2,017 research outputs found
Economic Criteria for Settling Federalism Disputes with an Application to Food Safety Regulation
Federal ism disputes arising from state regulations, particularly those pursuing health, safety, and environmental goals, are a common feature of the U.S . political system. Discussion of bases for settling such disputes often focuses on the in- and out-state incidence of benefits and costs but incidence is a complex concept that has not been systematically analyzed. We discuss five factors important to evaluating incidence and present spillover criteria for judging disputes based on them. When applied to a Massachusetts regulation of daminozide residues in heat-processed apple products, the criteria reach different conclusions on its appropriateness, although the main criteria suggest it should be invalidated by the courts or preempted by federal law. The application illustrates how the spillover criteria can clarify analysis of federalism disputes.Food Consumption/Nutrition/Food Safety,
VLA Observations of the "Eye of the Tornado"- the High Velocity \HII Region G357.63-0.06
The unusual supernova remnant candidate G357.7-0.1 and the compact source
G357.63-0.06 have been observed with the Very Large Array at 1.4 and 8.3 GHz.
The H92 line (8.3 GHz) was detected from the compact source with a
surprising velocity of about -210 km/s indicating that this source is an \HII
region, is most likely located at the Galactic center, and is unrelated to the
SNR. The \HI absorption line (1.4 GHz) data toward these sources supports this
picture and suggests that G357.7-0.1 lies farther away than the Galactic
center.Comment: Latex, 14 pages including 4 figures. Accepted to A
An analysis of the X-ray emission from the supernova remnant 3C397
The ASCA SIS and the ROSAT PSPC spectral data of the SNR 3C397 are analysed
with a two-component non-equilibrium ionization model. Besides, the ASCA SIS0
and SIS1 spectra are also fitted simultaneously in an equilibrium case. The
resulting values of the hydrogen column density yield a distance of \sim8\kpc
to 3C397. It is found that the hard X-ray emission, containing S and Fe
K lines, arises primarily from the hot component, while most of the
soft emission, composed mainly of Mg, Si, Fe L lines, and continuum, is
produced by the cool component. The emission measures suggest that the remnant
evolves in a cloudy medium and imply that the supernova progenitor might not be
a massive early-type star. The cool component is approaching ionization
equilibrium. The ages estimated from the ionization parameters and dynamics are
all much greater than the previous determination. We restore the X-ray maps
using the ASCA SIS data and compare them with the ROSAT HRI and the NRAO VLA
Sky Survey (NVSS) 20 cm maps. The morphology with two bright concentrations
suggests a bipolar remnant encountering a denser medium in the west.Comment: 20 pages, aasms4.sty, 3 figures To appear in ApJ (1999
What could be learnt from Positronium for Quarkonium?
In order to fulfill Low's theorem requirements, a new lowest order basis for
bound state decay computations is proposed, in which the binding energy is
treated non-perturbatively. The properties of the method are sketched by
reviewing standard positronium decay processes. Then, it is shown how applying
the method to quarkonia sheds new light on some longstanding puzzles.Comment: 12 pages, 10 figures. Talk given at the ETH Workshop on Positronium
Physics, May 30-31, 2003, Zurich, Switzerlan
Infrared study of the Southern Galactic star forming region associated with IRAS 14416-5937
Aims: We have carried out an infrared study of the southern Galactic massive
star forming region associated with IRAS 14416-5937. Methods: This star forming
region has been mapped simultaneously in two far infrared bands at ~ 150 & 210
micron using the TIFR 1-m balloon borne telescope with ~ 1' angular resolution.
We have used 2MASS JHK as well as Spitzer-GLIMPSE data of this region to
study the stellar populations of the embedded young cluster. This region
comprises of two sources, designated as A & B and separated by ~ 2 pc. The
spectrum of a region located close to the source A obtained using the Long
Wavelength Spectrometer (LWS) on-board the Infrared Space Observatory (ISO), is
presented. Emission from warm dust and from Unidentified Infrared Bands (UIBs)
is estimated using the mid-infrared data of the MSX survey. Results: The
spatial distributions of (1) the temperature of cool dust and (2) optical depth
at 200 micron have been obtained taking advantage of the similar beams in both
the TIFR bands. A number of atomic fine structure lines have been detected in
the ISO-LWS spectrum, which have been used to estimate the electron density and
the effective temperature of the ionising radiation in this region. From the
near and mid infrared images, we identify a dust lane due north-west of source
A. The dust lane is populated by Class I type sources. Class II type sources
are found further along the dust lane as well as below it. Self consistent
radiative transfer models of the two sources (A and B) are in good agreement
with the observed spectral energy distributions. Conclusions: The spatial
distribution of young stellar objects in and around the dust lane suggests that
active star formation is taking place along the dust lane and is possibly
triggered by the expanding HII regions of A and B.Comment: Accepted by the Astronomy and Astrophysics (21 pages, 7 tables and 13
figures
Intermittent maser flare around the high mass young stellar object G353.273+0.641 I: data & overview
We have performed VLBI and single-dish monitoring of 22 GHz HO maser
emission from the high mass young stellar object G353.273+0.641 with VERA (VLBI
Exploration of Radio Astrometry) and Tomakamai 11-m radio telescope. Two maser
flares have been detected, separated almost two years. Frequent VLBI monitoring
has revealed that these flare activities have been accompanied by structural
change of the prominent shock front traced by H2O maser alignments. We have
detected only blue-shifted emissions and all maser features have been
distributed within very small area of 200 200 au in spite of
wide velocity range (> 100 km s). The light curve shows notably
intermittent variation and suggests that the HO masers in G353.273+0.641
are excited by episodic radio jet. The time-scale of \sim2 yr and
characteristic velocity of \sim500 km s also support this
interpretation. Two isolated velocity components of C50 (-53 \pm 7 km s)
and C70 (-73 \pm 7 km s) have shown synchronised linear acceleration of
the flux weighted V_{\rmn{LSR}} values (\sim-5 km s yr) during
the flare phase. This can be converted to the lower-limit momentum rate of 1.1
\times 10 M_{\sun} km s yr. Maser properties are quite
similar to that of IRAS 20126+4104 especially. This corroborates the previous
suggestion that G353.273+0.641 is a candidate of high mass protostellar object.
The possible pole-on geometry of disc-jet system can be suitable for direct
imaging of the accretion disc in this case.Comment: 13 pages, 5 figures accepted for publication in MNRA
A Survey of OH Masers Towards High Mass Protostellar Objects
We present a survey of OH maser emission towards a sample of high mass
protostellar objects made using the Nancay and GBT telescopes.OH maser emission
was detected towards 63 objects with 36 new detections. There are 56
star-forming regions and 7 OH/IR candidates. There is no evidence that sources
with OH masers have a different range of luminosities from the non-maser
sources. The results of this survey are compared with previous water and class
II methanol maser observations of the same objects. Some of the detected
sources are only associated with OH masers and some sources are only associated
with the 1720 MHz OH maser line. The velocity range of the maser emission
suggests that the water maser sources may be divided into two groups. The
detection rates and velocity range of the OH and Class II methanol masers
support the idea that there is a spatial association of the OH and Class II
methanol masers. The sources span a wide range in R, the ratio of the methanol
maser peak flux to OH 1665 MHz maser peak flux, however there are only a few
sources with intermediate values of R, 8<R<32, which has characterised previous
samples. Sources which have masers of any species, OH, water or methanol, have
redder [100um-12um] IRAS colours than those without masers. However, there is
no evidence for different maser species tracing different stages in the
evolution of these young high mass sources. Previous observations which have
shown that the OH maser emission from similar sources traces the circumstellar
disks around the objects. This combined with the sensitivity of the OH emission
to the magnetic field, make the newly detected sources interesting candidates
for future follow-up at high angular resolution.Comment: Accepted for publication in A&
X-ray Observation and Analysis of The Composite Supernova Remnant G327.1-1.1
Based on the data from the observation of the SNR G327.1-1.1 by ASCA and
ROSAT, we find that G327.1-1.1 is a composite remnant with both a nonthermal
emission component and a diffuse thermal emission component. The nonthermal
component is well fitted by a power-law model with photon index about 2.2. This
component is attributed to the emission from the synchrotron nebula powered by
an undiscovered central pulsar. The thermal component has a temperature of
about 0.4 keV. We attribute it to the emission from the shock-heat swept-up
ISM. Its age, explosion energy and density of ambient medium are derived from
the observed thermal component. Some charactistics about the synchrotron nebula
are also derived. We search for the pulsed signal, but has not found it. The
soft X-ray(0.4 - 2 keV) and hard X-ray(2 - 10 keV) images are different, but
they both elongate in the SE-NW direction. And this X-ray SE-NW elongation is
in positional coincidence with the radio ridge in MOST 843MHz radio map. We
present a possibility that the X-ray nonthermal emission mainly come from the
trail produced by a quickly moving undiscoverd pulsar, and the long radio ridge
is formed when the pulsar is moving out of the boundary of the plerionic
structure.Comment: 20 pages, 4 Postscript figures, aasms4.sty and psfig.sty, to be
published in Astrophysical Journal, January 20, 1999, Vol. 51
The Australia Telescope campaign to study southern class I methanol masers
The Australia Telescope Compact Array (ATCA) and the Mopra facility have been
used to search for new southern class I methanol masers at 9.9, 25 (J=5) and
104 GHz, which are thought to trace more energetic conditions in the interface
regions of molecular outflows, than the widespread class I masers at 44 and 95
GHz. One source shows a clear outflow association.Comment: 2 pages, 1 figure (composed from 3 files), to appear in proceedings
of IAU Symposium 242 "Astrophysical masers and their environment" (eds. J.
Chapman and W. Baan
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