Impact fatigue of an alumina ceramic

A new type of pendulum impact apparatus is described for determining single and repeated impact strength of ceramics, It has been demonstrated that specimens of a Sintox alumina ceramic exhibit fatigue behaviour, having a high stress plateau followed by progressively increasing endurance with decrease in applied impact energy. A fatigue limit, at least from the engineering view point, has been drawn at high endurances (10⁵ impacts). The influence of environment (static fatigue) and/or plastic deformation to explain the fatigue behaviour is suggested.     

Antiredeposition additives face new opportunities

Recent trends in fabric composition, choice of raw materials, and government regulations are placing new demands on the use and utility of antiredeposition additives.     

Generation of Bessel functions of complex order and argument

Recurrence techniques are described for the generation of Bessel functions of the first and second kinds where both the argument and order may be complex. The method is shown to be accurate for several well known forms of functions, including Kelvin and spherical Bessel functions. The accuracy of the general case of complex order and argument is determined by computing the Wronskians and by verifying some addition theorems of the Bessel functions over wide ranges of order and argument. Procedures for the accurate generation of complex-argument gamma functions are also described.     

Algebraic relations between system response and system parameters for linear time-invariant systems

By means of a rational-fraction approximation to the delay function, and through use of a generalised technique for evaluating convolution integrals, it is possible to approximately evaluate the inverse Laplace transform. The time-domain response is approximated by a ratio of polynomials in t, with coefficients which are algebraic functions of the system parameters.     

Precipitation phase transformation in nanocrystalline Fe-Mo alloys

Precipitation phase transformation was studied in nanocrystalline Fe-rich Fe-Mo alloys with the use of X-ray diffraction and M?ssbauer spectroscopy. Alloys up to 5 at% Mo in Fe were synthesized by mechanical alloying and formed in alpha phase bcc solid solutions with average grain sizes in the range of 10-13 nm. The precipitation transformation (alpha-->alpha + lambda) was found to proceed via a Mo clustering that was correlated with the size of the nanograins. This was understood in terms of the Gibbs Thomson effect with a concept of negative surface energy contribution to the Gibbs free energy of mixing in a nanocrystalline alloy with positive internal energy of mixing. This contribution increased the stability of the solid solution for nanosized grains, and the Mo precipitation started once the grains grew beyond a critical size. We argue that the Mo precipitation takes place in the grain boundary regions, and the Mo-rich lambda phase also precipitates directly in the grain boundary regions, in contrast to the microcrystalline alloys, where the Mo clusters formed within the grains and were first dissolved in the Fe matrix before the lambda phase was formed.     

Hybrid Wireless-Optical Broadband-Access Network (WOBAN): A Review of Relevant Challenges

The hybrid wireless-optical broadband-access network (WOBAN) is a promising architecture for future access networks. Recently, the wireless part of WOBAN has been gaining increasing attention, and early versions are being deployed as municipal access solutions to eliminate the wired drop to every wireless router at customer premises. This architecture saves on network deployment cost because the fiber need not penetrate each end-user, and it extends the reach of emerging optical-access solutions, such as passive optical networks. This paper first presents an architecture and a vision for the WOBAN and articulates why the combination of wireless and optical presents a compelling solution that optimizes the best of both worlds. While this discussion briefly touches upon the business drivers, the main arguments are based on technical and deployment considerations. Consequently, the rest of this paper reviews a variety of relevant research challenges, namely, network setup, network connectivity, and fault-tolerant behavior of the WOBAN. In the network setup, we review the design of a WOBAN where the back end is a wired optical network, the front end is managed by a wireless connectivity, and, in between, the tail ends of the optical part [known as optical network unit (ONU)] communicate directly with wireless base stations (known as ldquogateway routersrdquo). We outline algorithms to optimize the placement of ONUs in a WOBAN and report on a survey that we conducted on the distribution and types of wireless routers in the Wildhorse residential neighborhood of North Davis, CA. Then, we examine the WOBAN's routing properties (network connectivity), discuss the pros and cons of various routing algorithms, and summarize the idea behind fault-tolerant design of such hybrid networks.     

TD‐CFIE Formulation for Transient Electromagnetic Scattering from 3‐D Dielectric Objects

In this paper, we present a time domain combined field integral equation formulation (TD‐CFIE) to analyze the transient electromagnetic response from dielectric objects. The solution method is based on the method of moments which involves separate spatial and temporal testing procedures. A set of the RWG functions is used for spatial expansion of the equivalent electric and magnetic current densities, and a combination of RWG and its orthogonal component is used for spatial testing. The time domain unknowns are approximated by a set of orthonormal basis functions derived from the Laguerre polynomials. These basis functions are also used for temporal testing. Use of this temporal expansion function characterizing the time variable makes it possible to handle the time derivative terms in the integral equation and decouples the space‐time continuum in an analytic fashion. Numerical results computed by the proposed formulation are compared with the solutions of the frequency domain combined field integral equation.     

Dynamic power density, wavelength, and switching time modulation of optically triggered power transistor (OTPT) performance parameters

Optical modulation by varying the intensity, wavelength, or switching time can dynamically alter the performance parameters of direct optically controlled power semiconductor device. Understanding the effect of optical parameters on these parameters from a first principle approach is necessary for making optimal design choices and gaining design insights. We focus on performance parameters whose variations with direct optical modulation have not been reported previously for a power semiconductor such as switching times and on-state resistance. We carry out analytical modeling and two-dimensional (2D) finite-element simulations for a GaAs/AlGaAs based superjunction lateral optically controlled power transistor that has been fabricated and successfully tested for high-voltage capability. It is shown that optical power density can modulate on-state resistance and more importantly the trade-off curve between breakdown voltage and on-state resistance. A closed-form analytical equation relating switching times with optical parameters via logarithmic function is derived and the nonlinear variation of on-state resistance and switching time with optical wavelength is illustrated. We also derive the analytical expression for power device rise time as a function of optical signal rise time and show that they are related by Lambert's W-function with exponential coefficients.