scholarly journals Simulations on the Collisional Properties of Gas in Galaxies

2004 ◽  
Vol 217 ◽  
pp. 228-229
Author(s):  
Yves Revaz ◽  
Daniel Pfenniger
Keyword(s):  
Disk Galaxies ◽  
Simple Method ◽  
Free Parameters ◽  
Slow Cycling ◽  
Cold Gas

In this work, we explore a simple method with few free parameters, which describes the global dynamical consequences on disk galaxies of a slow cycling of gas between the interstellar, almost collisionless very cold gas and the warm collisional phases, with a secular transformation of a fraction of warm gas into stars.

scholarly journals Transparent silver and other metallic films

1908 ◽  
Vol 81 (548) ◽  
pp. 301-310 ◽  
Keyword(s):  
White Light ◽  
Electric Resistivity ◽  
Metallic Film ◽  
Moderate Temperature ◽  
Metallic Films ◽  
Remarkable Change ◽  
Simple Method ◽  
Glass Plates ◽  
Cold Gas

It is well known that when thin leaves of gold or silver are mounted upon glass and heated to a temperature which is well below a red heat, a remarkable change of properties takes place, whereby the continuity of the metallic film is destroyed. The result is that white light is now freely transmitted, reflection is correspondingly diminished, while the electric resistivity is enormously increased. A simple method of illustrating this extraordinary change is to mount a sheet of silver leaf between two clean lantern plates, clip them lightly together by means of wire paper fasteners or other suitable means, and then heat gradually to a temperature of not more than 500°C. This can be done con­veniently by placing the plates on a thin fire-brick in a cold gas muffle, and then raising the temperature to the desired point. The gas should now be turned off, and the glass plates allowed to cool slowly, so as to avoid cracking. They can then be bound with strips like an ordinary lantern plate, and a permanent example of transparent silver is obtained. It will be found that such a plate transmits the light of the electric lantern almost as readily as ordinary glass, and does not produce any change of colour. The great trans­parency of the film may be shown by placing the plate upon printing or writing, and photographing the characters through the plate. Every detail of the characters can be reproduced with remarkable clearness. At first sight it is perhaps difficult to conceive that so distinct an impression could be obtained through what was originally a perfectly opaque sheet of silver, and which has only been once heated to a moderate temperature.

A Simple but Efficient Method for Nonlinear Parameter Estimation Based on Comparing Phase Space Structures

2006 ◽  
Vol 61 (5-6) ◽  
pp. 239-248 ◽  
Author(s):  
Kazuhiro Matsumoto ◽  
Hans H. Diebner
Keyword(s):  
Parameter Estimation ◽  
Structural Difference ◽  
Coarse Graining ◽  
Nonlinear Parameter ◽  
Model Systems ◽  
Space Structures ◽  
Structural Comparison ◽  
Simple Method ◽  
Nonlinear Parameter Estimation ◽  
Free Parameters

We introduce a simple method for nonlinear parameter estimation based on a structural comparison of target and model attractor. The parameters of the model are adapted by means of minimizing the structural difference of the attractors. For this quantitative comparison histograms derived from a coarse graining of the phase spaces are used. We present a time discrete as well as a continuous example to demonstrate the efficiency of this method. The target attractors are computed from the Hénon map and the Rössler system, respectively. The model systems are chosen to be fairly universal endowed with free parameters that are adapted so that the model attractor resembles the target. The estimations work accurate and acceptably fast up to four parameters

scholarly journals Dynamics of Mergers & Remnants

1999 ◽  
Vol 186 ◽  
pp. 137-144
Author(s):  
Joshua E. Barnes
Keyword(s):  
Power Law ◽  
Tail Length ◽  
Disk Galaxy ◽  
Disk Galaxies ◽  
Galaxy Mergers ◽  
Halo Structure ◽  
Unequal Mass ◽  
Cold Gas

This review focus on some issues which seem relevant to recent discussions: (1) how halo structure influences tail length, (2) the fate of power-law density cusps, (3) the results of unequal-mass disk galaxy mergers, and (4) the behavior of hot and cold gas in merging disk galaxies.

Evolution of disk galaxies in MOdified Gravity (MOG)

2019 ◽  
Vol 14 (S353) ◽  
pp. 152-153
Author(s):  
Neda Ghafourian ◽  
Mahmood Roshan
Keyword(s):  
Modified Gravity ◽  
Disk Galaxies ◽  
Galactic Disks ◽  
Free Parameters

AbstractEvolution and the formation of bars in the galactic disks is studied in the context of Modified Gravity (MOG) by using N-body simulations. It is found that changing the value of free parameters of the model can effectively alter the strength of the bar and disk’s stability.

scholarly journals Star formation in galaxy mergers: ISM turbulence, dense gas excess, and scaling relations for disks and starbusts

2010 ◽  
Vol 6 (S271) ◽  
pp. 160-169
Author(s):  
Frédéric Bournaud ◽  
Leila C. Powell ◽  
Damien Chapon ◽  
Romain Teyssier
Keyword(s):  
Star Formation ◽  
Theoretical Models ◽  
Quantitative Agreement ◽  
Star Formation History ◽  
Scaling Relations ◽  
Disk Galaxies ◽  
Galaxy Mergers ◽  
Galaxy Interactions ◽  
History Of ◽  
Cold Gas

AbstractGalaxy interactions and mergers play a significant, but still debated and poorly understood role in the star formation history of galaxies. Numerical and theoretical models cannot yet explain the main properties of merger-induced starbursts, including their intensity and their spatial extent. Usually, the mechanism invoked in merger-induced starbursts is a global inflow of gas towards the central kpc, resulting in a nuclear starburst. We show here, using high-resolution AMR simulations and comparing to observations of the gas component in mergers, that the triggering of starbursts also results from increased ISM turbulence and velocity dispersions in interacting systems. This forms cold gas that are denser and more massive than in quiescent disk galaxies. The fraction of dense cold gas largely increases, modifying the global density distribution of these systems, and efficient star formation results. Because the starbursting activity is not just from a global compacting of the gas to higher average surface densities, but also from higher turbulence and fragmentation into massive and dense clouds, merging systems can enter a different regime of star formation compared to quiescent disk galaxies. This is in quantitative agreement with recent observations suggesting that disk galaxies and starbursting systems are not the low-activity end and high-activity end of a single regime, but actually follow different scaling relations for their star formation.

scholarly journals A PORTRAIT OF COLD GAS IN GALAXIES AT 60 pc RESOLUTION AND A SIMPLE METHOD TO TEST HYPOTHESES THAT LINK SMALL-SCALE ISM STRUCTURE TO GALAXY-SCALE PROCESSES

2016 ◽  
Vol 831 (1) ◽  
pp. 16 ◽  
Author(s):  
Adam K. Leroy ◽  
Annie Hughes ◽  
Andreas Schruba ◽  
Erik Rosolowsky ◽  
Guillermo A. Blanc ◽  
...  
Keyword(s):  
Small Scale ◽  
Simple Method ◽  
Ism Structure ◽  
Cold Gas

Density waves in disk galaxies

1967 ◽  
Vol 31 ◽  
pp. 313-317 ◽  
Author(s):  
C. C. Lin ◽  
F. H. Shu
Keyword(s):  
Mathematical Analysis ◽  
Spiral Structure ◽  
Stellar System ◽  
Collective Modes ◽  
Disk Galaxies ◽  
Spiral Pattern ◽  
Density Waves ◽  
The Galaxy ◽  
Detailed Mathematical Analysis

Density waves in the nature of those proposed by B. Lindblad are described by detailed mathematical analysis of collective modes in a disk-like stellar system. The treatment is centered around a hypothesis of quasi-stationary spiral structure. We examine (a) the mechanism for the maintenance of this spiral pattern, and (b) its consequences on the observable features of the galaxy.

A simple way for producing holographic filters suitable for image improvement

1978 ◽  
Vol 36 (1) ◽  
pp. 226-227
Author(s):  
K.-H. Herrmann ◽  
E. Reuber ◽  
P. Schiske
Keyword(s):  
Transfer Functions ◽  
Diffraction Order ◽  
Lateral Position ◽  
Simple Method ◽  
Spatial Frequencies ◽  
Resolution Electron ◽  
Wiener Filters ◽  
Image Improvement ◽  
Optical Reconstruction ◽  
Set Up

Aposteriori deblurring of high resolution electron micrographs of weak phase objects can be performed by holographic filters [1,2] which are arranged in the Fourier domain of a light-optical reconstruction set-up. According to the diffraction efficiency and the lateral position of the grating structure, the filters permit adjustment of the amplitudes and phases of the spatial frequencies in the image which is obtained in the first diffraction order.In the case of bright field imaging with axial illumination, the Contrast Transfer Functions (CTF) are oscillating, but real. For different imageforming conditions and several signal-to-noise ratios an extensive set of Wiener-filters should be available. A simple method of producing such filters by only photographic and mechanical means will be described here.A transparent master grating with 6.25 lines/mm and 160 mm diameter was produced by a high precision computer plotter. It is photographed through a rotating mask, plotted by a standard plotter.

Rotary Beveling for In Situ Thin-Section Microscopy of Cell Cultures

1981 ◽  
Vol 39 ◽  
pp. 550-551
Author(s):  
Dean A. Handley ◽  
Jack T. Alexander ◽  
Shu Chien
Keyword(s):  
Cell Growth ◽  
Cell Cultures ◽  
Molecular Interactions ◽  
Convenient Method ◽  
Petri Dish ◽  
Simple Method ◽  
Thin Section Microscopy ◽  
Thin Sectioning ◽  
Organic Fluids

In situ preparation of cell cultures for ultrastructural investigations is a convenient method by which fixation, dehydration and embedment are carried out in the culture petri dish. The in situ method offers the advantage of preserving the native orientation of cell-cell interactions, junctional regions and overlapping configurations. In order to section after embedment, the petri dish is usually separated from the polymerized resin by either differential cryo-contraction or solvation in organic fluids. The remaining resin block must be re-embedded before sectioning. Although removal of the petri dish may not disrupt the native cellular geometry, it does sacrifice what is now recognized as an important characteristic of cell growth: cell-substratum molecular interactions. To preserve the topographic cell-substratum relationship, we developed a simple method of tapered rotary beveling to reduce the petri dish thickness to a dimension suitable for direct thin sectioning.

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