bluuebunny/crossref_metadata_2025 huggingface dataset:
On discrete homology of a free pro--group
Authors: Ivanov Sergei O. , Mikhailov Roman
Published: October 2018

For a prime $p$, let $\hat{F}_{p}$ be a finitely generated free pro-$p$-group of rank at least $2$. We show that the second discrete homology group $H_{2}(\hat{F}_{p},\mathbb{Z}/p)$ is an uncountable $\mathbb{Z}/p$-vector space. This answers a problem of A. K. Bousfield.
A Tilted-Axes Tool for Introductory Mechanics and Mathematics Courses
Authors: Licini Jerome C.
Published: October 2018

An important but challenging problem-solving technique in introductory mechanics is that of using “tilted axes.” For inclined plane and centripetal motion problems, using axes that are aligned relative to the ramp direction or the radial direction (rather than the horizontal and vertical) yields equations that are conceptually more straightforward and algebraically more tractable. Of necessity, textbooks tend to present this as a static choice of alternate axes, while experts often think of this as a continuous rotation. Simply printing orthogonal axes onto transparency film produces an inexpensive student handout that bridges this gap in an effective way for those students who have difficulty with the standard textbook presentation.
Accurate Radar Measurements of Drag Coefficients in Free Flight
Authors: Courtney Elya , Morris Collin , Courtney Michael
Published: October 2018

Undergraduate lab design balances several factors: 1) simple experiments connected with learning objectives, 2) experiments sufficiently accurate for comparisons between theory and measurements without gaps when students ascribe discrepancies to confounding factors (imperfect simplifying assumptions, measurement uncertainties, and “human error”), and 3) experiments capturing student attention to ensure due diligence in execution and analysis. Drag coefficient measurements are a particular challenge, though there has been some success using accurate measurements of terminal velocities. Video shows promise in several areas of kinematics, but the number of trials in a reasonable time is limited, and analysis techniques to determine drag coefficients often include numerical integration of differential equations. Here we demonstrate a technique with potential to measure drag coefficients to near 1% accuracy using an affordable 2.4 GHz Doppler radar system and round plastic pellets from an Airsoft launcher.
Cell Membrane Potential Model Circuit Lab
Authors: Kutzner Mickey D. , Bryson J. Michael
Published: October 2018

There remains a strong movement for Introductory Physics for Life Sciences (IPLS) courses to better integrate physics and biology. Part of the challenge for IPLS educators is to introduce fundamental physical law while simultaneously establishing the relevance of physics to biological science. Life science relevant laboratory experiences are essential to the training of future biologists and health professionals. The physiology of neurotransmission can be especially challenging to life science majors, but may be somewhat clarified in the IPLS course by model circuit labs. A realistic axon model lab using rubber tubing and gelatin recently reported by Dyer highlights the motivational value of lab experiences bridging biophysics and neurophysiology. Time-independent and time-dependent circuit labs modeling passive spread of charge within an axon absent the action potential have been described. In this paper, we describe a progressive complex circuit lab sequence introducing students to Kirchhoff’s rules, a model of the cell membrane resting potential, and a model representing key features of the action potential in an axon. In this context, “complex” describes a circuit that cannot be reduced to a single battery and resistor.
Friction block used for demonstrating vectors
Authors: Vetrone James
Published: October 2018

Students often struggle to understand the independence of velocity vectors in two-dimensional motion. Despite seeing classic projectile demonstrations, it is probably not obvious to most new students why the path of motion is parabolic. Likewise, first-year students might not predict that the path of motion is linear in two-dimensional vector problems such as a boat traveling at constant velocity across a river moving at constant velocity. There do exist excellent computer simulations, but students are more likely to believe the results if they can create the motion themselves. Fortunately, students can directly explore such motion using blocks of wood that are commonly used in the classroom to measure friction. The instructor only needs to make a few inexpensive modifications to the blocks to not just teach vector motion, but with a little imagination teach many more concepts in physics. In this article I will elaborate on those modifications and uses.
Using a Vortx to Teach Kepler’s Laws and Potential Energy
Authors: Ogawara Yasuo
Published: October 2018

For more than 10 years, I had taught Kepler’s laws and the law of universal gravity without a corresponding experiment. I sometimes remember how these topics were difficult for me in my high school days to understand. At that time, I thought that one of the reasons for my difficulty was that these phenomena cannot be visualized using physical objects. In this paper, I report on a method I developed by which students can actually watch some of the phenomena of Kepler’s laws and the law of universal gravity. In an earlier paper, theoretical and experimental results for a ball that rolls without slipping on a surface of revolution in cones and other funnels have been reported. Here I would like to introduce some experiments using a coin bank named Vortx®. The Vortx is a familiar and inexpensive apparatus (less than $50), and many Japanese physics teachers already have one. The Vortx, when used with the following experiments, can help students visualize a gravitational potential well, where the radius represents the distance to a massive body and the height from the funnel tip represents the potential energy per kg (for a description of a gravitational potential well, please refer to, for example, Ogborn). However, when we use the Vortx, we need to take care of some points as described in the following. One goal of this paper is to inform TPT readers how the Vortx can be used in the classroom.
Experiment in an Aircraft Cabin
Authors: Sinebar Wijen , Abdullah Mikrajuddin
Published: October 2018

Students have been taught that atmospheric temperature drops linearly with altitude, up to approximately 15 km. However, even after completing an undergraduate degree program, most students have only memorized such information and have never had the experience of measuring it. Students often assume that experimental tasks must involve the use of complex techniques and equipment. For example, they may assume that atmospheric temperatures can be measured using only advanced tools, such as a balloon equipped with a radiosonde or satellites equipped with sensors and transmitters. Actually, some measurement tasks can easily be accomplished using tools that are already available around us or simple equipment that can be self-designed. Here, we report on an experiment where students measure temperature vs. atmospheric height while seated on a commercial airplane.
Selecting your reference potential energy in a vertically hanging spring!
Authors: Podolak Ken , Lamsal Chiranjivi
Published: October 2018

When defining the gravitational potential energy of an object in a system, the reference point where you define a potential energy can be overlooked. Consider this cartoon you may have seen in Fig. 1. The cartoon is a light-hearted way to look at potential; however, it can be misleading. When considering potential energy in this situation, we examine the ball and Earth together as a system. Potential energy is due to an interaction between the object and what influences it.
A coupler-based calibration method for ear-probe microphones
Authors: Nørgaard Kren Rahbek , Fernandez-Grande Efren , Laugesen Søren
Published: October 2018

The calibration of ear-probe microphones can increase the precision of calibrating stimulus levels in situ and of measuring acoustic responses from the ear. This paper proposes a methodology to measure the sensitivity of an ear-probe microphone, requiring only an acoustic coupler and a calibrated reference microphone. The input impedance of the coupler is measured, enabled by a preliminary acoustic Thévenin calibration of the ear probe, and the plane-wave transfer impedance of the coupler is calculated analytically. Using these two quantities, the pressure transfer function between the reference microphone and the ear-probe microphone is estimated. This enables estimating the sensitivity of the ear-probe microphone. The proposed and an existing method were compared, resulting in substantially similar ear-probe microphone sensitivities. The proposed method is practically feasible in producing reliable measurements of sound pressure in the ear canal and calibrating stimulus levels in a clinical setting.
Using the new ASHRAE 189.1 Standard for the Design of High-Performance Green Buildings—Acoustical Control Section
Authors: Miller-Klein Erik , Boldt Jeff
Published: October 2018

The 2017 ASHRAE 189.1 Standard for the Design of High-Performance Green Buildings includes a complete rewrite of the acoustical control section. This section of the standard provides both performance and prescriptive paths to acoustical compliance and permits either acoustic commissioning or visual inspections to ensure the materials and assemblies are built to optimize acoustical performance. We will outline the importance of this new standard and review the basic parameters of the acoustical performance requirements, and how this standard can be used for your projects. This session will discuss the basis for this updated section and how you can use this standard to help guide your clients, and satisfy the LEED v4 for BD + C. The 189.1/IgCC aligns well with LEED, WELL, and other green building and improves on the LEED certification standard, so basic compliance will often garner the acoustic performance points.
Case study and lessons learned through achieving WELL Platinum
Authors: Shook Ken
Published: October 2018

This paper will present a case study of one of the first projects to achieve a Platinum rating through the WELL Certification program. We will review the acoustic requirement outlined by WELL and issues faced during the design of a WELL Platinum project. These will include conflicting features that were discovered between multiple features, the limitations that base-building can present, conflicts between WELL and LEED and how to satisfy both requirements. We well summarize our lessons learned and how we have applied these into recommendations to the WELL acoustic committee through our advisory role.
Two case studies of acoustical design in new construction using sustainable criteria: The living building challenge and WELL building design at The Georgia Institute of Technology
Authors: Clements Jessica S.
Published: October 2018

The Georgia Institute of Technology is updating their campus through a series of sustainably designed buildings to create an educational eco-commons. The ongoing renewal includes the Kendeda Building for Innovated Design and the Dalney Building. These buildings are designed to meet the International Living Future Institute’s Living Building Challenge Design Standard and the International Well Building Institute’s WELL certification criteria, respectively. The Kendeda building consists of classrooms, commons, offices, an auditorium, and open collaborative areas. The Dalney building is primarily office and conference spaces but includes some unique challenges for adaptable open and enclosed office areas. Substantial construction for the Kendeda building is scheduled for spring of 2019 and for the Dalney building in fall of 2019. The case studies cover the design phases of the two projects and discuss the acoustical challenges in meeting these specific designs, including credit compliance, unforeseen ramifications across disciplines, and areas of problematic interpretation.
Assessing impacts of offshore pile driving noise on the antipredator defense and shoaling behaviors of squid (Doryteuthis pealeii)
Authors: Jones Ian T. , Stanley Jenni , Mooney T. Aran
Published: October 2018

Impulsive pile driving occurs during construction of marine platforms, producing intense sounds that may adversely impact animals’ physiology and behavior. Little is known regarding how this noise impacts sound-sensitive invertebrates such as squid, which is surprising given squids’ relative abundance and key ecological role. We quantified how a commercially important squid species (Doryteuthis pealeii) behaviorally responded (in a controlled environment) to pile driving sounds recorded from an offshore windfarm installation within this species' habitat. Both sound pressure and particle motion components of the sound were quantified. Fifteen-minute portions of the recordings were played to individual squid. Body pattern changes, inking, jetting, and startle responses were observed during sound exposure and all squid exhibited at least one response. These responses occurred primarily during the first few noise impulses and diminished quickly over the first minute of playback, indicating short-term habituation. Responses returned after a 24-hr rest, indicating re-sensitization. Separate experiments investigated changes in shoaling behaviors by quantifying shoal cohesion and polarity in groups of squid during ten-minute noise exposures. Rapid habituation of antipredator alarm responses and changes in shoaling dynamics may alter squids’ susceptibility to predation. Noise exposure may also disrupt normal intraspecific communication and ecologically relevant behavioral responses to sounds.
Arctic Beaufort Gyre duct transmission measurements and simulations
Authors: Duda Timothy F. , Lin Ying-Tsong , Zhang Weifeng G. , Colosi John A. , Badiey Mohsen
Published: October 2018

Transmissions of 100–300 Hz sound over distances of 220–505 km in the Beaufort Sea area for 10 months revealed strong long-term trends and short-term variability. The sound was emitted by Canada Basin Acoustic Propagation Experiment (CANAPE) Deep Water sources, and received by CANAPE Shallow Water receivers close to the Chukchi Sea. Much of the sound that arrives at these distances is trapped in the Pacific Water duct. A dynamical model of the area driven by representative forcing, which includes eddies that have propagation consequences, is used to examine changes to the water column at small eddy scales and at broader scales that can influence the sound. Processes such as variable excitation of ducted normal modes, time-variable duct sound-speed mean profile, and coupling of ducted modes to other modes by range dependent eddy features are examined with the model. The effects of these processes are quantified and compared to field observations.
The effects of ice cover and oceanography on medium-frequency acoustic propagation on the Chukchi Shelf
Authors: Pecknold Sean , Whitt Christopher , Urazghildiiev Ildar R. , Weirathmueller Michelle , Badiey Mohsen , Turgut Altan , Sagers Jason D. , Ballard Megan S.
Published: October 2018

The Canada Basin Acoustic Propagation Experiment (CANAPE) was a year-long experiment exploring the changing nature of sound propagation and ambient noise in the Arctic ocean. As part of this experiment, medium-frequency signals at 0.7–1 kHz and 1–4 kHz were transmitted by two sources on the Chukchi Shelf. One of these sources was located in an area of 150 m of water depth, approximately 350 m from a directional receiver array and 50 km from an 8-element vertical line array in a water depth of about 125 m. Oceanographic sensors were located both on the arrays and on a set of moorings on the shelf, and an ice-profiling sonar was located between the arrays about 15 km from the source. In this talk, we will focus on using the measured environmental data and propagation modeling to characterize the variability observed in the short-range and long-range received acoustic signals over the course of CANAPE.
Measured acoustic intensity fluctuations on the Chukchi continental shelf during Canada Basin Acoustic Propagation Experiment 2017
Authors: Badiey Mohsen , Eickmeier Justin , Wan Lin , Lin Ying-Tsong , Turgut Altan , Pecknold Sean , Ballard Megan S.
Published: October 2018

One of the main objectives of the Shallow Water (SW) CANAPE experiment was to gain a thorough understanding of a yearlong propagation of broadband signals from deep to shallow water with simultaneous oceanographic and acoustic measurements together along the and across the shelf break region. Using more than eleven acoustic arrays and seven oceanographic moorings in a 30 km2 region on the Chukchi shelf this task is being done by assessing both deep water sound signatures and shallow water source transmissions. In this paper with present analysis of acoustic signals from both shallow and deep water sources on the Chukchi continental shelf for a specific time period between June and August 2017 where a 20 dB intensity drop from along-the-shelf source (S2) at 150 m water depth was observed for more than few weeks. This intensity drop is strongly correlated with occurrence of a large oceanographic event spanning the top 150 m water column due to Pacific Water outflow from Bering sea and retreat of Marginal Ice Zone (MIZ). During the same period, cross-the-shelf source (S1) was not transmitting signal but the reception from the deep water acoustic transmitters also show variability that could be correlated with the basin scale water column variability and the ice coverage. [Work supported by ONR.]
Beamforming shallow water propagation of mid-frequency acoustics on the Chukchi Shelf
Authors: Eickmeier Justin , Badiey Mohsen , Pecknold Sean , Turgut Altan
Published: October 2018

The shallow water Canadian Basin Acoustic Propagation Experiment (CANAPE 2016–2017) was designed to study the effect of oceanographic variability on the acoustic field in the Arctic. The physics of the acoustic waveguide on the Northeastern edge of the Chukchi Shelf are influenced by dynamic boundary conditions and spatio-temporal fluctuations in temperature/salinity profiles, including the upwelling of Atlantic bottom water, sinking Bering Sea surface water and sub-mesoscale eddy formation. These fluctuations influence the acoustic waveguide characteristics of a persistent sound speed channel centered at 150 m depth. The University of Delaware (UDel) deployed seven oceanographic moorings (OM) perpendicular to the isobaths on the Chukchi Shelf (145–700 m depth). A Naval Research Lab source (S1) was deployed in-line with the OMs, generating Linear Frequency Modulated (LFM) signals in alternating 700–1100 Hz and 1400–4000 Hz bands. A Vertical Line Array (VLA) was deployed in-line and within the span of the OMs. The array aperture spanned the depth of the sound speed channel. Beamforming measurements from the VLA in combination with environmental measurements and 2D PE model output will determine the degree of influence of individual physical oceanography processes on the spatio-temporal structure of the sound channel and internal acoustic wave propagation.
Ultrasound lung spectroscopy: Preliminary in-vivo results
Authors: Demi Libertario , Demi Marcello , Soldati Gino
Published: October 2018

Nowadays, lung pathologies are mainly diagnosed by X-ray imaging, with the golden-standard being computed tomography (CT). However, CT is not available at patients’ bed, not always accessible, and expensive. Additionally, CT delivers a relatively high radiation-dose, with the risk of an increased possibility to develop cancer. Recently, attention is shifting toward ultrasound imaging, which would offer a more portable, more accessible, cheaper, and safer alternative. However, despite promising clinical findings, technical development is lacking. In fact, ultrasound imaging is not optimal for lung investigation being designed for low acoustical impedance mismatches. As a consequence, clinicians base their decisions on qualitative interpretations and imaging artifacts, such as the well-known B-line artifact. In this work, following a recently published in-vitro study (L. Demi et al., “Determination of a potential quantitative measure of the state of the lung using lung ultrasound spectroscopy,” Scientific Reports, 2017), we report on the first preliminary in-vivo results. Standard B-mode, multi-frequency imaging-sequences, and RF-data, were acquired. Consistently with the in-vitro study, clinical data show that B-lines can be characterized on their frequency content. These results further support the hypothesis that the analysis of ultrasound spectral features can be used to develop a quantitative method dedicated to the lung.
A review of pulmonary injury by diagnostic ultrasound
Authors: Miller Douglas , Dong Zhihong , Dou Chunyan , Raghavendran Krishnan
Published: October 2018

Diagnostic ultrasound (DUS) induction of pulmonary capillary hemorrhage (PCH) presents a unique clinical safety issue. Pulmonary DUS has become routine in clinical and point-of-care settings worldwide for diagnosis of edema, effusion, pneumonia, etc. Our experiments in rats have shown that DUS-induced PCH increased rapidly above exposure thresholds, which depended on specific conditions. Using a linear array at 6.6 MHz, peak rarefactional pressure amplitude thresholds were 1.5 MPa for B mode, 1.1 MPa for Angio Doppler, 1.1 MPa for M mode, and 0.6 MPa for pulsed Doppler. Thresholds were nearly constant from 1.5 MHz to 12 MHz, suggesting involvement of a frequency-independent mechanism, such as radiation pressure. Physiological conditions were found to be as important as physical exposure parameters. Infusion of saline reduced the effect. Xylazine in the normal ketamine/xylazine anesthesia enhanced PCH relative to ketamine only, and the clinical sedative dexmedetomidine also lowered thresholds. Rats with positive-pressure ventilation had DUS-induced PCH inhibited by only + 4 cm H2O, or enhanced by only -4 cm H2O end expiratory pressure acting on the blood-air barrier. With subsequent studies and better understanding of this phenomenon, DUS-induced PCH will be avoidable by use of sub-threshold output by sonographers using DUS machines with output control.
Localization of directional noise sources from high-performance military aircraft through subarray beamforming analysis
Authors: Van Komen David F. , Neilsen Tracianne B. , Harker Blaine M. , Gee Kent L. , Swift S. Hales , Downing Micah , James Michael M. , Wall Alan T.
Published: October 2018

High-performance military aircraft noise is created by multiple sound generation mechanisms that need to be understood to guide noise reduction efforts and for adequate sound field predictions. Phased-array methods can be used to produce frequency-dependent equivalent acoustic source models. The Hybrid (beamforming) method [Padois et al., J. Sound Vib. 333 (2014)] is applied to an acoustical measurement along a 71-microphone ground-based array, spanning 32 m, placed in the vicinity of a high-performance military aircraft as the engine was operated at different powers. Application of the Hybrid method to the full-array creates an overall equivalent source model that is sufficient for predicting overall field radiation but fails to separate the different noise sources. Applying the Hybrid method to subarrays separates broadband shock-associated noise from the main radiation lobes of turbulent mixing noise. Results show that the subarray-based equivalent source distributions for the different types of noise originate from overlapping source locations. Further analysis of the subarray-based equivalent noise sources using coherence and directionality from the unwrapped phase of the cross-spectral source reconstructions identifies overlapping, frequency-dependent source regions with characteristics unique to broadband shock-associated noise and turbulent mixing noise. [Work supported by an Air Force Research Laboratory SBIR.]
Meteorological effects on long-range nonlinear propagation of jet noise from a static, high-performance military aircraft
Authors: Reichman Brent O. , Gee Kent L. , Wall Alan T.
Published: October 2018

The impact of nonlinearity on the propagation of noise from military jet aircraft has been fairly well documented, but only within a few hundred meters from the aircraft. This paper describes analysis of nonlinear propagation for morning static runups of F-35 aircraft at greater distances, out to 1220 m near the direction of maximum radiation and at heights ranging from 0 m up to 30.5 m. A comparison of overall levels with distance and height reveals evidence of significant atmospheric refraction effects, and a general trend of decreasing level with height. Examination of nonlinearity metrics reveals opposite behavior, however. At these distances, nonlinear propagation effects are often strongest in waveforms with lower sound levels, which is counterintuitive. One important finding, however, is that acoustic shock strength can vary greatly from runup to runup, even for seemingly small changes in atmospheric conditions. This analysis demonstrates the need for further research into long-range nonlinear propagation of jet noise through realistic atmospheric conditions.
Large-eddy simulation of supersonic jet noise emanating from an F404 nozzle at model scale
Authors: Liu Junhui , Ramamurti Ravi
Published: October 2018

Large-eddy simulations of supersonic jet noise emanating from an F404 nozzle at the model scale have been carried out using the JENRE flow solver. A wall-model method that was previously validated for a high subsonic flow over a flat plate is used to model the boundary layer effect inside the nozzle. The nozzle geometry is a faceted bi-conic convergent-divergent nozzle with a design Mach number equal to 1.65 and the nozzle-exit diameter equal to 5.07 inches. Both mildly and highly overexpanded conditions are tested for heated jets. The time averaged flow field, turbulence intensities, and the far-field noise are compared with available experimental data. The effects of both the boundary-layer thickness and turbulence intensity at the nozzle exit are investigated to assess their impact on jet noise generation and the noise source characteristics.
Launch vehicle acoustic measurements for community noise model development and validation
Authors: Salton Alexandria R. , James Michael M. , Calton Matthew F. , Gee Kent L. , Rasband Reese D. , Novakovich Daniel J. , Reichman Brent O.
Published: October 2018

A measurement campaign is being conducted under ACRP Project 02-81 to compile a database of high-fidelity modern rocket propulsion noise measurements for facilitating community noise model development and validation. As part of this measurement campaign, acoustic measurements of the Orbital ATK Antares rocket, launched as part of NASA’s eighth cargo resupply mission (OA-8E) to the International Space Station, were collected. The OA-8E acoustic measurement test plan was based on guidelines from the community noise measurement protocol being developed under the same effort. Pressure measurements were collected from 46 microphones at 19 unique geographic locations ranging from 0.2 to 19.1 km of the launch pad. The acoustic measurements and the resultant initial data products related to the OA-8E Antares launch will be presented. Comparisons of the multiple recording systems and microphone heights/orientations will be discussed in relation to their relevance in informing equipment recommendations and site layout related to the protocol design.
Super-resolution using a microscale membrane array metasurface
Authors: Lani Shane W. , Sabra Karim G. , Degertekin F. Levent
Published: October 2018

A metasurface or 2D metamaterial composed of a membrane array can support an interesting acoustic wave field. These waves are evanescent in the direction normal to the array and propagate in the immersion fluid along the metasurface. These waves are a result of the resonant membranes coupling to the fluid medium and propagate with a group and phase speed lower than that of the bulk waves in the surrounding fluid. Additionally these membranes can generate and detect membrane displacement capacitively such as in an array of Capacitive Micromachined Ultrasonic Transducers (CMUT) as a specific example. A model is developed that can solve for the modes of the membrane array in addition to transiently modeling the behavior of the array to help show the performance of the array in relation to wave propagation. Potential applications of this wave field are examined in the context of subwavelength focusing and imaging. Several methods of acoustic focusing are used on an array consisting of dense grid of membranes and several membranes spatially removed from the structure. Subwavelength acoustic focusing to a resolution of λ/5, limited by the size of one membrane, is shown in simulations and verified with experiments. This fundamental work in characterizing the waves above the membrane metasurfaces is expected to have impact and implications for transducer design, resonant sensors, 2D acoustic lenses, and subwavelength focusing and imaging.
Superresolution through regular sampling: Theory and applications
Authors: Cuyt Annie , Lee Wen-shin
Published: October 2018

Estimating fine-scale spectral information from coarse-scale measurements is an important issue in many signal processing applications. The problem of superresolution is therefore receiving considerable attention. We offer a technique that allows to overcome the Shannon-Nyquist sampling rate limitation and at the same time may improve the conditioning of the numerical linear algebra problems involved. The technique is exploiting aliasing rather than avoiding it and maintains a regular sampling scheme [3]. It relies on the concept of what we call an identification shift [1, 2], which is the additional sampling at locations shifted with respect to the original locations in order to overcome any ambiguity in the analysis. Neither the original sampling nor the identification shift need to respect the Shannon-Nyquist sampling theorem. So far the technique shows great potential in magnetic resonance spectroscopy, vibration analysis, echolocation, music signal processing, ISAR radar problems, and DOA or direction of arrival. [1] Annie Cuyt and Wen-shin Lee, “Smart data sampling and data reconstruction,” US patent 9,690,749. [2] Annie Cuyt and Wen-shin Lee, “Smart data sampling and data reconstruction,” EP2745404B1. [3] Annie Cuyt and Wen-shin Lee, “How to get high resolution results from sparse and coarsely sampled data,” ArXiv e-print 1710.09694 [math.NA].
Noise correlation in a metamaterial: From laboratory to field data
Authors: Hejazi Nooghabi Aida , de Rosny Julien , Boschi Lapo , Roux Philippe
Published: October 2018

In the METAFORET experiment, a seismic survey is conducted in a 120 m×120 m flat area, partly occupied by a relatively regular grid of tall pine trees, and partly by a canola field. We study the scattering effects of trees on cross correlations of ambient signal. A wave field is generated by several arrays of sources and recorded at a dense array of receivers within the area of interest. In parallel, we conduct a lab experiment, where the Earth's subsurface and the trees ("resonators") are idealized by a thin elastic (aluminum) plate and an array of rods, respectively. The Lamb waves propagating in plate are inherently 2-D and dispersive; thus, a good analogue of seismic surface waves observed in field data. Based on the reciprocity theorem, we can treat receivers as sources and vice-versa, resulting in a virtually uniform source distribution. We auto-correlate recordings corresponding to each virtual source-receiver pair, and visualize the auto-correlation maximum as a function of virtual-source location: this provides a map of energy contributed by virtual sources, inside and outside the region of resonators. From that, we identify the metamaterial position as well as bandgap and propagation band. Results from field and laboratory data are compared.
Inverse design method in acoustic wave manipulation
Authors: Gao He , Zhu Jie
Published: October 2018

We present here the involvement of inverse design method with the acoustic wave modulation, to simplify how we get the required material parameters and design novel acoustic devices that can perform certain prescribed operation. As an example, the acoustic cloaking will be discussed. The existing acoustic invisibility design based on coordinate transformation method needs negative index media which can be realized through complicate structures. With inverse design method, we have designed a circular cloak device with positive index materials, that successfully make a circular scatterer acoustically invisible. This inverse design method takes a significant step towards realizing practical cloaking devices and would open up new possibilities for manipulating acoustic wavefront with simplified parameter distribution and optimized properties.
A kind of polar coordinate system adaptable metasurface and its broadband wavefront manipulation
Authors: Liang Shanjun , Liu Tuo , Gao He , CHEN Fei , Zhu Jie
Published: October 2018

We report a type of polar coordinate system adaptable metasurface by which a three-dimensional Bessel beam in broadband of 2–6 kHz is realized. For the common design of metasurface, many kinds elements are for a square lattice in the Cartesian coordinate system while sometimes a cylindrical symmetric source can be more suitable for practical working conditions, the 3D Bessel beam for example. Here, we present a unit cell for metasurface by embedding helical blades into an element of required shape. Thus, the lattice structure can be adjusted easily to the distinct coordinate systems. Hence, the arrangement of the elements can be more flexible, which means a larger freedom of design for the requirement of bi-anisotropic metasurfaces can be obtained. With the advantage of helical blades, an ideal control over energy transmission efficiency can be achieved too. Based on this, we investigated the characteristics and performance of the elements and realized a better performed Bessel beam in three dimensional. This design thinking can also be utilized to other kinds of wavefront modulation in broadband for both transmission and reflection control.
Modeling of acoustic pulse propagation and beamforming in forests
Authors: Muhlestein Michael B. , Ostashev Vladimir E. , Wilson D. K.
Published: October 2018

Acoustic pulse propagation through forests is important for many applications, including noise attenuation by stands of trees, and localization of sound sources. Due to the highly complicated distribution of trees in natural forests, it is appropriate to consider a forest as a continuous distribution of scatterers of various shapes and sizes. A propagation model based on radiative transfer theory under a modified Born approximation may be developed for this situation to describe both the coherent and diffuse sound propagation . The simple case of an impulse in an infinite homogeneous forest of diffuse scatterers is first considered, and then the effects of successively including non-diffuse scatterers, ground reflections in a forest of finite height, and, finally, a realistic forest model are analyzed. These theoretical findings are then compared with experimental results. Lastly, a numerical example describing the effect of a forest on a simple beamforming array is considered.
An improved numerical scheme for predicting sound propagation in a vertically stratified medium
Authors: Wang Yiming , Li Kai Ming
Published: October 2018

Propagation of sound in a stratified medium has been studied for many decades. The ray tracing method, which is one of the most popular ways to solve this kind of problems, involves identifying the sound rays connecting the source with the receiver. However, the ray method does not yield accurate solutions when either the source or the receiver is placed near a turning point. Under these circumstances, it is found necessary to use a wave-based approach leading to a more accurate solution for predicting the sound fields. Typically, the solution is written in a form of a highly oscillatory integral that can be evaluated numerically. High computational times are required to obtain accurate solutions. There have been significant developments in the numerical approximation of highly oscillatory integrals. An improved scheme, which is known as Levin’s collocation method, has low computational costs but it gives accurate numerical solutions for high-frequency sound fields. In this paper, the propagation of sound in a stratified and unbounded medium is considered where there is only one turning point. The Levin collocation method is explored for calculating the sound fields efficiently. In addition, an asymptotic solution is also derived for comparison with the Levin collocation method.
Estimating Poisson’s ratio of a free, rectangular panel using video-based modal analysis
Authors: Shepherd Micah R. , Robin Olivier , Hambric Stephen , O'Donoughue Patrick
Published: October 2018

Recent work has shown that the Poisson’s ratio of an isotropic material can be determined using the anticlastic curvature that exists in certain mode shapes of a free, rectangular panel of that material. The shapes must be measured experimentally in order to determine the curvature that exists. The curvature is then related to Poisson’s ratio based on a relationship that depends on thickness and length-to-width ratio. For accurate determination of the anticlastic curvature, high spatial resolution is required. In this paper, high speed video is used to experimentally measure the mode shapes of a free, rectangular panel. The spatial resolution achieved is much higher than that obtained using traditional methods due to the inherent resolution of the camera. The high-speed video results are demonstrated and compared to modes using traditional modal techniques. The Poisson’s ratio is then computed and found to agree well with published values.
Machine learning for behavior classification of passively tracked vessels
Authors: Fischell Erin M. , Viquez Oscar A. , Schmidt Henrik
Published: October 2018

Situational awareness is a constant challenge for autonomous underwater vehicles (AUVs) due to limited communication to the surface, navigation drift, and a need to operate in busy areas around other vessels. One piece of information that would be valuable to both keep AUVs safe and inform autonomous monitoring missions is the location and behavior of nearby surface vessels. Passive acoustic data collected on a hydrophone array and processed on an on-board computer can provide bearing and time-to-intercept (TTI). This information can be used to classify overall boat behavior and inform AUV response: for example, investigating an area a boat has circled or avoiding an approaching vessel for vehicle safety reasons. Simulation studies were used to characterize trajectories for simple vehicle behaviors based on the bearing and TTI data produced by an existing passive tracking system. A classifier based on K-nearest-neighbor with dynamic time warping as a distance metric was used to classify simulation data. The simulation-based classifier was applied to classify experimental tracking data on boats completing different types of behaviors using bearing/TTI from dock-based and AUV-based hydrophone arrays.
Assessment of the temporal and spatial dependence of reverberation mechanisms for KOREX-17
Authors: Tang Dajun , Hefner Brian T. , Shim Taebo
Published: October 2018

Mid-frequency reverberation data were obtained over a 9-day period off Geoje Island, Republic of Korea, complemented by transmission loss and backscatter measurements. The reverberation data were collected using the Autonomous Reverberation Measurement System (ARMS), a benthic lander with a source and receive array mounted on a rotation stage in order to collect reverberation data as a function of bearing angle. The ARMS was repeatedly deployed in roughly the same location over the course of the experiment. The surficial sediments close to the ARMS are known to be composed primarily of mud with occasional rock outcrops. Beyond a range of 2 km, the sediment composition is uncertain and a geoacoustic measurement survey has been planned to collect additional data in this region. Using contemporaneous measurements of the sea surface directional wave spectrum and the currently limited geoacoustic data, modeling is used to estimate the relative importance of sea bottom and surface reverberation. [Work supported by of the Office of Naval Research.]
Measurements of mid-frequency bottom backscattering during KOREX-17
Authors: Han Dong-Gyun , Oh Raegeun , Choi Jee Woong , Tang Dajun , Hefner Brian T.
Published: October 2018

Measurements of mid-frequency bottom backscattering strength were made on May 30, 2017, as part of the Korea Reverberation Experiment (KOREX-17) in a shallow water region located at the south coast of Korea. The acoustic data were transmitted and received as functions of frequency (4, 6, and 8 kHz) and pulse length (2 and 4 ms) using semi-monostatic sonar system composed of omni-directional acoustic source and receiver, which was deployed from the R/V Mirae. The bottom backscattering strength were extracted from intensity-averaged reverberation level for 30 individual pings. The water depth measured by an echo sounder was about 35 m and bottom was approximately flat, having a slope less than 1° over the experimental area. The surficial sediment was estimated to be silty sediment, having a mean grain size of 6 phi from grain size analysis. In this talk, the measurement results of bottom backscattering strengths will be presented as a function of grazing angle and compared to the predictions obtained by Lambert’s law and APL-UW scattering model. [Work supported by Agency for Defense Development, Korea(UD160006DD).]
Dynamic imaging of a gravity wave caused by laser-induced breakdown in a fluid waveguide using multi-reverberated ultrasonic waves
Authors: van Baarsel Tobias , Roux Philippe , Nicolas Barbara , MARS JEROME I. , Arrigoni Michel , Bonnel Julien , Kerampran Steven
Published: October 2018

The dynamic imaging of a gravity wave propagating at the air-water interface is a complex task that requires the sampling of every point at this interface during the gravity wave propagation. Using two source-receiver vertical arrays facing each other in a shallow water environment, we manage to isolate and identify each multi-reverberated eigenbeam that interacts with the air-water interface. The travel-time and amplitude variations of each eigenbeam are then measured during the crossing of the gravity wave. In this work, we present an ultrasonic experiment in a 1 m-long, 5 cm-deep waveguide at the laboratory scale. The waveguide transfer matrix is recorded 100 times per second at a sample rate of 1.1 MHz between two source-receiver arrays while a low-amplitude gravity wave is generated by a laser-induced breakdown at the middle of the waveguide above the water surface. The controlled and therefore repeatable breakdown causes a blast wave that interacts with the air-water interface and penetrates into the water, creating ripples at the surface that propagate in both directions. The surface deformation induced by these two wave packets is also measured by two cameras which allows for independent validation of the ultrasonic inversion. The ultrasonic inversion performed from a few thousand eigenbeams lead to accurate quantitative imaging of the dynamic of the air-water interface, using either the travel-time or the amplitude variation of the ultrasonic arrivals.
Modeling acoustic interactions with a dynamic rough sea surface boundary
Authors: Higgins Alex , Siderius Martin , Hines Paul C. , Abraham Douglas
Published: October 2018

The acoustic wave scattering properties of a dynamic pressure-release surface boundary are analyzed using a numeric technique based on the finite-difference time-domain (FDTD) method. Of primary interest is to study the impact of assuming a “frozen” sea-surface on long duration sonar transmissions. Although relatively uncommon in ocean acoustics, the FDTD approach is well suited for modeling boundary roughness and motion. This technique has the additional benefit that the pressure fields are resolved over time, which allows for transient analysis of the observed wave scattering effects. The method is adapted from electromagnetic wave scattering and can properly model the physics of the observed system, which shows a frequency modulated reflection that includes a double-Doppler effect. First, a traditional analytic solution for the static smooth surface boundary ocean half-space model, the Lloyd Mirror, is compared to an equivalent simulation using the FDTD method. Then a dynamic smooth surface boundary is investigated using a modified Lloyd-mirror solution and the FDTD method. Finally, surface roughness for both static and dynamic boundary cases will be considered. Agreement is shown between FDTD simulations and the modified Lloyd Mirror model for both one-dimension and two-dimension cases. [Work supported by the Office of Naval Research.]
Examination of extensions to transport theory that includes rough surface scattering
Authors: Thorsos Eric I. , Henyey Frank
Published: October 2018

Sea surface forward scattering has important effects on shallow water propagation and reverberation at mid frequencies (i.e., 1–3 kHz) under typical sea surface roughness conditions. Coupled-mode or rough surface PE modeling of these effects require averaging results over many rough surface realizations, increasing the computational effort. An alternative method is based on transport theory, where equations are developed for propagating the moments of the field, avoiding the need for utilizing rough surface realizations. Our transport theory method is based on expanding the field in unperturbed modes, and the equations of motion are for moments of the mode amplitudes. The approach has been based on keeping terms to only first-order in the surface height h(x), making the method linear in surface height. Methods for extending the approach beyond the linear model will be described, both with using realizations with coupled modes and with attempts to extend these approaches to obtain a transport theory. A key part of the approach is the use of the Differential Algebraic Equation (DAE) method in which the range-derivative of the effective boundary condition on the mean plane of the rough surface is used instead of the effective boundary condition itself. [Work supported by ONR Ocean Acoustics.]
Scale model test for the acoustical design of Arts Center Incheon concert hall and acoustic measurement after construction
Authors: Kwak Kee Hyun , Jang Hyung Suk , Jeon Jin Yong
Published: October 2018

The Arts Center Incheon (ACI) concert hall was designed to have 1,760 seats, the volume of 18,000 m3 and the reverberation time of 2.1s with seats fully occupied. To achieve the auditory and visual intimacy, the concert hall had a reverse fan shape with a combination of vineyard and balcony. Various scale models and computer simulation were used to determine the acoustical design including the volume of hall, locations of walls and shapes of finishing materials. Three types of sound diffusers were applied according to wall locations. Appropriate protrusion heights were determined based on sound diffusion targets by each part such as the stage and the sides and back of the auditorium. During the execution design stage, a 1:10 scale model of this concert hall was fabricated to measure acoustic characteristics. An auralization experiment was conducted to assess psycho-acoustic responses to the diffusion design. The acoustic measurements after construction matched the design objectives.