2,829 research outputs found
Non-Fermi Liquid behavior at the Orbital Ordering Quantum Critical Point in the Two-Orbital Model
The critical behavior of a two-orbital model with degenerate and
orbitals is investigated by multidimensional bosonization. We find
that the corresponding bosonic theory has an overdamped collective mode with
dynamical exponent , which appears to be a general feature of a
two-orbital model and becomes the dominant fluctuation in the vicinity of the
orbital-ordering quantum critical point. Since the very existence of this
overdamped collective mode induces non-Fermi liquid behavior near the quantum
critical point, we conclude that a two-orbital model generally has a sizable
area in the phase diagram showing non-Fermi liquid behavior. Furthermore, we
show that the bosonic theory resembles the continuous model near the d-wave
Pomeranchuk instability, suggesting that orbital order in a two-orbital model
is identical to nematic order in a continuous model. Our results can be applied
to systems with degenerate and orbitals such as iron-based
superconductors and bilayer strontium ruthenates SrRuO.Comment: 5 pages, 2 figure
Pomeranchuk Instability in a non-Fermi Liquid from Holography
The Pomeranchuk instability, in which an isotropic Fermi surface distorts and
becomes anisotropic due to strong interactions, is a possible mechanism for the
growing number of experimental systems which display transport properties that
differ along the and axes. We show here that the gauge-gravity duality
can be used to describe such an instability in fermionic systems. Our
holographic model consists of fermions in a background which describes the
causal propagation of a massive neutral spin-two field in an asymptotically AdS
spacetime. The Fermi surfaces in the boundary theory distort spontaneously and
become anisotropic once the neutral massive spin-two field develops a
normalizable mode in the bulk. Analysis of the fermionic correlators reveals
that the low-lying fermionic excitations are non-Fermi liquid-like both before
and after the Fermi surface shape distortion. Further, the spectral weight
along the Fermi surface is angularly dependent and can be made to vanish along
certain directions.Comment: Updated version to appear in PRD. New version has WKB analysis of
spectral intensity in ordered phas
Supercontinuum generation in the vacuum ultraviolet through dispersive-wave and soliton-plasma interaction in noble-gas-filled hollow-core photonic crystal fiber
We report on the generation of a three-octave-wide supercontinuum extending
from the vacuum ultraviolet (VUV) to the near-infrared, spanning at least 113
to 1000 nm (i.e., 11 to 1.2 eV), in He-filled hollow-core kagome-style photonic
crystal fiber. Numerical simulations confirm that the main mechanism is a novel
and previously undiscovered interaction between dispersive-wave emission and
plasma-induced blueshifted soliton recompression around the fiber zero
dispersion frequency. The VUV part of the supercontinuum, which modeling shows
to be coherent and possess a simple phase structure, has sufficient bandwidth
to support single-cycle pulses of 500 attosecond duration. We also demonstrate,
in the same system, the generation of narrower-band VUV pulses, through
dispersive-wave emission, tunable from 120 to 200 nm with efficiencies
exceeding 1% and VUV pulse energies in excess of 50 nJ.Comment: 7 pages, 5 figure
Non-invasive computer-assisted measurement of knee alignment
The quantification of knee alignment is a routine part of orthopaedic practice and is important for monitoring disease progression, planning interventional strategies, and follow-up of patients. Currently available technologies such as radiographic measurements have a number of drawbacks. The aim of this study was to validate a potentially improved technique for measuring knee alignment under different conditions. An image-free navigation system was adapted for non-invasive use through the development of external infrared tracker mountings. Stability was assessed by comparing the variance (F-test) of repeated mechanical femoro-tibial (MFT) angle measurements for a volunteer and a leg model. MFT angles were then measured supine, standing and with varus-valgus stress in asymptomatic volunteers who each underwent two separate registrations and repeated measurements for each condition. The mean difference and 95% limits of agreement were used to assess intra-registration and inter-registration repeatability. For multiple registrations the range of measurements for the external mountings was 1° larger than for the rigid model with statistically similar variance (p=0.34). Thirty volunteers were assessed (19 males, 11 females) with a mean age of 41 years (range: 20-65) and a mean BMI of 26 (range: 19-34). For intra-registration repeatability, consecutive coronal alignment readings agreed to almost ±1°, with up to ±0.5° loss of repeatability for coronal alignment measured before and after stress maneuvers, and a ±0.2° loss following stance trials. Sagittal alignment measurements were less repeatable overall by an approximate factor of two. Inter-registration agreement limits for coronal and sagittal supine MFT angles were ±1.6° and ±2.3°, respectively. Varus and valgus stress measurements agreed to within ±1.3° and ±1.1°, respectively. Agreement limits for standing MFT angles were ±2.9° (coronal) and ±5.0° (sagittal), which may have reflected a variation in stance between measurements. The system provided repeatable, real-time measurements of coronal and sagittal knee alignment under a number of dynamic, real-time conditions, offering a potential alternative to radiographs
Attitudes towards the use and acceptance of eHealth technologies : a case study of older adults living with chronic pain and implications for rural healthcare
Acknowledgements The research described here is supported by the award made by the RCUK Digital Economy programme to the dot.rural Digital Economy Hub; award reference: EP/G066051/1. MCâs time writing the paper is funded by the Scottish Governmentâs Rural and Environmental Science and Analytical Services Division (RESAS) under Theme 8 âVibrant Rural Communitiesâ of the Food, Land and People Programme (2011â2016). MC is also an Honorary Research Fellow at the Division of Applied Health Sciences, University of Aberdeen. The input of other members of the TOPS research team, Alastair Mort, Fiona Williams, Sophie Corbett, Phil Wilson and Paul MacNamee who contributed to be wider study and discussed preliminary findings reported here with the authors of the paper is acknowledged. We acknowledge the feedback on earlier versions of this paper provided by members of the Trans-Atlantic Rural Research Network, especially Stefanie Doebler and Carmen Hubbard. We also thank Deb Roberts for her comments.Peer reviewedPublisher PD
On the structure of the Figueroa unital and the existence of OâNan configurations
AbstractThe finite Figueroa planes are non-Desarguesian projective planes of order q3 for all prime powers q>2, constructed algebraically in 1982 by Figueroa, and Hering and Schaeffer, and synthetically in 1986 by Grundhöfer. All Figueroa planes of finite square order are shown to possess a unitary polarity by de Resmini and Hamilton in 1998, and hence admit unitals. Hui and Wong (2012) have shown that these polar unitals do not satisfy a necessary condition, introduced by Wilbrink in 1983, for a unital to be classical, and hence they are not classical. In this article we introduce and make use of a new alternative synthetic description of the Figueroa plane and unital to demonstrate the existence of OâNan configurations, thus providing support to Piperâs conjecture (1981)
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