几种新型分子筛对催化裂化汽油的改质性能研究

在固定床微反装置上,对比考察了几种新型分子筛材料对催化裂化汽油的催化改质反应性能及β沸石在不同反应温度下的催化反应规律。结果表明,β沸石具有较好的异构化和芳构化能力,并随反应温度的升高,其裂解和芳构化能力逐渐增强,异构烃产率逐渐降低;工业低硅ZSM-5型分子筛的裂化活性较强;催化裂化汽油经改质后其烯烃含量均有所降低,且辛烷值基本不变。     

A high-capacity wireless network by quad-sector cell andinterleaved channel assignment

We propose an improved sectorization scheme, called narrow-beam quad-sector cell (NBQC) for cellular networks, in which each cell is divided into four sectors and each sector is covered by a 60° antenna. The NBQC structure allows easy implementation of the concept of interleaved channel assignment (ICA), which can take full advantage of antenna directivity. With ICA, the NBQC system can enhance the system performance from several perspectives. First, the NBQC has better coverage performance than the current three-sector cellular architecture. Second, we demonstrate that in a typical radio environment, the NBQC system ran achieve a reuse cluster size N=2 with the signal-to-interference ratio (SIR) as high as 11 dB in 90% of the cell area, which is a 3-5-dB improvement over the existing cellular architectures. Third, as compared to the most advanced three-sector clover-leaf cell architecture with reuse cluster size N=3, the NBQC system with ICA can achieve reuse cluster size N=2 with very slight degradation in SIR performance, thereby still improving the system capacity by about 10% over a wide range of ninetieth percentile SIR requirements     

Epidemiology of falls among the elderly community dwellers in Singapore

AIM: Falling is a serious medical problem for elderly persons. This study was done to look at prevalence and risk factors for falls in community dwelling elderly in Singapore. METHOD: A random sample of 3,000 persons aged 60 years and above was chosen from a database based on the 1990 population census. Letters were sent out to 2,582 subjects who had local and complete addresses. In the letter, they were informed about the purpose of the survey, and invited to participate in a questionnaire and clinical health screening at an appointed date at a polyclinic. Participants were reminded the day before their appointment by telephone, and a new appointment could be given at the subject's convenience. RESULTS: We found a prevalence rate of falls of 17.2%. Two-thirds of these had single falls, while one-third had recurrent falls, defined as having more than one fall within the previous one year. The following factors were found to be significantly associated with increase falling in the elderly: age > or = 75 years (O.R. = 1.82, 95% C.I. 0.95-3.50), female sex (O.R. = 2.5, 95% C.I. 1.40-4.48), Malay race (O.R. = 2.66, 95% C.I. 1.21-5.86), poor vision (O.R. = 1.7, 95% C.I. 0.99-2.90), Barthel's score of less than 20 (O.R. = 1.76, 95% C.I. 0.94-3.28), those taking 2 or more drugs daily (O.R. = 2.1, 95% C.I. 1.22-3.72) and the presence of hypertension (O.R. = 1.78, 95% C.I. 1.06-3.01). Fall rate is also twice as high in women as in men. At the same time, we found that women in the group we studied also tend to exercise less than the men. Fallers also had significantly more mobility and activities of daily living (ADL) disabilities (reflected by a lower Barthel's score) and this is consistent with other results. The only factor that reduced the risk of falling was regular exercise (O.R. = 1.64, 95% C.I. 0.93-2.93). CONCLUSION: In our study, we found differences between the group with single and recurrent falls. In the group with single falls, the fall tend to occur outdoors (O.R. = 2.97, 95% C.I. 1.03-8.60) and during the day (O.R. = 3.47, 95% C.I. 1.20-10.0), tend to be accidental (O.R. = 3.16, 95% C.I. 1.05-9.50) and tend to seek medical attention (O.R. = 3.68, 95% C.I. 1.23-11.0). Overall, 32 persons (46.4%) seek medical treatment after their falls, and of these, 65.6% were women. Risk factors for falls should be screened for all elderly.     

高速高阶可编程数字滤波技术与实现

本文讨论了频率范围宽,连续可调的高速高阶数字滤波技术及其工程实现。运用IMSA100级联信号处理技术和8097BH单片机可编程控制技术,实现了数字滤波中心频率在50～500000Hz,数字滤波归一化带宽在7‰～5%范围内连续可变的功能。应用该技术所研制的数字滤波设备在卫星测控遥测系统中获得了良好的效果。     

含各向异性介质的三维不均匀涡流场有限元法计算

本文用有限元法分析、计算含各向异性介质的三维不均匀涡流场。按加权余量法导出了对应的等价变分式及矢量磁位的三个分量式。采用三棱柱单元离散,研究出系数矩阵建立的方法并导出上机计算公式。     

Fuzzy concepts in expert systems

The authors present a comprehensive expert-system building tool, called System Z-II, that can deal with exact, fuzzy (or inexact), and combined reasoning, allowing fuzzy and normal terms to be freely mixed in the rules and facts of an expert system. This fully implemented tool has been used to build several expert systems in the fields of student curriculum advisement, medical diagnosis, psychoanalysis, and risk analysis. System Z-II is a rule-based system that uses fuzzy logic and fuzzy numbers for its inexact reasoning. It uses two basic inexact concepts, fuzziness and uncertainty, which are distinct from each other in the system     

国内外工业炉发展趋势

介绍了６０年代中期以来，由于冶金工厂轧制设备生产能力的不断提高、对坯料或产品加热质量的严格要求、不定形耐火材料的发展和节省能源的要求，以及计算机技术的发展所导致的国内外工业炉在设计、炉型、砌筑、环保和热工过程控制等方面的发展趋势。     

Simplified power control method for cellular mobile communication

The centralised power control (CPC) method measures the gain of the communication links between every mobile and every base station in the cochannel cells and determines optimal transmitter power to maximise the minimum carrier-to-interference ratio. The authors propose a simplified power control method which has nearly the same performance as the CPC method but which involves much smaller measurement overhead     

A syntax-directed translation for the synthesis ofdelay-insensitive circuits

A syntax-directed translation procedure for the synthesis of delay-insensitive circuits from graph-theoretic specifications is presented. No isochronic fork assumption is required for the correct operation of the synthesized circuits. The synthesized circuits are different from those obtained from Ebergen's synthesis method. In Ebergen's circuits, the voltage levels of a set of wires are used to encode which input events are most recently received. Special circuit elements (the N-element or the RCEL element) and two-phase to four-phase converters are needed to change the voltage levels of the encoding wires when input events are received. In the circuits obtained from the method in this paper, the wires encoding which input events are most recently received are the outputs of the toggles. When input events are received, they are sent directly or via demultiplexers to the toggles to change the voltage levels at their outputs. Two-phase to four-phase converters are not needed. The synthesis method is compared with Ebergen's synthesis method