Identifying biotic determinants of historic American eel (Anguilla rostrata) distributions

Traditionally, ecologists studying large scale patterns in species distributions emphasize abiotic variables over biotic interactions. Noting that both abiotic & biotic variables likely determine distributions of all organisms, many ecologists now aim for a more comprehensive view of species distributions, inclusive of both abiotic and biotic components (Soberón 2007)

Virtual Exploration of the Human Vocal Tract

Hypothesis: By simulating the acoustic field throughout the entire vocal tract the evolution of speech sounds within the tract can be directly and quantitatively related to physical variations in the tract geometry. This insight into speech production could then be applied to a variety of fields where the ability to alter or investigate speech characteristics in a targeted way could be useful for example in the teaching of speech science, in speech coaching, or as part of the planning of medical procedures. In this research, a bespoke acoustic simulation package has been produced using a continuous 3-dimensional Digital Waveguide Mesh (DWM) which can produce acoustic output throughout the entire simulation domain containing the tract at every time step. This package has been shown to reproduce formant frequencies for a variety of vocal tract shapes with an average mean absolute error of 10.12% at the lips, which is comparable to other research. These results have been investigated by comparing simulation output to recorded output from physical models. This simulation package has also been used to perform studies into the shifting of formant frequencies during speech sound production along the length of the tract, and into the effect on formant frequencies of the removal of geometric features of the tract such as the piriform fossae. These studies have been compared to physical internal measurements of vocal tract models from living subjects, showing preliminary agreement with further development required. A large emphasis has been placed on the accessibility of this research, with the production of several tools for visualisation of the data contained within, and with decisions made during the production of the simulation package itself

On the use of mechanical and acoustical excitations for selective heat generation in polymer-bonded energetic materials

To address security issues in both military and civilian settings, there is a pressing need for improved explosives detection technologies suitable for trace vapor detection. In light of the strong dependence of vapor pressure on temperature, trace vapor detection capabilities may be enhanced by selectively heating target materials by external excitation. Moreover, polymer-bonded energetic materials may be particularly susceptible to heating by mechanical or acoustical excitation, due to the high levels of damping and low thermal conductivities of most polymers. In this work, the thermomechanical response of polymer-based energetic composites and methods for acoustical excitation are investigated in order to improve the understanding of the temperature rises induced by applied excitation, and to uncover waveforms which may efficiently transmit excitation energy to generate heat and enhance trace vapor detection capabilities. The heat generation in the binder material of energetic and surrogate systems under harmonic excitation was investigated analytically through the application of a viscoelastic material model. Specifically, structural-scale heating was considered under low-frequency direct mechanical excitation as applied to a beam geometry. Experiments were conducted with a mock mechanical material, wherein the mechanical and thermal responses were recorded by scanning laser Doppler vibrometry and infrared thermography, respectively. Direct comparisons between the model and experimental results demonstrated good agreement with the predicted response, with low-order, bulk-scale heating observed along the modal structure in areas of higher strains. In addition, localized heating near individual crystals was investigated analytically by extending the viscoelastic heating model to general three-dimensional stress-strain states. Application of the model to a Sylgard 184 binder system with an embedded HMX (octogen) crystal under ultrasonic excitation revealed predictions of significant heating rates, particularly near the front edge of the crystal, due to the wave scattering and the resulting stress concentrations. In considering methods for such excitation through incident acoustical or ultrasonic waves, the form of the wave profile was tuned in this work for the purpose of maximizing the energy transmission into solid materials. That transmission is generally limited by the large impedance mismatch at typical fluid--solid interfaces, but by varying the spatial distribution of the incident wave pressure, significant transmission increases can be achieved. In particular, tuned incident inhomogeneous plane waves were found to predict much lower values of the reflection coefficient, and hence large increases in the energy transmission in the context of lossless and low-loss dissipative media. Also, material dissipation was found to have a strong effect on the optimal incident waveform, generally causing a shift to lower inhomogeneity values. Similar results were obtained for parameterized forms of bounded incident waves with respect to the local reflection phenomena and surface wave excitation. These results suggest that, depending on the targeted solid material, substantial energy transmission and heat generation increases may be achieved by tailoring the spatial form of the incident wave profile

Unpacking the Impact of Restorative Justice in the Rise Experiments: Facilitators, Offenders, and Conference Non-Delivery

Restorative Justice (RJ) programs are often evaluated in terms of their outcomes, with little attention to the process. Typically we analyze average effects across individuals who experience RJ differently. The present dissertation unpacks these different effects in three separate inquiries utilizing data from the Reintegrative Shaming Experiments (RISE) conducted in Canberra, Australia from 1995 - 2000. First, we descriptively assess the extent RJ conference facilitators engender perceptions of procedural justice and legitimacy in offenders. We examine the number of conferences delivered (experience), sequential conferences (practice-makes-perfect) and the timing between conferences (skill maintenance). Certain conference facilitators are better than others from the outset. We recommend the identification of RJ facilitators who are good at promoting perceptions of procedural justice and legitimacy. Second, we utilize trajectory analysis and find the impact of RJ varies by offending group, with negative effects observed for Aboriginal offenders. Finally, utilizing multinomial logistic regression, we examine the characteristics associated with non-delivery of RJ. Randomized controlled trials, such as RISE, rely on treatment integrity to best assess the impact of the assigned treatment. From a policy standpoint, the most efficient use of resources would rely on successful conference delivery. We find that the time between random assignment and the first conference attempt is significantly related to successful delivery. This dissertation takes important steps in understanding the importance of unpacking the impact of RJ and helps inform who should conduct RJ conferences, what groups of individuals to include in future studies, and what impacts non-delivery of RJ conferences

Overview of Dr. L. L. Beranek\u27s 2006 paper on Analysis of Sabine and Eyring Equations and their Application to Concert Hall Audience and Chair Absorption

Overview of Dr. L. L. Beranek\u27s 2006 paper on Analysis of Sabine and Eyring Equations and their Application to Concert Hall Audience and Chair Absorptio

On the Maximum Mass of Accreting Primordial Supermassive Stars

Supermassive primordial stars are suspected to be the progenitors of the most massive quasars at z~6. Previous studies of such stars were either unable to resolve hydrodynamical timescales or considered stars in isolation, not in the extreme accretion flows in which they actually form. Therefore, they could not self-consistently predict their final masses at collapse, or those of the resulting supermassive black hole seeds, but rather invoked comparison to simple polytropic models. Here, we systematically examine the birth, evolution and collapse of accreting non-rotating supermassive stars under accretion rates of 0.01-10 solar masses per year, using the stellar evolution code KEPLER. Our approach includes post-Newtonian corrections to the stellar structure and an adaptive nuclear network, and can transition to following the hydrodynamic evolution of supermassive stars after they encounter the general relativistic instability. We find that this instability triggers the collapse of the star at masses of 150,000-330,000 solar masses for accretion rates of 0.1-10 solar masses per year, and that the final mass of the star scales roughly logarithmically with the rate. The structure of the star, and thus its stability against collapse, is sensitive to the treatment of convection, and the heat content of the outer accreted envelope. Comparison with other codes suggests differences here may lead to small deviations in the evolutionary state of the star as a function of time, that worsen with accretion rate. Since the general relativistic instability leads to the immediate death of these stars, our models place an upper limit on the masses of the first quasars at birth.Comment: 5 pages, 4 figures. Accepted ApJ letter

The Evolution of Supermassive Population III Stars

Supermassive primordial stars forming in atomically-cooled halos at $z \sim15-20$ are currently thought to be the progenitors of the earliest quasars in the Universe. In this picture, the star evolves under accretion rates of $0.1 - 1$ $M_\odot$ yr$^{-1}$ until the general relativistic instability triggers its collapse to a black hole at masses of $\sim10^5$ $M_\odot$. However, the ability of the accretion flow to sustain such high rates depends crucially on the photospheric properties of the accreting star, because its ionising radiation could reduce or even halt accretion. Here we present new models of supermassive Population III protostars accreting at rates $0.001 - 10$ $M_\odot$ yr$^{-1}$, computed with the GENEVA stellar evolution code including general relativistic corrections to the internal structure. We use the polytropic stability criterion to estimate the mass at which the collapse occurs, which has been shown to give a lower limit of the actual mass at collapse in recent hydrodynamic simulations. We find that at accretion rates higher than $0.001$ $M_\odot$ yr$^{-1}$ the stars evolve as red, cool supergiants with surface temperatures below $10^4$ K towards masses $>10^5$ $M_\odot$, and become blue and hot, with surface temperatures above $10^5$ K, only for rates $\lesssim0.001$ $M_\odot$ yr$^{-1}$. Compared to previous studies, our results extend the range of masses and accretion rates at which the ionising feedback remains weak, reinforcing the case for direct collapse as the origin of the first quasars

On the Rotation of Supermassive Stars

Supermassive stars born from pristine gas in atomically-cooled haloes are thought to be the progenitors of supermassive black holes at high redshifts. However, the way they accrete their mass is still an unsolved problem. In particular, for accretion to proceed, a large amount of angular momentum has to be extracted from the collapsing gas. Here, we investigate the constraints stellar evolution imposes on this angular momentum problem. We present an evolution model of a supermassive Population III star including simultaneously accretion and rotation. We find that, for supermassive stars to form by accretion, the accreted angular momentum has to be about 1% of the Keplerian angular momentum. This tight constraint comes from the $\Omega\Gamma$-limit, at which the combination of radiation pressure and centrifugal force cancels gravity. It implies that supermassive stars are slow rotators, with a surface velocity less than 10-20% of their first critical velocity, at which the centrifugal force alone cancels gravity. At such low velocities, the deformation of the star due to rotation is negligible