Disaster relief logistics under demand-supply incongruence environment: A sequential approach
APPLIED MATHEMATICAL MODELLING
Authors: Zhan, Sha-lei; Liu, Sen; Ignatius, Joshua; Chen, Daqiang; Chan, Felix T. S.
Several logistics problems involving disaster relief have attracted growing research interest in the recent decade. A commonality among these problems is that demand-supply incongruence is always observed in post-disaster logistics operations due to the limited relief supplies and the randomly increasing relief demands. In such situations, the decision maker fails to meet the total relief demands simultaneously. This study employs a novel decision-making framework, where the traditional disaster relief logistics actions (e.g., vehicles routing and relief allocation) are replaced by periodic, sequential actions involving demand point location and assignment. A sequential approach allows the decision maker, in the face of every demand-point, to decide whether to locate and assign it to relief suppliers immediately or later, which sequentially influences the decision in the next period. A dynamic optimization model is built and solved by using particle swarm optimization algorithm. The results of a case study indicate the advantages of the sequential approach. (C) 2020 Elsevier Inc. All rights reserved.
A modeling study of predator-prey interaction propounding honest signals and cues
APPLIED MATHEMATICAL MODELLING
Authors: Al-Salman, Ahd Mahmoud; Chavez, Joseph Paez; Wijaya, Karunia Putra
Honest signals and cues have been observed as part of interspecific and intraspecific communication among animals. Recent theories suggest that existing signaling systems have evolved through natural selection imposed by predators. Honest signaling in the interspecific communication can provide insight into the evolution of anti-predation techniques. In this work, we introduce a deterministic three-stage, two-species predator-prey model, which modulates the impact of honest signals and cues on the interacting populations. The model is built from a set of first principles originated from signaling and social learning theory in which the response of predators to transmitted honest signals or cues is determined. The predators then use the signals to decide whether to pursue the attack or save their energy for an easier catch. Other members from the prey population that are not familiar with signaling their fitness observe and learn the technique. Our numerical bifurcation analysis indicates that increasing the predator's search rate and the corresponding assimilation efficiency gives a journey from predator-prey abundance and scarcity, a stable transient cycle between persistence and near-extinction, a homoclinic orbit pointing towards extinction, and ultimately, a quasi-periodic orbit. A similar discovery is met under the increment of the prey's intrinsic birth rate and carrying capacity. When both parameters are of sufficiently large magnitudes, the separator between honest signal and cue takes the similar journey from a stable equilibrium to a quasi-periodic orbit as it increases. In the context of modeling, we conclude that under prey abundance, transmitting error-free honest signals leads to not only a stable but also more predictable predator-prey dynamics. (C) 2020 Elsevier Inc. All rights reserved.