Optimization of a laval nozzle for energy-efficient cold spraying of microparticles

An application of cold spraying is the microstructuring of surfaces by particles in the size range of 1–10?µm, for example, to improve tribological properties. Since the particle acceleration is crucial for the cold spray process, this work is focused on the optimization of a Laval nozzle. Therefore, a nozzle was designed using analytic models for the fluid and particles behavior. The new nozzle design was improved by CFD simulations considering the effects of friction between the gas and the inner nozzle wall. Moreover, the effects of the distance between the nozzle outlet and the sample, as well as the particle position by entering the nozzle on the particle trajectories and impact velocity were studied numerically. The optimization of nozzle design has been validated experimentally by cold spraying small TiO₂ particles with mean size of 1?µm and larger Ti particles with the mean size of 10?µm. The optimized nozzle showed an improved spray performance. This work has been presented at the conference SMT30 (ID 267)     

Prioritizing test cases with string distances

Test case prioritisation aims at finding an ordering which enhances a certain property of an ordered test suite. Traditional techniques rely on the availability of code or a specification of the program under test. We propose to use string distances on the text of test cases for their comparison and elaborate a prioritisation algorithm. Such a prioritisation does not require code or a specification and can be useful for initial testing and in cases when code is difficult to instrument. In this paper, we also report on experiments performed on the “Siemens Test Suite”, where the proposed prioritisation technique was compared with random permutations and four classical string distance metrics were evaluated. The obtained results, confirmed by a statistical analysis, indicate that prioritisation based on string distances is more efficient in finding defects than random ordering of the test suite: the test suites prioritized using string distances are more efficient in detecting the strongest mutants, and, on average, have a better APFD than randomly ordered test suites. The results suggest that string distances can be used for prioritisation purposes, and Manhattan distance could be the best choice.     

Evaluating a Country For Offshore Outsourcing: Software Development Providers in the Ukraine

IS outsourcing is increasingly viewed as a cost-effective and fast way to get access to highly skilled, scarce resources located abroad. Locations such as India and Ireland are recognized as established offshore outsourcing locations. When evaluating other countries as potential outsourcing locations, Western managers need to consider a wide range of factors. This article uses a published framework to evaluate the software industry within the Ukraine.     

Crystal growth of copper-rich ytterbium compounds: The predicted giant unit cell structures YbCu4.4 and YbCu4.25

Two new phases YbCu_4.4 and YbCu_4.25 are found as a result of careful phase diagram investigations. Between the congruent and peritectic formation of YbCu_4.5 and YbCu_3.5, respectively, the phases YbCu_4.4 and YbCu_4.25 are formed peritectically at 934(2) °C and 931(3) °C.Crystal growth was realised using a Bridgman technique and single crystalline grains of about 50–100 μm were analysed by electron diffraction and single crystal X-ray diffraction. Due to the only slight differences in both compositions and formation temperatures the growth of larger single crystals of a defined phase is challenging. The compounds YbCu_4.4 and YbCu_4.25 fit in ?ernýs [J Solid State Chem 2003;174:125] building principle {(RECu₅)_n·(RECu₂)} where RE = Yb with n = 4 and 3. YbCu_4.4 and YbCu_4.25 are based on AuBe₅/MgCu₂-type substructures and contain approximately 4570 and 2780 atoms per unit cell. The new phases close the gap in the series of known copper-rich rare-earth compounds for n = 1, 2 (DyCu_3.5, DyCu_4.0) and n = 5 (YbCu_4.5, DyCu_4.5).     

液晶共面取向的等离子处理方法

在受等离子辐照过的一些有机和无机的基板上，获得了高质量的液晶共面取向。与已知的用来改善顶部锚定及预倾角各向同性的等离子处理方法不同，新方法是将等离子束调整到倾斜射向待取向的基板。在所用的辐射参数范围内，所有基板上的LC取向的易取向轴(easy axis)都平行于等离子体传播方向。研究了LC的预倾角和锚定能与等离子束的入射角、辐照时间、能量以及辐照电流密度等的依赖关系。经等离子处理过的基板上，方位角、锚定能与用光取向方法得到的相近，而预倾角与摩擦产生的类似。透过率-电压曲线与等离子处理的和摩擦工艺处理的非常接近。与摩擦取向相同，等离子诱导的取向具有很高的温度和光照的稳定性。也考虑了采用等离子／偏振紫外光和等离子／摩擦处理等组合方法来制作LC图形。     

Conformation of single polyelectrolyte chains vs. salt concentration: Effects of sample history and solid substrate

Using AFM single polymer molecule experiments we compare conformations of adsorbed on the mica substrate (in the isoelectric point) polyelectrolyte molecules (PE) of poly(methacryloyloxyethyl dimethylbenzylammonium chloride) at different concentrations of Na₃PO₄ salt. We compare the conformations at solid-liquid interface (1) with the conformations of dry samples obtained if the samples of the adsorbed PE were slowly dried (2) and if the PE chains were rapidly deposited and dried on the surface (3). The experiments demonstrate very similar conformations for the cases (1) and (2), while the case (3) differs substantially. The results suggest that the conformations (1) and (2) are formed under strong influence of the substrate. In all cases we observed very pronounced transitions from the extended coil conformation to the pearl necklace-like globule with an increase of salt concentration. The necklace-globules in the cases (1) and (2) appear at a higher salt concentration as compared to the case (3). The strong van der Waals interactions with the solid substrate stabilize the PE globule.