The study on the fracture of multiple flaw specimens

The fracturing processes of a rock-model material with three and sixteen flaws are investigated in uniaxial compression. From the tests, wing and secondary cracks are observed. Wing cracks are tensile cracks that initiate at or near the tips of the flaw and propagate in a stable manner towards the direction of maximum compression. Secondary cracks are shear cracks that initiate from the tips of the flaw; they initially propagate in a stable manner but may become unstable near coalescence. From the tests two different types of secondary cracks are observed: quasi-coplanar and oblique secondary cracks. Oblique secondary cracks are a new type of secondary crack observed in this study. Quasi-coplanar secondary cracks initiate and propagate along a direction parallel or quasi-parallel to the plane of the flaws. Oblique secondary cracks initiate and propagate at an angle with the flaws, in the opposite direction of initiation of the wing crack. The geometry of the flaws determines the stress at which wing and secondary cracks occur. Wing and secondary cracks initiate at higher stresses with higher flaw angles, overlapping ratios and spacing. In three flaw specimens, initiation of the cracks occurs at lower stress in left-stepping than in right stepping geometries. A total of nine different types of coalescence are observed in the three flaw specimens, and four different types in the sixteen flaw specimens. In sixteen flaw specimens, columnar coalescence types are generally predominant. A strong correlation is observed between flaw geometry and type of coalescence, which applies to specimens with two, three, and sixteen flaws. Micro-observations of wing and secondary cracks can be used to distinguish tensile and shear cracks. Tensile cracks are characterized by a narrower damage area (about 10 to 20 μm) than shear cracks (about 100 μm), propagation along the boundary of crystals and across crystals, and unbroken crystals on the surface of the cracks. The characteristics of shear cracks are wider damage area, separation of grains and crystals around the pores, generation of columns by microtensile cracks at an angle with the direction of shearing, breakage of such columns and formation of angular crystals with further shearing, and discontinuous contact between the crack surface due to dilation

Combined effects of ultrasound and surfactants to reduce Bacillus cereus spores on lettuce and carrots

This study was performed to compare the effectiveness of ultrasound treatment singly and in combination with surfactants as an alternative method to conventional sanitizers containing chlorine for reducing numbers of Bacillus cereus spores on fresh produce. A cocktail of three strains of B. cereus (10876, ATCC 13061, and W-1) spores was inoculated onto iceberg lettuce and then treated with ultrasound for 0, 5, 10, 20 and 60 min. Five minutes was foudn to be an adequate ultrasound (40 kHz, 20W/L) treatment time which also caused no damage to lettuce leaf surfaces as observed thorugh a field-emission scanning electron microscope (FE-SEM). Iceberg lettuce and carrots were inoculated with a cocktail of three stains of B. cereus spores and treated with combinations of ultrasound and various concentrations (0.03 to 0.3%) of surfactants (Tween 20, 40, 60, 80 and Span 20, 80, 85) solutions for 5 min. The efficacy of the combination of ultrasound and surfactant increased depending on the hydrophile-lipophile balance (HLB). The most effective treatment for reducing levels of B. cereus spores was the combination of ultrasound and 0.1% Tween 20, yielding reductions of 2.49 and 2.22 log CFU/g on lettuce and carrots, respectively, without causing deterioration of quality. These reductions were 1 log greater than those obtained by immersion in 200 ppm chlorine for 5 min. Further research for elimination of B. cereus spores involving study of spore adhesion and removal mechanisms from food surfaces is needed, as well as devising an industrial-scale ultrasound system for the food industry.OAIID:oai:osos.snu.ac.kr:snu2013-01/102/0000047059/1SEQ:1PERF_CD:SNU2013-01EVAL_ITEM_CD:102USER_ID:0000047059ADJUST_YN:NEMP_ID:A077087DEPT_CD:5321CITE_RATE:3.327FILENAME:13-01-Int J Food Microbiol 160(3).pdfDEPT_NM:농생명공학부EMAIL:[email protected]_YN:YCONFIRM:

Genetic Characterization and Pathogenesis of H5N1 High Pathogenicity Avian Influenza Virus Isolated in South Korea during 2021–2022

High pathogenicity avian influenza (HPAI) viruses of clade 2.3.4.4 H5Nx have been circulating in poultry and wild birds worldwide since 2014. In South Korea, after the first clade 2.3.4.4b H5N1 HPAI viruses were isolated from wild birds in October 2021, additional HPAIV outbreaks occurred in poultry farms until April 2022. In this study, we genetically characterized clade 2.3.4.4b H5N1 HPAIV isolates in 2021–2022 and examined the pathogenicity and transmissibility of A/mandarin duck/Korea/WA585/2021 (H5N1) (WA585/21) in chickens and ducks. Clade 2.3.4.4b H5N1 HPAI viruses caused 47 outbreaks in poultry farms and were also detected in multiple wild birds. Phylogenetic analysis of HA and NA genes indicated that Korean H5N1 HPAI isolates were closely related to Eurasian viruses isolated in 2021–2022. Four distinct genotypes of H5N1 HPAI viruses were identified in poultry, and the majority were also found in wild birds. WA585/21 inoculated chickens showed virulent pathogenicity with high mortality and transmission. Meanwhile, ducks infected with the virus showed no mortality but exhibited high rates of transmission and longer viral shedding than chickens, suggesting that they may play an important role as silent carriers. In conclusion, consideration of both genetic and pathogenic traits of H5N1 HPAI viruses is required for effective viral control

Analytic model of S/D series resistance in trigate finfets with polygonal epitaxy

In this paper, a simple but accurate model is presented to analyze source/drain (S/D) series resistance in trigate fin field-effect transistors, particularly on triangular or pentagonal rather than rectangular epitaxy. The model includes the contribution of spreading, sheet, and contact resistances. Although the spreading and sheet resistances are evaluated modifying standard models, the contact resistance is newly modeled using equivalent models of lossy transmission lines and transformations of 3-D to 2-D geometry. Compared with series resistance extracted from 3-D numerical simulations, the model shows excellent agreement, even when the S/D geometry, silicide contact resistivity, and S/D doping concentration are varied. We find that the series resistance is influenced more by contact surface area than by carrier path from the S/D extension to the silicide contact. To meet the series resistance targeted in the semiconductor roadmap, both materials and geometry will need to be optimized, i.e., lowering the silicide contact resistivity and keeping high doping concentration as well as maximizing the contact surface area, respectively.X111312sciescopu