Coupling a branching process to an infinite dimensional epidemic process

Branching process approximation to the initial stages of an epidemic process has been used since the 1950's as a technique for providing stochastic counterparts to deterministic epidemic threshold theorems. One way of describing the approximation is to construct both branching and epidemic processes on the same probability space, in such a way that their paths coincide for as long as possible. In this paper, it is shown, in the context of a Markovian model of parasitic infection, that coincidence can be achieved with asymptotically high probability until o(N^{2/3}) infections have occurred, where N denotes the total number of hosts.Comment: 16 page

An Evaluation of Operation Street Sweeper - 2006

Operation Street Sweeper (OSS) was a multi-level, interagency collaboration with multiple purposes. According to OSS documents, Operation Street Sweeper goals included the following: (1) to reduce gang-related criminal and violent activity in Nampa and Caldwell, Idaho through aggressive, proactive, and coordinated street enforcement between the Bureau of Alcohol, Tobacco and Firearms (ATF) and local law enforcement; (2) to deter criminal activity through high profile enforcement activity; (3) to develop and/or increase the number of positive community contacts; (4) to show the community and gang members that law enforcement is serious about reducing gang and violent crime in the area; and (5) to use the media to showcase a law enforcement effort to reduce gang violence and activity

Diagnosis of Combination Faults in a Planetary Gearbox using a Modulation Signal Bispectrum based Sideband Estimator

This paper presents a novel method for diagnosing combination faults in planetary gearboxes. Vibration signals measured on the gearbox housing exhibit complicated characteristics because of multiple modulations of concurrent excitation sources, signal paths and noise. To separate these modulations accurately, a modulation signal bispectrum based sideband estimator (MSB-SE) developed recently is used to achieve a sparse representation for the complicated signal contents, which allows effective enhancement of various sidebands for accurate diagnostic information. Applying the proposed method to diagnose an industrial planetary gearbox which coexists both bearing faults and gear faults shows that the different severities of the faults can be separated reliably under different load conditions, confirming the superior performance of this MSB-SE based diagnosis scheme

Simulation Visualization Rhetoric and It\u27s Practical Implications

Modeling and simulation has moved far beyond simple data representation into the world of visual communication over the past 15 years; ultimately, the acceptance of M&S within mainstream science and society will depend on the results that are produced visually. A simulation’s function is of primary importance to its end result, but it cannot be denied that the discipline of M&S now prizes fancy graphics to communicate. Rhetorical methodological decisions have the greatest impact on the end user, and considerations that bring visual rhetoric to modeling and simulation should be examined as a necessity to application. This paper will expose the community to existing research on the rhetoric of visualization, highlights and addresses current problems with simulation visualization, and bring visualization’s inherent rhetoric to the forefront of consideration and utilization

A tribological study of the design and performance of automotive cams

Analytical methods to enable the evaluation of important lubrication operational parameters at the contact between any cam and follower mechanism (excluding valve trains incorporating rolling element followers or hydraulic lash adjusters) have been collated, critically assessed and developed. A robust and user friendly computer program, which incorporated these methods, was written in order that the tribological conditions existing at the cam/follower interface of any type of valve train in common use in today's internal combustion engines could be studied. The output from the program included graphical displays of frictional torque, minimum lubricant film thickness and Hertzian stress around the cam cycle. Such studies were performed on a cam and flat faced follower system, a cam and centrally pivoted follower system, a cam and end pivoted follower system and a desmodromic system (comprising a conventional cam and centrally pivoted. system and a desmodromic cam and end pivoted follower system). The computer program also allowed parametric studies to be carried out on valve train mechanisms. Parametric studies of three different valve trains, including the valve trains from the Rover 2300 and the Ford 2.0 litre Pinto engines, have been presented, the results being presented in graphical and tabular form. The loadings, orbits, and power losses associated with the camshaft bearings of the Ford 2.0 litre Pinto engine were evaluated using existing dynamically loaded bearing analysis techniques. The total frictional power loss predicted for the three camshaft bearings was found to be equal to approximately one fifth of that calculated for all of the cam/follower interfaces throughout the operational speed range of the engine. An experimental single valve desmodromic valve train apparatus was designed and commissioned to test the accuracy of the valve train lubrication analysis computer program. The apparatus allowed studies to be made of the running-in of valve trains operating at lubricant temperatures of 40C, 60C and. 80C, by applying the electrical resistivity technique. Analytical models used to predict which cam/follower pair was in control of the valve at any point around the cam cycle were tested using an electrical continuity technique and were found to show good agreement with practice. Good agreement was also found between the theoretically predicted and measured torque and power required to drive the valve train

Hearing through your eyes: neural basis of audiovisual cross-activation, revealed by transcranial alternating current stimulation

Some people experience auditory sensations when seeing visual flashes or movements. This prevalent synaesthesia-like ‘visual-evoked auditory response’ (vEAR) could result either from over-exuberant cross-activation between brain areas, and/or reduced inhibition of normally-occurring cross-activation. We have used transcranial alternating current stimulation (tACS) to test these theories. We applied tACS at 10Hz (alpha-band frequency) or 40Hz (gamma-band), bilaterally either to temporal or occipital sites, while measuring same/different discrimination of paired auditory (A) versus visual (V) 'Morse code' sequences. At debriefing, participants were classified as vEAR or non-vEAR depending on whether they reported 'hearing' the silent flashes. In non-vEAR participants, temporal 10Hz tACS caused impairment of A performance, which correlated with improved V; conversely under occipital tACS, poorer V performance correlated with improved A. This reciprocal pattern suggests that sensory cortices are normally mutually inhibitory, and that alpha-frequency tACS may bias the balance of competition between them. vEAR participants showed no tACS effects, consistent with reduced inhibition, or enhanced cooperation between modalities. In addition, temporal 40Hz tACS impaired V performance, specifically in individuals who showed a performance advantage for V (relative to A). Gamma-frequency tACS may therefore modulate the ability of these individuals to benefit from recoding flashes into the auditory modality, possibly by disrupting cross-activation of auditory areas by visual stimulation. Our results support both theories, suggesting that vEAR may depend on disinhibition of normally-occurring sensory cross-activation, which may be expressed more strongly in some individuals. Furthermore, endogenous alpha and gamma-frequency oscillations may function respectively to inhibit or promote this cross-activation

Helical gear wear monitoring: Modelling and experimental validation

Gear tooth surface wear is a common failure mode. It occurs over relatively long periods of service nonetheless, it degrades operating efficiency and leads to other major failures such as excessive tooth removal and catastrophic breakage. To develop accurate wear detection and diagnosis approaches at the early phase of the wear, this paper examines the gear dynamic responses from both experimental and numerical studies with increasing extents of wear on tooth contact surfaces. An experimental test facility comprising of a back-to-back two-stage helical gearbox arrangement was used in a run-to-failure test, in which variable sinusoidal and step increment loads along with variable speeds were applied and gear wear was allowed to progress naturally. A comprehensive dynamic model was also developed to study the influence of surface wear on gear dynamic response, with the inclusion of time-varying stiffness and tooth friction based on elasto-hydrodynamic lubrication (EHL) principles. The model consists of an 18 degree of freedom (DOF) vibration system, which includes the effects of the supporting bearings, driving motor and loading system. It also couples the transverse and torsional motions resulting from time-varying friction forces, time varying mesh stiffness and the excitation of different wear severities. Vibration signatures due to tooth wear severity and frictional excitations were acquired for the parameter determination and the validation of the model with the experimental results. The experimental test and numerical model results show clearly correlated behaviour, over different gear sizes and geometries. The spectral peaks at the meshing frequency components along with their sidebands were used to examine the response patterns due to wear. The paper concludes that the mesh vibration amplitudes of the second and third harmonics as well as the sideband components increase considerably with the extent of wear and hence these can be used as effective features for fault detection and diagnosis

A validated finite element model for predicting dynamic responses of cylinder liners in an IC engine*

Vibration of cylinder liners affects not only engine combustion performances but also tribological behaviour and noise radiations. However, it is difficult to characterize it experimentally due to multiple sources, strong background noise, and nonlinear transfer paths. Therefore, a finite element model is established in this study to predict the dynamic responses of cylinder liners under respective sources. The model takes into account both the characteristics of structural modes and nonlinearities of assembly constraints when selecting adequate elements for efficient computation of the responses under both the highly nonlinear combustion pressure excitations and subsequent piston slap impacts. The predictions are then evaluated against experimental results under different engine operating conditions. In addition, continuous wavelet analysis is employed to process the complicated responses for key response events and their frequency ranges. The results show agreeable correspondences between the numerical predictions and measured vibration signals, paving the way for investigating its effect on combustion and lubrication processes