2,040 research outputs found
Sound attenuation apparatus
An apparatus is disclosed for reducing acoustic transmission from mechanical or acoustic sources by means of a double wall partition, within which an acoustic pressure field is generated by at least one secondary acoustic source. The secondary acoustic source is advantageously placed within the partition, around its edges, or it may be an integral part of a wall of the partition
Statistics of Conductances and Subleading Corrections to Scaling near the Integer Quantum Hall Plateau Transition
We study the critical behavior near the integer quantum Hall plateau
transition by focusing on the multifractal (MF) exponents describing the
scaling of the disorder-average moments of the point contact conductance
between two points of the sample, within the Chalker-Coddington network model.
Past analytical work has related the exponents to the MF exponents
of the local density of states (LDOS). To verify this relation, we
numerically determine the exponents with high accuracy. We thereby
provide, at the same time, independent numerical results for the MF exponents
for the LDOS. The presence of subleading corrections to scaling
makes such determination directly from scaling of the moments of virtually
impossible. We overcome this difficulty by using two recent advances. First, we
construct pure scaling operators for the moments of which have precisely
the same leading scaling behavior, but no subleading contributions. Secondly,
we take into account corrections to scaling from irrelevant (in the
renormalization group sense) scaling fields by employing a numerical technique
("stability map") recently developed by us. We thereby numerically confirm the
relation between the two sets of exponents, (point contact conductances)
and (LDOS), and also determine the leading irrelevant (corrections
to scaling) exponent as well as other subleading exponents. Our results
suggest a way to access multifractality in an experimental setting.Comment: 7 pages and 4 figures, plus Supplemental materia
Large Civil Tiltrotor (LCTR2) Interior Noise Predictions due to Turbulent Boundary Layer Excitation
The Large Civil Tiltrotor (LCTR2) is a conceptual vehicle that has a design goal to transport 90 passengers over a distance of 1800 km at a speed of 556 km/hr. In this study noise predictions were made in the notional LCTR2 cabin due to Cockburn/Robertson and Efimtsov turbulent boundary layer (TBL) excitation models. A narrowband hybrid Finite Element (FE) analysis was performed for the low frequencies (6-141 Hz) and a Statistical Energy Analysis (SEA) was conducted for the high frequency one-third octave bands (125- 8000 Hz). It is shown that the interior sound pressure level distribution in the low frequencies is governed by interactions between individual structural and acoustic modes. The spatially averaged predicted interior sound pressure levels for the low frequency hybrid FE and the high frequency SEA analyses, due to the Efimtsov turbulent boundary layer excitation, were within 1 dB in the common 125 Hz one-third octave band. The averaged interior noise levels for the LCTR2 cabin were predicted lower than the levels in a comparable Bombardier Q400 aircraft cabin during cruise flight due to the higher cruise altitude and lower Mach number of the LCTR2. LCTR2 cabin noise due to TBL excitation during cruise flight was found not unacceptable for crew or passengers when predictions were compared to an acoustic survey on a Q400 aircraft
Reverberation Time Measurements in the NASA Langley Exterior Effects Room (EER)
One-third octave band background noise and reverberation time measurements were conducted in the Exterior Effect Room (EER) at the NASA Langley Research Center. The related overall acoustic absorption of the room was calculated. The acoustic field in the room was characterized. Reverberation time measurements were performed using the integrated impulse response method. The results were compared with independent measurements using the interrupted noise reverberation time method and different instrumentation. Reasonable agreement was obtained between the reverberation times of the two methods
COMBINING TASTE PANELS WITH FOCUS GROUPS TO ELICIT CONSUMER PREFERENCES TOWARD A NEW SHRIMP PRODUCT
Consumer/Household Economics,
Preliminary Assessment of the Interior Noise Environment in the Large Civil Tiltrotor (LCTR2)
The second-generation Large Civil Tiltrotor (LCTR2) serves as a representative vehicle under the NASA Fundamental Aeronautics Program (FAP) Subsonic Rotary Wing (SRW) project with a design goal to transport 90 passengers over a distance of 1800 km at a speed of 550 km/hr. The tiltrotor combines the vertical lift capability of a helicopter with the speed, altitude, and range of a turboprop airplane. The blade-passage frequency of the four-bladed rotor is as low as 6.9 Hz during cruise conditions. The resulting low-frequency acoustic excitation and its harmonics, combined with the anticipated use of lightweight composite and sandwich materials for the fuselage sidewall, may pose a challenge to achieving acceptable interior noise levels. The objective of the present study is to perform a preliminary assessment of the expected interior noise environment in the LCTR2 cabin. The approach includes a combination of semi-empirical, analytical, and statistical energy analysis methods. Because the LCTR2 is a notional vehicle, the prediction approach was also applied to the XV-15 tiltrotor and Bombardier Q400 turobprop aircraft to compare predictions with publicly available experimental data. Guidance for the expected interior noise levels in the LCTR2 was obtained by considering both the predicted exterior noise levels and the transmission loss of a basic fuselage sidewall consisting of a skin, porous layer and a trim panel. Structural and acoustic resonances are expected to coincide with low order harmonics of the blade passage frequency. The estimated sound pressure levels in the LCTR2 may not be acceptable when evaluated against known characteristics of human response to low frequency sound
Ising model on nonorientable surfaces: Exact solution for the Moebius strip and the Klein bottle
Closed-form expressions are obtained for the partition function of the Ising
model on an M x N simple-quartic lattice embedded on a Moebius strip and a
Klein bottle for finite M and N. The finite-size effects at criticality are
analyzed and compared with those under cylindrical and toroidal boundary
conditions. Our analysis confirms that the central charge is c=1/2.Comment: 8 pages, 3 eps figure
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