Surface Roughness and Load in Boundary Lubrication

Using the Bowden-Leben apparatus, the effects of load and surface roughness on the frictional behavior of various steels are studied over a range of temperature and of additive concentration. Cetyl amine and long-chain acids were used as surfactants, cetane and squalane being the carriers.

The critical temperatures associated with sharp rises in friction and in track width decreased linearly with increasing load. When extrapolated to zero load, these temperatures corresponded to the temperature at which serious surface damage occurred.

An explanation of this effect is given in terms of a desorption work term.

Thermodynamic analysis is shown to be very powerful using the Langmuir adsorption model.

The heat of adsorption and entropy changes were found to be functions of surface roughness for all the steels investigated. Optimum adsorption occurred at about 15 microinches CLA. This offers an additional thermodynamic explanation for the known danger of having machine parts too smooth.     

Probabilistic cuing in large-scale environmental search.

Finding an object in our environment is an important human ability that also represents a critical component of human foraging behavior. One type of information that aids efficient large-scale search is the likelihood of the object being in one location over another. In this study we investigated the conditions under which individuals respond to this likelihood, and the reference frames in which this information is coded, using a novel, large-scale environmental search paradigm. Participants searched an array of locations, on the floor of a room, for a hidden target by pressing switches at each location. We manipulated the probability of the target being at a particular set of locations. Participants reliably learned target likelihoods when the possible search locations were kept constant throughout the experiment and the starting location was fixed. There was no evidence of such learning when room-based and body-based reference frames were dissociated. However, when this was combined with a more salient perceptual landmark, an allocentric cuing effect was observed. These data suggest that the encoding of this type of statistical contingency depends on the combination of spatial cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Power and politics in requirements engineering: embracing the dark side?

This paper considers the role of power and politics in requirements engineering (RE). It presents a brief working definition of both terms and provides an overview of existing literature both in RE and related disciplines. It argues that, given the increased complexity, uncertainty, and organisational embeddedness faced by RE in practice, power and politics have necessarily become increasingly relevant factors, but that they have not yet been given adequate consideration. A framework for analysis is presented, examining power and politics in turn through the structure of power relations and the process of decision-making. This framework is explored by applying it to a case study of a website development in a publishing company. The use of a case study is intended to demonstrate the proposed framework, perform an initial validation of it, and an assessment of its utility to RE.     

Growth of Salmonella enterica Serovar Enteritidis PT4 in media containing glucose results in enhanced RpoS-independent heat and acid tolerance but does not affect the ability to survive air-drying on surfaces

The heat and acid tolerance of isolates of Salmonella enterica serovar Enteritidis PT4 was markedly higher if cells were grown to stationary phase in either commercially produced Tryptone Soya (TSBG) or brain–heart infusion (BHI) broth containing glucose than when cells were grown in either nutrient or Tryptone Soya broth without glucose. Differences between the populations were found to be related to the production of acid in either TSBG or BHI which caused the culture media pH values to fall to pH 5·8–4·7 during overnight incubation. This led to habituation, which increased both heat- and acid-tolerance, although there was no effect on the abilities of cells to survive air-drying on surfaces. The acid tolerance mechanisms, induced by fermentative growth in complex media, responsible for survival at pH 2·8, were RpoS-independent. In addition, although growth rates as measured by cfu were essentially the same in all media, optical density measurements were very different, with those of cells in media containing glucose being much higher. This was found to be due to the formation of larger cells by the Salmonella in these media.     

Analysis of Crushing Response of Composite Crashworthy Structures

The paper describes quasi-static and dynamic tests to characterise the energy absorption properties of polymer composite crash energy absorbing segment elements under axial loads. Detailed computer tomography scans of failed specimens are used to identify local compression crush failure mechanisms at the crush front. The varied crushing morphology between the compression strain rates identified in this paper is observed to be due to the differences in the response modes and mechanical properties of the strain dependent epoxy matrix. The importance of understanding the role of strain rate effects in composite crash energy absorbing structures is highlighted in this paper.     

A coupled CFD-population balance approach for nanoparticle synthesis in turbulent reacting flows

This paper investigates the first part of a two-stage methodology for the detailed fully coupled modelling of nanoparticle formation in turbulent reacting flows. We use a projected fields (PF) method to approximate the joint composition probability density function (PDF) transport equation that describes the evolution of the nanoparticles. The method combines detailed chemistry and the method of moments with interpolative closure (MoMIC) population balance model in a commercial computational fluid dynamics (CFD) code. We show details of the implementation and present an extensive set of numerical experiments and validation. We consider the example of the chloride process for the industrial synthesis of titania. We show good agreement with experimental data and present fully coupled detailed chemistry CFD simulations of nanoparticle formation in a representative ‘slot’ reactor geometry. The simulations show that inception occurs in a mixing zone near the reactor inlets. Most of the nanoparticle mass is due to surface growth downstream of the mixing zone with a narrower size distribution occurring in the regions of higher surface growth. The predicted temperature and particle properties are compared to a perfect mixing case. The implications for the second part of the methodology, where it is proposed to post-process the data using a more detailed particle model, are discussed critically.     

Formation and Lifetime of Polycyclic Aromatic Compounds During a National-Scale Transient Pollution Episode

Concentrations of selected particle-borne parent, alkylated, oxygenated, and nitrated polycyclic aromatic compounds (PACs) have been monitored before, during, and after a large national-scale wood-burning pollution episode (5 November 1994 and 4-5 November 1995). Toluene-modified supercritical CO 2 was used for the extraction of PACs from the collected particulate matter. Analysis was performed using an on-line multidimensional chromatographic technique using coupled liquid and gas chromatography (LC-GC) with loop interface. Comparison of average urban and wood smoke particulate PAC profiles identified a marked change in the ambient PAC profile for the pollution episode period, caused by the change in emission source from predominantly vehicular to wood smoke. A chemical mass balance model has been used to calculate the relative contributions from general urban and wood smoke PAC sources and from them, an estimation of the atmospheric life-time of the PAC emissions has been made. When monitored with 24 hr resolution in 1994, the concentrations of quinone-PAC oxidation products were found to peak 1 day after the maximum concentrations in the parent PAH were recorded, consistent with photochemically driven reactions with singlet state molecular oxygen. When concentrations were monitored on a more frequent basis in 1995, the concentrations of oxygenated species were seen to begin increasing in concentration before sunrise but still peaking after the maximum concentrations of parent PAH were recorded. The nighttime rise in product PAC suggests dark reactions with ozone or the NO 3 radical also may be occurring.     

Diet shift of double-crested cormorants in eastern Lake Ontario associated with the expansion of the invasive round goby

The proliferation of the invasive round goby (Apollonia melanostoma) in the Great Lakes has caused shifts in the trophic ecology in some areas. We examined the diet of double-crested cormorants (Phalacrocorax auritas) prior to, and immediately after, round goby population expansion at two colonies, Pigeon and Snake Islands, in eastern Lake Ontario from 1999 to 2007. Cormorant diet was determined from the examination of 10,167 pellets collected over the nine-year period. By the second year round gobies were found in the diet (2002 at Snake Island and 2003 at Pigeon Island) they were the main species consumed by cormorants at each colony. The dominance of round goby in cormorant diets had a significant effect on both daily fish consumption and seasonal trends in fish consumption compared to the pre-goby years. Seasonal differences that were observed during the pre-goby years were lost once gobies became the main diet component of cormorants. The rapid switch to a benthic prey such as round goby, from a largely limnetic fish diet demonstrates the adaptive foraging ability of cormorants. Round goby may act as a buffer for yellow perch and smallmouth bass, two sport fish impacted by cormorant predation in eastern Lake Ontario.