1,343 research outputs found
Impact of Caloric Intake on Parenteral Nutrition–Associated Intestinal Morphology and Mucosal Barrier Function
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142275/1/jpen0474.pd
Galactic Coronae in the Intracluster Environment: Semi-confined Stellar-feedback-driven Outflows
Recently X-ray observations have shown the common presence of compact
galactic coronae around intermediate-mass spheroid galaxies embedded in the
intracluster/intragroup medium (ICM). We conduct 2-D hydrodynamic simulations
to study the quasi-steady-state properties of such coronae as the natural
products of the ongoing distributed stellar feedback semi-confined by the
thermal and ram pressures of the ICM. We find that the temperature of a
simulated corona depends primarily on the specific energy of the feedback,
consistent with the lack of the correlation between the observed hot gas
temperature and K-band luminosity of galaxies. The simulated coronae typically
represent subsonic outflows, chiefly because of the semi-confinement. As a
result, the hot gas density increases with the ICM thermal pressure. The ram
pressure, on the other hand, chiefly affects the size and lopsidedness of the
coronae. The density increase could lead to the compression of cool gas clouds,
if present, and hence the formation of stars. The increase also enhances
radiative cooling of the hot gas, which may fuel central supermassive black
holes, explaining the higher frequency of active galactic nuclei observed in
clusters than in the field. The radiation enhancement is consistent with a
substantially higher surface brightness of the X-ray emission detected from
coronae in cluster environment. The total X-ray luminosity of a corona,
however, depends on the relative importance of the surrounding thermal and ram
pressures. These environment dependences should at least partly explain the
large dispersion in the observed diffuse X-ray luminosities of spheroids with
similar stellar properties. Furthermore, we show that an outflow powered by the
distributed feedback can naturally produce a positive radial gradient in the
hot gas entropy, mimicking a cooling flow.Comment: accepted by MNRAS, comments are welcom
The Geometry of an Electron Scale Magnetic Cavity in the Plasma Sheet
Electron scale magnetic cavities are electron vortex structures formed in turbulent plasma, while the evolution and electron dynamics of these structures have not been fully understood. Recently, highâ energy, angular, and temporal electron measurements from Magnetospheric Multiscale have enabled the application of an energetic particle sounding technique to these structures. This study analyzes an electron scale magnetic cavity observed by Magnetospheric Multiscale on 7 May 2015 in the plasma sheet. A comprehensive sounding technique is applied to obtain the geometry and propagation velocities of the boundaries. The result shows that the scale size of the structure is â ¼90 km, and the leading and trailing boundaries are moving in the same direction but with different speeds (â ¼11.5 ± 2.2 and â ¼18.1 ± 3.4 km/s, respectively). The speed difference suggests a shrinking of the structure that may play a significant role in magnetic energy dissipation and electron energization of electron scale magnetic cavities.Plain Language SummaryElectron scale magnetic cavities are extremely small vortices frequently found in space plasma environments, where a cavity of the depressed magnetic field contains energetic electrons forming a ringâ like current at electron scale. The formation of these structures is thought to be linked to energy cascade in plasma turbulence, while the mechanism and process of the energy transformation are not clear. In this paper we discuss an electron scale magnetic cavity in the terrestrial plasma sheet with a modified particle sounding technique proposed and applied to the boundaries, suggesting that the structure is shrinking. This analysis may provide new insight into understanding the evolution and electron energization of these structures.Key PointsA comprehensive energetic particle sounding technique is applied to detect the geometry of an electron scale magnetic cavityThe boundary loss plays a significant role in forming electron nonâ gyrotropic distributions in the cavityMoving speed obtained by the technique is higher for the trailing boundary than the leading boundary suggesting a shrinkage of the cavityPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151894/1/grl59390.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151894/2/grl59390_am.pd
Does Sensory Function Decline Independently or Concomitantly with Age? Data from the Baltimore Longitudinal Study of Aging
Objectives. To investigate whether sensory function declines independently or in parallel with age within a single individual. Methods. Cross-sectional analysis of Baltimore Longitudinal Study of Aging (BLSA) participants who underwent vision (visual acuity threshold), proprioception (ankle joint proprioceptive threshold), vestibular function (cervical vestibular-evoked myogenic potential), hearing (pure-tone average audiometric threshold), and Health ABC physical performance battery testing. Results. A total of 276 participants (mean age 70 years, range 26–93) underwent all four sensory tests. The function of all four systems declined with age. After age adjustment, there were no significant associations between sensory systems. Among 70–79-year-olds, dual or triple sensory impairment was associated with poorer physical performance. Discussion. Our findings suggest that beyond the common mechanism of aging, other distinct (nonshared) etiologic mechanisms may contribute to decline in each sensory system. Multiple sensory impairments influence physical performance among individuals in middle old-age (age 70–79)
Chalcogenide Glass-on-Graphene Photonics
Two-dimensional (2-D) materials are of tremendous interest to integrated
photonics given their singular optical characteristics spanning light emission,
modulation, saturable absorption, and nonlinear optics. To harness their
optical properties, these atomically thin materials are usually attached onto
prefabricated devices via a transfer process. In this paper, we present a new
route for 2-D material integration with planar photonics. Central to this
approach is the use of chalcogenide glass, a multifunctional material which can
be directly deposited and patterned on a wide variety of 2-D materials and can
simultaneously function as the light guiding medium, a gate dielectric, and a
passivation layer for 2-D materials. Besides claiming improved fabrication
yield and throughput compared to the traditional transfer process, our
technique also enables unconventional multilayer device geometries optimally
designed for enhancing light-matter interactions in the 2-D layers.
Capitalizing on this facile integration method, we demonstrate a series of
high-performance glass-on-graphene devices including ultra-broadband on-chip
polarizers, energy-efficient thermo-optic switches, as well as graphene-based
mid-infrared (mid-IR) waveguide-integrated photodetectors and modulators
Interference in interacting quantum dots with spin
We study spectral and transport properties of interacting quantum dots with
spin. Two particular model systems are investigated: Lateral multilevel and two
parallel quantum dots. In both cases different paths through the system can
give rise to interference. We demonstrate that this strengthens the multilevel
Kondo effect for which a simple two-stage mechanism is proposed. In parallel
dots we show under which conditions the peak of an interference-induced orbital
Kondo effect can be split.Comment: 8 pages, 8 figure
A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles
In recent years, there has been a dramatic increase in the use of unmanned
aerial vehicles (UAVs), particularly for small UAVs, due to their affordable
prices, ease of availability, and ease of operability. Existing and future
applications of UAVs include remote surveillance and monitoring, relief
operations, package delivery, and communication backhaul infrastructure.
Additionally, UAVs are envisioned as an important component of 5G wireless
technology and beyond. The unique application scenarios for UAVs necessitate
accurate air-to-ground (AG) propagation channel models for designing and
evaluating UAV communication links for control/non-payload as well as payload
data transmissions. These AG propagation models have not been investigated in
detail when compared to terrestrial propagation models. In this paper, a
comprehensive survey is provided on available AG channel measurement campaigns,
large and small scale fading channel models, their limitations, and future
research directions for UAV communication scenarios
CHANG-ES XXIX: the sub-kpc nuclear bubble of NGC 4438
Active galactic nucleus (AGN) bubbles could play an important role in accelerating high-energy cosmic rays (CRs) and galactic feedback. Only in nearby galaxies could we have high enough angular resolution in multiwavelengths to study the sub-kpc environment of the AGN, where the bubbles are produced and strongly interact with the surrounding interstellar medium. In this paper, we present the latest Chandra observations of the Virgo cluster galaxy NGC 4438, which hosts multiscale bubbles detected in various bands. The galaxy also has low current star formation activity, so these bubbles are evidently produced by the AGN rather than a starburst. We present spatially resolved spectral analysis of the Chandra data of the ∼3 arcsec × 5 arcsec (∼200 pc×350 pc) nuclear bubble of NGC 4438. The power-law tail in the X-ray spectra can be most naturally explained as synchrotron emission from high-energy CR leptons. The hot gas temperature increases, while the overall contribution of the non-thermal X-ray emission decreases with the vertical distance from the galactic plane. We calculate the synchrotron cooling time-scale of the CR leptons responsible for the non-thermal hard X-ray emission to be only a few tens to a few hundreds of years. The thermal pressure of the hot gas is about three times the magnetic pressure, but the current data cannot rule out the possibility that they are still in pressure balance. The spatially resolved spectroscopy presented in this paper may have important constraints on how the AGN accelerates CRs and drives outflows. We also discover a transient X-ray source only ∼5 arcsec from the nucleus of NGC 4438. The source was not detected in 2002 and 2008, but became quite X-ray bright in 2020 March, with an average 0.5–7 keV luminosity of ∼1039 erg s−1. © 2022 The Author(s)
Published by Oxford University Press on behalf of Royal Astronomical Society.The authors also acknowledge the financial support from NASA and the Chandra X-ray Center through the grant GO9-20074X. TW acknowledges financial support from the coordination of the participation in SKA-SPAIN, financed by the Ministry of Science and Innovation (MCIN), and from the State Agency for Research of the Spanish Ministry of Science, Innovation and Universities through the ‘Centre of Excellence Severo Ochoa’ award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709).Peer reviewe
Estimation and inference under economic restrictions
Estimation of economic relationships often requires imposition of constraints such as positivity or monotonicity on each observation. Methods to impose such constraints, however, vary depending upon the estimation technique employed. We describe a general methodology to impose (observation-specific) constraints for the class of linear regression estimators using a method known as constraint weighted bootstrapping. While this method has received attention in the nonparametric regression literature, we show how it can be applied for both parametric and nonparametric estimators. A benefit of this method is that imposing numerous constraints simultaneously can be performed seamlessly. We apply this method to Norwegian dairy farm data to estimate both unconstrained and constrained parametric and nonparametric models
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