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The subject of the study are alumina foams produced by gelcasting method. The results of micro-computed tomography of the foam samples are used to create the numerical model reconstructing the real structure of the foam skeleton as well as the simplified periodic open-cell structure models. The aim of the paper is to present a new idea of the energy-based assessment of failure strength under uniaxial compression of real alumina foams of various porosity with use of the periodic structure model of the same porosity. Considering two kinds of cellular structures: the periodic one, for instance of fcc type, and the random structure of real alumina foam it is possible to justify the hypothesis, computationally and experimentally, that the same elastic energy density cumulated in the both structures of the same porosity allows to determine the close values of fracture strength under compression. Application of finite element computations for the analysis of deformation and failure processes in real ceramic foams is time consuming. Therefore, the use of simplified periodic cell structure models for the assessment of elastic moduli and failure strength appears very attractive from the point of view of practical applications. [ABSTRACT FROM AUTHOR]

This paper is concerned with numerical modeling of deformation and fracture of a metal ligament bridging the crack faces in ceramic–metal composites, as a prerequisite for the determination of the J integral for composites with interpenetrating microstructure. A finite element model is proposed of an elasto-plastic crack-reinforcing fiber undergoing large plastic deformations and progressive debonding from the elastic matrix through a cohesive matrix–fiber interface. The σ-u relationships are derived first in the case of pullout of an elasto-plastic fiber embedded in an elastic matrix and then in uniaxial tension of the elasto-plastic fiber bridging the crack faces in elastic matrix. The obtained numerical results are discussed and compared with the theoretical predictions reported by other authors. [ABSTRACT FROM AUTHOR]

In the present study we investigated the pattern and efficacy of respiratory autoresuscitation in spontaneously breathing adult male rats across three separate anesthetic backgrounds. Each animal was administered one of three injectable anesthetics to achieve a surgical plane of anesthesia: ketamine-xylazine (KET, n = 10), pentobarbital (PEN, n = 10), or urethane (URE, n = 10). Animals were tracheostomized and equipped with a femoral artery catheter to record airflow and arterial pressures. In response to a bout of breathing anoxic air, none of the 10 URE animals were able to mount a successful autoresuscitation response. In contrast, all KET and PEN animals survived all four consecutive anoxic exposures, restoring eupneic breathing in all cases. Moreover, only 4/10 URE animals expressed gasping breaths following the onset of respiratory arrest, and these were temporally delayed (p < 0.001) and much smaller in volume (P ≤ 0.012) compared to KET and PEN animals. URE animals showed no clear aberrations in their cardiovascular responses to anoxia, with the exception of lower arterial pulse pressures compared to either KET or PEN animals at specific points following RA. Ketamine-xylazine and pentobarbital anesthesia can be reliably and effectively used to create models for the study of autoresuscitation in adult rats. In contrast, urethane causes catastrophic failure of respiratory autoresuscitation, by delaying or outright preventing the elaboration of gasping breaths following anoxia-induced respiratory arrest. The neuronal and synaptic alterations accompanying urethane anesthesia may therefore provide a means of understanding potential pathological alterations in rhythm generation that can predispose the respiratory control system to failed autoresuscitation following an episode of acute severe hypoxemia. [ABSTRACT FROM AUTHOR]

The mechanical properties and numerical model of ceramic alumina open-cell foam, which is produced by the chemical method of gelcasting with different cell sizes (porosities) are presented. Geometric characteristics of real foam samples were estimated from tomographic and scanning electron microscopy images. Using this information, numerical foam model was proposed. A good agreement between the numerical model and the results elaborated from microtomography was obtained. To simulate the deformation processes the finite element program ABAQUS was used. The main goal of this computation was to obtain macroscopic force as a function of applied vertical displacement in compression test. As a result of numerical simulation of compression test of alumina foam for different values of porosity, the Young modulus and the strength of such foams were estimated. [ABSTRACT FROM AUTHOR]

Ultrafine grained (UFG) and nanocrystalline metals (nc-metals) are studied. Experimental investigations of the behaviour of such materials under quasistatic as well as dynamic loading conditions related with microscopic observations show that in many cases the dominant mechanism of plastic strain is a multiscale development of shear deformation modes. The comprehensive discussion of these phenomena in UFG and nc-metals is given in M.A. Meyers, A. Mishra and D.J. Benson [Mechanical properties of nanocrystalline materials, Progr. Mater. Sci. 51 (2006), pp. 427-556], where it has been shown that the deformation mode of nanocrystalline materials changes as the grain size decreases into the ultrafine region. For smaller grain sizes (d < 300 nm) shear band development occurs immediately after the onset of plastic flow. Significant strain-rate dependence of the flow stress, particularly at high strain rates, was also emphasized. Our objective is to identify the parameters of Perzyna constitutive model, a new description of viscoplastic deformation, which accounts for the observed shear banding. The viscoplasticity model proposed earlier by Perzyna [Fundamental problems in viscoplasticity, Adv. Mech. 9 (1966), pp. 243-377] was extended in order to describe the shear banding contribution in Z. Nowak, P. Perzyna, R.B. Pȩcherski [Description of viscoplastic fow accounting for shear banding, Arch. Metall. Mater. 52 (2007), pp. 217-222]. The shear banding contribution function, which was introduced formerly by Pȩcherski [Modelling of large plastic deformation produced by micro-shear banding, Arch. Mech. 44 (1992), pp. 563-584] and applied in continuum plasticity accounting for shear banding in R.B. Pȩcherski [Macroscopic measure of the rate of deformation produced by micro-shear banding, Arch. Mech. 49 (1997), pp. 385-401] plays pivotal role in the viscoplasticity model. The derived constitutive equations were identified and verified with the application of experimental data provided in the article by D. Jia, K.T. Ramesh and E. Ma [Effects of nanocrystalline and ultrafne grain sizes on constitutive behavior and shear bands in iron, Acta Mat. 51 (2003), pp. 3495-3509], where quasistatic and dynamic compression tests with UFG and nanocrystalline iron specimens of a wide range of mean grain size were reported. Numerical simulation of the compression of the prismatic specimen was made by the ABAQUS FEM program with UMAT subroutine. Comparison with experimental results proved the validity of the identified parameters and the possibilities of the application of the proposed description for other high strength metals. [ABSTRACT FROM AUTHOR]

The production of interleukin 1 (IL-l) and interleukin 2 (IL-2) by peripheral blood mononuclear cells (PBMC) stimulated with human myelin basic protein (MBP) was assessed in vitro in multiple sclerosis (MS) patients in relapse, patients with other neurological diseases (OND) and healthy subjects. Myelin basic protein significantly increased both IL-1 and IL-2 production by PBMC from MS patients during relapse when compared to OND patients or healthy controls. The most efficient concentration of MBP for the induction of IL-I and IL-2 was 50 μg/ml. The optimal IL-I production occurred after 48 h of PBMC culture and optimal IL-2 production after 72 h of PBMC culture. Anti- Tac monoclonal antibody (MoAb) was used lo study IL-2 receptor expression on the same sample of PBM used for IL-2 study in MS patients in relapse. In addition IL-2 receptor expression was studied in PBMC from chronic progressive MS patients. In both MS groups IL-2 receptor expression on PBMC stimutated with MBP appeared higher than in control groups, but these differences were not statistically significant. IL-2 receptor expression on cerebrospinal fluid lymphocytes (CSF-L) either unstimulated or MBP-stimulated was, however, significantly higher in both MS groups when compared lo OND patients. These results confirm the presence of activated lymphocytes in the CSF of MS patients during active stages of disease and suggest that this activation may be related to expansion of MBP specific cells. [ABSTRACT FROM AUTHOR]

In the last 20 years, a new meshless computational method has been developed that is called peridynamics. The method is based on the parallelized code. The subject of the study is the deformation of open-cell copper foams under dynamic compression. The computational model of virtual cellular material is considered. The skeleton structure of such a virtual cellular material can be rescaled according to requirements. The material of the skeleton is assumed as the oxygen free high conductivity (OFHC) copper. The OFHC copper powder can be applied in additive manufacturing to produce the open-cell multifunctional structures, e.g., crush resistant heat exchangers, heat capacitors, etc. In considered peridynamic computations the foam skeleton is described with the use of an elastic-plastic model with isotropic hardening. The dynamic process of compression and crushing with different impact velocities is simulated. [ABSTRACT FROM AUTHOR]

The aim of the paper is to formulate physically well founded yield condition for initially anisotropic solids revealing the asymmetry of elastic range. The initial anisotropy occurs in material primarily due to thermo-mechanical pre-processing and plastic deformation during the manufacturing processes. Therefore, materials in the "as-received" state become usually anisotropic. After short account of the known limit criteria for anisotropic solids and discussion of mathematical preliminaries the energy-based criterion for orthotropic materials was formulated and confronted with experimental data and numerical predictions of other theories. Finally, possible simplifications are discussed and certain model of isotropic material with yield condition accounting for a correction of shear strength due to initial anisotropy is presented. The experimental verification is provided and the comparison with existing approach based on the transformed-tensor method is discussed. [ABSTRACT FROM AUTHOR]

Contents: Wisent, or European bison (Bison bonasus), is listed as “vulnerable” on the IUCN Red List of Threatened Species and is therefore protected by international law. For the first time, a Wisent embryo has been obtained in vitro. This procedure creates a new opportunity to protect and increase Wisent reproductive potential and thereby opens new possibilities for the establishment of a controlled and broad reserve of the gene pool. [ABSTRACT FROM AUTHOR]

Ectromelia virus (ECTV) is an orthopoxvirus (OPV) that causes mousepox, the murine equivalent of human smallpox. Fas receptor-Fas ligand (FasL) signaling is involved in apoptosis of immune cells and virus-specific cytotoxicity. The Fas/FasL pathway also plays an important role in controlling the local inflammatory response during ECTV infection. Here, the immune response to the ECTV Moscow strain was examined in Fas (-) (lpr), FasL (-) (gld) and C57BL6 wild-type mice. During ECTV-MOS infection, Fas- and FasL mice showed increased viral titers, decreased total numbers of NK cells, CD4 and CD8 T cells followed by decreased percentages of IFN-γ expressing NK cells, CD4 and CD8 T cells in spleens and lymph nodes. At day 7 of ECTV-MOS infection, Fas- and FasL-deficient mice had the highest regulatory T cell (Treg) counts in spleen and lymph nodes in contrast to wild-type mice. Furthermore, at days 7 and 10 of the infection, we observed significantly higher numbers of PD-L1-expressing dendritic cells in Fas (-) and FasL (-) mice in comparison to wild-type mice. Experiments in co-cultures of CD4 T cells and bone-marrow-derived dendritic cells showed that the lack of bilateral Fas-FasL signalling led to expansion of Tregs. In conclusion, our results demonstrate that during ECTV infection, Fas/FasL can regulate development of tolerogenic DCs and Tregs, leading to an ineffective immune response. [ABSTRACT FROM AUTHOR]