1,894 research outputs found

    Semiclassical action based on dynamical mean-field theory describing electrons interacting with local lattice fluctuations

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    We extend a recently introduced semiclassical approach to calculating the influence of local lattice fluctuations on electronic properties of metals and metallic molecular crystals. The effective action of electrons in degenerate orbital states coupling to Jahn-Teller distortions is derived, employing dynamical mean-field theory and adiabatic expansions. We improve on previous numerical treatments of the semiclassical action and present for the simplifying Holstein model results for the finite temperature optical conductivity at electron-phonon coupling strengths from weak to strong. Significant transfer of spectral weight from high to low frequencies is obtained on isotope substitution in the Fermi-liquid to polaron crossover regime.Comment: 10 pages, 7 figure

    Numerical optimisation of forced convection in a vascularised solid with triagular channels

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    Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.In this paper we employ the constructal design and theory to seek the optimal cooling channels in forced convection of vascularised material with the localised self-cooling property subject to heat flux. The isosceles right triangular channel configuration was studied for family of porosities. The isosceles right triangle is special case of triangle which can easily and uniformly be packed and arranged to form a larger constructs. The objective was to optimise the configurations in such a way that the peak temperature was minimised at every point in the solid body. The optimisation was subject to the constraint of fixed global volume of solid material, but the elemental volume was allowed to morph. The solid material was subject to heat flux on one side and the cooling fluid was forced through the channels in opposite direction of the heated side of the solid body by the specified pressure differencecf201

    Numerical optimisation of conjugate Hexagonal cooling channels with internal heat generation using Al2O3-water nanofluid

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    Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.This paper presents a three-dimensional geometric optimisation of conjugate cooling channels in forced convection with internal heat generation within the solid. Hexagonal cooling channels configuration are considered and Al2O3-water nanofluid is used as cooloing fluid because of its promising superior thermal properties over traditional cooling fluids The main objective is to optimise the configuration in such a way that the peak temperature is minimised subject to the constraint of fixed global volume of solid material. The cooling fluid is driven through the channels by the pressure difference across the channel.The elemental volume of the structure and hydraulic diameter of the cooling channel were considered as design variables. Also, different values of volume fraction of Al2O3 nanoparticles added into water that enhanced the cooling effect are considered. The shape of the channel is allowed to morph to determine the best configuration that gives the lowest peak temperature. A gradient-based mathematic optimisation algorithm (Dynamic-Q) is applied in order to search for the best optimal geometric configuration that improves thermal performance by minimising peak temperature for a wide range of pressure difference. Results obtained show that there are unique optimal geometry for a given pressure difference. Also, the results show that the effects of pressure difference, volume fraction of Al2O3 nanoparticles on minimum peak temperature and hydraulic diameter of the channel are consistent with those obtained in the open literature.The funding obtained from NRF, TESP, Stellenbosch University / University of Pretoria, SANERI/SANEDI, CSIR, EEDSM Hub and NAC is acknowledged and duly appreciated. Also, Olabode Olakoyejo appreciates the support received from the National Centre for Energy Efficiency and conservation, University of Lagos, Nigeria.am201

    Odderon and Pomeron from the Vacuum Correlator Method

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    Glueball masses with J<=7 are computed both for C=+1 and C=-1 using the string Hamiltonian derived in the framework of the Vacuum Correlator Method. No fitting parameters are used, and masses are expressed in terms of string tension σ\sigma and effective value of αs\alpha_s. We extend the calculations done for J<=3 using the same Hamiltonian, which provided glueball masses in good agreement with existing lattice data, to higher mass states. It is shown that 3^{--}, 5^{--} and 7^{--} states lie on the odderon trajectories with the intercept around or below 0.14. Another odderon trajectory with 3g glueballs of Y-shape, corresponds to 11% higher masses and low intercept. These findings are in agreement with recent experimental data, setting limits on the odderon contribution to the exclusive γp\gamma p reactions.Comment: 16 pages. Journal version. To be published in Phys.Lett.

    Statewide geographic variation in outcomes for adults with acute myeloid leukemia in North Carolina

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    BACKGROUND: Population-based studies have demonstrated survival disparities related to socioeconomic factors for patients with acute myeloid leukemia (AML). The objective of the current study was to determine whether the local health care infrastructure, represented by Area Health Education Centers (AHEC) region, or treating center experience, represented by National Cancer Institute Comprehensive Cancer Center (NCICCC) designation, were associated with outcomes among patients with AML in North Carolina. METHODS: Patients who were diagnosed with AML from 2003 to 2009 were identified using the University of North Carolina Lineberger Integrated Cancer Information and Surveillance System, a database linking insurance claims to the North Carolina Cancer Registry. A Cox proportional-hazards model was used to explore survival based on AHEC region. A subset of patients who received inpatient chemotherapy was examined to evaluate the impact of treatment at an NCICCC. RESULTS: Nine hundred patients were identified in the study period, 553 of whom received inpatient chemotherapy therapy within 30 days of diagnosis. Almost one-half of these patients (n5294) received chemotherapy at a non-NCICCC. Among the patients who received intensive inpatient therapy, residence in 3 of 9 AHEC regions was associated with a higher risk of mortality (hazard ratio: range, 1.97-4.03; P<.01) at 1 year in multivariate analysis. Treatment at a non-NCICCC was not associated with an increased risk of mortality at 1 year (hazard ratio, 1.25; 95% confidence interval, 0.95-1.65). CONCLUSIONS: Survival among patients with AML in North Carolina varies according to geographic region. Further examination of local practice and referral patterns may inform strategies to improve AML outcomes across the state

    A purely algebraic construction of a gauge and renormalization group invariant scalar glueball operator

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    This paper presents a complete algebraic proof of the renormalizability of the gauge invariant d=4d=4 operator Fμν2(x)F_{\mu\nu}^2(x) to all orders of perturbation theory in pure Yang-Mills gauge theory, whereby working in the Landau gauge. This renormalization is far from being trivial as mixing occurs with other d=4d=4 gauge variant operators, which we identify explicitly. We determine the mixing matrix ZZ to all orders in perturbation theory by using only algebraic arguments and consequently we can uncover a renormalization group invariant by using the anomalous dimension matrix Γ\Gamma derived from ZZ. We also present a future plan for calculating the mass of the lightest scalar glueball with the help of the framework we have set up.Comment: 17 page
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