1,721,201 research outputs found
Theoretical interpretation of Warburg's impedance in unsupported electrolytic cells
No full textWe discuss the origin of Warburg's impedance in unsupported electrolytic cells containing only one group of positive and one group of negative ions. Our analysis is based on the Poisson-Nernst-Planck model, where the generation-recombination phenomenon is neglected. We show that to observe Warburg-like impedance the diffusion coefficient of the positive ions has to differ from that of the negative ones, and furthermore the electrodes have to be not blocking. We assume that the non-blocking properties of the electrodes can be described by means of an Ohmic model, where the charge exchange between the cell and the external circuit is described by means of an electrode conductivity. For simplicity we consider a symmetric cell. However, our analysis can be easily generalized to more complicated situations, where the cell is not symmetric and the charge exchange is described by the Chang-Jaffe model, or by a linearized version of the Butler-Volmer equation. Our analysis allows justification of the expression for Warburg's impedance proposed previously by several groups, based on wrong assumptions
Analisi di pluviogrammi registrati a Cascina Scala (Pavia) e determinazione di ietogrammi di progetto
No full textGenova (Italia
Dati pluviometrici ed idrometrici dettagliati, relativi ad eventi selezionati, registrati nel bacino urbano sperimentale di Cascina Scala (Pavia) nel biennio 1989-1990
No full textPubblicazione n. 177 del Dipartimento di Ingegneria Idraulica e Ambientale dell'Università degli Studi di Pavi
Nonlinear nematic elasticity
No full textThe nonlinear elastic properties of nematic liquid crystals have acquired new interest with the recent experimental observation of bulk modulated nematic phases which are composed by achiral molecules. We extend the Oseen-Zocher-Frank's elastic theory for nematic liquid crystals by including gradients of the nematic strain tensor in the elastic deformation energy. The invariants of the elastic tensor fields, up to the fourth order in the nematic director spatial derivatives, are calculated. An alternative approach that consists in the extension of the linear elastic energy to higher powers of the nematic strain tensor. as in classical elasticity of solids, is also developed. The twist-bend nematic modulated phase is investigated by both approaches and the results are critically compared. The conical angle of the twist-bend phase is calculated as function of the elastic constants. Surface-like effects are considered. Finally, we demonstrate that a splay-bend nematic phase with small oscillations of the nematic director around an axis is prohibited
Precipitazioni e deflussi nel bacino urbano sperimentale di Cascina Scala (Pavia) dal 1° settembre 1989 al 31 Agosto 1990
No full textPubblicazione n. 173 del Dipartimento di Ingegneria Idraulica e Ambientale dell'Università degli Studi di Pavi
Experimental validation of a discrete free gas model for numerical simulation of hydraulic transients with cavitation
No full textValenci
Il modello dell'invaso lineare per i bacini di drenaggio urbano. Una verifica sperimentale
No full textNapoli, Itali
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