High-order terms in the renormalized perturbation theory for the Anderson impurity model

We study the renormalized perturbation theory of the single-impurity Anderson model, particularly the high-order terms in the expansion of the self-energy in powers of the renormalized coupling $\tilde{U}$. Though the presence of counter-terms in the renormalized theory may appear to complicate the diagrammatics, we show how these can be seamlessly accommodated by carrying out the calculation order-by-order in terms of skeleton diagrams. We describe how the diagrams pertinent to the renormalized self-energy and four-vertex can be automatically generated, translated into integrals and numerically integrated. To maximize the efficiency of our approach we introduce a generalized $k$-particle/hole propagator, which is used to analytically simplify the resultant integrals and reduce the dimensionality of the integration. We present results for the self-energy and spectral density to fifth order in $\tilde{U}$, for various values of the model asymmetry, and compare them to a Numerical Renormalization Group calculation.Comment: 11 pages, 8 figure

Semantically annotated hypermedia services

Hypermedia systems’ researchers investigate the various approaches in the way documents and resources are linked, navigated and stored in a distributed environment. Unfortunately, those systems fail to provide effortlessly usable discrete services, since it is difficult both to discover and to invoke any of them. This paper proposes the usage of emerging technologies that try to augment the Web resources with semantics in order to provide Hypermedia services that can be easily discovered, and integrated by potential third party developers. In this context, we analyze the benefits for the Hypermedia community upon the adoption of Semantic Web technologies for the description of Hypermedia services, and we implement an initial corresponding ontology

SOSTITUTI BIOLOGICI VASCOLARI A BASE DI ACIDO IALURONICO

The discovery of an adequate tissue substitute for the regeneration of small vessels has become one of the most debated issues in the last years. This is due to recent advances in regenerative medicine, which offers new cellular types and biomaterials, and the large clinical applications that this product may have, ranging from the replacement of the coronary vessels to correction of peripheral vascular malformations in pediatric patients. The biomaterials used so far for large caliber vascular prostheses have yielded disappointing results when applied in vessels with a smaller diameter than 6 mm, leading to occlusion of the vessel lumen in short periods. The finding of an ideal product in this area is difficult to reach first of all for the cellular complexity of the vascular tissue but also for involvedness of cellular interactions (vascular cells - red blood cells), mechanical properties and convolution of experimental models in vivo and in vitro. The aim of this observational study was to test a biomaterial based on hyaluronic acid in three different experimental models and to develop a model of tissue healing, to prove venous regeneration and functionality of this construct in similar to daily clinical practice conditions. The study is constituted of 3 different projects on animal models. In the first project patches of hyaluronic acid have been used to repair defects on the vascular wall of abdominal aorta of rat, there were operated 20 animals ( 250-350 g ). After isolation of the abdominal aorta, a breach was opened in it (1 x 5 mm) and the defect was repaired by placing the patch of hyaluronic acid. Tissue samples were evaluated after their removal to 1, 2, 4, 8 and 16 weeks with histological and immunohistochemical studies. In the second project a tubular conduit of hyaluronic acid ( 2 mm diameter, 1.5 cm length ) was placed after interruption of cava vein of the rat as a resorbable guide to vein regeneration . The tissue samples were evaluated after 30, 90 and 60 days with histological and immunohistochemical methods. In the third project the conduits of hyaluronic acid have been placed in vessels forming the vascular pedicle of a free tissue flap (groin flap) in the rabbit. 16 animals were operated, 8 of them were a control group, where microanastomosis were executed without interposition of any conduit. The vitality of the flaps was evaluated after 1, 2 and 3 weeks postoperatively. In the first project was detected a progressive regeneration of the arterial vessel in all its components, starting from the intima and adventitia and continuing with the muscularis. After 16 weeks, the biomaterial was completely degraded and replaced by a new vascular wall composed of endothelial cells, smooth muscle cells, collagen and elastin arranged in layers. In the project with the installation of venous ducts was documented a progressive venous regeneration already complete after 30 days of implantation but consolidated in 60 days. The total degradation after 4 months proved a protected environment for the regeneration during the initial stages . In the last project all flaps were viable after 3 weeks in cases of replacement and in control group , ¾ of them were vital in the case of venous replacement. There were recorded some complications such as dehiscence of the surgical wound and the seromas formation, which however did not appear to be related to implanted prosthesis but to surgical procedures and the specific animal. After these observations is claimable that the hyaluronic acid patch is able to support vascular regeneration. From this experiment was extrapolated a three-dimensional model of vascular tissue healing with the various stages. With the use of the tubular duct into the cavavein was obtained regeneration without the occlusion up to 4 months after implantation. Finally, tubular conduits successfully supported the vascularization of a free flap, and in this way was proved the functionality of the vascular component. These results open new perspectives in vascular , pediatric and cardiac surgery. Specifically in reconstructive surgery, these products could be used for the elongation of vascular pedicles in transplantation free flaps surgery or replants

Hypothesis testing for two population means: parametric or non-parametric test?

The parametric Welch $t$-test and the non-parametric Wilcoxon-Mann-Whitney test are the most commonly used two independent sample means tests. More recent testing approaches include the non-parametric, empirical likelihood and exponential empirical likelihood. However, the applicability of these non-parametric likelihood testing procedures is limited partially because of their tendency to inflate the type I error in small sized samples. In order to circumvent the type I error problem, we propose simple calibrations using the $t$ distribution and bootstrapping. The two non-parametric likelihood testing procedures, with and without those calibrations, are then compared against the Wilcoxon-Mann-Whitney test and the Welch $t$-test. The comparisons are implemented via extensive Monte Carlo simulations on the grounds of type I error and power in small/medium sized samples generated from various non-normal populations. The simulation studies clearly demonstrate that a) the $t$ calibration improves the type I error of the empirical likelihood, b) bootstrap calibration improves the type I error of both non-parametric likelihoods, c) the Welch $t$-test with or without bootstrap calibration attains the type I error and produces similar levels of power with the former testing procedures, and d) the Wilcoxon-Mann-Whitney test produces inflated type I error while the computation of an exact p-value is not feasible in the presence of ties with discrete data. Further, an application to real gene expression data illustrates the computational high cost and thus the impracticality of the non parametric likelihoods. Overall, the Welch t-test, which is highly computationally efficient and readily interpretable, is shown to be the best method when testing equality of two population means.Comment: Accepted for publication in the Journal of Statistical Computation and Simulatio

Mathematical modeling of acid deposition due to radiation fog

A Lagrangian model has been developed to study acidic deposition due to radiation fog. The model couples submodels describing the development and dissipation of radiation fog, the gas-phase chemistry and transfer, and the aqueous-phase chemistry. The model is applied to a radiation fog episode in Bakersfield in the San Joaquin Valley of California over the period January 4–5, 1985. Model predictions for temperature profile, fog development, liquid water content, gas-phase concentrations of SO_2, HNO_3, and NH_3, pH, aqueous-phase concentrations of SO_4^(2−), NH_4^+, and NO_3^−, and finally deposition rates of the above ions are compared with the observed values. The deposition rates of the major ions are predicted to increase significantly during the fog episode, the most notable being the increase of sulfate deposition. Pathways for sulfate production that are of secondary importance in a cloud environment may become significant in a fog. Expressing the mean droplet settling velocity as a function of liquid water content is found to be quite influential in the model's predictions

The effectiveness of laceback ligatures during initial orthodontic alignment: a systematic review and meta-analysis

Lacebacks may be used to limit unwanted incisor proclination during initial orthodontic alignment; however, their use has not met with universal approval. This systematic review aims to appraise the evidence in relation to the effectiveness of lacebacks in controlling incisor position during initial alignment. Electronic database searches of published literature (MEDLINE via Ovid, Cochrane Central Register of Controlled Trials, LILACS, and IBECS) and unpublished literature were performed. Search terms used included randomized controlled trial, controlled clinical trial, random allocation, double blind method, orthodontics, and laceback. Data were extracted using custom forms. Risk of bias assessment was made using the Cochrane Collaboration risk of bias tool. The quality of the evidence was also assessed using GRADE. Mean differences in incisor inclination and antero-posterior changes in incisor and molar position during alignment were calculated. Two studies involving 97 participants were found to be at low risk of bias and were included in the quantitative synthesis. The random effects meta-analysis demonstrated that the use of lacebacks was associated with 0.5 mm greater posterior movement of the incisors during alignment; this finding was of limited clinical importance and statistically non-significant [95 per cent confidence interval (CI): −1.25, 0.25, P = 0.19]. Little difference (0.46 mm) was also found between laceback and non-laceback groups with regards to mesial molar movement (95 per cent CI: −0.33, 1.24, P = 0.26). According to the GRADE assessment, the overall quality of evidence relating to the use of lacebacks was high. There is no evidence to support the use of lacebacks for the control of the sagittal position of the incisors during initial orthodontic alignmen

A simple model to estimate atmospheric concentrations of aerosol chemical species based on snow core chemistry at Summit, Greenland

A simple model is presented to estimate atmospheric concentrations of chemical species that exist primarily as aerosols based on snow core/ice core chemistry at Summit, Greenland. The model considers the processes of snow, fog, and dry deposition. The deposition parameters for each of the processes are estimated for SO42− and Ca2+ and are based on experiments conducted during the 1993 and 1994 summer field seasons. The seasonal mean atmospheric concentrations are estimated based on the deposition parameters and snow cores obtained during the field seasons. The ratios of the estimated seasonal mean airborne concentration divided by the measured mean concentration ( ) for SO42− over the 1993 and 1994 field seasons are 0.85 and 0.95, respectively. The ratios for Ca2+ are 0.45 and 0.90 for the 1993 and 1994 field seasons. The uncertainties in the estimated atmospheric concentrations range from 30% to 40% and are due to variability in the input parameters. The model estimates the seasonal mean atmospheric SO42− and Ca2+ concentrations to within 15% and 55%, respectively. Although the model is not directly applied to ice cores, the application of the model to ice core chemical signals is briefly discussed