Vibrational Spectroscopy of Phenols and Phenolic Polymers. Theory,Experiment, and Applications

In the first part of this review, the authors give a survey on the literature of vibrational spectroscopy of phenol, phenol derivatives, and other phenolic componds from the last decade of the last century through today. The classical and modern methods of vibrational spectroscopy are also introduced and a glossary is included to aid comprehension. The second part deals with the literature regarding the importance of vibrational spectroscopy in the investigation and identification of phenolic compounds in natural substances, the application of vibrational spectroscopy in composite and synthetic polymer chemistry, and following of chemical processes and investigating their resulting products. Vibrational spectroscopy is a very good tool for determination of molecular structures and is important in chemical analysis and in the chemical industry.     

Fiber Optic Excitation of Silicon Microspheres in Amorphous and Crystalline Fluids

ABSTRACT

This study investigates the optical resonance spectra of free-standing monolithic single crystal silicon microspheres immersed in various amorphous fluids, such as air, water, ethylene glycol, and 4-Cyano-4’-pentylbiphenyl nematic liquid crystal. For the various amorphous fluids, morphology-dependent resonances with quality factors on the order of 10⁵ are observed at 1428 nm. The mode spacing is always on the order of 0.23 nm. The immersion in various amorphous fluids affects the spectral response of the silicon microsphere and heralds this technique for use in novel optofluidics applications. Even though the nematic liquid crystal is a highly birefringent, scattering, and high-index optical medium, morphology-dependent resonances with quality factors on the order of 10⁵ are observed at 1300 nm in the elastic scattering spectra of the silicon microsphere, realizing a liquid-crystal-on-silicon geometry. The relative refractive index and the size parameter of the silicon microsphere are the parameters that affect the resonance structure. The more 4-Cyano-4’-pentylbiphenyl interacting with the silicon microsphere, the lower the quality factor of the resonances is. The more 4-Cyano-4’-pentylbiphenyl is interacting with the silicon microsphere, the lower the mode spacing Δλ of the resonances is. The silicon microspheres wetted with nematic liquid crystal can be used for optically addressed liquid-crystal-on-silicon displays, light valve applications, or reconfigurable optical networks.     

Compressive matched-field processing

Source localization by matched-field processing (MFP) generally involves solving a number of computationally intensive partial differential equations. This paper introduces a technique that mitigates this computational workload by "compressing" these computations. Drawing on key concepts from the recently developed field of compressed sensing, it shows how a low-dimensional proxy for the Green's function can be constructed by backpropagating a small set of random receiver vectors. Then the source can be located by performing a number of "short" correlations between this proxy and the projection of the recorded acoustic data in the compressed space. Numerical experiments in a Pekeris ocean waveguide are presented that demonstrate that this compressed version of MFP is as effective as traditional MFP even when the compression is significant. The results are particularly promising in the broadband regime where using as few as two random backpropagations per frequency performs almost as well as the traditional broadband MFP but with the added benefit of generic applicability. That is, the computationally intensive backpropagations may be computed offline independently from the received signals, and may be reused to locate any source within the search grid area.     

Characterization of AZ91D Granules Covered with a Flux during In‐Situ Melting

Oxidation and melting behaviors of AZ91D granules throughout the in‐situ melting process using flux were investigated. The granules were heated under unprotected environment at four different temperatures between 650 and 800 °C, for the durations of 30 and 60 min. The products of heating process were characterized macroscopically and the oxides formed on the granules were examined using field emission scanning electron microscope, energy dispersive X‐ray spectroscopy and X‐ray diffraction analysis. Thermal analysis was used to reveal the response of the granules to heating during the in‐situ melting. The results showed that the granules experienced severe oxidation even in the presence of the flux, and significant amount of them changed to a powdered state due to oxidation and combustion, especially at 800 °C. It was discovered that the granules melted during heating; however, oxides formed on their surface encapsulated the molten metal and prevented the liquids from merging. The results also revealed that increasing heating temperature and time enhanced mold‐magnesium reaction resulted in the entrance of mold materials into the oxidation residues.     

Simultaneous Determination of Acetylsalicylic Acid and Caffeine in Pharmaceutical Formulation by First Derivative Synchronous Fluorimetric Method

A sensitive, rapid, and specific assay has been developed for the simultaneous determination of acetylsalicylic acid and caffeine in commercial tablets based on their natural fluorescence. The mixture of these drugs was resolved by first derivative synchronous fluorimetric technique using two scans. At Δλ=106 nm, using first derivative synchronous scanning, only acetylsalicylic acid yields a detectable signal at 316 nm (peak to zero method) which is unaffected by caffeine. At Δλ=30 nm, the signal of caffeine at 288 nm (peak to zero method) is not affected by acetylsalicylic acid. The range of application is between 0.021 and 41.62 μg ml⁻¹ (correlation coefficient, R=0.9995) for acetylsalicylic acid and between 0.4486 and 44.86 μg ml⁻¹ (correlation coefficient, R=0.99786) for caffeine. The recovery range of 98.40–102% for acetylsalicylic acid and 90–100.5% for caffeine from their synthetic mixture was reported. Overall recovery of both compounds about 97–99% for acetylsalicylic acid and 97–98% for caffeine was obtained from real sample analysis. The detection limits are 0.0013 μg ml⁻¹ and 0.0306 μg ml⁻¹ for acetylsalicylic acid and caffeine, respectively. The relative standard deviation (n=10) for 20 μg ml⁻¹ of acetylsalicylic acid is 2.75% and for 2.2 μg ml⁻¹of caffeine is 1.7%.     

Heavy ion interactions of (14.0 MeV/u) Pb with U

The interactions of ²⁰⁸Pb projectiles with ^natU target have been studied at 14.0 MeV/u beam energy using two different threshold detectors; mica and lexan. The elastic scattering data have been separated from the binary events and used for the determination of quarter-point angle θ_1/4 (≡ grazing angle θ_gr). The values of maximum angular momentum , radius of interaction R_int and reaction cross-section σ_R^exp(el.) were then deduced by making use of the value of θ_1/4. The data of inelastic events of different multiplicities have been used to determine partial reaction cross-sections. The sum of the partial cross-sections, therefore, yielded another independent value of reaction cross-section σ_R^exp(inel.) that in turn was used to derive the alternative values of , θ_gr, and R_int independently. The average of these quantities provided the experimental values of the reaction parameters that are comparable to the theoretical predictions.     

In-situ electrical characterisation of a photodiode during nano-structuring with a focussed ion beam

We study the fabrication and power conversion efficiency of GaAs photodiodes, which have been nano-structured and covered with colloidal quantum dots. A focussed ion beam is used to etch vertical channels into the photodiodes and the detrimental effects of this treatment are characterised in-situ during the fabrication process. A novel experimental configuration allows the electrical characterization of the photodiodes under laser illumination during the nano-fabrication process and reveals the gradual decrease of the photodiodes’ shunt resistance with increasing laterally revealed surface along the etched channels. This is interpreted as evidence for leakage currents through redeposited material and surface states on the lateral channel surface. After the fabrication step the channels are filled with colloidal quantum dots, which upon absorption of light transfer electronic excitations to the photodiode via resonance energy transfer. It is found that after the addition of quantum dots the nano-structured photodiodes show larger enhancements of the energy conversion efficiency under simulated solar irradiance than the pristine photodiodes. Nevertheless, the device degradation induced by the ion beam treatment itself cannot be compensated for.     

Theoretical estimates for proton-NMR spin–lattice relaxation rates of heterometallic spin rings

Heterometallic molecular chromium wheels are fascinating new magnetic materials. We reexamine the available experimental susceptibility data on MCr₇ wheels in terms of a simple isotropic Heisenberg Hamiltonian for M=Fe, Ni, Cu, and Zn and find in that FeCr₇ needs to be described with an iron–chromium exchange that is different from all other cases. In a second step we model the behavior of the proton spin lattice relaxation rate as a function of applied magnetic field for low temperatures as it is measured in nuclear magnetic resonance (NMR) experiments. It appears that CuCr₇ and NiCr₇ show an unexpectedly reduced relaxation rate at certain level crossings.     

The Efficient Synthesis of 3,4-Dihydropyrimidin-2-(1H)-Ones and Their Sulfur Derivatives with H2SO4 Immobilized on Activated Charcoal

Abstract

Various 3,4-dihydropyrimidin-2-(1H)-ones (DHPMs) and their sulfur derivatives were efficiently synthesized by a one-pot cyclocondensation reaction of aromatic and aliphatic aldehydes, β-dicarbonyl compounds and urea (or thiourea) in the presence of sulfuric acid immobilized on activated charcoal (133% w/w). The reactions were carried out in refluxing n-hexane-acetonitrile (2.5:0.5 mL) within 5–150 min to give 3,4-dihydropyrimidinones (or thiones) in high to excellent yields (81–97%).     

Spectrophotometric determination of Chromium(VI) using cyclam as a reagent

A simple, rapid, sensitive, and inexpensive method for spectrophotometric determination of chromium(VI), based on the absorbance of its complex with 1,4,8,11-tetraazacyclotetradecane (cyclam) is presented. The complex showed a molar absorbtivity of 1.5?×?10⁴?L?mol^?1?cm^?1 at 379?nm. Under optimum experimental conditions, a pH of 4.5 and 1.960?×?10³?mg?L^?1 cyclam were selected, and all measurements were performed 10?min after mixing. Major cations and anions did not show any interference; Beer's law was applicable in the concentration range 0.2–20?mg?L^?1 with a detection limit of 0.001?mg?L^?1. The standard deviation in the determination is ±0.5?mg?L^?1 for a 15.0?mg?L^?1 solution (n?=?7). The described method provides a simple and reliable means for determination of Cr(VI) in real samples.