2,038 research outputs found
Superfluidity in a Doped Helium Droplet
Path Integral Monte Carlo calculations of the superfluid density throughout
^4He droplets doped with linear impurities (HCN)_n are presented. After
deriving a local estimator for the superfluid density distribution, we find a
decreased superfluid response in the first solvation layer. This effective
normal fluid exhibits temperature dependence similar to that of a
two-dimensional helium system.Comment: 4 pages, 6 figure
Bose Condensation at He-4 Interfaces
Path Integral Monte Carlo was used to calculate the Bose-Einstein condensate fraction at the surface of a helium film at T = 0:77 K, as a function of density. Moving from the center of the slab to the surface, the condensate fraction was found to initially increase with decreasing density to a maximum value of 0.9, before decreasing. Long wavelength density correlations were observed in the static structure factor at the surface of the slab. A surface dispersion relation was calculated from imaginary-time density-density correlations. Similar calculations of the superfluid density throughout He-4 droplets doped with linear impurities (HCN)(sub n) are presented. After deriving a local estimator for the superfluid density distribution, we find a decreased superfluid response in the first solvation layer. This effective normal fluid exhibits temperature dependence similar to that of a two-dimensional helium system
An integrated study of earth resources in the State of California using remote sensing techniques
The author has identified the following significant results. The supply, demand, and impact relationships of California's water resources as exemplified by the Feather River project and other aspects of the California Water Plan are discussed
Bose-Einstein Condensation at a Helium Surface
Path Integral Monte Carlo was used to calculate the Bose-Einstein condensate
fraction at the surface of a helium film at , as a function of
density. Moving from the center of the slab to the surface, the condensate
fraction was found to initially increase with decreasing density to a maximum
value of 0.9 before decreasing. Long wavelength density correlations were
observed in the static structure factor at the surface of the slab. Finally, a
surface dispersion relation was calculated from imaginary-time density-density
correlations.Comment: 8 pages, 5 figure
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Understanding the Mechanism of Human P450 CYP1A2 Using Coupled Quantum-Classical Simulations in a Dynamical Environment
The reaction mechanism of the human P450 CYP1A2 enzyme plays a fundamental role in understanding the effects of environmental carcinogens and mutagens on humans. Despite extensive experimental research on this enzyme system, key questions regarding its catalytic cycle and oxygen activation mechanism remain unanswered. In order to elucidate the reaction mechanism in human P450, new computational methods are needed to accurately represent this system. To enable us to perform computational simulations of unprecedented accuracy on these systems, we developed a dynamic quantum-classical (QM/MM) hybrid method, in which ab initio molecular dynamics are coupled with classical molecular mechanics. This will provide the accuracy needed to address such a complex, large biological system in a fully dynamic environment. We also present detailed calculations of the P450 active site, including the relative charge transfer between iron porphine and tetraphenyl porphyrin
The Debye-Waller Factor in solid 3He and 4He
The Debye-Waller factor and the mean-squared displacement from lattice sites
for solid 3He and 4He were calculated with Path Integral Monte Carlo at
temperatures between 5 K and 35 K, and densities between 38 nm^(-3) and 67
nm^(-3). It was found that the mean-squared displacement exhibits finite-size
scaling consistent with a crossover between the quantum and classical limits of
N^(-2/3) and N^(-1/3), respectively. The temperature dependence appears to be
T^3, different than expected from harmonic theory. An anisotropic k^4 term was
also observed in the Debye-Waller factor, indicating the presence of
non-Gaussian corrections to the density distribution around lattice sites. Our
results, extrapolated to the thermodynamic limit, agree well with recent values
from scattering experiments.Comment: 5 figure
Molar volume of solid isotopic helium mixtures
Solid isotopic helium mixtures have been studied by path-integral Monte Carlo
simulations in the isothermal-isobaric ensemble. This method allowed us to
study the molar volume as a function of temperature, pressure, and isotopic
composition. At 25 K and 0.2 GPa, the relative difference between molar volumes
of isotopically-pure crystals of 3He and 4He is found to be about 3%. This
difference decreases under pressure, and for 12 GPa it is smaller than 1%. For
isotopically-mixed crystals, a linear relation between lattice parameters and
concentrations of helium isotopes is found, in agreement with Vegard's law. The
virtual crystal approximation, valid for isotopic mixtures of heavier atoms,
does not give reliable results for solid solutions of helium isotopes.Comment: 7 pages, 5 figure
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