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Negative Charge Density (negative + charge_density)
Selected AbstractsGauge-independent quantum dynamics on phase-space of charged scalar particlesFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 2-3 2003S. Varró On the basis of the Hamiltonian form of the Klein-Gordon equation of a charged scalar particle field introduced by Feshbach and Villars, the gauge-invariant 2×2 Wigner matrix has been constructed whose diagonal elements describe positive and negative charge densities and the off-diagonal elements correspond to cross-densities in phase-space. The system of coupled transport equations has been derived in case of interaction with an arbitrary external electromagnetic field. A gauge-independent generalization of the free particle representation due to Feshbach and Villars is given, and on the basis of it both the nonrelativistic and the classical limits of the general relativistic quantum Boltzmann-Vlasov equation(RQBVE) is discussed. In the non-relativistic limit (p/mc,0) the set of equations of motion decouple to two independent quantum transport equations describing the dynamics of oppositely charged positon and negaton densities separately. In the classical limit(,,0) two relativistic Boltzmann-Vlasov equations result for the diagonal positon and negaton densities. It is obtained that, though in the latter equations the Planck constant , is absent, the real part of the cross-density does not vanish. [source] Existence of front solutions for a nonlocal transport problem describing gas ionizationMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 12 2010M. Günther Abstract We discuss a moving boundary problem arising from a model of gas ionization in the case of negligible electron diffusion and suitable initial data. It describes the time evolution of an ionization front. Mathematically, it can be considered as a system of transport equations with different characteristics for positive and negative charge densities. We show that only advancing fronts are possible and prove short-time well posedness of the problem in Hölder spaces of functions. Technically, the proof is based on a fixed-point argument for a Volterra-type system of integral equations involving potential operators. It crucially relies on estimates of such operators with respect to variable domains in weighted Hölder spaces and related calculus estimates. Copyright © 2010 John Wiley & Sons, Ltd. [source] Activated carbon surface modifications by adsorption of bacteria and their effect on aqueous lead adsorptionJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 12 2001J Rivera-Utrilla Abstract The adsorption of Escherichia coli on different activated carbons has been studied. The activated carbon samples used have been characterized, determining their surface area, pore size distribution, elemental analysis, mineral matter analysis and pH of the point of zero charge. The adsorption capacity of these carbons increased with their hydrophobicity and macropore volume. The number of bacteria adsorbed on the demineralized activated carbon in a solution of pH value equal to the iso-electric point of the carbon was negligible. However, in the presence of cations the proportions of bacterial cells adsorbed were 87.8% (Fe3+), 54.7% (Ca2+) and 24.8% (Mg2+) respectively. This increase in adsorption capacity in the presence of electrolytes has been explained on the basis of both the reduction in electrostatic free energy and the increase in cell surface hydrophobicity due to the metal bound by some compounds of the cell membrane. When the solution pH was intermediate between the pH values of the point of zero charge of the carbon and bacteria the number of bacteria adsorbed increased due to the attractive interactions between the carbon and bacteria. The adsorption of bacteria on activated carbons decreased the porosity and increased the negative charge density of the latter. Depending on the experimental conditions used, the presence of bacteria can enhance the capacity of activated carbons to adsorb lead. © 2001 Society of Chemical Industry [source] Colorimetric Sensing of Adenosine Based on Aptamer Binding Inducing Gold Nanoparticle AggregationCHINESE JOURNAL OF CHEMISTRY, Issue 10 2009Xueping Liu Abstract A simple and rapid colorimetric approach for the determination of adenosine has been developed via target inducing aptamer structure switching, thus leading to Au colloidal solution aggregation. In the absence of the analytes, the aptamer/gold nanoparticle (Au NP) solution remained well dispersed under a given high ionic strength condition in that the random-coil aptamer was readily wrapped on the surface of the Au NPs, which resulted in the enhancement of the repulsive force between the nanoparticles due to the high negative charge density of DNA molecules. While in the presence of adenosine, target-aptamer complexes were formed and the conformation of the aptamer was changed to a folded structure which disfavored its adsorption on the Au NP surface, thus leading to the reduction of the negative charge density on each Au NP and then the reduced degree of electrostatic repulsion between Au nanoparticles. As a result, the aggregation of the Au colloidal solution occurred. The changes of the absorption spectrum could be easily monitored by a UV-Vis spectrophotometer. A linear correlation exists between the ratio of the absorbance of the system at 522 to 700 nm (A522 nm/A700 nm) and the concentration of adenosine between 100 nmol·L,1 and 10 µmol·L,1, with a detection limit of 51.5 nmol·L,1. [source] | ||||||||||