Optimal allocation of blood products

The high cost of collection and the short shelf life of apheresis platelets demand efficient inventory management to reduce outdates and shortages. Apheresis platelets are licensed for seven days, and blood centers are keen on knowing the consequences of various product collection and distribution strategies. To reduce outdates, inventory managers typically distribute the older units first, thereby following first-in first-out (FIFO) policy; however, hospital blood banks would prefer that the blood center issues out the freshest units first, equivalent to a last-in first-out (LIFO) policy. This study addresses the optimal distribution policy to achieve a desired outdate, shortage and average age of apheresis platelets. A comprehensive literature review was conducted on previous models studied to efficiently distribute blood products. However, most of the research on blood inventory management has been restricted to the hospital blood bank level in terms of ordering policies and inventory levels. This study takes the approach from the perspective of the inventory manager at the regional blood center. The inventory manager needs a reliable forecast of the quantity and timing of future blood supply (collection from donors) and blood demand from hospital blood banks to make an effective decision on blood inventory control. A forecasting method is used in this study to predict collection and demand for Single Donor Platelets (SDPs), and solves the blood inventory problem using a heuristic method and a Linear Programming (LP) with a rolling horizon method to find the near optimal issuing policy, the expected average age, outdate rate, and shortage rate of a blood product from the perspective of the blood center. It is concluded that regional blood centers can distribute with a ‘mixed’ FIFO/LIFO strategy and not significantly affect outdates or ability to cover shortages. For the LP model with a rolling horizon schedule, the inventory manager at the blood center would have to use forecast windows of five to achieve good issuing policies. A simulation study comparing the heuristic method and an LP-based with a rolling horizon method indicated that LP models with forecast windows of five and heuristics methods with a ‘mixed’ FIFO/LIFO strategy can be used to optimize this inventory problem

Platelet inventory management in blood supply chain under demand and supply uncertainty

Supply chain management of blood and its products are of paramount importance in medical treatment due to its perishable nature, uncertain demand, and lack of auxiliary substitutes. For example, the Red Blood Cells (RBC's) have a life span of approximately 40 days, whereas platelets have a shelf life of up to five days after extraction from the human body. According to the World Health Organization, approximately 112 million blood units are collected worldwide annually. However, nearly 20 percent of units are discarded in developed nations due to being expired before the final use. A similar trend is noticed in developing countries as well. On the other hand, blood shortage could lead to elective surgeries cancellations. Therefore, managing blood distribution and developing an efficient blood inventory management is considered a critical issue in the supply chain domain. A standard blood supply chain (BSC) achieves the movement of blood products (red blood cells, white blood cells, and platelets) from initial collection to final patients in several echelons. The first step comprises of donation of blood by donors at the donation or mobile centers. The donation sites transport the blood units to blood centers where several tests for infections are carried out. The blood centers then store either the whole blood units or segregate them into their individual products. Finally, they are distributed to the healthcare facilities when required. In this dissertation, an efficient forecasting model is developed to forecast the supply of blood. We leverage five years' worth of historical blood supply data from the Taiwan Blood Services Foundation (TBSF) to conduct our forecasting study. With the generated supply and demand distributioins from historial supply and demand data as inputs, a single objective stochastic model is developed to determine the number of platelet units to order and the time between orders at the hospitals. To reduce platelet shortage and outdating, a collaborative network between the blood centers and hospitals is proposed; the model is extended to determine the optimal ordering policy for a divergent network consisting of multiple blood centers and hospitals. It has been shown that a collaborative system of blood centers and hospitals is better than a decentralized system in which each hospital is supplied with blood only by its corresponding blood center. Furthermore, a mathematical model is proposed based on multi-criteria decision-making (MCDM) techniques, in which different conflicting objective functions are satisfied to generate an efficient and satisfactory solution for a blood supply chain comprising of two hospitals and one blood center. This study also conducted a sensitivity analysis to examine the impacts of the coefficient of demand and supply variation and the settings of cost parameters on the average total cost and the performance measures (units of shortage, outdated units, inventory holding units, and purchased units) for both the blood center and hospitals. The proposed models can also be applied to determine ordering policies for other supply chain of perishable products, such as perishable food or drug supply chains.Includes bibliographical references

Performance measures of nonstationary inventory models for perishable products under the EWA policy

Accurately estimating key performance indicators in inventory models for perishable items is essential in order to assess and improve the management strategy of these systems. We analyse the production of platelet concentrates at blood banks under the EWA replenishment policy. We give analytical approximations of the most important performance measures, such as the size of orders, the size of stocks, the percentage of outdating, the age distribution of stocks and the freshness of units issued, among others. The production of platelet concentrates is a prototypical example of inventory models for short life items with random demand and a weekly pattern, where a high service level is required. The methodology and the approximations presented here can be easily adapted to other inventory systems with similar characteristics. Most of the formulae in this article are new for nonstationary models under the EWA policy; indeed, formulae for the age distribution of units in stock and of units issued have not appeared in the literature even for the simpler base-stock replenishment policy. We apply our results to a real blood bank and find very close agreement between the formulae and the results of Monte Carlo simulations. The accuracy of our approximations is also tested in several scenarios, depending on the lifetime of units, safety stock levels and the probabilistic distribution of demand.Carlos Gorria and Mikel Lezaun have received funding from the Department of Education of the Basque Government through the Consolidated Research Group MATHMODE (IT1294-19) and the Spanish Ministry of Science and Inovation Ref. PID2019-108111RB-I00 (FEDER/AEI). F. Javier López has received funding from Grant PID2020-116873GB-I00 funded by MCIN/AEI/ 10.13039/501100011033. He is a member of the research group Modelos Estocásticos (DGA). The authors thank CVTTH for providing the data on platelet demand in 2012

A Metaheuristic-Based Simulation Optimization Framework For Supply Chain Inventory Management Under Uncertainty

The need for inventory control models for practical real-world applications is growing with the global expansion of supply chains. The widely used traditional optimization procedures usually require an explicit mathematical model formulated based on some assumptions. The validity of such models and approaches for real world applications depend greatly upon whether the assumptions made match closely with the reality. The use of meta-heuristics, as opposed to a traditional method, does not require such assumptions and has allowed more realistic modeling of the inventory control system and its solution. In this dissertation, a metaheuristic-based simulation optimization framework is developed for supply chain inventory management under uncertainty. In the proposed framework, any effective metaheuristic can be employed to serve as the optimizer to intelligently search the solution space, using an appropriate simulation inventory model as the evaluation module. To be realistic and practical, the proposed framework supports inventory decision-making under supply-side and demand-side uncertainty in a supply chain. The supply-side uncertainty specifically considered includes quality imperfection. As far as demand-side uncertainty is concerned, the new framework does not make any assumption on demand distribution and can process any demand time series. This salient feature enables users to have the flexibility to evaluate data of practical relevance. In addition, other realistic factors, such as capacity constraints, limited shelf life of products and type-compatible substitutions are also considered and studied by the new framework. The proposed framework has been applied to single-vendor multi-buyer supply chains with the single vendor facing the direct impact of quality deviation and capacity constraint from its supplier and the buyers facing demand uncertainty. In addition, it has been extended to the supply chain inventory management of highly perishable products. Blood products with limited shelf life and ABO compatibility have been examined in detail. It is expected that the proposed framework can be easily adapted to different supply chain systems, including healthcare organizations. Computational results have shown that the proposed framework can effectively assess the impacts of different realistic factors on the performance of a supply chain from different angles, and to determine the optimal inventory policies accordingly

Transshipment in supply chain networks with perishable items

Supply chain management is an efficient approach to managing the flow of information, goods, and services in fulfillment of customer demand. The implementation of supply chain management significantly affects the cost, benefit level, and quality. Over the past decades, multiple strategies for effective supply chain management have been developed in both academia and industry. One such strategy is named lateral transshipment which allows movement of stock between locations at the same echelon level or even across different levels. Although transshipment has been considered in the literature for a long time, there has been limited studies of transshipment for perishable items, most likely because of the complex structure of perishable inventories. The analysis of perishable-inventory systems has been considered in numerous articles because of its potential application in sectors such as chemicals, food, photography, pharmaceuticals, and blood bank management. Blood services in Australia rely on voluntary, non-remunerated donors to satisfy the demand for blood. Blood services confront ongoing challenges in providing an adequate supply of blood and blood products. One of the powerful tools that could improve the efficiency of the blood supply chain is lateral transshipment. This thesis presents three models that have application in the transshipment of perishable items such as blood. The first model (presented in Chapter 2) outlines the development of a new transshipment policy for perishable items, to enhance supply chain performance. A Poissondistributed customer demand is assumed and the effect of reactive transshipment on expected costs are evaluated. A heuristic solution is developed, using partial differential equations to compute performance measures and cost function. The performance of this model is evaluated through a numerical study. The results indicate that this transshipment policy is effective under lost-sale and backordering scenarios. In addition, the performance of the suggested transshipment policy is compared with the current transshipment policy that is practiced in some Australian hospitals. The results suggest that by setting the optimal threshold, a significant cost saving could be obtained with the same average issuing age of the current policy. The second model (presented in Chapter 3) considers a finite-horizon multi-period inventory system with one main hospital connected to several smaller hospitals. The hospitals face random demand and small hospitals are allowed to transship to the big hospital to mitigate their wastage. The problem is formulated as an infinite-horizon dynamic programming model. The objective of this model is to determine an optimal ordering and transshipment policy that minimizes the total expected cost. An approximate dynamic programming (ADP) model is used to approximate the value function with a linear combination of basis functions, using column generation to cope with the course of dimensionality. The numerical results suggest that considerable cost saving can be achieved by using an ADP model. The third model (presented in Chapter 4) proposes a proactive transshipment policy for a network of hospitals with uncertain demand. At the beginning of each review period, each hospital makes decisions on the quantity to order from a central blood bank and to transship to other hospitals. The problem is formulated as a two-stage stochastic programming model where the Quasi-Monte Carlo (QMC) sampling approach is used to generate scenarios and the optimal number of scenarios is determined by conducting stability tests. The performance of the developed model is evaluated through numerical experiences. The numerical results indicate significant potential cost savings in comparison with the current policy in use and the no-transshipment policy

Comparing conventional and distributed approaches to simulation in complex supply-chain health systems

Decision making in modern supply chains can be extremely daunting due to their complex nature. Discrete-event simulation is a technique that can support decision making by providing what-if analysis and evaluation of quantitative data. However, modelling supply chain systems can result in massively large and complicated models that can take a very long time to run even with today's powerful desktop computers. Distributed simulation has been suggested as a possible solution to this problem, by enabling the use of multiple computers to run models. To investigate this claim, this paper presents experiences in implementing a simulation model with a 'conventional' approach and with a distributed approach. This study takes place in a healthcare setting, the supply chain of blood from donor to recipient. The study compares conventional and distributed model execution times of a supply chain model simulated in the simulation package Simul8. The results show that the execution time of the conventional approach increases almost linearly with the size of the system and also the simulation run period. However, the distributed approach to this problem follows a more linear distribution of the execution time in terms of system size and run time and appears to offer a practical alternative. On the basis of this, the paper concludes that distributed simulation can be successfully applied in certain situations

Grocery omnichannel perishable inventories: performance measures and influencing factors

Purpose- Perishable inventory management for the grocery sector has become more challenging with extended omnichannel activities and emerging consumer expectations. This paper aims to identify and formalize key performance measures of omnichannel perishable inventory management (OCPI) and explore the influence of operational and market-related factors on these measures. Design/methodology/approach- The inductive approach of this research synthesizes three performance measures (product waste, lost sales and freshness) and four influencing factors (channel effect, demand variability, product perishability and shelf life visibility) for OCPI, through industry investigation, expert interviews and a systematic literature review. Treating OCPI as a complex adaptive system and considering its transaction costs, this paper formalizes the OCPI performance measures and their influencing factors in two statements and four propositions, which are then tested through numerical analysis with simulation. Findings- Product waste, lost sales and freshness are identified as distinctive OCPI performance measures, which are influenced by product perishability, shelf life visibility, demand variability and channel effects. The OCPI sensitivity to those influencing factors is diverse, whereas those factors are found to moderate each other's effects. Practical implications- To manage perishables more effectively, with less waste and lost sales for the business and fresher products for the consumer, omnichannel firms need to consider store and online channel requirements and strive to reduce demand variability, extend product shelf life and facilitate item-level shelf life visibility. While flexible logistics capacity and dynamic pricing can mitigate demand variability, the product shelf life extension needs modifications in product design, production, or storage conditions. OCPI executives can also increase the product shelf life visibility through advanced stock monitoring/tracking technologies (e.g. smart tags or more comprehensive barcodes), particularly for the online channel which demands fresher products. Originality/value- This paper provides a novel theoretical view on perishables in omnichannel systems. It specifies the OCPI performance, beyond typical inventory policies for cost minimization, while discussing its sensitivity to operations and market factors

Solving large structured Markov Decision Problems for perishable inventory management and traffic control

Published data revealed that Tagetes spp. suppress polyphagous endoparasitic root nematodes, that the effect varies, perhaps between Tagetes spp. and cultivars, certainly between nematode genera and perhaps between species and strains. The effect is sometimes striking but the picture in general is far from complete and not clear. This situation determined the three objectives of our investigation: occurrence and significance of Tagetes effect, interpretation, and possibilities of application in agriculture.For most of the trials plants were cultivated under controlled and field conditions, and their growth evaluated; nematode populations were collected, cultivated, maintained and transferred; nematodes in soil and plant tissues were counted and results were analysed statistically. Several special techniques were used occasionally as indicated in the relevant sections.The occurrence and significance of special Tagetes effects on plant nematode population were determined with species of Pratylenchus, Meloidogyne, Tylenchorhynchus, Rotylenchus and Helicotylenchus, other ectoparasitic nematodes, Ditylenchus and Aphelenchoides.Pratylenchus spp. were markedly suppressed by Tagetes spp. in tube cultures (Tables 1-5) and in field trials (Tables 6 and 7, Figs 1 and 2). This was true for P. penetrans, P. crenatus, P. neglectus and probably P. thornei. Soil type may be of influence on the result. There were great differences in effectiveness between Tagetes spp. and cultivars. The effectiveness against Pratylenchus spp. decreases in the order T. patula, T. erecta, T. minuta, with T. patula markedly better. T. patula Harmony suppresses field populations of Pratylenchus spp. in a few months and fallow requires a few years to reach a comparable low final density of these nematodes. Density never fell to zero, probably because of limited reproduction on weeds and limited reproduction on Tagetes itself if it is grown for a full season. There was no evidence that resistance of Tagetes was broken or that nematode strains resistant to Tagetes effects arose even after 7-10 successive crops of T. patula. Biennial rotations of T. patula and good hosts kept Pratylenchus spp. at a low density, except the population of P. thornei on heavy soil which fluctuated at a rather high level (Fig. 2).Tagetes spp. were generally as effective or better than fallow in suppressing Meloidogyne spp. in tube cultures (Tables 8-12), although with some notable exceptions. Meloidogyne larvae were less persistent than Pratylenchus larvae in fallow soil. T.patula severely suppressed M. hapla, M. incognita, M. arenaria and M.javanica. T. erecta was also suppressive but slightly more syncytia formed in all four Meloidogyne spp.; M. hapla reproduced and maintained a small population on T. erecta. T. minuta differed markedly from the earlier species in that it suppressed M. hapla and M. incognita completely and M.javanica almost completely, whereas M. arenaria could breed on this plant and reach considerable densities in both roots and soil. Any general effect by Tagetes on Meloidogyne is therefore complicated by certain exceptions which may account for conflicting published results.Tube and field trials showed that Tylenchorhynchus spp. were suppressed by T. patula in different soils (Table 7), that Tyl. dubius was suppressed better and more rapidly by T. patula than by fallow (Fig. 3A, B; literature), and that T. erecta and T. minuta were about as effective as T. patula against Tyl. dubius (Table 6). Tyl. dubius was suppressed slightly less effectively and less rapidly than Pratylenchus spp. in the same soil by T. patulaThe data on R.robustus supports the view that Tagetes spp., at any rate T. patula Golden Harmony and Harmony, maintains a rather high density. Unexplained peaks of the density under Tagetes and fallow make it difficult to indicate any Tagetes effect at all; factors other than the presence of higher plants may govern the population dynamics of this species.The genera Hemicycliophora, Paratylenchus and Trichodorus are not generally suppressed by Tagetes cultivars. Specific host-nematode relationships may vary as widely as is the case with these nematodes on other plants, and no special Tagetes effect can be demonstrated against these ectoparasites. Some species breed profusely on certain Tagetes spp. but are not affected by other Tagetes spp.The stem nematode D. dipsaci may reproduce to a limited extent and cause typical symptoms in T. patula and T. erecta, but not in T. minuta. The same is true for the foliar nematode A. ritzemabosi (Plate 1A and B).The data leave no doubt that certain Tagetes spp. suppress certain species of plant nematodes unusually strongly. The Tagetes effect manifested itself most clearly with Pratylenchus spp., Meloidogyne spp. and Tyl. dubius, but was evidently not present or not marked against R. robustus and several other ectoparasitic genera, nor against D. dipsaci and A. ritzemabosi. The results alone or combined with published data do not fully explain the mechanism. For a further analysis the exoradicular effects, the effects on the surface of the plant or during penetration, and the endoradicular effects were subsequently studied.Exoradicular effects may contribute to, but not explain the larger part of the Tagetes effect. As with the good host red clover, P. penetrans is not particularly attracted nor deterred by growing roots of T. patula on agar plates, but there was some aggregation around the roots in soil (Table 14), though it concerned only part of the soil population (Fig. 5). Percolates from pots of T. patula, red clover, apple or without a plant did not differ in effect on activity or mortality of P. penetrans in vitro. Survival of P. penetrans in water cultures of T. patula and T. minuta was only slightly less than in water culture of apple, control solution or distilled water, and the effect was at any rate slight and unspecific (Table 15). Tagetes soil was distinctly nematicidal for some days after the roots have been removed. This effect, however, was not very strong and was not specific for Tagetes , because red clover was equally and apple even more effective than T. patula and T. minuta (Table 16). Damage or kill of nematodes outside the root may therefore play a role, but it is apparently not the essential part of the Tagetes effect.Root systems of three different Tagetes spp. were penetrated by M. hapla larvae as much as root systems of a suitable host. The same holds for penetration by P. penetrans , except perhaps for T. patula which fewer nematodes entered than other Tagetes spp. or good hosts in most trials (Table 17). As a rule only a few of the larvae around the roots succeed in penetrating.Endoradicular influences comprise nematode survival and development, nematicidal effects and histological reactions in Tagetes tissues. M. hapla larvae enter Tagetes spp. to the same amount as tomato within a week. Only a few of the larvae around the roots succeed, although potential sites for penetration are present in excess. The unsuccessful nematodes outside the root decrease rapidly in number, more rapidly in the presence of growing plants than in fallow soil, which may be important for the population dynamics of nematodes in general. M. hapla survives for at least 4 weeks within roots of Tagetes spp., but development beyond the infective second larval stage is hardly noticeable in T. patula and T. minuta , whereas only a few larvae develop and reach adulthood in T. erecta (Table 18).The picture is similar with P. penetrans . The percentage penetration is generally low in all plants, but significantly lower in T. patula than in T. erecta , T. minuta or red clover (Table 19, Fig. 6). T. patula may resist penetration by this nematode The main difference between a suitable host such as red clover, and T. patula is that nematodes reproduce in the first plant and decline or remain few in T. patula. In T. minuta the nematodes survive and may even develop and multiply, though at slower rate than in red clover (Figs. 6, 7 and 8). T. patula , T. minuta and red clover represent degrees of host suitability from almost zero through low to very high (Fig. 7, Table 20). The equilibrium density under T. patula is very low but not zero because some reproduction occurs when the plants have grown a long while. The percentage males among the sexually differentiated nematodes is not higher in the very resistant T. patula and does not increase with ageing of host plants, as has often been published. T. patula allows very little escape or survival of P. penetrans once the nematodes have entered the roots, whereas the population in T. minuta roots does escape and may be infective as in suitable hosts (Tables 21 and 22).Root extracts of Tagetes spp., contrary to root exudates, contain a nematicidal principle which manifests itself against P. penetrans in vitro from the third day on (Fig. 9A, B, C). Extract of T. patula is more effective than extract of T. minuta and the latter is more effective than extract of potato or control solutions. Fractioning of root extracts of T. patula over a column of Sephadex G-75 indicate high mortality in a later fraction. No attempt was made to identify the active principle(s) in this fraction. This effect in vitro may be related to the Tagetes effect on nematodes in soil. It may be caused by the nematicides such as the thiophenes isolated from Tagetes roots by Uhlenbroek & Bijloo (1958, 1959). There was some nematode kill in potato root extract too, distinctly less than in Tagetes extract but distinctly higher than in the control solutions. This indicates the presence of a weak nematicidal effect in potato root extract and may support the indication recorded earlier that plants establish or induce in general an "antinemic potential" by means of their exudates or other substances in water or soil. The Tagetes effects are much stronger and evidently differ from it.Histological reactions as part of the endoradicular influences of Tagetes on penetrated nematodes are not conspicuous. Tagetes cultures, unlike most other plants, normally grow well and have well-developed root systems without discoloration in soils with dense populations of Meloidogyne and Pratylenchus spp. Despite this healthy appearance Tagetes roots may show barely visible histological reactions after such nematode infestations.M. hapla larvae penetrate the root apex of T. patula in much the same way as that of tomato. They do not normally develop nor cause marked necrosis or swelling in the roots of T. patula . Occasionally, however, small syncytia or sometimes even small galls occur associated with a developing larva. Unlike tomato, T.patula develops few and very small syncytia and galls and only slowly, and the nematode often dies and syncytia often abort in T. patula .P. penetrans penetrates young roots of T. patula , T. minuta and red clover at random sites on their surface except at the apex and causes cortical lesions in all three plants. The lesions in T. patula are small, dark and necrotic but do not abort from surrounding cortex tissue; they normally harbour only 1-3 nematodes, often dead, dying or twisted. In T. minuta the lesions appear slower, are larger and less dark than in T. patula ; the number of nematodes per lesion may be up to 38 and often occur outside lesions. Red clover lesions appear still slower, are usually larger and contain a large breeding population. Histological reactions, therefore, largely coincide with nematode development.The endoradicular effects are apparently instrumental in the nematode suppression by Tagetes spp. They are incorporated in or super-imposed upon the common plant-nematode relationships which are different for each association and may therefore influence the result. It is suggested that the special nematicidal principle in Tagetes is made up of more components, of which thiophenes recorded up to now from T. erecta , and that the components or their relative weights vary between Tagetes spp. Some other Compositae related closely to Tagetes spp. were also found to be effective against P. penetrans and also contained the same thiophenes as found in Tagetes or hitherto unidentified active principles. T. patula is probably superior to other Tagetes spp. in its effect against P. penetrans because necrosis appears earlier and more acutely. This may be a consequence of more rapid intoxication of the nematodes, as in root extracts.Ectoparasitic cortex feeders of the genus Tylenchorynchus are affected less and root-vessel feeders are evidently not influenced by the nematicidal principles in Tagetes roots, probably because they do not undergo the same type or degree of contact with the Tagetes tissue. The Tagetes effect, therefore, seems to be generally strong for endoparasitic root nematodes or cortical feeders, but varies even within this group with the different plant-nematode associations.The agricultural value of Tagetes as a source of organic matter, stains, therapeutics, or other chemicals, and as ornamentals is limited and has up to now supported only small-scale cultivation. The use of Tagetes crops for suppression of plant nematodes and the marked growth improvement obtained in main crops, is handicapped by the lack of value of the crop. Furthermore Tagetes spp. and cultivars are limited in their agricultural applicability. Nematode suppression is the primary determinant of their practical value so that T. patula particularly the cultivars Golden Harmony or Harmony are recommended. They are more effective against Pratylenchus and at least as effective against Meloidogyne populations, and appear to be as good or better than other Tagetes cultivars for growing and handling as a crop. Seed characteristics, rapid development as an autumn crop and winter-hardiness could all be improved, whereas a search for profitable use of the crop is desirable. Breeding of Tagetes spp. have resulted in a great assortment of ornamentals, and prospects seem good for the plant breeder of combining strong nematicidal effect with useful agricultural properties.The desired characters will depend on the type of agriculture. Tagetes grown as a full-season crop has been found effective by several workers and may cause striking growth and yield increments, it may find use in areas where valuable main crops are grown and where land rent is low, as in some tropical and subtropical countries. Tagetes as a spring crop does not seem promising in temperate climates due to its slow seedling growth. Even when sown densely, 10 cm apart on 15 May, minimum densities of Pratylenchus could be achieved only after about 2 months; these densities appear later when greater plant distances are taken (Fig. 10). Tagetes grown as an autumn crop has better possibilities. The degree of development of autumn Tagetes is evidently critical for its effect, and this varies strongly from year to year. Autumn Tagetes may be very effective in nematode suppression as well as in yield increase of main plants in certain years (Tables 23, 24 and 25), but the earliest sowing dates after an early pea crop varied in the period 1961-1968 from 6 July to 14 August, and a good development was obtained in only 4 out of 8 years (Table 6). Continuous autumn Tagetes , however, may be effective despite failure in certain years. Autumn Tagetes should be sown not later than the end of July and 10 rather than 25 cm apart is advisable.Simultaneous culture of Tagetes with a main crop appeared to be effective around and between trees and woody ornamentals and may be promising in more cases, especially since sowing at 60 cm apart completely suppressed nematodes, though slower than when closer sown. Sowing between rows is practized incidentally (Plate IIC and D). Sowing under cereals and other high crops to give the crop a quicker start after harvesting the main crop has not so far been promising, because only few weak plants survived.Autumn application after a main crop and application between rows of a main crop may be promising under certain conditions. The technical possibilities increase when climatic conditions allow a better growth in the autumn or when agricultural systems allow a full-season crop.Yield of main crops after Tagetes may be increased by nematological or other growth factors or both. Tagetes promoted growth of apple seedlings in soil with P. penetrans to 167 % of fallow infested soil, though Tagetes decreased growth in uninfested soil; allowance for the nitrogen used by Tagetes would lead to a higher growth promotion in infested soil (Table 27). The decline in nematode population continued markedly after the growth of Tagetes had been disrupted by removal of the tops. Direct mulch with a natural dosage of Tagetes roots suppresses P. penetrans much better than other mulches or fallow. It is probable that there is a significant aftereffect also under field conditions. Leaf mulches were also effective in suppressing P. penetrans , but Tagetes leaves were less effective than apple and no specific nematicidal effect of Tagetes leaves could be demonstrated. The results in uninfested soil show that cultivation of Tagetes and removal of tops decreases soil fertility in unfertilized soil (Table 27). The addition of root or leaf mulch generally increases soil fertility and therefore growth of test plants (Tables 30, 31, 32). These effects, however, are unspecific, and would have been smaller in fertilized soils, uninfested or infested. The dominance of nematicidal over non- nematicidal effects of Tagetes is clear for the growth of apple seedlings in soil infested with P. penetrans . The relative weight of these factors may of course be different in other plant nematode relationships.Our results, therefore, confirm or substantiate the marked Tagetes effect, but also the variation between plant-nematode relationships. The Tagetes effect is exceptional in nature, though not completely restricted to the genus Tagetes because it does occur in some genera ofthe Heleniae. The effect appears to be centred inside the roots and is evidently correlated with the presence in these plants of strongly nematicidal thiophenes, which are rare elsewhere in nature. The fact that it is conspicuous against endoparasitic polyphagous root nematodes and not against epidermal and vessel feeders is understandable from the difference in parasitic way of life.Histopathological reactions to nematode invasion vary between Tagetes spp. This may explain the stronger effect of T. patula on P. penetrans than of other Tagetes spp. The concept of nematode intoxication by nematicidal thiophenes and histopathological resistance phenomena may be interrelated and are not necessarily contradictory.Use of Tagetes spp. often markedly increases yield of main crops, but is limited by type of agriculture. In temperate regions Tagetes grown simultaneously with the main crop or grown in the autumn after the main crop is considered promising. Slow seedling growth, high light requirement and frost susceptibility of available cultivars are disadvantages. Tagetes has better prospects in tropical and subtropical agriculture

Facilitating the analysis of a UK national blood service supply chain using distributed simulation

In an attempt to investigate blood unit ordering policies, researchers have created a discrete-event model of the UK National Blood Service (NBS) supply chain in the Southampton area of the UK. The model has been created using Simul8, a commercial-off-the-shelf discrete-event simulation package (CSP). However, as more hospitals were added to the model, it was discovered that the length of time needed to perform a single simulation severely increased. It has been claimed that distributed simulation, a technique that uses the resources of many computers to execute a simulation model, can reduce simulation runtime. Further, an emerging standardized approach exists that supports distributed simulation with CSPs. These CSP Interoperability (CSPI) standards are compatible with the IEEE 1516 standard The High Level Architecture, the defacto interoperability standard for distributed simulation. To investigate if distributed simulation can reduce the execution time of NBS supply chain simulation, this paper presents experiences of creating a distributed version of the CSP Simul8 according to the CSPI/HLA standards. It shows that the distributed version of the simulation does indeed run faster when the model reaches a certain size. Further, we argue that understanding the relationship of model features is key to performance. This is illustrated by experimentation with two different protocols implementations (using Time Advance Request (TAR) and Next Event Request (NER)). Our contribution is therefore the demonstration that distributed simulation is a useful technique in the timely execution of supply chains of this type and that careful analysis of model features can further increase performance