Inventory management of spare parts in an energy company

We address the problem of how to determine control parameters for the inventory of spare parts of an energy company. The prevailing policy is based on an (s, S) system subject to a fill rate constraint. The parameters are decided based mainly on the expert judgment of the planners at different plants. The company is pursuing to conform all planners to the same approach, and to be more cost efficient. Our work focuses on supporting these goals. We test seven demand models using real-world data for about 21?000 items. We find that significant differences in cost and service level may appear from using one or another model. We propose a decision rule to select an appropriate model. Our approach allows us to recommend control parameters for 97.9% of the items. We also explore the impact of pooling inventory for different demand sources and the inaccuracy arising from duplicate item codes.     

Asymptotic analysis of solutions to parabolic systems

We study asymptotics as of solutions to a linear, parabolic system of equations with time-dependent coefficients in , where is a bounded domain. On we prescribe the homogeneous Dirichlet boundary condition. For large values of t, the coefficients in the elliptic part are close to time-independent coefficients in an integral sense which is described by a certain function . This includes in particular situations when the coefficients may take different values on different parts of and the boundaries between them can move with t but stabilize as . The main result is an asymptotic representation of solutions for large t. A consequence is that for , the solution behaves asymptotically as the solution to a parabolic system with time-independent coefficients.     

Approximately central matrix units and the structure of noncommutative tori

The property of approximate divisibility forC*-algebras is introduced and studied. Simple approximately divisibleC*-algebras are shown to have nice nonstableK-theory properties. Non-rational noncommutative tori are shown to be approximately divisible. It follows that every simple noncommutative torus (in particular, every irrational rotation algebra) has stable rank one and real rank zero.     

Optical absorption spectra of PtO and Pt2 in rare-gas matrices

The diatomic molecules, PtO and Pt₂, as well as atomic Pt, were isolated in Ar and Kr matrices at a temperature of ca.12K. The absorption spectra of these species were photographed in the wavelength region 2500–9000 Å. Probably three systems of PtO were observed but none of them seemed to correspond to the earlier analyzed intense systems of gaseous PtO having a ¹Σ state, designated X¹Σ, as their common lower state. The assumption that this state should be the ground state of PtO is thus rather uncertain. A single progression of sharp bands in the near-infrared spectrum was ascribed to the dimer Pt₂. In addition, some absorption lines due to Pt atoms were found in the ultraviolet region.     

A purely infinite AH-algebra and an application to AF-embeddability

We show that there exists a purely infinite AH-algebra. The AH-algebra arises as an inductive limit ofC*-algebras of the formC ₀([0, 1),M _k ) and it absorbs the Cuntz algebra ctive limit of the finite and elementaryC*-algebrasC ₀([0, 1),M _k ). As an application we give a new proof of a recent theorem of Ozawa that the cone over any separable exactC*-algebra is AF-embeddable, and we exhibit a concrete AF-algebra into which this class ofC*-algebras can be embedded.     

Unified treatment of fluorescence and raman scattering processes near metal surfaces

We present a general model study of surface-enhanced resonant Raman scattering and fluorescence focusing on the interplay between electromagnetic effects and the molecular dynamics. Our model molecule is placed close to two Ag nanoparticles and has two electronic levels. A Franck-Condon mechanism provides electron-vibration coupling. Using realistic parameter values for the molecule we find that an electromagnetic enhancement by 10 orders of magnitude can yield Raman cross sections sigma(R) of the order 10(-14) cm(2). We also discuss the dependence of sigma(R) on incident laser intensity.     

Semiclassical calculations of collision line broadening in Raman spectra of N2 and CO mixtures

We present a detailed theoretical study of pressure-broadened Raman line shapes in binary mixtures of nitrogen and carbon monoxide. The semiclassical Robert-Bonamy theory was used to calculate self-broadened Q-branch linewidths of N(2) and CO, and Lennard-Jones (LJ) potential energy surface parameters were fixed by comparing our results with extensive experimental linewidth data. For the case of N(2), the ab initio PES8 potential energy surface was investigated, however, the anisotropic repulsive part had to be reduced to ensure a good agreement with experimental linewidths. The agreement between calculations and experiments was remarkably good, both for self-broadened N(2) and CO Q-branch linewidths. Yet, our calculations were not able to predict the experimentally observed difference between Q- and S-branch linewidths of self-broadened N(2). The central results of this work are the Q-branch linewidths of N(2)-CO and CO-N(2), which have been calculated through an extrapolation of the parameters of the potential energy surfaces used for self-broadened linewidths by common combination rules.     

Optimized interactions for targeted self-assembly: application to a honeycomb lattice

We devise an inverse statistical-mechanical methodology to find optimized interaction potentials that lead spontaneously to a target many-particle configuration. Target structures can possess varying degrees of disorder, thus extending the traditional idea of self-assembly to incorporate both amorphous and crystalline structures as well as quasicrystals. For illustration purposes, our computational technique is applied to yield an optimized isotropic (nondirectional) pair potential that spontaneously yields the three-coordinated honeycomb lattice as the ground state structure in two dimensions. This target choice is motivated by its three-dimensional analog, the diamond lattice, which is known to possess desirable photonic band gap properties.     

Self assembly,structure and properties of the decanuclear lanthanide ring complex,Dy10(OC2H4OCH3)30

Self assembly produced high yields of the lanthanide ring complex Dy10(OC2H4OCH3)30, the largest lanthanide ring known, characterized by X-ray diffraction methods and by magnetic susceptibility as a function of temperature.