4,178 research outputs found
Kondo effect in "bad metals"
We study the low-temperature properties of a Kondo lattice using the large-N
formalism. For a singular density of conduction states (DOS), we generalize the
single-impurity result of Withoff and Fradkin: the strong-coupling fixed point
becomes irrelevant if the DOS vanishes at the Fermi level E_F. However, for E_F
close enough to the singularity, and close to half-filling, the Kondo
temperature, , can become much smaller than the characteristic Fermi
liquid scale. At T=0, a meta-magnetic transition occurs at the critical
magnetic field H_c ~ (k_B/mu_B) T_K. Our results provide a qualitative
explanation for the behavior of the YbInCu_4 compound below the valence-change
transition.Comment: 4 pages, 1 figur
Numerical simulation of hydraulic processes in anaerobic bioreactors
The aim of the work was to determine the rate and uniformity of temperature distribution in the amount of biogas plant constructed by UrFU, "Avanguard" PLC and "Gildia-M" Ltd on the stage of warming and achieving the rated work conditions corresponding to the mesophilic fermentation process. A computer model of the biogas reactor, considering the main unit features, was created. The installation heating was carried out by uniform thermal energy supply through the outer surface of the vessel full of substrate. Numerical solution was achieved by the finite volume method which has the following features. The calculation results in the form of temperature fields and the substrate particle trajectories for several time moments are given in this paper. The results analysis shows the possibility to use the model for the thermohydraulic computation of various operation modes of the bioreactor. © 2014 WIT Press.International Journal of Safety and Security Engineering;International Journal of Sustainable Development and Planning;WIT Transactions on Ecology and the Environmen
A device to characterize optical fibres
ATLAS is a general purpose experiment approved for the LHC collider at CERN.
An important component of the detector is the central hadronic calorimeter; for
its construction more than 600,000 Wave Length Shifting (WLS) fibres
(corresponding to a total length of 1,120 Km) have been used.
We have built and put into operation a dedicated instrument for the
measurement of light yield and attenuation length over groups of 20 fibres at a
time.
The overall accuracy achieved in the measurement of light yield
(attenuation length) is 1.5% (3%).
We also report the results obtained using this method in the quality control
of a large sample of fibres.Comment: 17 pages 20 figeres submitted to NIM journa
Evidence of phi --> pi0 pi0 gamma and phi --> pi0 eta gamma decays in SND experiment at VEPP-2M
Preliminary results on the study of e+e- --> phi(1020) --> pi0 pi0 gamma, eta
pi0 gamma processes from SND experiment at VEPP-2M collider in Novosibirsk are
presented. Branching ratios of rare radiative phi --> pi0 pi0 gamma and phi -->
pi0 eta gamma decays are measured:
B(phi --> pi0 pi0 gamma ) = (1.1 +- 0.2) * 10^-4
(invariant mass (pi0 pi0) < 800 MeV),
B(phi --> eta pi0 gamma ) = (1.3 +- 0.5) * 10^-4.Comment: Talk at the HADRON97 conference, BNL, Aug 24-30 1997; LaTeX, 4 pages,
4 eps figure
Heavy-fermion and spin-liquid behavior in a Kondo lattice with magnetic frustration
We study the competition between the Kondo effect and frustrating exchange
interactions in a Kondo-lattice model within a large- dynamical
mean-field theory. We find a T=0 phase transition between a heavy Fermi-liquid
and a spin-liquid for a critical value of the exchange , the
single-impurity Kondo temperature. Close to the critical point, the Fermi
liquid coherence scale is strongly reduced and the effective mass
strongly enhanced. The regime is characterized by spin-liquid
magnetic correlations and non-Fermi-liquid properties. It is suggested that
magnetic frustration is a general mechanism which is essential to explain the
large effective mass of some metallic compounds such as LiVO.Comment: 7 pages, 1 figure. Late
Electronic states and magnetic excitations in LiV2O4: Exact diagonalization study
Motivated by recent inelastic neutron scattering experiment we examine
magnetic properties of LiV2O4. We consider a model which describes the
half-filled localized A1g spins interacting via frustrated antiferromagnetic
Heisenberg exchange and coupled by local Hund's interaction with the 1/8-filled
itinerant Eg band, and study it within an exact diagonalization scheme. In the
present study we limited the analysis to the case of the cluster of two
isolated tetrahedrons. We obtained that both the ground state structure and
low-lying excitations depend strongly on the value of the Hund's coupling which
favors the triplet states. With increasing temperature the triplet states
become more and more populated which results in the formation of non-zero
residual magnetic moment. We present the temperature dependence of calculated
magnetic moment and of the spin-spin correlation functions at different values
of Hund's coupling and compare them with the experimental results.Comment: 7 pages. 6 eps figure
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