38,687 research outputs found
The density of mid-sized Kuiper belt objects from ALMA thermal observations
The densities of mid-sized Kuiper belt objects are a key constraint into
understanding the assembly of objects in the outer solar system. These objects
are critical for understanding the currently unexplained transition from the
smallest Kuiper belt objects with densities lower than that of water to the
largest objects with significant rock content. Mapping this transition is made
difficult by the uncertainties in the diameters of these objects, which maps
into an even larger uncertainty in volume and thus density. The substantial
collecting area of the Atacama Large Millimeter Array allows significantly more
precise measurements of thermal emission from outer solar system objects and
could potentially greatly improve the density measurements. Here we use new
thermal observations of four objects with satellites to explore the
improvements possible with millimeter data. We find that effects due to
effective emissivity at millimeter wavelengths make it difficult to use the
millimeter data directly to find diameters and thus volumes for these bodies.
In addition, we find that when including the effects of model uncertainty, the
true uncertainties on the sizes of outer solar system objects measured with
radiometry are likely larger than those previously published. Substantial
improvement in object sizes will likely require precise occultation
measurements.Comment: AJ, in pres
Probing Hadronic Structure with The Decay
We compute the branching ratio for and
in chiral perturbation theory and find that
both decays should be observable at CEBAF. With sufficiently low thresholds on
the invariant mass a branching ratio of may be observed
for . For the decay
mode we predict a branching ratio of . The dependence of the
M1 and E2 amplitudes on the momentum transfer will provide a useful test of
chiral perturbation theory which predicts variation over the
allowed kinematic range.Comment: 6 pages, 3 figures, UCSD/PTH 93-06, QUSTH-93-02, Duke-TH-93-4
SOFIP: A Short Orbital Flux Integration Program
A computer code was developed to evaluate the space radiation environment encountered by geocentric satellites. The Short Orbital Flux Integration Program (SOFIP) is a compact routine of modular compositions, designed mostly with structured programming techniques in order to provide core and time economy and ease of use. The program in its simplest form produces for a given input trajectory a composite integral orbital spectrum of either protons or electrons. Additional features are available separately or in combination with the inclusion of the corresponding (optional) modules. The code is described in detail, and the function and usage of the various modules are explained. A program listing and sample outputs are attached
Decuplet baryon magnetic moments in a QCD-based quark model beyond quenched approximation
We study the decuplet baryon magnetic moments in a QCD-based quark model
beyond quenched approximation. Our approach for unquenching the theory is based
on the heavy baryon perturbation theory in which the axial couplings for baryon
- meson and the meson-meson-photon couplings from the chiral perturbation
theory are used together with the QM moment couplings. It also involves the
introduction of a form factor characterizing the structure of baryons
considered as composite particles. Using the parameters obtained from fitting
the octet baryon magnetic moments, we predict the decuplet baryon magnetic
moments. The magnetic moment is found to be in good agreement with
experiment: is predicted to be compared to the
experimental result of (2.02 0.05) .Comment: 19 pages, 2 figure
ALMA Thermal Observations of Europa
We present four daytime thermal images of Europa taken with the Atacama Large
Millimeter Array. Together, these images comprise the first spatially resolved
thermal dataset with complete coverage of Europa's surface. The resulting
brightness temperatures correspond to a frequency of 233 GHz (1.3 mm) and a
typical linear resolution of roughly 200 km. At this resolution, the images
capture spatially localized thermal variations on the scale of geologic and
compositional units. We use a global thermal model of Europa to simulate the
ALMA observations in order to investigate the thermal structure visible in the
data. Comparisons between the data and model images suggest that the
large-scale daytime thermal structure on Europa largely results from bolometric
albedo variations across the surface. Using bolometric albedos extrapolated
from Voyager measurements, a homogenous model reproduces these patterns well,
but localized discrepancies exist. These discrepancies can be largely explained
by spatial inhomogeneity of the surface thermal properties. Thus, we use the
four ALMA images to create maps of the surface thermal inertia and emissivity
at our ALMA wavelength. From these maps, we identify a region of either
particularly high thermal inertia or low emissivity near 90 degrees West and 23
degrees North, which appears anomalously cold in two of our images.Comment: 9 pages, 3 figures, accepted for publication in the Astronomical
Journa
A knowledge-based flight status monitor for real-time application in digital avionics systems
The Dryden Flight Research Facility of the National Aeronautics and Space Administration (NASA) Ames Research Center (Ames-Dryden) is the principal NASA facility for the flight testing and evaluation of new and complex avionics systems. To aid in the interpretation of system health and status data, a knowledge-based flight status monitor was designed. The monitor was designed to use fault indicators from the onboard system which are telemetered to the ground and processed by a rule-based model of the aircraft failure management system to give timely advice and recommendations in the mission control room. One of the important constraints on the flight status monitor is the need to operate in real time, and to pursue this aspect, a joint research activity between NASA Ames-Dryden and the Royal Aerospace Establishment (RAE) on real-time knowledge-based systems was established. Under this agreement, the original LISP knowledge base for the flight status monitor was reimplemented using the intelligent knowledge-based system toolkit, MUSE, which was developed under RAE sponsorship. Details of the flight status monitor and the MUSE implementation are presented
Thermal control characteristics of a diffuse bladed specular base louver system Final report
Diffuse bladed specular base louver system for spacecraft temperature contro
The relational ethics of conflict and identity
The contemporary psychoanalytically inflected vocabulary of relational ethics centres on acknowledgement, witnessing and responsibility. It has become an important code for efforts to connect with otherness across fractures of hurt, oppression and suffering. One can see the deployment of this vocabulary to challenge patterns of exclusion and dehumanisation in zones of intense political conflict in many situations in which destructive hatred reigns. This paper traces some of the use of and disputes over this ‘acknowledgement-based’ relational ethics in the recent work of Jessica Benjamin and Judith Butler. The field of application is their response to Israel’s treatment of the Palestinians, given their position as Jews. The challenge of the acknowledgement agenda leads back to an issue of general concern – the degree to which relational ethics can prise open apparently closed and defensive psychosocial identities
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