An analytical insight into the buckling paradox for circular cylindrical shells under axial and lateral loading

A large number of authors in the past have concluded that the flow theory of plasticity tends to overestimate significantly the buckling load for many problems of plates and shells in the plastic range, while the deformation theory generally provides much more accurate predictions and is consequently used in practical applications. Following previous numerical studies by the same authors focused on axially compressed cylinders, the present work presents an analytical investigation which comprises the broader and different case of nonproportional loading. The analytical results are discussed and compared with experimental and numerical findings and the reason for the apparent discrepancy on the basis of the so-called “buckling paradox” appears once again to lay in the overconstrained kinematics on the basis of the analytical and numerical approaches present in the literature

Proline Metabolism Increases katG Expression and Oxidative Stress Resistance in \u3ci\u3eEscherichia coli\u3c/i\u3e

The oxidation of L-proline to glutamate in Gram-negative bacteria is catalyzed by the proline utilization A (PutA) flavoenzyme, which contains proline dehydrogenase (PRODH) and _1-pyrroline-5-carboxylate (P5C) dehydrogenase domains in a single polypeptide. Previous studies have suggested that aside from providing energy, proline metabolism influences oxidative stress resistance in different organisms. To explore this potential role and the mechanism, we characterized the oxidative stress resistance of wild-type and putA mutant strains of Escherichia coli. Initial stress assays revealed that the putA mutant strain was significantly more sensitive to oxidative stress than the parental wild-type strain. Expression of PutA in the putA mutant strain restored oxidative stress resistance, confirming that depletion of PutA was responsible for the oxidative stress phenotype. Treatment of wild-type cells with proline significantly increased hydroperoxidase I (encoded by katG) expression and activity. Furthermore, the _katG strain failed to respond to proline, indicating a critical role for hydroperoxidase I in the mechanism of proline protection. The global regulator OxyR activates the expression of katG along with several other genes involved in oxidative stress defense. In addition to katG, proline increased the expression of grxA (glutaredoxin 1) and trxC (thioredoxin 2) of the OxyR regulon, implicating OxyR in proline protection. Proline oxidative metabolism was shown to generate hydrogen peroxide, indicating that proline increases oxidative stress tolerance in E. coli via a preadaptive effect involving endogenous hydrogen peroxide production and enhanced catalase-peroxidase activity

On the Eigenvalue Density of Real and Complex Wishart Correlation Matrices

Wishart correlation matrices are the standard model for the statistical analysis of time series. The ensemble averaged eigenvalue density is of considerable practical and theoretical interest. For complex time series and correlation matrices, the eigenvalue density is known exactly. In the real case, however, a fundamental mathematical obstacle made it forbidingly complicated to obtain exact results. We use the supersymmetry method to fully circumvent this problem. We present an exact formula for the eigenvalue density in the real case in terms of twofold integrals and finite sums.Comment: 4 pages, 2 figure

Fast and Accurate Computation of Orbital Collision Probability for Short-Term Encounters

International audienceThis article provides a new method for computing the probability of collision between two spherical space objects involved in a short-term encounter under Gaussian-distributed uncertainty. In this model of conjunction, classical assumptions reduce the probability of collision to the integral of a two-dimensional Gaussian probability density function over a disk. The computational method presented here is based on an analytic expression for the integral, derived by use of Laplace transform and D-finite functions properties. The formula has the form of a product between an exponential term and a convergent power series with positive coefficients. Analytic bounds on the truncation error are also derived and are used to obtain a very accurate algorithm. Another contribution is the derivation of analytic bounds on the probability of collision itself, allowing for a very fast and - in most cases - very precise evaluation of the risk. The only other analytical method of the literature - based on an approximation - is shown to be a special case of the new formula. A numerical study illustrates the efficiency of the proposed algorithms on a broad variety of examples and favorably compares the approach to the other methods of the literature

Ethylic esters as green solvents for the extraction of intracellular polyhydroxyalkanoates produced by mixed microbial culture

Volatile fatty acids obtained from the fermentation of the organic fraction of municipal solid waste can be used as raw materials for non-toxic ethyl ester (EE) synthesis as well as feedstock for the production of polyhydroxyalkanoates (PHAs). Taking advantage of the concept of an integrated process of a bio-refinery, in the present paper, a systematic investigation on the extraction of intracellular poly(3-hydroxybutyrate-co-3-hydroxyvalerate), produced by mixed microbial culture by using EEs was reported. Among the tested EEs, ethyl acetate (EA) was the best solvent, dissolving the copolymer at the lowest temperature. Then, extraction experiments were carried out by EA at different temperatures on two biomass samples containing PHAs with different average molecular weights. The parallel characterization of the extracted and non-extracted PHAs evidenced that at the lower temperature (100◦C) EA solubilizes preferentially the polymer fractions richer in 3HV comonomers and with the lower molecular weight. By increasing the extraction temperature from 100◦C to 125◦C, an increase of recovery from about 50 to 80 wt% and a molecular weight reduction from 48% to 65% was observed. The results highlighted that the extracted polymer purity is always above 90 wt% and that it is possible to choose the proper extraction condition to maximize the recovery yield at the expense of polymer fractionation and degradation at high temperatures or use milder conditions to maintain the original properties of a polymer

A numerical investigation into the plastic buckling of circular cylinders

It has been long known that finding a thoroughly good agreement with experimental results for the buckling loads of circular cylinders in the plastic range constitutes a very difficult task, beyond the same as well challenging problem in the elastic range. This paper attempts to contribute to the understanding of this issue by discussing a few numerical examples in comparison with some classical experimental results reported by Blachut et al. (1996) and Batterman (1965). It is shown that finite-element analyses grounded on the hypo-elasticity-based extension of small-strain theory of plasticity to geometrically nonlinear problems lead to good agreement with experimental results, although in some cases the sensitivity to the amount and shape of imperfection plays an important role, a fact which leaves open issues in terms of fully predictive capability of the computational models

Hemolytic Anemia as Presentation of T-Cell Large Granular Lymphocytic Leukemia After Kidney Transplantation: A Case Report

T-cell large granular lymphocytic (T-LGL) leukemia is a rare clonal proliferation presenting with cytopenia, splenomegaly, and autoimmune manifestations. It has rarely been described in recipients of solid organ transplants. We report the clinical case of a young kidney transplant recipient that developed T-LGL leukemia 3 years after kidney transplantation. The disorder manifested with a severe form of autoimmune hemolytic anemia in the absence of other laboratory abnormalities. The anemia was successfully treated with an intense course of corticosteroids ands witch of immunosuppressive therapy from a calcineurin inhibitor to sirolimus, a mammalian target of rapamycin inhibitor. Our case shows that autoimmune hemolytic anemia can be a life-threatening manifestation of T-LGL disease. The antiproliferative effects of sirolimus may be useful in the treatment of symptoms of T-LGL leukemia in kidney transplantation

On the elasto-plastic stability analysis of circular cylindrical shells

Copyright ©: SDSS'2016. The stability of thin circular shells under proportional and non-proportional loading, i.e. axial tensile stress and external pressure is extensively investigated. Two plasticity theories are considered; the flow and the deformation theory of plasticity. The results obtained confirm that under over-constrained kinematic assumptions the deformation theory tends to provides lower values of buckling pressure and the discrepancies in the results from the two plasticity theories increase with increasing thickness ratios, tensile stresses, boundary clamping E/σy and ratio