643 research outputs found
Serotonin reuptake inhibitors and cardiovascular disease
Selective serotonin re-uptake inhibiting drugs (SSRIs) are widely used for endogenous depression. In addition to depleting the nerve terminals of serotonin they also lower blood platelet serotonin levels. Platelet aggregation is a major component of acute coronary syndromes, including sudden death, and also of limb ischaemia. Platelet-released serotonin causes constriction of diseased blood vessels. The recent literature has revealed a number of reports of association between the treatment of depression with SSRIs and reduced events caused by intra-arterial thrombosis. The effects of serotonin and serotonin depletion upon intracoronary thrombosis, diseased blood vessels, blood platelets and bleeding are discussed with recommendations for future research into the potential cardiovascular benefits of SSRIs and serotonin 5HT2A antagonists
Coronary vessel supersensitivity to noradrenaline in the presence of chronic sympathetic denervation.
It is well known that there is usually super-sensitivity to the normal neurotransmitter in chronically denervated organs. The present consensus of opinion is that there is no super-sensitivity of response of myocardial arteriolar resistance vessels to nor-adrenaline after chronic sympathetic denervation; this opinion was tested. We re-analysed the data in the literature on innervated myocardium, plus the effect of chronic sympathetic myocardial denervation induced by surgery plus phenol application. We found that the opinion is based on studies of isolated epicardial arteries. Studies of resistance vessels mostly ignore an important confounding factor, in that myocardial blood flow (MBF) within myocardium is heterogeneous under all circumstances. This heterogeneity is partly related to similar heterogeneity in myocardial oxygen consumption (MVO2), and partly to heterogeneity in local noradrenaline, as assessed by 11C-hydroxyephidrine positron emission tomography. The local volume of distribution of 11C-hydroxyephedrine in innervated myocardium was inversely correlated to local MBF, at the same perfusion pressure, i.e., increasing vasoconstriction with increasing tissue noradrenaline. In chronically denervated myocardium, local MBF was lower for any given amount of noradrenaline, showing the existence of supersensitivity of the resistance vessels. This factor may have a deletereous effect in diabetic patients with cardiac autonomic neuropathy
Shear mechanical properties of repair grafts—how well do they match normal and torn human rotator cuff tendons?
Ocean forcing of glacier retreat in the western Antarctic Peninsula
In recent decades, hundreds of glaciers draining the Antarctic Peninsula (63° to 70°S) have undergone systematic and progressive change. These changes are widely attributed to rapid increases in regional surface air temperature, but it is now clear that this cannot be the sole driver. Here, we identify a strong correspondence between mid-depth ocean temperatures and glacier-front changes along the ~1000-kilometer western coastline. In the south, glaciers that terminate in warm Circumpolar Deep Water have undergone considerable retreat, whereas those in the far northwest, which terminate in cooler waters, have not. Furthermore, a mid-ocean warming since the 1990s in the south is coincident with widespread acceleration of glacier retreat. We conclude that changes in ocean-induced melting are the primary cause of retreat for glaciers in this region
Chiral properties of SU(3) sextet fermions
SU(3) gauge theory with overlap fermions in the 2-index symmetric (sextet)
and fundamental representations is considered. A priori it is not known what
the pattern of chiral symmetry breaking is in a higher dimensional
representation although the general expectation is that if two representations
are both complex, the breaking pattern will be the same. This expectation is
verified for the sextet at N_f = 0 in several exact zero mode sectors. It is
shown that if the volume is large enough the same random matrix ensemble
describes both the sextet and fundamental Dirac eigenvalues. The number of zero
modes for the sextet increases approximately 5-fold relative to the fundamental
in accordance with the index theorem for small lattice spacing but zero modes
which do not correspond to integer topological charge do exist at larger
lattice spacings. The zero mode number dependence of the random matrix model
predictions correctly match the simulations in each sector and each
representation.Comment: 38 pages (12 pages text and gazillion tables/figures), minor
modification, references adde
Brief Communication: Newly developing rift in Larsen C Ice Shelf presents significant risk to stability
An established rift in the Larsen C Ice Shelf, formerly constrained by a suture zone containing marine ice, grew rapidly during 2014 and is likely in the near future to generate the largest calving event since the 1980s and result in a new minimum area for the ice shelf. Here we investigate the recent development of the rift, quantify the projected calving event and, using a numerical model, assess its likely impact on ice shelf stability. We find that the ice front is at risk of becoming unstable when the anticipated calving event occurs
Feshbach resonances in a quasi-2D atomic gas
Strongly confining an ultracold atomic gas in one direction to create a
quasi-2D system alters the scattering properties of this gas. We investigate
the effects of confinement on Feshbach scattering resonances and show that
strong confinement results in a shift in the position of the Feshbach resonance
as a function of the magnetic field. This shift, as well as the change of the
width of the resonance, are computed. We find that the resonance is strongly
damped in the thermal gas, but in the condensate the resonance remains sharp
due to many-body effects. We introduce a 2D model system, suited for the study
of resonant superfluidity, and having the same scattering properties as the
tightly confined real system near a Feshbach resonance. Exact relations are
derived between measurable quantities and the model parameters.Comment: 8 pages, 2 figure
Ground-state energy and entropy of the two-dimensional Edwards-Anderson spin-glass model with different bond distributions
We study the two-dimensional Edwards-Anderson spin-glass model using a
parallel tempering Monte Carlo algorithm. The ground-state energy and entropy
are calculated for different bond distributions. In particular, the entropy is
obtained by using a thermodynamic integration technique and an appropriate
reference state, which is determined with the method of high-temperature
expansion. This strategy provide accurate values of this quantity for
finite-size lattices. By extrapolating to the thermodynamic limit, the
ground-state energy and entropy of the different versions of the spin-glass
model are determined.Comment: 18 pages, 5 figure
Tree-body loss of of trapped ultracold Rb atoms due to a Feshbach resonance
The loss of ultracold trapped atoms in the vicinity of a Feshbach resonance
is treated as a two-stage reaction, using the Breit-Wigner theory. The first
stage is the formation of a resonant diatomic molecule, and the second one is
its deactivation by inelastic collisions with other atoms. This model is
applied to the analysis of recent experiments on Rb, leading to an
estimated value of cms for the deactivation rate
coefficient.Comment: LaTeX, 4 pages with 1 figures, uses REVTeX4, uses improved
experimental dat
Fermionic superfluidity: From high Tc superconductors to ultracold Fermi gases
We present a pairing fluctuation theory which self-consistently incorporates
finite momentum pair excitations in the context of BCS--Bose-Einstein
condensation (BEC) crossover, and we apply this theory to high
superconductors and ultracold Fermi gases. There are strong similarities
between Fermi gases in the unitary regime and high Tc superconductors. Here we
address key issues of common interest, especially the pseudogap. In the Fermi
gases we summarize recent experiments including various phase diagrams (with
and without population imbalance), as well as evidence for a pseudogap in
thermodynamic and other experiments.Comment: Expanded version, invited talk at the 5th International Conference on
Complex Matter -- Stripes 2006, 6 pages, 6 figure
- …