3,634 research outputs found
Rheology at the micro-scale: new tools for bio-analysis
We present a simple and non-invasive experimental procedure to measure the linear viscoelastic properties of cells by passive particle tracking microrheology. In order to do this, a generalised Langevin equation is adopted to relate the timedependent thermal fluctuations of a probe sensor, immobilised to the cell’s membrane, to the frequency-dependent viscoelastic moduli of the cell. The method has been validated by measuring the linear viscoelastic response of a soft solid and then applied to cell physiology studies. It is shown that the viscoelastic moduli are related to the cell’s cytoskeletal structure, which in this work is modulated either by inhibiting the actin/myosin-II interactions by means of blebbistatin or by varying the solution osmolarity from iso- to hypo-osmotic conditions. The insights gained from this form of rheological analysis promises to be a valuable addition to physiological studies; e.g. cell physiology during pathology and pharmacological response
FRW Universe in Ho\~rava Gravity
Recently, a field theoretic model for a UV complete theory of gravity has
been proposed by Ho\~{r}ava. This theory is a non-relativistic renormalizable
gravity theory which coincides with Einstein's general relativity at large
distances. Subsequently L\"{u} et al have formulated the modified Friedmann
equations and have presented a solution in vacuum. In the present work, we
rewrite the modified FRW equations in the form of usual FRW equations in
Einstein gravity and consequences has been analyzed. Also the thermodynamics of
the FRW universe has been studied
Numerical study of scars in a chaotic billiard
We study numerically the scaling properties of scars in stadium billiard.
Using the semiclassical criterion, we have searched systematically the scars of
the same type through a very wide range, from ground state to as high as the 1
millionth state. We have analyzed the integrated probability density along the
periodic orbit. The numerical results confirm that the average intensity of
certain types of scars is independent of rather than scales with
. Our findings confirm the theoretical predictions of Robnik
(1989).Comment: 7 pages in Revtex 3.1, 5 PS figures available upon request. To appear
in Phys. Rev. E, Vol. 55, No. 5, 199
MIMO free-space optical communication employing subcarrier intensity modulation in atmospheric turbulence channels
In this paper, we analyse the error performance of transmitter/receiver array free-space optical (FSO) communication system employing binary phase shift keying (BPSK) subcarrier intensity modulation (SIM) in clear but turbulent atmospheric channel. Subcarrier modulation is employed to eliminate the need for adaptive threshold detector. Direct detection is employed at the receiver and each subcarrier is subsequently demodulated coherently. The effect of irradiance fading is mitigated with an array of lasers and photodetectors. The received signals are linearly combined using the optimal maximum ratio combining (MRC), the equal gain combining (EGC) and the selection combining (SelC). The bit error rate (BER) equations are derived considering additive white Gaussian noise and log normal intensity fluctuations. This work is part of the EU COST actions and EU projects
Willmore minimizers with prescribed isoperimetric ratio
Motivated by a simple model for elastic cell membranes, we minimize the
Willmore functional among two-dimensional spheres embedded in R^3 with
prescribed isoperimetric ratio
Comparison of Temperature-Dependent Hadronic Current Correlation Functions Calculated in Lattice Simulations of QCD and with a Chiral Lagrangian Model
The Euclidean-time hadronic current correlation functions, and
, of pseudoscalar and vector currents have recently been
calculated in lattice simulations of QCD and have been used to obtain the
corresponding spectral functions. We have used the Nambu-Jona-Lasinio (NJL)
model to calculate such spectral functions, as well as the Euclidean-time
correlators, and have made a comparison to the lattice results for the
correlators. We find evidence for the type of temperature dependence of the NJL
coupling parameters that we have used in previous studies of the mesonic
confinement-deconfinement transition. We also see that the spectral functions
obtained when using the maximum-entropy-method (MEM) and the lattice data
differ from the spectral functions that we calculate in our chiral model.
However, our results for the Euclidean-time correlators are in general
agreement with the lattice results, with better agreement when our
temperature-dependent coupling parameters are used than when
temperature-independent parameters are used for the NJL model. We also discuss
some additional evidence for the utility of temperature-dependent coupling
parameters for the NJL model. For example, if the constituent quark mass at T=0
is in the chiral limit, the transition temperature is for the NJL model with a standard momentum cutoff parameter. (If a
Gaussian momentum cutoff is used, we find in the chiral limit,
with at T=0.) The introduction of a weak temperature dependence
for the coupling constant will move the value of into the range 150-170
MeV, which is more in accord with what is found in lattice simulations of QCD
with dynamical quarks
Entropy and the variational principle for actions of sofic groups
Recently Lewis Bowen introduced a notion of entropy for measure-preserving
actions of a countable sofic group on a standard probability space admitting a
generating partition with finite entropy. By applying an operator algebra
perspective we develop a more general approach to sofic entropy which produces
both measure and topological dynamical invariants, and we establish the
variational principle in this context. In the case of residually finite groups
we use the variational principle to compute the topological entropy of
principal algebraic actions whose defining group ring element is invertible in
the full group C*-algebra.Comment: 44 pages; minor changes; to appear in Invent. Mat
Finding co-solvers on Twitter, with a little help from Linked Data
In this paper we propose a method for suggesting potential collaborators for solving innovation challenges online, based on their competence, similarity of interests and social proximity with the user. We rely on Linked Data to derive a measure of semantic relatedness that we use to enrich both user profiles and innovation problems with additional relevant topics, thereby improving the performance of co-solver recommendation. We evaluate this approach against state of the art methods for query enrichment based on the distribution of topics in user profiles, and demonstrate its usefulness in recommending collaborators that are both complementary in competence and compatible with the user. Our experiments are grounded using data from the social networking service Twitter.com
The asymptotic iteration method for the angular spheroidal eigenvalues with arbitrary complex size parameter c
The asymptotic iteration method is applied, to calculate the angular
spheroidal eigenvalues with arbitrary complex size
parameter . It is shown that, the obtained numerical results of
are all in excellent agreement with the available
published data over the full range of parameter values , , and .
Some representative values of for large real are
also given.Comment: 15 pages, 1 figur
Spin-dependent structure functions and for inclusive spin-half baryon production in electron-positron annihilation
Two spin-dependent structure functions and for the
inclusive spin-half baryon production in electron-positron annihilation are
studied in the context of QCD factorization as well as in the naive quark
parton model. As a result, it is found that the sum of and is related to and , two quark fragmentation functions
defined by Jaffe and Ji. In connection with the measurement of quark
fragmentation functions, the possible phenomenological consequences are
discussed.Comment: RevTex, four Ps figures, to appear in Phys. Rev.
- …