On Certain Kähler Quotients of Quaternionic Kähler Manifolds

We prove that, given a certain isometric action of a two-dimensional Abelian group A on a quaternionic Kähler manifold M which preserves a submanifold N ? M, the quotient M′ = N/A has a natural Kähler structure. We verify that the assumptions on the group action and on the submanifold N ? M are satisfied for a large class of examples obtained from the supergravity c-map. In particular, we find that all quaternionic Kähler manifolds M in the image of the c-map admit an integrable complex structure compatible with the quaternionic structure, such that N ? M is a complex submanifold. Finally, we discuss how the existence of the Kähler structure on M′ is required by the consistency of spontaneous ${\mathcal{N} = 2}$ to ${\mathcal{N} = 1}$ supersymmetry breaking.     

Vortex structure in ferromagnetic superconductors

It is shown that in ferromagnetic superconductors the polarization of the local spins induced by the persistent current in a vortex is quantized along with the magnetic field due to the current. Because of the polarization the vortex structure strongly depends on temperature. Near the ferromagnetic transition temperatures T_M all the superconductors become type I even if they are extremely of type II far above T_M.     

Effect of 4d metal impurities on the structure, electronic properties, and stability of hexagonal WC from data of FLAPW-GGA calculations

This paper reports on the results of systematic ab initio full-potential linearized augmented plane wave (FP-LAPW) calculations of the band structure and a number of properties of hexagonal tungsten carbide h-WC doped by all 4d metals (M = Y, Zr, ..., Ag). The lattice parameters, distributions of the density of states, energies of formation and cohesion, low-temperature heat capacity coefficients, and Pauli paramagnetic susceptibilities of the WC: M systems have been determined for the first time and discussed in comparison with those for h-WC doped by 3d atoms. It has been found that the change in these properties of the WC: M systems as a function of the type of M atom has a nonmonotonic character.     

Function groups associated with constraint submanifolds

Let M be a submanifold of a manifold Q which has a generalized symplectic form ω. The submanifold M of Q is locally Hamiltonian if its vector fields are locally generated as a C^∞_ω- module by Hamiltonian vector fields of Q. If M is a first class submanifold, i.e., M is defined by first class constraints, then it is shown that M is locally Hamiltonian. It follows that if M is first class then M is a leaf of the singular foliation associated with the function group of all first class functions.     

Study of the magnetic and structural properties of Mn-, Fe-, and Co-doped ZnO powder

A study of the magnetic and structural properties of Zn_1−xM_xO powder (where x=0 or 0.01, and M=Mn, Fe or Co) produced by the proteic sol–gel process was undertaken. The sample crystal structure was analyzed by XRD and magnetic measurements were carried out in a SQUID magnetometer. Of the XRD analysis, all samples had hexagonal wurtzite crystal structure with P63mc space group, and no secondary phase was observed. It is observed of the M(H) measures at 2 K, that the Co- and Mn-doped ZnO displayed saturation magnetizations (M_s) of approximately 2 and 3.2 emu/g, respectively, and no remanence (M_r) was observed, indicating a superparamagnetic behavior in these samples. However, the Fe-doped sample showed a ferromagnetic behavior with M_s∼0.34 emu/g, M_r∼0.05 emu/g, and coercivity (H_c)∼1090 Oe. Already at room temperature, the M(H) measurements reveal a purely paramagnetic behavior for Mn- and Fe-doped ZnO, indicating that the Curie temperature (T_c) is below 300 K. However, a weak superparamagnetic behavior was observed in the Co-doped sample, indicating that T_c>300 K.     

Magnetic and electrical transport properties in the self-doped manganite La0.9Mn0.9M0.1O3 (M=Mn,Zn and Ti)

The magnetic and electrical transport properties of La_0.9Mn_0.9M_0.1O₃ (M=Mn, Zn and Ti) were investigated. The temperature and magnetic field dependence of electrical resistivity (ρ) and dc magnetization were studied. All the compounds are found in rhombohedral structure. The excess oxygen in all three compounds was detected through iodometric titration. A modification in resistivity is observed when M=Mn is replaced by M=Zn and Ti. The high temperature resistivity above T_C follow variable range hopping model for both Zn and Ti compounds. For Zn doping, the observation of large field-cool effect and decrease in resistivity at room temperature and is assumed to be due to the implant of Mn⁴⁺ in Mn³⁺ matrix, which favor Mn³⁺/Mn⁴⁺ double exchange. The ferromagnetic behavior below T_C for the compound with M=Ti is correlated to the excess oxygen in it, which implants Mn⁴⁺ and thus incorporates ferromagnetic interactions. The substitutions lead to a reduction of T_c and magnetization.     

Anisotropy modulated stepwise magnetization in triangular Heisenberg antiferromagnet

During the course of tuning anisotropy from Ising type to zero, the variation of magnetization (M) steps against magnetic field (h) is investigated in a triangular antiferromagnetic Heisenberg model using Monte Carlo techniques. It is revealed that the anisotropy is an essential key to induce the temperature-dependent stepwise M(h) curve observed in frustrated magnetic system, and it can be employed to modulate this steplike magnetic behavior effectively. When the anisotropy is strengthened, a ground state transition occurs from the homogeneous 120° triangular structure to the collinear partially disordered antiferromagnetic state. No M step is detected in the system without anisotropy. But if the anisotropy is nonzero, the M₀/3 step (where M₀ is the saturated M) will emerge on M(h) curve, which is due to an h-induced quasi-collinear ferrimagnetic state. This M₀/3 step can be extended by increasing the anisotropy. When the M₀/3 plateau dominates the h-range broad enough, the equidistant metastable substeps, which originates from the disorders frozen in the frustrated collinear spin structure, appear to be superposed on the M₀/3 plateau. Thus the system with a strong anisotropy presents the whole temperature evolution of stepwise M(h) curve in quantitative agreement with the experiments of Ca₃Co₂O₆.     

Zeeman topologies on space-times of general relativity theory

In 1964 Zeeman published a paper showing [independently of Alexandrov (1953)] that the causal structure of the light cones on Minkowski spaceM determines the linear structure ofM. This initiated the question whether a topology (more physically than the ordinary one) onM, related to the light cones also implies the linear structure ofM. In 1967 Zeeman defined such a new topology — here called Zeeman-topology ?₀ — on Minkowski space and solved this question forM. In that paper he asked whether it is possible to generalize this program to general relativity. Two of his main questions were: (a) What is the structure of the groupG(S) of all homeomorphisms of a space-timeS with respect to the general relativistic analogue of ?₀ (defined in § 3)? (b) What are the world lines (defined in § 1) with respect to ?₀? Without any restrictions on the space-timeS we will give the answers: (a)G(S) is the group of all homothetic transformations onS (for an explicite discussion of this result we refer to § 5). (b) World lines are broken geodesics. Including external fields (like Maxwell fields and deviations of ?₀) the answer (b) can be generalized in different physical directions; cf. § 3. Ein Fernrohr wird gezeigt, womit man seinen eigenen Rücken sieht. Es führt durchs Weltall deinen Blick im Kreis zurück auf dein Genick. Zwar braucht es so geraume Frist, daß du schon längst verstorben bist, doch wird ein Standbild dir geweiht, empfängt es ihn zu seiner Zeit. Christian Morgenstern, ?Böhmischer Jahrmarkt“     

Europium silicides and germanides of the EuM2X2 type: Crystal structure and the valence states of europium

X-ray diffraction studies of EuM₂X₂ compounds (M = Fe, Co, Ni, Cu; X = Si, Ge) revealed that these compounds crystallize in the ThCr₂Si₂ type body-centered tetragonal structure, with the space group $\text{I4}\text{mmm}$. Distribution of the atoms among the lattice sites, the free parameter of the Si and Ge atoms, and the interatomic distances of the compounds were determined by crystal structure calculations. Europium, as determined by Mössbauer spectroscopy, is present in the di- and tri-valent states in the EuM₂Si₂ compounds, the relative amounts of the two states being different in each of the compounds. In EuNiSi₃, EuNi₂Ge₂ and EuCu₂Ge₂ all the Eu are divalent. The relationship between the structure properties and the valence states of Eu in the compounds is discussed.     

Nondynamical structure of inelastic scattering or reactions of spin type 1+0 → 1+0

The nondynamicalM-matrix formalism is applied to the inelastic scattering or to reactions of spin type 1+0→1+0. It is shown how the parameters of theM-matrix, which contain all dynamical information, can be determined by experiments. There are twoM-matricesM ₊ andM _?, one (M ₊) for the case in which the product of the intrinsic parities of all interacting particles is +1 and one (M _?) where this product is ?1. In the case ofM _? one can avoid triple scattering parameters to determine fully theM _?-matrix.     

Size analysis and magnetic structure of nickel nanoparticles

The size distribution of an assembly of fcc nickel nanoparticles is studied by measuring the temperature dependent magnetization curves fitted by a uniform model and a core-shell model, both based on the Langevin function for superparamagnetism with a log-normal particle volume distribution. The uniform model fits lead to a spontaneous magnetization M_s much smaller than the M_s for bulk nickel and to particle sizes larger than the ones evaluated by transmission electron microscopy; the core-shell model fits can result in a correct size distribution but the M_s in the core becomes significantly greater than the M_s for bulk nickel. It is concluded that there is a core-shell magnetic structure in nickel particles. Although the enhanced M_s in the core may be related to the narrowing of the energy bands of 3d electrons in small fcc nickel particles, the modeling values of M_s are over large compared with previous calculations on nickel clusters of different structures, which implies possible existence of an exchange interaction between the core and the shell, which is not considered in the simple core-shell model.     

Dielectric and magnetic properties of Bi1−xYxFeO3 ceramics

Y doped BiFeO₃ polycrystalline ceramics were prepared by sol–gel method. Crystal structure examined by X-ray diffraction indicates that the samples were single-phase and crystallize in rhombohedral structure. An anomaly in the dielectric constant and dielectric loss in the vicinity of the antiferromagnetic Neel temperature (T_N) was observed. Saturated magnetization loops were observed for all sample with saturated magnetization M_s=0.678 emu/g and remnant magnetization M_r=0.084 emu/g for x=0.3.     

Electronic structure of the Np<Emphasis Type="Italic">MT</Emphasis> <Subscript>5</Subscript> (<Emphasis Type="Italic">M</Emphasis> = Fe,Co, Ni; <Emphasis Type="Italic">T</Emphasis> = Ga,In) series of neptunium compounds

Evolution of the electronic structure of the NpMGa₅ (M = Fe, Co, Ni) series of neptunium compounds, whose crystal structure is similar to that of the known family of Pu115 superconductors, was studied by the LDA + U + SO method. The calculations took into account both the strong electron correlations and the spin?orbit coupling in the 5f shell of neptunium. For the first time, the electronic structure was calculated for a hypothetical series of compounds in which gallium is replaced with indium. Parameters of the crystal structure of the given series were obtained using the relationship between the parameters of the crystal structure of the earlier-studied compounds PuCoGa₅ and PuCoIn₅. The analysis of the electronic structure and characteristics of neptunium ions calculated in the framework of the LDA + U + SO method showed that the neptunium ions in NpMIn₅ with M = Fe, Co, and Ni should have an electron configuration closer to f⁴, but a spin and magnetic characteristics close to those in NpMGa₅.     

Non-abelian D = 11 supermembrane

We obtain a U(M) action for super membranes with central charges in the Light Cone Gauge (LCG). The theory realizes all of the symmetries and constraints of the supermembrane together with the invariance under a U(M) gauge group with M arbitrary. The worldvolume action has (LCG) N = 8 supersymmetry arid it corresponds to M parallel supermembranes minimally immersed on the target M g × T ² (MIM2). In order to ensure the invariance under the symmetries and to close the corresponding algebra, a star-product determined by the central charge condition is introduced. It is constructed with a nonconstant symplectic two-form where curvature terms are also present. The theory is in the strongly coupled gauge-gravity regime. At low energies, the theory enters in a decoupling limit and it is described by an ordinary N = 8 SYM in the IR phase for any number of M2-branes.     

Instantons, Poisson Structures and Generalized Kähler Geometry

Using the idea of a generalized Kähler structure, we construct bihermitian metrics on CP² and CP¹×CP¹, and show that any such structure on a compact 4-manifold M defines one on the moduli space of anti-self-dual connections on a fixed principal bundle over M. We highlight the role of holomorphic Poisson structures in all these constructions.     

Energy-dependent X-ray lines in the M-series X-ray spectrum of lanthanum

Using the theory of plasmon oscillations in solids, an alternative explanation is given for the line-like structure observed by Liefeld, Burr and Chamberlain [1] which moves with incident electron energy, resonates in intensity near the excitation energy of the M_α and M_β lines, and leaves residual shoulders on the low-energy side of the lanthanum M_α and M_β lines.     

Electrical relaxation studies of olivine type nanocrystalline LiMPO4 (M=Ni,Mn and Co) materials

The olivine type LiMPO₄ (M=Ni, Mn and Co) materials were synthesized by solution combustion technique using glycine as fuel. The structural characterizations were explored to confirm the phase formation of materials. The scanning electron microscope was used to identify the morphology of olivine materials. The local structure and chemical bonding between MO₆ octahedral and (PO₄)^3- tetrahedral groups were probed by Raman spectroscopy. Grain and grain boundaries were contributed for ion relaxation and dc conduction in olivine materials. Two orders of enhancement in ionic conductivity was observed in these olivine materials than the reported value. Among all the explored olivine samples, LiMnPO₄ showed highest enhancement in conductivity due to weak Li–O bonding and largest unit cell volume.     

Raman scattering in stage 1 europium intercalated graphite

The Raman spectrum of stage 1 europium intercalated graphite, EuC₆, has been recorded at room temperature. EuC₆ has a p(√3 × √3)R30° in-plane superlattice structure, the same as that of LiC₆. The c-axis stacking sequences of EuC₆ and LiC₆ are different. The Raman spectrum of EuC₆ exhibits a broad asymmetric Fano resonance peak at 1500 ± 5 cm^-1, similar to that observed in MC₈ (M = K, RbandCs). However, there is no evidence of any spectral feature around 580 cm^-1 as what has been observed in MC₈. Considering the Raman features of various graphite intercalation compounds in light of their superlattice structures, we suggest that: (1) The feature around 580 cm^-1 is a characteristic associated only with the MC₈p(2 × 2)R0° in-plane superlattice structure. It should originate from the M point phonons of pristine graphite, which become Raman active as predicted by phonon band structure calculations. (2) The continuous background in the spectra of EuC₆ and MC₈, which results in the Fano resonance peak at 1500 cm^-1, is associated with the staggered stacking sequence. Stacking faults are easy to occur in crystals with staggered stacking sequences, but not in crystals with complete elliptical sequences. Therefore, a disorder induced continuum is observed in the Raman spectra of EuC₆ and MC₈, but not in that of LiC₆.     

On the stability of the A 15 structure

The pair potential model is applied to problems of thermodynamic stability involving the A 15 structure. Many such problems have been clarified and answered by this procedure. Among the problems considered are the stability of A 15V₃Al and Nb₃Si; the stability of Nb₃(M₁, M₂) and V₃(M₁, M₂) A 15 pseudobinary stability of stoichiometric A15 phases; long range order of A 15 phases; the effect of pressure on the stability of the A 15 structure; the type of phase diagram that is stable in the vicinity of the A 15 phase.     

Influence of superalkali oxides on structural,electrical and optical properties of C24 fullerene nanocluster: A theoretical study

The influence of superalkali oxides on structural, electrical and the optical properties of 6-5 isomer of C₂₄ fullerene nanocluster was investigate using DFT calculations. It was shown that the structure of fullerene was drastically affected by adsorption of M₃O on its surface and as a result of all bonding lengths, was subsequently changed. DOS results showed that the E_g of C₂₄ in presence of M₃O (M=Li, Na, K) was fairly changed so that the electronic properties and electrical conductance of C₂₄ were not affected by M₃O adsorption. Based on the results of NBO calculations, specifically on MEP surfaces and HOMO-LUMO distribution, the charge was transferred from M₃O to C₂₄ fullerene; therefore, the M₃O is the positive head of complexes and in an electric field it is oriented toward the negative pole. The calculated polarisability(α) and the first hyperpolarisability(β₀) values indicated that the adsorption of M₃O on exterior surface of C₂₄ fullerene has had a drastic effect on the optical response of C₂₄ fullerene and caused a large increase in α and β₀ values. TD-DFT calculations were also carried out in order to confirm the β₀ values. This work theoretically devises novel C₂₄-based nanostructures via interaction with Superalkali Oxides in order to promote, their potential applications in electronic devices and high-performance NLO materials.