Pesticide residue analysis by off-line SPE and on-line reversed-phase LC-GC using the through-oven-transfer adsorption/desorption interface

A new method to determine pesticide residue in water is presented. The described method includes using off-line solid-phase extraction (SPE) and on-line reversed-phase liquid chromatography-gas chromatography (RPLC-GC). An interface, based on a modified programmed temperature vaporizer (PTV) injector, packed with a suitable trapping material, is used for on-line RPLC-GC. The changes made in the PTV injector affect the pneumatic system, sample introduction, and solvent elimination. The new interface is easily capable of automation. Methanol/wate (70/30) is used as the eluent in the LC preseparation step. The LC column flow during elution is different from the flow during the transfer step. The transferred volumes range from 500 to 1400 microL (volume of the fractions of interest). Solvent elimination is almost 100% before the sample reaches the GC column. The described system does not show any variation of the peak retention times. The detection limit for real samples ranges from 0.04 to 1.5 ng/L, using NP detection.     

Control system to counteract axial displacement during the welding of huge pipes

Development research has been carried out in order to solve a practical industrial problem: to counteract axial displacement (axial drift or axial creep) of workpieces during the welding process. Solutions found in the literature generally provide adequate results; however, they are mechanically complex with high purchase and maintenance costs. A mechanically simple and inexpensive solution is proposed in this paper. Axial drift is measured with a low-cost custom-built contact displacement sensor. This sensor can measure axial drift without calibration or set-up operations. It is highly robust in order to function correctly in industrial conditions. A pneumatic cylinder moves the idle turning roll along a rail, modifying the longitudinal position of the idle turning roll in order to counteract axial drift. The position of the idle turning roll is controlled by a control algorithm, which consists of a set of rules. Tests were carried out in order to validate the proposed solution, which can be applied to existing turning rolls thereby significantly reducing costs.     

Manual performance and laterality in twins of known chorion type

Manual performance, direction, and degree of laterality were tested in monozygotic (MZ) twins (8-12 years old) of known chorion type and dizygotic (DZ) twins. Three manual tasks rarely employed in twin studies were used; dot-filling, tapping, and peg-moving tasks. No chorion effect was observed: the monochorionic and dichorionic MZs differed neither for frequency of discordant pairs nor for handedness, laterality measurements, and manual performance. The pooled MZs and DZs were then compared in a classic twin design. The within-pair resemblance was not higher in MZs than in DZs for variables measuring level of manual performance. For laterality scores intraclass correlations were close to zero in MZ and DZ twin groups.     

Metabolic response to halothane in piglets susceptible to malignant hyperthermia: an in vivo 31P-NMR study

Using in vivo 31P-nuclear magnetic resonance spectroscopy, we studied the skeletal muscle metabolism of 17 anesthetized malignant hyperthermia-susceptible piglets and 25 control piglets during and after a halothane stress test. At rest, the phosphocreatine- (PCr) to-ATP ratio was 12% higher in the anesthetized piglets than in the control piglets, which may reflect a higher proportion of fast glycolytic fibers in the former. About 15 min of halothane administration sufficed to provoke onset of a reaction, which was characterized by a reciprocal drop in PCr and an increase in Pi with commencing intracellular acidosis. Halothane was withdrawn after a 20% drop in PCr. Within the next few minutes, intracellular pH dropped sharply and phosphomonoesters (PME) accumulated excessively. ATP was observed to decrease in 8 of the 17 animals. Halothane inhalation provoked a switch of metabolism toward glycolysis. Accumulation of PME suggests a mismatch between glycogenolysis and glycolysis. Despite severe acidification, glycolysis was not completely halted. Recovery of PCr and Pi started approximately 5 min after halothane withdrawal, with a longer time constant for recovery of the former. PME and intracellular pH aberrations lingered and started to recover later. Lost ATP was never restored within the observed recovery period of approximately 20 min.     

A Far IR Study of NbN in the Normal and Superconductive State

A thin film of NbN (thickness t = 300 Å), has been deposited on an MgO and a Si wafer. Both samples have been studied by transmission from 10 or 20 to 120 cm^?1, and have exhibited one maximum of transmission at a given frequency like the classical superconductors as Pb, Sn or Hg in the superconductive state. From the Far IR experimental data, the characteristic temperature θ_c, and the gap frequency (ν_gap (θ) = 2 Δ (θ), Δ(θ) being the energy gap) are immediately obtained (for instance for the NbN / MgO sample, θ_c = 15.5 K; ν_g (5 K) = 39.7 cm^?1), and it is seen that $\frac{{{\text{2}}\vartriangle (4{\text{K)}}}}{{{\text{k}}_{\text{B}} \theta _c }} \approx 3.5$ as expected from the BCS theory for a weak coupling. To fit the data we had to adjust only two additionnal parameters: collision and plasma frequency, ν_c (θ) and ν_p (including all carriers). At θ = 5 K, thebest fit for the NbN / MgO sample is obtained with ν_c = 371 cm^?1 and ν_p = 12,600cm^?1.     

The incorporation of quantum effects in enzyme kinetics modeling

We present an overview of new procedures for including quantum mechanical effects in enzyme kinetics. Quantum effects are included in three ways: (1) The electronic structure of the atoms in the catalytic center is treated quantum mechanically in order to calculate a realistic potential energy surface for the bond rearrangement process. (2) The discrete nature of quantum mechanical vibrational energies is incorporated in the treatment of nuclear motion for computing the potential of mean force. (3) Multidimensional tunneling contributions are included. These procedures are illustrated by applications to proton abstractions catalyzed by enolase and methylamine dehydrogenase and hydride-transfer reactions by alcohol dehydrogenase and xylose isomerase.     

Analysis of volatile components by direct injection of real-life samples by using a programmed-temperature vaporizer

A Chromatographic method is presented which allows the analysis of the volatile components of real-life samples without requiring the previous isolation and concentration of the compounds of interest. A programmed-temperature vaporizer (PTV) is used to enable the direct injection of the sample. A comparison of the proposed method with one involving a liquid-liquid extraction of the sample is also included.     

Current-Temperature Diagram of Resistive States in Long Superconducting YBa2Cu3O7 Strips

Using a sequence of stepped bias currents in the nanosecond range, we have studied the destruction of superconductivity in c-axis textured YBa₂Cu₃O₇ strips of various thickness and structure (single or multi-layers). Sufficiently far from T _c, vortex flow fades out and gradually gives way to localized dissipative structures, which can be interpreted either as Phase-Slip Centers (PSC) or normal Hot Spots (HS). A plot of the corresponding threshold currents in the current–temperature (I–T) plane indicates when each of them will occur, and how to switch over from one to the other, in a manner similar to that demonstrated for metallic materials (cf. Ladan et al., J. Low Temp. Phys. 153:103, 2008). The capability of some YBCO strips to support PSC’s at arbitrarily low temperatures escapes the common picture.