Structural,mechanicalandsuperconductingpropertiesofBi2Sr2Ca1xYxCu2Oy superconductorswith various x values(0.00rxr0.50) areinvestigatedbyX-raydiffraction,scanningelectronmicroscopy, Vickershardnessandresistivitymeasurements.ItisfoundthatthereplacementofCa2þ by Y3þ does not influencethephasepurityofBi:2212whilelatticeparameters,orthorhombicdistortion,surface morphology,oxygencontentandholecarrierperCuion(P)areaffected.Furthermore,thecritical temperatures Tc are increasedbyincreasing Y contentupto0.30,followedbyadecreasewithfurther increaseof Y contentupto0.50.Thevaluesof Tc are 88,94,101,104and501 K for x¼0.00,0.075,0.15, 0.30 and0.50,respectively.Similarbehaviorisobtainedfortheabsolutevaluesoftruehardness Ht and surface energy g against Y contentwhiletheoppositebehaviorisrecordedfortheholecarrierperCu ion (P),deducedfrom Tc values,against Y content.Similarbehaviorisobtainedfortheabsolutevalues of truehardness Ht and surfaceenergy g against Y content.Theseresultsarediscussedintermsof possiblereasonsforsuppressionofsuperconductivityby Y substitutionattheCasiteintheBi:2212 superconductingsystem.

Mechanical and magnetic properties of the ZnO/Fe2O3 ceramic varistors have been examined by using mechanical analyzer, digital microhardness tester and vibrating sample magnetometer. The initial stress–strain behavior is found to be linear (elastic) then becomes nonlinear (plastic deformation) without reaching the failure limit up to the maximum available stress (0.07 MPa). The compressive elastic modulus varies between 0.2 and 0.8 MPa with Fe addition up to 0.50. Furthermore, an approximately monotonically linear decrease in VHN with increasing Fe content up to 50% has been observed for all applied loads, which closely resembles the behavior of the true hardness and the surface energy. The magnetic measurements revealed an antiferromagnetic to paramagnetic to transition for all Fe doped samples. The Fe free sample showed paramagnetic behavior down to 2 K. The Neel temperature moderately increased from 18 K at 0.05% Fe to 25 K at 0.5% Fe. The magnetization (M) versus applied magnetic field (H) did not reach saturation for all samples up to 9 Tesla. The saturated magnetization (per Fe contents) is low and found to decreases linearly at a rate of (35 emu/g-Fe) in a clear manifestation of the strengthening of the antiferromagnetic exchange interaction with increasing Fe contents.

In this paper, the Kelvin-Helmholtz instability of viscous incompressible magnetic fluid fully saturated porous media is achieved through the viscous potential theory. The flow is considered to be through semi-permeable boundaries above and below the fluids through which the fluid may either be blown in or sucked out, in a direction normal to the main streaming direction of the fluid flow. An oblique magnetic field, mass, heat transfer, and surface tension are present across the interface. Through the linear stability analysis, a general dispersion relation is derived and the natural curves are plotted. Therefore, the linear stability condition is discussed in some depth. In view of the multiple time scale technique, the Ginzburg–Landau equation, which describes the behavior of the system in the nonlinear approach, is obtained. The effects of the orientation of the magnetic fields on the stability configuration in linear, as well as nonlinear approaches, are discussed. It is found that the Darcy’s coefficient for the porous layers plays a stabilizing role. The injection of the fluids at both boundaries has a stabilizing effect, in contrast with the suction at both

The cleavage of F!CN bond in the presence of Fe(II) silyl complex, [Cp(CO)FeSiMe3], was studied using density functional theory calculations and compared with the mechanisms for E!CN (E = C, N, and O) bond cleavages, which have previously been clarified to be a silyl-migration-induced reaction.

Using hybrid density functional theory calculations with the B3LYP functional, the reaction mechanisms for cleavage of R2N−CN (R  H, Me) and MeO−CN bonds in the presence of an unsaturated iron(II) silyl complex, CpFe(CO)SiMe3, were studied. The following sequence of reactions was shown to be favorable: (i) coordination of a nitrile through the lone pair of electrons on the nitrile N atom (NCN) to form an end-on complex, (ii) isomerization of the endon complex to a side-on complex, (iii) migration of the silyl group to NCN facilitated by the hypervalent character of the Si atom and its electrostatic attraction with NCN to form a stable Fe−C−NCN three-membered-ring intermediate with an Fe−NCN dative bond, (iv) dissociation of the NCN atom from Fe and coordination of an amino N atom (NNR2) or methoxy O atom to Fe leading to an Fe−C−NNR2 or Fe−C−O three-membered-ring intermediate, and (v) cleavage of the R2N−C or MeO−C bond to form a silyl isocyanide ligand. Step iv possesses the largest activation energy in the sequence of reactions. The activation energies for the reactions of H2NCN, Me2NCN, and MeOCN were calculated to be 29.9, 28.0, and 19.1 kcal/mol, respectively, on the basis of potential energies with zero-point energy correction. This accounts for the experimental observation that the intermediates formed by silyl group migration can be isolated. The effects of the amino and methoxy groups are discussed by comparing their reaction profiles with that for the reaction of acetonitrile. Localized orbital analysis showed that in the three-membered-ring intermediates formed in step iv, the R2N−C and MeO−C bonds are activated by ring strain, whereas the Me−CN bond is activated by interaction of the Me−C bond with the vacant coordination site that is produced in the dissociation of NCN.

O−CN bond cleavage of cyanates (ROCN) has been achieved at room temperature in the reaction of ROCN with a methyl Fe, Mo, or W complex. A mechanistic investigation involving DFT calculations revealed that silyl migration from Mo to the CN nitrogen gave an N-silylated η2-imidato Mo complex. This intermediate analogue was isolated and characterized by X-ray analysis. Catalytic O−CN bond cleavage was achieved using Cp(CO)3MoMe under thermal conditions.

In this work, a viscous potential flow analysis is used to investigate capillary surface waves between two horizontal finite fluid layers. The two layers have finite conductivities and admit mass and heat transfer. A general dispersion relation is derived. The presence of finite conductivities together with the dielectric permeabilities makes the horizontal electric field play a dual role in the stability criterion. The phenomenon of negative viscosity is observed. A new growth rate parameter, depending on the kinematical viscosity of the lower fluid layer, is found and has a stabilizing effect on the unstable modes. The growth rates and neutral stability curve are given and applied to air-water interface. The effects of various parameters are discussed for the Kelvin-Helmholtz and the Rayleigh-Taylor instabilities.

In the view of viscous potential flow theory, the hydromagnetic stability of the interface between two infinitely conducting, incompressible plasmas, streaming parallel to the interface and subjected to a constant magnetic field parallel to the streaming direction will be considered. The plasmas are flowing through porous media between two rigid planes and surface tension is taken into account. A general dispersion relation is obtained analytically and solved numerically. For Kelvin-Helmholtz instability problem, the stability criterion is given by a critical value of the relative velocity. On the other hand, a comparison between inviscid and viscous potential flow solutions has been made and it has noticed that viscosity plays a dual role, destabilizing for Rayleigh-Taylor problem and stabilizing for Kelvin-Helmholtz. For Rayleigh-Taylor instability, a new dispersion relation has been obtained in terms of a critical wave number. It has been found that magnetic field, surface tension, and rigid planes have stabilizing effects, whereas critical wave number and porous media have destabilizing effects.