Experimental results on mhd homogeneous turbulence

2005 ◽  
pp. 369-384 ◽  
Author(s):  
R. Moreau ◽  
A. Alemany
Keyword(s):  
Experimental Results ◽  
Homogeneous Turbulence

An Improved Model for the Return to Isotropy of Homogeneous Turbulence

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Hari Warrior ◽  
Sajo Mathews ◽  
Subhendu Maity ◽  
Kaushik Sasmal
Keyword(s):  
Kinetic Energy ◽  
Strain Rate ◽  
Turbulent Kinetic Energy ◽  
Reynolds Stress ◽  
Experimental Results ◽  
Homogeneous Turbulence ◽  
Cfd Modeling ◽  
Present Formulation ◽  
Improved Model ◽  
Stress Models

In CFD modeling, the most widely used Reynolds stress models is the Speziale, Sarkar, Gatski (SSG) model. The present formulation, though similar in structure to the SSG model, is a mathematical variation assuming homogeneity of turbulence and is an improved model for the slow pressure strain of turbulence. The basic thrust is that anisotropy of dissipation tensor is not negligible when compared to the anisotropy of turbulent kinetic energy and affects the slow pressure strain rate. After an exhaustive survey of the available experimental results on return to isotropy, graphical plots reveal that the model performs as good as the SSG model.

The relaxation of stress in a ≠-fluid with reference to the decay of homogeneous turbulence

1972 ◽  
Vol 56 (4) ◽  
pp. 641-656 ◽  
Author(s):  
J. M. Dowden
Keyword(s):  
Reynolds Number ◽  
Stress Tensor ◽  
High Reynolds Number ◽  
Experimental Results ◽  
Homogeneous Turbulence ◽  
Third Order ◽  
Isotropic Tensor ◽  
Differential Structure ◽  
Homogeneous Stress ◽  
High Reynolds

It was suggested by Proudman (1970) that many of the phenomena of turbulence at high Reynolds number could be modelled by a suitably chosen member of a class of non-Newtonian fluids, ν-fluids, all of whose properties depend only on a single dimensional constant with the dimensions of viscosity. This paper investigates the relaxation of homogeneous stress in a doubly degenerate third-order ν-fluid (which is the simplest member of the class that can possibly be used to model turbulence) in the limit ν → 0.The equation which governs the stress tensor S is of the form \[ AS\ddot{S} + B\dot{S}^2 = 0, \] where A and B are isotropic tensor constants of the fluid; its differential structure can be of four distinct types. A list of properties required of the solutions of the equation is set out, and it is shown that only one of the four types has all the properties demanded of it. The behaviour of solutions of this equation is found to be consistent with the theoretical and experimental results on the decay of homogeneous turbulence.

Diagnostics of Gold Laser Plasmas

1988 ◽  
Vol 102 ◽  
pp. 357-360
Author(s):  
J.C. Gauthier ◽  
J.P. Geindre ◽  
P. Monier ◽  
C. Chenais-Popovics ◽  
N. Tragin ◽  
...  
Keyword(s):  
Experimental Results ◽  
Pure Gold ◽  
Electronic Temperature ◽  
X Ray ◽  
Laser Plasmas ◽  
Collisional Radiative Model ◽  
Radiative Model

AbstractIn order to achieve a nickel-like X ray laser scheme we need a tool to determine the parameters which characterise the high-Z plasma. The aim of this work is to study gold laser plasmas and to compare experimental results to a collisional-radiative model which describes nickel-like ions. The electronic temperature and density are measured by the emission of an aluminium tracer. They are compared to the predictions of the nickel-like model for pure gold. The results show that the density and temperature can be estimated in a pure gold plasma.

Observation of Phase Contrast Images in STEM and CTEM Modes by Using 100 kV Field Emission Electron Gun

1974 ◽  
Vol 32 ◽  
pp. 390-391
Author(s):  
Y. Harada ◽  
T. Goto ◽  
H. Koike ◽  
T. Someya
Keyword(s):  
Field Emission ◽  
Phase Contrast ◽  
Image Formation ◽  
Fresnel Diffraction ◽  
Experimental Results ◽  
Electron Gun ◽  
Scanning Microscopy ◽  
Emission Electron ◽  
Lattice Images

Since phase contrasts of STEM images, that is, Fresnel diffraction fringes or lattice images, manifest themselves in field emission scanning microscopy, the mechanism for image formation in the STEM mode has been investigated and compared with that in CTEM mode, resulting in the theory of reciprocity. It reveals that contrast in STEM images exhibits the same properties as contrast in CTEM images. However, it appears that the validity of the reciprocity theory, especially on the details of phase contrast, has not yet been fully proven by the experiments. In this work, we shall investigate the phase contrast images obtained in both the STEM and CTEM modes of a field emission microscope (100kV), and evaluate the validity of the reciprocity theory by comparing the experimental results.

A new dissociation mode for dislocations in silicon

1978 ◽  
Vol 36 (1) ◽  
pp. 346-347
Author(s):  
A. Ourmazd ◽  
G.R. Booker ◽  
C.J. Humphreys
Keyword(s):  
Detailed Examination ◽  
Experimental Results ◽  
Dislocation Network ◽  
Weak Beam ◽  
Phosphorus Doped

A (111) phosphorus-doped Si specimen, thinned to give a TEM foil of thickness ∼ 150nm, contained a dislocation network lying on the (111) plane. The dislocation lines were along the three <211> directions and their total Burgers vectors,ḇt, were of the type , each dislocation being of edge character. TEM examination under proper weak-beam conditions seemed initially to show the standard contrast behaviour for such dislocations, indicating some dislocation segments were undissociated (contrast A), while other segments were dissociated to give two Shockley partials separated by approximately 6nm (contrast B) . A more detailed examination, however, revealed that some segments exhibited a third and anomalous contrast behaviour (contrast C), interpreted here as being due to a new dissociation not previously reported. Experimental results obtained for a dislocation along [211] with for the six <220> type reflections using (g,5g) weak-beam conditions are summarised in the table below, together with the relevant values.

Multislice calculations of RHEED patterns from vicinal Si (001)

1993 ◽  
Vol 51 ◽  
pp. 1000-1001
Author(s):  
Scott Lordi
Keyword(s):  
Misorientation Angle ◽  
Incident Angle ◽  
Incident Beam ◽  
Experimental Results ◽  
Bragg Condition ◽  
Vicinal Surfaces ◽  
Kinematic Theory ◽  
Step Edges

Vicinal Si (001) surfaces are interesting because they are good substrates for the growth of III-V semiconductors. Spots in RHEED patterns from vicinal surfaces are split due to scattering from ordered step arrays and this splitting can be used to determine the misorientation angle, using kinematic arguments. Kinematic theory is generally regarded to be inadequate for the calculation of RHEED intensities; however, only a few dynamical RHEED simulations have been attempted for vicinal surfaces. The multislice formulation of Cowley and Moodie with a recently developed edge patching method was used to calculate RHEED patterns from vicinal Si (001) surfaces. The calculated patterns are qualitatively similar to published experimental results and the positions of the split spots quantitatively agree with kinematic calculations.RHEED patterns were calculated for unreconstructed (bulk terminated) Si (001) surfaces misoriented towards [110] ,with an energy of 15 keV, at an incident angle of 36.63 mrad ([004] bragg condition), and a beam azimuth of [110] (perpendicular to the step edges) and the incident beam pointed down the step staircase.

Appropriation des Savoirs et Mémoire Collective

2013 ◽  
Vol 72 (2) ◽  
pp. 71-78
Author(s):  
Sophie Richardot
Keyword(s):  
Collective Memory ◽  
Factorial Analysis ◽  
Experimental Results ◽  
Ancient History ◽  
Historical Events ◽  
Memoire Collective ◽  
Obedience To Authority

The aim of this study is to understand to what extent soliciting collective memory facilitates the appropriation of knowledge. After being informed about Milgram’s experiment on obedience to authority, students were asked to mention historical or contemporary events that came to mind while thinking about submission to authority. Main results of the factorial analysis show that the students who do not believe in the reproducibility of the experimental results oppose dramatic past events to a peaceful present, whereas those who do believe in the reproducibility of the results also mention dramatic contemporary events, thus linking past and present. Moreover, the students who do not accept the results for today personify historical events, whereas those who fully accept them generalize their impact. Therefore, according to their attitude toward this objet of knowledge, the students refer to two kinds of memory: a “closed memory,” which tends to relegate Milgram’s results to ancient history; and an “open memory,” which, on the contrary, transforms past events into a concept that helps them understand the present. Soliciting collective memory may contribute to the appropriation of knowledge provided the memory activated is an “open” one, linking past to present and going beyond the singularity of the event.

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