11,586 research outputs found
Temporal changes of the flare activity of Proxima Cen
We study temporal variations of the emission lines of Halpha, Hepsilon, H and
K Ca II, D1 and D2 Na I, 4026 and 5876 A He I in the HARPS spectra of Proxima
Centauri across an extended time of 13.2 years, from May 27, 2004, to September
30, 2017.
Aims. We analyse the common behaviour and differences in the intensities and
profiles of different emission lines in flare and quiet modes of Proxima
activity.
Methods. We compare the pseudo-equivalent widths (pEW) and profiles of the
emission lines in the HARPS high-resolution (R ~ 115,000) spectra observed at
the same epochs.
Results. All emission lines show variability with a timescale of at least 10
min. The strength of all lines except He I 4026 A correlate with \Halpha.
During strong flares the `red asymmetry' appears in the Halpha emission line
indicating the infall of hot condensed matter into the chromosphere with
velocities greater than 100 km/s disturbing chromospheric layers. As a result,
the strength of the Ca II lines anti-correlates with Halpha during strong
flares. The He I lines at 4026 and 5876 A appear in the strong flares. The
cores of D1 and D2 Na I lines are also seen in emission. During the minimum
activity of Proxima Centauri, Ca II lines and Hepsilon almost disappear while
the blue part of the Na I emission lines is affected by the absorption in the
extending and condensing flows.
Conclusions. We see different behaviour of emission lines formed in the flare
regions and chromosphere. Chromosphere layers of Proxima Cen are likely heated
by the flare events; these layers are cooled in the `non-flare' mode. The
self-absorption structures in cores of our emission lines vary with time due to
the presence of a complicated system of inward and outward matter flows in the
absorbing layers.Comment: 22 pages, 12 Figures, accepted by A
Characteristic molecular properties of one-electron double quantum rings under magnetic fields
The molecular states of conduction electrons in laterally coupled quantum
rings are investigated theoretically. The states are shown to have a distinct
magnetic field dependence, which gives rise to periodic fluctuations of the
tunnel splitting and ring angular momentum in the vicinity of the ground state
crossings. The origin of these effects can be traced back to the Aharonov-Bohm
oscillations of the energy levels, along with the quantum mechanical tunneling
between the rings. We propose a setup using double quantum rings which shows
that Aharonov-Bohm effects can be observed even if the net magnetic flux
trapped by the carriers is zero.Comment: 16 pages (iopart format), 10 figures, accepted in J.Phys.Cond.Mat
Radiation Testing of Electronics for the CMS Endcap Muon System
The electronics used in the data readout and triggering system for the
Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC)
particle accelerator at CERN are exposed to high radiation levels. This
radiation can cause permanent damage to the electronic circuitry, as well as
temporary effects such as data corruption induced by Single Event Upsets. Once
the High Luminosity LHC (HL-LHC) accelerator upgrades are completed it will
have five times higher instantaneous luminosity than LHC, allowing for
detection of rare physics processes, new particles and interactions. Tests have
been performed to determine the effects of radiation on the electronic
components to be used for the Endcap Muon electronics project currently being
designed for installation in the CMS experiment in 2013. During these tests the
digital components on the test boards were operating with active data readout
while being irradiated with 55 MeV protons. In reactor tests, components were
exposed to 30 years equivalent levels of neutron radiation expected at the
HL-LHC. The highest total ionizing dose (TID) for the muon system is expected
at the inner-most portion of the CMS detector, with 8900 rad over ten years.
Our results show that Commercial Off-The-Shelf (COTS) components selected for
the new electronics will operate reliably in the CMS radiation environment
Abundance trend with condensation temperature for stars with different Galactic birth places
During the past decade, several studies reported a correlation between
chemical abundances of stars and condensation temperature (also known as Tc
trend). However, the real astrophysical nature of this correlation is still
debated. The main goal of this work is to explore the possible dependence of
the Tc trend on stellar Galactocentric distances, Rmean. We used high-quality
spectra of about 40 stars observed with the HARPS and UVES spectrographs to
derive precise stellar parameters, chemical abundances, and stellar ages. A
differential line-by-line analysis was applied to achieve the highest possible
precision in the chemical abundances. We confirm previous results that [X/Fe]
abundance ratios depend on stellar age and that for a given age, some elements
also show a dependence on Rmean. When using the whole sample of stars, we
observe a weak hint that the Tc trend depends on Rmean. The observed dependence
is very complex and disappears when only stars with similar ages are
considered. To conclude on the possible dependence of the Tc trend on the
formation place of stars, a larger sample of stars with very similar
atmospheric parameters and stellar ages observed at different Galactocentric
distances is neededComment: Accepted by A&
Quantum correlations versus Multisimultaneity: an experimental test
Multisimultaneity is a causal model of relativistic quantum physics which
assigns a real time ordering to any set of events, much in the spirit of the
pilot-wave picture. Contrary to standard quantum mechanics, it predicts a
disappearance of the correlations in a Bell-type experiment when both analysers
are in relative motion such that, each one in its own inertial reference frame,
is first to select the output of the photons. We tested this prediction using
acousto-optic modulators as moving beam-splitters and interferometers separated
by 55 m. We didn't observe any disappearance of the correlations, thus refuting
Multisimultaneity.Comment: 4 pages, 3 figures, RevTex 4 versio
Film blowing of PHB-based systems for home compostable food packaging
One of the routes to minimize the environmental impact of plastics waste is the use of bio-sourced and biodegradable alternatives, particularly for packaging applications. Although Polyhydroxyalkanoates (PHA) are attractive candidates for food packaging, they have poor processability, particularly for extrusion film blowing. Thus, one relatively successful alternative has been blending PHA with a biodegradable polymer. This work proposes film blowing of a co-extruded Poly (hydroxybutyrate) (PHB) layer with a poly butylene adipate-co-terephtalate (PBAT) layer to enhance bubble stability, mechanical and barrier properties. Co-extrusion is detailed, together with the different strategies followed to improve adhesion between film layers and the PHB content in the films. Films with thicknesses below 50 micron and elongation at break beyond 500 % were consistently produced.This project has received funding from the European Union’s Horizon 2020 research and
innovation programme under grant agreement No. 774088. LH also acknowledges
funding from the Portuguese Foundation for Science and Technology Investigator
Programme through grant IF/00606/2014
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