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1.
We define currents on a Grassmann algebra Gr( N) with N generators as distributions on its exterior algebra (using the symmetric wedge product). We interpret the currents in terms of
2-graded Hochschild cohomology and closed currents in terms of cyclic cocycles (they are particular multilinear forms on Gr( N). An explicit construction of the vector space of closed currents of degree p on Gr( N) is given by using Berezin integration. 相似文献
2.
The observation of an anomalous temperature dependence of Mn 2+ EPR spectra linewidth and nonaxial crystal-field parameter in K 3H(SO 4) 2 and Rb 3H(SO 4) 2 allows one to suggest the presence of “local mode” predicted by Yamada (Ferroelectrics 170 (1995) 23). The activation energy for this kind of excitation was found and equals 11.3 (0.5) and 7.4 (0.3) meV for Mn 2+ doped K 3H(SO 4) 2 and Rb 3H(SO 4) 2, respectively. 相似文献
3.
Anomalies are found in the near-band-edge luminescence properties of Δ 2-light-hole indirect excitons in Si 1−yC y-based tensilely strained quantum wells (QWs). The experimental spectra exhibit a clear signature of phonon-assisted transitions on the lower energy side of the “no-phonon” transition, which indicates the relevance of “virtual” indirect valleys and in-plane k-dispersion, as opposed to the theoretical prediction that the zone-centered Δ 2 valleys take over the conduction band edge. Intervalley scattering between [0 0 1]-Δ 2 valleys and in-plane Δ 4 valleys is suggested as the underlying mechanism. On the other hand, the experimental evidence was found for “apparently enhanced” quantum-confined Stark red shifts for Si 1−yC y-based QWs. However, quantitative estimates are in conflict with the experimental results and predict a blue shift due to exciton weakening which masks the Stark effect as in the case of Δ 4-heavy hole excitons in Si 1−xGe x-based QWs. 相似文献
4.
Several magnets with different Zr contents were studied: Sm(Co balFe 0.2Cu 0.1Zr x) 8 (bal=balance; x=0, 0.02, 0.04, 0.06 and 0.08). The microstructure of the magnets includes three main phases, all crystallographically coherent: the cell phase Sm 2(Co,Fe) 17, the cell boundary phase Sm(Co,Cu) 5 and a lamellar Zr-rich phase, rhombohedral (ZrSm) 1Co 3. The hysteresis curves were compared with the Callen, Liu and Cullen (CLC) modification of the Stoner–Wohlfarth model for an isotropic distribution of interacting single-domain particles. Choosing reasonable values for the saturation magnetization Ms, the anisotropy field Ha, and the mean-field interactions of the CLC model, we were able to reproduce the main features of the hysteresis curves for the x=0.02 and 0.04 samples. For higher x values, X-ray diffraction Rietveld analysis revealed the presence of other “impurity” phases, among them cubic Zr 6(Co,Fe) 23, rhombohedral (SmZr) 5(CoFeCu) 19 and rhombohedral (SmZr) 2(CoFeCu) 7. 相似文献
5.
We give a theoretical analysis of a “stimulated photorefractive backscattering and four-wave mixing” (SPB-FWM) self-pumped phase conjugator (SPPC) in which the generation of the phase conjugate wave relies on both stimulated photorefractive backscattering (SPB) and four-wave mixing (FWM) processes. The two pumping beams in the FWM process are, respectively, the forward-propagating beam of which the generation is seeded by the fanning effect, and the backward-propagating beam that is generated by the SPB process. Assuming that the SPB interaction is seeded by the scattering centers in the crystal, we have calculated the threshold four-wave mixing coupling strength (γ 1l1) th as a function of the SPB two-wave mixing coupling strength (γ 2l2) corresponding to the 2k grating and of the reflectivity R′ of the scattering centers. Above threshold, we have also calculated the phase-conjugate reflectivity with a numerical method. Our calculations show that the threshold as well as the reflectivity of a SPB-FWM SPPC strongly depend on γ 2l2 and R′. It is also shown that a high phase-conjugate reflectivity can be easily realised in doped barium titanate crystals which are shown to have much larger γ 1 and γ 2 than an undoped one. 相似文献
6.
Yb(Ba 1−xSr x) 2Cu 4O 8 (0.1 x0.3) superconductors of the YBa 2Cu 4O 8(“124”) structure were successfully synthesized using an O 2-hot-isostaticc-pressing (HIP) technique. The samples were characterized with respect to the crystal structure and superconducting properties. The lattice parameters of the samples decreased as the substitution of Sr for Ba proceeded. The superconducting transition temperatures of all the Yb-“124” samples were more or less the same, being around 80 K. 相似文献
7.
We present constraints on the relative photoproduction cross sections of positive parity pentaquark states, Σ 5, Λ 5, and N5, based on a minimum phenomenology gained in
and their baryon–meson couplings as in the work of Close and Dudek. The possibility of anomalous signals in γ p→ K0S(Θ +;Σ d+) is discussed. We emphasize the importance of comparing
with “conventional” states such as γ N→ KΣ(1660). 相似文献
8.
Thin films of Bi 2Sr 2CaCu 2O 8 and (Bi, Pb) 2Sr 2Ca 2Cu 3O 10 have been prepared on monocrystalline (100) MgO substrates, using a laser ablation method with post annealing treatment. The influence of substrate temperature and oxygen pressure during deposition were investigated. SEM observations, EDS analysis, electric and magnetic measurements have been used to characterize the films. Superconducting “2212” films, with Tc( R = 0) at 80–83 K and Jc (50 K) up to 5 × 10 5 A/cm 2, have been currently achieved, while Pb-doped “2223” films exhibit Tc as high as 110 K with Jc = 5 × 10 4 A/cm 2 at 77 K. The effect of annealing at low temperature (350°C) in an argon flow has been studied for the 2212 phase, it shows the influence of the oxygen non-stoichiometry, i.e. of the hole carrier density upon Tc's which can be measured up to 89 K (zero resistance). 相似文献
9.
The influence of addition of sliver ions on the redox properties and catalytic performance of molybdenum-phosphate catalyst in oxidative dehydrogenation (ODH) of propane has been investigated. MoO 3 and AgMoO 2PO 4 have been detected in Ag-doped Mo-P-O catalysts. The redox properties have been characterized by H 2-temperature-programmed reduction (TPR), electronic paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS). The catalytic performance of MoO 3, Ag 2O, AgMoO 2PO 4 and Ag-doped Mo-P-O catalysts has also been examined. The incorporation of Ag improved the number of Mo 5+ species and the reducibility of the catalysts. The Ag-doped catalysts favor activity and selectivity in ODH of propane higher than the undoped catalyst. The best catalyst was obtained with Ag/Mo ratio of 0.3 and MoO 3/AgMoO 2PO 4 ratio of 1.1. The influence of promoter Ag + on redox properties and catalytic performance is due to forming redox couple “Ag 0+Mo 6+Ag ++Mo 5+” and the synergetic effect originating from “ coherent interface” between MoO 3 and AgMoO 2PO 4. 相似文献
10.
The phase structure of a large N, O( N) supersymmetric model in three dimensions is studied. Of special interest is the spontaneous breaking of scale invariance which occurs at a fixed value of the coupling constant, λ 0=λ c=4π. In this phase the bosons and fermions acquire a mass while a Goldstone boson (dilaton) and Goldstone fermion (“dilatino”) are dynamically generated as massless bound states. The absence of renormalization of the dimensionless coupling constant λ 0 leaves these Goldstone particles massless. 相似文献
11.
The antifield formalism is extended so as to incorporate the rigid symmetries of a given theory. To that end, it is necessary to introduce global ghosts not only for the given rigid symmetries, but also for all the higher order conservation laws, associated with conserved antisymmetric tensors jμ13μk fulfilling μ1jμ13μk 2˜ 0. Otherwise, one may encounter obstructions of the type discussed in by the authors. These higher order conservation laws are shown to define additional rigid symmetries of the master equation and to form — together with the standard symmetries — an interesting algebraic structure. They lead furthermore to independent Ward identities which are derived in the standard manner, because the resulting master (“Zinn-Justin”) equation capturing both the gauge symmetries and the rigid symmetries of all orders takes a known form. Issues such as anomalies or consistent deformations of the action preserving some set of rigid symmetries can be also systematically analysed in this framework. 相似文献
12.
A noncommutative associative algebra of the N= 2 fuzzy supersphere is introduced. It turns out to possess a nontrivial automorphism which relates twisted chiral to twisted
anti-chiral superfields and hence makes it possible to construct noncommutative nonlinear σ-models with extended supersymmetry.
Received: 29 March 1999 / Accepted: 8 April 1999 相似文献
13.
Silver-sheathed (Bi,Pb) 2Sr 2Ca 2Cu 3O x (Bi(2223)) tapes were fabricated by the “oxide-powder-in-tube” technique. After the tapes were shaped and sintered, an additional cold rolling and a re-sintering were applied in order to enhance the critical current density Jc. The influence of the additional rolling conditions (roll diameter, number of passes, lubrication) on the Jc (77 K, 0 T) was made clear. The influence of the sintering conditions (temperature, heating rate) on Jc was also investigated. As for the rolling conditions, a small redundant shear deformation or a small contact angle leads to a good grain alignment, texturing, and a higher Jc value. As for the temperature of the first sintering, 1113 K is superior to 1118 K because of the volume fraction of the Bi(2223) phase. 相似文献
14.
The differential geometry of an imbedded (e.g. string or membrane world sheet) surface in a higher-dimensional background is shown to be conveniently describable (except in the null limit case) in terms of what are designated as its first, second, and third fundamental tensors, which will have the respective symmetry properties η μν = η (μν) as a trivial algebraic identity, Kμνρ = K(μν)ρ as the “generalised Weingarten identity”, which is the (Frobenius type) integrability condition for the imbedding, and Ξ λμνρ = Ξ (λμν)ρ as a “generalised Codazzi equation”, which depends on the background geometry being flat or of constant curvature, needing replacement by a more complicated expression for a generic value of the background curvature Bκλμν. The “generalised Gauss equation” expressing the dependence on this background curvature of the internal curvature tensor Rκλμν of the imbedded surface is converted into terms of the first and second fundamental tensors, and it is thereby demonstrated that the vanishing of the (conformally invariant) “conformation tensor”, i.e. the trace free part Cμνρ of the second fundamental tensor Kμvρ, is a sufficient condition for conformal flatness of the imbedded surface (and thus in particular for the vanishing of its (Weyl type) conformal curvature tensor Cκλμν) provided the background is itself conformally flat. In a trio of which the first two members are the generalised Gauss and Codazzi equations, the “third” member is shown to give an expression in terms of Cμνρ for the (trace free, conformally invariant) “outer curvature” tensor Ω κλμν whose vanishing is the condition for feasibility of the natural generalisation of the Walker frame transportation ansatz. The vanishing of Cμνρ is shown to be sufficient in a conformally flat background for the vanishing also of Ω κλμν. 相似文献
15.
Magnetization measurements in fields up to 38 T performed at low temperature on single crystals of the hexagonal Pr(Ni 1-xCo x) 5 compounds for x = 0, 0.05, 0.10 and 0.20 are presented. In PrNi 5 we observe highly original behaviour predicted by the knowledge of the Crystalline Electric Field parameters and arising from the existence of a non-magnetic singlet ground state; namely transitions associated with the field induced “anticrossing” and “crossing” of the two lowest states along the [100] and [120] directions, respectively. The measurements performed on the other compounds have allowed us to study the dependence of this behaviour on Co substitutions. 相似文献
16.
采用密度泛函理论与Wagner-Schottky热力学模型计算了金属间化合物L1 2-A1 3Sc中点缺陷浓度与温度、成分间的关系. 结果表明: 在考察的温度区间(T=300-1200 K), 理想化学计量比L1 2-A1 3Sc中的点缺陷主要为Al空位和Sc空位, 且缺陷浓度较低(在1200 K时仅约为10 -6). 当L1 2-A1 3Sc偏离化学计量比成分时, 富Al成分端的点缺陷主要为Al反位与Sc空位, 且两种缺陷的浓度相当; 富Sc成分端的点缺陷则主要为Sc反位. 利用超胞模型进一步计算了含点缺陷L1 2-A1 3Sc晶体的弹性常数, 并计算预测了点缺陷形式和浓度对其弹性性能的影响. 结果表明: 在理想化学计量比成分附近, 点缺陷的引入均会降低非化学计量比L1 2-Al 3Sc晶体的杨氏、剪切和体积弹性模量, 增加非化学计量比L1 2-Al 3Sc弹性性能的各向异性, 但是对其脆-韧性的影响不大. 相似文献
17.
New Pb based layered superconducting cuprates (Pb 0.5Cd 0.5)(Sr 0.9R 0.1) 2(R′ 0.7Ce 0.3) 2Cu 2O y with (R,R′) = (Eu,Gd), (Eu,Dy) and (Nd,Gd), have been successfully synthesized. The structure of (Pb,Cd)(Sr,Eu) 2(Gd,Ce) 2Cu 2O y is determined using XRD data. The X-ray powder diffraction pattern can be indexed by the tetragonal structure with lattice parameters a = 3.8250 Å, C = 29.2235 Å and a space group of I4/mmm. The effects of synthesis conditions on (Pb,Cd)(Sr,Eu) 2(Gd,Ce) 2Cu 2O y are studied and a Tc(onset) of 26 K is obtained by resistance measurements. It is isostructural to the superconductor (Pb,Cu)(Sr,Eu) 2(Eu,Ce) 2Cu 2O y. 相似文献
18.
High-temperature 23Na MAS NMR experiments up to 873 K for a number of different sodalites (Na 8[AlSiO 4] 6(NO 3) 2, Na 8[AlSiO 4] 6(NO 2) 2, Na 8[AlSiO 4] 6I 2, Na 7.9[AlSiO 4] 6(SCN) 7.9 · 0.5H 2O, Na 8[AlGeO 4] 6(NO 3) 2, and Na 7[AlSiO 4] 6(H 3O 2) · 4H 2O) were carried out. The spectra of the first five sodalites consist of a quadrupolar MAS pattern with different quadrupolar coupling constants. The quadrupolar interaction for the thiocyanate sodalite, the nitrate aluminosilicate, and germanate sodalite decreases strongly passing a coalescence state on heating, while the quadrupolar interaction of the iodide and nitrite sample shows nearly no change. The basic hydrosodalite shows an asymmetric lineshape at room temperature and, between 350 and 370 K, a second line due to the evaporation of cage-water emerges. The linewidth increases with rising temperature. The temperature dependence of the quadrupolar interaction seems to be a function of the sodalite β-cage expansion. Two conceivable jump mechanisms are proposed for a tetrahedral two-site jump between occupied and unoccupied tetrahedral sites. 相似文献
19.
系统研究了核磁共振碳谱与化学位移和规律,以及分子拓扑指数在定量[结]构[波]谱关系(QSSR)中的应用.本文基于矢量路径长度矢量p=(P 1, P 2, P 3,…, P m)与分子中原子相互作用,提出了一种新型分子距边矢量并发现它与烷烃 13C NMR 化学位移和有良好线性相关性, 回归方程及其统计参数为:
CSS=bν+p 3=Σ mj=0b jν j+b 10p 3=b 0ν+b 1ν 1+b 2ν 2+b 3ν 3+b 4ν 4+b 5ν 5+b 6ν 6+b 7ν 7+b 8ν 8+b 9ν9 ν+b 10P 3 =-13.6011+22.2133 ν 1+28.4121 ν 2+25.9416 ν 3+26.6709 ν 4+14.4976 ν 5+5.7240 ν 6-5.3830 ν 7-3.2152 ν 8-15.0213 ν 9-25.7099 ν 10+12.2786P 3 (n=63, R=0.9970, EV=99.68%, RMS=3.7348, F=2418.2; 交互校验CV为: R=0.9893, EV=98.83%, RMS=7.1261, F=664.046); 结果良好. 相似文献
20.
In this work, we compare positon capture and photo-beta disintegration probabilities in several stellar conditions. We show that the second process can be neglected with regard to the first one in strongly endothermic nuclear transitions, whereas photo-beta disintegration can be competitive with positon capture and even can have a greater likelihood than the latter process in weakly endothermic and exothermic transitions. In the range of temperature we consider here (T ≈ 109 °K), it appears that the lifetime ratio τ(ph)/τ(ec+) against photo-beta disintegration and positon capture is the smallest for densities in the neighbourhood of 106 g/cm3. Thus, we arrive at the conclusion that the photo-beta process can play a role in the synthesis of two “p” elements at least, 62144Sm and 80196Hg, for which the ratios τ(ph)/τ(ec+) are close to 10 and 20, respectively, in the most favourable stellar conditions. 相似文献
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