1,628 research outputs found
The first close-up of the "flip-flop" phenomenon in a single star
We present temperature maps of the active late-type giant FK Com which
exhibit the first imagining record of the ``flip-flop'' phenomenon in a single
star. The phenomenon, in which the main part of the spot activity shifts 180
degrees in longitude, discovered a decade ago in FK Com, was reported later
also in a number of RS CVn binaries and a single young dwarf. With the surface
images obtained right before and after the ``flip-flop'', we clearly show that
the ``flip-flop'' phenomenon in FK Com is caused by changing the relative
strengths of the spot groups at the two active longitudes, with no actual spot
movements across the stellar surface, i.e. exactly as it happens in other
active stars.Comment: 4 pages, accepted by A&A Letter
Magnetic Structure of Rapidly Rotating FK Comae-Type Coronae
We present a three-dimensional simulation of the corona of an FK Com-type
rapidly rotating G giant using a magnetohydrodynamic model that was originally
developed for the solar corona in order to capture the more realistic,
non-potential coronal structure. We drive the simulation with surface maps for
the radial magnetic field obtained from a stellar dynamo model of the FK Com
system. This enables us to obtain the coronal structure for different field
topologies representing different periods of time. We find that the corona of
such an FK Com-like star, including the large scale coronal loops, is dominated
by a strong toroidal component of the magnetic field. This is a result of part
of the field being dragged by the radial outflow, while the other part remains
attached to the rapidly rotating stellar surface. This tangling of the magnetic
field,in addition to a reduction in the radial flow component, leads to a
flattening of the gas density profile with distance in the inner part of the
corona. The three-dimensional simulation provides a global view of the coronal
structure. Some aspects of the results, such as the toroidal wrapping of the
magnetic field, should also be applicable to coronae on fast rotators in
general, which our study shows can be considerably different from the
well-studied and well-observed solar corona. Studying the global structure of
such coronae should also lead to a better understanding of their related
stellar processes, such as flares and coronal mass ejections, and in
particular, should lead to an improved understanding of mass and angular
momentum loss from such systems.Comment: Accepted to ApJ, 10 pages, 6 figure
Creating novel approaches to mitigate aflatoxin risk in food and feed with lactic acid bacteria - mold growth inhibition and aflatoxin binding
Aflatoxins, produced by Aspergillus fungi, are ubiquitous toxins and they can present a severe health risk to humans and animals if contaminated food and feed is consumed. Fungi live in the soil and on the surface of the crop and Aspergillus species are dominant in favorable conditions of maize cultivation areas. Climate change could threaten the production of safe food by promoting Aspergillus growth and aflatoxin production in food and feed. A novel biological approach using lactic acid bacteria (LAB) could reduce the health risks of aflatoxins through inhibiting mold growth, thus aflatoxin production and by binding existing aflatoxins. LAB are commonly used in fermented food production; they are also known to inhibit mold growth and interact with aflatoxins. LAB provide a potential novel approach to mitigate the mould growth and aflatoxin production in maize during storage and after food consumption. Mold growth inhibition by certain LAB strains may be caused by competition for resources between bacterial cells and fungi and/or production of antifungal compounds such as organic acids. Aflatoxin binding is more complex. Binding is a reversible reaction, which occurs on bacterial surfaces and involves interaction with carbohydrates, peptidoglycan and to some extent protein structures. Aflatoxin binding seems to be highly related to strain, matrix, temperature, pH, incubation time and related conditions. There are two different aspects of aflatoxin risk mitigation in this research. First is the fungal growth inhibition with LAB and second is aflatoxin binding from food and feed with LAB. We have isolated 200 strains of bacteria from 21 different indigenous fermented dairy and cereal products prepared locally in different parts of Kenya. Firstly, these strains are being tested for their growth inhibition abilities against aflatoxin producing Aspergillus fungi in laboratory conditions. Secondly, the same strains are tested for their abilities to bind and retain aflatoxin M1 and B1. Later, these same effective strains will be tested in various food and feed matrices against Aspergillus growth and then the ones with most potential will be identified. This approach aims at providing a safe method of reducing aflatoxin absorption in human gastrointestinal tract after ingesting fermented maize or dairy products, which are contaminated with aflatoxins. Novel biological methods can have a role in preventing toxic effects of aflatoxins in food and feed. Exploitation of LAB is a good option for existing methods as LAB are generally recognized as safe.
This research is done as part of FoodAfrica programme, which is a research, and development programme and the main funding agency being Finnish Ministry for Foreign Affairs. The research is partnering with MTT Agrifood Research Finland and ILRI International Livestock Research Institute
Structural perspective on constraint-based learning of Markov networks
Markov networks are probabilistic graphical models that employ undirected
graphs to depict conditional independence relationships among variables. Our
focus lies in constraint-based structure learning, which entails learning the
undirected graph from data through the execution of conditional independence
tests. We establish theoretical limits concerning two critical aspects of
constraint-based learning of Markov networks: the number of tests and the sizes
of the conditioning sets. These bounds uncover an exciting interplay between
the structural properties of the graph and the amount of tests required to
learn a Markov network. The starting point of our work is that the graph
parameter maximum pairwise connectivity, , that is, the maximum number
of vertex-disjoint paths connecting a pair of vertices in the graph, is
responsible for the sizes of independence tests required to learn the graph. On
one hand, we show that at least one test with the size of the conditioning set
at least is always necessary. On the other hand, we prove that any
graph can be learned by performing tests of size at most . This
completely resolves the question of the minimum size of conditioning sets
required to learn the graph. When it comes to the number of tests, our upper
bound on the sizes of conditioning sets implies that every -vertex graph can
be learned by at most tests with conditioning sets of sizes at
most . We show that for any upper bound on the sizes of the
conditioning sets, there exist graphs with vertices that require at
least tests to learn. This lower bound holds even when the
treewidth and the maximum degree of the graph are at most . On the
positive side, we prove that every graph of bounded treewidth can be learned by
a polynomial number of tests with conditioning sets of sizes at most .Comment: AISTATS 202
First measurement of the magnetic field on FK Com and its relation to the contemporaneous starspot locations
In this study we present simultaneous low-resolution longitudinal magnetic
field measurements and high-resolution spectroscopic observations of the cool
single giant FK Com. The variation of the magnetic field over the rotational
period of 2.4 days is compared with the starspot location obtained using
Doppler imaging techniques, V-band photometry and V-I colours. The
chromospheric activity is studied simultaneously with the photospheric activity
using high resolution observations of the Halpha, Hbeta and Hgamma line
profiles. Both the maximum (272 +/- 24 G) and minimum (60 +/- 17 G) in the mean
longitudinal magnetic field, , are detected close to the phases where cool
spots appear on the stellar surface. A possible explanation for such a
behaviour is that the active regions at the two longitudes separated by 0.2 in
phase have opposite polarities.Comment: 10 Pages, 11 figures (quality of Figures 7,8 and 10 reduced),
accepted for publication in MNRA
Longitudinal Associations of High-Volume and Vigorous-Intensity Exercise With Hip Fracture Risk in Men
Maintenance of vigorous exercise habits from young to old age is considered protective against hip fractures, but data on fracture risk in lifelong vigorous exercisers are lacking. This longitudinal cohort study examined the hazard of hip fractures in 1844 male former athletes and 1216 population controls and in relation to exercise volume and intensity in later years. Incident hip fractures after age 50 years were identified from hospital discharge register from 1972 to 2015. Exercise and covariate information was obtained from questionnaires administered in 1985, 1995, 2001, and 2008. Analyses were conducted using extended proportional hazards regression model for time-dependent exposures and effects. During the mean +/- SD follow-up of 21.6 +/- 10.3 years, 62 (3.4%) athletes and 38 (3.1%) controls sustained a hip fracture. Adjusted hazard ratio (HR) indicated no statistically significant difference between athletes and controls (0.84; 95% confidence interval [CI], 0.55-1.29). In subgroup analyses, adjusted HRs for athletes with recent high (>= 15 metabolic equivalent hours [MET-h]/week) and low (= 6 METs at least 75 minutes/week) had initially 77% lower hazard rate (adjusted HR 0.23; 95% CI, 0.06-0.86) than controls. However, the HR was time-dependent (adjusted HR 1.04; 95% CI, 1.01-1.07); by age 75 years the HRs for the athletes with vigorous-intensity exercise reached the level of the controls, but after 85 years the HRs for these athletes increased approximately 1.3-fold annually relative to the controls. In conclusion, these data suggest that continuation of vigorous-intensity exercise is associated with lower HR of hip fracture up to old age. (c) 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).Peer reviewe
FK Comae Berenices, King of Spin: The COCOA-PUFS Project
COCOA-PUFS is an energy-diverse, time-domain study of the ultra-fast
spinning, heavily spotted, yellow giant FK Com (HD117555; G4 III). This single
star is thought to be a recent binary merger, and is exceptionally active by
measure of its intense ultraviolet and X-ray emissions, and proclivity to
flare. COCOA-PUFS was carried out with Hubble Space Telescope in the UV
(120-300 nm), using mainly its high-performance Cosmic Origins Spectrograph,
but also high-precision Space Telescope Imaging Spectrograph; Chandra X-ray
Observatory in the soft X-rays (0.5-10 keV), utilizing its High-Energy
Transmission Grating Spectrometer; together with supporting photometry and
spectropolarimetry in the visible from the ground. This is an introductory
report on the project.
FK Com displayed variability on a wide range of time scales, over all
wavelengths, during the week-long main campaign, including a large X-ray flare;
"super-rotational broadening" of the far-ultraviolet "hot-lines" (e.g., Si IV
139 nm (T~80,000 K) together with chromospheric Mg II 280 nm and C II 133 nm
(10,000-30,000 K); large Doppler swings suggestive of bright regions
alternately on advancing and retreating limbs of the star; and substantial
redshifts of the epoch-average emission profiles. These behaviors paint a
picture of a highly extended, dynamic, hot (10 MK) coronal magnetosphere around
the star, threaded by cooler structures perhaps analogous to solar prominences,
and replenished continually by surface activity and flares. Suppression of
angular momentum loss by the confining magnetosphere could temporarily postpone
the inevitable stellar spindown, thereby lengthening this highly volatile stage
of coronal evolution.Comment: to be published in ApJ
CCN activation and cloud processing in simplified sectional aerosol models with low size resolution
International audienceWe investigate the influence of low size resolution, typical to sectional aerosol models in large scale applications, on cloud droplet activation and cloud processing of aerosol particles. A simplified cloud scheme with five approaches to determine the fraction of activated particles is compared with a detailed reference model under different atmospheric conditions. In general, activation approaches which assume a distribution profile within the critical model size sections predict the cloud droplet concentration most accurately under clean and moderately polluted conditions. In such cases, the deviation from the reference simulations is below 15% except for very low updraft velocities. In highly polluted cases, the concentration of cloud droplets is significantly overestimated due to the inability of the simplified scheme to account for the kinetic limitations of the droplet growth. Of the profiles examined, taking into account the local shape of the particle size distribution is the most accurate although in most cases the shape of the profile has little relevance. While the low resolution cloud model cannot reproduce the details of the out-of-the-cloud aerosol size distribution, it captures well the amount of sulphate produced in aqueous-phase reactions as well as the distribution of the sulphate between the cloud droplets. Overall, the simplified cloud scheme with low size resolution performs well for clean and moderately polluted regions that cover most of the Earth's surface and is therefore suitable for large scale models
Fixed-Parameter Tractability of Maximum Colored Path and Beyond
We introduce a general method for obtaining fixed-parameter algorithms for
problems about finding paths in undirected graphs, where the length of the path
could be unbounded in the parameter. The first application of our method is as
follows.
We give a randomized algorithm, that given a colored -vertex undirected
graph, vertices and , and an integer , finds an -path
containing at least different colors in time . This is the
first FPT algorithm for this problem, and it generalizes the algorithm of
Bj\"orklund, Husfeldt, and Taslaman [SODA 2012] on finding a path through
specified vertices. It also implies the first time algorithm for
finding an -path of length at least .
Our method yields FPT algorithms for even more general problems. For example,
we consider the problem where the input consists of an -vertex undirected
graph , a matroid whose elements correspond to the vertices of and
which is represented over a finite field of order , a positive integer
weight function on the vertices of , two sets of vertices , and integers , and the task is to find vertex-disjoint paths
from to so that the union of the vertices of these paths contains an
independent set of of cardinality and weight , while minimizing the
sum of the lengths of the paths. We give a
time randomized algorithm for this problem.Comment: 50 pages, 16 figure
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