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Sci Transl Med-2011-Rozen-92ps31

B ETA DEFENSIN 126An estimated 10 to 15% of couples at some point su er from infertility, which is de ned as the inability to conceive a er 1 year of unprotected intercourse (1). O en, multiple factors contribute to infertility, and many treatment decisions rely on trial and error (2–4). In many couples, genetically deter-mined characteristics of the male’s semen probably play at least some role, and this may be compounded by reduced fertility in the female partner. However, little is known about the genetic determinants of male fer-tility beyond e ects mediated by reduced sperm count (5–9), as well as a few addition-al rare variants that account for a small frac-tion of male infertility (10–12). In this issue of Science Translational Medicine , Tollner et al . (13) o er a welcome advance showing that a common variant in the gene encoding beta defensin 126, DEFB126, probably con-tributes to infertility.DEFB126 is a member of a diverse yet underinvestigated family of genes, many of which encode antimicrobial proteins pres-ent in the skin or mucous membranes (14). Some beta defensins are expressed primarily in the epididymis (15), a small organ on the side of each testis that serves to store sperm and contributes to their maturation (Fig. 1A). It is hypothesized that some of the beta defensins expressed in the epididymis help to protect the organ from infection-causing microbes. However, among the epididymal beta defensins, the DEFB126 protein has a di erent function. In a model organism, itcoats the plasma membrane of sperm (16)(Fig. 1B). Functional studies in macaques show that the DEFB126 protein coat helps sperm to penetrate cervical mucus (17), shields them from recognition by the female immune system (18), and promotes their at-tachment to the epithelium of the oviduct (fallopian tube) (Fig. 1A) (19).A COMMON FUNCTIONAL GENETICVARIANT IN DEFB126In examining the nucleotide sequence of hu-man DEFB126, Tollner and colleagues no-ticed an extremely common sequence variant (13). is variant, denoted “del,” involves the deletion of two cytosine nucleotides starting at position 317 of the reference coding se-quence (CDS) of the gene (Concensus CDS no. 12990.1). us, although the reference variant encodes a predicted 111–amino acid protein, the del variant results in a frame shi that removes the stop codon. is results in a “nonstop” mRNA in which the last six amino acids of the reference protein product (PVSPTG) are predicted to be replaced by a 26–amino acid sequence: RFSHWLNIP AS-VSCSRIP DSLKQRGL. e authors further reported that in the epididymis, a del/del homozygote had DEFB126 mRNA levels that were only 10% of those in a reference-allele homozygote (13). ey hypothesize that this might be the result of suppression of the non-stop mRNA by cellular surveillance mecha-nisms. In any case, the surface of sperm from del/del homozygotes showed dramati-cally less glycosylation of the type associated with DEFB126 (20)—speci cally, O-linked galactose-GalNAc (N -acetylgalactosamine) glycans (13). is lack of sperm glycosylation is presumably due to reduced levels of the DEFB126 protein itself, although this was notmeasured directly. Importantly, the amount of this coating correlates with the ability of sperm to penetrate hyaluronic acid (HA) (13). Because HA is an established surrogate for cervical mucus (21, 22), the near inability of sperm from del/del men to penetrate HA indicates that these sperm would have great di culty penetrating cervical mucus.DEL/DEL AND FERTILITYNaturally, some questions then followed: Does homozygosity for the del variant im-pede sperm penetration of cervical mucus or other functions mediated by DEFB126 in vivo? Furthermore, does this then a ect fer-tility? To address the latter question, Tollner et al . studied DEFB126 genotypes and fertil-ity in approximately 500 newlywed couples (13). ey found that a er 2 years, couples in which the man’s genotype was del/del were signi cantly less likely to have had a pregnancy than were the other couples. A second, con rmatory analysis found that in any given month, couples in which the man’s genotype was del/del were 30% less likely than were the other couples to have a birth. e con uence of the experimental and human genetic studies provides strong evidence that men with the del/del genotype have reduced fertility. Nevertheless, the ge-netic ndings will need to be replicated in a larger cohort of couples or over a longer period of time before we can be con dent in the e ects of the del/del DEFB126 genotype on male fertility.It is also important to recognize that re-duced penetration of cervical mucus might not be the only reason that del/del homo-zygotes have lower fertility. In macaques, DEFB126 also helps sperm avoid recogni-tion by the female immune system (18). In addition, DEFB126 promotes sperm attach-ment to the epithelium of the oviduct (19), the organ in which fertilization normally takes place. us, beyond reducing sperm penetration of cervical mucus, the del/del genotype could conceivably contribute to infertility by abrogating these or other, still-unknown, functions of DEFB126. e geographically widespread, high prevalence of the del variant—close to 50% of alleles in populations from Asia, Europe, and Africa—is surprising in light of the ob-served reduced fertility of del/del homozy-gotes. Fundamentally, we can only specu-late about why the del variant is extremely common in so many populations. Tollner and colleagues show possible evidence ofI N F E R T I L I T YDefending Male FertilitySteve Rozen**E-mail: steve.rozen@.sgDuke–NUS Graduate Medical School Singapore, 8 Col-lege Road, 169857 Singapore. A n estimated 10 to 15% of couples su er from infertility, and many treatment decisions rely on trial and error. In this issue of Science Translational Medicine , Tollner and colleagues provide strong evidence from a human genetics study that a common variant in the beta defensin 126 gene, the “del” variant, can reduce male fertility substantially. In addition, they show a plausible mechanism for reduced fertility: Sperm from del/del homozygotes lack an important component of their glycoprotein coat and have di culty penetrating a surrogate for cervical mucus. If replicated in future studies, these ndings promise to guide choices about the timing and type of assisted reproduction interventions—and further hint at the possibility of treating sperm from del/del homozygotes to promote fertility.o n J u l y 21, 2011s t m .s c i e n c e m a g .o r g D o w n l o a d e d f r o mC R ED I T : P . H UE Y /S C I E N C E T R A N S L A T I O N A L M E D I C I N Ebalancing selection, in which heterozygotes mig ht have a selective advantag e over ho-mozygotes for either allele. But the authors’ genetic studies (13) show no evidence that heterozy otes have any advanta e over reference-allele homozyg otes in terms of time to pregnancy or birth. us, any het-erozygote advantage would have to be medi-ated by other e ects, such as, speculatively, resistance to infection.CLINICAL IMPLICATIONS e g enetic nding s by Tollner et al . o er two clinical opportunities. A future oppor-tunity is the possibility of treating sperm from del/del men to restore g lycosylated DEFB126. In previous work, the authors showed that it is possible to remove and then restore the DEFB126 coat from ma-caque sperm (Fig. 1B) (23). Restoring g ly-cosylated DEFB126 would depend on iden-tifying an abundant source of the protein with the necessary pattern of glycosylation. e more immediate clinical opportunity is that of guiding choices about the timing andtype of assisted reproduction intervention (Fig. 1A). In g eneral terms, if it is known that time to preg nancy is likely to be longbecause the man has the del/del genotype, then resorting immediately to assisted re-production may be attractive. is would beespecially true if the woman has dwindlingovarian reserves and is also contributing to the couple’s infertility. is situation is be-coming more common as women increas-ing ly delay childbearing , which results indecreased female fertility (24–28).If it is con rmed that the del/del geno-type depresses fertility by impeding sperm penetration of the cervical mucus, then apossible intervention is intrauterine insemi-nation (Fig. 1A). In this technique, washed sperm are deposited directly into the uterusvia a catheter inserted throug h the cervi-cal canal, thus mechanically bypassing the cervical mucus. is can be combined withovarian hyperstimulation to increase thechances of successful fertilization. If, how-ever, it turns out that the del/del genotypedepresses fertility through additional mech-anisms [such as poor evasion of the femaleimmune system (18) or suboptimal interac-tions with the oviductal epithelium (19)],possible interventions would include in vi-tro fertilization (IVF) or intracytoplasmicsperm injection (ICSI) (Fig. 1A). For IVF,the sperm and an egg are combined in a mi-crodroplet, and the sperm can fertilize the egg naturally, albeit outside of the body. For ICSI, the sperm is injected directly into the cytoplasm of the egg. For both assisted re-production techniques, embryos are placed in the uterus a few days a er fertilization; if an embryo implants, a pregnancy results.With either technique, any requirement for the DEFB126 protein coat would be by-passed because DEFB126 must be removedfrom the sperm as a nal step before fertil-ization (23).It is too soon to predict how this new knowledg e about the DEFB126 g enotype(13) may aect the multifaceted decisions reg arding the use of assisted reproduc-tion technolog ies for human preg nancy. Itis clear that this genetic information could lead to more informed assisted reproduc-tion, in addition to possible new methods of treating sperm. In the meantime, we eagerly await a more complete understanding of the epidemiolog y of the DEFB126 del variant and of the mechanisms by which it increases time to pregnancy.REFERENCES AND NOTES 1. M. G. Hull, C. M. Glazener, N. J. Kelly, D. I. Conway, P. A.Foster, R. A. Hinton, C. Coulson, P. A. Lambert, E. M. Watt,K. M. Desai, Population study of causes, treatment, andoutcome of infertility. Br. Med. J. (Clin. Res. Ed.) 291, 1693–1697 (1985).2. P. J. Rowe, F. H. Comhaire, T. B. Hargreave, H. J. Mellows, WHO Manual for the Standardized Investigation and Diag-nosis of the Infertile Couple (Cambridge Univ. Press, Cam-birdge, 1993).3. American Urological Association Infertility Best P ractice Statement P anel, ed., 2010. “The Optimal Evaluation of the Infertile Male: AUA Best P ractice Statement,” down-Fig. 1. DEFB126 in the human male and female reproductive tracts. (A ) Sperm are created in thetestis and subsequently stored in the epididymis. Here, they also obtain a coating of glycoproteins,of which DEFB126 is a major component. After ejaculation, the sperm ﬁ nd themselves at the open-ing of the cervical canal, which is ﬁ lled with mucus. The sperm must swim through the cervical mucus and make their way through the uterus to the oviducts (fallopian tubes), where they mightmanage to fertilize an egg. DEFB126 helps the sperm to penetrate the cervical mucus, probably helps them to evade the female immune system, and promotes their attachment to the epithelial lining of the oviducts. (B ) Macaque sperm stained with an antibody for DEFB126. Reproduced with permission from (16). CervixFertile sperm with DEFB126 coating Less-fertile sperm, which lack the DEFB126 coatingClinical implication: Treat sperm to provide a coating of glycosylated DEFB126Location of cervical mucusUterusOvary Oviduct AB Oviduct OvaryTestisEpididymisClinical implication: Intrauterine insemination Clinical implications:In vitro fertilizationIntracytoplasmic sperm injectiono n J u l y 21, 2011s t m .s c i e n c e m a g .o r g D o w n l o a d e d f r o mloaded from /content/media/op-timalevaluation2010.pdf.4. P. J. Rowe, F. H. Comhaire, T. B. Hargreave, A. M. A. Mah-moud, WHO Manual for th e Standardized Investigation and Diagnosis of the Infertile Male (Cambridge Univ. Press, Cambridge, 2000).5. C. Krausz, S. Degl’Innocenti, Y chromosome and male in-fertility: Update, 2006. Front. Biosci.11,3049–3061(2006).6. M. J. Noordam, S. Repping, The human Y chromosome:A masculine chromosome. Curr. Opin. Genet. Dev.16,225–232 (2006).7. M. Simoni, E. Bakker, C. Krausz, EAA/EMQN best practiceguidelines for molecular diagnosis of y-chromosomal microdeletions. State of the art 2004. Int. J. Androl.27, 240–249 (2004).8. S. Repping, H. Skaletsky, J. Lange, S. Silber, F. Van Der Veen,R. D. Oates, D. C. Page, S. Rozen, Recombination between palindromes P5 and P1 on the human Y chromosome causes massive deletions and spermatogenic failure. Am.J. Hum. Genet.71, 906–922 (2002).9. T. Kuroda-Kawaguchi, H. Skaletsky, L. G. Brown, P. J. Minx,H. S. Cordum, R. H. Waterston, R. K. Wilson, S. Silber, R.Oates, S. Rozen, D. C. Page, The AZFc region of the Y chro-mosome features massive palindromes and uniform re-current deletions in infertile men. Nat. Genet.29, 279–286 (2001).10. A. Anguiano, R. D. Oates, J. A. Amos, M. Dean, B. Gerrard, C.Stewart, T. A. Maher, M. B. White, A. Milunsky, Congenital bilateral absence of the vas deferens. A primarily genital form of cystic ﬁ brosis. JAMA267, 1794–1797 (1992). 11. R. J. Aitken, A. Ross, M. M. Lees, Analysis of sperm functionin Kartagener’s syndrome. Fertil. Steril.40, 696–698 (1983).12. B. A. Afzelius, R. Eliasson, O. Johnsen, C. Lindholmer, Lackof dynein arms in immotile human spermatozoa. J. Cell Biol.66, 225–232 (1975).13. T. L. Tollner, S. A. Venners, E. J. Hollox, A. I. Yudin, X. Liu, G.Tang, H. Xing, R. J. Kays, T. Lau, J. W. Overstreet, X. Xu, C. L.Bevins, G. N. Cherr, A common mutation in the defensinDEFB126 causes impaired sperm function and subfertility.Sci. Transl. Med.3, 92ra65 (2011).14. R. I. Lehrer, Primate defensins. Nat. Rev. Microbiol.2, 727–738 (2004).15. Y. Yamaguchi, T. Nagase, R. Makita, S. Fukuhara, T. Tomita,T. Tominaga, H. Kurihara, Y. Ouchi, Identiﬁ cation of mul-tiple novel epididymis-speciﬁ c beta-defensin isoforms inhumans and mice. J. Immunol.169, 2516–2523 (2002).16. A. I. Yudin, T. L. Tollner, M. W. Li, C. A. Treece, J. W. Over-street, G. N. Cherr, ESP13.2, a member of the beta-defen-sin family, is a macaque sperm surface-coating proteininvolved in the capacitation process. Biol. Reprod.69,1118–1128 (2003).17. T. L. Tollner, A. I. Yudin, C. A. Treece, J. W. Overstreet, G. N.Cherr, M acaque sperm coating protein DEFB126 facili-tates sperm penetration of cervical mucus. Hum. Reprod.23, 2523–2534 (2008).18. A. I. Yudin, S. E. Generao, T. L. Tollner, C. A. Treece, J. W.Overstreet, G. N. Cherr, Beta-defensin 126 on the cell sur-face protects sperm from immunorecognition and bind-ing of anti-sperm antibodies. Biol. Reprod.73, 1243–1252(2005).19. T. L. Tollner, A. I. Yudin, A. F. Tarantal, C. A. Treece, J. W.Overstreet, G. N. Cherr, Beta-defensin 126 on the surfaceof macaque sperm mediates attachment of sperm to ovi-ductal epithelia. Biol. Reprod.78, 400–412 (2008).20. A. I. Yudin, C. A. Treece, T. L. Tollner, J. W. Overstreet, G. N.Cherr, The carbohydrate structure of DEFB126, the majorcomponent of the cynomolgus Macaque sperm plasmamembrane glycocalyx. J. Membr. Biol.207, 119–129(2005).21. R. J. Aitken, H. Bowie, D. Buckingham, D. Harkiss, D. W.Richardson, K. M. West, Sperm penetration into a hyal-uronic acid polymer as a means of monitoring functionalcompetence. J. Androl.13, 44–54 (1992).22. S. Tang, C. Garrett, H. W. Baker, Comparison of human cer-vical mucus and artiﬁ cial sperm penetration media. Hum.Reprod.14, 2812–2817 (1999).23. T. L. Tollner, A. I. Yudin, C. A. Treece, J. W. Overstreet, G. N.Cherr, Macaque sperm release ESP13.2 and PSP94 duringcapacitation: The absence of ESP13.2 is linked to sperm-zona recognition and binding. Mol. Reprod. Dev.69, 325–337 (2004).24. S. Sunderam, J. Chang, L. Flowers, A. Kulkarni, G. Sentelle,G. Jeng, M. M acaluso; Centers for Disease Control andPrevention (CDC), Assisted reproductive technology sur-veillance—United States, 2006. MMWR Surveill. Summ.58,1–25 (2009).25. A. Nyboe Andersen, V. Goossens, A. P. Ferraretti, S. Bhat-tacharya, R. Felberbaum, J. de M ouzon, K. G. Nygren;The European IVF-monitoring (EIM) Consortium, forthe European Society of Human Reproduction and Em-bryology (ESHRE), Assisted reproductive technology inEurope, 2004: Results generated from European registersby ESHRE. Hum. Reprod.23, 756–771 (2008).26. S. C. Tough, C. Newburn-Cook, D. W. Johnston, L. W. Sven-son, S. Rose, J. Belik, Delayed childbearing and its impacton population rate changes in lower birth weight, mul-tiple birth, and preterm delivery. Pediatrics109, 399–403(2002).27. H.-P. Kohler, F. C. Billari, J. A. Ortega, The emergence oflowest-low fertility in Europe during the 1990s. Popul. Dev.Rev.28, 641–680 (2002).28. P. Katz, R. Nachtigall, J. Showstack, The economic impactof the assisted reproductive technologies. Nat. Cell Biol.4,(Suppl. 1), S29–S32 (2002).29. Funding: The author is supported by the Singapore Min-istry of Health and the Agency for Science, Technology,and Research. Competing Interests: The author declaresno competing interests.Citation: S. Rozen, Defending male fertility. Sci. Transl. Med.3, 92ps31 (2011).10.1126/scitranslmed.3002743onJuly21,211stm.sciencemag.orgDownloadedfrom。

igcse英语article范文

igcse英语article范文Title: The Impact of Social Media on TeenagersIn today's digital age, social media has become an integral part of most teenagers' lives. With the rise of platforms such as Instagram, Snapchat, and TikTok, young people are constantly connected and exposed to a world of information and communication. While social media has its undeniable benefits, it also poses various challenges and risks, particularly for teenagers.One of the biggest impacts of social media on teenagers is its influence on mental health. Studies have shown that excessive use of social media can lead to feelings of loneliness, anxiety, and depression among young people. The constant need for validation through likes and comments can also trigger feelings of insecurity and inferiority in teenagers, as they compare themselves to others on social media.Furthermore, social media has also been found to contribute to cyberbullying, which can have devastating effects on teenagers' mental and emotional well-being. With the anonymity that social media provides, bullies can easily targettheir victims without fear of consequences, leading to a rise in cases of online harassment and abuse.Another impact of social media on teenagers is its effect on interpersonal relationships. While social media allows teenagers to stay connected with friends and family members, it can also hinder face-to-face communication and intimacy. Many young people are more comfortable expressing themselves through texts and emojis than in person, leading to a decline in social skills and emotional intelligence.In addition, social media can also have a negative impact on teenagers' academic performance. With the constant distraction of notifications and updates, many young people find it difficult to focus on their studies and assignments. The pressure to maintain a social media presence and keep up with the latest trends can also consume a significant amount of teenagers' time and energy, leaving little room for academic pursuits.Despite these challenges, social media also has its benefits for teenagers. It can provide a platform for self-expression, creativity, and activism, allowing young people to share their ideas and opinions with a global audience. Social media has also been instrumental in raising awareness about social issues,promoting diversity and inclusion, and mobilizing youth-led movements for change.In conclusion, the impact of social media on teenagers is complex and multifaceted. While it offers numerous opportunities for connection and communication, it also poses risks and challenges for young people's mental health, relationships, and academic performance. As such, it is essential for parents, educators, and policymakers to be mindful of the effects of social media on teenagers and work together to promote healthy and responsible use of these platforms.References:- Twenge, J.M. & Campbell, W.K. (2018). Associations between screen time and lower psychological well-being among children and adolescents: Evidence from a population-based study. Preventive Medicine Reports, 12, 271-283.- Kowalski, R.M., Giumetti, G.W., Schroeder, A.N., & Lattanner, M.R. (2014). Bullying in the digital age: A critical review and meta-analysis of cyberbullying research among youth. Psychological Bulletin, 140(4), 1073-1137.。

冠词 Article 的用法

in hospital in the hospital
在住院在医院里
in school in the school
在学习；在学校上课在学校里
out of question 不成问题；豪无疑问 out of the question 不可能；办不到
go to school
上学
go to the school 到学校去
6）在称呼或表示官衔，职位的名词前不加冠词： The guards took the American to General Lee. 士兵们把这个美国人送到李将军那里。
7）在三餐、球类运动和娱乐运动的名称前，不加冠词如：
have breakfast，play chess 8）当两个或两个以上名词并用时，常省去冠词：
go to hospital go to the hospital
go to bed go to the bed
去看病到医院去
去睡觉向那张床走去
5
冠词用法歌诀
名词是秃子，常要戴帽子。可数名词单，须用a或an。辅音前用a，an用元音前。若为特指时，则须用定冠。复数不可数，泛指the不见。碰到代词时，冠词均不现。
12）如果名词前已有this, that, these, those, whose, which, my, your, their, his, her, it词，意义不同
试比较：
at table at the table
在进餐在餐桌旁
Where do you live? I live on the second floor. 你住在哪？我住在二层。
That‘s the very thing I’ve been looking for. 那正是我要找的东西。

WEARING ARTICLE

专利名称：WEARING ARTICLE发明人：ICHIKAWA, Makoto,OHASHI, Naoto 申请号：JP2008066675申请日：20080916公开号：WO09/054206P1公开日：20090430专利内容由知识产权出版社提供摘要：A wearing article in which a front waist region and a rear waist region can be easily and accurately engaged with each other. A first fastening element (13) is installed on a front edge section (11) of the front waist region (8), and a second fastening element (14) engageable with the first fastening element (13) is installed on a rear edge section (12) of the rear waist region (9). The second fastening element (14) has a bellows structure extending in the lateral direction (X) and having crests (17) spaced in the longitudinal direction (Y). Even if a bellows region (16) where the bellows structure is formed makes contact with the first fastening element (13) with the bellows contracted, they are engaged with each other with a weak force and can be easily disengaged from each other. When the bellows region (16) is stretched in the longitudinal direction (Y) and made to make contact with the first fastening element (13), they can be in contact with each other in a large area to be firmly engaged with each other.申请人：ICHIKAWA, Makoto,OHASHI, Naoto地址：JP,JP,JP国籍：JP,JP,JP代理机构：SHIRAHAMA, Yoshiharu更多信息请下载全文后查看。

山东大学博士学位论文怀特的历史书...

山东大学博士学位论文海登?怀特的历史书写理论与文学观念姓名:杨杰申请学位级别:博士专业:文艺学指导教师:马龙潜20060320山东大学博士学位论文中文提要海登?怀特是当代美国著名思想史家、历史学家、文学批评家,他主导了世纪年代以后的历史哲学领域中的语言学转向,并将历史意识与历史方法引入文学批评领域,成为跨学科研究的典范。

怀特享誉世界,是新历史主义文学批评研究所不能忽视的重要理论家,称其为“理论家”的原因是??在新历史主义“庞杂”的队伍中只有他对“历史”进行了系统化的理论阐述,而其他人如格林布拉特等更擅长批评实践而非理论阐述。

怀特的理论在史学界激起轩然大波,褒贬不一。

可是,失之东隅,收之桑榆,其理论竟成了文学批评界的必读经典。

怀特理论虽被广泛引用,但对其学术进行较为全面、深入研究的却是相当有限,我们能查阅到的仅仅是在对新历史主义文学批评进行宏观研究时所做的篇幅不过是一节的介绍,至于更为细致、深入的针对其个人的研究却是相当稀少。

鉴于此,不论是否赞赏怀特的理论观点,都应回到对其理论本身的探讨上来,在对其理论进行较为全面分析、鉴别的基础之上再作出得失评判。

这不失为一种科学的态度。

选取怀特的历史书写理论为研究课题不是一件轻松的事情。

因为怀特知识渊博,学术功底深厚,不仅涉及多个学科领域知识,而且还大量论及学界泰斗的理论观点,其中的如海德格尔、伽达默尔、杰姆逊、福柯、利科等人的理论本身就很深奥,再加上怀特本人的生涩文笔,更令人有仰之弥高之感;尤其是在查阅他的原文资料时经常遇到夹杂意大利文、法文、德文等非英文词句,这也增加了理解的难度。

怀特的理论代表了“回归历史”的呼声。

历史问题作为人类本体存在的时间维度必然引发我们的思考,更是文学研究不能回避、也绝对无法回避的问题。

他的理论具有“多声部?复调”①式的特点,可以概括为“一个核心、两个维度、两种视角”。

所谓的“一个核心”是指怀特始终坚持文史相通的观念;“两个维度”指形式主义与“回归历史”是支撑其理论大厦的两个轴;“两种视角”是指“在文学中审视历史”和“在历史中研究文学”。

(完整版)CISG中英文对照版

联合国国际货物销售合同公约中英文对照字体大小：大- 中- 小quanzhoufanyi 发表于08-08-07 10:42 阅读(288) 评论(0) 联合国国际货物销售合同公约(United Nations Convention on Contractsfor the International Sale of Goods (1980) )PreambleThe States Parties to this Convention Bearing in Mind the broad objectives in the resolutions adopted by the sixth special session of the General Assembly of the United Nations on the establishment of a New International Economic Order. Considering that the development of international trade on the basis of equality and mutual benefit is an important element in promoting friendly relations among States, Being of the Opinion that the adoption of uniform rules which govern contracts for the international sale of goods and take into account the different social, economic and legal systems would contribute to the removal of legal barriers in international trade and promote the development of international trade, have decreed as follows: 本公约个缔约国: 铭记联合国大会第六界特别会议通过的关于建立新的国际经济次序的各项决议的广泛目标, 考虑到在平等互利基础上发展国际贸易, 是促进各国间友好关系的一个重要因素, 认为采用照顾到不同的社会, 经济和法律制度的国际货物销售合同统一规则，将有助于减少国际贸易的法律障碍, 促进国际贸易的发展. 兹协议如下.PART ISphere of Application and General ProvisionsChapter ISphere of ApplicationArticle 1(1) This Convention applies to contracts of sale of goods between parties whose places of business are in different States: ( 本公约适用于营业地在不同国家的当事人之间所订立的货物销售合同，)(a) when the States are Contracting States; or ( 如果这些国家是缔约国, 或)(b) when the rules of private international law lead to the application of the law of a Contracting State. ( 如果国际私法规则导致适用某一缔约国的法律，)(2) The fact that the parties have their places of business in different States is to be disregarded whenever this fact does not appear either from the contract or from any dealings between, or from information disclosed by, the parties at any time before or at the conclusion of the contract. ( 当事人营业地在不同国家的事实，如果从合同或从订立合同前任何时候或订立合同时, 当事人之间的任何交易或当事人透露的情报均看不出, 应不予考虑)(3) Neither the nationality of the parties nor the civil or commercial character of the parties or of the contract is to be taken into consideration in determining the application of this Convention. ( 在确定本公约的适用时, 当事人的国籍和当事人或合同的民事或商业性质，应不予考虑) Article 2This Convention does not apply to sales: ( 本公约不适用以下的销售)(a) of goods bought for personal, family or household use, unless the seller, at any time before or at the conclusion of the contract, neither knew nor ought to have known that the goods were bought for any such use; ( 购供私人, 家人或家庭使用的货物销售, 除非卖方再订立合同前任何时候或订立合同时不知道而且没有理由知道这些货物是购供任何这种使用)(b) by auction; ( 经由拍卖销售的)(c) on execution or otherwise by authority of law; ( 根据法律执行令状或其他领状的销售)(d) of stocks, shares, investment securities, negotiable （可通过谈判解决的）instruments （手段）or money;( 公债，股票，投资证券, 流通票据或是货币的销售)(e) of ships, vessels （船只）, hovercraft （水翼船）or aircraft;( 船舶船只，气垫船或是飞机的销售)(f) of electricity. ( 电力的销售)Article 3(1) Contracts for the supply of goods to be manufactured or produced are to be considered sales unless the party who orders the goods undertakes to supply a substantial part of the materials necessary for such manufacture or production.( 供应尚待制造或生产的货物的合同应视为销售合同, 除非订购货物的当事人保证供应这种制造或生产所需的大部分重要材料.)(2) This Convention does not apply to contracts in which the preponderant( 优势的) part of the obligations of the party （当事人）who furnishes the goods consists in the supply of labour or other services.( 本公约不适用于供应货物一方的绝大部分义务在于供应劳力或其它服务的合同)Article 4This Convention governs only the formation （形成）of the contract of sale and the rights and obligations of the seller and the buyer arising from （产生）such a contract. In particular, except as otherwise expressly （明确地）provided in this Convention, it is not concerned with: ( 本公约只适用于销售合同的订立和卖方和买方因此种合同而产生的权利和义务. 特别是本公约除非另有明文规定, 与以下事项无关:)(a) the validity （效力）of the contract or of any of its provisions （供应）or of any usage;( 合同的效力，或其任何条款的效力，或任何惯例的效力)(b) the effect which the contract may have on the property in the goods sold. （合同对所销售物所有权可能产生的影响。

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Effect of shearing on crystallization behavior ofpoly(ethylene naphthalate)W.J.Yoon,H.S.Myung,B.C.Kim,S.S.Im *Department of Textile Engineering,Hanyang University,Haengdang,Seongdong,Seoul 133-791,South KoreaReceived 11August 1999;received in revised form 24September 1999;accepted 30September 1999AbstractThe effect of shear history on the isothermal crystallization behavior of poly(ethylene naphthalate)(PEN)was investigated by rheological and morphological measurements.Time sweep measurements of storage modulus (G H )and dynamic viscosity (h H )were carried out on the molten PEN by Advanced Rheometric Expansion System (ARES)in the parallel-plate geometry at several different temperatures and frequencies,followed by structural analysis by differential scanning calorimeter (DSC),X-ray diffractometer,and polarizing microscopy for the shear-induced crystallized PEN specimens in the ARES measurements.The rate of isothermal crystallization of PEN was notably affected by temperature,while the shear rate has an important effect on the structures of the resultant crystals.At a constant shear rate,the rate of crystallization by shear-induced structuring mechanism was increased with lowering temperature over the temperature range 230–250ЊC.The rate of crystallization was increased with increasing shear rate at a given temperature.An increase in shear rate increased both nucleation and number of crystallites.Further,it increased the content of the a -form crystal in the specimen.On the other hand,lower shear rate offered more favorable conditions for forming the b -form crystal.DSC analysis exhibited that the b -form crystal had higher melting temperature (T m )than the a -form crystal.The wide angle X-ray diffraction (WAXD)patterns also ascertained that higher content of the a -form crystal was produced in the PEN specimen crystallized at higher frequency.᭧2000Elsevier Science Ltd.All rights reserved.Keywords :Poly(ethylene naphthalate);Rheology;Shear-induced crystallization1.IntroductionShear-induced structural changes in polymeric materials take an increasing interest in the ﬁeld of polymer proces-sing.In real polymer processing very complex deformation histories are involved,which can inﬂuence ultimate proper-ties of plastics.Recent advances in experimental techniques that allow in situ measurements of materials under deforma-tion have escalated research in this subject area.It has been known for a long time that ﬂow stress have accelerating effect on the crystallization of semi-crystalline polymers [1–6].It is supposed that the application of a shear stress to a polymer melt should lead to formation of orientation and reduce the entropy of the melt,which results in a higher melting temperature and,hence,lead to an increased super-cooling [3,7].Several experiments have been described in the literature where attempts were made to quantify the shear stress-induced crystallization in molten semi-crystal-line polymers such as polypropylene [3,8,9],polyethylene oxide [10],polypropylene [11–13],and polybutene-1[3,14].Some investigators used rotational viscometers andmeasured either the volume change [15]or the number of nuclei formed during shearing [11,14].The polymers enum-erated above are apt to process because of low melting point and viscosity.On the other hand,PEN has good thermal and mechanical properties and is being used as engineering plastics.PEN is reported to have two different triclinic crystalline structures,a -form and b -form crystals.Of two crystal forms,the b -form crystal is known to be more stable than the a -form.The effect of crystallization temperature on the resultant crystal structure is well recognized;lower temperature favors formation of the a -form crystal.The critical temperature is reported about 230ЊC.However,the effect of shear history on the crystal structure of PEN has not been reported.In this study,the shear-induced crystallization behavior of PEN was investigated on the rheological basis.The effect of shear history on the crystalline structure was also discussed in terms of thermal and morphological properties.2.Experimental 2.1.MaterialThe PEN tested was a commercially available gradePolymer 41(2000)4933–49420032-3861/00/$-see front matter ᭧2000Elsevier Science Ltd.All rights reserved.PII:S0032-3861(99)00703-X*Corresponding author.Tel.:ϩ82-2-2292-0495;fax:ϩ82-2-2297-5859.E-mail address:imss007@email.hanyang.ac.kr (S.S.Im).supplied by Kolon Group in South Korea.The inherent viscosity,0.344dl/g was determined in a mixture of triﬂuoroacetic acid and chloroform (1/3v/v%)with an Ubbelohde viscometer at 25^0:1ЊC :The polymer was dried in a vacuum oven at 120ЊC for 24h prior to use.2.2.Measurement of physical propertiesThe dynamic rheological properties were measured by ARES (Rheometric Scientiﬁcs)in the parallel plate geome-try.The plate diameter was 12.5mm,strain level was 5%,and gap between the plates was 1mm.The PEN chips were melted at 300ЊC.The initial gap was set to a value equiva-lent to ﬁnal gap plus 50m m.The excess sample squeezed out by reducing the gap was carefully trimmed off.The value was reset to the ﬁnal gap value,1mm.To remove the residual stress the newly set PEN specimen was relaxed for about 5min at the temperature in nitrogen atmosphere,then cooled to the predetermined temperature for rheologi-cal measurements.A time-sweep experiment was continued for the specimen till the G H reached the ceiling value of the apparatus.After ARES measurement,the molten PEN sample was detached from the plates for measuring other properties such as thermal and morphological properties by DSC,X-ray diffractometer and polarizing optical micro-scopy.Thermal properties were measured by Perkin–Elmer DSC-7over the temperature 50–300ЊC at the heating rate of 10ЊC/min under nitrogen purge.The isothermalcrystallization experiment was performed by two different methods.Firstly,the PEN sample was heated to 300ЊC at the heating rate of 200ЊC/min,and held for about 5min,then they were cooled to the preset temperature to bring about the isothermal crystallization for same time required in ARES experiment.Secondly,the PEN chips were melted at 300ЊC between two slide glasses for 5min on the hot stage.They were moved to an oil bath very quickly and isothermally crystallized at 230,240,and 250ЊC for 4,10,and 24h,respectively.Wide angle X-ray diffraction patterns of the isothermally crystallized PEN specimen in the oil bath and ARES were obtained by X-ray diffractometer (Rigaku Denki)with Ni-ﬁltered CuK a radiation at 35kV and 35mA.Morphology of quiescent and shear-induced crystallized PEN specimen was observed by polarized microscopy (Nikon HFX-IIA).The spherulite structure was observed by microtoming the specimen.3.Results and discussionIn the plot of G H and h H versus time at a given frequency for a polymer,the two parameters may give information on the change in physicochemical properties of the polymer.For thermally sensitive polymer melts,an irreversible decrease of viscosity with time at a constant shear rate suggests the possibility of thermal degradation of polymer molecules,whereas an irreversible increase of viscosityW.J.Yoon et al./Polymer 41(2000)4933–49424934Fig.1.Variation of G H with time for PEN melt at 240ЊC at three different frequencies.with time indicates the possibility of chemical crosslinkingbetween polymer molecules.Both thermal degradation andchemical crosslinking show irreversibility in the rheologicalresponses.On the other hand,a reversible change in G H and h H with time at a constant frequency may be caused by changing in the physical state of the polymer melts.A typi-cal example of the physical change is the isothermal crystal-lization.As the crystallites grow to larger sized spheruliteswithin the PEN melt through nucleation and growth,thehomogeneous melt system changes to the heterogeneoussystem.Thus the G H and h H increase with the crystallization time.Figs.1and2show the variation of the G H and h H of PEN melt with time at240ЊC at three different shear rates(1,3, and5rad/s).At the early stage of experiment,both G H and h H are increased slowly,indicating an induction time for crystallization.The induction period is the stage when randomly entangled polymer chains transform to the regular aligned lattice.Because of topological obstruction of such entanglements,the polymer crystallization is extremely slow[16].However,an abrupt increase of both parameters follows in some minutes.This phenomenon can be ascribed to the formation of tiny crystals so-called crystallites prob-ably due to shear-induced crystallization.It can be easily imagined that the homogeneous PEN melt changes to a suspension system with proceeding crystallization,in which numerous crystallites are dispersed in the homo-geneous molten polymer matrix.The viscosity increases due to increasing the volume fraction of dispersed crystal-lites with progressing crystallization,which is also reportedby others[7,9,11,14,17].The ceiling value of G H is the same regardless of frequen-cies and temperatures whenﬁnishing crystallization asshown in Fig.1.On the other hand,the ceiling value of h H is gradually decreased with increasing the applied frequency as shown in Fig.2.This is attributable to pseudo-plasticity.That is,the heterogeneous system is expected toshow yield behavior[18].At low shear rates the hetero-geneous systems exhibit very high viscosity,and almostunbounded viscosity at zero shear rate.The viscosity,however,is rapidly decreased if the shear rate exceeds acritical value.Consequently,the ceiling viscosity at1rad/sis greater than at5rad/s.In addition,the ceiling value of h H shows a gradual decrease with time after having reached maximum as shown in Fig.2,which is more noticeable at the higher frequency.The gradual decrease of h H seems to result from the restructuring of the heterogeneous systems. That is,the viscosity is decreased with shearing on account of destruction of the orderedﬁller particle structure.The destruction of the pseudostructure ofﬁller particles is increased as shear rate is increased.Fig.2reﬂects this.It is also noted in Figs.1and2that the induction time forcrystallization is decreased as frequency is increased.Anapplication of shear stress to a polymer melt would giverise to two characteristic responses,orientation and slippageof polymer molecules.They are associated with theW.J.Yoon et al./Polymer41(2000)4933–49424935Fig.2.Variation of h H with time for PEN melt at240ЊC at three different frequencies.W.J.Yoon et al./Polymer41(2000)4933–49424936Fig.3.Variation of G H(A)and h H(B)for PEN melt at3rad/s at three different temperatures.W.J.Yoon et al./Polymer41(2000)4933–49424937Fig.4.DSC thermograms of PEN isothermally crystallized at(A)230ЊC,(B)240ЊC and(C)250ЊC at various frequencies.macroscopic phenomena of elasticity and ﬂow,respectively.That is,the oriented polymer molecule has fewer possible conformations than the unoriented one,which results in lower entropy.At the melting temperature,the free energy of the crystal equals the free energy of the melt as written by [3]T mD H f D S f H m ϪH cS m ϪS c1Hence,for an oriented melt,the ensuing reduction in entropy raises T m .Further,it increases the degree of super-cooling,accelerating the rate of crystallization.In general,higher shear rate gives better chance for orientation.Con-sequently,the induction time for cystallization is decreased with increasing shear rate.In Fig.3(A)and (B)shows that the annealing temperaturehas a profound effect on the nucleation and crystallization mechanism of PEN melts.The increase of G H and h H with annealing time represents the extent of crystallization of the melts with annealing time.Fig.3suggests that the number and growth rate of the nucleated crystallites is greater at 230ЊC than at 250ЊC.That is,both nucleation density and growth rate of crystallites are diminished with raising the annealing temperature.This stands to reason because the maximum rate of the homogeneous crystallization of PEN melts is observed in the vicinity of 215ЊC.The viscosity behavior of the PEN melt with crystalliza-tion in Fig.3may be accounted for by adopting the Mooney equation in a qualitative manner [19].ln h =h 1K E F 21ϪF 2=F m2W.J.Yoon et al./Polymer 41(2000)4933–49424938Fig.4.(continued )Table 1The values of T m H and T m HH of PEN with frequency (230,240and 250indicate temperature.(a)and (b)indicate v 0 a and v 0 b ;respectively (see Fig.6).1,3and 5indicate frequencyT m HT m HH T m HT m HH T m HT m HH PEN230(a)259.2272.1PEN240(a)266.7PEN250(a)270.1PEN230(b)264.1270.9PEN240(b)272.1PEN250(b)280.1PEN2301255.6270.3PEN2401259.3269.3PEN2501269.1PEN2303256.0270.0PEN2403261.9268.7PEN2503270.4PEN2305256.2269.7PEN2405263.6268.0PEN2505270.7F m true volume of fillerapparent volume occupied by the filler3 in which h is the viscosity of the suspension,h l is the viscosity of the suspending medium,f2is the volume frac-tion of theﬁller,f m is the maximum volume fraction that theﬁller can have,and K E is the Einstein coefﬁcient,whose value is known to be2.5for the dispersed sphericalﬁller.W.J.Yoon et al./Polymer41(2000)4933–49424939Fig.5.WAXD patterns of PEN isothermally crystallized at(A)230ЊC,(B)240ЊC and(C)250ЊC at various frequencies.Referring to the Mooney equation,the crystallization patterns of PEN melts at 230ЊC and at 250ЊC are distinc-tively different from each other.The Mooney equation predicts that the degree of increasing the suspension visc-osity with increasing f 2is greatly increased if the spheres form aggregates because the aggregation of spheres (spheru-litic crystallites or crystals in this study)increases the appar-ent ﬁller volume fraction.That is,the immobile portions (homogeneous molten PEN matrix in this study)caged by aggregated spheres also act as ﬁller portion.On this assump-tion,it may be suggested that an application of higher shear rate during isothermal crystallization tends to increase the heterogeneous crystallization characteristics.Hence,the higher nucleation density and higher growth rate of the nucleated crystallites is obtained at higher frequency,and the resultant is more abundant with less stable a -form crys-tals (this will be discussed later in detail).The melt endotherms of quiescently and shear-induced crystallized PEN were shown in Fig.4and the correspond-ing peak temperatures are listed in Table 1.The double melting endotherm behavior is displayed during heating the PEN sample in the DSC cell.In the melting process of the shear-induced crystallized PEN sample,three endother-mic peaks are identiﬁed;a broad endotherm,a low endotherm (T m H ),and a high endotherm (T m HH )as shown in Fig.4.The broad endotherm might be due to the thermal history during cooling and reheating,and both low and high endotherms are due to the melting of original lamella and recrystallized one,respectively.These results well coincide with the results of Zachman et al.[20]:(1)no change of crystal modiﬁcation is observed during DSC scanning;(2)the double melting behavior of PEN is due to the mechan-ism based on melting and recrystallization;(3)the b -form crystal has the T m higher than the a -form crystal by 2ЊC;and (4)the peaks of two forms of crystal are not separated in DSC thermogramsIn Fig.4(A)–(C)v 0rad =s indicates quiescent crystal-lization.(A)indicates that the PEN sample was crystallized at 230,240,and 250ЊC for the same time that required in the ARES experiments,and (B)expresses the PEN sample crys-tallized in an oil bath at the same temperature as in (A)for the time long enough to fully crystallize.Since the crystal-lization time in (A)is much shorter than in (B),an exother-mic peak is observed in the thermogram (A)at around 205ЊC.The v 0rad =s (b)curves in Fig.4(B)show a single melting peak.The T m shifts to higher temperature and peak width gets narrower as the crystallization time and tempera-ture are increased.This is attributable to the increased perfectness of the resultant crystal structure,which is observed more clearly when the sample is crystallized at higher temperature as can be seen in Fig.4(C).Only the b -form crystal exists when the sample is isothermally crys-tallized at 250ЊC after having melted at 300ЊC.This result matches well with the X-ray data.As mentioned the T m of the b -form crystal is higher than the a -form crystal by 2–4ЊC.It has been known that PEN has two different triclinic crystal structures.Buchner et al.reported that crystalW.J.Yoon et al./Polymer 41(2000)4933–49424940Fig.5.(continued )structures are inﬂuenced by both melting and isothermal crystallization temperature.They observed that the b -form crystal appeared mainly when PEN was isothermally crys-tallized above 230ЊC quiescently and the a -form crystal did below 230ЊC after having melted at 300ЊC [20].Fig.5presents WAXD patterns of PEN specimens shear-inducedcrystallized at (A)230ЊC,(B)240ЊC,(C)250ЊC at several frequencies.In Fig.5(A)the WAXD patterns for v 0rad =s shows diffraction peaks at 15.6and 23.3Њwhich correspond to (010)and (100)plane of the a -form crystal,respectively.The intensity of these peaks has a tendency to increase with increasing frequency.It means that the appli-cation of shear promotes the formation of the a -form crystal and the increase of frequency increases the content of the a -form crystal.In Fig.5(B)the (010)plane peak of the a -form crystal is smaller than that of the sample crystallized at 230ЊC in Fig.5(A)for v 0rad =s :However,the plane peak is increased with increasing frequency.In the case of the (100)plane peak,a shoulder appears at v 0rad =s :As frequency increases,the intensity of the plane peak standing for the a -form crystal shows tendency to increase.Particu-larly,for v 0rad =s in Fig.5(C)any plane peak of the a -form crystal is not observed,which is consistent with the results reported by Buchner et al.[20].The (010)and (100)plane peaks appear simultaneously,and keep on growing with increasing frequency.In addition,all diffraction peaks of Fig.5shift to lower angle when frequency is increased.This suggests that there is deformation in the crystal struc-tures as well.Thus,this X-ray trace of the sample is similar to those of Fig.5(A)and (B),suggesting similarity in the crystallization behavior at 230–250ЊC.In general,the b -form crystal is thermodynamically more stable but more difﬁcult to nucleate than the a -form crystal and the form of the crystal is largely determined by kinetic factors during crystallization such as the rate of nucleation and spherulite growth [21].In the case of the a -form crystal,one chain passes through the unit cell and the chains in the crystal are extended.In the case of the b -form crystal,however,four chains pass through the unit cell and the chains in the crystal are not completely extended.When the polymer is sheared,the number of crystallites increases with shear rate,representing faster nucleation.Wolkowicz [14]mentioned that the number of crystallites increased exponentially with time at all shear rates.Also,this can be conﬁrmed in Fig.6,which indicates that nuclea-tion becomes increasingly profuse with increasing frequency until the crystalline structure formed is no longer distinguishable with a microscope [3,22].Hence,the content of the a -form crystal in the speci-men increases with frequency because the a -form crys-tal is apt to nucleate due to fast nucleation.Consequently,the resultant a -form crystal is thermody-namically less stable than the b -form crystal because of much reduced entropy by molecular orientation under high shear force.References[1]Hill MJ,Keller A.J Macromol Sci (Phys)1969;B3(1):153.[2]Andrews EH.J Polym Sci 1966;A-2(4):663.[3]Haas TW,Maxwell B.Polym Eng Sci 1969;9:226.W.J.Yoon et al./Polymer 41(2000)4933–49424941(B)(A)(C)Fig.6.Polarizing optical micrographs of PEN crystallized at 240ЊC (A)v 0;(B)v 1;and (C)v 5:[4]Pennings AJ,van der Mark JMAA,Booj HC.kolloid Z v Z Polym1970;236:99.[5]Mackley MR,Keller A.Polymer1973;14:16.[6]Peterlin A.Polym Eng Sci1976;16:126.[7]Kobayashi K,Nagasawa T.J Macromol Sci(Phys)1970;B4:331.[8]Lagasse RR,Maxwell B.Polym Eng Sci1976;16:189.[9]Titomanlio G,Brucato V.Plastics Processing Society,The TenthAnnual Meeting,Akron,OH,1965,p.93.[10]Ulrich RD,Price FP.J Appl Polym Sci1976;14:401.[11]Eder G,Janeschizt-Kriehl H,Liedauer S.Progr Polym Sci1989;15:629.[12]Liedauer S,et al.Int Polym Proc VIII1993;3:236–44.[13]Moitzi J,Skallcky P.Polymer1993;34:3168.[14]Wolkowicz MD.J Polym Sci:Polym Symp1978;63:365.[15]Sherwood CH,Price FP,Stein RS.J Polym Sci;Polym Symp1977;63:77.[16]Imai M,et al.Phys.Rev.1995;B52:12696.[17]Kim JG,Park HJ,Lee JW.Korean J Rheol1997;4:174.[18]Carreau PJ,De Kee DCR,Chhabra RP.Rheology of polymericsystems,New York:Hanser,1997.[19]Nielsen LE.Polymer rheology,New York:Marcel Dekker,1977.[20]Buchner S,Wiswe D,Zachman HG.Polymer1989;30:480.[21]Zachman HG,Wiswe D,Riekel C.Macromol Chem Suppl1985;12:175.[22]Kim SP,Kim SC.Polym Eng Sci1993;33:83.W.J.Yoon et al./Polymer41(2000)4933–4942 4942。

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雅思剑桥11高分范文Unfortunately, as an AI language model, I am unable to provide specific content from copyrighted sources such as the Cambridge IELTS 11 book. However, I can help you generate a high-scoring IELTS essay by providing you with a structure and some guidance on how to approach the task.Title: "The Impact of Social Media on Society"Introduction:- Introduce the topic and state the importance of social media in today's society.- Present the thesis statement, conveying the overall impact of social media on individuals and communities.Body Paragraph 1: Positive Effects- Discuss the positive impacts of social media, such as fostering communication and networking.- Provide examples of how social media has facilitated connections between people worldwide.- Emphasize the role of social media in disseminating information and enhancing education.Body Paragraph 2: Negative Effects- Address the negative effects of social media, such as addiction and privacy concerns.- Discuss the impact of excessive social media use on mental and physical health.- Examine the potential manipulation of social media platforms for political purposes.Body Paragraph 3: Mitigating the Negative Effects- Suggest ways to mitigate the negative impact of social media.- Highlight the importance of digital literacy and critical thinking. - Explain the role of individuals, families, educational institutions, and governments in addressing the challenges posed by social media.Conclusion:- Summarize the main points discussed in the essay.- Reiterate the overall impact of social media on individuals and communities.- Call for a balanced approach towards social media usage, focusing on maximizing the benefits while minimizing the drawbacks.Remember to carefully analyze the essay question and adapt your response accordingly. Additionally, enhance your essay with relevant vocabulary, transitional phrases, and well-structured sentences. Practice time management to ensure you have enough time to revise and proofread your essay. Good luck with your IELTS preparation!。

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my first article散文

my first article散文I still remember the day when I wrote my first article. It was a sunny afternoon, and I was sitting at my desk, pen in hand, staring at a blank piece of paper. I had always loved writing, but I had never actually written an article before. I was nervous and excited at the same time.I started by jotting down some ideas. I thought about the things that mattered to me, the experiences that had shaped me, and the ideas that I wanted to share with the world. As I wrote, the words seemed to flow effortlessly from my pen. I was surprised at how easily the ideas came to me, and how clearly I was able to express them.Before I knew it, an hour had passed, and I had a page full of handwritten notes. I read through them, feeling a sense of pride and accomplishment. Those were my thoughts, my words, my voice. It was a powerful feeling.Over the next few days, I typed up my article and edited it carefully. I revised it several times, making sure that every sentence was clear and every word was chosen with care. Finally, I was ready to publish my first article.I submitted it to a local newspaper, and a few weeks later, I received a letter in the mail. My article had been accepted, and it wasgoing to be published in the next issue. I was overjoyed. My dream of becoming a writer was finally coming true.Looking back on that experience, I realize that writing that first article was more than just a成就感. It was a journey of self-discovery. It taught me that I had something valuable to say, and that my voice mattered. It gave me the confidence to keep writing, to keep sharing my ideas with the world.I will always cherish that first article, and the memories of the process of creating it. It will always remind me of the power of words, and the importance of following your dreams.。

article的例句

∙ 1. We cannot put a or the in front of names.∙姓名前不能用不定冠词或定冠词.∙来自互联网∙ 2. We can't use the indefinite article with this noun.∙我们不可以在这个名词前用不定冠词.∙来自互联网∙ 3. There arein English two articles: definite article and the indefinite article.∙英语中有两种冠词:定冠词和不定冠词.∙来自互联网∙2∙ 4. A and an are indefinite articles, any is an indefinite pronoun. ∙a和an是不定冠词,any是不定代词.∙来自互联网∙ 5. There are in English two articles:the definite article and the indefinite article.∙英语中有两个冠词, 即定冠词和不定冠词.∙来自互联网∙ 6.As I've already told you, articles can be classified into definite articles andindefinite articles.∙我早就讲过,冠词可以分为定冠词和不定冠词.∙来自互联网∙7. Complete the following sentences by fillingthe blanks with properprepositions and adverbs.∙用适当的冠词和副词填空,完成下列句子.∙来自《简明英汉词典》∙12∙8. The article is a part of speech in the English language.∙冠词是英语的一种词类.∙来自辞典例句∙2∙9. Fill in the blanks with articles where needed.∙需要的地方在空白处填入冠词.∙来自辞典例句∙51∙10. Fill in the blanks with articles where necessary.∙在需要的地方,用冠词填空.。

article英文作文格式

article英文作文格式1. I woke up late this morning, feeling groggy and disoriented. My alarm clock had failed me, leaving me scrambling to get ready for the day. I rushed through my morning routine, throwing on clothes and grabbing a quick breakfast. It was a chaotic start to the day, but I managed to make it out the door on time.2. As I walked to work, I noticed the sun shining brightly in the clear blue sky. The weather was perfect not too hot, not too cold. It put me in a good mood and made the walk more enjoyable. I couldn't help but smile as I passed by people on the street, feeling the warmth of the sun on my skin.3. When I arrived at the office, I was greeted by a mountain of paperwork on my desk. It seemed like there was no end to the tasks that needed to be completed. I took a deep breath and dove right in, determined to tackle each item one by one. The day was going to be busy, but I was upfor the challenge.4. During lunchtime, I decided to take a break and go for a walk outside. The fresh air and change of scenery helped clear my mind and recharge my energy. I strolled through the nearby park, admiring the colorful flowers and listening to the birds chirping. It was a peaceful moment amidst the chaos of the workday.5. Back at the office, I found myself in a meeting with my colleagues. We discussed upcoming projects and brainstormed ideas. It was a collaborative and productive session, with everyone sharing their thoughts and opinions.I enjoyed the lively discussion and felt inspired by the creativity in the room.6. As the workday came to a close, I felt a sense of accomplishment. Despite the challenges and busyness, I had managed to complete all my tasks. I packed up my things and headed home, looking forward to a relaxing evening.7. At home, I decided to unwind by watching a movie. Itwas a comedy that had me laughing out loud. The humor was a welcome distraction from the stresses of the day. I curled up on the couch with a bowl of popcorn, enjoying the movie and letting the laughter wash over me.8. Finally, it was time to go to bed. I crawled under the covers, feeling grateful for the day that had passed. It had been a rollercoaster of emotions, but ultimately a fulfilling and rewarding experience. As I closed my eyes, I looked forward to what tomorrow would bring.。

General 期刊——Sdarticle

1998
H.-J. Lai et al. / Discrete Mathematics 306 (200 of r (G), it follows immediately that (G) = 1 (G), and so r (G) is a generalization of the classical graph coloring. The purpose of this paper is to investigate the behavior of r (G) and to generalize certain properties on (G) to r (G). 2. The conditional chromatic number of certain graph families In this section, we determine the conditional chromatic number of a certain families of graphs, including complete bipartite graphs, and cycles. Throughout this section, r > 0 denotes an integer. Proposition 2.1. Let G be a connected graph. Each of the following holds: (i) (ii) (iii) (iv) (v) ··· (G). r (G) r −1 (G) 2 (G) |V (G)| r (G) min{r, (G)} + 1. Let n 1 be an integer. Then r (Kn ) = n. If |V (G)| 2 and r 2, then r (G) = 2 if and only if G

英文作文article格式

英文作文article格式Title: The Power of Music。

Music is a universal language that has the ability to transcend cultural barriers and connect people from all walks of life. It has the power to evoke emotions, bring back memories, and even inspire change. Whether it's the soothing melodies of a lullaby or the energetic beats of a rock concert, music has the ability to touch our souls and leave a lasting impact.In today's fast-paced world, music serves as a form of escapism for many. It provides a temporary refuge from the stresses and pressures of everyday life. With just a few notes, a song can transport us to a different time and place, allowing us to momentarily forget our worries and immerse ourselves in the rhythm and melody. It is a form of therapy that can heal our souls and rejuvenate our spirits.Furthermore, music has the power to unite people in away that few other things can. It brings together individuals from different backgrounds and cultures, creating a sense of community and belonging. Whether it's through a shared love for a particular genre or acollective experience at a concert, music has the ability to break down barriers and foster a sense of togetherness. It is a language that everyone can understand, regardless of their native tongue.Moreover, music has the ability to evoke strong emotions and memories. A single song can transport us back in time, evoking memories of past experiences and emotions. It has the power to make us laugh, cry, or feel a sense of nostalgia. It has the ability to capture the essence of a moment and preserve it forever in our hearts and minds.In addition, music has the power to inspire change and bring about social awareness. Throughout history, musicians have used their platform to raise awareness about important social issues and advocate for change. From Bob Dylan's protest songs to Beyoncé's empowering anthems, music has the ability to spark conversations and ignite movements. Ithas the power to give a voice to the voiceless and inspire individuals to take action.In conclusion, music is a powerful force that has the ability to transcend boundaries and connect people on a deeper level. It serves as a form of therapy, a means of unity, a source of emotional connection, and a catalyst for change. Whether we're singing in the shower or attending a live concert, music has the power to touch our souls and leave a lasting impact. So, let's embrace the power of music and let it guide us on our journey through life.。

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Usefulness of Intravascular Low-Power Laser Illumination in Preventing Restenosis After Percutaneous Coronary InterventionArkadiusz Derkacz,MD,PhD a,*,Marcin Protasiewicz,MD,PhD b,Rafal Poreba,MD,PhD a, Andrzej Szuba,MD,PhD a,and Ryszard Andrzejak,MD,PhD aDespite the several years of studies,no factor that could reduce the restenosis rate withoutsigniﬁcant limitations has been introduced.The aim of the present study was to evaluatethe inﬂuence of low-power808-nm laser illumination of coronary vessels after percutane-ous angioplasty in preventing restenosis.The procedure of laser intravascular illuminationwas performed on52patients(laser group),and another49patients formed the controlgroup.All patients were monitored for major adverse cardiac events(MACE)at the6-and12-month follow-up points.The MACE rate after6and12months was7.7%in the lasergroup at both points.The MACE rate was14.3%and18.5%at6and12months offollow-up in the control group,respectively(p؍NS).Follow-up coronary angiography wasperformed after6months.The difference in the restenosis rate was insigniﬁcant(15.0%vs32.4%);however,signiﬁcant differences were observed in the minimal lumen diameter(2.18؎0.70vs1.76؎0.74mm;p<0.05),late lumen loss(0.53؎0.68vs0.76؎0.76mm;p<0.01),and the late lumen loss index(0.28؎0.39vs0.46؎0.43;p<0.005)in favor of the lasergroup.In conclusion,the new therapy seemed effective and safe.Marked differencesbetween late loss,late loss index,and minimal lumen diameter were observed.The latelumen loss in the laser group was only slightly greater than that in studies of drug-elutingstents,and MACE rate remained within very comparable ranges.This suggests thatintravascular laser illumination could bring advantages comparable to those of drug-eluting stents without the risk of late thrombosis.©2010Elsevier Inc.All rights reserved.(Am J Cardiol2010;106:1113–1117)Restenosis represents the principal problem associated with the long-term efﬁcacy of percutaneous coronary inter-vention(PCI).The application of intravascular low-power laser illumination(LPLI)in PCI constitutes one of potential methods to reduce the occurrence of restenosis.The results of in vitro,1–3animal model,4,5and clinical studies6–9have seemed to conﬁrm the hypothesis and have pointed to the safety of such procedures in humans.The present study, conducted using randomized,angiographically controlled, clinical material,evaluated the efﬁcacy of LPLI in prevent-ing restenosis.MethodsAfter approval of the appropriate bioethical commission, the clinical study was performed on a group of patients with stable coronary heart disease who had undergone PCI.The lesion to be dilated was10to20mm long and involved native coronary arteries with a diameter notϽ2.5mm. Those with a totally occluded or left main artery and those with ostial,restenotic,thrombotic,or strongly calciﬁed le-sions were excluded from the present study.Balloon angio-plasty was performed in all patients.If the effect of the procedure was not satisfactory(Ͼ30%of residual stenosis), it was followed by bare metal stent implantation.The pos-sibility of drug-eluting stent implantation was not consid-ered.Directly after PCI,a single LPLI of the dilated vessel was performed.Patients with diabetes mellitus or diseases potentially restricting the survival period were excluded from the present study.The included patients were random-ized to the laser group or control group using a toss-up randomization process.A semiconductor laser with a diode pig-tailed using a lightﬁber(Optel,Opole,Poland)was used for the coronary illumination procedure.The laser was connected to a bal-loon catheter,with an in-built lightﬁber,through a submin-iature A(SMA905)ﬁber connector.Theﬁber was termi-nated with a special diffuser.10The diffuser,located at the distal end of the catheter with its20-mm,low-pressure balloon,made it possible to irradiate the coronary artery at the previously performed dilation point with uniform inten-sity(Figure1).Radiation with a808-nm wavelength,100 mW/cm2,and9J/cm2energy was applied in all cases.The method of intravascular illumination has been precisely described in previous publications.10–12To assess the restenosis rate,control angiography was performed6months after PCI.The analyzed variables in-cluded restenosis,late loss of vascular lumen(LLL),and the late lumen loss index(LLLI).At the6-and12-month follow-up points,all patients were monitored for majorDepartments of a Internal Medicine,Occupational Disease and Hyper-tension and b Cardiology,Wroclaw Medical University,Wroclaw,Poland.Manuscript received March9,2010;manuscript received and acceptedJune2,2010.This study was supported by grant4P05C04318from the Polish StateCommittee for Scientiﬁc Research,Warsaw,Poland.*Corresponding author:Tel:(ϩ48)71-784-2520;fax:(ϩ48)71-784-2527.E-mail address:aderkacz@chirs.am.wroc.pl(A.Derkacz).0002-9149/10/$–see front matter©2010Elsevier Inc.All rights doi:10.1016/j.amjcard.2010.06.017adverse cardiac events (MACE)—death,Q-and non–Q-wave myocardial infarction,coronary artery bypass graft-ing,and target vessel revascularization.Angioplasty and control angiography were conducted using the Innova 2000angiograph (GE Medical Systems,Fairﬁeld,Connecticut).Quantitative coronary angiographic calculations were per-formed with the investigator unaware of whether the patient had undergone laser illumination.All patients received acetylsalicylic acid at a dose of 75to 150mg/day and clopidogrel at a dose of 75mg/day Ն3days before PCI.After PCI,the patients received acetylsal-icylic acid,statins,angiotensin-converting enzyme inhibi-tors,␤blockers,and clopidogrel indeﬁnitely but for Ն2months.Just before the angioplasty procedure,the patients were given nonfractionated heparin in a single dose of 100IU/kg body weight.None of the patients received drugs blocking the glycoprotein IIb/IIIa platelet receptors.Statistical analysis was performed using Statistica,ver-sion 6.0(StatSoft,Krakow,Poland),statistical software.The arithmetic mean (X)and SD were calculated.When quantitative variables manifested normal distribution,the subsequent statistical analysis used Student’s t test or anal-ysis of variance.In the case of a distribution distinct from normal,the independent quantitative variables were ana-lyzed using the Mann-Whitney U test or the nonparametric equivalent of variance analysis,the Kruskal-Wallis analysis of variance test.Quantitative dependent variables were eval-uated using Wilcoxon’s test of pair sequences or the non-parametric variance analysis (Friedman’s analysis of vari-ance test).The chi-square test was used for independent qualitative variables and the McNemara test for dependent qualitative variables.Differences at p Ͻ0.05were consid-ered statistically signiﬁcant.ResultsThe study included 101patients.Of the 101patients,29underwent conventional balloon angioplasty and 72re-quired additional bare metal stent implantation.Intravascu-lar illumination was performed with LPLI in 52patients (laser group)and 49patients formed the control group.The demographic data between the 2groups were not signiﬁ-cantly different (Table 1).Moreover,the 2groups were not signiﬁcantly different in the type,spread,or degree of nar-rowing in the affected lesions,and no difference was seen in the stent implantation frequency or the ﬁnal effect of the procedure (Table 2).Figure 1.Scheme of device for intravascular laser illumination.Table 1Most important constitutional and clinical indexes in 2compared groups VariableLaser (n ϭ52)Control (n ϭ49)p Value Gender 0.583Women 1214Men4035Age (years)Total 57Ϯ1160Ϯ90.487Women 64Ϯ1263Ϯ90.746Men55Ϯ1057Ϯ90.348Myocardial infarction 0.742Total*3229In region supplied by dilated artery2926In another region63Canadian CardiovascularSociety class 0.644I 126II 2122III 1214IV77Arterial hypertension 24300.315Tobacco smoker34310.685*Patients who experienced cardiac infarction in past (in laser group 3persons experienced infarctions,in control group 1person experienced 2infarctions);determination of whether infarction developed in area supplied by dilated artery might have been only tentative in some cases.Table 2Most important indexes linked to angioplasty technique VariableLaser (n ϭ52)Control (n ϭ49)p Value Dilated coronary artery 0.215Left anterior descending 2923Left circumﬂex 1113Right1213Lesions supplied with stents 0.458Total3834Left anterior descending 2220Circumﬂex 77Right97Lesions supplied with balloons 0.227Total1415Left anterior descending 73Circumﬂex 46Right36Reference diameter of bloodvessel (mm)3.20Ϯ0.44 3.11Ϯ0.430.756Narrowing of blood vessel beforepercutaneous coronary intervention (%)74.1Ϯ14.072.4Ϯ12.80.712Lesion length (mm)13.6Ϯ5.012.0Ϯ3.10.695Narrowing of blood vessel afterpercutaneous coronary intervention (%)15.3Ϯ12.219.0Ϯ11.90.248Diameter of applied balloon (mm) 3.40Ϯ0.47 3.25Ϯ0.380.746Pressure used for balloon dilation(atm)15.3Ϯ3.614.7Ϯ3.50.648Length of applied stent (mm)19.2Ϯ5.517.6Ϯ5.60.3481114The American Journal of Cardiology ()At the6-month follow-up point,the total MACE rate was 7.7%in the laser group(3target vessel revascularizations and1non–Q-wave myocardial infarction).The total MACE rate was14.3%in the control group(5target vessel revas-cularizations,1death from myocardial infarction,and1 coronary artery bypass grafting).At the12-month point,the MACE rate remained unchanged in the laser group(7.7%). However,in the control group,the MACE rate had in-creased to18.4%(2additional coronary artery bypass graft-ing procedures;pϭNS).After6months,angiography was performed in the laser group in40patients(76.9%).An-giography showed restenosis in6patients(15.0%).In the control group,follow-up angiography was performed in37 patients(75.5%),and12(32.4%)had signs of restenosis. The difference between the2groups was insigniﬁcant.The remaining patients did not report angina complaints and did not agree to undergo follow-up angiography.Thus,6(11.5%)of 52patients in the laser group had developed angiographi-cally conﬁrmed restenosis and12(24.5%)of49patients in the control group had done so.The intergroup difference was insigniﬁcant.The average extent of narrowing did not differ signiﬁcantly between the2groups,either before or directly after PCI.However,the average percentage of nar-rowing on the follow-up angiogram was signiﬁcantly greater in the control group.The results obtained during from follow-up angiography were evaluated by dividing the laser and control groups into subgroups of those with and without restenosis.No signiﬁcant differences were detected between the subgroups without restenosis.In contrast,in the subgroups with restenosis,the narrowing within the lumen was signiﬁcantly more pronounced in the control group(no previous laser illumination;Table3).A comparison of the2groups did not reveal signiﬁcant differences in the minimal lumen diameter before or after the procedure nor in the average increase in vascular lumen after PCI.The same was observed when the groups were divided into the subgroups of balloon angioplasty versus stent implantation.In contrast,the minimal lumen diameter at follow-up angiography was signiﬁcantly greater in the laser group than in the control group.At follow-up angiog-raphy,the laser group also had a signiﬁcantly lower LLL and LLLI.The latter was signiﬁcantly smaller in both laser subgroups than in the control subgroups.The average val-ues of the vascular measurements are listed in Table4. DiscussionDespite the introduction of drug-eluting stents,restenosis and late thrombosis within the stent constitute a signiﬁcant clinical problem.13Studies published to date have empha-sized the beneﬁcial role of laser illumination in preventing restenosis,1–9although the mechanisms are not entirely known.The present study evaluated the inﬂuence of808-mn laser illumination on the frequency of restenosis after PCI.The808-nm laser wavelength used in our study was chosen because of the propagation of radiation in the blood, vessel walls,and surrounding tissues.14Moreover,the wavelength was selected because of its anti-inﬂammatory effect and the ability to stimulate endothelial renewal.15To date,632-nm wavelengths(helium–neon laser)3,6or650-nm wavelengths(semiconductor laser)5,7–9have been used in LPLI procedures.The radiation dose used in our studies could be perceived as being relatively high.It resulted from the requirement of a1-step illumination procedure.Several-fold repeated illu-mination procedures are known to provide the best effects; however,such procedures,which are relatively simple to conduct in easily accessible sites,cannot be applied intra-vascularly.The necessity for several-day maintenance of the artery access and the repetition of coronary vessel illumi-nation process would probably nullify the advantages re-lated to using the method because of the potential risk of complications.Table3Major adverse cardiac events(MACE)and mean extent of narrowing on follow-up coronary angiogram at6months,stratiﬁed by diagnosis of restenosisVariable Laser(nϭ52)Control(nϭ49)p ValueMean narrowing on angiogram(%)32.0Ϯ22.143.5Ϯ23.6Ͻ0.05 Patients with restenosis(%)59.1Ϯ22.071.8Ϯ16.3Ͻ0.01 Patients without restenosis(%)27.5Ϯ13.032.2Ϯ17.80.128 Major adverse cardiac eventsAt6months4(7.7%)7(14.3%)0.525 At12months4(7.7%)9(18.4%)0.266 Table4Vascular measurements before and after angioplasty and at follow-upVariable Laser(nϭ52)Control(nϭ49)p ValueDiameter of blood vessel(mm)Reference 3.20Ϯ0.44 3.11Ϯ0.430.459 Balloon 3.32Ϯ0.37 3.19Ϯ0.470.517 Stent 3.26Ϯ0.35 3.08Ϯ0.390.526 Minimal lumen diameter(mm)Before percutaneous coronaryintervention0.83Ϯ0.450.85Ϯ0.420.685Balloon0.84Ϯ0.380.85Ϯ0.610.595 Stent0.82Ϯ0.470.85Ϯ0.390.573 Minimum lumen diameter(mm)After percutaneous coronaryintervention2.71Ϯ0.38 2.52Ϯ0.370.314 Balloon 2.71Ϯ0.67 2.51Ϯ0.920.425 Stent 2.72Ϯ0.45 2.53Ϯ0.470.563 Minimal lumen diameter(mm)On follow-up angiogram 2.18Ϯ0.70 1.76Ϯ0.74Ͻ0.05 Balloon 2.18Ϯ0.41 1.75Ϯ0.120.075 Stent 2.19Ϯ0.27 1.76Ϯ0.820.088 Acute gain(mm)After percutaneous coronaryintervention1.88Ϯ0.68 1.67Ϯ0.730.462 Balloon 1.87Ϯ0.61 1.66Ϯ0.640.369 Stent 1.89Ϯ0.52 1.68Ϯ0.650.281 Late lumen loss(mm)At follow-up examination0.53Ϯ0.680.76Ϯ0.76Ͻ0.01 Balloon0.53Ϯ0.570.76Ϯ0.580.092 Stent0.53Ϯ0.690.77Ϯ0.750.072 Late lumen loss indexAt follow-up examination0.28Ϯ0.390.46Ϯ0.43Ͻ0.005 Balloon0.28Ϯ0.420.46Ϯ0.89Ͻ0.05 Stent0.28Ϯ0.370.46Ϯ0.73Ͻ0.051115Coronary Artery Disease/Laser Therapy in Restenosis PreventionFrom the available data,our study represents the only research in which the effectiveness of LPLI in preventing restenosis was controlled with a placebo group.The2com-pared groups had the same extent of arterial narrowing,both before and directly after the procedure.This not only em-phasizes the absence of differences in selecting the patients for each group,but also the lack of inﬂuence arterial illu-mination has on the direct outcome of PCI.Thisﬁnding supports the hypothesis that the differences observed at6 months of follow-up resulted from modifying the restenosis cascade with LPLI.The follow-up angiographic studies revealed more ex-tensive narrowing in the control group than in the laser group.This reﬂected not only the greater number of patients with restenosis in the control group,but also the more pronounced narrowing compared to the laser group.Simi-larly,the percentage of narrowing and the real size of the affected vessel on the follow-up angiogram disclosed a signiﬁcantly lower minimal lumen diameter and greater LLL and LLLI in the control group compared to the laser group.Of the40patients in the laser group who underwent follow-up angiography,restenosis was found in6(15.0%). Thus,considering all52patients in the laser group,the rate of restenosis was11.5%(6of52patients).We believe the real incidence of restenosis was probably between the2 values and approached11.5%,because those who had not undergone angiography at6months after PCI had not man-ifested any clinical signs of restenosis.Despite the insignif-icant differences in the rate of restenosis between the2 groups,a marked difference was noted in the rate of reste-nosis(15.0%of the laser group that underwent follow-up angiography compared to32.4%of the control group that had done so).It might be expected that a signiﬁcant differ-ence would have been detected between the2groups if more patients had been included in the study.The illumi-nation procedure was partially performed in patients who had undergone balloon angioplasty exclusively.No signif-icant differences were detected in the rate of restenosis, regardless whether the stent had been implanted within the lesion.The results might emphasize an additional advantage of LPLI,namely the reduction of restenosis after balloon angioplasty.16However,it is essential to remember that the lack of a difference in the restenosis rate between those with and without a vascular stent could have resulted from the relatively low number of treated patients.In2previous studies of650-nm laser light illumination in preventing restenosis,the restenosis rate was18.2%to 11.8%.7,9In those studies,the LLL was0.49and0.42mm, and the LLLI was0.21and0.27mm.The values did not vary much from present results in the laser group.The results were much better than those observed in our control group or previous studies,which appraised the values after bare metal stenting.Nevertheless,the LLL and LLLI were greater than those in studies evaluating theﬁrst-generation drug-eluting stents,which had a LLLϽ0.2mm.However, subsequent studies demonstrated a comparable or even greater LLL(0.61mm),even if a drug-eluting stent was used.17–19Also,the signiﬁcant difference in LLL among various types of drug-eluting stent has not translated into long-term efﬁcacy for the angioplasty procedure(as evalu-ated by MACE and target vessel revascularization).20The value of LLL in our study might suggest that,compared to bare metal stent implantation,LPLI could bring advantages comparable to that of some types of drug-eluting stents in preventing restenosis but free of the risk related to stent thrombosis owing to stent strut coverage with moderate neointimal hyperplasia.The6-and12-month observation showed that the new treatment method,in addition to its effectiveness in preventing restenosis,is safe,as character-ized by the very low MACE rate,comparable to the results from previous design studies.Study LimitationsThe present study included a relatively small and heter-ogenous(with or without a bare metal stent)group of patients(according to approval from the bioethics commit-tee).The inﬂuence of radiation in patients more threatened with restenosis(lesion type C,diabetes,ostial lesions)was not evaluated.An evaluation concerning the inﬂuence of LPLI on the frequency of restenosis and MACE after drug-eluting stent implantation would be interesting,although it would require entirely different examinations.1.Deckelbaum LI,Scott JJ,Stetz ML,O’Brien KL,Sumpio BE,MadriJA,Bell L.Photoinhibition of smooth muscle cell migration:potential therapy for sers Surg Med1993;13:4–11.2.Kipshidze N,Keelan M,Nikolaychik V.Impact of red light on reste-nosis.In:Waksman R,King S,Crocker I,Mould R,eds.Vascular Brachytherapy.Amsterdam:Nucleotron;1996:165–175.3.Kipshidze N,Nikolaychik V,Keelan MH,Shankar LR,Khanna A,Kornowski R,Leon M,Moses J.Low-power helium neon laser illu-mination enhances production of vascular endothelial growth factor and promotes growth of endothelial cells in sers Surg Med 2001;28:355–364.4.De Scheerder IK,Wang K,Zhou XR,Verbeken E,Keelan MH Jr,Horn JB,Sahota H,Kipshidze N.Intravascular low power red laser light as an adjunct to coronary stent implantation evaluated in a porcine coronary model.J Invas Cardiol1998;10:263–268.5.Kipshidze N,Sahota H,Komorowski R,Nikolaychik V,Keelan MHJr.Photoremodeling of arterial wall reduces restenosis after balloon angioplasty in an atherosclerotic rabbit model.J Am Coll Cardiol 1998;31:1152–1157.6.Kaul U,Singh B,Sudan D,Ghose T,Kipshidze N.Intravascular redlight therapy after coronary stenting—angiographic and clinical fol-low-up study in humans.J Invas Cardiol1998;10:534–538.7.De Scheerder I,Wang K,Nikolaychik V,Kaul U,Singh B,Sahota H,Keelan MH,Kipshidze N.Long-term follow-up after coronary stenting and intravascular red laser therapy.Am J Cardiol2000;86:927–930.8.De Scheerder IK,Wang K,Kaul U,Singh B,Sahota H,Keelan MH,Kipshidze NN,Moses J.Intravascular low-power laser illumination after coronary stenting:Long-term sers Surg Med2001;28:212–215.9.Derkacz A,Protasiewicz M,Kipshidze N,Bialy D,Poreba R,Beres-Pawlik E,Abramski K,Mazurek W.Endoluminal photo-therapy for prevention of restenosis.Preliminary result at6-month follow-up.Photomed Laser Surg2005;23:536–542.10.Pawlik E,Grobelny A,Palasz Z,Abramski K,Derkacz A,Bialy D,Protasiewicz M.Method of intravascular low power laser illumination.Opt Appl2001;31:761–767.11.Derkacz A,Bialy D,Protasiewicz M,Beres-Pawlik E,Abramski K.Intravascular low power laser light illumination—a new method in restenosis prevention.Proc SPIE2004;5505:51–55.12.Derkacz A,Bialy D,Protasiewicz M,Pawlik E,Abramski K,GrobelnyA,Palasz Z,Nowosad H.Photostimulation of coronary arteries with low power laser radiation:preliminary results for a new method in invasive cardiology therapy.Med Sci Monit2003;9:335–339.13.Jaffe R,Strauss te and very late thrombosis of drug-elutingstents:evolving concepts and perspectives.J Am Coll Cardiol2007;50:119–127.1116The American Journal of Cardiology()14.Hahn A.Optimalization of Laser Measuring Methods For Their Use inExtracorporeal Circulation.Wroclaw:Technical University of Wro-claw;1996:10–66.15.Almeida-Lopez L,Rigau J,Zangaro RA,Guidugli-Neto J,Jaeger MM.Comparison of low level laser therapy effects on cultured human gingivalﬁbroblast proliferation using different irradiance and same ﬂsers Surg Med2001;29:179–184.16.Faxon D.Restenosis:do we need to understand it to treat it?J Am CollCardiol2002;40:2090–2091.17.Morice MC,Serruys PW,Sousa JE,Fajadet J,Ban Hayashi E,Perin M,Colombo A,Schuler G,Barragan P,Guagliumi G,Molnar F,Falotico R.A randomized comparison of a sirolimus-eluting stent with a standard stentfor coronary revascularization.N Engl J Med2002;346:1773–1780.18.Fajadet J,Wijns W,Laarman GJ,Kuck KH,Ormiston J,Munzel T,Popma JJ,Fitzgerald PJ,Bonan R,Kuntz RE.Randomized,double-blind,multicenter study of the endeavor zotarolimus-eluting phospho-rylcholine-encapsulated stent for treatment of native coronary artery lesions:clinical and angiographic results of the ENDEAVOR II trial.Circulation2006;114:798–806.19.Mauri L,Orav EJ,O’Malley AJ,Moses JW,Leon MB,Holmes DR Jr,Teirstein PS,Schofer J,Breithardt G,Cutlip DE,Kereiakes DJ,Shi C, Firth BG,Donohoe DJ,Kuntz RE.Relationship of late loss in lumen diameter to coronary restenosis in sirolimus-eluting stents.Circulation 2005;111:321–327.20.Leon MB,Mauri L,Popma JJ,Cutlip DE,Nikolsky E,O’ShaughnessyC,Overlie PA,McLaurin BT,Solomon SL,Douglas JS,Ball MW, Caputo RP,Jain A,Tolleson TR,Reen BM,Kirtane AJ,Fitzgerald PJ, Thompson K,Kandzari DE.A randomized comparison of the EN-DEAVOR zotarolimus-eluting stent versus the TAXUS paclitaxel-eluting stent in de novo native coronary lesions12-month outcomes from the ENDEAVOR IV trial.J Am Coll Cardiol2010;55:543–554.1117Coronary Artery Disease/Laser Therapy in Restenosis Prevention。

S-011 Safety equipment data sheets

NORSOK STANDARDCOMMON REQUIREMENTSSAFETY EQUIPMENT DATA SHEETSS-011Rev. 2, August 1999This NORSOK standard is developed by NTS with broad industry participation.Please note that whilst every effort has been made to ensure the accuracy of this standard, neither OLF nor TBL or any of their members will assume liability for any use thereof. NTS is responsible for the administration and publication of this standard.Norwegian Technology Standards InstitutionOscarsgt. 20, Postbox 7072 MajorstuaN-0306 Oslo, NORWAYTelephone: + 47 22 59 01 00 Fax: + 47 22 59 01 29Email: norsok@nts.no Website: http://www.nts.no/norsokCopyrights reservedFOREWORDNORSOK (The competitive standing of the Norwegian offshore sector) is the industry initiative to add value, reduce cost and lead time and eliminate unnecessary activities in offshore field developments and operations.The NORSOK standards are developed by the Norwegian petroleum industry as a part of the NORSOK initiative and supported by OLF (The Norwegian Oil Industry Association) and TBL (Federation of Norwegian Manufacturing Industries). NORSOK standards are administered and issued by NTS (Norwegian Technology Standards Institution).The purpose of NORSOK standards is to contribute to meet the NORSOK goals, e.g. by replacing individual oil company specifications and other industry guidelines and documents for use in existing and future petroleum industry developments.The NORSOK standards make extensive references to international standards. Where relevant, the contents of a NORSOK standard will be used to provide input to the international standardisation process. Subject to implementation into international standards, the NORSOK standard will be withdrawn.INTRODUCTIONThe revision 2 of this document is an update of S-CR-001, Rev 1 issued December 1994.This standard outlines common requirements to data sheets for safety equipment as listed below. These data sheets should be used when enquiring, trading and purchasing such equipment.SDS-100Liferaft and Davit Data SheetSDS-101Firewater Monitors Data SheetSDS-102Firewater Hosereels w/nozzle Data SheetSDS-103Evacuation Chute Data SheetSDS-104Firewater Hydrant Data SheetSDS-105Fire fighting Cabinet Data SheetSDS-106Mob Equipment Station Data SheetSDS-107Lifejacket Cabinet Data SheetSDS-108Survival Suits Cabinet Data SheetSDS-109Fireman's Equipment Cabinet Data SheetSDS-110Firewater Valve Skid Data SheetSDS-111Portable Extinguisher Data SheetSDS-112Eye Bath Data SheetSDS-113Breathing Air Recharge Unit Data SheetSDS-114Personnel Basket Data SheetSDS-115Medical Basket Data SheetSDS-116Safety Station Cabinet Data SheetSDS-117Safety Shower/Eye Bath (outdoor) Data SheetSDS-118Lifeboat and Davit Data SheetMade by NORSOK LIFERAFT AND DAVIT Checked byS-011DATA SHEET DateRev. 2 Aug. 1999Data sheet SDS-100 Package no.Doc. no.Rev.Page 1 of 1Tag no. Location/moduleUnit No. req'dService Inquiry no.Size & type Quote no.Supplier P.O. no.Manufacturer Job no.Model Serial no.1 SERVICE CONDITIONS2 Blast pressure resistance:3 Electrical area hazard: Zone 1Gas/temp class: llA/T34:5:6 PERFORMANCE REQUIREMENTS7 Design standard: SOLAS 1983, NMD approved8 Capacity, no. of persons: 209 Marking of liferafts:10:11:12 WEIGHT AND DIMENSIONS13 Container dimensions (length x diameter)m:14 Weight raft kg:15:1617 WINCH:18Equip. No.:19Supplier/Type20Hoisting capacity Kg:21Hoisting height m:22Hoisting speed with max. load m/s:23Lowering speed m/s:24Drum details25WIRE ROPE AND HOOK26Diameter mm:27Core material28Wire material29Tensile strength Kg/mm2:30Total breaking load Kn:31Wire length32No. of falls33NOTES343536373839404142434445Made by NORSOK FIREWATER MONITORS Checked byS-011DATA SHEET DateRev.2 Apr. 1999Data Sheet SDS-101 Package no.Doc. no.Rev.Page 1 of 2Tag no. Location/moduleUnit No. req'dService Inquiry no.Size & type Quote no.Supplier P.O. no.Manufacturer Job no.Model Serial no.SECONDARY MANUFACTURER DATAPart Manufacturer Type Model Serial No NozzleAFFF Prop.1FLUID DATA2 AFFF::3 Temperature ºC:4 Viscosity at T & P cP:5 Density at T & P kg/m³:6 Specific gravity 15.6/15.6 ºC:7 :89PERFORMANCE REQUIREMENTS10 Firewater:11Available inlet pressure (design cond barg :12 Min inlet pressure barg :13 Max inlet presure barg :14 Design flow per outlet m³/h:15 Inlet flange size:16:17:18 AFFF::19 Design pressure barg :20 Design flow m³/h:21 Differential pressure req.:22 Inlet flange:23:24:25 NOTES:2627282930313233343536373839Made by NORSOK FIREWATER MONITORS Checked byS-011DATA SHEET DateRev.2. Apr. 1999Data sheet SDS-101 Package no.Doc. no.Rev.Page 2 of 242PERFORMANCE REQUIREMENTS(CONT.)43Monitor:44Throw at min inlet pressure m:45Rotation in degrees:46Vertical movement:47Lockable in any direction:48Remote release:49Self oscillating with adjustable setting degrees:50Colour: Red (RAL 3002)51:52Nozzle::53Type:54Connection:55Spray angle:56:57:58AFFF proportioner:59Proportion%:60Proportioning tolerance:61Differential pressure req.:62:63:64WEIGHT AND DIMENSIONS65Monitor:66Nozzle:67AFFF proportioner:68:69:70MATERIALS71Monitor:72Nozzle:73AFFF proportioner:74Paint coatings:75:76 NOTES:777879808182838485868788899091Made by NORSOK FIREWATER HOSEREELS W/NOZZLE Checked byS-011DATA SHEET DateRev. 2, Apr. 1999Data Sheet SDS-102 Package no.Doc. no.Rev.Page 1 of 1Tag no. Location/moduleUnit No. req'dService Inquiry no.Size & type Quote no.Supplier P.O. no.Manufacturer Job no.Model Serial no.1 SERVICE CONDITIONS2 Ambient temperature min/maxºC:3 Relative humidity%:4 Environment:5 Indoor/outdoor:6 PERFORMANCE REQUIREMENTS7 Available inlet pressure (design conditions) barg:8 Design temperature F.WºC:9 Design pressure barg:10 Min. Inlet pressure barg:11 Max. inlet pressure barg:12 Design flow per outlet m³/h:13 Inlet flange size:14 Hose length m:15 Throw length at min. inlet press.m:16 Throw length at available inlet pressure m17 Nozzle inlet pressure barg:18 Spray angleº:19 Cabinet: Red (RAL 3002)20 Winterization heater:21 Heater type:22 Heater rating:23 Heater maximum temperatureºC:24 Hinge details:25 Protection degree IP:26:27 WEIGHT AND DIMENSIONS28 Hose reel weight kg:29 Hose reel dimension (WxHxL)m:30 Hose diameter m:31 Support frame dim's (WxHxL)m:32 Cabinet dimensions (WxHxL)m:33:34 MATERIALS35 Hose:36 Nozzle:37 Cabinet:38 Support frame:39 Isolation valve:4041 LIFTING42 No. of lifting lugs support frame:43:44NOTES:4546Made by NORSOK EVACUATION CHUTE Checked byS-011DATA SHEET DateRev. 2, Apr. 1999Data Sheet SDS-103 Package no.Doc. no.Rev.Page 1 of 1Tag no. Location/moduleUnit No. req'dService Inquiry no.Size & type Quote no.Supplier P.O. no.Manufacturer Job no.Model Serial no.1 SERVICE CONDITIONS2 Electrical area hazard: Zone 1 Gas/temp class: llA/T33 Location open/exposed:4 PERFORMANCE REQUIREMENTS5 Special project requirements:6 Design standard - chute:7 Design standard - collection raft: SOLAS 1983/NMD Approved8 Design standard - container:9 Chute dimensions Length x Dia:10 Container dimensions LxWxH:11 Lowering height m:12 No. of persons/capacity collection raft: 2513 Weight (package)kg:14 Electrical power supply:15:16:17 MATERIALS18 Chute:19 Collection raft:20 Container:21 Painting: Yellow outside (RAL 1023) , White inside (RAL 9016).22:23:24 NOTES:25262728293031323334353637383940414243444546Made by NORSOK FIREWATER HYDRANT Checked byS-011DATA SHEET DateRev. 2, Apr. 1999Data Sheet SDS-104 Package no.Doc. no.Rev.Page 1 of 2Tag no. Location/moduleUnit No. req'dService Inquiry no.Size & type Quote no.Supplier P.O. no.Manufacturer Job no.Model Serial no.SECONDARY MANUFACTURER DATAPart Manufacturer Type Model Serial no Hydrant valveHoseHose couplingNozzleAFFF proportionerN2 press. system1SERVICE CONDITIONS2 Zone: Zone 1 Gas/temp. class:llA/T33 Explosion protection:4:5:6FLUID DATA7 AFFF:8 Temperature ºC:9 Viscosity at T & P cP:10 Density at T & P kg/m³:11 Specific gravity 15.6/15.6 ºC:12 Available inlet pressure (design conditions)barg:13:14:15PERFORMANCE REQUIREMENTS16 Firewater:17 Available inlet pressure (design conditions) barg :18 Min inlet pressure barg :19 Max inlet presure barg :20 Design flow per outlet m³/h:21 Inlet flange size:22:23:24:25 Hose (Common for FW/AFFF):26 Hose length m:27 Number off:28 Throw length at min. inlet press.m:29 Hose size mm:30 Nozzle inlet pressure barg:31 Hydrant/hose/nozzle:32:33:34:35 AFFF:36 Design pressure barg:37 Design flow m3/h:38 Inlet flange:Made by NORSOK FIREWATER HYDRANT Checked byS-011DATA SHEET DateRev. 2, Apr. 1999Data Sheet SDS-104 Package no.Doc. no.Rev.Page 2 of 240PERFORMANCE REQUIREMENTS (CONT)41 Hydrant valve:42 Turning direction for closing:43 Operating direction marked:44Colour: Red (RAL 3002)45 Nozzle:46 Spray angle:47:48 AFFF proportioner:49 Differential pressure req.50 Proportion%:51 Proportioning tolerance:52:53 Nitrogen pressurisation system54 Number of cylinders:55:56 Cabinet:57 Type:58 Winterization heater fitted:59 Heater type:60 Heater rating:61 Heater max. temperature ºC62 Door lock details:63 Hinge details:64 Hose cradle material:65 Hose cradle pivots:66 Protection degree IP:67Colour: Red (RAL 3002)68WEIGHT AND DIMENSIONS69 Hydrant valve:70 Hose:71 Hose coupling:72 Nozzle:73 Manifold:74 AFFF proportioner:75 Cabinet (LxWxH):76:77MATERIALS78 Hydrant valve:79 Hose :80 Hose coupling:81 Nozzle:82 Manifold:83 AFFF proportioner:84 Cabinet:85:86 NOTES:8788899091Made by NORSOK MOB - EQUIPMENT STATION Checked byS-011DATA SHEET DateRev. 1, Dec. 1994Data Sheet SDS-106 Package no.Doc. no.Rev.Page 1 of 1Tag no. Location/moduleUnit No. req'dService Inquiry no.Size & type Quote no.Supplier P.O. no.Manufacturer Job no.Model Serial no.QUANTITY1 Contents2 Rescue suits medium: 23 Rescue suits large: 24 Rescue suits extra large: 25 Wet gloves: 66 Lifejackets: 67 Rescue stretcher blanket: 18 Bags each containing: 29- 1 Off lifeline w/snap hook10- 1 Pair fins11- 1 Off diving knife12- 1 Off mask and snorkel13- 1 Off strobe light14- 1 Off waterproof torch15- 1 Off weight belt 6 kg16 Marking: MOB BÅT UTSTYR / MOB BOAT EQUIPMENT17 Painting: White RAL 900118:19:20 NOTES:212223242526272829303132333435363738394041424344454647Made by NORSOK LIFEJACKET CABINET Checked byS-011DATA SHEET DateRev. 2, Apr. 1999Data Sheet SDS-107 Package no.Doc. no.Rev.Page 1 of 1Tag no. Location/moduleUnit No. req'dService Inquiry no.Size & type Quote no.Supplier P.O. no.Manufacturer Job no.Model Serial no.1 CABINET2 No off lifejackets in each cabinet: (Insert actual number)3 Type and model:4 Material: Fire retardent GRP5 Length mm:6 Width mm:7 Height mm:8 Weight (empty)kg:9 Weight (including equipment)kg:10 Door size mm:11 Door opening angle min.º: Can be completely removed12 Door opens to: On top13 Marking: Redningsvester / Life jackets (Insert actual number)14 Painting: White RAL 901015 Degree of protection: IP 5516 Explosion blast pressure:17 Electric heater:18 Lighting:19 LIFEJACKETS20 Approving authority: NMD21 Type and model: "T-vesten"22 Fitted with whistle: YES23 Fitted with reflective strip: YES24 Marking according to NMD regulations:25 Fitted with light:26 Light type:27 Beacon (type):28 Sprayhood:29 Thigh strap :30 Twin chamber:31 Buoyancy N:32 NOTES:333435363738394041424344454647Made by NORSOK SURVIVAL SUITS CABINET Checked byS-011DATA SHEET DateRev. 2, Apr. 1999Data Sheet SDS-108 Package no.Doc. no.Rev.Page 1 of 1Tag no. Location/moduleUnit No. req'dService Inquiry no.Size & type Quote no.Supplier P.O. no.Manufacturer Job no.Model Serial no.1 CABINET2 No off survival suits in each cabinet: (Insert actual number)3 Type and model:4 Material: GRP Fire retardent5 Length mm:6 Width mm:7 Height mm:8 Weight (empty)kg:9 Weight (including equipment)kg:10 Door size mm:11 Door opening angle min.º: 27012 Door opens to: Both sides13 Marking: Redningsdrakter / Life suits (Insert actual number)14 Painting: White RAL 901015 Degree of protection: IP 5516 Explosion blast pressure:17 Electric heater:18 Lighting19 SURVIVAL SUITS20 Approving authority: NMD21 Type and model:22 Size: One size23 Marking according to NMD regulations:24 Fitted with light:No25 Attachments:26:27:28 NOTES:29303132333435363738394041424344454647Made by NORSOK FIREMANS EQUIPMENT CABINET Checked byS-011DATA SHEET DateRev. 2, Apr. 1999Data sheet SDS-109 Package no.Doc. no.Rev.Page 1 of 4Tag no. Location/moduleUnit No. req'dService Inquiry no.Size & type Quote no.Supplier P.o. no.Manufacturer Job no.Model Serial no.1DESIGN REQUIREMENTS2 Cabinet:3 Type and model:4 Material:5 Length mm:6 Width mm:7 Height mm:8 Weight (Empty)kg:9 Weight (Including equipment)kg:10 Door size mm:11 Door opening angle min.º: 27012 Door opens to: Both sides13 Marking according to:14 Painting according to: Red (RAL 3002)15 Electric heater: YES16 Lighting: YES17 Degree of protection: IP 5518 Explosion blast pressure:19 Marking: BRANNMANNS UTSTYR / FIREMANS EQUIPMENT20:21:22:23:24:25CONTENTS OF CABINET2627 Firemans suit with hood:28 No in cabinet: 429 Type, model and size:30 Material:31 Weight kg:32Approved by:33:34 Firemans helmet with visor:35 No in cabinet: 436 Type and model:37 Material:38 Weight kg:39 Approved by:4041 Firemans boots:42 No in cabinet: 443 Type and model:44 Material:45 Weight kg:46 Approved by:Made by NORSOK FIREMANS EQUIPMENT CABINET Checked byS-011DATA SHEET DateRev. 2, Apr. 1999Data sheet SDS-109 Package no.Doc. no.Rev.Page 2 of 448CONTENTS OF CABINET (CONT)4950 Gloves aluminized:51 No in cabinet: 452 Type and model:53 Material:54 Approved by:5556 Gloves electricians:57 No in cabinet: 458 Type and model:59 Material:60 Approved by:6162 Rescue belt:63 No in cabinet: 464 Type and model:65 Material:66 Weight kg:67 Approved by:6869 Breathing apparatus:70 No in cabinet: 471 Type and model:72 Material:73 Complete set weight kg:74 Mask type and model:75 Set stored dimensions mm:76 Number of cylinders per set:77 Nominal work duration:78 Operating temperature ºC:79 Approved by:8081 Air cylinders for breathing apparatus:82 No in cabinet: 1283 Type and model:84 Material:85 Weight kg:86 Dimensions (DxH)mm:87 Water capacity ltr:88 Air capacity ltr:89 Working pressure barg:90 Test presure barg:91 Approved by:9293 Radio sets:94 No in cabinet: 495 Type and model:96 Material:97 Weight kg:98 Electrical area hazard:99 Zone:100 Gas/temp class:101 Approved by:102:Made by NORSOK FIREMANS EQUIPMENT CABINET Checked byS-011DATA SHEET DateRev. 2, Apr. 1999Data Sheet SDS-109 Package no.Doc. no.Rev.Page 3 of 4103CONTENTS OF CABINET (CONT.)104105 Radio sets (cont.)106 Output power:107 Frequencies:108 Sensitivity:109 Modulation:110 Battery capacity:111112 Charger for radio sets:113 No in cabinet: 1114 Type and model:115 Dimensions (LxWxH)mm:116 Material:117 Weight kg118 Area classification119 Supply:120 Recharging time hr:121122 Torches:123 No in cabinet: 6124 Type and model:125 Material:126 Weight kg:127 Dimensions (LxWxH)mm:128 Electrical area hazard:129 Zone:130 Gas/temp class:131 Operation time hr:132 Recommended time between:133 Recharging (when not used):134135 Batteries for torches:136 Type and model:137 Battery charger supply:138139 Boiler suit with hood:140 No in cabinet: 4141 Type and model:142 Material:143 Weight kg:144 Approved by:145146 Rescue mask:147 No in cabinet: 2148 Type and model:149 Material:150 Weight kg:151 Approved by:152153 Body Line:154 No in cabinet: 4155 Type and model:156 Material:157:Made by NORSOK FIREMANS EQUIPMENT CABINET Checked byS-011DATA SHEET DateRev. 2, Apr. 1999Data Sheet SDS-109 Package no.Doc. no.Rev.Page 4 of 4 CONTENTS OF CABINET(CONT.)158 Body line (cont.)159 Weight kg:160 Approved by:161:162163 Force Tool:164 No in cabinet: 2165 Type and model:166 Material:167 Weight kg:168:169170 Stroke bar:171 No in cabinet: 2172 Type and model:173 Material:174 Weight kg:175:176177 Bolt cutter:178 No in cabinet: 2179 Type and model:180 Material:181 Weight kg:182:183184 NOTES:185186187188189190191192193194195196197198199200201202203204205206207208209210211212Made by NORSOK FIREWATER VALVE SKID Checked byS-011DATA SHEET DateRev. 2,Apr. 1999Data Sheet SDS-110 Package no.Doc. no.Rev.Page 1 of 2Tag no. Location/ModuleUnit No. req'dService Inquiry no.Size & type Quote no.Supplier P.O. no.Manufacturer Job no.Model Serial no.1SERVICE CONDITIONS2 Module/area protected:3 Explosion blast pressure:4 Electrical area hazard: Zone 1 Gas/temp class: II A/T35 Equipment designed according to:6:7:8PERFORMANCE REQUIREMENTS9 Design standard:10 Special project requirements:11 Design flowrate water m³/hr:12 Design flowrate foam m³/hr:13 Design downstream operating press.barg:14 Max. pressure downstream barg:15 Design upstream operating press. water barg:16 Design upstream max. pressure water barg:17 Design upstream operating press. foam barg:18 Design upstream max. pressure foam barg:19 Electric heater:20 Lighting:21 Foam mixing ratio:22 Required differential pressure foam prop. bar:23 Proportional tolerance foam prop:24Colour: Red (RAL 3002) 25:26WEIGHT27 Weight dry kg:28 Weight oper kg:29 Lifting lugs:30:31:32MATERIALS33 Deluge valve:34 Enclosure:35 Foam proportioning:36:37:38NOTES:3940414243444546Made by NORSOK FIREWATER VALVE SKID Checked byS-011DATA SHEET DateRev. 2,Apr. 1999Data sheet SDS-110 Package no.Doc. no.Rev.Page 2 of 248DIMENSIONS49A H50B I51C J52D K53E L54F M55G N5657NOZZLES5859MARK No.DN PN TYPE SERVICE6061626364656667686970 NOTES:717273Made by NORSOK PORTABLE EXTINGUISHER Checked byS-011DATA SHEET DateRev. 2, Apr. 1999Data Sheet SDS-111 Package no.Doc. no.Rev.Page 1 of 2Tag no. Location/moduleUnit No. req'dService Inquiry no.Size & type Quote no.Supplier P.O. no.Manufacturer Job no.Model Serial no.1DESIGN REQUIREMENTS2 Extinguisher:3 Charge capacity kg:4 Fire rating/class:5:6:7 Extinguishing agent:8 Type:9 Manufacturer:10 Trade name:11 Approvals:12:13:14WEIGHT AND DIMENSIONS15 Dimensions (DxH)mm:16 Total weight kg:17:18:19NOTES:202122232425262728293031323334353637383940414243444546Made by NORSOK PORTABLE EXTINGUISHER Checked byS-011DATA SHEET DateRev. 2, Apr. 1999Data Sheet SDS-111 Package no.Doc. no.Rev.Page 2 of 2 TAG Number AREA DESCRIPTION COMMENTSMade by NORSOK EYE BATH Checked byS-011DATA SHEET DateRev. 2, Apr. 1999Data Sheet SDS-112 Package no.Doc. no.Rev.Page 1 of 1Tag no. Location/moduleUnit No. req'dService Inquiry no.Size & type Quote no.Supplier P.O. no.Manufacturer Job no.Model Serial no.1 DESIGN REQUIREMENTS2 No off:3 Type :4 Weight kg: MDS:5 Material:6 Stay open valve:7 Method of valve opening:8 Max. working pressure barg:9 Min. working pressure barg:10 Test pressure barg:11 Flow rate m³/h:12 Water temperatureºC:13 Inlet connection diameter mm:14 Inlet connection type :15 Dimensions overall mm:16:17:18:19:20 NOTES:21222324252627282930313233343536373839404142434445Made byNORSOK BREATHING AIR RECHARGE UNIT Checked byS-011DATA SHEET Date Rev.2, Apr. 1999Data Sheet SDS-113 Package no.Doc. no.Rev.Page 1 of 1Tag no. Location/moduleUnit No. req'dService Inquiry no.Size & type Quote no.Supplier P.O. no.Manufacturer Job no.Model Serial no.1 DESIGN REQUIREMENTS2 Nominal capacity m³/hr: 19.23 Working pressure barg: 3004 Filling pressure barg:5 Power supply V: 6606 Power rating:7 Frequency Hz:8:9:10:11 CONSTRUCTION12 Classification::13 Length mm:14 Width mm:15 Height mm:16 Weight kg:17 Material:18 Surface protecton (panel):19 Surface protection (rack):20 Colour: GREY21 Approvals: Manufacturers Standard22:23:24:25 Air testing kit:26 Manufacturer:27 Model:28 Utility consumption:29 Approvals:30:31:32:33 NOTES:3435363738394041424344Made by NORSOK PERSONNEL BASKET Checked byS-011DATA SHEET DateRev. 2, Apr. 1999Data Sheet SDS-114 Package no.Doc. no.Rev.Page 1 of 1Tag no. 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Clamping eﬀects on the dynamic characteristics of compositemachine tool structuresHui Yun Hwang,Hak Gu Lee,Dai Gil Lee*Mechanical Design Laboratory with Advanced Materials,Department of Mechanical Engineering,ME3221,Korea Advanced Institute of Scienceand Technology,373-1Guseong-dong,Yuseong-gu,Daejeon 305-701,South KoreaAvailable online 2June 2004AbstractSubstituting composite structures for conventional metallic structures has many advantages for structural dynamic characteristics because composite materials have the higher speciﬁc stiﬀness and damping characteristics than conventional materials.However,the dynamic characteristics such as the fundamental natural frequency and damping of composite structures are inﬂuenced much by their joints.In this work,the eﬀects of clamping conditions on the dynamic characteristics of cantilever type composite machine tool structures with clamped joint were investigated to increase the natural frequency and damping of structures.In order to improve the shear property of the clamping part of composite machine tool bar,a new method for the clamping part was developed with metal core or sleeve inserted in the composite body at the clamping part.From the ﬁnite element and experimental results,suitable clamping conditions for the maximum dynamic stiﬀness were obtained for the composite structures with clamped joint.Ó2004Elsevier Ltd.All rights reserved.Keywords:Composite machine tool structures;Clamped joint;Clamping condition;Dynamic characteristics;Composite boring bar1.IntroductionSince the dynamic characteristics of carbon ﬁber composite structures are superior to conventional metallic structures due to the higher speciﬁc stiﬀness and damping characteristics of composite materials,they have been used in precise mechanical elements such as rollers for thin ﬁlm processing,machine tool spindles and power-transmission shafts of aircraft,ships and cars,which enables high operating speed and suppres-sion of the external or internal vibration [1–6].Espe-cially,composite tool bars such as boring bar or reaming bar have been successfully developed with high stiﬀness carbon ﬁber epoxy composites because the functional requirements of machine tool bars are higher operating speed and machining stability which can be satisﬁed simultaneously with the high stiﬀness carbon ﬁber epoxy composite [7,8].For the analysis of dynamic characteristics of struc-tures,ideal boundary conditions such as clamped,sim-ply supported or free conditions were considered [9,10].However,the exact estimation of clamping characteris-tics is essential for the dynamic characteristics such as the fundamental natural frequency and damping of structures because they are inﬂuenced much by their joints.In particular,the dynamic characteristics of ma-chine tool bars depend on the clamping conditions such as clamping force,stiﬀness and surface characteristics of clamping parts [11].Furthermore,the relatively large shear deformation of the clamping part due to the low shear modulus of composite materials decreases the fundamental natural frequency of the composite struc-tures,while it may increase the damping capacity of structures.Therefore,in this work,the clamping eﬀects on the dynamic characteristics of cantilever type com-posite machine tool bar were investigated because the cantilever type machine tool bars are suitable cases for composite application to increase the natural frequency and damping of structures.In order to increase the shear property of the clamping part of composite machine tool bar,a new method of clamping part was designed with metal core or sleeve inserted in the composite body at the clamping part.The fundamental natural fre-quency and damping ratio of circular shape composite *Corresponding author.Tel.:+82-42-869-3221;fax:+82-42-869-Composite Structures 66(2004)399–407/locate/compstructconditions such as the overhang length,clamping length,the dimension of metal core and sleeve,and properties of composite materials.From the results of the ﬁnite element analysis and the impulse response tests,suitable clamping conditions for the maximum dynamic stiﬀness,deﬁned as the product of the fundamental natural fre-quency and damping ratio,were obtained for the com-posite structures with clamped joint.2.Finite element analysis of the clamped jointThe cross-section of the circular shape composite bar,used in this work,consists of the permanent mandrel and the composite body as shown in Fig.1.The com-posite bar in Fig.1is the simplest design for composite tool bars,which could eliminate other eﬀects such as the constrained damping when adhesive joints exist,the structural damping due to the complicated shape and so on.In order to improve the shear properties of the clamping part and the dynamic characteristics of the composite bar,two types of the clamping part design,the sleeve type and the core type,were devised.The sleeve type clamping part as shown in Fig.2(a)has the steel sleeve outside the composite body in the clamping part,and the core type clamping part as shown in Fig.2(b)has the steel core between the composite body and the permanent mandrel in the clamping part.For two types of the clamping part design,the natural frequencywere obtained by ﬁnite element method using ABAQUS 6.3(Hibbitt,Karsson &Sorensen,USA)with respect to the clamping conditions.Mechanical properties of the permanent mandrel,the steel sleeve and core,and the epoxy adhesive for joining the steel sleeve or core to the clamping part were listed in Table 1.Parameters considered during the ﬁnite element analysis were overhang length (L ),clamping length (L c )and sleeve or core thickness (t )of composite bars,and tensile modulus (E 1)of composite materials.The shear modulus,Pois-son’s ratio and density of composite materials used were 5.5GPa,0.29and 1750kg/m 3,respectively.Finite ele-ment analysis results were represented by the funda-mental natural frequency (f )and the natural frequency ratio (f 0)as following equation:f 0¼f =f withoutsleeve or core :ð1Þ2.1.Sleeve type clamping partFig.3shows the ﬁnite element mesh for the modal analysis of the composite tool bar with the sleeve type clamping part.The 20-node three-dimensional solid elements (C3D20)of ABAQUS were used for the clamping part and overhang part near the clamping part,and the 8-node three-dimensional solid element (C3D8)of ABAQUS were used for the remained part.In the analysis,outer surface of the clamping part was ﬁxed as shown in Fig.3.Fig.4shows the ﬁnite element analysis results of composite bars with respect to the overhang length-to-diameter ratio (L =D )of the composite bar when the clamping length and tensile modulus were 50mm and 380GPa,respectively.The natural frequency ratio in-creased fast when the sleeve thickness-to-bar radius ratioTable 1Mechanical properties of the permanent mandrel,sleeve or core and epoxy adhesivePermanent mandrelSleeve/core Epoxy adhesive Material Lead Steel DP460,3M (USA)Tensile modulus (GPa)–207 2.5Poisson’s ratio –0.300.40Density (kg/m 3)11,40078601100400H.Y.Hwang et al./Composite Structures 66(2004)399–407(t=R)was less than0.3,and then decreased slowly.The natural frequency ratio was highest in the range of0.3–0.4of t=R for the considered L=D.The maximum value of the natural frequency ratio increased as the value of L=D decreased.Fig.5shows theﬁnite element analysis results of composite bars with respect to the clamping length-to-overhang length ratio(L c=L)of the composite bar when the overhang length and tensile modulus were250 mm and380GPa,respectively.Since the shear defor-mation at the clamping part decreased as the clamping length increased,the fundamental natural frequency of composite bars increased as L c=L increased as shown in Fig.5(a).For the small value of L c=L,the natural fre-quency ratio increased fast when the value of t=R was less than0.3,and then the ratio saturated.For the large value of L c=L,the natural frequency ratio increased fast when the value of t=R was less than0.3,and then de-creased slowly.The natural frequency ratio was highest in the range of0.4–0.5of t=R for large L c=L.The max-imum value of the natural frequency ratio increased asFig.6shows theﬁnite element analysis results of composite bars with respect to the shear modulus-to-tensile modulus ratio(G12=E1)of composite materials when the overhang length and clamping length were250 and30mm,respectively.For the large value of G12=E1, the natural frequency ratio increased fast when the value of t=R was less than0.3,and then increased slowly.For the small value of G12=E1,the natural frequency ratio increased fast when the value of t=R was less than0.3, and then decreased slowly.The natural frequency ratio was highest in the range of0.2–0.4of t=R for the small value of G12=E1.The maximum value of the maximum natural frequency ratio increased as the value of G12=E1 ratio increased.Additionally,the value of t=R at the maximum dynamic stiﬀness decreased from0.40to0.24 as the value of G12=E1decreased from0.014to0.009.2.2.Core type clamping partFig.7shows theﬁnite element mesh for the modalH.Y.Hwang et al./Composite Structures66(2004)399–407401clamping part.The20-node three-dimensional solid elements(C3D20)of ABAQUS were used for the clamping part and overhang part near the clamping part,and the8-node three-dimensional solid element (C3D8)of ABAQUS were used for the remained part. In the analysis,outer surface of the clamping part was ﬁxed as shown in Fig.5.Fig.8shows theﬁnite element analysis results of composite bars with respect to the overhang length-to-diameter ratio(L=D)of the composite bar when the creased fast when the value of t=R was less than0.3,and then decreased slowly when the value of t=R was over 0.5.The natural frequency ratio was highest in the range of0.4–0.5of t=R for the considered L=D.The maximum value of the natural frequency ratio increased as the value of L=D decreased.Fig.9shows theﬁnite element analysis results of composite bars with respect to the clamping length-to-overhang length ratio(L c=L)of the composite bar when the overhang length and tensile modulus were500mm and380GPa,respectively.For the small value of L c=L, the natural frequency ratio increased as the value of t=R increased.For the case of the value of L c=L of0.2,the natural frequency ratio increased fast when the value of t=R was less than0.4,and then the ratio saturated.The maximum value of the natural frequency ratio increased as the value of L c=L decreased.Fig.10shows theﬁnite element analysis results of composite bars with respect to the shear modulus-to-tensile modulus ratio(G12=E1)of composite materials402H.Y.Hwang et al./Composite Structures66(2004)399–407the natural frequency ratio increased as the value of t=R increased.For the small value of G12=E1,the natural frequency ratio increased fast when the value of t=R was less than0.4,and then decreased slowly.The natural frequency ratio was highest in the range of0.3–0.5of t=R for the small value of G12=E1.The maximum value of the maximum natural frequency ratio increased as the value of G12=E1decreased.Through theﬁnite element analysis of composite bars,it was found that the improvement of the natural frequency of composite bars with the sleeve type clamping part was higher than that of composite bars with the core type clamping part.The large clamping-to-overhang length ratio and small shear-to-tensile modulus ratio should be used in order to improve the natural frequency of composite tool bars.On the other hand,the maximum natural frequency ratio,i.e. improvement rate of the fundamental natural frequency, is higher when the length-to-diameter and the clamping-3.ExperimentalThe eﬀects of the clamping part conditions on the dynamic characteristics of the composite tool bar were measured by performing impulse response tests of composite tool bars.Since the composite bar with the sleeve type clamping part have higher improvement of the natural frequency than that with the core type clamping part,in the experiments,only the composite bar with the sleeve type clamping part was considered.3.1.Specimens and composite materialsFor the impulse response tests,composite tool bars as shown in Fig.2(a)were manufactured with various overhang length(L),clamping length(L c)and sleeve thickness(t).Composite bodies with the permanent mandrel were manufactured by autoclave vacuum bag degassing molding,and then the steel sleeves wereH.Y.Hwang et al./Composite Structures66(2004)399–407403materials were used for the diﬀerent shear-to-tensile modulus ratio (G 12=E 1).The mechanical properties of the carbon ﬁber epoxy composites were listed in Table 2.3.2.Impulse response testsFig.11shows the experimental set-up for the impulse response test of the composite bar.In order to give the same clamped joint conditions,the composite bar was joined to the ﬁxture by giving a same clamping torque on the bolts with a torque wrench.The impulse frequency responses were measured using an accelerometer (type 4374,B&K,Denmark),impact hammer (type 8202,B&K,Denmark),and FFT analyzer (type 3560C,B&K,Table 2Mechanical properties of carbon ﬁber epoxy composite materials Composite materialUSN 150SK chemicals,Korea URN 300SK chemicals,Korea HYEJ25M80D Mitsubishi chemical,Japan Longitudinal modulus,E 1(GPa)130380480Transverse modulus,E 2(GPa)8.2 5.1 5.2Shear modulus,G 12(GPa) 4.5 5.5 3.5Poisson’s ratio,m 120.280.290.27Density,q (kg/m 3)156017501750404H.Y.Hwang et al./Composite Structures 66(2004)399–407Denmark).The fundamental natural frequency and damping of composite tool bars were obtained through the analysis of impulse frequency responses.Then,dy-namic stiﬀness D,deﬁned as the product of the bending static stiﬀness K and the damping ratio f,which are ex-pressed in Appendix A,was calculated as follows[8]:D¼f K¼0:243L f f2ðq SÞequivð2Þwhere f andðq SÞequiv represent the fundamental naturalfrequency of the composite bar and the equivalent area density of the composite body,respectively.3.3.Impulse response test resultsFig.12shows the impulse response test results of the composite bar with respect to the overhang length-to-diameter ratio(L=D)of the composite bar when the clamping length and composite material were50mm and URN300(SK chemicals,Korea)whose tensile modulus is380GPa,respectively.The fundamental natural frequency of composite tool bars increased as the value of t=R increased below0.3,and then decreased as the value of t=R increased over0.4as shown Fig. 12(a).The maximum values of the natural frequency ratio(f0)were in the region of0.3–0.4of t=R,and in-creased as the value of L=D decreased as shown in Fig. 12(b).These results agreed well with theﬁnite element results.The damping ratio increased when the value of t=R was less than0.2,while it decreased as the value of t=R increased over0.2as shown in Fig.12(c).Since the epoxy adhesive used to join the composite body and sleeve plays a role of the viscoelastic material for the constrained damping,composite bars with the sleeve have higher damping compared with the composite bars without the sleeve[13].The dynamic stiﬀness,calculated from Eq.(2)using the measured natural frequencies and damping ratios,was highest in the range of0.1–0.2of t=R,which was inﬂuenced much by the damping ratio as shown in Fig.12(d).Fig.13shows the impulse response test results of the composite bar with respect to the clamping-to-overhang length ratio(L c=L)of the composite bar when the clamping length and composite material were250mm and URN300(SK chemicals,Korea)whose tensile modulus is380GPa,respectively.For the small value of L c=L,the fundamental natural frequency of composite tool bars increased as the value of t=R increased.On the other hand,for the large value of L c=L,the fundamental natural frequency of composite tool bars increased when the value of t=R was below0.4,and then saturated whenH.Y.Hwang et al./Composite Structures66(2004)399–407405the value of t=R was over0.5as shown in Fig.13(a).The maximum values of the natural frequency ratio(f0)were in the region of0.4–0.5of t=R for the large value of L c=L, and increased as the value of L c=L decreased as shown in Fig.13(b).These results agreed well with theﬁnite ele-ment results.The damping ratio increased when the value of t=R was less than0.2,while it decreased as the value of t=R increased over0.2as shown in Fig.13(c). The dynamic stiﬀness was highest in the range of0.1–0.4 of thickness-to-radius ratio,which was inﬂuenced much by damping ratio as shown in Fig.13(d).Additionally, the value of t=R at the maximum dynamic stiﬀness de-creased from0.40to0.16as the value of L c=L increased from0.04to0.20.Fig.14shows the impulse response test results of the composite bar with respect to the shear-to-tensile mod-ulus ratio(G12=E1)of the composite bar when the overhang length and clamping length were250and50 mm,respectively.For the value of G12=E1of0.035,i.e. low tensile modulus carbonﬁber epoxy composite material,the fundamental natural frequency ratio of composite tool bars increased slowly as the value of t=R increased.On the other hand,for the small value of below0.2,and then decreased when the value of t=R was over0.4as shown in Fig.14(b).The maximum values of the natural frequency ratio(f0)were in the region of0.2–0.4of t=R for the small value of G12=E1and increased as the value of G12=E1increased as shown in Fig.14(b). These results agreed well with theﬁnite element results. The damping ratio increased when the value of t=R was less than0.2,while it decreased when the value of t=R was over0.2as shown in Fig.14(c).The dynamic stiﬀ-ness was highest in the range of0.1–0.3of thickness-to-radius ratio,which was inﬂuenced much by damping ratio as shown in Fig.14(d).Through the impulse response tests,it was found that the higher dynamic stiﬀness of composite tool bars could be obtained when the clamping-to-overhang length ratio was larger,the shear-to-tensile modulus ratio was smaller,and the sleeve thickness-to-bar radius ratio was in the region of0.1–0.3.4.ConclusionIn this work,the eﬀects of clamping conditions on the406H.Y.Hwang et al./Composite Structures66(2004)399–407tigated.In order to overcome the low shear property of composite materials,two types of clamping part design, the sleeve type and core type,were devised.The dynamic characteristics of composite tool bar with the newly designed clamping parts were analyzed and tested through theﬁnite element method and the impulse re-sponse tests with respect to the clamping part conditions such as the overhang length,clamping length,dimension of sleeves and cores,and mechanical properties of composite materials.From impulse response tests,it was found that the tendency of the natural frequency ratio by impulse re-sponse tests was similar to that by theﬁnite element analysis.Also,the dynamic stiﬀness was inﬂuenced much by the damping ratio and was highest in the region of0.1–0.3of sleeve thickness-to-bar radius.Finally,the higher dynamic stiﬀness of composite tool bars could be obtained when the clamping-to-overhang length ratio was larger,the shear-to-tensile modulus ratio was smaller,and the sleeve thickness-to-bar radius ratio was in the region of0.1–0.3. AcknowledgementsThis work was supported in part by the National Research Laboratory Project of Ministry of Science and Technology and in part by the BK21Project of the Ministry of Education.Appendix AThe dynamic stiﬀness D of the composite bar with the clamped-free boundary condition in Eq.(2)can be cal-culated as shown below[8].The dynamic stiﬀness D of the composite bar with the clamped-free boundary condition can be calculated by employing the equivalent bending static stiﬀness K and the damping ratio f as follows:D¼f K¼f 3ðEIÞequivL3ðA:1ÞwhereðEIÞequiv and L represent the equivalent bendingstiﬀness and overhang length of the composite bar.The fundamental natural frequency of the composite bar with the clamped-free boundary condition can be obtained as follows[12]:f¼3:516L2ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃðEIÞequivðq SÞequivsðA:2Þðq SÞequiv¼ðq SÞcompositeþðq SÞmandrelðA:3Þwhereðq SÞequivrepresents the equivalent area density (density per unit length)of the composite bar.From Eqs.((A.1)–(A.3)),the dynamic stiﬀness D was calculated as follows using measurable parameters,the fundamental natural frequency f,damping ratio f,overhang length L and equivalent area densityðq SÞequiv:D¼f K¼0:243L f f2ðq SÞequivð2ÞReferences[1]Reinhart posites.ASM International;1987.[2]Lee DG,Kim KS,Kwak YK.Manufacturing of a SCARA typedirect-drive robot with graphite epoxy composite materials.Robotica1991;9:219–29.[3]Bang KG,Choi JK,Kim HS,Lee DG,Jeon HS.Development ofguide roller using electroplated carbonﬁber composite for thin polymerﬁlm pos Struct1997;38:321–8.[4]Choi JK,Lee DG.Manufacturing of a carbonﬁber–epoxycomposite spindle bearing system for a machine pos Struct1997;37:241–51.[5]Cho DH,Lee DG,Choi JH.Manufacturing of one-pieceautomotive drive shafts with aluminum and composite materials.Compos Struct1997;38:309–19.[6]Cheon SS,Lee DG,Jeong posite side door impact beamsfor passenger pos Struct1997;38:229–39.[7]Lee DG,Suh NP.Manufacturing and testing of chatter freeboring bars.Ann CIRP1988;37:365–8.[8]Lee DG,Hwang HY,Kim JK.Design and manufacturing of acarbonﬁber epoxy rotating boring pos Struct 2003;60:115–24.[9]Warburton GB.The dynamical behaviour of structures.Perg-amon Press,Inc.;1976.[10]Gorman DJ.Free vibration analysis of beams and shafts.JohnWiley&Sons,Inc.;1975.[11]Marul E,Hahimoto M,Kato S.Damping capacity of turningtools.Part1:eﬀect of clamping conditions and optimum clamping load.J Eng Ind1993;115:362–5.[12]Harris GM.Shock and vibration bandbook.McGraw-Hill;1988.[13]Nashif AD,Jones DI,Henderson P.Vibration damping.JohnWiley&Sons,Inc.;1985.H.Y.Hwang et al./Composite Structures66(2004)399–407407。

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bearing capacity of strip footings on a broken rock mass. These solutions are obtained using the numerical techni-ques developed by Lyamin and Sloan[1,2]which have been modiﬁed to incorporate the well-known Hoek–Brown yield criterion[7].The applicability and background of the Hoek–Brown criterion will be discussed in the following section in more detail.2.The generalised Hoek–Brown failure criterion2.1.ApplicabilityIt is well known that the strength of jointed rock masses is notoriously difﬁcult to assess.The behaviour of a rock mass is complicated greatly because deformations and sliding along naturally occurring discontinuities can occur in addition to deformations and failure in the intact parts (blocks)of the rock mass.Unfortunately,laboratory tests on speciﬁc core samples is often not representative of a rock mass atﬁeld scale,while in situ strength testing of the rock mass is seldom practically or economically feasible. Nonetheless,engineers and geologists are required to predict the strength of large-scale rock masses when designing such things as drifts,foundations,slopes,tunnels and caverns.Many criteria have been developed that seek to capture the important elements of measured rock strength or seek to modify theoretical approaches to accommodate experi-mental evidence.One currently accepted approach to estimating rock mass strength is to use the Hoek–Brown failure criterion where the required parameters are estimated with the help of a rock mass classiﬁcation system.The Hoek–Brown failure criterion is an empirical criterion developed through curve-ﬁtting of triaxial test data.It was originally developed in the1980s[8]for intact rock and jointed rock masses,and has been subject to continual reﬁnement[7].The Hoek–Brown criterion is one of the few non-linear criteria used by practising engineers [9]to estimate rock mass strength.It is therefore appropriate to use this yield criterion when predicting the bearing capacity of surface foundations on rock.It is important to note that the Hoek–Brown failure criterion,which assumes isotropic rock and rock mass behaviour,should only be applied to those rock masses in which there are a sufﬁcient number of closely spaced discontinuities,with similar surface characteristics,that isotropic behaviour involving failure on discontinuities can be assumed.When the structure being analysed is large and the block size small in comparison,the rock mass can be treated as a Hoek–Brown material.Where the block size is of the same order as that of the structure being analysed,or when one of the discontinuity sets is signiﬁcantly weaker than the others,the Hoek–Brown criterion should not be used.In these cases,the stability of the structure should be analysed by considering failure mechanisms involving the sliding or rotation of blocks and wedges deﬁned by intersecting structural features.With reference to the bearing capacity problem con-sidered herein,the applicability of the Hoek–Brown criterion is best described by referring to Fig. 1.After Hoek[10]it appears three main structural groups can be differentiated for rock masses,namely GROUP I,GROUP II,and GROUP III.Fig.1shows the transition from an isotropic intact rock(GROUP I),through a highly anisotropic rock mass(GROUP II),to an isotropic heavily jointed rock mass(GROUP III),with increasing sample size for a surface foundation on a hypothetical rock mass. Which of these structural groups will apply in a given case will depend on the width of the foundation relative to the discontinuity spacing,and the orientations and strengths of the discontinuities.In this paper it has been assumed that the underlying rock mass is either:(1)intact or;(2)heavily jointed with‘‘small spacing’’between discontinuities so that,on the scale of the problem,it can be regarded as an isotropic assembly of interlocking particles.Consequently, the results presented are valid for‘‘intact rock’’(GROUP I)and‘‘several discontinuities’’and‘‘jointed rock mass’’(GROUP III)conditions,respectively.The relative concept of‘‘small spacing’’as mentioned above,was proposed by Serrano and Olalla[11]as a means of quantifying the validity of using the Hoek–Brown failure criterion for bearing capacity predictions.A new para-meter,the‘‘spacing ratio of a foundation’’(SR)was proposed that depends,among other things,on the width of the foundation.It is deﬁned by the expression;SR¼BX ni¼11S mi¼BX ni¼1l i,where B is the foundation width;S mi is the joint spacing of the i th discontinuity family;l i is the frequency of the i th discontinuity family;and n is the number of discontinuity families.Serrano and Olalla suggest a relatively‘‘small spacing’’is whenðSRÞis greater than60.This would imply that there are four families of discontinuities each appearing15times across the foundation width.Therefore the Hoek–Brown criterion is not valid when SR o60, except when the value of SR is so low that the rock mass can be considered as intact and belonging to the aforementioned GROUP I.It should be noted that,in the case of intact rock (GROUP I),common sense needs to be exercised when using the results presented in this paper since the failure of the foundation may be brittle rather than plastic.The effect of scale on the bearing capacity of founda-tions on rock needs to be considered,particularly when the underlying assumption is that the rock mass behaves as a homogeneous isotropic continuous medium.There will be a distinct difference in the ultimate behaviour of‘‘large’’and‘‘small’’foundations.For the case of‘‘large’’founda-tions where the load covers an extensive area,a consider-able volume of the rock mass is affected and the stresses caused by gravity on the potentialﬂow surfaces are comparable to that part of the strength which is due toR.S.Meriﬁeld et al./International Journal of Rock Mechanics&Mining Sciences43(2006)920–937921the rock cohesion.In this case it seems reasonable toassume that such a problem can be studied using plasticitytheories.However,‘‘small’’foundations only inﬂuence asmall volume of the rock mass and the stresses caused byself-weight will be negligible when compared to thestrength of the rock.In this case the ultimate behaviourmay be brittle in nature and the theories of plasticity maynot be appropriate.Unfortunately,there is currently noguidance for engineers regarding what constitutes a ‘‘large’’or ‘‘small’’foundation.As pointed out by Serrano andOlalla [11]more research is required to quantify thisproblem.2.2.Limit analysis implementationOne of the key features of the Lyamin and Sloan [1,2]formulations is that they can deal with general yield criteriaincluding multi-surface ones where several convex domainsare combined to constrain the stresses at each node of themesh.These combinations can be different for differentparts of the discretised body.Because they are employed intheir native form,a wide range of yield criteria can be usedin the analysis.Each of the surfaces must be convex andsmooth but the resulting composite surface,thoughconvex,is generally non-smooth.An example of a multi-surface yield function is where the conventional (non-smooth)Tresca criterion is combined with a transition surface to round the corners in the octahedral plane.Another example is the use of a simple plane to cut the apex of a cone-like yield surface.This type of cut-off is often used for modelling materials such as rock,and leads to a cup-shaped surface.In this section,details of the latest version of the Hoek–Brown yield criterion [7]and how it has been incorporated into the limit analysis formulations of Lyamin and Sloan [1,2]are discussed.The Hoek–Brown failure criterion for rock masses was ﬁrst described in 1980[8]and has been subsequently updated in 1983,1988,1992,1995,1997,2001and 2002.A brief history of its development can be found in Hoek [12].The latest version that is used here can be written as s 01¼s 03þs ci m b s 03s 0ci þs a .(1)The relationships between m b =m i ,s and a and the geological strength index (GSI )are as follows:m b ¼m i exp GSI À10028À14D ,(2)s ¼exp GSI À1009À3D ,(3)GROUP IGROUP II GROUP III INTACTROCK JOINTED ROCKMASSSINGLE DISCONTINUITY TWO DISCONTINUITIES SEVERAL DISCONTINUITIES Jointed Rockci , GSI , m i ,Fig.1.Applicability of the Hoek–Brown yield criterion for shallow foundations.R.S.Meriﬁeld et al./International Journal of Rock Mechanics &Mining Sciences 43(2006)920–937922a ¼1þ1e ÀGSI =15Àe À20=3 .(4)The GSI was introduced because Bieniawski’s rock mass rating (RMR )system [13]and the Q-system [14]were deemed to be unsuitable for poor rock masses.The GSI ranges from about 10,for extremely poor rock masses,to 100for intact rock.The parameter D is a factor that depends on the degreeof disturbance.The suggested value of the disturbance factoris D ¼0for undisturbed in situ rock masses and D ¼1fordisturbed rock mass properties.For the analyses presentedhere,a value of D ¼0has been adopted.The unconﬁned compressive strength is obtained bysetting s 3¼0in Eq.(1),givings c ¼s ci s a(5)and the tensile strength iss t ¼Às s ci m b .(6)In a similar manner to the Mohr–Coulomb failure envelope,the Hoek–Brown yield surface has apex and corner singularities in stress space.The direct computation of the derivatives at these locations,which are required for1.00.90.80.70.60.50.40.30.20.10.0× 10−3J 2I 1 × 10−3√Fig.2.Meridian plane section of Hoek–Brown yield surface and its smoothapproximation.Q = q u BfFig.3.Problem deﬁnition.R.S.Meriﬁeld et al./International Journal of Rock Mechanics &Mining Sciences 43(2006)920–937923the non-linear programming (NLP)solver,becomesimpossible.This issue can be resolved using three differentapproaches;namely,global smoothing,local smoothingand multi-surface representation (which includes both apriori and dynamic linearisation).As the current study islimited to the case of plain strain conditions,the cornersare automatically avoided and the only singularity whichneeds to be dealt with is the apex of the yield surface.The easiest options to implement are a simple tension cut-off (which is a multi-surface technique)or a quasi-hyperbolic approximation (which is a global smoothing technique).The authors decided to adopt the later approach as a similar method has been previously employed by Abbo and Sloan [15]for smoothing the Mohr–Coulomb yield criteria.The preﬁx ‘‘quasi’’is used here because the Hoek–Brown yield surface is already curved in the meridional plane and the suggested approx-imation is not a pure hyperbolic one.A brief description of the procedure is provides as follows (more details can be found in [15]).ZONE I ZONE II ZONE Iq u q u = [s a + (m b s a + s )a ] ciQ us a ci s a ci s a ciBFig.4.Lower bound solution for bearing capacity (after Kulhawy and Carter[20]).141210864N 20.00010.00100.01000.1000 1.0000ζn Fig.5.Bearing capacity factor for weightless rock (after Serrano et al.[24]).R.S.Meriﬁeld et al./International Journal of Rock Mechanics &Mining Sciences 43(2006)920–937924First,the Hoek–Brown yield function given in Eq.(1)is expressed in terms of stress invariants asf HB¼ﬃﬃﬃﬃﬃJ2pgðyÞþﬃﬃﬃﬃﬃJ2phðyÞþb I1þwa,(7)where I1is theﬁrst stress invariant,J2is the second deviatoric stress invariant and y is the Lode angle related to the third deviatoric stress invariant J3,whereas parameters b and w,and functions gðyÞand hðyÞare given by the following expressions:gðyÞ¼À2cosðyÞ,(8)hðyÞ¼Àm b sð1ÀaÞ=acicosðyÞþsinðyÞﬃﬃﬃ3p,(9)b¼m b sð1ÀaÞ=aci,(10)w¼s s1=aci.(11)Next,quasi-hyperbolic smoothing is applied by permutingJ2with a small term according to^J2¼ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃJ2þ 2p,(12)on condition that is related to the tensile strength ofmaterial by the rule¼minðd;mr j r gð0Þþðr hð0ÞþwÞa¼0Þ.(13)The constants d and m must be chosen to balance theefﬁciency of the NLP solver against the accuracy of theSee insetFig.6.Typicalﬁnite element mesh.R.S.Meriﬁeld et al./International Journal of Rock Mechanics&Mining Sciences43(2006)920–937925representation of the original yield surface.The values usedin the current study are d ¼10À6and m ¼10À1.The resulting approximation of the Hoek–Brown yieldcriterion can be written asf HB ¼^J 2g ðy Þþ^J 2h ðy Þþb I 1þw ÀÁa (14)and is now a smooth and convex function in the meridionalplane.An illustration of the original and smoothed Hoek–Brown curves in the ðI 1;ﬃﬃﬃﬃﬃJ 2p Þplane for zero y isgiven in Fig. 2.It should be noted that the differencebetween the smooth approximation and the original yieldsurface has been greatly exaggerated in this ﬁgure byselecting values of m and r that are much larger than whatwas actually adopted.The original and smoothed yieldsurfaces are almost indistinguishable when the actualvalues of m and r are used.2.3.Equivalent Mohr–Coulomb parametersSince many geotechnical analysis methods still use theMohr–Coulomb failure criterion,it is sometimes necessaryfor practising engineers to determine equivalent angles offriction and cohesive strengths for each rock mass andstress range.In the context of this paper,estimating theseequivalent parameters will enable a direct comparison to bemade between Hoek–Brown solutions and equivalent Mohr–Coulomb solutions.The choice of method to use for determining equivalent cohesion and friction angle is largely a matter of taste and experience.An equivalent cohesion and friction angle at a speciﬁed normal stress or minor principal stress,as determined by an elastic analysis,may give locally accurate values for a small stress variation.Alternatively,average values applicable to a wider range of stress conditions may be obtained by using a regression procedure.However,this may lead to an underestimate of the strength for low stresses and an overestimate for high stresses.Nonetheless,a regression approach appears to be the most widely accepted method and is typically performed by ﬁtting a linear relationship to the curve generated by Eq.(1)for a range of minor principal stress values deﬁned by s t o s 3o s 03max .This has been performed recently by Hoek et al.[7]where the ﬁtting process involves balancing the areas above and below the Mohr–Coulomb relation.This results in the following equations for the angle of friction and cohesive strength:c 0¼s ci ½ð1þ2a Þs þð1Àa Þm b s 03n ðs þm b s 03n Þa À1ð1þa Þð2þa Þﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ1þð6a m b ðs þm b s 03n Þa À1Þ=ð1þa Þð2þa Þq ,(15)Table 1Values of the bearing capacity factor for a weightless rockGSIm i N s 0Average N s 0Kulhawy and Carter [20]N s 0Serrano et al.[24]GSI m i N s 0Average N s 0Kulhawy and Carter [20]N s 0Serrano et al.[24]1010.0150:009ðÀ40%Þ0:010ðÀ35%Þ6010.4650:299ðÀ36%Þ0:458ðÀ1%Þ1050.0420:016ðÀ61%Þ0:035ðÀ17%Þ605 1.0130:479ðÀ53%Þ1:006ðÀ1%Þ10100.0770:022ðÀ71%Þ0:072ðÀ7%Þ6010 1.5970:623ðÀ61%Þ1:588ðÀ1%Þ10200.1560:032ðÀ80%Þ0:159ðþ2%Þ6020 2.6670:830ðÀ69%Þ2:658ð0%Þ10300.2380:039ðÀ83%Þ0:259ðþ9%Þ6030 3.6440:990ðÀ73%Þ3:673ðþ1%Þ10350.2880:043ðÀ85%Þ0:314ðþ9%Þ6035 4.1861:060ðÀ75%Þ4:170ð0%Þ2010.0440:026ðÀ41%Þ0:036ðÀ16%Þ7010.7650:503ðÀ34%Þ0:759ðÀ1%Þ2050.1190:046ðÀ61%Þ0:111ðÀ6%Þ705 1.5820:785ðÀ50%Þ1:574ðÀ1%Þ20100.2090:062ðÀ70%Þ0:204ðÀ2%Þ7010 2.4441:012ðÀ59%Þ2:434ð0%Þ20200.3890:086ðÀ78%Þ0:397ðþ2%Þ7020 4.0121:339ðÀ67%Þ3:998ð0%Þ20300.5750:106ðÀ82%Þ0:600ðþ4%Þ7030 5.4911:592ðÀ71%Þ5:470ð0%Þ20350.6700:114ðÀ83%Þ0:704ðþ5%Þ7035 6.0681:703ðÀ72%Þ6:187ðþ2%Þ3010.0920:054ðÀ41%Þ0:084ðÀ8%Þ801 1.2600:847ðÀ33%Þ1:254ðÀ1%Þ3050.2350:095ðÀ60%Þ0:227ðÀ3%Þ805 2.4731:284ðÀ48%Þ2:463ð0%Þ30100.3970:127ðÀ68%Þ0:393ðÀ1%Þ8010 3.7451:640ðÀ56%Þ3:732ð0%Þ30200.7130:174ðÀ76%Þ0:716ð0%Þ8020 6.0402:154ðÀ64%Þ6:019ð0%Þ3030 1.0220:210ðÀ79%Þ1:038ðþ2%Þ80308.1952:553ðÀ69%Þ8:171ð0%Þ3035 1.1930:226ðÀ81%Þ1:200ðþ1%Þ80359.2422:727ðÀ70%Þ9:210ð0%Þ4010.1650:101ðÀ39%Þ0:158ðÀ4%Þ901 2.0831:428ðÀ31%Þ2:076ð0%Þ4050.4010:171ðÀ57%Þ0:393ðÀ2%Þ905 3.8812:102ðÀ46%Þ3:869ð0%Þ40100.6590:226ðÀ66%Þ0:654ðÀ1%Þ9010 5.7582:658ðÀ54%Þ5:741ð0%Þ4020 1.1490:306ðÀ73%Þ1:147ð0%Þ90209.1253:466ðÀ62%Þ9:100ð0%Þ4030 1.6300:368ðÀ77%Þ1:626ð0%Þ903012.2704:092ðÀ67%Þ12:237ð0%Þ4035 1.8730:395ðÀ79%Þ1:863ðÀ1%Þ903513.7944:367ðÀ68%Þ13:738ð0%Þ5010.2810:176ðÀ37%Þ0:274ðÀ3%Þ1001 3.4612:414ðÀ30%Þ3:449ð0%Þ5050.6440:290ðÀ55%Þ0:638ðÀ1%Þ1005 6.1243:449ðÀ44%Þ6:114ð0%Þ5010 1.0370:380ðÀ63%Þ1:031ðÀ1%Þ100108.8964:317ðÀ51%Þ8:875ð0%Þ5020 1.7650:510ðÀ71%Þ1:760ð0%Þ1002013.8475:583ðÀ60%Þ13:809ð0%Þ5030 2.4670:610ðÀ75%Þ2:458ð0%Þ1003018.4446:568ðÀ64%Þ18:390ð0%Þ5035 2.8170:654ðÀ77%Þ2:801ðÀ1%Þ1003520.6687:000ðÀ66%Þ20:628ð0%ÞR.S.Meriﬁeld et al./International Journal of Rock Mechanics &Mining Sciences 43(2006)920–937926f 0¼sin À16a m b ðs þm b s 03n Þa À12ð1þa Þð2þa Þþ6a m b ðs þm b s 03n Þ"#,(16)where s 3n ¼s 03max =s ci .Note that the value of s 03max ,the upper limit of conﬁningstress over which the relationship between the Hoek–Brownand the Mohr–Coulomb criteria is considered,has to bedetermined for each individual case.Of course it is likelythat the stresses will vary greatly throughout the rock masswhich will make it difﬁcult to select a representative value ofs 03max .As far as the authors are aware,there are notheoretically correct methods for choosing this range and atrial and error method,based upon practical compromise,is suggested by Hoek [16].From experience and trial and error,Hoek and Brown [17]suggest a value of s 03max ¼0:25s ci will provide consistent results.More speciﬁc guidance is provided by Hoek [16]for selecting appropriate values of s 03max speciﬁcally for tunnels and slopes.However,no guidance is provided for the case of a surface footing.3.Problem deﬁnition The plane strain bearing capacity problem to be considered is illustrated in Fig.3.A strip footing of width B rests upon a jointed rock mass with an intact uniaxial compressive strength s ci ,geological strength index GSI ,2.82.42.01.6N o N o 1.20.80.422201816141210864200.0051015202530GSI = 50GSI = 40GSI = 30GSI = 100GSI = 90GSI = 80GSI = 70GSI = 60GSI = 20GSI = 1035m i 05101520253035m iFig.7.Bearing capacity factor for weightless rock.R.S.Meriﬁeld et al./International Journal of Rock Mechanics &Mining Sciences 43(2006)920–937927rock mass unit weight g ,and intact rock yield parameterm i .The ultimate capacity can be written asq u ¼s ci N s ,(17)where N s is deﬁned as the bearing capacity factor.For a weightless rock mass ðg ¼0Þ,the above expression is valid but the bearing capacity factor N s is replaced with N s 0.The form of Eq.(17)is a convenient way of expressing the ultimate bearing capacity as a ‘‘fraction’’of the uniaxial compressive strength and is historically consistent with previous bearing capacity representations.In the following,the ultimate bearing capacity will be estimated for a practical range of GSI ,g and m i values.4.Previous studiesA review of the literature reveals that very few thoroughnumerical analyses have been performed to determine theultimate bearing capacity of shallow foundations on rock.Of the numerical studies that have been presented,few canbe considered as rigorous.The ultimate tip bearingcapacity of pile foundations,on the other hand,has m i = 1m i = 1m i = 5m i = 10m i = 10m i = 30GSI = 20GSI = 50Fig.8.Upper bound velocity ﬁelds and plastic zones for weightless rock.R.S.Meriﬁeld et al./International Journal of Rock Mechanics &Mining Sciences 43(2006)920–937928received much more attention and is discussed by Serranoand Olalla [11,18].Carter and Kulhawy [19]and Kulhawy and Carter [20]proposed a simple lower bound solution for the bearingcapacity of a weightless rock mass obeying a non-linearHoek–Brown yield criterion.The details of the lowerbound stress ﬁeld are shown in Fig.4.A lower bound tothe failure load q u is calculated by ﬁnding a stress ﬁeld thatsatisﬁes both equilibrium and the failure criterion.Therock mass beneath the strip footing is divided into twozones as shown.The vertical stress s 3in zone I is assumedto be zero (weightless),while the horizontal stress ðs 1Þisequal to the unconﬁned compressive strength of the rockmass,as given by Eq.(5).For equilibrium,continuity ofthe normal stress across the discontinuity between the zones must be maintained.The bearing capacity of the strip footing may thus be evaluated from Eq.(1)(with s 3¼s a s ci )as q u ¼½s a þðm b s a þs Þa s ci ,(18)which to be consistent with Eq.(17)can be written as q u ¼N s 0s ci ,where N s 0¼½s a þðm b s a þs Þa (19)is the bearing capacity factor for a weightless rock mass as deﬁned previously.0.90.80.70.60.5NN0.40.30.20.10.01.41.21.00.80.60.40.20.0510152025303540m i 510152025303540m i= 125= 125(a)(b)Fig.9.Average ﬁnite element limit analysis values of the bearing capacity factor N s .R.S.Meriﬁeld et al./International Journal of Rock Mechanics &Mining Sciences 43(2006)920–937929Eq.(18),along with the categories of rock type and rock mass condition presented by Hoek [10],have been used to produce guidelines for estimating the bearing capacity of rock masses [21].Serrano and Olalla [22,23]and Serrano et al.[24]proposed a method for estimating the ultimate bearing capacity for a strip footing on a weightless rock mass with or without a surface surcharge.The method is based upon the slip-line method developed by Soko-lovskii [25].The ultimate bearing capacity q u ,as proposed by Serrano et al.[24]using the Hoek–Brown criterion presented by Hoek et al.[26],is expressed as q u ¼P h ¼b n ðN b Àz n Þ,(20)where z n and b n are constants for the rock mass and depend on m b ,a ,s and s ci according toA n ¼m b ð1Àa Þ2a =ð1Àa Þ;b n¼A n s ci ;z n ¼sm b A n .z n is referred to as the ‘‘rock mass toughness’’while b n isreferred to as the ‘‘strength modulus’’[27,28].N b is a function of the normalised external load on the boundary adjacent to the footing.If there is no surface surcharge on this boundary,then N b can be determined using the method outlined by Serrano and Olalla [22]and is shown graphically in Fig. 5.Note that this ﬁgure has been produced using the most recent version of the Hoek–Brown yield criterion,and not the earlier version [26]used in the paper by Serrano et al.[24].2.01.81.61.41.21.00.80.60.40.20.02.82.42.01.61.20.80.40.0m iNN= 125= 10000(a)More recently,Xiaoli et al.[29]formulated an analytical lower bound for the bearing capacity of a strip footing resting on a Hoek–Brown material.Very few results,however,were presented.5.Results and discussionThe computed upper and lower bound estimates of the bearing capacity factor N s for both the weightless and ponderable rock analyses were found to be within 5%of each other.This indicates that,for practical design purposes,the true collapse load has been bracketed to within Æ2:5%or better.As a consequence,average values of the upper and lower bound bearing capacity factor have been calculated and will be used in the following discussions.Typical upper and lower bound meshes for the problem,along with the applied stress and velocity boundaryconditions,are shown in Fig.6.The results presented are for the case of a perfectly rough rigid footing.For the lower bound,this boundary condition is achieved by assuming the individual normal stresses at element nodes on the soil/footing interface are unrestricted in magnitude.In the upper bound case,a uniform velocity is prescribed for all the nodes along the footing.The overall upper bound and lower bound mesh dimensions were selected such that they adequately contained all plastic zones.5.1.Weightless rock massesFor the weightless rock case the bearing capacity factor has been deﬁned as N s 0.The average upper and lower bound estimates of N s 0are summarised in Table 1and Fig.7for a range of GSI and m i values.As expected,for a given GSI ,increasing m i leads to an increase in the ultimate4.03.52.53.02.01.51.00.50.06543210510152025303540m i510152025303540NN= 125ci Bci B= 10000(a)bearing capacity.Fig.7indicates that N s 0increases non-linearly with m i and GSI .Fig.8presents several of the observed upper bound velocity ﬁelds and plastic zones.For a given GSI ,as m i increases,so does the extent of the observed velocity ﬁeld and zone of plastic yielding.This is expected as an increase in m i will,in essence,increase the strength of the rock and the equivalent Mohr–Coulomb parameters.Interestingly the same effect is not observed when,for a given m i ,an increase in GSI leads to a reduction in the extent of both the velocity ﬁeld and zone of plastic shearing.5.2.Rock masses with unit weightThe effect of rock weight and rock strength has been incorporated in the analyses using the non-dimensionalfactor s ci =g B which varies between 125and 10000.This range will cover most problems of practical interest.The average upper and lower bound estimates of the bearing capacity factor N s are summarised in Figs.9–12for a range of GSI and m i values.For a given GSI ,increasing m i leads to an almost linear increase in the bearing capacity factor N s .Referring to the above ﬁgures,the effects of including self-weight in the analyses may be explained as follows.For any given rock mass ðs ci ;GSI ;m i Þand foundation width B (i.e.s ci =B ¼constant),the addition of self-weight g (i.e.decrease in the ratio s ci =g B )will lead to an increase in the bearing capacity factor N s and thus the ultimate bearing capacity.That is,the bearing capacity factor for a weightless rock N s 0is always less than the bearing capacity factor N s for a rock with unit weight ðN s X N s 0Þ.The effect of a small increase or decrease in the estimated rock weight121086420m i510152025303540NN= 125= 10000= 125= 10000(a)。