Dislocation Structure in Deformed Fe-35%Ni Invar Alloy Single Crystals(Metallurgy)

Dislocation structures of Fe-35%Ni invar alloy single crystals deformed at room temperature have been observed by transmission electron microscopy. The peculiar characteristics of dislocation structures are as follows : 1) most of the residual dislocations after plastic deformation are cusped screw ones in the early stage of deformation and increase in edge components with increasing strain, 2) dislocation loops exist with high density, distributed homogeneously and form weak obstacles against other dislocation motion, 3) a dislocation accumulation is observed, but does not tangle heavily. It is shown that these experimental results can be explained by the invar properties of these alloys

Exchange Effects in the Invar Hardening: Fe0.65Ni0.35Fe_{0.65}Ni_{0.35} as a test case

An increase of the critical resolved shear stress of Invar alloys (Invar hardening) with a lowering temperature is explained. The effect is caused by a growth of the exchange interaction between dangling $d$-electron states of dislocation cores and paramagnetic obstacles (e.g., Ni atoms in FeNi alloys) which occurs below the Curie temperature. The spins of the two electrons align along the magnetization due to the exchange interaction with the surrounding atoms of the ferromagnetic. The exchange interaction between the dislocations and obstacles is enhanced in Invars due to a strong growth of the magnetic moments of atoms under the action of elastic strains near the dislocation cores. Parameters characterizing the exchange interaction are determined for the case of the Fe$_{0.65}$Ni$_{0.35}$ Invar. The influence of the internal magnetic field on the dislocation detachment from the obstacles is taken into account. The obtained temperature dependence of the critical resolved shear stress in the Fe$_{0.65}$Ni$_{0.35}$ Invar agrees well with the available experimental data. Experiments facilitating a further check of the theoretical model are suggested.Comment: 8 pages, 2 figure

Growth and Perfection of Nickel and Cobalt Single Crystals Using the Floating-Zone Method(Physics)

Using the floating-zone method, Ni and Co single crystals were grown under various experimental conditions. Detailed observations of low angle boundaries or striations and of the dislocation arrangements in the grown crystals were carried out using an optical microscope. Ni single crystals grew preferentially along the direction and were striation-free. As the growth direction deviated from the , sharp striations were formed. The dislocation density in the crystals was about 10^6 cm^, which were distributed at random. Co single crystals grew along the direction and were also striation-free. As the growth direction deviated from the , many striations were formed with more complex shapes. These experimental results are discussed on the basis of the growth mechanism of crystals and of dislocation behaviour during the solidification process

In Silico Screening Based on Predictive Algorithms as a Design Tool for Exon Skipping Oligonucleotides in Duchenne Muscular Dystrophy

The use of antisense 'splice-switching' oligonucleotides to induce exon skipping represents a potential therapeutic approach to various human genetic diseases. It has achieved greatest maturity in exon skipping of the dystrophin transcript in Duchenne muscular dystrophy (DMD), for which several clinical trials are completed or ongoing, and a large body of data exists describing tested oligonucleotides and their efficacy. The rational design of an exon skipping oligonucleotide involves the choice of an antisense sequence, usually between 15 and 32 nucleotides, targeting the exon that is to be skipped. Although parameters describing the target site can be computationally estimated and several have been identified to correlate with efficacy, methods to predict efficacy are limited. Here, an in silico pre-screening approach is proposed, based on predictive statistical modelling. Previous DMD data were compiled together and, for each oligonucleotide, some 60 descriptors were considered. Statistical modelling approaches were applied to derive algorithms that predict exon skipping for a given target site. We confirmed (1) the binding energetics of the oligonucleotide to the RNA, and (2) the distance in bases of the target site from the splice acceptor site, as the two most predictive parameters, and we included these and several other parameters (while discounting many) into an in silico screening process, based on their capacity to predict high or low efficacy in either phosphorodiamidate morpholino oligomers (89% correctly predicted) and/or 2'O Methyl RNA oligonucleotides (76% correctly predicted). Predictions correlated strongly with in vitro testing for sixteen de novo PMO sequences targeting various positions on DMD exons 44 (R² 0.89) and 53 (R² 0.89), one of which represents a potential novel candidate for clinical trials. We provide these algorithms together with a computational tool that facilitates screening to predict exon skipping efficacy at each position of a target exon

Genetic Diversity, Morphological Uniformity and Polyketide Production in Dinoflagellates (Amphidinium, Dinoflagellata)

Dinoflagellates are an intriguing group of eukaryotes, showing many unusual morphological and genetic features. Some groups of dinoflagellates are morphologically highly uniform, despite indications of genetic diversity. The species Amphidinium carterae is abundant and cosmopolitan in marine environments, grows easily in culture, and has therefore been used as a ‘model’ dinoflagellate in research into dinoflagellate genetics, polyketide production and photosynthesis. We have investigated the diversity of ‘cryptic’ species of Amphidinium that are morphologically similar to A. carterae, including the very similar species Amphidinium massartii, based on light and electron microscopy, two nuclear gene regions (LSU rDNA and ITS rDNA) and one mitochondrial gene region (cytochrome b). We found that six genetically distinct cryptic species (clades) exist within the species A. massartii and four within A. carterae, and that these clades differ from one another in molecular sequences at levels comparable to other dinoflagellate species, genera or even families. Using primers based on an alignment of alveolate ketosynthase sequences, we isolated partial ketosynthase genes from several Amphidinium species. We compared these genes to known dinoflagellate ketosynthase genes and investigated the evolution and diversity of the strains of Amphidinium that produce them

Dislocation Motion in Antiferromagnetic γ-Fe-Mn Alloys

The plastic deformation of γ-Fe-Mn alloys has been investigated by tensile and stress relaxation tests and transmission electron microscopy. The flow stress increases below the Neel temperature and reaches about 1 kp/mm^2 at room temperature, but the activation volume and dislocation configuration do not change. This may be understood by the magnetic friction for dislocation motion in antiferromagnetic γ-Fe-Mn alloys, which is associated with the newly-produced ferromagnetic coupling at the nearest neighbour site rather than a change of the deformation process

Plastic Deformation of Iron-Nickel Invar Alloys

Plastic deformation of Fe-Ni invar alloys which have peculiar magnetic properties is studied by means of the tensile and stress relaxation tests. The plastic properties of these alloys in comparison with other face centred cubic alloys are characterized by the large temperature dependence of the flow stress, the straight dislocation configuration, and not having clearly defined three-stage hardening. These results reveal a contribution to the resistance to dislocation motion from the drag due to making the new region of the magnetization decrease around a dislocation