KINETICS AGGREGATION OF MAGNETIC SUSPENSIONS

International audienceWe present results of theoretical and computer study of the kinetics of chain-like aggregate formation in suspensions of non-Brownian magnetizable particles. An analytical model for calculation of the time-dependent function of distribution over chain size is suggested. This model describes the evolution of the chain structure due to the chain-chain aggregation. In order to verify this model we have compared it with the results of computer simulations of two-dimensional model of this suspension. Results of computer simulations and of the analytical model are in reasonable agreement up to 5% of the surface concentration of the particles

Structurization of ferrofluids in the absence of an external magnetic field

Structural transformations in a model ferrofluid in the absence of an external magnetic field have been theoretically studied. The results agree with well-known laboratory experiments and computer simulations in showing that, if the concentration of particles and their magnetic interaction energy are below certain critical values, most particles form separate linear chains. If these parameters exceed the critical values, most particles concentrate so as to form branched network structures. The passage from chains to network has a continuous character rather than represents a discontinuous first-order phase transition. © Pleiades Publishing, Inc., 2013

Shear thickening of dense suspensions due to energy dissipation in lubrication layers between particles

This paper deals with a theoretical study of the shear thickening effects in concentrated suspensions of non-Brownian particles. Our analysis shows that an increase of the shear rate of the suspension flow leads to a decrease of the mean thickness of the gaps between the nearest particles in dense suspensions. In turn, this leads to the growth of energy dissipation in these gaps, which means an increase of the suspension effective viscosity with the shear rate. © 2013 American Physical Society

Association between 28 single nucleotide polymorphisms and type 2 diabetes mellitus in the Kazakh population: a case-control study.

We evaluated the associations between single nucleotide polymorphisms and different clinical parameters related to type 2 diabetes mellitus (T2DM), obesity risk, and metabolic syndrome (MS) in a Kazakh cohort. A total of 1336 subjects, including 408 T2DM patients and 928 control subjects, were recruited from an outpatient clinic and genotyped for 32 polymorphisms previously associated with T2DM and obesity-related phenotypes in other ethnic groups. For association studies, the chi-squared test or Fisher's exact test for binomial variables were used. Logistic regression was conducted to explore associations between the studied SNPs and the risk of developing T2DM, obesity, and MS, after adjustments for age and sex. After excluding four SNPs due to Hardy-Weinberg disequilibrium, significant associations in age-matched cohorts were found betweenT2DM and the following SNPs: rs9939609 (FTO), rs13266634 (SLC30A8), rs7961581 (TSPAN8/LGR5), and rs1799883 (FABP2). In addition, examination of general unmatched T2DM and control cohorts revealed significant associations between T2DM and SNPsrs1799883 (FABP2) and rs9939609 (FTO). Furthermore, polymorphisms in the FTO gene were associated with increased obesity risk, whereas polymorphisms in the FTO and FABP2 genes were also associated with the risk of developing MS in general unmatched cohorts. We confirmed associations between polymorphisms within the SLC30A8, TSPAN8/LGR5, FABP2, and FTO genes and susceptibility to T2DM in a Kazakh cohort, and revealed significant associations with anthropometric and metabolic traits. In particular, FTO and FABP2 gene polymorphisms were significantly associated with susceptibility to MS and obesity in this cohort

Kinetics of internal structures growth in magnetic suspensions

The kinetics of aggregation of non Brownian magnetizable particles in the presence of a magnetic field is studied both theoretically and by means of computer simulations. A theoretical approach is based on a system of Smoluchowski equations for the distribution function of the number of particles in linear chain-like aggregates. Results obtained in the two dimensional (2D) and three dimensional (3D) models are analyzed in relation with the size of the cell, containing the particles, and the particle volume fraction φ. The theoretical model reproduces the change of the aggregation kinetics with the size of the cell and with the particle volume fraction as long as the lateral aggregation of chains is negligible. The simulations show that lateral aggregation takes place when, roughly, φ2D>5% and φ3D>1.5%. Dependence of the average size of the chains with time can be described by a power law; the corresponding exponent decreases with the particle volume fraction in relation with the lateral aggregation. In the 3D simulations, dense labyrinthine-like structures, aligned along the applied field, are observed when the particle concentration is high enough (φ3D>5%). © 2012 Elsevier B.V. All rights reserved

Polymorphisms in genes involved in the absorption, distribution, metabolism, and excretion of drugs in the Kazakhs of Kazakhstan

A list of SNPs that were not found in heterozygous or homozygous variants. (DOC 83 kb

Optimisation of a transcription-translation coupled in vitro system

Cell-free protein synthesis exploits the catalytic machinery of the cell to produce active proteins. An in vitro system is flexible and well controlled, and it offers several advantages over conventional in vivo technologies such as easy ways for purification, synthesis of regulatory and/or toxic proteins, incorporation of artificial or modified amino acids that might be doted with isotopes required for NMR. Here I describe experiments exploring optimisation possibilities concerning yield and quality of the synthesised protein. Some experimental strategies also include expression of eukaryotic genes in prokaryotic expression systems. The following results have been achieved: 1: Quality criteria developed that allow a critical evaluation of parameters important for the coupled transcription/translation system or improving the yield and quality of the synthesized protein exploiting the features of the green fluorescent protein GFP. 2: The standard transcriptase used in overexpression studies in vivo and in vitro is the T7 polymerase. The fundamental difficulty with this enzyme is the fact that it is about six times faster than the E. coli transcriptase and thus uncouples transcription from translation, a possible reason for the fact that in vitro systems usually produce proteins with an activity of 30 to 60% only. We tested some slow mutants of T7 polymerase that approached the rate of the E. coli transcriptase and observed indeed a significant improvement up to 100% of the active fraction, although at the cost of lower yields. 3: A similar improvement of the active fraction was observed at lower incubation temperatures down to 20°C, again at the cost of lower yields. 4: According to literature data some amino acids are metabolised during in vitro incubations and thus could cause a limitation of protein synthesis. Indeed, we demonstrate that a second addition of amino acids in the middle of the incubation triggers a burst of further protein synthesis. Using this trick at 20°C pushed the yield of protein to almost that seen at 30°C, but now with an active fraction of 100%. In contrast, our analysis revealed that NTPs are not limiting the gene expression in vitro in our system (modified Roche RTS). 5: It is known that the codon usage of highly and lowly expressed proteins in E. coli differs dramatically. When we examined this point with human genes, to our surprise a corresponding difference could not be observed. Due to this fact it was possible to identify 11 tRNAs the corresponding codon are quite often used in human genes but rarely in E. coli genes. Therefore, for a good expression of eukaryotic genes in E. coli systems these 11 tRNAs should be added (and not only the 7 tRNAs supplied in systems from Novagen). 6: I outlined some ways to improve further the expression system