Effect of grain size on slow fatigue crack propagation and plastic deformation near crack tip

Fatigue crack growth and its threshold are investigated at a stress ratio of 0.5 for the three-point bend specimen made of Austenitic stainless steel. The effect of grain size on the crack tip plastic deformation is investigated. The results show that the threshold value Δkth increases linearly with the square root of grain size d and the growth rate is slower for materials with larger grain size. The plastic zone size and ratio for different grain sizes are different at the threshold. The maximum stress intensity factor is kmax and σys is the yield strength. At the same time, the characteristics of the plastic deformation development is discontinuous and anti-symmetric as the growth rate is increased from 2·10—8 to 10−7 mm/cycle.

Splitting the fast and slow motions in molecular dynamics simulations based on the change of cold potential well bottom

Abstract. The atomic motion is coupled by the fast and slow components due to the high frequency vibration of atoms and the low frequency deformation of atomic lattice, respectively. A two-step approximate method was presented to determine the atomic slow motion. The first step is based on the change of the location of the cold potential well bottom and the second step is based on the average of the appropriate slow velocities of the surrounding atoms. The simple tensions of one-dimensional atoms and two-dimensional atoms were performed with the full molecular dynamics simulations. The conjugate gradient method was employed to determine the corresponding location of cold potential well bottom. Results show that our two-step approximate method is appropriate to determine the atomic slow motion under the low strain rate loading. This splitting method may be helpful to develop more efficient molecular modeling methods and simulations pertinent to realistic loading conditions of materials.

Ultra-slow atomic beam generation by velocity selective resonance

We describe a method to generate an ultra-slow atomic beam by velocity selective resonance (VSR). A VSR experiment on a metastable helium beam in a magnetic field is presented and the results show that the transverse velocity of the defected beam can be cooled and precisely controlled to less than the recoil velocity, depending on the magnitude of the magnetic field. We extend this idea to a cold atomic cloud to produce an ultra-slow Rb-87 beam that can be used as a source of an atomic fountain clock or a space clock.

Protein polymorphism and genetic divergence in slow loris (Genus nycticebus)

In this study, protein electrophoresis was assayed to detect genetic variation in Genus Nycticebus. A total of 29 samples (2 N. coucang and 27 N. pygmaeus) were analyzed for 42 genetic loci. In the 27 samples of N. pygmaeus, 4 loci were observed to be polymorphic. Therefore, the estimated P value (proportion of polymorphic loci) is 0.095, the A value (average number of alleles each locus) is 1.045, and the H value (mean individual heterozygosity) is 0.040. After comparing the H of N. pygmaeus with those of other primates reported, we found that the protein variation in N. pygmaeus is slightly lower than the average level. Additionally, we also observed obvious allele difference between N. pygmaeus and N. coucang. There are no shared alleles between these two species in eight loci. The NEI's genetic distance between them was calculated as 0.2541, which falls in the spectrum of genetic difference between species in primates.

Molecular Phylogeny of Slow Lorises ( Nycticebus) Revealed by D2loop Sequences and Complete Cytochrome bGene Sequences of Mitochondrial DNA

本研究测定了懒猴属( Nycticebus) D 环的部分序列和细胞色素b 基因的全序列(1 140 bp) , 分析了 该属物种之间的系统发育进化关系。在DNA 水平上, 序列分析结果一致地提供了新的分类学证据: 支持Rata2 jszczak 和Groves 的观点, 即N1intermedus 只是N1 pygmaeus 的成体(Ratajszczak , 1998 ; Groves , 1971) 。对两种 序列的数据做了联合及个别分析, 获得相似的系统树, 支持懒猴属由两个单系群组成: 第一群由N1 pygmaeus 聚成, 第二群由N1coucang 聚成。该结果也提供了新的分子遗传证据, 支持懒猴属由N1coucang 和 N1 pygmaeus 两物种组成。

PHYLOGENY OF THE SLOW LORISES (GENUS NYCTICEBUS) - AN APPROACH USING MITOCHONDRIAL-DNA RESTRICTION ENZYME ANALYSIS

Mitochondrial DNA polymorphisms in 15 specimens of three species of slow lorises-Nycticebus coucang, N. intermedius, and N. pygmaeus-were analyzed in order to study the evolutionary relationships among the species. Eight restriction types were observed in the samples. Phylogenetic trees constructed on the basis of genetic distances showed that the slow lorises sort into two clusters: four types of N. coucang and three types of N. intermedius plus one type of N. pygmaeus. Our results suggest that there are two valid species in the genus Nycticebus-N. coucang and N. pygmaeus-and that N. intermedius should be included within N. pygmaeus. Divergence between the two species may have begun 2.7 Ma (million years ago). Evolution of gross morphology, chromosomes, and mitochondrial DNA in the slow lorises appears to be concordant.

Molecular evolution of GH in primates: characterisation of the GH genes from slow loris and marmoset defines an episode of rapid evolutionary change

Pituitary growth hormone (GH), like several other protein hormones, shows an unusual episodic pattern of molecular evolution in which sustained bursts of rapid change are imposed on long periods of very slow evolution (near-stasis). A marked period of rap

Cryopreservation of Kunming mouse oocytes using slow cooling, ultrarapid cooling and vitrification protocols

The cryopreservation of oocytes has been only marginally successful with any of the current protocols, including slow cooling, rapid cooling and vitrification. We wished to test the hypothesis that oocytes from a single mouse strain would freeze successfully by 1 of the 3 mentioned protocols. Unfertilized Kunming mouse oocytes obtained 14 h after PMSG/hCG administration were randomly assigned to be cryopreserved after slow cooling, ultra rapid cooling and vitrification. Oocytes were thawed by straws being placed into 37 degrees C water, and their morphological appearance and in vitro fertilization capability were compared with that of oocytes that had not undergone cryopreservation. Survival of oocytes was indicated by the absence of darkened ooplasm or by broken membranes or zona pellucida. Functional integrity was evaluated by the formation of a 2-cell embryo after IVF. Survival rate of slow cooled oocytes did not differ from that seen in vitrified oocytes (55.1 vs 65.9%) but was significantly lower in the rapidly cooled oocytes (24.2%; P<0.01). The results of NF of slow cooled and vitrified oocytes were similar to those of the control group (72 and 73 vs 77%; P>0.05). It appears that Kunming mouse oocytes can be successfully cryopreserved using the slow cooling method with 1,2-propanediol and vitrification, which contains both permeating and nonpermeating cryoprotectants. (C) 1997 by Elsevier Science Inc.

High transmission of slow light in the photonic crystal waveguide bends

We present the research on the transmission characteristic of slow-light-mode in the photonic crystal line-defect waveguide bends on SOL After optimizing the structure parameters in the vicinity of the bends, the normalized transmission efficiency of slow-light-mode through the photonic crystal 60 degree and 120 degree waveguide bends are as high as 80% and 60% respectively, which are 10 times higher than that in the undeformed case. To slow down light further, we design novel coupled cavity waveguide bend structures with high quality-factor. High normalized transmission efficiency of 75% and low group velocity of c/170 ( c is the light velocity in vacuum) are realized. These results are beneficial to enhance the slow light effect of photonic crystal structures and improve the miniaturization and integration of photonic crystal slow light devices.

Slow wave effect of 2-D photonic crystal coupled cavity array

We designed a two-dimensional coupled photonic crystal resonator array with hexagonal lattice. The calculation by plane-wave-expansion method shows that the dispersion curve of coupled cavity modes in the bandgap are much flattened in all directions in the reciprocal space. We simulated the transmission spectra of transverse electric (TE) wave along the Gamma K direction. Compared with the PC single cavity structure, the transmission ratio of the coupled cavity array increases more than three orders of magnitude, while the group velocity decreases to below 1/10, reaching 0.007c. The slow wave effect has potential application in the field of miniaturized tunable optical delay components and low-threshold photonic crystal lasers.

Defects around self-organized InAs quantum dots measured by slow positron beam

Self-organized InAs quantum dots (QDs) have been fabricated by molecular beam epitaxy. The authors try to use a slow positron beam to detect defects in and around self-organized QDs, and point defects are observed in GaAs cap layer above QDs. For the self-organized InAs QDs without strain-reducing layer, it is free of defects. However, by introducing a strain-reducing layer, the density of point defects around larger sized InAs QDs increased. The above results suggest that low energy positron beam measurements may be a good approach to detect depth profiles of defects in QD materials. (c) 2007 American Institute of Physics.

Slow light at terahertz frequencies in surface plasmon polariton assisted grating waveguide

National Natural Science Foundation of China 60677045 60876049