Showing papers by "Conservatoire national des arts et métiers published in 2010"

Accounting for multiple comparisons in a genome-wide association study (GWAS)

Abstract: Background: As we enter an era when testing millions of SNPs in a single gene association study will become the standard, consideration of multiple comparisons is an essential part of determining statistical significance. Bonferroni adjustments can be made but are conservative due to the preponderance of linkage disequilibrium (LD) between genetic markers, and permutation testing is not always a viable option. Three major classes of corrections have been proposed to correct the dependent nature of genetic data in Bonferroni adjustments: permutation testing and related alternatives, principal components analysis (PCA), and analysis of blocks of LD across the genome. We consider seven implementations of these commonly used methods using data from 1514 European American participants genotyped for 700,078 SNPs in a GWAS for AIDS. Results: A Bonferroni correction using the number of LD blocks found by the three algorithms implemented by Haploview resulted in an insufficiently conservative threshold, corresponding to a genome-wide significance level of a = 0.15 - 0.20. We observed a moderate increase in power when using PRESTO, SLIDE, and simpleℳ when compared with traditional Bonferroni methods for population data genotyped on the Affymetrix 6.0 platform in European Americans (a = 0.05 thresholds between 1 × 10 -7 and 7 × 10 -8 ). Conclusions: Correcting for the number of LD blocks resulted in an anti-conservative Bonferroni adjustment. SLIDE and simpleℳ are particularly useful when using a statistical test not handled in optimized permutation testing packages, and genome-wide corrected p-values using SLIDE, are much easier to interpret for consumers of GWAS studies.

Geophysical muon imaging: feasibility and limits

Abstract: SUMMARY We study the possibility of muon radiography as a tool to investigate space and time changes in the internal density distribution inside geological structures. Previous work has shown the practical applicability of this method. Nevertheless, quantitative information on factors which impose limitations on it are still sorely lacking in the literature. We discuss the main issues that can influence the final result of a geophysical imaging experiment. In particular, with the view of optimizing the signal-to-noise ratio, we address issues concerning (i) the energy spectrum for muons arriving at different zenith angles, (ii) the muon propagation model through matter and (iii) the characteristics of the muon detector (telescope) that we have designed to perform experiments of muon radiography against the harsh environment usually encountered in the active zone of a volcano. We thus identify factors that can induce either static or dynamic effects and that should be taken into account. We also define a feasibility eq. (32) relating the geometrical characteristics of the telescope and the duration of the experiment to the expected density resolution, in turn a function of the geometrical characteristics of the target structure. This relation is especially important to define the applicability domain of muon radiography and it is utilized to test the suitability of the method to investigate the density distribution inside some candidate target structures.

Carotenoid biosynthesis in diatoms.

Abstract: Diatoms are ubiquitous and constitute an important group of the phytoplankton community having a major contribution to the total marine primary production. These microalgae exhibit a characteristic golden-brown colour due to a high amount of the xanthophyll fucoxanthin that plays a major role in the light-harvesting complex of photosystems. In the water column, diatoms are exposed to light intensities that vary quickly from lower to higher values. Xanthophyll cycles prevent photodestruction of the cells in excessive light intensities. In diatoms, the diadinoxanthin–diatoxanthin cycle is the most important short-term photoprotective mechanism. If the biosynthetic pathways of chloroplast pigments have been extensively studied in higher plants and green algae, the research on carotenoid biosynthesis in diatoms is still in its infancy. In this study, the data on the biosynthetic pathway of diatom carotenoids are reviewed. The early steps occur through the 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway. Then a hypothetical pathway is suggested from dimethylallyl diphosphate (DMAPP) and isopentenyl pyrophosphate (IPP). Most of the enzymes of the pathway have not been so far isolated from diatoms, but candidate genes for each of them were identified using protein similarity searches of genomic data.

Real-time vision based respiration monitoring system

Abstract: Respiration rate is an important indicator of an individual's health. Existing respiration monitoring systems are usually contact based, and so the sensing device is attached to the subject's body. This creates discomfort to the patient and can interfere with normal breathing. This paper presents a vision based contactless method of monitoring respiration rate. The method involves image and signal processing techniques to extract chest and abdominal movements' information from a sequence of video images recorded using a single video camera. The system provided a real-time respiration monitoring information consisting of a plot of respiration signal and the value of respiration rate. The respiration data could also be stored to allow for off-line analysis to be performed. A caparison of the developed method against a number of contact-based respiration monitoring systems confirmed its effectiveness. The system is currently being further developed to make its operation more robust.

Improved Constraints on Models of Glacial Isostatic Adjustment: A Review of the Contribution of Ground-Based Geodetic Observations

Abstract: The provision of accurate models of Glacial Isostatic Adjustment (GIA) is presently a priority need in climate studies, largely due to the potential of the Gravity Recovery and Climate Experiment (GRACE) data to be used to determine accurate and continent-wide assessments of ice mass change and hydrology. However, modelled GIA is uncertain due to insufficient constraints on our knowledge of past glacial changes and to large simplifications in the underlying Earth models. Consequently, we show differences between models that exceed several mm/year in terms of surface displacement for the two major ice sheets: Greenland and Antarctica. Geodetic measurements of surface displacement offer the potential for new constraints to be made on GIA models, especially when they are used to improve structural features of the Earth’s interior as to allow for a more realistic reconstruction of the glaciation history. We present the distribution of presently available campaign and continuous geodetic measurements in Greenland and Antarctica and summarise surface velocities published to date, showing substantial disagreement between techniques and GIA models alike. We review the current state-of-the-art in ground-based geodesy (GPS, VLBI, DORIS, SLR) in determining accurate and precise surface velocities. In particular, we focus on known areas of need in GPS observation level models and the terrestrial reference frame in order to advance geodetic observation precision/accuracy toward 0.1 mm/year and therefore further constrain models of GIA and subsequent present-day ice mass change estimates.

The Centrality of Work

Abstract: This article briefly presents some of the main features of the notion of "centrality of work" within the framework of the "psychodynamic" approach to work developed by Christophe Dejours The paper argues that we should distinguish between at least four separate but related ways in which work can be said to be central: psychologically, in terms of gender relations, social-politically and epistemically

Physical layer for future broadband radio systems

Abstract: Future broadband radio systems have ambitious objectives in terms of performance and quality of service. Moreover, new network topologies are likely to be introduced. Therefore, the physical layer has to evolve to meet the new requirements. With this in mind, the filter bank multicarrier (FBMC) technique is proposed as an enhancement to the present OFDM technique. After a brief presentation of the FBMC principle, the adaptation to the radio context is described. Then, the main features which impact radio networks are reviewed with emphasis on the potential benefits of the evolution. The paper provides an overview of the work carried out in the European research project EC-FP7-Phydyas (physical layer for dynamic access and cognitive radio).

The alamouti scheme with CDMA-OFDM/OQAM

Abstract: This paper deals with the combination of OFDM/OQAM with the Alamouti scheme. After a brief presentation of the OFDM/OQAM modulation scheme, we introduce the fact that the well-known Alamouti decoding scheme cannot be simply applied to this modulation. Indeed, the Alamouti coding scheme requires a complex orthogonality property; whereas OFDM/OQAM only provides real orthogonality. However, as we have recently shown, under some conditions, a transmission scheme combining CDMA and OFDM/OQAM can satisfy the complex orthogonality condition. Adding a CDMA component can thus be seen as a solution to apply the Alamouti scheme in combination with OFDM/OQAM. However, our analysis shows that the CDMA-OFDM/OQAM combination has to be built taking into account particular features of the transmission channel. Our simulation results illustrate the 2 × 1 Alamouti coding scheme for which CDMA-OFDM/OQAM and CP-OFDM are compared in two different scenarios: (i) CDMA is performed in the frequency domain, (ii) CDMA is performed in time domain.

Multiple-cohort genetic association study reveals CXCR6 as a new chemokine receptor involved in long-term nonprogression to AIDS

Abstract: a Background. The compilation of previous genomewide association studies of AIDS shows a major polymor- phism in the HCP5 gene associated with both control of the viral load and long-term nonprogression (LTNP) to AIDS. Methods. To look for genetic variants that affect LTNP without necessary control of the viral load, we reanalyzed the genomewide data of the unique LTNP Genomics of Resistance to Immunodeficiency Virus (GRIV) cohort by excluding "elite controller" patients, who were controlling the viral load at very low levels (!100 copies/mL). Results. The rs2234358 polymorphism in the CXCR6 gene was the strongest signal ( ; odds ratio, 7 P p 2.5 10 1.85) obtained for the genomewide association study comparing the 186 GRIV LTNPs who were not elite controllers with 697 uninfected control subjects. This association was replicated in 3 additional independent European studies, reaching genomewide significance of . This association with LTNP is independent of the 10 P p 9.7 10 combined CCR2-CCR5 locus and the HCP5 polymorphisms. Conclusions. The statistical significance, the replication, and the magnitude of the association demonstrate that CXCR6 is likely involved in the molecular etiology of AIDS and, in particular, in LTNP, emphasizing the power of extreme-phenotype cohorts. CXCR6 is a chemokine receptor that is known as a minor coreceptor in human immunodeficiency virus type 1 infection but could participate in disease progression through its role as a mediator of inflammation.

Barrier properties of poly(lactic acid) and its morphological changes induced by aroma compound sorption

Abstract: The barrier properties of poly(lactic acid) (PLA) play a key role in food packaging applications. For their optimization, the influence of crystallinity on the barrier properties of PLA and the interaction of PLA with the aroma compound ethyl acetate were investigated. PLA film samples with various crystallinities were fabricated by flat die extrusion and thermocompression and compared to PLA Biophan (TM). The degree of crystallinity had no effect on the oxygen permeability. However, an increase of crystallinity caused a decrease in ethyl acetate sorption. The sorption isotherm of ethyl acetate obtained using microgravimetry showed a steep increase with increasing aroma activity, a form which is consistent with a plasticization effect. This behaviour was verified using differential scanning calorimetry and dynamic mechanical analysis. Sorption caused a marked decrease in the glass transition temperature well below room temperature to approximately 0 degrees C. Furthermore, PLA underwent a solvent-induced crystallization when equilibrated in ethyl acetate atmosphere at an activity of 0.5. The results obtained show the importance of considering possible interactions between polymer and foodstuff during the optimization step of polymeric materials for food packaging applications.

MHC heterozygote advantage in simian immunodeficiency virus-infected Mauritian cynomolgus macaques.

Abstract: The importance of a broad CD8 T lymphocyte (CD8-TL) immune response to HIV is unknown. Ex vivo measurements of immunological activity directed at a limited number of defined epitopes provide an incomplete portrait of the actual immune response. We examined viral loads in simian immunodeficiency virus (SIV)-infected major histocompatibility complex (MHC)-homozygous and MHC-heterozygous Mauritian cynomolgus macaques. Chronic viremia in MHC-homozygous macaques was 80 times that in MHC-heterozygous macaques. Virus from MHC-homozygous macaques accumulated 11 to 14 variants, consistent with escape from CD8-TL responses after 1 year of SIV infection. The pattern of mutations detected in MHC-heterozygous macaques suggests that their epitope-specific CD8-TL responses are a composite of those present in their MHC-homozygous counterparts. These results provide the clearest example of MHC heterozygote advantage among individuals infected with the same immunodeficiency virus strain, suggesting that broad recognition of multiple CD8-TL epitopes should be a key feature of HIV vaccines.

Optical, thermal, electrical, damage, and phase-matching properties of lithium selenoindate

Abstract: Lithium selenoindate (LiInSe2) is a new nonlinear chalcogenide biaxial crystal, related to LiInS2 and transparent from 0.54 to 10 μm at the 50% level (10 mm thickness), which has been successfully grown in large sizes and with good optical quality. We report on what we believe to be new physical properties that are relevant for laser and nonlinear optical applications and summarize all relevant characteristics, both from the literature and as measured in the present work. With respect to AgGaS(e)2 ternary chalcopyrite materials, LiInSe2 displays a nearly isotropic thermal expansion behavior with three- to five-times-larger thermal conductivities associated with high optical damage thresholds, and low intensity-dependent absorption, allowing direct high-power downconversion from the near-infrared, especially 1064 nm, to the deep mid-infrared. Continuous-wave difference-frequency generation (5.9–8.1 μm) of Ti:sapphire laser sources is reported for the first time as well as nanosecond optical parametric oscillation with a Nd:YAG laser as the pump source at 100 Hz and idler tuning between 4.7 and 8.7 μm.

Study of nuclear stopping in central collisions at intermediate energies.

Abstract: Nuclear stopping has been investigated in central nuclear collisions at intermediate energies by analyzing kinematically complete events recorded with the help of the 4π multidetector INDRA for a large variety of symmetric systems. It is found that the mean isotropy ratio defined as the ratio of transverse to parallel momenta (energies) reaches a minimum near the Fermi energy, saturates or slowly increases depending on the mass of the system as the beam energy increases, and then stays lower than unity, showing that significant stopping is not achieved even for the heavier systems. Close to and above the Fermi energy, experimental data show no effect of the isospin content of the interacting system. A comparison with transport model calculations reveals that the latter overestimates the stopping power at low energies.

Spectral efficiency comparison of OFDM/FBMC for uplink cognitive radio networks

Abstract: Cognitive radio (CR) is proposed to automatically detect and exploit unused spectrum while avoiding harmful interference to the incumbent system. In this paper, we emphasize the channel capacity comparison of a CR network using two types of multicarrier communications: conventional Orthogonal Frequency Division Multiplexing (OFDM) with Cyclic Prefix (CP) and Filter Bank based MultiCarrier (FBMC) modulations. We use a resource allocation algorithm in which subcarrier assignment and power allocation are carried out sequentially. By taking the impact of Inter-Cell Interference (ICI) resulting from timing offset into account, the maximization of total information rates is formulated under an uplink scenario with pathloss and Rayleigh fading, subject to maximum power constraint as well as mutual interference constraint between primary user (PU) and secondary user (SU). Final simulation results show that FBMC can achieve higher channel capacity than OFDM because of the low spectral leakage of its prototype filter.

Individual Differences in Working Memory Moderate Stereotype-Threat Effects

Abstract: Research on stereotype threat has shown that negative stereotypes hinder stigmatized individuals’ performance on difficult tasks (Schmader, Johns, & Forbes, 2008; Steele & Aronson, 1995; for stereotype threat among children, see Huguet & Régner, 2007, 2009). Stereotype threat typically affects those who excel in—and are strongly identified with—the stereotyped domain being evaluated and who have much to lose by confirming the negative characterization of their group in this domain (Schmader et al., 2008; Steele, 1997; Steele, Spencer, & Aronson, 2002; Walton & Cohen, 2003). This threat appears to lower performance by reducing working memory (WM) capacity (Beilock, Rydell, & McConnell, 2007; Rydell, McConnell, & Beilock, 2009; Schmader & Johns, 2003), an executive resource used to perform complex tasks (Kane, Conway, Hambrick, & Engle, 2007). Recently, Schmader et al. (2008) raised the crucial question of whether stigmatized individuals with a dispositionally high WM capacity resist stereotype threat. On the basis of the idea that WM involves an executive-control mechanism that is recruited to combat interference (Conway, Kane, & Engle, 2003), Schmader et al. (2008) suggested that high-WM individuals should therefore be better equipped to cope with stereotype threat than lowWM individuals are. Not only does this hypothesis remain untested, but it is challenged by research on “choking under pressure” (Beilock & Carr, 2005; Beilock & DeCaro, 2007; Gimmig, Huguet, Caverni, & Cury, 2006), in which suboptimal performance under strong evaluative pressure has been shown to be limited to high-WM individuals. It appears that pressure is likely to consume the resources that high-WM individuals rely on to achieve superior performance. To determine if stereotype threat is limited to either lowor high-WM individuals, we selected outstanding students in their last or second-to-last year (out of 5 years) at highly selective engineering schools. This selection criterion ensured that the participants’ identification with engineering and their intention to pursue an engineering career were unquestionable. In a pretest (consisting of self-assessments and importance ratings) on a group of students similar to those participating in the experiment, we confirmed that logical reasoning is an ability with which engineers identify strongly. Because women are typically assumed to reason less well than men (Davies, Spencer, Quinn, & Gerhardstein, 2002), we thought that women might experience stereotype threat in this domain. The question here is whether women with a high WM capacity are more able than their low-WM counterparts to resist stereotype threat.

Efficiency of Filter Bank Multicarrier Techniques in Burst Radio Transmission

Abstract: The filter bank multicarrier (FBMC) technique has been proposed in the FP7 European research program, as an enhancement to the OFDM technique for future broadband radio systems. Besides gains in efficiency, mainly due to the absence of cyclic prefix, an important feature of FBMC is the absence of spectral leakage, which makes it particularly appealing for cognitive radio. However, in burst transmission, the filter impulse response introduces transitions which extend the length of the burst with respect to OFDM and may reduce the gains in efficiency. After a brief overview of the FBMC technique, the exploitation in burst transmission is discussed. The effect of cutting the initial and final transitions of the burst is investigated. The level of temporary spectral leakage introduced by this operation is assessed. It is shown that cuts leading to an increase in burst length of half a symbol with respect to OFDM affect the first and the last symbol only, resulting in a minor reduction in bit loading for these symbols. Application to the time division duplex access mode is considered, as well as the case of the presence of a preamble in the burst. For implementation, it is proposed to resort to a simple memory preloading technique, which has the advantage of compatibility with OFDM in dual mode systems.

Selective Adsorption of Neutral Nitrogen Compounds from Fuel Using Ion-Exchange Resins

Abstract: Adsorptive removal of hydrodesulfurization inhibitors, that is, nitrogen-containing compounds (N-compounds), was studied using model fuel which contains carbazole and dibenzothiophene in an n-dodecane−toluene mixture over ion-exchange resins (IXRs) in batch and in fixed-bed adsorption systems. The adsorptive capacity and selectivity for neutral N-compounds were examined. The high affinity for neutral N-compounds present in hydrocarbon feed was explained by hydrogen bonding between the chloride anion (with nonbonding electrons) and the neutral N-compounds. However, the presence of a flat charged cation, that is, N-alkylated pyridinium, is essential to ensure the adsorption of neutral N-compounds. The regeneration of the sorbent could be easily performed using polar organic solvent like methanol. Commercially available IXR bearing pyridinium chloride functionality (HPQ) was further evaluated with straight-run fuel oil. The N/S selectivity decreases, but analysis of the adsorbed compounds by gas chromatograp...

Acoustic Resonator Experiments at the Triple Point of Water: First Results for the Boltzmann Constant and Remaining Challenges

Abstract: We report on two sets of isothermal acoustic measurements made with argon close to the triple point of water using a 50 mm radius, thin-walled, diamond-turned quasisphere. Our two isotherms yielded values for the Boltzmann constant, k B, which differ by 0.9 parts in 106, and have an average value of k B = (1.380 649 6 ± 0.000 004 3) × 10−23J · K−1. The relative uncertainty is 3.1 parts in 106, and the average value is 0.58 parts in 106 below the 2006 CODATA value (Mohr et al. Rev Mod Phys 80:633, 2008), and so the values are consistent within their combined (k = 1) uncertainties.

Structural Vibration Reduction by Switch Shunting of Piezoelectric Elements: Modeling and Optimization

Abstract: This work deals with the reduction of structural vibrations by means of synchronized switch damping techniques on piezoelectric elements. Piezoelectric patches are attached to the vibrating structure and connected to an electrical circuit that includes a switch. The latter allows to continuously switch the piezoelectric elements from an open-circuit state to a specific electric impedance, synchronously with the mechanical oscillations. The present study focuses on two goals: (i) the quantification of the added damping, (ii) the optimization of the electric circuit parameters, carried out on a one degree of freedom model. The free and forced responses of one mode of the mechanical structure are studied in detail. The precise time response of the system is obtained with semi-analytical models for the two cases where the electrical impedance is a simple resistance (synchronized switch damping on short circuit) or a resistance in series with an inductance (synchronized switch damping on inductor). The damping...

Simulation of fractionally damped mechanical systems by means of a Newmark-diffusive scheme

Abstract: A Newmark-diffusive scheme is presented for the time-domain solution of dynamic systems containing fractional derivatives. This scheme combines a classical Newmark time-integration method used to solve second-order mechanical systems (obtained for example after finite element discretization), with a diffusive representation based on the transformation of the fractional operator into a diagonal system of linear differential equations, which can be seen as internal memory variables. The focus is given on the algorithm implementation into a finite element framework, the strategies for choosing diffusive parameters, and applications to beam structures with a fractional Zener model.

Maximum likelihood detection in spatial multiplexing with FBMC

Abstract: In FBMC transmission systems, the bit rate is maximized when OQAM modulation is employed. One of the characteristics of this modulation is that the received data symbols are accompanied by interference terms, which complicates the application of ML techniques in optimal decoders. Two approaches are proposed to cope with this situation. The first one exploits the MMSE estimation of the interference terms and it introduces no additional delay. In the second one, the interference terms are calculated from past, present and future data symbols, either already decided or estimated. The gains provided by these approaches, with respect to MMSE, are assessed and illustrated by simulation.