474 research outputs found
Kosterlitz-Thouless transition of the quasi two-dimensional trapped Bose gas
We present Quantum Monte Carlo calculations with up to N=576000 interacting
bosons in a quasi two-dimensional trap geometry closely related to recent
experiments with atomic gases. The density profile of the gas and the
non-classical moment of inertia yield intrinsic signatures for the
Kosterlitz--Thouless transition temperature T_KT. From the reduced one-body
density matrix, we compute the condensate fraction, which is quite large for
small systems. It decreases slowly with increasing system sizes, vanishing in
the thermodynamic limit. We interpret our data in the framework of the
local-density approximation, and point out the relevance of our results for the
analysis of experiments.Comment: 4 pages, 4 figure
Off-diagonal long-range order, cycle probabilities, and condensate fraction in the ideal Bose gas
We discuss the relationship between the cycle probabilities in the
path-integral representation of the ideal Bose gas, off-diagonal long-range
order, and Bose--Einstein condensation. Starting from the Landsberg recursion
relation for the canonic partition function, we use elementary considerations
to show that in a box of size L^3 the sum of the cycle probabilities of length
k >> L^2 equals the off-diagonal long-range order parameter in the
thermodynamic limit. For arbitrary systems of ideal bosons, the integer
derivative of the cycle probabilities is related to the probability of
condensing k bosons. We use this relation to derive the precise form of the
\pi_k in the thermodynamic limit. We also determine the function \pi_k for
arbitrary systems. Furthermore we use the cycle probabilities to compute the
probability distribution of the maximum-length cycles both at T=0, where the
ideal Bose gas reduces to the study of random permutations, and at finite
temperature. We close with comments on the cycle probabilities in interacting
Bose gases.Comment: 6 pages, extensive rewriting, new section on maximum-length cycle
Adding a Myers Term to the IIB Matrix Model
We show that Yang-Mills matrix integrals remain convergent when a Myers term
is added, and stay in the same topological class as the original model. It is
possible to add a supersymmetric Myers term and this leaves the partition
function invariant.Comment: 8 pages, v2 2 refs adde
Driven interfaces in random media at finite temperature : is there an anomalous zero-velocity phase at small external force ?
The motion of driven interfaces in random media at finite temperature and
small external force is usually described by a linear displacement at large times, where the velocity vanishes according to the
creep formula as for . In this paper,
we question this picture on the specific example of the directed polymer in a
two dimensional random medium. We have recently shown (C. Monthus and T. Garel,
arxiv:0802.2502) that its dynamics for F=0 can be analyzed in terms of a strong
disorder renormalization procedure, where the distribution of renormalized
barriers flows towards some "infinite disorder fixed point". In the present
paper, we obtain that for small , this "infinite disorder fixed point"
becomes a "strong disorder fixed point" with an exponential distribution of
renormalized barriers. The corresponding distribution of trapping times then
only decays as a power-law , where the exponent
vanishes as as . Our
conclusion is that in the small force region , the divergence of
the averaged trapping time induces strong
non-self-averaging effects that invalidate the usual creep formula obtained by
replacing all trapping times by the typical value. We find instead that the
motion is only sub-linearly in time , i.e. the
asymptotic velocity vanishes V=0. This analysis is confirmed by numerical
simulations of a directed polymer with a metric constraint driven in a traps
landscape. We moreover obtain that the roughness exponent, which is governed by
the equilibrium value up to some large scale, becomes equal to
at the largest scales.Comment: v3=final versio
Emotional reactions to the French colonization in Algeria: the normative nature of collective guilt
Fifty years after the end of the Algerian war of independence, French colonization in Algeria (1830-1962) is still a very controversial topic when sporadically brought to the forefront of the public sphere. One way to better understand current intergroup relationships between French of French origin and French with Algerian origins is to investigate how the past influences the present. This study explores French students' emotional reactions to this historical period, their ideological underpinnings and their relationship with the willingness to compensate for past misdeeds, and with prejudice. Results show that French students with French ascendants endorse a no-remorse norm when thinking about past colonization of Algeria and express very low levels of collective guilt and moral-outrage related emotions, especially those students with a right-wing political orientation and a national identification in the form of glorification of the country. These group-based emotions are significantly related to pro-social behavioral intentions (i.e. the willingness to compensate) and to prejudice toward the outgroup.info:eu-repo/semantics/acceptedVersio
Absence of a structural glass phase in a monoatomic model liquid predicted to undergo an ideal glass transition
We study numerically a monodisperse model of interacting classical particles
predicted to exhibit a static liquid-glass transition. Using a dynamical Monte
Carlo method we show that the model does not freeze into a glassy phase at low
temperatures. Instead, depending on the choice of the hard-core radius for the
particles the system either collapses trivially or a polycrystalline hexagonal
structure emerges.Comment: 4 pages, 4 figures, minor changes in introduction and conclusions,
additional reference
Vacancy localization in the square dimer model
We study the classical dimer model on a square lattice with a single vacancy
by developing a graph-theoretic classification of the set of all configurations
which extends the spanning tree formulation of close-packed dimers. With this
formalism, we can address the question of the possible motion of the vacancy
induced by dimer slidings. We find a probability 57/4-10Sqrt[2] for the vacancy
to be strictly jammed in an infinite system. More generally, the size
distribution of the domain accessible to the vacancy is characterized by a
power law decay with exponent 9/8. On a finite system, the probability that a
vacancy in the bulk can reach the boundary falls off as a power law of the
system size with exponent 1/4. The resultant weak localization of vacancies
still allows for unbounded diffusion, characterized by a diffusion exponent
that we relate to that of diffusion on spanning trees. We also implement
numerical simulations of the model with both free and periodic boundary
conditions.Comment: 35 pages, 24 figures. Improved version with one added figure (figure
9), a shift s->s+1 in the definition of the tree size, and minor correction
The silicon trypanosome
African trypanosomes have emerged as promising unicellular model organisms for the next generation of systems biology. They offer unique advantages, due to their relative simplicity, the availability of all standard genomics techniques and a long history of quantitative research. Reproducible cultivation methods exist for morphologically and physiologically distinct life-cycle stages. The genome has been sequenced, and microarrays, RNA-interference and high-accuracy metabolomics are available. Furthermore, the availability of extensive kinetic data on all glycolytic enzymes has led to the early development of a complete, experiment-based dynamic model of an important biochemical pathway. Here we describe the achievements of trypanosome systems biology so far and outline the necessary steps towards the ambitious aim of creating a , a comprehensive, experiment-based, multi-scale mathematical model of trypanosome physiology. We expect that, in the long run, the quantitative modelling enabled by the Silicon Trypanosome will play a key role in selecting the most suitable targets for developing new anti-parasite drugs
Glassy features of a Bose Glass
We study a two-dimensional Bose-Hubbard model at a zero temperature with
random local potentials in the presence of either uniform or binary disorder.
Many low-energy metastable configurations are found with virtually the same
energy as the ground state. These are characterized by the same blotchy pattern
of the, in principle, complex nonzero local order parameter as the ground
state. Yet, unlike the ground state, each island exhibits an overall random
independent phase. The different phases in different coherent islands could
provide a further explanation for the lack of coherence observed in experiments
on Bose glasses.Comment: 14 pages, 4 figures
Exact Quantum Monte Carlo Process for the Statistics of Discrete Systems
We introduce an exact Monte Carlo approach to the statistics of discrete
quantum systems which does not rely on the standard fragmentation of the
imaginary time, or any small parameter. The method deals with discrete objects,
kinks, representing virtual transitions at different moments of time. The
global statistics of kinks is reproduced by explicit local procedures, the key
one being based on the exact solution for the biased two-level system.Comment: 4 pages, latex, no figures, English translation of the paper
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