The High‐Excitation Planetary Nebula NGC 246: Optical and Near‐Ultraviolet Observations and Two‐dimensional Numerical Models

We present the results of a comparative theoretical analysis of the electron beam bunching in a single-stage klystron amplifier using analytical models, a one-dimensional disk program, and a two-dimensional program. Data on the influence of various one-dimensional and two-dimensional nonlinear effects on the efficiency of electron beam bunching at different values of the space charge parameter and the modulation amplitude are presented. The limits of applicability of analytical and one-dimensional numerical models for electron beam bunching analysis in high-power klystron amplifiers are found.

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Observations of Planetary-Nebula Spectra in the near Ultraviolet

Planetary Nebulae ◽

10.1007/978-94-010-3473-9_10 ◽

1968 ◽

pp. 62-62

Author(s):

E. B. Kostjakova

Keyword(s):

Planetary Nebula ◽

Near Ultraviolet

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N 66: A High Excitation N Rich Planetary Nebula in the LMC

Planetary Nebulae ◽

10.1007/978-94-009-0865-9_130 ◽

1989 ◽

pp. 353-353

Author(s):

M. Peña ◽

M. T. Ruiz

Keyword(s):

Planetary Nebula ◽

High Excitation

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Experience of employment of computational models for water quality modelling

E3S Web of Conferences ◽

10.1051/e3sconf/20199705030 ◽

2019 ◽

Vol 97 ◽

pp. 05030 ◽

Cited By ~ 16

Author(s):

Anatoly Krutov ◽

Dilshod Bazarov ◽

Begzod Norkulov ◽

Bakhtiyar Obidov ◽

Bobur Nazarov

Keyword(s):

Computational Models ◽

Numerical Models ◽

Qualitative Difference ◽

Three Dimensional ◽

Sufficient Conditions ◽

Aral Sea ◽

Two Dimensional ◽

Dimensional Model ◽

Two Dimensional Model ◽

Wind Currents

The purpose of the article is to develop the required and sufficient conditions under which numerical methods can be used for engineering calculations and for scientific research of hydrodynamic processes in solving practical problems related to predicting the spread of pollutants in water bodies and streams. The conducted studies consisted in comparing the results of laboratory experiments and mathematical modelling, in particular the distribution of heat in a stream with different temperature in water layers was studied. To check the adequacy of the proposed numerical models, calculations were performed and comparisons were made with the results of experimental data. The obtained results allowed to determine the boundaries of the qualitative difference in the flow behaviour for different numbers of Froude and Reynolds. The accuracy of the method was also studied. A number of additional requirements for numerical models were proposed in addition to approcsimation and stability, such as requirements of conservativeness (divergence), existence of trivial solutions on grids, possibility to calculate highly unsteady, quasi-stable, pulsating and stationary flows, requirement of invariance of linearized equations, as well as the requirement of a one-dimensional scheme to be a consequence of a two-dimensional scheme. Distribution of velocities of wind currents using a three-dimensional and two-dimensional model was studied for a real object. A shallow-water bay of the Aral Sea was chosen as the object for the research. Comparison of the calculation results for both models showed that the flow velocity fields, as well as the distribution of pollutants in shallow waters, can be performed using a two-dimensional model.

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Models of Planetary Nebulae: Generalisation of the Multiple Winds Model

Symposium - International Astronomical Union ◽

10.1017/s0074180900138811 ◽

1989 ◽

Vol 131 ◽

pp. 411-424 ◽

Cited By ~ 5

Author(s):

F. D. Kahn

Keyword(s):

Planetary Nebula ◽

High Speed ◽

Planetary Nebulae ◽

Central Star ◽

Theoretical Description ◽

Basic Theory ◽

Spectral Lines ◽

High Excitation ◽

General Shape ◽

Fast Wind

According to the multiple winds model a planetary nebula forms as the result of the interaction of a fast wind from the central star with the superwind that had previously been emitted by the progenitor star. The basic theory which deals with the spherically symmetrical case is briefly summarised. Various improvements are then considered in turn. A better history is clearly needed of the way that the central star becomes hotter, it is unrealistic to make the assumption that the superwind is spherically symmetrical, and finally there are likely to be important instabilities at some of the interfaces in the PN, notably that between the shocked superwind and the HII layer. These changes in the theoretical description produce a better understanding of the conditions in the outer parts of a PN and of the nature of its general shape, and they should lead to an explanation for the occurrence of high speed motions, and of highly ionized species and high excitation spectral lines.

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Mass loss from the exoplanet WASP-12b inferred from Spitzer phase curves

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2018 ◽

2019 ◽

Vol 489 (2) ◽

pp. 1995-2013 ◽

Cited By ~ 12

Author(s):

Taylor J Bell ◽

Michael Zhang ◽

Patricio E Cubillos ◽

Lisa Dang ◽

Luca Fossati ◽

...

Keyword(s):

Mass Loss ◽

Infrared Radiation ◽

High Energy ◽

The Other ◽

Phase Curve ◽

Near Ultraviolet ◽

Energy Irradiation ◽

Ultraviolet Observations ◽

Host Stars ◽

Co Emission

ABSTRACT The exoplanet WASP-12b is the prototype for the emerging class of ultrahot, Jupiter-mass exoplanets. Past models have predicted – and near-ultraviolet observations have shown – that this planet is losing mass. We present an analysis of two sets of 3.6 and 4.5 $\mu \rm{m}$Spitzer phase curve observations of the system which show clear evidence of infrared radiation from gas stripped from the planet, and the gas appears to be flowing directly toward or away from the host star. This accretion signature is only seen at 4.5 $\mu \rm{m}$, not at 3.6 $\mu \rm{m}$, which is indicative either of CO emission at the longer wavelength or blackbody emission from cool, ≲600 K gas. It is unclear why WASP-12b is the only ultrahot Jupiter to exhibit this mass-loss signature, but perhaps WASP-12b’s orbit is decaying as some have claimed, while the orbits of other exoplanets may be more stable; alternatively, the high-energy irradiation from WASP-12A may be stronger than the other host stars. We also find evidence for phase offset variability at the level of 6.4σ (46.2°) at 3.6 $\mu \rm{m}$.

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Two-Dimensional, Time-dependent Modelling of an Arbitrarily Shaped Ice Mass with the Finite-Element Technique

Journal of Glaciology ◽

10.1017/s0022143000006699 ◽

1985 ◽

Vol 31 (109) ◽

pp. 350-359 ◽

Cited By ~ 8

Author(s):

Steven M. Hodge

Keyword(s):

Finite Element ◽

Numerical Models ◽

Basis Functions ◽

Time Dependent ◽

Small Computer ◽

Two Dimensional ◽

Maximum Increase ◽

Steady State Condition ◽

Finite Element Technique ◽

Element Technique

AbstractThe two-dimensional, time-dependent flow of an arbitrarily shaped ice mass can be successfully modeled with the finite-element technique on a small computer. Methods developed for automatically generating the mesh data greatly simplify the data preparation and optimize the numerical simulations. Using quadratic basis functions permits the flow to be approximated quite adequately by only two element rows (five nodes vertically). Mixed-order basis functions, however, must be used so that numerical oscillations do not set in, and the ends of the ice mass, where the thickness tends to zero, must be treated carefully. Time simulations to a steady-state condition are necessary to test such numerical models adequately.South Cascade Glacier, Washington, is currently close to equilibrium. A bedrock sill dominates the bed topography in the lower half of the glacier, rising to a height of about 20% of the ice thickness. This sill produces a maximum increase in the overall thickness of about 6–7% compared to what the thickness would have been if the sill were not present. Finally, this glacier does not appear to be sliding much, if at all, despite its maritime alpine environment. This could help explain the difficulties encountered when trying to measure sliding and basal water pressures on the same glacier (Hodge, 1979), or it could imply that drag exerted by the valley walls has a significantly greater effect than conventional shape-factor concepts imply.

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