长期贮存对填充聚乙烯机械性能的影响

研究填充塑料在人工和自然环境下长期贮存后的性能具有极大的实际意义。在贮存聚合物及其制品时,会出现材料的静力疲劳变态—使聚合物及其制品性能改变的老化。本报道介绍了填充的和未填充的低压聚乙烯管状试样经仓库贮存不同时间后机械性能研究的结果。在工作中采用了鉴定评价法。管材是由低压聚乙烯、10％石棉填充聚     

高浓度二氧化硫以工业用氧在沸腾层转化器氧化

使用工业用氧焙烧铜精矿和黄铁矿精矿可得到高浓度二氧化硫(50%—90%SO_2)的炉气。在接触法硫酸生产中用氧来氧化,过程可增强3—7倍,并直接制得100%SO_3和65%发烟硫酸。在固定层转化器进行此过程,对于从触媒层排出热和在过剩氧很小时氧化二氧化硫,都有一定的困难。而且设备体积大,管理和操作复杂。至于循环法仅适于处理洁净的SO_2和O_2(不少于99%)。     

纳米粒子/环氧树脂复合材料的固化动力学研究

在纳米Al2O3、Si3N4、SiC填充环氧树脂复合材料体系中,纳米粒子表面活性及粒子与环氧树脂之间的相互作用影响着环氧树脂的固化过程.本文利用傅立叶红外光谱表征了纳米粒子与环氧树脂之间的化学作用情况,并利用差视扫描量热仪研究了不同纳米粒子/环氧树脂复合材料的固化动力学.结果表明,具有相对最强表面活性的纳米Al2O3粒子与基体之间的相互作用最强,同时该粒子对环氧树脂固化过程的促进作用最显著.     

立方型状态方程结合Eyring理论在液体混合物黏度计算中的应用

Cubic equations of state (EOS) have been combined with the absolute rate theory of Eyring to calculate viscosities of liquid mixtures. A modified Huron Vidal gE-mixing rule is employed in the calculation and in comparison with the van Laar and the Redlich-Kister-type mixing rule. The EOS method gives an accurate correlation of liquid viscosities with an overall average deviation less than 1% for 67 binary systems including aqueous solutions. It is also successful in extrapolating viscosity data over a certain temperature range using parameters obtained from the isotherm at a given temperature and in predicting viscosities of ternary solutions from binary parameters for either polar or associated systems.     

磺酰脲除草剂与土壤的关系

自1975年杜邦公司George Levit博士发现磺酰脲类除草剂以来,已经成为一类主要的新颖除草剂,并促进化学除草技术的重大进步。目前世界范围内,共有8种磺酰脲除草剂已经商品化(表1),估计到九十年代中期会成倍增加,它们具有前所未有的除草活性,其使用量从千克/公顷惊人地下降到克/公顷。如今,甲黄隆每年用量为2～8克/公顷,使用200年也不过相当于过去传统除草剂一次使用量(1～4千克/公顷)。杀草谱广、用量低、对作物又有较大选择性,这些都是磺酰脲除草剂迅速成功的重要因素。同样重要的,它具有令人称     

用buprofezin和其他昆虫生长调节剂防治棉田害虫

苯甲酰苯基脲类化合物杀虫活性的发现揭示了化学防治公害的新途径.第一个商品化的化合物除虫脲能干扰昆虫蜕皮过程,因而作为昆虫生长调节剂使用.其主要作用方式为摄入,对某些昆虫也可通过触杀而起作用.其部分活性似乎与对于几丁质形成的生物化学过程的抑制作用有关.对于更有前途的酰脲化合物的探索工作得到了三个对农业害虫较除虫脲有更高活性的新型化合物:石原公司的chlorfluazuron、Calemerck公司的teflubenzuron     

Assessment of response function in two PET scanners with and without interplane septa

The authors have assessed the response function both experimentally and theoretically for two commercial tomographs: CTI 931/08-12 and CTI 953B with and without interplane septa. Monte Carlo simulations were undertaken using the GEANT package from CERN. Spatial resolution (tomographic and axial) was calculated for line sources at various positions in the field of view. Sensitivity and scatter fraction (SF) were calculated for various source geometries as a function of energy discrimination. A very realistic response function in positron emission tomography (PET) is obtained by Monte Carlo methods, using global parameters to account for unsimulated phenomena such as scintillation light transport inside a detector block and its sharing among the various phototubes. Minor discrepancies remain for sensitivity and SF at high energy thresholds and may probably be explained by introducing the observed dispersion in the energy response for the various crystals within a detector block.     

Noise equivalent count measurements in a neuro-PET scanner with retractable septa

The noise-equivalent count-rate (NEC) performance of a neuro-positron emission tomography (PET) scanner has been determined with and without interplane septa on uniform cylindrical phantoms of differing radii and in human studies to assess the optimum count rate conditions that realize the maximum gain. In the brain, the effective gain in NEC performance for three-dimensions (3-D) ranges from >5 at low count rates to approximately 3.3 at 200 kcps (equivalent to 37 kcps in 2-D). The gains of the 3-D method assessed by this analysis are significant, and are shown to be highly dependent on count rate and object dimensions.     

Sequencing of multi‑robot behaviors using reinforcement learning

Given a collection of parameterized multi-robot controllers associated with individual behaviors designed for particular tasks, this paper considers the problem of how to sequence and instantiate the behaviors for the purpose of completing a more complex, overarching mission. In addition, uncertainties about the environment or even the mission specifications may require the robots to learn, in a cooperative manner, how best to sequence the behaviors. In this paper, we approach this problem by using reinforcement learning to approximate the solution to the computationally intractable sequencing problem, combined with an online gradient descent approach to selecting the individual behavior parameters, while the transitions among behaviors are triggered automatically when the behaviors have reached a desired performance level relative to a task performance cost. To illustrate the effectiveness of the proposed method, it is implemented on a team of differential-drive robots for solving two different missions, namely, convoy protection and object manipulation.     

自动称重装置的国际建议

一、目的与回顾本文回顾自动称重装置国际建议发展的过程,并对已采纳的新建议的一些部分做说明。这些建议由OIML TC9/SC分会负责,秘书处仍为UK（NW/ML）（即英国、国家称重和测量实验室）。该工作始于1963年,当时为了非连续累计称重的需要,首次纳入国际建议。之后,原有的三个建议：R50皮带秤、