Dipole potentials indicate restructuring of the membrane interface induced by gadolinium and beryllium ions.

The dipole component of the membrane boundary potential, phi(d), is an integral parameter that may report on the conformational state of the lipid headgroups and their hydration. In this work, we describe an experimental approach to measurements of the dipole potential changes, Deltaphi(d), and apply it in studies of Be(2+) and Gd(3+) interactions with membranes composed of phosphatidylserine (PS), phosphatidylcholine (PC), and their mixtures. Deltaphi(d) is determined as the difference between the changes of the total boundary potential, phi(b), measured by the IFC method in planar lipid membranes and the surface potential, phi(s), determined from the electrophoretic mobility of liposomes. The Gouy-Chapman-Stern formalism, combined with the condition of mass balance, well describes the ion equilibria for these high-affinity cations. For the adsorption of Be(2+) and Gd(3+) to PC membranes, and of Mg(2+) to PS membranes, the values of Deltaphi(b) and Deltaphi(s) are the same, indicative of no change of phi(d). Binding of Gd(3+) to PS-containing membranes induces changes of phi(d) of opposite signs depending on the density of ionized PS headgroups in the bilayer. At low density, the induced Deltaphi(d) is negative (-30 mV), consistent with the effect of dehydration of the surface. At maximal density (pure PS, neutral pH), adsorption of Be(2+) or Gd(3+) induces an increase of phi(d) of 35 or 140 mV, respectively. The onset of the strong positive dipole effect on PS membranes with Gd(3+) is observed near the zero charge point and correlates with a six-fold increase of membrane tension. The observed phenomena may reflect concerted reorientation of dipole moments of PS headgroups as a result of ion adsorption and lipid condensation. Their possible implications to in-vivo effects of these high-affinity ions are discussed

Integrated production and outbound distribution scheduling problems with job release dates and deadlines

International audienceIn this paper, we study an integrated production and outbound distribution scheduling model with one manufacturer and one customer. The manufacturer has to process a set of jobs on a single machine and deliver them in batches to the customer. Each job has a release date and a delivery deadline. The objective of the problem is to issue a feasible integrated production and distribution schedule minimizing the transportation cost subject to the delivery deadline constraints. We consider three problems with different ways how a job can be produced and delivered: non-splittable production and delivery (NSP-NSD) problem, splittable production and non-splittable delivery (SP-NSD) problem and splittable production and delivery (SP-SD) problem. We provide a polynomial-time algorithm that solves two special cases of SP-NSD and SP-SD problems. Solving these problems allows us to compute a lower bound for the NP-hard problem NSP-NSD, which we use in a branch and bound (B&B) algorithm to solve problem NSP-NSD. The computational results show that the B&B algorithm outperforms a MILP formulation of the problem implemented on a commercial solver. keywords: single machine scheduling production and delivery release dates deadlines transportation costs branch and bound

p-Center Problems

Language of publication: enInternational audienceno abstrac

Integrated production scheduling and distribution planning with time windows

Ensuring timely product deliveries in supply chains depends on the decisions made at various stages of the supply chain, including the production stage where commodities are made available, and the distribution stage where shipments are made to customers within requested time windows. Delivery times depend on the distribution plans, which are inherently linked to the production schedules, as a commodity must first be produced or procured before being sent onwards in the supply chain. One way to ensure that the delivery times are respected is to perform direct shipments, but this is often costly. In contrast, products can be consolidated whereby several customers are visited on a given vehicle route, but this may result in either early or late deliveries. The challenge is then to devise lean production and distribution schedules that eliminate any redundancy in delivery times. In this chapter, we present an integrated production and outbound distribution scheduling problem with time windows arising in a supply chain. The problem involves jointly deciding on production and distribution operations where a manufacturer is committed first to processing a given set of orders and then to distributing them to the respective customers in different locations. The orders first undergo single processing through a set of identical parallel machines. Once completed, they are delivered by a fleet of vehicles in such a way so as to meet the customer time windows. The objective is to improve the timeliness of the deliveries, which is achieved by minimizing the earliness or tardiness of each order in reaching the customer. The chapter formally introduces the problem, describes integer linear programming formulations for two variants of the problem, and presents computational results on solving randomly generated instances with the proposed formulations.</p