bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluid Inclusion and Stable Isotope Studies at Don Sixto, a Precious Metal Low Sulfidation Deposit in Mendoza Province, Argentina
Authors: Mugas Lobos Ana Cecilia , Márquez‐Zavalía María Florencia
Published: October 2013

The Don Sixto mining area in Mendoza province, central‐western Argentina, contains an epithermal low sulfidation Au–Ag deposit. It is a small deposit (∼4 km2), with a gold resource of 36 t. In Don Sixto, ore minerals are disseminated in the hydrothermal quartz veins and hydrothermally altered volcanic‐pyroclastic rock units of Permian–Triassic age. On the basis of the texture, ore mineral paragenesis and cross cutting relationship of gangue minerals, seven stages of mineralization were recognized and described. The first six stages are characterized by quartz veins with minor amounts of base metal minerals and the last stage is represented by fluorite veins with minimal quantities of base metal minerals; the precious metal mineralization is mainly related to the fourth stage. The hydrothermal veins exhibit mainly massive, crustiform and comb infilling textures; the presence of bladed quartz replacement textures and quartz veins with adularia crystals are indicative of boiling processes in the system. Fluid inclusion and complementary stable isotope studies were performed in quartz, fluorite, and pyrite samples from the vein systems. The microthermometric data were obtained from primary, biphasic (liquid‐vapor) fluid inclusion assemblages in quartz and fluorite. The maximum values for salinity and homogenization temperature (Th) came from the stage IV where quartz with petrographic evidence of boiling has average values of 4.96 wt% NaClequiv. and 286.9°C respectively. The lower values are related to the last stage of mineralization, where the fluid inclusions in fluorite have average salinities of 1.05 wt% NaClequiv. and average homogenization temperatures of 173.1°C. The oxygen and sulfur isotopic fractionation was analyzed in quartz and pyrite. The calculated isotopic fractionation for oxygen in the hydrothermal fluid is in the range of δ18OH2O = −6.92 up to −3.08‰, which indicates dominance of a meteoric source for the water, while sulfur reaches δ34SH2S = 1.09‰, which could be reflecting a possible magmatic, or even a mixed source.
Labor Skills and Foreign Investment in a Dynamic Economy: Estimating the Knowledge‐capital Model for Singapore
Authors: Chellaraj Gnanaraj , Maskus Keith E. , Mattoo Aaditya
Published: October 2013

Singapore is an interesting example of how the pattern of foreign investment changes with economic development. This paper studies inbound and outbound investment between Singapore and a sample of industrialized and developing countries over the period 1984–2007. Singapore's investments from industrialized nations shifted into skill‐seeking activities, while its investments in developing countries became concentrated in labor‐seeking production. The knowledge‐capital model is used to analyze the determinants of these shifts. The estimates suggest that a 10% increase in Singapore's skill differences with developing countries resulted in a 15.2% increase in outbound stocks of investment to the average recipient nation. A 10% decline in skill differences with industrialized countries after 1995 resulted in a 3.6% increase in inbound stocks from the average parent nation.
Foreign Capital and Urban Congestion in Emerging Markets
Authors: Batra Ravi , Beladi Hamid
Published: October 2013

Traditional literature emphasizes the role of foreign capital, especially foreign direct investment (FDI) in explaining the high growth rates that many emerging economies have enjoyed during 1990s and 2000s. The present paper accepts this conventional wisdom but argues that theFDIhas also created problems of urban sprawl and congestion that would not be so intense if economic development had primarily come from domestic sources. This is because theFDIis typically concentrated in urban areas that abound in manufacturing and it neglects the rural areas where agriculture predominates. The paper suggests that a small tax on foreign capital tends to mitigate the side effects of foreign investment.
Bounded Biofuels? Sustainability of Global Biogas Developments
Authors: Mol Arthur P.J.
Published: October 2013

Compared to liquid biofuels biogas has hardly drawn any attention from social sciences researchers lately. Although the share of biogas and liquid biofuels in the energy portfolio of many countries are comparable, biogas systems are strongly place‐based and are non‐controversial in terms of sustainability. But is that a fundamental distinction between the two biofuel systems; or is it just a matter of time before biogas becomes globally integrated and subject to sustainability controversies? In using a sociology of networks and flows frame, the current state of and developments in biogas systems around the world are analysed. It is concluded that biogas systems are most likely to further globally integrate, but that it remains to be seen whether that will result in similar sustainability controversies as with respect to liquid biofuels. One determining factor is whether governance arrangements manage to condition the sustainability of globalising biogas developments.
Virtual Coast Guard: An Open and Crowdsourced GIS Portal for Stewardship of India's Coast
Authors: Gajbe Alpesh , Shankar Adya , Rodriguez Sudarshan
Published: October 2013

India's coastline is under tremendous pressure. The current processes of development are becoming a threat to the ecology and livelihoods housed on the coast. If left unchecked, there will not be much of a coast left for our future generations. GIS provides tremendous opportunities to map spatial information for better decision‐making. Government agencies generate maps, but they are localized and inaccessible, preventing an actual assessment of the damage that is already happening to our coast. The Coastal Area Mapping Project (CAMP) envisions creating a collaborative GIS platform using open source technologies. CAMP's vision is to use Free and Open Source Software (FOSS) for collaboration and cocreation and collective problem solving. CAMP foresees a vision for India's coastline where power is equalized among all constituencies (Government, corporations, media, communities, civil societies, etc.), by capturing the big picture and patterns, thus enabling the creation of strategies for stewardship of India's coastline for human wellbeing, coastal protection and sustainable coastal development.
Registering medicines for low‐income countries: how suitable are the stringent review procedures of the World Health Organisation, the US Food and Drug Administration and the European Medicines Agency?
Authors: Doua Joachim Y. , Geertruyden Jean‐Pierre Van
Published: October 2013

New medicines are registered after a resource‐demanding process. Unfortunately, in low‐income countries (LICs), demand outweighs resources. To facilitate registration in LICs, stringent review procedures of the European Medicines Agency (EMA Article‐58), Food and Drug Administration (FDA PEPFAR‐linked review) and WHO Prequalification programme have been established. Only the PEPFAR‐linked review gives approval, while the others make recommendations for approval. This study assessed the performance and discussed the challenges of these three stringent review procedures. Data from WHO, FDA, EMA, Medline and Internet were analysed. Over 60% of medicines reviewed by stringent review procedures are manufactured in India. Until 2012, WHO prequalified 400 medicines (211 vaccines, 130 antiretrovirals, 29 tuberculostatics, 15 antimalarials and 15 others). PEPFAR‐linked review approved 156 antiretrovirals, while EMA Article 58 recommended approval of 3 antiretrovirals, 1 vaccine and 1 antimalarial. WHO Prequalification and PEPFAR‐linked review are free of charge and as a result have accelerated access to antiretrovirals. They both built capacity in sub‐Saharan Africa, although WHO prequalification relies technically on stringent regulatory authorities and financially on donors. Article‐58 offers the largest disease coverage and strongest technical capacities, is costly and involves fewer LICs. To meet the high demand for quality medicines in LICs, these stringent review procedures need to enlarge their disease coverage. To improve registration, EMA Article 58 should actively involve LICs. Furthermore, LIC regulatory activities must not be fully resigned to stringent review procedure.
Soil seedbanks in slash‐and‐burn rice fields of northern Laos
Authors: de Rouw A , Casagrande M , Phaynaxay K , Soulileuth B , Saito K
Published: October 2013

Crops in shifting cultivation fields often suffer from severe weed infestation when long fallow periods are replaced by short fallow periods. The soil seedbank as a source of weed infestation was studied in four fields that differed in their last fallow duration. The effect of burning was analysed by comparing adjacent pre‐burn and post‐burn samples (two sites). Surface vegetation was monitored from burning to harvest in the plots from which soil samples were taken to determine the fraction of the seedbank germinating (three sites). Seedbank size (1700–4000 seedlings m−2) varied depending on a single species, Mimosa diplotricha. Burning reduced emergence of most species, but stimulated emergence in others. Densities in the seedbank were not correlated with above‐ground abundances in the field, except for some species. Most species emerging after 50 days from the soil samples (40% of seedlings) were absent from the field after 190 days. Whilst the data from this study are derived from only four fields, the weed problems after short‐term fallowing appeared to be due to a larger fraction of the seedbank emerging, possibly due to shallow burial, and to a floristic shift towards adaption to burning, rather than the size of the seedbank per se.
Cytoprotective effects of opioids on irradiated oral epithelial cells
Authors: Charbaji Nada , Rosenthal Peter , Schäfer‐Korting Monika , Küchler Sarah
Published: October 2013

Oral mucositis is a common side effect of chemotherapy and radiation therapy accompanied with acute inflammation and ulceration of the oral mucosa. Opioids can improve the wound healing of dermal and oral tissue when applied locally. The aim of this study was to investigate if morphine exhibits cytoprotective effects on oral epithelial cells postirradiation. Hence, oral epithelial cells were exposed to increasing doses (3–30 Gy) of ionization radiation. We assessed the effects of the radiation on cell viability, proinflammatory cytokine release (interleukin [IL]‐1α, IL‐6), and matrix metalloproteinase (MMP‐1, ‐8, and ‐9) expression. As expected, radiation significantly impaired cell viability and morphology and resulted in enhanced IL release. However, morphine‐treated cells consistently showed higher cell viability postirradiation: 9.19 ± 1.16% after 24 hours and 7.45 ± 0.93% after 48 hours compared with the control. In terms of proinflammatory cytokines, the release of IL‐1α and IL‐6 was significantly reduced, too, being most pronounced at 48 hours postradiation. Additionally, we observed a significant reduction of MMP‐1 and especially MMP‐9 expression in morphine‐treated cells. The results clearly indicate anti‐inflammatory as well as cytoprotective effects of morphine on irradiated oral epithelial cells. Interestingly, the protective effects of morphine are not related to a decrease in cell apoptosis or necrosis. Before final conclusions can be drawn, further studies in more complex systems in vitro and in vivo are required. Nevertheless, these findings further underline the high potential of opioids for the treatment of topical wounds and inflammatory conditions.
Isoflux Nusselt Number and Slip Length Formulae for Superhydrophobic Microchannels
Authors: Enright Ryan , Hodes Marc , Salamon Todd , Muzychka Yuri
Published: October 2013

We analytically and numerically consider the hydrodynamic and thermal transport behavior of fully developed laminar flow through a superhydrophobic (SH) parallel-plate channel. Hydrodynamic slip length, thermal slip length and heat flux are prescribed at each surface. We first develop a general expression for the Nusselt number valid for asymmetric velocity profiles. Next, we demonstrate that, in the limit of Stokes flow near the surface and an adiabatic and shear-free liquid–gas interface, both thermal and hydrodynamic slip lengths can be found by redefining existing solutions for conduction spreading resistances. Expressions for the thermal slip length for pillar and ridge surface topographies are determined. Comparison of fundamental half-space solutions for the Laplace and Stokes equations facilitate the development of expressions for hydrodynamic slip length over pillar-structured surfaces based on existing solutions for the conduction spreading resistance from an isothermal source. Numerical validation is performed and an analysis of the idealized thermal transport behavior suggests conditions under which superhydrophobic microchannels may enhance heat transfer.
Managing of a Strategic Crude Oil Pipeline for Maximum Transportation Capacity
Authors: Abdou Hesham A. M.
Published: October 2013

The aged crude oil pipeline; 16″ × 166 km since November 1984, extends from Meleiha field at western desert to El-Hamra terminal at coast of the Mediterranean sea. Its original capacity was 100,000 BOPD using two pumping stations; one at Meleiha and the other is a boosting station, 83 km far from Meleiha. Planned pumped flow rate increased to 177,000 BOPD at the time that Maximum Allowable Working Pressure (MAWP) reduced from 1440 psi to 950 psi. This paper shows managing procedures led to pumping higher flow rate without exceeding MAWP, where two solutions to accommodate such increase in production were applied; firstly by looping the existing pipeline with a (16″ × 56 km), secondly by using a Drag Reducing Agent (DRA), so that could reduce hydraulic friction losses and Total Dynamic Pressure (TDP) in the system and could pumped more with reduced initial pumping pressure at Meleiha. So, the intermediate station was temporarily abandoned. Mathematical models are designed to simulate pumping operation through the whole system, where TDP is predicted for the three pipeline cases: 1- normal case without both looping & DRA. 2- case without DRA & with looping. 3- case with both looping & DRA. Laws of hydraulics are applied with the deduced formula represents performance of DRA in which percentage of drop in pressure losses is modeled as a function of DRA dose in ppm. Close agreement is remarked between values of the deduced theoretical values and actual values obtained for TDP, confirming validity of such mathematical models.
Design and Processing of Niobium Microalloyed Cost Effective Line Pipe Steel With Enhanced Strength and Fracture Toughness
Authors: Subramanian S. V. , Gray J. M.
Published: October 2013

The functional role of niobium in the original HTP X-80 design of high niobium (0.1wt%), low interstitial ( C 0.03 to 0.04, N<0.005wt%) cost-effective base chemistry is (i) to use Zener drag from strain induced precipitation of NbC during thermo-mechanical rolling and solute drag from solute niobium to retard static recrystallization, (ii) to impart adequate rolling reduction below temperature of no recrystallization to promote large strain accumulation in pancaked austenite, and (iii) to promote fine ferrite grain size by strain induced phase transformation under accelerated cooling conditions, thereby obtain high strength and fracture toughness at low temperature through grain size effect. Residual niobium in austenite is used to impart additional strength through transformation hardening, dislocation hardening from accelerated cooling and precipitation strengthening of ferrite through accelerated cooling and interrupted cooling at coiling temperature.

Recent research has confirmed the importance of control of density and dispersion of crystallographic high angle boundaries which are superimposed on the morphological microstructure in order to prevent the initiation of brittle fracture. Extensive research has been carried out in HTP base chemistry to determine the processing options to control the density and dispersion of high angle boundaries to produce higher grade (>X-80) line pipe steels with enhanced fracture toughness. Whereas the resistance to ductile fracture is measured by Charpy toughness, the resistance to brittle fracture is inferred from ductile to brittle transition temperature and percentage shear in DWTT. The research has underscored the importance of austenite grain refinement in upstream processing of HTP before pancaking in finish rolling to control density and dispersion of high angle boundaries in order to prevent brittle fracture initiation. Experimental results are presented which demonstrate that HTP base chemistry is a cost effective design to produce higher grade line pipe steels, not only to achieve high resistance to ductile and brittle fracture in the base plate, but also in HAZ regions associated with relatively high heat input welding in weld fabrication of pipes from plates, and Girth field welding of pipes involving low heat input multi-pass welding.
A multi-channel high-intensity focused ultrasound (HIFU) system for image-guided therapy (IGT)
Authors: Kaczkowski Peter J. , Vaezy Shahram , Martin Roy , Crum Lawrence A. , Keilman George
Published: October 2013

Recent success in using high-intensity focused ultrasound (HIFU) for surgical applications has stimulated the development of image-guided systems for noninvasive therapy. With the goal of developing an all-ultrasound modality, we have developed a clinical HIFU system comprising an integrated transducer probe that permits precisely registered HIFU therapy delivery and high-quality ultrasound imaging, a multi-channel signal generator and rf amplifier system, and a software program that provides the clinician with a graphical overlay of the ultrasound image and therapeutic protocol controls. Electronic phasing of the 2-MHz HIFU annular array allows adjusting the focus within the range of about 4–12 cm from the face. A central opening in the transducer permits mounting of a commercial medical imaging scanhead (ATL P7-4) that is held in place within a special housing. This mechanical fixture ensures precise registration between the HIFU transducer axis and the image plane of the imaging probe. We will present a description of the various system components along with experimental in vitro results of therapy targeting and lesion visualization.
Computational time-reversal and object localization
Authors: Devaney Anthony J.
Published: October 2013

The problem of detecting and locating point scatterers embedded in a known, nonrandom, background medium from multi-static scattering data specified at one or more temporal frequencies is addressed within the context of the acoustic wave equation. It is shown that the singular value decomposition (SVD) of the multi-static data matrix leads to a general theory for both target detection and location that applies for arbitrary distributions of sources and receivers and that reduces to the standard method of computational time-reversal in the special case where the sources and receivers are co-located. The developed theory employs both standard backpropagation as well as vector subspace methods such as music to perform target location estimation and is shown to apply to such diverse applications as ultrasound imaging, acoustic wave tomography, and offset vertical seismic profiling (VSP). The talk includes computer simulations as well as results from experimental data.
Propagation through an imperfectly layered fine-structure
Authors: McCoy John J. , Steinberg Ben Z.
Published: October 2013

The ‘‘fine-structure’’ refers to spatial variations that obtain on a length scale, l, that is small when compared to the acoustic wavelength, λ, in a reference medium, i.e., λ≫l. The ‘‘imperfection’’ refers to variations in measures of the fine structure, which obtain on a much larger length scale, L. A precise definition of a useful ‘‘global’’ measure of the fine-structure variation is determined by the mathematical model of the experiment described. The variations that apply to this measure are required to be weakly varying and stochastic. Prediction models can be expressed in statistical moments of a spatially smoothed component of the complete propagating wavefield; the first two moments are considered. The model constructions are accomplished in two steps, the first of which is a ‘‘generalization’’ of classical homogenization theory, now based on a multiresolution decomposition using wavelets. The second step is to derive equations that govern the statistical moments of solutions of the homogenized equations. An alternate construction, for which an equation that determines the statistical moments of the complete acoustic field is obtained before accomplishing the homogenization, is discussed.
Prediction of the characteristic of sound fields in long enclosures by a hybrid computer model
Authors: Zeng Xiangyang , Chen Kean , Sun Jincai
Published: October 2013

A combined ray tracing and image source model RATISM has been developed specially for the simulation of sound propagation throughout long enclosures such as a corridor. How the algorithm models sound source, sound propagation, and sound receiver was described. The ways in which more complex long enclosures can be modeled were also given. The methods of the prediction of reverberation time and sound pressure level were presented in detail. Three different enclosures were modeled and the results were analyzed. The reverberation room of Northwestern Polytechnic University was measured and predicted to show RATISM can be used for both diffused and nondiffused sound field. A rectangular long enclosure was then predicted by RATISM and NORMAL [L. N. Yang and B. M. Shield, J. Sound Vib. 229, 133–146 (2000)] and the comparison showed that both the two models can correctly simulate the sound field in rectangular long enclosures. A more complicated long enclosure was also simulated and the results showed that the sound field in it had similar characteristic to that in the rectangular one, in which the sound field is nondiffused and sound distribution was mainly dependent on the distance of receiver to source. [Work supported by the Doctorate Foundation of Northwestern Polytechnical University.]
Influence of airway wall properties on respiratory system response characteristics
Authors: Al-Jumaily Ahmed , Al-Fakhri Younis
Published: October 2013

Changes of airway wall physical properties are associated with inflammation and swelling of the airway passages. This contributes to airway obstruction and increased work of breathing. A model is developed to study the effect of changes in the wall properties on the dynamic characteristics of the respiratory system. Both symmetric and asymmetric structures are considered. By developing some insight into the correlation between the respiratory system structure and its acoustical response, groundwork is set for the analytical interpretation of high frequency response data in clinical and laboratory tests. The response of the lung structure indicates that when the airway wall elastance and inertance are varied, as the case during asthma attack (airway walls get swollen results in airway constriction and tissue properties changing), the overall normalized input impedance frequency spectrum measured at the throat gives a reasonable signature for identifying such abnormality. The identification procedure is based on comparing the frequency spectrums of healthy and unhealthy lungs. The branching structure of the airway walls and its dynamical properties appear to significantly influence the lung response.
The music technology program at York
Authors: Howard David M.
Published: October 2013

For the last 8 years, undergraduate degrees (fully accredited by the Institution of Electrical Engineers) in Electrical Engineering with Music Technology Systems have been available in the Department of Electronics at the University of York (UK). These courses maintain a thread of music technology related material alongside the core electronics material throughout the 3 (BEng) or 4 (MEng) years of the program which includes acoustics and psychoacoustics, digital computer music, recording studio techniques, music technology ECAD (MATLAB) exercise, and advanced music synthesis. Students have to participate in a concert (as a group exercise), and in recording exercises (group and individual). Entry requirements are: three grade B passes at A-level including Mathematics and a science subject (usually Physics) as well as musical performance skills [Grade VII from the Associated Board of the Royal School of Music (ABRSM) or equivalent] and some music theory background (ABRSM Grade V Theory or equivalent). Employers have noted that graduates from these Music Technology programs have an added range of creative skills beyond music and audio that they can apply to other areas of engineering design, such as printed circuit board layout and user interface design.
The teaching of musical technology at London Guildhall University
Authors: Jones Lewis , Seago Allan
Published: October 2013

London Guildhall University has recently fundamentally reformed its undergraduate teaching of musical technologies. There are now two broad streams, one concentrating on the study, making, design, and restoration of musical instruments, and one on audio systems. Central to both is teaching in acoustics and a range of course units which explore the relationship between music and technology in its historical, contemporary, and ethnographic aspects. New MMus and MSc courses in ‘‘Music and Technology’’ will provide research training and opportunities for advanced project work. The rationale for these developments is accounted for, and the approach to the teaching of musical acoustics to music technologists and instrument technicians is described. A number of Java-based programs and Quicktime animations have been developed. The animations serve simply to demonstrate such phenomena as simple harmonic motion and standing waves. The Java applet which has been developed by Allan Seago is intended to demonstrate resonance, and the factors which affect it. Unlike the animations, the software is interactive, and enables the student to vary such aspects of the system as mass, spring constant, and damping, and to observe the effect.
Application of acoustic resonators in photoacoustic trace gas detection and metrology
Authors: Hess Peter
Published: October 2013

The application of different types of acoustic resonators such as pipes, cylinders, and spheres in photoacoustics will be considered. This includes a discussion of the fundamental properties of these resonant cavities. Modulated and pulsed laser excitation of acoustic modes will be discussed. The theoretical and practical aspects of high-Q and low-Q resonators and their integration into complete photoacoustic detection systems for trace gas monitoring and metrology will be covered. The main characteristics of the available laser sources and the performance of the photoacoustic resonators, such as signal amplification will be discussed including setup properties and noise features. Recent results will be presented for a state-of-the-art dual-resonator differential cell suitable for sensitive trace gas detection with low electronic and acoustic noise. With this resonant cell and a near-infrared DFB diode laser radiating at 1.53 μm (42 mW) polar ammonia molecules have been detected with a sensitivity of 200 ppbv under flow conditions to reduce adsorption effects. By excitation of fundamental vibrations in methane using a pulsed optical parametric oscillator (OPO), with 60 mW output power, a sensitivity of 1.2 ppbv has been achieved employing this resonant cell. This setup allows accurate detection of the greenhouse gas methane which has a concentration of about 1.7 ppmv in ambient air.
Acoustic resonators as air quality sensors
Authors: Muehleisen Ralph T.
Published: October 2013

The past decade has seen a dramatic rise in concern for the quality of air that we breathe in our homes and workplace. Inexpensive sensors to measure changes of the composition of air are required. One can measure changes in the speed of sound of air by measuring the change in the resonance frequency of an open air acoustic resonator. If the air is treated as an ideal gas, changes in the speed of sound are directly related to changes in the gas composition. This presentation will discuss common indoor contaminants and the concentrations at which they contribute to poor indoor air quality (IAQ) and occupational safety. It is found that acoustic resonant sensors are not sensitive enough for use as IAQ sensors but are sensitive enough to be used as occupational safety monitors. [Work supported by ONR.]
Use of radiation pressure to move small particles in an air flow-through resonator
Authors: Budwig Ralph S. , Frankel Joseph G. , Anderson Michael J. , Line K. Scott
Published: October 2013

It has been demonstrated many times in the past that particles suspended in a fluid medium can be manipulated with radiation pressure. Resonant cavities are often used to achieve large acoustic amplitudes. While most investigations have used water as the fluid medium, few have reported using a gas such as air. Little is known about the effect of openings, required for mean fluid flow through the cavity, on acoustic resonant amplification. Finally, few investigations report actual sound pressures that can be achieved, and correlate them to the movement of the particles. We present experimental measurements that quantify the ability of a flow-through resonator to move small water particles in air as the flow velocity and sound pressure levels are changed. The small water particles were generated with an ultrasonic humidifier. A commercial electrostatic transducer was employed to excite a one-wavelength longitudinal resonance of the cavity at a frequency near 60 kHz. Preliminary results show that sound pressure levels in excess of 150 dB re: 20 μPa can be attained, and significant particle movement is observed at flow velocities up to 11 cm/s. Observed particle movements will be compared to simple theoretical predictions based upon measured sound pressure levels and flow velocities.
Resonant sonic spectroscopic studies of aerogel solids
Authors: Tucholski Edward , Larraza Andres , Droege Michael
Published: October 2013

Measurements similar to those performed using resonant ultrasound spectroscopy (RUS) were carried out in the audible frequency range for isotropic silica aerogels in air. This solid material has attracted significant attention due to its interesting physical properties. It has a density only 100 times greater than air, an optical index of refraction nearly equal to air (1.0–1.05), and a thermal conductivity of ∼0.017 W/mK (∼R10/in.). The acoustic measurements, conducted on a series of aerogel spheres ranging in diameter from 1.1 to 4.6 cm, demonstrated the two elastic moduli are four orders of magnitude less than that of dense silica and correspond to a longitudinal wave speed one-third that in air. The results are compared to pulse-receiver sound speed measurements. Sample spherical imperfections are demonstrated.
Including acoustics in the RESOUND hybrid approach to the mid-frequency problem
Authors: Shorter Philip J. , Gardner Bryce K.
Published: October 2013

The prediction of the response of a complex structural acoustic system across a broad frequency range presents a number of challenges to an analyst. It is quite common to find that (i) the uncertainty associated with the local modal properties of a subsystem, (ii) the wave number content of the local modes, and (iii) the local modal density, can all vary significantly across the various subsystems of a system. This mismatch in the local statistical and dynamic properties of a system is often referred to as the mid-frequency problem. One approach to the mid-frequency problem is to construct a hybrid model that combines deterministic and statistical representations of the system dynamics. Previously, this approach has been applied to in-vacuo structural problems. In this presentation we discuss the extension of the hybrid formulation to encompass enclosed acoustic cavities. The various mechanisms by which energy flows between the deterministic and statistical parts of the structural–acoustic model are discussed, and numerical examples are presented that illustrate radiation into a large (statistical) acoustic cavity and a small (deterministic) acoustic cavity.
Modeling acoustic time reversal in random shallow water sound channels
Authors: Dowling David R.
Published: October 2013

The robust spatial and temporal focusing properties of time-reversing arrays (TRAs) are limited or lost when the environment is dynamic, acoustic absorption losses are prevalent, or noise contaminates the received signal(s). This talk presents theoretical and simulated performance results for TRAs deployed in shallow ocean sound channels containing a random linear superposition of internal waves or having a random rough bottom. In both cases, TRA retrofocusing is improved by random propagation and vertical linear TRAs are predicted to have significant azimuthal directivity. Scaling laws for this azimuthal directivity that include the signal frequency, the characteristics of the sound channel, the properties of the randomness, and the assumption of weak azimuthal coupling are presented. These scaling laws are found to successfully collapse results for a wide parametric range of N by 2-D parabolic equation simulations of TRA retrofocusing in shallow ocean sound channels with random propagation. As expected, the TRA retrofocusing improvements derived from random propagation are typically degraded and are eventually lost when the environmental randomness is time varying. However, the time scales of the oceanic fluctuations appear to be long enough to allow successful TRA operations in shallow ocean waters. [Work sponsored by ONR.]
Time reversal through a solid–liquid interface and super-resolution
Authors: Tsogka Chrysoula , Papanicolaou George C.
Published: October 2013

Time-reversal can be used to refocus optimally a signal back onto the source that emitted it. An active array antenna is used to record the wave as a function of time and then, the recorded field is time reversed and retransmitted. The time reversed wave backpropagates through the medium and refocuses approximately on the initial source position. From the experimental point of view, time-reversal devices are designed to work primarily in a fluid environment. However, time reversal refocusing can be realized also in solids. To do so, the solid is surrounded by a fluid in which the active antenna is located. We propose a numerical formulation describing the time reversal phenomenon through a fluid–solid interface and we analyze with numerical simulations the refocusing resolution obtained in homogeneous media. We also show numerically that multipathing caused by random inhomogeneities improves the focusing of the back-propagated elastic waves beyond the diffraction limit. This phenomenon is called super-resolution and was seen previously in acoustic wave propagation.
Propagation model predictions and comparisons with measurements for broadband acoustic transmission in the Florida Straits
Authors: DeFerrari Harry , Williams Neil , Nguyen Hien
Published: October 2013

Parabolic equation and normal mode propagation models are used to predict the channel pulse responses for comparison with experimental observations in the Straits of Florida. The model inputs for range dependent sound speed and bathymetry are known in detail but geoacoustic properties of the bottom are not well understood. In order to compensate, bottom input parameters are tuned so that predictions agreed with measurements. The tuned models are then used to explain the observed pulse arrival patterns and to predict other patterns that may come about from combinations of sound speed profiles and bottom properties that are known to exist and form interesting acoustic waveguides. Specifically, the models are used to examine the very intense focused arrivals from a deep source located in a downward refracting sound speed profile, the coupling of surface ducted and refracted modes to form ducted precursors and the possibility of strong attenuation of shipping noise with channel depth. Some of the predicted arrival patterns suggest experimental geometries that would enable ocean acoustic tomographic and geoacoustic inversions in shallow water.
Shallow water acoustic wave propagation experiments between three rigid bottom mounted acoustic sonar towers
Authors: Yamaoka Haruhiko , Yamamoto Tokuo
Published: October 2013

Shallow water acoustic wave propagation experiments were conducted between three bottom mounted 5-m tall towers as a part of the SWAT (Shallow Water Acoustic Technology) 2000 Experiment. Each sonar tower was self-contained to support a broadband sound transmitter and a hydrophone 5 m above seafloor. The Gold code of 1023 digits with a center frequency of 5.5 kHz was transmitted from each tower at 2- and 20-min intervals. The three towers were located in a triangle with ranges of 3, 4, and 5 km in the SS and OS sites. The results show a large difference in propagation characters. In the SS site, the peaks of arrivals are scattered over 10–15 ms from the first arrival peak. The envelopes of these signals are not stable during the 32-h experiment period. However, in the OS site the peak arrival is almost single within the 3-ms width. Also, the structure of arrival is very simple and includes the tidal effect. Parabolic equation (PE) model results based on CTD and bottom observation data indicate that there is a waveguide providing stable transmission just above the seafloor in the OS site. Comparison between acoustics data and broadband PE results will be discussed. [Work supported by ONR 321OA.]
Temporal coherence and time spread of ocean surface scattered high-frequency acoustic signals
Authors: Lutz Steven , Bradley David , Culver R. L. , Keranen Joe , Reeves Jon
Published: October 2013

The influence of the ocean environment on the temporal coherence and time spread of high-frequency, surface scattered acoustic signals over intervals ranging from a few seconds to tens of hours have been investigated experimentally. Pulses transmitted every 128 ms reveal persistent micro-path arrivals subsequent to the main surface reflected signal. The observed structure has implications for channel equalization update rate requirements and optimal range resolution for target detection. The measurements were made during the (BBCoh/PasSAS) joint experiment with the Marine Physical Laboratory, Scripps Institution of Oceanography conducted in Fall 2000 off the coast of San Diego in water depths of 200 m to 700 m. Signals transmitted include 0.1-ms pure-tone pulses and 8-ms 13-kHz bandwidth linear frequency modulated (LFM) sweeps centered at 18, 32, and 46 kHz. The projector was suspended from the Floating Instrument Platform (FLIP) at a water depth of 170 m while the receive hydrophones were suspended from a moored buoy at two different ranges, 640 m and 2350 m, with water depths of 200 m and 700 m, respectively. Environmental measurements included water temperature, current speed and direction, directional wave height, and wind speed. [Work sponsored by ONR Code 321US under the ARL Program.]
Measurement and modeling of sound penetration into sandy sediment: Absolute pressure levels
Authors: Jackson Darrell R. , Williams Kevin L. , Thorsos Eric I. , Kargl Steven G.
Published: October 2013

As part of the SAX99 high-frequency sediment acoustics experiment, a buried array was used to measure the pressure field in a sandy sediment with sources in the water column. The sediment was a medium sand with pronounced directional ripples. The buried array consisted of five vertical subarrays of six elements each spanning a horizontal aperture of approximately 30 cm and a vertical aperture of approximately 45 cm. Sources operating over the frequency range 11–50 kHz were moved to obtain various propagation directions relative to the ripple field with ranges and elevations that provided incident grazing angles both larger and smaller than the 30-deg critical angle. Signal levels measured by the buried hydrophones were compared with calculations based on a fluid sediment model and small-roughness perturbation theory, with both directional ripple and small-scale isotropic roughness. Under the assumption that hydrophone sensitivity in-sediment is the same as the value measured in water, data-model comparisons show similar azimuthal dependence and agree in absolute level to within about 2 dB for above-critical incidence and about 3 dB for below-critical incidence. [Work supported by ONR.]
An effective density model for acoustic propagation in sediments derived from the Biot theory
Authors: Williams Kevin L.
Published: October 2013

An acoustic propagation model that approximates a porous medium as a fluid with a bulk modulus and effective density derived from the Biot theory will be presented. Within the framework of the Biot theory it is assumed that the porous medium has low values of frame bulk and shear moduli relative to the other moduli of the medium and these low values are approximated as zero. This leads to an effective density fluid model. It is shown that, for saturated sand sediments, the dispersion, transmission, reflection, and in-water backscattering predicted with this effective density fluid model are in close agreement with the predictions of the Biot theory. This agreement demonstrates that the frame bulk and shear moduli play only a minor role in determining several aspects of sand acoustics. Thus for many applications the effective density fluid model is an accurate alternative to full Biot theory and is much simpler to implement. [Work supported by ONR.]
Perception of sound by goldfish
Authors: Fay Richard R.
Published: October 2013

Psychophysical experiments have helped define the sense of hearing of goldfish with respect to detection and discrimination thresholds within many acoustic dimensions. Generally, these data reveal aspects of peripheral and early brain processing that are qualitatively, and sometimes quantitatively, indistinguishable from those of most other vertebrates. This correspondence suggests that goldfish share an essentially common sense of hearing with other vertebrates, and motivated new experiments that investigate more complex aspects of sound perception in goldfish using the phenomenon of stimulus generalization to study perceived similarities among simple and complex sounds. We have found that goldfish listen analytically to simultaneous tones, have perceptual dimensions analogous to pitch, timbre, and roughness in human listeners, and can segregate simultaneous, complex sources in perception. Several of these processes will be illustrated. These results are in accord with the hypothesis that the sense of hearing in goldfish is essentially similar to that revealed in other vertebrates studied. We suggest that it is useful to view the sense of hearing of any given vertebrate species as representing a general vertebrate pattern as an alternative to assuming that individual species are specially adapted to process particular sounds in its species-specific niche. [Work supported by NIH, NIDCD.]
Pulsed sound production by Sciaenid fishes
Authors: Sprague Mark W.
Published: October 2013

Many fishes, including members of the family Sciaenidae, produce pulses of sound by driving their swimbladders with sonic muscles. The swimbladder functions as a damped oscillator driven by the sonic muscles in a transient response. The radiated waveform contains information about the excitation function generated by the sonic muscles and the properties of the swimbladder. A theoretical model for pulsed sound production based on a driven damped oscillator [M. W. Sprague, J. Acoust. Soc. Am. 108, 2430–2437 (2000)] can be used to establish relationships between sonic muscle excitation, swimbladder motion, and the radiated waveform. Analysis of sonic muscle excitations and corresponding waveforms produced by weakfish (Cynoscion regalis) (Sciaenidae) suggest that the swimbladder continues to oscillate or ‘‘ring’’ after the sonic muscle driving force stops. Portions of the waveform produced during this ringing of the swimbladder depend solely on swimbladder properties such as volume, which relates to fish size, and damping.
Bubbles and acoustic image-guided high intensity focused ultrasound
Authors: Bailey Michael R. , Vaezy Shahram , Yuen Jonathan C. , Anand Ajay , Miller Nathan A. , Kaczkowski Peter J. , Crum Lawrence A.
Published: October 2013

Clinical diagnostic ultrasound (US) can be used to target and to monitor in real-time high-intensity focused ultrasound (HIFU) therapy. In our system, the HIFU transducer (3.5 MHz, 35 mm aperture, 55 mm radius of curvature) and US scan head (several were tested, center frequencies 3–8 MHz) are fixed with the HIFU focus in the imaging plane. HIFU and US are either synchronized real time to relegate interference to the image fringe or HIFU and US are interlaced for nearly real-time imaging. HIFU produces a localized hyperechoic region visible on B-mode US. Coagulatively necrosed lesions produced have similar size, shape, and location to measurements made from the corresponding US images. Thresholds are also comparable. However, in vivo, if HIFU is turned off as soon as hyperecho appears, no lesion is seen (the tissue was fixed within four hours of treatment). Thus, a short HIFU burst can be used to target treatment. Bubbles appear to be largely but perhaps not entirely responsible for the increase in echogenicity. Times for dissipation of the hyperecho and dissolution of a bubble as a function of hydrostatic pressure compare well. Significant overpressure (50 bar) can suppress hyperecho produced by HIFU. [Work supported by NSF, NSBRI, DARPA/ONR, and NIH SBIR.]
Turbulence induced distortion in hearing aid receivers
Authors: Warren Daniel M.
Published: October 2013

The quality of resonances in hearing aid receivers can be reduced by adding damping in various places in the electroacoustic system. Acoustic damping may be implemented by means of tiny (≊0.001 in. diam) holes in the diaphragm separating the front and rear cavities of the receiver. The holes are very small, ≊1/10 of the boundary layer thickness. As noted previously [P. M. Morse and K. U. Ingard, Theoretical Acoustics (Princeton University Press, Princeton, 1968)], ‘‘fortunately, such a minute hole is of no practical interest.’’ However, in hearing aid receivers such holes are of practical interest, and are identified as causing high distortion at frequencies below 500 Hz. The experiment described demonstrates that the distortion is caused by turbulence in air flow through holes in the diaphragm. The experiment also shows that distributing the air flow among multiple smaller holes raises the threshold for turbulent flow, alleviating distortion at the nominal drive level. [Work supported by Knowles Electronics, LLC.]