scholarly journals Evolutionary sequence of expanding Hydrogen shells

2006 ◽  
Vol 2 (S237) ◽  
pp. 467-467
Author(s):  
M. Relaño ◽  
J. E. Beckman ◽  
O. Daigle ◽  
C. Carignan
Keyword(s):  
Evolutionary Sequence ◽  
Dynamical Models ◽  
Ob Stars ◽  
Ob Associations ◽  
Hi Shells ◽  
The Impact

AbstractGiant HI shells, with diameters of hundreds of parsecs and expansion velocities of 10-20 s−1 are characteristic observed features of local gas rich galaxies. Although a predictable consequence of the impact of OB associations on the ISM doubts have been raised, as OB stars are not present in the centres of the majority of these shells. Here we combine our observations of expanding ionized shells in luminous H II regions with basic dynamical models to give support to the scenario in which OB associations do produce the HI shells.

PRICING COUNTERPARTY RISK INCLUDING COLLATERALIZATION, NETTING RULES, RE-HYPOTHECATION AND WRONG-WAY RISK

2013 ◽  
Vol 16 (02) ◽  
pp. 1350007 ◽  
Author(s):  
DAMIANO BRIGO ◽  
AGOSTINO CAPPONI ◽  
ANDREA PALLAVICINI ◽  
VASILEIOS PAPATHEODOROU
Keyword(s):  
Interest Rate ◽  
Credit Derivatives ◽  
Credit Default Swaps ◽  
Credit Spread ◽  
Counterparty Risk ◽  
Default Correlation ◽  
Dynamical Models ◽  
Credit Default ◽  
The Impact

This article is concerned with the arbitrage-free valuation of bilateral counterparty risk through stochastic dynamical models when collateral is included, with possible rehypothecation. The payout of claims is modified to account for collateral margining in agreement with International Swap and Derivatives Association (ISDA) documentation. The analysis is specialized to interest-rate and credit derivatives. In particular, credit default swaps are considered to show that a perfect collateralization cannot be achieved under default correlation. Interest rate and credit spread volatilities are fully accounted for, as is the impact of re-hypothecation, collateral margining frequency, and dependencies.

scholarly journals Hydrodynamic and frictional modulation of deformations in switchable colloidal crystallites

2020 ◽  
Vol 117 (23) ◽  
pp. 12700-12706
Author(s):  
Young Ki Lee ◽  
Xiaoguai Li ◽  
Paris Perdikaris ◽  
John C. Crocker ◽  
Celia Reina ◽  
...  
Keyword(s):  
Principal Component Analysis ◽  
Diffusion Coefficients ◽  
Particle Shape ◽  
Colloidal Crystals ◽  
Principal Component ◽  
Nucleation And Growth ◽  
Spherically Symmetric ◽  
Dynamical Models ◽  
Micrometer Scale ◽  
The Impact

Displacive transformations in colloidal crystals may offer a pathway for increasing the diversity of accessible configurations without the need to engineer particle shape or interaction complexity. To date, binary crystals composed of spherically symmetric particles at specific size ratios have been formed that exhibit floppiness and facile routes for transformation into more rigid structures that are otherwise not accessible by direct nucleation and growth. There is evidence that such transformations, at least at the micrometer scale, are kinetically influenced by concomitant solvent motion that effectively induces hydrodynamic correlations between particles. Here, we study quantitatively the impact of such interactions on the transformation of binary bcc-CsCl analog crystals into close-packed configurations. We first employ principal-component analysis to stratify the explorations of a bcc-CsCl crystallite into orthogonal directions according to displacement. We then compute diffusion coefficients along the different directions using several dynamical models and find that hydrodynamic correlations, depending on their range, can either enhance or dampen collective particle motions. These two distinct effects work synergistically to bias crystallite deformations toward a subset of the available outcomes.

scholarly journals Study of HI and Star Formation Sites in the Magellanic Bridge

2004 ◽  
Vol 217 ◽  
pp. 506-508 ◽  
Author(s):  
Erik Muller ◽  
Lister Staveley-Smith ◽  
William Zealey
Keyword(s):  
Star Formation ◽  
Spatial Correlation ◽  
Spatial Scales ◽  
Neutral Hydrogen ◽  
Important Process ◽  
Ob Associations ◽  
Active Processes ◽  
Hi Shells

Tidal features represent an important process for the recycling of matter across extremely large spatial scales. The Magellanic Bridge is the closest gaseous tidal feature to our own Galaxy, and offers an ideal opportunity to study the active processes in such phenomena at high spatial resolutions otherwise unavailable. The neutral hydrogen of the western Magellanic Bridge, has been observed with both the Parkes 64m telescope and ATCA interferometer and the resulting dataset has revealed an extremely complex and chaotic morphology. We discuss these observations here with reference to a variety of analyses: the spatial correlation of apparently expanding HI shells with OB associations and the outcome of sensitive Hα and CO surveys.

scholarly journals Magnetic fields, winds and X-rays of massive stars in the Orion nebula cluster

2010 ◽  
Vol 6 (S272) ◽  
pp. 208-209 ◽  
Author(s):  
Véronique Petit ◽  
Gregg A. Wade ◽  
Evelyne Alecian ◽  
Laurent Drissen ◽  
Thierry Montmerle ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Massive Stars ◽  
Theoretical Models ◽  
Magnetic Star ◽  
X Rays ◽  
Orion Nebula ◽  
X Ray ◽  
Ob Stars ◽  
The Impact ◽  
The Relationship

AbstractIn some massive stars, magnetic fields are thought to confine the outflowing radiatively-driven wind. Although theoretical models and MHD simulations are able to illustrate the dynamics of such a magnetized wind, the impact of this wind-field interaction on the observable properties of a magnetic star - X-ray emission, photometric and spectral variability - is still unclear. The aim of this study is to examine the relationship between magnetism, stellar winds and X-ray emission of OB stars, by providing empirical observations and confronting theory. In conjunction with the COUP survey of the Orion Nebula Cluster, we carried out spectropolarimatric ESPaDOnS observations to determine the magnetic properties of massive OB stars of this cluster.

scholarly journals The Impact of Stellar Rotation on the Nitrogen Abundance Gradient from OB Stars in the Galactic Disk

2004 ◽  
Vol 215 ◽  
pp. 226-227
Author(s):  
Simone Daflon ◽  
Katia Cunha
Keyword(s):  
Milky Way ◽  
Galactic Disk ◽  
Young Stars ◽  
Evolutionary Models ◽  
Rotating Stars ◽  
Stellar Rotation ◽  
Ob Stars ◽  
Nitrogen Abundance ◽  
N Enrichment ◽  
The Impact

Massive young stars can be used to trace the current chemical composition of the Galactic disk and to define its metallicity gradient. However, evolutionary models of massive rotating stars predict changes of the surface abundances due to rotationally induced mixing. The abundance analysis of elements sensitive to mixing, such as CNO, can be used to test these rotating stellar models. In this study we identify those stars that show one particular signature of mixing, N-enrichment, in our sample of 70 OB stars for which we have conducted an abundance analysis. This sample is used to define radial metallicity gradients in the Milky Way and we investigate the variation of the calculated nitrogen gradient after the exclusion of these, probably mixing-induced, N-rich stars.

Changing Patterns of Corporate Headquarter Influence, 1974–89

1994 ◽  
Vol 26 (5) ◽  
pp. 733-747 ◽  
Author(s):  
D I Lyons
Keyword(s):  
New York ◽  
Metropolitan Region ◽  
Evolutionary Sequence ◽  
Metropolitan Regions ◽  
Corporate Influence ◽  
Us Economy ◽  
The Us ◽  
Changing Patterns ◽  
Regional Centers ◽  
The Impact

Research on the changing geography of metropolitan corporate headquarters (CH) influence has pointed to a decrease in importance for national centers and an increase in the importance of regional centers throughout the country. Theoretical explanations of this change have posited a linear evolutionary sequence from spatial and hierarchical concentration to dispersal. In this paper, the nature of change in metropolitan CH influence between 1974 and 1989 is examined, with a focus on three aspects of this process. First, the detailed sequence of dispersal within types of metropolitan region is explored. Second, the issue of how metropolitan CH influence changes over space is examined. Third, the impact of the recent restructuring of the US economy on metropolitan corporate influence is investigated. The results suggest that the linear evolutionary sequence model needs some modification. The major proportional shifts in CH influence are from New York to a select set of diversified regional centers that may be emerging as national centers in their own right. Dispersion of CH influence is not simply a matter of shifts from one level of the hierarchy to another, rather it is the outcome of a continuous struggle by existing and new corporations in metropolises among and within all levels of the hierarchy to capture new growth opportunities as older opportunities decline. Finally, the impact of restructuring was twofold. Among some metropolitan regions dominated by sectors that declined during the period 1974–89 the consequences were a dramatic decrease in influence. The CHs of the new growth sectors were concentrated among national centers and hence contributed to increased influence at the apex of the hierarchy.

scholarly journals Migration & Extra-solar Terrestrial Planets: Watering the Planets

2012 ◽  
Vol 8 (S293) ◽  
pp. 229-234
Author(s):  
Jade C. Carter-Bond ◽  
David P. O'Brien ◽  
Sean N. Raymond
Keyword(s):  
Chemical Equilibrium ◽  
Formation Process ◽  
Giant Planet ◽  
Terrestrial Planet ◽  
Dynamical Models ◽  
Diverse Range ◽  
Refractory Elements ◽  
Planet Migration ◽  
The Impact ◽  
Host Stars

AbstractA diverse range of terrestrial planet compositions is believed to exist within known extrasolar planetary systems, ranging from those that are relatively Earth-like to those that are highly unusual, dominated by species such as refractory elements (Al and Ca) or C (as pure C, TiC and SiC)(Bond et al. 2010b). However, all prior simulations have ignored the impact that giant planet migration during planetary accretion may have on the final terrestrial planetary composition. Here, we combined chemical equilibrium models of the disk around five known planetary host stars (Solar, HD4203, HD19994, HD213240 and Gl777) with dynamical models of terrestrial planet formation incorporating various degrees of giant planet migration. Giant planet migration is found to drastically impact terrestrial planet composition by 1) increasing the amount of Mg-silicate species present in the final body; and 2) dramatically increasing the efficiency and amount of water delivered to the terrestrial bodies during their formation process.

scholarly journals Sources of predictability over the Mediterranean at seasonal time-scale: building up an empirical forecasting model

2021 ◽  
Author(s):  
Esteban Rodríguez-Guisado ◽  
Ernesto Rodríguez-Camino
Keyword(s):  
Time Series ◽  
Global Climate ◽  
Supplementary Information ◽  
Climate Indices ◽  
Least Squares Regression ◽  
Dynamical Models ◽  
Flexible Tool ◽  
Probabilistic Forecasts ◽  
The Mediterranean ◽  
The Impact

<p>Although most operational seasonal forecasting systems are based on dynamical models, empirical forecasting systems, built on statistical relationships between present and future at seasonal time horizons conditions of the climate system, provide a feasible and realistic alternative and a source of supplementary information. Here, a new empirical model based on partial least squares regression is presented. Originally designed as a flexible tool, the model can be run with many configurations including different predictands, resolutions, leads and aggregation times. To be able of producing forecast for any selected configuration, the model automatically selects predictors from an initial pool, containing global climate indices and specific predictors for the Mediterranean region unveiled in the frame of the MEDSCOPE project. Additionally, the model explores spatial fields, generating time series based on spatial averages of areas well correlated with the predictand. These time series are added to the initial pool of candidate predictors.  We present here results from a configuration producing probabilistic forecasts of seasonal (3 month averages) temperature and precipitation, their verification and comparison against a selection of state-of-the-art seasonal forecast systems based on dynamical models in a hindcast period (1994-2015). The model is able to produce spatially coherent anomaly patterns, and reach levels of skill comparable to those based on dynamical models. As predictors can be easily removed or incorporated, the model can provide information on the impact of a particular predictor on skill, so it can be used to help in the search and understanding of new sources of predictability. Evaluation of soil moisture impact on summer temperature predictability is shown as an example</p>

scholarly journals Evolutionary Models of Interstellar Chemistry

1987 ◽  
Vol 120 ◽  
pp. 259-272
Author(s):  
Sheo S. Prasad
Keyword(s):  
Evolutionary Models ◽  
Evolutionary Sequence ◽  
Dynamical Models ◽  
Interstellar Chemistry ◽  
Interstellar Clouds ◽  
The Way

The goal of evolutionary models of interstellar chemistry is to understand how interstellar clouds came to be the way they are, how they will change with time, and to place them in an evolutionary sequence with other celestial objects such as stars. To this end, we present an improved Mark II version of our earlier model of chemistry in dynamically evolving clouds. The Mark II model suggests that the conventional elemental C/O ratio less than one can explain the observed abundances of CI and the non-detection of O2 in dense clouds. Coupled chemical-dynamical models seem to have the potential to generate many observable discriminators of the evolutionary tracks. This is exciting, because, in general, purely dynamical models do not yield enough verifiable discriminators of the predicted tracks.

Variability Survey of Massive Stars in OB-Associations: Preliminary Results on the Cygnus Region

2012 ◽  
Vol 21 (4) ◽  
Author(s):  
J. Laur ◽  
T. Tuvikene ◽  
T. Eenmäe ◽  
I. Kolka ◽  
L. Leedjärv
Keyword(s):  
Massive Stars ◽  
Light Curves ◽  
Ob Stars ◽  
Preliminary Results ◽  
Red Supergiants ◽  
Ob Associations

AbstractWe present V - and I-passband photometry of massive stars in the Cyg OB1 and Cyg OB2 associations, based on about 80 observing nights spanning 300 days in the 2011 season. The variability of 22 supergiants and 48 OB-stars with luminosity classes III-V is analyzed. We report two new variable OB stars and 15 variable supergiants of which four are new discoveries. The light variations of Schulte 12 are interpreted as microvariability. We also present light curves of the red supergiants BC Cyg and BI Cyg which exhibit brightness drop of more than 0.4 mag during the season.

Sign in / Sign up

Export Citation Format

Share Document