色散方程的两类高效率差分格式

使用组合差商法求解色散方程的一类空间宽度为二个步长的两层隐格式和仅为一个步长的两层半显格式.半显格式是一个可显式计算的盒式格式,隐格式则是一个对角占优三对角方程组,可用追赶法求解.且计算时都不受网比r的符号和大小限制,也都不需要提供数值内边界条件,是迄今为止计算最简单、效率最高的两类差分格式.既为其它差分格式解决了数值内边界条件的计算问题,也为色散方程差分格式的并行化提供了条件.

矿产开发利用效率指标研究

讨论了已有的资源利用效率研究成果,分析了矿产开发利用效率的内涵,在此基础上定义了矿产开发利用效率及其计算公式。为了消除价格因素影响,进一步提出了基于时间要素的效率增量概念及其计算公式。两项指标能较好地反映矿山企业状况,可以比较不同企业之间技术水平。最后,给出了不同矿山企业的矿产开发利用效率和差分效率的汇总计算办法以及计算实例。

Species- and Habitat-variability of Photosynthesis, Transpiration and Water Use Efficiency of Different Plant Species in Maowusu Sand Area

Photosynthesis ( P n ), transpiration ( E ) and water use efficiency ( WUE ) of more than 66 arid sand species from different environmental habitats, shifting sand dune, fixed sand dune, lowland and wetland in the Maowusu Sand Area were analyzed and the relation among these characteristics and the resource utilization efficiency, taxonomic categories and growth forms of the species were assessed. The results showed that species from Chenopodiaceae, Gramineae, Leguminosae which possessed the C 4 photosynthesis pathway, or C 3 pathway and also with nitrogen_fixation capacities had higher or the highest P n values, i.e., 20～30 μmol CO 2·m -2 ·s -1 , while that of evergreen shrub of Pinaceae had the lowest P n values, i.e., 0～5 μmol CO 2·m -2 ·s -1 . Those species from Compositae, Scrophulariaceae, and Gramineae with C 3 pathway but no N_fixation capacity had the highest E rates, i.e., 20～30 mmol H 2O·m -2 ·s -1 and again the evergreen shrub together with some species from Salicaceae and Compositae had the lowest E rates, i.e., 0～5 mmol H 2O·m -2 ·s -1 . Species from Leguminosae, Gramineae and Chenopodiaceae with C 4 pathway or C 3 pathway with N_fixation capacity, both shrubs and grasses, generally had higher WUE . However, even the physiological traits of the same species were habitat_ and season_specific. The values of both P n and E in late summer were much higher than those in early summer, with average increases of 26%, 40% respectively in the four habitats. WUE in late summer was, however, 12% lower. Generally, when the environments became drier as a result of habitats changed, i.e., in the order of wetland, lowland, fixed sand dune and shifting sand dune, P n and E decreased but WUE increased.

Investigation of a Design Modification for Double Helical Gears Reducing Vibration and Noise

To reduce vibration and noise and increase transmission efficiency, a three segment method for modifying the pinion profile was proposed. Cutter surface equations were deduced by changing the shape of the cutter-edge, substituting three segment parabolas for the line. The influence of longitudinal tooth modifications on tooth surface load distributions was discussed. Transmission error minimization and uniformity of tooth surface load distribution were chosen as optimization goals and the modified parameters were obtained by applying the complex method. Finally, an experiment comparing the loaded transmission error, vibration, and noise both before and after modifications was carried out. The results indicate that the modified design is reliable.

Numerical simulation and model of control-efficiency of thermal crown of work rolls in cold rolling

Aiming at accuracy control of the thermal crown of work rolls in cold rolling,new parameters such as regulation domain and control-efficiency factors were proposed and a numerical analysis model of the thermal crown of work rolls was established using finite difference method to study roll's thermal deformation.Based on simulation results,the influences of control-efficiency factors on thermal crown are presented and the thermal crown of work rolls is analyzed after taking sub-cooling of sprinkling beam into consideration.It has been found that the control-efficiency factor of any position on the roll's surface is linear function of the temperature and the control ability of water temperature is stronger than other control parameters.In addition,the verification of the model has been carried out based on the producing technology data in some factories and the numerical simulation results coincide well with the experimental data.Therefore,this work has important value for on-line control of roll's crown in cold rolling.

Technology Gaps, Resource Allocation and Economic Growth of Large Late-starting Countries

In the evolution of economic growth drivers, technology gaps are a key variable that determines the efficiency of resource allocation. Analysis of an optimal resource allocation path based on an extended endogenous growth model reveals that economic growth drivers evolve from productive investment to R＆D investment and a shift from imitation to innovation. Empirical analysis based on China＇s provincial-level panel data suggests that the effect of productive investment and R＆D investment, as well as innovation and imitation, on economic growth and technological progress varies greatly among regions of disparate technology levels. As a late-starting country, China should properly allocate resources between productive investment and R＆D investment, and between imitational investment and innovative investment while advancing the transformation of economic growth patterns on a differentiated basis in light of regional technology disparities.

A high quality factor photonic crystal channel-drop filter with a linear gradient microcavity

We design a channel-drop filter(CDF)with a linear gradient microcavity in a two-dimensional(2D)photonic crystal(PC).The model of three-port CDF with reflector is used to achieve high quality factor(Q-factor)and 100%channel-drop efficiency.The research indicates that adjusting the distance between reference plane and reflector can simultaneously influence the Q-factor due to coupling to a bus waveguide and the phase retardation occurring in the round trip between a microcavity and a reflector.The calculation results of 2D finite-difference time-domain(FDTD)method show that the designed filter can achieve the drop efficiency of 96.7%and ultra-high Q-factor with an ultra-small modal volume.

FDTD analysis of the optical properties of vertical ZnO nanorod array

Based on the structure and dimensions of a vertical ZnO nanorod array(V-ZNA)sample,an ideal 2-D photonic crystal model was established.The optical properties of the V-ZNAs were analyzed with finite-difference time-domain(FDTD)method,and the influences of the geometry parameters,including the circumcircle diameters of the top and bottom surfaces(Dt and Db)and the height(H)of the nanorods,and the pitch between each column(L),were discussed.High transmittance and low reflectance in the waveband of 400–800 nm were proved,and the highest transmittance can be obtained with Dt<50 nm,H=200 nm,and Db/L=0.85,which was verified by Effective Index Method(EIM).The result indicates that V-ZNAs can be used as excellent light coupling element and antireflection material for solar energy applications.