On the stability of time-marching schemes for the general surfaceelectric-field integral equation

We demonstrate that time marching algorithms which use the electric-field integral equation to compute the current induced on a perfect conductor by a transient electric field, may have unstable modes that are due to the particular basis functions used to represent the current on the conductor. These modes are not removed by averaging the solution in time, but they can be eliminated by averaging in space appropriately     

Strange attractors in multipath propagation

The estimation of the correlation dimension of multipath propagation signals in an indoor environment, indicates the presence of a strange attractor of dimension between four and five, suggesting deterministic chaos. The authors stress that although the profiles they examined show saturation in all three experimental configurations, indicating that they would be able to describe their data with a set of at most five nonlinear differential equations, investigation in other propagation situations is needed. An example of the detection of the presence of strange attractors in radar clutter is presented     

Stagewise Weak Gradient Pursuits

Finding sparse solutions to underdetermined inverse problems is a fundamental challenge encountered in a wide range of signal processing applications, from signal acquisition to source separation. This paper looks at greedy algorithms that are applicable to very large problems. The main contribution is the development of a new selection strategy (called stagewise weak selection) that effectively selects several elements in each iteration. The new selection strategy is based on the realization that many classical proofs for recovery of sparse signals can be trivially extended to the new setting. What is more, simulation studies show the computational benefits and good performance of the approach. This strategy can be used in several greedy algorithms, and we argue for the use within the gradient pursuit framework in which selected coefficients are updated using a conjugate update direction. For this update, we present a fast implementation and novel convergence result.     

Uncooled DBR laser directly Modulated at 3.125 gb/s as athermal transmitter for low-cost WDM systems

An uncooled three-section tunable distributed Bragg reflector laser is demonstrated as an athermal transmitter for low-cost uncooled wavelength-division-multiplexing (WDM) systems with tight channel spacing. A /spl plusmn/0.02-nm thermal wavelength drift is achieved under continuous-wave operation up to 70/spl deg/C. Dynamic sidemode suppression ratio of greater than 35 dB is consistently obtained under 3.125-Gb/s direct modulation over a 20/spl deg/C-70/spl deg/C temperature range, with wavelength variation of as low as /spl plusmn/0.2 nm. This indicates that more than an order of magnitude reduction in coarse WDM channel spacing is possible using this source.     

The Future of Web Services

Much of the Web's success can be attributed to its simplicity. It offers a straightforward means by which static information could be published and interconnected on a global basis. The Web Services initiative effectively adds computational objects to the static information of yesterday's Web and as such offers a distributed services capability over a network. Web Services have the potential to create new paradigms for both the delivery of software capabilities and the models by which networked enterprises will trade. Today's Web Services technology, useful though it is, will be enhanced over the next 2-5 years by the harnessing of Semantic Web technology to deliver a step change in capability. Web Services provide an easy way to make existing (or indeed new) components available to applications via the Internet. However, currently, Web Services are essentially described using semi-structured natural language mechanisms, which means that considerable human intervention is needed to find and combine Web Services into an end application. The Semantic Web will enable the accessing of Web resources by semantic content rather than just by keywords. Resources (in this case Web Services) are defined in such a way that they can be automatically ‘understood’ and processed by machine. This will enable the realisation of Semantic Web Services, involving the automation of service discovery, acquisition, composition and monitoring. Software agents will be able automatically to create new services from already published services, with potentially huge implications for models of eBusiness. Having identified limitations in current Web Services technology, this paper will survey existing research in Semantic Web Services, most notably USA's DAML-S initiative and the European WSMF work, and describe BT's research into creating a set of tools to support next-generation Semantic Web Services. This revised version was published online in July 2006 with corrections to the Cover Date.     

A 0.9-V microcontroller for portable applications

A 0.9-1.6-V, 1-MHz, 8-b microcontroller based on the 68HC08 architecture is presented. In addition to standard digital microcontroller functions, the chip features RAM, ROM, phase-locked loop (PLL) clock synthesis, and liquid crystal displays (LCD) drive capabilities operating from the voltage supply range of a single AA or AAA battery. The design used a library of CMOS microcontroller building blocks, converted into a low-voltage technology using unilateral transistors. The design approach was to optimize the conversion strategy for each functional block and to provide new designs when the conversion was insufficient. The chip exceeded specifications with blocks showing full functionality down to 0.7 V     

铝－锂合金中δ’（Al＿3Li）沉淀相时效粗化行为及体积分数的测定

对经固溶处理的二种Ａｌ－Ｌｉ合金（１．９４ｗｔ．％Ｌｉ和２．７５ｗｔ．％Ｌｉ）的时效过程进行了研究。结果表明：δ’的生长速率遵从Ｏｓｔｗａｒｄ粗化动力学。１．９４ｗｔ．％Ｌｉ合金δ’产生于时效过程中，而２．７５ｗｔ．％Ｌｉ合金的δ’产生于时效的前期阶段。前者的表现体积分数明显大于根据相图估算的数伍，真实体积分数则与此值接近；后者的体积分数低于根据相图估算的数值，这可能归咎于δ’固相线的位置、统计学误差及Ｌｉ更易在时效过程中贫化。     

Noise performance of a GaAs MESFET as an optical detector and as an optoelectronic mixer in analogue optical links

Noise measurements with a GaAs MESFET employed as a photodetector or as an optoelectronic mixer are reported. Despite its higher noise it is shown that with proper biasing the GaAs MESFET provided a higher carrier-to-noise ratio than a pin photodiode, and as an optoelectronic mixer provided a comparable signal-to-noise ratio to that of a conventional pin and microwave mixer combination. The implications of using GaAs MESFETs in these configurations are discussed.<>     

Implantation annealing by thermal imaging

Elliptical mirrors have been used to image incoherent light sources onto silicon for the purpose of annealing implanted layers. It is found that ~1 s of illumination is sufficient for annealing areas that approximate the dimensions of the source. Low-dose boron implants are found to be fully activated without any significant diffusive redistribution. Amorphous layers produced by implanting arsenic can be annealed to exhibit minimum yields of ~4% from back-scattering and give sheet resistivities comparable with thermal annealed values. It is envisioned that the annealing can be expanded to large areas and throughputs by physically moving wafers through the 2 in-long heating strip produced by the present configuration.