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排序方式: 共有1824条查询结果,搜索用时 93 毫秒
11.
Paulo S. André António L. Teixeira Armando N. Pinto Lara P. Pellegrino Berta B. Neto José F. Rocha Joäo L. Pinto Paulo N. Monteiro 《ETRI Journal》2006,28(2):257-259
In this letter, we will evaluate the performance degradation of a 40 km high‐speed (40 Gb/s) optical system, induced by optical fiber variations of the chromatic dispersion induced by temperature changes. The chromatic dispersion temperature sensitivity will be estimated based on the signal quality parameters. 相似文献
12.
A novel directive and nondispersive antenna is presented: the ultrawideband (UWB) leaky lens. It is based on the broad band Cherenkov radiation occurring at a slot printed between different infinite homogeneous dielectrics. The first part of the paper presents the antenna concept and the UWB design. The issues that are specifically addressed include the impedance matching, the radiation pattern and the phase purity. Subsequently the hardware demonstrator and the results of the measurement campaign are shown. The results fully validate the antenna concept. The antenna presents decade bandwidth impedance matching, directive and frequency independent patterns in the H-plane over two octaves, negligible cross-polarization levels, weak amplitude dispersivity and, according to the authors, the most stable phase center for a directive antenna over an ultra wide frequency range. 相似文献
13.
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
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16.
Susana Criado Norman A. García Maria I. Gutirrez Vicente Avila Sonia G. Bertolotti Rio Cuarto 《European Journal of Lipid Science and Technology》1996,98(5):172-175
The ability of mono-, di-, tri-and tetra-hydroxyflavones (7-and 3-hy-droxyflavones, 7, 8-dihydroxyflavone, baicalein and fisetin) to act as photoprotectors against singlet molecular oxygen [O2(Δg)]-initiated photooxidation of fats has been established by a kinetic study. The overall quenching rate constants for a series of five hydroxyflavones perfectly parallel their respective behaviour as inhibitors of the sensitized photooxidation of linoleic acid. The best antioxidative effect was exerted by 7-hydroxyflavone which does not chemically react with O2(1Δg). Nevertheless for the remaining flavonoids of the series, the physical deactivation of O2(1Δg) largely prevails over the chemical process. As for the cases of phenols and related hydroxy-aromatic derivatives, the ionization of the -OH group in the flavones, dramatically accelerates the rate of photooxidation. Under these conditions, the 7-hydroxyflavone also reacts effectively with O2(1Δg). Given that flavonoids are natural oil components, this medium effect should be taken into account during the oil-refining process, in order to avoid the flavonoid photodestruction. 相似文献
17.
Lima A.M.N. Deep G.S. Neto J.S.R. Freire R.C.S. Lobo P.C. 《IEEE transactions on instrumentation and measurement》1994,43(2):133-138
An identification procedure to estimate the parameters of a thermoresistive solar radiation sensor is presented. The proposed technique employs only electrical excitation for the sensor. The estimation algorithm is recursive and is applied to the sensor model derived from the thermodynamic equilibrium differential equations. The simulation and the experimental results demonstrate the validity of the proposed approach 相似文献
18.
The authors present experimental results which indicate that a Dy 3+-doped Ga:La:S glass fibre amplifier may be operated efficiently at 1.3 μm with an optimum device length significantly shorter than a comparable Pr3+-doped glass fibre amplifier. Moreover, the efficiency exceeds that obtained from the Pr3+-doped ZBLAN devices currently available 相似文献
19.
Joaquim J. Barroso Pedro J. Castro Joaquim P. Leite Neto 《Journal of Infrared, Millimeter and Terahertz Waves》2003,24(1):79-86
We present a method for measuring the electrical conductivity of metallic materials that relies on the ratio of two loaded Q factors, QR/QX, with QR corresponding to a TE011-mode reference cavity made of aluminum, and QX the Q that results upon replacing the aluminum plate with the one fabricated from the material to be examined. Electrical conductivity is mathematically inferred from the ratio QR/QX where the loaded Q factors are measured by using the transmission-type method. Within a 3.0 percent accuracy, conductivities determined at 8.7 GHz for electrolytic copper (5.6 times 107 S/m) and brass (1.6 times 107 S/m) show to be in good agreement with those reported in the literature. 相似文献
20.