We propose and experimentally demonstrate a method based on Brillouin optical time-domain analysis to measure the longitudinal signal power distribution along phase-sensitive fiber-optical parametric amplifiers (PS-FOPAs). Experimental results show that the amplification of a PS-FOPA could go through different longitudinal profiles and yet finish with the same overall gain. This behavior is in sheer contrast with theoretical expectations, according to which longitudinal gain distribution should follow certain profiles determined by the initial relative phase difference but can never end up in the same overall gain. The gap between theory and experiment only becomes evident when the pump wavelength is within the fluctuation range of the zero dispersion wavelength (ZDW) of the PS-FOPA.
We used complexes between a fourth generation polyamidoamine (PAMAM) dendrimer and one of two heterocyclic compounds - 1-(6-hydroxyhexyl)-3-(5-phenyl-isoxazole-3-yl)-urea or 5-phenyl-isoxazole-3-carboxylic acid - to reduce oxygen consumption in transverse slices of the hippocampus taken from 4-week old male rats. In vitro electrophysiological experiments revealed that the inhibitory effect of the hypoxic state on the evoked responses was enhanced in the presence of the complexes. The data were analyzed in terms of the potential antitumor effects of these complexes.
Signals recorded from neurons with extracellular planar sensors have a wide range of waveforms and amplitudes. This variety is a result of different physical conditions affecting the ion currents through a cellular membrane. The transmembrane currents are often considered by macroscopic membrane models as essentially a homogeneous process. However, this assumption is doubtful, since ions move through ion channels, which are scattered within the membrane. Accounting for this fact, the present work proposes a theoretical model of heterogeneous membrane conductivity. The model is based on the hypothesis that both potential and charge are distributed homogeneously on the membrane surface, concentrated near channel pores, as the direct consequence of the inhomogeneous transmembrane current. A system of continuity equations having non-stationary and quasi-stationary forms expresses this fact mathematically. The present work performs mathematical analysis of the proposed equations, following by the synthesis of the equivalent electric element of a heterogeneous membrane current. This element is further used to construct a model of the cell-surface electric junction in a form of the equivalent electrical circuit. After that a study of how the heterogeneous membrane conductivity affects parameters of the extracellular electrical signal is performed. As the result it was found that variation of the passive characteristics of the cell-surface junction like conductivity of the cleft and the cleft height could lead to different shapes of the extracellular signals.
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