291,297 research outputs found
Evolution of Intermediate-Mass Black Hole X-Ray Binaries
The majority of the ultraluminous X-ray sources (ULXs) in external galaxies
are believed to be accreting black holes in binary systems; some of the black
holes could be as massive as \sim 100-1000 \ms. We have performed evolution
calculations for intermediate-mass black hole X-ray binaries, assuming they are
formed in dense star clusters via tidal capture. The results are compared with
those for stellar-mass black holes X-ray binaries. We find that these two types
of black holes may have similar companion stars and binary orbits if observed
as ULXs. However, intermediate-mass black holes seem to be favored in
explaining the most luminous ULXs. We also discuss the possibilities of
transient behavior and beamed emission in the evolution of these binary
systems.Comment: 11 pages, 3 figures. Accepted for publication in ApJ
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A golden block based self-refining scheme for repetitive patterned wafer inspections
This paper presents a novel technique for detecting possible defects in two-dimensional wafer images with repetitive patterns using prior knowledge. It has a learning ability that is able to create a golden block database from the wafer image itself, modify and refine its content when used in further inspections. The extracted building block is stored as a golden block for the detected pattern. When new wafer images with the same periodical pattern arrives, we do not have to re-calculate its periods and building block. A new building block can be derived directly from the existing golden block after eliminating alignment differences. If the newly derived building block has better quality than the stored golden block, then the golden block is replaced with the new building block. With the proposed algorithm, our implementation shows that a significant amount of processing time is saved. And the storage overhead of golden templates is also reduced significantly by storing golden blocks only
On quantum vertex algebras and their modules
We give a survey on the developments in a certain theory of quantum vertex
algebras, including a conceptual construction of quantum vertex algebras and
their modules and a connection of double Yangians and Zamolodchikov-Faddeev
algebras with quantum vertex algebras.Comment: 18 pages; contribution to the proceedings of the conference in honor
of Professor Geoffrey Maso
The Coupled Cluster Method Applied to Quantum Magnets: A New LPSUB Approximation Scheme for Lattice Models
A new approximation hierarchy, called the LPSUB scheme, is described for
the coupled cluster method (CCM). It is applicable to systems defined on a
regular spatial lattice. We then apply it to two well-studied prototypical
(spin-1/2 Heisenberg antiferromagnetic) spin-lattice models, namely: the XXZ
and the XY models on the square lattice in two dimensions. Results are obtained
in each case for the ground-state energy, the ground-state sublattice
magnetization and the quantum critical point. They are all in good agreement
with those from such alternative methods as spin-wave theory, series
expansions, quantum Monte Carlo methods and the CCM using the alternative
LSUB and DSUB schemes. Each of the three CCM schemes (LSUB, DSUB
and LPSUB) for use with systems defined on a regular spatial lattice is
shown to have its own advantages in particular applications
Transverse Magnetic Susceptibility of a Frustrated Spin- ---- Heisenberg Antiferromagnet on a Bilayer Honeycomb Lattice
We use the coupled cluster method (CCM) to study a frustrated
spin- ---- Heisenberg antiferromagnet
on a bilayer honeycomb lattice with stacking. Both nearest-neighbor (NN)
and frustrating next-nearest-neighbor antiferromagnetic (AFM) exchange
interactions are present in each layer, with respective exchange coupling
constants and . The two layers are
coupled with NN AFM exchanges with coupling strength . We calculate to high orders of approximation within the CCM
the zero-field transverse magnetic susceptibility in the N\'eel phase.
We thus obtain an accurate estimate of the full boundary of the N\'eel phase in
the plane for the zero-temperature quantum phase diagram. We
demonstrate explicitly that the phase boundary derived from is fully
consistent with that obtained from the vanishing of the N\'eel magnetic order
parameter. We thus conclude that at all points along the N\'eel phase boundary
quasiclassical magnetic order gives way to a nonclassical paramagnetic phase
with a nonzero energy gap. The N\'eel phase boundary exhibits a marked
reentrant behavior, which we discuss in detail
Collinear antiferromagnetic phases of a frustrated spin- ---- Heisenberg model on an -stacked bilayer honeycomb lattice
The zero-temperature quantum phase diagram of the spin-
---- model on an -stacked bilayer honeycomb
lattice is investigated using the coupled cluster method (CCM). The model
comprises two monolayers in each of which the spins, residing on
honeycomb-lattice sites, interact via both nearest-neighbor (NN) and
frustrating next-nearest-neighbor isotropic antiferromagnetic (AFM) Heisenberg
exchange iteractions, with respective strengths and . The two layers are coupled via a comparable Heisenberg
exchange interaction between NN interlayer pairs, with a strength
. The complete phase boundaries of two
quasiclassical collinear AFM phases, namely the N\'{e}el and N\'{e}el-II
phases, are calculated in the half-plane with .
Whereas on each monolayer in the N\'{e}el state all NN pairs of spins are
antiparallel, in the N\'{e}el-II state NN pairs of spins on zigzag chains along
one of the three equivalent honeycomb-lattice directions are antiparallel,
while NN interchain spins are parallel. We calculate directly in the
thermodynamic (infinite-lattice) limit both the magnetic order parameter
and the excitation energy from the ground state to the
lowest-lying excited state (where is the total
component of spin for the system as a whole, and where the collinear ordering
lies along the direction) for both quasiclassical states used (separately)
as the CCM model state, on top of which the multispin quantum correlations are
then calculated to high orders () in a systematic series of
approximations involving -spin clusters. The sole approximation made is then
to extrapolate the sequences of th-order results for and to the
exact limit,
A high-order study of the quantum critical behavior of a frustrated spin- antiferromagnet on a stacked honeycomb bilayer
We study a frustrated spin-
------ Heisenberg antiferromagnet on an
-stacked bilayer honeycomb lattice. In each layer we consider
nearest-neighbor (NN), next-nearest-neighbor, and next-next-nearest-neighbor
antiferromagnetic (AFM) exchange couplings , , and ,
respectively. The two layers are coupled with an AFM NN exchange coupling
. The model is studied for arbitrary values of
along the line that includes the most
highly frustrated point at , where the classical ground
state is macroscopically degenerate. The coupled cluster method is used at high
orders of approximation to calculate the magnetic order parameter and the
triplet spin gap. We are thereby able to give an accurate description of the
quantum phase diagram of the model in the plane in the window , . This includes two AFM phases with
N\'eel and striped order, and an intermediate gapped paramagnetic phase that
exhibits various forms of valence-bond crystalline order. We obtain accurate
estimations of the two phase boundaries, , or
equivalently, , with (N\'eel) and 2
(striped). The two boundaries exhibit an "avoided crossing" behavior with both
curves being reentrant
Ground-state phases of the spin-1 -- Heisenberg antiferromagnet on the honeycomb lattice
We study the zero-temperature quantum phase diagram of a spin-1 Heisenberg
antiferromagnet on the honeycomb lattice with both nearest-neighbor exchange
coupling and frustrating next-nearest-neighbor coupling , using the coupled cluster method implemented to high orders
of approximation, and based on model states with different forms of classical
magnetic order. For each we calculate directly in the bulk thermodynamic limit
both ground-state low-energy parameters (including the energy per spin,
magnetic order parameter, spin stiffness coefficient, and zero-field uniform
transverse magnetic susceptibility) and their generalized susceptibilities to
various forms of valence-bond crystalline (VBC) order, as well as the energy
gap to the lowest-lying spin-triplet excitation. In the range
we find evidence for four distinct phases. Two of these are quasiclassical
phases with antiferromagnetic long-range order, one with 2-sublattice N\'{e}el
order for , and another with 4-sublattice
N\'{e}el-II order for . Two different
paramagnetic phases are found to exist in the intermediate region. Over the
range we find a gapless
phase with no discernible magnetic order, which is a strong candidate for being
a quantum spin liquid, while over the range we find a gapped phase, which is most likely a lattice nematic
with staggered dimer VBC order that breaks the lattice rotational symmetry
Large- expansions for the low-energy parameters of the honeycomb-lattice Heisenberg antiferromagnet with spin quantum number
The coupled cluster method (CCM) is employed to very high orders of
approximation to study the ground-state (GS) properties of the spin-
Heisenberg antiferromagnet (with isotropic interactions, all of equal strength,
between nearest-neighbour pairs only) on the honeycomb lattice. We calculate
with high accuracy the complete set of GS parameters that fully describes the
low-energy behaviour of the system, in terms of an effective magnon field
theory, viz., the energy per spin, the magnetic order parameter (i.e., the
sublattie magnetization), the spin stiffness and the zero-field (uniform,
transverse) magnetic susceptibility, for all values of the spin quantum number
in the range . The CCM data points are
used to calculate the leading quantum corrections to the classical () values of these low-energy parameters, considered as
large- asymptotic expansions
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