Reconfigurable wavefront sensor for ultrashort pulses

A highly flexible Shack-Hartmann wavefront sensor for ultrashort pulse diagnostics is presented. The temporal system performance is studied in detail. Reflective operation is enabled by programming tilt-tolerant microaxicons into a liquid-crystal-on-silicon spatial light modulator. Nearly undistorted pulse transfer is obtained by generating nondiffracting needle beams as subbeams. Reproducible wavefront analysis and spatially resolved second-order autocorrelation are demonstrated at incident angles up to 50° and pulse durations down to 6 fs.     

Chemical degradation of crosslinked ethylene-propylene-diene rubber in an acidic environment. Part I. Effect on accelerated sulphur crosslinks

The time-dependent chemical degradation of accelerated sulphur cured ethylene propylene diene rubber containing 5-ethylidene-2-norbornene as diene in an acidic environment (20% Cr/H₂SO₄) was investigated. Two different rubbers with a similar ethylene to propylene ratio and diene content but with a significant difference in molar mass and level of long chain branching were used in the study. The molecular mechanisms of the chemical degradation occurring at the surface were determined using surface analysis (X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy). The results reveal formation of several oxygenated species on the surface as a consequence of the acid attack. Furthermore, the crosslink sites of the exposed rubber samples are also found vulnerable to hydrolytic attack as evidenced by the decrease in crosslink density. The extent of surface degradation was strong enough to affect the bulk mechanical properties. Changes in mechanical properties were also monitored through determining retention in tensile strength, (%) elongation at break, modulus at 50% elongation, and change in micro-hardness. A negative correlation is also established between retention in modulus at 50% elongation and decrease in crosslink density. Scanning electron microscopy reveals the topographical damage at the surface due to the aqueous acid induced chemical degradation. The results indicate that the chemical degradation proceeds mainly via hydrolysis of crosslinks but upon prolonged exposure, the oxygenated species tend to combine with each other. The effect of molar mass and level of long chain branching also influences the chemical degradation.     

Iridoid glucosides from Wendlandia tinctoria roots

Four new iridoid glucosides, 5-dehydro-8-epi-adoxosidic acid, 5-dehydro-8-epi-mussaenoside, 10-O-dihydroferuloyldeacetyldaphylloside, and wendoside, together with one known iridoid glucoside, 8-epi-mussaenoside, beta-D-glucose, D-mannitol and beta-sitosterol have been isolated from the roots of Wendlandia tinctoria. On the basis of chemical and spectral analyses, the structures of new iridoid glucosides have been elucidated.     

Effect of platinum on the photoelectrochemical behavior of lead oxide thin film

The effect of Pt on the photoelectrochemical behavior of lead oxide prepared from anodization of Pb-Pt alloy containing various concentrations of Pt has been studied. It is observed that, while Pt reduces the resistivity of the oxide film, it also reduces the photoconversion efficiency of the photoelectrochemical cell prepared from this material. The reason for this low efficiency is discussed. Received: 19 November 1997 / Accepted: 9 March 1998     

Synthesis and characterization of new aromatic poly(ether imide)s and their gas transport properties

A series of processable fluorinated poly(ether imide)s (PIs) were synthesized by reacting a diamine monomer, 1,4-bis-[{2′-trifluromethyl 4′-(4″-aminophenyl)phenoxy}] benzene (HQA) with six different aromatic dianhydrides e.g., BPADA, 6FDA, ODPA, BPDA, BTDA and PMDA. The polyimides showed reasonably high glass-transition temperature (T_g up to 280 °C) and high thermal stability (T_d,10 up to 558 °C). The membranes of these polymers showed tensile strength up to 107 MPa with elongation at break up to 15%, low water absorption (0.61–1.29%), low dielectric constant (2.10–3.13 at 1 MHz) and high optical transparency (λ_cut-off up to 466 nm). The PI membrane prepared from 6FDA exhibited high permeability and permselectivity for O₂/N₂ (P_O2 = 11.8 and P_O2/P_N2 = 9.44) gas pair which eventually surpassed the present upper boundary limit drawn by L.M. Robeson.     

Simultaneous production and separation of no-carrier-added 111In, 109Cd from alpha particle induced silver target

A natural silver foil was bombarded by 30 MeV α-particles which produced ¹¹¹In, ¹⁰⁹Cd and ^106mAg in the target matrix. ¹¹¹In and ¹⁰⁹Cd were separated from the Ag target matrix employing ion-exchange chromatography and liquid–liquid extraction (LLX). In the chromatographic separation, the active solution containing the NCA products were adsorbed in the column containing Dowex 50 and were eluted with HNO₃. Bulk silver and ¹⁰⁹Cd were sequentially eluted with 1 M HNO₃. After complete elution of ¹⁰⁹Cd and the bulk, ¹¹¹In was eluted with 1.5 M HNO₃. In the LLX, the NCA ¹¹¹In was extracted to 1 % HDEHP (di-2(ethylhexyl)phosphoric acid) from 10^?2 M HNO₃ solution, leaving cadmium and bulk silver quantitatively in the aqueous phase. The NCA ¹⁰⁹Cd was separated from the bulk Ag by precipitating Ag as AgCl. NCA ¹¹¹In was stripped back quantitatively from HDEHP phase using 8 M HNO₃.     

Cloud point extraction of 99Mo with Triton X-114

This paper reports the cloud point extraction (CPE) extraction behaviour of ⁹⁹Mo in non-ionic Triton X-114 (TX-114), sodiumdodecyl sulphate (SDS) + TX-114 and sodium diethyldithiocarbamate (DDTC) + TX-114. The high extraction of ⁹⁹Mo observed in all the CPE systems in pH 5 or less. The extent of extraction was almost unchanged with addition of SDS and DDTC in TX-114. Extraction behaviour was also studied in presence of common salts. It was observed the presence of salts dramatically decreased the amount of molybdenum extraction in the surfactant-rich phase.     

Effective method of characterization of the phase and intensity profiles of asymmetrically distorted light pulses in optical fiber systems

We address the problem of characterization of light pulses that propagate in long-haul high-bit-rate optical communication systems, under strongly perturbed conditions. We show that the conventional technique for characterization of the phase and intensity profile of such pulses becomes qualitatively inconsistent when the pulse’s profile is asymmetrically distorted with respect to its center-of-mass. We resolve these inconsistencies by partially reformulating the conventional technique by means of appropriate pulse parameters, which we call upgraded parameters, which allow a fair characterization of the intensity and phase of all types of light pulses, including those which are asymmetrically distorted. We illustrate the effectiveness of the upgraded parameters by applying them to a meticulous characterization of light pulses in a dispersion-managed optical fiber system in which third-order dispersion is acting as a strong perturbation.     

Slow magnetic relaxation and electron delocalization in an S = 9/2 iron(II∕III) complex with two crystallographically inequivalent iron sites

The magnetic, electronic, and Mo?ssbauer spectral properties of [Fe(2)L(μ-OAc)(2)]ClO(4), 1, where L is the dianion of the tetraimino-diphenolate macrocyclic ligand, H(2)L, indicate that 1 is a class III mixed valence iron(II∕III) complex with an electron that is fully delocalized between two crystallographically inequivalent iron sites to yield a [Fe(2)](V) cationic configuration with a S(t) = 9∕2 ground state. Fits of the dc magnetic susceptibility between 2 and 300 K and of the isofield variable-temperature magnetization of 1 yield an isotropic magnetic exchange parameter, J, of -32(2) cm(-1) for an electron transfer parameter, B, of 950 cm(-1), a zero-field uniaxial D(9∕2) parameter of -0.9(1) cm(-1), and g = 1.95(5). In agreement with the presence of uniaxial magnetic anisotropy, ac susceptibility measurements reveal that 1 is a single-molecule magnet at low temperature with a single molecule magnetic effective relaxation barrier, U(eff), of 9.8 cm(-1). At 5.25 K the Mo?ssbauer spectra of 1 exhibit two spectral components, assigned to the two crystallographically inequivalent iron sites with a static effective hyperfine field; as the temperature increases from 7 to 310 K, the spectra exhibit increasingly rapid relaxation of the hyperfine field on the iron-57 Larmor precession time of 5 × 10(-8) s. A fit of the temperature dependence of the average effective hyperfine field yields |D(9∕2)| = 0.9 cm(-1). An Arrhenius plot of the logarithm of the relaxation frequency between 5 and 85 K yields a relaxation barrier of 17 cm(-1).