11,841 research outputs found
Propagating and evanescent internal waves in a deep ocean model
We present experimental and computational studies of the propagation of
internal waves in a stratified fluid with an exponential density profile that
models the deep ocean. The buoyancy frequency profile (proportional to
the square root of the density gradient) varies smoothly by more than an order
of magnitude over the fluid depth, as is common in the deep ocean. The
nonuniform stratification is characterized by a turning depth , where
is equal to the wave frequency and .
Internal waves reflect from the turning depth and become evanescent below the
turning depth. The energy flux below the turning depth is shown to decay
exponentially with a decay constant given by , which is the horizontal
wavenumber at the turning depth. The viscous decay of the vertical velocity
amplitude of the incoming and reflected waves above the turning depth agree
within a few percent with a previously untested theory for a fluid of arbitrary
stratification [Kistovich and Chashechkin, J. App. Mech. Tech. Phys. 39,
729-737 (1998)].Comment: 13 pages, 4 figures, 4 table
Exploiting structure in piecewise affine identification of LFT systems
Identification of interconnected systems is a challenging problem in which it is crucial to exploit the available knowledge about the interconnection structure. In this paper, identification of discrete-time nonlinear systems composed by interconnected linear
and nonlinear systems, is addressed. An iterative identification procedure is proposed, which alternates the estimation of the linear and the nonlinear components. Standard identification techniques are applied to the linear subsystem, whereas recently developed piecewise affine (PWA) identification techniques are employed for modelling the nonlinearity. A numerical
example analyzes the benefits of the proposed structure-exploiting identification algorithm compared to applying black-box PWA identification techniques to the overall system
The Implementation of the power supply system of the CMS Silicon Strip Tracker
The power supply system of the silicon strip tracker of the CMS experiment provides HV bias and LV power to the 15000 modules of the detector, arranged into 1944 âpower groupsâ and 256 âcontrol ringsâ. Around 1200 power supply modules, disposed on 29 racks, operate in a âhostileâ radiation and magnetic field environment, 10 m away from the beam crossing region. They power the detector throughâ 50 m long custom-designed âLow Impedanceâ cables, adopting the sensing wire technique to compensate voltage drops. Detector âpower groupsâ and âcontrol groupsâ are powered bymodules of different architecture,which are fed by 48 V sources, provided by AC-DC converters installed in the racks. This paper reports the experience acquired in the implementation of the system, the rack layout, the grounding scheme, the power budget, the heat dissipation on racks. A comprehensive Quality Assurance program ensured the performance, using a well defined protocol, shared with the boardâs manufacturer, for acceptance tests and failure detection
Local trace formulae and scaling asymptotics in Toeplitz quantization
A trace formula for Toeplitz operators was proved by Boutet de Monvel and
Guillemin in the setting of general Toeplitz structures. Here we give a local
version of this result for a class of Toeplitz operators related to continuous
groups of symmetries on quantizable compact symplectic manifolds. The local
trace formula involves certain scaling asymptotics along the clean fixed locus
of the Hamiltonian flow of the symbol, reminiscent of the scaling asymptotics
of the equivariant components of the Szeg\"o kernel along the diagonal
Scaling asymptotics for quantized Hamiltonian flows
In recent years, the near diagonal asymptotics of the equivariant components
of the Szeg\"{o} kernel of a positive line bundle on a compact symplectic
manifold have been studied extensively by many authors. As a natural
generalization of this theme, here we consider the local scaling asymptotics of
the Toeplitz quantization of a Hamiltonian symplectomorphism, and specifically
how they concentrate on the graph of the underlying classical map
Reflection High-Energy Electron Diffraction oscillations during epitaxial growth of artificially layered films of (BaCuOx)m /(CaCuO2)n
Pulsed Laser Deposition in molecular-beam epitaxy environment (Laser-MBE) has
been used to grow high quality BaCuOx/CaCuO2 superlattices. In situ Reflection
High Energy Electron Diffraction (RHEED) shows that the growth mechanism is
2-dimensional. Furthermore, weak but reproducible RHEED intensity oscillations
have been monitored during the growth. Ex-situ x-ray diffraction spectra
confirmed the growth rate deduced from RHEED oscillations. Such results
demonstrate that RHEED oscillations can be used, even for (BaCuOx)2/(CaCuO2)2
superlattices, for phase locking of the growth.Comment: 9 pages, 5 figures. Corresponding author: Dr. A. Tebano:
[email protected]
Feedback Linearization in Systems with Nonsmooth Nonlinearities
This paper aims to elucidate the application of feedback linearization in systems having nonsmooth nonlinearities. With the aid of analytical expressions originating from classical feedback linearization theory, it is demonstrated that for a subset of nonsmooth systems, ubiquitous in the structural dynamics and vibrations community, the theory holds soundly. Numerical simulations on a three-degree-of-freedom aeroservoelastic system are carried out to illustrate the application of feedback linearization for a specific control objective, in the presence of dead-zone and piecewise linear structural nonlinearities in the plant. An in-depth study of the arising zero dynamics, based on a combination of analytical formulations and numerical simulations, reveals that asymptotically stable equilibria exist, paving the way for the application of feedback linearization. The latter is demonstrated successfully through pole placement on the linearized system
No more time to stay âsingleâ in the detection of Anisakis pegreffii, A. simplex (s. s.) and hybridization events between them: a multi-marker nuclear genotyping approach
A multi-marker nuclear genotyping approach was performed on larval and adult specimens of Anisakis spp. (N = 689) collected from fish and cetaceans in allopatric and sympatric areas of the two species Anisakis pegreffii and Anisakis simplex
(s. s.), in order to: (1) identify specimens belonging to the parental taxa by using nuclear markers (allozymes loci) and sequence analysis of a new diagnostic nuclear DNA locus (i.e. partial sequence of the EF1 뱉1 nDNA region) and (2) recognize hybrid categories. According to the Bayesian clustering algorithms, based on those markers, most of the individuals
(N = 678) were identified as the parental species [i.e. A. pegreffii or A. simplex (s. s.)], whereas a smaller portion (N = 11)
were recognized as F1 hybrids. Discordant results were obtained when using the polymerase chain reactionârestriction
fragment length polymorphisms (PCRâRFLPs) of the internal transcribed spacer (ITS) ribosomal DNA (rDNA) on
the same specimens, which indicated the occurrence of a large number of âhybridsâ both in sympatry and allopatry.
These findings raise the question of possible misidentification of specimens belonging to the two parental Anisakis and
their hybrid categories derived from the application of that single marker (i.e. PCRâRFLPs analysis of the ITS of
rDNA). Finally, Bayesian clustering, using allozymes and EF1 뱉1 nDNA markers, has demonstrated that hybridization
between A. pegreffii and A. simplex (s. s.) is a contemporary phenomenon in sympatric areas, while no introgressive hybridization takes place between the two species
A Low Cost Ultrasound-based Localisation System
This paper presents a low-cost localisation system based on ultrasonic sensing and time of flight measurements. A
compact ultrasound emitter has been designed to generate omnidirectional train of ultrasound pulses which are then picked up
by several fixed receivers measuring the time difference of arrival. A least squares approach is used to analytically obtain a
first estimate of the emitter position, which is then refined through steepest descent optimisation. All processing is done via a
standard Arduino platform, proving the low computational demands of the method. Localisation results are validated against
a state-of-the-art Optitrack motion capture system. It is shown that the system can cover a 4.3x3.1m arena with a mean error
localisation error of 1.57cm and an average standard deviation of 1.39cm throughout the arena
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