3,140 research outputs found
Lattice and q-difference Darboux-Zakharov-Manakov systems via -dressing method
A general scheme is proposed for introduction of lattice and q-difference
variables to integrable hierarchies in frame of -dressing
method . Using this scheme, lattice and q-difference Darboux-Zakharov-Manakov
systems of equations are derived. Darboux, B\"acklund and Combescure
transformations and exact solutions for these systems are studied.Comment: 8 pages, LaTeX, to be published in J Phys A, Letters
New Perturbation Theory for Nonstationary Anharmonic Oscillator
The new perturbation theory for the problem of nonstationary anharmonic
oscillator with polynomial nonstationary perturbation is proposed. As a zero
order approximation the exact wave function of harmonic oscillator with
variable frequency in external field is used. Based on some intrinsic
properties of unperturbed wave function the variational-iterational method is
proposed, that make it possible to correct both the amplitude and the phase of
wave function. As an application the first order correction are proposed both
for wave function and S-matrix elements for asymmetric perturbation potential
of type The transition amplitude
''ground state - ground state'' is analyzed in detail
depending on perturbation parameter (including strong coupling
region ) and one-dimensional refraction coefficient .Comment: LaTeX, 13 page
Intermediate phase in the spiral antiferromagnet Ba_2CuGe_2O_7
The magnetic compound Ba_2CuGe_2O_7 has recently been shown to be an
essentially two-dimensional spiral antiferromagnet that exhibits an
incommensurate-to-commensurate phase transition when a magnetic field applied
along the c-axis exceeds a certain critical value H_c. The T=0 dynamics is
described here in terms of a continuum field theory in the form of a nonlinear
sigma model. We are thus in a position to carry out a complete calculation of
the low-energy magnon spectrum for any strength of the applied field throughout
the phase transition. In particular, our spin-wave analysis reveals
field-induced instabilities at two distinct critical fields H_1 and H_2 such
that H_1 < H_c < H_2. Hence we predict the existence of an intermediate phase
whose detailed nature is also studied to some extent in the present paper.Comment: 15 pages, 11 figures, 2 table
Functional representations of integrable hierarchies
We consider a general framework for integrable hierarchies in Lax form and
derive certain universal equations from which `functional representations' of
particular hierarchies (like KP, discrete KP, mKP, AKNS), i.e. formulations in
terms of functional equations, are systematically and quite easily obtained.
The formalism genuinely applies to hierarchies where the dependent variables
live in a noncommutative (typically matrix) algebra. The obtained functional
representations can be understood as `noncommutative' analogs of `Fay
identities' for the KP hierarchy.Comment: 21 pages, version 2: equations (3.28) and (4.11) adde
Magnetic phases and reorientation transitions in antiferromagnetically coupled multilayers
In antiferromagnetically coupled superlattices grown on (001) faces of cubic
substrates, e.g. based on materials combinations as Co/Cu, Fe/Si, Co/Cr, or
Fe/Cr, the magnetic states evolve under competing influence of bilinear and
biquadratic exchange interactions, surface-enhanced four-fold in-plane
anisotropy, and specific finite-size effects. Using phenomenological
(micromagnetic) theory, a comprehensive survey of the magnetic states and
reorientation transitions has been carried out for multilayer systems with even
number of ferromagnetic sub-layers and magnetizations in the plane. In
two-layer systems (N=2) the phase diagrams in dependence on components of the
applied field in the plane include ``swallow-tail'' type regions of
(metastable) multistate co-existence and a number of continuous and
discontinuous reorientation transitions induced by radial and transversal
components of the applied field. In multilayers (N \ge 4) noncollinear states
are spatially inhomogeneous with magnetization varying across the multilayer
stack. For weak four-fold anisotropy the magnetic states under influence of an
applied field evolve by a complex continuous reorientation into the saturated
state. At higher anisotropy they transform into various inhomogeneous and
asymmetric structures. The discontinuous transitions between the magnetic
states in these two-layers and multilayers are characterized by broad ranges of
multi-phase coexistence of the (metastable) states and give rise to specific
transitional domain structures.Comment: Manuscript 34 pages, 14 figures; submitted for publicatio
Limb-Darkening of a K Giant in the Galactic Bulge: PLANET Photometry of MACHO 97-BLG-28
We present the PLANET photometric dataset for the binary-lens microlensing
event MACHO 97-BLG-28 consisting of 696 I and V-band measurements, and analyze
it to determine the radial surface brightness profile of the Galactic bulge
source star. The microlensed source, demonstrated to be a K giant by our
independent spectroscopy, crossed the central isolated cusp of the lensing
binary, generating a sharp peak in the light curve that was well-resolved by
dense (3 - 30 minute) and continuous monitoring from PLANET sites in Chile,
South Africa, and Australia. Our modeling of these data has produced stellar
profiles for the source star in the I and V bands that are in excellent
agreement with those predicted by stellar atmospheric models for K giants. The
limb-darkening coefficients presented here are the first derived from
microlensing, among the first for normal giants by any technique, and the first
for any star as distant as the Galactic bulge. Modeling indicates that the
lensing binary has a mass ratio q = 0.23 and an (instantaneous) separation in
units of the angular Einstein ring radius of d = 0.69 . For a lens in the
Galactic bulge, this corresponds to a typical stellar binary with a projected
separation between 1 and 2 AU. If the lens lies closer, the separation is
smaller, and one or both of the lens objects is in the brown dwarf regime.
Assuming that the source is a bulge K2 giant at 8 kpc, the relative lens-source
proper motion is mu = 19.4 +/- 2.6 km/s /kpc, consistent with a disk or bulge
lens. If the non-lensed blended light is due to a single star, it is likely to
be a young white dwarf in the bulge, consistent with the blended light coming
from the lens itself.Comment: 32 Pages, including 1 table and 9 postscript figures. (Revised
version has slightly modified text, corrected typo, and 1 new figure.)
Accepted for publication in 1999 Astrophysical Journal; data are now
available at http://www.astro.rug.nl/~plane
Polarization ququarts
We discuss the concept of polarization states of four-dimensional quantum
systems based on frequency non-degenerate biphoton field. Several quantum
tomography protocols were developed and implemented for measurement of an
arbitrary state of ququart. A simple method that does not rely on
interferometric technique is used to generate and measure the sequence of
states that can be used for quantum communication purposes.Comment: 13 pages, 10 figure
Spin and orbital dynamics through the metal-to-insulator transition in CdOsO probed with high-resolution RIXS
High-resolution resonant inelastic x-ray scattering (RIXS) measurements
(E = 46 meV) have been performed on CdOsO through the
metal-to-insulator transition (MIT). A magnetic excitation at 125 meV evolves
continuously through the MIT, in agreement with recent Raman scattering
results, and provides further confirmation for an all-in, all-out magnetic
ground state. Asymmetry of this feature is likely a result of coupling between
the electronic and magnetic degrees of freedom. We also observe a broad
continuum of interband excitations centered at 0.3 eV energy loss. This is
indicative of significant hybridization between Os 5 and O 2 states, and
concurrent itinerant nature of the system. In turn, this suggests a possible
break down of the free-ion model for CdOsO.Comment: Accepted in Physical Review B (10 pages
Strongly Gapped Spin-Wave Excitation in the Insulating Phase of NaOsO3
NaOsO3 hosts a rare manifestation of a metal-insulator transition driven by
magnetic correlations, placing the magnetic exchange interactions in a central
role. We use resonant inelastic x-ray scattering to directly probe these
magnetic exchange interactions. A dispersive and strongly gapped (58 meV)
excitation is observed indicating appreciable spin-orbit coupling in this 5d3
system. The excitation is well described within a minimal model Hamiltonian
with strong anisotropy and Heisenberg exchange (J1=J2=13.9 meV). The observed
behavior places NaOsO3 on the boundary between localized and itinerant
magnetism
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