79 research outputs found
Swimming pool deck as environmental reservoir of Fusarium
While investigations on fungal contamination of swimming pools usually focus on dermatophytes, data on other potentially pathogenic molds are scarce. Here, we report the investigation of fungal colonization of the deck surrounding a hospital physical therapy swimming pool. Five series of samples from 8 sites were collected over one year from the pool surroundings. Concomitantly, 58 patients using the swimming pool were examined and samples obtained from those with suspected onychomycosis. All surface samples were positive for fungi, with Fusarium the most frequently recovered from 22 of 27 samples of sites surrounding the pool. Among the outpatients evaluated, two presented with a mixed onychomycosis from which Fusarium and Trichophyton rubrum were isolated. The questions of possible acquisition from the swimming pool area must be considered in both cases as the ungual lesions had developed within the previous three months. This warrants further studies to better understand the epidemiology of potentially pathogenic molds in areas surrounding pools in order to adopt appropriate measures to avoid contamination. This is of particular importance within medical institutions, considering the potential role of Fusarium onychomycosis as a starting point for disseminated infections in immunocompromised patient
Data-Discriminants of Likelihood Equations
Maximum likelihood estimation (MLE) is a fundamental computational problem in
statistics. The problem is to maximize the likelihood function with respect to
given data on a statistical model. An algebraic approach to this problem is to
solve a very structured parameterized polynomial system called likelihood
equations. For general choices of data, the number of complex solutions to the
likelihood equations is finite and called the ML-degree of the model. The only
solutions to the likelihood equations that are statistically meaningful are the
real/positive solutions. However, the number of real/positive solutions is not
characterized by the ML-degree. We use discriminants to classify data according
to the number of real/positive solutions of the likelihood equations. We call
these discriminants data-discriminants (DD). We develop a probabilistic
algorithm for computing DDs. Experimental results show that, for the benchmarks
we have tried, the probabilistic algorithm is more efficient than the standard
elimination algorithm. Based on the computational results, we discuss the real
root classification problem for the 3 by 3 symmetric matrix~model.Comment: 2 table
Charging effects in the ac conductance of a double barrier resonant tunneling structure
There have been many studies of the linear response ac conductance of a
double barrier resonant tunneling structure (DBRTS). While these studies are
important, they fail to self-consistently include the effect of time dependent
charge density in the well. In this paper, we calculate the ac conductance by
including the effect of time dependent charge density in the well in a
self-consistent manner. The charge density in the well contributes to both the
flow of displacement currents and the time dependent potential in the well. We
find that including these effects can make a significant difference to the ac
conductance and the total ac current is not equal to the average of
non-selfconsitently calculated conduction currents in the two contacts, an
often made assumption. This is illustrated by comparing the results obtained
with and without the effect of the time dependent charge density included
properly
A topological Dirac insulator in a quantum spin Hall phase : Experimental observation of first strong topological insulator
When electrons are subject to a large external magnetic field, the
conventional charge quantum Hall effect \cite{Klitzing,Tsui} dictates that an
electronic excitation gap is generated in the sample bulk, but metallic
conduction is permitted at the boundary. Recent theoretical models suggest that
certain bulk insulators with large spin-orbit interactions may also naturally
support conducting topological boundary states in the extreme quantum limit,
which opens up the possibility for studying unusual quantum Hall-like phenomena
in zero external magnetic field. Bulk BiSb single crystals are
expected to be prime candidates for one such unusual Hall phase of matter known
as the topological insulator. The hallmark of a topological insulator is the
existence of metallic surface states that are higher dimensional analogues of
the edge states that characterize a spin Hall insulator. In addition to its
interesting boundary states, the bulk of BiSb is predicted to
exhibit three-dimensional Dirac particles, another topic of heightened current
interest. Here, using incident-photon-energy-modulated (IPEM-ARPES), we report
the first direct observation of massive Dirac particles in the bulk of
BiSb, locate the Kramers' points at the sample's boundary and
provide a comprehensive mapping of the topological Dirac insulator's gapless
surface modes. These findings taken together suggest that the observed surface
state on the boundary of the bulk insulator is a realization of the much sought
exotic "topological metal". They also suggest that this material has potential
application in developing next-generation quantum computing devices.Comment: 16 pages, 3 Figures. Submitted to NATURE on 25th November(2007
Self-Similar Interpolation in Quantum Mechanics
An approach is developed for constructing simple analytical formulae
accurately approximating solutions to eigenvalue problems of quantum mechanics.
This approach is based on self-similar approximation theory. In order to derive
interpolation formulae valid in the whole range of parameters of considered
physical quantities, the self-similar renormalization procedure is complimented
here by boundary conditions which define control functions guaranteeing correct
asymptotic behaviour in the vicinity of boundary points. To emphasize the
generality of the approach, it is illustrated by different problems that are
typical for quantum mechanics, such as anharmonic oscillators, double-well
potentials, and quasiresonance models with quasistationary states. In addition,
the nonlinear Schr\"odinger equation is considered, for which both eigenvalues
and wave functions are constructed.Comment: 1 file, 30 pages, RevTex, no figure
Prediction of Anisotropic Single-Dirac-Cones in BiSb Thin Films
The electronic band structures of BiSb thin films can be
varied as a function of temperature, pressure, stoichiometry, film thickness
and growth orientation. We here show how different anisotropic
single-Dirac-cones can be constructed in a BiSb thin film for
different applications or research purposes. For predicting anisotropic
single-Dirac-cones, we have developed an iterative-two-dimensional-two-band
model to get a consistent inverse-effective-mass-tensor and band-gap, which can
be used in a general two-dimensional system that has a non-parabolic dispersion
relation as in a BiSb thin film system
Quantum Energy-Transport and Drift-Diffusion Models
We show that Quantum Energy-Transport and Quantum Drift-Diffusion models can be derived through diffusion limits of a collisional Wigner equation. The collision operator relaxes to an equilibrium defined through the entropy minimization principle. Both models are shown to be entropic and exhibit fluxes which are related with the state variables through spatially non-local relations. Thanks to an � expansion of these models, � 2 perturbations of the Classical Energy-Transport and Drift-Diffusion models are found. In the Drift-Diffusion case, the quantum correction is the Bohm potential and the model is still entropic. In the Energy-Transport case however, the quantum correction is a rather complex expression and the model cannot be proven entropic.
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