Ka频段ATC-OFDM传输体制的性能分析

分析了Ka频段移动信道特性,建立了Ka频段自适应Turbo编码-OFDM传输体制（ATC-OFDM）,并提出了3种自适应方案和相应算法。通过新传输体制中的自适应功率、自适应调制和自适应功率调制同固定分配功率和调制方案的TC-OFDM传输体制相比,在不同的天气环境下,其系统误码性能有着明显的改善。系统的吞吐量在信噪比大于8dB时,相比于BPSK调制,可提高2bps/Hz,验证了该传输体制的可行性和有效性。     

四氢萘催化裂化研究进展

加氢处理油中含有一定量的环烷基单环芳烃,研究四氢萘催化裂化有利于加强对更多环数环烷基单环芳烃催化裂化的认识。综述了四氢萘催化裂化过程的反应机理,认为四氢萘主要遵循单分子裂化机理;从反应活化能、扩散、吸附等动力学角度对四氢萘裂解行为进行了解释;催化剂适宜的孔径和BrØnsted酸强度有利于四氢萘开环;随着反应温度升高、剂/油质量比增大、质量空速减小,四氢萘反应活性增强,同时氢转移反应愈发明显。适宜的催化剂孔径和Brnsted酸强度、反应温度、剂/油质量比以及质量空速有利于四氢萘裂化生成低碳烯烃。     

过偏晶Cu-40%Pb合金凝固组织的深过冷细化

利用电磁模拟微重力设备获得S(Pb)均匀分布的过偏晶Cu-40%Pb合金实验样品,然后用熔融玻璃净化与循环过热相结合获得熔体深过冷的方法,对上述获得的均质化实验样品进行深过冷快速凝固实验和凝固组织演化规律的研究.结果表明:经过深过冷技术进行二次处理试样的凝固组织中,随着过冷度的增加弥散的S(Pb)比模拟微重力环境下得到的S(Pb)明显细化.     

基于EZW的水下作战环境应用产品压缩研究

如何有效利用海军数据链系统传输战术水声环境产品是海军作战环境保障的关键问题之一.然而,战术水声环境数据具有较强的时空变化性,其数据量相对来说较为庞大,且在实际作战环境中,传输信道存在着各种干扰,特别是在海洋战场环境中,通信传输条件较差,传输时间紧迫,致使图像信息的传输容易受到外部因素的非正常干扰甚至中断,从而影响用户端对图像信息的接收.因此.寻求一种不依赖于通信时间和其它外部情况限制町随时结束编码实现数据压缩与渐进传输的编码方法是作战环境信息处理的一项必不可少的工作.运用目前较为先进的嵌入式小波零树编码算法对战术水声环境数据进行压缩,取得了较好的压缩效果,并在此基础上实现了图像的渐进传输,能够较好的适应复杂海洋战场的需求.     

Bithalamic hyperintensity on T2-weighted MR: vascular causes and evaluation with MR angiography

PURPOSE: To determine whether MR angiography can be used to differentiate between the two vascular causes of bithalamic hyperintensity on T2-weighted MR images: "top of the basilar" artery occlusion and deep cerebral vein thrombosis. METHODS: A retrospective review identified six patients with bithalamic T2 hyperintensity of vascular causes. MR angiography was performed in four patients, MR angiography and conventional angiography in one patient, and conventional angiography in one patient. Data pertaining to clinical presentation and hospital course were collected. MR angiographic techniques were multislab overlapping three-dimensional time-of-flight, 2-D time-of-flight, and 2-D phase-contrast. RESULTS: Three cases of top of the basilar artery occlusion and three cases of deep cerebral vein thrombosis were recognized. In all cases, T2 hyperintensity in a vascular distribution suggested cerebral occlusive disease. Infarction involving the thalami and basal ganglia was present in two cases of deep cerebral vein thrombosis. Infarction of the thalami, mesodiencephalic region, and cerebellar hemispheres was present in two cases of basilar artery occlusion. Bithalamic infarction alone was seen in one case of deep cerebral vein thrombosis and one case of basilar artery occlusion. In the five cases in which MR angiography was used, this technique accurately distinguished the vessels involved (arterial or venous). CONCLUSION: MR angiography is a useful adjunct to MR imaging in the evaluation of bithalamic T2 hyperintensity. It does help distinguish between the two vascular causes: top of basilar artery occlusion and deep cerebral vein thrombosis.     

Medical specialists prefer to withdraw familiar technologies when discontinuing life support

OBJECTIVE: To assess how members of different specialties vary in their decisions about which form of life support to withdraw. The hypothesis was that each specialty would be more comfortable withdrawing its "own" form of life support relative to other forms and other specialties. DESIGN: Mail survey. SETTING: 24 medical centers. PARTICIPANTS: 225 specialists in six specialties and 225 comparison physicians randomly matched according to percentage of time devoted to clinical practice. MEASUREMENTS: The six specialties were linked with six life-sustaining technologies related to their special expertise: 1) pulmonologists with mechanical ventilation, 2) nephrologists with hemodialysis, 3) gastroenterologists with tube feedings, 4) hematologists with blood products, 5) cardiologists with intravenous vasopressors, and 6) infectious disease specialists with antibiotics. The subjects ranked different forms of life support in the order in which they would prefer to withdraw them. They also expressed their preferences in response to hypothetical clinical vignettes. RESULTS: In five of the six specialties, the specialists had a relative preference for withdrawing their "own" form of life support, compared with the preferences of the comparison physicians. Overall, the physicians tended to prefer withdrawing a form of life support closely linked with their own specialty. CONCLUSIONS: Just as some specialist physicians tend to reach for different technologies first in treating patients, they also tend to reach for different technologies first when ceasing treatment. Specialists' preferences for different ways to withdraw life support not only may reflect a special understanding of the limits of certain technologies, but also may reveal how ingrained are physicians' patterns of practice.     

Effect of contrast concentration on abdominal enhancement in the rabbit: spiral computed tomography evaluation

BACKGROUND: Langerhans' cell histiocytosis (LCH) is an uncommon, poorly understood granulomatous disease, characterized by the idiopathic proliferation of Langerhan's cells or their marrow precursors. In 1985, the Philadelphia Work-shop adopted the term "Langerhans' cell histiocytosis" (LCH) to differentiate it from reactive and neoplastic causes of histiocytosis. METHODS: This study includes 73 pediatric patients diagnosed with this condition in Dublin, Ireland, and Nottingham, England, during a 34-year period (1959 to 1993). These patients are reviewed with respect to clinical presentation, difficulty with making a histological diagnosis, their management, and outcome. RESULTS: A total of 49 patients (67%) had head and neck involvement. Bony involvement was the most frequent sign, most frequently located in the skull. There were 11 deaths (15%) in this series, all associated with multisystem disease, and nine of these deaths were in children younger than 2 years of age. CONCLUSIONS: The role of otolaryngologists is important in the early and accurate evaluation, staging, and diagnosis of LCH. It may mimic more common diseases, such as otitis externa, acute mastoiditis, skin rash, gingivitis, or cervical lymphadenopathy. Patients with multisystem disease may be so ill at presentation that the head and neck lesions may be overlooked. The current management of LCH has become increasingly conservative, and in the 1990s, fewer cases are given chemotherapy or radiotherapy. The prognosis is very good for single-system disease and poor for multisystem disseminated disease with early onset.     

视场非完全重叠的分布式雷达多目标跟踪方法

在探测能力、波形设计及天线指向等因素制约下,分布式雷达视场并非完全重合,由此造成的观测信息差异给后续信息融合带来了巨大挑战。该文基于高斯混合实现的集势概率假设密度(CPHD)滤波器,提出了一种视场部分重叠下的分布式雷达多目标跟踪方法。首先,利用多目标密度乘积切分出概率假设密度(PHD)中表征共同观测信息的部分;之后,标准的分布式融合(算术平均或几何平均融合)方法作用于切分出的共同观测目标信息以提升跟踪性能,补偿融合则作用于雷达单独观测目标信息以扩展视场范围。该文方法无须视场先验信息,能够适应雷达视场未知时的分布式融合多目标跟踪场景。仿真实验验证了所提出方法在未知、时变雷达视场下跟踪多目标的性能,表明了该文方法比基于高斯混合的聚类方法性能更好。      

硅基单结太阳能电池的制备技术、缺陷及其性能的研究

首先综述了硅基单结太阳能电池的分类、制备方法及进展,介绍了化学气相沉积法、液相外延法(LPPE)、金属诱导结晶法(MIC)、磁控溅射法以及分子束外延法等各种硅基太阳能电池的制备方法,阐述了各种制备工艺的优缺点。其次,总结了单晶硅、多晶硅以及非晶硅太阳能电池在组织结构、缺陷方面的研究现状。最后,对硅基太阳能电池的机械、电学、光学以及光电性能等方面的研究进展做了论述。     

高性能混凝土结构在热带海洋环境下的服役寿命

近些年,高性能混凝土以其高强度,高抗渗性、抗冻融性、耐腐蚀性的特点得到了越来越广泛的应用。本文通过实验所得数据,简要分析了高性能混凝土在南海热带海洋环境下对混凝土结构服役寿命的影响。结果表明:运用高性能混凝土能大幅度延长混凝土结构的使用寿命。对于港口、防波堤等结构,在热带海洋环境下按照现行规范《水运工程混凝土施工规范》(JTS 202-2011)中规定的最小保护层厚度(65mm)进行设计,不能达到50年的寿命要求,必须增加保护层的厚度至75mm,或者施加附加防护措施,才能满足寿命要求。