Interprétation géométrique de la capacité et des performances de systèmes à diversité

- Notre étude a pour cadre les systèmes de transmission à diversité. Nous analysons tout d'abord l'influence d'une erreur d'estimation du canal, et déduisons l'expression analytique de la capacité ainsi dégradée d'un système OPRA (Optimal Power and Rate Adaptation). Ensuite, nous proposons une interprétation géométrique de cette capacité en nous basant sur la théorie des courbes dites de Bézier. Après avoir passé en revue certaines propriétés héritées de cette structure particulière, nous proposons alors une expression matricielle de cette capacité, ainsi qu'une méthodologie de construction graphique. Pour conclure, nous présentons une application concernant le dimensionnement de motif de pilotes, pour des systèmes multi-porteuse à étalement fréquentiel (Multi-Carrier Spread-Spectrum)

Nouveau décodeur à complexité réduite pour codes convolutifs de rendement 1/2

Les codes convolutifs peuvent être décodés de façon optimale à l'aide l'algorithme de Viterbi (VA). Nous proposons un décodeur à entrée souple dans lequel l'algorithme de Viterbi est employé pour identifier le vecteur d'erreur plutôt que le message d'information avec une métrique appropriée. Ce type de décodage permet d'éviter la mise en oeuvre d'un nombre important d'opérations ACS (Add Compare Select). Nous montrons que les performances atteintes sont proches de l'optimum tout en bénéficiant d'une réduction de la complexité qui est d'autant plus importante que le rapport signal à bruit (SNR) est favorable. Par exemple, pour des SNR supérieurs à 3 dB et dans le cas d'une transmission avec la modulation BPSK sur canal gaussien, au moins 88% des ACS peuvent être évités

Reductive Metabolism of AGE Precursors: A Metabolic Route for Preventing AGE Accumulation in Cardiovascular Tissue

OBJECTIVE—To examine the role of aldo-keto reductases (AKRs) in the cardiovascular metabolism of the precursors of advanced glycation end products (AGEs). RESEARCH DESIGN AND METHODS—Steady-state kinetic parameters of AKRs with AGE precursors were determined using recombinant proteins expressed in bacteria. Metabolism of meth-ylglyoxal and AGE accumulation were studied in human umbil-ical vein endothelial cells (HUVECs) and C57 wild-type, akr1b3 (aldose reductase)-null, cardiospecific-akr1b4 (rat aldose reduc-tase), and akr1b8 (FR-1)-transgenic mice. AGE accumulation and atherosclerotic lesions were studied 12 weeks after streptozoto-cin treatment of C57, akr1b3-null, and apoE- and akr1b3-apoE– null mice. RESULTS—Higher levels of AGEs were generated in the cytosol than at the external surface of HUVECs cultured in high glucose

Accumulation of advanced glycation end (AGEs) products in intensive care patients: an observational, prospective study

<p>Abstract</p> <p>Background</p> <p>Oxidative stress plays an important role in the course and eventual outcome in a majority of patients admitted to the intensive care unit (ICU). Markers to estimate oxidative stress are not readily available in a clinical setting. AGEs accumulation has been merely described in chronic conditions, but can also occur acutely due to oxidative stress. Since AGEs have emerged to be stable end products, these can be a marker of oxidative stress. Skin autofluorescence (AF) is a validated marker of tissue content of AGEs. We hypothesized that AGEs accumulate acutely in ICU patients.</p> <p>Methods</p> <p>We performed an observational prospective study in a medical surgical ICU in a university affiliated teaching hospital. All consecutively admitted ICU patients in a 2 month period were included. Skin AF was measured using an AGE reader in 35 consecutive ICU patients > 18 yrs. As a comparison, historical data of a control group (n = 231) were used. These were also used to calculate age-adjusted AF-levels (AF_adj). Values are expressed as median and interquartile range [P₂₅-P₇₅]. Differences between groups were tested by non parametric tests. P < 0.05 was considered statistically significant.</p> <p>Results</p> <p>AF_adjvalues were higher in ICU patients (0.33 [0.00 - 0.68]) than in controls (-0.07 [-0.29 - 0.24]; P < 0.001). No differences in skin AF_adjwere observed between acute or planned admissions, or presence of sepsis, nor was skin AF_adjrelated to severity of disease as estimated by APACHE-II score, length of ICU, hospital stay or mortality.</p> <p>Conclusion</p> <p>Acute AGE accumulation in ICU patients was shown in this study, although group size was small. This can possibly reflect oxidative stress in ICU patients. Further studies should reveal whether AGE-accumulation will be a useful parameter in ICU patients and whether skin AF has a predictive value for outcome, which was not shown in this small study.</p

Age-related impairment of mesenchymal progenitor cell function

In most mesenchymal tissues a subcompartment of multipotent progenitor cells is responsible for the maintenance and repair of the tissue following trauma. With increasing age, the ability of tissues to repair themselves is diminished, which may be due to reduced functional capacity of the progenitor cells. The purpose of this study was to investigate the effect of aging on rat mesenchymal progenitor cells. Mesenchymal progenitor cells were isolated from Wistar rats aged 3, 7, 12 and 56 weeks. Viability, capacity for differentiation and cellular aging were examined. Cells from the oldest group accumulated raised levels of oxidized proteins and lipids and showed decreased levels of antioxidative enzyme activity. This was reflected in decreased fibroblast colony-forming unit (CFU-f) numbers, increased levels of apoptosis and reduced proliferation and potential for differentiation. These data suggest that the reduced ability to maintain mesenchymal tissue homeostasis in aged mammals is not purely due to a decline in progenitor cells numbers but also to a loss of progenitor functionality due to the accumulation of oxidative damage, which may in turn be a causative factor in a number of age-related pathologies such as arthritis, tendinosis and osteoporosis. © 2006 The Authors Journal compilation © Blackwell Publishing Ltd/Anatomical Society of Great Britain and Ireland 2006

Higher Plasma Levels of Advanced Glycation End Products Are Associated With Incident Cardiovascular Disease and All-Cause Mortality in Type 1 Diabetes: A 12-year follow-up study

OBJECTIVE - To investigate the associations of plasma levels of advanced glycation end products (AGEs) with incident cardiovascular disease (CVD) and all-cause mortality in type 1 diabetes and the extent to which any such associations could be explained by endothelial and renal dysfunction, low-grade inflammation, and arterial stiffness. RESEARCH DESIGN AND METHODS - We prospectively followed 169 individuals with diabetic nephropathy and 170 individuals with persistent normoalbuminuria who were free of CVD at study entry and in whom levels of N ε -(carboxymethyl)lysine, N ε -(carboxyethyl) lysine, pentosidine and other biomarkers were measured at baseline. The median follow-up duration was 12.3 (interquartile range 7.6-12.5) years. RESULTS - During the course of follow-up, 82 individuals (24.2%) died; 85 (25.1%) suffered a fatal (n = 48) and/or nonfatal (n = 53) CVD event. The incidence of fatal and nonfatal CVD and of all-cause mortality increased with higher baseline levels of AGEs independently of traditional CVD risk factors: hazard ratio (HR) = 1.30 (95% CI = 1.03-1.66) and HR = 1.27 (1.00-1.62), respectively. These associations were not attenuated after further adjustments for markers of renal or endothelial dysfunction, low-grade inflammation, or arterial stiffness. CONCLUSIONS - Higher levels of AGEs are associated with incident fatal and nonfatal CVD as well as all-cause mortality in individuals with type 1 diabetes, independently of other risk factors and of several potential AGEs-related pathophysiological mechanisms. Thus, AGEs may explain, in part, the increased cardiovascular disease andmortality attributable to type 1 diabetes and constitute a specific target for treatment in these patients. 2011 by the American Diabetes Association

A nonlinear Lagrangian particle model for grains assemblies including grain relative rotations

International audienceWe formulate a discrete Lagrangian model for a set of interacting grains, which is purely elastic. The considered degrees of freedom for each grain include placement of barycenter and rotation. Further, we limit the study to the case of planar systems. A representative grain radius is introduced to express the deformation energy to be associated to relative displacements and rotations of interacting grains. We distinguish inter‐grains elongation/compression energy from inter‐grains shear and rotations energies, and we consider an exact finite kinematics in which grain rotations are independent of grain displacements. The equilibrium configurations of the grain assembly are calculated by minimization of deformation energy for selected imposed displacements and rotations at the boundaries. Behaviours of grain assemblies arranged in regular patterns, without and with defects, and similar mechanical properties are simulated. The values of shear, rotation, and compression elastic moduli are varied to investigate the shapes and thicknesses of the layers where deformation energy, relative displacement, and rotations are concentrated. It is found that these concentration bands are close to the boundaries and in correspondence of grain voids. The obtained results question the possibility of introducing a first gradient continuum models for granular media and justify the development of both numerical and theoretical methods for including frictional, plasticity, and damage phenomena in the proposed model