Halo abundances within the cosmic web

We investigate the dependence of the mass function of dark-matter haloes on their environment within the cosmic web of large-scale structure. A dependence of the halo mass function on large-scale mean density is a standard element of cosmological theory, allowing mass-dependent biasing to be understood via the peak-background split. On the assumption of a Gaussian density field, this analysis can be extended to ask how the mass function depends on the geometrical environment: clusters, filaments, sheets and voids, as classified via the tidal tensor (the Hessian matrix of the gravitational potential). In linear theory, the problem can be solved exactly, and the result is attractively simple: the conditional mass function has no explicit dependence on the local tidal field, and is a function only of the local density on the filtering scale used to define the tidal tensor. There is nevertheless a strong implicit predicted dependence on geometrical environment, because the local density couples statistically to the derivatives of the potential. We compute the predictions of this model and study the limits of their validity by comparing them to results deduced empirically from $N$-body simulations. We have verified that, to a good approximation, the abundance of haloes in different environments depends only on their densities, and not on their tidal structure. In this sense we find relative differences between halo abundances in different environments with the same density which are smaller than 13%. Furthermore, for sufficiently large filtering scales, the agreement with the theoretical prediction is good, although there are important deviations from the Gaussian prediction at small, non-linear scales. We discuss how to obtain improved predictions in this regime, using the 'effective-universe' approach.Comment: 14 pages, 6 figures. Revision matching journal versio

Distribution, habitat preferences and population sizes of two threatened tree ferns, Cyathea cunninghamii and Cyathea x marcescens, in south-eastern Australia

The distribution, population sizes and habitat preferences of the rare tree ferns Cyathea cunninghamii Hook.f. (Slender Tree Fern) and F1 hybrid Cyathea x marcescens N.A.Wakef. (Skirted Tree Fern) in south-eastern Australia are described, together with the extension of the known distribution range of Cyathea cunninghamii from eastern Victoria into south-eastern New South Wales. Floristic and ecological data, encompassing most of the known habitat types, vegetation associations and population sizes, were collected across 120 locations. Additional information was sought from literature reviews, herbarium collections and field surveys of extant populations. Cyathea cunninghamii is widespread, with the majority of populations occurring in Tasmania and Victoria, one population in south-eastern NSW and a disjunct population in south-eastern Queensland; Cyathea x marcescens is confined to south and eastern Victoria and south and north eastern Tasmania. Both taxa occur on King Island in Bass Strait. Both taxa have a near coastal distribution with most populations occurring in sub-coastal hinterland and escarpment forests with a median altitude of 288 m. Hierarchical cluster analysis of floristic data across the species’ geographic range identified six vegetation communities ranging from rainforest to damp sclerophyll forest. Their micro-habitat preferences were consistently identified as steeply incised gullies of minor headwater streams of coastal and sub-coastal ranges with a plentiful moisture regime and geomorphic protection from extreme stream flow events, flooding and bank scouring. Sporophyte recruitment was associated with exposed soil of stream banks and edges of constructed walking tracks. Population sizes of both taxa are small with the majority of populations consisting of less than five adult individuals, with total populations of Cyathea cunninghamii and Cyathea x marcescens estimated at 919 and 221 mature individuals respectively. Population extinctions in Victoria and Tasmania have primarily been associated with outlier populations in regions subject to agricultural land clearance, habitat modification and changes to fire regimes in crown forests. Nonanthropogenic mortality was associated with land slips, tree falls and stream bank scouring by flood water. Conservation of the hybrid Cyathea x marcescens necessitates the preservation of habitats where both Cyathea cunninghamii and Cyathea australis occur in close proximity to substrates suitable for spore germination. In future, molecular techniques may prove useful for field identification of juvenile stages, facilitating selection of progeny of Cyathea cunninghamii and Cyathea x marcescens for cultivation and re-introduction to sites of previous or possible future extinctions

FINANCIAL PROSPECTS, BUSINESS ORGANIZATION, AND MANAGEMENT: FARM BUSINESS CHALLENGES

Farm Management,

Palladium-Mediated Formation of Alkyl–Nitrogen Bonds

The following dissertation discusses reactions of palladium complexes to form sp3 carbon–nitrogen bonds. Both stoichiometric reductive elimination reactions to form alkylamines from characterized alkylpalladium(II) complexes and new palladium-catalyzed methods for the synthesis of N-alkylbenzophenone imines are reported.Chapter 1 provides an overview of methods for the N-alkylation of nitrogen nucleophiles. Metal-catalyzed substitution reactions of nitrogen nucleophiles with alkyl electrophiles are discussed with a focus on the fundamental organometallic reactions that may form carbon–nitrogen bonds in these reactions. Examples of reductive elimination reactions from characterized alkylmetal complexes are covered in more detail because of their relevance to later chapters.Chapter 2 discusses continued work in the Hartwig group studying the reductive elimination of norbornylamines from syn-2-methylnorbornylpalladium(II) amido complexes. This work focuses on the effects of phosphine ancillary ligands on the rate of reductive elimination and yield of alkylamine. These studies led to the design of bidentate P,O ligands that stabilize Pd(II) amido complexes while still enabling the reductive elimination of alkylamines to occur in good yield.Chapter 3 presents the reductive elimination of N-neopentyl anilines and N-neopentyl imines from palladium(II) complexes. The P,O ligand structures developed as part of the work described in Chapter 2 proved particularly valuable to the study of neopentylpalladium(II) complexes and enabled the synthesis of stable, four-coordinate Pd(II) anilido and methyleneamido complexes that undergo reductive elimination to form N-neopentyl anilines and N-neopentyl imines in good yields.Chapter 4 discusses the development of palladium catalysts for the cross-coupling of imines and primary alkyl bromides. The addition of fluorinated iminoquinolines as ancillary ligands was found to greatly increase the rate of the reaction. Mechanistic studies suggest that this reaction occurs through a two-electron pathway that may involve oxidative addition to a cyclometallated palladium(II) complex.Chapter 5 expands the palladium-catalyzed cross-coupling of imines to include reactions with synthetically valuable secondary and tertiary alkyl halides. This method was applied to form a variety of imines bearing secondary and tertiary alkyl groups on nitrogen. Mechanistic studies suggest that this reaction occurs through single-electron transfer from a palladium(0) complex to form an alkyl radical intermediate. The intermediacy of this alkyl radical enabled this method to be expanded to include the intramolecular carboamination of unsaturated alkyl bromides

A mathematical study of Voigt viscoelastic Love wave propagation

This research is a mathematical investigation of the propagation of a Love wave in a Voigt viscoelastic medium. A solution to the partial differential equation of motion is assumed and is shown to satisfy the three necessary boundary conditions. Velocity restrictions on the wave and the media are developed and are shown to be of the same form as those governing the elastic Love wave --Abstract, page ii

Discrimination of signal and noise events on seismic recordings by linear threshold estimation theory

The object of this study is the investigation of a linear threshold element technique for identifying surface multiples on a single seismic trace. Traces of seismic events were generated which contained primaries, surface multiples, and various levels of Gaussian random noise. Since it was necessary to separate the events as much as possible, the traces were subjected to pulse-compression deconvolution processing prior to LTE analysis. Mean frequency, peak frequency, amplitude spectrum variance, periodicity, and polarity were employed as pattern parameters. A set of weights was found that would maximize the moment of inertia of the S line distribution of the patterns subject to the constraint that the sum of the squared values of the weights was minimized. It is shown that the problem of the maximization of the moment of inertia reduces to the solution of a simple eigenvalue problem. Furthermore, the optimum set of weights is the eigenvector corresponding to the largest eigenvalue of a matrix proportional to the autocovariance matrix of the pattern vectors. The classes of patterns representing primaries and multiples on traces with high signal-to-noise ratios were clustered and separated, making identification by inspection a simple procedure. Clustering and separation of classes on traces with low signal-to-noise ratios was less than optimum --Abstract, page ii

Women Leading University-Community Engagement: Disruption, Resistance; Resilience

This paper explores the identity jolts and professional responses of female leaders of institutionalized university-community engagement in Canada, the U.S., the U.K. and Australia. Using a feminist narrative approach we explored the disorienting dilemmas, critical events and identity jolts related to women’s participation in the institutional leadership of social change initiatives, in particular university-community engagement (UCE). Themes of disruption, resistance and resilience in the neoliberal institutional cultures and practices in which university-community engagement (UCE) is situated are shared through participants’ stories of praxis. This paper is one of a series exploring sociocultural influences on the institutionalization of university-community engagement and the development of engaged and engagement scholarship as an intellectual domain in higher education

Basement highs: definitions, characterisation and origins

A glossary of commonly used terms related to the geometric forms and geological settings of basement highs is presented to assist cross-disciplinary understanding, qualifying prefixes for the term basement are discussed and a scheme for characterising basement highs is presented. This scheme is designed to standardise, and to add rigour to, description of basement highs. It will thereby enhance basement high comparisons and assist understanding of basement highs across technical disciplines. The scheme enables systematic characterisation of: the geometry of a basement high; the lithologic units and structures in, above and around it; timings; tectonics and origins of the basement high and play elements relating to resource prospectivity. Use of this scheme is demonstrated using the southern Rona Ridge (West of Shetland, UK Continental Shelf). The tectonic, isostatic, erosional and stratigraphic processes that form basement highs are also discussed, and examples in proven petroleum systems are presented.publishedVersio

Transforming lives through international community service-learning : a case study

Through a case study of the experiences of eight undergraduate students participating in the St. Thomas More College/Intercordia Canada international community service-learning programme (2008), this thesis seeks to assess whether the participants’ learning has proved transformational through an analysis of the forms and processes of transformative learning as developed by Richard Kiely (2002, 2004, 2005). Content analysis of semi-structured student interviews (pre and post-participation), programme materials, student journals, academic reflections and essays reveal transformative shifts across the political, moral, intellectual, cultural, personal and spiritual learning domains. The study adds to the research on international community service-learning through an analysis of Kiely’s transformative learning theory in a new context, and explores how context affects learning processes. Findings indicate the dynamics of participant vulnerability and acceptance from host communities can provide for transformational relationships of solidarity across difference

The Axiverse Extended: Vacuum Destabilisation, Early Dark Energy and Cosmological Collapse

A model is presented in the philosophy of the "String Axiverse" of Arvanitaki et al (arXiv:0905.4720v2 [hep-th]) that incorporates a coupling of ultralight axions to their corresponding moduli through the mass term. The light fields roll in their potentials at late times and contribute to the dark sector energy densities in the cosmological expansion. The addition of a coupling and extra field greatly enrich the possible phenomenology of the axiverse. There are a number of interesting phases where the axion and modulus components behave as Dark Matter or Dark Energy and can have considerable and distinct effects on the expansion history of the universe by modifying the equation of state in the past or causing possible future collapse of the universe. In future such a coupling may help to alleviate fine tuning problems for cosmological axions. We motivate and present the model, and briefly explore its cosmological consequences numerically.Comment: 13 pages, 17 figures, published in PRD. v3: corrected SUSY interpretation of axion potential scal