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COVID-19 has, at least temporarily, reshaped the teaching and learning environment. Virtual learning classrooms have replaced physical classrooms and require teachers to think of new and creative ways to keep students motivated to learn. Understandably, these thoughts for creative teaching strategies are critical when considering changing demographics in student populations and existing linguistic barriers more commonly found in English language learners (ELLs). To this end, the purpose of this paper is to discuss how within the virtual learning environment, meaningful interactions, student motivation to learn, vocabulary instruction, the partnership model, and graphic organizers remain important factors impacting ELLs’ reading comprehension. The paper culminates with implications for the professional development of teachers and school administration. Keywordssupport strategies, virtual learning, English language learners

Acoustic tweezers are a method of using sound radiation forces to trap and manipulate objects. Previously, we demonstrated an acoustic tweezer capable of first creating the objects, droplets of CCl4 from a reservoir, before trapping and manipulating them. We achieved this using a single transducer whose field was modified by a low-profile fraxicon (Fresnel axicon) lens exhibiting specific near-field trapping zones and far-field Bessel beam behavior which enable the trapping process. Here, we extend the method to include another class of fluids, complex hydrocarbons, using conventional SAE30 motor oil in water. Furthermore, with the higher power levels used in this study we demonstrate the discovery of a second trapping region in the field generated by our transducer. The non-contact extraction and manipulation of organic and hydrocarbon fluid samples could have significant biological and environmental applications where a container would contaminate, destroy, or otherwise change the samples under investigation.

Helical coils serve many functions in mechanical systems and are often subjected to a variety of impulsive forces. In this talk we examine the dynamics of a helix modeled after an L-Band helical antenna used for satellite communications in low Earth orbit (LEO). Since the components of a deployed satellite are not accessible, it is critical to understand the dynamics of the antenna given its position outside of the main body. The intent of this work is to identify the frequencies, shapes and Q-values of the vibrational modes of the helix subject to impulsive stimuli and evaluate changes due to environmental exposures and structural modifications. We report on coil-by-coil measurements of the spectra using eight distinct stimulus-response polarizations. Two specific studies are emphasized in this talk. To gauge the sensitivity of the element to thermal variations under (LEO) conditions, we report on the impact of thermal cycling on the vibrational spectra of the helix. We also report on changes in the dynamic response of the helix due to the addition of structural support elements.

Radiation pressure from acoustic and electromagnetic fields can generate forces sufficient to trap and manipulate objects. In most cases, the objects are pre-existing, but it is also possible for the forces to essentially create the target objects. Recently, we reported on the ability of high power ultrasound to extract and controllably manipulate droplets from the organic solvent CCl4 using a near-field type of acoustic tweezers [Lirette et al., Phys. Rev. Appl. 12, 061001 (2019)]. The extraction used a fraxicon lens which produced trapping zones in the near-field. With the addition of extraction to trapping and manipulation, the process can be considered a form of contact-free pipetting. In the present work, we demonstrate the capability of this system to co-axially extract two droplets of SAE30ND motor oil (between 70%–80% liquid hydrocarbon) at a water interface against a positive radiation pressure. In the experiments with oil, several differences in the process have been observed relative to the CCl4 study: a second near-field trapping zone is revealed; the surface deformation is small and opposite to the direction of extraction; the extraction and trapping forces are sufficient to overcome both interfacial tension and buoyancy; and the target liquid has distinct physical properties, such as density, viscosity, and acoustic impedance. Non-contact and label-free extraction of oil droplets remotely in an aqueous environment could have significant biological and environmental applications. Finding that the process works with two distinct liquids demonstrates its more general applicability and broadens its potential uses.

Cylindrical containers, such as liquid tanks and pressure vessels, are ubiquitous in storage applications. Traditional lines of non-destructive evaluation (NDE) are mostly focused on the integrity of containers, but studies on solid contents within using external sensors are lacking. In previous work, metrics were developed to estimate the structural integrity of mock-up fuel assemblies inside a lab-scale nuclear dry storage cask. Linear acoustic resonance techniques were shown to be sensitive down to single assembly level. In this work, this problem is further examined by studying contact nonlinearity in a simplified system using Nonlinear Ultrasound Resonance Spectroscopy (NRUS). This system consists of a single layer of identical spheres with varying composition and size evenly distributed at the bottom of a cylindrical aluminum container. The resonance frequency shifts due to varying amplitudes were mostly affected by the total mass of spheres inside, while diameter and composition of spheres played minor roles. A phenomenological model was developed based on the resulting shifts and was studied numerically using finite element simulations. The agreement between simulations and experiments suggests that the contact nonlinearity is predominated by a contact loss mechanism. This NRUS technique may complement linear acoustic techniques for solid cargo NDE inside sealed vessels.

A fraxicon is a stepped phase plate lens designed to be a discrete approximation of the axicon, a refractive cone-shaped lens. Both lenses generate minimally diffractive Bessel beams with long depths of focus. Here the characteristics of broadband pulses modified by these lenses to compare and contrast the dynamics of the propagating wave packets were examined. Pulses from a spherically focused Fresnel lens are also examined to provide the context of a conventional design. The wave packets generated through the fraxicon exhibit many of the same characteristics of those from the axicon such as lateral compactness and axial integrity, although the fraxicon packets do exhibit noticeable dispersion in comparison. Both the fraxicon and axicon wave packets have a much tighter lateral extent than those of the Fresnel throughout the propagation region. The most significant difference between the fraxicon and axicon is with the group speeds of the packets with the fraxicon group subsonic and the axicon supersonic across a 50 mm path. Supplemental movies are provided for direct visualization of the propagation (for movies of the waveforms and energy profiles of the wave packet propagation that was experimentally obtained). To assess the conformity of the low profile lenses to their design parameters, frequency domain comparisons of measurements with simulations are also presented and are in good agreement.

The objectives of a series of our researches are to determine the feasibility of applying ultrasonic pretreatment prior to biochar gasification. As per the initial results, the heating value (HV) of biochar significantly increased after acoustic treatment in water with dissolved CO2 (AIChE Journal, 2014;60:1054–1065). Accordingly, emphasis of the current work is placed on the parameters governing the HV of biochar in the early stage of the treatment. Switchgrass and miscanthus biochars were treated under different conditions. The reactant ratio, biochar:water:CO2, exhibited profound impacts on the synergism. The highest (but not yet systematically optimized) ratio of HV increase (or HV Gain, HG) to ultrasound energy supplied (ES) takes place when biochar-to-water ratio, or BC:W, equals 0.06 g/ml. The observed HG/ES is about 10, suggesting that the energy consumption is only a fraction of the acoustic energy supplied. Miscanthus biochar’s HV increases by up to 4.6% after treatment at 5% amplitude for 135 s (HG = 33 cal/g). For the same run, miscanthus biochar's H content increased by 42.7%. Changes in HV can be mediated by mineral leaching, C or H fixation, or O content loss. Mineral leaching is influenced by pH and CO2 concentration. CO2 and water are the sole contributors to C and H gains, respectively. CO2 concentration in the solution during the treatment is also affected by mass transfer limitations, ultrasound power, and design of the three-phase reactor. Increasing the BC:W ratio initially enhances the cavitation nuclei on the fluid/solid surface, and therefore sonolysis. The subsequent decrease in HV with increasing BC:W may be due to the limitation in ultrasound penetration and H supply from water. Carbon and hydrogen fixation may be connected to the formation of H2, CO, formic acid, formaldehyde, and associated radicals during sonolysis of aqueous CO2.

The acoustic radiation force and associated trapping by ``acoustic tweezers'' is an efficient means of particle manipulation in a variety of applications, although this trapping is highly sensitive to parameters of the object and beam. The authors show how to extract and manipulate droplets from a fluid interface without mechanical contact, using near-field acoustic tweezers, with the near-field pressure gradient allowing automatic trapping after extraction. The strong, flexible trapping here is an advantage over traditional tweezers based on focused beams or standing waves, and can be of great importance in both laboratory and industrial settings.

The angular spectrum method (ASM) is an effective tool for propagating wave fields between parallel planes through decomposition of the field into a series of independent plane waves. One source of error is interference from mirror sources introduced through the inherent periodicity of the fast Fourier transform (FFT) used to implement this method numerically. Here, spatial filters attenuate waves propagating at large angles, which are sensitive to mirror sources. Simulations show that this suppresses the ripple artifact whilst preserving the accuracy of the ASM-computed fields. To achieve comparable performance without filtering requires up to a 13.5-fold increase in computation time.

In many countries, permanent repositories for high burnup spent nuclear fuel assemblies have yet to be established. As a result, much of the spent fuel from nuclear reactors is contained within dry storage casks, with many being beyond their designed service life. The assessment of the internal structural integrity of these casks and the fuel assemblies contained therein is of critical importance for both extended storage and transport to permanent repositories. The large size, structural complexity, and inaccessibility of the interior of the casks make this task challenging. To address these difficulties, a 1:6 scaled model based closely on the design of a Transnuclear (TN-32) dry storage cask was fabricated to facilitate controlled studies of these structures in the laboratory. Vibrational spectroscopy was used to evaluate the state of the cargo and internal structures within the cask utilizing only measurements on the outer surface. Using modes identified through Finite Element modeling corresponding to those previously measured on a full-scale TN-32 cask, we report on the development of amplitude- and phase-based metrics that are sensitive to internal conditions in the lab cask. Steel rod bundles and steel shot were used as surrogates for intact and damaged fuel assemblies, and various internal configurations of these materials were investigated. The metrics were based on acquired spectra involving the (1, 2) global bending mode and the (2, 1) radial-with-shearing mode. The results show that the metrics are sensitive to the condition of a single assembly and have some ability to determine the locations of damaged and empty slots.

Constructing tissue-mimicking phantoms of the brain for ultrasonic studies is complicated by the low backscatter coefficient of brain tissue, causing difficulties in simultaneously matching the backscatter and attenuation properties. In this work, we report on the development of a polyvinyl alcohol-based tissue-mimicking phantom with properties approaching those of human brain tissue. Polyvinyl alcohol was selected as the base material for the phantom as its properties can be varied by freeze–thaw cycling, variations in concentration and the addition of scattering inclusions, allowing some independent control of backscatter and attenuation. The ultrasonic properties (including speed of sound, attenuation and backscatter) were optimized using these methods with talc powder as an additive. It was determined that the ultrasonic properties of the phantom produced in this study are best matched to brain tissue in the frequency range 1–3 MHz, indicating its utility for laboratory ultrasonic studies in this frequency range.

The assessment of the internal structural integrity of dry storage casks for used high burnup nuclear fuel assemblies is of critical importance before transporting these to permanent repositories. The large size and structural complexity of the Transnuclear-32 (TN-32) cask as well as the inability to access its interior make this a challenging task. To address these difficulties, we use an active acoustics approach to develop metrics that are sensitive to the internal configuration of these casks. A 6:1 scaled model of the TN-32 cask was constructed in order to study the internal configuration of the fuel assemblies including various damage scenarios. Each mock-up fuel assembly consists of bundled steel rods, and their structural failure is mimicked by steel shot of equal weight. This talk will report the amplitude- and phase-based active acoustics metrics that we developed to characterize different levels of internal damage. Our studies indicate that vibrometric signatures of various internal conditions can be measured using sources and sensors mounted on the exterior shell. Our current methodology is sensitive enough to detect structural failures at the single fuel assembly level. [Work supported by DOE NEUP Award No. DENE0008400.]

The assessment of the internal structural integrity of dry storage casks with high burnup nuclear fuel assemblies is of critical importance for their transport to permanent repositories and during their extended storage service lives. The large size, structural complexity, and inability to access the interiors of the casks make this task challenging. The aim of this work is to evaluate the ability of vibrational characterization to assess the state of the internal cargo (i.e., fuel assemblies) in a cask strictly using measurements on the outer surface. In this study, we report on the identification of five modes of an unloaded full-scale Transnuclear-32 (TN-32) cask and examine the potential of using these modes to assess the internal configuration in a loaded condition. Vibrational spectra were acquired using impulse and continuous-wave techniques on both storage and transportation configurations from which the modal frequencies and the associated quality factors were determined. A finite element model of the TN-32 was constructed and used to identify the observed modes. The model was extended to include loaded configurations to assess how the presence of assemblies impacts the modal structure of the cask and its surface vibrations.

Ultrasound focused at a fluid-fluid boundary creates an acoustic radiation pressure on the boundary that is dependent on the incident energy density and the relative density and sound speed of each fluid. For different fluid combinations, this radiation pressure can either be positive or negative. For this study, ultrasound propagating from water to carbon tetrachloride was used to create a negative radiation pressure at the interface. This fluid combination is impedance matched eliminating reflections and heating effects at the boundary. A fraxicon phase plate lens is a low profile analog of an axicon and generates an approximate Bessel beam in the far field. The near field exhibits a complex diffraction pattern including shadow zones capable of acoustic trapping. Starting with a planar interface, we demonstrate the extraction, capture, and manipulation of a carbon tetrachloride droplet. The negative radiation pressure draws the carbon tetrachloride surface up into the water, eventually breaking a drople...

Fresnel and fraxicon phase plate lenses modify incident acoustic radiation by a series of phasing steps. A Fresnel lens is designed to approximate a spherical lens, and a fraxicon is designed to approximate an axicon generating a non-diffracting Bessel beam out to a depth of focus. For this study, two lenses were manufactured out of aluminum, a Fresnel with a focal point of 5 cm and a fraxicon with a DOF of 10 cm. Each lens was bonded to a 1.2-MHz piezoelectric driver with epoxy and the assemblies mounted in PVC housings for use under water. The field from each was measured by a hydrophone scanned in the transverse planes. Using an acoustic force balance, the electromechanical conversion efficiency was measured to be roughly 50% for each. The focal power fraction, defined as the ratio of the power within the -6 dB boundary of the focus to the total emitted power, was determined for both transducers. The results are compared to numerical simulations and previously published results.

The assessment of the internal structural integrity of dry storage casks for used high burnup nuclear fuel assemblies is of critical importance before these are transported to permanent repositories. The size of the casks (5.2 m in height and 2.4 m in diameter), structural complexity and the inability to access the interior make this a challenging task. This project addresses these difficulties through a multi-modal approach involving nuclear, charged particle and acoustic methods. This paper reports on measurements of the vibrational spectra and mode shapes using a 6:1 scaled TN-32 model cask constructed in house. 2-D vibrometric scans were performed with a laser Doppler vibrometer to measure the vibrational mode shapes exhibited by the intact cask. Good agreement is observed between the experimentally measured mode shapes on both full-scale and scaled cask and those determined numerically using a detailed finite element model. Several modes identified will be important in assessing the internal characteristics from external measurements. Furthermore, compared to linear techniques, nonlinear responses acquired suggest higher sensitivity to changes in internal structure.

The assessment of the internal structural integrity of dry storage casks for used high burnup nuclear fuel assemblies is of critical importance before these are transported to permanent repositories. The size of the casks (5.2 m in height and 2.4 m in diameter), structural complexity and the inability to access the interior make this a challenging task. This project addresses these difficulties through a multi-modal approach involving nuclear, charged particle and acoustic methods. This paper reports on linear and nonlinear vibrational spectra of an unloaded full-scale TN-32 cask. These studies use both impulsive and swept continuous-wave excitations with a variety of sensor placement and cask configurations. From the resulting spectra, resonant frequencies, quality factors and harmonic responses of various vibrational modes were determined. A detailed finite element model of the TN-32 was constructed and the experimental results are compared to the modal structure determined numerically.

Recent investigations of cavitation in fluids pressurized up to 30 MPa found that the intensity of light emissions increased by 1000-fold over that measured for single bubble sonoluminescence. A series of measurements is reported here to extend this original work by resolving the static pressure dependence of the shock wave and light emissions from the first and the most energetic collapses, along with the total shock wave energy and light emissions for the event. Each of these parameters was found to increase with the static pressure of the fluid. Furthermore, the energy of these shock wave and light emissions was found to increase in proportion to the stored acoustic energy in the system. These findings were corroborated using the Gilmore equation to numerically compute the work done by the liquid during the bubble collapse. The overall findings suggest that the increased collapse strength at high static pressure is due to the increased tension required to generate inertial cavitation, and not an increased pressure gradient between the interior of the vaporous bubble and the surrounding liquid.

The amplitude of the acoustic pressure required to nucleate a gas or vapor bubble in a fluid, and to have that bubble undergo an inertial collapse, is termed the inertial cavitation threshold. The magnitude of the inertial cavitation threshold is typically limited by mechanisms other than homogeneous nucleation such that the theoretical maximum is never achieved. However, the onset of inertial cavitation can be suppressed by increasing the static pressure of the fluid. The inertial cavitation threshold was measured in ultrapure water at static pressures up to 30 MPa (300 bars) by exciting a radially symmetric standing wave field in a spherical resonator driven at a resonant frequency of 25.5 kHz. The threshold was found to increase linearly with the static pressure; an exponentially decaying temperature dependence was also found. The nature and properties of the nucleating mechanisms were investigated by comparing the measured thresholds to an independent analysis of the particulate content and available models for nucleation.

Low frequency (61 Hz) shear wave speeds have been measured in viscoelastic wormlike micellar (WM) fluids for a concentration range of 20/12-500/300 mM CTAB/NaSAL where CTAB is the surfactant and NaSAL is the salt and the concentration ratio was fixed at 0.6 for all experiments. The birefringent property of the WM fluids was exploited to visually track the the shear pulse using crossed optical polarizing filters and high speed video. Several scalings of shear wave speed as a function of concentration were discovered: c(s) ~ √C for 20-200 mM and c(s) ~ C for higher concentrations, but with a break in the slope at 400 mM CTAB. Over this full concentration range, the shear wave speed varied from 0.08-0.7 m/s. The shear wave speed was also found to be sensitive to the time between fluid synthesis and measurement indicating a long equilibrium time. Further, comparison with elastic and loss moduli obtained from rheology data show that shear wave propagation is dominated by the elastic modulus for this frequency range. Also briefly discussed are potential applications of this fluid in elastography.

The assessment of the internal structural integrity of dry storage casks for used high burnup nuclear fuel assemblies is of critical importance before these are transported to permanent repositories. The size of the casks (5.2 m in height and 2.4 m in diameter), structural complexity and the inability to access the interior make this a challenging task. This project addresses these difficulties through a multi-modal approach involving nuclear, charged particle and acoustic methods. In this work, we report on measurements of the vibrational spectra and mode shapes using a 6:1 scaled TN-32 model cask constructed in our lab. 2-D vibrometric scans were performed with a laser Doppler velocimeter to measure the vibrational mode shapes exhibited by the cask. Good agreement is observed between the experimentally measured mode shapes and those determined numerically using a detailed finite element model. Several modes are identified that will be important in assessing the internal characteristics from external mea...

Low frequency (61 Hz) shear wave speeds have been measured in viscoelastic wormlike micellar (WM) fluids for a concentration range of 20/12-160/96 mM CTAB/NaSAL. The strain induced birefringence of the WM fluids was exploited to optically track the shear pulse using crossed polarizing filters and high speed video. It was found that shear speed increases roughly linearly with concentration at a rate of 3.5 mm s(-1) mM(-1) CTAB. Further, comparison with elastic and loss moduli obtained from rheology data show that shear wave propagation is dominated by the elastic modulus for this frequency range.

Using a broadband through-transmission technique, the attenuation coefficient and phase velocity spectra have been measured for a set of multi-wall carbon nanotube (MWCNT)-nylon composites (from pure nylon to 20% MWCNT by weight) in the ultrasonic frequency band from 4 to 14 MHz. The samples were found to be effectively homogeneous on spatial scales from the low end of ultrasonic wavelengths investigated and up (>0.2 mm). Using Kramers–Kronig relations, the attenuation and dispersion data were found to be consistent with a power-law attenuation model with a range of exponents from y=1.12 to y=1.19 over the measurement bandwidth. The attenuation coefficients of the respective samples are found to decrease with increasing MWCNT content and a similar trend holds also for the dispersion. In contrast, the mean phase velocities for the samples rise with increasing MWCNT content indicating an increase in the mechanical moduli.

This paper reports the first intensified biochip system for chemiluminescence detection and the feasibility of using this system for the analysis of biological warfare agents is demonstrated. An enzyme-linked immunosorbent assay targeting Bacillus globigii spores, a surrogate species for Bacillus anthracis, using a chemiluminescent alkaline phosphatase substrate is combined with a compact intensified biochip detection system. The enzymatic amplification was found to be an attractive method for detection of low spore concentrations when combined with the intensified biochip device. This system was capable of detecting approximately 1 × 105Bacillus globigii spores. Moreover, the chemiluminescence method, combined with the self-contained biochip design, allows for a simple, compact system that does not require laser excitation and is readily adaptable to field use. Figure Schematic diagram of the miniature biochip detection system

In the wake of recent reports of superluminal acoustic group velocities in sonic and ultrasonic regions of the acoustic spectrum, this paper describes the time-domain manifestation of such group velocities through simulations of the linear propagation of ultrasonic wave packets in a suspension of elastic microspheres. Conditions under which arbitrarily large and negative group velocities can be observed as the speed of a peak in the envelope of an acoustic pulse are described. Propagation simulations demonstrate the physical signature of negative group velocities, as well as the causal compliance of the superluminal acoustic pulses examined in this work.

Kramers-Kronig (KK) analyses of experimental data are complicated by the conflict between the inherently bandlimited data and the requirement of KK integrals for a complete infinite spectrum of input information. For data exhibiting localized extrema, KK relations can provide accurate transforms over finite bandwidths due to the local-weighting properties of the KK kernel. Recently, acoustic KK relations have been derived for the determination of the group velocity (cg) and the derivative of the attenuation coefficient (alpha') (components of the derivative of the acoustic complex wave number). These relations are applicable to bandlimited data exhibiting resonant features without extrapolation or unmeasured parameters. In contrast to twice-subtracted finite-bandwidth KK predictions for phase velocity and attenuation coefficient (components of the undifferentiated wave number), these more recently derived relations for cg and alpha' provide stricter tests of causal consistency because the resulting shapes are invariant with respect to subtraction constants. The integrals in these relations can be formulated so that they only require the phase velocity and attenuation coefficient data without differentiation. Using experimental data from suspensions of encapsulated microbubbles, the finite-bandwidth KK predictions for cg and alpha' are found to provide an accurate mapping of the primary wave number quantities onto their derivatives.

We report the development of a battery-powered portable chemical identification device for field use consisting of an acousto-optic tunable filter (AOTF)-based Raman spectrometer with integrated data processing and analysis software. The various components and custom circuitry are integrated into a self-contained instrument by control software that runs on an embedded single-board computer (SBC), which communicates with the various instrument modules through a 48-line bidirectional TTL bus. The user interacts with the instrument via a touch-sensitive liquid crystal display unit (LCD) that provides soft buttons for user control as well as visual feedback (e.g., spectral plots, stored data, instrument settings, etc.) from the instrument. The control software manages all operational aspects of the instrument with the exception of the power management module that is run by embedded firmware. The SBC-based software includes both automated and manual library searching capabilities, permitting rapid identification of samples in the field. The use of the SBC in tandem with the LCD touchscreen for interfacing and control provides the instrument with a great deal of flexibility as its function can be customized to specific users or tasks via software modifications alone. The instrument, as currently configured, can be operated as a research-grade Raman spectrometer for scientific applications and as a “black-box” chemical identification system for field use. The instrument can acquire 198-point spectra over a spectral range of 238–1620 cm−1, perform a library search, and display the results in less than 14 s. The operating modes of the instrument are demonstrated illustrating the utility and flexibility afforded the system by the SBC–LCD control module.

A novel method for the simultaneous acquisition of optical absorption and ultrasonic attenuation spectra is described. The technique is based on the photoacoustic generation of bi-directional ultrasonic pulses by a thin optical absorber that is remote from the sample. A single piezoelectric transducer ultimately detects the two pulses of ultrasound, and the captured signals are used to determine both the optical absorption and ultrasonic attenuation properties of the sample. Measurements on a polycarbonate resin sample using the simultaneous photoacoustic method and conventional techniques show good agreement, indicating the validity of the method.

Laser-induced fluorescence (LIF) spectroscopy can serve as a rapid analytical method for the quantitative analysis of polycyclic aromatic hydrocarbons (PAHs). The high quantum yields of this class of compounds, along with large absorption cross-sections, make fluorescence a very attractive technique for trace analysis determination of PAHs. Furthermore, fluorescence can provide in situ and online information regarding the composition and concentration of PAHs formed during combustion or pyrolysis processes. In this paper, we utilize a fiber-optic probe coupled to a spectrometer to collect fluorescence spectra of several PAH vapors at elevated temperatures using excitation at 337 nm. We have collected the fluorescence of standards as well as complex mixtures of PAHs at 300 °C. The expected band broadening induced by temperature effects was observed, but did not compromise the spectrum signature for each PAH studied. We have measured fluorescence spectra of benzo[a]pyrene, pyrene, anthracene, and phenanthrene vapors. Determination of trace amounts of the toxicologically important benzo[a]pyrene has been shown to be feasible. Experimental results show that at 337 nm, benzo[a]pyrene is the most quantum efficient fluorophore among the PAHs studied. Furthermore, fluorescence lifetime measurements were found to be helpful in the characterization of PAH mixtures.

A band gap in the transmission spectrum of a finite two dimensional phononic crystal is examined in the time domain using pulsed ultrasonic fields. The phononic crystal consists of a hexagonal array of copper cylinders (r = 1.19 mm) in an aqueous matrix with a lattice constant of 2.9 mm. Measurements of the transmission properties of the sample are performed using ultrasonic wave groups of various center frequencies and bandwidths. Among the band gaps in the low-MHz range, we concentrate on the gap from 1.48 MHz—1.70 MHz. The phase velocity, group velocity, and attenuation coefficient spectra are determined and compared with expectations.

The feasibility of using a novel detection scheme for the analysis of biological warfare agents is demonstrated using Bacillus globigii spores, a surrogate species for Bacillus anthracis. In this paper, a sensitive and selective enzyme-linked immunosorbent assay using a novel fluorogenic alkaline phosphatase substrate (dimethylacridinone phosphate) is combined with a compact biochip detection system, which includes a miniature diode laser for excitation. Detection of aerosolized spores was achieved by coupling the miniature system to a portable bioaerosol sampler, and the performance of the antibody-based recognition and enzyme amplification method was evaluated. The bioassay performance was found to be compatible with the air sampling device, and the enzymatic amplification was found to be an attractive amplification method for detection of low spore concentrations. The combined portable bioaerosol sampler and miniature biochip system detected 100 B. globigii spores, corresponding to 17 aerosolized spores/L of air. Moreover, the incorporation of the miniature diode laser with the self-contained biochip design allows for a compact system that is readily adaptable to field use. In addition, these studies have included investigations into the tradeoff between assay time and sensitivity.

Three-dimensional optical random access memory (3D ORAM) materials with enormous capacity and fast access speed have shown a great potential in overcoming limitations of access and storage capacity in current memory devices. As another useful development of this 3D ORAM, we have shown the application of 3D ORAM materials as a practical dosimeter. The local heating of the polymer matrix by the deposited energy of ionizing radiation is thought to contribute to the conversion of the fluorescent photochromic dye to a nonfluorescent form. The two-photon readout system is very useful in tracking the interactions of energy of ionizing radiation deposited in a polymer matrix. However, the polymer fracturing that has occurred during two-photon readout has been an obstacle in utilization of 3D ORAM materials as a dosimeter. In this work, we further evaluated the readout system using a high-energy variable attenuator in order to prevent polymer fracturing due to the strong absorption of the 1064 nm beam by the polymer matrix. Through adjustment of the 1064 nm beam intensity using this attenuator, two-photon excited fluorescence of anthracene-doped 3D ORAM materials could be obtained without polymer fracturing. As a result of this improved procedure, a highly spatially resolved fluorescence image of anthracene-doped 3D ORAM material could be observed with the two-photon readout system.

In this paper, we describe the use of an integrated circuit (IC) microchip system as a detector in multiplex capillary electrophoresis (CE). This combination of multiplex capillary gel electrophoresis and the IC microchip technology represents a novel approach to DNA analysis on the microchip platform. Separation of DNA ladders using a multiplex CE microsystem of four capillaries was monitored simultaneously using the IC microchip system. The IC microchip–CE system has advantages such as low cost, rapid analysis, compactness, and multiplex capability, and has great potential as an alternative system to conventional capillary array gel electrophoresis systems based on charge-coupled device (CCD) detection.

The ability to determine particle type and energy plays an important role in the dosimetry of heavy charged particles (HCP) and neutrons. A new approach to radiation dosimetry is presented, which is shown to be capable of particle type and energy discrimination. This method is based on utilising radiation induced changes in the digital information stored on three-dimensional optical random access memories (3D ORAM). 3D ORAM is a small cube (a few mm 3 ) composed of poly(methyl methacrylate) doped with a photochromic dye, and it was originally proposed as a memory device in high speed parallel computers. A Nd:YAG laser system is used to write and read binary information (bits) on the ORAM, which functions as a charged particle detector. Both the read and the write processes use two laser beams that simultaneously strike the material to cause a colour change at their intersection (similar to the darkening of light-sensitive sunglasses when exposed to sunlight.) The laser produces colour changes in the ORAM, which then reverts to the original colour ('bit-flips') at sites where energy is deposited from interaction with incident HCP or neutron-recoil protons. The feasibility of this approach was demonstrated both theoretically and experimentally. Calculations based on track structure theory (TST) predict that when HCP interact with the ORAM material, the local energy deposition is capable of inducing measurable 'bit-flips'. These predictions were recently confirmed experimentally using two types of ORAM systems, one based on spirobenzopyran and the other on anthracene, as the photochromic dyes.

Wormlike micellar (WM) fluids, which flow when subjected to long term stresses, are mechanically viscoelastic over shorter durations. These fluids are birefringent under shear, allowing the study of shear wave propagation using both optical and acoustic modalities. In this work, the thermal and spectral behavior of ultrasonically generated shear waves in a WM fluid are studied. A fluid consisting of hexadecyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSAL) combined in a 5:3 ratio is used in a 200 mM concentration. A high intensity focused ultrasound (HIFU) beam generates radiation pressure in the fluid and can induce shear waves of sufficient amplitude to be visualized optically when the beam is modulated. By pulsing the HIFU beam, a train of shear waves are generated which propagate laterally from the focal region. The temperature and frequency dependent behavior of the HIFU generated shear waves are correlated with the rheological and microstructural properties of the fluid.Wormlike micellar (WM) fluids, which flow when subjected to long term stresses, are mechanically viscoelastic over shorter durations. These fluids are birefringent under shear, allowing the study of shear wave propagation using both optical and acoustic modalities. In this work, the thermal and spectral behavior of ultrasonically generated shear waves in a WM fluid are studied. A fluid consisting of hexadecyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSAL) combined in a 5:3 ratio is used in a 200 mM concentration. A high intensity focused ultrasound (HIFU) beam generates radiation pressure in the fluid and can induce shear waves of sufficient amplitude to be visualized optically when the beam is modulated. By pulsing the HIFU beam, a train of shear waves are generated which propagate laterally from the focal region. The temperature and frequency dependent behavior of the HIFU generated shear waves are correlated with the rheological and microstructural properties of the fluid.

The assessment of the internal structural integrity of dry storage casks for used high burnup nuclear fuel assemblies is of critical importance before these are transported to permanent repositories. The size of the casks (5.2 m in height and 2.4 m in diameter), structural complexity, and the inability to access the interior make this a challenging task. This project addresses these difficulties through a multi-modal approach involving nuclear, charged particle, and acoustic methods. In this talk, we report on linear and nonlinear vibrational spectra of intact TN-32 casks. These studies use both impulsive and swept continuous-wave excitations with a variety of sensor placement configurations. From the resulting spectra, resonant frequencies, quality factors, and harmonic responses of various vibrational modes were determined. A detailed finite element model of the TN-32 was constructed and the experimental results are compared to the modal structure determined numerically. [This work was supported by DOE ...

Metamaterial and metasurface-based passive phased arrays provide novel means for the manipulation of acoustic fields. As passive elements, metasurfaces can provide local phase delays which enable the steering of sound fields and facilitate extraordinary wave phenomena. Some aspects that affect the performance of these passive elements include the spatial resolution/aliasing effect, the component resonances that shape the transmission spectra, and the thermoviscous losses that limit the transmission efficiency [X. Jiang, L. Yong, and L. Zhang, J. Acoust. Soc. Am. 141(4), EL363–368, April 2017]. Efficient acoustic field characterization is essential for investigating these issues with the ultimate aim of optimizing the geometrical parameters of the structure. This talk will address some details of the physics of metamaterial-based passive arrays and the broadband approach for assessing their transmission properties, with the aim of improving the design cycle and exploring novel uses.

Constructing tissue-mimicking phantoms of the brain for ultrasonic studies is complicated by the low backscatter coefficient of brain tissue, causing difficulties in simultaneously matching the backscatter and attenuation properties. In this work, we report on the development of a polyvinyl alcohol (PVA) based tissue-mimicking phantom with properties approaching those of white matter tissue. PVA was selected as the base material for the phantom as its properties can be varied by temperature cycling, variations in concentration and the addition of scattering inclusions, allowing some independent control of backscatter and attenuation. The ultrasonic properties (including speed of sound, attenuation, and backscatter) were optimized using these three methods with talcum powder as a scatterer. It was determined that the ultrasonic properties of the phantom produced in this study are best matched to brain tissue in the frequency range 1.0–2.5 MHz, indicating its utility for benchtop ultrasonic studies in this ...

Negative refraction and the associated lensing effect of a two-dimensional (2D) phononic crystal (PC) in the MHz regime were studied both experimentally and numerically. The PC consists of a hexagonal array of steel cylinders (r = 0.4 mm, a = 0.5 mm) in a methanol matrix for use in an aqueous medium. FEM simulations of the pressure field show negative refraction of plane waves through a prism shaped crystal and superresolution lensing through a rectangular crystal. These phenomena were observed with hydrophone scans of the transmitted pressure fields through the steel-methanol PC in a water tank.

Polycyclic aromatic hydrocarbons (PAHs) are generated from the incomplete combustion of organic matters in a wide variety of natural and man-made materials, such as fuels. It is important to develop an analytical technique for rapidly monitoring PAH generation at high temperatures during pyrolysis processes. This work describes a real-time and in situ technique using laser-induced fluorescence to detect PAH vapors at elevated temperatures. We report fluorescence spectra of several typical PAH model compounds, such as pyrene, phenanthrene and chrysene. We have also examined the temperature effects on PAH fluorescence spectra such as spectral shift, intensity and band width.

In this work, we present the fluorescence spectra of anthracene and pyrene vapors at different elevated temperatures (from 150 to 650 degrees C) excited with the 337 nm line of a nitrogen laser. We describe the high temperature effects on the resulting spectral properties including spectral intensity, spectral bandwidth and spectral shift. We found that the PAH fluorescence spectral bandwidths become very broad as the temperature increases. The broadening is mainly due to thermal vibrational sequence congestion. We also have found that the fluorescence intensity of pyrene vapor increases with increasing temperature, which results from the increase of the pyrene vapor absorption cross section at 337 nm.

In this work, the Kramers-Kronig (K-K) relations are applied to experimental data of resonant nature by limiting the interval of integration to the measurement spectrum. The data are from suspensions of encapsulated microbubbles (Albunex) and have the characteristics of an ultrasonic notch filter. The goal is to test the consistency of this dispersion and attenuation data with the Kramers-Kronig relations in a strict manner, without any parameters from outside the experimental bandwidth entering in to the calculations. In the course of reaching the goal, the artifacts associated with the truncation of the integrals are identified and it is shown how their impacts on the results can be minimized. The problem is first approached analytically by performing the Kramers-Kronig calculations over a restricted spectral band on a specific Hilbert transform pair (Lorentzian curves). The resulting closed-form solutions illustrate the type of artifacts that can occur due to truncation and also show that accurate results can be achieved. Next, both twice-subtracted and lower-order Kramers-Kronig relations are applied directly to the attenuation and dispersion data from the encapsulated microbubbles. Only parameters from within the experimental attenuation coefficient and phase velocity data sets are used. The twice-subtracted K-K relations produced accurate estimates for both the attenuation coefficient and dispersion across all 12 data sets. Lower-order Kramers-Kronig relations also produced good results over the finite spectrum for most of the data. In 2 of the 12 cases, the twice-subtracted relations tracked the data markedly better than the lower-order predictions. These calculations demonstrate that truncation artifacts do not overwhelm the causal link between the phase velocity and the attenuation coefficient for finite bandwidth calculations. This work provides experimental evidence supporting the validity of the subtracted forms of the acoustic K-K relations between the phase velocity and attenuation coefficient.

This article describes a lightweight, self-contained, field portable Raman instrument that has been developed for rapid on-site determination of primary mixture components. The instrument consists of a helium neon (HeNe) laser for excitation, an acousto-optic tunable filter (AOTF) for wavelength discrimination, and an avalanche photodiode for detection. The AOTF is the primary component of this system and has been selected based on its spectral range (600–900 nm) along with its high resolution, ∼7.5 cm−1. Labview™ based software for controlling the AOTF frequency and the signal acquisition has also been developed. Several different samples were analyzed (both solids and liquids) using this instrument for the evaluation of parameters such as spectral resolution, sensitivity, and data acquisition speed for certain environmentally important compounds. The results from these measurements are compared with those using a conventional laboratory Raman system consisting of a grating-based spectrograph and a charg...