Fundamentals of picosecond laser ultrasonics.

The aim of this article is to provide an introduction to picosecond laser ultrasonics, a means by which gigahertz-terahertz ultrasonic waves can be generated and detected by ultrashort light pulses. This method can be used to characterize materials with nanometer spatial resolution. With reference to key experiments, we first review the theoretical background for normal-incidence optical detection in opaque single-layer isotropic thin films. The theory is extended to handle isotropic multilayer samples, and again compared to experiment. We then review applications to anisotropic samples, including oblique-incidence optical probing, and treat the generation and detection of shear waves. Solids including metals and semiconductors are mainly discussed, although liquids are briefly mentioned. © 2014 Elsevier B.V. All rights reserved

Deep-Learning-Assisted Resonant Ultrasound Spectroscopy for Cubic Solids

This paper solves a long-standing problem in resonant ultrasound spectroscopy (RUS) for cubic solids through the use of two-dimensional deep learning (DL). By means of inverse methods, conventional RUS can determine all independent elastic constants of a crystalline solid specimen by comparing measured and calculated free-vibration resonance frequencies. However, to avoid invalid local minima in the inverse process, good initial guesses of the elastic constants must be available. Here, we propose a DL scheme to remedy this problem, which utilizes an input elasticity image composed of three layers obtained from resonance frequency data. After network training, this scheme is executed in two steps: DL processing by a neural network to output elastic constants in a Blackman diagram classification, followed by the use of a regression network around the classified point in this diagram for more accurate determination. By means of simulations, we demonstrate that this DL scheme yields the principal elastic constants within an error of approximately 5% without any inverse processing even in the unfavorable case of five missing modes for 111 existing cubic crystals.Fukuda Hiroki, Nagakubo Akira, Wright Oliver B., et al. Deep-Learning-Assisted Resonant Ultrasound Spectroscopy for Cubic Solids. Physical Review Applied 20, 228 (2023); https://doi.org/10.1103/physrevapplied.20.034048

PSL Icing Facility Upgrade Overview

The NASA Glenn Research Center Propulsion Systems Lab (PSL) was recently upgraded to perform engine inlet ice crystal testing in an altitude environment. The system installed 10 spray bars in the inlet plenum for ice crystal generation using 222 spray nozzles. As an altitude test chamber, the PSL is capable of simulating icing events at altitude in a groundtest facility. The system was designed to operate at altitudes from 4,000 to 40,000 ft at Mach numbers up to 0.8M and inlet total temperatures from -60 to +15 degF. This paper and presentation will be part of a series of presentations on PSL Icing and will cover the development of the icing capability through design, developmental testing, installation, initial calibration, and validation engine testing. Information will be presented on the design criteria and process, spray bar developmental testing at Cox and Co., system capabilities, and initial calibration and engine validation test. The PSL icing system was designed to provide NASA and the icing community with a facility that could be used for research studies of engine icing by duplicating in-flight events in a controlled ground-test facility. With the system and the altitude chamber we can produce flight conditions and cloud environments to simulate those encountered in flight. The icing system can be controlled to set various cloud uniformities, droplet median volumetric diameter (MVD), and icing water content (IWC) through a wide variety of conditions. The PSL chamber can set altitudes, Mach numbers, and temperatures of interest to the icing community and also has the instrumentation capability of measuring engine performance during icing testing. PSL last year completed the calibration and initial engine validation of the facility utilizing a Honeywell ALF502-R5 engine and has duplicated in-flight roll back conditions experienced during flight testing. This paper will summarize the modifications and buildup of the facility to accomplish these tests

Intergroup contact and social change: Implications of negative and positive contact for collective action in advantaged and disadvantaged groups

Previous research has shown that (1) positive intergroup contact with an advantaged group can discourage collective action among disadvantaged-group members and (2) positive intergroup contact can encourage advantaged-group members to take action on behalf of disadvantaged outgroups. Two studies investigated the effects of negative as well as positive intergroup contact. Study 1 (N = 482) found that negative but not positive contact with heterosexual people was associated with sexual-minority students’ engagement in collective action (via group identification and perceived discrimination). Among heterosexual students, positive and negative contact were associated with, respectively, more and less LGB activism. Study 2 (N = 1,469) found that only negative contact (via perceived discrimination) predicted LGBT students’ collective action intentions longitudinally while only positive contact predicted heterosexual/cisgender students’ LGBT activism. Implications for the relationship between intergroup contact, collective action, and social change are discussed

Active chiral control of GHz acoustic whispering-gallery modes

We selectively generate chiral surface-acoustic whispering gallery modes in the gigahertz range on a microscopic disk by means of an ultrafast time-domain technique incorporating a spatial light modulator. Active chiral control is achieved by making use of an optical pump spatial profile in the form of a semicircular arc, positioned on the sample to break the symmetry of clockwise- and counterclockwise-propagating modes. Spatiotemporal Fourier transforms of the interferometrically monitored two-dimensional acoustic fields measured to micron resolution allow individual chiral modes and their azimuthal mode order, both positive and negative, to be distinguished. In particular, for modes with 15-fold rotational symmetry, we demonstrate ultrafast chiral control of surface acoustic waves in a micro-acoustic system with picosecond temporal resolution. Applications include nondestructive testing and surface acoustic wave devices

IRAC Imaging of Lockman Hole

IRAC imaging of a 4'7x4'7 area in the Lockman Hole detected over 400 galaxies in the IRAC 3.6 micron and 4.5 micron bands, 120 in the 5.8 micron, and 80 in the 8 micron bandin 30 minutes of observing time. Color-color diagrams suggest that about half of these galaxies are at redshifts 0.6<z<1.3 with about a quarter at higher redshifts (z>1.3). We also detect IRAC counterparts for 6 of the 7 SCUBA sources and all 9 XMM sources in this area. The detection of the counterparts of the SCUBA sources and galaxies at z>1.3 demonstrates the ability of IRAC to probe the universe at very high redshifts.Comment: 11 pages, 2 figures. accepted by ApJS, Spizter Special Issu

Rapid progression is associated with lymphoid follicle dysfunction in SIV-infected infant rhesus macaques.

HIV-infected infants are at an increased risk of progressing rapidly to AIDS in the first weeks of life. Here, we evaluated immunological and virological parameters in 25 SIV-infected infant rhesus macaques to understand the factors influencing a rapid disease outcome. Infant macaques were infected with SIVmac251 and monitored for 10 to 17 weeks post-infection. SIV-infected infants were divided into either typical (TypP) or rapid (RP) progressor groups based on levels of plasma anti-SIV antibody and viral load, with RP infants having low SIV-specific antibodies and high viral loads. Following SIV infection, 11 out of 25 infant macaques exhibited an RP phenotype. Interestingly, TypP had lower levels of total CD4 T cells, similar reductions in CD4/CD8 ratios and elevated activation of CD8 T cells, as measured by the levels of HLA-DR, compared to RP. Differences between the two groups were identified in other immune cell populations, including a failure to expand activated memory (CD21-CD27+) B cells in peripheral blood in RP infant macaques, as well as reduced levels of germinal center (GC) B cells and T follicular helper (Tfh) cells in spleens (4- and 10-weeks post-SIV). Reduced B cell proliferation in splenic germinal GCs was associated with increased SIV+ cell density and follicular type 1 interferon (IFN)-induced immune activation. Further analyses determined that at 2-weeks post SIV infection TypP infants exhibited elevated levels of the GC-inducing chemokine CXCL13 in plasma, as well as significantly lower levels of viral envelope diversity compared to RP infants. Our findings provide evidence that early viral and immunologic events following SIV infection contributes to impairment of B cells, Tfh cells and germinal center formation, ultimately impeding the development of SIV-specific antibody responses in rapidly progressing infant macaques

The challenges of intersectionality: Researching difference in physical education

Researching the intersection of class, race, gender, sexuality and disability raises many issues for educational research. Indeed, Maynard (2002, 33) has recently argued that ‘difference is one of the most significant, yet unresolved, issues for feminist and social thinking at the beginning of the twentieth century’. This paper reviews some of the key imperatives of working with ‘intersectional theory’ and explores the extent to these debates are informing research around difference in education and Physical Education (PE). The first part of the paper highlights some key issues in theorising and researching intersectionality before moving on to consider how difference has been addressed within PE. The paper then considers three ongoing challenges of intersectionality – bodies and embodiment, politics and practice and empirical research. The paper argues for a continued focus on the specific context of PE within education for its contribution to these questions