145 research outputs found
Experimental implications of quantum phase fluctuations in layered superconductors
I study the effect of quantum and thermal phase fluctuations on the in-plane
and c-axis superfluid stiffness of layered d-wave superconductors. First, I
show that quantum phase fluctuations in the superconductor can be damped in the
presence of external screening of Coulomb interactions, and suggest an
experiment to test the importance of these fluctuations, by placing a metal in
close proximity to the superconductor to induce such screening. Second, I show
that a combination of quantum phase fluctuations and the linear temperature
dependence of the in-plane superfluid stiffness leads to a linear temperature
dependence of the c-axis penetration depth, below a temperature scale
determined by the magnitude of in-plane dissipation.Comment: 6 pgs, 1 figure, minor changes in comparison with c-axis expt, final
published versio
Effective Actions and Phase Fluctuations in d-wave Superconductors
We study effective actions for order parameter fluctuations at low
temperature in layered d-wave superconductors such as the cuprates. The order
parameter lives on the bonds of a square lattice and has two amplitude and two
phase modes associated with it. The low frequency spectral weights for
amplitude and relative phase fluctuations is determined and found to be
subdominant to quasiparticle contributions. The Goldstone phase mode and its
coupling to density fluctuations in charged systems is treated in a
gauge-invariant manner. The Gaussian phase action is used to study both the
-axis Josephson plasmon and the more conventional in-plane plasmon in the
cuprates. We go beyond the Gaussian theory by deriving a coarse-grained quantum
XY model, which incorporates important cutoff effects overlooked in previous
studies. A variational analysis of this effective model shows that in the
cuprates, quantum effects of phase fluctuations are important in reducing the
zero temperature superfluid stiffness, but thermal effects are small for .Comment: Some numerical estimates corrected and figures changed. to appear in
PRB, Sept.1 (2000
Quantum interference between multiple impurities in anisotropic superconductors
We study the quantum interference between impurities in d-wave
superconductors within a potential scattering formalism that easily applies to
multiple impurities. The evolution of the low-energy local density of states
for both magnetic and nonmagnetic short-ranged scatterers are studied as a
function of the spatial configuration of the impurities. Further we discuss the
influence of subdominant bulk superconducting order parameters on the
interference pattern from multiple impurities.Comment: 4 pages, 6 figure
Natural Orbitals and BEC in traps, a diffusion Monte Carlo analysis
We investigate the properties of hard core Bosons in harmonic traps over a
wide range of densities. Bose-Einstein condensation is formulated using the
one-body Density Matrix (OBDM) which is equally valid at low and high
densities. The OBDM is calculated using diffusion Monte Carlo methods and it is
diagonalized to obtain the "natural" single particle orbitals and their
occupation, including the condensate fraction. At low Boson density, , where and is the hard core diameter, the condensate is
localized at the center of the trap. As increases, the condensate moves
to the edges of the trap. At high density it is localized at the edges of the
trap. At the Gross-Pitaevskii theory of the condensate
describes the whole system within 1%. At corrections are
3% to the GP energy but 30% to the Bogoliubov prediction of the condensate
depletion. At , mean field theory fails. At , the Bosons behave more like a liquid He droplet than a trapped Boson
gas.Comment: 13 pages, 14 figures, submitted Phys. Rev.
Momentum distribution and correlation function of quasicondensates in elongated traps
We calculate the spatial correlation function and momentum distribution of a
phase-fluctuating, elongated three-dimensional condensate, in a trap and in
free expansion. We take the inhomogeneous density profile into account
{\it{via}} a local density approximation. We find an almost Lorentzian momentum
distribution, in stark contrast with a Heisenberg-limited Thomas-Fermi
condensate.Comment: 5 pages, 2 figures; final version, references update
Neutralizing antibody vaccine for pandemic and pre-emergent coronaviruses
Betacoronaviruses (betaCoVs) caused the severe acute respiratory syndrome (SARS) and Middle East Respiratory Syndrome (MERS) outbreaks, and the SARS-CoV-2 pandemic1–4. Vaccines that elicit protective immunity against SARS-CoV-2 and betaCoVs circulating in animals have the potential to prevent future betaCoV pandemics. Here, we show that macaque immunization with a multimeric SARS-CoV-2 receptor binding domain (RBD) nanoparticle adjuvanted with 3M-052/Alum elicited cross-neutralizing antibody (cross-nAb) responses against batCoVs, SARS-CoV-1, SARS-CoV-2, and SARS-CoV-2 variants B.1.1.7, P.1, and B.1.351. Nanoparticle vaccination resulted in a SARS-CoV-2 reciprocal geometric mean neutralization ID50 titer of 47,216, and protection against SARS-CoV-2 in macaque upper and lower respiratory tracts. Importantly, nucleoside-modified mRNA encoding a stabilized transmembrane spike or monomeric RBD also induced SARS-CoV-1 and batCoV cross-nAbs, albeit at lower titers. These results demonstrate current mRNA vaccines may provide some protection from future zoonotic betaCoV outbreaks, and provide a platform for further development of pan-betaCoV vaccines
Interferência e controle de milho voluntário tolerante ao glifosato na cultura da soja
Resumo: O objetivo deste trabalho foi estimar o efeito da infestação de milho voluntário tolerante ao glifosato na produtividade da cultura da soja, bem como avaliar o controle dessas plantas com o herbicida cletodim. Seis experimentos foram desenvolvidos, na safra de 2013/2014, nos estados da Bahia, de Minas Gerais, de Mato Grosso, do Paraná, do Rio Grande do Sul e de São Paulo. Espigas de milho sem palha, segmentadas ao meio, foram uniformemente distribuídas nas parcelas, à densidade de 1, 2 ou 4 segmentos por metro quadrado. Como tratamento herbicida, utilizou-se cletodim, nas seguintes doses: aplicação única, 108 g ha-1, sobre a soja com três trifólios (3T); aplicação única, 108 g ha-1, sobre soja com seis trifólios (6T); e duas aplicações, 108 e 84 g ha-1, sobre soja nos estágios 3T e 6T. Adicionou-se, ainda, um tratamento com a soja plenamente capinada. O aumento de densidade dos segmentos de espiga reduziu a produtividade da soja em até 69,9%. A produtividade da soja foi assegurada com o controle eficaz das plantas voluntárias de milho tolerante ao glifosato, oriundas de espigas, em aplicação única de cletodim (108 g ha-1) no estádio 6T; ou por meio de duas aplicações sequenciais do graminicida, com a soja em 3T e 6T
The Sudbury Neutrino Observatory
The Sudbury Neutrino Observatory is a second generation water Cherenkov
detector designed to determine whether the currently observed solar neutrino
deficit is a result of neutrino oscillations. The detector is unique in its use
of D2O as a detection medium, permitting it to make a solar model-independent
test of the neutrino oscillation hypothesis by comparison of the charged- and
neutral-current interaction rates. In this paper the physical properties,
construction, and preliminary operation of the Sudbury Neutrino Observatory are
described. Data and predicted operating parameters are provided whenever
possible.Comment: 58 pages, 12 figures, submitted to Nucl. Inst. Meth. Uses elsart and
epsf style files. For additional information about SNO see
http://www.sno.phy.queensu.ca . This version has some new reference
Burden and risk factors for Pseudomonas aeruginosa community-acquired pneumonia:a Multinational Point Prevalence Study of Hospitalised Patients
Pseudornonas aeruginosa is a challenging bacterium to treat due to its intrinsic resistance to the antibiotics used most frequently in patients with community-acquired pneumonia (CAP). Data about the global burden and risk factors associated with P. aeruginosa-CAP are limited. We assessed the multinational burden and specific risk factors associated with P. aeruginosa-CAP.
We enrolled 3193 patients in 54 countries with confirmed diagnosis of CAP who underwent microbiological testing at admission. Prevalence was calculated according to the identification of P. aeruginosa. Logistic regression analysis was used to identify risk factors for antibiotic-susceptible and antibiotic-resistant P. aeruginosa-CAP.
The prevalence of P. aeruginosa and antibiotic-resistant P. aeruginosa-CAP was 4.2% and 2.0%, respectively. The rate of P. aeruginosa CAP in patients with prior infection/colonisation due to P. aeruginosa and at least one of the three independently associated chronic lung diseases (i.e. tracheostomy, bronchiectasis and/or very severe chronic obstructive pulmonary disease) was 67%. In contrast, the rate of P. aeruginosa-CAP was 2% in patients without prior P. aeruginosa infection/colonisation and none of the selected chronic lung diseases. The multinational prevalence of P. aeruginosa-CAP is low.
The risk factors identified in this study may guide healthcare professionals in deciding empirical antibiotic coverage for CAP patients
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