Fear of contagion: a response to stress?

Alterations of neutrophil functions by tobacco products may play a central role in the pathogenesis of periodontal diseases and several smoking-related systemic diseases. In the present study, we examined the in vitro effects of cigarette smoke on neutrophils at times and concentrations that may be encountered during smoke exposure. We measured the level of smoke exposure in the in vitro system by measuring the levels of nicotine and comparing these to levels in the oral cavity in smokers before and after smoking. We examined both the unstimulated and stimulated release of 2 oxidative burst products: superoxide (O-2) and hydrogen peroxide (H2O2). Salivary washings were collected from 7 smokers (> 1 pack/day) before smoking a cigarette. Immediately after they smoked a cigarette, a second set of washings was collected. In vitro exposure to smoke involved incubating aliquots of neutrophils in phosphate-buffered saline for 1 to 5 minutes. Nicotine and cotinine levels were quantitated using gas chromatography, with detection by electron impact mass spectrometry. Peripheral neutrophils were isolated from medically healthy non-smoking volunteers via a double-density gradient technique and incubated in vitro with whole cigarette smoke for 0 to 5 minutes. Phorbol myristate acetate (PMA; 10(-7) M) was used to stimulate half of the cell aliquots. Superoxide generation was assessed through the superoxide dismutase (SOD) inhibitable reduction of ferricytochrome c. H2O2 production was assessed through the H2O2-dependent breakdown of dichlorofluorescin diacetate to its fluorophore and measured by flow cytometry. There was a marked elevation in salivary nicotine concentration from before smoking (mean: 80.8 ng) to after smoking (mean 1,685 ng/mL). In the in vitro smoke box system, there was a time-related elevation in nicotine from 1 to 5 minutes (50-->136 ng/mL). In PMA-stimulated cells exposed to smoke, there was a time-related inhibition of both superoxide and H2O2 production. However, in unstimulated cells exposed to smoke, there was a time-related increase in the release of superoxide and H2O2. A novel finding in unstimulated cells exposed to smoke was that there appeared to be 2 distinct populations of cells--one of "high" H2O2 producers and one of "low" H2O2 producers. The proportion of high H2O2 producers increased relative to smoke exposure. The relative production of H2O2 in the unstimulated high producers was comparable to PMA-stimulated cells at 5 minutes. This release of superoxide and H2O2 in unstimulated cells exposed to smoke may alter the pathogenic processes both in periodontal diseases and other systemic diseases.     

Recall of interrupted tasks under stress: A phenomenon of memory or of learning?

The study proposed to answer three questions: "1. Is superior recall of successes in an intelligence test situation (S-recall) a function of selective forgetting (repression) of failures or selective learning in favor of successes? 2. Is superior recall of failures in this situation (F-recall) a function of selective remembering or selective learning in favor of failures? 3. Is there a mnemonic reaction to the test as a whole?" Findings indicate that: "1. Both the S- and f-recall tendencies were due to a selective learning rather than a selective remembering mechanism. 2. A repression was demonstrated for S-recallers with regard to the stress situation as a whole. 3. A comparable process of enhanced retention of the total stress situation was not demonstrated for F-recallers; rather the effect here was due to enhanced registration." Implications of results are discussed. It is suggested that "experimental tests of repression… fulfill a criterion of cognitive relevance of test materials." 23 references. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Are traumatic events necessary to elicit symptoms of posttraumatic stress?

A diagnosis of posttraumatic stress disorder (PTSD) has been conceptualized as being precipitated by a particularly traumatic stressor (e.g., combat exposure, rape, and violent assault). Recent research suggests that common stressful events (e.g., relational problems, divorce, and expected death of a loved one) may also be capable of eliciting posttraumatic symptomatology. The current study replicated and extended these previous findings, examining three groups of event exposure: those who reported experiencing only traumatic events in the past year, those who reported experiencing only significant stressful life events in the last year, and those who experienced both types of events. Consistent with previous findings, we found that all three groups of event exposure, including those experiencing only stressful life events, experienced similar amounts of PTSD symptomatology across symptom clusters. These data add to the growing literature that suggests that the type of events that cause symptoms of PTSD may be broader than the current diagnostic criteria indicate, and as such calls for more rigorous research in this area to better understand the diagnostic implications of these findings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of cyclic stress on the high temperature creep behavior of AlMg alloys

The effect of cyclic stress on high temperature creep and also the dislocation structures developed during cyclic creep for three AlMg solid solutions have been studied. When the steady state creep rate is the range of 10⁻⁸ s⁻¹, cyclic creep with complete unloading (R = 0) exhibited only the transition from class M to class A creep instead of the two transitions from class M to class A and then to class M again ihe corresponding static creep. The threshold stress for the transition in cyclic creep was found to be close to or larger than that for the class A to class M transition in the static creep. With increase in magnesium content, cyclic creep retardation became stronger at lower stresses. However the transition from retardation to acceleration in the cyclic creep has been observed at higher stress levels only in the high magnesium alloys. Also found were two types of relationships between the unloading amount and steady state creep rate. The micromechanisms of cyclic creep, especially the interaction of dislocations with solute atoms, have also been discussed.     

Effect of strain rate and temperature on the flow stress of β-phase titanium- hydrogen alloys

Compression tests were carried out on seven titanium-hydrogen alloys containing hydrogen concen-trations up to 31 at. pct. All the experiments were performed within the β-phase field at strain rates of 0.001 to 1.0s ^~1 The dependences of the steady-state flow stress on strain rate, temperature, and hydrogen concentration were determined. The strain rate sensitivity increases with temperature but decreases with hydrogen concentration. The experimental activation energy of deformation decreases when the flow stress or strain rate is increased. At a fixed strain rate, it decreases when the hydrogen concentration is increased. However, when measured at a fixed steady-state stress, the activation energies are nearly the same for all the alloys. The steady-state flow stress increases with hydrogen concentration as can be expressed by both linear and quadratic dependences. The flow behavior of the alloys can also be described in terms of thermally activated glide and the relation $$\dot \varepsilon = K\sigma ^4 \exp \left( { - \frac{{\Delta H_0 }}{{kT}}} \right)\exp \left( {\frac{{v\sigma }}{{kT}}} \right)$$ where the constantsv and ΔH₀ are independent of hydrogen concentration, while the parameterK decreases exponentially when the hydrogen concentration is increased.     

Near-threshold fatigue crack growth behavior of 2195 aluminum-lithium-alloy—prediction of crack propagation direction and influence of stress ratio

Tensile properties and fatigue crack propagation behavior of a 2195-T8 Al-Li alloy were investigated at different stress ratios, with particular emphasis on their dependence on specimen orientation. Specimens with orientations of 0, 15, 30, 45, and 90 deg to the rolling direction were tested. The alloy contained a strong brass-type texture and a profuse distribution of platelike precipitates of T ₁ (Al₂CuLi) phase on {111} matrix planes. Both tensile strength and fatigue thresholds were found to be strongly dependent on the specimen orientation, with the lowest values observed along the direction at 45 deg to the rolling direction. The effect of stress ratio on fatigue threshold could generally be explained by a modified crack closure concept. The growth of fatigue crack in this alloy was found to exhibit a significant crystallographic cracking and especially macroscopic crack deflection. The specimens oriented in the L-T + 45 deg had the smallest deflection angle, while the specimens in the L-T and T-L orientations exhibited a large deflection angle. The dependence of the fatigue threshold on the specimen orientation could be rationalized by considering an equivalent fatigue threshold calculated from both mode I and mode II values due to the crack deflection. A four-step approach on the basis of Schmid’s law combined with specific crystallographic textures is proposed to predict the fatigue crack deflection angle. Good agreement between the theoretical prediction and experimental results was observed.     

Microstructure based modelling of stress–strain relationship on dual phase steels

The deformation in microstructures of DP600, DP800 and DP1000 commercial advanced high strength steels have been researched through using the representative volume element method. For this purpose, deformation analyses have been carried out by transferring geometrical models and mechanical properties of phases of each material to the finite element software. Deformation relation between ferrite and martensite phases was determined. According to the loading direction, Shear bands have been observed to occur in the range of approximately 40°–45°. It has been understood that the failure mode is shear for DP600, DP800 and DP1000 steels. Crack propagation has been observed to occur in the ferrite phase trapped at the martensite grain boundary.     

Is the stress test useful in the detection of post-angioplasty restenosis?

Restetenosis is still the greatest limitation of coronary angioplasty (PTCA). The systematic use of ergometry (PE) with the objective of identifying restenosis is controversial and, namely, the ACC/AHA does not recommend its routine use. Our objective was to conduct a retrospective study of the use of PE when performed late (3 to 6 months) for the detection of restenosis. As a protocol, our group performed "late" PE on all the patients without contraindications, the patients with positive ergometry or CCS class II-IV angor submitted to angiographic control. Between January 1996 and July 1997, 121 patients (pts) were submitted to PTCA. Our study population was composed of patients submitted to complete revascularisation with follow-up in our centre: 59 pts (49%) with an average age of 58 +/- 12 years, 82% male. Eighty-three percent of the pts had revascularisation in a context of unstable angina, 10% in the acute phase of myocardial infarction and 7% due to chronic angina. Stents were implanted in 42% of the pts. In the follow-up after six months, 7 pts complained of CCS class II or III angor. The ergometry showed positive electrocardiographic criteria in 11 pts (18.6%). All pts with angor had positive PE. All these pts were submitted to angiographic control; restenosis (residual stenosis equal to or above 50%) was observed in all the patients who complained of angor (100% positive predictive value); restenosis occurred in 9 pts with positive ergometry (82% positive predictive value). In asymptomatic pts, PE indicated 2 pts with restenosis (2/59-3.4%) and two false positive (2/11-18%). At six months, PE detected 22% of the pts with restenosis. In conclusion, complete post-revascularisation angor due to coronary angioplasty has a higher positive predictive value than ergometry. However, the stress test, performed systematically, can identify an additional percentage of pts with restenosis with an acceptable percentage of false positives.     

Observations of the effect of an applied stress on the morphology of discontinuous precipitation in a CuCd alloy

The influence of an applied tensile stress on the morphology and growth rate of the discontinuous precipitation product in a Cu−3.8 wt% Cd alloy was first reported by Sulonen. In this contribution, we investigate and further quantify a number of factors associated with the role of applied stress in this alloy, including absolute and relative growth rates of interfaces with normals parallel to and perpendicular to the tensile axis, and the morphological stability of discontinuous precipitation front as a function of the applied stress. Once morphological instability has occurred, the amplitude and wavelength of the protuberences formed depends on the value of the applied stress, and on the angle between the average interface normal and the tensile axis. It is suggested that the process is best viewed as one of transformation-assisted viscoelastic deformation.     

Does stress exacerbate parental differential treatment of siblings? A pattern-analytic approach.

To develop a typology based on family members' perspectives on parental differential treatment of siblings, data from mothers, fathers, firstborn adolescent siblings (M?=?15 years), and second-born adolescent siblings (M?=?12.5 years) from 187 families were submitted to cluster analysis. A 4-cluster solution based on the convergence or divergence of reports and the levels of parental differential treatment was identified and replicated: convergent/all below average (n?=?94), convergent/all above average (n?=?48), divergent/all below average except older sibling (n?=?20), and divergent/all above average except mother (n?=?25). Analyses revealed cluster differences in family structure (e.g., sex of siblings, age spacing) and in parents' perceived levels of stress across several domains (e.g., work, marriage, and individual mental health). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The critical resolved shear stress of a superalloy as a combination of those of its γ matrix and γ′ precipitates

The critical resolved shear stress (CRSS), τ ₀, of peak-aged single crystals of the γ′-hardened commercial nickel-base superalloy NIMONIC 105 has been measured as a function of temperature T and orientation [hkl] of the compression axis. The same measurements have been carried out for the two constituent phases of NIMONIC 105: for the single-phase γ matrix and for the single-phase L1₂-long-range ordered γ′ phase. The value of T ranged from 283 to 1150 K, and the following orientations were studied: [001], [011], , and . The specimens were compression tested. The τ ₀ values of NIMONIC 105 and of the γ′ phase are anisotropic; the anisotropy of NIMONIC 105 is similar to that of the γ′ phase, but less pronounced. The τ ₀ of the γ phase is isotropic. The τ ₀ values of the γ and of the γ′ phase vary with T, whereas the τ ₀ of NIMONIC 105 is nearly independent of T for 400 K≤T≤1000 K. A model is presented that relates the function τ ₀ ([h, k, l], T) of NIMONIC 105 to the analogous functions of its constituent γ and γ′ phase.     

The Hertzian stress field and formation of cone cracks—I. Theoretical approach

A complete three-dimensional solution has been derived for the Hertzian stress field. The solution was used to define an expression for the largest tensile stress under a spherical indenter. A numerical method was developed to solve the fracture mechanics equation related to cone crack formation, leading to a simple expression for fracture toughness. Examination of the relation between load, cone crack size and stress intensity showed that the critical stress intensity factor is independent of load and crack size. This suggests a new method to determine fracture toughness of brittle materials using Hertzian indentation.     

Anisotropy of the critical resolved shear stress of a superalloy containing 6 vol.% L12-ordered γ′-precipitates

Single crystals of the γ′-strengthened nickel-base superalloy NIMONIC PE16 have been compression tested in the temperature range 683–1143 K. Four different orientations of the specimens have been studied: [0 0 1].[1¯23].[011] and [1¯11]. They were either in the homogenized, single-phase state or in the peak-aged state. The critical resolved shear stress (CRSS) of the homogenized specimens was isotropic at 683 K. The CRSS of the peak-aged specimens, containing 6 vol.% of L1₂-long-range ordered γ′-precipitates of 25 nm radius, was anisotropic at 683 K and at 989 K: the [001]-orientated specimens were the softest ones, the CRSS increased as the orientation moved towards [011] or [11¯1]. This is the same orientation dependence found for the CRSS of single-phase L1₂-ordered materials. The interpretation of the anisotropy of the CRSS of NIMONIC PE16 follows that given for single-phase L1₂-long-range ordered materials.     

Effect of stress and temperature on the creep and rupture behavior of a 1.25 Pct chromium—0.5 Pct molybdenum steel

The creep and stress rupture behavior of a normalized 1.25 pct chromium-0.5 pct molybdenum steel has been investigated over a temperature (T) range of 510 to 620°C and a stress(σ) range of 65 to 425 MN/m². The creep rate ( ) and time to rupture (t _r ) data have been analyzed in terms of the general expression ort _r -A σⁿ exp (Q/RT), whereA is a constant,n is the power exponent of stress,Q is an empirical activation energy for the rate controlling process andR is the universal gas constant. At each temperature, the logarithmic plots of creep rate and time to rupture as functions of stress consist of two linear segments, separating the data into low stress and high stress regimes. The stress exponent has approximate values of 4 and 10 in the low stress and high stress regimes respectively in the appropriate expressions for both creep rate and for time to rupture. The activation energy has values of 367 and 420 kJ/mole in the low stress regime for time to rupture and creep rate respectively. In the high stress regime, the respective values of activation energy are 581 and 670 kJ/mole. Fractographic observations show that the changes from low stress to high stress behavior in creep rate and time to rupture approximately coincide with the transition in fracture mode from intergranular to transgranular cracking as well as with the transition in the rupture ductility from a region of linear variation with stress to one of constant ductility. These observations suggest that the transition from low stress to high stress behavior may be associated with a change in deformation mode from predominantly grain boundary sliding at low stress to transgranular matrix deformation at high stress. Analysis of the creep rate data based on this premise enables calculation of the ratio of the contributions of the grain boundary sliding mode to the total deformation (ε _gb /ε _T ) at various values of stress and temperature. Results of this analysis are consistent with numerous experimental observations reported in the literature.