14,303 research outputs found
Space shuttle pogo active controller design using frequency domain optimization
A frequency domain parameter optimization technique was used to design active pogo suppression controls for the space shuttle. The technique uses a conjugate gradient search procedure and is well suited for designing low-order controllers for higher order systems. The shuttle model was a two-pump and six-structural-mode linear model representing a worst-case condition. A promising feedback controller structure was found to be a lead-lag design
Exact Lagrangian submanifolds in simply-connected cotangent bundles
We consider exact Lagrangian submanifolds in cotangent bundles. Under certain
additional restrictions (triviality of the fundamental group of the cotangent
bundle, and of the Maslov class and second Stiefel-Whitney class of the
Lagrangian submanifold) we prove such submanifolds are Floer-cohomologically
indistinguishable from the zero-section. This implies strong restrictions on
their topology. An essentially equivalent result was recently proved
independently by Nadler, using a different approach.Comment: 28 pages, 3 figures. Version 2 -- derivation and discussion of the
spectral sequence considerably expanded. Other minor change
Giant phonon anomalies in the pseudo-gap phase of TiOCl
We report infrared and Raman spectroscopy results of the spin-1/2 quantum
magnet TiOCl. Giant anomalies are found in the temperature dependence of the
phonon spectrum, which hint to unusual coupling of the electronic degrees of
freedom to the lattice. These anomalies develop over a broad temperature
interval, suggesting the presence of an extended fluctuation regime. This
defines a pseudo-gap phase, characterized by a local spin-gap. Below 100 K a
dimensionality cross-over leads to a dimerized ground state with a global
spin-gap of about 2~430 K.Comment: 4 pages, 3 figures, for further information see
http://www.peter-lemmens.d
A Textured Silicon Calorimetric Light Detector
We apply the standard photovoltaic technique of texturing to reduce the
reflectivity of silicon cryogenic calorimetric light detectors. In the case of
photons with random incidence angles, absorption is compatible with the
increase in surface area. For the geometrically thin detectors studied, energy
resolution from athermal phonons, dominated by position dependence, is
proportional to the surface-to-volume ratio. With the CaWO4 scintillating
crystal used as light source, the time constants of the calorimeter should be
adapted to the relatively slow light-emission times.Comment: Submitted to Journal of Applied Physic
Effects of self-assembled gold nanoparticles on YBa 2 Cu 3 O 7−δ thin films and devices
In our work we prepared YBa 2 Cu 3 O 7−δ (YBCO) thin films with self-assembled gold nanoparticles on SrTiO 3 (STO) substrates. We carried out different experiments to determine the effects on the crystallographic properties of the YBCO matrix as well as of the gold nanoparticles. Furthermore, we investigated how the particles influence the superconducting parameters of the film, e.g. the critical temperature T C and the critical current density j C . To ascertain j C we employed magneto-optical Faraday microscopy. In addition, the YBCO film was deposited and structured on STO bi-crystal substrates, thus producing grain boundary Josephson junctions. We studied those junctions with respect to the normal state resistance R N , and the dependence of the critical current I C on the temperature T as well as on the magnetic flux Φ. Finally, we prepared direct current superconducting quantum interference device (dc-SQUID) gradiometers and embedded gold nanoparticles at well-defined areas such as only the antenna or the SQUID region. We measured the flux noise in a shielded environment using an ac-bias reversal technique and compared it with that of sensors without gold nanoparticles. Thus, we demonstrate a new preparation method and an innovative application of gold nanoparticles
Robust Structured Low-Rank Approximation on the Grassmannian
Over the past years Robust PCA has been established as a standard tool for
reliable low-rank approximation of matrices in the presence of outliers.
Recently, the Robust PCA approach via nuclear norm minimization has been
extended to matrices with linear structures which appear in applications such
as system identification and data series analysis. At the same time it has been
shown how to control the rank of a structured approximation via matrix
factorization approaches. The drawbacks of these methods either lie in the lack
of robustness against outliers or in their static nature of repeated
batch-processing. We present a Robust Structured Low-Rank Approximation method
on the Grassmannian that on the one hand allows for fast re-initialization in
an online setting due to subspace identification with manifolds, and that is
robust against outliers due to a smooth approximation of the -norm cost
function on the other hand. The method is evaluated in online time series
forecasting tasks on simulated and real-world data
XNect: Real-time Multi-person 3D Human Pose Estimation with a Single RGB Camera
We present a real-time approach for multi-person 3D motion capture at over 30 fps using a single RGB camera. It operates in generic scenes and is robust to difficult occlusions both by other people and objects. Our method operates in subsequent stages. The first stage is a convolutional neural network (CNN) that estimates 2D and 3D pose features along with identity assignments for all visible joints of all individuals. We contribute a new architecture for this CNN, called SelecSLS Net, that uses novel selective long and short range skip connections to improve the information flow allowing for a drastically faster network without compromising accuracy. In the second stage, a fully-connected neural network turns the possibly partial (on account of occlusion) 2D pose and 3D pose features for each subject into a complete 3D pose estimate per individual. The third stage applies space-time skeletal model fitting to the predicted 2D and 3D pose per subject to further reconcile the 2D and 3D pose, and enforce temporal coherence. Our method returns the full skeletal pose in joint angles for each subject. This is a further key distinction from previous work that neither extracted global body positions nor joint angle results of a coherent skeleton in real time for multi-person scenes. The proposed system runs on consumer hardware at a previously unseen speed of more than 30 fps given 512x320 images as input while achieving state-of-the-art accuracy, which we will demonstrate on a range of challenging real-world scenes
The dimension of splines of arbitrary degree on a tetrahedral partition
We consider the linear space of piecewise polynomials in three variables which are globally smooth, i.e., trivariate splines. The splines are defined on a uniform tetrahedral partition , which is a natural generalization of the four-directional mesh. By using Bernstein-B{\´e}zier techniques, we establish formulae for the dimension of the splines of arbitrary degree
Strain-induced magnetic phase transition in SrCoO thin films
It has been well established that both in bulk at ambient pressure and for
films under modest strains, cubic SrCoO () is a
ferromagnetic metal. Recent theoretical work, however, indicates that a
magnetic phase transition to an antiferromagnetic structure could occur under
large strain accompanied by a metal-insulator transition. We have observed a
strain-induced ferromagnetic to antiferromagnetic phase transition in
SrCoO films grown on DyScO substrates, which provide a large
tensile epitaxial strain, as compared to ferromagnetic films under lower
tensile strain on SrTiO substrates. Magnetometry results demonstrate the
existence of antiferromagnetic spin correlations and neutron diffraction
experiments provide a direct evidence for a G-type antiferromagnetic structure
with Ne\'el temperatures between and depending on the oxygen content of the samples. Therefore, our
data experimentally confirm the predicted strain-induced magnetic phase
transition to an antiferromagnetic state for SrCoO thin films
under large epitaxial strain.Comment: 6 pages, 4 figure
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