Diffusion-controlled growth in ternary systems

Diffusion-controlled growth of particles, dendrites, and plates in infinite media is examined for ternary systems. The growth kinetics associated with planar, cylindrical, and spherical particles are shown to be limiting cases of a more complete analysis (also presented) for shape-preserving growth. The theory is applied to the growth of allotriomorphic ferrite from austenite in ternary Fe-C-X steels, where X represents a substitutional alloying element. Numerical results are given, the analysis relying on the ability to predict multicomponent phase equilibria. The work represents an attempt at coupling together thermodynamic and kinetic models for the diffusion-controlled3 phase transformations that occur in steels.     

Diffusion-controlled precipitate growth in ternary systems I

Diffusion-controlled precipitation in isothermal ternary systems of arbitrary constitution is analyzed theoretically. The treatment is applicable to isolated precipitates whose morphology is preserved during growth;i.e., planar surfaces, cylinders, spheres, spheroids, and ellipsoids. The analysis does not account for ternary diffusional interaction. For a particular bulk alloy composition, the problem is essentially to determine the precipitatematrix interface velocity and the phase diagram tie-line which defines the equilibrium concentrations at this interface. The concepts of interface composition and interface velocity contours on the ternary phase diagram are introduced as instruments for solution of this problem. The influence on these contours of various diffusivity ratios for the independent components and of precipitate morphology is investigated. The assumption that local equilibrium maintains at the precipitate-matrix interface is critically examined and it is suggested that there are many instances in which the assumption is invalid. Therefore, Hultgren’s concept of paraequilibrium is discussed and is incorporated into the present theoretical framework. The techniques developed in the analysis are applied to ferrite growth in the Fe-C-Mn system.     

Diffusion-controlled growth of disordered interphase boundaries in finite matrix

The diffusion-controlled growth of interphase boundaries in finite matrices, which is influenced by the enrichment or depletion of solute in the untransformed matrix, is investigated using the solution to the diffusion equation obtained from the general formulation of free boundary problems by Kolodner. The integro-differential equation for the boundary position and velocity derived from the flux balance of solute is numerically solved for both one-dimensional (planar growth) and three-dimensional cases (growth of a spherical interface toward its center) and compared with the quasi-stationary solution in corresponding situations. The results show that the latter solution coupled with the mass balance of solute between precipitate and matrix as previously utilized by some authors tends to overestimate the progress of transformation. The error becomes quite large at higher supersaturations where the quasi-stationary approximation obviously breaks down.     

Diffusion-controlled kink motion

A simple model for the growth of kinks by volume diffusion is discussed, and singular perturbation methods, valid for supersaturations much less than one, are used to derive coupled integral equations for the motion of trains of (well-spaced) kinks. Numerical results are presented for the motion of two-and three-kink trains. This paper is based on a presentation made in the symposium “The Role of Ledges in Phase Transformations” presented as part of the 1989 Fall Meeting of TMS-MSD, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Phase Transformations Committee of the Materials Science Division, ASM INTERNATIONAL.     

Diffusion-controlled thermal aging of 15X2HMΦA structural steel

At nuclear power plants, metal equipment is subjected to temperatures of 290–320°C. That may lead to thermal aging and reduce the resistance to brittle failure. The degradation of the steel’s properties may be taken into account in terms of the shift in the critical brittleness temperature. The thermal aging of steel is controlled by the diffusion of carbon and associated with carbide deposition. The results permit prediction of the properties of steel and the shift in the critical brittleness temperature corresponding to a life of 60 years.     

Experimental diabetic renal growth: role of growth hormone and insulin-like growth factor-I

We have compared the kidneys of two inbred strains of rats (Lewis and Lewis-Dwarf) 7 days after the induction of diabetes mellitus with streptozotocin, in order to examine the influence of a selective growth hormone (GH) deficiency on diabetic renal growth and insulin-like growth factor-I (IGF-I) content of the kidneys. Insulin-like growth factor-I (IGF-I) content of the kidneys. Insulin-like growth factor-I was measured by radioimmunoassay and its distribution within the kidney by immunohistochemical staining. We detected a significant increase in both the wet weight (32.9 +/- 5.3%, P = 0.0085) and dry weight (16.3 +/- 6.3%, P = 0.046) of the kidneys of diabetic Lewis rats but dwarf rats, selectively deficient in GH, did not show a significant increase in either parameter. Extractable IGF-I increased within the kidneys of diabetic rats of both strains but to a lesser extent in the dwarf rats (+105 +/- 28% and +65 +/- 21% respectively, P < 0.01). In diabetic Lewis rats a positive correlation was noted between the severity of glycaemia and kidney IGF-I content (r = 0.604, P < 0.05) but no such correlation was noted in dwarf rats. Inulin-like growth factor-I immunostaining increased in diabetic rats of both strains, mainly within cells of the thick ascending limb of the loop of Henle including damaged and vacuolated cells. However, morphometric analysis of the staining showed that it was significantly less widespread in the diabetic dwarf rats (P = 0.026).(ABSTRACT TRUNCATED AT 250 WORDS)     

Epidermal growth factor modulates fetal thymocyte growth and differentiation

In the present study, we used the fetal organ culture (FTOC) technique in order to study a putative effect of epidermal growth factor (EGF) on the thymus ontogeny. Functional EGF receptors and more recently the EGF molecule itself, respectively, on the membrane of epithelial components of thymic stroma and on a few thymocytes in adult thymus, had been reported in the literature. We could observe a dose-dependent decrease in cellularity and a progressive retention of thymocytes in the double-negative (CD4-/CD8-) stage of differentiation when exogenous EGF was added. Epidermal growth factor interfered with both fetal stroma growth and thymocyte development at a precise moment, that is, in the passage from double-negative to the double-positive (CD4+/CD8+) stage. After a 7-day FTOC in the presence of EGF, most cells recovered were Thy-1.2+, c-kit+, TSA1-/int, CD3-, and one of CD44high/CD25int, CD44-/CD25int, or CD44/CD25-. Some developed into gammadeltaTCR+ cells with a mature (CD3+) phenotype, but not into alphabetaTCR+ thymocytes. It seems that EGF addition makes the cultures "nonpermissible" for alphabetaTCR+ thymocyte generation. We report here the presence of a high Mr "EGF-like" molecule on the membrane of fetal thymocytes, which role in the observed effects is under investigation. Further biochemical characterization of this molecule is still required, because its presence was only evidenced on the basis of its antigenicity.     

The growth of pain and the pain of growth.

Reviews the book, Textbook of pain by Patrick D. Wall and Ronald Melzack (1984). A clinical specialty has come of age when it is represented by a textbook of this stature. Wall and Melzack's 79-chapter Textbook of Pain attempts, as Noordenbos describes in his prologue, to represent the state of the art today, to be a guideline on how to tackle the subject, and finally, to prescribe how to act in a given situation. As a textbook, it also must accomplish these goals through chapters that are accessible to readers at less advanced levels or working in different disciplines. In this instance, the difficulty of the textbook creators' task is compounded by the nature of the specialty of studying and treating pain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Regulation of prostatic growth and function by peptide growth factors

Polypeptide growth factors are positive and negative regulators of prostatic growth and function. Expression and biological effects of epidermal growth factor (EGF), transforming growth factors (TGFs) alpha and beta, fibroblast growth factors (FGFs), and insulin-like growth factors (IGFs) in the prostate have been extensively studied. EGF and TGF alpha, which share the same receptor, are strong mitogens for prostatic epithelial and stromal cells. Their paracrine mode of action in normal tissue and early-stage tumors is apparently altered towards an autocrine stimulation in hormone-independent tumors, which gain the ability to produce TGF alpha by themselves. TGF beta has a dual role in the regulation of prostatic growth. It inhibits growth of prostatic epithelial cells in culture and mediates programmed cell death after androgen withdrawal. However, advanced prostatic carcinomas become insensitive to the inhibitory effect of TGF beta. Several members of the FGF family have been identified in the prostate. They are mainly or exclusively expressed in the stromal cells, and stimulate the epithelial cells. In the rat Dunning tumor model, progression is accompanied by distinct changes in the expression of FGFs and their receptors. In the hyperplastic tissue, basic FGF (bFGF) is accumulated. This growth factor is also a potent angiogenic inducer, expression of which may determine the metastatic capability of a tumor. IGFs are paracrine growth stimulators in the normal and hyperplastic prostate. It is still under consideration whether prostatic cancer cells gain the ability to produce IGF-I by themselves and thus shift to an autocrine mode of IGF-I stimulation. Growth factors also interact with the androgen-signaling pathway. IGF-I in particular, other growth factors as well, can activate the androgen receptor.     

Chaos and growth.

Chaotic states of mind are often encountered by clients at critical points in psychotherapy when growth is initiated, and this form of client chaos differs from the chaos that arises as a result of regression or in the service of resistance. During these chaotic "gestation" periods clients are preconsciously organizing new adaptive and representational patterns, and from this activity emerge new syntheses and directions for living. Psychotherapists can be helpful by recognizing these gestation states and responding in ways that facilitate this reorganizing activity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Correlation between longitudinal bone growth, growth hormone, and insulin-like growth factor-I in prepubertal dogs

OBJECTIVE: To determine the association between longitudinal bone growth and concentrations of growth hormone (GH) and insulin-like growth factor-I (IGF-I) in serum from prepubertal dogs. Animals-6 male 14-week-old German Shepherd Dogs. PROCEDURE: Blood was obtained every 30 minutes for 14 consecutive days. Concentrations of GH and IGF-I in serum were determined, using a canine-specific radioimmunoassay and conventional radioimmunoassay after acid-ethanol extraction, respectively. Simultaneous biplanar radiography was performed daily to measure bone growth. Spectral analysis was used to estimate specific features of GH secretion during an extended period. Multiple linear regression with different lag times between independent and dependent variables was used to determine the strongest predictors of bone growth. RESULTS: The power spectra of GH concentrations in serum had a primary peak at a frequency of 0.02 cycles/h or a periodicity of 50 h/cycle. A significant determinant of longitudinal bone growth was a lag time of 1 day in concentration of GH in serum. The relationship between IGF-I concentration in serum and bone growth was not significant. CONCLUSIONS: The primary frequency of GH secretion is outside the time frame of a single day and the concentration of GH in serum is a primary determinant of bone growth. CLINICAL RELEVANCE: A better understanding of the components of bone growth provide discernment to improved diagnosis and treatment of abnormal bone growth.     

Postnatal catch-up growth induced by growth hormone and insulin-like growth factor-I in rats with intrauterine growth retardation caused by maternal protein malnutrition

In an earlier study, we found that yellow-rumped warblers had in vitro active uptake rates of D-glucose that were only a few percent of the glucose absorption rate achieved at the whole-animal level. Here we used a pharmacokinetic technique to test whether a substantial amount of sugar can be absorbed passively. We used yellow-rumped warblers (Dendroica coronata), known for their seasonal frugivory, freely feeding on a synthetic mash formulated with naturally occurring concentrations of D-glucose. Birds absorbed 89.8% +/- 1.0% (SE) of the D-glucose in the mash. When fed the same mash with trace-labeled 3H L-glucose, the stereoisomer that does not interact with the intestinal Na(+)-glucose cotransporter, 3H appeared in plasma, an indication that this stereoisomer of glucose was absorbed. We used 3H levels in plasma and excreta in a pharmacokinetic model to calculate L-glucose extraction efficiency (i.e., the percent absorbed). Calculated mean extraction efficiency for the passively absorbed L-glucose averaged 91% +/- 23%. Our finding of considerable passive absorption reconciles the in vitro and in vivo results for D-glucose absorption and is in concert with results from five other avian species. The passive pathway appears to provide birds with an absorptive process that can respond quickly to changing luminal concentration and that is energetically inexpensive to maintain and modulate in real time but that may bear a cost. Less discriminate passive absorption might increase vulnerability to toxins and thus constrain foraging behavior and limit the breadth of the dietary niche.