Influence of fluorine-containing lubricant on properties of NR/BR rubber

K95 experimental lubricant being a product of fluorine reaction with a blend of mutually soluble poly(fluorine alcohols) and poly(fluorine esters) with molecular weight 240-900 g/mol was studied as an additive for rubber compounds based on blend of NR and BR. It was thermally stable till 270-300 °C. For comparison, it was tested simultaneously with homogenizing agent, Struktol MS40. Lubricant K95 added in a quantity of 0.5 wt% reduced the viscosity of rubber compound; it also improved compound flow in the mold. Mechanical properties of cured rubber not decrease while resistance to abrasion and fatigue increased. K95 participated in forming strong physical junctions (lower molecular weight between junctions of thermally stable network) while Struktol MS40 reduced the networking degree of rubber. As a result, it acts a multifunctional additive for NR/BR rubber.     

Genomic Imprinting—The Struggle of the Genders at the Molecular Level

Genomic imprinting, the parent of origin‐dependent expression of genes, has been discovered as a fascinating example of the control of gene expression by epigenetic processes in the human body. It affects about 100 genes, which are often involved in growth and development. In this Review, we discuss the mechanisms leading to the generation of gender‐specific imprints in form of DNA methylation marks, their preservation during growth and development of the organism, and the processes that translate parental methylation marks into monoallelic gene expression. We discuss the gender‐specific dimorphic nature of imprints from an evolutionary point of view and present the prevalent model that molecular imprinting mediates a conflict of interest between the parents that occurs in viviparous animals. Finally, we summarize the relevance of parental imprinting for human health.     

Analysis of the area of material really tested by TMA

Deformation distribution within the specimen beneath the thermomechanical analysis (TMA) probe, found by using the finite element method (FEM), depends mainly on penetration depth, specimen thickness and diameter as well as on radius of the probe tip when the Poisson’s ratio influences it just slightly. For standard radius of the tip R_o=1 mm, most deformation is distributed in a material layer up to 0.5 mm thick independently on elastic modulus of a polymer at a glassy state. It is caused by the fact that maximal penetration depth for the polymers usually equals to about 0.05 mm. Because of this, the contact surface area is less than 0.17 mm² for the standard radius of the tip. This evidences that predominantly the specimen volume equal to  mm² (depth×area) is tested by the TMA at compression mode. For R_o=5 mm is tested the layer 2.5 mm thick. This makes possible to evaluate the material properties in the zone of different thickness depending on radius of the tip.     

Comparison of results from the more informative version of TMA with other methods of polymer testing

Summary Several characteristics of the topological regions determined by the more informative version of TMA for cured rubbers based on NR/CPE and NR/ENR blends as well as PA6/cured rubber blends correlate with static and dynamic mechanical properties. These rubbers differ substantially in the structure of their network and the related topological structure because CPE does not participate in cross-links when ENR can do it. The physical interactions caused by these additives also vary, due to the different polarity that influences the formation of physical networking junctions. In blends of PA6 and cured rubber the networking junctions are assumed as being physical nature only. From these facts and the above-mentioned results it could be preliminarily concluded that the correlation depends on the formulation and related structure of the composite, and on which of the characteristics have been compared. To understand the reasons for the existence, or lack of, correlation observed, further investigations are needed.     

Specificity of Dnmt1 for methylation of hemimethylated CpG sites resides in its catalytic domain

The maintenance methylation of hemimethylated CpG sites by the DNA methyltransferase Dnmt1 is the molecular basis of the inheritance of DNA methylation patterns. Based on structural data and kinetics obtained with a truncated form of Dnmt1, an autoinhibition model for the specificity of Dnmt1 was proposed in which unmethylated DNA binds to Dnmt1's CXXC domain, which prevents its methylation. We have prepared CXXC domain variants that lost DNA binding. Corresponding full-length Dnmt1 variants did not display a reduction in specificity, indicating that the autoinhibition model does not apply in full-length Dnmt1. Furthermore, we show that the Dnmt1 M1235S variant, which carries an exchange in the catalytic domain of the enzyme, has a marked reduction in specificity, indicating that the recognition of the hemimethylated state of target sites resides within the catalytic domain.     

A COUPLED FLUID-STRUCTURE ANALYSIS FOR 3-D INVISCID FLUTTER OF IV STANDARD CONFIGURATION

A three-dimensional non-linear time-marching method and numerical analysis for aeroelastic behaviour of an oscillating blade row is presented. The approach is based on the solution of the coupled fluid-structure problem in which the aerodynamic and structural equations are integrated simultaneously in time. In this formulation of a coupled problem, the interblade phase angle at which a stability (or instability) would occur is a part of the solution. The ideal gas flow through multiple interblade passage (with periodicity on the whole annulus) is described by the unsteady Euler equations in the form of conservative laws, which are integrated by use of the explicit monotonic second order accurate Godunov-Kolgan volume scheme and a moving hybrid H-H (or H-O) grid. The structure analysis uses the modal approach and 3-D finite element model of the blade. The blade motion is assumed to be a linear combination of modes shapes with the modal coefficients depending on time. The influence of the natural frequencies on the aerodynamic coefficient and aeroelastic coupled oscillations for the Fourth Standard Configuration is shown. The stability (instability) areas for the modes are obtained. It has been shown that interaction between modes plays an important role in the aeroelastic blade response. This interaction has an essentially non-linear character and leads to blade limit cycle oscillations.