10,051 research outputs found
A robust loop-shaping approach to fast and accurate nanopositioning
Peer reviewedPreprin
Clarification of the Nature of the Galaxy CFC97 Cen 05
The galaxy CFC97 Cen 05 has in the past been considered an HI-rich dwarf
galaxy in the nearby Centaurus A group. We have used Australia Telescope
Compact Array observations to show that the HI associated with CFC97 Cen 05 by
Cote et al. (1997) is most likely a Galactic High Velocity Cloud that is
centered ~17' from the optical image of the galaxy. At the optical location of
the galaxy, which is not that tabulated by Banks et al. (1999), there is no
indication of the presence of HI for velocities less than the upper limit of
the HIPASS survey at ~12,500 km/s. In addition, WFPC2 images of CFC97 Cen 05
obtained from the HST Archive reveal that this galaxy is in fact not a dwarf at
all, but rather is a distant background spiral not associated with the
Centaurus A group.Comment: accepted for publication in the PASP (November 2004
The catalytic role of beta effect in barotropization processes
The vertical structure of freely evolving, continuously stratified,
quasi-geostrophic flow is investigated. We predict the final state
organization, and in particular its vertical structure, using statistical
mechanics and these predictions are tested against numerical simulations. The
key role played by conservation laws in each layer, including the fine-grained
enstrophy, is discussed. In general, the conservation laws, and in particular
that enstrophy is conserved layer-wise, prevent complete barotropization, i.e.,
the tendency to reach the gravest vertical mode. The peculiar role of the
-effect, i.e. of the existence of planetary vorticity gradients, is
discussed. In particular, it is shown that increasing increases the
tendency toward barotropization through turbulent stirring. The effectiveness
of barotropisation may be partly parameterized using the Rhines scale . As this parameter decreases (beta increases) then
barotropization can progress further, because the beta term provides enstrophy
to each layer
Ubiquitous diffraction resonances in positronium formation from fullerenes
Due to the dominant electron capture by positrons from the molecular wall and
the spatial dephasing across the wall-width, a powerful diffraction effect
universally underlies the positronium (Ps) formation from fullerenes. This
results into trains of resonances in the Ps formation cross section as a
function of the positron beam energy, producing uniform structures in recoil
momenta in analogy with classical single-slit diffraction fringes in the
configuration space. The prediction opens a hitherto unknown avenue of Ps
spectroscopy with nanomaterials.Comment: 6 pages, 3 figures, submitte
Online Convex Optimization with Binary Constraints
We consider online optimization with binary decision variables and convex
loss functions. We design a new algorithm, binary online gradient descent
(bOGD) and bound its expected dynamic regret. We provide a regret bound that
holds for any time horizon and a specialized bound for finite time horizons.
First, we present the regret as the sum of the relaxed, continuous round
optimum tracking error and the rounding error of our update in which the former
asymptomatically decreases with time under certain conditions. Then, we derive
a finite-time bound that is sublinear in time and linear in the cumulative
variation of the relaxed, continuous round optima. We apply bOGD to demand
response with thermostatically controlled loads, in which binary constraints
model discrete on/off settings. We also model uncertainty and varying load
availability, which depend on temperature deadbands, lockout of cooling units
and manual overrides. We test the performance of bOGD in several simulations
based on demand response. The simulations corroborate that the use of
randomization in bOGD does not significantly degrade performance while making
the problem more tractable
Labor Market Regulation and Employment in the Caribbean
This research project focuses on the demand side of the labor market by examining the impact which labor market regulations have had on employment creation in the English-speaking Caribbean countries of Barbados, Jamaica and Trinidad and Tobago. Although a recent IADB report on labor market reform in Latin America and the Caribbean indicates that the English-speaking Caribbean countries have a lower level of labor market inflexibility than Latin American countries, the regulatory environment in both the labor and commodity markets has had some adverse impact on employment creation in the region (IADB, 1996). Results from a study of the operations of the labor market in the Caribbean Group for Cooperation in Economic Development (CGCED) suggest that these regulatory measures do have some effect on the operation of businesses in the region (see Abt Associates, 1998).
Importance of electronic correlations for structural and magnetic properties of the iron pnictide superconductor LaFeAsO
We present calculations of structural and magnetic properties of the
iron-pnictide superconductor LaFeAsO including electron-electron correlations.
For this purpose we apply a fully charge self-consistent combination of
Density-Functional Theory with the Dynamical Mean-Field theory, allowing for
the calculation of total energies. We find that the inclusion of correlation
effects gives a good agreement of the Arsenic z position with experimental data
even in the paramagnetic (high-temperature) phase. Going to low temperatures,
we study the formation of the ordered moment in the striped spin-density-wave
phase, yielding an ordered moment of about 0.60, again in good agreement with
experiments. This shows that the inclusion of correlation effects improves both
structural and magnetic properties of LaFeAsO at the same time.Comment: 7 pages, 5 figures, published versio
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