Numerical evaluation of the viscoelastic and viscoplastic behavior of composites

This paper is concerned with the development of homogenization methods in order to obtain the effective material parameters of viscoelastic and viscoplastic composites. In the case of a viscoelastic behavior, the constitutive laws at the heterogeneous scale are transposed into a LAPLACE-CARSON domain where the equations become similar to those of linear elasticity and classical homogenization procedures can be applied. Afterward, the results have to be converted by an inverse transformation. Mostly, this procedure is combined with analytical or semi-analytical models such as the self-consistent or Mori-Tanaka model. Since the application of this approach is limited to simple structured composites it is not suitable for materials with a complex internal architecture. In order to avoid this limitation, this paper is focused on the development of a homogenization procedure which is based on the LAPLACE-CARSON transformation and a numerical solution of the field problem. For heterogeneous material with viscoplastic or nonlinear viscoelastic properties, an additional linearization step is required. A new algorithm is proposed in order to combine this affine formulation with the numerical homogenization method. Finally, these procedures are used to estimate the effective material behavior of different types of composites. With that, the accuracy of the results and efficiency of the methodologies is assessed

The nucleotide and partial amino acid sequences of rat fetuin

Fetuins are among the major plasma proteins, yet their biological role has remained elusive. Here we report the molecular cloning of rat fetuin and the sequence analysis of a full-length clone, RF619 of 1456 bp with an open reading frame of 1056 bp encoding 352 amino acid residues. The coding part of RF619 was identical with the cDNA sequence of the natural inhibitor of the insulin receptor tyrosine kinase from rat (pp63) except for four substitutions and a single base insertion causing divergence of the predicted protein sequences. Partial amino acid sequences of rat plasma fetuin were in agreement with the predictions based on the RF619 cDNA. Purified rat fetuin inhibited the insulin receptor tyrosine kinase in vitro. Therefore, we conclude that RF619 and pp63 cDNA encode the same protein, i.e. authentic rat fetuin which is a functional tyrosine kinase inhibitor

A Hepatic Protein, Fetuin-A, Occupies a Protective Role in Lethal Systemic Inflammation

A liver-derived protein, fetuin-A, was first purified from calf fetal serum in 1944, but its potential role in lethal systemic inflammation was previously unknown. This study aims to delineate the molecular mechanisms underlying the regulation of hepatic fetuin-A expression during lethal systemic inflammation (LSI), and investigated whether alterations of fetuin-A levels affect animal survival, and influence systemic accumulation of a late mediator, HMGB1.LSI was induced by endotoxemia or cecal ligation and puncture (CLP) in fetuin-A knock-out or wild-type mice, and animal survival rates were compared. Murine peritoneal macrophages were challenged with exogenous (endotoxin) or endogenous (IFN-γ) stimuli in the absence or presence of fetuin-A, and HMGB1 expression and release was assessed. Circulating fetuin-A levels were decreased in a time-dependent manner, starting between 26 h, reaching a nadir around 24-48 h, and returning towards base-line approximately 72 h post onset of endotoxemia or sepsis. These dynamic changes were mirrored by an early cytokine IFN-γ-mediated inhibition (up to 50-70%) of hepatic fetuin-A expression. Disruption of fetuin-A expression rendered animals more susceptible to LSI, whereas supplementation of fetuin-A (20-100 mg/kg) dose-dependently increased animal survival rates. The protection was associated with a significant reduction in systemic HMGB1 accumulation in vivo, and parallel inhibition of IFN-γ- or LPS-induced HMGB1 release in vitro.These experimental data suggest that fetuin-A is protective against lethal systemic inflammation partly by inhibiting active HMGB1 release

Numerical evaluation of the viscoelastic and viscoplastic behavior of composites

This paper is concerned with the development of homogenization methods in order to obtain the effective material parameters of viscoelastic and viscoplastic composites. In the case of a viscoelastic behavior, the constitutive laws at the heterogeneous scale are transposed into a LAPLACE-CARSON domain where the equations become similar to those of linear elasticity and classical homogenization procedures can be applied. Afterward, the results have to be converted by an inverse transformation. Mostly, this procedure is combined with analytical or semi-analytical models such as the self-consistent or Mori-Tanaka model. Since the application of this approach is limited to simple structured composites it is not suitable for materials with a complex internal architecture. In order to avoid this limitation, this paper is focused on the development of a homogenization procedure which is based on the LAPLACE-CARSON transformation and a numerical solution of the field problem. For heterogeneous material with viscoplastic or nonlinear viscoelastic properties, an additional linearization step is required. A new algorithm is proposed in order to combine this affine formulation with the numerical homogenization method. Finally, these procedures are used to estimate the effective material behavior of different types of composites. With that, the accuracy of the results and efficiency of the methodologies is assessed