Mixed mode crack growth in curved beams with radial edge crack

Mixed mode crack growth in curved beams with radial edge crack is predicted by the prominent S-theory. An improved simple engineering method for obtaining approximate stress intensity factors of curved cracked beams is also used. It takes into account the elastic crack tip stress singularity while using the elementary beam theory. The results are in reasonable agreement with the more accurate calculations in literature.     

Detection of crack location using cracked beam element method for structural analysis

The local flexibility introduced by cracks changes the dynamic behavior of the structure and, by examining this change, crack position and magnitude can be identified. In order to model the structure for FEM analysis, a special finite element for a cracked Timoshenko beam is developed. Shape functions for rotational and translational displacements are used to obtain the consistent mass matrix for the cracked beam element. Effect of the crack on the stiffness matrix and consistent mass matrix is investigated. Proposed is a procedure for identifying cracks in structures using modal test data.     

Analysis of a subdomain‐based error estimator for finite element approximations of elliptic problems

In this article we analyze a subdomain residual error estimator for finite element approximations of elliptic problems. It is obtained by solving local problems on patches of elements in weighted spaces and provides an upper bound on the energy norm of the error when the local problems are solved in sufficiently enriched discrete spaces. A guaranteed lower bound on the error is also derived by a simple postprocess of the solutions to the local problems. Numerical tests show very good effectivity indices for both the upper and lower bounds and a strong reliability of this estimator even for coarse meshes. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 20: 165–192, 2004     

Multinuclear and dynamic NMR study of trans-[Pt(Cl)(PHCy2)2(PCy2)], [Pt(Cl)(PHCy2)3][BF4], [Pt(Cl)(PHCy2)3][Cl], trans-[Pt(Cl)(PHCy2)2[P(S)Cy(2)]], and trans-[Pt(Cl)(PHCy2)2[P(O)Cy2]]. Influence of intramolecular P=O...H-P and Cl...H-P interactions on restricted rotation about Pt-P bond. X-ray structure of trans-[Pt(Cl)(PHCy2)2[P(O)Cy2]

Dynamic NMR experiments on trans-[Pt(Cl)(PHCy2)2[P(X)Cy2]]z where X is a lone pair (1, z = 0), H (2, z = +1), S (3, z = 0), or O (4, z = 0) show that the rotation around the P(X)-Pt bond is hindered for all molecules studied, with deltaG++ ranging from 8.2 to 11.0 kcal/mol. The highest value of the series was calculated for trans-[Pt(Cl)(PHCy2)2[P(O)Cy2]] (4) where intramolecular P=O...H-P interactions act as a molecular brake at room temperature. Single-crystal X-ray diffraction confirms the presence of both intra and intermolecular P=O...H interactions in solid 4. In the case of [Pt(Cl)(PHCy2)3]Cl, multinuclear NMR analysis indicates the presence of a P-H...Cl- interaction in aromatic or halogenated solvents which could have also a minor effect on the rotational barrier around the P(X)-Pt bond.     

Fast and Cysteine-Specific Modification of Peptides,Proteins and Bacteriophage Using Chlorooximes

This work reports a novel chlorooxime mediated modification of native peptides and proteins under physiologic conditions. This method features fast reaction kinetics (apparent k₂=306±4 M⁻¹s⁻¹ for GSH) and exquisite selectivity for cysteine residues. This cysteine conjugation reaction can be carried out with just single-digit micromolar concentrations of the labeling reagent. The conjugates show high stability towards acid, base, and external thiol nucleophiles. A nitrile oxide species generated in situ is likely involved as the key intermediate. Furthermore, a bis-chlorooxime reagent is synthesized to enable facile Cys-Cys stapling in native peptides and proteins. This highly efficient cysteine conjugation and stapling was further implemented on bacteriophage to construct chemically modified phage libraries.     

Intramolecular cyclisation of isosorbide by dimethylcarbonate chemistry

In this work the synthesis of a tricyclic isosorbide derivative in moderate yield directly from the dicarboxymethyl isosorbide in a continuous-flow apparatus is reported. The tricyclic structure has been isolated as pure and fully characterized. This product confirms the potentiality of dimethylcarbonate (DMC) as dehydrating agent also for complicated structure and opens up further investigation and application of DMC chemistry on renewable starting materials.     

On plastic dynamics of discrete structural models

Summary This paper discusses the dynamic loading of rigid-perfectly plastic structures by adopting a structural model discretized with constant stress finite elements. This assumption together with the hypothesis of small displacements and of a piecewise linear yield surface leads to the formulation of a problem in linear inequalities, which is, implicitly, time discretized. It is shown how the non linearity of the associated plastic flow laws leads to an equivalent extremal formulation. A numerical algorithm for solving the problem is directly derived from the mechanical statements. Numerical examples illustrate this approach. In the appendix an approximate technique is developed, which takes into account the influence of the strain-hardening and the strain rate sensitivity of material.

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Sommario Il problema del caricamento dinamico delle strutture rigido-plastiche viene affrontato attraverso un modello discretizzato per elementi finiti a stato di sollecitazione costante. Tale assunzione insieme alle ipotesi di superficie di plasticizzazione lineare a tratti e di piccoli spostamenti, conduce alla formulazione di un problema retto da diseguaglianze lineari che si presenta discretizzato, implicitamente, nel tempo. Si mostra che la non linearità delle leggi del flusso plastico associato conduce ad una equivalente formulazione di estremo.È esposto un algoritmo risolvente affatto aderente alla formulazione meccanica. Alcuni esempi illustrano il procedimento. Una proposta di adattamento al caso di materiali incrudenti e sensibili alle velocità di deformazione è presentata in appendice.

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Research supported by the National Research Council (C.N.R. - P.A.d.I.S.) of Italy.