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Heat stress occupational exposure limits (OELs) were developed in the 1970s to prevent heat-related illnesses (HRIs). The OELs define the maximum safe wet bulb globe temperature (WBGT) for a given physical activity level. This study's objectives were to compute the sensitivity of heat stress OELs and determine if Heat Index could be a surrogate for WBGT. We performed a retrospective analysis of 234 outdoor work-related HRIs reported to the Occupational Safety and Health Administration in 2016. Archived NOAA weather data were used to compute each day's maximum WBGT and Heat Index. We defined the OELs' sensitivity as the percentage of incidents with WBGT OEL. Sensitivity of the OELs was between 88% and 97%, depending upon our assumption about acclimatization status. In fatal cases, the OELs' sensitivity was somewhat higher (92-100%). We also computed the sensitivity of each possible Heat Index discrimination threshold. A Heat Index threshold of 80 °F (26.7 °C) was exceeded in 100% of fatalities and 99% of non-fatal HRIs. In a separate analysis, we created simulated weather data to assess associations of WBGT with Heat Index over a range of realistic outdoor heat conditions. These simulations demonstrated that for a given Heat Index, when radiant heat was included, WBGT was often higher than previously reported. The imperfect correlation between WBGT and Heat Index precluded a direct translation of OELs from WBGT into Heat Index. We conclude that WBGT-based heat stress exposure limits are highly sensitive and should be used for workplace heat hazard assessment. When WBGT is unavailable, a Heat Index alert threshold of approximately 80 °F (26.7 °C) could identify potentially hazardous workplace environmental heat.

We propose a novel mixed integer programming formulation for the capacitated lot-sizing problem with set-up times and set-up carryover. We compare our formulation to two earlier formulations, the Classical and Modified formulations, and a more recent formulation due to Suerie and Stadtler. Extensive computational experiments show that our formulation consistently outperforms the Classical and Modified formulations in terms of CPU time and solution quality. It is competitive with the Suerie–Stadtler (S&S) formulation, but outperforms all other formulations on the most challenging instances, those with low-capacity slack and a dense jobs matrix. We show that some of the differences in the performance of these various formulations arise from their different use of binary variables to represent production or set-up states. We also show that the LP relaxation of our Novel formulation provides a tighter lower bound than that of the Modified formulation. Our experiments demonstrate that, while the S&S formulatio...

Computational models provide a framework through which to predict impurity in-growth in reactor generated radiological sources. However, the energy group structure and methodology used in these cod...

The Economic Lot Scheduling Problem is a classical scheduling problem with the objective of minimising the long-run inventory and set-up costs of a single machine, multi-product inventory system. Demand rates, production rates and set-up times are assumed to be deterministic. The problem has been extensively studied and methods exist to obtain cyclic schedules which minimise total cost. In order to apply a cyclic schedule without a stock-out occurring, certain initial inventory levels are required. This paper considers the scenario where inventory levels are critically low and the cyclic schedule cannot be applied. Analytical methods are developed to determine: if the initial inventory is sufficient to prevent a stock-out from occurring; the maximum time until a stock-out will occur if a stock-out is unavoidable; and the minimum time required to obtain the necessary inventory to resume the cyclic schedule if a stock-out can be avoided.

We present a modelling approach for quantifying the value of information in supply chains using Markov decision processes (MDP). The case where information sharing occurs is modelled using a completely observable MDP. A restricted observation MDP is used to model the case where no information sharing occurs. We illustrate the use of this framework on a two-stage capacity-constrained supply chain consisting of a supplier and a retailer. We quantify the value of information sharing in this setting and construct several performance measures to identify the benefits to both the retailer and supplier as a result of the information sharing partnership.

The valuation of French Canadian paintings is analysed empirically. Using a sample of auction prices for major French Canadian painters for the period 1968 to 2005, we run hedonic regressions to determine the influence of various factors, including painter identity, on auction prices, as well as to construct a market price index. This is then used in a second stage analysis of the properties of these art works viewed as investment assets. We consider the extent to which standard asset pricing theory, as represented by the capital asset pricing model, can account for price movements in the market for French Canadian paintings.

This article presents a study of a between-subjects design experiment on the comprehension of telicity in simple telic predicates (e.g., John filled the bucket) and locatum predicates (e.g., the water filled the bucket) in L1 Spanish. Weist, Wysocka, and Lyytinen (1991) for English and Finnish, and Van Hout (1997, 1998b) for English and Dutch have shown that children up to age 6;06 allow simple telic predicates to have both telic and atelic interpretations. The main objective of this article is to show that children aged 3;09 allow locatum structures to be interpreted as telic, like adults, but allow simple telic predicates to have telic and atelic interpretations. The central claim is that in simple telic predicates, telicity is checked by covert movement, while in locatum predicates, telicity is checked by overt movement. Children misinterpret simple telic predicates because covert movement is an operation that takes place after the branching off to the PF component, but perform like adults when overt m...

Water mites (Hydracarina) are not consumed by some fish because of their distastefulness or toxicity. We obtained evidence that some individual largemouth bass (Micropterus salrnoides) specifically targeted mites as prey in a small unproductive and unexploited lake in Michigan's Upper Peninsula, USA. Bass stomachs that contained water mites tended to have high numbers of mites, with up to 780 mites in individual stomachs. Stronger evidence for foraging specialization was provided by repeated examination of stomach contents from recaptured bass; many bass contained water mites more often than would be expected by chance (one-sample t-test [H0=0], t = 3.54, P

The operative findings are presented in two patients following inadequate coil embolization. At craniotomy, part of the coil mass had extruded through the fundus of both aneurysms. It is unclear if this phenomenon is confined to aneurysms that demonstrate significant regrowth and if there is an increased risk of rebleeding.

Developing detailed production schedules for dyeing and finishing operations is a very difficult task that has received relatively little attention in the literature. In this paper, a scheduling procedure is presented for a knitted fabric dyeing and finishing plant that is essentially a flexible job shop with sequence-dependent setups. An existing job shop scheduling algorithm is modified to take into account the complexities of the case plant. The resulting approach based on family scheduling is tested on problems generated with case plant characteristics.

A fundamental scheduling problem is to determine a production start (ready) time for jobs based on customer-specified due dates. Typically, the objective is to delay the ready time in an attempt to minimize work-in-process inventory and maximize production system utilization. In many practical situations, notably remanufacturing operations, highly variable operation times and intricate process plans complicate this problem. In such a case, a specific ready time implies a confidence of on-time completion. Prior analytical results imply the optimal solution is a function of: (i) customer due dates; (ii) desired confidence levels; and (iii) stochastic makespan minimization. This paper proposes the use of a network flow model to represent a remanufacturing flowshop and then presents a structured heuristic approach that is able to develop sequences and ready times for remanufacturing systems by balancing the three factors. A broad experimental design is used to demonstrate that the proposed scheduling method o...

We obtain semiparametric efficiency bounds for estimation of a location parameter in a time series model where the innovations are stationary and ergodic conditionally symmetric martingale differences but otherwise possess general dependence and distributions of unknown form. We then describe an iterative estimator that achieves this bound when the conditional density functions of the sample are known. Finally, we develop a “semi-adaptive” estimator that achieves the bound when these densities are unknown by the investigator. This estimator employs nonparametric kernel estimates of the densities. Monte Carlo results are reported.

Femoral head resurfacing is re-emerging as a surgical option for younger patients who are not yet candidates for total hip replacement. However, this procedure is more difficult than total hip replacement, and the mechanical jigs typically used to align the implant produce significant variability in implant placement and take a significant amount of time to position properly. We propose that a computer-assisted surgical (CAS) technique could reduce implant variability with little or no increase in operative time. We describe a new CAS technique for this procedure and demonstrate in a cadaver study of five paired femurs that the CAS technique in the hands of a novice surgeon markedly reduced the varus/valgus variability of the implant relative to the pre-operative plan (2 degrees standard deviation for CAS versus 5 degrees for a mechanical jig operated by an expert surgeon). We also show that the mechanical jig resulted in significantly retroverted implant placement. There was no significant difference in operative time between the two techniques.

The academic literature in 2000 presented a procedure for solving the job-shop-scheduling problem of minimizing L max. The iterative-adaptive simulation-based procedure is shown here to perform well on large-scale problems. However, there is potential for improvement in closing the gap between best-known solutions and the lower bound. In the present paper, a simulated annealing post-processing procedure is presented and evaluated on large-scale problems. A new neighbourhood structure for local searches in the job-shop scheduling problem is developed. The procedure is also evaluated using benchmark problems and new upper bounds are established.

A procedure for the single machine-scheduling problem of minimizing the maximum lateness for jobs with sequence independent set-ups is presented. The procedure provides optimal/near-optimal solutions over a wide range of problems. It performs well compared with other heuristics, and it is effective in finding solutions for large problems.

Optical fibre cable manufacturing is a multistep process that combines individual fibres into colour-coded buffer tubes. These tubes are grouped together to make cables in which individual fibres are protected from external loads and environmental factors. This assembly process has a tree structure in which components are progressively combined into a finished cable. The main component, optical fibre, is held in inventory on spools in varying lengths and in both pre-coloured and natural states. Orders are received for lengths of finished cable. Since the glass fibre is the highest cost component of the cable, the allocation of fibre inventory to orders should be accomplished so that fibre scrap is minimized. In this paper a heuristic procedure for minimizing glass fibre scrap is presented. Computational results are given.

A semiparametric efficient estimation procedure is developed for the parameters of multivariate generalized autoregressive conditional heteroscedasticity-in-mean models when the disturbances have a conditional distribution assumed to be elliptically symmetric but otherwise unrestricted. Under high-level assumptions, the resulting estimator achieves the asymptotic semiparametric efficiency bound. The elliptical symmetry assumption allows us to avert the curse of dimensionality problem that would otherwise arise in estimating the unknown error distribution. This framework is suitable for the estimation and testing of conditional asset-pricing models, such as the conditional capital asset-pricing model. We apply our procedure in an empirical study of stock prices, with Monte Carlo simulation results also reported.

The authors describe a longitudinal assessment of intervention effectiveness in response to an outbreak of hypersensitivity pneumonitis (HP) at a metalworking facility. Thirty-five (29%) of the plant's 120 production workers were given a clinical diagnosis of HP during the two years of the investigation. Although quantitative exposure assessment tools were of limited utility, the investigators successfully used qualitative observations and the patients' return-to-work experiences to iteratively evaluate their exposure control recommendations. Recommended interventions included improving metalworking fluid management practices, enclosing selected metalworking fluid machining operations, eliminating mist cooling, exhausting two additional water-based industrial processes, increasing general dilution ventilation, and worker training. As of November 1999, 26 months into the outbreak, 51 percent (18) of the employees with a clinical diagnosis of hypersensitivity pneumonitis had been able to return to work. The symptom onset of the 35 workers who were given a clinical diagnosis of hypersensitivity pneumonitis during the two-year study period predated the implementation of the interventions. The collaboration of a multidisciplinary team appears to have allowed for successful intervention in this setting. A specific etiological agent(s) associated with the outbreak was not confirmed during the investigation. An acid fast isolate identified as being in the Mycobacterium chelonae group was detected in only one of the submitted metalworking fluid (MWF) sump samples. Longitudinally, there was a statistically significant difference in MWF sump bacteria (X(2) = 286.4, df = 17, p.0001) and MWF sump fungi (X(2) = 28.1, df = 7, p.0002). Measured oil mist air levels did not exceed the Occupational Safety and Health Administration's (OSHA's) permissible exposure limit (PEL), and in fact, did not exceed 0.5 mg/m(3).

We address the problem of releasing jobs to the factory floor while meeting delivery dates and minimizing the work-in-process inventory. Heuristic algorithms were developed that used an efficient, detailed shop-floor scheduling model to determine the release times of new jobs. The process starts with the current shop floor conditions and determines the sequencing of both in-process and new jobs on machines in order to minimize the maximum lateness (L max ). The approach is tractable for industrial-sized problems and provides solutions close to a calculated lower bound for WIP. Computational experience is given.

A procedure is developed for the simultaneous scheduling of multi-factory supply chains, including inter-factory transportation. A job-shop scheduling procedure, known to provide near-optimal solutions to industrial-sized problems, is enhanced to include transportation elements in the fundamental model. In order to demonstrate the quality of the solutions, a lower bound calculation is compared to the procedure's solutions on a number of large-scale test problems. The lower bound is an enhancement of the classic lower bound calculation for the N-job, M-machine job shop. The computational effort in scheduling is linear in the size of the problem, and high quality solutions to large-scale problems can be obtained in seconds.

In this paper, a dry-or-buy cost model for a dry kiln scheduling problem in the furniture manufacturing industry is considered. Factory-specified due-dates for jobs, kiln availability, kiln capacity, and drying and buying costs are incorporated into an Integer-Programming (IP) model. As it may be difficult (i.e., because of due-dates, kiln availability, processing times, etc.) to meet all the due-dates, certain jobs may have to be out-sourced. The objective of the model is to minimize the total drying and buying costs while satisfying all due-dates. Because of the computational complexity of the problem, a heuristic approach is developed. Computational experience indicates that the heuristic gives high quality solutions with significant savings in time over standard IP algorithms.

We consider parametric non-linear regression models with additive innovations which are serially uncorrelated but not necessarily independent, and consider the consequences of maximum likelihood and related one-step iterative estimation when the innovations are treated as being iid from their unconditional density. We find that the estimators' asymptotic covariance matrices will generally differ from those that would obtain if the errors actually were iid, except for the special case of strictly exogenous regressors. One important application of these results is to analysis of the properties of adaptive estimators, which employ nonparametric kernel estimates of the unconditional density of the disturbances in the construction of one-step iterative estimators. In the presence of strictly exogenous regressors, adaptive estimators are found to be asymptotically equivalent to the one-step iterative estimators that use the correct unconditional density. We illustrate our results through a brief Monte Carlo study.

The objective of this research is to develop and evaluate effective, computationally efficient procedures for scheduling jobs in a large-scale manufacturing system involving, for example, over 1000 jobs and over 100 machines. The main performance measure is maximum lateness; and a useful lower bound on maximum lateness is derived from a relaxed scheduling problem in which preemption of jobs is based on the latest finish time of each job at each machine. To construct a production schedule that minimizes maximum lateness, an iterative simulation-based scheduling algorithm operates as follows: (a) job queuing times observed at each machine in the previous simulation iteration are used to compute a refined estimate of the effective due date (slack) for each job at each machine; and (b) in the current simulation iteration, jobs are dispatched at each machine in order of increasing slack. Iterations of the scheduling algorithm terminate when the lower bound on maximum lateness is achieved or the iteration limit is reached. This scheduling algorithm is implemented in Virtual Factory, a Windows-based software package. The performance of Virtual Factory is demonstrated in a suite of randomly generated test problems as well as in a large furniture manufacturing facility. To further reduce maximum lateness, a second scheduling algorithm also incorporates a tabu search procedure that identifies process plans with alternative operations and routings for jobs. This enhancement yields improved schedules that minimize manufacturing costs while satisfying job due dates. An extensive experimental performance evaluation indicates that in a broad range of industrial settings, the second scheduling algorithm can rapidly identify optimal or nearly optimal schedules.

In this paper, a dry kiln scheduling problem from the furniture manufacturing industry is considered. Factory-specified due dates for orders, kiln availability, kiln capacity, and travel time from the kilns to the factories are all incorporated in a model which is formulated as an integer linear program. The objective of the formulation is to minimize the maximum tardiness of orders arriving at the plants by solving a special case of scheduling n independent jobs on m non-identical parallel machines. Because of the computational complexity, and the fact that standard integer programming packages appear to perform very poorly on the problem, a heuristic approach is developed. Computational experience is provided which indicates that the heuristic gives very high quality solutions to problems in near real-time.

The authors conducted a cross-sectional telephone survey of patients and employers to evaluate the effectiveness of conducting industrial hygiene work site visits as part of the medical management of clinic patients with suspected occupational disease. Industrial hygiene interventions were intended to keep the index patient from ongoing exposure while simultaneously protecting co-workers from future disease. The demographics of the 76 work sites and patients are summarized. According to the employers, 78 percent had implemented at least one recommended intervention, and 52 percent of the employers had implemented the priority intervention. The factors associated with the employers' implementation of the recommended industrial hygiene controls are presented. Employers were 3.7 times more likely to implement the priority intervention (p = .04) if they believed a worker's illness was work-related. Employers with joint labor-management health and safety committees were 3.8 times as likely to implement the priority intervention (p = 0.04). The factors associated with changes in the patients' self-reported disease status are explored and the social and economic implications of this model, are discussed. Patients who reported an improvement in disease status were 5.5 times more likely to have maintained or increased their salary (p = 0.03). Patients were 10.4 times more likely to be working if the employer had implemented any intervention (p = 0.02) and 13.3 times more likely if the priority intervention (p = 0.01) had been adopted. Those patients who left their original employer suffered a median decrease in salary of 35 percent if they found work with a different employer and a 90 percent decrease when they failed to find a new job.

A soft scale genus, Pounamococcus Henderson & Hodgson, new genus, is introduced to take two new species, P. tubulus Henderson & Hodgson and P. cuneatus Henderson & Hodgson, from New Zealand. The adult males and females, lst‐instar nymphs and 2nd‐instar male, and female nymphs and pupae of both species are described. Some details with regard to habit and distribution are also included. All known stages except the pupae of both species have campaniform pores on the tarsus of all legs, a feature so far unique within the family Coccidae, but a common feature in most other families of Coccoidea; this character is considered to be primitive. In addition, the adult males have no glandular pouch, a rare condition in known male soft scales outside New Zealand.

This paper is concerned with the modeling and analysis of a single-machine, multi-product, integrated production-inventory system. A semi-Markov model is developed that incorporates a state-dependent control system. Control optimization is achieved through the use of Markov-renewal programming. Three- and four-product models are developed. The model(s) are exercised over a range of parameters in order to determine the characteristics of the system, and to identify the structure of the optimal control rules of the system. The result is that one can identify simple basic rules of operation that are near-optimal in a dynamic environment, and that make sense intuitively.

The U.S. Consumer Product Safety Commission is investigating chemical emissions from carpet systems in order to determine whether the emissions may be responsible for the numerous health complaints associated with carpet installation. As part of this effort, a study was conducted to identify and quantify volatile organic compounds (VOCs) released into the air by five major product types of new carpet cushions. Cushion samples were tested in small-volume dynamic chambers over a six-hour exposure period. Airborne VOCs collected on multisorbent samplers were identified using sensitive gas chromatography/mass spectrometry. The emissions of selected VOCs were quantitated with the small-scale chamber method and further characterized in larger environmental chambers conducted over a 96-hour period under conditions more representative of indoor environments. A separate chamber method was developed to screen polyurethane cushions for emissions of toluene diisocyanates (TDI). Over 100 VOCs, spanning a broad range of chemical classes, were emitted from 17 carpet cushions. The pattern of emitted VOCs varied between and among product types, which reflects probable differences in manufacturing processes and ingredients. No significant quantities of TDI or formaldehyde were released by any cushions. Emission profiles were characterized for total VOCs and for the predominant individual VOCs. As a group, the synthetic fiber cushion samples emitted the lowest quantities of VOCs. Cushion samples purchased from carpet retailers released lesser amounts of VOCs than samples of the same cushion types obtained directly from the manufacturing mills, suggesting that chemical losses from the bulk material may ensue as a result of transport, handling, and storage prior to installation. The data suggest that placement of carpet on top of a carpet cushion, as would occur in a residential installation, reduced the rate of some VOC emissions when compared to the cushion alone.

This paper revises a species‐complex in the eriococcid genus Eriochiton. In addition to E. spinosus (Maskell), about whose status there is still some uncertainty, the complex contains E. armatus Brittin and five new species, E. brittini, E. deboerae, E. dracophylli, E. dugdalei and E. pseudohispidus. Descriptions, illustrations and diagnostic keys are provided for most scale‐like stages of all seven species. The prepupa, pupa and adult male of Eriochiton are described for the first time; the structure of the latter confirms the placement of Eriochiton in the Eriococcidae. A phylogenetic study of the Eriochitonini concludes that it is monophyletic and suggests some evolutionary trends within the tribe. Neoeriochiton clareae is considered the most primitive known taxon in the Eriochitonini and its placement in a separate genus is discussed. Also discussed are the importance of the immature stages in scale insect taxonomy and the narrow host range of most species in this tribe.

The performance and probing behaviour of three cowpea aphid clones were studied on four cowpea cultivars reared under bright and poor light conditions. The cowpea cultivars included two resistant (TVu 801, TVu 3000), a semi‐resistant (TVu 36) and a susceptible cv. (Ife Brown). The general trends under the two light conditions were similar: a Nigerian clone off groundnut had the poorest performance, producing no offspring, even off Ife Brown; a Philippines clone performed well on all cultivars, with high mean relative growth rates and fecundity, while a Nigerian clone off cowpea performed well on Ife Brown and TVu 36 but very poorly on the resistant cultivars, particularly under bright light conditions. Almost all aphid performance parameters were significantly improved on plants grown under low light, particularly with the Philippines clone. It was concluded that (a) some clones do not readily transfer from groundnut to cowpea; (b) the resistance in TVu 801 and TVu 3000 appeared to be effective a...

This paper considers the relationships of the genus Eriochiton, previously placed in the Coccidae. The adult females of E. hispidus and E. spinosus are redescribed, and the crawler and second‐instar males and females are described for the first time. In addition, three new species are described along with their available immature stages. One of these new species is placed in a new genus Neoeriochiton, close to Eriochiton. The morphology of these two genera indicates that they are members of the Eriococcidae belonging to a new tribe, the Eriochitonini, subfamily Eriococcinae. It is considered that they may illustrate the evolutionary events leading to the position and structure of the anal plates in the Coccidae, although the presence of anal plates in the Eriochitonini is thought to be due to parallel evolution. Other points discussed are: the importance of the structure of immature stages in the taxonomy of scale insects, features considered to be diagnostic for the Coccidae and the segmentation of the a...

Effective sequencing and scheduling of the material handling system can have a major impact on the productivity of the manufacturing system. This is especially true in the case where material handling times are on par with machine processing times. In a dynamic, real-time environment, the optimal solution of this scheduling problem may be computationally infeasible. In this paper, we develop a branch and bound approach which is coupled with quick, effective bounds to optimize the movement of a robot which serves the material handling requirements within a manufacturing cell. Computational results are given which explore the tradeoff between computation time and deviation from optimal for different scenarios.

In order to solve a large-scale Markov decision process which optimizes the control strategy of a multistaged production/inventory system, a computation reduction and memory management system was used. A ‘nuclear’ state space of relatively small size was found to substitute for the original state space. A circular comparison technique and a location index storage method were used to save computer memory used for storing the model

Approaches to multistage production scheduling can be conveniently classified into push type (i.e., Materials Requirements Planning (MRP) systems) or pull type (i.e., kanban systems). Each is generally thought to have both advantages and disadvantages. In this paper, a hybrid push/pull strategy is developed with the aim of gaining the advantages of both approaches. Material flow between work centers is regulated using the standard single card kanban/pull arrangement. Superimposed on this is the MRP-type information flow which feeds forward demand information directly to one or more (but not necessarily all) work centers. A general N-stage hybrid push/pull model is developed. The use of the approach is illustrated using 3-stage and 4-stage serial flowlines. The results indicate that the push/pull approach has lower inventory levels and a better response to demand changes than the pure pull system. The hybrid approach seems to combine many of die advantages of MRP approaches while retaining much of the simp...

A multistage production/inventory system is modelled. The system structure, which has the form of an assembly network, is abstracted from the production process of a typical integrated iron and steel works. The system is modelled as a Markov Decision Process (MDP). Combinations of Just-In-Time (pull) and MRP (push) policies are used as alternatives in the MDP. Optimal hybrid strategies are developed. In part II, we extend our observations to a more general case.

Estimating component reliability from system life data can be a valuable method for estimating new product reliability. It is presented a framework for applying the approach based upon the well-known theory of competing risks. The advantage of the approach lies in its ability to estimate the reliability of components after their assembly into an operational system. It can therefore account for the degrading effects induced by the assembly/manufacturing process

Possible mechanisms of resistance to the bean flower thrips (BFT) M. sjostedti (Trybom) in cowpea (Vigna unguiculata (L.) Walp. genotype TVx 3236 were studied in field and screenhouse experiments. Nonpreference was evaluated through measuring differences in populations and damage of BFT on TVx 3236 compared with susceptible genotypes. TVx 3236 consistently had lower thrips populations in field experiments, and was observed to sustain less damage in screenhouse choicefeeding. Antibiosis was evaluated through rearing thrips on flower buds of TVx 3236 and a susceptible standard (VITA7), and antibiosis was manifested by extended immature developmental period and decreased survival of adults. Nonpreference and antibiosis are discussed as modalities underlying the resistance of TVx 3236.

On etend la comparaison entre la procedure d'approximation de Clark et Scarf et la procedure basee sur les processus de decision de Markov aux problemes a trois etapes. Il s'avere que les ecarts de cout moyen par periode s'accentuent sensiblement avec l'augmentation du nombre des etapes

Seed of P. elliottii, P. taeda and P. patula was immersed for periods of 5, 15, 30 and 60 minutes in absolute or 50% organic liquids having densities in the range 0,71 to0,93g/cm3. Both absolute and 50% ethyl alcohol had a significant detrimental effect on the germination of P. elliottii seed. The seeds of P. taeda and P. patula are more tolerant of ethyl alcohol for short periods of immersion. Methyl alcohol and ethyl ether do not adversely affect germination whilst petroleum ether has a significant deleterious effect on the germination of P. elliottii seed within the first 5 minutes but continued immersion causes no further loss in viability.

In a recent paper the first author developed a dynamic-programming-based heuristic for the two-dimensional pallet loading problem. This note presents improvements to that procedure which have resulted in reductions in CPU run times of up to 1/20, as well as drastic lowering of memory requirements. A fundamental improvement in the bounding function is developed, and another improvement taken from observations of real-world pallet loaders and furniture movers is presented. Other implications of the improvements are also discussed, and results are compared.

Past research on the lot size scheduling problem has relied heavily on the following assumptions: (1)Each product is to be produced on a regular invariant cycle. (2)The inventory level at the onset of each production run is zero. In this paper these two restrictions have been dropped. It is shown that the inventory cost function can be expressed as a linear function. This allows the use of linear programming methods to determine the optimal lengths for a given sequence of production runs.