Analysis of thin walled structures using the boundary element method

In this article the direct boundary element formulations of stretching and bending plate problems are combined together to solve thin walled structures and other similar frames. The final system is obtained by assuming each individual plane structural element as a subregion. After the necessary transforms of these equations they can be combined together taking into account the displacement compatibility and equilibrium conditions.     

Experimental densities for compressed R134a

This paper reports densities of compressed R134a (1,1,1,2-tetrafluoroethane) determined by using a contiuously weighed pycnometer at 20 K intervals between 180 and 380 K at pressures from slightly greater than the vapour pressure to 70 MPa. The results are accurate to within ±0.1%. Saturated liquid densities derived by extrapolation from the experimental values agree with other reported values to within ±0.3%.     

An alternative approach to weight function evaluation for an orthotropic crack

The use of the analytically decoupled near-tip displacement solutions as an alternative approach, is presented in this paper for the efficient finite element evaluation of the decoupled weight functions for an orthotropic 2-D crack. This alternative approach has been validated by directly comparing the prior weight function results with a symmetric mesh approach in the crack-tip neighborhood, and indirectly by comparing the calculated stress intensity factors (K_I(II)) values using the computed weight functions with available K_I(II) solutions of the 2-D mixed mode orthotropic cracks. In addition, this approach with analytically decoupled near-tip displacement solutions for calculating weight functions at all locations, can facilitate further extension of weight function evaluations to a more general 2-D anisotropic crack.     

Influence of lips on thin-walled sections

Turning the free edge of an unstiffened flange inwards or outwards to form a ‘lip’, can substantially improve the local buckling resistance of a member. The lip is the most common type of edge stiffener used in cold-rolled, thin-walled sections. In this paper the behaviour of plate elements of thin-walled sections stiffened by compound lips (i.e. lips which are folded twice to form ‘lips on the lips’) is examined both theoretically and experimentally. An outline of a series of tests on compound edge-stiffened thin-walled sections of various geometries is given and some load-end compression displacement paths are compared with the theoretical predictions. Reasonably good agreement is obtained between the experimental and theoretical results. Comparisons of the theoretical predictions with experimental results of other researchers are also presented in this paper.     

Kinetics of acid toxicity in cultures ofXanthomonas campestris

By adding acetic, pentanoic and octanoic acids to batch cultures ofXanthomonas campestrisa close correlation between the acid concentration and the length of the lag phase and the value of the specific growth rate was obtained. The specific growth rate was largely affected by acid toxicity. As the amount of acetic acid was increased the specific growth rate dropped to 0.08 h⁻¹at 5 m and 0.07 h⁻¹at 9.99 m . Pentanoic acid produced a decrease of the specific growth rate to 0.06 h⁻¹at 3.92 m . Octanoic acid produced a greater effect on the specific growth rate. At 0.69 m the specific growth rate was reduced to 0.09 h⁻¹and then it dropped to 0.06 h⁻¹at 1.39 m . The lag phase length was increased as the result of the activation of the tolerance mechanism. The octanoic acid produced a 40 h lag in the culture containing 1.39 m total acid concentration. The cells in contact with 0.69 m octanoic acid had a lag phase of 5 h, twice that obtained in the acid-free cultures. Acetic and pentanoic acids at 9.99 and 3.92 m , increased the lag phases to 30 and 6 h, respectively.     

Influence of mixed-mode loading on fatigue-crack propagation

The subject of fatigue which comprises crack nucleation, crack propagation and final failure or fracture has, over the years, been the subject of numerous theoretical and experimental studies. These studies have highlighted the extrinsic influence of mixed-mode loading in governing the fatigue behavior of a wide spectrum of engineering materials and structures. In this paper we review the basic criteria and models that have been proposed and used to predict crack behavior and response for structures containing large cracks and subject to mixed-mode loading. Since the aspect of crack growth is the focus of this review, the effects or contributions from intrinsic microstructural effects are largely excluded. Specific criteria discussed are the maximum tangential stress, minimum strain-energy density and the maximum energy-release rate criteria. The use of these criteria to predict the behavior of structures is examined based on results published in the open literature. The characteristics and implications of each criterion are examined and discussed with particular relevance to threshold conditions on crack growth, direction of crack growth and crack-growth rate. The limitations of each criterion are highlighted.     

Stress function with finite magnitude of stress concentration around an interface crack

A new mathematical model for study of an interface crack between two dissimilar elastic half planes is proposed. A process zone is formed along the interface between the physical crack and the continuous part. Both the crack opening (and sliding) displacement with a smooth shape and the finite magnitude of stress concentration appear in this zone. The analytical model is expressed by closed elastic solutions using complex variables, but with no oscillations at the crack tip.     

激光结晶a-Si:H SOI离子注入和快速退火

本文对激光结晶a-Si∶H SOI结构砷注入和快速退火行为作了研究.a-Si∶H激光结晶有Lp-LCR,OD,FCR-2,FCR-1四个结晶区.用剖面电镜观察了结晶区的结构.扩展电阻测量表明Lp-LCR区中有两种扩散机制,即杂质在晶粒体内扩散和沿缺陷扩散.OD区中有三种扩散形式,除有上述两种以外,还有沿缺陷的扩散.首次比较了沿晶界和缺陷的扩散速度.     

A frame-based knowledge representation model and its mapping to nested relations

The first part of this paper introduces the basic constructs of a frame representation model and gives a formal definition for them. Subsequently the nested relational model (NF²) is described as an extension of the classical relational model to support relation-valued attributes. In the second part of this paper both models are compared with each other and a mapping of frame representation structures to NF² structures is specified. The structural similarities between frames and NF² relations are made clear and it is shown that their main difference is due to the type polymorphism introduced by the concept hierarchy of the frame model. This causes type collisions to occur in the strictly typed NF² model when frames are directly mapped to NF² structures. Two solutions to this problem are suggested and compared. The paper concludes with a reformulation of query operations of the frame model in terms of NF² algebra operations.     

退火损伤对Er注入GaAs和Yb注入InP发光的影响

本文报道了CaAs∶Er、InP∶Yb发光样品的二次离子质谱、X-射线双晶衍射测量结果及其与Er离子的表面成份的关系.分析讨论了退火损伤对GaAs∶Er和InP∶Yb发光的影响以及Er~(3+)复合体发光中心模型.