Generating NC tool paths from random scanned data using point-based models

This paper presents a new approach for the generation of NC tool paths from random scanned data. Instead of using smooth or triangulated surfaces reconstructed from raw data, which is usually a time-consuming reverse engineering approach, the point-based surfel models computed by a GPU (graphics processing unit) are used to generate NC tool paths. The tool-path generation is highly efficient and still maintains the advantage of having accurate and smooth machining result. The word “surfel” itself is the combination of the two words “surface” and “element”. It is originally applied to the rendering of scanned data. In this paper, the point-based model is created using an elliptical Gaussian re-sampling filter that is based on a signal re-sampling algorithm. Since the input scanned data is of discrete and random nature, the warping process is utilized to transform the input data into a continuous surface and then re-sample the continuous surface by using GPU. Because the re-sampled data can accurately represent the original surface, tool paths can be generated based on the point data set. For cutting tools with various sizes, adaptive re-sampling schemes are employed to generate sufficient sampled points for the generation of accurate and smooth tool-paths.     

Suprathermal plasma analyzer for the measurement of low-energy electron distribution in the ionosphere

It is commonly believed that an energy transfer from thermal to suprathermal electrons (相似文献   

多病床非典病房的气流分布研究

到2003年8月7日止，在全球34个国家和地区相继出现了严重急性呼吸系统综合症(SARS或者非典)，其中，共报告有8422例疑似案例，916例死亡案例。2002年11月到2003年6月间的非典流行中，医院医护人员受感染情况最为严重，世界范围内20％的感染群体为医护人员，香港地区22％的确诊案例为医护人员。因此，为减少交叉感染，加强有关工程控制，特别是在非典病房里进行通风设计是非常必要的。本文总结了非典病房气流分布的最新研究。这项研究由非典特工队于2003年4～7月间完成。非典特工队是由香港工程师协会组织，来自7个专家协会的工程师组成的研究小组。在对香港治疗非典医院的现有空调系统进行了解后，非典特工队首先运用计算流体力学模拟确定了在6个床位的病房里减少交叉感染和改善污染物稀释的通风设计；接着，对新设计在香港大学屋宇设备实验室里的全尺寸非典病房里进行了测试。测试表明，新设计方案在这个接近现实的全尺寸非典病房里运行良好。采用床头回风口回风设计可有效地对病人产生的含病毒颗粒进行局部捕获。根据这项研究，作者提出了原则性的设计建议。2003年里，香港政府和医院管理局医院采纳了非典特工队提出的设计基本原理建造了1200多个床位的可用于非典治疗的新病房。另外，气流分布是复杂的紊流过程，送风格栅结构如导流器或散流器的微小改动以及送风参数如风速、温度和风向的微小变化都会引起气流的改变。适当的设计对于减少病人间、病人与医护人员之间的交叉感染以及有效稀释和排除含病菌颗粒都是至关重要的。     

On Radiant Network Models of Thermocouple Error in Pre and Post Flashover Compartment Fires

Thermocouples are often used to obtain gas temperature measurements in compartment fires. Such measurements are subject to a thermal lag during fire growth, but the main problem is a steady-state error induced by radiant heat transfer at the thermocouple surface. This error is sensitive to thermal parameters of the flame, compartment structure, thermocouple surface and combustion products; and is also influenced by the size and position of both the flame and thermocouple. The literature contains models of varying sophistication to enable an assessment of steady-state error. A model is now proposed that makes use of the concept of radiosity. Developed from radiant network theory, the model can be applied to both pre-flashover and post-flashover conditions. Experiments have been performed using different sizes of thermocouple and the models compared. The simpler models pre-date the more sophisticated and predict much larger errors than the latest published and current versions.     

Hot-carrier degradation of submicrometer p-MOSFETs withthermal/LPCVD composite oxide

It is shown that while gate oxides containing thermal/LPCVD composite oxide have lower defect densities than gates using only thermal oxides, they are more susceptible to hot-carrier degradation. The hot-carrier-induced degradation of composite oxides is worse in p-channel MOSFETs than in n-channel MOSFETs. This sensitivity of p-channel MOSFETs is caused by higher electron trapping levels in LPCVD oxides. For 150-Å gate technology, the hot-carrier-degradation resistance of thermal/LPCVD composite gate oxides with a 70-Å or thicker thermal oxide layer approaches that of high-quality pure thermal oxide     

High efficiency ultra-thin sputtered CdTe solar cells

Large scale manufacturing of CdTe PV modules at the GW/yr level may be constrained due to the limited availability of the relatively rare (Te) element and the volume of potentially hazardous (Cd) material being used in the typically 3–8 μm thick CdTe absorber layer. However, we find that it is possible to reduce the CdTe layer thickness without much compromise in efficiency. The CdS/CdTe solar cells were fabricated using magnetron sputtering with ultra-thin CdTe layers in the range of 0.5–1.28 μm. The ultra-thin films and cells were characterized using X-ray diffraction (XRD), optical transmission, scanning electron microscopy (SEM), current–voltage and quantum efficiency measurements. These results were compared with those of standard 2.3 μm thick CdTe sputtered cells. Different post-deposition processing parameters were required for cells with ultra-thin and standard CdTe thicknesses to achieve high efficiency. Ultra-thin CdTe cells showed crystallographic texture and CdTe_1−xS_x alloy formation after CdCl₂ treatment very similar to standard CdTe cells. Optimization of the post-deposition CdCl₂ treatment and back-contact processing yielded cells of 11.2% efficiency with 0.7 μm CdTe compared to 13.0% obtained with standard 2.3 μm CdTe cells.     

Sputtered Cd1−xZnxTe films for top junctions in tandem solar cells

Cd_1−xZn_xTe alloy films with 1.6 and 1.7 eV band gaps were deposited by RF magnetron sputtering from targets made either of mixed powders or alloys of CdTe and ZnTe (25% and 40%). High-quality polycrystalline films with the (1 1 1) preferred orientation were obtained. The films were characterized using X-ray diffraction (XRD), scanning electron microscopy, resistivity, optical absorption, Raman, and photoluminescence. The EDS, XRD, and optical absorption analysis indicated that the x-value of the as-grown films were typically 0.20 and 0.30 for films sputtered from 25% and 40% ZnTe containing targets, respectively. The as-deposited alloy films exhibit quite low photovoltaic performance when used to make cells with CdS as the hetero-junction partner. Therefore, we have studied various post-deposition treatments with vapors of chlorine-containing materials, CdCl₂ and ZnCl₂, in dry air or H₂/Ar ambient at 390 °C. The best performance of a Cd_1−xZn_xTe cell (, ) was found for treatment with vapors of the mixed CdCl₂+0.5%ZnCl₂ in an H₂/Ar ambient after pre-annealing at 520 °C in pure H₂/Ar.     

An efficient algorithm for superresolution in medium field imaging

In this paper, we study the problem of reconstruction of a high-resolution (HR) image from several blurred low-resolution (LR) image frames in medium field. The image frames consist of blurred, decimated, and noisy versions of a HR image. The HR image is modeled as a Markov random field (MRF), and a maximum a posteriori (MAP) estimation technique is used for the restoration. We show that with the periodic boundary condition, a HR image can be restored efficiently by using fast Fourier transforms. We also apply the preconditioned conjugate gradient method to restore HR images in the aperiodic boundary condition. Computer simulations are given to illustrate the effectiveness of the proposed approach. This research was conducted with support from the Army Research Office Grant DAAD 19-03-1-0261 and the National Science Foundation Grant CCF-0429481. Research supported in part by RGC Grant Nos. 7130/02P, 7046/03P, 7035/04P and 7035/04P and FRG/04-05/II-51.     

Immersive electronic books for surgical training

Immersive electronic books (IEBooks) for surgical training will let surgeons explore previous surgical procedures in 3D. The authors describe the techniques and tools for creating a preliminary IEBook, embodying some of the basic concepts.     

On the robustness of parameter estimation of superimposed signalsby dynamic programming

We analyze a recently proposed dynamic programming algorithm (REDP) for maximum likelihood (ML) parameter estimation of superimposed signals in noise. We show that it degrades gracefully with deviations from the key assumption of a limited interaction signal model (LISMO), providing exact estimates when the LISMO assumption holds exactly. In particular, we show that the deviations of the REDP estimates from the exact ML are continuous in the deviation of the signal model from the LISMO assumption. These deviations of the REDP estimates from the MLE are further quantified by a comparison to an ML algorithm with an exhaustive multidimensional search on a lattice in parameter space. We derive an explicit expression for the lattice spacing for which the two algorithms have equivalent optimization performance, which can be used to assess the robustness of REDP to deviations from the LISMO assumption. The values of this equivalent lattice spacing are found to be small for a classical example of superimposed complex exponentials in noise, confirming the robustness of REDP for this application