3,162 research outputs found
Chiral phase transition at high temperature and density in the QCD-like theory
The chiral phase transition at finite temperature T and/or chemical potential
is studied using the QCD-like theory with a variational approach. The
``QCD-like theory'' means the improved ladder approximation with an infrared
cutoff in terms of a modified running coupling. The form of
Cornwall-Jackiw-Tomboulis effective potential is modified by the use of the
Schwinger-Dyson equation for generally nonzero current quark mass. We then
calculate the effective potential at finite T and/or and investigate the
phase structure in the chiral limit. We have a second-order phase transition at
MeV for and a first-order one at MeV for T=0. A
tricritical point in the T- plane is found at T=107 MeV, MeV.
The position is close to that of the random matrix model and some version of
the Nambu-Jona-Lasinio model.Comment: 10 pages, 6 figures. Accepted for publication in Physical Review
Rotor vibration caused by external excitation and rub
For turbomachinery with low natural frequencies, considerations have been recently required for rotor vibrations caused by external forces except unbalance one, such as foundation motion, seismic wave, rub and so forth. Such a forced vibration is investigated analytically and experimentally in the present paper. Vibrations in a rotor-bearing system under a harmonic excitation are analyzed by the modal technique in the case of a linear system including gyroscopic effect. For a nonlinear system a new and powerful quasi-modal technique is developed and applied to the vibration caused by rub
Queue lengths and workloads in polling systems
We consider a polling system: a queueing system of queues with
Poisson arrivals visited in a cyclic order (with or without
switchover times) by a single server. For this system we derive the probability
generating function of the joint queue length distribution
at an arbitrary epoch in a stationary cycle, under no assumptions on service
disciplines. We also derive the Laplace-Stieltjes transform
of the joint workload distribution at an arbitrary epoch. We express and in the probability generating functions of the joint queue
length distribution at visit beginnings, , and visit
completions, , at , . It is well
known that and can be computed in a
broad variety of cases. Furthermore, we establish a workload decomposition
result
Generic phase diagram of "electron-doped" T' cuprates
We investigated the generic phase diagram of the electron doped
superconductor, Nd2-xCexCuO4, using films prepared by metal organic
decomposition. After careful oxygen reduction treatment to remove interstitial
Oap atoms, we found that the Tc increases monotonically from 24 K to 29 K with
decreasing x from 0.15 to 0.00, demonstrating a quite different phase diagram
from the previous bulk one. The implication of our results is discussed on the
basis of tremendous influence of Oap "impurities" on superconductivity and also
magnetism in T' cuprates. Then we conclude that our result represents the
generic phase diagram for oxygen-stoichiometric Nd2-xCexCuO4.Comment: 12 pages, 4 figures; International Symposium on Superconductivity
(ISS) 200
Comparative investigation of the coupled-tetrahedra quantum spin systems Cu2Te2O5X2, X=Cl, Br and Cu4Te5O12Cl4
We present a comparative study of the coupled-tetrahedra quantum spin systems
Cu2Te2O5X2, X=Cl, Br (Cu-2252(X)) and the newly synthesized Cu4Te5O12Cl4
(Cu-45124(Cl)) based on ab initio Density Functional Theory calculations. The
magnetic behavior of Cu-45124(Cl) with a phase transition to an ordered state
at a lower critical temperature T=13.6K than in Cu-2252(Cl) (T=18K) can
be well understood in terms of the modified interaction paths. We identify the
relevant structural changes between the two systems and discuss the
hypothetical behavior of the not yet synthesized Cu-45124(Br) with an ab initio
relaxed structure using Car-Parrinello Molecular Dynamics.Comment: 2 pages, 1 figure; submitted to Proceedings of M2S-HTSC VIII, Dresden
200
Inversion of the Diffraction Pattern from an Inhomogeneously Strained Crystal using an Iterative Algorithm
The displacement field in highly non uniformly strained crystals is obtained
by addition of constraints to an iterative phase retrieval algorithm. These
constraints include direct space density uniformity and also constraints to the
sign and derivatives of the different components of the displacement field.
This algorithm is applied to an experimental reciprocal space map measured
using high resolution X-ray diffraction from an array of silicon lines and the
obtained component of the displacement field is in very good agreement with the
one calculated using a finite element model.Comment: 5 pages, 4 figure
Iterative Perturbation Theory for Strongly Correlated Electron Systems with Orbital Degeneracy
A new scheme of the iterative perturbation theory is proposed for the
strongly correlated electron systems with orbital degeneracy. The method is
based on the modified self-energy of Yeyati, et al. which interpolates between
the weak and the strong correlation limits, but a much simpler scheme is
proposed which is useful in the case of the strong correlation with orbital
degeneracy. It will be also useful in the study of the electronic structures
combined with the band calculations.Comment: 6 pages, 3 Postscript figures, to appear in J. Phys. Cond. Matte
Commensurate structural modulation in the charge- and orbitally-ordered phase of the quadruple perovskite (NaMn)MnO
By means of synchrotron x-ray and electron diffraction, we studied the
structural changes at the charge order transition =176 K in the
mixed-valence quadruple perovskite (NaMn)MnO. Below we
find satellite peaks indicating a commensurate structural modulation with the
same propagation vector q =(1/2,0,-1/2) of the CE magnetic order that appears
at low temperature, similarly to the case of simple perovskites like
LaCaMnO. In the present case, the modulated structure
together with the observation of a large entropy change at gives
evidence of a rare case of full Mn/Mn charge and orbital order
consistent with the Goodenough-Kanamori model.Comment: Accepted for publication in Phys. Rev. B Rapid Communication
Generalized Numerical Renormalization Group for Dynamical Quantities
In this paper we introduce a new approach for calculating dynamical
properties within the numerical renormalization group. It is demonstrated that
the method previously used fails for the Anderson impurity in a magnetic field
due to the absence of energy scale separation. The problem is solved by
evaluating the Green function with respect to the reduced density matrix of the
full system, leading to accurate spectra in agreement with the static
magnetization. The new procedure (denoted as DM-NRG) provides a unifying
framework for calculating dynamics at any temperature and represents the
correct extension of Wilson's original thermodynamic calculation.Comment: 4 pages RevTeX, 6 eps figures include
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