Simulation of Rarefied Gas Flows in Atmospheric Pressure Interfaces for Mass Spectrometry Systems

The understanding of the gas dynamics of the atmospheric pressure interface is very important for the development of mass spectrometry systems with high sensitivity. While the gas flows at high pressure (>1 Torr) and low pressure (<10^–3 Torr) stages are relatively well understood and could be modeled using continuum and molecular flows, respectively, the theoretical modeling or numeric simulation of gas flow through the transition pressure stage (1 to 10^–3 Torr) remains challenging. In this study, we used the direct simulation Monte Carlo (DMSC) method to develop the gas dynamic simulations for the continuous and discontinuous atmospheric pressure interfaces (API), with different focuses on the ion transfer by gas flows through a skimmer or directly from the atmospheric pressure to a vacuum stage, respectively. The impacts by the skimmer location in the continuous API and the temporal evolvement of the gas flow with a discontinuous API were characterized, which provide a solid base for the instrument design and performance improvement.

Standing wave design of a four-zone thermal SMB fractionator and concentrator (4-zone TSMB-FC) for linear systems

For a dilute feed, a four-zone SMB with temperature gradient (4-zone TSMB-FC) can fractionate and simultaneously concentrate two solutes. Optimization of the operating parameters for this system, which include four zone flow rates and port switching time, is a major challenge because of the five variables. Initial choice of the variables using the triangle theory followed by a systematic search using rate model simulations is time-consuming. In this study, the SWD developed previously for isothermal systems is modified for the first time for a 4-zone TSMB-FC. The optimum operating parameters are determined with the new method. Only linear isotherm systems with significant mass transfer resistances are considered. For a dilute feed, a 4-zone SMB-FC can produce pure desorbent, in addition to extract and raffinate products with high purities. For the separation of p-xylene and toluene with silica gel in the temperature range from 0 to 80 °C, the enrichment factor in the linear region can be as high as 80 fold for an extract purity of 99.99 % and tenfold for raffinate purity of 99.8 %, while withdrawing the desorbent at a desorbent to feed flow rate ratio of 0.53 and 0.78, respectively.     

Quantitative SIMS depth profiling of Al in AlGaN/AlN/GaN HEMT structures with nanometer‐thin layers

The possibilities of quantitative secondary ion mass spectrometry (SIMS) depth profiling of Al in AlxGa1 ? xN/AlN/GaN transistor heterostructures are shown. Using a series of test structures for a TOF.SIMS‐5 time‐of‐flight mass spectrometer, we obtained a refined linear calibration dependence of the secondary‐ion yield on the composition ×, namely, Y(CsAl+)/Y(CsGa+) = K × x/(1 ? x), with a high linear correlation coefficient, Rl = 0.9996, which permits quantitative SIMS analysis of relatively thick AlGaN barrier layers. The method of profile reconstruction with allowance for the main artifacts of ion sputtering has been first applied for the analysis of GaN/AlGaN/AlN/GaN high electron mobility transistor structure. This method permits to perform quantitative analysis of the thickness and composition of a nanometer‐thin AlN sublayer and to estimate the measurement error. For the structure being studied, the AlN sublayer is 1.2 ± 0.2 nm thick. Copyright © 2016 John Wiley & Sons, Ltd.     

Determination of major nonmetallic impurities in magnesium by glow discharge mass spectrometry with a fast flow source using sintered and pressed powder samples

Fast flow glow discharge mass spectrometry with a Grimm-type ion source providing a high sputter rate was used for the determination of major nonmetallic impurities in magnesium. The analytical signal was found to be strongly influenced by the electrical discharge parameters. For calibration by standard addition, synthetic standard samples were produced in two different ways—namely, by pressing and by sintering doped metal powders. The observed sensitivity of the calibration curves was shown to depend on the particle size of the powder. For the magnesium powders, the mass fractions of oxygen, nitrogen, boron, and silicon were determined to be about 0.01 kg?kg^-1 (relative standard deviation approximately 10–20 %), 2,700 mg?kg^-1, 150 mg?kg^-1, and 300 mg?kg^-1, respectively.     

Synthetic boron-doped carbonado,a new electrode material: synthesis in C–metal–B growth systems aimed at the lowering of the synthesis temperature without loss of electrochemical activity

New electrode material—boron-doped synthetic carbonado (bulk polycrystalline diamond)—was synthesized at high pressures and high temperatures in the C–metal (Co, Ni, or Fe) –B growth systems. The metal borides were used as the growth medium-forming substances for graphite-to-diamond transformation at a temperature of ~?1300 °C and pressure of 8 GPa. For comparison, etalon carbonado-type electrode with nearly limiting concentration of boron in diamond was synthesized by subjecting the mixture of amorphous boron with graphite to much higher temperatures (2200–2500 °C) under the same pressure. Despite the lower content of boron in diamond synthesized in the presence of metal borides, these new boron-doped carbonado electrodes are not inferior to the etalon compact in their electrochemical activity, as judging by the onset potential of anodic chlorine evolution from KCl solution. The presence of metal-containing structural defects in boron-doped diamond matrix is supposed to be responsible for the somewhat enhanced catalytic activity of the electrodes. High-pressure synthesis of bulk metal-modified boron-doped diamond opens a new avenue in the development of superior functional electrode materials.     

Platinum nanoparticles on gallium nitride surfaces: effect of semiconductor doping on nanoparticle reactivity

Platinum nanoparticles supported on n- and p-type gallium nitride (GaN) are investigated as novel hybrid systems for the electronic control of catalytic activity via electronic interactions with the semiconductor support. In situ oxidation and reduction were studied with high pressure photoemission spectroscopy. The experiments revealed that the underlying wide-band-gap semiconductor has a large influence on the chemical composition and oxygen affinity of supported nanoparticles under X-ray irradiation. For as-deposited Pt cuboctahedra supported on n-type GaN, a higher fraction of oxidized surface atoms was observed compared to cuboctahedral particles supported on p-type GaN. Under an oxygen atmosphere, immediate oxidation was recorded for nanoparticles on n-type GaN, whereas little oxidation was observed for nanoparticles on p-type GaN. Together, these results indicate that changes in the Pt chemical state under X-ray irradiation depend on the type of GaN doping. The strong interaction between the nanoparticles and the support is consistent with charge transfer of X-ray photogenerated free carriers at the semiconductor-nanoparticle interface and suggests that GaN is a promising wide-band-gap support material for photocatalysis and electronic control of catalysis.     

Atmospheric pressure chemical ionization of alkanes,alkenes, and cycloalkanes

Normal and cyclic alkanes and alkenes form stable gas-phase ions in air at atmospheric pressure from 40 to 200°C when moisture is below 1 ppm. Ionization of alkanes in a ⁶³Ni source favored charge transfer over proton transfer through pathways involving [M?1]⁺ and [M?3]⁺ ions. Ion mobility spectra for alkanes showed sharp and symmetrical profiles while spectra for alkenes suggested fragmentation. Ion identifications were made by using mass spectrometry, and ionization pathways were supported by using deuterated analogs of alkanes and alkenes. Alkanes were ionized seemingly through a hydrogen abstraction pathway and did not proceed through an alkene intermediate. New methods for interpretation of mobility spectra utilizing ion mobility spectrometry, atmospheric pressure chemical ionization mass spectrometry, chemical ionization mass spectrometry, and ion mobility spectrometry-mass spectrometry data were demonstrated.     

Development and validation of two LC-MS/MS methods for the detection and quantification of amphetamines, designer amphetamines, benzoylecgonine, benzodiazepines, opiates, and opioids in urine using turbulent flow chromatography

In the context of driving ability diagnostics in Germany, administrative cutoffs for various drugs and pharmaceuticals in urine have been established. Two liquid chromatography–tandem mass spectrometry methods for simultaneous detection and quantification of amphetamines, designer amphetamines, benzoylecgonine, benzodiazepines, opiates, and opioids in urine were developed and validated. A 500-μL aliquot of urine was diluted and fortified with an internal standard solution. After enzymatic cleavage, online extraction was performed by an ion-exchange/reversed-phase turbulent flow column. Separation was achieved by using a reversed-phase column and gradient elution. For detection, a Thermo Fisher TSQ Quantum Ultra Accurate Mass tandem mass spectrometer with positive electrospray ionization was used, and the analytes were measured in multiple-reaction monitoring mode detecting two transitions per precursor ion. The total run time for both methods was about 15 min. Validation was performed according to the guidelines of the Society of Toxicological and Forensic Chemistry. The results of matrix effect determination were between 78 % and 116 %. The limits of detection and quantification for all drugs, except zopiclone, were less than10?ng/mL and less than 25 ng/mL, respectively. Calibration curves ranged from 25 to 200 ng/mL for amphetamines, designer amphetamines, and benzoylecgonine, from 25 to 250 ng/mL for benzodiazepines, from 12.5 to 100 ng/mL for morphine, codeine, and dihydrocodeine, and from 5 to 50 ng/mL for buprenorphine and norbuprenorphine. Intraday and interday precision values were lower than 15 %, and bias values within?±?15 % were achieved. Turbulent flow chromatography needs no laborious sample preparation, so the workup is less time-consuming compared with gas chromatography–mass spectrometry methods. The methods are suitable for quantification of multiple analytes at the cutoff concentrations required for driving ability diagnostics in Germany.     

Synthesis of two-dimensional gallium nitride via spin coating method: influences of nitridation temperatures

This paper reports the synthesis and characterization of gallium nitride (GaN) thin films deposited on p-type silicon (100) substrates by using low cost spin coating method under various nitridation temperatures. This work demonstrated that spin coating with the new prepared precursor solution can be used as a versatile method for the successfully growth of GaN thin films. Furthermore, the influence of varying nitridation temperatures on the structural, morphological, and optical properties of synthesized GaN thin films were studied in this work. The GaN thin films were characterized by X-ray diffraction, field-emission scanning electron microscopy, atomic force microscopy, photoluminescence and Raman spectroscopy. All the characteristics of the GaN thin films were effectively improved with the increasing of the nitridation temperatures from 750 to 950 °C and degraded at temperature of 1,050 °C. The measured results show that nitridation temperature plays an important role in improving the crystalline quality of the GaN thin films and the most efficient nitridation temperature was at 950 °C.     

The study of wet etching on GaN surface by potassium hydroxide solution

Potassium hydroxide solution was used to etch un-doped GaN grown on the sapphire substrate at 180 and 260 °C. We illustrated the etching phenomenon in detail and probed its mechanism in the wet etching process. By multiplying the planar density and the number of dangling bonds on the N atom, we proposed the etching barrier index (EBI) to describe the difficulty degree of each lattice facet. The raking of EBI will be +c-plane > a-plane > m-plane > ?c-plane > (10-1-1) plane > r-plane. Combining the EBI with SEM results, we thoroughly studied the whole etching process. We confirmed that in our research, KOH wet etching on GaN starts from the r-plane instead of the +c-plane or ?c-plane, which differs from other studies. We also found that during the high-temperature etching process, there are two etching approaches. In one, the etching begins vertically from the top to the bottom, then horizontally, and finally reversely from the bottom to the top. In the other, etching pits will develop into a hexagonal hole of the sidewall of m-plane.     

Kristallines Phoshor(V)-nitrid-imid,HPN2 bzw. DPN2 – Strukturbestimmung mit Röntgen-, Synchrotron- und Neutronenstrahlung

Crystalline Phosphorus(V) Nitride Imide, HPN₂ and DPN₂, respectively, – Structure Determination with X-Ray, Synchrotron, and Neutron Radiation Microcrystalline HPN₂ resp. DPN₂ was obtained by the reaction of P₃N₅ with NH₃ resp. ND₃ in high-pressure autoclaves under ammonothermal conditions (T = 550°C, p(NH₃ resp. ND₃) = 6 kbar) within 14 d.     

Characterization of Simultaneous Heat and Mass Transfer Phenomena for Water Vapour Condensation on a Solid Surface in an Abiotic Environment—Application to Bioprocesses

The phenomenon of heat and mass transfer by condensation of water vapour from humid air involves several key concepts in aerobic bioreactors. The high performance of bioreactors results from optimised interactions between biological processes and multiphase heat and mass transfer. Indeed in various processes such as submerged fermenters and solid-state fermenters, gas/liquid transfer need to be well controlled, as it is involved at the microorganism interface and for the control of the global process. For the theoretical prediction of such phenomena, mathematical models require heat and mass transfer coefficients. To date, very few data have been validated concerning mass transfer coefficients from humid air inflows relevant to those bioprocesses. Our study focussed on the condensation process of water vapour and developed an experimental set-up and protocol to study the velocity profiles and the mass flux on a small size horizontal flat plate in controlled environmental conditions. A closed circuit wind tunnel facility was used to control the temperature, hygrometry and hydrodynamics of the flow. The temperature of the active surface was controlled and kept isothermal below the dew point to induce condensation, by the use of thermoelectricity. The experiments were performed at ambient temperature for a relative humidity between 35?C65% and for a velocity of 1.0?ms^?1. The obtained data are analysed and compared to available theoretical calculations on condensation mass flux.     

Electrocatalytic studies of covalently immobilized metal tetra-amino phthalocyanines onto derivatized screen-printed gold electrodes

Metal tetra-amino phthalocyanine complexes (MTAPc; where M is Co or Mn) were immobilized on screen-printed gold electrodes pre-modified with monolayers of benzylamino groups. The functionalized electrodes were then activated using benzene-1,4-dicarbaldehyde as a linker before MTAPc complexes were immobilized. The surface coverages for the modified electrodes confirmed the perpendicular orientation of the MTAPcs. The apparent electron transfer constant (k_app) for the electrodes is 2.2?×?10^?5 cm.s^?1 for both CoTAPc and MnTAPc modified electrodes as calculated with data from impedance measurements. The k_app values for the bare and benzylamino modified electrodes were found to be 1.2?×?10^?4 cm.s^?1 and 4.9?×?10^?6 cm.s^?1, respectively. The electrocatalysis of the modified electrodes towards detection of H₂O₂ gave significant peak current densities and electrocatalytic potentials at ?0.28 V and ?0.31 V for the MnTAPc and CoTAPc modified electrodes, respectively.     

Evaluation of an alternative convenient irradiation system for determination of emission rate of radio-isotopic neutron sources

In present work, an alternative irradiation system based on a symmetric cylindrical tank filled with a moderator containing hydrogen, which was equipped with a NaI(Tl) scintillation detector, was proposed for using in determination of neutron flux. This irradiation system was designed by MCNP4C code, with considering a ²⁴¹Am–Be neutron source in several volumes and different materials. When the neutron is captured by hydrogen, a 2.22 MeV prompt gamma-ray is emitted. The gamma pulse-height spectrum shows a photo-peak around 2.22 MeV whose net area is proportional to the total emission rate of neutron. The simulation result showed that a cylindrical tank with 110 cm diameter and height filled with water can be a suitable system for neutron source strength calibration. Furthermore, a proper two-layer shielding must be placed between the source and detector for preventing neutrons and gamma rays to directly enter the detector.     

Modeling of thermal processes in very high pressure liquid chromatography for column immersed in a water bath: Application of the selected models

Currently, chromatographic analyses are carried out by operating columns packed with sub-2 μm particles under very high pressure gradients, up to 1200 bar for 5 cm long columns. This provides the high flow rates that are necessary for the achievement of high column efficiencies and short analysis times. However, operating columns at high flow rates under such high pressure gradients generate a large amount of heat due to the viscous friction of the mobile phase stream that percolates through a low permeability bed. The evacuation of this heat causes the formation of significant or even large axial and radial gradients of all the physico-chemical parameters characterizing the packing material and the mobile phase, eventually resulting in a loss of column efficiency. We previously developed and successfully applied a model combining the heat and the mass balances of a chromatographic column operated under very high pressure gradients (VHPLC). The use of this model requires accurate estimates of the dispersion coefficients at each applied mobile phase velocity. This work reports on a modification of the mass balance model such that only one measurement is now necessary to accurately predict elution peak profiles in a wide range of mobile phase velocities. The conditions under which the simple equilibrium-dispersive (ED) and transport-dispersive (TD) models are applicable in VHPLC are also discussed. This work proves that the new combination of the heat transfer and the ED model discussed in this work enables the calculation of accurate profiles for peaks eluted under extreme conditions, like when the column is thermostated in a water bath.     

Insights into electrocatalytic activity of epitaxial graphene on SiC from cyclic voltammetry and ac impedance spectroscopy

Electrocatalytic activity of graphene grown epitaxially on SiC is studied using cyclic voltammetry and electrochemical impedance spectroscopy. AFM images show step-like topography of SiC-graphene. For ferri-/ferrocyanide redox couple, no voltammetric response is observed at the pristine graphene. Basal planes of graphite are electrochemically inactive as well. After electrochemical oxidation, apparent redox peaks appear at both the graphene and graphite electrode. However, more intensive redox peaks are observed at graphene, where simultaneous redox reaction with the adsorbed and the diffused ferri-/ferrocyanide ions occurs. Electrochemical impedance measurements show that the graphene electrode behaves like an array of microelectrodes. We used the partially blocked electrode model to fit impedance data. Using the fitting parameters, a size of microelectrodes was found to be 23.8?±?2.1 μm and the active surface of graphene was estimated to be 21 %. A value of the standard electron transfer rate constant found for the anodized epitaxial graphene (2.16?±?0.32)?×?10^??3cm???s^??1) is by one order of magnitude lower than the standard rate constant estimated for the anodized graphite basal planes (～5?×?10^??2cm???s^??1). Electrochemical reduction causes total disappearance of electrochemical responses at the graphene electrode, whereas only slight decrease of the peak currents is observed at the reduced graphene. Such behavior proves that different activation mechanisms occur at the graphene and graphite electrodes.     

Principles and Latest Developments in the Field of Metallic and Nonmetallic Hard Materials

A survey of some fundamental aspects of the theory of hardness is followed by a discussion of recent developments in the field of sintered hard metal alloys. For example, good results have been obtained by the addition of hafnium carbide to hard metals. Niobium carbide can sometimes replace the more expensive tantalum carbide; vanadium carbide can be used to inhibit grain growth, especially in the case of ultrafine carbides. A brief outline is given of the results of investigations on ternary and quaternary systems with the components TiC, HfC, NbC, TaC, and WC. The utilization of sintered nitride and carbonitride hard metals in the field of machining appears feasible. Recently developed high-pressure/high-temperature autoclaves permit work on nitride systems under a high nitrogen pressure. The authors comment on the latest work in the field of non-metallic hard materials and on diamond synthesis.     

Application of thermovision for estimation of the optimal and safe parameters of the whole body cryotherapy

Exposure to the extreme low temperatures, ranging between ?60 and ?140 °C, has many beneficial effects on the human body what is exploited for example in sport medicine, for treatment of locomotory system diseases or even some psychiatric disorders. To insure the safe treatment in a cryochamber, careful planning of the procedure and proper qualification of patients, is required. Cardiovascular system, especially skin vasculature plays the major role of the body response to the extreme cold. The changes in skin blood flow are reflected in changes of the temperature distribution. Therefore, the thermal imaging, which allows to analyze the temperature distribution on the human body, may be successfully exploited to examine the influence of extremely low temperatures on the skin vascular system. The aim of this work was to examine the temperature, blood pressure, and heart rate changes after the whole body cryotherapy in healthy subjects to determine the safety conditions of the treatment. 480 healthy students of the Wroc?aw University School of Physical Education were divided into two groups (each 240 persons). All subjects were exposed for 1–3 min to the extremely low temperatures: ?60, ?100, ?120, and ?140 °C. In one group, the thermograms were recorded before and 5 and 30 min after the cryotherapy by means of ThermoVision A20 M thermal camera. In the other one, heart rate and blood pressure were measured before and 5 min after the cryotherapy. It was demonstrated that 3-min exposure in the cryochamber and the temperature ?120 °C are the optimal and safe cryotherapy parameters.     

Experimental study of extraction fraction and mass transfer coefficient in a microchannel using butyl acetate/acetic acid/water chemical system

The droplet flow regime in microchannels can increase the mass transfer and chemical reactions considerably. In this work, the mass transfer of immiscible fluids of water as the solvent and butyl acetate containing 5 vol% of acetic acid as the feed is experimentally studied in a vertical flow inside a microchannel with the inner diameter of 8 mm. Effect of total flow velocity, Re number and volumetric flux ratio of two phases (Q_aq/Q_or) on the extraction fraction of acetic acid, mass transfer coefficient and droplet size were investigated. Based on the experiments, increasing the flux ratio can shift the flow regime from the plug to the droplet. Compared to the plug flow, the extraction fraction increased by 2–3 times in the droplet regime, depending on the total velocity, while the average diameter of the droplets decreased. Moreover, with the increase in the total velocity, the extraction fraction is reduced by 22%. However, in the case of the plug flow, the extraction fraction does not change appreciably with the increase in the total flow velocity. The mass transfer coefficient was found to increase monotonously with increasing Re number and an enhancement of 133% was achieved in the droplet flow regime.     

Effects of nitridation durations on the synthesis of wurtzite GaN thin films by spin coating method

In this paper, the effects of nitridation durations on the structural, surface morphologies and lattice vibrational properties of gallium nitride (GaN) thin films grown via spin coating method were reported. X-ray diffraction (XRD) results revealed that all the deposited GaN thin films have wurtzite structure and with GaN(002) preferred orientation. In addition, the crystallinity of the GaN thin films increases with increasing of nitridation durations from 15 to 75 min while it degrades at 105 min. Field-emission scanning electron microscopy observations showed that GaN thin films with hexagon grains were formed at nitridation duration of 45 and 75 min, whereas rose-like microstructures were formed at nitridation duration of 105 min. P-polarized infrared reflectance measurements demonstrated that the reststrahlen feature of GaN thin films gradually increases from 15 to 75 min and diminished at 105 min, which is consistent with the XRD results. Finally, all the results revealed that the duration of 75 min was the most efficient time for the nitridation process.