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81.
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 相似文献
82.
83.
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. 相似文献
84.
85.
F. PALUTAN D. DE MARTINO S. FALZINI M. MELIS 《International Journal of Satellite Communications and Networking》1996,14(1):1-9
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. 相似文献
86.
87.
D. Van Oevelen F. DE L'Escaille H. Verachtert 《Journal of the Institute of Brewing》1976,82(6):322-326
Lambic is a type of Belgian beer obtained by spontaneous fermentation of wort. The fermentation in casks takes almost two years, and after that period the beer may be re-fermented in bottles and is then called gueuze. To gain insight into the many microbiological transformations occurring during this process, a qualitative and quantitative study of several components formed over a two-year period was undertaken. It was found that lambic and gueuze are characterized by high contents of ethyl acetate, ethyl lactate, lactic acid and acetic acid. Two phases of fermentation may be distinguished: a primary phase lasting for about three months during which almost all the ethanol and higher alcohols are formed and a very long secondary phase during which lactic acid is formed first, followed by ethyl lactate. Some lower fatty acids, including all the acetic acid, are made at the very beginning of the first phase. An important part of the ethyl acetate is made during the first phase but the amounts increase slowly to high levels during the second phase. Unusually low amounts of isoamyl acetate are detected. Several components are above the reported threshold levels of taste and are thus probably involved in the genesis of the typical aroma of lambic and gueuze. These results will allow a further study of the relations between the components found and the microbial populations involved in the spontaneous fermentation inherent in the brewing of lambic and gueuze. 相似文献
88.
Zhouyan XIA Jan-Willem G. VAN DE KUILEN Andrea POLASTRI Ario CECCOTTI Minjuan HE 《Frontiers of Structural and Civil Engineering》2021,15(1):213
This study analyzes the feasibility of the use of cross-laminated timber (CLT) as a load-bearing structural element in a 40-story building based on Chinese design requirements. The proposed design of the high-rise concrete–CLT building utilizes the core–outrigger system. Concrete is used for the central core and outriggers, and CLT is used for the rest of the structure of the building. Finite element models with different types of connections were developed using SAP2000 to analyze the lateral behavior of the building under wind action. The finite element models with rigid connections deduce the wind load distributions on individual structural elements, which determine the total number and the stiffness of fasteners of the CLT panels. Accordingly, spring links with equivalent stiffness that simulate the mechanical fasteners were employed in SAP2000. The results indicate that CLT increases the lateral flexibility of the building. A closed concrete core was substituted by two half cores to measure the requirement of the maximum lateral deflection. However, the acceleration at the building top still exceeded the limitation prescribed in Chinese Code JGJ 3–2010 owing to the lightweight of CLT and decreased stiffness of the hybrid building. To restrict this top acceleration within the limit, further approaches to increase the stiffness in the weak direction of the building are required. Methods such as the modification of the floor layout, increase in the thickness of walls, and addition of extra damping capacity should be considered and verified in the future. 相似文献
89.
ALONZO A. GABRIEL KRISTELLE GAY S. CRUZ JEANE AUBREY D. DE GUZMAN 《Journal of Food Processing and Preservation》2009,33(S1):136-144
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.
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. 相似文献
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. 相似文献
90.
PATRICIA L. ALVES DE LIMA DANIEL A RIBEIRO MARINA M SUGUI ANA PAULA TEREZAN MARIA APARECIDA C DOMINGUES E R FILHO LUCIANA AZEVEDO DAISY M F SALVADORI LUCIA R RIBEIRO 《Journal of Food Biochemistry》2010,34(1):206-228
In this study, we have investigated the stability of the antigenotoxic properties of dried of Lentinula edodes (Berk.) Singer mushroom powder stored at room and at − 20C. Mice were pretreated by gavage for 15 consecutive days with 0.6 mL/day of an aqueous extract of dried L. edodes powder prepared at 60C. On day 15, the mice were intraperitoneally injected with 50 mg/kg N-ethyl-N-nitrosourea (ENU); 3 h later, peripheral blood was withdrawn from the animals and used to evaluate DNA damage using the comet assay. The mice were sacrificed 24 h after the ENU treatment and the bone marrow used to measure the frequency of micronucleated polychromatic erythrocytes. The results indicated that storage at both room temperature and at − 20C significantly reduced the antigenotoxic effects of the mushroom powder. In addition, whereas freshly dried mushroom powder was nongenotoxic, storage of the powder at − 20C resulted in genotoxic activity ( P < 0.05). Taken together, our data indicate that constituents of L. edodes powder are altered during storage, resulting in both genotoxicity and a reduction in antigenotoxicity. 相似文献