712 research outputs found
High Resolution BIMA Observations of CO, HCN, and 13CO in NGC 1068
We present high-resolution CO, HCN, and 13CO maps of the inner arcminute of
NGC 1068 made with the BIMA interferometer. Several features appear in the CO
map which have not previously been observed: (1) a firm detection of CO line
emission from a compact region centered on the nucleus of the galaxy; (2) the
detection of a triplet velocity structure characteristic of kinematically
independent regions shown on the spectrum of the unresolved nuclear emission ;
and (3) the detection of a molecular bar, the extent and position angle of
which are in good agreement with the 2 m stellar bar. The most intense CO
emission is nonnuclear; the structure and kinematics of this emission imply
that this gas is distributed along the inner spiral arms and not in a ring. The
bar's kinematic influence on the molecular gas in the spiral arms is modest,
with typical ordered noncircular motions of \la\ 30 \kms\ in the plane of the
galaxy. Interior to the spiral arms, the bar's influence is more dramatic, as
reflected by the twisted isovelocity contours in the CO and HCN velocity
fields. The surface density of molecular gas within the central 100 pc radius
of NGC 1068 is the same as that in the central 200 pc radius in the Milky Way
to within the uncertainties. There is evidence for an kinematic mode in
NGC 1068; we find the kinematic center of rotation to be displaced from the
radio continuum center by about 2.9", or 200 pc. The HCN image, in contrast to
the CO map, shows a strong concentration of emission centered on the nucleus.
The ratio of integrated intensities of the HCN emission to that of CO is about
0.6 and is the highest ratio measured in the central region of any galaxy.Comment: 35 pages of uuencoded, compressed postscript, 20 postscript figures
not included but available from [email protected] or from
ftp://astro.astro.umd.edu/pub/thelfer/n1068_figs.ps.Z To appear in The
Astrophysical Journal, V. 450, Sept. 199
Dense Gas in the Milky Way
We present a study of dense gas emission in the Milky Way in order to serve
as a basis for comparison with extragalactic results. This study combines new
observations of HCN, CS, and CO in individual GMCs and in the Milky Way plane
with published studies of emission from these molecules in the inner 500 pc of
the Milky Way. We find a strong trend in the fraction of emission from dense
gas tracers as a function of location in the Milky Way: in the bulge,
I_{HCN}/I_{CO} = 0.081 \pm 0.004, in the plane, I_{HCN}/I_{CO} = 0.026 \pm
0.008 on average, and over the full extent of nearby GMCs, I_{HCN}/I_{CO} =
0.014 \pm 0.020. Similar trends are seen in I_{CS}/I_{CO}. The low intensities
of the HCN and CS emission in the plane suggests that these lines are produced
by gas at moderate densities; they are thus not like the emission produced by
the dense, pc-scale star forming cores in nearby GMCs. The contrast between the
bulge and disk ratios in the Milky Way is likely to be caused by a combination
of higher kinetic temperatures as well as a higher dense gas fraction in the
bulge of the Milky Way.Comment: 34 pages LaTeX, AASTEX macros, includes 11 postscript figures. To
appear in ApJ 478, March 199
Backlash Against International Courts in West, East and Southern Africa: Causes and Consequences
This paper discusses three credible attempts by African governments to restrict the jurisdiction of three similarly-situated sub-regional courts in response to politically controversial rulings. In West Africa, when the ECOWAS Court upheld allegations of torture by opposition journalists in the Gambia, that country’s political leaders sought to restrict the Court’s power to review human rights complaints. The other member states ultimately defeated the Gambia’s proposal. In East Africa, Kenya failed in its efforts to eliminate the EACJ and to remove some of its judges after a decision challenging an election to a sub-regional legislature. However, the member states agreed to restructure the EACJ in ways that have significantly affected the court’s subsequent trajectory. In Southern Africa, after the SADC Tribunal ruled in favor of white farmers in disputes over land seizure, Zimbabwe prevailed upon SADC member states to suspend the Tribunal and strip its power to review complaints from private litigants. Variations in the mobilization efforts of Community secretariats, civil society groups and sub-regional Parliaments explain why efforts to eliminate the three courts or narrow their jurisdiction were defeated in ECOWAS, scaled back in the EAC, and largely succeeded in SADC
Moving Mirrors and Thermodynamic Paradoxes
Quantum fields responding to "moving mirrors" have been predicted to give
rise to thermodynamic paradoxes. I show that the assumption in such work that
the mirror can be treated as an external field is invalid: the exotic
energy-transfer effects necessary to the paradoxes are well below the scales at
which the model is credible. For a first-quantized point-particle mirror, it
appears that exotic energy-transfers are lost in the quantum uncertainty in the
mirror's state. An accurate accounting of these energies will require a model
which recognizes the mirror's finite reflectivity, and almost certainly a model
which allows for the excitation of internal mirror modes, that is, a
second-quantized model.Comment: 7 pages, Revtex with Latex2
Counting cycles in labeled graphs: The nonpositive immersion property for one-relator groups
We prove a rank 1 version of the Hanna Neumann Theorem. This shows that every
one-relator 2-complex without torsion has the nonpositive immersion property.
The proof generalizes to staggered and reducible 2-complexes.Comment: 12 pages, 2 figure
Insertion reliability studies for the RBC-type control rods in ASTRID
International audienceThis paper reports on preliminary studies performed regarding the insertion reliability of theRBC-type Control Rods designed for the ASTRID Sodium-cooled Fast Reactor. At this stage, the primary aim of the analysis is to evaluate the mechanical behavior of RBC Control Rods under Emergency Shutdown conditions, for which reactor core structures are subjected to significant misalignments (including earthquakeimposed displacements). Using a Finite Element Model based on the Cast3M solver and developed specifically for these studies, computations are performed that allow assessing contact reactions (and the associated friction forces and contact pressures), deformations and stresses (mostly due to bending-induced deformations) which are considered for design. Based on these preliminary results, some optimization of the Control Rod design is proposed that ensures some stable behavior all along the rod drop, with substantial design margin
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