9,311 research outputs found
Inversion of spinning sound fields
A method is presented for the reconstruction of rotating monopole source
distributions using acoustic pressures measured on a sideline parallel to the
source axis. The method requires no \textit{a priori} assumptions about the
source other than that its strength at the frequency of interest vary
sinusoidally in azimuth on the source disc so that the radiated acoustic field
is composed of a single circumferential mode. When multiple azimuthal modes are
present, the acoustic field can be decomposed into azimuthal modes and the
method applied to each mode in sequence.
The method proceeds in two stages, first finding an intermediate line source
derived from the source distribution and then inverting this line source to
find the radial variation of source strength. A far-field form of the radiation
integrals is derived, showing that the far field pressure is a band-limited
Fourier transform of the line source, establishing a limit on the quality of
source reconstruction which can be achieved using far-field measurements. The
method is applied to simulated data representing wind-tunnel testing of a
ducted rotor system (tip Mach number~0.74) and to control of noise from an
automotive cooling fan (tip Mach number~0.14), studies which have appeared in
the literature of source identification.Comment: Revised version of paper submitted to JASA; five more figures;
expanded content with more discussion of error behaviour and relation to
Nearfield Acoustical Holograph
Recommended from our members
Pituophis ruthveni
Number of Pages: 16Geological SciencesIntegrative Biolog
Implications of Constraints on Mass Parameters in the Higgs Sector of the Nonlinear Supersymmetric SU(5) Model
The Higgs sector of the minimal nonlinear supersymmetric SU(5) model contains
three mass parameters. Although these mass parameters are essentially free at
the electroweak scale, they might have particular values if they evolve from a
particular constraints at the GUT scale through the RG equations. By assuming a
number of simple constraints on these mass parameters at the GUT scale, we
obtain their values at the electroweak scale through the RG equations in order
to investigate the phenomenological implications. Some of them are found to be
consistent with the present experimental data.Comment: 23 pages, 10 figure
Introduction to Categories and Categorical Logic
The aim of these notes is to provide a succinct, accessible introduction to
some of the basic ideas of category theory and categorical logic. The notes are
based on a lecture course given at Oxford over the past few years. They contain
numerous exercises, and hopefully will prove useful for self-study by those
seeking a first introduction to the subject, with fairly minimal prerequisites.
The coverage is by no means comprehensive, but should provide a good basis for
further study; a guide to further reading is included. The main prerequisite is
a basic familiarity with the elements of discrete mathematics: sets, relations
and functions. An Appendix contains a summary of what we will need, and it may
be useful to review this first. In addition, some prior exposure to abstract
algebra - vector spaces and linear maps, or groups and group homomorphisms -
would be helpful.Comment: 96 page
Quantum Films Adsorbed on Graphite: Third and Fourth Helium Layers
Using a path-integral Monte Carlo method for simulating superfluid quantum
films, we investigate helium layers adsorbed on a substrate consisting of
graphite plus two solid helium layers. Our results for the promotion densities
and the dependence of the superfluid density on coverage are in agreement with
experiment. We can also explain certain features of the measured heat capacity
as a function of temperature and coverage.Comment: 13 pages in the Phys. Rev. two-column format, 16 Figure
A (1,2) Heterotic String with Gauge Symmetry
We construct a (1,2) heterotic string with gauge symmetry and determine its
particle spectrum. This theory has a local N=1 worldsheet supersymmetry for
left movers and a local N=2 worldsheet supersymmetry for right movers and
describes particles in either two or three space-time dimensions. We show that
fermionizing the bosons of the compactified N=1 space leads to a particle
spectrum which has nonabelian gauge symmetry. The fermionic formulation of the
theory corresponds to a dimensional reduction of self dual Yang Mills. We also
give a worldsheet action for the theory and calculate the one-loop path
integral.Comment: 17 pages, added reference
Recombinant factorVIII Fc fusion protein for the prevention and treatment of bleeding in children with severe hemophilia A
This work was supported
by funding from Biogen, including funding for the
editorial and writing support in the the development of
this paper
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