Luminescent Properties of Borosilicate Glass Doped with Cerium

Physics of the Solid State - ABS–BGP glasses (Al2O3–B2O3–SiO2–BaCO3–Gd2O3–P2O5) doped with different concentrations of Ce3+ ions are synthesized by the...     

Kinetic studies of the reaction of phenacyl bromide derivatives with sulfur nucleophiles

The reaction of the substituted phenacyl bromides 1a–e and 2a–e with thioglycolic acid 3 and thiophenol 6 in methanol underwent nucleophilic substitution S_N2 mechanism to give the corresponding 2‐sulfanylacetic acid derivatives 4a–e, 5a–e and benzenethiol derivatives 9a–e, 10a–e. The reactants and products were identified by mass spectra, infrared and nuclear magnetic resonance. We measured the kinetics of these reactions conductometrically in methanol at a range of temperatures. The rates of the reactions were found to fit the Hammett equation and correlated with σ‐Hammett values. The ρ values for thioglycolic acid were 1.22–1.21 in the case of 4‐substituted phenacyl bromide 1a–e, while in the case of the nitro derivatives 2a–e they were 0.39–0.35. The ρ values for thiophenol were 0.97–0.83 in the case of 4‐substituted phenacyl bromide 1a–e, while in the case of the nitro derivatives 2a–e they were 0.79–0.74. The Brønsted‐type plot was linear with a α = ?0.41 ± 0.03. The kinetic data and structure‐reactivity relationships indicate that the reaction of 1a–e and 2a–e with thiol nucleophiles proceeds by a concerted mechanism. The plot of log k₄₅ versus log k₃₀, the plot log(k_x,3‐NO2/k_H) versus log(k_x/k_H), and the Brønsted‐type correlation indicate that the reactions of the thiol nucleophiles with the substituted phenacyl bromides 1a–e and 2a–e are attributed to the electronic nature of the substituents. Copyright © 2011 John Wiley & Sons, Ltd.     

Some Thermodynamic Characteristics of Paracetamol Dispersing with the SEDS Method

The solubility of paracetamol in supercritical carbon dioxide and its mixtures with acetone is experientially studied. The isobaric heat capacity of paracetamol and the systems “paracetamol–CO₂” and “paracetamol–acetone–CO₂” is measured under pressures 7–29 MPa and temperatures 303–523 K. The results of paracetamol dispersing using the SEDS method (Solution Enhanced Dispersion by Supercritical Fluids) are presented.     

Magnetic properties of 3D nanocomposites consisting of an opal matrix with embedded spinel ferrite particles

The magnetic properties of 3D nanocomposites representing Mn–Zn, Ni–Zn, Co–Zn, La–Co–Zn, and Nd–Co–Zn spinel ferrite particles embedded in the interspherical spaces of opal matrices are studied. Experimental data are obtained in the temperature interval 2–300 K by measuring the magnetization at a static magnetic field strength of up to 50 kOe and the ac magnetic susceptibility at an alternating magnetic field amplitude of 4 kOe and a frequency of 80 Hz.     

Intercalation of graphene on iridium with samarium atoms

Intercalation of graphene on Ir (111) with Sm atoms is studied by methods of thermal desorption spectroscopy and thermionic emission. It is shown that adsorption of samarium at T = 300 K on graphene to concentrations of N ≤ 6 × 10¹⁴ atoms cm^–2 followed by heating of the substrate leads to practically complete escape of adsorbate underneath the graphene layer. At N > 6 × 10¹⁴ atoms cm^–2 and increasing temperature, a fraction of adsorbate remains on graphene in the form of two-dimensional “gas” and samarium islands and are desorbed in the range of temperatures of 1000–1200 K. Samarium remaining under the graphene is desorbed from the surface in the temperature range 1200–2150 K. Model conceptions for the samarium–graphene–iridium system in a wide temperature range are developed.     

Hydrogen-bonding studies of amino acid side-chains with DNA base pairs

The interactions of the amino acid side-chains arginine (ARG), aspartic acid (ASP), asparagine (ASN), lysine (LYS) and serine (SER) with nucleic acid base pairs have been investigated using theoretical methods. The interaction energy of the short intermolecular N–H?···?N, N–H?···?O, O–H?···?O, O–H?···?N, C–H?···?O and C–H?···?N hydrogen bonds present in both isolated base pairs and complexes and its role in providing stability to the complexes have been explored. The homonuclear interactions are found to be stronger than the heteronuclear interactions. An improper hydrogen bond has been observed for some of the N–H?···?O and N–H?···?N hydrogen-bond interactions with the contraction of the N–H bond varying from 0.001 to 0.0260?Å and the corresponding blue shift of the stretching frequency by 4–291?cm^?1. Localized molecular orbital energy decomposition analysis (LMOEDA) reveals that the major contributions to the energetics are from the long-range polarization (PL) interaction, and the short-range attractive (ES, EX) and repulsive (REP) interactions. The Bader's atoms in molecules (AIM) theory shows good correlation for the electron density and its Laplacian at the bond critical points (BCP) with the N–H?···?N and N–H?···?O hydrogen-bond lengths in the complexes, and gives a proper explanation for the stability of the structure. The charge-transfer from the proton acceptor to the antibonding orbital of the X–H bond in the complexes was studied using natural bond orbital (NBO) analysis.     

Rigidity of Compact Riemannian Spin Manifolds with Boundary

In this article, we prove new rigidity results for compact Riemannian spin manifolds with boundary whose scalar curvature is bounded from below by a nonpositive constant. In particular, we obtain generalizations of a result of Hang–Wang (Pac J Math 232(2):283–288, 2007) based on a conjecture of Schroeder and Strake (Comment Math Helv 64:173–186, 1989).     

Growth of silica nanowire arrays by reaction of Si substrate with oxygen using Ga as catalyst

Silica nanowire arrays were grown by oxidizing Si substrates with Ga catalyst in temperatures of 520–900 °C. The Si substrates, painted with a layer of molten Ga, were placed on a quartz boat, and heated up in a tube furnace. At high temperatures, Ga atoms condense into spheres, along with a small amount of silicon atoms. Si–O–Ga then formed on the surface of Ga–Si alloy sphere, and silica nanowire arrays were eventually grown with typical diameters of about 15–20 nm. A growth model based on extended vapor–liquid–solid mechanism is suggested.     

Optical Spectra of Gamma-Irradiated LiF Crystals with Anisotropic Lithium Nanoparticles

The optical response of Li anisotropic defects and nanoparticles from three faces of cubic LiF crystals with 10-mm edges to γ radiation from a ⁶⁰Со source with doses of 10⁵–10⁹ R at 320 K in air is studied. After a maximum dose of 10⁹ R, scanning electron microscopy revealed submicron metal lithium flakes ordered into long parallel nanofilaments. The resonance absorption band, which shifts from 272 to 295 nm with increasing dose, is assigned to lithium nanocolloids in the (110) plane. The band at 202–225 nm observed only from the (100) face narrows at doses below 10⁵ R and is assigned to diatomic fluorine molecules in interstitial sites. The appearance of the 209–212–215-nm triplets at 2.7 × 10⁵ R from the (100) plane and the 211–213–215-nm triplets at 0.9 × 10⁵ R from the (010) plane is related to radiation-induced axially symmetric bipolarons with a high oscillator strength. The splitting of the 445-nm band into a 438–445–450-nm triplet is observed only for the (010) plane after a dose of 10⁶ R and is related to surface plasmon polaritons (longitudinal and transverse) of elongated Li nanoparticles. The (F₂–F₃) complexes are oriented in the most imperfect (111) plane and are seen along three cubic axes.     

The integrability of an extended fifth-order KdV equation with Riccati-type pseudopotential

The extended fifth-order KdV equation in fluids is investigated in this paper. Based on the concept of pseudopotential, a direct and unifying Riccati-type pseudopotential approach is employed to achieve Lax pair and singularity manifold equation of this equation. Moreover, this equation is classified into three categories: extended Caudrey–Dodd–Gibbon–Sawada–Kotera (CDGSK) equation, extended Lax equation and extended Kaup–Kuperschmidt (KK) equation. The corresponding singularity manifold equations and auto-Bäcklund transformations of these three equations are also obtained. Furthermore, the infinitely many conservation laws of the extended Lax equation are found using its Lax pair. All conserved densities and fluxes are given with explicit recursion formulas.     

Field emission of multitip silicon structures with protection coatings

(0.1–0.3 cm²) area multipoint silicon emitters with two-layer metal–fullerene coatings are studied. Field-emission sources that generate currents of several tens of milliamperes that are sufficient for several millimeter- and submillimeter-wavelength microwave sources and compact X-ray sources are developed. Stable operation of multitip silicon field emitters with two-layer metal–fullerene coatings in high-voltage electronic devices is demonstrated at relatively high current output under technical vacuum conditions.     

Enhanced thermal–mechanical properties of polymer composites with hybrid boron nitride nanofillers

The present work focuses on the investigation of the thermal–mechanical properties of the epoxy composites with hybrid boron nitride nanotubes (BNNTs) and boron nitride nanosheets (BNNSs). The stable dispersions of BNNTs–BNNSs were achieved by a noncovalent functionalization with pyrene carboxylic acid. The resulting epoxy/BNNTs–BNNSs composites exhibited homogeneously dispersed BNNTs–BNNSs and a strong filler–matrix interface interaction. The composites showed a 95 % increase in thermal conductivity and a 57 % improvement in Young’s modulus by addition of only 1 vol. % BNNTs–BNNSs. Meanwhile, the composites also retained a high electrical resistance of pure epoxy. Our study thus shows the potential for hybrid BNNTs–BNNSs to be successfully used as the nanofillers of polymer composites for applications in electrically insulating thermal interface materials.     

Ultrasonic-assisted electrodeposition of Cu-Sn-TiO2 nanocomposite coatings with enhanced antibacterial activity

Copper-based coatings are known for their high antibacterial activity. In this study, nanocomposite Cu–Sn–TiO₂ coatings were obtained by electrodeposition from an oxalic acid bath additionally containing 4 g/dm³ TiO₂ with mechanical and ultrasonic agitation. Ultrasound treatment was performed at 26 kHz frequency and 32 W/dm³ power. The influence of agitation mode and the current load on the inclusion and distribution of the TiO₂ phase in the Cu–Sn metallic matrix were evaluated. Results indicated that ultrasonic agitation decreases agglomeration of TiO₂ particles and allows for the deposition of dense Cu–Sn–TiO₂ nanocomposites. It is shown that nanocomposite Cu–Sn–TiO₂ coatings formed by ultrasonic-assisted electrodeposition exhibit excellent antimicrobial properties against E. coli bacteria.     

Cold brittleness and fracture of metals with various crystal lattices: Dislocation mechanisms

The dislocation mechanisms of formation of the ductile–brittle transition temperature and the low-temperature brittle fracture of metals (single crystals, polycrystals) with various crystal lattices (bcc, fcc, hcp) are considered. The conditions of appearance of cold shortness and intracrystalline crack propagation (brittle fracture) are determined. These conditions can be met in bcc and some hcp metals and cannot be met in fcc and many hcp metals. The nondestructive internal friction (at 100 kHz) method is used to determine the temperature ranges of cold shortness (ductile–brittle transition temperatures) in bcc metals (ferritic–martensitic EK-181 steel, V–4Ti–4Cr alloy), which depend on their structure–phase state and strength (yield strength).     

Thermal properties of graphite intercalation compounds with acids

This work is devoted to systematic thermal analysis of first to fifth stages of binary graphite intercalation compounds (GIC) with HNO₃ and ternary GICs with HNO₃–R (R=CH₃COOH, H₃PO₄) by simultaneous TG–DSC thermoanalyses (Netzsch). Thermolysis of GIC leads to the full deintercalation of acid and significant expansion of samples. The thermal properties of co-intercalated GICs-HNO₃-R and the thermal expanding coefficient of GIC depend on the nature of the intercalate. The endopeak at 110–150 °C corresponds to the loss of nitric acid was observed in DSC- curve of binary second to fifth stages of GICs with HNO₃. A wide endopeak which is characterized by the increasing of decomposition temperature in comparison with GIC-HNO₃ was observed in DSC—curve of ternary GIC with HNO₃–CH₃COOH. Thus, acetic acid stabilizes the graphite nitrate matrix. Two endoeffects due to the deintercalation of HNO₃ (110–180 °C) and H₃PO₄ (450–800 °C) were observed in the DSC-curves of co-intercalated GICs with HNO₃–H₃PO₄ of second and third stages. The value of decomposition heat (ΔH) and weight loss decrease with the increasing of the stage number of GICs. The values of ΔH are equal to 0.40–14.8 kJ/g-at C.     

Modifying a cylindrical surface irradiated with a radial beam of argon ions with energies of up to 5 keV

Aspects of the ion modification of the outer surfaces of tubular samples of E110 (Zr–1% Nb) alloy is studied. The samples are irradiated with a radial beam of argon ions (0.5–5.0 keV, (5–10) × 10¹⁸ ion/cm²) on the ILUR-03 setup. It is found that such ion bombardment smooths the relief formed by mechanical abrasive treatment. It is demonstrated that the effect of ion polishing is most pronounced for surface irregularities of a certain size.     

Photocatalytic reduction of carbon dioxide with water using InNbO4 catalyst with NiO and Co3O4 cocatalysts

InNbO₄ was prepared by the solid-state reaction method. Various cocatalysts were added on InNbO₄ by the incipient-wetness impregnation method. The effects of co-catalyst and pretreatment conditions on the photocatalytic activity of InNbO₄ for photoreduction of carbon dioxide were investigated. NiO–InNbO₄ and Co₃O₄–InNbO₄ were pretreated by reduction at 500 °C for 2 h and subsequent oxidation at 200 °C for 1 h. The catalysts were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectroscopy. The characterization results of NiO–InNbO₄ catalysts after pretreatment showed the presence of highly crystalline NiO and monoclinic Nb₂O₅. NiO–InNbO₄ with reduction–oxidation pretreatment exhibited the highest activity due to the presence of core–shell type Ni⁰ and NiO on the surface and the presence of a small amount of Nb₂O₅ as a promoter.     

Attenuation of sound in shallow-water areas with gas-saturated bottoms

Acoustical Physics - We investigated the specific features low-frequency (50–300 Hz) sound propagation in shallow-water areas to relatively small distances r ≈ 3H–50H from the...     

Mean Field Evolution of Fermions with Coulomb Interaction

We study the many body Schrödinger evolution of weakly coupled fermions interacting through a Coulomb potential. We are interested in a joint mean field and semiclassical scaling, that emerges naturally for initially confined particles. For initial data describing approximate Slater determinants, we prove convergence of the many-body evolution towards Hartree–Fock dynamics. Our result holds under a condition on the solution of the Hartree–Fock equation, that we can only show in a very special situation (translation invariant data, whose Hartree–Fock evolution is trivial), but that we expect to hold more generally.     

Higher-order solutions of a matrix AKNS system associated with a Hermitian symmetric space

In this paper, we study a matrix Ablowitz–Kaup–Newell–Segur (AKNS) system associated with a Hermitian symmetric space as a follow-up study of an earlier paper. A multi-fold generalized Darboux transformation of the matrix AKNS system associated with a Hermitian symmetric space is constructed by means of determinants. Subsequently, we derive various higher-order solutions for this system, including fan-shaped rogue wave and (truncated) Kuznetsov–Ma breather solutions. Specifically, we show the fusion and fission processes for two truncated Kuznetsov–Ma breathers by taking different free parameters.