The Dislocation Bias

Bias factors for dislocations quantify the preferential diffusion of self-interstitials relative to the diffusion of vacancies to dislocations. These parameters are essential for rate theory computer codes that model nucleation and growth of voids, helium bubbles, dislocation loops, and the evolution of microstructures in materials subject to high dose irradiations. Compact formulae for these factors are derived and the accuracy of several approximations is explored.     

α-Quaterthiophene–polyethylene blends: Phase behaviour and electronic properties

We demonstrate that blending α-quaterthiophene (4T) with high-density polyethylene (HDPE) under judiciously chosen processing conditions allows preparation of continuous thin films of insulator content as high as 90 wt% without considerably sacrificing the electronic properties of the semiconducting species, as measured in field-effect transistors (FETs). Similar behaviour was recently reported for all-polymeric crystalline–crystalline semiconducting blends such as poly(3-hexylthiophene):HDPE. However, while that previous work focussed on the sequence in which the two components crystallize, we show here that for the present small molecule:polymer binaries – in addition to the crystallization sequence – the extent of solid–solid phase separation that occurs during blend preparation strongly affects the electronic properties of the active layers.     

On the meaning of sink capture efficiency and sink strength for point defects

The concepts of sink capture efficiency and sink strength for point defects are central to the theory of point defect reactions in materials undergoing irradiation. Two fundamentally different definitions of the capture efficiency are in current use. The essential difference can be stated simply. The conventional meaning denotes a measure of the loss rate of point defects to sinks per unit mean point defect concentration. A second definition of capture efficiency, introduced recently, gives a measure of the point defect loss rate without normalization to the mean point defect concentration. The relationship between the two capture efficiencies is here derived. By stating the relationship we hope to eliminate confusion caused by comparisons of the two types of capture efficiencies at face value and to provide a method of obtaining one from the other. Internally consistent usage of either of the capture efficiencies leads to the same results for the calculation of measuable quantities, as is required physically.     

Investigation of cascade-induced point-defect fluctuations

High energy irradiation produces collision cascades, which occur randomly in space and time. Any given point in the material will therefore to subject to intermittent arrival of interstitials and vacancies, even under steady irradiation. The conventional rate theory formulation of the point-defect concentrations, which contains spatial and time averaging and a uniform production rate, may not always adequately describe processes such as void nucleation and irradiation creep. We develop in this paper a theoretical approach to describe the cascade-induced point-defect fluctuations by their moments.The first moment, giving the average point-defect concentration, is used in the traditional rate theory. However, the second moment provides the variance of the point defect concentration, and it becomes important for processes such as void nucleation, dislocation climb, and loop growth. An approximate analytical expression is given for the second moment. The obtained concentration variances compare well with numerical results.We demonstrate with the example of climb-induced dislocation glide how the moments can be used to extend rate theory results. Large enhancement in the creep rate due to point defect fluctuations can be obtained if the barrier size and the average climb rate are small and if the cascade size is large.     

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Void nucleation, growth, and coalescence in irradiated metals

A novel computational treatment of dense, stiff, coupled reaction rate equations is introduced to study the nucleation, growth, and possible coalescence of cavities during neutron irradiation of metals. Radiation damage is modeled by the creation of Frenkel pair defects and helium impurity atoms. A multi-dimensional cluster size distribution function allows independent evolution of the vacancy and helium content of cavities, distinguishing voids and bubbles. A model with sessile cavities and no cluster–cluster coalescence can result in a bimodal final cavity size distribution with coexistence of small, high-pressure bubbles and large, low-pressure voids. A model that includes unhindered cavity diffusion and coalescence ultimately removes the small helium bubbles from the system, leaving only large voids. The terminal void density is also reduced and the incubation period and terminal swelling rate can be greatly altered by cavity coalescence. Temperature-dependent trapping of voids/bubbles by precipitates and alterations in void surface diffusion from adsorbed impurities and internal gas pressure may give rise to intermediate swelling behavior through their effects on cavity mobility and coalescence.     

Phenotype of Mrps5-Associated Phylogenetic Polymorphisms Is Intimately Linked to Mitoribosomal Misreading

We have recently identified point mutation V336Y in mitoribosomal protein Mrps5 (uS5m) as a mitoribosomal ram (ribosomal ambiguity) mutation conferring error-prone mitochondrial protein synthesis. In vivo in transgenic knock-in animals, homologous mutation V338Y was associated with a discrete phenotype including impaired mitochondrial function, anxiety-related behavioral alterations, enhanced susceptibility to noise-induced hearing damage, and accelerated metabolic aging in muscle. To challenge the postulated link between Mrps5 V338Y-mediated misreading and the in vivo phenotype, we introduced mutation G315R into the mouse Mrps5 gene as Mrps5 G315R is homologous to the established bacterial ram mutation RpsE (uS5) G104R. However, in contrast to bacterial translation, the homologous G → R mutation in mitoribosomal Mrps5 did not affect the accuracy of mitochondrial protein synthesis. Importantly, in the absence of mitochondrial misreading, homozygous mutant MrpS5^G315R/G315R mice did not show a phenotype distinct from wild-type animals.     

Accurate Mean Field Void Bias Factors for Radiation Swelling Calculations

A fast numerical approximation is introduced for the interaction of vacancies and interstitials with a spherical cavity in an isotropic elastic medium. The image interaction is evaluated from a fit which is accurate and simple enough to obtain bias factors for rate theories of radiation swelling by direct numerical integration.     

The Dislocation Bias

Bias factors for dislocations quantify the preferential diffusion of self-interstitials relative to the diffusion of vacancies to dislocations. These parameters are essential for rate theory computer codes that model nucleation and growth of voids, helium bubbles, dislocation loops, and the evolution of microstructures in materials subject to high dose irradiations. Compact formulae for these factors are derived and the accuracy of several approximations is explored.