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271.
Eynard C. Lenti M. Lombardo A. Marengo O. Palazzo S. 《Selected Areas in Communications, IEEE Journal on》1995,13(5):893-907
The anticipated emergence of third-generation mobile systems, referred to as universal mobile telecommunication systems (UMTS), raises the problem of reconsidering the design of the databases destined to contain the user information. In particular, it is expected that the key concepts of the new database architectures will be high distribution and fast updating of information. So far, the problem of determining the most appropriate distributed database (DDB) architectures for third-generation mobile systems has not been widely dealt with in literature. This paper presents a methodology for evaluating hierarchical DDB architectures by means of an analytical model of the data querying operation. This methodology allows for structural alternatives, differing on account of the number of levels and branches in the hierarchy, to be evaluated in terms of query loads and mean response times, according to a given user mobility characterization and a given search protocol operation. By way of illustration, the paper discusses a case study, concerning a query operation arising from a location updating procedure and applied to a hierarchical tree-like DDB in which some structural alternatives are considered 相似文献
272.
Switched reluctance (SR) motors with differing structures are compared in terms of their torque prediction capabilities. The first structure is doubly salient with conventional laminations, also referred to as the CRS motor. The second has semiclosed stator slots and a cylindrical rotor with anisotropic magnetic properties arising from axial laminations interleaved with nonmagnetic material, also referred to as the CRR motor. The second structure has been claimed, on theoretical grounds, to be the superior structure in terms of torque per stator volume. The present comparison, based on RMS currents, concludes that the torque produced by the conventionally laminated motor is approximately 2.5 times that of the anisotropic design when the two copper losses are equalized. However, when the CRR motor has been optimized in terms of magnetic and electric loading, the CRS motor is still twice as torque productive. These results reverse the benefits previously claimed for the anisotropic motor design 相似文献
273.
274.
The discrete time decoding of data in pulse position modulation calls for accurate timing synchronisation, particularly at the frame rate. The spectral properties of optical fibre digital PPM are considered. An original expression is presented for predicting the spectrum and it is shown that, unlike satellite PPM, a component exists at the frame rate which may be used for timing extraction purposes. Further, it is illustrated that the modulation index can be used to enhance this component by up to 19 dB. This has been verified practically, with the results agreeing to within 1 dB of those predicted from the original expression presented.<> 相似文献
275.
A modal expansion method is used with the reciprocity and Poynting theorems to derive the admittance of inclined slots cut in the metal wall of a nonradiating dielectric (NRD) waveguide. Theoretical values of normalised conductance and susceptance are compared with previously reported experimental results and are found to be in good agreement.<> 相似文献
276.
J. Kircher M. Cardona M. Alouani S. Gopalan O. Jepsen O. K. Andersen
E. Kaldis
J. Karpinski S. Rusieki 《Physica C: Superconductivity and its Applications》1992,200(3-4):413-417We report results of ellipsometric measurements of the dielectric tensor of YBa2Cu4O8 as well as calculations employing density functional theory in the local density approximation (LDA). For the computation of the one-electron eigenvalues and states the linear-muffin-tin-orbital method (LMTO) was used. Measured and calculated results show good agreement. In particular, the calculation predicts different band structures for YBa2Cu3O7 and YBa2Cu4O8 in the vicinity of the Fermi energy which lead to significant differences in the optical spectra. One such difference is a region of small ε2 in the near infrared which is a fingerprint of the high (relative to the top of the highest fully occupied band) Fermi energy as compared to the situation in YBa2Cu3O7. Our experimental results confirm the theoretical findings. 相似文献
277.
Many cognitive tasks that are easy for humans to perform are proving difficult to emulate in computer systems. Combining the disciplines of psychology and engineering may offer a solution to some of these problems. A connectionist or neural network model of face recognition by humans which incorporates aspects of a model proposed by cognitive psychologists is presented. A comparative set of experiments has been performed using this simulation and human subjects for familiar face recognition. By employing the same stimuli for both humans and the computer model, it is possible to advance not only our understanding of human cognition but also to develop improved automated systems for face recognition 相似文献
278.
This paper develops a method for simultaneously designing the power stage and controller for a switching power supply. The method utilizes a numerical optimization procedure, which facilitates computer-aided design. It is found that better performance can be achieved than with a traditional two-step design process, where the power stage and controller are designed sequentially. Optimization and simulation results for a buck power converter are presented to illustrate the design process and benefits 相似文献
279.
A technique is proposed for improving the accuracy of the heat of fusion of semicrystalline polymers by DSC. The results of three commercially available instruments are compared. 相似文献
280.
We generalize literature data and our own experimental data on using 1,3-dipolar cycloaddition reactions for synthesis of fullerene C60 derivatives containing annelated heterocyclic moieties.M. V. Lomonosov Moscow State University, Moscow 119899, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 291–297, March, 1998. 相似文献