428 research outputs found
Stability of thin liquid films and sessile droplets under confinement
The stability of nonvolatile thin liquid films and of sessile droplets is
strongly affected by finite size effects. We analyze their stability within the
framework of density functional theory using the sharp kink approximation,
i.e., on the basis of an effective interface Hamiltonian. We show that finite
size effects suppress spinodal dewetting of films because it is driven by a
long-wavelength instability. Therefore nonvolatile films are stable if the
substrate area is too small. Similarly, nonvolatile droplets connected to a
wetting film become unstable if the substrate area is too large. This
instability of a nonvolatile sessile droplet turns out to be equivalent to the
instability of a volatile drop which can attain chemical equilibrium with its
vapor.Comment: 14 pages, 13 figure
An Inverse Problem for Localization Operators
A classical result of time-frequency analysis, obtained by I. Daubechies in
1988, states that the eigenfunctions of a time-frequency localization operator
with circular localization domain and Gaussian analysis window are the Hermite
functions. In this contribution, a converse of Daubechies' theorem is proved.
More precisely, it is shown that, for simply connected localization domains, if
one of the eigenfunctions of a time-frequency localization operator with
Gaussian window is a Hermite function, then its localization domain is a disc.
The general problem of obtaining, from some knowledge of its eigenfunctions,
information about the symbol of a time-frequency localization operator, is
denoted as the inverse problem, and the problem studied by Daubechies as the
direct problem of time-frequency analysis. Here, we also solve the
corresponding problem for wavelet localization, providing the inverse problem
analogue of the direct problem studied by Daubechies and Paul.Comment: 18 pages, 1 figur
Pädiatrisches stumpfes thorakoabdominales Trauma: Damage-Control-Resuscitation-Therapie
Zusammenfassung: Die Primärversorgung von Kindern mit schwerem stumpfem Bauchtrauma und begleitender Azidose, Koagulopathie und Hypothermie (letale Trias) erfordert ein effizientes multidisziplinäres Therapieregime zur Reduktion der Mortalität. Ein 5,5Jahre alter Junge wurde auf einem Bergbauernhof zwischen Traktorhinterrad und Hoftorumrandung im Torsobereich eingequetscht. Es kam zu einer Milzruptur Grad IV, einer Leberruptur Grad III, einer Pankreaslazeration Grad III, einer beidseitigen Lungenkontusion und einem begleitenden Weichteiltrauma mit Rhabdomyolyse. Aufgrund des schweren Traumas mit Auftreten einer Koagulopathie und einer kombinierten metabolisch-respiratorischen Azidose erfolgten die Gabe von Blutprodukten anstelle der von Kristalloiden, Akzeptanz einer permissiven Hypotension, Stabilisierung der Körpertemperatur im Sinne einer Damage-Control-Resuscitation-Strategie sowie eine Milz erhaltende operative Versorgung mittels Laparotomie. Es wird ein mögliches Therapieregime für das pädiatrische schwere Trauma mit Massentransfusion (MT) diskutier
On orthogonal projections for dimension reduction and applications in augmented target loss functions for learning problems
The use of orthogonal projections on high-dimensional input and target data
in learning frameworks is studied. First, we investigate the relations between
two standard objectives in dimension reduction, preservation of variance and of
pairwise relative distances. Investigations of their asymptotic correlation as
well as numerical experiments show that a projection does usually not satisfy
both objectives at once. In a standard classification problem we determine
projections on the input data that balance the objectives and compare
subsequent results. Next, we extend our application of orthogonal projections
to deep learning tasks and introduce a general framework of augmented target
loss functions. These loss functions integrate additional information via
transformations and projections of the target data. In two supervised learning
problems, clinical image segmentation and music information classification, the
application of our proposed augmented target loss functions increase the
accuracy
Convergence of simple adaptive Galerkin schemes based on h − h/2 error estimators
We discuss several adaptive mesh-refinement strategies based on (h − h/2)-error estimation. This class of adaptivemethods is particularly popular in practise since it is problem independent and requires virtually no implementational overhead. We prove that, under the saturation assumption, these adaptive algorithms are convergent. Our framework applies not only to finite element methods, but also yields a first convergence proof for adaptive boundary element schemes. For a finite element model problem, we extend the proposed adaptive scheme and prove convergence even if the saturation assumption fails to hold in general
MIMO Grid Impedance Identification of Three-Phase Power Systems: Parametric vs. Nonparametric Approaches
A fast and accurate grid impedance measurement of three-phase power systems
is crucial for online assessment of power system stability and adaptive control
of grid-connected converters. Existing grid impedance measurement approaches
typically rely on pointwise sinusoidal injections or sequential wideband
perturbations to identify a nonparametric grid impedance curve via fast Fourier
computations in the frequency domain. This is not only time-consuming, but also
inaccurate during time-varying grid conditions, while on top of that, the
identified nonparametric model cannot be immediately used for stability
analysis or control design. To tackle these problems, we propose to use
parametric system identification techniques (e.g., prediction error or subspace
methods) to obtain a parametric impedance model directly from time-domain
current and voltage data. Our approach relies on injecting wideband excitation
signals in the converter's controller and allows to accurately identify the
grid impedance in closed loop within one injection and measurement cycle. Even
though the underlying parametric system identification techniques are
well-studied in general, their utilization in a grid impedance identification
setup poses specific challenges, is vastly underexplored, and has not gained
adequate attention in urgent and timely power systems applications. To this
end, we demonstrate in numerical experiments how the proposed parametric
approach can accomplish a significant improvement compared to prevalent
nonparametric methods.Comment: 7 pages, 7 figure
Rotational state-changing collisions between N and Rb at low energies
We present a theoretical study of rotationally elastic and inelastic
collisions between molecular nitrogen ions and Rb atoms in the sub-Kelvin
temperature regime prevalent in ion-atom hybrid trapping experiments. The cross
sections for rotational excitation and de-excitation collisions were calculated
using quantum-scattering methods on ab-initio potential energy surfaces for the
energetically lowest singlet electronic channel of the system. We find that the
rotationally inelastic collision rates are at least an order of magnitude
smaller than the charge-exchange rates found in this system, rendering
inelastic processes a minor channel under the conditions of typical hybrid
trapping experiments.Comment: 6 pages, 5 figures, Computational study of rotational state changing
collision
Cascade Failure in a Phase Model of Power Grids
We propose a phase model to study cascade failure in power grids composed of
generators and loads. If the power demand is below a critical value, the model
system of power grids maintains the standard frequency by feedback control. On
the other hand, if the power demand exceeds the critical value, an electric
failure occurs via step out (loss of synchronization) or voltage collapse. The
two failures are incorporated as two removal rules of generator nodes and load
nodes. We perform direct numerical simulation of the phase model on a
scale-free network and compare the results with a mean-field approximation.Comment: 7 pages, 2 figure
A high-quality annually laminated sequence from Lake Belau, Northern Germany: Revised chronology and its implications for palynological and tephrochronological studies
The annually laminated record of Lake Belau offers an exceptional opportunity to investigate with high temporal resolution Holocene environmental change, aspects of climate history and human impact on the landscape. A new chronology based on varve counts, 14C-datings and heavy metal history has been established, covering the last 9400 years. Based on multiple varve counting on two core sequences, the easily countable laminated section spans about 7850 varve years (modelled age range c. 9430 to 1630 cal. BP). Not all of the record is of the same quality but approximately 69% of the varves sequence is classified to be of high quality and only c. 5% of low quality. The new chronology suggests dates generally c. 260 years older than previously assumed for the laminated section of the record. The implications for the vegetation and land-use history of the region as well as revised datings for pollen stratigraphical events are discussed. Tephra analysis allowed the identification of several cryptotephra layers. New dates for volcanic eruptions are presented for the Lairg B event (c. 6848 cal. BP, 2s range 6930–6713 cal. BP), the Hekla 4 event (c. 4396 cal. BP, 2s range 4417–4266 cal. BP), and Hekla 3 eruption (c. 3095 cal. BP, 2s range 3120–3068 cal. BP)
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