A tree-based approach for secure key distribution in wireless sensor networks

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Persistent Authenticated Dictionaries and TheirApplications⋆Aris Anagnostopoulos1,Michael T.Goodrich2,and Roberto Tamassia1 puter Science,Brown University.Email:{aris,rt}@puter Science,University of California,Irvine.Email:goodrich@ Abstract.We introduce the notion of persistent authenticated dictio-naries,that is,dictionaries where the user can make queries of the type“was element e in set S at time t?”and get authenticated answers.Appli-cations include credential and certiﬁcate validation checking in the past(as in digital signatures for electronic contracts),digital receipts,andelectronic tickets.We present two data structures that can eﬃcientlysupport an infrastructure for persistent authenticated dictionaries,andwe compare their performance.1IntroductionAt its core,nonrepudiation involves making cryptographically strong statements about the past.Although we digitally sign statements in the present,we only worry about enforcing statements made in the past.Consider,for example,the following scenarios:–Alice executed a digital mortgage two years ago and now is in default.The bank can only sue Alice if it can prove that she was in fact the one who digitally signed the mortgage contract.(Moreover,the exact history of Alice’s digital certiﬁcates may be crucial here,for her signature should remain valid even if her private key was compromised and her digital certiﬁcate revoked even just a few weeks after she signed the contract.)–Bob signed a digital receipt for Alice’s electronic payment and then shipped her a defective item.Alice must be able to prove that Bob truly was the one who signed that receipt.–A company,,issued a signed digital ticket to Alice for the opera,but Alice is refused entry to the performance.She needs to be able to prove that indeed issued that ticket and was also authorized to do so.–A company,,has published an online catalog that advertised widgets at$1a piece on the day they accepted a digital purchase order(PO) for100widgets from Alice.Now the company has raised the price to$100 and is demanding$10,000from Alice.She needs to be able to prove that$1 was the valid price for widgets on the day they accepted her digital PO.Thus,in order to enforce nonrepudiation on important contractual statements, such as in these examples,we need to have in place a mechanism for checking credentials,certiﬁcates,and published information in the past.Ideally,we would like there to be a collection of potentially untrusted directories that can answer historical queries about such items.1.1Problem Deﬁnition and ApplicationsPut more abstractly,the problem we address involves three types of parties: a trusted source,untrusted directories,and users.The source deﬁnes aﬁnite set S of elements that evolves over time through insertions and deletions of elements.Each directory,acting as a query agent for the source maintains a copy of set S and receives time-stamped updates from the source together with update authentication information,such as signed statements about the update and the current elements of the set.A user performs membership queries on the set S of the type“was element e in S at time t?”but instead of contacting the source directly,it queries one of the directories.The contacted directory provides the user with a yes/no answer to the query together with query authentication information,which yields a cryptographic proof of the answer assembled by combining statements signed by the source.The user then veriﬁes the proof by relying solely on its trust in the source and the availability of public information about the source that allows the user to check the source’s signature.We call the data structure used by the directory to maintain the set S,together with the protocol for queries and updates a persistent authenticated dictionary(PAD).The PAD abstract data type extends the usual notion of an authenticated dictionary[15],where the queries are only of the form“is element e currently in S?”.Thus,a PAD has the added burden of having to archive the entire history of updates sent by the source to the directories.Moreover,the directories must be able to provide answers and proofs for queries related to any time,past or present.We show,in Fig.1,a schematic view of a persistent authenticated dictionary.The design of a persistent authenticated dictionary should address the fol-lowing goals:–Low computational cost:The computations performed internally by each entity(source,directory,and user)should be simple and fast.More impor-tantly,the space needed to archive historical copies of S should be small.–Low communication overhead:source-to-directory communication(update authentication information)and directory-to-user communication(query au-thentication information)should be kept as small as possible.–High security:the authenticity of the data provided by a directory should be veriﬁable with a high degree of certainty.In addition to the motivating examples given above,applications of persis-tent authenticated dictionaries include third-party publication of historical data on the Internet[3]and historical certiﬁcate revocation checking in public keyFig.1.Persistent authenticated dictionary.infrastructures[9,15,1,2,8,5].In the third-party publication application[3], the source is a trusted organization(e.g.,a stock exchange)that produces and maintains historical integrity-critical content(e.g.,stock prices)and allows third parties(e.g.,Web portals),to publish this content on the Internet so that it be-comes widely disseminated.The publishers store copies of the content produced by the source and process queries on such content made by the users.In the certiﬁcate revocation application[9,15,1,2,8,5],the source is a cer-tiﬁcation authority(CA)that digitally signs certiﬁcates binding entities to their public keys,thus guaranteeing their validity.Nevertheless,certiﬁcates are some-times revoked(e.g.,if a private key is lost or compromised,or if someone loses his authority to use a particular private key).Thus,the user of a certiﬁcate must be able to verify that a given certiﬁcate used to validate someone for a historic contract was not revoked at the time the contract was executed.To facilitate such queries,certiﬁcate revocation directories process historic revocation status queries on behalf of users.The results of such queries need to be trustworthy, for they often form the basis for electronic commerce transactions.In this paper,we present a new scheme for persistent authenticated dictio-naries,based on eﬃcient persistent data structures known as red-black trees and skip lists.Our structures are secure,as well as being fast and space eﬃcient in terms of the parameters n,which denotes the current number of elements of the set S,and m,which denotes the total number of updates the source has performed.1.2Previous and Related WorkWe are not aware of any previous work on persistent authenticated dictionaries. We summarize prior work on ephemeral authenticated dictionaries,where only the current version of S is maintained,and on persistent(non-authenticated) dictionaries.Ephemeral Authenticated Dictionaries.Work has been done on ephemeral au-thenticated dictionaries primarily in the context of certiﬁcate revocation.The traditional method for certiﬁcate revocation(e.g.,see[9])is for the CA(source) to sign a statement consisting of a timestamp plus a hash of the list of all re-voked certiﬁcates,called certiﬁcate revocation list(CRL),and periodically send the signed CRL to the directories.A directory then just forwards that entire signed CRL to any user who requests the revocation status of a certiﬁcate.This approach is secure,but it is ineﬃcient:the update and query authentication information has sizeΘ(n).Moreover,to turn the CRL approach into a persis-tent authenticated dictionary requires that every CRL ever issued be archived at the directories.Thus,if m CRLs have been issued,this solution requires in the worst case quadratic O(m2)storage space at each directory.In other words,the CRL-based approach is a simple but very ineﬃcient solution for the persistent authenticated dictionary problem.There are other more space-eﬃcient methods for implementing ephemeral authenticated dictionaries.But methods for adapting them to the persistent context are not obvious.The hash tree scheme introduced by Merkle[13]can be used to implement a static authenticated dictionary,which supports the initial construction of the data structure followed by query operations,but not update operations(without complete rebuilding).Still,the only obvious way to make a hash tree persistent is to checkpoint the entire tree at each time quantum,which is clearly not space eﬃcient.Kocher[12]also advocates a static hash tree approach for realizing an au-thenticated dictionary,but simpliﬁes somewhat the processing done by the user to validate that an item is not in the set ing techniques from incremental cryptography,Naor and Nissim[15]dynamize hash trees to support the inser-tion and deletion of elements using2-3trees.Other certiﬁcate revocation schemes based on variations of hash trees have been recently proposed in[2,5,10],as well,but do not deviate signiﬁcantly from the above approaches.Goodrich and Tamassia[6,7]have proposed an authenticated-dictionary scheme based on the skip-list data structure that has asymptotically the same performance as[15]but it is simpler to implement.Still,like other previous so-lutions,their data structure is ephemeral—it only stores the most recent copy of the set S.Persistent Data Structures.Researchers have worked on persistent data struc-tures for other abstract data types besides authenticated dictionaries.The idea of path copying in a tree,for example,which is a component in some of our so-lutions,has been used in non-authenticated contexts by several researchers(e.g. Myers[14]and Reps,Teitelbaum and Demers[17]).Sarnak and Tarjan[18]pro-posed the node-copying method and use persistent trees to solve the planar point location problem,while Driscoll,Sarnak,Sleator and Tarjan[4]developed tech-niques for making linked data structures persistent.Nevertheless,none of these previous schemes for making data structures persistent have directly addressed the need for authentication or directory distribution.1.3Summary of ResultsWe present two data structures for implementing PADs,based on the dictionary data structures known as red-black trees and skip lists.Our solutions allow for element insertions and removals in the current set S to run in O(log n) time and queries in the past to run in O(log m)time.More importantly,our solutions use only O(log n)additional space per update.(Recall that n is the number of elements in the current set S and m is number of updates that have occurred so far.)Thus,our solutions are signiﬁcantly more eﬃcient than the CRL-based approach or checkpointing-based approaches,which requireΘ(n) additional space for archiving S at each historic time quantum.We describe the theoretical foundations behind our solution to the persistent authenticated dictionary problem in Section2.In addition,we claim that our methods are simple,which is an often ne-glected,but important aspect of computer security solutions,for implementa-tion correctness is as important as theoretic soundness.To support this claim,we have implemented our solutions and have performed a number of benchmarking tests,which we report on in Section3.2Making Authenticated Dictionaries PersistentWe use and extend some ideas from previous work on persistent data structures to create our solutions to the persistent authenticated dictionary(PAD)abstract data type.Let us therefore begin with a quick review.A Quick Review of Persistent Data Structures.Most of the data structures are ephemeral in the sense that whenever the user performs an update to them he destroys the previous version.If the previous version is retained and we can do queries to them we talk about persistent data structures.We can even talk about fully persistent data structures if we can make updates and not only queries to previous versions.In more detail,the operations that a persistent data structure S supports areﬁnd(e,t),which determines whether element e was in S at time t,insert(e), which inserts element e into S(at current time),and delete(e),which removes element e from S(at current time).In our case,we maintain the data structure in both the source and the di-rectories.When the user queries a directory if an element e was in the source at some time t,the directory returns“yes”if e existed in the source at time t along with a proof of its existence,or“no”if e did not exist in the source at time t along with a proof of its nonexistence.The proof must permit the user to verify that the answer is authentic(i.e.,it is as trustworthy as if it were directly signed by the source)and that it is current(i.e.,it corresponds to time t).Depending on the application we can use one of the two versions of the PADs which diﬀer in the way they deﬁne time.In particular we can have:–Discrete time where we can think that the dictionary holds several versions whose time is numbered sequentially with integers starting at0.When a user performs a query,t equals the time of one of the versions,and the dictionary searches the corresponding version and returns an answer that allows the user to verify that indeed the dictionary searched version at time t.–Continuous time where we can deﬁne the time over any set for which there exist a complete order.The versions of the dictionary are ordered according to that order.Whenever a user queries the directory about time t,the direc-tory must provide an answer corresponding to the latest dictionary version at time t′that is earlier than t;moreover,it must provide information for the user to verify that indeed t′is the time of the version that should have been queried and that does not exist a version at time t′′such that t′<t′′≤t.We have developed two data structures that implement PADs,one based on the red-black tree and the other based on the skip-list data structures.2.1PADs Based on Red-Black TreesWe denote the element stored at a node v as elem(v).The version of the red-black tree we use,has all the values stored only at the external nodes.We use the internal nodes to make queries to the tree and to store authentication information.The value stored at each internal node equals the maximum value of the left subtree;the values at the right subtree are greater than that value.When we want to make an insertion to the tree of an element with value e that does not exist into the tree,ﬁrst weﬁnd the external node v containing the minimum element elem(v),such that elem(v)>e.We then create a new internal node w to replace v and we set as the left child of w a new external node u such that elem(u)=e and as the right child the node v.1 Finally we perform the necessary reconstructions and recolorings.A deletion of a node is performed in the opposite manner.The persistent red-black tree is a modiﬁcation of the red-black tree.Each node u has also aﬁeld time(u)where we store the timestamp of its creation. Each addition or deletion to the tree does not change the current tree nodes but instead it adds new nodes with timestamp value that of the current time.In Fig.2we can see an example of an instance of a red-black tree.The bold lines denote black nodes and edges,while the normal ones denote red.The label at the top of each node(in Fig.2all are0for simplicity)denotes the timestamp value.Suppose we want to add a new element(e=18).We can see the new tree created in Fig.3,where the timestamp of the new nodes has taken the current time value(here just1for simplicity).Because at each update operation we copy the whole path from a node up to the root,this method is called path-copying method.Note that we have as many signed roots as update operations.Details of the operations follow in the next paragraphs.66101520615000000Fig.2.The tree before the inser-tion.661015206151820615180000001111Fig.3.The tree after the insertion of ele-ment 18.In our scheme we use an authenticated persistent red-black tree.Each node u has stored one more value,auth(u ),that is used for authentication;auth(u )equals elem(u )if u is an external node,and the concatenation of the auth()values of u ’s children if u is an internal node.h must be a collision-free hash function.Finally the root of every version of the tree (for the diﬀerent update times)is signed.In summary,each node u contains three ﬁelds:elem(u ),time(u ),and auth(u ).We describe now the details of the operations.Insertion.At every insert operation,the old version of the tree doesn’t change at all (except for the colors of the nodes and edges as we will see later).We ﬁnd the external node u that will be the father of the new node.Then we make a copy of the nodes on the path,from the root down to u to which we assign a timestamp value equal to the current time.We perform then the insertion by creating a new node as we saw before.We denote here a node x as x 0for the old version,and x 1for the new version that is copied.If along the path,a node v that is copied has a child w that is also copied,we add the edge from the node v 1to w 1.For the rest of the edges of v 0to some other node z 0we add an edge from v 1to z 0.We can see an example in Figures 2,3.Since we have a red-black tree,we must color the new nodes.Every node v 1will be colored with the same color with v 0,and the insertion will be done normally.After the insertion we may have to perform some transformations on the tree,namely some rotations and recolorings.The recolorings are easy,since we can overwrite the old colors of any node of any previous version of the tree.The colors are used only for the update operations,so we do not need to keep track of the old ones—we do not make updates in the past.Rotations are also simple;they will be done only on the new version of the tree and they will aﬀect only the new nodes and the links originating from them.Finally we must compute the values elem()and auth()for all the new nodes created.These operations are straightforward and we can perform them as we create the new nodes,in O (log n )time.In particular,we must compute only two elem()values,the one of the new external node,and that of its parent (which has the same value).We must compute the auth()values of all the O (log n )new nodes.Finally,if r 1is the root of the last version of the tree(just created)and r0is the root of the just previous version,then the source signs(auth(r1),time(r1),time(r0)).(The previous timestamp is necessary only in the case of continuous time;we give more details later.)Deletion.A delete operation is similar to an insert.We copy the path from the root down to the node to be deleted,we remove the nodes(one external and one internal node will be deleted),and then perform the necessary rotations and recolorings.Here we must be careful,since the rotations in this case may also aﬀect nodes not existing in the new path created.So before the rotation,these nodes must also be copied.During the deletion we may require to perform in the worst case at most a logarithmic number of recolorings and two rotations.In total,except for the path of the node deleted,it may be necessary to copy at most4additional nodes; therefore,we copy only a logarithmic number of nodes.Finally we compute the necessary elem()and auth()values and sign the new root,by the method we described in the Insertion paragraph.Again,we must compute all the auth()values of the O(log n)new nodes,and the only internal elem()value that we must alter is the value of the node that followed the removed external node in the inﬁx traversal of the tree.Query.Aﬁnd operation can query the PAD at any time in the past(or present) toﬁnd if an element e existed at that time.Say that we want to query for time t1and we have the two consecutive tree versions for times t0and t2,where t0≤t1<t2,assuming that t2exists.In the following,assume that r0is the root with timestamp t0,r2is the root with timestamp t2and r3is the root with the largest timestamp that is less than t0,if it exists.In order to search for e we work on the tree originating from the root r0of time t0.We distinguish two cases:–The element e exists in the tree at time t0:The dictionary returns to the user the answer“yes”,the root r0signed by the source(i.e.,the signature of(auth(r0),time(r0),time(r3))),the root r2signed by the source, that is,the signature of(auth(r2),time(r2),time(r0)),the element e,and the sequence Q(e)of the hashes of the siblings of the nodes of the path from the root of the tree to e.The user can verify that the answer is valid from the sequence Q(e)and the source’s signature of the root.–The element e does not exist in the tree at time t0:In this case,let e′be the maximum element that exists in the tree and is smaller than e,and e′′the minimum element that exists in the tree and is greater than e.The dictionary returns to the user the answer“no”,the root r0with timestamp t0 and the root r1with timestamp t1,signed by the source like in the previous case,the elements e′and e′′,and the sequences Q(e′)and Q(e′′)deﬁned as before.The user can verify now that both e′and e′′exist in the tree and that they are consecutive external nodes(hence e is not between them).The root r2has to be included only in the case of continuous time.The reason is to prove that there is not another version of the tree at time t4suchthat t 0<t 4≤t 1<t 2which may have diﬀerent information concerning C .The user can now verify that the version that immediately follows the one that corresponds to time t 0is at time t 2since it is included in the signature.Summarizing the above results,we have the following theorem:Theorem 1.A persistent authenticated dictionary can be implemented with a persistent authenticated red-black tree.The time needed for an update operation is O (log n )and for a query operation is O (log m ),where n is the number of elements of the last version and m is the total number of versions.The total space requirement is O ( m i =1log n i ),where n i is the number of elements of version i .Proof.We perform an update to the last version of the tree,which has n el-ements.The update operation requires the addition of O (log n )new nodes,O (log n )changes to the tree structure (including recolorings)and the computa-tion of O (log n )new hash values.Therefore,it can be performed in time O (log n ).A query on version i requires a binary search on the root of the trees to ﬁnd the appropriate version of the tree,which takes time O (log m ),a search in the tree to ﬁnd the appropriate node(s),which needs O (log n i )steps,and the creation and return of the response,which is done in O (log n i )steps.Since n i cannot be greater than m ,the overall time requirement of a query is O (log m ).The space required for the i -th update is O (log n i ):the insert operations need to copy only the nodes of the path of the new node,while the delete operations may need to copy at most 4additional nodes.By the property of red-black trees the total path length is O (log n i ),hence,the total space is O ( m i =1log n i ).2Note that the above time complexity results hold when we have continuous time.In the case of discrete time,we can ﬁnd the appropriate root for a query just by a table lookup in constant time,and in this case the total query time is O (log n i ).Also,note that when we query the last version,the time is reduced to O (log n ),as in the ephemeral authenticated dictionary.2.2PADs Based on Skip ListsThe skip-list data structure [16]is an eﬃcient means for storing a set S of elements from an ordered universe.Brieﬂy,a skip list consists of a collection of linked lists S 0,S 1,...,S k (where S i contains a randomly selected subset of the items in S i −1,plus two additional values −∞and +∞),and links between them.We can see an example in Fig.4.With high probability (whp 2),skip lists have the same asymptotic performance as red-black trees.However,experimental studies (e.g.,see [16])have shown that they often outperform in practice 2-3trees,red-black trees,and other deterministic search tree structures.S5S4S3S2S1S0Fig.4.(a)An example of a skip list.All the lines indicate links of the data structure.(b)The answer authentication information for the presence of element x=39(and for the absence of element42)consists of the signed time-stamped value f(v11)of the source element and the sequence Q(x)=(44,39,38,f(w3),f(u4),f(u6),f(w7),f(u8),f(u10)). The user recomputes f(v11)by accumulating the elements of the sequence with the hash function h,and veriﬁes that the computed value of f(v11)is equal to the value signed by the source[6,7].The arrows denote theﬂow of authentication information. Commutative Hashing.To simplify the veriﬁcation process,commutative crypto-graphic hash functions are introduced in[6].A hash function h is commutative if h(x,y)=h(y,x)for all x and y.A commutative hash function is commu-tatively collision resistant[6]if,given(a,b),it is diﬃcult to compute a pair (c,d)such that h(a,b)=h(c,d)while(a,b)=(c,d)and(a,b)=(d,c).Given a cryptographic hash function g that is collision resistant in the usual sense,the commutative hash function,h(x,y)=g(min{x,y},max{x,y})is commutatively collision resistant if x and y have the same length[6].Authenticated Dictionary Based on a Skip ing the skip-list data structure and commutative hashing,we can design a scheme for authenticated dictionaries, similar to the one based on balanced trees.It has the same asymptotic perfor-mance but it avoids many complications that arise in the implementation of the hash trees,leading to easier and less error-prone implementations.An example of the data structure and of an authenticated query is in Fig.4.For more details refer to[6,7].PAD Based on a Skip List.We can apply the path-copying idea to the au-thenticated skip list and create a persistent authenticated skip list.First,we make the following observation,which allows us to have an eﬃcient implemen-tation:for the operations supported by the skip list,some of the nodes and links are unnecessary and can be omitted.The skip list then looks like that of Fig.5. We can see now that in this form the skip list is essentially a binary tree(whose root is the node in the highest-level list with the value−∞)and so we can apply the path-copying method.We have to be careful however to copy all the nodes whose out-links or authentication information change.S5S4S3S2S1S0Fig.5.(a)A tree-like representation of a skip list.(b)Insertion of element21with height5.The new nodes and links are bold,while the dashed ones exist only in the previous version.It is important to mention that when we do an update,we do not change the existing nodes of the skip list—we only add new nodes.Therefore,by storing links to the appropriate root nodes we can make queries to any version of the dictionary.We describe now in detail the operations.Insertion.Assume that we want to insert element e and that e′is the largest element that is smaller than e.On the search path p we will reach element e′that belongs to the list S0.We insert the element e and hence the authentication data of e′in S0changes;the change of the authentication data propagates up to the root node along the path p that we followed to reach e′.In other words, the nodes of p(and of course the nodes of the new element)are the only nodes whose authentication data changes.Finally,some of the links to the right of the nodes on p—basically,those that belong to nodes that are lower than the height of the new element—must be set to null and be replaced by links that originate from the new elements.Therefore,the new nodes that we create are exactly those that belong to p plus those of the new element e.Fig.5shows an example of an insertion.The number of the new nodes that we create equals the length of the search path to the element e′plus the number of the new nodes for the new element. Both of these are O(log n)whp.The number of hashes that we have to compute is at most equal to the number of the new nodes(although for some of the nodes the authentication data is equal to that of the node below and does not have to be recomputed).Deletion.Assume that we want to remove element e from the skip list and that e′is the element immediately preceding e.We follow the path p to element e′. Since we remove the element next to e′(i.e.,e),the authentication data of e′in S0changes.Again,the change propagates up to the root node only along p,and the only links to the right that must change are in p.Therefore,the only nodes that we must duplicate are those in p,which with high probability are O(log n). Also,the number of the hashes to compute equals at most the number of the new nodes and so it is O(log n)whp.。

介绍数学知识的英语文章

介绍数学知识的英语文章Mathematics is a fundamental and universal languagethat provides a framework for understanding and analyzing the world around us. It encompasses a wide range of concepts, including numbers, shapes, patterns, and relationships, and plays a crucial role in fields such as science, engineering, economics, and technology. In this article, we will explore some key aspects of mathematics, its significance, and its applications.First and foremost, mathematics is the study of numbers and their operations, such as addition, subtraction, multiplication, and division. It also includes the study of abstract structures, such as sets, groups, and fields, which serve as the foundation for more advanced mathematical concepts. Through the use of symbols and notation, mathematicians are able to express complex ideas and relationships in a concise and precise manner.One of the most fascinating aspects of mathematics isits ability to describe and analyze patterns and relationships in the natural world. For example, mathematical principles govern the motion of celestial bodies, the growth of populations, and the behavior of waves and particles. By using mathematical models, scientists and researchers can make predictions and test hypotheses, leading to a deeper understanding of the underlying mechanisms of the universe.Furthermore, mathematics provides powerful tools for problem-solving and decision-making. Whether it's calculating the trajectory of a spacecraft, optimizing the efficiency of a manufacturing process, or designing cryptographic algorithms for secure communication, mathematics offers a systematic approach to tackling real-world challenges. Its applications in fields such as computer science, finance, and logistics have revolutionized the way we live and work.In addition to its practical applications, mathematics also fosters critical thinking and reasoning skills. Through the process of formulating and proving theorems,students of mathematics learn to analyze problems, construct logical arguments, and think abstractly. This not only enhances their problem-solving abilities but also equips them with a valuable mindset for approaching complex issues in other disciplines.In conclusion, mathematics is a rich and diverse field with profound implications for our understanding of the world and our ability to shape it. Its role in science, technology, and everyday life cannot be overstated, and its beauty lies in its ability to reveal the hidden order and structure underlying the universe. By studying mathematics, we gain not only knowledge but also a powerful set of tools for exploring the unknown and making meaningful contributions to society.。

论文参考文献标准格式

规范的参考文献格式一、参考文献的类型参考文献(即引文出处）的类型以单字母方式标识，具体如下：M——专著C——论文集N—-报纸文章J-—期刊文章D——学位论文R——报告S-—标准P-—专利A——文章对于不属于上述的文献类型，采用字母“Z”标识。

常用的电子文献及载体类型标识：［ＤＢ/OL]-—联机网上数据（database online)[DB/MT］—-磁带数据库（database on magnetic tape)［Ｍ/CD]--光盘图书(monograph on CD ROM）［ＣＰ／DK］-—磁盘软件（computer program on disk）［Ｊ／ＯＬ］——网上期刊(serial online)［ＥＢ/OL］——网上电子公告(electronic bulletin board online)对于英文参考文献，还应注意以下两点：①作者姓名采用“姓在前名在后”原则，具体格式是：姓，名字的首字母。

如：Malcolm Richard Cowley 应为：Cowley, M。

R.,如果有两位作者,第一位作者方式不变，&之后第二位作者名字的首字母放在前面，姓放在后面，如：Frank Norris 与Irving Gordon应为：Norris, F。

& I。

Gordon.；②书名、报刊名使用斜体字，如：Mastering English Literature，English Weekly。

二、参考文献的格式及举例1．期刊类【格式】［序号]作者.篇名［J].刊名,出版年份,卷号(期号）：起止页码.【举例】[1] 周融，任志国，杨尚雷，厉星星。

对新形势下毕业设计管理工作的思考与实践［J]。

电气电子教学学报，2003（6）：107-109。

［2] 夏鲁惠。

高等学校毕业设计（论文）教学情况调研报告［J]。

高等理科教育，2004（1):46-52。

[3］Heider，E.R.＆D.C。

Oliver。

树屋英语作文

树屋英语作文Tree HouseTree houses have always been a fascinating concept for many people. The idea of living high up in the trees, surrounded by nature, is both thrilling and peaceful. In this essay, I will discuss the appeal of tree houses, their benefits, and the potential challenges of living in one.Firstly, the appeal of tree houses lies in their close connection to nature. Being elevated off the ground allows for a unique perspective of the surrounding environment. The sounds of birds chirping, leaves rustling, and the wind blowing through the branches create a serene atmosphere. Additionally, the feeling of being nestled among the trees provides a sense of tranquility that is hard to find elsewhere.Moreover, tree houses offer a sense of adventure and freedom. Climbing up to the house and having the ability to peek out at the world below can be exhilarating. It provides a break from the hustle and bustle of everydaylife, allowing one to escape and find solace in thepeaceful surroundings.Furthermore, there are numerous benefits to living in a tree house. For one, the environmental impact is minimal.By utilizing the existing trees as a foundation, the needfor extensive construction is reduced. This eco-friendly approach aligns with the growing trend of sustainable living. Additionally, tree houses often require creativeand innovative design solutions, making them an exciting architectural challenge.In terms of challenges, living in a tree house does come with its own set of obstacles. One of the primary concernsis safety. Ensuring that the structure is stable and secure is essential, as living at a height presents inherent risks. Weather conditions must also be taken into account, as strong winds and heavy rain can pose a threat to theintegrity of the tree house.Another challenge is the practicality of daily living. Access to amenities such as running water, electricity, and waste disposal can be more complicated in a tree house. However, with advancements in technology and design, thesechallenges can be overcome through the use of sustainable and off-grid solutions.In conclusion, the allure of tree houses lies in their unique connection to nature and the sense of adventure they offer. While there are challenges to consider, the benefits of living in a tree house, such as minimal environmental impact and the opportunity for creative design, make them an appealing housing option. Whether for a weekend getaway or a permanent residence, tree houses continue to capture the imagination of people of all ages.树屋树屋一直以来都是许多人着迷的概念。

中山大学软件学院本科生期末考试《数据库系统原理》(A卷)

中山大学软件学院本科生期末考试考试科目：《数据库系统原理》（A卷）学年学期：2014学年第3学期姓名：学院/系：软件学院学号：考试方式：开卷年级专业：考试时长：120分钟班别：第八条：“考试作弊者，不授予学士学位。

”------------以下为试题区域，共7道大题，总分100分,考生请在答题纸上作答------------1. (10 marks) Let R = {A, B, C, D, E, F, G} and F = {AB→C, A→C, A→E, B→C, EF→EG, G→F}. Answer the following three questions.1)(4 marks) Compute the minimal cover of F.B→CA→CA→EEF→GG→F2)(4 marks) Decompose R into 3NF relations.{B, C}, {A, C, E}, {E, F, G} and {A, B, D, F} (OR {A, B, D, G})3)(2 marks) Is the composition in (b2) in BCNF? Briefly explain your answer.No. For {E, F, G} and G→F, G is not a candidate key.2. (10 marks)Assume there is an employee database Employee (eid: 8 bytes, ename: 16 bytes, did: 4 bytes, email: 12 bytes), where eid and ename are respectively the id and name of an employee and did is the id of the department in which the employee works. Suppose there are 50,000 employee records and 500 departments (i.e. each department has 100 employees on average). A page size is 1,000 bytes and a pointer costs 4 bytes.1)(4 marks) Assume that the employee file is sorted sequentially on did and there is noindex. Estimate the page access cost for retrieving the records of all employees working in a department with a given did. (You should show your argument and the main steps of the estimation clearly in the answer.)AnswerRecord size = 40 bytes, 25 records per page, 2,000 pages.Finding the first record requires log22000 + 3 more pages to search theremaining records (each dept has 100 employees which are distributed in 4pages).2)(6 marks) Assume only 20 pages of main memory are available for running theexternal sorting of the employee file on did.•How many PASSes are needed for the external sorting?•In each PASS, how many runs are created?•What is the total cost of the sorting in terms of pages?Answer:3 PASSes:PASS 0: 2000 pages / 20 pages per run = 100 runsPASS 1: ceil (100 runs / 19 runs per run) = 6 runsPASS 2: 1 runTotal cost: (2000 pages read per pass + 2000 pages write per pass) * 2 PASSes +2000 pages read per pass = 10000 pages (Note: Output is not counted!)Or: 2000 * (2 * 2 + 1) = 10000 pages transfer.3. (10 marks) Suppose a bookstore has the following five relational tables:BOOK (BID, TITLE, AID, SUBJECT, QUANTITY_IN_STOCK)AUTHOR (AID, NAME) CUSTOMER (CID, NAME)ORDER_DETAILS (OID, BID , QUANTITY) ORDER (OID, CID , ORDER_YEAR)In the above tables, keys are underlined and foreign keys are in italics . Each author has authored at least one book in the store. Each book has exactly one author. Each order is made by exactly one customer and has one or more associated record in ORDER_DETAILS (e.g., an order may contain different books).Express the following query using (i) SQL expressions, (ii) the relational algebra (RA).Find the distinct customer IDs (CID) of customers who have purchased more than 10 identical books in one order at least once.(i) SELECT DISTINCT CIDFROM ORDER_DETAILS od, ORDER oWHERE QUANTITY >= 10 AND od.OID = o.OID(ii)CID (σQUANTITY ≥ 10 (ORDER_DETAILSOID ORDER ))4. (10 marks) A B+ tree with n=5 is shown in Figure 1, in which only search keys are shown and pointers to the file system are hidden. We want to insert a data entry with search key “23”.Figure 1. A B+ Tree Structure1) Which of the following descriptions about the insertion operation is correct?A.The B+ tree contains 2 levels after insertion. 2 node splits are needed duringinsertion. The root node contains search key “15”.B.The B+ tree contains 3 levels after insertion. 1 node split is needed duringinsertion. The root node contains search key “20”.C.The B+ tree contains 3 levels after insertion. 2 node splits are needed duringinsertion. The root node contains search key “15”.D.The B+ tree contains 3 levels after insertion. 2 node splits are needed duringinsertion. The root node contains search key “20”.Answer: C2)We want to delete the data entry with search key “7”. How many leaf nodes store onlytwo data values after deletion?A.2B. 3C. 4D.5Answer: A5. (20 marks)You are given an initial hash structure with three keys already inserted as below. The hash function is h(x) = x mod 16. Draw five extendable hash structures corresponding for each insertion of the following search key values K: 7, 15, 20, 37, 18. Assume each bucket can hold two keys and the search key values arrive in the given order (i.e. 7 being the first coming key and 18 being the last one).You should follow the convention used by lecture slides: binary hash indices starting from the least significant bit. (E.g. 1 is the least significant bit of the 4 digit binary number 0001.)AnswerInsert 7Insert 15 and 20Insert 37Insert 186. (25 Marks) Consider a database consisting of the following three relation schemas:SAILORS (sid, sname, rating, age)BOATS (bid, bname, color)RESERVES (sid, bid, date, rname)The meaning of the attributes in the above schemas is self-explanatory. For example, sid is the sailor identity number and bname is the name of the boat. The primary keys of the relations are underlined. The attribute sid in RESERVES is a foreign key referencing SAILORS. The attribute bid in RESERVES is a foreign key referencing BOATS.The relation SAILORS has 100,000 tuples and 100 tuples of SAILORS fit into one page. The relation BOATS has 50,000 tuples and 25 tuples of BOATS fit into one page. The relation RESERVES has 10,000 tuples and 20 tuples of RESERVES fit on one page. We assume all attribute values and pointers in these three relations, if needed to be considered, are of the same size.(a)(10 marks) Assume that we use Indexed Nested Loop Join to computeSAILORS RESERVES using SAILORS as the outer relation. RESERVES have a primary B+-tree index with 2 levels on the join attribute. Estimate the cost of the join in terms of pages.Number of SAILORS pages: br = 100,000/100 = 1,000Number of SAILORS Tuples: nr = 100,000.The cost is br+ c * nr = 1,000 + (2+1) * 100,000 = 301,000.(b)(5 mark)Assume that 26% of the sailors have the rating bigger than 5. Estimate theresult size of sid(σrating>5 SAILORS) in terms of pages.Size = 26% * 100,000 / 100/4 = 65 pages260 divided by 4, for there is projection and all the attributes have same size(c)(10 marks) Consider the following two strategies to compute the join operationSAILORS BOATS RESERVES.Strategy 1: (SAILORS BOATS) RESERVESStrategy 2: (SAILORS RESERVES) BOATSWhich strategy is better? Explain the reason(s) of your choice based on the size of the intermediate result using the above strategies.Strategy 2 is better.Because in Strategy 1, SAILORS BOATS is equal to the cross-product of the two relations and the size of the join result will become as large as 100,000 * 50,000 = 5,000,000,000 tuples. This intermediate result is very large and later when joining this intermediate result with RESERVES, the cost is also large.In comparison, in Strategy 2, SAILORS RESERVES has only 10,000 tuples. And later when joining this intermediate result with BOATS, the cost is also small.7. (15 Marks) Consider a schedule S which consists of four transactions as follows:S = <T3_R(U), T2_R(X), T2_W(X), T3_R(X), T1_R(Y), T1_W(Y), T3_W(X), T1_R(Z), T4_R(Z), T4_W(Z), T2_W(Y), T3_R(Y)>The notation is self-explanatory. For example, T1_R(X) means that transaction T1 reads item X.(a)(5 marks) Fill in the following table representing S with the usual notations in lectureslides. The first operation R(U) has been shown in the table. Show clearly all conflicting pairs with downward arrows on the operations.(b)(5 marks) Construct the precedence graph of S. Explain why or why not the schedule isconflict-serializable.Precedence Graph of S:No cycle.(c)(5 marks) Suppose the format of the “commit” operation is Ci where i = 1, 2, 3, or 4.For example, the operation C1 means that the transaction T1 commits. Append all the commit statements to S so that the schedule becomes recoverable. For example, one append can be SC4C3C2C1 which means running S and then C4, C3, C2, C1. (Note that you should NOT change the sequence of the operations in S other than appending S with the four commit statements to make the schedule recoverable.)Recoverable (but not cascadeless) schedule: SC1C2C3C4 or (SC1C2C4C3) or (SC1C4C2C3) (Note: any permutation of Ci satisfies the commit order constraints: C1→C2, C1→C3, C1→C4, C2→C3 is correct)。

Lessons learnt

NDIA CMMI Technology conference
How to Incorporate “Lessons Learned” for Sustained Process Improvements
Anil Midha BAE Systems, CNIR Wayne, NJ
Process Commonality and Durability
The Issue is …
In today’s competitive environment, organizations cannot afford missed opportunities and repeated mistakes The Resolution is …
Organizations must: Constantly and quickly leverage from each other’s experiences Provide organizational, cultural, and technological infrastructure to facilitate cross-team learning Enforce the process discipline
Process improvement will be a trivial exercise
Projects will usually be on time, within budget, and deliver high quality products
Customer and user satisfaction will be higher
But these are exceptions!
092605 7
Challenges are …

组织种树的作文英语

组织种树的作文英语Organizing a Tree Planting EventPlanting trees is a simple yet impactful action that can contribute to a healthier and more sustainable environment. As individuals and communities, we have the power to make a positive difference by organizing tree planting events. These events not only beautify our surroundings but also provide numerous environmental benefits that can have a lasting impact on our local ecosystems.One of the primary reasons to organize a tree planting event is to increase the overall tree canopy in a given area. Trees play a crucial role in absorbing and storing carbon dioxide, a greenhouse gas that contributes to climate change. By planting more trees, we can help mitigate the effects of climate change and improve air quality. Additionally, trees provide shade, which can help reduce energy consumption by lowering the need for air conditioning, and they also help prevent soil erosion and improve water quality by filtering runoff.Another important aspect of organizing a tree planting event is the educational and community-building opportunities it presents. Byinvolving members of the community, especially young people, in the tree planting process, we can foster a sense of environmental stewardship and encourage a deeper appreciation for the natural world. Participants can learn about the importance of trees, proper planting techniques, and the various species that thrive in the local ecosystem.When planning a tree planting event, it is crucial to consider several key factors to ensure its success. The first step is to identify a suitable location for the event. This may involve working with local authorities or landowners to secure a suitable site, such as a public park, a school campus, or a community green space. It is important to consider factors like soil quality, sunlight exposure, and accessibility when selecting the planting site.Next, it is necessary to determine the types of trees that will be planted. This decision should be based on the local climate, soil conditions, and the desired aesthetic and environmental benefits. Consulting with local horticulturists or environmental organizations can help identify the most appropriate tree species for the area.Organizing the logistics of the event is another essential aspect. This includes securing the necessary equipment and materials, such as shovels, gloves, and the trees themselves. It is also important to ensure that the event is well-publicized and that participants areaware of the date, time, and location. Collaborating with local organizations, schools, or community groups can help increase the event's visibility and attract a larger turnout.On the day of the event, it is crucial to have a well-organized plan in place to ensure a smooth and efficient tree planting process. This may involve dividing participants into smaller groups, providing clear instructions on proper planting techniques, and designating specific areas for each group to work in. It is also important to have a plan in place for the ongoing maintenance and care of the newly planted trees, such as regular watering and monitoring.One of the most rewarding aspects of organizing a tree planting event is the sense of community and environmental stewardship that it can foster. By bringing people together to work towards a common goal, we can create a sense of shared responsibility and ownership over the local environment. This can lead to increased civic engagement, a greater appreciation for the natural world, and a stronger commitment to environmental conservation.In conclusion, organizing a tree planting event is a powerful way to make a positive impact on our local environment and communities. By increasing the tree canopy, providing educational opportunities, and fostering a sense of environmental stewardship, we can contribute to a more sustainable and livable future for all. Whetherit's a small-scale event in a local park or a large-scale initiative involving multiple organizations, every tree planted can make a difference in the fight against climate change and the preservation of our natural resources.。

网络交换机用户手册说明书

16 Port Nway Fast EthernetPoE Web Smart SwitchUser’s ManualVer:1.3.3- 0 -- 1 -Web Smart Switch ConfigurePlease follow the steps to configure this Web Smart switch.Step 1: Use a twisted pair cable to connect this switch to your PC.Step 2: Set your PC’s IP to 192.168.2.xx.Step 3: Open the web browser (like IE…), and go to 192.168.2.1 Then you will see the login screen.ID and the password: admin- 2 -Step 4: After the authentication procedure, the home page shows up.Select one of the configurations by clicking the icon.- Administrator - Port Management - VLAN Setting - Per Port Counter - QoS Setting - Security- Spanning Tree - Trunking- Backup/Recovery - Miscellaneous - LogoutAdministrator: Authentication Configuration1. Change the user name and the password.2. Click “Update” to confirm the new change. Now, you can use the new user name and the password.- 3 -Administrator: System IP Configuration1. Change the IP address: type the new IP address or selectDHCP IP configuration.2. Click “Update” to confirm the new change.“Setting Process OK!!” will be shown on the screen.Now, the setting of “System IP Configuration” is finished.- 4 -Administrator: System StatusMAC address and system version will be shown on the screen.1.Change the new comment of this switch by typing the newcomment.2.Click “Update” to confirm the new change.Now, the setting of “System Status” is finished.- 5 -Administrator: Load Default Setting1.Click “Load” to back to the factory default setting.**Note: Recover switch default setting excluding the IP address, User name and Password.Now, the default is loaded.- 6 -Administrator: Firmware UpdateFollow the instruction on the screen to update the new firmware. Please contact with your sales agents to get the latest firmware information.- 7 -Administrator: Reboot Device1. Click “Confirm” to reboot the device. Now, the setting of “Reboot Device” is finished.- 8 -Port Management: Port ConfigurationSelect the “Port No.” - configure the mode below:1. “Auto-Nego” - enable/disable Auto-Negotiation.2. “Speed” - 10M or 100M mode for the selected port.3.“Duplex” - Full or Half-Duplex mode for the selected port.4. “Pause” - enable/disable for the selected port.5. “Backpressure” - enable/disable for the selected port.6. “Tx Cap (Capability) ” - enable/disable for the selected port.7. “Addr. Learning” - enable/disable for the selected port. Now, the setting of “Port Configuration” is finished.- 9 -Port Management: Port MirroringPort Mirroring is used to mirror traffic, RX, TX or TX&RX, from Source port to Destination port for analysis.1.Select the Destination port: you can choose port 1 to port 162.Select the Source port: by clicking the checking box of theport.3.Click “Update” to save the setting.Now, the setting of “Port Mirroring” is finished.- 10 -Port Management: Bandwidth Control1.Select the “Port No.”: you can choose port 1 to port 162.“TX Rate Value”: set the transmission rate of the selected port.(0:Full speed; 1~255:Specified bandwidth.)3.“RX Rate Value”: set the receiving rate of the selected port. (0:Full speed; 1~255: Specified bandwidth.)4.“Resolution” : Low: 32 kbps / High: 512 kbps5.Click “Update” to confirm the setting or “LoadDefault”. Now, the setting of “Bandwidth Control” is finished.- 11 -Port Management: Broadcast Storm Control1.“Threshold” - Set the threshold from 1~63.2.“Enable Port” - per port to define the status of broadcast packets.3.Click “Update” to confirm the setting.Now, the setting of “Broadcast Storm Control” is finished.- 12 -Port Management: PoE ConfigurationRemote access and monitor the attached PD (Powered Device) status by using Enable/Disable function.1.Enable: POE of the port is able to supply power to the attachedPD (Powered Device)2.PSE Current & Minimum Output Power: The status of theport current and minimum output power.3. POE class: each POE port will detect the class of the attachedPD (Powered Device)4. Click “Update” to confirm and finish the setting.Now, the setting of “PoE Configuration” is finished.- 13 -VLAN Setting: VLAN ModeThere are two VLAN modes : Port Based VLAN and Tagged VLAN. Click “Change VLAN mode” to select the mode.**If the Port Based VLAN function is enabled, Multi to 2 setting and tag Based VLAN will be disabled automatically.Now, the setting of “VLAN Mode” is finished.- 14 -VLAN Setting: VLAN Member Setting (Port Based)You can select a port group.1. Click the port numbers: which you want to put them into theselected VLAN group.2. Click “Update” to confirm and finish the setting.3. Click “LoadDefualt” to back to the original factory setting. Now, the setting of “VLAN Mode” is finished.- 15 -VLAN Setting: Multi to 2 SettingThis is a special design for easily setting the switch VLAN into “VLAN Per Port“.1.Choose “Destination Port No”.2.Choose “Disable Port”3.“Disable Port” – choose the port which you don’t want to use4.Click “Update” to confirm and finish the setting.After this setting, all ports can only connect to destination ports.- 16 -Per Port Counter: Counter CategoryYou can read the transmitting and receiving packet of the connecting port.Click “Refresh” or “Clear” the data.- 17 -QoS Setting: Priority ModeThere are three Priority Modes to select.1.“First-in-First-Out” - the first receiving packet will be firstlytransmitted.2.“All-High-before-Low” – All packets will be assigned to eitherQ2(high) piority queue or Q1(low)priority queue.3.“4 Queue WRR (Weight-Round-Robin)” - set the ratio ofthe transmitting packet for the low priority to high priority. 4.Click “Update” to confirm and finish the setting.- 18 -- 19 - QoS Setting: Class of ServiceYou can set QoS mode of per port by different bases.TCP/UDP > TP TPS/DS > 802.1P > Physical port1.“TCP/UDP Port” – Q1 ~ Q4 options are effective for theselected physical port only. “Drop” option is the global setting for all physical ports.The packet queue will be transferred based on the number of “4 Queue WRR” on QoS Setting: Priority Mode.**WRR –Q1/Q2/Q3/Q4**“Drop” - packets will be dropped.2. “IP TOS/DS” – “Priority Setting”: Q1 ~ Q4; “IP TOS/DS PortSetting” - It means the packets with special IP will befirstly transmitted.3. “802.1p” – Priority mapping table as the screen shown.4. “Physical port” - you can select the port which you want toconfigure as Q1~Q4 priority.5. Click “Update” to confirm and finish the setting.Now, the setting of “Class of Service” is finished.- 20 -Security: MAC Address FilterSet special MAC address to activate on the selected port1.Choose “Select Port” – port 1~162.“Binding” – “Enable”: allow the packet with the specifiedsource MAC address to enter this port.3.Click “Update” to confirm and finish the setting.Now, the setting of “MAC Address Filter” is finished.- 21 -Security: TCP_UDP Filter ConfigurationYou can enable or disable this function of per port.If the “Function Enable” is “Enable”, please kindly check the following setting:1.“Port Filtering Rule” –“Deny”: the outgoing packets to the selected port with selected- 22 -protocol will be dropped and other protocols will beforwarded.“Allow”: the selected protocol will be forwarded and otherprotocol will be dropped.2.“Secure Port” – choose secure ports which you want.**Note 1:a.The secure WAN port should be set at the physical portwhich is connected to the server.b.Once this function is enabled, the switch will check thedestination TCP/UTP port number at the outgoing directionof the secure WAN port.If the condition matches, this packet will be dropped or forwarded.**Note 2: The description of Secure WAN port is shown on the bottom of this screen.3. “Protocol” – choose protocols which you want.4. Click “Update” to confirm and finish the setting.Now, the setting of “TCP/UDP Filter Configuration” is finished.- 23 -Spanning Tree: STP Bridge SettingsThis setting is to avoid the loop network.1.Select the “STP Mode”- choose “Disable”, “STP” or “RSTP”2.Set the “Bridge Priority” – Set the priority of the Bridge3.Set the period of “Hello Time” packet – Provides the time periodbetween root bridge configuration messages.4.Set the “Max Age” – Indicates when the current configurationmessage should be deleted.5.Set the “Forward Delay” time – Provides the length of time thatbridges should wait before transitioning to a new state after a topology change. (If a bridge transitions too soon, not all network links might be ready to change their state, and loops can result.)6. Click “Update” to confirm and finish the setting.Now, the setting of “STP Bridge Settings” is finished.- 24 -Spanning Tree: STP Port Settings1.Choose “Port No.” : Port 1 ~ Port 162. Choose “Priority”: 0~ 2403. “RPC” = Root Path Cost: 0 = AUTO. When the loop is found, the STP/RSTP will calculate the cost of its path.- 25 -Trunking: Link Aggregation SettingsThere are two groups to choose and max. for each group is 4 ports. Click “Submit” to confirm and finish the setting.“State” – Enable / Disable“Type” – LACP/ Static“Activity” – Active/Passive: Both switches use “LACP” to configure the Trunk, at least one of them should be “Active”.- 26 -Backup/RecoveryFollow the instruction on the screen to update the original setting. “Backup” - Click “Download” to confirm the setting. “Recovery” – select a file and key in the password Click “Update”to confirm the setting.- 27 -Miscellaneous: Miscellaneous Setting1.“Output Queue Aging Time” - You can set queue aging time intodifferent milliseconds or disable this function.2.“VLAN Striding” – You can enable/disable this function.3.“IGMP Snooping V1 & V2” – You can enable/disable thisfunction.4.“VLAN Uplink Setting” – Set “uplink1 or uplink2” or “Clearuplink1” or “Clear uplink2”5.Click “Update” to confirm and finish the setting.6.- 28 -Logout: You can click “Logout” to logout.- 29 -。

小学上册第五次英语第二单元暑期作业

小学上册英语第二单元暑期作业英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.The chemical symbol for yttrium is ______.2.I love going to the park with my __________. (家人)3.The currency of India is the ________ (印度的货币是________).4.I love to play with my ________ (玩具名称) at the playground.5.This ________ (玩具) can help me make friends.6.The squirrel's _______ (灵巧) allows it to climb trees.7.I enjoy visiting the ______ (博物馆) to learn about science and history.8.I love to ________ (探索) new places.9. A ______ (刺猬) curls up when it feels threatened.10.Many plants have ______ (独特的特征).11.What is the tallest mountain in the world?A. K2B. Mount EverestC. KilimanjaroD. Mont Blanc12.What is the opposite of "safe"?A. SecureB. DangerousC. ProtectedD. Guarded13.The capital of Panama is __________.14.My dad enjoys cooking on the ____.15.What do you call a young horse?A. CalfB. FoalC. KidD. Puppy16.The butterfly has beautiful ________________ (翅膀).17.The ________ (交通安全) is a priority for everyone.18.The chemical formula for baking soda is _______.19.The __________ is bright and sunny today. (天空)20.Flammable substances can easily ______.21.The __________ is known for its warm climate.22. A reaction that results in a change of state is called a ______ reaction.23.We have ___ (gym/music) class next week.24.I have a _____ (collection) of rocks.25.My uncle is a fantastic ____ (musician).26.My aunt has a pet ____ (dog) that likes to play.27.The park is _______ (full) of children.28.The _______ of a wave can be increased by adding energy.29.What do we call the distance around a circle?A. AreaB. CircumferenceC. RadiusD. DiameterB30.The _______ (The fall of the Berlin Wall) symbolized the end of the Cold War.31.Carbon dioxide is produced during ______ respiration.32.The pig loves to roll in ______ (泥).33.What is the sum of 5 + 6?A. 10B. 11C. 12D. 13B34.What do you call the planet known for its rings?A. EarthB. SaturnC. MarsD. Neptune35.My sister is a ______. She loves fashion design.36. A _____ (植物教学) can engage students in science.37.My _________ (玩具) can talk and tell stories!38.What do you call a large area of sand?A. DesertB. BeachC. DuneD. OasisA39.What do we call the study of the mind and behavior?A. SociologyB. PsychologyC. AnthropologyD. PhilosophyB40.The first settlers in America were looking for _______. (新机会)41.The Louisiana Purchase doubled the size of the _______.42.I find ________ (心理学) fascinating.43.The bee buzzes around the _______ (花).44.My sister plays on the school ____ (basketball) team.45.The process of chromatography separates mixtures based on _____.46.The leaves on the _______ turn green in spring.47.What is the term for the gravitational attraction that keeps planets in orbit around the sun?A. GravityB. MagnetismC. ElectromagnetismD. Nuclear Force48.My dad is a ______. He helps people solve problems.49.What do we call the device used to cook food using electricity?A. OvenB. StoveC. MicrowaveD. ToasterC50.What do you call a person who studies space?A. BiologistB. AstronomerC. GeologistD. Physicist51.Roses are beautiful _______ that smell sweet.52.__________ are important for the production of biofuels.53.The dog is _____ (chasing/playing) its tail.54. A ____ swims in lakes and has webbed feet.55.__________ are substances that can conduct electricity when dissolved in water.56.Which of these is a type of tree?A. RoseB. OakC. TulipD. Daisy57.The chemical formula for -dodecanol is ______.58.What do we call a person who travels to space?A. CosmonautB. AstronautC. PilotD. EngineerB59.The __________ (moon) affects the tides in the ocean.60.We bake _____ (bread/cake) for the festival.61.The Great Wall of China was built to:A. Keep out animalsB. Protect against invasionsC. Mark boundariesD. Serve as a roadB62.The ____ has bright eyes and is often seen in gardens.63.What is the name of the fairy tale character who had long hair?A. RapunzelB. ArielC. BelleD. JasmineA64.I ride my ______ to school.65.I have a special ________ that reminds me of adventures.66.ts are known for their _____ (香味). Some pla67.My sister is a good ________.68.The __________ (历史的传承价值) shape identities.69.What is the capital of Panama?A. Panama CityB. ColonC. DavidD. SantiagoA70. A _______ is a process that involves the absorption of light.71.I want to travel to ________ (日本) one day.72.The __________ is a mountain range that runs along the east coast of the United States. (阿巴拉契亚山脉)73.Which holiday is celebrated on December 25th?A. ThanksgivingB. HalloweenC. ChristmasD. EasterC74.How many zeros are in one hundred?A. OneB. TwoC. ThreeD. Four75.The manatee is often called a "sea ______ (牛)."76.I like to _______ (参加) community service.ets have distinctive tails made of gas and ______.78.I like to ______ my grandparents during holidays. (visit)79.The _____ (cup/plate) is on the table.80.How many legs does an octopus have?A. 6B. 8C. 10D. 12B 881.I have a toy _______ that can dig and scoop.82.Materials that do not conduct electricity are called ________.83. of Terror occurred during the _____ Revolution. The Rena84.My sister is _____ a song. (singing)85.What is the name of the famous statue in Rio de Janeiro?A. Christ the RedeemerB. Statue of LibertyC. DavidD. Venus de Milo答案:A86._____ (sunlight) is essential for growth.87.The clock shows ______ o'clock. (three)88. A __________ is a substance that speeds up a chemical reaction.89.What is the capital of England?A. ParisB. LondonC. MadridD. Rome90.The __________ is known for its rich history and artifacts. (博物馆)91. A ______ is a type of rodent that loves to run.92.I want to be a ______ (teacher) when I grow up.93.I see a _____ (彩虹) after the rain.94.The ________ is full of life.95.What color do you get when you mix blue and yellow?A. RedB. GreenC. PurpleD. OrangeB96.Chlorine is used to disinfect _____ (water) in pools.97.My cousin is very good at ____ (acting).98.When it rains, I can’t play with my __________ (玩具名).99.What is the name of the famous mouse created by Walt Disney?A. Donald DuckB. Mickey MouseC. GoofyD. Bugs BunnyB 100.ers bloom in ______ (夜间). Some flo。

Spanning-tree based coverage of continuous areas by a mobile robot

time O(N), but requires O(N) memory for its implementation. The third version of STC is
\ant"-like. In this version, too, the robot has no apriori knowledge of the environment, but it may leave pheromone-like markers during the coverage process. The ant-like STC algorithm
algorithm computes an optimal covering path in linear time O(N), where N is the number
of cells comprising the area. The second version of STC is on-line, where the robot uses its on-board sensors to detect obstacles and construct a spanning tree of the environment while covering the work-area. The on-line STC algorithm completes an optimal covering path in
Spanning-Tus Areas by a Mobile Robot
Yoav Gabriely and Elon Rimon
Dept. of Mechanical Engineering Technion, Israel Institute of Technology yoav@robots.technion.ac.il,elon@robby.technion.ac.il

基础的英文

基础的英文基础的英语读法1：foundation英 [faunˈdeiʃən] 美 [faʊnˈdeʃən]基础的英语读法2：basis英 [ˈbeisis] 美 [ˈbesɪs]基础的英语读法3：understructure基础相关英语表达：economic base经济基础theoretical basis理论基础material base物质基础基础英语读法例句：1. They will concentrate on teaching the basics of reading, writing and arithmetic.他们将集中教授阅读、写作和算术基础知识。

2. The degree provides a thorough grounding in both mathematics and statistics.该学位课程将为数学和统计学打下扎实的基础。

3. This basic utilitarian model gives a relatively unsophisticated account of human behaviour.这个实用的基础模型较为简略地解释了人类的行为。

4. Canadian libel law is based on English mon law.加拿大的诽谤法是以英国的习惯法为基础的。

5. All vessels were to be built on a cost-plus basis.所有的船只都将在成本加利润的基础上制造。

6. A substantial proportion of the population speak a French-based patois.人口中有一大部分说以法语为基础的混合语。

7. Dr. Mesibov set forth the basis of his approach to teaching students.梅西伯夫博士阐述了他的教学方法的基础。

植树造林 Tree Plantation 英语作文

Tree PlantationTrees plantation is the process where seedlings are moved from one location to another for land reclamation, forestry or landscaping purposes. Tree plantation has many apparent advantages – it contributes to the environment by improving air quality, oxygen, conserving water and supporting wildlife.Tree Plantation Essay aims to educate the readers and students about the importance of tree plantation. In today’s world, globalization and industrialization have led to the destruction of millions of acres of forests and wildlifesanctuaries. This has displaced the homes of many animals, which consequently led to them straying into inhabited areas. Hence, drastic measures have to be undertaken to reverse the damage humans have done.From an academic perspective, a tree plantation essay is an important topic as it is usually asked in the exams. The topic may be easy to comprehend, however, to write an engaging essay on the same may not be as simple. With these sample essays and useful tips, securing marks is much easier. Consideradopting these tips and guidelines to deliver the perfect essay.Tree Plantation Essay – Writing Tips and TricksAdopting these writing tips will help to secure more marks/ grades for the essay. Moreover, it can also improve general writing and presentation skills:Always begin the essay with an introductory paragraphThe introductory paragraph must contain relevant background information or any other pertinent information about the topicIncorporate specifics such as names, dates, places or any other information that provides clarity and contextDo not use jargons unless required by the topicEnsure that the content is broken down into digestible chunks. Long, monotonous texts may make it difficult for the reader.Try to present the content in points wherever possibleAlways organize the content by using headings and subheadingsEnd the essay with a concluding paragraphThe concluding paragraph must summarize all the relevant points or key takeawaysIf time permits, read through the essay before final submission. This will help weed out grammatical errors and spelling mistakesTree Plantation Essay Sample 1 (250+ Words –High School Level)What is Tree Plantation?Tree Plantation is the process of transplanting seedlings from one place to another for forestry, landscaping or land reclamation. It has many ecological implications, such as preservation of soil, supporting wildlife and more.Implications of Tree PlantationIn today’s day and age, globalization ha s taken a toll on the environment. Our carbon footprinthas drastically increased ever since the Industrial Revolution. Moreover, to make matters worse, millions of acres of forests have been encroached to expand for commercialization and industrialization. This has accelerated global warming, which has resulted in higher global temperatures. Polar ice caps are melting, and global sea levels are rising as a consequence. Many animals are now at risk of losing their habitat and eventually becoming extinct.A Possible Solution?Most of these ill-effects can be pushed back if more trees are planted. As a result, one of theprimary goals of tree plantation is offsetting carbon emissions. Trees can act as carbon offsets based on the notion that they capture and use carbon as they grow. This has a significant impact on climate change, as sequestering carbon can help reduce the greenhouse effect.Trees also act as carbon sinks, a natural reservoir that absorbs more carbon than it releases. This adds a “cooling effect” where water vapour enters the earth’s atmosphere, thereby increasing cloudiness. Also, studies have found that trees in the tropical rainforestsannually remove close to 22 kilos of carbon dioxide from the atmosphere every year.ConclusionIn conclusion, tree plantation must be seen as not just a social responsibility, but one among many solutions to our environmental crisis.Tree Plantation Essay Sample 2 (250+ Words –Primary School Level)What is Tree Plantation?Tree Plantation is a process where seedlings are transplanted from one place to another.There are many reasons why trees are transferred – it can be for either land reclamation, forestry, or even landscaping. Moreover, this process has many ecological benefits, as well.Applications of Tree PlantationForestry:Forestry is the science of creating, managing and conserving forests for its resources, typically for human consumption or benefits. Hence, tree plantation is one of the most commonly used methods to procure trees or plants of economic importance such as timber and wood fuel.However, forestry also embraces other goals, such as recreational activities, wildlife habitats, and erosion control.Land Reclamation:Land reclamation is the process of creating new land areas from seas, riverbeds, and lake beds. These new areas are usually created for human habitation. Common examples include man-made beaches and the coastlines of Mumbai. Land Reclamation can also be used to develop sanctuaries and habitats for wildlife.Landscaping: Landscaping is any activity that is used to alter the visible features of a land area. It is primarily done for visual aesthetics. Importance of Tree PlantationCarbon emissions are at an all-time high because of globalization and industrialization. As a result, the rate of global warming has increased, leading to a rise in global temperatures. Furthermore, many other negative repercussions also begin to plague the planet, such as rising sea levels and melting ice caps. These drastically affect wildlife as well as human activities.The only feasible solution to these problems would be to plant trees. Trees act as natural carbon sinks, which means they absorb more carbon than they release. This results in a reduction of carbon dioxide levels in the atmosphere.In conclusion, tree plantation has many applications, but we need to focus on the most important one- which is to reverse the effects of global warming and deforestation.Important FAQs on Tree Plantation EssayQuestion 1.What is Tree Plantation?Answer:Trees plantation is the process where seedlings are moved from one location to another for land reclamation, forestry or landscaping purposes.。

cybersecurity 网络安全

The Comprehensive National Cybersecurity Initiative President Obama has identified cybersecurity as one of the most serious economic and national security challenges we face as a nation, but one that we as a government or as a country are not adequately prepared to counter. Shortly after taking office, the President therefore ordered a thorough review of federal efforts to defend the U.S. information and communications infrastructure and the development of a comprehensive approach to securing America’s digital infrastructure.In May 2009, the President accepted the recommendations of the resulting Cyberspace Policy Review, including the selection of an Executive Branch Cybersecurity Coordinator who will have regular access to the President. The Executive Branch was also directed to work closely with all key players in U.S. cyberse-curity, including state and local governments and the private sector, to ensure an organized and unified response to future cyber incidents; strengthen public/private partnerships to find technology solutions that ensure U.S. security and prosperity; invest in the cutting-edge research and development necessary for the innovation and discovery to meet the digital challenges of our time; and begin a campaign to promote cybersecurity awareness and digital literacy from our boardrooms to our classrooms and begin to build the digital workforce of the 21st century. Finally, the President directed that these activities be conducted in a way that is consistent with ensuring the privacy rights and civil liberties guaranteed in the Constitution and cherished by all Americans.The activities under way to implement the recommendations of the Cyberspace Policy Review build on the Comprehensive National Cybersecurity Initiative (CNCI) launched by President George W. Bush in National Security Presidential Directive 54/Homeland Security Presidential Directive 23 (NSPD-54/ HSPD-23) in January 2008. President Obama determined that the CNCI and its associated activities should evolve to become key elements of a broader, updated national U.S. cybersecurity strategy. These CNCI initiatives will play a key role in supporting the achievement of many of the key recommendations of President Obama’s Cyberspace Policy Review.The CNCI consists of a number of mutually reinforcing initiatives with the following major goals designed to help secure the United States in cyberspace:••To•establish•a•front•line•of•defense•against•today’s•immediate•threats•by creating or enhancing shared situational awareness of network vulnerabilities, threats, and events within the Federal Government—and ultimately with state, local, and tribal governments and private sector partners—and the ability to act quickly to reduce our current vulnerabilities and prevent intrusions.••To•defend•against•the•full•spectrum•of•threats•by enhancing U.S. counterintelligence capabili-ties and increasing the security of the supply chain for key information technologies.••To•strengthen•the•future•cybersecurity•environment•by expanding cyber education; coordi-nating and redirecting research and development efforts across the Federal Government; and working to define and develop strategies to deter hostile or malicious activity in cyberspace. In building the plans for the CNCI, it was quickly realized that these goals could not be achieved without also strengthening certain key strategic foundational capabilities within the Government. Therefore, the CNCI includes funding within the federal law enforcement, intelligence, and defense communities to enhance such key functions as criminal investigation; intelligence collection, processing, and analysis; and information assurance critical to enabling national cybersecurity efforts.The CNCI was developed with great care and attention to privacy and civil liberties concerns in close consultation with privacy experts across the government. Protecting civil liberties and privacy rights remain fundamental objectives in the implementation of the CNCI.In accord with President Obama’s declared intent to make transparency a touchstone of his presidency, the Cyberspace Policy Review identified enhanced information sharing as a key component of effective cybersecurity. To improve public understanding of Federal efforts, the Cybersecurity Coordinator has directed the release of the following summary description of the CNCI. CNCI•Initiative•DetailsInitiative•#1.•Manage•the•Federal•Enterprise•Network•as•a•single•network•enterprise•with•Trusted•Internet•Connections.•The Trusted Internet Connections (TIC) initiative, headed by the Office of Management and Budget and the Department of Homeland Security, covers the consolidation of the Federal Government’s external access points (including those to the Internet). This consolidation will result in a common security solution which includes: facilitating the reduction of external access points, establishing baseline security capabilities; and, validating agency adherence to those security capabilities. Agencies participate in the TIC initiative either as TIC Access Providers (a limited number of agencies that operate their own capabilities) or by contracting with commercial Managed Trusted IP Service (MTIPS) providers through the GSA-managed NETWORX contract vehicle.Initiative•#2.•Deploy•an•intrusion•detection•system•of•sensors•across•the•Federal•enterprise.•Intrusion Detection Systems using passive sensors form a vital part of U.S. Government network defenses by identifying when unauthorized users attempt to gain access to those networks. DHS is deploying, as part of its EINSTEIN 2 activities, signature-based sensors capable of inspecting Internet traffic entering Federal systems for unauthorized accesses and malicious content. The EINSTEIN 2 capability enables analysis of network flow information to identify potential malicious activity while conducting automatic full packet inspection of traffic entering or exiting U.S. Government networks for malicious activity using signature-based intrusion detection technology. Associated with this investment in technology is a parallel investment in manpower with the expertise required to accomplish DHS’s expanded network security mission. EINSTEIN 2 is capable of alerting US-CERT in real time to the presence of malicious or potentially harmful activity in federal network traffic and provides correlation and visualization of the derived data. Due to the capabilities within EINSTEIN 2, US-CERT analysts have a greatly improved understanding of the network environment and an increased ability to address the weaknesses and vulnerabilities in Federal network security. As a result, US-CERT has greater situational awareness and canT h eComp reh ensivenaT i onalCyberseCuri T yi ni T iaT ivemore effectively develop and more readily share security relevant information with network defenders across the U.S. Government, as well as with security professionals in the private sector and the American public. The Department of Homeland Security’s Privacy Office has conducted and published a Privacy Impact Assessment for the EINSTEIN 2 program.Initiative•#3.•Pursue•deployment•of•intrusion•prevention•systems•across•the•Federal•enterprise.•This Initiative represents the next evolution of protection for civilian Departments and Agencies of the Federal Executive Branch. This approach, called EINSTEIN 3, will draw on commercial technology and specialized government technology to conduct real-time full packet inspection and threat-based decision-making on network traffic entering or leaving these Executive Branch networks. The goal of EINSTEIN 3 is to identify and characterize malicious network traffic to enhance cybersecurity analysis, situational awareness and security response. It will have the ability to automatically detect and respond appropriately to cyber threats before harm is done, providing an intrusion prevention system supporting dynamic defense. EINSTEIN 3 will assist DHS US-CERT in defending, protecting and reducing vulner-abilities on Federal Executive Branch networks and systems. The EINSTEIN 3 system will also support enhanced information sharing by US-CERT with Federal Departments and Agencies by giving DHS the ability to automate alerting of detected network intrusion attempts and, when deemed necessary by DHS, to send alerts that do not contain the content of communications to the National Security Agency (NSA) so that DHS efforts may be supported by NSA exercising its lawfully authorized missions. This initiative makes substantial and long-term investments to increase national intelligence capabilities to discover critical information about foreign cyber threats and use this insight to inform EINSTEIN 3 systems in real time. DHS will be able to adapt threat signatures determined by NSA in the course of its foreign intelligence and DoD information assurance missions for use in the EINSTEIN 3 system in support of DHS’s federal system security mission. Information sharing on cyber intrusions will be conducted in accordance with the laws and oversight for activities related to homeland security, intelligence, and defense in order to protect the privacy and rights of U.S. citizens.DHS is currently conducting a exercise to pilot the EINSTEIN 3 capabilities described in this initiative based on technology developed by NSA and to solidify processes for managing and protecting informa-tion gleaned from observed cyber intrusions against civilian Executive Branch systems. Government civil liberties and privacy officials are working closely with DHS and US-CERT to build appropriate and necessary privacy protections into the design and operational deployment of EINSTEIN 3. Initiative•#4:•Coordinate•and•redirect•research•and•development•(R&D)•efforts.•No single individual or organization is aware of all of the cyber-related R&D activities being funded by the Government. This initiative is developing strategies and structures for coordinating all cyber R&D sponsored or conducted by the U.S. government, both classified and unclassified, and to redirect that R&D where needed. This Initiative is critical to eliminate redundancies in federally funded cybersecurity research, and to identify research gaps, prioritize R&D efforts, and ensure the taxpayers are getting full value for their money as we shape our strategic investments.Initiative•#5.•Connect•current•cyber•ops•centers•to•enhance•situational•awareness. There is a pressing need to ensure that government information security offices and strategic operations centers share data regarding malicious activities against federal systems, consistent with privacy protectionsfor personally identifiable and other protected information and as legally appropriate, in order to have a better understanding of the entire threat to government systems and to take maximum advantage of each organization’s unique capabilities to produce the best overall national cyber defense possible. This initiative provides the key means necessary to enable and support shared situational awareness and collaboration across six centers that are responsible for carrying out U.S. cyber activities. This effort focuses on key aspects necessary to enable practical mission bridging across the elements of U.S. cyber activities: foundational capabilities and investments such as upgraded infrastructure, increased bandwidth, and integrated operational capabilities; enhanced collaboration, including common tech-nology, tools, and procedures; and enhanced shared situational awareness through shared analytic and collaborative technologies.The National Cybersecurity Center (NCSC) within the Department of Homeland Security will play a key role in securing U.S. Government networks and systems under this initiative by coordinating and integrating information from the six centers to provide cross-domain situational awareness, analyzing and reporting on the state of U.S. networks and systems, and fostering interagency collaboration and coordination.Initiative•#6.•Develop•and•implement•a•government-wide•cyber•counterintelligence•(CI)•plan.•A government-wide cyber counterintelligence plan is necessary to coordinate activities across all Federal Agencies to detect, deter, and mitigate the foreign-sponsored cyber intelligence threat to U.S. and private sector information systems. To accomplish these goals, the plan establishes and expands cyber CI education and awareness programs and workforce development to integrate CI into all cyber opera-tions and analysis, increase employee awareness of the cyber CI threat, and increase counterintelligence collaboration across the government. The Cyber CI Plan is aligned with the National Counterintelligence Strategy of the United States of America (2007) and supports the other programmatic elements of the CNCI. Initiative•#7.•Increase•the•security•of•our•classified•networks.•Classified networks house the Federal Government’s most sensitive information and enable crucial war-fighting, diplomatic, counterterrorism, law enforcement, intelligence, and homeland security operations. Successful penetration or disruption of these networks could cause exceptionally grave damage to our national security. We need to exercise due diligence in ensuring the integrity of these networks and the data they contain. Initiative•#8.•Expand•cyber•education. While billions of dollars are being spent on new technologies to secure the U.S. Government in cyberspace, it is the people with the right knowledge, skills, and abilities to implement those technologies who will determine success. However there are not enough cybersecurity experts within the Federal Government or private sector to implement the CNCI, nor is there an adequately established Federal cybersecurity career field. Existing cybersecurity training and personnel development programs, while good, are limited in focus and lack unity of effort. In order to effectively ensure our continued technical advantage and future cybersecurity, we must develop a technologically-skilled and cyber-savvy workforce and an effective pipeline of future employees. It will take a national strategy, similar to the effort to upgrade science and mathematics education in the 1950’s, to meet this challenge.Initiative•#9.•Define•and•develop•enduring•“leap-ahead”•technology,•strategies,•and•programs.•One goal of the CNCI is to develop technologies that provide increases in cybersecurity by orders of magnitude above current systems and which can be deployed within 5 to 10 years. This initiative seeksT h eComp reh ensivenaT i onalCyberseCuri T yi ni T iaT iveto develop strategies and programs to enhance the component of the government R&D portfolio that pursues high-risk/high-payoff solutions to critical cybersecurity problems. The Federal Government has begun to outline Grand Challenges for the research community to help solve these difficult problems that require ‘out of the box’ thinking. In dealing with the private sector, the government is identifying and communicating common needs that should drive mutual investment in key research areas. Initiative•#10.•Define•and•develop•enduring•deterrence•strategies•and•programs.•Our Nation’s senior policymakers must think through the long-range strategic options available to the United States in a world that depends on assuring the use of cyberspace. To date, the U.S. Government has been implementing traditional approaches to the cybersecurity problem—and these measures have not achieved the level of security needed. This Initiative is aimed at building an approach to cyber defense strategy that deters interference and attack in cyberspace by improving warning capabilities, articulat-ing roles for private sector and international partners, and developing appropriate responses for both state and non-state actors.Initiative•#11.•Develop•a•multi-pronged•approach•for•global•supply•chain•risk•management. Globalization of the commercial information and communications technology marketplace provides increased opportunities for those intent on harming the United States by penetrating the supply chain to gain unauthorized access to data, alter data, or interrupt communications. Risks stemming from both the domestic and globalized supply chain must be managed in a strategic and comprehensive way over the entire lifecycle of products, systems and services. Managing this risk will require a greater awareness of the threats, vulnerabilities, and consequences associated with acquisition decisions; the development and employment of tools and resources to technically and operationally mitigate risk across the lifecycle of products (from design through retirement); the development of new acquisition policies and practices that reflect the complex global marketplace; and partnership with industry to develop and adopt supply chain and risk management standards and best practices. This initiative will enhance Federal Government skills, policies, and processes to provide departments and agencies with a robust toolset to better manage and mitigate supply chain risk at levels commensurate with the criticality of, and risks to, their systems and networks.Initiative•#12.•Define•the•Federal•role•for•extending•cybersecurity•into•critical•infrastructure•domains.•The U.S. Government depends on a variety of privately owned and operated critical infra-structures to carry out the public’s business. In turn, these critical infrastructures rely on the efficient operation of information systems and networks that are vulnerable to malicious cyber threats. This Initiative builds on the existing and ongoing partnership between the Federal Government and the public and private sector owners and operators of Critical Infrastructure and Key Resources (CIKR). The Department of Homeland Security and its private-sector partners have developed a plan of shared action with an aggressive series of milestones and activities. It includes both short-term and long-term recommendations, specifically incorporating and leveraging previous accomplishments and activities that are already underway. It addresses security and information assurance efforts across the cyber infrastructure to increase resiliency and operational capabilities throughout the CIKR sectors. It includes a focus on public-private sharing of information regarding cyber threats and incidents in both govern-ment and CIKR.。

有关自然灾害的知识竞赛英语作文

有关自然灾害的知识竞赛英语作文Disaster Preparedness: A Crucial Skill in an Unpredictable WorldNatural disasters are a sobering reality that humanity must face with resilience and adaptability. From earthquakes and hurricanes to wildfires and floods, these catastrophic events have the power to devastate communities, disrupt lives, and leave lasting scars. As such, it is imperative that we equip ourselves with the knowledge and skills necessary to navigate these challenging circumstances.One of the most effective ways to prepare for natural disasters is through knowledge-based competitions. These contests not only test our understanding of various disaster scenarios but also challenge us to think critically about emergency response strategies and disaster mitigation techniques. By engaging in such competitions, we can develop a deeper appreciation for the complexities of disaster management and the importance of being proactive in the face of these unpredictable events.At the heart of these competitions lies a fundamental understanding of the different types of natural disasters and their unique characteristics. Earthquakes, for instance, can strike without warning,causing widespread structural damage and potentially triggering tsunamis. Hurricanes, on the other hand, are often preceded by advanced warning systems, allowing for more time to prepare and evacuate vulnerable areas. Wildfires, fueled by dry conditions and strong winds, can rapidly spread, threatening both human lives and valuable natural resources.Participants in these knowledge-based competitions are expected to demonstrate a comprehensive grasp of the causes, effects, and mitigation strategies for a wide range of natural disasters. This includes understanding the underlying geological, meteorological, and environmental factors that contribute to these events, as well as the latest advancements in early warning systems and emergency response protocols.One of the key aspects of disaster preparedness is the ability to assess risks and vulnerabilities within a given community. Competitors may be tasked with identifying the potential hazards faced by a particular region, evaluating the resilience of critical infrastructure, and developing comprehensive emergency plans that address the unique needs of the local population. This requires a deep understanding of geographic, demographic, and socioeconomic factors that can influence the impact of a natural disaster.In addition to understanding the science behind natural disasters, successful participants in these competitions must also possess strong problem-solving and decision-making skills. When faced with a disaster scenario, they must be able to quickly analyze the situation, weigh the available options, and make informed choices that prioritize the safety and well-being of affected individuals. This often involves the ability to think creatively, communicate effectively, and collaborate with diverse stakeholders, such as emergency responders, government agencies, and community organizations.Beyond the immediate response to a natural disaster, these knowledge-based competitions also emphasize the importance of long-term recovery and resilience-building efforts. Participants may be required to develop strategies for rebuilding infrastructure, restoring essential services, and supporting the mental and emotional well-being of disaster survivors. This holistic approach to disaster management recognizes that the impacts of these events can reverberate for years, and that effective recovery and mitigation efforts are essential for building stronger, more resilient communities.Ultimately, the knowledge gained through these disaster preparedness competitions can have far-reaching implications. By equipping individuals with the skills and understanding necessary to navigate the challenges posed by natural disasters, these competitions contribute to a more informed and resilient globalcommunity. As the frequency and intensity of natural disasters continue to rise due to climate change and other environmental factors, the ability to anticipate, respond to, and recover from these events will become increasingly crucial.In conclusion, disaster preparedness knowledge-based competitions are not merely academic exercises but rather critical tools for building a more secure and resilient future. By fostering a deeper understanding of natural disasters and their management, these competitions empower individuals and communities to take proactive steps in safeguarding their well-being and ensuring the long-term sustainability of our shared planet. As we face the unpredictable challenges of the years to come, the knowledge and skills gained through these competitions will prove invaluable in our collective efforts to adapt, survive, and thrive in the face of natural disasters.。

如何使我们居住的城市更好英语作文

How to Make Our City a Better Place to LiveImproving our city to make it a more desirable place to live involves a multi-faceted approach that encompasses various aspects of urban life. Here are some key considerations for creating a better city:1. Enhancing InfrastructureA city's infrastructure is its backbone. Improving transportation systems, such as roads, public transportation, and cycling lanes, can make commuting easier and more efficient. Additionally, investing in renewable energy sources and improving water and waste management systems are crucial for environmental sustainability and public health.2. Promoting Green SpacesGreen spaces, such as parks, gardens, and tree-lined streets, not only enhance the aesthetics of a city but also provide important ecological benefits. They improve air quality, reduce noise pollution, and offer spaces for recreation and relaxation. Encouraging the development of these areas can significantly improve the quality of life in a city.3. Encouraging Community EngagementCreating a sense of community and belonging is essential for making a city more attractive. Encouraging community events, cultural activities, and volunteer opportunities can foster a sense of unity and participation among residents. This, in turn, can lead to a more vibrant and inclusive city.4. Emphasizing Safety and SecurityA safe and secure environment is paramount for any city. Improving policing, lighting, and surveillance in areas prone to crime can help reduce criminal activity. Additionally, promoting educational programs and resources on safety and security can empower residents to take proactive measures to protect themselves and their communities.5. Prioritizing Affordability and InclusivityEnsuring that housing, education, and other essential services are affordable and accessible to all residents is crucial for a city's inclusivity. Implementing policies that promote affordable housing, provide educational opportunities, and support economic development can help create a more inclusive and diverse city.In conclusion, making our city a better place to live requires a concerted effort from all stakeholders. By enhancing infrastructure, promoting green spaces, encouraging community engagement, emphasizing safety and security, and prioritizing affordability andinclusivity, we can create a city that is not only more desirable but also more sustainable and inclusive.。

江苏省盐城市亭湖高级中学高二暑假作业英语试题2 含答案

高二英语暑假作业 2I.单项填空（共15小题；每小题1分，满分15分）1. The "Chinese Dream" is ____ dream to improve people's well-being and ____ dreamof harmony, peace and development.A. the; aB. a; aC. a; theD. the; the2. While intelligent people can often ______ the complex, a fool is more likely tocomplicate the simple.A. sacrificeB. substituteC. simplifyD. survive3. If what your friend comes up with surprises you, don’t reject it immediately. ________,imagine that it is true.A. ThusB. BesidesC. RatherD. Otherwise4. Mrs. Smith finds it hard to clear up the mess, as her children are always ____whenever she tries to.A. in the wayB. on watchC. in sightD. on the line5. Anyone, once ____ positive for H7N9 flu virus, will receive free medical treatment from ourgovernment.A. to be testedB. being testedC. testedD. to test6. With inspiration from other food cultures, American food culture can take a __ for the better.A. shareB. chanceC. turnD. lead7. He was unhappy when he sold his guitar. After all, he _________if for a very long time.A. has had.B. had hadC. hasD. had8. It will be a big help if you go to the store and get what we need for dinner. ________, I will set the table.A. As a resultB. On the wholeC. In the meanwhileD. As a matter of fact9. Team leaders must ensure that all members ______ their natural desire to avoid theembarrassment associated with making mistakes.A. get overB. look overC. take overD. come over10. It be the vocabulary that caused you the problem in the exercise because youknow a lot of words.A. mayB. couldn’tC. shouldD. needn’t11. The subway was crowded with passengers going home from market, most of _____ carrying heavy bags and baskets full of fruit and vegetables they had bought there.A. whomB. themC. whoD. which12. When asked to explain _____ he did to make his students so fascinated with his lessons, the teacher paused and thought deeply.A. what was it thatB. that what it wasC. what it was thatD. what was it13. The president of the World Bank says he has a passion for China, ______ he remembers starting as early as his childhood.A. whereB. whichC. whatD. when14. At no time ________the rules of the game. It was unfair to punish them.A. they actually brokeB. do they actually breakC. did they actually breakD. they had actually broken15. —Would you mind answering some questions on shopping habits?— ________.A. Yes, with great pleasureB. No, I am afraid I can't make itC. Yes, it is worth the timeD. No, as long as it doesn't take longII：完形填空（共20小题；每小题1分，满分20分）New genetic analysis has revealed that many Amazon tree species are likely to survive human-made climate warming in the coming century, contrary to previous findings that temperature increases would cause them to die out. A study, 16 in the latest edition of Ecology and Evolution, reveals the 17 age of some Amazonian tree species -- more than 8 million years -- and 18 shows that they have survived previous periods as warm as many of the global warming imagined periods 19 for the year 2100.The authors write that, having survived warm periods in the past, the trees will 20 survive future warming, provided there are no other major environmental changes. 21 extreme droughts and forest fires will impact Amazonia as temperatures 22 , the trees will stand the direct impact of higher temperatures. The authors 23 that as well as reducing greenhouse gas emissions to minimize the risk of drought and fire, conservation policy should remain 24 on preventing deforestation（采伐森林）for agriculture and mining.The study disagrees with other recent researches which predicted tree species’ extinctions 25 relatively small increases in global average air temperatures.Study co-author Dr Simon Lewis (UCL Geography) said the 26 were good news for Amazon tree species, but warned that drought and over-exploitation of the forest remained major 27 to the Amazon’s future.Dr Lewis said: “The past cannot be compared directly with the future. while tr ee species seem likely to 28 higher air temperatures than today, the Amazon forest is being transformed for agriculture and 29 , and what remains is being degraded by logging, and increasingly split up by fields and roads.“Species will not move as freely in today’s Amazon as they did in previous warm periods, when there was no human 30 . Similarly, today’s climate change is extremely fast, making comparisons with slower changes in the past 31 .”“With a clearer 32 of the relative risks to the Amazon forest, we 33 that direct human impacts -- such as forest clearances for agriculture or mining -- should remain a key point of conservation policy. We also need more aggressive 34 to reduce greenhouse gas emissions in order to make minimum the risk of drought and fire impacts and 35 the future of most Amazon tree species.”16. A. advertised B. described C. published D. presented17. A. frightening B. surprising C. exciting D. interesting18. A. still B. nevertheless C. however D. therefore19. A. assess B. confirm C. forecast D. promise20. A. particularly B. probably C. merely D. possibly21. A. Since B. Although C. When D. If22. A. rise B. change C. drop D. end23. A. consider B. decide C. guarantee D. recommend24. A. based B. built C. focused D. made25. A. in relation to B. in response to C. in reply to D. in reference to26. A. findings B. thoughts C. inventions D. writings27. A. threats B. disadvantages C. embarrassments D. instructions28. A. accept B. tolerate C. permit D. require29. A. farming B. planting C. catering D. mining30. A. power B. influence C. desire D. violence31. A. difficult B. clear C. easy D. important32. A. belief B. direction C. understanding D. suggestion33. A. doubt B. conclude C. calculate D. prefer34. A. thought B. guidance C. protection D. action35. A. secure B. advance C. sacrifice D. evaluateIII：阅读理解（共15小题；每小题2分，满分30分）AWe observe today not a victory of party but a celebration of freedom, symbolizing an end as well as a beginning, signifying renewal as well as change for I have sworn before you and Almighty God the same solemn oath our forbears (ancestors) prescribed nearly a century and three-quarters ago.The world is very different now, for man holds in his mortal hands the power to abolish all forms of human poverty and all forms of human life. And yet the same revolutionary beliefs for which our forbears fought are still at issue around the globe, the belief that the rights of man come not from the generosity of the state but from the hand of God. We dare not forget today that we are the heirs（继承人）of that first revolution.Let the word go forth from this time and place, to friend and foe (enemy) alike, that the torch has been passed to a new generation of Americans born in this century, tempered by war, disciplined by a hard and bitter peace, proud of our ancient heritage and unwilling to disciplined by a hard and bitter peace, proud of our ancient heritage and unwilling to disciplined by a hard and bitter peace, proud of our ancient heritage and unwilling to witness or permit the slow undoing of those human rights to which this nation has always been committed, and to which we are committed today at home and around the world.Let every nation know whether it wishes us well or ill that we shall pay any price, bear any burden, meet any hardship, support any friend, oppose any foe, to assure the survival and the success of liberty. This much we pledge (promise solemny) and more.In the long history of the world, only a few generations have been granted the role of defending freedom in its hour of maximum danger. I do not shrink from this responsibility. I welcome it. I do not believe that any of us would exchange places with any other people or any other generation. The energy, the faith, the devotion which we bring to this endeavor will light our country and all who serve it and the glow from that fire can truly light the world.And so, my fellow Americans ask not what your country can do for you; ask what you can do for your country. My fellow citizens of the world ask not what America will do for you, but what together we can do for the Freedom of Man.Finally, whether you are citizens of America or citizens of the world, ask of us here the same high standards of strength and sacrifice which we ask of you. With a good conscience our only sure reward, with history the final judge of our deeds, let us go forth to lead the land we love, asking His blessing and His help, but knowing that here on earth God’s work must truly be our own.36. What should friends and foes know?A. That the United States is powerful.B. That a new generation of Americans are responsible for their government.C. That the United States is governed by liberals.D. The rights of man come from the hand of God.37. What is Kennedy’s promise to the world?A. To support liberty.B. To abolish all forms of human poverty.C. To visit each country at least once.D. To support and friend.38. What should citizens of the world ask of America?A. How America can help them.B. If America plans to invade their country.C. What they can do for freedom.D. What they can do for America.39. Which of the following statement is NOT true according to the passage?A. Human beings have the power to put an end to all forms of poverty.B. We should remember we are the first revolution.C. Our nation has always been committed to human rights.D. We should assure the survival and the success of liberty.BWhat's the one word of advice a well-meaning professional would give to a recent college graduate? China! India! Brazil! How about trade!When the Commerce Department reported last week that the trade deficit (赤字) in June approached $50 billion, it set off a new round of economic doomsaying（末日说）. Imports, which increasedto $200.3 billion in the month, are subtracted in the calculation of gross domestic product. The larger the trade deficit, the smaller the GDP. Should such imbalances continue, pessimists say, they could contribute to slower growth.But there's another way of looking at the trade data. Over the past two years, the figures on imports and exports seem not to signal a double-dip recession – a renewed decline in the broad level of economic activity in the United States – but an economic expansion.The rising volume of trade –more goods and services shuttling in and out of the United States –is good news for many sectors. Companies engaged in shipping, trucking, rail freight, delivery, and logistics (物流) have all been reporting better than expected results. The rising numbers shows growing vitality in foreign markets – when we import more stuff, it puts more cash in the hands of people around the world, and U.S. exports are rising because more foreigners have the ability to buy the things we produce and market. The rising tide of trade is also good news for people who work in trade-sensitive businesses, especially those that produce commodities for which global demand sets the price – agricultural goods, mining, metals, oil.And while exports always seem to lag, U.S. companies are becoming more involved in the global economy with each passing month. General Motors sells as many cars in China as in America each month. While that may not do much for imports, it does help GM's balance sheet –and hence makes the jobs of U.S.-based executives more stable.One great challenge for the U.S. economy is slack domestic consumer demand. Americans are paying down debt, saving more, and spending more carefully. That's to be expected, given what we've been through. But there's a bigger challenge. Can U.S.-based businesses, large and small, figure out how to get a piece of growing global demand? Unless you want to pick up and move to India, or Brazil, or China, the best way to do that is through trade. It may seem obvious, but it's no longer enough simply to do business with our friends and neighbors here at home.Companies and individuals who don't have a strategy to export more, or to get more involved in foreign markets, or to play a role in global trade, are shutting themselves out of the lion's share of economic opportunity in our world.40. How do pessimists interpret the U.S. trade deficit in June?A. It reflects Americans' preference for imported goods.B. It signifies a change in American economic structure.C. It is the result of America's growing focus on domestic market.D. It could lead to slower growth of the national economy.41. What does the author say about the trade data of the past two years?A. It indicates that economic activities in the U.S. have increased.B. It shows that U.S. economy is slipping further into recession.C. It signals decreasing domestic demand for goods and services.D. It reflects the fluctuations in the international market.42.. Who particularly benefit from the rising volume of trade?A. People who have expertise in international trade.B. Consumers who favor imported goods and services.C. Producers of agricultural goods and raw materials.D. Retailers dealing in foreign goods and services.43. What is the author's advice to U.S. companies and individuals?A. To import more cheap goods from developing countries.B. To move their companies to where labor is cheaper.C. To increase their market share overseas.D. To be alert to fluctuations in foreign markets.CA MENTORING (导师制) program is giving life changing opportunities to Banbury youth.Young Inspirations was founded two years ago to provide mentoring sessions for students and unemployed young adults aged 11 to 21.Alex Goldberg, the program's founder, said; "We set up Young Inspirations because we wanted to give young people experiences which will potentially be life changing and broaden their outlook."We try to create work experience opportunities that will really make a difference to our youth. For example, we've secured internships (实习) with world-famous firms such as Honda."At a time of funding cutbacks where schools are finding it more and more difficult to offer this kind of mentoring, it is extremely important that these opportunities are available both to help youth with their school work and grades and to give them opportunities which may help shape their futures. " Kieran Hepburn, 14, is one of a group of Banbury youth who has benefited from the program so far. In October the Banbury School pupil was accompanied by Young Inspirations staff to Paris where he was an observer at the United Nations Educational, Scientific and Cultural Organization's (UNESCO) International Youth Forum (论坛).The event was held for young people from around the world, to seek their views on how the future of youth and education should look. Kieran joined several hundred observers mostly in their 20s and was the only UK school pupil to attend the event. Kieran thinks the trip was a life changing experience. " Before we left I didn't quite know what to make of it but when we got there we didn't stop, it was amazing," he said, " We went to three or four hours of debates each day and then did something cultural each afternoon. "The main theme of the forum was how youth can drive change in political and public life. It dealt with issues (问题) such as drug abuse, violence and unemployment.Kieran said: " It has really helped me to improve my confidence and social skills as well as my school grades and I was voted most improved pupil at school in August. "The Young Inspirations mentoring sessions take place each Friday in Banbury. For details visit.44. According to the passage, the forum focused on how youth can ____.A. build up their confidence at schoolB. find work experience opportunitiesC. improve their social skills for the futureD. play an active role in the change of society45. We can learn from the passage that _____.A. the visit to the United Kingdom was amazingB. Kieran has made great progress in many aspectsC. the youth have found a way to solve their problemsD. the mentoring sessions are held every day except Friday46. What would be the best title for the passage?A. Alex Goldberg, Founder of Young InspirationsB. Young People Find a World of OpportunityC. Kieran, Banbury School Pupil to ParisD. Debates Help Youth with Their GradesDIn 1974, after filling out fifty applications, going through four interviews, and winning one offer, I look what I could get — a teaching job at what I considered a distant wild area: western New Jersey. My characteristic optimism was alive only when I reminded myself that I would be doing what I had wanted to do since I was fourteen -- teaching English.School started, but I felt more and more as if I were in a foreign country. Was this rural area really New Jersey? My students have a week off when hunting season began. I was told they were also frequently absent in late October to help their fathers make hay on the farms. I was a young woman from New York City, who thought that “Make hay while the sun shines” just meant to have a good time.But, still, I was teaching English. I worked hard, taking time off only to eat and sleep. And then there was my sixth-grade class -- seventeen boys and five girls who were only six years younger than me. I had a problem long before I knew it. I was struggling in my work as a young idealistic teacher. I wanted to make literature come alive and to promote a love of the written word. The students wanted to throw spitballs and whisper dirty words in the back of the room.In college I had been taught that a successful educator should ignore bad behavior. So I did, confident that, as the textbook had said, the bad behavior would disappear as I gave ray students positive attention. It sounds reasonable, but the text evidently ignored the fact that humans, particularly teenagers, rarely seem reasonable. By the time ray boss, who was also ray taskmaster known to be the strictest, most demanding, most quick to fire inexperienced teachers, came into the classroom to observe me, the students exhibited very little good behavior to praise.My boss sat in the back of the room. The boys in the class were making animal noises, hitting each other while the girls filed their nails or read magazines. I just pretended it all wasn’t happening, and went on lecturing and tried to ask some inspiring questions. My boss, sitting in the back of the room, seemed to be growing bigger and bigger. After twenty minutes he left, silently. Visions of unemployment marched before my eyes.I felt mildly victorious that I got through the rest of class without crying, but at my next free period I had to face him. I wondered if he would let me finish out the day. I walked to his office, took a deep breath, and opened the door.He was sitting in his chair, and he looked at me long and hard. I said nothing. All I could thinkof was that I was not an English teacher; I had been lying to myself, pretending that everything was fine.When he spoke, he said simply, without accusation, “You had nothing to say to them.”“You had nothing to say to them," he repeated. “No wonder they’re bored. Why not get to the meal of the literature and stop talking about symbolism. Talk with them, not at them. And more important, why do you ignore their bad behavior?” We talked. He named the problems and offered solutions. We role-played. He was the bad student, and I was the forceful, yet, warm, teacher.As the year progressed, we spent many hours discussing literature and ideas about human beings and their motivations. He helped me identify my weaknesses and my strengths. In short, he made a teacher of me by teaching me the reality of Emerson's words: “The secret to education lies in respecting the pupil.”Fifteen years later I still drive that same winding road to the same school. Thanks to the helpI received that difficult first year, the school is my home now.47. It can be inferred from the story that in 1974 ______.A. the writer became an optimistic personB. the writer was very happy about her new jobC. it was rather difficult to get a job in the USAD. it was easy to get a teaching job in New Jersey48. According to the passage, which of the following is most probably the writer’s problem as a new teacher?A. She had blind trust in what she learnt at college.B. She didn’t ask experienced teachers for advice.C. She took too much time off to eat and sleep.D. She didn’t like teaching English literature.49. The students behaved badly in the writer's classes because ______.A. they were eager to embarrass herB. she didn't really understand themC. they didn't regard her as a good teacherD. she didn’t have a good command of English50. The taskmaster’s a ttitude towards the writer after his observation of her class can be best described as ______.A. cruel but encouragingB. fierce but forgivingC. sincere and supportiveD. angry and aggressiveIV：任务型阅读（共 10 小题，每小题 1 分，满分 10 分）阅读下面短文，根据所读内容在文后第71至第80小题的空格里填上适当的单词。

APIC Quick Guide for API Sourcing_September08final

ACTIVE PHARMACEUTICAL INGREDIENTS COMMITTEEAPIC QUICK GUIDE FORAPI SOURCINGFinal Version: 30 September 2008APIs from Legitimate and Reliable Sources1. IntroductionCounterfeit and sub-standard APIs are increasingly present. Not only are they a fact of non-compliance but also they form a serious and increasing risk for patient safety.Various initiatives have been taken such as the founding of the FDA Counterfeit Drug Task Force, the European Commission’s current “Public consultation in preparation of a legal proposal to combat counterfeit medicines for human use” and the WHO Program “IMPACT” (International Medical Products Anti-Counterfeiting Taskforce).This document focuses on the interaction between the API manufacturer and themedicinal product manufacturer and provides possible measures that may be taken by both partners in order to ensure only non-rogue APIs are used in the manufacture of medicinal products. The proposed measures are considered as elements out of a whole puzzle. A risk-based approach should be applied to determine the necessity and value of the individual proposals, alone or in combination.The document does not address in detail the vendor qualification process as it is taken for granted that APIs are only purchased from suppliers that have been thoroughlyevaluated and approved by Quality Assurance in line with GMP requirements.2. Supply Chain: Agents, Brokers, Distributors, Repackers, RelabelersAs a general principle, the shorter the supply chain, the more secure it will be. This is reflected in the EU GMP Guidelines, Part 1 (5.26) specifying that starting materials (APIs, excipients) should be purchased, where possible, directly from the producer.In addition to the length of the supply chain, any changes on the original container – e.g.by repackaging, relabeling – should be considered as an additional risk for alteration and should therefore, whenever possible, be avoided.There is no doubt that the entire supply chain needs to be assessed from a qualityperspective, covered by an effective supplier qualification program and the sameprinciples as described in the following sections for the direct supply form APImanufacturer to drug product manufacturer should be applied.This already starts at the point of selecting the contractor for transportation of the API (see also ICH Q7, 10.23).3. On Site Visits / Audits3.1. VisitsA thorough knowledge of the supplier is a key element. Therefore, a close and stablerelationship between the manufacturer of the API and the drug product manufacturer should be achieved by using various means of contact. A regular exchange betweensourcing- and purchasing people and the supplier contributes to strengthening this relationship, especially if the contact also includes regular visits on site. Site visits should not be restricted to the manufacturing site alone; intermediaries in the supply chain should be covered as well. It should be ensured that representatives of the purchasing department have a good GMP- and regulatory awareness and technical understanding so that these visits are as beneficial as possible, also in relation to compliance.3.2. AuditsAn audit is considered the most effective way of verifying concrete and compliant manufacturing incl. distribution of APIs. However, apart from the fact that an audit is very time-consuming it only provides a snapshot of the situation and there is no 100% guarantee that evidence for any occurring counterfeiting activities may be identified. Nonetheless, there are various elements in a quality audit that may increase that probability and that respectively may confirm the reliability of the manufacturer.3.2.1 GeneralWhenever possible, the audit should be executed when an actual productioncampaign is ongoing.Requests for changing the agenda at short notice during the audit, e.g.revisiting areas on another time or day, may be a useful approach to confirmthe consistency of operations on site.3.2.2 WarehouseThe walk-through in the warehouse supports the verification of the materialsmanagement capability with respect to claimed annual production of the APIand storage capacity.Checking for the presence of intermediates or APIs in the warehouse thathave been purchased and could be subject for relabeling or of APIs intendedto undergo a reprocessing may lead to the identification of different sources ofmaterials than claimed. The list of approved vendors should also be reviewedfor this purpose.The review of the materials management system and material movements(booking in/out) of concerned API starting materials, intermediates and thefinal API is another possible source of information in the warehouse. However,confidentiality with respect to other customers’ names needs to be respected.3.2.3 ProductionThe walk-through in production should cover the verification of the necessaryequipment and necessary utilities by cross-checking with the productioninstruction and/or process flow chart.3.2.4 Document ReviewThe review of master production instructions as well as analytical methodsand specifications for raw materials, intermediates and the API as well as ofexecuted documents/raw data and cross-checks with the regulatory document(e.g. DMF, CMC section, CEP dossier) is an important element in verifyingregulatory compliance.One can also verify the availability of production records and/or analytical rawdata as well as retained samples (where applicable) of raw material,intermediates and API batches for specific batches that were either identifiedfrom the review of the stock cards/materials management system, productquality review or from supplied batches.The timely and sequential correlation of equipment use logbooks in productionand QC laboratory, production batch records (incl. electronic raw data),cleaning records and analytical raw data (incl. date/time on equipment print-outs such as balances, chromatographic systems etc.) is a good indicator foron site production.The review of the documentation related to seals (specifications –testing/approval according to specifications – reconciliation documentation –authorized persons identified and documented…) may be added.A spot wise review of analytical raw data from stability studies (not only thesummary table) as well as of the logbook of the stability chambers (e.g. dateof sample in/out) and the check for physical availability of the stability samplesshould be included.The adequate involvement of the drug product manufacturer in case ofchanges that can impact the quality and/or regulatory compliance of the APImay be verified by the reviewing the history of changes and individual changerequest cases related to the production and testing of the API (incl.intermediates, raw materials),4. Supporting DocumentationThe availability of certain documents that are regularly available and up-dated, where applicable, may be considered as one efficient element in the continuous suppliermonitoring process.4.1 Inspections, Inspection historyAs part of the initial evaluation of a potential API supplier the GMP inspection history, with respect to inspecting regulatory body, inspection date, inspected areas (as far as this information is / is made available) and the inspection results should be reviewed. Aregular up-date of the inspection history as part of the supplier monitoring and re-qualification process should be performed.On the other hand, as these inspections are not mandatory for APIs e.g. used inmedicinal products for the EU, the non-availability of an inspection history may not lead to the conclusion that this API supplier is less reliable.4.2 GMP certificatesGMP certificates of the API manufacturer, where available (see 4.1), should be provided, ideally as authentic copies.4.3 Certificate of AnalysisA thorough review of Certificate of Analysis, against regulatory documents (e.g. DMF, CMC section, CEP dossier) and in-house specification respectively, and with respect to GMP compliance (ICH Q7, 11.14) should be performed as part of incoming release testing of APIs. Suppliers involved in counterfeiting could apply improper documentation practices.In case of agents, brokers etc. being involved in the supply chain it is recommended to insist on a certificate of analysis issued by the original manufacturer of the API (see also 2.). Where a new certificate of analysis is prepared by agent, broker, distributor, there should be a reference to the name and address of the original manufacturer and a copy of the original batch Certificate should be attached, as specifically required by ICH Q7 11.43, 444.4 Certificate of Compliance, Compliance CommitmentA certificate of compliance issued by the API manufacturer, either as a separate document or as part of the certificate of analysis, which certifies that a specific batch has been manufactured according to ICH Q7 GMP requirements and in line with the applicable Registration Documents can provide additional assurance related to the awareness of the manufacturer on the quality and regulatory expectations of the customers.4.5 On-going stability programA GMP compliant manufacturer has an on-going stability program for its APIs (ICH Q7,11.5). At least one batch of the API manufactured per year is added to the stability program and tested at least annually. A regular up-date of the program provided by the API manufacturer, not necessarily including stability data, gives additional assurance for actual and compliant systems.4.6 Product Quality ReviewThe major objective of the Product Quality Review (ICH Q7, 2.5) is to evaluate the compliance status of the manufacture (process, packaging, labelling and tests) and to identify areas of improvement based on the evaluation of key data. It includes a review of critical in-process controls and critical API test results, of batches that failed to meet specification, of changes carried out, of the stability monitoring program, of quality-related returns/complaints/recalls and of the adequacy of corrective actions. Due to the comprehensive information included, the Product Quality Review provides a good overview of the manufacture of a certain API.The document should be reviewed during an audit or as a minimum an approved executive summary should be made available by the API manufacturer.4.7 Quality AgreementThe quality agreement as a tool to clearly define the GMP responsibilities strengthens the awareness of liabilities of both partners. The extent and level of detail of the agreement may vary and can depend on the material supplied, e.g. generic API versus exclusively synthesized API, but it should at least address- name of the product- mutually agreed specification (if not covered by supply agreement)- manufacturing site- applicable cGMP standards, e.g. ICH Q7- compliance with the DMF or with other registration documentation- GMP audits related to the API (e.g. 3rd party auditing)- documents to be provided by the manufacturer, e.g. certificate of analysis,certificate of compliance, inclusion of copies of respective master documents may be addressed- arrangements for transportation and transport packaging (see 5.), e.g. description and degree of tampering proof seal to be used, inclusion of a copy of the master drum label may be considered- deviation handling- handling of and response to complaints- change management: involvement of the customer with respect to notification andapproval- list of approved signatories may be included5 Packaging: labeling, tamper-proof sealingIf the API manufacturer provides examples/templates of master labels, which he uses to label the containers, this supports the drug product manufacturer in identifying anymanipulation on the material on its way from the manufacturer to the recipient.The use of tamper-resistant packaging closure by the manufacturer provides additional assurance that the material was not adulterated on its way from the manufacturer to the drug product manufacturer. A manufacturer-specific design of the seal is recommended to be used; the use of unique seals may be considered. The communication of the type of seal, by the manufacturer to the user, completes the information chain.6. Material Inspection, Sampling, Analysis, Impurity ProfileAt the point of receipt the first relevant action is to carefully perform the visual inspection of all the containers of the API. Attention shall be paid to the integrity and type of the sealing as well as to the special attributes added by the manufacturer (see above 4.7, 5.) such as label design, seal number and design.The applied sampling regime related to the number of containers sampled, number of samples taken per container, analysis of individual and/or pooled samples as well as the extent of analysis, varying from identity test to full analysis may influence the probability of identifying counterfeiting, provided it may be identified by analytical means.A risk-based approach, considering the qualification status of the supplier, may bechosen to define the extent of sampling and testing, considering the requirements for drug product manufacturers (e.g. Annex 8 to EU GMP Guidelines).The impurity profile is normally dependent on the production process and origin of the API. The comparison of the impurity profile of a current batch with either previous batches or data provided by the manufacturer (e.g. as part of the regulatory submission) may help in order to identify changes related to modifications in the production process and may indicate whether the API might originate from a different manufacturer than the supposed one.It is recommended to check the current (im)purity profile and compare it with former quality in regular intervals, at least once a year.GLOSSARYAPIActive pharmaceutical ingredient (synonym: drug substance)Counterfeit APIActive pharmaceutical ingredient for which source and/or quality are falsely represented on the label, on the certificate of analysis or otherwiseRogue APIAPI that is counterfeit or severely, deliberately non-compliant.ACKNOWLEDGEMENTSThis document was originally prepared by a group of experts within CEFIC/ APIC. We thank them for their work and efforts spent as well as for their kindly co-operation, intensive discussions and fruitful comments:- Claudia Stampfli (Lonza)- Stephan Rosenberger (Lonza)- Ricardo Giralt (Boehringer-Ingelheim)- Luisa Paulo (Hovione)- Tony Storey (Pfizer)- Iain Moore (Croda)- Henri Leblanc (Rhodia)- Rodney Horder (Abbott)- Rainer Fendt (BASF)- François Vandeweyer (Janssen Pharmaceutica)- Chris Oldenhof (DSM)- José Luis Ortega (Pharma Mar)- Tom Buggy (DSM)。

密码编码学与网络安全-原理与实践课后答案

数学综合讨论区论坛管理团队及部分会员来源于山东大学数学院七大专业（基础数学、应用数学、运筹学、控制论、计算数学、统计学、信息安全），在数学方面均为思维活跃、成绩优秀的研究生，相信会给您的数学学习带来很大的帮助。
密码学与网络安全山东大学数学院的信息安全专业师资雄厚，前景广阔，具有密码理论、密码技术与网络安全技术三个研究方向。有一大批博士、硕士及本科生活跃于本论坛。本版块适合从事密码学或网络安全方面学习研究的朋友访问。
Third Edition WILLIAM STALLINGS
Copyright 2002: William Stallings -1-
TABLE OF CONTENTS
Chapter 2: Chapter 3: Chapter 4: Chapter 5: Chapter 6: Chapter 7: Chapter 8: Chapter 9: Chapter 10: Chapter 11: Chapter 12: Chapter 13: Chapter 14: Chapter 15: Chapter 16: Chapter 17: Chapter 18: Chapter 19: Chapter 20:
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SOLUTIONS MANUAL
CRYPTOGRAPHY AND NETWORK SECURITY
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CHAPTER 2 CLASSICAL ENCRYPTION TECHNIQUES

英语分级教学实践总结(3篇)

第1篇Abstract:This paper summarizes the practical experience of implementing a graded English teaching approach in a primary school setting. It discusses the rationale behind the approach, the methods employed, the challenges faced, and the outcomes achieved. The paper also reflects on the lessons learned and provides recommendations for future implementation.I. IntroductionThe implementation of a graded English teaching approach in our primary school has been a significant endeavor aimed at catering to the diverse needs and abilities of our students. English, being a critical language for global communication, is an essential subject in our curriculum. However, students come to English with varying levels of proficiency, backgrounds, and learning styles. To address this diversity, we adopted a graded English teaching method, which has proven to be both challenging and rewarding. This paper provides a comprehensive summary of our experiences, highlighting the process, outcomes, and insights gained from the implementation.II. Rationale for Graded English TeachingThe primary rationale for adopting a graded English teaching approach was to ensure that each student receives an education that is appropriate to their individual needs. By grouping students based on their English proficiency levels, we could tailor our teaching methods and materials to cater to their specific strengths and weaknesses. This approach aimed to provide a more personalized learning experience, fostering better engagement and achievement among students.III. Methods Employed1. Assessment and Grouping:- Standardized tests and informal assessments were conducted to evaluate students' English proficiency.- Students were grouped into four levels: beginner, elementary, intermediate, and advanced.2. Curriculum Development:- Tailored curricula were designed for each level, focusing on key language skills such as listening, speaking, reading, and writing.- Textbooks and supplementary materials were selected based on the needs of each group.3. Teaching Strategies:- Interactive and student-centered approaches were adopted to promote active learning.- Differentiated instruction was used to cater to students' varying abilities and learning styles.4. Assessment and Feedback:- Formative and summative assessments were conducted regularly to monitor student progress.- Constructive feedback was provided to students and their parents to encourage continuous improvement.IV. Challenges Faced1. Resource Allocation:- Allocating sufficient resources, including qualified teachers and materials, for each level was a significant challenge.2. Teacher Training:- Ensuring that teachers were adequately trained to implement differentiated instruction was crucial.3. Parental Involvement:- Engaging parents in the grading system and encouraging their support was essential for the success of the program.V. Outcomes Achieved1. Increased Student Engagement:- Students showed higher levels of engagement and motivation in their English classes.2. Improved Learning Outcomes:- There was a noticeable improvement in students' English proficiency across all levels.3. Positive Parental Feedback:- Parents were satisfied with the personalized approach and the progress of their children.VI. Lessons Learned1. Importance of Continuous Assessment:- Regular assessments are crucial for monitoring student progress and adjusting teaching strategies accordingly.2. Value of Differentiated Instruction:- Tailoring instruction to meet the needs of diverse learners can significantly enhance learning outcomes.3. Need for Ongoing Teacher Training:- Continuous professional development for teachers is essential to implement effective graded teaching methods.VII. Recommendations for Future Implementation1. Enhanced Resource Allocation:- Allocate additional resources, including qualified teachers and materials, to support the graded teaching approach.2. Regular Teacher Training:- Provide ongoing training for teachers to enhance their skills in differentiated instruction and grading systems.3. Parental Engagement Programs:- Develop programs to engage parents in the grading system and encourage their support.VIII. ConclusionThe implementation of a graded English teaching approach in our primary school has been a transformative experience. By catering to the diverse needs of our students, we have been able to foster a more inclusive and effective learning environment. While challenges were faced, the outcomes achieved justify the efforts invested. As we move forward, we are committed to refining our grading system and continuously improving the quality of English education provided to our students.第2篇Introduction:As the globalization of the world continues to progress, the importance of English language proficiency has become increasingly evident. Inorder to cater to the diverse needs and learning abilities of students, the implementation of English language分级教学 has gained popularity in recent years. This summary aims to reflect on the practical experienceof implementing English language分级教学，including its benefits, challenges, and future directions.I. Background and Rationale1.1 BackgroundThe concept of English language分级教学 originated from the need to address the varying levels of students' English proficiency. Traditional teaching methods often ignored the individual differences among students, leading to a lack of personalized instruction and reduced learning effectiveness.1.2 RationaleThe implementation of English language分级教学 is based on thefollowing principles:a. Individualized instruction: cater to the different learning needs of students.b. Improved learning outcomes: enhance students' English proficiency and promote their overall development.c. Increased motivation: encourage students to actively participate in the learning process.II. Implementation Process2.1 Preparing for the Implementationa. Conducting a comprehensive needs analysis: identify the strengths and weaknesses of students' English language abilities.b. Developing a clear grading system: categorize students into different levels based on their language proficiency.c. Designing appropriate teaching materials: tailor teaching content and activities to each level.2.2 Classroom Teachinga. Using a variety of teaching methods: incorporate different teaching techniques, such as task-based learning, cooperative learning, and project-based learning.b. Adjusting teaching strategies: adapt teaching methods and materials to cater to the specific needs of each level.c. Providing individualized attention: offer guidance and support to students who require additional assistance.2.3 Assessment and Feedbacka. Using a variety of assessment methods: employ formative and summative assessments to evaluate students' progress.b. Providing timely feedback: offer constructive comments and suggestions to help students improve their language skills.c. Monitoring students' progress: track students' development and make necessary adjustments to the teaching plan.III. Benefits of English Language分级教学3.1 Improved Learning OutcomesStudents at different levels can learn at their own pace, which enhances their learning outcomes and promotes their overall development.3.2 Increased MotivationBy catering to individual needs, students are more likely to be motivated and actively participate in the learning process.3.3 Enhanced Teacher-Employee RelationshipsTeachers can better understand and support students, leading to improved teacher-student relationships and a more positive learning environment.IV. Challenges and Solutions4.1 Challenge: Lack of ResourcesSolution: Seek external funding or collaborate with other educational institutions to secure necessary resources.4.2 Challenge: Teacher TrainingSolution: Provide professional development opportunities for teachers to enhance their knowledge and skills in implementing English language分级教学.4.3 Challenge: Parental InvolvementSolution: Establish communication channels with parents to keep them informed about their children's progress and encourage their participation in the learning process.V. Future Directions5.1 Continuously Refining the Grading SystemRegularly assess the effectiveness of the grading system and make adjustments to ensure it remains relevant and accurate.5.2 Expanding the Scope of English Language分级教学Consider extending the application of English language分级教学到其他学科领域， such as mathematics and science.5.3 Embracing TechnologyLeverage technology to support English language分级教学， such asonline platforms, educational apps, and virtual reality tools.Conclusion:The implementation of English language分级教学 has proven to be a valuable approach to catering to the diverse needs of students. By addressing the challenges and continuously improving the teaching methods, English language分级教学 can play a crucial role in fostering students' English proficiency and promoting their overall development.第3篇Introduction:As a language teacher, implementing a分级教学（Graduated English Teaching）model has proven to be a transformative approach in enhancing the learning experience for students of diverse abilities and backgrounds. This practice summary aims to reflect on the experiences and outcomes of a year-long English分级教学实践, highlighting the strategies employed, challenges faced, and the overall impact on student learning.I. Background and ObjectivesThe purpose of the English分级教学 practice was to cater to the varied needs of students in terms of their English proficiency levels. The objectives were as follows:1. To identify and group students based on their current English proficiency.2. To create a supportive learning environment that challenges and motivates students at their respective levels.3. To develop a curriculum that addresses the individual needs of each group.4. To monitor and assess student progress regularly and adjust teaching strategies accordingly.II. Implementation Strategies1. Assessment and Grouping:- Conducted initial assessments using standardized tests and teacher observations.- Formed groups with similar proficiency levels, ensuring a balanced mix of abilities within each group.- Reassessed students periodically to accommodate any changes intheir abilities.2. Curriculum Design:- Designed differentiated lesson plans for each group, focusing on core language skills (reading, writing, listening, and speaking).- Included a variety of teaching methods such as cooperative learning, project-based learning, and technology integration to cater to different learning styles.- Adapted materials and activities to match the level of each group, ensuring a challenging yet achievable curriculum.3. Classroom Management:- Implemented a tiered system of classroom management to provide support and accountability for each student.- Encouraged peer tutoring and collaborative learning to foster a sense of community and mutual support among students.- Created a positive and inclusive classroom culture where all students felt valued and motivated.4. Assessment and Feedback:- Utilized formative and summative assessments to monitor student progress and identify areas of improvement.- Provided constructive feedback to students, focusing on their strengths and areas that needed further development.- Adjusted teaching strategies based on the feedback received and observed changes in student performance.III. Challenges and Solutions1. Time Management:- Challenging to allocate sufficient time to cater to the diverse needs of each group within the limited class hours.- Solution: Scheduled additional time for group work and collaborative activities, allowing students to receive personalized attention and support.2. Student Motivation:- Some students felt overwhelmed or bored due to the differentiation in the curriculum.- Solution: Encouraged students to set personal goals and celebrated their achievements, regardless of their proficiency level.3. Parental Involvement:- Limited parental awareness and involvement in the differentiated teaching approach.- Solution: Communicated regularly with parents through newsletters, parent-teacher meetings, and online platforms, ensuring they were informed and supportive of the teaching strategies.IV. Impact on Student Learning1. Increased Student Engagement:- Students showed higher levels of engagement and motivation in their English classes.- Evidence: Improved attendance rates, increased participation in class activities, and positive feedback from students regarding their learning experience.2. Enhanced Academic Performance:- Students from all proficiency levels demonstrated improved academic performance.- Evidence: Increased scores on standardized tests, better understanding of English language concepts, and enhanced communication skills.3. Improved Self-Esteem:- Students felt more confident in their abilities and were more willing to take risks in their learning.- Evidence: Increased number of students participating in class discussions, willingness to share their work with peers, and a positive attitude towards learning English.Conclusion:The implementation of English分级教学 in our classroom has been a rewarding experience, offering a personalized approach to language learning that caters to the diverse needs of students. By employing a variety of strategies and adapting teaching methods to suit different proficiency levels, we have seen significant improvements in student engagement, academic performance, and self-esteem. As we continue torefine and expand our practices, we remain committed to providing an inclusive and effective English learning environment for all students.。