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Book
Open Access
Eine Stadttour durch Hamburg im Jahr 1686. Die App Hidden Hamburg als erlebbare Geschichte und Digital-Public-History-Experiment (2. Auflage)
(edition lumière, 2024-05-02) Bellingradt, Daniel; Heise, Claudia
Mit der App Hidden Hamburg liegt ein kostenloses und zweisprachiges Angebot zu einer Stadttour im Hamburg des Jahres 1686 vor. Die App ist ein digitales Experiment, das historisches story telling als „erlebbare Geschichte“ mal anders akzentuiert: bequem am Computer-Bildschirm daheim oder als echte Stadttour durch Hamburg mit GPS-Tracking und einem Smartphone. In diesem Begleitbuch, das mit didaktischen Hinweisen, vertiefenden Themeninseln und stadthistorischen Einordnungen für den Einsatz in Klassenzimmern und Seminarräumen ebenso geeignet ist wie für den Museumsbesuch, werden die Ideen und Kontexte der vorbereiteten Stadttour beleuchtet. Rund um den virtuellen Stadtführer Johann, der in der Nachrichtenhochburg Hamburg im Jahr 1686 lebt, bietet dieses reich bebilderte Begleitbuch neue Einblicke in das frühneuzeitliche Hamburg als eine „Stadt der Neuigkeiten“, bekannt für ihre vielen Druckereien, stete Publizistik-Herstellung und Fülle an medialen Echos.
Dieses Buch führt zu Buchhandlungen in Kirchen, zu Zeitungsständen auf Marktplätzen, in ein Kaffeehaus, zum Opernhaus, und bietet in Kombination mit App und Webseite einen alternativen Einstieg in Mediengeschichte, Stadtgeschichte und Pressegeschichte. Viele integrierte Museumsobjekte aus Hamburg, u.a. aus dem Museum für Hamburgische Geschichte, vermitteln einen lebendigen Eindruck von Hamburg vor rund 350 Jahren.
Article
Open Access
Rolf Krafft Ligniez: Bild der Nacht
(Verlag der Starnberger Hefte, 2024-04-01) Schöntag, Roger
Rolf Krafft Ligniez (1916-1944), gebürtig aus Frankfurt a.M., gefallen an der Westfront (in Floverich bei Aachen), studierte Germanistik, Theater-Wissenschaft, Kunstgeschichte und Philosophie in Frankfurt sowie für ein Gastsemester in München. Ligniez selbst gehörte in seinen Studienjahren in Frankfurt zum Dichterkreis um Max Kommerell (1902-1944), der in seiner Jugend Sekretär (1924-1928) Stefan Georges (1868-1933) und Teil dessen Dichterkreises war, mit dem er aber 1930 brach. Die Gedichte Ligniez' lassen sich in dieser schwierigen Zeit am ehesten als eskapistisch einordnen, mit einer teilweisen Anknüpfung an eine späte Neo-Romantik.
Doctoral thesis
Open Access
Ultraschallbasiertes Sensorprinzip für die eingriffsfreie Messung des hydrostatischen Drucks
FAU Studien aus der Elektrotechnik : 24, (FAU University Press, 2024) Ponschab, Michael; Rupitsch, Stefan J.
In dieser Arbeit wird ein Sensorprinzip zur Messung der statischen mechanischen Spannung in der Rohrwand und damit des hydrostatischen Drucks basierend auf geführten elastischen Wellen entwickelt. Dabei wird auf die Verwendbarkeit von parasitär in der Rohrwand laufender Signalanteile in neuen Durchflusssensoren abgezielt, die auf der gezielten Anregung geführter elastischer Wellen in der Rohrwand basieren. Idealerweise ist so der Einbau weiterer Sensorik verzichtbar.
Zur Modellierung des Messprinzips wurde eine effiziente Methode zur Lösung des linearen Randwertproblems der geführten Wellenausbreitung implementiert und der Einfluss der statischen mechanischen Spannung basierend auf dem akustoelastischen Effekt integriert.
Ein weiterer Schwerpunkt der Arbeit ist die messtechnische Verifikation der implementierten Modelle und der empirische Nachweis der Verwendbarkeit des Effekts zur Messung des hydrostatischen Drucks. Sowohl Sende-Empfänger-Messungen, wie sie das entwickelte Sensorprinzip vorsieht, als auch Mehrkanalmessungen an verteilten Empfangsorten mittels eines Laser-Doppler-Vibrometers wurden durchgeführt. Die Genauigkeit der Modelle konnte durch eine eigens entwickelte inverse Materialcharakterisierungsmethode verbessert werden. Es wurde außerdem ein neuer Ansatz zur inversen Charakterisierung der Elastizitätskonstanten dritter Ordnung entwickelt. Das neue Sensorprinzip konnte anhand eines Versuchsstands demonstriert werden.
Doctoral thesis
Open Access
Approximate and Reconfigurable Precision Instruction Set Processors for Tightly Coupled Processor Arrays
(2024) Brand, Marcel; Teich, Jürgen
With the decline of Moore’s law, the trend of processor architecture design
shifts from powerful single-core processors to compensating for the stagnating
increase of single-core frequency with the parallelism provided by many- and
multi-core systems. For the increasing degree of parallelism, it also becomes
more and more important to have access to small processing elements that are
not only energy efficient but have a compact instruction set and use the costly
instruction memory efficiently. This thesis presents a set of novel processor
architectures that can be particularly beneficial when used in loop accelerator
architectures like Tightly Coupled Processor Arrays (TCPAs) to not only save
hardware but also energy and time under constraints for computational accuracy.
Already the current generation of processor-array-on-chip architectures, e.g.,
coarse-grained reconfigurable or programmable arrays, include more than 100s
or even 1,000s of processing elements. Thus, it becomes essential to keep the
on-chip configuration/instruction memories of each processing element as small
as possible. Even compilers must take into account the scarceness of available
instruction memory and create the code as compact as possible. However,
compilers for Very Long Instruction Word (VLIW) processors have the well-known
problem that they typically produce lengthy codes, especially for pipelined
instruction sequences. Barely utilized Functional Units (FUs) as well as
repeating operations of single FUs inside pipelined instruction sequences may
lead to unnecessary or redundant code. Techniques like software pipelining can
be used to improve the utilization of the FUs, yet with the risk of code
explosion due to the overlapped scheduling of multiple loop iterations or other
control flow statements. The proposed Orthogonal Instruction Processing (OIP)
processor architecture by Brand et al. shows that the size of pipelined code of
compute-intensive loop programs can be reduced significantly compared to the
size of an equivalently pipelined VLIW program. The general concept of OIP is
to have each FU process a microprogram orthogonally to each other but share
control flow and access to the peripheral infrastructure. Contrary to VLIW
processors, each FU is equipped with its own instruction memory, branch unit,
and program counter. Each FU has access to shared register files and the flags
from all functional units inside the processor. The synchronization of the
microprograms may necessitate the repeated execution of single instructions for
a fixed number of cycles. This can be encoded in the branch instruction and
capsuled by only a single instruction to prevent redundant code. To utilize OIP
processors to their full potential, they have to be programmed in a way that
minimizes the idle time of FUs (e.g., due to data dependencies) and maximizes
throughput. To solve this resource-constrained modulo scheduling problem,
techniques based on mixed integer linear programming have been proposed. The
necessary hardware extensions of OIP do not produce an overhead of resources,
especially of needed instruction memory, compared to VLIW processors.
Therefore, the architecture in conjunction with a set of benchmark applications
has been analyzed and evaluated regarding program size, memory size, and
overall architecture cost (based on a cost model by Müller et al.) in relation
to VLIW processors. It could be shown that OIP produces no computational or
memory overhead as soon as the program size of the OIP application is at least
50% less than the VLIW application. The necessary code size reduction is not
only achieved for all investigated benchmarks, but depending on the
application, the code size can even go down to 4.6% compared to its VLIW
counterpart. Thus, expensive instruction memory can be saved which reduces the
area and power requirements of an OIP processor in comparison to a VLIW
processor with an equal number of functional units.
Besides memory requirements, many relevant applications from domains like image
processing or machine learning are compute-intensive. But not always do they
rely on perfectly accurate results, e.g., even though reasonably inaccurate
computations of Convolutional Neural Networks (CNNs) may influence the exact
probabilities of each class, they rarely change the final decision. With this
motivation in mind, Anytime Instruction Processing (AIP) has been defined and
investigated, a concept for programmable accuracy floating-point computations.
AIP gives a programmer or compiler control over the accuracy of computed
floating-point (FP) operations. The accuracy of the computations is encoded on
bit granularity into the instruction, which leads to the executed operation
only computing that many most significant bits (MSBs) and may even terminate
earlier than when it had been computed at full accuracy. This is achieved by
encoding an intended accuracy into the instruction’s opcode which specifically
defines how many most significant mantissa bits of the FP operation shall be
computed. Thus, only errors in the resulting mantissa are to be expected, while
the resulting exponent and sign are computed accurately.
An anytime division capitalizes on the fact that divisions are classically
already computed MSB first and is implemented by a non-restoring division that
can terminate early based on the instructed accuracy. Implementations for the
typically non-MSB first operations of addition and multiplication were
presented in. One implementation uses on-line arithmetic to compute the
addition or multiplication of the mantissa MSB first, and the alternative uses
a bitmasking scheme to mask the least significant bits that should not be
computed. In on-line arithmetic, a recurrence equation is derived for an
operation in which the dependencies between two consecutive result bits are
removed (e.g., the carry chain of an addition). Without those dependencies,
each result bit can be computed independently of all others, enabling MSB first
computation. By computing MSB first, on-line arithmetic also provides a high
potential for pipelining: the execution of consecutive on-line instructions can
start as soon as the first digit of the preceding instruction has been
computed. Furthermore, operating in a redundant number format can help to
reduce the complexity of the recurrence equation and the number of iterations
required. Thus, binary operations in on-line arithmetic are usually performed
in the redundant Signed Digit Radix-2 (SDR2) number format. The redundant FP
number format SDFP has been defined based on SDR2 and enables the use of
on-line arithmetics in anytime instructions. An alternative implementation of
anytime additions and multiplications, the bitmasking approach, is based on
masking the operand bits that do not contribute to the specified a MSBs of the
result mantissa. In case of a multiplication, this masking is applied to the
partial products, instead of directly to the operands to reduce a possible
error. Compared to on-line arithmetic, computations may have a higher error,
but the hardware overhead is negligible.
After integrating the anytime instruction paradigm into the C++ arbitrary
precision framework Aarith, this framework was then used to evaluate the error
behavior of anytime addition, multiplication, and division operations. Power
and area were evaluated through the use of synthesis and simulation tools. The
experiments clearly show a favor of computing iterative applications with
anytime instructions. It is shown that the computation of an iterative Jacobi
solver can on average save up to 39% of energy with a computational error of
below 0.1% when compared to single-precision FP computations. Further, the
applicability of anytime instructions for CNNs has been specifically
investigated by setting an individual accuracy per layer of the inference of a
ResNet-18 CNN implementation. It could be shown by a design space exploration
that by using AIP, the energy of the inference can be reduced by up to 62%,
again, compared to single-precision FP computations.
Besides the programmable accuracy provided by anytime instructions,
reconfigurable-precision floating-point functional units have been investigated
that not only provide different floating-point formats that can be selected
dynamically but also vectorization and sub-word parallelism to potentially
increase the performance of applications even further.
In summary, by using the concepts presented in this thesis implemented into the
novel OIP processor architecture, it is possible to save not only hardware area
and instruction memory but also tremendously energy and time when executing
loop applications under constraints for computational accuracy, in specific
circumstances even without reducing the result accuracy.
Doctoral thesis
Open Access
Transport phenomena on the nanoscale: from isotropic systems to extreme confinement
(2024-04-29) Baer, Andreas; Smith, Ana-Suncana
Nanoscale systems, including particles or macromolecules as well as fluids confined to nanochannels and liquid films, are fascinating as they feature a transition between macroscopic continuum hydrodynamics and the intrinsically discrete molecular scale. A wealth of new phenomena arises due to this cross over as the separation of time or length scales between the different components (liquid – confinement – particle) is often not satisfied. The present thesis tackles this transition region focusing on diffusive transport in a series of six peer-reviewed articles [P1] to [P6]. Molecular dynamics (MD) simulations are applied as primary method, that is a unique tool allowing to resolve molecular details and sampling statistical averages on the mesoscopic scale.
The thesis starts with addressing the validity of the Stokes-Einstein-Sutherland (SES) equation [P1]. It captures a fundamental relation between the diffusion coefficient of a particle or molecule, its hydrodynamic radius and the surrounding fluid viscosity. The derivation of the SES equation at equilibrium assumes a continuous description of the fluid and a separation of time and length scales: the particle is required to be large and heavy compared to solvent molecules such that the momentum of the particle changes slowly compared to molecular time scales of the fluid. With these conditions violated for a nanoparticle, a breakdown at the nanoscale was often proposed and the latter even confirmed by several MD studies. Contrastingly, most experiments including those of our collaborators confirmed its validity for particles down to 1 nm in diameter. This discrepancy is tackled in the thesis by extensive MD simulations of the C60 buckminsterfullerene diffusing in toluene. This system clearly violates crucial conditions underlying the SES equation, yet the law is restored in simulations in the framework of the linear response to a constant drag force. This explains the success of the experiments that typically rely on the analysis of particle sedimentation when applying the SES equation. Notably, consistent with the Knudsen number, small deviations from perfect stick boundary conditions at the particle interface are required to obtain uniform results in experiments and simulations.
The study of bulk systems is extended to understand diffusion in confined liquids. Here the ordering of the solvent at the interface with the solid or the vapour phase may occur on similar length scales as the characteristic length scale of the confinement and the size of the diffusing object. Similarly, the characteristic time scales of diffusion life times of structural fluctuations become comparable to those of interactions of molecules with interfaces and other molecules. The anisotropy due to confinement also requires separate handling of the directions parallel and orthogonal to the confining walls when analysing transport properties. These issues are first tackled in MD simulations of the solvent phase within solid pores or thin films in [P2] to [P4]. Using the analysis tools developed in the PULS group it is possible to show that significant anisotropic oscillations of transport coefficients may take place due to effective interactions with the interfaces.
Understanding the behaviour of confined solvents is a prerequisite for the investigation of diffusive transport of nanoparticles as solutes in such confined systems [P5]. Using the fullerenes C60 and C70 in toluene filled alumina pores as model systems, it is shown that an effective diffusion coefficient can be well estimated by measuring the diffusivity in the centre of a pore and at the interface, as well as the transition rates between these two regions. These rates are estimated from the potential of mean force (PMF) of the particle with the solid. This approach is of particular relevance for understanding separation techniques including chromatography, as the direct relation between the effective transport coefficients in the pore and the particle retention time is established.
With equilibrium transport properties at the nanoscale extensively analysed, the attention finally shifts towards non-equilibrium systems, specifically addressing the viscosity of water in electric fields [P6]. Due to their dipole moment, water molecules couple to such fields, altering its intrinsic structure as well as relaxation processes in an anisotropic manner. In the extensive analysis of relaxations of thermal excitations and changes in the first and second hydration shell it is possible to study the competition between order imposed by the intrinsic tetrahedral structure and order imposed by the field. It is furthermore possible to assign different modes to time dependent viscosity, each relating to different molecular relaxation processes, and ultimately explain the anisotropic response of the system.
The transport phenomena of nanoscale systems tackled in the present thesis demand further research to be conducted in this area. The theoretical foundations of the SES equation are recapped and brought into the context of experiments and simulations, providing a solid framework for studying the diffusion of small dispersed nanoparticles. Relaxing the stick boundary condition demands an in-depth analysis covering various systems and particle sizes to allow for an a priori estimate of the boundary condition, e.g. from the Knudsen number. Furthermore, the study on the transport of dispersions through narrow pores paves the way for establishing a unified view of the relationship between interactions and transport properties of such systems in general. For systems with polar components, the investigations of water in an electric field furthermore provide valuable insights, into how the transport phenomena are altered in the presence of these fields, most relevant for water-filled nanopores. Therefore, the tools and concepts developed in this work shall find applications well beyond the systems studied herein.