La0.789Yb0.20Ho0.001Tm0.01F3纳米立方体的溶剂热合成及白色上转换发光性质

采用溶剂热方法制备了La0.789Yb0.20Ho0.001Tm0.01F3纳米立方体,并利用粉末X射线衍射仪、透射电子显微镜和X射线能谱仪表征了其组成、结构和形貌,用荧光分光光度计测量了样品的室温上转换发射光谱,结果表明,样品具有红、绿和蓝色3个发射带,其辐射跃迁分别归属于Tm3+的1G4→3H6(蓝色)和1G4→3...     

Disruption of urogenital biofilms by lactobacilli

The process that changes a relatively sparse vaginal microbiota of healthy women into a dense biofilm of pathogenic and potentially pathogenic bacteria is poorly understood. Likewise, the reverse step whereby an aberrant biofilm is displaced and returns to a healthy lactobacilli dominated microbiota is unclear. In order to study these phenomena, in vitro experiments were performed to examine the structure of biofilms associated with aerobic vaginosis, urinary tract infections, and bacterial vaginosis (BV). Uropathogenic Escherichia coli were able to form relatively thin biofilms within five days (6 μm height), while Atopobium vaginae and Gardnerella vaginalis formed thicker biofilms 12 μm in height within two days. Challenge of E. coli biofilms with lactobacilli did not result in pathogen displacement. However, the resulting thicker lactobacilli infused biofilms, caused significant E. coli killing. E. coli biofilms challenged with secreted products of L. rhamnosus GR-1 caused a marked decrease in cell density, and increased cell death. Similarly challenge of BV biofilms with lactobacilli infiltrated BV biofilms and caused bacterial cell death. Metronidazole produced holes in the biofilm but did not eradicate the organisms. The findings provide some evidence of how lactobacilli probiotics might interfere with an aberrant vaginal microbiota, and strengthen the position that combining probiotics with antimicrobials could better eradicate pathogenic biofilms.     

High-resolution FTIR spectrum of vinyl chloride: rovibrational analysis of the v 10 and v 11 fundamental bands

The Fourier transform gas-phase infrared spectra of the v ₁₀ and v ₁₁ bands of natural CH₂=CHCl have been measured with a resolution of 0.005 cm^?1 in the frequency range 820–1010 cm^?1. These vibrations of symmetry species A″ give rise to c-type bands and the transitions observed are characterized by δK _a = ±1 and δK _c = 0, ±2. Both J and K structures have been resolved in different subbranches and about 1800 (J ≤ 64, K _a ≤ 13) and 2800 (J ≤ 72, K _a ≤ 14) transitions for the v ₁₀ and v ₁₁ fundamentals, respectively, have been identified for the ³⁵Cl isotopomer. Combined analysis of the assigned data with the available ground state constants allowed the determination of the band origins, rotational and centrifugal distortion parameters for the v ₁₀ = 1 and v ₁₁ = 1 excited states of CH₂=CH³⁵Cl isotopic species. The molecular constants obtained account for slight perturbations in the v ₁₀ vibrational level.     

Direct correlation functions and bridge functions in additive hard-sphere mixtures

A method to obtain (approximate) analytical expressions for the radial distribution functions in a multicomponent mixture of additive hard spheres that was recently introduced is used to obtain the direct correlation functions and bridge functions in these systems. This method, which yields results practically equivalent to the generalized mean spherical approximation and includes thermodynamic consistency, is an alternative to the usual integral equation approaches and requires as input only the contact values of the radial distribution functions and the isothermal compressibility. Calculations of the bridge functions for a binary mixture using the Boublik-Mansoori-Carnahan-Starling-Leland equation of state are compared to parallel results obtained from the solution of the Percus-Yevick equation. We find that the conjecture recently proposed by Guzman and del Rio (1998, 98, Molec. Phys., 95, 645), stating that the zeros of the bridge functions occur approximately at the same value of the shifted distance for all pairs of interactions, is at odds with our results. Moreover, in the case of disparate sizes, even the Percus-Yevick bridge functions do not have this property. It is also found that the bridge functions are not necessarily non-positive.     

Exploring the MRCI method for calculating interaction energies: application to the HeNe potential curve

A multi-reference configuration interaction (MRCI) method is described, which is devised for the calculation of interaction energies of van der Waals complexes and applied to calculating the HeNe potential energy curve. The MRCI calculations make use of a generalized Pople-correction in order to account for the lack of size consistency. The orbital space is partitioned into three subspaces: the first active space (AS1), which contains the strongly occupied orbitals; the second active space (AS2), which contains the main intra-correlating orbitals; and the external space (ES). It is shown that, to keep the error below ± 0.2 K in the excitation scheme and the active orbital space it is sufficient to include only σ-orbitals in AS2 and to use an excitation scheme (labelled Qq-MRCI) that encompasses only up to quadruply excited configurations. The final active orbital space (AS2) turned out to be 2s(He), 2pσ(He), 3s(Ne), 3σ(Ne) and 3dσ(Ne). Other MRCI variants, in which most or all quadruply excited configurations were deleted from the CI expansion (Qt- and Tt-MRCI), were found to be inadequate. Using the Qq-MRCI scheme together with a 197-orbital ‘interaction optimized’ basis set (IO197), the MRCI interaction energy at R = 5.7 _a0 was calculated to be -21.12K. The corresponding values at the MP4 and CCSD(T) levels of theory are -20.06 K and -20.99 K, respectively, indicating that the MP4 method is inappropriate for highly accurate calculations on this system. Fitting the calculated data using a generalized Morse function, including an additional C₆/R⁶ term to account for a correct long-range behaviour of the potential, the MRCI well depth was calculated to be -21.16K at R_eq = 5.73a ₀. The MRCI and CCSD(T) potentials have the same quality and are found to be in good agreement with the Hartree-Fock dispersion (HFD-B) potential of Keil, M., Danielson, L. J., and Dunlop, P. J., 1991, J. Chem. Phys., 94, 296. It is concluded that, for basis IO197, the CCSD(T) method is sufficiently accurate for calculating the HeNe interaction. To recover the small, missing contributions (a few tenths of a Kelvin), MRCI should be used.     

Dynamics on reactive potential energy surfaces: hyperspherical view and signatures of ‘quantum chaos’

Adiabatic energy levels for two prototypical reactions, F + H₂ → HF + H and He + H⁺ ₂ → HeH⁺ + H, are analysed by means of statistical tests. These levels result from quantum mechanical calculations of dynamics based on the hyperspherical approach, and are given as a function of the total inertia of the system measured by the hyperradius ρ The nearest neighbour level spacing distributions of Brody and of Berry and Robnik, the spectral rigidity δ₃ of Dyson and Mehta and the correlation coefficient are reported, together with other properties, such as variance, skewness and kurtosis of the distributions. Trends are studied as a function of ρ, proposed as a natural control variable. For low ρ, which correspond to the transition state, evidence is found of Wigner-like behaviour, which is interpreted as the signature of quantum chaos. On the passage of the systems through intermediate ρ a mixture of Wigner- and Poisson-like behaviour emerges. The situation for high ρ where reactants and products of the reactions are well separated, is characterized by a tendency towards regular Poisson-like behaviour. A comparison between the two investigated systems shows that the chaotic regime in the transition state region is more pronounced for the He reaction, which proceeds through a deep well and whose dynamics are characterized by a rich resonance pattern.     

Density functional theory calculations of nuclear quadrupole coupling constants with calibrated 14N quadrupole moments

Density functional calculations of the electric field gradient tensor at the nitrogen nucleus in 13 test molecules, containing 14 nitrogen sites, have been performed using the linear combination of Gaussian-type orbital Kohn-Sham density functional theory (LCGTO-KSDFT) approach. Local and gradient corrected functionals were used for all-electron calculations. All the molecular structures were optimized at their respective levels of theory with extended basis sets. Calibrated ¹⁴N nuclear quadrupole moments were obtained through a fitting procedure between calculated electric field gradients and experimental nuclear quadrupole coupling constants of the test set of molecules for each basis set and functional considered. With these calibrated ¹⁴N nuclear quadrupole moments, the nuclear quadrupole coupling constants of the following selected systems were determined: fluoromethylisonitrile, pyridine, pyrrole, imadazole, pyrazole, 1,8-bis(dimethyl-amino)naphthalene, cyclotetramethylenetetranitramine, cocaine and heroin.     

Graphitic carbon nitride C6N9H3·HCl: Characterisation by UV and near-IR FT Raman spectroscopy

The graphitic layered compound C₆N₉H₃·HCl was prepared by reaction between melamine and cyanuric chloride under high pressure-high temperature conditions in a piston cylinder apparatus and characterised using SEM, powder X-ray diffraction, UV Raman and near-IR Fourier transform Raman spectroscopy with near-IR excitation. Theoretical calculations using density functional methods permitted evaluation of the mode of attachment of H atoms to nitrogen sites in the structure and a better understanding of the X-ray diffraction pattern. Broadening in the UV and near-IR FT Raman spectra indicate possible disordering of the void sites within the graphitic layers or it could be due to electron-phonon coupling effects.     

High pressure effects on liquid viscosity and glass transition behaviour,polyamorphic phase transitions and structural properties of glasses and liquids

Since the pioneering work of Bridgman it has been known that pressure affects the glass transition of polymers and liquid state viscosities. Usually the T_g and viscosity both increase as a function of pressure as expected from ‘free volume’ theories. However, H₂O provided a notable exception in that the viscosity passes through a minimum at low temperature. It was thought that this might be linked to the anomalous thermal expansion behavior. However further research on geologically important aluminosilicate liquids revealed that they could show anomalous viscosity decreases with increasing pressure and this behavior is given a structural interpretation as five-fold coordinated Si⁴⁺ and Al³⁺ species are formed. Also the existence of polyamorphism or density-driven liquid–liquid phase transitions in certain systems can lead to anomalies in the T_g or η vs. P relations. This may be the case for H₂O, for example. Current research is focusing on investigating structural changes in liquids and glasses at high pressure as the rich variety of behavior is becoming recognized. Both experimental studies and computer simulations are important as the underlying phenomonology is linked to changes in the glass or liquid structure as a function of densification.     

Water-soluble amorphous alumina-based ceramic precursors and alumosols: Structural and chemical characterization

We examined the solid-state water-soluble amorphous precursors that are formed by partial thermal decomposition of Al(NO₃)₃·9H₂O (aluminum nitrate nonahydrate: ANN) using Raman and FTIR and solid-state magic-angle spinning NMR spectroscopy. We also studied the species formed in the aqueous alumosols formed by dissolution of the pre-ceramic precursors using ²⁷Al NMR spectroscopy. Species identified in the alumosols included the Al³⁺(H₂O)₆ monomer, the [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺(Al₁₃) Keggin ion, and the Al₃₀ polycation, [Al₃₀O₈(OH)₅₆(H₂O)₂₄]¹⁸⁺, as well as various other oligomers or nanoparticles containing IV-, V- and VI-coordinated Al³⁺ ions.