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排序方式: 共有768条查询结果,搜索用时 15 毫秒
91.
92.
T Babia JW Kok C Hulstaert H de Weerd D Hoekstra 《Canadian Metallurgical Quarterly》1993,54(5):839-845
Trafficking and metabolism of sphingolipids were examined in undifferentiated (G+) and differentiated (G+ reversed) HT29 human colon adenocarcinoma cell lines. Metabolic experiments employing a fluorescently labeled sphingolipid precursor, 6-[N-(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]hexanoylceramide++ + (C6-NBD-ceramide) revealed that both qualitative and quantitative differences exist in sphingolipid synthesis between the 2 cell lines. One of the C6-NBD-sphingolipids synthesized in G+ cells is not found in the G+ reversed cells. Furthermore, the ratio of the 2 main products, C6-NBD-glucosylceramide and C6-NBD-sphingomyelin, differs: in G+ cells glucosylceramide is by far the main product, whereas G+ reversed cells synthesize C6-NBD-sphingomyelin in slight excess. Once established, these ratios of sphingolipids are quickly restored metabolically when distortion of the ratio is caused by experimental manipulation. This indicates that they represent a true metabolic equilibrium situation of the 2 sphingolipids in these cells, while the distinct ratios are mainly determined by the NBD-lipid pool in the plasma membrane. Preferential synthesis and transfer of glucosylceramide from its site of synthesis to the cell surface do not occur when the plasma membrane pool of glucosylceramide is selectively removed. This suggests that instantaneous replenishment via specific signalling is probably not involved as a mechanism in re-establishing perturbed lipid pools. In conjunction with observations on distinct lipid trafficking pathways of glucosylceramide in G+ and G+ reversed cells, the present metabolic studies emphasize a relation between the expression of this glycolipid and the state of differentiation of HT29 cells. 相似文献
93.
André J. Kok 《Expert Systems》1995,12(4):347-351
Abstract: Retrieving ad hoc data from information systems is difficult for non-expert users. Despite the efforts made in improving query tools (e.g. visual query construction, Query By Example, query templates), empirical research shows that constructing a request is still difficult (Reisner 1988). The core of the problem seems to be in the difference between the way the user perceives the application domain and the way the system requires the user to see it (Carroll & Olsen 1988).
In this paper we describe the design and implementation of an ad hoc query tool developed by RCC for a personnel information system, and how AI techniques contributed to this module. The main novel idea incorporated in the query tool is to present the user with a means to question the conceptual model of the system instead of the technical model. To support this, a blackboard architecture has been designed and implemented with knowledge sources that translate the user's questions to database queries. The query tool is used in daily practice by over 100 users. 相似文献
In this paper we describe the design and implementation of an ad hoc query tool developed by RCC for a personnel information system, and how AI techniques contributed to this module. The main novel idea incorporated in the query tool is to present the user with a means to question the conceptual model of the system instead of the technical model. To support this, a blackboard architecture has been designed and implemented with knowledge sources that translate the user's questions to database queries. The query tool is used in daily practice by over 100 users. 相似文献
94.
P.J.J. Kok K. Abrahams H. Postma W.J. Huiskamp 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1985,12(3):325-330
Capture of unpolarized thermal neutrons has been used to gain information on the 7Li level scheme. Two reactions have been investigated. Firstly, a study has been made of the decay scheme of 7Li through the 6Li(n, γ)7Li reaction. Three γ-transitions were observed and placed. The binding energy value of this reaction turned out to be Q = 7251.02(9) keV. Secondly, investigation of radiation from excited Li produced by the 10B(n,α)7Li reaction, made it possible to deduce a more precise lifetime of the 478 keV level of 7Li; namely τ = 102 ± 5 fs. This value is compared with existing data; it agrees with previous less accurate independent values and an average could be made in order to reduce the error further. As a byproduct the analysis of the peak shape of the 478 keV transition offered a new method for estimating the size of boron grains embedded in other materials. 相似文献
95.
A van den Berg RF Kooy MM Hulsbeek D de Jong K Kok AY van der Veen CH Buys 《Canadian Metallurgical Quarterly》1996,72(2-3):225-228
Starting from five markers, with a well-defined order from distal to proximal 3p21, nine other markers could be inserted in this 3p21 map. Five were precisely mapped genetically. The other markers were ordered by FISH and/or deletion hybrid mapping. The overall 3p21 order from distal to proximal is as follows: D3S1298-D3S1260-(D3S966, D3S1448 (= D3S1449)-D3S1029-D3S32-D3S643-D3F15S2 -D3S2968-D3S1235-D3S1289-D3S1447-D3S1295. 相似文献
96.
An extended study of the effect of moderate thermal stress on the performance of tasks simulating aspects of industrial work has been under way since 1977. Factory workers were used as test subjects, each being exposed to a single test condition for a full shift in a mobile climate laboratory.Analyses completed so far reveal a fall in the performance of manipulative tasks of approximately 10% when finger skin temperatures (FST) fall to 20°C, and a further 10% at about 12°C. The FST of black male subjects typically reached these values at air temperatures about 4°C higher than gave rise to similar FST's in white subjects.For many of the tasks the air temperature which produced best performance in the range 20–38°C, was 32°C at a relative humidity of 25%. The subjects nevertheless reported preferred temperatures in the expected range of 20–23°C. 相似文献
97.
Eric-Wubbo?Lameijer Thomas?B?ck Joost?N.?Kok AD?P.?IjzermanEmail author 《Natural computing》2005,4(3):177-243
Designing a drug is the process of finding or creating a molecule which has a specific activity on a biological organism. Drug design is difficult since there are only few molecules that are both effective against a certain disease and exhibit other necessary physiological properties, such as absorption by the body and safety of use. The main problem of drug design is therefore how to explore the chemical space of many possible molecules to find the few suitable ones. Computational methods are increasingly being used for this purpose, among them evolutionary algorithms. This review will focus on the applications of evolutionary algorithms in drug design, in which evolutionary algorithms are used both to create new molecules and to construct methods for predicting the properties of real or yet unexisting molecules. We will also discuss the progress and problems of application of evolutionary algorithms in this field, as well as possible developments and future perspectives. 相似文献
98.
BACKGROUND: Vitamin A deficiency remains a public health problem in Burkina Faso and elsewhere in the developing world. Dietary diversification is a promising strategy that needs to be explored to strengthen the country's ongoing supplementation program. OBJECTIVE: The purpose of this study was to identify locally available and acceptable (pro)vitamin A-rich foods to be included in a dietary intervention addressing vitamin A deficiency in children aged six months to three years. METHODS: A food ethnographic study combining recall methods, observation, and focused group discussion was conducted in the dry and rainy seasons. Thirty-five mother-child pairs were randomly selected and included in the study. RESULTS: The dietary pattern of children was characterized by low diversity with extremely low energy and vitamin A intake in both seasons. The study identified the availability of numerous (pro)vitamin A-rich foods, but these foods are either not consumed or consumed by few in low amounts and/or in low frequencies. The main constraining factors identified are related to financial accessibility (for liver), seasonal availability (for egg, milk, mango, papaya, and green leafy vegetables), and beliefs related to consumption and preparation (for green leafy vegetables). However, the study also revealed that the study population associated all identified (pro)vitamin A-rich foods with positive attributes such as health, strength, and vitamin richness, which might offer an entry point for designing and implementing dietary interventions. CONCLUSIONS: Based on the findings of this formative research, intervention strategies with mango and liver are proposed to improve the vitamin A intake and status of children in the rural areas of Burkina Faso. 相似文献
99.
A.G.J. Voragen H.A.M. de Kok A.J. Kelholt H.A. Schols Ko Swan Djien 《Food chemistry》1982,9(3):167-174
An HPLC method for the determination of bongkrek acid and toxoflavin extracted from laboratory made tempe bongkrek is described. The method appeared to be reliable and simple; samples containing 0·5–80 μg/ml of bongkrek acid or 1–300 μg/ml of toxoflavin could be analysed. 相似文献
100.
Open access for new broadcasting organizations "has led not to an increase, but a decrease in diversity" and a greater dependence on group membership. 相似文献