Exsolution of Nickel Nanoparticles from Mixed-Valence Metal Oxides: A Quantitative Evaluation by Magnetic Measurements

A fast and accurate experimental method is demonstrated to assess the fraction of exsolved metallic nanoparticles using magnetic measurements. As a benchmark, nanometric metallic nickel exsolved from (La_1−xSr_x)(Cr_1−yNi_y)O_3−δ is used for its high relevance as a solid oxide fuel cell component. The method is based on the difference in the magnetic response of the exsolved metallic nickel (ferromagnetic) and Sr-doped lanthanum chromite ceramic matrix (paramagnetic). The exsolved nickel results in coherent nanoparticles pinned on the surface of the Sr-doped lanthanum chromite ceramic matrix, as evidenced by electron microscopy analyses. The results obtained indicate the procedure as a fast and sensitive method to study the exsolution of ferromagnetic nanoparticles.     

Synthesis and optical and transport properties of a phenyl‐substituted polythiophene

The synthesis and characterization of a novel polythiophene substituted with a 2′‐pentyloxy‐5′‐(1″′‐oxooctyl) phenyl group (PPOPT) is reported. The bulk transport properties of thin films of PPOPT are investigated by admittance spectroscopy. The dramatic effect of the phenyl side chain on the mobility of positive carriers in films of PPOPT is described. The photophysics of PPOPT in both solution and thin film is also investigated and correlated to substituent‐driven intrachain and interchain arrangements. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Experimental and Theoretical Study of Helium Broadening and Shift of HCO+ Rotational Lines

An experimental and theoretical study of pressure broadening and pressure shift of HCO⁺ rotational lines perturbed by collisions with He is presented. Results are reported from measurements at 88 K for the lines j=4←3, 5←4 and 6←5 with frequencies ranging from 0.35 to 0.54 THz. Using a new CCSD(T)/aug‐cc‐pVQZ potential energy surface for the He–HCO⁺ interaction, the collisional line shape parameters are studied from fully quantum and semiclassical calculations. Results from the quantum treatment are in satisfactory agreement with experiments whereas the semiclassical approach can lead to appreciable differences. A study of the dependence of line width Γ and shift s as a function of the translational energy shows the presence of quantum oscillations. Calculations on a previous Hartree–Fock‐based potential energy surface lead to quite similar results for the collisional line shape parameters. Using a simplified version of the potential morphing method it is found that the line width Γ is particularly sensitive to the long‐range part of the potential energy surface. This also explains the success of the first line‐broadening calculations which date back to the 1950s.     

On the solution of indefinite systems arising in nonlinear programming problems

This work is concerned with the convergence properties and the numerical analysis of the preconditioned conjugate gradient (PCG) method applied to the solution of indefinite linear systems arising in nonlinear optimization. Our approach is based on the choice of quasidefinite preconditioners and of a suitable factorization routine. Some theoretical and numerical results about these preconditioners are obtained. Furthermore, we show the behaviour of the PCG method for different formulations of the indefinite system and we compare the effectiveness of the proposed variants. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

Optical and ODMR investigation of the low lying excited states of neat α-oxalic acid dihydrate

The lowest excited singlet and triplet states of neat α-oxalic acid dihydrate have been investigated by optical, optical Zeeman, and zero-field optically detected magnetic resonance (ODMR) spectroscopy at T ? 4 K. The observed electronic transitions in absorption are assigned as ¹A_u ← ¹A_g (ν₀ = 34131 cm^?1) from its normal polarizatio These correspond to the expected lowest lying ^1,3nπ* excitations in trans-α-dicarbonyls. The ³A_u → ¹A_g phosphorescence is also observed. Monitoring the phosphorescence intensity, the fine structure splittings and principal axes' orientation and the kinetic parameters of the ³A_u s The fine structure constants are X = 2510.0, Y = ?1800.3, and Z = ?709.7 MHZ where the x axis is in-plane and parallel to the carbo The absolute signs of the constants have been established by optical Zeeman measurements. The τ_x zero-field spin state has the largest total phosphorescence rate, radiative rate, and populating rate. The τ_x activity in the 0 - 0 band is polarized mainly along the x axis. However, considerable normal polarization associated with an in-p     

The ideal relativistic rotating gas as a perfect fluid with spin

We show that the ideal relativistic spinning gas at complete thermodynamical equilibrium is a fluid with a non-vanishing spin density tensor σ_μν. After having obtained the expression of the local spin-dependent phase-space density f(x, p)_στ in the Boltzmann approximation, we derive the spin density tensor and show that it is proportional to the acceleration tensor Ω_μν constructed with the Frenet-Serret tetrad. We recover the proper generalization of the fundamental thermodynamical relation, involving an additional term −(1/2)Ω_μνσ^μν. We also show that the spin density tensor has a non-vanishing projection onto the four-velocity field, i.e. t^μ = σ_μνu^ν ≠ 0, in contrast to the common assumption t^μ = 0, known as Frenkel condition, in the thus-far proposed theories of relativistic fluids with spin. We briefly address the viewpoint of the accelerated observer and inertial spin effects.     

Remarkable variations in the luminescence of frozen solutions of [Au[C(NHMe)(2)](2)](PF(6)) x 0.5(acetone). Structural and spectroscopic studies of the effects of anions and solvents on Gold(I) carbene complexes

The unusual luminescence behavior of the two-coordinate gold(I) carbene complex, [Au[C(NHMe)(2)](2)](PF(6)) x 0.5(acetone), is reported. Upon freezing in a liquid N(2) bath, the colorless, nonluminescent solutions of [Au[C(NHMe)(2)](2)](PF(6)) x 0.5(acetone) become intensely luminescent. Strikingly, the colors of the emission differ in different solvents and appear only after the solvent has frozen. Solid [Au[C(NHMe)(2)](2)](PF(6)) x 0.5(acetone) is also luminescent, and the luminescence is attributed to the formation of extended chains of gold(I) centers that are connected through aurophilic attractions. Crystallographic studies of [Au[C(NHMe)(2)](2)](PF(6)) x 0.5(acetone) and [Au[C(NHMe)(2)](2)](BF(4)), which is also luminescent, reveal that both involve extended chains of cations and that the anions are hydrogen bonded to the cations through cation N-H groups. However, these chains differ in the Au...Au separations in each and in the carbene ligand orientations. In contrast, [Au[C(NMe(2))(NHMe)](2)](PF(6)) forms a colorless, nonluminescent solid, and in that solid there are no Au...Au interactions, a factor which supports the contention that aggregated species are responsible for the luminescence of [Au[C(NHMe)(2)](2)](PF(6)) x 0.5(acetone) in the solid state and in frozen solutions.     

Diazocinones: synthesis and conformational analysis

1,2,4,5-Tetrazines (prepared from aryl nitriles) condense with isoxazolylcyclobutanones (prepared from 3-benzenesulfonyl-3-vinylcyclobutanol) in methanolic KOH to give conformationally restricted 6-isoxazol-5-yl-6,7-dihydro-5H-[1,2]diazocin-4-ones. The solution 1H NMR spectra of dihydrodiazocinone 1a with phenyl moieties at C3 and C8 reveal two conformations of the eight-membered heterocycle that are non-interconverting on the NMR time scale at ambient temperature. The kinetics of the conversion process, followed by 1H NMR between 21 and 70 degrees C in DMSO solution, yield an activation energy of approximately 21 kcal/mol relative to the kinetic conformer and show an equilibrated ratio of approximately 5:1 of the thermodynamic to the kinetic conformers. The electronic structure calculations on a model dihydrodiazocinone predict geometries for the two conformations. One of these geometries agrees with the X-ray crystallographic analysis of the thermodynamic conformation of 1a.     

New structural motifs in the aggregation of neutral gold(I) complexes: structures and luminescence from (alkyl isocyanide)AuCN

The preparation and X-ray crystal structures of (CyNC)Au(I)CN, (n-BuNC)Au(I)CN, and (i-PrNC)Au(I)CN.0.5CH(2)Cl(2) are reported and compared with those of (MeNC)Au(I)CN and (t-BuNC)Au(I)CN, which were previously described. These linear molecules are all organized through aurophilic interactions into three structural classes: simple chains ((CyNC)Au(I)CN and (t-BuNC)Au(I)CN), side-by-side chains in which two strands make Au...Au contact with each other ((n-BuNC)Au(I)CN), and nets in which multiple aurophilic interactions produce layers of gold(I) centers ((i-PrNC)Au(I)CN and (MeNC)Au(I)CN). All of these five solids dissolve to produce colorless, nonluminescent solutions with similar UV/vis spectra. However, each of the solids displays a unique luminescence with emission maxima occurring in the range 371-430 nm.