We are investigating the fluid dynamics of high-speed (500 m/s) small size (200 μm in diameter) droplet impact on a rigid substrate. Utilizing a high-resolution axisymmetric solver for the Euler equations, we show that the compressibility of the liquid medium plays a dominant role in the evolution of the phenomenon. Compression of the liquid in a zone defined by a shock wave envelope, very high velocity lateral jetting, and expansion waves in the bulk of the medium are the most important mechanisms identified, simulated, and discussed. Comparisons of computationally obtained jetting inception times with analytic results show that agreement improves significantly if the radial motion of liquid in the compressed area is taken into account.

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The early phase of high-speed liquid droplet impact on a rigid wall is characterized by compressibility effects through the creation of a shock wave attached to the contact area periphery. Initially, the area of compressed liquid is assumed to be bounded by the shock envelope, which propagates both laterally and upwardly into the bulk of the liquid. In this paper, an analytical model accounting for the lateral liquid motion in the compressed area is developed and compared to the axisymmetric numerical solution of the inviscid (Euler) flow equations. It is shown that the often employed assumption that the compressed area is separated from the liquid bulk by a single shock wave attached to the contact line breaks down and results in an anomaly. This anomaly emerges prior to the time when the shock wave departs from the contact line, initiating lateral liquid jetting. In order to remove this anomaly, the analytical model presented in this paper proposes the transition from a single to a multiple wave structure in the contact line region, prior to jetting eruption. The occurrence of this more complex multiple wave structure is also supported by the numerical results.

Mobile apps are everywhere. Some apps entertain and others enable business transactions. Apps increasingly interact with complex IT landscapes. For example, a banking app on a mobile device acts as a front end that invokes services on a back-end server of the bank, which might contact even more servers. Mobile testing becomes crucial and challenging. This paper follows a user-centric testing approach. The app's architecture matters for testing, as does its user base and usage context. Addressing these factors ensures that test cases cover all relevant areas. Most apps need test automation for two reasons: agility and compatibly. Agile projects test frequently, such as every night, to detect bugs early. Compatibility tests ensure that an app runs on all relevant devices and operating system versions on the market. Thus, testers execute test scripts on many devices. This demands for a private device cloud and a mobile test automation framework. Swisscom IT Services followed this path, enabling us to address the major quality issues we identified for mobile apps: pre-usage failures (installation fails, app crashes during startup) and lack of basic regression testing (upgrades buggier than predecessor).

Abstract-New business models, constant technological progress, as well as ever-changing legal regulations require that companies replace their business applications from time to time. As a side effect, this demands for migrating the data from the existing source application to a target application. Since the success of the application replacement as a form of IT maintenance is contingent on the underlying data migration project, it is crucial to accomplish the migration in time and on budget. This however, calls for a stringent data migration process model combined with well-defined quality assurance measures. The paper presents, first, a field-tested process model for data migration projects. Secondly, it points out the typical risks we have frequently observed in the course of this type of project. Thirdly, the paper provides practice-based testing and quality assurance techniques to reduce or even eliminate these data migration risks.