4,020 research outputs found
Contractile stresses in cohesive cell layers on finite-thickness substrates
Using a minimal model of cells or cohesive cell layers as continuum active
elastic media, we examine the effect of substrate thickness and stiffness on
traction forces exerted by strongly adhering cells. We obtain a simple
expression for the length scale controlling the spatial variation of stresses
in terms of cell and substrate parameters that describes the crossover between
the thin and thick substrate limits. Our model is an important step towards a
unified theoretical description of the dependence of traction forces on cell or
colony size, acto-myosin contractility, substrate depth and stiffness, and
strength of focal adhesions, and makes experimentally testable predictions.Comment: 5 pages, 3 figure
Mobility through Heterogeneous Networks in a 4G Environment
Serving and Managing users in a heterogeneous environment. 17th WWRF Meeting in Heidelberg, Germany, 15 - 17 November 2006. [Proceeding presented at WG3 - Co-operative and Ad-hoc Networks]The increase will of ubiquitous access of the users to the requested services points towards the integration of heterogeneous networks. In this sense, a user shall be able to access its services through different access technologies, such as WLAN, Wimax, UMTS and DVB technologies, from the same or different network operators, and to seamless move between different networks with active communications. In this paper we propose a mobility architecture able to support this users’ ubiquitous access and seamless movement, while simultaneously bringing a large flexibility to access network operators
Translational Correlations in the Vortex Array at the Surface of a Type-II Superconductor
We discuss the statistical mechanics of magnetic flux lines in a
finite-thickness slab of type-II superconductor. The long wavelength properties
of a flux-line liquid in a slab geometry are described by a hydrodynamic free
energy that incorporates the boundary conditions on the flux lines at the
sample's surface as a surface contribution to the free energy. Bulk and surface
weak disorder are modeled via Gaussian impurity potentials. This free energy is
used to evaluate the two-dimensional structure factor of the flux-line tips at
the sample surface. We find that surface interaction always dominates in
determining the decay of translational correlations in the asymptotic
long-wavelength limit. On the other hand, such large length scales have not
been probed by the decoration experiments. Our results indicate that the
translational correlations extracted from the analysis of the Bitter patterns
are indeed representative of behavior of flux lines in the bulk.Comment: 23 pages, 1 figure (not included), harvmac.tex macro needed (e-mail
requests to [email protected] SU-CM-92-01
Spin-charge gauge approach to metal-insulator crossover and transport properties in High-T cuprates
The spin-charge gauge approach to consider the metal-insulator crossover
(MIC) and other anomalous transport properties in High-T cuprates is
briefly reviewed. A U(1) field gauging the global charge symmetry and an SU(2)
field gauging the global spin-rotational symmetry are introduced to study the
two-dimensional model in the limit . The MIC as a clue to the
understanding of the ``pseudogap'' (PG) phase, is attributed to the competition
between the short-range antiferromagnetic order and dissipative motion of
charge carriers coupled to the slave-particle gauge field. The composite
particle formed by binding the charge carrier (holon) and spin excitation
(spinon) via the slave particle gauge field exhibits a number of peculiar
properties, and the calculated results are in good agreement with experimental
data for both PG and ``strange metal'' phases. Connections to other gauge field
approaches in studying the strong correlation problem are also briefly
outlined.Comment: 32 pages, to appear in the special issue on "Correlated Electrons" of
J. Phys.: Condens. Mat
CLINICAL IMPACT OF TOBI® ON CYSTIC FIBROSIS PATIENTS WITH CHRONIC PSEUDOMONAS AERUGINOSA COLONISATION: RESULT OF A POST-MARKETING SURVEILLANCE
In-Plane Conductivity Anisotropy in Underdoped Cuprates in the Spin-Charge Gauge Approach
Applying the recently developed spin-charge gauge theory for the pseudogap
phase in cuprates, we propose a self-consistent explanation of several peculiar
features of the far-infrared in-plane AC conductivity, including a broad peak
as a function of frequency and significant anisotropy at low temperatures,
along with a similar temperature-dependent in-plane anisotropy of DC
conductivity in lightly doped cuprates. The anisotropy of the metal-insulator
crossover scale is considered to be responsible for these phenomena. The
obtained results are in good agreement with experiments. An explicit proposal
is made to further check the theory.Comment: 5 pages, 3 figures, to appear in Phys. Rev.
Theory of Double-Sided Flux Decorations
A novel two-sided Bitter decoration technique was recently employed by Yao et
al. to study the structure of the magnetic vortex array in high-temperature
superconductors. Here we discuss the analysis of such experiments. We show that
two-sided decorations can be used to infer {\it quantitative} information about
the bulk properties of flux arrays, and discuss how a least squares analysis of
the local density differences can be used to bring the two sides into registry.
Information about the tilt, compressional and shear moduli of bulk vortex
configurations can be extracted from these measurements.Comment: 17 pages, 3 figures not included (to request send email to
[email protected]
Metal-insulator crossover in superconducting cuprates in strong magnetic fields
The metal-insulator crossover of the in-plane resistivity upon temperature
decrease, recently observed in several classes of cuprate superconductors, when
a strong magnetic field suppresses the superconductivity, is explained using
the Chern-Simons gauge field theory. The origin of this
crossover is the same as that for a similar phenomenon observed in heavily
underdoped cuprates without magnetic field. It is due to the interplay between
the diffusive motion of the charge carriers and the ``peculiar'' localization
effect due to short-range antiferromagnetic order. We also calculate the
in-plane transverse magnetoresistance which is in a fairly good agreement with
available experimental data.Comment: 4 pages, 3 .eps figures, to appear in Physical Review Letter
Critical States in Disordered Superconducting Films
When subject to a pair-breaking perturbation, the pairing susceptibility of a
disordered superconductor exhibits substantial long-ranged mesoscopic
fluctuations. Focusing on a thin film subject to a parallel magnetic field, it
is proposed that the quantum phase transition to the bulk superconducting
condensate may be preempted by the formation of a glass-like phase with
multi-fractal correlations of a complex order parameter. Although not
universal, we argue that such behavior may be a common feature of quantum
critical phenomena in disordered environments.Comment: 7 pages, 1 eps figur
HerMES: A Statistical Measurement of the Redshift Distribution of Herschel-SPIRE Sources Using the Cross-correlation Technique
The wide-area imaging surveys with the Herschel Space Observatory at submillimeter (sub-mm) wavelengths have now resulted in catalogs of the order of one-hundred-thousand dusty, starburst galaxies. These galaxies capture an important phase of galaxy formation and evolution, but, unfortunately, the redshift distribution of these galaxies, N(z), is still mostly uncertain due to limitations associated with counterpart identification at optical wavelengths and spectroscopic follow-up. We make a statistical estimate of N(z) using a clustering analysis of sub-mm galaxies detected at each of 250, 350 and 500 μm from the Herschel Multi-tiered Extragalactic Survey centered on the Boötes field. We cross-correlate Herschel galaxies against galaxy samples at optical and near-IR wavelengths from the Sloan Digital Sky Survey, the NOAO Deep Wide Field Survey, and the Spitzer Deep Wide Field Survey. We create optical and near-IR galaxy samples based on their photometric or spectroscopic redshift distributions and test the accuracy of those redshift distributions with similar galaxy samples defined with catalogs from the Cosmological Evolution Survey (COSMOS), which has superior spectroscopic coverage. We model the clustering auto- and cross-correlations of Herschel and optical/IR galaxy samples to estimate N(z) and clustering bias factors. The S_(350) > 20 mJy galaxies have a bias factor varying with redshift as b(z) = 1.0^(+1.0)_(–0.5)(1 + z)^1.2^(+0.3)_(–0.7). This bias and the redshift dependence is broadly in agreement with galaxies that occupy dark matter halos of mass in the range of 1012 to 10^(13) M_☉. We find that galaxy selections in all three Spectral and Photometric Imaging Receiver (SPIRE) bands share a similar average redshift, with = 1.8 ± 0.2 for 250 μm selected samples, and = 1.9 ± 0.2 for both 350 and 500 μm samples, while their distributions behave differently. For 250 μm selected galaxies we find the a larger number of sources with z ≤ 1 when compared with the subsequent two SPIRE bands, with 350 and 500 μm selected SPIRE samples having peaks in N(z) at progressively higher redshifts. We compare our clustering-based N(z) results to sub-mm galaxy model predictions in the literature, and with an estimate of N(z) using a stacking analysis of COSMOS 24 μm detections
- …