1,829 research outputs found
A Dust Twin of Cas A: Cool Dust and 21-micron Silicate Dust Feature in the Supernova Remnant G54.1+0.3
We present infrared (IR) and submillimeter observations of the Crab-like
supernova remnant (SNR) G54.1+0.3 including 350 micron (SHARC-II), 870 micron
(LABOCA), 70, 100, 160, 250, 350, 500 micron (Herschel) and 3-40 micron
(Spitzer). We detect dust features at 9, 11 and 21 micron and a long wavelength
continuum dust component. The 21 micron dust coincides with [Ar II] ejecta
emission, and the feature is remarkably similar to that in Cas A. The IRAC 8
micron image including Ar ejecta is distributed in a shell-like morphology
which is coincident with dust features, suggesting that dust has formed in the
ejecta. We create a cold dust map that shows excess emission in the
northwestern shell. We fit the spectral energy distribution of the SNR using
the continuous distributions of ellipsoidal (CDE) grain model of pre-solar
grain SiO2 that reproduces the 21 and 9 micron dust features and discuss grains
of SiC and PAH that may be responsible for the 10-13 micron dust features. To
reproduce the long-wavelength continuum, we explore models consisting of
different grains including Mg2SiO4, MgSiO3, Al2O3, FeS, carbon, and Fe3O4. We
tested a model with a temperature-dependent silicate absorption coefficient. We
detect cold dust (27-44 K) in the remnant, making this the fourth such SNR with
freshly-formed dust. The total dust mass in the SNR ranges from 0.08-0.9 Msun
depending on the grain composition, which is comparable to predicted masses
from theoretical models. Our estimated dust masses are consistent with the idea
that SNe are a significant source of dust in the early Universe.Comment: MNRAS: accepted on June 28, 2018 and published on July 4, 201
The Solar hep Process in Effective Field Theory
Using effective field theory, we calculate the S-factor for the hep process
in a totally parameter-free formulation. The transition operators are organized
according to chiral counting, and their matrix elements are evaluated using the
realistic nuclear wave functions obtained in the
correlated-hyperspherical-harmonics method. Terms of up to
next-to-next-to-next-to-leading order in heavy-baryon chiral perturbation
theory are considered. Fixing the only parameter in the theory by fitting the
tritium \beta-decay rate, we predict the hep S-factor with accuracy better than
\sim 20 %.Comment: 4 pages, Revtex. Minor revision has been mad
Parameter-Free Calculation of the Solar Proton Fusion Rate in Effective Field Theory
Spurred by the recent complete determination of the weak currents in
two-nucleon systems up to in heavy-baryon chiral perturbation
theory, we carry out a parameter-free calculation of the solar proton fusion
rate in an effective field theory that combines the merits of the standard
nuclear physics method and systematic chiral expansion. Using the tritium
beta-decay rate as an input to fix the only unknown parameter in the effective
Lagrangian, we can evaluate with drastically improved precision the ratio of
the two-body contribution to the well established one-body contribution; the
ratio is determined to be (0.86\pm 0.05) %. This result is essentially
independent of the cutoff parameter for a wide range of its variation (500 MeV
\le \Lambda \le 800 MeV), a feature that substantiates the consistency of the
calculation.Comment: 10 pages. The argument is considerably more sharpened with a reduced
error ba
Exchange Current Corrections to Neutrino--Nucleus Scattering
Relativistic exchange current corrections to neutrino--nucleus cross sections
are presented assuming non--vanishing strange quark form factors for the
constituent nucleons. For charged current processes the exchange current
corrections can lower the impulse approximation results by 10\% while these
corrections are found to be sensitive to both the nuclear density and the
strange quark axial form factor of the nucleon for neutral current processes.
Implications on the LSND experiment to determine this form factor are
discussed.Comment: 11 pages, 2 figures, revtex 3.0, full postscript version of the file
and figures available at
http://www.nikhefk.nikhef.nl/projects/Theory/preprints/preprints.html To
appear in Phys. Rev. Lett
Discovery of X-rays from the supernova remnant G0.9+0.1
During the survey of the Galactic Center region, we have
discovered X-ray emission from the central region of the supernova remnant
G0.9+0.1. The high interstellar absorption (N_H about 3 times 10^{23} cm^-2) is
consistent with a distance of order of 10 kpc and, correspondingly, an X-ray
luminosity of about 10^{35} erg s^{-1}. Although we cannot completely rule out
a thermal origin of the X-ray emission, its small angular extent (radius of
about 2'), the good fit with a power law, the presence of a flat spectrum radio
core, and the estimated SNR age of a few thousand years, favour the
interpretation in terms of synchrotron emission powered by a young, energetic
pulsar.Comment: 4 pages, 1 figure. Uses espcrc2.sty (included). To appear in The
Active X-ray Sky: Results from BeppoSAX and Rossi-XTE, Nuclear Physics B
Proceedings Supplements, L. Scarsi, H. Bradt, P. Giommi and F. Fiore (eds.),
Elsevier Science B.
Cyber-threat detection system using a hybrid approach of transfer learning and multi-model image representation
Currently, Android apps are easily targeted by malicious network traffic because of their constant network access. These threats have the potential to steal vital information and disrupt the commerce, social system, and banking markets. In this paper, we present a malware detection system based on word2vec-based transfer learning and multi-model image representation. The proposed method combines the textual and texture features of network traffic to leverage the advantages of both types. Initially, the transfer learning method is used to extract trained vocab from network traffic. Then, the malware-to-image algorithm visualizes network bytes for visual analysis of data traffic. Next, the texture features are extracted from malware images using a combination of scale-invariant feature transforms (SIFTs) and oriented fast and rotated brief transforms (ORBs). Moreover, a convolutional neural network (CNN) is designed to extract deep features from a set of trained vocab and texture features. Finally, an ensemble model is designed to classify and detect malware based on the combination of textual and texture features. The proposed method is tested using two standard datasets, CIC-AAGM2017 and CICMalDroid 2020, which comprise a total of 10.2K malware and 3.2K benign samples. Furthermore, an explainable AI experiment is performed to interpret the proposed approach
Magnetic properties of pure and Gd doped EuO probed by NMR
An Eu NMR study in the ferromagnetic phase of pure and Gd doped EuO was
performed. A complete description of the NMR lineshape of pure EuO allowed for
the influence of doping EuO with Gd impurities to be highlighted. The presence
of a temperature dependent static magnetic inhomogeneity in Gd doped EuO was
demonstrated by studying the temperature dependence of the lineshapes. The
results suggest that the inhomogeneity in 0.6% Gd doped EuO is linked to
colossal magnetoresistance. The measurement of the spin-lattice relaxation
times as a function of temperature led to the determination of the value of the
exchange integral J as a function of Gd doping. It was found that J is
temperature independent and spatially homogeneous for all the samples and that
its value increases abruptly with increasing Gd doping.Comment: 14 pages, 10 figures, to be published in Physical Review
Lattice dynamics and the electron-phonon interaction in CaRuO
We present a Raman scattering study of CaRuO, in which we investigate
the temperature-dependence of the lattice dynamics and the electron-phonon
interaction below the metal-insulator transition temperature ({\it T}). Raman spectra obtained in a backscattering geometry with light polarized
in the ab-plane reveal 9 B phonon modes (140, 215, 265, 269, 292, 388,
459, 534, and 683 cm) and 9 A phonon modes (126, 192, 204, 251, 304,
322, 356, 395, and 607 cm) for the orthorhombic crystal structure
(PbcaD). With increasing temperature toward {\it T},
the observed phonon modes shift to lower energies and exhibit reduced spectral
weights, reflecting structural changes associated with the elongation of the
RuO octahedra. Interestingly, the phonons exhibit significant increases in
linewidths and asymmetries for {\it T} {\it T}. These results
indicate that there is an increase in the effective number of electrons and the
electron-phonon interaction strengths as the temperature is raised through {\it
T}, suggesting the presence of orbital fluctuations in the
temperature regime {\it T} {\it T} {\it T}.Comment: 6 pages, 4 figure
- …