Comment on "Topological stability of the half-vortices in spinor exciton-polariton condensates"

We show that recent paper by Flayac et al. [Phys. Rev. B 81, 045318 (2010) and arXiv:0911.1650] is misleading. We demonstrate the existence of static half-quantum vortices in exciton-polariton condensates and calculate the warping of their polarization texture produced by TE-TM splitting of polariton band.Comment: 4 pages, 1 figure. More material was added (in particular, on the current flow)

Vortices in exciton-polariton condensates with polarization splitting

The presence of polarization splitting of exciton-polariton branches in planar semiconductor microcavities has a pronounced effect on vortices in polariton condensates. We show that the TE-TM splitting leads to the coupling between the left and right half-vortices (vortices in the right and left circular components of the condensate), that otherwise do not interact. We analyze also the effect of linear polarization pinning resulted from a fixed splitting between two perpendicular linear polarizations. In this case, half-vortices acquire strings (solitons) attached to them. The half-vortices with strings can be detected by observing the interference fringes of light emitted from the cavity in two circular polarizations. The string affects the fringes in both polarizations. Namely, the half-vortex is characterized by an asymmetric fork-like dislocation in one circular polarization; the fringes in the other circular polarization are continuous, but they are shifted by crossing the string.Comment: 4 pages, 2 figs, Optics of Excitons in Confined Systems 11 (Madrid, 7-11 september 2009

Exocytosis of single chromaffin granules in cell-free inside-out membrane patches.

In chromaffin cells, exocytosis of single granules and properties of the fusion pore — the first connection between vesicular lumen and extracellular space1 — can be studied by cell-attached patch amperometry2, 3, which couples patch-clamp capacitance measurements4, 5, 6, 7 with simultaneous amperometric recordings of transmitter release8, 9. Here we have studied exocytosis of single chromaffin granules and endocytosis of single vesicles in cell-free inside-out membrane patches by patch capacitance measurements and patch amperometry. We excised patches from chromaffin cells by using methods developed for studying properties of single ion channels10. With low calcium concentrations in the pipette and bath, the patches showed no spontaneous exocytosis, but exocytosis could be induced in some patches by applying calcium to the cytoplasmic side of the patch. Exocytosis was also stimulated by calcium entry through the patch membrane. Initial conductances of the fusion pore were undistinguishable in cell-attached and excised patch recordings, but the subsequent pore expansion was slower in excised patches. The properties of exocytotic fusion pores in chromaffin cells are very similar to those observed in mast cells and granulocytes. Excised patches provide a tool with which to study the mechanisms of fusion pore formation and endocytosis in vitro

Exocytosis of catecholamine (CA)-containing and CA-free granules in chromaffin cells.

Recent evidence suggests that endocytosis in neuroendocrine cells and neurons can be tightly coupled to exocytosis, allowing rapid retrieval from the plasma membrane of fused vesicles for future use. This can be a much faster mechanism for membrane recycling than classical clathrin-mediated endocytosis. During a fast exo-endocytotic cycle, the vesicle membrane does not fully collapse into the plasma membrane; nevertheless, it releases the vesicular contents through the fusion pore. Once the vesicle is depleted of transmitter, its membrane is recovered without renouncing its identity. In this report, we show that chromaffin cells contain catecholamine-free granules that retain their ability to fuse with the plasma membrane. These catecholamine-free granules represent 7% of the total population of fused vesicles, but they contributed to 47% of the fusion events when the cells were treated with reserpine for several hours. We propose that rat chromaffin granules that transiently fuse with the plasma membrane preserve their exocytotic machinery, allowing another round of exocytosis

Proton fraction in the inner neutron-star crust

Monte Carlo simulations of neutron-rich matter of relevance to the inner neutron-star crust are performed for a system of A=5,000 nucleons. To determine the proton fraction in the inner crust, numerical simulations are carried out for a variety of densities and proton fractions. We conclude---as others have before us using different techniques---that the proton fraction in the inner stellar crust is very small. Given that the purported "nuclear pasta" phase in stellar crusts develops as a consequence of the long-range Coulomb interaction among protons, we question whether pasta formation is possible in such proton-poor environments. To answer this question, we search for physical observables sensitive to the transition between spherical nuclei and exotic pasta structures. Of particular relevance is the static structure factor S(k)---an observable sensitive to density fluctuations. However, no dramatic behavior was observed in S(k). We regard the identification of physical observables sensitive to the existence---or lack-thereof---of a pasta phase in proton-poor environments as an open problem of critical importance.Comment: 24 pages and 7 figure

Nutrientes vegetais no meio ambiente: ciclos bioquímicos, fertilizantes e corretivos.

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Entrance-channel Mass-asymmetry Dependence of Compound-nucleus Formation Time in Light Heavy-ion Reactions

The entrance-channel mass-asymmetry dependence of the compound nucleus formation time in light heavy-ion reactions has been investigated within the framework of semiclassical dissipative collision models. the model calculations have been succesfully applied to the formation of the $^{38}$Ar compound nucleus as populated via the $^{9}$Be+$^{29}$Si, $^{11}$B+$^{27}$Al, $^{12}$C+$^{26}$Mg and $^{19}$F+$^{19}$F entrance channels. The shape evolution of several other light composite systems appears to be consistent with the so-called "Fusion Inhibition Factor" which has been experimentally observed. As found previously in more massive systems for the fusion-evaporation process, the entrance-channel mass-asymmetry degree of freedom appears to determine the competition between the different mechanisms as well as the time scales involved.Comment: 12 pages, 3 Figures available upon request, Submitted at Phys. Rev.