60,186 research outputs found
The Angular Separation of the Components of the Cepheid AW Per
The 6.4 day classical Cepheid AW Per is a spectroscopic binary with a period
of 40 years. Analyzing the centroids of HST/STIS spectra obtained in November
2001, we have determined the angular separation of the binary system. Although
we currently have spatially resolved data for a single epoch in the orbit, the
success of our approach opens the possibility of determining the inclination,
sini, for the system if the measurements are repeated at additional epochs.
Since the system is potentially a double lined spectroscopic binary, the
combination of spectroscopic orbits for both components and the visual orbit
would give the distance to the system and the masses of its components, thereby
providing a direct measurement of a Cepheid mass.Comment: 12 pages, accepted version -- minor change
NASA/JPL Aircraft SAR Workshop Proceedings
Speaker-supplied summaries of the talks given at the NASA/JPL Aircraft SAR Workshop on February 4 and 5, 1985, are provided. These talks dealt mostly with composite quadpolarization imagery from a geologic or ecologic prespective. An overview and summary of the system characteristics of the L-band synthetic aperture radar (SAR) flown on the NASA CV-990 aircraft are included as supplementary information. Other topics ranging from phase imagery and interferometric techniques classifications of specific areas, and the potentials and limitations of SAR imagery in various applications are discussed
Axisymmetric Self-Similar Equilibria of Self-Gravitating Isothermal Systems
All axisymmetric self-similar equilibria of self-gravitating, rotating,
isothermal systems are identified by solving the nonlinear Poisson equation
analytically. There are two families of equilibria: (1) Cylindrically symmetric
solutions in which the density varies with cylindrical radius as R^(-alpha),
with 0 <= alpha <= 2. (2) Axially symmetric solutions in which the density
varies as f(theta)/r^2, where `r' is the spherical radius and `theta' is the
co-latitude. The singular isothermal sphere is a special case of the latter
class with f(theta)=constant. The axially symmetric equilibrium configurations
form a two-parameter family of solutions and include equilibria which are
surprisingly asymmetric with respect to the equatorial plane. The asymmetric
equilibria are, however, not force-free at the singular points r=0, infinity,
and their relevance to real systems is unclear. For each hydrodynamic
equilibrium, we determine the phase-space distribution of the collisionless
analog.Comment: 13 pages, 7 figures, uses emulateapj.sty. Submitted to Ap
New observations regarding deterministic, time reversible thermostats and Gauss's principle of least constraint
Deterministic thermostats are frequently employed in non-equilibrium
molecular dynamics simulations in order to remove the heat produced
irreversibly over the course of such simulations. The simplest thermostat is
the Gaussian thermostat, which satisfies Gauss's principle of least constraint
and fixes the peculiar kinetic energy. There are of course infinitely many ways
to thermostat systems, e.g. by fixing . In
the present paper we provide, for the first time, convincing arguments as to
why the conventional Gaussian isokinetic thermostat () is unique in this
class. We show that this thermostat minimizes the phase space compression and
is the only thermostat for which the conjugate pairing rule (CPR) holds.
Moreover it is shown that for finite sized systems in the absence of an applied
dissipative field, all other thermostats () perform work on the system
in the same manner as a dissipative field while simultaneously removing the
dissipative heat so generated. All other thermostats () are thus
auto-dissipative. Among all -thermostats, only the Gaussian
thermostat permits an equilibrium state.Comment: 27 pages including 10 figures; submitted for publication Journal of
Chemical Physic
Schooling and Labor Market Consequences of the 1970 State Abortion Reforms
This study uses the 1970 state abortion reforms to estimate the effect of teen and out-of-wedlock childbearing on the schooling and labor market outcomes of mothers observed in 1980 and 1990 Census microdata. Reduced-form estimates suggest that state abortion reforms had a negative impact on teen marriage, teen fertility, and teen out- of-wedlock childbearing. The teen marriage effects are largest and most precisely estimated for white women while the teen fertility and out-of-wedlock childbearing effects are largest and most precisely estimated for black women. The relatively modest fertility and marriage consequences of abortion reform for white women do not appear to have changed schooling or labor market outcomes. In contrast, black women who were exposed to abortion reforms experienced large reductions in teen fertility and teen out-of-wedlock fertility that appear to have led to increased schooling and employment rates. Instrumental variables estimates of the effects of teen and out-of- wedlock childbearing on the schooling and employment status of black women, using measures of exposure to abortion reform as instruments, are marginally significant and larger than the corresponding OLS estimates.
New Velocity Distribution in the Context of the Eddington Theory
Exotic dark matter together with the vacuum energy (associated with the
cosmological constant) seem to dominate the Universe. Thus its direct detection
is central to particle physics and cosmology. Supersymmetry provides a natural
dark matter candidate, the lightest supersymmetric particle (LSP). One
essential ingredient in obtaining the direct detection rates is the density and
velocity distribution of the LSP. The detection rate is proportional to this
density in our vicinity. Furthermore, since this rate is expected to be very
low, one should explore the two characteristic signatures of the process,
namely the modulation effect, i.e. the dependence of the event rate on the
Earth's motion and the correlation of the directional rate with the motion of
the sun. Both of these crucially depend on the LSP velocity distribution. In
the present paper we study simultaneously density profiles and velocity
distributions based on the Eddington theory.Comment: 40 LaTex pages, 19 figures and one table. The previous version was
expanded to include new numerical solutions to Poisson's equation. Sheduled
to appear in vol. 588, ApJ, May 1, 300
A class of symplectic integrators with adaptive timestep for separable Hamiltonian systems
Symplectic integration algorithms are well-suited for long-term integrations
of Hamiltonian systems because they preserve the geometric structure of the
Hamiltonian flow. However, this desirable property is generally lost when
adaptive timestep control is added to a symplectic integrator. We describe an
adaptive-timestep symplectic integrator that can be used if the Hamiltonian is
the sum of kinetic and potential energy components and the required timestep
depends only on the potential energy (e.g. test-particle integrations in fixed
potentials). In particular, we describe an explicit, reversible, symplectic,
leapfrog integrator for a test particle in a near-Keplerian potential; this
integrator has timestep proportional to distance from the attracting mass and
has the remarkable property of integrating orbits in an inverse-square force
field with only "along-track" errors; i.e. the phase-space shape of a Keplerian
orbit is reproduced exactly, but the orbital period is in error by O(1/N^2),
where N is the number of steps per period.Comment: 24 pages, 3 figures, submitted to Astronomical Journal; minor errors
in equations and one figure correcte
A sub-regional management framework for South Pacific longline fisheries
The principal objective of this study was to determine if additional net benefits can be derived from the sub-regional longline fishery by the introduction of a new management agreement that would centre on the provision of licensing arrangements that would allow access by eligible
longline vessels to multiple Exclusive Economic Zones, i.e. Multi-zone Access. [90pp.
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