13,303 research outputs found
Physics at the B Factories
We review recent progress at the two B factories. The first
measurement of CP violation and the prospects for measuring all the angles of
the unitarity triangle are discussed.Comment: To appear in the Proceedings of From the Smallest to the Largest
Distances, a conference in honor of Tranh Thanh Van in Moscow, Russi
The effect of electromechanical coupling on the strain in AlGaN/GaN heterojunction field effect transistors
The strain in AlGaN/GaN heterojunction field-effect transistors (HFETs) is
examined theoretically in the context of the fully-coupled equation of state
for piezoelectric materials. Using a simple analytical model, it is shown that,
in the absence of a two-dimensional electron gas (2DEG), the out-of-plane
strain obtained without electromechanical coupling is in error by about 30% for
an Al fraction of 0.3. This result has consequences for the calculation of
quantities that depend directly on the strain tensor. These quantities include
the eigenstates and electrostatic potential in AlGaN/GaN heterostructures. It
is shown that for an HFET, the electromechanical coupling is screened by the
2DEG. Results for the electromechanical model, including the 2DEG, indicate
that the standard (decoupled) strain model is a reasonable approximation for
HFET calculataions. The analytical results are supported by a self-consistent
Schr\"odinger-Poisson calculation that includes the fully-coupled equation of
state together with the charge-balance equation.Comment: 6 figures, revte
GOexpress: an R/Bioconductor package for the identification and visualisation of robust gene ontology signatures through supervised learning of gene expression data
Background: Identification of gene expression profiles that differentiate experimental groups is critical for discovery and analysis of key molecular pathways and also for selection of robust diagnostic or prognostic biomarkers. While integration of differential expression statistics has been used to refine gene set enrichment analyses, such approaches are typically limited to single gene lists resulting from simple two-group comparisons or time-series analyses. In contrast, functional class scoring and machine learning approaches provide powerful alternative methods to leverage molecular measurements for pathway analyses, and to compare continuous and multi-level categorical factors. Results: We introduce GOexpress, a software package for scoring and summarising the capacity of gene ontology features to simultaneously classify samples from multiple experimental groups. GOexpress integrates normalised gene expression data (e.g., from microarray and RNA-seq experiments) and phenotypic information of individual samples with gene ontology annotations to derive a ranking of genes and gene ontology terms using a supervised learning approach. The default random forest algorithm allows interactions between all experimental factors, and competitive scoring of expressed genes to evaluate their relative importance in classifying predefined groups of samples. Conclusions: GOexpress enables rapid identification and visualisation of ontology-related gene panels that robustly classify groups of samples and supports both categorical (e.g., infection status, treatment) and continuous (e.g., time-series, drug concentrations) experimental factors. The use of standard Bioconductor extension packages and publicly available gene ontology annotations facilitates straightforward integration of GOexpress within existing computational biology pipelines.Department of Agriculture, Food and the MarineEuropean Commission - Seventh Framework Programme (FP7)Science Foundation IrelandUniversity College Dubli
A Firefly-inspired method for protein structure prediction in lattice models
We introduce a Firefly-inspired algorithmic approach for protein structure prediction over two different lattice models in three-dimensional space. In particular, we consider three-dimensional cubic and three-dimensional face-centred-cubic (FCC) lattices. The underlying energy models are the Hydrophobic-Polar (H-P) model, the Miyazawa–Jernigan (M-J) model and a related matrix model. The implementation of our approach is tested on ten H-P benchmark problems of a length of 48 and ten M-J benchmark problems of a length ranging from 48 until 61. The key complexity parameter we investigate is the total number of objective function valuations required to achieve the optimum energy values for the H-P model or competitive results in comparison to published values for the M-J model. For H-P instances and cubic lattices, where data for comparison are available, we obtain an average speed-up over eight instances of 2.1, leaving out two extreme values (otherwise, 8.8). For six M-J instances, data for comparison are available for cubic lattices and runs with a population size of 100, where, a priori, the minimum free energy is a termination criterion. The average speed-up over four instances is 1.2 (leaving out two extreme values, otherwise 1.1), which is achieved for a population size of only eight instances. The present study is a test case with initial results for ad hoc parameter settings, with the aim of justifying future research on larger instances within lattice model settings, eventually leading to the ultimate goal of implementations for off-lattice models
Electromechanical coupling in free-standing AlGaN/GaN planar structures
The strain and electric fields present in free-standing AlGaN/GaN slabs are
examined theoretically within the framework of fully-coupled continuum elastic
and dielectric models. Simultaneous solutions for the electric field and strain
components are obtained by minimizing the electric enthalpy. We apply
constraints appropriate to pseudomorphic semiconductor epitaxial layers and
obtain closed-form analytic expressions that take into account the wurtzite
crystal anisotropy. It is shown that in the absence of free charges, the
calculated strain and electric fields are substantially differently from those
obtained using the standard model without electromechanical coupling. It is
also shown, however, that when a two-dimensional electron gas is present at the
AlGaN/GaN interface, a condition that is the basis for heterojunction
field-effect transistors, the electromechanical coupling is screened and the
decoupled model is once again a good approximation. Specific cases of these
calculations corresponding to transistor and superlattice structures are
discussed.Comment: revte
Differences in Dopamine Function in Fibromyalgia
poster abstractObjective: Fibromyalgia (FM) is a debilitating pain disorder that affects 2% of the population. Many of the drugs prescribed to fibromyalgia sufferers are highly addictive, have limited clinical efficacy, and do not treat the cognitive symptoms of fibromyalgia. The neurobiological substrates of fibromyalgia are unknown, but there is evidence for involvement of altered dopaminergic transmission in pain disorders. Given that dopamine is essential for proper cognitive function, it is possible that fibromyalgia symptoms are partly mediated by abnormal dopaminergic functioning. However, the in vivo dopamine system in fibromyalgia patients has not been assessed. Thus, the objective of the current study was to ascertain how the dopamine system in fibromyalgia differs from healthy controls. Methods: [18F]-Fallypride (FAL) PET scanning was used to assess DA changes during a working memory task relative to a baseline task. Twelve patients with FM and twelve controls completed study procedures. Subjects received one FAL PET scan during a 2-back working-memory condition and one during a 0-back (attentional control) task. Results: Fibromyalgia subjects had higher baseline FAL binding potential (BPND) in the right amygdala and ventral pallidum relative to controls. FM subjects had lower baseline FAL BPND in frontal, temporal, and cingulate cortices. Voxel-wise paired t-tests were used to infer increases or decreases in FAL BPND (indicative of decreases or increases in dopamine, respectively) during 2-back performance. Fibromyalgia subjects had significant dopamine release in the ACC, left insula, OFC, and bilateral hippocampus during the 2-back task. Conversely, decreases in DA were detected in the posterior parietal cortex and vmPFC. In controls, dopamine appeared to decrease in the posterior parietal lobe, left hippocampus, and vmPFC during the 2-back task. No significant DA release was detected in controls. Self-reported pain ratings in fibromyalgia subjects were significantly associated with baseline FAL BPND in the ACC, bilateral ventral pallidum, amygdalae, and PAG. Conclusion: These data suggest that in fibromyalgia, abnormalities in dopamine function may be associated with both working memory and pain perception. Further studies are needed to further explore the potential associations between dopamine and cognitive performance and pain perception in FM
Effects of Possible Transitions in Neutral Meson Decays}
We explore the possibility that the existing data on like-sign dileptons at
the resonance consist of events arising from mixing and also from transitions. The
consequences of these nonstandard transitions for certain time-asymmetries
which are likely to be measured at the factories are studied.Comment: {\LARGE \bf 10 pages, no figures, process using latex, TIFR/TH/93-5
Highlights from Five Years at the B Factories
The highlights and conflicts at the B Factories are briefly reviewed.
violation was established in 2001 in and related modes,
which has now become a precision measurement of CP violation in - mixing. However, the situation for the and charmless
modes, which probe also CP violation in the {\it decay} amplitude, are
not quite settled yet. They could be hinting at presence of both strong (CP
conserving) and new physics (CP violating) phases. We critically assess the
developments and discuss some related discrepancies and highlights, such as
observation of direct CP violation, and make a projection towards the next few
years.Comment: 16 pages, 5 figures, to appear as Brief Review in Mod. Phys. Lett.
Transport signatures of quasiparticle poisoning in a Majorana island
We investigate effects of quasiparticle poisoning in a Majorana island with
strong tunnel coupling to normal-metal leads. In addition to the main Coulomb
blockade diamonds, "shadow" diamonds appear, shifted by 1e in gate voltage,
consistent with transport through an excited (poisoned) state of the island.
Comparison to a simple model yields an estimate of parity lifetime for the
strongly coupled island (~ 1 {\mu}s) and sets a bound for a weakly coupled
island (> 10 {\mu}s). Fluctuations in the gate-voltage spacing of Coulomb peaks
at high field, reflecting Majorana hybridization, are enhanced by the reduced
lever arm at strong coupling. In energy units, fluctuations are consistent with
previous measurements.Comment: includes supplementary materia
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