Dual-Frequency Behavior of Stacked High <Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> Superconducting Microstrip Patches

The dual-frequency behavior of stacked high T _c superconducting rectangular microstrip patches fabricated on a two-layered substrate is investigated using a full-wave spectral analysis in conjunction with the complex resistive boundary condition. Using a matrix representation of each layer, the dyadic Green’s functions of the problem are efficiently determined in the vector Fourier transform domain. The stationary phase method is used for computing the radiation electric field of the antenna. The proposed approach is validated by comparison of the computed results with previously published data. Variations of the lower and upper resonant frequencies, bandwidth and quality factor with the operating temperature are given. Results showing the effects of the bottom patch thickness as well as the top patch thickness on the dual-frequency behavior of the stacked configuration are also presented and discussed. Finally, for a better comprehension of the dual-frequency operation, a comparison between the characteristics of the lower and upper resonances is given.     

Polysorbate20 adsorption layers below and above the critical micelle concentration over aluminum; cloud point and inhibitory role investigations at the solid/liquid interface

Non‐ionic polysorbate20 surfactant was used to produce adsorption protective layers below and above its critical micelle concentration (CMC) at the liquid/solid interface. The well‐ordered accumulation of surfactant molecules on the metal surface below the CMC led to the formation of oriented surfactant monolayers. On the other hand, as the surfactant concentration increased above the CMC, the monodisperse micelles, free surfactant molecules and oriented surfactant monolayers undergo aggregate formation and produce a turbid solution. The gradual increase in the number and size of aggregates leads to phase separation and hence disassembled protective layers that allow easier penetration of corrosive HCl at a metal surface. This was demonstrated by inhibition efficiency, activation energy, enthalpy and entropy of activation values. Two‐dimensional irregular crystalline sheets accumulated at the surface of aluminum, as shown by scanning electron micrographs. Adsorption of polysorbate20 at the aluminum surface exhibited a Temkin isotherm fit. Larger desorption processes at the cloud point demonstrate aggregate formation and phase separation, and hence poorer adsorption layers at the metal surface. Copyright © 2012 John Wiley & Sons, Ltd.     

The reduced basis method for the electric field integral equation

We introduce the reduced basis method (RBM) as an efficient tool for parametrized scattering problems in computational electromagnetics for problems where field solutions are computed using a standard Boundary Element Method (BEM) for the parametrized electric field integral equation (EFIE). This combination enables an algorithmic cooperation which results in a two step procedure. The first step consists of a computationally intense assembling of the reduced basis, that needs to be effected only once. In the second step, we compute output functionals of the solution, such as the Radar Cross Section (RCS), independently of the dimension of the discretization space, for many different parameter values in a many-query context at very little cost. Parameters include the wavenumber, the angle of the incident plane wave and its polarization.     

Three-dimensional pore evolution of nanoporous metal particles for energy storage

A well characterized and predictable aging pattern is necessary for practical energy storage applications of nanoporous particles that facilitate rapid transport of ions or redox species. Here we use STEM tomography with segmentation to show that surface diffusion and grain boundary diffusion are responsible for pore evolution at intermediate and higher temperatures, respectively. This unprecedented three dimensional understanding of pore behavior as a function of temperature suggests routes for optimizing pore stability in future energy storage materials.     

Complexity-reduced Volterra series model for power amplifier digital predistortion

This paper expounds a complexity-reduced Volterra series model for radio frequency power amplifier (PA) behavioral modeling and digital predistortion (DPD). An analysis was conducted, which took into account the memory effect mechanisms of the PA. This led to a closed-form expression that relates the memoryless behavior of the PA to the finite impulse response feedback filter, which approximates the memory effects’ behavior. The analysis resulted in a complexity-reduced Volterra series model which allows for a substantial reduction in the requirements for digital signal processors and the time needed to construct and implement the DPD in a real-time environment. The proposed model was validated as a behavioral model and a DPD using two different PA architectures, employing two different transistor technologies, driven by both 20 MHz 1001 wideband code division multiple access and long term evolution signals. The results obtained demonstrate the excellent modeling and linearization capability of the complexity-reduced Volterra series model.     

Micro mobility in the IP networks

Wireless access to Internet services will become typical, rather than the exception as it is today. Such a vision presents great demands on mobile networks. Mobile IP represents a simple and scalable global mobility solution but lacks the support for fast handoff control and paging found in cellular telephony networks. In contrast, second- and third-generation cellular systems offer seamless mobility support but are built on complex and costly connection-oriented networking infrastructure that lacks the inherent flexibility, robustness, and scalability found in IP networks. This paper presents an overview and performance comparison of two of the main micro-mobility protocols, namely Cellular IP and Hierarchical Mobile IP with regards to the handoff process for UDP applications. The differences in the handoff quality of the two protocols are small and can be traced to design choices within the typical model. There are however significant differences regarding the processing requirement, routing efficiency and parameters relating to implementation and deployment.     

High-speed bridges for fiber optic local area networks

Progress in optical fiber communications allows ever-increasing channel capacity for local area networks (LANs). However, there are still many problems to solve with respect to bridges interconnecting these LANs, which constitute a system bottleneck. To eliminate the bridge bottleneck in the interconnection of fiber optic LANs, a high-speed bridge using optical technology is proposed. The proposed optical bridge uses bistable optical devices, such as interference filters, as essential components of its design. As these devices can be easily fabricated, the implementation of this optical bridge is feasible.     

A differential equation for approximate wall distance

A partial differential equation to compute the distance from a surface is derived and solved numerically. The benefit of such a formulation especially in combination with turbulence models is shown. The details of the formulation as well as several examples demonstrating the influence of its parameters are presented. The proposed formulation has computational advantages and can be favourably incorporated into one‐ and two‐equation turbulence models like e.g. the Spalart–Allmaras, the Secundov or Menter's SST model. Copyright © 2002 John Wiley & Sons, Ltd.     

Integration of Mobile-IP and OLSR for a Universal Mobility

Trends in fourth generation (4G) wireless networks are clearly identified by the full-IP concept where all traffic (data, control, voice and video services, etc.) will be transported in IP packets. Many proposals are being made to enhance IP with the functionalities necessary to manage the mobility of nodes, so that networks can provide global seamless roaming between heterogeneous wireless and wired networks. In this paper, we focus on the management of universal mobility, including both large scale macro-mobility and local scale micro-mobility. We propose a hierachical architecture (i) extending micro-mobility management of a wireless access network to an ad-hoc access network, (ii) connecting this ad-hoc network to the Internet and (iii) integrating Mobile IP and OLSR, a routing protocol for ad-hoc networks, to manage universal mobility. This architecture is validated by an implementation based on DynamicsMobile-IP and OLSR version 7. We show how the brodcast of Mobile-IP Agent Advertisement can be optimized using OLSR MPR-flooding.