Emergent rotational symmetries in disordered magnetic domain patterns

Uniaxial systems often form labyrinthine domains that exhibit short-range order but are macroscopically isotropic and would not be expected to exhibit precise symmetries. However, their underlying frustration results in a multitude of metastable configurations of comparable energy, and driving such a system externally might lead to pattern formation. We find that soft x-ray speckle diffraction patterns of the labyrinthine domains in CoPd/IrMn heterostructures reveal a diverse array of hidden rotational symmetries about the magnetization axis, thereby suggesting an unusual form of emergent order in an otherwise disordered system. These symmetries depend on applied magnetic field, magnetization history, and scattering wave vector. Maps of rotational symmetry exhibit intriguing structures that can be controlled by manipulating the applied magnetic field in concert with the exchange bias condition.     

A Born scatterer in an acoustical waveguide

Scattering from a Born inhomogeneity in a homogeneous, acoustical waveguide is considered and results compared to the corresponding scattering in a homogeneous, unbounded medium. It is found that the Ewald sphere in the unbounded medium case is replaced by a Ewald "strip" in a waveguide, the strip consisting of many individual Ewald spheres embedded in a ball the radius of which is twice that of an individual sphere. The physics behind the Ewald strip is discussed along with the implications of waveguide Born data.     

Scheduling and control,performance measures and discrete event simulation

There are a growing number of finite capacity scheduling tools which are in use and available to industry. To be fully effective, a scheduling system needs to be incorporated within a control methodology which enables shop-floor performance to be analysed and, when necessary, corrective actions to be formulated. Manufacturing system performance, however, is not only dependent upon short-term planning decisions, but is also constrained by the capability for which it is designed. Hence, any control methodology should be based on a consistent set of performance measures and well defined procedures which help to integrate decision making at all levels in the order fulfilment process. The paper examines the distinctive roles of process optimisation and process control in the decision hierarchy; it classifies a set of measures of performance and other system variables according to the functions they serve in manufacturing control, and suggests a hierarchical process control methodology. The role of discrete event simulation techniques in linking decisions on manufacturing system design and production planning/control is also discussed.     

Stress in polycrystalline GaN films prepared by r.f sputtering

Undoped, Be-doped and Si-doped polycrystalline GaN films were deposited by R.F. sputtering onto fused silica substrates. The films were deposited at various deposition temperatures ranging from 300 K to 623 K and characterized by optical measurements while the microstructural information was obtained from SEM and XRD studies. The compositional study for the GaN film was carried out using SIMS. Residual stresses in these films were evaluated from the band tail of the absorption spectra as well as from direct measurements of hardness by commercially available depth sensing indentometer. It was observed that undoped GaN films had the highest hardness followed by that for Be-doped and Si-doped films. The values of hardness obtained form the above optical measurement tallied quite well with those obtained from direct indentation measurement.     

Diastereoselective arylithium addition to an alpha-trifluoromethyl imine. Practical synthesis of a potent cathepsin K inhibitor

A practical, chromatography-free synthesis of potent cathepsin K inhibitor 1 is described. The addition of 4-bromophenyllithium to an alpha-trifluoromethylimine derived from commercially available (S)-leucinol was accomplished in a highly diastereoselective manner (97.6% de, 91% yield). Subsequent Suzuki cross-coupling afforded biaryl 7. Oxidation of the alcohol and sulfide functionalities led to the formation of carboxylic acid 8. Crystallization of 7 and acid 8 as its dicyclohexylamine salt gave excellent impurity rejection. The final amide coupling with commercially available aminoacetonitrile hydrochloride afforded 1 in excellent purity (99.6A% by HPLC, 100% de, <3 ppm Pd, W, Cr).     

Thermal hysteresis of some important physical properties of nanoparticles

Gold nanoparticles show thermal hysteresis with properties such as surface plasmon absorption, conductivity, and zeta potential. The direction of the incremental change in plasmon peak position and its extinction depend on the nature of surface conjugation. The thermal profile of a surface plasmon resonance spectrum for nanoparticles may serve as a signature for the associated small molecule or macromolecule on which it is seeded. The thermal responses of zeta potential and conductivity profile are found to be independent of the surface conjugation with the later being subjected to a phase transition phenomenon as revealed by a temperature criticality.     

Synthesis of S-Glycosyl Xanthates by Phase Transfer Catalyzed Substitution of Glycosyl Halides

Abstract

Peracetylated glycosyl- and glycobiosyl bromides and chlorides 1-4 including acetochloroneuraminic acid 5 were stereoselectively transformed into their corresponding S-glycosyl xanthates 6-10 in high yield (91-98%) under phase transfer catalyzed conditions. The reactions occurred at room temperature using tetrabutylammonium hydrogen sulfate as the catalyst. The substitutions gave complete inversion of configuration and thus proceeded by an S_N2 type mechanism. Changing the organic solvent from methylene chloride to ethyl acetate had no detrimental effect on the outcome of the reactions but avoided an undesirable side reaction between the xanthate anion and methylene chloride.     

A chemometric analysis of ab initio vibrational frequencies and infrared intensities of methyl fluoride

Factorial design and principal component analyses are applied to CH₃F infrared frequencies and intensities calculated from ab initio wave functions. In the factorial analysis, the quantitative effects of changing from a 6–31G to a 6–311G basis, of including polarization and diffuse orbitals, and of correcting for electron correlation using the second-order Møller-Plesset procedure are determined for all frequencies and intensities. The most significant main effect observed for the frequencies corresponds to the shift from Hartree-Fock to MP2 calculations, which tends to lower all frequency values by approximately 100 cm⁻¹. For the intensities, the main effects are larger for the CF stretching and the CH₃ asymmetric stretching modes. Interaction effects between two or more of the four factors are found to be of minor importance, except for the interaction between correlation and polarization. The principal component analysis indicates that wave functions with polarization and diffuse orbitals at the second-order Møller-Plesset level provide the best estimates for the harmonic frequencies, but not for the intensities. For the frequencies, the first principal component distinguishes between MP2 and Hartree-Fock calculations, while the second component separates the wave functions with polarization orbitals from those without these orbitals. For the intensities, the separation is similar but less well defined. This analysis also shows that wave function optimization to calculate accurate intensities is more difficult than an optimization for frequencies. © 1996 by John Wiley & Sons, Inc.     

The non-commutative oscillator, symmetry and the Landau problem

The isotropic oscillator on a plane is discussed where the coordinate and momentum space are both considered to be non-commutative. We also discuss the symmetry properties of the oscillator for three separate cases when the non-commutative parameters Θ and for x and p-space, respectively, satisfy specific relations. We compare the Landau problem with the isotropic oscillator on non-commutative space and obtain a relation between the two non-commutative parameters and the magnetic field of the Landau problem.     

Self-consistent perturbation theory

The density matrix form of Hartree-Fock perturbation theory is developed for the case in which the basis functions themselves are perturbation-dependent. Energy expressions are derived, through second order, for both single and double perturbations.

The theory is applied in the calculation of electric dipole polarizabilities and hyperpolarizabilities for atoms (He, Be) and molecules (H₂, LiH), with excellent results. The high computational efficiency of the method is discussed and possibilities of further development are outlined.