Symbol Error Rate Performance of QS-CDMA over Frequency Selective Time Non-Selective Multipath Generalized Gamma Fading Channels

Quasisynchronous (QS) Code Division Multiple Access (CDMA) is currently being considered for a variety of wireless applications and services because QS-CDMA enables information transmission with a good quality of service. In this paper, for M-ary signaling, the Symbol Error Rate (SER) performance of QS-CDMA communication system with a maximal ratio combiner (MRC) over frequency-selective, time-nonselective multipath Generalized Gamma (GG3) fading channels is derived not only for any deterministic spreading sequences but also for any chip-limited chip waveforms, and it is investigated for Rectangular, Half-Sine, and Raised-Cosine chip waveforms by means of numerical and simulation results. Numerical and simulation results show that the performance of QS-CDMA is as good as or slightly better than synchronous CDMA (S-CDMA) when the maximum quasisynchronous delays do not need to be less than some specific values depending on the path power scattering. With this flexibility of quasisynchronous delays, both the transmitter and receiver complexities are reduced as quasisynchronous communication is a challenging task for researchers. Additionally, since not only the spreading sequences but also the partial autocorrelation functions of the chip waveform are influential on the performance of multipath QS-CDMA, a measure, Partial Power Ratio (PPR) is defined based on these partial autocorrelation functions in order to select or design a chip waveform for quasisynchronous communication. Furthermore, results show that QS-CDMA using the chip waveform whose PPR is greater has better performance.

Restoring Coastal Wetlands: The Californian Experience

Coastal wetlands are an important natural resource, providing habitat for fish and wildlife, particularly many rare or endangered species. These wetlands also serve important functions for the treatment of urban runoff and effluent discharges, the dissipation of wave energy, and shore protection. The US Fish and Wildlife Service estimates that approximately 45 000 km² of US wetlands have been destroyed in the past two centuries.
The importance of wetlands in the ecosystem has only begun to be understood during the past two decades, and there has been a major legislative effort to preserve, protect, and enhance existing coastal wetlands. The productivity of tidal wetlands is related directly to the hydrologic characteristics of the system, and some considerations for the hydrologic design for the enhancement or construction of tidal wetlands are outlined. Recent attention has focused on the use of dredged spoil materials from harbours or shippping channels to restore historic tidal wetlands. The hydrologic design criteria are illustrated through a series of case studies in California.     

Sensitivity of Field Data Estimates in One-Dimensional Hydraulic Modeling of Channels

A hydraulic simulation study was carried out for Red Hill Creek, an urban stream channel in Ontario, Canada. Over one million simulations were conducted using the HEC-RAS4b model to evaluate the sensitivity of model predictions to field data accuracy, density and estimation techniques and provide guidance toward balancing human resource allocation with model accuracy. Increased cross-sectional discretization and improved estimates of floodplain roughness dominate the accuracy of the results of computed water surface elevations. For a range of field hours available for data collection, a sampling strategy focused on maximizing the number of sparsely detailed cross sections is shown to outperform a sampling strategy using the same number of field hours to sample fewer cross sections with a higher resolution.     

Hydraulic Performance of a Steep Single Layer Riprap Drainage Channel

Highway drainage channels often approach slopes of 0.5 (50%). Single layer riprap-lined channels at this slope have been constructed for highway drainage and appear to perform satisfactorily, but no quantitative information is available to guide their hydraulic design. A 1/6 scale laboratory hydraulic model, using a single layer of sized crushed limestone, was constructed to determine the relationship between depth of flow and discharge. The flow range investigated took place at depths near or below the top of the riprap, since riprap instability occurred at greater depths. Standing waves and localized hydraulic jumps dominated the surface of the flow, which held streamwise-averaged Froude numbers in a narrow range near the critical condition for those flow depths for which the channel is designed. This resulted in a simple relationship between unit discharge and depth of flow that applies to the model and prototype channels.     

Semianalytical Model for Shear Stress Distribution in Simple and Compound Open Channels

Semianalytical equations were derived for distribution of shear stress in straight open channels with rectangular, trapezoidal, and compound cross sections. These equations are based on a simplified streamwise vorticity equation that includes secondary Reynolds stresses. Reynolds stresses were then modeled and their different terms were evaluated based on the work of previous researchers and experimental data. Substitution of these terms into the simplified vorticity equation yielded the relative shear stress distribution equation along the width of different channel cross sections. In compound channels the effect of additional secondary flows due to the shear layer between the main channel and the flood plain were also considered. Comparisons between predictions of the model and experimental data, predictions of other analytical or three dimensional numerical models with advanced turbulent closures, were made with good agreement.     

Numerical Simulation of Longitudinal and Lateral Channel Deformations in the Braided Reach of the Lower Yellow River

Bank erosion frequently occurs in the Lower Yellow River (LYR), playing an important role in the evolution of this braided river. A two-dimensional (2D) composite model is developed herein that consists of a depth-averaged 2D flow and sediment transport submodel and a bank-erosion submodel. The model incorporates a new technique for updating bank geometry during either degradational or aggradational bed evolution, allowing the two submodels to be closely combined. Using the model, the fluvial processes in the braided reach of the LYR between Huayuankou and Laitongzhai are simulated, and the calculated results generally agree with the field measurements, including the water-surface elevation, variation of water-surface width, and variations of cross-sectional profiles. The calculated average water-surface elevation in the study reach was 0.09?m greater than the observed initial value, and the calculated mean bed elevation for six cross sections was 0.11?m lower than the observed value after 24 days. These errors are attributed to the large variability of flow and sediment transport processes. Sensitivity tests of three groups of parameters are conducted, and these groups of parameters are related to flow and sediment transport, bank erosion, and model application, respectively. Analysis results of parameter sensitivity tests indicate that bank erodibility coefficient and critical shear stress for bank material are sensitive to the simulated bank erosion process. The lateral erosion distance at Huayuankou will increase by 19% as the value of bank erodibility coefficient changes from 0.1 to 0.3, and it will decrease by 57% as the value of critical shear stress for bank increases from 0.6 to 1.2?N/m2. Limited changes of other parameters have relatively small effects on the simulated results for this reach, and the maximum change extent of calculated results is less than 5%. Because the process of sediment transport and bank erosion in the braided reach of the LYR is very complicated, further study is needed to verify the model.     

Vulnerability-Based Risk Assessment for Stream Instability at Bridges

The Federal Highway Administration recommends that stream stability analyses at bridges over water begin with a Level 1 assessment. Following this assessment of the physical condition of the stream in the vicinity of the bridge, the user must determine whether or not the relative risk is low. If it is low, then no action is needed. If the risk is greater than low, then a Level 2 analysis is recommended; however, no method is given for determining the risk. In this paper, the relative risk of unsatisfactory conditions at bridge foundations is assessed as a simple function of vulnerability and criticality. Vulnerability is based on a stream stability assessment and data from the National Bridge Inventory (NBI). Criticality is determined indirectly as a function of the bridge serviceability and cost by using data extracted from the NBI. Relative risk is then qualitatively determined by combining vulnerability and criticality. Three examples in central Pennsylvania are provided in which the relative level of risk is used to determine the need for a Level 2 analysis.     

Design of Hydraulically Efficient Power-Law Channels with Freeboard

A power-law channel is a generalized form of the parabolic channel. The exponent of the governing equation is a variable that for certain maximum permissible side slopes can be determined by maximizing the cross-sectional area of flow (or minimizing the wetted perimeter). Using this exponent rather than the constant allows a hydraulically more efficient open channel section to be designed. In earlier work on power-law channels freeboard was neglected to simplify the analysis. However as pointed out by several authors, a channel without freeboard is of academic interest only and not practical. All open channels are in practice designed and constructed with freeboard as a factor of safety. In this paper freeboard has been introduced as an additional parameter to be taken into account when designing a power-law channel. The work from this paper is applied to an earlier example of a parabolic channel to demonstrate a practical design.     

双通道时延脉冲耦合神经网络的AOV-网拓扑排序

在时延脉冲耦合神经网络DPCNN的基础上提出了双通道时延脉冲耦合神经网络(DCDPCNN,Dual Channels DPCNN)模型,并提出了利用DCDPCNN来实现AOV-网拓扑排序算法。该算法在深度优先搜索的同时兼顾广度优先搜索,同时忽略节点进栈顺序,在求得的拓扑序列的个数、计算中的临时数据量、有向环判断、计算速度方面,比传统算法有了较大的改进。     

多总线的系统扩展方法

分析系统在多总线下的扩展。局部内存扩展（ＩＬＢＸ）总线、多通道Ｉ／Ｏ总线、系统扩展Ｉ／Ｏ（ＩＳＢＸＩ／Ｏ）总线在多总线中的作用和结构。最后讨论了多总线系统扩展方法、系统运用多总线的情况下，板上ＣＰＵ和多总线接口是如何占用双端口总线，对双端口总线，对双端口ＲＡＭ进行资源共享的。