3,214 research outputs found
Coordinate systems for differential correction
System of state transition partial derivatives for which tracking information normal matrix for lunar orbiter is nearly diagonalize
A universal formulation for conic trajectories. Basic variables and relationships
Truncated trigonometric functions for conic trajectory formulation in space flight application
Shape oscillations of a charged diamagnetically-levitated droplet
We investigate the effect of electrical charge on the normal mode frequencies
of electrically-charged diamagnetically levitated water droplets with radii
4.5-7.5 mm using diamagnetic levitation. This technique allows us to levitate
almost spherical droplets and therefore to directly compare the measured
vibrational frequencies of the first seven modes of the charged droplet with
theoretical values calculated by Lord Rayleigh, for which we find good
agreement
Probing the hydrogen melting line at high pressures by dynamic compression
We investigate the capabilities of dynamic compression by intense heavy ion beams to yield information about the high pressure phases of hydrogen. Employing ab initio simulations and experimental data, a new wide range equation of state for hydrogen is constructed. The results show that the melting line up to its maximum as well as the transition from molecular fluids to fully ionized plasmas can be tested with the beam parameters soon to be available. We demonstrate that x-ray scattering can distinguish between phases and dissociation states
Gaussian-Charge Polarizable Interaction Potential for Carbon Dioxide
A number of simple pair interaction potentials of the carbon dioxide molecule
are investigated and found to underestimate the magnitude of the second virial
coefficient in the temperature interval 220 K to 448 K by up to 20%. Also the
third virial coefficient is underestimated by these models. A rigid,
polarizable, three-site interaction potential reproduces the experimental
second and third virial coefficients to within a few percent. It is based on
the modified Buckingham exp-6 potential, an anisotropic Axilrod-Teller
correction and Gaussian charge densities on the atomic sites with an inducible
dipole at the center of mass. The electric quadrupole moment, polarizability
and bond distances are set to equal experiment. Density of the fluid at 200 and
800 bars pressure is reproduced to within some percent of observation over the
temperature range 250 K to 310 K. The dimer structure is in passable agreement
with electronically resolved quantum-mechanical calculations in the literature,
as are those of the monohydrated monomer and dimer complexes using the
polarizable GCPM water potential. Qualitative agreement with experiment is also
obtained, when quantum corrections are included, for the relative stability of
the trimer conformations, which is not the case for the pair potentials.Comment: Error in the long-range correction fixed and three-body dispersion
introduced. 32 pages (incl. title page), 7 figures, 9 tables, double-space
QCD Viscosity to Entropy Density Ratio in the Hadronic Phase
Shear viscosity (eta) of QCD in the hadronic phase is computed by the coupled
Boltzmann equations of pions and nucleons in low temperatures and low baryon
number densities. The eta to entropy density ratio eta/s maps out the nuclear
gas-liquid phase transition by forming a valley tracing the phase transition
line in the temperature-chemical potential plane. When the phase transition
turns into a crossover, the eta/s valley gradually disappears. We suspect the
general feature for a first-order phase transition is that eta/s has a
discontinuity in the bottom of the eta/s valley. The discontinuity coincides
with the phase transition line and ends at the critical point. Beyond the
critical point, a smooth eta/s valley is seen. However, the valley could
disappear further away from the critical point. The eta/s measurements might
provide an alternative to identify the critical points.Comment: 16 pages, 4 figures. Minor typos corrected and references adde
Quantification of Viscosity for Solvents−Heavy Oil/Bitumen Systems in the Presence of Water at High Pressures and Elevated Temperatures
In this study, a new and pragmatic methodology has been developed to accurately predict the viscosity for light solvents (i.e., methane, ethane, propane, n-butane, n-pentane, N2, and CO2)–heavy oil/bitumen/water systems as a function of pressure in the temperature range of 287.9–463.4 K. The LV and ALV (L is the oleic phase, V is the vapor phase, and A is the aqueous phase) phase equilibria of the aforementioned systems are calculated using the Peng–Robinson equation of state (PR EOS) with modified alpha functions and binary interaction parameters (BIPs). The six widely used mixing rules for predicting viscosity of solvents−heavy oil/bitumen systems pertaining to vapor–liquid equilibria are compared and evaluated, while the linear mixing rule is used for hydrocarbons−water mixtures. Plus, effective density is for the first time successfully introduced into the volume-based mixing rules. The volume-based power law, weight-based power law, and weight-based Cragoe’s mixing rules are found to well reproduce the viscosity for the aforementioned systems with AARDs of 15.5%, 19.0%, and 32.6%, respectively. Effective density rather than real density of dissolved gas(es) should be used for all of the volume-based mixing rules, while the adjustable parameter in the power law mixing rule has a potential to achieve high generalization if adequate measurements are made available. Although water has a lower diluting ability than other solvents in the same amount of dissolution, it can outperform methane and CO2 in diluting heavy oil/bitumen at high temperatures due to its high solubility. Addition of water can reduce or increase the viscosity of a solvents–heavy oil/bitumen mixture, depending on the ability of solvents and water to dilute heavy oil/bitumen and effects of water on the solvent dissolution. Water molar fraction in feed can exert an effect on the mixture viscosity in LV equilibria through affecting the solvent dissolution but cannot impose an impact on the mixture viscosity at ALV equilibria
Bulk Viscosity of a Gas of Massless Pions
In the hadronic phase, the dominant configuration of QCD with two flavors of
massless quarks is a gas of massless pions. We calculate the bulk viscosity
(zeta) using the Boltzmann equation with the kinetic theory generalized to
incorporate the trace anomaly. We find that the dimensionless ratio zeta/s, s
being the entropy density, is monotonic increasing below T=120 MeV, where
chiral perturbation theory is applicable. This, combined with previous results,
shows that zeta/s reaches its maximum near the phase transition temperature Tc,
while eta/s, eta being the shear viscosity, reaches its minimum near Tc in QCD
with massless quarks.Comment: 12 pages, 1 figure; the version to appear in PR
Performance of a cryogenic system prototype for the XENON1T Detector
We have developed an efficient cryogenic system with heat exchange and
associated gas purification system, as a prototype for the XENON1T experiment.
The XENON1T detector will use about 3 ton of liquid xenon (LXe) at a
temperature of 175K as target and detection medium for a dark matter search. In
this paper we report results on the cryogenic system performance focusing on
the dynamics of the gas circulation-purification through a heated getter, at
flow rates above 50 Standard Liter per Minute (SLPM). A maximum flow of 114
SLPM has been achieved, and using two heat exchangers in parallel, a heat
exchange efficiency better than 96% has been measured
Statistical Mechanics of Membrane Protein Conformation: A Homopolymer Model
The conformation and the phase diagram of a membrane protein are investigated
via grand canonical ensemble approach using a homopolymer model. We discuss the
nature and pathway of -helix integration into the membrane that results
depending upon membrane permeability and polymer adsorptivity. For a membrane
with the permeability larger than a critical value, the integration becomes the
second order transition that occurs at the same temperature as that of the
adsorption transition. For a nonadsorbing membrane, the integration is of the
first order due to the aggregation of -helices.Comment: RevTeX with 5 postscript figure
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