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991.
992.
采用激光烧结的原理加工三维(3D)功能化零件, 利用高性能的Nd∶YAG激光器(波长1.06 μm)和光学系统, 通过计算机高精度控制的喷嘴送粉、数控平台配合运动, 在光束焦点处烧结粉状颗粒, 层状生长, 加工生长出由二种金属粉末组成的合金钢管零件。此激光辅助加工系统的主要难点在于激光加工头的设计与加工, 给出了激光加工头的机械结构, 送粉喷嘴的结构设计和整个激光辅助加工系统的总体布局。整个加工过程通过友好的人机界面, 由UG软件设计的每个3D部分的界面层依次切片, 然后在加工平台上一层层的堆砌起来。零件通过金相法观测其金属组成分布, 并利用微硬度仪检测钢管垂直方向上的微硬度分布, 结果表明钢管的微硬度分布完全取决于材料组分的分布, 证明了此激光辅助加工系统制造功能化零件的实用性。 相似文献
993.
P.Y. Emelie S. Velicu C.H. Grein J.D. Phillips P.S. Wijewarnasuriya N.K. Dhar 《Journal of Electronic Materials》2008,37(9):1362-1368
The general approach and effects of nonequilibrium operation of Auger-suppressed HgCdTe infrared photodiodes are well understood.
However, the complex relationships of carrier generation and dependencies on nonuniform carrier profiles in the device prevent
the development of simplistic analytical device models with acceptable accuracy. In this work, finite element methods are
used to obtain self-consistent steady-state solutions of Poisson’s equation and the carrier continuity equations. Experimental
current–voltage characteristics between 120 K and 300 K of HgCdTe Auger-suppressed photodiodes with cutoff wavelength of λ
c = 10 μm at 120 K are fitted using our numerical model. Based on this fitting, we study the lifetime in the absorber region, extract
the current mechanisms limiting the dark current in these photodiodes, and discuss design and fabrication considerations in
order to optimize future HgCdTe Auger-suppressed photodiodes. 相似文献
994.
The proliferation of wireless technologies and services has intensified the demand for the radio spectrum. However, the currently existing fixed spectrum assignment policy leads to an inefficient and unevenly distributed spectrum utilization. Cognitive radio paradigm has been proposed to alleviate these drawbacks by employing dynamic spectrum access (DSA) methodology. Federal Communications Commission (FCC) has proposed the interference temperature model, which enables the unlicensed users to utilize the licensed frequencies simultaneously with the licensed users as long as they conform to the interference temperature constraints. Recently, throughput and delay optimal schedulers that meet the interference temperature constraints in cognitive radio networks have been formulated in the literature. However, these schedulers have high computational complexity. In this paper, we propose genetic algorithm (GA)‐based suboptimal methods addressing these throughput and delay optimal scheduling problems. The simulation results corroborate that our GA‐based approach yields very close performance to the optimal solutions and operates with much lower complexity. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
995.
996.
Ilja Vladimirov Sebastian Müller Roelf‐Peter Baumann Thomas Geßner Zahra Molla Souren Grigorian Anna Khler Heinz Bssler Ullrich Pietsch Ralf Thomas Weitz 《Advanced functional materials》2019,29(12)
The fundamental nature of charge transport in highly ordered organic semiconductors is under constant debate. At cryogenic temperatures, effects within the semiconductor such as traps or the interaction of charge carriers with the insulating substrate (dipolar disorder or Fröhlich polarons) are known to limit carrier motion. In comparison, at elevated temperatures, where charge carrier mobility often also decreases as function of temperature, phonon scattering or dynamic disorder are frequently discussed mechanisms, but the exact microscopic cause that limits carrier motion is debated. Here, the mobility in the temperature range between 200 and 420 K as function of carrier density is explored in highly ordered perylene‐diimide from 3 to 9 nm thin films. It is observed that above room temperature increasing the gate electric field or decreasing the semiconducting film thickness leads to a suppression of the charge carrier mobility. Via X‐ray diffraction measurements at various temperatures and electric fields, changes of the thin film structure are excluded as cause for the observed mobility decrease. The experimental findings point toward scattering sites or traps at the semiconductor–dielectric interface, or in the dielectric as limiting factor for carrier mobility, whose role is usually neglected at elevated temperatures. 相似文献
997.
State-of-the-art devices in the consumer electronics market are relying more and more on Multi-Processor Systems-On-Chip (MPSoCs) as an efficient solution to meet their multiple design constrains, such as low cost, low power consumption, high performance and short time-to-market. In fact, as technology scales down, logic density and power density increase, generating hot spots that seriously affect the MPSoC performance and can physically damage the final system behavior. Moreover, forthcoming three-dimensional (3D) MPSoCs can achieve higher system integration density, but the aforementioned thermal problems are seriously aggravated. Thus, new thermal exploration tools are needed to study the temperature variation effects inside 3D MPSoCs. In this paper, we present a novel approach for fast transient thermal modeling and analysis of 3D MPSoCs with active (liquid) cooling solutions, while capturing the hardware-software interaction. In order to preserve both accuracy and speed, we propose a close-loop framework that combines the use of Field Programmable Gate Arrays (FPGAs) to emulate the hardware components of 2D/3D MPSoC platforms with a highly optimized thermal simulator, which uses an RC-based linear thermal model to analyze the liquid flow. The proposed framework offers speed-ups of more than three orders of magnitude when compared to cycle-accurate 3D MPSoC thermal simulators. Thus, this approach enables MPSoC designers to validate different hardware- and software-based 3D thermal management policies in real-time, and while running real-life applications, including liquid cooling injection control. 相似文献
998.
介绍了裂解炉工作中对炉管表面温度掌握的重要性,利用比色测温理论对炉管温度进行监测的方法,以及CCD的光电特性对于曝光量的要求。通过对几组标定温度与计算温度的比较得出温度T的计算方法,并通过实验证实用这种测温方法的可行性。 相似文献
999.
大功率LED热问题是制约大功率 LED的稳定性、可靠性和寿命的技术瓶颈之一,有效的低热阻封装LED热设计是提高LE D性能的关键。本文提 出一种应用于大功率LED散热的铜-水回路热管(LHP),研究了加热方 式、充液率、风压和倾角 等对LHP均温性、起动性和热阻等的影响。研究结果表明:在输入功率为30W时,LHP的启动时间约为 6.5min;热阻范围为0.48~1.62K/W;在热 负荷为30W时,蒸发器的温度可以稳定控制在75℃以下;蒸发器表 面均温差被控制在1.6℃以下;LHP的最佳的充液率为60%;冷凝器侧 风压在一定范围内(小于130Pa)时,冷凝器侧风压力越大,LED产 品的散热性能越好。 相似文献
1000.
用冠层温度计算作物缺水指标的一种简化模式 总被引:10,自引:1,他引:10
本文对Jacskon等人提出利用作物冠层温度计算作物缺水指标的模式进行了简化,并根据甘肃民勤县棉花和宁夏吴忠春小麦的田间试验资料进行了验证,结果表明该简化模式可用于诊断作物缺水状况。 相似文献