12,014 research outputs found
Regularized Renormalization Group Reduction of Symplectic Map
By means of the perturbative renormalization group method, we study a
long-time behaviour of some symplectic discrete maps near elliptic and
hyperbolic fixed points. It is shown that a naive renormalization group (RG)
map breaks the symplectic symmetry and fails to describe a long-time behaviour.
In order to preserve the symplectic symmetry, we present a regularization
procedure, which gives a regularized symplectic RG map describing an
approximate long-time behaviour succesfully
Electric Control of Spin Helicity in a Magnetic Ferroelectric
Magnetic ferroelectrics or multiferroics, which are currently extensively
explored, may provide a good arena to realize a novel magnetoelectric function.
Here we demonstrate the genuine electric control of the spiral magnetic
structure in one of such magnetic ferroelectrics, TbMnO3. A spin-polarized
neutron scattering experiment clearly shows that the spin helicity, clockwise
or counter-clockwise, is controlled by the direction of spontaneous
polarization and hence by the polarity of the small cooling electric field.Comment: 4 pages, 3 figure
Collinear-to-Spiral Spin Transformation without Changing Modulation Wavelength upon Ferroelectric Transition in Tb1-xDyxMnO3
Lattice modulation and magnetic structures in magnetoelectric compounds
Tb1-xDyxMnO3 have been studied around the ferroelectric (FE) Curie temperature
T_C by x-ray and neutron diffraction. Temperature-independent modulation
vectors through T_C are observed for the compounds with 0.50< x < 0.68. This
indicates that ferroelectricity with a polarization (P) along the c axis in the
RMnO3 series cannot be ascribed to such an incommensurate-commensurate
transition of an antiferromagnetic order as was previously anticipated. Neutron
diffraction study of a single crystal with x=0.59 shows that the FE transition
is accompanied by the transformation of the Mn-spin alignment from sinusoidal
(collinear) antiferromagnetism into a transverse spiral structure. The observed
spiral structure below T_C is expected to produce P along the c axis with the
`inverse' Dzialoshinski-Moriya interaction, which is consistent with the
observation.Comment: 9 pages, 4 figure
Derivation of Non-isotropic Phase Equations from a General Reaction-Diffusion Equation
A non-isotropic version of phase equations such as the Burgers equation, the
K-dV-Burgers equation, the Kuramoto-Sivashinsky equation and the Benney
equation in the three-dimensional space is systematically derived from a
general reaction-diffusion system by means of the renormalization group method.Comment: 21pages,no figure
Environmental dependence of 8um luminosity functions of galaxies at z~0.8: Comparison between RXJ1716.4+6708 and the AKARI NEP deep field
We aim to reveal environmental dependence of infrared luminosity functions
(IR LFs) of galaxies at z~0.8 using the AKARI satellite. We construct restframe
8um IR LFs in the cluster region RXJ1716.4+6708 at z=0.81, and compare them
with a blank field using the AKARI North Ecliptic Pole deep field data at the
same redshift. AKARI's wide field of view (10'x10') is suitable to investigate
wide range of galaxy environments. AKARI's 15um filter is advantageous here
since it directly probes restframe 8um at z~0.8, without relying on a large
extrapolation based on a SED fit, which was the largest uncertainty in previous
work. We have found that cluster IR LFs at restframe 8um have a factor of 2.4
smaller L^* and a steeper faint-end slope than that of the field. Confirming
this trend, we also found that faint-end slopes of the cluster LFs becomes
flatter and flatter with decreasing local galaxy density. These changes in LFs
cannot be explained by a simple infall of field galaxy population into a
cluster. Physics that can preferentially suppress IR luminous galaxies in high
density regions is required to explain the observed results.Comment: Accepted for publication in A&A AKARI special issu
Realization of Strong Coupling Fixed Point in Multilevel Kondo Models
Impurity four- and six-level Kondo model, in which an ion is tunneling among
four- and six-stable points and interacting with surrounding conduction
electrons, are investigated by using the perturbative and numerical
renormalization group methods. It is shown that purely orbital Kondo effects
occur at low temperatures in these systems which are direct generalizations of
the Kondo effect in the so-called two-level system. This result offers a good
explanation for the enhanced and magnetically robust Sommerfeld coefficient
observed in SmOs_4Sb_12 and some other filled-skutterudites.Comment: 3 pages, 3 figures, for proceedings of ASR-WYP-2005. To be published
in Journal of Physical Society Japan supplemen
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