2010 Vol. 23, No. 1

Article
A wide-range and phase-locked Michelson interferometer technique is described.This technique combined with femtosecond laser is used to measure the spectrum of the rare-earth ion Nd:YVO4, which presents very high signal to noise ratio of interferometric intensity output and higher spectral resolution than traditional grating spectrophotometer.
The structural and electronic properties of Li2Mg(NH)2 for hydrogen storage have been studied by first-principles calculation. The optimal unit cell parameters and the distance of N-H are determined, which are in good agreement with the experimental data. The bulk modules and the energies of zero pressure are obtained by using Murnaghan equation of states. The results show that the α-Li2Mg(NH)2 is a ground state configuration. The overlap population analysis shows that the N-Li/Mg ionic characteristics and N-H interaction of αphase are weaker than those of βphase. The valence band is dominated by the presence of N s and p states, hybridized with the H s state.
Elastic behaviors of protein-like chains are investigated by Pruned-Enriched-Rosenbluth method and modified orientation-dependent monomer-monomer interactions model. The protein-like chain is pulled away from the attractive surface slowly with elastic force acting on it. Strong adsorption interaction and no adsorption interaction are both considered. We calculate the characteristic ratio and shape factor of protein-like chains in the process of elongation. The conformation change of the protein-like chain is well depicted. The shape of chain changes from “rod” to “sphere” at the beginning of elongation. Then, the shape changes from “sphere” to “rod”. In the end, the shape becomes a “sphere” as the chain leaves away from the surface. In the meantime, we discuss average Helmoholtz free energy per bond, average energy per bond, average adsorbed energy per bond, average α-helical energy per bond, average β-sheet energy per bond and average contact energy per bond.On the other hand, elastic force is also studied. It is found that elastic force has a long plateau during the tensile elongation when there exists adsorption interaction. This result is consistent with SMFS experiment of general polymers. Energy contribution to elastic force and contact energy contribution to elastic force are both discussed. These investigations can provide some insights into the elastic behaviors of adsorbed protein chains.
The reconstructed structures of Cu(100) surface induced by O2 dissociative adsorption wereinvestigated by low energy electron diffraction and scanning tunneling microscopy. At lower oxygen coverage, it was found that two reconstructed structures, i.e. c(2×2)-O and (√2×2√2)R45°-O are coexistent. The domain size of the c(2×2)-O structure decreased with the increasing of O2 exposure. The reconstructed structure at very small coverage was also investigated and a “zigzag” structure was observed at this stage. The “zigzag” structure was identified as boundaries of local c(2×2) domains. It was found that the strip region shows much stronger molecule-substrate interaction than that of oxygen covered regions, making it a proper template for patterned organic films. The sequence of the thermal stability was found as zigzag structure>c(2×2)>(√2×2√2)R45°-O.
The effects of random long-range connections (shortcuts) on the transitions of neural firing patterns in coupled Hindmarsh-Rose neurons are investigated, where each neuron is subjected to an external current. It is found that, on one hand, the system can achieve the transition of neural firing patterns from the fewer-period state to the multi-period one, when the number of the added shortcuts in the neural network is greater than a threshold value, indicating the occurrence of in-transition of neural firing patterns. On the other hand, for a stronger coupling strength, we can also find the similar but reverse results by adding some proper random connections. In addition, the influences of system size and coupling strength on such transition behavior, as well as the internality between the transition degree of firing patterns and its critical characteristics for different external stimulation current, are also discussed.
A two dimensional model approach for the photodetachment dynamics of closed shell an-ionic systems in presence of external light field have been proposed in the context of polar environmental media. The effects of strong coupling between the solvent polarization and the extra charge in the system were studied by a simple model. The electronic states of con-cerned halide ions are represented by a two dimensional model Hamiltonian with a potential V(x,y)=-V0e-σ(x2+y2). The time dependent Fourier grid Hamiltonian method have beenused to follow the detachment process with fairly high intensities of light. The environmentaleffects on the dynamics are sought to be modeled by two different ways. The first one was the presence of polar solvents which perturb the energy levels of anionic systems by changing the effective potential surface and the second one was allowing the fluctuation of the well depth randomly to mimic the system in a more realistic view point. The average detachment rate constant is calculated as a function of important parameters of the used light field to explain the effects of solvent field on the dynamical behavior of dipole bound anionic system at least in a qualitative way.
The density functional theory on the level of B3LYP/6-31G was empolyed to study the chain growth mechanism in polymerization process of α-linear olefin in TiCl3/AlEt2Cl catalytic system to synthesize drag reduction agent. Full parameter optimization without symmetryrestrictions for reactants, products, the possible transition states, and intermediates wascalculated. Vibration frequency was analyzed for all of stagnation points on the potential energy surface at the same theoretical level. The internal reaction coordinate was calculated from the transition states to reactants and products respectively. The results showed as flloes:(i) Coordination compounds were formed on the optimum configuration of TiCl3/AlEt2Cl.(ii) The transition states were formed. The energy di?erence between transition states and the coordination compounds was 40.687 kJ/mol. (iii) Double bond opened and Ti-C(4) bond fractured, and the polymerization was completed. The calculation results also showedthat the chain growth mechanism did not essentially change with the increase of carbon atom number of α-linear olefin. From the relationship between polymerization activation energy and carbon atom number of the α-linear olefin, it can be seen that the α-linear olefin monomers with 6-10 carbon atoms had low activation energy and wide range. It was optimum to synthesize drag reduction agent by polymerization.
Based on the structure of glass (or liquid) polymers consisting of α-domain, β-co-domain, and entanglement constituent chain networks, and the nonexponentially viscoelastic behavior, a “heterophase fluctuation” model was proposed. It was found that the dynamics of cooperative rearrangement on the “fluidized domain” has a great shear rate, domain size, and temperature dependences. When the shear rate, domain size, and temperature dependences were taken account into the cooperatively localized rearrangement on the fluidized domain by the degradation of primary α-domain and the reformation of secondary β-co-domain constituent chains. A new dynamic theory of cooperatively localized rearrangement on the fluidized domain constituent chains with different size and different network chain length during physical and mechanical aging was established. The total viscoelastic free en-ergy of deformation resulting from the change in conformations of α-domain, β-co-domain, crytallite, crosslinked, and trapped entanglement constituent chains during aging processes was calculated by the combining method of kinetics and statistical mechanics. The constitu-tive equations and reduced stress relaxation modulus and creep compliances for three types of polymers were also derived. Finally, two reduced universal equations on creep compliance and stress relaxation modulus with a non-linear and two nonexponential parameters α and β were theoretically derived from the dynamic theory and a statistically extended mode coupling theory for double aging effects of polymers was developed. Results show that the two reduced universal equations have the same form as Kohlraush-Williams-Watts (K-W-W) stretched exponential function. The nonlinearity and the nonexponentiality are, respectively, originated from the memory effects of nonthermal and thermal history. The correlation of nonlinearity, α and β to the aging time, aging temperature, and the mesomorphic structure of fluidized domains was also established.
One dimensional periodic hopping model is useful to understand the motion of microscopic particles in thermal noise environment. In this research, by formal calculation and based on detailed balance, the explicit expressions of the limits of mean velocity and diffusion constant of this model as the number of internal mechanochemical sates tend to infinity are obtained.These results will be helpful to understand the limit of the one dimensional hopping model.At the same time, the work can be used to get more useful results in continuous form from the corresponding ones obtained by discrete models.
The difference of energy and electronic structure of V, Nb, and Ta in different crystalline structures were investigated by different methods in density functional theory (DFT). Latticeconstants, total energies, and densities of states of these metals were calculated using the plane-wave pseudopotential method in DFT. Results were compared with those of projector augmented wave method, CALPHAD method, and experiments. Total energy and electronic structure analyses showed that valence electrons mostly transferred from s to p or d state, changing obviously with both the crystal structure and the elemental period number from V to Ta and leading to stronger cohesion, higher cohesive energy and more stable lattice of heavier metals.
Er-doped BiVO4 composite photocatalyst was hydrothermal synthesized and characterizedby X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray Spectroscopy, X-ray photoelectron spectroscopy, and UV-Vis diffuse reflectance spectra techniques. The activity of the catalyst was determined by oxidative decomposition of methyl orange in aqueous solution under visible-light irradiation. X-ray photoelectron spectroscopy and energy-dispersive X-ray Spectroscopy analysis revealed that the doped Er existed in the form of Er2O3. It also showed that the Er doping can enhance the visible-light absorption abilities of catalysts and their visible-light-driven photocatalytic activities in comparison with those of pure BiVO4.
ZnO nanobelts, hollow microspheres, and urchins have been prepared on copper foil via a simply low temperature evaporation route. The microstructure, morphologies, and photolu-minescence of the ZnO nanostructures were studied with X-ray diffraction, Raman spectra, scanning electron microscopy and photoluminescence spectra. The width of the nanobelts was about 500 nm and the length was longer than 10μm. The diameter of the hollow microspheres was between 5 and 10μm. A possible growth mechanism of the nanobelts, microspheres and urchins was proposed. The photoluminescence spectrum exhibited strong deep level energy emissions and a weak near band edge emission. These ZnO nanostructures on a copper substrate have the advantages of naturally good adhesion and electrical connection between the ZnO nanostructures and the conductive substrate.
The role of bathophenanthroline (Bphen) as a buffer layer inserted between fullerene (C60) and Ag cathode in organic photovoltaic (OPV) cell was discussed. By introducing Bphen as a buffer layer with thicknes from 0 to 2.5 nm, the power conversion efficiency of the OPV cell based on copper phthalocyanine (CuPc) and C60 was increased from 0.87% to 2.25% under AM 1.5 solar illumination at an intensity of 100 mW/cm2, which was higher than that of bathocuproine used as a buffer layer. The photocurrent-voltage characteristics showed that Bphen effectively improves electron transport through C60 layer into Ag electrode and leads to balance charge carrier transport capability. The influence of Bphen thickness on OPV cells was also investigated. Furthermore, the absorption spectrum shows that an additional Bphen layer enhances the light harvest capability of CuPc/C60.
A La-modified Al2O3 catalyst was prepared with deposition-precipitation method. The effect of calcination temperature on the reactivity for vapor phase hydrofluorination of acetylene to vinyl fluoride. The catalysts calcined at different temperatures were characterized using NH3-TPD, pyridine-FTIR, X-ray diffraction, and Raman techniques. It was found that the calcination process could not only change the structure of these catalysts but also modify the amount of surface acidity on the catalysts. The catalyst calcined at 400 oC exhibited the highest conversion of acetylene (94.6%) and highest selectivity to vinyl fluoride (83.4%) and lower coke deposition selectivity (0.72%). The highest activity was related to the largest amount of surface acidity on the catalyst, and the coke deposition was also related to the total amount of surface acidic sites.
We developed a novel approach for the preparation of N-doped TiO2 photocatalysts by calcining ammonium titanium oxalate at different temperatures. The structures of N-TiO2 were characterized by powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, diffuse reflectance UV-Vis spectroscopy, and scanning electron microscope. The N-doped TiO2 photocatalysts calcined below 700 oC are the pure anatase phase but that calcined at 700 oC is a mixture of anatase and rutile phases. The doped N locates at the interstitial site of TiO2 which leads to the narrowing of bad gap of pure anatase N-TiO2. Among all photocatalysts, N-TiO2 photocatalysts calcined at 600 and 400 oC exhibit the best performance in the photodegradation of methyl orange under the UV light and all-wavelength light illuminations, respectively; however, because of the perfect crystallinity and the existence of anatase-rutile phase junctions, N-TiO2 photocatalyst calcined at 700 oC exhibits the highest specific photodegradation rate, i.e., the highest quantum yield, under both the UV light and all-wavelength light illuminations.
Rhombus-like SmCO3OH microplates with the edge lengths ranging from 5 μm to 10 μm and the thickness about 1.5 μm were synthesized through a simple hydrothermal method using urea as the precipitance. The structure and properties of the rhombus-like SmCO3OH microplates were characterized by X-ray diffraction, field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The optical property of the rhombus-like SmCO3OH microplates doped with Eu3+ was investigated by photoluminescence. A broad and strong emission band at 677 nm was obtained, which can be contributed to producing light conversion film.
The miscibility and crystallization of solution casting biodegradable poly(3-hydroxybuty-rate)/poly(ethylene succinate) (PHB/PES) blends was investigated by differential scanning calorimetry, rheology, and optical microscopy. The blends showed two glass transition temperatures and a depression of melting temperature of PHB with compositions in phase diagram, which indicated that the blend was partially miscible. The morphology observation supported this result. It was found that the PHB and PES can crystallize simultaneously or upon stepwise depending on the crystallization temperatures and compositions. The spherulite growth rate of PHB increased with increasing of PES content. The influence of compositions on the spherulitic growth rate for the partially miscible polymer blends was discussed.
TiO2 nanotube arrays (TNTs) electrode loaded with Zn nanoparticles was prepared by anodization and the size of Zn nanoparticle loaded on TNTs electrode was controlled bychronoamperometry deposition time. Results of SEM and XRD analysis show that Zn nanoparticles had a diameter of about 15-25 nm when the deposition time was 3-5 s. The UV-Vis diffuse reflectance spectra show the Zn loaded harvest light with 480-780 nm more effectively than the unloaded sample. The photocurrent response of Zn loaded TNTs electrodes were studied, the results showed that TNTs electrodes loaded with Zn nanoparti-cles has 50% increased photocurrent response under high-pressure mercury lamp irradiation compared with unloaded TNTs electrode.
A small shielding effect on the hydrogen atoms of chiral carbons of β-cyclodextrin (β-CD) was detected by 1H nuclear magnetic resonance, but a large environmental change of the chiral carbon atoms at high concentration ratios of lithium carbonate (Li2CO3) to β-CD was observed by polarimetry in aqueous solution. These findings urged us to investigate whether different formation conditions of the molecule-ion system between Li2CO3 and β-CD in solid state were involved in different spectral performances. To answer the question, we prepared three adducts of Li2CO3 to β-CD, i.e., samples 1, 2, and 3, by magnetic stirring, solvothermal and grinding conditions, respectively. Powder X-ray diffraction and Fourier transformation infrared spectroscopy provided the information of formation of the three molecule-ion adducts. Besides, scanning electron microscope images provided different surface information of the three adducts. Further, significant spectral differences in thermal behavior of these adducts were found by thermogravimetry and derivative thermogravimetry.