21,310 research outputs found
A systematic program of cometary spectroscopy
Some early results of a systematic program of observing the spectroscopic behavior of comets as a function of heliocentric distance are presented. An ultraviolet sensitive microchannel plate intensifier spectrograph was used to record the 3000-5000A spectrum of comets brighter than magnitude 17 with a spectral resolution of 8 or 16A, followed by direct image for better interpretation of the spatial distribution of spectral features. Although the goals of the program require much more time and data, some interesting results from Comets Schwassmann-Wachmann, 1, Bradfield and Bowell were obtained
Validity of adiabaticity in Cavity QED
This paper deals with the concept of adiabaticity for fully quantum
mechanically cavity QED models. The physically interesting cases of Gaussian
and standing wave shapes of the cavity mode are considered. An analytical
approximate measure for adiabaticity is given and compared with numerical wave
packet simulations. Good agreement is obtained where the approximations are
expected to be valid. Usually for cavity QED systems, the large atom-field
detuning case is considered as the adiabatic limit. We, however, show that
adiabaticity is also valid, for the Gaussian mode shape, in the opposite limit.
Effective semiclassical time dependent models, which do not take into account
the shape of the wave packet, are derived. Corrections to such an effective
theory, which are purely quantum mechanical, are discussed. It is shown that
many of the results presented can be applied to time dependent two-level
systems.Comment: 10 pages, 9 figure
Evaluating some computer enhancement algorithms that improve the visibility of cometary morphology
The observed morphology of cometary comae is determined by ejection circumstances and the interaction of the ejected material with the local environment. Anisotropic emission can provide useful information on such things as orientation of the nucleus, location of active areas on the nucleus, and the formation of ion structure near the nucleus. However, discrete coma features are usually diffuse, of low amplitude, and superimposed on a steep intensity gradient radial to the nucleus. To improve the visibility of these features, a variety of digital enhancement algorithms were employed with varying degrees of success. They usually produce some degree of spatial filtering, and are chosen to optimize visibility of certain detail. Since information in the image is altered, it is important to understand the effects of parameter selection and processing artifacts can have on subsequent interpretation. Using the criteria that the ideal algorithm must enhance low contrast features while not introducing misleading artifacts (or features that cannot be seen in the stretched, unprocessed image), the suitability of various algorithms that aid cometary studies were assessed. The strong and weak points of each are identified in the context of maintaining positional integrity of features at the expense of photometric information
Gravitational Radiation from Black Hole Binaries in Globular Clusters
A populations of stellar mass black hole binaries may exist in globular
clusters. The dynamics of globular cluster evolution imply that there may be at
most one black hole binary is a globular cluster. The population of binaries
are expected to have orbital periods greater than a few hours and to have a
thermal distribution of eccentricities. In the LISA band, the gravitational
wave signal from these binaries will consist of several of the higher harmonics
of the orbital frequency. A Monte Carlo simulation of the galactic globular
cluster system indicates that LISA will detect binaries in 10 % of the clusters
with an angular resolution sufficient to identify the host cluster of the
binary.Comment: 7 pages, 2 eps figures, uses iopart styl
Determination of lunar ilmentite abundances from remotely sensed data
The mapping of ilmenite on the surface of the moon is a necessary precursor to the investigation of prospective lunar base sites. Telescopic observations of the moon using a variety of narrow bandpass optical interference filters are being performed as a preliminary means of achieving this goal. Specifically, ratios of images obtained using filters centered at 0.40 and 0.56 microns provide quantitative estimates of TiO2 abundances. Analysis of preliminary distribution maps of TiO2 concentrations allows identification of specific high-Ti areas. Investigations of these areas using slit spectra in the range 0.03 to 0.85 microns are underway to search for discrete spectral signatures attributable to ilmenite
A NEW APPROACH FOR ASSESSING THE COSTS OF LIVING WITH WILDLIFE IN DEVELOPING COUNTRIES
The costs of living with wildlife are assessed using Namibian subsistence farmers willingness to pay (WTP) for deterrents to attacks on crops and livestock as a measure of damage costs. A utility-theoretic approach jointly estimates household WTP for deterrent programs in two currencies, maize and cash. This has a double payoff. Use of a noncash staple increases respondent comprehension and provides more information about preferences, improving the accuracy of results. The household shadow value of maize is also identified. Significant costs from living with elephants and other types of wildlife are demonstrated. Compensation for farmers may be warranted on equity and efficiency grounds. Uncontrolled domestic cattle generate even higher costs to farmers than wildlife, highlighting the need to clarify property rights among these farmers.Resource /Energy Economics and Policy,
Quantum fluctuations in the mazer
Quantum fluctuations in the mazer are considered, arising either from the
atomic motion or from the quantized intracavity field. Analytical results, for
both the meza and the hyperbolic secant mode profile, predict for example an
attenuation of tunneling resonances due to such fluctuations. The case of a
Gaussian mode profile is studied numerically using a wave packet propagation
approach. The method automatically takes into account fluctuations in the
atomic motion and the dynamics is especially considered at or adjacent to a
tunnel resonance. We find that the system evolution is greatly sensitive to the
atom-field detuning, bringing about a discussion about the concept of
adiabaticity in this model. Further, a novel collapse-revival phenomena is
demonstrated, originating from the quantum fluctuations in the atomic motion
rather from field fluctuations as is normally the case.Comment: 15 pages, 8 figures. Replaced with final versio
The LISA Gravitational Wave Foreground: A Study of Double White Dwarfs
Double white dwarfs are expected to be a source of confusion-limited noise
for the future gravitational wave observatory LISA. In a specific frequency
range, this 'foreground noise' is predicted to rise above the instrumental
noise and hinder the detection of other types of signals, e.g., gravitational
waves arising from stellar mass objects inspiraling into massive black holes.
In many previous studies only detached populations of compact object binaries
have been considered in estimating the LISA gravitational wave foreground
signal. Here, we investigate the influence of compact object detached and
Roche-Lobe Overflow Galactic binaries on the shape and strength of the LISA
signal. Since >99% of remnant binaries which have orbital periods within the
LISA sensitivity range are white dwarf binaries, we consider only these
binaries when calculating the LISA signal. We find that the contribution of
RLOF binaries to the foreground noise is negligible at low frequencies, but
becomes significant at higher frequencies, pushing the frequency at which the
foreground noise drops below the instrumental noise to >6 mHz. We find that it
is important to consider the population of mass transferring binaries in order
to obtain an accurate assessment of the foreground noise on the LISA data
stream. However, we estimate that there still exists a sizeable number (~11300)
of Galactic double white dwarf binaries which will have a signal-to-noise ratio
>5, and thus will be potentially resolvable with LISA. We present the LISA
gravitational wave signal from the Galactic population of white dwarf binaries,
show the most important formation channels contributing to the LISA disc and
bulge populations and discuss the implications of these new findings.Comment: ApJ accepted. 28 pages, 11 figures (low resolution), 5 tables, some
new references and changed content since last astro-ph versio
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