1,250 research outputs found
Anisotropic eddy viscosity models
A general discussion on the structure of the eddy viscosity tensor in anisotropic flows is presented. The systematic use of tensor symmetries and flow symmetries is shown to reduce drastically the number of independent parameters needed to describe the rank 4 eddy viscosity tensor. The possibility of using Onsager symmetries for simplifying further the eddy viscosity is discussed explicitly for the axisymmetric geometry
Tagging single muons and other long-flying relativistic charged particles by ultra-fast timing in air Cherenkov telescopes
Atmospheric air Cherenkov telescopes are successfully used for ground-based,
very high-energy (VHE) gamma ray astronomy. Triggers from the so-called single
muon and other long-flying relativistic charged particle events are an unwanted
background for the Cherenkov telescope. Because of low rate at TeV energies the
muon background is unimportant. It is much more intense for telescopes with
high photon sensitivity and low energy threshold. Below a few hundred GeV
energy, the so-called muon background becomes so intense, that it can
deteriorate the sensitivity of telescopes (the so-called muon-wall problem).
From general considerations it can be anticipated that the signature of these
particles should be a light pulse with a narrow time structure. In fact,
simulations show that the pulses from muons have a very narrow time profile
that is well below the time resolutions of nearly all currently operating
telescopes. In this report we elaborate on the time profile of Cherenkov light
from the so-called single muons and show that a telescope with ultra-fast time
response can open a new dimension allowing one to tag and to reject those
events.Comment: Accepted by Astroparticle Physic
Ensemble averaged dynamic modeling
The possibility of using the information from simultaneous equivalent Large Eddy Simulations (LAS) for improving the subgrid scale modeling is investigated. An ensemble average dynamic model is proposed as an alternative to the usual spatial average versions. It is shown to be suitable independently of the existence of any homogeneity directions, and its formulation is thus universal. The ensemble average dynamic model is shown to give very encouraging results for as few as 16 simultaneous LES's
Vorticity Budget of Weak Thermal Convection in Keplerian disks
By employing the equations of mean-square vorticity (enstrophy) fluctuations
in strong shear flows, we demonstrate that unlike energy production of
turbulent vorticity in nonrotating shear flows, the turbulent vorticity of weak
convection in Keplerian disks cannot gain energy from vortex stretching/tilting
by background shear unless the asscoiated Reynolds stresses are negative. This
is because the epicyclic motion is an energy sink of the radial component of
mean-square turbulent vorticity in Keplerian disks when Reynolds stresses are
positive. Consequently, weak convection cannot be self-sustained in Keplerian
flows. This agrees with the results implied from the equations of mean-square
velocity fluctuations in strong shear flows. Our analysis also sheds light on
the explanation of the simulation result in which positive kinetic helicity is
produced by the Balbus-Hawley instability in a vertically stratified Keplerian
disk. We also comment on the possibility of outward angular momentum transport
by strong convection based on azimuthal pressure perturbations and directions
of energy cascade.Comment: 8 pages, 1 figure, emulateapj.sty, revised version in response to
referee's comments, accepted by Ap
Recommended from our members
A Wavelet Based Dissipation Method for ALE Schemes
Wavelet analysis is natural tool to detect the presence of numerical noise, shocks and other features which might drive a calculation to become unstable. Here we suggest ways where wavelets can be used effectively to define a dissipation flag to replace dissipation flags traditionally used in ALE numerical schemes
The μ opioid agonist morphine modulates potentiation of capsaicin-evoked TRPV1 responses through a cyclic AMP-dependent protein kinase A pathway
BACKGROUND: The vanilloid receptor 1 (TRPV1) is critical in the development of inflammatory hyperalgesia. Several receptors including G-protein coupled prostaglandin receptors have been reported to functionally interact with the TRPV1 through a cAMP-dependent protein kinase A (PKA) pathway to potentiate TRPV1-mediated capsaicin responses. Such regulation may have significance in inflammatory pain. However, few functional receptor interactions that inhibit PKA-mediated potentiation of TRPV1 responses have been described. RESULTS: In the present studies we investigated the hypothesis that the μ opioid receptor (MOP) agonist morphine can modulate forskolin-potentiated capsaicin responses through a cAMP-dependent PKA pathway. HEK293 cells were stably transfected with TRPV1 and MOP, and calcium (Ca(2+)) responses to injection of the TRPV1 agonist capsaicin were monitored in Fluo-3-loaded cells. Pre-treatment with morphine did not inhibit unpotentiated capsaicin-induced Ca(2+ )responses but significantly altered capsaicin responses potentiated by forskolin. TRPV1-mediated Ca(2+ )responses potentiated by the direct PKA activator 8-Br-cAMP and the PKC activator Phorbol-12-myristate-13-acetatewere not modulated by morphine. Immunohistochemical studies confirmed that the TRPV1 and MOP are co-expressed on cultured Dorsal Root Ganglion neurones, pointing towards the existence of a functional relationship between the G-protein coupled MOP and nociceptive TRPV1. CONCLUSION: The results presented here indicate that the opioid receptor agonist morphine acts via inhibition of adenylate cyclase to inhibit PKA-potentiated TRPV1 responses. Targeting of peripheral opioid receptors may therefore have therapeutic potential as an intervention to prevent potentiation of TRPV1 responses through the PKA pathway in inflammation
- …