245 research outputs found
New reactions and strategies in divergent syntheses of macrolide antibiotics
No full textFrom the microbial world, antibiotics are structurally complex and highly potent chemical weapons that co-evolved with bacteria. Macrolide (glycosylated cyclic polyketides) antibiotics have been used extensively as first-line antibacterial agents since the discovery of the broad-spectrum antibiotic erythromycin A in 1952. However wide-spread use of antibiotics has led pathogens to develop drug resistance. Therefore new and enhanced antibiotics are constantly in need. Described in this dissertation is my effort to emulate the synthetic capabilities of erythromycin-producing bacteria by accessing novel erythromycin-inspired polyketides via divergent total synthesis. New allene oxidation methods have been developed and implemented in a modular and divergent route to produce a diversified portfolio of cyclic polyketides and their glycoconjugates. I will disclose a total synthesis of 4,10-didesmethyl-(9S)-dihydroerythronolide A (Chapter 2), preparation of glycosylated erythromycin analogs (Chapter 3) and progress towards synthesis of 9(S)-dihydroerythronolide A (Chapter 4).Ph.D.Includes bibliographical referencesby Libing Y
ON GEODESICS OF FINSLER METRICS VIA NAVIGATION PROBLEM
No full textThis paper is devoted to a study of geodesics of Finsler metrics via Zermelo navigation. We give a geometric description of the geodesics of the Finsler metric produced from any Finsler metric and any homothetic field in terms of navigation representation, generalizing a result previously only known in the case of Randers metrics with constant S-curvature. As its application, we present explicitly the geodesics of the Funk metric on a strongly convex domain.Mathematics, AppliedMathematicsSCI(E)0ARTICLE83015-302413
On Finsler surfaces of constant curvature with two-dimensional isometry group
No full textIn this paper, we study Finsler surfaces of constant (flag) curvature. We show that the space of those, with two-dimensional isometric group depends on two arbitrary constants. We also give a new technique to recover Finsler metrics from the specified two constants. Using this technique we obtain some new Finsler surfaces of constant flag curvature with two-dimensional isometry group.National Natural Science Foundation of China [11371032, 11301283]SCI(E)[email protected]; [email protected]
Projectively flat Finsler metrics with orthogonal invariance
No full textWe study Finsler metrics with orthogonal invariance. By determining an expression of these Finsler metrics we find a PDE equivalent to these metrics being locally projectively flat. After investigating this PDE we manufacture projectively flat Finsler metrics with orthogonal invariance in terms of error functions.MathematicsSCI(E)6ARTICLE3259-27010
Research on the relationship between the elements and pharmacological activities in velvet antler using factor analysis and cluster analysis
No full textOn spherically symmetric Finsler metrics of scalar curvature
No full textSpherically symmetric Finsler. metrics form a rich class of Finsler metrics. In this paper we find equations that characterize spherically symmetric Finsler metrics of scalar flag curvature. By using these equations, we construct infinitely many non-projectively flat spherically symmetric Finsler metrics of scalar curvature. (C) 2012 Elsevier B.V. All rights reserved.Mathematics, AppliedPhysics, MathematicalSCI(E)3ARTICLE112279-22876
On some dually flat Finsler metrics with orthogonal invariance
No full textInspired by the integral representation of two-dimensional reversible projective Finsler metrics due to A. V. Pogorelov, we explicitly construct two new families of dually flat (not necessarily reversible) Finsler metrics with orthogonal invariance of arbitrary dimension. (C) 2014 Elsevier Ltd. All rights reserved.Mathematics, AppliedMathematicsSCI(E)[email protected]; [email protected]
A conclusive theorem on Finsler metrics of sectional flag curvature
No full textIf the flag curvature of a Finsler manifold reduces to sectional curvature, then locally either the Finsler metric is Riemannian, or the flag curvature is isotropic
Influence of Number of Pole Pairs on Torque Ripple of Magnetic Gear
No full textThe field modulation magnetic gear is a kind of transmission device with broad development prospects. It has the advantages of no friction， no pollution， less maintenance and easy installation. The magnetic gear models with different transmission ratio are established. The input and output torque waveforms of different models are compared. The influences of the number of pole pairs of inner rotor （P1） and the number of pole pairs of outer rotor （P2） on torque ripple are analyzed. According to the principle of magnetic field modulation and spatial magnetic field harmonic distribution， the torque ripple of magnetic gear is greatly affected by P1 and P2. The research results show that the torque ripple can be effectively reduced by selecting the magnetic gear with P1=4， P1:P2=1:n+0.25 or 1:n+0.75 （n is a natural number）
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