Showing papers on "Standing wave published in 1983"

Stable standing waves of nonlinear Klein-Gordon equations

Abstract: In this paper we give sufficient conditions for the stability of the standing waves of least energy for nonlinear Klein-Gordon equations.

Diffraction of an Atomic Beam by Standing-Wave Radiation

Abstract: Preliminary experimental results are reported for the deflection of Na atoms in an atomic beam by a transverse standing-wave laser field whose frequency is tuned between the two ground-state hyperfine components of the ${D}_{2}$ line In contrast to the two experiments done previously, a splitting of the beam into two symmetric peaks whose separation increases with the electric-field is seen here In addition, the data show evidence for atomic diffraction: a tendency for scattered atoms to acquire momentum in multiples of $2\ensuremath{\hbar}k$

Numerical study of drift wave turbulence with simple models for wave–wave nonlinear coupling

Abstract: Scattering experiments in tokamaks show a broad drift wave frequency spectrum Δω/ω∼O(1) at fixed wavenumbers indicating a strong turbulent state with unstable drift modes strongly decorrelated at a rate Δω by nonlinear wave–wave coupling to stable modes. In this paper a two‐dimensional study of homogeneous stationary drift wave turbulence with simple models of the wave–wave coupling is described. It shows that linearly driven‐damped stationary states exist and demonstrates that approximate weak coupling theories based on the direct interaction approximation (DIA) can provide a faithful and practical description of the turbulence. In addition, it is found that simple models which include nonlinear E×B as well as nonlinear polarization drift coupling are in rough agreement with the experimental turbulence levels, transport coefficients, and decorrelation rates.

Discrimination by the cod of sounds from opposing directions

Abstract: 1. The ability of cod (Gadus morhua L.) to discriminate between sound waves coming from opposing directions was studied by means of cardiac conditioning in approximately free field conditions under a raft in a Scottish sea loch. The sound sources were positioned at 0° (frontal), 60° or 120° in the fish's median vertical plane, or at 60° or 90° in the transverse plane, other sources occupying diametrically opposed locations. Radial distances varied between 3.05 m and 4.20 m. 2. Switching a continually pulsed 120 Hz pure tone stimulus from a reference source to an opposing source was detected under all conditions. 3. Discrimination was absent when a standing wave was added to the opposing source, locally inverting the phase of sound pressure with respect to the acoustic particle motion without influencing the direction of propagation. 4. Switching to a completely synthesized standing wave field, simulating the phase relations of the reference source, was not detected. Switching to a simulation of the opposite source was detected. 5. It is concluded that the detection of sound propagation direction is based on the characteristic phase relationship between particle motion and sound pressure. Cues resulting from sound propagation itself are irrelevant, and do not appear to be perceived. 6. It appears that the 180° ambiguity in determining sound propagation direction by means of acoustic particle oscillation alone can be eliminated by the cod. This ability seems to hold for all stimulus directions, thus providing a basis for truly three-dimensional directional hearing.

Flutter and forced response of mistuned rotors using standing wave analysis

Abstract: A standing wave approach is applied to the analysis of the flutter and forced response of tuned and mistuned rotors. The traditional traveling wave cascade airforces are recast into standing wave arbitrary motion form using Pade approximants, and the resulting equations of motion are written in the matrix form. Applications for vibration modes, flutter, and forced response are discussed. It is noted that the standing wave methods may prove to be more versatile for dealing with certain applications, such as coupling flutter with forced response and dynamic shaft problems, transient impulses on the rotor, low-order engine excitation, bearing motions, and mistuning effects in rotors.

Dynamic bottom feed for microwave ovens

Abstract: An excitation system for a microwave cooking appliance includes a waveguide along one wall arranged to support a standing wave therein, with an array of apertures spaced along the length of the waveguide to couple energy from the waveguide to the cooking cavity. A phase shifting device periodically shifts the phase of the standing wave between a first phase relationship and a second phase relationship. The array of radiating apertures is configured to support a first and a second substantially stationary radiating pattern when the first and second phase relationships, respectively, are established for the standing wave in the waveguide. Each radiating pattern at the cooking plane has regions of relatively high energy density interspersed wth regions of relatively low energy density, with the high energy regions of one pattern overlying low energy regions of the other, such that by periodically switching between patterns the uniformity of the time-averaged energy density at the cooking plane is enhanced.

Charged particle behavior in low-frequency geomagnetic pulsations: 3. Spin phase dependence

Abstract: Low-frequency modulations of the fluxes of magnetospheric charged particles are often observed in conjunction with geomagnetic pulsations. In some cases, the flux modulations depend on detector look direction even after effects arising from pitch angle anisotropy have been removed. For a detector on a spinning spacecraft, the look direction dependence creates flux modulations ordered by the spin phase angle, so the term ‘spin phase dependence’ provides a convenient description of the phenomenon considered in this paper. Spin phase dependence occurs only when the gyroradius of the detected particles (charge, q; energy, W) is comparable with some other characteristic length of the problem. In particular, spin phase dependence occurs when the particle gyroradius aL is comparable with λ⊥, the wavelength transverse to B. ATS 6 and GEOS have provided examples of this type of ‘finite gyroradius’ effect. Wave-related spin phase dependence may also arise with aL ≪ λ⊥. For example, a wave convecting a steep spatial gradient in the particle density n(W) back and forth creates spin phase dependent flux oscillations if aL ≃ n(W)/|▽n(W)|. This situation is described and related to ISEE boundary wave studies. Gyration acceleration, i.e., acceleration by the wave electric field E, leads to spin phase dependence of the flux of particles for which aL ≃ W/γqE, where γ is the power law coefficient of the differential particle flux, again without any restriction to short wavelengths. Some OGO 5 and ISEE wave analyses have relied on this type of spin phase dependence. Gyration acceleration has also been invoked to explain particle pulsations seen on the nonspinning ATS 6 spacecraft, albeit in circumstances where the spin dependence cannot be checked. Finally, spin phase dependences may be produced by large-scale standing wave structure parallel to the ambient magnetic field, an effect which appears in some ISEE particle data.

X-Ray-Standing-Wave Atom Location in Heteropolar Crystals and the Problem of Extinction

Abstract: By monitoring the characteristic fluorescent radiation excited by x-ray standing waves we have been able to distinguish the two different kinds of lattice sites in a heteropolar crystal of GaAs. The strong extinction effects that mask the position-dependent fluorescent signal were minimized by adopting a suitable detector geometry.

Structural analysis of the NiSi2/(111)Si interface by the X-ray standing-wave method

Abstract: The atomic structure of the NiSi2/(111)Si interface was investigated by the X-ray standing wave method using synchrotron radiation at Photon Factory. The angular yield of Ni K fluorescent X-rays was measured around the Bragg peak of a substrate Si. By comparing the profile of the experimental curve with that of calculated one, the interface atomic structure was determined.

Measurement of the acoustic internal source impedance of an internal combustion engine

Abstract: The standing wave tube technique has been adapted to measure the acoustic internal source impedance of an internal combustion engine. In order to implement this technique an extensive experimental facility was designed and constructed and simple test cases were evaluated for validity. In addition an adaptation of the standing wave tube method incorporating a random signal as the external driver sound source and digital data analysis techniques were introduced to reduce the experimental difficulty and time consumption. Normalized specific acoustic impedance data at a constant engine speed of 2200 rpm show little change with varying engine load conditions. Similar data at a constant engine load condition of 254‐mm Hg exhibit more significant dependence on engine speed.

Apparatus for generating or detecting field components in a magnetic resonance system

Abstract: Apparatus for generating and detecting magnetic field components oscillating at a radio frequency in a direction transverse to a static magnetic field in a nuclear-magnetic-resonance (NMR) system. The apparatus has a plurality of conductive elements spaced from one another and from the axis along which the static magnetic field is directed. The relative amplitudes of alternating currents in the conductive elements are controlled to generate a spatially uniform field. A preferred embodiment uses a standing wave in a coil assembly to control relative current amplitudes, which takes advantage of the current-phase characteristics of such waves. Detection of RF magnetic fields results from an EMF generated in the coil assembly in response to the time-varying magnetic field; the high Q of the coil assembly enhances detection properties.

Geos 2 plasma drift velocity measurements associated with a storm time Pc5 pulsation

Abstract: The Geos 2 electron gun experiment has been used to obtain electric field data during the compressional Pc5 pulsation event of Day 300, 1979. The phase relationships between the electric field and magnetic field observations show that the oscillation in the meridian plane appears to be a transverse Alfven standing wave in the second harmonic, while the compressional oscillation is symmetrical about the equatorial plane. Computations of the fields of a guided poloidal wave fit the transverse oscillation well. The oscillation is not completeley explained by existing theories. A comprehensive model of the oscillation is presented.

Microwave phase shifting device

Abstract: An improved phase shifting device for varying the phase of the standing wave in a hollow rectangular waveguide is provided which is particularly applicable to microwave cooking appliances. A metallic septum is constructed at the end of the waveguide remote from the microwave source which extends inwardly into the waveguide from the adjacent waveguide end wall parallel to the narrow walls of the waveguide and electrically connects the broad walls of the waveguide, thereby dividing the waveguide into two sub-waveguides, each of which exhibits a cut-off characteristic at the operating frequency. The leading edge of the septum provides a short circuit termination reference point for the waveguide. The moving parts comprise a pair of dielectric plugs, each of which is received in a respective one of the sub-waveguides for selective movement in tandem from a reference position completely within the sub-waveguides to one or more phase shifting positions in which the plugs extend forward of the septum leading edge toward the microwave source. The shift in the phase of the standing wave varies linearly with the extent of forward displacement of the plugs relative to the septum leading edge. The plugs are selectively moved in tandem relative to the reference position in the sub-waveguides to provide the desired phase shift.

Visualization of acoustic scattering by elastic cylinders at low ka

Abstract: Theoretical studies have shown the great importance of circumferential waves in acoustic scattering by infinite elastic cylinders immersed in a fluid. The ‘‘Resonance Isolation and Identification Method’’ (RIIM) has allowed us to separate the resonances produced by circumferential standing waves by recording the free vibrations which are still present for some frequencies after the forced excitation has stopped. In this paper, the problem of acoustic scattering is studied by a stroboscopic Schlieren visualization method at low frequencies (0

The Effect of the Interference of Traveling and Stationary Waves on Time Variations of the Large-Scale Circulation.

Abstract: It is hypothesized that the interference of stationary and traveling waves of the same longitudinal can cause some of the observed time variations in the large-scale circulation. To explore this hypothesis the eight-winter average structure of a regularly occurring, westward propagating disturbance which we earlier called the “16-day wave” is further documented. Energy quantities are calculated as this 16-day wave moves in and out of phase with the stationary or time-mean wave. The resulting time variations are similar to some already reported in the literature. Eddy heat momentum transport associated with energy conversions have phase relationships between pressure levels that can be approximately predicted by a simple linear superposition of the observed stationary waves and traveling external Rossby waves. In further support of the hypothesis, cross-spectral results determined from independent data show a reasonable agreement with these predictions.

Detection of insulation deterioration through electrical spectrum analysis

Abstract: Several types of insulation deterioration common to large rotating electrical machines produce Electromagnetic Interference (EMI) at discrete frequencies or within bands of frequencies This paper employs the use of standing wave calculations to predict these natural resonant points Curves of measured impedance variation with frequency are presented to verify calculated values Determination of these resonants is an important first step in real time monitoring and later physically locating a defect before failures occur

Frequency splitting and collisional de-correlation for removing superadiabatic barriers in ECRH experiments

Abstract: A series of test-particle calculations are presented which measure the ECRH velocity diffusion coefficients for two mirror devices – the simple mirror SM-1 and the tandem mirror TMX-U – for monochromatic electron-cyclotron waves. The diffusion coefficients are compared to those from quasi-linear theory. The role of wave-particle resonance overlap and collisional de-correlation for producing stochastic instead of superadiabatic particle motion is investigated. The use of two or more waves with different frequencies is found to increase the number of resonances and thus the chance of resonance overlap; a frequency separation of the axial bounce frequency is optimum for two waves. A spectrum of axial wavenumbers making up a standing wave does not increase the number of resonances and thus does not increase stochasticity. Pitch-angle collisions can also produce significant de-correlation between the wave and particle, owing to the large geometrical enhancement of the gyrophase diffusion in an inhomogeneous magnetic field. Results for fundamental (ω = ωc) heating in SM-1 show that using two frequencies instead of one increases heating at an energy of ~ 10 keV by a factor of about three. Calculations for the tandem mirror TMX-U for an energy of SO keV show that stochasticity is assured by either resonance overlap or collisional gyrophase diffusion.

Dynamics of the Toda lattice: A soliton-phonon phase-shift analysis

Abstract: The dynamics of the Toda lattice can be described in terms of solitons and nonlinear phonons (ripples). The latter are shown to be obtainable from a general multisoliton solution by allowing the soliton parameters to become imaginary. This device yields phonon phase shifts due to a soliton via a linearization procedure and shows that the zone-edge phonon (standing wave) is removed in the presence of a soliton. An expansion of the soliton-ripple solution up to the second order in the phonon amplitude allows the calculation of typical nonlinear quantities such as momentum and mass of the ripple and the spatial shift of a soliton due to its collision with a ripple. Finally, the relationship is established between the form of a ripple, viewed as a phonon wave packet, and its associated action variable within the framework of inverse scattering theory.

Magnetoelastic Wave Excitation Properties of Amorphous Iron-Boron Films Prepared by RF-High Rate Sputtering

Abstract: We investigated the magneto-acoustic excitation properties of amorphous iron-boron films prepared by rf-high rate sputtering by observing magnetoelastic wave resonance in linear samples. The longitudinal complex susceptibility was measured as a function of the external applied field. Films about 10 µm thick were deposited onto aluminum foil substrates. The observed magnetoelastic wave was a standing wave of the lowest mode. The controllable change in the velocity of sound by the application of an external field ΔC/C was about 4.7% for films with substrates. This value increased to 17% when films were removed from the substrate, the new value being comparable to that obtained in rapid-quenched Fe80B20 ribbons. The experimental results are explained very well by the one-dimensional string model, from which important magneto-acoustic quantities are derived.

Scale effects in a wave-refraction experiment

Abstract: The experimental results of Provis (1975, 1976) for wave amplification at a conical island bear little resemblance to the theoretical predictions of Smith & Sprinks (1975). Here Provis's suggestion is confirmed: that his experiments were dominated by viscous damping and by standing waves between the island and the wavemaker. Estimates are given as to how large an experiment needs to be to avoid these important scale effects.

Ponderomotive effects in nonneutral plasmas

Abstract: The ponderomotive effects which arise in a single species plasma, i.e., a nonneutral plasma, are considered. The important difference from a neutral plasma is that quasineutral density cavities given by δn/n0≂−‖E‖2/16πn0T cannot arise in a single species plasma. Instead, it is found that the ponderomotive force is balanced by self‐consistent space charge fields, and results in δn≂∇2‖E∥‖2/16πmω2, where ω is the frequency and E∥ refers to the wave electric field parallel to the confining magnetic field. In addition to the density rearrangement, the zero order E×B rotation is modified. The self‐consistent nonlinear state has been found for a large‐amplitude l=0 axially standing Gould–Trivelpiece wave. The linear dispersion relation is modified by the presence of the large‐amplitude wave and results in a nonlinear frequency shift. This shift produces an interesting hysteresis effect in the nonlinear resonant response of the plasma when the frequency of the external driver is swept slowly.

New ultrasonic resonator method using optical diffraction for liquids

Abstract: A new resonator method has been developed for measuring ultrasonic absorption in liquids in the frequency range 0.3–10 MHz. This method utilizes Raman–Nath light diffraction to detect a resonance spectrum of standing waves in a cylindrical cavity. Comparison with the spectrum obtained by conventional resonator method demonstrates that distortion of plane‐wave peaks by higher modes can be avoided with the present method. The use of a concave reflector is found to reduce a cavity loss considerably, enabling us to measure absorption down to a few hundred kHz. Results for water obtained using three types of reflectors with curvature radius 100–400 mm are shown.

Identification of the Fortnightly Wave Observed Along the Northern Coast of the Gulf of Guinea

Abstract: Numerical calculations of coastally trapped wave modes along the northern coast of the Gulf of Guinea using representative bottom topography and continuous stratification on a β-plane were carried out to identify the observed fortnightly propagating coastal wave Results showed that the propagation speed of the observed wave (approximately 53 cm s−1 for sea level and 54 cm s−1 for sea surface temperature) is close to that of the second mode (64 cm s−1) and no other Off the shelf this mode has a baroclinic structure, having considerable amplitude at 2 km depth Ray theory calculations indicate that if, as is likely, the observed wave were generated on the shelf, a vertically standing modal structure with large amplitude at 2 km depth is not possible Therefore, no coastally trapped vertically standing wave modes are consistent with the observed wave Consequently, it is most likely that the wave is a vertically propagating coastally trapped wave as has been observed recently in other contexts Th

Breakdown of the atmosphere by emission from a millimeter‐wave free‐electron maser

Abstract: Production of an atmospheric pressure air breakdown plasma using the emission from a short‐pulse millimeter‐wave free‐electron maser is used to demonstrate frequency tunability over the range 50–100 GHz, via breakdown standing wave patterns, and very high peak power.

Standing wave patterns in VLF Hiss

Abstract: Observations have been made of systematic patterns in VLF hiss, which can be interpreted as a standing wave pattern formed by reflection in the lower ionosphere. Multicomponent VLF electric and magnetic field experiments were flown on three sounding rockets (Nike-Tomahawk 18.203-205) from Siple Station. Antarctica during December 1980 to January 1981. One feature of the natural emissions was observed in a very similar form during each flight. A band of hiss, typically from 1.5 to 3 kHz, was seen on the upleg to form a series of closely spaced stripes with whistler-like dispersion. These first appeared at an altitude of 90–95 km and extended for as much as 40 km in altitude. On the downleg the stripes were observed at the same altitude with the pattern reversed in time. No such patterns were observed by the VLF receivers operating at the same time on the ground at Siple or at its conjugate point. It is suggested that the patterns are interference effects due to downcoming waves reflecting from a layer in the E region and forming a standing wave pattern. The observed stripes are then due to the rocket traversing the standing wave pattern in opposite directions on upleg and downleg. If this interpretation is correct, the fringe spacing should be related to the wavelength and permits a calculation of the refractive index. In one example we calculate n = 43.7 in good agreement with two independent determinations of the refractive index.