24,548 research outputs found
Layered Kondo lattice model for quantum critical beta-YbAlB4
We analyze the magnetic and electronic properties of the quantum critical
heavy fermion superconductor beta-YbAlB4, calculating the Fermi surface and the
angular dependence of the extremal orbits relevant to the de Haas--van Alphen
measurements. Using a combination of the realistic materials modeling and
single-ion crystal field analysis, we are led to propose a layered Kondo
lattice model for this system, in which two dimensional boron layers are Kondo
coupled via interlayer Yb moments in a state. This model fits
the measured single ion magnetic susceptibility and predicts a substantial
change in the electronic anisotropy as the system is pressure-tuned through the
quantum critical point.Comment: Fig.3 and 4 have been updated, typos corrected in v2. Published at
http://link.aps.org/doi/10.1103/PhysRevLett.102.07720
Two-fluid behavior of the Kondo lattice in the 1/N slave boson approach
It has been recently shown by Nakatsuji, Pines, and Fisk [S. Nakatsuji, D.
Pines, and Z. Fisk, Phys. Rev. Lett. 92, 016401 (2004)] from the
phenomenological analysis of experiments in Ce1-xLaxCoIn5 and CeIrIn5 that
thermodynamic and transport properties of Kondo lattices below coherence
temperature can be very successfully described in terms of a two-fluid model,
with Kondo impurity and heavy electron Fermi liquid contributions. We analyze
thermodynamic properties of Kondo lattices using 1/N slave boson treatment of
the periodic Anderson model and show that these two contributions indeed arise
below the coherence temperature. We find that the Kondo impurity contribution
to thermodynamics corresponds to thermal excitations into the flat portion of
the energy spectrum.Comment: 7 pages, 2 figure
Locally critical point in an anisotropic Kondo lattice
We report the first numerical identification of a locally quantum critical
point, at which the criticality of the local Kondo physics is embedded in that
associated with a magnetic ordering. We are able to numerically access the
quantum critical behavior by focusing on a Kondo-lattice model with Ising
anisotropy. We also establish that the critical exponent for the q-dependent
dynamical spin susceptibility is fractional and compares well with the
experimental value for heavy fermions.Comment: 4 pages, 3 figures; published versio
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Atmospheric observations of the water vapour continuum in the near-infrared windows between 2500 and 6600 cm-1
Water vapour continuum absorption is potentially important for both closure of the Earth's energy budget and remote sensing applications. Currently, there are significant uncertainties in its characteristics in the near-infrared atmospheric windows at 2.1 and 1.6 µm. There have been several attempts to measure the continuum in the laboratory; not only are there significant differences amongst these measurements, but there are also difficulties in extrapolating the laboratory data taken at room temperature and above to temperatures more widely relevant to the atmosphere. Validation is therefore required using field observations of the real atmosphere. There are currently no published observations in atmospheric conditions with enough water vapour to detect a continuum signal within these windows or where the self-continuum component is significant. We present observations of the near-infrared water vapour continuum from Camborne, UK, at sea level using a Sun-pointing, radiometrically calibrated Fourier transform spectrometer in the window regions between 2000 and 10 000 cm−1. Analysis of these data is challenging, particularly because of the need to remove aerosol extinction and the large uncertainties associated with such field measurements. Nevertheless, we present data that are consistent with recent laboratory datasets in the 4 and 2.1 µm windows (when extrapolated to atmospheric temperatures). These results indicate that the most recent revision (3.2) of the MT_CKD foreign continuum, versions of which are widely used in atmospheric radiation models, requires strengthening by a factor of ∼5 in the centre of the 2.1 µm window. In the higher-wavenumber window at 1.6 µm, our estimated self- and foreign-continua are significantly stronger than MT_CKD. The possible contribution of the self- and foreign-continua to our derived total continuum optical depth is estimated by using laboratory or MT_CKD values of one, to estimate the other. The obtained self-continuum shows some consistency with temperature-extrapolated laboratory data in the centres of the 4 and 2.1 µm windows. The 1.6 µm region is more sensitive to atmospheric aerosol and continuum retrievals and therefore more uncertain than the more robust results at 2.1 and 4 µm. We highlight the difficulties in observing the atmospheric continuum and make the case for additional measurements in both the laboratory and field and discuss the requirements for any future field campaign
Atomic Model of Susy Hubbard Operators
We apply the recently proposed susy Hubbard operators to an atomic model. In
the limiting case of free spins, we derive exact results for the entropy which
are compared with a mean field + gaussian corrections description. We show how
these results can be extended to the case of charge fluctuations and calculate
exact results for the partition function, free energy and heat capacity of an
atomic model for some simple examples. Wavefunctions of possible states are
listed. We compare the accuracy of large N expansions of the susy spin
operators with those obtained using `Schwinger bosons' and `Abrikosov
pseudo-fermions'. For the atomic model, we compare results of slave boson,
slave fermion, and susy Hubbard operator approximations in the physically
interesting but uncontrolled limiting case of N->2. For a mixed representation
of spins we estimate the accuracy of large N expansions of the atomic model. In
the single box limit, we find that the lowest energy saddle-point solution
reduces to simply either slave bosons or slave fermions, while for higher boxes
this is not the case. The highest energy saddle-point solution has the
interesting feature that it admits a small region of a mixed representation,
which bears a superficial resemblance to that seen experimentally close to an
antiferromagnetic quantum critical point.Comment: 17 pages + 7 pages Appendices, 14 figures. Substantial revision
Reply to the comment by Carmelo Anile on the paper "Complexity analysis of the cerebrospinal fluid pulse waveform during infusion studies"
Veterinary technology is an emerging profession within the veterinary and allied animal health fields in Australia and affords graduates the opportunity to contribute to the small but growing body of literature within this discipline. This study describes the introduction of a contextualised assessment task to develop students’ research capability, competence and confidence in professional writing, and to engage them with the academic publishing process. Students worked in self-selected dyads to author a scientific case report, of publishable standard, based on authentic cases from their clinical practicum. Intrinsic to the task, students attended a series of workshops that explored topics such as critiquing the literature, professional writing styles and oral presentation skills. Assessment was multi-staged with progressive feedback, including peer review, and culminated with students presenting their abstracts at a mock conference. Students reported the task to be an enjoyable and valuable learning experience which improved their competence and confidence in scientific writing; supported by a comparison of previously submitted work. Linking scientific writing skills to clinical practice experiences enhanced learning outcomes and may foster the professionalisation of students within this emerging discipline
Defects in Heavy-Fermion Materials: Unveiling Strong Correlations in Real Space
Complexity in materials often arises from competing interactions at the
atomic length scale. One such example are the strongly correlated heavy-fermion
materials where the competition between Kondo screening and antiferromagnetic
ordering is believed to be the origin of their puzzling non-Fermi-liquid
properties. Insight into such complex physical behavior in strongly correlated
electron systems can be gained by impurity doping. Here, we develop a
microscopic theoretical framework to demonstrate that defects implanted in
heavy-fermion materials provide an opportunity for unveiling competing
interactions and their correlations in real space. Defect-induced perturbations
in the electronic and magnetic correlations possess characteristically
different spatial patterns that can be visualized via their spectroscopic
signatures in the local density of states or non-local spin susceptibility.
These real space patterns provide insight into the complex electronic structure
of heavy-fermion materials, the light or heavy character of the perturbed
states, and the hybridization between them. The strongly correlated nature of
these materials also manifests itself in highly non-linear quantum interference
effects between defects that can drive the system through a first-order phase
transition to a novel inhomogeneous ground state.Comment: 11 pages, 7 figure
Information of Structures in Galaxy Distribution
We introduce an information-theoretic measure, the Renyi information, to
describe the galaxy distribution in space. We discuss properties of the
information measure, and demonstrate its relationship with the probability
distribution function and multifractal descriptions. Using the First Look
Survey galaxy samples observed by the Infrared Array Camera onboard Spitzer
Space Telescope, we present measurements of the Renyi information, as well as
the counts-in-cells distribution and multifractal properties of galaxies in
mid-infrared wavelengths. Guided by multiplicative cascade simulation based on
a binomial model, we verify our measurements, and discuss the spatial selection
effects on measuring information of the spatial structures. We derive structure
scan functions at scales where selection effects are small for the Spitzer
samples. We discuss the results, and the potential of applying the Renyi
information to measuring other spatial structures.Comment: 25 pages, 8 figures, submitted to ApJ; To appear in The Astrophysical
Journal 2006, 644, 678 (June 20th
Study of low frequency hydromagnetic waves using ATS-1 data
Low frequency oscillations of the magnetic field at ATS-1 were analyzed for the 25 month data interval, Dec., 1966 through 1968. Irregular oscillations and those associated with magnetic storms were excluded from the analysis. Of the 222 events identified, 170 were found to be oscillating predominantly transverse to the background magnetic field. The oscillations were observed to occur most frequently in the early afternoon hours. They also seemed to occur more frequently during Dec., Jan., and Feb. than at any other time of the year. During a given event, the frequency was fairly constant. The event duration varied between a minimum of 10 min. and a maximum of 14 hrs and 26 min. During a given event the amplitude varied
Who responds to a placebo? Factors associated with response to placebo during a double-blind randomised controlled trial
INTRODUCTION:
The placebo effect, a desirable outcome resulting from a person’s expected and/or learned response to a treatment or situation, may significantly influence the interpretation of double-blind, randomised controlled trials (RCT). High placebo responder rates may under-estimate the true efficacy of a treatment. It is therefore important for researchers conducting RCTs to be cognisant of factors influencing the placebo response. In this study, we performed a retrospective analysis of a RCT of participants’ response to placebo beetroot juice on 5-km running performance.
METHODS:
Participants were 70 recreational runners (male 51.2%; mean ± SD = age = 32.0 ± 10.4 years, hours per week training = 6.16 ± 3.98, 5-km personal best = 24:28 minutes:seconds). After completing measures of sport supplement use and their beliefs about sport supplements, participants completed 5-km time-trials at baseline and with the ingestion of nitrate depleted placebo (containing ~0.04 mmol of nitrate, Beet It Sport®). The smallest worthwhile change was calculated to identify placebo responders and backward linear regression identified variables associated with the placebo response.
RESULTS:
Nearly two-thirds of participants were identified as placebo responders (63%). Compared to baseline, time to run 5-km among placebo responders was 2.76 ± 0.36%, whereas for non-responders it was -1.45 ± 0.46%. Sport supplement use (β = -2.162, p = 0.042), sport supplement beliefs (β = -0.712, p = 0.034) and being male (β = -2.030, p = 0.022) predicted the response to placebo. Stronger beliefs about sport supplements also influenced the magnitude of improvement in 5-km times in the placebo condition compared to baseline (β = 0.820, p = 0.028).
CONCLUSION:
Results demonstrate that participants recruited to a RCT of beetroot juice on 5-km running performance were more likely to respond to a placebo if they used sport supplements, reported strong beliefs in their effectiveness and were male. Given that interpretation of RCTs can be influenced by the placebo effect, researchers using these research designs should consider measuring and controlling for these variables in their analyses. Further data on what may influence the response to a placebo is needed to help inform interpretation of RCTs
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