106 research outputs found
Small-scale Dynamo in Cool Stars: I. Changes in stratification and near-surface convection for main-sequence spectral types
Some of the small-scale solar magnetic flux can be attributed to a
small-scale dynamo (SSD) operating in the near-surface convection. The SSD
fields have consequences for solar granular convection, basal flux, as well as
chromospheric heating. A similar SSD mechanism is expected to be active in the
near-surface convection of other cool main-sequence stars, but this has never
been investigated. We aim to investigate changes in stratification and
convection due to inclusion of SSD fields for F3V, G2V, K0V and M0V spectral
types in the near-surface convection. 3D magnetohydrodynamic (MHD) models of
the four stellar boxes, covering the subsurface convection zone up to the lower
photosphere in a small cartesian box, are studied using the \textit{MURaM}
radiative-MHD simulation code. The SSD runs are compared against reference
hydrodynamic runs. An SSD is found to efficiently produce magnetic field with
energies ranging between 5\% to 80\% of the plasma kinetic energy at different
depths. This ratio tends to be larger for larger . The
relative change in density and gas pressure stratification for the deeper
convective layers due to SSD magnetic fields is negligible, except for the
F-star. For the F-star, there is a substantial reduction in convective
velocities due to Lorentz force feedback from magnetic fields, which, in turn,
reduces the turbulent pressure. SSD in near-surface convection for cool
main-sequence stars introduces small but significant changes in thermodynamic
stratification (especially for the F-star) due to reduction in convective
velocities.Comment: 10 pages, 7 figures, accepted for publication in A&
âA very orderly retreatâ: Democratic transition in East Germany, 1989-90
East Germany's 1989-90 democratisation is among the best known of East European transitions, but does not lend itself to comparative analysis, due to the singular way in which political reform and democratic consolidation were subsumed by Germany's unification process. Yet aspects of East Germany's democratisation have proved amenable to comparative approaches. This article reviews the comparative literature that refers to East Germany, and finds a schism between those who designate East Germany's transition âregime collapseâ and others who contend that it exemplifies âtransition through extricationâ. It inquires into the merits of each position and finds in favour of the latter. Drawing on primary and secondary literature, as well as archival and interview sources, it portrays a communist elite that was, to a large extent, prepared to adapt to changing circumstances and capable of learning from âreference statesâ such as Poland. Although East Germany was the Soviet state in which the positions of existing elites were most threatened by democratic transition, here too a surprising number succeeded in maintaining their position while filing across the bridge to market society. A concluding section outlines the alchemy through which their bureaucratic power was transmuted into property and influence in the ânew Germanyâ
Magnetic Imaging of the Outer Solar Atmosphere (MImOSA): Unlocking the driver of the dynamics in the upper solar atmosphere
The magnetic activity of the Sun directly impacts the Earth and human life.
Likewise, other stars will have an impact on the habitability of planets
orbiting these host stars. The lack of information on the magnetic field in the
higher atmospheric layers hampers our progress in understanding solar magnetic
activity. Overcoming this limitation would allow us to address four paramount
long-standing questions: (1) How does the magnetic field couple the different
layers of the atmosphere, and how does it transport energy? (2) How does the
magnetic field structure, drive and interact with the plasma in the
chromosphere and upper atmosphere? (3) How does the magnetic field destabilise
the outer solar atmosphere and thus affect the interplanetary environment? (4)
How do magnetic processes accelerate particles to high energies? New
ground-breaking observations are needed to address these science questions. We
suggest a suite of three instruments that far exceed current capabilities in
terms of spatial resolution, light-gathering power, and polarimetric
performance: (a) A large-aperture UV-to-IR telescope of the 1-3 m class aimed
mainly to measure the magnetic field in the chromosphere by combining high
spatial resolution and high sensitivity. (b) An extreme-UV-to-IR coronagraph
that is designed to measure the large-scale magnetic field in the corona with
an aperture of about 40 cm. (c) An extreme-UV imaging polarimeter based on a 30
cm telescope that combines high throughput in the extreme UV with polarimetry
to connect the magnetic measurements of the other two instruments. This mission
to measure the magnetic field will unlock the driver of the dynamics in the
outer solar atmosphere and thereby greatly advance our understanding of the Sun
and the heliosphere.Comment: Submitted to Experimental Astronomy (on 28. Jul. 2020). Based on a
proposal submitted in response to a call for white papers in the Voyage 2050
long-term plan in the ESA science programme. 36 pages, 10 figure
All-sky search for time-integrated neutrino emission from astrophysical sources with 7 years of IceCube data
Since the recent detection of an astrophysical flux of high energy neutrinos,
the question of its origin has not yet fully been answered. Much of what is
known about this flux comes from a small event sample of high neutrino purity,
good energy resolution, but large angular uncertainties. In searches for
point-like sources, on the other hand, the best performance is given by using
large statistics and good angular reconstructions. Track-like muon events
produced in neutrino interactions satisfy these requirements. We present here
the results of searches for point-like sources with neutrinos using data
acquired by the IceCube detector over seven years from 2008--2015. The
discovery potential of the analysis in the northern sky is now significantly
below , on average
lower than the sensitivity of the previously published analysis of four
years exposure. No significant clustering of neutrinos above background
expectation was observed, and implications for prominent neutrino source
candidates are discussed.Comment: 19 pages, 17 figures, 3 tables; ; submitted to The Astrophysical
Journa
The contribution of Fermi-2LAC blazars to the diffuse TeV-PeV neutrino flux
The recent discovery of a diffuse cosmic neutrino flux extending up to PeV
energies raises the question of which astrophysical sources generate this
signal. One class of extragalactic sources which may produce such high-energy
neutrinos are blazars. We present a likelihood analysis searching for
cumulative neutrino emission from blazars in the 2nd Fermi-LAT AGN catalogue
(2LAC) using an IceCube neutrino dataset 2009-12 which was optimised for the
detection of individual sources. In contrast to previous searches with IceCube,
the populations investigated contain up to hundreds of sources, the largest one
being the entire blazar sample in the 2LAC catalogue. No significant excess is
observed and upper limits for the cumulative flux from these populations are
obtained. These constrain the maximum contribution of the 2LAC blazars to the
observed astrophysical neutrino flux to be or less between around 10
TeV and 2 PeV, assuming equipartition of flavours at Earth and a single
power-law spectrum with a spectral index of . We can still exclude that
the 2LAC blazars (and sub-populations) emit more than of the observed
neutrinos up to a spectral index as hard as in the same energy range.
Our result takes into account that the neutrino source count distribution is
unknown, and it does not assume strict proportionality of the neutrino flux to
the measured 2LAC -ray signal for each source. Additionally, we
constrain recent models for neutrino emission by blazars.Comment: 18 pages, 22 figure
A weak scientific basis for gaming disorder: let us err on the side of caution
We greatly appreciate the care and thought that is evident in the 10 commentaries that discuss our debate paper, the
majority of which argued in favor of a formalized ICD-11 gaming disorder. We agree that there are some people
whose play of video games is related to life problems. We believe that understanding this population and the nature
and severity of the problems they experience should be a focus area for future research. However, moving from
research construct to formal disorder requires a much stronger evidence base than we currently have. The burden of
evidence and the clinical utility should be extremely high, because there is a genuine risk of abuse of diagnoses. We
provide suggestions about the level of evidence that might be required: transparent and preregistered studies, a better
demarcation of the subject area that includes a rationale for focusing on gaming particularly versus a more general
behavioral addictions concept, the exploration of non-addiction approaches, and the unbiased exploration of clinical
approaches that treat potentially underlying issues, such as depressive mood or social anxiety first. We acknowledge
there could be benefits to formalizing gaming disorder, many of which were highlighted by colleagues in their
commentaries, but we think they do not yet outweigh the wider societal and public health risks involved. Given the
gravity of diagnostic classification and its wider societal impact, we urge our colleagues at the WHO to err on the side
of caution for now and postpone the formalization
Reduced Estradiol-Induced Vasodilation and Poly-(ADP-Ribose) Polymerase (PARP) Activity in the Aortas of Rats with Experimental Polycystic Ovary Syndrome (PCOS)
Polycystic ovary syndrome (PCOS) is a complex endocrine disorder characterized by hyperandrogenism and insulin resistance, both of which have been connected to atherosclerosis. Indeed, an increased risk of clinical manifestations of arterial vascular diseases has been described in PCOS. On the other hand endothelial dysfunction can be detected early on, before atherosclerosis develops. Thus we assumed that vascular dysfunction is also related directly to the hormonal imbalance rather than to its metabolic consequences. To detect early functional changes, we applied a novel rodent model of PCOS: rats were either sham operated or hyperandrogenism was achieved by implanting subcutaneous pellets of dihydrotestosterone (DHT). After ten weeks, myograph measurements were performed on isolated aortic rings. Previously we described an increased contractility to norepinephrine (NE). Here we found a reduced immediate relaxation to estradiol treatment in pre-contracted aortic rings from hyperandrogenic rats. Although the administration of vitamin D3 along with DHT reduced responsiveness to NE, it did not restore relaxation to estradiol. Poly-(ADP-ribose) polymerase (PARP) activity was assessed by poly-ADP-ribose immunostaining. Increased PAR staining in ovaries and circulating leukocytes from DHT rats showed enhanced DNA damage, which was reduced by concomitant vitamin D3 treatment. Surprisingly, PAR staining was reduced in both the endothelium and vascular smooth muscle cells of the aorta rings from hyperandrogenic rats. Thus in the early phase of PCOS, vascular tone is already shifted towards vasoconstriction, characterized by reduced vasorelaxation and vascular dysfunction is concomitant with altered PARP activity. Based on our findings, PARP inhibitors might have a future perspective in restoring metabolic disorders in PCOS
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Analysis of the African coelacanth genome sheds light on tetrapod evolution
It was a zoological sensation when a living specimen of the coelacanth was first discovered in 1938, as this lineage of lobe-finned fish was thought to have gone extinct 70 million years ago. The modern coelacanth looks remarkably similar to many of its ancient relatives, and its evolutionary proximity to our own fish ancestors provides a glimpse of the fish that first walked on land. Here we report the genome sequence of the African coelacanth, Latimeria chalumnae. Through a phylogenomic analysis, we conclude that the lungfish, and not the coelacanth, is the closest living relative of tetrapods. Coelacanth protein-coding genes are significantly more slowly evolving than those of tetrapods, unlike other genomic features . Analyses of changes in genes and regulatory elements during the vertebrate adaptation to land highlight genes involved in immunity, nitrogen excretion and the development of fins, tail, ear, eye, brain, and olfaction. Functional assays of enhancers involved in the fin-to-limb transition and in the emergence of extra-embryonic tissues demonstrate the importance of the coelacanth genome as a blueprint for understanding tetrapod evolution
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