lecture7(process,cause-effect,example)

内容提要★结构型设计模式小结包装型模式群设计模式实例分析Structural Patterns结构模式描述如何将类或者对象结合在一起形成更大的结构。

类的结构模式：类的结构模式使用继承把类、接口等组合在一起，以形成更大的结构。

当一个类从父类继承并实现某接口时，这个新的类就把父类的结构和接口的结构组合起来。

类的结构模式是静态的。

对象的结构模式：对象的结构模式描述了怎样把各种不同类型的对象组合在一起，以实现新功能的方法。

可以在运行时刻改变对象组合关系，对象的结构模式是动态的。

结构模式主要有：Adapter 适配器模式Bridge 桥接模式Composite组合模式Decorator 装饰模式Facade 门面模式Flyweight享元模式Proxy 代理模式1 AdapterAliases：WrapperIntent将一个类的接口转换成客户希望的另外一个接口。

Adapter模式使得原本由于接口不兼容而不能一起工作的那些类可以一起工作Motivation有时为复用而设计的工具箱类不能够被复用的原因仅仅是因为它的接口与专业应用领域所需要的接口不匹配图示：1. 对象Adapter：Adapter与Adaptee是委派关系图示：2. 类Adapter：Adapter与Adaptee是继承关系Adapter 模式的关键特征Adapter 模式的关键特征用一个满足现有接口需求的新类包含已有类，调用已有类的方法实现新类中的方法实现Adapter 模式使得先前存在的对象可以匹配新的类型，而不受该对象原有接口的限制效果Adapter 对Adaptee 进行适配，使其满足Adapter’s Target 的要求。

这是的用户可以实际使用Adaptee ，就好像它是一种Target 一样。

参与者和协作者Adapter 面向所需的接口提供一个包装器解某系统拥有合适的数据和行为，但接口并不合要求。

问题将一个你难以控制（如无法修改其内部代码）的对象匹配到特定的接口上意图2 BridgeAliases：Handle/BodyIntent将抽象部分与它的实现部分分离，使它们都可以独立地变化Motivation要做到“抽象(接口)与实现分离”，最常用的办法是定义一个抽象类，然后在子类中提供实现。

Producer Theory1Technology1.Production is a process of transforming inputs into outputs.Thefundamental problem…rms must contend with in this process is the technological feasibility.The state of technology determines and restricts what is possible in combining inputs to produce out-put.2.We…rst concentrate on the case in which the…rm produces onlyone output.The case of multiple outputs will be dealt with later.When there is only one output,we will use q2R+to denote the …rm’s output and x2R n+to denote the…rm’s inputs.3.We de…ne the production function as:q=f(x):The production function captures the technology of production.It tells us how much input x is needed to produce a a…xed amount of output q.4.Assumption3.1.The production f:R n+!R+,is continuous,strictly increasing,and strictly quasiconcave on R n+,and f(0)=0.5.The marginal product of x i,MP i=@f @x i;tell us how many extra units of output an extra unit of x i produces. Unlike marginal utility in consumer theory,marginal product is objective and measurable.6.The strict quasiconcavity assumption means that any convex com-bination of two input vectors can produce at least as much output as one of the original two.This would be the case if we have diminishing marginal product.7.For any…xed level of output q,the set of input vectors producingq is called q-level isoquant.This plays the same role as indi¤erence curve in consumer theory.An isoquant traces out all the combina-tions of inputs that allow that…rm to produce the same quantity of output.8.The substitutability between any pair of inputs x i and x j is themarginal rate of technical substitution(MRTS).MRTS measures the amount of one input i the…rm would require in exchange for using a little less of another input j in order to just be able to produce the same output as before.A q-level isoquant is de…ned as:f(x)=q:Given x ij,let x j(x i)be the amount of x j required to keep out-put constant.If we di¤erentiate the isoquant with respect to x i, holding x ij constant,we get@f @x j dx jdx i+@f@x i=0:Rearranging the terms gives the slopeMRT S ij(x)= dx jdx i=@f@x i@fj:Since f is strictly quasiconcave,MRTS is diminishing.9.Elasticity of substitution:for a production function q=f(K;L);the elasticity of substitution ;measures the proportionate change in K=L relative to the proportionate change in the MRTS along the isoquant.That is,=% KL% MRT S L;K=dK=LdMRT SMRT SK=L=d ln(K=L)d ln MRT S:The shape of the isoquants indicates the degree of substitutability.10.De…nition:we classify the returns to scale of a production function,f(K;L),as follows:E¤ect of Output(m>1)Returns to Scale f(mx)=mf(x)Constantf(mx)<mf(x)Decreasingf(mx)>mf(x)Increasing11.Constant returns to scale means if you multiply all inputs by factorm>1,the output is increased by factor m.Increasing returns to scale means if you multiply all inputs by a factor m,the out-put increases by a factor more than m.That is,you can get proportionally more as you expand.Decreasing returns to scale is just the opposite to increasing returns.A production function can have increasing returns over some range and decreasing returns over another.In fact,a lot of times there is some optimal scale in between:it is ine¢cient to be too small and ine¢cient to be too big.12.Locally,the elasticity of scale at point x is de…ned by(x) limm!1d ln[f(mx)]d ln(m)=P n i=1f i(x)x if(x):1.1Special production functions1.Linear production function:perfect substitutes2.Cobb-Douglas production functionsq=AL K ;where A; ; >0.3.Leontief production functionsq=min K; L :4.CES production functionq=A h L 1 +(1 )K 1 i 1where A>0; 2(0;1); >0. is the elasticity of substitution.(a) =+1,linear production function.(b) =1,Cobb-Douglas production function.(c) =0,Leontief production function.5.Homothetical production function:homothetical production pro-duces a linear expansion path starting from the origin,optimal input ratio at various output level is constant given…xed input prices.2Cost Minimization2.1Long-run Cost minimization1.Some cost de…nition(a)Opportunity cost:the value of a resource in its best alterna-tive use.(b)Sunk costs are those unrecoverable costs that have alreadybeen incurred and the resources have no alternative use.2.Short-run vs.long-run cost minimization(a)Long-run:free to vary quantities of all its inputs as much asit desires.(b)Short-run:unable to adjust the quantities of some of its in-puts.3.Long-run cost-minimization.Let w denote input prices.The costminimization problem is de…ned as:minxwxs:t:f(x) q:L=wx+ (q f(x)):The…rst-order conditions:@L@x i=w i f x i=0;i=1;:::;n@L@=q f(x)=0;From the…rst n equations,we get for all iw if xi= .4.Recall f xi is the extra output the…rm can make from one extraunit input i,so1x i is the amount of input i required to produceone unit of output,and wf xi is the cost for producing one extraunit of output using input i.A cost-minimizing…rm chooses an input combination such that the cost for producing one extra unit of output is the same no matter what input mixes the…rm choose to increase output.5.Example 1:Cobb-Douglas production functionq =50L 1=2K 1=2:MRT S L;K =K L =w r =)K (r;w )=w rL:Plugging K (r;w )into the production functionq =50L 1=2 w r L 1=2=)L =q 50 r w1=2:Similarly,K =q 50 w r 1=2:parative statics of change in output(a)The cost minimizing input combinations,as q 0varies,traceout the expansion path .(b)If the cost minimizing quantities of labor and capital rise asoutput rises,labor and capital are normal inputs .(c)If the cost minimizing quantity of an input decreases as the…rm produces more output,the input is called an inferior input .7.Properties of Cost FunctionIf f is continuous and strictly increasing,then the cost functionc (w;q ) min x wx s:t:f (x ) q is(a)Zero when q =0.(b)Continuous on its domain.(c)For all w >>0,strictly increasing and unbounded above inq .(d)Increasing in w:(e)Homogeneous of degree one in w:(f)Concave in w .(g)Shephard’s lemma:c (w;q )is di¤erentiable in w at (w 0;q 0)whenever w 0>>0;and @c (w 0;q 0)@w i=x i w 0;q 0 ;i =1;:::;n:2.2Conditional Input DemandsSuppose the production function satis…es Assumption 3.1and that the associated cost function is twice continuously di¤erentiable.Then1.x (w;q )is homogeneous of degree zero in w:2.The substitution matrix,0B B B @@x 1(w;q )@w 1@x 1(w;q )@w n::::@x n (w;q )@w 1@x n (w;q )@w n1C C C A is symmetric and negative semide…nite.In particular,the semidef-initeness property implies that for all i@x i (w;q )@w i0.2.3Short-run cost-minimization1.The …rm’s short-run cost minimization problem is to choose quan-tities of the variable inputs so as to minimize total costs,given that the …rm wants to produce an output level q and under the constraint that the quantities of the …xed factors do not change.min xwx + w x s:t:f (x; x ) q:2.Three inputs short-run cost-minimizationmin L;MwL +mM +r K s:t:q =f (L;K;M )Note:L;M are the variable inputs and wL +mM is the total variable cost. Kis the …xed input and r K is the total …xed cost.Tangency condition:MP L w =MP M m:Constraint:q =f (L;K;M ):3.Suppose that K is the long run cost minimizing level of capital foroutput level q .Then when the…rm produces q ,the short-run demands for L and M must yield the long-run cost minimizing levels of L and M4.Exampleq=K1=2L1=4M1=4;r=2;w=16;m=1: The short-run cost-minimization condition when q=16, K=32:(a)Short-run Tangency condition:MP L MP M =ML=wm=161=)M=16L:Constraint16=321=2L1=4(16L)1=4;which gives L=2,and M=16L=32.Thus when q= 16; K=32,the short-run cost minimization inputs combina-tion isL=2;M=32:(b)Long-run cost minimization when q=16:Two tangency conditionMP L MP M =ML=wm=161=)M=16L;MP L MP K =2KL=wr=162=)K=16LConstraint16=(16L)1=2L1=4(16L)1=4=)1634L=16=)L=1614=2: Plugging L=2into tangency conditionM=16L=32;K=16L=32:Hence when K=32is the long-run cost minimizing level of capital for the output level q=16,the short-run cost minimization yields the long-run cost minimizing levels of L and M.5.For the previous example,the long-run cost given input pricesr=1;w=16;m=1isc(q)=8q:The short-run cost…xing K=32issc(q; K)=64+q2 4 :Clearly sc(q; K) c(q)for all q 0:3Pro…t Maximization1.To…nd the optimal outputmaxf q gpq c(w;q) The…rst order condition implies thatp=@c@q(1)and the second order condition is that@2c@q2>0:By the…rst order conditions,we can get the…rm’s output supply function,q =q(p;w):2.To…nd the optimal inputsmaxf x gpf(x) wxUsing the…rst order condition we havep @f@x i=w i;for i=1;:::;n:The…rst-order conditions mean that the marginal revenue product (MRP)of each input i should equal the input price.MRP gives the rate at which revenue increases per additional unit of input i employed.The…rst-order conditions will give us the input demand function of the…rm,x =x(p;w):3.Theorem3.7.If f satis…es Assumption3.1,then for p 0andw 0;the pro…t function(p;w) max pq c(w;q)when well-de…ned,is continuous and(a)Increasing in p:(b)Decreasing in w:(c)Homogeneous of degree one in(p;w):(d)Convex in(p;w):(e)Di¤erentiable in(p;w)>>0.Moreover,(Hotelling’s lemma),@@p=q;@ @wi=x i:4.Theorem3.8.Suppose is well-de…ned and twice continuouslydi¤erentiable,then(a)q and x i are homogeneity of degree zero.(b)The substitution matrix0B B B B B @@q@p@q@w1:::@q@w n@x1(p;w)@p @x1(p;w)@w1::: @x1(p;w)@w n ::::::::::::@x n(p;w)@p @x n(p;w)@w1::: @x n(p;w)@w n1CC C C CAis symmetric and positive semide…nite.In particular,@q 0and@x i(p;w)@w i 0for all i.5.Example:Price P,input prices(w1;w2)q=x 1x 2where ; >0.The…rst order condition givesP x 11x 2 w1=0;(2)P x 1x 12 w2=0;(3)q x 1x 2=0:(4) The…rst two conditions imply that x2= x2=w1=w2and thus, x2=( w1= w2)x1.Plugging it back into(4)yieldsx1=q1 + w2 w1 + ;x2=q1 + w1 w2 + :Plugging the two conditional input demands into (2)gives P q + 1+ w 2w 1 + =w 1=)q+ 1 + =P 1w + 1w + 2 + + =)q =P +1 w + 11w + 12 1 1 ;x 1(P;w )=P 11 w 1 ( + 1)1w ( + 1)2 1 (1 ) 1 ;x 2(P;w )=P 11 w ( + 1)1w 1 ( + 1)2 (1 ) 1 1 :Plugging q (P;w )back into the conditional input demand gives x i (P;w ).And the pro…t function(P;w )=P q (P;w ) wx (P;w ):Note that when + <1,dq (P;w )dP >0@x i (P;w )@w i<0:6.When + =1or + >1;q (P;w )and x i (P;w )are unde…ned,therefore,the pro…t function is not de…ned.To show this,the pro…t function de…ned as before:(p;w ) max pf (x ) wx:Suppose that x 0and f (x 0)maximize pro…ts at p and w:With in-creasing returns,f (tx 0)>tf (x 0)for all t >1:Thus,pf (tx 0) wtx 0>tf (x 0) wtx 0 f (x 0) wx 0for all t >1:This says higher pro…t can always be had by increasing inputs in proportion t >1;which contradicts our assumption that x 0and f (x 0)maximized pro…t.7.Note that in the special case of constant returns,no such problem arises if the maximal level of pro…t happens to be 0.In that case,though,the scale of the …rm’s operation is indeterminate because (f (x 0);x 0)and (tf (x 0);tx 0)give the same level of 0pro…ts for all t >0:4Multiple outputs1.Another way to represent the technology constraint is to think ofthe…rm as having a production possibility set,Y R n;where each vector y=(y1;y2;:::y n)2Y is a production plan,where y i>0means outputs and y j<0means inputs.2.A production plan y2Y is technological e¢cient if there isno b y2Y such that b y>y:A production plan is economically e¢cient if it maximizes pro…ts =py of a given price vector p:3.Economic e¢ciency implies technological e¢ciency.No matterwhat the prices of inputs and outputs are,the…rm needs to achieve technological e¢ciency in order to achieve pro…t maximization.We can think of the…rm’s choice problem in two steps:…rst,the…rm has to achieve technological e¢ciency;second,the…rm obtain eco-nomic e¢ciency on the e¢cient production set or the production possibility frontier(PPF).The PPF is de…ned to be the set of all technologically e¢cient production plans.4.Formally,given a production plan y=(y1;y2;:::y n)2Y;thereis a twice di¤erentiable function G:R n!R that de…nes the production possibility set:Y f y2R n j G(y) 0g:5.Assumption1.Strict Monotonicity.That is,G yi >0;8i;y:By thisassumption,since G yi >0,any y such that G(y)<0is technolog-ically ine¢cient:one can increase the production(or decrease theuse)of one product y i while keeping others constant(some y i areinputs).Therefore,f y2R n j G(y)=0g is the technologically e¢-cient production set and is thus called the production possibilityfrontier(PPF).6.We de…ne the marginal rate of transformation(MRT)asMRT ij @y i@yj =G yjG yi>0:MRT is the slope the PPF.7.Assumption2.G is quasi-convex.The…rm’s problem is then:(p) maxy2R npys:t:G(y) 0:Since technological e¢ciency is necessary for economic e¢ciency (pro…t maximization),the above problem is equivalent to(p) maxpyy2R n s:t:G(y)=0:。

Lecture 7 Second Language Learning Theories(1)Learning guidance:Goals: 1.to be familiar with Krashen's five hypotheses2.to grasp the main idea of the Output Hypothesis3.to grasp the main idea of the Interaction Hypothesis4.to grasp the main idea of the Multiple Intelligences TheoryKey Points: knowing how to use these learning theories in real language teachingDifficulties: identifying the differences between learning and acquisitionPeriods: One periodLanguage acquisition especially, second language acquisition, is a dynamic process which can be explained from many perspectives. It can be linked to the process of human being's rounded growth, including affective development, cognitive development, and behavior changes. Such process should be psychological and physiological as well.Many physiologists, linguists, language teachers and some policy makers of language teaching have tried to explain language acquisition phenomenon from various aspects. In the following parts, we will mention some influential theories based on existing studies, whose contributions to the language acquisition process are provocative and overwhelming.7.1 Krashen's Five Hypotheses and Second Language Acquisition (SLA)Krashen, a professor from the linguistic department of the University of South California, mentions five hypotheses about second language learning in the late 1970s. He refines and expands his theories in the early 1980s as follows.1.The Acquisition-Learning Hypothesis2.The Monitor Hypothesis3.The Natural Order Hypothesis4.The Input Hypothesis5.The Affective Filter Hypothesis7.1.1The Acquisition-Learning Hypothesis and Second Language Acquisition (SLA)Five hypotheses are very important theories in second language learning. They deal with the laws of second language learning. In so far as, they are the most comprehensive of existing theories. Krashen (1982) claims that adult second language learners have two distinct and independent means for developing competence and internalizing the target language. The first way is "acquisition", and the other is "learning". He considers that acquisition is primary and first and foremost; through acquisition, learners acquire language abilities and skills. Learning is auxiliary. It can not improve learners' language development. It can only assist acquisition. Next we will introduce these two ways in detail in the following.7.1.1.1 Contents of the Acquisition-Learning HypothesisAcquisition is a natural way, which refers to implicit, informal, natural learning. Acquisition is an unconscious process that includes natural interaction through using language for meaningful communication. According to Krashen, acquisition is the process used by children to pick up their mother language. Children only concentrate on communication instead of language form, and the result of acquisition is acquired competence. Krashen holds that second language learning is the same as first language acquisition, which means that second language learners also can acquire language competence in a natural and unconscious way through using language in real communication, and second language performance should base on acquired knowledge.However, learning is an unnatural way, which refers to the conscious, explicit, and formal studying. In other words, learning is the result of formal teaching, which makes learners concentrate on form and linguistic rules of the target language.Krashen also pays attention to the distinction between language acquisition and learning. He considers that learning takes place between "learning" and "teaching", however, acquisition takes place between "learning" and "getting", and he also thinks that acquisition is relevant to oral communication, while learning to exams and homework. He holds that process of acquisition plays a vital role in the adults. The performance of second language depends on what learners have acquired, not what they have learned. He proposes that error correction has no effect on unconscious acquisition, but has positive effect on conscious learning. During the process of conscious learning, both teachers and learners use their grammatical knowledge to correct errors from their speeches or writings. However, meaningful communication should be the final goal in unconscious acquisition process, so we should focus on fluency not accuracy.Based on the Acquisition-Learning Hypothesis, Krashen and Terrel (1983) propose The Natural Approach. This approach attracted a wider interest than some other languageteaching proposals. They consider communication as the primary function of language, and since their approach focuses on communication ability, they refer to the Natural Approach as an example of communicative approach. This theory is based on an empirically grounded theory of second language acquisition, which has been supported by a large number of scientific studies in a wide variety of language acquisition and learning context.The Natural Approach divides language acquisition into four stages:(1) Pre-ProductionIn the first stage, teachers can communicate with students naturally with basic vocabulary and sentence patterns. Some important points should be reviewed and repeated. Teachers can also provide students with objects and pictures to help them have a deep understanding. In this stage, learners need to understand some simple teaching instructions and have non-language reaction. Many students have a "silent" stage before expression, which is a normal phenomenon, and teachers should have patience with learners instead of pressing.(2) Early ProductionIn the second stage, teachers should focus on the conversation of students. Basic vocabulary and sentence patterns are still primary and accurate reactions to instructions are also important. In addition, teachers can use some interrogative sentences to question learners in classes and let students answer them by using some phrases and simple words. In this stage, students should understand these instructions totally and give correct answers.(3) Speech EmergenceIn the third stage, teachers may communicate with students by some sentences and let students explain some points by phrases and complete sentences, namely express themselves freely. In this stage, teachers should encourage students express themselves in real life and communicate with others by target language.(4) Intermediate FluencyIn the fourth stage, teachers can use some teaching aids to lay stress on the important points. At the same time, teachers may choose a topic or describe a situation to guide learners to express actively. In this stage, learners can communicate with others naturally, join in the activities, and express themselves accurately and fluently. Krashen and T errel hold that teachers should not concentrate on correction in any stage. Errors are common phenomenon in second language acquisition; therefore, teachers should create a totally relaxed situation for learners instead of stressing accuracy all the time.The Natural Approach, based on the Acquisition-Learning Hypothesis, shows the differences between acquisition and learning to illustrate that we should follow gradual improvement to learn language.7.1.1.2 Comments on the Acquisition-Learning HypothesisMclaughlin (1978) holds that the difference between acquisition and learning can not be explained clearly, and the process of learning and acquisition also can not be observed and proved by experiments. Krashen doesn't give the detailed conditions about distinguishing learning and acquisition process. Some linguists also propose that learning and acquisition can not be separable from consciousness. Brown(1994) holds that without consciousness, input can not become intake. Therefore, consciousness and unconsciousness can not be the standard to tell learning from acquisition.Some linguists also propose that acquisition and learning are the different stages of second language acquirement, and they have the same destination to use language accurately and fluently. Rivers and Stevick (1980) think that acquisition is inseparable from learning, because learners internalize what we have learned with the help of usage (practice and training), then what we have learned becomes what we have acquired in daily life. In addition, what we learned can permeate into the whole system of what we required and can compensate what we required. They also hold that meaningful practice can become habitual knowledge, so learners can use habitual knowledge in some real situations. Therefore, learned knowledge can become acquired knowledge.In addition, some linguists also think that learned knowledge not only can monitor output from learners, but also can help learners comprehend materials better. However, Krashen thinks that learned knowledge only has one function that is to monitor the output, which denies other functions of learned knowledge. Learners use learned knowledge to monitor and correct their speech and writing errors, and also use them to comprehend listening and reading materials. For example, either bottom-up processing or top-down processing reading model needs learned knowledge to understand reading materials.However, the Acquisition-Learning Hypothesis still makes a great contribution to SLA. Although this hypothesis has many shortcomings, it provides teachers with two ways of language development. In addition, the Acquisition-Learning Hypothesis focuses on the importance of language acquisition, and proposes that mechanical practices which only focus on accuracy are not enough for second language learners, but the meaningfulpractices which focus on the communicative competence are the best choices for fluency.The Monitor Hypothesis and Second Language Acquisition (SLA)Krashen holds that each time second language learners produce output, there is amonitor overseeing the language output. Monitor device plays important role in conscious learning, which has a positive effect on editing and correcting learners' output.7.1.2.1 Contents of the Monitor HypothesisKrashen (2003) proposes that learner's old knowledge system acts as a monitor when they are acquiring new knowledge and producing something new. In other words, the acquired system is only able to produce spontaneous speech, while the learned system is used to check the accuracy of the utterance. Before a learner produces an utterance, he or she internally uses the conscious learning system to make correction and modification. Self-correction occurs when the learner uses the monitor to correct errors. According to the hypothesis, self-monitoring and self-correction only can be applied to conscious learning system.It also holds that learners can use learned knowledge to correct themselves when they are involved in a communication. According to the hypothesis, language learning and language acquisition have different functions on development of language proficiency. The acquisition system (unconscious learning) is the real language competence, but learned system (conscious learning) plays monitoring and editing roles in second language communication. Learned competence functions as a monitor and exerts its role during the learning process. The following chart has shown to us the whole process.The successful use of the monitor depends on three conditions:(1) The acquirer/learner must know the ruleThis is a very difficult condition to meet because it means that the speaker must have explicit instructions on the linguistic rules that he or she is trying to apply to.(2) The acquirer must focus on correctnessHe or she must think about form, and it is difficult to focus on meaning and form at the same time, especially for beginners.(3) The acquirer/learner must have time to use the monitorUsing the monitor requires the speaker to slow down and focus on form.As far as language learners are concerned, we may divide them into following three types according to their using of learned competence.•The monitor over-users. They are performers who are constantly checking their output with their conscious knowledge of the SL.• The monitor under-users. They are people who prepare not to use their conscious knowledge even when conditions allow it. They use "feeling" for correctness and rely completely on the acquired system.•The optimal monitor users. They are those who use the monitor when it is appropriate and when it does interfere with communication.7.1.2.2 Comments on the Monitor HypothesisThere are some criticisms about Monitor Hypothesis. Lightbown & Spada (2002) propose that the only evidence for monitoring lies in the language users' own accounts of applying explicit rules, which is impossible to observe.Monitoring does not account for reception of utterances.In addition,Mithell & Myles (1988) propose Monitoring is limited to syntax, lacking sufficient attentions on pronunciation, lexis, and most importantly, their discourse.However, it makes contribution to second language teaching. When our goal of teaching is to help learners acquire the competence to use language appropriately and fluently, it is neither reasonable nor realistic to expect them to be concerned with the accurate grammatical rules when they are speaking in free conversation. Teachers should guide learners to use the monitor moderately in writing and planned speech.7.1.3 The Natural Order Hypothesis and Second Language Acquisition (SLA)The Natural Order Hypothesis is another important hypothesis from Krahen's Five Hypothese. It studies the orders of second language learning. One of the most exciting discoveries in language acquisition research in the 1980s has been the finding that there is a predictable, natural order for the acquisition of grammatical structures of second language, regardless of age differences and language backgrounds of learners.7.1.3.1 Contents of the Natural Order HypothesisSome scholars such as H. Dulay and M. Burt and others find that learners from different language backgrounds undergo the same process of second language learning.Krashen once said we acquire the rules of language in a predictable order, some rules tending to come early and others late. The order does not appear to be determined solely by formal simplicity and there is evidence that it is independent of the order in which rules are taught in language classes."According to the Natural Order Hypothesis, the acquisition of grammatical structures proceeds in a predictable order." (Jack C. Richards & Theodore S. Rodgers, 2008, 182)According to Krashen, this order is a "natural and predictable order for the acquisition of grammatical structures of the second language regardless age differences and language backgrounds." (Wang Lifei, 2001, 97)Brown thinks that children acquiring English as second language tend to obtain certain grammatical morphemes, or function words, earlier than others, irrespective of their first language. For example, the progressive marker \ ing \ and plural marker \ s \ are acquired earlier than the third person singular marker \ s \ and the possessive \ s \. Although the order of acquisition for the second language is not the same as that in the first language process, there are some similarities. Besides, Krashen proposes a natural order for adults subjects, quite similar to that seen in the child second language acquisition.7.1.3.2 Comments on the Natural Order HypothesisThis theory is criticized by some scholars for three reasons. The first is that the studies of the natural order are limited to part of grammatical morphemes, negative sentences and attributive clauses. It is not systematic and complete.The second one is related with the fact that the hypothesis which holds that L1 has no influence on L2 is not convincing, as ‘chinglish' does exist among Chinese English learners. The hypothesis only focuses on the second language grammatical order, but ignores the interference from the first language. Different learners from different cultures are easily influenced by their own native languages, so the learning order can not be exactly the same.The third is that the hypothesis ignores the varieties of learners. There surely exist some learner differences, such as different age, cultural backgrounds, knowledge backgrounds, and cognitive development, but the hypothesis ignores all of the factors that also play vital roles in SLA.Although this theory is criticized by so many scholars, it still has some significance.According to Krashen, this theory has positive effect on conscious learning. He also proposes three requirements for presenting linguistic rules (Wang Lifei, 2001, 98) The first principle is learnable, which means that simple rules should be presented first; the second is portable, which means that grammatical rules that could be memorized easily should be presented firstly; the last one relates itself with certain knowledge, which has not yet been acquired. Rules which have not been acquired need to be taught, however, those rules that have been acquired before do not need to be taught.7.1.4 The Input Hypothesis and Second Language Acquisition (SLA)The input hypothesis has both theoretical and practical importance in that it attempts to answer what is perhaps the most important question in the second language learning byemphasizing the comprehensible input in SLA.7.1.4.1 Contents of the Input HypothesisThe Input Hypothesis claims to explain the relationship between what the learner is exposed to get of a language (the input) and language acquisition. He thought that humans acquire language by understanding messages or by receiving comprehensible input. Comprehensible Input refers to utterances that the learner understands based on the context in which they are used as well as the language in which they are phrased. In other words, "Comprehensible Input is defined as second language input just beyond the learners' current second language competence. If a learner's current competence is "i" then comprehensible input is "i+1", the next step is the developmental sequence."(Hodder Arnold, 1998, 47) It means that input materials can not be too simple (already required) nor too complex (i+2\3\4…)The more comprehensible input one receives the greater progress one makes in acquisition.According to Krashen, "comprehensible input is the only true cause of second language acquisition."(Krashen, 1984, 61) Krashen considers Input Hypothesis as the centre of the second language acquisition. He also believes if the input is understood, the necessary grammar is automatically provided. He proposes that it is unavoidable that early speech is grammatically inaccurate, but the accuracy develops as acquirers hear and understand more input. It means that learners will get the grammar rules automatically if the teacher provides enough comprehensible input.He also holds that input materials that teachers provide must be relevant and interesting so that learners could acquire knowledge in a totally relaxed environment.At last, he draws a conclusion that people acquire language best by understanding comprehensible input that is slightly beyond their current level (I+1), and when they acquire enough, they get the ability to speak fluently automatically. In a short, his Input hypothesis shares four characteristics:comprehension, interesting and relevant, not grammatically sequenced, and enough input materials.There are four ways to make materials become more comprehensible: learners have already known; secondly, to let students get help from the context or extra-linguistic information; thirdly, to modify the interaction structure of conversation; fourthly, to teach materials with modification.7.1.4.2 Comments on Input HypothesisThe Input Hypothesis provides foreign language teachers with some useful information. Teacher should provide students with appropriate environment to help them get an idealinput. According to Krashen, language environment determines the quality of language output. During the input process, teachers should try their best to put learners in real communicative situation. Therefore, teachers can design some functional teaching activities according to their teaching goal to improve learners' communicative competence.Based on Input hypothesis, Input materials should be beyond their current level so that learners can understand most of the materials but still have some challenges to make progress. In addition, enough and comprehensible examples should be presented before linguistic forms are presented. It means that grammar can not be taught independently, but should be concluded by learners themselves after enough examples are provided.Another important point is that input materials should be relevant so that learners will intake new knowledge more easily. Teacher should help learners build up a chain between old knowledge and new knowledge to form a clear knowledge structure.Although the Input Hypothesis makes a great contribution to foreign language teaching, it has some shortcomings.Some linguists propose that it is difficult to judge students' current level "i", and it is also difficult to suit different students' levels, because different students may have different levels. Therefore, it would be difficult for teachers to design accurate teaching materials and teaching activities to suit each learner's level.It simplifies the way of learning foreign language, because it treats foreign language the same as mother tongue. As everyone knows, native language acquisition is in the real and natural language environment, and native speakers acquire a large number of language input, most of which is disordered. However, most of second language learners study foreign language after acquiring native language, so they do not have the physiological basis needed by native language acquisition for second language learning, in addition, the input of target language is also limited, which leads negative transference.In addition, it emphasizes too much the importance of language input. The Input Hypothesis can not reveal how language input becomes learners' intake. It ignores learners' internal factors and external environment factors. During the process of language learning, brain firstly notices materials, and then context and learners' competence begin to process the materials. At last, input becomes learners' internal knowledge structure naturally, but this hypothesis ignores this process.7.1.5 The Affective Filter Hypothesis and Second Language Acquisition (SLA)The Affective Filter Hypothesis plays a more important role in language teaching, and the hypothesis states how affective factors relate to the second language acquisition.7.1.5.1 Contents of the Affective Filter HypothesisH. Dulay and M. Burt propose this concept of Affective Filter Hypothesis in 1977. Three kinds of emotions including motivation, self-confidence, and anxiety, which may affect students' learning, are proposed first. These emotions have a close relationship with results of second language learning.Krashen regards learners' emotion or states as an affective filter which passes or blocks input during the process of second language learning. According to the theory, a large number of inputs do not guarantee that learners can learn the target language well. If the filter is weak, learners' emotion will have a positive effect on second language learning, so the input will become intake more easily. If the filter is high or strong, less input will become intake. Input refers to the environment and materials the teacher can offer, and the intake refers to what learners have acquired. The process of second language acquisition is affected by many affective factors, so input must overcome the affective filter to become intake.Affective Filter Hypothesis (Wang Lifei, 2001, 101)From this chart, we can find that input must overcome the affective filter to become intake. Affective factors are "outside" the language acquisition device, and may add, impede or facilitate the delivery of input to the LAD. The input which can overcome affective filter and then be processed by LAD can become acquired competence.Therefore, a large number of input and a low affective filter are desirable. There are three kinds of affective variables related to second language acquisition (Jack C. Richards & Theodore S. Rodgers, 2008, 183):• Motivation. Learners with high motivation generally do better.•Self- confidence. Learners with self-confidence and a good self-image tend to be more successful.•Anxiety. Low personal anxiety and low classroom anxiety are more conductive to second language acquisition, which we have already talked about in chapter four.7.1.5.2 Comments on the Affective Filter HypothesisThe Affective Filter Hypothesis implies that the teaching goals should not only focus onthe comprehensible input but also a relaxed situation that can create a low filter. Therefore, foreign language teachers should provide learners with enough and comprehensible input and reduce affective filter to help them acquire new knowledge and make a great progress.These five hypotheses play very vital roles in second language learning, and some scholars consider them as the most comprehensive theories which also give foreign language researchers and teachers many applications in language teaching.Krashen summarizes his five hypotheses as followings: acquisition is more important in the process of second language learning; • acquisition is the ultimate goal of language teaching;Whether acquisition can be reached or not depends on two conditions: ①comprehensible input, which includes these characteristics, is beyond learners' current level, relevant and interesting, and enough. ②a low affective filter, which allows input to turn into intake. Therefore, Krashen holds that the comprehensible input and low or weak affective filter are the two important keys to the successful second language learning. 7.2 Output Hypothesis and Second Language Acquisition (SLA)Mclaughlin (1987) mentions that Input Hypothesis ignores the importance of output, but excessively emphasizes comprehension of new knowledge. As a result of such criticism, the Output Hypothesis emerged, as time requires, because of the shortcomings of input hypothesis. "Most language learning researchers agree that output is necessary to increase fluency, that is, learners must practice producing second language utterances if they are to learn to use their interlanguage system confidently and routinely."(Hodder Arnold, 1998, 174)7.2.1 Contents of Output HypothesisSwain proposes that through producing language, either spoken or written, language acquisition or learning may occur. Furthermore, as to in what way output works in SLA, she (1995) puts forward three functions of output, which, in her opinion, have much more to do with linguistic accuracy, rather than fluency.The first function is the noticing or triggering function."(Swain, 1995) That is to say, Swain believes that the activity of producing the target language may push learners to become aware of gaps and problems in their current second language system. It means that what learners want to express in the target language cannot exactly be the same as what they can produce. A linguistic gap thus comes into being. In addition, linguistic gap is also called linguistic problem, and linguistic deficiency. These problems in producing enable language learners to be aware of what they do not know or know only partially。

句子汉英笔记法练习I.经济商贸专题II.外交政治专题III.能源环境专题IV.体育旅游专题V.文化教育专题一、汉译英I. 经济商贸专题1.人民币的汇率问题一直是国际上很关心的一个问题，中国很多重要的贸易伙伴都敦促中国要采取更为灵活的人民币汇率机制。

The RMB question has been the focus of world attention，with many foreign trading partners urging China to adopt a more flexible exchange rate.2.中国民间贸易在对外贸易中起着重要的作用，与此同时，中国与世界各国政府间的贸易联系，也得到了巨大而持续的发展。

While China’s nongovernmental businesses are playing a more pivotal role in foreign trade, governmental business contacts between China and the rest of the world also saw remarkable and continuous growth.3.我们必须坚持国际建设与经济建设协调发展。

We must maintain a balance between the nation's defense construction and its economic development.4.我们成功地避免了经济的大起大落，避免了物价的过度上涨。

We have been successful in avoiding major ups and downs in the economy and preventing excessive price hikes.5.双方贸易与合作迅速发展的主要原因在于两国的经济有着很强的互补性。