265 research outputs found
A Quantitative Examination of Black and Hispanic Students’ Time-to-Graduation
What factors influence Black and Hispanic students’ time-to-graduation, and is it different for their special opportunity program peers? Using theoretical lenses including intersectionality, class struggle, justice, and sociological practice, this dissertation employs data from a large urban public university system to examine the relative impact of demography, academic preparedness, and financial background on students’ time-to-graduation performance.
Time-to-graduation, operationalized in this dissertation as the duration of years before a student earns a bachelor’s degree, for full-time students often represents an investment of time at the expense of earning a wage or salary in the job market. The economic gain that accrues to students who have at least a bachelor’s degree is well documented. Little attention, however, has been given to how much demographic, academic preparedness, and financial background factors account for student time-to-graduation. For this reason, this dissertation interrogates the relationship between the foregoing variables for Black and Hispanic students, and includes a stratification that bifurcates between traditional first-time, full-time students, and those enrolled in the special opportunity program at the City University of New York’s (CUNY) senior colleges known as the Searching for Education, Elevation, and Knowledge (SEEK) program.
In all, the most important findings in this dissertation include: 1) the SEEK program appears to decrease time-to-graduation gaps for Black and Hispanic students, 2) high school GPA and the English Regents exam are better predictors of time-to-graduation than the SAT Verbal and Math test scores, and 3) financial background as a predictor of time-to-graduation for Black students is no better than chance
Energy versus information based estimations of dissipation using a pair of magnetic colloidal particles
Using the framework of stochastic thermodynamics, we present an experimental
study of a doublet of magnetic colloidal particles which is manipulated by a
time-dependent magnetic field. Due to hydrodynamic interactions, each bead
experiences a state-dependent friction, which we characterize using a
hydrodynamic model. In this work, we compare two estimates of the dissipation
in this system: the first one is energy based since it relies on the measured
interaction potential, while the second one is information based since it uses
only the information content of the trajectories. While the latter only offers
a lower bound of the former, we find it to be simple to implement and of
general applicability to more complex systems.Comment: Main text: 5 pages, 4 figures. Supplementary material: 5 pages, 5
figure
HI asymmetry in the isolated galaxy CIG 85 (UGC 1547)
We present the results from the Giant Metrewave Radio Telescope (GMRT)
interferometric HI and 20 cm radio continuum observations of CIG 85, an
isolated asymmetric galaxy from the AMIGA (Analysis of the Interstellar Medium
of Isolated GAlaxies) sample. Despite being an isolated galaxy, CIG 85 showed
an appreciable optical and HI spectral asymmetry and therefore was an excellent
candidate for resolved HI studies to understand the reasons giving rise to
asymmetries in isolated galaxies. The galaxy was imaged in HI and 20 cm radio
continuum using the GMRT. For a detailed discussion of the results we also made
use of multi-wavelength data from archival SDSS, GALEX and Halpha imaging. We
find the HI in CIG 85 to have a clumpy, asymmetric distribution which in the NW
part is correlated with optical tail like features, but the HI velocity field
displays a relatively regular rotation pattern. Evaluating all the
observational evidence, we come to a conclusion that CIG 85 is most likely a
case of a disturbed spiral galaxy which now appears to have the morphology of
an irregular galaxy. Although it is currently isolated from major companions,
the observational evidence is consistent with HI asymmetries, a highly
disturbed optical disk and recent increase in star formation having been caused
by a minor merger, remnants of which are now projected in front of the optical
disk. If this is correct, the companion will be fully accreted by CIG 85 in the
near future.Comment: 10 pages, 9 figures, accepted in A&
Modified Fluctuation-dissipation theorem for non-equilibrium steady-states and applications to molecular motors
We present a theoretical framework to understand a modified
fluctuation-dissipation theorem valid for systems close to non-equilibrium
steady-states and obeying markovian dynamics. We discuss the interpretation of
this result in terms of trajectory entropy excess. The framework is illustrated
on a simple pedagogical example of a molecular motor. We also derive in this
context generalized Green-Kubo relations similar to the ones derived recently
by Seifert., Phys. Rev. Lett., 104, 138101 (2010) for more general networks of
biomolecular states.Comment: 6 pages, 2 figures, submitted in EP
The AMIGA sample of isolated galaxies - II. Morphological refinement
We present a complete POSS II-based refinement of the optical morphologies
for galaxies in the Karatchenseva's Catalog of Isolated Galaxies that forms the
basis of the AMIGA project. Comparison with independent classifications made
for an SDSS overlap sample of more than 200 galaxies confirms the reliability
of the early vs. late-type discrimination and the accuracy of spiral subtypes
within DeltaT = 1-2. CCD images taken at the OSN were also used to solve
ambiguities. 193 galaxies are flagged for the presence of nearby companions or
signs of distortion likely due to interaction. This most isolated sample of
galaxies in the local Universe is dominated by 2 populations: 1) 82% spirals
(Sa-Sd) with the bulk being luminous systems with small bulges (63% between
types Sb-Sc) and 2) a significant population of early-type E-S0 galaxies (14%).
Most of the types later than Sd are low luminosity galaxies concentrated in the
local supercluster where isolation is difficult to evaluate. The late-type
spiral majority of the sample spans a luminosity range M_B-corr = -18 to -22
mag. Few of the E/S0 population are more luminous than -21.0 marking an absence
of, an often sought, super L* merger (eg fossil elliptical) population. The
rarity of high luminosity systems results in a fainter derived M* for this
population compared to the spiral optical luminosity function (OLF). The E-S0
population is from 0.2 to 0.6 mag fainter depending how the sample is defined.
This marks the AMIGA sample as almost unique among samples that compare early
and late-type OLFs separately. In other samples, which always involve galaxies
in higher density environments, M*(E/S0) is almost always 0.3-0.5 mag brighter
than M*(S), presumably reflecting a stronger correlation between M* and
environmental density for early-type galaxies.Comment: A&A accepted, 13 pages, 9 figures, 8 tables. Higher resolution Fig. 1
and full tables are available on the AMIGA (Analysis of the interstellar
Medium of Isolated GAlaxies) website at http://www.iaa.es/AMIGA.htm
Setting the normalcy level of HI properties in isolated galaxies
Studying the atomic gas (HI) properties of the most isolated galaxies is
essential to quantify the effect that the environment exerts on this sensitive
component of the interstellar medium. We observed and compiled HI data for a
well defined sample of ~ 800 galaxies in the Catalog of Isolated Galaxies, as
part of the AMIGA project (Analysis of the ISM in Isolated GAlaxies,
http://amiga.iaa.es), which enlarges considerably previous samples used to
quantify the HI deficiency in galaxies located in denser environments. By
studying the shape of 182 HI profiles, we revisited the usually accepted result
that, independently of the environment, more than half of the galaxies present
a perturbed HI disk. In isolated galaxies this would certainly be a striking
result if these are supposed to be the most relaxed systems, and has
implications in the relaxation time scales of HI disks and the nature of the
most frequent perturbing mechanisms in galaxies. Our sample likely exhibits the
lowest HI asymmetry level in the local Universe. We found that other field
samples present an excess of ~ 20% more asymmetric HI profiles than that in
CIG. Still a small percentage of galaxies in our sample present large
asymmetries. Follow-up high resolution VLA maps give insight into the origin of
such asymmetries.Comment: 4 pages, 2 figures, Conference 'Galaxies in Isolation: Exploring
Nature vs. Nurture', Granada, 12-15 May 2009. To be published in the ASP
Conference Serie
Brownian Carnot engine
The Carnot cycle imposes a fundamental upper limit to the efficiency of a
macroscopic motor operating between two thermal baths. However, this bound
needs to be reinterpreted at microscopic scales, where molecular bio-motors and
some artificial micro-engines operate. As described by stochastic
thermodynamics, energy transfers in microscopic systems are random and thermal
fluctuations induce transient decreases of entropy, allowing for possible
violations of the Carnot limit. Despite its potential relevance for the
development of a thermodynamics of small systems, an experimental study of
microscopic Carnot engines is still lacking. Here we report on an experimental
realization of a Carnot engine with a single optically trapped Brownian
particle as working substance. We present an exhaustive study of the energetics
of the engine and analyze the fluctuations of the finite-time efficiency,
showing that the Carnot bound can be surpassed for a small number of
non-equilibrium cycles. As its macroscopic counterpart, the energetics of our
Carnot device exhibits basic properties that one would expect to observe in any
microscopic energy transducer operating with baths at different temperatures.
Our results characterize the sources of irreversibility in the engine and the
statistical properties of the efficiency -an insight that could inspire novel
strategies in the design of efficient nano-motors.Comment: 7 pages, 7 figure
PACS and SPIRE photometer maps of M33: First results of the Herschel M33 extended survey (HERM33ES)
Within the framework of the HERM33ES key project, we are studying the star
forming interstellar medium in the nearby, metal-poor spiral galaxy M33,
exploiting the high resolution and sensitivity of Herschel. We use PACS and
SPIRE maps at 100, 160, 250, 350, and 500 micron wavelength, to study the
variation of the spectral energy distributions (SEDs) with galacto-centric
distance. Detailed SED modeling is performed using azimuthally averaged fluxes
in elliptical rings of 2 kpc width, out to 8 kpc galacto-centric distance.
Simple isothermal and two-component grey body models, with fixed dust
emissivity index, are fitted to the SEDs between 24 and 500 micron using also
MIPS/Spitzer data, to derive first estimates of the dust physical conditions.
The far-infrared and submillimeter maps reveal the branched, knotted spiral
structure of M33. An underlying diffuse disk is seen in all SPIRE maps (250-500
micron). Two component fits to the SEDs agree better than isothermal models
with the observed, total and radially averaged flux densities. The two
component model, with beta fixed at 1.5, best fits the global and the radial
SEDs. The cold dust component clearly dominates; the relative mass of the warm
component is less than 0.3% for all the fits. The temperature of the warm
component is not well constrained and is found to be about 60K plus/minus 10K.
The temperature of the cold component drops significantly from about 24K in the
inner 2 kpc radius to 13K beyond 6 kpc radial distance, for the best fitting
model. The gas-to-dust ratio for beta=1.5, averaged over the galaxy, is higher
than the solar value by a factor of 1.5 and is roughly in agreement with the
subsolar metallicity of M33.Comment: 5 pages, 3 figures, accepted for publication in the A&A Herschel
Special Issu
Modified fluctuation-dissipation theorem near non-equilibrium states and applications to the Glauber-Ising chain
In this paper, we present a general derivation of a modified
fluctuation-dissipation theorem (MFDT) valid near an arbitrary non-stationary
state for a system obeying markovian dynamics. We show that the method to
derive modified fluctuation-dissipation theorems near non-equilibrium
stationary states used by J. Prost et al., PRL 103, 090601 (2009), is
generalizable to non-stationary states. This result follows from both standard
linear response theory and from a transient fluctuation theorem, analogous to
the Hatano-Sasa relation. We show that this modified fluctuation-dissipation
theorem can be interpreted at the trajectory level using the notion of
stochastic trajectory entropy, in a way which is similar to what has been done
recently in the case of MFDT near non-equilibrium steady states (NESS). We
illustrate this framework with two solvable examples: the first example
corresponds to a brownian particle in an harmonic trap submitted to a quench of
temperature and to a time-dependent stiffness. The second example is a classic
model of coarsening systems, namely the 1D Ising model with Glauber dynamics.Comment: 25 pages, 4 figure
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