Experimental evidence of thermal fluctuations on the X-ray absorption near-edge structure at the aluminum K-edge

After a review of temperature-dependent experimental x-ray absorption near-edge structure (XANES) and related theoretical developments, we present the Al K-edge XANES spectra of corundum and beryl for temperature ranging from 300K to 930K. These experimental results provide a first evidence of the role of thermal fluctuation in XANES at the Al K-edge especially in the pre-edge region. The study is carried out by polarized XANES measurements of single crystals. For any orientation of the sample with respect to the x-ray beam, the pre-edge peak grows and shifts to lower energy with temperature. In addition temperature induces modifications in the position and intensities of the main XANES features. First-principles DFT calculations are performed for both compounds. They show that the pre-edge peak originates from forbidden 1s to 3s transitions induced by vibrations. Three existing theoretical models are used to take vibrations into account in the absorption cross section calculations: i) an average of the XANES spectra over the thermal displacements of the absorbing atom around its equilibrium position, ii) a method based on the crude Born-Oppenheimer approximation where only the initial state is averaged over thermal displacements, iii) a convolution of the spectra obtained for the atoms at the equilibrium positions with an approximate phonon spectral function. The theoretical spectra so obtained permit to qualitatively understand the origin of the spectral modifications induced by temperature. However the correct treatment of thermal fluctuation in XANES spectroscopy requires more sophisticated theoretical tools

fMRI visualization of transient activations in the rat olfactory bulb using short odor stimulations

International audienceOdor-evoked activity in the olfactory bulb displays both spatial and temporal organization. The difficulty when assessing spatio-temporal dynamics of olfactory representation is to find a method that reconciles the appropriate resolution for both dimensions. Imaging methods based on optical recordings can reach high temporal and spatial resolution but are limited to the observation of the accessible dorsal surface. Functional magnetic resonance imaging (fMRI) may be useful to overcome this limitation as it allows recording from the whole brain. In this study, we combined ultra fast imaging sequence and short stimulus duration to improve temporal resolution of odor-evoked BOLD responses. Short odor stimulations evoked high amplitude BOLD responses and patterns of activation were similar to those obtained in previous studies using longer stimulations. Moreover, short odor exposures prevented habituation processes. Analysis of the BOLD signal time course in the different areas of activation revealed that odorant response maps are not static entities but rather are temporally dynamic as reported by recent studies using optical imaging. These data demonstrated that fMRI is a non-invasive method which could represent a powerful tool to study not only the spatial dimension of odor representation but also the temporal dimension of information processing

Vaginal microbiota diversity and paucity of Lactobacillus species are associated with persistent hrHPV infection in HIV negative but not in HIV positive women.

Funder: Maryland Department of Health and Mental Hygiene; doi: http://dx.doi.org/10.13039/100006671The vaginal microbiota is thought to play a role in modulating risk of high-risk human papillomavirus (hrHPV) infection. We examined the relationship between the vaginal microbiota and persistent hrHPV infection in HIV-negative and HIV-positive women. We used 16S-rRNA sequencing to characterize the vaginal microbiota of two serial samples taken six months apart from 211 Nigerian women (67%, 142/211 HIV-positive and 33%, 69/211 HIV-negative) and evaluated the association between the vaginal microbiota and persistent hrHPV infection using generalized estimating equation logistic regression models and linear discriminant analysis effect size (LEfSe) algorithm to identify phylotypic biomarkers of persistent hrHPV infection. The high diversity microbiota, Community State Type IV-B, was the most prevalent in both HIV-negative (38% at baseline, 30% at the follow-up visit) and HIV-positive (27% at baseline, 35% at the follow-up visit) women. The relationship between the vaginal microbiota and persistent hrHPV was modified by HIV status. In HIV-negative women, women with Lactobacillus dominant microbiota had lower odds (OR: 0.35, 95% CI 0.14-0.89, p = 0.03) of persistent hrHPV compared to women with Lactobacillus deficient microbiota. While among HIV-positive women, the odds of being persistently infected with hrHPV was higher in women with Lactobacillus dominant microbiota (OR: 1.25, 95% CI 0.73-2.14 p = 0.41). This difference in effect estimates by HIV was statistically significant (p = 0.02). A high diversity vaginal microbial community with paucity of Lactobacillus species was associated with persistent hrHPV infection in HIV-negative women but not in HIV-positive women

Transcriptional Responses of Different Brain Cell Types to Oxygen Decline

Brain hypoxia is associated with a wide range of physiological and clinical conditions. Although oxygen is an essential constituent of maintaining brain functions, our understanding of how specific brain cell types globally respond and adapt to decreasing oxygen conditions is incomplete. In this study, we exposed mouse primary neurons, astrocytes, and microglia to normoxia and two hypoxic conditions and obtained genome-wide transcriptional profiles of the treated cells. Analysis of differentially expressed genes under conditions of reduced oxygen revealed a canonical hypoxic response shared among different brain cell types. In addition, we observed a higher sensitivity of neurons to oxygen decline, and dissected cell type-specific biological processes affected by hypoxia. Importantly, this study establishes novel gene modules associated with brain cells responding to oxygen deprivation and reveals a state of profound stress incurred by hypoxia

Early MicroRNA expression profile as a prognostic biomarker for the development of pelvic inflammatory disease in a mouse model of chlamydial genital infection

It is not currently possible to predict the probability of whether a woman with a chlamydial genital infection will develop pelvic inflammatory disease (PID). To determine if specific biomarkers may be associated with distinct chlamydial pathotypes, we utilized two Chlamydia muridarum variants (C. muridarum Var001 [CmVar001] and CmVar004) that differ in their abilities to elicit upper genital tract pathology in a mouse model. CmVar004 has a lower growth rate in vitro and induces pathology in only 20% of C57BL/6 mouse oviducts versus 83.3% of oviducts in CmVar001-infected mice. To determine if chemokine and cytokine production within 24 h of infection is associated with the outcome of pathology, levels of 15 chemokines and cytokines were measured. CmVar004 infection induced significantly lower levels of CXCL1, CXCL2, tumor necrosis factor alpha (TNF-α), and CCL2 in comparison to CmVar001 infection with similar rRNA (rs16) levels for Chlamydiae. A combination of microRNA (miRNA) sequencing and quantitative real-time PCR (qRT-PCR) analysis of 134 inflammation-related miRNAs was performed 24 h postinfection to determine if the chemokine/cytokine responses would also be reflected in miRNA expression profiles. Interestingly, 12 miRNAs (miR-135a-5p, miR298-5p, miR142-3p, miR223-3p, miR299a-3p, miR147-3p, miR105, miR325-3p, miR132-3p, miR142-5p, miR155-5p, and miR-410-3p) were overexpressed during CmVar004 infection compared to CmVar001 infection, inversely correlating with the respective chemokine/cytokine responses. To our knowledge, this is the first report demonstrating that early biomarkers elicited in the host can differentiate between two pathological variants of chlamydiae and be predictive of upper tract disease. © 2014 Yeruva et al

Stabilisation of beta and gamma oscillation frequency in the mammalian olfactory bulb

International audienceThe dynamics of the mammalian olfactory bulb (OB) is characterized by local field potential (LFP) oscillations either slow, in the theta range (2-10Hz, tightly linked to the respiratory rhythm), or fast, in the beta (15-30Hz) or gamma (40-90Hz) range. These fast oscillations are known to be modulated by odorant features and animal experience or state, but both their mechanisms and implication in coding are still not well understood. In this study, we used a double canulation protocol to impose artificial breathing rhythms to anesthetized rats while recording the LFP in the OB. We observed that despite the changes in the input air flow parameters (frequency or flow rate), the main characteristics of fast oscillations (duration, frequency or amplitude) were merely constant. We thus made the hypothesis that fast beta and gamma oscillations dynamics are entirely determined by the OB network properties and that external stimulation was only able put the network in a state which permits the generation of one or the other oscillations (they are never present simultaneously)

Capteur RF à 4 canaux pour la détection de signaux BOLD par IRMf de réponses olfactives chez le rat à 7T

National audienceIntroduction Les capteurs RMN multiéléments ont été introduits en 1990 pour augmenter la sensibilité en réduisant le diamètre des boucles tout en gardant un large volume d'exploration [1] en juxtaposant plusieurs bobines simples. Ces bobines doivent être découplées entre elles pour acquérir simultanément et indépendamment les signaux. Le moyen de découplage le plus utilisé est le découplage géométrique combiné à l'utilisation de préamplificateurs faible bruit à basse impédance d'entrée. Une technique alternative consistant à joindre les bobines par un conducteur commun a permis de réaliser une bobine constituée de deux-canaux sans utilisation de préamplificateurs et avec un découplage approprié entre les canaux [2]. Le principe du découplage était fondé sur la transformation d'impédance [3]. Dans ce travail nous présentons la réalisation d'un capteur constitué de quatre canaux et basée sur ce même principe de découplage. Ce capteur est dédié à la détection de signaux BOLD (blood oxygen level-dependent) par IRMf dans le cerveau du rat. Une expérience d'activation des zones olfactives du rat a été réalisée sur un système Bruker à 7T. Nous présentons les premiers résultats d'activation observée dans le bulbe olfactif (BO) et dans le cortex piriforme (CP) pour lesquels la géométrie du capteur a été optimisée. Matériel et Méthode La figure 1 présente le capteur de réception à quatre canaux conçu pour s'adapter à la morphologie du rat et pour imager les régions d'activation visées. Ce capteur est constitué de quatre boucles rectangulaires de 20x24 mm 2 intérieur avec des pistes de cuivre de 4 mm de large. Il est collé sur un cylindre de 35 mm de diamètre extérieur permettant de couvrir de la tête de l'animal. Des diodes PIN placées sur chacune des boucles assurent le découplage actif avec la bobine d'émission. Le découplage entre les canaux est obtenu par un report du plan de masse à l'intersection de deux canaux voisin, à la fréquence de résonance. Ce découplage est réalisé lors de la construction par l'ajustement des capacités constituant les boucles. Une capacité supplémentaire, annulant la partie imaginaire de l'inductance parasite du plan de masse assure le découplage entre les deux canaux extérieurs. L'adaptation des 4 canaux à 50 Ω pour une fréquence de 300 MHz est réalisé avec un boitier qui a été conçu pour s'interfacer avec le système Bruker avance I et II. Un masque permet de délivrer aux rats anesthésiés une odeur de façon synchronisée avec la séquence d'imagerie (séquence EPI, TR/TE=1000/19ms, FOV 2.5x2.5 cm, 128x128 pixels) de manière à détecter la réponse à ces stimulations olfactives. Résultats La mesure des paramètres S du capteur est présentée sur la figure 2. Cette mesure, réalisée à l'aide d'un analyseur de réseau vectoriel 4 ports, montre l'adaptation de chacun des canaux et un couplage entre eux inférieur à-20 dB. Le rapport signal sur bruit du capteur réalisé est environ 2 fois plus élevé dans la zone du cortex piriforme que celui d'une antenne quatre canaux Rapid Biomed pur le cerveau de rat. La figure 3 montre un premier résultat d'activation BOLD par IRMf obtenu dans le bulbe olfactif et dans le cortex piriforme d'un rat pendant une stimulation olfactive (extrait de verveine). Conclusion Le principe de découplage par conducteur commun a été montré sur un capteur quatre-canaux. Les performances de ce capteur ont été validées par la mesure des paramètres S et par des résultats d'activation BOLD en IRMf du cerveau de rat

Radio emission of extensive air shower at CODALEMA: Polarization of the radio emission along the v*B vector

Cosmic rays extensive air showers (EAS) are associated with transient radio emission, which could provide an efficient new detection method of high energy cosmic rays, combining a calorimetric measurement with a high duty cycle. The CODALEMA experiment, installed at the Radio Observatory in Nancay, France, is investigating this phenomenon in the 10^17 eV region. One challenging point is the understanding of the radio emission mechanism. A first observation indicating a linear relation between the electric field produced and the cross product of the shower axis with the geomagnetic field direction has been presented (B. Revenu, this conference). We will present here other strong evidences for this linear relationship, and some hints on its physical origin.Comment: Contribution to the 31st International Cosmic Ray Conference, Lodz, Poland, July 2009. 4 pages, 8 figures. v2: Typo fixed, arxiv references adde