15,049 research outputs found
Report by the ESA-ESO Working Group on Fundamental Cosmology
ESO and ESA agreed to establish a number of Working Groups to explore
possible synergies between these two major European astronomical institutions.
This Working Group's mandate was to concentrate on fundamental questions in
cosmology, and the scope for tackling these in Europe over the next ~15 years.
One major resulting recommendation concerns the provision of new generations of
imaging survey, where the image quality and near-IR sensitivity that can be
attained only in space are naturally matched by ground-based imaging and
spectroscopy to yield massive datasets with well-understood photometric
redshifts (photo-z's). Such information is essential for a range of new
cosmological tests using gravitational lensing, large-scale structure, clusters
of galaxies, and supernovae. Great scope in future cosmology also exists for
ELT studies of the intergalactic medium and space-based studies of the CMB and
gravitational waves; here the synergy is less direct, but these areas will
remain of the highest mutual interest to the agencies. All these recommended
facilities will produce vast datasets of general applicability, which will have
a tremendous impact on broad areas of astronomy.Comment: ESA-ESO Working Groups Report No. 3, 125 pages, 28 figures. A PDF
version including the cover is available from
http://www.stecf.org/coordination/esa_eso/cosmology/report_cover.pdf and a
printed version (A5 booklet) is available in limited numbers from the Space
Telescope-European Coordinating Facility (ST-ECF): [email protected]
Heat Transfer Mechanism In Particle-Laden Turbulent Shearless Flows
Particle-laden turbulent flows are one of the complex flow regimes involved in a wide range of environmental, industrial, biomedical and aeronautical applications. Recently the interest has included also the interaction between scalars and particles, and the complex scenario which arises from the interaction of particle finite inertia, temperature transport, and momentum and heat feedback of particles on the flow leads to a multi-scale and multi-physics phenomenon which is not yet fully understood. The present work aims to investigate the fluid-particle thermal interaction in turbulent mixing under one-way and two-way coupling regimes. A recent novel numerical framework has been used to investigate the impact of suspended sub-Kolmogorov inertial particles on heat transfer within the mixing layer which develops at the interface of two regions with different temperature in an isotropic turbulent flow. Temperature has been considered a passive scalar, advected by the solenoidal velocity field, and subject to the particle thermal feedback in the two-way regime. A self-similar stage always develops where all single-point statistics of the carrier fluid and the suspended particles collapse when properly re-scaled.
We quantify the effect of particle inertial, parametrized through the Stokes and thermal Stokes numbers, on the heat transfer through the Nusselt number, defined as the ratio of the heat transfer to the thermal diffusion. A scale analysis will be presented. We show how the modulation of fluid temperature gradients due to the statistical alignments of the particle velocity and the local carrier flow temperature gradient field, impacts the overall heat transfer in the two-way coupling regime
Review of the Synergies Between Computational Modeling and Experimental Characterization of Materials Across Length Scales
With the increasing interplay between experimental and computational
approaches at multiple length scales, new research directions are emerging in
materials science and computational mechanics. Such cooperative interactions
find many applications in the development, characterization and design of
complex material systems. This manuscript provides a broad and comprehensive
overview of recent trends where predictive modeling capabilities are developed
in conjunction with experiments and advanced characterization to gain a greater
insight into structure-properties relationships and study various physical
phenomena and mechanisms. The focus of this review is on the intersections of
multiscale materials experiments and modeling relevant to the materials
mechanics community. After a general discussion on the perspective from various
communities, the article focuses on the latest experimental and theoretical
opportunities. Emphasis is given to the role of experiments in multiscale
models, including insights into how computations can be used as discovery tools
for materials engineering, rather than to "simply" support experimental work.
This is illustrated by examples from several application areas on structural
materials. This manuscript ends with a discussion on some problems and open
scientific questions that are being explored in order to advance this
relatively new field of research.Comment: 25 pages, 11 figures, review article accepted for publication in J.
Mater. Sc
Flow induced ultrasound scattering: experimental studies
Sound scattering by a finite width beam on a single rigid body rotation
vortex flow is detected by a linear array of transducers (both smaller than a
flow cell), and analyzed using a revised scattering theory. Both the phase and
amplitude of the scattered signal are obtained on 64 elements of the detector
array and used for the analysis of velocity and vorticity fields. Due to
averaging on many pulses the signal-to-noise ratio of the phases difference in
the scattered sound signal can be amplified drastically, and the resolution of
the method in the detection of circulation, vortex radius, vorticity, and
vortex location becomes comparable with that obtained earlier by time-reversal
mirror (TRM) method (P. Roux, J. de Rosny, M. Tanter, and M. Fink, {\sl Phys.
Rev. Lett.} {\bf 79}, 3170 (1997)). The revised scattering theory includes two
crucial steps, which allow overcoming limitations of the existing theories.
First, the Huygens construction of a far field scattering signal is carried out
from a signal obtained at any intermediate plane. Second, a beam function that
describes a finite width beam is introduced, which allows using a theory
developed for an infinite width beam for the relation between a scattering
amplitude and the vorticity structure function. Structure functions of the
velocity and vorticity fields deduced from the sound scattering signal are
compared with those obtained from simultaneous particle image velocimetry (PIV)
measurements. Good quantitative agreement is found.Comment: 14 pages, 23 figures. accepted for publication in Phys. Fluids(June
issue
Machining-based coverage path planning for automated structural inspection
The automation of robotically delivered nondestructive evaluation inspection shares many aims with traditional manufacture machining. This paper presents a new hardware and software system for automated thickness mapping of large-scale areas, with multiple obstacles, by employing computer-aided drawing (CAD)/computer-aided manufacturing (CAM)-inspired path planning to implement control of a novel mobile robotic thickness mapping inspection vehicle. A custom postprocessor provides the necessary translation from CAM numeric code through robotic kinematic control to combine and automate the overall process. The generalized steps to implement this approach for any mobile robotic platform are presented herein and applied, in this instance, to a novel thickness mapping crawler. The inspection capabilities of the system were evaluated on an indoor mock-inspection scenario, within a motion tracking cell, to provide quantitative performance figures for positional accuracy. Multiple thickness defects simulating corrosion features on a steel sample plate were combined with obstacles to be avoided during the inspection. A minimum thickness mapping error of 0.21 mm and a mean path error of 4.41 mm were observed for a 2 m² carbon steel sample of 10-mm nominal thickness. The potential of this automated approach has benefits in terms of repeatability of area coverage, obstacle avoidance, and reduced path overlap, all of which directly lead to increased task efficiency and reduced inspection time of large structural assets
Scan and paint: theory and practice of a sound field visualization method
Sound visualization techniques have played a key role in the development of acoustics throughout history. The development of measurement apparatus and techniques for displaying sound and vibration phenomena has provided excellent tools for building understanding about specific problems. Traditional methods, such as step-by-step measurements or simultaneous multichannel systems, have a strong tradeoff between time requirements, flexibility, and cost. However, if the sound field can be assumed time stationary, scanning methods allow us to assess variations across space with a single transducer, as long as the position of the sensor is known. The proposed technique, Scan and Paint, is based on the acquisition of sound pressure and particle velocity by manually moving a P-U probe (pressure-particle velocity sensors) across a sound field whilst filming the event with a camera. The sensor position is extracted by applying automatic color tracking to each frame of the recorded video. It is then possible to visualize sound variations across the space in terms of sound pressure, particle velocity, or acoustic intensity. In this paper, not only the theoretical foundations of the method, but also its practical applications are explored such as scanning transfer path analysis, source radiation characterization, operational deflection shapes, virtual phased arrays, material characterization, and acoustic intensity vector field mapping
Black-hole binaries, gravitational waves, and numerical relativity
Understanding the predictions of general relativity for the dynamical
interactions of two black holes has been a long-standing unsolved problem in
theoretical physics. Black-hole mergers are monumental astrophysical events,
releasing tremendous amounts of energy in the form of gravitational radiation,
and are key sources for both ground- and space-based gravitational-wave
detectors. The black-hole merger dynamics and the resulting gravitational
waveforms can only be calculated through numerical simulations of Einstein's
equations of general relativity. For many years, numerical relativists
attempting to model these mergers encountered a host of problems, causing their
codes to crash after just a fraction of a binary orbit could be simulated.
Recently, however, a series of dramatic advances in numerical relativity has
allowed stable, robust black-hole merger simulations. This remarkable progress
in the rapidly maturing field of numerical relativity, and the new
understanding of black-hole binary dynamics that is emerging is chronicled.
Important applications of these fundamental physics results to astrophysics, to
gravitational-wave astronomy, and in other areas are also discussed.Comment: 54 pages, 42 figures. Some typos corrected & references updated.
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