Showing papers on "Standing wave published in 1982"

Two-dimensional surf beat: Long wave generation by a time-varying breakpoint

Abstract: A two-dimensional parametrization of a surf zone with a time-dependent breakpoint due to groupiness in the incident wave field is developed. The breakpoint is defined in terms of a mean position X plus a modulation Δa. Free wave solutions are obtained on a plane beach at the group frequency and its harmonics. Shoreward of the breakpoint, standing waves are found, while seaward an outgoing progressive wave exists. The amplitude of the standing wave is relatively insensitive to the incident wave field. The amplitude of the outgoing wave depends on X, the group frequency σ, and the beach slope tan β. For certain values of X = (σ2X/g tan β) the amplitude of the outgoing wave goes to zero. It appears that any ‘resonant’ response of the standing wave shoreward of the breakpoint is suppressed by seaward radiation of energy by the outgoing wave.

Charged particle behavior in low-frequency geomagnetic pulsations, 2. Graphical approach

Abstract: The behavior of charged particles in an ultralow frequency magnetospheric pulsation with standing wave structure along the magnetic field is interpreted by using a graphical approach. Attention is directed principally to the way in which particles are accelerated as they bounce and drift through a wave with which they are in resonance, but nonresonant particles are also discussed. Under appropriate conditions, passage through the wave leads to modulation of particle energy. Applications emphasize the necessity of considering the large-scale structure of a wave in interpreting the particle behavior seen at a particular point in space.

Solution to the surface registration problem using X-ray standing waves

Abstract: Standing waves of x rays have been used to determine the positions of bromine atoms in submonolayer coverages on a (111) silicon surface. In addition to the bromine position normal to the crystal surface its components relative to a plane inclined to the surface are also measured. This information suffices to establish the registration of the surface atoms relative to the crystal below.

Standing hydromagnetic waves observed by ISEE 1 and 2: Radial extent and harmonic

Abstract: Direct measurements of the spatial extent of the resonant hydromagnetic waves associated with Pc 4 and 5 magnetic pulsations made by the closely spaced ISEE 1 and 2 satellites are presented together with ISEE 1 determinations of the harmonic of the resonant waves The use of two satellites in similar orbits, which makes it possible to distinguish between spatial and temporal features, has shown the resonant region widths to extend over about 02 to 16 L shells for three events detected on the dayside between L = 4 and L = 7 The two events for which plasma density data was available occurred at plasma density gradients in the vicinity of the plasmapause The standing wave harmonic was determined by the combination of two techniques: the comparison of the observed wave period with that predicted by standing wave theory, and the comparison of the phases of the observed wave electric and magnetic field The two events analyzed are found to be second harmonic oscillations, suggesting internal generation in the magnetosphere by a bounce resonant mechanism

Apparatus and method for in situ controlled heat processing of hydrocarbonaceous formations

Abstract: A system and method for the controlled in situ heat processing of hydrocarbonaceous earth formations involves the application of electromagnetic energy at a selected frequency or at selected frequencies to a waveguide structure formed by electrodes bounding a particular volume of hydrocarbonaceous material. Terminating one end of the structure with different impedances at different times produces electric field standing waves of different respective phase at that end at a selected frequency. Two standing waves substantially 90° out of phase in formations having relatively uniform dielectric properties result in substantially uniform application of heating power if the product of the amplitude-squared of the electric field standing wave and dwell time is substantially the same in each of the two modes. Feeding the line at both ends provides partial offset for attenuation. Various desired controlled heating patterns other than uniform may be effected by utilizing different dwell times or applied fields. Different frequencies provide further flexibility, particularly where the line is terminated differently at the respective frequencies. Energy at the different frequencies may be applied simultaneously.

Pressure diffusion sepn. method for mixts. - uses perpendicular identical frequency wave fields with differing phases

Abstract: The sepn. of mixts. of two gases, two liqs., a gas with a colloid, or a liq. with a solid, and based on differing molecular weights or specific gravities is effected by pressure diffusion using varying pressure fields. These fields are two-dimensional mutually perpendicular wave fields operating at the same frequency but with pi/2 phase shift. The mixt. for sepn. is fed by co-current or counter-flow perpendicular to the vibration plane along the longitudinal axis of a prismatic sepn. chamber with the sepd. components leaving at the roof of the chamber. The wave-fields can be formed by two vibrating walls, each tuned to the natural frequency of the standing waves. A circular polarised wave field produced by a single vibrating wall and reflecting wall, or by tubular valves, may be used. The method separates a variety of mixtures, in particular gaseous isotopes, with high efficiency and low power consumption. No moving parts or pressure compressors are involved.

Lateral waves: a new formula and interference patterns

Abstract: A new simple formula is derived as an approximation for the general exact integrals for the radial component of the electric field generated by a horizontal electric dipole in a half-space of water or earth near its boundary with air. The field in the water or earth is investigated as a function of radial distance from the source for er = 80, 20, and 4, over wide ranges of conductivities and frequencies. Special attention is paid to the ranges in which the direct wave from the dipole produces an interference pattern of standing waves when it interacts with the lateral wave. For selected values of the parameters the radial electric field computed from the new simple formula is compared with the field evaluated numerically from the exact integrals. The agreement is excellent when the ratio of wave numbers characteristic of the denser half-space and air is large, quite good even when this ratio is as small as 2.

Optical bistability for two-level atoms in a standing-wave cavity.

Abstract: Observations of optical bistability are reported for a system composed of multiple atomic beams passing through a high-finesse optical cavity. Both the transmitted power and the intracavity fluorescent intensity have been recorded as functions of incident laser power for zero cavity and atomic detunings. A quantitative study has been made of the evolution of the steady-state switching intensities from well below the critical onset of bistability to well above this point. The results show reasonable agreement with a Gaussian-beam theory of optical bistability, but systematic departures are noted.

Effects of lateral ionospheric gradients on ELF propagation

Abstract: This paper analyzes the propagation of the transverse electromagnetic (TEM) ELF mode when the earth-ionosphere waveguide is not stratified. It treats a localized disturbance by recasting the wave equation as a two-dimensional integral equation. Numerical solutions show that such a disturbance behaves like a cylindrical lens filling a narrow aperture. Lateral diffraction, focusing, and reflection can cause the TEM mode to exhibit a standing wave pattern before the disturbance, and a transverse pattern of maxima and minima beyond it. Such phenomena can contribute to the spatial fluctuations occasionally observed in ELF transmissions. The focusing and diffraction diminish when the transverse dimension of the disturbance approaches the width of the first Fresnel zone—typically, several megameters. The analysis models exceedingly widespread inhomogeneities, such as a disturbed polar cap or the day/night hemispheres, as semi-infinite regions having diffuse boundaries. It then derives full-wave analytic expressions for the lateral reflection and transmission coefficients of the TEM mode. Reflection can be important in two situations: first, when a great-circle propagation path is nearly tangential to the boundary of the disturbed polar cap and second, when the TEM mode is obliquely incident on the day/night terminator, in which case a phenomenon analogous to internal reflection can occur.

Plasma wave collapse generated by the interaction of two oppositely propagating electron beams with a plasma

Abstract: The nonlinear stage of the evolution of unstable Langmuir waves excited by two oppositely-propagating beams is studied experimentally. When a pump at frequency omega p is applied, the two monochromatic Langmuir waves thus generated ( omega p, k) and ( omega p, -k) form a standing wave. The ponderomotive force and the generation of cavitons lead to the process of plasma wave collapse to a spatial width of 7 lambda D and an intensity E2/4 pi nT approximately=0.4. Experimental evidence showing that transit time damping is the limiting mechanism for the collapse process is also discussed.

Steep standing waves at a fluid interface

Abstract: An algorithm is formulated for computing perturbation-series solutions for standing waves on the interface between two semi-infinite fluids of different but uniform densities. Using a comppter, the series solutions are computed to fifth order for a general value of r, the ratio of the density of the upper fluid to that of the lower fluid (0 ≤ r ≤ l), and to 21st order for five specific values of this ratio: r = 0, 10−3, 0·1, 5·0, 1·0. The series for the period, the energy, and the interface profile of the waves are summed using Pade approximants. The maximum wave height for each of the above five density ratios is estimated from the locations of the poles of the Pade approximants for the wave period and the wave energy. At maximum height the interface appears to be vertical at a point on the interface that is very near the crest for r = 10−3 and approaches the midpoint between the crest and the trough as r approaches 1·0.

A Simulation of the January Standing Wave Pattern Including the Effects of Transient Eddies

Abstract: A steady-state, linear, two-level primitive equation model is used to simulate the January standing wave pattern as a response to mountain, diabatic and transient eddy effects. The model equations are linearized around an observed zonal mean state which is a function of latitude and pressure. The mountain effect is the vertical velocity field resulting from zonal mean wind over the surface topography. The diabatic heating is calculated using parameterized forms of the heating processes. The transient-eddy effects, i.e., the flux convergence of momentum and heat by transient eddies, are computed from observations. Separate responses of the model are computed for each of the three forcing functions. The amplitude of the response to diabatic heating is small compared to observed values. The vertical structure is highly baroclinic. At the upper level, the phase of the waves is approximately in agreement with the observations. The amplitude of the response to mountain forcing is comparable with observ...

Motional side-band resonances in the microwave spectrum of stored ions

Abstract: Side‐band resonances were investigated in the radio‐frequency (rf) spectrum of free ions stored in a radio‐frequency quadrupole ion trap. The magnetic resonance signals occur at the center frequency and at the center frequency plus or minus integral multiples of the characteristic ion macromotion frequencies. The experiment was performed on 3He+ using the ion storage exchange collision technique. Contributions of the side‐band intensity arose predominantly from the standing microwave field inside the cavity. The effect of a small traveling wave component was also included. The microwave field was fed into the trap structure which, in addition to being used for trapping, was also employed as a broad band cavity in the TE013 mode. The dependence of the intensity distribution of the side‐band spectrum on different ion motion temperatures and energy distributions of the ions was studied numerically. It was demonstrated experimentally that initially the stored ions have a uniform energy distribution. Since the...

Acoustic agglomeration methods and apparatus

Abstract: Methods are described for using acoustic energy to agglomerate fine particles on the order of one micron diameter that are suspended in gas, to provide agglomerates large enough for efficient removal by other techniques. The gas with suspended particles, is passed through the length of a chamber (24) while acoustic energy at a resonant chamber mode is applied to set up one or more acoustic standing wave patterns (40,42,44) that vibrate the suspended particles to bring them together so they agglomerate. Several widely different frequencies can be applied to efficiently vibrate particles of widely differing sizes. The standing wave pattern can be applied along directions (R in FIG. 3) transversed to the flow of the gas. The particles can be made to move in circles by applying acoustic energy in perpendicular directions (P,Q in FIG. 6) with the energy in both directions being of the same wavelength but 90° out of phase.

A Study on Circular Disk Resonators on a Ferrite Substrate

Abstract: In this paper, an exact analysis of a circular disk resonator on a magnetized ferrite substrate which can be used for tunable filters and circular polarizing radiators is presented. The method makes use of Galerkin's method applied in the Hankel transform domain and is quite suitable for numerical calculation. The calculated values of the resonant frequencies and unloaded Q's are shown to be in good agreement with the measured data and the validity of the present theory is confirmed. Furthermore, the characteristics of the traveling wave filters are investigated theoretically and experimentally, and their advantages over the standing wave filters are demonstrated in terms of reflection and sensitivity of the Q/sub L/ on the coupling strength.

Standing Waves along a Microwave Generated Surface Wave Plasma

Abstract: Two surface wave plasma columns, generated by microwave power in argon at gas pressures of 0.05 torr to 330 torr, interact in the same discharge tube to form standing surface waves. Radial electric field Er and azimuthal magnetic field H? outside the discharge tube are measured to be 90° out of phase with respect to axial position and to decay exponentially with radial distance from the tube axis. Maximum light emission occurs at the position of maximum H?, and minimum Er. Electron temperature and density are measured at low pressures with double probes inserted into the plasma at a null of Er. Measured electron densities compare well with those predicted by Gould-Trivelpiece (GT) surface wave theory. Measured electron temperatures are the same order of magnitude as temperatures predicted by positive column theory.

A Further Study of Spectral Energetics in the Winter Atmosphere

Abstract: The contributions of standing (time-mean) and transient (time-departure) waves to the atmospheric spectral energetics are analyzed using the NMC (National Meteorological Center) data of winter 1976-1977. It is found that the standing long waves are responsible for the major horizontal sensible heat transport and also for the significant horizontal momentum transport. Furthermore, the major contents of eddy available energy and eddy kinetic energy of standing waves are in the long-wave regime. However, the spectral energetics analysis indicates that the standing long waves are energetically less efficient than the transient long and short waves. It is suggested that the lower efficiency of the standing long waves in the atmospheric energetics may be one of the physical factors causing the underforecast of the standing long waves in the numerical weather prediction models.

Observations on tides in the equatorial mesosphere

Abstract: Backscatter observations of the mesosphere (62–86 km), using the 50 MHz coherent scatter radar at Jicamarca, Peru (12°S, 77°W), are analyzed to obtain tidal and prevailing wind components. The observation periods are four 48-hour intervals covering December 20–22, 1976, and April 11–13, July 15–17, and October 3–5, 1977. The effects of missing nighttime data on the 12- and 24-hour estimates are taken into account. The diurnal and semidiurnal tidal components appear to show an evanescent mode or higher order propagating modes superimposed on the main diurnal (1,1) mode and the main semidiurnal (2,2) mode, respectively. There are a few indications of complete phase reversal from one height to the next, indicating the presence of standing wave patterns. The diurnal tide amplitudes never realize the amplitude growth with height predicted by theory partly due to interference effects and other loss processes at work in the upper mesosphere.

Self-consistent potential for a two-level atom in a standing-wave field

Abstract: It is shown that the effects of a standing electromagnetic wave of cosinusoidal form on a neutral two-level atom can be represented by an effective static potential, which is obtained by a local unitary transformation to dress the atom by the field. The form of the effective potential is obtained self-consistently by minimizing fluctuations of the atomic kinetic energy induced by the locality of the dressing transformation. Moreover this effective potential is shown to depend on the atom-field detuning and on the field intensity, and to exhibit discontinuities in some ranges of these parameters. The band structure which characterizes the eigenvalue spectrum of the dressed Hamiltonian is discussed in the spirit of the tight-binding approximation, and the fluctuations of the kinetic energy near resonance are shown to induce splitting of the bands; a physical interpretation of the atomic dynamics associated with these splittings is presented. Off resonance the fluctuations are shown to induce exchange of real photons and variations of the atomic kinetic energy. The results are compared with those of previous theories, leading to an improved understanding of the dynamics of a two-level atom in a standing-wave field.

Radiation impedance of an unflanged pipe with mean flow

Abstract: Methods used in estimating tail pipe radiation characteristics are reviewed. The pressure reflection coefficient and the radiation impedance of a tail pipe with a moving medium are evaluated form standing wave measurements at discrete positions. Empirical relations of the pressure reflection coefficient (modulus and phase angle) and the radiation resistance and reactance in the presence of mean flow, are derived from experiments observations in circular pipes of different diameters.

Microwave Power Absorption in a Biological Specimen Inside a Standing-Wave Irradiation Waveguide

Abstract: An irradiation system consisting of a standing-wave in a waveguide is a convenient way to study biological effects of the individual components of the microwave fields. This paper describes microwave power absorption in a biological specimen exposed to standing waves inside the waveguide with a reflection plate. A method is presented to obtain the absorbed power distribution and total power absorption in a prolate spheroidal model of a specimen having small dimensions compared to the guide wavelength. Numerical results on the pupa of Tenebrio molitor are given, and also verified experimentally.

Experimental and theoretical study of drift-waves in a quadrupole. II. Radial eigenfunctions

Abstract: Drift waves in a plasma with a density gradient are expected to behave like standing waves in the direction parallel to the density gradient, confined to a region around the point of maximum gradient and evanescent outside this region. Because of finite Larmor radius effects the higher radial harmonics are predicted to have lower frequencies. The authors show that in the quadrupole, confinement at the inner boundary is probably due to a layer of rapid velocity shear and with this assumption the observed radial eigenfunctions are in reasonable agreement with those predicted; the lower frequency drift wave observed in earlier work is identified as the first radial harmonic. There is a significant departure from the theory, however, in that the drift wave is observed to become a radially propagating wave in the outer regions of the plasma. The energy outflow associated with this propagation is evaluated and shown to be small compared with the input rate due to the drift wave instability mechanism.

Sheet levitational support

Abstract: An array of acoustic transducers (100) is operated to generate progressive air pressure waves. Sheets (106, 107) are introduced by feed rolls (105) and reflect the progressive waves to establish interference and a pattern of standing waves which includes a planar array of high pressure antinodes to support a sheet against gravity approximately at the level of a planar array of low pressure nodes. The initial portion of the array of transducers is horizontal to provide levitational support. A succeeding portion is inclined to the horizontal to provide movement under gravity for the sheets to a bin (112). The height of support by the standing waves may be changed by altering the frequency, and they may be rendered non-supporting by turning off or greatly reducing the amplitude of the standing waves. Various controls and guides may be provided to direct sheets being transported.

Opto-optical light deflector/modulator

Abstract: An opto-optical light deflector/modulator has means for providing first and second coherent wave fronts of wavelength (λ0) to travel in a transparent optical active medium to produce an optically generated standing wave that induces a periodic refractive index variation in the medium suitable for diffraction purposes. The device also includes means for providing a third wavefront (λ1) to travel in said medium which is diffracted by the periodic refractive index variation induced by the first and second wavefronts.

Wave soldering apparatus and method

Abstract: An apparatus for wave soldering component leads to a conductor on a printed circuit board surface includes a fountain for forming a standing wave of hot molten solder. A pool of hot oil having a specific gravity lower than the solder floats in a depression in the surface of the solder adjacent to the standing wave. A printed circuit board whose surface is to be soldered is passed through the crest of the molten solder standing wave and then while the solder adhering to the component leads and conductor is still molten, into contact with the pool of hot oil.