Minimizing Labor Requirements in a Periodic Vehicle Loading Problem

In this paper, we address a logistics problem that a manufacturer of auto parts in the north of Spain described to the authors. The manufacturer stores products in its warehouse until customers retrieve them. The customers and the manufacturer agree upon an order pickup frequency. The problem is to find the best pickup schedule, which consists of the days and times during the day that each customer is expected to retrieve his/her order. For a given planning horizon, the optimization problem is to minimize the labor requirements to load the vehicles that the customers use to pick up their orders. Heuristically, we approach this situation as a decision problem in two levels. At the first level, customers are assigned to a calendar, consisting of a set of days with the required frequency during the planning horizon. Then, for each day, the decision at the second level is to assign each customer to a time slot. The busiest time slot determines the labor requirement for a given day. Therefore, once customers have been assigned to particular days in the planning horizon, the second-level decision is a multiprocessor scheduling problem, where each time slot is the equivalent of a processor, and where the objective is to minimize the makespan. A metaheuristic procedure is developed for the problem of minimizing labor requirements in this periodic vehicle-loading problem and artificial as well as real data are used to assess its performance.     

Stochastic Bounds for the Sparre Andersen Process

In this paper we define two stochastic processes that are smaller and greater in usual stochastic order than the Sparre Andersen process. We derive, as a consequence, upper and lower bounds of its marginal distributions, and of the distributions of its first passage times above fixed thresholds. We also present a generalization of these stochastic bounds for risk processes perturbed by diffusion.AMS 2000 Subject Classification: 60K10, 60E15Partially supported by the italian PRIN-Cofin 2004 “Stochastic models in mathematical finance” (F. Pellerey) and PRIN-Cofin 2003 “Numerical, analytical and simulation methods with reference to reliability in neuronal signal transmission” (C. Zucca).     

DTI of trabecular bone marrow

The development of NMR diffusion imaging and diffusion tensor imaging (DTI) has offered the possibility of studying the porous structures beyond anatomical imaging. In fact, random molecular motions, within tissue components, probe tissue microstructures. Up to now, the DTI method was mainly used to investigate cerebral morphology and study white matter diseases. In this study, it has been applied to trabecular bone marrow analysis to obtain structural information on spongy bone tissue. Our first results show that DTI could represent an important tool in studying the microstructural architecture of the trabecular bone as well as the microarchitecture of porous media.     

Membrane receptor probes: solid-phase synthesis of biotin-Asp-PEG-arvanil derivatives

[structure: see text] A modular, flexible solid-phase synthetic route for the preparation of biotinylated cross-linking probes of membrane receptors is described. The route utilizes an orthogonal protection strategy employing a Pd[0] cleavable allyl linker attached to the probe via an aspartate residue. The versatility of the method is illustrated through the synthesis of a number of arvanil-derived cannabinoid receptor ligands displaying either a photoaffinity or a chemical cross-linking group.     

Thermal behavior of some aromatic copolyethers containing a propylenic spacer

The main objective of this paper is to study the thermal stability of some aromatic copolyethers containing a propylenic spacer. Some of the investigated copolyethers displayed a liquid crystalline (LC) behavior, with the presence of the mesogenic groups in the main chain, inducing high values of the thermal transition temperatures. As a consequence, a thermal stability study was necessary to establish the maximum temperature value for the LC behavior characterization. A thermal degradation mechanism is proposed, taking into consideration the azobenzenic unit as the weakest link in the polymer chain and thus, the starting point of the thermal degradation process. The degradation mechanisms were correlated with the chemical structure and the polarity and conformation of the chains. Conformational analysis was performed using molecular simulations. Freeman-Caroll and Coats-Redfern methods were used to calculate some kinetic characteristics.     

The methoxycarbonylation of aryl chlorides catalysed by palladium complexes of bis(di-tert-butylphosphinomethyl)benzene

A catalyst system based on palladium-1,2-bis-(di-tert-butylphosphinomethyl)benzene (BDTBPMB) shows good activity for the methoxycarbonylation of strongly activated aryl chlorides, like 4-chloromethylbenzoate or 4-chlorocyanobenzene. Surprisingly, the use of less activated aryl chlorides, like 4-chloroacetophenone, leads to the formation of dimethyl terephthalate amongst other products arising from organic reactions of methoxide ion and/or CO. Less nucleophilic alcohols such as 2,2,2-trifluoroethanol promote the formation of carbonylation products even from 4-chloroacetophenone and chlorobenzene. Labelling studies involving CD3OH, CD3OD or 13CO give information on the origin of many of the products.     

Constructive techniques for approximating collocation linear systems

A high order discretization by spectral collocation methods of the elliptic problem $$\begin{gathered} \left\{ \begin{gathered} A_{A,b} u \equiv - \nabla [A(x)\nabla u(x)] + b(x)u(x) = c(x){\text{ on}}\;\Omega \; = ( - 1,1)^2 \hfill \\ u\left| {\partial \Omega \equiv 0,} \right. \hfill \\ \end{gathered} \right. \hfill \\ \hfill \\ \end{gathered} $$ is considered where A(x)=a(x)I ₂, x=(x ^[1],x ^[2]) and I ₂ denotes the 2×2 identity matrix, giving rise to a sequence of dense linear systems that are optimally preconditioned by using the sparse Finite Difference (FD) matrix-sequence {A _n } _n over the nonuniform grid sequence defined via the collocation points [11]. Here we propose a preconditioning strategy for {A _n } _n based on the “approximate factorization” idea. More specifically, the preconditioning sequence {P _n } _n is constructed by using two basic structures: a FD discretization of (1) with A(x)=I ₂ over the collocation points, which is interpreted as a FD discretization over an equidistant grid of a suitable separable problem, and a diagonal matrix which adds the informative content expressed by the weight function a(x). The main result is the proof that the sequence {P _n ^?1 A _n } _n is spectrally clustered at unity so that the solution of the nonseparable problem (1) is reduced to the solution of a separable one, this being computationally more attractive [2,3]. Several numerical experiments confirm the goodness of the discussed proposal.     

Synthesis and electrochemical characterization of dipyrroles separated by diphenyleneoxide and diphenylenesulfide spacers via the Trofimov reaction

4,4′-Bis[2-(1-vinylpyrrolyl)]diphenyloxide, 4,4′-bis(2-pyrrolyl)diphenylsulfide, 4-(2-pyrrolyl)-4′-[2-(1-vinylpyrrolyl)]diphenylsulfide and 4,4′-bis[2-(1-vinylpyrrolyl)]diphenylsulfide have been synthesized in a one-pot procedure from oximes of corresponding diacetylphenylenoxide and -sulfide through their reaction with acetylene in the MOH-DMSO systems (M=Li, K) at 80-130 °C under pressure of 10-15 atm, thus illustrating applicability and general character of the reaction of synthesis of diverse dipyrrole-phenylene assemblies and their N-vinyl derivatives. Two of the pipyrroles are promising for creating new conducting polymers with sulfur and oxygen atoms in the conjugation chain and for the study of the influence of the diphenyleneheteroatom moiety on conductivity of final polymer products. For the dipyrroles with the diphenyleneheteroatom moieties and 1,4-phenylene spacer the luminescence characteristics were determined.