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Publications

Publications by Maria João Santos

2023

Green reverse logistics: Exploring the vehicle routing problem with deliveries and pickups

Authors
Santos, MJ; Jorge, D; Ramos, T; Barbosa-Povoa, A;

Publication
OMEGA-INTERNATIONAL JOURNAL OF MANAGEMENT SCIENCE

Abstract
The Vehicle Routing Problem with Divisible Deliveries and Pickups (VRPDDP) is under-explored in literature, yet it has a wide application in practice in a reverse logistics context, where the collection returnable items must also be ensured along with the traditional delivery of products to customers. problem considers that each customer has both delivery and pickup demands and may be visited twice in the same or different routes (i.e., splitting customers' visits). In several reverse logistics problems, capacity restrictions are required to either allow the movement of the driver inside the vehicle to arrange the loads or to avoid cross-contamination between delivery and pickup loads. In this work, explore the economic and the environmental impacts of the VRPDDP, with and without restrictions the free capacity, and compare it with the traditional Vehicle Routing Problem with Simultaneous Deliveries and Pickups (VRPSDP), on savings achieved by splitting customers visits. An exact method, solved through Gurobi, and an ALNS metaheuristic are coded in Python and used to test well-known and newly generated instances. A multi-objective approach based on the augmented e-constraint method is applied to obtain and compare solutions minimizing costs and CO2 emissions. The results demonstrate that splitting customer visits reduces the CO2 emissions for load-constrained distribution problems. Moreover, savings percentage of the VRPDDP when compared to the VRPSDP is higher for instances with a random network than when a clustered network of customers is considered.

2023

Minimizing Food Waste in Grocery Store Operations: Literature Review and Research Agenda

Authors
Riesenegger, L; Santos, MJ; Ostermeier, M; Martins, S; Amorim, P; Hübner, A;

Publication
Sustainability Analytics and Modeling

Abstract

2009

Comparison of adsorption equilibrium of fructose, glucose and sucrose on potassium gel-type and macroporous sodium ion-exchange resins

Authors
Nobre, C; Santos, MJ; Dominguez, A; Torres, D; Rocha, O; Peres, AM; Rocha, I; Ferreira, EC; Teixeira, JA; Rodrigues, LR;

Publication
ANALYTICA CHIMICA ACTA

Abstract
Adsorption equilibrium of fructose, glucose and sucrose was evaluated on sulfonated poly(styrene-co-divinylbenzene) cation-exchange resins. Two types of resins were used: potassium (K(+)) gel-type and sodium (Na(+)) macroporous resins. Influence of the cation and effect of the resin structure on adsorption were studied. The adsorption isotherms were determined by the static method in batch mode for mono-component and multi-component sugar mixtures, at 25 and 40 degrees C, in a range of concentrations between 5 and 250gL(-1). All adsorption isotherms were fitted by a linear model in this range of concentrations. Sugars were adsorbed in both resins by the following order: fructose > glucose > sucrose. Sucrose was more adsorbed in the Na(+) macroporous resin, glucose was identically adsorbed, and fructose was more adsorbed in the K(+) gel-type resin. Data obtained from the adsorption of multi-component mixtures as compared to the mono-component ones showed a competitive effect on the adsorption at 25 degrees C, and a synergetic effect at 40 degrees C. The temperature increase conducted to a decrease on the adsorption capacity for mono-component Sugar mixtures, and to an increase for the multi-component mixtures. Based on the selectivity results, K(+) gel-type resin seems to be the best choice for the separation of fructose, glucose and sucrose, at 25 degrees C.

2011

Fractionation and recovery of whey proteins by hydrophobic interaction chromatography

Authors
Santos, MJ; Teixeira, JA; Rodrigues, LR;

Publication
JOURNAL OF CHROMATOGRAPHY B-ANALYTICAL TECHNOLOGIES IN THE BIOMEDICAL AND LIFE SCIENCES

Abstract
A method for the recovery and fractionation of whey proteins from a whey protein concentrate (80%, w/w) by hydrophobic interaction chromatography is proposed. Standard proteins and WPC 80 dissolved in phosphate buffer with ammonium sulfate 1 M were loaded in a HiPrep Octyl Sepharose FF column coupled to a fast protein liquid chromatography (FPLC) system and eluted by decreasing the ionic strength of the buffer using a salt gradient. The results showed that the most hydrophobic protein from whey is alpha-lactalbumin and the less hydrophobic is lactoferrin. It was possible to recover 45.2% of beta-lactoglobulin using the HiPrep Octyl Sepharose FF column from the whey protein concentrate mixture with 99.6% purity on total protein basis.

2012

Fractionation of the major whey proteins and isolation of beta-Lactoglobulin variants by anion exchange chromatography

Authors
Santos, MJ; Teixeira, JA; Rodrigues, LR;

Publication
SEPARATION AND PURIFICATION TECHNOLOGY

Abstract
A method for the separation and fractionation of the major whey proteins from a whey protein concentrate (WPC80) by anion-exchange chromatography coupled to a Fast Protein Liquid Chromatography (FPLC) system is proposed. The method is based on the use of an ionic column (Mono Q) and a salt gradient elution by increasing the ionic strength of the elution buffer (Tris-HCl 20 mM plus 0 to 1 M NaCl). The proposed method was found to be suitable to fractionate the major whey proteins from the WPC80 in different fractions, namely one fraction containing all the alpha-Lactalbumin and immunoglobulins; another fraction containing all the bovine serum albumin; and two distinct fractions each containing a different variant of p-Lactoglobulin. A 60.5% (w/w) recovery of the two main p-Lactoglobulin variants was obtained.

2024

Enhancing logistics through a vehicle routing problem with deliveries, pickups, and backhauls

Authors
Santos, MJ; Jorge, D; Bonomi, V; Ramos, T; Póvoa, A;

Publication
International Transactions in Operational Research

Abstract
Today, logistics activities are driven by the pressing need to simultaneously increase efficiency, reduce costs, and promote sustainability. In our research, we tackle this challenge by adapting a general vehicle routing problem with deliveries and pickups to accommodate different types of customers. Customers requiring both delivery and pickup services are mandatory, while those needing only a pickup service (backhaul customers) are optional and are only visited if profitable. A mixed-integer linear programming model is formulated to minimize fuel consumption. This model can address various scenarios, such as allowing mandatory customers to be served with combined or separate delivery or pickup visits, and visiting optional customers either during or only after mandatory customer visits. An adaptive large neighborhood search is developed to solve instances adapted from the literature as well as to solve a real-case study of a beverage distributor. The results show the effectiveness of our approach, demonstrating the potential to utilize the available capacity on vehicles returning to the depot to create profitable and environmentally friendly routes, and so enhancing efficient, cost-effective, and sustainable logistics activities. © 2024 International Federation of Operational Research Societies.

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