Extension and partial optimization of a modified Smith predictor and controller for unstable processes with time delay

Extension and partial parameter optimization are applied to a modified Smith predictor and controller, designed by de Paor( 1985) for a class of unstable processes having transfer functions of the form k₁A exp(—sT)/B, where A is a monic, Hurwitz polynomial of degree (n — l) and the nth degree monic polynomial B has a single right half-plane root at s=λ It is found that for l = 1,2,3 asymptotic stability can be achieved for λ T> 1, which more than doubles the best result obtained earlier. For a specific process, responses are compared with those obtained using the optimum stability PI controller of de Paor and O'Malley (1989). The advantages of the optimized, modified predictor in terms of tightness of control and faster settling time are highlighted     

The measurements of autonomy and technology for task svstems design

Numerous experiments in job enlargement, direct worker participation and autonomous workgroups have been reported. However, little cumulative knowledge has been gained through a lack of conceptual and theoretical bases. Moreover, worker autonomy and technology, the major variables in those experiments either were measured by questioning workers and supervisors and are consequently modified by their perception, or were measured in a very broad fashion.

In the present work more objective and specific measures for technology and autonomy, which can link job design research and experiments with job design practice, were developed and validated. Automony and technology are of course multidimensional concepts. Relevant aspects for job design are derived from a model for task related decision making which shows that the degree of worker autonomy is contingent on task technology and worker characteristics.

Technology is measured by cycle time, task repetitiveness, task skill level, disturbance level of a task and the disruption potential of a task system, through observation. A distinction is made between autonomy in regulation, which keeps the process on target by counteracting disturbances and autonomy in control which specifies targets. Measures for both types of autonomy are developed. The measures of technology and autonomy were tested in a sample consisting of 411 work stations in industry and proved to be effective and efficient for job design purposes.     

GEOSTATIONARY STATION-KEEPING BY ION THRUSTERS: GENETIC ALGORITHMS OPTIMIZATION

The orbital control of geostationary satellites requires the periodic execution of manoeuvres for gravitational and solar radiation perturbation compensation. To maintain a fine control of the satellite position, it is usually sufficient to perform orbit corrections every two weeks, firing chemical thrusters. The operational load for the manoeuvre's planning and execution is usually quite low. Innovative technologies for station-keeping are available now, based on high efficiency ion thrusters, which allow a significant propellant saving. They are included in Artemis, a telecommunications satellite developed by the European Space Agency. When low acceleration ion thrusters are adopted, a near continuous orbit control is required; the resulting long firing arcs can be in conflict with some operational or technical constraints. The station-keeping planning is a critical process, since it is not based on periodic impulsive manoeuvres, but rather on quasi-continuous firings. Furthermore the orbit control should be planned more on a seasonal or a yearly cycle rather than on short weekly cycles. Since each manoeuvre is defined by its start time and duration, the total number of parameters involved in a station-keeping optimization process amounts to several tens. The presence of many variables and logical constraints makes the use of classical optimization methods quite complex. The model proposed here is based on genetic algorithms, which allows the convergence to an optimum solution through successive iterations, in which a random set of solutions is progressively selected on the basis of a factor of merit tailored to the target. This paper presents some innovative concepts for station-keeping optimization when ion propulsion is adopted for orbital control; furthermore, the general properties of genetic algorithms are discussed, together with the results obtained in the specific station-keeping application.     

Analysis of hexamidine, dibromohexamidine, dibromopropamidine and chlorhexidine in cosmetic products by high-performance liquid chromatography

A method of determining qualitatively and quantitatively hexamidine, dibromohexamidine, dibromopropamidine and chlorhexidine in cosmetic products by means of paired ion, reverse-phase high-performance liquid chromatography (HPLC) and ultraviolet detection (UV) at 264 nm.
Détermination de l'hexamidine, du dibromohexamidine, du dibromopropamidine et de la chlorhexidine dans les produits cosmétiques     

大青叶抗菌物质提取及抗菌效果研究

研究了用水浸提法抽提大青叶中抗菌物质的方法，并通过抑菌实验检验了对细菌和霉菌的抑菌能力。正交实验结果表明最佳抽提工艺为：料水比1：20，加热时间40min，回流温度100℃：滤纸片法抑菌实验发现：大青叶提抽浓缩液(浓缩比为5：1)对大肠杆菌及枯草杆菌的最低抑菌浓度为2．77％(ml，100ml)左右，青霉，黄曲霉为0．55％(ml／100ml)左右，金黄色葡萄球为0．055％(ml／100ml)左右。     

运用模糊聚类分析方法整编翰林桥站流量资料初探

主要对水文资料整编采用模糊聚类分析的方法进行尝试，利用计算机定线，使得水文资料整编全面计算机化作了初步的探索，取得一定的效果。     

THERMAL DEATH TIMES OF ESCHERICHIA COLI IN YOUNG COCONUT ENDOSPERM BEVERAGE

The decimal reduction times (D values) of Escherichia coli (American Type Culture Collection 25922) were established in a young coconut endosperm beverage, a famous local drink in the Philippines and in many tropical countries. Artificially inoculated cells were heated to 60, 70 and 80C at various heating times prior to survivor enumeration by surface plating onto pre-solidified Eosine Methylene Blue Agar. Results showed that the surviving populations significantly (P  <  0.05) decreased with increasing exposure time and temperature. The calculated D values ranged from 0.26  ±  0.01 to 0.56  ±  0.08   min. Validation of the results by establishing the thermal resistance of other E. coli isolates in the coconut beverage medium was recommended.

PRACTICAL APPLICATION

The study established the thermal inactivation rates of Escherichia coli (American Type Culture Collection 25922) in a young coconut endosperm beverage medium in various heating temperatures. The results obtained from this study may be used in the calculations of appropriate thermal process schedules for the test beverage against the test organism.