M/G/c/c state dependent queuing model for a road traffic system of two sections in tandem

We propose in this article a M/G/c/c state dependent queuing model for road traffic flow. The model is based on finite capacity queuing theory which captures the stationary density-flow relationships. It is also inspired from the deterministic Godunov scheme for the road traffic simulation. We first present a reformulation of the existing linear case of M/G/c/c state dependent model, in order to use flow rather than speed variables. We then extend this model in order to consider upstream traffic demand and downstream traffic supply. After that, we propose the model for two road sections in tandem where both sections influence each other. In order to deal with this mutual dependence, we solve an implicit system given by an algebraic equation. Finally, we derive some performance measures (throughput and expected travel time). A comparison with results predicted by the M/G/c/c state dependent queuing networks shows that the model we propose here captures really the dynamics of the road traffic.     

Conformance checking and performance improvement in scheduled processes: A queueing-network perspective

Service processes, for example in transportation, telecommunications or the health sector, are the backbone of today׳s economies. Conceptual models of service processes enable operational analysis that supports, e.g., resource provisioning or delay prediction. In the presence of event logs containing recorded traces of process execution, such operational models can be mined automatically.In this work, we target the analysis of resource-driven, scheduled processes based on event logs. We focus on processes for which there exists a pre-defined assignment of activity instances to resources that execute activities. Specifically, we approach the questions of conformance checking (how to assess the conformance of the schedule and the actual process execution) and performance improvement (how to improve the operational process performance). The first question is addressed based on a queueing network for both the schedule and the actual process execution. Based on these models, we detect operational deviations and then apply statistical inference and similarity measures to validate the scheduling assumptions, thereby identifying root-causes for these deviations. These results are the starting point for our technique to improve the operational performance. It suggests adaptations of the scheduling policy of the service process to decrease the tardiness (non-punctuality) and lower the flow time. We demonstrate the value of our approach based on a real-world dataset comprising clinical pathways of an outpatient clinic that have been recorded by a real-time location system (RTLS). Our results indicate that the presented technique enables localization of operational bottlenecks along with their root-causes, while our improvement technique yields a decrease in median tardiness and flow time by more than 20%.     

The effect of workers with different capabilities on customer delay

Many service facilities operate seven days per week. The operations managers of these facilities face the problem of allocating personnel of varying skills and work speed to satisfy the demand for services. Furthermore, for practical reasons, periodic staffing schedule is implemented regularly. We introduce a novel approach for modeling periodic staffing schedule and analyzing the impact of employee variability on customer delay. The problem is formulated as a multiple server vacation queueing system with Bernoulli feedback of customers. At any point in time, at most one server can serve the customers. Each server incur a durations of set-up time before they can serve the customers. The customer service time and server set-up time may depend on the server. The service process is unreliable in the sense that it is possible for the customer at service completion to rejoin the queue and request for more service. The customer arrival process is assumed to satisfy a linear–quadratic model of uncertainty. We will present transient and steady-state analysis on the queueing model. The transient analysis provides a stability condition for the system to reach steady state. The steady-state analysis provides explicit expressions for several performance measures of the system. For the special case of M^X/G/1 vacation queue with a gated or exhaustive service policy and Bernoulli feedback, our result reduces to a previously known result. Lastly, we show that a variant of our periodic staffing schedule model can be used to analyze queues with permanent customers. For the special case of M/G/1 queue with permanent customers and Bernoulli feedback of ordinary customers, we obtain results previously given by Boxma and Cohen (IEEE J. Select. Areas Commun. 9 (1991) 179) and van den Berg (Sojourn Times in Feedback and Processor Sharing Queues, CWI Tracts, vol. 97, Amsterdam, Netherlands, 1993).Scope and purposeWorkforce scheduling is a classical problem and has been studied by many researchers. The problem is usually formulated with homogeneous workforce as part of the assumption. Clearly, non-homogeneous workforce is a fact of life for many organizations. Operations manager would prefer to have skills and experience worker as it would improve the quality of the services provided. Ignoring the effect of employees with varying skills and work speed would seriously undermine the effectiveness of the services provided and lead to significant undesirable outcomes for the organization. This paper aims as a first step to fill the gap of past research. We present a novel approach to analyze the issue of non-homogeneous workforce on stability of work flows and the effect of workers with different capabilities on customers’ waiting time. We believe that the results are useful for operations manager dealing with non-homogeneous workforce.     

CFD assisted modeling for control system design: A case study

This paper presents a novel modeling approach of coupling transient computational fluid dynamics (CFD) simulation with system identification for control system involving fluid flow and heat transfer. In order to illuminate the feasibility of this method, a fluid flow and heat transfer related process, i.e. a three dimension (3-D) spatio-temporal air temperature distribution and input (inlet air temperature) dependent process in the desert climate chamber, is considered. The distributed parameter models of the chamber temperature are identified using transient CFD simulation results and are then validated against the results obtained from the CFD simulations with high RT² (more than 0.97) and negative Young’s information criterion (YIC, less than ?11.8). The PI controllers embedded in CFD simulation are then developed based on the models. The performance of the closed-loop systems is also evaluated within the full-scale CFD model. The results show that CFD-based system identification is feasible to model fluid flow and heat transfer related processes.     

Production/inventory systems with a stochastic production rate under a continuous review policy

A single production facility is dedicated to producing one product with completed units going directly into inventory. The unit production time is a random variable. The demand for the product is given by a Poisson process and is supplied directly from inventory when available, or is backordered until it is produced by the production facility. Relevant costs are a linear inventory holding cost, a linear backorder cost, and a fixed setup cost for initiating a production run. The objective is to find a control policy that minimizes the expected cost per time unit.The problem may be modeled as an M/G/1 queueing system, for which the optimal decision policy is a two-critical-number policy. Cost expressions are derived as functions of the policy parameters, and based on convexity properties of these cost expressions, an efficient search procedure is proposed for finding the optimal policy. Computational test results demonstrating the efficiency of the search procedure and the behavior of the optimal policy are presented.     

k-out-of-n: G system with repair: the D-policy

In this paper we consider a k-out-of-n: G system with repair under D-policy. According to this policy whenever the workload exceeds a threshold D a server is called for repair and starts repair one at a time. He is sent back as soon as all the failed units are repaired. The repaired units are assumed to be as good as new. The repair time and failure time distributions are assumed to be exponential. We obtain the system state distribution, system reliability, expected length of time the server is continuously available, expected number of times the system is down in a cycle and several other measures of performance. We compute the optimal D value which maximizes a suitably defined cost function.Scope and purposeThis paper considers a repair policy, called D-policy, of a k-out-of-n: G system. In a k-out-of-n: G system, the system functions as long as there are atleast k operational units. The server activation cost is high once it becomes idle due to all failed units repaired. Hence it is activated when the accumulated amount of work reaches D. This paper examines the optimal D-value by bringing in costs such as the cost of system being down, the server activation cost. Activating the server the moment the first failure takes place may involve very heavy fixed cost per cycle (a cycle is the duration from a point at which the server becomes idle to the next epoch at which it becomes idle after being activated). The other extreme of server activation only after n−k+1 units fail leads to the system being down for a long duration in each cycle. Hence the need for the optimal D-policy. A brief account of k-out-of-n: G system can be had in Ross (Ross, SM. Introduction to probability models, 6th ed., New York: Academic Press, 1997). The results obtained here find direct applications in reliability engineering, Production systems, Satellite communication, etc.     

The evaluation of pedestrians’ behavior using <Emphasis Type="Italic">M/G/C/C</Emphasis> analytical,weighted distance and real distance simulation models

M/G/C/C analytical and simulation models have long been used to evaluate the performance of a large and complex topological network. However, such evaluation is only founded on a network’s total arrival rate and its weighted distance. Thus, this paper discusses some concepts and issues in building an M/G/C/C simulation model of a complex geometric system where all its arrival sources and their exact distances to the end of their networks (i.e., corridors) have been taken into consideration in measuring the impacts of various evacuation rates to its throughput, blocking probability, expected service time and expected number of pedestrians. For this purpose, the Dewan Tuanku Syed Putra hall, Universiti Sains Malaysia, Malaysia has been selected as a case study for various evaluations of complex pedestrian flows. These results were analyzed and compared with the results of our analytical and weighted distance simulation models. We then documented the ranges of arrival rates for each of the model where their results exhibited significant discrepancies and suggest ideal rates to best evacuate occupants from the hall. Our model can be utilized by policy makers to recommend suitable actions especially in emergency cases and be modified to build and measure the performance of other real-life complex systems.     

Randomized control of T-policy for an M/G/1 system

We study an M/G/1 queueing system with a server that can be switched on and off. The server can take a vacation time T after the system becomes empty. In this paper, we investigate a randomized policy to control a server with which, when the system is empty, the server can be switched off with probability p and take a vacation or left on with probability (1 − p) and continue to serve the arriving customers. For this system, we consider the operating cost and the holding cost where the operating cost consists of the system running and switching costs (start up and shut down costs). We describe the structure and characteristics of this policy and solve a constrained problem to minimize the average operating cost per unit time under the constraint for the holding cost per unit time.     

An inspection policy for shredder equipment used in steel production lines considering buffer level and operating time

On the basis of scrap metal recycling, the shredding process transforms a large variety of objects composed predominantly of steel in crunched scrap. The main equipment used in this process is called shredder: a device consisting of several hammers attached in a horizontal rotor. Due to high efforts involved in the transformation process, the maintenance is an essential aspect to ensure the continuity of the shredder operation. A non-efficient maintenance policy can have negative consequences for the shredder performance, whose failure can stop all downstream processes for which it provides the basic input (crunched scrap). In order to improve the performance of the steel production line, we are introducing an opportunistic inspection policy that makes use of the crushed scrap buffer level. The policy guides the execution of an inspection after a time T of continuous operation, when the system fails, when the buffer is full or empty, or when the opportunity criterion (operation time ≥ t AND buffer level ≥ h) is verified, whichever occurs first. At an inspection, the shredder is stopped, the hammers are inspected, and the failed and defective ones are replaced by new units. A discrete-event simulation model was developed and applied to the context of a real steel production line of a company. The optimal opportunistic inspection policy was obtained, and its performance was compared with that of the policy currently adopted by the company. The results showed the possibility of obtaining significant economic savings. A sensitivity analysis showed a cost reduction of around 95 %.     

WCOID-DG: An approach for case base maintenance based on Weighting, Clustering, Outliers, Internal Detection and Dbsan-Gmeans

The success of the Case Based Reasoning system depends on the quality of the case data and the speed of the retrieval process that can be costly in time, especially when the number of cases gets bulky. To guarantee the system?s quality, maintaining the contents of a case base (CB) becomes unavoidably. In this paper, we propose a novel case base maintenance policy named WCOID-DG: Weighting, Clustering, Outliers and Internal cases Detection based on Dbscan and Gaussian means. Our WCOID-DG policy uses in addition to feature weights and outliers detection methods, a new efficient clustering technique, named DBSCAN-GM (DG) which is a combination of DBSCAN and Gaussian-Means algorithms. The purpose of our WCOID-GM is to reduce both the storage requirements and search time and to focus on balancing case retrieval efficiency and competence for a CB. WCOID-GM is mainly based on the idea that a large CB with weighted features is transformed to a small CB with improving its quality. We support our approach with empirical evaluation using different benchmark data sets to show its competence in terms of shrinking the size of the CB and the research time, as well as, getting satisfying classification accuracy.     

A solution of the syntactical induction-inference problem for regular languages

A Teacher knows a regular language L(G), in the form of a finite state acceptor. A method is described for selecting a set of examples, strings X, each in L(G) as inputs to the Pupil. The Set X is mapped into a lattice W (in Pupil) of finite state machines. A mapping is defined from pairs of machines in the lattice W into strings y, each of which serves as a ”crucial experiment”. The Teacher is asked to decide if the string y belongs to L(G). The process then repeats or terminates.This procedure is shown to converge (if Teacher answers truthfully) to a finite state acceptor accepting only strings of L(G)(which obviously may be brought into canonical, minimal state form). However, this process does not depend on state minimization as an inference method.The only necessary condition for the inference process is that every move (edge) of that finite state acceptor U(X) chosen to correspond to L(G) must be applied at least once in generating some string x in X. A proof is given that if the Teacher answers correctly, the Pupil will infer a machine behaviorally equivalent to the original acceptor U.Elements of the lattice W are constructed by successive refinement of the partitions of the state set of the initial finite state machine U(X). Pairs are chosen in an ordered process and converted to deterministic and completely specified machines, if necessary. The two machines are tested for behavioral equivalence. If they are equivalent, one is eliminated. If not, a testing string y belonging to one machine, but not the other, is constructed and output to the teacher. If y belongs to L(G), one machine is eliminated. If not, y is tested by the Pupil against a sequence of machines generated internally. If only one machine is left, the process terminates, otherwise two new candidate machines are chosen. The algorithm described is relatively simple and easy to understand, but does not necessarily produce a minimal time solution.     

Symmetry,groups, and boundary value problems. A progressive introduction to noncommutative harmonic analysis of partial differential equations in domains with geometrical symmetry

Let Ω be a plane or spatial domain and G a group of isometries which leave Ω invariant. Suppose one has to solve on Ω a boundary value problem Au = f or an eigenvalue problem Au = μu. It is assumed (‘equivariance’) that the coefficients of A are also invariant by the action of G (but this is not required of the right-hand side ƒ). Then, instead of solving the original problem on the whole domain, one can solve a set of related problems (whose number does not exceed the order n of G) on a reduced domain, the ‘symmetry cell’, n times smaller than the original Ω. The process, which obviously promises interesting savings in structural analysis and other fields, generalizes Fourier analysis and may be referred to as “non-commutative harmonic analysis” [1]. The theoretical foundations are essentially those of group representation theory. The paper, which is mainly expository, aims at introducing the minimal amount of this theory necessary to understand how the process works and how it can be implemented in finite element codes. It also addresses the question (which seems to have been neglected in the literature) of the derivation of proper boundary conditions for the subproblems to be solved on the symmetry cell.     

SPGProfile: Speak Group Profile

In this paper, we propose an XML-based recommender system, called SPGProfile. It is a type of collaborative information filtering system. SPGProfile uses ontology-driven social networks, where nodes represent social groups. A social group is an entity that defines a group based on demographic, ethnic, cultural, religious, age, or other characteristics. In the SPGProfile framework, query results are filtered and ranked based on the preferences of the social groups to which the user belongs. If the user belongs to social group G_x, results will be filtered based on the preferences of G_x and the preferences of each ancestor social group of G_x in the social network. SPGProfile can be used for various practical applications, such as Internet or other businesses that market preference-driven products. In the ontology, the preferences of a social group are identified from either: (1) the preferences of its member users or (2) from published studies about the social group. We describe and experimentally compare these two approaches. We also experimentally evaluate the search effectiveness and efficiency of SPGProfile and compare it to two existing search engines.     

Self-similar scalar cosmologies

We study several scalar cosmological models under the self-similar approach. We deduce, by stating and proving general theorems, which is the exact form that must follow the scalar field and the potential in the frameworks of a single scalar field and non-interacting (with a perfect fluid) models. The proofs are carried out by two methods: the matter collineation approach and the Lie group method. The results obtained are absolutely general and valid for all Bianchi models and the flat FRW one. In order to study how the “constant” G may vary we propose, in a phenomenological way, how to incorporate a variable G in the framework of scalar models by modifying the Klein-Gordon equation. This approach is more general than the usual one in the context of the FRW symmetries. We deduce the exact form to be followed by each quantity in these new models. Therefore, to study how the “constants” G and Λ may vary, we propose three scenarios where such constants are considered as time functions: modified general relativity with a perfect fluid, the scalar cosmological models (“quintessence”) in the non-interacting case and a scalar-tensor model with a dynamical Λ. As an example, we study the case of Bianchi VI₀ geometry.     

An M/G/C/C state-dependent network simulation model

A discrete-event digital simulation model is developed to study traffic flows in M/G/C/C state-dependent queueing networks. Several performance measures are evaluated, namely (i) the blocking probability, (ii) throughput, (iii) the expected number of the customers in the system, and (iv) expected travel (service) time. Series, merge, and split topologies are examined with special application to pedestrian planning evacuation problems in buildings. Extensive computational experiments are presented showing that the simulation model is an effective and insightful tool to validate analytical expressions and also to analyze general accessibility in network evacuation problems especially in high-rise buildings.     

Modelling worker fatigue and recovery in dual-resource constrained systems

The operational benefits that dual-resource constrained (DRC) job shop systems bring have captured the attention of researchers for some time. Although several studies that investigate DRCs are available in the literature, none has investigated a DRC system for the effects of human fatigue and recovery, which poses important parameters to avoiding overload and injury to employees. The purpose of this paper is to address this limitation by presenting a mixed-integer linear programming (MILP) model that describes fatigue and recovery in a DRC system with one worker performing n tasks (flexibility level) within m cycles. Later, the complexity of the MILP problem was reduced to four practical cases. These cases were investigated to evaluate several research questions. The results obtained from the MILP model and the four practical cases suggest that short rest breaks after each task, short cycle times and faster recovery rates improve the system’s performance and that reduced force levels in the work tasks will reduce recovery needs and further increase performance. Further research is still needed to identify or to develop better models of physiological and mental fatigue that can be integrated to the modelling framework presented here.     

Spectral Sparsification in the Semi-streaming Setting

Let G be a graph with n vertices and m edges. A sparsifier of G is a sparse graph on the same vertex set approximating G in some natural way. It allows us to say useful things about G while considering much fewer than m edges. The strongest commonly-used notion of sparsification is spectral sparsification; H is a spectral sparsifier of G if the quadratic forms induced by the Laplacians of G and H approximate one another well. This notion is strictly stronger than the earlier concept of combinatorial sparsification. In this paper, we consider a semi-streaming setting, where we have only $\tilde{O}(n)$ storage space, and we thus cannot keep all of G. In this case, maintaining a sparsifier instead gives us a useful approximation to G, allowing us to answer certain questions about the original graph without storing all of it. We introduce an algorithm for constructing a spectral sparsifier of G with O(nlogn/? ²) edges (where ? is a parameter measuring the quality of the sparsifier), taking $\tilde{O}(m)$ time and requiring only one pass over G. In addition, our algorithm has the property that it maintains at all times a valid sparsifier for the subgraph of G that we have received. Our algorithm is natural and conceptually simple. As we read edges of G, we add them to the sparsifier H. Whenever H gets too big, we resparsify it in $\tilde{O}(n)$ time. Adding edges to a graph changes the structure of its sparsifier’s restriction to the already existing edges. It would thus seem that the above procedure would cause errors to compound each time that we resparsify, and that we should need to either retain significantly more information or reexamine previously discarded edges in order to construct the new sparsifier. However, we show how to use the information contained in H to perform this resparsification using only the edges retained by earlier steps in nearly linear time.     

修正的Gödel逻辑系统中子代数的广义重言式理论

将修正的Gödel逻辑系统中的广义重言式理论进行推广,讨论其序稠密子代数的广义重言式理论,并利用可达广义重言式概念和α-矛盾式概念在G的序稠密子代数中给出F（S）关于┐同余的一个分划.     

Self-averaging property of queuing systems

We establish an averaging property for a one-server queuing process, M(t)/G/1. It is a new relation between the output flow rate and the input flow rate, crucial in the study of the Poisson hypothesis. Its implications include the statement that the output flow always possesses more regularity than the input flow.     

Parallel string acceptance using lattice graphs

This paper describes a method of string acceptance with respect to a given grammar G by repeatedly applying the rules of G in parallel. The process differs from previous work in parallel string recognition in that when a rule, say α→β, is applied, β is not replaced by α; rather, a ‘string bypass’, consisting of α, is created that joins the left context of β to its right context. Thus, the process creates a ‘lattice graph’ in which any directed path from the least element to the greatest element is a string derivable (in reverse) by a sequence of rewritings of σ. For context-free grammars, this process does not lead to a combinatorial explosion, and could thus be used to parse strings very rapidly if suitable parallel hardware were available.