1,268 research outputs found
Deciphering Solar Magnetic Activity: The (Solar) Hale Cycle Terminator of 2021
McIntosh and colleagues identified an event in the solar timeline that
appeared to play a role in how Sunspot Cycle 23 (SC23) transitioned into
Sunspot Cycle 24 (SC24). The timeframe for this transition was rapid, taking
place in as short as time as a solar rotation. M2014 inferred that the
transition observed was a critical episode for the Sun's global-scale magnetic
field that was being manifest in the spatially and temporally overlapping and
magnetic systems belonging to the Sun's 22-year (Hale) magnetic cycle. These
events have been dubbed as Hale Cycle terminations, or `terminators' for short.
Further exploration revealed a relationship between terminator separation (as a
measure of overlap in the Hale Cycles) and the upcoming sunspot cycle
amplitude. McIntosh and colleagues extrapolated upon this relationship to
identify the termination of the SC24 carrying Hale Cycle band in Mid-2020 and
inferred that this would result in a very large Sunspot Cycle 25 (SC25). This
paper presents observational analysis of the end of SC24 and the initial months
of SC25 growth following a terminator that occurred in mid-December 2021
(approximately 12/13/2021). We use the December 2021 terminator to finalize the
forecast of SC25 amplitude 184 (17 with 95\% confidence, and 63 with
68\% confidence). Finally, we use other terminator-related superposed epoch
analyses to project the timing of SC25 maxima in late 2023 to mid 2024.Comment: 16 pages, 10 figures - Submitted to Frontier
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Multiple, discrete arcs on sunward convecting field lines in the 14-15 MLT region
Ionospheric plasma flow measurements and simultaneous observations of thin (∼0.2° invariant latitude (ILAT)), multiple, longitudinally extended auroral arcs of transient nature within 74°-76° ILAT and 1030-1130 UT (∼14-15 MLT) on January 12, 1989, are reported. The auroral structures appeared within the luminous belt of strong 630.0-nm emissions located predominantly on sunward convecting field lines equatorward of the convection reversal boundary as identified by the European Incoherent Scatter UHF radar. The events occurred during a period of several hours quasi-steady solar wind speed (∼ 700 km s−1) and a radially orientated interplanetary magnetic field (IMF) with a weak northward tilt (IMF Bz>0). These typical dayside auroral features are related to previous studies of auroral activity related to the upward region 1 current in the postnoon sector. The discrete auroral events presented here may result from magnetosheath plasma injections into the low-latitude boundary layer (LLBL) and an associated dynamo mechanism. An alternative explanation invokes kinetic Alfvén waves, triggered either by Kelvin-Helmholtz instability at the inner (or outer) edge of the LLBL or by pressure pulse induced magnetopause surface waves
Solar Magnetic Activity and Solar-Stellar Connections
Prediction of solar magnetic activity on various temporal scales is a fundamental element of space weather, which requires a wide range of theoretical and observational expertise in solar phenomena from the deep interior to the corona. Historical observations have revealed many features of cyclic variations of the solar activity; but these data are dramatically insufficient to draw a physical picture of global magnetic field evolution. New observational data, currently available from space missions and ground-based observatories, provide us with detailed information about solar dynamics and magnetism. However, because of the relatively short duration of data series and the great variety of data types and quality, it is challenging to assimilate these data in theoretical models and make reliable forecasts. The recent unexpectedly weak solar activity cycles, as well as observations of rotational and magnetic topology transitions in solar-type stars, suggest that the Sun and its magnetic dynamo are currently in a very interesting evolutionary stage. This could relate to the difficulty in getting a model of the Sun to produce solar-like rather than anti-solar-like differential rotation, to reproduce the rotation profile obtained from helioseismology, and to predict solar activity cycles
The origin of the Acheulean: the 1.7 million-year-old site of FLK West, Olduvai Gorge (Tanzania)
The appearance of the Acheulean is one of the hallmarks of human evolution. It represents the
emergence of a complex behavior, expressed in the recurrent manufacture of large-sized tools, with
standardized forms, implying more advance forethought and planning by hominins than those required
by the precedent Oldowan technology. The earliest known evidence of this technology dates back to
c. 1.7 Ma. and is limited to two sites (Kokiselei [Kenya] and Konso [Ethiopia]), both of which lack fauna.
The functionality of these earliest Acheulean assemblages remains unknown. Here we present the
discovery of another early Acheulean site also dating to c. 1.7 Ma from Olduvai Gorge. This site provides
evidence of the earliest steps in developing the Acheulean technology and is the oldest Acheulean site in
which stone tools occur spatially and functionally associated with the exploitation of fauna. Simple and
elaborate large-cutting tools (LCT) and handaxes co-exist at FLK West, showing that complex cognition
was present from the earliest stages of the Acheulean. Here we provide a detailed technological study
and evidence of the use of these tools on the butchery and consumption of fauna, probably by early
Homo erectus sensu lato
Photospheric and chromospheric magnetic activity of seismic solar analogs. Observational inputs on the solar/stellar connection from Kepler and Hermes
We identify a set of 18 solar analogs among the seismic sample of solar-like
stars observed by the Kepler satellite rotating between 10 and 40 days. This
set is constructed using the asteroseismic stellar properties derived using
either the global oscillation properties or the individual acoustic
frequencies. We measure the magnetic activity properties of these stars using
observations collected by the photometric Kepler satellite and by the
ground-based, high-resolution Hermes spectrograph mounted on the Mercator
telescope. The photospheric (Sph) and chromospheric (S index) magnetic activity
levels of these seismic solar analogs are estimated and compared in relation to
the solar activity. We show that the activity of the Sun is comparable to the
activity of the seismic solar analogs, within the maximum-to-minimum temporal
variations of the 11-year solar activity cycle 23. In agreement with previous
studies, the youngest stars and fastest rotators in our sample are actually the
most active. The activity of stars older than the Sun seems to not evolve much
with age. Furthermore, the comparison of the photospheric, Sph, with the
well-established chromospheric, S index, indicates that the Sph index can be
used to provide a suitable magnetic activity proxy which can be easily
estimated for a large number of stars from space photometric observations.Comment: Accepted for publication in A&
The spherical probe electric field and wave experiment
The experiment is designed to measure the electric field and density fluctuations with sampling rates up to 40,000 samples/sec. The description includes Langmuir sweeps that can be made to determine the electron density and temperature, the study of nonlinear processes that result in acceleration of plasma, and the analysis of large scale phenomena where all four spacecraft are needed
Magnetic variability in the young solar analog KIC 10644253: Observations from the Kepler satellite and the HERMES spectrograph
The continuous photometric observations collected by the Kepler satellite
over 4 years provide a whelm of data with an unequalled quantity and quality
for the study of stellar evolution of more than 200000 stars. Moreover, the
length of the dataset provide a unique source of information to detect magnetic
activity and associated temporal variability in the acoustic oscillations. In
this regards, the Kepler mission was awaited with great expectation. The search
for the signature of magnetic activity variability in solar-like pulsations
still remained unfruitful more than 2 years after the end of the nominal
mission. Here, however, we report the discovery of temporal variability in the
low-degree acoustic frequencies of the young (1 Gyr-old) solar analog KIC
10644253 with a modulation of about 1.5 years with significant temporal
variations along the duration of the Kepler observations. The variations are in
agreement with the derived photometric activity. The frequency shifts extracted
for KIC 10644253 are shown to result from the same physical mechanisms involved
in the inner sub-surface layers as in the Sun. In parallel, a detailed
spectroscopic analysis of KIC 10644253 is performed based on complementary
ground-based, high-resolution observations collected by the HERMES instrument
mounted on the MERCATOR telescope. Its lithium abundance and chromospheric
activity S-index confirm that KIC 10644253 is a young and more active star than
the Sun.Comment: Accepted for publication in A&A, 12 pages, 8 figure
Low serum magnesium concentrations are associated with a high prevalence of premature ventricular complexes in obese adults with type 2 diabetes
<p>Abstract</p> <p>Background</p> <p>Premature ventricular complexes (PVC) predict cardiovascular mortality among several adult populations. Increased arrhythmia prevalence has been reported during controlled magnesium (Mg) depletion studies in adults. We thus hypothesized that serum magnesium (sMg) concentrations are inversely associated with the prevalence of PVC in adults at high cardiovascular risk.</p> <p>Methods</p> <p>Anthropometric, demographic and lifestyle characteristics were assessed in 750 Cree adults, aged > 18 yrs, who participated in an age-stratified, cross-sectional health survey in Quebec, Canada. Holter electrocardiograms recorded heart rate variability and cardiac arrhythmias for two consecutive hours. Multivariate logistic regression was used to evaluate the associations between sMg and PVC.</p> <p>Results</p> <p>PVC prevalence in adults with hypomagnesemia (sMg ≤ 0.70 mmol/L) was more than twice that of adults without hypomagnesemia (50% vs. 21%, <it>p </it>= 0.015); results were similar when adults with cardiovascular disease history were excluded. All hypomagnesemic adults with PVC had type 2 diabetes (T2DM). Prevalence of PVC declined across the sMg concentration gradient in adults with T2DM only (<it>p </it>< 0.001 for linear trend). In multivariate logistic regressions adjusted for age, sex, community, body mass index, smoking, physical activity, alcohol consumption, kidney disease, antihypertensive and cholesterol lowering drug use, and blood docosahexaenoic acid concentrations, the odds ratio of PVC among T2DM subjects with sMg > 0.70 mmol/L was 0.24 (95% CI: 0.06-0.98) <it>p </it>= 0.046 compared to those with sMg ≤ 0.70 mmol/L.</p> <p>Conclusions</p> <p>sMg concentrations were inversely associated with the prevalence of PVC in patients with T2DM in a dose response manner, indicating that suboptimal sMg may be a contributor to arrhythmias among patients with T2DM.</p
In situ oligonucleotide synthesis on poly(dimethylsiloxane): a flexible substrate for microarray fabrication
In this paper, we demonstrate in situ synthesis of oligonucleotide probes on poly(dimethylsiloxane) (PDMS) microchannels through use of conventional phosphoramidite chemistry. PDMS polymer was moulded into a series of microchannels using standard soft lithography (micro-moulding), with dimensions <100 μm. The surface of the PDMS was derivatized by exposure to ultraviolet/ozone followed by vapour phase deposition of glycidoxypropyltrimethoxysilane and reaction with poly(ethylene glycol) spacer, resulting in a reactive surface for oligonucleotide coupling. High, reproducible yields were achieved for both 6mer and 21mer probes as assessed by hybridization to fluorescent oligonucleotides. Oligonucleotide surface density was comparable with that obtained on glass substrates. These results suggest PDMS as a stable and flexible alternative to glass as a suitable substrate in the fabrication and synthesis of DNA microarrays
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