Intrinsic second-order nonlinearity in chalcogenide glasses containing HgI2

Frequency conversion using nonlinear optical (NLO) crystals is widely used in advanced photonic technologies to produce coherent light in the spectral regions where the available laser sources are missing. Isotropic glasses usually do not show second order nonlinear processes like second harmonic or difference frequency generation (SHG, DFG) except for temporarily induced anisotropy under external stimuli. Here, we show that a HgI₂–Ga₂S₃–GeS₂ homogeneous glass exhibits a strong intrinsic SHG response comparable with that of the well-known NLO single crystal LiNbO₃. The origin of this extremely rare phenomenon seems to be noncentrosymmetric bent HgI₂ molecules embedded in a sulfide glassy host. Taking into account the unique properties of chalcogenide glasses (wide IR transmission, low phonon density, unlimited ability to be modified changing the appropriate glass properties, fiber drawing and thin layer design), the observed phenomenon opens up the possibility of creating fundamentally new devices for mid-IR photonics.     

Photochemische Primärprozesse von Xanthenfarbstoffen. I. Blitzlichtspektroskopische Untersuchung der Primärprozesse von Selenopyronin

Photochemical Primary Processes of Xanthene Dyes. I. Investigations of the Primary Processes of Selenopyronine by Flash Excitation The triplet-state of selenopyronine absorbs light in the whole investigated spectral range (λ_max = 400 nm, 480 nm, 690 nm). As results of the bimolecular triplet decay a half-reduced (λ_max = 430 nm) and a half-oxidized (λ_max = 475 nm) form of the dye are observed. p-Benzoquinone quenches the triplet-state (k₇ = 1,5 · 10⁹ l/mol s) and the results are the half-oxidized form and the p-benzosemiquinone ion. For these two products different decay processes exist. The reducing agents DABCO, EDTA and Hydroquinone also quench the triplet state (k₁₀ = 1,2 · 10⁶ l/mol s, k₁₁ = 1,0 · 10⁶ l/mol s, k₁₂ = 1,0 · 10⁹ l/mol s) and as result the half-reduced form is observed. Measurements with thiopyronine give analogous results, which are in good agreement with investigations published in the literature.     

Photophysical Parameters of Functional Transparent Polymethyl-Methacrylate/Double-Walled Carbon Nanotubes Nanocomposite Sheet Under UV-Irradiation

Polymethyl-methacrylate (PMMA)/double-walled carbon nanotubes DWCNTs was prepared by using casting technique and studying with different spectroscopic techniques. UV/Vis spectral analysis shows that, the transmittance reaches to 92 % for blank PMMA and decreases to 87 % for PMMA doped with 0.01 DWCNTs composite. The calculated refractive index and absorption coefficient increase, while the estimated values of Urbach energy decreased after embedding CNT into PMMA matrix. The optical band gap values were observed to vary slightly with doping amount. Photoluminescence (PL) spectra show that there is no shift in the emission peak position upon doping with CNTs, but PL intensity is enhanced.     

Photochemische Primärprozesse von Xanthenfarbstoffen. III. Blitzlichtspektroskopische Untersuchungen zum Einfluß von kationischen Mizellen auf die Photoredoxprozesse von Selenopyronin

Photochemical Primary Processes of Xanthene Dyes. III. Investigations of the Influence of Cationic Micelles on the Photoredox Processes of Selenopyronine by Flash Excitation Cationic micelles have no influence on the decay of the triplet state of selenopyronine (³F⁺). The products of photoredox reactions ³F⁺ + ³F⁺ (F⁺) → F^· + F and ³F⁺ + DABCO → F^· + DABCO live longer in the presence of the cationic micelles. The reason for the change of the lifetime is a separation of the photoredox products by micelles. F^. is stored in the interior of the micelles. The positively charged F and DABCO are repelled from the micelles and the electron back transfer is hindered.     

Photochemische Primärprozesse von Xanthenfarbstoffen. II. Blitzlichtspektroskopische Untersuchungen zum Einfluß von anionischen Mizellen auf die photochemischen Primärprozesse von Selenopyronin

Photochemical Primary Processes of Xanthene Dyes. II. Investigations of the Influence of Anionic Micelles on the Primary Processes of Selenopyronine by Flash Excitation In aqueous solutions containing anionic micelles, the dye cations of selenopyronine are present at the micellar surface. If the concentration of the dye ions is much lower than the concentration of micelles, only monomolecular triplet decay (k₁^aM = 2 · 10⁻³s⁻¹) is observed. Under these conditions, the half-oxidized and half-reduced form of selenopyronin is not formed. If the concentration of the dye ions is much higher than the concentration of micelles, two or more dye ions are present at every micelle, and a fast bimolecular decay of the triplet state during the flash is observed. The quenching of the triplet state with p-benzoquinone (k₇^aM = 1,9 · 10⁹ l/mol s), DABCO (k₁₀^aM = 1,6 · 10⁷ l/mol s) and EDTA (k₁₁^aM = 1,3 · 10⁵ l/mol s) and the decay processes of the half-reduced and half-oxidized form in the micellar solution are investigated.     

Computations of shear driven vortex flow in a cylindrical cavity using a modified k-ε turbulence model

In this paper, a new variant of the k-ε turbulence model (Saqr et al., CFD Letters, 1(2) pp. 87–94) is used to compute the shear driven vortex flow in an open cylindrical cavity. The results are compared with published LDA measurements for such flow configuration. The modified turbulence model demonstrated good agreement with experimental results, which further supports its validity in computing vortex dominated flows.     

Evaluation of ageing in asphalt cores using low-field nuclear magnetic resonance

This paper introduces an innovative methodology for estimating the ageing of asphalt concrete cores without extracting the binder. Asphalt concrete samples at different ageing stages (unaged, 3-month and 6-month aged) and with different percent air voids (4%, 7% and 10%) were analysed with low-field nuclear magnetic resonance (NMR). The transverse relaxation time T₂ and relative hydrogen index (RHI) obtained from NMR measurements were related to the viscosity of the asphalt binder. The samples were analysed during cooling from 70°C to room temperature, showing increase in viscosity with decreasing temperature. There was a clear trend indicating higher viscosities in samples that were aged for a longer period and samples with higher percent air voids. The RHI and T₂ values obtained from low-field NMR measurements and the viscosity data calculated from measurements using a dynamic shear rheometer were correlated to develop a model that relates viscosity with RHI.     

In situ STM and EQCM studies of tantalum electrodeposition from TaF5 in the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide

The electroreduction of 0.5 M TaF₅ on Au(1 1 1) and on polycrystalline gold substrates was investigated at room temperature in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py_1,4]TFSA, by cyclic voltammetry, in situ scanning tunneling microscopy (STM) and electrochemical quartz crystal microbalance (EQCM). The electrochemical reduction of TaF₅ in the employed ionic liquid occurs in several steps. The first redox process is attributed to the reduction of TaF₅ to TaF₃, which likely occurs in the solution, as EQCM indicates no mass change. The electrodeposition of tantalum occurs only in a very narrow potential window and is preceded by the formation of various non-stoichiometric tantalum subhalides. Attempts to deposit micrometer thick tantalum layers at room temperature fail, presumably because of kinetic reasons.     

Influence of Panthenol, Chlorphenesin and Lignocaine on the Physical Characteristics of Solidified Sodium Stearate-Based Sticks(SSSS)

Cosmetic sticks provide many consumer advantages over the more readily used aerosol sprays, creams and lotions. In view of the many advantages offered by solidified sodium stearate-based sticks (SSSS), a program was set up to evaluate them as potential bases for the inclusion of topically active medicaments. The present publication elucidates the influence of Panthenol, Chlorphenesin and Lignocaine on the main physical characteristics of some SSSS bases, including their disintegration time, hardness, penetrability, softening point, yield by abrasion and rate of drying by evaporation. The investigated SSSS bases contained glycerol, propylene glycol (PG), polyethylene glycol 400 (PEG 400) or PEG 600 as humectant.

-The disintegration time of the studied bases was generally lowered by the three medicaments; however, glycerol or PG-formulated stick bases had their disintegration time slightly prolonged or unaffected by the addition of Chlorphenesin or Lignocaine;

-Panthenol generally lowered the hardness of SSSS bases but the least variation in this parameter was noticed with PG bases; hardness was generally increased with Chlorphenesin or Lignocaine, but to a lesser extent with the latter;

-generally speaking, Panthenol markedly increased the penetrability of the investigated stick bases; Chlorphenesin and Lignocaine did the same thing but to a lesser extent;

-the softening point of SSSS bases was generally lowered in presence of Panthenol or Lignocaine; Chlorphenesin did not generally affect the softening point of the stick bases; anyhow, the softening point of the investigated medicated sticks moved within the limits of safety, as far as the resistance to handling and storage in areas with occasional hot summers is concerned;

-Panthenol appreciably increased the yield by abrasion of all investigated bases; Lignocaine and Chlorphenesin did not appreciably influence this parameter except in the case of PEG 400 bases where the yield was markedly increased in presence of Lignocaine;

-the rate of drying of all the investigated stick bases was greatly lowered on addition of Panthenol; Chlorphenesin and Lignocaine affected this parameter to a much lesser extent.