299 research outputs found
Ising Ferromagnet: Zero-Temperature Dynamic Evolution
The dynamic evolution at zero temperature of a uniform Ising ferromagnet on a
square lattice is followed by Monte Carlo computer simulations. The system
always eventually reaches a final, absorbing state, which sometimes coincides
with a ground state (all spins parallel), and sometimes does not (parallel
stripes of spins up and down). We initiate here the numerical study of
``Chaotic Time Dependence'' (CTD) by seeing how much information about the
final state is predictable from the randomly generated quenched initial state.
CTD was originally proposed to explain how nonequilibrium spin glasses could
manifest equilibrium pure state structure, but in simpler systems such as
homogeneous ferromagnets it is closely related to long-term predictability and
our results suggest that CTD might indeed occur in the infinite volume limit.Comment: 14 pages, Latex with 8 EPS figure
Zero Temperature Dynamics of 2D and 3D Ising Ferromagnets
We consider zero-temperature, stochastic Ising models with nearest-neighbor
interactions in two and three dimensions. Using both symmetric and asymmetric
initial configurations, we study the evolution of the system with time. We
examine the issue of convergence of the dynamics and discuss the nature of the
final state of the system. By determining a relation between the median number
of spin flips per site, the probability p that a spin in the initial spin
configuration takes the value +1, and lattice size, we conclude that in two and
three dimensions, the system converges to a frozen (but not necessarily
uniform) state when p is not equal to 1/2. Results for p=1/2 in three
dimensions are consistent with the conjecture that the system does not evolve
towards a fully frozen limiting state. Our simulations also uncover `striped'
and `blinker' states first discussed by Spirin et al., and their statistical
properties are investigated.Comment: 17 pages, 12 figure
Phase formation in hole- and electron-doped rare-earth nickelate single crystals
The recent discovery of superconductivity in hole-doped infinite-layer
nickelates has triggered a great interest in the synthesis of novel nickelate
phases, which have primarily been examined in thin film samples. Here, we
report the high-pressure optical floating zone (OFZ) growth of various
perovskite and perovskite-derived rare-earth nickelate single-crystals, and
investigate the effects of hole-, electron-, and self-doping. For hole-doping
with Ca and Sr, we observe phase separations during the growth process when a
substitution level of 8% is exceeded. A similar trend emerges for
electron-doping with Ce and Zr. Employing lower doping levels allows us to grow
sizeable crystals in the perovskite phase, which exhibit significantly
different electronic and magnetic properties than the undoped parent compounds,
such as a decreased resistivity and a suppressed magnetic response. Our
insights into the doping-dependent phase formation and the resulting properties
of the synthesized crystals reveal limitations and opportunities for the
exploration and manipulation of electronic states in rare-earth nickelates
Directional emission of light from a nano-optical Yagi-Uda antenna
The plasmon resonance of metal nanoparticles can enhance and direct light
from optical emitters in much the same way that radio frequency (RF) antennas
enhance and direct the emission from electrical circuits. In the RF regime, a
typical antenna design for high directivity is the Yagi-Uda antenna, which
basically consists of a one-dimensional array of antenna elements driven by a
single feed element. Here, we present the experimental demonstration of
directional light emission from a nano-optical Yagi-Uda antenna composed of an
array of appropriately tuned gold nanorods. Our results indicate that
nano-optical antenna arrays are a simple but efficient tool for the spatial
control of light emission.Comment: 4 pages, including 4 figure
Metastability in zero-temperature dynamics: Statistics of attractors
The zero-temperature dynamics of simple models such as Ising ferromagnets
provides, as an alternative to the mean-field situation, interesting examples
of dynamical systems with many attractors (absorbing configurations, blocked
configurations, zero-temperature metastable states). After a brief review of
metastability in the mean-field ferromagnet and of the droplet picture, we
focus our attention onto zero-temperature single-spin-flip dynamics of
ferromagnetic Ising models. The situations leading to metastability are
characterized. The statistics and the spatial structure of the attractors thus
obtained are investigated, and put in perspective with uniform a priori
ensembles. We review the vast amount of exact results available in one
dimension, and present original results on the square and honeycomb lattices.Comment: 21 pages, 6 figures. To appear in special issue of JPCM on Granular
Matter edited by M. Nicodem
Numerical Modeling of Plasmonic Nanoantennas with Realistic 3D Roughness and Distortion
Nanostructured plasmonic metamaterials, including optical nanoantenna arrays, are important for advanced optical sensing and imaging applications including surface-enhanced fluorescence, chemiluminescence, and Raman scattering. Although designs typically use ideally smooth geometries, realistic nanoantennas have nonzero roughness, which typically results in a modified enhancement factor that should be involved in their design. Herein we aim to treat roughness by introducing a realistic roughened geometry into the finite element (FE) model. Even if the roughness does not result in significant loss, it does result in a spectral shift and inhomogeneous broadening of the resonance, which could be critical when fitting the FE simulations of plasmonic nanoantennas to experiments. Moreover, the proposed approach could be applied to any model, whether mechanical, acoustic, electromagnetic, thermal, etc, in order to simulate a given roughness-generated physical phenomenon
Lumbar hernia diagnosed after laparoscopic hiatal hernia surgery
The presence of a new lumbar swelling or pain in the postoperative period following laparoscopic surgery should raise the suspicion of a lumbar hernia. Cross‐sectional imaging can be used to establish an early diagnosis to enable successful management
Systematic profiling of DNMT3A variants reveals protein instability mediated by the DCAF8 E3 ubiquitin ligase adaptor
Clonal hematopoiesis is a prevalent age-related condition associated with greatly increased risk of hematologic disease; mutations in DNA methyltransferase 3A (DNMT3A) are the most common driver of this state. DNMT3A variants occur across the gene with some particularly associated with malignancy, but the functional relevance and mechanisms of pathogenesis of the majority of mutations is unknown. Here, we systematically investigated the methyltransferase activity and protein stability of 253 disease-associated DNMT3A mutations, finding that 74% were loss-of-function mutations. Half of these variants exhibited reduced protein stability and, as a class, correlated with greater clonal expansion and AML development. We investigated the mechanisms underlying the instability using a CRISPR screen and uncovered regulated destruction of DNMT3A mediated by the DCAF8 E3 ubiquitin ligase adaptor. We establish a new paradigm to classify novel variants that has prognostic and potential therapeutic significance for patients with hematologic disease
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