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The ignition and combustion behaviors of titanium aluminide (TiAl alloy) were studied by using laser oxygen concentration experimental method combined with ultra-high temperature infrared thermometer, high-speed camera in-situ observation, scanning electron microscopy and X-ray diffraction. The formation and movement laws of the molten body, types and structural characteristics during the combustion process were revealed, and the molten body mechanism was further explored. The results show that the critical conditions of laser power and oxgyen concentration for the ignition and sustained burning of TiAl alloy follow parabolic and parabolic+linear laws, respectively, which are significantly higher than those of near α high temperature titanium alloy, indicating the better flame retardant properties of TiAl alloy. The ignition temperature of TiAl alloy is higher than the melting point. During the ignition period, the partial melting of the matrix causes the transition of Al element from internal oxidation to external oxidation. The oxides formed during the sustained burning stage are characterized as Al2O3, Al2Ti7O15, Al2TiO5, and Al6Ti2O13 phases from the inner side to the burning surface. The continuous network Al2O3 layer formed in the fusion zone can hinder the movement of the melt. The Ti-Al-O ternary phase formed in the combustion zone can improve the stability of the Al2O3 protective layer by reducing the decomposition pressure of Al2O3, thus leading to the better flame retardant performance of TiAl alloy.

With the improvement of thrust-to-weight ratio and other properties of future aero-engine，the high temperature mechanical property and structural stability of titanium alloy components are required. The limitation of traditional experiments in time and space scale has become increasingly prominent，and it is difficult to deeply study the microscopic transient phenomena and mechanisms. Moreover，the molecular dynamics（MD）calculation method takes the atomic/molecular model as the calculation object，on the basis of Newton classical mechanics and empirical parameters，the calculation efficiency is greatly improved compared with the quantum calculation method. Therefore，MD has become an important method to optimize the process parameters and calculate the microstructure properties of aero-engine titanium alloy. Based on an overview of the basic principle of MD computing space and time scale advantages，this paper reviews the relevant domestic and foreign achievements in the study of molding，microstructure characterization and performance testing of aero-engine titanium alloys by MD method in recent years，as well as representative conclusions that contribute to the improvement of high temperature resistance of aero-engine titanium alloys. Finally，the future prospect is discussed based on the demand for MD computing technology for aircraft engine titanium alloys，thus pointing out the challenges faced on the following aspects，including high-throughput composition design based on MD computing method，training molecular force fields for mature titanium alloy systems，and introducing the new ReaxFF（Reactive Force Field）into the study of combustion mechanisms.

A versatile reactor system analysis code RESYS for advanced nuclear reactor was developed by using object-oriented language C++. Based on RESYS code, the model of thermionic nuclear reactor TOPAZ-Ⅱ developed in the former Soviet Union was established, and its start-up process was simulated. The established TOPAZ-Ⅱ reactor system model included reactor core thermal model, thermionic conversion system model and the radiator model. The current density model of cesium thermionic converter used model by Rasor. And the 6 groups of delayed neutron point reactor kinetic model was used to consider the influence of various structural components on reactivity. The point reactor equation with strong rigidity was solved using the Gear algorithm in the RESYS code. The reactivity feedback model of TOPAZ-Ⅱ reactor took into account the Doppler reactivity feedback of the fuel, the reactivity feedback of the electrodes, the reactivity feedback of the moderator and reflector, and the introduction of reactivity control drums. The steady state and start-up transient were simulated based on established thermal-hydraulic model and RESYS code. At steady state, the maximum temperature on the inner surface of the central thermionic fuel element is 2 291 K, the maximum temperature on the outer surface is 2 066.55 K, the maximum temperature on the emitter is 1 961 K, the maximum temperature difference between the electrodes is close to 1 200 K, the temperature at the coolant inlet is 743 K, and the temperature at the core outlet is 837 K. The comparison between the steady-state operating conditions calculated by the RESYS code and the TOPAZ-Ⅱ design values was carried out. The calculated steady-state electric power output is consistent with the calculation results of TITAM code. The calculation results verify the correctness of the developed RESYS code and the established TOPAZ-Ⅱ system model. During the startup process, the reactivity feedback of the moderator and reflection layer is positive feedback, which dominates all feedback effects. The overall reactivity feedback of the TOPAZ-Ⅱ reactor core is positive and does not have a self-stable negative feedback effect, which increases the difficulty of reactor control. During the start-up process of TFE, due to changes in the gas thermal conductivity of the electrode gap, the temperature of the fuel pellets and emitter rapidly increases. At this time, some of the thermal energy generated by fission is stored in the fuel pellets, causing a decrease in coolant temperature and the power of the radiation radiator.

In this work, the distribution and segregation behaviors of helium (He) and the effect of yttrium (Y) on these behaviors in the symmetrical tilt tungsten (W) Σ5(310)/[001] grain boundary (GB) region were studied using first-principles calculations. The results revealed that the GB has a significant impact on the behaviors of He in W. The solution and segregation energies of He in the W Σ5(310)/[001] GB region increase with increasing the distance from He to the GB and are inversely proportional to the effective electrons of He. The density of states analysis showed that the GB can suppress partial hybridization between He and W atoms. In addition, we find that the strengthening element Y facilitates the dissolution of He in the W GB region. [ABSTRACT FROM AUTHOR]

The rapid development of the Internet industry and the emergence of new business models have reshaped the spatial structure and spatial relationships of cities.The development of Internet enterprises has profoundly reshaped the established venture capital network by establishing investment departments and expanding the ecosystem in the form of venture capital.As venture capital and the Internet industry are mutually attractive and highly geographically coupled, the analysis of the structure and location of the venture capital network of Internet enterprises has become an important foundation for the development of the regional "new economy".This paper examined the spatial dynamics and location selection mechanism of venture capital activities of Chinese Internet companies by constructing a factor flow network, using spatial analysis, network analysis, and negative binomial regression models.The study demonstrated that venture capital investment in Chinese Internet enterprises has developed rapidly over the past 20 years in three phases: initial development from 2001 to 2012, rapid development from 2013 to 2016, and adjustment development from 2017 to 2019, with Internet venture capital showing the characteristics of cumulative development.Compared with traditional venture capital activities, the location choice of Internet venture capital is more concentrated, with a high concentration in a few major cities in the eastern region of China.The three major regions of Beijing-Tianjin-Hebei, Yangtze River Delta, and Pearl River Delta are the main places of occurrence and association of Internet venture capital activities in China, with a significant tendency of localization of venture capital.The cumulative development of corporate venture capital and the spatial evolution of both investors and financiers have contributed to the formation of a 'core-periphery' structure of the venture capital network.In addition, an assessment of the network density of the cities where the investment and financing occurs showed that the current Internet investment and financing network is still in its developmental stage, and most of the cities are not directly connected, showing a sparse matrix.Three time windows (2012, 2015, and 2017) were selected to analyze the location selection factors of Chinese Internet venture capital in different development periods in terms of enterprise growth environment, investment proximity, and transportation accessibility.The results showed that marketization, policy guidance, investment proximity, and spatial proximity were the main forces shaping the spatial pattern of Internet venture capital activities and had different degrees of influence on the various stages of Internet industry development.This study facilitates an in-depth examination of the spatial distribution characteristics of venture capital activities in the Internet economy and provides a detailed empirical basis for understanding the changes in venture capital investments in Internet enterprises and their locational influences.

The fuel assembly and fuel rod bundle of sodium-cooled fast reactor are arranged in a triangle form. The fuel assembly adopts closed structure deign without mixing of coolant between assemblies, which is cooled by the sodium coolant through the distribution header on the bottom of the core to accomplish the matching of coolant and nuclear power and flattening the outlet temperature of the reactor core. It is of great significance for the core design and flow distribution scheme to carry out the whole core pinbypin refinement power distribution and neutronicthermal coupling calculation. There are many internal components and complex structures in the pool type fast reactor container including the core, the internal shielding structure, the primary main pump, intermediate heat exchanger, independent heat exchanger and loading and unloading elevators which are arranged around the core. The design of neutron extraction channel in the direction of loading and unloading lifting devices leads to the asymmetry of the structure in the reactor container. It causes obvious anisotropic scattering in the process of neutron transport calculation, which is also a typical deep penetration problem, so more reliable and accurate calculation results require threedimensional calculation with the whole range of the reactor container. The above problems pose challenges to modeling and neutron transport calculation. The highperformance simulation system of sodiumcooled fast reactor adopts advanced modeling technology, largescale parallel computing technology, transportburnup coupling function, coreassemblylattice multilevel mapping and conversion technology to realize the full range threedimensional fine modeling and multiphysical coupling calculation, including the shielding calculation of the container of pool structure fast reactor, the deep penetration calculation of neutron transport of detectors outside the reactor, pinbypin refined power distribution calculation, transport burnup coupling calculation and full core neutronic-thermal sub-channel coupling calculation with the parallel computation scale, and reaches thousands of cores. Through CAD preprocessing modeling, mesh generation, highperformance calculation and visualization, the threedimensional calculation results of large pool type fast reactor can be given more comprehensively and finely, and a clearer physical image of the core or reactor container can be obtained. The comparison between the local key position and the existing calculation program verifies that the highperformance simulation system of fast reactor is reasonable and feasible which provides support for further reducing the conservative margin of design and local structure optimization.