A Study of the Coronal Plasma in RS CVn binary systems

XMM-Newton has been performing comprehensive studies of X-ray bright RS CVn binaries in its Calibration and Guaranteed Time programs. We present results from ongoing investigations in the context of a systematic study of coronal emission from RS CVns. We concentrate in this paper on coronal abundances and investigate the abundance pattern in RS CVn binaries as a function of activity and average temperature. A transition from an Inverse First Ionization Potential (FIP) effect towards an absence of a clear trend is found in intermediately active RS CVn systems. This scheme corresponds well into the long-term evolution from an IFIP to a FIP effect found in solar analogs. We further study variations in the elemental abundances during a large flare.Comment: to appear in The Twelfth Cool Stars, Stellar Systems and the Sun, eds. A. Brown, T.R. Ayres, G.M. Harper, (Boulder: Univ. of Colorado), in pres

Bifurcation Diagram for Compartmentalized Granular Gases

The bifurcation diagram for a vibro-fluidized granular gas in N connected compartments is constructed and discussed. At vigorous driving, the uniform distribution (in which the gas is equi-partitioned over the compartments) is stable. But when the driving intensity is decreased this uniform distribution becomes unstable and gives way to a clustered state. For the simplest case, N=2, this transition takes place via a pitchfork bifurcation but for all N>2 the transition involves saddle-node bifurcations. The associated hysteresis becomes more and more pronounced for growing N. In the bifurcation diagram, apart from the uniform and the one-peaked distributions, also a number of multi-peaked solutions occur. These are transient states. Their physical relevance is discussed in the context of a stability analysis.Comment: Phys. Rev. E, in press. Figure quality has been reduced in order to decrease file-siz

Coronal density diagnostics with Helium-like triplets: CHANDRA--LETGS observations of Algol, Capella, Procyon, Eps Eri, Alpha Cen A&B, UX Ari, AD Leo, YY Gem, and HR1099

We present an analysis of ten cool stars (Algol, Capella, Procyon, Eps Eri, Alpha Cen A&B, UX Ari, AD Leo, YY Gem, and HR1099) observed with the Low Energy Transmission Grating Spectrometer (LETGS) on board the Chandra X-ray Observatory. This sample contains all cools stars observed with the LETGS presently available to us with integration times sufficiently long to warrant a meaningful spectral analysis. Our sample comprises inactive, moderately active, and hyperactive stars and samples the bulk part of activity levels encountered in coronal X-ray sources. We use the LETGS spectra to carry out density and temperature diagnostics with an emphasis on the H-like and the He-like ions. We find a correlation between line flux ratios of the Lyman-Alpha and He-like resonance lines with the mean X-ray surface flux. We determine densities using the He-like triplets. For active stars we find no significant deviations from the low-density limit for the ions of Ne, Mg, and Si, while the measured line ratios for the ions of C, N, and O do show evidence for departures from the low-density limit in the active stars, but not in the inactive stars. Best measurements can be made for the OVII triplet where we find significant deviations from the low-density limit for the stars Algol, Procyon, YY Gem, Eps Eri, and HR1099. We discuss the influence of radiation fields on the interpretation of the He-like triplet line ratios in the low-Z ions, which is relevant for Algol, and the influence of dielectronic satellite lines, which is relevant for Procyon. For the active stars YY Gem, Eps Eri, and HR1099 the low f/i ratios can unambiguously be attributed to high densties in the range 1--3 10^10 cm^-3 at OVII temperatures. We find our LETGS spectra to be an extremely useful tool for plasma diagnostics of stellar coronae.Comment: 17 pages, Latex2e, 12 figures. accepted for A&A under MS262

Variability in basal metabolic rate of a long-distance migrant shorebird (Red Knot, <i>Calidris canutus</i>) reflects shifts in organ sizes

We studied differences in body composition and basal metabolic rate (BMR, measured in postabsorptive birds under thermoneutral conditions at night) in two subspecies of red knots, Calidris canutus: one that spends the nonbreeding season under energetically costly climatic conditions at temperate latitudes (subspecies islandica in western Europe) and one that winters in the hot and humid tropics (subspecies canutus in West and South Africa). To examine whether the possible differences would be upheld under identical conditions, we kept both groups in captivity as well. Body composition was quantified with respect to the fat and lean components of 10 ''organs'' (breast muscles, leg muscles, stomach, intestine, liver kidneys, lungs, heart, and the skin, and skeleton and attached muscle). Captive birds had lighter lean tissues than wild birds, especially those of the stomach, intestine, kidneys, and liver (the nutritional organs). During the northern winter wild islandica knots had higher lean masses than canutus knots in tropical Africa. Tropically wintering red knots had lower BMRs than their temperate-wintering conspecifics, and birds in long-term captivity had lower BMR values than their free-living counterparts. Average BMR values per category of birds (wild or captive of either subspecies) were strongly correlated with the group averages of lean mass. Prediction of BMR on the basis of total lean mass of red knots undergoing incipient starvation follows this same relationship because metabolically active tissue is being depleted. That the two subspecies converged to similar body composition in captivity indicates that individual red knots may possess considerable flexibility. We argue that red knots, and probably most other long-distance migrants, have metabolic machinery that is able to adjust continuously, depending on the ecological conditions and food types encountered in the course of the year. We further argue that variation in (functional components of) lean mass is the vehicle for seasonal adjustments in metabolic physiology to variable demand levels. Body mass adjustments offer a flexible response enabling red knots to economize on total daily metabolic expenditure whenever conditions allow a relaxation of metabolic scope, such as during winter in the Tropics.</p

Investigating the function of single-pass leucine-rich repeat transmembrane proteins in cell signalling and early neural development

Single-pass leucine-rich (LRR) repeat transmembrane proteins contain a diverse number of repeating motifs of approximately 24 amino acid residues with a large number being conserved leucines. Flrt expression is observed in the developing embryo in important developmental regions such as the central nervous system and developing skeletal muscle. Knockout of Flrt3 during embryogenesis results in early embryonic lethality making in vivo analysis of endogenous Flrt3 function difficult. No cell based model exists for studying Flrt function. Flrt family members have previously been shown to interact with FgfR1 and 2, with the Flrt1 FgfR1 interaction resulting in an increase in FgfR1 signalling activity. Immunofluorescent microscopy reveals that Flrt3 from mouse (Mus musculus) co-localises with FgfR1 both intracellularly and at the plasma membrane, with the interaction resulting in a trend of increased FgfR1 signalling being observed, and phosphorylation of tyrosine residues within Flrt3. An attempt was made to identify domains of the protein important in the trend of increased FgfR1 signalling, but no domains could be identified as contributing to this outcome. To study endogenous Flrt3 function, the P19 embryonic carcinoma retinoic acid-induced neural differentiation model was used, and the results showed a rapid and robust induction of Flrt3 mRNA and protein expression. A region of the promoter between 4 kb and 6 kb upstream of the Flrt3 start site was found to be partially responsible for the induction of Flrt3. Interestingly, this response element was not within a region of promoter that showed conservation among higher-order mammals. An effect of increased Flrt3 expression during neural differentiation was observed, resulting in decreased MAPK pathway activation. Induction of Flrt3 is found to occur prior to that of Sox1, accepted to be one of the first genes up-regulated in early neurectoderm differentiation, yet was found to be not solely responsible for the induction of Sox1. The individual cell expression of Flrt3 and Sox1 was analysed by immunofluorescence, although it did not reveal details regarding induction of Sox1 in cells with increased Flrt3 expression. The potential for a common feature of single-pass LRR transmembrane proteins to function as modulators of receptor signalling during embryonic development was investigated, using Lrrtm3 and FgfR1 as an example. Lrrtm3 was investigated as a modulator of FgfR1 signalling due to overlapping region of expression with FgfR1 in the developing embryo. Lrrtm3 was found to co-localise and form an interaction with FgfR1, with this interaction resulting in an increase in FgfR1 signalling. The data obtained in this thesis provides further insight into not only the role of the Flrt protein family as FgfR1 modulators, but potentially identifies a role for similar, if not all single-pass LRR transmembrane proteins as regulators of receptor signalling during embryonic development. While the results of Chapter 3 and 5 were obtained using a protein over-expression system, the first model for studying endogenous Flrt3 was identified and characterised in Chapter 4, providing the opportunity to study Flrt3 function during development with protein expression levels closely resembling those that are found in the embryo.Thesis (M.Phil.) -- University of Adelaide, School of Biological Sciences, 201

Confirmatory factor analysis and differential relationships of the two subdomains of negative symptoms in chronically ill psychotic patients

Research suggests a two factor structure for negative symptoms in patients with psychotic disorders: social amotivation (SA) and expressive deficits (ED). Applying this two-factor structure in clinical settings may provide valuable information with regard to outcomes and to target treatments. We aimed to investigate 1) whether the factor structure is also supported in chronically ill patients with a psychotic disorder and 2) what the relationship is between these factors and functioning (overall functioning and living situation), depressive symptoms and quality of life. 1157 Patients with a psychotic disorder and a duration of illness of 5 years or more were included in the analysis (data selected from the Pharmacotherapy Monitoring Outcome Survey; PHAMOUS). A confirmatory factor analysis was performed using items of the Positive and Negative Syndrome Scale that were previously identified to reflect negative symptoms (N1-4, N6, G5, G7, G13, G16). Subsequently, regression analysis was performed on outcomes. The results confirmed the distinction between SA (N2, N4, G16) and ED (N1, N3, N6, G5, G7, G13) in chronically ill patients. Both factors were related to worse overall functioning as measured with the Health of the Nation Outcome Scales, ED was uniquely associated with residential living status. Higher scores for SA were associated with more depressive symptoms and worse quality of life. Thus, SA is most strongly related to level of social-emotional functioning, while ED are more related to living situation and thereby are indicative of level of everyday functioning. This subdivision may be useful for research purposes and be a valuable additional tool in clinical practice and treatment development