172 research outputs found
New Optical Reddening Maps of the Large and Small Magellanic Clouds
We present new reddening maps of the SMC and LMC based on the data of the
third phase of the Optical Gravitational Lensing Experiment (OGLE III). We have
used two different methods to derive optical reddening maps. We adopt a
theoretical mean unreddened colour for the red clump in the SMC and LMC,
respectively. We subdivide the photometric data for both Clouds into subfields
and calculate the difference between the observed red clump position and the
theoretical value for each field, which provides us with the reddening value in
(V-I). Furthermore reddening values are obtained for 13490 LMC RR Lyrae ab and
1529 SMC RR Lyrae ab stars covering the whole OGLE III region of the MCs. The
observed colours (V-I) of the RR Lyrae stars are compared with the colour from
the absolute magnitudes. The absolute magnitude of each RR Lyrae star is
computed using its period and metallicity derived from Fourier decomposition of
its lightcurve. In general we find a low and uniform reddening distribution in
both Magellanic Clouds. The red clump method indicates a mean reddening of the
LMC of E(V-I) = 0.09 +/- 0.07 mag, while for the SMC E(V-I) = 0.04 +/- 0.06 mag
is obtained. With RR Lyrae stars a median value of E(V-I) = 0.11 +/- 0.06 mag
for the LMC and E(V-I) = 0.07 +/- 0.06 mag for the SMC is found. The LMC shows
very low reddening in the bar region, whereas the reddening in the star-forming
leading edge and 30 Doradus is considerably higher. In the SMC three pronounced
regions with higher reddening are visible. Two are located along the bar, while
the highest reddening is found in the star-forming wing of the SMC. In general
the regions with higher reddening are in good spatial agreement with infrared
reddening maps as well as with reddening estimations of other studies. The
position-dependent reddening values from the red clump method are available via
the Virtual Observatory interface.Comment: 15 pages, 22 Figures, AJ publishe
The Role of Dwarf Galaxy Interactions in Shaping the Magellanic System and Implications for Magellanic Irregulars
We present a novel pair of numerical models of the interaction history
between the Large and Small Magellanic Clouds (LMC and SMC, respectively) and
our Milky Way (MW) in light of recent high precision proper motions
(Kallivayalil et al. 2006a,b). Given the new velocities, cosmological
simulations of structure formation favor a scenario where the Magellanic Clouds
(MCs) are currently on their first infall towards our Galaxy (Boylan-Kolchin et
al. 2011, Busha et al. 2011). We illustrate here that the observed irregular
morphology and internal kinematics of the MCs (in gas and stars) are naturally
explained by interactions between the LMC and SMC, rather than gravitational
interactions with the MW. This picture further supports a first infall scenario
(Besla et a. 2007). In particular, we demonstrate that the Magellanic Stream, a
band of HI gas trailing behind the MCs 150 degrees across the sky, can be
accounted for by the action of LMC tides on the SMC before the system was
accreted by the MW. We further demonstrate that the off-center, warped stellar
bar of the LMC and its one-armed spiral, can be naturally explained by a recent
direct collision with the SMC. Such structures are key morphological
characteristics of a class of galaxies referred to as Magellanic Irregulars (de
Vaucouleurs & Freeman 1972), the majority of which are not associated with
massive spiral galaxies. We infer that dwarf-dwarf galaxy interactions are
important drivers for the morphological evolution of Magellanic Irregulars and
can dramatically affect the efficiency of baryon removal from dwarf galaxies
via the formation of extended tidal bridges and tails. Such interactions are
important not only for the evolution of dwarf galaxies but also have direct
consequences for the buildup of baryons in our own MW, as LMC-mass systems are
believed to be the dominant building blocks of MW-type halos.Comment: 33 pages, 21 figures, Accepted for publication in MNRAS, Dec 23 201
Geodesic rewriting systems and pregroups
In this paper we study rewriting systems for groups and monoids, focusing on
situations where finite convergent systems may be difficult to find or do not
exist. We consider systems which have no length increasing rules and are
confluent and then systems in which the length reducing rules lead to
geodesics. Combining these properties we arrive at our main object of study
which we call geodesically perfect rewriting systems. We show that these are
well-behaved and convenient to use, and give several examples of classes of
groups for which they can be constructed from natural presentations. We
describe a Knuth-Bendix completion process to construct such systems, show how
they may be found with the help of Stallings' pregroups and conversely may be
used to construct such pregroups.Comment: 44 pages, to appear in "Combinatorial and Geometric Group Theory,
Dortmund and Carleton Conferences". Series: Trends in Mathematics.
Bogopolski, O.; Bumagin, I.; Kharlampovich, O.; Ventura, E. (Eds.) 2009,
Approx. 350 p., Hardcover. ISBN: 978-3-7643-9910-8 Birkhause
The manipulation of massive ro-vibronic superpositions using time-frequency-resolved coherent anti-Stokes Raman scattering (TFRCARS): from quantum control to quantum computing
Molecular ro-vibronic coherences, joint energy-time distributions of quantum
amplitudes, are selectively prepared, manipulated, and imaged in
Time-Frequency-Resolved Coherent Anti-Stokes Raman Scattering (TFRCARS)
measurements using femtosecond laser pulses. The studies are implemented in
iodine vapor, with its thermally occupied statistical ro-vibrational density
serving as initial state. The evolution of the massive ro-vibronic
superpositions, consisting of 1000 eigenstates, is followed through
two-dimensional images. The first- and second-order coherences are captured
using time-integrated frequency-resolved CARS, while the third-order coherence
is captured using time-gated frequency-resolved CARS. The Fourier filtering
provided by time integrated detection projects out single ro-vibronic
transitions, while time-gated detection allows the projection of arbitrary
ro-vibronic superpositions from the coherent third-order polarization. Beside
the control and imaging of chemistry, the controlled manipulation of massive
quantum coherences suggests the possibility of quantum computing. We argue that
the universal logic gates necessary for arbitrary quantum computing - all
single qubit operations and the two-qubit controlled-NOT (CNOT) gate - are
available in time resolved four-wave mixing in a molecule. The molecular
rotational manifold is naturally "wired" for carrying out all single qubit
operations efficiently, and in parallel. We identify vibronic coherences as one
example of a naturally available two-qubit CNOT gate, wherein the vibrational
qubit controls the switching of the targeted electronic qubit.Comment: PDF format. 59 pages, including 22 figures. To appear in Chemical
Physic
An evolutionary perspective on the co-occurrence of social anxiety disorder and alcohol use disorder
Social Anxiety Disorder (SAD) commonly co-occurs with, and often precedes, Alcohol Use Disorder (AUD). In this paper, we address the relationship between SAD and AUD by considering how natural selection left socially anxious individuals vulnerable to alcohol use, and by addressing the underlying mechanisms. We review research suggesting that social anxiety has evolved for the regulation of behaviors involved in reducing the likelihood or consequences of threats to social status. The management of potential threats to social standing is important considering that these threats can result in reduced cooperation or ostracism â and therefore to reduced access to coalitional partners, resources or mates. Alcohol exerts effects upon evolutionarily conserved emotion circuits, and can down-regulate or block anxiety (or may be expected to do so). As such, the ingestion of alcohol can artificially signal the absence or successful management of social threats. In turn, alcohol use may be reinforced in socially anxious people because of this reduction in subjective malaise, and because it facilitates social behaviors â particularly in individuals for whom the persistent avoidance of social situations poses its own threat (i.e., difficulty finding mates). Although the frequent co-occurrence of SAD and AUD is associated with poorer treatment outcomes than either condition alone, a richer understanding of the biological and psychosocial drives underlying susceptibility to alcohol use among socially anxious individuals may improve the efficacy of therapeutic interventions aimed at preventing or treating this comorbidity
The WOCEâera 3âD Pacific Ocean circulation and heat budget
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Progress In Oceanography 82 (2009): 281-325, doi:10.1016/j.pocean.2009.08.002.To address questions concerning the intensity and spatial structure of the 3âdimensional
circulation within the Pacific Ocean and the associated advective and diffusive property flux
divergences, data from approximately 3000 highâquality hydrographic stations collected on
40 zonal and meridional cruises have been merged into a physically consistent model. The
majority of the stations were occupied as part of the World Ocean Circulation Experiment
(WOCE), which took place in the 1990s. These data are supplemented by a few preâWOCE
surveys of similar quality, and timeâaveraged directâvelocity and historical hydrographic
measurements about the equator.
An inverse box model formalism is employed to estimate the absolute alongâisopycnal
velocity field, the magnitude and spatial distribution of the associated diapycnal flow and
the corresponding diapycnal advective and diffusive property flux divergences. The resulting
largeâscale WOCE Pacific circulation can be described as two shallow overturning cells
at midâ to low latitudes, one in each hemisphere, and a single deep cell which brings abyssal
waters from the Southern Ocean into the Pacific where they upwell across isopycnals and
are returned south as deep waters. Upwelling is seen to occur throughout most of the basin
with generally larger dianeutral transport and greater mixing occurring at depth. The derived
pattern of ocean heat transport divergence is compared to published results based
on airâsea flux estimates. The synthesis suggests a strongly east/west oriented pattern of
airâsea heat flux with heat loss to the atmosphere throughout most of the western basins,
and a gain of heat throughout the tropics extending poleward through the eastern basins.
The calculated meridional heat transport agrees well with previous hydrographic estimates.
Consistent with many of the climatologies at a variety of latitudes as well, our meridional
heat transport estimates tend toward lower values in both hemispheres.This work was funded by National Science Foundation grants OCEâ9710102, OCEâ
9712209 and OCEâ0079383, and also benefited from work on closely related projects funded
by NSF grants OCEâ0223421 and OCEâ0623261, and NOAA grant NA17RJ1223 funded
through CICOR. For G.C.J. NASA funding came under Order Wâ19,314
Experiments in the Control of a Flexible Robot Arm
©1985 Society of Mechanical EngineersPresented at the 9th Robots Conference, June 2 - 6, 1985, Detroit, Michigan.Control of flexible manipulator arms offers high performance, light weight, and low cost over conventional rigid members. Presented is an experimental system for evaluating control systems. A dynamic modeling procedure is outlined and an optimal control system is discussed. Reconstruction of flexible modes is accomplished using strain gage data. Velocity of flexible modes is estimated with a reduced order observer. Experimental data is presented to verify dynamic modeling and modal reconstruction. Initial results using a deterministic optimal controller are presented
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