881 research outputs found
The Origin of Magnetic Interactions in Ca3Co2O6
We investigate the microscopic origin of the ferromagnetic and
antiferromagnetic spin exchange couplings in the quasi one-dimensional cobalt
compound Ca3Co2O6. In particular, we establish a local model which stabilizes a
ferromagnetic alignment of the S=2 spins on the cobalt sites with trigonal
prismatic symmetry, for a sufficiently strong Hund's rule coupling on the
cobalt ions. The exchange is mediated through a S=0 cobalt ion at the
octahedral sites of the chain structure. We present a strong coupling
evaluation of the Heisenberg coupling between the S=2 Co spins on a separate
chain. The chains are coupled antiferromagnetically through super-superexchange
via short O-O bonds.Comment: 5 Pages, 3 Figures; added anisotropy term in eq. 9; extended
discussion of phase transitio
Comparison of stimulation patterns for FES-cycling using measures of oxygen cost and stimulation cost
<b>Aim</b><p></p>
The energy efficiency of FES-cycling in spinal cord injured subjects is very much lower than that of normal cycling, and efficiency is dependent upon the parameters of muscle stimulation. We investigated measures which can be used to evaluate the effect on cycling performance of changes in stimulation parameters, and which might therefore be used to optimise them. We aimed to determine whether oxygen cost and stimulation cost measurements are sensitive enough to allow discrimination between the efficacy of different activation ranges for stimulation of each muscle group during constant-power cycling. <p></p>
<b>Methods</b><p></p>
We employed a custom FES-cycling ergometer system, with accurate control of cadence and stimulated exercise workrate. Two sets of muscle activation angles (âstimulation patternsâ), denoted âP1â and âP2â, were applied repeatedly (eight times each) during constant-power cycling, in a repeated measures design with a single paraplegic subject. Pulmonary oxygen uptake was measured in real time and used to determine the oxygen cost of the exercise. A new measure of stimulation cost of the exercise is proposed, which represents the total rate of stimulation charge applied to the stimulated muscle groups during cycling. A number of energy-efficiency measures were also estimated. <p></p>
<b>Results</b><p></p>
Average oxygen cost and stimulation cost of P1 were found to be significantly lower than those for P2 (paired <i>t</i>-test, <i>p</i> < 0.05): oxygen costs were 0.56 ± 0.03 l min<sup>â1</sup> and 0.61 ± 0.04 l min<sup>â1</sup>(mean ± S.D.), respectively; stimulation costs were 74.91 ± 12.15 mC min<sup>â1</sup> and 100.30 ± 14.78 mC min<sup>â1</sup> (mean ± S.D.), respectively. Correspondingly, all efficiency estimates for P1 were greater than those for P2. <p></p>
<b>Conclusion</b><p></p>
Oxygen cost and stimulation cost measures both allow discrimination between the efficacy of different muscle activation patterns during constant-power FES-cycling. However, stimulation cost is more easily determined in real time, and responds more rapidly and with greatly improved signal-to-noise properties than the ventilatory oxygen uptake measurements required for estimation of oxygen cost. These measures may find utility in the adjustment of stimulation patterns for achievement of optimal cycling performance. <p></p>
PTPα regulates integrin-stimulated FAK autophosphorylation and cytoskeletal rearrangement in cell spreading and migration
We investigated the molecular and cellular actions of receptor protein tyrosine phosphatase (PTP) α in integrin signaling using immortalized fibroblasts derived from wild-type and PTPα-deficient mouse embryos. Defects in PTPαâ/â migration in a wound healing assay were associated with altered cell shape and focal adhesion kinase (FAK) phosphorylation. The reduced haptotaxis to fibronectin (FN) of PTPαâ/â cells was increased by expression of active (but not inactive) PTPα. Integrin-mediated formation of srcâFAK and fynâFAK complexes was reduced or abolished in PTPαâ/â cells on FN, concomitant with markedly reduced phosphorylation of FAK at Tyr397. Reintroduction of active (but not inactive) PTPα restored FAK Tyr-397 phosphorylation. FN-induced cytoskeletal rearrangement was retarded in PTPαâ/â cells, with delayed filamentous actin stress fiber assembly and focal adhesion formation. This mimicked the effects of treating wild-type fibroblasts with the src family protein tyrosine kinase (Src-PTK) inhibitor PP2. These results, together with the reduced src/fyn tyrosine kinase activity in PTPαâ/â fibroblasts (Ponniah et al., 1999; Su et al., 1999), suggest that PTPα functions in integrin signaling and cell migration as an Src-PTK activator. Our paper establishes that PTPα is required for early integrin-proximal events, acting upstream of FAK to affect the timely and efficient phosphorylation of FAK Tyr-397
An interaction network of mental disorder proteins in neural stem cells
Mental disorders (MDs) such as intellectual disability (ID), autism spectrum disorders (ASD) and schizophrenia have a strong genetic component. Recently, many gene mutations associated with ID, ASD or schizophrenia have been identified by high-throughput sequencing. A substantial fraction of these mutations are in genes encoding transcriptional regulators. Transcriptional regulators associated with different MDs but acting in the same gene regulatory network provide information on the molecular relation between MDs. Physical interaction between transcriptional regulators is a strong predictor for their cooperation in gene regulation. Here, we biochemically purified transcriptional regulators from neural stem cells, identified their interaction partners by mass spectrometry and assembled a protein interaction network containing 206 proteins, including 68 proteins mutated in MD patients and 52 proteins significantly lacking coding variation in humans. Our network shows molecular connections between established MD proteins and provides a discovery tool for novel MD genes. Network proteins preferentially co-localize on the genome and cooperate in disease-relevant gene regulation. Our results suggest that the observed transcriptional regulators associated with ID, ASD or schizophrenia are part of a transcriptional network in neural stem cells. We find that more severe mutations in network proteins are associated with MDs that include lower intelligence quotient (IQ), suggesting that the level of disruption of a shared transcriptional network correlates with cognitive dysfunction
Equilibration processes in the Warm-Hot Intergalactic Medium
The Warm-Hot Intergalactic Medium (WHIM) is thought to contribute about 40-50
% to the baryonic budget at the present evolution stage of the universe. The
observed large scale structure is likely to be due to gravitational growth of
density fluctuations in the post-inflation era. The evolving cosmic web is
governed by non-linear gravitational growth of the initially weak density
fluctuations in the dark energy dominated cosmology. Non-linear structure
formation, accretion and merging processes, star forming and AGN activity
produce gas shocks in the WHIM. Shock waves are converting a fraction of the
gravitation power to thermal and non-thermal emission of baryonic/leptonic
matter. They provide the most likely way to power the luminous matter in the
WHIM. The plasma shocks in the WHIM are expected to be collisionless.
Collisionless shocks produce a highly non-equilibrium state with anisotropic
temperatures and a large differences in ion and electron temperatures. We
discuss the ion and electron heating by the collisionless shocks and then
review the plasma processes responsible for the Coulomb equilibration and
collisional ionisation equilibrium of oxygen ions in the WHIM. MHD-turbulence
produced by the strong collisionless shocks could provide a sizeable
non-thermal contribution to the observed Doppler parameter of the UV line
spectra of the WHIM.Comment: 13 pages, 4 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 8; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics
For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types
The Wave-Driver System of the Off-Disk Coronal Wave 17 January 2010
We study the 17 January 2010 flare-CME-wave event by using STEREO/SECCHI EUVI
and COR1 data. The observational study is combined with an analytic model which
simulates the evolution of the coronal-wave phenomenon associated with the
event. From EUV observations, the wave signature appears to be dome shaped
having a component propagating on the solar surface (v~280 km s-1) as well as
off-disk (v~600 km s-1) away from the Sun. The off-disk dome of the wave
consists of two enhancements in intensity, which conjointly develop and can be
followed up to white-light coronagraph images. Applying an analytic model, we
derive that these intensity variations belong to a wave-driver system with a
weakly shocked wave, initially driven by expanding loops, which are indicative
of the early evolution phase of the accompanying CME. We obtain the shock
standoff distance between wave and driver from observations as well as from
model results. The shock standoff distance close to the Sun (<0.3 Rs above the
solar surface) is found to rapidly increase with values of ~0.03-0.09 Rs which
give evidence of an initial lateral (over-)expansion of the CME. The
kinematical evolution of the on-disk wave could be modeled using input
parameters which require a more impulsive driver (t=90 s, a=1.7 km s-2)
compared to the off-disk component (t=340 s, a=1.5 km s-2).Comment: accepted for publication in Solar Physic
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in âs = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fbâ1 of protonâproton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment
This paper describes an analysis of the angular distribution of W->enu and
W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with
the ATLAS detector at the LHC in 2010, corresponding to an integrated
luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and
the missing transverse energy, the W decay angular distribution projected onto
the transverse plane is obtained and analysed in terms of helicity fractions
f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV
and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw
> 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour,
are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017
+/- 0.030, where the first uncertainties are statistical, and the second
include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables,
revised author list, matches European Journal of Physics C versio
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