Near surface flaw detection by ultrasonic critical angle imaging

Acoustic critical angle measurements usually involve broad beam or global isonification of a water-solid interface. In order to obtain local interface data, it is convenient to use a focused acoustic source with lens axis at incident angle and point-receiver at specular reflection angle . By scanning this combination at various critical angles (=_crit), interface waves are generated locally near the lens focus. These waves penetrate the solid to a depth of approximately one shear wavelength _T and are modulated by discontinuities such as flaws, inclusions, and debonds that may be present there. A radiated longitudinal wave in water accompanies these modulated interface waves and carries information on subsurface flaws to the point-detector along the direction of a specularly reflected wave. By scanning the focus-receiver combination along the interface, the receiver output may be used to form images of local subsurface detail. We show that in anisotropic materials, such as crystals, there are generally two different _crit where a radiating interface wave provides subsurface information. We also discuss special problems associated with the use of a focused acoustic source including nonlinear effects (generation of harmonics) in the water.     

Initiation of tantalum oxide pores grown on tantalum by potentiodynamic anodic oxidation

The initiation and growth of porous oxide on Ta was investigated in mixed H₂SO₄/HF electrolytes. Under selected potentiodynamic anodic oxidation conditions the formation of nearly uniform porous Ta₂O₅ layer was observed. The porous Ta₂O₅ layers consist of self-organized pore arrays with single pore diameters ranging from 2 to 10 nm. The morphology and the thickness of the layer depend strongly on the applied potential, the scan rate and on HF presence. The composition of the porous oxide layer is Ta₂O₅.     

基于PD控制的机器人轨迹跟踪性能研究与比较

定义同一个Lyapunov函数，分析了基于PD的3种常用机器人轨迹跟踪算法的稳定性和鲁棒性，得到了新的结论，PD加前馈控制按指数收敛到0，PD及修改的PD加前馈控制收敛到一封闭球，增大反馈系数可使球半径任意小，基于PD的轨迹跟踪算法对模型误差及有界不确定性干扰具有鲁棒性，实验研究验证了分析结果，并对3种轨迹跟踪算法的控制性能进行比较。     

A review on assessment of fatigue strength in welded studs

Welding is one of the most important and highly developed joining methods; nevertheless unwanted side effects occur like thermal strains and altering of certain material properties induced by heating and melting. These effects lead to distortions and high residual stresses which should be kept to a minimum. To minimize distortion, various strategies are being developed. Stud welding is widely used in steel structures, power plants, and ship buildings due to the significantly technology including highest quality of production processes by continuous electrical control and the efficiency of such a process. Therefore, varying the heat input typically will affect the material properties including yield strength, tensile strength, hardness, and notch toughness in the stud arc welding. Well-defined heat sources offer a reproduced heat input into a highly localized area. The fatigue strength of stud welding has been investigated by performing welding process and microstructural observations. This paper is going to discuss the influence of heat input on the structural changes in stud arc welding.     

Turning wine (waste) into water: Toward technological advances in the use of constructed wetlands for winery effluent treatment

The research presented in this article describes an investigation into the use of vegetated submerged reedbeds (VSR) as a practicable alternative for effluent treatment for small‐scale wine producers. In this study, we found that the hydraulic processes occurring within the VSR display significantly nonideal behavior. If the feed to the VSR was located on the surface the dead volume accounted for approximately 25% of the nonideal behavior of the system and bypass accounted for a further 6%. A preferential flow pattern was found within the VSR with the greatest flow occurring closest the surface and in the center, and the least at the sidewalls. We propose that the flow profile can be conceptualized as being hull shaped and found that this profile was the same for irregularly shaped gravel and for spherically shaped gelatinous beads. We, therefore, hypothesize that it is not dependent on the geometry of the VSR or the packing medium. © 2013 American Institute of Chemical Engineers AIChE J 60: 420–431, 2014     

Chromatographische Untersuchungen zur Polydispersität von Hydroxyethylstärke

Chromatographic Studies on the Polydispersity of Hydroxyethyl Starch. A representative sample of clinically used hydroxyethyl starch was separated by semipreparative HPSEC into narrow fractions in the range of approx. 3.000 to 800.000 D. The original sample and selected fractions were characterised by gaschromatographic methylation analysis according to their substitution degrees MS and DS, which were differentiated by the substitution positions at C2, C3 and C6 of the anhydroglucoses and their kind of glycosidic bonding α-1, α-1,4 or α-1,4,6, respectively. Furthermore, polydispersity in relations to the degree of branching was determined. Mark-Houwink and molecular weight distribution parameters determined by multi-detection HPSEC are reported. The presented data demonstrate a extensive homogeneity of the original sample. The clinical relevance is discussed.