scholarly journals Link to the Physical Modelling with an Emphasis on Chemical Peculiarities

1995 ◽  
Vol 10 ◽  
pp. 415-418
Author(s):  
G. Mathys
Keyword(s):  
Physical Modelling ◽  
Physical Processes ◽  
Distribution Fitting ◽  
Physical Conditions ◽  
Elemental Abundances ◽  
Abundance Patterns ◽  
Spectral Ranges ◽  
Ap Stars ◽  
Selection Of ◽  
Broad Continuum

Frequently, the atmospheres of stars of spectral types B to F, on which the attention is particularly focussed in this Joint Discussion, are characterized by non-standard physical conditions: non-solar abundance patterns, surface in homogeneities, strong magnetic fields. The most extreme anomalies are found in the chemically peculiar (CP) stars but more moderate departures from standard atmospheres are observed in many stars in the considered temperature range. This can affect the derivation of fundamental stellar parameters in a number of ways, some of which will be presented in this contribution. The emphasis is set on those physical processes which are specific to CP stars. Due to lack of space, this review is necessarily incomplete: a selection of recent results of interest will be pointed out and some directions of investigation will be suggested.CP stars have an anomalous continuous energy distribution. Fitting this distribution by standard model atmospheres can only be achieved using models corresponding to different effective temperatures to represent different spectral ranges (e.g., Leone & Catalano 1991). This is obviously not physically meaningful: the effective temperature characterizes the total flux of a star, thus is unique. “Realistic” models must incorporate the anomalous elemental abundances. Such models are presently being developed by Kurucz (ATLAS12) and by the Vienna group (Weiss 1994, private communication). The latter is adapted from Muthsam’s (1979) code. One important result obtained by Muthsam is that the relation T(τ) appears steeper in magnetic Ap stars than in normal stars. This view recently received support from observations of rapid oscillations (Matthews et al. 1990). But even such realistic models may not represent satisfactorily CP star atmospheres, as some potentially important opacity sources may still be unknown. For instance, the broad continuum depressions observed in many magnetic CP stars have not been fully explained yet.

Extended Observations and New Insights of Dynamically Triggered Tremor in Parkfield

2021 ◽  
Author(s):  
Allie Hutchison ◽  
Piero Poli
Keyword(s):  
San Andreas Fault ◽  
Peak Ground Velocity ◽  
Dynamic Strain ◽  
Frequency Content ◽  
Physical Processes ◽  
Dynamic Triggering ◽  
Physical Conditions ◽  
San Andreas ◽  
Triggered Tremor ◽  
Selection Of

<p>We create an extended catalog of dynamically triggered tremor in the Parkfield region of the San Andreas Fault for teleseismic and regional earthquakes from 2001-2020 with a magnitude threshold of M >7. After selection of clear dynamic triggering episodes, each tremor event is precisely located using a multi station approach. Using this new catalog of triggered tremor, we quantitatively evaluate the conditions under which tremor is triggered. In particular, we study the effect of frequency dependent peak dynamic strain, peak ground velocity, and the incident azimuth of triggering waves. We further try to assess if the triggering potential in the San Andreas Fault evolves as function of time. Finally, we search for differences and similarities (e.g. frequency content, location) between triggered and regular tremor. Our observations provide new insights about the physical conditions necessary for triggering tremor, and in general, on the physical processes generating non-volcanic tremors.</p>

scholarly journals A New Opacity-Sampling Model Atmosphere Program for Arbitrary Abundances

1993 ◽  
Vol 138 ◽  
pp. 87-97 ◽  
Author(s):  
Robert L. Kurucz
Keyword(s):  
Distribution Function ◽  
Energy Level ◽  
Lower Energy ◽  
Van Der Waals ◽  
Model Atmosphere ◽  
Function Model ◽  
Elemental Abundances ◽  
Lower Energy Level ◽  
Molecular Lines ◽  
Ap Stars

AbstractI have developed a new version of my model atmosphere program called ATLAS12. It recognizes more than 1000 species, each in up to 10 isotopic forms, including all ions of the elements up through Zn and the first 5 ions of heavier elements up through Es. The elemental abundances are treated as variable with depth. ATLAS12 has 6 input files of line data containing 58,000,000 atomic and molecular lines. For each line the wavelength, identification, lower energy level, gf, radiative, Stark, and van der Waals damping constants are packed into 16 bytes. At each wavelength point in a frequency integration the profiles of all the significant nearby lines are computed and summed. The program and line files will be distributed in the fall of 1992.There are no significant differences at A0 between an opacity-sampled model computed with ATLAS12 and opacity-distribution-function model computed with ATLAS9. ATLAS12 allows arbitrary abundances but is slower. The new program can be used to produce improved models for Am and Ap stars that include the effects of millions of lines.

scholarly journals Spectrophotometry of the Broad Continuum Features in Magnetic AP Stars

1986 ◽  
Vol 90 ◽  
pp. 201-204
Author(s):  
Diane M. Pyper ◽  
Saul J. Adelman
Keyword(s):  
Color Temperature ◽  
Absorption Feature ◽  
Intensity Maximum ◽  
Energy Distributions ◽  
Broad Absorption ◽  
Solar Abundance ◽  
Normal Star ◽  
Ap Stars ◽  
Relationship Of ◽  
Broad Continuum

The strongest broad absorption feature in the peculiar energy distributions of the Ap stars is that centered at about 5200 Å, thus the Stromgren y band and the Geneva VI band are most affected in stars in which this feature is strong. Fig. 1 shows bandpasses (full width at ½ intensity maximum) of three widely used photometric systems superimposed on two of our scans of Ap stars and two solar abundance line blanketed model atmospheres (Kurucz 1979). It is seen that both the y and VI bands fall entirely within the λ5200 feature. The plot (Fig. 2a) of b-y vs. Tpc (the color temperature of the red end of the Paschen continuum), shows that the b-y colors for most of our sample of Ap stars are displaced to the blue of the b-y, Teff relationship of Relyea and Kurucz (1978). In Fig. 2b, Δ(b−y) = (model b−y) − (observed b−y), for a given temperature is plotted vs. ΔWS2(5200), a spectrophotometric index measuring the equivalent width of the λ5200 feature. There is a strong correlation between Δ(b-y) and ΔWS2(5200), indicating quantitatively the large effect of the λ5200 feature on the y band, previously discussed by Adelman (1979). The deviations in Ap star B2-G values from the normal star B2-G vs. T curve are much less than for b-y, as the Geneva G band is largely outside the λ5200 feature (Fig. 2c). Thus B2-G is a better temperature indicator for Ap stars than is b-y (also see Hauck and North 1982).

scholarly journals Discovery of Secular Evolution of the Atmospheric Abundances of Ap Stars

2014 ◽  
Vol 9 (S307) ◽  
pp. 365-366
Author(s):  
J. D. Bailey ◽  
J. D. Landstreet ◽  
S. Bagnulo
Keyword(s):  
Main Sequence ◽  
Chemical Abundance ◽  
Mixing Processes ◽  
Chemical Tracers ◽  
Secular Evolution ◽  
Abundance Patterns ◽  
Chemically Peculiar ◽  
Peculiar Stars ◽  
Chemically Peculiar Stars ◽  
Ap Stars

AbstractThe stars of the middle main-sequence have relatively quiescent outer layers, and unusual chemical abundance patterns may develop in their atmospheres, revealing the action of such subsurface phenomena as gravitational settling and radiatively driven levitation of trace elements, and their competition with mixing processes such as turbulent diffusion. We report the discovery of the time evolution of such chemical tracers through the main-sequence lifetime of magnetic chemically peculiar stars.

Stochastic accretion of the Earth

2020 ◽  
Author(s):  
Paolo Sossi ◽  
Ingo Stotz ◽  
Seth Jacobson ◽  
Alessandro Morbidelli ◽  
Hugh O'Neill
Keyword(s):  
Building Blocks ◽  
Physical Processes ◽  
Volatile Elements ◽  
Volatile Element ◽  
Elemental Abundances ◽  
Stable Isotope Fractionation ◽  
The Earth ◽  
Gravitational Pull ◽  
Atmospheric Loss ◽  
Impact Events

<p>The Earth is depleted in volatile elements relative to chondritic meteorites, its possible building blocks. Abundances of volatile elements descend roughly log-linearly with their calculated volatilities during solar nebula condensation [1, 2]. This depletion, however, is not accompanied by any stable isotope fractionation, which would otherwise be expected during vaporisation/condensation and atmospheric loss attending accretion [3, 4]. Thus, the physical processes that led to the formation of the Earth are yet to be reconciled with its chemical composition. Here, we integrate N-body simulations of planetary formation [5] within a framework that combines estimates for the compositions of planetary building blocks with volatile element losses during collisions, to link Earth’s elemental- and isotopic make-up with accretion mechanisms. The smooth pattern of volatile depletion in the Earth reflects the stochastic accretion of numerous, smaller, partially-vaporised precursor bodies whose elemental abundances are set by the heliocentric distances at which they formed. Impact events engender vaporisation, but atmospheric loss is only efficient during the early stages of accretion when volatile species can readily escape the gravitational pull of the proto-Earth. The chemical and isotopic compositions of the most volatile elements are controlled by that of late-accreting material, during which time the proto-Earth is sufficiently large so as to limit atmospheric loss. Stable isotopes of moderately- and highly volatile elements thus retain near-chondritic compositions.</p> <p>[1] O’Neill and Palme (2008), <em>Phil. Trans. R. Soc.</em> 4205-38 [2] Braukmüller et al. (2019), <em>Nat. Geosci.</em>, 564-9 [3] Wang and Jacobsen (2016), <em>Nature</em>, 521-4 [4] Sossi et al. 2018, <em>Chem. Geol.</em> 73-84 [5] Jacobson and Morbidelli (2014), <em>Phil. Trans. R. Soc.</em> 20130174</p>

Ice lines and the formation of Uranus and Neptune

2020 ◽  
Author(s):  
Olivier Mousis ◽  
Artyom Aguichine ◽  
Ravit Helled ◽  
Patrick Irwin ◽  
Jonathan I. Lunine
Keyword(s):  
Chemical Composition ◽  
Transport Model ◽  
Outer Region ◽  
Building Blocks ◽  
Planetary Formation ◽  
Physical Conditions ◽  
Elemental Abundances ◽  
Self Consistent ◽  
Protosolar Nebula ◽  
Do So

<p>We aim at investigating whether the chemical composition of the outer region of the protosolar nebula can be consistent with current estimates of the elemental abundances in the ice giants. To do so, we use a self-consistent evolutionary disc and transport model to investigate the time and radial distributions of H<sub>2</sub>O, CO, N<sub>2</sub>, and H<sub>2</sub>S, i.e., the main O-, C-, N, and S-bearing volatiles in the outer disc. We show that it is impossible to accrete a mixture composed of gas and solids from the disc with a C/H ratio presenting enrichments comparable to the measurements (70 times protosolar). We also find that the C/N and C/S ratios measured in Uranus and Neptune are compatible with those acquired by building blocks agglomerated from grains and pebbles condensed in the vicinities of N<sub>2</sub> and CO ice lines in the nebula. In contrast, the presence of protosolar C/N and C/S ratios in Uranus and Neptune would imply that their building blocks agglomerated from particles condensed at higher heliocentric distances. Our study demonstrates the importance of measuring the elemental abundances in the ice giant atmospheres, as they can be used to trace the planetary formation location and/or the chemical and physical conditions of the protosolar nebula.<span class="Apple-converted-space"> </span></p>

THE SYNTHESIS OF SEISMOGRAMS FROM WELL LOG DATA

Geophysics ◽  
1955 ◽  
Vol 20 (3) ◽  
pp. 516-538 ◽  
Author(s):  
R. A. Peterson ◽  
W. R. Fillippone ◽  
F. B. Coker
Keyword(s):  
Analogue Computer ◽  
Physical Processes ◽  
Physical Conditions ◽  
Interesting Insight ◽  
Close Relationship ◽  
Seismic Records ◽  
Set Up ◽  
Well Data ◽  
Seismic Reflections ◽  
Insight Into

Under certain simplified but realistic physical assumptions, the basic data from continuous velocity surveys in wells can be used to simulate the variations in acoustic impedance in the ground which give rise to seismic reflections. An analogue computer is described which makes use of the basic well data to produce synthetic seismic records which resemble actual seismograms from shothole explosions. This process provides an interesting insight into the requisite physical conditions, as well as the physical processes, whereby seismic reflections are set up in the earth. The close relationship between seismograms and well logs is brought out. Illustrations are given of field results.

Food Consumption and Handling Survey for Quantitative Microbiological Consumer Phase Risk Assessments

2016 ◽  
Vol 79 (7) ◽  
pp. 1221-1233 ◽  
Author(s):  
JURGEN CHARDON ◽  
ARNO SWART
Keyword(s):  
Food Consumption ◽  
Parameter Estimates ◽  
Food Handling ◽  
Distribution Fitting ◽  
Uncertainty Estimates ◽  
Data Gaps ◽  
Consumption Practices ◽  
Mathematical Equations ◽  
Fitting In ◽  
Selection Of

ABSTRACT In the consumer phase of a typical quantitative microbiological risk assessment (QMRA), mathematical equations identify data gaps. To acquire useful data we designed a food consumption and food handling survey (2,226 respondents) for QMRA applications that is especially aimed at obtaining quantitative data. For a broad spectrum of food products, the survey covered the following topics: processing status at retail, consumer storage, preparation, and consumption. Questions were designed to facilitate distribution fitting. In the statistical analysis, special attention was given to the selection of the most adequate distribution to describe the data. Bootstrap procedures were used to describe uncertainty. The final result was a coherent quantitative consumer phase food survey and parameter estimates for food handling and consumption practices in The Netherlands, including variation over individuals and uncertainty estimates.

scholarly journals On content, migration and concentration of heavy metals in oils (by the example of the Dnieper-Donets Depression)

2019 ◽  
Vol 4 (181) ◽  
pp. 96-103
Author(s):  
Artem YEROFIEIEV ◽  
Ihor BEREZOVSKY
Keyword(s):  
Heavy Metals ◽  
Measurement Errors ◽  
Oil And Gas ◽  
Geological Structure ◽  
X Ray ◽  
Physical Conditions ◽  
Sediment Formation ◽  
Abnormal Accumulation ◽  
Ore Mineralization ◽  
Selection Of

Literature review and analysis of previous studies of the problem was carried. The main scientific works on the research topic, as well as the main directions and stages of the study are indicated. Similar studies that were conducted on the territory of Ukraine are considered. The results of the study of heavy metals in oil samples taken from a large oil and gas region from more than thirty deposits of Ukraine are presented. All current and non-working fields are considered. The geological structure of the oil and gas province, as well as the main geochemical features of the formation of mineral deposits are considered. The main forms of finding target metals, as well as possible ways of transferring these elements in the earth’s crust are given. Samples were investigated using x-ray fluorescence and neutron activation analysis. The obtained research data in the framework of two selected methods are combined for analysis. The results obtained within the same geological structure are compared with each other to determine the effect of the physical conditions of sediment formation on the microcomponent composition of crude oil. They also compared the effect of physical conditions on the properties of oil and their ability to accumulate heavy metals. Possible causes of the abnormal accumulation of heavy metals due to the close occurrence of oil and formation water are noted. According to the results obtained, a graph is constructed of the dependence of the mineralization of oil on its depth. An exponential graphical approximation is presented to display the general trend of dependence. Possible sources and ways of migration and accumulation of heavy metals in hydrocarbons are analyzed. The concept of the migration of heavy metals in oil is proposed in conjunction with the ore mineralization of adjacent and adjacent deposits. Possible causes of differences in the concentrations of heavy metals in oil of various geological structures are indicated, as well as the main possible causes of measurement errors and complications in the selection of each of the analysis methods are specified.

scholarly journals Behaviour of Al2O3 in aluminium matrix composites: An overview

2021 ◽  
Vol 309 ◽  
pp. 01028
Author(s):  
Lokesh Singh ◽  
Shankar Sehgal ◽  
K. Saxena Kuldeep
Keyword(s):  
Metal Matrix Composite ◽  
Matrix Composite ◽  
Metal Matrix ◽  
Aluminium Matrix ◽  
Matrix Composites ◽  
Aluminium Matrix Composites ◽  
Physical Conditions ◽  
Alumina Particles ◽  
Composite Properties ◽  
Selection Of

In this paper, behaviour of Al2O3 in aluminium matrix composites is reviewed for its properties and applications. In addition, many metal matrix composite fabrication processes are also elaborated. In the present days the aluminium metal matrix composite is in high demand because of its superior properties. Its demand is still on rise because of its widespread use in automotive industries, aerospace industries and marine industries. The method of the fabrication of aluminium matrix-based composite is also a deciding factor for its resultant properties. Desired composite-properties are achievable by proper selection of reinforcing materials as well as the physical conditions. Various sections of current information compile the details about the behaviour of alumina particles in aluminium-based matrix for formation of metal matrix composites.

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