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Dissertations / Theses on the topic 'Polar Science'

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Published: 10 December 2022
Last updated: 28 January 2023

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1

Riddolls, Ryan James 1974. "Structure of the polar electrojet antenna." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/16945.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.
Includes bibliographical references (p. 153-156).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Field experiments were performed in Gakona, Alaska in August and November 2002. The ionospheric conductivity was periodically perturbed using amplitude-modulated radiation from the HAARP HF transmitter (1 MW power, 14 dB gain, 3.3-5.8 MHz carrier, 0.1-40 kHz modulation). The conductivity perturbations lead to perturbations to the natural flow of electrojet current in the lower ionosphere, resulting in ELF/VLF radiation at the modulation frequency. Measurements of the radiation, along with analytic and numerical models, suggest that a vertical loop with a scale size of 10 km is the dominant current structure excited during the experiments.
by Ryan James Riddolls.
Ph.D.
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2

Ba, Demba Elimane. "Nonlinear transform coding with lossless polar coordinates." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37937.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.
Includes bibliographical references (p. 51-52).
In conventional transform coding, the importance of preserving desirable quantization partition cell shapes prevents one from considering the use of a nonlinear change of variables. If no linear transformation of a given source would yield independent components, this means having to encode it at a rate higher than its entropy, i.e. suboptimally. This thesis proposes a new transform coding technique where the source samples are first uniformly scalar quantized and then transformed with an integer-to-integer approximation to a nonlinear transformation that would give independent components. In particular, we design a family of integer-to-integer approximations to the Cartesian-to-polar transformation and analyze its behavior for high rate transform coding. Among the benefits of such an approach is the ability to achieve redundancy reduction beyond decorrelation without limitation to orthogonal linear transformations of the original variables. A high resolution analysis is given, and for source models inspired by a sensor network application and by image compression, simulations show improvements over conventional transform coding. A comparison to state-of-the-art entropy-coded polar quantization techniques is also provided.
by Demba Elimane Ba.
S.M.
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3

Schild, Ingrid. "The politics of international collaboration in Polar research." Doctoral thesis, University of Sussex, 1996. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-42850.

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This thesis investigates the tension between science and politics in contemporary polar research. Twin objectives underpin this central theme. The first is to investigate the relationship between science and politics when analysed through an understanding of international collaboration in Arctic and Antarctic research. The second is to gain an understanding of the nature of research collaboration as an important mode of working in modern science. A framework for analysing collaboration as a work process is proposed. The empirical research interprets how and why polar researchers collaborate. This is done by investigating a number of collaborative projects with reference to their policy and political context. Three countries with contrastive polar political interests were chosen within which to conduct the empirical work: the UK, Norway and Germany. Science logistics (the means of supporting research in the field, e.g. transport, research platforms) are identified as the most significant enabling factor in experimental polar research. They also perform a symbolic political role for governments. In the three countries forming the focus of this study, science logistics are controlled bygovernment polar research institutes which also house multidisciplinary research programmes. Logistics are traced to the heart of collaboration; they bring researchers together, and shape the nature of collaborative research. Differences in ease of access to national logistics structure collaboration. The interface between these politics of access andnational political agendas is blurred, owing to the central role played by logistics in both science and politics. However, the apparent conflict between scientists' careers and polar politics masks the finding that scientists shape their careers in creative ways, despite, or perhaps because of the constraints imposed by structural conditions. Viewing science as work reveals the importance of taking account of what scientists do when analysing the relation between science and politics.
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4

Jin, Menglin. "Interpolation of surface radiative temperature measured from polar orbiting satellites to a diurnal cycle." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/282883.

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The land surface skin temperature diurnal cycle (LSTD) is very important for the understanding of surface climate and for evaluating climate models. This variable, however, cannot be obtained globally from polar-orbiting satellites because the satellites usually pass a given area twice per day and because their infrared channels cannot observe the surface when the sky is cloudy. In order to more optimally use the satellite data, this research is designed, for the first time, to solve the above two problems by advance use of remote sensing techniques and climate modeling. Specifically, this work is divided into two parts. Part one deals with obtaining the skin temperature diurnal cycle for cloud-free cases. We have developed a "cloud-free algorithm" to combine model results with satellite and surface-based observations, thus interpolating satellite twice-daily observations to the diurnal cycle. Part two studies the cloudy cases. The "cloudy-pixel treatment" presented here is a hybrid technique of "neighboring-pixel" and "surface air temperature" approaches. The whole algorithm has been tested against field experiments and climate model CCM3/BATS in global and single column mode simulations. It shows that this proposed algorithm can obtain skin temperature diurnal cycles with an accuracy of 1-2 K at the monthly pixel level.
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5

Walsh, Stephen Anthony. "Between the Arctic & the Adriatic: Polar Exploration, Science & Empire in the Habsburg Monarchy." Thesis, Harvard University, 2014. http://nrs.harvard.edu/urn-3:HUL.InstRepos:13070045.

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Exploration was a defining aspect of how European societies encountered and established relations with the wider world. It set the stage for worldwide empires and laid the foundations for understandings of planetary existence. Exploration facilitated the exchange of commodities and ideas, the migration of peoples and the construction of scientific knowledge. This dissertation examines the nexus between ice and imperium through a study of how citizens of the Habsburg Monarchy contributed to polar exploration. In the long nineteenth century, the two main objects of European exploration were Africa and the polar regions. In the former, the dynamic between exploration and empire was fairly straightforward. But how did imperialism function in the frozen, uninhabited, latitudes of the world? This question becomes more problematic for the Habsburg Monarchy, a multinational polity with eleven officially recognized languages, and a self-professed empire that was the one European "Great Power" at the time without overseas colonies. This dissertation analyzes how the symbology and practice of polar exploration was used in the service of sundry - and frequently contradictory - political projects, including various nationalist activisms, Habsburg loyalism, and the liberal politics of notables. The analysis incorporates a case study in the convoluted road between discovery and empire, Franz Josef Land, the northernmost terrain in Eurasia, discovered by an Austro-Hungarian expedition in 1873. This dissertation then traces fractures within the Austro-Hungarian culture of exploration, as explorer/scientists could reach little consensus on the goals and practices for expeditions to the farthest latitudes of the globe. Finally, it examines how the rise of mass-data driven inductive sciences, such as geomagnetism, caused a fundamental redefinition in the practice of polar research toward a model of corporate, coordinated scientific effort and transnational cooperation. With the emergence of nation states and colonial empires, the basic frameworks of sovereignty, legitimacy and political meaning were changing and this study highlights how Habsburg subjects contributed to these modernization processes. In so doing, it brings to light neglected but lasting aspects of nineteenth century imperialism and treats both nationalism and empire as research problems rather than given ends.
History
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6

Davis, Jason Michael. "Reconsidering Antarctic Bioprospecting through Territorialities of Science, Property, and Governance." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1299535648.

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7

Becerra, Patricio, and Patricio Becerra. "The Poles of Mars, Past and Present: A High-Resolution Observational Study of the Martian Polar Regions and their Connection to Climate." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/621066.

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The poles of Mars, much like Earth's polar regions, are covered by kilometer-thick sheets of ice that interact with the Martian atmosphere and can record climatic changes in their stratigraphy. These polar caps are composed of several icy sections that interact with the Martian environment over different timescales. This dissertation describes my investigation of two of these units: The South Polar Residual Cap (SPRC), and the North Polar Layered Deposits (NPLD). The overarching theme of my work is to explore the connections between these caps and the current (SPRC) and past (NPLD) climate of Mars using a wide variety of data from spacecraft missions, and applying numerical models of surface properties and processes to interpret the observations. The SPRC is a ~10 meter thick slab of bright carbon dioxide ice that is covered by pits and scarps formed by differential sublimation. It is unclear whether this cap is in a state of net accumulation or net ablation. During the summer of Mars Year 28 (2006/2007), The High Resolution Imaging Science Experiment (HiRISE) observed an apparent increase in brightness near the edges of these pits that had not been seen before, and was not seen in the few years following. I analyzed hundreds of images from HiRISE and the Mars Orbiter Camera (MOC), as well as data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) to search for compositional and/or grain-size changes in the ice that could explain these "halos". I coupled my observations with numerical modeling of the spectral reflectance of the ice, to explore the effects of different ice grain sizes and minuscule dust inclusions on the observed brightness. I concluded that the features were caused by the occurrence of a global dust storm, after which the depositing dust actually acted to darken the SPRC. The halos were thus areas that had been kept relatively "clean" of the depositing dust, thanks to winds driven by enhanced sublimation from the pit walls. The fact that the halos did not show up in subsequent years means that they had not been exhumed, and that flat areas of the SPRC are in a state of net accumulation. It is likely that events like these result in new flat surfaces formed by snowfall driven by the depositing dust, which could explain the persistence of the cap throughout history. The polar layered deposits (PLD) are kilometer-thick stratified dome structures composed of dusty water ice that make up the bulk of the polar caps. The layers that make up the PLD are thought to record climatic variations over timescales of millions of years, in a similar way to Earth's ice caps. These caps are dissected by deep troughs that allow us to observe outcrops of their internal layers and map the stratigraphy. In the past, researchers have done this using layer brightness. However, remotely observed brightness has been shown to be affected by many external factors and may not represent an intrinsic property of the layers. Using Digital Terrain Models (DTM) made from HiRISE stereo images of NPLD outcrops, I mapped the change with depth of each layer's topographic protrusion from the scarp slope, defining the stratigraphy with a property related to the layers' resistance to erosion. I mapped the protrusion stratigraphy of 16 sites throughout the NPLD, and correlated the stratigraphic profiles from a subset of these sites, with Context Camera (CTX) images and signal-matching algorithms. This correlation combined topographic information with brightness information, resulting in an improvement of the current state of stratigraphic mapping of the NPLD, providing further evidence that layer sequences are continuous across the NPLD, and setting lower limits on relative accumulation rates for large sections of the cap.In order to search for a connection between the Martian paleoclimate and the NPLD stratigraphic record, I identified overlapping periodicities in the stratigraphic structure and compared them to periodicities in the climatic history, represented by the change in insolation with time at the North Pole over the last 5 Myr. I found that the ratio of stratigraphic wavelengths is systematically lower than the ratio between dominant modes of oscillation of the north polar insolation. However, a similar wavelet analysis of synthetic stratigraphic profiles created with a simple climate-driven model of accumulation revealed that a detectable non-linear relationship exists between the variation of insolation on the North Polar region of Mars and the stratigraphic record preserved in the NPLD. The dissertation is organized into four principal chapters and one final chapter with concluding remarks and future directions. Chapter 1 gives an introduction to Mars' polar regions and to the history of research in astronomically forced climate change through cyclostratigraphy, along with a short summary of the scope and main questions of this study. Chapter 2 details my study of the SPRC halos. Chapter 3 deals with the stratigraphic mapping of the NPLD through high-resolution topography, and Chapter 4 presents the results of my search for an astronomical forcing signal in the NPLD stratigraphy. Chapter 2 was published in the journal Icarus, in a special issue on the dynamic geologic processes of Mars and the science learned from continuous monitoring of these processes through remote sensing. Chapter 3 has been accepted for publication in the Journal of Geophysical Research. A modified version of Chapter 4 will be submitted to Nature Geoscience.
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8

Mancini, Duane Joseph. "Large Scale Synthesis of Amphiphiles for Biological Use and Analytical Profile of Polar Extracts from Mastic Gum." University of Toledo Health Science Campus / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=mco1404224303.

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9

Okunev, Oleg. "Observations and modeling of polar faculae on the sun." Doctoral thesis, [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=975320157.

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10

Finnie, Sean McIlwain. "Wheat polar lipids : sources of variation among near-isogenic wheat lines with different endosperm hardness." Diss., Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/1384.

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11

Jones, Megan E. "Sixty Years of Widespread Warming in the Southern Mid- and High-Latitudes (1957-2016)." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1525542816174135.

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12

Bonev, Boncho Peichev. "Towards a chemical toxonomy of comets : infrared spectroscopic methods for quantitative measurements of cometary water (with an independent chapter on Mars polar science) /." See Full Text at OhioLINK ETD Center (Requires Adobe Acrobat Reader for viewing), 2005. http://www.ohiolink.edu/etd/view.cgi?toledo1133980701.

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Thesis (Ph. D.)--University of Toledo, 2005.
Typescript. "A dissertation [submitted] as partial fulfillment of the requirements of the Doctor of Philosophy degree in Physics." Includes bibliographical references (leaves 295-304).
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13

Bonev, Boncho P. "Towards a Chemical Taxonomy of Comets: Infrared Spectroscopic Methods for Quantitative Measurements of Cometary Water (With an Independent Chapter on Mars Polar Science)." University of Toledo / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1133980701.

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14

Zhou, Albert Lihong. "Bioactivities of Milk Polar Lipids in Influencing Intestinal Barrier Integrity, Systemic Inflammation, and Lipid Metabolism." DigitalCommons@USU, 2013. http://digitalcommons.usu.edu/etd/1517.

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The purpose of lactation is for nutrient provision and also importantly for protection from various environmental stressors. Milk polar lipids reduce cholesterol, protect against bacterial infection, reduce inflammation and help maintain gut integrity. Dynamic interactions within dietary fat, lipid metabolism, gut permeability and inflammatory cytokines remain unclear in the context of obesity and systemic inflammation. A rat model and three mouse models were developed to test the hypotheses that dietary milk polar lipids may affect lipid metabolism and intestinal integrity and may protect against systemic inflammation in the context of stressful diet, systemic inflammation, and obesity. The milk polar lipids isolates had complex effects on lipid metabolism and associated gene expression in the rat model. There were complex dynamics in lipid metabolism, gut permeability and systemic inflammation at different time points in all mouse models. The milk phospholipids increased gut permeability in genetic and diet-induced obesity and during the lipopolysaccharide (LPS) -induced inflammation. The phospholipids increased the plasma LPS level in genetic obesity and during the LPS stress. The phospholipids reduced liver mass and liver lipids in genetic obesity and during the LPS-induced inflammation. The phospholipids increased the body fat in the diet-induced obesity model. The milk gangliosides did not significantly affect gut permeability, systemic inflammation, and lipid metabolism in all three mouse models. Current estimate by the Centers for Disease Control is that about 1/3 Americans are obese (body mass index, BMI ≥ 30) and 1/3 Americans are overweight (25 ≤ BMI < 30). More than 25% of Americans today have a fatty liver which could lead to further health problems. The data from this dissertation shed light on the complicated interrelationships between gut permeability, systemic inflammation, and lipid metabolism in obesity. The results contribute to our understanding of the bioactivities of milk polar lipids and provide scientific evidence for the role of milk polar lipids rich materials in affecting biological functions. The study of the influence of milk polar lipids on gut barrier integrity adds new information on understanding the mechanisms of gut leakiness and recovery. The investigation of the impact of milk polar lipids on lipid metabolism reveals new perspectives for the development of diet-induced obesity.
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15

Seibel, Harry Andrew II. "Psuedo-Oxides: Property Tailoring Through the Integration of Nitrogen and Fluorine." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1250624527.

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16

Popendorf, Kimberly J. (Kimberly Julia). "Marine microbial intact polar diacylglycerolipids and their application in the study of nutrient stress and bacterial production." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/79293.

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Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), February 2013.
"February 2013." Cataloged from PDF version of thesis.
Includes bibliographical references.
Intact polar diacylglycerolipids (IP-DAGs) were used to study microbial dynamics in the surface ocean. IP-DAGs from surface ocean seawater were quantified using high performance liquid chromatography-mass spectrometry (HPLC-MS), after first developing a sensitive, high throughput molecular ion independent triple quadrupole MS method for quantification. Using this analytical technique I examined the distribution of the nine most abundant classes of IPDAGs across the Mediterranean, and found that phospholipids as a percent of total IP-DAGs correlated with phosphate concentration. Furthermore, phospholipids were a higher percent of total particulate phosphorus where phosphate was higher, ranging from 1-14%. Thus IP-DAGs can play not only a significant but also a dynamic role in defining planktonic nutrient needs and cellular C:N:P ratios in the environment. Additionally, microcosm incubations were amended with phosphate and ammonium, and in the course of several days this elicited a shift in the ratios of IP-DAGs. This study was the first to demonstrate the dynamic response of membrane lipid composition to changes in nutrients in a natural, mixed planktonic community, and indicated that the change in IP-DAG ratios in response to changing nutrients may be a useful indicator of microbial nutrient stress. In the surface waters of the western North Atlantic I used three experimental approaches to identify the microbial sources of the nine most abundant classes of IP-DAGs. Phytoplankton are the primary source of one class of sulfolipid, sulfoquinovosyldiacylglycerol, and one class of betaine lipid, diacylglyceryl-trimethyl-homoserine, while heterotrophic bacteria are the dominant source of the phospholipids phosphatidylglycerol and phosphatidylethanolamine. In regrowth experiments in the Sargasso Sea and the North Pacific I demonstrated that phospholipid specific production rate is representative of heterotrophic bacterial cell specific growth rate. I measured phospholipid specific production rate and bacterial production rate using uptake of 3H-leucine (³H-Leu) and 3H-thymidine (³H-TdR) across the North Atlantic, across the Mediterranean, and in the North Pacific subtropical gyre. I found that phospholipid specific production rates estimate heterotrophic bacterial cell specific growth rates that are on the order of 1 per day, an order of magnitude faster than cell specific growth rates suggested by uptake of ³H-Leu and ³H-TdR.
by Kimberly J. Popendorf.
Ph.D.
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17

Suciu, Loredana G. "Indirect Determination of Integrated Chlorine and Bromine Concentration from Hydrocarbons in Barrow, Alaska." Ohio University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1179950576.

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18

Henri, Dominique. "Managing nature, producing cultures : Inuit participation, science and policy in wildlife governance in the Nunavut Territory, Canada." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:2cde7bcb-4818-4f61-9562-179b4ee74fee.

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In this thesis, a critical analysis is proposed of the relationships between Inuit participation, science and policy in wildlife governance in the Nunavut Territory, Canada. This analysis situates the emergence of a participatory regime for the governance of wildlife in Nunavut, explores its performance and examines the relations between the ways in which wildlife governance arrangements are currently represented in policy and how they are played out in practice across the territory. To pursue these objectives, this research draws upon a number of theoretical perspectives and methodological strategies poised at a crossroads between environmental geography, science and technology studies, political ecology and ecological anthropology. It combines participant observation, semi-directed interviews and literature-based searches with approaches to the study of actor-networks, hybrid forums and scientific practices associated with Latour and Callon, as well as with Foucauldian and post-Foucauldian analyses of power, governmentality and subjectivity. This analysis suggests that the overall rationale within which wildlife governance operates in Nunavut remains largely based on a scientific and bureaucratic framework of resource management that poses significant barriers to the meaningful inclusion of Inuit views. In spite of their participation in wildlife governance through a range of institutional arrangements, consultation practices and research initiatives, the Inuit of Nunavut remain critical of the power relations embedded within existing schemes, where significant decision-making authority remains under the control of the territorial (or federal) government, and where asymmetries persist with regard to the capacity of various actors to produce and mediate their claims. In addition, while the use of Inuit knowledge, or Inuit Qaujimajatuqangit, in wildlife governance in Nunavut has produced some collaborative research and management endeavours, it has also crystallised a divide between ‘Inuit’ and ‘scientific’ knowledge, generated unresolved conflicts, fuelled mistrust among wildlife co-management partners and led to an overall limited inclusion of Inuit observations, values and beliefs in decision-making.
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19

Tulip, David F. "Preservice primary teachers' constructions of themselves as science teachers." Thesis, Queensland University of Technology, 1999. https://eprints.qut.edu.au/36598/1/36598_Digitised%20Thesis.pdf.

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The research reported in this thesis investigated preservice primary teachers' constructions of themselves as science teachers. This was done in response to Seddon' s (1991) claim that an approach to teaching the science component of a preservice Bachelor of Education course should be proposed that was congruent with preservice teachers' beliefs about themselves as science teachers. The nature of the research undertaken was interpretive and conversational. It was set in a context of postmodern students in contemporary universities and depended upon preservice teachers sharing their beliefs about themselves with the researcher. To achieve this end and elicit substantive data from individuals, that is, beliefs that affect individuals' behaviour in a consistent manner, the research was couched within a framework of Personal Construct Theory (Kelly, 1955/1991). A variety of data collection methods were used, including characterisation sketches, career snakes, repertory grids, semi-structured interviews, and questionnaires. The data received from these sources were reduced through processes of classification to produce profiles of hierarchical personal characteristics for each of the twelve preservice teachers who volunteered to take part in the project. During the collection and classification processes data were triangulated and personal profiles were memberchecked to establish trustworthiness. Based on the Commonality and Sociality Corollaries of Personal Construct Theory (Kelly, 1955/1991) and precedents well established in curriculum development and text writing, the researcher construed the commonalities between individuals' profiles to propose a profile of personal characteristics for a hypothetical preservice primary teacher. This construction was used as a platform from which to propose an approach to teaching science to preservice primary teachers that would be congruent with individual's beliefs about themselves as science teachers. Because of the nature of this derived profile and the manner in which it corresponded with conclusions reached by Shulman (1986, 1987a), the approach to teaching that was adopted was based on Shulman's (1987a) model of pedagogical reasoning and action. Importantly, this approach to teaching science is not prescriptive. It provides science educators with opportunities to recognise and build upon their preservice teacher students' prior experiences, to cater for a wide diversity of personalities, pedagogical skills and interests in science and science teaching, and, most importantly, to treat preservice teachers as social actors. These are conditions that Seddon (1991) claimed would be essential ifthe science pedagogical ideals of tertiary primary teacher education are ever to survive the transition from tertiary studies to primary classroom teaching practices.
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20

Nath, de Oliveira Daniela. "Thermal properties of starch from transgenic isolines of wheat differing in starch surface components." Thesis, Kansas State University, 2010. http://hdl.handle.net/2097/4319.

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Master of Science
Department of Grain Science and Industry
Jon M. Faubion
Endosperm texture is an important characteristic in determining wheat processing and end-use. The presence of puroindoline proteins on the starch surface is the biochemical marker for wheat hardness. Near-isogenic samples over expressing puroindolines have been used to assess the effect of wheat hardness on final product characteristics. The objective of this study was to determine differences among starch isolated from near-isogenic samples and to investigate the role starch surface components play in pasting. The use of near-isogenic samples over expressing puroindolines combined with the use of two methods of starch isolation (batter and dough) was an effective means to create samples with varied amounts of surface components. Starch thermal properties were characterized and surface proteins and lipids were quantified. Starch isolated from hard wheat cultivars presented more similarities with starch isolated from its soft near-isogenic line when a dough method was used than when a batter method was used. Starch from soft experimental lines isolated using a batter method showed increased MVA peak viscosity, breakdown and swelling power. Increased levels of LysoPC in starch isolated from hard wheat cultivars or soft experimental lines by dough method could have complexed with amylose and restricted granule swelling. Thereby, decreasing peak viscosity, breakdown and swelling power.
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21

Haines, Wesley Adam. "Acceleration of the Weather Research & Forecasting (WRF) Model using OpenACC and Case Study of the August 2012 Great Arctic Cyclone." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1373472482.

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22

Smith, Erik T. "HISTORICAL AND FUTURE CHANGES IN COLD AIR OUTBREAKS ACROSS THE GLOBE AND THE INFLUENCE OF ATMOSPHERIC TELECONNECTIONS." Kent State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=kent1615739656563986.

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23

Cheng, Jian. "Estimation and Processing of Ensemble Average Propagator and Its Features in Diffusion MRI." Phd thesis, Université Nice Sophia Antipolis, 2012. http://tel.archives-ouvertes.fr/tel-00759048.

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L'IRM de diffusion est a ce jour la seule technique a meme d'observer in vivo et de fac¸on non-invasive les structures fines de la mati'ere blanche, en modelisant la diffusion des molecules d'eau. Le propagateur moyen (EAP pour Ensemble average Propagator en anglais) et la fonction de distribution d'orientation (ODF pour Orientation Distribution Function en anglais) sont les deux fonctions de probabilites d'int'erˆet pour caracteriser la diffusion des molecules d'eau. Le probleme central en IRM de diffusion est la reconstruction et le traitement de ces fonctions (EAP et ODF); c'est aussi le point de depart pour la tractographie des fibres de la mati'ere blanche. Le formalisme du tenseur de diffusion (DTI pour Diffusion Tensor Imaging en anglais) est le modele le plus couramment utilise, et se base sur une hypothese de diffusion gaussienne. Il existe un cadre riemannien qui permet d'estimer et de traiter correctement les images de tenseur de diffusion. Cependant, l'hypothese d'une diffusion gaussienne est une simplification, qui ne permet pas de d'écrire les cas ou la structure microscopique sous-jacente est complexe, tels que les croisements de faisceaux de fibres. L'imagerie 'a haute resolution angulaire (HARDI pour High Angular Resolution Diffusion Imaging en anglais) est un ensemble de methodes qui permettent de contourner les limites du modele tensoriel. La plupart des m'ethodes HARDI 'a ce jour, telles que l'imagerie spherique de l'espace de Fourier (QBI pour Q-Ball Imaging en anglais) se basent sur des hypoth'eses reductrices, et prennent en compte des acquisitions qui ne se font que sur une seule sphere dans l'espace de Fourier (sHARDI pour single-shell HARDI en anglais), c'est-a-dire une seule valeur du coefficient de ponderation b. Cependant, avec le developpement des scanners IRM et des techniques d'acquisition, il devient plus facile d'acquerir des donn'ees sur plusieurs sph'eres concentriques. Cette th'ese porte sur les methodes d'estimation et de traitement de donnees sur plusieurs spheres (mHARDI pour multiple-shell HARDI en anglais), et de facon generale sur les methodes de reconstruction independantes du schema d'echantillonnage. Cette these presente plusieurs contributions originales. En premier lieu, nous developpons l'imagerie par transformee de Fourier en coordonnees spheriques (SPFI pour Spherical Polar Fourier Imaging en anglais), qui se base sur une representation du signal dans une base de fonctions a parties radiale et angulaire separables (SPF basis pour Spherical Polar Fourier en anglais). Nous obtenons, de fac¸on analytique et par transformations lineaires, l'EAP ainsi que ses caracteristiques importantes : l'ODF, et des indices scalaires tels que l'anisotropie fractionnelle generalisee (GFA pour Generalized Fractional Anisotropy en anglais). En ce qui concerne l'implementation de SPFI, nous presentons deux methodes pour determiner le facteur d'echelle, et nous prenons en compte le fait que E(0) = 1 dans l'estimation. En second lieu, nous presentons un nouveau cadre pour une transformee de Fourier analytique en coordonnees spheriques (AFT-SC pour Analytical Fourier Transform in Spherical Coordinate en anglais), ce qui permet de considerer aussi bien les methodes mHARDI que sHARDI, d'explorer les relations entre ces methodes, et de developper de nouvelles techniques d'estimation de l'EAP et de l'ODF. Nous presentons en troisieme lieu d'importants crit'eres de comparaison des differentes methodes HARDI, ce qui permet de mettre en lumiere leurs avantages et leurs limites. Dans une quatrieme partie, nous proposons un nouveau cadre riemannien invariant par diffeomorphisme pour le traitement de l'EAP et de l'ODF. Ce cadre est une generalisation de la m'ethode riemannienne precedemment appliquee au tenseur de diffusion. Il peut etre utilise pour l'estimation d'une fonction de probabilite representee par sa racine carree, appelee fonction d'onde, dans une base de fonctions orthonormale. Dans ce cadre riemannien, les applications exponentielle et logarithmique, ainsi que les geodesiques ont une forme analytique. La moyenne riemannienne ponderee ainsi que la mediane existent et sont uniques, et peuvent etre calculees de facon efficace par descente de gradient. Nous developpons egalement un cadre log-euclidien et un cadre affine-euclidien pour un traitement rapide des donnees. En cinquieme partie, nous comparons, theoriquement et sur un plan exp'erimental, les metriques euclidiennes et riemanniennes pour les tenseurs, l'ODF et l'EAP. Finalement, nous proposons l'anisotropie geodesique (GA pour Geodesic Anisotropy en anglais) pour mesurer l'anisotropie de l'EAP; une parametrisation par la racine carrée (SRPE pour Square-Root Parameterized Estimation en anglais) pour l'estimation d'un EAP et d'une ODF positifs; la mediane et la moyenne riemanniennes ponderees pour l'interpolation, le lissage et la construction d'atlas bas'es sur l'ODF et de l'EAP. Nous introduisons la notion de valeur moyenne raisonnable pour l'interpolation de fonction de probabilites en general.
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24

Smith, Erik T. "The Characteristics of Cold Air Outbreaks in the eastern United States and the influence of Atmospheric Circulation Patterns." Kent State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=kent1499870942487366.

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25

Seal, Gavin J. "Morphisms of polar spaces and related structures." Doctoral thesis, Universite Libre de Bruxelles, 2000. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211809.

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26

Ashraf, Hina. "Investigation of the Symmetries of the Phonons in 4H and 6H-SiC by Infrared Absorption and Raman Spectroscopy." Thesis, Linköping University, The Department of Physics, Chemistry and Biology, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-6079.

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The goal of the project work has been to study the symmetry of the phonons in 4H and 6H-SiC for different measuring geometries by using two experimental techniques, Raman and infrared absorption (IR) spectroscopy, and a theoretical model. The Raman spectra were measured in different scattering configurations in order to obtain experimental data for detailed investigation of the phonon symmetries.

The gross features of the spectra obtained in different geometries can be explained using general group-theoretical arguments. Using a lattice-dynamics model, we have also calculated the angular dependence of the phonon energies near the centre of the Brillouin zone, as well as the phonon displacements in some high-symmetry directions. The theoretical results are used to interpret the Raman lines in different configurations, and it was possible to estimate that if ionicity of the bonding of 12% is taken in the theoretical model for 4H-SiC, the splitting of the polar TO mode and the shift of the polar LO mode observed in our spectra are well reproduced theoretically. It was also observed that these polar modes have to be classified as longitudinal and transversal with respect to the direction of phonon wave vector, while the rest of the modes remain longitudinal or transversal with respect to the c-axis of the crystal. The Raman lines in the case of 4H SiC have been tentatively labelled with the irreducible representations of the point group of the crystal (C6v).

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27

O'Neill, Morgan E. "A theory for polar cyclones on giant planets." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/97335.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2015.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 135-145).
features, with a deep, hot and rapid cyclone situated directly over each pole, and a rapid jet marking the cyclone boundary at 3° from the pole. Extant theories for the zonal jets preclude the possibility of a jet at such high latitudes. This thesis proposes and tests a moist convective hypothesis for polar cyclone formation. Using purely baroclinic forcing, with statistical characteristics motivated by moist convection observed on Jupiter and Saturn, a robust tendency to form a barotropic polar cyclone is identified. A 2 1/2 layer shallow water model is built to test our hypothesis. An 11-dimensional parameter space is explored to determine the most importance controls on cyclone formation. Two sets of experiments are performed: 1) Barotropic and baroclinic 'storms' are briefly forced and then allowed to freely evolve on the polar beta plane, and 2) Forced-dissipative simulations are run, with periodic and randomly placed storms, until statistical equilibrium is reached. Results confirm the well known tendency of positive vorticity anomalies to self-advect poleward if they are intense enough for nonlinear advection to be significant. Likewise, strong negative vorticity anomalies move equatorward. Simulations span several orders of magnitude of energy density, ranging from weak wave-dominated flows to strong cyclones that experience instabilities. We find that a range of behavior, including what is observed on all four giant planets as well as previous simulation studies, can be expressed by varying only 2 nondimensional control parameters: a second baroclinic deformation radius scaled by the planetary radius, LD2=a; and a total energy parameter Êp that scales with the kinetic+potential energy density of the system at statistical equilibrium. In the context of an idealized model, the difference between Jupiter's and Saturn's polar flow regimes may be explained by their different planetary and deformation radii.
by Morgan E. O'Neill.
Ph. D.
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28

Tarnoff, David. "Episode 3.11 – Polar and Bipolar Line Coding." Digital Commons @ East Tennessee State University, 2020. https://dc.etsu.edu/computer-organization-design-oer/27.

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In this episode, we continue our discussion of line codes by examining five schemes used with polar and bipolar signaling: NRZ-L, NRZ-I, RZ-AMI, Manchester, and differential Manchester. We also discuss differential coding and its benefits.
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29

Rosenqvist, Tobias, and Joël Sloof. "Implementation and evaluation of Polar Codes in 5G." Thesis, Karlstads universitet, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-72467.

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In today’s society the ability to communicate with one another has grown, were a lot of focus is aimed towards speed in the telecommunication industry. For transmissions to become even faster, there are many ways to enhance transmission speeds of which error correction is one. Padding messages such that they are protected from noise, while using as few bits as possible and ensuring safe transmit is handled by error correction codes. Short codes with low complexity is a solution to faster transmission speeds. An error correction code which has gained a lot of attention since its first appearance in 2009 is Polar Codes. Polar Codes was chosen as the 3GPP standard for 5G control channel. The goal of the thesis is to develop and implement Polar Codes and rate matching according to the 3GPP standard 38.212. Polar Codes are then to be evaluated with different block sizes and rate matching settings. Finally Polar Code is compared with Convolutional code in a LTE-simulation environment. The performance evaluations are presented using BLER/(Eb/N0)-graphs. In this thesis a Polar encoder, rate matching and a Polar decoder (with Successive Cancellation algorithm) were successfully implemented. The simulation results show that Polar Codes performs better with longer block sizes and also has a better BLER-performance than Convolutional Codes when given the same message lengths.
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30

Achtert, Peggy. "Lidar Measurements of Polar Stratospheric Clouds in the Arctic." Doctoral thesis, Stockholms universitet, Meteorologiska institutionen (MISU), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-88054.

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Polar Stratospheric Clouds (PSCs) play a key role for ozone depletion in the polar stratosphere. Its magnitude depends on the type of PSC and its lifetime and extent. This thesis presents PSC observations conducted with the Esrange lidar and the space-borne CALIPSO lidar. PSCs are separated into three types according to their optical properties. The occurrence rate of the different types which are often observed simultaneously as well as their interaction and connection is not well understood. To better understand the processes that govern PSC formation, observations need to be combined with a detailed view of the atmospheric background in which PSCs develop, exist, and are transformed from one type to another. This thesis introduces a new channel of the Esrange lidar for temperature profiling at heights below 35 km. The design of this channel and first temperature measurements within PSCs and cirrus clouds are presented. This is an important step since the majority of PSC-related literature extracts temperatures within PSCs from reanalysis data. In contrast to ground–based measurements space–borne lidar does not rely on cloud–free conditions. Hence, it provides an unprecedented opportunity for studying the connection between PSCs and the underlying synoptic–scale conditions which manifest as tropospheric clouds. This thesis shows that most of the PSCs observed in the Arctic during winter 2007/08 occurred in connection with tropospheric clouds. A combined analysis of ground-based and space-borne lidar observation of PSCs in combination with microphysical modeling can improve our understanding of PSC formation. A first case study of this approach shows how a PSC that was formed by synoptic-scale processes is transformed into another type while passing the Scandinavian mountains. Today a variety of classification schemes provides inconsistent information on PSC properties and types. This thesis suggests a unified classification scheme for lidar measurements of PSCs.

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Submitted. 

 

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Zhang, Hengfang. "Hot-wall MOCVD of N-polar group-III nitride materials." Licentiate thesis, Linköpings universitet, Halvledarmaterial, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-175502.

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Group III-Nitride semiconductors: indium nitride (InN), gallium nitride (GaN), aluminum nitride (AlN) and their alloys continue to attract significant scientific interest due to their unique properties and diverse applications in photonic and electronic applications. Group-III nitrides have direct bandgaps which cover the entire spectral range from the infrared (InN) to the ultraviolet (GaN) and to the deep ultraviolet (AlN). This makes III-nitride materials suitable for high-efficient and energy-saving optoelectronic devices, such as light-emitting diodes (LEDs) and laser diodes (LDs). The Nobel Prize in Physics 2014 was awarded for the invention of efficient GaN blue LEDs, which further accelerated the research in the field of group III-nitride materials. GaN and related alloys are also suitable for high-temperature, high-power and high-frequency electronic devices with performance that cannot be delivered by other semiconductor technologies such as silicon (Si) and gallium arsenide (GaAs). For example, GaN-based high electron mobility transistors (HEMTs) have been widely adopted for radio frequency (RF) communication and power amplifiers, high-voltage power switches in radars, satellites, and wireless base stations for 5G.  Recently, nitrogen (N)-polar group-III nitrides have drawn much attention due to their advantages over their metal-polar counterparts in e.g. HEMTs. These include feasibility to fabricate ohmic contacts with low resistance, an enhanced carrier confinement with a natural back barrier, and improved device scalability. Despite intensive research, the growth of micrometer-thick high-quality N-polar GaN based materials remains challenging. One of the major problems to develop device-quality N-polar nitrides is the high surface roughness, which results from the formation of hexagonal hillocks or step-bunching. Another significant hurdle is the unintentional polarity inversion, which reduces the crystalline quality and prohibits device fabrication.  This licentiate thesis focuses on the development of N-polar AlN and GaN heterostructures on SiC substrates for HEMT RF applications. The overall aim is to exploit the advantages of the hot-wall MOCVD concept to grow high-quality N-polar HEMT structures for higher operational frequencies and improved device performance. In order to achieve this goal, special effort is dedicated to understanding the effects of growth conditions and substrate orientation on the structural properties and polarity of AlN, GaN and AlGaN grown by hot-wall MOCVD. N-polar AlN nucleation layers (NLs) with layer by layer growth mode and step-flow growth mode can be achieved on on-axis and 4_ offaxis SiC (000¯1), respectively, by carefully controlling V/III ratio and growth temperature. Utilizing scanning transmission electron microscopy (STEM) we have established a comprehensive picture of the atomic arrangements, local polarity and polarity evolution in AlN, GaN/AlN and AlGaN/GaN/AlN in the cases of low-temperature and high-temperature AlN NLs both for on-axis and off-axis substrates. We have shown that typically employed methods for polarity determination using potassium hydroxide wet etching could not provide conclusive results in the case of mixed-polar AlN as Al-polar domains may be easily over-etched and remain undetected. Atomic scale electron microscopy is therefore needed to accurately determine the polarity. We further have developed growth strategy and have optimized the epitaxial process for N-polar GaN, and have demonstrated high quality N-polar AlGaN/GaN/AlN heterostructures.

Additional funding agencies: Chalmers University of technology; ABB; Ericsson; Epiluvac; FMV; Gotmic; Saab; SweGaN; UMS; Swedish Foundation for Strategic Research under Grants No. FL12-0181, No. RIF14-055, and No. EM16-0024; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University, Faculty Grant SFO Mat LiU No.2009- 00971.

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32

Arrell, Russell 1975. "Implications of Martian polar insolation levels on the climatic cycling of volatiles." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/53045.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2000.
Includes bibliographical references (leaves 35-36).
Solar insolation at the poles is the driving force in Mars' seasonal climatic cycle. Mars' obliquity has varied greatly in the geologically recent past and this would have had a profound effect on the past climate. Previous studies have always assumed a spherical planet when calculating insolation. This study uses a geodetic elevation model (GEM) of the elevation data from the Mars Orbiter Laser Altimeter, to provide accurate insolation calculations. This method takes into account the long and shortwavelength topography, the planetary curvature, and the planetary flattening. This paper outlines the design and implementation of a GEM, and presents insolation calculations for Mar's north polar cap for obliquities of 150, 250 and 450. This study found that the elevation of the northern ice cap above the surroundings results in the ice cap having more days of sunlight than previously thought.
by Russell Arrell.
S.M.
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33

Evaratt, Matthew. "Stress ecophysiology of polar terrestrial invertebrates and the impact of climate change." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5020/.

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Terrestrial invertebrates are small poikilothermic ectotherms and are thus susceptible to chronic cold, rapid temperature change and desiccation. In the polar regions, where buffered microhabitat temperatures regularly fall below 0°C and water availability is low, they are particularly vulnerable. However, polar terrestrial invertebrates successfully exist within these climes. Using whole organism experimental techniques, this thesis aims to further understand the capacity of invertebrates to tolerate different stressors, the underpinning physiological adaptations, and the potential impact of continued climate change. For just the second time in a freeze-tolerant polar insect, rapid cold hardening is observed. Acclimation to sub-lethal low temperatures is also demonstrated, through depression of the critical thermal minimum (CTmin) and chill coma temperature. Contrasting strategies of desiccation tolerance vs. resistance are noted, as well as evidence of cross-tolerance to temperature stress. At the opposite extreme, water submergence experiments confirm the first example of an amphibious terrestrial midge. A remarkable capacity to tolerate high temperatures, including those that may occur as a result of climate change, is also observed. This body of work underscores the physiological flexibility of polar invertebrates, which allows them to flourish in environments considered too extreme and inhospitable for most terrestrial species.
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34

Biddle, M. B., S. E. Rickert, J. B. Lando, and André Laschewsky. "The use of the Langmuir-Blodgett technique to obtain ultra-thin polar films." Universität Potsdam, 1989. http://opus.kobv.de/ubp/volltexte/2009/1718/.

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The piezoelectric and pyroelectric properties of oriented films possessing dipole moments are increasingly being used in pressure, acoustic, thermal and optical devices. The performance of these devices in many applications may be enhanced by thin-film technology.The developing Langmuir-Blodgett thin-film deposition technique offers the opportunity to obtain highly oriented and uniform organic-based films in the 10–5000 nm thickness range. Special techniques must be used, however, to assemble these molecules in such a way as to result in polar multilayer films. Several possible deposition techniques are investigated, with one resulting in a polar and pyroelectric film about 50 nm thick.
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35

Carron, Delphine. "Figures du détective dans le polar américain contemporain." Phd thesis, Université d'Angers, 2013. http://tel.archives-ouvertes.fr/tel-00961471.

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Le polar américain contemporain se pose en continuité et en rupture avec l'âge d'or des années 1930-1950 en reprenant les codes et représentations mythiques du hard-boiled et du modèle anglais pour les confronter au monde contemporain. A la ville des années 1930, terrain privilégié du détective progressant méthodiquement vers la clé de l'énigme, s'oppose l'univers urbain contemporain - New York et plus particulièrement Brooklyn - au coeur duquel l'énigme initiale reste sans véritable dénouement. Les méthodes traditionnelles n'ont plus cours, laissant place à l'incertitude et au doute ; il n'est plus question de héros triomphant contre le Mal au coeur de l'univers urbain, mais des efforts d'un détective perdu dans sa propre fragmentation. Ainsi, la focalisation ne porte plus sur l'aboutissement de l'enquête mais sur la quête interne du détective qui, avant même d'élucider le mystère, est d'abord en quête de lui-même. Le polar d'avant-garde sous toutes ses formes, et en particulier la bande dessinée et le roman, détrône le statut mythique du détective pour en proposer de multiples figures, prétextes à la redéfinition des codes bien connus du genre et à l'exploration métaphysique du monde contemporain.
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36

Sheshadri, Aditi. "Variability of the polar stratospheric vortex and its impact on surface climate patterns." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98674.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, June 2015.
Cataloged from PDF version of thesis. "June 2015."
Includes bibliographical references (pages 133-145).
This thesis investigates various aspects of the variability of the stratospheric polar vortex and the effect of this variability on tropospheric weather and climate patterns on various timescales. In the first part of this work, an improved idealized model was developed to study the coupled stratosphere-troposphere system. The model is forced by relaxation to a specified equilibrium temperature profile, which varies seasonally only in the stratosphere. This model setup permits the investigation of stratosphere-troposphere interactions on seasonal timescales, without the complication of an internal tropospheric seasonal cycle. The model is forced with different shapes and amplitudes of simple bottom topography, resulting in a range of stratospheric climates. The effect of these different kinds of topography on the seasonal variability of the strength of the polar vortex, the average timing and variability in timing of the final breakup of the vortex (final warming events), the conditions of occurrence and frequency of midwinter warming events, and the impact of the stratospheric seasonal cycle on the troposphere are explored. The inclusion of wavenumber 1 and wavenumber 2 topographies results in very different stratospheric seasonal variability. Hemispheric differences in stratospheric seasonal variability are recovered in the model with appropriate choices of wave-2 topography. In the model experiment with a realistic Northern Hemisphere-like frequency of midwinter warming events, the distribution of the intervals between these events suggest that the model has no year to year memory. When forced with wave-1 topography, the gross features of seasonal variability are similar to those forced with wave-2 topography, but the dependence on forcing magnitude is weaker. Further, the frequency of major warming events has a non-monotonic dependence on forcing magnitude, and never reaches the frequency observed in the northern hemisphere. In the second part of the thesis, the impact of stratospheric ozone depletion on the Antarctic polar vortex and its subsequent influences on southern hemisphere surface climate patterns is investigated. It is verified that stratospheric final warming events have an impact on tropospheric circulation in a simplified GCM with seasonal variations in the stratosphere only. The model produces qualitatively realistic final warming events whose influence extends down to the surface, much like what has been reported in observational analyses. The hypothesis that recent observed trends in surface westerlies in the Southern Hemisphere are directly consequent on observed trends in the timing of stratospheric final warming events is tested. It is confirmed that there is a statistically significant shift towards later final warming events in the years with large ozone depletion. However it is found that the observed trends in surface westerlies cannot be attributed simply to this shift towards later final warming events. Finally, responses of the idealized AGCM to polar stratospheric cooling that mimics the radiative effects of stratospheric ozone depletion are studied. It is found that there are two factors that play a role in setting the magnitude and persistence of the model's surface response to cooling: the seasonal cycle of tropospheric annular mode timescales, and whether or not the imposed cooling leads to the presence of stratospheric westerlies at a time when easterlies were prevalent in the control run. That is, the surface response is sensitive to the timing of the imposed polar stratospheric cooling.
by Aditi Sheshadri.
Ph. D.
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37

Smirnova, Maria. "Long-term observations of polar mesosphere summer echoes using the ESRAD MST radar." Doctoral thesis, Luleå tekniska universitet, Rymdteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18134.

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Polar Mesosphere Summer Echoes (PMSE) are strong radar echoes observed from altitudes of 80-90 km in polar regions, during summer time. PMSE are closely related to the fascinating atmospheric phenomenon known as noctilucent clouds (NLC). Since it has been suspected that NLC could respond to climate change in the mesosphere, they have attracted considerable interest in the scientific community during recent years. However, continuous visual or photographic NLC observations suffer from weather restrictions and the human factor. In contrast, PMSE radar measurements can easily be made over a long interval and are very attractive for long-term studies of the atmospheric parameters at the polar mesopause. This thesis uses the world’s longest data set of PMSE observations made by the same radar at the same place. Since 1997 these measurements have been carried out with the 52 MHz ESRAD MST radar located near Kiruna in Northern Sweden. The data set for 1997-2008 has been used for studies of diurnal, day-to-day and year-to-year variations of PMSE. We showed that PMSE occurrence rate and volume reflectivity on a daily scale show predominantly semidiurnal variations with the shape of the diurnal curves remaining consistent from year to year. We found that day-to-day and inter-annual variations of PMSE correlate with geomagnetic activity while they do not correlate with mesopause temperature or solar activity. We did not find any statistically significant trends in PMSE occurrence rate and length of PMSE season over 1997-2008. The thesis also presents also a new, independent calibration method, which can be used to estimate changes in transmitter output and antenna feed losses from year to year (for example due to changes of antenna configuration) and allows making accurate calculations of PMSE strength. This method is based on radar-radiosonde comparisons in the upper troposphere/lower stratosphere region simultaneously with PMSE observations. Using this calibration we calculated the distribution of PMSE strength over magnitudes; it varies from year to year with the peak of the distribution varying from 2×10−15 to 3×10−14 m−1. We found that inter-annual variations of PMSE volume reflectivity strongly correlate with the local geomagnetic k-index and anticorrelate with solar 10.7 cm flux. We did not identify any significant trend in PMSE volume reflectivity over 1997–2009. Finally, using 11 years of measurements, we calculated in-beam the PMSE aspect sensitivities using the FCA technique. We showed that half of PMSE detected each year cannot be explained by isotropic turbulence since they are highly aspect sensitive echoes. The distribution of these echoes remains consistent from year to year with median values of aspect sensitivity from 2.9 to 3.7°. The remaining half of the PMSE have aspect sensitivity parameters larger than 9-11°. We found that PMSE aspect sensitivity has altitude dependence: the scatter becomes more isotropic with increasing height. We did not identify any dependence of PMSE aspect sensitivity on backscattered power for any year. We analysed limitations of the in-beam and off-zenith beam methods and concluded that the former is suitable for highly aspect sensitive echoes while the latter is needed for more isotropic scatterers.

Godkänd; 2011; 20110926 (marsmi); DISPUTATION Ämnesområde: Rymdteknik/Space Technology Opponent: Professor Patrick Joseph Espy, Dep of Physics, Norwegian University of Science and Technology (NTNU), Trondheim, Norway, Ordförande: Docent Evgenia Belova, Swedish Institute of Spaces Physics, Kiruna Tid: Måndag den 31 oktober 2011, kl 10.00 Plats: Aulan, Swedish Institute of Spaces Physics, Kiruna

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Greenberg, Marc Samuel. "Defining Benthic Organism Exposure: Bioavailability and Effects of Non-Polar Organics." Wright State University / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=wright1074096654.

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39

Harris, Carolyn Louise. "Water mass distribution and Polar Front structure in the Southwestern Barents Sea." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/54421.

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, and Woods Hole Oceanographic Institution, 1996.
Includes bibliographic references (leaves 63-66). Includes bibliographical references (leaves 63-66).
by Carolyn Louise Harris.
M.S.
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40

Mount, Christopher P. "Spatial, temporal, and inter-annual variability of the Martian northern seasonal polar cap." Thesis, Northern Arizona University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1537795.

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Earth and Mars have nearly the same axial tilt, so seasons on these two bodies progress in a similar manner. During fall and winter on Mars, the primarily CO2 atmosphere (~95% by volume) condenses out onto the poles as ice. Approximately 25% of the entire Martian atmosphere condenses, and then sublimes in the spring, making this cycle a dominant driver in the global climate. Because the water and dust cycles are coupled to this CO2 cycle, we must examine seasonal CO2 processes to understand the global (seasonal) distribution of H2O on Mars. The density of the ice may indicate whether it condensed in the atmosphere and precipitated as “snow” or condensed directly onto the surface as “slab”. Variations in density may be controlled by geographic location and surface morphology. The distribution and variations in densities of seasonal deposits on the Martian poles gives us insight to the planet’s volatile inventories. Here we analyze density variations over time on Mars’ Northern Polar Seasonal Cap (NPSC) using observational data and energy balance techniques.

We calculate the bulk density of surface CO2 ice by dividing the column mass abundance (the mass of CO2 per unit area) by the depth of the ice cap at a given location. We use seasonal rock shadow measurements from High Resolution Imaging Science Experiment (HiRISE) images to estimate ice depth. The length of a rock’s shadow is related to its height through the solar incidence angle and the slope of the ground.

From differences in the height of a rock measured in icy vs. ice-free images, we estimate the depth of surface ice at the time of the icy observation. Averaging over many rocks in a region yields the ice depth for that region. This technique yields minimums for ice depth and therefore maximums for density.

Thermal properties of rocks may play an important role in observed ice depths. Crowns of ice may form on the tops of rocks with insufficient heat capacity to inhibit ice condensation, and may cause an artificial increase in shadow length. This increases the apparent height of a rock and thus decreases the apparent surface ice depth. Additionally, moats may form around rocks with sufficient heat capacity to sublime ice as it is deposited. Moating will also artificially increase the shadow lengths (decreasing apparent surface ice depth). We correct for these effects in our depth-estimation technique.

We balance incoming solar flux with outgoing thermal radiation from Thermal Emission Spectrometer (TES) observations to calculate the column mass abundance. TES thermal bolometer atmospheric albedo and temperature observations are a good proxy to the surface bond albedo and effective surface temperature. These parameters are needed to balance the incoming and outgoing flux.

Mars’ atmosphere is tenuous so we assume homogeneous radiance from the surface to the top of the atmosphere, no lateral diffusion of heat, and that any excess heat goes into subliming surface ice in our flux balance. Using a Monte Carlo model, we integrate the net flux until reaching the time where Cap Recession Observations indicate CO2 has Ultimately Sublimed (the CROCUS date) to obtain the column mass abundance.

We study seasonal ice at three distinct geomorphic units: plains, dune fields, and craters. Two plains regions, four dunes regions, and two crater regions are analyzed over springtime sublimation. Data for these regions spanned three Mars Years.

Our results indicate that the evolution of seasonally deposited CO 2 ice on the Northern Polar Cap of Mars is highly dependent on complex relationships between various processes. The grain size, dust contamination, water doping, and density vary dramatically over time. The initially deposited material varies according to local geomorphic features and topography, as well as latitude and longitude. The inter-annual variability of ice may play a role in its evolution over sublimation, but likely plays a smaller role than anticipated. Low normalized initial and time-averaged densities suggest that NPSC deposits are initially low and remain relatively low throughout spring. These densities are very similar to estimates made by previous studies. Thus, we conclude that the NPSC is indeed pervaded by low density deposits. These deposits densify over time, but rarely reach typical characteristics for pure slab ice.

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41

Jones, Matthew. "The social construction of a threatened species: a critical analysis of a polar bear discourse." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97131.

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The recent listing of the polar bear (Ursus maritimus) as 'threatened' under the United States Endangered Species Act occurred despite widespread debate about the validity of, and need for listing. In this thesis, I conduct a Critical Discourse Analysis on a prevalent discourse in the polar bear debate, that of the Center for Biological Diversity. I aim to denaturalize this discourse by addressing two key questions: How is this polar bear discourse constructed through texts? And, what are the broader discursive practices and sociocultural contexts supporting these texts? I find the Center for Biological Diversity's polar bear discourse is comprised of multiple constructs linked to broader discursive and sociocultural practices through four inextricably associated elements: a scientific, an ethical, a political and a metaphorical element. This discovery is of potential use to less powerful actors in the polar bear debate, like Inuit communities, because avenues may be created for critiquing dominant positions and for articulating their own.
Dans cette thèse, je réalise une analyse de discours critique concernant le débat de l'ours polaire; plus précisément, le discours du Centre de la Diversité Biologique sera analysé. Une vulgarisation de ce discours sera faite en en adressant deux questions clef : Comment est construit ce discours en forme textuelle? Quelles sont les pratiques discursives principales et quelles sont leurs contextes socioculturels qui supportent ces textes? Les résultats de mon analyse démontrent que le discours de l'ours polaire du Centre de la Diversité Biologique est construit de multiples facettes qui sont liées par des pratiques discursives et socioculturelles. Ces pratiques sont eux même attachées à quatre éléments: scientifiques, étiques, politiques et métaphoriques. Cette découverte est potentiellement utile pour des acteurs qui on moins de pouvoir décisive dans ce débat, comme les communautés Inuit, puisque de nouvelles voies peuvent être créées en critiquant les positions dominantes et en exprimant leur propre.
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42

Patil, Ravikant Amogisidha. "Production of acetic acid in kraft pulp mill biorefinery using bi-polar membrane electrodialysis." Thesis, The University of Maine, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10300301.

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The objective of this dissertation was to develop a process for the production of acetic acid in kraft mills. Acetyl groups in hardwood can be hydrolyzed using alkali at 50 °C. The product from this process contains about 15 g/L of sodium acetate and was determined to be suitable for the production of acetic acid.

Experiments performed using aqueous sodium acetate to evaluate the ability of electrodialysis (ED) to separate and concentrate sodium acetate showed that sodium acetate can be concentrated up to 275 g/L starting with an initial concentration of 17 g/L. The transport of water with sodium and acetate ions through ED membranes limited the maximum obtainable concentration.

To avoid the deleterious effects of white liquor on ED, selectivity experiments were performed using synthetic oxidized white liquor extract. These experiments showed a decrease in the efficiency of ED process due to the presence of sodium carbonate and sodium sulphate in the extract. Hence, it was concluded that caustic should be used as the extraction solvent.

Bi-polar electrodialysis (BPMED) experiments performed using sodium acetate showed that up to 200-280 g/L of acetic acid can be produced using BPMED. Although higher concentrations of sodium hydroxide can also be produced using BPMED, 30 g/L concentration was considered to be sufficient for recycle to the extraction process.

Feed and bleed mode BPMED experiments were performed to determine the current efficiencies and the suitable inlet concentration of sodium acetate for the production of up to 200 g/L of acetic acid. Both feed and bleed mode and batch experiments showed that the current density was the major driving force for BPMED.

Two types of concentrated wood extracts; namely (1) clarified and (2) unclarified were prepared with and without the lignin removal pre-treatment, respectively. The results of the ED and BPMED experiments performed using these extracts were similar to those of the synthetic sodium acetate. A major difference involved an increase of about 15% in electric energy consumption arising from the transport of formate, lactate and glycolate salts. The color of the anionic membranes slightly changed after processing unclarified extract through ED and BPMED.

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43

Norin, Gustav. "Development of UPLC-MS/MS method for the determination of polar metabolites." Thesis, Örebro universitet, Institutionen för naturvetenskap och teknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-69074.

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Trimethylamine-n-oxide (TMAO) is a metabolite found in plasma/serum in humans. Elevated levels of TMAO have been associated with several types of heart disease. It’s therefore of interest to make a simple analytical method to analyse TMAO and other metabolites that are degraded to TMAO, including betaine. In this study, the goal was to develop a method for the sample preparation and analysis of these compounds in human plasma. Sample preparation was performed with an Ostro 96-well method for sample clean-up. The analysis was performed by ultraperformance liquid chromatography – hydrophilic interaction liquid chromatography – tandem masspectrometry (UPLC-HILIC-MS/MS) in multiple reaction monitoring (MRM)-mode using electrospray ionization in positive mode (ESI+)-mode as the ion source. The analytes eluted under five minutes and were all baseline separated in the chromatogram. TMAO and betaine were quantified in quality control (QC) plasma samples using external calibration. Concentration of TMAO ranged from 132 ng/mL – 253 ng/mL and 1025-2084 ng/mL for betaine. Due to the lack of isotopically labelled standards for TMAO and betaine, valine-d8 was tested as an internal standard for the extraction; however, it was not a suitable option due to the low recovery obtained (5-34%) and the low response in ESI+. The recovery needs to be investigated further using isotopically labelled TMAO or betaine. Overall, the developed UPLC-HILIC-MS/MS method was found to be suitable for analysis of TMAO and betaine in human plasma. Further development and validation is required before application to samples from clinical studies.
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44

Saxin, Jonathan. "Jämförelse av Polar Vantage V ”Konditionstest” med direkt mätning av VO2max." Thesis, Linnéuniversitetet, Institutionen för idrottsvetenskap (ID), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-104215.

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Bakgrund: Det finns flertalet modeller av pulsklockor på marknaden med funktioner som skall kunna uppskatta individens maximala syreupptagningsförmåga. En av dessa modeller är Polar Vantage V, som enligt tillverkaren kan uppskatta individens VO2max genom funktionen”konditionstest”. Testet utförs genom ett fem minuters vilotest. Testvärdet beräknas sedan från hjärtfrekvens samt personliga faktorer. Syfte: Studien jämförde Polar Vantage V uppskattade testvärde med en direkt mätning av VO2max, med frågeställningen om detta test var pålitligt och användbart i praktiken. Metod: En experimentell studiedesign användes som inkluderade 11 män samt 5 kvinnor som deltagare (N=16). Alla deltagare utförde Polar Vantage V’s konditionstest i vila, för att sedan utföra en maximal prestation utfört på löpband. För mätning av VO2max användes ergospirometri-systemet Jaeger®Vyntus CPX med halvmask. Resultat:Kendall Tau-b test visade signifikant starkt positivt samband mellan Vantage V’s testvärde och VO2max från Vyntus CPX. Wilcoxon Signed Rank test visade ingen signifikant skillnad mellan testvärdet (grupp medelvärde) från Vantage V och Vyntus CPX. Slutsats: På grund av stora individuella skillnader i testvärdet mätt med ”Konditionstestet” från Vantage V, bör individen tolka resultatet med aktsamhet. Vantage V’s ”Konditionstest” verkar emellertid kunna ge en bra uppskattning av VO2max på gruppnivå för friska vuxna i 20-36 års ålder.
Background: There are several models of fitness devices on the market with functions that claims to have the capability to estimate the capacity of a individuals maximum oxygen uptake. One of these models is the Polar Vantage V fitness watch, which according to the manufacturer can estimate the VO2max through the function "Fitness test". The test is performed through a five-minute rest test. The test result is then calculated thru various variables such as the individuals resting heart rate and personal factors. Purpose: To assess the estimated test value of the Polar Vantage V “Fitness test” with a direct measurement of VO2max, with the research question whether this test was valid and useful in practice. Method: This study used an experimental design and included 11 men and 5 women as participants (N = 16). All participantsfirst performed the Polar Vantage V's “Fitness test”, then proceeded to perform a maximum performance using a treadmill. For measurement of VO2max, the cardiopulmonary exercisetesting system Jaeger®Vyntus CPX with half mask was used. Results: Kendall Tau-b test presented a significant strong positive relationship between Vantage V’s “Fitness test” and VO2max -value from the Vyntus CPX. The Wilcoxon Signed Rank test presented a nonsignificant difference between the test value (group mean value) from Vantage V “Fitness test”and VO2max from Vyntus CPX. Conclusion: Due to large individual differences in the test value measured by the "Fitness test" from Vantage V, one should interpret the test-result with care. However, the Vantage V "Fitness test" seems to be able to provide a good estimate of theVO2max at group level in healthy adults aged between 20-36.
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45

Dowsley, Martha. "The development of multi-level governance for the management of polar bears in Nunavut Territory, Canada." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18694.

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This thesis examines the complex social ecological system involving polar bear management in Nunavut and its conversion from a top-down system to a multi-level governance system. The interactions of the governance scale with the biophysical, economic and social/cultural scales are explored, with emphasis placed on the local levels of these scales. Co-management, as an instituted method of governance, is also examined to evaluate the incorporation of the Euro-Canadian and Inuit ideologies regarding polar bears. The hypothesis that Inuit would gain power through the authority granted to them in co-management was supported. However, the hypothesis that individual polar bear harvesters and other Inuit involved in the formal governance system would adopt the Euro-Canadian ideology due to the influences of the market economy and historic power of the top-down governance system was not well supported. Instead, Inuit used the Euro-Canadian tools of science and the market economy, but resisted top-down management views and the commoditization of polar bears in the market economy. Traditional understandings of social relationships among humans and between humans and bears based on the social economy of subsistence were used to oppose Euro-Canadian views in co-management and in structuring the use of polar bears for economic reasons.
Cette thèse compare le système socio-écologique, impliquant la gestion des ours polaire du Nunavut, et la conversion d'un système de gestion directionel (« top-down ») vers un système de gouvernance multi-niveaux . Les interactions des échelles de gouvernance avec les éléments biophysiques, économiques et socio-culturelles sont abordées, en mettant l'accent sur les échelles locales. La co-gestion, comme méthode de gouvernance, est également examinée afin d'évaluer l'incorporation des idéologies Euro-Canadiennes et Inuits en ce qui concerne les ours polaires. Notre hypothèse de recherche stipule stipulant que les Inuits gagnent du pouvoir par l'acquisition d'une autorité accordée par la co-gestion. Toutefois, nos recherches n'ont pas corroboré l'hypothèse voulant que les individus chassant l'ours polaire et les autres Inuits impliqués dans le système formel de gouvernement adopteraient les idéologies Euro-Canadienne, en raison de l'influence du pouvoir du marché économique et historique présent dans le système de gestion directionnel. Au contraire, les Inuits utilisent les outils scientifiques Euro-Canadiens et l'économie de marché, mais résistent aux idées de gestion directive et la commercialisation des ours polaires dans l'économie de marché. La compréhension traditionelle des relations entre les Hommes, entre les Hommes et les ours polaires sur l'économie sociale de substistance a été utilisée afin d'opposer les idées Euro-Canadiennes de la co-gestion et pour rationaliser l'utilisation de l'ours polaire pour des raisons économiques.
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46

Tewelde, Yodit. "Constraining the average fill densities of Mars' lowlands and fluvial erosion of Titan's polar regions." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/84910.

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Thesis (S.M. in Planetary Science)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 67-78).
Other than Earth, Mars and Titan are the only bodies in our Solar System where we have observed widespread fluvial activity. In this thesis I present two approaches for constraining the extent of multiple resurfacing processes in order to gain insight into the early history of Mars and Titan. One of the most distinctive features of the Martian surface is the dichotomy between the heavily cratered southern highlands and the relatively smooth northern lowlands. The northern lowlands appear smooth because many of the craters in the north have been partially or completely buried beneath volcanic and sedimentary fill of unknown relative proportions. In Chapter 1, we use the Mars Orbiter Laser Altimeter (MOLA) topography data, the Mars Reconnaissance Orbiter (MRO) gravity model and a Wiener filter to map these buried craters and estimate minimum fill thickness and volume as well as maximum fill density. The overall trend observed for the northern lowlands is more sedimentation near the dichotomy and less sedimentation further north and near the Tharsis region, which is consistent with the geology of the region. Titan has few impact craters, suggesting that its surface is geologically young. In Chapter 2 we evaluate whether fluvial erosion has caused significant resurfacing by estimating the cumulative erosion around the margins of polar lakes. Images of drowned fluvial features around the lake margins, where elevated levels of hydrocarbon liquids appear to have partly flooded fluvial valleys, allow us to map topographic contours that trace the fluvially dissected topography. We then used a numerical landscape evolution model to calibrate a relationship between contour sinuosity, which reflects the extent of fluvial valley incision, and cumulative erosion. We find that cumulative fluvial erosion around the margins of Titan's polar lakes, including Ligeia Mare, Kraken Mare, and Punga Mare in the north and Ontario Lacus in the south, ranges from 4% to 31% of the initial relief. Additional model simulations show that this amount of fluvial erosion does not render craters invisible at the resolution of currently available imagery, suggesting that fluvial erosion is not the only major resurfacing mechanism operating in Titan's polar regions.
by Yodit Tewelde.
S.M.in Planetary Science
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47

Baucher, Marie. "Modification of lignin quality in transgenic poplar and alfalfa." Doctoral thesis, Universite Libre de Bruxelles, 1996. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212365.

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48

Egekwu, Chioma. "Influence of nitrogen and sink competition on shoot growth of poplar." Thesis, University of Maryland, College Park, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10130093.

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Terrestrial and oceanic biomass carbon sinks help reduce anthropogenic CO2 emissions and mitigate the long-term effect of increasing atmospheric CO2. Woody plants have large carbon pools because of their long residence time, however N availability can negatively impact tree responses to elevated CO2. Seasonal cycling of internal N in trees is a component that contributes to fitness especially in N limited environments. It involves resorption from senescing leaves of deciduous trees and storage as vegetative storage proteins (VSP) in perennial organs. Populus is a model organism for tree biology that efficiently recycles N. Bark storage proteins (BSP) are the most abundant VSP that serves as seasonal N reserves. Here I show how poplar growth is influenced by N availability and how growth is influenced by shoot competition for stored N reserves. I also provide data that indicates that auxin mediates BSP catabolism during renewed shoot growth. Understanding the components of N accumulation, remobilization and utilization can provide insights leading to increasing N use efficiency (NUE) of perennial plants.

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49

Chard, Julie K. "Uptake and Transformation of Trichloroethylene by Hybrid Poplar: Laboratory Studies." DigitalCommons@USU, 1999. https://digitalcommons.usu.edu/etd/3647.

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Trichloroethylene (TCE) was widely used as an industrial solvent and degreasing agent for most of the twentieth century. It is now a widespread groundwater contaminant. Phytoremediation may be a cost-effective cleanup method for TCEii contaminated soils and groundwater. Studies of environmental TCE fate are complicated by its volatility. The literature repons both significant and insignificant plant uptake of TCE. Conflicting findings may be due to differences in exposure level, conditions, and duration of the studies, or to experimental artifacts from laboratory systems. This research quantified plant uptake and volatilization of TCE using a unique laboratory system. Hybrid poplar trees were exposed to 1 or 10 ppm TCE over a 43-d period. [14C]TCE was added to four high-flow, aerated, hydroponic plant growth chamber systems designed to provide high mass recoveries, an optimal plant environment and complete separation between foliar and root uptake. Transpiration stream concentration factors (TSCFs) for TCE, calculated from total [14C]TCE in shoot tissues plus phytovolatilized 14C, were 0.11 for two 1 ppm treatments and 0.15 for a 10 ppm treatment with roughly 25% attributed to phytovolatilization. Though extending study duration from 26 to 43 d resulted in accumulation of more mass of 14C in plant tissues, it had no effect on TSCF. These TSCF values are much lower than other published experimental values and values predicted by a theoretical relationship between TSCF and octanol-water partition coefficient. The TCE metabolites trichloroethanol (TCEt), trichloroacetic acid (TCAA), and dichloroacetic acid (DCAA)were identified in plant tissues of the 10-mg/L treatment. Hybrid poplar uptake ofTCAA and TCEt was quantified using a simpler aerated hydroponic system. TSCF values were calculated based on extractable parent compound in shoot tiss ues. TSCF for TCEt was < 0.01. Presence of TCAA in hydroponic solution and in leaf and root tissues indicated transformation of TCEt to TCAA. TSCF for TCAA was < 0.03 and decreased with increasing exposure concentration. TSCF also decreased under oxygen-limited root-zone conditions. Presence of DCAA in leaf and root tissues indicated transformation ofTCAA to DCAA. Transformation of parent compound, coupled with low extractability, may contribute to low TSCFs.
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Labrecque, Jeremy. "Indicator species of soil nutrients and poplar plantation productivity in southeastern Quebec." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66757.

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Two sites, situated approximately 60 kilometers apart in southern Quebec, were studied to determine what nutrients were most limiting and to compare growth variation on microsite (3-9m) and landscape scales (100-1000m). One site was found to be 20% more productive than the other growing at 6.9 m3 ha-1 in its fifth year of growth. Principal component analysis found no nutrients to be limiting at the more productive site while the other site appeared to be N and K limited. Microsite scale variation was found to be at least as important as landscape scale variation in explaining measures of productivity in most cases. Potential problems posed by microsite scale variation could be addressed using an indicator species analysis. Empirical distribution function analysis revealed that some species present in hybrid poplar plantations (e.g. Fragaria spp. and Polytrichum spp.) may be good indicators of low and high productivity sites respectively.
Deux sites de plantations situés approximativement 60 kilomètres l'un de l'autre ont été étudiés afin de déterminer quels nutriments était les plus limitants et de comparer la variance à l'échelle de 3-9m (microsite) à la variance à l'échelle de 100-1000m. Un site était 20% plus productif que l'autre avec un taux de croissane de 6.9 m3 ha-1 dans ça cinquième année. L'analyse de la composante principale a dévoilé que aucun des nutriments n'était limitant tandis qu'à l'autre site le N et la K parassait être limitants. La variance à l'échelle 3-9m semble être au moins aussi importante que la variance à l'échelle 100-1000m dans son explication des mesures de productivité, dans la majorité des cas. Le potentiel de problèmes rencontrés dans l'échelle de variation des microsites peut être expliqué en se servant d'une analyse d'espèces indicatrices. L'analyse de la fonction de distribution empirique a révèlé que certaines espèces présentes dans les plantations de peupliers hybrides (e.g. Fragaria spp. et Polytrichum spp.) pourraient être de bons indicateurs de sites à productivité élevé ou basse.
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