608 research outputs found
Shoulder posture and median nerve sliding
Background: Patients with upper limb pain often have a slumped sitting position and poorshoulder posture. Pain could be due to poor posture causing mechanical changes (stretch; localpressure) that in turn affect the function of major limb nerves (e.g. median nerve). This studyexamines (1) whether the individual components of slumped sitting (forward head position, trunkflexion and shoulder protraction) cause median nerve stretch and (2) whether shoulderprotraction restricts normal nerve movements.Methods: Longitudinal nerve movement was measured using frame-by-frame cross-correlationanalysis from high frequency ultrasound images during individual components of slumped sitting.The effects of protraction on nerve movement through the shoulder region were investigated byexamining nerve movement in the arm in response to contralateral neck side flexion.Results: Neither moving the head forward or trunk flexion caused significant movement of themedian nerve. In contrast, 4.3 mm of movement, adding 0.7% strain, occurred in the forearm duringshoulder protraction. A delay in movement at the start of protraction and straightening of thenerve trunk provided evidence of unloading with the shoulder flexed and elbow extended and thescapulothoracic joint in neutral. There was a 60% reduction in nerve movement in the arm duringcontralateral neck side flexion when the shoulder was protracted compared to scapulothoracicneutral.Conclusion: Slumped sitting is unlikely to increase nerve strain sufficient to cause changes tonerve function. However, shoulder protraction may place the median nerve at risk of injury, sincenerve movement is reduced through the shoulder region when the shoulder is protracted andother joints are moved. Both altered nerve dynamics in response to moving other joints and localchanges to blood supply may adversely affect nerve function and increase the risk of developingupper quadrant pain
Highly Efficient Source for Indistinguishable Photons of Controlled Shape
We demonstrate a straightforward implementation of a push-button like
single-photon source which is based on a strongly coupled atom-cavity system.
The device operates intermittently for periods of up to 100 microseconds, with
single-photon repetition rates of 1.0 MHz and an efficiency of 60 %. Atoms are
loaded into the cavity using an atomic fountain, with the upper turning point
near the cavity's mode centre. This ensures long interaction times without any
disturbances induced by trapping potentials. The latter is the key to reaching
deterministic efficiencies as high as obtained in probabalistic
photon-heralding schemes. The price to pay is the random loading of atoms into
the cavity and the resulting intermittency. However, for all practical
purposes, this has a negligible impact
Nontelomeric TRF2-REST Interaction Modulates Neuronal Gene Silencing and Fate of Tumor and Stem Cells
SummaryRemoval of TRF2, a telomere shelterin protein, recapitulates key aspects of telomere attrition including the DNA-damage response and cell-cycle arrest [1]. Distinct from the response of proliferating cells to loss of TRF2 [2, 3], in rodent noncycling cells, TRF2 inhibition promotes differentiation and growth [4, 5]. However, the mechanism that couples telomere gene-silencing features [6–8] to differentiation programs has yet to be elucidated. Here we describe an extratelomeric function of TRF2 in the regulation of neuronal genes mediated by the interaction of TRF2 with repressor element 1-silencing transcription factor (REST), a master repressor of gene networks devoted to neuronal functions [9–12]. TRF2-REST complexes are readily detected by coimmunoprecipitation assays and are localized to aggregated PML-nuclear bodies in undifferentiated pluripotent human NTera2 stem cells. Inhibition of TRF2, either by a dominant-negative mutant or by RNA interference, dissociates TRF2-REST complexes resulting in ubiquitin-proteasomal degradation of REST. Consequentially, REST-targeted neural genes (L1CAM, β3-tubulin, synaptophysin, and others) are derepressed, resulting in acquisition of neuronal phenotypes. Notably, selective damage to telomeres without affecting TRF2 levels causes neither REST degradation nor cell differentiation. Thus, in addition to protecting telomeres, TRF2 possesses a novel role in stabilization of REST thereby controlling neural tumor and stem cell fate
Coefficient of restitution for elastic disks
We calculate the coefficient of restitution, , starting from a
microscopic model of elastic disks. The theory is shown to agree with the
approach of Hertz in the quasistatic limit, but predicts inelastic collisions
for finite relative velocities of two approaching disks. The velocity
dependence of is calculated numerically for a wide range of
velocities. The coefficient of restitution furthermore depends on the elastic
constants of the material via Poisson's number. The elastic vibrations absorb
kinetic energy more effectively for materials with low values of the shear
modulus.Comment: 25 pages, 12 Postscript figures, LaTex2
Spatial Structure and Coherent Motion in Dense Planetary Rings Induced by Self-Gravitational Instability
We investigate the formation of spatial structure in dense, self-gravitating
particle systems such as Saturn's B-ring through local -body simulations to
clarify the intrinsic physics based on individual particle motion. In such a
system, Salo (1995) showed that the formation of spatial structure such as
wake-like structure and particle grouping (clump) arises spontaneously due to
gravitational instability and the radial velocity dispersion increases as the
formation of the wake structure. However, intrinsic physics of the phenomena
has not been clarified. We performed local -body simulations including
mutual gravitational forces between ring particles as well as direct
(inelastic) collisions with identical (up to ) particles. In the
wake structure particles no longer move randomly but coherently. We found that
particle motion was similar to Keplerian motion even in the wake structure and
that the coherent motion was produced since the particles in a clump had
similar eccentricity and longitude of perihelion. This coherent motion causes
the increase and oscillation in the radial velocity dispersion. The mean
velocity dispersion is rather larger in a more dissipative case with a smaller
restitution coefficient and/or a larger surface density since the coherence is
stronger in the more dissipative case. Our simulations showed that the
wavelength of the wake structure was approximately given by the longest
wavelength \hs{\lambda}{cr} = 4\pi^2 G\Sigma/\kappa^2 in the linear theory of
axisymmetric gravitational instability in a thin disk, where , , and
are the gravitational constant, surface density, and a epicyclic
frequency.Comment: Accepted by Earth, Planets, and Space. 39 pages, 20 figures.
PostScript files also available from
http://www.geo.titech.ac.jp/nakazawalab/hdaisaka/works
Evidence for a common physical description of non-Fermi-liquid behavior in f-electron systems
The non-Fermi-liquid (NFL) behavior observed in the low temperature specific
heat and magnetic susceptibility of f-electron systems is
analyzed within the context of a recently developed theory based on Griffiths
singularities. Measurements of and in the systems
, , and (M = Pd,
Pt) are found to be consistent with predicted by this model with in the NFL regime.
These results suggest that the NFL properties observed in a wide variety of
f-electron systems can be described within the context of a common physical
picture.Comment: 4 pages, 4 figure
Unusual behaviors in the transport properties of REFeP (RE: La, Ce, Pr, and Nd)
We have investigated the resistivity (), thermoelectric power (TEP) and
Hall coefficient () on high quality single crystals of
REFeP. TEP in CeFeP is extremely large (
0.5mV/K at 290K) with a peak of 0.75mV/K at around 65K. The Hall
mobility also shows a peak at 65K, suggesting carriers with heavy masses
developed at lower temperatures related with the f-hybridized band. Both Pr-
and Nd- systems exhibit an apparent increase of with decreasing
temperature far above their magnetic transition temperatures. In the same
temperature ranges, TEP exhibits unusually large absolute values of -50V/K
for PrFeP and -15V/K for NdFeP, respectively.
For PrFeP, such anomalous transport properties suggest an unusual
ground state, possibly related with the Quadrupolar Kondo effect.Comment: 5 pages, 8 figure
A model for collisions in granular gases
We propose a model for collisions between particles of a granular material
and calculate the restitution coefficients for the normal and tangential motion
as functions of the impact velocity from considerations of dissipative
viscoelastic collisions. Existing models of impact with dissipation as well as
the classical Hertz impact theory are included in the present model as special
cases. We find that the type of collision (smooth, reflecting or sticky) is
determined by the impact velocity and by the surface properties of the
colliding grains. We observe a rather nontrivial dependence of the tangential
restitution coefficient on the impact velocity.Comment: 11 pages, 2 figure
Elastic-to-plastic crossover below the peak effect in the vortex solid of YBa2Cu3O7 single crystals
We report on transport and ac susceptibility studies below the peak effect in
twinned YBa2Cu3O7 single crystals. We find that disorder generated at the peak
effect can be partially inhibited by forcing vortices to move with an ac
driving current. The vortex system can be additionally ordered below a
well-defined temperature where elastic interactions between vortices overcome
pinning-generated stress and a plastic to elastic crossover seems to occur. The
combined effect of these two processes results in vortex structures with
different mobilities that give place to history effects.Comment: 4 pages, 4 figures. Published in PRB Rapid Comm., February 1, 200
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