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- Role of synaptic phosphatidylinositol 3-kinase in a behavioral learning response in C. elegans. [Journal Article, Research Support, Non-U.S. Gov't]
- Science 2014 Jul 18; 345(6194):313-7.
The phosphatidylinositol 3-kinase (PI3K) pathway regulates many cellular functions, but its roles in the nervous system are still poorly understood. We found that a newly discovered insulin receptor isoform, DAF-2c, is translocated from the cell body to the synaptic region of the chemosensory neuron in Caenorhabditis elegans by a conditioning stimulus that induces taste avoidance learning. This translocation is essential for learning and is dependent on the mitogen-activated protein kinase-regulated interaction of CASY-1 (the calsyntenin ortholog) and kinesin-1. The PI3K pathway is required downstream of the receptor. Light-regulated activation of PI3K in the synaptic region, but not in other parts of the cell, switched taste-attractive behavior to taste avoidance, mimicking the effect of conditioning. Thus, synaptic PI3K is crucial for the behavioral switch caused by learning.
- Electro-optical frequency division and stable microwave synthesis. [Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.]
- Science 2014 Jul 18; 345(6194):309-13.
Optical frequency division by using frequency combs has revolutionized time keeping and the generation of stable microwave signals. We demonstrate optical frequency division and microwave generation by using a tunable electrical oscillator to create dual combs through phase modulation of two optical signals that have a stable difference frequency. Phase-locked control of the electrical oscillator by means of optical frequency division produces stable microwaves. Our approach transposes the oscillator and frequency reference of a conventional microwave frequency synthesizer. In this way, the oscillator experiences large phase noise reduction relative to the frequency reference. The electro-optical approach additionally relaxes the need for highly linear photodetection of the comb mode spacing. As well as simplicity, the technique is also tunable and scalable to higher division ratios.
- Dielectric gradient metasurface optical elements. [Journal Article, Research Support, Non-U.S. Gov't]
- Science 2014 Jul 18; 345(6194):298-302.
Gradient metasurfaces are two-dimensional optical elements capable of manipulating light by imparting local, space-variant phase changes on an incident electromagnetic wave. These surfaces have thus far been constructed from nanometallic optical antennas, and high diffraction efficiencies have been limited to operation in reflection mode. We describe the experimental realization and operation of dielectric gradient metasurface optical elements capable of also achieving high efficiencies in transmission mode in the visible spectrum. Ultrathin gratings, lenses, and axicons have been realized by patterning a 100-nanometer-thick Si layer into a dense arrangement of Si nanobeam antennas. The use of semiconductors can broaden the general applicability of gradient metasurfaces, as they offer facile integration with electronics and can be realized by mature semiconductor fabrication technologies.
- A hole-conductor-free, fully printable mesoscopic perovskite solar cell with high stability. [Journal Article, Research Support, Non-U.S. Gov't]
- Science 2014 Jul 18; 345(6194):295-8.
We fabricated a perovskite solar cell that uses a double layer of mesoporous TiO2 and ZrO2 as a scaffold infiltrated with perovskite and does not require a hole-conducting layer. The perovskite was produced by drop-casting a solution of PbI2, methylammonium (MA) iodide, and 5-ammoniumvaleric acid (5-AVA) iodide through a porous carbon film. The 5-AVA templating created mixed-cation perovskite (5-AVA)x(MA)1- xPbI3 crystals with lower defect concentration and better pore filling as well as more complete contact with the TiO2 scaffold, resulting in a longer exciton lifetime and a higher quantum yield for photoinduced charge separation as compared to MAPbI3. The cell achieved a certified power conversion efficiency of 12.8% and was stable for >1000 hours in ambient air under full sunlight.
- High-turnover hypoiodite catalysis for asymmetric synthesis of tocopherols. [Journal Article, Research Support, Non-U.S. Gov't]
- Science 2014 Jul 18; 345(6194):291-4.
The diverse biological activities of tocopherols and their analogs have inspired considerable interest in the development of routes for their efficient asymmetric synthesis. Here, we report that chiral ammonium hypoiodite salts catalyze highly chemo- and enantioselective oxidative cyclization of γ-(2-hydroxyphenyl)ketones to 2-acyl chromans bearing a quaternary stereocenter, which serve as productive synthetic intermediates for tocopherols. Raman spectroscopic analysis of a solution of tetrabutylammonium iodide and tert-butyl hydroperoxide revealed the in situ generation of the hypoiodite salt as an unstable catalytic active species and triiodide salt as a stable inert species. A high-performance catalytic oxidation system (turnover number of ~200) has been achieved through reversible equilibration between hypoiodite and triiodide in the presence of potassium carbonate base. We anticipate that these findings will open further prospects for the development of high-turnover redox organocatalysis.
- Imaging charge transfer in iodomethane upon x-ray photoabsorption. [Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.]
- Science 2014 Jul 18; 345(6194):288-91.
Studies of charge transfer are often hampered by difficulties in determining the charge localization at a given time. Here, we used ultrashort x-ray free-electron laser pulses to image charge rearrangement dynamics within gas-phase iodomethane molecules during dissociation induced by a synchronized near-infrared (NIR) laser pulse. Inner-shell photoionization creates positive charge, which is initially localized on the iodine atom. We map the electron transfer between the methyl and iodine fragments as a function of their interatomic separation set by the NIR-x-ray delay. We observe signatures of electron transfer for distances up to 20 angstroms and show that a realistic estimate of its effective spatial range can be obtained from a classical over-the-barrier model. The presented technique is applicable for spatiotemporal imaging of charge transfer dynamics in a wide range of molecular systems.
- Slicing the wheat genome. Introduction. [Introductory Journal Article]
- Science 2014 Jul 18; 345(6194):285-7.
- Outside the tower. A night at the museum. [Letter]
- Science 2014 Jul 18; 345(6194):279.
- Delisted whales good news for pipeline. [Letter]
- Science 2014 Jul 18; 345(6194):278-9.
- Partnering with Cuba: earthquake hazards. [Comment, Letter]
- Science 2014 Jul 18; 345(6194):278.