A Central Limit Theorem for the SINR at the LMMSE Estimator Output for Large-Dimensional Signals

This paper is devoted to the performance study of the linear minimum mean squared error (LMMSE) estimator for multidimensional signals in the large-dimension regime. Such an estimator is frequently encountered in wireless communications and in array processing, and the signal-to-interference-plus-noise ratio (SINR) at its output is a popular performance index. The SINR can be modeled as a random quadratic form which can be studied with the help of large random matrix theory, if one assumes that the dimension of the received and transmitted signals go to infinity at the same pace. This paper considers the asymptotic behavior of the SINR for a wide class of multidimensional signal models that includes general multiple-antenna as well as spread-spectrum transmission models. The expression of the deterministic approximation of the SINR in the large-dimension regime is recalled and the SINR fluctuations around this deterministic approximation are studied. These fluctuations are shown to converge in distribution to the Gaussian law in the large-dimension regime, and their variance is shown to decrease as the inverse of the signal dimension.     

Cross-sectional study of in-vehicle exposure to ultrafine particles and black carbon inside Lebanese taxicabs

Taxi drivers’ exposure to traffic-related air pollutants inside their vehicles has been reported in different countries but not yet in Lebanon. Thus, we conducted a cross-sectional study on 20 Lebanese taxi drivers to (1) assess their exposure to ultrafine particles (UFP) and black carbon (BC) inside their vehicles and (2) identify determinants of this exposure. UFP and BC were measured using Diffusion Size Classifier Miniature^® and microAeth ^® Model AE51, respectively, for 5 hours. Data on characteristics of vehicles and trips were collected by face-to-face interviews. Associations between pollutant levels and their determinants were analyzed by multiple linear regression. The mean of UFP count (35.2 ± 17.6 x 10³ particles cm^-3) and BC (5.2 ± 1.9 μg m^-3) concentrations in-taxis was higher in the morning measurements compared with those in the afternoon measurements. UFP count increased in-taxis by 60% for every 10 minutes spent in blocked traffic and by 84% starting from two trips with smokers compared to trips without smokers. Conversely, UFP count decreased by 30% for every 10 minutes under both air-conditioning and air recirculation mode with windows closed. BC was not affected by any of these factors. Our findings suggest easy ways to reduce UFP exposure inside vehicles for all commuters.     

Parametric investigation of geometric form effects on solar potential of housing units

The paper presents a study of the solar potential of different shapes of two-story single family housing units, located in mid-latitude climate. Seven plan geometries are studied: square, rectangle, trapezoid, L, U, H and T shapes. The study investigates the effect of these shapes on two major response variables - Solar radiation incident on equatorial-facing facades and transmitted by the fenestration of such facades, and electricity production potential of building integrated photovoltaic (BIPV) covering roof surfaces with optimal solar exposure. The parameters, whose effects on the response variables are investigated, include, in addition to the basic shapes and roof design, variations to the geometry of L and U shapes and variations to the roof design. Shape variations include varying values of the relative dimensions of shading and shaded facades and variations to the angle enclosed by the wings of these shapes. Variations of roof design consist of modifications to the tilt and side angles of hip roofs. The results indicate that the number of shading facades in-self shading geometries and their relative dimensions are the major parameters affecting solar incident and transmitted radiation. Manipulation of the orientation of wings in L shape units can result in increased peak electricity generation potential, and in shifting the timing of the peak by up to 2 h either side of solar noon. The shift of peak load may be economically beneficial, facilitating more even distribution of electricity production over an assemblage of buildings. Judicious manipulation of unit shapes and window location can lead to optimization of solar radiation and its utilization for electricity generation and passive solar gain.     

Emerging Role of Phospholipids and Lysophospholipids for Improving Brain Docosahexaenoic Acid as Potential Preventive and Therapeutic Strategies for Neurological Diseases

Docosahexaenoic acid (DHA, 22:6n-3) is an omega-3 polyunsaturated fatty acid (PUFA) essential for neural development, learning, and vision. Although DHA can be provided to humans through nutrition and synthesized in vivo from its precursor alpha-linolenic acid (ALA, 18:3n-3), deficiencies in cerebral DHA level were associated with neurodegenerative diseases including Parkinson’s and Alzheimer’s diseases. The aim of this review was to develop a complete understanding of previous and current approaches and suggest future approaches to target the brain with DHA in different lipids’ forms for potential prevention and treatment of neurodegenerative diseases. Since glycerophospholipids (GPs) play a crucial role in DHA transport to the brain, we explored their biosynthesis and remodeling pathways with a focus on cerebral PUFA remodeling. Following this, we discussed the brain content and biological properties of phospholipids (PLs) and Lyso-PLs with omega-3 PUFA focusing on DHA’s beneficial effects in healthy conditions and brain disorders. We emphasized the cerebral accretion of DHA when esterified at sn-2 position of PLs and Lyso-PLs. Finally, we highlighted the importance of DHA-rich Lyso-PLs’ development for pharmaceutical applications since most commercially available DHA formulations are in the form of PLs or triglycerides, which are not the preferred transporter of DHA to the brain.     

Stopping powers of gases for 40 MeV/u tellurium ions

The stopping powers of six gaseous media have been measured for incident 40 MeV/u ¹²⁵Te heavy ions. The energy losses of ions in various “thicknesses” of gas have been accurately determined. The gases were confined in a cell. The amount of matter traversed by the ions was determined from temperature and pressure measurements. The beam energy before and after slowing down were measured using the LISE magnetic spectrometer at GANIL. These experimental gas stopping powers are lower by about 10% than the corresponding tabulated values for solid media. This means that the gas–solid effect is still significant at 40 MeV/u for Te ions. The projectile effective charges derived from these measurements depend on the target atomic number, thus confirming the trend observed in previous experiments performed with lighter ions or at lower energies.     

A decomposition approach for the solution of the unit loading problem in hydroplants

This paper presents a decomposition approach for the solution of the dynamic programming formulation of the unit loading problem in hydroplant management. This decomposition approach allows the consideration of network and canal constraints without additional computational effort.     

Asymptotic analysis of optimum and suboptimum CDMA downlink MMSE receivers

In this paper, we investigate the performance of two linear receivers for code-division multiple-access (CDMA) downlink transmissions over frequency-selective channels, the users having possibly different powers. The optimum minimum mean-square error (MMSE) receiver is first considered. Because this receiver requires the knowledge of the code vectors attributed to all the users within the cell when these vectors are time varying, its use may be unrealistic in the forward link. A classical suboptimum receiver, consisting in a chip rate equalizer followed by a despreading with the code of the user of interest, is therefore studied and compared to the optimum MMSE receiver. Performance of both receivers is assessed through the signal-to-interference-plus-noise ratio (SINR) at their outputs. The analytical expressions of these SINRs depend in a rather nonexplicit way on the codes allocated to the users of the cell, and are therefore not informative. This difficulty is dealt with by modeling the users code matrix by a random matrix. Because the code matrices used in the forward link are usually isometric, the code matrix is assumed to be extracted from a Haar-distributed random unitary matrix. The behavior of the SINRs is studied when the spreading factor and the number of users converge to /spl infin/ at the same rate. Using certain results of the free probability theory, we establish the fact that the SINRs converge almost surely toward quantities that depend only on the complex amplitudes of propagation channel paths. We then use the expressions of these SINR limits to discuss the influence of the various parameters on the performance of the receivers.     

Resource Allocation for Downlink Cellular OFDMA Systems—Part I: Optimal Allocation

In this pair of papers (Part I and Part II in this issue), we investigate the issue of power control and subcarrier assignment in a sectorized two-cell downlink OFDMA system impaired by multicell interference. As recommended for WiMAX, we assume that the first part of the available bandwidth is likely to be reused by different base stations (and is thus subject to multicell interference) and that the second part of the bandwidth is shared in an orthogonal way between the different base stations (and is thus protected from multicell interference). Although the problem of multicell resource allocation is nonconvex in this scenario, we provide in Part I the general form of the global solution. In particular, the optimal resource allocation turns out to be “binary” in the sense that, except for at most one pivot-user in each cell, any user receives data either in the reused bandwidth or in the protected bandwidth, but not in both. The determination of the optimal resource allocation essentially reduces to the determination of the latter pivot-position.