Spontaneous emission of a moving atom in a waveguide of rectangular cross section

We study the spontaneous emission(SE) of an excited nonrelativistic two-level system(TLS) interacting with the vacuum in a waveguide of rectangular cross section. All TLS’s transitions and the center-of-mass motion of the TLS are taken into account. The SE rate and the carried frequency of the emitted photon for the TLS initially being at rest are obtained, it is found that in the first order of the mass M, the frequency of the emitted photon is smaller than the transition frequency of the TLS and the SE rate is smaller than the SE rate Γfof the TLS fixed in the same waveguide. The SE rate for the TLS initially being moving is obtained in the second order of the mass M. The SE rate is smaller than Γfbut it is dependent not only on the atomic mass but also on the initial momentum. The carried frequency of the emitted photon is decreased when it travels along the direction of the initial momentum, whereas it is increased when it travels in the opposite direction of the initial momentum.

Sensitivity of springback and section deformation to process parameters in rotary draw bending of thin-walled rectangular H96 brass tube

In order to study the effects of the process parameters on springback and section deformation, a sensitivity analysis model was established based on the combination use of the multi-parameter sensitivity analysis method and the springback/section deformation prediction finite element model, and by using this model the sensitivities of the springback and the section deformation to process parameters were analyzed and compared. The results show that the most sensitive process conditions for springback angle are the boost speed and the pressure of pressure die, and the most sensitive process condition for section deformation is the number of cores. When the clamp force, the boost speed and the pressure of pressure die are utilized to control section deformation, the effect of these process parameters on springback should be considered. When the process parameters are mainly used to control springback, the effect of these process parameters on the section deformation should be always considered.

Development of component stiffness equations for thread-fixed one-side bolt connections to an enclosed rectangular hollow section column under tension

The derivation and validation of analytical equations for predicting the tensile initial stiffness of threadfixed one-side bolts(TOBs),connected to enclosed rectangular hollow section(RHS)columns,is presented in this paper.Two unknown stiffness components are considered:the TOBs connection and the enclosed RHS face.First,the trapezoidal thread of TOB,as an equivalent cantilevered beam subjected to uniformly distributed loads,is analyzed to determine the associated deformations.Based on the findings,the thread-shank serial-parallel stiffness model of TOB connection is proposed.For analysis of the tensile stiffness of the enclosed RHS face due to two bolt forces,the four sidewalls are treated as rotation constraints,thus reducing the problem to a two-dimensional plate analysis.According to the load superposition method,the deflection of the face plate is resolved into three components under various boundary and load conditions.Referring to the plate deflection theory of Timoshenko,the analytical solutions for the three deflections are derived in terms of the variables of bolt spacing,RHS thickness,height to width ratio,etc.Finally,the validity of the above stiffness equations is verified by a series of finite element(FE)models of T-stub substructures.The proposed component stiffness equations are an effective supplement to the component-based method.

Experimental study of hollow rectangular bridge column performance under vertical and cyclically bilateral loads

To investigate the seismic performance of hollow reinforced concrete （RC） bridge columns of rectangular cross section under constant axial load and cyclically biaxial bending, five specimens were tested. A parametric study is carried out for different axial load ratios, longitudinal reinforcement ratios and lateral reinforcement ratios. The experimental results showed that all tested specimens failed in the flexural failure mode and their ultimate performance was dominated by flexural capacity, which is represented by the rupture/buckling of tensile longitudinal rebars at the bottom of the bridge columns. Biaxial force and displacement hysteresis loops showed significant stiffness and strength degradations, and the pinching effect and coupling interaction effect of both directions severely decrease the structural seismic resistance. However, the measured ductility coefficient varying from 3.5 to 5.7 and the equivalent viscous damping ratio varying from 0.19 and 0.26 can meet the requirements of the seismic design. The hollow RC rectangular bridge columns with configurations of lateral reinforcement in this study have excellent performance under bidirectional earthquake excitations, and may be considered as a substitute for current hollow RC rectangular section configurations described in the Guideline for Seismic Design of Highway Bridges （JTG/T B02-01-2008）. The length of the plastic hinge region was found to approach one sixth of the hollow RC rectangular bridge column height for all specimen columns, and it was much less than those specified in the current JTG/T. Thus, the length of the plastic hinge region is more concentrated for RC rectangular hollow bridge columns.

Influence of Axial Feeding on Hydroforming of Aluminum Alloy Tubular Part with Rectangular Section

The hydroforming experiment of aluminum tubular part with rectangular section was carried out to investigate influence of axial feeding on thickness distribution and calibration pressure of the corner.Thickness distribution and relation between corner radius and internal pressure were analyzed.The influence of lubricant was discussed.Microstructure and hardness of different region were observed.It is shown that thickness reduction in the transition region between the corner and center region is the biggest.Friction condition has influence both on the thickness distribution and calibration pressure of the corner.As the increase of the axial feeding,the calibration pressure is decreased.There is only little change for the microstructure,but the hardness is increased by 23.3% for the transition region.

Plate reinforced square hollow section X-joints subjected to in-plane moment

The static test of 13 square hollow section(SHS) X-joints with different β and different types of plate reinforcement under in-plane moment in brace was carried out. Experimental test schemes, failure modes of specimens, moment-vertical displacement curves, moment-deformation of the chord, and strain strength distribution curves were presented. The effect of β and plate reinforcement types on in-plane flexural property of SHS X-joints was studied. Results show that punching shear of chord face disappears, brace material fracture appears and concave and convex deformation of chord decrease when either collar plates or doubler plates were welded on chord face. Moment-vertical displacement curves of all specimens have obvious elastic, elastic-plastic and plastic stages. As β increases, the in-plane flexural ultimate capacity and initial stiffness of joints of the same plate reinforcement type increase, but ductility of joints decreases. With the same β, the in-plane flexural initial stiffness and ultimate capacity of doubler plate reinforced joints, collar plate reinforced joints, and unreinforced joints decrease progressively. Thickness of reinforcement plate has no obvious effect on in-plane flexural initial stiffness and ultimate capacity of joints. As thickness of reinforcement plate increases, the ductility of reinforced X-joints decreases. The concave and convex deformation of every specimen has good symmetry;as β increases, the yield and ultimate deformation of chord decrease.

ANALYTICAL SOLUTION OF RESTRAINED TORSIONAL STRESSES AND DISPLACEMENT FOR RECTANGULAR- SECTION BOX BAR WITH HONTYCOMB CORE

Differential equation of restrained torsion for rectangular-section box bar with honeycomb core was established and solved by using the method of undetermined function.Non-dimension normal stress, shear stress acting in the faceplate and shear stress acting in the honeycomb-core and warping displacement were deduced. Numerical analysis shows the normal stress attenuates quickly along x-axis. Normal stress acting on the cross section at a distance of 20 h from the fixed end is only one per cent of that acting on the fixed end.

The Possibilities of Determining the Effective Thermal Conductivity of Steel Rectangular Section Bundles Based on the Selected Literature Models

The article presents the results of calculations of the effective thermal conductivity kef for bundles of steel rectangular sections obtained for a few analytical models. This coefficient expresses the ability of the bundles to heat transfer. The knowledge about the values of the kef coefficient of the section bundles is essential to correctly identify the parameters of their heat treatment process. The quality of the Calculation results were verified by the experimental measurement data. These measurements were performed in the guarded hot plate apparatus. It should be noted, that none of the eleven analyzed models of effective thermal conductivity is suitable for evaluation of thermal properties of the section bundles.

Ultimate Load Capacity and Reinforcement of Circular-Hollow-Section N-Joint

Experimental research and numerical analysis were applied to study the ultimate load capacity(ULC) and reinforcement of circular-hollow-section N-joint.Four specimens were tested under static load.The ULC of each specimen was obtained and the detailed failure conditions were discussed.Based on the results, both welding a plate on the chord member and filling concrete in the chord member are effective to reinforce the N-joint, but it is suggested that these two methods should not be applied simultaneously.Mo...

Physical Principles of Optimization of the Static Regime of a Cantilever-Type Power-effect Sensor with a Constant Rectangular Cross Section

In this paper an analysis of the physical principles of two-criterion optimization Pareto static mode of operation of power sensors cantilever type of rectangular type with a stable cross-section.The proposed criterion based on the Cauchy number is one of the characteristic numbers of the proportional miniaturization of microsystem technology.It is established that,for a rectangular cantilever with a stable cross-section,the value of the Cauchy does not depend on the width of the microconsole and the material from which it is made.

PLASTIC POST－BUCKLING OF A SIMPLY SUPPORTED COLUMN WITH A SOLID RECTANGULAR CROSS－SECTION

The plastic post-buckling of a simply supported column with a solid rectangularcross-section is analysed by a new approach. High order terms in the asymptotic post-buckling expansions are carried out. In some aspects, the method proposed in thispaper is similar io Hutchinson's. However, the computation is simple since theintroduction is avoided of stretched coordinates. The method can be used to analyseinitial post-bifurcation of plates and shells in the plastic range.

Saint-Venant torsion analysis of bars with rectangular cross-section and effective coating layers

This paper investigates the torsion analysis of coated bars with a rectangular cross-section. Two opposite faces of a bar are coated by two isotropie layers with different materials of the original substrate that are perfectly bonded to the bar. With the Saint- Venant torsion theory, the governing equation of the problem in terms of the warping function is established and solved using the finite Fourier cosine transform. The state of stress on the cross-section, warping of the cross-section, and torsional rigidity of the bar are evaluated. Effects of thickness of the coating layers and material properties on these quantities are investigated. A set of graphs are provided that can be used to determine the coating thicknesses and material properties so as to keep the maximum von Mises stress on the cross-section below an allowable value for effective use of the coating layer.

Numerical simulation of small section rectangular tube in parallel welding

The welding temperature field and deformation of parallel arrangement small-section rectangular tubes is calculated by using a non-contact model. After comparing the computed results with the experimentally measured results, it shows that there exist big errors when applying this model to the numerical simulation of small-section rectangular tube＇ s welding temperature field and deformation. Based on a simple analysis of the errors, a contact model is presented. The heat transfer and stress analysis between small-section rectangular tubes and clamping fixture are simulated by using direct constraints method, and then the laws of the temperature distribution, which coincide with experiment, are obtained. A further numerical analysis of the stress and deformation are made, it shows that a ＂T＂ shaped stress-field is formed in the vicinity of the weld. As the stress-field departs from the centroid of tubes＇, this leads to the small rectangular tubes not only have a longitudinal deflection, but also have a transverse bending and deformation.

工字形钢梁-矩形钢管柱单向螺栓节点抗弯承载力理论计算方法

针对工字形纯钢梁和钢-混凝土组合梁分别与矩形钢管柱和矩形钢管混凝土柱采用单向螺栓(也称单边拧紧螺栓)连接形成的4种节点形式,对其在弯矩作用下的受力机理及破坏模式进行分析,讨论导致节点失效的因素。总结节点在弯矩作用下的9种失效模式,包括:单向螺栓拉断、端板受弯屈服、矩形钢管柱壁翼板受拉屈服、矩形钢管柱壁翼板受压屈服、矩形钢管柱壁腹板受压屈曲、混凝土楼板局部压溃、钢筋屈服、矩形钢管柱内混凝土局部压溃、矩形钢管柱壁腹板受压屈服,进而基于破坏模式给出节点各组件承载力的计算公式。对4种节点在不同破坏模式下的正弯矩承载力和负弯矩承载力进行分析,给出节点承载力计算公式。将节点抗弯承载力的理论计算结果与试验结果进行对比,验证理论计算方法的可靠性。

平面KK型矩形钢管节点静力试验研究

依托某主题广场月牙形艺廊单层网壳钢屋架结构,选取其最不利受力节点,设计了中心插板节点和毂节点两种KK型矩形钢管节点,分别对其足尺模型进行静载试验,测试分析模型节点区域的应变及应力分布规律,对比分析支管端部的位移变化。结果表明:1)设计荷载水平下,两个节点均满足受力要求;毂节点和中心插板节点的最大试验荷载约为等效设计荷载的2.85倍和3.25倍,节点安全储备较高;2)在最大试验荷载作用下,两个节点支管根部与中心构件相贯焊缝附近部分均不同程度地屈服,毂节点圆筒内加劲肋焊缝局部出现开裂;3)相同荷载作用下,中心插板节点相应位置应力应变水平相对较低,故中心插板节点的承载强度较高;4)由试验荷载-位移曲线分析得出毂节点的各肢平均位移比中心插板节点约大13.3%,表明中心插板节点弹性刚度较大。

大跨度铁路桥附属构件对不同宽高比矩形断面涡振性能的影响

在已建成的大跨度鳊鱼洲长江大桥原设计宽高比为6.7∶1的四线铁路桥矩形箱型主梁断面的基础上,通过调整断面宽高比,设计宽高比为4∶1的二线铁路和宽高比为9∶1的六线铁路桥矩形箱梁断面。通过节段模型风洞试验,在0°,±3°和±5°风攻角的均匀来流下,对以上3种常用二线、四线和六线铁路桥矩形箱梁断面与对应相同宽高比纯矩形断面之间的涡振特性关系,以及铁路桥附属构件对不同宽高比矩形断面涡振性能的影响进行研究。结果表明:在宽高比分别为4∶1和6.7∶1的矩形断面上布置铁路桥附属构件能增大断面在负风攻角下的涡振振幅,在-5°风攻角下竖向涡振振幅增大率高达277.5%,但对正风攻角下的涡振响应起到一定的抑制作用,而在宽高比为9∶1的矩形断面布置六线铁路桥附属构件则能明显增大该断面在各风攻角下的涡振振幅,其扭转涡振振幅增大率均在48.3%以上;铁路桥附属构件对矩形断面涡振性能的降低作用随着断面宽高比的增大而提升,针对气动外形较钝的二线和四线铁路桥箱梁,可参考相似宽高比矩形断面涡振特性,并重点考察箱梁在负风攻角下的涡振响应,而针对宽高比较大的六线铁路桥箱梁,由于附属构件影响较大,参考相似宽高比矩形断面涡振特性的意义较小,均应详细研究其在各风攻角下的涡振性能。

思政元素融入混凝土结构课程的教学设计--以单筋矩形截面梁承载力设计为例

土木工程专业的课程思政设计是实现专业课程与思政课同步前行的重要举措,也是培养社会主义合格建设者和可靠接班人的重要途径。混凝土结构系列课程在土木工程专业课程体系中占据重要的地位,因此,在对课程教学背景和学情分析的基础上,以单筋矩形截面梁承载力设计知识单元为例,基于OBE理念,将思政元素融入教学设计,从课程目标、课程内容、教学过程设计、教学方法设计及教学实施方面,探讨如何合理、科学地将思政元素引入课程教学设计的各个环节,不仅解决专业教育和思政教育“两张皮”问题,且对学生的自主学习能力和学习热情起到积极的促进作用,另外对其他专业课具有引领和示范作用。

钢筋混凝土薄壁空心高墩塑性铰长度计算方法

针对我国现行抗震设计规范尚未明确给出钢筋混凝土(RC)薄壁空心高墩塑性铰长度计算方法的问题,首先收集整理了既有RC桥墩塑性铰长度计算方法以及试验数据,分析影响塑性铰计算长度的主要因素;同时对实际桥梁工程采用的RC薄壁空心墩构造参数进行统计归纳.在验证有限元建模方法准确性后,采用ABAQUS软件建立了高度为40~120 m的8种典型RC薄壁空心高墩的精细化有限元模型,并开展非线性推覆分析,得到不同高度桥墩的等效塑性铰长度.最后讨论不同塑性铰长度计算方法的适用性,发现Eurocode 8规范的计算公式精度最高,可用于计算RC薄壁空心高墩的塑性铰长度.

从肥袋足鬲看商时期北方长城地带东段地区的文化互动

肥袋足鬲是商时期在北方长城地带东段地区不同考古学文化中共有的一类器物。虽然不同地区的考古学文化中肥袋足鬲形态存在差异,但在面对商文化的扩张过程中,不同地区的肥袋足鬲消长、中断与复兴的时间却几乎相同。肥袋足鬲所体现的文化传播,反映了华北平原北缘地区与晋陕高原地区人群的交流与互动。晚商时期使用肥袋足鬲的人群往往与佩戴卷云形金耳饰的人群在空间上重合,反映了北方长城地带东段不同考古学文化之间的共性。

典型浅埋矩形框架地铁车站地下结构地震易损性分析

该文旨在研究典型浅埋矩形框架形式地铁车站结构的震后失效概率模型。以9座已建典型矩形框架地铁车站工程实例为研究对象,通过Abaqus/standard有限元软件平台建立了土-结构相互作用三维数值模型。基于地下结构Pushover分析获得的抗震性能曲线,定义了各个车站结构的层间位移角限值。采用IDA方法计算得到了地铁车站结构的概率地震需求模型,并绘制了不同地铁车站结构的地震易损性曲线。通过对比研究发现,地铁车站结构之间的震后失效概率相差巨大,场地平均剪切波速对地下结构地震易损性分析结果起主导作用,尤其是与结构等高分布土层的自由场响应结果,但地下框架结构本身的变形能力也是影响结构震后失效概率的重要因素之一。上述研究成果能够有效加强对现行浅埋地下框架结构抗震性能的认识,可为基于性能的浅埋地铁车站地下框架结构抗震设计提供科学参考。