21,186 research outputs found
Infrared absorption and Raman scattering on coupled plasmon--phonon modes in superlattices
We consider theoretically a superlattice formed by thin conducting layers
separated spatially between insulating layers. The dispersion of two coupled
phonon-plasmon modes of the system is analyzed by using Maxwell's equations,
with the influence of retardation included. Both transmission for the finite
plate as well as absorption for the semi-infinite superlattice in the infrared
are calculated. Reflectance minima are determined by the longitudinal and
transverse phonon frequencies in the insulating layers and by the density-state
singularities of the coupled modes. We evaluate also the Raman cross section
from the semi-infinite superlattice.Comment: 20 pages,14 figure
Field and temperature dependence of the NMR relaxation rate in the magnetic quadrupolar liquid phase of spin-1/2 frustrated ferromagnetic chains
It is generally difficult to experimentally distinguish magnetic multipolar
orders in spin systems. Recently, it was proposed that the temperature
dependence of the nuclear magnetic resonance relaxation rate 1/T_1 can involve
an indirect, but clear signature of the field-induced spin nematic or
multipolar Tomonaga-Luttinger (TL) liquid phase [Phys. Rev. B79, 060406(R)
(2009)]. In this paper, we evaluate accurately the field and temperature
dependence of 1/T_1 in spin-1/2 frustrated J1-J2 chains combining
field-theoretical techniques with numerical data. Our results demonstrate that
isotherms of 1/T_1 as a function of magnetic field also exhibit distinctive
non-monotonic behavior in spin nematic TL liquid, in contrast with the standard
TL liquid in the spin-1/2 Heisenberg chain. The relevance of our results to
quasi one-dimensional edge-sharing cuprate magnets, such as LiCuVO4, is
discussed.Comment: 11 pages (2 column), 5 figures, published versio
Exact evaluation of density matrix elements for the Heisenberg chain
We have obtained all the density matrix elements on six lattice sites for the
spin-1/2 Heisenberg chain via the algebraic method based on the quantum
Knizhnik-Zamolodchikov equations. Several interesting correlation functions,
such as chiral correlation functions, dimer-dimer correlation functions, etc...
have been analytically evaluated. Furthermore we have calculated all the
eigenvalues of the density matrix and analyze the eigenvalue-distribution. As a
result the exact von Neumann entropy for the reduced density matrix on six
lattice sites has been obtained.Comment: 33 pages, 4 eps figures, 3 author
String correlation functions of the spin-1/2 Heisenberg XXZ chain
We calculate certain string correlation functions, originally introduced as
order parameters in integer spin chains, for the spin-1/2 XXZ Heisenberg chain
at zero temperature and in the thermodynamic limit. For small distances, we
obtain exact results from Bethe Ansatz and exact diagonalization, whereas in
the large-distance limit, field-theoretical arguments yield an asymptotic
algebraic decay. We also make contact with two-point spin-correlation functions
in the asymptotic limit.Comment: 23 pages, 4 figures. An incomplete discussion on the limit to the
spin-spin correlation function is corrected on page 1
Quantum Hall Effect Wave Functions as Cyclic Representations of U_q(sl(2))
Quantum Hall effect wave functions corresponding to the filling factors
1/2p+1, 2/2p+1, ..., 2p/2p+1, 1, are shown to form a basis of irreducible
cyclic representation of the quantum algebra U_q(sl(2)) at q^{2p+1}=1. Thus,
the wave functions \Psi_{P/Q} possessing filling factors P/Q<1 where Q is odd
and P, Q are relatively prime integers are classified in terms of U_q(sl(2)).Comment: Version to appear in Jour. Phys.
Akns Hierarchy, Self-Similarity, String Equations and the Grassmannian
In this paper the Galilean, scaling and translational self--similarity
conditions for the AKNS hierarchy are analysed geometrically in terms of the
infinite dimensional Grassmannian. The string equations found recently by
non--scaling limit analysis of the one--matrix model are shown to correspond to
the Galilean self--similarity condition for this hierarchy. We describe, in
terms of the initial data for the zero--curvature 1--form of the AKNS
hierarchy, the moduli space of these self--similar solutions in the Sato
Grassmannian. As a byproduct we characterize the points in the Segal--Wilson
Grassmannian corresponding to the Sachs rational solutions of the AKNS equation
and to the Nakamura--Hirota rational solutions of the NLS equation. An explicit
1--parameter family of Galilean self--similar solutions of the AKNS equation
and the associated solution to the NLS equation is determined.Comment: 25 pages in AMS-LaTe
Produção integrada.
Resumo: O morango é um produto de forte apelo entre os consumidores e uma ótima fonte de renda para os agricultores familiares. No entanto, problemas com contaminações por agrotóxicos, principalmente, prejudicam a imagem do produto e do produtor. A produção integrada surgiu como um sistema de produção agrícola alternativo em que, embora ainda seja permitido o uso de agrotóxicos, esta prática deve ser feita de forma criteriosa, de preferência depois de esgotadas as formas de controle físicas e biológicas. Essa é a base do Programa Produção Integrada Agropecuária (PI Brasil), dentro do qual foram estabelecidos requisitos técnicos específicos para a produção de morangos seguros e de qualidade. Apresentam-se os objetivos, desafios e avanços do Programa Produção Integrada de Morango (PI Morango)
Young diagrams and N-soliton solutions of the KP equation
We consider -soliton solutions of the KP equation,
(-4u_t+u_{xxx}+6uu_x)_x+3u_{yy}=0 . An -soliton solution is a solution
which has the same set of line soliton solutions in both
asymptotics and . The -soliton solutions include
all possible resonant interactions among those line solitons. We then classify
those -soliton solutions by defining a pair of -numbers with , which labels line solitons in the solution. The
classification is related to the Schubert decomposition of the Grassmann
manifolds Gr, where the solution of the KP equation is defined as a
torus orbit. Then the interaction pattern of -soliton solution can be
described by the pair of Young diagrams associated with . We also show that -soliton solutions of the KdV equation obtained by
the constraint cannot have resonant interaction.Comment: 22 pages, 5 figures, some minor corrections and added one section on
the KdV N-soliton solution
- …