Reply to Peter Hubral by the Author

Geophysics ◽  
1978 ◽  
Vol 43 (5) ◽  
pp. 1024-1025
Author(s):  
Paul Michaels
Keyword(s):  
Velocity Gradient ◽  
Horizontal Velocity ◽  
Lateral Velocity ◽  
Velocity Gradients ◽  
Coordinate Rotation

Peter Hubral’s extension of the raypath migration calculator program to include a lateral velocity gradient is quite ingenious. In such cases where the vertical and horizontal velocity gradients are constant, the net effect is a simple coordinate rotation. The theoretical raypath remains circular, but is only rotated about its intersection with the datum plane.

scholarly journals Velocity Gradient Separation Reveals a New Extracellular Vesicle Population Enriched in miR-155 and Mitochondrial DNA

Pathogens ◽  
2021 ◽  
Vol 10 (5) ◽  
pp. 526
Author(s):  
Myriam Vaillancourt ◽  
Audrey Hubert ◽  
Caroline Subra ◽  
Julien Boucher ◽  
Wilfried Wenceslas Bazié ◽  
...  
Keyword(s):  
Mitochondrial Dna ◽  
Velocity Gradient ◽  
Messenger Rna ◽  
Sucrose Density Gradient ◽  
Extracellular Vesicle ◽  
Therapeutic Interventions ◽  
Optimal Separation ◽  
Velocity Gradients ◽  
Commercial Kits ◽  
Hiv 1

Extracellular vesicles (EVs) and their contents (proteins, lipids, messenger RNA, microRNA, and DNA) are viewed as intercellular signals, cell-transforming agents, and shelters for viruses that allow both diagnostic and therapeutic interventions. EVs circulating in the blood of individuals infected with human immunodeficiency virus (HIV-1) may provide insights into pathogenesis, inflammation, and disease progression. However, distinguishing plasma membrane EVs from exosomes, exomeres, apoptotic bodies, virions, and contaminating proteins remains challenging. We aimed at comparing sucrose and iodixanol density and velocity gradients along with commercial kits as a means of separating EVs from HIV particles and contaminating protein like calprotectin; and thereby evaluating the suitability of current plasma EVs analysis techniques for identifying new biomarkers of HIV-1 immune activation. Multiple analysis have been performed on HIV-1 infected cell lines, plasma from HIV-1 patients, or plasma from HIV-negative individuals spiked with HIV-1. Commercial kits, the differential centrifugation and density or velocity gradients to precipitate and separate HIV, EVs, and proteins such as calprotectin, have been used. EVs, virions, and contaminating proteins were characterized using Western blot, ELISA, RT-PCR, hydrodynamic size measurement, and enzymatic assay. Conversely to iodixanol density or velocity gradient, protein and virions co-sedimented in the same fractions of the sucrose density gradient than AChE-positive EVs. Iodixanol velocity gradient provided the optimal separation of EVs from viruses and free proteins in culture supernatants and plasma samples from a person living with HIV (PLWH) or a control and revealed a new population of large EVs enriched in microRNA miR-155 and mitochondrial DNA. Although EVs and their contents provide helpful information about several key events in HIV-1 pathogenesis, their purification and extensive characterization by velocity gradient must be investigated thoroughly before further use as biomarkers. By revealing a new population of EVs enriched in miR-155 and mitochondrial DNA, this study paves a way to increase our understanding of HIV-1 pathogenesis.

The influence of agitation on aggregates formed during treatment of water with a content of humic substances

2006 ◽  
Vol 6 (1) ◽  
pp. 211-218 ◽  
Author(s):  
L. Pivokonska ◽  
M. Pivokonsky
Keyword(s):  
Humic Substances ◽  
Velocity Gradient ◽  
Laboratory Tests ◽  
Treatment Plant ◽  
Water Treatment Plant ◽  
Aluminium Chloride ◽  
Velocity Gradients ◽  
Perforated Baffle ◽  
Wide Size Distribution

This study aims to evaluate the influence of agitation conditions on the efficiency of the aggregation process when treating surface water containing humic substances. Laboratory tests were conducted by the jar tests using a variable speed paddle gang stirrer. Optimization of agitation intensity was determined by a Couette flocculator. Suspension was prepared using aluminium chloride as a destabilising reagent. Aggregation efficiency was evaluated by the determination of the degree of aggregation and by the test of aggregation. For all surface waters treated, the optimum treatability was demonstrated by applying higher velocity gradients (G=200–250 s−1). In addition to the laboratory tests, the plant measurements with water containing increased amounts of humic substances were taken to evaluate the aggregation efficiency. The results obtained by the aggregation efficiency measurements show that the intensity of agitation, with the assistance of perforated baffle-type flocculation chamber, attains a low level of velocity gradient (G=22–113 s−1), in contrast to the optimized velocity gradient level (G=200–250 s−1). The aggregates formed in the water treatment plant have an unsuitably wide size-distribution.

scholarly journals Self-gravitating filament formation from shocked flows: velocity gradients across filaments

2020 ◽  
Vol 494 (3) ◽  
pp. 3675-3685 ◽  
Author(s):  
Che-Yu Chen ◽  
Lee G Mundy ◽  
Eve C Ostriker ◽  
Shaye Storm ◽  
Arnab Dhabal
Keyword(s):  
Velocity Gradient ◽  
Unit Length ◽  
Selection Effect ◽  
Major Axis ◽  
Large Area ◽  
North West ◽  
Preferred Direction ◽  
The North ◽  
Velocity Gradients ◽  
Field Lines

ABSTRACT In typical environments of star-forming clouds, converging supersonic turbulence generates shock-compressed regions, and can create strongly magnetized sheet-like layers. Numerical magnetohydrodynamic simulations show that within these post-shock layers, dense filaments and embedded self-gravitating cores form via gathering material along the magnetic field lines. As a result of the preferred-direction mass collection, a velocity gradient perpendicular to the filament major axis is a common feature seen in simulations. We show that this prediction is in good agreement with recent observations from the CARMA Large Area Star Formation Survey (CLASSy), from which we identified several filaments with prominent velocity gradients perpendicular to their major axes. Highlighting a filament from the north-west part of Serpens South, we provide both qualitative and quantitative comparisons between simulation results and observational data. In particular, we show that the dimensionless ratio Cv ≡ Δvh2/(GM/L), where Δvh is half of the observed perpendicular velocity difference across a filament, and M/L is the filament’s mass per unit length, can distinguish between filaments formed purely due to turbulent compression and those formed due to gravity-induced accretion. We conclude that the perpendicular velocity gradient observed in the Serpens South north-west filament can be caused by gravity-induced anisotropic accretion of material from a flattened layer. Using synthetic observations of our simulated filaments, we also propose that a density-selection effect may explain observed subfilaments (one filament breaking into two components in velocity space) as reported in recent observations.

High magnitude global seismicity and lateral velocity gradients

1970 ◽  
Vol 80 (1) ◽  
pp. 92-101
Author(s):  
Harsh K. Gupta ◽  
Janardan G. Negi
Keyword(s):  
Lateral Velocity ◽  
Velocity Gradients ◽  
High Magnitude ◽  
Global Seismicity

scholarly journals The Fluid Dynamical Performance of the Carpentier-Edwards PERIMOUNT Magna Ease Prosthesis

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Philipp Marx ◽  
Wojciech Kowalczyk ◽  
Aydin Demircioglu ◽  
Gary Neil Brault ◽  
Hermann Wendt ◽  
...  
Keyword(s):  
Velocity Gradient ◽  
Aortic Wall ◽  
Particle Image ◽  
In Vitro Study ◽  
Maximal Velocity ◽  
Flow Parameters ◽  
Velocity Gradients ◽  
Image Velocimetry ◽  
Maximal Strain

The aim of the present in vitro study was the evaluation of the fluid dynamical performance of the Carpentier-Edwards PERIMOUNT Magna Ease depending on the prosthetic size (21, 23, and 25 mm) and the cardiac output (3.6–6.4 L/min). A self-constructed flow channel in combination with particle image velocimetry (PIV) enabled precise results with high reproducibility, focus on maximal and local peek velocities, strain, and velocity gradients. These flow parameters allow insights into the generation of forces that act on blood cells and the aortic wall. The results showed that the 21 and 23 mm valves have a quite similar performance. Maximal velocities were 3.03±0.1 and 2.87±0.13 m/s; maximal strain Exx, 913.81±173.25 and 896.15±88.16 1/s; maximal velocity gradient Eyx, 1203.14±221.84 1/s and 1200.81±61.83 1/s. The 25 mm size revealed significantly lower values: maximal velocity, 2.47±0.15 m/s; maximal strain Exx, 592.98±155.80 1/s; maximal velocity gradient Eyx, 823.71±38.64 1/s. In summary, the 25 mm Magna Ease was able to create a wider, more homogenous flow with lower peak velocities especially for higher flow rates. Despite the wider flow, the velocity values close to the aortic walls did not exceed the level of the smaller valves.

Lagrangian investigations of velocity gradients in compressible turbulence: lifetime of flow-field topologies

2019 ◽  
Vol 872 ◽  
pp. 492-514 ◽  
Author(s):  
Nishant Parashar ◽  
Sawan Suman Sinha ◽  
Balaji Srinivasan
Keyword(s):  
Mach Number ◽  
Velocity Gradient ◽  
Direct Numerical Simulations ◽  
Compressible Turbulence ◽  
Lagrangian Particle ◽  
Gradient Tensor ◽  
Velocity Gradient Tensor ◽  
Conditional Mean ◽  
Velocity Gradients ◽  
Decaying Turbulence

We perform Lagrangian investigations of the dynamics of velocity gradients in compressible decaying turbulence. Specifically, we examine the evolution of the invariants of the velocity-gradient tensor. We employ well-resolved direct numerical simulations over a range of Mach number along with a Lagrangian particle tracker to examine trajectories of fluid particles in the space of the invariants of the velocity gradient tensor. This allows us to accurately measure the lifetimes of major topologies of compressible turbulence and provide an explanation of why some selective topologies tend to exist longer than the others. Further, the influence of dilatation on the lifetime of various topologies is examined. Finally, we explain why the so-called conditional mean trajectories (CMT) used previously by several researchers fail to predict the lifetime of topologies accurately.

scholarly journals On the Progenitors of Type Ia Supernovae

2011 ◽  
Vol 7 (S281) ◽  
pp. 303-308
Author(s):  
Mario Livio
Keyword(s):  
Velocity Gradient ◽  
Degenerate Case ◽  
Type Ia Supernovae ◽  
Spherically Symmetric ◽  
Velocity Gradients ◽  
Main Class ◽  
Type Ia ◽  
The Asymmetry ◽  
Ia Supernovae

AbstractI propose two new means of identifying the main class of progenitors of Type Ia supernovae – single or double degenerate: (i) If the range of supernova properties is significantly determined by the range of viewing angles of non-spherically symmetric explosions, then the nature of the correlation between polarization and another property (for example, the velocity gradient) can be used to determine the geometry of the asymmetry and hence the nature of the progenitor, and (ii) in the double- but not in the single-degenerate case, the range in the observed properties (e.g., velocity gradients) is likely to increase with the amount of carbon seen in the ejecta.

Velocity gradient as a tool to characterise the link between mixing and biogas production in anaerobic waste digesters

2013 ◽  
Vol 67 (12) ◽  
pp. 2800-2806 ◽  
Author(s):  
R. Sindall ◽  
J. Bridgeman ◽  
C. Carliell-Marquet
Keyword(s):  
Velocity Gradient ◽  
Biogas Production ◽  
Gas Production ◽  
Valuable Contribution ◽  
Anaerobic Digesters ◽  
Mixing Speed ◽  
Cfd Models ◽  
Specific Effects ◽  
Velocity Gradients ◽  
Computational Fluid Dynamics Cfd

Whilst the importance of mixing in anaerobic digesters to enhance process performance and gas production is well recognised, the specific effects of mixing regime on biogas production are not clear. Here, the velocity gradient is used to demonstrate the importance of minimally mixed zones in a digester, with computational fluid dynamics (CFD) models indicating that 20–85% of a laboratory-scale digester experiences local velocity gradients of less than 10 s−1, dependent on mixing speed. Experimental results indicate that there is a threshold above which increased mixing speed (and hence velocity gradient) becomes counter-productive and biogas production falls. The effects of minimal mixing on digester microbiology are considered with the creation or destruction of localised pockets of high acetate concentration providing a possible explanation for the velocity gradient threshold. The identification of this threshold represents a valuable contribution to the understanding of the effects of mixing on gas production in anaerobic digesters.

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