217 research outputs found
Trigger, an active release experiment that stimulated auroral particle precipitation and wave emissions
The experiment design, including a description of the diagnostic and chemical release payload, and the general results are given for an auroral process simulation experiment. A drastic increase of the field aligned charged particle flux was observed over the approximate energy range 10 eV to more than 300 keV, starting about 150 ms after the release and lasting about one second. The is evidence of a second particle burst, starting one second after the release and lasting for tens of seconds, and evidence for a periodic train of particle bursts occurring with a 7.7 second period from 40 to 130 seconds after the release. A transient electric field pulse of 200 mv/m appeared just before the particle flux increase started. Electrostatic wave emissions around 2 kHz, as well as a delayed perturbation of the E-region below the plasma cloud were also observed. Some of the particle observations are interpreted in terms of field aligned electrostatic acceleration a few hundred kilometers above the injected plasma cloud. It is suggested that the acceleration electric field was created by an instability driven by field aligned currents originating in the plasma cloud
Lossless quantum data compression and variable-length coding
In order to compress quantum messages without loss of information it is
necessary to allow the length of the encoded messages to vary. We develop a
general framework for variable-length quantum messages in close analogy to the
classical case and show that lossless compression is only possible if the
message to be compressed is known to the sender. The lossless compression of an
ensemble of messages is bounded from below by its von-Neumann entropy. We show
that it is possible to reduce the number of qbits passing through a quantum
channel even below the von-Neumann entropy by adding a classical side-channel.
We give an explicit communication protocol that realizes lossless and
instantaneous quantum data compression and apply it to a simple example. This
protocol can be used for both online quantum communication and storage of
quantum data.Comment: 16 pages, 5 figure
Energy Requirements for Quantum Data Compression and 1-1 Coding
By looking at quantum data compression in the second quantisation, we present
a new model for the efficient generation and use of variable length codes. In
this picture lossless data compression can be seen as the {\em minimum energy}
required to faithfully represent or transmit classical information contained
within a quantum state.
In order to represent information we create quanta in some predefined modes
(i.e. frequencies) prepared in one of two possible internal states (the
information carrying degrees of freedom). Data compression is now seen as the
selective annihilation of these quanta, the energy of whom is effectively
dissipated into the environment. As any increase in the energy of the
environment is intricately linked to any information loss and is subject to
Landauer's erasure principle, we use this principle to distinguish lossless and
lossy schemes and to suggest bounds on the efficiency of our lossless
compression protocol.
In line with the work of Bostr\"{o}m and Felbinger \cite{bostroem}, we also
show that when using variable length codes the classical notions of prefix or
uniquely decipherable codes are unnecessarily restrictive given the structure
of quantum mechanics and that a 1-1 mapping is sufficient. In the absence of
this restraint we translate existing classical results on 1-1 coding to the
quantum domain to derive a new upper bound on the compression of quantum
information. Finally we present a simple quantum circuit to implement our
scheme.Comment: 10 pages, 5 figure
The Properties of Fast Yellow Pulsating Supergiants: FYPS Point the Way to Missing Red Supergiants
Fast yellow pulsating supergiants (FYPS) are a recently-discovered class of
evolved massive pulsator. As candidate post-red supergiant objects, and one of
the few classes of pulsating evolved massive stars, these objects have
incredible potential to change our understanding of the structure and evolution
of massive stars. Here we examine the lightcurves of a sample of 126 cool
supergiants in the Magellanic Clouds observed by the Transiting Exoplanet
Survey Satellite (\tess~) in order to identify pulsating stars. After making
quality cuts and filtering out contaminant objects, we examine the distribution
of pulsating stars in the Hertzprung-Russel (HR) diagram, and find that FYPS
occupy a region above . This luminosity boundary
corresponds to stars with initial masses of 18-20 , consistent
with the most massive red supergiant progenitors of supernovae (SNe) II-P, as
well as the observed properties of SNe IIb progenitors. This threshold is in
agreement with the picture that FYPS are post-RSG stars. Finally, we
characterize the behavior of FYPS pulsations as a function of their location in
the HR diagram. We find low frequency pulsations at higher effective
temperatures, higher frequency pulsations at lower temperatures, with a
transition between the two behaviors at intermediate temperatures. The observed
properties of FYPS make them fascinating objects for future theoretical study.Comment: Consistent with published version which contains significantly
improved detection and rejection of contaminant objects. Comments welcom
The R136 star cluster dissected with Hubble Space Telescope/STIS. I. Far-ultraviolet spectroscopic census and the origin of HeII 1640 in young star clusters
We introduce a HST/STIS stellar census of R136a, the central ionizing star
cluster of 30 Doradus. We present low resolution far-ultraviolet STIS/MAMA
spectroscopy of R136 using 17 contiguous 52x0.2 arcsec slits which together
provide complete coverage of the central 0.85 parsec (3.4 arcsec). We provide
spectral types of 90% of the 57 sources brighter than m_F555W = 16.0 mag within
a radius of 0.5 parsec of R136a1, plus 8 additional nearby sources including
R136b (O4\,If/WN8). We measure wind velocities for 52 early-type stars from CIV
1548-51, including 16 O2-3 stars. For the first time we spectroscopically
classify all Weigelt & Baier members of R136a, which comprise three WN5 stars
(a1-a3), two O supergiants (a5-a6) and three early O dwarfs (a4, a7, a8). A
complete Hertzsprung-Russell diagram for the most massive O stars in R136 is
provided, from which we obtain a cluster age of 1.5+0.3_-0.7 Myr. In addition,
we discuss the integrated ultraviolet spectrum of R136, and highlight the
central role played by the most luminous stars in producing the prominent HeII
1640 emission line. This emission is totally dominated by very massive stars
with initial masses above ~100 Msun. The presence of strong HeII 1640 emission
in the integrated light of very young star clusters (e.g A1 in NGC 3125)
favours an initial mass function extending well beyond a conventional upper
limit of 100 Msun. We include montages of ultraviolet spectroscopy for LMC O
stars in the Appendix. Future studies in this series will focus on optical
STIS/CCD medium resolution observations.Comment: 20 pages plus four Appendices providing LMC UV O spectral templates,
UV spectral atlas in R136, wind velocities of LMC O stars and photometry of
additional R136 source
Three-dimensional distribution of ejecta in Supernova 1987A at 10 000 days
Due to its proximity, SN 1987A offers a unique opportunity to directly
observe the geometry of a stellar explosion as it unfolds. Here we present
spectral and imaging observations of SN 1987A obtained ~10,000 days after the
explosion with HST/STIS and VLT/SINFONI at optical and near-infrared
wavelengths. These observations allow us to produce the most detailed 3D map of
H-alpha to date, the first 3D maps for [Ca II] \lambda \lambda 7292, 7324, [O
I] \lambda \lambda 6300, 6364 and Mg II \lambda \lambda 9218, 9244, as well as
new maps for [Si I]+[Fe II] 1.644 \mu m and He I 2.058 \mu m. A comparison with
previous observations shows that the [Si I]+[Fe II] flux and morphology have
not changed significantly during the past ten years, providing evidence that it
is powered by 44Ti. The time-evolution of H-alpha shows that it is
predominantly powered by X-rays from the ring, in agreement with previous
findings. All lines that have sufficient signal show a similar large-scale 3D
structure, with a north-south asymmetry that resembles a broken dipole. This
structure correlates with early observations of asymmetries, showing that there
is a global asymmetry that extends from the inner core to the outer envelope.
On smaller scales, the two brightest lines, H-alpha and [Si I]+[Fe II] 1.644
\mu m, show substructures at the level of ~ 200 - 1000 km/s and clear
differences in their 3D geometries. We discuss these results in the context of
explosion models and the properties of dust in the ejecta.Comment: Accepted for publication in Ap
Saliva molecular inflammatory profiling in female migraine patients responsive to adjunctive cervical non-invasive vagus nerve stimulation : the MOXY Study
BackgroundRising evidence indicate that oxytocin and IL-1 impact trigemino-nociceptive signaling. Current perspectives on migraine physiopathology emphasize a cytokine bias towards a pro-inflammatory status. The anti-nociceptive impact of oxytocin has been reported in preclinical and human trials. Cervical non-invasive vagus nerve stimulation (nVNS) emerges as an add-on treatment for the preventive and abortive use in migraine. Less is known about its potential to modulate saliva inflammatory signaling in migraine patients. The rationale was to perform inter-ictal saliva measures of oxytocin and IL-1 ss along with headache assessment in migraine patients with 10weeks adjunctive nVNS compared to healthy controls.Methods12 migraineurs and 12 suitably matched healthy control were studied with inter-ictal saliva assay of pro- and anti-neuroinflammatory cytokines using enzyme-linked immuno assay techniques along with assessment of headache severity/frequency and associated functional capacity at baseline and after 10weeks adjunctive cervical nVNS.ResultsnVNS significantly reduced headache severity (VAS), frequency (headache days and total number of attacks) and significantly improved sleep quality compared to baseline (pPeer reviewe
AT 2021loi: A Bowen Fluorescence Flare with a Rebrightening Episode, Occurring in a Previously-Known AGN
AT 2021loi is an optical-ultraviolet transient located at the center of its
host galaxy. Its spectral features identify it as a member of the ``Bowen
Fluorescence Flare'' (BFF) class. The first member of this class was considered
to be related to a tidal disruption event, but enhanced accretion onto an
already active supermassive black hole was suggested as an alternative
explanation. AT 2021loi, having occurred in a previously-known unobscured AGN,
strengthens the latter interpretation. Its light curve is similar to those of
previous BFFs, showing a rebrightening approximately one year after the main
peak (which was not explicitly identified, but might be the case, in all
previous BFFs). An emission feature around 4680 A, seen in the pre-flare
spectrum, strengthens by a factor of 2 around the optical peak of the
flare, and is clearly seen as a double peaked feature then, suggesting a blend
of NIII with HeII as its origin. The appearance of
OIII 3133 and possible NIII (blended with
H) during the flare further support a Bowen Fluorescence
classification. Here, we present ZTF, ATLAS, Keck, Las Cumbres Observatory,
NEOWISE-R, , AMI and VLA observations of AT 2021loi, making it one of
the best observed BFFs to date. AT 2021loi thus provides some clarity on the
nature of BFFs but also further demonstrates the diversity of nuclear
transients.Comment: Submitted to ApJ. This version addresses comments from the refere
SAGUARO: Time-domain Infrastructure for the Fourth Gravitational-wave Observing Run and Beyond
We present upgraded infrastructure for Searches after Gravitational Waves
Using ARizona Observatories (SAGUARO) during LIGO, Virgo, and KAGRA's fourth
gravitational-wave (GW) observing run (O4). These upgrades implement many of
the lessons we learned after a comprehensive analysis of potential
electromagnetic counterparts to the GWs discovered during the previous
observing run. We have developed a new web-based target and observation manager
(TOM) that allows us to coordinate sky surveys, vet potential counterparts, and
trigger follow-up observations from one centralized portal. The TOM includes
software that aggregates all publicly available information on the light curves
and possible host galaxies of targets, allowing us to rule out potential
contaminants like active galactic nuclei, variable stars, solar-system objects,
and preexisting supernovae, as well as to assess the viability of any plausible
counterparts. We have also upgraded our image-subtraction pipeline by
assembling deeper reference images and training a new neural network-based
real-bogus classifier. These infrastructure upgrades will aid coordination by
enabling the prompt reporting of observations, discoveries, and analysis to the
GW follow-up community, and put SAGUARO in an advantageous position to discover
kilonovae in the remainder of O4 and beyond. Many elements of our open-source
software stack have broad utility beyond multimessenger astronomy, and will be
particularly relevant in the "big data" era of transient discoveries by the
Vera C. Rubin Observatory.Comment: submitted to AAS Journal
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