401 research outputs found
Basic properties of three-leg Heisenberg tube
We study three-leg antiferromagnetic Heisenberg model with the periodic
boundary conditions in the rung direction. Since the rungs form regular
triangles, spin frustration is induced. We use the density-matrix
renormalization group method to investigate the ground state. We find that the
spin excitations are always gapped to remove the spin frustration as long as
the rung coupling is nonzero. We also visibly confirm spin-Peierls dimerization
order in the leg direction. Both the spin gap and the dimerization order are
basically enhanced as the rung coupling increases.Comment: 4 pages, 2 figure
Spinon excitations in the XX chain: spectra, transition rates, observability
The exact one-to-one mapping between (spinless) Jordan-Wigner lattice
fermions and (spin-1/2) spinons is established for all eigenstates of the
one-dimensional s = 1=2 XX model on a lattice with an even or odd number N of
lattice sites and periodic boundary conditions. Exact product formulas for the
transition rates derived via Bethe ansatz are used to calculate asymptotic
expressions of the 2-spinon and 4-spinon parts (for large even N) as well as of
the 1-spinon and 3-spinon parts (for large odd N) of the dynamic spin structure
factors. The observability of these spectral contributions is assessed for
finite and infinite N.Comment: 19 pages, 10 figure
A Survey of Hydroxyl Toward Supernova Remnants: Evidence for Extended 1720 MHz Maser Emission
We present the results of GBT observations of all four ground-state hydroxyl
(OH) transitions toward 15 supernova remnants (SNRs) which show OH(1720 MHz)
maser emission. This species of maser is well established as an excellent
tracer of an ongoing interaction between the SNR and dense molecular material.
For the majority of these objects we detect significantly higher flux densities
with a single dish than has been reported with interferometric observations. We
infer that spatially extended, low level maser emission is a common phenomenon
that traces the large-scale interaction in maser-emitting SNRs. Additionally we
use a collisional pumping model to fit the physical conditions under which OH
is excited behind the SNR shock front. We find the observed OH gas associated
with the SNR interaction having columns less than approximately 10^17 per
square cm, temperatures of 20 to 125 K, and densities 10^5 per cubic cm.Comment: 24 pages, 23 figures, Accepted to ApJ, March 26, 2008; v2 - added
Figure 6, minor clarifications to text in Sections 3 and
Photoreceptor spectral sensitivities of the Small White butterfly Pieris rapae crucivora interpreted with optical modeling
The compound eye of the Small White butterfly, Pieris rapae crucivora, has four classes of visual pigments, with peak absorption in the ultraviolet, violet, blue and green, but electrophysiological recordings yielded eight photoreceptors classes: an ultraviolet, violet, blue, double-peaked blue, green, blue-suppressed-green, pale-red and deep-red class. These photoreceptor classes were identified in three types of ommatidia, distinguishable by the different eye shine spectra and fluorescence; the latter only being present in the eyes of males. We present here two slightly different optical models that incorporate the various visual pigments, the light-filtering actions of the fluorescent, pale-red and deep-red screening pigment, located inside or adjacent to the rhabdom, and the reflectance spectrum of the tapetum that abuts the rhabdom proximally. The models serve to explain the photoreceptor spectral sensitivities as well as the eye shine
Dynamical Properties of One-Dimensional Multicomponent Quantum Liquids in Metallic Phase
We investigate low-energy dynamical properties of one-dimensional
multicomponent quantum liquids with the short-range interaction as well as the
-type long-range interaction. By calculating the single-particle spectrum
and the dynamical spin susceptibility by means of the bosonization method, we
discuss how the orbital degeneracy and the band splitting affect the dynamical
response functions. The effect of the long-range interaction is also addressed.
Although the long-range interaction suppresses charge fluctuations, it
effectively enhances spin fluctuations via the formation of the Wigner crystal.Comment: 17 pages, 8 figure
12mm line survey of the dense molecular gas towards the W28 field TeV gamma-ray sources
We present 12mm Mopra observations of dense molecular gas towards the W28
supernova remnant (SNR) field. The focus is on the dense molecular gas towards
the TeV gamma-ray sources detected by the H.E.S.S. telescopes, which likely
trace the cosmic-rays from W28 and possibly other sources in the region. Using
the NH3 inversion transitions we reveal several dense cores inside the
molecular clouds, the majority of which coincide with high-mass star formation
and HII regions, including the energetic ultra-compact HII region G5.89-0.39. A
key exception to this is the cloud north east of W28, which is well-known to be
disrupted as evidenced by clusters of 1720MHz OH masers and broad CO line
emission. Here we detect broad NH3, up to the (9,9) transition, with linewidths
up to 16 km/s. This broad NH3 emission spatially matches well with the TeV
source HESS J1801-233 and CO emission, and its velocity dispersion distribution
suggests external disruption from the W28 SNR direction. Other lines are
detected, such as HC3N and HC5N, H2O masers, and many radio recombination
lines, all of which are primarily found towards the southern high-mass star
formation regions. These observations provide a new view onto the internal
structures and dynamics of the dense molecular gas towards the W28 SNR field,
and in tandem with future higher resolution TeV gamma-ray observations will
offer the chance to probe the transport of cosmic-rays into molecular clouds.Comment: 18 pages, 10 figures, 5 tables, accepted for publication in MNRAS.
Online appendices containing additional molecular line: fit parameters, maps,
PV plots & spectra, will be available through MNRA
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