Scheduling Functions Research Articles

Generation of alternative process plans in integrated manufacturing systems.

The availability of alternative process plans is a key factor for integration of design, process planning, and scheduling functions. The availability of alternative process plans can speed up the process of incremental process plan generation which can help in providing real time cost feed back to the designer after each design modification. Also alternative process plans relax the constraints in the optimization of production schedules, which in turn results in more efficient use of production resources and better delivery schedules. This paper describes a methodology for generation of alternative process plans in the integrated manufacturing environment. The procedure consists of: selection of alternative machining processes, clustering and sequencing of machining processes, and generation of a process plan network. Each of these steps is explained in detail. The result of the procedure is the process plan network that provides all alternative process plans for the given part. Methods for the selection of an optimal process plan are also described. Computational complexity of the procedure is discussed and experimental results on several realistic examples are shown.

Adolescent leisure across European nations.

The amount and uses of leisure time among adolescents vary across European countries as a function of culture, school schedules, and wealth.

Testing Concurrent Java Programs using Randomized Scheduling

The difficulty of finding errors caused by unexpected interleavings of threads in concurrent programs is well known. Model checkers can pinpoint such errors and verify correctness but are not easily scalable to large programs. The approach discussed here is more scalable but less systematic. We transform a given Java program by inserting calls to a scheduling function at selected points. The scheduling function either does nothing or causes a context switch. The simplest scheduling function makes the choice blindly using a pseudo-random number generator; more sophisticated scheduling functions use heuristics to weight the choices. We try to insert as few calls as possible while still ensuring that for each reachable deadlock and assertion violation, there is a sequence of choices by the scheduling function that leads to it; thus, there is a non-zero probability of finding it by testing the transformed program, regardless of the scheduling policies of the underlying Java Virtual Machine.

Performance of Spatially and Temporally Distributed Displays as a Function of Continuous versus Discrete Update Schedules

Generally, there are two ways to present monitored information: a traditional display that spatially distributes information across a screen or a temporally distributed display, which is the presentation of information serially in the center of a screen. Previous studies comparing these display formats have used methodologies in which changes in numerical information only occurred in view of the participant. This is beneficial for tight experimental control, but is not realistic since information can constantly change. The current study compared a spatially distributed display with a temporally distributed display and manipulated the updates to occur either in view, as in previous research, or continuously, even if out of view. Results showed a system response lag time in addition to participant reaction time for realistic settings and an increase in missed events not shown in previous research. These findings suggest that while a temporally distributed display is currently far from implementation, research shows promise for this technology.

A case study on the integration of APS and ERP in a steel processing plant

This article describes the implementation of information systems to support the production planning and scheduling functions in two steel processing business units of a steel plant. In particular, the integration of the implementation of two systems is described: Enterprise Resource Planning (ERP) and Advanced Planning and Scheduling (APS). The article presents a functional architecture that integrates the two systems, and discusses typical issues that have to be solved when ERP and APS systems have to be integrated. Lessons learnt included the importance of an architecture to facilitate discussions, issue management, the importance of the primary process, differences between an ERP and APS implementation and differences in process descriptions.

Maîtrise de lˈasthme et atteinte des petites voies aériennes : enquête transversale Jacinte (Juniper Asthma Control In a National Transversal Evaluation) en pneumologie libérale

A transversal survey was performed in order to assess asthma control in usual practice, and to evaluate, the existence and extent of small airway impairment in non-controlled asthma. This survey was performed between September and November 2000 by 420 urban pneumologists on 1,333 adult asthmatic patients referring for scheduled pulmonary function tests. Asthma control was assessed following two approaches: qualitatively by the physician’s interview about functional signs, and quantitatively by the patient with the help of the Juniper questionnaire for asthma control. Small airway impairment was defined as a decrease in the distal flows greater than 50% or distension (residual volume or forced vital capacity > 120% of predicted values). Compared to clinical evaluation, a value < 1.25 for the Juniper score is predictive of good asthma control: P < 0.0001, sensibility 84%, specificity 91%, confidence interval between 0.65 and 0.73. Distal airway impairment was more frequent in case of poorly controlled asthma (score ≥ 1.25). This survey shows the interest of the quantitative evaluation of asthma control by the patients by means of the questionnaire of Juniper, a mean score of 1.25 having the best comparative value with the clinical assessment by the physician. It also shows a good correlation between an elevated score of Juniper and the degree of small airway impairment, suggesting to optimise the anti-inflammatory treatment while directing it on the whole bronchial tract, including small airways.

Integrated ANN approach to forecast load

The demand for electricity is known to vary by the time of the day, week, month, temperature, and usage habits of the consumers. Though usage habit is not directly observable, it may be implied in the patterns of usage that have occurred in the past. A short-term load-forecasting (STLF) program that uses an integrated artificial neural network (ANN) approach is capable of predicting load for basic generation scheduling functions, assessing power system security, and providing timely dispatcher information. How well training data is chosen in an ANN is the defining factor in how well the network's output will match the event being modeled.

Incorporating Practicability into Genetic Algorithm-Based Time-Cost Optimization

Optimization problems in construction scheduling, such as time-cost optimization, can be effectively solved using genetic algorithms (GAs). This paper presents an approach that makes GA-based time-cost optimization viable for real world problems. Practicability is incorporated through the integration of a project management system to the GA system. The approach takes advantage of the powerful scheduling functionality of the project management system in evaluating project completion dates during optimization. The approach ensures that all scheduling parameters, including activity relationships, lags, calendars, constraints, resources, and progress, are considered in determining the project completion date, thus allowing comprehensive and realistic evaluations to be made during optimization.

Heuristics for hybrid flow shops with controllable processing times and assignable due dates

This paper considers a generalization of the permutation flow shop problem that combines the scheduling function with the planning stage. In this problem, each work center consists of parallel identical machines. Each job has a different release date and consists of ordered operations that have to be processed on machines from different machine centers in the same order. In addition, the processing times of the operations on some machines may vary between a minimum and a maximum value depending on the use of a continuously divisible resource. We consider a nonregular optimization criterion based on due dates which are not a priori given but can be fixed by a decision-maker. A due date assignment cost is included into the objective function. For this type of problems, we generalize well-known approaches for the heuristic solution of classical problems and propose constructive algorithms based on job insertion techniques and iterative algorithms based on local search. For the latter, we deal with the design of appropriate neighborhoods to find better quality solution. Computational results for problems with up to 20 jobs and 10 machine centers are given. Scope and purpose Traditional research to solve multi-stage scheduling problems has focused on regular measures of performance based on a single criterion and assumes that several decisions related to due dates and processing times have already been made. However, in many industrial scheduling practices, managers develop schedules based on multicriteria and have to decide the due dates and processing times as part of the scheduling activities. Further, in practical scheduling situations, there are multiple machines at each stage and the objective function often reflects the total cost of processing, earliness and tardiness. Such scheduling problems require significantly more effort in finding acceptable solutions and hence have not received much attention in the literature. For this reason, this paper considers one such hybrid flow shop scheduling problem involving nonregular measures of performance, controllable processing times, and assignable due dates. We combine and generalize the existing approaches for the classical flow shop problem to the problem under consideration. Computational experiments are used to evaluate the utility of the proposed algorithms for the generalized scheduling problems. Brah and Hunsucker (European Journal of Operational Research 1991;51:88–99) and Nowicki and Smutnicki (European Journal of Operational Research 1998;106:226–253) describe branch and bound and tabu search algorithms for the approach used in the development of heuristic algorithms can also be adapted to several other complex practical scheduling problems.

Planning, scheduling and control systems: why cannot they work together

The decisions made by the planning, scheduling, and control functions have a large economic impact on process industry operations—estimated to be as high as 10 dollars increased margin per ton of feed for many plants. The current process industry environment places even more of a premium on effective execution of these functions. In spite of the incentives, or maybe because of them, there exists significant disagreement about the proper organization and integration of these functions, indeed even which decisions are properly considered by the planning, scheduling or control business process. Advances in data capture and conditioning, sophisticated analytical techniques, and high performance computing environments have provided improved support for all three functions. High-speed communications can transfer information and data almost without limits. Yet, maintaining consistency among the decisions in most process companies continues to be difficult and the lack of consistency has real economic consequences. In this paper, we examine the following questions: what are the key issues, similarities, and differences for these functions in support of process industry decision making? What are the roadblocks in achieving the integration that seems technically feasible? The answers have significant financial implications as well as implications with regard to technology selection, infrastructure design, and staffing requirements.

Implementing a Laboratory Information Management System (LIMS) in an Army Corps of Engineers' Water Quality Testing Laboratory

Today's environmental laboratory faces numerous challenge such as enhanced regulatory oversight, decreasing costs per tests, and numerous laboratory accreditations that are offered and/or required. Selecting the LIMS that will “fit” your laboratory is important, but so is finding a system that has the flexibility to conform to the changes that will be required by the laboratory over the years. These changes will occur not only in terms of reporting, but also in terms of the ability to integrate new instrumentation, calculations, screens and future software. When selecting a LIMS, it is important to have a good understanding of the requirements of current and future laboratory needs. Equally as important in selecting the functionality that matches the laboratory requirements is selecting a technology platform that is easily managed and utilizes open architecture. The Army Corps of Engineers' Laboratory chose SQL Server as the backend database because of the robustness of the product. Microsoft® Access was chosen as the front-end database partially because of its provision for seamless integration. These functions allow users to export directly from the LIMS to any of the programs in the Microsoft Office suite and vice versa. Synergy such as this enhances the flexibility of the LIMS. There are many features in a LIMS; however, the primary functionalities include sample tracking, data entry, sample scheduling, QA/QC, electronic data entry, chemical and reagent inventory and personnel and equipment management. Other features that help increase productivity and efficiency include the use of bar codes, data loggers, instrument integration and specialized software modules such as cost accounting/time tracking. The Washington Aqueduct, a division of the US Army Corps of Engineers, operates two water treatment facilities and a water quality laboratory in Washington, D.C., which perform testing on a wide array of water and wastewater samples. Washington Aqueduct is a wholesale water producer serving one million residents in Washington, D.C., Arlington County, Virginia and Falls Church, Virginia. Challenges faced by many environmental laboratories include enhanced regulatory oversight, decreasing costs per tests, and numerous laboratory accreditations that are offered and/or required. The Washington Aqueduct laboratory implemented a Laboratory Information Management System (LIMS) as its data management solution to combat some of these challenges. Sample Master® Pro LIMS offered Washington Aqueduct their ability to track samples, data entry capabilities, sample scheduling functions, QA/QC, electronic data entry, chemical and reagent inventory and personnel and equipment management. The Washington Aqueduct also needed to increase productivity and efficiency. These challenges were met through the use of bar coding, instrument integration and specialized software, which offered a cost accounting/time tracking module. This paper will focus on the process of implementing a Laboratory Information Management System, flow-charting through software installation, instrument integration and full automation.

A Model for the Control of Complexity in Manufacturing Systems

Information variety and uncertainty are the key elements of complexity in manufacturing systems. An information-theoretic model based on entropy is proposed here. The model shows the interaction between the scheduling function and the production function, which provides a realistic framework for the control of complexity in manufacturing systems. The usefulness of the model can be summarised as supporting the understanding, monitoring and decision-making when controlling complexity. Some results of a case study are presented to prove the applicability of the model. Furthermore, the model has provided a basis for the investigation on related topics.

Experiences with Mixed Integer Linear Programming-Based Approaches in Short-Term Hydro Scheduling

This paper describes experiences with mixed integer linear programming (MILP)-based approaches on the short-term hydro scheduling (STHS) function. The STHS is used to determine the optimal or near-optimal schedules for the dispatchable hydro units in a hydro-dominant system for a user-definable study period at each time step while respecting all system and hydraulic constraints. The problem can be modeled in detail for a hydro system that contains both conventional and pumped-storage units. Discrete and dynamic constraints such as unit startup/shutdown and minimum-up/minimum-down time limits are also included in the model for hydro unit commitment (HUC). The STHS problem is solved with a state-ofthe-art package that includes an algebraic modeling language and an MILP solver. The usefulness of the proposed solution algorithm is illustrated by testing the problem with actual hydraulic system data. Numerical experiences show that the solution technique is computationally efficient, simple, and suitable for decision support of short-term hydro operations planning. In addition, the proposed approaches can be easily extended for scheduling applications in deregulated environments.

Fleet scheduling and dispatching for demand-responsive passenger services

This paper describes a software system designed to manage the deployment of a fleet of demand-responsive passenger vehicles such as taxis or variably routed buses. Multiple modes of operation are supported both for the fleet and for individual vehicles. Booking requests can be immediate (i.e. with zero notice) or in advance of travel. An initial implementation is chosen for each incoming request, subject to time-window and other constraints, and with an objective of minimising additional travel time or maximising a surrogate for future fleet capacity. This incremental insertion scheme is supplemented by post-insert improvement procedures, a periodically executed steepest-descent improvement procedure applied to the fleet as a whole, and a “rank-homing” heuristic incorporating information about future patterns of demand. A simple objective for trip-insertion and other scheduling operations is based on localised minimisation of travel time, while an alternative incorporating occupancy ratios has a more strategic orientation. Apart from its scheduling functions, the system includes automated vehicle dispatching procedures designed to achieve a favourable combination of customer service and efficiency of vehicle deployment. Provision is made for a variety of contingencies, including travel slower or faster than expected, unexpected vehicle locations, vehicle breakdowns and trip cancellations. Simulation tests indicate that the improvement procedures yield substantial efficiencies over more naı̈ve scheduling methods and that the system will be effective in real-time applications.

Fuzzy Logic Scheduling in PI Control of the Servo System Under High Stiction Torque

This paper is concerned with a controller design for a servo system with a high stiction torque. A complete friction model is adopted that caters for a dynamic stiction torque. A classical cascaded control structure that is composed of the inner velocity and outer position control loops is employed. The PI controllers are used in this loops. Due to a high stiction torque a high accuracy of servo tracking in the steady-state and a high dynamic performance cannot be simultaneously achieved by fixed parameter controller under uncertainty in the friction model parameters. High gains of the controller needed to reject friction in order to obtain required steady-state error would lead to a loss of stability. Gain scheduling is proposed based on the servo speed measurements. The gain scheduling functions cannot be derived using classical techniques due to the uncertainty and nonlinearities. A fuzzy logic approach is then applied that easily utilises available qualitative representation of the functions. Performance of the controller is illustrated by simulation results.

Motor Learning as a Function of KR Schedule and Characteristics of Task-Intrinsic Feedback

Forty participants (age range = 18–35 years) practiced 1 of 2 versions of an aiming task (with or without spring resistance). Knowledge of results (KR) was provided to them either immediately or after a delay of 2 trials. Immediate KR led to significantly more accurate performance during the 80 trials in acquisition but significantly less accurate performance on a 40-trial retention test given 24 hr after practice. In addition, the spring version of the task was performed significantly less accurately than the no-spring version on the 24-hr retention test. Most important, a significant interaction on the 24-hr retention test revealed that performance of the no-spring version of the task, when KR had been given after a 2-trial delay, was significantly more accurate than performance of the other 3 combinations of task version and KR schedule. The results suggest that KR dependency in motor skill learning is related to familiarity with task-intrinsic feedback in addition to the schedule on which KR is presented.

A Method for Parallelizing Algorithms by Vector Scheduling Functions

A technique for parallelizing multidimensional algorithms with uniform dependencies designed for the implementation on parallel architectures of smaller dimensionalities is suggested. The technique is based on multidimensional separate scheduling of the basic operations of the algorithm. A procedure for the construction of a scheduling (parallelizing) function on the basis of theoretical results is suggested.

ROLE OF SCHOOL SCHEDULE, AGE, AND PARENTAL SOCIOECONOMIC STATUS ON SLEEP DURATION AND SLEEPINESS OF PARISIAN CHILDREN

The aim of the study was to assess the duration and quality of sleep of prepubertal (Tanner Scale level 1) physically and mentally healthy children as a function of school schedule (4 versus 4.5 days per week), age and grade (median age of 9.5 years for 4th grade versus median age of 10.5 years for 5th grade), school district (wealthy versus nonwealthy) in Paris, France, and parental socioeconomic status (high, medium, or low). We studied 51 girl and 44 boy volunteer pupils with written parental consent. The study lasted 2 weeks during the month of March. During the first study week, the children attended school 4.5 days, and during the second week, they attended school only 4 days without difference in the length of the school day. A sleep log was used to ascertain time of lights off for sleep and lights on at awakening, nighttime sleep duration, and self-rated sleep quality. A visual analog scale (VAS) was also used by pupils to self-rate the level of perceived sleepiness at four specific times of the school day. Conventional statistical methods (e.g., t and χ2tests) were used to examine differences in mean values. Sleep duration, self-rated sleepiness, and subjective sleep quality were comparable (P >. 05) by gender, school schedule, school district, and parental socioeconomic status. Overall, the sleep of this sample of Parisian children around 10 years of age was rather stable in its duration and timing, suggesting flexibility to adjust to the different school schedules. (Chronobiology International, 18 (6), 1005–1017, 2001)

Sintering temperature effects on the in vitro bioactive response of tape cast and sintered bioactive glass-ceramic in Tris buffer.

Tape casting procedures were used to form thin polymeric sheets (100 microm thickness) loaded with bioactive glass particulate. Blanks were punched from the sheets, stacked, laminated, and heated in air to 500 degrees C to remove the organic phase. The resulting bioactive glass discs were sintered at 800 degrees C, 900 degrees C, or 1000 degrees C. Because the material is built up in layers and can be machined in the green state, such a processing technique can be used to form complex-shaped materials. The in vitro bioactivity of the tape cast sintered (TCS) bioactive glass-ceramic discs was then assessed in Tris buffer. The sample surface area to volume buffer (SA/V) ratio was approximately 0.1 cm(2)/mL. Tape cast bioactive glass-ceramic sintered at 900 degrees C and 1000 degrees C formed crystalline hydroxyapatite layers after 24 h in Tris buffer as indicated by FTIR, SEM, and EDS analysis. Decreasing the SA/V ratio to 0.013 cm(2)/mL allowed for the formation of crystalline hydroxyapatite layers on the surface of 800C TCS bioactive glass-ceramic. Given the dependence of the bioactive response as a function of the processing schedule and SA/V ratio, it may be possible to tailor the response to that desired in vivo or in vitro for tissue engineering studies. Biaxial flexural strength of TCS bioactive glass-ceramic increased with increasing sintering temperature. Strength of samples sintered at 1000 degrees C for 3 h increased from 87 to 120 MPa after 2 weeks' immersion in Tris buffer.

Design of Processor Arrays for Reconfigurable Architectures

This paper deals with the design of processor arrays for regular algorithms. The design is constrained by limited implementation cost characterizing a reconfigurable architecture. The objective of the design is to minimize the latency of the processor array. The presented approach to determine a scheduling function leading to the minimal latency of the processor array is formulated as a linear program that incorporates 1) the selection of modules to be implemented in processors to execute operations of the algorithm, 2) the binding of operations to modules, 3) the computation of the number of registers, 4) the limitation of implementation cost for modules and registers, 5) the determination of the size of partitions that allows to match the limited implementation cost.