Atmospheric DMSO degradation in the gas phase: Cl-DMSO reaction. Temperature dependence and products

The reactions of Cl atoms and ClO radicals with CH3-SOCH3 (DMSO) have been studied using the discharge flow method with direct detection of DMSO, CO, and products by mass spectrometry. The absolute rate constant at room temperature measured for reaction 1, (CH3)2SO + Cl --> products, was k(1) = (1.7 +/- 0.3) x 10(-11) cm3 molecule(-1) s(-1). For reaction 2, (CH3)2SO + ClO --> products, only an upper limit could be established, k(2) < or = 6 x 10(-14) cm3 molecule(-1) s(-1) Reaction 1 has been found to proceed through adduct formation and further decomposition involving the cleavage of the C-S bound. The pressure effect on the Cl-DMSO reaction from 0.5 to 3 Torr was negligible, and the temperature dependence in the range 273-335 K was also very slight. The results obtained are related to previous studies of sulfur compounds, and the atmospheric implications are also discussed in relation to the homogeneous sinks of DMSO. Tropospheric lifetimes of DMSO based on average Cl and ClO concentrations and the measured rate constants have been calculated showing that the contribution of reaction 1 must be of minor relevance in the marine boundary layer. Reaction 2 is so slow that it does not play any role within the atmospheric sulfur chemistry.     

Application of the Tauc-Lorentz formulation to the interband absorption of optical coating materials

Recent progress in ellipsometry instrumentation permits precise measurement and characterization of optical coating materials in the deep-UV wavelength range. Dielectric coating materials exhibit their first electronic interband transition in this spectral range. The Tauc-Lorentz model is a powerful tool with which to parameterize interband absorption above the band edge. The application of this model for the parameterization of the optical absorption of TiO2, Ta2O5, HfO2, Al2O3, and LaF3 thin-film materials is described.     

SENTIMENT CLASSIFICATION of MOVIE REVIEWS USING CONTEXTUAL VALENCE SHIFTERS

We present two methods for determining the sentiment expressed by a movie review. The semantic orientation of a review can be positive, negative, or neutral. We examine the effect of valence shifters on classifying the reviews. We examine three types of valence shifters: negations, intensifiers, and diminishers. Negations are used to reverse the semantic polarity of a particular term, while intensifiers and diminishers are used to increase and decrease, respectively, the degree to which a term is positive or negative. The first method classifies reviews based on the number of positive and negative terms they contain. We use the General Inquirer to identify positive and negative terms, as well as negation terms, intensifiers, and diminishers. We also use positive and negative terms from other sources, including a dictionary of synonym differences and a very large Web corpus. To compute corpus-based semantic orientation values of terms, we use their association scores with a small group of positive and negative terms. We show that extending the term-counting method with contextual valence shifters improves the accuracy of the classification. The second method uses a Machine Learning algorithm, Support Vector Machines. We start with unigram features and then add bigrams that consist of a valence shifter and another word. The accuracy of classification is very high, and the valence shifter bigrams slightly improve it. The features that contribute to the high accuracy are the words in the lists of positive and negative terms. Previous work focused on either the term-counting method or the Machine Learning method. We show that combining the two methods achieves better results than either method alone.     

Evaluation of various slip estimation techniques for an inductionmachine operating under field-oriented control conditions

Six published methods of rotor slip estimation for sensorless speed control were evaluated using simulated data. Only two of these showed signs of being usable. Both are based on the steady-state machine model and produce a fair slip accuracy for a machine running under perfect field alignment conditions. It was not determined whether the other four techniques were unsuccessful because they require a closed-loop speed controller, were presented incorrectly in the literature, or contain fundamental deficiencies. On the basis of these evaluations, a new technique was developed, and both measured and predicted results are presented to show that it works well. Moreover, this new technique has many features that make it theoretically and practically more attractive than most existing techniques     

Freeze-substitution

Freeze-substitution is a technique suitable for the preparation of unicellular and multicellular plant and animal specimens for conventional light microscopy, TEM and SEM. It is also widely used as a means of preparing animal and plant tissues for the localization of water soluble substances by analytical electron microscopy, autoradiography or visual detection of precipitates. The technical requirements of preparation, together with an evaluation of the procedures, are presented for various applications. Careful selection and evaluation of freezing technique, substitution solvent and regime are required for meaningful results.     

Volatile compounds on the surface and within Iberian dry-cured loin

The profile of volatile compounds from external and internal areas of Iberian dry-cured loin was studied by headspace solid-phase microextraction. Higher levels of 16 volatile compounds (hexane, decane, 3-methylbutanal, several sulphur compounds and some aromatic hydrocarbons) were detected in the outer part of the loins. These differences could be owing to several factors, such as greater exposure to oxygen and dehydration conditions in the surface of the product, which favour oxidation reactions and Strecker degradation of amino acids. Moreover, the addition of spices on the surface and the proximity of a mould layer growing on the surface of the product could also contribute to the higher levels of these compounds on the external layer. However, other sulphur compounds coming from spices showed similar levels on the surface and within the loins. This different behaviour could be a consequence of different diffusion rates depending on the features of the compound and the matrix.     

Identification of a photooxygenation product of chlortetracycline in hog lagoons using LC/ESI-ion trap-MS and LC/ESI-time-of-flight-MS

In the present work, a photoproduct of chlortetracycline (CTC) was identified for the first time in hog lagoon samples from confined animal feeding operations. Screening of several samples by LC/ESI-MS indicated the presence of a potential photooxygenation product of CTC with a nominal mass that was 32 Da higher than the parent drug. Generation of this assumed photoproduct (designated M510) was achieved in a 24-h irradiation experiment of an oxygenated alkaline medium containing 50 mg L(-)(1) CTC. Accurate mass measurements with an ESI-TOF-MS of the protonated isomerization product of CTC (iCTC) and the postulated photooxygenation product, bearing two oxygen atoms more than iCTC, were m/z 479.1229 and 511.1109, respectively. These corresponded to errors of -2.8 ppm for iCTC and +1.0 ppm for M510 relative to the theoretical masses. The generation of second- and third-stage mass spectra in an ESI-ion trap-MS showed similar characteristic fragmentation patterns for iCTC and the photoproduct M510, leading to the conclusion that the M510 structure consisted of an iCTC-like skeleton bearing two additional hydroxy groups. The site and configuration of one hydroxylation was confidently assigned, while the position of the other hydroxy group was tentatively assigned. Comparison of the (+)-ESI-MS(3) spectrum and the retention time of M510 in the sample from the irradiation experiment with those from the hog lagoon samples yielded excellent agreement, suggesting that the compounds were identical. Quantitative analysis of seven hog lagoon samples showed iCTC concentrations of 1910-15 800 microg L(-)(1), while the levels of M510 were found to be between 46 and 303 microg L(-)(1).