Interplanetary gas. viii - on the importance of radiative losses.
Radiative losses for all ions in the extended solar corona
INTERPLANETARY GAS↗
SEARCH · Engineering Papers
Results for “Radiation losses”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
INTERPLANETARY GAS. VIII. ON THE ROLE OF RADIATIVE LOSSES INTERPLANETARY GAS. VIII. ON THE ROLE OF RADIATIVE LOSSES
Radiative losses evaluated for all significant ions present in interplanetary gas from 4 to 215 radii - solar corona energy balance
INTERPLANETARY GAS↗
Radiative Losses in the Chromosphere During A C-Class Flare
Context. Solar flares release an enormous amount of energy (~10(exp 32) erg) into the corona. A substantial fraction of this energy is transported to the lower atmosphere, which results in chromospheric heating. The mechanisms that transport energy to the lower solar atmosphere during a flare are still not fully understood. Aims. We aim to estimate the temporal evolution of the radiative losses in the chromosphere at the footpoints of a C-class flare, in order to set observational constraints on the electron beam parameters of a RADYN flare simulation. Methods. We estimated the radiative losses from hydrogen, and singly ionized Ca and Mg using semiempirical model atmospheres, which were inferred from a multiline inversion of observed Stokes profiles obtained with the CRISP and CHROMIS instruments on the Swedish 1-m Solar Telescope. The radiative losses were computed taking into account the effect of partial redistribution and non-local thermodynamic equilibrium. To estimate the integrated radiative losses in the chromosphere, the net cooling rates were integrated between the temperature minimum and the height where the temperature reaches 10 kK. We also compared our time series of radiative losses with those from the RADYN flare simulations. Results. We obtained a high spatial-resolution map of integrated radiative losses around the flare peak time. The stratification of the net cooling rate suggests that the Ca IR triplet lines are responsible for most of the radiative losses in the flaring atmosphere. During the flare peak time, the contribution from Ca II H and K and Mgii h and k lines are strong and comparable to the Ca IR triplet (~32kW m(exp -2)). Since our flare is a relatively weak event, the chromosphere is not heated above 11 kK, which in turn yields a subdued Lyα contribution (~7kW m(exp -2)) in the selected limits of the chromosphere. The temporal evolution of total integrated radiative losses exhibits sharply rising losses (0.4kW m(exp -2) (s(exp -1)) and a relatively slow decay (0.23kW m(exp -2) s(exp -1)). The maximum value of total radiative losses is reached around the flare peak time and can go up to 175kWm2 for a single pixel located at footpoint. After a small parameter study, we find the best model-data consistency in terms of the amplitude of radiative losses and the overall atmospheric structure with a RADYN flare simulation in the injected energy flux of 5 × 10(exp 10) erg s(exp -1) cm(exp -2).
Chromosphere↗
Extinction of premixed flames by stretch and radiative loss
The extinction of laminar premixed flames by stretch and radiative loss is studied for the model problem of counterflow opposed-jet combustion by using the matched asymptotic expansion technique for the highly temperature sensitive processes of radiative heat loss and large-activation-energy reaction kinetics. Explicit expressions for the critical Damkoehler number at extinction are derived and the influence of upstream vs downstream heat losses assessed. Results show that stretch exerts a much stronger influence than radiative loss on flame extinction.
Sohrab, S. H.↗
Radiation losses in resonant tubes
The role of radiation losses in a resonant tube - the transfer of sound energy from the test gas through the confines of the tube to the ambient atmosphere - is investigated both theoretically and experimentally. It is concluded that losses of this sort make no noticeable contribution to the background losses, even at high gas pressures. Nevertheless, if an axial resonant frequency of the test gas closely matches a longitudinal resonant frequency of the tube wall, the internal sound pressure can excite tube displacements of disproportionate magnitude and thus cause excessive losses, not due to radiation but rather to frictional dissipation related to the motion of the tube structure. This mechanism is effective when the mode numbers of the gas and tube have opposite parity, and makes sound absorption measurements at the fundamental gas frequency particularly problematical. An experimental investigation confirms the existence of such additional losses when the parity condition is fulfilled.
Zuckerwar, A. J.↗
Chromospheric structure in relation to radiation losses
It is assumed that cool star chromospheres are heated by mechanical energy dissipation that depends quasilinearly on density and cooled by radiation loss and it is shown that the basic properties of chromospheres are determined by the ionization of hydrogen. It is hydrogen ionization that provides the freedom for chromospheres to adjust their radiation losses to balance the prescribed heat input, resulting in an extended region of low temperature gradient. Chromospheric radiation losses in cool stars occur mainly in the strongest spectral lines at wavelengths greater than about 2000 A and the fraction of the chromosphere is effectively thin. The most important lines include Ca II H and K and the infrared triplet and Mg II h and k. The strong lines of other abundant species, are less important because their high excitation energies reduce the collisional excitation rates. Lyman alpha losses are important because of the overwhelming abundance of hydrogen. However, the inability of chromospheres to adjust their Lyman alpha losses limits the geometrical thickness of the effectively thin region in Lyman alpha and limits the total Lyman alpha flux.
Athay, R. G.↗
Effect of coronal elemental abundances on the radiative loss function
The solar photosphere and corona abundances tabulated by Meyer (1985) and the chromospheric abundances given by Murphy (1985) are used here to recalculate radiative loss functions for equilibrium, low-density, optically thin plasmas. Results from a representative standard photospheric abundance set and from coronal and chromospheric abundance sets showing depletions of up to a factor of four in certain elemental abundances are compared. A significant difference is found for both the coronal and chromospheric abundance sets, with the peak of the radiative loss curve shifted closer to 10 to the 6th K than to the standard 2 x 10 to the 5th K found from photospheric abundances. Consequences of these new calculations, in particular for the cool loop model of Antiochos and Noci (1986), are discussed.
Cook, J. W.↗
Opacity effects on the radiative losses of coronal loops
This paper presents calculations of radiative losses, which include the effects of geometry and optical depth, that can be used to improve the energy losses in many flux-tube calculations for loops with constant and variable cross sections. The results include the non-LTE ionization state of hydrogen and helium, thus allowing the determination of the ionization energy in the gas and the relative importance of collisional and radiative processes. These calculations show that optical depth effects are important under solar conditions in the temperature range of 8000-40,000 K.
Kuin, N. P. M.↗
The Effects of Pressure and Optical Thickness on Radiative Losses in Spherical Diffusion Flames in Microgravity
In microgravity combustion, heat loss due to radiation plays a large role. Combustion products are able to accumulate in the flame region and radiate heat, while the heat release from the flame remains relatively constant. This causes the flame temperature to decrease until combustion can no longer be sustained, a phenomenon known as radiative extinction.
Kendyl A. Waddell↗
Stellar model chromospheres. VI - Empirical estimates of the chromospheric radiative losses of late-type stars
A method is developed for estimating the nonradiative heating of stellar chromospheres by measuring the net radiative losses in strong Fraunhofer line cores. This method is applied to observations of the Mg II resonance lines in a sample of 32 stars including the sun. At most a small dependence of chromospheric nonradiative heating on stellar surface gravity is found, which is contrary to the large effect predicted by recent calculations based on acoustic-heating theories.
Linsky, J. L.↗
Public Data Set: Impurity Dynamics and Radiative Losses During Local Helicity Injection Startup in the Pegasus-III Spherical Tokamak
This public dataset contains openly-documented, machine readable digital research data corresponding to figures published in C. Rodriguez Sanchez et al., “ Impurity Dynamics and Radiative Losses During Local Helicity Injection Startup in the Pegasus-III Spherical Tokamak,” accepted for publication in Physics of Plasmas .
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Outer atmospheres of cool stars. II - Mg II flux profiles and chromospheric radiative loss rates
International Ultraviolet Explorer high-resolution spectra of the Mg II lines at 2796, 2803 A in 15 stars of spectral type G2-M2 including a wide range of luminosities are presented. These spectra are calibrated in absolute flux units at earth and at the stellar surface, and the chromospheric radiative loss rates in the Mg II lines are compared with corresponding rates in the Ca II H, K, and 8542 lines. The ratio of Mg II surface flux to total surface flux is found to be independent of stellar luminosity and thus gravity; may decrease slowly with decreasing effective temperature, and increases with decreasing period among RS Canum Venaticorum binaries. The factor of 10 range in this ratio at each effective temperature may be due to differences in the fractional surface area covered by plages and may indicate that stars of all luminosity classes have chromospheric plages. In this small data sample no evidence is found that the Mg II line surface fluxes indicate whether a star possesses a transition region and hot corona.
Basri, G. S.↗
3D hybrid fluid-particle jet simulations and the importance of synchrotron radiative losses
Context. Relativistic jets in active galactic nuclei are known for their exceptional energy output, and imaging the synthetic synchrotron emission of numerical jet simulations is essential for a comparison with observed jet polarization emission. Aims. Through the use of 3D hybrid fluid-particle jet simulations (with the PLUTO code), we overcome some of the commonly made assumptions in relativistic magnetohydrodynamic (RMHD) simulations by using non-thermal particle attributes to account for the resulting synchrotron radiation. Polarized radiative transfer and ray-tracing (via the RADMC-3D code) highlight the differences in total intensity maps when (i) the jet is simulated purely with the RMHD approach, (ii) a jet tracer is considered in the RMHD approach, and (iii) a hybrid fluid-particle approach is used. The resulting emission maps were compared to the example of the radio galaxy Centaurus A. Methods. We applied the Lagrangian particle module implemented in the latest version of the PLUTO code. This new module contains a state-of-the-art algorithm for modeling diffusive shock acceleration and for accounting for radiative losses in RMHD jet simulations. The module implements the physical postulates missing in RMHD jet simulations by accounting for a cooled ambient medium and strengthening the central jet emission. Results. We find a distinction between the innermost structure of the jet and the back-flowing material by mimicking the radio emission of the Seyfert II radio galaxy Centaurus A when considering an edge-brightened jet with an underlying purely toroidal magnetic field. We demonstrate the necessity of synchrotron cooling as well as the improvements gained when directly accounting for non-thermal synchrotron radiation via non-thermal particles.
79 ASTRONOMY AND ASTROPHYSICS↗
The effects of nonequilibrium ionization on the radiative losses of the solar corona
The emissivity of the ions of carbon and oxygen has been recalculated for a set of solar coronal loop models with a steady state siphon flow. The ion densities were calculated from the plasma velocities, temperatures, and densities of the models, and large departures from equilibrium were found. For purposes of comparison, the emissivity was calculated with and without the approximation of ionization equilibrium. Considerable differences in the radiative loss function Lambda(T) curve between equilibrium and nonequilibrium conditions were found. The nonequilibrium Lambda(T) function was then used to solve again the steady state flow equations of the loop models. The differences in the structure of these models with respect to the models calculated adopting the Lambda(T) curve in equilibrium are discussed.
Spadaro, D.↗
Regulation of Side‐Chain Symmetry for Delaying Triplet Formation and Suppressing Non‐Radiative Loss in Organic Solar Cells
Abstract The structural revolutions of non‐fullerene acceptors (NFAs) have driven continuous efficiency breakthroughs in organic solar cells (OSCs). Rational regulation of NFA structures toward efficient exciton dissociation and mitigated non‐radiative recombination is pivotal for OSCs. The incorporation of asymmetric side chains on NFAs can often achieve these goals by inducing a desirable aggregate state. However, it lacks the studies to directly correlate the side‐chain symmetry of NFAs with the exciton delocalization and triplet dynamics in OSCs. Herein, The influence of structural symmetry on the aggregate properties is systematically investigated and exciton/charge dynamics based on two developed biaxial‐conjugated NFAs with varied side‐chain symmetry. The symmetric NFA having diverse molecular packing orientations can form multiple charge transfer channels in its blend with polymer donor, which cannot be found in that comprising the asymmetric ones. Moreover, a slower rate and lower ratio of the spin‐triplet state are formed in the blend of symmetric NFA, resulting in a much lower non‐radiative voltage loss in corresponding OSCs. This study reveals the distinct advantages of symmetric NFAs in both aggregate properties and exciton/charge dynamics over those of asymmetric ones, paving the way for developing high‐performance OSCs using easier‐to‐prepare, low‐cost symmetric materials.
Chemistry↗
Effects of Oxygen Concentration on Radiative Loss from Normal-Gravity and Microgravity Methane Diffusion Flames
Laminar diffusion flames of methane, burning in quiescent oxidizing environments at atmospheric pressure, have been studied under both normal-gravity and microgravity conditions. Radiation from these flames is measured using a wide-view-angle, thermopile detector radiometer. The oxidizer was 18, 21, and 30 percent oxygen in nitrogen.
Bahadori, M. Y.↗
Suppressed non-radiative loss and efficient hole transfer at a small highest occupied molecular orbital offset endows binary organic solar cells with 19.73% efficiency and a small efficiency-cost gap
Two novel acceptors are designed and synthesized, and the PTQ11:PEH-F binary system is highly promising for industrial cost-effective organic photovoltaics.
Kong, Xiaolei [College of Chemistry, Zhengzhou Uni↗
Nearly simultaneous observations of chromospheric and coronal radiative losses of cool stars
The flux-flux relationships of cool stars are studied on the basis of nearly simultaneous measurements of Ca II H+K, Mg II h+k, and soft X-ray fluxes. A linear relationship is derived between IUE Mg II h+k fluxes and Mount Wilson Ca II H+K fluxes which were obtained within 36 hr of each other for a sample of 26 F5-K3 main-sequence stars. Nearly simultaneous EXOSAT soft X-ray fluxes are compared with Ca II H+K fluxes for a sample of 20 dwarfs and gaints with spectral types ranging from F6 to K2, and 72 additional cool stars for which noncontemporaneous Ca II H+K and EINSTEIN soft X-ray fluxes are available are compared. It is confirmed that a nonradiatively heated chromosphere exists on even the least active main-sequence stars. This basal chromosphere is probably independent of stellar magnetic activity.
Schrijver, C. J.↗