大学生网络购物行为研究

互联网的普及为网络购物奠定了良好的基础,网上银行以及现代物流业务的日趋频繁也为网络购物产业发展开拓了良好的市场。大学生网上购物行为已成为时尚,如何看待大学生网上消费,对该现象进行简要的分析和研究是十分必要的。     

A direct position determination method with combined TDOA and FDOA based on particle filter

The localization of a stationary transmitter using moving receivers is considered. The original Direct Position Determination (DPD) methods, with combined Time Difference of Arrival (TDOA) and Frequency Difference of Arrival (FDOA), do not perform well under low Signal-to-Noise Ratio (SNR), and worse still, the computation cost is difficult to accept when the computational capabilities are limited. To get better positioning performance, we present a new DPD algorithm that proves to be more computationally efficient and more precise for weak signals than the conventional approach. The algorithm partitions the signal received with the same receiver into multiple non-overlapping short-time signal segments, and then uses the TDOA, the FDOA and the coherency among the short-time signals to locate the target. The fast maximum likelihood estimation, one iterative method based on particle filter, is designed to solve the problem of high computation load. A secondary but important result is a derivation of closed-form expressions of the Cramer-Rao Lower Bound (CRLB). The simulation results show that the algorithm proposed in this paper outperforms the traditional DPD algorithms with more accurate results and higher computational efficiency, and especially at low SNR, it is more close to the CRLB.     

Development of a coupled supersonic inlet-fan Navier–Stokes simulation method

A coupled supersonic inlet-fan Navier–Stokes simulation method was developed by using COMSOL-CFD code. The flow turning, pressure rise and loss effects across blade rows of the fan and the inlet-fan interactions were taken into account as source terms of the governing equations without a blade geometry by a body force model. In this model, viscous effects in blade passages can also be calculated directly, which include the exchange of momentum between fluids and detailed viscous flow close to walls. NASA Rotor 37 compressor test rig was used to validate the ability of the body force model to estimate the real performance of blade rows. Calculated pressure ratio characteristics and the distribution of the total pressure, total temperature, and swirl angle in the span direction agreed well with experimental and numerical data. It is shown that the body force model is a promising approach for predicting the flow field of the turbomachinery. Then, coupled axisymmetric mixed compression supersonic inlet-fan simulations were conducted at Mach number 2.8 operating conditions. The analysis includes coupled steady-state performance, and effects of the fan on the inlet. The results indicate that the coupled simulation method is capable of simulating behavior of the supersonic inlet-fan system.     

晚清衡州教案特点述评

鸦片战争后,西方传教士搭乘殖民主义列车闯入中国,从事精神上的殖民活动。由于这些活动与中国传统的道德文化相抵触,加之传教士的种种不法行为,从而引发了一系列的教案。其中在衡州发生的教案最具特色,它与全国的反侵略斗争紧密相联,具有较为浓厚的政治、经济斗争色彩,并且得到了地方官绅的支持与响应。这些特点使其地位突出,激发基层民众的爱国热情,推动全国反帝爱国运动的进一步发展。     

浅谈降低国内航空复合材料结构成本的途径

从20世纪60年代末至今,先进树脂基复合材料(以下简称复合材料)以其轻质、高强、抗疲劳等优异性能及耐腐蚀、可设计、易于整体成型等特点,在航空领域得到极大的推崇.     

从IP组播数据中断故障谈网络地址设计

首先描述了在IP网络环境中出现的组播数据偶断现象,分析定位了故障出现的原因。然后,详细阐述了组播维护机理,从组播管理协议的运行机制上进一步分析了组播数据偶断的过程。最后,给出了通过网络地址重新设计的方法解决问题的方案,并提出了交换机、路由器-VLAN（虚拟局域网）-主机的网络地址按顺序进行由小到大地分级分配的原则。     

Reactant jetting in unstable detonation

We note the common existence of a supersonic jet structure locally embedded within a surrounding transonic flow field in the hitherto unrelated phenomena of unstable gaseous detonation and hypervelocity blunt body shock wave interaction. Extending prior results that demonstrate the consequences of reduced endothermic reaction rate for the supersonic jet fluid in the blunt body case, we provide an explanation for observations of locally reduced OH PLIF signal in images of the keystone reaction zone structure of weakly unstable detonations. Modeling these flow features as exothermically reacting jets with similarly reduced reaction rates, we demonstrate a mechanism for jetting of bulk pockets of unreacted fluid with potentially differing kinetic pathways into the region behind the primary detonation front of strongly unstable mixtures. We examine the impact of mono-atomic and diatomic diluents on transverse structure. The results yield insight into the mechanisms of transition and characteristic features of both weakly and strongly unstable mixtures.     

液冷模块的热仿真分析

运用基于CFD的热仿真软件Flotherm对液冷模块进行了热仿真分析,分别研究了在不同环境温度,不同冷却液流量以及不同冷却液温度条件下,液冷模块内部温度场的变化规律。仿真分析结果表明,环境温度对液冷模块的温度场影响非常小;液冷模块冷却液流量的增幅与元器件温度的降幅并非正比关系;元器件温度的升幅与冷却液温度的增幅相同。     

新型弹簧床结构的HAN基发动机技术

为改善硝酸羟胺(HAN)基发动机催化剂在长时间工作的工况下容易发生破碎而产生空穴的现象，本文提出一种新型弹簧床结构发动机设计方法，对发动机催化床进行改进优化设计。该设计可实现，常温环境下弹簧所提供的最大弹力不足以压碎催化剂；同时在高温环境下，弹簧的最小弹力足以克服催化床受到的流动阻力，可大幅提高发动机工作寿命、性能和可靠性。为验证该设计方法的有效性，分别开展了传统结构和新型弹簧床结构的HAN基1N发动机温启动试验。试验结果表明：在相同试验条件下，传统结构1N发动机温启动次数不超过150次，而使用新型弹簧床结构的1N发动机温启动次数超过了500次，且工作性能更优。试验结果证明了该设计方法的有效性，为HAN基发动机长寿命可靠工作奠定了良好的技术基础。