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Effect of layer thickness on spatters oxidation of Hastelloy X alloy during powder bed fusion-laser beam processing
Full text linkThis study investigates the impact of powder layer thickness on spatter generation and oxidation behavior during the processing of Hastelloy X. In-situ monitoring using optical tomography reveals that thicker powder layers result in a higher number of hot spatters generated during laser-melt-powder interaction. Scanning electron microscopy and Auger electron spectroscopy analysis demonstrate the presence of different types of spatters that oxidize differently depending on their origin. X-ray photoelectron spectroscopy analysis further shows that the surface enrichment of oxide-forming elements such as Al, Ti, Cr, and Fe varies with the type of spatter particle. Additionally, depth profile analysis using X-ray photoelectron spectroscopy indicates that the average oxide layer thickness increases from ∼2.5 nm in virgin to ∼68 nm in spatters generated at 150 μm powder layer thickness. The findings suggest that powder layer thickness is a crucial factor in controlling spatter generation and oxidation behavior during powder bed fusion-laser beam processing
VLBI astrometry on the white dwarf pulsar AR Scorpii
Full text linkAR Scorpii (AR Sco), the only-known radio-pulsing white dwarf binary, shows unusual pulsating emission at the radio, infrared, optical, and ultraviolet bands. To determine its astrometric parameters at the radio band independently, we conducted multi-epoch Very Long Baseline Interferometry (VLBI) phase-referencing observations with the European VLBI Network at 5 GHz and the Chinese VLBI Network plus the Warkworth 30-m telescope (New Zealand) at 8.6 GHz. By using the differential VLBI astrometry, we provide high-precision astrometric measurements on the parallax (pi = 8.52(-0.07)(+0.04) mas) and proper motion (mu(alpha) = 9.48(-0.07)(+0.04) mas yr(-1), mu(delta) = -51.32(-0.38)(+0.22) mas yr (-1)). The new VLBI results agree with the optical Gaia astrometry. Our kinematic analysis reveals that the Galactic space velocities of AR Sco are quite consistent with that of both intermediate polars and polars. Combined with the previous tightest VLBI constraint on the size, our parallax distance suggests that the radio emission of AR Sco should be located within the light cylinder of its white dwarf
Classifiability of crossed products by nonamenable groups
Full text linkWe show that all amenable, minimal actions of a large class of nonamenable countable groups on compact metric spaces have dynamical comparison. This class includes all nonamenable hyperbolic groups, many HNN-extensions, nonamenable Baumslag-Solitar groups, a large class of amalgamated free products, lattices in many Lie groups, A2-groups, as well as direct products of the above with arbitrary countable groups. As a consequence, crossed products by amenable, minimal and topologically free actions of such groups on compact metric spaces are Kirchberg algebras in the UCT class, and are therefore classified by K-theory
Social Regulation of Learning in Tracks
No full textA presentation on my current research into the Tracks program
Chokepoint capitalism [Brief Reviews of Books and Products]
Full text linkThis is a book review of: Giblin, R., & Doctorow, C. (2022).\ua0Chokepoint Capitalism. Beacon Press.\ua0312\ua0pp.,\ua0ISBN\ua0978-080700706-8,\ua026.95\ua0USD (hardcover);\ua0ISBN 9780807007075 (ebook)
Charge Localization in Acene Crystals from Ab Initio Electronic Structure
Full text linkThe performance of Koopmans-compliant hybrid functionals in reproducing the electronic structure of organic crystals is tested for a series of acene crystals. The calculated band gaps are found to be consistent with those achieved with the GW method at a fraction of the computational cost and in excellent accord with the experimental results at room temperature, when including the thermal renormalization. The energetics of excess holes and electrons reveals a struggle between polaronic localization and band-like delocalization. The consequences of these results on the transport properties of acene crystals are discussed
Optimization of Channel Structures in InP HEMT Technology for Cryogenic Low-Noise and Low-Power Operation
No full textWe report the impact from channel composition on the cryogenic low-noise performance at low dc power for a 100-nm gate-length InGaAs-InAlAs-InP high-electron mobility transistor (HEMT). Two indium (In) channel compositions, 65% and 80%, were studied by dc and RF characterization at 300 and 5 K. For the cryogenic low-noise optimization, it was important to increase the transconductance to gate–source capacitance ratio in the weak inversion region implying that a higher maximum cutoff frequency in the HEMT does not guarantee lower noise. The HEMT noise performance was obtained from noise measurements in a hybrid three-stage 4–8-GHz ( -band) low-noise amplifier (LNA) down to 300- W dc power dissipation. While the HEMT LNA noise performance for both the channel compositions at 300 K was found to be comparable, the HEMT LNA at 5 K with 65% In channel showed a minimum noise temperature of 1.4 K, whereas the noise temperature in the HEMT LNA with 80% In channel HEMTs increased to 2.4 K. The difference in the noise became more pronounced at reduced dc power dissipation. The ultralow dc power of 300 W demonstrated for a cryogenic -band LNA with an average noise temperature of 2.9 K and 24-dB gain is of interest for future qubit read-out electronics at 4 K
Wisp: Drones as Companions for Breathing
No full textThe spectrum of applications for social drones is broadening as they become an increasingly accessible technology. In order to expand on the immensely rich but poorly researched field of Human-Drone Interaction (HDI), we present a minimal, explorative, and anti-solutionist design. We describe the first steps of a Research through Design (RtD) project focused on the concept-driven exploration of an unlikely pairing: drones and breathing. We present Wisp, a micro-drone probe controlled by a user’s breath. Informed by experts on breathing, drawing inspiration from soma design, Wisp is described as platform for the development of defamiliarising views towards intimate somatic interactions between humans and drones. In this paper we describe the initial studies in a RtD development process, including expert interviews, prototyping, and informal evaluations. We contribute to the field of HDI with a design composite framework combining soma design and slow technology for exploratory somatic slow interactions between humans and drones
Nonlinear modelling of unimorph and bimorph magneto-electro-elastic energy harvesters
No full textThis paper nonlinearly models cantilever-based functionally graded magneto-electro-elastic energy harvesters (FGMEEEH) for the first time. The coupled magneto-electro-mechanical model is obtained on the basis of the Euler-Bernoulli beam theory. A hybrid procedure including Ritz\u27s method is then utilized to generate reduced order models for both asymmetric unimorph and symmetric bimorph configurations. The resulting sets of initial value problems, whose convergence will be examined, are then analytically solved using the method of multiple time scales for both the free vibrations and primary resonance cases. The analytical time-histories of the system are compared by those obtained numerically and excellent agreements between them are observed. In addition, simplifying the frequency response function of the system in the primary resonance case, the present findings are validated by those available in the literature for linear unimorph systems. The influences of the harvester configurations, base acceleration amplitude, the value of the tip mass, the material gradation index as well as the resistances of the piezoelectric and magnetic circuits on the nonlinear response of the system are also studied in detail. It is observed that FGMEEEEHs enjoy much more efficiency in comparison to piezoelectric-based systems
Defecation, littering and other acts of public disturbance in pandemic times – A study of a Scandinavian city
Full text linkThe spatiotemporal patterns of public disturbance acts are investigated in Stockholm, the capital of Sweden. Using crowdsourced data, the number of records is compared 15 months before and after the stay-at-home measures of the COVID-19 pandemic, controlling for seasonal trends. Poisson-Gamma-CAR regression models are implemented to assess the potential impact of land use on the spatial distribution of public disturbance acts, accounting for the effect of pandemic restrictions and differences in neighborhood context. Findings show that, with the exception of abandoned vehicles, there was a significant increase in records of public disturbance after the 2020 stay-at-home pandemic restrictions. Parks, transport hubs and less importantly, schools were significantly associated with public disturbances, controlling for neighborhood characteristics and reporting practices. Recommendations are made for research and practice