Search

In an ecosystem multiple predator species often forages on a common prey and the interactions between the predators are neutral. In view of these facts and based on a one-prey-multiple-predators system with Holling IV functional response, an impulsive differential equation to model the process of periodically releasing natural enemies and spraying pesticides at different fixed times for pest control is proposed and investigated.It is proved that there exists a locally asymptotically stable pest-eradication periodic solution when some condition is satisfied(or the impulsive period is less than some critical value). Numerical results show that the system we considered has more complex dynamics including period-doubling cascade, period halfing cascade, quasi-periodic oscillation, chaos, intermittency and crises.

An UHF Radio Frequency Identification (RFID) transponder, which can function according to either standard ISO 18000–6B or security ISO 18000–6B with Advanced Encryption Standard (AES), is presented in this paper. The UHF RFID transponder is composed of analog front-end (AFE) and digital signal processing unit. A novel demodulator in AFE is presented in this paper. Silicon area occupied by the demodulator is only 21% of traditional structure and it could demodulate input signal with data rate ranging from 10Kbps to 870Kbps. In digital processing unit, 128-bit AES algorithm is built in to ensure security communication between transponder and reader. Total chip area without test pads is 0.7mm2@0.18µm CMOS process and consumes 15µW without writing Memory.

In order to optimize the population structure of nitrifying bacteria, several factors were analyzed in this paper to make partial nitrification start up. Lab-scale SBR was employed to treat the domestic wastewater of low COD/TN ratio. Steady partial nitrification can be achieved through real-time control in 32 cycles with dissolved oxygen(DO)1.8±0.1mg/L and SRT 7 days at 30℃. The nitrite accumulation rate (NO2 - - N /NOx - - N) was over 90% under the premise of TN removal ratio above 95%. In the next 64 days, the system was also successfully operated at ambient temperature (20 ~ 24℃). Fluorescent in-situ hybridization(FISH)analysis showed that the population of ammonia oxidizing bacteria (AOB) increased by 58.9% while nitrite oxidizing bacteria(NOB) decreased by 83.2% during 32 cycles. NOB can be gradually washed out by the process control of DO and aerobic duration based on DO and pH on-line sensors so steady partial nitrification and nitrogen removal efficiency can be achieved and enhanced, respectively. Keywords-rapid achievement; process optimization; on-line control; partial nitrification; FISH; SBR process

Nowadays, wireless sensor networks are widely used in many environmental monitoring applications. However, due to the limitation of the current hardware technology, sensors are often battery powered and it is very difficult to change batteries. Therefore, for applications over wireless sensor networks, it is a critical issue to save the energy of sensors. Many attempts have been made to answer various types of queries energy-efficiently, such as max, top-k, and skylines. However, all of them return the readings of individual sensors that satisfy the query constraint. In practice, query results based on individual sensor readings are unreliable because sensor readings are often noisy. Thus, in this paper, we present a new type of query, max aggregate query over a region (i.e. max regional aggregate), which aims to find a fixed-size region whose regional aggregate is the maximum among all the possible regions with the same size. Compared to traditional max queries, max regional aggregate is more reliable in detecting events. Designing an energy-efficient approach to answer max regional aggregate is non-trivial because a huge number of regions need to be investigated. Thus, in this paper, we propose a novel two-level sampling approach, with region and sensor sampling, to collect the sensor readings intelligently and compute the approximate max regional aggregate based on the collected results. Specifically, region sampling is used to select regions and sensor sampling isused to choose the sensors within a selected region. Our extensive simulation results demonstrate that the proposed two-level sampling approach can answer the max regional aggregate energy-efficiently with a desirable accuracy.

Intrusion detection has become the important component of the network security. Many intelligent intrusion detection models are proposed, but the performance and efficiency are not satisfied to real computer network system. This paper extends these works by applying a new high efficient technique, named twin support vector machines (TWSVM), to intrusion detection. Using the KDD'99 data set collected at MITpsilas Lincoln Labs evaluates the performance and efficiency of the proposed intrusion detection models. The experimental results indicate that the proposed models based on TWSVM is more efficient and has higher detection rate than conventional SVM based model and other models.

In ad hoc networks, any concurrent transmission will add to the level of interference and collision experienced by other users. The spatial density of transmissions that could be supported subject to two constraints: the excessive interference of attempted receivers, the channel access collision of attempted transmitters. We combine two constraint factors and define channel interference and access delay (CIAD) routing metric. CIAD may balance interference, access delay and length of a route. CIAD can avoid accessing the areas with high interference and overfull channel competition. In this paper, we implement a more realistic channel model to calculate the aggregate interference and the bite error rate (BER) in NS-2. We show through simulation that our proposal increases throughput, reduces the end-to-end delay. The simulation results illustrate that our protocol is able to achieve better performance than dynamic source routing (DSR).

This paper presents a communication protocol of streaming media to ensure secure live transferring of scalable quality video programs over network. In our protocol, client, authentication server and video server collaborate for authentication, generation of session keys and transferring of encrypted streaming media. Bi-direction authentication is carried out by bi-direction challenge method and method base on public-key cryptography. Perfect forward secrecy is provided by adoption of Diffie-Hellman key exchange steps.

Spatial reuse in a wireless network can allow multiple communications to proceed concurrently. Usually it seems that the more concurrent transmissions are allowed, the more the aggregate throughput can be sought. Unfortunately, to increase the level of spatial reuse, medium access control (MAC) protocols should either reduce the transmit power or increase the carrier sense (CS) threshold dynamically, which will make the SINR at the receiver decrease. With the decrease of SINR, the data rate sustained by each transmitter will also decrease, which counteracts the gain of simultaneously transmissions and leads to the degradation of network performance. The conflict among SINR and spatial reuse of the data rate suggests that there should be a tradeoff between them. In this paper, on the basis of theoretical analysis, we propose a dynamic joint control (JC) mechanism to adjust transmit power, sense threshold and data rate, based on the former transmit status, to increase the level of spatial reuse and improve performance in terms of aggregate throughput and energy efficiency.

In this paper, the electrical tree initiation characteristics of high-density polyethylene (HDPE) under AC voltage with frequency ranging from 50 Hz to 100 kHz were studied. With the increase of frequency, the tree initiation voltage (TIV) firstly increases and then decreases after a peak value at 10 kHz is reached. However, the increase of frequency results in the decrease of the minimum of TIV and the increase of the dispersivity of TIV. There are 4 kinds of tree initiation shape (TIS): branch tree, bush tree, trunk tree and breakdown tree. With the increase of frequency, the kinds of TIS increase and the primary TIS changes from branch tree to bush tree. The influence of frequency on TIV and TIS were discussed.

Topology control in wireless ad hoc networks can be considered the task of given a network connectivity graph computing a sub graph with specific desired properties, such as connectivity, symmetry, sparsity, low interference. All previous approaches used for topology control have in common that they model wireless networks as purely geometric graphs, hence neglecting one of the most crucial aspects of wireless communication: capture effect. From a theoretical point of view, the graph-based model of topology control really does not bear any significance when it comes to actually scheduling messages in an SINR environment. Therefore, we integrate SINR-based model into graph-based model. Then we present a hybrid interference model-based topology control (HIMTC) algorithm. The proposed algorithm is distributed and only requires the local information. It can lower the graph interference of networks and increases the network capacity.

Interference in the mobile ad hoc networks (MANET) influences performances of the networks badly. In this paper, we propound a new interference-aware probability forwarding (IPF) mechanism to reduce interference. Firstly, IPF is to adjust the carrier sensing threshold, resulting in a higher level of spatial reuse. Secondly, IPF distributes a probability to every node. The probability is related with the real time interference and the maximal interference in the MANET. Thirdly, nodes rebroadcast received route request packets with this probability. In this way, the IPF finally controls the direction of routes to avoid nodes or areas with more interference and reduce the total interference the packets will suffer from the source to the destination. Simulation results have highlighted that our IPF mechanism can improve several performance metrics, such as throughput, average end to end delay, control overhead.

In the reactive routing algorithms of mobile ad hoc networks (MANET), preemptive routing method tries to warn the source node and to tell it to change route in time before a link is about to break. This method alleviates the problem from packet losses, and shortens the delay of route change after a route failure. However, it also decreases the number of route error packets which play an important role in removing stale route entries from node cache, i.e. it disables the cache function. In this paper, we propose a protocol called Cache-enabled Preemptive Dynamic Source Routing (CPDSR), and try to reserve the cache function in preemptive routing method. Simultaneously, we give a definition of Reaction Time which determines exactly when a link is regarded as unstable and is a key ingredient in preemptive routing method. Our definition is in accordance with our method and proves to be more reasonable. The simulation result shows that our work can improve the performance of preemptive routing greatly in overhead and end-to-end delay.

By environmental scanning electron microscopy and X-ray electron probe microanalysis, Al content was studied in the grains of 21 genotypes of rice. The Al content differed as follows: inner surface of glume > aleurone layer > outer surface of glume > surface of caryopsis > sub-aleurone layer > centre of caryopsis. There were genetic differences in Al enrichment among the 21 genotypes, with differences in distribution of Al within the grain and hence differences among genotypes in the Al content of each part of the grain. There were significant non-linear correlations as follows: Al content in the centre with that in the surface and the sub-aleurone layer; Al content in the aleurone layer with that in the centre and sub-aleurone layer; and Al content in the inner surface of the glume with that in the aleurone layer. The results indicated that the Al enrichment in the centre of the caryopsis is regulated by the glume and the aleurone layer.

The total nitrogen content, alkali-soluble nitrogen content, ammonification intensity, nitrogen fixation intensity, urease activity, protinase activity, nitrite reductase activity and nitrate reductase activity of alkalized soil of which Puccinellia tenuiflora grown for different years increased that compared with alkali spot soil, and there are difference between the soil of which P. tenuiflora grown for different years. The total nitrogen content of the soil of which P. tenuiflora grown for different years has significant difference with alkali spot soil, and the alkali- soluble nitrogen content of the soil of P. tenuiflora grown for three or four years has significant difference with alkali spot soil, but the ammonification intensity, nitrogen fixation intensity, urease, proteinase, nitrite reductase and nitrate reductase activity of alkalized soil of which P. tenuiflora grown for three, four or five years have the significant difference with that of alkali spot soil. All of above indicated that the growth of P. tenuiflora has the improvement effect upon nitrogen nutrition status of alkalized soil, and which grown for 3~5 years is the best of all.

Physical carrier sensing plays an important role in collision avoidance in wireless networks, and the size of the physical carrier sense threshold has a great impact on the system performance. As the channel access activities and packet reception rate of a node is affected by the accumulative interference, we present a new analytical approach that demonstrates how to tune the sense threshold to reduce the interference. The optimum carrier sensing range should balance the spatial reuse and the impact of interference in order to optimize the aggregate throughput of nodes (users). Then we present a new heuristic algorithm to optimize the physical carrier sense threshold by measuring the state of the channel in IEEE 802.11 ad hoc networks. The proposed algorithm can approach the optimum carrier sense threshold to maximize the throughput through both analysis and simulations.

To meet the requirements of services with various quality of service (QoS) in future wireless communication systems, a traffic satisfaction factor(TSF) is defined to describe the satisfaction degree of traffic QoS experience. Based on this TSF, a satisfaction based scheduling scheme with multi-beam zero-forcing beamforming (ZFBF) strategy in multi-antenna downlink systems is presented in this paper. This scheduler schedules users with joint considerations of their QoS satisfaction and their channel condition. Punishment mechanism of the scheduler is proposed to prevent traffics from occupying too much more resource than their requirements. Simulation results show that the proposed scheduler can guarantee the traffic QoS experience and exploit radio resource utilization better than that of existed scheduling methods.

Based on interpreting the conception of antenna's spacial polarization especially for instantaneous polarization detailedly, the description framework of spacial polarization characteristics for antenna is introduced in this paper. Some classical descriptors and instantaneous descriptors are given. On the basis of this, the spacial polarization characteristics of theoretical orthogonal dipole antenna and a practical jammer antenna is analyzed. The corresponding computer simulation is completed. The result indicates that antenna's polarization characteristics often changes by rule in different radiation direction. The research in this paper also provide theoretical base and support for the application of the spacial polarization characteristics of antenna.

Nowadays, wireless sensor networks have been widely used in many monitoring applications. Due to the low quality of sensors and random effects of the environments, however, it is well known that the collected sensor data are noisy. Therefore, it is very critical to clean the sensor data before using them to answer queries or conduct data analysis. Popular data cleaning approaches, such as the moving average, cannot meet the requirements of both energy efficiency and quick response time in many sensor related applications. In this paper, we propose a hybrid sensor data cleaning approach with confidence. Specifically, we propose a smart weighted moving average (WMA) algorithm that collects confidence data from sensors and computes the weighted moving average. The rationale behind the WMA algorithm is to draw more samples for a particular value that is of great importance to the moving average, and provide higher confidence weight for this value, such that this important value can be quickly reflected in the moving average. Based on our extensive simulation results, we demonstrate that, compared to the simple moving average (SMA), our WMA approach can effectively clean data and offer quick response time.

The intrinsic flexibility and independence of infrastructure enable mobile ad hoc networks (MANET) to be widely used in various environments such as disaster rescue, and battlefield. Recently, researches have shown that interference can impose a significant impact on the performance of a MANET. However, there is no unified definition of interference in MANETs currently. Therefore, in this paper, we first introduce an explicit definition of interference. Based on this definition, we present a series of formulas for computing node-interference, link-interference and path-interference, and then propose an interference-aware routing protocol selecting paths with the minimum average link-interference between the source and destination. Paths found by our protocol tend to avoid the areas with high interferences, reducing the number of collisions and packet retransmissions, resulting in higher network throughput and longer lifetime. We implement our average link interference-aware routing protocol (ALIR) on dynamic source routing (DSR). The simulation results illustrate that our protocol is able to achieve better performance than DSR.

This paper is dedicated to the application of artificial neural networks in building prediction models of mechanical properties of new high-speed steel, including predictions of hardness (H) and impact toughness (Ak) according to quenching and tempering temperatures (T1, T2). Multilayer backpropagation (BP) networks are created and trained using comprehensive datasets tested by the authors. And very good performances of the neural networks are achieved. The prediction values sufficiently mine the basic domain knowledge of heat treatment process of HSS. A new application field of neural network was developed by the authors.

Firstly, the statistics of random polarized wave's instantaneous Stokes sub-vector is analyzed and its probability density function (PDF) is obtained. Secondly, the target detection problem is skillfully translated into the detection problem of three equivalent polarization signals. Thereby, a novel fusion detection algorithm is presented based on the difference statistical distribution of Stokes sub-vector between targets and clutters. Experimental results show that no matter the target is random polarization or invariable polarization, the algorithm is effective. Its performance can be comparative to that of the optimal polarization detector (OPD) and better than that of the polarization white filtering detector (PWF). Considering variable conditions of polarimetric measurements, it can be used more widely than the optimal polarization detector

The newly emerging wireless backhaul network has fundamental difficulties in supporting Voice over IP (VoIP) applications due to the MAC overheads introduced by huge amounts of small packets. Packet aggregation is a promising approach to mitigate these overheads. However, previous approaches to such problems are often stringent, not adaptive to the change of channel conditions. They are operated by each TAP (Transit Access Point) separately without any coordination in the use of shared channels. As a result, they fail to ensure the VoIP quality in terms of delay and loss. The major contribution of this paper is the proposal of a coordinated aggregation algorithm, which is adaptive and distributed. By coordinating with neighboring TAPs, the proposed algorithm is able to assign an appropriate aggregation rate to each TAP, aiming at better channel utilization and lower packet loss and delay. We evaluate this design by comprehensive analysis and simulations. The simulation results show that our algorithm significantly improves the VoIP capacity in wireless backhaul networks and outperforms existing aggregation algorithms.

Volume data compression is very important for transmission and display of very large 3D volume data sets. Based on adaptive wavelet, an efficient compression scheme was proposed, which mainly exploited intra-band dependencies of wavelet coefficients. Blockwise hierarchy wavelet decomposition was performed to obtain approximate and detail coefficient block. Because significant coefficients were clustered in certain areas in wavelet domain, corresponding to the edge and textual regions in the volume, we repeatedly applied a process in which each coefficient block was subdivided into eight sub-blocks if there were significant coefficients in the block. Finally, we used one bit to indicate block or sub-block significant map, resulting in fewer bits for storing significant map and that all the coefficients stored in data area were significant. Due to adopt adaptive wavelet in which homogeneous regions are smoothed while discontinuities are preserved, high quality image can be obtained at low resolution, which is useful for transmission between data server and browsing clients over low-bandwidth networks.

The commercial operation of future "4G" mobile wireless networks, comprising both IP-based voice and data uniformly, is widely considered as the next challenge for service providers. Within such an IP-environment, with its implicit integration of the control and data plane, passive measuring and metering will be one of the key elements for AAA and QoS provision, for performance and fault management purposes. Within the IETF, a real-time flow measurement framework has been developed for measurement and accounting for the fixed Internet infrastructure. The article first briefly introduces the IETF "real-time flow measurement" (RTFM) architecture, a pure IP 4G-architecture, together with its key signalling scenarios, and Java/J2EE and Web middleware technology. It then describes "FlowVis", a highly scalable and distributed IP based protocol visualization and verification framework for both signalling and data traffic. Combining the near-real-time capabilities of the existing IETF RTFM with current middleware technology, this "FlowVis" framework can serve as a starting point for distributed protocol analysis in future 4G networks. We use NeTraMet, an open-source implementation of the RTFM architecture as the key metering component of "Moby Dick", a 4G mobile access network architecture.

Summary form only given. We designed and fabricated the hybrid integrated CMOS-VCSEL multiple chip modules. The VCSEL operate at 850nm wavelength. A typical VCSEL has a threshold current of 4 mA, and quantum efficiency of 0.3 mW/mA. Operating at 8 mA modulation current, the VCSEL 3-dB modulation bandwidth was measured more than 5 GHz.

A large phonemic time-delay neural network (LPTDNN) technique has been developed to recognize all Mandarin consonants of the entire set of Chinese syllables. By modular construction, six component networks, viz. (b,d,g,ot), (l,m,n,r,ot), (j,z,zh,ot), (c,q,ch,ot), (f,s,x,h,sh,ot) and (p,t,k,ot), are formed to represent all 21 Mandarin consonants (where ot=others). The technique was thoroughly tested with 8 sets of 1157 isolated Hanyu Pinyin syllables, with 6 sets used for training and 2 sets used for testing. The overall result shows a high recognition performance with 99.2% for the inside test (i.e. testing on the datasets which were used entirely in training) and 92.7% for the outside test (i.e. testing on the remaining datasets which were never used in training). >

Modern power generation control areas consist of large power plants and many industrial customers. High quality supply of the electricity increases the demand for automatic generation control in North-China Electric Power Network. For quickly satisfying the large load changes or other disturbances and enhancing the safety of the power system, the feed forward strategy and the nonlinear governor-boiler model in automatic generation control are investigated in this paper. Some new concepts, such as developing a new algorithm for more effective control; considering the whole boiler-turbine-generator model instead of only the governor-boiler model for the load disturbances; understanding the interaction between the fast area control error loop and slow governor-boiler inner loop, are discussed. Simulations of the automatic generation control with feed forward and PI controller have shown that these ideas are helpful to the automatic generation control realization.

The problem of wideband high-resolution radar target detection in cluttered circumstances is studied. A high-resolution polarization target detection scheme is presented based on intense scatterer integration. Because of the intrinsic high-resolution characteristic of the wideband waveform, a one dimensional range profile of a radar target can be obtained. In connection with the target's polarization characteristics, the number and distribution of intense scatterers in the target's echo can be estimated. SCR (signal-to-clutter ratio) can be improved efficiently by integration of these intense scatterers in corresponding resolution cells. Experimental results show that the radar's detection performance can be improved significantly by using the presented algorithm.

To meet the increasing need of modern ballistic missile countermeasure, it becomes more and more important to study chaff cloud's scattering characteristics in outer space more accurately. A coherent scattering model is presented to depict the polarization scattering process of chaff cloud in outer space instead of the traditional noncoherent model. Chaff cloud's polarization scattering matrix and RCS formulae are derived. These formulae reflect the fluctuation law of chaff cloud's RCS due to the variation of cloud's spatial distribution.