605 research outputs found
Theory of short-range magnetic order for the t-J model
We present a self-consistent theory of magnetic short-range order based on a
spin-rotation-invariant slave-boson representation of the 2D t-J model. In the
functional-integral scheme, at the nearest-neighbour pair-approximation level,
the bosonized t-J Lagrangian is transformed to a classical Heisenberg model
with an effective (doping-dependent) exchange interaction which takes into
account the interrelation of ``itinerant'' and ``localized'' magnetic
behaviour. Evaluating the theory in the saddle-point approximation, we find a
suppression of antiferromagnetic and incommensurate spiral long-range-ordered
phases in the favour of a paramagnetic phase with pronounced antiferromagnetic
short-range correlations.Comment: 2 pages, 1 Postscript figure, LTpaper.sty, Proc. XXI Int. Conf. on
Low Temp. Phys. Prague 9
Pauli crystal melting in shaken optical traps
Pauli crystals are ordered geometric structures that emerge in trapped
noninteracting fermionic systems due to their underlying Pauli repulsion. The
deformation of Pauli crystals - often called melting - has been recently
observed in experiments, but the mechanism that leads to it remains unclear. We
address this question by studying the melting dynamics of N=6 fermions as a
function of periodic driving and experimental imperfections in the trap
(anisotropy and anharmonicity) by employing a combination of numerical
simulations and Floquet theory. Surprisingly, we reveal that the melting of
Pauli crystals is not simply a direct consequence of an increase in system
energy, but is instead related to the trap geometry and the population of the
Floquet modes. We show that the melting is absent in traps without
imperfections and triggered only by a sufficiently large shaking amplitude in
traps with imperfections.Comment: 14 pages, 9 figure
Detection of the Filarial Parasite Mansonella streptocerca in Skin Biopsies by a Nested Polymerase Chain Reaction-Based Assay
To differentiate the skin-dwelling filariae Mansonella streptocerca and Onchocerca volvulus, a nested polymerase chain reaction (PCR) assay was developed from small amounts of parasite material present in skin biopsies. One nonspecific and one specific pair of primers were used to amplify the 5S rDNA spacer region of M. streptocerca. Biopsies with different microfilaria densities obtained from 104 Ugandans living in an area endemic forM. streptocerca were tested using both the nested PCR assay and standard parasitologic assessment of microfilariae. All 82 samples from microfilaria carriers were positive when tested using the nested PCR assay. In addition, M. streptocerca DNA could be detected in 16 samples thought to be microfilaria negative. Furthermore, six days follow- ing ivermectin treatment, M. streptocerca DNA was found in 12 of 14 microfilaria-negative biopsies. Control skin samples from patients infected with O. volvulus were all negative in the nested PCR assay. This assay improves the diagnosis of M. streptocerca and will facilitate further epidemiologic studies
Immunohistological studies on neoplasms of female and male Onchocerca volvulus: filarial origin and absence of Wolbachia from tumor cells
Up to 5% of untreated female Onchocerca volvulus filariae develop potentially fatal pleomorphic neoplasms, whose incidence is increased following ivermectin treatment. We studied the occurrence of 8 filarial proteins and of Wolbachia endobacteria in the tumor cells. Onchocercomas from patients, untreated and treated with antibiotics and anthelminthics, were examined by immunohistology. Neoplasms were diagnosed in 112 of 3587 female and in 2 of 1570 male O. volvulus. The following proteins and other compounds of O. volvulus were expressed in the cells of the neoplasms: glutathione S-transferase 1, lysosomal aspartic protease, cAMP-dependent protein kinase, alpha-enolase, aspartate aminotransferase, ankyrin E1, tropomyosin, heat shock protein 60, transforming growth factor-beta, and prostaglandin E2. These findings prove the filarial origin of the neoplasms and confirm the pleomorphism of the tumor cells. Signs indicating malignancy of the neoplasms are described. Wolbachia were observed in the hypodermis, oocytes, and embryos of tumor-harbouring filariae using antibodies against Wolbachia surface protein, Wolbachia HtrA-type serine protease, and Wolbachia aspartate aminotransferase. In contrast, Wolbachia were not found in the cells of the neoplasms. Further, neoplasm-containing worms were not observed after more than 10 months after the start of sufficient treatment with doxycycline or doxycycline plus ivermectin
Thermodynamics of quantum Brownian motion with internal degrees of freedom: the role of entanglement in the strong-coupling quantum regime
We study the influence of entanglement on the relation between the
statistical entropy of an open quantum system and the heat exchanged with a low
temperature environment. A model of quantum Brownian motion of the
Caldeira-Leggett type - for which a violation of the Clausius inequality has
been stated by Th.M. Nieuwenhuizen and A.E. Allahverdyan [Phys. Rev. E 66,
036102 (2002)] - is reexamined and the results of the cited work are put into
perspective. In order to address the problem from an information theoretical
viewpoint a model of two coupled Brownian oscillators is formulated that can
also be viewed as a continuum version of a two-qubit system. The influence of
an additional internal coupling parameter on heat and entropy changes is
described and the findings are compared to the case of a single Brownian
particle.Comment: 10 pages, 11 figure
Assessing uncertainties in flood forecasts for decision making: prototype of an operational flood management system integrating ensemble predictions
Ensemble forecasts aim at framing the uncertainties of the potential future development of the hydro-meteorological situation. A probabilistic evaluation can be used to communicate forecast uncertainty to decision makers. Here an operational system for ensemble based flood forecasting is presented, which combines forecasts from the European COSMO-LEPS, SRNWP-PEPS and COSMO-DE prediction systems. A multi-model lagged average super-ensemble is generated by recombining members from different runs of these meteorological forecast systems. A subset of the super-ensemble is selected based on a priori model weights, which are obtained from ensemble calibration. Flood forecasts are simulated by the conceptual rainfall-runoff-model ArcEGMO. Parameter uncertainty of the model is represented by a parameter ensemble, which is a priori generated from a comprehensive uncertainty analysis during model calibration. The use of a computationally efficient hydrological model within a flood management system allows us to compute the hydro-meteorological model chain for all members of the sub-ensemble. The model chain is not re-computed before new ensemble forecasts are available, but the probabilistic assessment of the output is updated when new information from deterministic short range forecasts or from assimilation of measured data becomes available. For hydraulic modelling, with the desired result of a probabilistic inundation map with high spatial resolution, a replacement model can help to overcome computational limitations. A prototype of the developed framework has been applied for a case study in the Mulde river basin. However these techniques, in particular the probabilistic assessment and the derivation of decision rules are still in their infancy. Further research is necessary and promising
Effects of spin-elastic interactions in frustrated Heisenberg antiferromagnets
The Heisenberg antiferromagnet on a compressible triangular lattice in the
spin- wave approximation is considered. It is shown that the interaction
between quantum fluctuations and elastic degrees of freedom stabilizes the low
symmetric L-phase with a collinear Neel magnetic ordering. Multi-stability in
the dependence of the on-site magnetization on an unaxial pressure is found.Comment: Revtex, 4 pages, 2 eps figure
The Infrared Behavior of Gluon and Ghost Propagators in Landau Gauge QCD
A solvable systematic truncation scheme for the Dyson-Schwinger equations of
Euclidean QCD in Landau gauge is presented. It implements the Slavnov-Taylor
identities for the three-gluon and ghost-gluon vertices, whereas irreducible
four-gluon couplings as well as the gluon-ghost and ghost-ghost scattering
kernels are neglected. The infrared behavior of gluon and ghost propagators is
obtained analytically: The gluon propagator vanishes for small spacelike
momenta whereas the ghost propagator diverges stronger than a massless particle
pole. The numerical solutions are compared with recent lattice data for these
propagators. The running coupling of the renormalization scheme approaches a
fixed point, , in the infrared.Comment: 4 pages, 2 figures, Revtex; revised version accepted for publication
in Physical Review Letter
Технологические решения для строительства разведочной вертикальной скважины глубиной 2520 метров на нефтяном месторождении (Томская область)
Данная работа содержит следующие ключевые слова: буровая установка, бурение, буровой раствор, заканчивание скважин, скважина, нефть охрана окружающей среды, ресурсоффективность. Объектом исследования является разведочная вертикальная скважина глубиной 2540 метров на нефтегазовом месторождении (Томская область).
Целью работы является – спроектировать технологические решения для бурения вертикальной разведочной скважины глубиной 2540 м на месторождении Томской области.This work contains the following keywords: rig, drilling, drilling mud, well completion, well, oil, environmental protection, resource efficiency. The object of the study is a vertical exploration well with a depth of 2540 meters in an oil and gas field (Tomsk region). The aim of the work is to design technological solutions for drilling a vertical exploration well with a depth of 2540 m in the field of the Tomsk region
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