ABSTRACT
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 Rb = 1.08 ± 0.03RJ, a mass of Mb = 64.4 ± 2.3MJ, an orbital period of P = 7.200865 ± 0.00002 d, and an eccentricity of e = 0.337 ± 0.002. The host star has a mass of M⋆ = 0.53 ± 0.02M⊙, a radius of R⋆ = 0.50 ± 0.01R⊙, an effective temperature of Teff = 3621 ± 48K, and a metallicity of $\rm Fe/H=+0.06\pm 0.08$. 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 q = Mb/M⋆ ≈ 0.1−0.2, 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 2030 ± 84K, which is consistent with predictions by substellar evolutionary models.
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.
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 \(R_b = 1.08 \pm 0.03{\rm R_J}\), a mass of \(M_b = 64.4 \pm 2.3{\rm M_J}\), an orbital period of \(P = 7.200865 \pm 0.00002\) days, and an eccentricity of \(e=0.337\pm 0.002\). The host star has a mass of \(M_\star = 0.53 \pm 0.02{\rm M_\odot}\), a radius of \(R_\star= 0.50 \pm 0.01{\rm R_\odot}\), an effective temperature of \(T_{\rm eff} = 3621 \pm 48\)K, and a metallicity of \(\rm Fe/H=+0.06\pm 0.08\). 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 \(q = M_b/M_\star \approx 0.1-0.2\), 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 \(2030\pm 84\)K, which is consistent with predictions by substellar evolutionary models.
Research shows that approximately 14% of school age children with mild traumatic brain injury (TBI) including sports-related concussions (SRCs) remain symptomatic three months after injury. Advanced ...imaging studies early after injury have shown evidence of axonal damage, reduced N-acetyl aspartate (NAA) and impaired cerebral blood flow (CBF) in individuals with mild TBI. This study was undertaken to determine whether these techniques can provide valuable information in pediatric SRC patients with persistent post-concussive symptoms. Fifteen pediatric subjects ages 8 to 17 years with persistent post-concussive symptoms were evaluated using perfusion-weighted imaging (PWI), three-dimensional (3D) magnetic resonance spectroscopic imaging, and diffusion tensor imaging (DTI) three to 12 months post-SRC. Data were compared with 15 demographically similar (age, gender, and body mass index) controls. In the bilateral thalami, SRC patients showed reduced CBF (p=0.02 and p=0.02) and relative cerebral blood volume (CBV; p=0.05 and p=0.03), compared with controls. NAA/creatine (Cr) and NAA/choline (Cho) ratios were reduced in the corpus callosum (p=0.003; p=0.05) and parietal white matter (p<0.001; p=0.006) of SRC subjects, compared with controls. Significant differences in DTI metrics differentiated patients with cognitive symptoms, compared with those without cognitive symptoms and controls. Advanced imaging methods detect a spectrum of injury including impaired axonal function, neuronal metabolism and perfusion, suggesting involvement of the neurovascular unit in the presence of persistent symptoms in pediatric SRC patients.
We report the design, fabrication, and characterization of colloidal PbSe nanocrystal (NC)-based photovoltaic test structures that exhibit an excitonic solar cell mechanism. Charge extraction from ...the NC active layer is driven by a photoinduced chemical potential energy gradient at the nanostructured heterojunction. By minimizing perturbation to PbSe NC energy levels and thereby gaining insight into the “intrinsic” photovoltaic properties and charge transfer mechanism of PbSe NC, we show a direct correlation between interfacial energy level offsets and photovoltaic device performance. Size dependent PbSe NC energy levels were determined by cyclic voltammetry and optical spectroscopy and correlated to photovoltaic measurements. Photovoltaic test structures were fabricated from PbSe NC films sandwiched between layers of ZnO nanoparticles and PEDOT:PSS as electron and hole transporting elements, respectively. The device current−voltage characteristics suggest a charge separation mechanism that is distinct from previously reported Schottky devices and consistent with signatures of excitonic solar cells. Remarkably, despite the limitation of planar junction structure, and without film thickness optimization, the best performing device shows a 1-sun power conversion efficiency of 3.4%, ranking among the highest performing NC-based solar cells reported to date.
HERACLES: A high-voltage DC test beamline for high average current photocathodes Andorf, Matthew; Bae, Jai Kwan; Bartnik, Adam ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
July 2023, 2023-07-00, 2023-07-01, Letnik:
1052, Številka:
C
Journal Article
Recenzirano
We present commissioning results of the High ElectRon Average Current for Lifetime ExperimentS (HERACLES) beamline at Cornell University. 10 mA average beam current at 200 keV was achieved with a ...Cs3Sb photocathode operated with an Argon laser at 488 nm. HERACLES is intended to be a test facility to improve the robustness of photocathodes developed for high average current beam operation in conjunction with the Cornell photocathode laboratory.
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 demonstrate that improved chemical resistance of Cs–Sb–O activated GaAs photocathodes allowed them to survive a day-long transport process from a separate vacuum system using a vacuum suitcase. During beam running, we observed spectral dependence on lifetime improvement. In particular, we saw a 45% increase in the lifetime at 780 nm on average for Cs–Sb–O activated GaAs compared to Cs–O activated GaAs.
•Identified Capto adhere condition separating antibody large hinge fragment.•Hydrophobic interactions and hydrogen bonding mediated removal.•Labeling with sulfo-NHS acetate showed hinge region ...interaction with the resin.•Operation at high pH favored mixed mode interactions between LHF hinge and ligand.•Optimization of separation for successful use in a manufacturing process.
Efforts to increase monoclonal antibody expression in cell culture can result in the presence of fragmented species requiring removal in downstream processing. Capto adhere, HEA Hypercel, and PPA Hypercel anion exchange/hydrophobic interaction mixed mode resins were evaluated for their fragment removal capabilities and found to separate large hinge IgG1 antibody fragment (LHF) from monomer. Removal of greater than 75% of LHF population occurred at pH 8 and low conductivity. The mechanism of fragment removal was investigated in two series of experiments. The first experimental series consisted of comparison to chromatographic behavior on corresponding single mode resins. Both single mode anion exchange and hydrophobic interaction resins failed to separate LHF. The second experimental series studied the impact of phase modifiers, ethylene glycol, urea, and arginine on the mixed mode mediated removal. The addition of ethylene glycol decreased LHF removal by half. Further decreases in LHF separation were seen upon incubation with urea and arginine. Therefore, it was discovered that the purification is the result of a mixed mode phenomena dominated by hydrophobic interaction and hydrogen bonding effects. The site of interaction between the LHF and mixed mode resin was determined by chemical labeling of lysine residues with sulfo-NHS acetate. The labeling identified the antibody hinge and light chain regions as mediating the fragment separation. Sequence analysis showed that under separation conditions, a hydrophobic proline patch and hydrogen bonding serine and threonine residues mediate the hinge interaction with the Capto adhere ligand. Additionally, a case study is presented detailing the optimization of fragment removal using Capto adhere resin to achieve purity and yield targets in a manufacturing facility. This study demonstrated that mixed mode resins can be readily integrated into commercial antibody platform processes when additional chromatographic abilities are required.
Cognitive reserve is one's mental resilience or resistance to the effects of structural brain damage. Reserve effects are well established in people with multiple sclerosis (PwMS) and Alzheimer's ...disease, but the neural basis of this phenomenon is unclear. We aimed to investigate whether preservation of functional connectivity explains cognitive reserve. Seventy‐four PwMS and 29 HCs underwent neuropsychological assessment and 3 T MRI. Structural damage measures included gray matter (GM) atrophy and network white matter (WM) tract disruption between pairs of GM regions. Resting‐state functional connectivity was also assessed. PwMS exhibited significantly impaired cognitive processing speed (t = 2.14, p = .037) and visual/spatial memory (t = 2.72, p = .008), and had significantly greater variance in functional connectivity relative to HCs within relevant networks (p < .001, p < .001, p = .016). Higher premorbid verbal intelligence, a proxy for cognitive reserve, predicted relative preservation of functional connectivity despite accumulation of GM atrophy (standardized‐β = .301, p = .021). Furthermore, preservation of functional connectivity attenuated the impact of structural network WM tract disruption on cognition (β = −.513, p = .001, for cognitive processing speed; β = −.209, p = .066, for visual/spatial memory). The data suggests that preserved functional connectivity explains cognitive reserve in PwMS, helping to maintain cognitive capacity despite structural damage.
Negative Electron Affinity (NEA) activated GaAs photocathodes are the most popular option for generating a high current (Formula: see text1 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 demonstrate that improved chemical resistance of Cs–Sb–O activated GaAs photocathodes allowed them to survive a day-long transport process from a separate vacuum system using a vacuum suitcase. During beam running, we observed spectral dependence on lifetime improvement. In particular, we saw a 45% increase in the lifetime at 780 nm on average for Cs–Sb–O activated GaAs compared to Cs–O activated GaAs.
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