Locally stationary covariance and signal estimation with macrotiles

A macrotile estimation algorithm is introduced to estimate the covariance of locally stationary processes. A macrotile algorithm uses a penalized method to optimize the partition of the space in orthogonal subspaces, and the estimation is computed with a projection operator. It is implemented by searching for a best basis among a dictionary of orthogonal bases and by constructing an adaptive segmentation of this basis to estimate the covariance coefficients. The macrotile algorithm provides a consistent estimation of the covariance of locally stationary processes, using a dictionary of local cosine bases. This estimation is computed with a fast algorithm. Macrotile algorithms apply to other estimation problems such as the removal of additive noise in signals. This simpler problem is used as an intuitive guide to better understand the case of covariance estimation. Examples of removal of white noise from sounds illustrate the results.     

Enantioselective hydrogenation of carbonyl compounds over Pd-Pt/alumina catalysts

A series of Pd-Pt/alumina catalysts were prepared by consecutive deposition of Pd onto supported Pt particles. Electrochemical model studies indicated that under very mild conditions in aqueous acetic acid the reduction of Pd²⁺ ions occurred partly via the ionization of hydrogen adsorbed on Pt and partly by the slow oxidation of acetic acid. There was only a moderate change in the surface Pd/Pt atomic ratio during heat treatment in flowing hydrogen at 400°C, as determined by XPS analysis. The catalytic performance of the bimetallic catalysts was tested in the enantioselective hydrogenation of ethyl pyruvate and ketopantolactone, in the presence of cinchonidine. Pd was virtually inactive and acted as a site blocker, which decreased the size of Pt ensembles and hindered the formation of the bulky transition complex between the reactant and the chiral modifier. The intrinsically low activity and selectivity of Pd are discussed in the light of H/D exchange studies in deuterated ethanol. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cryogenic millimeter-wave ring filter for space application

A tunerless cryogenic millimeter-wave ring filter has been designed for a space application. Detuning of the center frequency caused by thermal deformations has been compensated by a novel mechanism based on the use of two materials with different temperature expansion coefficients. An improvement of 1:8 in the detuning of the center frequency, compared to an uncompensated ring filter, is reported. By applying the new design, external tuning aids can be avoided even in applications where a wide operational temperature range is of interest. Thus, the new ring filter is especially advantageous in space-borne millimeter-wave receivers     

A feed scanning based APC technique for compact antenna test ranges

The measurement accuracy of a compact antenna test range (CATR) depends on the level of spurious signals. To improve the measurement accuracy, several error compensation methods have been developed, but most of them are not feasible at submillimeter wavelengths. This paper introduces an error compensation technique for compact antenna test ranges, which is especially suitable at submillimeter wavelengths. The method is based on antenna pattern comparison (APC). In the original APC technique the antenna pattern is recorded several times at different positions of the quiet-zone field, and the corrected pattern is obtained by averaging the measured patterns. In the proposed method, the lightweight transmitter is moved instead of moving the heavy combination of the antenna under test (AUT) and the rotation stage. The feasibility of the method is studied and the method is tested with measurements in a hologram based compact antenna test range at 310 GHz. The accuracy provided by the proposed method is compared to the accuracy provided by the conventional APC. The accuracies provided by both methods are practically equal.     

The relationship of hydroxyeicosatetraenoic acids and F2-isoprostanes to plaque instability in human carotid atherosclerosis

Evidence for increased oxidant stress has been reported in human atherosclerosis. However, no information is available about the importance of in situ oxidant stress in relation to plaque stability. This information is relevant because the morbidity and mortality of atherosclerosis are essentially the consequences of acute ischemic syndromes due to unstable plaques. We studied 30 carotid atherosclerotic plaques retrieved by endarterectomy from 18 asymptomatic (stable plaques) and 12 symptomatic patients (unstable plaques). Four normal arteries served as controls. After lipid extraction and ester hydrolysis, quantitation of different indices of oxidant stress were analyzed, including hydroxyeicosatetraenoic acids (HETEs), epoxyeicosatetraenoic acids (EETs), ketoeicosatetraenoic acids (oxo-ETEs), and F2-isoprostanes using online reverse-phase high-performance liquid chromatography tandem mass spectrometry (LC/MS/MS). All measurements were carried out in a strictly double-blind procedure. We found elevated levels of the different compounds in atherosclerotic plaques. Levels of HETEs were 24 times higher than EETs, oxo-ETEs, or F2-isoprostanes. Levels of HETEs, but not those of EETs, oxo-ETEs or F2-isoprostanes, were significantly elevated in plaques retrieved from symptomatic patients compared with those retrieved from asymptomatic patients (1, 738 +/- 274 vs. 1,002 +/- 107 pmol/ micromol lipid phosphorous, respectively; P < 0.01). One monooxygenated arachidonate species, 9-HETE, which cannot be derived from known enzymatic reactions, was the most abundant and significant compound observed in plaques, suggesting that nonenzymatic lipid peroxidation predominates in advanced atherosclerosis and may promote plaque instability.     

Past, present and future of mobile payments research: A literature review

The mobile payment services markets are currently under transition with a history of numerous tried and failed solutions, and a future of promising but yet uncertain possibilities with potential new technology innovations. At this point of the development, we take a look at the current state of the mobile payment services market from a literature review perspective. We review prior literature on mobile payments, analyze the various factors that impact mobile payment services markets, and suggest directions for future research in this still emerging field. To facilitate the analysis of literature, we propose a framework of four contingency and five competitive force factors, and organize the mobile payment research under the proposed framework. Consumer perspective of mobile payments as well as technical security and trust are best covered by contemporary research. The impacts of social and cultural factors on mobile payments, as well as comparisons between mobile and traditional payment services are entirely uninvestigated issues. Most of the factors outlined by the framework have been addressed by exploratory and early phase studies.     

Dielectric rod waveguide antenna for W band with good input match

Antennas based on dielectric rod waveguide made of GaAs and fused sapphire cut along its optical axis inserted in the end of a standard WR-10 metal waveguide are investigated with computer simulations and experiments in the W band. The radiation pattern is found to be similar to that of the open metal waveguide end, but less frequency-dependent beamwidth and input match: measured return loss is more than 25 dB.     

Sparse geometric image representations with bandelets.

This paper introduces a new class of bases, called bandelet bases, which decompose the image along multiscale vectors that are elongated in the direction of a geometric flow. This geometric flow indicates directions in which the image gray levels have regular variations. The image decomposition in a bandelet basis is implemented with a fast subband-filtering algorithm. Bandelet bases lead to optimal approximation rates for geometrically regular images. For image compression and noise removal applications, the geometric flow is optimized with fast algorithms so that the resulting bandelet basis produces minimum distortion. Comparisons are made with wavelet image compression and noise-removal algorithms.     

Enhanced Transient Heat Transfer From Arrays of Jets Impinging on a Moving Plate

This article addresses the numerical analysis of single and multiple circular jets impinging perpendicularly on a flat plate for heating and cooling purposes. Computational fluid dynamics (CFD) is used to evaluate heat transfer calculations for different configurations and different flow boundary conditions. The commercial CFD package FLUENT is employed with various turbulence models. Results for a single jet are validated against experimental data. The SST k ? ω turbulence model is compared with the elliptic V2F model, and both were validated against experimental data. Results were obtained for a range of jet Reynolds numbers and jet-to-target distances. Optimization results for the single jet case are validated against experimental data. The SST k ? ω and V2F turbulence models succeeded with a reasonable accuracy (within 20% error) in reproducing experimental results. The heat transfer rates from the use of multijet configurations are discussed in the article. Transient heat transfer between multiple jets and a moving plate is more difficult to study due to the changing boundaries but is also very relevant in engineering applications. This article presents full CFD calculations of the transient heat transfer between a bank of circular jets and a moving plate. Design optimization has also been achieved for the single- and multiple-jet configurations.