title: Spikes and matter inhomogeneities in massless scalar field models

authors: Coley, A.A.

subjects: Science & Technology

abstract: We shall discuss the general relativistic generation of spikes in a massless scalar field or stiff perfect fluid model. We first investigate orthogonally transitive (OT) G 2 stiff fluid spike models both heuristically and numerically, and give a new exact OT G 2 stiff fluid spike solution. We then present a new two-parameter family of non-OT G 2 stiff fluid spike solutions, obtained by the generalization of non-OT G 2 vacuum spike solutions to the stiff fluid case by applying Geroch's transformation on a Jacobs seed. The dynamics of these new stiff fluid spike solutions is qualitatively different from that of the vacuum spike solutions in that the matter (stiff fluid) feels the spike directly and the stiff fluid spike solution can end up with a permanent spike. We then derive the evolution equations of non-OT G 2 stiff fluid models, including a second perfect fluid, in full generality, and briefly discuss some of their qualitative properties and their potential numerical analysis. Finally, we discuss how a fluid, and especially a stiff fluid or massless scalar field, affects the physics of the generation of spikes.

text: Spikes and matter inhomogeneities in massless scalar field models We shall discuss the general relativistic generation of spikes in a massless scalar field or stiff perfect fluid model. We first investigate orthogonally transitive (OT) G 2 stiff fluid spike models both heuristically and numerically, and give a new exact OT G 2 stiff fluid spike solution. We then present a new two-parameter family of non-OT G 2 stiff fluid spike solutions, obtained by the generalization of non-OT G 2 vacuum spike solutions to the stiff fluid case by applying Geroch's transformation on a Jacobs seed. The dynamics of these new stiff fluid spike solutions is qualitatively different from that of the vacuum spike solutions in that the matter (stiff fluid) feels the spike directly and the stiff fluid spike solution can end up with a permanent spike. We then derive the evolution equations of non-OT G 2 stiff fluid models, including a second perfect fluid, in full generality, and briefly discuss some of their qualitative properties and their potential numerical analysis. Finally, we discuss how a fluid, and especially a stiff fluid or massless scalar field, affects the physics of the generation of spikes.

year: 2016-01-07

title: Orthogonal grid generation software

authors: Delbourgo, Daniel

abstract: Calculates transformations between physical and index space within a numerical grid

text: Orthogonal grid generation software Calculates transformations between physical and index space within a numerical grid

year: 1992

title: Spatial and temporal characteristics of the underwater soundscape around the Motiti Protection Area: Ōtaiti/Astrolabe Reef and Motiti Island

authors: Riegel, Maria Sophie

subjects: Underwater Soundscapes

abstract: Marine ecosystems around the world have been impacted by degradation and loss of biodiversity as a result of human impacts and climate change. The monitoring and management of ecologically significant areas is vital in understanding the effects of habitat degradation on marine ecosystems. Traditional monitoring methods are often expensive, time consuming, labour intensive and invasive. Soundscapes offer a unique opportunity for monitoring habitats in a way that is cost effective, minimally invasive and efficient. The aim of this study was to use passive acoustic monitoring to create a baseline data set using ambient sound data to investigate the spatial and temporal changes in ambient sound pressure levels, and to identify biotic, abiotic and anthropogenic sound sources which make up the marine soundscapes at the Motiti Island and Ōtaiti/Astrolabe Reef. Five diverse and ecologically significant sites in the Motiti Protection Area – at Ōtaiti/Astrolabe Reef and Motiti Island, in the Bay of Plenty, New Zealand were selected and monitored over the course of a year. This provided a wide variety of data to show the diel, lunar and seasonal patterns and trends in acoustic biological activity in order to represent the ecosystems accurately. The results showed that all sites showed strong diel patterns, with a sound pressure level increase of ~6-10dB during daylight hours compared to dark hours, and evident peaks during dawn and dusk hours as a result of biological choruses composed largely of sea urchins. There were also strong seasonal trends among the five sites, with Summer having the overall highest sound pressure level compared to Spring, Autumn and Winter, this also had an effect on the peaks in dusk choruses, which were also found to be highest during Summer. Lunar phases were also found to have an impact on the sound pressure levels of all five sites, with increased sound pressure levels during the new moon, compared to sound pressure levels during the full moon. This study created a baseline data set for a culturally, ecologically, and economically valuable area. Passive acoustic monitoring was found to be an incredibly useful tool in understand the ecosystems health and biological condition, and offers an alternative to traditional monitoring which is an effective, minimally invasive, and less labour intensive way of monitoring marine ecosystems.

text: Spatial and temporal characteristics of the underwater soundscape around the Motiti Protection Area: Ōtaiti/Astrolabe Reef and Motiti Island Marine ecosystems around the world have been impacted by degradation and loss of biodiversity as a result of human impacts and climate change. The monitoring and management of ecologically significant areas is vital in understanding the effects of habitat degradation on marine ecosystems. Traditional monitoring methods are often expensive, time consuming, labour intensive and invasive. Soundscapes offer a unique opportunity for monitoring habitats in a way that is cost effective, minimally invasive and efficient. The aim of this study was to use passive acoustic monitoring to create a baseline data set using ambient sound data to investigate the spatial and temporal changes in ambient sound pressure levels, and to identify biotic, abiotic and anthropogenic sound sources which make up the marine soundscapes at the Motiti Island and Ōtaiti/Astrolabe Reef. Five diverse and ecologically significant sites in the Motiti Protection Area – at Ōtaiti/Astrolabe Reef and Motiti Island, in the Bay of Plenty, New Zealand were selected and monitored over the course of a year. This provided a wide variety of data to show the diel, lunar and seasonal patterns and trends in acoustic biological activity in order to represent the ecosystems accurately. The results showed that all sites showed strong diel patterns, with a sound pressure level increase of ~6-10dB during daylight hours compared to dark hours, and evident peaks during dawn and dusk hours as a result of biological choruses composed largely of sea urchins. There were also strong seasonal trends among the five sites, with Summer having the overall highest sound pressure level compared to Spring, Autumn and Winter, this also had an effect on the peaks in dusk choruses, which were also found to be highest during Summer. Lunar phases were also found to have an impact on the sound pressure levels of all five sites, with increased sound pressure levels during the new moon, compared to sound pressure levels during the full moon. This study created a baseline data set for a culturally, ecologically, and economically valuable area. Passive acoustic monitoring was found to be an incredibly useful tool in understand the ecosystems health and biological condition, and offers an alternative to traditional monitoring which is an effective, minimally invasive, and less labour intensive way of monitoring marine ecosystems.

year: 2022