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.     

Production scheduling of single-stage multi-product batch chemical processes with fixed batch sizes

We address the problem of scheduling a single-stage multi-product batch chemical process with fixed batch sizes. We present a mixed-integer nonlinear programming model to determine the schedule of batches, the batch size, and the number of overtime shifts that satisfy the demand at minimum cost for this process. We introduce a polynomial-time algorithm to solve the problem when the processing times of all batches are identical and the setup and cleaning times are sequence-independent. The solution procedure is based on recognizing that the optimal fixed batch size is a member of a set whose cardinality is polynomial. Given a batch size, the problem may be formulated as an assignment problem. Thus, an optimal solution may be found by iteratively solving a polynomial number of assignment problems. This work was motivated by a pesticide manufacturing company in the design of a new plant where the assumptions of a single bottleneck machine, fixed batch sizes, sequence-independent setup times, and identical batch processing times are all valid. An example is developed for this application.     

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.     

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.     

The effects of spatial resolution on the classification of Thematic Mapper data

Actual and degraded LANDSAT-4 Thematic Mapper (TM) data were analysed to examine the effect of spatial resolution on the performance of a per pixel, maximum-likelihood classification algorithm. Analysis of variance (ANOVA) and a balanced, three-factor, eight-treatment, fixed-effects model were used to investigate the interactions between spatial resolution and two other TM refinements, spectral band configuration and data quantization. The goal was to evaluate quantitatively the effects of these attributes on classification accuracies obtained with all pixels (pure pixels plus mixed pixels) and on accuracies obtained with pure pixels alone.

A comparison of results from these separate analyses supported previous explanations of the effects of increasing spatial resolution. First, the difficulty in classifying mixed pixels was demonstrated by an average 21 per cent decrease in percentage accuracy from the pure-pixel case to the pure-plus-mixed-pixel case for the eight ANOVA treatments. In the pure-pixel case, an increase in spatial resolution from 80 to 30 m caused an average 6·1 per cent decrease in percentage accuracy when the other factors were held constant. This decrease was attributed to increased within-class spectral variability at the TM resolution. Finally, in the pure-plus-mixed-pixel case, increasing the spatial resolution did not significantly affect accuracy. This insignificance was attributed to a reduced proportion of mixed pixels at the TM resolution which counteracted the detrimental effects of increased spectral variability. These results point to a need for the development of new approaches to classification which take full advantage of the TM spatial resolution.     

The influence of radiation on the skin and the basis of protection

This paper reviews current ideas concerning the reactions involved in sunburn, suntanning, premature ageing and carcinogenesis due to acute or chronic exposure to sunlight. The physiological mechanisms of protection involving melanin pigmentation, thickening of the epidermal horny layer and urocanic acid are briefly discussed. The importance of wavelengths from 290-315 nm (UV-B) for these reactions is emphasized as is the need to investigate further the involvement of longer wavelength (UV-A, 315-400 nm).
L'influence des radiations sur la peau et les principes de la protection solaire
Cet article passe en revue les données actuelles concernant les réactions impliquées dans les processus de brûlure, bronzage, vieillissement prématuré et carcinogenese dus aux expositions aigues ou chroniques de la peau à la lumière solaire. Les mécanismes physiologiques de protection qui mettent en oeuvre la pigmentation par la mélanine, l'épais-sissement de la couche cornée, et l'acide urocanique sont brièvement discutés. On insiste sur l'importance des UV-B (longueurs d'onde de 290 à 315 nm) dans ces réactions, de même que sur la nécessité d'entreprendre des études plus approfondies sur le rôle des UV-A (315-400 nm).