Kinetic Modeling of Plasma Methane Conversion Using Gliding Arc

Plasma methane (CH4) conversion in gliding arc discharge was examined. The result data of experiments regarding the performance of gliding arc discharge were presented in this paper. A simulation which is consisted some chemical kinetic mechanisms has been provided to analyze and describe the plasma process. The effect of total gas flow rate and input frequency refers to power consumption have been studied to evaluate the performance of gliding arc plasma system and the reaction mechanism of decomposition.Experiment results indicated that the maximum conversion of CH4 reached 50% at the total gas flow rate of 1 L/min. The plasma reaction was occurred at the atmospheric pressure and the main products were C (solid), hydrogen, and acetylene (C2H2). The plasma reaction of methane conversion was exothermic reaction which increased the product stream temperature around 30～50℃.     

Plasma Chemical and Electrical Modeling of a Dielectric Barrier Discharge in Kr–Cl2 Gas Mixtures

This paper reports the study of the Kr–Cl₂ plasma chemistry in terms of the homogenous model of a dielectric barrier discharge and for two kinds of the applied voltage excitation shape. The effect of Cl₂ concentration in the gas mixture, as well as gas pressure and power frequency on the discharge efficiency and the 222 nm photon generation, under typical experimental operating conditions, have been investigated and discussed. Calculations suggest that the overall conversion efficiency from electrical energy to ultraviolet emission in the lamp is in the range of 4.4–12 %, and it will be very affected at high chlorine percentage (>1 %) and high gas pressure (>200 Torr). A comparison between the sinusoidal and the burst excitation waveforms reveals that the burst excitation method provides an enhanced light source performance compared to the sinusoidal wave.     

Characteristics of Analyte Ionization in Low Power Microwave Plasma Torch

The ionization characteristics of the analytes in a low power Ar microwave plasma torch (MPT) was studied. The influence of forward microwave power, the flow rate of carrier gas and matrix element on the degree of ionization were observed. The axial profiles of the degree of the ionization of some elements were determined. The experimental results are very important for developing the new analytical source——microwave plasma torch (MPT).     

Modelling of the Plasma–Sheath Boundary Region in Wall-Stabilized Arc Plasmas: Unipolar Discharge Properties

A two-dimensional model of the non-equilibrium unipolar discharge occurring in the plasma–sheath boundary region of a transferred-arc was developed. This model was used to study the current transfer to the nozzle (1 mm diameter) of a 30 A arc cutting torch operated with oxygen. The energy balance and chemistry processes in the discharge were described by using a kinetic block of 45 elementary reactions and processes with the participation of 13 species including electronically excited particles. The nonlocal transport of electrons was accounted for into the fluid model. The dependence of the ion mobility with the electric field was also considered. Basic discharge properties were described. It has been found that a large part (~ 80%) of the total electric power (1700 mW) delivered in the bulk of the sheath region is spent in heating the positive ions and further dissipated through collisions with the neutral particles. The results also showed that the electron energy loss in inelastic collisions represents only ~ 25% of the electron power and that about 63% of the power spent on gas heating is produced by the ion–molecule reaction, the electron–ion and ion–ion recombination reactions, and by the electron attachment. The rest of the power converted into heat is contributed by dissociation by electron-impact, dissociative ionization and quenching of O(¹D). Some fast gas heating channels which are expected to play a key role in the double-arcing phenomena in oxygen gas were also identified.     

LC–MS–MS Analysis of Strictosamide in Rat Plasma, and Application of the Method to a Pharmacokinetic Study

A rapid and simple high-performance liquid chromatographic tandem mass spectrometric method has been developed and validated for analysis of strictosamide in rat plasma. Chromatographic separation was achieved on a C₁₈ column by gradient elution with mixtures of methanol, water, and acetonitrile containing 0.05% acetic acid. Digoxin was used as internal standard. Selected reaction monitoring (SRM) was used for MS quantitation. Linearity was good in the range 0.05–20 ng mL^?1 in rat plasma. The lower limit of quantitation was 0.04 ng mL^?1. The method is precise and reliable and can be applied to pharmacokinetic studies.     

Turbulent Convective Heat Transfer and Pressure Drop of Graphene–Water Nanofluid Flowing Inside a Horizontal Circular Tube

Turbulent convective heat transfer of graphene–water nanofluids with various concentrations inside a uniformly heated circular tube is studied experimentally. For this purpose, experiments are conducted to measure thermal conductivity, viscosity, pressure drop, and heat transfer coefficient. Results show enhancement of thermal conductivity and moderate increment of viscosity with addition of low amounts of nanoparticles. Moreover, heat transfer coefficient shows relatively high augmentation, and pressure drop remains unchanged. The maximum enhancements are 10.30%, 4.95%, and 6.04% for thermal conductivity, viscosity, and heat transfer coefficient, respectively. UV–Vis spectroscopy results show that the nanofluids are highly stable.     

Spatially Dependent Kinetics of Electrons and Excited Atoms in the Column Plasma of a He–Xe dc Discharge

The radially varying kinetics of electrons and excited atoms in the cylindrical axially homogeneous positive column of a dc glow discharge in a gas mixture of helium and 2% xenon was studied. The experimental investigations comprise the radially resolved measurements of the isotropic part of the electron velocity distribution function (EVDF) using a single-probe technique and of the densities of atoms in the lower excited states by using a laser diode absorption method. The theoretical investigations are based on the solution of the space-dependent kinetic equation for the EVDF and the balance equations of excited gas atoms. Besides a strict solution, various simplified treatments of the electron kinetics as the conventional homogeneous approach and the nonlocal approach have been applied. The electron kinetic behavior in the helium–xenon column plasma changes remarkably with increasing helium gas pressure from a distinctly nonlocal behavior at a low pressure of 100 Pa to a nearly local behavior at a medium pressure of 600 Pa.     

Temperature and Heat Flow Calibration of A DSC-instrument in the Temperature Range Between −100 and 160°C

Thermoanalytical instruments are extensively used in R&D as well as in industrial quality control. A quantitative analysis of the data of a thermoanalytical measurement requires a careful calibration of the instrument. In differential scanning calorimetry (DSC) the quantities that have to be calibrated are the temperature and the heat flow. These two quantities are usually calibrated by evaluating melting or solid-solid transitions of some reference materials with well known transition enthalpies and temperatures. In this contribution we investigate temperature and heat flow calibration in the temperature range between −100 and 160°C. We included 9 different samples for the analysis and established some general rules for the calibration process. As a result we found that with a well calibrated instrument the heat flow can be measured with 90% confidence to about ± 3% accuracy in this temperature range. With respect to temperature calibration we find that accuracies of ±0.8°C (90% confidence) may be expected. These values represent general accuracy limitations of DSC’s due to varying heat transfer conditions within the samples. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rapid and Sensitive UPLC-MS–MS for the Determination of Trimetazidine in Human Plasma

A specific and sensitive UPLC-MS–MS was developed for the determination of trimetazidine in human plasma. The sample preparation was based on a single-step liquid–liquid extraction with acetic ether. The chromatographic separation was on a C₁₈ analytical column (50 mm × 2.1 mm, 1.7 μm) with acetonitrile and 10 mM ammonium acetate (30:70, v/v) as the mobile phase, and a triple-quadrupole mass spectrometer equipped with an electrospray ionization source (ESI) applied for detection. The method was linear over the concentration ranges of 0.25–100.00 ng mL^?1 for trimetazidine, and the lower limit of quantification (LLOQ) was 0.25 ng mL^?1. The intra- and inter-day relative standard deviation (RSD) were less than 15% and the relative error (RE) were all within 15%. Finally, this method has been successfully applied to analyze plasma samples from a bioequivalence study with 18 volunteers.     

Rapid and Sensitive UPLC-MS–MS for the Determination of Trimetazidine in Human Plasma

A specific and sensitive UPLC-MS–MS was developed for the determination of trimetazidine in human plasma. The sample preparation was based on a single-step liquid–liquid extraction with acetic ether. The chromatographic separation was on a C₁₈ analytical column (50 mm × 2.1 mm, 1.7 μm) with acetonitrile and 10 mM ammonium acetate (30:70, v/v) as the mobile phase, and a triple-quadrupole mass spectrometer equipped with an electrospray ionization source (ESI) applied for detection. The method was linear over the concentration ranges of 0.25–100.00 ng mL⁻¹ for trimetazidine, and the lower limit of quantification (LLOQ) was 0.25 ng mL⁻¹. The intra- and inter-day relative standard deviation (RSD) were less than 15% and the relative error (RE) were all within 15%. Finally, this method has been successfully applied to analyze plasma samples from a bioequivalence study with 18 volunteers.

     

Development and Validation of a Sensitive LC–Tandem-MS Method for the Quantitative Determination of Picroside II in Rat Plasma

A rapid and sensitive method for the quantitative determination of picroside II in rat plasma was developed and validated using liquid chromatographic separation with tandem mass spectrometric detection. The analytes of interest were extracted from rat plasma samples by ethyl acetate after acidification with 1.0% acetic acid solution. Chromatographic separation was achieved on a Hypersil GOLD column (50 × 2.1 mm I.D., 5 μm) using a mobile phase consisting of acetonitrile–0.1% formic acid solution (30:70, v/v) at a flow rate of 0.2 mL min^?1. Detection was performed on a triple quadrupole tandem mass spectrometer by selected reaction monitoring (SRM) mode via electrospray ionization (ESI). The calibration curve was linear in the concentration range of 1.00–400 ng mL^?1 in rat plasma, with a 1.00 ng mL^?1 lower limit of quantification (LLOQ). Satisfactory results were achieved for intraday repeatability [relative standard deviation (RSD) = 6.4–12.4%] and inter-day precision (RSD = 6.8–14.7%). The accuracy in terms of relative error ranged from ?2.1 to 10.0%. The extraction recoveries of picroside II and icariin (internal standard) were 80.0 and 89.3%, respectively. The developed method was successfully employed to determine picroside II plasma concentrations after oral administration to Wistar rats.     

Heat capacity and thermodynamic functions of cadmium tellurites in the range of 298.15–673 K

The isobaric heat capacity of cadmium tellurites is studied by dynamic calorimetry in the range of 298.15–673 K to derive the equation for the C _p ^○ ～ f(T) dependence, and to determine the thermodynamic functions. The C _p ^○ ～ f(T) dependences exhibit sharp λ-shaped anomalous effects due apparently to secondorder phase transitions.     

Modeling the molecular dynamics of cytochrome C in aqueous and water–methanol environment

One-microsecond molecular dynamics of horse heart cytochrome C was modeled in aqueous and water–methanol environment. It was shown that the coordination bond between Met-80 sulfur and heme iron is broken in water– methanol solution.     

LC–MS–MS Determination of Troxerutin in Plasma and Its Application to a Pharmacokinetic Study

A highly sensitive liquid chromatography–tandem mass spectrometry (LC–MS–MS) method for the determination of troxerutin in human plasma using tramadol as internal standard (IS) has been developed and validated. Sample preparation involved liquid–liquid extraction with ethyl acetate–isopropanol (95:5, v/v). The analyte and IS were separated by RP–LC with gradient elution using 10 mM ammonium acetate containing 0.1% formic acid and methanol at a flow rate of 0.9 mL min^?1. LC–MS–MS in the positive ion mode employed multiple reaction monitoring of the transitions at m/z 743.2→435.3 and m/z 264.1→58.0 for troxerutin and IS, respectively. The assay was linear in the concentration range 0.01–10 ng mL^?1 with precision and accuracy within assay variability limits as per FDA guidelines. The assay was successfully applied to a pharmacokinetic study involving oral administration of 300 mg troxerutin to eight healthy Chinese volunteers.     

SPE and LC–ESI–MS for Quantitative Analysis of Mitiglinide in Human Plasma in a Bioequivalence Study

Liquid chromatography–electrospray ionization mass spectrometry has been used for rapid, selective, and sensitive quantitative analysis of mitiglinide in human plasma. Sample pretreatment involved solid-phase extraction from plasma with gliclazide as internal standard. Separation was performed on a C₁₈ column (150 × 2.0 mm) with 71:29 (v/v) acetonitrile–water (containing 0.1% formic acid and 0.2 mmol L^?1 ammonium acetate) as mobile phase at a flow rate of 0.2 mL min^?1. The method was validated then successfully applied to a clinical bioequivalence study of mitiglinide in 20 healthy volunteers after oral administration.     

Heat capacity and thermodynamic functions of YVO4 in the 13–347 K region

The heat capacity of YVO₄ was measured by adiabatic calorimetry in the region of 13.11–347.14 K. The values of thermodynamic functions (the entropy, enthalpy change and reduced Gibbs function) were calculated using smoothed heat capacity values. The value of the Gibbs energy of formation from simple compounds was calculated.     

Numerical Modeling of an RF Argon–Silane Plasma with Dust Particle Nucleation and Growth

A one-dimensional numerical model and simulation results are presented for a capacitively-coupled radio frequency parallel-plate argon–silane dusty plasma. The model includes self-consistently coupled numerical modules, including a plasma fluid model, a sectional aerosol model, and a simple chemistry model to predict rates of particle nucleation and surface growth. Operating conditions considered include 13.56 MHz frequency, 100 mTorr pressure, a 4-cm electrode gap, gas flow through the top electrode with a 30:1 ratio of argon to silane, and applied radio frequency voltage amplitude of either 100 or 250 V. In the higher voltage case two lobes of relatively large particles are formed by ion drag, while fresh nucleation occurs in the void between these lobes. It is shown that the reason that fresh nucleation occurs in the void involves an interplay among several coupled phenomena, including nanoparticle transport, the plasma potential profile, and trapping of silicon hydride anions that drive nucleation in this system.     

Studies on Excitation and Rotational Temperatures of an Oxygenshielded Argon Microwave Plasma Torch Source

IntroductionPlasma sources have been widely used for traceelemental analysis in atomic emission spectrometry(AES)or mass spectrometry(MS).The microwaveplasma torch(MPT),as a relative new source,wasfirst developed by Jinet al.in1985[1,2]and modifiedby Jin …     

Modeling of three-phase vapor–liquid–liquid equilibria for a natural-gas system rich in nitrogen with the SRK and PC-SAFT EoS

In this work, we present the modeling of three-phase vapor–liquid–liquid equilibria for a mixture of natural gas (Hogback gas) containing high concentrations in nitrogen (51.8 mol%) with the SRK and PC-SAFT equations of state. The interest of studying this mixture is due to the experimental evidence of the occurrence of multiple equilibrium liquid phases for this mixture over certain ranges of temperature and pressure. The calculation of the multiphase equilibria was carried out by using an efficient numerical procedure based on the minimization of the system Gibbs energy and thermodynamic stability tests to find the most stable state of the system. The results of the calculated vapor–liquid–liquid equilibria (VLLE) show that the PC-SAFT equation of state predicts satisfactorily the phase behavior that experimentally exhibits this mixture, whereas the SRK equation of state predicts a three-phase region wider than the experimentally observed. The two-phase boundary for this mixture was also calculated through flash calculations, and the results showed that this mixture does not present any gas-liquid critical point.