Horizontal Array Research Articles

Morphology-Dependent Room-Temperature Ferromagnetism in Undoped ZnO Nanostructures.

Since Dietl et al. predicted that Co-doped ZnO may show room-temperature ferromagnetism (RTFM) in 2000, researchers have focused on the investigation of ferromagnetic ZnO doped with various transition metals. However, after decades of exploration, it has been found that undoped ZnO nanostructures can also show RTFM, which in general is dependent on ZnO morphologies. Here, we will give an overall review on undoped ZnO nanomaterials with RTFM. The advanced strategies to achieve multidimensional (quasi-0D, 1D, 2D, and 3D) ferromagnetic ZnO nanostructures and the mechanisms behind RTFM are systematically presented. We have successfully prepared ferromagnetic nanostructures, including thin films, horizontal arrays and vertical arrays. The existing challenges, including open questions about quantum-bound ZnO nanostructures, are then discussed.

Heat transfer of spray falling films over horizontal tubes with counter current airflows in an evaporative condenser

The spray film evaporative cooling equipment is useful to circumvent the scaling with expanded liquid coverage for attaining good thermal performance and energy efficiency. This paper examines the evaporative heat transfer phenomena of falling spray films over the horizontal circular tube array. In the experimental study, a high-speed camera with a LED fiber optic light source is implemented to capture the optical images for illuminating the distributions of spray films over the tube array under the counter current airflows. The average wall temperature, outlet temperature of spray nozzle and heat flux regulated by a programmable DC power supply are measured to determine the heat transfer coefficient. Moreover, the computational simulation is conducted using the CFD software ANSYS/ Fluent® in conjunction with a user defined function (UDF) to investigate the evaporative heat transfer of liquid spray films over the tubes. The calculated liquid film thicknesses and average heat transfer coefficients around the upper and lower tubes agree reasonably with the measured data to validate the numerical model. To explore the development of falling spray film dispersion and thermal performance over the tubes, the measurements and simulations are then extended to examine the characteristics of film thickness and heat transfer of splashed water sprays on the tube array at varying water flow rates of 3–7 l/min, heat fluxes of 10–50 kW/m2, tube placement positions of 0–142.5 mm (i.e. w1-w6) and counter current airflow velocities of 0.8–2.0 m/s, respectively. In measurements, the average heat transfer coefficients of four positions for the tubes at an upward airflow velocity of 2 m/s can reach 5.0 kW/m2 K for the water flow rate of 5 l/min and a heat flux of 30 kW/m2K.

Acoustic multipath structure in direct zone of deep water and bearing estimation of tow ship noise of towed line array

In the towed line array sonar system, the tow ship noise is the main factor that affects the sonar performance. Conventional noise cancelling methods assume that the noise is towards the endfire direction of the array. An acoustic experiment employing a towed line array is conducted in the western Pacific Ocean, and a strange bearing-splitting phenomenon of the tow ship noise is observed in the array. The tow ship noise is split into multiple noise signals whose bearings are distributed between 10° and 90° deviating from the endfire direction. The multiple interferences increase the difficulty in recognizing the target for the sonar operator and noise cancellation. Therefore, making the mechanism clear and putting forward the tow ship noise splitting bearing estimation method are imperative. In this paper, the acoustic multi-path structure of the tow ship in deep water is analyzed. Then it is pointed out that the bearing-splitting phenomenon is caused by the main lobe of direct rays and bottom-reflected rays, as well as several side lobes of direct rays. Meanwhile, the indistinguishability between the elevation angle and the bearing angle due to the axial symmetry of a strict horizontal line array causes the bearing to deviate from the endfire direction. Based on the theory above, a method of estimating bearing of the tow ship noise in deep water is proposed. The theoretical analysis results accord with the experimental results, which helps to identify the target and provide correct initial bearing guidance for noise cancelation methods.

Cross-species evidence that nicotine widens the attentional window.

The ability to spread attention over items or locations is as important for everyday functioning as the ability to focus narrowly. Little is known about neuronal processes involved in broad monitoring, but indirect evidence suggests a role of nicotinic acetylcholine receptors (nAChRs). The present study tested whether the prototypical nAChR agonist nicotine enhances the ability of humans and rodents to maintain a broad attentional window. Fifty-three never-smokers wearing a nicotine (7mg/24h) or placebo patch performed an attention task requiring detection of stimuli presented randomly in one of four peripheral locations, with a central cue predicting the target location or indicating the need to spread attention over all locations. Nineteen rats performed the 5-choice serial reaction time task requiring detection of stimuli presented randomly in a horizontal array of five locations. Performance after nicotine (0.1 and 0.2mg/kg) or vehicle administration was analyzed as a function of target location eccentricity. In human subjects, nicotine caused greater reaction time reduction when all locations were monitored than when a single location was cued. In rats, nicotine attenuated the decline in stimulus detections and the increase in omission errors with greater target location eccentricity. The findings represent cross-species evidence that nAChR agonism facilitates the ability to spread attention broadly. This suggests that nAChR hypofunction may be central to broad monitoring deficits as seen, for example, in schizophrenia. The homology of findings between the rodent and the human paradigm contributes to validating a translational strategy for treatment development.

Normal mode energy estimation based on reconstructing the incoherent beamformed outputs from a horizontal array.

The acoustic pressure field in many underwater environments is well described by a superposition of normal modes. The normal modes can be used for source localization and environmental inversion. However, the wavenumber resolution of traditional normal mode filtering methods for a small-aperture horizontal array is usually not sufficient to identify individual modes in a shallow water waveguide. This paper proposes an original method of normal mode energy estimation to remove the energy leakage between modes. The modal energy is defined as the square of the modal amplitude. This method is to reconstruct the incoherent beamformed outputs in wavenumber domain for a horizontally moving source. The adaptive beamforming is used to suppress interference and improve output signal-to-noise ratio. The uncertainty of modal phase velocity has also been considered in this method. The proposed method can provide more accurate estimates of modal energy for a small-aperture horizontal array than the traditional mode filtering methods, such as the matched filter, the least squares mode filter, the regularized-least squares mode filter, and the maximum a posteriori mode filter, in simulations and experiments.

Passive acoustic characterization of sub-seasonal sound speed variations in a coastal ocean

Acoustic noise interferometry is applied to retrieve empirical Green's functions (EGFs) from the ambient and shipping noise data acquired in the Shallow Water 2006 experiment on the continental shelf off New Jersey. Despite strong internal wave-induced perturbations of the sound speed in water, EGFs are found on 31 acoustic paths by cross-correlating the noise recorded on a single hydrophone with noise on the hydrophones of a horizontal linear array about 3.6 km away. Datasets from two non-overlapping 15-day observation periods are considered. Dispersion curves of three low-order normal modes at frequencies below 110 Hz are extracted from the EGFs with the time-warping technique. The dispersion curves from the first dataset were previously employed to estimate the seabed properties. Here, using this seabed model, we invert the differences between the dispersion curves obtained from the two datasets for the variation of the time-averaged sound speed profile (SSP) in water between the two observation periods. Results of the passive SSP inversion of the second dataset are compared with the ground truth derived from in situ temperature measurements. The effect of temporal variability of the water column during noise-averaging time on EGF retrieval is discussed and quantified.

Gridless Variational Direction-of-Arrival Estimation in Heteroscedastic Noise Environment

Horizontal line arrays are often employed in underwater environments to estimate the direction of arrival (DOA) of a weak signal. Conventional beamforming is robust but has wide beamwidths and high-level sidelobes. High-resolution methods, such as minimum-variance distortionless response and subspace-based MUSIC algorithm, produce low sidelobe levels and narrow beamwidths, but are sensitive to signal mismatch, and require many snapshots and the knowledge of number of sources. In addition, heteroscedastic noise (HN) where the variance varies across observations and sensors due to nonstationary environments degrades the conventional methods significantly. This article studies DOA in an HN environment, where the variance of noise is varied across the snapshots and the antennas. By treating the DOAs as random variables and the nuisance parameters of the noise variance different across the snapshots and the antennas, multisnapshot variational line spectral estimation dealing with HN (MVHN) is proposed, which automatically estimates the noise variance, nuisance parameters of the prior distribution, and number of sources, and provides the uncertain degrees of DOA estimates. When the noise variance only varies across the snapshots or the antennas, the variants of MVHN, i.e., MVHN-S and MVHN-A, can be naturally developed. Finally, substantial numerical experiments are conducted to illustrate the proposed algorithms’ performance, including a real data set in a DOA application.

Modeling and observation of low-frequency propagation into warm core ring on the New England shelf slope

Analytical and computational modeling is used to examine propagation of low-frequency sound into a warm core ring oceanic front. When the source is placed outside the front and the receiver is placed inside it, the sound field consists of the refracted path and the horizontal lateral wave, which decays exponentially into the front. The analytical solution is presented in 2D (x, y) assuming an adiabatic vertical mode solution in z, wherein the vertical mode-dependence of the propagation paths into the front are considered. A 3D computational acoustic model examines the additional effects of sloping bathymetry and frontal geometry. The modeled results are compared to experimental measurements of into-front propagation during the March 2021 New England Shelf Break Acoustics Experiment using a low-frequency (fc = 115 Hz), shallow towed chirp signal received on an L-shape vertical and horizontal hydrophone array. [Work supported by the Office of Naval Research.]

Abnormal interference of very low frequency sound field in shallow water

In a multi-channel seismic exploration experiment in the South Yellow Sea, a tuned air gun array with a shooting interval of 37.5m was used as broadband pulse source, and a horizontal line array with 336 elements is used to receive transmitted signals. The received single shot records in the range-time domain are transformed into an interference pattern in the range-frequency domain using Fourier transform. It is found that there is an abnormal interference pattern of the very low frequency (VLF) sound field in the stratified shallow water environment. It is a complex nonlinear structure, no longer regular striations in the range-frequency domain. The mechanism of this particular interference pattern is interpreted according to normal mode theory. In shallow water stratified leaky waveguide, VLF sound propagates as waterborne modes and bottom-trapped modes. These two kinds of normal mode interfere with each other and form the particular stable interference pattern. In the experimental environment, the group speeds for these two type normal modes change differently with frequency. And it causes slope of interference striations change from positive to negative with increase of frequency. The theoretical simulation results are in good agreement with the experimental data. It is shown that the structure of interference pattern is sensitive to bottom structure and geoacoustic parameters.

A look at reverberation received on a vertical array during the TREX13 experiment

The TREX13 Target and Reverberation Experiment was conducted in shallow water off Panama City, Florida. Previously published work focused on reverberation from a fixed horizontal array, which resolves scattering in the azimuthal direction, but has very limited information about the vertical dependence of the scattering. Here, we look at the TREX13 datai—LFM pulses of various bandwidths in the 1.8–3.6 kHz frequency range—received on the vertical line arrays (VLAs) to see what information can be gleaned. The depth and time dependence of the reverberation and echo from a target are investigated. Beams are formed at various vertical angles, which should provide information about the grazing angle dependence of the scattering. A complication arises in determining the scattering strength in non-uniform environments, since the reverberation comes from all azimuths, and since the source and vertical array receivers were not co-located. In such bistatic geometry, the energy arriving at any instant comes from different ranges, azimuths, and vertical angles. However, if the source and receiver are close together, at longer times the geometry approximates the simpler monostatic situation. To help interpretation, results are compared with predictions from a range-dependent bistatic reverberation model. [Work supported by ONR, Ocean Acoustics.]

Range estimation of a distant ship using a vertical array and a guide ship

In this talk, we present a method for estimating the range of a distant ship in shallow water using a vertical array and a guide ship at a known range close to the array. The method involves a combination of four well-known approaches: (1) blind deconvolution; (2) waveguide invariant; (3) virtual receiver; and (4) array invariant. The main idea is to transform theoriginal task of estimating the range of a distant ship using a vertical array into estimating the range with a synthesized horizontal array aroundthe guide source exploiting the waveguide invariant theory. The proposed method is demonstrated for a surface ship radiating broadband noise (100–500 Hz) at 10 km range, using a 56.25-m long vertical array in approximately 100-m water and the same ship at 2 km range as the guide ship.

Predicting the effect of hearing-protection devices on horizontal-plane sound localization

Hearing-protection devices (HPD) are critical to hearing health in hazardous noise environments, but can be detrimental to job effectiveness and safety when degrading a wearer’s sound localization accuracy. Understanding specifically how localization is disrupted by HPDs is critical for mitigating the deleterious effects of HPDs on situation awareness. This study attempts to better quantify the effects of the degradations by predicting horizontal sound localization. A 360 deg horizontal array with 10 deg between-speaker spacing is used to collect head-related transfer functions (HRTFs) and to measure localization [ANSI/ASA S3.71] for the different conditions (open-ear, passive plugs, and both passive and active muffs). Our model attempts to select the response location that was most likely to have elicited the observed stimulus for the trial, by comparing narrow-band statistics between prior knowledge (“templates”) and trial observations. Bone conduction related noise is added, and the degree to which the priors are “device-related” (i.e., based on HRTFs captured for the device) or “open ear” related is varied. Results are discussed in terms of two potential mechanisms: (1) the wrong location is chosen due to a prior/template mismatch in percent device-related and (2) multiple response locations are viable because cue variability is reduced between locations compared to within.

Peripheral Cues Can Repulse Unbound Features Closer to Fixation

Previous work has shown that, in the absence of focal attention, simple features (e.g., colors) can be misbound to incorrect locations. Here we show that attention-demanding cues in the periphery can repulse these features to be incorrectly seen at locations closer to fixation. Participants were cued with a shape (circle or square) either in the left or right periphery before seeing a horizontal array of diamonds in the center of the screen (a pair of diamonds on each side of fixation, each with one gray and one colored diamond). Participants reported the shape of the cue, and which two colors appeared at which of the four diamond locations. When the cue was absent or at fixation, participants were accurate in reporting the locations of both colored diamonds. But attending to peripheral cues created a perceptual repulsion, where colors on that side of fixation were consistently misperceived closer to fixation (and farther away from the cue). This illusion was found to be even stronger when the cue was presented in the right hemifield compared to the left hemifield, revealing an attentional hemifield asymmetry for the binding of simple features.

Spatially Confined CVD Growth of High‐Density Semiconducting Single‐Walled Carbon Nanotube Horizontal Arrays

AbstractHigh‐density horizontally aligned single‐walled carbon nanotube (SWNT) arrays with high‐purity semiconducting tubes are promising materials for energy‐efficient electronics. However, realizing high density and high semiconducting purity through the direct‐growth method is still a challenge. Here the problem is overcome through a spatially confined approach based on a floating solid catalyst chemical vapor deposition (FSCCVD) system. A confined space is designed to change the fluid dynamics in a chemical vapor deposition reactor, offering a trapping effect for both catalyst nanoparticles and carbon fragments. Therefore, densely and uniformly distributed catalyst nanoparticles are continuously deposited on substrates, greatly increasing the growth probability and efficiency of SWNTs. Besides, the solid catalyst TiC and the oxygen‐vacancy‐enriched catalyst TiO both facilitate the growth of semiconducting tubes. As a result, SWNT horizontal arrays with a high density of 65 tubes µm−1 and a semiconducting purity of >95% are realized, which hold the potential for future application in carbon nanotube electronics.

The Role of Acoustics in the Conservation of the Ivory-Billed Woodpecker (Campephilus principalis)

The Ivory-billed Woodpecker (Campephilus principalis) is an iconic species that has survived in barely detectable numbers for the past 100 years, during which it has been feared extinct only to be rediscovered several times. The most recent rediscovery was announced in an article that was featured on the cover of Science in 2005. The persistence of the Ivory-billed Woodpecker became controversial when ornithologists were unable to obtain a clear photo for documenting this ultra-elusive bird during multi-year searches at sites in Arkansas and Florida, where they had several sightings and were convinced these birds were present. Audio recordings of ‘kent’ calls and double knocks were obtained at both sites, but such recordings are not regarded as conclusive evidence of persistence. A debate on this issue that took place in Science and Nature focused on relatively weak video evidence obtained in Arkansas but excluded three videos obtained in Louisiana and Florida that show flights, field marks, and other behaviors and characteristics that are consistent with the Ivory-billed Woodpecker but no other species of the region. Kent calls were recorded in the 1930s, when other types of vocalizations were observed but not recorded, including a high-pitched alarm call. On two occasions in Louisiana, high-pitched calls were observed coming from the direction of an alarmed Ivory-billed Woodpecker, and several of them were recorded. The spectrograms of the high-pitched calls and all other known and putative vocalizations of the Ivory-billed Woodpecker consist of simultaneously excited harmonics. A harmonic oscillator model has been used to draw a connection between the drumming that is typical of most woodpeckers and the double knocks of the Ivory-billed Woodpecker and other Campephilus woodpeckers. Drumming corresponds to periodic forcing; double knocks correspond to impulsive forcing, and a single thrust of the body is sufficient to produce two impacts of the bill in rapid succession. The audio recordings from Arkansas and Florida were obtained with single microphones. A horizontal array of microphones would make it possible to detect weaker sounds and determine the directions of sources. This approach has the potential to lead to the discovery of a nest, and it might be more effective if the array is placed above the treetops, where sounds might propagate to longer ranges.

Directional Response of a Horizontal Linear Array to an Acoustic Source at Close Range in Deep Water

Directional Response of a Horizontal Linear Array to an Acoustic Source at Close Range in Deep Water

The NY-Ålesund TurbulencE Fiber Optic eXperiment (NYTEFOX): investigating the Arctic boundary layer, Svalbard

Abstract. The NY-Ålesund TurbulencE Fiber Optic eXperiment (NYTEFOX) was a field experiment at the Ny-Ålesund Arctic site (78.9∘ N, 11.9∘ E) and yielded a unique meteorological data set. These data describe the distribution of heat, airflows, and exchange in the Arctic boundary layer for a period of 14 d from 26 February to 10 March 2020. NYTEFOX is the first field experiment to investigate the heterogeneity of airflow and its transport of temperature, wind, and kinetic energy in the Arctic environment using the fiber-optic distributed sensing (FODS) technique for horizontal and vertical observations. FODS air temperature and wind speed were observed at a spatial resolution of 0.127 m and a temporal resolution of 9 s along a 700 m horizontal array at 1 m above ground level (a.g.l.) and along three 7 m vertical profiles. Ancillary data were collected from three sonic anemometers and an acoustic profiler (minisodar; sodar is an acronym for “sound detection and ranging”) yielding turbulent flow statistics and vertical profiles in the lowest 300 m a.g.l., respectively. The observations from this field campaign are publicly available on Zenodo (https://doi.org/10.5281/zenodo.4756836, Huss et al., 2021) and supplement the meteorological data set operationally collected by the Baseline Surface Radiation Network (BSRN) at Ny-Ålesund, Svalbard.

The Impact of Surface Temperature Heterogeneity on Near-Surface Heat Transport

Experimental closure of the surface energy balance during convective periods is a long-standing problem. With experimental data from the Idealized horizontal Planar Array experiment for Quantifying Surface heterogeneity, the terms of the temperature-tendency equation are computed, with an emphasis on the total derivative. The experiment occurred at the Surface Layer Turbulence and Environmental Science Test facility at the U.S. Army Dugway Proving Ground during the summer of 2019. The experimental layout contained an array of 21 flux stations over a 1 km $$^2$$ grid. Sensible heat fluxes show high spatial variability, with maximum variability occurring during convective periods. Maximum variability in the vertical heat flux is 50–80 W m $$^{-2}$$ (median variability of 40%), while in the horizontal flux, it is 200–500 W m $$^{-2}$$ (median variability of 48% for the streamwise and 40% for the spanwise fluxes). Ensemble averages computed during convective afternoon periods show large magnitudes of horizontal advection (48 W m $$^{-3}$$ or 172 K h $$^{-1}$$ ) and vertical flux divergence (13 W m $$^{-3}$$ or 47 K h $$^{-1}$$ ). Probability density functions of the total derivative from convective cases show mean volumetric heating rates of 43 W m $$^{-3}$$ (154 K h $$^{-1}$$ ) compared to 13 W m $$^{-3}$$ (47 K h $$^{-1}$$ ) on non-convective days. A conceptual model based on persistent mean flow structures from local-surface-temperature heterogeneities may explain the observed advection. The model describes the difference between locally-driven advection and advection driven by larger-scale forcings. Of the cases examined, 83% with streamwise and 81% with spanwise advection during unstable periods are classified as locally driven by nearby surface thermal heterogeneities.

Coordinate Transformations-Based Antenna Elements Embedded in a Metamaterial Shell with Scanning Capabilities

In this work transformation electromagnetics/optics (TE/TO) were employed to realize a non-homogeneous, anisotropic material-embedded beam-steerer using both a single antenna element and an antenna array without phase control circuitry. Initially, through theory and validation with numerical simulations it is shown that beam-steering can be achieved in an arbitrary direction by enclosing a single antenna element within the transformation media. Then, this was followed by an array with fixed voltages and equal phases enclosed by transformation media. This enclosed array was scanned, and the proposed theory was validated through numerical simulations. Furthermore, through full-wave simulations it was shown that a horizontal dipole antenna embedded in a metamaterial can be designed such that the horizontal dipole performs identically to a vertical dipole in free-space. Similarly, it was also shown that a material-embedded horizontal dipole array can perform as a vertical dipole array in free-space, all without the need of a phase shifter network. These methods have applications in scanning for wireless communications, radar, beam-forming, and steering.

Space-Constrained Arrays for Massive MIMO

We analyse the behavior of a massive multi-user MIMO (MU-MIMO) system comprising a base station (BS) equipped with one of five antenna topologies whose spatial apertures are either unconstrained, or space-constrained. We derive the normalized mean interference (NMI) with a ray-based channel model, as a metric for topology comparison. Using an existing derivation for a horizontal uniform rectangular array (HURA), we provide closed-form NMI equations for a uniform linear array (ULA) and uniform circular array (UCirA). We then derive the same for a vertical URA (VURA) and uniform cylindrical array (UCylA). Results for the often-considered unconstrained case confirm the prior understanding that topologies with wider azimuth footprints aid performance. However, in the constrained case, performance is dictated by the angular resolution of the topology, particularly in elevation. We confirm the behavioral patterns predicted by the NMI by observing the same patterns in the signal-to-interference-and-noise-ratio (SINR) with minimum mean-squared error (MMSE) processing.