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.
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.