79,299 research outputs found
Soluble kagome Ising model in a magnetic field
An Ising model on the kagome lattice with super-exchange interactions is
solved exactly under the presence of a nonzero external magnetic field. The
model generalizes the super-exchange model introduced by Fisher in 1960 and is
analyzed in light of a free-fermion model. We deduce the critical condition and
present detailed analyses of its thermodynamic and magnetic properties. The
system is found to exhibit a second-order transition with logarithmic
singularities at criticality.Comment: 8 pages, 8 figures, references adde
Dimers on two-dimensional lattices
We consider close-packed dimers, or perfect matchings, on two-dimensional
regular lattices. We review known results and derive new expressions for the
free energy, entropy, and the molecular freedom of dimers for a number of
lattices including the simple-quartic (4^4), honeycomb (6^3), triangular (3^6),
kagome (3.6.3.6), 3-12 (3.12^2) and its dual [3.12^2], and 4-8 (4.8^2) and its
dual Union Jack [4.8^2] Archimedean tilings. The occurrence and nature of phase
transitions are also analyzed and discussed.Comment: Typos corrections in Eqs. (28), (32) and (43
Novel method for refinement of retained austenite in micro/nano-structured bainitic steels
A comparative study was conducted to assess the effects of two different heat treatments on the amount and morphology of the retained austenite in a micro/nano-structured bainitic steel. The heat treatments used in this work were two-stage bainitic transformation and bainitic-partitioning transformation. Both methods resulted in the generation of a multi-phase microstructure containing nanoscale bainitic ferrite, and/or fresh martensitic phases and much finer retained austenite. Both heat treatments were verified to be effective in refining the retained austenite in micro/nano-structured bainite and increasing the hardness. However, the bainitic transformation followed by partitioning cycle was proved to be a more viable approach than the two-stage bainitic transformation due to much shorter processing time, i.e. ∼2 h compared to ∼4 day, respectively
Molecular line and continuum study of the W40 cloud
The dense cloud associated with W40, one of the nearby H II regions, has been
studied in millimeter-wave molecular lines and in 1.2 mm continuum. Besides,
1280 MHz and 610 MHz interferometric observations have been done. The cloud has
complex morphological and kinematical structure, including a clumpy dust ring
and an extended dense core. The ring is probably formed by the "collect and
collapse" process due to the expansion of neighboring H II region. Nine dust
clumps in the ring have been deconvolved. Their sizes, masses and peak hydrogen
column densities are: pc, and cm, respectively. Molecular lines are observed
at two different velocities and have different spatial distributions implying
strong chemical differentiation over the region. The CS abundance is enhanced
towards the eastern dust clump 2, while the NH, NH, and
HCO abundances are enhanced towards the western clumps. HCN and
HCO do not correlate with the dust probably tracing the surrounding gas.
Number densities derived towards selected positions are: cm. Two western clumps have kinetic temperatures 21 K and 16 K and
are close to virial equilibrium. The eastern clumps 2 and 3 are more massive,
have higher extent of turbulence and are probably more evolved than the western
ones. They show asymmetric CS(2--1) line profiles due to infalling motions
which is confirmed by model calculations. An interaction between ionized and
neutral material is taking place in the vicinity of the eastern branch of the
ring and probably trigger star formation.Comment: 16 pages, 6 figure
Ferrimagnetism of the magnetoelectric compound CuOSeO probed by Se NMR
We present a thorough Se NMR study of a single crystal of the
magnetoelectric compound CuOSeO. The temperature dependence of the
local electronic moments extracted from the NMR data is fully consistent with a
magnetic phase transition from the high-T paramagnetic phase to a low-T
ferrimagnetic state with 3/4 of the Cu ions aligned parallel and 1/4
aligned antiparallel to the applied field of 14.09 T. The transition to this
3up-1down magnetic state is not accompanied by any splitting of the NMR lines
or any abrupt modification in their broadening, hence there is no observable
reduction of the crystalline symmetry from its high-T cubic \textit{P}23
space group. These results are in agreement with high resolution x-ray
diffraction and magnetization data on powder samples reported previously by Bos
{\it et al.} [Phys. Rev. B, {\bf 78}, 094416 (2008)]. We also develop a mean
field theory description of the problem based on a microscopic spin Hamiltonian
with one antiferromagnetic ( K) and one ferromagnetic
( K) nearest-neighbor exchange interaction
Using Superconducting Qubit Circuits to Engineer Exotic Lattice Systems
We propose an architecture based on superconducting qubits and resonators for
the implementation of a variety of exotic lattice systems, such as spin and
Hubbard models in higher or fractal dimensions and higher-genus topologies.
Spin systems are realized naturally using qubits, while superconducting
resonators can be used for the realization of Bose-Hubbard models. Fundamental
requirements for these designs, such as controllable interactions between
arbitrary qubit pairs, have recently been implemented in the laboratory,
rendering our proposals feasible with current technology.Comment: 7 pages (two-column), 3 figure
Tunneling into d-wave superconductors: Effects of interface spin-orbit coupling
Tunneling conductance of a clean normal metal/d-wave superconductor junction
is studied by using the extended Blonder-Tinkham-Klapwijk formalism. We show
that the conductance is significantly affected by the interface spin-orbit
coupling of the Rashba type, which is inevitably present due to the asymmetry
of the junction.Comment: 4 pages, 4 figure
Critical frontier of the Potts and percolation models in triangular-type and kagome-type lattices I: Closed-form expressions
We consider the Potts model and the related bond, site, and mixed site-bond
percolation problems on triangular-type and kagome-type lattices, and derive
closed-form expressions for the critical frontier. For triangular-type lattices
the critical frontier is known, usually derived from a duality consideration in
conjunction with the assumption of a unique transition. Our analysis, however,
is rigorous and based on an established result without the need of a uniqueness
assumption, thus firmly establishing all derived results. For kagome-type
lattices the exact critical frontier is not known. We derive a closed-form
expression for the Potts critical frontier by making use of a homogeneity
assumption. The closed-form expression is new, and we apply it to a host of
problems including site, bond, and mixed site-bond percolation on various
lattices. It yields exact thresholds for site percolation on kagome, martini,
and other lattices, and is highly accurate numerically in other applications
when compared to numerical determination.Comment: 22 pages, 13 figure
Roles of the Bloom's syndrome helicase in the maintenance of genome stability
The RecQ family of DNA helicases is highly conserved in evolution from bacteria to humans. Of the five known human RecQ family members, three (BLM, WRN and RECQ4, which cause Bloom's syndrome, Werner's syndrome and Rothmund-Thomson syndrome respectively) are mutated in distinct clinical disorders associated with cancer predisposition and/or premature aging. BLM forms part of a multienzyme complex including topoisomerase IIIalpha, replication protein A and a newly identified factor called BLAP75. Together, these proteins play a role in the resolution of DNA structures that arise during the process of homologous recombination repair. In the absence of BLM, cells show genomic instability and a high incidence of sister-chromatid exchanges. In addition to a DNA structure-specific helicase activity, BLM also catalyses Holliday-junction branch migration and the annealing of complementary single-stranded DNA molecules
Nucleation of superconducting pairing states at mesoscopic scales at zero temperature
We find the spin polarized disordered Fermi liquids are unstable to the
nucleation of superconducting pairing states at mesoscopic scales even when
magnetic fields which polarize the spins are substantially higher than the
critical one. We study the probability of finding superconducting pairing
states at mesoscopic scales in this limit. We find that the distribution
function depends only on the film conductance. The typical length scale at
which pairing takes place is universal, and decreases when the magnetic field
is increased. The number density of these states determines the strength of the
random exchange interactions between mesoscopic pairing states.Comment: 11 pages, no figure
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