EPR experiment and two-photon interferometry: Report of a two-photon interference experiment

After a very brief review of the historical EPR experiments, this paper reports a new two-photon interference type EPR experiment. A two-photon state was generated by optical parametric down conversion. Pairs of light quanta with degenerate frequency but divergent directions of propagation were sent to two independent Michelson interferometers. First- and second-order interference effects were studied. Different from other reports, we observed that the second-order interference visibility vanished when the optical path difference of the interferometers were much less than the coherence length of the pumping laser beam. However, we also observed that the second-order interference behaved differently depending on whether the interferometers were set at equal or different optical path differences.Presented at the International Workshop on Squeezed and Correlated States, Moscow, December 3–7, 1990.     

A Branch and Bound Procedure for a Class of Discrete Resource Allocation Problems with Several Constraints

Journal of the Operational Research Society - A branch and bound algorithm is developed in this paper for a class of discrete resource allocation problems with many constraints. The algorithm...     

Determination of theophylline in tea and drug formulation using a Nafion(R)/lead-ruthenium oxide pyrochlore chemically modified electrode

Square-wave voltammetry was used for the determination of trace amounts of theophylline in tea and drug formulation at a Nafion(R)/lead-ruthenium oxide pyrochlore chemically modified electrode. This chemically modified electrode exhibits a marked enhancement of the current response compared to a bare glassy carbon electrode. The calibration graph for the determination of theophylline was linear up to 100 muM in 0.1 M, pH 3 phosphate solution with a detection limit (S/N=3) of 0.1 muM. The results of 15 successive repetitive measurement-regeneration cycles showed a relative standard deviation of 1.3% for 10 muM theophylline indicating that the electrode renewal gives a good reproducible surface. Quantitative analysis was performed by the standard addition method for the theophylline content in commercially available tea and drug.     

Photorefractive polymeric optical spatial solitons

We predict the formation of optical spatial solitons in photorefractive polymers. The orientational enhancement from the doped chromophores and the dependency of the quantum efficiency of generating mobile holes on the electric field make the polymeric solitons behave differently from other photorefractive solitons.     

Facile synthesis of 9-substituted 9-deazapurines as potential purine nucleoside phosphorylase inhibitors

A facile synthesis of 9-substituted 9-deazapurines as potential inhibitors of purine nucleoside phosphorylase has been achieved by the direct Friedel-Crafts aroylation or arylmethylation of 9-deazapurines using trifluoromethanesulfonic acid as catalyst. The aroylated 9-deazapurines could be transformed into the corresponding 9-aryimethyl derivatives by the Wolff-Kishner reaction. A novel synthesis of 9-deazahypoxanthine was also developed by treatment of 4-hydroxy-5-phenylazo-6-methylpyrimidin-2-thione with triethyl orthoformate in trifluoroacetic acid (TFA) to yield 8-oxo-7H-2-phenylpyrimido[5,4-c]pyridazin-6-thione followed by Raney nickel reduction.     

Kinetic analysis of the hydrogen oxidation reaction on Pt-black/Nafion electrode

The hydrogen oxidation reaction on Pt-black/Nafion electrode was investigated using a rotating disk electrode and cyclic voltammetry technique. The voltammetric results demonstrated that the electrode can be prepared with good reproducibility and that Pt-black particles without direct contact with Nafion were still electrochemically active in taking part in the H-adsorption/desorption process. For hydrogen oxidation, the limiting current density was reduced by the presence of Nafion coating. The H₂ diffusion resistance in Nafion film was avoided when the film thickness was less than 0.2 μm for a Pt-black loading of 20 μg. Moreover, the uncertainties in the kinetic results were discussed.     

An electrospray ionization tandem mass spectrometry based system with an online dual-loop cleanup device for simultaneous quantitation of urinary benzene exposure biomarkers trans,trans-muconic acid and S-phenylmercapturic acid

An electrospray ionization tandem mass spectrometry (ESI-MS/MS) system with an online dual-loop cleanup device was developed for simultaneous quantitation of the urinary benzene exposure biomarkers trans,trans-muconic acid (ttMA) and S-phenylmercapturic acid (SPMA). The cleanup device was constructed from an autosampler, two electrically operated two-position switching valves, a reversed-phase C18 trap cartridge, a 200-microL loop, and two solvent-delivery pumps. The device was interfaced directly with a triple-quadrupole mass spectrometer and fully controlled by computer software and hardware. Because isotope dilution by introducing 13C-labeled ttMA and SPMA as internal standards was employed, the precision of the analytical system was high (for ttMA, intra- and inter-day CV values ranged from 3.82-4.53%; for SPMA, 2.13-7.06%). The calibration curves obtained using human urine spiked with ttMA were linear from 15.6-4000 microg/L (R = 0.9998) and SPMA at concentrations from 0.78-200 microg/L (R = 0.9993). The method detection limit (MDL) for SPMA was 0.23 microg/L. The MDL of ttMA could not be determined accurately because of unavailability of an appropriate blank urine matrix, but was estimated to be lower than 7.43 microg/L. Without tedious manual sample cleanup procedures the analytical system is fully automated and is therefore useful for high-throughput simultaneous determination of urinary ttMA and SPMA. The sample throughput is roughly 100 samples per day. With the selectivity and the sensitivity provided by MS/MS detection, the analytical system can be used for large-scale monitoring of environmental or occupational exposure of humans to benzene.     

Full-capillary sample stacking/sweeping-MEKC for the separation of naphthalene-2,3-dicarboxaldehyde-derivatized tryptophan and isoleucine

In an attempt to improve the sensitivity of detection in capillary electrophoresis (CE), a novel online sample-concentration method, full-capillary sample stacking (FCSS)/sweeping-micellar electrokinetic chromatography (sweeping-MEKC) mode, is proposed. Naphthalene-2,3-dicarboxaldehyde (NDA)-derivatized tryptophan and isoleucine were selected as model compounds. In the initial step, the weakly acidic compounds, dissolved in a low-conductivity buffer (35.1 microS/cm; apparent ph (pH*) in a mixed solution of acetonitrile/methanol/water, 4.6), fill the entire capillary, two vials of a high-conductivity buffer (2.06 mS/cm; pH* 2.0) are placed on each end, and a negative polarity is then applied. Under these conditions, the direction of the electroosmotic flow (EOF) is toward the inlet. Meanwhile, the anionic analytes move in the reverse direction and are neutralized and stacked at the boundary of a dynamic pH-junction (between the sample matrix and the nonmicellar background solution (BGS)). When the sample concentration is completed, the BGS is quickly changed to solutions containing SDS-BGS for the subsequent separation. Since the mobility of SDS-analytes is then greater than the EOF, the following steps occur by the sweeping (for focusing) and MEKC (for separation) mode. Using these steps, a full-capillary sample injection/separation can be achieved.