460 research outputs found
Exporting Telecommunications Regulation: The U.S.-Japan Negotiations on Interconnection Pricing
Since 1997, the U.S. government has attempted to use the World Trade Organization (WTO) agreement on telecommunications services as a vehicle for 'exporting' American principles of telecommunications regulation to other nations. The United States took the position in 1997 that the WTO telecommunications agreement requires its signatory nations to follow the practices of the Federal Communications Commission (FCC) on telecommunications regulatory policy. Subsequently, the Office of the U.S. Trade Representative (USTR) has sought to influence, under the implicit threat of trade sanctions, Japan's domestic regulatory policy on the pricing of mandatory competitor access to the unbundled elements of the local network belonging to the operating companies of Nippon Telegraph and Telephone Corporation (NTT). In this Article, we examine the substantive difficulties of engrafting the FCC's interconnection policy onto the telecommunications marketplace of another nation. For more than five years, many American experts on telecommunications policy have disagreed whether American consumers have benefited from the very FCC policies that the USTR would have Japanese regulators emulate. The USTR's initiative appears to ignore that the transition to costoriented rates for interconnection and retail telecommunications services has been a difficult and unfinished process in the United States; that the cost models used by the FCC to set interconnection prices have significant deficiencies; that actual interconnection prices both within and outside the United States diverge considerably from the estimates of the FCC's cost models; that variations across countries in the prices of inputs have a significant effect on the costs of interconnection; and that, with respect to depreciation in particular, regulators treat this cost differently'and, from an economic perspective, more reasonably'in Japan than in the United States. Such substantive economic considerations suggest why the FCC's policy in this area has generated continuous litigation, including two Supreme Court cases, since 1996 and consequently is too unresolved at this point in the American experience for the United States to force on its trading partners. Next, we ask whether the USTR has the detailed knowledge required to negotiate trade agreements on interconnection pricing. We question the propriety of using the USTR to influence the domestic regulatory policy of another country on a topic as complex as the efficient pricing of mandatory access to unbundled network elements. The USTR's power to formulate trade policy on this subject resides in officials who are unlikely to possess the economic expertise and resources necessary to evaluate the consumer-welfare implications of the policies that they would have Japan and other nations adopt. For these reasons, the USTR cannot credibly make the interconnection pricing policies of another nation a legitimate concern of U.S. trade policy.
New Models for a Triaxial Milky Way Spheroid and Effect on the Microlensing Optical Depth to the Large Magellanic Cloud
We obtain models for a triaxial Milky Way spheroid based on data by Newberg
and Yanny. The best fits to the data occur for a spheroid center that is
shifted by 3kpc from the Galactic Center. We investigate effects of the
triaxiality on the microlensing optical depth to the Large Magellanic Cloud
(LMC). The optical depth can be used to ascertain the number of Massive Compact
Halo Objects (MACHOs); a larger spheroid contribution would imply fewer Halo
MACHOs. On the one hand, the triaxiality gives rise to more spheroid mass along
the line of sight between us and the LMC and thus a larger optical depth.
However, shifting the spheroid center leads to an effect that goes in the other
direction: the best fit to the spheroid center is_away_ from the line of sight
to the LMC. As a consequence, these two effects tend to cancel so that the
change in optical depth due to the Newberg/Yanny triaxial halo is at most 50%.
After subtracting the spheroid contribution in the four models we consider, the
MACHO contribution (central value) to the mass of the Galactic Halo varies from
\~(8-20)% if all excess lensing events observed by the MACHO collaboration are
assumed to be due to MACHOs. Here the maximum is due to the original MACHO
collaboration results and the minimum is consistent with 0% at the 1 sigma
error level in the data.Comment: 26 pages, 2 figures. v2: minor revisions. v3: expanded discussion of
the local spheroid density and minor revisions to match version published in
Journal of Cosmology and Astroparticle Physics (JCAP
Supernova Remnants in the Magellanic Clouds. IV. X-Ray Emission from the Largest SNR in the LMC
We present the first X-ray detection of SNR 0450-70.9 the largest known
supernova remnant (SNR) in the Large Magellanic Cloud. To study the physical
conditions of this SNR, we have obtained XMM-Newton X-ray observations, optical
images and high-dispersion spectra, and radio continuum maps. Optical images of
SNR 0450-70.9 show a large, irregular elliptical shell with bright filaments
along the eastern and western rims and within the shell interior. The interior
filaments have higher [S II]/Halpha ratios and form an apparent inner shell
morphology. The X-ray emission region is smaller than the full extent of the
optical shell, with the brightest X-ray emission found within the small
interior shell and on the western rim of the large shell. The expansion
velocity of the small shell is ~220 km/s, while the large shell is ~120 km/s.
The radio image shows central brightening and a fairly flat radio spectral
index over the SNR. However, no point X-ray or radio source corresponding to a
pulsar is detected and the X-ray emission is predominantly thermal. Therefore,
these phenomena can be most reasonably explained in terms of the advanced age
of the large SNR. Using hydrodynamic models combined with a nonequilibrium
ionization model for thermal X-ray emission, we derived a lower limit on the
SNR age of about 45,000 yr, well into the later stages of SNR evolution.
Despite this, the temperature and density derived from spectral fits to the
X-ray emission indicate that the remnant is still overpressured, and thus that
the development is largely driven by hot gas in the SNR interior.Comment: Accepted for publication in The Astrophysical Journa
Magnetohydrodynamics of Cloud Collisions in a Multi-phase Interstellar Medium
We extend previous studies of the physics of interstellar cloud collisions by
beginning investigation of the role of magnetic fields through 2D
magnetohydrodynamic (MHD) numerical simulations. We study head-on collisions
between equal mass, mildly supersonic diffuse clouds. We include a moderate
magnetic field and two limiting field geometries, with the field lines parallel
(aligned) and perpendicular (transverse) to the colliding cloud motion. We
explore both adiabatic and radiative cases, as well as symmetric and asymmetric
ones. We also compute collisions between clouds evolved through prior motion in
the intercloud medium and compare with unevolved cases.
We find that: In the (i) aligned case, adiabatic collisions, like their HD
counterparts, are very disruptive, independent of the cloud symmetry. However,
when radiative processes are taken into account, partial coalescence takes
place even in the asymmetric case, unlike the HD calculations. In the (ii)
transverse case, collisions between initially adjacent unevolved clouds are
almost unaffected by magnetic fields. However, the interaction with the
magnetized intercloud gas during the pre-collision evolution produces a region
of very high magnetic energy in front of the cloud. In collisions between
evolved clouds with transverse field geometry, this region acts like a
``bumper'', preventing direct contact between the clouds, and eventually
reverses their motion. The ``elasticity'', defined as the ratio of the final to
the initial kinetic energy of each cloud, is about 0.5-0.6 in the cases we
considered. This behavior is found both in adiabatic and radiative cases.Comment: 40 pages in AAS LaTeX v4.0, 13 figures (in degraded jpeg format).
Full resolution images as well as mpeg animations are available at
http://www.msi.umn.edu:80/Projects/twj/mhd-cc/ . Accepted for publication in
The Astrophysical Journa
Experimental Demonstration of Squeezed State Quantum Averaging
We propose and experimentally demonstrate a universal quantum averaging
process implementing the harmonic mean of quadrature variances. The harmonic
mean protocol can be used to efficiently stabilize a set of fragile squeezed
light sources with statistically fluctuating noise levels. The averaged
variances are prepared probabilistically by means of linear optical
interference and measurement induced conditioning. We verify that the
implemented harmonic mean outperforms the standard arithmetic mean strategy.
The effect of quantum averaging is experimentally tested both for uncorrelated
and partially correlated noise sources with sub-Poissonian shot noise or
super-Poissonian shot noise characteristics.Comment: 4 pages, 5 figure
Supernova Remnants in the Magellanic Clouds. V. The Complex Interior Structure of the N206 SNR
The N206 supernova remnant (SNR) in the Large Magellanic Cloud (LMC) has long
been considered a prototypical "mixed morphology" SNR. Recent observations,
however, have added a new twist to this familiar plot: an elongated,
radially-oriented radio feature seen in projection against the SNR face.
Utilizing the high resolution and sensitivity available with the Hubble Space
Telescope, Chandra, and XMM-Newton, we have obtained optical emission-line
images and spatially resolved X-ray spectral maps for this intriguing SNR. Our
findings present the SNR itself as a remnant in the mid to late stages of its
evolution. X-ray emission associated with the radio "linear feature" strongly
suggests it to be a pulsar-wind nebula (PWN). A small X-ray knot is discovered
at the outer tip of this feature. The feature's elongated morphology and the
surrounding wedge-shaped X-ray enhancement strongly suggest a bow-shock PWN
structure.Comment: 41 pages including 7 figures, accepted for publication by the
Astrophysical Journa
Magellanic Cloud Structure from Near-IR Surveys II: Star Count Maps and the Intrinsic Elongation of the LMC
I construct a near-IR star count map of the LMC and demonstrate, using the
viewing angles derived in Paper I, that the LMC is intrinsically elongated. I
argue that this is due to the tidal force from the Milky Way. The near-IR data
from the 2MASS and DENIS surveys are used to create a star count map of RGB and
AGB stars, which is interpreted through ellipse fitting. The radial number
density profile is approximately exponential with a scale-length 1.3-1.5 kpc.
However, there is an excess density at large radii that may be due to the tidal
effect of the Milky Way. The position angle and ellipticity profile converge to
PA_maj = 189.3 +/- 1.4 degrees and epsilon = 0.199 +/- 0.008 for r > 5 deg. At
large radii there is a drift of the center of the star count contours towards
the near side of the plane, which can be undrestood as due to viewing
perspective. The fact that PA_maj differes from the line of nodes position
angle Theta = 122.5 +/- 8.3 (cf. Paper I) indicates that the LMC disk is not
circular, but has an intrinsic ellipticity of 0.31. The LMC is elongated in the
general direction of the Galactic center, and is elongated perpendicular to the
Magellanic Stream and the velocity vector of the LMC center of mass. This
suggests that the elongation of the LMC has been induced by the tidal force of
the Milky Way. The position angle of the line of nodes differs from the
position angle Theta_max of the line of maximum line of sight velocity
gradient: Theta_max - Theta = 20-60 degrees. This could be due to: (a)
streaming along non-circular orbits in the elongated disk; (b) uncertainties in
the transverse motion of the LMC center of mass; (c) precession and nutation of
the LMC disk as it orbits the Milky Way (expected on theoretical grounds).
[Abridged]Comment: Astronomical Journal, in press. 34 pages, LaTeX, with 7 PostScript
figures. Contains minor revisions with respect to previously posted version.
Check out http://www.stsci.edu/~marel/lmc.html for a large scale (23x21
degree) stellar number-density image of the LMC constructed from RGB and AGB
stars in the 2MASS and DENIS surveys. The paper is available with higher
resolution color figures from
http://www.stsci.edu/~marel/abstracts/abs_R32.htm
Is a Classical Language Adequate in Assessing the Detectability of the Redshifted 21cm Signal from the Early Universe?
The classical radiometer equation is commonly used to calculate the
detectability of the 21cm emission by diffuse cosmic hydrogen at high
redshifts. However, the classical description is only valid in the regime where
the occupation number of the photons in phase space is much larger than unity
and they collectively behave as a classical electromagnetic field. At redshifts
z<20, the spin temperature of the intergalactic gas is dictated by the
radiation from galaxies and the brightness temperature of the emitting gas is
in the range of mK, independently from the existence of the cosmic microwave
background. In regions where the observed brightness temperature of the 21cm
signal is smaller than the observed photon energy, of 68/(1+z) mK, the
occupation number of the signal photons is smaller than unity. Neverethless,
the radiometer equation can still be used in this regime because the weak
signal is accompanied by a flood of foreground photons with a high occupation
number (involving the synchrotron Galactic emission and the cosmic microwave
background). As the signal photons are not individually distinguishable, the
combined signal+foreground population of photons has a high occupation number,
thus justifying the use of the radiometer equation.Comment: 4 pages, Accepted for publication in JCA
Equilibrium Disk-Bulge-Halo Models for the Milky Way and Andromeda Galaxies
We describe a new set of self-consistent, equilibrium disk galaxy models that
incorporate an exponential disk, a Hernquist model bulge, an NFW halo and a
central supermassive black hole. The models are derived from explicit
distribution functions for each component and the large number of parameters
permit detailed modeling of actual galaxies. We present techniques that use
structural and kinematic data such as radial surface brightness profiles,
rotation curves and bulge velocity dispersion profiles to find the best-fit
models for the Milky Way and M31. Through N-body realizations of these models
we explore their stability against the formation of bars. The models permit the
study of a wide range of dynamical phenomenon with a high degree of realism.Comment: 58 pages, 20 figures, submitted to the Astrophysical Journa
A Sample of Intermediate-Mass Star-Forming Regions: Making Stars at Mass Column Densities <1 g/cm^2
In an effort to understand the factors that govern the transition from low-
to high-mass star formation, we identify for the first time a sample of
intermediate-mass star-forming regions (IM SFRs) where stars up to - but not
exceeding - 8 solar masses are being produced. We use IRAS colors and Spitzer
Space Telescope mid-IR images, in conjunction with millimeter continuum and CO
maps, to compile a sample of 50 IM SFRs in the inner Galaxy. These are likely
to be precursors to Herbig AeBe stars and their associated clusters of low-mass
stars. IM SFRs constitute embedded clusters at an early evolutionary stage akin
to compact HII regions, but they lack the massive ionizing central star(s). The
photodissociation regions that demarcate IM SFRs have typical diameters of ~1
pc and luminosities of ~10^4 solar luminosities, making them an order of
magnitude less luminous than (ultra)compact HII regions. IM SFRs coincide with
molecular clumps of mass ~10^3 solar masses which, in turn, lie within larger
molecular clouds spanning the lower end of the giant molecular cloud mass
range, 10^4-10^5 solar masses. The IR luminosity and associated molecular mass
of IM SFRs are correlated, consistent with the known luminosity-mass
relationship of compact HII regions. Peak mass column densities within IM SFRs
are ~0.1-0.5 g/cm^2, a factor of several lower than ultra-compact HII regions,
supporting the proposition that there is a threshold for massive star formation
at ~1 g/cm^2.Comment: 61 pages, 6 tables, 20 figures. Accepted for publication in the
Astronomical Journa
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