19,709 research outputs found
Boundary monomers in the dimer model
The correlation functions of an arbitrary number of boundary monomers in the
system of close-packed dimers on the square lattice are computed exactly in the
scaling limit. The equivalence of the 2n-point correlation functions with those
of a complex free fermion is proved, thereby reinforcing the description of the
monomer-dimer model by a conformal free field theory with central charge c=1.Comment: 15 pages, 2 figure
The Bose gas beyond mean field
We study a homogeneous Bose gas with purely repulsive forces. Using the Kac
scaling of the binary potential we derive analytically the form of the
thermodynamic functions of the gas for small but finite values of the scaling
parameter in the low density regime. In this way we determine dominant
corrections to the mean-field theory. It turns out that repulsive forces
increase the pressure at fixed density and decrease the density at given
chemical potential (the temperature is kept constant). They also flatten the
Bose momentum distribution. However, the present analysis cannot be extended to
the region where the mean-field theory predicts the appearence of condensate.Comment: 19 pages, 3 figure
Discrete rearranging disordered patterns, part I: Robust statistical tools in two or three dimensions
Discrete rearranging patterns include cellular patterns, for instance liquid
foams, biological tissues, grains in polycrystals; assemblies of particles such
as beads, granular materials, colloids, molecules, atoms; and interconnected
networks. Such a pattern can be described as a list of links between
neighbouring sites. Performing statistics on the links between neighbouring
sites yields average quantities (hereafter "tools") as the result of direct
measurements on images. These descriptive tools are flexible and suitable for
various problems where quantitative measurements are required, whether in two
or in three dimensions. Here, we present a coherent set of robust tools, in
three steps. First, we revisit the definitions of three existing tools based on
the texture matrix. Second, thanks to their more general definition, we embed
these three tools in a self-consistent formalism, which includes three
additional ones. Third, we show that the six tools together provide a direct
correspondence between a small scale, where they quantify the discrete
pattern's local distortion and rearrangements, and a large scale, where they
help describe a material as a continuous medium. This enables to formulate
elastic, plastic, fluid behaviours in a common, self-consistent modelling using
continuous mechanics. Experiments, simulations and models can be expressed in
the same language and directly compared. As an example, a companion paper
(Marmottant, Raufaste and Graner, joint paper) provides an application to foam
plasticity
Fast acoustic tweezers for the two-dimensional manipulation of individual particles in microfluidic channels
This paper presents a microfluidic device that implements standing surface
acoustic waves in order to handle single cells, droplets, and generally
particles. The particles are moved in a very controlled manner by the
two-dimensional drifting of a standing wave array, using a slight frequency
modulation of two ultrasound emitters around their resonance. These acoustic
tweezers allow any type of motion at velocities up to few 10mm/s, while the
device transparency is adapted for optical studies. The possibility of
automation provides a critical step in the development of lab-on-a-chip cell
sorters and it should find applications in biology, chemistry, and engineering
domains
Non-Local Finite-Size Effects in the Dimer Model
We study the finite-size corrections of the dimer model on
square lattice with two different boundary conditions: free and periodic. We
find that the finite-size corrections depend in a crucial way on the parity of
, and show that, because of certain non-local features present in the model,
a change of parity of induces a change of boundary condition. Taking a
careful account of this, these unusual finite-size behaviours can be fully
explained in the framework of the logarithmic conformal field theory.Comment: This is a contribution to the Proc. of the O'Raifeartaigh Symposium
on Non-Perturbative and Symmetry Methods in Field Theory (June 2006,
Budapest, Hungary), published in SIGMA (Symmetry, Integrability and Geometry:
Methods and Applications) at http://www.emis.de/journals/SIGMA
Drosophila as a model system to study nonautonomous mechanisms affecting tumour growth and cell death
The study of cancer has represented a central focus in medical research for over a century. The great complexity and constant evolution of the pathology require the use of multiple research model systems and interdisciplinary approaches. This is necessary in order to achieve a comprehensive understanding into the mechanisms driving disease initiation and progression, to aid the development of appropriate therapies. In recent decades, the fruit fly Drosophila melanogaster and its associated powerful genetic tools have become a very attractive model system to study tumour-intrinsic and non-tumour-derived processes that mediate tumour development in vivo. In this review, we will summarize recent work on Drosophila as a model system to study cancer biology. We will focus on the interactions between tumours and their microenvironment, including extrinsic mechanisms affecting tumour growth and how tumours impact systemic host physiology
Variational solution of the Gross-Neveu model at finite temperature in the large N limit
We use a nonperturbative variational method to investigate the phase
transition of the Gross-Neveu model. It is shown that the variational procedure
can be generalized to the finite temperature case. The large N result for the
phase transition is correctly reproduced.Comment: 12 p., 1 fig, this is the version which will appear in the Phys Lett
B, it differs from the previous one in what concerns the introduction and
conclusions (re written), several references have been adde
Thermodynamic and rheological properties of rhyolite and andesite melts
The heat capacities of a rhyolite and an andesite glass and liquid have been investigated from relative-enthalpy measurements made between 400 and 1800 K. For the glass phases, the experimental data agree with empirical models of calculation of the heat capacity. For the liquid phases, the agreement is less good owing to strong interactions between alkali metals and aluminum, which are not currently accounted for by empirical heat capacity models. The viscosity of both liquids has been measured from the glass transition to 1800 K. The temperature dependence of the viscosity is quantitatively related to the configurational heat capacity (determined calorimetrically) through the configurational entropy theory of relaxation processes. For both rhyolite and andesite melts, the heat capacity and viscosity do not differ markedly from those obtained by additive modeling from components with mineral compositions
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