3,927 research outputs found
Sources, control, and effects of noise from aircraft propellers and rotors
Source noise predictions are compared with measurements for conventional low-speed propellers, for new high speed propellers (propfans), and for a helicopter. Results from a light aircraft demonstration program are described, indicating that about 5-dB reduction of flyover noise can be obtained without significant performance penalty. Sidewall design studies are described for interior noise control in light general aviation aircraft and in large transports using propfan propulsion. The weight of the added acoustic treatment is estimated and tradeoffs between weight and noise reduction are discussed. A laboratory study of passenger response to combined broadband and tonal propeller like noise is described. Subject discomfort ratings of combined tone broadband noises are compared with ratings of broadband (boundary layer) noise alone, and the relative importance of the propeller tones is examined
Model of aircraft noise adaptation
Development of an aircraft noise adaptation model, which would account for much of the variability in the responses of subjects participating in human response to noise experiments, was studied. A description of the model development is presented. The principal concept of the model, was the determination of an aircraft adaptation level which represents an annoyance calibration for each individual. Results showed a direct correlation between noise level of the stimuli and annoyance reactions. Attitude-personality variables were found to account for varying annoyance judgements
An investigation of ride quality rating scales
An experimental investigation was conducted for the combined purposes of determining the relative merits of various category scales for the prediction of human discomfort response to vibration and for determining the mathematical relationships whereby subjective data are transformed from one scale to other scales. There were 16 category scales analyzed representing various parametric combinations of polarity, that is, unipolar and bipolar, scale type, and number of scalar points. Results indicated that unipolar continuous-type scales containing either seven or nine scalar points provide the greatest reliability and discriminability. Transformations of subjective data between category scales were found to be feasible with unipolar scales of a larger number of scalar points providing the greatest accuracy of transformation. The results contain coefficients for transformation of subjective data between the category scales investigated. A result of particular interest was that the comfort half of a bipolar scale was seldom used by subjects to describe their subjective reaction to vibration
Ride quality meter
A ride quality meter is disclosed that automatically transforms vibration and noise measurements into a single number index of passenger discomfort. The noise measurements are converted into a noise discomfort value. The vibrations are converted into single axis discomfort values which are then converted into a combined axis discomfort value. The combined axis discomfort value is corrected for time duration and then summed with the noise discomfort value to obtain a total discomfort value
Metabolism of Nonessential N15-Labeled Amino Acids and the Measurement of Human Whole-Body Protein Synthesis Rates
Eight N-15 labeled nonessential amino acids plus (15)NH4Cl were administered over a 10 h period to four healthy adult males using a primed-constant dosage regimen. The amount of N-15 excreted in the urine and the urinary ammonia, hippuric acid, and plasma alanine N-15 enrichments were measured. There was a high degree of consistency across subjects in the ordering of the nine compounds based on the fraction of N-15 excreted (Kendall coefficient of concordance W = 0.83, P is less than 0.01). Protein synthesis rates were calculated from the urinary ammonia plateau enrichment and the cumulative excretion of N-15. Glycine was one of the few amino acids that gave similar values by both methods
Electron correlation effects in a wide channel from the quantum Hall edge states
The spatial behavior of Landau levels (LLs) for the quantum Hall
regime at the edge of a wide channel is studied in a self-consistent way by
using a generalized local density approximation proposed here. Both exchange
interaction and strong electron correlations, due to edge states, are taken
into account. They essentially modify the spatial behavior of the occupied
lowest spin-up LL in comparison with that of the lowest spin-down LL, which is
totally empty. The contrast in the spatial behavior can be attributed to a
different effective one-electron lateral confining potentials for the
spin-split LLs. Many-body effects on the spatially inhomogeneous spin-splitting
are calculated within the screened Hartree-Fock approximation. It is shown
that, far from the edges, the maximum activation energy is dominated by the gap
between the Fermi level and the bottom of the spin-down LL, because the gap
between the Fermi level and the spin-up LL is much larger. In other words, the
maximum activation energy in the bulk of the channel corresponds to a highly
asymmetric position of the Fermi level within the gap between spin-down and
spin-up LLs in the bulk. We have also studied the renormalization of the
edge-state group velocity due to electron correlations. The results of the
present theory are in line with those suggested and reported by experiments on
high quality samples.Comment: 9 pages, 4 figure
Effect of vibration in combined axes on subjective evaluation of ride quality
The effects of simultaneous sinusoidal vibration in the vertical and lateral axes on ratings of discomfort were investigated. The first experiment concentrated on the effects of variation of frequency in the two axes, and the second study concentrated on the effects of amplitude variation in the two axes
Correlations, inhomogeneous screening, and suppression of spin-splitting in quantum wires at strong magnetic fields
A self-consistent treatment of exchange and correlation interactions in a
quantum wire (QW) subject to a strong perpendicular magnetic field is presented
using a modified local-density approximation (MLDA). The influence of many-body
interactions on the spin-splitting between the two lowest Landau levels (LLs)
is calculated within the screened Hartree-Fock approximation (SHFA), for
filling factor \nu=1, and the strong spatial dependence of the screening
properties of electrons is taken into account. In comparison with the
Hartree-Fock result, the spatial behavior of the occupied LL in a QW is
strongly modified when correlations are included. Correlations caused by
screening at the edges strongly suppress the exchange splitting and smoothen
the energy dispersion at the edges. The theory accounts well for the
experimentally observed strong suppression of the spin-splitting pertinent to
the \nu=1 quantum Hall effect (QHE) state as well as the destruction of this
state in long, quasi-ballistic GaAlAs/GaAs QWs.Comment: Text 23 pages in Latex/Revtex/preprint format, 6 Postscript figures,
submitted to Physical Review
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