Characterization of Ni–Cu mixed spinel ferrite

Crystal structure, X-ray density, porosity, compressive strength of Ni_1−xCu_xFe₂O₄ have been investigated along with scanning electron microscopy (SEM) to study the effect of composition and microstructure on the magnetic and electrical properties. The formation of single-phase ferrite is confirmed by the X-ray diffraction. Tetragonal deformation is observed for the sample of composition x=1, i.e. for pure CuFe₂O₄ Crystal structure for samples of other compositions are face centered cubic (FCC). SEM micrographs exhibit increase in grain size with the increase of copper content. Compressive strength decreases with the increase of Cu. Initial magnetic permeability and saturation magnetization is maximum for the composition of x=0.2, i.e. for Ni_0.8Cu_0.2Fe₂O₄, which can be attributed to the maximum sintered density obtained for this composition. Resistivity decreases with the increase of Cu content.     

Study of the synthesis of nanocrystalline mixed tantalum–zirconium carbide

The synthesis conditions of refractory tantalum–zirconium carbide Ta_0.8Zr_0.2C on the basis of Ta₂O₅–ZrO₂–C ultrafine initial blend prepared via the sol–gel method are explored. The initial blend is prepared via hydrolysis in the presence of Ta(OC₅H₁₁)₅ and [Zr(O₂C₅H₇)_4–x (OC₅H₁₁) _x ] carbon source polymer solutions, gel drying, and carbonization at a temperature of 450°C. A series of the carbothermal synthesis experiments is implemented at various temperatures and exposure times. The synthesis conditions are shown to affect not only the phase composition of products but also their oxidation resistance related to the particle size.     

Photoemission studies of Cd1−xPbxF2 mixed crystals

Mixed Cd_1−xPb_xF₂ and pure PbF₂, CdF₂ crystals have been investigated using UPS spectroscopy. The CdF₂ valence density of states, due mainly to F _2p electrons, is reconstructed due to the presence of Pb 6s states. The width of the valence band increases from 3.9 eV for CdF₂ to 6.6 in PbF₂. The contributions of cationic s and anionic p electrons have been identified. The experimental results confirm the recent theoretical calculations of electronic states in mixed Cd_1−xPb_xF₂ crystals [1].     

A 23Na NMR study of mixed cation β-aluminas

The ²³Na NMR spectrum of Na, Ti β- and Na, Cd ß-alumina can be understood in the same terms of cation site occupation used to interpret the spectrum of the pure Na crystal. The monovalent Tl ion enters the conduction plane and, up to a level of 60% of exchange, occupies the cation site in the singly occupied cell. The divalent Cd ion, on the other hand, moves initially into the doubly occupied cell, the cell that also contains the charge compensating oxygen. This difference in exchange behavior, as observed by NMR, can be related to differences in mixed cation behavior between these two mixed crystals.     

Interface phonon-polaritons in quantum well systems of polar ternary mixed crystals

The interface phonon-polaritons in quantum well systems consisting of polar ternary mixed crystals are investi-gated. The numerical results of the interface phonon-polariton frequencies in the GaAs/AlxGa1-xAs, ZnSxSe1-x/ZnS, and ZnxCd1-xSe/ ZnSe quantum well systems are obtained and discussed. It is shown that there are six branches of interface phonon-polariton modes distributed in three bulk phonon-polariton forbidden bands in the systems. The electric fields of interface phonon-polaritons are also presented and show the interface locality of the modes. The effects of the ’two-mode’ and ’one-mode’ behaviours of the ternary mixed crystals on the interface phonon-polariton modes are shown in the dispersion curves.     

Effect of lithium-potassium mixed alkali on spectroscopic properties of Er^3＋-doped aluminophosphate glasses

Er^3＋-doped lithium-potassium mixed alkali aluminophosphate glasses belonging to the oxide system xK2O-（15-x）Li2O-4B2O3-11Al2O3-5BaO-65P2O5 are obtained in a semi-continuous melting quenching process. Spectroscopic properties of Er^3＋-doped glass matrix have been analysed by fitting the experimental data with the standard Judd-Ofelt theory. It is observed that Judd-Ofelt intensity parameters Ωt（t = 2, 4 and 6） of Er^3＋ change when the second alkali is introduced into glass matrix. The variation of line strength Sed[^4I13/2,^4I15/2] follows the same trend as that of the/26 parameter. The effect of mixed alkali on the spectroscopic properties of the aluminophosphate glasses, such as absorption cross-section, stimulated emission cross-section, spontaneous emission probability, branching ratio and the radiative lifetime, has also been investigated in this paper.     

Photophysics of mixed ligand complexes of ruthenium(II) with 2,2′-bipyridyl and phosphines

Luminescence of mixed ligand complexes of ruthenium(II) of the types cis-Ru(bpy)₂X₂(I), cis-[Ru(bpy)₂(PPh₃)X](BF₄)(II), and cis-Ru(bpy)(PP)X₂(III) (X = CN, NO₂, PPh₃ is triphenyl phosphine; PP is 1,2-bis(diphenylphospino)ethane (dppe) and cis-,2-bis(diphenylphosphino)ethylene (dppene)) is studied in alcohol matrices (EtOH/MeOH, 4:1) frozen at 77 K. A sequence of complexes I–III exhibits an additive (in the number of phosphorous atoms) blue shift of the absorption and luminescence bands and an increase in the quantum yield of luminescence and in the excited-state lifetime. The rate constant of nonradiative deactivation of the excited state decreases more than by an order of magnitude in the sequence I–III of cyano complexes and only by three times in a sequence of nitro complexes. This is assumed to be caused by a specific (in the hydrogen bond type) interaction of nitro groups of complexes with a proton solvent.     

Entanglement evolution of three-qubit mixed states in multipartite cavity—reservoir systems

We analyze the multipartite entanglement evolution of three-qubit mixed states composed of a GHZ state and a W state.For a composite system consisting of three cavities interacting with independent reservoirs,it is shown that the entanglement evolution is restricted by a set of monogamy relations.Furthermore,as quantified by the negativity,the entanglement dynamical property of the mixed entangled state of cavity photons is investigated.It is found that the three cavity photons can exhibit the phenomenon of entanglement sudden death(ESD).However,compared with the evolution of a generalized three-qubit GHZ state which has the equal initial entanglement,the ESD time of mixed states is later than that of the pure state.Finally,we discuss the entanglement distribution in the multipartite system,and point out the intrinsic relation between the ESD of cavity photons and the entanglement sudden birth of reservoirs.     

Seebeck-effect in the mixed state of Y−Ba−Cu−O

We report on measurements of the Seebeck-effect, the Nernst-effect, and the magnetoresistance in the mixed state of ac-axis oriented expitaxial film of Y–Ba–Cu–O. In contrast to conventional superconductors we find a large Seebeck-coefficientS, which is comparable in magnitude to the Nernst-effect. The broadening of the super-conducting transitions of magnetoresistance and Seebeck-effect are rather similar with respect to (1) the temperature dependence, (2) the dependence on the direction between magnetic field and crystal axis and (3) the dependence on the direction between magnetic field and driving forces. The large Seebeck-effect has to be attributed to dissipation due to normal quasiparticle-excitations, since the vortex-contribution to the Seebeck-effect is by far too small to account for the observed magnitude ofS. It is argued that such a quasiparticle contribution to the dissipation is large in the high-T _c superconductors because of the small coherence lengths and thus the small vortex cores. Another possibility is that granularity leads to dissipation proportional to the normal state transport properties. The Seebeck-voltage depends on all dissipative processes other than vortex motion, whereas the Nernst-effect depends only on the vortex motion. Therefore by measurements of thermomagnetic effects the various dissipative properties may be separated.     

Observation of a 〈100〉 mixed dumbbell at181HF in tungsten

TDPAC measurements were carried out in Tungsten foils and single crystals using implanted¹⁸¹Hf as a probe nucleus. After proton irradiation at 25 K the trapping of a defect at the Hf probe was observed, which lead to a quadrupole interaction frequency of _Q=354(5) MHz. The defect could be identified as a W self interstitial forming a 100 mixed dumbbell with a Hf impurity atom.     

Surface phonon–polaritons in rectangular quantum wires of polar ternary mixed crystals

In this paper, the dispersion relations of surface phonon–polaritons in freestanding rectangular quantum wire systems of polar ternary mixed crystals are derived. The numerical calculations for Al_xGa_1−xAs and Zn_xCd_1−xSe quantum wire systems are performed. The results reveal that the frequencies of surface phonon–polariton modes are sensitive to the geometric structures of the quantum wires, the wave-vectors in z-direction, and the compositions of the ternary mixed crystal materials. The effects of the “two-mode” and “one-mode” behaviors of the ternary mixed crystals on the surface phonon–polariton modes are also discussed.     

Bad behavior of Godunov mixed methods for strongly anisotropic advection–dispersion equations

We study the performance of Godunov mixed methods, which combine a mixed-hybrid finite element solver and a Godunov-like shock-capturing solver, for the numerical treatment of the advection–dispersion equation with strong anisotropic tensor coefficients. It turns out that a mesh locking phenomenon may cause ill-conditioning and reduce the accuracy of the numerical approximation especially on coarse meshes. This problem may be partially alleviated by substituting the mixed-hybrid finite element solver used in the discretization of the dispersive (diffusive) term with a linear Galerkin finite element solver, which does not display such a strong ill conditioning. To illustrate the different mechanisms that come into play, we investigate the spectral properties of such numerical discretizations when applied to a strongly anisotropic diffusive term on a small regular mesh. A thorough comparison of the stiffness matrix eigenvalues reveals that the accuracy loss of the Godunov mixed method is a structural feature of the mixed-hybrid method. In fact, the varied response of the two methods is due to the different way the smallest and largest eigenvalues of the dispersion (diffusion) tensor influence the diagonal and off-diagonal terms of the final stiffness matrix. One and two dimensional test cases support our findings.     

Fermions in the background of mixed vector–scalar–pseudoscalar square potentials

The general Dirac equation in 1+1$1+1$ dimensions with a potential with a completely general Lorentz structure is studied. Considering mixed vector–scalar–pseudoscalar square potentials, the states of relativistic fermions are investigated. This relativistic problem can be mapped into a effective Schrödinger equation for a square potential with repulsive and attractive delta-functions situated at the borders. An oscillatory transmission coefficient is found and resonant state energies are obtained. In a special case, the same bound energy spectrum for spinless particles is obtained, confirming the predictions of literature. We showed that existence of bound-state solutions is conditioned by the intensity of the pseudoscalar potential, which possess a critical value.     

Energy-momentum tensor of a spinor field in the “mixed universe” cosmological model

The energy-momentum tensor of a massless spinor field is constructed and studied based on the previously proposed interpretation of quantum effects of such a field in the anisotropic metric of Bianci type IX. The characteristic properties of the energy-momentum tensor in the mixed universe model are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 45–50, September, 1988.I am grateful to A. A. Grib and A. V. Nesteruk for their interest in this work and for useful discussions.     

Dynamics of mixed lump-solitary waves of an extended (2 + 1)-dimensional shallow water wave model

To explore the features of lump solutions, which are local in every direction of space, a ($2+1$)-dimensional extended shallow water wave model is studied, based on its bilinear representation. Several ansatzes have been utilized to determine single lump waves, lump-kink waves, single kinks and multi-lumps leading to breathers in terms of function patterns for the model. Through analyzing interactions between solitons, the impact of free parameters involved in the solutions on interaction types is exhibited. We determine a condition on the parameters under which a single kink wave can be converted into a multi-lump wave. To illustrate the interaction of exponential and periodic function waves, we show that multi-lump waves in the form of breather waves especially come into sight as a straight line or an X shape. To realize dynamics, we make various graphical analyses on the presented solutions, which gives an essential improvement in the physical realizing of higher-dimensional lump waves in oceanography and nonlinear optics.     

Infrared spectroscopy of solid mixed ammonia–water and acetylene–water aerosol particles

Mixed water aerosols are important components of planetary and lunar atmospheres. In this work, we use rapid-scan Fourier transform infrared (IR) spectroscopy to study solid ammonia–water and acetylene–water aerosol particles formed in a bath gas cooling cell at 78 K. With this set-up, we record time-dependent extinction spectra of particle ensembles in the mid-IR to monitor changes to the internal structure of the aerosol particles. Both ammonia–water and acetylene–water were found to form molecularly mixed structures. The mixing is observed by monitoring the profile for the ammonia ν₂ band and the acetylene ν₅ band, both of which are sensitive to particle properties. Depending on the injection conditions, the mixed particles form either immediately after sample injection or after a short mixing period of several tens of minutes. We confirm the formation of mixed particles by comparing the experimental spectra with spectra calculated with the vibrational exciton model.