Browsing by Subject "Ice"

Now showing 1 - 4 of 4
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    Fire and Ice: Thermoluminescent Temperature Sensing in High-Explosive Detonations and Optical Characterization Methods for Glacier Ice Boreholes
    (2017-07) Mah, Merlin
    The environment around a detonating high explosive is incredibly energetic and dynamic, generating shock waves, turbulent mixing, chemical reactions, and temperature excursions of thousands of Kelvin. Probing this violent but short-lived phenomena requires durable sensors with fast response times. By contrast, the glacier ice sheets of Antarctica and Greenland change on geologic time scales; the accumulation and compression of snow into ice preserves samples of atmospheric gas, dust, and volcanic ash, while the crystal orientations of the ice reflect its conditions and movement over hundreds of thousands of years. Here, difficulty of characterization stems primarily from the location, scale, and depth of the ice sheet. This work describes new sensing technologies for both of these environments. Microparticles of thermoluminescent materials are proposed as high-survivability, bulk-deployable temperature sensors for applications such as assessing bioagent inactivation. A technique to reconstruct thermal history from subsequent thermoluminescence observations is described. MEMS devices were designed and fabricated to assist in non-detonation testing: large-area electrostatic membrane actuators were used to apply mechanical stress to thermoluminescent Y2O3:Tb thin film, and microheaters impose rapid temperature excursions upon particles of Mg2SiO4:Tb,Co to demonstrate predictable thermoluminescent response. Closed- and open-chamber explosive detonation tests using dosimetric LiF:Mg,Ti and two experimental thermometry materials were performed to test survivability and attempt thermal event reconstruction. Two borehole logging devices are described for optical characterization of glacier ice. For detecting and recording layers of volcanic ash in glacier ice, we developed a lightweight, compact probe which uses optical fibers and purely passive downhole components to detect single-scattered long-wavelength light. To characterize ice fabric orientation, we propose a technique which uses reflection measurements from a small, fixed set of geometries. The design and construction of a borehole logger implementing these techniques is described, and its testing discussed.
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    Heterogeneous protein distribution during rapid and equilibrium freezing
    (2013-04) Twomey, Alan Michael
    Interactions between proteins and ice were studied in situ using FTIR and confocal Raman microspectroscopy under equilibrium and non-equilibrium conditions over a range of temperatures. During quasi-equilibrium freezing of aqueous solutions of dimethyl sulfoxide (DMSO) and bovine serum albumin, preferential exclusion of albumin and/or DMSO was observed. It was hypothesized that the albumin may be adsorbed onto the ice interface or entrapped in the ice phase. To investigate protein-ice interactions during freezing under non-equilibrium conditions, confocal Raman microspectroscopy was used to map the distribution of albumin and the cryoprotective agent trehalose. Microheterogeneity was found in the composition of the freeze-concentrated liquid phase that indicated that albumin was preferentially distributed near or at the boundary of the ice phase. The observed microheterogeneity did not occur under all freezing protocols, which suggests that the technique developed here could be used to develop freezing protocols that would reduce harmful protein-ice interactions.
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    MEMS Actuators for Tuning Nanometer-scale Airgaps in Heterostructures and Optical Instrumentation for Glacier Ice Studies
    (2016-01) Chan, Wing Shan
    MEMS Actuators for Tuning Nanometer-scale Airgaps in Heterostructures We developed a new actuator microstructure to control the spacing between closely spaced surfaces. Creating and controlling nanometer gaps is of interest in areas such as plasmonics and quantum electronics. For example, energy states in quantum well heterostructures can be tuned by adjusting the physical coupling distance between wells. Unfortunately, such an application calls for active control of a nano-scale air gap between surfaces which are orders of magnitude larger, which is difficult due to stiction forces. A vertical electrostatic wedge actuator was designed to control the air gap between two closely spaced quantum wells in a collapsed cantilever structure. A six-mask fab- rication process was developed and carried out on an InGaAs/InP quantum well het- erostructure on an InP substrate. Upon actuation, the gap spacing between the surfaces was tuned over a maximum range of 55 nm from contact with an applied voltage of 60 V. Challenges in designing and fabricating the device are discussed. Optical Instrumentation for Glacier Ice Studies We explored new optical instrumentation for glacier ice studies. Glacier ice, such as that of the Greenland and Antarctic ice sheets, is formed by the accumulation of snowfall over hundreds of thousands of years. Not all snowfalls are the same. Their isotopic compositions vary according to the planet’s climate at the time, and may contain part of the past atmosphere. The physical properties and chemical content of the ice are therefore proxies of Earth’s climate history. In this work, new optical methods and instrumentation based on light scattering and polarization were developed to more efficiently study glacier ice. Field deployments in Antarctica of said instrumentation and results acquired are presented.
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    A three-dimensional model of Lake Superior with ice and biogeochemistry: investigating interannual Lake Trends and the deep chlorophyll maximum
    (2013-12) White, Brooke
    The development of a realistically configured three-dimensional model for Lake Superior including prognostic ice and biogeochemistry models is documented. The addition of a prognostic ice model is a significant advance over previous modeling efforts. The hydrodynamic, ice and biogeochemical models are described and behavior of the model during the period 1985 to 2008 and focusing on the annual cycle of 2005 is discussed. The model is found to sufficiently reproduce many observed physical and biological characteristics of Lake Superior. It is also successfully applied in two scientific investigations: interannual trends in lake temperature, ice cover and primary productivity and elucidation of the causal mechanisms of Lake Superior's deep chlorophyll maximum. The formation of winter ice on Lake Superior has been shown to be important in determining the annual thermal cycle of the lake and long-term trends of surface water temperature increase. However, modeling studies of Lake Superior to date have not included dynamic and thermodynamic ice cover. These physical characteristics of the lake in turn can have significant impacts on biogeochemical cycling within the lake. Modeled long-term interannual trends in increasing water temperature and decreasing ice cover are compared with observed rates. In the model, total annual gross primary productivity is found to correlate positively with mean annual temperature and negatively with mean winter ice cover magnitude.The deep chlorophyll maximum (DCM) is a near ubiquitous feature in Lake Superior during the summer stratified season. Previous studies have elucidated observable characteristics of the DCM in Lake Superior but the physical and biological mechanisms controlling the creation and maintenance of the DCM remained unclear. Sensitivity runs are performed to explore the influence of photoadaptation, photoinhibition, zooplankton grazing, and phytoplankton sinking on the vertical distribution of chlorophyll in the water column. The role of a nutricline in determining the presence and nature of the DCM is also explored. The presence of the DCM is dependent upon the presence of thermal stratification in the model. The sensitivity runs reveal that photoadaptation plays a primary role in determining the depth of the DCM in the model while zooplankton grazing and phytoplankton sinking affected the magnitude but not the presence or depth of the DCM. Photoinhibition showed negligible effects on chlorophyll concentration distribution. The presence of a nutricline in the model is also a necessary condition for the formation of the DCM and it influences both the depth and magnitude of the DCM.