基于协同簇与模糊评判的无线传感器网络转发协议

提出一种基于协同簇的无线传感器网络转发协议CCRD。CCRD将传输路径上分布密集的节点组成多跳协同簇,进而使数据沿着多跳协同簇向信宿传递,并通过簇间的协同配合来保证转发的成功率和减少冗余发送能耗。每跳协同簇是通过分布式模糊综合评判与优先级竞争相结合的机制动态选出的,此机制能有效降低竞争过程中簇间的冲突概率,提高下一跳的选择效率。对CCRD的性能进行了理论计算与分析,实验结果表明,CCRD在保证端到端可靠转发的同时有效提高了数据的转发能效。

WSNs中一种基于EIETX的自适应功率控制的机会路由

为了延长无线传感器网络(WSNs)的生存时间,提出了一种基于EIETX的自适应功率控制的机会路由协议APExOR。考虑节点剩余能量,改进了IETX,给出基于EIETX的转发候选集选择策略;分析节点间链路状况,建立起相关的转发能效模型,提出了一种自适应优化转发候选集和发射功率的算法;利用以上策略和算法改进ExOR协议,提出了适合WSNs的APExOR协议。仿真实验表明:与固定功率下的ExOR协议相比,APExOR协议提高了网络吞吐量,降低了网络的能量消耗。

Multistage Stack with Multiple Pore Radii Applying the Temperature Gradient to a Thermoacoustic Engine

Conventional thermoacoustic engines have a stack pore radius that is almost constant in the axial direction. Hence, a thermoacoustic engine is expected to improve the energy conversion efficiency using a multistage stack with multiple pore radii. The stack comprises several bundles of numerous narrow tubes with specified pore radii. The optimum pore radius of the stack is determined by the oscillation frequency and the temperature in the stack. Consequently, the suitable pore radius changes in the axial direction, because the temperature gradient exists along the stack axis. Therefore, a multistage stack with multiple pore radii is introduced, which achieves a desired optimum pore radius everywhere in the stack. The energy conversion efficiency of the multistage stack, which was studied experimentally for a straight-tube type thermoacoustic engine, was compared with that of a conventional single-stage stack. In these experiments, the improvement of the energy conversion efficiency was confirmed. A numerical method with the transmittance matrix to include the effect of a multistage stack was used, and good agreement between experimental and numerical results was obtained. The results make a future possibilities for stack design intended to higher thermoacoustic engine efficiency expect.

Experimental Study on Load Characteristics in a Floating Type Pendulum Wave Energy Converter

A floating type pendulum wave energy converter(FPWEC) with a rotary vane pump as the power take-off system was proposed by Watabe et al.in 1998.They showed that this device had high energy conversion efficiency.In the previous research,the authors conducted 2D wave tank tests in regular waves to evaluate the generating efficiency of FPWEC with a power take-off system composed of pulleys,belts and a generator.As a result,the influence of the electrical load on the generating efficiency was shown.Continuously,the load characteristics of FPWEC are pursued experimentally by using the servo motors to change the damping coefficient in this paper.In a later part of this paper,the motions of the model with the servo motors are compared with that of the case with the same power take-off system as the previous research.From the above experiment,it may be concluded that the maximum primary conversion efficiency is achieved as high as 98%at the optimal load.

Concentration quenching in transparent glass ceramics containing Er^(3+):NaYF_4 nanocrystals

In this work, we have studied the concentration quenching in transparent glass ceramics containing Er^3＋：NaYF4 nanocrystals. For different concentrations, the emission spectra and decay curves of the ^4I/3/2 → ^4I15/2 emission were measured. The Er-concentration dependence of integrated intensity and lifetime of ^4I13/2→^4I15/2 emission are showed. With the increase of the Er^3＋ doping concentration, the 1.5 μm fluorescence emission first increases, then decreases, and the lifetime falls gradually. With 980 nm excitation, the efficiency of the energy transfer from Er^3＋ to quenching centers reaches 73.73% for the sample with 4 mol% Er^3＋. Meanwhile, owing to the relation of fluorescence integrated intensity and Er-concentration, a dipole-dipole quenching mechanism in the framework of a limited diffusion regime has been proved. Using the limited diffusion case, the critical concentration for quenching has been determined from a fitting equation of the lifetime and Er-concentration. The fit- ting result shows the critical concentration for quenching is higher than the values obtained in Er-doped different glass by an order of magnitude.

Boosting solar steam generation by structure enhanced energy management

Interfacial solar-steam generation is a promising and cost-effective technology for both desalination and wastewater treatment.This process uses a photothermal evaporator to absorb sunlight and convert it into heat for water evaporation.However solar-steam generation can be somewhat inefficient due to energy losses via conduction,convection and radiation.Thus,efficient energy management is crucial for optimizing the performance of solar-steam generation.Here,via elaborate design of the configuration of photothermal materials,as well as warm and cold evaporation surfaces,performance in solar evaporation was significantly enhanced.This was achieved via a simultaneous reduction in energy loss with a net increase in energy gain from the environment,and recycling of the latent heat released from vapor condensation,diffusive reflectance,thermal radiation and convection from the evaporation surface.Overall,by using the new strategy,an evaporation rate of 2.94 kg m^-2 h^-1,with a corresponding energy efficiency of solar-steam generation beyond theoretical limit was achieved.

Development of small-molecule materials for high-performance organic solar cells

With the rapid development in recent years, small-molecule organic solar cell is challenging the dominance of its counterpart, polymer solar cell. The top power conversion efficiencies of both single and tandem solar cells based on small molecules have surpassed 9%. In this mini review, achievements of small molecules with impressive photovoltaic performance especially reported in the last two years were highlighted. The relationship between molecular structure and device performance was analyzed, which draws some rules for rational molecular design. Five series of p- and n-type small molecules were selected based on the consideration of their competitiveness of power conversion efficiencies.

Characteristic of Local Boiling Heat Transfer of Ammonia and Ammonia/Water Binary Mixture on the Plate Type Evaporator

Power generation using small temperature difference such as ocean thermal energy conversion(OTEC)and discharged thermal energy conversion(DTEC)is expected to be the countermeasures against global warming problem.As ammonia and ammonia/water are used in evaporators for OTEC and DTEC as working fluids,the research of their local boiling heat transfer is important for improvement of the power generation efficiency.Measurements of local boiling heat transfer coefficients were performed for ammonia/water mixture(z=0.9-1)on a vertical flat plate heat exchanger in a range of mass flux(7.5-15 kg/m2s),heat flux(15-23 kW/m 2),and pressure(0.7-0.9 MPa).The result shows that in the case of ammonia/water mixture,the local heat transfer coefficients increase with an increase of mass flux and composition of ammonia,and decrease with an increase of heat flux.