Physical characterization of plastic surfaces in wearing and cleanability research

Plastic surfaces are a group of materials used for many purposes. The present study was focused on methods for investigation of surface topography, wearing and cleanability of polyvinyl chloride (PVC) model surfaces and industrial plastic surfaces. Contact profilometry, scanning electron microscopy (SEM) and atomic force microscopy (AFM) are powerful methods for studying the topography of plastic surfaces. Although they have their own limitations, they are together an effective tool providing useful information on surface topography, especially when studying laboratory-made PVC model surfaces with known chemical compositions and structures. All examined laboratory-made PVC plastic surfaces examined in this work could be considered as smooth according to both AFM and profilometer measurements because height differences are in the nanoscale on every surface. Industrial plastic surfaces are a complex group of materials because of their chemical and topographical heterogeneity, but they are nevertheless important reference materials when developing cleaning and wearing methods. According to the results of this study the Soiling and Wearing Drum and the Frick-Taber methods are very useful when simulating three-body wearing of plastic surfaces. Both the investigated wearing methods can be used to compare the wearing of different plastic materials using appropriate evaluation methods of wearing and industrial use. In this study, physical methods were developed and adapted from other fields of material research to cleanability studies. The thesis focuses on the methodology for investigating the cleanability of plastic surfaces under realistic conditions, where surface topography and the effect of wear cleanability were among the major topics. A colorimetric method proved to be suitable for examining the cleanability of the industrial plastic surfaces. The results were utilized to evaluate the relationship between cleanability and the surface properties of plastic surfaces. The devices and methods used in the work can be utilized both in material research and product development.

Surface instability of a current-carrying plasma under the influence of a high-frequency electric-field

Surface instability of a collisionless semi-infinite current carrying plasma is studied. The semi-infinite plasma bounded by a plane surface is under the influence of a high frequency (hf) field. There are two classes of surface modes. One is a normal extension of zero high frequency field and the other due entirely to the presence ofhf field. As expected, with the increase in thehf field, the growth rates of the surface instabilities decrease. There are regions defined by the electron drift velocityu where the unstable surface and bulk regions overlap. The interesting result is that unlike the bulk plasma, there is a stable region on theu-axis flanked by two unstable regions. The width of this stable region increases with the increase in the field strength.

Molecular motion in plastic crystals

Abstract is not available.

The Productivity of Strawberry Plants Growing Under Plastic High Tunnels in a Wet Subtropical Environment

The effect of plastic high tunnels on the performance of two strawberry (Fragaria ×ananassa) cultivars (Festival and Rubygem) and two breeding lines was studied in southeastern Queensland, Australia, over 2 years. Production in this area is affected by rain, with direct damage to the fruit and the development of fruit disease before harvest. The main objective of the study was to determine whether plants growing under tunnels had less rain damage, a lower incidence of disease, and higher yields than plants growing outdoors. Plants growing under the tunnels or outdoors had at best only small differences in leaf, crown, root, and flower and immature fruit dry weight. These responses were associated with relatively similar temperatures and relative humidities in the two growing environments. Marketable yields were 38% higher under the tunnels compared with yields outdoors in year 1, and 24% higher in year 2, mainly due to less rain damage. There were only small differences in the incidences of grey mold (Botrytis cinerea) and small and misshaped fruit in the plants growing under the tunnels and outdoors. There were also only small differences in postharvest quality, total soluble solids, and titratable acidity between the two environments. These results highlight the potential of plastic high tunnels for strawberry plants growing in subtropical areas that receive significant rainfall during the production season.

Plastic response of orthotropic spherical shells under blast loading

The plastic response of a segment of a simply supported orthotropic spherical shell under a uniform blast loading applied on the convex surface of the shell is presented. The blast is assumed to impart a uniform velocity to the shell surface initially. The material of the shell is orthotropic obeying a modified Tresca yield hypersurface conditions and the associated flow rules. The deformation of the shell is determined during all phases of its motion by considering the motion of plastic hinges in different regimes of flow. Numerical results presented include the permanent deformed configuration of the shell and the total time of shell response for different degrees of orthotropy. Conclusions regarding the plastic behaviour of spherical shells with circumferential and meridional stiffening under uniform blast load are presented.

Surface explosive instability for high frequency waves

High frequency three-wave nonlinear 'explosive' interaction of the surface modes of a semi-infinite beam-plasma system under no external field is investigated. The conditions that favour nonlinear instability, keep the plasma linearly stable. The beam runs parallel to the surface. If at least one of the three wave vectors of the surface modes is parallel to the beam, explosive interaction at the surface takes place after it has happened in the plasma bulk, provided the bulk waves propagate almost perpendicular to the surface and are of short wavelength. On the other hand if the bulk modes have long wavelength and propagate almost parallel to the surface, the surface modes can 'explode' first.

Nonlinear saturation of ion-acoustic instability

It is proposed that the wave mediated indirect wave-particle interaction may be responsible for nonlinear saturation of current driven low frequency ion-acoustic turbulence. This process decreases the growth rate and increases the damping rate of the wave. Comparison has been made with some experiments.

Nature of trapped particle instability

The amplification mechanism for the side bands which accompany a large amplitude electron wave on a plasma column are shown to arise due to two mode interaction between negative and positive energy waves.

Orbit perturbation theory of beam-plasma instability

The nonlinear theory of the instability caused by an electron beam-plasma interaction is studied. A nonlinear analysis has been carried out using many-body methods. A general formula for a neutral collisionless plasma, without external fields, is derived. This could be used for calculating the saturation levels of other instabilities. The effect of orbit perturbation theory on the beam-plasma instability is briefly reviewed.

Note on the Helmholtz instability in stratified flows with magnetic fields

The nature of the neutral curves for the stability of a Helmholtz velocity profile in a stratified, Boussinesq fluid in the presence of a uniform magnetic field for the cases (1) an infinite fluid (2) a semi-infinite fluid with a rigid boundary is discussed.

Effect of membrane action on the plastic collapse load of circular orthotropic slabs with fixed edges

In the case of reinforced concrete slabs fixed at the boundaries, considerable enhancement in the load carrying capacity takes place due to compressive membrane action. In this paper a method is presented to analyse the effects of membrane action in fixed orthotropic circular slabs, carrying uniformly distributed loads. Depending on the radial moment capacity being greater or less than the circumferential moment capacity, two cases of orthotropy have been considered. Numerical results are worked out for certain assumed physical parameters and for different coefficients of orthotropy. Variations of load and bending moments with the central deflection are presented.

Living on voles - plastic life of the Ural owl

Individuals face variable environmental conditions during their life. This may be due to migration, dispersion, environmental changes or, for example, annual variation in weather conditions. Genetic adaptation to a novel environment happens through natural selection. Phenotypic plasticity allows, however, a quick individual response to a new environment. Phenotypic plasticity may also be beneficial for individual if the environment is highly variable. For example, eggs are costly to produce. If the food conditions vary significantly between breeding seasons it is useful to be able to adjust the clutch and egg size according to the food abundance. In this thesis I use Ural owl vole system to study phenotypic plasticity and natural selection using a number of reproduction related traits. The Ural owl (Strix uralensis) is a long-lived and sedentary species. The reproduction and survival of the Ural owl, in fact their whole life, is tied to the dramatically fluctuating vole densities. Ural owls do not cause vole cycles but they have to adjust their behaviour to the rather predictable population fluctuations of these small mammals. Earlier work with this system has shown that Ural owl laying date and clutch size are plastic in relation to vole abundance. Further, individual laying date clutch size reaction norms have been shown to vary in the amount of plasticity. My work extends the knowledge of natural selection and phenotypic plasticity in traits related to reproduction. I show that egg size, timing of the onset of incubation and nest defense aggressiveness are plastic traits with fitness consequences for the Ural owl. Although egg size is in general thought to be a fixed characteristic of an individual, this highly heritable trait in the Ural owl is also remarkably plastic in relation to the changes in vole numbers, Ural owls are laying the largest eggs when their prey is most abundant. Timing of the onset of incubation is an individual-specific property and plastic in relation to clutch size. Timing of incubation is an important underlying cause for asynchronous hatching in birds. Asynchronous hatching is beneficial to offspring survival in Ural owl. Hence, timing of the onset of incubation may also be under natural selection. Ural owl females also adjust their nest defense aggressiveness according to the vole dynamics, being most aggressive in years when they produce the largest broods. Individual females show different levels of nest defense aggressiveness. Aggressiveness is positively correlated with the phenotypic plasticity of aggressiveness. As elevated nest defense aggressiveness is selected for, it may promote the plasticity of aggressive nest defense behaviour. All the studied traits are repeatable or heritable on individual level, and their expression is either directly or indirectly sensitive to changes in vole numbers. My work considers a number of important fitness-related traits showing phenotypic plasticity in all of them. Further, in two chapters I show that there is individual variation in the amount of plasticity exhibited. These findings on plasticity in reproduction related traits suggest that variable environments indeed promote plasticity.

Is there an athermal region of plastic flow in metals at intermediate temperatures?

The question of the existence or otherwise of an athermal temperature region of plastic flow in metals is examined. It is suggested that the athermal region is absent in metals with large dislocation densities. Such an explanation is provoked by a fairly recent proposition that the unzipping of attractive junctions is a plausible rate-controlling mechanism at high temperatures.

Instability of Combustion

THE following equations governing the phenomenon of intrinsic instability of combustion, leading to low frequency oscillations in a rocket motor using a single liquid propellant, were derived and investigated by L. Crocco.

A cyclostationary multi-domain analysis of fluid instability in Kaplan turbines

Hydraulic instabilities represent a critical problem for Francis and Kaplan turbines, reducing their useful life due to increase of fatigue on the components and cavitation phenomena. Whereas an exhaustive list of publications on computational fluid-dynamic models of hydraulic instability is available, the possibility of applying diagnostic techniques based on vibration measurements has not been investigated sufficiently, also because the appropriate sensors seldom equip hydro turbine units. The aim of this study is to fill this knowledge gap and to exploit fully, for this purpose, the potentiality of combining cyclostationary analysis tools, able to describe complex dynamics such as those of fluid-structure interactions, with order tracking procedures, allowing domain transformations and consequently the separation of synchronous and non-synchronous components. This paper will focus on experimental data obtained on a full-scale Kaplan turbine unit, operating in a real power plant, tackling the issues of adapting such diagnostic tools for the analysis of hydraulic instabilities and proposing techniques and methodologies for a highly automated condition monitoring system. © 2015 Elsevier Ltd.