486 research outputs found
On acceleration of Krylov-subspace-based Newton and Arnoldi iterations for incompressible CFD: replacing time steppers and generation of initial guess
We propose two techniques aimed at improving the convergence rate of steady
state and eigenvalue solvers preconditioned by the inverse Stokes operator and
realized via time-stepping. First, we suggest a generalization of the Stokes
operator so that the resulting preconditioner operator depends on several
parameters and whose action preserves zero divergence and boundary conditions.
The parameters can be tuned for each problem to speed up the convergence of a
Krylov-subspace-based linear algebra solver. This operator can be inverted by
the Uzawa-like algorithm, and does not need a time-stepping. Second, we propose
to generate an initial guess of steady flow, leading eigenvalue and eigenvector
using orthogonal projection on a divergence-free basis satisfying all boundary
conditions. The approach, including the two proposed techniques, is illustrated
on the solution of the linear stability problem for laterally heated square and
cubic cavities
NLSP Gluino Search at the Tevatron and early LHC
We investigate the collider phenomenology of gluino-bino co-annihilation
scenario both at the Tevatron and 7 TeV LHC. This scenario can be realized, for
example, in a class of realistic supersymmetric models with non-universal
gaugino masses and t-b-\tau Yukawa unification. The NLSP gluino and LSP bino
should be nearly degenerate in mass, so that the typical gluino search channels
involving leptons or hard jets are not available. Consequently, the gluino can
be lighter than various bounds on its mass from direct searches. We propose a
new search for NLSP gluino involving multi-b final states, arising from the
three-body decay \tilde{g}-> b\bar{b}\tilde{\chi}_1^0. We identify two
realistic models with gluino mass of around 300 GeV for which the three-body
decay is dominant, and show that a 4.5 \sigma observation sensitivity can be
achieved at the Tevatron with an integrated luminosity of 10 fb^{-1}. For the 7
TeV LHC with 50 pb^{-1} of integrated luminosity, the number of signal events
for the two models is O(10), to be compared with negligible SM background
event.Comment: 14 pages, 4 figures and 3 tables, minor modifications made and
accepted for publication in JHE
Phenomenological Implications of Deflected Mirage Mediation: Comparison with Mirage Mediation
We compare the collider phenomenology of mirage mediation and deflected
mirage mediation, which are two recently proposed "mixed" supersymmetry
breaking scenarios motivated from string compactifications. The scenarios
differ in that deflected mirage mediation includes contributions from gauge
mediation in addition to the contributions from gravity mediation and anomaly
mediation also present in mirage mediation. The threshold effects from gauge
mediation can drastically alter the low energy spectrum from that of pure
mirage mediation models, resulting in some cases in a squeezed gaugino spectrum
and a gluino that is much lighter than other colored superpartners. We provide
several benchmark deflected mirage mediation models and construct model lines
as a function of the gauge mediation contributions, and discuss their discovery
potential at the LHC.Comment: 29 pages, 9 figure
Visual Exploration and Object Recognition by Lattice Deformation
Mechanisms of explicit object recognition are often difficult to investigate and require stimuli with controlled features whose expression can be manipulated in a precise quantitative fashion. Here, we developed a novel method (called “Dots”), for generating visual stimuli, which is based on the progressive deformation of a regular lattice of dots, driven by local contour information from images of objects. By applying progressively larger deformation to the lattice, the latter conveys progressively more information about the target object. Stimuli generated with the presented method enable a precise control of object-related information content while preserving low-level image statistics, globally, and affecting them only little, locally. We show that such stimuli are useful for investigating object recognition under a naturalistic setting – free visual exploration – enabling a clear dissociation between object detection and explicit recognition. Using the introduced stimuli, we show that top-down modulation induced by previous exposure to target objects can greatly influence perceptual decisions, lowering perceptual thresholds not only for object recognition but also for object detection (visual hysteresis). Visual hysteresis is target-specific, its expression and magnitude depending on the identity of individual objects. Relying on the particular features of dot stimuli and on eye-tracking measurements, we further demonstrate that top-down processes guide visual exploration, controlling how visual information is integrated by successive fixations. Prior knowledge about objects can guide saccades/fixations to sample locations that are supposed to be highly informative, even when the actual information is missing from those locations in the stimulus. The duration of individual fixations is modulated by the novelty and difficulty of the stimulus, likely reflecting cognitive demand
Survivability Is More Fundamental Than Evolvability
For a lineage to survive over long time periods, it must sometimes change. This has given rise to the term evolvability, meaning the tendency to produce adaptive variation. One lineage may be superior to another in terms of its current standing variation, or it may tend to produce more adaptive variation. However, evolutionary outcomes depend on more than standing variation and produced adaptive variation: deleterious variation also matters. Evolvability, as most commonly interpreted, is not predictive of evolutionary outcomes. Here, we define a predictive measure of the evolutionary success of a lineage that we call the k-survivability, defined as the probability that the lineage avoids extinction for k generations. We estimate the k-survivability using multiple experimental replicates. Because we measure evolutionary outcomes, the initial standing variation, the full spectrum of generated variation, and the heritability of that variation are all incorporated. Survivability also accounts for the decreased joint likelihood of extinction of sub-lineages when they 1) disperse in space, or 2) diversify in lifestyle. We illustrate measurement of survivability with in silico models, and suggest that it may also be measured in vivo using multiple longitudinal replicates. The k-survivability is a metric that enables the quantitative study of, for example, the evolution of 1) mutation rates, 2) dispersal mechanisms, 3) the genotype-phenotype map, and 4) sexual reproduction, in temporally and spatially fluctuating environments. Although these disparate phenomena evolve by well-understood microevolutionary rules, they are also subject to the macroevolutionary constraint of long-term survivability
Where the Sidewalk Ends: Jets and Missing Energy Search Strategies for the 7 TeV LHC
This work explores the potential reach of the 7 TeV LHC to new colored states
in the context of simplified models and addresses the issue of which search
regions are necessary to cover an extensive set of event topologies and
kinematic regimes. This article demonstrates that if searches are designed to
focus on specific regions of phase space, then new physics may be missed if it
lies in unexpected corners. Simple multiregion search strategies can be
designed to cover all of kinematic possibilities. A set of benchmark models are
created that cover the qualitatively different signatures and a benchmark
multiregion search strategy is presented that covers these models.Comment: 30 pages, 8 Figures, 3 Tables. Version accepted at JHEP. Minor
changes. Added figur
General Gauge and Anomaly Mediated Supersymmetry Breaking in Grand Unified Theories with Vector-Like Particles
In Grand Unified Theories (GUTs) from orbifold and various string
constructions the generic vector-like particles do not need to form complete
SU(5) or SO(10) representations. To realize them concretely, we present
orbifold SU(5) models, orbifold SO(10) models where the gauge symmetry can be
broken down to flipped SU(5) X U(1)_X or Pati-Salam SU(4)_C X SU(2)_L X SU(2)_R
gauge symmetries, and F-theory SU(5) models. Interestingly, these vector-like
particles can be at the TeV-scale so that the lightest CP-even Higgs boson mass
can be lifted, or play the messenger fields in the Gauge Mediated Supersymmetry
Breaking (GMSB). Considering GMSB, ultraviolet insensitive Anomaly Mediated
Supersymmetry Breaking (AMSB), and the deflected AMSB, we study the general
gaugino mass relations and their indices, which are valid from the GUT scale to
the electroweak scale at one loop, in the SU(5) models, the flipped SU(5) X
U(1)_X models, and the Pati-Salam SU(4)_C X SU(2)_L X SU(2)_R models. In the
deflected AMSB, we also define the new indices for the gaugino mass relations,
and calculate them as well. Using these gaugino mass relations and their
indices, we may probe the messenger fields at intermediate scale in the GMSB
and deflected AMSB, determine the supersymmetry breaking mediation mechanisms,
and distinguish the four-dimensional GUTs, orbifold GUTs, and F-theory GUTs.Comment: RevTex4, 45 pages, 15 tables, version to appear in JHE
Bigger, Better, Faster, More at the LHC
Multijet plus missing energy searches provide universal coverage for theories
that have new colored particles that decay into a dark matter candidate and
jets. These signals appear at the LHC further out on the missing energy tail
than two-to-two scattering indicates. The simplicity of the searches at the LHC
contrasts sharply with the Tevatron where more elaborate searches are necessary
to separate signal from background. The searches presented in this article
effectively distinguish signal from background for any theory where the LSP is
a daughter or granddaughter of the pair-produced colored parent particle
without ever having to consider missing energies less than 400 GeV.Comment: 26 pages, 8 Figures. Minor textual changes, typos fixed and
references adde
The effects of an area-based intervention on the uptake of maternal and child health assessments in Australia: A community trial
Background
Recognition of the importance of the early years in determining health and educational attainment and promotion of the World Health Organization Health for All (HFA) principles has led to an international trend towards community-based initiatives to improve developmental outcomes among socio-economically disadvantaged children. In this study we examine whether, Best Start, an Australian area-based initiative to improve child health was effective in improving access to Maternal and Child Health (MCH) services.
Methods
The study compares access to information, parental confidence and annual 3.5 year Ages and Stages visiting rates before (2001/02) and after (2004/05) the introduction of Best Start. Access to information and parental confidence were measured in surveys of parents with 3 year old children. There were 1666 surveys in the first wave and 1838 surveys in the second wave. The analysis of visiting rates for the 3.5 year Ages and Stages visit included all eligible Victorian children. Best Start sites included 1,739 eligible children in 2001/02 and 1437 eligible children in 2004/05. The comparable figures in the rest of the state were and 45, 497 and 45, 953 respectively.
Results
There was a significant increase in attendance at the 3.5 year Ages and Stages visit in 2004/05 compared to 2001/02 in all areas. However the increase in attendance was significantly greater at Best Start sites than the rest of the state. Access to information and parental confidence improved over the course of the intervention in Best Start sites with MCH projects compared to other Best Start sites.
Conclusion
These results suggest that community-based initiatives in disadvantaged areas may improve parents' access to child health information, improve their confidence and increase MCH service use. These outcomes suggest such programmes could potentially contribute to strategies to reduce child health inequalities
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