基于理想饱和土体的有效应力原理几点辨思

提出了理想饱和土体的概念,以理想饱和土体水平截面为研究对象,首先从截面整体所受平均总应力的角度出发,推导了有效应力提出的过程,阐明了有效应力是一个虚拟物理量的实质,澄清了认识上的误区;其次从截面上液相接触面和固相接触面各自独立的角度出发,对两部分的实际应力情况进行分析,采用定量与定性相结合的方法,得出实际应力的表达式,比较了有效应力与实际应力之间的差量关系;最后,针对不同的实际土体,简单分析了有效应力原理的适用性程度。

Motion mechanism analysis of two contacting rollers

Two rollers contact each other under the normal load,and when the driving roller rotates,it drives the driven roller rotate by the tangential force on contact area.Finite Element Method analysis and experimental analysis are adopted to research the motion mechanism of two rollers which elasticity has big difference both on the condition of direct contact and indirect contact.From the analysis it is achieved that the relative sliding between the two rollers is due to the tangential force on the contact area and the radial compression deformation of the soft roller which has greater elasticity.For the condition of indirect contact in which a layer of inter-medium exists between the two rollers,the relative sliding is greater than that on the condition of direct contact,and the hardness of the intermedium layer affects the relative sliding between the two rollers.And for the condition of multiple rollers in the state of pressing contact,the number of contact areas on the soft roller also affects its motion characteristics.

In-situ preparation of TiO_(2)/N-doped graphene hollow sphere photocatalyst with enhanced photocatalytic CO_(2) reduction performance

Photocatalytic CO_(2)conversion efficiency is hampered by the rapid recombination of photogenerated charge carriers.It is effective to suppress the recombination by constructing cocatalysts on photocatalysts with high-quality interfacial contact.Herein,we develop a novel strategy to in-situ grow ultrathin/V-doped graphene(NG)layer on TiO_(2) hollow spheres(HS) with large area and intimate interfacial contact via a chemical vapor deposition(CVD).The optimized TiO^(2)/NG HS nanocomposite achieves total CO_(2)conversion rates(the sum yield of CO,CH_(3)OH and CH_(4))of 18.11μmol·g^(-1)h^(-1),which is about 4.6 times higher than blank T1O_(2)HS.Experimental results demonstrate that intimate interfacial contact and abundant pyridinic N sites can effectively facilitate photogenerated charge carrier separation and transport,realizing enhanced photocatalytic CO_(2)reduction performance.In addition,this work provides an effective strategy for in-situ construction of graphene-based photocatalysts for highly efficient photocatalytic CO_(2)conversion.

Effect of crack face contact on dynamic stress intensity factors for a hole-edge crack

In order to determine the dynamic stress intensity factors(DSIFs)for a single edge crack at the center hole of a finite plate under a compressive step loading parallel to the crack,the finite element method was employed to solve the cracked plate problem.The square-root stress singularity around the crack tip was simulated by quarter point singular elements collapsed by 8-node two-dimensional isoparametric elements.The DSIFs with and without considering crack face contact situations were evaluated by using the displacement correlation technique,and the influence of contact interaction between crack surfaces on DSIFs was investigated.The numerical results show that if the contact interaction between crack surfaces is ignored,the negative mode I DSIFs may be obtained and a physically impossible interpenetration or overlap of the crack surfaces will occur.Thus the crack face contact has a significant influence on the mode I DSIFs.

牛顿第一定律的修改

在17世纪前人们普遍认定力是维持物体运动的原因。用力推车子,车子才前进,停止用力,车子就停下来,古希腊的哲学家亚里士多德根据这类经验事实得出结论说:必须有力作用在物体上,物体才会运动,没有力的作用,物体就要静止下来。这与人们实际生活中的亲身体验非常相似,比如用手推车,只有你一直给车一个推力,车才能保持向前运动。

Influence of laser geometric morphology type on Si C surface wettability

To obtain effective surface morphology to control surface wettability, this work investigated the influence of protuberant and concave morphology, which are respectively represented by circle-dimpled and micro-square-convex morphology, on surface wettability. The geometric morphologies were processed on silicon carbide （SIC） surfaces by a laser-marking machine, and surface wettability was monitored by the measurement of contact angles using the sessile drop method. Correlation analysis between contact angles and morphology parameters was conducted to determine the extent of influence. The results showed that the circle-dimpled diameter had a signific^mt influence on surface wettability, whereas grooved width did not. Additionally the depth of dimples and grooves exerted less influence on controlling wetting behaviors. In addition, surface wettability transformed from a superhydrophilic state to a hydrophobic state on micro-square-convex surfaces; contact angles on cir- cle-dimpled surfaces showed a relatively slow transformation, though the surface wettability also underwent the state change.