Neuroprotective activity of Wedelia calendulacea on cerebral ischemia/reperfusion induced oxidative stress in rats

Objective: This study was undertaken to evaluate the neuroprotective activity of Wedelia calendulacea against cerebral ischemia/reperfusion induced oxidative stress in the rats. Materials and Methods: The global cerebral ischemia was induced in male albino Wistar rats by occluding the bilateral carotid arteries for 30 min followed by 1 h and 4 h reperfusion. At various times of reperfusion, the histopathological changes and the levels of malondialdehyde (MDA), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione-s-transferase (GST), and hydrogen peroxide (H(2)O(2)) activity and brain water content were measured. Results: The ischemic changes were preceded by increase in concentration of MDA, hydrogen peroxide and followed by decreased GPx, GR, and GST activity. Treatment with W. calendulacea significantly attenuated ischemia-induced oxidative stress. W. calendulacea administration markedly reversed and restored to near normal level in the groups pre-treated with methanolic extract (250 and 500 mg/kg, given orally in single and double dose/day for 10 days) in dose-dependent way. Similarly, W. calendulacea reversed the brain water content in the ischemia reperfusion animals. The neurodegenaration also conformed by the histopathological changes in the cerebral-ischemic animals. Conclusion: The findings from the present investigation reveal that W. calendulacea protects neurons from global cerebral-ischemic injury in rat by attenuating oxidative stress.

A deep‐level spectroscopic technique for determining capture cross‐section activation energy of Si‐related DX centers in AlxGa1-xAs

A deep‐level transient spectroscopy (DLTS) technique is reported for determining the capture cross‐section activation energy directly. Conventionally, the capture activation energy is obtained from the temperature dependence of the capture cross section. Capture cross‐section measurement is often very doubtful due to many intrinsic errors and is more critical for nonexponential capture kinetics. The essence of this technique is to use an emission pulse to allow the defects to emit electrons and the transient signal from capture process due to a large capture barrier was analyzed, in contrast with the emission signal in conventional DLTS. This technique has been applied for determining the capture barrier for silicon‐related DX centers in AlxGa1−xAs for different AlAs mole fractions.

Stress Evolution With Temperature in Titanium-Rich NiTi Shape Memory Alloy Films

The effect of deposition temperature on residual stress evolution with temperature in Ti-rich NiTi films deposited on silicon substrates was studied. Ti-rich NiTi films were deposited on 3? Si (100) substrates by DC magnetron sputtering at three deposition temperatures (300, 350 and 400 degrees C) with subsequent annealing in vacuum at their respective deposition temperatures for 4 h. The initial value of residual stress was found to be the highest for the film deposited and annealed at 400 degrees C and the lowest for the film deposited and annealed at 300 degrees C. All the three films were found to be amorphous in the as-deposited and annealed conditions. The nature of the stress response with temperature on heating in the first cycle (room temperature to 450 degrees C) was similar for all three films although the spike in tensile stress, which occurs at similar to 330 degrees C, was significantly higher in the film deposited and annealed at 300 degrees C. All the films were also found to undergo partial crystallisation on heating up to 450 degrees C and this resulted in decrease in the stress values around 5560 degrees C in the cooling cycle. The stress response with temperature in the second thermal cycle (room temperature to 450 degrees C and back), which is reflective of the intrinsic film behaviour, was found to be similar in all cases and the elastic modulus determined from the stress response was also more or less identical. The three deposition temperatures were also not found to have a significant effect on the transformation characteristics of these films such as transformation start and finish temperatures, recovery stress and hysteresis.

A Revisit to Capture the Entire Behavior of Ultrasonic Wave Dispersion Characteristics of Single Walled Carbon Nanotubes Based on Nonlocal Elasticity Theory and Flugge Shell Model

In this paper, an ultrasonic wave propagation analysis in single-walled carbon nanotube (SWCNT) is re-studied using nonlocal elasticity theory, to capture the whole behaviour. The SWCNT is modeled using Flugge's shell theory, with the wall having axial, circumferential and radial degrees of freedom and also including small scale effects. Nonlocal governing equations for this system are derived and wave propagation analysis is also carried out. The revisited nonlocal elasticity calculation shows that the wavenumber tends to infinite at certain frequencies and the corresponding wave velocity tends to zero at those frequencies indicating localization and stationary behavior. This frequency is termed as escape frequency. This behavior is observed only for axial and radial waves in SWCNT. It has been shown that the circumferential waves will propagate dispersively at higher frequencies in nonlocality. The magnitudes of wave velocities of circumferential waves are smaller in nonlocal elasticity as compared to local elasticity. We also show that the explicit expressions of cut-off frequency depend on the nonlocal scaling parameter and the axial wavenumber. The effect of axial wavenumber on the ultrasonic wave behavior in SWCNTs is also discussed. The present results are compared with the corresponding results (for first mode) obtained from ab initio and 3-D elastodynamic continuum models. The acoustic phonon dispersion relation predicted by the present model is in good agreement with that obtained from literature. The results are new and can provide useful guidance for the study and design of the next generation of nanodevices that make use of the wave propagation properties of single-walled carbon nanotubes.

Simulation of surface and volume stress for high voltage transmission insulators

The bulk of power transmission from the generating stations to the load centres is carried through overhead lines. The distances involved could span several hundreds of kilometres. To minimize line losses, power transmission over such long distances is carried out at high voltages (several hundreds of kV). A network of outdoor lines operating at different voltages has been found to be the most economical method of power delivery. The disc insulators perform dual task of mechanically supporting and electrically isolating the live phase conductors from the support tower. These insulators have to perform under various environmental conditions; hence the electrical stress distribution along the insulators governs the possible flashover, which is quite detrimental to the system. In view of this the present investigation aims to simulate the surface electric field stress on different types of porcelain/ceramic insulators; both normal and anti-fog type discs which are used for high voltage transmission/distribution systems are considered. The surface charge simulation method is employed for the field computation to simulate potential, electric field, surface and bulk/volume stress.

Characterization and finite element modeling of montmorillonite/polypropylene nanocomposites

Finite element modeling can be a useful tool for predicting the behavior of composite materials and arriving at desirable filler contents for maximizing mechanical performance. In the present study, to corroborate finite element analysis results, quantitative information on the effect of reinforcing polypropylene (PP) with various proportions of nanoclay (in the range of 3-9% by weight) is obtained through experiments; in particular, attention is paid to the Young's modulus, tensile strength and failure strain. Micromechanical finite element analysis combined with Monte Carlo simulation have been carried out to establish the validity of the modeling procedure and accuracy of prediction by comparing against experimentally determined stiffness moduli of nanocomposites. In the same context, predictions of Young's modulus yielded by theoretical micromechanics-based models are compared with experimental results. Macromechanical modeling was done to capture the non-linear stress-strain behavior including failure observed in experiments as this is deemed to be a more viable tool for analyzing products made of nanocomposites including applications of dynamics. (C) 2011 Elsevier Ltd. All rights reserved.

Anomalous Stress Profile in a Sheared Granular Column

We present measurements of the stress as a function of vertical position in a column of granular material sheared in a cylindrical Couette device. All three components of the stress tensor on the outer cylinder were measured as a function of distance from the free surface at shear rates low enough that the material was in the dense, slow flow regime. We find that the stress profile differs fundamentally from that of fluids, from the predictions of plasticity theories, and from intuitive expectation. We argue that the anomalous stress profile is due to an anisotropic fabric caused by the combined action of gravity and shear.

MODELING HETEROSTRUCTURES WITH SCHRODINGER-POISSON-NAVIER ITERATIVE SCHEMES, EFFECT OF CARRIER CHARGE, AND INFLUENCE OF ELECTROMECHANICAL COUPLING

This paper presents a detailed investigation of the erects of piezoelectricity, spontaneous polarization and charge density on the electronic states and the quasi-Fermi level energy in wurtzite-type semiconductor heterojunctions. This has required a full solution to the coupled Schrodinger-Poisson-Navier model, as a generalization of earlier work on the Schrodinger-Poisson problem. Finite-element-based simulations have been performed on a A1N/GaN quantum well by using both one-step calculation as well as the self-consistent iterative scheme. Results have been provided for field distributions corresponding to cases with zero-displacement boundary conditions and also stress-free boundary conditions. It has been further demonstrated by using four case study examples that a complete self-consistent coupling of electromechanical fields is essential to accurately capture the electromechanical fields and electronic wavefunctions. We have demonstrated that electronic energies can change up to approximately 0.5 eV when comparing partial and complete coupling of electromechanical fields. Similarly, wavefunctions are significantly altered when following a self-consistent procedure as opposed to the partial-coupling case usually considered in literature. Hence, a complete self-consistent procedure is necessary when addressing problems requiring more accurate results on optoelectronic properties of low-dimensional nanostructures compared to those obtainable with conventional methodologies.

Stress and texture development during sputtering of yttria, zirconia, and yttria stabilized zirconia films on Si substrates

Understanding and controlling growth stress is a requisite for integrating oxides with Si. Yttria stabilized zirconia (YSZ) is both an important functional oxide and a buffer layer material needed for integrating other functional oxides. Stress evolution during the growth of (100) and (111) oriented YSZ on Si (100) by radio frequency and reactive direct current sputtering has been investigated with an in-situ monitor and correlated with texture evolution. Films nucleated at rates <5 nm/min are found to be (111) oriented and grow predominantly under a compressive steady state stress. Films nucleated at rates >20 nm/min are found to be (100) oriented and grow under tension. A change in growth rate following the nucleation stage does not change the orientation. The value of the final steady state stress varies from -4.7 GPa to 0.3 GPa. The in-situ studies show that the steady state stress generation is a dynamic phenomenon occurring at the growth surface and not decided at film nucleation. The combination of stress evolution and texture evolution data shows that the adatom injection into the grain boundaries is the predominant source of compressive stress and grain boundary formation at the growth surface is the source of tensile stress. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4757924]

Catalytic activity of Peptidase N is required for adaptation of Escherichia coli to nutritional downshift and high temperature stress

Peptidase N (PepN), the sole M1 family member in Escherichia coli, displays broad substrate specificity and modulates stress responses: it lowers resistance to sodium salicylate (NaSal)-induced stress but is required during nutritional downshift and high temperature (NDHT) stress. The expression of PepN does not significantly change during different growth phases in LB or NaSal-induced stress; however, PepN amounts are lower during NDHT stress. To gain mechanistic insights on the roles of catalytic activity of PepN in modulating these two stress responses, alanine mutants of PepN replacing E264 (GAMEN motif) and E298 (HEXXH motif) were generated. There are no major structural changes between purified wild type (WT) and mutant proteins, which are catalytically inactive. Importantly, growth profiles of Delta pepN upon expression of WT or mutant proteins demonstrated the importance of catalytic activity during NDHT but not NaSal-induced stress. Further fluorescamine reactivity studies demonstrated that the catalytic activity of PepN is required to generate higher intracellular amounts of free N-terminal amino acids; consequently, the lower growth of Delta pepN during NDHT stress increases with high amounts of casamino acids. Together, this study sheds insights on the expression and functional roles of the catalytic activity of PepN during adaptation to NDHT stress. (C) 2012 Elsevier GmbH. All rights reserved.

Effect of stress orientation on microstructural evolution during creep of near-lamellar Ti-47Al-2Cr-2Nb

Microstructural evolution was studied in a near-lamellar two phase (alpha(2) + gamma) Ti-47Al-2Cr-2Nb alloy under high temperature creep and exposure conditions. The aim of this study was to probe the role of stress orientation, with respect to lamellar plates, on microstructural changes during primary creep. Creep testing was complemented with SEM and TEM based microstructural characterization. It was observed that retention of excess alpha(2) resulted in an unstable microstructure. Under stress and temperature, excess alpha(2) was lost and Cr-rich precipitates formed. Depending on stress orientation, the sequence of precipitates formed was different. alpha(2) loss was accompanied by formation of the non-equilibrium C14 Laves phase when lamellar plates were oriented parallel to the stress axis. In contrast, alpha(2) loss did not result in formation of the C14 phase in perpendicular samples. It was concluded that C14 formed preferentially in certain test orientations because of its effectiveness in relieving residual stresses in alpha(2) that arose from lattice misfit and modulus mismatch. (c) 2012 Elsevier B.V. All rights reserved.

Estimation of electric stress and surface potential for traction insulators

Traction insulators are solid core insulators widely used for railway electrification. Constant exposure to detrimental effects of vandalism, and mechanical vibrations begets certain faults like shorting of sheds or cracks in the sheds. Due to fault in one/two sheds, stress on the remaining healthy sheds increases, owing to atmospheric pollution the stress may lead to a flashover of the insulator. Presently due to non availability of the electric stress data for the insulators, simulation study is carried out to find the potential and electric field for most widely used traction insulators in the country. The results of potential and electric field stress obtained for normal and faulty imposed insulators are presented.

Predicting the lithospheric stress field and plate motions by joint modeling of lithosphere and mantle dynamics

The way in which basal tractions, associated with mantle convection, couples with the lithosphere is a fundamental problem in geodynamics. A successful lithosphere-mantle coupling model for the Earth will satisfy observations of plate motions, intraplate stresses, and the plate boundary zone deformation. We solve the depth integrated three-dimensional force balance equations in a global finite element model that takes into account effects of both topography and shallow lithosphere structure as well as tractions originating from deeper mantle convection. The contribution from topography and lithosphere structure is estimated by calculating gravitational potential energy differences. The basal tractions are derived from a fully dynamic flow model with both radial and lateral viscosity variations. We simultaneously fit stresses and plate motions in order to delineate a best-fit lithosphere-mantle coupling model. We use both the World Stress Map and the Global Strain Rate Model to constrain the models. We find that a strongly coupled model with a stiff lithosphere and 3-4 orders of lateral viscosity variations in the lithosphere are best able to match the observational constraints. Our predicted deviatoric stresses, which are dominated by contribution from mantle tractions, range between 20-70 MPa. The best-fitting coupled models predict strain rates that are consistent with observations. That is, the intraplate areas are nearly rigid whereas plate boundaries and some other continental deformation zones display high strain rates. Comparison of mantle tractions and surface velocities indicate that in most areas tractions are driving, although in a few regions, including western North America, tractions are resistive. Citation: Ghosh, A., W. E. Holt, and L. M. Wen (2013), Predicting the lithospheric stress field and plate motions by joint modeling of lithosphere and mantle dynamics.

Structure, molecular dynamics, and stress in a linear polymer

We present a study correlating uniaxial stress in a polymer with its underlying structure when it is strained. The uniaxial stress is significantly influenced by the mean-square bond length and mean bond angle. In contrast, the size and shape of the polymer, typically represented by the end-to-end length, mass ratio, and radius of gyration, contribute negligibly. Among externally set control variables, density and polymer chain length play a critical role in influencing the anisotropic uniaxial stress. Short chain polymers more or less behave like rigid molecules. Temperature and rate of loading, in the range considered, have a very mild effect on the uniaxial stress.

Intracellular reactive oxidative stress, cell proliferation and apoptosis of Schwann cells on carbon nanofibrous substrates

Despite considerable research to develop carbon based materials for biomedical applications, the toxicity of carbon remains a major concern. In order to address this issue as well as to investigate the cell fate processes of neural cells from the perspective of neural tissue engineering applications, the in vitro cytocompatibility of polyacrylonitrile (PAN) derived continuous carbon nanofibers and PAN derived carbon thin films were investigated both quantitatively and qualitatively using in vitro biochemical assays followed by extensive flow cytometry analysis. The experimental results of Schwann cell fate, i.e. cell proliferation, cell metabolic activity and cell apoptosis on amorphous carbon substrates are discussed in reference to the time dependent evolution of intracellular oxidative stress. Apart from providing evidence that an electrospun carbon nanofibrous substrate can physically guide the cultured Schwann cells, this study suggested that continuous carbon nanofibers and amorphous carbon films are not cytotoxic in vitro and do not significantly induce apoptosis of Schwann cells, but in fact even facilitate their proliferation and growth.