On causality, unitarity and perturbative expansions

We present a pedagogical case study how to combine micro-causality and unitarity based on a perturbative approach. The method we advocate constructs an analytic extrapolation of partial-wave scattering amplitudes that is constrained by the unitarity condition. Suitably constructed conformal mappings help to arrive at a systematic approximation of the scattering amplitude. The technique is illustrated at hand of a Yukawa interaction. The typical case of a superposition of strong short-range and weak long-range forces is investigated.Comment: 12 pages, 12 figure

A nonlinear drift which leads to κ\kappa-generalized distributions

We consider a system described by a Fokker-Planck equation with a new type of momentum-dependent drift coefficient which asymptotically decreases as $-1/p$ for a large momentum $p$. It is shown that the steady-state of this system is a $\kappa$-generalized Gaussian distribution, which is a non-Gaussian distribution with a power-law tail.Comment: Submitted to EPJB. 8 pages, 2 figures, dedicated to the proceedings of APFA

Constructive Dimension and Turing Degrees

This paper examines the constructive Hausdorff and packing dimensions of Turing degrees. The main result is that every infinite sequence S with constructive Hausdorff dimension dim_H(S) and constructive packing dimension dim_P(S) is Turing equivalent to a sequence R with dim_H(R) <= (dim_H(S) / dim_P(S)) - epsilon, for arbitrary epsilon > 0. Furthermore, if dim_P(S) > 0, then dim_P(R) >= 1 - epsilon. The reduction thus serves as a *randomness extractor* that increases the algorithmic randomness of S, as measured by constructive dimension. A number of applications of this result shed new light on the constructive dimensions of Turing degrees. A lower bound of dim_H(S) / dim_P(S) is shown to hold for the Turing degree of any sequence S. A new proof is given of a previously-known zero-one law for the constructive packing dimension of Turing degrees. It is also shown that, for any regular sequence S (that is, dim_H(S) = dim_P(S)) such that dim_H(S) > 0, the Turing degree of S has constructive Hausdorff and packing dimension equal to 1. Finally, it is shown that no single Turing reduction can be a universal constructive Hausdorff dimension extractor, and that bounded Turing reductions cannot extract constructive Hausdorff dimension. We also exhibit sequences on which weak truth-table and bounded Turing reductions differ in their ability to extract dimension.Comment: The version of this paper appearing in Theory of Computing Systems, 45(4):740-755, 2009, had an error in the proof of Theorem 2.4, due to insufficient care with the choice of delta. This version modifies that proof to fix the error

Development of EM-CCD-based X-ray detector for synchrotron applications

A high speed, low noise camera system for crystallography and X-ray imaging applications is developed and successfully demonstrated. By coupling an electron-multiplying (EM)-CCD to a 3:1 fibre-optic taper and a CsI(Tl) scintillator, it was possible to detect hard X-rays. This novel approach to hard X-ray imaging takes advantage of sub-electron equivalent readout noise performance at high pixel readout frequencies of EM-CCD detectors with the increase in the imaging area that is offered through the use of a fibre-optic taper. Compared with the industry state of the art, based on CCD camera systems, a high frame rate for a full-frame readout (50 ms) and a lower readout noise (<1 electron root mean square) across a range of X-ray energies (6–18 keV) were achieved

Development and characterisation of pressed packaging solutions for high-temperature high-reliability SiC power modules

SiC is a wide bandgap semiconductor with better electrothermal properties than silicon, including higher temperature of operation, higher breakdown voltage, lower losses and the ability to switch at higher frequencies. However, the power cycling performance of SiC devices in traditional silicon packaging systems is in need of further investigation since initial studies have shown reduced reliability. These traditional packaging systems have been developed for silicon, a semiconductor with different electrothermal and thermomechanical properties from SiC, hence the stresses on the different components of the package will change. Pressure packages, a packaging alternative where the weak elements of the traditional systems like wirebonds are removed, have demonstrated enhanced reliability for silicon devices however, there has not been much investigation on the performance of SiC devices in press-pack assemblies. This will be important for high power applications where reliability is critical. In this paper, SiC Schottky diodes in pressure packages have been evaluated, including the electrothermal characterisation for different clamping forces and contact materials, the thermal impedance evaluation and initial thermal cycling studies, focusing on the use of aluminium graphite as contact material

A prototype liquid Argon Time Projection Chamber for the study of UV laser multi-photonic ionization

This paper describes the design, realization and operation of a prototype liquid Argon Time Projection Chamber (LAr TPC) detector dedicated to the development of a novel online monitoring and calibration system exploiting UV laser beams. In particular, the system is intended to measure the lifetime of the primary ionization in LAr, in turn related to the LAr purity level. This technique could be exploited by present and next generation large mass LAr TPCs for which monitoring of the performance and calibration plays an important role. Results from the first measurements are presented together with some considerations and outlook.Comment: 26 pages, 27 figure

Dewetting of thin films on heterogeneous substrates: Pinning vs. coarsening

We study a model for a thin liquid film dewetting from a periodic heterogeneous substrate (template). The amplitude and periodicity of a striped template heterogeneity necessary to obtain a stable periodic stripe pattern, i.e. pinning, are computed. This requires a stabilization of the longitudinal and transversal modes driving the typical coarsening dynamics during dewetting of a thin film on a homogeneous substrate. If the heterogeneity has a larger spatial period than the critical dewetting mode, weak heterogeneities are sufficient for pinning. A large region of coexistence between coarsening dynamics and pinning is found.Comment: 4 pages, 4 figure

Negative Kaons in Dense Baryonic Matter

Kaon polarization operator in dense baryonic matter of arbitrary isotopic composition is calculated including s- and p-wave kaon-baryon interactions. The regular part of the polarization operator is extracted from the realistic kaon-nucleon interaction based on the chiral and 1/N_c expansion. Contributions of the Lambda(1116), Sigma(1195), Sigma*(1385) resonances are taken explicitly into account in the pole and regular terms with inclusion of mean-field potentials. The baryon-baryon correlations are incorporated and fluctuation contributions are estimated. Results are applied for K- in neutron star matter. Within our model a second-order phase transition to the s-wave K- condensate state occurs at rho_c \gsim 4 \rho_0 once the baryon-baryon correlations are included. We show that the second-order phase transition to the p-wave $K^-$ condensate state may occur at densities $\rho_c \sim 3\div 5 \rho_0$ in dependence on the parameter choice. We demonstrate that a first-order phase transition to a proton-enriched (approximately isospin-symmetric) nucleon matter with a p-wave K- condensate can occur at smaller densities, \rho\lsim 2 \rho_0. The transition is accompanied by the suppression of hyperon concentrations.Comment: 41 pages, 24 figures, revtex4 styl

Emergency department utilization after hospitalization discharge for acute stroke: The COMprehensive Post-Acute Stroke Services (COMPASS) study

Each year nearly 800,000 people in the United States experience a stroke. Those that survive are at high risk for complications after hospital discharge. Providing appropriate care during the recovery from this complex condition is a challenge for patients, caregivers, and health care providers. Understanding emergency department (ED) utilization after a stroke may provide insights into long-term management of stroke, inform interventions, improve patient outcomes, and reduce medical costs. A comprehensive transitional care model for post-acute stroke care may influence the need to seek ED care for downstream events after a stroke. To date, most transitional care trials exploring post-stroke healthcare utilization were conducted outside of the U.S. health-care system. We examined data from the Comprehensive Post-Acute Stroke Services (COMPASS) study, a cluster-randomized pragmatic trial of a post-discharge transitional care model for stroke survivors and their caregivers compared with usual care

Disease-modifying effects of an SCAF4 structural variant in a predominantly SOD1 ALS cohort

Objective To test the hypothesis that rs573116164 will have disease-modifying effects in patients with superoxide dismutase 1 (SOD1) familial amyotrophic lateral sclerosis (fALS), we characterized rs573116164 within a cohort of 190 patients with fALS and 560 healthy age-matched controls to assess the variant for association with various measures of disease. Methods Using a previously described bioinformatics evaluation algorithm, a polymorphic short structural variant associated with SOD1 was identified according to its theoretical effect on gene expression. An 12–18 poly-T repeat (rs573116164) within the 3′ untranslated region of serine and arginine rich proteins-related carboxy terminal domain associated factor 4 (SCAF4), a gene that is adjacent to SOD1, was assessed for disease association and influence on survival and age at onset in an fALS cohort using PCR, Sanger sequencing, and capillary separation techniques for allele detection. Results In a North American cohort of predominantly SOD1 fALS patients (n =190) and age-matched healthy controls (n = 560), we showed that carriage of an 18T SCAF4 allele was associated with disease within this cohort (odds ratio [OR] 6.6; 95% confidence interval [CI] 3.9–11.2; p = 4.0e-11), but also within non-SOD1 cases (n = 27; OR 5.3; 95% CI 1.9–14.5; p = 0.0014). This finding suggests genetically SOD1-independent effects of SCAF4 on fALS susceptibility. Furthermore, carriage of an 18T allele was associated with a 26-month reduction in survival time (95% CI 6.6–40.8; p = 0.014), but did not affect age at onset of disease. Conclusions The findings in this fALS cohort suggest that rs573116164 could have SOD1-independent and broader relevance in ALS, warranting further investigation in other fALS and sporadic ALS cohorts, as well as studies of functional effects of the 18T variant on gene expression