Observer dependent D-brane for strings propagating in pp-wave time dependent background

We study type IIB superstring in the pp-wave time-dependent background, which has a singularity at $t=0$. We show that this background can provide a toy model to study some ideas related to the stretched horizon paradigm and the complementary principle of black holes. To this end, we construct a unitary Bogoliubov generator which relates the asymptotically flat string Hilbert space, defined at $t =\pm \infty$, to the finite time Hilbert space. For asymptotically flat observers, the closed string vacuum close to the singularity appears as a boundary state which is in fact a D-brane described in the closed string channel. However, observers who go with the string towards to the singularity see the original vacuum.Comment: 12 pages, revtex 4, added references, corrected mistake

Cognitive changes under memantine according to vitamin D status in Alzheimer patients: An exposed/unexposed cohort pilot study

Memantine is a symptomatic treatment that partially prevents cognitive decline in Alzheimer disease (AD). The neuroprotective effects of memantine and vitamin D may potentiate each other, with benefits for cognition. The objective of this exposed/unexposed pilot study was to determine the cognitive changes among AD patients using memantine according to the presence or absence of vitamin D deficiency (VDD). Fifty-eight AD patients followed in a memory clinic during 6 months between 2009 and 2014 (mean±standard deviation, 82.9±5.0years; 56.9%female) were separated into four groups according to VDD (i.e., serum 25-hydroxyvitamin D≤25nM) at M0 and M6 (i.e., Group 1: no VDD-M0, no VDD-M6; Group 2: VDD-M0, no VDD-M6; Group 3: no VDD-M0, VDD-M6; Group 4: VDD-M0, VDD-M6). The 6-month cognitive change was examined with the Mini-Mental State Examination (MMSE) score in the 4 groups according to the use of memantine. Age, gender, body mass index, IADL score, GDS score, and use of pchychoactive drugs were measured at baseline. We found that participants using memantine had a lower MMSE score at M0 compared to those without memantine (P=0.006). After 6 months of follow-up, there was a memantine-related improvement of the MMSE score only in the participants with VDD-M6. This was significant in Group 3 with no VDD-M0 (P=0.039), but not in Group 4 who already had VDD-M0. Similarly, using memantine was associated with a 6-month improvement of MMSE only in Group 3 in whom VDD appeared during the follow-up (β=8.8, P=0.044). In conclusion, the use of memantine was associated with improved cognitive performance after 6 months of treatment in the presence of VDD at M6. Memantine may prevent the cognitive decline that accompanies the onset of VDD, which prompts to give to AD patients a regimen combining both memantine and vitamin D supplements

Test de double tâche sur cyclo-ergomètre : Recherches préliminaires sur l’acceptabilité et l’utilisation

Les perturbations motrices en condition de double tâche, visant à explorer le contrôle moteur cérébral, sont majoritairement examinées au moyen de tapis d\u27analyse spatio-temporelle de la marche. Pourtant, les patients âgés qui viennent pratiquer ces examens sont en partie sujets à un risque accru de chute du fait de troubles moteurs et/ou cognitifs probables. L\u27étude consiste donc à pratiquer ces tests de double tâche sur un nouveau dispositif, Cycléo BRAU, qui permet aux patients de réaliser une tâche attentionnelle, surajoutée à une tâche primaire, faire du vélo, en toute sécurité. De plus, le système est équipé d\u27un dispositif de réalité virtuelle qui projette un environnement prédéterminé permettant des tâches attentionnelles plus complexes. Le patient est donc rassuré à l\u27idée de faire son examen, non seulement parce qu\u27il n\u27a plus peur de tomber, mais également parce que cet examen devient ludique. L\u27objectif principal est d\u27établir la concordance des résultats des tests de double tâche obtenus avec le tapis de marche GAITRite et ceux obtenus avec le dispositif Cycléo BRAU. Ceci s\u27effectue grâce à l\u27analyse de la vitesse et de la variabilité de la vitesse de marche et de pédalage durant ces examens. Les résultats espérés sont l\u27obtention d\u27une bonne faisabilité, d\u27une bonne reproductibilité et de trouver une corrélation entre l\u27analyse de la marche et l\u27analyse avec Cycléo BRAU. Avec cette étude, les examens de la personne âgée atteinte de troubles moteurs et cognitifs pourront être plus rapides et plus sécurisants pour les patients

Quantum Theory of Noncommutative Fields

Generalizing the noncommutative harmonic oscillator construction, we propose a new extension of quantum field theory based on the concept of "noncommutative fields". Our description permits to break the usual particle-antiparticle degeneracy at the dispersion relation level and introduces naturally an ultraviolet and an infrared cutoff. Phenomenological bounds for these new energy scales are given.Comment: LaTeX file, JHEP3.cls, subequations.sty; 12 pages, no figures. Final version published in JHEP with some references adde

Calcium and vitamin D supplementation. Myths and realities with regard to cardiovascular risk

Vitamin D and calcium are considered crucial for the treatment of bone diseases. Both vitamin D and calcium contribute to bone homeostasis but also preserve muscle health by reducing the risk of falls and fractures. Low vitamin D concentrations result in secondary hyperparathyroidism and contribute to bone loss, although the development of secondary hyperparathyroidism varies, even in patients with severe vitamin D deficiency. Findings from observational studies have shown controversial results regarding to the association between bone mineral density and vitamin D/calcium status, thus sparking a debate regarding optimum concentrations of 25-hydroxyvitamin D and calcium for the best possible skeletal health. Although most of intervention studies reported a positive effect of supplementation with calcium and vitamin D on bone in patients with osteoporosis, this therapeutic approach has been a matter of debate regarding potential side effects on the cardiovascular (CV) system. Thus, the aim of this review is to consider the current evidence on the physiological role of vitamin D and calcium on bone and muscle health. Moreover, we provide an overview on observational and interventional studies that investigate the effect of vitamin D and calcium supplementation on bone health, also taking into account the possible CV side-effects. We also provide molecular insights on the effect of calcium plus vitamin D on the CV system

Painless local pressure application to test microvascular reactivity to ischemia

BACKGROUND: Forearm cutaneous blood flux (CBF) measurement with post-occlusive reactive hyperemia (PORH) is uncomfortable and may not be devoid of risks. We aimed to investigate post-compression reactive hyperemia (PCRH) with a custom-made indenter that was designed to be easily used routinely by inexperienced observers. METHODS: Medical students evaluated PCRH with 1- to 4-min pressure applications of 16 to 34 kPa and PORH with 3-min forearm cuff occlusion using laser speckle contrast imaging in 15 healthy volunteers. Participants were asked to quantify their discomfort with a visual analogue scale (VAS) of 10 cm. Total ischemia (ISCH) was quantified by the product of CBF during ischemia and ischemia duration (min). We subtracted the CBF changes in the skin from a reference ipsilateral (PCRH) or contralateral (PORH) non-stimulated area. RESULTS: The average VAS was 1.0 for PCRH vs. 6.0 for PORH (p < 0.001). A strong linear relationship between ISCH and peak PCRH (r = 0.915, p < 0.001) was noted. Peak PORH values (63.9 laser perfusion units (LPU)) were significantly lower than all values of the 3-min PCRH (72.6 LPU), including the one obtained with 16 kPa. CONCLUSION: Inexperienced observers could test microvascular reactivity with PCRH without inducing the discomfort that is typically experienced with PORH. Further, PCRH elicits a higher peak response to ischemia compared with PORH. This extremely simple method could influence a broad spectrum of routine cutaneous microcirculation investigations, especially when a painful approach is particularly inadequate or if the patient is fragile. CLINICAL TRIAL REGISTRATION: NCT02861924

A novel multiscale cross-entropy method applied to navigation data acquired with a bike simulator

International audienc

Profiling older community-dwellers with hypovitaminosis D: A classification tree analysis

Despite the high prevalence of hypovitaminosis D in older adults, universal vitamin D supplementation is not recommended due to potential risk of intoxication. Our aim here was to determine the clinical profiles of older community-dwellers with hypovitaminosis D. The perspective is to build novel strategies to screen for and supplement those with hypovitaminosis D. A classification tree (CHAID analysis) was performed on multiple datasets standardizedly collected from 1991 older French community-dwelling volunteers ≥ 65 years in 2009-2012. Hypovitaminosis D was defined as serum 25-hydroxyvitamin D ≤ 50 nmol/L. CHAID analysis retained 5 clinical profiles of older community-dwellers with different risks of hypovitaminosis D up to 87.3%, based on various combinations of the following characteristics: polymorbidity, obesity, sadness and gait disorders. For instance, the probability of hypovitaminosis D was 1.42-fold higher [95CI: 1.27-1.59] for those with polymorbidity and gait disorders compared to those with no polymorbidity, no obesity and no sadness. In conclusion, these easily-recordable measures may be used in clinical routine to identify older community-dwellers for whom vitamin D supplementation should be initiated