1,399 research outputs found
A Simple Geometrical Model for Solid Friction
We present a simple model for the friction of two solid bodies moving against
each other. In a self consistent way we can obtain the dependence of the
macroscopic friction force as a function of the driving velocity, the normal
force and the ruggedness of the surfaces in contact. Our results are discussed
in the context of friction laws used in earthquake models.Comment: 9 pages, plain TeX, preprint HLRZ 24/9
On the Use of Neural Networks for Full Waveform Inversion
Neural networks have recently gained attention in solving inverse problems.
One prominent methodology are Physics-Informed Neural Networks (PINNs) which
can solve both forward and inverse problems. In the paper at hand, full
waveform inversion is the considered inverse problem. The performance of PINNs
is compared against classical adjoint optimization, focusing on three key
aspects: the forward-solver, the neural network Ansatz for the inverse field,
and the sensitivity computation for the gradient-based minimization. Starting
from PINNs, each of these key aspects is adapted individually until the
classical adjoint optimization emerges. It is shown that it is beneficial to
use the neural network only for the discretization of the unknown material
field, where the neural network produces reconstructions without oscillatory
artifacts as typically encountered in classical full waveform inversion
approaches. Due to this finding, a hybrid approach is proposed. It exploits
both the efficient gradient computation with the continuous adjoint method as
well as the neural network Ansatz for the unknown material field. This new
hybrid approach outperforms Physics-Informed Neural Networks and the classical
adjoint optimization in settings of two and three-dimensional examples
Conception of an Eddy Current In-process Quality Control for the Production of Carbon Fibre Reinforced Components in the RTM Process Chain
The integration of quality control processes in immature production systems such as the resin transfer moulding (RTM) process in the
production of carbon fibre reinforced plastics (CFRP) faces numerous challenges. Requirements towards the reliability and product design as
well as the consideration of economic restrictions lead to challenging requirements for measurement systems. This paper presents the
development of a process integrated quality control using eddy current inspection. The concept focuses on an eddy current sensor array that is
integrated in a preforming tool and thus enables a 100% quality control of CRFP parts with minor effects on the production environment
Technical Performance and Energy Intensity of the Electrode-Separator Composite Manufacturing Process
AbstractEnergy storage is one of the key technological factors that determine the success of a sustainable future. Especially green mobility concepts for electric or hybrid electric vehicles highly depend upon storage technologies with high energy density and light-weight materials. At the same time, innovative production processes should be conceived that ensure energy and resource efficient manufacturing of these energy storage devices. This paper focuses on the technical as well as dynamic energetic performance analysis and evaluation of an innovative electrode-separator composite manufacturing process of lithium-ion batteries for automotive applications. The technical performance indicators such as battery capacity and the energy intensity of the manufacturing process are highly dependent upon process parameters, machine and product design. Hence, in-depth process knowledge must be acquired to understand interdependencies between all system components. Thus, the manufacturing process is analysed in terms of its dynamics, and correlations between process parameters, process energy demand and final product properties are assessed. The resulting knowledge is important for the subsequent design of large-scale products and processes involved design, as well as for characterisation of the manufacturing process for life cycle inventory databases or life cycle costing calculations
Self-Similar Law of Energy Release before Materials Fracture
A general law of energy release is derived for stressed heterogeneous
materials, being valid from the starting moment of loading till the moment of
materials fracture. This law is obtained by employing the extrapolation
technique of the self-similar approximation theory. Experiments are
accomplished measuring the energy release for industrial composite samples. The
derived analytical law is confronted with these experimental data as well as
with the known experimental data for other materials.Comment: Latex, 15 pages, no figure
Self-Similarity of Friction Laws
The change of the friction law from a mesoscopic level to a macroscopic level
is studied in the spring-block models introduced by Burridge-Knopoff. We find
that the Coulomb law is always scale invariant. Other proposed scaling laws are
only invariant under certain conditions.}Comment: Plain TEX. Figures not include
Functionally aberrant electrophysiological cortical connectivities in first episode medication-naive schizophrenics from three psychiatry centers
Functional dissociation between brain processes is widely hypothesized to
account for aberrations of thought and emotions in schizophrenic patients. The
typically small groups of analyzed schizophrenic patients yielded different
neurophysiological findings, probably because small patient groups are likely
to comprise different schizophrenia subtypes. We analyzed multichannel eyes-
closed resting EEG from three small groups of acutely ill, first episode
productive schizophrenic patients before start of medication (from three
centers: Bern N = 9; Osaka N = 9; Berlin N = 12) and their controls. Low
resolution brain electromagnetic tomography (LORETA) was used to compute
intracortical source model-based lagged functional connectivity not biased by
volume conduction effects between 19 cortical regions of interest (ROIs). The
connectivities were compared between controls and patients of each group.
Conjunction analysis determined six aberrant cortical functional
connectivities that were the same in the three patient groups. Four of these
six concerned the facilitating EEG alpha-1 frequency activity; they were
decreased in the patients. Another two of these six connectivities concerned
the inhibiting EEG delta frequency activity; they were increased in the
patients. The principal orientation of the six aberrant cortical functional
connectivities was sagittal; five of them involved both hemispheres. In sum,
activity in the posterior brain areas of preprocessing functions and the
anterior brain areas of evaluation and behavior control functions were
compromised by either decreased coupled activation or increased coupled
inhibition, common across schizophrenia subtypes in the three patient groups.
These results of the analyzed three independent groups of schizophrenics
support the concept of functional dissociation
Astroculture – Figurations of Cosmology in Media and Arts
Astroculture is a testament to the literary imagination and theoretical innovation of the late Sonja A.J. Neef, who devised the term as an expanding horizon of collaborative research – into the powerful gravitational force exerted on culture by astronomical phenomena and imagery. It is also the name of a conference on the topic inspired by Neef and held at the Center for Advanced Studies Morphomata at the University of Cologne in November, 2011. Indeed, Astroculture is a perfect instance of a morphome, the overall target of the Cologne College’s ongoing symposia: a persistent trope or topos of cultural fascination and transcription appearing across a gamut of civilizations and historical periods.
Commentary in this volume ranges from Claudius Ptolemy’s mapping of the universe and the emergence of a pluralistic cosmology in seventeenth-century Europe to the spread of planetariums, the Whole Earth Catalog, and the contemporary artwork of Ingo GĂĽnter. With interventions by David Aubin, LucĂa Ayala, Monika Bernold, Dietrich Boschung, Bruce Clarke, Gerd GraĂźhoff, Hans-Christian von Hermann, Martina Leeker, Patricia Pisters, and Henry Sussman
Feasibility of Coherent xuv Spectroscopy on the 1S-2S Transition in Singly Ionized Helium
The 1S-2S two-photon transition in singly ionized helium is a highly interesting candidate for precision tests of bound-state quantum electrodynamics (QED). With the recent advent of extreme ultraviolet frequency combs, highly coherent quasi-continuous-wave light sources at 61 nm have become available, and precision spectroscopy of this transition now comes into reach for the first time. We discuss quantitatively the feasibility of such an experiment by analyzing excitation and ionization rates, propose an experimental scheme, and explore the potential for QED tests
The complete nucleotide sequences of the five genetically distinct plastid genomes of Oenothera, subsection Oenothera: I. Sequence evaluation and plastome evolutionâ€
The flowering plant genus Oenothera is uniquely suited for studying molecular mechanisms of speciation. It assembles an intriguing combination of genetic features, including permanent translocation heterozygosity, biparental transmission of plastids, and a general interfertility of well-defined species. This allows an exchange of plastids and nuclei between species often resulting in plastome–genome incompatibility. For evaluation of its molecular determinants we present the complete nucleotide sequences of the five basic, genetically distinguishable plastid chromosomes of subsection Oenothera (=Euoenothera) of the genus, which are associated in distinct combinations with six basic genomes. Sizes of the chromosomes range from 163 365 bp (plastome IV) to 165 728 bp (plastome I), display between 96.3% and 98.6% sequence similarity and encode a total of 113 unique genes. Plastome diversification is caused by an abundance of nucleotide substitutions, small insertions, deletions and repetitions. The five plastomes deviate from the general ancestral design of plastid chromosomes of vascular plants by a subsection-specific 56 kb inversion within the large single-copy segment. This inversion disrupted operon structures and predates the divergence of the subsection presumably 1 My ago. Phylogenetic relationships suggest plastomes I–III in one clade, while plastome IV appears to be closest to the common ancestor
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