摘要：The uniform experiment design is an effective way of optimizing technology scheme for refining the grain size during multistage deformation. In this paper, it is adopted to evaluate the effect of each technology parameter on final grain size of AISI H13 hot work tool steel during multistage deformation. It has been verified that the technology scheme for refining the final grain size can be determined rapidly and efficiently with the aid of the uniform design. The results show that the deformation parameters and the intermission time after deformation of the first stage affect the final grain size remarkably. For AISI H13 hot work tool steel, the final grain size can be refined notably when deformation parameters for the first stage are set as follows: a deformation temperature range of 1?025 1?085 ℃; a true strain of above 0.26 and the interpass time between the first and the second stage of deformation less than 10 s.

摘要：Phase field models were established to simulate the grain growth of a nanostructured AZ31 magnesium alloy,which contain spherical particles of differing sizes and volume fractions, under realistic spatial and temporal *** effect of the second phase particles on the nanostructure evolution was studied. The simulated results were compared with those of the conventional microstructured *** expression of the local free energy density was improved by adding a second phase particle term. The right input parameters were selected for proper physical meaning. It was shown that the rules that govern the pinning effect of the second phase particles during the grain growth were different for the nanostructure and microstructure. There was a critical particle size value that affected the grain growth within the nanostructure. If the particle size was lower than the critical value, the pinning effect on grain growth increased with decreasing particle size. When the particle size was greater than the critical value, the particles had almost no pinning ***, in the conventional microstructured material,the larger particle size resulted in an enhanced pinning effect during grain growth for particle sizes smaller than 1 μm. The effect was reversed when the particle size was larger than the critical value. For the nanostructure, the critical value was200 nm when the particle content was 10 v.%, and the critical value decreased when the content increased. When the particle size was 30 nm, the particle pinning effect on the grain growth increased for increasing particle content.

摘要：New flat-oval groove rolling process of multi-direction deformation is proposed to manufacture ultra-fine grain bar. Application of new groove series can introduce uniform large plastic strain into whole cross section of the material, and meanwhile satisfy the requirements of shape and size. Principle of grain refinement, based on experimental research of small specimen, is that grain refinement of ferrite is mainly dynamic recrystallization when low-carbon alloy steel is at low temperature deformation. Relationship of grain size and z-factor is also obtained through experimental research, as well as ultra-fine ferrite grain less than 1 micron. To predict strain, shape, dimensions and grain size of the material in rolling process, numerical simulation model of the warm groove bar rolling process is established via nonlinear finite element method, and distribution of grain size of the final section is obtained via finite element subroutine. The result indicates that ultra-fine grain bar rolling can accomplish at low temperature region.

摘要：通过分析流密码算法grain-v1,提出了一种针对密钥流生成器的差分错误攻击。该攻击利用了前17轮密钥流次数较低的弱点,向LFSR的指定位置引入错误,通过差分得到17个线性无关的线性方程和80个内部状态,只需要猜测62bits的初始内部状态变量就可得到密钥种子。整个过程的计算复杂度为O(274.26)。结果表明,grain-v1抗差分错误攻击的计算复杂度低于设计者宣称的O(280),也就是说,算法存在安全漏洞。

摘要：Early season maize is harvested with high moisture content that makes it impossible to store. The sale of early season maize in green form is uneconomical to the farmer. Experience had shown that farmers could hardly make the cost of production from their sales. Also, grain losses are high when maize is harvested green. To minimize grain losses and thereby increase value and the profit margin of the farmer, a grain dryer is necessary for wet grains. Therefore, this paper presents the design and development of a batch in-bin maize grain dryer. Some properties of maize such as moisture content and bulk density were determined to get information required for design of the dryer. The dimension of drying chamber, amount of moisture to be removed in a batch, quantity of air required to effect drying, volume of air required to effect drying, blower capacity, quantity of heat required to effect drying and actual heat used to effect drying were all designed for. A maize dryer was developed with a batch size of100 kg of threshed wet maize. The dryer can be used in laboratory for experimental purpose as well as on the farm for commercial purposes. The dryer can be used to measure drying rates of maize at different initial moisture contents, drying air temperatures, drying air velocities and grain beds. The effects of different drying temperature, air velocity, loading and agitating speed on the quality of dried maize can be investigated with the dryer.