23,094 research outputs found
High Spectral and Spatial Resolution Observations of Shocked Molecular Hydrogen at the Galactic Center
The presence of OH (1720 MHz) masers, and the absence of counterparts at
1665/1667 MHz has proved to be a clear diagnostic of shocked molecular gas
associated with Galactic supernova remnants. This suggests that shocked
molecular gas should be associated with the OH (1720 MHz) masers that have been
detected in the circumnuclear disk (CND) and Sgr A East at the Galactic center.
In order to test this hypothesis, we observed the H 1--0 S(1) and Br
lines using NICMOS on the HST and UNSWIRF on the AAT, near the regions
where OH (1720 MHz) masers are detected in the CND and Sgr A East. We present
the distribution of H in the North and South lobes of the CND and in Sgr A
East. H emission accompanies almost all of the maser spots detected at the
Galactic center. In particular, we find a striking filamentary structure near
the Northwest of the CND and evidence that shocked molecular gas is associated
with the 70 \kms molecular cloud at the Galactic center. We argue that the
emission from the CND could arise in gas heated by the dissipation of the
random motion of clumps by collisions or the dissipation of turbulence in a
more homogeneous medium. In addition, highly red-shifted gas of up to 140 \kms\
close to the eastern edge of the Sgr A East shell is detected. These
observations combined with OH (1720 MHz) results suggest that the H gas is
shocked and accelerated by the expansion of Sgr A East into the 50 and the 70
\kms cloud and into the lobes of the CND.Comment: 31 pages plus 14 figures, ApJ (in press
Palatini Variational Principle for -Dimensional Dilaton Gravity
We consider a Palatini variation on a general -Dimensional second order,
torsion-free dilaton gravity action and determine the resulting equations of
motion. Consistency is checked by considering the restraint imposed due to
invariance of the matter action under simple coordinate transformations, and
the special case of N=2 is examined. We also examine a sub-class of theories
whereby a Palatini variation dynamically coincides with that of the "ordinary"
Hilbert variational principle; in particular we examine a generalized
Brans-Dicke theory and the associated role of conformal transformations.Comment: 16 pages, LaTe
Quantifying flow and stress in ice mĂ©lange, the worldâs largest granular material.
Tidewater glacier fjords are often filled with a collection of calved icebergs, brash ice, and sea ice. For glaciers with high calving rates, this âm Ìelangeâ of ice can be jam-packed, so that the flow of ice fragments is mostly determined by granular interactions. In the jammed state, ice m Ìelange has been hypothesized to influence iceberg calving and capsize, dispersion and attenuation of ocean waves, injection of freshwater into fjords, and fjord circulation. However, detailed measurements of ice m Ìelange are lacking due to difficulties in instrumenting remote, ice-choked fjords. Here we characterize the flow and associated stress in icem Ìelange, using a combination of terrestrial radar data, laboratory experiments, and numerical simulations. We find that, during periods of terminus quiescence, ice m Ìelange experiences laminar flow over timescales of hours to days. The uniform flow fields are bounded by shear margins along fjord walls where force chains between granular icebergs terminate. In addition, the average force per unit width that is transmitted to the glacier terminus, which can exceed 107N/m, increases exponentially with them Ìelange length-to-width ratio. These âbuttressingâ forces are sufficiently high to inhibit the initiation of large-scale calving events, supporting the notion that ice m Ìelange can be viewed as a weak granular ice shelf that transmits stresses from fjord walls back to glacier termini.Ye
Constructing sonified haptic line graphs for the blind student: first steps
Line graphs stand as an established information visualisation and analysis technique taught at various levels of difficulty according to standard Mathematics curricula. It has been argued that blind individuals cannot use line graphs as a visualisation and analytic tool because they currently primarily exist in the visual medium. The research described in this paper aims at making line graphs accessible to blind students through auditory and haptic media. We describe (1) our design space for representing line graphs, (2) the technology we use to develop our prototypes and (3) the insights from our preliminary work
Master agreement task order 2 - Analyses and limited evaluations of payload and landing system structures for the survivable soft landing of instrument payloads
Computer programs for analysis and evaluation of payload and landing system structures for soft landing of instrument package
The inexorable resistance of inertia determines the initial regime of drop coalescence
Drop coalescence is central to diverse processes involving dispersions of
drops in industrial, engineering and scientific realms. During coalescence, two
drops first touch and then merge as the liquid neck connecting them grows from
initially microscopic scales to a size comparable to the drop diameters. The
curvature of the interface is infinite at the point where the drops first make
contact, and the flows that ensue as the two drops coalesce are intimately
coupled to this singularity in the dynamics. Conventionally, this process has
been thought to have just two dynamical regimes: a viscous and an inertial
regime with a crossover region between them. We use experiments and simulations
to reveal that a third regime, one that describes the initial dynamics of
coalescence for all drop viscosities, has been missed. An argument based on
force balance allows the construction of a new coalescence phase diagram
CONSUMER PREFERENCES FOR ELECTRICITY FROM BIOENERGY AND OTHER RENEWABLES
This study ascertains residential electricity consumers' support and willingness to pay for electricity from renewable sources. Then, willingness to pay for specified renewable energy sources (solar, wind, landfill wastes, bioenergy from fast growing crops, and bioenergy from forest products wastes). Effects of demographics and environmental behaviors are estimated.Institutional and Behavioral Economics,
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