458 research outputs found
Membrane evaporator/sublimator investigation
Data are presented on a new evaporator/sublimator concept using a hollow fiber membrane unit with a high permeability to liquid water. The aim of the program was to obtain a more reliable, lightweight and simpler Extra Vehicular Life Support System (EVLSS) cooling concept than is currently being used
Membrane humidity control investigation
The basic performance data on a hollow fiber membrane unit that removes water from a breathing gas loop by diffusion is presented. Using available permeability data for cellulose acetate, a preliminary design was made of a dehumidifier unit that would meet the problem statement
Observability of atomic line features in strong magnetic fields
The physical properties of atoms in superstrong magnetic fields, characteristic of neutron stars, and the possibility of detecting magnetically strongly shifted atomic lines in the spectra of magnetized X-ray pulsars are discussed. It is suggested that it is recommendable to look for magnetically strongly shifted Fe 26 Lyman lines in rotating neutron stars of not too high luminosity using spectrometers working in the energy range 10 - 20 keV, with sensitivities to minus 4 power photons per sq cm and second, and resolution E/delta E approx. 10-100
Membrane water deaerator investigation
The purpose of the membrane water deaerator program was to develop data on a breadboard hollow fiber membrane unit that removes both dissolved and evolved gas from a water transfer system in order to: (1) assure a hard fill of the EVLSS expendable water tank; (2) prevent flow blockage by gas bubbles in circulating systems; and (3) prevent pump cavitation
Electron corrected Lorentz forces in solids and molecules in magnetic field
We describe the effective Lorentz forces on the ions of a generic insulating
system in an magnetic field, in the context of Born-Oppenheimer ab-initio
molecular dynamics. The force on each ion includes an important contribution of
electronic origin, which depends explicitly on the velocity of all other ions.
It is formulated in terms of a Berry curvature, in a form directly suitable for
future first principles classical dynamics simulations based {\it e.g.,} on
density functional methods. As a preliminary analytical demonstration we
present the dynamics of an H molecule in a field of intermediate strength,
approximately describing the electrons through Slater's variational
wavefunction.Comment: 5 pages, 2 figures; to appear in Phys. Rev.
Electronic screening and damping in magnetars
We calculate the screening of the ion-ion potential due to electrons in the
presence of a large background magnetic field, at densities of relevance to
neutron star crusts. Using the standard approach to incorporate electron
screening through the one-loop polarization function, we show that the magnetic
field produces important corrections both at short and long distances. In
extreme fields, realized in highly magnetized neutron stars called magnetars,
electrons occupy only the lowest Landau levels in the relatively low density
region of the crust. Here our results show that the screening length for
Coulomb interactions between ions can be smaller than the inter-ion spacing.
More interestingly, we find that the screening is anisotropic and the screened
potential between two static charges exhibits long range Friedel oscillations
parallel to the magnetic field. This long-range oscillatory behavior is likely
to affect the lattice structure of ions, and can possibly create rod-like
structures in the magnetar crusts. We also calculate the imaginary part of the
electron polarization function which determines the spectrum of electron-hole
excitations and plays a role in damping lattice phonon excitations. We
demonstrate that even for modest magnetic fields this damping is highly
anisotropic and will likely lead to anisotropic phonon heat transport in the
outer neutron star crust.Comment: 14 pages, 5 Figure
Magnetically Catalyzed Fusion
We calculate the reaction cross-sections for the fusion of hydrogen and
deuterium in strong magnetic fields as are believed to exist in the atmospheres
of neutron stars. We find that in the presence of a strong magnetic field (B
\gsim 10^{12}G), the reaction rates are many orders of magnitude higher than
in the unmagnetized case. The fusion of both protons and deuterons are
important over a neutron star's lifetime for ultrastrong magnetic fields (G). The enhancement may have dramatic effects on thermonuclear
runaways and bursts on the surfaces of neutron stars.Comment: 13 pages, 6 figure
Contribution of the second Landau level to the exchange energy of the three-dimensional electron gas in a high magnetic field
We derive a closed analytical expression for the exchange energy of the
three-dimensional interacting electron gas in strong magnetic fields, which
goes beyond the quantum limit (L=0) by explicitly including the effect of the
second, L=1, Landau level and arbitrary spin polarization. The inclusion of the
L=1 level brings the fields to which the formula applies closer to the
laboratory range, as compared to previous expressions, valid only for L=0 and
complete spin polarization. We identify, and explain, two distinct regimes,
separated by a critical density . Below , the per-particle exchange
energy is lowered by the contribution of L=1, whereas above it is
increased. As special cases of our general equation we recover various known,
more limited, results for higher fields, and identify and correct a few
inconsistencies in some of these earlier expressions.Comment: 7 pages, 2 figures, PRB accepte
Electronic Structure of Atoms in Magnetic Quadrupole Traps
We investigate the electronic structure and properties of atoms exposed to a
magnetic quadrupole field. The spin-spatial as well as generalized time
reversal symmetries are established and shown to lead to a two-fold degeneracy
of the electronic states in the presence of the field. Low-lying as well as
highly excited Rydberg states are computed and analyzed for a broad regime of
field gradients. The delicate interplay between the Coulomb and various
magnetic interactions leads to complex patterns of the spatial spin
polarization of individual excited states. Electromagnetic transitions in the
quadrupole field are studied in detail thereby providing the selection rules
and in particular the transition wavelengths and corresponding dipole
strengths. The peculiar property that the quadrupole magnetic field induces
permanent electric dipole moments of the atoms is derived and discussed.Comment: 17 pages, 13 figures, accepted for publication in PR
Hydrogen and Helium atoms in strong magnetic fields
The energy levels of hydrogen and helium atoms in strong magnetic fields are
calculated in this study. The current work contains estimates of the binding
energies of the first few low-lying states of these systems that are
improvements upon previous estimates. The methodology involves computing the
eigenvalues and eigenvectors of the generalized two-dimensional Hartree-Fock
partial differential equations for these one- and two-electron systems in a
self-consistent manner. The method described herein is applicable to
calculations of atomic structure in magnetic fields of arbitrary strength as it
exploits the natural symmetries of the problem without assumptions of any basis
functions for expressing the wave functions of the electrons or the commonly
employed adiabatic approximation. The method is found to be readily extendable
to systems with more than two electrons.Comment: 15 pages, 6 figure
- …