Showing papers on "Interference (wave propagation) published in 1972"
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TL;DR: A lower bound on the symbol error probability achieved by any estimator of a digital pulse-amplitude-modulated sequence in the presence of white Gaussian noise and intersymbol interference is presented and reduces to the well-known single-pulse error probability bound.
Abstract: A lower bound on the symbol error probability achieved by any estimator of a digital pulse-amplitude-modulated sequence in the presence of white Gaussian noise and intersymbol interference is presented. The bound reduces to the well-known single-pulse error probability bound when intersymbol interference is small, but is tighter when interference is large. For example, on the singlepole ( RC ) channel, the effective signal-to-noise ratio for any estimator is shown to decrease by at least 3 dB for every doubling in pulse rate T-1as T \rightarrow 0 and, on the double-pole channel, by at least 9 dB, thus disproving a recent conjecture [2] on the performance of nonlinear receivers.
121 citations
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TL;DR: In this article, a He-Ne laser beam is sent through a common path differential interferometer and the interference signal is detected by a p-i-n photodiode.
Abstract: A He-Ne laser beam is sent through a common path differential interferometer and the interference signal is detected by a p-i-n photodiode. Weak phase objects can be examined because optical path changes can be resolved to 0.1 A with a time resolution of about 20 ns. Examples for different gas-dynamic investigations show good results and demonstrate the wide field of application for this type of laser interferometer.
72 citations
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TL;DR: In this article, the authors reviewed and organized available experimental results to provide a logical explanation of aerodynamic support interference for dynamic wind-tunnel testing and proposed an analytical method of correcting the windtunnel results for dynamic support interference.
Abstract: Available experimental results are reviewed and organized to provide a logical explanation of aerodynamic support interference for dynamic wind-tunnel testing. Configurations involving bulbous bases, mass addition, boundary-layer transition near the base, and hypersonic low-density flows are shown to be particularly sensitive to sting interference effects. Transverse rod support interference occurs at all Mach numbers depending on oscillation amplitude and/or trim angle of attack. The postulated flow model predicts that cylindrical and flared stings can have opposite interference effects in agreement with experimental observations. An analytical method of correcting the wind-tunnel results for dynamic support interference is proposed.
50 citations
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TL;DR: A model to estimate the bandwidth and interference in an interleaved memory system in a multiprocessor system is described and allows queuing on busy modules, and the results obtained show that previous results are rather pessimistic.
Abstract: A model to estimate the bandwidth and interference in an interleaved memory system in a multiprocessor system is described. The model allows queuing on busy modules, and the results obtained show that previous results are rather pessimistic.
47 citations
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06 Jul 1972TL;DR: In this article, an interferometry of the matter waves accompanying particles such as neutral atoms, charged ions or electrons is described, and the resulting interference fringes can be measured by a suitable particle detector.
Abstract: An apparatus is disclosed which makes use of interferometry of the matter waves accompanying particles such as neutral atoms, charged ions or electrons. The apparatus includes a particle source and a beam splitter for splitting the original beam of particles into two beams having accompanying matter waves which are coherent with each other. The two beams are recombined by a pair of beam reflectors, and the resulting interference fringes may be measured by a suitable particle detector. Such an apparatus may be used for measuring variation of the gravitational field or the rate of rotation of the apparatus. In both cases the apparatus is capable of ultra precise measurement of acceleration, of the mass of an object or the rate of rotation. Alternatively, by utilizing charged particles it is possible to measure a magnetic field to obtain a magnetometer of great sensitivity. The apparatus may finally be used to carry out holography by matter waves.
40 citations
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TL;DR: A full-field, variable sensitivity technique for mapping the vibrational amplitude of a diffuse surface is demonstrated and the visibility of the fringe pattern obtained is found to be modulated by a function of the local amplitude of vibration.
Abstract: A full-field, variable sensitivity technique for mapping the vibrational amplitude of a diffuse surface is demonstrated. The surface under study is placed in an optical field consisting of two mutually coherent plane waves which propagate in different angular directions. At any instant of time the interference of these waves causes a fringe pattern to be formed on the surface under study. The time average, over one or more vibrational periods, of the intensity pattern on the surface can be obtained in real time by utilizing visual persistance or by making a time-average recording of an image of the surface. The visibility of the fringe pattern thus obtained is found to be modulated by a function of the local amplitude of vibration. This modulation can be observed directly or a photograph of the pattern can be optically processed to yield fringes that are loci of constant vibrational amplitude.
37 citations
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TL;DR: In this paper, the dependence of spectral variations within a reflected broad-band ultrasonic pulse on the size and orientation of the reflector was determined experimentally and an analytical model was developed on the assumption that interference of the waves received from the edges of the reflecting surface is responsible for the variations of the received frequency spectra.
Abstract: The dependence of spectral variations within a reflected broad‐band ultrasonic pulse on the size and orientation of the reflector was determined experimentally. An analytical model is developed on the assumption that interference of the waves received from the edges of the reflecting surface is responsible for the variations of the received frequency spectra. It explains the experimental results very well. The feasibility of determining the size and orientation of hidden flaws in metals by this method is demonstrated.
30 citations
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01 Jan 1972TL;DR: The long-range periodicity of a crystal lattice is not a necessary requirement for the production of diffraction effects as mentioned in this paper, and even in a dilute polyatomic gas the interference between waves scattered from different atoms within a molecule is sufficient to produce a characteristic diffraction pattern from which the molecular structure can be deduced.
Abstract: The long-range periodicity of a crystal lattice is not a necessary requirement for the production of diffraction effects. Even in a dilute polyatomic gas the interference between waves scattered from different atoms within a molecule is sufficient to produce a characteristic diffraction pattern from which the molecular structure can be deduced. The short-range positional and orientational correlation between molecules, negligible in the gas phase, is sufficient in a liquid to cause additional interference effects between waves scattered from atoms in different molecules. The diffraction pattern of a liquid contains information about these correlations.
28 citations
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TL;DR: In this paper, the interference pattern for a source towed past a hydrophone demonstrates a focusing effect predicted theoretically, and the number of modes effective is found to vary as (frequency) x (range) − 1 2, which has important implications.
26 citations
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TL;DR: The holo-diagram demonstrates the interference limits and diffraction limits of any method of optical information retrieval.
Abstract: Ordinary interferometry, hologram interferometry, contouring, speckle, moire, ordinary radar, Doppler radar, optical Doppler velocimeter, Doppler holography, and gated viewing are all discussed, and it is demonstrated how closely these methods are related to each other. One single diagram, the holo-diagram, can be used for the evaluation of each method and even for combinations of the methods. The diagram is constructed for the study of interference patterns when an object is placed in the vicinity of two focal points representing either one point of illumination and one point of observation or two points of illumination or two points of observation. It reveals interference surfaces in space and how ordinary interference fringes are formed where an object intersects these surfaces. With a common moire analogy the three-dimensional sensitivity distribution and the fringe patterns of each of the methods can be simulated. Finally it is pointed out that the diagram demonstrates the interference limits and diffraction limits of any method of optical information retrieval.
25 citations
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25 May 1972TL;DR: In this article, a short-coherence-length laser pulse is projected upon two optical surfaces separated by a distance, d The reflected, coincident beams are directed into a Michelson interferometer in which one plane mirror is replaced by a stepped mirror and the beams reflected from the two mirrors are directed onto a film where they form interference images.
Abstract: The invention comprises a method and means for measuring the separation been two optical surfaces A short-coherence-length laser pulse is projected upon two optical surfaces separated by a distance, d The reflected, coincident beams are directed into a Michelson interferometer in which one plane mirror is replaced by a stepped mirror The beams reflected from the two mirrors are directed onto a film where they form interference images A formula using the number of channels, n, between successive interference fringes and the step width of the stepped mirror is used to calculate d
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TL;DR: In this article, the three Josephson-junction asymmetric feed quantum interferometer has been analyzed and shown to have increased magnetic field sensitivity and amplitude deviation over the two junction interferometers.
Abstract: The three‐Josephson‐junction asymmetric‐feed quantum interferometer has been analyzed and shown to have increased magnetic field sensitivity and amplitude deviation over the two‐junction interferometer. The critical current at zero applied field is shown to be less than the critical current at zero flux in the interference loop.
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TL;DR: In this paper, the amplitude and phase of the received waves show variations with periods in the range from seconds to weeks and longer-term trends, which raises questions of modeling amplitude fluctuations from transport and temperature changes obtained from acoustic phase measurements.
Abstract: Sound waves of 420 Hz continuously transmitted across the Florida Current from a fixed source to fixed hydrophones are used to investigate relationships between temporal fluctuations of the waves and changes of Florida Current transport and water‐column temperatures. The amplitude and phase of the received waves show variations with periods in the range from seconds to weeks and longer‐term trends. Characteristically, variations of acoustic phase correspond to changes of transport and temperature, but fluctuations of acoustic amplitude are noiselike and not readily identifiable. Long period changes of transport and temperature result in slowly changing phases of the multipath arrivals and varying patterns of interference and amplitude fading. Spectra of the amplitude fluctuations show components over a wide frequency range which mask components corresponding to transport and temperature changes. The above characteristics also appear in calculations with ray‐propagation models in which sound speed versus depth was varied with time in accordance with measured variations. Since the models have plane parallel boundaries, characteristic features of the variations appear to be independent of surface and bottom irregularities. This raises questions of modeling amplitude fluctuations from transport and temperature changes obtained from acoustic phase measurements. The paper summarizes relevant observations and analyses.
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TL;DR: In this paper, interference experiments between elliptically polarized light beams are described, and it is shown that when beams of light in orthogonal states of elliptical polarization are used no interference fringes are observed.
Abstract: Interference experiments (Young's double slit) between elliptically polarized light beams are described. The results show that when beams of light in orthogonal states of elliptical polarization are used no interference fringes are observed.
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TL;DR: In this article, a Michelson interferometer has been used to analyze the complete spectrum of the collision-induced depolarized light scattered by compressed Ar. Precise measurements of the width and integrated intensities are given.
Abstract: A Michelson interferometer has been used to analyze the complete spectrum of the collision-induced depolarized light scattered by compressed Ar. Precise measurements of the width and integrated intensities are given. Some evidence for an intercollisional interference effect is found.
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TL;DR: In this paper, an interference experiment is described in which measurements are made of fringe-visibility when the interfering light beams are amplitude-modulated in anti-phase and the conditions were such that the mean density of quanta in the interferometer contributing to the interference was much less than unity; the electro-optic shutters were switched several times between the detection of successive quanta.
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01 Jan 1972TL;DR: In this article, the authors used polystyrene spheres suspended in a very thin liquid film formed on the surface of the solid to reveal the interference pattern present at the surface, which is a technique for the visualization of ultrasonic interference in solids.
Abstract: This paper reports a new technique for the visualization of ultrasonic interference in solids. The technique utilizes small (≈ 1 μm) polystyrene spheres suspended in a very thin liquid film formed on the surface of the solid. The nonlinear response of this film to acoustic waves is such that the spheres reveal the interference pattern present at the surface. There are two important advantages to this technique. The first is the simplicity of the technique, no elaborate equipment is required. The second is the easing of restrictions on ultimate resolution by our ability to visualize ultrasonic interference in solids.
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09 Nov 1972
TL;DR: In this article, the primary causation of undesired non-linear intermodulation interference developed from a plurality of known radio frequency sources is determined by the method and process of generating commensurate derivative signals from each of the known radios frequency sources, non-linearly amplifying and mixing the derivative signals to produce composite signals containing spectrally expanded frequencies, separating the frequency components of the composite signals for indicating the amplitude of each component, and then separately disconnecting each derivation signal in turn to identify which of the radio frequencies sources causes the unwanted inter modulation interference at a
Abstract: The primary causation of undesired non-linear intermodulation interference developed from a plurality of known radio frequency sources is determined by the method and process of generating commensurate derivative signals from each of the known radio frequency sources, non-linearly amplifying and mixing the derivative signals to produce composite signals containing spectrally expanded frequencies, separating the frequency components of the composite signals for indicating the amplitude of each component, and then separately disconnecting each derivation signal in turn to identify which of the plurality of known radio frequency sources causes the unwanted intermodulation interference at a particular selected frequency. The new method and process may be implemented by apparatus such as a current transformer electromagnetically coupled to each of the known radio frequency sources, and amplified by a broadband non-linear amplifier which also mixes the signals as well as spectrally expanding their frequency content; a multiple switch means connecting the derivative signals as inputs to the nonlinear amplifier is preferably adapted for selectively disconnecting each of the derivative signals in turn. Broadband frequency response means receives the resultant outputs of the amplifier and separately indicates the amplitude of each discrete frequency component. Disconnection of each derivative signal in turn identifies which of the known radio frequency sources contributes significantly to the undesired intermodulation interference at any particular selected frequency of concern.
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TL;DR: In this article, the complex cepstrum technique is used to remove undesirable modulations of surface wave spectra caused by interference of either multiple sources or multipath propagation, which has greatly enhanced the utility of the spectral features for characterization of seismic sources.
Abstract: summary
The complex cepstrum technique is found to provide an effective means for removing undesirable modulations of surface wave spectra caused by interference of either multiple sources or multipath propagation. This technique has greatly enhanced the utility of surface wave spectra for characterization of seismic sources. An empirical analysis of surface wave spectra on a regional basis is made on seismic events in the Arctic Ocean and the Eurasian Continent. The results indicate that: (1) the spectral shapes of Rayleigh waves often are similar among events in the same epicentral area but vary substantially from one epicentral area to another, (2) a great majority of earthquakes can be differentiated from underground nuclear explosions based on spectral shapes of Rayleigh waves, and (3) spectral shapes of Love waves do not vary as much as Rayleigh waves from one epicentral area to another. Finally, a method for systematically finding the source mechanism and focal depth of an earthquake using the observed and theoretical surface wave spectra are devised and tested. The results from tests of the method on several earthquakes are consistent with other independent evidence.
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TL;DR: In this paper, two beams derived from a mode-locked ruby laser were superimposed in an absorbing liquid and the absorbed light produced a spatial and temporal temperature modulation which excited an ultrasonic wave, this was detected by diffraction of light
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TL;DR: In this article, the rate of loss of phonons from a crystal covered with a thin film of liquid helium is calculated using a model of acoustic multiple beam interference with a bulk attenuation in the helium.
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TL;DR: In this article, the general principles of quantum mechanics imply restrictions upon the time and space dependence of interference effects produced by modulated particle beams, and theorems proved cover a wide range of phenomena, including the production of coherent radiation.
Abstract: The general principles of quantum mechanics imply restrictions upon the time and space dependence of interference effects produced by modulated particle beams. The theorems proved cover a wide range of phenomena, including the production of coherent radiation.
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