The relaxation of two-dimensional rolls in Rayleigh–Bénard convection

Large aspect ratio, two-dimensional, periodic convection layers containing a Boussinesq fluid of finite Prandtl number bounded by rigid or free horizontal surfaces are investigated numerically. The fluid equations are solved using both a standard pseudospectral and a Fourier integral method for the time evolution of finite initial perturbations, both random thermal perturbations and localized roll disturbances, into a final equilibrium state. The suggestion that a Fourier integral solution method is required to yield roll relaxation, the two-dimensional process increasing the convection wavelength to values larger than critical, is investigated. Roll relaxation is found for both free-slip and no-slip surfaces using either solution method as long as the initial state is chosen to be of the form of a localized roll disturbance. A wide variety of simulations are performed and roll relaxation is found to be independent of the periodic domain length, weakly dependent on the Rayleigh number and dependent upon the magnitude of the initial localized roll disturbances

Visualizing experience: using creative research methods with members of sexual and gender communities

This chapter argues that visual methods may be particularly appropriate for the study of non- heteronormative sexualities and genders, particularly the more marginal identities and practices which have tended to be pathologised in, and excluded from, past research. We focus here on three of these: bisexuality (attraction to more than one gender, or regardless of gender), trans (moving away from the gender which was assigned at birth), and polyamory (having multiple sexual and/or intimate relationships). Of course trans people may be heterosexual, or indeed of any sexuality, but have tended to be marginalised in many of the same ways as people from non-heterosexual sexualities, and are consequently included in this chapter for that reason. First we briefly overview the history of qualitative research on non-heterosexual sexualities and trans, arguing that qualitative methods, per se, do not prevent researchers from forming limiting understandings and problematic generalisations about such groups. Then we present an alternative to conventional interview/focus group discussion research involving the use of visual methods. We summarise key reasons why this may be particularly appropriate to the exploration of those in marginalised sexualities, genders and relationship forms, and then present three examples, based in our own research, of the ways in which such research provided data which confounded simple celebratory or critical conclusions about people in these communities. Finally, we summarise some methodological considerations which are of value to those considering the use of visual methods in their own research

Effects of reverberation conditions and physical versus virtual source placement on localization in virtual sound environments

Sound field synthesis systems vary in number and arrangement of loudspeakers and methods used to generate virtual sound environments to study human hearing perception. While previous work has evaluated the accuracy with which these systems physically reproduce room acoustic conditions, less is known on assessing subjective perception of those conditions, such as how well such systems preserve source localization. This work quantifies the accuracy and precision of perceived localization from a multi-channel sound field synthesis system at Boys Town National Research Hospital, which used 24 physical loudspeakers and vector-based amplitude panning to generate sound fields. Short bursts of broadband speech-shaped noise were presented from source locations (either coinciding with a physical loudspeaker location, or panned between loudspeakers) under free-field and modeled reverberant-room conditions. Listeners used a HTC Vive remote laser tracking system to point to the perceived source location.Results show that the system synthesizes source locations accurately for both physical and panned sources, in both azimuth and elevation. Panned sources, though, are localized less precisely than physical sources. Reverberant condition is also found to affect both the accuracy and precision of localization in the azimuthal plane, with dry conditions producing greater accuracy and better precision. Only accuracy (not precision) of localization in elevation was impacted by reverberant condition, with reverberant cases producing results closer to the target than dry cases. An interaction effect of reverberant condition with elevation on localization in elevation, though, indicates that dry conditions result in better localization in elevation than reverberant ones at an elevation close to head height, but the situations at higher elevations are where subjects localized dry sources lower than the target height, while reverberant ones were more accurately placed. Other laboratories with sound field synthesis systems are encouraged to gather similar data on the accuracy and precision of localization in azimuth and elevation, so that results from studies using these systems can be better interpreted in light of the capabilities of the system to generate accurate and precise reproductions of source locations. [Work supported by NIH GM109023.] Advisor: Lily M. Wan

Patronage in English literature to close of eighteenth century ..

Typewritten sheets in cover. Thesis (M.A.)--Boston University This item was digitized by the Internet Archive

Treatment of Emerging Contaminants in Wastewater by Advanced Oxidation Processes

This study evaluated the effectiveness of ozonation and activated carbon for the degradation and removal of three main emerging contaminants (ECs) in wastewater; fluoranthene (FLT), di (2- ethyl hexyl) phthalate (DEHP) and cypermethrin (CYM). The effects of key semi-batch ozonation parameters related to gas-liquid mass transfer and reaction kinetics were identified for all contaminants. The degradation rates were evaluated in solutions of DI water, using concentration change of ozone and EC versus time. With an ozone gas concentration of 20 g/m3 NTP, the change in concentration from an initial concentration of 0.05 mg/L over time was measured using HPLC. To decrease by 75 %, it took less than a minute for FLT, two minutes for DEHP and six minutes for CYM. The adsorption of the emerging contaminants with granulated activated carbon (GAC) were evaluated in solutions of DI water at an initial concentration of 1 mg/L. For the decrease in concentration of 60 %, the time for each contaminant varied. For FLT this was achieved in 5 minutes, DEHP was decreased within 20 minutes, and it took CYM 20 minutes to reach this decrease. The effects of ozonation and adsorption onto GAC were also investigated in samples of final wastewater effluent

Science And The Systematicity Of Nature: A Critique Of Nancy Cartwright\u27s Doctrine Of Nature And Natural Science

Whether nature is or is not systematic sounds at first like an idle metaphysical question, but considered in relation to (i) the aims of science and (ii) the methods of appraisal of scientific theories, it can be given clear (and quite plainly empirical) content. It is also necessary to ask the question in order to study (iii) the relation of causation, laws of nature, and theoretical structure.;(i) Aims. The doctrines (1) that science aims to provide explanations, (2) that science achieves success in this aim, (3) that explanation involves unification, and (4) that the principles on which explanations, properly so-called, are based, must be true, together imply that nature is a system. For a kind of explanation she calls causal , Nancy Cartwright affirms (1), (2) and (4) but denies (3); for a kind of explanation she calls theoretical , Cartwright affirms (1), (2) and (3) but denies (4). I show by historical examples (in particular, in the work of Copernicus, Kepler, Newton, Maxwell and Einstein) that Cartwright\u27s distinction between theoretical and causal explanation is often impossible to make out. I show, largely through discussions of Galileo and Newton, that Cartwright has a misleading view of the role of idealization in physical science, a view apt perhaps for physics before Newton, but not for Newtonian physics. I use my historical case studies to undermine numerous specific sceptical arguments by which Cartwright supports her novel conception of theoretical explanation.;(ii) Methods. I argue that the Newtonian, bootstrap method in terms of which Cartwright reconstructs low-level experiment- and measurement-based inferences to specific causal conclusions has its clearest and most cogent applications in inferences to high-level theoretical conclusions. Newton\u27s method, however, presupposes that nature is a system. Nature must be systematic in order to be well suited to study by the bootstrap method. I argue that the method has been notably successful, and that it consequently is appropriate to assimilate the method\u27s substantive presupposition concerning natural systematicity to what has been learned from the experience of the method\u27s successful application, and to say that we have evidence that this presupposition is true, that is, evidence that nature is systematic.;(iii) Causation, Laws, and Theory. Against Cartwright I defend a top-down, anti-metaphysical conception of this relation, and an internal realist conception of theoretical structure. By highlighting some facets of the mathematics appertaining to fundamental physical laws presumed true, I argue that certain phenomena concerning scientific practice from which Cartwright\u27s metaphysical view of causes gains apparent strength in fact are conformable to my own account

Aspects of sensory cues and propulsion in marine zooplankton hydrodynamic disturbances

The hydrodynamic disturbances generated by two types of free-swimming, marine zooplankton were quantified experimentally in the laboratory with a novel, infrared Particle Image Velocimetry (PIV) system. The study consisted of three main parts: (1) the flow fields of free-swimming and tethered Euchaeta antarctica were compared to determine the effects of tethering, (2) three species of copepods (Euchaeta rimana, Euchaeta elongata, and Euchaeta antarctica) that live in seawater in a range of temperatures (23 ºC - 0 ºC) and a corresponding range of fluid viscosity (0.97 - 1.88 mm2 s-1) were analyzed experimentally and with a computational fluid dynamics model (FLUENT) to assess the effect of size and fluid viscosity on the flow fields, (3) the flow fields were collected for individuals of two species of euphausiids (Euphausia pacifica and Euphausia superba) to compare the effect of size and Reynolds number on propulsion and the spatial extent of the flow disturbance. In addition to the measured flow fields around solitary krill, flow fields were collected around small, coordinated groups of E. superba to examine group sensory cues through hydrodynamics. In the first part of this investigation, it was determined that tethering zooplankton during data collection resulted in flow fields with increased asymmetry and larger spatial extent due to the unbalanced force applied to the fluid by the tether. In response to these findings, only flow fields collected for free-swimming organisms were used in the subsequent studies. In the second part of the study, the increase in viscosity between subtropical and temperate fluid environments in conjunction with increased size and species-specific swimming speeds resulted in similar Reynolds numbers among E. elongata and E. rimana (in both cruising and escaping modes). During cruising (Re ~10), the spatial extent of the copepod hydrodynamic disturbances and propulsion costs were similar between species. In the case of fluid distrubances of escape (Re ~ 100), the spatial extent and energetic cost were larger for the larger species ( E. elongata). In the third part of the study, the hydrodynamic disturbance produced by E. superba (larger krill species) was found to be longer in horizontal spatial extent and at scales more appropriate for communication within schools than the hydrodynamic disturbance produced by E. pacifica. However, the sensory cue in coordinated groups of krill was complicated by the interaction of multiple flow disturbance fields, which suggests that hydrodynamic cues between krill in groups are restricted to small distances. The energetic cost of propulsion was ten times greater for the larger species of krill, and energetic expenditure did not appear to decrease for krill swimming in coordinated groups.Ph.D.Committee Chair: Dr. Donald Webster; Committee Co-Chair: Dr. Jeannette Yen; Committee Member: Dr. Philip Roberts; Committee Member: Dr. Terry Sturm; Committee Member: Dr. Thorsten Stoesse