14,754 research outputs found
Quantum Monte Carlo simulation of overpressurized liquid 4He
A diffusion Monte Carlo simulation of superfluid He at zero temperature
and pressures up to 275 bar is presented. Increasing the pressure beyond
freezing ( 25 bar), the liquid enters the overpressurized phase in a
metastable state. In this regime, we report results of the equation of state
and the pressure dependence of the static structure factor, the condensate
fraction, and the excited-state energy corresponding to the roton. Along this
large pressure range, both the condensate fraction and the roton energy
decrease but do not become zero. The roton energies obtained are compared with
recent experimental data in the overpressurized regime.Comment: 5 pages, accepted for publication in Phys. Rev. Let
Progress in Monte Carlo calculations of Fermi systems: normal liquid 3He
The application of the diffusion Monte Carlo method to a strongly interacting
Fermi system as normal liquid He is explored. We show that the fixed-node
method together with the released-node technique and a systematic method to
analytically improve the nodal surface constitute an efficient strategy to
improve the calculation up to a desired accuracy. This methodology shows
unambiguously that backflow correlations, when properly optimized, are enough
to generate an equation of state of liquid He in excellent agreement with
experimental data from equilibrium up to freezing.Comment: 14 pages, 3 eps figure
High-quality variational wave functions for small 4He clusters
We report a variational calculation of ground state energies and radii for
4He_N droplets (3 \leq N \leq 40), using the atom-atom interaction HFD-B(HE).
The trial wave function has a simple structure, combining two- and three-body
correlation functions coming from a translationally invariant
configuration-interaction description, and Jastrow-type short-range
correlations. The calculated ground state energies differ by around 2% from the
diffusion Monte Carlo results.Comment: 5 pages, 1 ps figure, REVTeX, submitted to Phys. Rev.
Atomic kinetic energy, momentum distribution and structure of solid neon at zero-temperature
We report on the calculation of the ground-state atomic kinetic energy,
, and momentum distribution of solid Ne by means of the diffusion Monte
Carlo method and Aziz HFD-B pair potential. This approach is shown to perform
notably for this crystal since we obtain very good agreement with respect to
experimental thermodynamic data. Additionally, we study the structural
properties of solid Ne at densities near the equilibrium by estimating the
radial pair-distribution function, Lindemann's ratio and atomic density profile
around the positions of the perfect crystalline lattice. Our value for
at the equilibrium density is K, which agrees perfectly with the
recent prediction made by Timms {\it et al.}, K, based on their
deep-inelastic neutron scattering experiments carried out over the temperature
range K, and also with previous path integral Monte Carlo results
obtained with the Lennard-Jones and Aziz HFD-C2 atomic pairwise interactions.
The one-body density function of solid Ne is calculated accurately and found to
fit perfectly, within statistical uncertainty, to a Gaussian curve.
Furthermore, we analyze the degree of anharmonicity of solid Ne by calculating
some of its microscopic ground-state properties within traditional harmonic
approaches. We provide insightful comparison to solid He in terms of the
Debye model, in order to size the relevance of anharmonic effects in Ne.Comment: 20 pages, 7 figures. To be published in Physical Review
Random forest algorithm for algorithm for prediction of high school science students acceptance snmptn based on students assesment report
National Selection for State University (SNMPTN) is one of the selectionlines for admission of new students in Indonesia to enter State Universities byinvitation. Report card grades are one component of the assessment ofadmission of new students to enter state universities on this pathway. Thedifference in standards between universities in determining the admission ofSNMPTN applicants, causing the need to predict based on several relatedfactors. This research uses data mining techniques with Random forestalgorithm. From the results of research that has been done, it was found thatthe Random Forest algorithm can be used to predict students who are acceptedat SNMPTN based on report card grades, obtained from the results of theclassification process with the student report card report survey datasetreceived by SNMPTN, This is indicated by the accuracy, precision, and recallvalues of 93%. Optimization of the random forest algorithm using theoversampling technique with the SMOTE method can improve the classifier'sperformance due to the imbalanced class problem
Extraction conditions of polyphenol oxidase from banana peel
Polyphenol oxidase (PPO) is an enzyme containing copper, presents in various fruits and vegetables. It is responsible for the browning reactions when the cells are damaged during handling. The best conditions for extraction of polyphenol oxidase from banana peel was by using an extraction buffer containing phosphate buffer (0.05 M, pH 7), 0.01 M ascorbic acid and 0.5% polyethylene glycol, with extraction ratio 1:4 (w:v) for one minute by using blender. The enzyme activity was measured spectrophotometrically at 425 nm. PPO was studied to prevent the browning of banana peel which results in the loss of their marketability. The aim of this study was to determine the optimum conditions for polyphenol oxidase extraction from banana peel
Monte Carlo Calculations for Liquid He at Negative Pressure
A Quadratic Diffusion Monte Carlo method has been used to obtain the equation
of state of liquid He including the negative pressure region down to the
spinodal point. The atomic interaction used is a renewed version (HFD-B(HE)) of
the Aziz potential, which reproduces quite accurately the features of the
experimental equation of state. The spinodal pressure has been calculated and
the behavior of the sound velociy around the spinodal density has been
analyzed.Comment: 10 pages, RevTex 3.0, with 4 PostScript figures include
Scattering length for helium atom-diatom collision
We present results on the scattering lengths of ^4He--^4He_2 and ^3He--^4He_2
collisions. We also study the consequence of varying the coupling constant of
the atom-atom interaction.Comment: Contribution to Proceedings of the International Workshop ``Critical
Stability of Few-Body Quantum Systems'' (Dresden, October 17--22, 2005
Ferromagnetic GaâËâ Mnâ As produced by ion implantation and pulsed-laser melting
We demonstrate the formation of ferromagneticGaâËâMnâAsfilms by Mn ion implantation into GaAs followed by pulsed-laser melting. Irradiation with a single excimer laser pulse results in the epitaxial regrowth of the implanted layer with Mn substitutional fraction up to 80% and effective Curie temperature up to 29 K for samples with a maximum Mn concentration of xâ0.03. A remanent magnetization persisting above 85 K has been observed for samples with xâ0.10, in which 40% of the Mn resides on substitutional lattice sites. We find that the ferromagnetism in GaâËâMnâAs is rather robust to the presence of structural defects.The work at the Lawrence Berkeley National Laboratory
was supported by the Director, Office of Science, Office of
Basic Energy Sciences, Division of Materials Sciences and
Engineering, of the U.S. Department of Energy under Contract
No. DE-AC03-76SF00098. The work at Harvard was
supported by NASA Grant No. NAG8-1680. One of
the authors ~M.A.S.! acknowledges support from an NSF
Graduate Research Fellowship
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