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The properties of linear internal waves are well studied in deep ocean and are surprisingly well modeled by the Garrett–Munk model. The properties of linear internal waves in shallow water are not well studied. Experimental measurements may be hindered by the contributions of nonlinear internal waves, the complications caused by range‐dependent coastal oceanography, and possible interactions with the bottom boundary layers. There is no reason to expect the Garrett–Munk model to work in shallow water, as some of the assumptions made in the model may be violated. In this paper, the modal spectrum (the modal amplitudes) of the linear internal waves are deduced from approximately 2 h of CTD data collected during the SWARM 95 experiment during a period when nonlinear internal waves are absent or negligible. The method of empirical orthogonal decomposition is applied to the covariance matrix of the sound speed variations assuming that the internal waves modes are uncorrelated. One finds that the eigenvectors of this matrix agree well with the theoretical eigenfunctions of the first five modes of the internal waves. The mode amplitudes are deduced from the eigenvalues and compared with the Garrett–Munk model. The measured mode amplitudes agree with the measurements using a different method which projects the sound speed variations onto the theoretically calculated mode depth functions. [This work is supported by the Office of Naval Research.]

Source localization can be a difficult problem in temporally and spatially varying shallow‐water environments. The SWARM 95 data indicate that the acoustic fields at 225 and 400 Hz change drastically in the time scale of several minutes. Since it is practically impossible to model the replica field at this time scale, one expects degraded performance for matched field processing (assuming a time‐independent replica field). An alternate processing scheme is proposed here. First it is shown that internal waves cause mode conversions and that mode conversions degrade matched‐field source localization. This is illustrated for the Garret–Munk internal waves, the solitary internal waves and the combination of both. It is then shown that source localization can be achieved by using only the uncoupled modes. This concept was implemented using matched‐beam processing. The beam filter serves to suppress the contribution of the coupled modes. It is shown that this technique significantly improves the localization performance over conventional matched‐field processing. [Work supported by the Office of Naval Research.]

The performance of a vertical array for source localization and for target detection (array gain) is studied in shallow water under a directional noise field. The acoustic environment consists of a downward refractive sound‐speed profile. At mid (e.g., 500 Hz) frequencies the vertical directionality of the surface generated noise exhibits a notch near the signal arrival direction, i.e., which is close to horizontal for a submerged source. The ability of the beam filter in rejecting directional noise has been previously demonstrated using conventional beamforming. The same capability is carried over into full field processing by using matched‐beam processing which is an equivalent of matched‐field processing conducted in the beam domain. It is shown with simulated data that matched‐beam processing incorporating a beam filter of 10 deg enhances the array output signal‐to‐noise ratio (array gain) by more than 5 dB compared with conventional beamforming and matched‐field processing. For white noise, matched‐f...

The acoustic environment is known to influence the vertical directionality of the ambient noise. For example, in shallow water with a downward refractive (summer) sound‐speed profile, the noise vertical directionality is expected to show a deep (≳5 dB) null in the horizontal direction for wind generated noise below 1 kHz. This ‘‘horizontal null’’ is a consequence of the fact that low‐order modes are weakly excited by the noise sources which are located near the ocean surface. This phenomenon has been experimentally observed in limited cases. This paper concentrates on a quantitative analysis of when the vertical directionality will exhibit a notch in the horizontal direction. The answer will depend on the acoustic frequency, the sound‐speed profile, the water depth and bathymetry, the bottom properties, the vertical array aperture, and finally the noise source distribution. Currently no simple way exists to model the noise notch except to run the numerical noise model repeatedly. A modal analysis is prese...

Conventional beamforming, based on the concept of delay and sum of plane‐wave signals, has been the cornerstone for radar and underwater acoustic array processing for many years. Matched‐field processing, which has received much attention in recent years, represents a departure from conventional beamforming in that the signal propagation is an integral part of the processor. In this paper a framework is presented (i.e., matched beam processing) in which conventional beamforming and matched‐field processing can be unified and treated on an equal footing. Matched‐beam processing is matched‐field processing in the beam domain. The resulting benefits are (1) the extension of full field processing to conventional beams, (2) the ability to do spatial filtering based on the angle of arrival, and (3) the ease of integration of the (matched‐beam) processor into existing systems. For a horizontal array in shallow water, conventional beamforming would be the processor to use, but it suffers from signal gain degradation and bearing bias when the signal energy is split over many beams. Matched‐field processing can be used to estimate the bearing accurately, but it must simultaneously estimate the target range, depth, and bearing. Using matched‐beam processing, bearing can be estimated accurately while maintaining some tolerance to environmental mismatch.

Acoustic environment is known to influence the vertical directionality of the ambient noise. For example, in shallow water with a downward refractive (summer) sound‐speed profile, the noise vertical directionality is expected to show a deep (≳10 dB) null in the horizontal direction for wind‐generated noise below 1 kHz. This ‘‘horizontal null’’ is a consequence of the fact that low‐order modes are weakly excited by the noise sources which are located near the ocean surface. This phenomenon has been experimentally observed and is not expected to occur in an upward refractive (winter) sound‐speed profile environment. It is noted, however, that when internal waves are present, the deep null may disappear or sufficiently weaken due to the ‘‘strong’’ mode coupling effect caused by the scattering of the noise field from the internal waves. In the internal wave fields, the conversion of higher‐order modes (generated by the surface noise sources) to low‐order modes by the internal waves can fill in the deep (≳10 d...

During the AREA 88 experiment (Spring of 1988), an ice camp was deployed on an ice floe in the general neighborhood of 78 N and 55 W in the central Arctic. The ice floe became active on and off for a period of days. Many of the noise events were recorded on a planar array of geophones. The response of three‐axis geophones were used to analyze the forcing mechanism of the noise events by comparing the geophone response to the ice activities with that generated by man, i.e., hammer blows. Specifically, frequency‐wave‐number analysis was used to sort out the longitudinal, shear, and flexural waves in the geophone data. While the examples shown here indicate that floe bumping/rubbing was the likely cause for the very‐low‐frequency noise signals analyzed, long‐term accumulative geophone data indicate vertical forcing was the dominant source for ice generated noise.

A broadband signal (shot) received on a vertical array was processed for geoacoustic inversion of bottom sound‐speed profile. The data were beamformed to show the distribution of waterborne and bottom interacting signals. By correlating the (complex) beams containing the bottom interacting signals with the equivalently formed beams for the replica field (matched beam processing), one evaluates the ambiguity function maximum at the source location and searches for the bottom sound‐speed profile which yields the highest correlation for the matched beam processing. Different frequency bands of the signal are investigated to evaluate the sensitivity to bottom sound‐speed variations. The inverted sound‐speed profiles are found consistent (within the resolution of 50–100 m/s) with the sound‐speed profiles estimated from (1) core samples and other geoacoustic data at the site, and (2) the arrival time of the Head waves [J. Wolf, J. Acoust. Soc. Am. 94, 1769 (1993)].

Matched‐field inversion for ocean bottom compressional wave speeds using a synthetic horizontal aperture has been demonstrated previously in simulations and data analyses employing optimization by simulated annealing [M. Collins, W. Kuperman, and H. Schmidt, J. Acoust. Soc. Am. 92, 2770 (1992)] and genetic‐algorithm search [P. Gerstoft, J. Acoust. Soc. Am. 95, 770 (1994)]. The first reference noted a lack of sensitivity of the matched‐field ambiguity function to zero‐mean functional variations of the sound‐speed profile. This lack of sensitivity sometimes results in slow convergence of the search algorithm when applied to profiles with several unknown parameters. This problem is observed in simulations using genetic algorithm search. Improved convergence of the genetic algorithm is then achieved by using some nonstandard procedures, including autologous gene exchanges, to generate new solutions. The simulations indicate the practical feasibility of inversion for deep‐bottom (up to 500 m) compressional wave speeds at a shallow‐water site using a single receiver and coherent synthetic horizontal aperture processing of a towed‐source signal.

In shallow waters, the effective vertical aperture of an array composed of horizontal and vertical segments may be greater than the water column depth. The extended vertical aperture leads to better decomposition of bottom‐interacting normal modes and hence better range‐depth localization compared with the performance of the vertical subarray alone. The conditions under which the effective vertical aperture gives improved localization performance over a vertical array spanning the water column are demonstrated. The effect of source frequency, ratio of horizontal to vertical array length, and bottom properties on localization performance are discussed.

Acoustic inversion of geoacoustic properties in the ocean bottom has been investigated recently using matched‐field processing. In the shallow Arctic waters, the acoustic signal may still be dominated by waterborne modes. As a consequence, the matched‐field correlation may not be very sensitive to bottom sound‐speed variation. It is found that in a water depth of approximately 600 m the matched‐field correlation remains very high (≳0.95) even with a mismatch of 50 m/s in bottom sound‐speed profile. To improve the sensitivity to bottom mismatch, we include only the high‐order modes in the matched‐field/mode correlation. This method is investigated using a simulated broadband signal and also using SUS data received on a vertical array. The source is localized using broadband matched‐field/mode processing. Short‐range data are considered to maximize bottom interacting signals.

Low‐frequency reverberation data received on a large aperture planar array of hydrophones are used to estimate the under‐ice scattering strength over a basin wide area. The result is interpreted as a large scale under‐ice keel distribution which, unlike the ice surface ridge distribution, has not been measured over a wide area. The reverberation data were collected during the CEAREX 89 experiment using explosive sources. Scatterer localization was performed for each time segment. The range‐bearing ambiguity distributions at depth near the surface was range gated according to estimated two‐way travel times, and combined to form the ambiguity surface for a large area. Ice keel distribution is obtained by removing the two‐way transmission loss to and from the surface scatterers. This image is compared with that obtained using conventional beamforming techniques.

Time domain waveforms excited by an impulse, point force are modeled using fluid‐loaded thin plate theory and compared with measured data collected on ice‐implanted geophones. In the frequency domain, the solution, expressed as an integral over wave number, can be expressed in terms of poles (free waves) and branch cuts (forced waves). The time domain solution is obtained by taking a Fourier transform of the frequency response of the plate, weighted by the (measured) source spectrum. The modeled time domain waveform compared favorably with the received time series data. A simple direct time domain solution for the forced wave in a thin plate in air also approximates the data well. It is shown that the forced wave solution produces the ‘‘abnormal’’ dispersion relation observed in recent geophone data. The free‐wave solutions, which have been extensively studied before, also agree with the geophone data.

Benchmark tests of propagation models have been conducted by comparing transmission loss of individual phones. While various propagation models often yield the same (range) averaged transmission loss, they differ in the calculation of phases. The difference in the calculated pressure field is examined here in terms of source localization in a sloping shallow‐water environment. This study examines the impact on source localization due to boundary reflection loss, bottom bathymetry and profile, and mode coupling which are handled differently by different models. In particular, the coupled normal mode, adiabatic normal mode, and PE propagation codes are examined. The calculated pressure field from individual models are analyzed in terms of the normal mode amplitudes at the receiver site. The difference of mode amplitude surfaces are plotted as a function of source range to evaluate the range dependence of propagation model mismatch.

In the Arctic ocean, very low‐frequency (10–50 Hz) reverberation returns from the ice and bottom both contribute to the total received reverberation and are not easily distinguishable in long‐range reverberation data, except where there is a dominant bottom or ice feature. In this paper, a normal‐mode scattering model for surface and bottom protuberance is used to model long‐range reverberation data collected during the CEAREX 89 experiment in the Norwegian/Greenland Seas. Modeled reverberation spectrum levels at 23 Hz are compared with data to investigate the relative contributions of the ice and bottom to the measured reverberation. It is found that for a source at 91‐m depth in the 3000‐m‐deep basin, the reverberation level for a receiver at 91 m is dominated by scattering from the ice except for reverberation associated with certain identifiable bottom features. For the same environment but a deeper (244‐m) source, reverberation levels from the ice and bottom are more comparable. For a strongly range‐...

Acoustic reverberation data from SUS explosions collected during the CEAREX 89 experiment in the Norwegian–Greenland Seas are analyzed to estimate both under‐ice and bottom backscattering strengths. Data from the 1230‐m vertical array were previously used to measure scattering strengths from short‐range (

Where in the curriculum is the best place to teach experimental NMR methods that are so essential to chemists and chemistry? These authors are of the opinion that NMR must be given more than a cursory introduction involving a single experiment, and present a series of experiments.

A tank experiment was devised to measure forward and backscattering from single and multiple rods distributed on the water‐air interface oriented normal to the plane of scattering. The cylindrical rods made of acrylic simulate the soft half‐cylindrical protuberances used by Twersky in calculating scattering [J. Acoust. Soc. Am. 22, 539–546 (1950)]. (The Burke‐Twersky model has been used frequently to model under‐ice scattering in the Arctic Ocean.) To measure the scattering function (including the specular reflection and backscattering) from the cylindrical rods, a new experimental setup using an array of small diameter (0.05 in.) transducers was used to receive the scattering returns at different angles simultaneously. The source is a large diameter (3 in.) transducer operating at 100 kHz, with a narrow beam (

A method of mode decomposition by averaging over broadband components of impulse signals propagated over long ranges is investigated here for simulations and explosive data collected in the Arctic on a vertical array. This method is based on the assumption that cross‐modal terms of the covariance matrix are minimized when averaging over broadband components of an impulse signal [C. S. Clay, “Array steering in a layered waveguide,” J. Acoust. Soc. Am. 33, 865–870 (1961)]. Analysis of simulated data shows that both the mode amplitudes and modal depth functions can be deduced using this method; accuracy depends on how each mode is sampled by the vertical array. This method is developed for the purpose of investigating the modal structure of reverberation returns from explosive signals in the CEAREX 89 experiment. [Work supported by ONR.]

A technique to model under‐ice reflection loss based on new analysis of data from the Fram IV experiment is described. Using Burke‐Twersky scattering theory, the under‐ice/water boundary is modeled as a set of rigid, elliptical cylinders fixed to a free surface. Ice draft measurements taken during the Fram IV experiment are used to identify individual ice‐ridge keels resulting in a keel depth distribution function spatially coincident with the acoustic measurement track. The Burke‐Twersky scattering function is weighted against the keel depth distribution providing an effective scattering as a function of frequency. Ice reflectivity as a function of grazing angle is then calculated for a particular frequency, which provides predictions that are in good agreement with those inferred from low‐frequency, long‐range acoustic field measurements.

The vertical directionality of ambient noise in a wavegrade such as the Arctic is determined by the weighted contributions of near and distant sources. The weighting is determined by the source strength and the amount of transmission loss which in the Arctic is determined by the ice reflection loss. On a quiet day, i.e., when the local noise is minimal, the vertical directionality of the ambient noise is dominated by the contribution of distant noise sources. In other words, the vertical directionality could not be properly modeled without first modeling the ice reflection loss. A simple analytic expression for the mode intensity of ambient noise is given to relate the mode intensity with the mode arrival angles. This mode spectrum with respect to arrival angle is compared with the vertical directionality data on a quiet day to determine the angular dependence of ice reflection loss at low frequencies.

The Arctic Ocean, because of its unique sound‐speed profile, exhibits clear mode structure in long range data of explosive sources. Range estimation can be made from the time‐frequency dispersion of wideband pulses received at a single hydrophone. The method is discussed here. From the shot data, we find results using the lowest mode are in agreement with actual ranges within ten percent uncertainty. The method is insensitive to background noise, source spectrum shape, bottom profile, and the source‐receiver depths. Relations between the sound‐speed profile and the mode dispersions in the Arctic are discussed.

In a previous article [T. C. Yang, J. Acoust. Soc. Am. 82, 1736–1745 (1987)], range and depth were successfully estimated by modal beamforming. In this article, the modal beamforming array gain is derived in closed form for a vertical array of N hydrophones. For the case of white noise and a long well‐populated vertical array, the array gain nearly equals 10 log N. For the case of colored noise and a finite aperture, finite element vertical array, the array gain degrades from the theoretical by an amount determined by the mode depth amplitudes evaluated at the source and receiver depths and the modal covariance matrix of the noise. Numerical estimates of array gain are given for the FRAM IV vertical array for a colored noise environment in the Arctic sound channel. Approximately 1‐dB array gain degradation at 47 Hz is found. Proper array configuration and deployment depth are not only important for optimizing array gain but also critical for maximizing the input signal‐to‐noise ratio on a vertical array, ...

A towed array experiment was performed by NRL in 1982 in the vicinity of the ice edge in the Greenland Sea. The array was towed normal and parallel to and at ranges between 4–50 km from the ice edge; the received data were beamformed to study the horizontal directionality of the noise. The results indicated that a few localized ‘‘hot spots’’ (with dimensions

The group velocities of normal modes are not independent but are related to each other by a scaling law. The scaling law relates the frequencies of any two modes received at a particular time (associated with a particular group velocity) by a scaling parameter. The scaling parameter is a constant for mode energies fully contained in the water column; in the ray picture, this corresponds to refracted only, and refracted and surface reflected rays. Experimental data will be analyzed to see how well the ‘‘constant’’ behaves for a variety of frequencies and modes. For bottom‐limited acoustic propagation, the scaling parameter for the normal modes may not be a constant. For this case we can use the theory to deduce the phase change of reflection at the boundary from the measured scaling parameter data. The phase change for bottom reflection is deduced from shallow water shot data for grazing angles from 9° to 10.4° and is used to probe the sound speed in the bottom. This proves to be a useful technique since direct measurement of phase change is extremely difficult by other experimental techniques.

We have calculated charm pair production in νμN collisions using quantum chromodynamics (QCD). The resulting trimuon rate turns out to be small at present energies: σ(3μ) σ(1μ)≲10 −6 at Eν = 200 GeV for αs = 0.2. (However, this process may be measurable at the high energies attainable with colliding beam ep machines.) We emphasize the general importance of looking for inclusive J Ψ or the bound states of heavier flavors in deep inelastic reactions, as a signal for the pair production of heavy quarks.

Normal mode amplitudes are definite functions of depth and have a characteristic phase as a function of source range rs [i.e., exp(−ikirs), where ki is the ith mode wavenumber]. The range and depth of an acoustic source in the ocean can then be determined by decomposing array data and beamforming on the mode amplitudes. In particular, the product of the normal mode amplitudes with the steering vector Ui [where Ui=exp(ikir) ] is maximum for the true source range (r=rs). Similarly, the correlation of the measured (decomposed) mode amplitudes with the theoretically calculated mode amplitudes is maximum at the source depth. Accurate range and depth estimation with this approach, however, requires reliable estimates of the mode amplitudes. In this article, an eigenvector decomposition technique is used to extract the mode amplitudes for data received on a long (1‐km) vertical array. Range and depth are successfully estimated both for simulated data and for data from the 1982 FRAM IV experiment in the Arctic Oc...

(1975). SYNTHESIS OF TWO TOXIC 4-IPOMEANOL ANALOGS. Organic Preparations and Procedures International: Vol. 7, No. 5, pp. 221-224.

The production of heavy-lepton pairs by longitudinally polarized ${e}^{+}{e}^{\ensuremath{-}}$ colliding beams induces a parity-violating correlation in the angular distribution of the daughter leptons. The dependence of the parity asymmetry on the beam and lepton energy is studied in $V\ensuremath{-}A$ and $V+A$ current models for the heavy lepton. Large asymmetries are expected from the threshold of heavy-lepton production to very high energies. The energy-integrated angular distribution of the detected leptons becomes parity-symmetric at very high energies.

A new decentralized stabilization method is presented, in which l single-input/single-output local feedback controllers are designed to stabilize or to improve the stability of a large-scale system consisting of N subsystems with l

The time‐frequency structure of broadband pulses propagating to long ranges is analyzed with the stationary phase approximation. A method based on this analysis is proposed for measuring the fine structure of the frequency dispersion. The new method determines the mode frequencies to a precision of 0.5 Hz whereas the precision of the sonogram method is typically several Hz. Implications of this improved frequency dispersion measurement are discussed.

Potato spindle tuber viroid (PSTV) caused albinism in the new growth of Rutgers tomato under continuous light. The albinism response was obtained with 4 isolates causing severe symptoms in tomato and with 1 mild isolate which is normally symptomless.

If chiral U(1) symmetry is a gauge symmetry, CP is automatically conserved despite the instanton effects, and the weak neutral currents have a definite structure. A realistic SU(2) L ⊗U(1)⊗U(1) R model contains an axion which is consistent with present data. Furthermore the neutrino interactions to lowest order are identical to the Weinberg-Salam model. Implications for the chiral U(1) currents are discussed.

An experiment measuring sonic reflectivities below 1 kHz was done beneath large smooth ice floes in the Arctic Ocean north of Ellesmere Island. Reflectivity data are presented here for grazing angles between 14 ° and 26 °. The reflectivity is found strongly dependent on frequency as well as grazing angles. Theoretical discussions are given to interpret the data. The most significant finding of this report is that a smooth ice plate cannot be treated as totally reflective for frequencies between 200 Hz and 1 kHz, an assumption which has so far been taken for granted in the literature. In fact, the reflection loss at smooth, flat ice could account for a substantial part of the transmission loss in Arctic oceans for this frequency range.

We explore the possibility that charged Higgs bosons exist. The role of e + e − experiments carried out above heavy quark thresholds is stressed. Striking experimental signatures are predicted.

For the analytically important reaction of ozone with Fe/sup 2 +/ in aqueous solution, the stoichiometric ratio (SR), defined as the moles of Fe/sup 2 +/ oxidized per mole of ozone consumed, has been determined over a range of ratios of (Fe/sup 2 +/)/(O/sub 3/) between 3 and 200 and for pH values between 1.3 and 5.4. The SRs were referenced to the UV absorption of aqueous ozone using epsilon = 3300 M/sup -1/ cm/sup -1/ at 258 nm. The SR varied between 1.84 and 2.53 depending on pH and on the initial ratio of (Fe/sup 2 +/)/(0/sub 3/). While the consumption of ozone was complete within 0.1 s, attainment of the final stable value of the SR required at least 15 min. These results are rationalized in terms of a proposed reaction mechanism in which secondary oxidizing species of varying reactivity are generated in the rapid first oxidation step. The variable SR results from the differing effectiveness of competition for these secondary species by O/sub 3/, Fe/sup 2 +/, and H/sup +/ as their relative concentrations vary. While the SR does change in this complex way, it was found that the value is sufficiently reproducible at selected reasonable conditionsmore » to be analytically useful in the case of clean water.« less

It is demonstrated that low‐frequency ( 250 km) range‐averaged propagation data. It is also found that transmission loss varies significantly with source depth; consequently, transmission loss curves determined from data for multiple source depths have an inherent (not experimentally related) uncertainty of several dB and thus cannot shed light on the angular dependence of ice‐scattering loss.

A disorder of Michigan potatoes tentatively called speckle leaf is associated, in part, with air pollution injury. The disease is characterized by reduced yields following early vine maturity, premature vine death, and yellowing of the lower leaves. Necrotic spots developed on the upper surface of leaves, followed by bronzing, and upward leaf rolling. Severely affected leaves became chlorotic and remained attached to the stem. Potato plants were grown in two plastic houses through which was blown either ambient field air or ambient air filtered through activated charcoal. Plants grown in the plastic house receiving ambient air developed symptoms similar to nearby field plants. Plants grew normally in filtered ambient air and remained free of speckle leaf and air pollution injury symptoms. The potato varieties Haig, Norchip, and Superior were most sensitive, Sebago was intermediate, and Kennebec and Katahdin were most tolerant. Tobacco plants in ambient non-filtered air developed symptoms typical of ozone injury. Bean leaves became bronzed with brown necrotic flecks on both surfaces, and severely affected leaves dropped. Neither tobacco nor bean was affected in the filtered air. 24 references, 6 figures.

We propose a simple and unique asymptotic symmetry scheme to incorporate spins, SU (3), $\mathrm{CPT}$ invariance, and the generalized Bose statistics into the parton dual-resonance model for deep-inelastic lepton-hadron reactions. The scheme embodies Harari-Rosner quark duality diagrams, adopts Chan-Paton SU (3)-symmetry factors, identifies Mandelstam, Bardakci, and Halpern's multiplicative quark model in the Bjorken limit, and generates Fritzsch and Gell-Mann's light-cone structures identically. The dynamical (parton-dual-resonance-model) approach is therefore unified with the symmetry (light-cone) approach, and the complementarity between these two is established. Light-cone sum rules are derived, and a new sum rule is suggested. As a further application of this scheme, we calculate the complete sets of bilocal light-cone structures occurring in the two-heavy-boson processes.