The measurement of lubricant-film thickness using ultrasound

Ultrasound is reflected from a liquid layer between two solid bodies. This reflection depends on the ultrasonic frequency, the acoustic properties of the liquid and solid, and the layer thickness. If the wavelength is much greater than the liquid-layer thickness, then the response is governed by the stiffness of the layer. If the wavelength and layer thickness are similar, then the interaction of ultrasound with the layer is controlled by its resonant behaviour. This stiffness governed response and resonant response can be used to determine the thickness of the liquid layer, if the other parameters are known. In this paper, ultrasound has been developed as a method to determine the thickness of lubricating films in bearing systems. An ultrasonic transducer is positioned on the outside of a bearing shell such that the wave is focused on the lubricant-film layer. The transducer is used to both emit and receive wide-band ultrasonic pulses. For a particular lubricant film, the reflected pulse is processed to give a reflection-coefficient spectrum. The lubricant-film thickness is then obtained from either the layer stiffness or the resonant frequency. The method has been validated using fluid wedges at ambient pressure between flat and curved surfaces. Experiments on the elastohydrodynamic film formed between a sliding ball and a flat surface were performed. Film-thickness values in the range 50-500 nm were recorded, which agreed well with theoretical film-formation predictions. Similar measurements have been made on the oil film between the balls and outer raceway of a deep-groove ball bearing

Similarities and differences of pumping conventional and self-compacting concrete

In Practice, Self-Compacting Concrete (SCC) is Considered as a Simple Extension of Conventional Vibrated Concrete (CVC) When Pumping is Concerned. the Same Equipment, Materials, Pumping Procedures and Guidelines Used for CVC Are Applied When Pumping SCC. on the Other Hand, It Has Been Clearly Shown that the Rheological Properties and the Mix Design of SCC Are Different Than CVC. Can the Same Pumping Principles Employed for CVC Be Applied for SCC? This Paper Compares the Some Published Results of Pumping of CVC with Those for SCC. a First Striking Difference between Pumping of CVC and SCC is the Flow Behaviour in the Pipes. the Flow of CVC is a Plug, Surrounded by a Lubricating Layer, While during the Flow of SCC, Part of the Concrete Volume itself is Sheared Inside the Pipe. as a Result, the Importance of Viscosity Increases in Case of SCC. Due to the Low Yield Stress of SCC, the Behaviour in Bends is Different, But Quite Complex to Study. Due to the Lower Content of Aggregate and Better Stability of SCC, as It is Less Prone to Internal Water Migration, Blocking is Estimated to Occur at Lower Frequency in Case of SCC. © RILEM 2010

Representing CSCL macro-scripts using IMS LD lessons learned

Extended version of Hernández-Leo, D., Burgos, D., Tattersall, C., Koper, R. Representing Computer-Supported Collaborative Learning macro-scripts using IMS Learning Design Proceedings of the Second European Conference on Technology Enhanced Learning, CEUR Workshop Proceedings, EC-TEL'07, Crete, Greece, September 2007.This paper analyses how CSCL (Computer-Supported Collaborative Learning) macro-scripts can be implemented using IMS Learning Design (LD). CSCL macro-scripts are machine-readable collaboration scripts that structure the activities making up a learning process. In order to support a systematic analysis of the problem, we point out the requirements of CSCL macro-scripts for their representation using LD. These requirements include common collaborative learning mechanisms (group composition, role and resource distribution and coordination) and flexibility demands (such as flexible group composition). Each of these needs is described and illustrated by means of two examples proposed in the literature and which reflect the identified requirements well: Universanté and ArgueGraph Scripts. These scripts are used in the article to expose and exemplify the realization of the requirements using LD. The problem is approached from two angles – that of the LD notation itself and also from related tools and specifications. The paper positions related work and discusses the possibility of generalizing the lessons learned to the representation of CSCL micro-scripts

Fostering participation in learning networks by using reward systems and face-to-face meetings

Hummel, H. G. K., Tattersall, C., Burgos, D., Brouns, F. M. R., & Koper, E. J. R. (Submitted). Fostering participation in learning networks by using reward systems and face-to-face meetings. In Proceedings of ICALT 2006 Conference. July 5-7, Kerkrade, The NetherlandsThis paper investigates conditions for increasing participation in learning networks. ‘Lessons learned’ over a period of almost five years are phrased as recommendations for future learning network implementations. We describe three generations of facilities designed to promote learning of educational modelling languages, from a conventional website through a community site offering facilities for collaboration towards a learning network for the effective exchange of information. The paper focuses on the influence of incentive mechanisms and face-to-face meetings on participation in the LN4LD (Learning Network for Learning Design). These interventions are explained from Self-Organization and Social Exchange Theory. Repeated measurements show that the levels of both passive (accessing and reading information) and active participation (posting, replying and rating) are indeed significantly increased as a result of both interventions. Both the use of reward systems and face-to-face meetings can therefore be considered as valuable ‘add-ons’

How can field margin management contribute to invertebrate biodiversity?

Farmland invertebrates are vital for healthy ecosystem functioning. Many groups have declined due to agricultural intensification. Arable field margins potentially can increase food resources and provide winter refuges for invertebrates. They might also buffer them from agrochemical applications and farm operations. This chapter describes a series of field and farm-scale experiments which show that ways in which arable field margins are established and managed can have profound effects on their invertebrate assemblages. Field margin swards established by sowing with a grass and wildflower seed mixture attracted more butterflies than naturally regenerated swards. In the short term, larger and more species-rich invertebrate assemblages were fostered on unmanaged margins than on those managed by cutting. The timing of cutting was critical, with mid-summer cutting having the most persistent, negative effects on invertebrates, while cutting in spring and autumn was generally less damaging and may help maintain sward species richness. Fallowed land (set-aside) configured as blocks rather than margins constituted qualitatively different habitats for invertebrates. Margin width had complex effects on invertebrate abundance and species richness. Boundary hedgerows increased numbers of most invertebrate groups in the adjacent margin. The chapter suggests that blanket management approaches for invertebrates at the farm scale are not optimal. A diverse farmed landscape, with margins of different sizes and different sward structures, will provide for the different ecological requirements of invertebrate populations, and promote their diversity in the characteristically unstable environment of arable systems