969 research outputs found
Differential rotation decay in the radiative envelopes of CP stars
Stars of spectral classes A and late B are almost entirely radiative. CP
stars are a slowly rotating subgroup of these stars. It is possible that they
possessed long-lived accretion disks in their T Tauri phase. Magnetic coupling
of disk and star leads to rotational braking at the surface of the star.
Microscopic viscosities are extremely small and will not be able to reduce the
rotation rate of the core of the star. We investigate the question whether
magneto-rotational instability can provide turbulent angular momentum
transport. We illuminate the question whether or not differential rotation is
present in CP stars. Numerical MHD simulations of thick stellar shells are
performed. An initial differential rotation law is subject to the influence of
a magnetic field. The configuration gives indeed rise to magneto-rotational
instability. The emerging flows and magnetic fields transport efficiently
angular momentum outwards. Weak dependence on the magnetic Prandtl number
(~0.01 in stars) is found from the simulations. Since the estimated time-scale
of decay of differential rotation is 10^7-10^8 yr and comparable to the
life-time of A stars, we find the braking of the core to be an ongoing process
in many CP stars. The evolution of the surface rotation of CP stars with age
will be an observational challenge and of much value for verifying the
simulations.Comment: 8 pages, 11 figures; submitted to Astron. & Astrophy
Econobiophysics - game of choosing. Model of selection or election process with diverse accessible information
We propose several models applicable to both selection and election processes when each selecting or electing subject has access to different information about the objects to choose from. We wrote special software to simulate these processes. We consider both the cases when the environment is neutral (natural process) as well as when the environment is involved (controlled process)
Simple fractal method of assessment of histological images for application in medical diagnostics
We propose new method of assessment of histological images for medical diagnostics. 2-D image is preprocessed to form 1-D landscapes or 1-D signature of the image contour and then their complexity is analyzed using Higuchi's fractal dimension method. The method may have broad medical application, from choosing implant materials to differentiation between benign masses and malignant breast tumors
Binary coalescence from case A evolution -- mergers and blue stragglers
We constructed some main-sequence mergers from case A binary evolution and
studied their characteristics via Eggleton's stellar evolution code. Both total
mass and orbital angular momentum are conservative in our binary evolutions.
Some mergers might be on the left of the ZAMS as defined by normal surface
composition on a CMD because of enhanced surface helium content. The study also
shows that central hydrogen content of the mergers is independent of mass. As a
consequence, we fit the formula of magnitude and B-V of the mergers when they
return back to thermal equilibrium with maximum error 0.29 and 0.037,
respectively. Employing the consequences above, we performed Monte Carlo
simulations to examine our models in NGC 2682 and NGC 2660. In NGC 2682, binary
mergers from our models cover the region with high luminosity, but its
importance is much less than that of AML. Our results are well-matched to the
observations of NGC2660 if there is about 0.5Mo of mass loss in the merger
process.Comment: 14 pages, 12 figures. accepted by MNRA
Developing a gas rocket performance prediction technique
A simple, semi-empirical performance correlation/prediction technique applicable to gaseous and liquid propellant rocket engines is presented. Excellent correlations were attained for over 100 test firings by adjusting the computation of the gaseous mixing of an unreactive, coaxial jet using a correlation factor, F, which resulted in prediction of the experimental combustion efficiency for each firing. Static pressure, mean velocity and turbulence intensity in the developing region of non-reactive coaxial jets, typical of those of coaxial injector elements were determined. Detailed profiles were obtained at twelve axial locations (extending from the nozzle exit for a distance of five diameters) downstream from a single element of the Bell Aerospace H2/O2 19-element coaxial injector. These data are compared with analytical predictions made using both eddy viscosity and turbulence kinetic energy mixing models and available computer codes. Comparisons were disappointing, demonstrating the necessity of developing improved turbulence models and computational techniques before detailed predictions of practical coaxial free jet flows are attempted
Analysis of instagram® posts referring to cleft lip
Background: Social media has become a source of medical information. Cleft lip and palate is a visible congenital anomaly. The aim of the study was to analyze Instagram® posts on the topic of cleft lip. Methods: Instagram® posts with “#cleftlip” from March 2014–March 2017 were accessed. Separate lists of expressions (hashtags, meaningful words, words with emojis or emojis alone) were prepared for primary posts and for replies. Thirty expressions statistically most frequent in primary versus secondary posts and 30 in secondary versus primary posts were identified (Group 1) as well as 30 English words or hashtags (Group 2), non-English words or hashtags (Group 3) and emojis (Group 4). The frequencies of expressions were compared (Z-test for the difference of two population proportions). Results: There were 34,129 posts, (5427 primary posts and 28,702 replies), containing 62,163 expressions, (35,004 in primary posts). The occurrence of all expressions was 454,162, (225,418 in primary posts and 228,744 in replies). Posts with positive expressions such as “beautiful”, “love”, “cute”, “great”, “awesome” occurred more often than these with negative ones. In replies all emojis were positive. Conclusions: Numerous Instagram® posts referring to cleft lip are published and do provoke discussion. People express their solidarity and sympathize with persons affected by cleft
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