2+1 gravity, chaos and time machines

2+1 gravity for spacetimes with topology RxT^2 has been much studied. We add a description of how to extend these spacetimes across a Cauchy horizon into a region where the torus becomes Lorentzian. The result is a one parameter family of tori given by a geodesic in the "Teichmueller space" of Lorentzian tori. We describe this in detail. We also point out that if the modular group is regarded as part of the gauge group then these spacetimes offer a nice toy model for the dynamics of Bianchi IX models; in the region where the tori are spacelike the dynamics is described exactly by a hyperbolic billiard. On the other hand the modular group acts ergodically on the Teichmueller space of Lorentzian tori

A Linear Control Theory Analysis of Transverse Coherent Bunch Instabilities Feedback Systems (The Control Theory Approach to Hill's Equation)

There is an on-going effort to build a feedback system for transverse coherent bunch instabilities for ALS [1,2,3]. The beam dynamics issues were already addressed in the conceptual design report [ 4] and more detailed studies have been earned out [5]. On-going work is the development of a general simulation code including the full 6-dirnensional dynamics for coherent bunch instabilities (by using Taylor series maps) as well as related feedback systems [6]. Recently, there has been some confusion about how to choose the gain matrix in the feedback loop. In particular, the current analytical formulas were found (from numerical simulations by D. Briggs using the newly developed simulation code) to only be valid if ak = 0 at the kicker. This motivated us to perform a more careful design study of the transverse feedback system based on linear control theory. This paper presents the general formulas for tuning the system. Also, by a careful analytical study of the performance of the system, based on linear accelerator theory combined with linear control theory for sampled systems, we discovered that the performance of the system can be dramatically improved by slightly changing one of the two coefficients in the gain matrix

Adaptive Cruise Control and Driver Modeling

Many vehicle manufacturers have lately introduced advance driver support in some of their automobiles. One of those new features is Adaptive Cruise Control DACCE, which extends the conventional cruise control system to control of relative speed and distance to other vehicles. In order to design an ACC controller it is suitable to have a model of driver behavior. The approach in the thesis is to use system identification methodology to obtain dynamic models of driver behavior useful for ACC applications. Experiment with seven drivers participating in different traffic situations were performed both on public road and on a test track. Data analysis was made by means of system identification methodology, several models of drivers longitudinal behavior being proposed, including linear regression models, subspacebased models and behavioral models. The thesis also deals with detection of when a driver is changing his behavior in various situations to a deviant behavior. To that purpose, a GARCH model was used to model the driver in situations with timevarying behavior

Closed-Loop Control of HCCI Engine Dynamics

The topic of the thesis is control of Homogeneous Charge Compression Ignition (HCCI) engine dynamics. HCCI offers a potential to combine high efficiency with very low emissions. In order to fulfill the potential benefits, closed-loop control is needed. The thesis discusses sensors, feedback signals and actuators for closed-loop control of the HCCI combustion. Closed-loop control of the HCCI combustion using ion current is demonstrated. Models of the HCCI dynamics suitable for purposes of control design are presented. It is shown that low-order models are sufficient to describe the HCCI dynamics. Models of HCCI combustion have been determined both by system identification and by physical modeling. Different methods for characterizing and controlling the HCCI combustion are outlined and demonstrated. In cases where the combustion phasing in a six-cylinder heavy-duty engine was controlled, either by a Variable Valve Actuation system using the inlet valve or a dual-fuel system, results are presented. Combustion phasing is a limiting factor of the load control and emission control performance. A system where control of HCCI on a cycle-to-cycle basis is outlined and cylinder individual cycle-to-cycle control on a six-cylinder heavy duty engine is presented. Various control strategies are compared. Model-based control, such as LQG and Model Predictive Control MPC, and PID control are shown to give satisfactory controller performance. An MPC controller is proposed as a solution to the problem of load-torque control with simultaneous minimization of the fuel consumption and emissions, while satisfying the constraints on cylinder pressure

Mare Nostrum - A study of the oil price’s effect on Danish shipping companies

Large shipping vessels currently got no other valid source of fuel than the ones that are oil based. Crude oil hence becomes an essential necessity for the shipping industry. This thesis examines the effect of the oil price on the profits made by Danish logistic firms. This is done by studying the three Danish shipping companies Maersk A/S, Erria A/S and Norden A/S. The alternative profit effect caused by environmental impacts is also brought into this study

ABS and Anti-skid on a LEGO car : A project in Embedded Systems

This work is the result of a course project in Embedded Systems. The goal was to implement a whee-slip control system on a LEGO car using a microcontroller. The car allows front-wheel or back-wheel driven configuration. Experimental results are presented for dry and wet surfaces

The effect of different criteria on the number of patients blind from open-angle glaucoma

<p>Abstract</p> <p>Background</p> <p>The prevalence of blindness and visual impairment from glaucoma is influenced by the criteria used to define these entities, which differ between countries and regions, as well as among published reports. The objective of the present study was to ascertain the extent to which different criteria of blindness and visual impairment influence estimates of the number of patients classified as blind or visually impaired by glaucoma in a clinic-based population.</p> <p>Methods</p> <p>We conducted a retrospective chart review of 914 patients with open-angle glaucoma to compare numbers of patients identified as visually impaired with and without considering visual field status. We also compared proportions classified using World Health Organisation (WHO) and United States (US) blindness criteria, and applying a new US Social Security Administration (SSA) disability criterion: perimetric mean deviation (MD) ≤ -22 dB.</p> <p>Results</p> <p>Forty patients (4.4%) were bilaterally blind from glaucoma by the WHO criteria. Fifty-two (5.7%) were blind by the the US criterion. Assessing only visual acuity, 14 (1.5%) patients were blind by the WHO criteria and 24 (2.6%) by the US definition. Eighty-five (9.3%) met the US SSA disability criterion. Among those, 52 were impaired also by the WHO definition. No patients impaired according to the WHO criteria had MD values better than -22 dB.</p> <p>Conclusions</p> <p>Excluding visual field status will seriously underestimate the prevalence of glaucoma blindness. In our patient population, 30% more patients were classified as blind by the US than by the WHO definition. Also, 60% more were identified as visually impaired by the US SSA criterion than by the WHO criteria. Visual field assessment is vital to determine visual impairment caused by glaucoma.</p