1,150 research outputs found
Multistep cascading and fourth-harmonic generation
We apply the concept of multistep cascading to the problem of fourth-harmonic
generation in a single quadratic crystal. We analyze a new model of parametric
wave mixing and describe its stationary solutions for two- and three-color
plane waves and spatial solitons. Some applications to the optical frequency
division as well as the realization of the double-phase-matching processes in
engineered QPM structures with phase reversal sequences are also discussed.Comment: 3 pages, 3 figure
Autophagy Works Out
Autophagy is generally considered to be a cytoprotective response to stress, whether in the form of nutrient deprivation or the presence of dysfunctional organelles. He et al. now show in Nature that exercise-induced autophagy is needed for some of the beneficial effects of exercise on metabolism (He et al., 2012)
Spatial Optical Solitons due to Multistep Cascading
We introduce a novel class of parametric optical solitons supported
simultaneously by two second-order nonlinear cascading processes,
second-harmonic generation and sum-frequency mixing. We obtain, analytically
and numerically, the solutions for three-wave spatial solitons and show that
the presence of an additional cascading mechanism can change dramatically the
properties and stability of two-wave quadratic solitary waves.Comment: 6 pages, 4 figure
Generation of the second-harmonic Bessel beams via nonlinear Bragg diffraction
We generate conical second-harmonic radiation by transverse excitation of a
two-dimensional annular periodically-poled nonlinear photonic structure with a
fundamental Gaussian beam. We show that these conical waves are the far-field
images of the Bessel beams generated in a crystal by parametric frequency
conversion assisted by nonlinear Bragg diffraction.Comment: 4 pages, 5 figures. submitte
A theory of nonvertical triplet energy transfer in terms of accurate potential energy surfaces: The transfer reaction from Ï,Ïâ triplet donors to 1,3,5,7-cyclooctatetraene
Triplet energy transfer (TET) from aromatic donors to 1,3,5,7-cyclooctatetraene (COT) is an extreme case of ânonverticalâ behavior, where the transfer rate for low-energy donors is considerably faster than that predicted for a thermally activated (Arrhenius) process. To explain the anomalous TET of COT and other molecules, a new theoretical model based on transition state theory for nonadiabatic processes is proposed here, which makes use of the adiabatic potential energy surfaces (PES) of reactants and products, as computed from high-level quantum mechanical methods, and a nonadiabatic transfer rate constant. It is shown that the rate of transfer depends on a geometrical distortion parameter Îł = (2g2/Îș1)1/2 in which g stands for the norm of the energy gradient in the PES of the acceptor triplet state and Îș1 is a combination of vibrational force constants of the ground-state acceptor in the gradient direction. The application of the model to existing experimental data for the triplet energy transfer reaction to COT from a series of Ï,Ïâ triplet donors, provides a detailed interpretation of the parameters that determine the transfer rate constant. In addition, the model shows that the observed decrease of the acceptor electronic excitation energy is due to thermal activation of CïżœC bond stretchings and CâC bond torsions, which collectively change the ground-state COT bent conformation (D2d) toward a planar triplet state (D8h)[email protected]
The exocyst complex is required for targeting of Glut4 to the plasma membrane by insulin
Insulin stimulates glucose transport by promoting exocytosis of the glucose transporter Glut4 (refs 1, 2). The dynamic processes involved in the trafficking of Glut4-containing vesicles, and in their targeting, docking and fusion at the plasma membrane, as well as the signalling processes that govern these events, are not well understood. We recently described tyrosine-phosphorylation events restricted to subdomains of the plasma membrane that result in activation of the G protein TC10 (refs 3, 4). Here we show that TC10 interacts with one of the components of the exocyst complex, Exo70. Exo70 translocates to the plasma membrane in response to insulin through the activation of TC10, where it assembles a multiprotein complex that includes Sec6 and Sec8. Overexpression of an Exo70 mutant blocked insulin-stimulated glucose uptake, but not the trafficking of Glut4 to the plasma membrane. However, this mutant did block the extracellular exposure of the Glut4 protein. So, the exocyst might have a crucial role in the targeting of the Glut4 vesicle to the plasma membrane, perhaps directing the vesicle to the precise site of fusion.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62982/1/nature01533.pd
Phenotypic Switching of Adipose Tissue Macrophages With Obesity Is Generated by Spatiotemporal Differences in Macrophage Subtypes
OBJECTIVEâTo establish the mechanism of the phenotypic switch of adipose tissue macrophages (ATMs) from an alternatively activated (M2a) to a classically activated (M1) phenotype with obesity
Turning light into a liquid via atomic coherence
We study a four level atomic system with electromagnetically induced
transparency with giant and susceptibilities of
opposite signs. This system would allow to obtain multidimensional solitons and
light condensates with surface tension properties analogous to those of usual
liquids
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