49 research outputs found

    Complex-Temperature Singularities in the d=2d=2 Ising Model. III. Honeycomb Lattice

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    We study complex-temperature properties of the uniform and staggered susceptibilities χ\chi and χ(a)\chi^{(a)} of the Ising model on the honeycomb lattice. From an analysis of low-temperature series expansions, we find evidence that χ\chi and χ(a)\chi^{(a)} both have divergent singularities at the point z=1zz=-1 \equiv z_{\ell} (where z=e2Kz=e^{-2K}), with exponents γ=γ,a=5/2\gamma_{\ell}'= \gamma_{\ell,a}'=5/2. The critical amplitudes at this singularity are calculated. Using exact results, we extract the behaviour of the magnetisation MM and specific heat CC at complex-temperature singularities. We find that, in addition to its zero at the physical critical point, MM diverges at z=1z=-1 with exponent β=1/4\beta_{\ell}=-1/4, vanishes continuously at z=±iz=\pm i with exponent βs=3/8\beta_s=3/8, and vanishes discontinuously elsewhere along the boundary of the complex-temperature ferromagnetic phase. CC diverges at z=1z=-1 with exponent α=2\alpha_{\ell}'=2 and at v=±i/3v=\pm i/\sqrt{3} (where v=tanhKv = \tanh K) with exponent αe=1\alpha_e=1, and diverges logarithmically at z=±iz=\pm i. We find that the exponent relation α+2β+γ=2\alpha'+2\beta+\gamma'=2 is violated at z=1z=-1; the right-hand side is 4 rather than 2. The connections of these results with complex-temperature properties of the Ising model on the triangular lattice are discussed.Comment: 22 pages, latex, figures appended after the end of the text as a compressed, uuencoded postscript fil

    Study of the Potts Model on the Honeycomb and Triangular Lattices: Low-Temperature Series and Partition Function Zeros

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    We present and analyze low-temperature series and complex-temperature partition function zeros for the qq-state Potts model with q=4q=4 on the honeycomb lattice and q=3,4q=3,4 on the triangular lattice. A discussion is given as to how the locations of the singularities obtained from the series analysis correlate with the complex-temperature phase boundary. Extending our earlier work, we include a similar discussion for the Potts model with q=3q=3 on the honeycomb lattice and with q=3,4q=3,4 on the kagom\'e lattice.Comment: 33 pages, Latex, 9 encapsulated postscript figures, J. Phys. A, in pres

    Some New Results on Complex-Temperature Singularities in Potts Models on the Square Lattice

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    We report some new results on the complex-temperature (CT) singularities of qq-state Potts models on the square lattice. We concentrate on the problematic region Re(a)<0Re(a) < 0 (where a=eKa=e^K) in which CT zeros of the partition function are sensitive to finite lattice artifacts. From analyses of low-temperature series expansions for 3q83 \le q \le 8, we establish the existence, in this region, of complex-conjugate CT singularities at which the magnetization and susceptibility diverge. From calculations of zeros of the partition function, we obtain evidence consistent with the inference that these singularities occur at endpoints ae, aea_e, \ a_e^* of arcs protruding into the (complex-temperature extension of the) FM phase. Exponents for these singularities are determined; e.g., for q=3q=3, we find βe=0.125(1)\beta_e=-0.125(1), consistent with βe=1/8\beta_e=-1/8. By duality, these results also imply associated arcs extending to the (CT extension of the) symmetric PM phase. Analytic expressions are suggested for the positions of some of these singularities; e.g., for q=5q=5, our finding is consistent with the exact value ae,ae=2(1i)a_e,a_e^*=2(-1 \mp i). Further discussions of complex-temperature phase diagrams are given.Comment: 26 pages, latex, with eight epsf figure

    Determination of the bond percolation threshold for the Kagome lattice

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    The hull-gradient method is used to determine the critical threshold for bond percolation on the two-dimensional Kagome lattice (and its dual, the dice lattice). For this system, the hull walk is represented as a self-avoiding trail, or mirror-model trajectory, on the (3,4,6,4)-Archimedean tiling lattice. The result pc = 0.524 405 3(3) (one standard deviation of error) is not consistent with the previously conjectured values.Comment: 10 pages, TeX, Style file iopppt.tex, to be published in J. Phys. A. in August, 199

    Application and Validation of Case-Finding Algorithms for Identifying Individuals with Human Immunodeficiency Virus from Administrative Data in British Columbia, Canada

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    Objective To define a population-level cohort of individuals infected with the human immunodeficiency virus (HIV) in the province of British Columbia from available registries and administrative datasets using a validated case-finding algorithm. Methods Individuals were identified for possible cohort inclusion from the BC Centre for Excellence in HIV/AIDS (CfE) drug treatment program (antiretroviral therapy) and laboratory testing datasets (plasma viral load (pVL) and CD4 diagnostic test results), the BC Centre for Disease Control (CDC) provincial HIV surveillance database (positive HIV tests), as well as databases held by the BC Ministry of Health (MoH); the Discharge Abstract Database (hospitalizations), the Medical Services Plan (physician billing) and PharmaNet databases (additional HIV-related medications). A validated case-finding algorithm was applied to distinguish true HIV cases from those likely to have been misclassified. The sensitivity of the algorithms was assessed as the proportion of confirmed cases (those with records in the CfE, CDC and MoH databases) positively identified by each algorithm. A priori hypotheses were generated and tested to verify excluded cases. Results A total of 25,673 individuals were identified as having at least one HIV-related health record. Among 9,454 unconfirmed cases, the selected case-finding algorithm identified 849 individuals believed to be HIV-positive. The sensitivity of this algorithm among confirmed cases was 88%. Those excluded from the cohort were more likely to be female (44.4% vs. 22.5%; p&lt;0.01), had a lower mortality rate (2.18 per 100 person years (100PY) vs. 3.14/100PY; p&lt;0.01), and had lower median rates of health service utilization (days of medications dispensed: 9745/100PY vs. 10266/100PY; p&lt;0.01; days of inpatient care: 29/100PY vs. 98/100PY; p&lt;0.01; physician billings: 602/100PY vs. 2,056/100PY; p&lt;0.01). Conclusions The application of validated case-finding algorithms and subsequent hypothesis testing provided a strong framework for defining a population-level cohort of HIV infected people in BC using administrative databases

    The 2020 UV emitter roadmap

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    Solid state UV emitters have many advantages over conventional UV sources. The (Al,In,Ga)N material system is best suited to produce LEDs and laser diodes from 400 nm down to 210 nm—due to its large and tuneable direct band gap, n- and p-doping capability up to the largest bandgap material AlN and a growth and fabrication technology compatible with the current visible InGaN-based LED production. However AlGaN based UV-emitters still suffer from numerous challenges compared to their visible counterparts that become most obvious by consideration of their light output power, operation voltage and long term stability. Most of these challenges are related to the large bandgap of the materials. However, the development since the first realization of UV electroluminescence in the 1970s shows that an improvement in understanding and technology allows the performance of UV emitters to be pushed far beyond the current state. One example is the very recent realization of edge emitting laser diodes emitting in the UVC at 271.8 nm and in the UVB spectral range at 298 nm. This roadmap summarizes the current state of the art for the most important aspects of UV emitters, their challenges and provides an outlook for future developments

    Cross-talk between calpain and caspase proteolytic systems during neuronal apoptosis

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    Cross-talk between calpain and caspase proteolytic systems has complicated efforts to determine their distinct roles in apoptotic cell death. This study examined the effect of overexpressing calpastatin, the specific endogenous calpain inhibitor, on the activity of the two proteolytic systems following an apoptotic stimulus. Human SH-SY5Y neuroblastoma cells were stably transfected with full-length human calpastatin cDNA resulting in 20-fold overexpression based on Western blot and 5-fold greater calpain inhibitory activity in cell extracts. Wild type and calpastatin overexpressing (CST1) cells were neuronally differentiated and apoptosis-induced with staurosporine (0.1-1.0 µm). Calpastatin overexpression decreased calpain activation, increased caspase-3-like activity, and accelerated the appearance of apoptotic nuclear morphology. Following 0.1-0.2 µm staurosporine, plasma membrane integrity based on calcein-acetoxymethyl fluorescence was significantly greater at 24 h in differentiated CST1 compared with differentiated wild type cells. However, this protective effect was lost at higher staurosporine doses (0.5-1.0 µm), which resulted in pronounced caspase-mediated degradation of the overexpressed calpastatin. These results suggest a dual role for calpains during neuronal apoptosis. In the early execution phase, calpain down-regulates caspase-3-like activity and slows progression of apoptotic nuclear morphology. Subsequent calpain activity, facilitated by caspase-mediated degradation of calpastatin, contributes to plasma membrane disruption and secondary necrosis.Journal ArticleFinal article publishe
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