Structural stability of Supersonic solutions to the Euler-Poisson system

The well-posedness for the supersonic solutions of the Euler-Poisson system for hydrodynamical model in semiconductor devices and plasmas is studied in this paper. We first reformulate the Euler-Poisson system in the supersonic region into a second order hyperbolic-elliptic coupled system together with several transport equations. One of the key ingredients of the analysis is to obtain the well-posedness of the boundary value problem for the associated linearized hyperbolic-elliptic coupled system, which is achieved via a delicate choice of multiplier to gain energy estimate. The nonlinear structural stability of supersonic solution in the general situation is established by combining the iteration method with the estimate for hyperbolic-elliptic system and the transport equations together.Comment: The paper was revised substantially in this new version. In particular, we constructed the new multiplier under general conditions on the background solution

Ethyl 8-(4-nitro­phen­yl)imidazo[1,2-a]pyridine-7-carboxyl­ate

In the title compound, C16H13N3O4, the imidazo[1,2-a]pyridine and benzene rings make a dihedral angle of 56.21 (2)°. The crystal packing is stabilized by weak π–π stacking inter­actions [centroid–centroid distances = 3.787 (2) Å] and C—H⋯O inter­molecular hydrogen-bonding inter­actions

Simulating infrastructure networks in the Yangtze River Delta (China) using generative urban network models

This paper explores the urban-geographical potential of simulation approaches combining spatial and topological processes. Drawing on Vértes et al.'s (2012) economical clustering model, we propose a generative network model integrating factors captured in traditional spatial models (e.g., gravity models) and more recently developed topological models (e.g., actor-oriented stochastic models) into a single framework. In our urban network-implementation of the generative network model, it is assumed that the emergence of inter-city linkages can be approximated through probabilistic processes that speak to a series of contradictory forces. Our exploratory study focuses on the outline of the infrastructure networks connecting prefecture-level cities in the highly urbanized Yangtze River Delta (China). Possible hampering factors in the emergence of these networks include distance and administrative boundaries, while stimulating factors include a measure of city size (population, gross domestic product) and a topological rule stating that the formation of connections between cities sharing nearest neighbors is more likely (i.e., a transitive effect). Based on our results, two wider implications of our research are discussed: (1) it confirms the potential of the proposed method in urban network simulation in that the inclusion of a topological factor alongside geographical factors generates an urban network that better approximates the observed network; (2) it allows exploring the differential extent to which driving forces influence the structure of different urban networks. For instance, in the Yangtze River Delta, transitivity plays a less important role in the Internet-network formation; GDP and boundaries more strongly affect the rail network; and distance decay effects play a more prominent role in the road network

Biosynthesis of thiocarboxylic acid-containing natural products.

Thiocarboxylic acid-containing natural products are rare and their biosynthesis and biological significance remain unknown. Thioplatensimycin (thioPTM) and thioplatencin (thioPTN), thiocarboxylic acid congeners of the antibacterial natural products platensimycin (PTM) and platencin (PTN), were recently discovered. Here we report the biosynthetic origin of the thiocarboxylic acid moiety in thioPTM and thioPTN. We identify a thioacid cassette encoding two proteins, PtmA3 and PtmU4, responsible for carboxylate activation by coenzyme A and sulfur transfer, respectively. ThioPTM and thioPTN bind tightly to β-ketoacyl-ACP synthase II (FabF) and retain strong antibacterial activities. Density functional theory calculations of binding and solvation free energies suggest thioPTM and thioPTN bind to FabF more favorably than PTM and PTN. Additionally, thioacid cassettes are prevalent in the genomes of bacteria, implicating that thiocarboxylic acid-containing natural products are underappreciated. These results suggest that thiocarboxylic acid, as an alternative pharmacophore, and thiocarboxylic acid-containing natural products may be considered for future drug discovery

Learning management systems: one size fits all?

Learning management systems such as WebCT and Blackboard are rapidly becoming the principal systems behind institutions' moves to technology-based learning settings. In settings where lecturers have had no or limited exposure to ICT as a teaching tool, LMSs pave the way for quick introduction and eventual adoption of technology-based teaching practices. Many lecturers quickly progress and grow in the field. But there are those who argue that the use of LMS tend to be counter-productive and that in their current forms, they cannot be used effectively as a learning tool. Critics argue that they support only traditional forms of teaching and encourage poor learning designs in their implementation. This panel will explore LMSs as they exist today and will explore whether they are the solution to a pressing problem or in fact problems within themselves

Ethyl 1-(4-chloro­benz­yl)-3-phenyl-1H-pyrazole-5-carboxyl­ate

In the title compound, C19H17ClN2O2, the pyrazole ring makes dihedral angles of 6.97 (5) and 79.25 (1)°, respectively, with the phenyl and chlorophenyl rings, respectively. In the crystal, C—H⋯O hydrogen bonds are observed