47,899 research outputs found
A MERLIN Study of 6 GHz Excited-state OH & 6.7 GHz Methanol Masers in ON1
MERLIN observations of 6.668-GHz methanol and both 6.031- and 6.035-GHz
hydroxyl (OH) emission from the massive star-formation region ON1 are
presented. These are the first methanol observations made in full polarization
using 5 antennas of MERLIN, giving high resolution and sensitivity to extended
emission. Maser features are found to lie at the southern edge of the
ultra-compact HII region, following the known distribution of ground-state OH
masers. The masers cover a region ~1 arcsec in extent, lying perpendicular to
the H13CO+ bipolar outflow. Excited-state OH emission demonstrates consistent
polarization angles across the strongest linearly polarized features which are
parallel to the overall distribution. The linear polarizations vary between
10.0 and 18.5 per cent, with an average polarization angle of -60 deg +/- 28
deg. The strongest 6.668-GHz methanol features provide an upper limit to linear
polarization of ~1 per cent. Zeeman splitting of OH shows magnetic fields
between -1.1 to -5.8 mG, and a tentative methanol magnetic field strength of
-18 mG is measured.Comment: 10 Pages, 5 Figure
Tilting mutation of weakly symmetric algebras and stable equivalence
We consider tilting mutations of a weakly symmetric algebra at a subset of
simple modules, as recently introduced by T. Aihara. These mutations are
defined as the endomorphism rings of certain tilting complexes of length 1.
Starting from a weakly symmetric algebra A, presented by a quiver with
relations, we give a detailed description of the quiver and relations of the
algebra obtained by mutating at a single loopless vertex of the quiver of A. In
this form the mutation procedure appears similar to, although significantly
more complicated than, the mutation procedure of Derksen, Weyman and Zelevinsky
for quivers with potentials. By definition, weakly symmetric algebras connected
by a sequence of tilting mutations are derived equivalent, and hence stably
equivalent. The second aim of this article is to study these stable
equivalences via a result of Okuyama describing the images of the simple
modules. As an application we answer a question of Asashiba on the derived
Picard groups of a class of self-injective algebras of finite representation
type. We conclude by introducing a mutation procedure for maximal systems of
orthogonal bricks in a triangulated category, which is motivated by the effect
that a tilting mutation has on the set of simple modules in the stable
category.Comment: Description and proof of mutated algebra made more rigorous (Prop.
3.1 and 4.2). Okuyama's Lemma incorporated: Theorem 4.1 is now Corollary 5.1,
and proof is omitted. To appear in Algebras and Representation Theor
Cooperative Chiral Order in Copolymers of Chiral and Achiral Units
Polyisocyanates can be synthesized with chiral and achiral pendant groups
distributed randomly along the chains. The overall chiral order, measured by
optical activity, is strongly cooperative and depends sensitively on the
concentration of chiral pendant groups. To explain this cooperative chiral
order theoretically, we map the random copolymer onto the one-dimensional
random-field Ising model. We show that the optical activity as a function of
composition is well-described by the predictions of this theory.Comment: 13 pages, including 3 postscript figures, uses REVTeX 3.0 and
epsf.st
A New Symmetric Expression of Weyl Ordering
For the creation operator \adag and the annihilation operator of a
harmonic oscillator, we consider Weyl ordering expression of (\adag a)^n and
obtain a new symmetric expression of Weyl ordering w.r.t. \adag a \equiv N
and a\adag =N+1 where is the number operator. Moreover, we interpret
intertwining formulas of various orderings in view of the difference theory.
Then we find that the noncommutative parameter corresponds to the increment of
the difference operator w.r.t. variable . Therefore, quantum
(noncommutative) calculations of harmonic oscillators are done by classical
(commutative) ones of the number operator by using the difference theory. As a
by-product, nontrivial relations including the Stirling number of the first
kind are also obtained.Comment: 15 pages, Latex2e, the title before replacement is "Orderings of
Operators in Quantum Physics", new proofs by using a difference operator
added, some references added, to appear in Modern Physics Letters
Primordial black holes as a tool for constraining non-Gaussianity
Primordial Black Holes (PBH's) can form in the early Universe from the
collapse of large density fluctuations. Tight observational limits on their
abundance constrain the amplitude of the primordial fluctuations on very small
scales which can not otherwise be constrained, with PBH's only forming from the
extremely rare large fluctuations. The number of PBH's formed is therefore
sensitive to small changes in the shape of the tail of the fluctuation
distribution, which itself depends on the amount of non-Gaussianity present. We
study, for the first time, how quadratic and cubic local non-Gaussianity of
arbitrary size (parameterised by f_nl and g_nl respectively) affects the PBH
abundance and the resulting constraints on the amplitude of the fluctuations on
very small scales. Intriguingly we find that even non-linearity parameters of
order unity have a significant impact on the PBH abundance. The sign of the
non-Gaussianity is particularly important, with the constraint on the allowed
fluctuation amplitude tightening by an order of magnitude as f_nl changes from
just -0.5 to 0.5. We find that if PBH's are observed in the future, then
regardless of the amplitude of the fluctuations, non-negligible negative f_nl
would be ruled out. Finally we show that g_nl can have an even larger effect on
the number of PBH's formed than f_nl.Comment: 9 pages, 5 figures, v2: version to appear in Phys. Rev. D with minor
changes, v3: typos corrected (including factor of 1/2 in erfc prefactor), no
changes to result
D-instanton partition functions
Duality arguments are used to determine D-instanton contributions to certain
effective interaction terms of type II supergravity theories in various
dimensions. This leads to exact expressions for the partition functions of the
finite N D-instanton matrix model in d=4 and 6 dimensions that generalize our
previous expression for the case d=10. These results are consistent with the
fact that the Witten index of the T-dual D-particle process should only be
non-vanishing for d=10.Comment: 20 pages, harvmac, typos corrected, reference adde
The population of hot subdwarf stars studied with Gaia I. The catalogue of known hot subdwarf stars
In preparation for the upcoming all-sky data releases of the Gaia mission we
compiled a catalogue of known hot subdwarf stars and candidates drawn from the
literature and yet unpublished databases. The catalogue contains 5613 unique
sources and provides multi-band photometry from the ultraviolet to the far
infrared, ground based proper motions, classifications based on spectroscopy
and colours, published atmospheric parameters, radial velocities and light
curve variability information. Using several different techniques we removed
outliers and misclassified objects. By matching this catalogue with astrometric
and photometric data from the Gaia mission, we will develop selection criteria
to construct a homogeneous, magnitude-limited all-sky catalogue of hot subdwarf
stars based on Gaia data.Comment: 11 pages, A&A accepte
Quartz crystal microbalance use in biological studies
Design, development, and applications of quartz crystal microbalance are discussed. Two types of crystals are used. One serves as reference and other senses changes in mass. Specific application to study of bacterial spores is described
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