579 research outputs found

### Equilibrium correlations in charged fluids coupled to the radiation field

We provide an exact microscopic statistical treatment of particle and field
correlations in a system of quantum charges in equilibrium with a classical
radiation field. Using the Feynman-Kac-Ito representation of the Gibbs weight,
the system of particles is mapped onto a collection of random charged wires.
The field degrees of freedom can be integrated out, providing an effective
pairwise magnetic potential. We then calculate the contribution of the
transverse field coupling to the large-distance particle correlations. The
asymptotics of the field correlations in the plasma are also exactly
determined.Comment: 31 pages, 0 figures. PACS 05.30.-d, 05.40.-a, 11.10.Wx. Changes:
Improved comparison with existing literature on field correlations. Added
Concluding Remarks. References update

### Charge and Density Fluctuations Lock Horns : Ionic Criticality with Power-Law Forces

How do charge and density fluctuations compete in ionic fluids near
gas-liquid criticality when quantum mechanical effects play a role ? To gain
some insight, long-range $\Phi^{{\mathcal{L}}}_{\pm \pm} / r^{d+\sigma}$
interactions (with $\sigma>0$), that encompass van der Waals forces (when
$\sigma = d = 3$), have been incorporated in exactly soluble, $d$-dimensional
1:1 ionic spherical models with charges $\pm q_0$ and hard-core repulsions. In
accord with previous work, when $d>\min \{\sigma, 2\}$ (and $q_0$ is not too
large), the Coulomb interactions do not alter the ($q_0 = 0$) critical
universality class that is characterized by density correlations at criticality
decaying as $1/r^{d-2+\eta}$ with $\eta = \max \{0, 2-\sigma\}$. But screening
is now algebraic, the charge-charge correlations decaying, in general, only as
$1/r^{d+\sigma+4}$; thus $\sigma = 3$ faithfully mimics known
\textit{non}critical $d=3$ quantal effects. But in the \textit{absence} of full
($+, -$) ion symmetry, density and charge fluctuations mix via a transparent
mechanism: then the screening \textit{at criticality} is \textit{weaker} by a
factor $r^{4-2\eta}$. Furthermore, the otherwise valid Stillinger-Lovett sum
rule fails \textit{at} criticality whenever $\eta =0$ (as, e.g., when
$\sigma>2$) although it remains valid if $\eta >0$ (as for $\sigma<2$ or in
real $d \leq 3$ Ising-type systems).Comment: 8 pages, in press in J. Phys. A, Letters to the Edito

### Nyquist method for Wigner-Poisson quantum plasmas

By means of the Nyquist method, we investigate the linear stability of
electrostatic waves in homogeneous equilibria of quantum plasmas described by
the Wigner-Poisson system. We show that, unlike the classical Vlasov-Poisson
system, the Wigner-Poisson case does not necessarily possess a Penrose
functional determining its linear stability properties. The Nyquist method is
then applied to a two-stream distribution, for which we obtain an exact,
necessary and sufficient condition for linear stability, as well as to a
bump-in-tail equilibrium.Comment: 6 figure

### Quantitative evaluation of chromosomal rearrangements in gene-edited human stem cells by CAST-Seq

Genome editing has shown great promise for clinical translation but also revealed the risk of genotoxicity caused by off-target effects of programmable nucleases. Here we describe chromosomal aberrations analysis by single targeted linker-mediated PCR sequencing (CAST-Seq), a preclinical assay to identify and quantify chromosomal aberrations derived from on-target and off-target activities of CRISPR-Cas nucleases or transcriptional activator-like effector nucleases (TALENs), respectively, in human hematopoietic stem cells (HSCs). Depending on the employed designer nuclease, CAST-Seq detected translocations in 0%â0.5% of gene-edited human CD34+ HSCs, and up to 20% of on-target loci harbored gross rearrangements. Moreover, CAST-Seq detected distinct types of chromosomal aberrations, such as homology-mediated translocations, that are mediated by homologous recombination and not off-target activity. CAST-Seq is a sensitive assay able to identify and quantify unintended chromosomal rearrangements in addition to the more typical mutations at off-target sites. CAST-Seq analyses may be particularly relevant for therapeutic genome editing to enable thorough risk assessment before clinical application of gene-edited products

### Prognostic study of continuous variables (white blood cell count, peripheral blast cell count, haemoglobin level, platelet count and age) in childhood acute lymphoblastic leukaemia. Analysis of a population of 1545 children treated by the French Acute Lymphoblastic Leukaemia Group (FRALLE)

Many cutpoints have been proposed to categorize continuous variables in childhood acute lymphoblastic leukaemia (white blood cell count, peripheral blast cell count, haemoglobin level, platelet count and age), and have been used to define therapeutic subgroups. This variation in the choice of cutpoints leads to a bias called the âWill Rogers phenomenonâ. The aim of this study was to analyse variations in the relative risk of relapse or death as a function of continuous prognostic variables in childhood ALL and to discuss the choice of cutpoints. We studied a population of 1545 children with ALL enrolled in three consecutive protocols named FRALLE 83, FRALLE 87 and FRALLE 89. We estimated the risk of relapse or death associated with different values of each continuous prognostic variable by dividing the sample into quintiles of the distribution of the variables. As regards age, a category of children under 1 year of age was distinguished and the rest of the population was divided into quintiles. The floated variance method was used to calculate the confidence interval of each relative risk, including the reference category. The relation between the quantitative prognostic factors and the risk was monotonic for each variable, except for age. For the white blood cell count (WBC), the relation is log linear. The risk associated with WBC values in the upper quintile was 1.9 times higher than that in the lower quintile. The peripheral blast cell count correlated strongly with WBC (correlation coefficient: 0.99). The risk increased with the haemoglobin level, and the risk in the upper quintile was 1.3 times higher than that in the lower quintile. The risk decreased as the platelet count increased: the risk in the lower quintile was 1.2 times higher than that in the upper quintile. The risk increased gradually with increasing age above one year. The small subgroup of patients (2.5% of the population) under 1 year of age at diagnosis had a risk 2.6 times higher than the reference category of patients between 3 and 4.3 years of age. When the risk associated with a quantitative prognostic factor varies monotonously, the selection of a cutpoint is arbitrary and represents a loss of information. Despite this loss of information, such arbitrary categorization may be necessary to define therapeutic stratification. In that case, consensus cutpoints must be defined if one wants to avoid the Will Rogers phenomenon. The cutpoints proposed by the Rome workshop and the NCI are arbitrary, but may represent an acceptable convention. Â© 2000 Cancer Research Campaign http://www.bjcancer.co

### Interpretation, translation and intercultural communication in refugee status determination procedures in the UK and France

This article explores the interplay between language and intercultural communication within refugee status determination procedures in the UK and France, using material taken from ethnographic research that involved a combination of participant observation, semi-structured interviews and documentary analysis in both countries over a two-year period (2007â2009). It is concerned, in particular, to examine the role played by interpreters in facilitating intercultural communication between asylum applicants and the different administrative and legal actors responsible for assessing or defending their claims. The first section provides an overview of refugee status determination procedures in the UK and France, introducing the main administrative and legal contexts of the asylum process within which interpreters operate in the two countries. The second section compares the organisation of interpreting services, codes of conduct for interpreters and institutional expectations about the nature of interpretersâ activity on the part of the relevant UK and French authorities. The third section then explores some of the practical dilemmas for interpreters and barriers to communication that exist in refugee status determination procedures in the two countries. The article concludes by emphasising the complex and active nature of the interpreter's role in UK and French refugee status determination procedures

### Atom-wall dispersive forces: a microscopic approach

We present a study of atom-wall interactions in non-relativistic quantum
electrodynamics by functional integral methods. The Feynman-Kac path integral
representation is generalized to the case when the particle interacts with a
radiation field, providing an additional effective potential that contains all
the interactions induced by the field. We show how one can retrieve the
standard van der Waals, Casimir-Polder and classical Lifshiftz forces in this
formalism for an atom in its ground state. Moreover, when electrostatic
interactions are screened in the medium, we find low temperature corrections
that are not included in the Lifshitz theory of fluctuating forces and are
opposite to them.Comment: 4 figure

### Analysis of path integrals at low temperature : Box formula, occupation time and ergodic approximation

We study the low temperature behaviour of path integrals for a simple
one-dimensional model. Starting from the Feynman-Kac formula, we derive a new
functional representation of the density matrix at finite temperature, in terms
of the occupation times of Brownian motions constrained to stay within boxes
with finite sizes. From that representation, we infer a kind of ergodic
approximation, which only involves double ordinary integrals. As shown by its
applications to different confining potentials, the ergodic approximation turns
out to be quite efficient, especially in the low-temperature regime where other
usual approximations fail

### Anomalous Effects of "Guest" Charges Immersed in Electrolyte: Exact 2D Results

We study physical situations when one or two "guest" arbitrarily-charged
particles are immersed in the bulk of a classical electrolyte modelled by a
Coulomb gas of positive/negative unit point-like charges, the whole system
being in thermal equilibrium. The models are treated as two-dimensional with
logarithmic pairwise interactions among charged constituents; the
(dimensionless) inverse temperature $\beta$ is considered to be smaller than 2
in order to ensure the stability of the electrolyte against the collapse of
positive-negative pairs of charges. Based on recent progress in the integrable
(1+1)-dimensional sine-Gordon theory, exact formulas are derived for the
chemical potential of one guest charge and for the asymptotic large-distance
behavior of the effective interaction between two guest charges. The exact
results imply, under certain circumstances, anomalous effects such as an
effective attraction (repulsion) between like-charged (oppositely-charged)
guest particles and the charge inversion in the electrolyte vicinity of a
highly-charged guest particle. The adequacy of the concept of renormalized
charge is confirmed in the whole stability region of inverse temperatures and
the related saturation phenomenon is revised.Comment: 21 pages, 1 figur

### Production and reliability oriented SOFC cell and stack design

The paper presents an innovative development methodology for a production and reliability oriented SOFC cell and stack design aiming at improving the stacks robustness, manufacturability, efficiency and cost. Multi-physics models allowed a probabilistic approach to consider statistical variations in production, material and operating parameters for the optimization phase. A methodology for 3D description of spatial distribution of material properties based on a random field models was developed and validated by experiments. Homogenized material models on multiple levels of the SOFC stack were established. The probabilistic models were related to the experimentally obtained properties of base materials to establish a statistical relationship between the material properties and the most relevant load effects. Software algorithms for meta models that allow the detection of relationships between input and output parameters and to perform a sensitivity analysis were developed and implemented. The capabilities of the methodology is illustrated on two practical cases

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