Micromechanical combined stress analysis: MICSTRAN, a user manual

Composite materials are currently being used in aerospace and other applications. The ability to tailor the composite properties by the appropriate selection of its constituents, the fiber and matrix, is a major advantage of composite materials. The Micromechanical Combined Stress Analysis (MICSTRAN) code provides the materials engineer with a user-friendly personal computer (PC) based tool to calculate overall composite properties given the constituent fiber and matrix properties. To assess the ability of the composite to carry structural loads, the materials engineer also needs to calculate the internal stresses in the composite material. MICSTRAN is a simple tool to calculate such internal stresses with a composite ply under combined thermomechanical loading. It assumes that the fibers have a circular cross-section and are arranged either in a repeating square or diamond array pattern within a ply. It uses a classical elasticity solution technique that has been demonstrated to calculate accurate stress results. Input to the program consists of transversely isotropic fiber properties and isotropic matrix properties such as moduli, Poisson's ratios, coefficients of thermal expansion, and volume fraction. Output consists of overall thermoelastic constants and stresses. Stresses can be computed under the combined action of thermal, transverse, longitudinal, transverse shear, and longitudinal shear loadings. Stress output can be requested along the fiber-matrix interface, the model boundaries, circular arcs, or at user-specified points located anywhere in the model. The MICSTRAN program is Windows compatible and takes advantage of the Microsoft Windows graphical user interface which facilitates multitasking and extends memory access far beyond the limits imposed by the DOS operating system

Magnetic and magnetoelectric studies in pure and cation doped BiFeO3

We report magnetic and magnetoelectric studies on BiFeO3 and divalent cation (A) suvtitute Bi0.7A0.3FeO3 (A = Sr,Ba, and Sr0.5Ba0.5). It is shown that the rapid increase of magnetization at the Neel temperature (TN = 642 K) is suppressed in the co-doped compound A = Sr0.5Ba0.5. All the divalent subtituted compounds show enhanced magnetization and hysteresis loop. Both longitudinal and transverse magnetoelectric coefficients were measured using the dynamical lock-in technique. The co-doped compound shows the highest magnetoelectric coefficient at room temperature although it is not the compound with the highest saturation magnetization. It is found that as the size of the A-site cation increses, the transverse magnetoelectric coeffient increases and exceeds the longitudinal magnetoelectric coefficient. It is suggested that changes in magnetic domain structure and magnetostriction are possible reasons for the observed changes in the magnetoelectric coefficients.Comment: 16 pages, 6 figur

Electrical, magnetic, magnetodielectric and magnetoabsorption studies in multiferroic GaFeO3

We report electrical, magnetic, magnetodielectric and magnetoabsorption properties of a polycrystalline GaFeO3. The resistivity measurement shows that the sample is highly insulating below 200 K and the resistivity above 200 K obey the Arrhenius law with an activation energy of Ea = 0.67 eV. An anomaly occurs in the temperature dependence of permittivity (e) near the ferrimagnetic transition temperature (TC = 228 K) in a zero magnetic field and it is suppressed under H = 60 mT which indicates a possible magnetoelectric coupling in GaFeO3 with a fractional change of de/e = -1.8% at 60 mT around TC. The coercivity (HC) of the sample increases dramatically with lowering temperature below 200 K from 0.1 T at 200 K to 0.9 T at 5 K. Magnetoabsorption was studied with a LC resonance technique and we found a close correlation between the shift in the resonance frequency due to applied magnetic field and the coercive field measured using dc magnetization measurements. Our results obtained with multiple techniques suggest that GaFeO3 is an interesting ferrimagnet with potential applications in future multiferroic devices.Comment: 22 pages, 6 figures. submitted to J. Appl. Phy

A macro-micromechanics analysis of a notched metal matrix composite

A macro-micromechanics analysis was formulated to determine the matrix and fiber behavior near the notch tip in a center-notched metal matrix composite. Results are presented for a boron/aluminum monolayer. The macro-level analysis models the entire notched specimen using a three dimensional finite element program which uses the vanishing-fiber-diameter model to model the elastic-plastic behavior of the matrix and the elastic behavior of the fiber. The micro-behavior is analyzed using a Discrete Fiber-Matrix (DFM) model containing one fabric and the surrounding matrix. The dimensions of the DFM model were determined by the ply thickness and the fiber volume fraction and corresponded to the size of the notch-tip element in the macro-level analysis. The boundary conditions applied to the DFM model were determined from the macro-level analysis. Stress components within the DFM model were calculated and stress distributions are presented along selected planes and surfaces within the DFM model, including the fiber-matrix interface. Yielding in the matrix was examined at the notch tip in both the macro- and micro-level analyses. The DFM model predicted higher stresses (24 percent) in the fiber compared to the global analysis. In the notch-tip element, the interface stresses indicated that a multi-axial criterion may be required to predict interfacial failure. The DFM analysis predicted yielding to initiate in the notch-tip element at a stress level 28 percent lower than predicted by the global analysis

Cross-talk of genetically and environmentally modulated epigenetic factors in the development of anxiety-related behavior

Here, I studied the role of two candidate genes i.e. neuropeptide S receptor 1 (Npsr1) and transmembrane protein 132D (Tmem132d), in two psychopathological animal models of anxiety-related behavior because of recent studies showing importance of these candidates in limbic areas and the frontal cortex of panic disorder patients, respectively. The two animal models are rat (r) and mouse (m), high anxiety-related behavior (rHAB/mHAB) and low anxiety-related behavior(rLAB/mLAB). To understand the anxiolytic role of neuropeptide S (NPS), basal Npsr1 mRNA expression was studied in limbic brain regions of HAB vs. LAB rodents, i.e. the paraventricular nucleus of hypothalamus (PVN) and amygdala, because these regions have been implicated in anxiety and fear attenuating responses of NPS and also due to differences in long-term activity based on cytochrome c oxidase activity in mHAB vs. mLAB. There was significantly lower basal Npsr1 mRNA expression in the basolateral amygdala of mHAB and also in the PVN of rHAB compared to corresponding LABs. To study the genetic underpinnings underlying this differential expression, Npsr1 DNA sequencing was carried out, which revealed several polymorphisms including single-nucleotide polymorphisms (SNP), insertions and deletions. By using dual reporter (luciferase) assays, I could show that the SNPs in the whole HAB promoter construct cause a significant decrease in promoter activity, thus confirming our in vivo findings in both rats and mice. Interestingly, however, when the promoter constructs were shortened to 500 bp relative to translational (ATG) start site, there was a two-fold higher HAB promoter activity, which could be attributed to the introduction of a polymorphism with putative binding site for the glucocorticoid receptor (GR) transcription factor. The higher HAB promoter activity was suppressed by dexamethasone (a GR activator), thus suggesting the presence of a polymorphism that favors GR binding. These findings are analogous to the higher HAB specific allele expression in cross-mated F1 offspring, which allows us to study the HAB vs. LAB alleles in the same cellular environment, irrespective of any epigenetic or other environmentally mediated factors that might modulate or interact with cis-acting factors. In addition, there was no difference in Npsr1 mRNA expression in the basolateral amygdala of mHAB and mLAB subjected to environmental enrichment (EE) and unpredictable chronic mild stress (UCMS), respectively. Thus it is a non-plastic gene as it does not respond to environmental challenges faced by the susceptible animal models. Similarly, for Tmem132d, using dual luciferase assays, two SNPs in the mHAB promoter region were shown to cause an increase in its corresponding promoter activity, and there was no difference in DNA methylation in the mHAB vs. mLAB Tmem132d promoter region, which explains the observed higher Tmem132d mRNA expression in the anterior cingulate cortex of mHAB. However, mHABs subjected to EE had higher Tmem132d mRNA expression, while mLAB undergoing UCMS had corresponding lower gene expression. To study the cis-trans interaction, we also subjected cross-mated F1 offspring to EE or UCMS and found that both groups have higher mLAB allelic expression, which could be attributed to differences in DNA methylation. Finally, I could show that there was no difference in DNA methylation in the basal mHAB vs. mLAB Tmem132d promoter and that two SNPs in the mHAB promoter were sufficient to cause a higher corresponding promoter activity, which explains the in vivo findings observed in the anterior cingulate cortex. Furthermore, F1 offspring subjected to EE or UCMS had a significantly lower mHAB-specific allele expression which was negatively correlated with DNA methylation, in the Tmem132d promoter region, thus this suggests cross-talk between genetic and environmentally mediated epigenetic factors. In summary, the data suggests a strong evolutionary conserved role of the NPS system considering the similar findings in rats and mice. However, Npsr1 is a nonplastic gene as it is not amenable to the different environmental manipulations applied to the animals. On the other hand, the plastic gene Tmem132d, is differentially expressed, thus making the animals more susceptible to environmental influences. Here, it could be revealed, that SNPs in the mHAB Tmem132d promoter cause higher promoter activity and that environmental manipulation can modulate the gene?s corresponding expression through DNA methylation