Applications of intelligent methods in various types of heat exchangers: a review

Journal of Thermal Analysis and Calorimetry - Heat exchangers are applicable in different industries and technologies, and their performance is influenced by different parameters. In addition to...     

Trace determination of lead(II) ions by using a magnetic nanocomposite of the type Fe3O4/TiO2/PPy as a sorbent,and FAAS for quantitation

Microchimica Acta - The authors describe a magnetic nanoadsorbent consisting of magnetite nanoparticles coated first with titanium dioxide and then with polypyrrole (PPy). It is shown to be a...     

Ultralow-noise mode-locked laser with coupled optoelectronic oscillator configuration

We describe simultaneous generation of ultralow-noise optical pulses and microwave signal with a mode-locked fiber laser in a coupled optoelectronic oscillator configuration. We demonstrate 9.2-GHz optical and microwave signals with the measured phase noise of -140 dBc/Hz at 10-kHz offset frequency. We show that the mode-locked laser in the photonic oscillator serves as a high-Q filter and is responsible for the observed low phase noise.     

Vertically coupled whispering-gallery-mode resonator waveguide

We theoretically describe a novel configuration of a vertically coupled whispering-gallery-mode resonator waveguide. The waveguide is formed as a chain of doughnut-shaped low-contrast ripples on the surface of a vertical cylinder made from an optically transparent material. One can manipulate the properties of the waveguide by changing the shape of the resonators and the separation distance between them. Application of the structure as an optical delay line is discussed.     

Ultraviolet-assisted frequency trimming of optical microsphere resonators

We have demonstrated the engineering of a precise shift in the resonance frequency of high-Q (10(8))whispering-gallery modes in microspheres of germanium-doped silica with UV irradiation. With 600 mW of 351-nm radiation from an Ar-ion laser, 18-GHz permanent frequency shifts were obtained for modes of 1550-nm wavelength, enough to tune a resonance over a full free spectral range.     

Selective kinetic spectrophotometric determination of copper at nanograms per milliliter level

A sensitive and selective kinetic method is proposed for the determination of nanogram amounts of copper. The method is based on the catalytic effect of copper on the reduction of Ponceau S by sodium sulfide in an alkaline media. The rate of the reaction is monitored spectrophotometrically at 560 nm. The method allows determination of copper concentrations in the range 2-400 ng ml(-1) with a relative standard deviation of approximately 2%. The proposed method, which is highly selective to copper, has been applied satisfactory to its determination in real samples.     

Microtorus: a high-finesse microcavity with whispering-gallery modes

We demonstrate a 165-mu;m oblate spheroidal microcavity with a free spectral range of 383.7 GHz (3.06 nm), a resonance bandwidth of 23 MHz (quality factor Q approximately 10(7)) at 1550 nm, and finesse F>/=10(4) . The highly oblate spheroidal dielectric microcavity combines a very high Q factor, typical of microspheres, with a vastly reduced number of excited whispering-gallery modes (by 2 orders of magnitude). The very large free spectral range in this novel microcavity-a few hundred gigahertz instead of a few gigahertz as in typical microspheres-is desirable for applications in spectral analysis, narrow-linewidth optical and rf oscillators, and cavity QED.     

Palladium-catalyzed regiocontrolled internal heteroarylation of electron-rich olefins with heteroaryl halides

A highly efficient palladium-catalyzed Heck coupling reaction of heteroaryl halides with electron-rich vinyl ether and hydroxyalkyl vinyl ethers is described. It was found that the choice of solvent, ligand, and reaction temperature had a fundamental influence on the regioselectivity and reactivity of the reaction, and the combination of Pd(OAc)₂ and DPPF in ethylene glycol led to the most effective catalytic system. Under these conditions, a variety of heteroaryl halides reacted very quickly with electron-rich olefins to afford exclusively the branched products in good to excellent yields without employing triflates, halide scavengers, or ionic liquids.