小型可变坡水槽的结构及其特点

可变坡水槽作为研究水流及泥沙运动特性和水力学实验的一种设备已被广泛应用，本文论述了作者所研制的小型可变坡水槽的结构及其特点。     

Signature of relations in mapping class groups and non-holomorphic Lefschetz fibrations

We introduce the notion of signature for relations in mapping class groups and show that the signature of a Lefschetz fibration over the 2-sphere is the sum of the signatures for basic relations contained in its monodromy. Combining explicit calculations of the signature cocycle with a technique of substituting positive relations, we give some new examples of non-holomorphic Lefschetz fibrations of genus and which violate slope bounds for non-hyperelliptic fibrations on algebraic surfaces of general type.

     

基于自适应斜坡补偿的双环电流模DC/DC混沌控制

提出了一种自适应斜坡补偿方法,将该方法引入到双环电流模buck DC/DC的混沌控制中,并给出实现该方法的电路结构.建立了双环电流模DC/DC系统稳定性分析的离散模型,理论分析了自适应斜坡补偿在双环控制下系统的稳定性条件,推导出了自适应因子k与系统工作的最大占空比的关系式.仿真结果表明该方法可有效控制系统的分岔和混沌现象,提高系统的工作范围和动态响应速度.     

Design considerations of depressed clad W-shaped single mode dispersion compensating fibers

Dispersion compensating fibers (DCFs) are being widely used as dispersion compensation techniques because of its superior characteristics. This work reports the theoretical modelling of a single mode DCF having W-shaped shallow as well as deeply depressed clad profile. The DCFs have been designed and optimized by suitable adjusting different fiber parameters such as, central relative index difference (Δ⁺), inner core radius (a), depression depth parameter (ρ), normalized end position of the depressed clad (p), etc. at a given spot size . The figure of merit (FOM) characteristics including the bend loss as well as other losses associated with fiber manufacturing technique have been thoroughly investigated. Performances of these DCFs for recent wavelength division multiplexing (WDM) transmission system have also been discussed. By adjusting different fiber parameters, the effective core area (A_eff) of the above DCFs can be controlled to minimize the effect of non-linearities on them.     

求一类多元多峰函数全局极小的区间斜率方法

Based on the interval analysis, an interval slope method is proposed for finding all global minimizers of a several peaks function f on domain X^0包含于R^n, which is given by interval slope discard tests and interval extension of objective function.Numerical results of representative test functions show that this method is practical and effective.     

Conceptualizations of slope in Mexican intended curriculum

Slope is a fundamental mathematics concept in middle and high school that transcends to the university level. An understanding of slope is needed at the university level since slope plays an important role in understanding problems involving variation and change. In this study Mexican curricula documents were examined to determine which conceptualizations of slope are addressed in the intended mathematics curriculum. To explain the results, we use conceptualizations of slope identified in previous research. Our findings reveal that, to a certain extent, the conceptualizations proposed in the Mexican intended mathematics curriculum differ slightly in terms of the emphasis and timing of instruction from what others have identified in the U.S., with slope as a geometric ratio receiving less emphasis in the Mexican curriculum. There was also noted discontinuity within the Mexican curriculum in introducing slope in grade 9 and subsequently introducing of linear functions in grade 10 without explicit mention of slope. Suggestions are made for future studies, both to consider the conceptualizations of slope promoted in the Mexican textbooks and the impact they have in classroom instruction and student learning of slope.     

Effective reaction rates of a thin catalyst layer

The catalyst layer in a fuel cell can be described with a system of reaction diffusion eq uations for the oxygen concentration and the protonic overpotential. The Tafel law gives an exponential expression for the reaction rate, and the Tafel slope is a coefficient in this law. We present a rigorous thin layer analysis for two reaction regimes. In the case of thin catalyst layers and bounded potentials, the original Tafel law enters as an effective boundary condition. Instead, in the case of large protonic overpotentials, we derive an exponential law that contains the doubled Tafel slope. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of inclined impermeable bed on the turbulent characteristics of the flow using particle image velocimetry

In this study, the turbulent characteristics of the flow in an open channel with horizontal and inclined impermeable beds were studied experimentally using two-dimensional particle image velocimetry (PIV). The experiments were conducted in a channel of 6.5 m in length, 7.5 cm in width and 25 cm in height. The slope of the channel was S = 0 for the horizontal impermeable bed and for S = ?0.002, S = ?0.004 and S = ?0.006 for the inclined impermeable bed. Hydraulic characteristics such as distributions of velocities, turbulent intensities and Reynolds stress are investigated at a fine resolution using the PIV. Velocity is measured above the horizontal and inclined impermeable bed for the same different heights (h = 5, 7, 9, 11 and 13 cm) and for the same different discharges (Q = 0.735, 0.845 and 0.970 lt/s). Results show that the channel slope influences significantly near the impermeable bed but not near the free surface the variation of turbulent characteristics of the flow and also the alteration of the channel slope from ?0.002 to ?0.006 doesn't influence the variation of turbulent characteristics of the flow, which are the longitudinal turbulent intensity u′U_*, the vertical turbulent intensity v′/U_* and the turbulent kinetic energy. The channel slope doesn't influence the Reynolds stress.     

Laser Light and X-Ray Diffraction Studies of Oriented Isotactic Polypropylene (iPP) Prepared by Temperature Slope Crystallization

Isotactic polypropylene (iPP) film was melt-crystallized in a temperature gradient. The iPP film showed well oriented α- and β-crystalline textures along the gradient. The crystalline structure, phase transition boundary and lamellar twisting were examined by X-ray diffraction and laser light diffraction (LLD). On the α-β boundary, LLD shows a sharp streak perpendicular to the boundary, where the a-axis of the β-crystal is oriented perpendicular to the temperature gradient. Apart from the boundary, the a-axis of the β-crystal becomes parallel to the gradient. The β-crystal shows lamellar twisting with a pitch of 200 μm at room temperature. When heated the β-crystal, the lamellar distance of 295Å at room temperature decreases to 285Å at 80–100°C and then increases to more than 300Å above 120°C. During the heating, the value of the twist period increases from 200 to 210 μm at 90–100°C, and then to above 224 μm at 140°C. The increase of the twist period is related to the increasing crystalline thickness of the β-lamellae.     

三维非连续变形分析方法碰撞分析及其应用

将具有完备动力学理论的非连续变形分析(DDA)方法应用于块体碰撞研究。基于三维DDA(3D DDA)方法,按时步输出块体碰撞过程速度变化和接触嵌入量,进而得到块体碰撞恢复系数、冲量、冲击力。以此为参考指标,采用斜抛、面-面对心等碰撞模型,验证3D DDA方法模拟块体碰撞的有效性,并将3D DDA方法应用于多米诺骨牌倾倒、滚石边坡成灾及防护等算例分析,探讨了多米诺骨牌倾倒机制、滚石启动及运动行为、滚石灾害防护方案。结果表明:多米诺骨牌间距越大,同一块体被碰撞时间越迟,其最终稳定时间也越迟,与下一块体碰撞的动能越大;滚石运动呈侧向平动及转动三维运动特征,每一次碰撞,均引起动能、轨迹或状态的显著变化;滚石拦挡设施弹簧刚度越大,越先达到最大冲击力,最大冲击力随弹簧刚度的增加而减小;可结合树木阻挡效应,耗散滚石动能,降低滚石飞跃高度,使滚石灾害减轻或控制在防护范围以内。