1,915 research outputs found
Harmonic Labeling of Graphs
Which graphs admit an integer value harmonic function which is injective and
surjective onto ? Such a function, which we call harmonic labeling, is
constructed when the graph is the square grid. It is shown that for any
finite graph containing at least one edge, there is no harmonic labeling of
Competency Corner, Part Three: Practice-based Weightings of the CBPS
The ïŹrst two articles in this series outlined the task, research, terminology and processes the Competence Committee used to develop the Competency-based Performance Standards (CBPS). These standards were designed as a framework for revision of the Canadian Standard Assessment in Optometry (CSAO) to directly link the exam and practice requirements of Canadian Optometrists. This linkage required determination of the relative weight to be assigned to each of the various competencies. Working groups of practising optometrists rated the frequency and criticality of performance of each of the competencies using a standardized rating system. Results indicated that the majority of a revised CSAO would focus on providing comprehensive eye and vision care (78%), followed by management (11%) and collaboration (10%). The ratings also allowed calculation of the appropriate weighting of the underlying general attributes. The heaviest weighting was assigned to candidatesâ professional optometric knowledge and the ability to apply this knowledge (41%), followed by communication (27%), planning (13%), ethics (11%) and self-directed learning (8%). The last article in this series will describe work to evaluate the competence-based weightings of the current CSAO and to describe plans for future versions of the CSAO
Obsessive and Compulsive Characteristics of Craving for Alcohol in Alcohol Abuse and Dependence
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65211/1/j.1530-0277.1992.tb01375.x.pd
Fermi-surface transformation across the pseudogap critical point of the cuprate superconductor LaNdSrCuO
The electrical resistivity and Hall coefficient R of the
tetragonal single-layer cuprate Nd-LSCO were measured in magnetic fields up to
T, large enough to access the normal state at , for closely
spaced dopings across the pseudogap critical point at .
Below , both coefficients exhibit an upturn at low temperature, which
gets more pronounced with decreasing . Taken together, these upturns show
that the normal-state carrier density at drops upon entering the
pseudogap phase. Quantitatively, it goes from at to at . By contrast, the mobility does not change appreciably, as
revealed by the magneto-resistance. The transition has a width in doping and
some internal structure, whereby R responds more slowly than to the
opening of the pseudogap. We attribute this difference to a Fermi surface that
supports both hole-like and electron-like carriers in the interval , with compensating contributions to R. Our data are in excellent
agreement with recent high-field data on YBCO and LSCO. The quantitative
consistency across three different cuprates shows that a drop in carrier
density from to is a universal signature of the pseudogap
transition at . We discuss the implication of these findings for the
nature of the pseudogap phase.Comment: 11 pages, 12 figure
Effects of exercise and environmental complexity on deficits in trace and contextual fear conditioning produced by neonatal alcohol exposure in rats
In rodents, voluntary exercise and environmental complexity increases hippocampal neurogenesis and reverses spatial learning and long-term potentiation deficits in animals prenatally exposed to alcohol. The present experiment extended these findings to neonatal alcohol exposure and to delay, trace, and contextual fear conditioning. Rats were administered either 5.25g/kg/day alcohol via gastric intubation or received sham-intubations (SI) between Postnatal Day (PD) 4 and 9 followed by either free access to a running wheel on PD 30-41 and housing in a complex environment on PD 42-72 (wheel-running plus environmental complexity; WREC) or conventional social housing (SHSH) from PD 30 to 72. Adult rats (PD 80 +/- 5) received 5 trials/day of a 10-s flashing-light conditioned stimulus (CS) paired with .8mA footshock either immediately (delay conditioning) or after a 10-s trace interval (trace conditioning) for 2 days. Neonatal alcohol exposure impaired context and trace conditioning, but not short-delay conditioning. The WREC intervention did not reverse these deficits, despite increasing context-related freezing in ethanol-exposed and SI animals. (c) 2012 Wiley Periodicals, Inc. Dev Psychobiol 55: 483-495, 201
ETHOS -- An Effective Theory of Structure Formation: Impact of Dark Acoustic Oscillations on Cosmic Dawn
Upcoming data of the 21-cm hydrogen line during cosmic dawn ()
will revolutionize our understanding of the astrophysics of the first galaxies.
Here we present a case study on how to exploit those same measurements to learn
about the nature of dark matter (DM) at small scales. Focusing on the Effective
Theory of Structure Formation (ETHOS) paradigm, we run a suite of simulations
covering a broad range of DM microphysics, connecting the output of -body
simulations to dedicated 21-cm simulations to predict the evolution of the
21-cm signal across the entire cosmic dawn. We find that observatories
targeting both the global signal and the 21-cm power spectrum are sensitive to
all ETHOS models we study, and can distinguish them from CDM if the suppression
wavenumber is smaller than Mpc, even when accounting for
feedback with a phenomenological model. This is an order of magnitude smaller
comoving scales than currently constrained by other data sets, including the
Lyman- forest. Moreover, if a prospective 21-cm detection confirmed a
deficiency of power at small scales, we show that ETHOS models with strong dark
acoustic oscillations can be discriminated from the pure suppression of warm
dark matter, showing the power of 21-cm data to understand the behavior of DM
at the smallest physical scales.Comment: 16 pages, 16 figures. Comments are welcom
Lifshitz critical point in the cuprate superconductor YBa2Cu3Oy from high-field Hall effect measurements
The Hall coefficient R_H of the cuprate superconductor YBa2Cu3Oy was measured
in magnetic fields up to 60 T for a hole concentration p from 0.078 to 0.152,
in the underdoped regime. In fields large enough to suppress superconductivity,
R_H(T) is seen to go from positive at high temperature to negative at low
temperature, for p > 0.08. This change of sign is attributed to the emergence
of an electron pocket in the Fermi surface at low temperature. At p < 0.08, the
normal-state R_H(T) remains positive at all temperatures, increasing
monotonically as T \to 0. We attribute the change of behaviour across p = 0.08
to a Lifshitz transition, namely a change in Fermi-surface topology occurring
at a critical concentration p_L = 0.08, where the electron pocket vanishes. The
loss of the high-mobility electron pocket across p_L coincides with a ten-fold
drop in the conductivity at low temperature, revealed in measurements of the
electrical resistivity at high fields, showing that the so-called
metal-insulator crossover of cuprates is in fact driven by a Lifshitz
transition. It also coincides with a jump in the in-plane anisotropy of ,
showing that without its electron pocket the Fermi surface must have strong
two-fold in-plane anisotropy. These findings are consistent with a
Fermi-surface reconstruction caused by a unidirectional spin-density wave or
stripe order.Comment: 16 pages, 13 figures, see associated Viewpoint: M. Vojta, Physics 4,
12 (2011
Properties of High-Latitude CME-Driven Disturbances During Ulysses Second Northern Polar Passage
Ulysses observed five coronal mass ejections (CMEs) and their associated disturbances while the spacecraft was immersed in the polar coronal hole (CH) flow above 70° N in late 2001. Of these CMEs, two were very fast (\u3e850 km sâ1) driving strong shocks in the wind ahead, and two others were over-expanding. The two fast CMEs were observed leaving the Sun by LASCO/SOHO, and were observed in the ecliptic by Genesis and ACE. These were large events, spanning at least from the northern heliospheric pole to the ecliptic. One-dimensional hydrodynamic simulations indicate that these could be described as overpressured CMEs launched from the Sun at speeds initially faster than ambient, but then decelerating to the ambient solar wind speed as they propagated outward. The two over-expanding CMEs mark their first occurrence since Ulyssesâ first orbit when such CMEs were only observed in polar CH flow
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