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Traffic classification on the fly

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Traffic Classification On The FlyLaurent Bernaille†Renata T eixeira†Ismael Akodjenou†Augustin Soule‡Kave Salamatian††Universit´e Pierre et Marie Curie-Paris VI‡Thomson Paris LabABSTRACTThe early detection of applications associated with TCP flows is an essential step for network security and traffic engineering.The classic way to identifyflows,i.e.looking at port numbers,is not effective anymore.On the other hand,state-of-the-art techniques cannot determine the ap-plication before the end of the TCPflow.In this editorial, we propose a technique that relies on the observation of the firstfive packets of a TCP connection to identify the ap-plication.This result opens a range of new possibilities for online traffic classification.Categories and Subject DescriptorsC.2.3[Network Monitoring]:Network Management;I.2.6 [Learning]:Unsupervised LearningGeneral TermsMeasurement,Algorithms,ManagementKeywordsTraffic classification,Applications,Machine Learning1.INTRODUCTIONEnterprise or campus networks usually impose a set of rules for users to access the network in order to protect network resources and enforce institutional policies(for in-stance,no sharing of musicfiles or gaming).This leaves network administrators with the daunting task of(1)iden-tifying the application associated with a trafficflow on-the fly and(2)control user’s traffic when needed.Therefore, accurate classification of trafficflows is an essential step for administrators to detect intrusion or malicious attacks,for-bidden applications,or simply new applications(which may impact the future provisioning of network resources). Previous work has proposed a number of methods to iden-tify the application associated with a trafficflow.The sim-plest approach consists in examining TCP port numbers. Port-based methods are simple because many well-known applications have specific port numbers(for instance,HTTP traffic uses port80and FTP port21).However,the research community now recognizes that port-based classification is inadequate[1,2,3,4],mainly because many applications use dynamic port-negotiation mechanisms to hide fromfirewalls and network security tools.An alternative approach is to inspect the payload of every packet.This technique can be extremely accurate when the payload is not encrypted,but it is unrealistic alternative.First,there are privacy concerns with examining user data.Second,there is a high storage and computational cost to study every packet that traverses a link(in particular at very high-speed links).Detecting the application associated associated with a flow is of limited interest once theflow isfinished(except for provisioning and maybe for pricing).To address these chal-lenges,we propose a novel technique that only uses the size of thefirst few data packets of each TCPflow to identify the application associated with a TCPflow.Our method runs at the edge of the network,i.e.,where the network connects to the Internet,and hence is able to capture all packets as-sociated with a TCPflow in both directions(from sender to receiver and vice-versa).The accurate classification of flows based on information contained only in thefirst few packets opens new possibilities for online classification(i.e. security,SLAs,etc.).Our method is in sharp contrast with the current state of the art.2.STATE OF THE ARTAfter port-based classification has been debunked and given the limitations of searching payloads for signatures,there has been a new trend to classify traffic based on summa-rizedflow information such as duration,number of packets and mean inter-arrival time[2],[5],[6],[3].BLINC[4]intro-duced a new approach for traffic classification.It associates Internet hosts with applications.Instead of studying TCP (or UDP)flows individually,it looks at all theflows gen-erated by specific hosts.BLINC is able to accurately asso-ciate hosts with the services they provide or use(application server,web client,etc.).However,it cannot classify a single TCPflow.All classification techniques that useflow statistics can only identify the nature of aflow when theflow isfinsihed. BLINC has to gather information from severalflows for each host before it can decide on the role of a host.These require-ments prevent the use of these methods online.In contrast, our method relies only on thefirst few packets of a TCP flow.This early classification is essential to allow automatic blocking,filtering,or recording of specific applications.It also limits the amount of memory required to store informa-tion associated with eachflow.3.KEY POINTSThis section discusses our assumptions and the two main insights of our method:the analysis of only thefirst few packets of theflow,and the use of unsupervised clustering to detect a set offlows that share a common behavior.3.1AssumptionsOur goal is to build a classifier that runs online and ac-curately identifies the application associated with a TCP flow as early as possible.Our work levarages the following observations:•Access to both directions of a TCP connection.Edge networks usually connect to the Internet at few locations.The vast majority in one or two locations.We assume that the network administrator monitors both directions of all the edge links.•Offline access toflows of a number of applica-tions.Our method only needs packet size information.However,for training purpose,we need to know the ap-plication associated with a sample offlows.There are two alternative techiniques for collecting this training trace:(i)directly from one of the monitored links us-ing high-end packet monitoring cards,we can analyze the payloads to identify the application corresponding to a givenflow;or(ii)generated in a controlled fashion by explicitly launching instances of each of the desired applications and collecting all packets exchanged.•Online access to header of all packets.We use only the information on the packet header to do our online classification,which is much smaller and offixed size.3.2Intuition behind the methodOur goal is to identify the application associated with a TCPflow as early as possible.We design a classifier that uses information available in the header of thefirst P packets of theflow to identify the application associated to aflow. Specifically,we use only the size of the data packets,not using TCP control packets(SYN,ACKs,etc).The size of thefirst few packets is a good predictor of the application associated with aflow because it captures the application’s negotiation phase,which is usually a pre-defined sequence of messages and distinct among applications.We illustrate our approach with SMTP and E-Donkey flows captured at the edge of a large university network to shed light on the behaviors of applications.Figure1presents the size of thefirst packet versus the size of the second(neg-ative values represents packets sent from the TCP server to the client and positive from client to server)for every TCP flow of these two applications.E-Donkey clients initialize request forfiles,hence the positive sign for the size of the first packet,whereas the SMTP sever initiates negotiation. This simple example illustrates the expressiveness of this two-dimensional representation of TCPflows to distinguish the application associated with eachflow.In fact,the traces we study consist of ten major applications and we found that 5packets were enough to distinguish their behaviors.3.3Unsupervised clusteringTo extract groups offlows that share a common communi-cation behavior,we borrow techniques from machine learn-ing.We use unsupervised clustering as it relies on unlabeled data samples(in our case,the size of thefirst few pack-ets of a TCPflow)tofind natural groups(or clusters)in a dataset,whereas supervised clustering uses a pre-labeled set of samples to construct a model for each cluster.Figure1:SMTP versus Edonkeyflows. Although the traffic classification mechanism presented in[3]uses Naive Bayes Classifiers,an example of supervised clustering,unsupervised learning is more appropriate for traffic classification because it does not rely on pre-defined classes.A single application can have multiple behaviors that should each have a model.For example,Figure2 presents the size of thefirst packet versus the size of the second of a set of FTPflows.Thisfigure shows that FTP has three very distinct behaviors:(i)commandflows cor-respond to a controlflow,in which a data connection is negotiated and in which clients ask for data;(ii)download flows corresponds tofiles transfer from client to server;and (iii)uploadflows arefiletransfers from server to client.Figure2:Example of a multi-modal application: FTP.FTP is one example of a multi-modal application,in our traces we observe many other such applications.Unsuper-vised learningfinds groups offlows that share the same be-havior,which are easier to model.4.METHODOLOGYBased on the observations from the previous section,we propose a traffic classification mechanism that works in two phases:an offline learning phase and an online traffic classi-fication phase.First,the learning phase uses a set of train-ing data to cluster TCPflows that have common behavior. Then,the traffic classification phase uses these classes to de-termine the application associated with each TCPflow.To verify that the behaviors of applications do not vary with time,we use one data set for the learning phase and an-other for the evaluation of the derived classification method. These two traces were collected several month apart on the same link.4.1Learning phaseThe learning phase is performed offline and consists in detecting common behaviors in a set offlows.It takes as input a short packet trace with TCPflows from a mix of applications.Our study uses a one hour trace collected at the edge of a university network.This trace also includes packet payloads.We apply a packet trace analyzer to this data set to extract TCPflows.First,to groupflows into clusters,we need to evaluate the similarity between them. We associate eachflow with a spatial representation based on the sizes of itsfirst P packets.The representation we use is quite simple:flows are represented by points in a P-dimensional space where each packet is associated to a dimension.The coordinate on the dimension p is the size of packet p in theflow.In order to differentiate packets sent by the TCP-server and the TCP-client,packets sent by the server have a negative coordinate.The similarity between flows is then evaluated with a simple metric:the Euclidean distance between their associated spatial representation.In order to extract common behaviors in such a space we rely on the well-known K-Means algorithm[7].Once we have found natural clusters in the training set,we model and analyze each cluster.The modeling step consists in defining a heuristic to associate a newflow to a cluster.We use a simple heuristic:we compute the euclidean distance between the newflow and the center of each predefined cluster,and then choose the cluster for which this distance is minimum. The analysis step consists in examining the composition of each cluster.We process the trainingflows with a payload analysis tool[8]that is a able to accurately determine the application associated with eachflow.This step allow us to decide how to label aflow once it has be assigned to a cluster.We studied different numbers of packets and found that the best separation of applications among clusters was ob-served with5packets.We also tried different numbers of clusters for the K-Means algorithm and found that,for5 packets,50clusters was the best trade-offbetween behavior separation and complexity.The learning phase outputs two sets:one with the de-scription of each cluster(or the center of the cluster)and the other with their composition(or the set of applications represented in the cluster).We use both these sets to classify flows online.4.2Online classificationFigure3presents the structure of the online classifier. This classifier can run either at a management host that has online access to packet headers or in a network processor at the router.We assume that the network administrators deploy a monitoring card that is able to process the header of all packets traversing the link[9].This process is very light since it only involves retrieving information from the IP and TCP headers(the size of the packet and theflow id).Figure3:Design of online classifier.Our classifier takes as input the series of packet headers for both directions of an edge link.A packet analyzer ex-tracts the5-tuple(protocol,source IP,destination IP,source port,destination port)and the packet size.The analyzerfil-ters out control traffic(the three packets of the TCP hand-shake)and stores the size of every packet in both directions of the connection.When it has the size for thefirst P pack-ets of the connection,it sends this information to theflow conversion module,which maps the newflow to a spa-tial representation.Then,the cluster assignment module searches all the cluster descriptions tofind the bestfit for the newflow and the application identification module selects which application is most likely associated with the flow given the set of applications that compose the cluster. We chose a simple heuristic to label associate unknownflows with applications:it is labeled with the application that is the most common in the cluster.5.EARLY EV ALUATION RESULTSThis section gives a proof of concept of ourflow classi-fication method.Further work is necessary to conclude in the applicability of the method.We build a prototype clas-sifier using matlab.First,we use a training data set for the learning phase.Based on the cluster descriptions and clus-ter compositions found in the learning phase,we emulate the online classification using a trace collected six month afterwards on the same link.For validation purposes,we label this trace using the payload analysis tool used in the learning phase[8].Table1presents the accuracy of our classifier when it considers thefirstfive packets of eachflow.We measure accuracy by comparing the application labels given by our classifier to the ones obtained through payload analysis.We were able to correctly identify more than80%offlows of al-most of the applications.The only exception is POP3.Ourclassifier labels86.8%of POP3flows as NNTP and12.6%as SMTP,because POP3flows always belong to clusters where POP3is not the dominant application.This error can be easilyfixed if we consider extra information.In this ex-ample,if we had used the destination port to label POP3flows,we would achieve over90%accuracy.We are currently working on more sophisticated labeling techniques.Application Accuracyedonkey84.2%ftp87%http99%kazaa95.24%nntp99.6%pop30%smtp84.4%ssh96.92%https81.8%pop3s89.8%Table1:Accuracy offlow classification.6.LIMITATIONS AND CHALLENGESThe initial results observed with our method on a small trace are encouraging.The method is promising as it al-lows early classification of applications and is quite simple. However,the method has some limitations that we discuss below.Most of these limitations are easy to overcome,while others are more fundamental and affect most classification methods to date.Multi-homed rge networks often have multiple connections to the Internet.In this case,we can extend our approach to monitor all access links and aggre-gate information on a machine where the classification will take place.Packet order.In IP networks,packets may be out of order or may appear more than once.Out-of-order packets will change the spatial representation of theflow,which will impact the quality of our classification.Fortunately,we only need thefirstfive packets to arrive in order,which is more likely.On the network we studied,less than4%of TCP flows had an out-of-order packet within thefirstfive data packets of theflow.Sampling.On high speed links,monitors cannot col-lect all packets.The accuracy of our method will degrade fairly quickly under packet sampling.If instead the net-work adoptsflow sampling[10],then our method will work unaltered.Applications with similar behaviors.If two distinct applications start by exchangingfive packets of approxi-mately the same size,then we classify both with the same label.To solve this problem,we are working on more so-phisticated labeling heuristics that take into account other information available in thefirst few packets(such as port numbers and inter-arrival times).Applications with unknown behaviors.The learning phase gives a model for the traffic present in the training ing this model on other networks could be ineffi-cient.Although a specific behavior for an application pre-cisely described on a trace should not change when observed on another network or at a different time,a new network can (and most likely will)have different application behaviors.We can identify new behaviors using limited cluster radiuses. Using this limit,the we return an accurate application label to previously-defined behaviors and classify as“unknown”allflows that are not represented in the training data. Shortflows.It is well known that the traffic is made of a large majority of shortflows and a small number of very largeflows.We need to test our method on these very shortflows.In this scenario,if it is successful,it will not work better than most other techniques.However,previous classification techniques have not specifically studied these shortflows and they may exhibit some limitations that have not been observed yet.False matches.Most classifiers to date are based on heuristics and may misclassify aflow.This possibility of error,even if small,prevents the use of traffic classification techniques to automaticallyfilter or blockflwork administrators can use our method to identify suspicious flows early and store all packets in them.They can later audit the stored dataEvasion.The main challenge to traffic classification tech-niques is evasion.For instance,an“attacker”could eas-ily evade our method by padding packet payloads in order to modify sizes.Payload analysis tools cannot classify en-crypted packets,port-based methods are deceived by a sim-ple change of port,and approaches relying on summarized flow information are sensitive to simple alterations of packet sizes and inter-arrival times.To summarize,we now need to analyze our method on a much broader panel of traces.This is a difficult task as(i)we need the full trace with full payload for validation purposes (such traces are rare in the community);and(ii)we more sophisticated techniques to label aflow after it has been assigned to a cluster.We are also working on circumventing the limitation and the weaknesses of our method.7.REFERENCES[1]T.Karagiannis,A.Broido,N.Brownlee,K.Claffy,andM.Faloutsos,“Is p2p dying or just hiding?,”in Globecom, 2004.[2]M.Roughan,S.Sen,O.Spatscheck,and N.Duffield,“Class-of-service mapping for qos:A statisticalsignature-based approach to ip traffic classification,”inIMC2004,2004.[3] A.Moore and D.Zuev,“Internet traffic classification usingbayesian analysis,”in Sigmetrics2005,2005.[4]T.Karagiannis,D.Papagiannaki,and M.Faloutsos,“Blinc:Multilevel traffic classification in the dark,”in SIGCOMM 2005,2005.[5] A.McGregor,M.Hall,P.Lorier,and J.Brunskill,“Flowclustering using machine learning techniques,”in PAM2004,2004.[6] D.Zuev and A.Moore,“Traffic classification using astatistical approach,”in PAM2005,2005.[7]J.McQueen,“Some methods for classification and analysisof multivariate tions,”in Proceedings of the5th BerkeleySymposium on Mathematical Statistics and Probability,pp.281–2297,1967.[8]Qosmos,“Traffic designer().”[9]Endace,“Endace().”[10]N.Hohn and D.Veitch,“Inverting sampled traffic,”in IMC’03:Proceedings of the3rd ACM SIGCOMM conference on Internet measurement,(New York,NY,USA),pp.222–233, ACM Press,2003.。

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辨认交通标志英语作文

辨认交通标志英语作文

The Importance of Recognizing Traffic Signs:A Guide for Safe DrivingIn the fast-paced world of modern driving, traffic signs play a crucial role in ensuring the safety and efficiency of road users. They serve as silent guardians, guiding drivers through various road conditions and regulations. However, the ability to recognize and understand these signs is essential for responsible and safe driving.Traffic signs are designed to convey important information quickly and effectively. From warning signsthat alert drivers to potential hazards, to regulatory signs that outline rules and regulations, each sign has a specific purpose. For instance, the stop sign, a red octagon, is a command sign that tells drivers to come to a complete stop before proceeding. On the other hand, the yield sign, a red triangle, warns drivers to slow down and prepare to stop if necessary to yield the right-of-way to other traffic.Moreover, traffic signs are not just limited to roadsides. They can also be found on road surfaces, such aspavement markings, which indicate various drivingdirectives like parking spaces, stop lines, and lane markings. These markings are crucial for maintaining the flow of traffic and ensuring safety.Recognizing traffic signs is not just about memorizing their shapes and colors. It's about understanding their meaning and applying that knowledge in real-time driving situations. For instance, drivers need to be able to interpret the meaning of a yield sign and act accordingly, slowing down and preparing to stop if necessary. Similarly, drivers must be aware of the different speed limit signs and adjust their speed accordingly to ensure safe driving. However, with the ever-changing landscape of traffic regulations and the introduction of new signs, it's important for drivers to stay updated and informed. This can be achieved by taking driving courses, reading driving manuals, and staying attentive to road signs while driving. By doing so, drivers can ensure that they are well-equipped to handle various road conditions and situations.In conclusion, recognizing traffic signs is an integral part of safe and responsible driving. It's aboutunderstanding the language of the road and applying that knowledge to make informed decisions while on the road. By staying updated, attentive, and respectful of traffic signs, drivers can ensure a safer and smoother driving experience for themselves and other road users.**辨认交通标志的重要性：安全驾驶指南**在现代驾驶的快节奏世界中，交通标志在确保道路使用者安全和效率方面发挥着至关重要的作用。

COMAC航空科技英语等级考试B样题

COMAC航空科技英语等级考试B样题

COMAC航空科技英语等级考试B样题COMAC航空科技英语等级考试B1（技术类）样题Test Time：120 minutes部门_______________ 姓名____________ ⼯号____________Part I Listening （30%）Section 1 Conversation and Lecture（10%）Directions: In this section, you will hear a long conversation and a lecture. At the end of the conversation or the lecture, you will hear five questions. The conversation, the lecture and the questions will be spoken ONLY ONCE. After you hear a question, you must choose the best answer from the four choices.Conversation1. A) They get you directly to holiday destination.B) Their tickets can be bought on the internet.C) They offer excellent services to customers.D) They’re much cheaper than famous airlines.2. A) They have sprung up recently and become successful.B) They change prices on the basis of customers’ demand.C) They always offer travelers the extremely cheap flight.D) They do much advertising but few people ever watch it.3. A) By travelling before public holidays.B) By buying tickets a day in advance.C) By booking at the very last minute.D) By flying at peak time like Fridays.4. A) They try every possible means to reduce expenses.B) They charge different prices depending on demand.C) They don’t serve any food on any of their flights.D) They have increased the speed of their aero planes.5. A) They only offer cheap tickets online.B) They fail to offer satisfactory service.C) They spend little time on the ground.D) They fly to and from smaller airports.Lecture6. A) The 845m2 wing area is large enough to park 70 cars.B) The plane has the potential to carry 550 passengers.C) The tail is about as long as the Great Sphinx in Egypt.D) The two deck fuselage is as high as a 7-storey building.7. A) It is as economical to run as a common jet.B) It burns more fuel than other jumbo jets.C) It can fly an amazing 15,000 km non-stop.D) It can carry more fuel than other planes.8. A) Toulouse in France.B) England and Wales.C) All over the Europe.D) Spain and Germany.9. A) It is remarkably expensive.B) It is impressively efficient.C) It is a nation-wide project.D) It is extremely complicated.10.A) The expenses.B) The designing.C) The electronics.D) The cooperation.Section 2 Compound Dictation （10%）Directions: In this section, you will hear a passage TWICE. You have its script in the following, but with eleven blanks in it. You are required to fill in the first eight blanks with the exact words you have just heard. For last three blanks, you can either use the exact words you have just heard or write down the main points in your own words. Remember, there will be a pause for the last three blanks.Laurence Barron, President of Airbus China, defended the A380 superjumbo jet as its safety performance has been called into question.“The Qantas A380 suffered an (1) ______________ engine failure, a fairly rare event, which also damaged the aircraft itself. The aircraft performed as expected and (2) ______________ safely, so no, there is nothing wrong with the A380. It’s a (3)______________ aircraft.”Barron also says the engine issue will not (4) ______________ next summer’s scheduled delivery of the A380 to China Southern Airlines, the only (5) ______________ carrier to purchase the plane.Meanwhile, Barron explains that the lack of orders for its A350 aircraft, which is under development, from Chinese carriers is due to the country’s (6) ______________ planning structure.“The Chinese government, as you are well aware, works on a 5-year-plan basis, and they are about to (7) ______________ the 12th 5-year-plan which runs from 2011 to 2015. The A350 deliveries that we can offer are now in the what will become the 13th 5-year-plan period.”Eric Chen, Airbus China‘s Vice President, adds that the Chinese carriers’ timid (8) _____________ to the A350 is due to its competing product, Boeing’s 787.“Several years ago, Chinese airlines ordered more than 60 Boeing 787’s and for various reasons, airlines lack this kind of courage and determination to be a launching customer for a new program again. In other words, we are buying the bill for our rivals’ dilemma and consequences.”(9) __________________________________________________________________________________________________________________________________“I don’t really understand the world ‘challenge’. Our industry is challenging. There are lots of challenges but this is not a challenge, this is a competitor. (10) __________________________________________________________________________ Beverly Wyse, Vice President of Boeing’s 737 program, says Boeing is open to work with C919’s manufacturer.“I think (11) __________________________________________________________________________________________________________________________”Four Chinese airlines and two aircraft leasing companies have signed agreements to purchase 100 C919’s as launching costumers.Section 3 Listening and translating （10%）Directions: In this section you are going to hear five short passages. You will hear them ONLY ONCE. In each of these passages some of the sentences are already printed. You are required to translate the missing parts into Chinese. After each of the passages there will be a pause lasting one and a half minutes. The pause is intended for you to do the translation.1)The ARJ21-700 jetliner, China’s first self-designed aircraft, will undertake itsmaiden flight before the end of the year. COMAC chairman, Zhang Qingwei says this first homegrown regional jet has aroused great interest from aviation companies at home and abroad.”I just came back from the United States and Canada. ___________________________________________________________________________________________________________________________________________________________________________________________.”2)Nine top tier US manufacturing companies won competitive contracts to buildand supply the aviation system for China‘s new aircraft program, the C919.Airport infrastructure needs are filling opportunities in the US companies as well.___________________________________________________________________________________________________________________________________________________________________________________________________ 3)The Deputy Chief of the China’s Civic Aviation Administration, Xia Xinghua,says more cooperation is crucial for the Chinese side. “Firstly, we need to strengthen our cooperation on sustainable security development, expanding the relationship in a pragmatic way.________________________________________________________________________________________________________________________________________________________________________”4)The Transportation Secretary Ray LaHood said that the review would becomprehensive covering design, manufacturing and assembly of the Dreamliner.Michael Huerta of the Federal Aviation Administration said emphasis would be put on electrical systems and how these and the plane’s sophisticated mechanical systems interact._____________________________________________________________________________________________________________________________________________________________________________________.5)Though the tricycle arrangement may be most popular today, that was not alwaysthe case. The tail wheel undercarriage dominated aircraft design for the first four decades of flight and is still widely used on many small piston-engine planes.What makes this form of landing gear most attractive is its simplicity. Another potential advantage results from the fact that_____________________________ __________________________________________________________________________________________________________________________________ Part II Reading Comprehension（30%）Section 1 Skimming and Scanning (10%)Directions: In this section there are 10 incomplete statements. Based on the following passage, please complete the statements with the information given in the passage.Commercial aviation is an essential component of the global economy. The cost of aviation fuel is directly determined by the prevailing world price of oil, and it accounts for a major proportion of airplane operating costs. Several airline companies now add a fuel surcharge to the ticket cost of a commercial flight to compensate for the recent rapid rise in fuel costs. World oil prices are expected to remain high for several years. The prospect of sustained high aviation fuel prices could propel airline companies to seek alternative aviation fuels. Seeking alternative fuel could become paramount（最⾼的）for the airlineindustry should the peak-oil phenomenon actually occur.Breakthroughs and ResearchIt may become possible for super-cooled liquid hydrogen（氢）to eventually be used as an alternative fuel for some types of commercial airline service. Other alternative fuels may include high-density energy-storage technologies that result from breakthroughs in research in the areas of nanotechnology(纳⽶技术) and in high-temperature superconductivity(超导性). High-temperature superconductivity holds great promise for use in high-density energy-storage technology. Advances in nanotechnology could enable superconductive materials to eventually be manufactured at a cost that could justify their application in airliner propulsion. Electrical Storage and PropulsionEnergy stored in a superconductive storage technology could power electric motors that drive the identical propulsion fans that are found at the front-end of modern, “high-bypass” turbo-fan aircraft engines. Such fans provide up to 90% of the propulsive thrust of the turbo-fan engine. Each electrically powered propulsion fan may be driven by multiple (induction) lightweight electric motors during take-off. Some electric motors would “cut-out”under reduced power demand at cruising altitude so that the remaining motors will operate at higher efficiency (electric motors have poor part-load efficiency). Coanda fans may propel subsonic commercial aircraft that use high-density electrical storage technology. Such units were originally developed by physicist Henri Coanda and can operate at comparable efficiency and at comparable flight speeds as turbine-driven propulsion fans. Electrically powered aircraft that use either turbine propulsion fans or Coanda fans could be flown in thinner air at higher altitude (up to 65,000-feet) to reduce energy consumption (less drag on aircraft) on extended flights.The cooler air found at such altitudes could assist in keeping the superconductive energy storage systems functioning properly.Superconductive energy storage systems used in future commercial aircraft would likely be cooled by liquid nitrogen(氮). Both systems would need to be frequently recharged, which would likely be both energy-intensive as well as time consuming.It may be possible to design the energy storage systems along with their cooling systems to be removed and replaced during shorts layovers—such technology could help reduce the turn-around time of the aircraft. The introduction of superconductive energy storage systems in commercial aircraft in the long-term future would require that future airport terminals be equipped with power generation technology at or near the premises.Power GenerationThe number of electrically powered and hydrogen powered road and railway vehicles would likely increase during a post peak-oil period. Commuter aircraft that operate short-haul service could be powered by ethanol(⼄醇) or by hydrogen while future supersonic aircraft could use liquid hydrogen as fuel. The commercial aviation industry of the future (post peak oil) could likely require vast amounts of electric power to recharge superconductive energy storage systems, recharge liquid nitrogen cooling systems as well as to generate, compress and supercool large amounts of hydrogen.Modern commercial aircraft are energy intensive during take-off. Airports that serve metropolitan areas presently process continual processions of large long-distance aircraft during peak periods. Such aircraft could require between 300-Mw-hr and 1000-Mw-hr of power to undertake trans-oceanic flights at subsonic speed. The power requirements of a future electrically based commercial aviation industry could likely overwhelm the power generation industry of most developed nations. Major international airports may eventually need to generate electric power on-site to meet the energy needs of future fleets of electrically powered and hydrogen-fueled commercial aircraft. Airport power stations may be nuclear; use hydrogen fusion or be based on some other unconventional power generation technology that is still subject to research.Energy StorageThe ability to store large amounts of energy at or near major airports could gain importance during a post peak-oil period. Electric power could be purchased from the grid during their off-peak periods and put into short-term storage. Airport power stations that encounter off-peak periods could replenish(装满) airport energy storage systems that may include superconductive storage, flow batteries, hydraulic storage in hydroelectric dams in nearby mountains (coastal airports) or off-site pneumatic storage (subterranean salt domes that were emptied). Air that is exhausted from pneumatic storage systems may be sufficiently cold to assist in “replenishing” liquid nitrogen super-cooling systems.Power Regulation (Airports)Power stations that provide energy for air transportation use may have to be excluded from the regulatory framework. Most of the electrically powered airliners that will be recharged would be “foreign”owned, that is, the owners would be domiciled in adifferent jurisdiction(司法权) to where the aircraft would be recharged. The idea of regulators in one jurisdiction looking after the interests of parties who live, do business and pay taxes in another jurisdiction is quite ludicrous. Power stations that supply a future airline industry with electric power would need to be regulatory-free despite the “foreign”airline owners being “captive”customers. It would be possible for power to be supplied to a single airport by several small providers who compete against each other. Power providers and airline companies could negotiate deals, perhaps even on a daily basis. ConclusionFuture scientific breakthroughs are likely to occur in both nanotechnology and in superconductivity. High-density energy storage technologies could be the likely result and appear in the distant future. Electrically powered commercial aircraft that fly at subsonic speeds could appear in the future irrespective of whether or not peak-oil actually occurs. Alternative liquid fuels that are cost-competitive to fossil oil are also likely to appear and find applications in aviation. Large ground-effect aircraft （地效飞⾏器）that fly above water and that carry either passengers or freight between coastal cities are also likely appear in the future.1.The prospect of sustained high aviation fuel prices could propel airline companiesto seek _______________________.2.Breakthroughs in nanotechnology could enable _______________________ to beavailable in their application in airliner propulsion.3.Coanda fans were first developed by _______________________ .4._______________________ could be used to cool superconductive energystorage system used in future commercial aircraft.5._______________________, which operates short-haul service, could be poweredby ethanol(⼄醇) or by hydrogen.6.Future airport power stations may be_______________________; use hydrogenfusion or be based on some other unconventional power generation technology. 7.During a post peak-oil period, the ability to_______________________ at or nearmajor airports could gain importance.8.Power stations that provide energy for air transportation use are likely to be_______________________ from the regulatory framework.9.Electrically powered commercial aircraft that fly at _______________________speeds could appear in the future.10.Aircrafts flying above water and carrying either passengers or freight betweencoastal cities are called _______________________.Section 2 Reading Comprehension (10%)Directions: The following passage is followed by some questions. For each of them there are four choices marked A), B), C) and D). You should choose the best answer from the four choices.Living standards have soared during the twentieth century, and economists expect them to continue rising in the decades ahead. Does that mean that we humans can look forward to increasing Happiness?Not necessarily, warns Richard A. Easterlin, an economist at the University of Southern California, in his new book, Growth Triumphant: The Twenty-first Century in Historical Perspective. Easterlin concedes that richer people are more likely to report themselves as being happy than poorer people are. But steady improvements in the American economy have not been accompanied by steady increases in people’s self-assessments of their own Happiness.The explanation for this paradox(悖论) may be that people become less satisfied over time with a given level of income. In Easterlin’s word: “As incomes rise, the aspiration level does too, and the effect of this increase in aspirations is to vitiate (破坏) the expected growth in Happiness due to higher income.”Money can buy Happiness, Easterlin seems to be saying, but only if one’s amounts get bigger and other people aren’t getting more. His analysis helps to explain sociologist Lee Rainwater’s finding that Americans’perception of the income “necessary to get along” rose between 1950 and 1986 in the same proportion as actual per capita income. We feel rich if we have more than our neighbors, poor if we have less, and feeling relatively well-off is equated with being happy.Easterlin’s findings, challenge psychologist Abraham Maslow’s “hierarchy(等级) of wants” as a reliable guide to future human motivation. Maslow suggested that as people’s basic material wants are satisfied they seek to achieve nonmaterial or spiritual goals. But Easterlin’s evidence points to the persistence of materialism.“Despite a general level of affluence never before realized in the history of the world.” Easterlin observes, “Material concerns in the wealthiest nations today are as pressing as ever and the pursuit of material need as intense.” The evidence suggests there is no evolution toward higher order goals. Rather, each step upward on the ladder of economic development merely stimulates new economic desires that lead the chase ever onward.Needs are limited, but not greeds. Science has developed no cure for envy, so our wealth boosts our Happiness only briefly while shrinking that of our neighbors. Thus the outlook for the future is gloomy in Easterlin’s view. “The triumph of economic growth is not a triumph of humanity over material wants; rather, it is the triumph of material wants over humanity.”1.What does Easterlin warn in his new book?A)Humans can look forward to increasing happiness with soaring livingstandards.B)Humans might not be able to enjoy increasing happiness with soaring livingstandards.C)Richer people tend to report themselves as being happy more than poorerpeople do.D)Richer people tend to report themselves as being happy less than poorerpeople do.2.Which of the following statements may account for the paradox(悖论) mentionedin paragraph 3?A)People become less satisfied though the income rises over time.B)A general level of affluence never before realized in the history of the world.C)Though the American economy improved steadily, there isn’t a steadyincrease in people’s self-assessments of their own happiness.D)As incomes rise, there will be an increase in the aspiration level, which willhamper the expected growth in Happiness due to higher income.3.Whose finding is against the theory of “Hierarchy of wants”?A)Easterlin’s B) Maslow’s C) Rainwater’s D) Lee’s4.According to Easterlin, the outlook of the future of happiness is ________.A)bright B) sad C) unclear D) thrilling5.From the quotation in the end of the passage (paragraph 7), we can infer that___________?A)The triumph of economic growth results in more humanity.B)The triumph of economic growth results in more material wants.C)Humanity contributes more to the triumph of economic growth.D)Material wants contributes more to the triumph of economic growth.Section 3 Short Answer Questions (10%)Directions: Read the following passage and then answer the questions. The answer should not be more than 25 words.The maximum allowable weight for an aircraft is determined by design considerations. However, the maximum operational weight may be less than the maximum allowable weight due to such considerations as high-density altitude or high-drag field conditions caused by wet grass or water on the runway. The maximum operational weight may also be limited by the departure or arrival airport’s runway length.One important preflight consideration is the distribution of the load in the aircraft. Loading the aircraft so the gross weight is less than the maximum allowable is not enough. This weight must be distributed to keep the center of gravity (CG) within the limits specified in the POH or AFM.If the CG is too far forward, a heavy passenger can be moved to one of the rear seats or baggage can be shifted to a rear compartment. If the CG is too far aft, passenger weight or baggage can be shifted forward. The fuel load should be balanced laterally: the pilot should pay special attention to the POH or AFM regarding the operation of the fuel system, in order to keep the aircraft balanced in flight. Weight and balance of a helicopter is far more critical than for an airplane. With some helicopters, they may be properly loaded for takeoff, but near the end of a long flight when the fuel tanks are almost empty, the CG may have shifted enough for the helicopter to be out of balance laterally or longitudinally. Before making any long flight, the CG with the fuel available for landing must be checked to ensure it will be within the allowable range.Changes of fixed equipment may have a major effect upon the weight of the aircraft. The replacement of older, heavy electronic equipment with newer, lightertypes results in a weight reduction, which will probably cause the CG to shift and must be computed and annotated in the weight and balance record.Repairs and alteration are the major sources of weight changes. The A&P mechanic must compute the CG and record the new empty weight and EWCG in the aircraft weight and balance record.The A&P mechanic or repairman conducting an annual or condition inspection must ensure the weight and balance data in the aircraft records is current and accurate. It is the responsibility of the pilot in command to use the most current weight and balance data when operating the aircraft.Questions:1.What conditions might cause the operational weight of a plane to be less than themaximum allowable weight?2.What should be done if the CG is too far aft in an aircraft?3.Why is the weight and balance for a helicopter far more critical than for anairplane?4.According to the passage, what might lead to weight changes and cause the CG toshift in an aircraft?5.Who are responsible for recording and using the most current and accurate data ofthe weight and balance?Part III Translation (15%)Section 1 English-Chinese Translation (10%)Direction: In this section there are two passages in English. Please read these passages and translate the underlined parts into Chinese.Passage 1The airplane propeller consists of two or more blades and a central hub to which the blades are attached. 1) Each blade of an airplane propeller is essentially a rotating wing. As a result of their construction, the propeller blades are like airfoils and produce forces that create the thrust to pull, or push, the airplane through the air.The power needed to rotate the propeller blades is furnished by the engine. The engine rotates the airfoils of the blades through the air at high speeds, and the propeller transforms the rotary power of the engine into forward thrust.2) An airplane moving through the air creates a drag force opposing its forward motion. Consequently, if an airplane is to fly, there must be a force applied to it that is equal to the drag, but acting forward. This force is called “thrust.”Passage 2Aircraft flight control systems are classified as primary and secondary. 3) The primary control systems consist of those that are required to safely control an airplane during flight. Secondary control systems improve the performance characteristics of the airplane, or relieve the pilot of excessive control forces. Those included in the primary control systems are the ailerons, elevator (or stabilator), and rudder. Examples of secondary control systems are wing flaps and trim systems.Airplane control systems are carefully designed to provide a natural feel, and at the same time, allow adequate responsiveness to control inputs. 4) At low airspeeds, the controls usually feel soft and sluggish, and the airplane responds slowly to controlapplications. At high speeds, the controls feel firm and the response is more rapid.Movement of any of the three primary flight control surfaces changes the airflow and pressure distribution over and around the airfoil. These changes affect the lift and drag produced by the airfoil/control surface combination, and allow a pilot to control the airplane about its three axes of rotation.Design features limit the amount of deflection of flight control surfaces. For example, control-stop mechanisms may be incorporated into the flight controls, or movement of the control column and/or rudder pedals may be limited. The purpose of these design limits is to prevent the pilot from inadvertently overcontrolling and overstressing the aircraft during normal maneuvers.5) A properly designed airplane should be stable and easily controlled during maneuvering. Control surface inputs cause movement about the three axes of rotation. The types of stability an airplane exhibits also relate to the three axes of rotation. Section 2 Chinese-English Translation (5%)Direction: In this section there are five sentences in Chinese. Please translate them into English.1.太阳能动⼒飞机的平均飞⾏时速为70公⾥，暂时不会对商⽤飞机构成威胁。

上下学路上注意交通安全英语作文

上下学路上注意交通安全英语作文

Pay Attention to Traffic Safety on the Way toSchool and BackThe safety of students commuting to and from school isa crucial concern for parents, teachers, and society at large. Every day, millions of children traverse busy roads, intersections, and bridges, making it imperative toprioritize their safety. Traffic accidents are a leading cause of fatalities and injuries among school-aged children, highlighting the need for enhanced awareness and vigilance. The first step in ensuring safe travel is to educate children about basic traffic rules and regulations. They should be taught to cross the road only at designated crossings, to look both ways before stepping onto the street, and to use pedestrian crossings whenever available. Additionally, they should be instructed to avoid jaywalking and never to dart into the road unexpectedly.Parents and guardians play a pivotal role in instilling these habits in their children. They should lead by example, following traffic rules and setting a positive standard for their young ones. Encouraging children to walk in groups orwith an adult can provide an added layer of safety, especially during peak traffic hours.Schools also have a responsibility to promote traffic safety awareness. They can organize workshops, campaigns, and assemblies to educate students about the importance of following traffic rules. These activities can be made interactive and engaging to capture the attention of young learners.Moreover, the authorities must ensure that school zones are well-marked and equipped with safety features such as speed bumps, crosswalks, and traffic lights. They should also enforce strict traffic regulations during school hours to reduce the risk of accidents.Community members can also contribute to creating a safer environment for schoolchildren. They can volunteer to monitor crossings or organize patrols to ensure that children are safely crossing the road. Such initiatives can foster a sense of community responsibility and encourage everyone to play their part in keeping the streets safe.In conclusion, ensuring the safety of children commuting to and from school requires a concerted effortfrom all stakeholders. Education, vigilance, and enforcement of traffic rules are crucial components of this endeavor. By working together, we can create a safer environment for our young ones and protect them from the perils of the road.**上下学路上注意交通安全**学生上下学途中的安全问题，是家长、老师和社会各界共同关注的焦点。

交通违法行为行政处罚归责原则探析

交通违法行为行政处罚归责原则探析

摘要交通违法行为行政处罚以国家强制力作为后盾，是国家行政权的一个重要内容。

德国、奥地利、俄罗斯以及我国台湾地区在行政处罚立法中均引入了过错归责理论，通过确定行为的主观因素，即“故意”或“过失”，全面考虑行为人违法行为时的主观状态，保障行政相对人的合法权益，有效限制行政权的不当实施。

从我国当下行政处罚归责原则的研究来看，存在不同学说，整体研究的不够深入，在具体的实践应用上存在较大争议。

随着我国道路交通车辆及参与者的不断增长，交通违法领域行政处罚不管在数量上还是情形上都有很大变化，在交通违法行政处罚领域实行过错归责原则必定引起强烈反响，能够提升公众交通安全领域的权利保障意识，有效制约交通处罚权的不当实施，并对整个行政处罚领域的归责原则构建产生积极影响。

除了引言和结语，本文共有四个部分。

第一部分对行政处罚归责原则概况进行了全面介绍，系统的阐释了行政处罚归责原则的基本概念、分类，指明行政处罚归责原则研究对于我国行政法发展的重要作用，并从域外国家或有关地区过错归责原则的实践适用研究以及我国行政法归责现状，试图为国内交通违法行政处罚归责原则的研究提供借鉴方向。

第二部分全面分析了过错归责原则在我国交通领域应当适用的理由，为我国交通领域归责原则理论的未来适用指明方向。

从现实情况并结合道路交通安全案例分析，客观归责原则已不再适应我国行政处罚适用现状，不仅会侵害行政相对人利益，也会引发严重社会矛盾；从理论层面讲，我国行政法理念不断发展，“服务论”“控权论”“平衡论”的本质内涵、宪法保障人权的精神期待、行政处罚教育与处罚相结合的实质要求，都呼唤着过错归责的加快出台；从法律溯源角度分析，主观过错归责原则在立法之初便在立法者的考虑之中。

第三部分构思了过错归责在交通行政处罚中的具体适用。

目前，大部分学者在过错归责原则适用机制的研究上，大多停留于过错推定原则。

本章构思在道路交通安全领域，人身罚处罚方面的归责适用严格过错原则，非人身限制性处罚方面适用过错推定原则，并提出交通违法行政处罚应该根据行为人的主观过错设定不同的处罚幅度，构建处罚幅度过错调节机制。