Ultrasonic reflection from mixed liquid-solid contacts and the determination of interface stiffness

In thin film or boundary lubricated contacts there is a possibility of potentially damaging asperity contact occurring. Whilst there are many models of this contact mechanism, experimental verification of the proportion of solid contact is difficult to achieve. Electrical methods will only indicate that contact has occurred. Whereas, optical methods can be used to determine the proportion of contact, but only when one surface is transparent. In this work the use of ultrasonic reflection is investigated as a means to analyse these types of mixed solid-liquid contacts. A pulse of ultrasound is partially reflected at the contact between two rough surfaces. The proportion of the wave reflected can be readily used to determine the stiffness of the interface. Experimental data has been obtained from grit-blasted surfaces pressed together, both with and without liquid at the interface. The interface stiffness can be modelled by two springs in series, one of them representing the solid contact stiffness, Ksolid and the other the stiffness of the liquid fluid, Kliquid. The variation of these stiffness values with contact pressure has been investigated. At this stage it is not possible to directly determine the proportion of liquid or solid contact from the stiffness. The results however, give qualitative comparisons and information about the approach of the surfaces and hence the mean thickness of the liquid layer at the interface

Evaluation of an ultrasonic method for measurement of oil film thickness in a hydraulic motor piston ring

The efficiency of a hydraulic motor depends on the lubrication performance of the piston ring. If the film is too thin then wear occurs quickly, if it is too thick then oil is lost into the cylinder and efficiency is reduced. In this paper a technique for oil film measurement based on ultrasonic reflection is investigated. This has the potential to be used non-invasively on real components. An ultrasonic pulse will reflect from a thin film interposed between two solids. The proportion of the pulse that is reflected depends on the stiffness of the intermediate layer. If the acoustic properties of the film material are known, then the stiffness can readily be used to determine the film thickness. This principle has been employed for the piston ring lubrication case. A piston/cylinder test bench has been used to evaluate the ultrasonic method. A focusing piezo-electric transducer is mounted outside the cylinder and ultrasonic pulses reflected back from the inner bore. The variation of these pulses as the piston ring passes underneath is investigated and used to determine oil film thickness. Films in the range 0.7 to 1.3 μm were measured; the thickness did not depend strongly on either ring speed or sealed pressure. Several practical aspects were investigated such as, attenuation in the cylinder material, response time, and transducer resolution. Whilst this study demonstrated that film thickness measurement is feasible, there are a number of practical considerations that require further work, principally the focusing and coupling of the ultrasonic transducer and the response time

Homotopy nilpotent groups

We study the connection between the Goodwillie tower of the identity and the lower central series of the loop group on connected spaces. We define the simplicial theory of homotopy n-nilpotent groups. This notion interpolates between infinite loop spaces and loop spaces. We prove that the set-valued algebraic theory obtained by applying $\pi_0$ is the theory of ordinary n-nilpotent groups and that the Goodwillie tower of a connected space is determined by a certain homotopy left Kan extension. We prove that n-excisive functors of the form $\Omega F$ have values in homotopy n-nilpotent groups.Comment: 16 pages, uses xy-pic, improved exposition, submitte

Normalizers of tori

We determine the groups which can appear as the normalizer of a maximal torus in a connected 2-compact group. The technique depends on using ideas of Tits to give a novel description of the normalizer of the torus in a connected compact Lie group, and then showing that this description can be extended to the 2-compact case.Comment: Published by Geometry and Topology at http://www.maths.warwick.ac.uk/gt/GTVol9/paper31.abs.htm

Retired EU migrants, healthcare rights and European social citizenship

Drawing on a set of 210 qualitative interviews conducted in six European countries, this paper investigates the citizenship status and experiences of retired EU migrants at both national and European levels. The paper focuses upon the experiences of two types of respondents: ‘Retired Migrants’ (retired nationals of one EU country who moved on retirement and reside in another EU host state) and ‘Returnees’, that is, those migrants who have chosen to return to their country of origin after a period of residence abroad. In particular, this paper will attempt to explore three issues: (a) The extent to which retired migrants have access to, and make use of, the public healthcare systems of the countries in which they reside. (b) Retired migrants’ perceptions and experiences of those systems. (c) Whether or not a lack of access to and/or the quality of public healthcare is an important determinant of return migration decisions, i.e. moves back to the country of origin. By focusing on healthcare the paper combines an analysis of the formal welfare rights available to EU citizens who migrate on retirement (both in terms of their EU rights and their status in the receiving and exporting countries) with qualitative evidence that documents the substantive reality of such rights

Twisted equivariant K-theory for proper actions of discrete groups

We give a construction for twisted equivariant K-theory in the case of a proper action of a discrete group using twisted bundles. Our construction uses results of Lueck and Oliver to extend a construction of Adem and Ruan. We also show the existence of a Chern character to twisted Bredon cohomology. This gives a partial answer to the question of when you can construct twisted equivariant K-theory out of finite rank twisted bundles.Comment: 13 page

Climate Change and Adaptation on Karajarri Country and ‘Pukarrikarra’ Places

I am a Karajarri woman and one of the Traditional Owners of Karajarri Country. I come from Bidyadanga Aboriginal Community which is on Karajarri Country, approximately 190 km south of the township of Broome in the Kimberley region of Western Australia. I am a linguist, interpreter and researcher at the Nulungu Research Institute, located on the Broome campus of the University of Notre Dame Australia, on Yawuru Country. I am often required to bring together traditional knowledge and Western rationalist approaches to knowledge generation in my research endeavours. The aim of the project described in this paper was to explore people’s concerns around climate change on Karajarri Country. It reflects on my cultural background, knowledge, traditional language and beliefs concerning changes to Country caused by changing climate. It also includes the ways my people adapt to changes to Country. During the research, Karajarri People talked about the importance of culture and heritage, and the importance of protecting Karajarri ‘Pukarrikarra’ (dreaming) places from changes to the land and waters. The importance and connectedness of language to Country is highlighted, and the significance and value of Country is demonstrated through our spiritual understandings and cultural practices, especially around climate change on Karajarri Country.https://researchonline.nd.edu.au/nulungu_research/1000/thumbnail.jp

Localization of high-energy electron scattering from atomic vibrations

Electrons with kinetic energies of the order 100 keV are capable of exciting atomic vibrational states from a distance of microns. Despite such a large interaction distance, our detailed calculations show that the scattering physics permits a high-energy electron beam to locate vibrational excitations with atomic-scale spatial resolution. Pursuits to realize this capability experimentally could potentially benefit numerous fields across the physical sciences