无线传感器网络中一种能量有效的分簇算法

传感器网络中簇头与基站的通信方式可分为两种:多跳和单跳.如果采用多跳方式,靠近基站的簇头因传送数据较多而导致较早死亡;而在单跳方式中,远离基站的簇头因传送数据能耗太高而很快死亡.针对上述问题,提出一种基于非均衡分簇的数据收集算法,使靠近基站的簇的大小小于远离基站的簇.仿真实验表明,非均衡分簇的数据收集算法能有效地延长网络的生命周期.     

Oxygen distribution on a multicrystalline silicon ingot grown from upgraded metallurgical silicon

Oxygen precipitation creates centers of recombination of carriers. Therefore, oxygen concentration and its chemical configuration must be controlled. In this study, the oxygen distribution on a multicrystalline silicon ingot produced by directional solidification of upgraded metallurgical silicon is investigated. The highest amount of oxygen was detected close to the bottom of the ingot. Most of the oxygen present was interstitial but there were approximately 5-10 ppma oxygen present as precipitates. FT-IR and TEM confirmed the presence of many oxygen precipitates, mainly segregated at grain boundaries and dislocations. Lifetime measurements by QSSPC were performed on as grown- and passivated wafers, and after P-gettering. A correlation between the lifetime values and the presence of oxygen precipitates has been found and it has been shown that the electrical properties could be improved if an appropriate annealing step would be applied. Oxygen content may dramatically reduce the solar cell performances and efficiencies (estimated reduction of 1-3% absolute values).     

The risk of power loss in crystalline silicon based photovoltaic modules due to micro-cracks

Micro-cracks in wafer based silicon solar cell modules are nowadays identified by a human observer with the electroluminescence (EL) method. However, the essential question of how the micro-cracks affect the PV module performance has yet to be answered. We experimentally analyze the direct impact of micro-cracks on the module power and the consequences after artificial aging. We show that the immediate effect of micro-cracks on the module power is small, whereas the presence of micro-cracks is potentially crucial for the performance of the module after artificial ageing. This confirms the necessity to develop the means of quantifying the risk of power loss in PV modules with cracked solar cells in their lifetime, in order to enable manufacturers to discard defective modules with high risk of failure while keeping modules with uncritical micro-cracks. As a first step towards risk estimation we develop an upper bound for the potential power loss of PV modules due to micro-cracks in the solar cells. This is done by simulating the impact of inactive solar cell fragments on the power of a common PV module type and PV array. We show that the largest inactive cell area of a double string protected by a bypass diode is most relevant for the power loss of the PV module. A solar cell with micro-cracks, which separate a part of less than 8% of the cell area, results in no power loss in a PV module or a PV module array for all practical cases. In between approximately 12 and 50% of inactive area of a single cell in the PV module the power loss increases nearly linearly from zero to the power of one double string.     

Oscillator strengths of allowed transitions for O III

The electric dipole oscillator strengths for lines in O III between some singlet and triplet levels have been calculated using the weakest bound electron potential model theory and the quantum defect orbital theory. In the calculations, both multiplet and fine-structure transitions are studied. The calculated oscillator strengths have been compared with available theoretical and experimental results. Good agreement with results in the literature has been obtained.     

Porous silicon and aluminum co-gettering experiment in p-type multicrystalline silicon substrate

The lifetimes of non-equilibrium minority carriers, which bound with the diffusion length, are considered as two important parameters of the low-quality multicrystalline silicon (mc-Si) substrate. Its value defines the quality of the initial substrate. It is also subjected to change as a result of many high-temperature operations during the device fabrication. Therefore, it is necessary to incorporate certain processing steps that either improve or preserve the electronic quality of the mc-Si substrate. In this study, a novel porous silicon and aluminum co-gettering experiment has been applied as a beneficial approach to improve the electronic quality of the low-resistivity mc-Si substrates. Porous silicon layers were prepared by anodization of the n⁺ silicon region by a simple electrochemical etching process using an aqueous HF-based electrolyte, which leads to the creation of porous silicon microcavities. Besides making porous silicon and aluminum co-gettered samples, both phosphorous and aluminum alloy-gettered samples and reference samples were made. The gettering-induced lifetime enhancement in the test samples was monitored by measuring the lifetime/diffusion length of the test samples using two independent methods such as photoconductivity decay (PCD) measurement and the photocurrent generation method (PCM), respectively. The result in both the measurements has shown a reasonably good agreement with each other. Therefore, it is inferred that the applied co-gettering experiment has a synergetic effect to improve the lifetime of the mc-Si substrate.     

I: Dispersibility of robust alumina particles in non-aqueous solution

This article presents the preparation of well dispersed alumina slurries containing relatively large alumina particles that can withstand accelerated weather conditions. Besides using conventional dispersants such as phosphate esters and menhaden fish oil, dispersants widely used in the surface coatings industries such as Disperbyk 110 and Triton X 100 have also been employed. However, sedimentation tests, sediment density, viscosity and gloss measurements indicate the failure of the anionic dispersants as well as menhaden fish oil to disperse the alumina particles in non-aqueous medium. Instead the binder polyvinyl butyral itself acts as the best dispersant. The well dispersed alumina slurry is stabilized in the presence of a commercially available rheology modifier, Bentone SD2 for a period of 144 h at 60 °C. The rheological behavior of the aged sample was studied under various conditions. Although a rise in viscosity of the suspension was observed when the slurry was exposed to accelerated weather conditions, a lower shear thinning index and higher gloss values indicate a better dispersion state with aging.     

Yb2O3 and Gd2O3 doped strontium zirconate for thermal barrier coatings

Yb₂O₃ (10 mol%) and Gd₂O₃ (20 mol%) doped SrZrO₃ was investigated as a material for thermal barrier coating (TBC) applications. The thermal expansion coefficients (TECs) of sintered bulk Sr(Zr_0.9Yb_0.1)O_2.95 and Sr(Zr_0.8Gd_0.2)O_2.9 were recorded by a high-temperature dilatometer and revealed a positive influence on phase transformations of SrZrO₃ by doping Yb₂O₃ or Gd₂O₃. The results for the thermal conductivities of Sr(Zr_0.9Yb_0.1)O_2.95 and Sr(Zr_0.8Gd_0.2)O_2.9 indicated that both dopants can reduce the thermal conductivity of SrZrO₃. Mechanical properties (Young's modulus, hardness, and fracture toughness) of dense Sr(Zr_0.9Yb_0.1)O_2.95 and Sr(Zr_0.8Gd_0.2)O_2.9 showed lower Young's modulus, hardness and comparable fracture toughness with respect to YSZ. The cycling lifetimes of Sr(Zr_0.9Yb_0.1)O_2.95/YSZ and Sr(Zr_0.8Gd_0.2)O_2.9/YSZ double layer coatings (DLC), which were prepared by plasma spraying, were comparable to that of YSZ at operating temperatures <1300 °C. However, the cycling lifetime of Sr(Zr_0.9Yb_0.1)O_2.95/YSZ DLC was 25% longer, whereas Sr(Zr_0.8Gd_0.2)O_2.9/YSZ DLC had a shorter lifetime compared to the optimized YSZ coating at operating temperatures >1300 °C.     

Enhanced red emission in LiAl5O8:Fe phosphor by B doping

Fe³⁺, B³⁺ co-doping LiAl₅O₈ phosphor has been successfully synthesized by a solid-state reaction method assisted with wet chemical mixing route. Photoluminescence emission peak is observed at around 672 nm excited at both 290 nm ultraviolet and 565 nm green light. With introduction of a small amount of boric acid, the red emission intensity can be enhanced by 2.62 times under 290 nm excitation and 2.31 times under 565 nm excitation, respectively. It is believed that the substitution of B³⁺ ions for Al³⁺ sites decreases the symmetry of the luminescence center, intensifying the red emission.     

Load balancing techniques for lifetime maximizing in wireless sensor networks

Energy consumption has been the focus of many studies on Wireless Sensor Networks (WSN). It is well recognized that energy is a strictly limited resource in WSNs. This limitation constrains the operation of the sensor nodes and somehow compromises the long term network performance as well as network activities. Indeed, the purpose of all application scenarios is to have sensor nodes deployed, unattended, for several months or years.This paper presents the lifetime maximization problem in “many-to-one” and “mostly-off” wireless sensor networks. In such network pattern, all sensor nodes generate and send packets to a single sink via multi-hop transmissions. We noticed, in our previous experimental studies, that since the entire sensor data has to be forwarded to a base station via multi-hop routing, the traffic pattern is highly non-uniform, putting a high burden on the sensor nodes close to the base station.In this paper, we propose some strategies that balance the energy consumption of these nodes and ensure maximum network lifetime by balancing the traffic load as equally as possible. First, we formalize the network lifetime maximization problem then we derive an optimal load balancing solution. Subsequently, we propose a heuristic to approximate the optimal solution and we compare both optimal and heuristic solutions with most common strategies such as shortest-path and equiproportional routing. We conclude that through the results of this work, combining load balancing with transmission power control outperforms the traditional routing schemes in terms of network lifetime maximization.     

环形器在少子寿命测试仪中的应用研究

针对少子寿命测试仪中存在的信号较弱导致的测试结果重复性较低的问题,先对矩形波导中微波的传输特性进行了理论分析。然后对测试仪中关键传输耦合模块魔T进行了研究。研究发现微波在魔T中的传播导致了大量能量的损失,严重削减了信噪比。环流器的特性很好地弥补了魔T的不足,既保证了微波正常的传输耦合又提高了装置中微波的能量利用率,保证了信噪比。用环流器替代魔T并进行改进后,测试结果重复性由原来的7%提升至3%