Elasto-visco-plastic modeling of mild steels for sheet forming applications over a large range of strain rates

A physically based elasto-visco-plastic constitutive model is presented and compared to experimental results for three different mild steels. The experiments consist of tensile tests ranging from quasi-static conditions up to strain rates of 10³ s^?1 as well as quasi-static simple and reverse shear tests at different amounts of pre-strain. Additional two-step sequential mechanical tests (Bauschinger and orthogonal effects) have been performed to further evaluate the ability of the model to describe strain-path changes at moderate/large strains. The model requires significantly fewer material parameters compared to other visco-plasticity models from the literature, while being able to describe some of the main features of the strain-rate sensitivity of mild steels. Accordingly, the parameter identification is simple and intuitive, requiring a relatively small set of experiments. The strain-rate sensitivity modeling is not restricted to a particular hardening law and thus provides a general framework in which advanced hardening equations can be adopted.     

Reaction Between Isocyanides and Dialkyl Acetylenedicarboxylates in the Presence of Hydantoins – A One-pot Synthesis of Stable Ketenimines

Summary. The reactive 1:1 intermediate produced in the reaction between isocyanides and dialkyl acetylenedicarboxylates was trapped by hydantoins to yield highly functionalized stable ketenimines in fairly good yields.     

Gas‐phase fragmentation study of biotin reagents using electrospray ionization tandem mass spectrometry on a quadrupole orthogonal time‐of‐flight hybrid instrument

In this study, we evaluated, by electrospray ionization mass spectrometry (ESI‐MS) and collision‐induced dissociation tandem mass spectrometry (CID‐MS/MS) using a quadrupole orthogonal time‐of‐flight (QqToF)‐MS/MS hybrid instrument, the gas‐phase fragmentations of some commercially available biotinyl reagents. The biotin reagents used were: psoralen‐BPE 1, p‐diazobenzoyl biocytin (DBB) 2, photoreactive biotin 3, biotinyl‐hexaethyleneglycol dimer 4, and the sulfo‐SBED 5. The results showed that, during ESI‐MS and CID‐MS/MS analyses, the biotin reagents followed a similar gas‐phase fragmentation pattern and the cleavages usually occurred at either end of the spacer arm of the biotin reagents. In general we have observed that the CID‐MS/MS fragmentation routes of the five precursor protonated molecules obtained from the biotin linkers 1–5 afforded a series of product ions formed essentially by similar routes. The genesis and the structural identities of all the product ions obtained from the biotin linkers 1–5 have been assigned. All the exact mass assignments of the protonated molecules and the product ions were verified by conducting separate CID‐MS/MS analysis of the deuterium‐labelled precursor ions. Copyright © 2009 John Wiley & Sons, Ltd.     

Quantification of Greenland halibut serum vitellogenin: a trip from the deep sea to the mass spectrometer

This paper focuses on the sequential steps involved in developing a technique for quantifying Greenland halibut vitellogenin, a serum protein biomarker, using a comprehensive mass spectrometric approach. In the first phase of this study, in‐gel trypsin digestions of serum proteins separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS‐PAGE) were analyzed by matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS). A characteristic band around a molecular mass of 185 kDa, present in the mature female specimens, but absent in the male samples, was identified as vitellognin according to the peptide mass fingerprint obtained by MALDI‐MS. Subsequently, MALDI and electrospray ionization tandem mass spectrometry (ESI‐MS/MS) analyses were performed on the digest of the vitellogenin band for de novo sequencing. From these studies, a characteristic 'signature' peptide (sequence: FFGQEIAFANIDK) was selected from a list of candidate peptides as a surrogate analytical standard used for quantification purposes. Sample preparation for vitellogenin quantification consisted of a simple one‐step overnight trypsin digestion. Samples were spiked with an isotopologue signature peptide standard and analyzed by high‐performance liquid chromatography (HPLC) coupled in‐line to an electrospray quadrupole‐hexapole‐quadrupole tandem mass spectrometer, operated in selective reaction monitoring mode. Transitions [(m/z 750.0 → 1020.4 and 750.0 → 1205.4) and (754.8 → 1028.6 and 754.8 → 1213.2)] were monitored for the signature peptide and the internal standard, respectively. Samples obtained from the field showed that vitellogenin levels were in accordance with fish maturity determined by macroscopic examination of the gonad, proving this technique suitable for measuring vitellogenin as a serum protein biomarker for reproductive maturity in female fish. Copyright © 2009 John Wiley & Sons, Ltd.     

Null-controllability of some reaction–diffusion systems with one control force

This work is concerned with the null-controllability of semilinear parabolic systems by a single control force acting on a subdomain.     

Unstable crack motion is predictable

Yoffe's linear theory of dynamic brittle fracture suggests that crack motion will be unstable beyond ∼70% of the Rayleigh speed, a prediction that is not supported by experiment. We show by atomistic simulations that hyperelasticity, the elasticity of large strains, plays a governing role in the instability dynamics of brittle fracture. A simple, yet remarkable, scaling model based on an effective elastic modulus (the secant modulus at the stability limit) gives successful predictions for the onset speed of the crack instability.     

Phenylglycine racemization in Fmoc-based solid-phase peptide synthesis: Stereochemical stability is achieved by choice of reaction conditions

Phenylglycine-containing peptides have broad applications in medicinal chemistry, but their synthetic accessibility is complicated by the risk of epimerization during solid-phase peptide synthesis (SPPS). Phenylglycine is therefore often considered a troublesome residue. This work studies the extent of Phg racemization under different Fmoc-SPPS reaction conditions. It is shown that the base-catalyzed coupling of Fmoc-Phg is the critical step for racemization. However, racemization can be reduced to a negligible level if DEPBT or COMU combined with TMP or DMP are employed during this step. Resin-bound peptides are remarkably resistant against epimerization during extended incubation under basic conditions and the free peptides were stable in buffer solutions used for biological assays.     

On toric locally conformally Kähler manifolds

We study compact toric strict locally conformally Kähler manifolds. We show that the Kodaira dimension of the underlying complex manifold is \(-\infty \), and that the only compact complex surfaces admitting toric strict locally conformally Kähler metrics are the diagonal Hopf surfaces. We also show that every toric Vaisman manifold has lcK rank 1 and is isomorphic to the mapping torus of an automorphism of a toric compact Sasakian manifold.     

Computation of the Coefficients Appearing in the Uniform Asymptotic Expansions of Integrals

The coefficients that appear in uniform asymptotic expansions for integrals are typically very complicated. In the existing literature, the majority of the work only give the first two coefficients. In a limited number of papers where more coefficients are given, the evaluation of the coefficients near the coalescence points is normally highly numerically unstable. In this paper, we illustrate how well‐known Cauchy‐type integral representations can be used to compute the coefficients in a very stable and efficient manner. We discuss the cases: (i) two coalescing saddles, (ii) two saddles coalesce with two branch points, and (iii) a saddle point near an endpoint of the interval of integration. As a special case of (ii), we give a new uniform asymptotic expansion for Jacobi polynomials in terms of Laguerre polynomials as that holds uniformly for z near 1. Several numerical illustrations are included.