Transport and relaxation properties of isotopomeric hydrogen–helium binary mixtures. I. H2–He mixtures

An extensive comparison has been carried out between calculated and measured bulk properties of H₂–helium mixtures. Detailed comparisons are presented for the interaction second virial coefficient, binary diffusion, mixture shear viscosity and thermal conductivity, rotational relaxation, thermal diffusion field-effects, collision broadening of the depolarized Rayleigh light scattering spectrum, and flow birefringence. Scattering calculations have been carried out for the ab initio potential energy surfaces obtained by Tao (1994, J. chem. Phys., 100, 4947) and Schaefer and Köhler (1985, Physica A, 129, 469). The values for the various bulk gas properties calculated from these two potential surfaces are generally found to lie within or near the experimental uncertainties.     

Transport and relaxation properties of isotopomeric hydrogen–helium binary mixtures. II. HD,D2, T2–He mixtures

The comprehensive comparison between calculated bulk non-equilibrium properties of hydrogen–helium isotopomeric mixtures and experiment that has previously been carried out for H₂–helium mixtures [2004, Molec. Phys., submitted] has been extended to mixtures of HD, D₂ and T₂ with ³He and ⁴He. For HD–⁴He mixtures, comparison is also made, where possible, with previous calculations of Köhler and Schaefer [1983, Physica A, 120, 185]. The phenomena examined herein include low temperature interaction second virial coefficients, binary diffusion and thermal conductivity coefficients, rotational relaxation, transport property field effects and flow birefringence. Scattering calculations have been carried out for the HD–He PES of Schaefer and Köhler [1985, Physica A, 129, 469], and for both the Köhler–Schaefer and Tao [1994, J. chem. Phys., 100, 4947] potential surfaces for the D₂–He and T₂–He interactions. Comparisons between calculated and experimental results for HD, D₂, T₂–He mixtures confirm the conclusion, reached earlier from the H₂–He comparisons, that these potential surfaces are very close to the correct one for the hydrogen–helium interaction, and that the small differences between them cannot be distinguished readily by measurements of bulk gas phenomena unless the attendant experimental uncertainties are better than ±0.3%.     

Pressure loading of detonation waves through 90-degree bend in high pressure H2–O2–N2 mixtures

Detonation experiments are conducted to investigate the detonation wave behavior in steam pipelines of boiling water reactors. Accumulated gases in BWRs are stoichiometric hydrogen/oxygen mixtures diluted with steam at 7 MPa. In the experiment, flammable gas mixture diluted with nitrogen at room temperature and up to 5 MPa is used to achieve equivalent detonation condition. Two test pieces are used, one is straight tube and the other is 90-degree bend. No initial pressure dependency in detonation wave behavior is observed in the experiments. However, in the straight tube tests, detonation velocities higher than theoretical values are measured when the initial pressures are greater than 2.3 MPa. This result is considered as attribution of real gas effect. In the 90-degree bend experiments, pressure time histories reveal pressure loads greater than the straight tube portion at two locations. One is a high pressure peak at the extrados of the bend and the other is a double pressure peak just downstream of the bend outlet. Second pressure peak just downstream of the bend outlet is due to transverse wave propagation. Additionally, the largest impulse is observed not at the extrados of the bend but at the intrados of bend outlet. These results show the importance of more investigations on transverse wave behaviors in failure potential evaluation.     

Detailed modeling of planar transcritical H2–O2–N2 flames

We first investigate a detailed high pressure flame model. Our model is based on the thermodynamics of irreversible processes, statistical mechanics, statistical thermodynamics, and the kinetic theory of dense gases. We study thermodynamic properties, chemical production rates, transport fluxes, and establish that entropy production is non-negative. We next investigate the structure of planar transcritical H₂–O₂–N₂ flames and perform a sensitivity analysis with respect to the model. Non-idealities in the equation of state and in the transport fluxes have a dramatic influence on the cold zone of the flame. Non-idealities in the chemical production rates – consistent with thermodynamics and important to insure positivity of entropy production – may also strongly influence flame structures at very high pressures. At sufficiently low temperatures, fresh mixtures of H₂–O₂–N₂ flames are found to be thermodynamically unstable, in agreement with experimental results. We finally study the influence of various parameters associated with the initial reactants on the structure of transcritical planar H₂–O₂–N₂ flames as well as lean and rich extinction limits.     

Thermodynamic properties of gold–water nanolayer mixtures using molecular dynamics

The physical behavior of a fluid in contact with solid layers is still not fully understood. The present work focuses on the study and understanding of thermodynamic and structural properties of gold–water nanolayer mixtures using molecular dynamics simulations. Two different systems are considered, where approximately 1,700 water molecules are confined between gold nanolayers with separations of 7.4 and 6.2 nm, respectively. Novelties of the present work are in the use of accurate force fields for modeling the inter- and intra-molecular interactions of the components, and providing comprehensive thermodynamic properties of the mixtures. The results are validated by examination of the pure fluid and pure solid properties. Results indicate that the thermodynamics of the system does not behave as an ideal mixture. The structure of the pure fluid is also analyzed and compared against the structure of the confined fluid in the mixture. Anisotropicity is observed in the fluid structure close to the surface of the nanolayer. Higher ordering and higher flux are detected in the fluid molecules close to the fluid–solid interface. Unusual thermodynamic behavior, anisotropicity, liquid layering, and higher interfacial fluid flux could be just some of the factors leading to the enhanced energy transport observed in mixtures involving at least one nanoscale component, such as nanofluids.     

Hydrogen CARS thermometry in H2–N2 mixtures at high pressure and medium temperatures: influence of linewidths models

In order to improve the accuracy of H₂ CARS thermometry, H₂ Q-branch CARS spectra have been recorded for various H₂-N₂ mixtures in a high-pressure cell at different pressures and temperatures (up to 40 bar and 875 K). Due to the low spectral resolution of broadband CARS experiments, the relevant spectral lineshape factor is the linewidth ratio &(Q(3))/&(Q(1)), since Q(1) and Q(3) are the most intense lines of the Q-branch spectrum in this temperature range. For the first time, the speed-inhomogeneous effects are accounted for in the simulation of the CARS profiles. The evaluated temperatures are in good agreement with reference values obtained by thermocouples. The specific role on the accuracy of H₂ CARS thermometry of the speed inhomogeneity is carefully analyzed, in connection with the influence of the nitrogen concentration.     

On the structural properties of B–C–N nanotubes

We apply a first-principles method, based on the density functional theory, to calculate the structural stability of B–C–N armchair nanotubes, comparing such results with the ones obtained for zigzag configuration. Analysis of the corresponding strain energies confirm that the stability of BC₂N nanotubes is independent of their chirality and demonstrate that such nanostructures have lower strain than BCN and carbon nanotubes. The results show that the formation energy decreases with the tube diameter and indicate that the most stable nanotubes have the maximum number of B–N and C–C bonds. Therefore, from the experimental point of view, larger diameter BC₂N model-I nanotubes should be more probable to be synthesized.     

Theoretical and experimental analysis of N2–H2 stimulated Raman spectra

The paper reports on a detailed study of the N₂–H₂ collisional line broadening coefficient. High resolution stimulated Raman spectra of nitrogen–hydrogen mixtures have been recorded at liquid nitrogen and room temperatures. Corresponding linewidth calculations have been performed at temperatures between 77 and 500?K using the semiclassical Robert and Bonamy model for J rotational quantum numbers varying between 0 and 11. Comparison between experimental data and calculated results shows good agreement at room temperature using an adjusted value for the kinetic diameter.     

Stability of the H2–(He,Ne, Ar) fluid mixtures

A theory of mixtures based on a statistical mechanical perturbation scheme is used to compute the excess free energy of mixing, the excess entropy of mixing and the concentration fluctuations in the long wavelength limit as functions of composition (c) over a wide range of temperature (T = 150 to 350 K) and pressure (p = 10 MPa to 10 GPa). This has been utilized to investigate the effects of c, T and p on the solubility of H₂ (the first element of the periodic table) to He, Ne and Ar (the first three elements of the last group) and the thermodynamic stability of the mixture. The long-range correlations among the constituent species are included through the double Yukawa potential which acts as a perturbation to the hard sphere reference mixture. The non-additivity of the potentials of the constituent species is linked to the second virial coefficients which can be determined from the experimental data. Necessary corrections to the equation of state for dimerisation of H₂ molecule and quantum effects are included. At a given T = 150 K and p = 100 MPa, H₂–Ar mixture exhibits greater thermodynamic stability than H₂–Ne and H₂–Ar.     

Transport properties in monolayer–bilayer–monolayer graphene planar junctions

The transport study of graphene based junctions has become one of the focuses in graphene research. There are two stacking configurations for monolayer–bilayer–monolayer graphene planar junctions. One is the two monolayer graphene contacting the same side of the bilayer graphene, and the other is the two-monolayer graphene contacting the different layers of the bilayer graphene. In this paper, according to the Landauer–Büttiker formula, we study the transport properties of these two configurations. The influences of the local gate potential in each part, the bias potential in bilayer graphene,the disorder and external magnetic field on conductance are obtained. We find the conductances of the two configurations can be manipulated by all of these effects. Especially, one can distinguish the two stacking configurations by introducing the bias potential into the bilayer graphene. The strong disorder and the external magnetic field will make the two stacking configurations indistinguishable in the transport experiment.     

Enhancement of the electrical properties of carbon nanotubes with Ar–N2 plasma treatment

Optical emission spectroscopy and Langmuir probe are used to investigate the low pressure inductively coupled Ar–N₂ plasmas as function of rf power, filling pressure and Ar content in N₂ discharge. It is observed that the active species generation, dissociation fraction and electron temperature significantly depends on discharge parameters and may be used to optimize the plasma reactor. Mixture of SWCNTs and MWCNTs are treated for different treatment time (0–120 min) at optimum discharge conditions. Changes induced in the elemental composition, surface morphology, crystallographic structure, and structural disorder in the plasma irradiated CNTs are analyzed by EDX, FTIR, SEM, XRD and Raman spectroscopy, respectively. Ar–N₂ mixture plasma treatment of CNTs lead to a significant increase in the electrical conductivity, modify the microstructure and induce structural disorder and cause a transition of crystalline phase from well crystalline to an amorphous structure.     

Transport properties of YBa2−xLayCu3On high temperature superconductors

The lattice parameters of the defect and La(III) substituted YBa_2–xLa_yCu₃O_n (0.05 x0.4,0y0.2) superconductors prepared in presence of the K₂CO₃ flux indicate substitution of La(III) on Ba(II) sites and intercalation of oxygen on 0(5) sites. This is manifested by a lowering ofT _c values. The presence of metastable phases with a sharp drop in resistivity around 200 K, which have been reported by Suzuki et al. (1989) for samples of similar composition, was not confirmed. The conductivity measurements show an increase of resistivity above 673 K, which is a consequence of gradual deoxygenation and the loss of metallic character. The full reversibility of this process in the bulk sample is modified by the oxygen diffusion into the sample.     

Improved lasing properties of the HêN 2 + system at 391 nm and 428 nm by H2 admixture

The He/N₂ system lasing on the N ₂ ⁺ (B)N ₂ ⁺ (X, 0) transition at 391 nm and on the N ₂ ⁺ (B)N ₂ ⁺ (X, 1) transition at 428 nm was investigated by e-beam excitation. By adding H₂ the lower laser state is efficiently quenched, which leads to a drastic improvement of the laser properties. A kinetic model is proposed which accounts for the experimental results. For a laser amplifier operated at 5 bar total efficiencies of 0.6% and 0.7% are predicted for the 391 nm and the 428 nm transitions respectively.     

The 2CH excitation band in C2H2–N2O and 2CH+torsion combination bands in C2H2–N2O and C2H2–CO2

A preliminary analysis of the 2CH excitation band in C₂H₂–N₂O in the 1.5 µm range (K. Didriche, C. Lauzin, P. Macko, M. Herman and W.J. Lafferty, Chem. Phys. Letters 469, 35 (2009).), only considering 117 low J-, and K_a - vibration-rotation lines, is significantly extended thanks to the analysis of new spectra including very regular series of lines with J/K_a up to 31/15. 1271 b-type lines were assigned. Perturbations are briefly discussed. The rotational temperature in the experiments is estimated to be 20?K and the upper state mean half-time is 1.6?ns for non perturbed levels. The previous analyses of the 2CH + torsion band in C₂H₂–N₂O and in C₂H₂–CO₂ (C. Lauzin, K. Didriche, T. Földes and M. Herman, Mol. Phys. 109, 2105 (2011).), are also extended to include 286 and 234 lines, respectively, also correcting for calibration errors. New rotational constants are obtained using a rigid rotor Hamiltonian by simultaneously fitting the ground, 2CH and 2CH + torsion states in C₂H₂–N₂O, and the latter state, only, in C₂H₂–CO₂.     

Transport properties of p-type semiconducting oxides—influence of aliovalent impurities

The effect of aliovalent impurities on the chemical diffusion coefficient of an oxide AO having a p-type semiconducting behavior has been determined. This treatment shows that for an oxide doped by a monovalent impurity the chemical diffusion coefficient in the extrinsic range is equal to the diffusion coefficient of the prevailing defects. In the case of doping by higher-valent ions, it predicts an increase of the chemical diffusion coefficient. The above predictions are in agreement with the experimental results obtained from electrical conductivity measurements on single crystals ofcobaltous oxide doped either by chromium or aluminium or lithium. In the case of pure or chromium doped nickel oxide, this analysis is in qualitative agreement with the experimental results but lack of data does not allow any calculation.     

Dielectric properties of magnetic-ferroelectric CoO–NaNO2–porous glass nanocomposite

Physics of the Solid State - Dielectric properties of the nanostructured multiferroic composite on the basis of silicate porous glass simultaneously filled with ferromagnetic (cobalt oxide CoO) and...     

Shock wave dispersion of gas–particle mixtures

The decay of a discontinuity in a two-component homogeneous gas mixture and the dispersion of a gas–particle mixture with a two-component carrier medium are numerically simulated. The mathematical model of the dynamics of heterogeneous media takes into account the interphase force interaction and interphase heat exchange. Experimental results known from the literature are compared with numerical results describing the dispersion of a gas–particle mixture in a shock tube.     

Theoretical Study of the Electronic and Transport Properties of Lateral 2D–1D–2D Graphene–CNT–Graphene Structures

JETP Letters - The electronic and transport properties of new hybrid 2D–1D–2D structures of carbon atoms, which are graphene sheets continuously connected through a fragment of a...