Radiation tolerance of nanocrystalline ceramics: insights from Yttria Stabilized Zirconia.

Materials for applications in hostile environments, such as nuclear reactors or radioactive waste immobilization, require extremely high resistance to radiation damage, such as resistance to amorphization or volume swelling. Nanocrystalline materials have been reported to present exceptionally high radiation-tolerance to amorphization. In principle, grain boundaries that are prevalent in nanomaterials could act as sinks for point-defects, enhancing defect recombination. In this paper we present evidence for this mechanism in nanograined Yttria Stabilized Zirconia (YSZ), associated with the observation that the concentration of defects after irradiation using heavy ions (Kr(+), 400 keV) is inversely proportional to the grain size. HAADF images suggest the short migration distances in nanograined YSZ allow radiation induced interstitials to reach the grain boundaries on the irradiation time scale, leaving behind only vacancy clusters distributed within the grain. Because of the relatively low temperature of the irradiations and the fact that interstitials diffuse thermally more slowly than vacancies, this result indicates that the interstitials must reach the boundaries directly in the collision cascade, consistent with previous simulation results. Concomitant radiation-induced grain growth was observed which, as a consequence of the non-uniform implantation, caused cracking of the nano-samples induced by local stresses at the irradiated/non-irradiated interfaces

EFFECT OF SiC PARTICLE SIZE ON THE MATERIAL AND MECHANICAL PROPERTIES OF MULLITE BONDED SiC CERAMICS PROCESSED BY INFILTRATION TECHNIQUE

The influence of SiC particles size on the bonding phase content, microstructure, SiC oxidation degree, flexural strength, porosity and pore size distribution of mullitebonded porous SiC ceramics were studied and compared with oxidebonded porous SiC ceramics. The SEM morphologies and EDS elemental analysis results showed the presence of needle shaped crystals of mullite and fish scaled cristobalite in the bond phase. It was found that increase of SiC particle size effectively enhanced the porosity and decreased the strength. The porosity decreased as the size of SiC particles decreased from 36 vol. % at 99 μm to 25 vol. % at 4.47 μm. The oxidation degree of SiC was found to be reduced by infiltration of mullite precursor sol and enhanced with sintering temperature. Bimodal pore size distributions were obtained for mullite-bonded porous SiC ceramics and the average pore diameter varied in the range of 2 - 30 μm with variation of particle size

A Dual-Plasmid-Based CRISPR/Cas9-Mediated Strategy Enables Targeted Editing of pH Regulatory Gene pacC in a Clinical Isolate of Trichophyton rubrum

Trichophyton rubrum is the most prevalent causative agent responsible for 80–90% of all known superficial fungal infections in humans, worldwide. Limited available methods for genetic manipulations have been one of the major bottlenecks in understanding relevant molecular mechanisms of disease pathogenesis in T. rubrum. Here, a dual-plasmid-based CRISPR/Cas9 strategy to edit pH regulatory transcription factor, pacC, of a clinical isolate of T. rubrum by non-homologous end joining (NHEJ) repair is presented. A cas9–eGFP fusion that aids pre-screening of primary transformants through detection of GFP fluorescence is expressed from one plasmid while target-specific sgRNA from the other brings about mutagenesis of pacC with an overall efficiency of 33.8–37.3%. The mutants had reduced transcript levels of pacC at both acidic and alkaline pH with several morphological abnormalities. We believe this dual-plasmid-based CRISPR/Cas9 strategy will aid functional genomics studies, especially in non-lab-adapted clinical strains of T. rubrum

Effect of SiC particle size on the material and mechanical properties of mullite bonded SiC ceramics processed by infiltration technique

The influence of SiC particles size on the bonding phase content. microstructure. SiC oxidation degree, flexural strength, porosity and pore size distribution of mullitebonded porous SiC ceramics were studied and compared with oxide bonded porous SiC ceramics. The SEM morphologies and EDS elemental analysis results showed the presence of needle shaped crystals of mullite and fish scaled cristobalite in the bond phase. It was found that increase of SiC particle size effectively enhanced the porosity and decreased the strength. The porosity decreased as the size of SiC particles decreased from 36 vol. % at 99 mu m 10 25 vol. % at 4.47 mu m. The oxidation degree of SiC was found to be reduced by infiltration of mullite precursor sol and enhanced with sintering temperature. Bimodal pore size distributions were obtained for mullite-bonded porous SiC ceramics and the average pore diameter varied in the range of 2 - 30 mu m with variation of particle size

Heterochromatin extension: a possible cytogenetic fate of primary amenorrhea along with normal karyotype

Primary amenorrhoea (PA) is considered to be one of the challenging and taxing problems for the gynaecologist. Previous studies suggested that different numerical and structural chromosome abnormalities are associated with this. Heterochromatin polymorphisms are considered to be normal variant but considering the recent research on crucial cellular effects of heterochromatin, we have aimed to find out the prevalence of heteromorphism along with other standard chromosomal abnormalities. This was an observational study which was conducted in Diamond Harbour Govt. Medical College and Hospital, West Bengal during March 2019–February 2021. Clinical features of 178 patients were noted and peripheral venous blood was taken following informed consent. This comprehensive study reveals that there are 10.11% of the females among 178 females having a heterochromatin extension which is significantly high. We hence suggest that heteromorphism may be associated with ovarian dysfunction leading to amenorrhoea as the region of heterochromatin acts as a key part in chromosome structure, histone modification and gene regulation. Analysis at the molecular level may be needed to unveil any relationship between heteromorphism and PA. Impact Statement What is already known on this subject? Primary amenorrhoea (PA) is a menstrual abnormality found in females with the prevalence of 1–3%. It may be associated with different types of numerical and structural chromosomal anomalies. Among them Turner’s syndrome (pure and in variant form) is the commonest chromosomal aberration associated with PA. Some patients with PA are found to have a normal karyotype with heterochromatin extension on the large arm (q) of either chromosome 9 or chromosome 16. Chromosomal polymorphism with increase in heterochromatin region consists of highly repetitive sequences of satellite DNA, which normally does not encode any protein and thus considered to be a normal variant. What do the results of this study add? This comprehensive study reveals that there are 10.11% of the females among 178 females having a heterochromatin extension which is significantly high. PA and certain association of phenotypical stigmata like short stature in these patients with heterochromatin extension can be explained on the basis of histone modification and gene regulation by heterochromatin. What are the implications of these findings for clinical practice and/or further research? We will be able to know about involved transcription factors those are responsible for the histone modification directly linked to the heterochromatin extension by further molecular study. That will definitely help to find out the reason for PA as well as implementation of gene therapy in these cases

Thermodynamic Strengthening of Heterointerfaces in Nanoceramics

Thermodynamic Strengthening of Heterointerfaces in Nanoceramic