Technische Universität Darmstadt

About: Technische Universität Darmstadt is a education organization based out in Darmstadt, Germany. It is known for research contribution in the topics: Neutron & Finite element method. The organization has 17316 authors who have published 40619 publications receiving 937916 citations. The organization is also known as: Darmstadt University of Technology & University of Darmstadt.

Radiochromic film imaging spectroscopy of laser-accelerated proton beams

Abstract: This article reports on an experimental method to fully reconstruct laser-accelerated proton beam parameters called radiochromic film imaging spectroscopy (RIS). RIS allows for the characterization of proton beams concerning real and virtual source size, envelope- and microdivergence, normalized transverse emittance, phase space, and proton spectrum. This technique requires particular targets and a high resolution proton detector. Therefore thin gold foils with a microgrooved rear side were manufactured and characterized. Calibrated GafChromic radiochromic film (RCF) types MD-55, HS, and HD-810 in stack configuration were used as spatial and energy resolved film detectors. The principle of the RCF imaging spectroscopy was demonstrated at four different laser systems. This can be a method to characterize a laser system with respect to its proton-acceleration capability. In addition, an algorithm to calculate the spatial and energy resolved proton distribution has been developed and tested to get a better idea of laser-accelerated proton beams and their energy deposition with respect to further applications.

Size‐Dependent Lattice Expansion in Nanoparticles: Reality or Anomaly?

Abstract: Size-dependent lattice expansion of nanoparticles is observed for many ionic compounds, including metal oxides, while lattice contraction prevails for pure metals. However, the physical origin of this effect, which is of importance for the thermodynamic, chemical and electronic properties of nanoparticles, is discussed controversially. After a survey of the experimental literature, revealing a wide variety of materials with size-dependent lattice expansion, we show that the negative surface stress is the key reason for lattice expansion, while the excess of lattice sums or point defects of various charge states can be excluded as general explanations. Ab initio calculations of surface stresses for various surface structures of metal oxides confirm the model of a surface-induced lattice expansion.

Bootstrap techniques for signal processing

Abstract: The statistical bootstrap is one of the methods that can be used to calculate estimates of a certain number of unknown parameters of a random process or a signal observed in noise, based on a random sample. Such situations are common in signal processing and the bootstrap is especially useful when only a small sample is available or an analytical analysis is too cumbersome or even impossible. This book covers the foundations of the bootstrap, its properties, its strengths and its limitations. The authors focus on bootstrap signal detection in Gaussian and non-Gaussian interference as well as bootstrap model selection. The theory developed in the book is supported by a number of useful practical examples written in MATLAB. The book is aimed at graduate students and engineers, and includes applications to real-world problems in areas such as radar and sonar, biomedical engineering and automotive engineering.

Pareto Local Optimum Sets in the Biobjective Traveling Salesman Problem: An Experimental Study

Abstract: In this article, we study Pareto local optimum sets for the biobjective Traveling Salesman Problem applying straightforward extensions of local search algorithms for the single objective case. The performance of the local search algorithms is illustrated by experimental results obtained for well known benchmark instances and comparisons to methods from literature. In fact, a 3-opt local search is able to compete with the best performing metaheuristics in terms of solution quality. Finally, we also present an empirical study of the features of the solutions found by 3-opt on a set of randomly generated instances. The results indicate the existence of several clusters of near-optimal solutions that are separated by only a few edges.

How open is this platform? The meaning and measurement of platform openness from the complementors’ perspective

Abstract: Software platforms’ success largely depends on complementors’ willingness to repeatedly invest their time and effort to the development of platform applications that attract users and increase the platform’s installed base. But how can platform providers encourage desirable behaviours by complementors (i.e., application developers) in the absence of formal roles and hierarchical control structures? Although previous studies of software-based platforms have identified openness as critical instrument at the macro (i.e., platform) level and have provided initial attempts to measure the construct, no research has been dedicated to comprehensively conceptualize and operationalize platform openness at the micro level from the perspective of application developers. To go beyond these preliminary findings and to theorize about the nature and effects of platform openness as perceived by application developers, we develop a construct called perceived platform openness (PPO). Drawing on recently advanced scale development methodologies, we conceptualize PPO as a multidimensional construct and empirically validate it with important consequent variables linked to developers’ continuous platform contributions. Empirical evidence from several rounds of qualitative and quantitative steps supports the conceptual validity of the construct and empirical relevance of the scale across different smartphone platform contexts (i.e., Apple iOS and Google Android). Researchers will benefit from the study’s systematic and comprehensive conceptualization of PPO, how it is measured, and how it relates to critical application developer beliefs and attitudes. Platform managers may use our results to target the underlying facets of PPO most likely to contribute to the platform’s long-term goals.