3,378 research outputs found
Ground State Properties of Anderson Impurity in a Gapless Host
Using the Bethe ansatz method, we study the ground state properties of a
Anderson impurity in a ``gapless'' host, where a density of band
states vanishes at the Fermi level as . As
in metals, the impurity spin is proven to be screened at arbitrary parameters
of the system. However, the impurity occupancy as a function of the bare
impurity energy is shown to acquire novel qualitative features which
demonstrate a nonuniversal behavior of the system. The latter explains why the
Kondo screening is absent (or exists only at quite a large electron-impurity
coupling) in earlier studies based on scaling arguments.Comment: 5 pages, no figure, RevTe
Strategies for Supporting Teachers’ Instructional and Mental Health Needs during the COVID Pandemic in Maine and Other States
The Maine Educational Policy Research Institute (MEPRI) report based on a study of the strategies and challenges involved in supporting preK–12 students and teachers during the COVID-19 pandemic
Strategies for Supporting Student Learning Needs during the COVID Pandemic in Maine and Other States
Maine Educational Policy Research Institute (MEPRI) report based on a study of the strategies and challenges involved in supporting preK–12 students and teachers during the COVID-19 pandemic
Effects of Activation Drills Combined with Dynamic Warmup on Performance Field Tests
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Multi-Wavelength Coverage of State Transitions in the New Black Hole X-Ray Binary Swift J1910.2-0546
Understanding how black holes accrete and supply feedback to their
environment is one of the outstanding challenges of modern astrophysics. Swift
J1910.2-0546 is a candidate black hole low-mass X-ray binary that was
discovered in 2012 when it entered an accretion outburst. To investigate the
binary configuration and the accretion morphology we monitored the evolution of
the outburst for ~3 months at X-ray, UV, optical (B,V,R,I), and near-infrared
(J,H,K) wavelengths using Swift and SMARTS. The source evolved from a hard to a
soft X-ray spectral state with a relatively cold accretion disk that peaked at
~0.5 keV. A Chandra/HETG spectrum obtained during this soft state did not
reveal signatures of an ionized disk wind. Both the low disk temperature and
the absence of a detectable wind could indicate that the system is viewed at
relatively low inclination. The multi-wavelength light curves revealed two
notable features that appear to be related to X-ray state changes. Firstly, a
prominent flux decrease was observed in all wavebands ~1-2 weeks before the
source entered the soft state. This dip occurred in (0.6-10 keV) X-rays ~6 days
later than at longer wavelengths, which could possibly reflect the viscous time
scale of the disk. Secondly, about two weeks after the source transitioned back
into the hard state, the UV emission significantly increased while the X-rays
steadily decayed. We discuss how these observations may reflect changes in the
accretion flow morphology, perhaps related to the quenching/launch of a jet or
the collapse/recovery of a hot flow.Comment: 8 pages, 5 figures, 1 table. To be published in Ap
Multichannel pseudogap Kondo model: Large-N solution and quantum-critical dynamics
We discuss a multichannel SU(N) Kondo model which displays non-trivial
zero-temperature phase transitions due to a conduction electron density of
states vanishing with a power law at the Fermi level. In a particular large-N
limit, the system is described by coupled integral equations corresponding to a
dynamic saddle point. We exactly determine the universal low-energy behavior of
spectral densities at the scale-invariant fixed points, obtain anomalous
exponents, and compute scaling functions describing the crossover near the
quantum-critical points. We argue that our findings are relevant to recent
experiments on impurity-doped d-wave superconductors.Comment: 4 pages, 3 figs; extended discussion of large-N spin representations,
added references; accepted for publication in PR
The Effects of Ketone Supplementation on Recovery in Collegiate Male Soccer Players: Pilot Trial
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Correlated variability in the blazar 3C 454.3
The blazar 3C 454.3 was revealed by the Fermi Gamma-ray Space Telescope to be
in an exceptionally high flux state in July 2008. Accordingly, we performed a
multi-wavelength monitoring campaign on this blazar using IR and optical
observations from the SMARTS telescopes, optical, UV and X-ray data from the
Swift satellite, and public-release gamma-ray data from Fermi. We find an
excellent correlation between the IR, optical, UV and gamma-ray light curves,
with a time lag of less than one day. The amplitude of the infrared variability
is comparable to that in gamma-rays, and larger than at optical or UV
wavelengths. The X-ray flux is not strongly correlated with either the
gamma-rays or longer wavelength data. These variability characteristics find a
natural explanation in the external Compton model, in which electrons with
Lorentz factor gamma~10^(3-4) radiate synchrotron emission in the
infrared-optical and also scatter accretion disk or emission line photons to
gamma-ray energies, while much cooler electrons (gamma~10^(1-2)) produce X-rays
by scattering synchrotron or other ambient photons.Comment: 7 pages, 3 figures, submitted to ApJ Letter
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