32,786 research outputs found
Signature of a universal statistical description for drift-wave plasma turbulence
This Letter provides a theoretical interpretation of numerically generated
probability density functions (PDFs) of intermittent plasma transport events.
Specifically, nonlinear gyrokinetic simulations of ion-temperature-gradient
turbulence produce time series of heat flux which exhibit manifestly
non-Gaussian PDFs with enhanced tails. It is demonstrated that, after the
removal of autocorrelations, the numerical PDFs can be matched with predictions
from a fluid theoretical setup, based on the instanton method. This result
points to a universality in the modeling of intermittent stochastic process,
offering predictive capability.Comment: 4 pages, 5 figure
The impact of the metallicity and star formation rate on the time-dependent galaxy-wide stellar initial mass function
The stellar initial mass function (IMF) is commonly assumed to be an
invariant probability density distribution function of initial stellar masses
being represented by the canonical IMF. As a consequence the galaxy-wide IMF
(gwIMF), defined as the sum of the IMFs of all star forming regions, should
also be invariant. Recent observational and theoretical results challenge the
hypothesis that the gwIMF is invariant. In order to study the possible reasons
for this variation we use the IMF determined in resolved star clusters and
apply the IGIMF-theory to calculate a grid of gwIMF models for metallicities,
-3<[Fe/H]<1, and galaxy-wide star formation rates,
<SFR<. For a galaxy with metallicy
[Fe/H]/yr, which is a common condition in the early
Universe, we find that the gwIMF is top-heavy (more massive stars), when
compared to the canonical IMF. For a SFR the gwIMF
becomes top-light regardless of the metallicity. For metallicities
the gwIMF can become bottom-heavy regardless of the SFR.
The IGIMF models predict that massive elliptical galaxies should have formed
with a gwIMF that is top-heavy within the first few hundred Myr of the galaxy's
life and that it evolves into a bottom-heavy gwIMF in the metal-enriched
galactic center. We study the SFRH relation, its dependency on
metallicity and the SFR, the correction factors to the Kennicutt SFRH relation, and provide new fitting functions Late-type dwarf
galaxies show significantly higher SFRs with respect to Kennicutt SFRs, while
star forming massive galaxies have significantly lower SFRs than hitherto
thought. This has implications for the gas-consumption time scales and for the
main sequence of galaxies. The Leo P and ultra-faint dwarf galaxies are
discussed explicitly. [abridged]Comment: Astronomy and Astrophysics (A&A) in press. 15 pages, 8 figure
Deep Multi-instance Networks with Sparse Label Assignment for Whole Mammogram Classification
Mammogram classification is directly related to computer-aided diagnosis of
breast cancer. Traditional methods rely on regions of interest (ROIs) which
require great efforts to annotate. Inspired by the success of using deep
convolutional features for natural image analysis and multi-instance learning
(MIL) for labeling a set of instances/patches, we propose end-to-end trained
deep multi-instance networks for mass classification based on whole mammogram
without the aforementioned ROIs. We explore three different schemes to
construct deep multi-instance networks for whole mammogram classification.
Experimental results on the INbreast dataset demonstrate the robustness of
proposed networks compared to previous work using segmentation and detection
annotations.Comment: MICCAI 2017 Camera Read
Effective Hamiltonians of polymethineimine, polyazine and polyazoethene: A density matrix variation approach
A new variation method is proposed to determine the effective Hamiltonians for conjugated π-electron systems. This method is based on the minimization of the difference between the ground state reduced single electron density matrix calculated from the effective Hamiltonian and its ab initio counterpart under a set of well-defined constraints. Applications are made to various oligomers of polymethineimine (PMI), polyazine (PAZ) and polyazoethene (PAE) at the Hartree-Fock level. Calculated are also the optical gaps of these oligomers. The effective Hamiltonians contain electron-electron Coulomb interactions and are suitable for the study of excited state dynamic processes such as nonlinear optical properties in π-conjugated systems. © 1998 American Institute of Physics.published_or_final_versio
A parity-breaking electronic nematic phase transition in the spin-orbit coupled metal CdReO
Strong electron interactions can drive metallic systems toward a variety of
well-known symmetry-broken phases, but the instabilities of correlated metals
with strong spin-orbit coupling have only recently begun to be explored. We
uncovered a multipolar nematic phase of matter in the metallic pyrochlore
CdReO using spatially resolved second-harmonic optical anisotropy
measurements. Like previously discovered electronic nematic phases, this
multipolar phase spontaneously breaks rotational symmetry while preserving
translational invariance. However, it has the distinguishing property of being
odd under spatial inversion, which is allowed only in the presence of
spin-orbit coupling. By examining the critical behavior of the multipolar
nematic order parameter, we show that it drives the thermal phase transition
near 200 kelvin in CdReO and induces a parity-breaking lattice
distortion as a secondary order.Comment: 9 pages main text, 4 figures, 10 pages supplementary informatio
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