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排序方式: 共有260条查询结果,搜索用时 15 毫秒
1.
2.
Cdc7 kinase is essential for initiation of DNA replication. Cdc7(-/-) mouse embryonic stem (ES) cells are non-viable but their growth can be rescued by an ectopically expressed transgene (Cdc7(-/-)tg). Here we report that, despite the normal growth capability of Cdc7(-/-)tg ES cells, the mice with the identical genetic background exhibit growth retardation. Concomi tantly, Cdc7(-/-)tg embryonic fibroblasts (MEFs) display delayed S phase entry and slow S phase progression. Furthermore, spermatogenesis of Cdc7(-/-)tg mice is disrupted prior to pachytene stage of meiotic prophase I. The impairment in spermatogenesis correlates with the extremely low level of Cdc7 protein in testes, and is rescued by introducing an additional allele of transgene, which results in increase of Cdc7 expression. The increased level of Cdc7 also recovers the growth of Cdc7(-/-)tg MEFs and mice, indicating that the developmental abnormalities of Cdc7(-/-)tg mice are due to insufficiency of Cdc7 protein. Our results indicate the requirement of a critical level of a cell-cycle regulator for mouse development and provide genetic evidence that Cdc7 plays essential roles in meiotic processes in mammals. 相似文献
3.
K Blasko LV Schagina G Agner YA Kaulin JY Takemoto 《Canadian Metallurgical Quarterly》1998,1373(1):163-169
The syndrome of hypoparathyroidism associated with growth retardation, developmental delay, and dysmorphism (HRD) is a newly described, autosomal recessive, congenital disorder with severe, often fatal consequences. Since the syndrome is very rare, with all parents of affected individuals being consanguineous, it is presumed to be caused by homozygous inheritance of a single recessive mutation from a common ancestor. To localize the HRD gene, we performed a genomewide screen using DNA pooling and homozygosity mapping for apparently unlinked kindreds. Analysis of a panel of 359 highly polymorphic markers revealed linkage to D1S235. The maximum LOD score obtained was 4.11 at a recombination fraction of 0. Analysis of three additional markers-GGAA6F06, D1S2678, and D1S179-in a 2-cM interval around D1S235 resulted in LOD scores >3. Analysis of additional chromosome 1 markers revealed evidence of genetic linkage disequilibrium and place the HRD locus within an approximately 1-cM interval defined by D1S1540 and D1S2678 on chromosome 1q42-43. 相似文献
4.
Active 4-dodecanoyl-2-nitrophenyl esters of β-alanine, β-alanyl-β-alanine, and β-alanyl-β-alanyl-β-alanine were prepared, and tried to polymerize in various solvents. Nonpolar solvents were found to be convenient for the polycondensation reaction. The yield of the polycondensation was high for the monopeptide ester, and less for the dipeptide and tripeptide esters. The effect of temperature on the polycondensation reaction was also studied. 相似文献
5.
Satoru Sano Noriko Saito Shin-ichi Matsuda Naoki Ohashi Hajime Haneda You Arita Minoru Takemoto 《Journal of the American Ceramic Society》2006,89(2):568-574
Forsterite (Mg2 SiO4 ) ceramics were prepared using Mg(OH)2 and SiO2 as precursors, and the effect of powder characteristics of Mg(OH)2 on calcination and sintering was investigated. The use of highly dispersed Mg(OH)2 powder (HD powder) resulted in a lower calcination temperature. Forsterite powder of high homogeneity and small particle size prepared from the HD powder enabled synthesis of high-density forsterite ceramics by ordinary sintering without applying external pressure. Moreover, transparent forsterite ceramics were successfully synthesized through addition of excess Mg to the precursors to compensate for Mg evaporated during the sintering process. Subsequent dielectric measurements revealed that the transparent forsterite ceramics had a very low dielectric loss (tan δ<10−4 ). 相似文献
6.
To improve the corrosion resistance and to study the effect of yttrium in the behavior of coatings produced by thermal spraying MCrAlY (M=Ni, Co) powders, CO2 laser processing was conducted. Three methods were used: (1) a combination of gas flame and plasma spraying in air followed by laser glazing in argon, (2) low-pressure plasma spraying (LPPS) and laser glazing in argon, and (3) LPPS and laser-gas (O2) alloying. Laser glazing in argon of the MCrAlY coatings sprayed in air promoted formation of weakly adherent agglomerates of Al–Y oxides and an alumina-chromia solid solution. Glazing in argon atmosphere of LPPS CoNiCrAlY and NiCrAlY coatings caused the formation of nickel aluminides besides the formation of Y–Al compounds. Gas (O2)-alloying of these coatings produces continuous and adherent (yttrium-containing) alumina and chromia layers. The effects of yttrium on the characteristics of the oxides formed in the coatings during laser glazing, laser-gas alloying, and high-temperature oxidation is discussed. This work also investigated the oxidation resistance of the laser-processed MCrAlY coatings in air and in the presence of 85 mol/o V2O5–Na2SO4 fused salt at 900°C. 相似文献
7.
The proportion of non-conforming items has been traditionally utilised as an evaluation criterion for quality of items. However, the proportion of non-conforming items is not necessarily useful as a proper evaluation criterion for controlling high-quality manufacturing in recent years. Accordingly, in order to achieve further quality improvement and innovation, more careful quality evaluation has been required newly. Then, a concept of quality loss in the Taguchi methods has been devised as a severe criterion of quality evaluation. Hereby, a variable single sampling plan having desired operating characteristics (OCs) indexed by quality loss has been proposed in the area of statistical quality control. By the way, the most economical sampling inspection in the average sample number (ASN) is the sequential sampling plan based on the Wald’s sequential probability ratio test. Then, from the viewpoint of cost reduction, we discuss a variable sequential sampling plan having desired OC indexed by quality loss with the aim of expansion of the utility of variable sampling plan for quality loss. As the result, the design procedure of the sequential sampling plan for satisfying some required design conditions indexed by quality loss is provided. In addition, the effectiveness of the proposed sequential sampling plan is verified through some numerical examples. 相似文献
8.
A study on the kinetics and mechanism of the polymerization of acrylonitrile initiated by imidazole and 2-substituted imidazole-copper-(II) complexes was made in dimethyl sulfoxide solution at 40–70°C. The rate of polymerization, Rp, could be expressed as follows: The overall activation energies of these polymerization processes are in a range from 14.2 to 69.1 KJ mole-1. From the data of electronic spectra and electron paramagnetic resonance, it was confirmed that the polymerization in question could be initiated by free radicals which were formed by the reduction of copper-(II) complex to copper-(I) complex, and the latter formed a new complex with polyacrylonitrile resulted. 相似文献
9.
A new elastic wave (EW) or acoustic emission (AE) monitoring and signal processing system has been developed and used to elucidate
the fracture behavior of sprayed and laser-glazed ceramic coatings. The system measures the minute surface displacements excited
by the propagation of elastic waves. It enables elucidation of the fracture dynamics (fracture mode and kinetics) of stressed
coatings. The surface displacement at the sensor position was computed by the convolution integral of an assumed source wave
with the dynamic Green’s function until signals resembled the measured wave. This new signal processing method was used to
determine the fracture strength and dynamics of microcracks in sprayed and laser-glazed titania subjected to four-point bending.
It was found that mode II shear cracking along the interface between the coating and substrate occurred prior to mode I cleavage
cracking. The fracture strength of laser-glazed titania was higher than that of as-sprayed titania in most cases; however,
this depended on the coating structure. This article introduces the principle of source inversion processing of elastic waves,
the monitoring system, laser glazing of sprayed titania, and experimental work on the fracture behavior of titania coatings. 相似文献
10.