Effects of composition on catalytic activities of molybdenum doped platinum nanoparticles

The physical and chemical properties of bimetallic nanoparticles can be optimized by tuning the particle composition. In this study, we identified CO adsorption and dissociation energetics on five Pt-Mo nanoparticles at different concentrations, the lowest energy Pt₇, Pt₆Mo, Pt₅Mo₂, Pt₄Mo₃, and Mo₇ clusters. We have shown that the CO adsorption and dissociation energies and preferred CO adsorption sites are largely dependent on the composition of the nanoparticles. As the Mo concentration increases, the strength of the C-O internal bond in the adsorption complex decreases, as indicated by a decrease in the C-O stretching frequency. Also, more Mo sites in the nanoparticle become available for CO adsorption, and the preferred CO adsorption site switches from Pt to Mo. For these reasons, dissociation of CO is energetically favorable on Pt₄Mo₃ and Mo₇. On both compositions, we have shown that the dissociation paths begin with CO adsorbed on a Mo site in a multifold configuration, in particular in a tilted configuration. These findings provide insight on the effects of the composition on the chemical and catalytical properties of Pt-Mo nanoparticles, thereby guiding future experiments on the synthesis of nanoparticles, especially those that may be suitable for various desired applications containing CO.     

Reactions of aldehyde with collagen: a DFT study

Structural Chemistry - The reaction mechanisms of several amino acids (Asn, Gln, Arg, His, and Lys) in the collagen with aldehyde were studied using density functional theory method. Based on the...     

Real-time phase-resolved functional optical coherence tomography by use of optical Hilbert transformation

We have developed a novel real-time phase-resolved functional optical coherence tomography system that uses optical Hilbert transformation. When we use a resonant scanner in the reference arm of the interferometer, with an axial scanning speed of 4 kHz, the frame rate of both structural and Doppler blood-flow imaging with a size of 100 by 100 pixels is 10 Hz. The system has high sensitivity and a larger dynamic range for measuring the Doppler frequency shift that is due to moving red blood cells. Real-time images of in vivo blood flow in human skin obtained with this interferometer are presented.     

Zinc-ion implanted and deposited titanium surfaces reduce adhesion of Streptococccus mutans

While titanium (Ti) is a commonly used dental implant material with advantageous biocompatible and mechanical properties, native Ti surfaces do not have the ability to prevent bacterial colonization. The objective of this study was to evaluate the chemical composition and bacterial adhesive properties of zinc (Zn) ion implanted and deposited Ti surfaces (Zn-PIIID-Ti) as potential dental implant materials. Surfaces of pure Ti (cp-Ti) were modified with increasing concentrations of Zn using plasma immersion ion implantation and deposition (PIIID), and elemental surface compositions were characterized by X-ray photoelectron spectrometry (XPS). To evaluate bacterial responses, Streptococcus mutans were seeded onto the modifiedTi surfaces for 48 h and subsequently observed by scanning electron microscopy. Relative numbers of bacteria on each surface were assessed by collecting the adhered bacteria, reculturing and counting colony forming units after 48 h on bacterial grade plates. Ti, oxygen and carbon elements were detected on all surfaces by XPS. Increased Zn signals were detected on Zn-PIIID-Ti surfaces, correlating with an increase of Zn-deposition time. Substantial numbers of S. mutans adhered to cp-Ti samples, whereas bacterial adhesion on Zn-PIIID-Ti surfaces signficantly decreased as the Zn concentration increased (p < 0.01). In conclusion, PIIID can successfully introduce Zn onto a Ti surface, forming a modified surface layer bearing Zn ions that consequently deter adhesion of S. mutans, a common bacterium in the oral environment.     

Highly efficient photoluminescence of Er2SiO5 films grown by reactive magnetron sputtering method

E₂SiO₅ thin films were fabricated on Si substrate by reactive magnetron sputtering method with subsequent annealing treatment. The morphology properties of as-deposited films have been studied by scanning electron microscope. The fraction of erbium is estimated to be 23.5 at% based on Rutherford backscattering measurement in as-deposited Er-Si-O film. X-ray diffraction measurement revealed that Er₂SiO₅ crystalline structure was formed as sample treated at 1100 °C for 1 h in O₂ atmosphere. Through proper thermal treatment, the 1.53 μm Er³⁺-related emission intensity can be enhanced by a factor of 50 with respect to the sample annealed at 800 °C. Analysis of pump-power dependence of Er³⁺ PL intensity indicated that the upconversion phenomenon could be neglected even under a high photon flux of 10²¹(photons/cm²/sec). Temperature-dependent photoluminescence (PL) of Er₂SiO₅ was studied and showed a weak thermal quenching factor of 2. Highly efficienct photoluminescence of Er₂SiO₅ films has been demonstrated with Er³⁺ concentration of 10²²/cm³, and it opens a promising way towards future Si-based light source for Si photonics.     

Frequency splitting phenomenon of dual transverse modes in a Nd:YAG laser

We observed frequency splitting phenomenon of dual transverse modes (TEM_00q and TEM_01q) in a Nd:YAG microchip standing wave laser utilizing intracavity stress birefringence effects. Four resonance frequencies (ν_00qe, ν_00qo, ν_01qe, and ν_01qo, respectively) were produced and tuned by changing the diametral compression force applied on the laser crystal. The transverse mode frequency spacing for the same longitudinal mode number (Δν_trans) was 1.16 GHz, and the magnitude of frequency splitting (Δν) ranged from 0 MHz to 1.16 GHz. Based on this phenomenon, a four-mode differential standing wave laser, whose signal characteristics were a little like those of a four-mode differential travelling wave laser gyro however with a much larger frequency splitting range, was produced. The theoretical analysis is in good agreement with the experimental results. This phenomenon not only can be used to make lasers with two or more frequency differences, but also can be used to make high-resolution self-sensing laser sensors (e.g. laser force sensors and laser accelerometers).     

Criteria for Separability of Multipartite Quantum System

We first present the Hamel base of the density operator space for multipartite quantum system, and thus establish a representation of density matrix. Moreover, according to the structure of the density matrix for multipartite quantum system, we present two necessary criteria for separability of multipartite quantum system of arbitrary dimensions.     

Growth of high-quality ZnO thin films on (11\bar{2}0) a-plane sapphire substrates by plasma-assisted molecular beam epitaxy

High-quality ZnO thin films were grown on a-plane sapphire substrates by plasma-assisted molecular beam epitaxy. X-ray diffraction and transmission electron microscopy reveal that the ZnO films have high structural quality and an atomically sharp ZnO/Al₂O₃ interface. The full width at half maximum values of the 0002 and $30\bar{3}2$ ZnO ω-rocking curves are 467.8 and 813.5 arc sec for a 600 nm thick ZnO film. A screw dislocation density of 4.35×10⁸ cm^?2 and an edge dislocation density of 3.38×10⁹ cm^?2 are estimated by X-ray diffraction. The surface of the ZnO epilayers contains hexagonal pits, which can be observed in the Zn-polar ZnO. The films have a resistivity of 0.119 Ω?cm, an electron concentration of 6.85×10¹⁷ cm^?3, and a mobility of 76.5 cm²?V^?1?s^?1 at room temperature. Low temperature photoluminescence measurements show good optical properties comparable to ZnO single crystals.     

艾纳香中黄酮化合物的研究

从中药艾纳香(Blumea balsamifera DC)中分离得到两种新的黄酮化合物,应用NMR、MS、IR、UV等波谱数据,确定其化学结构为3,5,3'-三羟基-7,4'-二甲氧基黄酮(Ⅰ)和3,5,3',4'-四羟基-7-甲氧基黄酮(Ⅱ).     

Generalization of Drinfeld Quantum Affine Algebras

Drinfeld gave a current realization of the quantum affine algebras as a Hopf algebra with a simple comultiplication for the quantum current operators. In this Letter, we will present a generalization of such a realization of quantum Hopf algebras. As a special case, we will choose the structure functions for this algebra to be elliptic functions to derive certain elliptic quantum groups as a Hopf algebra, which degenerates into quantum affine algebras if we take certain degeneration of the structure functions.