587 research outputs found
Design and application of magneto-rheological fluid
Magneto-Rheological Fluid (MRF) technology is an old “newcomers” coming to the market at high speed. Various industries including the automotive industry are full of potential MRF applications. Magneto-Rheological Fluid technology has been successfully employed already in various low and high volume applications. A structure based on MRF might be the next generation in design for products where power density, accuracy and dynamic performance are the key features.
Additionally, for products where is a need to control fluid motion by varying the viscosity, a structure based on MRF might be an improvement in functionality and costs. Two aspects of this technology, direct shear mode (used in brakes and clutches) and valve mode (used in dampers) have been studied thoroughly and several applications are already present on the market. Excellent features like fast response, simple interface between electrical power input and mechanical power output, and precise controllability make MRF technology attractive for many applications.
This paper presents the state of the art of an actuator with a control arrangement based on MRF technology. The study shows that excellent features like fast response, simple interface between electrical power input and the mechanical power output, and controllability make MRF the next technology of choice for many applications
Design of magneto-rheological (MR) valve
Magneto-Rheological Fluid (“MRF”) technology has been successfully employed in various low and high volume automotive applications. Good understanding of specific design constraints is required to define and to optimize a magneto-rheological device. This article presents parametrical analyses with magnetic simulations, of a magneto-rheological valve and a magneto-rheological orifice. Experimental rig assemblies of two different control devices have been designed, built and the performances have been evaluated experimentally. Controlled pressure drops, of 0.6MPa @ 4.5A at 5cm³/s in the orifice mode, and 1.5MPa @ 4.5A at 0 cm³/s, in the valve mode, using MRF132-AD, have been achieved. The study shows that excellent features like the fast response and the contactless nature of MRF control are attractive for various control devices
Possible Effects of Noncommutative Geometry on Weak CP Violation and Unitarity Triangles
Possible effects of noncommutative geometry on weak CP violation and
unitarity triangles are discussed by taking account of a simple version of the
momentum-dependent quark mixing matrix in the noncommutative standard model. In
particular, we calculate nine rephasing invariants of CP violation and
illustrate the noncommutative CP-violating effect in a couple of charged
D-meson decays. We also show how inner angles of the deformed unitarity
triangles are related to CP-violating asymmetries in some typical B_d and B_s
transitions into CP eigenstates. B-meson factories are expected to help probe
or constrain noncommutative geometry at low energies in the near future.Comment: RexTev 16 pages. Modifications made. References added. Accepted for
publication in Phys. Rev.
Electromagnetic Polarization Effects due to Axion Photon Mixing
We investigate the effect of axions on the polarization of electromagnetic
waves as they propagate through astronomical distances. We analyze the change
in the dispersion of the electromagnetic wave due to its mixing with axions. We
find that this leads to a shift in polarization and turns out to be the
dominant effect for a wide range of frequencies. We analyze whether this effect
or the decay of photons into axions can explain the large scale anisotropies
which have been observed in the polarizations of quasars and radio galaxies. We
also comment on the possibility that the axion-photon mixing can explain the
dimming of distant supernovae.Comment: 18 pages, 1 figur
Pair Phase Fluctuations and the Pseudogap
The single-particle density of states and the tunneling conductance are
studied for a two-dimensional BCS-like Hamiltonian with a d_{x^2-y^2}-gap and
phase fluctuations. The latter are treated by a classical Monte Carlo
simulation of an XY model. Comparison of our results with recent scanning
tunneling spectra of Bi-based high-T_c cuprates supports the idea that the
pseudogap behavior observed in these experiments can be understood as arising
from phase fluctuations of a d_{x^2-y^2} pairing gap whose amplitude forms on
an energy scale set by T_c^{MF} well above the actual superconducting
transition.Comment: 5 pages, 6 eps-figure
Pairing of fermions in atomic traps and nuclei
Pairing gaps for fermionic atoms in harmonic oscillator traps are calculated
for a wide range of interaction strengths and particle number, and compared to
pairing in nuclei. Especially systems, where the pairing gap exceeds the level
spacing but is smaller than the shell splitting , are studied
which applies to most trapped Fermi atomic systems as well as to finite nuclei.
When solving the gap equation for a large trap with such multi-level pairing,
one finds that the matrix elements between nearby harmonic oscillator levels
and the quasi-particle energies lead to a double logarithm of the gap, and a
pronounced shell structure at magic numbers. It is argued that neutron and
proton pairing in nuclei belongs to the class of multi-level pairing, that
their shell structure follows naturally and that the gaps scale as - all in qualitative agreement with odd-even staggering of nuclear
binding energies. Pairing in large systems are related to that in the bulk
limit. For large nuclei the neutron and proton superfluid gaps approach the
asymptotic value in infinite nuclear matter: MeV.Comment: 11 pages, 5 figure
Shallow structure beneath the Central Volcanic Complex of Tenerife from new gravity data: implications for its evolution and recent reactivation
We present a new local Bouguer anomaly map of the Central Volcanic Complex (CVC) of Tenerife, Spain, constructed from the amalgamation of 323 new high precision gravity measurements with existing gravity data from 361 observations. The new anomaly map images the high-density core of the CVC and the pronounced gravity low centred in the Las Cañadas caldera in greater detail than previously available. Mathematical construction of a sub-surface model from the local anomaly data, employing a 3D inversion based on 'growing' the sub-surface density distribution via the aggregation of cells, enables mapping of the shallow structure beneath the complex, giving unprecedented insights into the sub-surface architecture. We find the resultant density distribution in agreement with geological and other geophysical data. The modelled sub-surface structure supports a vertical collapse origin of the caldera, and maps the headwall of the ca. 180 ka Icod landslide, which appears to lie buried beneath the Pico Viejo–Pico Teide stratovolcanic complex. The results allow us to put into context the recorded ground deformation and gravity changes at the CVC during its reactivation in spring 2004 in relation to its dominant structural building blocks. For example, the areas undergoing the most significant changes at depth in recent years are underlain by low-density material and are aligned along long-standing structural entities, which have shaped this volcanic ocean island over the past few million years
Complete solutions to the metric of spherically collapsing dust in an expanding spacetime with a cosmological constant
We present semi-analytical solutions to the background equations describing
the Lema\^itre-Tolman-Bondi (LTB) metric as well as the homogeneous Friedmann
equations, in the presence of dust, curvature and a cosmological constant
Lambda. For none of the presented solutions any numerical integration has to be
performed. All presented solutions are given for expanding and collapsing
phases, preserving continuity in time and radius. Hence, these solutions
describe the complete space time of a collapsing spherical object in an
expanding universe. In the appendix we present for completeness a solution of
the Friedmann equations in the additional presence of radiation, only valid for
the Robertson-Walker metric.Comment: 23 pages, one figure. Numerical module for evaluation of the
solutions released at
http://web.physik.rwth-aachen.de/download/valkenburg/ColLambda/ Matches
published version, published under Open Access. Note change of titl
Time-frequency scaling transformation of the phonocardiogram based of the matching pursuit method.
International audienceA time-frequency scaling transformation based on the matching pursuit (MP) method is developed for the phonocardiogram (PCG). The MP method decomposes a signal into a series of time-frequency atoms by using an iterative process. The modification of the time scale of the PCG can be performed without perceptible change in its spectral characteristics. It is also possible to modify the frequency scale without changing the temporal properties. The technique has been tested on 11 PCG's containing heart sounds and different murmurs. A scaling/inverse-scaling procedure was used for quantitative evaluation of the scaling performance. Both the spectrogram and a MP-based Wigner distribution were used for visual comparison in the time-frequency domain. The results showed that the technique is suitable and effective for the time-frequency scale transformation of both the transient property of the heart sounds and the more complex random property of the murmurs. It is also shown that the effectiveness of the method is strongly related to the optimization of the parameters used for the decomposition of the signals
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