13,559 research outputs found
Critical Currents of Josephson-Coupled Wire Arrays
We calculate the current-voltage characteristics and critical current
I_c^{array} of an array of Josephson-coupled superconducting wires. The array
has two layers, each consisting of a set of parallel wires, arranged at right
angles, such that an overdamped resistively-shunted junction forms wherever two
wires cross. A uniform magnetic field equal to f flux quanta per plaquette is
applied perpendicular to the layers. If f = p/q, where p and q are mutually
prime integers, I_c^{array}(f) is found to have sharp peaks when q is a small
integer. To an excellent approximation, it is found in a square array of n^2
plaquettes, that I_c^{array}(f) \propto (n/q)^{1/2} for sufficiently large n.
This result is interpreted in terms of the commensurability between the array
and the assumed q \times q unit cell of the ground state vortex lattice.Comment: 4 pages, 4 figure
Voluntary Funding for Generic Advertising Using a Provision Point Mechanism: An Experimental Analysis of Option Assurance
The mandatory nature of generic advertising funding remains a contentious issue. Theoretically and in laboratory environments, a provision point mechanism with a money-back guarantee offers an attractive voluntary alternative to the standard voluntary contribution mechanisms, yet in practice, few examples of multiple-round provision point mechanisms exist. A practical concern with applying these mechanisms is that even a slight shortfall in contributions relative to the designated funding threshold in one period would engender an irreversible shutdown of administrative capacity with negative consequences for subsequent periods. This paper uses experimental economics to test new two-threshold provision point mechanisms in the context of check-off programs for funding commodity marketing programs that would separately fund the minimum administrative capacity and the more costly full marketing program. In these mechanisms, even if a funding shortfall occurs for the full marketing program, the low threshold can maintain the administrative capacity and retain the option for future funding of advertising. We demonstrate that providing such "option assurance" does not lead to a decrease in overall contributions and, in some settings, can increase producer surplus.Marketing,
Spectro-Morphology of Galaxies
We present a quantitative method to classify galaxies, based on
multi-wavelength data and elaborated from the properties of nearby galaxies.
Our objective is to define an evolutionary method that can be used for low and
high redshift objects. We estimate the concentration of light (C) at the galaxy
center and the 180 degree-rotational asymmetry (A), computed at several
wavelengths, from ultraviolet (UV) to I-band. The variation of the indices of
concentration and asymmetry with the wavelength reflects the proportion and the
distribution of young and old stellar populations in galaxies. In general C is
found to decrease from optical to UV, and A is found to increase from optical
to UV: the patchy appearance of galaxies in UV with no bulge is often very
different from their counterpart at optical wavelengths, with prominent bulges
and more regular disks. The variation of C and A with the wavelength is
quantified. By this way, we are able to distinguish five types of galaxies that
we call spectro-morphological types: compact, ringed, spiral, irregular and
central-starburst galaxies, which can be differentiated by the repartition of
their stellar populations. We discuss in detail the morphology of galaxies of
the sample, and describe the morphological characteristics of each
spectro-morphological type. We apply spectro-morphology to three objects at a
redshift z=1 in the Hubble Deep Field North, that gives encouraging results for
applications to large samples of high-redshift galaxies. This method of
morphological classification could be used to study the evolution of the
morphology with the redshift and is expected to bring observational constraints
on scenarios of galaxy evolution.Comment: Accepted for publication in Astronomy & Astrophysic
Tomography of Collisionless Stellar Systems
In this paper the concept of tomography of a collisionless stellar system of
general shape is introduced, and a generalization of the Projected Virial
Theorem is obtained. Applying the tomographic procedure we then derive a new
family of virial equations which coincides with the already known ones for
spherically symmetric systems. This result is obtained without any use of
explicit expressions for the line-of-sight velocity dispersion, or spherical
coordinate system.Comment: BAP-06-1994-016-OAB. 7 pages, postscript file. In press on Celestial
Mechanic
Ferromagnetic resonance study of polycrystalline Fe_{1-x}V_x alloy thin films
Ferromagnetic resonance has been used to study the magnetic properties and
magnetization dynamics of polycrystalline FeV alloy films with
. Films were produced by co-sputtering from separate Fe and V
targets, leading to a composition gradient across a Si substrate. FMR studies
were conducted at room temperature with a broadband coplanar waveguide at
frequencies up to 50 GHz using the flip-chip method. The effective
demagnetization field and the Gilbert damping
parameter have been determined as a function of V concentration. The
results are compared to those of epitaxial FeV films
Epitaxial Ferromagnetic Nanoislands of Cubic GdN in Hexagonal GaN
Periodic structures of GdN particles encapsulated in a single crystalline GaN
matrix were prepared by plasma assisted molecular beam epitaxy. High resolution
X-ray diffractometery shows that GdN islands, with rock salt structure are
epitaxially oriented to the wurtzite GaN matrix. Scanning transmission electron
microscopy combined with in-situ reflection high energy electron diffraction
allows for the study of island formation dynamics, which occurs after 1.2
monolayers of GdN coverage. Magnetometry reveals two ferromagnetic phases, one
due to GdN particles with Curie temperature of 70K and a second, anomalous room
temperature phase.Comment: 4 pages, 3 figure
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