Semiclassical Dynamics of Electrons in Magnetic Bloch Bands: a Hamiltonian Approach

y formally diagonalizing with accuracy $\hbar$ the Hamiltonian of electrons in a crystal subject to electromagnetic perturbations, we resolve the debate on the Hamiltonian nature of semiclassical equations of motion with Berry-phase corrections, and therefore confirm the validity of the Liouville theorem. We show that both the position and momentum operators acquire a Berry-phase dependence, leading to a non-canonical Hamiltonian dynamics. The equations of motion turn out to be identical to the ones previously derived in the context of electron wave-packets dynamics.Comment: 4 page

From Feynman Proof of Maxwell Equations to Noncommutative Quantum Mechanics

In 1990, Dyson published a proof due to Feynman of the Maxwell equations assuming only the commutation relations between position and velocity. With this minimal assumption, Feynman never supposed the existence of Hamiltonian or Lagrangian formalism. In the present communication, we review the study of a relativistic particle using ``Feynman brackets.'' We show that Poincar\'e's magnetic angular momentum and Dirac magnetic monopole are the consequences of the structure of the Lorentz Lie algebra defined by the Feynman's brackets. Then, we extend these ideas to the dual momentum space by considering noncommutative quantum mechanics. In this context, we show that the noncommutativity of the coordinates is responsible for a new effect called the spin Hall effect. We also show its relation with the Berry phase notion. As a practical application, we found an unusual spin-orbit contribution of a nonrelativistic particle that could be experimentally tested. Another practical application is the Berry phase effect on the propagation of light in inhomogeneous media.Comment: Presented at the 3rd Feynman Festival (Collage Park, Maryland, U.S.A., August 2006

Orientation and distribution of recent gullies in the southern hemisphere of Mars: observations from HRSC/MEX and MOC/MGS data

Abstract not available

Élaboration de normes DRIS provisoires pour des transplants de céleri

Nous avons utilisé une banque de données contenant 215 observations pour obtenir des normes DRIS (Diagnosis and Recommandation Integrated System) provisoires pour des transplants de céleri (Apium graveolens var. Dulce). La détermination des normes s'est faite en considérant un groupe de tête au rendement supérieur ou égal à 1600 g/plant (27 % de la population). Sur 45 rapports nutritionnels mesurés dans la partie aérienne des transplants, 26 ont présenté des rapports de variance permettant de distinguer significativement le groupe produisant des rendements supérieurs. Le coefficient de corrélation entre l'indice de déséquilibre nutritionnel (IDN) et les rendements s'est révélé très significatif. Les normes provisoires ont été confrontées à un ensemble indépendant de données obtenues chez des producteurs de la région du sud de Montréal (Québec). Les IDN calculés sur ces plantes échantillonnées au stade implantation (environ 27 jours après la plantation) ont été significativement corrélés aux rendements, malgré le fait que le tissu échantillonné et le stade de croissance aient été relativement éloignés de ceux correspondant aux normes. Les normes ont permis d'identifier la cause probable d'un problème de croissance induit par l'utilisation d'une solution fertilisante ne convenant pas à la production de transplants.A data bank of 215 observations was used to elaborate preliminary DRIS norms for celery (Apium graveolens var.Dulce) transplants. The threshold yield for high yielders was set at 1600 g/plant (27% of the population). Of the 45 nutrient ratios obtained, 26 presented significant variance ratios between low and high yielders. The correlation coefficient between nutrient imbalance index (Nil) and yield was highly significant. The norms were tested on an independent set of data obtained from celery growers located south of Montreal (Quebec). The Nil obtained from plants at the implantation stage (about 27 days after transplanting) was significantly correlated to yield even if the sampled tissue was different from that used for norm calculations. The norms were also used to identify the likely cause of a growth problem induced by a nutrient solution not suited for transplant production

Space Shuttle Crawler Transporter Truck Shoe Qualification Tests and Analyses for Return-to-Flight

A vital element to Launch Complex 39 (LC39) and NASA's Kennedy Space Center (KSC) mobile launch transfer operation is a 3 million kilogram behemoth known as the Crawler Transporter (CT). Built in the 1960's, two CT's have accumulated over 1700+ miles each and have been used for the Apollo and the Space Shuttle programs. Recent observation of fatigue cracks on the CT shoes led to a comprehensive engineering, structural and metallurgical evaluation to assess the root cause that necessitated procurement of over 1000 new shoes. This paper documents the completed dynamic and compression tests on the old and new shoes respectively, so as to certify them for Space Shuttle's return-to-flight (RTF). Measured strain data from the rollout tests was used to develop stress/loading spectra and static equivalent load for qualification testing of the new shoes. Additionally, finite element analysis (FEA) was used to conduct sensitivity analyses of various contact parameters and structural characteristics for acceptance of new shoes

Spinal Cord T-Cell Infiltration in the Rat Spared Nerve Injury Model: A Time Course Study.

The immune system is involved in the development of neuropathic pain. In particular, the infiltration of T-lymphocytes into the spinal cord following peripheral nerve injury has been described as a contributor to sensory hypersensitivity. We used the spared nerve injury (SNI) model of neuropathic pain in Sprague Dawley adult male rats to assess proliferation, and/or protein/gene expression levels for microglia (Iba1), T-lymphocytes (CD2) and cytotoxic T-lymphocytes (CD8). In the dorsal horn ipsilateral to SNI, Iba1 and BrdU stainings revealed microglial reactivity and proliferation, respectively, with different durations. Iba1 expression peaked at D4 and D7 at the mRNA and protein level, respectively, and was long-lasting. Proliferation occurred almost exclusively in Iba1 positive cells and peaked at D2. Gene expression observation by RT-qPCR array suggested that T-lymphocytes attracting chemokines were upregulated after SNI in rat spinal cord but only a few CD2/CD8 positive cells were found. A pronounced infiltration of CD2/CD8 positive T-cells was seen in the spinal cord injury (SCI) model used as a positive control for lymphocyte infiltration. Under these experimental conditions, we show early and long-lasting microglia reactivity in the spinal cord after SNI, but no lymphocyte infiltration was found

Space Shuttle Crawler Transporter Vibration Analysis in Support of Rollout Fatigue Load Spectra Verification Program

The Crawler Transporter (CT), designed and built for the Apollo Program in the 1960's and surpassing its initial operational life, has become an integral part of the Space Shuttle Program (SSP). The CT transports the Space Shuttle Vehicle (SSV) stack, atop the Mobile Launch Platform (MLP), from the Vehicle Assembly Building (VAB) to the launch pad. This support structure provides hydraulic jacking, leveling and load equalization for the 12 million pound stack on its 3.5-5.0 mile rollout to the launch pad. Major elements of the SSV, consisting of the orbiter, solid rocket boosters (SRB) and external tank (ET) have required fatigue analyses as part of the mission life certification. Compared to rollout vibration, the SSV sees relatively high vibration loads during launch, ascent, descent and landing phases of the mission. Although preliminary measured SRB vibration levels during rollout were of low amplitude and frequency, the duration of the rollout phase is typically high, from 5-6 hours. As part of an expanded mission life assessment, additional certification effort was initiated to define fatigue load spectra for rollout. This study addresses the CT vibration analyses in support of the rollout fatigue study. Structural models developed for modal and vibration analyses were used to identify unique CT, CT/MLP and CT/MLP/SRB vibration characteristics for comparison to instrumented rollout tests. Whereas the main structural and vibration characteristics of the SSV are well defined, minimum analytical and vibration test data on the Crawler Transporter were available. Unique vibration characteristics of the CT are attributable to the drive mechanism, hydraulic jacking system, structural framing and the CT-to-MLP support pad restraints. Initial tests performed on the CT/MLP/SRB configuration showed reasonable correlation with predicted mode shapes and frequencies

HIV-1 selectively targets gut-homing CCR6+CD4+ T cells via mTOR-dependent mechanisms

Gut-associated lymphoid tissues are enriched in CCR6+ Th17-polarized CD4+ T cells that contribute to HIV-1 persistence during antiretroviral therapy (ART). This raises the need for Th17-targeted immunotherapies. In an effort to identify mechanisms governing HIV-1 permissiveness/persistence in gut-homing Th17 cells, we analyzed the transcriptome of CCR6+ versus CCR6- T cells exposed to the gut-homing inducer retinoic acid (RA) and performed functional validations in colon biopsies of HIV-infected individuals receiving ART (HIV+ART). Although both CCR6+ and CCR6- T cells acquired gut-homing markers upon RA exposure, the modulation of unique sets of genes coincided with preferential HIV-1 replication in RA-treated CCR6+ T cells. This molecular signature included the upregulation of HIV-dependency factors acting at entry/postentry levels, such as the CCR5 and PI3K/Akt/mTORC1 signaling pathways. Of note, mTOR expression/phosphorylation was distinctively induced by RA in CCR6+ T cells. Consistently, mTOR inhibitors counteracted the effect of RA on HIV replication in vitro and viral reactivation in CD4+ T cells from HIV+ART individuals via postentry mechanisms independent of CCR5. Finally, CCR6+ versus CCR6- T cells infiltrating the colons of HIV+ART individuals expressed unique molecular signatures, including higher levels of CCR5, integrin β7, and mTOR phosphorylation. Together, our results identify mTOR as a druggable key regulator of HIV permissiveness in gut-homing CCR6+ T cells

The gray matter volume of the amygdala is correlated with the perception of melodic intervals: a voxel-based morphometry study

Music is not simply a series of organized pitches, rhythms, and timbres, it is capable of evoking emotions. In the present study, voxel-based morphometry (VBM) was employed to explore the neural basis that may link music to emotion. To do this, we identified the neuroanatomical correlates of the ability to extract pitch interval size in a music segment (i.e., interval perception) in a large population of healthy young adults (N = 264). Behaviorally, we found that interval perception was correlated with daily emotional experiences, indicating the intrinsic link between music and emotion. Neurally, and as expected, we found that interval perception was positively correlated with the gray matter volume (GMV) of the bilateral temporal cortex. More important, a larger GMV of the bilateral amygdala was associated with better interval perception, suggesting that the amygdala, which is the neural substrate of emotional processing, is also involved in music processing. In sum, our study provides one of first neuroanatomical evidence on the association between the amygdala and music, which contributes to our understanding of exactly how music evokes emotional responses

Self-adjustment mechanisms and their application for orthosis design

Medical orthoses aim at guiding anatomical joints along their natural trajectories while preventing pathological movements, especially in case of trauma or injuries. The motions that take place between bone surfaces have complex kinematics. These so-called arthrokinematic motions exhibit axes that move both in translation and rotation. Traditionally, orthoses are carefully adjusted and positioned such that their kinematics approximate the arthrokinematic movements as closely as possible in order to protect the joint. Adjustment procedures are typically long and tedious. We suggest in this paper another approach. We propose mechanisms having intrinsic self-aligning properties. They are designed such that their main axis self-adjusts with respect to the joint’s physiological axis during motion. When connected to a limb, their movement becomes homokinetic and they have the property of automatically minimizing internal stresses. The study is performed here in the planar case focusing on the most important component of the arthrokinematic motions of a knee joint