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Results for “SUPERFLUID MODEL”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Heavy-ion transfer reactions at large internuclear distance

The transfer reaction for the {sup 116}Sn+{sup 60}Ni system has been studied using the PRISMA magnetic spectrometer at different bombarding energies from above to well below the Coulomb barrier. The experiment has been done in inverse kinematics and light target-like ions have been detected with PRISMA placed at very forward angles. Good mass, nuclear charge and kinetic energy resolutions have been achieved. Sufficient statistics has been accumulated to extract angular distributions for different bombarding energies have been extracted and the response function of the spectrometer has been studied to correct for the aberration due to the transport of the ions in PRISMA. The comparison between the present case and the previously measured {sup 96}Zr+{sup 40}Ca system, superfluid and near closed shells nuclei, respectively, should significantly improve our understanding of nucleon-nucleon correlation properties in multinucleon transfer processes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Quantum criticality from in situ density imaging

We perform large-scale quantum Monte Carlo (QMC) simulations for strongly interacting bosons in a two-dimensional optical lattice trap and confirm an excellent agreement with the benchmarking in situ density measurements by the Chicago group [N. Gemelke et al., Nature (London) 460, 995 (2009)]. We further present a general finite-temperature phase diagram for both the uniform and the trapped systems, demonstrating how the universal scaling properties near the superfluid-to-Mott insulator transition can be observed from the in situ density profile. The characteristic temperature to find such quantum criticality is estimated to be of the order of the single-particle bandwidth, which should be achievable in the present experiments. Finally, we examine the validity regime of the local fluctuation-dissipation theorem, which can be a used as a thermometry in the strongly interacting regime.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Glassy Behavior in a Binary Atomic Mixture

We experimentally study one-dimensional, lattice-modulated Bose gases in the presence of an uncorrelated disorder potential formed by localized impurity atoms, and compare to the case of correlated quasidisorder formed by an incommensurate lattice. While the effects of the two disorder realizations are comparable deeply in the strongly interacting regime, both showing signatures of Bose-glass formation, we find a dramatic difference near the superfluid-to-insulator transition. In this transition region, we observe that random, uncorrelated disorder leads to a shift of the critical lattice depth for the breakdown of transport as opposed to the case of correlated quasidisorder, where no such shift is seen. Our findings, which are consistent with recent predictions for interacting bosons in one dimension, illustrate the important role of correlations in disordered atomic systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

RAPID COOLING OF THE NEUTRON STAR IN CASSIOPEIA A AND r-MODE DAMPING IN THE CORE

We proposed an alternative explanation to the rapid cooling of neutron star in Cas A. It is suggested that the star experiences the recovery period following the r-mode heating process assuming the star is differentially rotating. Like the neutron-superfluidity-triggering model, our model predicts that the rapid cooling will continue for several decades. However, the behavior of the two models has slight differences, and they might be distinguished by observations in the near future.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Enhancement of α -particle formation near Sn 100

The superfluid tunneling model is applied to the calculation of ground-state-to-ground-state α decay in the even-even neutron-deficient Te-Ba nuclei. Here, we show that there is a larger α-particle formation probability in nuclei of this region above 100 Sn when compared to analogous nuclei above 208 Pb. This is consistent with the expected systematic variation of the pair gap Δ as a function of mass number. Finally, the recent experimental data on the α decay of the N=Z nuclei 104 Te and 108 Xe are shown to leave open the possibility of enhanced α-particle formation involving nucleon correlations beyond the standard treatment of like-nucleon pairing, which is the mechanism suggested as underlying "superallowed" α decay.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Role of quasiparticle structure in α decay of superheavy nuclei

Here, we use the superfluid tunneling model (STM) to calculate the half-lives of α decays of odd-A and odd-odd superheavy nuclei (SHN) with Z ≥ 100 and A ≥ 250. The experimental data are reproduced to accuracies comparable to other contemporary models of the α decay of the SHN. We then apply the STM to examine the influence of the quasiparticle structure on the properties of the chains of α decays arising from odd- A SHN. Using representative calculations of the one-quasi-particle structure of odd-Z and odd-N SHN, we illustrate the important role played by high-Ω orbitals in defining the observed characteristics of the α-decay chains. We point out sources of possible ambiguity that may arise due to the quasiparticle structure when assigning α-decay chains to specific SHN.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

α decay of high-spin isomers in N = 84 isotones

The superfluid tunneling model is applied to the calculation of half-lives of the observed α decays in N = 84 isotones. Here the results of our calculations are compared to experimental data on the ground-state α decays along the isotonic chain from 144 Nd to 159 Re. Good agreement is found. The α decays of the known high-spin isomers in 155 Lu, 156 Hf, 157 Ta, and 158 W are also well reproduced, once a reduction in the pairing strength is taken into account. This includes reproduction of the main features of the recently observed fine structure from 155 Lu(25/2 - ) and 156 Hf(8 + ). Predictions for the α-decay fine structure of 157 Ta(25/2 - ) and 158 W(8 + ) high-spin isomers are presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Nuclear level densities in {sup 208}Bi and {sup 209}Po from the neutron spectra in the (p, n) reactions on {sup 208}Pb and {sup 209}Bi nuclei

The spectra of neutrons from the (p, n) reactions on the {sup 208}Pb and {sup 209}Bi nuclei were measured in the proton-energy range 8-11 MeV. These measurements were performed by using a time-of-flight spectrometer of fast neutrons on the basis of the pulsed tandem accelerator EGP-15 of the Institute of Physics and Power Engineering (Obninsk, Russian Federation). A high resolution and stability of the time-of-flight spectrometermade it possible to identify reliably low-lying discrete levels alongwith the continuum section of the neutron spectra. The measured data were analyzed on the basis of the statistical equilibrium and preequilibrium models of nuclear reactions. The respective calculations were performed by using the precise formalism of Hauser-Feshbach statistical theory together with the generalized model of a superfluid nucleus and the back-shifted Fermi gas model for the nuclear-level density. The nuclear-level densities in {sup 208}Bi and {sup 209}Po were determined along with their energy dependencies and model parameters. Our results are discussed together with available experimental data and recommendations of model systematics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Mean-field theory for the Mott-insulator-paired-superfluid phase transition in the two-species Bose-Hubbard model

The standard mean-field theory for the Mott-insulator-superfluid phase transition is not sufficient to describe the Mott-insulator-paired-superfluid phase transition. Therefore, by restricting the two-species Bose-Hubbard Hamiltonian to the subspace of paired particles, and using perturbation theory, here we derive an analytic mean-field expression for the Mott-insulator-paired-superfluid transition boundary.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Dynamical critical exponent of the Jaynes-Cummings-Hubbard model

An array of high-Q electromagnetic resonators coupled to qubits gives rise to the Jaynes-Cummings-Hubbard model describing a superfluid to Mott-insulator transition of lattice polaritons. From mean-field and strong-coupling expansions, the critical properties of the model are expected to be identical to the scalar Bose-Hubbard model. A recent Monte Carlo study of the superfluid density on the square lattice suggested that this does not hold for the fixed-density transition through the Mott lobe tip. Instead, mean-field behavior with a dynamical critical exponent z=2 was found. We perform large-scale quantum Monte Carlo simulations to investigate the critical behavior of the superfluid density and the compressibility. We find z=1 at the tip of the insulating lobe. Hence the transition falls in the three-dimensional XY universality class, analogous to the Bose-Hubbard model.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1982

Orbital performance of a one-year lifetime superfluid helium dewar based on ground testing and computer modelling

The ground-test results of the 550-liter superfluid-He dewar built for IRAS are presented and discussed, and a computer projection of its orbital performance life is developed. The ground-testing program included flow-swap, cold-flow, power-off, hot/cold-viewport, and strap-thermal-efficiency tests. After one set of trials, some design changes were made, and the thermal-network computer model of the system was modified as well. The driving boundary conditions of dewar orbital operation used in this model are vacuum-shell temperature = 170 K, aperture heating = 8.0 mW, and focal-plane power dissipation = 16.2 mW. An operational lifetime of 319 days and an He loss rate of 2.54 mg/sec are predicted.

Hopkins, R. A.↗
DOE OSTI2010

Superfluid-insulator transitions in attractive Bose-Hubbard model with three-body constraint

By means of the method of the effective potential, the phase transitions from the Mott insulating state to either the atomic or the dimer superfluid state in the three-body constrained attractive Bose lattice gas are analyzed. Because of the appearance of the Feshbach resonance coupling between the two kinds of order parameters in the derived Ginzburg-Landau function, it is found that the continuous Mott-insulator-superfluid transitions can be preempted by first-order ones. Since the employed approach can provide accurate predictions of phase boundaries in the strong coupling limit, where the dimer superfluid phase can emerge, our work sheds light on the search of this phase in real ultracold Bose gases in optical lattices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2012

A Superfluid Pulse Tube Refrigerator Without Moving Parts for Sub-Kelvin Cooling

A report describes a pulse tube refrigerator that uses a mixture of He-3 and superfluid He-4 to cool to temperatures below 300 mK, while rejecting heat at temperatures up to 1.7 K. The refrigerator is driven by a novel thermodynamically reversible pump that is capable of pumping the He-3 He-4 mixture without the need for moving parts. The refrigerator consists of a reversible thermal magnetic pump module, two warm heat exchangers, a recuperative heat exchanger, two cold heat exchangers, two pulse tubes, and an orifice. It is two superfluid pulse tubes that run 180 out of phase. All components of this machine except the reversible thermal pump have been demonstrated at least as proof-of-concept physical models in previous superfluid Stirling cycle machines. The pump consists of two canisters packed with pieces of gadolinium gallium garnet (GGG). The canisters are connected by a superleak (a porous piece of VYCOR glass). A superconducting magnetic coil surrounds each of the canisters.

Miller, Franklin K.↗
NASA NTRS1990

Experimental verification of a tank to tank He II transfer model with trade study results

A computer program has been developed to study the thermodynamics of tank to tank superfluid helium transfer. The model includes a supply and a receiver tank connected by a transfer line. The convey of He II from one tank to the other is controlled by a fountain effect pump (FEP). Phase separators are present in both the supply and receiver tank to regulate the bath temperature. Description of this model has been published elsewhere. In the present paper, data from a transfer experiment are used to verify the accuracy of this model. The experiment consisted of an FEP made of a 2-micron sintered stainless steel porous plug. Superfluid has been transferred from a liquid helium bath into a glass beaker. Bath temperatures, flowrate and heater power records are available. These results are compared to the predictions of the computer program and good agreement is found between the two. This model is very useful for the study and design of superfluid transfer systems, e.g., the Superfluid Helium Tanker (SFHT) and the Particle Astrophysics Magnet Facility (ASTROMAG).

Yuan, S. W. K.↗
DOE OSTI2011

Decoupling of superfluid and normal modes in pulsating neutron stars

We show that equations governing pulsations of superfluid neutron stars can be split into two sets of weakly coupled equations, one describing the superfluid modes and another one, the normal modes. The coupling parameter s is small, |s|{approx}0.01-0.05, for realistic equations of state. Already an approximation s=0 is sufficient to calculate the pulsation spectrum within the accuracy of a few percent. Our results indicate, in particular, that emission of gravitational waves from superfluid pulsation modes is suppressed in comparison to that from normal modes. The proposed approach allows to drastically simplify modeling of pulsations of superfluid neutron stars.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Viscosity of liquid {sup 4}He and quantum of circulation: Are they related?

In the vicinity of the superfluid transition in liquid {sup 4}He, we explore the relation between two apparently unrelated physical quantities—the kinematic viscosity, ν, in the normal state and the quantum of circulation, κ, in the superfluid state. The model developed here leads to the simple relationship ν ≈ κ/6, and links the classical and quantum flow properties of liquid {sup 4}He. We critically examine available data relevant to this relation and find that the prediction holds well at the saturated vapor pressure. Additionally, we predict the kinematic viscosity for liquid {sup 4}He along the λ-line at negative pressures.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗