Eukaryotic cells use membrane organelles, like the endoplasmic reticulum or the Golgi, to carry out different functions. Vertebrate rod photoreceptors use hundreds of membrane sacs (the disks) for the detection of light. We have used fluorescent tracers and single cell imaging to study the properties of rod photoreceptor disks. Labeling of intact rod photoreceptors with membrane markers and polar tracers revealed communication between intradiskal and extracellular space. Internalized tracers moved along the length of the rod outer segment, indicating communication between the disks as well. This communication involved the exchange of both membrane and aqueous phase and had a time constant in the order of minutes. The communication pathway uses approximately 2% of the available membrane disk area and does not allow the passage of molecules larger than 10 kDa. It was possible to load the intradiskal space with fluorescent Ca(2+) and pH dyes, which reported an intradiskal Ca(2+) concentration in the order of 1 microM and an acidic pH 6.5, both of them significantly different than intracellular and extracellular Ca(2+) concentrations and pH. The results suggest that the rod photoreceptor disks are not discrete, passive sacs but rather comprise an active cellular organelle. The communication between disks may be important for membrane remodeling as well as for providing access to the intradiskal space of the whole outer segment.
The polarization singularities in vector wavefields have been extensively studied analytically and experimentally. The polarization singularities can be analyzed by using electromagnetic theory or Stokes parameters, or be described in terms of complex Stokes scalar fields. In some practical applications, partially coherent beams have more advantages than fully coherent beams. Recently, the concept of the polarization singularities has been extended from fully coherent beams to partially coherent beams. In this paper, using the representation of cross-spectral density matrix propagation, the explicit propagation expressions for the partially coherent edge dislocation beams are derived in free space, and based on the spectral Stokes parameters the spectral singularities are studied in detail. It is shown that there exist spectral s12, s23 and s31 singularities of partially coherent edge dislocation beams in free-space propagation. s12 singularities correspond to circular polarization (C-points) of the partially coherent edge dislocation beams, and s30 (s30) means right-(left-) handedness, where the orientations of the major and minor axes of the polarization ellipse become undefined. s23 and s31 singularities must be located on L-lines, where the handedness of the polarization ellipse is undetermined (linear polarization). The motion, creation and annihilation of spectral Stokes singularities may appear in the variation of a controlling parameter, such as off-axis distance, slope of edge dislocation, spatial correlation length, or in the variation of the propagation distance. By suitably varying the spatial correlation length or propagation distance the V-point, the handedness reversal of C-point, creation and annihilation for a pair of oppositely charged spectral singularities take place. The creation and annihilation occur for a pair of s12 singularities with opposite topological charge but same handedness. The critical points of the controlling parameters and propagation distance, at which pairs of different spectral singularities annihilate, are not the same. The collision of the C-point and L-line results in a V-point (vector singularity), which is unstable. A small perturbation leads to the handedness reversal. At such a point the state of polarization is undetermined and the degree of polarization P=0. The results obtained in this paper would be useful for a deep understanding of polarization singularities of stochastic electromagnetic beams.
Based on the methods of vector angular spectrum of electromagnetic beams and stationary phase, the analytical expressions of TE and TM terms and energy flux distributions of cosh-Gaussian (ChG) vortex beams in the far field are derived, and used to study the phase singularities and energy flux distributions of the ChG vortex beams. It is shown that the density and position of optical vortices will vary by changing decentered parameter or waist width in the ChG vortex beams. The vortex off-axis distance leads to an asymmetric spatial distribution of energy flux. With gradually increasing vortex off-axis distance, dark spots around the origin will move toward the origin center.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.