Site symmetry dependence of repulsive interactions between chemisorbed oxygen atoms on Pt{100}-(1×1)

[[abstract]]Ab initio total energy calculations using density functional theory with the generalized gradient approximation have been performed for the chemisorption of oxygen atoms on a Pt$100%-~131! slab. Binding energies for the adsorption of oxygen on different high-symmetry sites are presented. The bridge site is the most stable at a coverage of 0.5 ML, followed by the fourfold hollow site. The atop site is the least stable. This finding is rationalized by analyzing the ‘‘local structures’’ formed upon oxygen chemisorption. The binding energies and heats of adsorption at different oxygen coverages show that pairwise repulsive interactions are considerably stronger between oxygen atoms occupying fourfold sites than those occupying bridge sites. Analysis of the partial charge densities associated with Bloch states demonstrates that the O–Pt bond is considerably more localized at the bridge site. These effects cause a sharp drop in the heats of adsorption for oxygen on hollow sites when the coverage is increased from 0.25 to 0.5 ML. Mixing between oxygen p orbitals and Pt d orbitals can be observed over the whole metal d-band energy range.[[notice]]補正完畢[[journaltype]]國內[[booktype]]紙

Variational formulas of higher order mean curvatures

In this paper, we establish the first variational formula and its Euler-Lagrange equation for the total $2p$-th mean curvature functional $\mathcal {M}_{2p}$ of a submanifold $M^n$ in a general Riemannian manifold $N^{n+m}$ for $p=0,1,...,[\frac{n}{2}]$. As an example, we prove that closed complex submanifolds in complex projective spaces are critical points of the functional $\mathcal {M}_{2p}$, called relatively $2p$-minimal submanifolds, for all $p$. At last, we discuss the relations between relatively $2p$-minimal submanifolds and austere submanifolds in real space forms, as well as a special variational problem.Comment: 13 pages, to appear in SCIENCE CHINA Mathematics 201

Application of Instantons: Quenching of Macroscopic Quantum Coherence and Macroscopic Fermi-Particle Configurations

Starting from the coherent state representation of the evolution operator with the help of the path-integral, we derive a formula for the low-lying levels $E = \epsilon_0 - 2\triangle\epsilon cos (s+\xi)\pi$ of a quantum spin system. The quenching of macroscopic quantum coherence is understood as the vanishing of $cos (s+\xi)\pi$ in disagreement with the suppression of tunneling (i.e. $\triangle\epsilon = 0$) as claimed in the literature. A new configuration called the macroscopic Fermi-particle is suggested by the character of its wave function. The tunneling rate ($(2\triangle\epsilon)/(\pi)$) does not vanish, not for integer spin s nor for a half-integer value of s, and is calculated explicitly (for the position dependent mass) up to the one-loop approximation.Comment: 13 pages, LaTex, no figure

Graded reflection equation algebras and integrable Kondo impurities in the one-dimensional t-J model

Integrable Kondo impurities in two cases of the one-dimensional $t-J$ model are studied by means of the boundary ${\bf Z}_2$-graded quantum inverse scattering method. The boundary $K$ matrices depending on the local magnetic moments of the impurities are presented as nontrivial realizations of the reflection equation algebras in an impurity Hilbert space. Furthermore, these models are solved by using the algebraic Bethe ansatz method and the Bethe ansatz equations are obtained.Comment: 14 pages, RevTe

Tuning magnetic anisotropy of epitaxial Ag/Fe/Fe0.5Co0.5/MgO(001) films

Single crystalline Ag/Fe/Fe0.5Co0.5/MgO(001) films were grown by Molecular Beam Epitaxy and investigated by Magneto-Optic Kerr Effect (MOKE). We find that even though the 4-fold magnetic anisotropies of Ag/Fe/MgO(001) and Ag/Fe0.5Co0.5/MgO(001) films are different from the corresponding bulk values, their opposite signs allow a fine tuning of the 4-fold magnetic anisotropy in Ag/Fe/Fe0.5Co0.5/MgO(001) films by varying the Fe and Fe0.5Co0.5 film thicknesses. In particular, the critical point of zero anisotropy can be achieved in a wide range of film thicknesses. Using Rotational MOKE, we determined and constructed the anisotropy phase diagram in the Fe and Fe0.5Co0.5 thickness plane from which the zero anisotropy exhibits a linear relation between the Fe and Fe0.5Co0.5 thickness

Baryon content and dynamic state of galaxy clusters: XMM-Newton observations of A1095 and A1926

We have initiated a program to study the baryon content and dynamic state of galaxy clusters. Here we present results primarily from XMM-Newton observations of two optically-selected galaxy clusters, A1095 ($z \simeq 0.210$) and A1926 ($z \simeq 0.136$). We find that both of them are actually cluster pairs at similar redshifts. We characterize the temperatures of these individual clusters through X-ray spectral fits and then estimate their gravitational masses. We show a rich set of substructures, including large position offsets between the diffuse X-ray centroids and the brightest galaxies of the clusters, which suggests that they are dynamically young. For both A1095 and A1926, we find that the mass required for the cluster pairs to be bound is smaller than the total gravitational mass. Thus both cluster pairs appear to be ongoing major mergers. Incorporating SDSS and NVSS/FIRST data, we further examine the large-scale structure environment and radio emission of the clusters to probe their origins, which also leads to the discovery of two additional X-ray-emitting clusters ($z \simeq 0.097$ and $z \simeq 0.147$) in the field of A1926. We estimate the hot gas and stellar masses of each cluster, which compared with the expected cosmological baryonic mass fraction, leave ample room for warm gas.Comment: 21 pages, 12 figures, MNRAS accepte

High Performance Chinese OCR Based on Gabor Features, Discriminative Feature Extraction and Model Training

We have developed a Chinese OCR engine for machine printed documents. Currently, our OCR engine can support a vocabulary of 6921 characters which include 6707 simplified Chinese characters in GB2312-80, 12 frequently used GBK Chinese characters, 62 alphanumeric characters, 140 punctuation marks and symbols. The supported font styles include Song, Fang Song, Kat, He, Yuan, LiShu, WeiBei, XingKai, etc. The averaged character recognition accuracy is above 99% for newspaper quality documents with a recognition speed of about 250 characters per second on a Pentium III-450 MHz PC yet only consuming less than 2 MB memory. We describe the key technologies we used to construct the above recognizer. Among them, we highlight three key techniques contributing to the high recognition accuracy, namely the use of Gabor features, the use of discriminative feature extraction, and the use of minimum classification error as a criterion for model training.published_or_final_versio