14,592 research outputs found
A Whole Genome Association Study to Detect Loci Associated with Somatic Cell Score in Dairy Cattle
Frobenius theorem and invariants for Hamiltonian systems
We apply Frobenius integrability theorem in the search of invariants for
one-dimensional Hamiltonian systems with a time-dependent potential. We obtain
several classes of potential functions for which Frobenius theorem assures the
existence of a two-dimensional foliation to which the motion is constrained. In
particular, we derive a new infinite class of potentials for which the motion
is assurately restricted to a two-dimensional foliation. In some cases,
Frobenius theorem allows the explicit construction of an associated invariant.
It is proven the inverse result that, if an invariant is known, then it always
can be furnished by Frobenius theorem
Quantum kinetic theory of the filamentation instability
The quantum electromagnetic dielectric tensor for a multi species plasma is
re-derived from the gauge invariant Wigner-Maxwell system and presented under a
form very similar to the classical one. The resulting expression is then
applied to a quantum kinetic theory of the electromagnetic filamentation
instability. Comparison is made with the quantum fluid theory including a Bohm
pressure term, and with the cold classical plasma result. A number of
analytical expressions are derived for the cutoff wave vector, the largest
growth rate and the most unstable wave vector
Order by disorder from non-magnetic impurities in a two-dimensional quantum spin liquid
We consider doping of non-magnetic impurities in the spin-1/2, 1/5-depleted
square lattice. This structure, whose undoped phase diagram offers both
magnetically ordered and spin-liquid ground states, is realized physically in
CaV_4O_9. Doping into the ordered phase results in a progressive loss of order,
which becomes complete at the percolation threshold. By contrast, non-magnetic
impurities introduced in the spin liquids create a phase of weak but
long-ranged antiferromagnetic order coexisting with the gapped state. The
latter may be viewed as a true order-by-disorder phenomenon. We study the phase
diagram of the doped system by computing the static susceptibility and
staggered magnetization using a stochastic series-expansion quantum Monte Carlo
technique.Comment: 4 pages, 5 figure
Shadow features and shadow bands in the paramagnetic state of cuprate superconductors
The conditions for the precursors of antiferromagnetic bands in cuprate
superconductors are studied using weak-to-intermediate coupling approach. It is
shown that there are, in fact, three different precursor effects due to the
proximity to antiferromagnetic instability: i) the shadow band which associated
with new pole in the Green's function ii) the dispersive shadow feature due to
the thermal enhancement of the scattering rate and iii) the non-dispersive
shadow feature due to quantum spin fluctuation that exist only in
scan of the spectral function . I found
that dispersive shadow peaks in can exist at finite
temperature T in the renormalized classical regime, when ,
( is the characteristic energy of
spin fluctuations, is the thermal wave length of electron). In
contrast at zero temperature, only non-dispersive shadow feature in has been found. I found, however, that the latter
effect is always very small. The theory predict no shadow effects in the
optimally doped materials. The conditions for which shadow peaks can be
observed in photoemission are discussed.Comment: 6 pages, REVTEX, 2 ps figures, version to be published in PR
Quasiparticle spectrum of a type-II superconductor in a high magnetic field with randomly pinned vortices
We show that gapless superconductivity of a strongly type-II superconductor
in a high magnetic field prevails in the presence of disorder, suggesting a
topological nature. We calculate the density of states of the Bogoliubov-de
Gennes quasiparticles for a two-dimensional inhomogeneous system in both cases
of weak and strong disorder. In the limit of very weak disorder, the effect is
very small and the density of states is not appreciably changed. As the
disorder increases, the density of states at low energies increases and the
ratio of the low-energy density of states to its maximum increases
significantly
Static and Dynamical Properties of the Ferromagnetic Kondo Model with Direct Antiferromagnetic Coupling Between the localized Electrons
The phase diagram of the Kondo lattice Hamiltonian with ferromagnetic Hund's
coupling in the limit where the spin of the localized electrons is
classical is analyzed in one dimension as a function of temperature, electronic
density, and a direct antiferromagnetic coupling between the localized
spins. Studying static and dynamical properties, a behavior that qualitatively
resembles experimental results for manganites occurs for smaller than 0.11
in units of the hopping amplitude. In particular a coexistence of
ferromagnetic and antiferromagnetic excitations is observed at low-hole density
in agreement with neutron scattering experiments on
with. This effect is caused by the
recently reported tendency to phase separation between hole-rich ferromagnetic
and hole-undoped antiferromagnetic domains in electronic models for manganites.
As increases metal-insulator transitions are detected by monitoring the
optical conductivity and the density of states. The magnetic correlations
reveal the existence of spiral phases without long-range order but with fairly
large correlation lengths. Indications of charge ordering effects appear in the
analysis of charge correlations.Comment: 14 pages with 25 eps figures embeded in the tex
Dynamical properties of the spin-Peierls compound \alpha'--NaV2O5
Dynamical properties of the novel inorganic spin-Peierls compound
\alpha'--NaV2O5 are investigated using a one-dimensional dimerized Heisenberg
model. By exact diagonalizations of chains with up to 28 sites, supplemented by
a finite-size scaling analysis, the dimerization parameter \delta is determined
by requiring that the model reproduces the experimentally observed spin gap
\Delta. The dynamical and static spin structure factors are calculated. As for
CuGeO3, the existence of a low energy magnon branch separated from the
continuum is predicted. The present calculations also suggest that a large
magnetic Raman scattering intensity should appear above an energy threshold of
1.9 \Delta. The predicted photoemission spectrum is qualitatively similar to
results for an undimerized chain due to the presence of sizable short-range
antiferromagnetic correlations.Comment: 4 pages, latex, minor misprints corrected and a few references adde
miR-155 regulates differentiation of brown and beige adipocytes via a bistable circuit
Brown adipocytes are a primary site of energy expenditure and reside not only in classical brown adipose tissue but can also be found in white adipose tissue. Here we show that microRNA 155 is enriched in brown adipose tissue and is highly expressed in proliferating brown preadipocytes but declines after induction of differentiation. Interestingly, microRNA 155 and its target, the adipogenic transcription factor CCAAT/enhancer-binding protein beta, form a bistable feedback loop integrating hormonal signals that regulate proliferation or differentiation. Inhibition of microRNA 155 enhances brown adipocyte differentiation and induces a brown adipocyte-like phenotype ('browning') in white adipocytes. Consequently, microRNA 155-deficient mice exhibit increased brown adipose tissue function and 'browning' of white fat tissue. In contrast, transgenic overexpression of microRNA 155 in mice causes a reduction of brown adipose tissue mass and impairment of brown adipose tissue function. These data demonstrate that the bistable loop involving microRNA 155 and CCAAT/enhancer-binding protein b regulates brown lineage commitment, thereby, controlling the development of brown and beige fat cells
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