We explore the relationship between Eulerian and Lagrangian approaches for modeling movement in vector-borne diseases for discrete space. In the Eulerian approach we account for the movement of hosts ...explicitly through movement rates captured by a graph Laplacian matrix
L
. In the Lagrangian approach we only account for the proportion of time that individuals spend in foreign patches through a mixing matrix
P
. We establish a relationship between an Eulerian model and a Lagrangian model for the hosts in terms of the matrices
L
and
P
. We say that the two modeling frameworks are consistent if for a given matrix
P
, the matrix
L
can be chosen so that the residence times of the matrix
P
and the matrix
L
match. We find a sufficient condition for consistency, and examine disease quantities such as the final outbreak size and basic reproduction number in both the consistent and inconsistent cases. In the special case of a two-patch model, we observe how similar values for the basic reproduction number and final outbreak size can occur even in the inconsistent case. However, there are scenarios where the final sizes in both approaches can significantly differ by means of the relationship we propose.
Knowledge of creep forces at wheel-rail interface when high power is applied to the locomotive wheels has been the subject of many recent studies. The common wheel-rail interaction methods are ...generally divided by two theories - Hertzian and non-Hertzian. The first method uses Hertzian contact for the normal problem and the tangential problem is divided into two algorithms - Polach's theory and the Simplified theory-based algorithm referred to as Modified Fastsim. Kalker's original Fastsim-based method shows a better accuracy for these two Hertzian-based algorithms. The second method is based on the non-Hertzian theory, and it uses the Exact theory also developed by Kalker and implemented in the Extended Contact library to calculate forces at the wheel-rail interface. Considering that the second method is more accurate, this paper aims to present an adaptive simulation and integration method (ASIM) which is positioned in the middle between the two common methods and is designed to introduce a transition from the non-Hertzian to Hertzian contact in the normal problem with the application of the Modified Fastsim for the calculation of contact forces at the wheel-rail interface. The proposed method is aimed to be used in vehicle system dynamics studies performed in multibody software packages. A specially developed wheel-rail coupling incorporating geometrical, normal, and tangential modules is integrated into Gensys multibody software and benchmarked with the standard Extended Contact based wheel-rail coupling by means of locomotive traction tests that use a full mechatronic model of a high adhesion locomotive. The computational performance and accuracy of the proposed method are assessed and discussed.
•A co-simulation dynamics model for a locomotive is presented.•The electrical-mechanical dynamic interactions are revealed.•The effect of wheel flat defect with different sizes are investigated.•The ...wheel flat defects can be detected by the spectrum analysis of motor current.
As a form of wheel tread failure, a wheel flat becomes increasingly severe in a large axle-load heavy-haul locomotive due to emergency braking or skidding idling. The presence of a wheel flat will cause additional impact forces at the wheel-rail interface which is likely to cause a more rapid fatigue failure of locomotive and infrastructure components. Therefore, it is necessary to determine the dynamics effect of the wheel flat on the railway vehicle system so as to allow efficient monitoring and maintenance. In this paper, a co-simulation model which combines the electrical drive subsystem with a locomotive-track coupled dynamics model considering the complete mechanical transmission subsystem has been presented to analyze the dynamic responses of the locomotive under the effect of wheel flats of different sizes. The results show that the existence of a wheel flat will exacerbate the wheel-rail impact and the vibrations of the components in the locomotive. In addition, the frequency associated with the wheel flat and the gear transmission can be extracted from the frequency spectrum of the current signals in a traction motor, which makes it possible to identify the existence of wheel flats or other rotary component defects in time through analysis of the electrical signals without installing extra sensors.
The wear and rolling contact fatigue (RCF) testing approaches for wheels and rails have been reviewed and evaluated in this study. The study points out the advantages and limitations of the existing ...approaches. The broad analysis revealed that scaled laboratory-based wear testing is widely applied. However, it is necessary to predetermine the input parameters and observing parameters for scaled wear testing for three reasons: first, to emulate the real-world scenarios as closely as possible; second, to postprocess the results received from the scaled testing and transfer them into real practice at full scale; third, to present the results in a legible/appropriate format. Therefore, most of the important parameters required for wear testing have been discussed with fundamental and systematic explanations provided. Additionally, the transition of the parameters from the real-world into the test domain is explained. This study also elaborates on the challenges of the RCF and wear testing processes and concludes by providing major considerations toward successful testing.
Given the constant demand for heavier, longer, faster, and more efficient rail freight vehicles, onboard fault detection systems appear as a good approach for enhanced railway asset exploitation. ...Real-time condition monitoring reduces inefficient preventive and reactive maintenance actions, decreases waste from replacing parts that still have a useful life, and improves availability and safety by real-time rolling stock diagnosis. There have been considerable advances in wayside monitoring applications, but these cannot achieve real-time continuous monitoring. With the price reduction and miniaturization trends of electronic devices, the cost of deploying wireless sensor networks onboard freight trains continues to become more feasible and accessible. On the other hand, the lack of onboard electric power availability on freight wagons appears as the major limitation for the implementation of these technologies. This paper reviews recent onboard condition monitoring sensors, systems, methods and techniques, aiming to define the present state of the art and its potential application for freight wagons without onboard electric power.
In this paper, we propose a method to study a general vector–host mathematical model in order to explain how the changes in biodiversity could influence the dynamics of vector-borne diseases. We find ...that under the assumption of frequency-dependent transmission, i.e., the assumption that the number of contacts is diluted by the total population of hosts, the presence of a competent host is a necessary condition for the existence of an endemic state. In addition, we obtain that in the case of an endemic disease with a unique competent and resilient host, an increase in its density amplifies the disease.
Resumen Varios investigadores han reportado el grafeno como un refuerzo ideal para materiales compuestos debido a sus interesantes propiedades (1). El material compuesto de matriz de aluminio ...reforzado con grafeno se fabricó por procesos de pulvimetalurgia. En este estudio se investigó el efecto de la morfología del polvo de aluminio sobre la capacidad de compactación y la resistencia mecánica del material compuesto. Se utilizaron diferentes tiempos de molienda para determinar el tiempo óptimo requerido en la fabricación. Se determinó la carga de compactación adecuada variando sus valores y analizando el efecto de las diferentes cargas en las características del material. Se establecieron los parámetros de sinterizado de acuerdo con los estudios previos empleados por otros investigadores. Finalmente, se determina que con 0.5% wt de grafeno se presentan fenómenos de refinamiento del grano y mayor conductividad eléctrica del compuesto con respecto al aluminio pulvimetalúrgico.
The males of the species of frogs
Engystomops pustulosus
produce simple and complex calls to lure females, as a way of
intersexual selection
. Complex calls lead males to a greater reproductive ...success than what simple calls do. However, the complex calls are also more attractive to their main predator, the bat
Trachops cirrhosus
. Therefore, as M. Ryan suggests in (The túngara frog: a study in sexual selection and communication. University of Chicago Press, Chicago,
1985
), the complexity of the calls lets the frogs keep a trade-off between reproductive success and predation. In this paper, we verify this trade-off from the perspective of game theory. We first model the proportion of simple calls as a symmetric game of two strategies. We also model the effect of adding a third strategy, males that keep quiet and intercept females, which would play a role of
intrasexual selection
. Under the assumption that the decision of the males takes into account this trade-off between reproductive success and predation, our model reproduces the observed behavior reported in the literature with minimal assumption on the parameters. From the model with three strategies, we verify that the quiet strategy could only coexists with the simple and complex strategies if the rate at which quiet males intercept females is high, which explains the rarity of the quiet strategy. We conclude that the reproductive strategy of the male frog
E. pustulosus
is rational.
A wheel flat is a common fault in railway vehicles that may develop after incorrect brake application, or localised wheel-rail adhesion reduction. Operators detect wheel flats using wayside systems ...that are not capable of delivering real-time alarms. A wheel flat defect was modelled and introduced to a railway wagon multibody dynamic simulation to study the vehicle dynamic behaviour triggered by such wheel tread defect. Bogie-based and car body-based wheel flat detection was evaluated to determine eventual hardware robustness and signal processing requirements for on-board wheel flat detection devices. Various vehicle operating conditionds and wheel flat defects were simulated to analyse the wheel flat impact propagation throughout the railway vehicle bodies. Wheel defect detectability was assessed using detectability indicators (DIs) based on envelope power spectrum analysis, crest factor and RMS. It was found that bogie and car body-based wheel flat detectability is highly dependent on the track characteristics. The wheel flat signature was reduced in the wheelset-bogie and bogie-car body interfaces, indicating that advanced signal processing techniques are required for bogie-based and car body-based wheel flat detection systems. The DIs showed clear differences between healthy and faulty wheelset and bogie frame acceleration signals, which is promising for eventual on-board wheel flat detection systems.
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