57 research outputs found
Comment on "Diffusion Monte Carlo study of jellium surfaces: Electronic densities and pair correlation functions"
In a fixed-node diffusion Monte Carlo calculation of the total energy of
jellium slabs, Acioli and Ceperley [Phys. Rev. B {\bf 54}, 17199 (1996)]
reported jellium surface energies that at low electron densities were
significantly higher than those predicted in the local-density approximation
(LDA) of density-functional theory. Assuming that the fixed-node error in the
slab and the bulk calculations cancel out, we show that their data yield
surface energies that are considerably closer to the LDA and in reasonable
agreement with those obtained in the random-phase approximation.Comment: 3 pages, 2 figures, to appear in Phys. Rev.
Correlation energies of inhomogeneous many-electron systems
We generalize the uniform-gas correlation energy formalism of Singwi, Tosi,
Land and Sjolander to the case of an arbitrary inhomogeneous many-particle
system. For jellium slabs of finite thickness with a self-consistent LDA
groundstate Kohn-Sham potential as input, our numerical results for the
correlation energy agree well with diffusion Monte Carlo results. For a helium
atom we also obtain a good correlation energy.Comment: 4 pages,1 figur
Quantum Monte Carlo calculations of the one-body density matrix and excitation energies of silicon
Quantum Monte Carlo (QMC) techniques are used to calculate the one-body
density matrix and excitation energies for the valence electrons of bulk
silicon. The one-body density matrix and energies are obtained from a
Slater-Jastrow wave function with a determinant of local density approximation
(LDA) orbitals. The QMC density matrix evaluated in a basis of LDA orbitals is
strongly diagonally dominant. The natural orbitals obtained by diagonalizing
the QMC density matrix resemble the LDA orbitals very closely. Replacing the
determinant of LDA orbitals in the wave function by a determinant of natural
orbitals makes no significant difference to the quality of the wave function's
nodal surface, leaving the diffusion Monte Carlo energy unchanged. The Extended
Koopmans' Theorem for correlated wave functions is used to calculate excitation
energies for silicon, which are in reasonable agreement with the available
experimental data. A diagonal approximation to the theorem, evaluated in the
basis of LDA orbitals, works quite well for both the quasihole and
quasielectron states. We have found that this approximation has an advantageous
scaling with system size, allowing more efficient studies of larger systems.Comment: 13 pages, 4 figures. To appear in Phys. Rev.
Two-dimensional limit of exchange-correlation energy functional approximations in density functional theory
We investigate the behavior of three-dimensional (3D) exchange-correlation
energy functional approximations of density functional theory in anisotropic
systems with two-dimensional (2D) character. Using two simple models, quasi-2D
electron gas and two-electron quantum dot, we show a {\it fundamental
limitation} of the local density approximation (LDA), and its semi-local
extensions, generalized gradient approximation (GGA) and meta-GGA (MGGA), the
most widely used forms of which are worse than the LDA in the strong 2D limit.
The origin of these shortcomings is in the inability of the local (LDA) and
semi-local (GGA/MGGA) approximations to describe systems with 2D character in
which the nature of the exchange-correlation hole is very nonlocal. Nonlocal
functionals provide an alternative approach, and explicitly the average density
approximation (ADA) is shown to be remarkably accurate for the quasi-2D
electron gas system. Our study is not only relevant for understanding of the
functionals but also practical applications to semiconductor quantum structures
and materials such as graphite and metal surfaces. We also comment on the
implication of our findings to the practical device simulations based on the
(semi-)local density functional method.Comment: 21 pages including 9 figures, to be published in Phys. Rev.
Correlation energy of a two-dimensional electron gas from static and dynamic exchange-correlation kernels
We calculate the correlation energy of a two-dimensional homogeneous electron
gas using several available approximations for the exchange-correlation kernel
entering the linear dielectric response of the system.
As in the previous work of Lein {\it et al.} [Phys. Rev. B {\bf 67}, 13431
(2000)] on the three-dimensional electron gas, we give attention to the
relative roles of the wave number and frequency dependence of the kernel and
analyze the correlation energy in terms of contributions from the plane. We find that consistency of the kernel with the electron-pair
distribution function is important and in this case the nonlocality of the
kernel in time is of minor importance, as far as the correlation energy is
concerned. We also show that, and explain why, the popular Adiabatic Local
Density Approximation performs much better in the two-dimensional case than in
the three-dimensional one.Comment: 9 Pages, 4 Figure
Alternative Complement Pathway Deregulation Is Correlated with Dengue Severity
BACKGROUND:The complement system, a key component that links the innate and adaptive immune responses, has three pathways: the classical, lectin, and alternative pathways. In the present study, we have analyzed the levels of various complement components in blood samples from dengue fever (DF) and dengue hemorrhagic fever (DHF) patients and found that the level of complement activation is associated with disease severity. METHODS AND RESULTS:Patients with DHF had lower levels of complement factor 3 (C3; p = 0.002) and increased levels of C3a, C4a and C5a (p<0.0001) when compared to those with the less severe form, DF. There were no significant differences between DF and DHF patients in the levels of C1q, immunocomplexes (CIC-CIq) and CRP. However, small but statistically significant differences were detected in the levels of MBL. In contrast, the levels of two regulatory proteins of the alternative pathway varied widely between DF and DHF patients: DHF patients had higher levels of factor D (p = 0.01), which cleaves factor B to yield the active (C3bBb) C3 convertase, and lower levels of factor H (p = 0.03), which inactivates the (C3bBb) C3 convertase, than did DF patients. When we considered the levels of factors D and H together as an indicator of (C3bBb) C3 convertase regulation, we found that the plasma levels of these regulatory proteins in DHF patients favored the formation of the (C3bBb) C3 convertase, whereas its formation was inhibited in DF patients (p<0.0001). CONCLUSION:The data suggest that an imbalance in the levels of regulatory factors D and H is associated with an abnormal regulation of complement activity in DHF patients
Quantum Monte Carlo simulations of solids
Published versio
A gente é um passador de informação: práticas educativas de agentes de combate a endemias no serviço de controle de zoonoses em Belo Horizonte, MG
As zoonoses ocupam importante lugar entre as causas de adoecimento no Brasil. A revisão histórica das diretrizes dos programas governamentais de controle destas enfermidades revela avanços, mas a sua operacionalização no âmbito estadual e municipal depende de fatores socioambientais, institucionais e epidemiológicos. Esta pesquisa objetiva analisar as práticas educativas desenvolvidas por agentes de combate a endemias (ACEs), a partir de um estudo de caso numa região de Belo Horizonte, MG. A investigação envolveu análise documental, dois meses de observação participante da rotina de trabalho dos agentes e entrevistas com 16 ACEs e dois coordenadores do serviço. A região apresentou diversos elementos ambientais, socioeconômicos e culturais associados à ocorrência de zoonoses, mas tais fatores não foram considerados nas orientações dos ACEs aos moradores. Nas ações educativas, predomina a transmissão de informações técnico-cientÃficas relacionadas ao controle de focos, criadouros de vetores e reservatórios de zoonoses; os saberes e a lógica popular não são valorizados. Apesar da centralidade do papel educativo dos ACEs no discurso institucional, as atividades educativas dos agentes são limitadas diante das lacunas na formação profissional, na estrutura organizacional do serviço e no modelo de gerenciamento, pautado em indicadores quantitativos de produtividade. Para compreender a resistência da população ao discurso técnico-cientÃfico e incrementar as atividades educativas dos ACEs, é preciso mudar a organização do serviço e desenvolver cursos de formação dos ACEs, centrados na multideterminação do processo saúde-doença, na importância do contexto socioeconômico e ambiental no controle das zoonoses e na educação participativa.Zoonoses have an important place among illnesses causes in Brazil. A historical review of governmental programs guidelines to control such diseases reveals advances, but their implementation at the municipal and state level depends on socio-environmental factors and on institutional and epidemiological characteristics. This research aims to analyze the educational practices developed by agents that fight endemic diseases (ACE) through a case study in one of Belo Horizonte’s burroughs, MG. The research involved documental analysis, two months of observation of ACE work and interviews with 16 ACE and two coordinators of the service. The region presented several environmental, socioeconomics and cultural elements associated with the occurrence of zoonoses, but these factors were not considered by ACE. The educational activities’ developed by them were based on the transmission of technical-scientific information related to the control of zoonoses’ vectors and reservoirs ; the knowledge of the population was not valued. In spite of the central place attributed to ACE’s educational activities in the institutional discourse, those actions are limited by gaps in their training process and by the organizational structure of the service and management model, based on quantitative indicators of productivity. In order to understand the resistance of the population to technical-scientific discourse and to improve ACE’s educational activities it is necessary to review the service organization and to develop a training process for them based on the multiple determinations of health-disease process, on the importance of environmental and socioeconomic contexts in zoonoses control and on participatory education
Optics and Quantum Electronics
Contains table of contents for Section 3, reports on twenty-one research projects and a list of publications and meeting papers.Joint Services Electronics Program Contract DAAL03-92-C-0001U.S. Air Force - Office of Scientific Research Contract F49620-91-C-0091Charles S. Draper Laboratories Contract DL-H-441692MIT Lincoln LaboratoryNational Science Foundation Grant ECS 90-12787Fujitsu LaboratoriesU.S. Navy - Office of Naval Research Grant N00014-92-J-1302National Center for Integrated Photonic TechnologyNational Science Foundation Grant ECS 85-52701U.S. Navy - Office of Naval Research (MFEL) Grant N00014-91-C-0084U.S. Navy - Office of Naval Research (MFEL) Grant N00014-91-J-1956National Institutes of Health Grant R01-GM35459-08U.S. Air Force - Office of Scientific Research Grant F49620-93-1-0301MIT Lincoln Laboratory Contract BX-5098Electric Power Research Institute Contract RP3170-2
Optics and Quantum Electronics
Contains table of contents for Section 2 and reports on eleven research projects.Joint Services Electronics Program Contract DAAL03-89-C-0001National Science Foundation Grant EET 87-00474U.S. Air Force - Office of Scientific Research Contract F49620-88-C-0089Charles S. Draper Laboratory Contract DL-H-404179National Center for Integrated PhotonicsNational Science Foundation Grant ECS 87-18417NEC Research InstituteNational Science Foundation Grant ECS 85-52701Medical Free Electron Laser Program Contract N00014-86-K-0117National Institutes of Health Grant 5-RO1-GM35459Lawrence Livermore National Laboratory Contract B048704U.S. Department of Energy Grant DE-FG02-89-ER14012Columbia University Contract P016310
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