scholarly journals Theoretical relations between LBV’s and other stars

1989 ◽  
Vol 113 ◽  
pp. 221-228
Author(s):  
Norbert Langer
Keyword(s):  
Theoretical Work ◽  
Computer Code ◽  
Physical Processes ◽  
Evolutionary Computations ◽  
Future Evolution ◽  
Luminous Blue Variables ◽  
Different Types ◽  
Stellar Masses ◽  
Heterogeneous Class ◽  
Hr Diagram

The so called Luminous Blue Variables (LBVs) form a rather heterogeneous class of very active, luminous (and therefore massive) stars (c.f. R.M. Humphreys, this volume). The following two points are the aim of theoretical work concerning these objects: 1. to know their internal structure from the center up to the atmosphere, i.e. to find out the place of these objects in the course of thermonuclear evolution, or to identify the physical processes which are responsible for the different types of mass loss phenomena, and 2. to conclude which were their preceding evolutionary phases, and to predict their future evolution, i.e. to identify LBV progenitors and descendants, derive their ages, and so on. The basic tool of the theorists is a stellar evolution computer code, which allows to perform evolutionary computations (including different assumptions, which are necessary since several physical ingredients cannot yet be treated from first principles), leading stellar tracks through the part of the HR diagram where LBVs are found. But in this context we meet already a basic problem: in a certain small area of the HR diagram (which may correspond e.g. to some kind of error box) stars of several different types may be identified by the observers, each type may be even devided into several subtypes. Therefore, the correlation of computer models and observed stars is often very difficult or impossible. The various types of stars are mainly classified by spectroscopic criteria, while important “theoretical quantities” as stellar masses or the chemical composition are hard to derive from observations.

A New Algorithmic Identity

2011 ◽  
Vol 28 (6) ◽  
pp. 164-181 ◽  
Author(s):  
John Cheney-Lippold
Keyword(s):  
Theoretical Work ◽  
Computer Code ◽  
Online Marketing ◽  
Computer Algorithms ◽  
Surveillance Networks ◽  
Internet History ◽  
Web Surfing

Marketing and web analytic companies have implemented sophisticated algorithms to observe, analyze, and identify users through large surveillance networks online. These computer algorithms have the capacity to infer categories of identity upon users based largely on their web-surfing habits. In this article I will first discuss the conceptual and theoretical work around code, outlining its use in an analysis of online categorization practices. The article will then approach the function of code at the level of the category, arguing that an analysis of coded computer algorithms enables a supplement to Foucauldian thinking around biopolitics and biopower, of what I call soft biopower and soft biopolitics. These new conceptual devices allow us to better understand the workings of biopower at the level of the category, of using computer code, statistics and surveillance to construct categories within populations according to users’ surveilled internet history. Finally, the article will think through the nuanced ways that algorithmic inference works as a mode of control, of processes of identification that structure and regulate our lives online within the context of online marketing and algorithmic categorization.

Spontaneous Aggregation of Convective Storms

2021 ◽  
Vol 54 (1) ◽  
Author(s):  
Caroline Muller ◽  
Da Yang ◽  
George Craig ◽  
Timothy Cronin ◽  
Benjamin Fildier ◽  
...  
Keyword(s):  
Hydrological Cycle ◽  
Theoretical Work ◽  
Annual Review ◽  
Publication Date ◽  
Tropical Atmosphere ◽  
Physical Processes ◽  
Convective Storms ◽  
Warming Climate ◽  
Cloudy Region ◽  
Self Aggregation

Idealized simulations of the tropical atmosphere have predicted that clouds can spontaneously clump together in space, despite perfectly homogeneous settings. This phenomenon has been called self-aggregation, and it results in a state where a moist cloudy region with intense deep convective storms is surrounded by extremely dry subsiding air devoid of deep clouds. We review here the main findings from theoretical work and idealized models of this phenomenon, highlighting the physical processes believed to play a key role in convective self-aggregation. We also review the growing literature on the importance and implications of this phenomenon for the tropical atmosphere, notably, for the hydrological cycle and for precipitation extremes, in our current and in a warming climate. Expected final online publication date for the Annual Review of Fluid Mechanics, Volume 54 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

scholarly journals The Long-Term Variability of Luminous Blue Variables

1999 ◽  
Vol 169 ◽  
pp. 243-248
Author(s):  
Roberta M. Humphreys
Keyword(s):  
Light Curve ◽  
Luminous Blue Variables ◽  
Second Peak ◽  
Hr Diagram

AbstractThe stars known as Luminous Blue Variables include two very distinctive subgroups - the S Dor-type variables which basically define what we call an LBV and the much rarer ‘giant eruption’ LBV’s which include famous stars like η Car and P Cyg. The distinctive characteristics and long term variability of these two groups is reviewed. The lesser 1890 eruption of η Car is shown to have been much more significant than previously believed and resembles the second peak seen in the historic light curve of P Cyg. Because so many, if not all, stars in certain parts of the HR diagram appear to be luminous, blue, and variable, I suggest returning to our previous designation - S Dor variables and η Car variables for these two important groups of stars.

scholarly journals Observations and Interpretation of Luminous Blue Variables

1995 ◽  
Vol 155 ◽  
pp. 176-191
Author(s):  
Henny J.G.L.M. Lamers
Keyword(s):  
Effective Temperature ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Variable Mass ◽  
Mode Interaction ◽  
Stellar Radius ◽  
Luminous Blue Variables ◽  
Different Types ◽  
Apparent Variation ◽  
Eddington Limit

AbstractThe different types of variations of LBVs are discussed. The “typical LBV variations” have amplitudes of ΔV ≃ 0.5 to 2.0 magnitudes and irregular time-scales of months to years. This is due to changes in the stellar radius and the effective temperature. Modelling of this variability for one star, S Dor, shows that the radius of the star varies between 100 and 380 R⊙, the effective temperature between 20,000 and 9,000 K, and the luminosity between log L* = 6.10 to 5.9. The variation of the radius is not an apparent variation of the effective radius of the wind due to a variable mass loss rate (which has often been assumed) but it is a true variation of the radius of the star itself. The changes in L* suggest that about 10−3 to 10−2M* takes part in the expansion of the star. The irregular microvariations with amplitudes of about ΔV ≃ 0.2m on timescales of weeks are probably due to non-adiabatic pulsations with mode-interaction. We argue that LBVs are close to their effective Eddington Limit and discuss a qualitative scenario to explain their location in the HR-diagram.

scholarly journals The HR Diagram

1978 ◽  
Vol 80 ◽  
pp. 101-116
Author(s):  
Jesse L. Greenstein
Keyword(s):  
Chemical Composition ◽  
Broad Band ◽  
Wavelength Region ◽  
Absolute Magnitude ◽  
Coordinate Space ◽  
Evolutionary Status ◽  
Bolometric Luminosity ◽  
The Galaxy ◽  
Stellar Masses ◽  
Hr Diagram

The HR diagram is a useful shorthand locating a star in a two-coordinate space. For the astrophysicist, the y-coordinate is bolometric luminosity, Mbol, the x-coordinate, effective temperature, Teff. Objects of given chemical composition, age (or evolutionary status) are labeled in the xy plane by mass. For an observer, y may be apparent or absolute magnitude in a certain wavelength region and x may be spectral type or color. The HR diagrams for populations differ because of age, chemical composition and stellar masses present. HR diagrams are often of mixed nature; some involve observables others derived or semi-theoretical quantities. I will display various types of HR diagrams for low-luminosity stars. For galactic or extragalactic studies the HR diagram needs a further dimension, the frequency of stars at an x,y. The mass of the Galaxy, but not its light, may be dominated by M dwarfs. HR diagrams are also interesting for their nearly empty spaces. In Fig. 1 we show as a sample, the basic results of the U.S. Naval Observatory parallax program, in which broad band (B-V) colors define the visual luminosity, My, on the main (MS) and degenerate (WD) sequences.

HMOs and Health Services Research: The Penalty of Taking the Lead

1996 ◽  
Vol 53 (1_suppl) ◽  
pp. 18-43 ◽  
Author(s):  
Amy B. Bernstein ◽  
Jill Bernstein
Keyword(s):  
Health Care ◽  
Health Policy ◽  
Health Services Research ◽  
Health Services ◽  
Information Needs ◽  
Health Maintenance Organization ◽  
Services Research ◽  
Health Maintenance ◽  
Future Evolution ◽  
Different Types

Although health maintenance organization (HMO) structures and databases are not uniform across plans, there are unique characteristics of HMO data in general that make them useful in examining health policy and delivery issues. The authors examine differences in data generated by different types of HMOs. After discussing why health services research using HMO data is needed by HMOs, other providers, practitioners, payers, and consumers of health care, the authors examine ways in which HMOs can provide sound answers to crucially important questions about the future of health care. They conclude that although the need for research on HMOs is compelling, researchers need to understand the information needs of HMOs and the incentives that are shaping the industry's approach to system delivery and clinical outcomes research. If HMOs do not take the lead in conducting health services research, they will diminish their role in shaping policies that will shape their future evolution.

scholarly journals Nearshore Wave Transformation Domains from Video Imagery

2019 ◽  
Vol 7 (6) ◽  
pp. 186 ◽  
Author(s):  
Umberto Andriolo
Keyword(s):  
Sediment Transport ◽  
Intensity Variation ◽  
Wave Transformation ◽  
Physical Processes ◽  
Pixel Intensity ◽  
Wave Characteristics ◽  
Wide Range ◽  
Different Types ◽  
Propagation Properties ◽  
Wave Properties

Within the nearshore area, three wave transformation domains can be distinguished based on the wave properties: shoaling, surf, and swash zones. The identification of these distinct areas is relevant for understanding nearshore wave propagation properties and physical processes, as these zones can be related, for instance, to different types of sediment transport. This work presents a technique to automatically retrieve the nearshore wave transformation domains from images taken by coastal video monitoring stations. The technique exploits the pixel intensity variation of image acquisitions, and relates the pixel properties to the distinct wave characteristics. This allows the automated description of spatial and temporal extent of shoaling, surf, and swash zones. The methodology was proven to be robust, and capable of spotting the three distinct zones within the nearshore, both cross-shore and along-shore dimensions. The method can support a wide range of coastal studies, such as nearshore hydrodynamics and sediment transport. It can also allow a faster and improved application of existing video-based techniques for wave breaking height and depth-inversion, among others.

scholarly journals Comparing the host galaxies of different type supernovae

2015 ◽  
Vol 11 (S319) ◽  
pp. 139-139
Author(s):  
Y. C. Liang ◽  
X. Shao ◽  
M. Dennefeld ◽  
X. Y. Chen ◽  
L. Zhou ◽  
...  
Keyword(s):  
Stellar Mass ◽  
Significant Fraction ◽  
Host Galaxies ◽  
Global Properties ◽  
Different Types ◽  
Type Ia ◽  
Total Light ◽  
Stellar Masses ◽  
Almost All ◽  
Cross Matching

AbstractWe compare the host galaxies of 902 supernovae, including Type Ia, II and Ibc, which are selected by cross-matching the Asiago Supernova Catalog with the SDSS DR7. We further selected 213 galaxies by requiring the light fraction of spectral observations > 15%, which could represent well the global properties of the galaxies. The diagrams related to Dn(4000), HδA, stellar masses, SFRs and specific SFRs for the SNe hosts show that almost all SNe II and most of SNe Ibc occur in SF galaxies. A significant fraction of SNe Ia occurs in AGNs and Absorp galaxies. These results are compared with those of the 689 comparison galaxies where the SDSS fiber captures < 15% of the total light. These comparison galaxies appear biased towards higher 12+log(O/H) (~0.1dex) at a given stellar mass, suggesting the aperture effect should be kept in mind when the properties of the hosts for different types of SNe are discussed.

scholarly journals Planet forming disks, debris disks and the Solar System

2019 ◽  
Vol 15 (S350) ◽  
pp. 207-215
Author(s):  
Inga Kamp
Keyword(s):  
Chemical Composition ◽  
Solar System ◽  
Planetary Systems ◽  
Theoretical Work ◽  
Structure Evolution ◽  
Debris Disks ◽  
Physical Processes ◽  
Disk Structure ◽  
Open Questions ◽  
Evolution Modeling

AbstractVLT instruments and ALMA with their high spatial resolution have revolutionized in the past five years our view and understanding of how disks turn into planetary systems. This talk will briefly outline our current understanding of the physical processes occurring and chemical composition evolving as these disks turn into debris disks and eventually planetary systems like our own solar system. I will especially focus on the synergy between disk structure/evolution modeling and astrochemical laboratory/theoretical work to highlight the most recent advances, and open questions such as (1) how much of the chemical composition in disks is inherited from molecular clouds, (2) the relevance of snowlines for planet formation, and (3) what is the origin of the gas in debris disks and what can we learn from it. For each of the three, I will outline briefly how the combination of theory/lab astrochemistry, astrophysical models and observations are required to advance our understanding.

scholarly journals Are the Fractionation Corrections Correct: Are the Isotopic Shifts for 14C/12C Ratios in Physical Processes and Chemical Reactions Really Twice Those for 13C/12C?

Radiocarbon ◽  
2011 ◽  
Vol 53 (4) ◽  
pp. 691-704 ◽  
Author(s):  
John Southon
Keyword(s):  
Chemical Reactions ◽  
Isotopic Fractionation ◽  
Theoretical Work ◽  
Chemical Processes ◽  
Physical Processes ◽  
Isotopic Discrimination ◽  
True Value ◽  
A Value ◽  
Isotopic Shifts ◽  
Physical And Chemical

Conventional radiocarbon calculations correct for isotopic fractionation using an assumed value of 2.0 for the fractionation of 14C relative to 13C. In other words, isotopic discrimination in physical and chemical processes is assumed to cause relative shifts in 14C/12C ratios that are exactly double those of 13C/12C. This paper analyzes a 1984 experiment that produced a value for the fractionation ratio in photosynthesis of 2.3, which is used to this day by some researchers in the fields of hydrology and speleothem geochemistry. While the value of 2.3 is almost certainly incorrect, theoretical work suggests that the true value may indeed deviate from 2.0, which would have significant implications for 14C calculations.

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