Influence of Processing Conditions on Microstructure and Mechanical Properties of Large Thin-Wall Centrifugal Ti–6Al–4V Casting

In this work,the effects of mould pre-heating temperatures and hot isostatic pressing(HIPping)process on the microstructural characteristics and mechanical properties,including static tensile and damagetolerance properties of large thin-wall cylindrical Ti–6Al–4V casting,have been studied.The experimental results show that with the increasing mould pre-heating temperature from 673 to 873 K,the casting microstructures change from a mixture of Widmanst?tten and colony microstructure to a primary colony.The centre of the thick wall section has relatively coarse microstructure than the edge and thin section.Lower mould pre-heating temperature brings about more porosities.HIPping process,which not only reduces the casting pores effectively but also increases the priorβgrain boundary cohesion and coarsens the microstructure,is essential to improving the ductility of the casting.Due to the oxygen contamination and finer microstructure on the surface,micro-hardness profiles on the cross section present a decreasing tendency from the surface to inner.The thickness of the reaction layers for the different mould pre-heating temperatures is nearly the same(~450μm).On the whole,the tensile strength and microhardness decrease with increasing mould pre-heating temperature from 673 to 873 K.However,the fracture toughness and fatigue crack growth resistance of the castings increase with increasing mould preheating temperature.     

Improved results on the probabilistic theory of the joint linear complexity of multisequences

We improve previous results on the asymptotic behavior and the expected value of the joint linear complexity of random multisequences over finite fields.These results are of interest for word-based stream ciphers in cryptology.     

Unnormalized and normalized forms of gefura measures in directed and undirected networks

In some networks nodes belong to predefined groups(e.g.,authors belong to institutions).Common network centrality measures do not take this structure into account.Gefura measures are designed as indicators of a node’s brokerage role between such groups.They are defined as variants of betweenness centrality and consider to what extent a node belongs to shortest paths between nodes from different groups.In this article we make the following new contributions to their study:(1) We systematically study unnormalized gefura measures and show that,next to the ‘structural’ normalization that has hitherto been applied,a ‘basic’ normalization procedure is possible.While the former normalizes at the level of groups,the latter normalizes at the level of nodes.(2) Treating undirected networks as equivalent to symmetric directed networks,we expand the definition of gefura measures to the directed case.(3) It is shown how Brandes’ algorithm for betweenness centrality can be adjusted to cover these cases.     

Sensitivity of simulated short-range high-temperature weather to land surface schemes by WRF

The simulations of a heat wave occurring in southern Yangtze-Huaihe valley and southern China during late July,2003 were conducted to examine the sensitivity of simulated surface air temperature(SAT) to different land surface schemes(LSSs) using the Weather Research and Forecasting Model(WRF) Version 2.2 in the short-range mode for 24-h integrations.Initial and boundary conditions employed a National Centers for Environmental Prediction(NCEP) analysis.The results showed that,overall,simulated high-temperatu...     

Spatio-temporal framework of tectonic uplift stages of the Tibetan Plateau in Cenozoic

Four intensive uplift periods, i.e., 60–35, 25–17 and 12–8 Ma (but 18–13 Ma in the Himalayas of the southern Tibet), and since about 5 Ma, can be determined on the Tibetan Plateau by synthetical analysis of low-temperature thermo-chronology data, sedimentary deposit records, and structural deformation records of different areas. The strong tectonic uplift periods in different areas on the Tibetan Plateau are penecontemporaneous, except for the Himalayan area of the southern Tibet, where a rapid uplift and e...     

East Asian-North Indian Ocean thermal contrast and variation in the East Asian summer monsoon for the past 2650 years

Using observational data,the East Asian-North Indian Ocean index(IEANI),which reflects a tropospheric thermal contrast,is found to correlate well with the East Asian summer monsoon(EASM) and associated rainfall over eastern China.Corresponding to a higher(lower) IEANI,the EASM at mid-latitudes is stronger(weaker),and there is more(less) rainfall in North China and less(more) rainfall near the Yangtze River valley.To investigate long-term variation in the EASM,we reconstructed the BC 665-AD 1985 IEANI based ...     

Genomics,metagenomics,and microbial oceanography—A sea of opportunities

Microbial oceanography is an emerging discipline resulted from the interaction,cross-fertilization and integration of life science and ocean science.Microbial oceanography integrates the principles of marine microbiology,microbial ecology and oceanography to study the role of microorganisms in the biogeochemical dynamics of natural marine ecosystems.The application of genomics tools to study marine microbes is resulting in rapid advancements in microbial oceanography that has important implications in globa...     

Bi对AZ80镁合金凝固行为及显微组织的影响

采用加热-激冷方法和OM,SEM,XRD,DSC等分析手段,研究了AZ80-Bi镁合金的凝固行为,分析了合金的凝固组织特征及其演变过程,阐明了合金的凝固序列.AZ80-2%Bi(质量分数)合金的铸态显微组织由α-Mg,β-Mg17Al12和Mg3Bi2相组成,其中Mg3Bi2相以片状和颗粒状两种形态存在.将2%Bi加入...     

硼酸缓冲溶液中pH值和腐蚀产物对低碳钢活化/钝化敏感性的影响

研究了在pH值分别为8,9和10的除氧硼酸缓冲溶液中,低碳钢腐蚀产物对其活化/钝化敏感性的影响.实验结果表明,在pH值为8时,低碳钢一直处于活性溶解状态,不受腐蚀产物影响;在pH值为9和10时,表面腐蚀产物使低碳钢钝化,其腐蚀电位最后稳定于钝化区间.XPS和XRD等分析结果表明,腐蚀产物由FeB(OH)12B4O7和γ...