6,395 research outputs found
Trade Credit, International Reserves and Sovereign Debt
We present a unified model of sovereign debt, trade credit and international reserves. Our model shows that access to short-term trade credit and gross international reserves critically affect the outcome of sovereign debt renegotiations. Whereas competitive banks do optimally lend for the accumulation of borrowed reserves that strengthen the bargaining position of borrowers, they also have incentives to restrict the supply of short-term trade credit during renegotiations. We first show that they effectively do so and then derive propositions that : I) establish the size of sovereign debt haircuts as a function of economic fundamentals and preferences ; II) predict that defaults occur during recessions rather than booms, contrary to reputation based models ; III) provide a rationale for holding costly borrowed reserves and, IV) show that the stock of borrowed international reserves tends to increase when global interest rates are low.
Generalization of the Schott energy in electrodynamic radiation theory
We discuss the origin of the Schott energy in the Abraham-Lorentz version of
electrodynamic radiation theory and how it can be used to explain some apparent
paradoxes. We also derive the generalization of this quantity for the
Ford-O'Connell equation, which has the merit of being derived exactly from a
microscopic Hamiltonian for an electron with structure and has been shown to be
free of the problems associated with the Abraham-Lorentz theory. We emphasize
that the instantaneous power supplied by the applied force not only gives rise
to radiation (acceleration fields), but it can change the kinetic energy of the
electron and change the Schott energy of the velocity fields. The important
role played by boundary conditions is noted
Rotation and Spin in Physics
We delineate the role of rotation and spin in physics, discussing in order
Newtonian classical physics, special relativity, quantum mechanics, quantum
electrodynamics and general relativity. In the latter case, we discuss the
generalization of the Kepler formula to post-Newtonian order )
including spin effects and two-body effects. Experiments which verify the
theoretical results for general relativistic spin-orbit effects are discussed
as well as efforts being made to verify the spin-spin effects
On risk aversion in the Rubinstein bargaining game
We derive closed-form solutions for the Rubinstein alternating offers game for cases where the two players have (possibly asymmetric) utility functions that belong to the HARA class and discount the future at a constant rate. We show that risk aversion may increase a bargainers payoff. This result - which contradicts Roth’s 1985 theorem tying greater risk neutrality to a smaller payoff - does not rely on imperfect information or departures from expected utility maximization
Signatures of the Youngest Starbursts: Optically-thick Thermal Bremsstrahlung Radio Sources in Henize 2-10
VLA radio continuum imaging reveals compact (<8 pc) ~1 mJy radio sources in
the central 5" starburst region of the blue compact galaxy Henize 2-10. We
interpret these radio knots as extremely young, ultra-dense HII regions. We
model their luminosities and spectral energy distributions, finding that they
are consistent with unusually dense HII regions having electron densities, 1500
cm^-3 < n_e < 5000 cm^-3, and sizes of 3-8 pc. Since these H II regions are not
visible in optical images, we propose that the radio data preferentially reveal
the youngest, densest, and most highly obscured starforming events. Energy
considerations imply that each of the five \HII regions contains ~750 O7V
equivalent stars, greater than the number found in 30 Doradus in the LMC. The
high densities imply an over-pressure compared to the typical interstellar
medium so that such objects must be short-lived (<0.5 Myr expansion
timescales). We conclude that the radio continuum maps reveal the very young
(<0.5 Myr) precursors of ``super starclusters'' or ``proto globular clusters''
which are prominent at optical and UV wavelengths in He 2-10. If the
ultra-dense HII regions are typical of those which we predict will be found in
other starbursting systems, then super starclusters spend 15% of their lifetime
in heavily-obscured environments, similar to Galactic ultra-compact HII
regions. This body of work leads us to propose that massive extragalactic star
clusters (i.e. proto globular clusters) with ages <10^6 yr may be most easily
identified by finding compact radio sources with optically-thick thermal
bremsstrahlung spectral signatures.Comment: AASTeX, 8 figures 2 included with psfig in text; other 6 in jpeg
format; Postscript versions of figures may be found at
http://zem.ucolick.org/chip/Research/young_clusters.html -- Accepted for
publication in the Astrophysical Journa
Spatial Variation in the Relationship between Hispanic Concentration and County Poverty: A Migration Perspective
Balmer and Metal Absorption Feature Gradients in M32
Spectra from MDM Observatory are used to assess Lick/IDS feature strength
gradients inside the half-light radius of the compact Local Group elliptical
galaxy M32. All but a few (of 24 measured) indices show a statistically
significant gradient. Comparing with models, the index gradients indicate a
mean age and abundance gradient in the sense that the nucleus is a factor of
2.5 younger and a factor of 0.3 dex more metal-rich than at 1 effective radius.
This conclusion is only weakly dependent on which index combinations are used
and is robust to high accuracy. Stars near the M32 nucleus have a mean age and
heavy element abundance [M/H] of (4.7 Gyr, +0.02), judging from models by
Worthey with variable abundance ratios. This result has very small formal
random errors, although, of course, there is significant age-metallicity
degeneracy along an (age, abundance) line segment from (5.0 Gyr, 0.00) to (4.5
Gyr, +0.05). An abundance pattern of [C/M]=+0.077, [N/M]=-0.13, [Mg/M]=-0.18,
[Fe/M]~0.0, and [Na/M]=+0.12 is required to fit the feature data, with a
fitting precision of about 0.01 dex. Model uncertainties make the accuracies of
these values at least twice the magnitude of the precision. Forcing
scaled-solar abundances does not change the age very much, but it increases the
rms goodness of model-data fit by a factor of 3 and broadens the allowed range
of age to Gyr. The overall abundance pattern contrasts with larger
elliptical galaxies, in which all measurable lighter elements are enhanced
relative to iron and calcium.Comment: 23 pages, 9 figures, Astronomical Journal, in pres
A multi-layer extension of the stochastic heat equation
Motivated by recent developments on solvable directed polymer models, we
define a 'multi-layer' extension of the stochastic heat equation involving
non-intersecting Brownian motions.Comment: v4: substantially extended and revised versio
Transformed Dissipation in Superconducting Quantum Circuits
Superconducting quantum circuits must be designed carefully to avoid
dissipation from coupling to external control circuitry. Here we introduce the
concept of current transformation to quantify coupling to the environment. We
test this theory with an experimentally-determined impedance transformation of
and find quantitative agreement better than a factor of 2 between
this transformation and the reduced lifetime of a phase qubit coupled to a
tunable transformer. Higher-order corrections from quantum fluctuations are
also calculated with this theory, but found not to limit the qubit lifetime. We
also illustrate how this simple connection between current and impedance
transformation can be used to rule out dissipation sources in experimental
qubit systems.Comment: 4 pages, 4 figure
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