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排序方式: 共有1549条查询结果,搜索用时 15 毫秒
1.
Lopera J.M. Prieto M.J. Pernia A.M. Nuno F. 《Power Electronics, IEEE Transactions on》2003,18(3):896-906
This paper presents a method to obtain an electric model for transformers and inductors, including both frequency and geometry effects in the windings, which can be linked with existing core models. One-dimensional distributions for magnetic and electric fields are assumed, and from Maxwell's equations an equivalent electric circuit is easily obtained. This equivalent circuit has been included in analog simulators (Spice, AnalogWorkBench, Saber ...), and comparisons between measured and simulated results are shown, both in time domain and in AC sweep, which verify the model accuracy. The model described in this paper allows designers to deal with key issues in the design of high-frequency magnetic components (copper losses, leakage inductance, skin and proximity effects) by using analog simulators, which are usually more familiar to them than finite-element analysis tools. 相似文献
2.
The estimation of the link capacity and its available bandwidth in an end-to-end path is crucial for network management, admission
control and flow control for adaptive applications. This paper introduces an estimation mechanism able to accurately estimate
the available bandwidth of all links in an end-to-end path, through its capacity and cross-traffic estimation. The estimation
procedures resort to the dispersions of packet pairs and trains using the concepts of ICMP Timestamp and Traceroute that,
efficiently used together, enable the measurement of the dispersions in all links in the path. These mechanisms were evaluated
through simulation experiments, where we analyzed the influence of the several network parameters on each estimation mechanism.
The results show that these estimation methods are able to accurately estimate both the capacity and the cross-traffic of
all links in a path with moderate length and with low overhead. 相似文献
3.
Atmospheric corrosion of reference metals in Antarctic sites 总被引:1,自引:0,他引:1
Manuel Morcillo Beln Chico Daniel de la Fuente Elisabete Almeida Günter Joseph Susana Rivero Blanca Rosales 《Cold Regions Science and Technology》2004,40(3):165-178
This paper presents the results obtained at three Antarctic test sites participating in the “Ibero-American Map of Atmospheric Corrosiveness” (MICAT), a project on atmospheric corrosion carried out during the period 1988–1994 at some 70 sites distributed across 12 countries of the Latin-American region, Spain and Portugal. The three Antarctic sites are located near the coastline.The singular climatic characteristics of Antarctic regions are related with the purity of the air, the absence of rainfall and the formation of ice on the metallic surface during an important part of the exposure time. However, electrochemical activity is possible below ice layers. This situation affects the structure and morphology of corrosion product films and the resulting corrosion rates of metallic surfaces. 相似文献
4.
Do individual factors matter? A survey of scientists’ patenting in Portuguese public research organisations 总被引:1,自引:0,他引:1
Paula Susana Figueiredo Moutinho Margarida Fontes Manuel Mira Godinho 《Scientometrics》2007,70(2):355-377
This paper addresses scientists’ behaviour regarding the patenting of knowledge produced in universities and other public
sector research organisations (PSROs). Recent years have witnessed a rapid growth in patenting and licensing activities by
PSROs. We argue that the whole process depends to a certain extent on scientists’ willingness to disclose their inventions.
Given this assumption, we conduct research into individual behaviour in order to understand scientists’ views concerning the
patenting of their research results. Data from a questionnaire survey of Portuguese researchers from nine PSROs in life sciences
and biotechnology is presented and analysed and complemented with in-depth interviews. The results reveal that overall the
scientists surveyed show a low propensity to become involved in patenting and licensing activities, despite the fact that
the majority had no “ethical” objections to the disclosure of their inventions and the commercial exploitation of these. Perceptions
about the impacts of these activities on certain fundamental aspects of knowledge production and dissemination are however
divergent. This may account for the low participation levels. Furthermore, most scientists perceived the personal benefits
deriving from this type of activity to be low. Similarly, the majority also believed that there are many difficulties associated
with the patenting process and that they receive limited support from their organisations, which lack the proper competences
and structures to assist with patenting and licensing. 相似文献
5.
Birnessites containing Na, K or Li in the interlayer have been prepared by oxidation of Mn(II) cations with H2O2 in a basic medium with different alkaline cation/Mn molar ratios. The solids prepared have been characterised by elemental chemical analysis, powder X-ray diffraction, thermal analyses (differential thermal analysis and thermogravimetric analysis), FT-IR spectroscopy and surface texture assessment by adsorption of N2 at –196°C. Crystalline birnessites are obtained for A/Mn ratios (A = K, Li) larger than 3.4, but MnO(OH) has been also identificed when such a ratio is smaller than 3.4. Ion exchange is topotactic, but is not complete for exchanging Na, K, or Mg for pre-existing Li. The solids are stable up to 400°C, and formation of spinels and solids with tunnel structures is observed at this temperature. Li-containing birnessites are transformed to LiMn2O4 spinel at 400°C, and co-crystallization of bixbyte (Mn2O3) is observed at higher temperatures. Bixbyte and cryptomelane are formed at 500°C for the K-containing birnessites. 相似文献
6.
Malacoplakia of the prostate and seminal vesicle. Ultrastructural study and review of the literature
M Sánchez Chapado J Angulo Cuesta M Guil Cid R Lera Fernández A Dehaini L Prieto Chaparro 《Canadian Metallurgical Quarterly》1995,48(8):775-778
OBJECTIVES: The present study describes a case of malacoplakia of the genitourinary tract arising in the seminal vesicle and prostate and reviews similar cases previously reported in the literature. METHOD: A 67-year-old male consulted for hemospermia and voiding symptoms. Prostatic neoplasm was suspected on the basis of the clinical and radiological findings. RESULTS: The diagnosis was made only after biopsy and histological analysis. Electron microscopy is a very useful tool. Long-term antibiotic therapy may achieve optimal results. Treatment with fluoroquinolones was successful. CONCLUSION: To avoid unwarranted radical approaches, we underscore the possibility that prostatic pseudotumors may be misinterpreted as neoplasia. Malacoplakia is diagnosed only by histology and requires medical treatment. 相似文献
7.
A CMOS current-mode approach for implementing the defuzzification function in analogue fuzzy controllers is proposed. The circuit computes the centre of area of the output fuzzy conclusion using switched current adders and a current divider. Simulation results of the defuzzifier show how the circuit can produce a good approximation of the centre of area even if a small number of levels are used to quantise the output variable.<> 相似文献
8.
Acetylsalicylic acid (ASA) alone (at least 30 mg per day) in post-cerebral ischaemia patients reduces the relative risk of further vascular events by 13% compared with placebo. A meta-analysis of all studies shows that the combination of ASA with dipyridamole reduces the relative risk by 16% (95% confidence interval: 5-26%) compared with ASA alone, but confirmation by a major trial appears desirable, because of discrepant results of a recent trial and 4 previous ones. Clopidogrel might reduce the risk by 7% compared with ASA alone, but this drug is expected to be expensive. Anticoagulation therapy with an international normalized ratio (INR) of 2.0-4.0 is particularly efficacious for secondary prevention in patients with atrial fibrillation, but anticoagulation therapy with an INR of 3.0-4.5 is not safe in secondary prevention of cerebral ischaemia of presumed arterial origin. Finally, not all atherosclerotic vascular diseases are identical from the therapeutic point of view; the effect of treatment depends in part on the clinical manifestation form. 相似文献
9.
Single crystals of nylon 7 prepared by crystallization from glycerine were studied by both X-rays and electron microscopy. Electron diffraction proved that they consist of a twinned layered-structure with hydrogen bonds running parallel to their long dimension. Polyethylene decoration of such crystals showed that they are subdivided in folding domains so that both chain folding and hydrogen bonding take place along the same crystallographical planes. 相似文献
10.
Mateus Ferreira-Satler Francisco P. Romero Victor H. Menendez-Dominguez Alfredo Zapata Manuel E. Prieto 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2012,16(7):1129-1141
Nowadays, the impact of technological developments on improving human activities is becoming more evident. In e-learning, this situation is no different. There are common to use systems that assist the daily activities of students and teachers. Typically, e-learning recommender systems are focused on students; however, teachers can also benefit from these type of tools. A recommender system can propose actions and resources that facilitate teaching activities like structuring learning strategies. In any case, a complete user’s representation is required. This paper shows how a fuzzy ontology can be used to represent user profiles into a recommender engine and enhances the user’s activities into e-learning environments. A fuzzy ontology is an extension of domain ontologies for solving the problems of uncertainty in sharing and reusing knowledge on the Semantic Web. The user profile is built from learning objects published by the user himself into a learning object repository. The initial experiment confirms that the automatically obtained fuzzy ontology is a good representation of the user’s preferences. The experiment results also indicate that the presented approach is useful and warrants further research in recommending and retrieval information. 相似文献