Reverse logistics facility location using cyclical model of extended MRP theory

Grubbström’s well-developed MRP Theory has been mostly used in modeling production processes. Global supply chains also contain distribution, consumption and recycling processes. For this reason theory was recently further extended to incorporate all kinds of activities. Such extended model, which consists of four main sub-systems, is closed and can be used for several detailed analyses. Since the importance of reverse logistics is increasing, this paper will focus on parameters which determine Net Present Value of the whole system, depending on geographical location of recycling facilities. We will show how lead times, transportation costs, setup costs and price of labor and energy of individual location contribute to overall NPV of the system.     

Finding all systems of weight functions associated with a given extended Chebyshev space

Systems of weight functions and corresponding generalised derivatives are classically used to build extended Chebyshev spaces on a given interval. This is a well-known procedure. Conversely, if the interval is closed and bounded, it is known that a given extended Chebyshev space can always be associated with a system of weight functions via the latter procedure. In the present article we determine all such possibilities, that is, all systems of weight functions which can be used to define a given extended Chebyshev space on a closed bounded interval.     

Delimitation of service areas in reverse logistics networks with multiple depots

This paper describes a heuristic approach for the definition of service (or influence) areas of multiple depots in a reverse logistics network. This work is based on a case study: the recyclable waste collection system with 5 depots that covers seven municipalities in the Alentejo region, southern Portugal. The system optimization considers two objectives, related with economic and organizational issues: minimizing the variable costs (function of the travelled distances by the collection vehicles), and the pursuit of equity, aiming at minimizing the workload differences among depots. The goal of balancing workloads poses a problem not usually treated in the existing literature. This fact required the development of a new approach with innovative elements adjusted to the existing circumstances.     

Mathematical study of trade-off relations in logistics systems

This paper presents a mathematical model of trade-off relations arising in third party logistics using Pareto optimal solutions for multi-objective optimization problems. The model defines an optimal set of distribution costs and service levels constituting a trade-off relation. An analogy to the concept of the indifference curve in the field of economics is discussed. Numerical experiments for a simplified problem are performed, demonstrating an increasing process of the utility of logistics.     

Analytic solutions of unstable interfaces for all density ratios in axisymmetric flows

An interface between two fluids subject to an external force is hydrodynamically unstable. We extend the Layzer-type potential flow model for unstable interfaces to the system of finite density ratio in axially symmetric geometry and derive analytic solutions for growth rates of unstable interfaces over all times. The analytic expressions for bubble growth rates at finite times are given for arbitrary Atwood number. Predictions of the analytic solutions for growth rates are in excellent agreements with numerical results.     

Modeling reverse logistics process in the agro-industrial sector: The case of the palm oil supply chain

As today’s consumers are more and more concerned with the environmental impacts of products and services they buy, enterprises have been more and more concerned with “green operations”. One of the key aspects of green logistics management is reverse logistics. This paper shows how the potential of managing reverse logistics flows can be implemented in the agro-industrial sector. As an example, the palm oil supply chain is considered. This study is carried out under the focus of the “closed-loop supply chain (CLSC) framework” in which forward and backward product flows are considered simultaneously. A mathematical model is proposed in order to represent the dynamic interaction between flows. The objective function considers energy, cost and economic profits. Different implementation scenarios of recovery processes are proposed and interactions between direct and reverse flows in the chain are evaluated. Results are analyzed using proper statistical tools, showing that the simultaneous analysis of direct and reverse flows positively impact the net economic profits in this complex supply chain of the agro-industrial sector.     

Theory of nonstationary flows of Maxwell fluids in aqueous solutions of polymers

One proves theorems of existence in the small for the classical solutions of a periodic initial-boundary-value problem and of the Cauchy problem for the system of integrodifferential equations describing the motion of Maxwell fluids of order N=1, 2, ... and also theorems of existence in the small for weak (relative to t) solutions of a periodic intial-boundary-value problem and of the Cauchy problem for the system of differential equations describing the motion of aqueous solutions of polymers.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 127, pp. 158–168, 1983.     

Classification of the types of instability of vertical flows in geothermal systems

Stability of vertical flows in geothermal systems is investigated in the case when the domain occupied by water (heavy fluid) is located over the domain occupied by vapor. It is found that under the transition to an unstable regime in a neighborhood of the existing solution, a pair of new solutions appears as a result of the turning point bifurcation. We consider the dynamics of a narrow band of weakly unstable and weakly nonlinear perturbations of the plane surface of the water-to-vapor phase transition. It is shown that such perturbations obey the generalized Ginzburg-Landau-Kolmogorov-Petrovsky-Piscounov equation.     

The method of decomposition over velocities in the dynamics of extended systems

We propose a new method of solving multimodal problems of the dynamics of nonlinear extended shells, plates, and bars in a field of distributed mass and surface forces. We study the mode of motion of a towed system with the body in the steady state and under acceleration. We propose a new version of the method of decomposition based on identifying the characteristic times of propagation of various modes in the system, which can be used with success in the early stage of design of shell and bar structures, and also in problems of control of towed systems. Translated fromDinamicheskie Sistemy, No. 13, 1994. pp. 73-2-80.     

Cooperation in assembly systems: The role of knowledge sharing networks

Process improvement plays a significant role in reducing production costs over the life cycle of a product. We consider the role of process improvement in a decentralized assembly system in which a buyer purchases components from several first-tier suppliers. These components are assembled into a finished product, which is sold to the downstream market. The assembler faces a deterministic demand/production rate and the suppliers incur variable inventory costs and fixed setup production costs. In the first stage of the game, which is modeled as a non-cooperative game among suppliers, suppliers make investments in process improvement activities to reduce the fixed production costs. Upon establishing a relationship with the suppliers, the assembler establishes a knowledge sharing network – this network is implemented as a series of meetings among suppliers and also mutual visits to their factories. These meetings facilitate the exchange of best practices among suppliers with the expectation that suppliers will achieve reductions in their production costs from the experiences learned through knowledge sharing. We model this knowledge exchange as a cooperative game among suppliers in which, as a result of cooperation, all suppliers achieve reductions in their fixed costs. In the non-cooperative game, the suppliers anticipate the cost allocation that results from the cooperative game in the second stage by incorporating the effect of knowledge sharing in their cost functions. Based on this model, we investigate the benefits and challenges associated with establishing a knowledge sharing network. We identify and compare various cost allocation mechanisms that are feasible in the cooperative game and show that the system optimal investment levels can be achieved only when the most efficient supplier receives the incremental benefits of the cost reduction achieved by other suppliers due to the knowledge transfer.     

Some extended analyses concerning the physics and kinematics of wave propagation in moving systems

For studying the details of the physical processes concerning space-time relations of signal exchanges in moving inertial-systems, it is purposeful to make at first a short exposition of the kinematics of electromagnetic wave propagation from a moving source to a stationary or moving field point in the free unbounded space. An introductory analysis on the kinematics of wave propagation from a source to an observer in a moving inertial system follows thereafter, primarily for elucidating the natural causality of the source and the observer remaining centered at the common midpoint of the radiating waves, without undergoing any relative drift. Special emphasis is then put to study the space-time relations of wave propagation from a source to an observer in the moving inertial system. The use of the emitting and receiving signal-cones in the moving system, with their common plane-cut, provides all the details with convincing insights concerning the causality and effect, both in the absolute space and in the Lorentz-space. The essential findings are elucidated with application to numerical examples and corresponding illustrations.      

Nonlinear systems arising from nonisothermal, non-Newtonian Hele-Shaw flows in the presence of body forces and sources

In this paper, we give a formal derivation of several systems of equations for injection moulding. This is done starting from the basic equations for nonisothermal, non-Newtonian flows in a three-dimensional domain. We derive systems for both (T⁰, p⁰) and (T¹, p¹) in the presence of body forces and sources. We find that body forces and sources have a nonlinear effect on the systems. We also derive a nonlinear “Darcy law”. Our formulation includes not only the pressure gradient, but also body forces and sources, which play the role of a nonlinearity. Later, we prove the existence of weak solutions to certain boundary value problems and initial-boundary value problems associated with the resulting equations for (T⁰,p⁰) but in a more general mathematical setting.