13 research outputs found
Efficient optimization of hollow-core photonic crystal fiber design using the finite-element method
Multi-dimensional modeling and simulation of semiconductor nanophotonic devices
Self-consistent modeling and multi-dimensional simulation of semiconductor nanophotonic devices is an important tool in the development of future integrated light sources and quantum devices. Simulations can guide important technological decisions by revealing performance bottlenecks in new device concepts, contribute to their understanding and help to theoretically explore their optimization potential. The efficient implementation of multi-dimensional numerical simulations for computer-aided design tasks requires sophisticated numerical methods and modeling techniques. We review recent advances in device-scale modeling of quantum dot based single-photon sources and laser diodes by self-consistently coupling the optical Maxwell equations with semiclassical carrier transport models using semi-classical and fully quantum mechanical descriptions of the optically active region, respectively. For the simulation of realistic devices with complex, multi-dimensional geometries, we have developed a novel hp-adaptive finite element approach for the optical Maxwell equations, using mixed meshes adapted to the multi-scale properties of the photonic structures. For electrically driven devices, we introduced novel discretization and parameter-embedding techniques to solve the drift-diffusion system for strongly degenerate semiconductors at cryogenic temperature. Our methodical advances are demonstrated on various applications, including vertical-cavity surface-emitting lasers, grating couplers and single-photon sources
Route planning with transportation network maps: an eye-tracking study.
Planning routes using transportation network maps is a common task that has received little attention in the literature. Here, we present a novel eye-tracking paradigm to investigate psychological processes and mechanisms involved in such a route planning. In the experiment, participants were first presented with an origin and destination pair before we presented them with fictitious public transportation maps. Their task was to find the connecting route that required the minimum number of transfers. Based on participants' gaze behaviour, each trial was split into two phases: (1) the search for origin and destination phase, i.e., the initial phase of the trial until participants gazed at both origin and destination at least once and (2) the route planning and selection phase. Comparisons of other eye-tracking measures between these phases and the time to complete them, which depended on the complexity of the planning task, suggest that these two phases are indeed distinct and supported by different cognitive processes. For example, participants spent more time attending the centre of the map during the initial search phase, before directing their attention to connecting stations, where transitions between lines were possible. Our results provide novel insights into the psychological processes involved in route planning from maps. The findings are discussed in relation to the current theories of route planning
Reduzierte Basis Methode fĂŒr elektromagnetische Streuprobleme
A main objective of numerical analysis and modeling is the simulation of
complex technological problems, arising in engineering and natural sciences.
Numerical simulations help to understand, design and optimize, or control and
characterize systems or components. Usually the behaviour of a system is
described by physical quantities like temperature, stress, or electromagnetic
fields. These fields are solutions to partial differential equations (PDEs),
which are stated on the domain of interest with appropriate boundary
conditions. Since in general the analytical solution to a PDE is unavailable,
a discretization procedure such as finite element, finite, discontinuous
Galerkin, or finite volume method has to be applied. The discretized system is
then solved numerically. For real world problems the numerical solution is
usually expensive, regarding computational resources and time. Computational
times can be of the order of seconds, up to hours and days, and even many
problems can not be solved at all with reasonable effort due to their
complexity. In engineering applications like optimization or parameter
estimation the discretized models have to be solved multiply for different
configurations of the system under consideration, for example, regarding
geometrical or material parameters. Hence, a large number of solutions for
different parameters are required in reasonable time (many-query context), or
a single solution has to be computed very fast (real-time context). Even for
moderate problems these requirements can often not be met with above
discretization methods. In applications usually the output of interest is not
the solution of the PDE itself, but some derived quantities. Hence, a method
for fast and reliable evaluation of input-output relationships is desirable.
The input are, for example, geometrical or material parameters of the system
under consideration. The output is given implicitly as a functional of the
field variable, which is the solution to the input parameter dependent PDE.
The reduced basis method offers a way to construct approximations to such
input-output relationships, which can be evaluated very fast. The key is an
online-offline decomposition. In a so-called offline phase the reduced model
is built self-adaptively. In an actual application (online phase) only the
reduced model is solved. Rigorous error estimation techniques allow to control
and quantify the accuracy of the approximative reduced model, such that
reduced basis solutions are reliable. In the present work we developed
efficient techniques for the reduced basis method for electromagnetic
scattering problems, with a focus on application to real world nano-optical
problems. Especially in the field of a posteriori error estimation and
multiple sources, established techniques were found to be infeasible and had
to be further developed, in order to treat complex geometries in 2D and 3D and
complex sources. Savings of computational costs of several orders of
magnitude, could be demonstrated, compared to state-of-the-art methods. In
application examples our results showed that the reduced basis method is very
well suited for complex engineering tasks like real-time inverse
scatterometry, parameter estimation, and design optimization of optical
systems.Eine Hauptaufgabe von numerischer Analysis und Modellierung ist die Simulation
komplexer technologischer Probleme im ingenieur- und naturwissenschaftlichen
Bereich. Simulationen helfen, Systeme oder Komponenten besser zu verstehen, zu
designen, zu optimieren oder zu charakterisieren. In vielen Anwendungsfeldern,
wie numerischem Design, Parameterrekonstruktion oder bei inversen Problemen
werden im Allgemeinen eine Vielzahl von Simulationen eines gegebenen Systems
in AbhĂ€ngigkeit von z.B. Geometrie- oder Materialparametern durchgefĂŒhrt. Oft
besteht dabei Echtzeitanforderung, so dass kurze Rechenzeiten des
VorwĂ€rtsproblems unverzichtbar sind. Vor allem fĂŒr 3D-Probleme sind die Zeiten
fĂŒr die Berechnung einer einzigen VorwĂ€rtslösung dafĂŒr jedoch oft zu lang.
Thema der vorliegenden Arbeit ist die Reduzierte Basis Methode, die zum Ziel
hat, parametrisierte Probleme in obigen Anwendungsfeldern in Echtzeit zu
lösen. Die Grundidee besteht darin, den Lösungsprozess in eine langsame
Offline- und einen schnelle Online-Phase aufzuspalten. In der Offline-Phase
wird das zu Grunde liegende Problem mehrmals rigoros gelöst, wobei lÀngere
Rechenzeiten in Kauf genommen werden. Diese Lösungen bilden die Basis eines
reduzierten niedrigdimensionalen Systems, das man durch Projektion aus dem
ursprĂŒnglichen Problem erhĂ€lt. Im Online-Schritt wird lediglich das reduzierte
Problem gelöst. Da die Reduzierte Basis Methode NÀherungslösungen liefert, ist
es fĂŒr die QualitĂ€t und VerlĂ€sslichkeit der Rechnungen von groĂer Bedeutung,
rigorose FehlerschÀtzer zu konstruieren. Anwendungsfeld dieser Arbeit ist das
Gebiet "Computational Nano-Optics'', das sich mit der Lösung der
Maxwellgleichungen in nanostrukturierten Systemen beschÀftigt. Speziell werden
Streuprobleme auf unbeschrÀnkten, geometrisch parametrisierten 3D-Gebieten
betrachtet. Vor allem auf dem Gebiet der a posteriori FehlerschÀtzung sind
bisherige ``State-of-the-Art'' Reduzierte Basis Methoden aufgrund extrem hohen
Aufwands praktisch nicht durchfĂŒhrbar, um komplexe geometrisch parametrisierte
Systeme in 2D und 3D zu behandeln. Daher wurde in der vorliegenden Arbeit ein
neuer FehlerschÀtzer entwickelt, der den Rechen- und Speicheraufwand um
mehrere GröĂenordnungen reduziert. Dieser basiert auf
Gebietszerlegungsmethoden, die auch fĂŒr FehlerschĂ€tzung von Finite Elemente
Lösungen verwendet werden. Desweiteren wurde eine neue Technik fĂŒr die
Reduzierte Basis Methode entwickelt, die es erlaubt, die Reaktion von Systemen
unter dem EinfluĂ einer Vielzahl von Quellen extrem effizient zu berechnen.
Dies ist eine typische Situation in vielen nanooptischen Anwendungen, z.B. in
der Lithographie. Als numerische Beispiele wurde die Optimierung von
Photomasken und die inverse Scatterometrie von EUV (extrem ultraviolett)
Masken untersucht. Die Arbeiten zur inversen Scatterometrie wurden in
Kollaboration mit der Physikalisch-Technischen Bundesanstalt (PTB) am Berliner
Elektronensynchrotron BESSY II (experimentelle Messungen) und dem Advanced
Mask Technology Center (Herstellung einer EUV Testmaske und Mikroskopie)
durchgefĂŒhrt. Aufgrund der vielversprechenden Ergebnisse wird eine
Prototypimplementierung der in dieser Arbeit entwickelten Methoden fĂŒr die
Auswertung von Streuexperimenten an der PTB eingesetzt
Paramilitaarne vÀgivald kui poliitilise radikaliseerumise toitepinnas? [Paramilitary violence as fodder for political radicalisation?]
I maailmasĂ”ja jĂ€rel Baltikumis vĂ”idelnud Saksa vabakorpuste nĂ€ideThe example of the German Freikorpswhich fought in the Baltic region after WWIThe article discusses the history of the Freikorps (âFree Corpsâ) formed in Germany after WWI, in a comparative analysis of two Freikorps which were recruited in Germany and fought in the Baltic region, and two Freikorps which only fought in Germany. The article compares the members of those Freikorps â the Baden assault battalion Kurland and the Von Medem Freikorps which fought in the Baltic region and the WĂŒrzburg Freikorps and the Haas battalion which operated only in Germany â on the basis of their generational affiliation as well as their subsequent involvement in national socialist organisations. It is concluded that the claims that the Freikorps members who fought in the Baltic region mostly belonged to the âwar youthâ generation who did not fight in WWI and whose fighting in the Baltic region caused their radicalisation manifested by their higher than average membership in the NSDAP, SS and SA, cannot be corroborated on the basis of the analysed units.KeywordsWWI, Weimar Republic, Freikorps, wars of independence in the Baltic countries, war youth and WWI veterans, national socialist organisations
Certified reduced basis method for electromagnetic scattering and radar cross section estimation
Chemogenomic Profiling of Human and Microbial FK506-Binding Proteins
FK506-binding
proteins (FKBPs) are evolutionarily conserved proteins
that display peptidyl-prolyl isomerase activities and act as coreceptors
for immunosuppressants. Microbial macrophage-infectivity-potentiator
(Mip)-type FKBPs can enhance infectivity. However, developing druglike
ligands for FKBPs or Mips has proven difficult, and many FKBPs and
Mips still lack biologically useful ligands. To explore the scope
and potential of C<sup>5</sup>-substituted [4.3.1]-aza-bicyclic sulfonamides
as a broadly applicable class of FKBP inhibitors, we developed a new
synthesis method for the bicyclic core scaffold and used it to prepare
an FKBP- and Mip-focused library. This allowed us to perform a systematic
structureâactivity-relationship analysis across key human FKBPs
and microbial Mips, yielding highly improved inhibitors for all the
FKBPs studied. A cocrystal structure confirmed the molecular-binding
mode of the core structure and explained the affinity gained as a
result of the preferred substituents. The best FKBP and Mip ligands
showed promising antimalarial, antileginonellal, and antichlamydial
properties in cellular models of infectivity, suggesting that substituted
[4.3.1]-aza-bicyclic sulfonamides could be a novel class of anti-infectives