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871.
Elastic beads repel in a highly nonlinear fashion, as described by Hertz law, when they are compressed against one another. Vertical stacking results in significant compressions of beads at finite distances from the surface of the stack due to gravity. Analytic studies that have been reported in the literature assume acoustic excitations upon weak perturbation [J. Hong et al., Phys. Rev. Lett. 82, 3058 (1999)] and soliton-like excitations upon strong perturbation [V. Nesterenko, J. Appl. Mech. Tech. Phys. 5, 733 (1983); S. Sen and M. Manciu, Physica A 268, 644 (1999)]. The present study probes the position, velocity and acceleration and selected two-point temporal correlations and their power spectra for individual beads for cases in which the system has been (i) weakly, (ii) strongly, and (iii) moderately perturbed at the surface in the sense specified in the text. Our studies reveal the existence of distinctly different dynamical behavior of the tagged beads, in contrast to conventional acoustic response, as the strength of the perturbation is varied at fixed gravitational loading. We also comment on the effects of polydispersity on system dynamics and probe the relaxation of isolated light and heavy beads in the chain. (c) 2000 American Institute of Physics. 相似文献
872.
Marek Milewski Justyna Baksalary Paweł Antkowiak Włodzimierz Augustyniak Michał Binkowski Jerzy Karolczak Dariusz Komar Andrzej Maciejewski Marian Szymański Wojciech Urjasz 《Journal of fluorescence》2000,10(2):89-89
Spectral and photochemical properties of three aromatic thioketones, 4H-1-benzopyran-4-thione and its two alkyl derivatives, in their second excited singlet and two lowest triplet states have been a subject of stationary and time-resolved studies. Quantum yields of emissions from the above-mentioned states as well as lifetimes of these states have been measured. The results indicate an important role of intermolecular solvent-induced processes in deactivation of the excited states of the thioketones studied. The possible mechanism of these processes involves hydrogen atom abstraction and/or formation of exciplex. For relatively high thione concentrations, the contribution of self-quenching in deactivation of the triplet states becomes significant. The effect of the alkyl chain in a thione molecule on deactivation parameters is discussed. 相似文献
873.
Mariusz Szemień Marian Gryta Edward Grzywa 《Journal of inclusion phenomena and macrocyclic chemistry》2000,37(1-4):59-66
A method of separating Dianin'scompound from a complex mixture of by-productsobtained from the bisphenol-A industrial processis described using compounds which formcrystalline clathrate structures with Dianin'scompound. Under the conditions used the clathratestructure obtained could be crystallized with highpurity (above 99.5%). The described statistical modelof mixture design shows that the highest yield ofcrystallization was found by using a single solvent(ethyl alcohol) for separation of Dianin's compound. 相似文献
874.
B Anuradha CM Santosh V Hari Sai Priya G Suman Latha KJR Murthy Valluri Vijaya Lakshmi 《Journal of immune based therapies and vaccines》2007,5(1):8-7
Background
Mycobacterium bovis BCG vaccine has displayed inconsistent efficacy in different trials conducted in various geographical regions. Nevertheless, it significantly reduces the risk of severe childhood tuberculosis and continues to be used to prevent tuberculosis in many countries. Many studies revealed that efficacy of vaccine wanes with age. Most of the studies were based on in vivo and in vitro responses to tuberculin. With the advent of newer tests such as in vitro interferon-γ assays and identification of potent immunogenic mycobacterial proteins there is a need to corroborate the observations. This study aims at ascertaining the need for a booster at a later age as indicated by in vitro release of IFN-γ while evaluating Ag85A as an antigen. 相似文献875.
876.
Marian Aprodu Laura Costa Rosa Maria Miró-Roig 《Journal of Pure and Applied Algebra》2018,222(1):131-138
In this short note, we study the existence problem for Ulrich bundles on polarized ruled surfaces, focusing our attention on the smallest possible rank. We show that existence of Ulrich line bundles occurs if and only if the coefficient α of the minimal section in the numerical class of the polarization equals one. For other polarizations, we prove the existence of rank two Ulrich bundles. 相似文献
877.
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879.
Bismuth Film Voltammetric Sensor on Pyrolyzed Photoresist/Alumina Support for Determination of Heavy Metals 下载免费PDF全文
Voltammetric sensors based on bismuth film electrodes are an attractive alternative to other sensors for application in electroanalysis of heavy metals. Bismuth film electrodes can be formed by a similar method on the same substrates as mercury. These systems were used most frequently for simultaneous determination of heavy metals such as Pb, Cd and Zn by anodic stripping voltammetry. Our voltammetric sensor was fabricated on an alumina substrate. A photoresist film prepared by pyrolysis of positive photoresist S‐1813 SP15 on the alumina substrate was used as an electrode support for bismuth film deposition. The influence of the Nafion membrane on the measurement sensitivity of the sensor and mechanical stability of the bismuth film were investigated. The sensor was successfully applied for determination of Pb, Cd and Zn in an aqueous solution in the concentration range of 0.2 to 10 µg L?1 by square wave anodic stripping voltammetry on an in‐situ formed bismuth film electrode with Nafion‐coating. Parameters of the sensor such as sensitivity, linearity, detection limit, repeatability and life‐time were evaluated. In the best case, the detection limits were estimated as 0.07, 0.11 and 0.63 µg L?1 for Pb, Cd and Zn, respectively. Finally, the applicability of the sensor was tested in analysis of Pb, Cd and Zn in real samples of tap and river water using the method of standard additions. 相似文献
880.
We formulate a mathematical model for the daily activities of a cow (eating, lying down, and standing) in terms of a piecewise linear dynamical system. We analyze the properties of this bovine dynamical system representing the single animal and develop an exact integrative form as a discrete-time mapping. We then couple multiple cow “oscillators” together to study synchrony and cooperation in cattle herds. We comment on the relevant biology and discuss extensions of our model. With this abstract approach, we not only investigate equations with interesting dynamics but also develop biological predictions. In particular, our model illustrates that it is possible for cows to synchronize less when the coupling is increased. 相似文献