The quantum Heisenberg antiferromagnet on the square lattice

The pure-quantum self-consistent harmonic approximation, a semiclassical method based on the path-integral formulation of quantum statistical mechanics, is applied to the study of the thermodynamic behaviour of the quantum Heisenberg antiferromagnet on the square lattice (QHAF). Results for various properties are obtained for different values of the spin and successfully compared with experimental data.Comment: Proceedings of the Conference "Path Integrals from peV to TeV - 50 Years from Feynman's paper" (Florence, August 1998) -- 2 pages, ReVTeX, 2 figure

Formation and seasonal occurrence of xylem embolism in Alnus cordata.

We investigated the vulnerability of xylem to embolism and the seasonal occurrence of xylem embolism in Italian alder (Alnus cordata Loisel.) by acoustic and hydraulic methods. Wood anatomy was also studied. More than eighty percent of the vessels were less than 50 mm long and no vessels were longer than 120 mm. Mean vessel diameter was 48 μm. Ultrasound acoustic emissions from root and branch segments dehydrating in air followed a similar pattern: in both tissues, emission peaks were recorded when the relative water content of the xylem was around 0.2. In branches dehydrating in air, xylem embolism increased linearly as water potential decreased. In trees in the field, more than 80 percent of hydraulic conductivity was lost in the tree crowns during winter. Recovery from winter embolism occurred mostly before bud burst. In summer, xylem embolism was low (< 30%) and acoustic emissions from roots, stem and branches of trees in the field were also low

Superconducting Fluctuation Corrections to the Thermal Current in Granular Metals

The first-order superconducting fluctuation corrections to the thermal conductivity of a granular metal are calculated. A suppression of thermal conductivity proportional to $T_c/(T-T_c)$ is observed in a region not too close to the critical temperature $T_c$. As $T\simeq T_c$, a saturation of the correction is found, and its sign depends on the ratio between the barrier transparency and the critical temperature. In both regimes, the Wiedemann-Franz law is violated.Comment: 9 pages, 7 figures. Replaced with published version. Important change

Two-spin entanglement distribution near factorized states

We study the two-spin entanglement distribution along the infinite $S=1/2$ chain described by the XY model in a transverse field; closed analytical expressions are derived for the one-tangle and the concurrences $C_r$, $r$ being the distance between the two possibly entangled spins, for values of the Hamiltonian parameters close to those corresponding to factorized ground states. The total amount of entanglement, the fraction of such entanglement which is stored in pairwise entanglement, and the way such fraction distributes along the chain is discussed, with attention focused on the dependence on the anisotropy of the exchange interaction. Near factorization a characteristic length-scale naturally emerges in the system, which is specifically related with entanglement properties and diverges at the critical point of the fully isotropic model. In general, we find that anisotropy rule a complex behavior of the entanglement properties, which results in the fact that more isotropic models, despite being characterized by a larger amount of total entanglement, present a smaller fraction of pairwise entanglement: the latter, in turn, is more evenly distributed along the chain, to the extent that, in the fully isotropic model at the critical field, the concurrences do not depend on $r$.Comment: 14 pages, 6 figures. Final versio

Spectral shapes of solid neon

We present a Path Integral Monte Carlo calculation of the first three moments of the displacement-displacement correlation functions of solid neon at different temperatures for longitudinal and transverse phonon modes. The Lennard-Jones potential is considered. The relevance of the quantum effects on the frequency position of the peak and principally on the line-width of the spectral shape is clearly pointed out. The spectrum is reconstructed via a continued fraction expansion; the approximations introduced using the effective potential quantum molecular dynamics are discussed.Comment: 3 pages, 2 figures, 3 table

Image Gallery: Super‐high magnification dermoscopy can identify pigmented cells: correlation with reflectance confocal microscopy

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Effective Potential and Quantum Dynamical Correlators

The approach to the calculation of quantum dynamical correlation functions is presented in the framework of the Mori theory. An unified treatment of classic and quantum dynamics is given in terms of Weyl representation of operators and holomorphic variables. The range of validity of an approximate molucular dynamics is discussedComment: 8 pages, Latex fil