scholarly journals Validity of the Cloud Model of the Interstellar Medium

1958 ◽  
Vol 8 ◽  
pp. 940-942
Author(s):  
Bertram Donn
Keyword(s):  
Interstellar Medium ◽  
Velocity Distribution ◽  
Uniform Distribution ◽  
Density Fluctuation ◽  
Cloud Model ◽  
Point Of View ◽  
Simplified Model ◽  
Interstellar Matter ◽  
Idealized Model ◽  
Fluctuation Model

Because of the extreme irregularity in distribution of interstellar matter, some idealized model must be adopted in discussing the interstellar medium. Three simple models have been considered. The original one, long-since discarded, was a uniform distribution. This has been largely replaced by the random cloud picture in which space is visualized as filled with isolated clouds, 5–10 per kpc, about 10 pc in diameter, the array having an exponential velocity distribution with a mean of about 8 km/sec. Lastly, there is a turbulent or a random density fluctuation model.Although the random cloud hypothesis has received most attenuation from astronomers, it has been well recognized that it is an over simplified model and should be used with some caution. This point of view has been clearly stated by many workers in this field, as the following statements by Oort and by Minkowski, respectively, demonstrate.

NATURAL ORBITALS AND ELECTRON ELASTIC MAGNETIC SCATTERING BY NUCLEI

1996 ◽  
Vol 05 (04) ◽  
pp. 717-724 ◽  
Author(s):  
D.N. KADREV ◽  
A.N. ANTONOV ◽  
M.V. STOITSOV ◽  
S.S. DIMITROVA
Keyword(s):  
Density Fluctuation ◽  
Form Factors ◽  
Wave Functions ◽  
Magnetic Scattering ◽  
Correlation Effects ◽  
Valence Nucleon ◽  
Nucleon System ◽  
Natural Orbitals ◽  
Transverse Form Factor ◽  
Fluctuation Model

Natural orbitals obtained within the coherent density fluctuation model and containing nucleon correlation effects are used to calculate characteristics of the A-nucleon system, such as the electron elastic magnetic scattering form factors. The calculations are performed for nuclei with a doubly-closed core and a valence nucleon in a stretched configuration (j=l+1/2), such as the 17 O and 41 Ca nuclei. It is shown that the calculations of the transverse form factor using natural orbitals improve the agreement with the experimental data in comparison with the case when shell-model single-particle wave functions are used.

scholarly journals Interstellar and interplanetary solids in the laboratory

2015 ◽  
Vol 11 (A29B) ◽  
pp. 416-419 ◽  
Author(s):  
Emmanuel Dartois ◽  
Ivan Alata ◽  
Cécile Engrand ◽  
Rosario Brunetto ◽  
Jean Duprat ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Environmental Parameters ◽  
Interstellar Matter ◽  
Additional Information ◽  
Set Constraints ◽  
Physico Chemical ◽  
Space Environments ◽  
Chemical Conditions ◽  
Extraterrestrial Material ◽  
Shed Light

AbstractThe composition of interstellar matter is driven by environmental parameters and results from extreme interstellar medium physico-chemical conditions. Astrochemists must rely on remote observations to monitor and analyze the interstellar solids composition. They bring additional information from the study of analogues produced in the laboratory, placed in simulated space environments. Planetologists and cosmochemists access and spectroscopically examine collected extraterrestrial material in the laboratory. Diffuse interstellar medium and molecular clouds observations set constraints on the composition of organic solids that can then be compared with collected extraterrestrial materials analyses, to shed light on their possible links.

Experimental Modeling of Air Temperature and Velocity Distribution in an Engine Compartment

2006 ◽  
Author(s):  
A. A. Mozafari ◽  
M. H. Saidi ◽  
J. Neyestani ◽  
A. E. Sany
Keyword(s):  
Heat Transfer ◽  
Velocity Distribution ◽  
Air Temperature ◽  
Gasoline Engine ◽  
Point Of View ◽  
Vehicle Body ◽  
Air Distribution ◽  
Wind Effect ◽  
Engine Compartment ◽  
Air Velocity

Investigation of air distribution and wind effect on a vehicle body from the point of view of underhood heat transfer effect and proper positioning of vehicle elements such cooler, condenser and engine configuration is an important area for engine researchers and manufacturers as well. In this research, the effect of air velocity distribution and wind effect around a vehicle is simulated and temperature and velocity distribution around engine block which is influenced by the wind effect is investigated. Thermal investigation of the engine compartment components is performed using results of underhood air temperature and velocity distribution. The heat transfer from engine surface is calculated from the engine energy balance in which their input data are obtained from a comprehensive experimental study on a four cylinder gasoline engine.

scholarly journals Practical Model Proposed for the Structural Analysis of Segmental Tunnels

2020 ◽  
Vol 10 (23) ◽  
pp. 8514
Author(s):  
Jatziri Y. Moreno-Martínez ◽  
Arturo Galván ◽  
Fernando Peña ◽  
Franco Carpio
Keyword(s):  
Finite Element ◽  
Soft Soil ◽  
Limit State ◽  
Structural Response ◽  
3D Models ◽  
Complex Model ◽  
Numerical Results ◽  
Point Of View ◽  
Simplified Model ◽  
Ultimate Limit State

The construction of tunnels has become increasingly common in city infrastructure; tunnels are used to connect different places in a region (for transportation and/or drainage). In this study, the structural response of a typical segmental tunnel built in soft soil was studied using a simplified model which considers the coupling between segmental rings. From an engineering point of view, there is a need to use simple and reliable finite element models. Therefore, a 1D model based on the Finite Element Method (FEM) composed of beam elements to model the segments and elastic-linear springs and non-linear springs to model the mechanical behavior of the joints was performed. To validate the modeling strategy, the numerical results were compared to (lab-based) experimental results, under an Ultimate Limit State, obtained from the literature, and a comparison between numerical results considering a 3D numerical complex model which included the nonlinearity of concrete, reinforcing steel and the joints was performed. With this simplified model, we obtained a prediction of approximately 95% of the ultimate loading capacity compared to the results developed in the experimental and 3D models. This proposed model will help engineers in practice to create “rational” structural designs of segmental tunnel linings when a “low” interaction between rings is expected.

The Effect of Anisotropic Support on Rotor Instability Due to Fluid Leakage

1988 ◽  
Vol 110 (4) ◽  
pp. 585-591
Author(s):  
Jhy-Horng Wang ◽  
Ming-Te Tsai
Keyword(s):  
Point Of View ◽  
Simplified Model ◽  
Optimum Range ◽  
Energy Point ◽  
Fluid Leakage ◽  
Rotor Bearing ◽  
Anisotropic Stiffness ◽  
Bearing System

The instability caused by fluid leakage leads to limited performance in turbomachines. This instability may be improved by using flexible bearing supports with anisotropic stiffness. With a simplified model this effect is investigated, including the influence of many parameters. The results show that the optimum range of anistropy is strongly dependent on the parameters of the rotor-bearing system. In this paper an explanation from an energy point of view is presented to clarify the different stability behaviors with anisotropic bearing support.

scholarly journals The effect of wind tunnel interference on the characteristics of an aerofoil

1930 ◽  
Vol 129 (809) ◽  
pp. 135-145 ◽  
Keyword(s):  
Wind Tunnel ◽  
Uniform Distribution ◽  
Infinite Series ◽  
Rectangular Channel ◽  
Approximate Expression ◽  
Point Of View ◽  
Approximate Methods ◽  
Free Jet ◽  
Drag And Lift ◽  
Lift And Drag

The effect of the walls of the enclosure on the measured values of the lift and drag experienced by an aerofoil is quite appreciable and it has been known for a considerable time that correction must be applied to wind tunnel result before they can be applied to free air conditions. Prandtl* investigated the effect on an aerofoil in a free jet or circular tube both in the case where there is a uniform lift distribution, and in the case where there is an elliptic distribution of circulation. The elliptic distribution is of importance because it gives the minimum drag for a given lift. Glauert by means of an approximate method found the induced drag and lift in a rectangular channel when there is a uniform distribution of lift. Terazawa modified Glauert’s method and obtained the exact solution for an aerofoil with uniform distribution of circulation in a rectangular channel. It is The object of this note to extend these results and to obtain the induces drag and lift in a rectangular channel when there is an elliptic distribution of lift. In addition, the discussion of Prandtl is briefly gone through because Prandtl’s results are usually given as the first few terms of an infinite series, and it has not been noticed that the result can be obtained exactly. Glauert’s work on the effect of plane barries is briefly re-examined because, in his analysis, approximate expression were summed over an infinite series of points, and at first glance it appeared that this would introduce some error of the same order as the result. In this note the summation is carried out rigorously and the approximations to the actual values. The small divergences from Glauert’s result obtained by Terazawa in two numerical cases are, in effect, the result of a slightly more accurate approximation. From the practical point of view the results of this paper add little to what is known already, for the major corrections are given by the results of the approximate methods, but this note should fill in some small gaps in the theory of wind tunnel interference.

scholarly journals Looking for the bricks of the life in the interstellar medium: The fascinating world of astrochemistry

2020 ◽  
Vol 246 ◽  
pp. 00021
Author(s):  
Vincenzo Barone ◽  
Cristina Puzzarini
Keyword(s):  
Interstellar Medium ◽  
Gas Phase ◽  
Molecular Spectroscopy ◽  
Building Blocks ◽  
Point Of View ◽  
General View ◽  
Computational Point ◽  
Heterogeneous Processes ◽  
Life Itself ◽  
Complex Chemistry

The discovery in the interstellar medium of molecules showing a certain degree of complexity, and in particular those with a prebiotic character, has attracted great interest. A complex chemistry takes place in space, but the processes that lead to the production of molecular species are a matter of intense discussion, the knowledge still being at a rather primitive stage. Debate on the origins of interstellar molecules has been further stimulated by the identification of biomolecular building blocks, such as nucleobases and amino acids, in meteorites and comets. Since many of the molecules found in space play a role in the chemistry of life, the issue of their molecular genesis and evolution might be related to the profound question of the origin of life itself. Understanding the underlying chemical processes, including the production, reactions and destruction of compounds, requires the concomitant study of spectroscopy, gas-phase reactivity, and heterogeneous processes on dust-grains. The aim of this contribution is to provide a general view of a complex and multifaceted challenge, while focusing on the role played by molecular spectroscopy and quantum-chemical computations. In particular, the derivation of the molecular spectroscopic features and the investigation of gas-phase formation routes of prebiotic species in the interstellar medium are addressed from a computational point of view.

scholarly journals 34. Interstellar Matter

1985 ◽  
Vol 19 (1) ◽  
pp. 437-478
Author(s):  
M. Peimbert ◽  
J. Lequeux ◽  
S. D’Odorico ◽  
B. G. Elmegreen ◽  
E. B. Kostyakova ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Present State ◽  
Theoretical Models ◽  
Interstellar Matter ◽  
Evolution Of The Universe ◽  
Formation And Evolution ◽  
The Subject ◽  
Astronomical Research ◽  
Theories Of Evolution ◽  
The Universe

It has become more evident during the last three years that the study of interstellar matter is paramount to understand the evolution of the universe and its constituents. From observations of the present state of the interstellar medium, in our galaxy, in other galaxies, and between galaxies, it is possible to test theories of: evolution of the universe, formation and evolution of galaxies, formation and evolution of stars and of the evolution of the interstellar medium itself. The amount of information on the interstellar medium that has been gathered during the 1982-1984 period has been very large and the theoretical models that have been ellaborated to explain these observations have been very numerous, these facts show that the subject of our Commission constitutes a very active field of astronomical research.

scholarly journals Chromospheric Ejections Associated with Type III Radio-Bursts

1989 ◽  
Vol 104 (2) ◽  
pp. 181-184
Author(s):  
Mein Nicole ◽  
Mein Pierre
Keyword(s):  
Phase Diagram ◽  
Magnetic Flux ◽  
Velocity Distribution ◽  
Radial Velocity ◽  
Cloud Model ◽  
Radio Bursts ◽  
Line Profiles ◽  
Flux Tubes ◽  
Type Iii ◽  
Magnetic Flux Tubes

AbstractWe study the dynamics of an IIα absorbing structure associated with a type III radioburst. We use a “Differential Cloud Model” to analyse the observed line profiles, in order to determine radial velocity and microturbulence (or shear) as functions of time.We assume that the material is flowing inside magnetic flux tubes, with a given velocity distribution. We analyse the motions in a phase-diagram (position x,velocity V). The evolution of velocity and microturbulcnce is compared to the observations. The model accounts qualitatively for the evolution of velocity, and qualitatively for the decrease of microturbulence.

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