A modified coupled map car following model and its traffic congestion analysis

Based on the coupled map car following model which was presented by Konishi et al. [Konishi KJ, Kokame H, Hirate K. Phys Rev E 1999;60:4000-7.] (for short, KKH), a modified coupled map car following model is proposed. In this model two successive vehicles’ headway distances in front of the considered one are incorporated in the optimal velocity (for short, OV) function. The stability condition is given for the change of the speed of the preceding vehicle on the base of the control theory. The control scheme in KKH model is applied to the modified model and the feedback gains are determined. Comparison between the modified model and KKH model is carried out. And the corresponding numerical simulation results show that the temporal behavior obtained by our model is better than that by KKH model. The simulation results are in good agreement with the theoretical analysis.     

The estimation of the prevalence of delinquency: Two approaches and a correction of the literature†

The index “the proportion of a cohort that have become delinquent by a given age,” here called the “prevalence of delinquency,” is an important social indicator. In the present paper, we indicate methods by which this index can be estimated from data, and correct errors in previous sex‐ and race‐specific prevalence estimates published by Monahan (1960) for the city of Philadelphia. The difference between the sexes and between the races shown by these corrected prevalence estimates are of sufficient magnitude to render suspect any comparisons of prevalences of delinquency among cohorts which do not take account of the sex and race compositions of the cohorts to be compared.     

Adapting support vector machine methods for horserace odds prediction

The methodology of Support Vector Machine Methods is adapted in a straightforward manner to enable the analysis of stratified outcomes such as horseracing results. As the strength of the Support Vector Machine approach lies in its apparent ability to produce generalisable models when the dimensionality of the inputs is large relative to the the number of observations, such a methodology would appear to be particularly appropriate in the horseracing context, where often the number of input variables deemed as being potentially relevant can be difficult to reconcile with the scarcity of relevant race results. The methods are applied to a relatively small (200 races in-sample) sample of Australian racing data and tested on 100 races out-of-sample with promising results, especially considering the relatively large number (12) of input variables used.     

Planning midwifery services to deliver continuity of care

This paper describes a simulation model of maternity services which was developed to support the planning of midwifery services to meet demands for continuity of care. A Government report of maternity services in 1992 emphasised the need to replace the fragmented care offered to pregnant women by a more personalised type of approach. One way of doing this is by the implementation of team midwifery in which care is provided, antenatally, during labour, and then postnatally by either the same midwife or, more usually a small team of midwives.The model described in this paper attempts to assess the effects of team size upon the continuity of care provided to pregnant women under different implementations. Continuity is measured in terms of the percentage of occasions a team midwife will be available to meet the health care demands of pregnant women. The model may be used not only for the evaluation of services already in use, but also for the planning of alternative and better services.     

Optimal driving strategy for a solar car on a level road

Every three years, solar cars from all over the world come toAustralia to participate in the World Solar Challenge. In 1993there were 52 cars in the race. Five cars finished within fivedays, each one breaking the previous race record and achievingan average speed exceeding 70 km/h. The performance of thesecars depends on many factors: power, aerodynamics, tractionefficiency, weight, reliability, and (not least of all) drivingstrategy. On a level road, the optimal driving strategy foran ideal car is essentially a speed-holding strategy. For areal car with inefficient energy storage, however, there aretwo distinct holding speeds. The lower speed is held when solarpower is low and must be supplemented from stored energy. Theupper speed is held when solar poler is high, and excess energyis stored.     

Two local search approaches for solving real-life car sequencing problems

The NP-hard problem of car sequencing appears as the heart of the logistic process of many car manufacturers. The subject of the ROADEF’2005 challenge addressed a car sequencing problem proposed by the car manufacturer RENAULT, more complex than the academic problem generally addressed in the literature. This paper describes two local search approaches for this problem. In the first part, a new approach by very large-scale neighborhood search is presented. This approach, designed during the qualification stage preceding the final, is based on an original integer linear programming formulation. The second part is dedicated to the approach which enabled us to win the ROADEF’2005 challenge. Inspired by the latest works on the subject, this one is based on very fast explorations of small neighborhoods. Our contribution here is mainly algorithmic, in particular by showing how much exploiting invariants speeds up the neighborhood evaluation and contributes to the diversification of the search. Finally, the two approaches are compared and discussed through an extensive computational study on RENAULT’s benchmarks. The main conclusion drawn at this point is that sophisticated metaheuristics are useless to solve car sequencing problems. More generally, our victory on ROADEF’2005 challenge demonstrates that algorithmic aspects, sometimes neglected, remain the key ingredients for designing and engineering high-performance local search heuristics.     

Trajectory stabilization of a model car via fuzzy control

This paper deals with trajectory stabilization of a computer simulated model car via fuzzy control. Stability conditions of fuzzy systems are given in accordance with the definition of stability in the sense of Lyapunov. First, we approximate a computer simulated model car, whose dynamics is nonlinear, by T-S (Takagi and Sugeno) fuzzy model. Fuzzy control rules, which guarantee stability of the control system under a condition, are derived from the approximated fuzzy model. The simulation results show that the fuzzy control rules effectively realize trajectory stabilization of the model car along a given reference trajectory from all initial positions under a condition and the dynamics of the approximated fuzzy model agrees well with that of the model car.     

Fuzzy controller of the air system of a diesel engine: Real-time simulation

In this paper a fuzzy controller is proposed to regulate the intake manifold pressure and the fresh mass airflow of diesel engines simultaneously. The instrumentation set usually embedded in a mass-produced passenger car has been considered. Unlike many multi-variable controllers, the proposed structure requires neither an internal model nor identification algorithms. In comparison to controllers embedded at present in standard engine control units (ECUs), it improves the trajectory tracking of desired outputs during simulation of EURO cycles. Because of its performance, the fuzzy controller has been implemented in an electronics control unit. Some real-time results are presented.     

The effect of bearing cage run-out on the nonlinear dynamics of a rotating shaft

This paper presents an analytical model to investigate the nonlinear dynamic behavior of an unbalanced rotor-bearing system due to cage run-out. Due to run-out of the cage, the rolling elements no longer stay equally spaced. The mathematical model takes into account the sources of nonlinearity such as Hertzian contact forces and cage run-out, and the resulting transition from a state of no contact to contact between the rolling elements and the races. The contact between the rolling elements and races is treated as nonlinear springs and the system is analyzed for varying numbers of balls. The results are presented in the form of fast Fourier transformations and Poincaré maps. The results show that the ball passage frequency is modulated with the rotational frequency. The response falls into three regimes: periodic motion, quasi-periodic oscillations, and chaotic response.     

Virtual Teams: What are their Characteristics, and Impact on Team Performance?

To date, efforts to understand virtual teaming have been largely anecdotal and atheoretical. Therefore, drawing from the extant research in the groups domain, we attempt to ground the definition of a virtual team in well-established group-level constructs, and design a simulation study to investigate the impact of different virtual team characteristics on team performance. Essentially, we argue that the virtual team is defined by three key characteristics—the virtual team context, the virtual team composition, and the virtual team structure. Using the VDT computational discrete event simulation model as our experimental platform, we simulated different virtual team models, and examined their impact on various team performance dimensions. We found that virtual team characteristics have different effects on different aspects of team performance. The virtual context team had a lower rework volume but higher coordination volume and longer project duration than the virtual composition team. Interestingly, we also found that the virtual structure team performed better than the software development team baseline model in all aspects of team performance. Based on these results, we proposed strategies to improve performance in different types of virtual team. Specifically, we propose (1) increasing the ease of communication and availability of routines in the virtual context team; (2) clarifying role expectations and fostering a team culture in the virtual composition team; and (3) implementing a lateral structure in the virtual team. Our results also suggest that firms should consider situational demands, specifically tolerance for errors and coordination volume, when considering the design of virtual teams.     

Optimal yield improvement in multi-stage manufacturing systems

Multi-stage manufacturing systems producing some non-conforming items still present economic operational problems. A decomposition approach is presented to model multi-stage manufacturing systems with inspection stations. The concept of process improvement as developed is expressed in terms of a step-wise yield improvement path, along which the most profitable improvement stages are identified. It is shown that the model selects an ever increasing set of stations to improve, once the profitability of the best station-candidates reaches a level similar to that of some other station-candidates. The approach also extends the concept of an event (naturally connected to a time frame) by relating it to a dynamic profitability frame. From an operational perspective the findings suggest that a quality improvement project, initially undertaken by a cross-functional team at a multi-stage level, may be continued through concurrent projects, focusing on improving the quality of specific manufacturing stages. The research results may be directly extended to include integrated economic improvement-inspection decisions.     

Arms races as iterated prisoner's dilemma games

Many important aspects of arms races are captured by the iterated prisoner's dilemma (IPD) game. In this analysis, strategies are developed and analyzed for IPD games which most resemble arms races; those which are finite, uncertain and time varying in length. It is shown that, under certain conditions, it can be rational to unilaterally cooperate following a series of mutual defection. A number of conclusions concerning arms race behavior are drawn.     

Modelling and Simulation of Milling Forces Using an Arbitrary Lagrangian–Eulerian Finite Element Method and Support Vector Regression

A new method is presented to predict milling forces synthetically. Firstly, the 3D simulation model of the milling process is established using the arbitrary Lagrangian–Eulerian finite element method. And the simulated accuracy is calibrated by milling tests. Then the simulation model is taken as a virtual milling test system to replace extensive real milling experiments. Secondly, the specific cutting coefficients in the mechanistic milling forces model are identified by the support vector regression method using the training sample generated from the established virtual milling test system. Lastly, this methodology was validated by the slot milling operation of 2024-T3 aluminum sheets. The results show that this new approach can dramatically eliminate the experimental machining work and achieve good estimation accuracy.     

An Econometric Approach to Short-Run Analysis of the U.K. Economy, 1955-66

The structural approach to economic forecasting differs from familiar models based on the classical analysis of time series in that it requires the specification and estimation of the inter-relationships that are taken to represent economic structure. The first part of the paper deals briefly and rapidly with some of the problems encountered in specifying and estimating such structural models. The second part deals with the applications of such models and their implications for forecasting and policy analysis. These sections are intended to be fairly allusive and preparatory to the main body of the paper which discusses a specific example of a simple econometric model of the U.K. economy constructed at the London Business School. The model is described in terms of its structural relationships, and the results of some simulation work are presented. The paper concludes with some general evaluation of the approach in the light of the specific illustration discussed.     

Simulation of High-Speed Ball Bearings with MSC/ADAMS

High-speed-rotors can be supported by angular ball bearings. Therefore, the nonlinear, time-variant bearing reaction forces are modeled for high revolution rates in this approach. Assuming local deformations, bearing stiffness is modeled with Hertzian contact between balls and races. Centrifugal forces on balls and rings are considered. Under consideration of clearance ratio the contact angle changes due to bearing load, rotational frequency and tilting angle of the inner ring. Since the contact angle determines the direction of reaction force and moment, it is possible to analyze the non-planar inner ring movement. To be able to attach further machinery parts easily to the bearing model, this approach has been done with the multi-body simulation software package MSC/ADAMS. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Stochastic optimization of sailing trajectories in an upwind regatta

In a sailboat race, the navigator’s attempts to plot the fastest possible course are hindered by shifty winds. We present mathematical models appropriate for this situation, which use statistical analysis of wind fluctuations and are amenable to stochastic optimization methods. We describe the decision tool that was developed and used in the 2007 America’s Cup race and its impact on the races.     

Full velocity difference and acceleration model for a car-following theory

In order to describe the car-following behavior more actually in real traffic, a full velocity difference and acceleration model (for short, FVDAM) is proposed by synthetically taking into account headway, velocity difference and acceleration of the leading car on the basis of full velocity difference model. The analytical method and numerical simulation results show that the proposed model can describe the phase transition of traffic flow and estimate the evolution of traffic congestion, that incorporating the acceleration of the leading car into car-following model can stabilize traffic flow, suppress the traffic jam and increase capacity, and that the following car in FVDAM can accelerate more quickly than in FVDM.     

随机模糊需求报童问题

考虑到需求的随机模糊性,建立了随机模糊需求报童的利润模型。利用可信性测度理论给出了其期望利润模型,并揭示了期望利润函数的凹性,证明了最优订货量的存在性和唯一性。结合随机模糊模拟技术和随机扰动近似算法设计了求解最优订货量的混合算法。最后,通过数值算例说明了算法的有效性。     

Manufacturing lead time estimation using data mining

We explore use of data mining for lead time estimation in make-to-order manufacturing. The regression tree approach is chosen as the specific data mining method. Training and test data are generated from variations of a job shop simulation model. Starting with a large set of job and shop attributes, a reasonably small subset is selected based on their contribution to estimation performance. Data mining with the selected attributes is compared with linear regression and three other lead time estimation methods from the literature. Empirical results indicate that our data mining approach coupled with the attribute selection scheme outperforms these methods.