21 resultados para Liquid–liquid equilibria

em Deakin Research Online - Australia


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The theory of ‘punctuated equilibria’ was formulated by two paleontologists, Niles Eldredge and Stephen Gould, in 1972 and has been the focus of considerable controversy within the evolutionary sciences ever since. The primary intentions of this thesis are to relate the history of punctuated equilibria and to examine how it has affected evolutionary science. Several modes of analysis have been used to illuminate the history: The sociological perspectives of Pierre Bourdieu and Bruno Latour (who see scientific debate as a ‘struggle for authority’); Rhetorical analysis of some of the key documents; Communication with practising scientists via questionnaires and correspondence; Citation Analysis. Chapter 1 gives a short summary of the history and introduces the methods and socio-philosophical perspectives used to illuminate the history. Chapters 3 and 4 examine the rhetorical process by which Eldredge and Gould constructed the ‘punctuationist revolution’. Chapters 2, 3, 5 and 6 relate the history of punctuated equilibria.

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We characterize and compare closed-loop (feedback) price and quantity strategies within a full-fledged dynamic model of oligopolistic competition in which production requires exploitation of a renewable productive asset. Unlike previous papers on the strategic exploitation of productive assets, we allow for imperfect product substitutability, which enables us to deal with price competition. We show that the traditional result that the Bertrand equilibrium is more efficient than the Cournot equilibrium does not necessarily hold in a Markovian environment, either in the short-run or at the stationary equilibrium, or using the discounted sum of welfare as a criterion for relative efficiency.

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The syntheses of cyclo-[R2Sn(OPPh2O)2SnR2](O3SCF3)2 (R = Me (1), t-Bu (2)) by the consecutive reaction of R2SnO (R = Me, t-Bu) with triflic acid and diphenylphosphinic acid are presented. In the solid state, 1 and 2 were investigated by 119Sn MAS and 31P MAS NMR spectroscopy as well as X-ray crystallography and appear to exist as ion pairs of cyclo-[R2Sn(OPPh2O)2SnR2]2+ dications and triflate anions. In solution, 1 and 2 are involved in extensive equilibria processes featuring cationic diorganotin(IV) species with Sn-O-P linkages, as evidenced by 119Sn and 31P NMR spectroscopy, electrospray mass spectrometry, and conductivity measurements.

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We analyze a principal-agent model with moral hazard in which the principal has private information about the technology. We characterize Perfect Bayesian Equilibria of the contracting game that possess the following properties: (i) a principal with a more informative technology ends up earning less profits than a principal with a less informative one does; (ii) compared to the complete information case, the actions implemented by the privately informed principal can be distorted; (iii) the agent can end up being better off when the principal has private information.

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Coate and Loury (1993) suggest the impact of affirmative action on a negative stereotype is theoretically ambiguous leading to either: a benign equilibrium in which affirmative action eradicates the negative stereotype and leads to equal proportional representation of the two groups; or alternatively a patronising equilibrium in which the stereotype persists. The current paper examines this theoretical ambiguity within the context of a laboratory experiment. Although benign and patronising equilibria are equally plausible in theory, the laboratory experiments easily replicate most features of the benign equilibrium, but diverge from the theoretically predicted patronising equilibrium.

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This paper analyzes corruption as a collusive act which requires the participation of two willing partners. An agent intending to engage in a corrupt act must search for a like-minded partner. When many people in the economy are corrupt, such a search is more likely to be fruitful. Thus when an agent engages in a search, he raises the net benefit of searching for other similar agents in the economy, creating an externality. This introduces a non-convexity in the model, which consequently has multiple equilibria. The economy can be in stable equilibrium with a high or low level of corruption.

Starting from the high-corruption equilibrium, a sufficient increase in vigilance triggers a negative cascade, leading the economy to a new equilibrium in which no agent finds it profitable to search for corrupt partners. The no-corruption equilibrium continues to be stable if vigilance is then relaxed. This suggests that the correct way to deal with corruption is to launch a ``big push'' with large amounts of resources. Once the level of corruption declines, these resources can be withdrawn.

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The properties of the nickel(II)/2-hydroxy-5-nonylacetophenone oxime (HNAPO), an active ingredient in LIX 84, extraction system were characterised in a micellar system. The extinction coefficient, λmax of HNAPO (316 nm) and the Ni2+ complex (387 nm) in a neutral micellar system, poly dispersed octa-ethyleneglycol mono-n-dodecyl ether (G12A8) were determined as 3100 and 3500 M−1 cm−1, respectively. HNAPO was found to have a neutral micellar phase and bulk aqueous phase pKa of 11.5 and 12.5, respectively. The extraction equilibrium constant, Kex, was determined to be 10−8.0, and the deviation from theory observed at high pH can be accounted for by consideration of the competition for nickel(II) ions by hydroxide ions and HNAPO. A micellar phase of octa-ethyleneglycol mono-n-dodecyl ether (C12E8) was determined to be an appropriate model of the free oil/water interface from the solubilised location of HNAPO. Utilising the interfacial probe, 4-heptadecyl-7-hydroxy coumarin (HHC) allowed the determination of the electrostatic surface potential of mixed micelles of G12A8 and sodium dodecyl sulphate (SDS) or dodecyl trimethyl ammonium chloride (DTAC). The electrostatic surface potential was a linear function of the number of additional surfactant monomers within the G12A8 micelle, for the concentration range studied. For G12A8/DTAC mixed micelles, the surface potential was given by +1.1 mV per DTAC molecule per micelle, and for G12A8/SDS mixed micelles the relationship was −1.4 mV per SDS molecule per micelle.

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This thesis is a study of the establishment of the music curriculum in state-supported schools in South Australia from the beginnings of such schooling until 1920. There will be a discussion of issues to be explored and the method by which this investigation will proceed. A literature survey of relevant research will be included, after which there will be a sketch of the development of state-supported schooling in South Australia. Several broad themes have been chosen as the means of organising the historical material: the rationales offered for the inclusion of music in schooling, the methodologies, syllabi and materials of such music instruction, the provisions for teacher training in music, both preservice and as professional development for established teachers, and the place and function of music in schooling. Each of these themes will form the framework for a chronological narrative. Comparisons will be made with three neighbouring colonies/States concerning each of these themes and conclusions will be drawn. Finally, overall conclusions will be made concerning the initial contentions raised in this chapter in the light of the data presented. Although this study is principally concerned with the establishment of music in state-supported schooling, there will be a brief consideration of the colony of South Australia from its proclamation in 1836. The music pedagogical context that prevailed at that time will be discussed and this will, of necessity, include developments that occurred before 1836. The period under consideration will close in 1920, by which time the music curriculum for South Australia was established, and the second of the influential figures in music education was at his zenith. At this time there was a new school curriculum in place which remained essentially unchanged for several decades. As well as the broad themes identified, this thesis will investigate several contentions as it attempts to chronicle and interpret the establishment and development of music in state-supported schooling in South Australia up to 1920. The first contention of this thesis is that music in state-supported schooling, once established, did not change significantly from its inception throughout the period under consideration. In seeking a discussion of the existence and importance of the notion of an absence of change or stasis, the theory of punctuated equilibria, which identifies stasis as the norm in the evolutionary growth of species, will be employed as an insightful analogy. It should be recognised that stasis exists, should be expected and may well be the prevailing norm. The second contention of this thesis is that advocates were and continue to be crucial to the establishment and continued existence of music in state-supported schooling. For change to occur there must be pressure through such agencies as motivated individuals holding positions of authority, and thus able to influence the educational system and its provisions. The pedagogical method introduced into an educational system is often that espoused by the acknowledged advocate. During the period under consideration there were two significant advocates for music in state-supported schools. The third contention of this thesis is that music was used in South Australia, as in the other colonies/States, as an agent of social reform, through the selection of repertoire and the way in which music was employed in state-supported schooling. Music was considered inherently uplifting. During the nineteenth and early twentieth centuries, the music selected for school singing carried texts with messages deemed significant by those who controlled the education system. The repertoire was not that of the receiving class but came from a middle class tradition of fully notated art music in which correct performance and notational reading were emphasised. A sweet, pure vocal tone was desired, as strident, harsh, speaking tones were perceived as a symptom of incipient larrikinism which was not desired in schooling. Music was seen as a contributor to good order and discipline in schooling.

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The formation of Al2O3, MgAl2O4, and MgO has been widely studied in different Al base metal matrix composites, but the studies on thermodynamic aspects of the Al2O3/ MgAl2O4/MgO phase equilibria have been limited to few systems such as Al/Al2O3 and Al/SiC. The present study analyzes the Al2O3/MgAl2O4 and MgAl2O4/MgO equilibria with respect to the temperature and the Mg content in Al/SiO2 system using an extended Miedema model. There is a linear and parabolic variation in Mg with respect to the temperature for MgAl2O4/MgO and Al2O3/MgAl2O4 equilibria, respectively, and the influence of Si and Cu in the two equilibria is not appreciable. The experimental verification has been limited to MgAl2O4/MgO equilibria due to the high Mg content (≥0.5 wt pct) required for composite processing. The study has been carried out on two varieties of Al/SiO2 composites, i.e., Al/Silica gel and Al/Micro silica processed by liquid metallurgy route (stir casting route). MgO is found to be more stable compared to MgAl2O4 at Mg levels ≥5 and 1 wt pct in Al/Silica gel and Al/Micro silica composites, respectively, at 1073 K. MgO is also found to be more stable at lower Mg content (3 wt pct) in Al/Silica gel composite with decreasing particle size of silica gel from 180 micron to submicron and nanolevels. The MgO to MgAl2O4 transformation has taken place through a series of transition phases influenced by the different thermodynamic and kinetic parameters such as holding temperature, Mg concentration in the alloy, holding time, and silica particle size.

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Results of crack growth observations on mica in water-containing environments are described. The study focuses on equilibrium crack states for reversed loading cycles, i.e., for initial propagation through virgin solid and subsequent retraction-repropagation through healed or misoriented-healed interfaces. Departures from these equilibrium states are manifest as steady-state forward or backward crack velocities at specific applied loads. The equilibria are thereby interpreted as quiescent, threshold configurations G = WE, with G the Griffith mechanical-energy-release rate and WE the Dupré work of adhesion, on crack velocity (v-G) diagrams. Generally, WE is found to decrease with concentration of water, in accordance with a Gibbs formalism. Hysteresis is observed in the forward-backward-forward crack propagation cycle, signifying a reduction in the adhesion energy on exposure of the open interface to environmental species prior to healing. This hysteresis is especially marked for those interfaces that are misoriented before healing, indicating that the structure of the underlying solid substrate as well as of the intervening fluid is an important consideration in the interface energetics. The equilibrium states for different environments can be represented on a simple energy-level diagram, as differences between thermodynamic end-point states: initial, closed-interface states refer to crystallographic bonding configurations ahead of the crack-tip adhesion zone; final, open interface states refer to configurations behind the crack-tip zone. The significance of this diagram in relation to the fundamental atomic structure of interfaces in fracture and other adhesion geometries, including implications concerning kinetics, is discussed.

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This article proposes a stochastic foundation for the contest success function (CSF for short) with a richer structure on the set of possible outcomes of the contest. Specifically, the analysis allows for the possibility of a draw, so that no contestant can claim a victory over all other players. Under plausible conditions, this article not only discovers new functional forms of CSFs, but also shows the newly derived CSFs have very different properties in equilibrium to those of conventional CSFs. For example, in contrast to the CSFs discussed in the contest literature, which always generate a unique pure strategy Nash equilibrium, the newly discovered CSFs admit the possibility of multiple equilibria.

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We examine a mathematical model for the transmission of Streptococcus Pneumoniae amongst young children when the carriage transmission coefficient depends on the serotype. Carriage means pneumococcal colonization. There are two sequence types (STs) spreading in a population each of which can be expressed as one of two serotypes. We derive the differential equation model for the carriage spread and perform an equilibrium and global stability analysis on it. A key parameter is the effective reproduction number R e. For R e ≤ 1,  there is only the carriage-free equilibrium (CFE) and the carriage will die out whatever be the starting values. For R e > 1, unless the effective reproduction numbers of the two STs are equal, in addition to the CFE there are two carriage equilibria, one for each ST. If the ST with the largest effective reproduction number is initially present, then in the long-term the carriage will tend to the corresponding equilibrium.

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This paper discusses a simple mathematical model to describe the spread of Streptococcus pneumoniae. We suppose that the transmission of the bacterium is determined by multi-locus sequence type. The model includes vaccination and is designed to examine what happens in a vaccinated population if MLSTs can exist as both vaccine and non vaccine serotypes with capsular switching possible from the former to the latter. We start off with a discussion of Streptococcus pneumoniae and a review of previous work. We propose a simple mathematical model with two sequence types and then perform an equilibrium and (global) stability analysis on the model. We show that in general there are only three equilibria, the carriage-free equilibrium and two carriage equilibria. If the effective reproduction number Re is less than or equal to one, then the carriage will die out. If Re > 1, then the carriage will tend to the carriage equilibrium corresponding to the multi-locus sequence type with the largest transmission parameter. In the case where both multi-locus sequence types have the same transmission parameter then there is a line of carriage equilibria. Provided that carriage is initially present then as time progresses the carriage will approach a point on this line. The results generalize to many competing sequence types. Simulations with realistic parameter values confirm the analytical results.