Large Range Of Experimental Conditions Research Articles

A reaction mechanism for vibrationally-cold low-pressure CO2 plasmas

The use of plasmas for CO2 utilization has been under investigation in recent years following a wave of environmental awareness. In this work, previously published experimental results on vibrationally cold CO2 plasmas are modelled to define a reaction mechanism, i.e. a set of reactions and rate coefficients validated against benchmark experiments. The model couples self-consistently the electron and heavy particle kinetics. In turn, the simulated results are validated against measurements taken in CO2 DC glow discharges in a relatively large range of experimental conditions: at pressures from 0.4 to 5 Torr, reduced electric fields ranging from 50 to 100 Td and gas flowing from 2 to 8 sccm. The model predicts the measured values of product formation (CO and O) as well as discharge power and electric field. After validation, a thorough analysis of the model’s results is presented, including: electron properties, species densities, power distribution into different excitation channels and main creation and destruction mechanisms of the main species. It is shown that, although vibrational populations are low, they have a significant effect on the electron properties and thus on the electric field and conversion. Moreover, the shape of the EEDF is significantly dependent on the dissociation degree. The role of electronically excited states on CO2 dissociation is also analyzed, showing that the first electronic excited state of CO can have a beneficial or detrimental effect in further producing CO and O in the discharge.

Dynamics in closed and open capillaries

Capillary rise of a liquid displacing gas is analysed for both open and closed capillaries. We include menisci mass and hysteresis, and show that oscillations due to inertia are muted by friction at the advancing meniscus. From single-phase numerical computations in a no-slip/slip capillary, we quantify losses due to entry, flow development, meniscus slip, exit and acceleration of fluid within the reservoir. For closed capillaries, determining viscous drag due to gas requires inclusion of compressibility, and solving a moving boundary problem. This solution is derived through perturbation expansion with respect to two different small parameters for obtaining pressure above the liquid meniscus. Our rise predictions spanning a large range of experimental conditions and fluids for both open and closed capillaries match the data. The experimental data confirm the adequacy of the theoretically constructed dimensionless groups for predicting oscillatory behaviour.

Experimental and Theoretical Study of the Complexation of Cesium and Thallium Cations by a Water-Soluble Cryptophane

Cs (cesium) and Tl (thallium) are known to be very toxic for the environment and human health. Thus, the synthesis of molecular receptors aimed at extracting these two elements from the environment is strongly desired. In this Article, we report the synthesis of the two enantiomers of cryptophane-223(OH)$_7$ (1) and the study of their interaction with cesium and thallium cations in basic aqueous solutions. These two complexes have been studied by $^{133}$Cs and $^{205}$Tl NMR spectroscopy to reveal the complexation of the two metallic cations and by chiroptical techniques (electronic and vibrational circular dichroism) to provide valuable information about the conformational changes occurring during the binding process. The thermodynamic parameters of complexation K, $\Delta $$H^0$ and $\Delta $$S^0$ obtained from titration experiments reveal a strong interaction between 1 and the two cations under a large range of experimental conditions. A decomposition of the total binding energy, performed by DFT calculations, allows us to characterize the nature of the interactions existing between the cage-molecule and these two cations. These calculations also reveal the importance of the spin-orbit coupling for predicting correctly the large frequency difference between the free Tl$^+$ and Tl$^+$@1 NMR signals and to understand its origin. In addition to the development of a methodology enabling detailed understanding of the host-guest interaction, this study indicates a very pronounced selectivity of this cage-molecule towards both Cs$^+$ and Tl$^+$ cations in various experimental conditions.

Experimental microkinetic approach of the CO/H2 reaction on Pt/Al2O3 using the Temkin formalism. 1. Competitive chemisorption between adsorbed CO and hydrogen species in the absence of reaction

The present study is dedicated to the development of a Temkin model for competitive chemisorption (denoted Temkin-C) which can be applied in large range of experimental conditions (partial pressures and temperatures). It is based on experimental data from the adsorption/reaction of x% CO/H2 gas mixtures (x=1, 10−2 and 10−3, total pressure 1atm.) on a reduced 2.9% Pt/Al2O3 catalyst for two platinum dispersions (D≈0.6 and 0.26) in the temperature range 300–740K. FTIR spectroscopy (a) shows that three adsorbed CO species: linear, bridged and threefold coordinated CO species (denoted L, B and 3FC respectively) are formed at 300K and (b) provides the evolution of the coverage of the dominant L CO species (IR band at 2080cm−1 at 300K) for the three CO/H2 gas mixtures in the 300–740K temperature range. These data support the rigorous development of a Temkin-C model providing the theoretical coverage of the L CO and hydrogen species in the absence of the CH4 production. The comparison of the theoretical and experimental evolutions of the coverage of the L CO species shows that (a) the L CO species dominates the competitive chemisorption with the hydrogen species and (b) the heats of adsorption of the two species are not significantly modified by their co-adsorption. Moreover, in line with the debate dedicated to the paradox of kinetics on heterogeneous surface (briefly the catalytic activity of a heterogeneous surface can be well represented by assuming an homogeneous surface), the Temkin-C model is compared to models based on the Langmuir formalism currently used in the literature dedicated to kinetic studies. This reveals the clear advantage of the Temkin-C model for the representation of experimental data in large range of experimental conditions. In Part 2, the Temkin-C model is extended by considering that the L CO species is the adsorbed intermediate species of the CH4 formation from the CO/H2 reaction at T>500K.

Increasing the efficiency of magnetic heterogeneous Fenton catalysts with a simple halogen visible lamp

Abstract The effect of a simple visible halogen lamp was studied in the Fenton-type oxidation of three model aqueous pollutants differing in their structure and electrostatic charge, methylorange (MO), methylene blue (MB) and paranitrophenol (PNP), using maghemite nanoparticles (γ-Fe 2 O 3 NP), or maghemite/silica nanocomposite microspheres (γ-Fe 2 O 3 /SiO 2 MS) as heterogeneous catalysts. These materials, which were fully characterized, differ in size, morphology, porosity and microstructure, although their catalytic activity is related to the same γ-Fe 2 O 3 nanoparticles. Both have a strong magnetic susceptibility, but only the MS catalyst can be easily recovered by magnetic settlement. Whatever the catalyst, the pollutant tested, or the experimental conditions used, much better decolorization rates and mineralization efficiencies were recorded under illumination by visible light in comparison to the same tests in the dark. The large range of experimental conditions tested enabled us to propose a mechanism for photocatalytic activity. Experiments of long-term stability showed that the MS catalyst, although generally less active than the NP catalyst, retained almost all of its activity after five repeated experiments under visible light. The good stability of this catalyst was also confirmed by the low level of iron leaching, making it suitable candidate for an application as photo-Fenton catalyst in industrial wastewater treatment.

(Invited) On the Modeling of the Charge Pumping Curves

The Charge Pumping (CP) technique has been used to characterize insulator semiconductor interface traps in numerous device types and in a wealth of situations [1]. A few years ago and for the first time, the three basic CP curves types recorded from conventional silicon MOSFETs with thick SiO2insulating films have been simulated very accurately in a large range of experimental conditions [2, 3], demonstrating that the model derived satisfactorily accounts for the CP mechanisms and that the properties of the traps introduced, i.e. their distribution and electrical characteristics, were plausible. As far as we know no more recent results have been published in that field. Indeed, one may expect the electrical CP response of gate stacks with high-k dielectrics to be even more difficult to tackle [1]. A part of the above results has been used more recently to investigate the meaning of CP curve edges [4]. This study pointed out the role that surface potential plays in interface traps filling and in CP curves shape. It was also shown that the Si-SiO2interface trap density, Dit, usually extracted as proposed in [5], can be very simply obtained from the slope of the CP curve edges [4]. Besides, a few months ago, several Pbo centers, the amphoteric defect well-known to be the main trap type at the Si(100)-SiO2 interface after SiO2 growth have been identified in deep submicron area MOSFETs [6], pursuing the story of the Si-SiO2interface electrical characterization. In this paper, starting from the results presented in [2, 3], the essential of the model, the major advances with regard to previous work and the main conclusion that can be drawn concerning the CP mechanisms will be recalled. The impact of the gate signal parameters on carrier capture and emission will be detailed. The contributions to the overall CP signal of the different traps introduced along with the impact on the CP curve shape of their characteristics will be presented. The limitations of this approach will also be pointed out. [1] Nanoscale CMOS – Innovative Materials, Modeling and Characterization, Ch. 15, Characterization of interface defects, by P. Hurley, O. Engström, D. Bauza, and G. Ghibaudo, Edited by F. Balestra, Ed. ISTE-Wiley 2010. [2] D. Bauza, IEEE Trans. Electron Devices 56, 70, (2009). [3] D. Bauza, IEEE Trans. Electron Devices 56, 78, (2009). [4] D. Bauza, International Reliability Physics Symposium (IRPS) 2013, paper GD-2. [5] G. Groeseneken, H.E. Maes, N. Beltran, and R. F. De Keersmaeker, IEEE Trans. Electron. Devices 31, 42 (1984). [6] T. Tsuchyia and Y. Ono, Jap. J. Appl. Phys. 54, 04DC01 (2015).

Simulation of Laser-Based Two-Photon Absorption Induced Charge Carrier Generation in Silicon

Numerical simulation software is used to calculate quantitatively the two-photon absorption-induced carrier-density distributions generated under conditions that are experimentally relevant for single-event effects studies. The results provide valuable insight into how the magnitudes and shapes of the charge carrier distributions evolve over a large range of experimental conditions and the impacts this has for different device geometries. Furthermore, values of integrated charge are determined that can be more directly correlated with experimental observables.

Synaptic Consolidation: From Synapses to Behavioral Modeling

Synaptic plasticity, a key process for memory formation, manifests itself across different time scales ranging from a few seconds for plasticity induction up to hours or even years for consolidation and memory retention. We developed a three-layered model of synaptic consolidation that accounts for data across a large range of experimental conditions. Consolidation occurs in the model through the interaction of the synaptic efficacy with a scaffolding variable by a read-write process mediated by a tagging-related variable. Plasticity-inducing stimuli modify the efficacy, but the state of tag and scaffold can only change if a write protection mechanism is overcome. Our model makes a link from depotentiation protocols in vitro to behavioral results regarding the influence of novelty on inhibitory avoidance memory in rats.

Complexation and precipitation reactions in the ternary As(V)–Fe(III)–OM (organic matter) system

The predominant forms of arsenic (As) in anoxic and oxic environments are As(III) and As(V), respectively, and the fate of these forms is influenced by interactions with mineral surfaces and organic matter (OM). Interactions between As(V) and OM are believed to occur mainly via iron(Fe)-bridges in ternary Fe–arsenate complexes, but direct evidence for these interactions are scarce. Furthermore, since the speciation of Fe in the presence of organic matter varies as a function of pH and Fe concentration, a central question is how different chemical conditions will affect the As–Fe–OM interactions. In order to answer this, the As(V)–Fe(III)–OM system have been studied under a large range of experimental conditions (6485–67,243ppm Fe(III) and Fe(III):As(V) ratios of 0.5–20 at pH 3–7), with Suwannee River natural organic matter and Suwannee River fulvic acid as sources of OM, using Fe and As K-edge X-ray absorption spectroscopy (XAS), infrared (IR) spectroscopy and chemical equilibrium modeling. Our collective results showed that interactions in the ternary As(V)–Fe(III)–OM system were strongly influenced by pH, total concentrations and ratios among the reactive species. In particular, the high stability of the Fe(III)–OM complexes exerted a strong control on the speciation. The predominant species identified were mononuclear Fe(III)–OM complexes, Fe(III) (hydr)oxides and FeAsO4 solids. The experimental results also showed that at low concentrations the Fe(III)–OM complexes were sufficiently stable to prevent reaction with arsenate. The chemical equilibrium models developed corroborated the spectroscopic results and indicated that As(V) was distributed over two solid phases, namely FeAsO4(s) and Fe(OH)1.5(AsO4)0.5(s). Thus, neither ternary As(V)–Fe(III)–OM complexes nor As(V) surface complexes on Fe(III) (hydr)oxides were necessary to explain the collective results presented in this study.

Photolysis of CH₃CHO at 248 nm: evidence of triple fragmentation from primary quantum yield of CH₃ and HCO radicals and H atoms.

Radical quantum yields have been measured following the 248 nm photolysis of acetaldehyde, CH3CHO. HCO radical and H atom yields have been quantified by time resolved continuous wave Cavity Ring Down Spectroscopy in the near infrared following their conversion to HO2 radicals by reaction with O2. The CH3 radical yield has been determined using the same technique following their conversion into CH3O2. Absolute yields have been deduced for HCO radicals and H atoms through fitting of time resolved HO2 profiles, obtained under various O2 concentrations, to a complex model, while the CH3 yield has been determined relative to the CH3 yield from 248 nm photolysis of CH3I. Time resolved HO2 profiles under very low O2 concentrations suggest that another unknown HO2 forming reaction path exists in this reaction system besides the conversion of HCO radicals and H atoms by reaction with O2. HO2 profiles can be well reproduced under a large range of experimental conditions with the following quantum yields: CH3CHO + hν(248nm) → CH3CHO*, CH3CHO* → CH3 + HCO ϕ(1a) = 0.125 ± 0.03, CH3CHO* → CH3 + H + CO ϕ(1e) = 0.205 ± 0.04, CH3CHO*[Formula: see text]CH3CO + HO2 ϕ(1f) = 0.07 ± 0.01. The CH3O2 quantum yield has been determined in separate experiments as ϕ(CH₃) = 0.33 ± 0.03 and is in excellent agreement with the CH3 yields derived from the HO2 measurements considering that the triple fragmentation (R1e) is an important reaction path in the 248 nm photolysis of CH3CHO. From arithmetic considerations taking into account the HO2 and CH3 measurements we deduce a remaining quantum yield for the molecular pathway: CH3CHO* → CH4 + CO ϕ(1b) = 0.6. All experiments can be consistently explained with absence of the formerly considered pathway: CH3CHO* → CH3CO + H ϕ(1c) = 0.

Effect of operational parameters on distillate flux in direct contact membrane distillation (DCMD): Comparison between experimental and model predicted performance

Membrane distillation (MD) is a thermally driven process where hydrophobic membranes are used to separate saline hot feed solution and cold stream of water and allow water to evaporate due to temperature difference. This work presents a single stage DCMD process using rejected brine from Qatari desalination plants as a feed to augment the production of fresh water. An experimental and theoretical study of a direct contact membrane distillation unit is presented. The work aims to provide a detailed analysis of the simultaneous heat and mass transfer in such systems. The impact of a number of experimental conditions on the performance of the system is presented and compared to simulated results. The predictive models took into account the varying operating conditions (such as temperature, flow rate, flow modes and regimes, etc.). In the formulation of this predictive model, the active membrane area of the MD system was divided into n elements, which are treated as hot and cold control volumes that are related to each other through simultaneous mass and heat transfer. The model presented in this work was in good agreement with the experimental results. The model was able to predict the flux and temperature polarization and was applicable to a large range of experimental conditions and variables.

Prediction of non-isothermal ternary gas-phase breakthrough experiments based on binary data

The results of breakthrough experiments in an adsorption column packed with commercial activated carbon for three binary CO2/N2 mixtures as well as for two ternary CO2/N2/H2 mixtures are presented. The experiments were carried out at two different temperatures (25 and 45 °C), four different pressures (1, 5, 10 and 20 bar) and three different flow rates. To analyze the experiments, the breakthrough profiles are simulated using a one-dimensional model consisting of material and energy balances together with the necessary constitutive equations. Transport parameters such as the heat and mass transfer coefficients are fitted to the results from the experiments with the binary mixtures (CO2/N2) and then compared to parameters obtained in a previous work (Adsorption 18: 143–161, 2012) for binary CO2/H2 mixtures. Furthermore, the parameters obtained for binary mixtures are used to predict the outcome of breakthrough experiments with ternary CO2/N2/H2 mixtures. These simulations are then tested by experiments, showing that their prediction capability is rather satisfactory for a large range of experimental conditions.

Efficient Simulation and Acceleration of Convergence for a Dual Piston Pressure Swing Adsorption System

The dual piston pressure swing adsorption (DP-PSA) system offers the potential for the full characterization of adsorbent materials under a large range of experimental conditions. The analysis of these experiments requires an efficient tool for the simulation of the DP-PSA system to cyclic steady state (CSS). In this contribution, a simulation tool is developed and applied to a mathematical model of the DP-PSA system. The governing set of partial differential equations (PDEs) is solved with state-of-the-art discretization schemes, which are tailored to the character of the governing equations. PDEs with a strong hyperbolic character are discretized with the finite volume method (FVM) with a flux-limiting scheme; this guarantees the conservation of mass as well as correct tracking of the moving fronts. The mass transfer in the adsorbent materials is discretized with the orthogonal collocation on finite elements method which is a very efficient method for problems with steep, stationary gradients. The large...

Water-Soluble Molecular Capsule for the Complexation of Cesium and Thallium Cations

Binding properties of cesium and thallium cations by an enantiopure cryptophane derivative PP-1 have been investigated in water under basic conditions. The binding process has been evidenced using electronic circular dichroism (ECD), and binding constants of the Cs(+)@PP-1 and Tl(+)@PP-1 complexes have been determined from isothermal titration calorimetry (ITC) experiments in LiOH/H(2)O, NaOH/H(2)O, and KOH/H(2)O solutions. In addition, Tl(+)@PP-1 complex has been characterized for the first time by (205)Tl NMR spectroscopy. Cryptophane 1 exhibits an exceptionally high affinity for thallium and cesium cations in a large range of experimental conditions (nature, concentration of the counterion, and temperature). For example, binding constants as high as 2.9 × 10(9) M(-1) and 5.3 × 10(8) M(-1) have been measured by ITC at 298 K in NaOH/H(2)O (0.1 M) solution, for the Tl(+)@PP-1 and Cs(+)@PP-1 complexes, respectively. The high affinity of cryptophane 1 for Cs(+) and Tl(+) cations is preserved at higher LiOH, NaOH, and KOH concentrations and under extreme basic conditions, revealing the stability and the great selectivity of this supramolecular system toward Li(+), Na(+), and K(+) cations.

Mathematical Simulation of Signal Profiles in Flow Analysis

A mathematical model based on an analytical solution for the axial dispersion plug flow model is used for simulating the dispersion in flow injection analysis. The dispersion coefficients for the leading and trailing components of the profile are modeled as a function of the physical parameters of the system (reactor length, internal diameter of the reactor) and experimental conditions (flow rate and sample volume). Modeling the dispersion coefficients using all these parameters renders the model with a generality that has not been previously observed when simulating the dispersion profiles. The internal radius of the coiled manifold was observed to have a significant influence on the axial dispersion coefficient; an variable that has not been taken into account in many previous approaches. The volume of the sample plug did not significantly influence the axial dispersion coefficient. The model was set based on a spectrophotometric determination of a colored compound, bromocresol green. The full dispersion profile can be estimated for a large range of experimental conditions and the information retrieved from the simulation can be used in a rapid yet less reagent consuming optimization of the flow conditions.

Effect of some parameters on the rate of the catalysed decomposition of hydrogen peroxide by iron(III)-nitrilotriacetate in water

The decomposition rate of H 2O 2 by iron(III)-nitrilotriacetate complexes (Fe IIINTA) has been investigated over a large range of experimental conditions: 3 < pH < 11, [Fe(III)] T,0: 0.05–1 mM; [NTA] T,0/[Fe(III)] T,0 molar ratios : 1–250; [H 2O 2] 0: 1 mM–4 M) and concentrations of HO radical scavengers: 0–53 mM. Spectrophotometric analyses revealed that reactions of H 2O 2 with Fe IIINTA (1 mM) at neutral pH immediately lead to the formation of intermediates (presumably peroxocomplexes of Fe IIINTA) which absorb light in the region 350–600 nm where Fe IIINTA and H 2O 2 do not absorb. Kinetic experiments showed that the decomposition rates of H 2O 2 were first-order with respect to H 2O 2 and that the apparent first-order rate constants were found to be proportional to the total concentration of Fe IIINTA complexes, were at a maximum at pH 7.95 ± 0.10 and depend on the [NTA] T,0/[Fe(III)] T,0 and [H 2O 2] 0/[Fe(III)] T,0 molar ratios. The addition of increasing concentrations of tert-butanol or sodium bicarbonate significantly decreased the decomposition rate of H 2O 2, suggesting the involvement of HO radicals in the decomposition of H 2O 2. The decomposition of H 2O 2 by Fe IIINTA at neutral pH was accompanied by a production of dioxygen and by the oxidation of NTA. The degradation of the organic ligand during the course of the reaction led to a progressive decomplexation of Fe IIINTA followed by a subsequent precipitation of iron(III) oxyhydroxides and by a significant decrease in the catalytic activity of Fe(III) species for the decomposition of H 2O 2.

Electrochemical and Theoretical Investigation of Corannulene Reduction Processes

The voltammetric generation of corannulene anions was investigated over a large range of experimental conditions comprising either "traditional" electrochemical solvents, such as dimethylformamide, acetonitrile, and tetrahydrofuran, or "unconventional" solvents, such as liquid ammonia, liquid methylamine, or liquid dimethylamine, and several different supporting electrolytes. Strong ion pairing effects were found to dominate the electrochemical generation of corannulene higher anions, and through the suitable choice of the solvent/electrolyte system, we observed, for the first time, the reversible electrochemical generation of up to the triply reduced corannulene. The standard potentials obtained experimentally compared rather well with the theoretical values calculated by ab initio and density functional methods, in which solvation and ion pairing effect were explicitly taken into account. In particular, the calculations considered the effect of the electrolyte cation size on ion pairing in order to rationalize the occurrence of the third reduction within the experimental potential window.

Formation of a Three-Dimensional Multicellular Assembly Using Magnetic Patterning

We demonstrate a facile approach to design three-dimensional cellular assembly of tunable size and controlled geometry with applications for tissue engineering. Three-dimensional cell patterning was performed using external magnetic forces, without the need for substrate chemical or physical modifications. Human endothelial progenitor cells and mouse macrophages were magnetically labeled using anionic citrate-coated iron oxide nanoparticles. Two magnetic tips were designed, and their magnetic field cartographies were calibrated. The focalized magnetic force generated ensured an efficient entrapment of the cells at the tips vicinity. By tuning the magnetic field gradient geometry and intensity, the magnetic cellular load, and the number of cells, we fully described the formation of the three-dimensional multicellular assemblies, and estimated the corresponding packing factor for a large range of experimental conditions.

A General and Reliable Model for Charge Pumping—Part I: Model and Basic Charge-Pumping Mechanisms

Starting from a rigorous analysis of the charge-pumping (CP) mechanisms, a general CP model, which accounts for capture time constant distribution (TCD) that exists at Si -SiO2 interface, is derived. By doing so, CP curves of state-of-the-art MOS devices are extremely well simulated. It is remarkable as this is achieved in a large range of experimental conditions, confirming the reliability of the approach. The interpretation of the TCDs in terms of distance from the Si- SiO2 interface through carrier tunneling, as used initially, is discussed in the light of recent results which show that the traps which dominate at the Si-SiO2 interface in fully processed devices, at least down to 109 eV1middotcm-2, are acceptor-like in the upper part of the bandgap, donor-like in its lower part and are amphoteric, i.e., have the properties of the Pb0 centers. As the model allows the energy and depth regions probed to be known in all experimental conditions, this paper focuses on the basic CP features at the Si-SiO2 interface and toward the insulator depth. For that, one of the standard CP curves is used.

What regulates Na+/Ca2+ exchange? Focus on “Sodium-dependent inactivation of sodium/calcium exchange in transfected Chinese hamster ovary cells”

### The Necessity for NCX1 Regulation Considering that the cardiac Na+/Ca2+ exchanger (NCX1.1) is the predominant mechanism for transsarcolemmal Ca2+ efflux in cardiac myocytes, it is obvious that this transport system must be regulated actively. Sodium/calcium exchange removes roughly the same