232 research outputs found
Dynamic correlations of the Coulomb Luttinger liquid
The dynamic density response function, form-factor, and spectral function of
a Luttinger liquid with Coulomb electron-electron interaction are studied with
the emphasis on the short-range electron correlations. The Coulomb interaction
changes dramatically the density response function as compared to the case of
the short-ranged interaction. The form of the density response function is
smoothing with time, and the oscillatory structure appears. However, the
spectral functions remain qualitatively the same. The dynamic form-factor
contains the -peak in the long-wave region, corresponding to one-boson
excitations. Besides, the multi-boson-excitations band exists in the
wave-number region near to . The dynamic form-factor diverges at the
edges of this band, while the dielectric function goes to zero there, which
indicates the appearance of a soft mode. We develop a method to analyze the
asymptotics of the spectral functions near to the edges of the
multi-boson-excitations band.Comment: 11 pages, 3 figures, submitted to PR
Reliability of 2D ultrasound imaging associated with transient ShearWave Elastography method to analyze spastic gastrocnemius medialis muscle architecture and viscoelastic properties
PurposeThe aim of the study was to assess the reliability of pennation angle (PA) and muscle thickness (MT) 2D measurements and of shear elastic modulus measurement, using ultrasound imaging (US). Those measurements were made on spastic gastrocnemius medialis muscle at rest and at maximal passive stretching, in post-stroke hemiplegic patients. The paretic side measurements were compared to non-paretic side.Material and methodsFourteen patients took part in 2 inter-session reliability experiments, realized at a 7 days interval by the same operator. The Aixplorer® Supersonic US scanner with the transient ShearWave Elastography (SWE) software was used. The stretching experiments were made manually and controlled by a goniometer.ResultsThe reliability of the 2D measurements was good. The coefficient of variation (CV) was 6.30% for MT measurement at rest, 6.40% and 8.26% for PA at rest and at maximal passive stretching respectively. The reliability of the shear elastic modulus measurement in the sagittal plane was good only at rest with a CV of 9.86%, versus 40.58% at stretching. None of the shear elastic modulus measurements in the axial plane were good. At rest, MT and PA were weaker on the paretic side (14.25±3.12mm and 17.32±5.10°) versus non-paretic side (16.30±3.19mm and 21.08±5.05°) (P<0.0001 and P=0.006). At rest, there was a small difference in the shear elastic modulus between the paretic side and the non-paretic side (5.40±1.67kPa versus 6.20±2.18kPa, P=0.041).DiscussionThis is the first description of muscle spastic structure using SWE with Supersonic Shear Imaging. 2D US associated with SWE shows promise in terms of muscular atrophy quantification and muscle histological quality assessment. These structural properties reflect some of the functional abilities regardless of motor control. It should enable further research on therapies, which impact muscle tissue quality, such as botulinum neurotoxin injections
Restricted and unrestricted Hartree-Fock calculations of conductance for a quantum point contact
Very short quantum wires (quantum contacts) exhibit a conductance structure
at a value of conductance close to . It is believed that the
structure arises due to the electron-electron interaction, and it is also
related to electron spin. However details of the mechanism of the structure are
not quite clear. Previously we approached the problem within the restricted
Hartree-Fock approximation. This calculation demonstrated a structure similar
to that observed experimentally. In the present work we perform restricted and
unrestricted Hartree-Fock calculations to analyze the validity of the
approximations. We also consider dependence of the effect on the electron
density in leads. The unrestricted Hartree-Fock method allows us to analyze
trapping of the single electron within the contact. Such trapping would result
in the Kondo model for the ``0.7 structure''. The present calculation confirms
the spin-dependent bound state picture and does not confirm the Kondo model
scenario.Comment: 6 pages, 9 figure
Generation and characterisation of Friedreich ataxia YG8R mouse fibroblast and neural stem cell models
This article has been made available through the Brunel Open Access Publishing Fund.Background: Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disease caused by GAA repeat expansion in the first intron of the FXN gene, which encodes frataxin, an essential mitochondrial protein. To further characterise the molecular abnormalities associated with FRDA pathogenesis and to hasten drug screening, the development and use of animal and cellular models is considered essential. Studies of lower organisms have already contributed to understanding FRDA disease pathology, but mammalian cells are more related to FRDA patient cells in physiological terms. Methodology/Principal Findings: We have generated fibroblast cells and neural stem cells (NSCs) from control Y47R mice (9 GAA repeats) and GAA repeat expansion YG8R mice (190+120 GAA repeats). We then differentiated the NSCs in to neurons, oligodendrocytes and astrocytes as confirmed by immunocytochemical analysis of cell specific markers. The three YG8R mouse cell types (fibroblasts, NSCs and differentiated NSCs) exhibit GAA repeat stability, together with reduced expression of frataxin and reduced aconitase activity compared to control Y47R cells. Furthermore, YG8R cells also show increased sensitivity to oxidative stress and downregulation of Pgc-1α and antioxidant gene expression levels, especially Sod2. We also analysed various DNA mismatch repair (MMR) gene expression levels and found that YG8R cells displayed significant reduction in expression of several MMR genes, which may contribute to the GAA repeat stability. Conclusions/Significance: We describe the first fibroblast and NSC models from YG8R FRDA mice and we confirm that the NSCs can be differentiated into neurons and glia. These novel FRDA mouse cell models, which exhibit a FRDA-like cellular and molecular phenotype, will be valuable resources to further study FRDA molecular pathogenesis. They will also provide very useful tools for preclinical testing of frataxin-increasing compounds for FRDA drug therapy, for gene therapy, and as a source of cells for cell therapy testing in FRDA mice. © 2014 Sandi et al
Impact of transient groundwater storage on the discharge of Himalayan rivers
International audienceIn the course of the transfer of precipitation into rivers, water is temporarily stored in reservoirs with different residence times such as soils, groundwater, snow and glaciers. In the central Himalaya, the water budget is thought to be primarily controlled by monsoon rainfall, snow and glacier melt, and secondarily by evapotranspiration. An additional contribution from deep groundwater has been deduced from the chemistry of Himalayan rivers, but its importance in the annual water budget remains to be evaluated. Here we analyse records of daily precipitation and discharge within twelve catchments in Nepal over about 30 years. We observe annual hysteresis loops--that is, a time lag between precipitation and discharge--in both glaciated and unglaciated catchments and independent of the geological setting. We infer that water is stored temporarily in a reservoir with characteristic response time of about 45 days, suggesting a diffusivity typical of fractured basement aquifers. We estimate this transient storage capacity at about 28km3 for the three main Nepal catchments; snow and glacier melt contribute around 14km3yr-1, about 10% of the annual river discharge. We conclude that groundwater storage in a fractured basement influences significantly the Himalayan river discharge cycle
Mammalian Frataxin: An Essential Function for Cellular Viability through an Interaction with a Preformed ISCU/NFS1/ISD11 Iron-Sulfur Assembly Complex
Frataxin, the mitochondrial protein deficient in Friedreich ataxia, a rare autosomal recessive neurodegenerative disorder, is thought to be involved in multiple iron-dependent mitochondrial pathways. In particular, frataxin plays an important role in the formation of iron-sulfur (Fe-S) clusters biogenesis.. Fe-S cluster biosynthesis
Characterisation of Genome-Wide PLZF/RARA Target Genes
The PLZF/RARA fusion protein generated by the t(11;17)(q23;q21) translocation in acute promyelocytic leukaemia (APL) is believed to act as an oncogenic transcriptional regulator recruiting epigenetic factors to genes important for its transforming potential. However, molecular mechanisms associated with PLZF/RARA-dependent leukaemogenesis still remain unclear
Active Vision during Action Execution, Observation and Imagery: Evidence for Shared Motor Representations
The concept of shared motor representations between action execution and various covert conditions has been demonstrated through a number of psychophysiological modalities over the past two decades. Rarely, however, have
researchers considered the congruence of physical, imaginary and observed movement markers in a single paradigm and never in a design where eye movement metrics are the markers. In this study, participants were required to perform a forward reach and point Fitts’ Task on a digitizing tablet whilst wearing an eye movement system. Gaze metrics were used to compare behaviour congruence between action execution, action observation, and guided and unguided movement imagery conditions. The data showed that participants attended the same task-related visual cues between conditions but the strategy was different. Specifically, the number of fixations was significantly different between action execution and all covert conditions. In addition, fixation duration was congruent between action execution and action observation only, and
both conditions displayed an indirect Fitts’ Law effect. We therefore extend the understanding of the common motor representation by demonstrating, for the first time, common spatial eye movement metrics across simulation conditions
and some specific temporal congruence for action execution and action observation. Our findings suggest that action
observation may be an effective technique in supporting motor processes. The use of video as an adjunct to physical
techniques may be beneficial in supporting motor planning in both performance and clinical rehabilitation environments
Real-Time Definition of Non-Randomness in the Distribution of Genomic Events
Features such as mutations or structural characteristics can be non-randomly or non-uniformly distributed within a genome. So far, computer simulations were required for statistical inferences on the distribution of sequence motifs. Here, we show that these analyses are possible using an analytical, mathematical approach. For the assessment of non-randomness, our calculations only require information including genome size, number of (sampled) sequence motifs and distance parameters. We have developed computer programs evaluating our analytical formulas for the real-time determination of expected values and p-values. This approach permits a flexible cluster definition that can be applied to most effectively identify non-random or non-uniform sequence motif distribution. As an example, we show the effectivity and reliability of our mathematical approach in clinical retroviral vector integration site distribution
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