5,059 research outputs found
Non-Hamiltonian generalizations of the dispersionless 2DTL hierarchy
We consider two-component integrable generalizations of the dispersionless
2DTL hierarchy connected with non-Hamiltonian vector fields, similar to the
Manakov-Santini hierarchy generalizing the dKP hierarchy. They form a
one-parametric family connected by hodograph type transformations. Generating
equations and Lax-Sato equations are introduced, a dressing scheme based on the
vector nonlinear Riemann problem is formulated. The simplest two-component
generalization of the dispersionless 2DTL equation is derived, its differential
reduction analogous to the Dunajski interpolating system is presented. A
symmetric two-component generalization of the dispersionless elliptic 2DTL
equation is also constructed.Comment: 10 pages, the text of the talk at NEEDS 09. Notations clarified,
references adde
`Interpolating' differential reductions of multidimensional integrable hierarchies
We transfer the scheme of constructing differential reductions, developed
recently for the case of the Manakov-Santini hierarchy, to the general
multidimensional case. We consider in more detail the four-dimensional case,
connected with the second heavenly equation and its generalization proposed by
Dunajski. We give a characterization of differential reductions in terms of the
Lax-Sato equations as well as in the framework of the dressing method based on
nonlinear Riemann-Hilbert problem.Comment: Based on the talk at NLPVI, Gallipoli, 15 page
Precursor phenomena at the magnetic ordering of the cubic helimagnet FeGe
We report on detailed magnetic measurements on the cubic helimagnet FeGe in
external magnetic fields and temperatures near the onset of long-range magnetic
order at K. Precursor phenomena display a complex succession of
temperature-driven crossovers and phase transitions in the vicinity of .
The A-phase region, present below and fields kOe, is split in
several pockets. Relying on a modified phenomenological theory for chiral
magnets, the main part of the A-phase could indicate the existence of a
Skyrmion lattice, the adjacent A pocket, however, appears to be related to
helicoids propagating in directions perpendicular to the applied field.Comment: 5 pages, 4 figure
On a class of reductions of Manakov-Santini hierarchy connected with the interpolating system
Using Lax-Sato formulation of Manakov-Santini hierarchy, we introduce a class
of reductions, such that zero order reduction of this class corresponds to dKP
hierarchy, and the first order reduction gives the hierarchy associated with
the interpolating system introduced by Dunajski. We present Lax-Sato form of
reduced hierarchy for the interpolating system and also for the reduction of
arbitrary order. Similar to dKP hierarchy, Lax-Sato equations for (Lax
fuction) due to the reduction split from Lax-Sato equations for (Orlov
function), and the reduced hierarchy for arbitrary order of reduction is
defined by Lax-Sato equations for only. Characterization of the class of
reductions in terms of the dressing data is given. We also consider a waterbag
reduction of the interpolating system hierarchy, which defines
(1+1)-dimensional systems of hydrodynamic type.Comment: 15 pages, revised and extended, characterization of the class of
reductions in terms of the dressing data is give
Chandra X-ray Observations of 12 Millisecond Pulsars in the Globular Cluster M28
We present a Chandra X-ray Observatory investigation of the millisecond
pulsars (MSPs) in the globular cluster M28 (NGC 6626). In what is one of the
deepest X-ray observations of a globular cluster, we firmly detect seven and
possibly detect two of the twelve known M28 pulsars. With the exception of PSRs
B1821-24 and J1824-2452H, the detected pulsars have relatively soft spectra,
with X-ray luminosities 10^30-31 ergs s^-1 (0.3-8 keV),similar to most
"recycled" pulsars in 47 Tucanae and the field of the Galaxy, implying thermal
emission from the pulsar magnetic polar caps. We present the most detailed
X-ray spectrum to date of the energetic PSR B1821-24. It is well described by a
purely non-thermal spectrum with spectral photon index 1.23 and luminosity
1.4x10^33Theta(D/5.5 kpc)^2 ergs s^-1 (0.3-8 keV), where Theta is the fraction
of the sky covered by the X-ray emission beam(s). We find no evidence for the
previously reported line emission feature around 3.3 keV, most likely as a
consequence of improvements in instrument calibration. The X-ray spectrum and
pulse profile of PSR B1821--24 suggest that the bulk of unpulsed emission from
this pulsar is not of thermal origin, and is likely due to low-level
non-thermal magnetospheric radiation, an unresolved pulsar wind nebula, and/or
small-angle scattering of the pulsed X-rays by interstellar dust grains. The
peculiar binary PSR J1824-2452H shows a relatively hard X-ray spectrum and
possible variability at the binary period, indicative of an intrabinary shock
formed by interaction between the relativistic pulsar wind and matter from its
non-degenerate companion star.Comment: 9 pages, 6 figures. Accepted for publication in the Astophysical
Journa
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