bluuebunny/crossref_metadata_2025_split huggingface dataset:
CNO and Li abundances in Barium-enriched stars
Authors: Drake Natalia A. , Pereira Claudio B. 
Published: May 2007

AbstractCNO and Li abundances and 12C/13C isotopic ratios have been derived for two metal-poor Ba giants, HD 104340 and HD 206983, and two CH subgiants, HD 50264 and HD 87080. High resolution spectra obtained with the 1.52 m telescope and the FEROS echelle spectrograph at ESO, La Silla, Chile, were used in this study. CNO and Li abundances so as 12C/13C isotopic ratios were determined by applying the synthetic spectrum method to the lines of C2, CH, CN, [O I’ and Li I. Our analysis showed that the giant stars studied here have quite different natures: HD 206983 is a metal-poor barium star while HD 104340, although showing enhancement of s-process elements, should not be considered as a classical barium star: its barium syndrome can be explained by internal nucleosynthesis. The low metallicity giant HD 104340 can experience deeper convective mixing and, consequently, a larger dredge-up of CNO-cycle products compared to normal red giants. Light element abundance pattern of HD 104340 resembles anomalies resulting from the appearance on the stellar surface of material enriched in triple-α and CNO cycling.
Rotational properties of the Orion nebular cluster revised
Authors: Landin Natália R. , Ventura Paolo , D'Antona Francesca , Mendes Luiz T. S. , Vaz Luiz P. R. 
Published: May 2007

AbstractThe observational data of the Orion Nebula Cluster (ONC) is reanalyzed by means of new sets of pre-main sequence (PMS) evolutionary tracks including rotation, non-gray boundary conditions (BC's) and either low (LCE) or high convection efficiency (HCE), aiming better understanding of the appropriate physical constraints for the rotational evolution of the stars within the ONC. The role played by convection is a key aspect of our analysis, since there are conflicting results from theory and observations. We derived stellar masses and ages for the ONC by using both LCE and HCE and considered was the role of non-gray atmospheres. Our results show that the resulting mass distribution for the bulk of the ONC population is in the range 0.2-0.4M⊙ for our non-gray models, and in the range 0.1-0.3M⊙ for gray models. In agreement with previous works, we found that a large percentage (∼70%) of low-mass stars (M≤Mtr, where Mtr is a transition mass) in the ONC appears to be fast rotators (P<4days). Mtr depends on the model choosen, being Mtr=0.5 for LCE, Mtr=0.35 for HCE and, as found in previous works, Mtr=0.25 for gray models. Finally, our analysis indicates that a second parameter is needed for a proper description of convection in the PMS phase.
Numerical simulations of semiconvection
Authors: Bascoul Guillaume P. 
Published: May 2007

AbstractUsing a semiconvective model based on thermohaline convection, we investigate the case of an expanding core of a main-sequence massive star. The numerical simulations at high Prandtl number show a flow consistent with the assumption that a dynamically neutral layer sits between the core and the radiative envelope. More simulations at low Prandtl number are needed to infer scaling laws applicable to astrophysical regimes.
Application of convection simulations to oscillation excitation and local helioseismology
Authors: Stein Robert F. , Benson David , Georgobiani Dali , Nordlund Åke 
Published: May 2007

AbstractExcitation of f- and p- modes by Reynolds stresses and entropy fluctuations is reviewed. Approximations made to allow semi-analytic analysis are discussed. The spectrum of solar convection is presented and shown to NOT be separable into independent spatial and temporal factors. An appropriate fitting formula is presented.Time-distance local helioseismology has been analyzed using numerical simulations. One approach is simulation of solar surface convection on supergranule scales (48 Mm wide by 20 Mm deep). A surface shear layer develops. There is a continuous increase in the horizontal scale of the convective motions with increasing depth. Some small granular scale downflows at the surface are swept sideways by diverging larger scale upflows from below to merge into stronger downdrafts in these larger downflow boundaries. Elsewhere, some granular downflows have to beat their way against the upflows from below are halted. These simulations have a rich spectrum of f- and p- modes that turn within the computational domain. Cross-correlations between each surface location and each location below the surface reveals the wave propagation pattern from the surface. Waves at the surface that propagate into the interior, spread horizontally and are refracted back toward the surface. Time-distance diagrams have been constructed and inverted to determine the subsurface flows, which can then be compared with the average flows in the simulation.A second approach calculates the propagation of linearized waves through a fixed, but non-uniform, background state. Some examples of such analysis are presented.
Convection and pulsation in red giant stars
Authors: Wood P. R. 
Published: May 2007

AbstractConvection strongly influences the periods, stability and amplitudes of pulsation in red giant stars. For example, changing the efficiency of convection (the mixing length parameter) changes the radius and the effective temperature of a red giant, which in turn changes the pulsation period at a given luminosity. Since essentially all the energy flux outside the nuclear-burning core is carried by convection, it is the variation of convective energy transport throughout the pulsation cycle that determines pulsation stability. In both linear and nonlinear pulsation models, the turbulent viscosity that results from the interaction of pulsation with turbulent convection provides a strong damping effect on pulsation and, in nonlinear models, it determines the limiting amplitude. In this paper, these and other topics are discussed.
Probing turbulence with seismic observations of α Centauri
Authors: Straka C. W. , Demarque P. , Robinson F. J. 
Published: May 2007

AbstractWe present two 3D Large Eddy Simulations (LES) of the convection-radiation transition layer for both the A and the B component of the α Centauri binary system. Theoretical oscillation spectra are then calculated from stellar evolutionary models that include the effects of turbulence based on the LES simulations. By taking both non-seismic and seismic observational constraints into account we discuss the possibility to probe turbulence beyond standard 5mixing-length-theory in a star other than Sun.
Thermal convection in accretion disks
Authors: Klahr Hubert 
Published: May 2007

AbstractFor a long time it was believed that thermal convection could serve as the driving mechanism for turbulence and angular momentum transport in accretion disks. Even it is meanwhile accepted that convection had to leave that role to the magneto rotational instability, it is still an important effect arising in a realistic treatment of accretion disks, i.e. with proper thermodynamics and radiation transport. We review the history of thermal convection in astrophysical disks and show the relevant analytic and numerical work, including energy transport by convection and the effect of “negative” Reynolds stresses. We will also place the convective instability into the context of the magnetorotational instability and planet–disk interaction.
Effects of rotation and input energy flux on convective overshooting
Authors: Käpylä Petri J. , Korpi M. J. , Stix M. , Tuominen I. 
Published: May 2007

AbstractWe study convective overshooting by means of local 3D convection calculations. Using a mixing length model of the solar convection zone (CZ) as a guide, we determine the Coriolis number (Co), which is the inverse of the Rossby number, to be of the order of ten or larger at the base of the solar CZ. Therefore we perform convection calculations in the range Co = 0. . .10 and interpret the value of Co realised in the calculation to represent a depth in the solar CZ. In order to study the dependence on rotation, we compute the mixing length parameters αT and αu relating the temperature and velocity fluctuations, respectively, to the mean thermal stratification. We find that the mixing length parameters for the rapid rotation case, corresponding to the base of the solar CZ, are 3-5 times smaller than in the nonrotating case. Introducing such depth-dependent α into a solar structure model employing a non-local mixing length formalism results in overshooting which is approximately proportional to α at the base of the CZ. Although overshooting is reduced due to the reduced α, a discrepancy with helioseismology remains due to the steep transition to the radiative temperature gradient.In comparison to the mixing length models the transition at the base of the CZ is much gentler in the 3D models. It was suggested recently (Rempel 2004) that this discrepancy is due to the significantly larger (up to seven orders of magnitude) input energy flux in the 3D models in comparison to the Sun and solar models, and that the 3D calculations should be able to approach the mixing length regime if the input energy flux is decreased by a moderate amount. We present results from local convection calculations which support this conjecture.
Round table discussion of session F: convection and rotation
Authors: Roxburgh Ian W. 
Published: May 2007

AbstractThe Session F round table. and audience, considered the following questions:
(i)what determines the differential rotation in stellar convective zones?(ii)If there really is a rapid inward increase in angular velocity in giants will it have significant effects in the late stages of stellar evolution?(iii)How effective is penetration above a convective core?(iv)Why is the solar core nearly uniformly rotating?
The redistribution of the regions in radiative and convective equilibrium of the stars of the main sequence with rotation
Authors: Kuzmanovska O. 
Published: May 2007

AbstractWe study the redistribution of the mechanisms of the energy transport with rotation in the interiors of young stars of the Main sequence. In that purpose, we did numerical modelling of the structure of zero age stars of the Main sequence for 26 stellar masses in the interval 0.8–120 Solar masses (M⊙), with constant chemical composition X = 0.75, Y = 0.23, Z = 0.02 (N = 0.3 Z). Rotation of a solid body type with angular velocity varied from zero (spherically symmetrical models) till critical one (models at the border of dynamical stability) for each stellar mass is considered. For numerical integration of the differential equations we used Henyey's method for spherically symmetrical stars, modified by the technique of Kippenhahn and Thomas for rotating stars, with the algorithm used by J. Petrovic. Additional algorithms determine the mass and radius of convective core.Analysis of the results shows that the radius rf of the convective core decreases with increase of the angular velocity and has the lowest value for critical rotation. The radius of convective core has the lowest value for 1.2 M⊙ for spherically symmetric models, and in the interval 1–1.3 M⊙ for rotating stars at the border of dynamical stability. Absolute values (rf are in a range from 0.03–0.08, and increase with increase of the stellar mass for m >1.2 M⊙, while the relative changes are in the interval 15–22%. The lowest value of the mass qf of the convective core coincides with the lowest values of the radius. The change (qf >0, and increases with increase of the stellar mass for m >1.4 M⊙, while the greatest relative change with rotation is 7%. We show the dependence of qf from the structural parameters in the centre and on the surface of the star.We emphasize a “critical” mass of the star, or a characteristic interval of stellar masses (1.2–1.4 M⊙), in which a qualitative change in the local structure and the distribution of mechanisms of energy transport of both, spherically symmetric and rotating stars occurs. It is connected with the change of the heat regime of the star in hydrostatic equilibrium. Rotation additionally changes the structure and redistributes the regions in radiative and convective equilibrium.
Differential rotation and angular momentum
Authors: Botha G. J. J. , Evangelidis E. A. 
Published: May 2007

AbstractDifferential rotation not only occurs in astrophysical plasmas like accretion disks, it is also measured in laboratory plasmas as manifested in the toroidal rotation of tokamak plasmas. A re-examination of the Lagrangian of the system shows that the inclusion of the angular momentum's radial variation in the derivation of the equations of motion produces a force term that couples the angular velocity gradient with the angular momentum. This force term is a property of the angular velocity field, so that the results are valid wherever differential rotation is present.
Challenges of magnetism in the turbulent Sun
Authors: Brun Allan Sacha , Miesch Mark S. , Toomre Juri 
Published: May 2007

AbstractThree-dimensional global modelling of turbulent convection coupled to rotation and magnetism within the Sun are revealing processes relevant to many stars. We study spherical shells of compressible convection spanning many density scale heights using the MHD version of the anelastic spherical harmonic (ASH) code on massively parallel supercomputers. The simulations reveal that strong magnetic fields can be realized in the bulk of the solar convection zone while still attaining differential rotation profiles that make good contact with helioseismic findings. We find that the Maxwell and Reynolds stresses present in such a turbulent layer play an important role in redistributing angular momentum, with the latter maintaining the differential rotation, aided by baroclinic forcing at the base of the convection zone which is consistent with a tachocline there. The dynamo processes generate strong non-axisymmetric and intermittent fields and weak mean (axisymmetric) fields, but do not possess a regular cyclic magnetism. The explicit inclusion of penetrative convection into the tachocline below is modifying such behavior, serving to build strong toroidal magnetic fields there that may yield more prominent mean fields that have the potential of erupting upward.
“Negative magnetic buoyancy” effects and reconstruction of toroidal field in the solar convection zone
Authors: Krivodubskij Valery N. 
Published: May 2007

AbstractThis investigation is devoted to study the turbulent convective transport of mean (large-scale) magnetic field in the solar convection zone (SCZ). For the SCZ model by Stix (1989) the reconstruction of the toroidal field was calculated as a result of the balance of mean-field magnetic buoyancy and two “negative magnetic buoyancy” effects: i) macroscopic turbulent diamagnetism and ii) the ∇ρ effect. It is shown that at high latitudes negative buoyancy effects block the magnetic fields, about 3000 – 4000 G, near the bottom of the SCZ. This may be the most plausible reason why a deep-seated field here could not become as apparent at the solar surface as sunspots. However, at the near equatorial domain in the deep layers the ∇ρ effect, with allowance for rotation, causes the upward magnetic transport, that facilitates penetration of strong fields to the surface where they emerge as sunspot patters in the “royal zone”.
Magnetic activity in the atmospheres of F-type binaries: V963 XSCyg, XZ CMi, V965 Cyg
Authors: Samec R. G. , Jones S. M. , Scott T. , Branning J. , Miller J. , Chamberlain H. , Faulkner D. R. , Hawkins N. C. 
Published: May 2007

AbstractWe have found photometric indications that Interacting Eclipsing Binaries of early to mid F spectral type (and possibly A) have strong magnetic activity which would arise from convective atmospheres. Light curve solutions and periodicity studies revealing spots, magnetic breaking and magnetic cycles are presented in XZ CMi, V965 Cyg and V963 Cyg.
Numerical simulations of sunspots
Authors: Botha G. J. J. , Rucklidge A. M. , Hurlburt N. E. 
Published: May 2007

AbstractThe origin, structure and evolution of sunspots are investigated using a numerical model. The compressible MHD equations are solved with physical parameter values that approximate the top layer of the solar convection zone. A three dimensional (3D) numerical code is used to solve the set of equations in cylindrical geometry, with the numerical domain in the form of a wedge. The linear evolution of the 3D solution is studied by perturbing an axisymmetric solution in the azimuthal direction. Steady and oscillating linear modes are obtained.
Super-equipartition fields in simulations of photospheric magnetoconvection
Authors: Bushby Paul J. 
Published: May 2007

AbstractObservations of magnetic fields in the quiet Sun indicate that kilogauss-strength fields can be found in the intergranular lanes. Since the magnetic energy of these localised features greatly exceeds estimates of the kinetic energy of the surrounding granular convection, it is difficult to see how these features could be formed simply by convective flux concentration. Idealised, high-resolution simulations of three-dimensional compressible magnetoconvection are used to investigate the formation of these features numerically. Initially we take a fully developed non-magnetic convective state into which we insert a weak, uniform, vertical magnetic field. Magnetic flux is rapidly swept into the convective downflows, where it is concentrated into localised regions. As the field strength within these regions becomes dynamically significant, the high magnetic pressure leads to partial evacuation (via the convective downflows). Provided that the magnetic Reynolds number is large enough, the strength of the resulting magnetic fields significantly exceeds the (so called) “equipartition” value, with the dynamical effects of the surrounding convection playing an important role in confining these magnetic features to localised regions. These results can be related to the well-known convective collapse instability, although there are some important differences between the two models.
Plant immunomodulators for termination of unwanted pregnancy and for contraception and reproductive health
Authors: Talwar GP , Vanshi Poonam Raghu , Misra Rachna , Mukherjee Sutapa , Shah Sangeeta 
Published: May 2007

Neem (Azadirachta indica) seed and leaf extracts have spermicidal, anti‐microbial, anti‐fungal and anti‐viral properties. They are also immunomodulators that induce primarily a TH, type response. These properties are being exploited to develop two different useful methods of fertility control. Neem extracts given orally at early post‐implantation stage terminate pregnancy in rodents and primates. Treatment has no residual permanent effect and fertility is regained in subsequent cycles. The mechanism by which the action occurs is not fully clear. A transient increase in CD4 and more significantly in CD8 cells is noticed in mesenteric lymph nodes and spleen. A rise in immunoreactive and bioactive TNF‐α and IFN‐γ in draining lymph nodes, serum and foetal‐placental tissue is observed.A polyherbal cream and pessary have been developed containing three active ingredients of plant origin. These have synergistic spermicidal properties on human sperm as determined by the Sander Cramer test. Their use before mating has high contraceptive efficacy in rabbits and baboons. Another interesting property is their inhibitory action on a wide spectrum of micro‐organisms, including Candida albicans. C. tropicalis, Neisseria gonorrhoeae, the multidrug‐resistant Slaphylococcus aureus and urinary tract Escherichia coli. Herpes simplex‐2 and HIV‐1, Phase I clinical trials have been completed in India, Egypt and the Dominican Republic, and indicate the safety of the formulation, its acceptability and beneficial action invaginosis due to infections.
Interspecific competition between Sphagnum mosses at different water tables
Authors: ROBROEK B. J. M. , LIMPENS J. , BREEUWER A. , CRUSHELL P. H. , SCHOUTEN M. G. C. 
Published: May 2007

Summary

Effects of climate change may affect the Sphagnum species composition in bogs, and ultimately the functioning of the whole ecosystem. We investigated the effect of different water tables on the competition between six Sphagnum species in the glasshouse. The amount of precipitation (234 mm year−1) and precipitation frequency (every 2 weeks) were kept low to encourage water‐table effects. Relevant species combinations and monocultures were grown at different water tables for a 16‐month period. We studied changes in cover, height increment and capitulum water content (WCcap) in order to understand competitive responses.
Species naturally occurring further above the water table generally showed higher competitive strength than species naturally occurring closer to the water table. Surprisingly, this effect was irrespective of the water table, indicating a minor role for capillary water transport. Cover change seemed to be related to differences in length growth, but not to water table or WCcap.
The WCcap of species within a mixture did not differ, but was lower than the WCcap of the individual species growing in monoculture, indicating differences in ability to supply water to the capitula between mono‐ and mixed cultures. Subcapitulum bulk densities between mono‐ and mixed cultures did not differ, or were even lower in monocultures, but did differ between species within mixed cultures.
Our results indicate that structural heterogeneity of the peat in mixed cultures has a negative effect on WCcap of both species. Furthermore, we show that sustained periods of drought cause species that naturally occur further above the water table to oust species that naturally occur closer to the water table, even if the water table remains high. Ultimately, the Sphagnum vegetation in raised bogs may shift from hollow to hummock species, evening out the natural microtopography of raised bogs.
Trichuris suis excretory/secretory antigen‐specific antibodies in serum from single‐inoculated pigs
Authors: KRINGEL H. , ROEPSTORFF A. 
Published: May 2007

Summary The humoral immune response induced by Trichuris infections has mostly been described in mouse models and in infected humans, but as the immunomodulatory effect of Trichuris suis, the swine whipworm, becomes increasingly documented, the need for understanding the response induced by this specific parasite species grows. In the present study we describe changes in serum IgG1, IgG2, IgA and IgM antibodies specific to adult T. suis excretory/secretory (E/S) antigens in the time course of a primary infection in swine. The average levels of specific IgG1, IgG2 and IgM peaked at 9 weeks post‐inoculation and then declined within a few weeks of worm expulsion. The IgA level rose earlier and remained elevated after worm expulsion. The protective role of Trichuris‐specific antibodies is uncertain, but some of them presumably reflect the presence of worms in the intestine. Further development of this analysis could have diagnostic value in swine and humans infected with T. suis for experimental or therapeutic purposes.