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2019

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Articles 12901 - 12930 of 13000

Full-Text Articles in Physical Sciences and Mathematics

Development Of Facial Expression Detection Model For Stroke Patients, Rawinan Praditsangthong Jan 2019

Development Of Facial Expression Detection Model For Stroke Patients, Rawinan Praditsangthong

Chulalongkorn University Theses and Dissertations (Chula ETD)

A stroke patient should be cared and treated closely since the patient cannot speak, communicate, and move the body when needed. In addition, the number of stroke patients is increasing in Thailand and around the world. Unfortunately, the number of medical staffs does not vary by the number of stroke patient. Thus, the aim of this research is to develop a facial expression detection model for stroke patients during their treatments. This research proposes the facial expression detection model for stroke patients from facial features, such as Interpalpebral Fissure (IPF), Palpebral Fissure Length (PFL), Palpebral Fissure Region (PFR), Inner Brow …

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Binomial Characterizations Of Inner Product Spaces, Saranyachakri Roekrit Jan 2019

Binomial Characterizations Of Inner Product Spaces, Saranyachakri Roekrit

Chulalongkorn University Theses and Dissertations (Chula ETD)

We study the sufficient conditions for a normed space to be an inner product space. We found that some characterizations of inner product spaces are in a form [equation] satisfy some algebraic conditions. We then introduce some characterizations of inner product spaces relating to the binomial identity and conclude that a nomed linear space (X,II.II) is an inner product space if there exist positive integers k and m with 2m

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Solving Interval-Valued Returns Mean Absolute Deviation Portfolio Selection Model Under Basis Stability, Songkomkrit Chaiyakan Jan 2019

Solving Interval-Valued Returns Mean Absolute Deviation Portfolio Selection Model Under Basis Stability, Songkomkrit Chaiyakan

Chulalongkorn University Theses and Dissertations (Chula ETD)

This work discusses a portfolio selection model with interval linear programming arising from the uncertainty of future rates of return and the disagreement over their estimates. The risk of the overall portfolio is proposed as an objective function to obtain a well-diversified portfolio with a certain threshold rate of return. The optimization problem employs mean absolute deviation as a risk measure for the sake of risk diversification and time complexity. The possible ranges of optimal portfolio returns and associated risks are derived. The duality theory contributes to an enclosure of the optimal portfolios. When the bounds on future rates of …

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Aircraft Detection Using Single Shot Scale-Invariant Face Detector With Viridis Saliency Map From Remote Sensing Image, Teepakorn Lilek Jan 2019

Aircraft Detection Using Single Shot Scale-Invariant Face Detector With Viridis Saliency Map From Remote Sensing Image, Teepakorn Lilek

Chulalongkorn University Theses and Dissertations (Chula ETD)

Aircraft detection from remote sensing images is a useful task and essential in many fields; for example, in the military, aircraft detection systems are used to search and inspect an enemy aircraft from remote sensing images. Nowadays, aircraft detection from remote sensing images has gained increasing research attention because this task is very challenging. This task is difficult due to many occurred problems in remote sensing images, such as a shadow, a complicated background, and various aircraft scales. In this research, we create a Viridis saliency map using many techniques from image processing such as color mapping, morphological image processing, …

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Logo Classification Of Amphetamines By Surf And Bag-Of-Features Model, Tharaphon Nitijiramon Jan 2019

Logo Classification Of Amphetamines By Surf And Bag-Of-Features Model, Tharaphon Nitijiramon

Chulalongkorn University Theses and Dissertations (Chula ETD)

An amphetamine is one of the drugs apprehended by the policemen in Thailand. At present, when an amphetamine drug seller is arrested, captured amphetamines are sent to the Scientific Crime Detection Center Region 1 to identify the amphetamines' source. Each drug is classified based on the printed character to relevant information from the source of drugs. For each case, a large volume of drugs is sent to be classified by only three staff members. It is a time-consuming task. In this work, we propose a framework for classifying the image of amphetamines based on their logo using the SURF and …

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Covers For Leo Moser's Worm Problem, Thitipong Kanchai Jan 2019

Covers For Leo Moser's Worm Problem, Thitipong Kanchai

Chulalongkorn University Theses and Dissertations (Chula ETD)

Leo Moser’s worm problem was posted in 1966 stating that “What is the region of the smallest area that can cover every unit are?”. In 2018, N. Ploymaklam and W. Wichiramala illustrated a new cover, which is currently smallest. Their cover was adapted from the cover of R. Norwood and G. Poole. In this work, we modify the region from the work of R. Norwood and G. Poole and the work of N. Ploymaklam and W. Wichiramala. Our regions are modified by changing their upper boundary. However, the regions remain satisfying properties in the work of R. Norwood and G. …

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Continuous Synthesis Of Biodiesel And Glycerol Ether Using Homogeneous And Heterogeneous Catalysts, Natta Rattanapanya Jan 2019

Continuous Synthesis Of Biodiesel And Glycerol Ether Using Homogeneous And Heterogeneous Catalysts, Natta Rattanapanya

Chulalongkorn University Theses and Dissertations (Chula ETD)

In our study, a mixture of p-toluenesulfonic acid and sulfuric acid (TsOH-H2SO4) as a catalyst showed a good performance in transesterification of palm oil (PO) with methanol and etherification of biodiesel with isobutylene. For biodiesel production, the catalyst noticeably accelerated the reaction faster than TsOH and H2SO4 alone and also gave up to 99.8% of the conversion. Etherification of biodiesel with isobutylene in the etherification process using isobutylene/glycerol molar ratio 6:1 at 70°C, in the period of 5 h reaction time, gave high selectivity to produce DTBG and TTBG (81.4%). Furthermore, the catalyst can be reused for 6 cycles of …

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Formaldehyde Fluorescent Sensors From 1,8-Naphthalimide Derivatives, Apicha Maharat Jan 2019

Formaldehyde Fluorescent Sensors From 1,8-Naphthalimide Derivatives, Apicha Maharat

Chulalongkorn University Theses and Dissertations (Chula ETD)

Three derivatives of 1,8-naphthalimide were systematically designed and synthesized to investigate the effect of substitution pattern on their photophysical properties and sensing behaviors towards formaldehyde in aqueous media. The key substituents, the hydrazino (-NHNH2) and the 2-methoxyethylamino groups (-NHCH2CH2OCH3), were installed at the 4-position of 1,8-naphthalimide by a nucleophilic replacement, and at the imide position by a condensation reaction with 1,8-naphthalic anhydride precursor. All target compounds were obtained in good overall yields of 60-80%. Compounds with two hydrazine moieties (R3) showed excellent selective fluorescent responses towards formaldehyde with the 3.5-fold fluorescence enhancement in 5% aqueous acetic acid solution at 520 …

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Polyvinyl Alcohol/Starch Modified Cotton Thread For Glucose Distance-Based Colorimetric Detection, Pornchanok Punnoy Jan 2019

Polyvinyl Alcohol/Starch Modified Cotton Thread For Glucose Distance-Based Colorimetric Detection, Pornchanok Punnoy

Chulalongkorn University Theses and Dissertations (Chula ETD)

In this thesis, polyvinyl alcohol (PVA) and starch modified cotton thread was developed as a cotton thread-based device for distance-based colorimetric detection of hydrogen peroxide (H2O2) and glucose. PVA and starch, the biocompatible polymers, were modified on a cotton thread to enhance the enzymatic stability and reagent immobilization efficiency. The colorimetric glucose detection of the device was based on a bienzymatic reaction involving glucose oxidase (GOx) and horseradish peroxidase (HRP), incorporated with potassium iodide (KI) as an indicator, which was oxidized by H2O2 to provide blue-black color band of an iodine–starch complex. The length of color band on the cotton …

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Continuous Flow Selective Hydrogenation Of 5-Hydroxymethylfurfural To 2.5-Dimethylfuran Using Pd-Cu/Reduced Graphene Oxde Catalysts, Sareena Mhadmhan Jan 2019

Continuous Flow Selective Hydrogenation Of 5-Hydroxymethylfurfural To 2.5-Dimethylfuran Using Pd-Cu/Reduced Graphene Oxde Catalysts, Sareena Mhadmhan

Chulalongkorn University Theses and Dissertations (Chula ETD)

2,5-Dimethylfuran (DMF) has been considered a promising biofuel, potentially derived from biomass. There have been various reports on DMF production from hydrogenation of 5-hydroxymethylfurfural (HMF). However, most reports employed high hydrogen pressure, long reaction times, and reactions under batch reactor. In this study, Pd-Cu bimetallic catalysts incorporated on reduced graphene oxide (RGO) were used for hydrogenation of HMF to DMF using 2-propanol as hydrogen donor under continuous flow system. Synthesized catalysts were characterized by N2 physisorption, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and temperature programmed reduction of hydrogen …

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Preparation Of Starch-Filled Polyisocyanurate Foams Catalyzed By Zinc-Ammonia Complex/Potassium Octoate, Sirima Goonack Jan 2019

Preparation Of Starch-Filled Polyisocyanurate Foams Catalyzed By Zinc-Ammonia Complex/Potassium Octoate, Sirima Goonack

Chulalongkorn University Theses and Dissertations (Chula ETD)

The research aimed to reduce apparent density and improve fire resistance of polyisocyanurate (PIR) foam. PIR foams were prepared using zinc-ammonia complex and potassium octoate as catalyst for gelling/blowing and trimerization reactions, respectively. Three types of starch produced in Thailand, namely glutinous rice flour, rice flour and mung bean starch, were used as additives for PIR foams. The characterized properties of PIR foams modified with starches are reaction times (cream time, gel time, rise time and tack free time), polyisocyanurate/polyurethane (PIR/PUR) ratio, %isocyanate conversion, apparent density, compressive property, morphology and fire behavior. These properties are compared with PIR foam without …

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Magnetic Nanoparticles Stabilized By Phosphorylcholine-Containing Polymer For Antibody Free C-Reactive Protein Detection, Suttawan Saipia Jan 2019

Magnetic Nanoparticles Stabilized By Phosphorylcholine-Containing Polymer For Antibody Free C-Reactive Protein Detection, Suttawan Saipia

Chulalongkorn University Theses and Dissertations (Chula ETD)

This research aims to develop a simple, yet effective assay for C-reactive protein (CRP) detection based on a combination of magnetic separation and antibody-free colorimetric assay. Magnetic nanoparticles stabilized with phosphorylcholine-containing polymer, poly[methacrylic acid)-ran-(methacryloyloxyethyl phosphorylcholine)] (PMAMPC-MNPs) were prepared by co-precipitation of ferric and ferrous salts in the presence of PMAMPC. Carboxyl groups in the methacrylic acid (MA) repeat units chelate with Fe atoms during MNPs formation while the methacryloyloxyethyl phosphorylcholine (MPC) repeat units provide specifically binding sites and conjugate with CRP in presence of Ca2+. The PMAMPC-MNPs were characterized by ATR-FTIR, TEM, DLS, TGA and XRD. To determine the CRP …

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Electrospun Nylon 6,6 Nanofibers Functionalized With Β-Cyclodextrin As Solid Phase Extraction Sorbent For Determination Of Parabens, Tassanee Kuakul Jan 2019

Electrospun Nylon 6,6 Nanofibers Functionalized With Β-Cyclodextrin As Solid Phase Extraction Sorbent For Determination Of Parabens, Tassanee Kuakul

Chulalongkorn University Theses and Dissertations (Chula ETD)

In this study, electrospun nanofibers of nylon 6,6 functionalized with β-cyclodextrin (nylon 6,6/β-CD) were fabricated and applied as a sorbent in solid-phase extraction (SPE) for determination of parabens in water. The electrospinning parameters such as polymer concentration, nylon 6,6/β-CD ratio, and electric field strength were investigated in order to obtain uniform nanofibers. The morphology and physical properties of obtained fibers were characterized by scanning electron microscope (SEM), Fourier transforms infrared spectroscopy (FTIR), and BET surface area analysis. The electrospun nylon 6,6/β-CD nanofibers were achieved with diameter in the range of 120 - 150 nm. The additional of β-CD slightly increased …

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High Magnification Polymeric Lens For Smartphone Microscope, Wisansaya Jaikeandee Jan 2019

High Magnification Polymeric Lens For Smartphone Microscope, Wisansaya Jaikeandee

Chulalongkorn University Theses and Dissertations (Chula ETD)

In this work, we present a facile method for fabrication of plano-convex lenses, using high reflective optical polymer (Polydimethylsiloxane, Sylgard 184 by Dow Corning, n ~1.42 and Norland Optical adhesive 61, NOA61 by Norland Products, ~1.56) under the confined sessile drop technique. The confined sessile drop technique is a facile method and an adjustable lens geometry through controlled the weight of liquid polymer on the lens substrate, as PMMA circular disk and Sylgard circular disk, with different diameter (2.5-6.0 mm). The liquid polymer was gradually spread and radially over the surface of the lens substrate, and resistance to spreading of …

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Curling Probe Measurement In Plasma, Chatchai Sirithipvanich Jan 2019

Curling Probe Measurement In Plasma, Chatchai Sirithipvanich

Chulalongkorn University Theses and Dissertations (Chula ETD)

The curling probe is one of the active resonance absorption spectroscopic methods, the methods utilized the probe reflection coefficient spectrum to determine the plasma density. The proposed model of the curling probe uses the deviation of the most matched frequency, the frequency in which the minimum reflection coefficient occurs, when the probe is submerged in different mediums. The probe structure is simple and claimed to be robust and efficient. The experiments of a curling probe were performed and the simulations for the probe reflection coefficient for both previously reported probe and the constructed probe configuration have been conducted. The previously …

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Ads₄/Cft₃ Holography From Four-Dimensional Gauged Supergravity, Khem Upathambhakul Jan 2019

Ads₄/Cft₃ Holography From Four-Dimensional Gauged Supergravity, Khem Upathambhakul

Chulalongkorn University Theses and Dissertations (Chula ETD)

We study holographic RG flows from N = 3 and N = 4 gauged supergravities in four dimensions. The scalar manifold of N = 3 gauged supergravity is in the form of the coset space G/H = SU(3, n)/SU(3) × SU(n) × U(1). Possible gauge groups, in this study, are given by SO(3) × SO(3), SO(3, 1), SO(2, 2), SO(2, 1) × SO(2, 2), and SL(3, R). We then study N = 4 gauged supergravity from type II compactification on T⁶/Z₂ × Z₂ with non-semisimple gaugings. The scalar manifold of N = 4 gauged supergravity is in the form of …

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Multipole Resonance Probe Measurement In Plasma, Natthapong Jampaiboon Jan 2019

Multipole Resonance Probe Measurement In Plasma, Natthapong Jampaiboon

Chulalongkorn University Theses and Dissertations (Chula ETD)

Active plasma resonance spectroscopy (APRS) is one of the interesting methods which could avoid plasma contamination problem occurs in a conventional Langmuir probe measurement. It is because the probe conductors are covered by a dielectric material. The APRS probe can be of any shape. A multipole resonance probe is a hemisphere APRS probe since a sphere imposes the simplest way to find an analytical solution by solving the Laplace equation in the spherical coordinates with the azimuthal symmetry. In this study, the APRS probes in the hemisphere, microstrip, and parallel rod shapes were constructed. Plasma density was obtained by using …

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Effects Of Magnesium Substitution On Electronic Properties Of Calcium Difluoride, Natthasart Chintananon Jan 2019

Effects Of Magnesium Substitution On Electronic Properties Of Calcium Difluoride, Natthasart Chintananon

Chulalongkorn University Theses and Dissertations (Chula ETD)

We use density functional theory to find the phase transitions of CaF2. The results show that CaF2 adopts the fluorite structure, with the space group Fm-3m, in the range 0f 0-8 GPa and transforms into the cotunnite structure, with the space group Pnma, above 8 GPa. The electronic band structure of the Pnma-CaF2 structure expresses an insulating phase, and the bandgap collapses under pressure above 70 GPa. In this work, we proposed a new decoration of Ca/Mg-substituted fluorides MgxCa1-xF2, using the cluster expansion technique which is commonly used to study alloys. We found that the Mg0.25Ca0.75F2, with a Pm structure, …

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Effect Of Hydrogen Exposure On The Electronic And Optical Properties Of Insulating Titanates, John G. Connell Jan 2019

Effect Of Hydrogen Exposure On The Electronic And Optical Properties Of Insulating Titanates, John G. Connell

Theses and Dissertations--Physics and Astronomy

Hydrogen exposure of insulating d0-titanates, such as SrTiO3 (STO), has displayed the formation of intriguing conducting states. These conducting states form through the use of forming gas (N2/H2) annealing or hydrogen plasma exposure, where hydrogen gas is exposed to high energy microwaves. The exposure of STO to hydrogen causes metallic conductivity due to the introduction of hydrogen cations on some of the oxygen sites. However, the optical properties of this hydrogen-exposed STO have not been well-studied. Further, Ba0.5Sr0.5TiO3 (BST), an insulating dielectric, also shows changes in its conductivity …

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The Role Of Angular Momentum In The Interplay Between Disk Galaxies And Their Host Dark Matter Halos: Corollaries For The Hubble Fork Diagram, Angela Collier Jan 2019

The Role Of Angular Momentum In The Interplay Between Disk Galaxies And Their Host Dark Matter Halos: Corollaries For The Hubble Fork Diagram, Angela Collier

Theses and Dissertations--Physics and Astronomy

A majority of disk galaxies host stellar bars that regulate and amplify the flow of angular momentum, J, between disks and their parent dark matter (DM) halos. These bars constitute the prime factor driving internal galaxy evolution. Yet, a non-negligible fraction of disks lack this morphological feature, which led to adoption of the Hubble Fork Diagram. The complex evolution of barred galaxies has been studied by means of numerical simulations, complemented by observations. Despite prolonged efforts, many fundamental questions remain, in part because cosmological simulations still lack the necessary resolution to account for resonant interactions and simulations of isolated …

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Electronic Properties Of Atomically Thin Material Heterostructures, M. Javad Farrokhi Jan 2019

Electronic Properties Of Atomically Thin Material Heterostructures, M. Javad Farrokhi

Theses and Dissertations--Physics and Astronomy

There is a movement in the electronic industry toward building electronic devices with dimensions smaller than is currently possible. Atomically thin 2D material, such as graphene, bilayer graphene, hBN and MoS2 are great candidate for this goal and they have a potential set of novel electronic properties compare to their bulk counterparts due to the exhibition of quantum confinement effects. To this goal, we have investigated the electric field screening of multilayer 2D materials due to the presence of impurity charge in the interface and vertical electric fifield from back gate. Our result shows a dramatic difference of screening behavior …

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Magnetic Field Monitoring In The Sns Neutron Edm Experiment, Alina Aleksandrova Jan 2019

Magnetic Field Monitoring In The Sns Neutron Edm Experiment, Alina Aleksandrova

Theses and Dissertations--Physics and Astronomy

It is a well known fact that the visible universe is made almost entirely of baryonic matter. Yet, this is also one of the greatest puzzles that physicists are trying to solve: Where did all of this matter come from in the first place? The Standard Model (SM) of particle physics predicts a baryon asymmetry that is much smaller than what is observed in nature. In order to try and explain this discrepancy, Sakharov (1967) postulated three necessary conditions for baryogenesis in the early universe. One of these is the requirement that charge conjugation (C) and the product of C …

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Exploring The Molecular Origin Of Jet Fuel Thermal Oxidative Deposition Through Statistical Analysis Of Mass Spectral Data And Pyrolysis Gas Chromatography/Mass Spectrometry Of Deposits, Krege Matthew Christison Jan 2019

Exploring The Molecular Origin Of Jet Fuel Thermal Oxidative Deposition Through Statistical Analysis Of Mass Spectral Data And Pyrolysis Gas Chromatography/Mass Spectrometry Of Deposits, Krege Matthew Christison

University of the Pacific Theses and Dissertations

ASTM D3241 (Standard Test Method for Thermal Oxidation Stability of Aviation Turbine Fuels) measures the thermal oxidative stability of jet fuels under elevated temperature and pressure conditions. When jet fuels fail ASTM D3241, either at the refinery or in the distribution system, there can be supply disruptions and financial losses. Understanding the causes of poor thermal oxidative stability in jet fuels could help prevent or mitigate issues. In order to develop a deeper understanding of the molecular precursors that lead to ASTM D3241 failures, a number of analytical methodologies and data treatment techniques have been developed, applied, and reported here. …

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Ephemeral Gully Erosion Modeling And Surveying With Close-Range Digital Photogrammetry, M. A. Islam, C. Weerasekara, Y. Zhou, A. Y. Shesukov Jan 2019

Ephemeral Gully Erosion Modeling And Surveying With Close-Range Digital Photogrammetry, M. A. Islam, C. Weerasekara, Y. Zhou, A. Y. Shesukov

Conservation and Survey Division: Faculty and Staff Publications

No abstract provided.

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Exploring The Northwest Margin Of The High Plains Aquifer: Structure, Depositional History And Hydrogeology, Nebraska Geological Society Field Trip, Doug Hallum, Dennis O. Terry, Jr., Michael Leite, Jennifer Balmat Jan 2019

Exploring The Northwest Margin Of The High Plains Aquifer: Structure, Depositional History And Hydrogeology, Nebraska Geological Society Field Trip, Doug Hallum, Dennis O. Terry, Jr., Michael Leite, Jennifer Balmat

Conservation and Survey Division: Faculty and Staff Publications

The northwest portion of the High Plains Aquifer in Nebraska corresponds with the western Sandhills, Box Butte, Sioux and Dawes County tablelands, and the Nebraska Pine Ridge in northwest Nebraska. This field excursion will travel beyond the margins of the High Plains aquifer into the White River valley and onto the Oglala National Grasslands. These areas are not only rich in natural resources, but rich in history as well. While this excursion will explore earth history, depositional environments and a portion of the High Plains Aquifer, the authors encourage all attendees to take additional time to explore the cultural, military …

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Age And Pattern Of The Southern High-Latitude Continental End-Permian Extinction Constrained By Multiproxy Analysis, Christopher R. Fielding, Tracy D. Frank, Stephen Mcloughlin, Vivi Vajda, Chris Mays, Allen P. Tevyaw, Arne Winguth, Cornelia Winguth, Robert S. Nicoll, Malcom Bocking, James L. Crowley Jan 2019

Age And Pattern Of The Southern High-Latitude Continental End-Permian Extinction Constrained By Multiproxy Analysis, Christopher R. Fielding, Tracy D. Frank, Stephen Mcloughlin, Vivi Vajda, Chris Mays, Allen P. Tevyaw, Arne Winguth, Cornelia Winguth, Robert S. Nicoll, Malcom Bocking, James L. Crowley

Department of Earth and Atmospheric Sciences: Faculty Publications

Past studies of the end-Permian extinction (EPE), the largest biotic crisis of the Phanerozoic, have not resolved the timing of events in southern high-latitudes. Here we use palynology coupled with high-precision CA-ID-TIMS dating of euhedral zircons from continental sequences of the Sydney Basin, Australia, to show that the collapse of the austral Permian Glossopteris flora occurred prior to 252.3 Ma (~370 kyrs before the main marine extinction). Weathering proxies indicate that floristic changes occurred during a brief climate perturbation in a regional alluvial landscape that otherwise experienced insubstantial change in fluvial style, insignificant reorganization of the depositional surface, and no …

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Radar Quantification, Temporal Analysis And Influence Of Atmospheric Conditions On A Roost Of American Robins (Turdus Migratorius) In Oklahoma, Matthew S. Van Den Broeke Jan 2019

Radar Quantification, Temporal Analysis And Influence Of Atmospheric Conditions On A Roost Of American Robins (Turdus Migratorius) In Oklahoma, Matthew S. Van Den Broeke

Department of Earth and Atmospheric Sciences: Faculty Publications

Radar observations present a way to monitor large, mobile populations across long temporal scales, and are especially valuable when individual scatterers are challenging to count visually. The focus of this study is a large and relatively homogeneous wintertime roost of American Robins (Turdus migratorius) in central Oklahoma. Radar observations are used to estimate the roost population through winter 2010–2011, and the population time series is related to weather variables and radar beam propagation. Radar-estimated roost population gradually increased to an estimated peak of 1.5–2 million individuals from November 2010 to January 2011, and then decreased in a more …

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Hexagonal Fracture Patterns On Navajo Sandstone Crossbeds At Yellow Knolls, Washington County, David Loope Jan 2019

Hexagonal Fracture Patterns On Navajo Sandstone Crossbeds At Yellow Knolls, Washington County, David Loope

Department of Earth and Atmospheric Sciences: Faculty Publications

At this geosite, the main features of interest—remarkably uniform and beautiful fracture patterns dominantly composed of linked hexagons (fi gures 1 and 2)—are present on outcrops of the Jurassic Navajo Sandstone. Th e Navajo was deposited by large, southward- migrating desert dunes about 200 million years ago, but the fractures that defi ne the hexagons here are just a surfi cial veneer less than 20 inches (half a meter) deep. Th e fractures are a weathering phenomenon that developed under climate conditions similar to today’s. Steep thermal gradients develop in the sandstone because it is exposed to solar radiation and …

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Rinded, Iron-Oxide Concretions In Navajo Sandstone Along The Trail To Upper Calf Creek Falls, Garfield County, David Loope, Richard Kettler Jan 2019

Rinded, Iron-Oxide Concretions In Navajo Sandstone Along The Trail To Upper Calf Creek Falls, Garfield County, David Loope, Richard Kettler

Department of Earth and Atmospheric Sciences: Faculty Publications

Concretions are hard rock masses, usually spheroidal, but commonly oblate or discoidal, that are formed by strongly localized precipitation of minerals in the pores of an otherwise weaker sedimentary rock (see Bates and Jackson, 1980, for a more extensive definition). The iron-oxide-rich concretions in the Jurassic Navajo Sandstone in southern Utah are unusual in two fundamental ways. First, they are cemented by iron oxide (Fe2O3, or Fe(OH)3); most other concretions are cemented by silica (SiO2), calcite (CaCO3), dolomite (CaMg(CO3)2), or siderite (FeCO3). Second, unlike other concretions, they are not strongly cemented throughout, but instead, the iron oxide is concentrated in …

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Plant Root Systems Preserved In The Permian Cedar Mesa Sandstone At Moki Dugway, Southeastern Utah, David Loope Jan 2019

Plant Root Systems Preserved In The Permian Cedar Mesa Sandstone At Moki Dugway, Southeastern Utah, David Loope

Department of Earth and Atmospheric Sciences: Faculty Publications

Rooted green plants represent the base of the food chain for most terrestrial ecosystems, but, compared to animal burrows, root systems are relatively rarely recognized in ancient sedimentary rocks. Plant roots that penetrate unconsolidated sand dunes, especially those containing not only quartz grains, but also abundant grains of calcite (CaCO3), are commonly replaced by fine crystals of calcite (Klappa, 1980). These structures (known by geologists as rhizoliths from the Greek for “root rock”) are one form of calcite cemented soil and sediment called caliche (figure 1). Caliche crystallizes well above the water table and its calcite crystals are …

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