Specific features of magnetic and transport properties of La1−x Mn1+x O3 manganites

The magnetic and transport properties of La_1?x Mn_1+x O₃ manganites with excess manganese are studied. It is shown that magnetic and charge ordering heavily depends on the superstoichiometric manganese content, magnetic field, and pressure. The magnetoresistive effect (MRE) is enhanced as the manganese concentration increases. In addition to the paramagnet-ferromagnet transition, the temperature dependences of the magnetization exhibit anomalies at low temperatures in samples with x=0.1–0.4. The magnetization decreases at T<45 K in fields H<0.2 kOe and increases as H changes from 0.2 to 10 kOe. An analysis shows that the features observed at low temperatures are most probably related to the transition from the ferromagnetic state to the canted spin structure in clusters of mixed-valence manganese ions. The temperature dependences of the magnetization and resistivity remain unchanged as the pressure increases. It is demonstrated that the Curie and metal-dielectric transition temperatures shift to higher values as the manganese concentration increases under pressure. The temperature of the MRE peak increases under pressure, while the MRE decreases.     

Rotational invariance and the phonon-induced contributions to spin-Hamiltonian parameters for orbital singlet ions

The rotational invariant parts to the dynamic spin-phonon Hamiltonian are examined for ions having an orbital singlet ground state. From the known experimentally-determined values for the parameters in this dynamic Hamiltonian, the phonon-induced contributions to the static electronic spin Hamiltonian parameters are studied. The ratio of the infinitesimal strain to infinitesimal rotation contributions are calculated for several systems. It is found that the rotational contributions are significant in some cases particularly for Eu²⁺: CaF₂.     

Magnetic studies of phase separation in La2CuO4+° single crystals

The phase seperation effect in La₂CuO_4.015 single crystal has been studied by magnetic susceptibility and EPR experiments. The experiments confirm the percolative phase separation model based on the concept of magnetic polarons formed by hole doping. It has been shown that the superconducting subphase has specific spatial structure which is responsible for unconventional low temperature behavior of susceptibility. The EPR signal as well as the paramagnetic contribution to the lowtemperature susceptibility have been shown to arise from isolated Cu²⁺ ions located inside the phase domain walls.     

Optimal design of thin walled I beams for extreme natural frequency of torsional vibrations

The optimal design of thin-walled I beams so as to extremize the natural frequency of torsional vibration is considered. It is assumed that only one dimension of the cross-section, except for the web height, may be variable in given limits, along the axis of the beam. The optimality condition for the variable dimension is settled by means of Pontryagin's maximum principle. The effect of the constant, axial loads is also included. the solution of the problem formulated is generally found in an iterative way. Some numerical examples of optimization of the I beam with variable widt of flanges are given.     

Multiple discrete solutions of the incompressible steady-state Navier-Stokes equations

Summary This paper discusses the computation of multiple solutions of various discretizations of the steady state incompressible Navier-Stokes equations. Solution paths (,R) satisfying the discrete system of equationsH(,R)=0, where represents the discrete flow field andR is the Reynolds number, are computed using a pseudo arc-length continuation procedure. For flows over the back end of an axially symmetric body with a cusped tail in a coaxial circular cylinder, the solution paths often exhibit hairpin turning points. Dependence of the paths on the mesh spacing and various selections for the discretizations of the convective and diffusive terms are presented.Dedicated to Professor Ivo Babuka on the occasion of his 60th birthdayThis research was supported in part by the Naval Surface Warfare Center Independent Research Fund, the Naval Sea Systems Command, and the Office for Naval Research under Contracts N001484WR24012 and N0001486R24209, and was performed in part under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under contract number W-7405-ENG-48. Partial support under contract Number W-7405-ENG-48 was provided by the Applied Mathematical Sciences Program of the Office of Energy Research     

Hydrogen Bonds Dictate the Coordination Geometry of Copper: Characterization of a Square‐Planar Copper(I) Complex

6,6′′‐Bis(2,4,6‐trimethylanilido)terpyridine (H₂Tpy^NMes) was prepared as a rigid, tridentate pincer ligand containing pendent anilines as hydrogen bond donor groups in the secondary coordination sphere. The coordination geometry of (H₂Tpy^NMes)copper(I)‐halide (Cl, Br and I) complexes is dictated by the strength of the NH–halide hydrogen bond. The Cu^ICl and Cu^IICl complexes are nearly isostructural, the former presenting a highly unusual square‐planar geometry about Cu^I. The geometric constraints provided by secondary interactions are reminiscent of blue copper proteins where a constrained geometry, or entatic state, allows for extremely rapid Cu^I/Cu^II electron‐transfer self‐exchange rates. Cu(H₂Tpy^NMes)Cl shows similar fast electron transfer (≈10⁵ m ^?1 s^?1) which is the same order of magnitude as biological systems.