Kinetic equations for concurrent size and shape coarsening by the ledge mechanism

The kinetic equations describing concurrent size and shape coarsening of plate-and rod-shaped particles having shapes that deviate from equilibrium are presented. In the derivations, the assumption is made that some of the interfaces are fully or partially coherent and migrate by the ledge mechanism. Three different interfacial character combinations are considered. The analysis also assumes a small and constant volume fraction of particles so that the average matrix composition can be estimated from knowledge of the particle size distribution, the surface area available for atomic attachment/detachment, and the diffusion distance. The resultant flux equations are then used in a computer model to predict the coarsening behavior of an ensemble of nonequilibrium-shaped particles. Comparison of these results with those obtained from the traditional coarsening theory of Lifshitz and Slyosov¹ and Wagner² (LSW) show significant discrepancies. These differences are attributed to the invalidity of many assumptions made in the LSW theory when applied to solid:solid coarsening systems. Formerly Graduate Student, Michigan. Technological University. Formerly Graduate Student, University of Utah. Formerly Graduate Student, University of Utah, Salt Lake City, UT. 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.     

Simultaneous recovery of size and radioactivity concentration of small spheroids with PET data

Quantification of tumor activity is used to predict prognosis and discriminate benign from malignant lesions identified by PET. Accurate quantitation of small lesions requires correction for the partial volume effects. Such a correction is often based on the recovery coefficient (RC), which depends on the lesion size, the object-to-background ratio (OBR) and physical properties of the media. The purpose of this investigation was to determine whether a model-based optimization method to simultaneously recover the size and the activity concentration of small spheroids could improve estimates of lesion radioactivity when object size is unknown. For reference, we compared our method with a widely used approach, RC correction, that requires the object size to be known. METHODS: A three-dimensional, spatially varying, object size- and contrast-dependent Gaussian model of the point spread function (PSF) of an ECAT EXACT was developed. The observed dependence of the PSF on random coincidences and measured-peak/background activity were included in the PSF using three adjusting factors. Size and radioactivity concentration of a spheroid were estimated by adjusting size and concentration until model output best matched the image data. Elliptic and circular phantoms both containing seven hot spheroids, with OBRs ranging from 5.6 to 0 background, were evaluated. RESULTS: The proposed quantification method reduced the activity error by 11%-63% of the error obtained without correction. The greatest error reduction occurred for small spheroids. The average error in radius estimation ranged from 2% to 48%, wherein the smallest spheroid produced the largest errors. For spheroids with diameters from 8 to 22 mm, Student t test (paired, one-tail) showed the proposed method significantly improved accuracy (P < 0.05) in comparison with the RC method and also in comparison with optimization without the three adjusting factors. CONCLUSION: The model-based optimization method improved estimation of radioactivity concentration over that corrected by the RC method and that made without any correction. It also provided accurate estimation of size for spheroids larger than 6 mm in diameter.     

Measuring the shape and size of microcracks in bone

Microcracks in bone are normally measured from two-dimensional, transverse sections but this provides incomplete information about their three-dimensional shape and size. The methods of stereology can usefully be applied in such a case. This problem has been addressed using a theoretical model and a numerical simulation. Results show that the data are consistent with a crack shape which is elliptical, with axis ratio approximately 4.5:1 and with size variation (expressed as the ratio of standard deviation to mean length) of at least 0.1. Measured lengths will, on average, be smaller and have more scatter than true lengths. Errors caused by omitting small cracks are relatively unimportant. Knowledge of the true crack dimensions, and their variability, is important for the analysis of damage, stress fracture, remodelling and adaptation.     

The effect of biopsy-hole shape and size on bone strength

The erythrocyte cholesterol, total phospholipid and individual phospholipids content have been determined in patients with chronic renal failure, resulting from glomerulonephritis and pyelonephritis. The rise in total phospholipid, confined predominantly to the sphingomyelin and lecithin classes was found. It was often accompanied by decrease in the phosphatidylethanol-amine content. The cholesterol/phospholipid ratio was found to be reduced. The excessive lipid loss during incubation of erythrocytes in glucose-rich medium has been observed in some patients.     

Is blood pressure related to kidney size and shape?

OBJECTIVE: To examine the relationship between blood pressure and the size and shape of the kidneys in healthy volunteers from the community. DESIGN: A cross-sectional community-based study of normal volunteers in Portsmouth City, Hampshire, UK. SUBJECTS: Subjects numbered 185 (99 female), aged 19-66 years. RESULTS: Blood pressure was higher in men, and in those with higher body mass index. Both systolic and diastolic blood pressure were correlated with the derived kidney volume. However, when corrected for age, sex and BMI the relationship was not statistically significant. Blood pressure correlated inversely with the width : length ratio of the left kidney. CONCLUSIONS: Blood pressure was not correlated with kidney size in this group of adults.     

A unified model of microsegregation and coarsening

Using a coordinate transform in a standard microsegregation model it is shown that the effect of coarsening on the dilution of the liquid phase can be accounted for by adding a dimensionless parameter α ^c to the back-diffusion Fourier number. Through theory, for the case of parabolic growth, and numerical experiments for the constant cooling rate, it is shown that a constant value of α ^c =0.1 is a sound choice across a wide range of casting and alloy conditions. This finding allows for the development of a unified model for microsegregation and coarsening. In particular, previous approximate microsegregation models can be readily modified to account for coarsening.     

Grain shape and its influence on the experimental measurement of grain size

A procedure for determining grain size,N _V , from measurable two-dimensional parameters is presented. A variety of microstructures (ferritic, austenitic, and ferrite-pearlitic steels and zinc) are considered and all tend to obey the following relation:N _V = 122.23 (N _L /K _S )³, whereN _L is the average number of grains per unit length of the test line, and KS is the shape factor of the grains. A shape factor is proposed which can be used to examine quantitatively the influence of grain shape, and an analysis is made of possible errors resulting from the approximate equations used in the literature for theN _V determination. The presence of a nonnegligible percentage of nonequiaxial grains and the curvature of the surfaces of each grain make the variety and complexity of shape distribution in grains greater than could be expected from their topological features.     

Readily releasable pool size changes associated with long term depression

We have estimated, for hippocampal neurons in culture, the size of the autaptic readily releasable pool before and after stimulation of the sort that produces culture long term depression (LTD). This stimulation protocol causes a decrease in the pool size that is proportional to the depression of synaptic currents. To determine if depression in this system is synapse specific rather than general, we have also monitored synaptic transmission between pairs of cultured hippocampal neurons that are autaptically and reciprocally interconnected. We find that the change in synaptic strength is restricted to the synapses on the target neuron that were active during LTD induction. When viewed from the perspective of the presynaptic neuron, however, synapse specificity is partial rather than complete: synapses active during induction that were not on the target neuron were partially depressed.     

ERPs in anterior and posterior regions associated with duration and size discriminations.

The main objective of the present study was to determine whether event-related potentials (ERPs) predominant in prefrontal cortex (PFC) respond in a similar fashion to ERPs predominant in posterior parietal cortex (PPC) in duration and size discrimination tasks. The results indicate that contingent negative variation (CNV) and P300 components changed according to task demands. In the time-related task, amplitudes and duration of both components increased as a function of stimulus duration and easier discriminability. This was not the case in the size discrimination task. These results are in accordance with the hypothesis of a functional link between PFC and PPC in timing behavior. The later-appearing LPCt component was observed in both tasks, but its amplitude increased only as a function of stimulus duration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Changes in size and shape of chromatin particles after successive removal of histones

The preparations of whole chromatin, chromatin selectively depleted of histone f1, depleted of all lysine-rich histones (f1, f2b, f2a2), and DNA was studied by viscosimetric and light scattering methods. The obtained results were used for calculation of the dimensions and packing ratios of DNA for the preparations studied. The packing ratio in whole chromatin is 7.2 and is almost unaffected by selective removal of histone f1 (6.9), but decreases on successive removal of the remaining four histones, the decrease being dependent more on the quantity than the kind of the dissociated histones.     

Development of Fe-based shape memory alloys associated with face-centered cubic-hexagonal close-packed martensitic transformations: Part I. shape memory behavior

As part of a study on newly developed Fe-based shape memory alloys associated with face-centered cubic-hexagonal close-packed (fcc-hcp) martensitic transformations, the shape memory behavior is reported and various physical factors influencing it discussed, based on experimental results from dilatometry and bending tests. It is shown that the alloys studied exhibit a good shape memory effect (SME) without special training. The SME is significantly improved by prestraining at low temperatures. A higher net reversible strain is made available by over-prestraining, although the fully reversible prestrain usually does not exceed 2 pct. Super-elasticity, the two-way shape memory, and a softening effect of the matrix at low temperatures are briefly discussed.     

The measurement of fringing fields in a radio-frequency hyperthermia array with emphasis on bolus size

The limited aperture size through which the em-field of the applicator is emanated and the constraining of this em-field near the bolus' edge is related to the appearance of superficial 'hot spot' phenomena in radiative hyperthermia. Regarding systems based on the concept of the annular phased array two questions arise: (1) what is the relative strength of the radial component present in the incident field of the radiators, and (2) in what way are fringing fields related to the bolus size? To address both of the above questions, the spatial distribution of the em-field emanated through the aperture of an applicator of the Amsterdam four waveguide-array system has been investigated for a long bolus and a short bolus. The em vector field emanated by the applicator has been characterized in two perpendicular planes, i.e. the aperture midplane and the sagittal midplane. It should be noted that this distribution depends on the propagation conditions throughout the coupling bolus, the phantom and other volumes attached, such as other applicators. Therefore two sets of propagation conditions have been measured: (1) the minimum number of parameters determining the propagation of the em-field namely one single waveguide, one bolus and a homogeneous phantom, and (2) the propagation conditions as for the clinical setting. It is stressed that the study concerns one specific radiative hyperthermia system, namely the AMC four-waveguide array, but that, based on the similarities discussed above, results may be extrapolated towards other radiative hyperthermia systems. According to the current study, bolus prolongation might lead to a clear clinical improvement, which is due to a decrease of the fringing field amplitude compared to the field amplitude in the centre of the aperture midplane. Bolus prolongation will lead to an extended heating area, the field lines being more aligned to the patient's main axis.