Comparison of strain hardening in polycrystals and <111> single crystals: The example of copper

Tests on copper single crystals oriented about 2 deg from <111> were in agreement with earlier work on similar crystals. Comparison to polycrystals using the Taylor factor showed agreement only for large-grained material. Literature data for single crystals in plane strain compression also agreed only with large-grained copper strain hardening curves. These results suggest that grain size strengthening occurs which is not accounted for in the Taylor analysis. It is therefore concluded that polycrystal strain hardening in copper is not simply a Taylor-averaged single crystal process.     

The effect of curvature on the grain boundary migration induced by diffusional coherency strain in mo-ni alloy

When a liquid phase sintered Mo-Ni alloy is heat-treated at 1400°C after replacing the liquid matrix with a Cu melt, the grain boundaries between some grains migrate, producing a Ni depleted Mo-Ni solid solution behind them. The phenomenon is same as those commonly referred to as DIGM with the Cu melt acting as the sink for Ni atoms. When Fe of 1% by weight is added to the Cu melt, the grain boundaries do not migrate, because the compressive coherency strain produced by Ni diffusion from the lattice is exactly compensated by the tensile strain due to the Fe diffusion into it. The diffusional coherency strain energy is thus shown to be the driving force for the grain boundary migration. Because Mo is insoluble in liquid Cu, the grain boundaries are pinned at the grooved ends. The grain boundary curvature thus increases during the migration, causing a migration reversal and consequently an oscillatory motion. The observed critical curvature for the migration reversal falls closely into the range predicted on the basis of the generation of misfit dislocations when the migration velocity decreases to a critical value because of the curvature. The reversal of the grain boundary migration resulting in an oscillatory motion is thus shown to be a natural consequence of the coherency strain hypothesis for the driving force if the inhibiting effect of the grain boundary curvature is taken into account.     

On calculation of Ms and driving force for martensitic transformation in Fe-C

The approximate approach for evaluation of the critical driving force is briefly introduced, i.e. ΔG^α→M = 2.1 δ + 900 J mol⁻¹, where δ is the yield strength of parent phase and 900 is the stored energy. By application of this approach M_s can directly be deducted through various method for calculation of ΔG^γ→α, i.e. LFG, KRC, Fisher-Bhadeshia and Fisher-Hsu, with ΔG_Fe^γ→α given by Kaufman el al., Orr and Chipman and Mogutnov. The results of the combination of LFG-Mogutnov, KRC-Orr and Chipman, Fisher-Bhadeshia-Orr and Chipman and Fisher-Hsu-Orr and Chipman (-Mogutnov as χ < 0.02) are all in good agreement with the experimental M_s, verifying the validity of the above equation. The driving force obtained by substitution the experimental M_s of KRC to the above equation is very close to that from calculation through LFG-Mogutnov, KRC-Orr and Chipman and Fisher-Hsu-Orr and Chipman (χ ⩾ 0.02). fairly close to Fisher-Bhadeshia-Orr and Chipman. The driving force calculated from LFG-Orr and Chipman seems too low. The driving force increases monotonically with the carbon content. The present work emphasizes that the selection of M_s is a key factor and the value of ΔG_Fe^γ→α plays an important role in the calculation of the driving force.     

Numerical determination of the elastic driving force for directional coarsening in Ni-superalloys

We have developed a general methodology, in the framework of the finite element method, for locally evaluating the generalized force acting on a material interface which is work-conjugate with the normal displacement of the interface itself. This methodology has been applied to the study of directional coarsening of γ′ precipitates in Ni-superalloys. The flexibility of the proposed method has allowed us to closely model the actual microstructural morphology of the alloys and to account for the effects of applied boundary conditions, lattice misfit, elastic anisotropy and inelastic behavior of the crystals. We have positively compared the indications of our model with available experimental data for a few alloys, and a circumscribed parametric study has lead us to formulate a more general interpretation of the rafting phenomenon, which appears to give a satisfactory explanation for all the available experimental observations.     

Cell membrane fluctuations are regulated by medium macroviscosity: evidence for a metabolic driving force

Extracellular fluid macroviscosity (EFM), modified by macromolecular cosolvents as occurs in body fluids, has been shown to affect cell membrane protein activities but not isolated proteins. In search for the mechanism of this phenomenon, we examined the effect of EFM on mechanical fluctuations of the cell membrane of human erythrocytes. The macroviscosity of the external medium was varied by adding to it various macromolecules [dextrans (70, 500, and 2,000 kDa), polyethylene glycol (20 kDa), and carboxymethyl-cellulose (100 kDa)], which differ in size, chemical nature, and in their capacity to increase fluid viscosity. The parameters of cell membrane fluctuations (maximal amplitude and half-width of amplitude distribution) were diminished with the elevation of solvent macroviscosity, regardless of the cosolvent used to increase EFM. Because thermally driven membrane fluctuations cannot be damped by elevation of EFM, the existence of a metabolic driving force is suggested. This is supported by the finding that in ATP-depleted red blood cells elevation of EMF did not affect cell membrane fluctuations. This study demonstrates that (i) EFM is a regulator of membrane dynamics, providing a possible mechanism by which EFM affects cell membrane activities; and (ii) cell membrane fluctuations are driven by a metabolic driving force in addition to the thermal one.     

A thermodynamic model for composition and chemical driving force for nucleation of complex carbonitrides in microalloyed steel

The extent and degree of dispersion of carbonitrides in high strength low alloy (HSLA) steels is controlled by nucleation and growth processes. A thermodynamic model is presented enabling calculation of the composition of the carbonitride embryo as well as the chemical driving force for nucleation (CDF) in the austenite region of a multicomponent microalloyed steel. The analysis made for a Nb-Ti HSLA steel indicates that the critical carbonitride nucleus is richer in N and Ti than the bulk precipitate at equilibrium at a given temperature and the difference increases when the holding temperature decreases. The results also show that the Ti addition has an optimum value defined by the maximum in the ratio of bound Ti and Nb to their total content. The maximum CDF correlated with the minimum Ti content sufficient to form a carbonitride at the austenitizing temperature.     

Vocal fold strain and vocal pitch in singing: radiographic observations of singers and nonsingers

The relationship between vocal fold strain and vocal pitch in singers and nonsingers singing a rising pitch series has been indirectly investigated by means of lateral radiographs. Nonsingers tend to exhibit more strain than singers. To standardize the degree of strain, an index of strain per semitone is proposed. The semitone strain indicates the average amount of strain per 1 semitone of pitch increase or decrease. The index has been shown to be affected by several factors: gender, singing training, singing technique, voice class, age, and status of muscle function. Observations suggest that similar groups of individuals occupy different positions on the stress-strain curve, indicated by their semitone strain values.     

The loss of driving force due to volume diffusion ahead of a migrating boundary in a cellular precipitation reaction

Experimental confirmation has been obtained of the existence of a solute diffusion zone ahead of a migrating cell boundary during the cellular precipitation of Cr₂N in a high nitrogen CrNi austenitic steel. The solute profile has been measured directly using analytical electron microscopy and indirectly by optical microscopy of potentiostatically etched specimens. The width of the diffusion zone was observed to increase with reaction time; this corresponded to the deceleration of the migration rate of the cell boundary with reaction time.     

Comparison of group paper-and-pencil tests with certain psychophysical tests for measuring driving aptitude of Army personnel.

A battery of paper and pencil tests was developed and validated against a driver-aptitude criterion consisting of ratings of driver reactions to specific situations and a check list of driving habits. Using samples of Army drivers, a multiple R for the final battery of .38 was found. Comparable size batteries of individual psychophysical tests yielded validities of .25 or lower. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Phosphate load as the evolutionary driving force for the development of a high filtration rate based excretory organ: a hypothesis

It is proposed that the nutritional load of phosphate is the primary factor that led to the development of an excretory organ that is based on a high filtration rate of the extracellular fluid. This hypothesis is based on the following arguments: 1) phosphate and potassium impose the highest average nutritional load rates defined as the ratio between the average ion content in foods that satisfies the energy demands of the body per unit time and the respective ionic plasma concentration. Due to the much higher intracellular than extracellular potassium concentration it is argued that a secretory based excretory organ would be more useful for disposal of potassium. 2) Magnesium and calcium nutritional load rates are lower than that of phosphate; in addition the disposal of magnesium should have been dealt with preferably by secretion due to its slightly higher intracellular concentration. The nutritional load rate of calcium is tempered by the inherently low absorption capacity of the intestinal mucosa. 3) In aglomerular teleost fishes the phosphate plasma concentration is significantly elevated vis a vis the mammals and other marine fishes, in comparison to only slight differences in calcium, magnesium and potassium levels. It is suggested that the seemingly peculiar and costly way in which sodium excretion is accomplished in the kidney represents the outcome of the solution to the phosphate nutritional load.     

In situ hybridization with riboprobes: an overview for veterinary pathologists

Although preliminary reports indicate that fatigue is a common symptom of human immunodeficiency virus (HIV) disease, little empirical research has focused on its prevalence or characteristics among patients with acquired immunodeficiency syndrome (AIDS). We assessed the frequency of fatigue and its medical and psychological correlates, in a cross-sectional survey of ambulatory AIDS patients. Ambulatory patients with AIDS who participated in a study of quality life (N = 427) were classified into fatigue/no fatigue groups based on their responses to fatigue items on the Memorial Symptom Assessment Scale (MSAS) and the AIDS physical symptom checklist. Self-report inventories were also administered to assess psychological distress, depressive symptoms, and overall quality of life. Medical information was elicited through clinical interview and review of medical chart. Fifty-four percent of the patients endorsed both of the fatigue items from the MSAS and the AIDS physical symptom checklists, and were classified as having fatigue. Women were significantly more likely to report fatigue than men (chi square = 5.28, df = 1, P < 0.03), and patients reporting homosexual contact as their transmission risk factor were significantly less likely to report fatigue than were patients reporting injection drug use or heterosexual contact (chi square = 5.13, df = 2, P < 0.03). The presence of fatigue was significantly associated with the number of current AIDS-related physical symptoms [t(425) = 8.00, P < 0.0001], current treatment for HIV-related medical disorders (chi square = 12.51, df = 1, P < 0.0001), anemia [t(174) = -2.35, P < 0.02], and pain (chi square = 36.36, df = 1 P < 0.0001). Patients with fatigue also had significantly poorer physical functioning ability [Karnofsky: t(422) = -6.27, P < 0.0001], as well as greater degree of overall psychological distress and lower quality of life [F(5,418) = 23.79, P < 0.0001], as measured by the Brief Symptom Inventory, Beck Depression Inventory, Beck Hopelessness Scale, Functional Living Inventory for Cancer (modified for AIDS), and the MSAS Psychological Distress Subscale. Fatigue is a common symptom in ambulatory AIDS patients and is associated with significant physical and psychological morbidity.