10,677 research outputs found
Acoustic radiation patterns for a source in a hard-walled unflanged circular duct
Acoustic radiation patterns are measured over a 320 deg arc for a point source in a finite length, hard walled, unflanged circular duct. The measured results are compared with computed results which are based on the Wiener-Hopf solution for radiation from a semi-infinite unflanged duct. Measurements and computations are presented for frequencies slightly below and slightly above each of the first four higher order radial mode cutoff frequencies. It is found that the computed and measured patterns show better agreement below the mode cut-off frequencies than above and that the agreement is better at lower frequencies that at higher frequencies. The computed radiation patterns do not show fine lobes which are caused by diffraction from the back end of the duct
Two-component {CH} system: Inverse Scattering, Peakons and Geometry
An inverse scattering transform method corresponding to a Riemann-Hilbert
problem is formulated for CH2, the two-component generalization of the
Camassa-Holm (CH) equation. As an illustration of the method, the multi -
soliton solutions corresponding to the reflectionless potentials are
constructed in terms of the scattering data for CH2.Comment: 22 pages, 3 figures, draft, please send comment
Forward velocity effects on fan noise and the influence of inlet aeroacoustic design as measured in the NASA Ames 40 x 80 foot wind tunnel
The inlet radiated noise of a turbofan engine was studied. The principal research objectives were to characterize or suppress such noise with particular regard to its tonal characteristics. The major portion of this research was conducted by using ground-based static testing without simulation of aircraft forward speed or aircraft installation-related aeroacoustic effects
JT15D simulated flight data evaluation
The noise characteristics of the JT15D turbofan engine was analyzed with the objectives of: (1) assessing the state-of-art ability to simulate flight acoustic data using test results acquired in wind tunnel and outdoor (turbulence controlled) environments; and (2) predicting the farfield noise directivity of the blade passage frequency (BPF) tonal components using results from rotor blade mounted dynamic pressure instrumentation. Engine rotor tip speeds at subsonic, transonic, and supersonic conditions were evaluated. The ability to simulate flight results was generally within 2-3 dB for both outdoor and wind tunnel acoustic results. Some differences did occur in the broadband noise level and in the multiple-pure-tone harmonics at supersonic tip speeds. The prediction of blade passage frequency tone directivity from dynamic pressure measurements was accomplished for the three tip speed conditions. Predictions were made of the random and periodic components of the tone directivity. The technique for estimating the random tone component used hot wire data to establish a correlation between dynamic pressure and turbulence intensity. This prediction overestimated the tone level by typically 10 dB with the greatest overestimates occurring at supersonic conditions
Current-induced phase transition in ballistic Ni nanocontacts
Local phase transition from ferromagnetic to paramagnetic state in the region
of the ballistic Ni nanocontacts (NCs) has been experimentally observed. We
found that contact size reduction leads to an increase in the bias voltage at
which the local phase transition occurs. Presented theoretical interpretation
of this phenomena takes into the account the specificity of the local heating
of the ballistic NC and describes the electron's energy relaxation dependences
on the applied voltage. The experimental data are in good qualitative and
quantitative agreement with the theory proposed.Comment: 8 pages, 2 figure
Ballistic and Diffuse Electron Transport in Nanocontacts of Magnetics
The transition from the ballistic electron transport to the diffuse one is
experimentally observed in the study of the magnetic phase transition in Ni
nanocontacts with different sizes. It is shown that the voltage needed
for Joule heating of the near-contact region to the critical temperature does
not depend on the contact size only in the diffuse mode. For the ballistic
contact it increases with decrease in the nanocontact size. The reduction of
the transport electron mean free path due to heating of NCs may result in
change of the electron transport mode from ballistic to diffusive one.Comment: 7 pages, 2 figures accepted for the publication in JETPL
(http://www.jetpletters.ac.ru). Will be published on 25 april 201
Signalment risk factors for cutaneous and renal glomerular vasculopathy (Alabama rot) in dogs in the UK
Seasonal outbreaks of cutaneous and renal glomerular vasculopathy (CRGV) have been reported annually in UK dogs since 2012, yet the aetiology of the disease remains unknown. The objectives of this study were to explore whether any breeds had an increased or decreased risk of being diagnosed with CRGV, and to report on age and sex distributions of CRGV cases occurring in the UK. Multivariable logistic regression was used to compare 101 dogs diagnosed with CRGV between November 2012 and May 2017 with a denominator population of 446,453 dogs from the VetCompass database. Two Kennel Club breed groups—hounds (odds ratio (OR) 10.68) and gun dogs (OR 9.69)—had the highest risk of being diagnosed with CRGV compared with terriers, while toy dogs were absent from among CRGV cases. Females were more likely to be diagnosed with CRGV (OR 1.51) as were neutered dogs (OR 3.36). As well as helping veterinarians develop an index of suspicion for the disease, better understanding of the signalment risk factors may assist in the development of causal models for CRGV and help identify the aetiology of the disease
An integrable shallow water equation with peaked solitons
We derive a new completely integrable dispersive shallow water equation that
is biHamiltonian and thus possesses an infinite number of conservation laws in
involution. The equation is obtained by using an asymptotic expansion directly
in the Hamiltonian for Euler's equations in the shallow water regime. The
soliton solution for this equation has a limiting form that has a discontinuity
in the first derivative at its peak.Comment: LaTeX file. Figure available from authors upon reques
Breakdown of disordered media by surface loads
We model an interface layer connecting two parts of a solid body by N
parallel elastic springs connecting two rigid blocks. We load the system by a
shear force acting on the top side. The springs have equal stiffness but are
ruptured randomly when the load reaches a critical value. For the considered
system, we calculate the shear modulus, G, as a function of the order
parameter, \phi, describing the state of damage, and also the ``spalled''
material (burst) size distribution. In particular, we evaluate the relation
between the damage parameter and the applied force and explore the behaviour in
the vicinity of material breakdown. Using this simple model for material
breakdown, we show that damage, caused by applied shear forces, is analogous to
a first-order phase transition. The scaling behaviour of G with \phi is
explored analytically and numerically, close to \phi=0 and \phi=1 and in the
vicinity of \phi_c, when the shear load is close but below the threshold force
that causes material breakdown. Our model calculation represents a first
approximation of a system subject to wear induced loads.Comment: 15 pages, 7 figure
Generalized Euler-Poincar\'e equations on Lie groups and homogeneous spaces, orbit invariants and applications
We develop the necessary tools, including a notion of logarithmic derivative
for curves in homogeneous spaces, for deriving a general class of equations
including Euler-Poincar\'e equations on Lie groups and homogeneous spaces.
Orbit invariants play an important role in this context and we use these
invariants to prove global existence and uniqueness results for a class of PDE.
This class includes Euler-Poincar\'e equations that have not yet been
considered in the literature as well as integrable equations like Camassa-Holm,
Degasperis-Procesi, CH and DP equations, and the geodesic equations
with respect to right invariant Sobolev metrics on the group of diffeomorphisms
of the circle
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