1,010 research outputs found
Stability of 1-D Excitons in Carbon Nanotubes under High Laser Excitations
Through ultrafast pump-probe spectroscopy with intense pump pulses and a wide
continuum probe, we show that interband exciton peaks in single-walled carbon
nanotubes (SWNTs) are extremely stable under high laser excitations. Estimates
of the initial densities of excitons from the excitation conditions, combined
with recent theoretical calculations of exciton Bohr radii for SWNTs, suggest
that their positions do not change at all even near the Mott density. In
addition, we found that the presence of lowest-subband excitons broadens all
absorption peaks, including those in the second-subband range, which provides a
consistent explanation for the complex spectral dependence of pump-probe
signals reported for SWNTs.Comment: 4 pages, 4 figure
Perfect hypermomentum fluid: variational theory and equations of motion
The variational theory of the perfect hypermomentum fluid is developed. The
new type of the generalized Frenkel condition is considered. The Lagrangian
density of such fluid is stated, and the equations of motion of the fluid and
the Weyssenhoff-type evolution equation of the hypermomentum tensor are
derived. The expressions of the matter currents of the fluid (the canonical
energy-momentum 3-form, the metric stress-energy 4-form and the hypermomentum
3-form) are obtained. The Euler-type hydrodynamic equation of motion of the
perfect hypermomentum fluid is derived. It is proved that the motion of the
perfect fluid without hypermomentum in a metric-affine space coincides with the
motion of this fluid in a Riemann space.Comment: REVTEX, 23 pages, no figure
Self-affine Asperity Model for earthquakes
A model for fault dynamics consisting of two rough and rigid brownian
profiles that slide one over the other is introduced. An earthquake occurs when
there is an intersection between the two profiles. The energy release is
proportional to the overlap interval. Our model exhibits some specific features
which follow from the fractal geometry of the fault: (1) non-universality of
the exponent of the Gutenberg-Richter law for the magnitude distribution; (2)
presence of local stress accumulation before a large seismic event; (3)
non-trivial space-time clustering of the epicenters. These properties are in
good agreement with various observations and lead to specific predictions that
can be experimentally tested.Comment: TeX file, 14 pages, 3 figures available from [email protected]
Ki67 expression levels are a better marker of reduced melanoma growth following MEK inhibitor treatment than phospho-ERK levels
The loss of tumour phospho-extracellular responsive kinase (pERK) positivity is the major treatment biomarker for mitogen-activated protein kinase/extracellular responsive kinase (MEK) inhibitors. Here, we demonstrate that there is a poor correlation between pERK inhibition and the anti-proliferative effects of MEK inhibitors in melanoma cells. We suggest that Ki67 is a better biomarker for future clinical studies
The sub-millimetre evolution of V4334 Sgr (Sakurai's Object)
We report the results of monitoring of V4334 Sgr (Sakurai's Object) at 450
microns and 850 microns with SCUBA on the James Clerk Maxwell Telescope. The
flux density at both wavelengths has increased dramatically since 2001, and is
consistent with continued cooling of the dust shell in which Sakurai's Object
is still enshrouded, and which still dominates the near-infrared emission.
Assuming that the dust shell is optically thin at sub-millimetre wavelengths
and optically thick in the near-infrared, the sub-millimetre data imply a
mass-loss rate during 2003 of ~3.4(+/0.2)E-5 for a gas-to-dust ratio of 75.
This is consistent with the evidence from 1-5micron observations that the
mass-loss is steadily increasing.Comment: 5 pages, 4 eps figures, accepted for publication in MNRA
Earthquake statistics and fractal faults
We introduce a Self-affine Asperity Model (SAM) for the seismicity that
mimics the fault friction by means of two fractional Brownian profiles (fBm)
that slide one over the other. An earthquake occurs when there is an overlap of
the two profiles representing the two fault faces and its energy is assumed
proportional to the overlap surface. The SAM exhibits the Gutenberg-Richter law
with an exponent related to the roughness index of the profiles. Apart
from being analytically treatable, the model exhibits a non-trivial clustering
in the spatio-temporal distribution of epicenters that strongly resembles the
experimentally observed one. A generalized and more realistic version of the
model exhibits the Omori scaling for the distribution of the aftershocks. The
SAM lies in a different perspective with respect to usual models for
seismicity. In this case, in fact, the critical behaviour is not Self-Organized
but stems from the fractal geometry of the faults, which, on its turn, is
supposed to arise as a consequence of geological processes on very long time
scales with respect to the seismic dynamics. The explicit introduction of the
fault geometry, as an active element of this complex phenomenology, represents
the real novelty of our approach.Comment: 40 pages (Tex file plus 8 postscript figures), LaTeX, submitted to
Phys. Rev.
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