6,879 research outputs found
Perturbation Theory for Plasmonic Modulation and Sensing
We develop a general perturbation theory to treat small parameter changes in
dispersive plasmonic nanostructures and metamaterials. We specifically apply it
to dielectric refractive index, and metallic plasma frequency modulation in
metal- dielectric nanostructures. As a numerical demonstration, we verify the
theory's accu- racy against direct calculations, for a system of plasmonic rods
in air where the metal is defined by a two-pole fit of silver's dielectric
function. We also discuss new optical behavior related to plasma frequency
modulation in such systems. Our approach provides new physical insight for the
design of plasmonic devices for biochemical sensing and optical modulation, and
future active metamaterial applications.Comment: 17 pages, 6 figure
An Optically Plugged Quadrupole Trap for Bose-Einstein Condensates
We created sodium Bose-Einstein condensates in an optically plugged
quadrupole magnetic trap (OPT). A focused, 532nm laser beam repelled atoms from
the coil center where Majorana loss is significant. We produced condensates of
up to atoms, a factor of 60 improvement over previous work [1],
a number comparable to the best all-magnetic traps, and transferred up to atoms into a purely optical trap. Due to the tight axial
confinement and azimuthal symmetry of the quadrupole coils, the OPT shows
promise for creating Bose-Einstein condensates in a ring geometry
Quantum and Classical Dynamics of a BEC in a Large-Period Optical Lattice
We experimentally investigate diffraction of a Rb-87 Bose-Einstein condensate
from a 1D optical lattice. We use a range of lattice periods and timescales,
including those beyond the Raman-Nath limit. We compare the results to quantum
mechanical and classical simulations, with quantitative and qualitative
agreement, respectively. The classical simulation predicts that the envelope of
the time-evolving diffraction pattern is shaped by caustics: singularities in
the phase space density of classical trajectories. This behavior becomes
increasingly clear as the lattice period grows.Comment: 7 pages, 6 figure
Psychological outcomes following surgical and endoscopic bariatric procedures: A systematic review.
Obesity is a leading global epidemic. Bariatric surgery is the only treatment demonstrating substantial long-term weight loss and medical benefits. However, there is limited research on the psychological outcomes following surgery. Therefore, the primary aim of this study was to systematically review depression, anxiety, and binge eating outcomes at different time points following bariatric surgery and identify whether bariatric surgery significantly reduces psychological symptoms over time. These outcomes were also examined among endoscopic bariatric procedures as a secondary aim. Forty-eight studies met inclusion criteria. Findings suggested that most patients experience a short-term reduction in anxiety and depression symptoms from pre-surgery. Over time, however, these symptoms increase and may even return to pre-surgery levels. Furthermore, while binge eating was uncommon after surgery, other disordered eating patterns may emerge. Binge eating may also restart over time as the stomach enlarges again. Overall, the complex psychological difficulties faced by individuals with obesity continue after surgery and may contribute to longer-term weight recidivism. More comprehensive and standardised psychological assessment procedures, including clinical interviews and longer-term follow-up, may provide insight into the psychological mechanisms maintaining weight management issues, and may serve as a starting point for improving the long-term success of patients with obesity
Bragg Spectroscopy of Vortex Lattices in Bose-Einstein condensates
We have measured the velocity field of a vortex lattice within a sodium
Bose-Einstein condensate using Bragg scattering. The phase gradient of the
macroscopic wavefunction was mapped into the spatial structure of the
diffracted atom cloud, allowing for single shot measurement of the rotation
parameters. A combination of spectral and spatial information yields a complete
description of the superfluid flow, coarse-grained over the lattice structure,
including direct and independent measurements of the rate and sense of
rotation. Signatures of the microscopic quantum rotation have also been
observed.Comment: 5 pages, 5 Figures, A movie built from the CM data is available in
our Webpage: http://www.physics.gatech.edu/chandra/index.htm; added Fig.5
presents new data, showing signatures of the microscopic vortex structure in
the diffracted clou
The clinical obesity maintenance model: a structural equation model.
PURPOSE:Theoretical research on the psychological underpinnings of weight management is limited. Recently, the clinical obesity maintenance model (COMM) proposed a theoretical conceptualisation of salient psychological and neuropsychological mechanisms maintaining weight management issues. The current study aimed to empirically test the COMM and elucidate the results in the context of recent empirical findings. METHODS:Participants (N = 165) were recruited from university and community settings in Australia. The sample consisted of adults with normal weight (n = 41), overweight (n = 40), and obesity (n = 84). Participants completed self-report questionnaires and a brief neuropsychological test. Structural equation modelling was used to estimate the associations between the hypothesised variables of the COMM and evaluate the model fit. RESULTS:Findings suggested acceptable to good model fit. Furthermore, several direct effects were found. First, cognitive flexibility directly affected eating habit strength. Second, eating habit strength directly affected eating beliefs. Third, eating beliefs directly affected emotion dysregulation. Fourth, emotion dysregulation directly affected depression and binge eating with depression partially mediating this relationship. Finally, depression directly affected binge eating. CONCLUSION:This was the first study to empirically test the COMM. Overall, findings provide preliminary support for the COMM as a psychological model of weight management and highlight the underlying psychological and neuropsychological mechanisms that may contribute to weight management issues. As this study examined a simplified version of the COMM, future research should continue evaluating this model and consider incorporating these components into more holistic weight management models to improve long-term treatment outcomes. LEVEL OF EVIDENCE:V, cross-sectional descriptive study
Subset feedback vertex set is fixed parameter tractable
The classical Feedback Vertex Set problem asks, for a given undirected graph
G and an integer k, to find a set of at most k vertices that hits all the
cycles in the graph G. Feedback Vertex Set has attracted a large amount of
research in the parameterized setting, and subsequent kernelization and
fixed-parameter algorithms have been a rich source of ideas in the field.
In this paper we consider a more general and difficult version of the
problem, named Subset Feedback Vertex Set (SUBSET-FVS in short) where an
instance comes additionally with a set S ? V of vertices, and we ask for a set
of at most k vertices that hits all simple cycles passing through S. Because of
its applications in circuit testing and genetic linkage analysis SUBSET-FVS was
studied from the approximation algorithms perspective by Even et al.
[SICOMP'00, SIDMA'00].
The question whether the SUBSET-FVS problem is fixed-parameter tractable was
posed independently by Kawarabayashi and Saurabh in 2009. We answer this
question affirmatively. We begin by showing that this problem is
fixed-parameter tractable when parametrized by |S|. Next we present an
algorithm which reduces the given instance to 2^k n^O(1) instances with the
size of S bounded by O(k^3), using kernelization techniques such as the
2-Expansion Lemma, Menger's theorem and Gallai's theorem. These two facts allow
us to give a 2^O(k log k) n^O(1) time algorithm solving the Subset Feedback
Vertex Set problem, proving that it is indeed fixed-parameter tractable.Comment: full version of a paper presented at ICALP'1
The Clinical Obesity Maintenance Model: A Theoretical Framework for Bariatric Psychology.
Ranked highly in its association with serious medical comorbidities, obesity, a rapidly growing epidemic worldwide, poses a significant socio-economic burden. While bariatric procedures offer the most efficacious treatment for weight loss, a subset of patients risk weight recidivism. Due to the heterogeneity of obesity, it is likely that there are phenotypes or sub-groups of patients that require evidence-based psychological support to produce more sustainable outcomes. So far, however, characteristics of patients have not led to a personalized treatment algorithm for bariatric surgery. Maintenance of weight loss following bariatric surgery requires long-term modification of eating behaviors and physical activity. A recent Clinical Obesity Maintenance Model (COMM) proposed a conceptual framework of salient constructs, including the role of habit, behavioral clusters, emotion dysregulation, mood, health literacy, and executive function as interconnected drivers of obesity maintaining behaviors relevant to the field of bariatric psychology. The primary aim of this concise review is to bring together emerging findings from experimental and epidemiological studies relating to the COMM constructs that may inform the assessment and follow up of bariatric surgery. We also aim to explain the phenotypes that need to be understood and screened prior to bariatric surgery to enable better pre-surgery intervention and optimum post-surgery response
RLZAP: Relative Lempel-Ziv with Adaptive Pointers
Relative Lempel-Ziv (RLZ) is a popular algorithm for compressing databases of
genomes from individuals of the same species when fast random access is
desired. With Kuruppu et al.'s (SPIRE 2010) original implementation, a
reference genome is selected and then the other genomes are greedily parsed
into phrases exactly matching substrings of the reference. Deorowicz and
Grabowski (Bioinformatics, 2011) pointed out that letting each phrase end with
a mismatch character usually gives better compression because many of the
differences between individuals' genomes are single-nucleotide substitutions.
Ferrada et al. (SPIRE 2014) then pointed out that also using relative pointers
and run-length compressing them usually gives even better compression. In this
paper we generalize Ferrada et al.'s idea to handle well also short insertions,
deletions and multi-character substitutions. We show experimentally that our
generalization achieves better compression than Ferrada et al.'s implementation
with comparable random-access times
Succinct representation of triangulations with a boundary
We consider the problem of designing succinct geometric data structures while maintaining efficient navigation operations. A data structure is said succinct if the asymptotic amount of space it uses matches the entropy of the class of structures represented. For the case of planar triangulations with a boundary we propose a succinct representation of the combinatorial information that improves to 2.175 bits per triangle the asymptotic amount of space required and that supports the navigation between adjacent triangles in constant time (as well as other standard operations). For triangulations with faces of a surface with genus g, our representation requires asymptotically an extra amount of 36(g-1)lg m bits (which is negligible as long as g << m/lg m)
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