无线传感器网络中影响能源消耗的因素的研究

在传感器网络中,电源能量是各个节点最宝贵的资源。为了使传感器网络的使用时间尽可能地长,必须合理有效地利用能量。该文从无线传感器网络的体系结构出发,对影响网络能源消耗的因素进行了研究。     

Selective Idling: Experiments in Transport Layer Energy Conservation

In this paper we consider the potential of using an aggressive form of energy conservation for mobile computing environments. The estimators for the round-trip time and round-trip time variance used by TCP are used to direct the transceiver of a mobile node to idle over extended periods of time when packet activity is not anticipated. In addition, we consider data link layer extensions that provide additional control information allowing the mobile to be further selective as to when to idle and when to activate the network interface device. Simulations are conducted to examine the performance of the proposed scheme under various levels of congestion in the fixed part of the network, from completely unloaded to fully congested. The simulations reveal that the technique is promising but its effectiveness depends crucially on the control of the maximum window size used by TCP and on accurate knowledge of the congestion conditions in the network.     

一个农户生态经济系统的分析

对沈阳市桃仙镇荒山子村一个农户生态经济系统进行分析,结果表明：该农户正处于从传统农业向现代农业的过渡阶段,经济效益较好,整体技术水平和生态效益低,后两了该农户的进一步发展,以目前的生产水平,应采取户与户联合,取得规模效益,以当前农业产业化的发展。     

Estimation of energy expenditure in a work environment: Comparison of accelerometry and oxygen consumption/heart rate regression

The aim of this study was to compare estimation of energy expenditure (EE) in working environments, either from accelerometry or from an individual oxygen consumption/heart rate ([Vdot]O₂/HR) regression curve. The study participants were 46 volunteer workers aged 27±6 years old. A significant correlation between EE predicted by the [Vdot]O₂/HR curve and the accelerometer was observed (r=0.78, p <0.01). However, more disparities were observed between the two methods when the mean job intensity was not within 16% and 23% higher than resting HR. The accelerometer overestimated by a mean of 34.4% the prediction by [Vdot]O₂/HR regression if the intensity of the task was lower than a total of 1000 kcal/shift and underestimated the prediction by a mean of –24.9% if EE estimation of the work shift was higher than a total of 1500 kcal/shift. Despite a high correlation between both methods in the whole group, EE evaluated by accelerometry does not correspond to EE predicted by the [Vdot]O₂/HR regression curves when evaluated individually.     

Energy flux characteristics of seismic waves at the interface between soil layers with different saturations

Based on the multiphase poroelasticity theory describing the propagation of waves in the unsaturated fluid-saturated porous medium, the reflection and transmission coefficients of the seismic waves at the interface between soil layers with different saturations are obtained. Our unsaturated model consists of a deformable skeleton in which two compressible and viscous fluids (i.e., water and gas) flow in the interstices. Three compressional waves (i.e., P1, P2, and P3 waves) and one shear (i.e., S wave) wave exist in the unsaturated soils. The expressions for the energy ratios of the various reflected and transmitted waves at the interface during the transmission and reflection processes are presented in explicit forms accordingly. At last, numerical computations are performed and the results obtained are respectively depicted graphically. The variation of the energy ratios with the incident angle, wave frequency and saturation degrees of the upper and lower soil layers is illustrated in detail. The calculation results show that the allocation of incident seismic waves at the interface is influenced not only by the angle and frequency of the incident seismic waves, but also by the saturations of the upper and lower soil layers. It is also verified that, at the interface, the sum of energy ratios of the reflected and transmitted waves is approximately equal to unity as was expected. This study is of importance to several fields such as geotechnical engineering, seismology, and geophysics.     

数字式三相智能电能表的研制

介绍了一款基于单片机Atmega128的三相数字式智能电能表的研制,从电路硬件选型、电路设计及制作进行论述。所设计的智能电能表与同类产品相比具有集成度高、功能强、成本更低廉、抗干扰能力强、功耗低等优点。随着未来电能智能化管理及电能表集抄需求,该款表具有很大的应用前景。     

电能质量智能在线监测系统设计

论述了电能质量问题的内容及其对电力系统的影响,设计了一种基于嵌入式技术的电能质量在线监控系统,给出了系统的硬件结构图和软件结构图及流程图,进行了样机的功能性验证试验,证明该系统对于构成具有智能化的监控及通信系统具有一定的应用价值。     

Residual strength prediction of multiple cracked stiffened panels

Prediction of the coalescence of adjacent cracks is critical for residual strength estimation of structures under multiple site damage conditions. A methodology successfully developed for the case of crack link‐up prediction of un‐stiffened plates, is extended for the case of typical cracked stiffened aircraft panels. The proposed link‐up criterion is based on the change in the magnitudes of elastic and plastic strain energies of the stiffened panel, before and after the cracks coalesce. The strain energy magnitudes of interest are calculated using non‐linear elastic–plastic finite‐element analysis. For the application and verification of the method, experimental results from the open literature are used. Residual strength values calculated by the proposed methodology are in good agreement with the experimental results. The present criterion provides superior results when compared to the existing and commonly applied link‐up criteria.     

Energy transfer mechanism of GdPO4: RE3+ (RE = Tb, Tm) under VUV-UV excitation

Polycrystal of GdPO₄:RE³⁺ (RE=Tb, Tm) phosphors were prepared by solid-state method. Vacuum ultraviolet excitation and emission spectrum and the energy transfer mechanism between the host and dopants of Tb³⁺ and Tm³⁺ were investigated respectively. The emission of Gd³⁺ at 313 nm was enhanced by the strong absorption of CTS of Tm³⁺ at 180 nm in GdPO₄: Tm. It has also been concluded that the excitation of Gd³⁺ is transferred to Tb³⁺ and then emission peaks of ⁵D_J→⁷F_J of Tb³⁺ were observed.     

户用PV系统设计

由于能源短缺和环境污染的问题日益严重,改善能源结构,保护环境,已成为我国在新世纪经济发展高速期所面临的重要课题。尤其是在居住建筑中,采用清洁、储量巨大、无地域限制和能源质量高等诸多优点的太阳能,成为近些年国内研究的热点,引起了各界的关注和重视,科研院所、相关企业等部门都在积极的探索和实践。本文介绍一种户用太阳能光伏发电系统(又称PV系统)的计算流程,仅供参考。