67,965 research outputs found
Continuous Tracking of Lava Effusion Rate in a Lava Tube at Kilauea Volcano Using Very Low Frequency (VLF) Monitoring
Measurement of lava effusion rates is a key objective for monitoring basaltic eruptions because it helps constrain geophysical models of magma dynamics, conduit geometry, and both deep and shallow volcano processes. During these eruptions, lava frequently travels through a single master lava tube. A new method and instrument for continuously monitoring the crosssectional area of lava streams in tubes and estimating the instantaneous effusion rate (IER) is described. The method uses 2 stationary very low frequency (VLF) radio receivers to measure an unperturbed VLF signal and the influence of highly conductive molten lava on that signal. The difference between these signals is a function of the cross-sectional area of molten lava and the IER. Data from a short test of the instrument are described. This methodology represents a breakthrough in the continuous monitoring of IER because it provides higher temporal resolution than competing methods at a fraction of the cost
Sound propagation and scattering in bubbly liquids
In the ocean, natural and artificial processes generate clouds of bubbles which scatter and attenuate sound. Measurements have shown that at the individual bubble resonance frequency, sound propagation in this medium is highly attenuated and dispersive. Theory to explain this behavior exists in the literature, and is adequate away from resonance. However, due to excessive attenuation near resonance, little experimental data exists for comparison.
An impedance tube was developed specifically for exploring this regime. Using the instrument, unique phase speed and attenuation measurements were made for void fractions ranging from 6.2 × 10^−5 to 2.7 × 10^−3 and bubble sizes centered around 0.62 mm in radius. Improved measurement speed, accuracy and precision is possible with the new instrument, and both instantaneous and time-averaged measurements were obtained. Behavior at resonance was observed to be sensitive to the bubble population statistics and agreed with existing theory, within the uncertainty of the bubble population parameters.
Scattering from acoustically compact bubble clouds can be predicted from classical scattering theory by using an effective medium description of the bubbly fluid interior. Experimental verification was previously obtained up to the lowest resonance frequency. A novel bubble production technique has been employed to obtain unique scattering measurements with a bubbly-liquid-filled latex tube in a large indoor tank. The effective scattering model described these measurements up to three times the lowest resonance frequency of the structure.United States Navy Office of Naval Research Ocean Acoustics Progra
Continuous harmonic analysis and power quality measurements in three-phase systems
A virtual instrument, named Power Quality
Meter, is presented for (a) measuring power consumption and
harmonics in three-phase systems, under non-sinusoidal and
imbalance conditions (b) detecting, classifying and organizes
power disturbance events. Measurement of the power
consumption follows the formulation proposed by the members
of the IEEE Working Group on Nonsinusoidal Situations
(1996). So, definitions are based on the analysis of functions in
the frequency domain, separating the fundamental terms from
the harmonic terms of the Fourier series. The virtual instrument
has been developed too for monitoring and measuring power
disturbances, which are automatically classified and organized
in a database while they are being recorded. Software tools use
the database structure to present summaries of power
disturbances and locate an event by severity or time of
occurrence. Records of actual measurements are included to
demonstrate the versatility of the instrument
Vertical axis non-linearities in wavelength scanning interferometry
The uncertainty of measurements made on an areal surface topography instrument is directly influenced by its metrological characteristics. In this work, the vertical axis deviation from linearity of a wavelength scanning interferometer is evaluated. The vertical axis non-linearities are caused by the spectral leakage resulting from the Fourier transform algorithm for phase slope estimation. These non-linearities are simulated and the results are compared with experimental measurements. In order to reduce the observed non-linearities, a
modification of the algorithm is proposed. The application of a Hamming window and the exclusion of edge points in the extracted phase are shown to increase the accuracy over the whole instrument range
Urban air quality estimation study, phase 1
Possibilities are explored for applying estimation theory to the analysis, interpretation, and use of air quality measurements in conjunction with simulation models to provide a cost effective method of obtaining reliable air quality estimates for wide urban areas. The physical phenomenology of real atmospheric plumes from elevated localized sources is discussed. A fluctuating plume dispersion model is derived. Individual plume parameter formulations are developed along with associated a priori information. Individual measurement models are developed
Specifying and calibrating instrumentations for wideband electronic power measurements
The wideband electric power measurement related topics of electronic wattmeter calibration and specification are discussed. Tested calibration techniques are described in detail. Analytical methods used to determine the bandwidth requirements of instrumentation for switching circuit waveforms are presented and illustrated with examples from electric vehicle type applications. Analog multiplier wattmeters, digital wattmeters and calculating digital oscilloscopes are compared. The instrumentation characteristics which are critical to accurate wideband power measurement are described
A laser gyroscope system to detect the Gravito-Magnetic effect on Earth
Large scale square ring laser gyros with a length of four meters on each side
are approaching a sensitivity of 1x10^-11 rad/s/sqrt(Hz). This is about the
regime required to measure the gravitomagnetic effect (Lense Thirring) of the
Earth. For an ensemble of linearly independent gyros each measurement signal
depends upon the orientation of each single axis gyro with respect to the
rotational axis of the Earth. Therefore at least 3 gyros are necessary to
reconstruct the complete angular orientation of the apparatus. In general, the
setup consists of several laser gyroscopes (we would prefer more than 3 for
sufficient redundancy), rigidly referenced to each other. Adding more gyros for
one plane of observation provides a cross-check against intra-system biases and
furthermore has the advantage of improving the signal to noise ratio by the
square root of the number of gyros. In this paper we analyze a system of two
pairs of identical gyros (twins) with a slightly different orientation with
respect to the Earth axis. The twin gyro configuration has several interesting
properties. The relative angle can be controlled and provides a useful null
measurement. A quadruple twin system could reach a 1% sensitivity after 3:2
years of data, provided each square ring has 6 m length on a side, the system
is shot noise limited and there is no source for 1/f- noise.Comment: 9 pages, 6 figures. 2010 Honourable mention of the Gravity Research
Foundation; to be published on J. Mod. Phys.
First measurements of high frequency cross-spectra from a pair of large Michelson interferometers
Measurements are reported of the cross-correlation of spectra of differential
position signals from the Fermilab Holometer, a pair of co-located 39 m long,
high power Michelson interferometers with flat, broadband frequency response in
the MHz range. The instrument obtains sensitivity to high frequency correlated
signals far exceeding any previous measurement in a broad frequency band
extending beyond the 3.8 MHz inverse light crossing time of the apparatus. The
dominant but uncorrelated shot noise is averaged down over
independent spectral measurements with 381 Hz frequency resolution to obtain
sensitivity to stationary
signals. For signal bandwidths kHz, the sensitivity to strain
or shear power spectral density of classical or exotic origin surpasses a
milestone where
is the Planck time.Comment: 5 pages, 3 figure
Dual physiological rate measurement instrument
The object of the invention is to provide an instrument for converting a physiological pulse rate into a corresponding linear output voltage. The instrument which accurately measures the rate of an unknown rectangular pulse wave over an extended range of values comprises a phase-locked loop including a phase comparator, a filtering network, and a voltage-controlled oscillator, arranged in cascade. The phase comparator has a first input responsive to the pulse wave and a second input responsive to the output signal of the voltage-controlled oscillator. The comparator provides a signal dependent on the difference in phase and frequency between the signals appearing on the first and second inputs. A high-input impedance amplifier accepts an output from the filtering network and provides an amplified output DC signal to a utilization device for providing a measurement of the rate of the pulse wave
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