激光电容半桥串联谐振充电电源研究

在重复率脉冲固体激光器中,由于储能电容需要频繁的充放电,通常采用谐振充电电路以适应其负载的大范围变化。为此研制了开关频率为20kHz,充电电流为2.1A,最高充电电压为1.86kV的半桥串联谐振充电电路。该电路工作于电流断续模式,开关管的开通和关断均为软开关。通过对周期电压、电流递推公式的分析,表明该工作模式中每个周期的平均充电电流均为恒定。应用递推公式计算稳态和暂态谐振电容电压和电流,结果显示暂态最大工作电压是稳态最大电压的2倍,暂态最大电流为稳态最大峰值电流的1.5倍,为谐振电容和开关管的选取提供了依据。     

Remote sensing of suspended sediments and shallow coastal waters

Ocean color sensors were designed mainly for remote sensing of chlorophyll concentrations over the clear open oceanic areas (Case 1 water) using channels between 0.4-0.86 /spl mu/m. The Moderate Resolution Imaging Spectroradiometer (MODIS) launched on the National Aeronautics and Space Administration Terra and Aqua spacecrafts is equipped with narrow channels located within a wider wavelength range between 0.4-2.5 /spl mu/m for a variety of remote sensing applications. The wide spectral range can provide improved capabilities for remote sensing of the more complex and turbid coastal waters (Case 2 water) and for improved atmospheric corrections for ocean scenes. We describe an empirical algorithm that uses this wide spectral range to identify areas with suspended sediments in turbid waters and shallow waters with bottom reflections. The algorithm takes advantage of the strong water absorption at wavelengths longer than 1 /spl mu/m that does not allow illumination of sediments in the water or a shallow ocean floor. MODIS data acquired over the east coast of China, west coast of Africa, Arabian Sea, Mississippi Delta, and west coast of Florida are used.     

Maximum likelihood, least squares, and penalized least squares for PET

The EM algorithm is the basic approach used to maximize the log likelihood objective function for the reconstruction problem in positron emission tomography (PET). The EM algorithm is a scaled steepest ascent algorithm that elegantly handles the nonnegativity constraints of the problem. It is shown that the same scaled steepest descent algorithm can be applied to the least squares merit function, and that it can be accelerated using the conjugate gradient approach. The experiments suggest that one can cut the computation by about a factor of 3 by using this technique. The results are applied to various penalized least squares functions which might be used to produce a smoother image.     

The imperative for medical simulation

The practice of medicine has, for millennia, relied upon a master-apprentice system of learning, with patients providing the necessary anatomy from which one learns how to perform surgery and other procedures. The advent of high-power computing and real-time graphics representations allows medicine to advance beyond this traditional methods of teaching and to begin to educate physicians without putting patients at risk. With innovative haptics interface devices, computer-based training will enable novice physicians to learn procedures that have been developed since their training was completed. Specialty boards and credentialing organizations will, for the first, time, have metrics upon which to base the decisions regarding who is qualified to practice medicine, and both sides of the learning curve, the acquisition of skills and their deterioration, will be discovered. The paper presents the concepts, challenges, and visions of the authors, both of whom have been actively developing simulation for the specialty of interventional radiology. It includes expectations for the future of simulation in other procedural specialties     

Earth Observing System AM1 mission to Earth

In 1998, NASA launches EOS-AMI, the first of a series of the Earth Observing System (EOS) satellites. EOS will monitor the evolution of the state of the earth for 18 years, starting with the morning observations of EOS-AM1 (10:30 a.m. equatorial crossing time). An integrated view of the earth, as planned by EOS, is needed to study the interchange of energy, moisture, and carbon between the lands, oceans, and atmosphere. The launch of EOS-AM1 and other international satellites marks a new phase of climate and global change research. Both natural and anthropogenic climate change have been studied for more than a century. It is now recognized that processes that vary rapidly in time and space-e.g. aerosol, clouds, land use, and exchanges of energy and moisture-must be considered to adequately explain the temperature record and predict future climate change. Frequent measurements with adequate resolution, as only possible from spacecraft, are key tools in such an effort. The versatile and highly accurate EOS-AM1 data, together with previous satellite records, as well as data from ADEOS, TRMM, SeaWiFS, ATSR, MERIS, ENVISAT, EOS-PM1, Landsat and ground-based networks is expected to revolutionize the way scientists look at climate change. This article introduces the EOS-AM1 mission and the special issue devoted to it. Following a brief historical perspective for an insight into the purpose and objectives of the mission, the authors summarize the characteristics of the five instruments onboard EOS-AM1. Specifically, they concentrate on the innovative elements of these five instruments and provide examples of the science issues that require this type of data     

PET regularization by envelope guided conjugate gradients

The authors propose a new way to iteratively solve large scale ill-posed problems and in particular the image reconstruction problem in positron emission tomography by exploiting the relation between Tikhonov regularization and multiobjective optimization to obtain iteratively approximations to the Tikhonov L-curve and its corner. Monitoring the change of the approximate L-curves allows the authors to adjust the regularization parameter adaptively during a preconditioned conjugate gradient iteration, so that the desired solution can be reconstructed with a small number of iterations.     

煤岩破坏电磁辐射信号的短时分形模糊滤波

介绍了短时分形滤波的基础理论,在分析煤岩破坏电磁辐射信号噪声特点基础上,提出了煤岩破坏电磁辐射信号的短时分形模糊滤波模型及分形维确定方法,并应用于型煤和原煤两种煤岩破坏电磁辐射信号的滤波处理.结果表明,短时分形滤波法用于煤岩破坏电磁辐射信号滤波是可行的,实现了煤岩破坏电磁辐射信号的自适应模糊控制滤波.     

Analysis of flow between a wafer and pad during CMP processes

In this paper, we summarize the development of a numerical model for the chemical mechanical planarization (CMP) process and experimentally investigate the effects of pad conditioning on slurry transport and mixing. A simplified two-dimensional numerical model of slurry flow beneath a stationary wafer was developed to determine the pressure and shear stress beneath a wafer. The initial results indicate that in the hydrodynamic regime a positive upward pressure is exerted on the wafer. We also examined three cases to study pad effects on slurry transport; polishing with an Embossed Politex pad, an unconditioned IC1000 pad, and a conditioned IC1000 pad. Cab-O-Sperse SC1 slurry was used in a 1:1.5 dilution with water. Mixing data show that conditioning has a negligible effect on the rate of slurry entrainment and mixing; however, conditioning has a large effect on the thickness of the slurry layer between the wafer and pad. Conditioning was found to increase the slurry thickness by a factor of two. In addition the gradients in slurry age beneath the wafer were compared among the three cases. The IC1000 pads supported a gradient in the inner third of the wafer only, while the Embossed Politex pad showed a linear gradient across the wafer implying it retains pockets of unmixed slurry in the embossed topography.     

United colors and untied meanings: Benetton and the commodification of social issues

The Benetton United Colors campaign illustrates how modern advertising has been radicalized into an explicitly political forum. Although lifestyle companies often attempt to associate their products with progressive social movements, Benetton was the first company to eliminate pictures of its products from its advertisements. In 1989, ads depicting Benetton's sportswear were replaced with powerful and problematic visual images of AIDS, environmental disasters, terrorism, and racism. Social issues became the embodiment of Benetton's product and, through the transformation into commodities, lost their significance as problematic human conditions. The campaign illustrates how the decontextualization of placing issues within the framework of product promotion, creates a tone of discordant meaning not adequately explained by mass culture critiques of consumerism. This case study recommends that advertising should be studied as a complex and contested social discourse within 1990s consumer culture.     

一种面向大面阵焦平面阵列的低功耗多功能读出电路设计

大面阵焦平面成像探测器需要具有随机开窗和反转读出功能,同时需要降低功耗。文章基于标准数字电路设计流程。设计了一种新型的基于格雷码编码规律的寻址计数器,用于对阵列的行地址和列地址进行寻址,提高了寻址的可靠性。对设计进行RTL级仿真,结果表明该设计能够实现任意开窗和反转读出功能。采用TSMC90工艺库对1024×1024阵列规模的RTL级设计进行分析计算,结果显示供电电压为3.3V时,寻址计数器功耗仅为19.56μW,整体设计功耗仅为58.75μW,适用于大面阵焦平面读出电路的设计。