20,552 research outputs found
A new approach to mass spectrometer measurements of thermospheric density
The gas sampling problem in satellite and high velocity probes was investigated by applying the theory of a drifting Maxwellian gas. A lens system using a free stream ion source was developed and experimentally evaluated over the pressure range of 0.00001 to 0.01 N/m sq (approx. 10 to the minus 7th power to 0.0001 torr). The source has high beam transparency, which minimizes gas-surface collisions within, or near, the ionization volume. It is shown that for high ion energy (60 eV), the extracted ion beam has an on-axis energy spread of less than 4 eV, and that 90 percent of the ions are within 2.5 deg of the beam axis. It is concluded that the molecular beam mass spectrometer concept, developed for gas density measurements in the upper atmosphere, substantially reduces gas-surface scattering and gas-surface reactions in the sample, and preserves the integrity of the gas sample during the analysis process. Studies show that both the Scout and Delta launch vehicles have adequate volume, control, velocity, and data acquisition capability necessary to obtain thermospheric number density in real time
Thermally activated escape rates of uniaxial spin systems with transverse field
Classical escape rates of uniaxial spin systems are characterized by a
prefactor differing from and much smaller than that of the particle problem,
since the maximum of the spin energy is attained everywhere on the line of
constant latitude: theta=const, 0 =< phi =< 2*pi. If a transverse field is
applied, a saddle point of the energy is formed, and high, moderate, and low
damping regimes (similar to those for particles) appear. Here we present the
first analytical and numerical study of crossovers between the uniaxial and
other regimes for spin systems. It is shown that there is one HD-Uniaxial
crossover, whereas at low damping the uniaxial and LD regimes are separated by
two crossovers.Comment: 4 PR pages, 3 figures, final published versio
Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres
We present a comprehensive description of the theory and practice of opacity
calculations from the infrared to the ultraviolet needed to generate models of
the atmospheres of brown dwarfs and extrasolar giant planets. Methods for using
existing line lists and spectroscopic databases in disparate formats are
presented and plots of the resulting absorptive opacities versus wavelength for
the most important molecules and atoms at representative temperature/pressure
points are provided. Electronic, ro-vibrational, bound-free, bound-bound,
free-free, and collision-induced transitions and monochromatic opacities are
derived, discussed, and analyzed. The species addressed include the alkali
metals, iron, heavy metal oxides, metal hydrides, , , , ,
, , , and representative grains. [Abridged]Comment: 28 pages of text, plus 22 figures, accepted to the Astrophysical
Journal Supplement Series, replaced with more compact emulateapj versio
Integral Relaxation Time of Single-Domain Ferromagnetic Particles
The integral relaxation time \tau_{int} of thermoactivating noninteracting
single-domain ferromagnetic particles is calculated analytically in the
geometry with a magnetic field H applied parallel to the easy axis. It is shown
that the drastic deviation of \tau_{int}^{-1} from the lowest eigenvalue of the
Fokker-Planck equation \Lambda_1 at low temperatures, starting from some
critical value of H, is the consequence of the depletion of the upper potential
well. In these conditions the integral relaxation time consists of two
competing contributions corresponding to the overbarrier and intrawell
relaxation processes.Comment: 8 pages, 3 figure
Georgia\u27s New Battleground: Five Georgia Law Professors Examine the State\u27s New Tort Legislation
In February, after several years of debate, the Georgia General Assembly enacted a comprehensive set of tort reform provisions. This fairly complex body of legislation contains 16 separate sections dealing with procedure, evidence and substantive tort issues. Shortly after it was signed into law, five Georgia Law professors sat down with alumni and students to describe parts of the new legislation, to identify some issues that are likely to arise as the new laws go into effect and to speculate about what they think the likely impact will be on litigation
Fokker-Planck and Landau-Lifshitz-Bloch Equations for Classical Ferromagnets
A macroscopic equation of motion for the magnetization of a ferromagnet at
elevated temperatures should contain both transverse and longitudinal
relaxation terms and interpolate between Landau-Lifshitz equation at low
temperatures and the Bloch equation at high temperatures. It is shown that for
the classical model where spin-bath interactions are described by stochastic
Langevin fields and spin-spin interactions are treated within the mean-field
approximation (MFA), such a ``Landau-Lifshitz-Bloch'' (LLB) equation can be
derived exactly from the Fokker-Planck equation, if the external conditions
change slowly enough. For weakly anisotropic ferromagnets within the MFA the
LLB equation can be written in a macroscopic form based on the free-energy
functional interpolating between the Landau free energy near T_C and the
``micromagnetic'' free energy, which neglects changes of the magnetization
magnitude |{\bf M}|, at low temperatures.Comment: 9 pages, no figures, a small error correcte
Field dependence of the temperature at the peak of the ZFC magnetization
The effect of an applied magnetic field on the temperature at the maximum of
the ZFC magnetization, , is studied using the recently obtained
analytic results of Coffey et al. (Phys. Rev. Lett. {\bf 80}(1998) 5655) for
the prefactor of the N\'{e}el relaxation time which allow one to precisely
calculate the prefactor in the N\'{e}el-Brown model and thus the blocking
temperature as a function of the coefficients of the Taylor series expansion of
the magnetocrystalline anisotropy. The present calculations indicate that even
a precise determination of the prefactor in the N\'{e}el-Brown theory, which
always predicts a monotonic decrease of the relaxation time with increasing
field, is insufficient to explain the effect of an applied magnetic field on
the temperature at the maximum of the ZFC magnetization. On the other hand, we
find that the non linear field-dependence of the magnetization along with the
magnetocrystalline anisotropy appears to be of crucial importance to the
existence of this maximum.Comment: 14 LaTex209 pages, 6 EPS figures. To appear in J. Phys.: Condensed
Matte
Active microwave users working group program planning
A detailed programmatic and technical development plan for active microwave technology was examined in each of four user activities: (1) vegetation; (2) water resources and geologic applications, and (4) oceanographic applications. Major application areas were identified, and the impact of each application area in terms of social and economic gains were evaluated. The present state of knowledge of the applicability of active microwave remote sensing to each application area was summarized and its role relative to other remote sensing devices was examined. The analysis and data acquisition techniques needed to resolve the effects of interference factors were reviewed to establish an operational capability in each application area. Flow charts of accomplished and required activities in each application area that lead to operational capability were structured
Reanalysis of Farmer Willingness to Tolerate Deer Damage in Western New York
Crop depredation by white-tailed deer (Odocoileus uirginianus) has been examined and discussed by wildlife managers since at least the early 1930\u27s (Leopold 1933:283). As with most aspects of game management in those early years, managers\u27 efforts focused on the biological parameters of depredation and control. In the 1960\u27s a few researchers began examining the social implications of deer management and found farmers to be surprisingly tolerant of most deer damage (McDowell and Benson 1960, McNeil 1962:81, Flyger and Thoerig 1962:48). Because of changing agricultural, habitat, and deer population conditions, studies of farmer tolerance of deer damage were initiated in New York (Brown et al. 1977, 1978, 1979, 1980). This research helped to systematically quantify and apply the concept of farmer tolerance of deer damage as a determinant of deer range carrying capacity on agricultural lands in New York State
Branes, AdS gravitons and Virasoro symmetry
We consider travelling waves propagating on the anti-de Sitter (AdS)
background. It is pointed out that for any dimension d, this space of solutions
has a Virasoro symmetry with a non-zero central charge. This result is a
natural generalization to higher dimensions of the three-dimensional
Brown-Henneaux symmetry.Comment: 4 pages REVTe
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