14,779 research outputs found
Periodic-Orbit Bifurcation and Shell Structure in Reflection-Asymmetric Deformed Cavity
Shell structure of the single-particle spectrum for reflection-asymmetric
deformed cavity is investigated. Remarkable shell structure emerges for certain
combinations of quadrupole and octupole deformations. Semiclassical
periodic-orbit analysis indicates that bifurcation of equatorial orbits plays
an important role in the formation of this new shell structure.Comment: 5 pages, latex including 5 postscript figures, submitted to Physics
Letters
On the energy momentum dispersion in the lattice regularization
For a free scalar boson field and for U(1) gauge theory finite volume
(infrared) and other corrections to the energy-momentum dispersion in the
lattice regularization are investigated calculating energy eigenstates from the
fall off behavior of two-point correlation functions. For small lattices the
squared dispersion energy defined by is in both cases
negative ( is the Euclidean space-time dimension and the
energy of momentum eigenstates). Observation of has
been an accepted method to demonstrate the existence of a massless photon
() in 4D lattice gauge theory, which we supplement here by a study of
its finite size corrections. A surprise from the lattice regularization of the
free field is that infrared corrections do {\it not} eliminate a difference
between the groundstate energy and the mass parameter of the free
scalar lattice action. Instead, the relation is
derived independently of the spatial lattice size.Comment: 9 pages, 2 figures. Parts of the paper have been rewritten and
expanded to clarify the result
Changes in the secretory profile of NSCLC-associated fibroblasts after ablative radiotherapy: potential impact on angiogenesis and tumor growth
In the context of radiotherapy, collateral effects of ablative ionizing radiation (AIR) on stromal components of tumors remains understudied. In this work, cancer-associated fibroblasts (CAFs) isolated from freshly resected human lung tumors were exposed to AIR (1x18Gy) and analyzed for their release of paracrine factors. Inflammatory mediators and regulators of angiogenesis and tumor growth were analyzed by multiplex protein assays in conditioned medium (CM) from irradiated and non-irradiated CAFs. Additionally, the profile of secreted proteins was examined by proteomics. In functional assays, effects of CAF-CM on proliferative and migratory capacity of lung tumor cells (H-520/H-522) and endothelial cells (HUVECs), and on the tube-forming capacity of endothelial cells was assessed. Our data show that exposure of CAFs to ablative doses of ionizing radiation results in a) down-regulated release of angiogenic factors SDF-1, angiopoietin and thrombospondin-2; b) up-regulated release of growth factor bFGF from most donors, and c) unaffected expression-levels of HGF and inflammatory mediators IL-6, IL-8, IL-1ƒÒ and TNF-£. Conditioned medium from irradiated and control CAFs did not affect differently the proliferative or migratory capacity of tumor cells (H-520/H-522), whereas migratory capacity of endothelial HUVEC cells was partially reduced in the presence of irradiated CAF conditioned medium. Overall we conclude that AIR mediates a transformation on the secretory profile of CAFs that could influence the behavior of other cells in the tumor tissue and hence guide to some extent therapeutic outcomes. The downstream consequences of the changes observed in this study merits further investigations
Direct electronic measurement of Peltier cooling and heating in graphene
Thermoelectric effects allow the generation of electrical power from waste
heat and the electrical control of cooling and heating. Remarkably, these
effects are also highly sensitive to the asymmetry in the density of states
around the Fermi energy and can therefore be exploited as probes of distortions
in the electronic structure at the nanoscale. Here we consider two-dimensional
graphene as an excellent nanoscale carbon material for exploring the
interaction between electronic and thermal transport phenomena, by presenting a
direct and quantitative measurement of the Peltier component to electronic
cooling and heating in graphene. Thanks to an architecture including nanoscale
thermometers, we detected Peltier component modulation of up to 15 mK for
currents of 20 A at room temperature and observed a full reversal between
Peltier cooling and heating for electron and hole regimes. This fundamental
thermodynamic property is a complementary tool for the study of nanoscale
thermoelectric transport in two-dimensional materials.Comment: Final version published in Nature Communications under a Creative
Commons Attribution 4.0 International Licens
String Loop Corrections to Kahler Potentials in Orientifolds
We determine one-loop string corrections to Kahler potentials in type IIB
orientifold compactifications with either N=1 or N=2 supersymmetry, including
D-brane moduli, by evaluating string scattering amplitudes.Comment: 80 pages, 4 figure
Phase Structure of Z(3)-Polyakov-Loop Models
We study effective lattice actions describing the Polyakov loop dynamics
originating from finite-temperature Yang-Mills theory. Starting with a
strong-coupling expansion the effective action is obtained as a series of
Z(3)-invariant operators involving higher and higher powers of the Polyakov
loop, each with its own coupling. Truncating to a subclass with two couplings
we perform a detailed analysis of the statistical mechanics involved. To this
end we employ a modified mean field approximation and Monte Carlo simulations
based on a novel cluster algorithm. We find excellent agreement of both
approaches concerning the phase structure of the theories. The phase diagram
exhibits both first and second order transitions between symmetric,
ferromagnetic and anti-ferromagnetic phases with phase boundaries merging at
three tricritical points. The critical exponents nu and gamma at the continuous
transition between symmetric and anti-ferromagnetic phases are the same as for
the 3-state Potts model.Comment: 20 pages, 22 figure
Connectivity strategies to enhance the capacity of weight-bearing networks
The connectivity properties of a weight-bearing network are exploited to
enhance it's capacity. We study a 2-d network of sites where the weight-bearing
capacity of a given site depends on the capacities of the sites connected to it
in the layers above. The network consists of clusters viz. a set of sites
connected with each other with the largest such collection of sites being
denoted as the maximal cluster. New connections are made between sites in
successive layers using two distinct strategies. The key element of our
strategies consists of adding as many disjoint clusters as possible to the
sites on the trunk of the maximal cluster. The new networks can bear much
higher weights than the original networks and have much lower failure rates.
The first strategy leads to a greater enhancement of stability whereas the
second leads to a greater enhancement of capacity compared to the original
networks. The original network used here is a typical example of the branching
hierarchical class. However the application of strategies similar to ours can
yield useful results in other types of networks as well.Comment: 17 pages, 3 EPS files, 5 PS files, Phys. Rev. E (to appear
The relevance of aerosol optical depth to cumulus fraction changes: a five-year climatology at the ACRF SGP site
International audienceThe objective of this study is to investigate, by observational means, the magnitude and sign of the actively discussed relationship between cloud fraction N and aerosol optical depth ?a. Collocated and coincident ground-based measurements and Terra/Aqua satellite observations at the Atmospheric Radiation Measurement (ARM) Climate Research Facility (ACRF) Southern Great Plains (SGP) site form the basis of this study. The N??a relationship occurred in a specific 5-year dataset of fair-weather cumulus (FWC) clouds and mostly non-absorbing aerosols. To reduce possible contamination of the aerosols on the cloud properties estimation (and vice versa), we use independent datasets of ?a and N obtained from the Multi-filter Rotating Shadowband Radiometer (MFRSR) measurements and from the ARM Active Remotely Sensed Clouds Locations (ARSCL) value-added product, respectively. Optical depth of the FWC clouds ?cld and effective radius of cloud droplets re are obtained from the MODerate resolution Imaging Spectroradiometer (MODIS) data. We found that relationships between cloud properties (N,?cld, re) and aerosol optical depth are time-dependent (morning versus afternoon). Observed time-dependent changes of cloud properties, associated with aerosol loading, control the variability of surface radiative fluxes. In comparison with pristine clouds, the polluted clouds are more transparent in the afternoon due to smaller cloud fraction, smaller optical depth and larger droplets. As a result, the corresponding correlation between the surface radiative flux and ?a is positive (warming effect of aerosol). Also we found that relationship between cloud fraction and aerosol optical depth is cloud size dependent. The cloud fraction of large clouds (larger than 1 km) is relatively insensitive to the aerosol amount. In contrast, cloud fraction of small clouds (smaller than 1 km) is strongly positively correlated with ?a. This suggests that an ensemble of polluted clouds tends to be composed of smaller clouds than a similar one in a pristine environment. One should be aware of these time- and size-dependent features when qualitatively comparing N??a relationships obtained from the satellite observations, surface measurements, and model simulations
Floppy swimming: Viscous locomotion of actuated elastica
Actuating periodically an elastic filament in a viscous liquid generally
breaks the constraints of Purcell's scallop theorem, resulting in the
generation of a net propulsive force. This observation suggests a method to
design simple swimming devices - which we call "elastic swimmers" - where the
actuation mechanism is embedded in a solid body and the resulting swimmer is
free to move. In this paper, we study theoretically the kinematics of elastic
swimming. After discussing the basic physical picture of the phenomenon and the
expected scaling relationships, we derive analytically the elastic swimming
velocities in the limit of small actuation amplitude. The emphasis is on the
coupling between the two unknowns of the problems - namely the shape of the
elastic filament and the swimming kinematics - which have to be solved
simultaneously. We then compute the performance of the resulting swimming
device, and its dependance on geometry. The optimal actuation frequency and
body shapes are derived and a discussion of filament shapes and internal
torques is presented. Swimming using multiple elastic filaments is discussed,
and simple strategies are presented which result in straight swimming
trajectories. Finally, we compare the performance of elastic swimming with that
of swimming microorganisms.Comment: 23 pages, 6 figure
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