Mid infrared interband cascade lasers for sensing applications

The growth of Interband Cascade Laser material to cover the wavelength range from 3–4 μm is presented along with the fabrication and characterization of Broad Area (BA) and Ridge Waveguide (RWG) devices based on this material. Pulsed operation slightly below room temperature is observed for both device types, and a strong reduction of threshold currents can be observed in the RWG lasers. Variation of the active Quantum Well width in the epitaxial structures enables laser emission in the 3–4 μm wavelength region.     

On the Preparation of ZnO Single Crystals

ZnO single crystals were prepared by means of two methods:i slow cooling of ZnO/PbF₂ (PbO) high temperature solution, (ii) flux reaction technique, hydrolysis of ZnF₂ in PbF₂ as a solvent. At cooling rate ≥ 0.9 K/h the known plates, hexagonal prisms, and hollow crystals were obtained. At the cooling rate 0.6 K/h compact crystals have grown. This habit was also formed with the flux reaction technique. An estimation of the deposition rates of both methods has shown approximative agreement between the cooling runs with 0.6 K/h and the flux reaction technique under the chosen conditions. The deposition rate appears to be a relevant parameter for forming compact ZnO crystals in these systems.     

The weak tail dependence coefficient of the elliptical generalized hyperbolic distribution

The strong and the weak tail dependence coefficients are measures that quantify the probability of conjoint extreme events of two random variables. Whereas formulas for both tail dependence coefficients exist for the Gaussian and Student t distribution, only the strong tail dependence coefficient is known for their super-model, the elliptical generalized hyperbolic distribution, which is extremely popular in finance (see Schmidt 2003). In this work we derive a simple expression for the corresponding weak tail dependence coefficient using the mixture representation of the elliptical generalized hyperbolic distribution.     

Determination of polycyclic aromatic hydrocarbons in water samples using high-performance liquid chromatography with amperometric detection

The determination of polycyclic aromatic hydrocarbons (PAHs) using high-performance liquid chromatography (HPLC) with UV and fluorescence detection has been well established. Although most of the PAHs can be detected by these methods, some environmentally important polyaromatic compounds, such as acenaphthylene, do not show fluorescence and can only be determined by UV detection at higher concentrations. A sensitive and selective determination of acenaphthylene, acenaphthene and the six PAHs listed in the TVO, the German drinking water standard, is also possible by amperometric detection following HPLC separation. The method was applied to the determination of PAHs in different water samples after solid-phase extraction (SPE). The efficiency of the amperometric determination was found to be superior to UV detection (λ = 300 nm).     

Cascaded contributions to degenerate four-wave mixing in an acentric organic crystal

We show both theoretically and experimentally by degenerate four-wave mixing that the combined processes of optical rectification and the linear electro-optic effect contribute to the large effective third-order susceptibilities [14chi((3))(CS(2))] of the organic salt 4-N, N^- dimethylamino-4(?) -N(?) -methylstilbazolium toluene-p- sulfonate (DAST). Furthermore, the knowledge of the cascaded contributions was used to determine absolute values of the third-order susceptibilities as well as their sign.     

Zwitterionic titanoxanes {Cp[η-C5H4B(C6F5)3]Ti}2O and {(η-PrC5H4)[η-1,3-PrC5H3B(C6F5)3]Ti}2O as catalysts for cationic ring-opening polymerization

Zwitterionic titanoxanes {Cp[η⁵-C₅H₄B(C₆F₅)₃]Ti}₂O (I) and {(η⁵-ⁱPrC₅H₄)[η⁵-1,3-ⁱPrC₅H₃B(C₆F₅)₃]Ti}₂O (II), which contain two positively charged Ti(IV) centres in the molecule, are able to catalyse the ring-opening polymerization of -caprolactone (-CL) in toluene solution and in bulk. The process proceeds with a noticeable rate even at room temperature and accelerates strongly on raising the temperature to 60 °C. The best results have been obtained on carrying out the reaction in bulk. Under these conditions, the use of I as a catalyst (-CL:I = 1000:1) gives at 60 °C close to quantitative yield of poly--CL with the molecular mass of 197 000. An increase in the -CL:I ratio to 6000:1 increases the molecular mass of poly--CL to 530 000. Tetrahydrofuran (THF) is also polymerized under the action of I albeit with a lesser rate. However, the molecular mass of the resulting poly-THF can reach rather big values under optimal conditions (up to 217 000 at 20 °C and the THF:I ratio of 770:1). A rise in the reaction temperature from 20 to 60 °C results here to a decrease in the efficiency of the process. Titanoxane II is close to I in its catalytic activity in the -CL polymerization but it is much less active in the polymerization of THF. Propylene oxide (PO), in contrast to -CL and THF, gives with I only liquid oligomers in wide temperature and PO:I molar ratio ranges (−30 to +20 °C, PO:I = 500–2000:1). γ-Butyrolactone and 1-methyl-2-pyrrolidone are not polymerized under the action of I at room temperature. The reactions found are the first examples of catalysis of the cationic ring-opening polymerization by zwitterionic metallocenes of the group IVB metals.     

Production of vector and tensor mesons in proton-proton collisions at\sqrt s = 52.5 GeV

Inclusive production of ?⁰,f, andg ⁰ mesons and ofK _s ⁰ ,K ^*0 (892), ? andK ^*0(1430)mesons has been measured at <y>～2.6 and <p _T >～1.1 GeV/c in proton-proton interactions at \(\sqrt s = 52.5\) GeV. The negative particle from the two-body decays of these resonances were identified by a threshold Cerenkov counter and used for triggering. Starting from the measured differential cross section, total inclusive cross sections for the vector and tensor mesons were determined using various parametrizations for they andp _T dependence of the differential cross section. The experimental results are discussed in the framework of production models based on the parton picture. The strangeness suppresion factor λ=(0.30±0.10) due toSU(3) symmetry breaking of the quark sea is derived.     

Thermal Cyclization of 2-Acyl-1-azido-3-phenalenones to Phenaleno[1,2-c]isoxazol-7-ones

1-Azido-3-phenalenones 5 with acyl substituents in position 2, obtained by acylation and azidation of 1-hydroxy-3-phenalenones 1 , cyclized by thermolysis to give phenaleno[1,2-c]isoxazol-7-ones 9 . The thermolysis conditions were studied by differential scanning calorimetry.     

Quantization and clustering with Bregman divergences

This paper deals with the problem of quantization of a random variable X taking values in a separable and reflexive Banach space, and with the related question of clustering independent random observations distributed as X. To this end, we use a quantization scheme with a class of distortion measures called Bregman divergences, and provide conditions ensuring the existence of an optimal quantizer and an empirically optimal quantizer. Rates of convergence are also discussed.