2,207 research outputs found
Early appearance of 2, 3-butanediol in acute myocardial infarction. A new marker for ischaemia?
In 28 patients with acute myocardial infarction, the release pattern of 2, 3-butanediol (BD), a product of intermediary metabolism, and creatine kinase activity (CK) in blood were compared. Whereas CKat entry was low in all patients, the BD level was elevated in 18 (64%). However, BD returned to normal levels during the next 24 h whereas CK increased. The BD level at entry did not allow differentiation between patients with transmural or non-transmural infarction; it was independent of clinical findings and biochemical parameters. We suggest that, in patients with acute myocardial infarction, elevated levels of BD originates from myo-cardial metabolism. Whether it reflects ongoing ischaemia or reperfusion of the infarcted area remains unresolve
Renal transplant anastomotic time–Every minute counts!
The impact of anastomotic time in renal transplant is under recognized and not well studied. It is one of the few controllable factors that affect the incidence of delayed graft function (DGF). Our study aimed at quantifying the impact of anastomotic time. We performed a retrospective review of 424 renal transplants between the years 2006 and 2020. A total of 247 deceased donor renal transplants formed the study cohort. Patients were divided into two groups based on the presence or absence of DGF. Variables with p < 0.3 were analyzed using the binary logistic regression test. The final analysis showed anastomotic time to be significantly associated with DGF with odds ratio of 1.04 per minute corresponding to 4% increase in DGF incidence with every minute increment in anastomotic time. Other variables that had significant impact on DGF were DCD donor (odds ratio – 8.7) and donor terminal creatinine. We concluded that anastomotic time had significant impact on the development of DGF and hence should be minimized
2,3-butanediol in experimental myocardial ischaemia in pigs
To investigate the role of 2,3-butanediol in myocardial ischaemia we analysed this compound in pig's myocardium and blood. Ischaemia was induced by ligation of a coronary artery. In the first study we found significantly higher levels of 2,3-butanediol in the homogenate of ischaemic myocardium than in non-ischaemic myocardium. The lactate concentration was also significantly elevated. In the second study, where ischaemia was similarly induced, and where reperfusion was achieved by re-opening the ligated coronary artery after 20 min, 2,3-butanediol in peripheral blood was found to increase significantly. In the pigs in which the coronary artery was not re-opened, the 2,3-butanediol level in peripheral blood was unchanged. We conclude that in pigs' anaerobic myocardia accumulation of 2,3-butanediol occurs; if the myocardium is reperfused this metabolite also appears in the bloo
How harmonic is dipole resonance of metal clusters?
We discuss the degree of anharmonicity of dipole plasmon resonances in metal
clusters. We employ the time-dependent variational principle and show that the
relative shift of the second phonon scales as in energy, being
the number of particles. This scaling property coincides with that for nuclear
giant resonances. Contrary to the previous study based on the boson-expansion
method, the deviation from the harmonic limit is found to be almost negligible
for Na clusters, the result being consistent with the recent experimental
observation.Comment: RevTex, 8 page
Magnetothermoelectric transport in modulated and unmodulated graphene
We draw motivation from recent experimental studies and present a
comprehensive study of magnetothermoelectric transport in a graphene monolayer
within the linear response regime. We employ the modified Kubo formalism
developed for thermal transport in a magnetic field. Thermopower as well as
thermal conductivity as a function of the gate voltage of a graphene monolayer
in the presence of a magnetic field perpendicular to the graphene plane is
determined for low magnetic fields (~1 Tesla) as well as high fields (~8
Tesla). We include the effects of screened charged impurities on thermal
transport. We find good, qualitative as well as quantitative, agreement with
recent experimental work on the subject. In addition, in order to analyze the
effects of modulation, which can be induced by various means, on the thermal
transport in graphene, we evaluate the thermal transport coefficients for a
graphene monolayer subjected to a periodic electric modulation in a magnetic
field. The results are presented as a function of the magnetic field and the
gate voltage.Comment: 14 pages, 8 figure
The structural properties of the multi-layer graphene/4H-SiC(000-1) system as determined by Surface X-ray Diffraction
We present a structural analysis of the multi-layer graphene-4HSiC(000-1})
system using Surface X-Ray Reflectivity. We show for the first time that
graphene films grown on the C-terminated (000-1}) surface have a
graphene-substrate bond length that is very short (0.162nm). The measured
distance rules out a weak Van der Waals interaction to the substrate and
instead indicates a strong bond between the first graphene layer and the bulk
as predicted by ab-initio calculations. The measurements also indicate that
multi-layer graphene grows in a near turbostratic mode on this surface. This
result may explain the lack of a broken graphene symmetry inferred from
conduction measurements on this system [C. Berger et al., Science 312, 1191
(2006)].Comment: 9 pages with 6 figure
Cluster ionization via two-plasmon excitation
We calculate the two-photon ionization of clusters for photon energies near
the surface plasmon resonance. The results are expressed in terms of the
ionization rate of a double plasmon excitation, which is calculated
perturbatively. For the conditions of the experiment by Schlipper et al., we
find an ionization rate of the order of 0.05-0.10 fs^(-1). This rate is used to
determine the ionization probability in an external field in terms of the
number of photons absorbed and the duration of the field. The probability also
depends on the damping rate of the surface plasmon. Agreement with experiment
can only be achieved if the plasmon damping is considerably smaller than its
observed width in the room-temperature single-photon absorption spectrum.Comment: 17 pages and 6 PostScript figure
Raman Topography and Strain Uniformity of Large-Area Epitaxial Graphene
We report results from two-dimensional Raman spectroscopy studies of
large-area epitaxial graphene grown on SiC. Our work reveals unexpectedly large
variation in Raman peak position across the sample resulting from inhomogeneity
in the strain of the graphene film, which we show to be correlated with
physical topography by coupling Raman spectroscopy with atomic force
microscopy. We report that essentially strain free graphene is possible even
for epitaxial graphene.Comment: 10 pages, 3 figure
Semiclassical theory for spatial density oscillations in fermionic systems
We investigate the particle and kinetic-energy densities for a system of
fermions bound in a local (mean-field) potential V(\bfr). We generalize a
recently developed semiclassical theory [J. Roccia and M. Brack, Phys. Rev.\
Lett. {\bf 100}, 200408 (2008)], in which the densities are calculated in terms
of the closed orbits of the corresponding classical system, to
dimensions. We regularize the semiclassical results for the U(1) symmetry
breaking occurring for spherical systems at and near the classical
turning points where the Friedel oscillations are predominant and well
reproduced by the shortest orbit going from to the closest turning point
and back. For systems with spherical symmetry, we show that there exist two
types of oscillations which can be attributed to radial and non-radial orbits,
respectively. The semiclassical theory is tested against exact
quantum-mechanical calculations for a variety of model potentials. We find a
very good overall numerical agreement between semiclassical and exact numerical
densities even for moderate particle numbers . Using a "local virial
theorem", shown to be valid (except for a small region around the classical
turning points) for arbitrary local potentials, we can prove that the
Thomas-Fermi functional reproduces the oscillations in
the quantum-mechanical densities to first order in the oscillating parts.Comment: LaTeX, 22pp, 15 figs, 1 table, to be published in Phys. Rev.
Men and Women in Space: Bone Loss and Kidney Stone Risk after Long-Duration Space Flight
Bone loss on Earth is more prevalent in women than men, leading to the assumption that women may be at greater risk from bone loss during flight. Until recently, the number of women having flown long-duration missions was too small to allow any type of statistical analysis. We report here data from 42 astronauts on long-duration missions to the International Space Station, 33 men and 9 women. Bone mineral density (dual-energy X-ray absorptiometry), bone biochemistry (from blood and urine samples), and renal stone risk factors were evaluated before and after flight. Data were analyzed in two groups, based on available resistance exercise equipment. The response of bone mineral density to flight was the same for men and women, and the typical decrease in bone mineral density (whole body and/or regional) after flight was not observed for either sex for those using an Advanced Resistive Exercise Device. Bone biochemistry, specifically markers of formation and resorption, generally responded similarly in male and female astronauts. The response of urinary supersaturation risk to space flight was not significantly different between men and women, although risks were typically increased after flight in both groups and risks were generally greater in men than in women before and after flight. Overall, the bone and renal stone responses of men and women to space flight were not different
- …