39,710 research outputs found
Optimization of sensor locations for measurement of flue gas flow in industrial ducts and stacks using neural networks
This paper presents a novel application of neural network modeling in the optimization of sensor locations for the measurement of flue gas flow in industrial ducts and stacks. The proposed neural network model has been validated with an experiment based upon a case-study power plant. The results have shown that the optimized sensor location can be easily determined with this model. The industry can directly benefit from the improvement of measurement accuracy of the flue gas flow in the optimized sensor location and the reduction of manual measurement operation with Pitot tube
Sound Environments in Large Public Buildings for Crowd Transit: A Systematic Review
Sound environments in large public buildings are likely to be different from those of performance spaces, as well as those not specifically designed for acoustic âperformanceâ, but where sounds still play an important role because of the function they can promote (or disrupt). The aim of this study was identifying common strategies and empirical approaches researchers have been implementing for these acoustically complex enclosures and to provide some methodological indications for future studies on the topic. Studies conducted in three building types for crowd transit, such as museums/exhibition spaces, shopping malls, and transportation hubs/stations, which were collecting data about either physical outcomes or individual responses for such sound environments, were selected. The Scopus databases were searched for peer-reviewed journal papers published in English without time limitations. An additional manual search was performed on the reference lists of the retrieved items. The general consideration on inclusion was to meet the requirement that the case belonged to the three building types, and then the specific inclusion criteria were: (1) including at least an objective acoustic measure of the space; or (2) including at least a subjective measure of the space. The search returned 1060 results; after removing duplicates, two authors screened titles and abstracts and selected 117 papers for further analysis. Twenty-six studies were eventually included. Due to the limited number of items and differences in measures across studies, a quantitative meta-analysis could not be performed, and a qualitative approach was adopted instead. The most commonly used objective measures were SPL, and more specifically often considered as LAeq, and T. The intervals across studies were currently of inconsistency, and the selection is recommended to take space scale factor into account. The used subjective measures can be classified into four categories as annoyance, affective quality, room-acoustic quality, and acoustic spatiality. Four basic perceptual assessments concerning dynamic contents are accordingly suggested as âannoying-not annoyingâ, âcrowded-uncrowdedâ, âlong-short (reverberation)â, and âfar away-nearbyâ. The other descriptors can be project-specific. The methodologies involve measurement, questionnaire/interview, listening test, and software simulation. It is necessary for the former two to consider temporal and spatial features of such spaces, and the adoption of the latter two will lead to better understanding of usersâ exposure in such spaces, e.g., acoustic sequences and user amount. The outputs of investigations inform that background noise level, e.g., 90 dB in museum/exhibition spaces, and sound reverberation, e.g., 4.0 to 5.0 s in shopping malls and transportation hubs/station, are of fundamental importance to the design of such spaces. Sufficient acoustic comfort can be achieved with integrated design of indoor soundscape
Neutrino Background Flux from Sources of Ultrahigh-Energy Cosmic-Ray Nuclei
Motivated by Pierre Auger Observatory results favoring a heavy nuclear
composition for ultrahigh-energy (UHE) cosmic rays, we investigate implications
for the cumulative neutrino background. The requirement that nuclei not be
photodisintegrated constrains their interactions in sources, therefore limiting
neutrino production via photomeson interactions. Assuming a injection spectrum and
photodisintegration via the giant dipole resonance, the background flux of
neutrinos is lower than if UHE nuclei ubiquitously survive in
their sources. This is smaller than the analogous Waxman-Bahcall flux for UHE
protons by about one order of magnitude, and is below the projected IceCube
sensitivity. If IceCube detects a neutrino background, it could be due to other
sources, e.g., hadronuclear interactions of lower-energy cosmic rays; if it
does not, this supports our strong restrictions on the properties of sources of
UHE nuclei.Comment: 7 pages, 3 figure
Magnetic Interaction in the Geometrically Frustrated Triangular Lattice Antiferromagnet
The spin wave excitations of the geometrically frustrated triangular lattice
antiferromagnet (TLA) have been measured using high resolution
inelastic neutron scattering. Antiferromagnetic interactions up to third
nearest neighbors in the ab plane (J_1, J_2, J_3, with
and ), as well as out-of-plane coupling (J_z, with
) are required to describe the spin wave dispersion
relations, indicating a three dimensional character of the magnetic
interactions. Two energy dips in the spin wave dispersion occur at the
incommensurate wavevectors associated with multiferroic phase, and can be
interpreted as dynamic precursors to the magnetoelectric behavior in this
system.Comment: 4 pages, 4 figures, published in Phys. Rev. Let
Monoclinic and Correlated Metal Phase in VO_2 as Evidence of the Mott Transition: Coherent Phonon Analysis
In femtosecond pump-probe measurements, the appearance of coherent phonon
oscillations at 4.5 THz and 6.0 THz indicating the rutile metal phase of VO_2
does not occur simultaneously with the first-order metal-insulator transition
(MIT) near 68^oC. The monoclinic and correlated metal(MCM) phase between the
MIT and the structural phase transition (SPT) is generated by a photo-assisted
hole excitation which is evidence of the Mott transition. The SPT between the
MCM phase and the rutile metal phase occurs due to subsequent Joule heating.
The MCM phase can be regarded as an intermediate non-equilibrium state.Comment: 4 pages, 2 figure
Collecting and mapping soundscape data across the 15 UK National Parks
The soundscape approach, as understood by the ISO 12913 series, is most applied in urban settings, aiming beyond noise control in order to holistically employ its quantitative and qualitative facets. On the other side, the current understanding of the soundscape concept in bioacoustics and acoustic ecology is less focused on perception. There is generally a lot of public interest in how to preserve the opportunity for people to experience the ânatural quietâ and âthe sounds of natureâ, and the need to balance that with the protection of the natural areas and national parks from the noise that the visitors themselves generate while on site. However, specific investigations in these environments are scarce in the United Kingdom. Moreover, while there might be acoustic environments and sound sources that people identify with national parks, they are not systematically documented nor implemented in the national parks' management plans. Therefore, we propose a framework starting with a quasi-crowd-sourced acquisition of soundscape data and mapping those to a freely accessible GIS platform such as Google Earth, leading towards identifying soundscape conservation targets and management tools for the UK national parks, further raising the awareness of the value of sound as a resource
Efficiency of Nonlinear Particle Acceleration at Cosmic Structure Shocks
We have calculated the evolution of cosmic ray (CR) modified astrophysical
shocks for a wide range of shock Mach numbers and shock speeds through
numerical simulations of diffusive shock acceleration (DSA) in 1D quasi-
parallel plane shocks. The simulations include thermal leakage injection of
seed CRs, as well as pre-existing, upstream CR populations. Bohm-like diffusion
is assumed. We model shocks similar to those expected around cosmic structure
pancakes as well as other accretion shocks driven by flows with upstream gas
temperatures in the range K and shock Mach numbers spanning
. We show that CR modified shocks evolve to time-asymptotic states
by the time injected particles are accelerated to moderately relativistic
energies (p/mc \gsim 1), and that two shocks with the same Mach number, but
with different shock speeds, evolve qualitatively similarly when the results
are presented in terms of a characteristic diffusion length and diffusion time.
For these models the time asymptotic value for the CR acceleration efficiency
is controlled mainly by shock Mach number. The modeled high Mach number shocks
all evolve towards efficiencies %, regardless of the upstream CR
pressure. On the other hand, the upstream CR pressure increases the overall CR
energy in moderate strength shocks (). (abridged)Comment: 23 pages, 12 ps figures, accepted for Astrophysical Journal (Feb. 10,
2005
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