L'utilisation des moteurs de recherche par les jeunes : Impact des connaissances du domaine et des connaissances procédurales sur les stratégies d'exploration visuelle

International audienceDans une expérimentation conduite avec 53 élèves de CM2 utilisant la technique de l'oculométrie, nous tentons de mieux comprendre les stratégies d'exploration visuelle utilisées par de très jeunes usagers lors d'une tâche de recherche d'information sur le Web. Plus précisément, notre étude vise d'une part, à déterminer si plusieurs types de stratégies d'exploration visuelle d'une page de résultats proposés par un moteur de recherche (ou SERP) peuvent être déterminés et d'autre part, si des facteurs psychologiques (ici, les connaissances du domaine et les connaissances procédurales) peuvent influencer ces stratégies. Nos résultats ont principalement montré d'une part, que quatre stratégies d'exploration visuelle peuvent effectivement être distinguées et d'autre part, que le niveau de connaissances procédurales influence ces mêmes stratégies

Diffuse emission measurement with INTEGRAL/SPI as indirect probe of cosmic-ray electrons and positrons

Significant advances have been made in the understanding of the diffuse Galactic hard X-ray continuum emission using data from the INTEGRAL observatory. The diffuse hard power-law component seen with the INTEGRAL/SPI spectrometer has been identified with inverse-Compton emission from relativistic (GeV) electrons on the cosmic microwave background and Galactic interstellar radiation field. In the present analysis, SPI data from 2003 to 2009, with a total exposure time of ~ 10^8 s, are used to derive the Galactic ridge hard X-ray spatial distribution and spectrum between 20 keV and 2.4 MeV. Both are consistent with predictions from the GALPROP code. The good agreement between measured and predicted emission from keV to GeV energies suggests that the correct production mechanisms have been identified. We discuss the potential of the SPI data to provide an indirect probe of the interstellar cosmic-ray electron distribution, in particular for energies below a few GeV.Comment: 39 pages, 11 figures. Accepted for publication in The Astrophysical Journa

CD4+ T cells spontaneously producing human immunodeficiency virus type I in breast milk from women with or without antiretroviral drugs

<p>Abstract</p> <p>Background</p> <p>Transmission of human immunodeficiency virus type 1 (HIV-1) through breast-feeding may involve both cell-free and cell-associated virus. This latter viral reservoir remains, however, to be fully explored. CD4⁺T cell-associated virus production in breast milk was therefore investigated.</p> <p>Methods</p> <p>The <it>ex vivo </it>spontaneous production of HIV-1 antigen and HIV-1 RNA by CD4⁺T cells was measured in paired blood and breast milk samples from 15 HIV-1 infected women treated or not with antiretroviral drugs. Spontaneous antigen secreting cells (HIV-1-AgSCs) from breast milk and blood were enumerated by an ELISpot assay, and cell-associated HIV-1 RNA was quantified by real-time PCR in supernatants of CD4⁺T cells cultured for 18 hours without addition of polyclonal activators.</p> <p>Results</p> <p>Among the CD4⁺T cells present in breast milk, memory cells expressing high levels of cell-surface activation markers were predominant. Spontaneous HIV-1-AgSCs were detected and enumerated in the breast milk of all 15 women, with a median number of 13.0 and 9.5 HIV-1- AgSCs/106 CD4⁺T cells in aviremic (n = 7) and viremic (n = 8) women, respectively. Cell- associated HIV-1 RNA was detected in cell-free supernatants from 4/7 aviremic and 5/8 viremic individuals at median levels of 190 and 245 copies/ml, respectively.</p> <p>Conclusions</p> <p>Activated CD4⁺T cells producing HIV-1 are detected in the breast milk of untreated individuals as well as those receiving highly active antiretroviral therapy. This finding strongly suggests that HIV-1 replication occurs in latently infected CD4⁺T cells that, upon spontaneous activation, revert to productively infected cells. These cells might be responsible for a residual breast milk transmission despite maternal highly active antiretroviral therapy.</p

Increased mean aliphatic lipid chain length in left ventricular hypertrophy secondary to arterial hypertension: A cross-sectional study

About 77.9 million (1 in 4) American adults have high blood pressure. High blood pressure is the primary cause of left ventricular hypertrophy (LVH), which represents a strong predictor of future heart failure and cardiovascular mortality. Previous studies have shown an altered metabolic profile in hypertensive patients with LVH. The goal of this study was to identify blood metabolomic LVH biomarkers by H NMR to provide novel diagnostic tools for rapid LVH detection in populations of hypertensive individuals. This cross-sectional study included 48 hypertensive patients with LVH matched with 48 hypertensive patients with normal LV size, and 24 healthy controls. Two-dimensional targeted M-mode echocardiography was performed to measure left ventricular mass index. Partial least squares discriminant analysis was used for the multivariate analysis of the H NMR spectral data. From the H NMR-based metabolomic profiling, signals coming from methylene (-CH2-) and methyl (-CH3) moieties of aliphatic chains from plasma lipids were identified as discriminant variables. The -CH2-/-CH3 ratio, an indicator of the mean length of the aliphatic lipid chains, was significantly higher (P < 0.001) in the LVH group than in the hypertensive group without LVH and controls. Receiver operating characteristic curve showed that a cutoff of 2.34 provided a 52.08% sensitivity and 85.42% specificity for discriminating LVH (AUC = 0.703, P-value < 0.001). We propose the -CH2-/-CH3 ratio from plasma aliphatic lipid chains as a biomarker for the diagnosis of left ventricular remodeling in hypertension

Kinetic theory of Onsager's vortices in two-dimensional hydrodynamics

Starting from the Liouville equation, and using a BBGKY-like hierarchy, we derive a kinetic equation for the point vortex gas in two-dimensional (2D) hydrodynamics, taking two-body correlations and collective effects into account. This equation is valid at the order 1/N where N>>1 is the number of point vortices in the system (we assume that their individual circulation scales like \gamma ~ 1/N). It gives the first correction, due to graininess and correlation effects, to the 2D Euler equation that is obtained for $N\rightarrow +\infty$. For axisymmetric distributions, this kinetic equation does not relax towards the Boltzmann distribution of statistical equilibrium. This implies either that (i) the "collisional" (correlational) relaxation time is larger than Nt_D, where t_D is the dynamical time, so that three-body, four-body... correlations must be taken into account in the kinetic theory, or (ii) that the point vortex gas is non-ergodic (or does not mix well) and will never attain statistical equilibrium. Non-axisymmetric distributions may relax towards the Boltzmann distribution on a timescale of the order Nt_D due to the existence of additional resonances, but this is hard to prove from the kinetic theory. On the other hand, 2D Euler unstable vortex distributions can experience a process of "collisionless" (correlationless) violent relaxation towards a non-Boltzmannian quasistationary state (QSS) on a very short timescale of the order of a few dynamical times. This QSS is possibly described by the Miller-Robert-Sommeria (MRS) statistical theory which is the counterpart, in the context of two-dimensional hydrodynamics, of the Lynden-Bell statistical theory of violent relaxation in stellar dynamics

Growth, immune and viral responses in HIV infected African children receiving highly active antiretroviral therapy: a prospective cohort study

<p>Abstract</p> <p>Background</p> <p>Scale up of paediatric antiretroviral therapy in resource limited settings continues despite limited access to routine laboratory monitoring. We documented the weight and height responses in HIV infected Ugandan children on highly active antiretroviral therapy and determined clinical factors associated with successful treatment outcomes.</p> <p>Methods</p> <p>A prospective cohort of HIV infected children were initiated on HAART and followed for 48 weeks. Body mass index for age z scores(BAZ), weight and height-for-age z scores (WAZ & HAZ) were calculated: CD4 cell % and HIV-1 RNA were measured at baseline and every 12 weeks. Treatment outcomes were classified according to; both virological and immunological success (VS/IS), virological failure and immunological success (VF/IS). virological success and immunological failure (VS/IF) and both virological and immunological failure (VF/IF).</p> <p>Results</p> <p>From March 2004 until May 2006, 124 HIV infected children were initiated on HAART. The median age (IQR) was 5.0 years (2.1 - 7.0) and 49% (61/124) were female. The median [95% confidence interval (CI)] BAZ, WAZ and HAZ at baseline were 0.29 (-2.9, -1.2), -1.2 (-2.1, -0.5) and -2.06 (-2.9, -1.2) respectively. Baseline median CD4 cell % and log10 HIV-1 RNA were; 11.8% (7.5-18.0) and 5.6 (5.2-5.8) copies/ml. By 48 weeks, mean WAZ and HAZ in the VF/IS group, which was younger, increased from - 0.98 (SD 1.7) to + 1.22 (SD 1.2) and from -1.99 (1.7) to + 0.76 (2.4) respectively. Mean increase in WAZ and HAZ in the VS/IF group, an older group was modest, from -1.84 (1.3) to - 0.41 (1.2) and -2.25 (1.2) to -1.16 (1.3) respectively. Baseline CD4 cell % [OR 6.97 95% CI (2.6 -18.6)], age [OR 4.6 95% CI (1.14 -19.1)] and WHO clinical stage [OR 3.5 95%CI (1.05 -12.7)] were associated with successful treatment outcome.</p> <p>Conclusions</p> <p>HIV infected Ugandan children demonstrated a robust increase in height and weight z scores during the first 48 weeks of HAART, including those who failed to completely suppress virus. Older children initiating HAART with severe immune suppression were less likely to achieve a successful treatment outcome. These data emphasize the importance of initiating HAART early to ensure adequate immune and growth responses.</p

Blood Signature of Pre-Heart Failure: A Microarrays Study

International audienceBACKGROUND: The preclinical stage of systolic heart failure (HF), known as asymptomatic left ventricular dysfunction (ALVD), is diagnosed only by echocardiography, frequent in the general population and leads to a high risk of developing severe HF. Large scale screening for ALVD is a difficult task and represents a major unmet clinical challenge that requires the determination of ALVD biomarkers. METHODOLOGY/PRINCIPAL FINDINGS: 294 individuals were screened by echocardiography. We identified 9 ALVD cases out of 128 subjects with cardiovascular risk factors. White blood cell gene expression profiling was performed using pangenomic microarrays. Data were analyzed using principal component analysis (PCA) and Significant Analysis of Microarrays (SAM). To build an ALVD classifier model, we used the nearest centroid classification method (NCCM) with the ClaNC software package. Classification performance was determined using the leave-one-out cross-validation method. Blood transcriptome analysis provided a specific molecular signature for ALVD which defined a model based on 7 genes capable of discriminating ALVD cases. Analysis of an ALVD patients validation group demonstrated that these genes are accurate diagnostic predictors for ALVD with 87% accuracy and 100% precision. Furthermore, Receiver Operating Characteristic curves of expression levels confirmed that 6 out of 7 genes discriminate for left ventricular dysfunction classification. CONCLUSIONS/SIGNIFICANCE: These targets could serve to enhance the ability to efficiently detect ALVD by general care practitioners to facilitate preemptive initiation of medical treatment preventing the development of HF

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Synthesis and covalent assembly of patchy particles : toward new colloidal molecules

La notion de valence est très répandue à l’échelle de l’atome et est à l’origine de la diversité et des propriétés des composés covalents (molécules, macromolécules, cristaux). L’un des grands challenges à l’heure actuelle est de décliner cette notion de valence à l’échelle des particules, qui pourraient devenir des briques élémentaires programmées, c’est-à-dire la matière première de nouveaux matériaux qui seraient obtenus par assemblage spontané. Dans ce contexte, nous avons développé des particules à patchs possédant à leur surface des discontinuités chimiques et topologiques permettant de limiter le nombre de particules voisines et d’engendrer des interactions directionnelles avec ces dernières. L’objectif de nos travaux consiste dans un premier temps à imiter les hybridations simples de l’atome de carbone divalent (sp), trivalent (sp2) et tétravalent (sp3). Des particules de silice contenant un nombre spécifique de cavités dans lesquelles se trouvent des chaines de polystyrène ont été synthétisées et fonctionnalisées sélectivement. Des molécules colloïdales constituées d’une particule à patchs, au centre, entourée de nanoparticules satellites en nombre contrôlé ont été obtenues par assemblages covalents ou supramoléculaires. Ces premiers clusters miment la géométrie de molécules simples telles que CF4, BF3, CO2 ou H2O. En différenciant des lots de satellites soit par leur taille, soit par leur composition chimique, nous avons montré qu’il est possible d’étendre la formation de molécules colloïdales vers de structures plus complexes du type AXnYm (n+m = 4) ou encore des molécules colloïdales chirales. Enfin, nous avons développé une autre voie permettant d’obtenir de nouveaux atomes colloïdaux contenant un nombre défini de patchs surfaciques de taille contrôlée.The concept of valence is well-known at the atomic level and is at the origin of the diversity and properties of covalent compounds (molecules, macromolecules, crystals). Nowadays, one of the major challenges is to decline this notion of valence at the scale of colloidal particles, which could become programmed elementary bricks, that is to say the raw material of new materials that would be obtained by spontaneous assembly. In this context, we have developed patchy particles with chemical and topological discontinuities at their surface that limit the number of neighboring particles and induce directional interactions with them. The objective of our work consists first in imitating simple hybridizations of the divalent (sp), trivalent (sp2) and tetravalent (sp3) carbon atoms. The silica particles containing a specific number of cavities in which residues of polystyrene chains are chemically and selectively functionalized. Colloidal molecules consisting of a patchy particle, in the center, surrounded by satellite nanoparticles in controlled number were obtained by covalent or supramolecular routes. These first clusters mimic the geometry of simple molecules such as CF4, BF3, CO2 or H2O. By differentiating batches of satellites either by their size or by their chemical composition, we have shown that it is possible to extend the formation of colloidal molecules to more complex AXnYm (n + m = 4) structures or chiral colloidal molecules. Finally, we have developed another way to obtain new colloidal atoms containing a precise number of surface patches with a controlled area