176,877 research outputs found

    Counting integral points in certain homogeneous spaces

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    Highly efficient optogenetic cell ablation in C. elegans using membrane-targeted miniSOG.

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    The genetically encoded photosensitizer miniSOG (mini Singlet Oxygen Generator) can be used to kill cells in C. elegans. miniSOG generates the reactive oxygen species (ROS) singlet oxygen after illumination with blue light. Illumination of neurons expressing miniSOG targeted to the outer mitochondrial membrane (mito-miniSOG) causes neuronal death. To enhance miniSOG's efficiency as an ablation tool in multiple cell types we tested alternative targeting signals. We find that membrane targeted miniSOG allows highly efficient cell killing. When combined with a point mutation that increases miniSOG's ROS generation, membrane targeted miniSOG can ablate neurons in less than one tenth the time of mito-miniSOG. We extend the miniSOG ablation technique to non-neuronal tissues, revealing an essential role for the epidermis in locomotion. These improvements expand the utility and throughput of optogenetic cell ablation in C. elegans

    The radiation properties of an accretion disk with a non-zero torque on its inner edge

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    The structure of the inner edge of the accretion disk around a black hole can be altered, if the matter inside the marginally stable orbit is magnetically connected to the disk. In this case, a non-zero torque is exerted on its inner edge, and the accretion efficiency ϵ\epsilon can be much higher than that in the standard accretion disk model. We explore the radiation properties of an accretion disk at its sonic point around a black hole with a time-steady torque exerted on the inner edge of the disk. The local structure of the accretion flow at the sonic point is investigated in the frame of general relativity. It is found that the accretion flow will be optically thin at its sonic point for most cases, if the additional accretion efficiency δϵ\delta\epsilon caused by the torque is as high as \sim10 %. The results imply that the variable torque may trigger transitions of the flow between different accretion types.Comment: 6 pages, to appear in PASJ, Vol. 55, No. 1 (February 25, 2003

    Existence of log canonical closures

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    Let f:XUf:X\to U be a projective morphism of normal varieties and (X,Δ)(X,\Delta) a dlt pair. We prove that if there is an open set U0UU^0\subset U, such that (X,Δ)×UU0(X,\Delta)\times_U U^0 has a good minimal model over U0U^0 and the images of all the non-klt centers intersect U0U^0, then (X,Δ)(X,\Delta) has a good minimal model over UU. As consequences we show the existence of log canonical compactifications for open log canonical pairs, and the fact that the moduli functor of stable schemes satisfies the valuative criterion for properness

    Size dependence of second-order hyperpolarizability of finite periodic chain under Su-Schrieffer-Heeger model

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    The second hyperpolarizability γN(3ωω,ω,ω)\gamma_N(-3\omega\omega,\omega,\omega) of NN double-bond finite chain of trans-polyactylene is analyzed using the Su-Schrieffer-Heeger model to explain qualitative features of the size-dependence behavior of γN\gamma_N. Our study shows that γN/N\gamma_N/N is {\it nonmonotonic} with NN and that the nonmonotonicity is caused by the dominant contribution of the intraband transition to γN\gamma_N in polyenes. Several important physical effects are discussed to reduce quantitative discrepancies between experimental and our resultsComment: 3 figures, 1 tabl