4,297 research outputs found
Effective Actions for Heterotic M-Theory
We discuss the moduli space approximation for heterotic M-theory, both for
the minimal case of two boundary branes only, and when a bulk brane is
included. The resulting effective actions may be used to describe the
cosmological dynamics in the regime where the branes are moving slowly, away
from singularities. We make use of the recently derived colliding branes
solution to determine the global structure of moduli space, finding a boundary
at which the trajectories undergo a hard wall reflection. This has important
consequences for the allowed moduli space trajectories, and for the behaviour
of cosmological perturbations in the model.Comment: 21 pages, 4 figures. References added and some discussions clarifie
Designing a mobile augmented memory system for people with traumatic brain injuries
Augmented memory systems help people remember events in their lives. Individuals with Traumatic Brain Injury (TBI) often have memory impairments. We conducted a user study to learn about strategies individuals with TBI use to remember events in their lives. We explored what characteristics individuals with TBI expect of an augmented memory system. We then investigated these aspects in an initial mobile app design, and propose here a concept for a rehearsal application that addresses the issues found in our studies
Phasing of muscle gene expression with fasting-induced recovery growth in Atlantic salmon
Background: Many fish species experience long periods of fasting in nature often associated with seasonal reductions in water temperature and prey availability or spawning migrations. During periods of nutrient restriction, changes in metabolism occur to provide cellular energy via catabolic processes. Muscle is particularly affected by prolonged fasting as myofibrillar proteins act as a major energy source. To investigate the mechanisms of metabolic reorganisation with fasting and refeeding in a saltwater stage of Atlantic salmon (Salmo salar L.) we analysed the expression of genes involved in myogenesis, growth signalling, lipid biosynthesis and myofibrillar protein degradation and synthesis pathways using qPCR. Results: Hierarchical clustering of gene expression data revealed three clusters. The first cluster comprised genes involved in lipid metabolism and triacylglycerol synthesis (ALDOB, DGAT1 and LPL) which had peak expression 3-14d after refeeding. The second cluster comprised ADIPOQ, MLC2, IGF-I and TALDO1, with peak expression 14-32d after refeeding. Cluster III contained genes strongly down regulated as an initial response to feeding and included the ubiquitin ligases MuRF1 and MAFbx, myogenic regulatory factors and some metabolic genes. Conclusion: Early responses to refeeding in fasted salmon included the synthesis of triacylglycerols and activation of the adipogenic differentiation program. Inhibition of MuRF1 and MAFbx respectively may result in decreased degradation and concomitant increased production of myofibrillar proteins. Both of these processes preceded any increase in expression of myogenic regulatory factors and IGF-I. These responses could be a necessary strategy for an animal adapted to long periods of food deprivation whereby energy reserves are replenished prior to the resumption of myogenesis.Publisher PDFPeer reviewe
The tensor hypercontracted parametric reduced density matrix algorithm: coupled-cluster accuracy with O(r^4) scaling
Tensor hypercontraction is a method that allows the representation of a
high-rank tensor as a product of lower-rank tensors. In this paper, we show how
tensor hypercontraction can be applied to both the electron repulsion integral
(ERI) tensor and the two-particle excitation amplitudes used in the parametric
reduced density matrix (pRDM) algorithm. Because only O(r) auxiliary functions
are needed in both of these approximations, our overall algorithm can be shown
to scale as O(r4), where r is the number of single-particle basis functions. We
apply our algorithm to several small molecules, hydrogen chains, and alkanes to
demonstrate its low formal scaling and practical utility. Provided we use
enough auxiliary functions, we obtain accuracy similar to that of the
traditional pRDM algorithm, somewhere between that of CCSD and CCSD(T).Comment: 11 pages, 1 figur
Flavor-Changing Processes in Extended Technicolor
We analyze constraints on a class of extended technicolor (ETC) models from
neutral flavor-changing processes induced by (dimension-six) four-fermion
operators. The ETC gauge group is taken to commute with the standard-model
gauge group. The models in the class are distinguished by how the left- and
right-handed components of the quarks and charged leptons transform
under the ETC group. We consider and other pseudoscalar
meson mixings, and conclude that they are adequately suppressed if the and
components of the relevant quarks are assigned to the same (fundamental or
conjugate-fundamental) representation of the ETC group. Models in which the
and components of the down-type quarks are assigned to relatively conjugate
representations, while they can lead to realistic CKM mixing and intra-family
mass splittings, do not adequately suppress these mixing processes. We identify
an approximate global symmetry that elucidates these behavioral differences and
can be used to analyze other possible representation assignments.
Flavor-changing decays, involving quarks and/or leptons, are adequately
suppressed for any ETC-representation assignment of the and components
of the quarks, as well as the leptons. We draw lessons for future ETC model
building.Comment: 25 page
Predicting high utilization of emergency department services among patients with a diagnosis of psychosis in a Medicaid managed care organization
Studies have demonstrated increased utilization of medical services for patients with behavioral health diagnoses. Medicaid managed care organizations (MMCOs) that operate under behavioral health carve-outs face the challenge of effectively targeting disease management initiatives in the absence of information on behavioral diagnoses. This study sought to develop a predictive model of emergency department (ED) utilization for patients where a diagnosis of psychosis could be identified from a claim associated with a medical service provider visit. A retrospective cohort analysis was performed using medical and pharmacy claims from an MMCO in Philadelphia, Pennsylvania, to identify patients known to have a diagnosis of psychosis and to develop the predictive model. Demographics, comorbidities, medical utilization, and medications were assessed as predictor variables. Within the MMCO, 764 members were identified with at least one medical claim having a psychosis diagnosis. Ordinary least squares multiple regression analysis was performed to measure the correlation between independent variables and ED visits. Variables with significant F ratios in the regression analysis were retained as factors in a risk model to evaluate their additive and cumulative effects. Four variables were significant predictors of high ED utilization: prior number of ED visits, prior number of hospitalizations, history of alcohol abuse, and history of depression. ED utilization increased as the number of risk factors increased: With no risk factors, mean ED use was 0.58 visits (per 6 months), while the cumulative effects of all four factors equated to 8.5 ED visits. The model may be useful to other MMCOs, or similar organizations, seeking to risk-stratify their ED-related disease management activities for patients identified with psychosis
Radiation from relativistic jets in turbulent magnetic fields
Using our new 3-D relativistic electromagnetic particle (REMP) code
parallelized with MPI, we have investigated long-term particle acceleration
associated with an relativistic electron-positron jet propagating in an
unmagnetized ambient electron-positron plasma. The simulations have been
performed using a much longer simulation system than our previous simulations
in order to investigate the full nonlinear stage of the Weibel instability and
its particle acceleration mechanism. Cold jet electrons are thermalized and
ambient electrons are accelerated in the resulting shocks. The acceleration of
ambient electrons leads to a maximum ambient electron density three times
larger than the original value. Behind the bow shock in the jet shock strong
electromagnetic fields are generated. These fields may lead to the afterglow
emission. We have calculated the time evolution of the spectrum from two
electrons propagating in a uniform parallel magnetic field to verify the
technique.Comment: 3 pages, 2 figures, submitted for the Proceedings of The Sixth
Huntsville Gamma-Ray Burst Symposium 2008, Huntsville, AL, October 20-23,
200
- …