Growth and magnetic behavior of bismuth substituted yttrium iron garnet nanoparticles

Crystal growth and the magnetic properties of bismuth substituted yttrium iron garnet (Bi-YIG) nanoparticles were studied with particular focus on the bismuth composition dependence of the magnetic properties of the particles and the effects of annealing on the garnet phase formation. The Bi-YIG nanoparticles of 47–67 nm in size can be chemically synthesized when they are annealed at 650–850 °C. Both the lattice constant and the magnetization of the garnet nanoparticles linearly increase when the bismuth composition in the Bi-YIG particles increases. We have found that chemically synthesized nanoparticles transform from the amorphous to the garnet phase when annealed at temperatures below 650 °C, while the onset of magnetic moment of iron in the garnet nanoparticles is observed slightly above 650 °C. According to Mössbauer effect measurements, the hyperfine fields of ⁵⁷Fe at the tetrahedral and octahedral sites in the garnet are 39 and 48 T, respectively.     

Irradiation-induced magnetism in carbon nanostructures

Nitrogen (15N) and carbon (12C) ion implantations with implant energy of 100 keV for different doses were performed on nanosized diamond (ND) particles. Magnetic measurements on the doped ND show ferromagnetic hysteresis behavior at room temperature. The saturation magnetization (M(s)) in the case of 15N implanted samples was found to be higher compared to the 12C implanted samples for dose sizes greater than 10(14) cm(-2). The role of structural modification or defects along with the carbon-nitrogen (C-N) bonding states for the observed enhanced ferromagnetic ordering in 15N doped samples is explained on the basis of x-ray photoelectron spectroscopy measurements.     

BKLT equations for reactive scattering: a successful application to H + H2

The first successful solution of the BKLT equations for reactive scattering for a realistic potential and three finite mass atoms is reported. These equations are completely general, as is also our non-propagative method of solution and provide a new framework for treating arbitrary reactive scattering problems.     

Self-consistent band structures of higher stage graphite intercalation compounds

Self-consistent non-empirical band structures of third and fourth stage graphite intercalation compounds have been calculated by using the numerical-basis-set LCAO method within the local density functional formalism. The calculations are carried out for a thin film model consisting of n contiguous graphite layers bounded by two partially ionized intercalant layers. The calculated band structures show that most of electrons transferred from the intercalant layers occupy the states in the lowest two conduction π bands mainly localized on the bounding graphite layers. The low-energy optical transitions of higher stage GICs are discussed in terms of the obtained band structures.     

Carbon monoxide as an intrinsic ligand to iron in the active site of the iron-sulfur-cluster-free hydrogenase H2-forming methylenetetrahydromethanopterin dehydrogenase as revealed by infrared spectroscopy

The iron-sulfur-cluster-free hydrogenase Hmd (H(2)-forming methylenetetrahydromethanopterin dehydrogenase) from methanogenic archaea has recently been found to contain one iron associated tightly with an extractable cofactor of yet unknown structure. We report here that Hmd contains intrinsic CO bound to the Fe. Chemical analysis of Hmd revealed the presence of 2.4 +/- 0.2 mol of CO/mol of iron. Fourier transform infrared spectra of the native enzyme showed two bands of almost equal intensity at 2011 and 1944 cm(-)(1), interpreted as the stretching frequencies of two CO molecules bound to the same iron in an angle of 90 degrees . We also report on the effect of extrinsic (12)CO, (13)CO, (12)CN(-), and (13)CN(-) on the IR spectrum of Hmd.     

Nonlinear acoustic response through minute surface cracks: FEM simulation and experimentation

The second harmonic of a Rayleigh wave passing through a minute surface crack has been numerically analyzed by semi-explicit FEM including special elements which account for a nonlinear stress-strain relation at crack surfaces. Minute cracks perpendicular to a free, flat surface close under compressive stress when width of the crack opening is less than the longitudinal amplitude of the Rayleigh wave. Thereafter, compressive and shear stresses are partially transmitted through the closed cracks, whereas tensile and shear stresses are not transmitted through cracks that remain open. This leads to marked nonlinear ultrasonic response. Calculation was performed for an aluminum block having a surface crack. The transverse component of the Rayleigh wave propagating through the cracks shows distorted waveforms, making the second harmonic amplitude clearly noticeable. In an experiment, the second harmonic component of the leaky Rayleigh wave was detected for a simple crack model consisting of two aluminum blocks, by use of a PVDF line-focused transducer. The results of the experiment show that the second harmonic amplitude is a second-order function of the fundamental wave amplitude, and is more pronounced for low compressive stress applied to close the crack surfaces.     

Two novel long-chain alkanoic acid esters of lupeol from alecrim-propolis

Two new long-chain alkanoic acid esters of lupeol were isolated together with known triterpenoids, alpha-amyrin, beta-amyrin, cycloartenol, lanosta-7,24-diene-3beta-ol and lupeol from Alecrim-propolis collected in Brazil. The structures were characterized by spectroscopic means.     

AUSM-like expression of HLLC and its all-speed extension

Advection upstream splitting method (AUSM) and Harten-Lax-van Leer with contact (HLLC) are two popular families of flux functions. The AUSM is simple and requires no eigenstructure, which facilitates its extensions to general equations of state. Furthermore, one of its variants, simple low-dissipation AUSM (SLAU), is applicable to all speeds and features removal of parameter setting by the user. HLLC, on the other hand, clearly defines three distinct waves in Riemann problem, namely, left-running and right-running acoustic waves, and entropy wave. This paper demonstrates that HLLC can be written in a very similar form with the AUSM family and that the similar manner in extending AUSM family to all speeds is easily incorporated into HLLC in this AUSM-like form. Then, we combine the strengths of the both flux functions and offer a new inviscid numerical flux function within the framework of monotone upwind scheme for conservation laws (MUSCL) in computational fluid dynamics (CFD) for Euler and Navier-Stokes equations. The resultant HLLC with low dissipation (HLLCL) numerical flux can compute low Mach number flows and sound propagations at the same time with high accuracy, as demonstrated by one-dimensional and two-dimensional numerical examples. Furthermore, the results indicate that its extensions to general fluids such as supercritical fluids are encouraging.