3,151 research outputs found
Atomic Resolution Imaging of Currents in Nanoscopic Quantum Networks via Scanning Tunneling Microscopy
We propose a new method for atomic-scale imaging of spatial current patterns
in nanoscopic quantum networks by using scanning tunneling microscopy (STM). By
measuring the current flowing from the STM tip into one of the leads attached
to the network as a function of tip position, one obtains an atomically
resolved spatial image of "current riverbeds" whose spatial structure reflects
the coherent flow of electrons out of equilibrium. We show that this method can
be successfully applied in variety of network topologies, and is robust against
dephasing effects.Comment: 5 page
Classification and Spectral Evolution of Outbursts of Aql X-1
We present a broad classification of all outbursts detected with the All-Sky
Monitor (ASM) on the Rossi X-Ray Timing Explorer (RXTE) and the Monitor of All
Sky X-Ray Image (MAXI) of Aql X-1. We identify three types of outbursts;
long-high, medium-low, and short-low, based on the duration and maximum flux.
We analyse the trends in the "phase-space" of flux-derivative versus flux to
demonstrate the differences in the three identified outburst types. We present
a spectral analysis of the observations of Aql X-1 performed by the
Proportional Counter Array (PCA) onboard RXTE during the 2000 and 2011
outbursts of the long-high class and the 2010 outburst of the medium-low class.
We model the source spectrum with a hybrid thermal/non-thermal hot plasma
emission model (EQPAIR in XSPEC, Coppi 2000) together with a Gaussian component
to model the Fe K_alpha emission line. We construct time histories of the
source flux, the optical depth of the corona (tau), the seed photon temperature
(kT_bb) and the hard state compactness (l_h) for these three outbursts. We show
that the physical parameters of either classes reach the same values throughout
the outbursts, the only difference being the maximum flux. We discuss our
results in the terms of modes of interaction of the star with the disc and size
of the disc kept hot by irradiation. We conclude that irradiation is the
dominant physical process leading to the different classes of outbursts.Comment: MNRAS accepted. 12 pages, 9 figures, 3 table
Bianchi I Model: An Alternative Way To Model The Presentday Universe
Although the new era of high precision cosmology of the cosmic microwave
background (CMB) radiation improves our knowledge to understand the infant as
well as the presentday Universe, it also leads us to question the main
assumption of the exact isotropy of the CMB. There are two pieces of
observational evidence that hint towards there being no exact isotropy. These
are first the existence of small anisotropy deviations from isotropy of the CMB
radiation and second, the presence of large angle anomalies, although the
existence of these anomalies is currently a huge matter of debate. These hints
are particularly important since isotropy is one of the two main postulates of
the Copernican principle on which the FRW models are built. This almost
isotropic CMB radiation implies that the universe is almost a FRW universe, as
is proved by previous studies.
Assuming the matter component forms the deviations from isotropy in the CMB
density fluctuations when matter and radiation decouples, we here attempt to
find possible constraints on the FRW type scale and Hubble parameter by using
the Bianchi type I (BI) anisotropic model which is asymptotically equivalent to
the standard FRW. To obtain constraints on such an anisotropic model, we derive
average and late-time shear values that come from the anisotropy upper limits
of the recent Planck data based on a model independent shear parameter of
Maartens et al. (1995a,b) and from the theoretical consistency relation. These
constraints lead us to obtain a BI model which becomes an almost-FRW model in
time, and which is consistent with the latest observational data of the CMB.Comment: 16 pages, 4 figures, accepted in MNRA
transition in lattice QCD
We study the electromagnetic
transition in 2+1 flavor lattice QCD, which gives access to the dominant decay
mode of baryon. The magnetic dipole and the electric quadrupole
transition form factors are computed. The magnetic dipole form factor is found
to be mainly determined by the strange quark and the electric quadrupole form
factor to be negligibly small, in consistency with the quark model. We also
evaluate the helicity amplitudes and the decay rate.Comment: 8 pages, 1 figure. Added references and discussio
A look inside charmed-strange baryons from lattice QCD
The electromagnetic form factors of the spin-3/2 baryons, namely
, , and , are
calculated in full QCD on PACS-CS lattices with a pion mass of
156(9) MeV. The electric charge radii and magnetic moments from the and
multipole form factors are extracted. Results for the electric quadrupole
form factors, , are also given. Quark sector contributions are computed
individually for each observable and then combined to obtain the baryon
properties. We find that the charm quark contributions are systematically
smaller than the strange-quark contributions in the case of the charge radii
and magnetic moments. moments of the and
provide a statistically significant data to conclude that their electric charge
distributions are deformed to an oblate shape. Properties of the spin-1/2
and baryons are also computed and a thorough
comparison is given. This complete study gives valuable hints about the
heavy-quark dynamics in charmed hadrons.Comment: 14 pages, 14 figures. Includes a subsection on the systematic effect
Building Morphological Chains for Agglutinative Languages
In this paper, we build morphological chains for agglutinative languages by
using a log-linear model for the morphological segmentation task. The model is
based on the unsupervised morphological segmentation system called
MorphoChains. We extend MorphoChains log linear model by expanding the
candidate space recursively to cover more split points for agglutinative
languages such as Turkish, whereas in the original model candidates are
generated by considering only binary segmentation of each word. The results
show that we improve the state-of-art Turkish scores by 12% having a F-measure
of 72% and we improve the English scores by 3% having a F-measure of 74%.
Eventually, the system outperforms both MorphoChains and other well-known
unsupervised morphological segmentation systems. The results indicate that
candidate generation plays an important role in such an unsupervised log-linear
model that is learned using contrastive estimation with negative samples.Comment: 10 pages, accepted and presented at the CICLing 2017 (18th
International Conference on Intelligent Text Processing and Computational
Linguistics
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