bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solar-like oscillation amplitudes and line-widths as a probe for turbulent convection in stars
Authors: Samadi R. , Belkacem K. , Goupil M.-J. , Kupka F. , Dupret M.-A. 
Published: May 2007

AbstractExcitation of solar-like oscillations is attributed to turbulent convection and takes place at the upper-most part of the outer convective zones. Amplitudes of these oscillations depend on the efficiency of the excitation processes as well as on the properties of turbulent convection. We present past and recent improvements on the modeling of those processes. We show how the mode amplitudes and mode line-widths can bring information about the turbulence in the specific cases of the Sun and α Cen A.
Can we detect convection in the Sun?
Authors: Hanasoge Shravan M. , Duvall T. L. , Derosa M. L. , Miesch M. S. 
Published: May 2007

AbstractWe investigate the possibility of detecting deep convection in the Sun by computing travel-time shifts induced by convective flows interacting with propagating waves. The convection zone is modeled using a velocity profile taken from an Anelastic convection simulation. We present results obtained from a ray calculation of travel-time shifts. We compare these results with a full 3D calculation of the wave-flow interaction.
Testing Reynolds stress model in solar interior
Authors: Yang J. Y. , Li Y. 
Published: May 2007

AbstractThe Reynolds stress model (RSM) for turbulent convection motion is compared to the MLT in solar model. The free parameters involved in the RSM are also tested with the aid of helioseismology. It is found that, the structure of solar convection zone is differ from the MLT when using the RSM, especially for the Reynolds correlations and the temperature gradient. Both the local and non-local RSM can improve the calculated solar p-mode oscillation frequencies with the appropriate choice of the parameters' value.
A closure model for turbulent convection. Application to the excitation of p modes
Authors: Belkacem K. , Samadi R. , Goupil M.-J. , Kupka F. , Baudin F. 
Published: May 2007

AbstractOscillations of stellar p modes excited by turbulent convection are investigated. In the uppermost part of the solar convection zone, radiative cooling is responsible for the formation of turbulent plumes, hence the medium is characterized with downdrafts and updrafts. The motivation is to take the asymmetry of up- and downflows created by turbulent plumes into account through an adapted closure model. We built a generalized two-scale mass-flux model (GTFM) that considers both the skew introduced by the presence of two flows and the effect of turbulence onto each flow. In order to apply the GTFM to the solar case, we introduce the plume dynamics as modelled by Rieutord & Zahn (1995) and construct a closure model with plumes (CMP). The CMP enables to express third- and fourth-order velocity correlation products in terms of the second-order ones. When comparing with 3D numerical simulation results, the CMP improves the agreement for the fourth order moments in comparison with the quasi-normal approximation (QNA) or the classical mass-flux model (MFM). This excitation model reproduces the maximum of the power supplied to solar p modes, when compared with GOLF observations.
Monitoring of the cool ZZ Ceti star PG 2303+243
Authors: Pakštienė E. , Solheim J.-E. , Handler G. , Steininger B. , Rodler F. , Paparo M. , Bognar Z. , Patterson R. , Reed M. 
Published: May 2007

AbstractBecause PG 2303+243 had not been observed since 1992, we have arranged the mini-campaign of six observatories on PG 2303+243 in 2004 Sep. 5-21 for the more detailed frequency analysis of variations. The amplitudes of the most frequencies change even during the one night and some frequencies can disappear or appear in one year. Probably it is resonance effect. We have estimated 69 frequencies of pulsations and their amplitudes according the observations from 2004 and 36 frequencies and its amplitudes from 2005.
Effect of convection modeling on the non-adiabatic seismic observables of δ Scuti stars
Authors: Montalbán Josefina , Dupret Marc-Antoine 
Published: May 2007

AbstractPulsation frequencies in δ Scuti stars do not fall in the asymptotic domain, therefore, multi-band photometric methods are currently used to identify the pulsation modes. Theoretical photometric amplitude ratios and phase differences between photometric bands depend, however, on the treatment of convection in surface stellar layers. In this poster we present the results of applying the non-adiabatic analysis by Dupret et al. (2003) to δ Scuti stellar models computed by using the FST (Canuto et al. 1996, CGM) treatment of convection in the interior and in the atmosphere. We determine the amplitude ratios and phase difference for several bands in the Strömgren photometric system, and we compare the results obtained with the FST treatment and with the classical Mixing-length theory. We show that the differences in the external thermal structure are clearly reflected in the photometric phase differences.
Rotation of the solar convection zone from helioseismology
Authors: Christensen-Dalsgaard Jørgen 
Published: May 2007

AbstractHelioseismology has provided very detailed inferences about rotation of the solar interior. Within the convection zone the rotation rate roughly shares the latitudinal variation seen in the surface differential rotation. The transition to the nearly uniformly rotating radiative interior takes place in a narrow tachocline, which is likely important to the operation of the solar magnetic cycle. The convection-zone rotation displays zonal flows, regions of slightly more rapid and slow rotation, extending over much of the depth of the convection zone and converging towards the equator as the solar cycle progresses. In addition, there is some evidence for a quasi-periodic variation in rotation, with a period of around 1.3 yr, at the equator near the bottom of the convection zone.
Theoretical estimates of the convective turnover time for low-mass, rotating pre-main sequence stars
Authors: Mendes L. T. S. , Landin N. R. , Vaz L. P. R. 
Published: May 2007

AbstractThe Rossby number Ro is an important quantity related to the well-known magnetic activity-rotation correlation for main sequence, solar-type stars. For such stars, Ro can be obtained by a semi-empirical relationship between the convective turnover time τc and the B-V colour index, but an equivalent activity-rotation correlation seems not to exist for pre-main sequence stars. In this work we report theoretical estimates of τc for low-mass, rotating pre-main sequence stars under either the Full Spectrum of Turbulence (FST) or the classical Mixing Length Theory (MLT) convection models. The results for the MLT models show that the lower the convection efficiency the higher τc, while the FST models give τc lower than those for the MLT. The presence of a parametric magnetic field lowers the convection efficiency, resulting in smaller τc values.
Near-surface shear layer dynamics
Authors: Brandenburg Axel 
Published: May 2007

AbstractThe outer surface layers of the sun show a clear deceleration at low latitudes. This is generally thought to be the result of a strong dominance of vertical turbulent motions associated with strong downdrafts. This strong negative radial shear should not only contribute to amplifying the toroidal field locally and to expelling magnetic helicity, but it may also be responsible for producing a strong prograde pattern speed in the supergranulation layer. Using simulations of rotating stratified convection in cartesian boxes located at low latitudes around the equator it is shown that in the surface layers patterns move in the prograde direction on top of a retrograde mean background flow. These patterns may also be associated with magnetic tracers and even sunspot proper motions that are known to be prograde relative to the much slower surface plasma.
Dynamos of giant planets
Authors: Busse F. H. , Simitev R. 
Published: May 2007

AbstractPossibilities and difficulties of applying the theory of magnetic field generation by convection flows in rotating spherical fluid shells to the Giant Planets are outlined. Recent progress in the understanding of the distribution of electrical conductivity in the Giant Planets suggests that the dynamo process occurs predominantly in regions of semiconductivity. In contrast to the geodynamo the magnetic field generation in the Giant Planets is thus characterized by strong radial conductivity variations. The importance of the constraint on the Ohmic dissipation provided by the planetary luminosity is emphasized. Planetary dynamos are likely to be of an oscillatory type, although these oscillations may not be evident from the exterior of the planets.
Photospheric magnetoconvection
Authors: Cameron Robert , Vögler Alexander , Schüssler Manfred 
Published: May 2007

AbstractMagnetic fields, convective motions and radiative energy transport all strongly influence each other in the solar photosphere. Attempts to understand, at a quantitative level, the diverse phenomona seen in the photosphere have relied on increasingly powerful computers since the 1980's. This approach has been remarkably successful and some recent examples, particularly cases where all three ingredients are important, will be discussed.
Generation of coupled global and local magnetic fields by a cellular MHD dynamo
Authors: Getling A. V. , Simitev R. D. , Busse F. H. 
Published: May 2007

AbstractThe convection-driven MHD dynamo in a rotating spherical shell is simulated numerically. Convection cells are regarded as a connecting link between the global and local electromagnetic processes. Local (in many cases, bipolar) magnetic structures are regularly produced by convection cells. Dynamo regimes in “thick” and “thin” shells are discussed. In the first case, the “general” magnetic field maintained by the dynamo has a sign-alternating dipolar component, which varies cyclically, although not periodically. The local structures, as they disintegrate, change into background fields, which drift toward the poles. From time to time, reversals of the magnetic fields in the polar regions occur, as “new” background fields expel the “old” fields. In the second case, the system settles down to a nearly stationary regime without polarity reversals.
Round table discussion of session G: MHD convection and dynamos
Authors: Toomre Juri 
Published: May 2007

AbstractVigorous discussion ensued about conditions under which both small-scale and global-scale dynamo action would be realized within real stars where the flow fields are expected to be highly turbulent and the magnetic Prandtl numbers small. Our nearest star reminds us that intricate boundary-layer phenomena may have to also be considered, such as the presence of a tachocline of rotational shear at the base of the solar convection zone revealed by helioseismology, which suggests that an interface dynamo may be at work to produce the observed 22-year cycles of large-scale magnetic activity.
Is solar convection responsible for the local amplification and structuring of magnetic fields? (Observational test of the hypothesis)
Authors: Getling A. V. , Bao X. M. 
Published: May 2007

AbstractFull-vector magnetograms and Dopplergrams of selected areas of the solar photosphere are used to compute the vertical component of the right-hand side of the vector induction equation. We attempt to find a criterion for the action of the convective mechanism of amplification and structuring of magnetic fields using the distributions of this quantity and of the vertical magnetic-field component.
Quasi-regular structures in the solar photosphere (trenching in the brightness relief): Algorithmic treatment
Authors: Getling A. V. , Buchnev A. A. 
Published: May 2007

AbstractThe results of applying two algorithmic techniques to time-averaged images of the solar granulation are presented. Some quasi-regular structures, which are hidden in the intense noise due to the presence of light blotches in the images, can be detected in this way.
Spectral properties of magnetohydrodynamic convection with mean horizontal temperature gradient
Authors: Skandera D. , Müller W.-Ch. 
Published: May 2007

AbstractSpectral properties of convective magnetohydrodynamic (MHD) turbulence in two and three dimensions are studied by means of direct numerical simulations (Skandera D. & Müller W.-C. 2006). The investigated system is set up with a mean horizontal temperature gradient in order to avoid a development of elevator instabilities in a fully periodic box. All simulations are performed without mean magnetic field. The applied resolution is 5123 and 20482. The MHD equation are solved by a numerical code (Müller & Biskamp 2000) that uses a standard pseudospectral scheme. For removing of aliasing errors a spherical truncation method is employed. Obtained results are compared with predictions of various existing phenomenological theories for magnetohydrodynamic and convective turbulence (Müller & Biskamp 2000). While the three-dimensional system is found to operate in a Kolmogorov-like regime where buoyant forces have a negligible impact on the turbulence dynamics (relatively low Rayleigh number achieved in the simulation; Ra ∼106), the two-dimensional system exhibits interesting irregular quasi-oscillations between a buoyancy dominated Bolgiano-Obukhov-like regime of turbulence and a standard Iroshnikov-Kraichnan-like regime of turbulence (Müller & Biskamp 2000). The most important parameter determining the turbulent regime of 2D magnetoconvection, apart from a high Rayleigh number, seems to be the mutual alignment of velocity and magnetic fields. The non-linear dynamics and the interplay between individual fields are examined with different transfer functions that confirm basic assumptions about directions of energy transfer in spectral space. Kinetic, magnetic and temperature energy are transported by a turbulent cascade from large to smaller scales. The local/nonlocal character of the transport is tested for several individual terms in the governing equations. Moreover, other statistical quantities, e.g. probability density functions, are computed as well. A passive character of the temperature field in the investigated three-dimensional magnetoconvection is supported by computations of intermittency using extended self-similarity. The intermittency of the Elsasser field z+ is in agreement with results from numerical simulations of isotropic MHD turbulence (Müller & Biskamp 2000). The intermittency of the temperature field is found to approximately agree with results of passive scalar measurements in hydrodynamic turbulence (Ruiz-Chavarria, Baudet & Ciliberto 1996).
Tandem peptide epitopes facilitate CD4‐dependent activation of T cell clones
Authors: Hayball John D , Fidler Sarah J , Palliser Deborah , Rees Ann DM , Lamb Jonathan R , Lake Richard A 
Published: May 2007

Peptides that consist of two tandemly repeated epitopes joined by a flexible linker have an increased affinity for class II molecules and are more potent at inducing prolireration of T cell clones than monomeric epitopes. The increase in potency of peptides with two epitopes for individual T cell clones is proportional to the relative CD4 dependence of the clones. We show that epitope dimers activate T cell clones that respond sub‐optimally to monomeric epitopes presented by APC from HIV‐infected donors. We hypothesize that HIV+ APC normally fail to stimulate the clones because virally encoded gpl20 sequesters CD4 from the activation complex, but epitope dimers overcome this effect because they are better able to recruit CD4.The αβ heterodimer of human class II (HLA‐DR1) is further ordered as a dimer of heterodimers (superdimer) at least in its crystal form. Since class II molecules have an open‐ended antigen binding groove, the superdimer is theoretically permissive of stable binding of two peptide epitopes linked in tandem. Our data support a role for the MHC class II dimer of heterodimers in amplifying the proliforative response of T cells to antigen by dint of the superdimers having a higher affinity for CD4 than the nominal class II αβ heterodimers.
Elution and partial characterization of immunoglobulins bound to ovine placenta
Authors: Omwandho Charles A , Hall Amanda L , Falconer John , Roberts Timothy K 
Published: May 2007

Immunoglobulins were eluted from ovine placentae and characterized by immunoprecipitation, electrophoresis, western blotting and ELISA. IgG was shown to comprise the bulk of placental‐bound immunoglobulins while smaller amounts of IgM and only trace amounts of IgA were demonstrated. Results suggest that ovine placental IgG eluted by surgical cannulation of the uterine blood vessels in situ is similar to that eluted from postpartum placentae in vitro, implying that there may be some transfer of antibodies across the maternal side of the placental barrier to the trophoblast. These antibodies are rich in IgG, and IgG2, have a relative molecular weight of 158 kDa, and bind to an 80 kDa peptide prepared from pre‐acidified ovine placental cotyledons.We propose that the binding of placental IgG to the 80 kDa antigen may prevent immunological rejection of the foetus by competitively excluding cytotoxic cells of maternal origin such as NK cells. Also, given that a similar antigen (80 kDa) has been reported in humans and equines and shown to be saturated with IgG in term placentae, we propose that this antigen may be conserved in several mammalian species for reproductive purposes. Consequently, we suggest that the ovine placental IgG and the 80 kDa antigen may be suitable as models for the study of maternal‐foetal interactions in mammalian pregnancies.
Unassisted pelvic floor exercises for postnatal women: a systematic review
Authors: Wagg Ann , Bunn Frances 
Published: May 2007

AbstractAim.  This paper is a report of a systematic review on unassisted pelvic floor exercises for postnatal stress incontinence to identify effective interventions and highlight areas for further research.Background.  Stress incontinence is a common and embarrassing problem. Childbirth is a major cause and problems can be persistent for some. However women are often reluctant to seek help.Method.  We conducted a systematic literature search in December 2006 using the CINAHL, Medline and Cochrane Library databases, hand‐searching of selected textbooks, checking reference lists and contacting experts. There were no date restrictions. The review included randomized controlled trials, published in English, of unassisted pelvic floor exercises in postnatal women. Two reviewers independently extracted data and assessed study quality. Main outcomes were reduction in symptoms of incontinence, patient satisfaction and quality of life.Results.  Four randomized controlled trials met the inclusion criteria. Interventions ranged from written information to structured exercise classes, while usual care varied from a leaflet to group sessions with a midwife. Three out of four studies demonstrated short‐term improvement in incontinence symptoms, which was statistically significant in two. However, at later follow‐up there was no longer a statistically significant effect on continence. All trials found that women in the intervention group were more likely to do the exercises.Conclusion.  We found few trials, quality was variable, and comparisons were difficult because of variations in interventions and outcomes measured. Further high quality evaluations are needed, using standardized interventions and outcome measures, patient‐relevant outcomes such as quality of life, and follow‐up periods that enable evaluation of long‐term effectiveness.
Reduced apoptosis in BALB/c mice infected with Heligmosomoides polygyrus
Authors: DOLIGALSKA M. , DONSKOW‐SCHMELTER K. , RZEPECKA J. , DRELA N. 
Published: May 2007

SUMMARY We evaluated levels of apoptosis and the immune response ex vivo in BALB/c mice infected with Heligmosomoides polygyrus. Cell proliferation, apoptosis and cytokine production were measured in mesenteric lymph nodes (MLN) without exposure to H. polygyrus antigens in culture. The inhibited apoptosis and cytokine production reported might reflect a state of cell hyporesponsiveness in the prepatent phase of infection. These changes were accompanied by changes in the percentage of CD4+ cells in MLN and popliteal lymph nodes (PLN). The prolonged reduction in apoptosis coexisted with induced cell proliferation, elevated TNF‐α, IL‐12p70, IFN‐γ, IL‐6, IL‐10 and TGF‐β synthesis, but lowered IL‐4 and IL‐2 levels. In the chronic phase of infection an increasing production of IFN‐γ, monocyte chemotactic protein‐1 (MCP‐1), IL‐10 and TGF‐β with decreasing concentrations of other cytokines resulted in restored apoptosis. The cytokine response in serum showed moderate production of TNF‐α, temporary involvement of IL‐12p70, induction of IFN‐γ and IL‐10 synthesis, as well as growing IL‐6 and MCP‐1 production. It is suggested that a synchronized synthesis of distinct cytokines is accompanied by different levels of inhibited apoptosis during the prepatent and chronic phases of H. polygyrus infection in BALB/c mice. We suggest that immunosuppression provoked by the nematode is not the outcome of parasite‐induced apoptosis, but rather results from a hyporesponsiveness experienced by cells during H. polygyrus infection.
Role for CTLA‐4 but not CD25+ T cells during Schistosoma mansoni infection of mice
Authors: WALSH C. M. , SMITH P. , FALLON P. G. 
Published: May 2007

SUMMARYSchistosoma mansoni infection of mice increases the frequency of cells that are CD4+CD25+ in the acute (4 and 8 weeks) and chronic (16 week) stages of infection. Depletion of > 85% of CD25+ cells in the acute or chronic stages of schistosome infection caused no overt changes in morbidity or immunological responses. The absence of effect in mice with CD25+ cells depleted may be due to the preferential expression of IL‐4 and IL‐10, two cytokines that are protective in schistosome infection, on CD25− CD4+ cells. We also assessed infection‐induced changes of other regulatory markers, GITR, CD103 and CTLA‐4 on CD4+ cells. We identified a marked expansion of CTLA‐4+ population on CD25− CD4+ cells in acute and chronic infection. Blocking of CTLA‐4 during acute, but not chronic infection, caused significant weight loss and altered the type 2 cytokine response of mice, with increased IL‐4 and IL‐5 production associated with significantly more Th2 cells and eosinophils in the liver granuloma. This study illustrates the complexity of regulation of T cells in schistosome infection and highlights a specific role for CTLA‐4+, but not CD25+ cells, in the regulation of Th2 responses in helminth infection.