8,137 research outputs found
Valley polarization and susceptibility of composite fermions around nu=3/2
We report magnetotransport measurements of fractional quantum Hall states in
an AlAs quantum well around Landau level filling factor nu = 3/2, demonstrating
that the quasiparticles are composite Fermions (CFs) with a valley degree of
freedom. By monitoring the valley level crossings for these states as a
function of applied symmetry-breaking strain, we determine the CF valley
susceptibility and polarization. The data can be explained well by a simple
Landau level fan diagram for CFs, and are in nearly quantitative agreement with
the results reported for CF spin polarization.Comment: to appear in Phys. Rev. Let
Observation of Quantum Hall Valley Skyrmions
We report measurements of the interaction-induced quantum Hall effect in a
spin-polarized AlAs two-dimensional electron system where the electrons occupy
two in-plane conduction band valleys. Via the application of in-plane strain,
we tune the energies of these valleys and measure the energy gap of the quantum
Hall state at filling factor = 1. The gap has a finite value even at zero
strain and, with strain, rises much faster than expected from a single-particle
picture, suggesting that the lowest energy charged excitations at are
"valley Skyrmions".Comment: 4 pages, 3 figure
Evidence that MEK1 positively promotes interhomologue double-strand break repair
During meiosis there is an imperative to create sufficient crossovers for homologue segregation. This can be achieved during repair of programmed DNA double-strand breaks (DSBs), which are biased towards using a homologue rather than sister chromatid as a repair template. Various proteins contribute to this bias, one of which is a meiosis specific kinase Mek1. It has been proposed that Mek1 establishes the bias by creating a barrier to sister chromatid repair, as distinct from enforcing strand invasion with the homologue. We looked for evidence that Mek1 positively stimulates strand invasion of the homologue. This was done by analysing repair of DSBs induced by the VMA1- derived endonuclease (VDE) and flanked by directly repeated sequences that can be used for intrachromatid single-strand annealing (SSA). SSA competes with interhomologue strand inva- sion significantly more successfully when Mek1 function is lost. We suggest the increase in intrachromosomal SSA reflects an opportunistic default repair pathway due to loss of a MEK1 stimulated bias for strand invasion of the homologous chromosome. Making use of an inhibitor sensitive mek1-as1 allele, we found that Mek1 function influences the repair pathway throughout the first 4-5 h of meiosis. Perhaps reflecting a particular need to create bias for successful interhomologue events before chromosome pairing is complete. © The Author(s) 2010. Published by Oxford University Pres
Effect of kinetic resonances on the stability of Resistive Wall Mode in Reversed Field Pinch
The kinetic effects, due to the mode resonance with thermal particle drift
motions in the reversed field pinch (RFP) plasmas, are numerically investigated
for the stability of the resistive wall mode, using a non-perturbative
MHD-kinetic hybrid formulation. The kinetic effects are generally found too
weak to substantially change the mode growth rate, or the stability margin,
re-enforcing the fact that the ideal MHD model is rather adequate for
describing the RWM physics in RFP experiments.Comment: Submitted to: Plasma Phys. Control. Fusio
Analysis of dropout learning regarded as ensemble learning
Deep learning is the state-of-the-art in fields such as visual object
recognition and speech recognition. This learning uses a large number of
layers, huge number of units, and connections. Therefore, overfitting is a
serious problem. To avoid this problem, dropout learning is proposed. Dropout
learning neglects some inputs and hidden units in the learning process with a
probability, p, and then, the neglected inputs and hidden units are combined
with the learned network to express the final output. We find that the process
of combining the neglected hidden units with the learned network can be
regarded as ensemble learning, so we analyze dropout learning from this point
of view.Comment: 9 pages, 8 figures, submitted to Conferenc
Audio Features Affected by Music Expressiveness
Within a Music Information Retrieval perspective, the goal of the study
presented here is to investigate the impact on sound features of the musician's
affective intention, namely when trying to intentionally convey emotional
contents via expressiveness. A preliminary experiment has been performed
involving tuba players. The recordings have been analysed by extracting a
variety of features, which have been subsequently evaluated by combining both
classic and machine learning statistical techniques. Results are reported and
discussed.Comment: Submitted to ACM SIGIR Conference on Research and Development in
Information Retrieval (SIGIR 2016), Pisa, Italy, July 17-21, 201
High-Order Coupled Cluster Method (CCM) Calculations for Quantum Magnets with Valence-Bond Ground States
In this article, we prove that exact representations of dimer and plaquette
valence-bond ket ground states for quantum Heisenberg antiferromagnets may be
formed via the usual coupled cluster method (CCM) from independent-spin product
(e.g. N\'eel) model states. We show that we are able to provide good results
for both the ground-state energy and the sublattice magnetization for dimer and
plaquette valence-bond phases within the CCM. As a first example, we
investigate the spin-half -- model for the linear chain, and we show
that we are able to reproduce exactly the dimerized ground (ket) state at
. The dimerized phase is stable over a range of values for
around 0.5. We present evidence of symmetry breaking by considering
the ket- and bra-state correlation coefficients as a function of . We
then consider the Shastry-Sutherland model and demonstrate that the CCM can
span the correct ground states in both the N\'eel and the dimerized phases.
Finally, we consider a spin-half system with nearest-neighbor bonds for an
underlying lattice corresponding to the magnetic material CaVO (CAVO).
We show that we are able to provide excellent results for the ground-state
energy in each of the plaquette-ordered, N\'eel-ordered, and dimerized regimes
of this model. The exact plaquette and dimer ground states are reproduced by
the CCM ket state in their relevant limits.Comment: 34 pages, 13 figures, 2 table
Phase Transitions in the Spin-Half J_1--J_2 Model
The coupled cluster method (CCM) is a well-known method of quantum many-body
theory, and here we present an application of the CCM to the spin-half J_1--J_2
quantum spin model with nearest- and next-nearest-neighbour interactions on the
linear chain and the square lattice. We present new results for ground-state
expectation values of such quantities as the energy and the sublattice
magnetisation. The presence of critical points in the solution of the CCM
equations, which are associated with phase transitions in the real system, is
investigated. Completely distinct from the investigation of the critical
points, we also make a link between the expansion coefficients of the
ground-state wave function in terms of an Ising basis and the CCM ket-state
correlation coefficients. We are thus able to present evidence of the
breakdown, at a given value of J_2/J_1, of the Marshall-Peierls sign rule which
is known to be satisfied at the pure Heisenberg point (J_2 = 0) on any
bipartite lattice. For the square lattice, our best estimates of the points at
which the sign rule breaks down and at which the phase transition from the
antiferromagnetic phase to the frustrated phase occurs are, respectively, given
(to two decimal places) by J_2/J_1 = 0.26 and J_2/J_1 = 0.61.Comment: 28 pages, Latex, 2 postscript figure
Initial data transients in binary black hole evolutions
We describe a method for initializing characteristic evolutions of the
Einstein equations using a linearized solution corresponding to purely outgoing
radiation. This allows for a more consistent application of the characteristic
(null cone) techniques for invariantly determining the gravitational radiation
content of numerical simulations. In addition, we are able to identify the {\em
ingoing} radiation contained in the characteristic initial data, as well as in
the initial data of the 3+1 simulation. We find that each component leads to a
small but long lasting (several hundred mass scales) transient in the measured
outgoing gravitational waves.Comment: 18 pages, 4 figure
Cauchy-perturbative matching and outer boundary conditions I: Methods and tests
We present a new method of extracting gravitational radiation from
three-dimensional numerical relativity codes and providing outer boundary
conditions. Our approach matches the solution of a Cauchy evolution of
Einstein's equations to a set of one-dimensional linear wave equations on a
curved background. We illustrate the mathematical properties of our approach
and discuss a numerical module we have constructed for this purpose. This
module implements the perturbative matching approach in connection with a
generic three-dimensional numerical relativity simulation. Tests of its
accuracy and second-order convergence are presented with analytic linear wave
data.Comment: 13 pages, 6 figures, RevTe
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