Blockchain-oriented dynamic modelling of smart contract design and execution in the supply chain

Recently, the applications of Blockchain technology have begun to revolutionise different aspects of supply chain (SC) management. Among others, Blockchain is a platform to execute the smart contracts in the SC as transactions. We develop and test a new model for smart contract design in the SC with multiple logistics service providers and show that this problem can be presented as a multi-processor flexible flow shop scheduling. A distinctive feature of our approach is that the execution of physical operations is modelled inside the start and completion of cyber information services. We name this modelling concept ‘virtual operation’. The constructed model and the developed experimental environment constitute an event-driven dynamic approach to task and service composition when designing the smart contract. Our approach is also of value when considering the contract execution stage. The use of state control variables in our model allows for operations status updates in the Blockchain that in turn, feeds automated information feedbacks, disruption detection and control of contract execution. The latter launches the re-scheduling procedure, comprehensively combining planning and adaptation decisions within a unified methodological framework of dynamic control theory. The modelling complex developed can be used to design and control smart contracts in the SC.     

A High Order Compact Time/Space Finite Difference Scheme for the Wave Equation with Variable Speed of Sound

We consider fourth order accurate compact schemes, in both space and time, for the second order wave equation with a variable speed of sound. We demonstrate that usually this is much more efficient than lower order schemes despite being implicit and only conditionally stable. Fast time marching of the implicit scheme is accomplished by iterative methods such as conjugate gradient and multigrid. For conjugate gradient, an upper bound on the convergence rate of the iterations is obtained by eigenvalue analysis of the scheme. The implicit discretization technique is such that the spatial and temporal convergence orders can be adjusted independently of each other. In special cases, the spatial error dominates the problem, and then an unconditionally stable second order accurate scheme in time with fourth order accuracy in space is more efficient. Computations confirm the design convergence rate for the inhomogeneous, variable wave speed equation and also confirm the pollution effect for these time dependent problems.     

Product quality inspection in Bernoulli lines: analysis,bottlenecks, and design

This paper is devoted to serial production lines consisting of producing and inspection machines that obey the Bernoulli reliability and Bernoulli quality models. Such production lines are encountered in automotive assembly and painting operations where the downtime is relatively short and the defects are due to uncorrelated random events. For these systems, this paper develops analytical methods for performance analysis, bottleneck identification, and design. In addition, insights into the nature of bottlenecks in such systems are provided, and an empirical rule for placing an inspection machine that maximises the production rate of non-defectives is formulated.     

High Diffusion Permeability of Anion-Exchange Membranes for Ammonium Chloride: Experiment and Modeling

It is known that ammonium has a higher permeability through anion exchange and bipolar membranes compared to K⁺ cation that has the same mobility in water. However, the mechanism of this high permeability is not clear enough. In this study, we develop a mathematical model based on the Nernst–Planck and Poisson’s equations for the diffusion of ammonium chloride through an anion-exchange membrane; proton-exchange reactions between ammonium, water and ammonia are taken into account. It is assumed that ammonium, chloride and OH⁻ ions can only pass through membrane hydrophilic pores, while ammonia can also dissolve in membrane matrix fragments not containing water and diffuse through these fragments. It is found that due to the Donnan exclusion of H⁺ ions as coions, the pH in the membrane internal solution increases when approaching the membrane side facing distilled water. Consequently, there is a change in the principal nitrogen-atom carrier in the membrane: in the part close to the side facing the feed NH₄Cl solution (pH < 8.8), it is the NH₄⁺ cation, and in the part close to distilled water, NH₃ molecules. The concentration of NH₄⁺ reaches almost zero at a point close to the middle of the membrane cross-section, which approximately halves the effective thickness of the diffusion layer for the transport of this ion. When NH₃ takes over the nitrogen transport, it only needs to pass through the other half of the membrane. Leaving the membrane, it captures an H+ ion from water, and the released OH⁻ moves towards the membrane side facing the feed solution to meet the NH₄⁺ ions. The comparison of the simulation with experiment shows a satisfactory agreement.     

Energy-Based Micromechanics Analysis on Fatigue Crack Propagation Behavior in Sn-Ag Eutectic Solder

Sn-Ag-eutectic-based solders are replacing Sn-Pb eutectic solders in the electronics industry. The current paper extends the recently developed approach based on phase transformation theory, micromechanics, and fracture mechanics to treat fatigue crack nucleation and propagation for steels and alloys to predict fatigue crack propagation in solder alloys. To verify the proposed method, fatigue experiments were conducted on Sn-3.5Ag solder alloys. Finite element analysis is performed to predict the stress intensity factor range ΔK and the required energy U to increase the crack by a unit area. Unified creep-plasticity theory and a cohesive zone model are incorporated to predict the creep and hysteresis effects on fatigue crack propagation in solder and the interfacial behavior between the solder alloy and the intermetallic layer, respectively. With U determined numerically, the predicted fatigue crack propagation rate using phase transformation theory is compared with experimental data for Sn-3.5Ag and Sn-37Pb eutectic solders. Reasonable agreement between theoretical predictions and experimental results is obtained.     

Buffer capacity for accommodating machine downtime in serial production lines

This paper investigates the smallest level of buffering (LB), necessary to ensure the desired production rate in serial lines with unreliable machines. The reliability of machines is assumed to obey either exponential, or Erlang, or Rayleigh models. The LB is measured in units of the average downtime, T down . The dependence of LB on the reliability model, the number of machines, M , the average uptime, T up , and the efficiency, e = T up /( T up + T down ) is analysed. It is shown that reliability models with larger coefficient of variation require larger LB, and an empirical law that connects LB of the exponential model with those for other reliability models is established. It is shown that LB is an increasing function of M , but with an exponentially decreasing rate, saturating at around M = 10. Also, it is shown that LB does not depend explicitly on T up and is a decreasing function of e . Based on these results, rules-of-thumb are provided for selecting buffer capacity, which guarantee sufficiently high line efficiency.