专项练习 完形填空

Discovery in a Thunderstorm
w Many years ago I was on a bicycle trip through some exceedingly picturesque countryside. Suddenly, dark clouds piled up overhead and rain began to fall,     

浮华下一曲爱的呢喃--评《纯真年代》

From the willow walk projectend a slight wooden pier ending in a sort of pagoda-like summerhoust and in the pagoda a lady stood laening against from sleep That vision of the past was a dream and the reality was what awalted him in the house on the bank overhead     

The Colour of the Sky

1If we look at the sky on a perfectly fine summer’s day we shall find that the blue colour is the most pure and intense overhead,and when looking high up in a direction opposite to the sun.Near the horizon it is always less bright, while in the region immediately around the sun it is more or less yellow.     

Bobby Brontosaurus （u）

The songs of the birds awakened (弄醒) Bobby. He watched them dart(飞翔) happily back and forth overhead. Suddenly he noticed that his mother wasn‘t there. He began following her giant footprints from the clearing (开阔地),     

Software outsourcing risk management： establishing outsourcee evaluation item systems

INTRODUCTION Outsourcing offers several advantages, such as enabling existing staff to concentrate on core com-petencies, focusing on achieving key strategic objec-tives, lowering or stabilizing overhead costs, obtain-ing cost competitiveness over the competition, pro-viding flexibility in responding to market conditions, and reducing investments in high technology. Thus software outsourcing is becoming increasingly popular. However, because of the difference between outsourcers and outso…     

Effect of a semi electro-mechanical engine valve on performance and emissions in a single cylinder spark ignited engine

In this study, an electro-mechanical valve （EMV） system for the intake valve ofa fottr stroke, single cylinder, overhead valve and spark ignition （SI） engine was designed and constructed. An engine with the EMV system and a standard engine were tested to observe the effects of the EMV on engine performance and emissions at different speeds under full load. The EMV engine showed improved engine power, engine torque and break specific fuel consumption （BSFC）. A 66% decrease in CO emissions was also obtained with the EMV system, but hydrocarbons （HC） and NOx emissions increased by 12% and 13% respectively.     

Performance analyses and optimization based on iSCSI

1 Introduction With advances in networking technology, iSCSI allows for the deployment of storage networks over a commodity internet. However providing storage services across networks increases communication costs: requests and results must be transported between iSCSI Initiator and iSCSI target [1,2]. Intensive overhead caused by network I/O limits the capacity of servers. This makes the study of iSCSI performance an import research topic. Earlier researches closely measure the perfo…     

Ad hoc网络中一种自适应的负载均衡机制

An adaptive load balancing scheme is proposed to balance the load in ad hoc networks. The new scheme can be applied in most on-demand routing protocols resulting in significant performance improvement. The proposed scheme is applied to the ad hoc on-demand distance vector (AODV) routing protocol. Simulation results show that the network load is balanced on the whole, and performance in packet loss rate, routing overhead and average end-to-end delay is also improved.     

Secure and efficient multi-message and multi-receiver ID-based signcryption for rekeying in ad hoc networks

In this paper, the security technology of ad hoc networks is studied.To improve the previous multi-receiver signcryption schemes, an ID-based multi-message and multi-receiver signcryption scheme for rekeying in ad hoc networks is proposed.In this scheme, a sender can simultaneously signcrypt n messeges for n receivers, and a receiver can unsigncrypt the ciphertext to get his message with his own private key.An analysis of this scheme indicates that it achieves authenticity and confidentiality in the random oracle model while being of lower computation and communication overhead.Finally, for the application of our scheme in ad hoc, a threshold key updating protocol for ad hoc networks is given.     

Adaptive progressive download based on the MPEG-4 file format

In this paper we describe how progressive download and adaptive streaming can be combined into a simple and efficient streaming framework. Based on the MPEG-4 file format (MP4) we use HTTP for transport and argue that these two components are sufficient for specifying an open streaming architecture. The client selects appropriate chunks from the MP4 file to be transferred based on (1) the header information (i.e. the "moov" box) in the first part of the file and (2) his observation of network throughput. The framework is completely client driven which allows for better server scalability and reduces signalling overhead. We discuss architecture and implementation issues such as complexity, interoperability and scalability and compare to 3GPP PSS Re1-6 adaptive streaming when appropriate. Measurements from a simple MP4/HTTP streaming client are presented showing that appropriate chunks are selected such that increased reliability is achieved.     

Performance Improvement of Distributed Coordination Function in IEEE 802.11 Wireless LAN

This paper proposes a modification to distributed coordination function (DCF) to improve the channel utilization in IEEE 802.11 wireless local area networks (WLANs). In the modified DCF, when a station has contended for the channel, it may transmit multiple data frames continuously to the same destination, which is called transmission burst(TB). When the maximum number of data packets transmitted continuously in a TB is set to be 2, the performance is expected to be the best. The theoretical analysis and simulation results show that compared with the standard DCF, the modified DCF can increase the throughput and decrease the delay of the WLAN, and the modification does not introduce any additional control overhead.     

移动Ad-hoc网络的路由修复的优化

A main shortcoming of mobile Ad-hoc network‘s reactive routing protocols is the large volume of far-reaching control traffic required to support the route discovery (RD) and route repair (RR) mechanism.Using a random mobility model,this paper derives the probability equation of the relative distance (RDIS) between any two mobile hosts in an ad-hoc network.Consequently,combining with average equivalent hop distance (AEHD) ,a host can estimate the routing hops between itself and any destnation host each time the RD/RR procedure is triggered,and reduce the flooding area of RD/RR messages. Simulation results show that this optimized route repair (ORR) algorithm can significantly decreace the communication overhead of RR process by about 35％.     

Super Node Routing Strategy in Content-Centric Networking

There were two strategies for the data forwarding in the content-centric networking(CCN): forwarding strategy and routing strategy. Forwarding strategy only considered a separated node rather than the whole network performance, and Interest flooding led to the network overhead and redundancy as well. As for routing strategy in CCN, each node was required to run the protocol. It was a waste of routing cost and unfit for large-scale deployment.This paper presents the super node routing strategy in CCN. Some super nodes selected from the peer nodes in CCN were used to receive the routing information from their slave nodes and compute the face-to-path to establish forwarding information base(FIB). Then FIB was sent to slave nodes to control and manage the slave nodes. The theoretical analysis showed that the super node routing strategy possessed robustness and scalability, achieved load balancing,reduced the redundancy and improved the network performance. In three topologies, three experiments were carried out to test the super node routing strategy. Network performance results showed that the proposed strategy had a shorter delay, lower CPU utilization and less redundancy compared with CCN.     

Adaptive ant-based routing in wireless sensor networks using Energy*Delay metrics

To find the optimal routing is always an important topic in wireless sensor networks （WSNs）. Considering a WSN where the nodes have limited energy, we propose a novel Energy^＊Delay model based on ant algorithms （＂E＆D ANTS＂ for short） to minimize the time delay in transferring a fixed number of data packets in an energy-constrained manner in one round. Our goal is not only to maximize the lifetime of the network but also to provide real-time data transmission services. However, because of the tradeoff of energy and delay in wireless network systems, the reinforcement learning （RL） algorithm is introduced to train the model. In this survey, the paradigm of E＆D ANTS is explicated and compared to other ant-based routing algorithms like AntNet and AntChain about the issues of routing information, routing overhead and adaptation. Simulation results show that our method performs about seven times better than AntNet and also outperforms AntChain by more than 150% in terms of energy cost and delay per round.     

A three-level mobility management scheme for hierarchical mobile IPv6 networks

INTRODUCTION Mobile IPv6 (MIPv6) (Johnson et al., 2004) was proposed to maintain network connectivity in the next generation Internet. However, communication quality of MIPv6 degrades because of the high signaling overhead and the long signaling delay when a mobile node (MN) performs handover. Hierarchical Mobile IPv6 (HMIPv6) (Soliman et al., 2005) was proposed to improve the performance of MIPv6, where the Mobility Anchor Point (MAP) handles mobility in- side the local domain…     

阅读理解练与析(英文)

ATerry Thom as has a very boring job,although it pays very well.W hat Terry doesis sitting in a rowboat all day long.H em akes＄16.37an hour,w hich is certainlyan excellent wage for sitting in a little boatand doing nothing.The boat stays all day under a bridgethat is being rebuilt.There is a distance ofabout100feet between the boat and theworkers on the bridge overhead.The rest ofTerry’s fellow workers are up on thebridge working.Terry’s job is to rescueanyone who falls off the bridge in…     

勇往直前!

未来未必可靠,无论它多么诱人!让黯淡的过去入土安息!行动,行动,就在此时此刻!勇气在胸,皇天在上!即使失败了,那有什么打紧?站起来再努力一次,直至成功!Trust no Future,however pleasant!Let the dead past bury its dead!Act,act in the living present!Heart within,and God overhead!If you fail,let it be!Just try again until you make it!勇往直前!$江苏省泰兴市刁铺中学@殷华新…     

老生常谈

在吹嘘过自己的瞄准本领后,猎手瞄准了头顶上的一只孤雁。"看着,"他对听者命令道。他开了火,大雁却还在飞着。"朋友们,"他带着敬畏的神情说道,你们现在看见了奇迹。天上飞着一只死雁!"After boasting of his prowess as a marksman, the hunter took aim on a lone duck overhead. "Watch this," he commanded his listeners. He fired, and the bird flew on. "My friends," he said with awe, "you are now viewing a miracle. There flies a dead duck!"老生常谈…     

Time-domain training sequences design for MIMO OFDM channel estimation

This paper describes a Least Squares （LS） channel estimation scheme for MIMO OFDM systems based on time-domain training sequence. We first compute the minimum mean square error （MSE） of the LS channel estimation, and then derive the optimal criteria of the training sequence with respect to the minimum MSE. It is shown that optimal time-domain training sequence should satisfy two criteria. First, the autocorrelation of the sequence transmitted from the same antenna is an impulse function in a region longer than the channel maximum delay. Second, the cross-correlation between sequences transmitted from different antennas is zero in this region. Simulation results show that the estimator using optimal time-domain training sequences has better performance than that using optimal frequency training sequence at low signal-to-noise ratio （SNR）. To reduce the training overhead, a suboptimal training sequence is also proposed. Comparing with optimal training sequence, it has low computation complexity and high transmission efficiency at the expense of little performance degradation.     

Flying Color

White is the fluffy clouds rolling overhead. White is the hopping bunnies. White is the daisies in the freshly trimmed green grass. White is the pearly sand on a beach. White is the blinding sun rays. White is the thrashing waves in the ocean