1,978 research outputs found
Universal Cubic Eigenvalue Repulsion for Random Normal Matrices
Random matrix models consisting of normal matrices, defined by the sole
constraint , will be explored. It is shown that cubic
eigenvalue repulsion in the complex plane is universal with respect to the
probability distribution of matrices. The density of eigenvalues, all
correlation functions, and level spacing statistics are calculated. Normal
matrix models offer more probability distributions amenable to analytical
analysis than complex matrix models where only a model wth a Gaussian
distribution are solvable. The statistics of numerically generated eigenvalues
from gaussian distributed normal matrices are compared to the analytical
results obtained and agreement is seen.Comment: 15 pages, 2 eps figures. to appar in Physical Review
Réservoir extra-digestif d’entérobactéries productrices de bêtalactamase à spectre élargi chez des patients non infectés: étude à partir d’une recherche systématique dans les urines et d’autres prélèvements à visée diagnostique
Notre objectif était d’étudier le réservoir extra-digestif d’entérobactéries productrices de β-lactamases à spectre élargi (EBLSE) en les recherchant dans des prélèvements à visée diagnostique (PVD) pour lesquels les colonies bactériennes isolées sur les milieux de cultures utilisés ne sont pas obligatoirement analysées (identification bactérienne et antibiogramme) en routine. Pendant une période de 5 semaines, des identifications et des antibiogrammes ont été réalisés de manière systématique pour les colonies correspondant à des entérobactéries isolées dans certains PVD comme les urines, les prélèvements respiratoires, et un groupe de prélèvements appelé “divers”. Les prélèvements pour lesquels un antibiogramme a été réalisé conformément à la pratique de routine du laboratoire ont été considérés comme infectés. Les prélèvements pour lesquels les entérobactéries ont été recherchées et étudiées suivant le protocole de l’étude ont été considérés comme colonisés. Au cours de l’étude, 2 312 urines, 327 prélèvements respiratoires et 1 887 prélèvements divers ont été envoyés au laboratoire. Parmi les 114 urines colonisées par au moins une entérobactérie, 13 (11,4 %) comportaient une EBLSE, alors que cette proportion était de 5,1 % (35/682) dans les urines infectées (p < 0,01). Parmi les prélèvements respiratoires et divers, 3 EBLSE ont été isolées dans 55 prélèvements colonisés par au moins une entérobactérie. Au total, la recherche systématique d’EBLSE dans les PVD a permis une augmentation de 27,7 % du nombre de patients identifiés comme porteurs de ces bactéries. D’autres études pourraient être utiles pour évaluer l’intérêt de mettre en place une telle stratégie comme alternative au dépistage rectal habituellement pratiqué
Brain dynamics of meal size selection in humans.
Although neuroimaging research has evidenced specific responses to visual food stimuli based on their nutritional quality (e.g., energy density, fat content), brain processes underlying portion size selection remain largely unexplored. We identified spatio-temporal brain dynamics in response to meal images varying in portion size during a task of ideal portion selection for prospective lunch intake and expected satiety. Brain responses to meal portions judged by the participants as 'too small', 'ideal' and 'too big' were measured by means of electro-encephalographic (EEG) recordings in 21 normal-weight women. During an early stage of meal viewing (105-145ms), data showed an incremental increase of the head-surface global electric field strength (quantified via global field power; GFP) as portion judgments ranged from 'too small' to 'too big'. Estimations of neural source activity revealed that brain regions underlying this effect were located in the insula, middle frontal gyrus and middle temporal gyrus, and are similar to those reported in previous studies investigating responses to changes in food nutritional content. In contrast, during a later stage (230-270ms), GFP was maximal for the 'ideal' relative to the 'non-ideal' portion sizes. Greater neural source activity to 'ideal' vs. 'non-ideal' portion sizes was observed in the inferior parietal lobule, superior temporal gyrus and mid-posterior cingulate gyrus. Collectively, our results provide evidence that several brain regions involved in attention and adaptive behavior track 'ideal' meal portion sizes as early as 230ms during visual encounter. That is, responses do not show an increase paralleling the amount of food viewed (and, in extension, the amount of reward), but are shaped by regulatory mechanisms
Histogram Monte Carlo study of next-nearest-neighbor Ising antiferromagnet on a stacked triangular lattice
Critical properties of the Ising model on a stacked triangular lattice, with
antiferromagnetic first and second-neighbor in-plane interactions, are studied
by extensive histogram Monte Carlo simulations. The results, in conjunction
with the recently determined phase diagram, strongly suggest that the
transition from the period-3 ordered state to the paramagnetic phase remains in
the xy universality class. This conclusion is in contrast with a previous
suggestion of mean-field tricritical behavior.Comment: 13 pages (RevTex 3.0), 10 figures available upon request, CRPS-93-0
An Elementary Approach to Filtering in Systems with Fractional Brownian Observation Noise
The problem of optimal filtering is addressed for a signal observed through a possibly nonlinear channel driven by a fractional Brownian motion. An elementary and completely self-contained approach is developed. An appropriate Girsanov type result is proved and a process -- equivalent to the innovation process in the usual situation where the observation noise is a Brownian motion -- is introduced. Zakai's approach is partly extended to derive filtering equations when the signal process is a diffusion. The case of conditionally Gaussian linear systems is analyzed. Closed form equations are derived both for the mean of the optimal filter and the conditional variance of the filtering error. The results are explicit in various special cases
An Empirical Process Central Limit Theorem for Multidimensional Dependent Data
Let be the empirical process associated to an
-valued stationary process . We give general conditions,
which only involve processes for a restricted class of
functions , under which weak convergence of can be
proved. This is particularly useful when dealing with data arising from
dynamical systems or functional of Markov chains. This result improves those of
[DDV09] and [DD11], where the technique was first introduced, and provides new
applications.Comment: to appear in Journal of Theoretical Probabilit
Integrable structure of Ginibre's ensemble of real random matrices and a Pfaffian integration theorem
In the recent publication [E. Kanzieper and G. Akemann, Phys. Rev. Lett. 95, 230201 (2005)], an exact solution was reported for the probability p_{n,k} to find exactly k real eigenvalues in the spectrum of an nxn real asymmetric matrix drawn at
random from Ginibre's Orthogonal Ensemble (GinOE). In the present paper, we offer a detailed derivation of the above result by concentrating on the proof of the Pfaffian integration theorem, the
key ingredient of our analysis of the statistics of real eigenvalues in the GinOE. We also initiate a study of the correlations of complex eigenvalues and derive a formula for the joint probability density function of all complex eigenvalues of a
GinOE matrix restricted to have exactly k real eigenvalues. In the particular case of k=0, all correlation functions of complex eigenvalues are determined
Magnetic Phase Diagram of the Ferromagnetically Stacked Triangular Ising Antiferromagnet
Histogram Monte-Carlo simulation results are presented for the magnetic-field
-- temperature phase diagram of the Ising model on a stacked triangular lattice
with antiferromagnetic intraplane and ferromagnetic interplane interactions.
Finite-size scaling results for this frustrated system at three points along
the paramagnetic transition boundary are presented which strongly suggest a
line of triciritcal points at low field and a first-order transition line at
higher fields. These results are compared with the corresponding phase diagrams
from conventional mean-field theory as well as from the Monte Carlo mean-field
calculations of Netz and Berker [Phys. Rev. Lett. {\bf 66}, 377 (1991)].Comment: 6 pages (RevTex 3.0), 8 figures available upon reques
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