摘要：The impact of satellite motion on two-way satellite time and frequency transfer (TWSTFT) is analysed. Due to the two distances from two stations to the satellite being different, the non-reciprocal paths are produced, which impact the accuracy of TWSTFT. Choosing a satellite for which both elevations are about the same can minimise the effect, or offsetting the transmission time can eliminate this. In addition, due to Earth's rotation and the finite signal velocity, the non-reciprocal paths are also produced, and the error mainly results from the aviation of the satellite longitude and altitude.

摘要：The plotting of the frequency transfer function has been simplified for decades by using,logarithmic plots. One advantage of logarithmic plots is that the mathematical operations of multiplication and division are transformed to addition and subtraction. With this method the work of obtaining the phase of transfer function is largely graphical instead analytical. On the other hand, we need the factors of the transfer function. In case we have only gain samples this might be a sensitive issue. The difficulty increases if there is available only a part of the samples. Moreover, the distance between samples might be not very small and this is the most encountered case in practical situations. The goal of this paper is to address this special situation. Therefore we establish methods for approximating the phase values from the gain samples, in nepers, equally spaced in the logarithmic frequency domain. First a general approximation formula is proved, then two quadrature formulae are derived using Newton-Cotes and Simpson rules. Numerical examples are also presented.

摘要：Geophysical properties of acoustic, seismic, electric, and magnetic waveforms create opportunities and constraints for animals' communication and sensory monitoring of the environment. The geometric spreading of waves differs; at some frequencies, transmission is most efficient and has minimal noise. The spreading properties of seismic waves favor long-distance propagation for communication and environmental monitoring, and would benefit elephants (Elephas maximus and Loxodonta africana), such as in locating subsurface water. Extending C. E. O'Connell-Rodwell, B. T. Arnason, and L. A. Hart (2000), a man jumping at 1.11 km propagated seismic waves at 10-40 Hz. Given the noise of lightning and the Schumann resonances, near field magnetic and electric transmission by animals would be most efficient around 1000 Hz.

摘要：A field-jump device for fast stepping the electron paramagnetic resonance magnetic field around 3.4 T during pulsed electron-electron double resonance experiments at W-band (95 GHz) is described. Field jumps up to +/- 160 G and submicrosecond times for the full field-jump cycle allow precession frequency transfer experiments to be made for the determination of the nanometer distance and the orientation of nitroxide spin-label pairs in disordered samples.

摘要：Until recently, the Global Positioning System (GPS) was the only operational means of distributing time to an arbitrary number of users and of synchronizing clocks over large distances with a high degree of precision and accuracy. Over the last few years it has been shown that similar performance can be achieved using the Russian Global Navigation Satellite System (GLONASS). GLONASS time transfer between continents was initially hampered by the lack of postprocessed precise ephemerides. Results from the International GLONASS Experiment (IGEX) campaign are now available, however, and this paper reports on the first use of IGEX precise ephemerides for GLONASS P-code intercontinental time links. The results of GLONASS P-code and GPS C/A-code time transfer are compared under similar conditions.

摘要：In the Acoustic Thermometry of Ocean Climate (ATOC) program's Acoustic Engineering Test (AET), broadband 75-Hz center frequency transmissions were recorded on a 700-m-long vertical array, 3252 km distant from a midwater source suspended from R/P FLIP. The transmissions occurred over a 6-day period. Previously reported results from the AET using 12.7-min averaged data by Colosi et al. [J. Acoust. Sec. Am. 105(6), 3202-3218 (1999)], hereafter referred to as Colosi99) revealed surprisingly weak acoustic scattering for early arriving identifiable wavefronts. Colosi99 found pulse time spreads on the order of 0-5 ms and the probability density function (PDF) of peak intensity was close to log normal. In this paper these results are confirmed using 1.8-min averaged data. It is also shown that scintillation index (SI) is a strong function of position along the pulse with the smallest values occurring at the peak and larger values occurring at the tails. Intensity PDFs of identifiable wavefronts are reanalyzed in terms of both peak intensity and integrated pulse energy (IE) where the integration is over +/- 50 ms from the wavefront peaks. While SI for the IE are somewhat smaller than for the peak intensity, the PDFs are both very closely log normal. Regarding multipathing along the wavefronts, it is found that on average there are 1.7 peaks per wavefront segment per hydrophone and the intensity PDF of all multipath peaks is log normal. The combined observation of weak scattering and multipathing is a novel result. A reanalysis of the scintillations in the AET transmission finale where no wavefronts are evident is presented. Colosi99 analyzed the finale in terms of peak scintillations and found a near log-normal intensity PDF. Reprocessing the full field without limiting data to intensity peaks and accounting for mean intensity nonstationarity yields an intensity PDF which is much closer to the exponential distribution associated with full saturation; these results show that the finale region can be expected to behave much like Gaussian random noise. (C) 2001 Acoustical Society of America.

摘要：through testing and analyzing the impact caused by the electrified railway on audio-video program production, this paper indicates that the electrified railway will cause obvious impact on the audio-video system, especially the audio frequency, within a certain distance. The interference ways mainly are electromagnetic radiation coupling interference. Under the condition of bad earthing, static induction impact will also become an interference source not to be ignored. The protective measures should be laid particular emphasis on increasing the balance level of the audio-frequency transmission line, improving the earthing effect or implementing the electromagnetic screening measures.

摘要：FM-CW radar is capable of detecting subsurface anomalies by using linear sweep frequency transmission of a periodically repetitive continuous FM signal. Due to the continuous-wave nature, the peak power of the FM-CW radar is usually in the range of hundreds of milliwatts. In cases where high resolution is necessary, the FM-CW radar is preferred because of the simple hardware structure and the availability of low-power components. The distance from the antenna to an anomaly can be determined by FM-CW radar in lossless media. In this paper, we present both analytical and numerical methods for modelling FM-CW radar performance in lossless and lossy layered formations for 1D and 2D cases. The FM-CW operating frequency is set in the range of 1-2 GHz, and the sweep periods are 10 ms and 2 ms, respectively. An inversion formulation is discussed to invert the distance and dielectric constant simultaneously from the spectrum of the received signal by using FFT and the 'range equation'. The spatial resolution is about one-third of the center wavelength and the depth of penetration is about 4 m in a medium having a conductivity less than 1 mS/m. The FM-CW radar technique cannot be used in a lossy medium having conductivity more than 30 mS/m. The spectrum and images of multilayer formations is also studied. (C) 1999 Elsevier Science B.V. All rights reserved.

摘要：Butyrivibrio fibrisolvens strains resistant to tetracycline were isolated from the bovine rumen. Two of three Tc-r B. fibrisolvens tested were able to donate tetracycline resistance at frequencies ranging from 10(-7) to 10(-1) per donor cell in anaerobic filter matings to a rifampin-resistant mutant of the type strain of B. fibrisolvens, 2221(R). The recipient strain 2221(R) exhibited rapid autoaggregation, which might be a factor in the high transfer rates observed. Tc-r transconjugants of B. fibrisolvens 2221(R) were also capable of further transferring tetracycline resistance to a fusidic acid-resistant mutant, 2221(F). Comparison of genomic DNAs by pulsed-field gel electrophoresis demonstrated altered band profiles in transconjugants, consistent with the acquisition of a large mobile chromosomal element. The transferable elements from the two B. fibrisolvens donors 1.23 and 1.230 (TnB123 and TnB1230, respectively) showed the same preferred insertion site in the B. fibrisolvens 2221(R) chromosome and are likely to be similar, or identical, elements. Hybridization experiments showed no close relationship between TnB1230 and int-xis regions from Tn916 of Tn5253. Although DNA from the B. fibrisolvens donor stains hybridized with probes carrying tet(M) of tet(O) sequences, transconjugants were found to have acquired a distinct band that hybridized only weakly with these probes, suggesting that a second, distantly related Tc-r determinant had been transferred.

摘要：The National Institute of Standards and Technology (NIST) has built a two-way time-transfer device which uses any currently unused byte in the SONET (SDH) overhead to effect time transfer, The hardware shows stability which allows time transfer over short distances (km) with stabilities less than 10 ps. Time transfer over distances that require additional amplifiers in the fiber have not yet been investigated, Accuracy at the same level should also be possible.