7,153 research outputs found
Characterization in bi-parameter space of a non-ideal oscillator
The authors thank scientific agencies CAPES, CNPq (112952/2015-1), and FAPESP (2011/ 19269-11). M. S. Baptista also thanks EPSRC (EP/I03 2606/1).Peer reviewedPostprin
Electron Spin Resonance of SrCu2(BO3)2 at High Magnetic Field
We calculate the electron spin resonance (ESR) spectra of the
quasi-two-dimensional dimer spin liquid SrCu2(BO3)2 as a function of magnetic
field B. Using the standard Lanczos method, we solve a Shastry-Sutherland
Hamiltonian with additional Dzyaloshinsky-Moriya (DM) terms which are crucial
to explain different qualitative aspects of the ESR spectra. In particular, a
nearest-neighbor DM interaction with a non-zero D_z component is required to
explain the low frequency ESR lines for B || c. This suggests that crystal
symmetry is lowered at low temperatures due to a structural phase transition.Comment: 4 pages, 4 b&w figure
The S=1/2 chain in a staggered field: High-energy bound-spinon state and the effects of a discrete lattice
We report an experimental and theoretical study of the antiferromagnetic
S=1/2 chain subject to uniform and staggered fields. Using inelastic neutron
scattering, we observe a novel bound-spinon state at high energies in the
linear chain compound CuCl2 * 2((CD3)2SO). The excitation is explained with a
mean-field theory of interacting S=1/2 fermions and arises from the opening of
a gap at the Fermi surface due to confining spinon interactions. The mean-field
model also describes the wave-vector dependence of the bound-spinon states,
particularly in regions where effects of the discrete lattice are important. We
calculate the dynamic structure factor using exact diagonalization of finite
length chains, obtaining excellent agreement with the experiments.Comment: 16 pages, 7 figures, accepted by Phys. Rev.
Electron-Doped Manganese Perovskites: The Polaronic State
Using the Lanczos method in linear chains we study the ground state of the
double exchange model including an antiferromagnetic super-exchange in the low
concentration limit. We find that this ground state is always inhomogeneous,
containig ferromagnetic polarons. The extention of the polaron spin distortion,
the dispersion relation and their trapping by impurities, are studied for
diferent values of the super exchange interaction and magnetic field. We also
find repulsive polaron polaron interaction.Comment: 4 pages, 6 embedded figure
Electron Spin Resonance of defects in the Haldane System Y(2)BaNiO(5)
We calculate the electron paramagnetic resonance (EPR) spectra of the
antiferromagnetic spin-1 chain compound Y(2)BaNi(1-x)Mg(x)O(5) for different
values of x and temperature T much lower than the Haldane gap (~100K). The
low-energy spectrum of an anisotropic Heisenberg Hamiltonian, with all
parameters determined from experiment, has been solved using DMRG. The observed
EPR spectra are quantitatively reproduced by this model. The presence of
end-chain S=1/2 states is clearly observed as the main peak in the spectrum and
the remaining structure is completely understood.Comment: 5 pages, 4 figures include
HAC-Net: A Hybrid Attention-Based Convolutional Neural Network for Highly Accurate Protein-Ligand Binding Affinity Prediction
Applying deep learning concepts from image detection and graph theory has
greatly advanced protein-ligand binding affinity prediction, a challenge with
enormous ramifications for both drug discovery and protein engineering. We
build upon these advances by designing a novel deep learning architecture
consisting of a 3-dimensional convolutional neural network utilizing
channel-wise attention and two graph convolutional networks utilizing
attention-based aggregation of node features. HAC-Net (Hybrid Attention-Based
Convolutional Neural Network) obtains state-of-the-art results on the PDBbind
v.2016 core set, the most widely recognized benchmark in the field. We
extensively assess the generalizability of our model using multiple train-test
splits, each of which maximizes differences between either protein structures,
protein sequences, or ligand extended-connectivity fingerprints of complexes in
the training and test sets. Furthermore, we perform 10-fold cross-validation
with a similarity cutoff between SMILES strings of ligands in the training and
test sets, and also evaluate the performance of HAC-Net on lower-quality data.
We envision that this model can be extended to a broad range of supervised
learning problems related to structure-based biomolecular property prediction.
All of our software is available as open source at
https://github.com/gregory-kyro/HAC-Net/, and the HACNet Python package is
available through PyPI
Geometric Frustration and Dimensional Reduction at a Quantum Critical Point
We show that the spatial dimensionality of the quantum critical point
associated with Bose--Einstein condensation at T=0 is reduced when the
underlying lattice comprises a set of layers coupled by a frustrating
interaction. Our theoretical predictions for the critical temperature as a
function of the chemical potential correspond very well with recent
measurements in BaCuSiO [S. E. Sebastian \textit{et al}, Nature
\textbf{411}, 617 (2006)].Comment: 5 pages, 2 figure
Role of anisotropy in the spin-dimer compound BaCuSi2O6
We present results of magnetisation and electron paramagnetic resonance
experiments on the spin-dimer system BaCuSi2O6. Evidence indicates that the
origin of anisotropic terms in the spin Hamiltonian is from magnetic dipolar
interactions. Axial symmetry-breaking is on a very small energy scale of ~11
mK, confirming Bose Einstein condensation critical scaling over an extended
temperature range in the vicinity of the quantum critical point.Comment: 4 pages, 4 figure
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