Use of a genetic algorithm technique in solid-state laser pump cavity development

We apply a genetic algorithm to optimize the pump cavity of a complex miniaturized diode-pumped laser to find a balance between the efficient energy transfer of the pump light and the homogeneous illumination of the laser crystal. These two points are in contradiction to each other, whereby a complex optimization situation is given. The genome determines the geometry of the internal optical elements of the pump cavity in which a laser rod is placed. After optimization of the internal optical elements, a homogeneous illumination over the crystal length and a coupling efficiency of 59% were achieved. The results showed that genetic algorithms can find solutions and blueprints for laser pump cavities of consistent quality.     

In situ investigation of electrical inhomogeneity of ion exchange membrane surface using scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) is a relatively new, but well-developed method to study the electrochemical characteristics of the surface of heterogeneous materials, such as microelectrodes and biological cells. This paper presents the adaptation of this method to studying the distribution of electric potential near the surface of a heterogeneous ion exchange membrane. A special electrodialysis flow-through cell whose design allows for in situ 3D SECM measurements has been developed. The cell provides a laminar flow of liquid along the membrane surface, thereby making it possible to control the thickness of the diffusion layer. The SECM method has been verified by examining a model heterogeneous ion exchange membrane with preset surface and bulk properties. It has been found that the potential distribution is axisymmetric in the presence of cylindrical pores and the method allows the unambiguous determination of the position of the centers of conductive and nonconductive areas. An extremely nonuniform distribution of the potential with no signs of symmetry has been revealed in the case of MK-40 membrane. Unlike other methods for investigating inhomogeneous surfaces, SECM enable the determination of the distribution and evaluation of the size of conductive and nonconductive areas of heterogeneous ion exchange membranes in the swollen state.     

Multireflection pumping concept for miniaturized diode-pumped solid-state lasers

An innovative pump concept for diode-pumped, solid-state lasers is introduced as an example for an Er:YSGG laser, permitting its miniaturization. Embedded in a multireflective pump cavity, the laser crystal is simultaneously side and end pumped. Specially calculated and shaped deflecting optics distribute the coaxially input pumping light homogeneously over the lateral surface of the crystal, therefore reducing the size of the laser head, including the optical resonator, to a length of 27.5 mm and an outside diameter of 12.5 mm. The differential efficiency achieved is between 8.7% and 24%. The laser emits energy of 15.7 mJ at an absolute efficiency of 9.1% and a repetition rate of 4 Hz.     

SPL Conqueror: Toward optimization of non-functional properties in software product lines

A software product line (SPL) is a family of related programs of a domain. The programs of an SPL are distinguished in terms of features, which are end-user visible characteristics of programs. Based on a selection of features, stakeholders can derive tailor-made programs that satisfy functional requirements. Besides functional requirements, different application scenarios raise the need for optimizing non-functional properties of a variant. The diversity of application scenarios leads to heterogeneous optimization goals with respect to non-functional properties (e.g., performance vs. footprint vs. energy optimized variants). Hence, an SPL has to satisfy different and sometimes contradicting requirements regarding non-functional properties. Usually, the actually required non-functional properties are not known before product derivation and can vary for each application scenario and customer. Allowing stakeholders to derive optimized variants requires us to measure non-functional properties after the SPL is developed. Unfortunately, the high variability provided by SPLs complicates measurement and optimization of non-functional properties due to a large variant space. With SPL Conqueror, we provide a holistic approach to optimize non-functional properties in SPL engineering. We show how non-functional properties can be qualitatively specified and quantitatively measured in the context of SPLs. Furthermore, we discuss the variant-derivation process in SPL Conqueror that reduces the effort of computing an optimal variant. We demonstrate the applicability of our approach by means of nine case studies of a broad range of application domains (e.g., database management and operating systems). Moreover, we show that SPL Conqueror is implementation and language independent by using SPLs that are implemented with different mechanisms, such as conditional compilation and feature-oriented programming.     

Flexible feature binding in software product lines

A software product line (SPL) is a family of programs that share assets from a common code base. The programs of an SPL can be distinguished in terms of features, which represent units of program functionality that satisfy stakeholders’ requirements. The features of an SPL can be bound either statically at program compile time or dynamically at run time. Both binding times are used in SPL development and have different advantages. For example, dynamic binding provides high flexibility whereas static binding supports fine-grained customizability without any impact on performance (e.g., for use on embedded systems). However, contemporary techniques for implementing SPLs force a programmer to choose the binding time already when designing an SPL and to mix different implementation techniques when multiple binding times are needed. We present an approach that integrates static and dynamic feature binding seamlessly. It allows a programmer to implement an SPL once and to decide per feature at deployment time whether it should be bound statically or dynamically. Dynamic binding usually introduces an overhead regarding resource consumption and performance. We reduce this overhead by statically merging features that are used together into dynamic binding units. A program can be configured at run time by composing binding units on demand. We use feature models to ensure that only valid feature combinations can be selected at compile and at run time. We provide a compiler and evaluate our approach on the basis of two non-trivial SPLs.     

Effects of V and Mn Colorants on the Crystallization Behavior and Optical Properties of Ce-Doped Li-Disilicate Glass–Ceramics

The critical cooling rate and fluorescence properties of lithium (Li) disilicate glasses and glass–ceramics, doped with 2.0 wt% CeO₂ and with up to 0.7 wt% V₂O₅ and 0.3 wt% MnO₂ added as colorants, were investigated. The critical cooling rates, R _c, of glass melts were determined using differential thermal analysis and were found to be dependent on the relative concentrations of V₂O₅ and MnO₂, decreasing from 25±3° to 16±3°C/min. Annealed glasses were heat treated first to 670°C, and then to 850°C to form Li metasilicate and Li disilicate glass–ceramics, respectively. The fluorescence intensities of the Ce-doped glasses and glass–ceramics decrease by a factor of 100 with the addition of the transition metal oxides. This optical quenching effect is explained by the association of the Ce³⁺ ions with the transition metal ions in the residual glassy phase of the glass–ceramics.     

Coevolution of variability models and related software artifacts

Variant-rich software systems offer a large degree of customization, allowing users to configure the target system according to their preferences and needs. Facing high degrees of variability, these systems often employ variability models to explicitly capture user-configurable features (e.g., systems options) and the constraints they impose. The explicit representation of features allows them to be referenced in different variation points across different artifacts, enabling the latter to vary according to specific feature selections. In such settings, the evolution of variability models interplays with the evolution of related artifacts, requiring the two to evolve together, or coevolve. Interestingly, little is known about how such coevolution occurs in real-world systems, as existing research has focused mostly on variability evolution as it happens in variability models only. Furthermore, existing techniques supporting variability evolution are usually validated with randomly-generated variability models or evolution scenarios that do not stem from practice. As the community lacks a deep understanding of how variability evolution occurs in real-world systems and how it relates to the evolution of different kinds of software artifacts, it is not surprising that industry reports existing tools and solutions ineffective, as they do not handle the complexity found in practice. Attempting to mitigate this overall lack of knowledge and to support tool builders with insights on how variability models coevolve with other artifact types, we study a large and complex real-world variant-rich software system: the Linux kernel. Specifically, we extract variability-coevolution patterns capturing changes in the variability model of the Linux kernel with subsequent changes in Makefiles and C source code. From the analysis of the patterns, we report on findings concerning evolution principles found in the kernel, and we reveal deficiencies in existing tools and theory when handling changes captured by our patterns.