Mathematical modelling of heat transfer during electron-beam autocrucible melting by means of the steady-state Stefan problem

A two-dimensional axisymmetric mathematical model of electron-beam autocrucible melting is developed and examined. Here, the hypothesis is used that forced convective heat transfer in the melt may be modelled with the help of the coefficient of effective thermal conductivity, _E. A simplified approach is used in which _E is assumed to be known. In another approach the value of _E depends on a prescribed value of a mean melt-stirring velocity and a mean liquid-pool radius which is determined in the course of solving of the problem. With the help of the Kirchoff transformation and a Green function we may reduce the problem to a nonlinear Hammerstein integral equation. Here, a dependence of the thermal-conductivity coefficient on the temperature, _S(T), at the cooled surfaces is disregarded and constant (mean) values of _S are utilized. In order to solve the problem in the case where this dependence _S(T) is taken into account, an axuiliary Green-function method is proposed which also permits to take into account a change of the heat-exchange coefficients on the autocrucible. This reduces the problem to a system of three integral Hammerstein equations. Numerical solutions of the nonlinear integral equations are obtained with the help of a variational (projective-net) method for the case of circular scanning of an electron beam over the heated surface. The computational results are well consistent with experimental data.     

Effect of Erythropoietin on the Expression of Murine Transferrin Receptor 2

Erythropoietin (EPO) downregulates hepcidin expression to increase the availability of iron; the downregulation of hepcidin is mediated by erythroferrone (ERFE) secreted by erythroblasts. Erythroblasts also express transferrin receptor 2 (TFR2); however, the possible role of TFR2 in hepcidin downregulation is unclear. The purpose of the study was to correlate liver expression of hepcidin with the expression of ERFE and TFR2 in murine bone marrow and spleen at 4, 16, 24, 48, 72 and 96 h following administration of a single dose of EPO. Splenic Fam132b expression increased 4 h after EPO injection; liver hepcidin mRNA was decreased at 16 h. In the spleen, expression of TFR2 and transferrin receptor (TFR1) proteins increased by an order of magnitude at 48 and 72 h after EPO treatment. The EPO-induced increase in splenic TFR2 and TFR1 was associated with an increase in the number of Tfr2- and Tfr1-expressing erythroblasts. Plasma exosomes prepared from EPO-treated mice displayed increased amount of TFR1 protein; however, no exosomal TFR2 was detected. Overall, the results confirm the importance of ERFE in stress erythropoiesis, support the role of TFR2 in erythroid cell development, and highlight possible differences in the removal of TFR2 and TFR1 from erythroid cell membranes.     

Discrete structure of van der Waals domains in globular proteins

Most globular proteins are divisible by domains, distinct substructuresof the globule. The notion of hierarchy of the domains was introducedearlier via van der Waals energy profiles that allow one tosubdivide the proteins into domains (subdomains). The questionremains open as to what is the possible structural connectionof the energy profiles. The recent discovery of the loop-n-lockelements in the globular proteins suggests such a structuralconnection. A direct comparison of the segmentation by van derWaals energy criteria with the maps of the locked loops of nearlystandard size reveals a striking correlation: domains in generalappear to consist of one to several such loops. In addition,it was demonstrated that a variety of subdivisions of the sameprotein into domains is just a regrouping of the loop-n-lockelements.     

Amino acid composition of protein termini are biased in different manners

An exhaustive statistical analysis of the amino acid sequencesat the carboxyl (C) and amino (N) termini of proteins and ofcoding nucleic acid sequences at the 5' side of the stop codonswas undertaken. At the N ends, Met and Ala residues are over-representedat the first (+1) position whereas at positions 2 and 5 Thris preferred. These peculiarities at N-termini are most probablyrelated to the mechanism of initiation of translation (for Met)and to the mechanisms governing the life-span of proteins viaregulation of their degradation (for Ala and Thr). We assumethat the C-terminal bias facilitates fixation of the C endson the protein globule by a preference for charged and Cys residues.The terminal biases, a novel feature of protein structure, haveto be taken into account when molecular evolution, three-dimensionalstructure, initiation and termination of translation, proteinfolding and life-span are concerned. In addition, the bias ofprotein termini composition is an important feature which shouldbe considered in protein engineering experiments.     

COOH-terminal decamers in proteins are non-random

We have undertaken an exhaustive statistical analysis of the amino acid sequences at the carboxyl-terminal (C) ends of proteins. The composition of the C-terminal decapeptides differs from that expected for the given proteins from the overall amino acid composition. For E. coli, yeast, and H. sapiens it was shown that positively charged amino acid residues are over-represented while Gly residues are under-represented. The C-terminal bias, a novel feature of protein structure, should be taken into account when molecular evolution, spatial structure, translational termination and protein folding are concerned.     

Heart Ferroportin Protein Content Is Regulated by Heart Iron Concentration and Systemic Hepcidin Expression

The purpose of the study was to investigate the expression of ferroportin protein following treatments that affect systemic hepcidin. Administration of erythropoietin to C57BL/6J mice decreased systemic hepcidin expression; it also increased heart ferroportin protein content, determined by immunoblot in the membrane fraction, to approximately 200% of control values. This increase in heart ferroportin protein is very probably caused by a decrease in systemic hepcidin expression, in accordance with the classical regulation of ferroportin by hepcidin. However, the control of heart ferroportin protein by systemic hepcidin could apparently be overridden by changes in heart non-heme iron content since injection of ferric carboxymaltose to mice at 300 mg Fe/kg resulted in an increase in liver hepcidin expression, heart non-heme iron content, and also a threefold increase in heart ferroportin protein content. In a separate experiment, feeding an iron-deficient diet to young Wistar rats dramatically decreased liver hepcidin expression, while heart non-heme iron content and heart ferroportin protein content decreased to 50% of controls. It is, therefore, suggested that heart ferroportin protein is regulated primarily by the iron regulatory protein/iron-responsive element system and that the regulation of heart ferroportin by the hepcidin-ferroportin axis plays a secondary role.     

Loop fold nature of globular proteins

Protein chains make numerous returns in globules, thus formingloops, closed by tight residue-to-residue contacts—closedloops. Previous statistical analysis of the sizes and locationsof the closed loops in all major protein folds revealed thatthe loops have an almost standard contour length of 25–30amino acid residues and follow one after another along the chain.In this work the closed loops of the major folds are presentedin three dimensions. A special image filtering procedure isintroduced that allows one to visualize the standard size closedloops for the first time. The loop positions along the sequencesare verified by detection of loop-end clusters.     

Effects of carbontetrachloride and chenodeoxycholic acid on hepatic monooxygenase system, lipid peroxidation and some immunologic parameters in rats

BACKGROUND: Nutritional characteristics of the mediterranean diet, with a high intake of complex carbohydrates, fibre, monounsatured fatty acids and vegetables, are related to a lower prevalence of some nutritional associated diseases. The aim of our study was to perform a longitudinal analysis of the evolution of food intake in a mediterranean population in order to observe its influence on the energy and nutritional intake and their balance. The latter could have some effects on health status. METHODS: Dietary intake was evaluated using the 24 hours recall method in a representative sample (n = 941, age range = 10-69) of a Reus population. This longitudinal study consisted of 70% of the samples studied in 1983 using identical methodology. RESULTS: During this decade (1983-1993), energy intake decreased significantly 180 kcal/day for men and 158 kcal/day for women, carbohydrates being the main cause for this drop (132 and 84 kcal/day less for men and women, respectively). Protein intake decreased significantly in both sexes, 5.6% for men and 8.0% for women. However, the evolution of fat intake was different for men (no changes) and for women (a significant decrease of 5.7%). Saturated and monounsatured fatty acids did not show significant changes in this decade. Cholesterol intake decreased significantly in both sexes. Energy percents obtained from lipids, saturated and monounsaturated fatty acids significantly increased. However, in absolute values very little changes in fat intake in both sexes were observed. CONCLUSIONS: The dietary pattern evolved to a lower energy intake with an increment of the percentage of dietary lipids, but this feature was did not reflect a greater fat intake in absolute values. Moreover, the main characteristics of the typical mediterranean diet (which is basically different to the usual diet of other non mediterranean european countries mainly due to its richness in monounsaturated fatty acids) did not change in the period analyzed.     

Synthesis of halftone 3D images on an array processor

A fast generation of shaded images of CSG-defined objects could be accomplished by employing a general-purpose array processor. To fully exploit the computing power of such a machine, the visualization algorithm should be tailored to that specific kind of architecture. A parallel adaptation of the ray-tracing method and algorithm kernel operations is introduced. The performance analysis shows suitability of the approach for interactive CAD applications. Test pictures are presented.     

Thermal Properties of Biological Tissue Gel-Phantoms in a Wide Low-Temperature Range

Journal of Engineering Physics and Thermophysics - It is often impossible or impractical to conduct experiments on cooling, freezing, and thawing during medical cryoexposures with using biological...