3,516 research outputs found
Manipulation of a Bose-Einstein condensate by a time-averaged orbiting potential using phase jumps of the rotating field
We report on the manipulation of the center-of-mass motion (`sloshing') of a
Bose Einstein condensate in a time-averaged orbiting potential (TOP) trap. We
start with a condensate at rest in the center of a static trapping potential.
When suddenly replacing the static trap with a TOP trap centered about the same
position, the condensate starts to slosh with an amplitude much larger than the
TOP micromotion. We show, both theoretically and experimentally, that the
direction of sloshing is related to the initial phase of the rotating magnetic
field of the TOP. We show further that the sloshing can be quenched by applying
a carefully timed and sized jump in the phase of the rotating field.Comment: 11 pages, 9 figure
An experimental documentation of trailing-edge flows at high Reynolds number
Experiments documenting attached trailing-edge and near-wake flows at high Reynolds numbers are described. A long, airfoil-like model was tested at subsonic and low transonic Mach numbers, and both symmetrical and asymmetrical flows with pressure gradients upstream of the trailing edge were investigated. Model surface pressures and detailed mean and turbulence flow qualities were measured in the vicinity of the trailing edge and in the near-wake. The data obtained are of sufficient quality and detail to be useful as test cases in assessing turbulence models and calculation methods
A multiple mapping conditioning model for differential diffusion
This work introduces modeling of differential diffusion within the multiple mapping conditioning (MMC) turbulent mixing and combustion framework. The effect of differential diffusion on scalar variance decay is analyzed and, following a number of publications, is found to scale as Re. The ability to model the differential decay rates is the most important aim of practical differential diffusion models, and here this is achieved in MMC by introducing what is called the side-stepping method. The approach is practical and, as it does not involve an increase in the number of MMC reference variables, economical. In addition we also investigate the modeling of a more refined and difficult to reproduce differential diffusion effect - the loss of correlation between the different scalars. For this we develop an alternative MMC model with two reference variables but which also makes use of the side-stepping method. The new models are successfully validated against DNS results available in literature for homogenous, isotropic two scalar mixing
SDSS IV MaNGA - Rotation Velocity Lags in the Extraplanar Ionized Gas from MaNGA Observations of Edge-on Galaxies
We present a study of the kinematics of the extraplanar ionized gas around
several dozen galaxies observed by the Mapping of Nearby Galaxies at the Apache
Point Observatory (MaNGA) survey. We considered a sample of 67 edge-on galaxies
out of more than 1400 extragalactic targets observed by MaNGA, in which we
found 25 galaxies (or 37%) with regular lagging of the rotation curve at large
distances from the galactic midplane. We model the observed emission
velocity fields in the galaxies, taking projection effects and a simple model
for the dust extinction into the account. We show that the vertical lag of the
rotation curve is necessary in the modeling, and estimate the lag amplitude in
the galaxies. We find no correlation between the lag and the star formation
rate in the galaxies. At the same time, we report a correlation between the lag
and the galactic stellar mass, central stellar velocity dispersion, and axial
ratio of the light distribution. These correlations suggest a possible higher
ratio of infalling-to-local gas in early-type disk galaxies or a connection
between lags and the possible presence of hot gaseous halos, which may be more
prevalent in more massive galaxies. These results again demonstrate that
observations of extraplanar gas can serve as a potential probe for accretion of
gas.Comment: 13 pages, 11 figures, accepted for publication in Ap
Reconfiguration on sparse graphs
A vertex-subset graph problem Q defines which subsets of the vertices of an
input graph are feasible solutions. A reconfiguration variant of a
vertex-subset problem asks, given two feasible solutions S and T of size k,
whether it is possible to transform S into T by a sequence of vertex additions
and deletions such that each intermediate set is also a feasible solution of
size bounded by k. We study reconfiguration variants of two classical
vertex-subset problems, namely Independent Set and Dominating Set. We denote
the former by ISR and the latter by DSR. Both ISR and DSR are PSPACE-complete
on graphs of bounded bandwidth and W[1]-hard parameterized by k on general
graphs. We show that ISR is fixed-parameter tractable parameterized by k when
the input graph is of bounded degeneracy or nowhere-dense. As a corollary, we
answer positively an open question concerning the parameterized complexity of
the problem on graphs of bounded treewidth. Moreover, our techniques generalize
recent results showing that ISR is fixed-parameter tractable on planar graphs
and graphs of bounded degree. For DSR, we show the problem fixed-parameter
tractable parameterized by k when the input graph does not contain large
bicliques, a class of graphs which includes graphs of bounded degeneracy and
nowhere-dense graphs
Parallel Recursive State Compression for Free
This paper focuses on reducing memory usage in enumerative model checking,
while maintaining the multi-core scalability obtained in earlier work. We
present a tree-based multi-core compression method, which works by leveraging
sharing among sub-vectors of state vectors.
An algorithmic analysis of both worst-case and optimal compression ratios
shows the potential to compress even large states to a small constant on
average (8 bytes). Our experiments demonstrate that this holds up in practice:
the median compression ratio of 279 measured experiments is within 17% of the
optimum for tree compression, and five times better than the median compression
ratio of SPIN's COLLAPSE compression.
Our algorithms are implemented in the LTSmin tool, and our experiments show
that for model checking, multi-core tree compression pays its own way: it comes
virtually without overhead compared to the fastest hash table-based methods.Comment: 19 page
9.7 um Silicate Features in AGNs: New Insights into Unification Models
We describe observations of 9.7 um silicate features in 97 AGNs, exhibiting a
wide range of AGN types and of X-ray extinction toward the central nuclei. We
find that the strength of the silicate feature correlates with the HI column
density estimated from fitting the X-ray data, such that low HI columns
correspond to silicate emission while high columns correspond to silicate
absorption. The behavior is generally consistent with unification models where
the large diversity in AGN properties is caused by viewing-angle-dependent
obscuration of the nucleus. Radio-loud AGNs and radio-quiet quasars follow
roughly the correlation between HI columns and the strength of the silicate
feature defined by Seyfert galaxies. The agreement among AGN types suggests a
high-level unification with similar characteristics for the structure of the
obscuring material. We demonstrate the implications for unification models
qualitatively with a conceptual disk model. The model includes an inner
accretion disk (< 0.1 pc in radius), a middle disk (0.1-10 pc in radius) with a
dense diffuse component and with embedded denser clouds, and an outer clumpy
disk (10-300 pc in radius).Comment: Accepted for publication in ApJ, 14 pages, 5 figures. The on-line
table is available at http://cztsy.as.arizona.edu/~yong/silicate_tab1.pd
Observations of total peroxy nitrates and aldehydes: measurement interpretation and inference of OH radical concentrations
We describe measurements of total peroxy nitrates (ΣPNs), NO<sub>2</sub>, O<sub>3</sub> and several aldehydes at Granite Bay, California, during the Chemistry and Transport of the Sacramento Urban Plume-2001 (CATSUP 2001) campaign, from 19 July–16 September 2001. We observed a strong photochemically driven variation of ΣPNs during the day with the median of 1.2 ppb at noon. Acetaldehyde, pentanal, hexanal and methacrolein had median abundances in the daytime of 1.2 ppb, 0.093 ppb, 0.14 ppb, and 0.27 ppb, respectively. We compare steady state and time dependent calculations of the dependence of ΣPNs on aldehydes, OH, NO and NO<sub>2</sub> showing that the steady state calculations are accurate to ±30% between 10:00 and 18:00 h. We use the steady state calculation to investigate the composition of ΣPNs and the concentration of OH at Granite Bay. We find that PN molecules that have never been observed before make up an unreasonably large fraction of the ΣPNs unless we assume that there exists a PAN source that is much larger than the acetaldehyde source. We calculate that OH at the site varied between 2 and 7×10<sup>6</sup> molecule cm<sup>−3</sup> at noon during the 8 weeks of the experiment
Handwritten digit recognition by bio-inspired hierarchical networks
The human brain processes information showing learning and prediction
abilities but the underlying neuronal mechanisms still remain unknown.
Recently, many studies prove that neuronal networks are able of both
generalizations and associations of sensory inputs. In this paper, following a
set of neurophysiological evidences, we propose a learning framework with a
strong biological plausibility that mimics prominent functions of cortical
circuitries. We developed the Inductive Conceptual Network (ICN), that is a
hierarchical bio-inspired network, able to learn invariant patterns by
Variable-order Markov Models implemented in its nodes. The outputs of the
top-most node of ICN hierarchy, representing the highest input generalization,
allow for automatic classification of inputs. We found that the ICN clusterized
MNIST images with an error of 5.73% and USPS images with an error of 12.56%
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