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 $J_{z}=\pm 5/2$ 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

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