16,361 research outputs found
Synthetic Observations of the HI Line in SPH-Simulated Spiral Galaxies
Using the radiative transfer code Torus, we produce spectral-line cubes of
the predicted HI profile from global SPH simulations of spiral galaxies. Torus
grids the SPH galaxy using Adaptive Mesh Refinement, then applies a ray-tracing
method to infer the HI profile along the line(s) of sight. The gridded galaxy
can be observed from any direction, which enables us to model the observed HI
profile for galaxies of any orientation. We can also place the observer inside
the galaxy, to simulate HI observations taken from the Earth's position in the
Milky Way.Comment: 4 pages, 2 figures, conference proceedings for "Panoramic Radio
Astronomy: 1-2 Ghz Research on Galaxy Evolution" June 2-5, 2009 Groninge
Advanced launch system trajectory optimization using suboptimal control
The maximum-final mass trajectory of a proposed configuration of the Advanced Launch System is presented. A model for the two-stage rocket is given; the optimal control problem is formulated as a parameter optimization problem; and the optimal trajectory is computed using a nonlinear programming code called VF02AD. Numerical results are presented for the controls (angle of attack and velocity roll angle) and the states. After the initial rotation, the angle of attack goes to a positive value to keep the trajectory as high as possible, returns to near zero to pass through the transonic regime and satisfy the dynamic pressure constraint, returns to a positive value to keep the trajectory high and to take advantage of minimum drag at positive angle of attack due to aerodynamic shading of the booster, and then rolls off to negative values to satisfy the constraints. Because the engines cannot be throttled, the maximum dynamic pressure occurs at a single point; there is no maximum dynamic pressure subarc. To test approximations for obtaining analytical solutions for guidance, two additional optimal trajectories are computed: one using untrimmed aerodynamics and one using no atmospheric effects except for the dynamic pressure constraint. It is concluded that untrimmed aerodynamics has a negligible effect on the optimal trajectory and that approximate optimal controls should be able to be obtained by treating atmospheric effects as perturbations
Responsiveness of Demand for Irrigation Water: A Focus on the Southern Murray-Darling Basin
The Productivity Commission staff working paper, 'Responsiveness of Demand for Irrigation Water: A Focus on the Southern Murray-Darling Basin', was released August 2004. This paper explores the determinants of the elasticity of demand for irrigation water. It focuses on three main irrigated industries - rice, dairy and horticulture - to gain a greater understanding of the value that farmers place on water as an input. This paper provides detail relating to farm decision behaviour and biophysical production realities faced by irrigators in the southern Murray-Darling Basin. The views expressed in this paper are those of the staff involved and do not necessarily reflect those of the Productivity Commission.Resource /Energy Economics and Policy,
Heuristic Spike Sorting Tuner (HSST), a framework to determine optimal parameter selection for a generic spike sorting algorithm
Extracellular microelectrodes frequently record neural activity from more than one neuron in the vicinity of the electrode. The process of labeling each recorded spike waveform with the identity of its source neuron is called spike sorting and is often approached from an abstracted statistical perspective. However, these approaches do not consider neurophysiological realities and may ignore important features that could improve the accuracy of these methods. Further, standard algorithms typically require selection of at least one free parameter, which can have significant effects on the quality of the output. We describe a Heuristic Spike Sorting Tuner (HSST) that determines the optimal choice of the free parameters for a given spike sorting algorithm based on the neurophysiological qualification of unit isolation and signal discrimination. A set of heuristic metrics are used to score the output of a spike sorting algorithm over a range of free parameters resulting in optimal sorting quality. We demonstrate that these metrics can be used to tune parameters in several spike sorting algorithms. The HSST algorithm shows robustness to variations in signal to noise ratio, number and relative size of units per channel. Moreover, the HSST algorithm is computationally efficient, operates unsupervised, and is parallelizable for batch processing
Trade costs, 1870â2000
What has driven trade booms and trade busts in the past century and a half? Was it changes in global output or in the costs of international trade? To address this question, we derive a micro-founded measure of aggregate bilateral
trade costs based on a standard model of trade in differentiated goods. These trade costs gauge the difference between observed bilateral trade and frictionless trade in terms of an implied markup on retail prices of foreign goods. Thus, we are able to estimate the combined magnitude of tariffs, transportation costs, and all other macroeconomic frictions that impede international
trade but that are inherently difficult to observe. We use this measure to examine the growth of global trade between 1870 and 1913, its retreat from 1921 to 1939, and its subsequent rise from 1950 to 2000. We find that trade cost
declines explain roughly 55 percent of the preâWorld War I trade boom and 33 percent of the postâWorld War II trade boom, while a precipitous rise in trade costs explains the entire interwar trade bust
We haven't got a seat on the bus for you or All the seats are mine: Narratives and career transitions in professional golf
In this article we explore how the stories an athlete tells throughout life in sport affect her career transition experiences. We base our enquiry on a social constructionist conception of narrative theory which holds that storytelling is integral to the creation and maintenance of identity and sense of self. Life stories were gathered through interviews with two professional women golfers (Christiana and Kandy) over a sixâyear period. Through a narrative analysis of structure and form we explored each participantâs stories of living in and withdrawing from professional golf. We suggest Christiana told monological performanceâoriented stories which, while aligning with the culture of elite sport, resulted in an exclusive athletic identity and foreclosure of alternative selves and roles. On withdrawal, Christiana experienced narrative wreckage, identity collapse, mental health difficulties and considerable psychological trauma. In contrast, Kandy told dialogical discoveryâoriented stories which, while being in tension with the dominant performance narrative, created and sustained a multidimensional identity and self. Her stories and identity remained intact, authentic and continuous on withdrawal from tournament golf and she experienced few psychological problems
Exploring taboo issues in professional sport through a fictional approach
While the need to consider life course issues in elite sport research and practice is increasingly recognised, some experiences still seem to be considered too dangerous to explore. Consequently, stories of these experiences are silenced and the ethical and moral questions they pose fail to be acknowledged, understood or debated. This paper presents an ethnographic fiction through which we explore a sensitive set of experiences that were uncovered during our research with professional sportspeople. Through a multiâlayered reconstruction, the story reveals the complex, but significant, relationships that exist between identity, cultural narratives and embodied experiences. After the telling we consider how the story has stimulated reflective practice among students, researchers and practitioners. While there are risks involved in writing and sharing taboo stories, the feedback we have received suggests that storytelling can be an effective pedagogical tool in education and professional development
Flows and Solitary Waves in Unitary Matrix Models with Logarithmic Potentials
We investigate unitary one-matrix models coupled to bosonic quarks. We derive
a flow equation for the square-root of the specific heat as a function of the
renormalized quark mass. We show numerically that the flows have a finite
number of solitary waves, and we postulate that their number equals the number
of quark flavors. We also study the nonperturbative behavior of this theory and
show that as the number of flavors diverges, the flow does not reach
two-dimensional gravity.Comment: 26 pages + 4 figure
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