Anisotropy inc-axis oriented YBa2Cu3O7−δ

Muon spin relaxation (μSR) data taken at LAMPF on ac-axis oriented fine powder sample of YBa₂Cu₃O_7−δ (YBCO) embedded in epoxy are analyzed for relaxation rate anisotropy. Clear differences beyond simple magnetic field penetration depth anisotropy are observed forB‖c andB c. The low-temperature anisotropy ratio is consistent with oriented ceramic data. Small crystallite size and anisotropic flux pinning characteristics are suggested as the fundamental cause of the additional effects.     

Effective index method for planar lightwave circuits containing directional couplers

A simple and intuitive effective index method for planar lightwave circuits containing directional couplers is proposed. The optimal cladding refractive index of the effective two-dimensional planar waveguide is found according to the coupling length of the directional coupler involved. Numerical examples indicate that this proposed effective index method gives accurate results while saving significant computation time in simulation and design of planar lightwave circuits containing directional couplers.     

Designing SISO observers with unknown input

In this paper we investigate the observer design for Single-InputSingle-Output (SISO) systems with unknown input. We find thatthe design conditions proposed by several authors in the pastlead to unity relative degree of the plant and zeros of theplant in the open left half of the complex plane, for SISO systems.In other words an observer for a SISO plant with unknown inputcan be designed if and only if the plant is of unity relativedegree and the numerator of the transfer function is Hurwitz.These conditions have an interesting consequence in the contextof model reference adaptive control (MRAC) for the case of relativedegree one, in the sense that strictly real positive (SPR) conditionfor the model reference is not needed.     

Subharmonics near an equilibrium point for hamitonian systems

This work is devoted to the study of subharmonic solutions near an equilibrium for certain Hamiltonian systems. We impose a weak condition on the Floquet exponents of the linearized system, and a superquadratic condition on the higher order term. This last condition is reduced to the center manifold. This research was supported in part by the Air Force Office of Scientific Research under Grant AFOSR-87-0202.     

Ordered mesoporous silicates of MCM-41 type as support of pt catalysts for the enantioselective hydrogenation of 1-phenyl-1,2-propanedione

Summary Platinum catalysts (1 wt.%) supported on MCM-41 type and SiO₂have been prepared, characterized and evaluated in the enantioselective hydrogenation of 1-phenyl-1,2-propanedione at 298 K and 20 bar of hydrogen pressure, using cinchonidine (CD) as chiral modifier. Chemisorption and TEM results revealed that both catalysts posses similar metal dispersion, however, significant differences in the catalytic behavior were observed. With dichloromethane as solvent, high hydrogenation rates and ee values around 47% were obtained for the Pt/MCM-41 catalyst. This fact is attributed to a confinement effect. The initial reaction rate is strongly dependent on the CD concentration, and the reaction rate (or ee) vsCD concentration plot exhibits bell-type curves. The main products were (R) -1-hydroxy-1-phenylpropanone and (S) -1-hydroxy-1-phenylpropanone.</o:p>     

Closure Łukasiewicz algebras

In this paper, the variety of closure n-valued Łukasiewicz algebras, that is, Łukasiewicz algebras of order n endowed with a closure operator, is investigated. The lattice of subvarieties in the particular case in which the open elements form a three-valued Heyting algebra is obtained.     

Relativistic Multipoles and the Advance of the Perihelia

In order to shed some light in the meaning of the relativistic multipolar expansions we consider different static solutions of the axially symmetric vacuum Einstein equations that in the non-relativistic limit have the same Newtonian moments. The motion of test particles orbiting around different deformed attraction centers with the same Newtonian limit is studied paying special attention to the advance of the perihelion. We find discrepancies in the fourth order of the dimensionless parameter (mass of the attraction center)/(semilatus rectum). An evolution equation for the difference of the radial coordinate due to the use of different general relativistic multipole expansions is presented.     

An O(mlog logD) algorithm for shortest paths

A technique for implementing Dijkstra's shortest paths algorithm is proposed. This method runs in O(mlog logD) time in the worst case, where m is the number of edges and D the length of the longest edge in the graph.