13 research outputs found

    Conductivity in quasi two-dimensional systems

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    The conductivity in quasi two-dimensional systems is calculated using the quantum kinetic equation. Linearizing the Lenard-Balescu collision integral with the extension to include external field dependences allows one to calculate the conductivity with diagrams beyond the GW approximation including maximally crossed lines. Consequently the weak localization correction as an interference effect appears here from the field dependence of the collision integral (the latter dependence sometimes called intra-collisional field effect). It is shown that this weak localization correction has the same origin as the Debye-Onsager relaxation effect in plasma physics. The approximation is applied to a system of quasi two-dimensional electrons in hetero-junctions which interact with charged and neutral impurities and the low temperature correction to the conductivity is calculated analytically. It turns out that the dynamical screening due to charged impurities leads to a linear temperature dependence, while the scattering from neutral impurities leads to the usual Fermi-liquid behavior. By considering an appropriate mass action law to determine the ratio of charged to neutral impurities we can describe the experimental metal-insulator transition at low temperatures as a Mott-Hubbard transition.Comment: 7 pages 7 pages appendix 11 figure

    Steady states of a chi-three parametric oscillator with coupled polarisations

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    Polarisation effects in the microcavity parametric oscillator are studied using a simple model in which two chi-three optical parametric oscillators are coupled together. It is found that there are, in general, a number of steady states of the model under continuous pumping. There are both continuous and discontinuous thresholds, at which new steady-states appear as the driving intensity is increased: at the continuous thresholds, the new state has zero output intensity, whereas at the discontinuous threshold it has a finite output intensity. The discontinuous thresholds have no analog in the uncoupled device. The coupling also generates rotations of the linear polarisation of the output compared with the pump, and shifts in the output frequencies as the driving polarisation or intensity is varied. For large ratios of the interaction between polarisations to the interaction within polarisations, of the order of 5, one of the thresholds has its lowest value when the pump is elliptically polarised. This is consistent with recent experiments in which the maximum output was achieved with an elliptically polarised pump.Comment: 7 pages, 4 figure

    Data of Figure 1 of "Gapless fluctuations and exceptional points in semiconductor lasers"

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    Data of Figure 1 of "Gapless fluctuations and exceptional points in semiconductor lasers" by N.H. Kwong, M.Em. Spotnitz and R. Binder, University of Arizona. The figure shows fluctuation mode spectra (real and imaginary part) of semiconductor lasers. Refer to the publication in Physical Review B for details.For inquiries regarding the contents of this dataset, please contact the Corresponding Author listed in the README.txt file. Administrative inquiries (e.g., removal requests, trouble downloading, etc.) can be directed to [email protected]</p

    Supplementary Material for: A Clinical Score for Predicting Atrial Fibrillation in Patients with Cryptogenic Stroke or Transient Ischemic Attack

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    <strong><em>Objectives:</em></strong> Detection of atrial fibrillation (AF) in post-cryptogenic stroke (CS) or transient ischemic attack (TIA) patients carries important therapeutic implications. <b><i>Methods:</i></b> To risk stratify CS/TIA patients for later development of AF, we conducted a retrospective cohort study using data from 1995 to 2015 in the Stanford Translational Research Integrated Database Environment (STRIDE). <b><i>Results:</i></b> Of the 9,589 adult patients (age ≥40 years) with CS/TIA included, 482 (5%) patients developed AF post CS/TIA. Of those patients, 28.4, 26.3, and 45.3% were diagnosed with AF 1-12 months, 1-3 years, and >3 years after the index CS/TIA, respectively. Age (≥75 years), obesity, congestive heart failure, hypertension, coronary artery disease, peripheral vascular disease, and valve disease are significant risk factors, with the following respective odds ratios (95% CI): 1.73 (1.39-2.16), 1.53 (1.05-2.18), 3.34 (2.61-4.28), 2.01 (1.53-2.68), 1.72 (1.35-2.19), 1.37 (1.02-1.84), and 2.05 (1.55-2.69). A risk-scoring system, i.e., the HAVOC score, was constructed using these 7 clinical variables that successfully stratify patients into 3 risk groups, with good model discrimination (area under the curve = 0.77). <b><i>Conclusions:</i></b> Findings from this study support the strategy of looking longer and harder for AF in post-CS/TIA patients. The HAVOC score identifies different levels of AF risk and may be used to select patients for extended rhythm monitoring
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