250,857 research outputs found
Modelling of epitaxial film growth with a Ehrlich-Schwoebel barrier dependent on the step height
The formation of mounded surfaces in epitaxial growth is attributed to the
presence of barriers against interlayer diffusion in the terrace edges, known
as Ehrlich-Schwoebel (ES) barriers. We investigate a model for epitaxial growth
using a ES barrier explicitly dependent on the step height. Our model has an
intrinsic topological step barrier even in the absence of an explicit ES
barrier. We show that mounded morphologies can be obtained even for a small
barrier while a self-affine growth, consistent with the Villain-Lai-Das Sarma
equation, is observed in absence of an explicit step barrier. The mounded
surfaces are described by a super-roughness dynamical scaling characterized by
locally smooth (faceted) surfaces and a global roughness exponent .
The thin film limit is featured by surfaces with self-assembled
three-dimensional structures having an aspect ratio (height/width) that may
increase or decrease with temperature depending on the strength of step
barrier.Comment: To appear in J. Phys. Cond. Matter; 3 movies as supplementary
materia
Evaluation of attenuated tumor antigens and the implications for peptide-based cancer vaccine development
Performance Analysis of the Spaceborne Laser Ranging System
The 'spaceborne laser ranging system' is a proposed short pulse laser on board an orbiting spacecraft. It measures the distances between the spacecraft and many laser retroreflectors (targets) deployed on the earth's surface. The precision of these range measurements was assumed to be about plus or minus 2 cm. These measurements were then used together with the orbital dynamics of the spacecraft to derive the intersite vector between the laser ground targets. The errors associated with this vector were on the order of 1 to 2 cm. The baseline distances determined range from 25 km to 1200 km. By repeating the measurements of the intersite vector, strain and strain rate errors were estimated. The realizable precision for intersite distance determination was estimated to be on the order of 0.5 cm at 300 km and about 1.5 cm at 1200 km. The corresponding inaccuracies for the intersite distances were larger, than is 1 cm and 3.5 cm respectively. The corresponding precision in the vertical direction was 1 cm and 3 cm
Ghost wave-function renormalization in Asymptotically Safe Quantum Gravity
Motivated by Weinberg's asymptotic safety scenario, we investigate the
gravitational renormalization group flow in the Einstein-Hilbert truncation
supplemented by the wave-function renormalization of the ghost fields. The
latter induces non-trivial corrections to the beta-functions for Newton's
constant and the cosmological constant. The resulting ghost-improved phase
diagram is investigated in detail. In particular, we find a non-trivial
ultraviolet fixed point in agreement with the asymptotic safety conjecture,
which also survives in the presence of extra dimensions. In four dimensions the
ghost anomalous dimension at the fixed point is , supporting
space-time being effectively two-dimensional at short distances.Comment: 23 pages, 4 figure
Spectroscopic and photometric oscillatory envelope variability during the S Doradus outburst of the Luminous Blue Variable R71
To better understand the LBV phenomenon, we analyze multi-epoch and
multi-wavelength spectra and photometry of R71. Pre-outburst spectra are
analyzed with the radiative transfer code CMFGEN to determine the star's
fundamental stellar parameters. During quiescence, R71 has an effective
temperature of and a luminosity of
log = 5.78 and is thus a classical LBV, but at the lower
luminosity end of this group. We determine its mass-loss rate to yr. We present R71's spectral energy distribution
from the near-ultraviolet to the mid-infrared during its present outburst.
Mid-infrared observations suggest that we are witnessing dust formation and
grain evolution. Semi-regular oscillatory variability in the star's light curve
is observed during the current outburst. Absorption lines develop a second blue
component on a timescale twice that length. The variability may consist of one
(quasi-)periodic component with P ~ 425/850 d with additional variations
superimposed. During its current S Doradus outburst, R71 occupies a region in
the HR diagram at the high-luminosity extension of the Cepheid instability
strip and exhibits similar irregular variations as RV Tau variables. LBVs do
not pass the Cepheid instability strip because of core evolution, but they
develop comparable cool, low-mass, extended atmospheres in which convective
instabilities may occur. As in the case of RV Tau variables, the occurrence of
double absorption lines with an apparent regular cycle may be due to shocks
within the atmosphere and period doubling may explain the factor of two in the
lengths of the photometric and spectroscopic cycles.Comment: 18 pages, 14 figures, submitted to A&
Toroidal Soliton Solutions in O(3)^N Nonlinear Sigma Model
A set of N three component unit scalar fields in (3+1) Minkowski space-time
is investigated. The highly nonlinear coupling between them is chosen to omit
the scaling instabilities. The multi-soliton static configurations with
arbitrary Hopf numbers are found. Moreover, the generalized version of the
Vakulenko-Kapitansky inequality is obtained. The possibility of attractive,
repulsing and noninteracting channels is discussed.Comment: to be published in Mod. Phys. Lett.
Low frequency m=1 normal mode oscillations of a self-gravitating disc
A continuous system such as a galactic disc is shown to be well approximated
by an N-ring differentially rotating self-gravitating system. Lowest order
(m=1) non-axisymmetric features such as lopsidedness and warps are global in
nature and quite common in the discs of spiral galaxies. Apparently these two
features of the galactic discs have been treated like two completely disjoint
phenomena. The present analysis based on an eigenvalue approach brings out
clearly that these two features are fundamentally similar in nature and they
are shown to be very Low frequency Normal Mode (LNM) oscillations manifested in
different symmetry planes of the galactic disc. Our analysis also show that
these features are actually long-lived oscillating pattern of the N-ring
self-gravitating system.Comment: 5 figures. Accepted for publication in MNRAS Letter
Quantum effects in linguistic endeavors
Classifying the information content of neural spike trains in a linguistic
endeavor, an uncertainty relation emerges between the bit size of a word and
its duration. This uncertainty is associated with the task of synchronizing the
spike trains of different duration representing different words. The
uncertainty involves peculiar quantum features, so that word comparison amounts
to measurement-based-quantum computation. Such a quantum behavior explains the
onset and decay of the memory window connecting successive pieces of a
linguistic text. The behavior here discussed is applicable to other reported
evidences of quantum effects in human linguistic processes, so far lacking a
plausible framework, since either no efforts to assign an appropriate quantum
constant had been associated or speculating on microscopic processes dependent
on Planck's constant resulted in unrealistic decoherence times
One-electron states and interband optical absorption in single-wall carbon nanotubes
Explicit expressions for the wave functions and dispersion equation for the
band p - electrons in single-wall carbon nanotubes are obtained within the
method of zero-range potentials. They are then used to investigate the
absorption spectrum of polarized light caused by direct interband transitions
in isolated nanotubes. It is shown that, at least, under the above
approximations, the circular dichroism is absent in chiral nanotubes for the
light wave propagating along the tube axis. The results obtained are compared
with those calculated in a similar way for a graphite plane.Comment: 16 pages, 8 figures, 1 tabl
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