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Free-surface turbulence and air-water gas exchange

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2000This thesis investigates the physical mechanisms of air-water gas transfer through direct measurements of turbulence at the air--water interface. To enable this study, a new approach to the particle image velocimetry (PIV) technique is developed in order to quantify free-surface flows. Two aspects of this work are innovative. First, the use of a three-dimensional laser light cone and optical filtering of the camera allow for the motion of fluorescent flow tracers at the water surface to be isolated and measured. Validation experiments indicate that this measurement reflects the fluid motion within the upper few hundred microns. A key benefit to this approach is the ability to deal with deforming surfaces, provided the amplitudes are not prohibitively large. This feature was used in this thesis to explore the surface flow induced by mechanically generated waves. Second, a new hybrid PIV image processing algorithm was developed that provides high accuracy velocity estimation with improved computational efficiency. This algorithm combines the concepts of dynamic Fourier-domain cross-correlation with a localized direct multiplicative correlation. In order to explore relationships between free-surface hydrodynamics and air-water gas transfer, an oscillating grid-stirred tank was constructed. By its design, this tank can be managed for chemical cleanliness, offers an unobstructed free surface, and is suited for turbulent mixing and air--water gas-exchange studies. A series of acoustic Doppler velocimeter, PIV, and infrared imaging experiments are presented that characterize the flow for the grid forcing conditions studied. Results indicate that the flows are stationary and reasonably repeatable. In addition, the flows exhibit near-isotropic turbulence and are quasi-homogeneous in horizontal planes. Secondary circulations are revealed and investigated. Finally, PIV measurements of free-surface turbulence are performed with concurrent measurements of gas transfer in the grid tank for a range of turbulent mixing and surface conditions. Surface turbulence, vorticity, and divergence are all affected by the presence of a surface film, with significant effects realized for relatively small surface pressures. Results show that while a relationship between surface turbulence and the gas-transfer velocity is an obvious improvement over that found using an estimate of the bulk flow turbulence, this relationship is dependent on the flow regime. This is revealed through additional surface wave studies. However, the data from both the wave experiments and the grid turbulence experiments can be reconciled by a single relationship between the gas-transfer velocity and the 1/2-power of the surface divergence, which agrees with previous conceptual models. These results (1) further our understanding of interfacial transport processes, (2) demonstrate the important role of surface divergence in air-water gas exchange, and (3) relate, in a physically meaningful way, the interactions between surface renewal, surfactants, and gas transfer.I was supported as an Office of Naval Research Graduate Fellow. This assistance was the impetus for my pursuit of a doctoral degree and is gratefully acknowledged. Very special thanks also to the WHOI Ocean Ventures Fund Program, Mr. F. Thomas Westcott, and the WHOI Education Department for generous financial support over the past several years

Doctor of Philosophy

dissertationThis dissertation establishes a new visualization design process model devised to guide visualization designers in building more effective and useful visualization systems and tools. The novelty of this framework includes its flexibility for iteration, actionability for guiding visualization designers with concrete steps, concise yet methodical definitions, and connections to other visualization design models commonly used in the field of data visualization. In summary, the design activity framework breaks down the visualization design process into a series of four design activities: understand, ideate, make, and deploy. For each activity, the framework prescribes a descriptive motivation, list of design methods, and expected visualization artifacts. To elucidate the framework, two case studies for visualization design illustrate these concepts, methods, and artifacts in real-world projects in the field of cybersecurity. For example, these projects employ user-centered design methods, such as personas and data sketches, which emphasize our teams' motivations and visualization artifacts with respect to the design activity framework. These case studies also serve as examples for novice visualization designers, and we hypothesized that the framework could serve as a pedagogical tool for teaching and guiding novices through their own design process to create a visualization tool. To externally evaluate the efficacy of this framework, we created worksheets for each design activity, outlining a series of concrete, tangible steps for novices. In order to validate the design worksheets, we conducted 13 student observations over the course of two months, received 32 online survey responses, and performed a qualitative analysis of 11 in-depth interviews. Students found the worksheets both useful and effective for framing the visualization design process. Next, by applying the design activity framework to technique-driven and evaluation-based research projects, we brainstormed possible extensions to the design model. Lastly, we examined implications of the design activity framework and present future work in this space. The visualization community is challenged to consider how to more effectively describe, capture, and communicate the complex, iterative nature of data visualization design throughout research, design, development, and deployment of visualization systems and tools

The Fire Hazards of Insulation Materials

Insulation materials are widespread in the modern built environment. They have, particularly in recent years, been a major focus of fire safety research. That focus has been enhanced by the tragic Grenfell Tower Fire that resulted in the death of 72 people. This work aims to understand and quantitatively assess the fire hazards presented by modern insulation materials. 14 materials were selected for analysis, including 7 PIR foams, 4 phenolic foams and 3 mineral wool materials. These materials were tested for their elemental composition, fire toxicity, and reaction-to-fire properties. The data generated was then used to calculate the maximum safe loadings of the insulation materials. The methodology had originally only been used with estimated values based on Euroclass data. In order to practically apply the method, the cone calorimeter was used to generate the mass loss per unit area data, rather than SBI test data or estimated values. Fire toxicity data was generated using the ISO/TS 19700 Steady State Tube Furnace. Additional maximum safe loading values were calculated using material-IC50 values, as incapacitation is arguably a more important end point in fire toxicity assessment. The maximum safe loading values calculated were comparable to the estimated values outlined in the original methodology. This methodology could be used to provide quick estimations of the safe loading of insulation materials in construction, allowing for informed decision making in building design without an overwhelming amount of data for non-fire experts to consider. The results of this work demonstrate significant differences between the 3 types of insulation material. The mineral wool materials (both glass wool and stone wool) were of low toxicity and flammability. The foam insulation materials (PIR and phenolic) produced high yields of toxic gases in under-ventilated conditions, and had relatively high flammability. The PIR foams, in particular, had the highest toxicity due to the high yields of HCN produced during under-ventilated flaming, which has been linked to their nitrogen content and chemical composition. The phenolic foams lacked the high yields of HCN due to their low nitrogen content, but still produced high quantities of asphyxiating CO, like the PIR foams. Both types of foam insulation also produced hydrogen chloride gas during combustion, which would have a strongly irritating effect on exposed persons, potentially hindering their escape. FED analysis has demonstrated that the PIR foams increased toxicity is largely the result of the high toxicity of HCN. 1 kg of any of the 7 PIR samples burning in under-ventilated conditions is capable of producing enough HCN to create a lethal atmosphere in 50 m3. The maximum safe loading values calculated showed that, on average, phenolic foams present ~50 to 100x higher fire hazard than the mineral wool materials, and the average PIR foam presented a potential fire hazard ~1.5 to 2.5x higher than the average phenolic foam. Additional work was performed to optimise a method for the quantification of HCN in fires – the chloramine-T/isonicotinic acid method from ISO 19701. HCN is a highly toxic product of the combustion of nitrogen containing materials. As such, it was important to ensure sampling and analysis was both accurate and reliable. Analysis was performed to understand sample and standard stability, optimal time to analysis, analytical variation, and potential interferences as a result of commonly encountered acid gases in fire effluent. The cone calorimeter and SBI apparatus were also assessed for their viability in fire toxicity assessment, potentially negating the need to use the ISO/TS 19700 Steady State Tube Furnace. However, the resulting data demonstrated that both tests are inadequate due to their inability to recreate the more toxic fire condition – under-ventilated burning. This emphasises the need for dedicated fire toxicity tests, as most fire tests are well-ventilated reaction-to-fire tests, despite the fact that fire toxicity results in at least 50% of UK fire deaths

A Selective Culture System for Generating Terminal Deoxynucleotidyl Transferase-Positive Lymphoid Cells In Vitro. V. Detection of Stage-Specific Pro-B-Cell Stimulating Activity in Medium Conditioned by Mouse Bone Marrow Stromal Cells

The selective in vitro generation of rat, mouse, and human terminal deoxynucleotidyl transferase-positive (TdT+ lymphoid cells in our long-term xenogeneic bone marrow (BM) culture system is characterized by physical interaction between the developing lymphocytes and mouse BM-adherent stromal cells and macrophages. In the present study, experiments in which micropor)us membrane culture inserts were inoculated with rat BM cells demonstrated that although the generation of primitive B-lineage lymphoid cells requires the presence of a mouse BM feeder layer, cognitive recognition events are not necessary. Similarly, cell-free (and serum-free) medium conditioned with mouse BM (but not thymus or spleen) adherent cells and stromal-cell lines therefrom supported the proliferation of early rat lymphoid cells in a dose-dependent manner. Double immunofluorescence for incorporated bromo-deoxyuridine (BrdU) and early B-lineage markers of rat BM lymphoid cells maintained in culture inserts or conditioned medium (CM), and studies of their in vitro and in vivo developmental potentials, indicated that the lymphoproliferative response resulted from the selective stimulation of lymphoid stem and/or progenitor cells. The most primitive of these target cells had a HIS24+ HIS50- TdT- cμ- sIg-, pre-pro-B-cell phenotype. Whereas this subset normally constitutes less than 2% of B-lineage BM cells in vivo, it comprises more than 25% of total lymphoid cells in vitro. In addition, the number of TdT+ cells, predominantly of the early pro-B-cell phenotype (HIS24+ HIS50- TdT- cμ- sIg-), was increased approximately tenfold above input levels. Based on these and previous findings, a schematic model is proposed for the developmental pathway of early B-lineage cells in rat BM from the level of the committed (possibly common) lymphoid stem cell to that of the pre-B-cell

Design activity framework for visualization design

pre-printAn important aspect in visualization design is the connection between what a designer does and the decisions the designer makes. Existing design process models, however, do not explicitly link back to models for visualization design decisions. We bridge this gap by introducing the design activity framework, a process model that explicitly connects to the nested model, a well-known visualization design decision model. The framework includes four overlapping activities that characterize the design process, with each activity explicating outcomes related to the nested model. Additionally, we describe and characterize a list of exemplar methods and how they overlap among these activities. The design activity framework is the result of reflective discussions from a collaboration on a visualization redesign project, the details of which we describe to ground the framework in a real-world design process. Lastly, from this redesign project we provide several research outcomes in the domain of cybersecurity, including an extended data abstraction and rich opportunities for future visualization research

Evaluation of the Thermal Performance for a Wire Mesh/Hollow Glass Microsphere Composite Structure as a Conduction Barrier

An experimental investigation exploring the use of wire mesh/hollow glass microsphere combination for use as thermal insulation was conducted with the aim to conclude whether or not it represents a superior insulation technology to those on the market. Three primary variables, including number of wire mesh layers, filler material, and temperature dependence were studied using an apparatus that was part of L.I.C.H.E.N (LabVIEW Integrated Conduction Heat Experiment Network), a setup whose basic components allow three vertically stacked samples to be thermally and mechanically controlled. Knowing the temperature profile in the upper and lower samples allows for determination of thermal conductivity of the middle material through the use of Fourier?s law. The numbers of layers investigated were two, four, six, and eight, with each separated by a metallic liner. The filler materials included air, s15, s35 and s60HS 3MTM hollow glass microspheres. The experiments were conducted at four temperatures of 300, 330, 366, and 400K with an interface pressure of 20 Psi. The experimental results indicated the ?number of layers? used was the primary factor in determining the effective thermal conductivity value. The addition of hollow glass microspheres as filler material resulted in statistically insignificant changes in effective thermal conductivity. Increasing the number of wire mesh layers resulted in a corresponding increase in effective thermal conductivity of the insulation. Changes in temperature had little to no effect on thermal conductivity. The effective thermal conductivity values for the proposed insulation structure ranged from 0.22 to 0.65 W/m-K, the lowest of which came from the two layer case having air as filler material. The uncertainties associated with the experimental results fell between 10 to 20 percent in all but a few cases. In the best performing cases, when compared with existing insulation technologies, thermal conductivity was approximately 3 to 10 times higher than these methods of insulation. Thus, the proposed insulation scheme with hollow glass-sphere filler material does not represent superior technology, and would be deemed uncompetitive with those readily available in the insulation market

Transformative Geomorphic Research Using Laboratory Experimentation

Laboratory experiments in geomorphology is the theme of the 46th annual Binghamton Geomorphology Symposium (BGS). While geomorphic research historically has been dominated by field-based endeavors, laboratory experimentation has emerged as an important methodological approach to study these phenomena, employed primarily to address issues related to scale and the analytical treatment of the geomorphic processes. It is contended here that geomorphic laboratory experiments have resulted in transformative research. Several examples drawn from the fluvial and aeolian research communities are offered as testament to this belief, and these select transformative endeavors often share very similar attributes. The 46th BGS will focus on eight broad themes within laboratory experimentation, and a strong and diverse group of scientists have been assembled to speak authoritatively on these topics, featuring several high-profile projects worldwide. This special issue of the journal Geomorphology represents a collection of the papers written in support of this symposium

Probabilistic Approach to Site Characterization: MIU site, Tono Region, Japan

Geostatistical simulation is used to extrapolate data derived from site characterization activities at the MIU site into information describing the three-dimensional distribution of hydraulic conductivity at the site and the uncertainty in the estimates of hydraulic conductivity. This process is demonstrated for six different data sets representing incrementally increasing amounts of characterization data. Short horizontal ranges characterize the spatial variability of both the rock types (facies) and the hydraulic conductivity measurements. For each of the six data sets, 50 geostatistical realizations of the facies and 50 realizations of the hydraulic conductivity are combined to produce 50 final realizations of the hydraulic conductivity distribution. Analysis of these final realizations indicates that the mean hydraulic conductivity value increases with the addition of site characterization data. The average hydraulic conductivity as a function of elevation changes from a uniform profile to a profile showing relatively high hydraulic conductivity values near the top and bottom of the simulation domain. Three-dimensional uncertainty maps show the highest amount of uncertainty in the hydraulic conductivity distribution near the top and bottom of the model. These upper and lower areas of high uncertainty are interpreted to be due to the unconformity at the top of the granitic rocks and the Tsukyoshi fault respectively