scholarly journals The velocity shear tensor: tracer of halo alignment

2012 ◽  
Vol 428 (3) ◽  
pp. 2489-2499 ◽  
Author(s):  
N. I. Libeskind ◽  
Y. Hoffman ◽  
J. Forero-Romero ◽  
S. Gottlober ◽  
A. Knebe ◽  
...  
Keyword(s):  
Velocity Shear ◽  
Shear Tensor

scholarly journals The beaming of subhalo accretion

2014 ◽  
Vol 11 (S308) ◽  
pp. 456-461
Author(s):  
Noam I. Libeskind
Keyword(s):  
Large Scale ◽  
Local Group ◽  
High Redshift ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Velocity Shear ◽  
Strongly Correlated ◽  
Peculiar Velocities ◽  
Key Factor ◽  
Shear Tensor

AbstractWe examine the infall pattern of subhaloes onto hosts in the context of the large-scale structure. We find that the infall pattern is essentially driven by the shear tensor of the ambient velocity field. Dark matter subhaloes are preferentially accreted along the principal axis of the shear tensor which corresponds to the direction of weakest collapse. We examine the dependence of this preferential infall on subhalo mass, host halo mass and redshift. Although strongest for the most massive hosts and the most massive subhaloes at high redshift, the preferential infall of subhaloes is effectively universal in the sense that its always aligned with the axis of weakest collapse of the velocity shear tensor. It is the same shear tensor that dictates the structure of the cosmic web and hence the shear field emerges as the key factor that governs the local anisotropic pattern of structure formation. Since the small (sub-Mpc) scale is strongly correlated with the mid-range (∼ 10 Mpc) scale - a scale accessible by current surveys of peculiar velocities - it follows that findings presented here open a new window into the relation between the observed large scale structure unveiled by current surveys of peculiar velocities and the preferential infall direction of the Local Group. This may shed light on the unexpected alignments of dwarf galaxies seen in the Local Group.

On linear wave motions in magnetic-velocity shears

1977 ◽  
Vol 285 (1328) ◽  
pp. 607-636 ◽  
Keyword(s):  
Differential Equation ◽  
Critical Level ◽  
Velocity Shear ◽  
Linear Wave ◽  
Wave Amplification ◽  
Isothermal Fluid ◽  
Governing Differential Equation ◽  
Boussinesq Fluid ◽  
Propagation Properties ◽  
Background State

The propagation properties of linear wave motions in magnetic and/or velocity shears which vary in one coordinate z (say) are usually governed by a second order linear ordinary differential equation in the independent variable z. It is proved that associated with any such differential equation there always exists a quantity A which is independent of z. By employing A a measure of the intensity of the wave, this result is used to investigate the general propagation properties of hydromagnetic-gravity waves (e.g. critical level absorption, valve effects and wave amplification) in magnetic and/or velocity shears, using a full wave treatment. When variations in the basic state are included, the governing differential equation usually has more singularities than it has in the W.K.B.J. approximation, which neglects all variations in the background state. The study of a wide variety of models shows that critical level behaviour occurs only at the singularities predicted by the W.K.B.J. approximation. Although the solutions of the differential equation are necessarily singular at the irregularities whose presence is solely due to the inclusion of variations in the basic state, the intensity of the wave (as measured by A) is continuous there. Also the valve effect is found to persist whatever the relation between the wavelength of the wave and the scale of variations of the background state. In addition, it is shown that a hydromagnetic-gravity wave incident upon a finite magnetic and/or velocity shear can be amplified (or over-reflected) in the absence of any critical levels within the shear layer. In a Boussinesq fluid rotating uniformly about the vertical, wave amplification can occur if the horizontal vertically sheared flow and magnetic field are perpendicular. In a compressible isothermal fluid, on the other hand, wave amplification not only occurs in both magnetic-velocity and velocity shears but also in a magnetic shear acting alone.

scholarly journals Infrared effects in the late stages of black hole evaporation

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
Éanna É. Flanagan
Keyword(s):  
Black Hole ◽  
Angular Momentum ◽  
Center Of Mass ◽  
Planck Scale ◽  
Black Hole Mass ◽  
Order Unity ◽  
Intrinsic Angular Momentum ◽  
Hole Position ◽  
Late Stages ◽  
Shear Tensor

Abstract As a black hole evaporates, each outgoing Hawking quantum carries away some of the black holes asymptotic charges associated with the extended Bondi-Metzner-Sachs group. These include the Poincaré charges of energy, linear momentum, intrinsic angular momentum, and orbital angular momentum or center-of-mass charge, as well as extensions of these quantities associated with supertranslations and super-Lorentz transformations, namely supermomentum, superspin and super center-of-mass charges (also known as soft hair). Since each emitted quantum has fluctuations that are of order unity, fluctuations in the black hole’s charges grow over the course of the evaporation. We estimate the scale of these fluctuations using a simple model. The results are, in Planck units: (i) The black hole position has a uncertainty of $$ \sim {M}_i^2 $$ ∼ M i 2 at late times, where Mi is the initial mass (previously found by Page). (ii) The black hole mass M has an uncertainty of order the mass M itself at the epoch when M ∼ $$ {M}_i^{2/3} $$ M i 2 / 3 , well before the Planck scale is reached. Correspondingly, the time at which the evaporation ends has an uncertainty of order $$ \sim {M}_i^2 $$ ∼ M i 2 . (iii) The supermomentum and superspin charges are not independent but are determined from the Poincaré charges and the super center-of-mass charges. (iv) The supertranslation that characterizes the super center-of-mass charges has fluctuations at multipole orders l of order unity that are of order unity in Planck units. At large l, there is a power law spectrum of fluctuations that extends up to l ∼ $$ {M}_i^2/M $$ M i 2 / M , beyond which the fluctuations fall off exponentially, with corresponding total rms shear tensor fluctuations ∼ MiM−3/2.

scholarly journals Rheological Properties of Wood–Plastic Composites by 3D Numerical Simulations: Different Components

Forests ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 417
Author(s):  
Xingcong Lv ◽  
Xiaolong Hao ◽  
Rongxian Ou ◽  
Tao Liu ◽  
Chuigen Guo ◽  
...  
Keyword(s):  
Flow Field ◽  
Rheological Properties ◽  
Wood Fiber ◽  
Velocity Shear ◽  
Wood Plastic Composites ◽  
Shear Rates ◽  
Plastic Composites ◽  
Power Law Fluids ◽  
Field Information ◽  
Computational Fluid Dynamics Cfd

The rheological properties of wood–plastic composites (WPCs) with different wood fiber contents were investigated using a rotational rheometer under low shear rates. The flow field information was analyzed and simulated by Ansys Polyflow software. The results showed that the WPCs with different wood fiber contents behaved as typical power-law fluids. A higher wood fiber content increased the shear thinning ability and pseudoplasticity of the WPCs. The pressure, velocity, shear rate, and viscosity distributions of the WPC during extrusion could be predicted by computational fluid dynamics (CFD) Ansys Polyflow software to explore the effects of different components on the flow field of WPCs.

Predicting Sulfidic and Naphthenic Acid Corrosion

CORROSION ◽  
2009 ◽  
Vol 65 (12) ◽  
pp. 831-844 ◽  
Author(s):  
J. Hau
Keyword(s):  
Shear Stress ◽  
Exposure Time ◽  
Acid Corrosion ◽  
Naphthenic Acid ◽  
Naphthenic Acids ◽  
Sulfur Compounds ◽  
Velocity Shear ◽  
Threshold Behavior ◽  
Temperature Range ◽  
Si Content

Abstract This paper reviews the factors that are hindering the development of models to predict corrosion due to sulfur compounds, naphthenic acids, or both, acting simultaneously on steels within the temperature range typically from 230°C to 400°C. These factors are identified as data scattering that do not distribute normally, variables or factors that do not exert their influence in a gradual manner but as a threshold behavior, and the interactions between the factors of sulfidic and naphthenic acid corrosion; exposure time, temperature, and velocity (shear stress); and the chromium and molybdenum content of the steels (Si content is not discussed). Not dealing with the interactions is probably the largest obstacle, followed by data scattering.

Experimental study of the collisional parallel velocity shear instability

1997 ◽  
Vol 102 (A12) ◽  
pp. 27249-27255 ◽  
Author(s):  
J. Willig ◽  
R. L. Merlino ◽  
N. D'Angelo
Keyword(s):  
Experimental Study ◽  
Velocity Shear ◽  
Shear Instability

Dissipative instabilities of magnetic neutral layers with velocity shear

1983 ◽  
Vol 29 (3) ◽  
pp. 393-407 ◽  
Author(s):  
M. Dobrowolny ◽  
P. Veltri ◽  
A. Mangeney
Keyword(s):  
General Problem ◽  
Growth Rates ◽  
Velocity Shear ◽  
Singular Case ◽  
Tearing Modes

We consider, in the framework of dissipative MHD, the general problem of instability of magnetic neutral sheets in the presence of velocity shear. Both resistivity and viscosity are included in the treatment. We show that velocity shear and/or viscosity introduce different orderings with respect to resistive tearing modes and that the classical tearing modes represent a singular case. Possible orderings for growth rates are discussed and a specific example containing the effect of velocity shear is treated in detail.

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