Synthesis of copper nanoparticles catalyzed by pre-formed silver nanoparticles

Synthesis of well dispersed copper nanoparticles was achieved by reduction of copper nitrate in aqueous solution using hydrazine monohydrate as a reducer in the presence of preformed silver nanoparticles as catalysts. It has been demonstrated that addition of silver nanoparticles to the reaction mixture leads to formation of aqueous dispersion of copper nanoparticles and also results in a drastic reduction in reaction time compared to procedures reported in the literature. The absorption spectrum of the dispersions, HR-TEM and STEM images and XRD pattern indicate the formation of copper nanoparticles with particle size in the range of 5–50 nm.     

Frequency conversion in novel materials and its application to high resolution gas sensing

We have constructed a compact room-temperature mid-infrared spectrometer and gas sensor, based on quasi-phase matched difference-frequency generation in periodically poled ferroelectric crystals of the KTiOPO₄ family, namely: KTiOPO₄, KTiOAsO₄ and RbTiOAsO₄. The wide tunabilty of the spectrometer (3.1–3.75 μm) enables us to cover an entire vibrational band of gases such as methane and nitrous oxide. The high spectral resolution (1 MHz) is used to investigate the spectral profile of the hyperfine components of a single rotational transition. The sensitivity of the described spectrometer is 75 parts per million. Applications of this technology include the detection of polluting or toxic gases, biomedical sensing, atmospheric research, volcanic monitoring and industrial process control.     

Hyperfine Parameters for Muonium in Copper (I), Silver (I) and Cadmium Oxides

Muonium centres in Cu₂O, Ag₂O and CdO show hyperfine parameters spanning four orders of magnitude. They exemplify the three different categories of hydrogen defect centre in semiconducting and dielectric solids, with very different electronic structure and electrical activity, namely quasi-atomic (possibly deep acceptor), deep donor and shallow donor.     

关于Z^＊积分

我们曾在［１］中讨论了强导数及其引出的若干积分，本文进一步研究其中的Ｚ＊积分，并给出Ｚ＊可积的充分必要条件。     

La2-xSrxCu1-yZnyO4: Tc and ns/m* correlations seen with muon spin rotation

We report the muon spin rotation experiments on Zn substituted La_1-x Sr_x CuO₄, for four zinc concentrations y=0.0,0.0025,0.005,0.01, at strontium concentrations x=0.15,0.20. We find that T_ c in the optimally doped (x=0.15) and overdoped (x=0.20) 2:1:4 decreases linearly with increasing zinc concentration. Plotted against the planar zinc concentration, the T_c’s of both series seem to fall on the same line. The superconducting carrier density/effective mass ratio, n_ s/m^*, at first decreases linearly, rising above this line for higher zinc concentrations. This behavior may result from the localization of carriers in an area \xi_ab around each zinc atom. This revised version was published online in August 2006 with corrections to the Cover Date.     

Spin frustration in Y(Sc)Mn2

The relaxation rate of muon polarization of Y_0.97Sc_0.03Mn₂ with a magnetic lattice composed of corner‐shared tetrahedrons shows a broad peak around 2.5 K indicating a random spin freezing at low temperatures. The substitution by nonmagnetic Al atoms for 10% Mn atoms raises the spin freezing temperature to 45 K. The present work shows clearly that due to the strong geometrical frustration, the ground state of the system is singlet tetrahedrons mixed with frozen paramagnetic tetrahedrons. This revised version was published online in July 2006 with corrections to the Cover Date.     

Muon spin relaxation investigation of frustrated antiferromagnetic pyrochlores A2B2O7

In a system where magnetic ions occupy the vertices of edge or corner sharing triangular units, the natural antiferromagnetic coupling between ions is geometrically frustrated. A wide variety of interesting magnetic behaviour has been observed in pyrochlores, where magnetic ions form a network of corner sharing tetrahedra. The low temperature spin dynamics of a number of pyrochlores A₂B₂O₇ have been investigated using the technique of μ SR. For example, Y₂Mo₂O₇ shows a transition to a disordered magnetic state similar to a spin glass at T_F=22 K. However, unlike conventional metallic spin glasses, a non‐zero muon spin depolarization rate is observed to persist well below 0.1\ T_F. These results suggest that there is a finite density of states for magnetic excitations in this system near zero energy. This revised version was published online in July 2006 with corrections to the Cover Date.     

μ+SR study of two-dimensional antiferromagnets,delafossite-type compounds

⁺SR experiments were performed on delafossite-type compounds, CuCrO₂, AgCrO₂, CuFeO₂, which are model compounds of triangular lattice antiferromagnets. The initial asymmetries are much smaller than the expected value, implying muonium formation. The time spectra are composed of slow andfast relaxation components. We attributed the components to signals from ⁺ stopped at the center of O^2– ions andmuonium far from nuclear dipole moments, respectively. The asymmetries decrease belowT _N but no precession spectra were observed. Relaxation rates of slow andfast relaxation components show maxima atT _N.     

Neutral and ionic dissociation patterns in hexacoordinate silicon chelates: a model nucleophilic substitution at pentacoordinate silicon

A model nucleophilic-displacement reaction coordinate at pentacoordinate silicon is demonstrated by neutral and ionic dissociation equilibria through a stable hexacoordinate complex.     

Harborth constants for certain classes of metacyclic groups

The Harborth constant of a finite group $G$ is the smallest integer $k\ge exp\left(G\right)$ such that any subset of $G$ of size $k$ contains $exp\left(G\right)$ distinct elements whose product is 1. Generalizing previous work on the Harborth constants of dihedral groups, we compute the Harborth constants for the metacyclic groups of the form $H_{n,m}=〈x,y\mid x^n=1,y^2=x^m,yx=x^{?1}y〉$. We also solve the “inverse” problem of characterizing all smaller subsets that do not contain $exp\left(H_{n,m}\right)$ distinct elements whose product is 1.