Requirements engineering with interrelated conceptual models and real world scenes

Requirements Engineering (RE) is the process of creating requirements documents with the objective to establish a complete, consistent, and unambiguous description of intended changes (e.g. in respect to software, hardware, or business processes) for a given application domain on an abstract conceptual level. RE is also a cooperative learning process in which stakeholders from different backgrounds (having different experiences and objectives) and requirements analysts have to communicate with each other to gain a common understanding on the application domain as well as to elicit and validate requirements. Because in general, stakeholders are not trained to understand abstract descriptions/ models the use of scenarios (i.e. concrete stories of existing or desired system usage) and real world scenes (captured or animated observations of current or future system usage system usage employing rich media such as video) become more and more popular in industrial practice to improve communication about the application domain and desired changes. However, current scenariobased RE approaches and techniques utilising rich media in the analysis process (e.g., ethnographical or participatory design techniques) do not provide a tight and fine granular integration of scenarios and scenes with conceptual descriptions. The approach presented in this PhD thesis provides tool-supported fine-granular interrelations between parts of abstract concepts of conceptual models and parts of concrete real world scenes that have influenced the creation of the concept or have been used for validation. The established interrelations result in a special form of pre-requirements traceability which extends existing approaches in RE in the way that it provides i) traceability back to concrete instance examples from the real world instead of just tracing between different representations of abstractions and ii) traceability in a fine-grained way allowing interrelations of arbitrary parts of conceptual models with arbitrary parts of real world scenes and not just interrelationships on a document level. We developed methods and a supporting process-integrated modelling environment for three different conceptual modelling languages, which create and utilise the interrelations in a reference base kind of manner to support the explanation and negotiation as well as informal and formal inspections of the conceptual models. The interrelation are also used as a structuring mechanism for the (normally unstructured) real world scenes allowing, for instance, to compare different observations (e.g., two different usage situations of the same activity in different locations) in respect to the concepts they are related to or to evaluate the coverage of the current analysis. We have validated the approach in two case studies and experimental research in the industrial field of mechanical engineering

Time dependent and temperature dependent properties of the forward voltage characteristic of InGaN high power LEDs

Estimating the junction temperature and its dynamic behavior in dependence of various operating conditions is an important issue, since these properties influence the optical characteristics as well as the aging processes of a light-emitting diode (LED). Particularly for high-power LEDs and pulsed operation, the dynamic behavior and the resulting thermal cycles are of interest. The forward voltage method relies on the existence of a time-independent unique triple of forward-voltage, forward-current, and junction temperature. These three figures should as well uniquely define the optical output power and spectrum, as well as the loss power of the LED, which is responsible for an increase of the junction temperature. From transient FEM-simulations one may expect an increase of the temperature of the active semiconductor layer of some 1/10 K within the first 10 μs. Most of the well-established techniques for junction temperature measurement via forward voltage method evaluate the measurement data several dozens of microseconds after switching on or switching off and estimate the junction temperature by extrapolation towards the time of switching. In contrast, the authors developed a measurement procedure with the focus on the first microseconds after switching. Besides a fast data acquisition system, a precise control of the switching process is required, i.e. a precisely defined current pulse amplitude with fast rise-time and negligible transient by-effects. We start with a short description of the measurement setup and the newly developed control algorithm for the generation of short current pulses. The thermal characterization of the LED chip during the measurement procedures is accomplished by an IR thermography system and transient finite element simulations. The same experimental setup is used to investigate the optical properties of the LED in an Ulbricht-sphere. Our experiments are performed on InGaN LED chips mounted on an Al based insulated metal substrate (IMS), giving a comprehensive picture of the transient behavior of the forward voltage of this type of high power LED

Delivery of cellular factors to regulate bone healing

Bone tissue has a strong intrinsic regenerative capacity, thanks to a delicate and complex interplay of cellular and molecular processes, which tightly involve the immune system. Pathological settings of anatomical, biomechanical or inflammatory nature may lead to impaired bone healing. Innovative strategies to enhance bone repair, including the delivery of osteoprogenitor cells or of potent cytokines/morphogens, indicate the potential of ‘orthobiologics’ but are not fully satisfactory. Here, we review different approaches based on the delivery of regenerative cues produced by cells but in cell-free, possibly off-the-shelf configurations. Such strategies exploit the paracrine effect of the secretome of mesenchymal stem/stromal cells, presented in soluble form, shuttled through extracellular vesicles, or embedded within the network of extracellular matrix molecules. In addition to osteoinductive molecules, attention is given to factors targeting the resident immune cells, to reshape inflammatory and immunity processes from scarring to regenerative patterns