Suppressed ion chromatography for monitoring chemical impurities in steam for geothermal power plants

A suppressed ion chromatography (IC) technique has been evaluated as a chemical monitoring tool for detecting major anions (F-, Cl-, NO3- and SO4(2-)) of condensed steam in geothermal power plants. It is shown that the suppressed IC technique provides a suitable means for preventing possible damage to generating equipment in the geothermal industry. An electrical conductivity detector (0.1 microS sensitivity) with an anion-exchange column (IonPac AS4A-SC), a micro-membrane suppressor (AMMS II), and an isocratic high-pressure pump system were successfully used for detecting low concentrations of inorganic anions. Method detection limits for the anions of interest were <0.184 mg/L. Details of the IC methodology as well as some experimental results obtained during its application for the chemical monitoring of geothermal steam pipes are also described.     

Amplitude squared squeezed states in the Fock–Bargmann space

Squeezed states are normally studied in configuration space or using the Glauber formalism for the coherent states. Here we show that the use of the Fock–Bargmann space can lead to more general solutions, especially in the case of squeezed states associated with the square of field amplitude. The relations that we obtain are completely general and several well-known, approximate results can be obtained as the limit cases of our approach.© 1993 John Wiley & Sons, Inc.     

Fallout of uranium isotopes from the 1980 eruption of Mount St. Helens

A marked increase in the concentration of²³⁸U in rain was observed at Fayetteville (36 °N, 94 °W), Arkansas, after the 18 May 1980 eruption of Mount St. Helens. The fallout of natural uranium observed during the summer months of 1980 can be attributed to the 18 May 1980 events, which ejected an amount of ash material on the order of 4 km³ or about 8·10¹⁵ grams into the atmosphere.²³⁴U and²³⁵U were found to be highly enriched relative to²³⁸U in several rain samples collected at Fayetteville, Arkansas, prior to the volcanic eruption. The anomalous uranium seems to have originated from the Soviet satellite Cosmos-954, which fell over Canada, on 24 January 1978. The effect of the 25th Chinese nuclear test, which occurred on 16 October 1980, on the concentrations of uranium isotopes in rain appears to have been insignificant.     

Lipase from Carica papaya latex presents high enantioselectivity toward the resolution of prodrug (R,S)-2-bromophenylacetic acid octyl ester

Besides the well-known papain, lipolytic activity is another interesting enzymatic activity present in latex from Carica papaya. This lipolytic activity is strongly attached to the latex solid phase, resulting in a naturally immobilized biocatalyst. In this work we describe the kinetic resolution of (R,S)-2-bromophenylacetic acid octyl ester by Carica papaya crude latex and two partially purified latex fractions. Several parameters, such as substrate concentration and solvent effects were studied. The best results were obtained using decane as solvent with 50 mM of substrate and 50 mg/mL enzyme/reaction medium; under these conditions, a high enantioselectivity (E >200) was obtained with crude latex. A twofold increase of the initial rate maintaining E >200 was obtained using purified fractions without protease and without esterase. Lipase from Carica papaya latex is the most enantioselective wild-type enzyme ever described for the studied reaction.     

Enhanced Thermal Oxidation Stability of Reduced Graphene Oxide by Nitrogen Doping

Nitrogen‐doped reduced graphene oxide (N‐doped RGO) samples with a high level of doping, up to 13 wt. %, have been prepared by annealing graphene oxide under a flow of pure ammonia. The presence of nitrogen within the structure of RGO induces a remarkable increase in the thermal stability against oxidation by air. The thermal stability is closely related with the temperature of synthesis and the nitrogen content. The combustion reaction of nitrogen in different coordination environments (pyridinic, pyrrolic, and graphitic) is analyzed against a graphene fragment (undoped) from a thermodynamic point of view. In agreement with the experimental observations, the combustion of undoped graphene turns out to be more spontaneous than when nitrogen atoms are present.     

Recasting the (Synchrosqueezed) Short-Time Fourier Transform as an Instantaneous Spectrum

In a previous work, we proposed a time-frequency analysis called instantaneous spectral analysis (ISA), which generalizes the notion of the Fourier spectrum and in which instantaneous frequency is utilized to the fullest extent. In this paper, we recast both the Fourier transform (FT) and filterbank (FB) interpretations of the short-time Fourier transform (STFT) as instantaneous spectra. We show that to recast the FB interpretation of STFT as an instantaneous spectrum with valid structure, frequency reassignment is a fundamental necessity, thus demonstrating that this IS is closely related to the synchrosqueezed STFT. This result provides a new theoretical motivation for the synchrosqueezed STFT. Finally, we illustrate through example the instantaneous spectra corresponding to the FT and FB interpretations of STFT using two closed-form examples.     

New oleanan-type triterpene and cincholic acid glycosides from Peruvian "Uña de Gato" (Uncaria tomentosa)

A new oleanan-type triterpene and three new cincholic acid glycosides were isolated from Peruvian "Una de Gato" (Cat's claw, plant of origin: Uncaria tomentosa), a traditional herbal medicine in Peru. Their structures were determined by spectroscopic analysis.     

Synthesis,structural characterization and cytotoxic activity of organotin derivatives of indomethacin

The synthesis, characterization and cytotoxic properties in vitro of tri‐n‐butyltin 1‐(4‐chlorobenzoyl)‐5‐methoxy‐2‐methyl‐1H‐indole‐3‐acetate ( 1 ), tri‐phenyltin 1‐(4‐chlorobenzoyl)‐5‐methoxy‐2‐methyl‐1H‐indole‐3‐acetate ( 2 ), tetra‐n‐butyltin[bis‐1‐(4‐chlorobenzoyl)‐5‐methoxy‐2‐methyl‐1H‐indole‐3‐acetato]distannoxane ( 3 ) and di‐n‐butyltin bis‐1‐(4‐chlorobenzoyl)‐5‐methoxy‐2‐methyl‐1H‐indole‐3‐acetate ( 4 ) are described. These compounds have been characterized by ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy in solution and ¹¹⁹Sn NMR in the solid state, infrared spectroscopy, elemental analysis and X‐ray diffraction for compound 1 . The growth inhibition effects of compounds 1–4 against the lung adenocarcinoma cell line SK‐LU‐1 as well as the cervical cancer cell line HeLa were determined. Compounds 1 and 2 exhibit cytotoxic activity, whereas compounds 3 and 4 are inactive. Copyright © 2008 John Wiley & Sons, Ltd.     

Heteroscedastic controlled calibration model applied to analytical chemistry

In chemical analyses performed by laboratories, one faces the problem of determining the concentration of a chemical element in a sample. In practice, one deals with the problem using the so‐called linear calibration model, which considers that the errors associated with the independent variables are negligible compared with the former variable. In this work, a new linear calibration model is proposed assuming that the independent variables are subject to heteroscedastic measurement errors. A simulation study is carried out in order to verify some properties of the estimators derived for the new model and it is also considered the usual calibration model to compare it with the new approach. Three applications are considered to verify the performance of the new approach. Copyright © 2010 John Wiley & Sons, Ltd.