5,981 research outputs found
Civil protective orders effective in stopping or reducing partner violence: challenges remain in rural areas with access and enforcement
Civil protective orders are a low cost, effective solution in either stopping or significantly reducing partner violence for women. While all women benefit from civil protective orders, this brief finds there are greater obstacles to enforcement in rural places, which result in less benefit for rural than urban women. The authors suggest that policies and services should be tailored to address community-specific barriers and differences such as hours of access, time it takes to obtain or serve an order, and access to information about the process
Spectral scaling and quantum critical behaviour in the pseudogap Anderson model
The pseudogap Anderson impurity model provides a classic example of an
essentially local quantum phase transition. Here we study its single-particle
dynamics in the vicinity of the symmetric quantum critical point (QCP)
separating generalized Fermi liquid and local moment phases, via the local
moment approach. Both phases are shown to be characterized by a low-energy
scale that vanishes at the QCP; and the universal scaling spectra, on all
energy scales, are obtained analytically. The spectrum precisely at the QCP is
also obtained; its form showing clearly the non-Fermi liquid, interacting
nature of the fixed point.Comment: 7 pages, 2 figure
Single-particle dynamics of the Anderson model: a local moment approach
A non-perturbative local moment approach to single-particle dynamics of the
general asymmetric Anderson impurity model is developed. The approach
encompasses all energy scales and interaction strengths. It captures thereby
strong coupling Kondo behaviour, including the resultant universal scaling
behaviour of the single-particle spectrum; as well as the mixed valent and
essentially perturbative empty orbital regimes. The underlying approach is
physically transparent and innately simple, and as such is capable of practical
extension to lattice-based models within the framework of dynamical mean-field
theory.Comment: 26 pages, 9 figure
Ecological Effects of Fear: How Spatiotemporal Heterogeneity in Predation Risk Influences Mule Deer Access to Forage in a Sky‐Island System
Forage availability and predation risk interact to affect habitat use of ungulates across many biomes. Within sky‐island habitats of the Mojave Desert, increased availability of diverse forage and cover may provide ungulates with unique opportunities to extend nutrient uptake and/or to mitigate predation risk. We addressed whether habitat use and foraging patterns of female mule deer (Odocoileus hemionus) responded to normalized difference vegetation index (NDVI), NDVI rate of change (green‐up), or the occurrence of cougars (Puma concolor). Female mule deer used available green‐up primarily in spring, although growing vegetation was available during other seasons. Mule deer and cougar shared similar habitat all year, and our models indicated cougars had a consistent, negative effect on mule deer access to growing vegetation, particularly in summer when cougar occurrence became concentrated at higher elevations. A seemingly late parturition date coincided with diminishing NDVI during the lactation period. Sky‐island populations, rarely studied, provide the opportunity to determine how mule deer respond to growing foliage along steep elevation and vegetation gradients when trapped with their predators and seasonally limited by aridity. Our findings indicate that fear of predation may restrict access to the forage resources found in sky islands
Local quantum phase transition in the pseudogap Anderson model: scales, scaling and quantum critical dynamics
The pseudogap Anderson impurity model provides a paradigm for understanding
local quantum phase transitions, in this case between generalised fermi liquid
and degenerate local moment phases. Here we develop a non-perturbative local
moment approach to the generic asymmetric model, encompassing all energy scales
and interaction strengths and leading thereby to a rich description of the
problem. We investigate in particular underlying phase boundaries, the critical
behaviour of relevant low-energy scales, and single-particle dynamics embodied
in the local spectrum. Particular attention is given to the resultant universal
scaling behaviour of dynamics close to the transition in both the GFL and LM
phases, the scale-free physics characteristic of the quantum critical point
itself, and the relation between the two.Comment: 39 pages, 19 figure
Finite temperature dynamics of the Anderson model
The recently introduced local moment approach (LMA) is extended to encompass
single-particle dynamics and transport properties of the Anderson impurity
model at finite-temperature, T. While applicable to arbitrary interaction
strengths, primary emphasis is given to the strongly correlated Kondo regime
(characterized by the T=0 Kondo scale ). In particular the
resultant universal scaling behaviour of the single-particle spectrum
D(\omega; T) \equiv F(\frac{\w}{\omega_{\rm K}}; \frac{T}{\omega_{\rm K}})
within the LMA is obtained in closed form; leading to an analytical description
of the thermal destruction of the Kondo resonance on all energy scales.
Transport properties follow directly from a knowledge of . The -dependence of the resulting resistivity , which is
found to agree rather well with numerical renormalization group calculations,
is shown to be asymptotically exact at high temperatures; to concur well with
the Hamann approximation for the s-d model down to ,
and to cross over smoothly to the Fermi liquid form in the low-temperature limit. The underlying
approach, while naturally approximate, is moreover applicable to a broad range
of quantum impurity and related models
A longitudinal study of the development of expressive timing
Tempo arches have often been reported in polished music performances, but their development during the learning of a new piece has not been studied. We examined the development of expressive timing at three levels of musical structure (piece, section, phrase) as an experienced concert soloist (the second author) prepared the Prelude from J. S. Bach’s Suite No. 6 for solo cello for public performance. We used mixed effect models to assess the development of expressive timing and the effects of the performance cues (PCs) that the cellist used as mental landmarks to guide her performance. Tempo arches appeared early in practice at all three levels of musical structure and changed over time in complex ways, first becoming more pronounced and more asymmetrical and then shrinking somewhat in later performances. Arches were also more pronounced in phrases that contained PCs, suggesting that PCs reminded the cellist where to “breathe” between phrases. The early development of tempo arches suggests that they were an automatic product of basic cognitive or motor processes. The complex trajectory of their later development appeared to be the result, at least in part, of a deliberate communicative strategy intended to draw listeners’ attention to some musical boundaries more than others
Anderson impurities in gapless hosts: comparison of renormalization group and local moment approaches
The symmetric Anderson impurity model, with a soft-gap hybridization
vanishing at the Fermi level with power law r > 0, is studied via the numerical
renormalization group (NRG). Detailed comparison is made with predictions
arising from the local moment approach (LMA), a recently developed many-body
theory which is found to provide a remarkably successful description of the
problem. Results for the `normal' (r = 0) impurity model are obtained as a
specific case. Particular emphasis is given both to single-particle excitation
dynamics, and to the transition between the strong coupling (SC) and local
moment (LM) phases of the model. Scaling characteristics and asymptotic
behaviour of the SC/LM phase boundaries are considered. Single-particle spectra
are investigated in some detail, for the SC phase in particular. Here, the
modified spectral functions are found to contain a generalized Kondo resonance
that is ubiquitously pinned at the Fermi level; and which exhibits a
characteristic low-energy Kondo scale that narrows progressively upon approach
to the SC->LM transition, where it vanishes. Universal scaling of the spectra
as the transition is approached thus results. The scaling spectrum
characteristic of the normal Anderson model is recovered as a particular case,
and is captured quantitatively by the LMA. In all cases the r-dependent scaling
spectra are found to possess characteristic low-energy asymptotics, but to be
dominated by generalized Doniach-Sunjic tails, in agreement with LMA
predictions.Comment: 26 pages, 14 figures, submitted for publicatio
Principles of Discrete Time Mechanics: II. Classical field Theory
We apply the principles discussed in an earlier paper to the construction of
discrete time field theories. We derive the discrete time field equations of
motion and Noether's theorem and apply them to the Schrodinger equation to
illustrate the methodology. Stationary solutions to the discrete time
Schrodinger wave equation are found to be identical to standard energy
eigenvalue solutions except for a fundamental limit on the energy. Then we
apply the formalism to the free neutral Klein Gordon system, deriving the
equations of motion and conserved quantities such as the linear momentum and
angular momentum. We show that there is an upper bound on the magnitude of
linear momentum for physical particle-like solutions. We extend the formalism
to the charged scalar field coupled to Maxwell's electrodynamics in a gauge
invariant way. We apply the formalism to include the Maxwell and Dirac fields,
setting the scene for second quantisation of discrete time mechanics and
discrete time Quantum Electrodynamics.Comment: 23 pages, LateX, To be published in J.Phys.A: Math.Gen: contact email
address: [email protected]
A Local Moment Approach to magnetic impurities in gapless Fermi systems
A local moment approach is developed for the single-particle excitations of a
symmetric Anderson impurity model (AIM), with a soft-gap hybridization
vanishing at the Fermi level with a power law r > 0. Local moments are
introduced explicitly from the outset, and a two-self-energy description is
employed in which the single-particle excitations are coupled dynamically to
low-energy transverse spin fluctuations. The resultant theory is applicable on
all energy scales, and captures both the spin-fluctuation regime of strong
coupling (large-U), as well as the weak coupling regime. While the primary
emphasis is on single particle dynamics, the quantum phase transition between
strong coupling (SC) and (LM) phases can also be addressed directly; for the
spin-fluctuation regime in particular a number of asymptotically exact results
are thereby obtained. Results for both single-particle spectra and SC/LM phase
boundaries are found to agree well with recent numerical renormalization group
(NRG) studies. A number of further testable predictions are made; in
particular, for r < 1/2, spectra characteristic of the SC state are predicted
to exhibit an r-dependent universal scaling form as the SC/LM phase boundary is
approached and the Kondo scale vanishes. Results for the `normal' r = 0 AIM are
moreover recovered smoothly from the limit r -> 0, where the resultant
description of single-particle dynamics includes recovery of Doniach-Sunjic
tails in the Kondo resonance, as well as characteristic low-energy Fermi liquid
behaviour.Comment: 52 pages, 19 figures, submitted to Journal of Physics: Condensed
Matte
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