Aspects of Interacting Electromagnetic and Torsion Fields

The interaction energy is studied for the coupling of axial torsion fields with photons in the presence of an external electromagnetic field. To this end, we compute the static quantum potential. Our discussion is carried out using the gauge-invariant but path-dependent variables formalism, which is alternative to the Wilson loop approach. Our results show that the static potential is a Yukawa correction to the usual static Coulomb potential. Interestingly, when this calculation is done by considering a mass term for the gauge field, the Coulombic piece disappears leading to a screening phase.     

Optimal Planning of a Multi-Station System with Sojourn Time Constraints

This paper studies a dynamic production system where multiple products must visit stations where inventories are constrained by maximum and minimum sojourn times with neither negative flow nor backlog being allowed. A resource availability constraint limits the aggregate throughput of the stations. The objective is to minimize the sum of flow and inventory cost. The problem is broken down into several single-product serial systems that serve as subroutines of a Lagrangian relaxation routine. This model is implemented in a spreadsheet so that it can be used by the officials of a Chilean institution for planning the operations and defining the optimal allocation of resources.     

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.     

Observation of surface states of hydrogen on a Rh/TiO2 catalyst by NMR spectroscopy

The proton NMR spectra of H₂ adsorbed on a Rh/TiO₂ catalyst have been measured. The presence of two kinds of hydrogenic species has been observed.     

Trace metal concentrations in single specimens of the intestinal broad flatworm (Diphyllobothrium latum), compared to their fish host (Oncorhynchus mykiss) measured by total reflection X-ray fluorescence spectrometry

The aim of this study was to investigate (1) whether intestine endoparasites (Diphyllobothrium latum) accumulate trace elements related to its body size and (2) whether parasites bioconcentrate more trace elements than their host. Freshwater fish (rainbow trout Oncorhynchus mykiss) were sampled in the deep, oligotrophic and uncontaminated Lake Riñihue in Southern Chile. The element concentration of different organs (intestine, muscle, liver) and of the intestine endoparasites were analyzed using total reflection X-ray fluorescence spectrometry. The results showed that the mass fraction for Mn, Fe, Ni, Cu, and Pb decreased significantly with the body size (dry weight) of the endoparasite. Only Zn did not reveal such a relationship. Small parasites accumulated up to 80 times more Fe, Ni, Mn, Pb, and Cu than large parasites. Compared to the fish organs, small parasites accumulated in maximum 35 to 307 times more Mn, 5 to 255 times more Fe, 98 to 220 times more Ni, 3 to 175 times more Cu, and 0.4 to 12 times more Zn than the fish. Lead was only found in the endoparasite, but not in the fish organs. We conclude that (1) D. latum is a good indicator for trace element accumulation in fishes and that (2) small endoparasites are more sensitive as bioindicators because they showed higher bioconcentrations of trace metals than larger parasites.