Knowledge acquisition, modelling and inference through the World Wide Web

The development of knowledge-based systems involves the management of a diversity of knowledge sources, computing resources and system users, often distributed geographically. The knowledge acquisition, modelling and representation communities have developed a wide range of tools relevant to the development and management of large-scale knowledge-based systems, but the majority of these tools run on individual workstations and use specialist data formats making system integration and knowledge interchange very problematic. However, widespread access to the Internet has led to a new era of distributed client–server computing. In particular, the introduction of support forformson World Wide Web in late 1993 has provided an easily programmable, cross-platform graphic-user interface that has become widely used in innovative interactive systems. This article reports on the development of open architecture knowledge management tools operating through the web to support knowledge acquisition, representation and inference through semantic networks and repertory grids.     

A closed form solution for the G/M/r machine interference model

This paper solves the machine interference problem in which N different machines are looked after by a team of r operatives. The run time of each machine is assumed to have a general distribution, different for each machine and the repair times are assumed to have a negative exponential distribution with different means for the different machines. An explicit expression for the probability that a particular group of machines is found running in the steady state is derived. From this other useful measures for the system can be obtained. It is shown that these depend on the run time distributions only through the means of those distributions.     

AN EXPERIMENTAL STUDY OF POLYMER DIFFUSION IN CONCENTRATED SOLUTION: IMPLICATIONS FOR DIFFUSION IN POLYMERIZATION

The Trommsdorf or gel effect in free radical polymerization is due to the fact that the termination reaction becomes strongly diffusion controlled above a critical concentration associated with the onset of molecular entanglements. Therefore, an understanding of polymer self-diffusion in entangled systems becomes essential to understanding the Trommsdorf effect. Our group has previously proposed a molecular model for the gel effect which uses a specific theory for polymer diffusion (reptution). The present work represents an experimental attack on the same problem Experimental studies of polymer self-diffusion in entangled systems are scarce. Quasielastic light scattering from ternary systems composed of solvent(l)-polymer(2)-polymer(3), in which species (3) is isorefractive to the solvent (i.e. 0n/0c ₃ = 0), offers an attractive way to study the tracer diffusion coefficient of species (2) in a binary mixture of composition c ₃. In regimes of low momentum transfer (qR _G < 1,) where q is the scattered wave vector and R _G is the polymer radius of gyration, we have shown that the correlation function of the scattered electric field should decay with a single exponential decay time, given by (D₂₂ q ²)^?1 where D ₂₂(c ₂, c ₃) is the main ternary diffusion coefficient of component (2). Extrapolation to zero concentration of 2) at fixed concentration of (3) yields the tracer diffusion coefficient of (2) in the binary mixture of (1) and (3). The systems toluene(l)-polystyrene(2)-polymethylmethacrylate(3) (0n/0c ₃ ≈ 0.007 at 25°C) and toluene(l)-polystyrene(2)-polyvinylmethylether (3) (0n/0c ₃ ≈ 0.012 at 60°C) very nearly satisfy the above criteria. In both systems, we have found that the tracer diffusion coefficient of the polystyrene decreases with increasing concentration of the isorefractive polymer. Further studies have focused upon the dependence of the tracer diffusion coefficient upon polystyrene molecular weight, and upon the effect of incomplete index matching.     

影响农机购买的因素

购买农机的用户可分为集团购买和个人购买.集团购买农机时主要考虑的因素为产品的技术参数、性能特点、售后服务、价格等.农民个人购买农机除了考虑以上的因素外,他们还把品牌的社会影响力以及周围农机户的口碑也作为重要的因素.尽管有人认为集团购买更为理性,个人购买时感性的成分更多一些,但实际上所有的购买行为都会受到决策者心理因素的影响.     

Lead in wine: a case study on two varieties at two wineries in South Australia

Sources of lead in wine were inferred from systematic assay of grapes must and wine, during winemaking. Two Australian wineries were monitored during the 1994 vintage with respect to vinification of Riesling and Shiraz. Juice and wine samples were collected at several process stages from crushing through to bottling, and were analysed for their total lead concentration by graphite furnace atomic absorption spectrometry. Selected samples were subsequently analysed for lead isotope ratio (fingerprinting method) to infer possible sources of lead in samples. Lead concentration in fermenting must was found to vary during vinification. In particular, lead concentration increased significantly in open-top vessels, in holding bins and during pressing. Juice and wine stored in concrete or waxed wood also had a significantly higher concentration of lead compared to juice or wine stored in stainless steel. Moreover, fining with bentonite or filtering with diatomaceous earth contributed further to final lead concentration, while fermentation, both primary and secondary, removed lead Overall, wines processed via these different systems still contained only traces of lead, and generally less than 30 μg/L (30 micrograms per litre). These trace levels are of no concern to human health when such wines are consumed in moderation.     

The milk industry — a farmer's view

The impact of the historical changes in the dairy farming industry, and of the changes recently introduced by the EEC, is described in relation to the responses of an individual dairy farmer in the south west of England.