The E12-14-012 experiment, performed in Jefferson Lab Hall A, has measured the $(e, e'p)$ cross section in parallel kinematics using a natural argon target. Here, we report the full results of the ...analysis of the data set corresponding to beam energy 2.222 GeV, and spanning the missing momentum and missing energy range $15 \lesssim p_m \lesssim 300$ MeV/c and $12 \lesssim E_m \lesssim 80$ MeV. The reduced cross section, determined as a function of $p_m$ and $E_m$ with $\approx$4\% accuracy, has been fitted using the results of Monte Carlo simulations involving a model spectral function and including the effects of final state interactions. The overall agreement between data and simulations turns out to be quite satisfactory ($\chi^2$/n.d.o.f.=1.9). Furthermore, the resulting spectral function will provide valuable new information, needed for the interpretation of neutrino interactions in liquid argon detectors.
This review article provides an overview of a range of recent technical developments in advanced arterial spin labeling (ASL) methods that have been developed or adopted by the community since the ...publication of a previous ASL consensus paper by Alsop et al. It is part of a series of review/recommendation papers from the International Society for Magnetic Resonance in Medicine Perfusion Study Group. Here, we focus on advancements in readouts and trajectories, image reconstruction, noise reduction, partial volume correction, quantification of nonperfusion parameters, fMRI, fingerprinting, vessel selective ASL, angiography, deep learning, and ultrahigh field ASL. We aim to provide a high level of understanding of these new approaches and some guidance for their implementation, with the goal of facilitating the adoption of such advances by research groups and by MRI vendors. Topics outside the scope of this article that are reviewed at length in separate articles include velocity selective ASL, multiple-timepoint ASL, body ASL, and clinical ASL recommendations.
ABSTRACT
We present the first characterization of the average dust attenuation curve at z ∼ 1.3 by combining rest-frame ultraviolet through near-IR photometry with Balmer decrement (H α/H β) ...constraints for ∼900 galaxies with 8 ≲ log (M⋆/M⊙) < 10.2 at 0.75 < z < 1.5 in the HST WFC3 IR Spectroscopic Parallel and 3D-HST grism surveys. Using galaxies in SDSS, we establish that the (H α + N ii)/O iii line ratio and stellar mass are good proxies for the Balmer decrement in low-spectral resolution grism data when only upper limits on H β are available and/or H α is blended with N ii. The slope of the z ∼ 1.3 attenuation curve ($A(0.15\, \rm{\mu m})/A(V)=3.15$) and its normalization (RV = 3.26) lie in-between the values found for z = 0 and z ∼ 2 dust attenuation curves derived with similar methods. These provide supporting evidence that the average dust attenuation curve of star-forming galaxies evolves continuously with redshift. The z ∼ 1.3 curve has a mild 2175 Å feature (bump amplitude, Eb = 0.83; ∼25 per cent that of the MW extinction curve), which is comparable to several other studies at 0 < z ≲ 3, and suggests that the average strength of this feature may not evolve significantly with redshift. The methods we develop to constrain dust attenuation from HST grism data can be applied to future grism surveys with JWST, Euclid, and RST. These new facilities will detect millions of emission line galaxies and offer the opportunity to significantly improve our understanding of how and why dust attenuation curves evolve.
The Van Allen Probes Electric Fields and Waves (EFW) instrument provided measurements of electric fields and spacecraft floating potentials over a wide dynamic range from DC to 6.5 kHz near the ...equatorial plane of the inner magnetosphere between 600 km altitude and 5.8 Re geocentric distance from October 2012 to November 2019. The two identical instruments provided data to investigate the quasi-static and low frequency fields that drive large-scale convection, waves induced by interplanetary shock impacts that result in rapid relativistic particle energization, ultra-low frequency (ULF) MHD waves which can drive radial diffusion, and higher frequency wave fields and time domain structures that provide particle pitch angle scattering and energization. In addition, measurements of the spacecraft potential provided a density estimate in cold plasmas (
<
20
eV
) from 10 to
3000
cm
−
3
. The EFW instrument provided analog electric field signals to EMFISIS for wave analysis, and it received 3d analog signals from the EMFISIS search coil sensors for inclusion in high time resolution waveform data.
The electric fields and potentials were measured by current-biased spherical sensors deployed at the end of four 50 m booms in the spacecraft spin plane (spin period
∼
11
sec
) and a pair of stacer booms with a total tip-tip separation of 15 m along the spin axis. Survey waveform measurements at 16 and/or 32 S/sec (with a nominal uncertainty of 0.3 mV/m over the prime mission) were available continuously while burst waveform captures at up to 16,384 S/sec provided high frequency waveforms.
This post-mission paper provides the reader with information useful for accessing, understanding and using EFW data. Selected science results are discussed and used to highlight instrument capabilities. Science quantities, data quality and error sources, and analysis routines are documented.
ABSTRACT
We present the first measurement of pulse scattering close to the eclipse region of PSR B1957+20, which is in a compact binary system with a low-mass star. We measured pulse scattering ...time-scales up to 0.2 ms close to the eclipse and showed that it scales with the dispersion measure (DM) excess roughly as τ ∝ ΔDM2. Our observations provide the first evidence of strong scattering due to multipath propagation effects in the eclipsing material. We show that Kolmogorov turbulence in the eclipsing material with an inner scale of ∼100 m and an outer scale of the size of the eclipse region can naturally explain the observation. Our results show that the eclipsing material in such systems can be highly turbulent and suggest that scattering is one of the main eclipsing mechanisms at around 1.4 GHz.
A new class of more effective lubricants could lead to huge energy savings. Limited recent literature has suggested potential for using room-temperature ionic liquids as lubricants, however, only a ...few out of millions (or more) of species possible have been evaluated. In this study, a series of new protic alkylammonium ionic liquids were synthesized by neutralization and metathesis reactions, and have demonstrated promising lubricating properties as neat lubricants or lubricant additives, particularly for use with difficult-to-lubricate metals like aluminum. More than a 30% friction reduction was observed with ammonium-based ionic liquids compared to conventional hydrocarbon oils in reciprocating sliding tests of 52100 bearing steel on aluminum alloy 6061-T6511. The inherent polarity of ionic liquids is believed to provide strong adsorption to contact surfaces and can form a boundary lubricating film leading to friction and wear reductions. Other advantages of ionic liquids include (1) negligible volatility, (2) high thermal stability, (3) non-flammability, and (4) better intrinsic properties that may eliminate the need for more complex and expensive additive packages. With very flexible molecular structures, this new class of lubricants, particularly ammonium-based ionic liquids, can be tailored to fit a variety of applications.
We report on carrier recombination within self-catalyzed InAs/InAlAs core–shell nanowires (NWs), disentangling recombination rates at the ends, sidewalls, and interior of the NWs. Ultrafast optical ...pump–probe spectroscopy measurements were performed from 77293 K on the free-standing, variable-sized NWs grown on lattice-mismatched Si(111) substrates, independently varying NW length and diameter. We found NW carrier recombination in the interior is nontrivial compared to the surface recombination, especially at 293 K. Surface recombination is dominated by carrier recombination at the NW sidewall, while contributions from the highly strained, impure NW base are negligible.
We report the discovery, mass, and radius determination of TOI-1801 b, a temperate mini-Neptune around a young M dwarf. TOI-1801 b was observed in TESS sectors 22 and 49, and the alert that this was ...a TESS planet candidate with a period of 21.3 days went out in April 2020. However, ground-based follow-up observations, including seeing-limited photometry in and outside transit together with precise radial velocity (RV) measurements with CARMENES and HIRES revealed that the true period of the planet is 10.6 days. These observations also allowed us to retrieve a mass of 5.74 ± 1.46
M
⊕
, which together with a radius of 2.08 ± 0.12
R
⊕
, means that TOI-1801 b is most probably composed of water and rock, with an upper limit of 2% by mass of H
2
in its atmosphere. The stellar rotation period of 16 days is readily detectable in our RV time series and in the ground-based photometry. We derived a likely age of 600–800 Myr for the parent star TOI-1801, which means that TOI-1801 b is the least massive young mini-Neptune with precise mass and radius determinations. Our results suggest that if TOI-1801 b had a larger atmosphere in the past, it must have been removed by some evolutionary mechanism on timescales shorter than 1 Gyr.
We study the process e^{+}e^{-}→Λ_{c}^{+}Λover ¯_{c}^{-} at twelve center-of-mass energies from 4.6119 to 4.9509 GeV using data samples collected by the BESIII detector at the BEPCII collider. The ...Born cross sections and effective form factors (|G_{eff}|) are determined with unprecedented precision after combining the single and double-tag methods based on the decay process Λ_{c}^{+}→pK^{-}π^{+}. Flat cross sections around 4.63 GeV are obtained and no indication of the resonant structure Y(4630), as reported by Belle, is found. In addition, no oscillatory behavior is discerned in the |G_{eff}| energy dependence of Λ_{c}^{+}, in contrast to what is seen for the proton and neutron cases. Analyzing the cross section together with the polar-angle distribution of the Λ_{c}^{+} baryon at each energy point, the moduli of electric and magnetic form factors (|G_{E}| and |G_{M}|) are extracted and separated. For the first time, the energy dependence of the form factor ratio |G_{E}/G_{M}| is observed, which can be well described by an oscillatory function.
Abstract
We report on an unusually bright observation of PSR J1720−0533 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The pulsar is in a black widow system that was ...discovered by the Commensal Radio Astronomy FAST Survey (CRAFTS). By coincidence, a bright scintillation maximum was simultaneous with the eclipse in our observation, which allowed for precise measurements of flux density variations, as well as dispersion measure (DM) and polarization. We found that there are quasi-periodic pulse emission variations with a modulation period of ∼22 s during the ingress of the eclipse, which could be caused by plasma lensing. No such periodic modulation was found during the egress of the eclipse. The linear polarization of the pulsar disappears before the eclipse, even before there is a visually obvious change in DM. We also found that the pulse scattering may play an important role in the eclipse of PSR J1720−0533.
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