Home networking at 60 GHz: challenges and research issues

The recent developments in CMOS technology are about opening a new exciting door to affordable 60-GHz radio applications. One promising application area for 60-GHz radio is home networks in which there is an increasing demand for multi-gigabit wireless networking. The research efforts so far have generally focused on utilizing the 60-GHz band for point-to-point communication by addressing its physical aspects like propagation characteristics and channel models. The issues of 60-GHz networking at the system level have not been adequately considered. In this paper, the challenges and the research issues of 60-GHz networking are reviewed from the system-level perspective. We present them in the context of wireless local area networks for future home networks with discussions on some possible solutions for the introduced challenges.     

Engineering solid oxide fuel cell electrode microstructure by a micro-modeling tool based on estimation of TPB length

In this study, a typical solid oxide fuel cell (SOFC) electrode microstructure is numerically optimized in terms of the volume fraction of the catalyst, electrolyte and pore phases via a novel tool based on Dream.3D for the synthetic microstructure reconstruction and COMSOL Multiphysics® Modeling for visualizing and computing three/triple phase boundaries (TPBs). First, the properties of the representative volume element are studied by a parameter independence analysis based on the average particle size. The results indicate that the size of the representative volume element should be at least 10 times greater than the largest average particle size in the microstructure, while the number of mesh elements should be selected such that the smallest average particle size in the system is divided into at least 5. The method is then validated with the available studies in the literature and seems to agree well. Therefore, numerical reconstruction of SOFC electrodes by the proposed method is found to be a very useful tool in the viewpoints of accuracy, flexibility and cost. Finally, SOFC electrode microstructures having the same particle size distribution of an average particle size of 0.5 μm for each phase but with various phase volume fractions are generated and the resultant TPBs are computed similarly. It is found out that the volume fraction of each phase should be close to each other as much as possible to maximize the active TPB density and among the cases considered, the highest active TPB density of 9.53 μm/μm³ is achieved for an SOFC electrode including 35 vol% catalyst, 35 vol% electrolyte and 30 vol% porosity. The active TPB density is also found to be around 93% of the total TPB density.     

A regional analysis of federal reserve districts

The U.S. Federal Reserve System (Fed) has a unique regional structure, one with a large amount of autonomy and authority for its twelve regional district banks. In this paper we briefly review the history behind establishment of this structure in 1913, and address the question, “Does this unchanged regional structure of the Fed make sense today?” Three criteria are used to assess the appropriateness of the regional structure: 1) proportionality of representation in monetary policy decisions, 2) the functional economic nature of Fed district boundaries, and 3) the quality of regional economic reporting by regional district banks. After finding substantial shortcomings in all areas, we propose a more modern set of district boundaries, which improves proportionality of representation, recaptures the functional economic character of Fed districts, while maintaining the possibility of meaningful district-wide regional economic reporting and analysis. Received: March 2001/Accepted: August 2001     

Experimental investigation and numerical modelling of photocurrent oscillations in lattice matched Ga1?x In x N y As1?y /GaAs quantum well p-i-n photodiodes

Photocurrent oscillations, observed at low temperatures in lattice-matched Ga_1−xIn_xN_yAs_1−y/GaAs multiple quantum well (MQW) p-i-n samples, are investigated as a function of applied bias and excitation wavelength and are modelled with the aid of semiconductor simulation software. The oscillations appear only at low temperatures and have the highest amplitude when the optical excitation energy is in resonance with the GaInNAs bandgap. They are explained in terms of electron accumulation and the formation of high-field domains in the GaInNAs QWs as a result of the disparity between the photoexcited electron and hole escape rates from the QWs. The application of the external bias results in the motion of the high-field domain towards the anode where the excess charge dissipates from the well adjacent to anode via tunnelling.     

The influence of blood and/or hemostatic agent contamination on Micro-TBS to dentin

Aim: The purpose of this study was to evaluate the effects of blood contamination and hemostatic agent Ankaferd Blood Stopper (ABS: Ankaferd Drug Inc, Istanbul, Turkey) on the microtensile bond strength of a self-etching adhesive. Material and methods: Flat dentin surfaces were created from 40-M teeth and randomly divided to four groups according to contamination and adhesive procedure. The specimens of Group 1 are contaminated with blood; ABS was applied to the specimens of Group 2 after blood contamination and applied to the specimens of Group 3 without blood contamination. Group 4 is control group and self-etching adhesive was applied to all specimens. Teeth were restored with a nanohybrid composite. The specimens were sectioned to the beams and microtensile testing was carried out and the data were statistically analyzed with analysis of variance test. Tukey’s honestly significant difference post hoc test was also performed for multiple comparisons to compare subgroups. Results: Group 4 had the highest strength value, followed by Group 3, while Group 1, which contacts only with blood, had the lowest strength value. Conclusion: ABS has a negative effect on the bond strength of one-step self-etching adhesive system.     

Thermal optical properties of TiO2 films

A fibre optic experimental arrangement was used to determine the thermo-optic coefficient (dn/dT) of electron beam deposited titanium dioxide coatings on the cleaved end faces of multimode optical fibres for a wavelength range between 600 and 1050 nm. The temperature-induced change in the index of refraction (n) and extinction coefficient (k) were successfully determined from reflection spectra. Measurements of n and k at various wavelengths for different temperatures enabled the determination of dn/dT and dk/dT. It was found that dn/dT takes different values at different temperature ranges. For example, at 800 nm, dn/dT was (−1.77±0.7)×10⁻⁴ K⁻¹, between 18°C and 120°C, and took a value of (−3.04±0.7)×10⁻⁴ K⁻¹ between 220°C and 325°C.     

Evaluation the effects of edge banding type and thickness on the strength of corner joints in case-type furniture

Edge banding is used to cover the exposed sides of wood materials such as plywood, particleboard or medium-density fiberboard, giving the appearance of a solid (or more valuable) material. This study was carried out to determine the effects of the edge banding material, namely polyvinyl chloride (PVC), melamine and wood veneer, thickness of edge banding material (0.4, 1, and 2 mm), and wood composite panel type on the diagonal compression and tension strength properties of particleboard surfaced with synthetic resin sheet (LamPb) and MDF surfaced with synthetic resin sheet (LamMDF).     

Transposition of maxillary permanent left cuspid tooth: a case report

It was no accident that Warren Harvey's paper on 'Tooth temperature with reference to dental pain while flying' was published during the Second World War, as Harvey was given the opportunity to investigate this subject after aircrew reported dental problems during flight. Group Captain Peter Richardson of the RAF Institute of Dental Health and Training reviews the paper.