scholarly journals Predicted X-ray fluxes of stellar coronas

1970 ◽  
Vol 37 ◽  
pp. 238-241
Author(s):  
C. De Loore ◽  
C. De Jager
Keyword(s):  
Mechanical Energy ◽  
Energy Fluxes ◽  
X Ray ◽  
Effective Temperatures ◽  
Acceleration Of Gravity

Models of convection zones and corresponding mechanical energy fluxes were computed for 90 stellar photospheres with effective temperatures ranging from 2500 K to 41 600 K and acceleration of gravity values between 1 and 105. The most intense X-ray fluxes may be expected from stars with T ≈ 7200 K and logg ≈ 4. Detectable X-ray fluxes could be expected from Procyon, α Cen and β Cas.

scholarly journals Structural Disorder of Mechanically Activated δ-MgCl2 Studied by Synchrotron X-ray Total Scattering and Vibrational Spectroscopy

Catalysts ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1089
Author(s):  
Toru Wada ◽  
Ashutosh Thakur ◽  
Patchanee Chammingkwan ◽  
Minoru Terano ◽  
Toshiaki Taniike ◽  
...  
Keyword(s):  
Early Stage ◽  
Mechanical Energy ◽  
Structural Disorder ◽  
Reliable Determination ◽  
Total Scattering ◽  
X Ray ◽  
Powerful Approach ◽  
Ft Ir ◽  
Grinding Time

A combination of synchrotron X-ray total scattering and molecular simulation is a powerful approach for reliable determination of the structure of δ-MgCl2 as an indispensable component of heterogeneous Ziegler–Natta catalysts. Here, the same approach is applied to mechanically activated MgCl2. Four types of mechanically activated MgCl2 samples are prepared using ball-milling in the absence and presence of different donors. The development of structural disorder along the grinding time is compared. It was found that the presence of donors accelerates the formation of δ-MgCl2 in an early stage of grinding, while elongated grinding eventually results in δ-MgCl2 with similar extents of structural disorder in the absence and presence of different donors. The FT-IR investigation consistently verified the morphological similarity between the firmly ground samples. Thus, the structure of δ-MgCl2 is likely governed by mechanical energy when sufficiently ground.

Ball-Milling Stimulated Mechanochemical Processes in the System “Titanium-Toluene”

2019 ◽  
Vol 946 ◽  
pp. 351-356 ◽  
Author(s):  
Olga M. Kanunnikova ◽  
V.V. Aksenova ◽  
G.A. Dorofeev
Keyword(s):  
Ball Milling ◽  
Mechanical Energy ◽  
High Energy ◽  
X Ray Diffraction ◽  
X Ray ◽  
Liquid Phases ◽  
Ft Ir ◽  
Titanium Powders ◽  
Solid Phases ◽  
Ft Ir Spectroscopy

The present work deals with the investigation of the transformations of the solid and liquid phases at high energy planetary ball milling of toluene together with titanium powder. The sequence of structural toluene transformations using FT-IR spectroscopy was investigated. Phase constitutions and morphology of ball milled titanium powders were studied by X-ray diffraction and scanning electron microscopy. It is shown that mechanically induced destruction of toluene occurs by the mechanism of catalytic cracking. During ball milling, concentration of aromatic hydrocarbons in the liquid phase decreases, at the same time the content of alkenes, cycloalkanes, and isoalkanes increases. The main solid products of the mechanosynthesis were cubic and hexagonal titanium carbo-hydrides.Evolution of lattice parameters, crystallites sizes, and micro-stresses of the solid phases during ball milling as a function of the mechanical energy dose have been discussed.

scholarly journals Model Atmospheres for Cooling Neutron Stars

1987 ◽  
Vol 125 ◽  
pp. 459-459
Author(s):  
Roger W. Romani ◽  
Roger D. Blandford ◽  
Lars Hernquist
Keyword(s):  
Neutron Stars ◽  
Supernova Remnants ◽  
Equations Of State ◽  
Black Body ◽  
X Ray ◽  
Electron Heat ◽  
Parallel Field ◽  
Effective Temperatures ◽  
Calculated Model ◽  
Magnetic Case

The failure of Einstein X-ray observations to detect central neutron stars in most young supernova remnants (Helfand and Becker 1984) has provided interesting constraints on cooling theories (cf. review by Tsuruta 1985). The comparison of the measured fluxes with the predicted effective temperatures is sensitive to the nature of the emitted spectrum, commonly assumed to be blackbody. The presence of a substantial absorbing atmosphere can, however, produce significant departures. We have calculated model atmospheres for unmagnetized neutron stars with effective temperatures 105K ≦ Teff ≦ 106.5K using Los Alamos opacities and equations of state (Romani 1986). We consider a range of surface compositions, since the accretion of ∼10−19M⊙ will cover the surface to the X-ray photosphere and subsequent settling in the strong gravitational field can severely deplete the heavy species. In a low Z atmosphere (eg. He) the measured X-ray flux will substantially exceed the blackbody value–the Einstein limits on Teff are correspondingly lowered (eg. by ∼1.6 for SN1006 with a helium surface). For high Z atmospheres, the flux is close to the black body value, but prominent absorption edges are present. Recent calculations of the electron heat transport in magnetized neutron star envelopes (Hernquist 1984, 1985) have shown that, contrary to earlier estimates, magnetic fields will have a small effect on the heat flux (≳ 3 for parallel field geometries and ∼1 for tangled fields). Extension of the atmosphere computations to the magnetic case is important for comparison with X-ray observations of known pulsars.

scholarly journals Radio and White-Light Observations of Coronal Transients

1980 ◽  
Vol 86 ◽  
pp. 419-433 ◽  
Author(s):  
G. A. Dulk
Keyword(s):  
White Light ◽  
Driving Force ◽  
Magnetic Energy ◽  
Mechanical Energy ◽  
Interplanetary Shock ◽  
Radio Bursts ◽  
Thermal Emissions ◽  
X Ray ◽  
Magnetic Forces ◽  
Nature Frequency

Optical, radio and X-ray evidence of violent mass motions in the corona has existed for some years but only recently have the form, nature, frequency and implication of the transients become obvious. In this paper I review the observed properties of coronal transients, concentrating on the white-light and radio manifestations. The classification according to speeds seems to be meaningful, with the slow transients having thermal emissions at radio wavelengths and the fast ones non-thermal. I then discuss the possible mechanisms involved in the radio bursts and review the estimates of various forms of energy. It appears that the magnetic energy transported from the Sun by the transient exceeds that of any other form, and that magnetic forces dominate in the dynamics of the motions. The conversion of magnetic energy into mechanical energy, by expansion of the fields, provides a possible driving force for the coronal and interplanetary shock waves.

scholarly journals The Theory of Extended and Expanding Atmospheres

1973 ◽  
Vol 51 ◽  
pp. 148-170
Author(s):  
Karl-Heinz Böhm
Keyword(s):  
Theoretical Study ◽  
Transfer Problem ◽  
Mechanical Energy ◽  
Radiation Force ◽  
Mean Free Path ◽  
Stellar Radius ◽  
Order Of Magnitude ◽  
Acceleration Of Gravity ◽  
Expanding Atmospheres ◽  
Radiative Acceleration

(A) The possibilities and the difficulties of a theoretical study of extended atmospheres in binaries are briefly discussed.(B) We try to summarize and discuss critically the present status of the theory of three types of extended atmospheres (i.e. atmospheres in which the average photon mean-free-path is the same order of magnitude or larger than the stellar radius):(1) Extended atmospheres in hydrostatic and in grey or non-grey radiative equilibrium.(2) Dynamic (expanding) atmospheres which occur if the radiative acceleration is slightly smaller than the acceleration of gravity.(3) Stellar coronae which are formed in the presence of a mechanical energy flux.In (1) we study the importance of the ‘forward peaking’ of the radiation field in the outer layers of the atmosphere. The possibilities for the solution of the non-grey transfer problem in an extended atmosphere are discussed.In (2) we pay special attention to Marlborough's and Roy's (1970) result that the atmospheric gas cannot be accelerated directly to supersonic velocities by the action of the radiation force.In (3) the large differences in the coronal properties of stars of different chemical composition are emphasized. We draw attention to the partially unexplored but probably very interesting properties of coronae of helium-rich stars.

scholarly journals The Cross-Bridge Spring: Can Cool Muscles Store Elastic Energy?

Science ◽  
2013 ◽  
Vol 340 (6137) ◽  
pp. 1217-1220 ◽  
Author(s):  
N. T. George ◽  
T. C. Irving ◽  
C. D. Williams ◽  
T. L. Daniel
Keyword(s):  
Energy Storage ◽  
Elastic Energy ◽  
Molecular Motors ◽  
High Speed ◽  
Mechanical Energy ◽  
Elastic Strain Energy ◽  
Time Resolved ◽  
X Ray ◽  
Cross Bridge ◽  
Cross Bridges

Muscles not only generate force. They may act as springs, providing energy storage to drive locomotion. Although extensible myofilaments are implicated as sites of energy storage, we show that intramuscular temperature gradients may enable molecular motors (cross-bridges) to store elastic strain energy. By using time-resolved small-angle x-ray diffraction paired with in situ measurements of mechanical energy exchange in flight muscles of Manduca sexta, we produced high-speed movies of x-ray equatorial reflections, indicating cross-bridge association with myofilaments. A temperature gradient within the flight muscle leads to lower cross-bridge cycling in the cooler regions. Those cross-bridges could elastically return energy at the extrema of muscle lengthening and shortening, helping drive cyclic wing motions. These results suggest that cross-bridges can perform functions other than contraction, acting as molecular links for elastic energy storage.

scholarly journals Energy Flux Paths in Lakes and Reservoirs

Water ◽  
2021 ◽  
Vol 13 (22) ◽  
pp. 3270
Author(s):  
Sofya Guseva ◽  
Peter Casper ◽  
Torsten Sachs ◽  
Uwe Spank ◽  
Andreas Lorke
Keyword(s):  
Wind Energy ◽  
Turbulent Flows ◽  
Internal Waves ◽  
Energy Flux ◽  
Energy Content ◽  
Mechanical Energy ◽  
Energy Fluxes ◽  
Ecological Processes ◽  
Basin Scale ◽  
Lakes And Reservoirs

Mechanical energy in lakes is present in various types of water motion, including turbulent flows, surface and internal waves. The major source of kinetic energy is wind forcing at the water surface. Although a small portion of the vertical wind energy flux in the atmosphere is transferred to water, it is crucial for physical, biogeochemical and ecological processes in lentic ecosystems. To examine energy fluxes and energy content in surface and internal waves, we analyze extensive datasets of air- and water-side measurements collected at two small water bodies (<10 km2). For the first time we use directly measured atmospheric momentum fluxes. The estimated energy fluxes and content agree well with results reported for larger lakes, suggesting that the energetics governing water motions in enclosed basins is similar, independent of basin size. The largest fraction of wind energy flux is transferred to surface waves and increases strongly nonlinearly for wind speeds exceeding 3 m s−1. The energy content is largest in basin-scale and high-frequency internal waves but shows seasonal variability and varies among aquatic systems. At one of the study sites, energy dissipation rates varied diurnally, suggesting biogenic turbulence, which appears to be a widespread phenomenon in lakes and reservoirs.

scholarly journals Radio and X-Ray Emissions from Chemically Peculiar B- and A-Type Stars: Observations and a Model

1993 ◽  
Vol 138 ◽  
pp. 507-516 ◽  
Author(s):  
Jeffrey L. Linsky
Keyword(s):  
Energy Source ◽  
Stellar Wind ◽  
Mechanical Energy ◽  
Early Type ◽  
Late Type ◽  
X Ray ◽  
Nonthermal Radio ◽  
Chemically Peculiar ◽  
Early Type Stars

AbstractConventional wisdom holds that early-type and late-type stars have very different outer atmospheres, because the early-type stars lack deep convective zones. I argue that the magnetic chemically peculiar (CP) stars hotter than about spectral type A2 display many of the activity phenomena seen in the most active late-type stars. In particular, many CP stars are luminous nonthermal radio and coronal x-ray sources like the RS CVn systems. A wind-fed magnetosphere model has been proposed to explain both the nonthermal radio and the x-ray emission. In this model the stellar wind plays the role of a mechanical energy source analogous to the role played by convection in the active late-type stars.

scholarly journals Stellar population of the superbubble N 206 in the LMC

2017 ◽  
Vol 609 ◽  
pp. A7 ◽  
Author(s):  
Varsha Ramachandran ◽  
R. Hainich ◽  
W.-R. Hamann ◽  
L. M. Oskinova ◽  
T. Shenar ◽  
...  
Keyword(s):  
Energy Input ◽  
Large Scale ◽  
Massive Stars ◽  
Mechanical Energy ◽  
Mass Loss Rate ◽  
Large Magellanic Cloud ◽  
High Mass ◽  
Clear Correlation ◽  
Physical Parameters ◽  
X Ray

Context. Massive stars severely influence their environment by their strong ionizing radiation and by the momentum and kinetic energy input provided by their stellar winds and supernovae. Quantitative analyses of massive stars are required to understand how their feedback creates and shapes large scale structures of the interstellar medium. The giant H ii region N 206 in the Large Magellanic Cloud contains an OB association that powers a superbubble filled with hot X-ray emitting gas, serving as an ideal laboratory in this context. Aims. We aim to estimate stellar and wind parameters of all OB stars in N 206 by means of quantitative spectroscopic analyses. In this first paper, we focus on the nine Of-type stars located in this region. We determine their ionizing flux and wind mechanical energy. The analysis of nitrogen abundances in our sample probes rotational mixing. Methods. We obtained optical spectra with the multi-object spectrograph FLAMES at the ESO-VLT. When possible, the optical spectroscopy was complemented by UV spectra from the HST, IUE, and FUSE archives. Detailed spectral classifications are presented for our sample Of-type stars. For the quantitative spectroscopic analysis we used the Potsdam Wolf-Rayet model atmosphere code. We determined the physical parameters and nitrogen abundances of our sample stars by fitting synthetic spectra to the observations. Results. The stellar and wind parameters of nine Of-type stars, which are largely derived from spectral analysis are used to construct wind momentum − luminosity relationship. We find that our sample follows a relation close to the theoretical prediction, assuming clumped winds. The most massive star in the N 206 association is an Of supergiant that has a very high mass-loss rate. Two objects in our sample reveal composite spectra, showing that the Of primaries have companions of late O subtype. All stars in our sample have an evolutionary age of less than 4 million yr, with the O2-type star being the youngest. All these stars show a systematic discrepancy between evolutionary and spectroscopic masses. All stars in our sample are nitrogen enriched. Nitrogen enrichment shows a clear correlation with increasing projected rotational velocities. Conclusions. The mechanical energy input from the Of stars alone is comparable to the energy stored in the N 206 superbubble as measured from the observed X-ray and Hα emission.

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