Supply management of high-value components with a credit constraint

We examine the effect of stochastic lead times on Just-in-Time (JIT) delivery. We find that with stochastic lead times there is a possibility of order crossover, and what order crossover does is to transform the original lead times into effective lead times, which is an AR(1) process that is an autoregressive process of Order 1. The mean of this process is the same as the mean of the original lead time, but its variance could be much smaller. The implication is that when we consider order crossover in the analysis, the cost could be less than otherwise (but never less than that with deterministic lead times). The literature on JIT with stochastic lead times has never considered order crossover, which produces the effective delivery times (EDT). Here, we demonstrate some important properties of the EDT: that it is a Cauchy sequence, and hence it converges; that it is an AR(1) process; and that it stochastically dominates the parent lead time distribution.

We consider an inventory system for continuous decaying items with stochastic lead time and Poisson demand. Shortage is allowed and all the unsatisfied demands are backlogged. Moreover, replenishment is one for one. Our objective is to minimize the long-run total expected cost of the system. Firstly, we have developed the mathematical model with deterministic lead time. Since the stochastic lead time makes the model complex especially when lead time has complicated probability distribution and it is difficult to prove convexity of the objective function, we have applied simulation modeling approach. The simulation model has no limitation on lead time or any other parameters. The simulation model is validated by comparing its outputs and analytical model's results for the deterministic lead time case. Furthermore, we use optimizer module of the applied software to find near optimal solutions for a number of examples with stochastic lead time.

LT variance or LT mean reduction in supply chain management: Which one has a higher impact on SC performance?

Aims. We present an investigation into how the cooling of the background plasma influences the propagation of slow and fast MHD wave modes supported by an unbounded, homogenous plasma. Previous investigations have suggested that the cooling of the plasma and a reduction in density could lead to the damping of fast magneto-acoustic oscillations. We aim to investigate whether cooling of the background plasma at a constant density may be responsible for the damping of slow and fast modes. Methods. The plasma is assumed homogeneous and the background temperature (pressure) is decreasing with time. The temperature change is assumed to be due to optically thin radiation. A special case of the radiative function is chosen to allow an analytical assessment of the effects of cooling on magneto-acoustic MHD modes and ensures the temperature evolution of the background plasma due to this radiation also matches the observed cooling profile of coronal loops. Results. A time-dependent dispersion relation is obtained on the slow timescale of cooling and full time-dependent solutions are found. Leading order equations for the amplitude of the waves are obtained and solved analytically for the slow and fast MHD modes. The cooling of the plasma is found to cause the frequency of the magneto-acoustic modes to decrease with time. The slow modes are found to experience a greater change in frequency than the fast modes. More importantly, the radiative losses also provide a significant damping of the slow mode and a small damping of the component of the fast mode perpendicular to the magnetic field. The damping of the slow mode is found to be strong within typical lifetimes of oscillations observed in coronal structures. Cooling could have important consequences and needs to be assessed when trying to determine what mechanism is responsible for the observed damping of coronal oscillations.

Blood bank operation is a facility which involves the process of collecting, testing, processing and storing blood for later use in blood transfusion. Blood bank management faces a crucial problem due to shortage of blood supply that sometimes does not meet the demand. Blood inventory is difficult to organize and control especially in festive seasons when demand is high due to road accidents and casualties. Blood bank management needs to balance the demand and supply to avoid shortage, and since blood is perishable, the management also needs to avoid wastage. To solve this issue, an effective inventory method should be implemented. This study compares two policies: the continuous review policy and the periodic review policy. The continuous review policy observes the monitory level more accurately and on time, while the periodic policy applies only periodically inventory control. This study looks at the relationships between the service level, safety stock and inventory cost that are based on three case studies, which are variable demand and constant lead time, variable lead time and constant demand and variable demand and variable lead time. The result shows that the continuous review policy should be implemented in blood bank management due to lower inventory cost and being more systematic with higher efficiency.

In recent years, manufacturing firms have realized that a new, higher level of global competition causes them to compete simultaneously on multiple manufacturing goals, such as quality, delivery, cost, and flexibility. In response to this realization, considerable research now focuses on the relationship of manufacturing improvement programs to manufacturing goals. However, to date, this research has not investigated the specific underlying statistical relationships between manufacturing goals and the shop floor. This study investigates manufacturing lead time linkages with manufacturing programs and manufacturing goals. The basic purpose of this study is to understand and explain how programs affect the elements of manufacturing lead time and how manufacturing lead time affects manufacturing goal capabilities. By understanding these linkages, managers can logically trace the effects of specific programs to their eventual effects on manufacturing goal capabilities. This study's most important finding is that statistical variations in the elements of lead time cause a tendency for certain manufacturing goals to be more difficult to control and achieve than others because of canonical relationships of lead time variances. To control these lead time variances, successful firms concentrate their early program targets first on achieving “fitness for use” quality, followed by delivery reliability, short delivery lead time and cost, current product flexibility, and lastly, new product flexibility. This study mathematically illustrates which improvement programs most affect manufacturing goals through their relationship to manufacturing lead time variance reduction. It suggests that firms improve goal performance by initially targeting improvement through setup time reduction programs, defect reduction programs, and preventive maintenance programs, to facilitate quality improvements. By targeting specific programs and their related lead time variances, firms improve their manufacturing facility competitiveness with minimum obstacles.

ABSTRACTAdiabatic and nonadiabatic dynamics in classical systems composed of fast and slow modes are formulated. Theoretical consequences from both adiabatic and nonadiabatic dynamics are discussed. In particular, we aim to identify a possible physical origin for drastic change of the slow dynamics to be induced by instability that happens to emerge in the fast mode. The Haken slaving principle and other theories like the adiabatic elimination method focus on the order formation led by the growth of the slow modes, with slaving the fast modes so as to faithfully follow the system dynamics. In this context, the fast modes are quite often regarded as ‘noise’ or a factor of small fluctuation. However, in molecular nonadiabatic dynamics, due to the breakdown of the Born–Oppenheimer approximation, the roles of the fast mode (due to electron dynamics) is far from that of ‘noise’, and sometimes bring about a qualitative bifurcation of the dynamics of the slow subsystem, which we usually refer to as nonadiabatic transition. We show the similar sudden change can be caused by the fast mode in classical mechanics too. The similarity and difference between quantum and classical nonadiabatic dynamics will be discussed.

In the past, many laser light-scattering experimental results revealed that besides the fast relaxation mode, there existed an additional slow mode in semidilute solutions. This slow mode has been assigned to a variety of origins, but there has been no clear and well-accepted explanation. As the polymer concentration increases, the slow relaxation mode persists in the concentrated region, in melts and in gels in which polymer chains are crosslinked instead of entangled. The slow relaxation mode has also been reported for charged macromolecules in aqueous and nonaqueous solutions. However, it is generally thought to be different in nature from that observed in semidilute neutral polymer solution. In recent years, armed with novel solution preparation methods and some specially designed polymers, we have reexamined the dynamics of polymer chains, especially the slow mode, in semidilute neutral polymer solutions, dilute polyelectrolyte solutions and gels, which are reviewed here. Our results suggest that the slow mode can be qualitatively considered as hindered motions of interacting chains even though the nature of interaction can be very different; namely, from the weak segment–segment interaction in a less good solvent to strong electrostatic interaction among polyelectrolyte chains, and even to chemical crosslinking inside gel networks. The slow mode in semidilute neutral polymer solutions, dilute polyelectrolyte solutions and gels, is reviewed here. Our results suggest that the slow mode can be qualitatively considered as a hindered motion of interacting chains, even though the nature of interaction can be very different; namely, from the weak segment-segment interaction in a less good solvent to a strong electrostatic interaction among polyelectrolyte chains, and even to chemical crosslinking inside gel networks.

ABSTRACTThe pressure to reduce inventory investments in supply chains has increased as competition expands and product variety grows. Managers are looking for areas they can improve to reduce inventories without hurting the level of service provided. Two areas that managers focus on are the reduction of the replenishment lead time from suppliers and the variability of this lead time. The normal approximation of lead time demand distribution indicates that both actions reduce inventories for cycle service levels above 50%. The normal approximation also indicates that reducing lead time variability tends to have a greater impact than reducing lead times, especially when lead time variability is large. We build on the work of Eppen and Martin (1988) to show that the conclusions from the normal approximation are flawed, especially in the range of service levels where most companies operate. We show the existence of a service‐level threshold greater than 50% below which reorder points increase with a decrease in lead time variability. Thus, for a firm operating just below this threshold, reducing lead times decreases reorder points, whereas reducing lead time variability increases reorder points. For firms operating at these service levels, decreasing lead time is the right lever if they want to cut inventories, not reducing lead time variability.

In this paper, an incentive scheme based on crashing lead time is proposed to coordinate a supplier-retailer supply chain (SC). In the investigated SC, the supplier applies a lot-for-lot replenishment policy to replenish its stock and determines the replenishment multiplier. Moreover, the transportation lead time is considered under the control of the supplier. The retailer as downstream member manages his inventory system according to the periodic review replenishment system (R, T). The review period (T) and order-up-to level (R) decisions along with the retail price are simultaneously optimized by the retailer. These decisions are made by the retailer influence the profitability of SC as well as the supplier's profitability. The investigated SC is modeled under three different decision making structures, i.e., (1) decentralized decision making model, (2) centralized decision making model, and (3) coordinated decision making model. By developing a lead time reduction policy as an incentive strategy, the pricing and periodic review replenishment decisions are coordinated. In the proposed incentive approach, the supplier by spending more cost and changing a fast transportation mode aims to crash the lead time in order to entice the retailer to accept the joint decision making strategy. In the suggested incentive scheme, two transportation modes (one slow and one fast) are supposed. Further, maximum and minimum lead time reduction, which are acceptable for both members, are determined. Moreover, a set of numerical examples along with a real case are carried out to demonstrate the performance and applicability of the developed models. The results demonstrate that the proposed incentive strategy is able to achieve channel coordination. Moreover, the results show the applicability of the developed coordination model under the high demand uncertainty. In addition, the proposed coordination model will fairly share the obtained profits between two SC members.

In this paper, a socially responsible supply chain consisting of one supplier and one retailer is proposed. The supplier decides on replenishment cycle multiplier and the retailer invests in corporate social responsibility (CSR) and decides on the order-up-to-level under a periodic review replenishment policy. The retailer’s decisions impact on the supplier’s probability as well as the supply chain. Therefore, the supplier proposes a lead time crashing contract to entice the retailer to participate in the coordination model. In this paper, the supplier can reduce the lead time by spending more cost and select a faster transportation mode. Two transportation modes (fast and slow) are considered in the proposed contract. By selecting a fast transportation mode, the retailer’s inventory cost and shortage will be decreased. Therefore, the retailers’ profit will be increased, while the lead time reduction cost and carbon emissions tax are imposed on the supplier under the lead time crashing contract. Numerical experiments and sensitivity analyses also show that the lead time crashing contract can coordinate the proposed model and the profit of supply chain and both members will be improved. Moreover, according to this contract the extra profit that is achieved from the coordination model is shared between both members of the supply chain fairly.

Three methods for analyzing azimuthal anisotropy from dipole logging data are described and applied to ultrasonic dipole data in this paper, based on the phenomena of flexural wave splitting in anisotropic materials and analogous to the techniques used for VSP data processing. The laboratory measured dipole data are employed to simulate the flexural modes propagating in a transversely isotropic (TI) formation with symmetry axis perpendicular to the borehole, and to examine and compare these methods. Amplitude and particle motion analyses of the laboratory data demonstrate that, only the polarisation direction of the fast flexural mode is consistently in accordance with the fast principle direction of the TI material. The slower mode, which is much easier to be excited and is of much larger amplitude than the fast mode, turns out to be subject to interferences and very complicated. It has not been well understood. Among the three methods used in VSP data processing, namely linear-transform technique, the technique of rotating data matrix and the technique of identifying the eigen direction with polar energy spectrum, the last method works best for the data used in this study. This technique can also be carried out in frequency domain to handle the possiblemore » interferences due to the dispersion of flexural modes.« less

Computational algorithmic procedure of optimal inventory policy involving a negative exponential crashing cost and variable lead time demand

This paper studies a buyer sourcing a product from multiple suppliers under stochastic demand. The buyer uses a (Q, s) continuous review, reorder point, order quantity inventory control system to determine the size and timing of orders. Lead time is assumed to be deterministic and to vary linearly with the lot size, wherefore lead time and the associated stockout risk may be influenced by varying the lot size and the number of contracted suppliers. This paper presents mathematical models for a multiple supplier single buyer integrated inventory problem with stochastic demand and variable lead time and studies the impact of the delivery structure on the risk of incurring a stockout during lead time.

Involvement of controllable lead time and variable demand for a smart manufacturing system under a supply chain management