The Chaboche nonlinear kinematic hardening model: calibration methodology and validation

This work studies how a nonlinear kinematic model aimed for cyclic plasticity could be put into effect and used within a FEM code. A correct modeling of cyclic elasto-plastic behavior can be exploited in low-cycle fatigue life investigation as well as in manufacturing problems related to springback prediction. The chosen formulation has been proposed by Chaboche, and it is implemented in most of the commercial codes used for nonlinear FEM simulations. At first, a procedure for the proper identification of unknown material model parameters has been put forward. This calibration, based on the data collected from experimental low-cycle fatigue tests, has been performed by means of an inverse method. Laboratory tests differ according to the type of material under investigation. A classification can be operated distinguishing between specimens obtained from bulk materials or from sheet metals. For the former, standard tension-compression tests have been performed, while for the latter, a dedicated testing equipment for three-point bend cyclic tests has been devised. Then, further experimental tests have been run to check model transferability: different strain per cycle amplitudes, asymmetric strain cycling and different stress triaxiality levels have been investigated. For each of these tests, experimental vs. FEM results have been analyzed to show the level of agreement that has been reached.     

Factorization of analytic functions by means of Koenig's theorem and Toeplitz computations

Summary. By providing a matrix version of Koenig's theorem we reduce the problem of evaluating the coefficients of a monic factor r(z) of degree h of a power series f(z) to that of approximating the first h entries in the first column of the inverse of an Toeplitz matrix in block Hessenberg form for sufficiently large values of n. This matrix is reduced to a band matrix if f(z) is a polynomial. We prove that the factorization problem can be also reduced to solving a matrix equation for an matrix X, where is a matrix power series whose coefficients are Toeplitz matrices. The function is reduced to a matrix polynomial of degree 2 if f(z) is a polynomial of degreeN and . These reductions allow us to devise a suitable algorithm, based on cyclic reduction and on the concept of displacement rank, for generating a sequence of vectors that quadratically converges to the vector having as components the coefficients of the factor r(z). In the case of a polynomial f(z) of degree N, the cost of computing the entries of given is arithmetic operations, where is the cost of solving an Toeplitz-like system. In the case of analytic functions the cost depends on the numerical degree of the power series involved in the computation. From the numerical experiments performed with several test polynomials and power series, the algorithm has shown good numerical properties and promises to be a good candidate for implementing polynomial root-finders based on recursive splitting strategies. Applications to solving spectral factorization problems and Markov chains are also shown. Received September 9, 1998 / Revised version received November 14, 1999 / Published online February 5, 2001     

Organic Ion Exchangers. Synthesis and Their Behaviour in the Retention of Some Metal Ions

Summary: Three pyridine strong base anion exchangers as beads were obtained by quaternization reactions of a 4-vinylpyridine : 8% divinylbenzene copolymer of gel type. These resins possess methyl / ethyl / butyl radicals as substituents on N⁺ atoms and have exchange capacities of 4.80 mEq/g and 2.10 mEq/mL. For pyridine strong base anion exchangers, the behaviours in the retention processes of Cr(VI) as oxyanions and Ga(III) as [GaCl₄]⁻ complex anion were evaluated with the bath method. All the resins exhibited retention properties, but the retained amounts of the metal cations are different as a function of the alkyl length as substituent on N⁺ atoms and the complex anion nature. Thus, Cr(VI) oxyanions are best retained by the resin with  CH₃ as substituent on N⁺ atoms while [GaCl₄]⁻ complex anion by the resin with  C₄H₉ as substituent on N⁺ atoms. By aminolysis reaction of an ethylacrylate : acrylonitrile : divinylbenzene copolymer as beads of macroporous type with NH₂OH · HCl in the presence of C₂H₅OH a new chelating ion exchanger was performed which contains both amidoxime and hydroxamic acid functional groups. This ion exchanger has the retention property for different metal cations but its retention capacities values are strongly dependent of the nature of metal cation and the counterion as well as pH of the solution. Thus, in the static conditions Zn(II) cation with NOequation/tex2gif-stack-1.gif anion as counterion is retained with the best result at pH = 5. As an example, for the aqueous metal cation solution of 10⁻² M concentration for Zn(NO₃)₂ the resin possess at equilibrium a retention capacity of 6.70 mmol Zn/g dry resin and for Cu(II) from Cu(NO₃)₂ solution of same concentration, the retention capacity is 0.22 mmol Cu/g dry resin and Fe(III) from Fe(NO₃)₃ solution is not retained.     

On adaptive step-size selections in gradient methods

In recent years several proposals for the step-size selection have largely improved the gradient methods, in the case of both constrained and unconstrained nonlinear optimization. We introduce a new step-size rule with some crucial properties. We design step-size selection strategies where the new rule and a standard Barzilai-Borwein (BB) rule can be adaptively alternated to get meaningful convergence rate improvements in comparison with other BB-like gradient schemes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A series of diarylsubstituted oximes as potential substrate for new aldose reductase inhibitors

In the course of our research aimed at the discovery of new compounds acting as aldose reductase inhibitors, we tested a series of some (E)‐ and (Z)‐ω‐[[(aryldiazinylmethylene)amino]oxy]alkanoic acids, which were found to have moderate in vitro inhibitory activity. On this basis we have now prepared several new derivatives modified both at the length of the chain and at its terminal carboxylic group, together with compounds carrying various substituents at the phenyl ring. This paper describes their synthesis and biological properties.     

Multi-degree-of-freedom systems with a Coulomb friction contact: analytical boundaries of motion regimes

Nonlinear Dynamics - This paper proposes an approach for the determination of the analytical boundaries of continuous, stick-slip and no motion regimes for the steady-state response of a...     

Design and Synthesis of Hsp90 Inhibitors with B-Raf and PDHK1 Multi-Target Activity

The design of multi-target ligands has become an innovative approach for the identification of effective therapeutic treatments against complex diseases, such as cancer. Recent studies have demonstrated that the combined inhibition of Hsp90 and B-Raf provides synergistic effects against several types of cancers. Moreover, it has been reported that PDHK1, which presents an ATP-binding pocket similar to that of Hsp90, plays an important role in tumor initiation, maintenance and progression, participating also to the senescence process induced by B-Raf oncogenic proteins. Based on these premises, the simultaneous inhibition of these targets may provide several benefits for the treatment of cancer. In this work, we set up a design strategy including the assembly and integration of molecular fragments known to be important for binding to the Hsp90, PDHK1 and B-Raf targets, aided by molecular docking for the selection of a set of compounds potentially able to exert Hsp90-B-Raf-PDHK1 multi-target activities. The designed compounds were synthesized and experimentally validated in vitro. According to the in vitro assays, compounds 4 a , 4 d and 4 e potently inhibited Hsp90 and moderately inhibited the PDHK1 kinase. Finally, molecular dynamics simulations were performed to provide further insights into the structural basis of their multi-target activity.     

Effect of thermal treatment under high pressure on the quality of a meat sauce

Abstract

It is known that pressure alone is not able to make shelf-stable any food stored in room conditions. Acid products are normally spoiled by enzymes, and low acid products are spoiled even by spore-forming micro-organisms. To overcome the problem the role of heat in the process has been re-evaluated and the possibility of destroying at the same time spores and enzymes has been found. This work compares the effect of sterilisation by High Pressure Processing (HPP) with one of the conventional retort processing techniques. Two batches of meat sauce were kept in room conditions over a year and their quality was evaluated periodically during the shelf life simulation. The physico-chemical characteristics of the retorted ones showed a progressive appearance of the typical thermal damage. The High Pressure Sterilised samples on the contrary showed limited damage, related to the unavoidable pre-heating. Their quality markers were constant over the shelf life evaluated period.     

Platinum role in hydrophilicity enhancement of Cr-doped TiO2 thin films

In this paper, we have investigated the hydrophilic properties of the titania films doped with increasing chromium percentages (from 2.1 at.% till 4.0 at.%). Cr-doping induces an increase in the rutile weight %, a more compact structure, and a significant red shift of the TiO₂ absorption edge, the last property being very important in the self cleaning applications. For the chosen Cr concentrations, the films did not show promising hydrophilic properties. To improve them, we have applied a novel surface modification method, reported in literature mainly for powders, namely, surface metallisation. We have observed that, by depositing Pt islands on the film with the highest Cr content, its hydrophilic properties improve for a certain metal coverage area. The explanation was based on FT-IR and X-ray photoelectron spectroscopy analysis, performed on the UV irradiated and non-irradiated films, which gives information on the relationship between hydrophilicity and the amount of the adsorbed hydroxyl groups.     

Development and validation of a HPLC–UV based method for the extraction and quantification of methotrexate in the skin

An innovative and sensitive HPLC–UV method for the extraction and quantification of methotrexate (MTX) in skin layers was developed and validated. Owing to the physico-chemical characteristics of the drug and the nature of the tissue, it was necessary to use folic acid (FA) as an internal standard for MTX quantification in the dermis. MTX (and FA) analysis was performed on a Phenomenex Jupiter C₁₈ column, using a 50 mm sodium acetate buffer (pH 3.6) and methanol mixture (87:13, v/v) as mobile phase, pumped at 1 ml/min. The absorbance was monitored at 290 nm. The method was selective, linear in the range 0.11–8.49 μg/ml for extraction solvent and 0.05–8.94 μg/ml for pH 7.4 phosphate-buffered saline, precise and accurate, with lower limits of quantitation of 0.11 μg/ml (extraction solvent) and 0.05 μg/ml (pH 7.4 phosphate-buffered saline). The method developed is suitable for the quantification of MTX in skin layers at the end of in vitro permeation experiments; the overall mass balance was 96.5 ± 1.4%, in line with the requirements of the Organisation for Economic Co-operation and Development guideline for the testing of the chemicals (Skin absorption: in vitro method).