2,644 research outputs found
State-dependent Jastrow correlation functions for 4He nuclei
We calculate the ground-state energy for the nucleus 4He with V4 nucleon
interactions, making use of a Jastrow description of the corresponding
wavefunction with state-dependent correlation factors. The effect related to
the state dependence of the correlation is quite important, lowering the upper
bound for the ground-state energy by some 2 MeV.Comment: 10 pages, REVTeX, to be published in J. Phys. G: Nucl. Part. Phy
Neutron matter at zero temperature with auxiliary field diffusion Monte Carlo
The recently developed auxiliary field diffusion Monte Carlo method is
applied to compute the equation of state and the compressibility of neutron
matter. By combining diffusion Monte Carlo for the spatial degrees of freedom
and auxiliary field Monte Carlo to separate the spin-isospin operators, quantum
Monte Carlo can be used to simulate the ground state of many nucleon systems
(A\alt 100). We use a path constraint to control the fermion sign problem. We
have made simulations for realistic interactions, which include tensor and
spin--orbit two--body potentials as well as three-nucleon forces. The Argonne
and two nucleon potentials plus the Urbana or Illinois
three-nucleon potentials have been used in our calculations. We compare with
fermion hypernetted chain results. We report results of a Periodic Box--FHNC
calculation, which is also used to estimate the finite size corrections to our
quantum Monte Carlo simulations. Our AFDMC results for models of pure
neutron matter are in reasonably good agreement with equivalent Correlated
Basis Function (CBF) calculations, providing energies per particle which are
slightly lower than the CBF ones. However, the inclusion of the spin--orbit
force leads to quite different results particularly at relatively high
densities. The resulting equation of state from AFDMC calculations is harder
than the one from previous Fermi hypernetted chain studies commonly used to
determine the neutron star structure.Comment: 15 pages, 15 tables and 5 figure
surface interpolation and 3d relatability
Although the role of surface-level processes has been demonstrated, visual interpolation models often emphasize contour relationships. We report two experiments on geometric constraints governing 3D interpolation between surface patches without visible edges. Observers were asked to classify pairs of planar patches specified by random dot disparities and visible through circular apertures (aligned or misaligned) in a frontoparallel occluder. On each trial, surfaces appeared in parallel or converging planes with vertical (in Experiment 1) or horizontal (in Experiment 2) tilt and variable amounts of slant. We expected the classification task to be facilitated when patches were perceived as connected. We found enhanced sensitivity and speed for 3D relatable vs. nonrelatable patches. Here 3D relatability does not involve oriented edges but rather inducing patches' orientations computed from stereoscopic information. Performance was markedly affected by slant anisotropy: both sensitivity and speed were worse for patches with horizontal tilt. We found nearly identical advantages of 3D relatability on performance, suggesting an isotropic unit formation process. Results are interpreted as evidence that inducing slant constrains surface interpolation in the absence of explicit edge information: 3D contour and surface interpolation processes share common geometric constraints as formalized by 3D relatability
Microscopic calculation of the equation of state of nuclear matter and neutron star structure
We present results for neutron star models constructed with a new equation of
state for nuclear matter at zero temperature. The ground state is computed
using the Auxiliary Field Diffusion Monte Carlo (AFDMC) technique, with
nucleons interacting via a semi-phenomenological Hamiltonian including a
realistic two-body interaction. The effect of many-body forces is included by
means of additional density-dependent terms in the Hamiltonian. In this letter
we compare the properties of the resulting neutron-star models with those
obtained using other nuclear Hamiltonians, focusing on the relations between
mass and radius, and between the gravitational mass and the baryon number.Comment: modified version with a slightly different Hamiltonian and
parametrization of the EO
Spin susceptibility of neutron matter at zero temperature
The Auxiliary Field Diffusion Monte Carlo method is applied to compute the
spin susceptibility and the compressibility of neutron matter at zero
temperature. Results are given for realistic interactions which include both a
two-body potential of the Argonne type and the Urbana IX three-body potential.
Simulations have been carried out for about 60 neutrons. We find an overall
reduction of the spin susceptibilty by about a factor 3 with respect to the
Pauli susceptibility for a wide range of densities. Results for the
compressibility of neutron matter are also presented and compared with other
available estimates obtained for semirealistic nucleon-nucleon interactions by
using other techniques
Ab Initio Treatments of the Ising Model in a Transverse Field
In this article, new results are presented for the zero-temperature
ground-state properties of the spin-half transverse Ising model on various
lattices using three different approximate techniques. These are, respectively,
the coupled cluster method, the correlated basis function method, and the
variational quantum Monte Carlo method. The methods, at different levels of
approximation, are used to study the ground-state properties of these systems,
and the results are found to be in excellent agreement both with each other and
with results of exact calculations for the linear chain and results of exact
cumulant series expansions for lattices of higher spatial dimension. The
different techniques used are compared and contrasted in the light of these
results, and the constructions of the approximate ground-state wave functions
are especially discussed.Comment: 28 Pages, 4 Figures, 1 Tabl
Low-risk prostate cancer selected for active surveillance with negative MRI at entry: can repeat biopsies at 1 year be avoided? A pilot study
Purpose: In patients considered for active surveillance (AS), the use of MRI and targeted biopsies (TB) at entry challenges the approach of routine “per protocol” repeat systematic biopsies (SB) at 1 year. This pilot study aimed to assess whether an approach of performing repeat biopsies only if PSA kinetics are abnormal would be safe and sufficient to detect progression. /
Methods: Prospective single-centre study of 149 patients on AS with low-risk PCa, a negative MRI at entry, followed for a minimum of 12 months between 01/2007 and 12/2015. Group 1 (n = 78) patients had per-protocol 12-month repeat SB; group 2 (n = 71) patients did not. Surveillance tests for tumour progression were for both groups: for cause SB and MRI-TB biopsies if PSA velocity (PSA-V) > 0.75 ng/ml/year, or PSA doubling time (PSADT) < 3 years. The main objectives are to compare the 2-year rates of tumour progression and AS discontinuation between groups. The secondary objectives are to estimate the diagnostic power of PSA-V and PSA-DT, to predict the risk of tumour progression. /
Results: Overall, 21 out of 149 patients (14.1%) showed tumour progression, 17.1% for group 1 and 12.3% for group 2, and 31 (21.2%) discontinued AS at 2 years. There was no difference between the 2 groups (p = 0.56). The area under the PSA-V and PSADT curves to predict tumour progression was 0.92 and 0.83, respectively. /
Conclusions: We did not find any significant difference for progression and AS discontinuation rate between the 2 groups. The PSA kinetic seems accurate as a marker of tumour progression. These results support the conduct of a multi-centre prospective trial to confirm these findings
"Outfow occlusion" para parada circulatória em cães
The purpose of this study was to evaluate the possibility of producing circulatory arrest by occlusion of the pulmonary trunk as an alternative to the venous inflow occlusion through the left hemithorax. Eight healthy mongrel dogs were divided in two groups. Group I underwent 4 minutes of outflow occlusion and Group II was submitted to 8 minutes of circulatory arrest. Outflow occlusion was performed through left thoracotomy and pericardiotomy by passing a Rumel tourniquet around the pulmonary trunk. Physical examination, electrocardiography, echocardiography, blood gas analyses, hemodynamic, and oxygen transport variables were obtained before and after the procedure. The dogs from Group I did not have any clinical, electrocardiographic, echocardiographic, or hemo-dynamic abnormalities after anesthetic recover. In the Group II, only one dog survived, which had no clinical, electrocardiographic, or echocardiographic abnormalities. In this last dog, just after releasing the occlusion, it was detected increases in the following parameters: heart rate (HR), systolic, diastolic and mean arterial blood pressure (SAP; DAP; MAP), pulmonary artery pressure (PAP), pulmonary wedge pressure (PWP), central venous pressure (CVP), cardiac output (CO), systolic index (SI), cardiac index (CI), left and right ventricular stroke work (LVSW; RVSW), oxygen delivery index (DO2), oxygen consumption index (VO2), and oxygen extraction (O2 ext). Moreover, the oxygen content of arterial and mixed venous blood (CaO2; CvO2), and the arterial and mixed venous partial pressure of oxygen (PaO2; PvO2) were decreased 5 minutes after circulatory arrest. Outflow occlusion is a feasible surgical procedure for period of 4 minutes of circulatory arrest.O objetivo deste estudo foi avaliar a possibilidade de se produzir uma parada circulatória pela oclusão do tronco pulmonar, como alternativa ao "inflow occlusion", pelo hemitórax esquerdo. Oito cães sem raça definida foram divididos em dois grupos. O Grupo I foi submetido a quatro minutos de parada circulatória e o Grupo II, a 8 minutos de parada. Realizou-se o "outflow occlusion" por meio de toracotomia intercostal esquerda e pericardiotomia, passando-se um torniquete de Rumel ao redor do tronco pulmonar. Foram realizados exame físico, eletrocardiografia, ecocardiografia, hemogasometria, avaliação hemodinâmica e cálculo de variáveis de transporte de oxigênio, antes e após o procedimento. Os cães do Grupo I não sofreram alterações clínicas, eletrocardiográficas, ecocardiográficas e hemodinâmicas após a recuperação anestésica. No Grupo II, apenas um animal sobreviveu, sem apresentar alterações clínicas, eletrocardiográficas e ecocardiográficas. Neste cão, após a liberação do torniquete, houve aumento nas seguintes variáveis: freqüência cardíaca, pressões arteriais sistólica, média e diastólica, pressão arterial pulmonar, pressão da artéria pulmonar ocluída, pressão venosa central, débito cardíaco, índice sistólico, índice cardíaco, trabalho ventricular esquerdo e direito, índice de transporte de oxigênio, índice de consumo de oxigênio e taxa de extração de oxigênio. O conteúdo de oxigênio arterial e venoso misto e a pressão parcial de oxigênio arterial e venosa mista diminuíram, cinco minutos após a parada circulatória. Concluiu-se que o "outflow occlusion" é um procedimento viável para a realização de parada circulatória por um período de quatro minutos.Fundação para o Amparo da Pesquisa no Estado de São Paulo (FAPESP
The Role of Final State Interactions in Quasielastic Fe Reactions at large
A relativistic finite nucleus calculation using a Dirac optical potential is
used to investigate the importance of final state interactions [FSI] at large
momentum transfers in inclusive quasielastic electronuclear reactions. The
optical potential is derived from first-order multiple scattering theory and
then is used to calculate the FSI in a nonspectral Green's function doorway
approach. At intermediate momentum transfers excellent predictions of the
quasielastic Fe experimental data for the longitudinal response
function are obtained. In comparisons with recent measurements at ~GeV/c the theoretical calculations of give good agreement for
the quasielastic peak shape and amplitude, but place the position of the peak
at an energy transfer of about ~MeV higher than the data.Comment: 13 pages typeset using revtex 3.0 with 6 postscript figures in
accompanying uuencoded file; submitted to Phys. Rev.
Colour filtering in a-SiC : H based p-i-n-p-i-n cells: A trade-off between bias polarity and absorption regions
A large area colour imager optically addressed is presented. The colour imager consists of a thin wide band gap p-i-n a-SiC:H filtering element deposited on the top of a thick large area a-SiC:H(-p)/a-Si:H(-i)/a-SiC:H(-n) image sensor, which reveals itself an intrinsic colour filter. In order to tune the external applied voltage for full colour discrimination the photocurrent generated by a modulated red light is measured under different optical and electrical bias. Results reveal that the integrated device behaves itself as an imager and a filter giving information not only on the position where the optical image is absorbed but also on it wavelength and intensity.
The amplitude and sign of the image signals are electrically tuneable. In a wide range of incident fluxes and under reverse bias, the red and blue image signals are opposite in sign and the green signal is suppressed allowing blue and red colour recognition. The green information is obtained under forward bias, where the blue signal goes down to zero and the red and green remain constant. Combining the information obtained at this two applied voltages a RGB colour image picture can be acquired without the need of the usual colour filters or pixel architecture. A numerical simulation supports the colour filter analysis
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