N.m.r. study of the ferroelectric phase transition in a 7030mol% copolymer of vinylidene fluoride (VF2) and trifluoroethylene (TrFE)

Nuclear magnetic resonance (n.m.r.) studies of ¹⁹F nuclei in a $\text{70}\text{30}\text{mol}\text{\%}$ random copolymer of vinylidene fluoride and trifluoroethylene were performed at 9.14 MHz and 20.0 MHz. The free induction decays (FIDs) were analysed in terms of two T₂ components attributed to the amorphous and crystalline portions of the polymer. The changes in crystallinity as well as the effects of the ferroelectric transition were observed during cycles of heating and cooling between 20°C and 140°C. The crystalline component of the FID lengthens by a factor of 2 at 100°C on heating and decreases by this factor at 60°C on cooling, thus exhibiting the thermal hysteresis of this ferroelectric transition. The spin-lattice relaxation was also investigated. From measurements at 9.14 MHz the observed longitudinal relaxation time T₁ appears to be dominated by the dynamics of the amorphous phase and exhibits no anomaly through the phase transition. However, from measurements at 20 MHz, well defined minima of T₁ were observed, which are associated with the ferroelectric transition (especially after repeated annealing of the samples). Results are discussed in terms of the crystalline phase structure, which appears dynamically disordered above the ferroelectric phase transition. An analogy is considered with the plastic phase transitions encountered in molecular crystals.     

Means of enhancing and promoting the use of solar energy

The development of renewable technologies in the last decade has been exceptional. In photovoltaic (PV) for example, efforts were not only limited to merely improving their efficiency but also to the reduction of the cost of cells and modules via volume production for commercial markets. There are many national schemes promoting the use of PV technology and regional targets for a share of renewable energy production. This paper attempts to relay to the reader a journey, based on experience, approaches for enhancing the prospect of utilising solar energy within the society we live in. The issue of expansion or enhancing the utilisation of solar energy can be undertaken by individuals, groups, institutions and governments. The aim of this paper is to provide some examples, which could serve as a framework in which action could be taken to promote solar technology.     

3G中的QoS结构及无线资源分配策略

在3G（第3代移动通信系统）中，为了给不同类型的业务提供不同级别的端到端QoS，网络资源必须进行合理分配。QoS和资源分配是密不可分的，而无线资源分配显得尤为重要。文中提出了UMTS的QoS结构，分3部分对空中接口部分的QoS（即无线资源分配策略问题）进行了讨论：首先提出了一种RRA算法，接着讨论了W－CDMA和TD－CDMA系统的无线资源分配问题，最后讨论了下行链路及上行链路的呼叫允许控制（CAC）。     

杜84断块超稠油开发中后期稳产对策研究

对杜84断块超稠油生产中后期暴露的主要矛盾，即随着轮次升高，周期吞吐效果变差，井下技术状况日益变差。油层动用不均，汽窜加剧等问题进行了分析。并提出了相应的稳产对策-实施多井整体吞吐，大修复产，调剖等措施。现场应用证明，这些措施基本能够确保杜84断块超稠油中后期的稳产。     

纺织品在农业上的应用和发展

在现代农业中纺织品占有重要地位 ,它的广泛使用大大促进了农业科技的发展。农业纺织品可广泛应用在农田水土保持、排水灌溉、保护植物和促进植物生长、温室大棚 (包括遮阳降温、储能保温材料 )、农用覆盖材料、植物生长基质材料等方面 ,本文将就农用纺织品在一些领域的应用加以介绍。     

A stochastic maximum principle for systems with jumps, with applications to finance

We consider a stochastic control problem with linear dynamics with jumps, convex cost criterion, and convex state constraint, in which the control enters the drift, the diffusion, and the jump coefficients. We allow these coefficients to be random, and do not impose any L^p-bounds on the control.

We obtain a stochastic maximum principle for this model that provides both necessary and sufficient conditions of optimality. This is the first version of the stochastic maximum principle that covers the consumption–investment problem in which there are jumps in the price system.     

Upgrading coal-derived liquids to diesel fuel

Distilled fractions of a coal-derived liquid from the H-Coal process were upgraded to diesel fuel by catalytic hydrotreatment. The total hydrotreated products were distilled into naphtha (<180°C) and diesel fuel fractions (>180°C) and the diesel fractions were analysed for hydrocarbon-type composition, hydrogen content and some diesel fuel properties. GC—MS-analyses were carried out on the hydrocarbon-type fractions to identify individual chemical compounds. To investigate the effect of different distillation cut points on diesel fuel yield and properties, cut points for one hydrotreated product were varied. The diesel fuel cetane numbers were correlated with percentage hydrogen, total aromatics and saturates. Cetane numbers above 40 were obtained for diesel fuels containing (i) more than 75% saturates, (ii) less than 15% total aromatics and (iii) a hydrogen content above 12.8%. Compounds identified by GC—MS-analyses (in the diesel fractions) were typical aromatic and cycloparaffin compounds. Normal-and iso-paraffin compounds were not detected. By varying the distillation cut point from 135 to 180°C, the cetane number of the residual diesel fraction improved from 37 to 44. This increase is ascribed to the removal of aromatic compounds in the 135–180°C boiling point range.     

Treatment of Humic Waters By Ozone

Two different generators for ozone were tested, a traditional electrical discharge generator and a generator based upon UV–irradiation of air at 150–180 nm. It was demonstrated that the traditional generator gave slightly higher reductions in levels of color for equivalent ozone dosages. Both gases affected the molecular weight distribution in the way that the bigger molecules were broken down to smaller ones. No significant difference between the molecular weight reduction efficiency of the gases was found.     

HHD型核子秤电离室物理性能检测

HHD型核子秤电离室已成功地使用于HCS型核子秤.对它的各种物理性能指标进行了检测,各项性能指标都达到了设计要求。     

Ultrasonic measurement of the inter-electrode gap in electrochemical machining

During the process of electrochemical machining the dependency of the inter-electrode gap with time and process parameters can be used to determine process characteristics and to define the shape of the workpiece surface relative to the tool surface. Defining process variables to map out the required gap-time function requires the use of time-consuming iterative trials. In-line monitoring of the gap would enable process control and tool to workpiece transfer characteristics to be achieved (for ideal conditions) without the requirement to generate such parameter maps. This work explores the use of ultrasound applied as a passive, non-intrusive, in-line gap measurement system for ECM. The accuracy of this technique was confirmed through correspondence between the generated gap-time and current time data and theoretical models applicable to ideal conditions. Gap measurements are also used to demonstrate and quantify the degree of departure from ideal behaviour for an In718/chloride system as the electrolyte flow rate is reduced from 16 to 4 l min⁻¹. The monitoring of the gap size has also been shown to be effective when determining shape convergence under ideal conditions, for the example case of a 2D sinusoidal profile.