122,841 research outputs found
Exact two-dimensionalization of low-magnetic-Reynolds-number flows subject to a strong magnetic field
No full textWe investigate the behavior of flows, including turbulent flows, driven by a horizontal body-force and subject to a vertical magnetic field, with the following question in mind: for very strong applied magnetic field, is the flow mostly two-dimensional, with remaining weak three-dimensional fluctuations, or does it become exactly 2D, with no dependence along the vertical? We restrict attention to low-magnetic-Reynolds number (Rm) flow. Because liquid metals have low magnetic Prandtl number, such low- flows can have a kinetic Reynolds number as large as one million and therefore be strongly turbulent. We first focus on the quasi-static approximation, i.e. the asymptotic limit of vanishing magnetic Reynolds number Rm << 1: we prove that the flow becomes exactly 2D asymptotically in time, regardless of the initial condition and provided the interaction parameter N is larger than a threshold value. We call this property absolute two-dimensionalization: the attractor of the system is necessarily a (possibly turbulent) 2D flow. We then consider the full-magnetohydrodynamic equations and we prove that, for low enough Rm and large enough N, the flow becomes exactly two-dimensional in the long-time limit provided the initial vertically-dependent perturbations are infinitesimal. We call this phenomenon linear two-dimensionalization: the (possibly turbulent) 2D flow is an attractor of the dynamics, but it is not necessarily the only attractor of the system. Some 3D attractors may also exist and be attained for strong enough initial 3D perturbations. These results shed some light on the existence of a dissipative anomaly for magnetohydrodynamic flows subject to a strong external magnetic field
Archäologische Forschungsreise nach Peru und Bolivia, 1931-1932.
No full textDoering Heinrich U. Archäologische Forschungsreise nach Peru und Bolivia, 1931-1932.. In: Journal de la Société des Américanistes. Tome 25 n°1, 1933. pp. 201-203
Ein Symbol der Grabhöhle in der Nasca-Malerei.
No full textDoering Heinrich U. Ein Symbol der Grabhöhle in der Nasca-Malerei.. In: Journal de la Société des Américanistes. Tome 25 n°1, 1933. pp. 1-8
A modified all-in-one DMSO-activating and base releasing reagent for the Parikh-Doering-type benzylic oxidation reaction
No full textThe Parikh-Doering reaction, an example of the series of DMSO-mediated selective oxidation named reaction family, finds ongoing use in natural product synthesis when mild oxidative reaction conditions are required. The original conditions require the use of Py-SO3 and NEt3 along with DMSO and DCM. As part of our ongoing interest in sulfating agents, we recently disclosed the novel structure of tributylsulfoammonium betaine (TBSAB) that has a formal N-S bond (not dative) and may indicate that other N(sp3) amine-SO3 complexes have been misassigned.
Herein, we explore a commercial sulfating agent, triethylamine-sulfur trioxide complex, as an all-in-one sulfation and base releasing reagent for a modified Parikh-Doering reaction. Single crystal X-ray crystallography further confirms our hypothesis than triethylamine-sulfur trioxide complex exists as triethylsulfoammonium betaine (TESAB). Employing TESAB as an all-in-one reagent, a range of primary and secondary alcohols were screened for competency. Reactivity was observed for the first time with 1) a non Py-SO3 sulfating agent and 2) without the need for additional base. Moderate to good yields of aldehydes and ketones can be prepared in an atom-efficient improvement with concomitant removal of toxic pyridine by-products
Investigation of the asymmetric Doering-Moore-Skattebol synthesis of allenes and carbolithiation methodologies
No full textThe asymmetric Doering-Moore-Skattebøl synthesis of allenes has been investigated. A modest enantioselectivity was observed in the presence of (−)-sparteine as a chiral ligand. Kinetic resolution of racemic 1,2-cyclononadiene was observed under certain conditions. An intramolecular carbolithiation route to all isomeric azaindolines was developed by the cyclization of aryllithiums derived from (N,N-diallylamino)bromopyridines.
ChemInform Abstract: Regio- and Diastereoselective Synthesis of N-Aryl-5-alkylidene-5H-pyrrol-2-ones by a New Domino Reaction of 1,3-Dicarbonyl Dianions with Oxalic Acid-bis(imidoyl)chlorides.
No full textIntermittency in solutions of the three-dimensional Navier-Stokes equations
No full textPublished versio
Fowlerium acutum Gnezdilov 2018, comb. n.
No full textFowlerium acutum (Doering, 1941), comb. n. Thionia acuta Doering, 1941: 214. Thionia naso: Doering 1938: 463, Pl. 51: 5, Pl. 52: 10, Pl. 53: 4, Pl. 55: 1, Pl. 56: 10. Note. Transferred to the genus according to original description (Doering 1938, 1941).Published as part of Gnezdilov, Dimir M., 2018, To the revision of the genus Thionia Stål (Hemiptera, Fulgoroidea, Issidae), with description of new genera and new subtribe, pp. 158-170 in Zootaxa 4434 (1) on page 164, DOI: 10.11646/zootaxa.4434.1.10, http://zenodo.org/record/129088
Intermittency and regularity issues in 3D Navier-Stokes turbulence
No full textTwo related open problems in the theory of 3 D Navier-Stokes turbulence are discussed in this paper. The first is the phenomenon of intermittency in the dissipation field. Dissipation-range intermittency was first discovered experimentally by Batchelor and Townsend over fifty years ago. It is characterized by spatio-temporal binary behaviour in which long, quiescent periods in the velocity signal are interrupted by short, active ‘events’ during which there are violent fluctuations away from the average. The second and related problem is whether solutions of the 3 D Navier-Stokes equations develop finite time singularities during these events. This paper shows that Leray’s weak solutions of the three-dimensional incompressible Navier-Stokes equations can have a binary character in time. The time-axis is split into ‘good’ and ‘bad’ intervals: on the ‘good’ intervals solutions are bounded and regular, whereas singularities are still possible within the ‘bad’ intervals. An estimate for the width of the latter is very small and decreases with increasing Reynolds number. It also decreases relative to the lengths of the good intervals as the Reynolds number increases. Within these ‘bad’ intervals, lower bounds on the local energy dissipation rate and other quantities, such as || u (·, t )|| ∞ and ||∇ u (·, t )|| ∞ , are very large, resulting in strong dynamics at sub-Kolmogorov scales. Intersections of bad intervals for n ≧1 are related to the potentially singular set in time. It is also proved that the Navier-Stokes equations are conditionally regular provided, in a given ‘bad’ interval, the energy has a lower bound that is decaying exponentially in time.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46170/1/205_2005_Article_382.pd
A Multi-Language Comparison of Influences on Author Verification using Character N-Grams
No full textWe create a new multi-language corpus for author verification based on Wikipedia talkpages, and evaluate the influence that differences in topic and time have on character n-gram author profiles. Topic alignment between two texts is found to increase author verification precision, and an authors writing style is found to change over time, but not more significantly after 3 years than after 1 year.Information ArchitectureWISElectrical Engineering, Mathematics and Computer Scienc
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