Showing papers on "Harmonics published in 1974"

On the synthesis of random field sampling from the spectrum: An application to the generation of hydrologic spatial processes

Abstract: A procedure for the synthesis of processes exhibiting temporal and spatial variability is presented The method involves the addition of harmonics of random frequencies that are sampled from the spectral density function or the radial spectral density function The process obtained is asymptotically Gaussian and ergodic An estimate of the error in time or space averages due to the nonergodicity of the process as a function of the number of harmonics is also included

Nonlinear oscillations of gas bubbles in liquids: steady‐state solutions

Abstract: The nonlinear oscillations of a spherical gas bubble in an incompressible, viscous liquid subject to the action of a sound field are investigated by means of an asymptotic method. Approximate analytical solutions for the steady‐state oscillations are presented for the fundamental mode, for the first and second subharmonics, and for the first and second harmonics to second order in the expansion. These results are compared with some numerical ones and a very good agreement is found.

The Effects of Geomagnetic Storms on Electrical Power Systems

Abstract: Geomagnetic field fluctuations produce spurious, quasi-dc currents in power systems. The currents enter through system grounding points, and are of sufficient magnitude to cause half-cycle saturation in power transformers. These currents have been recorded and are summarized, and recommendations made in the significant problem areas of system disturbances and equipment effects due to geomagnetic storms. The major problem areas include increased VAR requirements and shifts in VAR flow, system-voltage fluctuations, generation of harmonics, protective relayiing misoperations, and possible localized internal heating in transformers. Recommendations relating to these effects have Pot been published previously.

Dynamic Interaction of Multi-Machine Power System and Excitation Control

Abstract: In this paper the dynamic interactions between mechanical and reactive modes of machines in a multi-machine power system are investigated. The dynamic interactions are expressed in terms of machine angles, transient voltages, and coefficients which are functions of system parameters and operation conditions. The effect of the dynamic interaction can be examined by the electric torque loci on the A6-Aw phase plane. It is found that the interaction between the mechanical modes of machines has significant effect on stability characterized by the natural mechanical oscillation frequency and damping of individual machines.

Device for synthesizing frequencies which are rational multiples of a fundamental frequency

Abstract: A frequency synthesizer is disclosed which can provide frequencies which are rational multiples of a fundamental reference frequency. The synthesizer includes a voltagecontrolled oscillator in a phase-locked loop with the reference frequency. A modulo-N counter is included to allow synthesis of harmonics of the reference frequency. To obtain rational fractional frequencies between harmonics a ''''cycle swallower'''' is provided to occasionally abruptly shift the phase of the oscillator output. The swallowing rate is determined by the contents of a storage register which is pre-loaded with a representation of the desired frequency. The contents of this storage register are periodically loaded into and accumulated in an accumulator which generates an overflow signal to the cycle swallower whenever the accumulated value exceeds its maximum storage capacity. In response to the average rate of phase shifting by the swallower, the loop stabilizes when the oscillator frequency is equal to the desired rational multiple of the reference frequency.

Real time analysis of voiced sounds

Abstract: A power spectrum analysis of the harmonic content of a voiced sound signal is conducted in real time by phase-lock-loop tracking of the fundamental frequency, fo, of the signal and successive harmonics hl through hn of the fundamental frequency, measuring the quadrature power and phase of each frequency tracked, differentiating the power measurements of the harmonics in adjacent pairs and analyzing successive differentials to determine peak power points in the power spectrum for display or use in analysis of voiced sound, such as for voice recognition.

Determination of absolute frequencies of 12C16O and 13C16O laser lines

Abstract: The absolute frequencies of one 13C16O and seven 12C16O laser lines have been determined with an uncertainty of about ±5 MHz by measuring the beat frequencies between these CO lines and second harmonics of CO2 laser transitions generated in a CdGeAs2 frequency‐doubling crystal. Beat frequencies up to 11 GHz have been measured using a high‐speed HgCdTe detector.

The third harmonic of type III solar radio bursts

Abstract: Two examples of pairs of ‘J-shaped’ type III bursts with 2∶3 frequency ratio are given. It is suggested that these could be the second and the third harmonics of undetected fundamental radiation. The 80 MHz heliograph source of the third harmonic showed an apparent brightness temperature of 109.6K, while the order of 1016K seems to be required theoretically. This may imply that the apparent radio source was composed of many unresolved small sources of much higher brightness temperature.

Problems in the design of power transformers

Abstract: The power loss of transformer cores can still be considerably reduced by improved joint design based on new knowledge of the localized flux distribution, both in the corners and in the limbs. Rotational flux has been measured in the T-joints of experimental cores, and it has been found to cause localized high loss regions dependent on the joint design. Circulating harmonic fluxes have been found in individual laminations in the limbs of three-phase cores. The path of the harmonics is independent of joint design although their magnitudes are dependent. Circulating 3rd harmonics as large as 0.3 T have been found in a core magnetized sinusoidally at 1.6 T. These cause additional losses calculated to be 20% of the nominal core loss, and great savings would be possible if the circulating harmonics could be reduced or eliminated.

Stimulation of the Harris instability in the ionosphere

Abstract: Observations made with a sweep frequency rf sounder on the satellite ISIS 1 in the topside ionosphere are reported, and the interpretation of diffuse signals at the lower harmonics of the electron cyclotron frequency is discussed. These signals are attributed to the stimulation of Harris instabilities of longitudinal plasma waves at multiples of the cyclotron frequency in a single electron distribution. The Harris instability is excited most readily when the frequency is near the midpoint between the harmonics of the cyclotron frequency. The cause of these instabilities is the large electron velocity anisotropy which results from collisionless cyclotron damping of the energy from the high power sounder pulse.

Nonlinearly generated harmonics and attenuation of Rayleigh waves on crystalline quartz

Abstract: Measurements have been made of the nonlinearly generated harmonics and attenuation of Rayleigh acoustic surface waves at microwave frequencies on crystalline quartz. The Rayleigh waves were generated using an interdigital transducer deposited on the x‐z surface of the quartz crystal aligned so that the surface wave propagates in the pure‐mode x direction. Attenuation coefficients α were measured using the laser diffraction technique at frequencies of ∼160, ∼280, and ∼492 MHz with resulting typical values of α=0.083 dB/μsec, α=0.206 dB/μsec, and α=0.812 dB/μsec, respectively. These results agree with previously reported values and with theoretical predictions. The growth and decay of nonlinearly generated harmonics of Rayleigh waves with a fundamental frequency of 281 MHz were observed also using the laser probe technique. A description of the variation of the Rayleigh waves' intensity for each of the three harmonics observed is provided by a set of coupled amplitude equations modified to include dispersio...

Harmonic Analysis of a Synchronized Pulse-Width-Modulated Three-Phase Inverter

Abstract: In pulsewidth-modulated inverters used for variable-frequency applications, a number of harmonic control policies can be used. Most of these policies are complex to implement by hardware. The most simple and yet effective technique is synchronizing or the synchronized harmonic control policy. This paper uses double Fourier analysis techniques to obtain the output harmonics as a function of pulsewidth, pulsing frequency, and output frequency. The method obtains the harmonics as analytical functions and thus provides the necessary relationships for control studies and system optimization. The more significant theoretical results are provided and theoretical and experimental results obtained from a 25-kW three-phase pulsewidth-modulated inverter, are compared.

Dynamic Analysis of Harmonic Interaction Between AC AND DC Power Systems

Abstract: This paper describes a method of computing harmonics and waveforms in HVdc conversion, taking into account interaction with the ac system, dynamically. The perfbrmance of filters tuned at a nominal frequency is examined when the ac system frequency varies. Computed values of harmonic currents and voltages are presented and the influence of the ac system short circuit ratio is demonstrated. Harmonic magnification can occur due to resonance effects, but the system is harmonically stable.

New Frequency Measurements and Techniques in the 30-THz Region

Abstract: It is proposed that the frequency differences between CO2 laser ines and the harmonics of these differences might be used as intermediate frequencies to bridge the gap between microwave frequency standards and infrared frequencies to simplify absolute measurements of the latter. Tungsten-nickel point-contact diodes would be used as harmonic generators and mixers. The preliminary results of an experimental feasibility study are presented. A description of a novel two-frequency laser, built for this study, is given. It is shown that beat frequencies between differences up to 715 GHz and microwave frequency harmonics up to the twelfth can be observed; interactions with at least the third harmonic of a CO2 frequency difference are possible, producing signals with an S/N of 51 dB in a 2.2-s time constant receiver; attempts to observe a beat between a CO2 frequency and the seventh harmonic of a difference were not successful.

Monolithic solid‐state traveling‐wave amplifier

Abstract: A new monolithic structure for solid‐state traveling‐wave amplifiers is proposed, which promises efficient interaction between a drifting charge carrier stream and a slow electromagnetic wave component. The suggested configuration is potentially suitable for operation in the far‐ir frequency regime. A one‐dimensional analysis of the interaction between the electromagnetic waveguide mode and the carrier current is presented, including the loss contribution due to the nonsynchronous space harmonics of the electromagnetic mode.

Sources of harmonic currents in slip-ring induction motors

Abstract: Several features which could cause an unsaturated 3-phase induction motor to draw nonsinusoidal currents from a supply of negligible harmonic content are examined. An analysis is developed which provides a simple method for the prediction of the harmonic-current magnitudes and frequencies. A comparison of predicted and measured current harmonics is presented to substantiate the theory.

High power fundamental and harmonic resonant ion cyclotron heating in a mirror machine

Abstract: Radio frequency heating at powers up to 1 MW and pulse widths of ∼700 μsec was applied to a turbulently preheated hydrogen plasma in a large pulsed mirror machine. Energy analysis of charge exchange neutrals indicates that resonant heating occurred when the radio frequency matched either the ion cyclotron frequency or one of its harmonics. The behavior of the induced rf fluctuations in the plasma was observed by means of microwave scattering. These measurements show resonance phenomena and the presence of rf fluctuations at harmonics of the rf heating frequency. Diamagnetic loop measurements indicate that 310 ≤ (Te+Ti) ≤ 380 eV as a result of the heating, while measurements of the ion energy distribution by charge exchange energy analysis shows the ion energy distribution to be non‐Maxwellian with a low temperature component of Ti ∼ 320 eV. Microwave interferometer measurements indicate densities of ∼2 to 3 × 1013 cm−3.

Filter arrangement for a converter circuit

Abstract: An improved filtering arrangement for a converter circuit in which a highpass filter, tuned to have a cutoff frequency which is less than the lowest harmonic to be filtered is provided instead of the customary plurality of filters tuned to individual harmonic currents. In a 12 pulse converter circuit, at least one highpass filter which is tuned to filter out harmonics starting with the fifth harmonic and which has a resonant frequency above the 11th harmonic is used.

Frequency spectrum generated by thyristor control

Abstract: This paper describes the measured harmonics in the load currents of thyristor circuits and shows that with firing angle control the harmonic amplitudes decrease sharply with increasing harmonic frequency, but that they extend to very high harmonic orders of around 6000. The amplitudes of the harmonics are a maximum for a firing delay angle of around 90°.Integral cycle control produces only low order harmonics and sub-harmonics.It is also shown that with firing angle control apparently random inter-harmonic noise is present and that the harmonics fall below this noise level at frequencies of approximately 250 KHz for a switched 50 Hz Waveform and for the resistive load used. The noise amplitude decreases with increasing frequency and is a maximum with 90° firing delay.

Detection of the contribution of harmonics to the diffracted X-ray intensity

Abstract: The appreciable differences between the absorption coefficients of a foil for the characteristic radiation and its harmonics can be utilized to determine the wavelength composition of X-rays diffracted by a monochromator or sample. A simple experimental procedure is proposed and used to determine the intensity of the λ/2 harmonic diffracted by the 400 reflection of gallium phosphide at the 200 position of the molybdenum Kα peak. At a tube voltage of 45 kV the λ/2 contribution was found to be 9%; it decreased to 2.5% when pulse-height discrimination blocked 10% of the total counts. Our procedure provides a direct check of the effectiveness of balanced filters and electronic discrimination against harmonic radiation.

Many-particle Coulomb interaction: an expansion in terms of hyperspherical harmonics

Abstract: The nucleus-electron, as well as the electron-electron potentials, in all atomic systems are shown to have a simple expansion into hyperspherical harmonics. This expansion is useful for the calculation of matrix elements.

Spatial Correlation in Arbitrary Noise Fields

Abstract: Explicit expressions are developed for the cross‐spectral density between pairs of sensors and the wavenumber‐frequency spectrum projected onto the line joining these sensors, when they are placed in arbitrary positions in noise fields which are described by an arbitrary directional distribution of uncorrelated plane waves. The approach is to expand the directional distribution in spatial harmonics. Each harmonic leads to a corresponding term, with the same coefficient, in series representations for the cross‐spectral density function and the wavenumber‐frequency spectrum. The approach is particularly attractive when the field can be adequately represented by a relatively small number of harmonics. Both two‐ and three‐dimensional fields are considered. [This work was performed at the University of California, San Diego, Marine Physical Laboratory of the Scripps Institution of Oceanography, San Diego, California 92132.]

Use of chirping to compensate for nonlinearities in Fourier spectroscopy

Abstract: Chirping introduced into a Michelson interferometer permits correction for nonlinearities, distortion, and intermodulation in the final spectrum. This is because the false harmonics of each frequency carry the characteristic phase of the original frequency, whereas true spectral components at higher frequencies have their own characteristic phase. In an unchirped interferogram, there is no such distinguishing phase. This paper explains how the distinguishing phase occurs, presents two algorithms for carrying out the distortion correction when the form of the distortion is known, and displays results of correcting selected distorted experimental interferograms. This capability is a new advantage of chirping in Fourier spectroscopy.

On the second spherical harmonics of the cosmic ray angular distribution

Abstract: Explicit expressions describing the semi-diurnal variation of cosmic ray intensity are obtained in the frame of the convection-diffusion theory. Convection-diflusion equations are extended by introducing a symmetric traceless tensor accounting for the second harmonics of the cosmic ray angular distribution. Starting from the statistical Boltzmann equation a new transport equation is deduced which relates the second harmonics of the angular distribution to the gradients of cosmic ray streaming. Thus, compared to models used hitherto, a more quantitative calculation is carried out. Expressing the free space anisotropy in terms of geographical coordinates, the predicted diurnal and semi-diurnal variations are given. The results obtained are essentially in agreement with those of Quenby and Lietti but also differences arise as a result of the bending and divergence of the large-scale interplanetary magnetic field lines. Arguments are brought forward that a sunward cosmic ray streaming along the interplanetary field lines gives rise to a pitch angle distribution with an excess of particles of large pitch angles.