EFFECT OF REVERT RECYCLE TIMES ON MICROSTRUCTURE AND FATIGUE PROPERTIES IN COBALT-BASE SUPERALLOY K640S

Effect of revert cycles on microstructure and fatigue properties of cast cobalt base superalloy K640S has been investigated. The results show that: at 70 times of cool heat cycles, there were microcracks found in seven times revert and ten times revert. With the increasing of thermal fatigue cycles, the crack of revert grows a little faster than virgin. When the cycle time reaches 200, the crack length for both virgin and reverts have been as long as 2mm. The low cycle fatigue life has no remarkable change, with the increase of revert cycles at 815℃, 360MPa ,0 5Hz. With the times of cycles increasing, it is found that the content of impurity and gas in alloy change a little, and there is no obvious change for dendrite microstructure.

Construction and Genetic Analysis of Murine Hepatitis Virus Strain A59 Nsp16 Temperature Sensitive Mutant and the Revertant Virus

Coronaviruses (CoVs) are generally associated with respiratory and enteric infections and have long been recognized as important pathogens of livestock and companion animals. Mouse hepatitis virus (MHV) is a widely studied model system for Coronavirus replication and pathogenesis. In this study,we created a MHV-A59 temperature sensitive (ts) mutant Wu"-ts18(cd) using the recombinant vaccinia reverse genetics system. Virus replication assay in 17C1-1 cells showed the plaque phenotype and replication characterization of constructed Wu"-ts18(cd) were indistinguishable from the reported ts mutant Wu"-ts18. Then we cultured the ts mutant Wu"-ts18(cd) at non-permissive temperature 39.5°C,which "forced" the ts recombinant virus to use second-site mutation to revert from a ts to a non-ts phenotype. Sequence analysis showed most of the revertants had the same single amino acid mutation at Nsp16 position 43. The single amino acid mutation at Nsp16 position 76 or position 130 could also revert the ts mutant Wu"-ts18 (cd) to non-ts phenotype,an additional independent mutation in Nsp13 position 115 played an important role on plaque size. The results provided us with genetic information on the functional determinants of Nsp16. This allowed us to build up a more reasonable model of CoVs replication-transcription complex.

Gas-solid flow field numerical simulation of different feeding and returning formations of flue-gas circulating fluidized bed

3D Euler double-fluid model was applied and three different feedstocks and reverts formations were simulated. By calculating and analyzing the state of gas and solid fluxion in absorber using three different methods of the feedstocks and reverts in recirculating fluidized bed, described the behavior of gas and solid through the gas-phase velocity, turbulence intensity, gas-solid sliding velocity, and density of particles. The results show that the feedstocks and reverts enters into absorption tower through two symmetrical feedings and are mixed with flue gas. Based on the respective analysis of each model and the com- parison analysis of the three models, this paper drew conclusions. The turbulence intensity of absorption tower is high, gas-solid sliding speed is big, and granule concentration near the axis is high, which has advantages for desulfurization and im- proving the utilization rate of absorbent.

Microstructures and mechanical properties of the third generation automobile steels fabricated by ART-annealing

The mechanical properties dependence on the microstructure was reviewed and analyzed,and the ultrafine grained duplex microstructure of BCC matrix and large fractioned austenite was given as one of the optimum structures to develop the third generation steel with high strength and high ductility.The medium-Mn steels with different carbon contents processed by austenite reverted transformation(ART-annealing) were studied thoroughly to fabricate the ultrafine duplex steels with large fractioned austenite.The lamellar typed ultrafine structure,the granular typed ultrafine duplex structure and the corresponding mechanical properties of the medium-Mn steels processed by ART-annealing were demonstrated in this paper.It was revealed that the duplex structure with large fraction of austenite and ultrafine grain structure is capable of producing steels with excellent combination of strength and ductility,i.e.,Rm A about 30-50 GPa%,which is about two times of that of the conventional automobile steels and close to that of the TWIP steels.It was concluded that the ART-annealing of the medium-Mn steels would be at least one of the promising ways to fabricate the third generation automobile steels in the near future.

2.47 GPa grade ultra-strong 15Co-12Ni secondary hardening steel with superior ductility and fracture toughness

This study investigated the effect of multi-step heat treatment on the microstructure, mechanical properties and fracture behavior of thick 15 Co-12 Ni secondary hardening steel. As-quenched sample was found to have elongated prior austenite grain(PAG) and coarse lenticular martensitic structure. On the other hand, heat-treated sample was observed to have fine lenticular martensitic structure due to fine PAG size and a lot of nano-sized carbides. Also, after heat treatment, nano-scale reverted austenite film was formed at the martensite interfaces. The heat-treated sample showed 2.47 GPa superior tensile strength and superior elongation of about 12 %. The high strength was mainly due to fine block size and high number density of nano-sized carbides. The average value of plane strain fracture toughness(KIC) was 29.3 MPa m1/2, which indicated a good fracture toughness even with the high tensile strength. The tensile fracture surface was observed to have ductile fracture mode(cup-and-cone) and the formation of about ~1 μm ultra-fine dimples. In addition to this, nano-sized carbides were observed within the dimples.The findings suggested that the nano-sized carbide had a positive effect not only on the strength but also on the ductility of the alloy. The fractured surface after toughness test, also showed ductile fracture mode with a lot of dimples. Based on the above results, correlation among microstructural evolution,deformation and fracture mechanisms along the heat-treatment was also discussed.

政治词语 词语政治——一个赛义德后殖民主义个案研究

西方批评理论是对西方社会现实的直接反应 ,关注的是不同文化交汇时弱势群体和强势权威的意识形态冲突。本文就中西媒体在香港“回归”问题上所进行的意识形态交锋 ,用赛义德后殖民主义理论分析了“revert”一词中隐含的殖民主义意义“痕迹” ,揭示出这个词里包含的东方主义者对东方人的殖民心态。通过这个赛义德后殖民主义个案研究 ,本文指出 ,在经济一体化、资本全球化的今天 ,不同文化间的冲撞有时将会十分激烈 ,在文化上消除西方殖民主义的影响、确保我们的文化身份不被曲解 ,将是一个漫长的过程 ,因此我们的文学批评理论应当和文化交流中的社会现实紧密地联系在一起 ,使理论研究担负起更大的历史责任。

Phase Transformation and Its Effect on Mechanical Properties of C300 Weld Metal after Aging Treatment at Different Temperatures

The influence of aging temperature on phase transformation and mechanical properties of weld metal of maraging steel （grade C300） was studied. Microstructure was analyzed by means of optical microscopy, transmission e leetron microscopy, scanning electron microscopy and energy dispersive spectrum analysis. Gibbs free energy of Nia Ti and Fez Mo at different temperature was calculated by Thermal-calc software. The microstructure of weld metal in as- welded state is martensite. The yield strength of weld metal after 430 ℃ aging process may increase to 1561 MPa from 890 MPa in as-welded state, which is ascribed to the formation of spinodal constitute and GP zones. After 480 ℃ aging process, there are great deal of NiaTi precipitates in the martensite matrix and 10% reverted austenite phase in the cellular grain boundary, and the yield strength increases to 1 801 MPa. After aging process at 580 ℃ , there are many Fe2 Mo precipitates in the martensite matrix and 30%o reverted austenite phase in the cellular grain boundary, and the yield strength is 1329 MPa, which ls the lowest among the three cases. The phase transformation may also influence the toughness. It is found that precipitates make the toughness decrease and reverted austenite increases it. The mechanism of phase transformation on strength and toughness is discussed.

Joint effects of heavy metal binary mixtures on seed germination,root and shoot growth,bacterial bioluminescence,and gene mutation

This investigation was to assess the joint effects of metal binary mixtures on seed germination,root and shoot growth,bacterial bioluminescence,and gene mutation based on the one toxic unit（1 TU）approach.Different sensitivities and orders of toxicity of metal mixtures were observed among the bioassays.In general,mostly additive or antagonistic effects were observed,while almost no synergistic effects by the binary metal mixtures in all bioassays.Therefore,the combined effects of heavy metals in the different bioassays were difficult to generalize since they were dependent on both chemical type and the organism used in each bioassay.However, these results indicate that a battery of bioassays with mixture chemicals as opposed to just a single assay with single metal is a better strategy for the bioassessment of environmental pollutants.

A NOTE ON CONSTRUCTION OF HIGHER-ORDERSYMPLECTIC SCHEMES FROM LOWER-ORDER ONE VIAFORMAL ENERGIES

In this paper, we will prove by the help of formal energies only that one can improve the order of any symplectic scheme by modifying the Hamiltonian symbol H, and show through examples that this action exactly and directly simplifies Feng's way of construction of higher-order symplectic schemes by using higher-order terms of generating functions.

Systematic and efficient GMPLS-based recovery mechanism with soft-protection using enhanced LMP

generalized multi-protocol label switching （GMPLS- based） protection and restoration technologies will play significant role in next-generation broadband IP network to ensure the survivability. In this article, a systematic GMPLS-based recovery mechanism is proposed using enhanced link management protocol （LMP）, which can support bidirectional fault notification relay more effectively. The major contributions and propositions in this article involve： 1） Soft-protection configuration for higher resource utilization with optimized routing; 2） Intelligent Shift from protection manner to restoration manner for the reduction of recovery latency; and 3） Toggleable revertive mode to increase restoration flexibility and to reduce loss of stability. Additionally, by leveraging valuable legacy including shared risk link group （SRLG） processing and fast reroute technique, the proposed recovery mechanism achieves higher resource utilization, fast and robust operation, satisfactory stability and flexibility, and is convenient in the apphcation over heterogeneous transport networks.

Optimal Rotation Age of Larix kaempferi Pulpwood Plantation by Real Options Approach

The economic benefits and optimal rotation age of Larix kaempferi pulpwood plantation were analyzed under stochastic pulpwood price using real options approach in order to more effectively management to L.kaempferi pulpwood plantation in northern sub-tropical alpine area.Flexible rotation age and threshold price to different stand age of different site index plantation were developed.The result indicated that:1) the optimal rotation age of L.kaempferi plantation in site index 15,17,19,21 was 25,23,21 and 19 a,respectively,as the current pulpwood price equals 500 yuan·m-3,and the shortest rotation age was 23,20,17 and 15 a when facing to better price;and 2) Wait option should be the optimum strategy in any pulpwood price level when the stand age is lower than the shortest rotation age.

一分为二看待美国教授的观点

拜读倪家耀教授大作“类析汉译英常见拙译”(《科技英语学习》2002.2期),受益匪浅。倪教授把中国学生的译文交给美国教授修改,然后把原译与改译相比较、分析,中国人汉译英的常见错误就一目了然了,这对汉译英教学有重大的指导意义。读完该文后,笔者一方面感觉收获很大,另一方面感觉美国教授也有打盹的时候。例如该文的第六部分“汉语式英语”中。

Tax evasion and debt in a dynamic general equilibrium model

The literature has long analysed optimal taxation policies in economies where tax evasion is widespread.Nevertheless,very little has been produced on the relationship between public debt,tax evasion,and long-term economic growth.In this article,we investigate the relationship between sovereign debt sustainability and tax evasion by computing under which conditions the debt/GDP ratio is endogenously mean reverting in the context where tax evasion may increase the public debt and public expenditure is used to finance public and merit goods.For a log utility consumer,the level of tax evasion has no effect on the mean reverting conditions while the same is not true for more general functional forms.Finally,we conclude that allowing for tax evasion is not a suitable policy to make the debt/GDP ratio stable over time,especially in low-growth economies.