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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Pairing Dynamics in Low-energy Nuclear Collisions

Superfluidity is a generic feature of various quantum systems at low temperatures and it is in particular important for the description of dynam- ics of low energy nuclear reactions. The Time-Dependent Density Func- tional Theory (TDDFT) is, to date, the only microscopic method which takes into account in a consistent way far-from-equilibrium dynamics of pairing field and single-particle degrees of freedom. Here, the local version of TDDFT, so-called TDSLDA, is particularly useful for the description of nuclear reactions and is well-suited for leadership class computers of hybrid (CPU+GPU) architecture. The preliminary results obtained for collisions involving both medium-mass and heavy nuclei at the energies around the Coulomb barrier are presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Local Dynamics in Liquids and Glassy Materials

Atomic dynamics in strongly disordered matter, such as liquids and glasses, is characterized by correlated local dynamics. The conventional descriptions of atomic dynamics in condensed matter in terms of phonons and diffusion are inadequate for their dynamics, and instead we have to describe the dynamics in terms of spatial and temporal atomic correlations. Experimentally this means that it is insufficient to describe the dynamics through the dispersion of collective excitations in the dynamic structure factor, S(Q,E), where Q and E are the momentum and energy exchanges in scattering. As an alternative, herein we propose a real-space description in terms of the dynamic pair-density function (DyPDF) and the Van Hove function (VHF), and discuss recent results on relaxor ferroelectrics and superfluid 4 He measured by inelastic neutron scattering and water by inelastic x-ray scattering. As the subjects of research in condensed matter physics and materials science turn to more complex materials, the real-space approach is likely to become the mainstream method of research in atomic dynamics.

36 MATERIALS SCIENCE↗
NASA NTRS1970

Low temperature uses of helium

Helium is used for purging and pressurizing cryogenic rocket propellants, welding, atmosphere control, leak detection, and refrigeration. It provides the lowest possible liquid-bath temperature and produces superconductivity in certain materials. Its superfluid effects are used in superconducting magnets.

Brown, G. V.↗
NASA NTRS1971

Physics of the neutron star

Neutron star models, discussing crystalline crust, particle superfluid properties, rotational vortices and relation to Crab Nebula pulsar

Cameron, A. G. W.↗
NASA NTRS1972

Neutron stars.

Current theories of stellar evolution are examined, giving attention to neutrino emission processes and stellar collapse. Neutrinos can transfer energy produced in the collapsing core to the outer parts of the star. If the remaining core does not exceed a certain mass, it can remain in this highly condensed state to form a neutron star. The properties of neutron matter are discussed, taking into account the superfluid state, the crystallization of matter at subnuclear densities, aspects of rotation, and the magnetic field.

Chiu, H. Y.↗
NASA NTRS1972

Quartz microbalance studies of an adsorbed helium film.

The resonant frequency of a quartz crystal oscillating in the thickness-shear mode changes by virtue of the mass loading due to any type of film laid down on its surfaces. For a helium film only the normal fraction remains rigidly coupled to the substrate motion. Adsorption isotherms of He-4 measured with this technique show clear departures from conventional nonsuperfluid behavior. We attribute this effect to the onset and presence of superfluidity in the film.

Chester, M.↗
NASA NTRS1972

Cooling of pulsars.

The effects of the magnetic field and superfluidity on the cooling of neutron stars during the stage when they can be observed as pulsars are considered. A neutron-star model with a stellar mass of 1.07 solar mass, a radius of 12.33 km, and a central energy density of 7.39 x 10 to the 14th power gauss/cu cm was chosen. It appears that during the earlier periods while the star cools by neutrino emission, surface temperatures are somewhat higher at a given age in the presence of stronger magnetic fields. An interesting result is that most pulsars may be very cold.

Tsuruta, S.↗
NASA NTRS1973

Theoretical and experimental investigations of superconductivity. Amorphous semiconductors, superconductivity and magnetism

The research activities from 1 March 1963 to 28 February 1973 are summarized. Major lectures are listed along with publications on superconductivity, superfluidity, electronic structures and Fermi surfaces of metals, optical spectra of solids, electronic structure of insulators and semiconductors, theory of magnetic metals, physics of surfaces, structures of metals, and molecular physics.

Cohen, M. H.↗
NASA NTRS1973

Temperature dependence of the accommodation coefficient of liquid-helium film.

We have determined the accommodation coefficient, gamma, of a helium film from 1.15 to 4 K by measuring the time constant of a rotating superconducting Nb sphere levitated in vapor and covered with a saturated helium film. The conventional assumption of the phenomenological theory of superfluidity, that the order parameter psi vanishes at the free surface of helium II, implies that gamma, is unity and independent of temperature. We find that gamma, is nearly unity above the lambda point, suffers an abrupt drop close to T-lambda, and gradually levels off to the value of about 0.8 at lower temperatures.

Wang, T. G.↗
NASA NTRS1974

CVT/GPL phase 2 integrated testing

Experiments representing earth observations, space physics, and material sciences disciplines were installed in the General Purpose Laboratory (GPL). The experiments and the GPL are described. The experiments interfaces the GPL and GPL support systems are assessed. The experiments were cloud physics, ionospheric disturbances, material sciences, high energy astronomy, and superfluid helium.

Shurney, R. E.↗
NASA NTRS1973

Applications of cryogenics in electron microscopy

Description of research and development efforts which resulted in a high-voltage cryoelectron microscope system capable of consistent operation at 1.8 to 4.2 K. Attention is given to the design and operation of superconducting objective lenses providing enhanced resolution during longer exposure times at lower beam intensities (thus reducing radiation damage of specimens). A specific system described combines a closed-cycle superfluid helium refrigerator integrated with a modified 200 kV electron microscope. Consistent resolutions of 8 to 16 A are attained with significantly reduced radiation damage, contamination, and thermal noise in prolonged vibration-free examination of specimens at temperatures from 1.8 to 4.2 K. Applications in specific disciplines are discussed, including membrane ultrastructure, cryobiology, microelectronics, and general superconductivity research.

Fernandez-Moran, H.↗
NASA NTRS1974

Quantum crystals in neutron stars

Using the many-body techniques appropriate for quantum crystals it is shown that the deep interior of a neutron star is most likely an orderly arrangement of neutrons, protons and hyperons forming a solid. It is shown that a liquid or gas arrangement would produce higher energy. If so, a neutron star can be viewed as two solids (crust and core) permeated by a layer of ordinary or (perhaps) superfluid liquid. Astronomical evidence is in favor of such a structure: the sudden jumps in the periods of the Crab and Vela pulsars that differ by a factor of about 100 can be easily explained by the star-quake model. If the Crab is less massive than Vela (i.e., if it is not dense enough to have a solid core), the star-quakes take place in the crust whereas for Vela they occur in the core.

Canuto, V.↗
NASA NTRS1975

High-energy lasers by using distributed reflection: A concept

Lasers may be made with higher energy photons than heretofore possible. It has been proposed that vacuum ultraviolet lasing can be obtained by bombarding superfluid helium with electron beam, while coupling acoustic energy into helium to set up standing waves in fluid.

Saffren, M. M.↗
NASA NTRS1974

Research Investigation Directed Toward Extending the Useful Range of the Electromagnetic Spectrum

The report discusses completed and proposed research in atomic and molecular physics conducted at the Columbia Radiation Laboratory from July 1972 to June 1973. Central topics described include the atomic spectra and electronic structure of alkali metals and helium, molecular microwave spectroscopy, the resonance physics of photon echoes in some solid state systems (including Raman echoes, superradiance, and two photon absorption), and liquid helium superfluidity.

Hartmann, S. R.↗
NASA NTRS1974

Many-particle theory of nuclear systems with application to neutron star matter

The energy-density relation was calculated for pure neutron matter in the density range relevant for neutron stars, using four different hard-core potentials. Calculations are also presented of the properties of the superfluid state of the neutron component, along with the superconducting state of the proton component and the effects of polarization in neutron star matter.

Chakkalakal, D. A.↗
NASA NTRS1975

Working model of the London moment readout system

The operating characteristics of a porous plug which has liquid helium on one side and which is pumped on under vacuum on the other side are discussed. The system investigated consists of a container of liquid helium which is well isolated, and the only means for mass flow out of the container is through a plug mode of porous material. The plug was assumed to have liquid helium on the container side while the other side of the plug is evacuated. Three cases were considered: (1) perfect evacuation with zero pressure, (2) evacuation through a chocked orifice, and (3) evacuation through a long, small diameter pipe with heating. Mass flow rates were determined along with mass flow at temperature above the lambda point temperature. Solutions were obtained for normal and superfluid velocity.

Hendricks, J. B.↗