Dynamics of Barred Galaxies

Some 30% of disc galaxies have a pronounced central bar feature in the disc plane and many more have weaker features of a similar kind. Kinematic data indicate that the bar constitutes a major non-axisymmetric component of the mass distribution and that the bar pattern tumbles rapidly about the axis normal to the disc plane. The observed motions are consistent with material within the bar streaming along highly elongated orbits aligned with the rotating major axis. A barred galaxy may also contain a spheroidal bulge at its centre, spirals in the outer disc and, less commonly, other features such as a ring or lens. Mild asymmetries in both the light and kinematics are quite common. We review the main problems presented by these complicated dynamical systems and summarize the effort so far made towards their solution, emphasizing results which appear secure. (Truncated)Comment: This old review appeared in 1993. Plain tex with macro file. 82 pages 18 figures. A pdf version with figures at full resolution (3.24MB) is available at http://www.physics.rutgers.edu/~sellwood/bar_review.pd

T-duality Twists and Asymmetric Orbifolds

We study some aspects of asymmetric orbifolds of tori, with the orbifold group being some $\mathbb{Z}_N$ subgroup of the T-duality group and, in particular, provide a concrete understanding of certain phase factors that may accompany the T-duality operation on the stringy Hilbert space in toroidal compactification. We discuss how these T-duality twist phase factors are related to the symmetry and locality properties of the closed string vertex operator algebra, and clarify the role that they enact in the modular covariance of the orbifold theory, mainly using asymmetric orbifolds of tori which are root lattices as working examples.Comment: 67 pages. v2: references added and typos correcte

Studies on Dynamics of Financial Markets and Reacting Flows

One of the central problems in financial markets analysis is to understand the nature of the underlying stochastic dynamics. Several intraday behaviors are analyzed to study trading day ensemble averages of both high frequency foreign exchange and stock markets data. These empirical results indicate that the underlying stochastic processes have nonstationary increments. The three most liquid foreign exchange markets and five most actively traded stocks each contains several time intervals during the day where the mean square fluctuation and variance of increments can be fit by power law scaling in time. The fluctuations in return within these intervals follow asymptotic bi-exponential distributions. Based on these empirical results, an intraday stochastic model with linear variable diffusion coefficient is proposed to approximate the real dynamics of financial markets to the lowest order, and to test the effects of time averaging techniques typically used for financial time series analysis. The proposed model replicates major statistical characteristics of empirical financial time series and only ensemble averaging techniques deduce the underlying dynamics correctly. The proposed model also provides new insight into the modeling of financial markets' dynamics in microscopic time scales. Also discussed are analytical and computational studies of reacting flows. Many dynamical features of the flows can be inferred from modal decompositions and coupling between modes. Both proper orthogonal (POD) and dynamic mode (DMD) decompositions are conducted on high-frequency, high-resolution empirical data and their results and strengths are compared and contrasted. In POD the contribution of each mode to the flow is quantified using the latency only, whereas each DMD mode can be associated a latency as well as a unique complex growth rate. By comparing DMD spectra from multiple nominally identical experiments, it is possible to identify "reproducible" modes in a flow. A similar differentiation cannot be made using POD. Time-dependent coefficients of DMD modes are complex. Even in noisy experimental data, it is found that the phase of these coefficients (but not their magnitude) exhibits repeatable dynamics. Hence it is suggested that dynamical characterizations of complex flows are best analyzed through the phase dynamics of reproducible DMD modes.Physics, Department o

Customer satisfaction with the guesthouse experience in Ghana

Guesthouse accommodation plays an important role in Ghana’s hospitality industry and was therefore the focus of this study as little research dealing with guesthouses in Ghana could be found. The number of guesthouses in Ghana continues to grow and they thus represent an important alternative to hotels. However, these establishments seem to perform poorly and face several challenges such as lack of managerial knowledge, insufficiently skilled employees, poor interaction with customers, and criticisms of the provision of low quality service. The main reason for undertaking this research was to provide guesthouse managers in Ghana with information that might assist them in making decisions about the experience they offer. Such knowledge could make this type of accommodation more competitive and eventually help the hospitality sector in Ghana attract tourists and grow. It is imperative that guesthouses focus on the experience they offer, because contemporary tourism and hospitality literature suggest that successful businesses require a shift from functional and financial interests to a more profound focus on total experiences which embody emotional aspects. It is thus argued that, if guesthouse managers in Ghana do not know how their guests perceive their guesthouse experience, they might make costly mistakes and allocate resources to aspects that already provide quality and value in a functional sense, instead of those elements perceived as providing quality and value in the total experience. Two dominating concepts, namely experience quality and experience value, formed the basis of the examination of guests’ experience with the guesthouses in Ghana. In addition, the relationships between the experience and satisfaction were also investigated. Four experience quality dimensions, namely hedonics, peace of mind, involvement, and recognition, and seven value dimensions were examined. The experience value dimensions included atmospherics, enjoyment, entertainment, efficiency, excellence, escape, and economic value. A proportional stratified random sampling procedure was followed to select the guesthouses for the study. Thereafter, a structured questionnaire was distributed to the guesthouse guests selected by means of convenience sampling. Five hundred and forty one useable questionnaires were received. The guesthouse guests formed the primary sampling unit for this study. The results of the empirical study showed a strong positive correlation between all the dimensions of experience quality and experience value, while the factor analysis confirmed that all these dimensions loaded on a single factor. Therefore, experience quality and experience value cannot be separated, and the resulting single multi-dimensional factor was subsequently renamed, overall experience. The results also indicated a positive relationship between hedonics, peace of mind, involvement, recognition, atmospherics, enjoyment, entertainment, efficiency, excellence, escape, economic value, and overall satisfaction. The inferentially established rank-order of the dimensions contributing to satisfaction can guide managers when allocating resources. Overall, atmospherics was ranked first, followed by economic value. Escape was the lowest ranked dimension. In addition, it was found that, except for escape, all the experience dimensions were perceived as basic satisfiers. This implies that guests will be dissatisfied when provision of these dimensions is inadequate. With regard to escape, listed as a performance factor, guests will be satisfied when performance is improved and dissatisfied when performance is low. A positive relationship was also found between overall experience and overall satisfaction. The latter include the likelihood of return and recommending the guesthouse to others. Finally, structural equation modelling confirmed a model representing the 11 experience dimensions (hedonics, peace of mind, involvement, recognition, atmospherics, enjoyment, entertainment, escape, efficiency, excellence, and economic value) and the relationships between overall experience and overall satisfaction pertaining to guesthouses in Ghana

Conceptual design for sensemaking

The focus of sensemaking research is often on process and resources such as "schemas" and "frames". Less attention has been paid to the conceptual structures that make up the schema or frame, or how visualisations can be designed to support users' conceptual structures. In this chapter, we present an approach to gathering user requirements based on the conceptual structures that people are working with when making sense of a domain. We illustrate the approach with examples drawn from our own experience of designing, prototyping and testing an interactive visualisation tool for making sense of academic literature and of studies of sensemaking by lawyers and journalists. We discuss how to move from requirements to design, drawing on a classification of visualisations that highlights their principal conceptual structuring basis. Since each individual makes sense in their own way, it is beneficial to include features that enable people to work with a representation in their own way; for this, appropriation tools are helpful. We discuss the design of such features. Finally, we present an approach to evaluating interactive visualisations in terms of their support for sensemaking, focusing on the quality of the fit between users and system

The representation of spatial mental models in long-term memory

This thesis is concerned with how people understand and remember spatial information derived from verbal descriptions. The thesis distinguishes between three different ways of representing spatial information in working memory. The first way is to represent the surface form of the source from which the spatial information is derived (the language of a description). The second is to represent the structure of the situation derived from that source (a spatial mental model). The third is to represent the perceptual characteristics of the situation from a particular perspective (a visual image). Considerable evidence exists that people construct and manipulate spatial mental models in working memory. The purpose of this thesis is to investigate the claim that mental models are represented in long-term memory. An outline of the spatial mental modeling processes required to understand a simple spatial description is proposed. It is proposed that spatial mental modeling is comprised of three processing stages. Firstly, comprehension processes are required to access the linguistic meaning of information presented in spatial description. Secondly, construction processes are required to build up a representation of the spatial structure of the situation derived from the language of the description. Thirdly, consultation processes are required to monitor construction and to access information from the spatial mental model. Nine experiments are reported which investigate evidence for and against the view that people remember the construction and consultation of a spatial mental model. In the final chapter this evidence is reviewed and a 'sketch' of a processing theory of memory for spatial descriptions is proposed. It is argued that memory for a spatial mental model is a product of the interaction between construction and consultation processes over a period of time rather than a simple 'copy' of a completed working memory spatial mental model

TRANSITIONS: Biophilia, Beauty and Endangered Plants

While the science continues to underline the increasing risks posed by climate change, rallying the public to the cause has proved increasingly difficult. A major challenge is finding alternatives to the despair, hopelessness and consequent sense of disempowerment that confronting the realities of climate change can provoke. It is also the case that particular silent aspects of the impact of climate change – for example on the future viability of certain plant species – receive less public and political attention than others, such as catastrophic weather events. Artists have been active in exploring the impact of climate change through a variety of aesthetic strategies in attempts to address these challenges and mobilise complex understandings of the phenomenon. The response of this thesis is to focus on a specific issue and location – endangered Australian plants – and to experiment with a range of different artistic approaches, filtered through the lens of biophilia and beauty. The experimental artwork produced builds and demonstrates a bridge between botanical science, endangered plant species, and art, in relation to climate change. The PhD research makes four substantial contributions. First, it presents a different perspective on the applied use of art as a mode of enquiry into climate change, through creative agency and advocacy on the focused theme of endangered Australian plants. Second, the research explores and assesses alternative methods for making and reconceptualising static drawings into moving images, as a strategy to engage artistically and positively with the negative ecopsychology and ecoanxiety of climate change. Third, newly initiated, collaborative projects with non-arts partners are deployed to enhance audience engagement through the application of drawings. In parallel to this, conventional international and national exhibitions, publications and workshops are also realised as additional contributions to knowledge within different communities. Fourth, the research results in a document which explores a hopeful reconnection with nature through applying and embracing an aesthetic of beauty and meditative mindfulness. A Transmedia Art method is utilised to enhance broader community understanding of Eco Art, using a mindful, practice based research process