Idle Machines Research Articles

The practical value of computer literacy: 2. Troubleshooting computerized imaging equipment.

Computers are a central component of all the newer imaging methods available to the medical imager. It is obvious that the radiologist with an understanding of computer science will have an advantage in dealing with this equipment. In part 1 of this series [1 ], the value of computer literacy in the prepurchase evaluation of imaging equipment was discussed. This article will deal with the daily troubleshooting of computerized machines. Nothing is more exasperating than having a million-dollar machine idle for half a day while waiting for the service engineer to arrive from some distant site, or having to abort an examination because of computer failure, especially when the patient has already been injected with contrast material. This article illustrates how computer literacy allows the radiologist to troubleshoot equipment, and fix many hardware and software “glitches.” While the radiologist cannot be expected to make complex repairs, our experience has shown that a significant number of breakdowns are due to relatively simple problems. When these occur, the radiologist with an understanding of computers can often rapidly bring equipment back to function without calling a repairman. This may result in decreased cost, as well as more rapid patient throughput. This paper gives examples of how a knowledge of cornputers is valuable to the radiologist in his everyday practice. Most simple hardware repairs are best learned from the field service engineers who are called when the machine is “down.” Minor hardware problems are often recurrent, and the radiologist who takes an active interest in these problems can gain enough knowledge to fix them rapidly. Several examples are detailed below. The acquisition of software literacy is somewhat more difficult. Courses and books on the fundamentals of computer programming are ubiquitous. Those interested in developing computer literacy should begin with a home computer and a good basic course in programming. In particular, attention should be paid to the methods by which computers handle files, as file-handling errors are the most common software problems encountered in imaging systems.

A Multifactor Priority Rule for Jobshop Scheduling Using Computer Search

Abstract Priority rules are widely used in jobshop scheduling to determine the sequence in which jobs are to be processed. The research in this area has been directed at developing generally applicable priority rules. This paper presents a method for determining an effective priority rule specific to the jobshop scheduling problem to be solved. First, a generalized objective function is formulated which is the sum of costs of tardiness, carrying in-process inventory and machine idleness. Second, a multifactor priority rule is developed which is a weighted average of four factors used in simple priority rules. Third, a method is presented for using a computer search technique to determine the best weights to use in the priority rule. Finally, a computer simulation for testing this approach versus using other priority rules is described and the experimental results are reported.

Extensions of the multiarmed bandit problem: The discounted case

There are N independent machines. Machine i is described by a sequence {X^{i}(s), F^{i}(s)} where X^{i}(s) is the immediate reward and F^{i}(s) is the information available before i is operated for the sth lime. At each time one operates exacfiy one machine; idle machines remain frozen. The problem is to schedule the operation of the machines so as to maximize the expected total discounted sequence of rewards. An elementary proof shows that to each machine is associated an index, and the optimal policy operates the machine with the largest current index. When the machines are completely observed Markov chains, this coincides with the well-known Gittins index rule, and new algorithms are given for calculating the index. A reformulation of the bandit problem yields the tax problem, which includes, as a special case, Klimov's waiting time problem. Using the concept of superprocess, an index rule is derived for the case where new machines arrive randomly. Finally, continuous time versions of these problems are considered for both preemptive and nonpreemptive disciplines.

Review of operator/machine interference models

A practical problem of significant importance for many manufacturing systems is machine interference. Interference is undesirable and unnecessary machine idleness that is caused by allowing one (or more) operator(s) to tend several machines. When the service demands of machines are not synchronized, both operators and machines can experience interference. Interference obviously decreases the productivity of a manufacturing system. Most interference models are designed to attempt to minimize the cost of interference, or simply the interference itself. In this paper, we survey the literature and classify various interference problems, models and associated assumptions, and solution techniques. Theoretical results are given. Industrial applications of the models that have been reported in the literature are also described. Finally, future applications of such interference models to robotics and flexible manufacturing systems are outlined.

A heuristic proǵramminǵ procedure for sequencinǵ the static flowshop

Abstract This paper describes a heuristic procedure for sequencing the n job m machine static flowshop. Basically, the procedure is performed in two overall steps. In the first step, each of the n jobs is tested as a potential immediate follower to each of the other jobs. In effect, this step of the procedure asks the question, ‘how well does a particular job fit in terms of job blocking or machine idleness if it were to follow some other job?’ An overall figure of merit, or cost cij, is determined for each job j as a follower to another job i. Six different heuristics are presented for determining sets of cij values. Using these values of cij, the second step then heuristically develops a job sequence by solving the travelling salesman problem. The paper also presents computational experience with the algorithm for a variety of randomly generated test problems (up to 50 jobs and 50 machines in size), and compares its performance with other published heuristic techniques.

The “worm” programs—early experience with a distributed computation

The “worm” programs were an experiment in the development of distributed computations: programs that span machine boundaries and also replicate themselves in idle machines. A “worm” is composed of multiple “segments,” each running on a different machine. The underlying worm maintenance mechanisms are responsible for maintaining the worm—finding free machines when needed and replicating the program for each additional segment. These techniques were successfully used to support several real applications, ranging from a simple multimachine test program to a more sophisticated real-time animation system harnessing multiple machines.

Productivity in project management

Generally the people employed fall into two basic categories as far as production is concerned: direct labour, and indirect labour. The ratio of the latter to the former has grown considerably over recent years, and the concept of productivity therefore should be applied to both. In the U.K. the productivity has decreased as compared with other countries. The cause lies with workers at all levels, including management, and the under-utilisation of resources, e.g. defensive labour practices, inept and weak management (it is responsible for 50% of idle machine time) and lack of communication.

The production capacity of job shops with limited storage space

Abstract Suppose the number of jobs which can be stored in front of the machines in a job shop is limited. As a result, arriving jobs for which there is no space in the shop will form a shop queue. The production capacity or maximum departure rate of jobs from the shop will depend on the way in which jobs are selected from the shop queue for release to the machine queues. For a job shop with two identical machines and random routing of jobs a number of release rules are compared. It is shown that the production capacity is increased when the number of jobs in the shop is kept less than the available storage space. Among release rules independent'of job processing times and number of operations the optimum release rule is shown, using dynamic programming, to be the idle machine rule, i.e. only release a job to the shop when a machine would otherwise be idle.

Computational Experience with a Cost-Based Algorithm for the Shop Scheduling Problem

This paper reports on the formulation and testing of an economically structured algorithm for the static shop scheduling problem. A lower bound on machine idle and job penalty cost as well as a rescheduling feature which treats job-waiting cost was developed.

Can a Moral Man Raise the Question, “Should I Be Moral?”

Let it be allowed, though virtue or moral rectitude does indeed consist in affection to and pursuit of what is right and good, as such; yet, that when we sit down in a cool hour, we can neither justify to ourselves this or any other pursuit, till we are convinced that it will be for our happiness, or at least not contrary to it.—Butler, Sermon XIThere are a number of different grounds on which philosophers have argued that the question “Should I be moral?” is unintelligible or at least somewhat odd. Some evidently are unable to understand ‘should’ in any other way than ‘morally ought’, with the consequence that the question can admit of no answer but the affirmative. Others, influenced by the later Wittgenstein, hold that, although ‘should ’-questions have a role within the moral language game, the ‘should’ in the question above has no real function, it is like a ‘machine idling,’ and we can attribute no real sense to it. Now I consider neither of these arguments to be successful or even very plausible, but I do wish to consider a further argument which is logically independent of the above and which appears, initially at least, to be quite plausible.

An EOQ model when production standards are assumed to be normally distributed

SUMMARY In this paper an EOQ model is developed especially for a production environment where the inventory to be controlled is raw material. The fundamental difference between this model and others is that a stochastic demand is placed upon the inventory in terms of the time for an individual to consume one unit of inventory rather than the number of units consumed in some time interval. A shortage cost for inventory is imposed via the idle machine (man) cost. The optimal re-order quantity is determined as a function of the stockout probability and the optimal stockout probability is obtained via a one-dimensional search, over some prescribed set of feasible stockout probabilities.

Heuristic Methods for Assigning Men to Machines: An Experimental Analysis

Abstract This paper describes a labor assignment decision frequently encountered in production operations where: 1) one operator can service several semi-automatic machines simultaneously, 2) the operator service and machine processing times vary considerably among machines, and 3) the combined costs of idle labor and machine time are to be minimized in preparing a work schedule. Two heuristics for determining labor assignments are described: the man-loading and labor-saved heuristics. Experimental results are reported that compare the heuristics with respect to: 1) the proximity of their solutions to an optimum solution derived using a branch and bound algorithm, 2) their computational efficiency, and 3) the dependency of their performance on the data considered in the experiments.

World Events

Economists still take sides on the question: Is the U.S. economy in a depression? Some say "Yes"; some say "No"; others hedge. Answers to the question depend, in the first instance, on definitions. They also depend on the interpretation of current facts and trends. On one point all agree: the economy is no longer expanding. Some facts are plain enough: the volume of unemployment, idle machines, the increase in welfare payments, decline in profits.This article can also be found at the Monthly Review website, where most recent articles are published in full.Click here to purchase a PDF version of this article at the Monthly Review website.

A Problem of Delayed Service—I

SUMMARY A system is considered possessing the following characteristics: A repairman tends a number of machines—liable to break down from time to time—and some of his time is possibly taken up by ancillary duties, inspection, walking, etc. It is assumed throughout this study that the time consumed by attendance to a particular machine is independent of the state of the machine—working or idle. On the basis of this assumption a variety of models is discussed differing among themselves by the following considerations: (a)successional as against simultaneous attendance to machines;(b)constant Poisson breakdown intensity of the whole system as against constant Poisson breakdown intensity of individual machines in working order;(c)different assumptions regarding attendance time distributions. Expressions are developed for the mean, variance and, in some cases, the functional form of the distribution of (i)the number of idle machines as observed by a random controller;(ii)the number of idle machines as observed by the repairman during one round; and(iii)the waiting time of an idle machine.

A Problem of Delayed Service—Ii

SUMMARY The system analysed in the preceding paper under the two alternative extreme assumptions of successional as against simultaneous attendance to machines is reconsidered under a “mixed” assumption: Machines are attended to in groups; repair of machines belonging to the same group is simultaneous, but different groups are dealt with in succession. Expressions are developed for the mean and variance of the number of idle machines as observed by a random controller and as observed by the repairman during one round.