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The aim of this study was to evaluate the vibration level attenuation of a common wooden floor structure and to present the results together with the statistical precision of the evaluation. Linear regression was used to determine the attenuation rate in the two main directions of the floor structure. The probability for the attenuation rate to be zero was calculated. The attenuation rate was found to be high in the direction perpendicular to the beams with a probability to be zero lower than 0.001. In the direction parallel to the beams the attenuation rate was found to be close to zero. 相似文献
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A film surface, modeled by a grating with rectangular grooves, is shown to give rise to both short and long ranged enhancements due to excitation of planar surface plasmon resonances, and to short ranged, more intense, enhancements due to excitation of waveguide resonances. The latter type of enhancement is shown to become more intense as the ratio of grating period to groove width increases and to be able to account for experimentally observed SERS signals at very low as well as at higher temperatures. 相似文献
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做实验的主人--写给学习物理实验的学生 总被引:3,自引:1,他引:2
在学习实验时应注意学习探索,本文从实验课上学什么,如何在探索中学习,如何进行误差分析,实验结果如何评价,怎样认识验证性实验,怎样理解实验的物理思想,怎样在实验过程中提出问题等几方面讨论了学生怎样做实验的主人. 相似文献
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The formation of ohmic contacts to n- and p-type ZnSe is reviewed. The mechanisms for forming reasonable low-resistance ohmic contacts to n-ZnSe are well understood. This results from the fact that the Fermi energy level of ZnSe is unpinned and metals with sufficiently large work functions can make contact to n-type material. However, the situation is reversed for p-ZnSe where a large band gap and large electron affinity make it impossible to find metals with sufficiently large work functions to create an ohmic contact. Instead, the use of HgSe to form low barrier height Schottky contacts and of ZnSe/ZnTe multiple quantum wells (MQWs) to form ohmic contacts is reviewed. Although the MQWs can be used to form ohmic contacts to p-ZnSe, they degrade at high temperatures and high current densities. This is reviewed and shown to be a serious problem for applications to laser diodes. 相似文献
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For many years, the problem of how to distribute students to the various universities in Germany according to the preferences of the students has remained unsolved. Various approaches, like the centralized method to let a central agency organize the distribution to the various universities or the decentralized method to let the students apply directly at their preferred universities, turned out to lead to a significant fraction of frustrated students ending up at universities not being on their preference list or even not having a place to study at all. With our centralized approach, we are able to decrease the fraction of frustrated students as well as the bureaucratic expenses for applicants and universities drastically. 相似文献
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为了测试人员能在平时使用模拟器系统进行测试训练。本文设计了一种筒弹测试故障模拟器系统,介绍了它的工作原理、系统的软硬件设计。该系统能对筒弹基本电气性能和测试接口进行模拟,在软件的控制下,实现模拟筒弹测试项目和模拟筒弹测试故障等功能,可以很好的完成筒弹测试设备测试人员对筒弹测试的操作训练。 相似文献
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Carl A. Batt Anna M. Waldron Natalie Broadwater 《Journal of nanoparticle research》2008,10(7):1141-1148
Nanotechnology will be an increasing part of the everyday lives of most people in the world. There is a general recognition
that few people understand the implications of the technology, the technology itself or even the definition of the word. This
lack of understanding stems from a lack of knowledge about science in general but more specifically difficulty in grasping
the size scale and symbolism of nanotechnology. A potential key to informing the general public is establishing the ability
to comprehend the scale of nanotechnology. Transitioning from the macro to the nanoscale seems to require an ability to comprehend
scales of one-billion. Scaling is a skill not common in most individuals and tests of their ability to extrapolate size based
upon scaling a common object demonstrates that most individuals cannot scale to the extent needed to make the transition to
nanoscale. Symbolism is another important vehicle to providing the general public with a basis to understand the concepts
of nanotechnology. With increasing age, individuals are able to draw representations of atomic scale objects, but these tend
to be iconic and the different representations not easily translated. Ball and stick models are most recognized by the public,
which provides an opportunity to present not only useful symbolism but also a reference point for the atomic scale. 相似文献
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介绍了虚构的法拉第定律与电子感应加速器不合理,用完整洛伦兹磁力解释电子感应加速器合理有效。 相似文献
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The rangefinder described here is a self-contained instrument for hand-held operation by a diver for searching, tracking, navigation and surveying applications. It has four modes: 1 — to measure range to a passive target directly to ± 1 m; 2 — to measure range to a passive target indirectly to ± 0.1 m; 3 — to measure range to a coded transponder to either ± 1 m or ± 0.1 m; 4 — to indicate the presence of multiple targets downrange where each target occurs in a selected range interval. The pulse echo principle is employed, with pulses typically 250 μs long. The carrier frequency of 300 kHz can be altered easily if required by changing the transducer array. 相似文献
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In the non-relativistic and quasi-static limit, it is possible to map exactly the system of galaxies in the observable universe onto an Ising magnet. Techniques from the theory of critical phenomena as applied to magnets can then be employed to calculate rigorously the galaxy-to-galaxy correlation function, whose critical exponent is predicted to be between 1.530 to 1.862, to be compared to the empirical/observational value of 1.6 to 1.8.This essay received the fifth award from the Gravity Research Foundation, 1996—Ed. 相似文献
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We suggest to use "fluctuation spectroscopy" as a method to detect granularity in a disordered metal close to a superconducting transition. We show that with lowering temperature T the resistance R(T) of a system of relatively large grains initially grows due to the fluctuation suppression of the one-electron tunneling but decreases with further lowering T due to the coherent charge transfer of the fluctuation Cooper pairs. Under certain conditions, such a maximum in R(T) turns out to be sensitive to weak magnetic fields due to a novel Maki-Thompson-type mechanism. 相似文献
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T. Jaravel O. Dounia Q. Malé O. Vermorel 《Proceedings of the Combustion Institute》2021,38(3):3529-3536
In the context of vapour cloud explosion, the flame acceleration process can lead to conditions promoting deflagration to detonation transition (DDT), potentially leading to increased damages in accidental scenarios. This study focuses on this phenomenon by performing simulations of detonation reinitiation for fast flames in the Chapman–Jouguet deflagration regime. It is obtained experimentally by the attenuation of an incident detonation by an array of obstacles. A primary objective of the paper is to demonstrate the ability of the numerical model to reproduce the major experimental trends, namely the variation of the reinitiation propensity for different initial pressures and blockage ratios (BRs). Chemical explosive mode analysis (CEMA) is also adapted to the context of this study, in order to identify locally the propagation regime and to provide insights on the reinitiation mechanism. An a priori validation of the CEMA methodology is first performed on relevant canonical one-dimensional configurations. Subsequently, ensembles of five realizations are computed at different initial pressures and BRs and compared to experimental data. They are shown to reproduce the major observed trends in terms of detonation reinitiation length with respect to the operating conditions, with significant variability from one realization to another. In addition, the reinitiation mechanism is also found to be consistent with experimental observations and a previous numerical study of the same configuration. The CEMA methodology adapted to this context is able to identify locally the different propagation regimes, and to track the highly reactive zones that coherently couple with transverse pressure perturbations, leading to the formation of a strongly reacting kernel which eventually triggers the detonation reinitiation. 相似文献
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Necessary and sufficient conditions are derived for three double polarisation measurements to complement cross section and single polarisation measurements in pseudoscalar meson photoproduction to enable amplitudes to be determined up to discrete ambiguities. Rules for choosing two further measurements to resolve the discrete ambiguities are given and practical applications of the rules to particular reactions are discussed. 相似文献
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We show the equivalence of semi-classical solutions to optical model coupled-channel equations derived from Watson's form of the nucleus-nucleus multiple-scattering series to the Glauber multiple-scattering series. A second-order solution to the semi-classical coupled-channel elastic amplitude is shown to be nearly equivalent to a second-order optical-phase-shift approximation to the Glauber amplitude if the densities of all nuclear excited states are approximated by the ground-state density. Using the Jastrow method to model the two-body density we find an average excited-state density to be of negligible importance in the double-scattering region of alpha-alpha scattering. 相似文献
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M. S. M. Nour El-Din J. A. Maruhn W. Greiner 《Zeitschrift für Physik A Hadrons and Nuclei》1986,325(4):415-420
The extended rotation-vibration model containing different deformations for protons and neutrons is applied to even-even Gd-isotopes and the results are compared to experiment and to other theoretical models. It is found to describe magnetic transitions reasonably well and to also give improved electric transition rates compared to the conventional model. 相似文献