18,342 research outputs found
Fitting Spectral Decay with the k-Support Norm
The spectral kk-support norm enjoys good estimation properties in low rank matrix learning problems, empirically outperforming the trace norm. Its unit ball is the convex hull of rank kk matrices with unit Frobenius norm. In this paper we generalize the norm to the spectral (k,p)(k,p)-support norm, whose additional parameter pp can be used to tailor the norm to the decay of the spectrum of the underlying model. We characterize the unit ball and we explicitly compute the norm. We further provide a conditional gradient method to solve regularization problems with the norm, and we derive an efficient algorithm to compute the Euclidean projection on the unit ball in the case p=∞p=∞. In numerical experiments, we show that allowing pp to vary significantly improves performance over the spectral kk-support norm on various matrix completion benchmarks, and better captures the spectral decay of the underlying model
Recombining Plasma in the Gamma-ray Emitting Mixed-Morphology Supernova Remnant 3C 391
A group of middle-aged mixed-morphology (MM) supernova remnants (SNRs)
interacting with molecular clouds (MC) has been discovered as strong GeV
gamma-ray emitters by Large Area Telescope on board Fermi Gamma Ray Space
Telescope (Fermi-LAT). The recent observations of the Suzaku X-ray satellite
have revealed that some of these interacting gamma-ray emitting SNRs, such as
IC443, W49B, W44, and G359.1-0.5, have overionized plasmas. 3C 391 (G31.9+0.0)
is another Galactic MM SNR interacting with MC. It was observed in GeV gamma
rays by Fermi-LAT as well as in the 0.3 10.0 keV X-ray band by Suzaku. In
this work, 3C 391 was detected in GeV gamma rays with a significance of
18 and we showed that the GeV emission is point-like in nature. The
GeV gamma-ray spectrum was shown to be best explained by the decay of neutral
pions assuming that the protons follow a broken power-law distribution. We
revealed radiative recombination structures of silicon and sulfur from 3C 391
using Suzaku data. In this paper we discuss the possible origin of this type of
radiative plasma and hadronic gamma rays.Comment: 10 pages, 7 figures; accepted by Ap
Localness of energy cascade in hydrodynamic turbulence, II. Sharp spectral filter
We investigate the scale-locality of subgrid-scale (SGS) energy flux and
inter-band energy transfers defined by the sharp spectral filter. We show by
rigorous bounds, physical arguments and numerical simulations that the spectral
SGS flux is dominated by local triadic interactions in an extended turbulent
inertial-range. Inter-band energy transfers are also shown to be dominated by
local triads if the spectral bands have constant width on a logarithmic scale.
We disprove in particular an alternative picture of ``local transfer by
nonlocal triads,'' with the advecting wavenumber mode at the energy peak.
Although such triads have the largest transfer rates of all {\it individual}
wavenumber triads, we show rigorously that, due to their restricted number,
they make an asymptotically negligible contribution to energy flux and
log-banded energy transfers at high wavenumbers in the inertial-range. We show
that it is only the aggregate effect of a geometrically increasing number of
local wavenumber triads which can sustain an energy cascade to small scales.
Furthermore, non-local triads are argued to contribute even less to the
space-average energy flux than is implied by our rigorous bounds, because of
additional cancellations from scale-decorrelation effects. We can thus recover
the -4/3 scaling of nonlocal contributions to spectral energy flux predicted by
Kraichnan's ALHDIA and TFM closures. We support our results with numerical data
from a pseudospectral simulation of isotropic turbulence with
phase-shift dealiasing. We conclude that the sharp spectral filter has a firm
theoretical basis for use in large-eddy simulation (LES) modeling of turbulent
flows.Comment: 42 pages, 9 figure
Searching for Overionized Plasma in the Gamma-ray Emitting Supernova Remnant G349.70.2
G349.70.2 is a supernova remnant (SNR) expanding in a dense medium of
molecular clouds and interacting with clumps of molecular material emitting
gamma rays. We analyzed the gamma-ray data of Large Area Telescope on board
Fermi Gamma Ray Space Telescope and detected G349.70.2 in the energy range
of 0.2300 GeV with a significance of 13 showing no extended
morphology. Modeling of the gamma-ray spectrum revealed that the GeV gamma-ray
emission dominantly originates from the decay of neutral pions, where the
protons follow a broken power-law distribution with a spectral break at
12 GeV. To search for features of radiative recombination continua in the
eastern and western regions of the remnant, we analyzed the Suzaku data of
G349.70.2 and found no evidence for overionized plasma. In this paper we
discuss possible scenarios to explain the hadronic gamma-ray emission in
G349.70.2 and the mixed morphology nature of this SNR.Comment: 10 pages, 7 figures; accepted by ApJ. arXiv admin note: text overlap
with arXiv:1406.217
Analysis of Ultrafast Transient Absorption Spectroscopy Data using Integrative Data Analysis Platform: 1. Data Processing, Fitting, and Model Selection
This manuscript describes a workflow for analysis of transient absorption (TA) spectroscopy data using Integrative Data Analysis Platforms (IDAP) software package. Time-dependent spectral series are analyzed through evaluation of the isosbestic point and kinetics of excited state and ground-state bleach decays. Model fitting and selection based on Akaike\u27s Information Criterion is discussed. As a practical example, we analyze excitation decays of a common protein label, Alexa Fluor 647
The Evolving Accretion Disc in the Black Hole X-ray Transient XTE J1859+226
We present HST, RXTE, and UKIRT observations of the broad band spectra of the
black hole X-ray transient XTE J1859+226 during the decline from its 1999-2000
outburst. Our UV spectra define the 2175A interstellar absorption feature very
well and based on its strength we estimate E(B-V)=0.58+/-0.12. Hence we
deredden our spectra and follow the evolution of the spectral energy
distribution on the decline from outburst. We find that the UV and optical
data, and the X-ray thermal component when detectable, can be fit with a simple
blackbody model of an accretion disc heated by internal viscosity and X-ray
irradiation, and extending to close to the last stable orbit around the black
hole, although the actual inner radius cannot be well constrained. During the
decline we see the disc apparently evolving from a model with the edge
dominated by irradiative heating towards one where viscous heating is dominant
everywhere. The outer disc radius also appears to decrease during the decline;
we interpret this as evidence of a cooling wave moving inwards and discuss its
implications for the disc instability model. Based on the normalisation of our
spectral fits we estimate a likely distance range of 4.6-8.0kpc, although a
value outside of this range cannot securely be ruled out.Comment: 10 pages including figures. Accepted for publication in MNRA
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