156,700 research outputs found
Dynamical Characterization of Galaxies at z~4-6 via Tilted Ring Fitting to ALMA [CII] Observations
Until recently, determining the rotational properties of galaxies in the
early universe (z>4, Universe age <1.5Gyr) was impractical, with the exception
of a few strongly lensed systems. Combining the high resolution and sensitivity
of ALMA at (sub-) millimeter wavelengths with the typically high strength of
the [CII] 158um emission line from galaxies and long-developed dynamical
modeling tools raises the possibility of characterizing the gas dynamics in
both extreme starburst galaxies and normal star forming disk galaxies at z~4-7.
Using a procedure centered around GIPSY's ROTCUR task, we have fit tilted ring
models to some of the best available ALMA [CII] data of a small set of
galaxies: the MS galaxies HZ9 & HZ10, the Damped Lyman-alpha Absorber (DLA)
host galaxy ALMA J0817+1351, the submm galaxies AzTEC/C159 and COSMOS
J1000+0234, and the quasar host galaxy ULAS J1319+0950. This procedure directly
derives rotation curves and dynamical masses as functions of radius for each
object. In one case, we present evidence for a dark matter halo of O(10^11)
solar masses. We present an analysis of the possible velocity dispersions of
AzTEC/C159 and ULAS J1319+0950 based on matching simulated observations to the
integrated [CII] line profiles. Finally, we test the effects of observation
resolution and sensitivity on our results. While the conclusions remain limited
at the resolution and signal-to-noise ratios of these observations, the results
demonstrate the viability of the modeling tools at high redshift, and the
exciting potential for detailed dynamical analysis of the earliest galaxies, as
ALMA achieves full observational capabilities.Comment: 20 pages, 6 figures, Accepted for publication in Ap
Field-Trial of Machine Learning-Assisted Quantum Key Distribution (QKD) Networking with SDN
We demonstrated, for the first time, a machine-learning method to assist the
coexistence between quantum and classical communication channels.
Software-defined networking was used to successfully enable the key generation
and transmission over a city and campus network
Evidence for magnetic clusters in NiV close to the quantum critical concentration
The d-metal alloy NiV undergoes a quantum phase transition from
a ferromagnetic ground state to a paramagnetic ground state as the vanadium
concentration is increased. We present magnetization, ac-susceptibility and
muon-spin relaxation data at several vanadium concentrations near the critical
concentration at which the onset of ferromagnetic order is
suppressed to zero temperature. Below , the muon data reveal a broad
magnetic field distribution indicative of long-range ordered ferromagnetic
state with spatial disorder. We show evidence of magnetic clusters in the
ferromagnetic phase and close to the phase boundary in this disordered
itinerant system as an important generic ingredient of a disordered quantum
phase transition. In contrast, the temperature dependence of the magnetic
susceptibility above is best described in terms of a magnetic quantum
Griffiths phase with a power-law distribution of fluctuation rates of dynamic
magnetic clusters. At the lowest temperatures, the onset of a short-range
ordered cluster-glass phase is recognized by an increase in the muon
depolarization in transverse fields and maxima in ac-susceptibility.Comment: 6 pages, 5 figures, submitted to Proceedings of SCES 201
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
Magnetic structure of solar flare regions producing hard X-ray pulsations
We present analysis of the magnetic field in seven solar flare regions
accompanied by the pulsations of hard X-ray (HXR) emission. These flares were
studied by Kuznetsov et al. (2016) (Paper~I), and chosen here because of the
availability of the vector magnetograms for their parent active regions (ARs)
obtained with the SDO/HMI data. In Paper~I, based on the observations only, it
was suggested that a magnetic flux rope (MFR) might play an important role in
the process of generation of the HXR pulsations. The goal of the present paper
is to test this hypothesis by using the extrapolation of magnetic field with
the non-linear force-free field (NLFFF) method. Having done this, we found that
before each flare indeed there was an MFR elongated along and above a magnetic
polarity inversion line (MPIL) on the photosphere. In two flare regions the
sources of the HXR pulsations were located at the footpoints of different
magnetic field lines wrapping around the central axis, and constituting an MFR
by themselves. In five other flares the parent field lines of the HXR
pulsations were not a part of an MFR, but surrounded it in the form of an
arcade of magnetic loops. These results show that, at least in the analyzed
cases, the "single flare loop" models do not satisfy the observations and
magnetic field modeling, while are consistent with the concept that the HXR
pulsations are a consequence of successive episodes of energy release and
electron acceleration in different magnetic flux tubes (loops) of a complex AR.
An MFR could generate HXR pulsations by triggering episodes of magnetic
reconnection in different loops in the course of its non-uniform evolution
along an MPIL. However, since three events studied here were confined flares,
actual eruptions may not be required to trigger sequential particle
acceleration episodes in the magnetic systems containing an MFR.Comment: 33 pages, 5 figures, 2 tables. Accepted for publication in Journal of
Atmospheric and Solar-Terrestrial Physics (28 April 2018
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