Stress induced ordering due interstitials in Nb-4.7 at.%Ta

The presence of interstitial elements in metals cause strong changes in their physical, chemical or mechanical properties. These interstitial impurities interact with the metallic matrix atoms by a relaxation process known as stress induced ordering. Relaxation processes give rise to a peak in the internal friction spectrum, known as Snock effect. The presence of substitutional solutes has a strong influence on Snoek effect, particularly if the substitutional solute element is the one, which interacts with the interstitial element. Anelastic spectroscopy measurements provide information of the behavior of these impurities in the metallic matrix. In this paper, polycrystalline samples of Nb-4.7 at.%Ta alloy have been analyzed in the as-received condition. Measurements of anelastic spectroscopy were carried out using an inverted torsion pendulum, operating with frequency of 2.0-30.0 Hz and in a temperature range between 300 and 700 K. It was observed the presence of a relaxation structure that have been attributed to stress induced ordering due to interstitial atoms around atoms of the metallic matrix. The relaxation structure have been decomposed in its constituent peaks, what it allowed to identify the following relaxation processes: Ta-O, Nb-O and Nb-N. (c) 2005 Elsevier B.V. All rights reserved.

Viscoelastic behavior of persimmons dried at constant air temperature

The viscoelastic behavior of dried persimmons at different air-drying temperatures and velocities was evaluated. Air temperatures and velocities were varied according to a second-order central composite design, with temperature ranging from 40degreesC to 70degreesC and air velocity from 0.8 to 2.0 m/s. After drying, persimmons were equilibrated at four different water activities: 0.432, 0.576, 0.625 and 0.751. The rheological behavior of dried and conditioned persimmons was studied under uniaxial compression-relaxation tests. Three different rheological models were fitted to the experimental relaxation curves: Maxwell, Generalized Maxwell and Peleg and Normand. Based on the root mean square of residuals, the Generalized Maxwell model showed the best fit and a regression analysis was applied to obtain response surfaces for the model parameters. The dependence of the rheological properties on water activity was also analysed. Results showed that only the linear effect of air temperature was significant at a 5% level on the equilibrium stress and relaxation times. In a general way, these parameters increased with increasing air temperature and decreasing water activity. (C) 2004 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.

Cadmium and exposure to stress increase aggressive behavior

Environmental toxicants and stress influence the health and behavior of people from different parts of the world. In the present study, aggressive behavior was evaluated in rats exposed to cadmium (Cd) for four weeks and subjected to immobilization stress (IS) based on the resident/intruder paradigm. Latency to the first bite (LB), total number of attacks (NA), total duration of attack manifestations (DAM), and a composite aggression score (CAS) were used to assess aggressiveness. Cadmium concentrations in the blood and the brain were determined. We observed that the parameters of aggressiveness were not altered by either Cd or IS when administered separately. However, animals exposed to Cd + IS had increased NA, DAM, and CAS. Cadmium was detected in the blood and the brain after treatment and Cd + IS exposure modified Cd distribution in these tissues. These results suggest that exposure to low levels of Cd associated with stress may lead to increased aggressiveness in rats. (C) 2011 Elsevier B.V. All rights reserved.

Anelastic relaxation due to interstitial solutes diffusion in Nb and Nb-1 wt% Zr

Metals and alloys containing solute atoms dissolved interstitially often show anelastic behavior due to a process know as stress-induced ordering. The application of mechanical spectroscopy measurements to diffusion studies in body-centered cubic metals has been extensively used in the last decades. However the kind of preferential occupation of interstitial solutes in body-centered cubic metals is still controversial. The anelastic properties of the Nb and Nb-1 wt% Zr polycrystalline alloys were determined by internal friction and oscillation frequency measurements using a torsion pendulum inverted performed between 300K and 650K, operating in a frequency oscillation in the hertz bandwidth. The interstitial diffusion coefficients of oxygen and nitrogen in Nb and Nb-1 wt% Zr samples were determined at two distinct conditions: (a) for low concentration of oxygen and (b) for high concentration of oxygen.

Strain relaxation and stress-driven interdiffusion in InAsInGaAsInP nanowires

The authors have investigated strain relaxation in InAsInGaAsInP nanowires (NW's). Transmission electron microscopy images show an additional stress field attributed to compositional modulation in the ternary layer, which disrupts NW formation and drives Ga interdiffusion into InAs, according to grazing incidence x-Ray diffraction under anomalous scattering conditions. The strain profile along the NW, however, is not significantly affected when interdiffusion is considered. Results show that the InAs NW energetic stability is preserved with the introduction of ternary buffer layer in the structure. © 2007 American Institute of Physics.

Fluoxetine exposure during pregnancy and lactation: effects on acute stress response and behavior in the novelty-suppressed feeding are age and gender-dependent in rats

Fluoxetine (FLX) is commonly used to treat anxiety and depressive disorders in pregnant women. Since FLX crosses the placenta and is excreted in milk, maternal treatment with this antidepressant may expose the fetus and neonate to increased levels of serotonin (5-HT). Long-term behavioral abnormalities have been reported in rodents exposed to higher levels of 5-HT during neurodevelopment. In this study we evaluated if maternal exposure to FLX during pregnancy and lactation would result in behavioral and/or stress response disruption in adolescent and adult rats. Our results indicate that exposure to FLX influenced restraint stress-induced Fos expression in the amygdala in a gender and age-specific manner. In male animals, a decreased expression was observed in the basolateral amygdala at adolescence and adulthood; whereas at adulthood, a decrease was also observed in the medial amygdala. A lack of FLX exposure effect was observed in females and also in the paraventricular nucleus of both genders. Regarding the behavioral evaluation, FLX exposure did not induce anhedonia in the sucrose preference test but decreased the latency to feed of both male and female adolescent rats evaluated in the novelty-suppressed feeding test. In conclusion, FLX exposure during pregnancy and lactation decreases acute amygdalar stress response to a psychological stressor in males (adolescents and adults) as well as influences the behavior of adolescents (males and females) in a model that evaluates anxiety and/or depressive-like behavior. Even though FLX seems to be a developmental neurotoxicant, the translation of these findings to human safe assessment remains to be determined since it is recognized that not treating a pregnant or lactating woman may also impact negatively the development of the descendants.

Mechanical behavior and residual stress field of dissimilar laser welded joints

The present investigation addresses the mechanical behavior and residual stress field of dissimilar joints produced by laser welding. Microstructure characterization and residual strain scanning, carried out by neutron diffraction, were used to assess the joints features. It was found that the heat source position influences the base metals dilution and the residual stress field associated to the welding process. The tensile behavior of the joint, different zones achieved by using a video-image based system (VIC-2D) reveals that the residual stress field, together with the positive difference in yield between the weld metal and the base materials protects the joint from being plastically deformed.

Dynamic behavior of cylindrical shells under initial stress,

"Project no. 9782. Contract AF 49 (638)-430 ... CU-11-60-AF-430-CE."

Behavior of Granular Materials Under Triaxial Compression with Pulsating Deviator Stress, HR-131, Special Report

Behavior of granular material subjected to repeated load triaxial compression tests is characterized by a model based on rate process theory. Starting with the Arrhenius equation from chemical kinetics, the relationship of temperature, shear stress, normal stress and volume change to deformation rate is developed. The proposed model equation includes these factors as a product of exponential terms. An empirical relationship between deformation and the cube root of the number of stress applications at constant temperature and normal stress is combined with the rate equation to yield an integrated relationship of temperature, deviator stress, confining pressure and number of deviator stress applications to axial strain. The experimental program consists of 64 repeated load triaxial compression tests, 52 on untreated crushed stone and 12 on the same crushed stone material treated with 4% asphalt cement. Results were analyzed with multiple linear regression techniques and show substantial agreement with the model equations. Experimental results fit the rate equation somewhat better than the integrated equation when all variable quantities are considered. The coefficient of shear temperature gives the activation enthalpy, which is about 4.7 kilocalories/mole for untreated material and 39.4 kilocalories/mole for asphalt-treated material. This indicates the activation enthalpy is about that of the pore fluid. The proportionality coefficient of deviator stress may be used to measure flow unit volume. The volumes thus determined for untreated and asphalt-treated material are not substantially different. This may be coincidental since comparison with flow unit volumes reported by others indicates flow unit volume is related to gradation of untreated material. The flow unit volume of asphalt-treated material may relate to asphalt cement content. The proposed model equations provide a more rational basis for further studies of factors affecting deformation of granular materials under stress similar to that in pavement subjected to transient traffic loads.

Topology Optimization of continuum structures with epsilon-relaxed stress constraints

Topology optimization of linear elastic continuum structures is a challenging problem when considering local stress constraints. The reasons are the singular behavior of the constraint with the density design variables, combined with the large number of constraints even for small finite element meshes. This work presents an alternative formulation for the s-relaxation technique, which provides an workaround for the singularity of the stress constraint. It also presents a new global stress constraint formulation. Derivation of the sensitivities for the constraint by the adjoint method is shown. Results for single and multiple load cases show the potential of the new formulation.

The Effect of Stress Management Program Using Cognitive Behavior Approach on Mental Health of the Mothers of the Children With Attention Deficit Hyperactivity Disorder

Background: Attention deficit hyperactivity disorder is one of the most common psychiatric disorders in children. Objectives: The study aimed to evaluate the effectiveness of stress management program using cognitive behavior approach on mental health of the mothers of the children with attention deficit hyperactivity disorder. Patients and Methods: In this interventional study, 90 mothers of the children with attention deficit hyperactivity disorder were randomly allocated into three intervention, placebo, and control groups. The general health questionnaire was used to measure mental health. Besides, stress was assessed through the depression-anxiety-stress scale. The two instruments were completed at baseline, immediately after, and one month after the intervention by the mothers. Afterwards, within group comparisons were made using one-sample repeated measurement ANOVA. One-way ANOVA was used for inter group comparisons. Mothers in the placebo group only participated in meetings to talk and express feelings without receiving any interventions. Results: At the baseline, no significant difference was found among the three groups regarding the means of stress, anxiety, depression, and mental health. However, a significant difference was observed in the mean score of stress immediately after the intervention (P = 0.033). The results also showed a significant difference among the three groups regarding the mean score of mental health (P < 0.001). One month after the intervention, the mean difference of mental health score remained significant only in the intervention group (P < 0.001). Conclusions: The study findings confirmed the effectiveness of stress management program utilizing cognitive behavior approach in mental health of the mothers of the children with attention deficit hyperactivity disorder.

Taurine Supplementation Reduces Blood Pressure And Prevents Endothelial Dysfunction And Oxidative Stress In Post-weaning Protein-restricted Rats.

Taurine is a sulfur-containing amino acid that exerts protective effects on vascular function and structure in several models of cardiovascular diseases through its antioxidant and anti-inflammatory properties. Early protein malnutrition reprograms the cardiovascular system and is linked to hypertension in adulthood. This study assessed the effects of taurine supplementation in vascular alterations induced by protein restriction in post-weaning rats. Weaned male Wistar rats were fed normal- (12%, NP) or low-protein (6%, LP) diets for 90 days. Half of the NP and LP rats concomitantly received 2.5% taurine supplementation in the drinking water (NPT and LPT, respectively). LP rats showed elevated systolic, diastolic and mean arterial blood pressure versus NP rats; taurine supplementation partially prevented this increase. There was a reduced relaxation response to acetylcholine in isolated thoracic aortic rings from the LP group that was reversed by superoxide dismutase (SOD) or apocynin incubation. Protein expression of p47phox NADPH oxidase subunit was enhanced, whereas extracellular (EC)-SOD and endothelial nitric oxide synthase phosphorylation at Ser 1177 (p-eNOS) were reduced in aortas from LP rats. Furthermore, ROS production was enhanced while acetylcholine-induced NO release was reduced in aortas from the LP group. Taurine supplementation improved the relaxation response to acetylcholine and eNOS-derived NO production, increased EC-SOD and p-eNOS protein expression, as well as reduced ROS generation and p47phox expression in the aortas from LPT rats. LP rats showed an increased aortic wall/lumen ratio and taurine prevented this remodeling through a reduction in wall media thickness. Our data indicate a protective role of taurine supplementation on the high blood pressure, endothelial dysfunction and vascular remodeling induced by post-weaning protein restriction. The beneficial vascular effect of taurine was associated with restoration of vascular redox homeostasis and improvement of NO bioavailability.

Biofilm And Saliva Affect The Biomechanical Behavior Of Dental Implants.

Friction coefficient (FC) was quantified between titanium-titanium (Ti-Ti) and titanium-zirconia (Ti-Zr), materials commonly used as abutment and implants, in the presence of a multispecies biofilm (Bf) or salivary pellicle (Pel). Furthermore, FC was used as a parameter to evaluate the biomechanical behavior of a single implant-supported restoration. Interface between Ti-Ti and Ti-Zr without Pel or Bf was used as control (Ctrl). FC was recorded using tribometer and analyzed by two-way Anova and Tukey test (p<0.05). Data were transposed to a finite element model of a dental implant-supported restoration. Models were obtained varying abutment material (Ti and Zr) and FCs recorded (Bf, Pel, and Ctrl). Maximum and shear stress were calculated for bone and equivalent von Misses for prosthetic components. Data were analyzed using two-way ANOVA (p<0.05) and percentage of contribution for each condition (material and FC) was calculated. FC significant differences were observed between Ti-Ti and Ti-Zr for Ctrl and Bf groups, with lower values for Ti-Zr (p<0.05). Within each material group, Ti-Ti differed between all treatments (p<0.05) and for Ti-Zr, only Pel showed higher values compared with Ctrl and Bf (p<0.05). FC contributed to 89.83% (p<0.05) of the stress in the screw, decreasing the stress when the FC was lower. FC resulted in an increase of 59.78% of maximum stress in cortical bone (p=0.05). It can be concluded that the shift of the FC due to the presence of Pel or Bf is able to jeopardize the biomechanical behavior of a single implant-supported restoration.

Dynamic and steady: shear rheological properties of xanthan and guar gums dispersed in yellow passion fruit pulp (Passiflora edulis f. flavicarpa)

Yellow passion fruit pulp is unstable, presenting phase separation that can be avoided by the addition of hydrocolloids. For this purpose, xanthan and guar gum [0.3, 0.7 and 1.0% (w/w)] were added to yellow passion fruit pulp and the changes in the dynamic and steady - shear rheological behavior evaluated. Xanthan dispersions showed a more pronounced pseudoplasticity and the presence of yield stress, which was not observed in the guar gum dispersions. Cross model fitting to flow curves showed that the xanthan suspensions also had higher zero shear viscosity than the guar suspensions, and, for both gums, an increase in temperature led to lower values for this parameter. The gums showed different behavior as a function of temperature in the range of 5 - 35ºC. The activation energy of the apparent viscosity was dependent on the shear rate and gum concentration for guar, whereas for xanthan these values only varied with the concentration. The mechanical spectra were well described by the generalized Maxwell model and the xanthan dispersions showed a more elastic character than the guar dispersions, with higher values for the relaxation time. Xanthan was characterized as a weak gel, while guar presented a concentrated solution behavior. The simultaneous evaluation of temperature and concentration showed a stronger influence of the polysaccharide concentration on the apparent viscosity and the G' and G" moduli than the variation in temperature.