18 research outputs found
New Critical Behavior in Einstein-Yang-Mills Collapse
We extend the investigation of the gravitational collapse of a spherically
symmetric Yang-Mills field in Einstein gravity and show that, within the black
hole regime, a new kind of critical behavior arises which separates black holes
formed via Type I collapse from black holes formed through Type II collapse.
Further, we provide evidence that these new attracting critical solutions are
in fact the previously discovered colored black holes with a single unstable
mode.Comment: 13 pages, 4 figure
TOI-2119: A transiting brown dwarf orbiting an active M-dwarf from NASA’s TESS mission
We report the discovery of TOI-2119b, a transiting brown dwarf (BD) that
orbits and is completely eclipsed by an active M-dwarf star. Using light curve
data from the Transiting Exoplanet Survey Satellite mission and follow-up
high-resolution Doppler spectroscopic observations, we find the BD has a radius
of , a mass of , an
orbital period of days, and an eccentricity of
. The host star has a mass of , a radius of , an effective
temperature of K, and a metallicity of . TOI-2119b joins an emerging population of transiting BDs
around M-dwarf host stars, with TOI-2119 being the ninth such system. These
M-dwarf--brown dwarf systems typically occupy mass ratios near , which separates them from the typical mass ratios for systems
with transiting substellar objects and giant exoplanets that orbit more massive
stars. The nature of the secondary eclipse of the BD by the star enables us to
estimate the effective temperature of the substellar object to be K, which is consistent with predictions by substellar evolutionary models.Comment: 14 pages, 13 figures, 4 tables, accepted in MNRA
Ejecta Evolution Following a Planned Impact into an Asteroid: The First Five Weeks
The impact of the DART spacecraft into Dimorphos, moon of the asteroid
Didymos, changed Dimorphos' orbit substantially, largely from the ejection of
material. We present results from twelve Earth-based facilities involved in a
world-wide campaign to monitor the brightness and morphology of the ejecta in
the first 35 days after impact. After an initial brightening of ~1.4
magnitudes, we find consistent dimming rates of 0.11-0.12 magnitudes/day in the
first week, and 0.08-0.09 magnitudes/day over the entire study period. The
system returned to its pre-impact brightness 24.3-25.3 days after impact
through the primary ejecta tail remained. The dimming paused briefly eight days
after impact, near in time to the appearance of the second tail. This was
likely due to a secondary release of material after re-impact of a boulder
released in the initial impact, through movement of the primary ejecta through
the aperture likely played a role.Comment: 16 pages, 5 Figures, accepted in the Astrophysical Journal Letters
(ApJL) on October 16, 202
Ejecta Evolution Following a Planned Impact into an Asteroid: The First Five Weeks
The impact of the Double Asteroid Redirection Test spacecraft into Dimorphos, moon of the asteroid Didymos, changed Dimorphos’s orbit substantially, largely from the ejection of material. We present results from 12 Earth-based facilities involved in a world-wide campaign to monitor the brightness and morphology of the ejecta in the first 35 days after impact. After an initial brightening of ∼1.4 mag, we find consistent dimming rates of 0.11–0.12 mag day−1 in the first week, and 0.08–0.09 mag day−1 over the entire study period. The system returned to its pre-impact brightness 24.3–25.3 days after impact though the primary ejecta tail remained. The dimming paused briefly eight days after impact, near in time to the appearance of the second tail. This was likely due to a secondary release of material after re-impact of a boulder released in the initial impact, though movement of the primary ejecta through the aperture likely played a role
Operation of Cs-Sb-O activated GaAs in a high voltage DC electron gun at high average current
Negative Electron Affinity (NEA) activated GaAs photocathodes are the most
popular option for generating a high current (> 1 mA) spin-polarized electron
beam. Despite its popularity, a short operational lifetime is the main drawback
of this material. Recent works have shown that the lifetime can be improved by
using a robust Cs-Sb-O NEA layer with minimal adverse effects. In this work, we
operate GaAs photocathodes with this new activation method in a high voltage
environment to extract a high current. We observed spectral dependence on the
lifetime improvement. In particular, we saw a 45% increase in the lifetime at
780 nm for Cs-Sb-O activated GaAs compared to Cs-O activated GaAs.Comment: 7 pages, 6 figure
Recommended from our members
Four-dimensional emittance measurements of ultrafast electron diffraction optics corrected up to sextupole order
Ultrafast electron diffraction (UED) is a technique in which short-pulse electron beams can probe the femtosecond-scale evolution of atomic structure in matter driven far from equilibrium. As an accelerator physics challenge, UED imposes stringent constraints on the brightness of the probe electron beam. The low normalized emittance employed in UED, often at the 10-nm scale and below, is particularly sensitive to both applied field aberrations and space-charge effects. The role of aberrations is increasingly important in small probe systems that often feature multiple orders of magnitude variations in beam size during transport. In this work, we report the correction of normal quadrupole, skew quadrupole, and sextupole aberrations via dedicated corrector elements in an ultrafast electron microdiffraction beamline. To do this, we generate precise four-dimensional phase space maps of rf-compressed electron beams and find excellent agreement with aberration-free space-charge simulations. Finally, we discuss the role a probe-forming aperture can play in improving the brightness of bunches with appreciable space-charge effects
Recommended from our members
Balloon pulmonary angioplasty outcomes in patients previously treated by pulmonary endarterectomy surgery are inferior to those of inoperable patients.
Funder: NonePulmonary endarterectomy (PEA) may not achieve full clearance of vascular obstructions in patients with more distal chronic thromboembolic pulmonary hypertension (CTEPH). Balloon pulmonary angioplasty (BPA) may be indicated to treat these residual vascular lesions. We compared whether patients post-PEA (PP) treated by BPA derived similar benefit to those who had inoperable CTEPH (IC), and assessed predictors of BPA response after surgery. We treated 109 patients with BPA-89 with IC and 20 PP. Serial right heart catheterization performed at baseline (immediately before BPA) and 3 months after completing BPA, compared pulmonary vascular resistance (PVR), mean pulmonary artery pressure (mPAP) as well as change in WHO functional class and 6-minute walk distance. We also assessed the impact of total thrombus tail length (TTTL) from photographed PEA surgical specimens and PP computed tomography pulmonary angiography (CTPA)-quantified residual disease burden on BPA response. PP and IC groups did not differ significantly in terms of demographics, baseline hemodynamics or procedural characteristics. However, IC derived greater hemodynamic benefit from BPA: ΔPVR (-27.9 ± 20.2% vs. -13.9 ± 23.9%, p < 0.05) and ΔmPAP (-17.1 ± 14.4% vs. -8.5 ± 18.0%, p < 0.05). There was a negative correlation between pre-BPA PVR and TTTL (r = -0.47, p < 0.05) which persisted post-BPA. PVR, mPAP, WHO FC and 6MWD were not improved significantly post-BPA in PP patients. BPA response was not related to TTTL terciles or CTPA-quantified residual disease burden. Patients PP experienced inferior response to BPA, despite similar baseline and procedural characteristics to IC. BPA does not abolish the relationship between TTTL and postsurgical PVR in PP patients, suggesting that BPA is less effective in treating residual PH after surgery in an experienced surgical center
Balloon pulmonary angioplasty outcomes in patients previously treated by pulmonary endarterectomy surgery are inferior to those of inoperable patients
Abstract Pulmonary endarterectomy (PEA) may not achieve full clearance of vascular obstructions in patients with more distal chronic thromboembolic pulmonary hypertension (CTEPH). Balloon pulmonary angioplasty (BPA) may be indicated to treat these residual vascular lesions. We compared whether patients post‐PEA (PP) treated by BPA derived similar benefit to those who had inoperable CTEPH (IC), and assessed predictors of BPA response after surgery. We treated 109 patients with BPA—89 with IC and 20 PP. Serial right heart catheterization performed at baseline (immediately before BPA) and 3 months after completing BPA, compared pulmonary vascular resistance (PVR), mean pulmonary artery pressure (mPAP) as well as change in WHO functional class and 6‐minute walk distance. We also assessed the impact of total thrombus tail length (TTTL) from photographed PEA surgical specimens and PP computed tomography pulmonary angiography (CTPA)‐quantified residual disease burden on BPA response. PP and IC groups did not differ significantly in terms of demographics, baseline hemodynamics or procedural characteristics. However, IC derived greater hemodynamic benefit from BPA: ΔPVR (−27.9 ± 20.2% vs. −13.9 ± 23.9%, p < 0.05) and ΔmPAP (−17.1 ± 14.4% vs. −8.5 ± 18.0%, p < 0.05). There was a negative correlation between pre‐BPA PVR and TTTL (r = −0.47, p < 0.05) which persisted post‐BPA. PVR, mPAP, WHO FC and 6MWD were not improved significantly post‐BPA in PP patients. BPA response was not related to TTTL terciles or CTPA‐quantified residual disease burden. Patients PP experienced inferior response to BPA, despite similar baseline and procedural characteristics to IC. BPA does not abolish the relationship between TTTL and postsurgical PVR in PP patients, suggesting that BPA is less effective in treating residual PH after surgery in an experienced surgical center
Challenges and opportunities for neuroimaging in young patients with traumatic brain injury: a coordinated effort towards advancing discovery from the ENIGMA pediatric moderate/severe TBI group
Traumatic brain injury (TBI) is a major cause of death and disability in children in both developed and developing nations. Children and adolescents suffer from TBI at a higher rate than the general population, and specific developmental issues require a unique context since findings from adult research do not necessarily directly translate to children. Findings in pediatric cohorts tend to lag behind those in adult samples. This may be due, in part, both to the smaller number of investigators engaged in research with this population and may also be related to changes in safety laws and clinical practice that have altered length of hospital stays, treatment, and access to this population. The ENIGMA (Enhancing NeuroImaging Genetics through Meta-Analysis) Pediatric Moderate/Severe TBI (msTBI) group aims to advance research in this area through global collaborative meta-analysis of neuroimaging data. In this paper, we discuss important challenges in pediatric TBI research and opportunities that we believe the ENIGMA Pediatric msTBI group can provide to address them. With the paucity of research studies examining neuroimaging biomarkers in pediatric patients with TBI and the challenges of recruiting large numbers of participants, collaborating to improve statistical power and to address technical challenges like lesions will significantly advance the field. We conclude with recommendations for future research in this field of study