3,626 research outputs found
Potassium channel activators protect the N-methyl-D-aspartate-induced cerebral vascular dilation after combined hypoxia and ischemia in piglets
Background and Purpose-Cerebral arteriolar dilation to N-methyl-D-aspartate (NMDA) is a neuronally mediated multistep process that is sensitive to cerebral hypoxia and ischemia (H/I). We tested the hypothesis that topical pretreatment with the selective potassium channel agonists NS1619 and aprikalim preserves the vascular response to NMDA after consecutive WI.
Methods-Pial arteriolar diameters were measured in anesthetized piglets with the use of a closed cranial window and intravital microscopy, Arteriolar responses to NMDA (10(-5), 5 x 10(-5), and 10(-4) mol/L) were recorded before and 1 hour after 10 minutes of hypoxia (8.5% O-2 in N-2) plus; 10 minutes of ischemia (WI), Ischemia was induced by increasing intracranial pressure, Subgroups were topically pretreated with 10(-5) mol/L NS1619, 10(-6) mol/L aprikalim, 10(-6) mol/L calcitonin gene-related peptide (CGRP), or 10(-5) mol/L papaverine. We also examined the effects of H/I on vascular responses to kainate (10(-4) mol/L) to assess specificity of neuronal injury.
Results-Arteriolar responses to NMDA were significantly attenuated after WI. Baseline compared with post-WI arteriolar diameters were 9+/-4% versus 3+/-2% at 10(-5) mol/L, 22+/-4% versus 4+/-2% at 5 x 10(-5) mol/L, and 33+/-4% versus 7+/-2% at 10(-4) mol/L (mean+/-SE; all P<.05, n=7), Pretreatment with NS1619 and aprikalim preserved the arteriolar responses to NMDA after WI, For NS1619 (n=6), values were as follows: 9+/-2% versus 6+/-4% at 10(-5) mol/L, 19+/-6% versus 21+/-5% at 5x10(-5) mol/L, and 35+/-3% versus 31+/-5% at 10(-4) mol/L, For aprikalim (n=7), values were as follows: 6+/-2% versus 8+/-2% at 10(-5) mol/L, 22+/-6% versus 15+/-3% at 5x10(-5) mol/L, and 41+/-5% versus 32+/-6% at 10(-4) mol/L. In contrast, piglets pretreated with CGRP (n=6) or papaverine (n=5) showed no preservation of the vascular response to NMDA after WI, although these compounds dilated the arterioles to an extent similar to that with NS1619/aprikalim. Kainate-induced arteriolar dilation (n=6) was largely preserved after H/I compared with preischemic responses,
Conclusions-(1) Vascular responses of cerebral arterioles to NMDA after H/I are preserved by pretreatment with NS1619 or aprikalim, indicating a neuroprotective effect, (2) CGRP and papaverine do not preserve the vascular response to NMDA despite causing vasodilation similar to that with NS1619 or aprikalim, This suggests that activation of potassium channels on neurons accounts for the protective effect of potassium channel agonists, (3) Preserved arteriolar dilation to kainate suggests largely intact functioning of neuronal nitric oxide synthase after H/I
Universal temperature dependence of optical excitation life-time and band-gap in chirality assigned semiconducting single-wall carbon nanotubes
The temperature dependence of optical excitation life-time, Gamma, and
transition energies, E_ii, were measured for bucky-papers of single-wall carbon
nanotubes (SWCNTs) and inner tubes in double-wall carbon nanotubes (DWCNTs)
using resonant Raman scattering. The temperature dependence of Gamma and E_ii
is the same for both types of samples and is independent of tube chirality. The
data proves that electron-phonon interaction is responsible for temperature
dependence of E_ii(T). The temperature independent inhomogeneous contribution
to Gamma is much larger in the SWCNT samples, which is explained by the
different SWCNT environment in the two types of samples. Gamma of the inner
tubes for the bucky-paper DWCNT sample is as low as \sim 30 meV, which is
comparable to that found for individual SWCNTs
A conceptual design of an advanced 23 m diameter IACT of 50 tons for ground-based gamma-ray astronomy
A conceptual design of an advanced Imaging Air Cherenkov Telescope with a 23
m diameter mirror and of 50 tons weight will be presented. A system photon
detection efficiency of 15-17%, averaged over 300-600 nm, is aimed at to lower
the threshold to 10-20 GeV. Prospects for a second generation camera with
Geiger-mode Avalanche Photo Diodes will be discussed.Comment: 4 pages, 1 figure, to appear in the proceedings of the 31th
International Cosmic Ray Conference, Lodz, Poland, 200
Infinite disorder scaling of random quantum magnets in three and higher dimensions
Using a very efficient numerical algorithm of the strong disorder
renormalization group method we have extended the investigations about the
critical behavior of the random transverse-field Ising model in three and four
dimensions, as well as for Erd\H os-R\'enyi random graphs, which represent
infinite dimensional lattices. In all studied cases an infinite disorder
quantum critical point is identified, which ensures that the applied method is
asymptotically correct and the calculated critical exponents tend to the exact
values for large scales. We have found that the critical exponents are
independent of the form of (ferromagnetic) disorder and they vary smoothly with
the dimensionality.Comment: 6 pages, 5 figure
Logarithmic delocalization of end spins in the S=3/2 antiferromagnetic Heisenberg chain
Using the DMRG method we calculate the surface spin correlation function,
, in the spin antiferromagnetic Heisenberg
chain. For comparison we also investigate the chain with S=1 impurity
end spins and the S=1 chain. In the half-integer spin models the end-to-end
correlations are found to decay to zero logarithmically, , with . We find no surface order, in clear contrast with
the behavior of the S=1 chain, where exponentially localized end spins induce
finite surface correlations. The lack of surface order implies that end spins
do not exist in the strict sense. However, the system possesses a
logarithmically weakly delocalizing boundary excitation, which, for any chain
lengths attainable numerically or even experimentally, creates the illusion of
an end spin. This mode is responsible for the first gap, which vanishes
asymptotically as , where is the
sound velocity and is the logarithmic decay exponent. For the half-integer
spin models our results on the surface correlations and on the first gap
support universality. Those for the second gap are less conclusive, due to
strong higher-order corrections.Comment: 10 pages, 8 figure
Entanglement entropy with localized and extended interface defects
The quantum Ising chain of length, L, which is separated into two parts by
localized or extended defects is considered at the critical point where scaling
of the interface magnetization is non-universal. We measure the entanglement
entropy between the two halves of the system in equilibrium, as well as after a
quench, when the interaction at the interface is changed for time t>0. For the
localized defect the increase of the entropy with log(L) or with log(t)
involves the same effective central charge, which is a continuous function of
the strength of the defect. On the contrary for the extended defect the
equilibrium entropy is saturated, but the non-equilibrium entropy has a
logarithmic time-dependence the prefactor of which depends on the strength of
the defect.Comment: 9 pages, 6 figure
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