scholarly journals Luminous Blue Variables & Mass Loss near the Eddington Limit

2007 ◽  
Vol 3 (S250) ◽  
pp. 71-82
Author(s):  
Stan Owocki ◽  
Allard Jan van Marle
Keyword(s):  
Mass Loss ◽  
Potential Role ◽  
Time Dependent ◽  
Substantial Fraction ◽  
Luminous Blue Variables ◽  
Flow Stagnation ◽  
On Line ◽  
Eddington Limit ◽  
Luminous Blue Variable

AbstractDuring the course of their evolution, massive stars lose a substantial fraction of their initial mass, both through steady winds and through relatively brief eruptions during their Luminous Blue Variable (LBV) phase. This talk reviews the dynamical driving of this mass loss, contrasting the line-driving of steady winds to the potential role of continuum driving for eruptions during LBV episodes when the star exceeds the Eddington limit. A key theme is to emphasize the inherent limits that self-shadowing places on line-driven mass loss rates, whereas continuum driving can in principle drive mass up to the “photon-tiring” limit, for which the energy to lift the wind becomes equal to the stellar luminosity. We review how the “porosity” of a highly clumped atmosphere can regulate continuum-driven mass loss, but also discuss recent time-dependent simulations of how base mass flux that exceeds the tiring limit can lead to flow stagnation and a complex, time-dependent combination of inflow and outflow regions. A general result is thus that porosity-mediated continuum driving in super-Eddington phases can explain the large, near tiring-limit mass loss inferred for LBV giant eruptions.

scholarly journals Instabilities in massive stars

2003 ◽  
Vol 212 ◽  
pp. 281-290 ◽  
Author(s):  
Stanley P. Owocki
Keyword(s):  
Physical Properties ◽  
Mass Loss ◽  
Stellar Wind ◽  
Massive Stars ◽  
Dynamical Instability ◽  
Radiation Hydrodynamics ◽  
Stellar Rotation ◽  
Eddington Limit ◽  
Luminous Blue Variable

A defining property of massive stars is the dominant, dynamical role played by radiation throughout the stellar interior, atmosphere, and wind. Associated with this radiation hydrodynamics are several distinct kinds of instabilities that can lead to convection in both core and envelope, clumping in atmosphere and wind outflow, and perhaps even the dramatic mass loss outbursts associated with Luminous Blue Variable phases. Here I review these instabilities with emphasis on basic physical properties of radiative driving. I draw on two specific examples of dynamical instability, namely the strong instability associated with line-driving of a stellar wind outflow, and the global stellar instabilities associated with approaching or exceeding a modified Eddington limit. I conclude with a brief mention of recent ideas on the role of stellar rotation in the shaping of bipolar LBV outbursts.

scholarly journals Mass loss and evolution of hot massive stars

2008 ◽  
Vol 4 (S252) ◽  
pp. 271-281 ◽  
Author(s):  
Jorick S. Vink
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Main Sequence ◽  
Gamma Ray ◽  
Massive Stars ◽  
Gamma Ray Bursts ◽  
Absorption Profile ◽  
Luminous Blue Variables ◽  
Progenitor Stars

AbstractWe discuss the role of mass loss for the evolution of the most massive stars, highlighting the role of the predicted bi-stability jump that might be relevant for the evolution of rotational velocities during or just after the main sequence. This mechanism is also proposed as an explanation for the mass-loss variations seen in the winds from Luminous Blue Variables (LBVs). These might be relevant for the quasi-sinusoidal modulations seen in a number of recent transitional supernovae (SNe), as well as for the double-throughed absorption profile recently discovered in the Hα line of SN 2005gj. Finally, we discuss the role of metallicity via the Z-dependent character of their winds, during both the initial and final (Wolf-Rayet) phases of evolution, with implications for the angular momentum evolution of the progenitor stars of long gamma-ray bursts (GRBs).

Carbamoylcholine and gastrin induce inositol lipid turnover in canine gastric parietal cells

1988 ◽  
Vol 255 (1) ◽  
pp. G99-G105 ◽  
Author(s):  
T. Chiba ◽  
S. K. Fisher ◽  
J. Park ◽  
E. B. Seguin ◽  
B. W. Agranoff ◽  
...  
Keyword(s):  
Potential Role ◽  
Inositol Phosphates ◽  
Selective Reduction ◽  
Parietal Cells ◽  
Time Dependent ◽  
Cell Uptake ◽  
Inositol Phospholipids ◽  
Lipid Turnover ◽  
Gastric Parietal Cells

The potential role of inositol phospholipid turnover in mediating acid secretion was examined in a preparation enriched for isolated canine gastric parietal cells. The stimulatory effects of carbamoylcholine (carbachol) and gastrin on parietal cell uptake of [14C]aminopyrine were linked to dose- and time-dependent selective reduction in cellular phosphatidylinositol content, although the specific fatty acid composition of the phosphoinositides was not altered. Analysis of [3H]inositol phosphates accumulated in cells prelabeled with [3H]inositol revealed an increase in labeled inositol trisphosphate by 5 min of incubation with either carbachol or gastrin. Furthermore, after preincubation of parietal cells in medium containing [32P]orthophosphate, the two secretagogues elicited a time-dependent decrease in 32P labeling of phosphatidylinositol 4,5-bisphosphate and concomitant increase in labeling of phosphatidic acid. These data demonstrate that the acid secretagogue actions of carbachol and gastrin are correlated with turnover of cellular inositol phospholipids in a preparation consisting predominantly of parietal cells.

Modifier Attachment in Sentence Parsing: Evidence from Dutch

1996 ◽  
Vol 49 (3) ◽  
pp. 664-695 ◽  
Author(s):  
Marc Brysbaert ◽  
Don C. Mitchell
Keyword(s):  
Relative Clauses ◽  
Potential Role ◽  
Structural Characteristics ◽  
Attachment Site ◽  
Linguistic Variation ◽  
Language Experience ◽  
Garden Path ◽  
Corpus Studies ◽  
On Line

Current theories of parsing suggest a wide variety of mechanisms by which modifiers, such as relative clauses, may be related to constituents that offer more than one potential attachment site. Some, like the tuning hypothesis, are based on the premise that people's parsing performance is shaped by prior exposure to language. Others (e.g. garden-path theory and construal theory) play down any potential role of past linguistic experience, stressing instead the varying influences of structural characteristics of the sentence in question. The two views encourage differing expectations about cross-linguistic variation in parsing preference. A questionnaire study and two on-line experiments were carried out to investigate attachment preferences in Dutch. The results pose a number of problems for the majority of the existing parsing models and are clearly inconsistent with some of the traditional theories. In contrast, the findings are compatible with models incorporating parsing mechanisms that are tuned by language experience. The results highlight the need for further corpus studies to subject these accounts to more searching scrutiny.

scholarly journals Chronoeffects of the Herbal Medicines Puerariae radix and Coptidis rhizoma in Mice: A Potential Role of REV-ERBα

2021 ◽  
Vol 12 ◽  
Author(s):  
Jinming Liu ◽  
Haiman Xu ◽  
Li Zhang ◽  
Shuai Wang ◽  
Danyi Lu ◽  
...  
Keyword(s):  
Drug Target ◽  
Potential Role ◽  
Target Genes ◽  
Herbal Medicines ◽  
Time Dependent ◽  
Dependent Manner ◽  
Active Constituent ◽  
Puerariae Radix ◽  
Coptidis Rhizoma

Identifying drugs with dosing time-dependent effects (chronoeffects) and understanding the underlying mechanisms would help to improve drug treatment outcome. Here, we aimed to determine chronoeffects of the herbal medicines Puerariae radix (PR) and Coptidis rhizoma (CR), and investigate a potential role of REV-ERBα as a drug target in generating chronoeffects. The pharmacological effect of PR on hyperhomocysteinemia in mice was evaluated by measuring total homocysteine, triglyceride levels and lipid accumulation. PR dosed at ZT10 generated a stronger effect on hyperhomocysteinemia than drug dosed at ZT2. Furthermore, PR increased the expression levels of REV-ERBα target genes Bhmt, Cbs and Cth (encoding three key enzymes responsible for homocysteine catabolism), thereby alleviating hyperhomocysteinemia in mice. Moreover, CR attenuated chronic colitis in mice in a dosing time-dependent manner based on measurements of disease activity index, colon length, malondialdehyde/myeloperoxidase activities and IL-1β/IL-6 levels. ZT10 dosing generated a stronger anti-colitis effect as compared to ZT2 dosing. This was accompanied by lower production of colonic inflammatory cytokines (i.e., Nlrp3, IL-1β, IL-6, Tnf-α and Ccl2, REV-ERBα target genes) in colitis mice dosed at ZT10. The diurnal patterns of PR and CR effects were respectively consistent with those of puerarin (a main active constituent of PR, a REV-ERBα antagonist) and berberine (a main active constituent of CR, a REV-ERBα agonist). In addition, loss of Rev-erbα in mice abolished the dosing time-dependency in PR and CR effects. In conclusion, the therapeutic effects of PR and CR depend on dosing time in mice, which are probably attributed to diurnal expression of REV-ERBα as the drug target. Our findings have implications for improving therapeutic outcomes of herbal medicines with a chronotherapeutic approach.

scholarly journals Mass and angular momentum loss of first stars via decretion disks

2009 ◽  
Vol 5 (S265) ◽  
pp. 69-70
Author(s):  
Jiří Krtička ◽  
Stanley P. Owocki ◽  
Georges Meynet
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Potential Role ◽  
Outer Edge ◽  
Stellar Rotation ◽  
First Stars ◽  
Near Surface ◽  
Stellar Interior ◽  
Angular Momentum Loss

AbstractAlthough the first stars were likely very hot and luminous, their low or zero metallicity implies that any mass loss through winds driven by line-scattering of radiation in metal ions was likely small or non-existent. Here we examine the potential role of another possible mechanism for mass loss in these first stars, namely via decretion disks associated with near-critical rotation induced from evolution of the stellar interior. In this case the mass loss is set by the angular momentum needed to keep the stellar rotation at or below the critical rate. In present evolutionary models, that mass loss is estimated by assuming effective release from a spherical shell at the surface. Here we examine the potentially important role of viscous coupling of the decretion disk in outward angular momentum transport, emphasizing that the specific angular momentum at the outer edge of the disk can be much larger than at the stellar surface. The net result is that, for a given stellar interior angular momentum excess, the mass loss required from a decretion disk can be significantly less than invoked in previous models assuming a direct, near-surface release.

Time-dependent cellular response in the liver and heart in a dietary-induced obese mouse model: the potential role of ER stress and autophagy

2015 ◽  
Vol 55 (6) ◽  
pp. 2031-2043 ◽  
Author(s):  
Hsiu-Ching Hsu ◽  
Chia-Hsin Liu ◽  
Yi-Chen Tsai ◽  
Sin-Jin Li ◽  
Ching-Yi Chen ◽  
...  
Keyword(s):  
Mouse Model ◽  
Er Stress ◽  
Cellular Response ◽  
Potential Role ◽  
Time Dependent ◽  
Obese Mouse

scholarly journals The neovasculature homing motif NGR: more than meets the eye

Blood ◽  
2008 ◽  
Vol 112 (7) ◽  
pp. 2628-2635 ◽  
Author(s):  
Angelo Corti ◽  
Flavio Curnis ◽  
Wadih Arap ◽  
Renata Pasqualini
Keyword(s):  
Tumor Growth ◽  
Targeted Delivery ◽  
Binding Sites ◽  
Potential Role ◽  
Time Dependent ◽  
Binding Properties ◽  
Cell Functions ◽  
Structural And Functional Properties ◽  
Asparagine Deamidation

Abstract A growing body of evidence suggests that peptides containing the Asn-Gly-Arg (NGR) motif can selectively recognize tumor neovasculature and can be used, therefore, for ligand-directed targeted delivery of various drugs and particles to tumors or to other tissues with an angiogenesis component. The neovasculature binding properties of these peptides rely on the interaction with an endothelium-associated form of aminopeptidase N (CD13), an enzyme that has been implicated in angiogenesis and tumor growth. Recent studies have shown that NGR can rapidly convert to isoaspartate-glycine-arginine (isoDGR) by asparagine deamidation, generating αvβ3 ligands capable of affecting endothelial cell functions and tumor growth. This review focuses on structural and functional properties of the NGR motif and its application in drug development for angiogenesis-dependent diseases. Furthermore, we discuss the time-dependent transition of NGR to isoDGR in natural proteins, such as fibronectins, and its potential role of as a “molecular timer” for generating new binding sites for integrins impli-cated in angiogenesis.

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