11,366 research outputs found
Metallic Continuum Quantum Ferromagnets at Finite Temperature
We study via renormalization group (RG) and large N methods the problem of
continuum SU(N) quantum Heisenberg ferromagnets (QHF) coupled to gapless
electrons. We establish the phase diagram of the dissipative problem and
investigate the changes in the Curie temperature, magnetization, and magnetic
correlation length due to dissipation and both thermal and quantum
fluctuations. We show that the interplay between the topological term (Berry's
phase) and dissipation leads to non-trivial effects for the finite temperature
critical behavior.Comment: Corrected typos, new discussion of T=0 results, to appear in
Europhys. Let
Wave polarizations for a beam-like gravitational wave in quadratic curvature gravity
We compute analytically the tidal field and polarizations of an exact
gravitational wave generated by a cylindrical beam of null matter of finite
width and length in quadratic curvature gravity. We propose that this wave can
represent the gravitational wave that keep up with the high energy photons
produced in a gamma ray burst (GRB) source.Comment: 5 pages, 3 figures, minor corrections, to appear in CQ
Tradeoffs in manipulator structure and control. Part 1: Summary
The study of various aspects of manipulator design and control is summarized, focusing on the interaction of the structure's flexible dynamics and the dynamics of the joint control system, including specific information on modeling and design, modal analysis and control, and the flexible manipulator analysis computer program, FMAP
Quantum Hall plateau transition in the lowest Landau level of disordered graphene
We investigate, analytically and numerically, the effects of disorder on the
density of states and on the localization properties of the relativistic two
dimensional fermions in the lowest Landau level. Employing a supersymmetric
technique, we calculate the exact density of states for the Cauchy (Lorentzian)
distribution for various types of disorders. We use a numerical technique to
establish the localization-delocalization (LD) transition in the lowest Landau
level. For some types of disorder the LD transition is shown to belong to a
different universality class, as compared to the corresponding nonrelativistic
problem. The results are relevant to the integer quantum Hall plateau
transitions observed in graphene.Comment: 18 pages and 11 figure
A Tale of Two Theories: Quantum Griffiths Effects in Metallic Systems
We show that two apparently contradictory theories on the existence of
Griffiths-McCoy singularities in magnetic metallic systems [1,2] are in fact
mathematically equivalent. We discuss the generic phase diagram of the problem
and show that there is a non-universal crossover temperature range T* < T < W
where power law behavior (Griffiths-McCoy behavior) is expect. For T<T* power
law behavior ceases to exist due to the destruction of quantum effects
generated by the dissipation in the metallic environment. We show that T* is an
analogue of the Kondo temperature and is controlled by non-universal couplings.Comment: 4 pages, 2 figure
Sistema portátil de fluorescência induzida por laser para análise de matéria orgânica em solos.
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