Multiphoton endoscopy

Despite widespread use of multiphoton fluorescence microscopy, development of endoscopes for nonlinear optical imaging has been stymied by the degradation of ultrashort excitation pulses that occurs within optical fiber as a result of the combined effects of group-velocity dispersion and self-phase modulation. We introduce microendoscopes (350-1000 microm in diameter) based on gradient-index microlenses that effectively eliminate self-phase modulation within the endoscope. Laser-scanning multiphoton fluorescence endoscopy exhibits micrometer-scale resolution. We used multiphoton endoscopes to image fluorescently labeled neurons and dendrites.     

Self-Consistent Model and Numerical Analysis of VCSEL''s Laser Diodes

A self-consistent model of vertical-cavity surface-emitting lasers (VCSEL's) is presented in this paper, in which the carrier diffusion rate equation, the photon density rate equation, and the thermal conduction equation are considered simultaneously. The nonuniform heat flux density distribution in the active region due to the current-spreading effect is taken into account. The effects of temperature on gain and transparency carrier density are also included in this model. It is nonlinearly and self-consistently solved in the Matlab environment. The transient and lateral distribution characteristics of the carrier and photon densities and the junction temperature are investigated. Some interesting results are gotten and analyzed.     

Short-term carbon dynamics in a temperate grassland and heathland ecosystem exposed to 104 days of drought followed by irrigation

Temperate ecosystems are susceptible to drought events. The effect of a severe drought (104 days) followed by irrigation on the plant C uptake, its assimilation and input of C in soil were examined using a triple ¹³CO₂ pulse-chase labelling experiment in model grassland and heathland ecosystems. First ¹³CO₂ pulse at day 0 of the experiment revealed much higher ¹³C tracer uptake for shoots, roots and soil compared to the second pulse (day 44), where all plants showed significantly lower ¹³C tracer uptake. After the third ¹³CO₂ pulse (day 70), very low ¹³C uptake in shoots led to a negligible allocation of ¹³C into roots and soil. During irrigation after the severe drought, the ¹³C tracer that was allocated in plant tissues during the second and third pulse labelling was re-allocated in roots and soil, as soon as the irrigation started. This re-allocation was higher and longer lasting in heathland compared to grassland ecosystems.     

The impedance caused by interfacial current constriction: a case study on BaF2/YSZ bicrystals

Abstract  

BaF₂/YSZ (yttria stabilized zirconia) bicrystals are investigated by means of impedance spectroscopy. The spectra show two semicircles in the complex impedance plane, and both arcs exhibit very similar temperature dependences. The high frequency semicircle can be attributed to the ideal (quasi one-dimensional) bulk resistance of BaF₂, and the low frequency arc is caused by an additional resistance in BaF₂ due to the current constriction taking place close to the contact spots at the imperfect bicrystal interface. This interpretation is supported by finite element calculations revealing that bicrystals with imperfect contacts indeed exhibit an additional semicircle in the complex impedance plane even without any ion transfer resistance between the two crystals. The low frequency arc of the BaF₂/YSZ bicrystal drastically increases upon bias voltage, but relaxes to its original value after removing the bias. This phenomenon can be associated with a strong decrease of the vacancy concentration in YSZ (close to the interfacial contact spots), which is caused by F⁻ ions being pumped into YSZ and acting as a counter dopant to Y³⁺.     

Polymer waveguides from alicyclic methacrylate copolymer fabricated by deep-UV exposure

We have investigated the fabrication of waveguides from alicyclic methacrylate copolymer based on refractive-index modification by deep-UV exposure. By optimizing the UV-exposure process, we were able to obtain single-mode waveguides with a propagation loss of 0.8 dB/cm at 1550 nm, which is due only to material losses in this wavelength range. The loss obtained here is comparable with that of poly(methyl methacrylate) (PMMA) waveguides fabricated by deep-UV exposure. The fabricated waveguide is also single mode at 808 nm, and its propagation loss is 0.6 dB/cm. This alicyclic methacrylate copolymer is a promising material for the fabrication of polymer waveguides by use of deep-UV exposure.     

On the Electronic States of S4+ and S4‐ Isomers.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.     

The nature of the surface species formed on Au/TiO2 during the reaction of H2 and O2: an inelastic neutron scattering study

Inelastic neutron spectroscopy (INS) has been employed to identify surface species formed during the H2-O2 reaction on Au/TiO2 catalysts. Determination of the surface intermediates formed in this reaction is crucial to develop a mechanistic understanding for the direct vapor-phase propylene epoxidation reaction and synthesis of H2O2. Although the presence of intermediate hydroperoxo species (during these reactions) has been suggested in literature, it has never been demonstrated. Our studies provide direct evidence for the formation of surface hydroperoxo species during the H2-O2 reaction.