4,534 research outputs found
Disorder and the effective Mn-Mn exchange interaction in GaMnAs diluted magnetic semiconductors
We perform a theoretical study, using {\it ab initio} total energy
density-functional calculations, of the effects of disorder on the
exchange interactions for diluted semiconductors. For a 128
atoms supercell, we consider a variety of configurations with 2, 3 and 4 Mn
atoms, which correspond to concentrations of 3.1%, 4.7%, and 6.3%,
respectively. In this way, the disorder is intrinsically considered in the
calculations. Using a Heisenberg Hamiltonian to map the magnetic excitations,
and {\it ab initio} total energy calculations, we obtain the effective \JMn,
from first () all the way up to sixth () neighbors. Calculated
results show a clear dependence in the magnitudes of the \JMn with the Mn
concentration . Also, configurational disorder and/or clustering effects
lead to large dispersions in the Mn-Mn exchange interactions, in the case of
fixed Mn concentration. Moreover, theoretical results for the ground-state
total energies for several configurations indicate the importance of a proper
consideration of disorder in treating temperature and annealing effects
An outlier-resistant -generalized approach for robust physical parameter estimation
In this work we propose a robust methodology to mitigate the undesirable
effects caused by outliers to generate reliable physical models. In this way,
we formulate the inverse problems theory in the context of Kaniadakis
statistical mechanics (or -statistics), in which the classical approach
is a particular case. In this regard, the errors are assumed to be distributed
according to a finite-variance -generalized Gaussian distribution.
Based on the probabilistic maximum-likelihood method we derive a
-objective function associated with the finite-variance
-Gaussian distribution. To demonstrate our proposal's
outlier-resistance, we analyze the robustness properties of the
-objective function with help of the so-called influence function. In
this regard, we discuss the role of the entropic index () associated
with the Kaniadakis -entropy in the effectiveness in inferring physical
parameters by using strongly noisy data. In this way, we consider a classical
geophysical data-inverse problem in two realistic circumstances, in which the
first one refers to study the sensibility of our proposal to uncertainties in
the input parameters, and the second is devoted to the inversion of a seismic
data set contaminated by outliers. The results reveal an optimum -value
at the limit , which is related to the best results.Comment: 37 pages, 23 figure
Montagem do sistema para dosimetria de nêutrons com detectores de bolhas
São descritos a montagem e o procedimento desenvolvido para a aquisição e analise de imagens obtidas com os novos detectores de bolha BDS, para dosimetria de nêutrons ou nas medições de fluência e distribuição de energia de nêutrons de uma instalação nuclear
Mortality due to systemic mycoses as a primary cause of death or in association with AIDS in Brazil: a review from 1996 to 2006
Deaths caused by systemic mycoses such as paracoccidioidomycosis, cryptococcosis, histoplasmosis, candidiasis, aspergillosis, coccidioidomycosis and zygomycosis amounted to 3,583 between 1996-2006 in Brazil. When analysed as the underlying cause of death, paracoccidioidomycosis represented the most important cause of deaths among systemic mycoses (~ 51.2%). When considering AIDS as the underlying cause of death and the systemic mycoses as associated conditions, cryptococcosis (50.9%) appeared at the top of the list, followed by candidiasis (30.2%), histoplasmosis (10.1%) and others. This mortality analysis is useful in understanding the real situation of systemic mycoses in Brazil, since there is no mandatory notification of patients diagnosed with systemic mycoses in the official health system.FAPESPCNP
Schwinger multichannel method: A study of a Feshbach resonance in e-H_2 collisions
We present results of the application of the Schwinger multichannel method to study the role of Feshbach resonances on the elastic and electronic excitation cross sections in e-H_2 collisions. Using a ^2Σ_g^+2 resonance associated with the a ^3Σ^+_g and E^1Σ^+_g states of H_2 as an example, we quantitatively illustrate the dramatic influence of open channels on the decay of such Feshbach resonances in electron-molecule collisions
Polymer optical fiber specklegram strain sensor with extended dynamic range
FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORA polymer optical fiber strain sensor with extended dynamic range is reported. The proposed algorithm resets the reference fiber status depending on the magnitude of the specklegram deviation so the correlation coefficient never saturates, yielding a continuous response over the full range for both positive and negative strains. The technique was evaluated on the measurement of axial strains using a ZEONEX core, poly(methyl methacrylate) cladding multimode fiber, presenting reproducible results with 3 x 10(-3) mu epsilon(-1) sensitivity (similar to 15 mu epsilon resolution) within a 22,600 mu epsilon interval. In contrast to the available approaches, the presented method can retrieve the strain direction and does not require intensive image processing, thus providing a simple and reliable technique for mechanical measurements using multimode optical fibers. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)571119FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIOR2014/50632-62017/25666-2sem informaçãosem informaçã
Semi-automatic rubble counting system for superheated droplet detectors
Neutron dose rate measurements are normally performed by means of PADC, CR-39 and TLD detectors.
Although, none of these devices can give instant reading of the neutron dose, recently new kind of detectors are
being developed, based on the formation of tiny drops in a superheated liquid suspended in a polymer or gel
solution, called superheated droplet detector (SDD) or also as bubble detectors (BD), with no response for
gamma radiation. This work describes the experimental setup and the developed procedures for acquiring and
processing digital images obtained with bubble detector spectrometer (BDS), developed by Bubble Technology
Industries, for personal neutron dosimeter and/or neutron energy fluence measurements in nuclear facilities. The
results of the neutron measurements obtained during the F-18 production, at the RDS-111 cyclotron, are
presented. These neutron measurements were the first ones with this type of BDS detectors in a particle
accelerator facility in Brazil and it was very important to estimate neutron dose rate received by occupationally
exposed individuals
- …