Densities,Refractive Indices,Ultrasonic Speeds and Excess Properties of Acetonitrile + Poly(ethylene glycol) Binary Mixtures at Temperatures from 298.15 to 313.15 K

The densities, ρ, refractive indices, n _D, and ultrasonic speeds, u, of binary mixtures of acetonitrile (AN) with poly(ethylene glycol) 200 (PEG200), poly(ethylene glycol) 300 (PEG300) and poly(ethylene glycol) 400 (PEG400) were measured over the entire composition range at temperatures (298.15, 303.15, 308.15 and 313.15) K and at atmospheric pressure. From the experimental data, the excess molar volumes, \( V_{\text{m}}^{\text{E}} \) , deviations in refractive indices, \( \Delta n_{\text{D}} \) , excess molar isentropic compressibility, \( K_{{s , {\text{m}}}}^{\text{E}} \) , excess intermolecular free length, \( L_{\text{f}}^{\text{E}} \) , and excess acoustic impedance, Z ^E, have been evaluated. The partial molar volumes, \( \overline{V}_{\text{m,1}} \) and \( \overline{V}_{\text{m,2}} \) , partial molar isentropic compressibilities, \( \overline{K}_{{s , {\text{m,1}}}} \) and \( \overline{K}_{{s , {\text{m,2}}}} \) , and their excess values over whole composition range and at infinite dilution have also been calculated. The variations of these properties with composition and temperature are discussed in terms of intermolecular interactions in these mixtures. The results indicate the presence of specific interactions among the AN and PEG molecules, which follow the order PEG200 < PEG300 < PEG400.     

On k-resonance of grid graphs on the plane,torus and cylinder

Grid graphs on the plane, torus and cylinder are finite 2-connected bipartite graphs embedded on the plane, torus and cylinder, respectively, whose every interior face is bounded by a quadrangle. Let \(k\) be a positive integer, a grid graph is \(k\) -resonant if the deletion of any \(i \le k\) vertex-disjoint quadrangles from \(G\) results in a graph either having a perfect matching or being empty. If \(G\) is \(k\) -resonant for any integer \(k \ge 1\) , then it is called maximally resonant. In this study, we provide a complete characterization for the \(k\) -resonance of grid graphs \(P_m\times P_n\) on plane, \(C_m\times C_n\) on torus and \(P_m\times C_n\) on cylinder.     

Infrared Spectroscopy of \hbox {CH}_4/\hbox {N}_{2} and \hbox {C}_{2}\hbox {H}_{m}/\hbox {N}_{2} ({m = 2, 4, 6}) Gas Mixtures in a Dielectric Barrier Discharge

Fourier transform infrared spectroscopy of \(\hbox {CH}_{4}/\hbox {N}_{2}\) and \(\hbox {C}_{2}\hbox {H}_{m}/\hbox {N}_2\) ( \(m = 2, 4, 6\) ) gas mixtures in a medium pressure (300 mbar) dielectric barrier discharge was performed. Consumption of the initial gas and formation of other hydrocarbon and of nitrogen-containing HCN and \(\hbox {NH}_{3}\) molecules was observed. \(\hbox {NH}_{3}\) formation was further confirmed by laser absorption measurements. The experimental result for \(\hbox {NH}_{3}\) is at variance with simulation results.     

Three–step method to determine the eutectic composition of binary and ternary mixtures

A three-step method to determine the eutectic composition of a binary or ternary mixture is introduced. The method consists in creating a temperature–composition diagram, validating the predicted eutectic composition via differential scanning calorimetry and subsequent T-History measurements. To test the three-step method, we use two novel eutectic phase change materials based on \(\mathrm{Zn}(\hbox {NO}_3)_2\cdot 6\mathrm{H}_{2}{\mathrm O}\) and \(\mathrm{NH}_4\mathrm{NO}_3\)   respectively \(\mathrm{Mn}(\hbox {NO}_3)_2\cdot 6\mathrm{H}_{2}{\hbox {O}}\) and \(\mathrm{NH}_4\mathrm{NO}_3\) with equilibrium liquidus temperatures of 12.4 and 3.9  \(\,^{\circ }\mathrm {C}\) respectively with corresponding melting enthalpies of 135 J \(\mathrm{g}^{-1}\) (237 J \(\mathrm{cm}^{-3}\) ) respectively 133 J \(\mathrm{g}^{-1}\) (225 J \(\mathrm{cm}^{-3}\) ). We find eutectic compositions of 75/25 mass% for \(\mathrm{Zn}(\hbox {NO}_3)_2\cdot \mathrm{6H}_{2}{\mathrm{O}}\) and \(\mathrm{NH}_4\mathrm{NO}_3\) and 73/27 mass% for \(\mathrm{Mn}(\hbox {NO}_3)_2\cdot 6\mathrm{H}_{2}{\mathrm{O}}\) and \(\mathrm{NH}_4\mathrm{NO}_3\) . Considering a temperature range of 15 K around the phase change, a maximum storage capacity of about 172 J \(\mathrm{g}^{-1}\) (302 J \(\mathrm{cm}^{-3}\) ) respectively 162 J \(\mathrm{g}^{-1}\) (274 J \(\mathrm{cm}^{-3}\) ) was determined for \(\mathrm{Zn}(\hbox {NO}_3)_2\cdot \mathrm{6H}_{2}{\mathrm{O}}\) and \(\mathrm{NH}_4\mathrm{NO}_3\) respectively \(\mathrm{Mn}(\hbox {NO}_3)_2\cdot \mathrm{6H}_{2}{\mathrm{O}}\) and \(\mathrm{NH}_4\mathrm{NO}_3\) .     

Chaos in oscillatory sorption of hydrogen in palladium

Aperiodic oscillations in the sorption of hydrogen and deuterium in palladium have been observed. An expression relating the square of a function, with the derivative and integral with variable upper limit of the same function has been proved and proposed to be used as a base for a chaos-vs.-random test. The result of one “branch” of the test is a real number \(D \in [0,2]\) ; close to zero for the deterministic and smooth datasets, and approaching two for the random or discrete datasets. Another “branch” of the test, based on the same mathematical relation, produces two functions that appear to be convergent for deterministic and smooth datasets, but run totally divergent for random or discrete ones. The \(D\) -values yielded by deterministic time series, recorded in the periodic and quasiperiodic sorptions of H \(_{2}\) or D \(_{2}\) in Pd, are around 0.001. On the other hand, the databases that were presumably random or non-smooth yielded the test results from \(D= 0.2\) to \(D= 1.9\) . Against these benchmarks, the experimental, aperiodic oscillations scored around 0.003 in \(D\) , which is much closer to the deterministic than to a random manner.     

Methane preconcentration by adsorption: a methodology for materials and conditions selection

Methane (CH \(_4\) ) adsorption has been widely studied, mainly in the context of natural gas purification. A much less prominent, but highly relevant application is the preconcentration of CH \(_4\) from ambient air. In this study, we compare six different commercial adsorbent materials with respect to their effectiveness for methane preconcentration: a macroporous polymeric resin (HayeSep D), multi-walled carbon nanotubes, two microporous metal-organic frameworks (HKUST-1 and ZIF-8), and two zeolites (5A and 13X). The most relevant properties, such as isosteric enthalpy of adsorption, specific surface area and the selectivity for CH \(_4\) adsorption over N \(_2\) were characterized by analyzing adsorption/desorption isotherms. Using these parameters, we discuss the tested adsorbents with respect to the most important properties and identify the most promising candidates. Furthermore we identify the experimental conditions that are expected to give the best results with respect to practical applications.     

A preliminary study of gross alpha/beta activity concentrations in drinking waters from Albania

A pilot study involving screening measurements of gross alpha/beta activity concentration in drinking water was performed in 12 cities with the highest population density in Albania. The aim of this study was to develop a first insight regarding the radiological quality of drinking and bottled water supplies. The tap and bottled water samples investigated are acceptable for consumption, complying with the WHO recommendations for drinking water. The average gross alpha and beta activity concentrations were \( 36_{ - 18}^{ + 37} \) and \( 269_{ - 150}^{ + 337} \)  mBq/L, respectively in tap waters. While for bottled water the gross alpha and beta activities were respectively \( 39_{ - 23}^{ + 55} \) and \( 220_{ - 132}^{ + 336} \)  mBq/L. The data obtained can provide information for authorities regarding the quality of drinking water and a baseline for future contaminations.     

Aspects of size extensivity in unitary group adapted multi-reference coupled cluster theories: the role of cumulant decomposition of spin-free reduced density matrices

We present in this paper a comprehensive study of the various aspects of size extensivity of a set of unitary group adapted multi-reference coupled cluster (UGA-MRCC) theories recently developed by us. All these theories utilize a Jeziorski–Monkhorst (JM) inspired spin-free cluster Ansatz of the form \(|\varPsi \rangle = \sum\nolimits_\mu \varOmega _\mu |\phi _\mu \rangle c_\mu\) with \(\varOmega _\mu =\{\exp ({T_\mu })\}\) , where \(T_\mu\) is expressed in terms of spin-free generators of the unitary group \(U(n)\) for n-orbitals with the associated cluster amplitudes. \(\{...\}\) indicates normal ordering with respect to the common closed shell \(core\) part, \(|0\rangle\) , of the model functions, \(\{\phi _\mu \}\) which is taken as the vacuum. We argue and emphasize in the paper that maintaining size extensivity of the associated theories is consequent upon (a) connectivity of the composites, \(G_\mu\) , containing the Hamiltonian \(H\) and the various powers of \(T\) connected to it, (b) proving the connectivity of the MRCC equations which involve not only \(G_\mu\) s but also the associated connected components of the spin-free reduced density matrices (RDMs) obtained via their cumulant decomposition and (c) showing the extensivity of the cluster amplitudes for non-interacting groups of orbitals and eventually of the size-consistency of the theories in the fragmentation limits. While we will discuss the aspect (a) above rather briefly, since this was amply covered in our earlier papers, the aspect (b) and (c), not covered in detail hitherto, will be covered extensively in this paper. The UGA-MRCC theories dealt with in this paper are the spin-free analogs of the state-specific and state-universal MRCC developed and applied by us recently.We will explain the unfolding of the proof of extensivity by analyzing the algebraic structure of the working equations, decomposed into two factors, one containing the composite \(G_\mu\) that is connected with the products of cumulants arising out of the cumulant decomposition of the RDMs and the second term containing some RDMs which is disconnected from the first and can be factored out and removed. This factorization ultimately leads to a set of connected MRCC equations. Establishing the extensivity and size-consistency of the theories requires careful separation of truly extensive cumulants from the ones which are a measure of spin correlation and are thus connected but not extensive. We have discussed in detail, using diagrams, the factorization procedure and have used suitable example diagrams to amplify the meanings of the various algebraic quantities of any diagram. We conclude the paper by summarizing our findings and commenting on further developments in the future.     

Thermodynamic investigations of 1-ethyl-3-methylimidazolium tetrafluoroborate and cycloalkanone mixtures

The densities, ρ, speeds of sound, u, and heat capacities, (C _P)_mix, for binary 1-ethyl-3-methylimidazolium tetrafluoroborate (1) + cyclopentanone or cyclohexanone (2) mixtures within temperature range (293.15–308.15 K) and excess molar enthalpies, H ^E, at 298.15 K have been measured over the entire composition range. The excess molar volumes, V ^E, excess isentropic compressibilities, \( \kappa_{\text{S}}^{\text{E}}, \) and excess heat capacities, \( C_{\text{P}}^{\text{E}}, \) have been computed from the experimental results. The V ^E, \( \kappa_{\text{S}}^{\text{E}} \) , H ^E, and \( C_{\text{P}}^{\text{E}} \) values have been calculated and compared with calculated values from Graph theory. It has been observed that V ^E, \( \kappa_{\text{S}}^{\text{E}} \) , H ^E, and \( C_{\text{P}}^{\text{E}} \) values were predicted by Graph theory compare well with their experimental values. The V ^E, \( \kappa_{\text{S}}^{\text{E}}, \) and H ^E thermodynamic properties have also been analyzed in terms of Prigogine–Flory–Patterson theory.     

Lamellar/Disorder Phase Transition in a Mixture of Water/2,6-Dimethylpyridine/Antagonistic Salt

The effects of adding an antagonistic salt, sodium tetraphenylborate ( \(\hbox {NaBPh}_4\) ), to a binary mixture of deuterated water and 2,6-dimethylpyridine were investigated by visual inspection, optical microscopy, and small-angle neutron scattering. With increasing salt concentration, the two-phase region shrinks. When the concentration of \(\hbox {NaBPh}_4\) is \(85\hbox { mmol}{\cdot} \hbox {L}^{-1}\) , a temperature-induced lamellar/disorder phase transition is observed at 338 K. These trends are similar to those observed for a mixture of water/3-methylpyridine/ \(\hbox {NaBPh}_4\) (Sadakane et al., Phys. Rev. Lett. 103, 167803 (2009)).     

Effect of adsorbate loading on selectivity during adsorption of C_{14}/C_{15} and C_{15}/C_{16} n-alkane binary mixtures in silicalite

Adsorption experiments of mixtures of long chain alkanes into silicalite under liquid phase conditions show selectivity inversion and azeotrope formation. These effects are due to the subtle interplay between the size of the adsorbed molecules and pore topology of the adsorbent. In this study, the selective uptake of lighter component during liquid phase adsorption of C \(_{14}\) /C \(_{15}\) and C \(_{15}\) /C \(_{16}\) n-alkane binary mixtures in the zeolite silicalite is understood through configurational bias grand-canonical Monte Carlo molecular simulation technique and a coarse-grained siting analysis. The simulations are conducted under conditions of low and intermediate levels of loading. The siting pattern of the adsorbates inside the zeolite pores explain the selectivity as seen in experiments.     

Volumetric and Viscometric Studies in Binary Liquid Mixtures of 2-Methyl-2-propanol with Some Ketones at Different Temperatures

Densities, ??, and viscosities, ??, of binary mixtures of 2-methyl-2-propanol with acetone (AC), ethyl methyl ketone (EMK) and acetophenone (AP), including those of the pure liquids, were measured over the entire composition range at 298.15, 303.15 and 308.15?K. From these experimental data, the excess molar volume $V_{\mathrm{m}}^{\mathrm{E}}$ , deviation in viscosity ????, partial and apparent molar volumes ( $\overline{V}_{\mathrm{m},1}^{\,\circ }$ , $\overline{V}_{\mathrm{m},2}^{\,\circ }$ , $\overline{V}_{\phi ,1}^{\,\circ}$ and $\overline{V}_{\phi,2}^{\,\circ} $ ), and their excess values ( $\overline{V}_{\mathrm{m},1}^{\,\circ \mathrm{E}}$ , $\overline{V}_{\mathrm{m,2}}^{\,\circ \mathrm{ E}}$ , $\overline {V}_{\phi \mathrm{,1}}^{\,\circ \mathrm{ E}}$ and $\overline{V}_{\phi \mathrm{,2}}^{\,\circ \mathrm{ E}}$ ) of the components at infinite dilution were calculated. The interaction between the component molecules follows the order of AP > AC > EMK.     

Spin correlation in Pr IV and Tm IV free ions

The coefficients \(c_{k}\) (k = 2, 4, 6) that pertain to spin-correlated matrix elements of the tensor operator \({{\varvec{U}}}^{{\varvec{(k)}}}\) have been evaluated by means of the differences \({{\varvec{U}}}^{{\varvec{(k)}}}\) (intermediate) \(-\) \({{\varvec{U}}}^{{\varvec{(k)}}}\) (LS) and the reduced matrix elements of the operator \({{\varvec{V}}}^{{\varvec{(1k)}}}\) . Only spin-allowed transitions have been considered from each ground level to the excited energy levels within the \(4\hbox {f}^{2}\) and \(4\hbox {f}^{12}\) configurations of the free ions Pr (3+) and Tm (3+), respectively. The values of the coefficients \(c_{k}\) thus found correspond in most cases by sign and order of magnitude to those determined in other sources as corrections to lanthanide (3+) crystal-field parameters.     

Magnesium ionophore III as an effective receptor for trivalent europium and americium

Solvent extraction of microamounts of trivalent europium and americium into nitrobenzene by using a synergistic mixture of hydrogen dicarbollylcobaltate (H⁺B^?) and magnesium ionophore III (L) was studied. The equilibrium data were explained assuming that the species HL⁺, \( \text{HL}_{2}^{ + } , \) \( {\text{ML}}_{2}^{3 + } , \) and \( {\text{ML}}_{3}^{3 + } \) (M³⁺ = Eu³⁺, Am³⁺; L = magnesium ionophore III) are extracted into the nitrobenzene phase. The values of extraction and stability constants of the cationic complex species in nitrobenzene saturated with water were determined and discussed.     

Densities,viscosities, and excess properties for binary mixtures of ethylene glycol with amides at 308.15 K

The densities, ρ, and viscosities, η, of binary mixtures of ethylene glycol with formamide, N,N-dimethyl formamide and N,N-dimethyl acetamide, have been measured over the entire composition range at 308.15 K. From this experimental data, excess molar volume, \( V_{\text{m}}^{\text{E}} \) , deviation in viscosity, Δη, and excess Gibbs free energy of activation of viscous flow, \( \Delta G^{{ * {\text{E}}}}, \) have been determined. Negative values of \( V_{\text{m}}^{\text{E}} \) , Δη, and \( \Delta G^{{ * {\text{E}}}} \) are observed over the entire composition range in the mixtures studied. The observed negative values of various excess and deviation parameters are attributed to the existence of strong interactions, like dipole–dipole interactions, H-bonding between the carbonyl group of amide molecules, and hydroxyl group of glycol molecules, geometrical fitting of smaller molecules into the voids created by larger molecules in the liquid mixtures. The excess properties have been fitted to Redlich–Kister-type polynomial, and the corresponding standard deviations have been calculated. The derived partial molar volumes and excess partial molar volumes also support the \( V_{\text{m}}^{\text{E}} \) results. The experimental viscosity data of all of these liquid mixtures have been correlated with four viscosity models.     

Hydrogen Peroxide Production in an Atmospheric Pressure RF Glow Discharge: Comparison of Models and Experiments

The production of \(\hbox {H}_2\hbox {O}_2\) in an atmospheric pressure RF glow discharge in helium-water vapor mixtures has been investigated as a function of plasma dissipated power, water concentration, gas flow (residence time) and power modulation of the plasma. \(\hbox {H}_2\hbox {O}_2\) concentrations up to 8 ppm in the gas phase and a maximum energy efficiency of 0.12 g/kWh are found. The experimental results are compared with a previously reported global chemical kinetics model and a one dimensional (1D) fluid model to investigate the chemical processes involved in \(\hbox {H}_2\hbox {O}_2\) production. An analytical balance of the main production and destruction mechanisms of \(\hbox {H}_2\hbox {O}_2\) is made which is refined by a comparison of the experimental data with a previously published global kinetic model and a 1D fluid model. In addition, the experiments are used to validate and refine the computational models. Accuracies of both model and experiment are discussed.     

Carbon nanotori and nanotubes encapsulating carbon atomic-chains

In this paper we investigate toroidal carbon nanotubes (carbon nanotori) encapsulating a single symmetrically located carbon atomic-chain. The interaction energy of the carbon chain is found from the Lennard-Jones potential using the continuous approach which assumes that atoms are uniformly distributed over the surface of the torus and the line of the circular chain with constant atomic surface and line densities, respectively. We assume that the chain is centrally located and that the carbon nanotorus is synthesized from a perfect carbon nanotube. We predict that the carbon chain can be encapsulated inside the carbon nanotorus when the cross-sectional radius \(r\) of the nanotorus is larger than 3.17 Å. At the minimum energy, a value of the toroidal radius \(R\) lies between 3.6 and 3.7 Å corresponding to each value of \(r\) . We also investigate the energy of carbon chains inside carbon nanotubes, which are (4,4), (5,5) and (10,0) tubes. We find that they are energetically favourable in (5,5) and (10,0) tubes, but not in a (4,4) tube, because it is geometrically too small, and these results are in agreement with existing studies. The same results for these three carbon nanotubes can also be obtained from the corresponding nanotori when \(R\) goes to infinity.     

Intrinsic viscosity of aqueous suspensions of cellulose nanofibrils

Cellulose nanofibrils (CNF) from wood fibers are of increasing interest to industry because they are from renewable sources and are biodegradable. Owing to their high aspect ratio, they produce viscous suspensions and stiff gels that are strengthened by interfibrillar hydrogen bonds. In this study, the viscosity of aqueous CNF suspensions, at dilute concentrations ( \(nL^{3}<1\) ), was measured at various pH values by addition of HCl, and at various ionic strengths by addition of NaCl and \(\hbox {CaCl}_{2}\) . The results show that the primary electroviscous effect significantly increases the intrinsic viscosity. The intrinsic viscosity under conditions where the surface charge of nanofibrils is fully screened is in good agreement with the predictions of classical theory for dispersions of rodlike particles at low shear rates. Increasing the ionic strength up to \(\kappa d\approx 1\) decreases the intrinsic viscosity; at \(\kappa d>1\) , the intrinsic viscosity increases because of fibril aggregation and increase of the effective volume fraction.     

Heat capacity and density of potassium iodide solutions in mixed N-methylpyrrolidone-water solvent at 298.15 K

The heat capacity and density of potassium iodide solutions in a mixed N-methylpyrrolidone (MP)-water solvent with a low content of the organic component are measured via calorimetry and densimetry at 298.15 K. Standard partial molal heat capacities \(\bar C_{p,2}^ \circ \) and volumes \(\bar V_2^ \circ \) of potassium iodide in MP-water mixtures are calculated. Standard heat capacities \(\bar C_{p,i}^ \circ \) and volumes \(\bar V_i^ \circ \) of potassium and iodide ions are determined. The character of the changes in heat capacity and volume are discussed on the basis of calculating additivity coefficients δ _c and δ _v upon the mixing of isomolal binary solutions KI-MP and KI-water, depending on the composition of the MP-H₂O mixture and the concentration of the electrolyte.     

The standard molar enthalpies of formation of chromone-3-carboxylic acid, 6-methylchromone-2-carboxylic acid,and 6-methyl-4-chromanone determined by micro-combustion calorimetry

The energies of combustion of chromone-3-carboxylic acid (C3CA), 6-methylchromone-2-carboxylic acid (6MCC), and 6-methyl-4-chromanone (6M4C) were determined using an isoperibolic micro-combustion calorimeter. The calorimeter used in the present work has been assembled, calibrated, and tested in our laboratory with the desired results. Prior to the measurement of the energies of combustion, the purities, heat capacities (C _p), fusion temperatures (T _fus), and enthalpies of melting (Δ_fus H) for each compound were determined by differential scanning calorimetry. The values of the energies of combustion were used to derive standard molar enthalpies of combustion ( \( \Delta _{{\text{c}}} H_{{\text{m}}}^{\circ } \) ) and standard molar enthalpies of formation ( \( \Delta _{{\text{f}}} H_{{\text{m}}}^{\circ } \) ) in the crystalline phase at T = 298.15 K. The values found for the \( \Delta _{{\text{f}}} H_{{\text{m}}}^{\circ } \) of C3CA, 6MCC, and 6M4C were ?(619.5 ± 2.6), ?(656.2 ± 2.2), and ?(308.9 ± 3.0) kJ mol^?1, respectively.