“实际测量”教学有感

教学“实际测量”,只局限于课堂纸上谈兵,教师讲,学生被动地听、算是不行的。即使组织学生实际测量,可只是按教材中的程序,让学生验证书上的结论也是不够的。我是用探究法,让学生主动探究,自悟自得教学这一课的。

Understanding BitTorrent Through Real Measurements

In this paper, we present the resuks of the BitTorrent measurement study. Two sources of BitTorrent data were utilised： meta- data files and the logs of one of the currently most popular BitTorrent clients--gTorrent. Experimental data were collected for fifteen days from the popular torrent-discovery site thepiratebay.org （more than 30 000 torrents were captured and analysed）. During this pe- riod the activity and logs of an unmodified version of μTorrent client downloading ses- sions were also captured. The obtained ex- perimental results are swarm-oriented, which allows us to look at BitTorrent and its users from an exchanged resources perspective. Moreover, comparative analysis of the clients＇ connections with and without the μTP proto- col is carried out to verify the extent to which μTP improves BitTorrent transmissions. To the authors＇ best knowledge, none of the previous studies have addressed these issues.

Location Refinement and Power Coverage Analysis Based on Distributed Antenna

To establish wireless channel suitable for the cabin environment, the power coverage was investigated with distributed antenna system and centralized antenna system based on the actual measurement of channel impulse response. The results indicated that the distributed antenna system has more uniform power coverage than the centralized antenna system. The average relative errors of receiving power of both antennas were calculated. The optimal position of the centralized antenna was obtained by Gaussian function refinement, making the system achieve a better transmission power with the same coverage effect, and providing a reference for antenna location in the future real communication in the cabin.

A new damping ratio identification method based on pattern search

In order to improve the effectiveness of traditional time domain identification methods in identifying damping ratios, a new damping ratio identification method based on pattern search is proposed by fluctuating the reliable natural frequency obtained through traditional time domain identification methods by about 10% to build the boundary conditions, using all the initial identification results to establish the free decay response of the system, and using the pattern search method to correct the initial identification results with the residual sum of squares between the free decay response and the actually measured free-decay signal as the objective function. The proposed method deals with the actually measured free-decay signal with curve fitting and avoids enlarging the identified error caused by intermediate conversion, so it can effectively improve the identified accuracy of damping ratios. Simulations for a room-sized vibration isolation foundation show that the relative errors of analyzed three damping ratios are down to 1.05%, 1.51% and 3.7% by the proposed method from 8.42%, 5.85% and 8.5% by STD method when the noise level is 10%.

Thermodynamic functions of ZrW_2O_8 from its heat capacity

It is interesting to maximize the amount of information we can obtain from one experiment on a single sample. In obtaining all the thermodynamic properties of some materials from their experimental heat capacity data only, we aim to get the tempera- ture-independent energy spectrum. However, all the practical measured energy spectra depend on the temperature of experi- ments. One promising method to obtain the temperature-independent energy spectrum is to solve the so-called specific heat-phonon spectrum inversion （SPI） problem. Here we show, by developing a new practical solution method of SPI, the phonon spectrum of the negative thermal expansion material ZrW208 is obtained. This phonon spectrum is tempera- ture-independent and almost method independent. Hence all the thermodynamic properties of ZrW208, such as thermodynamic potential, entropy, Helmholtz free energy, etc. are obtained by heat capacity only.

Field acoustic measurements of high-speed train sound along BTIR

In this paper,single-point field measurements of noise radiated from high-speed trains were performed at two sites along Beijing-Tianjin intercity railway(BTIR),aiming at acquiring the realistic acoustic data for validation and verification of physical model and computational prediction.The measurements showed that A-weighted sound pressure levels(SPLs) were between 80 and 87 dBA as trains passed.The maximum noise occurred at the moment when the pantograph arrived,suggesting that pantograph noise was one of the most significant sources.Sound radiated from high-speed trains of BTIR was a typical broadband spectrum with most acoustic power restricted in the range of medium-high frequency from about 400 Hz to 5 kHz.Aerodynamic noise was shown to be the dominant one over other acoustic sources for high-speed trains.

Uncertainty and Certainty Relations for Successive Projective Measurements of a Qubit in Terms of Tsallis' Entropies

We study uncertainty and certainty relations for two successive measurements of two-dimensional observables. Uncertainties in successive measurement are considered within the following two scenarios. In the first scenario, the second measurement is performed on the quantum state generated affer the first measurement with completely erased information. In the second scenario, the second measurement is performed on the post-first- tioned on the actual measurement outcome. Induced entropies. For two successive projective t state condiquantum uncertainties are characterized by means of the Tsallis t of a qubit, we obtain minimal and maximal values of related entropic measures of induced uncertainties. Some conclusions found in the second scenario are extended to arbitrary finite dimensionality. In particular, a connection with mutual unbiasedness is emphasized.