2005 JB---Induction of rapid detachment in Shewanella oneidensis MR-1 biofilms

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2005 Decoding by Linear Programming

IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. 51, NO. 12, DECEMBER 20054203Decoding by Linear ProgrammingEmmanuel J. Candes and Terence TaoAbstract—This paper considers a natural error correcting problem with real valued input/output. We wish to recover an from corrupted measurements . input vector Here, is an by (coding) matrix and is an arbitrary and unknown vector of errors. Is it possible to recover exactly from the data ? We prove that under suitable conditions on the coding matrix , the input is the unique solution to the 1 -minimization problem ( )=+:=min : =0 0provided that the support of the vector of errors is not too large, for some . In short, can be recovered exactly by solving a simple convex optimization problem (which one can recast as a linear program). In addition, numerical experiments suggest that this recovery procedure works unreasonably well; is recovered exactly even in situations where a signiﬁcant fraction of the output is corrupted. This work is related to the problem of ﬁnding sparse solutions to vastly underdetermined systems of linear equations. There are also signiﬁcant connections with the problem of recovering signals from highly incomplete measurements. In fact, the results introduced in this paper improve on our earlier work. Finally, underlying the success of 1 is a crucial property we call the uniform uncertainty principle that we shall describe in detail.:=Index Terms—Basis pursuit, decoding of (random) linear codes, duality in optimization, Gaussian random matrices, 1 minimization, linear codes, linear programming, principal angles, restricted orthonormality, singular values of random matrices, sparse solutions to underdetermined systems.linear code; a linear code is a given collection of codewords —the columns of the mawhich are vectors trix . We would like to emphasize, however, that there is a clear distinction between our real-valued setting and the ﬁnite alphabet one which is more common in the information theory (the “plaintext”) we can then literature. Given a vector in (the “ciphertext”); if has full rank, generate a vector then one can clearly recover the plaintext from the ciphertext . But now we suppose that the ciphertext is corrupted by giving rise to the corrupted cipheran arbitrary vector . The question is then: given the coding matrix text and , can one recover exactly? As is well known, if the fraction of the corrupted entries is too large, then of course we have no hope of reconstructing from ; for instance, assume and consider two distinct and form a vector by concatenating plaintexts , together with the second half of . Then the ﬁrst half of where both and are supported on . This simple example shows that sets of size at most accurate decoding is impossible when the size of the support of the error vector is greater or equal to a half of that of the . Therefore, a common assumption in the literature is output to assume that only a small fraction of the entries are actually damaged (1.1) For which values of can we hope to reconstruct with practical algorithms? That is, with algorithms whose complexity is at most polynomial in the length of the code ? To reconstruct , note that it is obviously sufﬁcient to reconstruct the vector since knowledge of together with gives , and consequently , since has full rank. Our approach is then as follows. We construct a matrix which annihimatrix on the left, i.e., such that . This lates the can be done in an obvious fashion by taking a matrix whose , which is an -dimensional subkernel is the range of in space (e.g., could be the orthogonal projection onto the cokand ernel of ). We then apply to the output obtain (1.2) . Therefore, the decoding problem is reduced to since that of reconstructing a sparse vector from the observations (by sparse, we mean that only a fraction of the entries of are nonzero). Therefore, the overarching theme is that of the sparse reconstruction problem, which has recently attracted a lot of attention as we are about to see.I. INTRODUCTION A. Decoding of Linear Codes HIS paper considers the model problem of recovering an input vector from corrupted measurements . Here, is an by matrix (we will assume throughout ), and is an arbitrary and unknown vector the paper that of errors. The problem we consider is whether it is possible to recover exactly from the data . And if so, how? Our problem has of course the ﬂavor of error correction problems which arise in coding theory as we may think of as aManuscript received February 2005; revised September 2, 2005. The work of E. J. Candes is supported in part by the National Science Foundation under Grants DMS 01-40698 (FRG) and ACI-0204932 (ITR), and by an A. P. Sloan Fellowship. The work of T. Tao is supported in part by a grant from the Packard Foundation. E. J. Candes is with the Department of Applied and Computational Mathematics, California Institute of Technology, Pasadena, CA 91125 USA (e-mail: emmanuel@acm. ). T. Tao is with the Department of Mathematics, University of California, Los Angeles, CA 90095 USA (e-mail: tao@). Communicated by M. P. Fossorier, Associate Editor for Coding Techniques. Digital Object Identiﬁer 10.1109/TIT.2005.858979T0018-9448/$20.00 © 2005 IEEEAuthorized licensed use limited to: Zhejiang University. Downloaded on October 20, 2009 at 04:47 from IEEE Xplore. Restrictions apply.4204IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. 51, NO. 12, DECEMBER 2005B. Sparse Solutions to Underdetermined Systems Finding sparse solutions to underdetermined systems of linear equations is in general NP-hard. For example, the sparsest solution is given by subject to (1.3)provided that the number of nonzero entries in the vector be [1], [11]. In the special case where of the order of is an by random matrix with independent standard normal entries, [12] proved that the number of nonzero entries , where is some very small and may be as large as unspeciﬁed positive constant independent of . C. Innovations This paper introduces the concept of a restrictedly almost orthonormal system—a collection of vectors which behaves like an almost orthonormal system but only for sparse linear combinations. Thinking about these vectors as the columns of the matrix , we show that this condition allows for the exact reconstruction of sparse linear combination of these vectors, i.e., . Our results are signiﬁcantly different than those mentioned above as they are deterministic and do not involve any kind of randomization, although they can of course be specialized to random matrices. For instance, we shall see that a Gaussian matrix with independent entries sampled from the standard normal distribution is restrictedly almost orthonormal with overwhelming probability, and that minimizing the -norm recovers sparse decompositions with a number of ; we shall actually give numerical nonzero entries of size values for . We presented the connection with sparse solutions to underdetermined systems of linear equations merely for pedagogical reasons. There is a more direct approach. To recover from , we consider solving the following corrupted data -minimization problem: (1.5) Now is the unique solution of if and only if is the unique solution of . In other words, and are equivalent programs. To see why this is true, observe on the one hand that , we may decompose as so that sinceand to the best of our knowledge, solving this problem essentially requires exhaustive searches over all subsets of columns of , a procedure which clearly is combinatorial in nature and has exponential complexity. matrix and an integer Formally, given an integer vector , the problem of deciding whether there is a vector , and with fewer than with rational entries such that a ﬁxed number of nonzero entries is NP-complete, see [2, Problem MP5]. In fact, the -minimization problem contains the subset-sum problem. Assume, for instance, that and , and consider the following set of vectors in :where are the usual basis vectors and are integers. Now let be another integer and consider the problem of deciding whetheris a -sparse linear combination of the above vectors ( -sparse is impossible). This is exactly the subset-sum problem, i.e., whether one can write as a sum of a subset of . It is well known that this is an NP-complete problem. This computational intractability has recently led researchers , and a frequently discussed apto develop alternatives to proach considers a similar program in the -norm which goes by the name of basis pursuit [3] (1.4) . Unlike the -norm where we recall that which enumerates the nonzero coordinates, the -norm is convex. It is also well known [4] that can be recast as a linear program (LP). Motivated by the problem of ﬁnding sparse decompositions of special signals in the ﬁeld of mathematical signal processing and following upon the ground breaking work of Donoho and Huo [5], a series of beautiful articles [6]–[9] showed exact and . In a equivalence between the two programs by matrices obnutshell, this work shows that for tained by concatenation of two orthonormal bases, the solution and are unique and identical provided that in to both the most favorable case, the vector has at most nonzero entries. This is of little practical use here since we are interested in procedures that might recover a signal when a constant fraction of the output is unreliable. Using very different ideas and together with Romberg [10], the authors proved that the equivalence holds with overwhelming probability for various types of random matricesOn the other hand, the constraint for some and, therefore,means thatwhich proves the claim. may also be re-expressed as an LP—hence, The program the title of this paper. Indeed, the -minimization problem is equivalent to (1.6) where the optimization variables are and (as means that is standard, the generalized vector inequality for all ). As a result, is an LP with inequality constraints and can be solved efﬁciently using standard optimization algorithms, see [13].Authorized licensed use limited to: Zhejiang University. Downloaded on October 20, 2009 at 04:47 from IEEE Xplore. Restrictions apply.CANDES AND TAO: DECODING BY LINEAR PROGRAMMING4205D. Restricted Isometries In the remainder of this paper, it will be convenient to use the some linear algebra notations. We denote by columns of the matrix and by the linear subspace spanned , we let be the by these vectors. Further, for any so that submatrix with column indices, the value only conveys magnitude inforin , . For mation about the vectors ; indeed is the best constant such that for all if and only if all of the In particular, length. Section II-C establishes that the higher . orthogonality numbers Lemma 1.1: We have for all , . To see the relevance of the restricted isometry numbers to the sparse recovery problem, consider the following simple observation. is such that , and let Lemma 1.2: Suppose that be such that . Let where is an arbitrary vector supported on . Then is the unique minimizer to (1.9) ’s have unit control theTo introduce the notion of almost orthonormal system, we ﬁrst observe that if the columns of are sufﬁciently “degenerate,” the recovery problem cannot be solved. In particular, if there of exists a nontrivial sparse linear combination the which sums to zero, and is any partition of into two disjoint sets, then the vectorhas two distinct sparse representations. On the other hand, linear which involve a large number dependencies of nonzero coefﬁcients , as opposed to a sparse set of coefﬁcients, do not present an obvious obstruction to sparse reare an orthonormal covery. At the other extreme, if the system, then the recovery problem is easily solved by setting . The main result of this paper is that if we impose a “restricted orthonormality hypothesis,” which is far weaker than assuming solves the recovery problem, even if orthonormality, then are highly linearly dependent (for instance, it is posthe to be much larger than the dimension of the sible for span of the ’s). To make this quantitative we introduce the following deﬁnition. Deﬁnition 1.1 (Restricted Isometry Constants): Let be the as matrix with the ﬁnite collection of vectors , we deﬁne the columns. For every integer restricted isometry constants to be the smallest quantity such obeys that (1.7) of cardinality at most , and all real cofor all subsets . Similarly, we deﬁne the -restricted orefﬁcients thogonality constants for to be the smallest quantity such that (1.8)so that can be reconstructed from knowledge of the vector (and the ’s). Proof: We prove that there is a unique with and obeying . Suppose for the sake of contradiction that had two distinct sparse representations where and were supported on sets obeying . ThenBy construction is supported on of size less or equal to . Taking norms of both sides and applying (1.7) and the hypothesis we conclude that , contradicting the hypothesis that the two representations were distinct.E. Main Results Note that the previous lemma is an abstract existence argument which shows what might theoretically be possible, but does not supply any efﬁcient algorithm to recover and from and other than by brute-force search—as discussed earlier. In contrast, our main theorem shows that, by imposing , the -minimization proslightly stronger conditions on recovers exactly. gram Theorem 1.3: Suppose that is such that (1.10) and let be a real vector supported on a set obeying . Put . Then is the unique minimizer toholds for all disjoint sets .of cardinalityandThe numbers and measure how close the vectors are to behaving like an orthonormal system, but only when restricting attention to sparse linear combinations involving no more than vectors. These numbers are clearly nondecreasingNote from Lemma 1.1 that (1.10) implies , and is in . Thus, the condition (1.10) turn implied byAuthorized licensed use limited to: Zhejiang University. Downloaded on October 20, 2009 at 04:47 from IEEE Xplore. Restrictions apply.4206IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. 51, NO. 12, DECEMBER 2005is roughly “three times as strict” as the condition required for Lemma 1.2. Theorem 1.3 is inspired by our previous work [1], see also [10], [11], but unlike those earlier results, our results here are deterministic, and thus do not have a nonzero probability of failure, verprovided of course one can ensure that the system iﬁes the condition (1.10). By virtue of the previous discussion, we have the companion result. and let Theorem 1.4: Suppose is such that be a number obeying the hypothesis of Theorem 1.3. Set , where is a real vector supported on a set of size at most . Then is the unique minimizer to(such that ) as a matrix with independent Gaussian entries. Observe that the range of is a random space of dimenso that the data is the projection sion embedded in of on a random space of dimension . The range of a by matrix with independent Gaussian entries precisely is a random subspace of dimension , which justiﬁes the claim. We would like to point out that the numerical bounds we derived in this paper are overly pessimistic. We are conﬁdent that ﬁner arguments and perhaps new ideas will allow to derive versions of Theorem 1.5 with better bounds. The discussion section will enumerate several possibilities for improvement. G. A Notion of Capacity We now develop a notion of “capacity;” that is, an upper bound on the support size of the error vector beyond which recovery is information-theoretically impossible. Deﬁne the cospark of the matrix as (1.11) We call this number the cospark because it is related to another quantity others have called the spark. The spark of a matrix is the minimal number of columns from that are linearly dependent [6], [7]. In other words subject to Suppose has full rank and assume that , then matrix such that simply follows from s. t. since of the form means that is in the range of and, therefore, where is nonzero since does not vanish. obeys (1.12) . then, exact decoding is achieved by minimizing , then accurate decoding is Conversely, if not possible. Proof: Suppose ﬁrst that the number of errors obeys and let be of full rank with . is equivalent to ﬁnding the Since minimizing , and that the proof of Lemma 1.2 shortest so that assures that is the unique vector with at most nonzero entries, the recovery is exact. be a vector such that The converse is immediate. Let and write where both and are less or equal to . Let be any vector in and set . Then is any full rank , whichF. Gaussian Random Matrices An important question is then to ﬁnd matrices with good restricted isometry constants, i.e., such that (1.10) holds for large values of . Indeed, such matrices will tolerate a larger fraction of output in error while still allowing exact recovery of the original input by linear programming. How to construct such matrices might be delicate. In Section III, however, we will argue that generic matrices, namely, samples from the Gaussian unitary ensemble obey (1.10) for relatively large values of . Theorem 1.5: Assume and let be a by matrix whose entries are independent and identically distributed (i.i.d.) . Then the condition Gaussian with mean zero and variance of Theorem 1.3 holds with overwhelming probability provided is small enough so that thatwhere is given in (3.23). (By “with overwhelming probability,” we mean with probability decaying exponentially only depends upon the in .) In the limit of large samples, ratio, and numerical evaluations show that the condition holds in the case where , for when , and when . In other words, Gaussian matrices are a class of matrices for which one can solve an underdetermined systems of linear equations by minimizing provided, of course, the input vector has nonzero entries with . We mentioned fewer than earlier that this result is similar to [12]. What is new here is that by using a very different machinery, one can obtain explicit numerical values which were not available before. In the context of error correcting, the consequence is that a fraction of the output may be corrupted by arbitrary errors and yet, solving a convex problem would still recover exactly—a rather unexpected feat. Corollary 1.6: Suppose is an by Gaussian matrix and . Under the hypotheses of Theorem 1.5, the set is unique and equal to . solution to This is an immediate consequence of Theorem 1.5. The only thing we need to argue is why we may think of the annihilatorLemma 1.7: Suppose the fraction of errorsand, therefore,andare indistinguishable.Corollary 1.8: Suppose the entries of are independent normal with mean and variance . Then with probability , . As a consequence, one canAuthorized licensed use limited to: Zhejiang University. Downloaded on October 20, 2009 at 04:47 from IEEE Xplore. Restrictions apply.CANDES AND TAO: DECODING BY LINEAR PROGRAMMING4207theoretically recover any plaintext if and only if the fraction error obeys (1.13) In other words, given a fraction of error , accurate decoding is obeys . possible provided that the “rate” This may help to establish a link between this work and other information literature. Proof: It is clear that as one can so that the ﬁrst entries of vanish. Furﬁnd an ther, all the by submatrices of are invertible with probability . This follows from the fact that each by submatrix is invertible with probability , and that there is a ﬁnite number of them. With probability one, therefore, it is impossuch that has vanishing entries. This sible to ﬁnd . gives H. Organization of the Paper The paper is organized as follows. Section II proves our main claim, namely, Theorem 1.3 (and hence Theorem 1.4) while Section III introduces elements from random matrix theory to establish Theorem 1.5. In Section IV, we present numerical exworks unreasonperiments which suggest that in practice, provided ably well and recovers the exactly from that the fraction of the corrupted entries be less than about 17% and less than about 34% in the case in the case where . Section V explores the consequences of our where results for the recovery of signals from highly incomplete data and ties our ﬁndings with some of our earlier work. Finally, we conclude with a short discussion section whose main purpose is to outline areas for improvement. II. PROOF OF MAIN RESULTS Our main result, namely, Theorem 1.3 is proved by duality. As we will see in Section II-A, is the unique minimizer if the has full rank and if one can ﬁnd a vector with the matrix two properties , for all ; i) ii) and , for all ; is the sign of ( , for ). where The two conditions above say that a speciﬁc dual program is feasible and is called the exact reconstruction property in [1], see also [10]. The reader might ﬁnd it helpful to see how these conditions arise and we ﬁrst informally sketch the argument (a rigorous proof follows in Section II-A). Suppose we wish to subject to , and that is differentiable. minimize , the classical Lagrange multiplier opTogether with timality condition (see [13]) asserts that there exists ( is a Lagrange multiplier) such thatwe ask that here meansbe a subgradient of if andat the point [13], which otherwise. , conditions i) and ii) areSince by deﬁnition now natural. A. Proof of Theorem 1.3Observe ﬁrst that standard convex arguments give that there exists at least one minimizer to the problem . . Since obeys the constraints of We need to prove that this problem, obeys (2.14) Now take a obeying properties i) and ii) (see the remark following Lemma 2.2). Using the fact that the inner product is equal to the sign of on and has absolute value strictly less than one on the complement, we then computeComparing this with (2.14) we see that all the inequalities in the was above computation must in fact be equality. Since , this in particular forces strictly less than for all for all . Thus,Applying (1.7) (and noting from hypothesis that ) we conclude that for all . Thus, as claimed. with obeying the hypothesis of Theorem 1.3, For has full rank since and thus, the proof simply consists in constructing a dual vector ; this is the object of the next section. This concludes the proof of our theorem. B. Exact Reconstruction Property We now examine the sparse reconstruction property and begin with Lemma 2.1 which establishes that the coefﬁcients , , are suitably bounded except for an exceptional set. Lemma 2.2 strengthens this results by eliminating the exceptional set. Lemma 2.1 (Dual Reconstruction Property, Version): Let be such that , and be a real vector supportedIn a nutshell, for to be a solution, we must have . In our case , and so for , but is otherwise not smooth at zero. In this case,Authorized licensed use limited to: Zhejiang University. Downloaded on October 20, 2009 at 04:47 from IEEE Xplore. Restrictions apply.4208IEEE TRANSACTIONS ON INFORMATION THEORY, VOL. 51, NO. 12, DECEMBER 2005on such that such that “exceptional set” most. Then there exists a vector for all . Furthermore, there is an which is disjoint from , of size at (2.15)wheneverand. In particular, if we setthen must obey , since otherwise we could conof of cardinality . The tradict (2.17) by taking a subset claims now follow. We now derive a solution with better control on the sup norm outside of , by iterating away the exceptional set (while keeping the values on ﬁxed). The proof of the following lemma is given in the Appendix. of Version): Let Lemma 2.2 (Dual Reconstruction Property, be such that , and be a real vector supported on obeying . Then there exists a vector such that for all . Furthermore, obeys for all (2.18) Lemma 2.2 actually solves the dual recovery problem. Indeed, our result states that one can ﬁnd a vector obeying both properties i) and ii) stated at the beginning of the section. To see why ii) holds, observe that and, therefore, (2.18) gives for alland with the properties for all andwhere for short. In addition, for only depending upon . some constant is the linear transforProof: Recall that where (we use the mation subscript in to emphasize that the input is a -dimenbe the adjoint transformation sional vector), and letProperty (1.7) giveswhere and are the minimum and maximum eigenvalues of the positive-deﬁnite operator . In particular, , we see that is invertible with since (2.16) Also note that to be the vector and setit is then clear that , i.e., for all . with . In addition, and Finally, if is any set in disjoint from with is any sequence of real numbers, then (1.8) and (2.16) giveprovided that . It is likely that one may push the condition a little further. The key idea is as follows. Each vector in the iteration scheme used to prove Lemma 2.2 was designed to on the exceptional set . annihilate the inﬂuence of But annihilation is too strong of a goal. It would be just as suitto moderate the inﬂuence of enough able to design is small rather so that the inner product with elements in than zero. However, we have not pursued such reﬁnements as the arguments would become considerably more complicated than the calculations presented here. C. Approximate Orthogonality Lemma 1.1 gives control of the size of the principal angle between subspaces of dimension and , respectively. This is useful because it allows to guarantee exact reconstruction from the knowledge of the numbers only. Proof Proof of Lemma 1.1: We ﬁrst show that . By homogeneity it will sufﬁce to show thatsince of thewas arbitrary, it follows from the variational deﬁnition norm, , that whenever , , , are disjoint, andIn other words Now (1.7) gives (2.17)Authorized licensed use limited to: Zhejiang University. Downloaded on October 20, 2009 at 04:47 from IEEE Xplore. Restrictions apply.CANDES AND TAO: DECODING BY LINEAR PROGRAMMING4209together withand the claim now follows from the parallelogram identityIt remains to show that geneity, it sufﬁces to establish that. Again by homo-tion inequalities to develop such a uniform bound. Note that for , we obviously have and and, therefore, attention may be restricted to matrices of size . Now, there are large devia[18]. For example, tion results about the singular values of (resp., ) be the largest singular value of letting so that (resp., ), Ledoux [19] applies the concentration inequality , obtains the defor Gaussian measures, and for each ﬁxed viation bounds (3.19)whenever and . To prove this where and property, we partition as and write and . Equation (1.7) together with (1.8) give(3.20) constant, and is a here the scaling of interest has and which can be calcusmall term tending to zero as lated explicitly, see [20]. For example, this last reference shows in (3.19) as . that one can select Lemma 3.1: Put and setandwhereHence,is the entropy function deﬁned for of a restricted isometry constant obeys (for and large enough). For each , the by Gaussian matrix (3.21)as claimed. (We note that it is possible to optimize this bound a little further but will not do so here.) III. GAUSSIAN RANDOM MATRICES In this section, we argue that with overwhelming probability, Gaussian random matrices have “good” isometry constants. matrix whose entries are i.i.d. Gaussian Consider a by and let be a subset of the with mean zero and variance . columns. We wish to study the extremal eigenvalues of Following upon the work of Marchenko and Pastur [14], Geman [15], and Silverstein [16] (see also [17]) proved that a.s. a.s. in the limit where and withProof: As discussed above, we may restrict our attention such that . Set for short and to sets where the maximum is over all sets let of size , and similarly . Then andIt will sufﬁce to prove that and as for we have . Both statements are proved in exactly the same way and we only include that for . Denote by the -term appearing in (3.19). Observe thatIn other words, this says that loosely speaking and in the limit for a ﬁxed of large , the restricted isometry constant behaves like where Restricted isometry constants must hold for all sets of cardinality less or equal to , and we shall make use of concentra-From Stirling’s approximation we have the well-known formulawhich givesWe haveAuthorized licensed use limited to: Zhejiang University. Downloaded on October 20, 2009 at 04:47 from IEEE Xplore. Restrictions apply.。

SAE J200-2005 橡胶材料分类系统(中文版)

ASTM D 395——橡胶特性试验方法—压缩试验 ASTM D 412——橡胶拉伸特性试验方法 ASTM D 429——橡胶特性试验方法—刚性衬层粘着 ASTM D 430——橡胶老化试验方法—动态疲劳 ASTM D 471——橡胶特性试验方法—液体的影响 ASTM D 573——空气烘箱中的橡胶老化试验方法 ASTM D 575——压缩状态下的橡胶特性试验方法 ASTM D 624——橡胶特性试验方法—耐撕裂性能 ASTM D 865——橡胶在空气中加热老化试验方法（封闭试管） ASTM D 925——橡胶特性试验方法—表面着色（接触、色移和扩散） ASTM D 945——挤压作用或剪切力作用下橡胶特性试验方法（机械脉冲记录仪） ASTM D 1053——橡胶特性试验方法—低温下的硬化；柔性聚合物和有涂层的织物 ASTM D 1171——橡胶老化试验方法—室外或试验箱中的臭氧表面龟裂（三角形试样） ASTM D 1329——鉴定橡胶特性的试验方法—低温下的收缩（TR 试验） ASTM D 1349——橡胶操作规程—试验的标准温度 ASTM D 1418——橡胶及橡胶骨架惯例—命名法 ASTM D 2137——橡胶特性试验方法—柔性聚合物和有涂层的织物的脆化点 ASTM D 2240——橡胶特性试验方法—硬度计硬度（邵氏硬度） ASTM D 3183——橡胶操作规程—从产品上制备试验所用的试样
3．5 字母符号的后面应总是跟随着指定硬度和拉伸强度的三位数字——例如，505。首位表示硬度计（邵氏）硬度，例如，5 为 50±5，6 为 60±5。后两位表示最小拉伸强度，例如，05 为 5MPa，14 为 14MPa。现有材料的期望的硬度及拉伸强度的相互关系是通过伸长率的值得到的（见第 6．2 节）。
1．1．2 该文件被制订成为可以增加对未来橡胶材料的描述而无须对分类系统进行完全改编，而且便于今后引入新的试验方法，从而与行业技术要求的变化保持步调一致。

汶川地震前的b值变化

汶川地震前的b值变化史海霞;孟令媛;张雪梅;常莹;杨振涛;谢蔚云;服部克巳;韩鹏【摘要】Gutenberg-Richter定理给出了地震频度随震级的分布特征.大量研究表明频度-震级关系的斜率(b值)在大地震孕育的过程中会出现减小.为了考察b值在汶川地震孕育过程中的时间演化特征,本文尝试基于破裂断层选取研究区域,考察了2000年1月至2008年4月间,汶川地震(Ms8.0)破裂区的地震活动性,并对该区域b值的变化进行了探讨.结果表明,在2005年中至2006年底,地震月频度及季度频度有一个较明显的下降.b值从2002年始至地震前呈现出一个长期趋势性减小;在地震前约半年,出现快速、显著的下降.b值的这一时间变化特征与其他研究者报道的日本东北Mw9.0级地震前的b值变化特征具有很高相似性,可能反映了大地震准备过程中的应力变化.以上结果有益于认识和理解大地震孕育演化过程,同时也表明b值在中长期地震灾害评估中具有潜在价值.【期刊名称】《地球物理学报》【年(卷),期】2018(061)005【总页数】9页(P1874-1882)【关键词】汶川地震;b值;地震活动性;孕震区【作者】史海霞;孟令媛;张雪梅;常莹;杨振涛;谢蔚云;服部克巳;韩鹏【作者单位】中国地震台网中心,北京 100045;中国地震台网中心,北京 100045;中国地震台网中心,北京 100045;南方科技大学地球与空间科学系,广东深圳 518055;南方科技大学地球与空间科学系,广东深圳 518055;Chiba University, Chiba,Japan;Chiba University, Chiba, Japan;南方科技大学地球与空间科学系,广东深圳518055【正文语种】中文【中图分类】P3150 引言古登堡和里克特(Gutenberg and Richter, 1944)提出了有关地震频度(N)与频度震级(M)的统计关系logN=a-bM，称为古登堡—里克特定理.其中常量a反映了区域的地震活动性，b值反映了区域内大小地震的相对比例.研究表明b值的变化可反应地下介质的应力状态(Narteau et al., 2009; Mousavi et al., 2017).地震学家试图利用b值寻找俯冲带的闭锁区域，以此来识别大地震的潜在震源位置(Sobiesiak et al., 2007; Ghosh et al., 2008).同时，一些室内试验也表明在岩石最终破裂前，b值会出现一个系统性的下降(Lei, 2003).特别是大震前的低b值特征，被多次震例检验：如1976年唐山MS7.8地震(李全林等，1979)；2004年印尼苏门答腊MW9.1级地震和2011年日本东北MW9.0级地震(Nanjo et al.，2012).因而，利用统计地震学分析复杂构造区域的地震活动，监测b值的动态变化，以此寻找潜在大震孕震区的相关研究一直备受关注(Smith, 1981).2008年汶川8.0级大地震为检验和改进现有的地震预测知识和理论模型提供了宝贵资料和震例.本文以汶川地震的主破裂区龙门山断裂带为研究区域，采用2000年1月—2008年4月间的地震目录(中国地震台网中心提供，全国地震编目系统(新)http:∥10.5.160.18/console/index.action),统计分析地震频度和b值的时间变化.尝试从b值动态变化中获取中长期与中短期的孕震信息, 进而探求利用b值估计孕震状态的方法，为大震风险评估提供有益参考.1 研究资料的选取汶川地震(31.01°N，103.42°E) 发生于北京时间2008年5月12日，面波震级8.0，震源深度19 km.该地震发生在青藏块体东缘龙门山断裂上，为西南向东北传播的单侧破裂，余震区长约330 km(田勤俭，2009).龙门山断裂带位于青藏高原与扬子地块挤压拼接的交汇部位，龙门山构造系及其相邻断裂带是新生代以来强烈的褶皱隆起区，呈现推覆逆掩断裂构造特征.包括3条近似平行的主要断裂，即都江堰—江油断裂(前山断裂)，映秀—北川—青川断裂(中央断裂)，茂县—汶川断裂(后山断裂).这3条断裂带均显示由北西向南东的逆冲运动，并兼有右旋走滑分量(朱介寿，2008)，其中中央断裂被认为是汶川地震的主破裂断层(贺鹏超和沈正康，2014).马瑾等(2013)提出汶川地震孕震范围的认识，认为汶川地震的孕育部位主要分布在汶川段映秀—北川断裂和后山断裂之间，解释为有限断层段上孕育的地震快速失稳过程.Nanjo等(2012)对日本东北9.0级地震的研究也表明，主破裂区的地震活动性参数(b值)在震前变化最明显，具有很好的前兆特征.因而，为了更加有效地考察汶川地震前地震活动性的变化，本研究选取龙门山断裂带附近(中央主破裂断层两侧60 km区域)作为研究区域.图1给出了汶川地震的震源及本研究的考察区域(蓝色矩形框内).其中绿色实线表示中央断裂(断层数据源于邓启东等，2002).本文使用中国地震台网中心提供的地震目录.在2000年，中国数字台网进行了更新，检测能力得到了大幅提升(Liu et al., 2003).因而，本文选用2000年1月至2008年4月的地震目录.图2展示了在此其间研究区域内的地震震级-频度分布图.从中可以发现完备震级为MC=ML1.5 .这一结果与Huang使用RTL方法研究汶川地震前的地震平静所用最小震级一致(Huang，2008).以往研究表明，余震序列可能具有与主震及背景地震不同的统计特征(Molchan and Dmitrieva，1992).因而在分析地震活动性变化时，需要考察余震序列的影响.图3展示了2000年1月至2008年4月研究区域内的地震在时间域的分布特征.最大震级为ML4.2级.图3a反映了累计地震数目的变化，图3b为震级-时间图.从中可以看出并无显著的余震序列.为了最大程度保持资料的原始性和完整性，本研究未进行去余震处理，而是使用所有大于等于下限震级的地震资料.图1 龙门山断裂带2000年1月—2008年4月(红色空心圈)ML≥ 1.5地震分布图及研究区范围图中蓝色实心框为研究区域，绿色曲线为汶川8.0级地震主破裂带，黑色细线为断层.Fig.1 Locations of earthquakes (red open circle) withML≥1.5 during January, 2000—April, 2008 surrounding the Longmenshan Fault The blue box indicates the study area, the green line represents the main rupture fault, and black lines show active faults.图2 研究区域2000年1月—2008年4月震级-频度图Fig.2 The frequency-magnitude distribution of earthquakes in the study area during January, 2000—April, 20082 震前地震活动性的变化2.1 地震频度变化地震活动在时间上的分布特征可以反映出研究区域应力场所处的状态.研究表明大地震发生之前可能会出现“地震平静”现象(Wyss and Habermann， 1988).这种现象通常直观的表现是地震活动性减弱，即地震频度相对于背景值减小(Huang，2004，2006；Huang and Nagao，2002).为了考察汶川地震的孕育演化过程，我们分析了图1中所选取的研究区域内的地震频度变化.图4a展示了地震月频度的变化，图4b展示了地震季度频度的变化.在两幅图中均可以发现，从2005年中至2006年底，地震频度相对于平均背景值(水平虚线)有一个较明显的减弱.Huang(2008)使用RTL方法研究汶川地震前的地震活动性，发现在2006年至2007年震源区附近有一个明显的地震平静(RTL值减小).考虑到在他的结果中所用的时间窗是1年，因而实际地震平静期应为2005—2006年，与本文图4所示结果一致.类似的地震平静及地震频度减小也被发现于神户地震(Huang et al., 2001)及玉树地震之前(陈学忠和李艳娥，2012).图3 研究区域地震时间分布特征 (a) 累计地震数目随时间的变化; (b) 震级-时间图.Fig.3 The temporal distribution of earthquakes in the study area (a) The temporal variation of cumulative number of earthquakes; (b) The temporal variation of magnitude.图4 研究区地震月累计频度(a)和季度累计频度(b). 各子图中水平虚线代表相应的(月频度或季度频度)均值Fig.4 Monthly frequency (a) and quarterly frequency (b) of earthquakes in the study area The dashed line in each subplot shows the corresponding average value2.2 b值变化目前最常用的b值计算方法有线性最小二乘拟合和最大似然估计，考虑到后者计算简便，不易受个别较大地震影响，且计算结果较为稳定，本研究采用最大似然估计法求取b值.研究采用Aki和Utsu 1965年提出最大似然法求解(Aki，1965; Utsu, 1965)，具体计算公式如下：(1)其中，为研究区域时间窗内的平均震级，MC为下限震级.在本研究中，基于第二节的讨论，MC取1.5. b值计算误差可用以下公式评估(Aki，1965)：(2)其中σb为b值的标准差，其值越大，表明b值的不确定性(误差)越大.N为时间窗内地震样本的个数.从公式(2)可以发现，较大的样本数N可以降低b值估算的不确定性，减小误差.同时为了保证在每一个窗内具有相同的地震样本数，本文选用500个地震样本为一个时间窗，计算b值.为了考察b值在时间域的变化，我们采用步长为50个地震，向后逐步滑动样本窗，计算每一个窗口内的b值.这种基于样本数选取窗口和步长的方法在统计意义上具有一定优势，但每一个窗口和步长的时间尺度可能存在差别.图5展示了研究区域内b值随时间的变化.其中蓝色圆圈给出了每一个窗口的b值，对应的横坐标为该窗口内最后一个地震的发生时间.这样标注的好处是各时刻对应的b值完全由该时刻之前已发生的地震事件决定，在实际应用中更具可操作性.灰色误差棒给出了b值一倍标准差区间.从图中可以看出，b值呈现一个长期的趋势性下降，并大致可分为如下三个阶段：从2002年初至2005年初有一个快速明显的下降；在2005年至2007年中b值相对稳定并略有上升趋势；自2007年中至发震前b值出现连续的的下降，且下降幅度越来越快，尤其是2008年初b值出现大幅度的显著下降.上述结果与日本东北9.0级地震前b值变化形态非常相似(Nanjo et al.,2012图3B)，但绝对b值有明显差异.相较而言，汶川地区b值水平较高，这与汶川地区的构造环境、岩性特征以及应力状态有关.图5 b值时间曲线 (震级下限Mc=1.5，统计样本数为500个地震)Fig.5 The temporal variation of b value (Mc=1.5, the sample size is 500)为了更详细直观地反映b值变化特征，我们在图5中每个阶段各选取一个窗口，考察各窗内地震的震级-频度分布.图6给出对应W1, W2, W3窗内具体的b值计算拟合线，其中W1对应绿色实线，b=1.48±0.07，W2对应蓝色实线，b=1.16±0.05，W3对应红色实线，b=1.08±0.05.从中可以看出，随着窗口时间越来越靠近汶川地震，窗口内较大地震的占比越来越大，对应b值越来越小.图6 各选取窗内地震样本的震级-频度分布Fig.6 The frequency-magnitude distribution in each selected window虽然图6可以直观地反映b值的变化特征，但并不能给出这些变化是否具有统计显著性.为了定量识别b值的变化，我们基于赤池信息量准则(AIC)(Akaike，1974)对两个样本窗内的b值进行P-检验.假设1：两个样本窗内的b值无差异；假设2：两个样本窗内的b值有差异，分别为b1，b2.假设1与假设2的AIC之差ΔAIC为(Utsu, 1992)：ΔAIC=-2(N1+N2)ln(N1+N2)(3)其中，N1，N2为两个样本窗内的地震数目，b1，b2为两个样本窗内的b值.Pb表示两个样本窗内的地震来自于同一个总体即b值无差异的概率, 当样本数较大时，Pb可近似表示为(Utsu, 1999)(4)在图6中，三个窗的地震数目均为500，基于公式(3)和(4)，我们分别计算了W2，W3相对于W1的ΔAIC 及他们之间b值无差异的概率. 其中，W2与W1之间ΔAIC12 = 12.80，Pb=2.247×10-4; W3与W1之间ΔAIC13=22.7170，Pb=1.58×10-6. 上述结果表明，两个窗中b值无差异的概率很低，如果取常用的95%置信区间，则可以判定图6中W2，W3中b值相对于W1中b值的变化是显著的.3 讨论地震活动性反映的是一定区域内地震的统计特征，因而不同选取研究区域的方法可能带来不同的结果.以往的研究更多的是把地震近似为点源，以震源为中心选取一定范围内的区域作为孕震区域进而考察震前地震活动性变化.对于较大震级的地震，孕震范围通常也较大.如果不考虑可能的实际孕震区域而简单地以震源为中心选取研究资料，可能会包含大量与地震准备过程无关的地震样本.这些无关的地震样本很可能影响总体的统计特征，使得包含在地震活动性中的孕震信息无法被识别.Nanjo等(2012)对日本东北9.0级地震的研究中，选用了考虑实际断层走向的研究区域，所得b值变化特征较好地反映了孕震过程.考虑到汶川地震是一个较为特殊的单侧破裂，本文选取了主破裂断层两侧的研究区域，考察了b值在汶川地震前的时间演化特征.这种基于实际断层模型选取研究区域的方法，可能具有一定的潜在优势，值得在今后的地震活动性研究中进一步试验和讨论.在2.2节中可以发现b值在汶川地震前呈现趋势性的衰减特征.根据公式(1)和(2)，b值的计算结果及可信度受地震样本数N和下限震级Mc的影响.因而，为了确认b值的衰减特征是真实客观存在的而非参数选择造成的，我们考察了不同N及Mc 对计算结果的影响.图7给出了应用不同地震样本数N选取窗口(地震数目分别50，100，200，400，500，600)计算所得的b值曲线.从图中可以看出，所有的曲线均呈现一个长期的下降趋势，地震样本数小于200的结果波动较大，绝对b值存在明显差异；自样本数400起至600的b值曲线基本一致，相似度较高，即地震样本数400及以上的b值计算结果具有很好的稳定性.因而图5中所反映的b值减小趋势不太可能是地震样本数选取造成的.理论上讲，样本数越多，b值计算结果可信度越高.然而，较小的窗口可以提供较高的时间解析度.因此，基于两者之间的平衡，本文选取500个地震样本作为窗长.图8给出了Mc=1.5，Mc=1.6，Mc=1.7的b值动态变化曲线.其中窗口长度均为500个地震样本，步长为50个地震样本.从图中可以发现，选用不同的下限震级，b值的计算结果存在差异.这一方面是因为最大似然法本身所存在的计算误差，对不同的震级下限较为敏感(Lombardi，2003)，另外一方面也因为选取不同震级下限时，包含相同地震数目的窗口在时间跨度上存在较大的不一致性，而不同时间的b值可能存在差异.从趋势上看，三条曲线特征具有很好的相似性. 因此，图5所展示的b值长期趋势性减小是客观真实的.值得注意的是，虽然选用更大Mc在理论上可使得地震目录的完备性更可靠，但会造成地震样本数大幅减小，使得b值计算结果的时间分辨率(固定窗口样本数目)或稳定性(固定窗口时间尺度)变差.实际上，我们也尝试计算了Mc大于1.7时的b值，仍可发现b值减小的整体趋势，但趋势变得越来越平缓.在图4中可以发现，2005—2006地震频度出现了下降，这与Huang(2008)基于RTL研究所得的汶川地震前的“地震平静”较为一致.b值在该段时间对应为相对稳定，两者之间可能具有某种内在联系.一种可能的解释是在该时间段应力达到了某种临界状态. 紧接着这一阶段，地震频度出现反弹，同时b值表现为连续性减小，且减小速率越来越大.这可能反映了临界状态被打破，进入了失稳阶段(Main et al., 1989).图7 不同样本窗的b值时间曲线 (震级下限Mc=1.5，步长为50个地震)Fig.7 b value variations of different window length (sample size) (Mc=1.5, step length=50)图8 不同震级下限Mc的b值时间曲线 (窗长为500个地震，步长为50个地震)Fig.8 b value variations of different Mc (The ample size is 500, and the step length is 50)4 结论与展望本文根据汶川地震的破裂特征及可能的孕震区，选取了主破裂断层两侧作为研究区域，考察了地震活动性在汶川地震前的时间演化特征，得到如下结论：(1) 从2005年中至2006年底，地震频度有一个较明显的减弱.这一结果与其他研究者报道的汶川地震的震前“平静”在时间上具有很好的一致性.(2) b值总体呈现一个长期的趋势性下降.这一下降趋势与地震样本窗口大小和下限震级的选取无关，是一个客观存在的事实，且在统计上具有显著性.(3) b值的具体变化特征可分为三个阶段：从2002年初至2005年初有一个快速明显的下降；在2005年至2007年中b值相对稳定并略有上升趋势；自2007年中至发震前b值出现连续的的下降，且下降幅度越来越快，尤其是2008年初b 值出现大幅度的显著下降.上述结果与Nanjo等(2012)报道的日本东北9.0级地震前b变化特征非常相似.b值的这一演化特征是否具有普适性及可能的内在物理含义需要进一步的研究.以上结论表明b值在中长期地震灾害评估中具有潜在价值，有益于认识和理解大地震孕育演化过程，尤其是b值变化显著性水平的定量分析，可在一定程度上为大地震的概率预测及震情会商提供量化信息.然而在现阶段，单纯依靠b值或其他地震活动性参数来预报地震仍面临很大困难(Zhao and Wu, 2008).其中一个关键的原因是，这些参数均是基于统计所得，反应的是一种整体趋势的变化，它们在中长期时间尺度上可能具有较好的参考价值(易桂喜等，2013；闻学泽等，2013；Zhang and Zhou, 2016)，对于最关键的短临预报，目前似乎很难给出有意义的信息.一种可能的解决方法是综合其他直接的地球物理观测结果，比如电磁场(Hattori et al., 2013; Han et al.，2014，2015，2016，2017)，地下水(Orihara et al., 2014)，氡气(Tsunomori and Tanaka, 2014)，及GPS地壳形变(Chen et al.，2014)等，建立一种从中长期到短临的预报模型.并对预报模型不断运用统计检验进行优化，最终找到一个最佳的预报模型.致谢两位匿名评审专家对本文提出了宝贵的修改意见和建议，在此一并致谢.本文使用地震目录由中国台网中心提供.ReferencesAkaike H. 1974. 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Removed_实验测定炸药猛度

实验一炸药猛度测定一、基本概念猛度是指炸药爆轰时粉碎与其接触介质破坏能力，它是衡量炸药爆炸时对介质产生的冲击波和应力波的强度，对与其接触的局部固体介质的破碎程度的指标。

爆速越大，猛度超高。

猛度测定的常采用方法是铅柱压缩法。

本实验是利用一定规格的铅柱体，在一定重量、一定形状尺寸炸药爆炸作用后的铝柱体被压缩剩余量，作为该炸药的猛度计量，单位以毫米计。

本实验为国家部颁标准WJ302-65。

二、实验目的通过实验掌握“铅柱压缩法”测试炸药猛度的方法，并进一步理解炸药猛度的概念。

三、实验用器材设备及耗材名称规格数量/组备注发爆器起爆能力100发1起爆线30m 以上爆破电表 1 天平0.5g 感量1台铅柱Φ40×60mm 1 钢片Φ41×10mm 1 钢板座200×200×20mm 纸筒Φ40×150 mm 1带孔园纸片 1.3～2.0mm 厚Φ外30mm×Φ内8.5mm1炸药硝铵p=1g/cm350g 本实验所需专用设备及耗材电雷管即发型8#1个四、实验准备试验时，按图1－1所示，将纯铅制的圆柱放置于钢垫板(钢)中央，将50g炸药放入装药纸筒内，密度控制在1g／cm3，在药卷中心插入雷管，深度为15mm将园钢片放在铅柱上面并对准中心，再将装好的雷管的药卷放在钢片上部中央，用线绳拉紧进行定位。

（a）（b）图1－1炸药猛度试验a—试验装置：b—压缩后的铅柱1—钢板； 2—铅柱； 3—钢片； 4—受试炸药； 5—雷管五、实验原理及方法实验场地应选在空旷，周围无人及无保护设施的地方，将铁板按上图1所示，水平放置，按照实验装置和测试原理，称量炸药，安装实验装置，测试连接起爆网络，完成以上工作后，学生撤至30米以外的安全距离，由实验安全组长负责拿发爆器钥匙，将起爆线与电雷管脚线相连接。

待全部实验人员回到安全起爆位置后，用爆破电表对电爆网路进行导通检测正常后，发出起爆命令，即可进行起爆。

2005年科学幻想摄影奖作品

2005 Visions of Science Photographic Awards科學幻想攝影獎(2005 Visions of Science Photographic Awards)是由諾華制藥公司(Novartis)和倫敦每日電訊報(London Daily Telegraph)共同發起的。

去年度由科學家、攝影師和新聞記者組成的評選小組分別選出了2005年度科學幻想攝影獎各個類別中的優勝作品，其中主要五大獎項為：Action, Close-up, People, Concepts and Art 。

Action：Shrimp cleaning the teeth of a lizard fish生物的的共生，攝影師吉姆‧格林非爾德(Jim Greenfield)是在荷蘭安地列斯群島(Netherlands Antilles)的古拉索島(Curacao)海岸下拍攝到這張照片的。

一隻狗母魚張開了寬寬的大嘴，讓一隻小蝦為它清理牙齒。

Close-up：Salt and Pepper照片的作者大衛‧麥卡錫(David McCarthy)是倫敦藥劑學校的一位研究人員。

他使用一台電子顯微鏡拍下了一個胡椒子和一粒海鹽的特寫照片，讓人們清楚地看到了這兩種生活中常見物體的真實構造。

People：Clinical skills tutor一位臨床技能師，抱著一把修護用手臂。

Concepts：The Origin of Life英國劍橋大學的講師約翰‧布拉肯伯裡(John Brackenbury)把一系列高速照片組合在一起，向人們闡述有生源說(panspermia)的概念。

這張照片顯示出，雞蛋擊打水面時，蛋殼發生破碎，從而將裡面的物質釋放了出來。

Art：Paracetamol Crystals這張照片的作者斯派克‧沃克(Spike Walker)使用一台顯微照相機捕捉到了一種解熱鎮痛藥物扑熱息痛(Paracetamol Crystals)溶液中的晶體成長畫面。

玫瑰香精微胶囊缓释性的影响因素研究

收稿日期:2005-03-11;修回日期:2005-08-22基金项目:河北省教育厅资助项目(000208)作者简介:王奎涛(1962-),男,回族,河北沧县人,副教授,学士,联系电话:(0311)8632236。

玫瑰香精微胶囊缓释性的影响因素研究王奎涛,葛艳蕊,冯　薇,袁中凯(河北科技大学化学与制药工程学院,河北　石家庄　050018)摘要:采用热重-差热分析测量了脲醛树脂玫瑰香精微胶囊的芯材缓释性能,用显微镜二次变焦法测量了微胶囊粒径大小及膜厚,用扫描电子显微镜测量微胶囊的结构,研究了香精微胶囊的壁厚、粒径、缩聚终点pH 值、脲甲醛摩尔比对其缓释性的影响。

实验表明,香精微胶囊的释放速率随着微胶囊膜厚的增加、粒径的减小而减小,缓释性增强,当缩聚终点pH 115、n (脲)∶n (甲醛)为1∶2时,形成的微胶囊表面结构紧密无凹陷,其缓释性较强。

关键词:玫瑰香精;微胶囊;缓释性;热分析中图分类号:T Q657 文献标识码:A 文章编号:1001-1803(2005)06-0368-03 微胶囊(MC )是一些由天然或合成高分子材料制成的包有某些物质的微小容器,一般粒子大小在微米或毫米范围,微胶囊的研究多着重于制囊工艺与应用,对微胶囊的性能测试及芯材缓释的研究较少[1]。

通过对微胶囊缓释性的影响因素研究,可以指导其生产工艺,以达到更好控制释放芯材的目的。

作者利用热重-差热分析(DT A -TG A )测量了香精微胶囊的芯材缓释性能,用显微镜测量微胶囊粒径大小及壁厚,用扫描电子显微镜(SE M )观测微胶囊的结构及表面形状,考察了试样的壁厚、粒径、缩聚终点pH 值和脲甲醛摩尔比等对香精微胶囊缓释性的影响。

1　实验111　主要原料及仪器玫瑰香精,市售;乙醇、氢氧化钠、氯化铵、尿素、甲醛均为化学纯。

LZ J -II 高剪切混合乳化机,涟水电讯厂;尼康-代福特倒置摄影显微镜,日本;S DT -2960热分析仪,美国T A 公司;JS M -35C 扫描电子显微镜,日本日立公司。

Finding community structure in networks using the eigenvectors of matrices

Finding community structure in networks using the eigenvectors of matrices
M. E. J. Newman
Department of Physics and Center for the Study of Complex Systems, University of Michigan, Ann Arbor, MI 48109–1040
We consider the problem of detecting communities or modules in networks, groups of vertices with a higher-than-average density of edges connecting them. Previous work indicates that a robust approach to this problem is the maximization of the beneﬁt function known as “modularity” over possible divisions of a network. Here we show that this maximization process can be written in terms of the eigenspectrum of a matrix we call the modularity matrix, which plays a role in community detection similar to that played by the graph Laplacian in graph partitioning calculations. This result leads us to a number of possible algorithms for detecting community structure, as well as several other results, including a spectral measure of bipartite structure in neteasure that identiﬁes those vertices that occupy central positions within the communities to which they belong. The algorithms and measures proposed are illustrated with applications to a variety of real-world complex networks.

Bisphenol A impairs follicle growth, inhibits steroidoge

TOXICOLOGICAL SCIENCES119(1),209–217(2011)doi:10.1093/toxsci/kfq319Advance Access publication October18,2010Bisphenol A Impairs Follicle Growth,Inhibits Steroidogenesis,and Downregulates Rate-Limiting Enzymes in the Estradiol BiosynthesisPathwayJackye Peretz,Rupesh K.Gupta,Jeffrey Singh,Isabel Herna´ndez-Ochoa,and Jodi A.Flaws1Department of Comparative Biosciences,University of Illinois,Urbana,Illinois618021To whom correspondence should be addressed at Department of Comparative Biosciences,University of Illinois,2001S.Lincoln Avenue,Room3223,Urbana,IL61802.Fax:(217)244-1652.E-mail:jﬂaws@.Received July27,2010;accepted October8,2010Bisphenol A(BPA)is used as the backbone for plastics and epoxy resins,including various food and beverage containers.BPA has also been detected in95%of random urine samples and ovarian follicularﬂuid of adult women.Few studies have investigated the effects of BPA on antral follicles,the main producers of sex steroid hormones and the only follicles capable of ovulation.Thus,this study tested the hypothesis that postnatal BPA exposure inhibits antral follicle growth and steroidogenesis. To test this hypothesis,antral follicles isolated from32-day-old FVB mice were cultured with vehicle control(dimethyl sulfoxide [DMSO]),BPA(4.4–440m M),pregnenolone(10m g/ml),pregnen-olone1BPA44m M,and pregnenolone1BPA440m M.During the culture,follicles were measured for growth daily.After the culture,media was subjected to ELISA for hormones in the estradiol biosynthesis pathway,and follicles were processed for quantitative real-time PCR of steroidogenic enzymes.The results indicate that BPA(440m M)inhibits follicle growth and that pregnenolone cotreatment was unable to restore/maintain growth. Furthermore,BPA44and440m M inhibit progesterone,dehy-droepiandrosterone,androstenedione,estrone,testosterone,and estradiol production.Pregnenolone cotreatment was able to increase production of pregnenolone,progesterone,and dehy-droepiandrosterone and maintain androstenedione and estrone levels in BPA-treated follicles compared with DMSO controls but was unable to protect testosterone or estradiol levels.Further-more,pregnenolone was unable to protect follicles from BPA-(44–440m M)induced inhibition of steroidogenic enzymes compared with the DMSO control.Collectively,these data show that BPA targets the estradiol biosynthesis pathway in the ovary. Key Words:bisphenol A;steroidogenesis;ovary;antral follicle growth;StAR;pregnenolone.Bisphenol A(BPA),2,2-bis-4-hydroxyphenyl propane,is an estrogenic compound originally synthesized in1963to prevent miscarriage.BPA eventually became widely used as the backbone for epoxy resins,durable clear polycarbonate plastics such as reusable plastic food containers,food and beverage can liners,infant formula cans,baby bottles,and dental sealants, among many other plastic-based products.Unfortunately, aging,heating,and contact with acids and bases,including those commonly found in cleaning supplies and detergents, cause the BPA polymers to break apart.In a process commonly referred to as‘‘leaching,’’BPA seeps into the contents of various food packages,into saliva,and/or into dust particles, providing ample entry ways for BPA into animal physiological systems,including humans(Can et al.,2005;Kang et al.,2006; Lenie et al.,2008;Vandenberg et al.,2007;vom Saal and Hughes,2005;Welshons et al.,2006).Although BPA exposure can occur via food and drink (ingested),BPA can also be inhaled.Once in the lungs,BPA can travel through the bloodstream and into enterohepaticﬂow, where it can act as if ingested orally and travel through the digestive system.Various studies have detected BPA in blood, saliva,and human tissues as well as in95%of human urine samples taken in a random sampling(Calafat et al.,2005, 2008;Ouchi and Watanabe,2002).Additionally,though BPA is thought to be conjugated to glucuronide in the digestive system and to exit the body via the urinary system,the chemical is not solely conﬁned to the digestive system.BPA has also been detected in mammary tissue,breast milk, amnioticﬂuid,and ovarian follicularﬂuid,indicating BPA travels not only through the digestive system but also through the venous network and thus into the many other organ and tissue systems of the body(Ikezuki et al.,2002;Lenie et al., 2008;Vandenberg et al.,2007,2009).Recent research has suggested that BPA persists in the human system longer than originally thought.In a study comparing BPA levels with fasting time,researchers found BPA persisting in the body well past the given4–6h half-life of BPA.Speciﬁcally,following17-h exposure,BPA levels only decreased56%instead of the expected100%elimination. This study suggests that BPA has a longer half-life than previously estimated;there are signiﬁcant non-food source exposures of BPA or,more likely,a combination of the twoÓThe Author2010.Published by Oxford University Press on behalf of the Society of Toxicology.All rights reserved. For permissions,please email:journals.permissions@ at Shanghai Jiao Tong University on June 6, Downloaded fromexplanations(Stahlhut et al.,2009;Tillet,2009).Collectively, theseﬁndings suggest that humans are constantly exposed to BPA.Studies focusing on the effects of BPA exposure on the rodent female reproductive system have shown that maternal exposure to BPA during gestation can cause adverse de-velopmental effects in the offspring.Speciﬁcally,BPA has been shown to induce early puberty onset,changes in weight gain,early vaginal opening(Honma et al.,2002),and ovarian morphological abnormalities in the offspring.The ovarian abnormalities include cystic ovaries(Hartshorne,1997)and cystadenomas,hemorrhagic follicles,and large antral-like follicles seemingly unable to ovulate(Hartshorne,1997). BPA also can cause progressive proliferative lesions of the oviduct(Savabieasfahani et al.,2006)and leiomyomas in the uterus(Newbold et al.,2007).Furthermore,BPA increases estrogen receptor alpha(Esr1)and estrogen receptor beta(Esr2) receptor expression levels in the uterus(Richter et al.,2007). Few studies have investigated the direct effects of BPA on the ovarian follicle itself,the functional unit of the ovary and the main steroid hormone producer of the female reproductive system.Previous studies have focused mainly on meiotic abnormalities,such as cell cycle arrest,meiotic aneuploidy,and congression failure during the cell cycle(Eichenlaub-Ritter et al.,2008;Hunt et al.,2003)or on morphological indicators of ovulation,such as observing a lack of corpora lutea in the ovary(Hartshorne,1997).Although BPA has been reported to be present in follicularﬂuid of adult human ovaries,previously published studies have not focused on antral follicles of adult humans,and as a result,little information is available regarding the effect of postnatal BPA exposure on the proper functioning of adult human ovarian follicles.Furthermore,little informa-tion is available on the effect of BPA on the proper functioning of ovarian antral follicles in the adult mouse model.Thus,this study tested the hypothesis that postnatal exposure to BPA inhibits growth and steroidogenesis of adult ovarian antral follicles in mice.MATERIALS AND METHODSChemicals.BPA powder(99%)was purchased from Sigma-Aldrich (St Louis,MO).A stock solution of BPA was dissolved and diluted in dimethyl sulfoxide(DMSO)(Sigma-Aldrich)to achieve various BPA treatment concentrations(1.3,13.3,and133mg/ml)forﬁnal working concentrations of 1.0,10,and100l g of BPA per milliliter of culture media(4.4,44,and440l M BPA,respectively).Additionally,using these treatment concentrations allowed each working concentration to contain the same volume of chemical and vehicle(0.75l l BPA:DMSO per milliliter of culture media).The concentrations chosen for the cultures were based on concentrations used in previous studies(Can et al.,2005;Lee et al.,2007;Lenie et al.,2008; Mlynarcikova et al.,2009;Vandenberg et al.,2007;Watson et al.,2007;Xu et al.,2002;Zhou et al.,2008).BPA concentrations were also chosen based on studies showing the effects of BPA on ovarian cells.For example,BPA exposure between100fM and100l M for24–72h results in an increase in apoptosis and G2-to-M arrest in cultured mouse ovarian granulosa cells (Xu et al.,2002).The selected concentrations of BPA are relevant to current regulatory levels set for BPA.The lowest observable adverse effect level (LOAEL)is50mg/kg/day.This equates to210.6l M.The doses used in the experiments were4.4,44,and440l M(or1,10,and100l g/ml),encompassing the LOAEL concentration.5-Pregnen-3b-ol-20-one(Pregnenolone;pregn)powder was purchased from Sigma-Aldrich.A stock solution of pregn was prepared in DMSO for aﬁnal concentration in culture of10l g/ml.Animals.Adult,cycling female FVB mice were purchased from Jackson Laboratory(Bar Harbor,ME)and allowed to acclimate to the facility for at least 5days before use.The mice were housed at the University of Illinois at Urbana-Champaign,Veterinary Medicine Animal Facility.Food(Harlan Teklad8626) and water were provided for ad libitum consumption.Temperature was maintained at22±1°C,and animals were subjected to12-h light-dark cycles. The Institutional Animal Use and Care Committee at the University of Illinois at Urbana-Champaign approved all procedures involving animal care, euthanasia,and tissue collection.In vitro follicle culture.Female FVB mice were euthanized on postnatal day32and their ovaries removed using aseptic technique.Antral follicles were mechanically isolated from the ovary based on relative size(250–400 l m),cleaned of interstitial tissue usingﬁne watchmaker forceps(Gupta et al., 2006;Miller et al.,2005),and individually placed in wells of a96-well culture plate and covered with unsupplemented a-minimal essential medium (a-MEM)prior to treatment.Sufﬁcient numbers of antral follicles for statistical power were isolated from unprimed mouse ovaries;follicles from two to three mice were isolated per experiment providing approximately 20–40antral follicles from each mouse.Each experiment contained a minimum of8–16follicles per treatment group.Doses of vehicle control (DMSO),BPA(4.4,44,and440l M),pregn(10l g/ml),pregnþBPA (44l M),and pregnþBPA(440l M)were individually prepared in supplemented a-MEM.Supplemented a-MEM was prepared with:1%ITS (10ng/ml insulin,5.5ng/ml transferrin,and5.5ng/ml selenium),100U/ml penicillin,100mg/ml streptomycin,5IU/ml human recombinant follicle-stimulating hormone(Dr A. F.Parlow,National Hormone and Peptide Program,Harbor-UCLA Medical Center,Torrance,CA),and5%fetal calf serum(Atlanta Biologicals,Lawrenceville,GA)(Gupta et al.,2006;Miller et al.,2005).An equal volume of chemical was added for each dose to control for the amount of vehicle in each preparation(0.75l l/ml of media:BPA treatments;1.0l l/ml of media:DMSO and pregn treatments).Antral follicles were cultured for120h in an incubator supplying5%CO2at37°C.Analysis of follicle growth.Follicle growth was examined at24-h intervals by measuring follicle diameter on perpendicular axes with an inverted microscope equipped with a calibrated ocular micrometer.Follicle diameter measurements were averaged among treatment groups and plotted to compare the effects of chemical treatments on growth over time.Data were presented as percent change over time.Analysis of hormone levels.Media was collected after120h of follicle culture and subjected to ELISA for measurement of estradiol,estrone, testosterone,androstenedione,dehydroepiandrosterone sulfate(DHEA-S),and progesterone levels.ELISA kits and reagents were obtained from ALPCO Diagnostics(estrone,testosterone,androstenedione,progesterone,and DHEA-S) and Diagnostics Research Group(estradiol).The assays were run using the manufacturer’s instructions.All samples were run in duplicate and all intra-and interassay coefﬁcients of variability were less than10%.Analysis of quantitative real-time PCR.Female FVB mouse antral follicles were cultured as described above for120h.At the end of culture, follicles were collected and snap frozen atÀ80°C for quantitative real-time PCR(qPCR)analysis.Total RNA was extracted from follicles using the RNeasy Micro Kit(Qiagen,Inc.,Valencia,CA)according to the manufac-turer’s protocol.Reverse transcriptase generation of complementary DNA (cDNA)was performed with0.3–1l g of total RNA using an iScript RT Kit (Bio-Rad Laboratories,Inc.,Hercules,CA).qPCR was conducted using the210PERETZ ET AL.at Shanghai Jiao Tong University on June 6, Downloaded fromCFX96Real-Time PCR Detection System(Bio-Rad Laboratories,Inc.)and accompanying software(CFX Manager Software)according to the manufac-turer’s instructions.The CFX96quantiﬁes the amount of PCR product generated by measuring a dye(SYBR Green)thatﬂuoresces when bound to double-stranded DNA.A standard curve was generated fromﬁve serial dilutions of one of the samples,thus allowing analysis of the amount of cDNA in the exponential phase.Speciﬁc qPCR primers for the genes of interest and annealing temperatures are listed in Table1,along with GenBank accession numbers(Akingbemi et al.,2003;Hernandez-Ochoa et al.,2010;Pakarainen et al.,2005;Sha et al.,1996;Weihua et al.,2000).qPCR analysis was performed using2l l cDNA,forward and reverse primers(5pmol)for steroidogenic acute regulatory protein(StAR),cytochrome P450side-chain cleavage(P450scc),3b-hydroxysteroid dehydrogenase(3b-HSD),17b-hydroxysteroid dehydrogenase(17b-HSD),cytochrome P450aromatase (Cyp19),cytochrome P45017a-hydroxylase/17,20lyase(Cyp17a),or b-actin, in conjunction with a SsoFast EvaGreen Supermix qPCR Kit(Bio-Rad Laboratories).An initial incubation of95°C for10min was followed by denaturing at94°C for10s,annealing from56to61°C for10s,and extension at72°C for10s,for40cycles(b-actin),followed byﬁnal extension at72°C for 10min.A melting curve was generated at55–90°C to monitor the generation of a single product.The software also generated a standard curve.b-Actin was used as reference gene for each sample.Final values were calculated and expressed as the ratio normalized to b-actin.All analyses were performed in duplicate for at least three separate experiments.Statistical analysis.Data were expressed as means±SEM,and multiple comparisons between experimental groups were made using ANOVA followed by Tukey’s post hoc comparison.Tests for trend were analyzed using linear regression analyses for the overall effect of BPA concentration(continuous variable).At least three separate experiments were conducted for each treatment prior to data analysis.Statistical signiﬁcance was assigned at p0.05.RESULTSEffect of BPA on Follicle GrowthExposure to BPA(440l M)signiﬁcantly decreased antral follicle growth compared with DMSO controls beginning at 72h,and this decrease in follicle growth remained throughout the120-h culture(Fig.1).No signiﬁcant differences in follicle growth were observed between follicles exposed to DMSO, BPA(44l M),or BPA(4.4l M).Effect of BPA on Sex Steroid Hormone ProductionBPA(440l M)exposure for120h signiﬁcantly decreased estradiol,estrone,testosterone,androstenedione,DHEA-S,and progesterone levels produced by the follicles compared with DMSO(Fig.2).BPA(44l M)exposure for120h signiﬁcantly decreased estradiol,estrone,testosterone,androstenedione, DHEA-S,and progesterone levels produced by the follicles. No signiﬁcant differences in steroid levels were found between DMSO and4.4l M BPA.Effect of BPA on Gene ExpressionBecause BPA decreased steroidogenesis in the cultured antral follicles,studies were conducted to see if it did so by decreasing the expression of enzymes required for steroido-genesis.Speciﬁcally,levels of steroidogenic enzymes StAR,TABLE1PrimersusedinQuantitativeReal-TimePolymeraseChainReactions(qPCR)GenenameGenesymbolPrimersequencesAnnealingtemperatureGenBankaccession#ForwardReverseBeta-actinActbF:GGGCACAGTGTGGGTGACR:CTGGCACCACACCTTCTAC56°CNM_7393SteroidogenicacuteregulatoryproteinStARF:CAGGGAGAGGTGGCTATGCAR:CCGTGTCTTTTCCAATCCTCTG57°CNM_781CytochromeP45cholesterolside-chaincleavageCyp11a1F:AGATCCCTTCCCCTGGCGACAATGR:CGCATGAGAAGAGTATCGACGCATC6°CNM_82933b-Hydroxysteroiddehydrogenase1HSD3b1F:CAGGAGAAAGAACTGCAGGAGGTCR:GCACACTTGCTTGAACACAGGC59.5°CNM_8293CytochromeP45aromataseCyp19a1F:CATGGTCCCGCAAACTGTGAR:GTAGTAGTTGCAGGCACTTC56°CNM_781CytochromeP45steroid17-a-hydroxylase1Cyp17a1F:CCAGGACCCAAGTGTGTTCTR:CCTGATACGAAGCACTTCTCG56°CNM_78917B-hydroxysteroiddehydrogenase1HSD17b1F:ACTGTGCCAGCAAGTTTGCGR:AAGCGGTTCGTGGAGAAGTAG58°CNM_1475THE EFFECTS OF BISPHENOL A ON ANTRAL FOLLICLES211at Shanghai Jiao Tong University on June 6, Downloaded from3b -HSD,and Cyp17a were compared in control and BPA-treated follicles.Only StAR messenger RNA (mRNA)expression levels were signiﬁcantly decreased following exposure to BPA44l M and BPA440l M compared with DMSO controls (Figs.3and 6;BPA-only treated follicles).Exposure to BPA440l M,however,resulted in a signiﬁcant trend for decreased 3b -HSD expression compared with controls.Furthermore,BPA44l M and BPA440l M signiﬁ-cantly decreased P450scc mRNA expression levels compared with DMSO controls (Fig.6;BPA-only treated follicles).Effect of Pregnenolone Cotreatment on BPA-Treated FolliclesThe BPA-induced inhibition of steroidogenesis and follicle growth could be the result of decreased StAR and P450scc levels in the follicles because these are rate-limiting enzymes for the estradiol biosynthesis pathway.Because addition of pregnenolone bypasses this disrupted enzyme,studies were conducted to investigate whether cotreatment of follicles with pregnenolone and BPA would protect follicles from the toxic effects of BPA on follicle growth and steroidogenesis.Addition of pregnenolone to the supplemented media did not protect follicles from BPA-induced follicle growth inhibition (Fig.4).However,cotreatment of follicles with pregnenolone and BPA did provide some protection against inhibition of steroidogenesis (Fig.5).Pregnenolone cotreatment with BPA increased pregnenolone,progesterone,and DHEA-S levels compared with DMSO controls and maintained androstene-dione and estrone levels similar to DMSO controls.Pregnen-olone cotreatment with BPA,however,did not increase levels of testosterone and estradiol production compared with DMSO controls.Speciﬁcally,progesterone levels were 2.9±0.4ng/ml with BPA44l M only and 14.1±2.5ng/ml with DMSO only,but progesterone levels were 5502.1±387.2ng/ml with pregn þBPA44l M.Androstenedione levels were 0.07±0.003ng/mL with BPA44l M only and 1.1±0.2ng/ml with DMSO only,but androstenedione levels were 1.0±0.04ng/ml with pregn þBPA44l M.Estradiol levels were 378.1±54.5pg/ml with BPA44l M only,5417.8±1849.9pg/ml with DMSO only,and 465.6±11.2pg/ml with pregn þBPA44lM.FIG.2.Effect of BPA exposure on antral follicle hormone production.After exposure of antral follicles to DMSO control or BPA (4.4–440l M)for 120h in vitro ,media was collected and subjected to various hormone measurements by ELISA.These graphs represent the means ±SEMs from separate experiments.A single asterisk (*)denotes a signiﬁcant p value for overall effect of BPA concentration as the continuous variable using linear regression.A double asterisk (**)denotes a signiﬁcant p value from the DMSO control via ANOVA,post hoc Tukey’s Honestly Signiﬁcant Difference (test)(n ¼3–4;p0.05).at Shanghai Jiao Tong University on June 6, 2011 Downloaded fromEffect of Pregnenolone þBPA on Gene ExpressionBecause levels of pregnenolone,DHEA-S,progesterone,androstenedione,and estrone were protected from BPA-induced inhibition in the pregnenolone-treated groups compared with their nonpregnenolone counterparts,geneexpression levels of the enzymes responsible for their metabolism along the biosynthesis pathway were measured.Addition of pregnenolone treatment did not protect the follicles from BPA-induced alterations in steroidogenic enzyme gene expression (Fig.6).Speciﬁcally,StAR mRNA expression levels were 0.09±0.04genomic equivalents (ge)with BPA44l M only and 0.41±0.04ge with DMSO,but StAR mRNA expression levels were 0.09±0.006ge with pregn þBPA44l M.P450scc mRNA expression levels were 0.08±0.01ge with BPA44l M only and 0.37±0.07ge with DMSO only,but P450scc mRNA expression levels were 0.03±0.13ge with pregn þBPA44l M.DISCUSSIONUsing an in vitro follicle culture system,we have shown that BPA inhibits follicle growth and decreases hormone pro-duction in mouse ovarian antral follicles.Furthermore,although cotreatment with pregnenolone did not protect follicles from BPA-induced inhibition of follicle growth,it partially protected follicles from BPA-induced inhibition of steroidogenesis.Sex steroid hormone production is required for proper development of antral follicles (Cain et al.,1995).These hormones produced in the ovary have an autocrine effect on the growth and development of follicles.Estrogens,such as estradiol,stimulate follicle growth and protect the follicle from atresia (Quirk et al.,2004).Progestins,such as progesterone,have an inhibitory effect and induce atresia,although the speciﬁc actions of progesterone on the follicle are not currently well understood (Fukuda et al.,1980).Androgens,such as androstenedione,testosterone,and dehydrotestosterone,have been reported to both stimulate follicle growth and induce atresia in antral follicles (Drummond,2006).FIG.3.Effect of BPA exposure on StAR,3b -HSD,and Cyp17a mRNA expression levels.After exposure of antral follicles to DMSO control of BPA (4.4–440l M)for 120h in vitro ,the follicles were collected and subjected to qPCR analysis for StAR,3b -HSD,and Cyp17a mRNA expression levels.All values were normalized to b -actin as a loading control.Graph represents means ±SEMs from separate experiments.A single asterisk (*)denotes a signiﬁcant p value for overall effect of BPA concentration as the continuous variable using linear regression.A double asterisk (**)denotes a signiﬁcant p value from the DMSO control via ANOVA,post hoc Tukey’s HSD (n ¼8–16follicles per treatment per experiment from three separate experiments;p0.05).FIG.4.Effect of pregnenolone cotreatment with BPA on antral follicle growth.Antral follicles were mechanically isolated from FVB mice and exposed in vitro to BPA (4.4–440l M),pregnenolone (10l g/ml)or pregnenolone,and BPA (44–440l M)for 120h.Growth of follicles was monitored during culture and recorded in micrometers and reported as percent change.The graph represents means ±SEMs from at least three separate experiments.Lines with asterisks (*)are signiﬁcantly different from DMSO controls (n ¼8–16follicles per treatment per experiment from at least three separate experiments;p 0.05).THE EFFECTS OF BISPHENOL A ON ANTRAL FOLLICLES213at Shanghai Jiao Tong University on June 6, 2011 Downloaded fromHormone production is dependent on the components of the estradiol biosynthesis pathway.More speciﬁcally,production of downstream hormones in the pathway,such as estradiol,is dependent on the availability of upstream hormones,such as progestins and androgens.All the hormones within the biosynthesis pathway are dependent on the availability of the lipid precursor,cholesterol.Furthermore,the rate-limiting step of the estradiol biosynthesis pathway is the transport of cholesterol by StAR from lipid droplets in the theca cells into the inner matrix of the mitochondria.Therefore,without this transport,cholesterol cannot be converted to pregnenolone via P450scc,and further hormone metabolism and production in the antral follicles is inhibited.Our results suggest that both StAR and P450scc mRNA expression are inhibited following exposure to BPA.This would prevent cholesterol uptake into the mitochondria and metabolism to pregnenolone,explaining the decrease in hormone production following exposure to BPA in our study.To try and bypass these enzymes,we added pregnenolone to the culture.We hypothesized that the pregnenolone addition would protect the follicles from inhibited growth and hormone production.Exposing the follicles concurrently to pregneno-lone and BPA did not prevent inhibition of follicle growth but protected hormone production in the theca cells,although not necessarily in the granulosa cells.These data support our ﬁnding that StAR and P450scc mRNA levels are inhibited by BPA.Thus,cholesterol uptake into the mitochondria and metabolism to pregnenolone is inhibited,impairing hormone production in the antral follicles.Without adequate hormone levels,late antral follicle growth and ovulation will be impaired,as well as further hormone production within the follicles,thus affecting fertility.Our results support previous work,indicating that BPA exposure affects progesterone production using porcine granulosa cells incubated for 24–72h,although this previous work was done in isolated granulosa cells not the wholefollicleFIG.5.Effect of pregnenolone cotreatment with BPA on antral follicle hormone production.After exposure of antral follicles to DMSO control,BPA (4.4–440l M)pregnenolone (10l g/ml)or pregnenolone,and BPA (44–440l M)for 120h in vitro ,media was collected and subjected to various hormone measurements by ELISA.These graphs represent the means ±SEMs from separate experiments.Asterisks (*)indicate a signiﬁcant difference between no pregnenolone and pregnenolone groups;symbols (†)indicate a signiﬁcant difference between BPA and control groups without pregnenolone;letters indicate a signiﬁcant difference between BPA and control groups with pregnenolone groups (n ¼3–4;p 0.05).214PERETZ ET AL.at Shanghai Jiao Tong University on June 6, 2011 Downloaded from。

MBN 10143_2005.11_DE

Mechanische Verbindungselemente, Annahmeprüfung, (ISO 3269:2000),
Deutsche Fassung EN ISO 3269:2000
DIN EN ISO 7085
Mechanische und funktionelle Eigenschaften von einsatzgehärteten und angelas-
1 Anwendungsbereich
Diese Norm enthält Festlegungen über Schrauben mit Außensechsrund mit großem Flansch, mit Regelgewinde und Feingewinde mit Gewinde-Nenndurchmessern von 5 mm bis 20 mm, mit Festigkeitsklassen 8.8 und 10.9 in der Produktklasse A und mit Gewinde-Nenndurchmesser von 4 bis 12 mm aus Al9, Al10.
Alle Werkstoffe, Verfahren, Prozesse, Bauteile und Systeme müssen den geltenden gesetzlichen Bestimmungen in Bezug auf geregelte Stoffe und Wiederverwertbarkeit entsprechen.
Sechsrundschraube MBN 10 143 - M10 x 80 - 10.9 DBL 9440.40 Sechsrundschraube MBN 10 143 - M10 x 80 - Al9

A Method for the Rapid and Efficient Elution of Native

A Method for the Rapid and Efficient Elution of NativeAffinity-Purified Protein A Tagged ComplexesCaterina Strambio-de-Castillia,†Jaclyn Tetenbaum-Novatt,†Brian S.Imai,‡Brian T.Chait,§andMichael P.Rout*,†The Rockefeller University,1230York Avenue,New York New York 10021-6399Received May 24,2005A problem faced in proteomics studies is the recovery of tagged protein complexes in their native and active form.Here we describe a peptide,Bio-Ox,that mimics the immunoglobulin G (IgG)binding interface of Staphylococcus aureus Protein A,and competitively displaces affinity-purified Protein A fusion proteins and protein complexes from IgG-Sepharose.We show that Bio-Ox elution is a robust method for the efficient and rapid recovery of native tagged proteins,and can be applied to a variety of structural genomics and proteomics studies.Keywords:Staphylococcus aureus •Protein A •affinity purification •proteomics •fusion proteinIntroductionProtein -protein interactions are central to the maintenance and control of cellular processes.The study of such protein -protein interactions has been greatly enhanced by fusion protein technology,wherein specific peptide or protein domain “tags”are fused to the protein of interest (generally at either its carboxyl-terminus or amino-terminus).These tags can facilitate the detection,increase the yield,and enhance the solubility of their associated proteins.1-3Most importantly,these fusion domains have been exploited to allow the single-step purification of the test protein either alone or in complexes with its in vivo binding partners.4-6The yield of these purifica-tion methods is often high enough to allow the identification of such binding partners by mass spectrometry.A commonly used affinity tagging method generates ge-nomically expressed Protein A (PrA)fusion proteins by modify-ing the coding sequence of the protein under study via PCR-directed approaches.7-9This method takes advantage of the ∼10nM binding affinity of PrA from S taphylococcus aureus for the constant region (Fc)of immunoglobulin G (IgG).10After purification on IgG-conjugated resins,PrA-tagged proteins or protein complexes are most commonly eluted from the resin using high or low pH conditions.These elution methods typically lead to the denaturation of the isolated proteins,the dissociation of complexes,and concomitant loss of activity.However,it is often desirable to recover soluble native protein or protein complexes.One method by which this can be achieved is by constructing a cleavable tag.Such tags carry a specific cleavage site for a protease placed proximal to the tagged protein,allowing the tag to be removed from the fusion protein.Proteases that are widely used for this purpose includeblood coagulation factors X (factor Xa),enteropeptidase (en-terokinase),alpha-thrombin,and the tobacco etch virus (TEV)protease.Nevertheless,this method has drawbacks.First,the literature is replete with reports of fusion proteins that were cleaved by these proteases at sites other than the canonical cleaving site.11-14Second,the removal of the tag destroys the ability to detect or further purify the protein of interest,necessitating the encumbrance of a second,tandem tag.15Here,we describe a rapid single step method for the efficient recovery of native and active PrA fusion proteins and protein complexes from IgG-Sepharose.This technique avoids the complications of having to use a protease and in addition has the advantage of retaining the original tag on the target protein after elution,permitting further purification steps and detection of the fusion protein in subsequent experiments.Our method takes advantage of a previously described peptide,termed FcIII,16which mimics the protein -protein binding interface of PrA for the hinge region on the Fc domain of human IgG.We modified FcIII by the addition of a biotin moiety to its amino-terminus to increase the peptide’s solubility while leaving its affinity for Fc intact s making it a more effective elution reagent.We termed this modified peptide,Bio-Ox.To investigate the properties of Bio-Ox,PrA-tagged proteins were isolated in their native state from yeast on an IgG-conjugated Sepharose resin,either alone or in combination with their in vivo interacting partners;the Bio-Ox peptide was then used to competitively displace the tagged proteins and elute them from the resin.The efficiency of elution was monitored by quantitatively comparing the amounts of proteins eluted to the amounts remaining on the resin under a variety of test conditions.We show that Bio-Ox elution is a robust method for the efficient and rapid recovery of native tagged proteins that can be applied to a variety of structural genomics and proteomics studies.*To whom correspondence should be addressed.Tel:+1(212)327-8135.E-mail:rout@.†Laboratory of Cellular and Structural Biology,Box 213.‡Proteomics Resource Center,Box 105.§Laboratory of Mass Spectrometry and Gaseous Ion Chemistry,Box 170.2250Journal of Proteome Research 2005,4,2250-225610.1021/pr0501517CCC:$30.25©2005American Chemical SocietyPublished on Web10/08/2005Experimental SectionPeptide Synthesis,Oxidation and Cyclization.Peptides were synthesized using standard Fmoc protocols.Typical deprotec-tion times with20%piperidine were2times10min and typical coupling times with4-10-fold excess of amino acids over resin were2to6h.Small batches of peptides were made on a Symphony synthesizer(Protein Technologies,Inc.),while larger batches were made manually.Peptides were cleaved from the resin using94.5%trifluoroacetic acid, 2.5%water, 2.5% ethanedithiol and1%triisopropylsilane for3h at25°C.The solubilized peptides were precipitated with10volumes of cold tert-butyl methyl ether and the precipitated peptide was washed several times with ether prior to air-drying.The air-dried peptide was dissolved in20%acetonitrile in water to approximately0.5mg/mL,the pH was adjusted to8.5using sodium bicarbonate and the peptide was allowed to air oxidize overnight to promote cyclization.The progress of cyclization was monitored by mass spectrometry.The cyclized crude peptide was purified using standard preparative reversed phase HPLC using a Vydac218TP1022C18column.Peptide Solubility.Eluting peptides were suspended at a concentration of440µM(0.77mg/mL for BioOx;0.67mg/mL for FcIII),in peptide buffer by extensive vortexing.The peptide concentration was verified by measuring the OD280nm of each solution(extinction coefficient:1OD280nm)0.13mg/mL).The peptide solutions/suspensions were then combined with equal amounts of a100mM buffer to obtain∼220µM peptide at a range of pH values(buffers:Na-Acetate pH4.8,Na-Citrate pH 5.4,Na-Succinate pH5.8,Na-MES pH6.2,BisTris-Cl pH6.5, Na-HEPES pH7.4,Na-TES pH7.5,Tris-Cl pH8.3,Na-CAPSO pH9.6).Samples were incubated at room temperature with gentle agitation for20min,and then insoluble material was removed by centrifugation at21000×g max for20min at25°C.The concentration of peptide in each remaining superna-tant was determined by measuring its OD280nm.To determine the maximum solubility of each peptide,the peptides were dissolved to saturation in peptide buffer by extensive vortexing and incubation with stirring at25°C overnight.Insoluble material was removed by centrifugation at15000×g for15min at25°C and the amount of dissolved peptide was measured directly by amino acid analysis.Peptide Competitive Displacement of Bound Recombinant PrA from IgG-Sepharose.Recombinant PrA(280µg;6.7nmol) from S.aureus(Pierce)was dissolved in1mL TB-T[20mM HEPES-KOH pH7.4,110mM KOAc,2mM MgCl2,0.1%Tween-20(vol/vol)]and added to280µL of packed pre-equilibrated Sepharose4B(Amersham Biosciences)conjugated with affinity-purified rabbit IgG(ICN/Cappel; 1.87nmoles IgG).After incubation on a rotating wheel overnight at4°C,the resin was washed twice with1mL TB-T,twice with1mL TB-T containing 200mM MgCl2,and twice with1mL TB-T.After the final wash, the resin was divided evenly into14equal aliquots.The peptide was dissolved in peptide buffer at concentrations ranging between0and440µM peptide.Aliquots of400µL of the appropriate peptide solution was added to each PrA-IgG-Sepharose containing tube,and the tubes were then incubated on a rotating platform for3h at4°C followed by1h at25°C. After displacement of bound PrA from the IgG-Sepharose,the resin was recovered by centrifugation on a Bio-Spin column (BioRad),and resuspended in one-bed volume of sample buffer.Samples were separated by SDS-PAGE.Yeast Strains.Strains are isogenic to DH5alpha unless otherwise specified.All yeast strains were constructed using standard genetic techniques.C-terminal genomically tagged strains were generated using the PCR method previously described.7,17Affinity Purification of Proteins and Protein Complexes on IgG-Sepharose.The protocol for the purification of PrA-containing complexes was modified from published methods.18-20For the purification of Kap95p-PrA,yeast cytosol was prepared essentially as previously described.21,22Kap95p-PrA cytosol was diluted with3.75volumes of extraction buffer 1[EB1:20mM Hepes/KOH,pH7.4,0.1%(vol/vol)Tween-20, 1mM EDTA,1mM DTT,4µg/mL pepstatin,0.2mg/mL PMSF]. The diluted cytosol was cleared by centrifugation at2000×g av for10min in a Sorvall T6000D tabletop centrifuge and at 181000×g max for1h in a Type80Ti Beckman rotor at4°C.10µL bed volume of IgG-Sepharose pre-equilibrated in EB1was added per0.5mL of cytosol and the binding reaction was incubated overnight at4°C on a rotating wheel.The resin was recovered by centrifugation at2000×g av for1min in a Sorvall T6000D tabletop centrifuge,transferred to1.5mL snap-cap tubes(Eppendorf),and washed6times with EB1without DTT. For the purification of Nup82p-PrA,cells were grown in Whickerham’s medium21to a concentration of4×107cells/ mL,washed with water and with20mM Hepes/KOH pH7.4, 1.2%PVP(weight/vol),4µg/mL pepstatin,0.2mg/mL PMSF, and frozen in liquid N2before being ground with a motorized grinder(Retsch).Ground cell powder(1g)was thawed into10 mL of extraction buffer2[EB2;20mM Na-HEPES,pH7.4,0.5% TritonX-100(vol/vol),75mM NaCl,1mM DTT,4µg/mL pepstatin,0.2mg/mL PMSF].Cell lysates were homogenized by extensive vortexing at25°C followed by the use of a Polytron for25s(PT10/35;Brinkman Instruments)at4°C.Clearing of the homogenate,binding to IgG-Sepharose,resin recovery and washing was done as above except that10µL of IgG-Sepharose bed volume was used per1g of cell powder and EB2without DTT was used for all the washes.Elution of the PrA tagged complexes was performed as described below.Peptide Elution of Test Proteins and Protein Complexes and Removal of Peptide by Size Exclusion.Kap95p-PrA or Nup82p-PrA bound IgG-Sepharose resin was recovered over a pre-equilibrated Bio-Spin column(BioRad)by centrifugation for1min at1000×g max.Three bed-volumes of440µM(unless otherwise indicated in the text)of eluting peptide in peptide buffer were added per volume of packed IgG Sepharose resin. The elution was carried out for various times(as indicated in the text)at either4°C or at25°C.When elution was complete, the eluate was recovered over a Bio-Spin column.Finally,the resin was washed with one bed-volume of elution buffer to displace more eluted material from the resin and the wash was pooled with the initial eluate.The peptide was removed by filtration of the eluate over a micro spin G25column(Amer-sham Biosciences)as described by the manufacturer.Kap95p-Nup2p in Vitro Binding Experiments.To demon-strate in vitro binding of proteins after elution from the resin, Kap95p-PrA from0.3mL of yeast cytosol was affinity-purified on17.5µL of packed IgG-Sepharose and eluted with52.5µL of440µM Bio-Ox for2.5h at4°C followed by1h at25°C. The resulting sample(total volume88µL)was mixed with0.1µL of E.coli total cell lysate containing Nup2p-GST(generous gift from David Dilworth and John Aitchison23)and brought to a total volume of500µL with TB-T,1mM DTT,4µg/mL pepstatin,0.2mg/mL PMSF.Controls were set up in the absence of either Kap95p-PrA or Nup2p-GST.The samples were incubated at25°C for30min after which40µL of packed,pre-Native Elution of PrA-Tagged Proteins research articlesJournal of Proteome Research•Vol.4,No.6,20052251equilibrated glutathione-Sepharose 4B resin (Amersham Bio-sciences)was added per sample and the incubation was continued at 4°C for 1h.After nine washes with 1mL of TB-T,1mM DTT,4µg/mL pepstatin,0.2mg/mL PMSF,at 25°C,the resin was recovered on Bio-Spin columns as described above and bound material was eluted with 40µL of sample buffer.The samples were resolved on SDS-PAGE alongside an aliquot of input peptide-eluted Kap95p-PrA.To demonstrate the recovery of in vitro reconstituted protein complexes from the resin,Kap95p-PrA from 0.3mL of yeast cytosol was affinity-purified on 10µL of packed IgG-Sepharose and the washed resin was equilibrated in TB-T,1mM DTT,4µg/mL pepstatin,0.2mg/mL PMSF.This pre-bound Kap95p-PrA was mixed with 50µL of E.coli total cell lysate containing Nup2p-GST in a total volume of 1mL of TB-T,1mM DTT,4µg/mL pepstatin,0.2mg/mL PMSF.A mock control experiment was set up in the absence of Nup2p-GST.The binding reaction was carried out for 1h at 4°C and the resin was washed 2times with 1mL of TB-T,2times with 1mL of TB-T containing 100µM ATP and 3times with peptide buffer (all washed were without DTT).Bound material was eluted with 30µL of 440µM Bio-Ox in peptide buffer at 4°C for 2.5h at 4°C followed by 1h at 25°C.Samples were resolved by SDS-PAGE.Figure 1.Addition of a Biotin moiety to the FcIII peptide does not alter the ability of the peptide to competitively displace bound PrA from IgG-Sepharose.(a)Primary sequence and chemical structure of the biotinylated FcIII peptide,Bio-Ox.(b)220µM suspensions of peptides were prepared in buffers of different pHs,and allowed to solubilize.The material remaining in the buffer after centrifugation is plotted for Bio-Ox (closed triangles,black trend line )and FcIII (open circles,gray trend line ;dashed horizontal line represents the starting 220µM level .(c)Increasing amounts of Bio-Ox (closed triangles )and FcIII (open diamonds )were used to competitively displace recombinant PrA from IgG-Sepharose.The amounts of PrA left on the resin after elution were resolved by SDS-PAGE alongside known amounts of PrA standards.The data are displayed on logarithmic scale on both axes.Data are displayed as a %recovery relative to the input PrA amount (i.e.,PrA amount remaining bound in the absence of eluting peptide).Linear regression for both data sets was used to calculate the IC50.research articlesStrambio-de-Castillia et al.2252Journal of Proteome Research •Vol.4,No.6,2005Quantitation and Image Analyses.Band intensities were quantified with the Openlab software (Improvision),and the data was plotted using Excel (Microsoft).Results and DiscussionDesign of the PrA Mimicking Peptide.The hinge region on the Fc fragment of immunoglobulin G (IgG)interacts with Staphylococcus aureus Protein A (PrA).This region was also found to be the preferred binding site for peptides selected by bacteriophage display from a random library.16The specific Fc binding interactions of a selected 13amino acid peptide (termed FcIII),were shown to closely mimic those of natural Fc binding partners.We reasoned that this peptide could be used to efficiently displace PrA tagged proteins from IgG-conjugated affinity resins.Initial trials with FcIII determined that,although it functioned as an eluant,it exhibited a strong tendency to aggregate and its solubility under physiological conditions was not sufficient for many practical purposes,leading to low yields and nonreproducible results.As the high peptide concentrations needed for elution are outside the conditions for which the FcIII peptide was designed,we synthesized several modified peptides based on FcIII,with the specific aim of increasing their solubility and decreasing their degree of aggregation under conditions that would be useful for the isolation of proteins and protein complexes.Among the different alternatives,the most efficient in the displacement of bound PrA-tagged Kap95p from IgG-Sepharose was a peptide in which the amino-terminus of the original FcIII peptide wasFigure 2.Bio-Ox can be used to efficiently compete bound PrA-tagged proteins and protein complexes from IgG-Sepharose in a temperature-dependent fashion.(a )Kap95p-PrA/Kap60p was affinity-purified on IgG-Sepharose from logarithmically growing yeast cells.440µM Bio-Ox was used to competitively displace the bound tagged proteins from the IgG-Sepharose resin.The elution reaction was carried out for the times indicated.At the end of the incubation time eluted proteins (E )and proteins remaining bound to the resin (B )were resolved on SDS-PAGE.(b )Kap95p-PrA (closed squares)and Nup82p-PrA (open squares )were affinity-purified on IgG-Sepharose from logarithmically growing yeast cells and eluted as described above.The amounts of eluted versus resin-bound protein was quantified using the OpenLab software and the elution efficiency for each time point is presented as the percentage of eluted material over the total amount of bound plus eluted material (%eluted).(c )440µM Bio-Ox was used to elute Kap95p-PrA or Nup82p-PrA for 1h at 4°C or 25°C as indicated.Native Elution of PrA-Tagged Proteinsresearch articlesJournal of Proteome Research •Vol.4,No.6,20052253modified by the addition of a Biotin moiety (data not shown).We termed this peptide Bio-Ox (Figure 1,panel a).The solubility of Bio-Ox was measured directly by amino acid analysis and was shown to be ∼3-fold greater than the solubility of FcIII at pH 7.4.In addition,comparison of the solubility of both peptides over a range of pHs indicated that the Bio-Ox was considerably more soluble than FcIII at all but the most extreme pHs tested;importantly,Bio-Ox is very soluble across the full physiological range of pHs (Figure 1,panel b).To determine whether the addition of the Biotin moiety could have altered the inhibiting ability of the peptide,we measured the inhibition constant for Bio-Ox and found it to be comparable with the reported K i for FcIII (∼11nM;data not shown).We then measured the IC 50for competitive displacement for FcIII and Bio-Ox,under conditions in which both were soluble.For this test,commercially available recom-binant PrA from S.aureus was first bound to IgG-Sepharose and then increasing concentrations of the peptide were used to displace the bound PrA from the immobilized IgG (Figure 1,panel c).The apparent IC 50was found to be 10.4(3.2µM for FcIII and 9.8(2.6µM for Bio-Ox (mean value of four independent trials (standard deviation of the mean).Taken together,Bio-Ox appears to be as efficient as FcIII at binding to the F c portion of antibodies and competing for this site with Protein A,but is far more soluble in physiologically compatible buffers,a key requirement for an efficient elution peptide (Figure 3).Experimental Design of the Competitive Elution Procedure.The principle of the method is as follows;genomically PrA-tagged proteins of interest are expressed in yeast and affinity isolated on IgG-conjugated Sepharose resin.Depending on the conditions used for lysis and extraction,the test protein can be recovered in native form either in isolation or in complexes with protein partners.After binding,the resin is recovered by centrifugation and washed extensively to remove unbound material.The bound material is competitively displaced from the IgG-Sepharose resin by incubation with 440µM Bio-Ox peptide in peptide buffer for 2h at 4°C.Finally,the peptide is rapidly (<1min)removed from the eluted sample by fraction-ation over a size exclusion spin column.Given a typical protein of average abundance,1-10µg of pure protein can be recovered from 1g of cells using this method.Figure 3.Elution of Kap95-PrA/Kap60p is dose dependent.(a )Kap95p-PrA was affinity-purified on IgG-Sepharose from loga-rithmically growing yeast cells and eluted using increasing concentrations of Bio-Ox peptide as indicated.(b )The elution efficiency measured as described in Figure 2was plotted versus the peptide concentration in logarithmic scale as indicated.Figure 4.Eluted Kap95p-PrA/Kap60complex retains its biological activity.(a )Kap95p-PrA was prepared by affinity purification followed by Bio-Ox peptide elution (Kap95-PrA eluate ).Three binding reactions were then set up containing eluted Kap95p-PrA and Nup2p-GST bacterial lysate,Kap95p-PrA alone or Nup2p-GST alone.At the end of the incubation,Nup2p-GST was affinity-purified on glutathione-Sepharose and the immobilized material was eluted from the resin with sample buffer and resolved on SDS -PAGE (GST bound ).(b )Kap95p-PrA was immobilized on IgG-Sepharose and incubated with (+)or without (-)bacterial lysate containing Nup2p-GST.The resulting material was eluted using Bio-Ox.Eluate (E )and resin bound (B )material was resolved on SDS-PAGE.*,indicates a Nup2p breakdown product.Table 1.Elution Efficiency for PrA Tagged Nupsname of nup%yieldNup53p 56Nup59p 81Nup84p 88Nup85p 81Nic96p 76Nsp1p 99Nup1p 99Nup120p 69Nup157p 82Nup159p 53Nup170p 80Nup192p 76Gle2p 90research articlesStrambio-de-Castillia et al.2254Journal of Proteome Research •Vol.4,No.6,2005To explore the characteristics of Bio-Ox elution under conditions that preserve native protein complexes,we chose to work with the yeast karyopherin Kap95p-PrA/Kap60p com-plex,24and with the yeast nucleoporin Nup82p-PrA/Nsp1p/ Nup159p complex.25,26This choice was dictated by our interest in the structure and function of the yeast nuclear pore complex (NPC).17,27Optimization of the Elution Conditions.An elution time course for Kap95p-PrA/Kap60p and Nup82p-PrA from IgG-Sepharose at4°C is shown in Figure2,panels a and b.In both cases,the elution was virtually complete after2h at4°C.The largest difference in elution efficiency between the two test proteins was found at the earlier time points.Thus,more than 50%of initially bound Kap95p-PrA was displaced by10min, while it took∼1h to obtain the same result with Nup82p-PrA. We also determined the temperature dependence of the elution process(Figure2,panel c).Elutions of Kap95p-PrA and Nup82p-PrA with Bio-Ox,for1h were compared at4°C and 25°C(Figure2,panel c),showing that elution was improved at25°C over4°C for both test proteins.These various factors underscore the need to conduct appropriate test experiments to determine the optimal conditions for any given application. For example,elution for shorter periods and at4°C is preferable when the proteins under study are sensitive to denaturation,dissociation or proteolytic degradation.We also tested the dependence of elution efficiency upon Bio-Ox concentration.For this test,Kap95p-PrA bound to IgG-Sepharose was competitively displaced using increasing amounts of Bio-Ox peptide for4h at4°C.(Figure3).Bio-Ox peptide displaced IgG-Sepharose bound PrA tagged Kap95p with an apparent IC50of60.8µM.For practical purposes,the protocol we use in most cases takes advantage of the high solubility of Bio-Ox to obtain maximally efficient elutions,utilizing a concentration of440µM of Bio-Ox peptide for2h at4°C.To test the general applicability of the method,we performed peptide elution experiments using a series of PrA tagged proteins that were available in our laboratories.17The yield for these proteins was in all cases>50%and in most cases was >80%(average yield78%(14%;Table1).Eluted Proteins Retain their Biological Activity.The trans-location of macromolecules between the nucleus and cytosol of eukaryotic cells occurs through the NPC and is facilitated by soluble transport factors termed karyopherins(reviewed in ref28).Nucleoporins that contain FG peptide repeats(FG Nups)function as binding sites for karyopherins within the NPC.One example of an FG Nup-karyopherin interaction is represented by the binding of the Kap95p/Kap60p complex to Nup2p,29an interaction that requires both karyopherins to be natively folded.30,31We took advantage of this interaction to demonstrate that the Bio-Ox eluted Kap95p-PrA/Kap60p com-plex retains its biological activity and is able to bind Nup2p in vitro(Figure4,panel a).In this test,Kap95p-PrA was affinity-purified and eluted from IgG-Sepharose as described above. The eluate was incubated with whole cell lysate from E.coli expressing Nup2p-GST,23and GST-tagged Nup2p was isolated over gluthatione-Sepharose resin.As a control,the same experiment was performed either in the absence of Nup2p-GST containing bacterial lysate or in the absence of Kap95p-PrA eluate.As shown,Nup2p-GST binds specifically and directly to the peptide-eluted Kap95p-PrA/Kap60p complex. This result is consistent with reported data and demonstrates that elution with Bio-Ox does not alter the native state and biological activity of Kap95p-PrA.Moreover,the apparent equimolar stoichiometry of the Nup2-GST/Kap95p-PrA/Kap60p complex indicates that essentially all of the peptide eluted karyopherins were in their native,active conformation.This result underscores the usefulness of this method for the preparation of native protein samples.The method can also be used for in vitro reconstitution experiments of biologically relevant protein-protein interac-tions of interest.For this test,Kap95p-PrA was affinity isolated on IgG-Sepharose,Nup2p-GST was bound to the immobilized Kap95p-PrA and then the reconstituted complex was competi-tively displaced from the resin by Bio-Ox peptide elution(Figure 4,panel b).This shows that the method can be used in vitro to study protein-protein interactions using purified compo-nents.ConclusionWe have used the Bio-Ox technology extensively in our laboratories for a wide variety of applications including:(1) the semipreparative purification of∼30PrA-tagged natively folded Nups for the determination of their sedimentation coefficient over a sucrose velocity gradient(S.Dokudovskaya, L.Veenhoff,personal communication);(2)the isolation of yeast cyclins and cyclin-Cdk associated proteins;32(3)the semi-preparative purification of enzymatically active Dpb4p-PrA chromatin remodeling/histone complexes;33and(4)the study of the in vitro binding property of proteins of interest using blot and resin binding experiments.34Thus,this method should be generally applicable to the native purification of most other proteins and protein complexes.Acknowledgment.We are very grateful to David Dil-worth and John Aitchison for the generous gift of bacterially expressed Nup2p-GST.We are deeply indebted to Rosemary Williams for her skilled technical assistance throughout the course of this study and to all members of the Rout and Chait laboratories and of the Proteomic Research Center,past and present,for their continual help and unwavering support.We are particularly grateful to Markus Kalkum,Bhaskar Chan-drasekhar,Svetlana Dokudovskaya and Liesbeth Veenhoff.This work was supported by grants from the American Cancer Society(RSG-0404251)and the NIH(GM062427,RR00862,and CA89810).References(1)Uhlen,M.;Forsberg,G.;Moks,T.;Hartmanis,M.;Nilsson,B.Fusion proteins in biotechnology.Curr.Opin.Biotechnol.1992, 3(4),363-369.(2)Nygren,P.A.;Stahl,S.;Uhlen,M.Engineering proteins to facilitatebioprocessing.Trends Biotechnol.1994,12(5),184-188.(3)Baneyx,F.Recombinant protein expression in Escherichia coli.Curr.Opin.Biotechnol.1999,10(5),411-421.(4)LaVallie,E.R.;McCoy,J.M.Gene fusion expression systems inEscherichia coli.Curr.Opin.Biotechnol.1995,6(5),501-506.(5)Nilsson,J.;Stahl,S.;Lundeberg,J.;Uhlen,M.;Nygren,P.A.Affinity fusion strategies for detection,purification,and im-mobilization of recombinant proteins.Protein Expr.Purif.1997, 11(1),1-16.(6)Einhauer,A.;Jungbauer,A.The FLAG peptide,a versatile fusiontag for the purification of recombinant proteins.J.Biochem.Biophys.Methods2001,49(1-3),455-465.(7)Aitchison,J. D.;Blobel,G.;Rout,M.P.Nup120p:a yeastnucleoporin required for NPC distribution and mRNA transport.J.Cell Biol.1995,131(6Pt2),1659-1675.(8)Grandi,P.;Doye,V.;Hurt,E.C.Purification of NSP1revealscomplex formation with‘GLFG’nucleoporins and a novel nuclear pore protein NIC96.EMBO J.1993,12(8),3061-3071.(9)Stirling,D.A.;Petrie,A.;Pulford,D.J.;Paterson,D.T.;Stark,M.J.Protein A-calmodulin fusions:a novel approach for investigat-ing calmodulin function in yeast.Mol.Microbiol.1992,6(6),703-713.Native Elution of PrA-Tagged Proteins research articlesJournal of Proteome Research•Vol.4,No.6,20052255。

Numerical Predication of Cracking Reaction of Particle Clusters in

Chinese Journal of Chemical Engineering, 16(5) 670ü678 (2008)Numerical Predication of Cracking Reaction of Particle Clusters in Fluid Catalytic Cracking Riser Reactors*WANG Shuyan ( )1,**, LU Huilin ( )1, GAO Jinsen ( )2, XU Chunming ( ҝ )2 and SUN Dan ( ӥ)11 School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, China2 State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, ChinaAbstract Behavior of catalytic cracking reactions of particle cluster in fluid catalytic cracking (FCC) riser reac-tors was numerically analyzed using a four-lump mathematical model. Effects of the cluster porosity, inlet gas ve-locity and temperature, and coke deposition on cracking reactions of the cluster were investigated. Distributions of temperature, gases, and gasoline from both catalyst particle cluster and an isolated catalyst particle are presented.The reaction rates from vacuum gas oil (VGO) to gasoline, gas and coke of individual particle in the cluster are higher than those of the isolated particle, but it reverses for the reaction rates from gasoline to gas and coke. Less gasoline is produced by particle clustering. Simulated results show that the produced mass fluxes of gas and gasoline increase with the operating temperature and molar concentration of VGO, and decrease due to the formation of coke.Keywords cluster, fluid catalytic cracking, numerical simulation, riser1 INTRODUCTIONFluid catalytic cracking (FCC) is considered to be one of the most important petroleum refining proc-esses. The fluid catalytic cracking involves the con-version of heavy oil feedstock into gasoline and other valuable products [1]. The FCC unit comprises mainly of a riser and a regenerator. The vacuum gas oil (VGO) is dispersed into the riser bottom in the form of drops through a feed nozzle system. The VGO drops contact hot regenerated catalyst particles from the regenerator and get vaporized. The vapor entrains the catalyst par-ticles and the liquid drops getting cracked on the cata-lyst surface along the riser. In this process, the catalyst is progressively deactivated due to the deposition of coke formed during cracking reactions on its surface. The deactivated catalyst leaving the riser top is trans-ferred to the regenerator where its activity is restored by burning the coke. Therefore, hydrodynamics of the catalyst particle in the riser controls the performance of the FCC unit.It is generally agreed that the suspended particles may partially form denser clusters in the riser. These clusters move upward through the center of the riser and fall down along the riser wall [2]. Flow charac-terization of clusters has been experimentally investi-gated in the circulating fluidized beds (CFBs) [3, 4]. The particle clustering leads to inefficient gas-solids contact, and therefore affects on CFB performance. Hence, in-depth knowledge of the cluster behavior is essential for designing and operating the FCC units.Many numerical simulations have been per-formed to obtain the performance of the FCC unit based on catalyst reaction kinetic models [5, 6]. Most of them represents oil components in a few lumps, including the three-lump cracking model [7] to study gasoline production in a FCC unit and the four-lump model [8, 9] to describe the catalytic cracking of gaso-line, the five-lump model to consider the heavy frac-tion and with the gas oil splitting into paraffins, naphthenes, and aromatics [10], and the more detailed ten-lump kinetic model to take into account for dif-ferent feed properties in addition to the boiling point range [11]. Flow and cracking reactions have been predicted by using a three-dimensional computational fluid dynamics (CFD) models for FCC riser with Eul-erian approach and reactions with lumping models. Gupta and Subbarao [12] developed a three-phase model for FCC riser to analyze the effect of feed at-omization on conversion. Obviously, the number of lumps of the proposed models for catalytic cracking reactions may be increased to obtain more detailed descriptions of catalytic cracking reactions and prod-uct distributions [13, 14]. However, the cracking reac-tion models mentioned above have not considered the particle clustering effect on the cracking reactions as well as the flow behavior in the FCC riser reactors.Experiments suggested that the flow behavior of particle clusters be significantly different from single particles in the same flow stream. The clustering plays an important role on performance of CFB risers. It is, therefore, desirable to know characteristic behavior of particles in the clusters compared with that of dis-persed particles. The effects of catalyst particle clus-ters on cracking reaction in a FCC riser reactor is here numerically analyzed. Chemical reactions involve heterogeneous and homogeneous reactions among gas, gasoline and coke. Numerical results provide distribu-tions of temperature, gas and gasoline in the cluster. Effects of inlet temperature and velocity of mixture gases, cluster porosity, and coke formation on the mass fluxes of gas and gasoline were also investigated.2 GOVERNING EQUATIONSFor simplicity, the cluster is assumed to be spherical with a diameter of Dc containing 65 spheri-cal particles as shown in Fig. 1. The particles in theReceived 2007-10-09, accepted 2008-08-06.* Supported by the National Natural Science Foundation of China (50776023) and NSFC-Petro China (20490200). ** To whom correspondence should be addressed. E-mail: wangshuyan@Chin. J. Chem. Eng., Vol. 16, No. 5, October 2008 671cluster are regularly arranged and assumed to be sta-tionary during simulations. The cluster porosity is de-fined as333g c p c /D nd D H . With the particle di-ameter of 100 μm and the cluster size of 688 μm con-taining 65 particles in the cluster, the corresponding porosity is 0.8. Following assumptions are made: (1) The catalyst particle diameter and shape remains con-stant during the reactions; (2) Radiation heat transfer between gases and particles is neglected because of the small temperature difference between gases and particles, and radiation heat transfer between particles and the riser walls is not considered; (3) The instanta-neous vaporization of feeding at the riser entry is as-sumed and the post combustion reaction is not con-sidered; (4) Catalyst particles are very small (and its thermal conductivity is very high), therefore, tem-perature difference between its surface and center may be neglected for individual particles.The vaporized vacuum gas oil (VGO) diffuses into particulate phase and is cracked at the catalyst sur-face. While produced gases diffuse back to gas phase, and the produced coke is simultaneously deposited onto the catalyst surface. The four-lump model (Fig. 2) for cracking reactions kinetics is used in present analysis. The four lumps are feed (VGO), gasoline, gas and coke. The primary cracking of gas-oil is as-sumed to be first order kinetics. The turbulent flow field is computed using a k -İ turbulent model. The conservation equations of mass, momentum, gas speciesand energy in Eulerian coordinates are given as follows.Figure 2 4-lump kinetic model2.1 Gas phase continuity equationThe mass conservation equation of gas can be written as [15, 16]:0j ju t x U U w w w w , 14j (1) 2.2 Gas phase momentum equationThe conservation of momentum for the gas phase is expressed as follows:g g g j i j i j i j i i jj u p u u u t x x x x u g x x U U P P U w §·w w w w¨¸w w w w w ©¹§·w w ¨¸¨¸w w ©¹(2) where g l t P P P is the effective gas viscosity, and the turbulent viscosity 2t /C k P P U H is determined from a k -İ turbulent model.2.3 Gas phase turbulent k -İ modelHere, we employ the standard k -İ turbulence model for simulating turbulent flow in the riser reactor. The standard k -İ turbulence model gives the following turbulent kinetic energy equation [16]:t g R ()j k j jk j k k u k G G t x x x P U U U H V §·w w ww¨¸¨¸w w w w ©¹(3)and the turbulent kinetic energy dissipation rate equationt 121R ()j j j j k u t x x x C G C C G k kP H UH U H V HHUH H §·w w w w¨¸¨¸w w w w ©¹(4)where G k is the production term. The empirical con-stants, C P , V H , C 1 and C 2, are listed in Table 1.2.4 Energy conservation of gas phaseFor the energy balance equation of the gas phaseis written as follows [15, 16]:g g g g g t g g h j ji i i jj C T u C T t x C T H R x x Q O V w w w w ªºw §·w'«»¨¸w w «»©¹¬¼¦(5)(a) Front view (b) Cross-sectional view (0z )Figure 1 The cluster studied in the simulationsChin. J. Chem. Eng., Vol. 16, No. 5, October 2008 672where R i is the reaction rates of route A, B, C, D and E.The heat capacity and the thermal conductivity of the mixture are calculated by the mixing-law:g g i i iC Y C ¦ (6)g g i i iY O O ¦(7) where C g i and Ȝg i are the heat capacity and the thermal conductivity of species i respectively. The heat capac-ity and the thermal conductivity of gas and gasoline were estimated respectively using a modified Lee-Kesler correlation [17] in which the pressure ef-fect is neglected since the typical FCC processes are operated under a relatively low pressure. 2.5 Conservation equation of gas speciesThe mass balance for a gas species k is:g g t Y k j k jk k k i i i jj Y u Y t x Y D M R x x U U P U V w ww w ªº§·w w «»¨¸w w «»©¹¬¼¦ (8) where ıY is the turbulent Schmidt number with ıY ˙0.7. The last term on the right hand side of Eq. (8) is the mass source from the reactions.2.6 Cracking reactions of single catalyst particleFour-lump reaction kinetic models were consid-ered in the present work to represent gas phase cata-lytic cracking reactions. The reaction schemes for these kinetic models are shown in Fig. 2. The four lumps are: VGO (feedstock), gasoline, gas and coke. VGO is cracked to gasoline, gas and coke [18]. Therate of consumption of reactant k per unit catalyst volume can be expressed as [19]:0nk k rk k k C R K C C M §·¨¸©¹ (9) where C k is the concentration of gas component, and C k 0 is the initial concentration of pure component k . The value of n is set to be unit for VGO cracking. Thisimplies that VGO evaporated at the beginning of the cracking reaction is easier to crack than VGO evapo-rated later since heavier components take longer to evaporate. For all other reactions the value of n is set to be zero. The temperature dependence of kineticparameters appearing in Eq. (9) is described by the Arrhenius expression:g exp /rk k k K A E RT (10)The FCC catalyst can be deactivated due to thecoke formation [18, 19]. The coke deposited on the surface of the spent catalyst affects coke-oxidation kinetics. The parameter, M , in Eq. (9) represents the activity factor. Non-selective deactivation of catalystis assumed. The activity factor Mis related to the coke deposition on the catalyst as [18, 19]:cc c c 1exp B B A C M(11)where C c is the coke concentration (mass percentage). The values for deactivation constants A c and B c were taken as 4.29 and 10.4, respectively. The kinetic con-stants for the four lump model used in present simula-tions are listed in Table 2 [20, 21].2.7 Boundary conditions and simulation proceduresInitially, both gas and particle temperatures were set to be 991 K. At the inlet, velocity, gas composition,Table 1 Parameters used in the simulationsinlet gas velocity 1.0 m·s ˉ1diameter of particle 100 m inlet temperature 991 K size of cluster 688 m inlet mass fraction of VGO 0.27 number of particles 65 inlet mass fraction of steam 0.73 porosity of cluster0.8 particle specific heat 1000 J·kg ˉ1·K ˉ1particle density 1730 kg·m ˉ3particle thermal conductivity 0.0454 W·m ˉ1·K ˉ1temperature of particle 991 Kmolecular mass of VGO 400 kg·kmol ˉ1viscosity of VGO 5.0×10ˉ5 kg·m ˉ1·s ˉ1 molecular mass of gas 50 kg·kmol ˉ1viscosity of gas 1.66×10ˉ5 kg·m ˉ1·s ˉ1molecular mass of gasoline 100 kg·kmol ˉ1viscosity of gasoline 1.66x10ˉ5 kg·m ˉ1·s ˉ1molecular mass of steam 18 kg·kmol ˉ1viscosity of steam 2.0x10ˉ5 kg·m ˉ1·s ˉ1molecular mass of coke 400 kg·kmol ˉ1viscosity of coke1.66×10ˉ5 kg·m ˉ1·s ˉ1diffusion coefficient of VGO 8.8×10ˉ6 m 2·s ˉ1diffusion coefficient of gasoline 1.7×10ˉ5 m 2·s ˉ1diffusion coefficient of gas2.064×10ˉ5 m 2·s ˉ1diffusion coefficient of steam2.178×10ˉ5 m 2·s ˉ1empirical constant C 1 1.44 empirical C 2 1.92 empirical constant C ȝ 0.09 empirical ık 1.0 empirical constant ıİ 1.3empirical ıh 1.0Chin. J. Chem. Eng., Vol. 16, No. 5, October 2008 673temperature, turbulent kinetic energy and energy dis-passion are specified:g,g y u u ; g,g,0x z u u ; ,0i i Y Y ; g g,0T T ;g 0.004k u ; 3/2m /k H O (12)where the turbulent mixing length m O is taken as m c 2D O . At the outlet, the boundary conditions are g,g,g,0y x z u u u y x z w w w w w w ; 0i Yyw w ; g 0T y w w ; 0kyw w ; 0y H w w (13) On the particle surface, no-slip boundary condi-tion for gas flow was assumed:0u k H (14)For an isothermal catalytic particle, the tempera-ture at the surface of particle is given, and the mass fractions of gases, gasoline and feedstock are0i Y (15)The governing Eqs. (1) (8) coupled with reaction kinetics and boundary conditions are solved using a finite volume method [22]. The modeled part of the three-dimensional riser and its dimensions are shown in Fig. 1. The cluster is assumed to be located in the center of the computational domain. Each particle in the cluster is labeled. Because the cluster size is so small compared with the riser size, the riser wall effect on the gas flow around the cluster can be ignored.The three-dimensional conjugate flow, heat trans-fer and reactions were solved using the CFD software FLUENT 6.2. Reactions and gases properties were incorporated to the solver code through user defined functions (UDF). Appropriate mixing rules were ap-plied to the model for making all variables composition- dependent. The SIMPLE algorithm was used to couple the pressure and the velocities with the second order upwind method used in the momentum equations and for the energy equation. Fresh gases flow into the cluster and react on the surface of catalyst particles. A set of simulation needs about 24 h of CPU time on PC computer (80 GB hard disk, 128 Mb Ram and of 600 MHz CPU).2.8 Computational domain and gridThe conservation equations of momentum, en-ergy and gas species have been solved numericallyusing the segregated solver module of FLUENT 6.2. Using GAMBIT, a structured grid of triangular cells was created. The unstructured mesh used about 300000 elements. Each particle had 200 300 nodes with 700 1000 elements. The mesh was continually refined up to the point beyond which any further re-finement changed the solution by less than 1.0% at the expense of an enormous increase in CPU time. The effect of number of nodes on the surface of a particle on the drag coefficient is shown in Table 3. Therefore, the results presented herein are believed to be free from domain and grid effects as the number of nodes on a particle is larger than 200.Table 3 Comparison of drag coefficient for anisolated particlePresent simulations (number of nodes on a particle)Re 100 200 300Johnson and Patel [23]10 5.445 4.013 3.986 3.9 20 3.673 2.587 2.515 2.50 50 2.036 1.583 1.534 1.50 1001.546 1.112 1.068 1.053 COMPUTED RESULTS AND ANALYSIS 3.1 Base case simulationsIn the base case simulation, the inlet gas velocity,inlet temperature and porosity were set to be 1.0 m·s ˉ1, 991 K and 0.8, respectively. The terminal velocity ofparticle is about 0.39 m·s ˉ1.In order to validate the simulation, a single sphere suspended in a computational domain was cre-ated. In this work, gas flow past an unconfined sphere which is similar to a particle located in the center of the cluster. The values of drag coefficient are calcu-lated for a range of particle Reynolds number. Table 3 shows the comparison between the present results with the literature values. Three different number of nodes on a particle are used. Present simulations are in agreement with the data in Ref. [23] at the nodes number of 200 300 on a particle.Figure 3 shows the distributions of mass fraction and temperature of gases through the catalyst particle cluster (0Y , 0Z ). The Reynolds number is 4145 based on cluster diameter. The calculated mean gasvelocity inside the cluster is about 0.057 m·s ˉ1 at theinlet gas velocity and porosity of cluster of 1.0 m·s ˉ1 and 0.8. The Reynolds number is 34.4 based on particleTable 2 Kinetics constants used in present simulationsCracking reactionPre-exponential factor A j /m 3·m ˉ3·s ˉ1 Activation energy E j /J·kmol ˉ1ǻH r /J·kg ˉ1route A: AVGO gasoline Ko 3.5890×106 6.836×107 195 route B: BVGO gas Ko 2.5410×107 8.936×107 670 route C: CVGO coke Ko 6.7910×107 6.468×107 745 route D: Dgasoline gas Ko 8.8572×102 5.280×107 512.5 route E: Egasoline coke Ko 5.3198×107 1.1565×108 550Chin. J. Chem. Eng., Vol. 16, No. 5, October 2008674diameter which indicates laminar flow inside the clus-ter. Flow behavior of gases around a particle inside thecluster is different from an isolated particle in the stream. This indicates that the flow around a cluster is similar to the flow around a porosity body. The mass fractions and temperature of gases are spatially varied continuously from the inside to outside of a cluster.Various rates for particle in the cluster and for the isolated particle are shown in Fig. 4. It is found that the reaction rates from VGO to gasoline, gas and coke are higher in the front than those in the back of the cluster, while the reaction rates from gasoline to gas and coke are lower in the front than those in the back of the cluster. For the isolated particle, the reaction rates from VGO to gasoline, gas and coke are higher, and the rate from gasoline to gas and coke is lower comparing with individual particle in the cluster. Fig. 5 shows the produced gas and gasoline molar dis-tributions from each particle in the cluster and from the isolated particle. It is found that the produced gas and gasoline from individual particle in the cluster are more than those from the isolated particle due to the accumulation effect along flow direction. There is avariation of the produced gas and gasoline from parti-cle to particle in the cluster. 3.2 Effect of porosity of clusterThe ratio of gas flux through the cluster to inlet gas flux with the same flowing cross-sectional area of the cluster is shown in Fig. 6 as a function of cluster porosity. With cluster diameters of 638, 757, 866 and 1090 μm, the corresponding cluster porosities are 0.75, 0.85, 0.9 and 0.95, respectively. With the increase of concentration of particles in the cluster, the ratio of gas flux is reduced due to the high flow resistance inside the cluster. Simulated results show that the variation of gas temperature inside the cluster is notobvious with the changes of cluster porosity.Figure 6 Profile of ratio of gas flux through cluster to inlet air flux and averaged gas temperature (u g ˙1 m·s ˉ1, T ˙991 K, mass fraction of VGO ˙0.27, mass fraction of steam ˙0.73, number of particles in the cluster ˙65)With the increase of cluster porosity, more VGO can pass through the cluster and results in the cracking reaction rate increment, as shown in Fig. 7. The reac-tion rates from VGO to gasoline, gas and coke are increased, while the reaction rates from gasoline to gas and coke are decreased with the increase of cluster porosity. The reaction rate of gasoline to gas is almost one magnitude order less than that of VGO to gasoline.These results in the more gasoline and less gas produced,Figure 3 Profile of mass fractions and temperature of gases through the cluster (0Y ,0Z )[u g ˙1 m·s ˉ1, İg ˙0.8, T ˙991 K, mass fraction of steam ˙0.73, mass fraction of VGO ˙0.27 (or concentration of VGO ˙0.2 mol·m ˉ3)]Figure 4 Profile of reaction rates of particles in the clus-ter and an isolated particle (u g ˙1 m·s ˉ1, T ˙991 K, mass fraction of VGO ˙0.27, mass fraction of steam ˙0.73) 1ü11particle in the cluster; 12 isolated particleFigure 5 Distribution of molar fraction of gas and gaso-line from particles in the cluster and isolated particle (u g ˙1.0 m·s ˉ1; İg ˙0.8; T ˙991 K; mass fraction of VGO ˙0.27, mass fraction of steam ˙0.73)1ü11 particles in cluster; 12 isolated particle; gas; gasolineChin. J. Chem. Eng., Vol. 16, No. 5, October 2008 675as shown in Fig. 8. More gasoline and less gas will beproduced with the increase of particle concentration of the cluster. Hence, the particle clustering on the cracking reactions in the FCC riser is obvious.Figure 8 Distribution of mass fluxes of gas and gasolinefrom isolated particle and particles in the cluster [Both num-bers of isolated particles and particles in the cluster are 65, u g ˙1 m·s ˉ1; T ˙991 K; mass fraction of VGO ˙0.27 (or concen-tration of VGO ˙0.2 mol·m ˉ3), mass fraction of steam ˙0.73] Ƶ gas; ƻ gasoline3.3 Effect of inlet gas velocityFigure 9 shows the reaction rates of the cluster and the isolated particle as a function of inlet gas ve-locity. Roughly, the reaction rates from VGO to gaso-line, gas, and coke increase, while the reaction rates from gasoline to gas and coke decrease with the in-crease of inlet gas velocity. For the isolated particle, the effects of inlet gas velocity on the reaction rates are not noticeable.The flow rates of gasoline and gas can be calcu-lated by summing the product of density and mass fraction and velocity with the product of the facet area vector and the facet velocity vector at each grid. Fig. 10 shows the yields of gas and gasoline from the cluster and from the isolated particle as a function of inlet gas velocity. Within the range of gas inlet veloci-ties of 0.4 m·s ˉ1 to 1.6 m·s ˉ1, the variation of produc-tions of gasoline and gases with the inlet gas velocity are not noticeable. It is expected that the clusterbreakup may occur when the inlet gas velocity reaches some point. However the cluster breakage is not con-sidered in present model.3.4 Effect of operating temperatureIncreasing the operating temperature has a posi-tive effect on cracking reactions. Fig. 11 shows the reaction rates of the cluster and an isolated particle as a function of inlet gas temperature. The reaction rates from VGO to gasoline, gas and coke of the isolated particle are higher than those of the cluster. While the reaction rates of gasoline to gas and coke of the cluster are larger than those of the isolated particle. Since the reaction rate from gasoline to gas is higher than that from gasoline to coke, more gasoline will be con-verted to gas.The yield profiles of gas and gasoline are shown in Fig. 12 as a function of inlet gas temperature. The reaction rates were increased as the temperature re-sults in more gas and gasoline produced. For the iso-lated particle, the gas and gasoline yields incrementswith the increase of temperature are expected. The gasFigure 7 Reaction rates as a function of cluster porosity (u g ˙1 m·s ˉ1, T ˙991 K, mass fraction of VGO ˙0.27, mass fraction of steam ˙0.73, number of isolated particle ˙65)Figure 9 Profile of mass fluxes of gas and gasoline as a function of inlet velocity (mass fraction of VGO ˙0.27, mass fraction of steam ˙0.73, İg ˙0.8; T ˙991 K) Ƶ average value of cluster; ƻisolated particleFigure 10 Profile of mass fluxes of gas and gasoline as a function of inlet temperature of mixture gases [Both numbers of isolated particles and particles in cluster are 65, mass frac-tion of VGO ˙0.27 (or concentration of VGO ˙0.2 mol·m ˉ3), mass fraction of steam ˙0.73, İg ˙0.8, T ˙991 K] isolated particle: Ƶ gas; Ʒ gasoline cluster: ƶ gas; Ƹ gasolineChin. J. Chem. Eng., Vol. 16, No. 5, October 2008676production increases much more rapidly than thegasoline production as the temperature increases. However because of the produced gasoline is partially converted to gas by reaction route D, an optimal oper-ating temperature may need to be determined for products selectivity.3.5 Effect of inlet mass fraction of VGOThe cracking reaction rate for route A is propor-tional to the square of the concentration of VGO, while for other reactions the rates are proportional to the concentration of VGO. Hence, the reaction rate increases with the increase of inlet mass fraction of VGO. Fig. 13 shows the reaction rates of the cluster and an isolated particle as a function of inlet mass fraction of VGO. The reaction rates from VGO to gaso-line, gas and coke of the isolated particle are higher than those of the cluster, while the reaction rates from gasoline to gas and coke of the cluster are higher than those of the isolated particle. This indicates that the particle clustering will reduce VGO cracking.Figure 14 shows the distributions of gas and gasoline as a function of inlet mass fraction of VGO.It is noticed that more gasoline produced and less gas production from the isolated particle than those from the individual particle in the cluster. Simulated results indicated that particle clustering will reduce the produc-tion of gasoline and increase the yield of gas in the riser. 3.6 Effect of coke activityIn the present model, the effect of coke deposited on the catalyst is considered by coke concentration C c in Eq. (11). With the increase of C c , the value of activ-ity factor Mdecreases. The cracking reactions of catalyst particle clusters were simulated with different values of the coke concentrations to understand the effect of coke formation on cracking reactions of the clusters. Fig. 15 shows the reaction rates of the cluster and an isolated particle as a function of coke concen-trations. With the formation of coke, the reaction rates of the cluster and the isolated particle are decreased.The predicted mass fluxes of gasoline and gas of the cluster and an isolated particle are shown in Fig. 16 as a function of coke concentrations. It can be seen that when a value 0 for C c was selected, the mass fluxes of gas and gasoline are highest due to the factthat the activity factor equals to unity without cokeFigure 11 Profile of mass fluxes of gas and gasoline as a function of inlet velocity (mass fraction of VGO ˙0.27, mass fraction of steam ˙0.73, İg ˙0.8, T ˙991 K) Ƶ average value of cluster; ƻisolated particle Figure 12 Profile of mass fluxes of gas and gasoline as afunction of inlet temperature of mixture gases [Both num-bers of isolated particles and particles in cluster are 65, u g ˙1 m·s ˉ1, İg ˙0.8, mass fraction of VGO ˙0.27 (or concentra-tion of VGO ˙0.2 mol·m ˉ3), mass fraction of steam ˙0.73] isolated particle: Ƶ gas; Ʒ gasoline cluster: ƶ gas; ƸgasolineFigure 13 Profile of mass fluxes of gas and gasoline as afunction on inlet molar concentration of VGO (u g ˙1.0 m·s ˉ1,İg ˙0.8, T ˙991 K) Ƶ average value of cluster; ƻisolated particleFigure 14 Effect of coke contents on mass fluxes of gasand gasoline (Both numbers of isolated particles and particles in cluster are 65, u g ˙1 m·s ˉ1, İg ˙0.8, T ˙991 K) isolated particle: Ƶ gas; Ʒ gasoline cluster: ƶ gas; Ƹ gasoline。

汞在不同粒径大气颗粒物中的分布

2004年5月7日收稿.　3973项目(2003CB415003)和中国科学院知识创新项目(KZCX 32SW 2424)资助.汞在不同粒径大气颗粒物中的分布3王章玮　张晓山　张　逸　权建农(中国科学院生态环境研究中心,北京100085)摘　要　采用DF G 21型五段分级采样装置及冷蒸汽原子荧光法,对北京市冬、春、夏和秋季不同粒径大气颗粒物(分别为≤111μm ,111—210μm ,210—313μm ,313—710μm 和≥710μm )中的汞进行分析.结果表明:北京大气颗粒物中汞的浓度在0160—3195ng ・m -3之间,冬季平均浓度为2185ng ・m -3,远大于其它季节;大气颗粒物中的汞呈双峰分布,在≤111μm 的细颗粒和粗粒径处各有一峰值;北京大气颗粒物中的汞主要分布在≤111μm 的细颗粒中,不同粒径颗粒物中汞的分布随季节变化而变化,冬季各粒径颗粒物中汞的浓度比其它季节高;大气颗粒物中汞的质量中值粒径(MMD )冬季为0171μm ,其它季节均大于110μm ;北京大气颗粒物中的汞至少有50%可进入人体呼吸系统,且冬季最为严重.关键词　汞,大气颗粒物,粒径,分布. 大气环境中存在不同形式的汞化合物,它们在传输和沉降过程中具有不同物理和化学特性[1].单质汞在大气中停留时间长达几个月甚至两年;颗粒态汞的停留时间仅为3—5天,其传输的距离主要由颗粒物的粒径及质量决定[2],颗粒物的粒径不同,在大气中传输的距离不同,其通过干、湿沉降从大气中的清除过程也不同,从而对汞在大气中的循环和分布,尤其对汞在陆地生态系统与水生生态系统中的沉降起着重要的影响.因此对汞在不同粒径大气颗粒物中分布特征的研究显得尤为重要. 本文通过采集北京市区不同粒径大气颗粒物样品,用冷蒸汽原子荧光法测定样品中汞的浓度,分析了不同季节大气颗粒物中汞的污染及分布规律.1　实验部分111　样品的采集采用HV 21000型大流量TSP 采样器,配有DF G 21型五段多孔冲击分级器采集大气颗粒物样品,其粒径分布为:≤111μm (F5),111—210μm (F4),210—313μm (F3),313—710μm (F2)和≥710μm (F1),各级段50%收集效率切割粒径值的选择基本与“ISO 标准”中呼吸道主要部位沉积粒径的中位径相接近,分级粒径范围及卫生意义为:≥710μm 颗粒物大多数被人体阻止在体外,710—313μm 范围的颗粒物可穿透滞留在人体呼吸道,313—210μm 之间的颗粒物能穿透滞留在人体支气管,210—111μm 能穿透滞留在支气管末梢,≤111μm 能穿透滞留在人体肺泡上. 于2003年1月(冬)、4月(春)、7月(夏)和10月(秋)在中国科学院生态环境研究中心楼顶采集不同粒径的大气颗粒物样品,采样高度离地15米,采样时气体流量566L ・min -1,采样月内上、下旬各采集一次样品,每次持续48h ,采样用滤膜为玻璃纤维滤膜,此滤膜在使用前需在马弗炉内450℃灼烧5h ,以减少空白对测定的影响,采样后滤膜用铝铂包好,立即置于-20℃保存,待分析.112　样品的分析样品采集后,取一定面积的采样滤膜,加入高锰酸钾2硫酸2过硫酸钾混合氧化剂溶液,超声萃取30min ,放置过夜,使附着在颗粒物上的各种形态的汞均被氧化为高价态,用盐酸羟胺还原过量的氧化剂,以0105%的K BH 4和215%的HNO 3为载流,冷蒸汽原子荧光测定样品中的汞.2　结果与讨论第24卷　第1期2005年 1月环　境　化　学ENV IRONM EN TAL CHEM ISTR Y Vol.24,No.1January 2005211　北京大气总悬浮颗粒物(TSP )中的汞将五级颗粒物样品中汞的浓度进行加和处理,得到大气总悬浮颗粒物(TSP )中汞的浓度.不同季图1　不同季节TSP 中汞的浓度g 11　The concentration of mercury in TSP for different seas ons 节北京大气总悬浮颗粒物中汞的浓度变化情况示于图11采样期间TSP 中汞的浓度在0160—3195ng ・m -3之间,冬季TSP 中汞的平均浓度为2185ng ・m -3,远大于其它季节,这与北京冬季采暖密切相关,虽然北京市对采暖用燃料进行改革,但大部分采暖仍以烧煤为主,煤中的汞是大气中汞污染的重要来源.从表1各地区大气总悬浮颗粒物中汞浓度的比较可以看出,北京大气TSP 中汞的浓度与重庆基本一致,与长春、底特律及北美城区水平相当,但远远高出背景地区大气颗粒物中的汞浓度,表明北京大气已受到一定程度汞的污染.表1　各地区大气TSP 中汞浓度的比较(ng ・m -3)T able 1　Compare of concentration of mercury in TSP for different areas地　点年　份范　围平　均出　处北美地区1993—199401015—1120—[5]底特律19950112—01550138[6]重庆1996018—518—[4]长春1999—200001022—1198401303[3]背景地区1993—199401001—01086—[5]北京20030160—31951129本文212　不同粒径大气颗粒物中汞的分布特征不同季节不同粒径大气颗粒物中汞的浓度示于图2.从图2可见,汞在不同粒径大气颗粒物中的浓度随季节而发生变化.冬季≤111μm 颗粒物中汞的浓度为1154ng ・m -3,分别是春、夏和秋季的513,519和610倍;从其它各粒径来看,冬季颗粒物中汞的浓度也比春、夏和秋季相应粒径中汞的浓度高,但不如≤111μm 颗粒物的明显,可见冬季大量的燃煤对不同粒径颗粒物中的汞均有影响,其中对≤111μm 的颗粒物影响最明显,煤燃烧时主要排放<110μm [6]的细颗粒物,同时011—110μm 的细粒子在大气中停留时间长且能够进行长距离的传输[7],北京冬季盛行西北风可能导致北京以北地区燃煤采暖排放的细粒子长距离传输,这也是北京地区冬季大气细粒子中汞浓度高的原因之一.从图2还可看出,除了冬季,春季各粒径颗粒物中汞的浓度比夏和秋季高,尤其是春季(≥710μm 和111—210μm ),这是由于北京春季风沙大、地面扬尘多,且春季部分居民继续燃煤取暖造成的. 另外,不同季节大气颗粒物中汞均呈双峰分布,尤其冬、秋季这一分布规律更明显,这与Keeler G [5]和Pirrone N [6]等的研究一致,这一现象也可以从图3不同粒径颗粒物中汞百分浓度看出.不同季节大气颗粒态汞主要分布在≤111μm 的颗粒中,其不同粒径颗粒态汞占总量的比例随季节而发生变化,冬季大气颗粒态汞主要分布在≤111μm 的细颗粒,其次是≥710μm 颗粒,所占百分比分别为5411%和1419%;春季大气颗粒态汞则分散在粗细颗粒上,不同粒径汞百分浓度差别不明显,≤111μm 的细颗粒仅占2814%,略高于其它粒径;夏季主要分布在≤210μm 的颗粒物中,占其总量的5517%;秋季以≤111μm 和313—710μm 为主,分别占3913%和2312%1这一分布规律可能与不同季节汞的排放源及空气扩散条件有关. 表2是不同季节≤210μm 颗粒物中汞的浓度及百分比.根据表2的结果可知,≤210μm 可吸入　1期王章玮等:汞在不同粒径大气颗粒物中的分布73　颗粒物中汞的浓度在0129—1193ng ・m -3之间,冬季最高,占全年PM 210的6211%,表明冬季北京大气可吸入颗粒物中汞的污染严重;不同季节≤210μm 的颗粒物中,汞占总悬浮颗粒物中汞的比例不一样,冬季最高为6716%,其它季节均在50%左右.这表明北京大气颗粒物中的汞至少有50%可进入人体呼吸系统.图2　不同季节不同粒径大气颗粒物中汞的浓度Fig 12　The concentration of mercury indifferent size particlesfor four seasons 图3　不同粒径颗粒物中汞的百分浓度Fig 13　Fractional concentration of mercury in different diameter airborne particles表2　不同季节≤210μm 颗粒物中汞的浓度及百分比T able 2　Concentration of mercury and propotion in ≤210μm particles for different seasons冬春夏秋PM 210/ng ・m -31193015101380129PM 210/TSP/%6716491255174614全年平均百分比/%621116141213913213　大气颗粒物中汞的富集特征将汞在不同粒径颗粒物中的累计百分数与颗粒物空气动力学直径的自然对数进行线性回归计算,可获得很好的一系列的直线,其相关系数在01995以上(表3),表明在不同季节里大气颗粒物中汞与粒径的自然对数呈正态分布1大气颗粒物中的污染物在人体呼吸系统内主要沉积部位和沉积量与颗粒物的质量中值直径(MMD )有关,MMD 可以很好的反映污染物在颗粒物中的集中趋势,由表3可知,在冬季颗粒物中汞的MMD =0171μm ,与Keeler 对底特律大气颗粒物中的汞基本一致,其它季节的MMD >110μm ,更进一步说明冬季颗粒物中的汞主要富集在<110μm 的细粒子中,而其它季节则分散在各粒径中. 从离散度(σg )来看,各季节σg 基本一致,无明显变化,这表明采样期间采样点周围无点排放源的影响,大气颗粒物中汞的来源主要是携带汞污染物的气溶胶不断扩散和输送所致.表3　不同季节大气中颗粒态汞随粒径回归关系T able 3　Regression coefficient on different size distribution of ambient particles季节r Y =aln x +b MMD/μm σg /μm 冬019969Y =016799ln x -01022701712108春019954Y =017663ln x -01487511891131夏01999Y =0173ln x -01391911721137秋019989Y =015474ln x -011426113011833　结　论北京大气颗粒物中汞的浓度在0160ng ・m -3—3195ng ・m -3之间,冬季颗粒物中汞的平均浓度为2185ng ・m -3,远大于其它季节1不同季节大气颗粒态汞主要分布在≤111μm 的颗粒中,其不同粒径74　环境化学24卷颗粒态汞占总量的比例随季节而发生变化;冬季不同粒径中汞浓度均大于其他季节,尤其是≤110μm 的细颗粒,春季也略比夏、秋季高;大气颗粒物中汞均呈双峰分布,在≤111μm 的细颗粒和粗粒径处各有一峰值,冬、秋季这一分布规律更明显;冬季MMD =0171μm ,其它季节MMD 均大于110μm ;不同季节大气颗粒物中汞来源主要是携带汞污染物的气溶胶不断扩散和输送所致;北京大气颗粒物中汞至少有50%可进入人体呼吸系统,且冬季最为严重1参　考　文　献[1]　Dean W Boening ,Ecological Effects ,Transport ,and Fate of Mercury :A G eneral Review.Chemosphere ,2000,40∶1335—1351[2]　William H Schroeder ,John Munthe ,Atmospheric Mercury —An Overiew.A t mospheric Envi ronment ,1998,32∶809—822[3]　方凤满,王启超,长春市大气颗粒汞污染特征及影响因子分析.环境科学学报,2001,21(3)∶368—372[4]　王定勇,李孝华,重庆大气汞初步调查.重庆环境科学,1996,18(4)∶59—62[5]　K eeler G ,Particulate Mercury in the Atmosphere :Its Significance ,Transport ,Transformation and Sources.W ater ,A i r and SoilPoll ution ,1995,80(1/4)∶159—168[6]　Pirrone N ,G linsorn G ,K eeler G ,Ambient Levels and Dry Deposition Fluxes of Mercury to Lakes Huron ,Eric and St.Clair.W ater ,A i r and Soil Poll ution ,1995,80∶179—188[7]　Andreae M ,Andreae T ,Annegarn H et al ,Airborne Studies Aerosol Emission From Savanna Fires in Southern Africa ,2,Aerosolchemical composition.J.G eophysical Research ,1998,103∶32119—32129PARTICL E SIZE DISTRIBUTIONS OF ATMOSPHERICMERCUR Y IN BEIJ NGW A N G Zhang 2wei ZHA N G Xiao 2shan ZHA N G Yi Q UA N Jian 2nong(Research Center for Eco 2Environment Sciences ,Chinese Academy of Sciences ,Beijing ,100085)ABSTRACT Mercury on different diameter airborne particles (≤111μm ,1.1—210μm ,210—313μm ,313—710μm 和≥710μm )were determined with cold vapor atomic fluorescence in different seasons in Beijing.The results were showed that the concentration of particulate Hg was 0160—3195ng ・m -3,and mean con 2centration was 2185ng ・m -3in winter ,which much higher than the other seasons.The distribution of particulate Hg was bimodal with an obvious fine and coarse mode.The main part of atmospheric particulate mercury was distributed fine particles (≤111μm ),and the percent of mercury in different diameter to that in total particulate matter was change with seasons ,and in winter the concentration of mercury in dif 2ferent sizes was highest of all seasons.The value of mass media diameter (MMD )of particulate mercury in winter was 0171μm ,and that was more than 110μm in other seasons.There was no less than 50%of particulate mercury can inhale into human body ,especially in winter. K eyw ords :mercury ,atmospheric particles ,particle size ,distribution.　1期王章玮等:汞在不同粒径大气颗粒物中的分布75　。

E-2005-53c

联合国E /2005/53经济及社会理事会 Distr.: General3 May 2005Chinese Original: English 05-33112 (C) 310505 3105052005年实质性会议2005年6月29日至7月27日，纽约临时议程*项目13(m)经济问题和环境问题：危险货物的运输危险货物运输和全球化学品统一分类标签制度专家委员会的工作秘书长的报告摘要摘要依照经济及社会理事会第645 G(XXIII)号决议，秘书长每两年向经社理事会提出关于危险货物运输和全球化学品统一分类标签制度专家委员会及其两个小组委员会工作的报告。

本报告涉及专家委员会2003-2004两年期的工作以及经济及社会理事会第2003/64号决议的实施情况。

依照这项决议，秘书处出版了《关于危险货物运输的建议：示范条例》的第十三修订版、《关于危险货物运输的建议：检验和标准手册》的第四修订版和《全球化学品统一分类和标签制度》（《全球统一制度》）第一版。

关于海上、空中、公路、铁路或内陆水道的危险货物国际运输的所有主要法律文书或规则均已作出相应修正，从2005年1月1日起生效，而许多国家政府也已将《示范条例》内的一些规定纳入本国的交通立法，从2005年起适用。

__________________* E/2005/100。

E/2005/53许多国家政府和国际组织采取了有关步骤修正现有的国内和国际立法，以便在2008年这一建议的目标日期之前实施《全球统一制度》。

委员会通过了《示范条例》及《检验和标准手册》的修正案，主要是关于事故报告；爆竹烟花分类；与《全球统一制度》协调一致；传染性物质、放射性物质和有害环境物质的运输；新型危险物质和物品；装载和运输作业条件；气溶胶喷罐；以及轻便油罐的冲击测试。

委员会还通过了对《全球统一制度》的修正案，主要是澄清有毒物质的分类标准、增加了吸入后有害的物质的标准，并增加了关于警告说明、安全数据表和标志的指导条文。

美国2005年版Prentice Hall《化学》教材中的单位教学

美国２００５年版ＰｒｅｎｔｉｃｅＨａｌｌ《化学》教材中的单位教学作者：朱雪莲周青来源：《化学教学》2008年第05期摘要：在中学化学教学中，教师常发现学生单位学习和运用方面存在着较大问题。

美国2005 年版Prentice Hall《化学》教材的设计对我们突破单位教学难点有一定的启示，文章介绍并分析该教材中的单位教学内容，以期从中得到一些有益的启示。

关键词：教材；单位；科学测量文章编号：1005－6629(2008)05－0044－04中图分类号：G633.2 文献标识码：B在中学化学教学中，教师常发现学生单位学习和运用方面存在着较大问题。

例如，七个SI 基本单位中，物质的量单位“摩尔(mol)”是高一学生学习化学的基本内容之一。

很多教师认为“物质的量”在教学中是个难点。

对高一学生而言，物质的量是以前从未听过的抽象概念，理解和掌握它有很大的难度，甚至有些学生在整个高中化学学习结束后，对物质的量的理解还是含糊不清，导致了教师在给学生介绍这个知识点时，有些不知所措，怎么讲学生都理解不了。

学生学习化学单位出现类似问题的原因主要有两方面：一是缺乏对单位意义和重要性的感性认识；二是对单位的意义及其计算缺乏系统性的训练。

要突破单位教学的难点，需要加强单位的意义、单位基础知识以及单位换算等方面的教学，从单位对于化学学科的整体意义方面进行教学。

美国2005 年版Prentice Hall《化学》教材[1]的设计对于我们突破单位教学难点有一定的启示，文章将该教材中单位教学内容与国内的进行比较分析，以期为中学化学教师提供参考。

1美国《化学》教材中单位教学内容及特点美国2005 年版Prentice Hall《化学》教材将关于单位及其换算问题编排在第3章“科学测量(SCIENTIFIC MEASUREMENT)”和第10章“化学量(CHEMICAL QUANTITIES )”内容中[2]。

“科学测量”主要由3节内容构成，分别为：测量及其不确定性(Measurements and Their Uncertainty)；国际单位制(The International System of Units)；转换问题(Conversion Problems)。

贫铀合金球对Q235_钢靶侵彻性能研究

第20卷第11期装备环境工程2023年11月EQUIPMENT ENVIRONMENTAL ENGINEERING ·1·收稿日期：2023-05-25；修订日期：2023-08-14 Received ：2023-05-25；Revised ：2023-08-14基金项目：国家安全重大基础研究（14021005020302）Fund ：Major Basic Research Projects on National Security (14021005020302)引文格式：王存洪, 郑文凯, 吴翰林, 等. 贫铀合金球对Q235钢靶侵彻性能研究[J]. 装备环境工程, 2023, 20(11): 1-7.WANG Cun-hong, ZHENG Wen-kai, WU Han-lin, et al. Penetration Performance of Depleted Uranium Alloy Ball on Q235 Steel Target[J]. Equipment Environmental Engineering, 2023, 20(11): 1-7. *通信作者（Corresponding author ）贫铀合金球对Q235钢靶侵彻性能研究王存洪，郑文凯，吴翰林，曹玉武，孙兴昀*（西安近代化学研究所，西安 710065）摘要：目的研究贫铀合金球对Q235钢靶的侵彻行为，为贫铀合金材料侵彻行为的深入研究以及在战斗部中广泛应用提供支撑。

方法采用Johnson-Cook 强度模型和失效模型建立贫铀合金球撞击Q235钢靶的模型，利用Abaqus/explicit 模块模拟研究贫铀合金球初速与尺寸对剩余速度、扩孔面积、侵彻深度的影响，并对结果进行分析。

结果通过试验与模拟得到了贫铀合金球的穿靶极限速度，两者结果基本吻合，验证了模型参数的准确性。

控制燃气轮机排放的CLN技术

第 12 卷第 3/4 期2010 年 10 月燃气轮机发电技术控制燃气轮机排放的CLN技术董斌，马正军，俞世康，刘晗（中国船舶重工集团公司第七O三研究所，黑龙江哈尔滨150001）摘要：环保要求推动燃气轮机排放污染物控制技术的发展，程大酉博士领导开发的Cheng Low NO x System （CLN）技术可以同时减少NO x、CO，十年来该技术完成了理论研究、试验室验证和工程应用，受到人们的关注。

在Alison、LM2500等航改型燃气轮机上应用CLN技术，NO x可低至5×10-6，同时CO可保持在一位数，CO2可以减少20%，同样在工业燃气轮机上采用CLN技术也能取得良好的效果。

虽然还有需要继续研究的内容，但该技术的市场前景预期令人期待。

关键词：燃气轮机；低排放；CLN技术。

0 引言全球环境污染已成为世界性问题，京都议定书等对污染物排放提出限制。

燃气轮机需要高效、低排放、可靠的燃烧室，以满足越来越严格的NO x及CO的排放控制要求。

目前燃气轮机控制NO x主要有三种方式：控制燃烧、催化燃烧和燃烧后还原处理。

控制燃烧通过降低峰值火焰温度来控制热力NO x，峰值火焰温度可以通过燃料和空气混合、燃烧区局部过量空气、燃料停留时间长短以及燃烧功率密度等影响因素进行控制[1]，主要有贫预混DLN/DLE和注水/蒸汽技术；催化燃烧涉及燃料和空气在催化表面的无火焰燃烧，无火焰燃烧温度需低于NO x形成的极限温度；燃烧后还原技术主要是选择性催化还原（SCR），燃烧生成物中的NO x在催化剂表面与氨等还原剂作用，从而减少NO x排放[2]。

DLN/DLE、SCR和注水/蒸汽等技术在控制NO x排放的同时，热耗率会增加，CO排放也会升高。

目前工程项目中，注水/蒸汽是减少NO x 生成的主要方法，无需改动主要燃烧设备，但减少NO x生成是以增加CO排放为代价，因此应用和发展有其局限性；DLN/DLE和燃烧后还原处理等方法需要改进主要燃烧设备或增加昂贵的设备，而且DLN/DLE方法受到燃烧稳定性以及CO、UHC（未燃碳氢化合物）排放高的限制。

特种高分子材料

研究生课程
(1) 功能性小分子单体直接发生聚合反应

通过在功能性小分子中引入可聚合基团得到单体，然后进行均聚或共聚反应生成功能聚合物。这些可聚合功能性单体中的可聚合基团一般为：双键、羟基、羧基、氨基、环氧基、酰氯基、吡咯基、噻吩基等基团。可以发生加成聚合反应，开环聚合反应，缩聚反应以及氧化偶合反应。
研究生课程
(2) 功能性小分子通过聚合包埋与高分子材料结合(高分子微胶囊)

该方法是利用生成高分子的束缚作用将功能性小分子以某种形式包埋固定在高分子材料中来制备功能高分子材料。在聚合反应之前，向单体溶液中加入小分子功能化合物，在聚合过程中小分子被生成的聚合物所包埋。这种方法得到的功能高分子材料，聚合物骨架与小分子功能化合物之间没有化学键连接，固化作用通过聚合物的包络作用来完成。优点是方法简便，功能小分子的性质不受聚合物性质的影响，因此特别适宜酶等对环境敏感材料的固化。缺点是在使用过程中包络的小分子功能化合物容易逐步失去，特别是在溶胀条件下使用，将加快固化酶的失活过程。
吡咯基、噻吩基 (Z为连接基团，R为功能型小分子)
研究生课程

丙烯酸分子中带有双键，同时又带有活性羧基。经过自由基均聚或共聚，即可形成聚丙烯酸及其共聚物，可以作为弱酸性离子交换树脂、高吸水性树脂等应用。这是带有功能性基团的单体聚合制备功能高分子的简单例子。

含双键的环氧丙烯酸酯单体，可用于制备功能性粘合剂。
研究生课程

30年代，一系列烯烃类加聚物被合成出来并工业化，PVC （1927～1937），PVAc（1936），PMMA（1927～ 1931），PS（1934～1937），LDPE（1939）。自由基聚合发展。

赛门铁克诺顿网络安全特警2005版被选作HP全球个人电脑的最新安全解决方案

赛门铁克诺顿网络安全特警2005版被选作HP全球个人电脑
的最新安全解决方案
无
【期刊名称】《数字化工》
【年(卷),期】2005(000)008
【摘要】本刊讯信息安全厂商赛门铁克公司日前宣布，该公司的诺顿网络安全特警2005版解决方案将预装在所有新的惠普台式个人电脑上，从而为全球的客户提供更广泛的保护。

笔记本电脑将在夏季销售中换装诺顿网络安全特警2005版。

【总页数】1页(P63)
【作者】无
【作者单位】《数字化工》
【正文语种】中文
【中图分类】TP368.3
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