How far is far?

Recent comparisons of computed and measured backscattering cross sections of cylindrical bodies revealed unexpectedly large discrepancies which were apparently due to the finite range used in the measurements. This led to a reexamination of the farfield criterion for a variety of two-dimensional scatterers and one three-dimensional object. It was found that large errors can be incurred in measurements at the standard far-field distance, especially of bodies characterized by strong edge scattering. Errors as great as 6 dB can occur and it may be necessary to exceed the usual farfield distance by a factor of 5 or more in order to reduce the error to 1 dB.     

Target reconstruction from scattered far field data

The problem of finding the shape of a perfectly conducting cylinder when illuminated by an E-polarized incident electromagnetic wave is considered. The given problem is cast in the form of a penalized optimization problem in which we seek a surface in some suitably constrained class which minimizes a functional involving two terms. The first term measures the mean square deviation of the far field of the solution to the direct scattering problem for a surface in the admissible class from given, measured, far field data whilst the second term, penalty, measures the error in satisfying the imposed boundary conditions. An optimisation algorithm is used which does not require that a direct problem be solved in the updating process. Explicit reconstructions are presented which illustrate the effectiveness of the method. Some results indicating the sensitivity of the algorithm to the choice of penalty parameter and the number of incident waves are also given.     

远离平衡系统临界指数的标度理论

以Ｄｉｃｋｅ模型为具体事例,并运用耗散系统准热力学关系式,研究了远离热平衡体系临界指数问题。所取得的结果符合临界指数的标度律与Ｗｉｄｏｍ的标度理论。     

涉及各方重大利益 网络中立之争远未结束

从2010年底美国FCC通过《网络中立条例》至今,整整一年过去了,从全球特别是美欧各国市场的反应和发展态势来看,虽然争论多年的“网络中立”政策终于向前迈出了探索性的关键一步,但仍处在博弈和纠结中,各方的争论也远远没有结束,尤其是,一年来随着以应用商店为特征的移动互联网的深入发展,围绕着未来网络控制权和接人权的争夺愈演愈烈。这不仅要求我们对其进行认真的梳理,也需要更进一步地深入思考。     

Equivalent-step-index-fibre determination from wavelength dependence of far field

We compare two simple techniques for determination of equivalent-step-index parameters in single-mode fibres from measurement of the wavelength dependence of the far-field intensity profile. In one case the data is fitted directly by the step-index formula to yield the core radius and the v-value. In the other, wavelength dependence of the half-intensity angle is fitted to an empirical expression recently reported to give the core radius and the cutoff wavelength.     

动力赋全球 携手赢天下——-2009年度伊顿代理商大会在珠海召开

2009年2月20日，以“动力赋全球携手赢天下”为主题的伊顿公司2009年度代理商大会在风景秀丽的珠海德翰大酒店隆重举行。能容纳400人的会议厅中座无虚席，人们交流畅谈，气氛热烈。会场中，巨幅蓝色背板上“动力赋全球携手赢天下”十个大字分外醒目，这是伊顿在并购飞瑞后，三大UPS产品系列的首次代理商全体会议。     

Calculation of antenna mutual coupling from far radiated fields

Mutual coupling between a pair of identical array elements is calculated from far field radiation. The reaction theorem is used on a single element to carry out a mutual coupling calculation. Evaluation of the reaction integral over a spherical surface surrounding a single waveguide element produces results better than the conventional aperture surface integral when using far fields. The method provides a simple tool for the estimate of mutual coupling given knowledge of the far field radiation of a single element. This is of great advantage during the development of array elements of unusual geometry, where analysis or other measurement techniques are difficult or less convenient.<>     

Dielectric losses in a tin-zirconium titanate ceramics computed from the far infrared spectrum

It is shown from observations in both microwaves and far infrared that dielectric losses are smaller than computed from the assumption of far infrared Lorentz oscillators. An explanation is suggested.     

Quantum cascade lasers: from sketch to mainstream in the mid and far infrared

Electrically-pumped semiconductor lasers based on monolithic chip configuration possess plenty of advantages such as small volume,light weight,long lifetime and stable performance.Nevertheless this type of lasers rely on the interband transition,which sets the bounds for emission wavelength typically below 4μm,and state of the art performance has been attained below 3μm.Attempts to employ small bandgap meterials like antimonide or lead salts ended with poor performance mainly due to imperfect crystal quality and severe Auger recombination.In view of the broad application prospects of infrared spectral range above 3μm,more attention was casted again on the low-dimensional quantum structure materials,such as quantum wells and quantum dots,which have been applied in the near infrared successfully decades ago.