Single-Reference Coupled-Cluster Calculations of the Triplet Ground-State O2 Dissociation Potential

Three single-reference coupled-cluster single and double (CCSD) substitution models, CCSD + T(CCSD), CCSDT-1, and CCSD(T), exact through the fourth order of perturbation theory, are tested on the triplet ground-state dissociation potential of O₂. For the unrestricted Hartree-Fock (UHF) initial approximation, the interatomic distance region R ˜ 2.4–2.7 a.u. is problematic due to large multireference character, and beyond R ˜ 3.0 a.u. spin contamination causes difficulties. To a large extent these deficiencies are cured by the coupled-cluster treatments. Fourth-order triples as well as higher-order singles and doubles play a significant role. A more flexible basis set than DZP is important, too. None of the methods tried reproduce the experimental potential curve to the desired accuracy (2 kcal/mol). However, in a 6–311 + + G(2df, 2p) basis, the CCSD(T) model does give spectroscopic constants that are correct within 0.2 eV for the dissociation energy D_e, 70 cm⁻¹ for the harmonic vibrational frequency v_e, and 0.5 cm⁻¹ for the first anharmonicity constant v_eX_e. This model also reproduces the potential throughout the dissociative region to better than 0.2 eV. Overall CCSD + T(CCSD) is considerably less satisfactory than CCSD(T); CCSDT-1 is similar to CCSD(T) in a DZP basis, but large basis calculations proved to be too time consuming.     

Spin lattice relaxation and lithium motion in lithium-sodium beta-alumina

Pulsed nmr techniques were used to determine Li⁺ activation energies, spin lattice relaxation (T₁) times, observed linewidth (T*₂) and motional narrowing behavior in polycrystalline Li-Na beta-alumina having a nominal 1:1 Li⁺/Na⁺ ratio. Specimen heat treatment induced significant changes in all of the measured quantities.     

Transparent Beryllia Ceramics for Laser Technology and Ionizing Radiation Dosimetry

A technology for preparation of transparent beryllia ceramics has been developed using Li₂CO₃ as a modifier at relatively low temperatures (not above 1570 K) and moderate molding pressures (up to 40.0 MPa). Optimum pressure molding time, average grain size, and dopant concentrations (Li₂CO₃ + rare-earth oxides) to increase luminescence intensity are specified. The transparent dense BeO ceramic may be of interest for laser technology (especially in the middle infrared) as material for fabrication of dielectric resonant tubes, waveguides, and dielectric nontransmitting mirrors. The transparent BeO ceramic is a promising material for developing a new generation of tissue-equivalent scintillators for the dosimetry of ionizing radiation.     

Color change of white spot lesions after resin infiltration

This study evaluates color change of the enamel lesion before and after resin infiltration and after thermocycling (TC) in order to assess clinical usefulness of resin infiltrant in restoring esthetics of incipient enamel caries lesions. Twenty‐five healthy premolars were prepared and crown portions were vertically cut. Specimens were emerged in acryl blocks with relatively flat proximal surface facing outside. Specimens were put in decalcification solution (50 mM acetic acid solution, 3 mM CaCl₂·H₂O, 3 mM KH₂PO₄, 6 µM methylhydroxydiphosphonate, pH 4.95, 37°C), and were kept for 160 h, in order to make white spot lesions on the exposed enamel. Degree of decalcification was observed with microscope and nine specimens were excluded because of inadequate decalcification (n = 41). L^*, a^*, and b^* were measured with colorimeter at the baseline (T₁), after production of white spot lesions (T₂), after infiltration of resin infiltrants (ICON^®, DMG, Hamburg, Germany) (T₃), after 3000 (T₄), 6000 (T₅), and 10,000 cycles (T₆) of TC. L^* was highest at T₂, but significantly decreased until T₆ which was the closest value to T₁ (P < 0.05). a^* was highest at T₂ and decreased gradually until T₆, whereas b^* was lowest at T₂ and was highest at T₃ and decreased gradually until T₆. Δ less than 3.7 showed between T₁ and T₄, between T₁ and T₅, and between T₁ and T₆, which suggested that it was hard to differentiate one from the other clinically. Resin infiltrated lesions showed recovery of CIE value close to that of healthy enamel over time. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 506–510, 2014     

Tracer method in numerical simulation of combustion processes

Fuel-rich laminar flat hydrogen-methane-air flames are studied numerically using the tracer method. It is found that, in the near-limit mixture, hydrogen has an advantage in the oxidation by oxygen. As the stoichiometric compositions are approached, this advantage decreases and then disappears. It is shown that H ₂ ^* O and CO ₂ ^* labeled additives participate in the reactions and the labels from these molecules move to other products. Small additives of CH ₄ ^* in the mixture completely react to form HH*O, H ₂ ^* O, CO, CO₂, HH*, and H ₂ ^* . Quantitative data on the distribution of the tracer atoms in products are given. The interaction of the hydrogen and methane oxidation schemes is studied. It is shown that in the presence of restriction on the interaction of these schemes, the laminar flame velocity increases by a factor of 5–7. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 3–12, November–December, 2007.     

Density Functional Study of Structures and Electron Affinities of BrO4F/BrO4F?

The structures, electron affinities and bond dissociation energies of BrO₄F/BrO₄F⁻ species have been investigated with five density functional theory (DFT) methods with DZP++ basis sets. The planar F-Br…O₂…O₂ complexes possess ³A′ electronic state for neutral molecule and ⁴A′ state for the corresponding anion. Three types of the neutral-anion energy separations are the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The EA_ad value predicted by B3LYP method is 4.52 eV. The bond dissociation energies D_e (BrO₄F → BrO_4-mF + O_m) (m = 1–4) and D_e⁻ (BrO₄F⁻ → BrO_4-mF⁻ + O_m and BrO₄F⁻ → BrO_4-mF + O_m⁻) are predicted. The adiabatic electron affinities (EA_ad) were predicted to be 4.52 eV for F-Br…O₂…O₂ (³A′←⁴A′) (B3LYP method).     

Method for separating intramolecular and intermolecular interactions which influence polymer glass temperatures

It is shown that the glass temperature (T_g) for homopolymers of the type ? CH₂? CXY? can be expressed by a simple additive equation involving two terms: (1) a parameter E which is directly related to the molar cohesion energy and (2) a parameter E_s^* which is a measure of restricted rotation about valence bonds. E_s^*, at least for a large number of polymers, is related to the Mark-Houwink K_θ value (as measured in θ solvents at T_θ) via anti-log E_s^* ∝ 1/K_θ^2/3. It is also shown that for homologous series [e.g., poly(n-alkyl methacrylates)], there is a constant relationship between E and antilog E_s^*. The T_g values for copolymers may be estimated by a simple weighted (via mole fraction) summation of the E and E_s^* values of the components. When used in this form, a linear variation between T_g and composition is assumed, which may not be strictly correct but still yields useful approximations.     

Domain epitaxy of crystalline BeO films on GaN and ZnO substrates

We demonstrated the growth of wurtzite-crystalline beryllium oxide (BeO) thin films on GaN and ZnO substrates using atomic layer deposition (ALD). Single-crystalline BeO were epitaxially grown on GaN. Despite the inherently large lattice mismatch of BeO and GaN atoms, the 6/5 and 7/6 domain-matched structures dramatically reduced the residual strain in BeO thin films. On the other hand, the lattice mismatch of BeO and ZnO was not effectively accommodated in the mixed domains. X-ray diffraction (XRD) confirmed the in-plane crystallization of BeO-on-substrates in the (002){102}_BeO||(002){102}_Sub orientation and relaxation degrees of 20.8% (GaN), 100% (ZnO). The theoretical critical thicknesses of BeO for strain relaxation were 2.2 μm (GaN) and 1.6 nm (ZnO), calculated using a total film energy model. Transmission electron microscopy (TEM) and Fourier-filtered imaging supported the bonding configuration and crystallinity of wurtzite BeO thin films on GaN and ZnO substrates.     

Theoretical in-Solution Conformational/Tautomeric Analyses for Chain Systems with Conjugated Double Bonds Involving Nitrogen(s)

Conformational/tautomeric transformations for X=CH–CH=Y structures (X = CH₂, O, NH and Y = NH) have been studied in the gas phase, in dichloromethane and in aqueous solutions. The paper is a continuation of a former study where s-cis/s-trans conformational equilibria were predicted for analogues. The s-trans conformation is preferred for the present molecules in the gas phase on the basis of its lowest internal free energy as calculated at the B97D/aug-cc-pvqz and CCSD(T)_CBS (coupled-cluster singles and doubles with non-iterative triples extrapolated to the complete basis set) levels. Transition state barriers are of 29–36 kJ/mol for rotations about the central C–C bonds. In solution, an s-trans form is still favored on the basis of its considerably lower internal free energy compared with the s-cis forms as calculated by IEF-PCM (integral-equation formalism of the polarizable continuum dielectric solvent model) at the theoretical levels indicated. A tetrahydrate model in the supermolecule/continuum approach helped explore the 2solute-solvent hydrogen bond pattern. The calculated transition state barrier for rotation about the C–C bond decreased to 27 kJ/mol for the tetrahydrate. Considering explicit solvent models, relative solvation free energies were calculated by means of the free energy perturbation method through Monte Carlo simulations. These calculated values differ remarkably from those by the PCM approach in aqueous solution, nonetheless the same prevalent conformation was predicted by the two methods. Aqueous solution structure-characteristics were determined by Monte Carlo. Equilibration of conformers/tautomers through water-assisted double proton-relay is discussed. This mechanism is not viable, however, in non-protic solvents where the calculated potential of mean force curve does not predict remarkable solute dimerization and subsequent favorable orientation.     

Copolymerization of styrene. IV. Copolymerization with esters of benzylidenecyanoacetic acid

Styrene was copolymerized in bulk with a number of esters of benzylidenecyanoacetic acid. The kinetic scheme of all pairs fitted the improved scheme of copolymerization, taking into account the effect of the penultimate unit. The Alfrey-Price Q and e values were calculated. Using the modified Taft equation, log (1/r₁) = ρ^*σ^* + δE_s, it was found that the relative reactivities of the ester monomers toward the polystyryl radical were correlated by the polar substituent constants σ^* of the ester alkyl groups (ρ^* = 0.14) and not by their steric substituent constants E_s (δ = 0.008).     

Evaluation of Sodium Relaxation Times and Concentrations in the Achilles Tendon Using MRI

Sodium magnetic resonance imaging (MRI) can be used to evaluate the change in the proteoglycan content in Achilles tendons (ATs) of patients with different AT pathologies by measuring the ²³Na signal-to-noise ratio (SNR). As ²³Na SNR alone is difficult to compare between different studies, because of the high influence of hardware configurations and sequence settings on the SNR, we further set out to measure the apparent tissue sodium content (aTSC) in the AT as a better comparable parameter. Ten healthy controls and one patient with tendinopathy in the AT were examined using a clinical 3 Tesla (T) MRI scanner in conjunction with a dual tuned ¹H/²³Na surface coil to measure ²³Na SNR and aTSC in their ATs. ²³Na T₁ and T₂* of the AT were also measured for three controls to correct for different relaxation behavior. The results were as follows: ²³Na SNR = 11.7 ± 2.2, aTSC = 82.2 ± 13.9 mM, ²³Na T₁ = 20.4 ± 2.4 ms, ²³Na T_2s* = 1.4 ± 0.4 ms, and ²³Na T_2l* = 13.9 ± 0.8 ms for the whole AT of healthy controls with significant regional differences. These are the first reported aTSCs and ²³Na relaxation times for the AT using sodium MRI and may serve for future comparability in different studies regarding examinations of diseased ATs with sodium MRI.     

Ge-doped Li4Ti5-xGexO12 (x = 0.05) as a fast-charging,long-life bi-functional anode material for lithium- and sodium-ion batteries

We explored the doping effect of Ge⁴⁺ on the Li₄Ti_5-xGe_xO₁₂ (x = 0.0 and 0.05) anode material by looking at its electrochemical performance in both Li- and Na-ion batteries. Combined analysis using Rietveld refinement of high-resolution powder diffraction (HRPD) and transmission electron microscopy (TEM) unambiguously identified homogeneous Ge doping into the 16c octahedral Ti site of the Li₄Ti₅O₁₂ (LTO) cubic spinel structure. This Ge doping leads to a much-reduced particle size, slightly expanded lattice and increased electrical conductivity due to the increased Ti³⁺ to Ti⁴⁺ ratio, these results were verified by HRPD, scanning electron microscopy (SEM), 4-point probe and x-ray photoelectron spectroscopy (XPS) analysis. The Li₄Ti_4.95Ge_0.05O₁₂ (Ge0.05-LTO) electrode shows much-improved capacity, high-rate capability and excellent cycling stability in a Li-half cell compared with an un-doped LTO electrode. This performance improvement is due to the reduced Li⁺ diffusion path and faster Li⁺ insertion/extraction kinetics that originate from Ge doping. In addition to these results, when tested as an anode for SIBs, the Ge0.05-LTO electrode exhibits enhanced capacity and cycling stability compared to un-doped LTO electrode, demonstrating its bi-functional, advantageous features in both LIB and SIB systems.     

Structural,magnetic and magnetostrictive properties of Co1-xLixFe2O4 synthesized by cathode materials of spent Li-ion batteries

In this study, we investigated the effects of substituting Li⁺ for Co²⁺ at the B sites of the spinel lattice on the structural, magnetic and magnetostrictive properties of cobalt ferrites. The Li⁺ substituted cobalt ferrites, Co_1-xLi_xFe₂O₄, with x varying from 0 to 0.7 in 0.1 increments, were synthesized with a sol-gel auto-combustion method using the cathode materials of spent Li-ion batteries. X-ray diffraction analysis revealed that all the Co_1-xLi_xFe₂O₄ nanopowders had a single-phase spinel structure and the lattice parameters decreased with increasing Li⁺ content, which can be proved by slight shifts towards higher diffraction angle values of the (311) peak. Field emission scanning electron microscopy was used to observe the fractured inner surface of the sintered cylindrical rods and the increased porosity resulted in a decreased magnetostriction. The oxidation states of Co and Fe in the cobalt ferrite samples were examined by X-ray photoelectron spectroscopy. High resolution transmission electron microscopy micrographs showed that most particles were roughly spherical and with sizes of 25–35?nm. Li⁺ substitution had a strong effect on the saturation magnetization and coercivity, which were characterized with a vibrating sample magnetometer. The Curie temperature was reduced due to the decrease in magnetic cations and the weakening of the exchange interactions. The magnetostrictive properties were influenced by the incorporation of Li⁺ at the B sites of the spinel structure and correlated with the changes in porosity, magnetocrystalline anisotropy and the cation distribution.     

Structure and electrical conductivity of Li2O-B2O3 glasses

The temperature-concentration dependence of the electrical conductivity of Li₂O-B₂O₃ glasses in the temperature range of ～180–310°C has been studied. For pure boron anhydride, the dependence logσ = f([1/T]) is linear, whereas for glasses with ～2 mol % ≤ [Li₂O] < ～10 mol %, similar curves are kinked. At higher Li₂O concentration the kinks disappear. Occurrence of kinks is attributed to variation of essence of current carriers from proton pattern for B₂O₃ to mixed proton-ion pattern for low-alkali glasses. Conductivity of glasses at [Li₂O] ≥ 20 mol % is stipulated by the formation of a continuous sublattice of polar structuralchemical entities (entities) [BO_4/2]^?Li⁺ and the migration of lithium ions.     

Reaction kinetics to infer the effect of dopants on ion transport - A case study for Mo+6 doped lithium titanates (Li2TiO3-δ and Li4Ti5O12-δ)

In this paper, a unique approach to correlate influence of doping on ionic mobility, through thermo-kinetic analysis, is reported. Formation kinetics of Li₂TiO₃ and Li₄Ti₅O₁₂, with Mo⁺⁶ doping, were successfully analyzed in ultra-pure Ar atmosphere using differential scanning calorimetry. The results were compared with formation kinetics of pure Li₂TiO₃ and Li₄Ti₅O₁₂ under identical conditions. Field emission scanning electron microscopy (FE-SEM) with electron diffraction spectroscopy (EDS), X-ray diffraction and Raman spectroscopy were employed for the characterization of resulting phases and presence of oxygen vacancy. The results indicate that for doped samples, oxygen vacancy concentration was reduced due to the charge compensation mechanism of the doped ion. The activation energy (E_α) of the different reactions with and without Mo⁺⁶ doping was determined by Kissinger-Akahira-Sunose method. The most probable reaction mechanism was predicted through Master plot approach. The reaction rate controlling step shifted from three-dimensional diffusion (D₃) for undoped Li₂TiO₃ to a chemical reaction (F_n) for doped Li₂TiO₃. For Li₄Ti₅O₁₂ the reaction mechanism (or rate controlling step) was a chemical reaction (F_n) for undoped and nucleation (A_n) for doped material. The results show that diffusion of ions becomes faster in the Mo⁺⁶ doped materials by reducing the charge transfer resistance. Finally, the thermodynamic functions of the transition complex were calculated from kinetic triplets and correlated with thermo-kinetic data.     

Structures and Stabilities of the Metal Doped Gold Nano-Clusters: M@Au10 (M = W,Mo, Ru,Co)

The structures and stabilities of a series of endohedral gold clusters containing ten gold atoms M@Au₁₀ (M = W, Mo, Ru, Co) have been determined using density functional theory. The gradient-corrected functional BP86, the Tao-Perdew-Staroverov-Scuseria TPSS meta-GGA functional, and the hybrid density functionals B3LYP and PBE1PBE were employed to calculate the structures, binding energies, adiabatic ionization potentials, and adiabatic electron affinities for these clusters. The LanL2DZ effective core potentials and the corresponding valence basis sets were employed. The M@Au₁₀ (M = W, Mo, Ru, Co) clusters have higher binding energies than an empty Au₁₀ cluster. In addition, the large HOMO–LUMO gaps suggest that the M@Au₁₀ (M = W, Mo, Ru, Co) clusters are all likely to be stable chemically. The ionization potentials and electron affinities for these clusters are very high, and the W@Au₁₀ and Mo@Au₁₀ clusters have electron affinities similar to the super-halogen Al₁₃.     

Li+ enrichment to improve the microwave dielectric properties of Li2ZnTi3O8 ceramics and the relationship between structure and properties

Herein, Li⁺-enriched Li_(1+x)2ZnTi₃O₈ ceramics are prepared via the solid-phase methods. As x increases, the unit cell volume gradually increases, while the grain size initially increases and then decreases gradually. The Li_(1+0.06)2ZnTi₃O₈ ceramics exhibit the best dielectric properties: ε_r = 25.92, Q × f = 109534 GHz (@7.37 GHz, which is a 48 % increase compared with the stoichiometric counterpart.), and τ_f = ?8.21 ppm/°C. The complex chemical bond theory and Raman spectroscopy reveal that Ti-O bonds have a significant effect on the dielectric properties. An optimal Li⁺ enrichment leads to an overall reduction in the distortion of the Li/ZnO₄ tetrahedra, resulting in a reduction in τ_f. First-principles calculations demonstrate that a suitable excess of Li⁺ leads to an increase in the band-gap as well as an enhanced electron cloud density in the internal space of the Li1/ZnO₄ tetrahedra, thereby increasing the Q × f. In summary, Li⁺-enriched Li_(1+0.06)2ZnTi₃O₈ ceramics are promising for a wide array of applications in microwave communications.     

Structure and electrical properties evolution of B-site complex ions (Li1/4Nb3/4) modification BNT–BT ceramics

Abstract

B-site complex ions (Li_1/4Nb_3/4)⁴⁺ modification (Bi_1/2Na_1/2)_0·94Ba_0·06TiO₃ ceramics with compositions of (Bi_1/2Na_1/2)_0·94Ba_0·06Ti_1?x(Li_1/4Nb_3/4)_xO₃ (x?=?0, 0·01, 0·03 and 0·06) have been synthesised via the conventional solid state reaction. The effect of (Li_1/4Nb_3/4)⁴⁺ content and sintering temperature on structures and electrical properties were investigated. It was found that both compositions and sintering temperatures have no significant effect on the crystal structure, and trace (Li_1/4Nb_3/4)⁴⁺ addition and sintering temperatures have a great influence on the microstructure. Two obvious dielectric anomaly peaks (T_d and T_m) were observed and dielectric constant for all poled specimens displayed significant frequency dispersion at T_d and diffusion phase transition at T_m. The piezoelectric properties of the ceramics are insensitive to the sintering temperatures, and the composition with x?=?0·03 sintering at 1150°C exhibits favourable piezoelectric properties of d₃₃?=?155 pC N^?1 and k_p?=?0·312.     

Influence of helium ion radiation on the nano-grained Li2TiO3 ceramic for tritium breeding

Lithium titanium oxide (Li₂TiO₃) tritium breeder ceramic plates with nano- and coarse-grain size were fabricated. The preparation methods contained CTAB-modifying precursor, combining dry-pressing with isostatically cold-pressing, and calcinating at optimized sintering temperature in turn. Then their properties were characterized after radiation by 280 keV helium (He⁺) ion. Extensive characterization analyses were performed to reveal the changes in nano-grained and coarse-grained Li₂TiO₃ after radiation. They contained glancing angle X-ray diffraction (GIXRD), atomic force microscopy (AFM), electron spin resonance (ESR), and scanning electron microscopy (SEM). The results showed as follows, GIXRD peak position of the nano-grained Li₂TiO₃ was more stable than the coarse-grained Li₂TiO₃ after radiation. Nano-grained Li₂TiO₃ was less rough and swollen than the coarse-grained one after radiation. Nano-grained Li₂TiO₃ had more excellent structural stability and less defect concentration of Eʹ-center after radiation. As a result, nano-grained Li₂TiO₃ might have much better radiation tolerance than the coarse-grained one by comparing characterization results.     

A theory of pseudo cross-link

Summary The calculation of entanglement is reexamined and it is expressed by two factors nc² and n²c², n and c being the length of the polymer and its concentration, respectively. Both factors are concerned with the inter-coil interaction revealing in the melt viscosity so that is proportional to n^3.5c^4.5. At the melt temperature T_B, a critical chain length n_B is 256 and T_B is twice as high as t_A, i.e. a liquid-solid transition. At T_B the entropy of cross-linking becomes 2/3 times of that at T_A. The osmotic pressure increases in the semi-dilute solution by a factor of (c/c^*)^4/3, c^* being a critical concentration for overlapping. In the dilute solution in -solvents the cohesion of segments enables the independent coil to form an intra-coil linking even below c^* and induces the coil-globule transition at the -point to give rise to self-coaguration.