SuperW n gravity on compactified moduli space

We study the divergent behavior ofW gravity theories. As a tool, we use the Grothendieck-Riemann-Roch theorem on the compactified moduli space. We show thatW _n gravity has severe divergences caused by negative masses. However, for superextension ofW _n gravity the divergences by negative masses are miraculously cured by the counterpart contribution of superpartners.     

A false color image fusion method based on multi-resolution color transfer in normalization YCBCR space

In this paper, a false color image fusion method for merging visible and infrared images is proposed. Firstly, the source images and reference image are decomposed respectively by Laplacian pyramid transform. Then the grayscale fused image and the difference images between the normalized source images are assigned to construct YC_BC_R components. In the color transfer step, all the three channels of the color space in each decomposition level are processed with the statistic color mapping according to the color characteristics of the corresponding sub-images of the reference image. Color transfer is designed based on the multi-resolution scheme in order to significantly improve the detailed information of the final image, and to reduce excessive saturation phenomenon to have a comparatively natural color appearance compared with the classical global-coloring algorithm. Moreover, the differencing operation between the normalized source images not only provides inter-sensor contrast to make popping the potential targets but also weakens the influence of the ambient illumination variety to a certain degree. Finally, the fused results and several metrics for evaluation of fused images subjectively and objectively illustrate that the proposed color image fusion algorithm can yield a more complete mental representation of the perceived scene, resulting in better situational awareness.     

Crystal chemistry of the Tl2−xBa2Ca n Cu n+1O2n+6 (n=0, 1, 2) high-T c superconductors

We report on a comparative crystal chemical study of the Tl_2–xBa₂Ca _n Cu _n+1O_2n+6(n=0, 1, 2) high-T _c superconductors. Superconducting properties were determined by DC-conductivity and-susceptibility measurements. An X-ray diffraction analysis reveals the nonstoichiometry of the compounds as a link between structural and superconducting behavior. A comparison of the different structures gives evidence that T1 deficiency in the TlO double layers increases with increasingn; this deficiency causes apparent Cu valences larger than 2+in the superconducting phases thus maintaining the charge balance. By extracting appropriate chemical formulas and performing a bond strength calculation we obtained the mixed-valent oxidation state of copper for the superconducting tetragonal phases as being 2.17+(n=0), 2.25+(n=1) and 2.31+(n=2) respectively; for the non-superconducting orthorhombic phase Tl_2–xBa₂CuO_6–y a Cu valence of about 2+is suggested.     

Additivity and non-additivity of dissociation energies in intermolecular interactions. Theoretical studies on (H2)n,n = 2-8, (CO2)n,n = 2-6 and (HF)n,n = 2-8

CCSD(T) and MP2 results using the aug-cc-pV5Z basis set are reported for chain, cyclic and other structures of the clusters (H₂)_n, n?=?2-8, (CO₂)_n, n?=?2-6 and (HF)_n, n?=?2-8. In chain-like structures of (H₂)_n and (CO₂)_n, with the bonding type of the dimer maintained, the dissociation energy D_e of the dimer doubles for the trimer, triples for the tetramer, and so on. Due to these systems being dominated by short-range forces, interactions are essentially restricted to neighbouring monomers. For other types of (H₂)_n and (CO₂)_n structures, the multipliers relative to the dimerisation energy can be much higher. Dissociation energies for the hexamers in S₆ symmetry of both H₂ (379?cm^?1) and CO₂ (4925?cm^?1) are over ten times the respective dimerisation energies. For the chain-like trimer of HF, however, D_e is in excess of double the dimer value. Mainly due to longer-range dipolar forces, the interactions reach beyond the neighbouring monomers. The interaction energy between HF monomers in chains follows an approximate R^?2 (R being the F–F distance) relationship, The calculated dissociation energies of the HF octamer are 15,985?cm^?1 (factor of 10.4) for the chain, and 21,003?cm^?1 (factor of 13.7) for the C_6h cyclic structure.     

Structural and magnetic properties of Ni<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 2–21) clusters

Extensive studies of structural and magnetic properties of pure Ni _n (n=2–21) clusters are carried out using density functional theory with generalized gradient approximation. A new structural growth pattern is reported and the icosahedron sequence is not the global minima structures for size n < 16. The evolution pattern of Ni₅–Ni₁₀ clusters is based on square pyramid. For cluster between n = 9 and n = 14, structures of them are trilayered stacking pattern. Especially for Ni₁₃, it seriously deviates from icosahedral pattern which was frequently assumed in previous studies. Ni₁₀, Ni₁₃ and Ni₁₄ are pieces of a double tetrahedron. For cluster size larger than 16, icosahedron based configurations are found to be the dominative structure pattern with exception of Ni₁₉. But trilayered structure is a strong competitor due to small difference in energy between this pattern and icosahedral family. The comparison of magnetic behavior between the calculations and experimental results are conducted. The average coordination mainly dominates on the magnetic behavior in the size range we considered.     

A novel double-recessed 4H-SiC MESFET with partly undoped space region

In this paper, a novel double-recessed 4H-SiC metal semiconductor field effect transistor (MESFET) with partly undoped space region (DRUS-MESFET) is introduced. The key idea in this work is to improve the DC and RF characteristics of the device by introducing an undoped space region. Using two-dimensional and two-carrier device simulation, we demonstrate that breakdown voltage (V_BR) increases from 109 V in conventional double recessed MESFET (DR-MESFET) structure to 144.5 V in the DRUS-MESFET structure due to the modified channel electric field distribution of the proposed structure. The maximum output power density of the DRUS-MESFET structure is about 25.4% larger than that of the DR-MESFET structure. Furthermore, lower gate-drain capacitance (C_GD), higher cut-off frequency (f_T), larger maximum available gain (MAG), and higher maximum oscillation frequency (f_max) are achieved for the DRUS-MESFET structure. The results show that the f_max and f_T of the proposed structure improve 95.6% and 13.07% respectively, compared with that of the DR-MESFET structure. Also, the MAG of the DRUS-MESET is 4.5 dB higher than that of the DR-MESFET structure at 40 GHz. The results show that the DRUS-MESFET structure has superior electrical characteristics and performances in comparison with the DR-MESFET structure.     

T-duality as permutation of coordinates in double space

We introduce the 2D dimensional double space with the coordinates Z~M=(x~μ,y_μ),whose components are the coordinates of initial space x~μ and its T-dual y_μ.We shall show that in this extended space the T-duality transformations can be realized simply by exchanging the places of some coordinates x~a,along which we want to perform T-duality,and the corresponding dual coordinates y_a.In such an approach it is evident that T-duality leads to the physically equivalent theory and that a complete set of T-duality transformations forms a subgroup of the 2D permutation group.So,in double space we are able to represent the backgrounds of all T-dual theories in a unified manner.     

Testing CIELAB-based color-difference formulae using large color differences

Three advanced CIELAB-based color-difference formulae, CMC, CIE94, and CIEDE2000, together with the basic CIELAB equation, were tested using large color-difference visual data (maximum average size was 12 CIELAB ΔE units) produced in this study. The color-difference comparison experiment was carried out at CIE Gray and Blue centers by a panel of 6 normal color-vision observers using CRT-generated stimuli based on the psychophysical method of constant stimuli. The experimental data, processed via probit analysis, were well fitted to chromaticity ellipses with a high reliance according to the observer accuracy in terms ofPF/3 measure. A detailed comparison was performed to analyze the agreement between predicted color differences from all formulae and their corresponding visual scales in all measurement planes of CIELAB space. The results show that the CIEDE2000 marginally outperformed the others at all color centers while CIE94 was the worst in original formulae or with optimizedk _L value, but the CIELAB performed worst when the parametric factors ofk _L,k_c, andk _H were all optimized, with the CMC always lying between these extremes.     

幻数尺寸Li-n-1,Lin,Li+ n+1(n=20,40)团簇的几何结构、电子与光学性质的第一性原理研究

基于密度泛函理论,采用第一性原理分子动力学模拟退火方法,对Li^-_n-1,Li_n,Li⁺_n+1 (n=20,40)的最低能量结构进行了全局搜索. 发现锂团簇的生长模式是以单个或多个嵌套的正多面体为核心,其余原子以五角锥为基本单元围绕核心生长. 基于最低能量结构的第一性原理电子结构计算得到锂团簇的分子轨道能级分布与无结构凝胶模型给出的电子壳层完全一致. 在总电 关键词： 团簇 电子结构 极化率 光吸收     

Spectroscopic studies of real space indirect symmetric GaAs/AlAs short period superlattices

The band structure and the optical transitions of symmetric ultra-short period (GaAs) _m /(AlAs) _n superlattices (n=m is the number of monolayers) have been studied using different spectroscopic techniques, namely photoacoustic spectroscopy, reflectivity and luminescence, photoluminescence excitation and high excitation intensity time-resolved luminescence. Direct observation of the transition from type I to type II energy band alignment is reported for superlattices whose configuration consists of more than 12 monolayers (i.e. m=n>12). The radiative recombination processes associated with the real space indirect transitions have been investigated as a function of the density of photogenerated electron-hole pairs, revealing an unusual density-dependent behaviour. A tentative interpretation in terms of a condensed electron-hole state at the indirect gap is given, which accounts for the long decay time of the type II luminescence at high excitation rate.     

基于多光谱和sRGB空间的自然植物色的重现

多光谱成像技术在颜色科学方面的应用主要在于准确的记录和复制拍摄场景的颜色信息。针对目前基于光谱的颜色重现设备昂贵、复杂和实现起来困难的问题,提出了物体颜色从反射光谱空间向sRGB颜色空间变换的方案。在遵循sRGB标准的设备上重现了D65光源下的218种自然植物颜色,所显示的颜色与植物反射光谱实物对应的名称一致。对8个自然植物在9种不同光源下和在sRGB空间下的颜色进行了预测显示。所提出的方案对在网络环境下实现相同实物在不同照明环境下的场景显示提供了可行的途径。     

Algebra of Screening Operators for the Deformed W n Algebra

We construct a family of intertwining operators (screening operators) between various Fock space modules over the deformed W _n algebra. They are given as integrals involving a product of screening currents and elliptic theta functions. We derive a set of quadratic relations among the screening operators, and use them to construct a Felder-type complex in the case of the deformed W ₃ algebra. Received: 3 March 1997 / Accepted: 20 May 1997     

基于HSI颜色空间的彩色边缘检测方法研究

针对在RGB空间中很难有效区分颜色相似性的问题,通过选择更加符合颜色视觉特性的HSI颜色空间进行图像处理与分析,提出了一种新的色差度量方法,在此基础上设计了一种彩色边缘检测方法。首先计算色度、饱和度、亮度等三个分量的边缘信息,然后对三个分量进行加权得到彩色边缘信息,通过非极大值抑制和阈值选取后,得到彩色图像的边缘。实验结果表明,该方法可以充分利用彩色图像的色度、饱和度和亮度信息来有效地检测彩色边缘。     

Geometry of the submanifoldsESX n . III. Parallelism inESX n and its submanifolds

A connection which is both Einstein and semisymmetric is called anES connection. And a generalizedn-dimensional Riemannian manifold on which the differential geometric structure is imposed byg through anES connection, is called ann-dimensionalES manifold and denoted byESX _n . This paper is the third part of a systematic study of the submanifoldsX _m ofESX _n . In the first part, we introduced a new concept of theC-nonholonomic frame of reference inESX _n at points ofX _m and dealt with its consequences. In the second part, the generalized fundamental equations on a hypersubmanifold ofESX _n were derived as an application of theC-nonholonomic frame of reference. The purpose of the present paper is to study parallelism inESX _n and in its submanifoldX _m , using theC-nonholonomic frame of reference and the new concept ofES _i curves.     

Symplectic structure of the moduli space of flat connection on a Riemann surface

We consider the canonical symplectic structure on the moduli space of flatg-connections on a Riemann surface of genusg withn marked points. Forg being a semisimple Lie algebra we obtain an explicit efficient formula for this symplectic form and prove that it may be represented as a sum ofn copies of Kirillov symplectic form on the orbit of dressing transformations in the Poisson-Lie groupG ^* andg copies of the symplectic structure on the Heisenberg double of the Poisson-Lie groupG (the pair (G, G ^*) corresponds to the Lie algebrag).Supported by Swedish Natural Science Research Council (NFR) under the contract F-FU 06821-304Supported in part by a Soros Foundation Grant awarded by the American Physical Society     

Theoretical investigation of selected hydrogenated germanium clusters (Ge5Hn,n = 0–12) from density functional theory calculations

ABSTRACT

We reported the selected hydrogen absorption of Ge₅H_n isomers and their Ge₅H_n^? anions in the size range of n?=?0–12 for the first time by B3LYP, BPW91, BHandHLYP and BP86 methods in combination with 6-311++G** basis sets. The optimum geometrical structure, relative stability, electronic properties and dissociation behaviour of Ge₅H_n (n?=?0–12) cluster and their Ge₅H_n^? anions were systematically analysed by a series of methods and can be applied to the study of more complex cluster systems. H bridged structure and double H bridged structures were found in the size range of n?=?1–6 in neutral clusters and corresponding anion with triangular bipyramidal framework of Ge₅. The visible odd-even oscillations were observed in the study of change rules with increasing size from the Δ₂E(n), H-dissociation energy (De), HOMO–LUMO band-gap (E_gap) and electron affinity (EA) energy. This conclusion indicated that Ge₅H_n clusters with even H atoms were more stable than clusters with odd H atoms. The infrared spectra of the Ge₅H_n (n?=?0–12) clusters were also simulated which will further stimulate study on germanium-based nanomaterials.     

Distributions on Minkowski space and their connection with analytic representations of the conformal group

Unitary analytic representations of the conformal group are relized on Hilbert spaces of holomoprhic or antiholomorphic functions over a tube domain in complex Minkowski space. The distributional boundary values of these functions are tempered distributions on real Minkowski space. The representations are characterized by an integral scale dimension labeln and two spin labelsj ₁ andj ₂. The connection between the dimensionn and the degree of singularity of the tempered distribution is investigated. We propose an application to inclusive reactions of elementary particles.     

CIELAB与CIECAM02色空间均匀性比较研究

采用均匀色空间Munsell系统检验和验证了CIELAB和色貌模型CIECAM02色空间的均匀性。利用Mun- sell色卡所对应的三刺激值X,Y,Z作为模型的输入值,预测色空间模型的明度、彩度和色调,并通过预测结果比较和检验了CIELAB色空间和CIECAM02模型色空间的均匀性。研究表明:在预测明度方面,两个色空间的结果相似;在预测彩度时,CIECAM02模型较好于CIELAB色空间;在预测色调时,当色调逐渐从BG变化到B时,CIELAB所预测的色调角与由Munsell色空间计算出来的色调角之差逐渐增大,最大时超过6%,而CIECAM02所预测的色调角与Munsell色空间的色调角之差在2.5%以内,CIECAM02优于CIELAB色空间。     

Effect of B-site dopants on magnetic and transport properties of LaSrCoRuO<Subscript>6</Subscript>

Effect of Co, Ru and Cu substitution at B and B’ sites on the magnetic and transport properties of LaSrCoRuO₆ have been investigated. All the doped compositions crystallize in the monoclinic structure in the space group P2₁/n indicating a double perovskite structure. While the magnetization and conductivity increase in Co and Ru doped compounds, antiferromagnetism is seen to strengthen in the Cu doped samples. These results are explained on the basis of a competition between linear Co-O-Ru-O-Co and perpendicular Co-O-O-Co antiferromagnetic interactions and due to formation of Ru-O-Ru ferromagnetic networks.     

Coexistence of color superconductivity and chiral symmetry breaking within the NJL model

The phase diagram for quark matter is investigated within a simple Nambu-Jona-Lasinio model without vector correlations. It is found that the phase structure in the temperature-density plane depends sensitively on the parametrization of the model. We present two schemes of parametrization of the model where, within the first one, a first-order phase transition from a phase with broken chiral symmetry to a color superconducting phase for temperatures below the triple point at T _t = 55 MeV occurs, whereas for the second one a second-order phase transition for temperatures below T _t = 7 MeV is found. In the latter case, there is also a coexistence phase of broken chiral symmetry with color superconductivity, which is a new finding within this class of models. Possible consequences for the phenomenology of the QCD phase transition at high baryon densities are discussed. Received: 3 January 2003 / Accepted: 21 February 2003 / Published online: 24 April 2003