25,927 research outputs found
Data taking strategy for the phase study in
The study of the relative phase between strong and electromagnetic amplitudes
is of great importance for understanding the dynamics of charmonium decays. The
information of the phase can be obtained model-independently by fitting the
scan data of some special decay channels, one of which is . To find out the optimal data taking strategy for a scan experiment
in the measurement of the phase in , the
minimization process is analyzed from a theoretical point of view. The result
indicates that for one parameter fit, only one data taking point in the
vicinity of a resonance peak is sufficient to acquire the optimal precision.
Numerical results are obtained by fitting simulated scan data. Besides the
results related to the relative phase between strong and electromagnetic
amplitudes, the method is extended to analyze the fits of other resonant
parameters, such as the mass and the total decay width of .Comment: 13 pages, 7 figure
MSS0472. John C.Z. Thomas collection finding aid
The collection comprises newspapers, newsletters and documents related to activist organizations at Memphis State University and in Memphis, Tennessee, during the mid-1960s
Molecular geometry optimization with a genetic algorithm
We present a method for reliably determining the lowest energy structure of
an atomic cluster in an arbitrary model potential. The method is based on a
genetic algorithm, which operates on a population of candidate structures to
produce new candidates with lower energies. Our method dramatically outperforms
simulated annealing, which we demonstrate by applying the genetic algorithm to
a tight-binding model potential for carbon. With this potential, the algorithm
efficiently finds fullerene cluster structures up to starting
from random atomic coordinates.Comment: 4 pages REVTeX 3.0 plus 3 postscript figures; to appear in Physical
Review Letters. Additional information available under "genetic algorithms"
at http://www.public.iastate.edu/~deaven
Far-infrared optical properties of the pyrochlore spin ice compound Dy2Ti2O4
Near normal incident far-infrared reflectivity spectra of [111] dysprosium
titanate (Dy2Ti2O4) single crystal have been measured at different
temperatures. Seven phonon modes (eight at low temperature) are identified at
frequency below 1000 cm-1. Optical conductivity spectra are obtained by fitting
all the reflectivity spectra with the factorized form of the dielectric
function. Both the Born effective charges and the static optical primitivity
are found to increase with decreasing temperature. Moreover, phonon linewidth
narrowering and phonon modes shift with decreasing temperature are also
observed, which may result from enhanced charge localization. The redshift of
several low frequency modes is attributed to the spin-phonon coupling. All
observed optical properties can be explained within the framework of nearest
neighbor ferromagnetic(FM) spin ice model
Effect of Samarium doping on the nucleation of fcc-Aluminum in undercooled liquids
The effect of Sm doping on the fcc-Al nucleation was investigated in Al-Sm
liquids with low Sm concentrations (xSm) with molecular dynamics simulations.
The nucleation in the moderately undercooled liquid is achieved by the recently
developed persistent-embryo method. Systematically computing the nucleation
rate with different xSm (xSm=0%, 1%, 2%, 3%, 5%) at 700 K, we found Sm dopant
reduces the nucleation rate by up to 25 orders of magnitudes with only 5%
doping concentration. This effect is mostly associated with the increase in the
free energy barrier with a minor contribution from suppression of the
attachment to the nucleus caused by Sm doping.Comment: 4 figure
Weak Localization and Antilocalization in Topological Materials with Impurity Spin-Orbit Interactions
Topological materials have attracted considerable experimental and
theoretical attention. They exhibit strong spin-orbit coupling both in the band
structure (intrinsic) and in the impurity potentials (extrinsic), although the
latter is often neglected. Here we discuss weak localization and
antilocalization of massless Dirac fermions in topological insulators and
massive Dirac fermions in Weyl semimetal thin films taking into account both
intrinsic and extrinsic spin-orbit interactions. The physics is governed by the
complex interplay of the chiral spin texture, quasiparticle mass, and scalar
and spin-orbit scattering. We demonstrate that terms linear in the extrinsic
spin-orbit scattering are generally present in the Bloch and momentum
relaxation times in all topological materials, and the correction to the
diffusion constant is linear in the strength of the extrinsic spin-orbit. In
TIs, which have zero quasiparticle mass, the terms linear in the impurity
spin-orbit coupling lead to an observable density dependence in the weak
antilocalization correction. They produce substantial qualitative modifications
to the magnetoconductivity, differing greatly from the conventional HLN formula
traditionally used in experimental fits, which predicts a crossover from weak
localization to antilocalization as a function of the extrinsic spin-orbit
strength. In contrast, our analysis reveals that topological insulators always
exhibit weak antilocalization. In WSM thin films having intermediate to large
values of the quasiparticle mass extrinsic spin-orbit scattering strongly
affects the boundary of the weak localization to antilocalization transition.
We produce a complete phase diagram for this transition as a function of the
mass and spin-orbit scattering strength. We discuss implications for
experiments and provide a brief comparison with transition metal
dichalcogenides.Comment: arXiv admin note: text overlap with arXiv:1705.0761
Radiomics-Based Outcome Prediction for Pancreatic Cancer Following Stereotactic Body Radiotherapy
(1) Background: Radiomics use high-throughput mining of medical imaging data to extract unique information and predict tumor behavior. Currently available clinical prediction models poorly predict treatment outcomes in pancreatic adenocarcinoma. Therefore, we used radiomic features of primary pancreatic tumors to develop outcome prediction models and compared them to traditional clinical models. (2) Methods: We extracted and analyzed radiomic data from pre-radiation contrast-enhanced CTs of 74 pancreatic cancer patients undergoing stereotactic body radiotherapy. A panel of over 800 radiomic features was screened to create overall survival and local-regional recurrence prediction models, which were compared to clinical prediction models and models combining radiomic and clinical information. (3) Results: A 6-feature radiomic signature was identified that achieved better overall survival prediction performance than the clinical model (mean concordance index: 0.66 vs. 0.54 on resampled cross-validation test sets), and the combined model improved the performance slightly further to 0.68. Similarly, a 7-feature radiomic signature better predicted recurrence than the clinical model (mean AUC of 0.78 vs. 0.66). (4) Conclusion: Overall survival and recurrence can be better predicted with models based on radiomic features than with those based on clinical features for pancreatic cancer
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