36,286 research outputs found
Translational perspectives on perfusion-diffusion mismatch in ischemic stroke
Magnetic resonance imaging has tremendous potential to illuminate ischemic stroke pathophysiology and guide rational treatment decisions. Clinical applications to date have been largely limited to trials. However, recent analyses of the major clinical studies have led to refinements in selection criteria and improved understanding of the potential implications for the risk vs. benefit of thrombolytic therapy. In parallel, preclinical studies have provided complementary information on the evolution of stroke that is difficult to obtain in humans due to the requirement for continuous or repeated imaging and pathological verification. We review the clinical and preclinical advances that have led to perfusion–diffusion mismatch being applied in phase 3 randomized trials and, potentially, future routine clinical practice
Dynamics in the Sherrington-Kirkpatrick Ising spin glass at and above Tg
A detailed numerical study is made of relaxation at equilibrium in the
Sherrington-Kirkpatrick Ising spin glass model, at and above the critical
temperature Tg. The data show a long time stretched exponential relaxation q(t)
~ exp[-(t/tau(T))^beta(T)] with an exponent beta(T) tending to ~ 1/3 at Tg. The
results are compared to those which were observed by Ogielski in the 3d ISG
model, and are discussed in terms of a phase space percolation transition
scenario.Comment: 6 pages, 7 figure
Time-Domain Measurement of Spontaneous Vibrational Decay of Magnetically Trapped NH
The v = 1 -> 0 radiative lifetime of NH (X triplet-Sigma-, v=1,N=0) is
determined to be tau_rad,exp. = 37.0 +/- 0.5 stat +2.0 / -0.8 sys miliseconds,
corresponding to a transition dipole moment of |mu_10| = 0.0540 + 0.0009 /
-0.0018 Debye. To achieve the long observation times necessary for direct
time-domain measurement, vibrationally excited NH (X triplet-Sigma-, v=1,N=0)
radicals are magnetically trapped using helium buffer-gas loading. Simultaneous
trapping and lifetime measurement of both the NH(v=1, N=0) and NH(v=0,N=0)
populations allows for accurate extraction of tau_rad,exp. Background helium
atoms are present during our measurement of tau_rad,exp., and the rate constant
for helium atom induced collisional quenching of NH(v=1,N=0) was determined to
be k_q < 3.9 * 10^-15 cm^3/s. This bound on k_q yields the quoted systematic
uncertainty on tau_rad,exp. Using an ab initio dipole moment function and an
RKR potential, we also determine a theoretical value of 36.99 ms for this
lifetime, in agreement with our experimental value. Our results provide an
independent determination of tau_rad,10, test molecular theory, and furthermore
demonstrate the efficacy of buffer-gas loading and trapping in determining
metastable radiative and collisional lifetimes.Comment: 10 pages + 3 figures (11 pages total) v2 has minor corrections and
explanations accepted for publication in PR
Dynamic critical behaviour in Ising spin glasses
The critical dynamics of Ising spin glasses with Bimodal, Gaussian, and
Laplacian interaction distributions are studied numerically in dimensions 3 and
4. The data demonstrate that in both dimensions the critical dynamic exponent
, the non-equilibrium autocorrelation decay exponent
, and the critical fluctuation-dissipation ratio
all vary strongly and systematically with the form of the
interaction distribution.Comment: 8 pages, 4 figures, version to appear in Phys. Rev.
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A tale of one city: intra-institutional variations in migrating VLE platform
City University London committed in 2009 to make Moodle the Virtual Learning Environment (VLE) at the core of a new Strategic Learning Environment (SLE) comprised of VLE, externally facing website and related systems such as video streaming and virtual classrooms. Previously, the WebCT VLE had been separate from most of the other systems at the institution with very limited connections to other tools. Each of the schools within the institution was able to pursue their own strategy and timeframe for the migration and embedding of Moodle within their subject areas, within an absolute limit of 2 years. This paper outlines the approaches taken by the various schools, highlighting similarities and differences, and draws out common aspects from the project to make recommendations for institutions seeking to undertake similar migrations
Towards spin injection from silicon into topological insulators: Schottky barrier between Si and Bi2Se3
A scheme is proposed to electrically measure the spin-momentum coupling in
the topological insulator surface state by injection of spin polarized
electrons from silicon. As a first approach, devices were fabricated consisting
of thin (<100nm) exfoliated crystals of Bi2Se3 on n-type silicon with
independent electrical contacts to silicon and Bi2Se3. Analysis of the
temperature dependence of thermionic emission in reverse bias indicates a
barrier height of 0.34 eV at the Si-Bi2Se3 interface. This robust Schottky
barrier opens the possibility of novel device designs based on sub-band gap
internal photoemission from Bi2Se3 into Si
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