2,498 research outputs found
On the relevance of bubbles and potential flows for stellar convection
Recently Pasetto et al. have proposed a new method to derive a convection
theory appropriate for the implementation in stellar evolution codes. Their
approach is based on the simple physical picture of spherical bubbles moving
within a potential flow in dynamically unstable regions, and a detailed
computation of the bubble dynamics. Based on this approach the authors derive a
new theory of convection which is claimed to be parameter free, non-local and
time-dependent. This is a very strong claim, as such a theory is the holy grail
of stellar physics.
Unfortunately we have identified several distinct problems in the derivation
which ultimately render their theory inapplicable to any physical regime. In
addition we show that the framework of spherical bubbles in potential flows is
unable to capture the essence of stellar convection, even when equations are
derived correctly.Comment: 14 pages, 3 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Society. (Comments and criticism are welcomed
Simulation pour l'aide Ă l'optimisation et fabrication intelligente des composites par injections sous renfort
Injection sous renfort -- Moulage par transfert de résine -- Composites -- Modéliser l'injection sous renfort -- Outils de caractérisation -- Instrumentation de moule -- Délimiter l'espace de faisabilité -- Méthodes d'optimisation -- Exemples d'optimisation -- Review of numerical filling algorithms used in resin transfer molding simulations and new hybrid formulation -- Guiding selection for reduced process development time in RTM -- Processing parameters -- Moldability diagram -- General mathematical models -- Mathematical models simplification -- Test case -- Building the moldability diagram -- Méthodology -- Développement d'un outil de caratésisation de résine thermodurcissable pour les besoins industriels -- Concept de mini-moule thermique et sommaire du travail réalisé -- Détail du travail réalisé
Explanation for Anomalous Shock Temperatures Measured by Neutron Resonance Spectroscopy
Neutron resonance spectrometry (NRS) has been used to measure the temperature
inside Mo samples during shock loading. The temperatures obtained were
significantly higher than predicted assuming ideal hydrodynamic loading. The
effect of plastic flow and non-ideal projectile behavior were assessed. Plastic
flow was calculated self-consistently with the shock jump conditions: this is
necessary for a rigorous estimate of the locus of shock states accessible.
Plastic flow was estimated to contribute a temperature rise of 53K compared
with hydrodynamic flow. Simulations were performed of the operation of the
explosively-driven projectile system used to induce the shock in the Mo sample.
The simulations predicted that the projectile was significantly curved on
impact, and still accelerating. The resulting spatial variations in load,
including radial components of velocity, were predicted to increase the
apparent temperature that would be deduced from the width of the neutron
resonance by 160K. These corrections are sufficient to reconcile the apparent
temperatures deduced using NRS with the accepted properties of Mo, in
particular its equation of state.Comment: near-final version, waiting for final consent from an autho
On the relevance of bubbles and potential flows for stellar convection
Recently Pasetto et al. have proposed a new method to derive a convection theory appropriate for the implementation in stellar evolution codes. Their approach is based on the simple physical picture of spherical bubbles moving within a potential flow in dynamically unstable regions, and a detailed computation of the bubble dynamics. Based on this approach, the authors derive a new theory of convection which is claimed to be parameter-free, non-local and time-dependent. This is a very strong claim, as such a theory is the holy grail of stellar physics. Unfortunately, we have identified several distinct problems in the derivation which ultimately render their theory inapplicable to any physical regime. In addition, we show that the framework of spherical bubbles in potential flows is unable to capture the essence of stellar convection, even when equations are derived correctly.Facultad de Ciencias AstronĂłmicas y GeofĂsicasInstituto de AstrofĂsica de La Plat
Lipid profiling of the filarial nematodes Onchocerca volvulus, Onchocerca ochengi and Litomosoides sigmodontis reveals the accumulation of nematode-specific ether phospholipids in the host
Onchocerciasis, a neglected tropical disease prevalent in western and central Africa, is a major health problem and has been targeted for elimination. The causative agent for this disease is the human parasite Onchocerca volvulus. Onchocerca ochengi and Litomosoides sigmodontis, infectious agents of cattle and rodents, respectively, serve as model organisms to study filarial nematode infections. Biomarkers to determine infection without the use of painful skin biopsies and microscopic identification of larval worms are needed and their discovery is facilitated by an improved knowledge of parasite-specific metabolites. In addition to proteins and nucleic acids, lipids may be suitable candidates for filarial biomarkers that are currently underexplored. To fill this gap, we present the phospholipid profile of the filarial nematodes O. ochengi, O. volvulus and L. sigmodontis. Direct infusion quadrupole time-of flight (Q-TOF) mass spectrometry was employed to analyze the composition of phospholipids and their molecular species in the three nematode species. Analysis of the phospholipid profiles of plasma or serum of uninfected and infected hosts showed that nematode-specific phospholipids were below detection limits. However, several phospholipids, in particular ether lipids of phosphatidylethanolamine (PE), were abundant in O. ochengi worms and in bovine nodule fluid, suggesting that these phospholipids might be released from O. ochengi into the host, and could serve as potential biomarkers. (C) 2017 The Author(s). Published by Elsevier Ltd on behalf of Australian Society for Parasitology
Thrombocytopenia in the ICU: disseminated intravascular coagulation and thrombotic microangiopathies-what intensivists need to know
Catalytic Arene-forming Aldol Condensation: Stereoselective Synthesis of Rotationally Restricted Aromatic Compounds
By taking inspiration from the fascinating biosynthetic machinery that creates aromatic polyketides, our group investigates analogous reactions catalyzed by small molecules. We are particularly captivated by the prospects of intramolecular aldol condensation reactions to generate different rotationally restricted aromatic compounds. In a first project of our independent research group, a highly stereoselective amine catalyzed synthesis of axially chiral biaryls, tertiary aromatic amides and oligo-1,2-naphthylenes has been developed. In this article, we outline the twists and turns for our escape from the aromatic flatland to structurally intriguing chiral arene scaffolds relevant for various fields of application
Developed turbulence: From full simulations to full mode reductions
Developed Navier-Stokes turbulence is simulated with varying wavevector mode
reductions. The flatness and the skewness of the velocity derivative depend on
the degree of mode reduction. They show a crossover towards the value of the
full numerical simulation when the viscous subrange starts to be resolved. The
intermittency corrections of the scaling exponents of the pth order velocity
structure functions seem to depend mainly on the proper resolution of the
inertial subrange. Universal scaling properties (i.e., independent of the
degree of mode reduction) are found for the relative scaling exponents rho
which were recently defined by Benzi et al.Comment: 4 pages, 5 eps-figures, replaces version from August 5th, 199
- …