The spatial evolution of acoustic waveforms produced by a laboratory-scale Mach 3 jet are investigated using both 1∕4 in. and 1∕8 in. pressure field microphones located along rays emanating from the postpotential core where the peak sound emission is found to occur. The measurements are acquired in a fully anechoic chamber, where ground or other large surface reflections are minimal. Various statistical metrics are examined along the peak emission path, where they are shown to undergo rapid changes within 2m from the source region. An experimentally validated wave-packet model is then used to confirm the location where the pressure amplitude along the peak emission path transitions from cylindrical to spherical decay. Various source amplitudes, provided by the wave-packet model, are then used to estimate shock formation distance and Gol’dberg numbers for diverging waves. The findings suggest that cumulative nonlinear distortion is likely to occur at laboratory scale near the jet flow, where the waveform amplitude decays cylindrically, but less likely to occur farther from the jet flow, where the waveform amplitude decays spherically. Direct inspection of the raw time series reveals how steepened waveforms are generated by rogue like waves that form from the constructive interference of waves from neighboring sources as opposed to classical cumulative nonlinear distortion.
Abstract. We illustrate wide-field imaging of skin using a structured light (SL) approach that highlights the contrast from superficial tissue scattering. Setting the spatial frequency of the SL in a regime that limits the penetration depth effectively gates the image for photons that originate from the skin surface. Further, rendering the SL images in a color format provides an intuitive format for viewing skin pathologies. We demonstrate this approach in skin pathologies using a custom-built handheld SL imaging system.
A theoretical combustion model is developed to simulate the influence of ideal gas effects on various aeroacoustic parameters over a range of equivalence ratios. The motivation is to narrow the gap between laboratory and full-scale jet noise testing. The combustion model is used to model propane combustion in air and kerosene combustion in air. Gas properties from the combustion model are compared to real lab data acquired at the National Center for Physical Acoustics at the University of Mississippi as well as outputs from NASA’s Chemical Equilibrium Analysis code. Different jet properties are then studied over a range of equivalence ratios and pressure ratios for propane combustion in air, kerosene combustion in air and heated air. The findings reveal negligible differences between the three constituents where the density and sound speed ratios are concerned. Albeit, the area ratio required for perfectly expanded flow is shown to be more sensitive to gas properties, relative to changes in the temperature ratio.
This study develops synthetic strategies for N,N-trans and N,N-cis Re(O)(LO–N)2Cl complexes and investigates the effects of the coordination spheres and ligand structures on ancillary ligand exchange dynamics and catalytic perchlorate reduction activities of the corresponding [Re(O)(LO–N)2]+ cations. The 2-(2′-hydroxyphenyl)-2-oxazoline (Hhoz) and 2-(2′-hydroxyphenyl)-2-thiazoline (Hhtz) ligands are used to prepare homoleptic N,N-trans and N,N-cis isomers of both Re(O)(hoz)2Cl and Re(O)(htz)2Cl and one heteroleptic N,N-trans Re(O)(hoz)(htz)Cl. Selection of hoz/htzligands determines the preferred isomeric coordination sphere, and the use of substituted pyridine bases with varying degrees of steric hindrance during complex synthesis controls the rate of isomer interconversion. The five corresponding [Re(O)(LO–N)2]+ cations exhibit a wide range of solvent exchange rates (1.4 to 24,000 s–1 at 25 °C) and different LO–N movement patterns, as influenced by the coordination sphere of Re (trans/cis), the noncoordinating heteroatom on LO–N ligands (O/S), and the combination of the two LO–N ligands (homoleptic/heteroleptic). Ligand exchange dynamics also correlate with the activity of catalytic reduction of aqueous ClO4– by H2 when the Re(O)(LO–N)2Cl complexes are immobilized onto Pd/C. Findings from this study provide novel synthetic strategies and mechanistic insights for innovations in catalytic, environmental, and biomedical research.
Aqueous dispersions of iron oxide nanoparticles with a high initial magnetic susceptibility (χi) are of interest as contrast agents in electromagnetic tomography. Nanoclusters composed of iron oxide primary particles were formed by co-precipitation of Fe(II) and Fe(III) chlorides at alkaline conditions and high temperature of 95 °C. Two-step addition of citrate was used to produce large primary particles and then stabilize the nanoclusters. The size of the primary particles was tuned from 5 nm to 15 nm by varying the citrate/iron precursor ratio during the normal phase hydrolysis reaction, while the second iteration of citrate stabilized the nanoclusters with hydrodynamic diameters of 30–75 nm. The crystallinity of the iron oxide nanoparticles was promoted by annealing at 95 °C and systematically studied with Superconducting Quantum Interference Device (SQUID), Vibrating Sample Magnetometer (VSM), Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD). The dependence of χi was examined over a range of low volume fractions (0.005 < θ < 0.02) to understand the magnetic behavior of dispersions. The χi of the dispersions increased markedly with the size and concentration of the constituent primary particles, reaching an unusually high value of 0.85 at 1.6% v/v for 15 nm primary particles, which is 2–3 times higher than that for typical commercial ferrofluids. The high χi values are favored by the high crystallinity and the large magnetic diameter of 9.3 nm, indicating a relatively thin surface nonmagnetic layer where the spin orientations are disordered.
Coherent thermal phonons (CTPs) play an important role in thermal transport in superlattice (SL) structures. To have a profound understanding of CTP transport in SL, direct measurement of CTP properties is necessary. In this study, coherent phonon spectroscopy has been utilized to generate and detect CTP in Bi2Te3/Sb2Te3 SL. Phonon lifetimes have been extracted from experimental data, with which mode-wise thermal conductivities have been calculated. Comparing with bulk Bi2Te3, the estimated mode-wise thermal conductivity of longitudinal acoustic phonons shifts to higher frequencies, due to constructive coherent phonon interference. Our results suggest that it is possible to use SL structure to manipulate coherent phonon propagation and to tailor thermal conductivity.
BACKGROUND: Dietary canthaxanthin (CX), 25-hydroxycholecalciferol (25-OH-D 3 ) and vitamins have been widely reported to be involved in productive and reproductive performance of broiler breeders. However, limited information is available for duck breeders. In this study, a total of 1,560 Cherry Valley SM3 duck breeder females and 312 males were used to assess if the addition of CX and 25-OH-D3 could increase the performance of duck breeders under two different dietary vitamin regimens. Four diets were used under a 2 x 2 factorial arrangement with 2 kinds of vitamin premixes (REGULAR and HIGH; HIGH premix had higher levels of all vitamins except K3 than REGULAR premix), and with or without the supplementation of the mixture of CX (6 mg/kg) and 25-OH-D3 (0.069 mg/kg). The ducks were fed ad libitum with pelleted diets based on corn-soybean meal from 38 to 77 wk of age. RESULTS: HIGH vitamin premix decreased malondialdehyde (MDA) level (P < 0.001) of egg yolk, increased hatchability of fertile eggs (P = 0.029), increased hatchability of total eggs (P = 0.029), and decreased serum protein carbonyl level (P = 0.037) of breeder males. The mixture of CX and 25-OH-D3 increased serum calcium of breeder females (P = 0.010), decreased the cracked egg rate (P = 0.001), increased the pigmentation of egg yolk (P < 0.001) and male bill (P < 0.001), and decreased MDA level of egg yolk (P < 0.001) and male serum (P = 0.034). Interactive effects were observed in cracked egg rate (P = 0.038), shell thickness (P = 0.011) and serum phosphorus (P = 0.026) of breeder females. HIGH vitamin premix together with the mixture of CX and 25-OH-D3 decreased cracked egg rate and increased shell thickness of duck breeders. Serum phosphorus was decreased in duck breeder females fed REGULAR vitamin premix without the addition of the CX and 25-OH-D3 mixture. CONCLUSIONS: Dietary HIGH vitamin premix increased antioxidant status of eggs and breeder males, and increased hatchability. The mixture of CX and 25-OH-D3 enhanced egg shell quality, and promoted pigmentation and antioxidant status of eggs and breeder males.
The effect of stagger startup on the vibro-acoustic loads that form during the end-effects regime of clustered rockets is studied using both full-scale (hot-gas) and laboratory scale (cold gas) data with vehicle geometry. Both configurations comprise three nozzles with thrust optimized parabolic contours that undergo free shock separated flow and restricted shock separated flow as well as an end-effects regime prior to flowing full. Acoustic pressure waveforms recorded at the base of the nozzle cluster are analyzed using various statistical metrics as well as time-frequency analysis. The findings reveal a significant reduction in end-effects regime loads when engine ignition is staggered. However, regardless of stagger, both the skewness and kurtosis of the acoustic pressure time derivative elevate to the same levels during the end-effects regime thereby demonstrating the intermittence and impulsiveness of the acoustic waveforms that form during engine startup.