The Hydrogen Clouds of M33

Quasi-one-dimensional iron chalcogenides possess various magnetic states depending on the lattice distortion, electronic correlations, and presence of defects. We present neutron diffraction and inelastic neutron scattering experiments on the spin ladder compound BaFe2−δS1.5Se1.5 with ∼6% iron vacancies. The data reveal that long-range magnetic order is absent, while the characteristic magnetic excitations that correspond to both the stripe- and block-type antiferromagnetic correlations are observed. First-principles calculations support the existence of both stripe- and block-type antiferromagnetic short-range orders in the experimental sample. The disappearance of long-range magnetic order may be due to the competition between these two magnetic orders, which is greatly enhanced for a certain concentration of iron vacancies, which we calculate to be about 6%, consistent with the measured iron vacancy concentration. Our results highlight how iron vacancies in the iron-based spin ladder system strongly influence the magnetic ground state.

This paper presents an analysis of acoustic radiation characteristics of a T-7A-installed F404 engine, as derived from far-field measurements. Radiated directivity at different engine conditions is compared with contemporary investigations into Mach wave radiation. The peak directivity angles observed in the far-field are used to evaluate appropriate values for the convective Mach number. It is shown that velocity from the convective Mach number is approximately 70% of the centerline jet velocity, agreeing with contemporary supersonic jet noise literature. Spatiospectral maps from far-field data indicate the presence of spatiospectral lobes, like those observed in the near field. These spatiospectral maps also illustrate interference nulls caused by ground reflection interference. A ground reflection model is used to attempt to correct these errors. Using these corrected data, the overall sound power level is calculated and is used to find the acoustic radiation efficiency, a value rarely calculated for jet engines. The F404 OAPWL is proportional to Uₑ⁸ subsonically, and Uₑ³ supersonically. The efficiency at afterburner exists between 0.5% and 0.8%, exhibiting similar acoustic efficiency trends as those seen in launch vehicles 50 years ago.

Acoustic source characterization of full-scale supersonic jets remains a vital component of understanding jet noise. Identification of fundamental characteristics such as source location(s) and directivity will better inform physical understanding, noise models, engine design, and noise reduction technologies. This paper investigates an installed F404-GE-103 engine as an acoustic source using statistically optimized near-field acoustical holography (SONAH) for engine conditions ranging from 50% thrust to afterburner. Partial field decomposition is used to characterize the coherent nature of the source as a function of frequency. Spatiospectral reconstructions along the nozzle lipline show distinct behavior at different engine conditions. Lower engine conditions show two energetic spatial regions along the lipline from 200-300 Hz. Three distinct local maxima are observed at AB. These maxima are correlated with other studies about supersonic jet noise sources in the literature. Mach wave radiation is thought to be tied to the first two local maxima, which occur throughout the shear layer, ending ahead of the approximate supersonic core tip. The third, lower-frequency maximum is proposed to be correlated with noise from large-scale turbulence structures.

Spatiospectral lobes are still-unexplained phenomena seen in noise radiation from multiple high-performance aircraft. These lobes are observed as multiple peaks in noise spectra at a given field location or as multiple local maxima in noise directivity at a single frequency. Using hybrid beamforming with a 120-microphone near-field array, the lobe characteristics are studied for a GE F404 engine installed on a T-7A aircraft at different engine conditions. Both the measured and reconstructed fields show multiple spatiospectral lobes at different engine conditions, and the overall noise directivity is identified as being the superposition of multiple distinct lobes. The individual lobes appear, shift aft, and then disappear with increasing frequency, which is opposite the behavior of overall noise directivity. The lobes are ray-traced back to the jet centerline to determine an apparent acoustic source location and it is concluded that each lobe originates from a different source within the jet.

The VERsatile DIffractometer will set a new standard for a world-class magnetic diffractometer with versatility for both powder and single crystal samples and capability for wide-angle polarization analysis. The instrument will utilize a large single-frame bandwidth and will offer high-resolution at low momentum transfers and excellent signal-to-noise ratio. A horizontal elliptical mirror concept with interchangeable guide pieces will provide high flexibility in beam divergence to allow for a high-resolution powder mode, a high-intensity single crystal mode, and a polarized beam option. A major science focus will be quantum materials that exhibit emergent properties arising from collective effects in condensed matter. The unique use of polarized neutrons to isolate the magnetic signature will provide optimal experimental input to state-of-the-art modeling approaches to access detailed insight into local magnetic ordering.

Traditional collimators typically require large optics and/or long pathlengths which makes miniaturization difficult. Carbon nanotube templated microfabrication offers a solution to pattern small 3D structures, such as parallel hole collimators. Here we present the characterization of a carbon nanotube parallel hole collimator design and its efficacy in visible and short wavelength infrared light. Comparison to geometric and far field diffraction models are shown to give a close fit, making this a promising technology for miniaturized diffuse light collimation.