The Non-Abelian Self Dual String on the Light Cone

We construct the scalar profile for the non-abelian self dual string connecting two M5-branes compactified on a light-like circle. The construction is based on a conjectured modified version of Nahm's equations describing a D2-brane, with a magnetic field on it, suspended between two D4-branes. Turning on a constant magnetic field on the D2-brane corresponds to a boost in the eleventh direction. In the limit of infinite boost the D4-branes correspond to light-like compactified M5-branes. The solution for the scalar profile of the brane remains finite in this limit and displays all the correct expected features such as smooth interpolation between the unbroken and broken phase with the correct value for the Higgs field at infinity.Comment: 13 pages, LaTeX 2e, 2 figure

Infinite spin particles

We show that Wigner's infinite spin particle classically is described by a reparametrization invariant higher order geometrical Lagrangian. The model exhibit unconventional features like tachyonic behaviour and momenta proportional to light-like accelerations. A simple higher order superversion for half-odd integer particles is also derived. Interaction with external vector fields and curved spacetimes are analyzed with negative results except for (anti)de Sitter spacetimes. We quantize the free theories covariantly and show that the resulting wave functions are fields containing arbitrary large spins. Closely related infinite spin particle models are also analyzed.Comment: 43 pages, Late

Threshold intensity factors as lower boundaries for crack propagation in ceramics

BACKGROUND: Slow crack growth can be described in a v (crack velocity) versus K(I )(stress intensity factor) diagram. Slow crack growth in ceramics is attributed to corrosion assisted stress at the crack tip or at any pre-existing defect in the ceramic. The combined effect of high stresses at the crack tip and the presence of water or body fluid molecules (reducing surface energy at the crack tip) induces crack propagation, which eventually may result in fatigue. The presence of a threshold in the stress intensity factor, below which no crack propagation occurs, has been the subject of important research in the last years. The higher this threshold, the higher the reliability of the ceramic, and consequently the longer its lifetime. METHODS: We utilize the Irwin K-field displacement relation to deduce crack tip stress intensity factors from the near crack tip profile. Cracks are initiated by indentation impressions. The threshold stress intensity factor is determined as the time limit of the tip stress intensity when the residual stresses have (nearly) disappeared. RESULTS: We determined the threshold stress intensity factors for most of the all ceramic materials presently important for dental restorations in Europe. Of special significance is the finding that alumina ceramic has a threshold limit nearly identical with that of zirconia. CONCLUSION: The intention of the present paper is to stress the point that the threshold stress intensity factor represents a more intrinsic property for a given ceramic material than the widely used toughness (bend strength or fracture toughness), which refers only to fast crack growth. Considering two ceramics with identical threshold limits, although with different critical stress intensity limits, means that both ceramics have identical starting points for slow crack growth. Fast catastrophic crack growth leading to spontaneous fatigue, however, is different. This growth starts later in those ceramic materials that have larger critical stress intensity factors

An introduction to analytical mechanics

The present edition of this compendium is intended to be a complement to the textbook “Engineering Mechanics” by J.L. Meriam and L.G. Kraige (MK) for the course ”Mekanik F del 2” given in the first year of the Engineering physics (Teknisk fysik) programme at Chalmers University of Technology, Gothenburg. Apart from what is contained in MK, this course also encompasses an elementary understanding of analytical mechanics, especially the Lagrangian formulation. In order not to be too narrow, this text contains not only what is taught in the course, but tries to give a somewhat more general overview of the subject of analytical mechanics. The intention is that an interested student should be able to read additional material that may be useful in more advanced courses or simply interesting by itself. The chapter on the Hamiltonian formulation is strongly recommended for the student who wants a deeper theoretical understanding of the sub ject and is very relevant for the connection between classical mechanics (”classical” here denoting both Newton’s and Einstein’s theories) and quantum mechanics. The mathematical rigour is kept at a minimum, hopefully for the benefit of physical understanding and clarity. Notation is not always consistent with MK; in the cases it differs our notation mostly conforms with generally accepted conventions. The text is organised as follows: In Chapter 1 a background is given. Chapters 2, 3 and 4 contain the general setup needed for the Lagrangian formalism. In Chapter 5 Lagrange’s equation are derived and Chapter 6 gives their interpretation in terms of an action. Chapters 7 and 8 contain further developments of analytical mechanics, namely the Hamiltonian formulation and a Lagrangian treatment of constrained systems. Exercises are given at the end of each chapter. Finally, a translation table from English to Swedish of some terms used is found. Many of the exercise problems are borrowed from material by Ture Eriksson, Arne Kihlberg and G\uf6ran Niklasson. The selection of exercises has been focused on Chapter 5, which is of greatest use for practical applications

Experiences of demand responsive transport among vulnerable travellers - a handbook on need, demeanour, and interaction

This research-based handbook provides an understanding about the experiences that vulnerable travellers have when they use demand responsive transport (DRT) modes. It deals with issues of importance when conducting this form of service: ways to interact with travellers, being sensitive to their needs and adapt to situations in the traffic environment. The handbook starts with a detailed description of the phases that a trip typically consists of and the different demands that needs to be accounted for. It details how important social structures are produced in interaction. Further, some concrete issues of driver-traveller interaction are discussed, followed by an identification of critical touchpoints during travel. It is argued that providers need to go beyond the mere managerial discourse on being ‘service-minded’, and pay more attention to the embodied, behavioural, multimodal and sequential aspects during training and education since these are important mechanisms for traveller and employee well-being. Travellers may be guided in how to more distinctively and actively use their own and the provider’s resources, e.g. knowledge, capabilities and equipment.The handbook also highlights general problems and challenges, having a user-perspective on the trip and suggests some solutions and opportunities that DRT-systems provide. The section discusses crucial aspects, such as service employee demeanour, traveller coping behaviour, and traveller misbehaviour. It is argued that transport providers should be aware of the principal forms of vulnerability, i.e. physical discomfort, commodification, and disorientation, which travellers may experience during traveller-driver interactions. Environmental designers may benefit from using this type of data on traveller behaviour, paying particular attention to the communication environment from a processual perspective. Marketing personnel in provider organizations could provide more accurate and timely information to travellers during, before, and after trips.Armed with a more profound knowledge of travellers’ real-time perceptions, transport operators might increase their ability to design more user-friendly services. This, in turn, could have a substantial impact in inducing travellers to switch from costly road-based special transport vehicles (such as various kinds of taxis for disabled travellers) to public transport. Travellers’ real-time perceptions could be an alternative starting-point for design of DRT-service—especially in integrating various responsible organisations. In the case of public transport there are many actors—including the operators of various transport modes (bus, train, and tram), the various transport authorities, different regional authorities, and various traveller representatives. All of these parties could use this kind of concrete visual information as a platform for a more profound dialogue that promotes a long-term, accessible, and sustainable service system.The handbook ends with some recommendations on how to develop methods for a better understanding of vulnerable travellers and how more specifically conduct group sessions where participants may analyse and develop co-designed future transport solutions. It is argued that transport provider awareness of the value co-formation activities in the practices described enables a more precise strategy for employee education and traveller involvement in the services. More service staff training in interactional techniques can thus be beneficial. Further, employee education could include discussions about general practices in services for functionally limited travellers and the delicate balance of assisting the traveller and letting the traveller decide how much assistance that is needed. The latter requires sensitivity to verbal and non-verbal cues that only can be picked up in the meeting with each traveller. All sections include suggestions for managerial implications.RESPONSE - Demand-Responsive Transport to ensure accessibility, availability and reliability of rural public transpor

Bi-directional and Stratified Demeanour in Value Forming Service Encounter Interactions

The purpose of this paper is to unearth the bi-directional and stratified nature of service encounter interactions. Drawing on a detailed empirical study of service demeanour in mobility services, seen from a customer perspective, we outline a classification of 6 overarching demeanour practices, 20 sub-activities, and interactional sequences, explaining how value co-formation is realized. We suggest that value derives from bi-directional activities mutually combined in congruent ways, avoiding counterproductive interactions