Search

Search Results

• 301. [Article] Comparisons of Linear Regression Models for Properties of Alkaliactivated Binder Concrete

  Concrete with alkali-activated binder (AAB) is increasingly considered as a better alternative to conventional portland cement (PC) concrete due to its superior sustainable and green properties. In order ...

  Citation × Citation Citation Abstract Copy Title: Comparisons of Linear Regression Models for Properties of Alkaliactivated Binder Concrete Author: Kar, Arkamitra, Halabe, Udaya B., Ray, Indrajit, Unnikrishnan, Avinash Year: 2015 Concrete with alkali-activated binder (AAB) is increasingly considered as a better alternative to conventional portland cement (PC) concrete due to its superior sustainable and green properties. In order to promote the practical usage of AAB concrete, a previous study by the present authors proposed models on correlations among their mechanical and nondestructive properties. The present study extends the previous knowledge by proposing new improved models using linear regressions to predict compressive strengths and modulus of elasticity from ultrasonic pulse velocities. The models are developed for both unstressed and stressed AAB concrete with different curing temperatures. The accuracies of the models are compared with both sum of squares due to errors (SSE) and R2 depending on the type of equations; and the new models are found to be more accurate compared to the previous models. Title: Comparisons of Linear Regression Models for Properties of Alkaliactivated Binder Concrete Author: Kar, Arkamitra, Halabe, Udaya B., Ray, Indrajit, Unnikrishnan, Avinash Year: 2015 Concrete with alkali-activated binder (AAB) is increasingly considered as a better alternative to conventional portland cement (PC) concrete due to its superior sustainable and green properties. In order to promote the practical usage of AAB concrete, a previous study by the present authors proposed models on correlations among their mechanical and nondestructive properties. The present study extends the previous knowledge by proposing new improved models using linear regressions to predict compressive strengths and modulus of elasticity from ultrasonic pulse velocities. The models are developed for both unstressed and stressed AAB concrete with different curing temperatures. The accuracies of the models are compared with both sum of squares due to errors (SSE) and R2 depending on the type of equations; and the new models are found to be more accurate compared to the previous models. Close

• 302. [Article] Biogeography of the American Pika (Ochotona princeps) in Oregon and Southern Washington : illuminating genetic relationships among disjunct populations

  The American pika (Ochotona princeps) finds moderately warm temperatures (>25°C) lethally stressful, and at the end of the last Ice Age 10,000 years ago was forced to disperse to cooler, "sky island" mountaintops ...

  Citation × Citation Citation Abstract Copy Title: Biogeography of the American Pika (Ochotona princeps) in Oregon and Southern Washington : illuminating genetic relationships among disjunct populations Author: Batten, George Washington, III Year: 2010 The American pika (Ochotona princeps) finds moderately warm temperatures (>25°C) lethally stressful, and at the end of the last Ice Age 10,000 years ago was forced to disperse to cooler, "sky island" mountaintops where they are almost exclusively found today. Thirty six subspecies are recognized, all established using morphological characters, and it is uncertain whether these subspecies' designations are corroborated by genetic analyses. This study elucidates three hypotheses regarding populations in Oregon and southern Washington: 1) O. p. fumosa constitutes a subspecies distinct form O. p. brunnescens, 2) the Columbia River constitutes a barrier to gene flow giving rise to two subspecies rather than the single subspecies O. p. brunnescens, and 3) populations in eastern Oregon ( O. p. jewetti and O. p. taylori) are genetically distinct from populations in the Cascade Range ( 0. p. brunnescens and O. p. fumosa). Title: Biogeography of the American Pika (Ochotona princeps) in Oregon and Southern Washington : illuminating genetic relationships among disjunct populations Author: Batten, George Washington, III Year: 2010 The American pika (Ochotona princeps) finds moderately warm temperatures (>25°C) lethally stressful, and at the end of the last Ice Age 10,000 years ago was forced to disperse to cooler, "sky island" mountaintops where they are almost exclusively found today. Thirty six subspecies are recognized, all established using morphological characters, and it is uncertain whether these subspecies' designations are corroborated by genetic analyses. This study elucidates three hypotheses regarding populations in Oregon and southern Washington: 1) O. p. fumosa constitutes a subspecies distinct form O. p. brunnescens, 2) the Columbia River constitutes a barrier to gene flow giving rise to two subspecies rather than the single subspecies O. p. brunnescens, and 3) populations in eastern Oregon ( O. p. jewetti and O. p. taylori) are genetically distinct from populations in the Cascade Range ( 0. p. brunnescens and O. p. fumosa). Close

• 303. [Article] Reversible Control of the Magnetization of Fe₃O₄ via Lithium Ions

  In this report, a reversible control of Fe₃O₄ saturated magnetization by Li ions is demonstrated. A miniature Li ion battery (LIB) was assembled using a Fe₃O₄ nanoparticle layer as the active cathode. ...

  Citation × Citation Citation Abstract Copy Title: Reversible Control of the Magnetization of Fe₃O₄ via Lithium Ions Author: Wei, Guodong, Wei, Lin, Wang, Dong, Tian, Yufeng, Chen, Yanxue, Yan, Shishen, Mei, Liangmo, Jiao, Jun Year: 2017 In this report, a reversible control of Fe₃O₄ saturated magnetization by Li ions is demonstrated. A miniature Li ion battery (LIB) was assembled using a Fe₃O₄ nanoparticle layer as the active cathode. A stable magnetism modulation is realized by a nondestructive electrochemical process in which the lithium insertion results in a valence change and partial redistribution of Fe cations in the crystal structure. The relation between the discharge voltage and the chemical phases were studied by ex situ X-ray diffraction and magnetic measurement. In a suitable discharge potential range, a reversible control of Fe₃O₄ saturated magnetization was obtained without structural damage to the magnetic electrode. The experimental results indicate by further optimizing the LIB's performance, a large reversible change in magnetization could be realized at room temperature, suggesting the potential for future practical applications. Title: Reversible Control of the Magnetization of Fe₃O₄ via Lithium Ions Author: Wei, Guodong, Wei, Lin, Wang, Dong, Tian, Yufeng, Chen, Yanxue, Yan, Shishen, Mei, Liangmo, Jiao, Jun Year: 2017 In this report, a reversible control of Fe₃O₄ saturated magnetization by Li ions is demonstrated. A miniature Li ion battery (LIB) was assembled using a Fe₃O₄ nanoparticle layer as the active cathode. A stable magnetism modulation is realized by a nondestructive electrochemical process in which the lithium insertion results in a valence change and partial redistribution of Fe cations in the crystal structure. The relation between the discharge voltage and the chemical phases were studied by ex situ X-ray diffraction and magnetic measurement. In a suitable discharge potential range, a reversible control of Fe₃O₄ saturated magnetization was obtained without structural damage to the magnetic electrode. The experimental results indicate by further optimizing the LIB's performance, a large reversible change in magnetization could be realized at room temperature, suggesting the potential for future practical applications. Close

• 304. [Article] ZnO Nanoneedle/H2O Solid-Liquid Heterojunction-Based Self-Powered Ultraviolet Detector

  ZnO nanoneedle arrays were grown vertically on a fluorine-doped tin oxide-coated glass by hydrothermal method at a relatively low temperature. A self-powered photoelectrochemical cell-type UV detector ...

  Citation × Citation Citation Abstract Copy Title: ZnO Nanoneedle/H2O Solid-Liquid Heterojunction-Based Self-Powered Ultraviolet Detector Author: Li, Qinghao, Wei, Lin, Xie, Yanru, Zhang, Kai, Liu, Lei, Zhu, Dapeng, Jiao, Jun, Chen, Yanxue, Yan, Shishen, Liu, Guolei, Mei, Liangmo Year: 2013 ZnO nanoneedle arrays were grown vertically on a fluorine-doped tin oxide-coated glass by hydrothermal method at a relatively low temperature. A self-powered photoelectrochemical cell-type UV detector was fabricated using the ZnO nanoneedles as the active photoanode and H2O as the electrolyte. This solid-liquid heterojunction offers an enlarged ZnO/water contact area and a direct pathway for electron transport simultaneously. By connecting this UV photodetector to an ammeter, the intensity of UV light can be quantified using the output short-circuit photocurrent without a power source. High photosensitivity, excellent spectral selectivity, and fast photoresponse at zero bias are observed in this UV detector. The self-powered behavior can be well explained by the formation of a space charge layer near the interface of the solid-liquid heterojunction, which results in a built-in potential and makes the solid-liquid heterojunction work in photovoltaic mode. Title: ZnO Nanoneedle/H2O Solid-Liquid Heterojunction-Based Self-Powered Ultraviolet Detector Author: Li, Qinghao, Wei, Lin, Xie, Yanru, Zhang, Kai, Liu, Lei, Zhu, Dapeng, Jiao, Jun, Chen, Yanxue, Yan, Shishen, Liu, Guolei, Mei, Liangmo Year: 2013 ZnO nanoneedle arrays were grown vertically on a fluorine-doped tin oxide-coated glass by hydrothermal method at a relatively low temperature. A self-powered photoelectrochemical cell-type UV detector was fabricated using the ZnO nanoneedles as the active photoanode and H2O as the electrolyte. This solid-liquid heterojunction offers an enlarged ZnO/water contact area and a direct pathway for electron transport simultaneously. By connecting this UV photodetector to an ammeter, the intensity of UV light can be quantified using the output short-circuit photocurrent without a power source. High photosensitivity, excellent spectral selectivity, and fast photoresponse at zero bias are observed in this UV detector. The self-powered behavior can be well explained by the formation of a space charge layer near the interface of the solid-liquid heterojunction, which results in a built-in potential and makes the solid-liquid heterojunction work in photovoltaic mode. Close

• 305. [Article] The Impact of a Large-Scale Climate Event on Antarctic Ecosystem Processes

  Extreme climate and weather events, such as a drought, hurricanes, or ice storms, can strongly imprint ecosystem processing and may alter ecosystem structure. Ecosystems in extreme environments are particularly ...

  Citation × Citation Citation Abstract Copy Title: The Impact of a Large-Scale Climate Event on Antarctic Ecosystem Processes Author: Fountain, Andrew G., Saba, Grace, Adams, Byron, Doran, Peter, Fraser, William, Gooseff, Michael N., Obryk, Maciej K., Priscu, John Charles, Stammerjohn, Sharon, Virginia, Ross A. Year: 2016 Extreme climate and weather events, such as a drought, hurricanes, or ice storms, can strongly imprint ecosystem processing and may alter ecosystem structure. Ecosystems in extreme environments are particularly vulnerable because of their adaptation to severe limitations in energy, water, or nutrients. The vulnerability can be expressed as a relatively long-lasting ecosystem response to a small or brief change in environmental conditions. Such an event occurred in Antarctica and affected two vastly different ecosystems: a marine-dominated coastal system and a terrestrial polar desert. Both sites experienced winds that warmed air temperatures above the 0°C threshold, resulting in extensive snow and ice melt and triggering a series of cascading effects through the ecosystems that are continuing to play out more than a decade later. This highlights the sensitivity of Antarctic ecosystems to warming events, which should occur more frequently in the future with global climate warming. Title: The Impact of a Large-Scale Climate Event on Antarctic Ecosystem Processes Author: Fountain, Andrew G., Saba, Grace, Adams, Byron, Doran, Peter, Fraser, William, Gooseff, Michael N., Obryk, Maciej K., Priscu, John Charles, Stammerjohn, Sharon, Virginia, Ross A. Year: 2016 Extreme climate and weather events, such as a drought, hurricanes, or ice storms, can strongly imprint ecosystem processing and may alter ecosystem structure. Ecosystems in extreme environments are particularly vulnerable because of their adaptation to severe limitations in energy, water, or nutrients. The vulnerability can be expressed as a relatively long-lasting ecosystem response to a small or brief change in environmental conditions. Such an event occurred in Antarctica and affected two vastly different ecosystems: a marine-dominated coastal system and a terrestrial polar desert. Both sites experienced winds that warmed air temperatures above the 0°C threshold, resulting in extensive snow and ice melt and triggering a series of cascading effects through the ecosystems that are continuing to play out more than a decade later. This highlights the sensitivity of Antarctic ecosystems to warming events, which should occur more frequently in the future with global climate warming. Close

• 306. [Article] Spindle Shaped Virus (SSV) : Mutants and Their Infectivity

  SSV1 is an archaeal virus that infects the thermoacidophile Sulfolobus residing in hot springs. The lemon shaped/spindle-shaped fuselloviruses (SSV) that infect Sulfolobus solfataricus is quite morphologically ...

  Citation × Citation Citation Abstract Copy Title: Spindle Shaped Virus (SSV) : Mutants and Their Infectivity Author: Hoang, Thien Year: 2014 SSV1 is an archaeal virus that infects the thermoacidophile Sulfolobus residing in hot springs. The lemon shaped/spindle-shaped fuselloviruses (SSV) that infect Sulfolobus solfataricus is quite morphologically different from almost all other viruses. Because these archaeal viruses live in hot springs with high temperatures and low pH, their genomes and structures have adapted to withstand such harsh conditions. Little research has been done on these extreme viruses, and of the little research, SSV has been the most prominent. Not much is known about the genes that the genome encodes and so I have inserted transposons randomly into genome to determine functionality. The only highly conserved genes whose functions we know for sure are the VP1-3, encoding for the capsids and DNA packaging. I tried to isolate transposons that have inserted into a very small region of the genome, approx. 800bp, but have not had any luck. So far the transposon only inserted into ORFs B-49, F-93, A-132, A-100, and between F-112 and B-49. Title: Spindle Shaped Virus (SSV) : Mutants and Their Infectivity Author: Hoang, Thien Year: 2014 SSV1 is an archaeal virus that infects the thermoacidophile Sulfolobus residing in hot springs. The lemon shaped/spindle-shaped fuselloviruses (SSV) that infect Sulfolobus solfataricus is quite morphologically different from almost all other viruses. Because these archaeal viruses live in hot springs with high temperatures and low pH, their genomes and structures have adapted to withstand such harsh conditions. Little research has been done on these extreme viruses, and of the little research, SSV has been the most prominent. Not much is known about the genes that the genome encodes and so I have inserted transposons randomly into genome to determine functionality. The only highly conserved genes whose functions we know for sure are the VP1-3, encoding for the capsids and DNA packaging. I tried to isolate transposons that have inserted into a very small region of the genome, approx. 800bp, but have not had any luck. So far the transposon only inserted into ORFs B-49, F-93, A-132, A-100, and between F-112 and B-49. Close

• 307. [Article] Validation of an ANN Flow Prediction Model Using a Multt-Station Cluster Analysis

  The objective of this study is to validate a flow prediction model for a hydrometric station using a multistation criterion in addition to standard single-station performance criteria. In this contribution ...

  Citation × Citation Citation Abstract Copy Title: Validation of an ANN Flow Prediction Model Using a Multt-Station Cluster Analysis Author: Demirel, Mehmet, Booij, Martijn, Kahya, Ercan Year: 2012 The objective of this study is to validate a flow prediction model for a hydrometric station using a multistation criterion in addition to standard single-station performance criteria. In this contribution we used cluster analysis to identify the regional flow height, i.e., water-level patterns and validate the output of an artificial neural network (ANN) model of the Alportel River in Portugal. Measurements of precipitation, temperature, and flow height were used as input variables to the ANN model with a lead time of 12 h. The lead time of 12 h is assumed to be appropriate for a short-term hydrological prediction since it is meaningful for physical processes. The ANN model with three inputs, four hidden neurons, and ten epochs was tested using the new model-validation criterion. The high performance of the model (i.e., Nash-Sutcliffe coefficient is equal to 0.922) was confirmed by the cluster-analysis criterion. It can be concluded that a multistation-based approach can be used as an additional validation criterion and might result in a rejection of a model which initially passed a single-station validation criterion. Title: Validation of an ANN Flow Prediction Model Using a Multt-Station Cluster Analysis Author: Demirel, Mehmet, Booij, Martijn, Kahya, Ercan Year: 2012 The objective of this study is to validate a flow prediction model for a hydrometric station using a multistation criterion in addition to standard single-station performance criteria. In this contribution we used cluster analysis to identify the regional flow height, i.e., water-level patterns and validate the output of an artificial neural network (ANN) model of the Alportel River in Portugal. Measurements of precipitation, temperature, and flow height were used as input variables to the ANN model with a lead time of 12 h. The lead time of 12 h is assumed to be appropriate for a short-term hydrological prediction since it is meaningful for physical processes. The ANN model with three inputs, four hidden neurons, and ten epochs was tested using the new model-validation criterion. The high performance of the model (i.e., Nash-Sutcliffe coefficient is equal to 0.922) was confirmed by the cluster-analysis criterion. It can be concluded that a multistation-based approach can be used as an additional validation criterion and might result in a rejection of a model which initially passed a single-station validation criterion. Close

• 308. [Article] Centennial Drought Outlook Over the CONUS Using NASA-NEX Downscaled Climate Ensemble

  Drought is a natural hazard developing slowly and affecting large areas which may have severe consequences on society and economy. Due to the effects of climate change, drought is expected to exacerbate ...

  Citation × Citation Citation Abstract Copy Title: Centennial Drought Outlook Over the CONUS Using NASA-NEX Downscaled Climate Ensemble Author: Ahmadalipour, Ali, Moradkhani, Hamid, Svoboda, Mark Year: 2017 Drought is a natural hazard developing slowly and affecting large areas which may have severe consequences on society and economy. Due to the effects of climate change, drought is expected to exacerbate in various regions in future. In this study, the impact of climate change on drought characteristics is assessed, and statistical methods are employed to analyse the significance of projections. This is the first study utilizing 21 recently available downscaled global climate models generated by NASA (NEX-GDDP) to evaluate drought projections over various regions across the United States. Drought is investigated through a multi-model dual-index dual-scenario approach to probabilistically analyse drought attributes while characterizing the uncertainty in future drought projections. Standardized Precipitation Index and Standardized Precipitation Evapotranspiration Index values at the seasonal scale (3 months) are used to project and analyse meteorological drought conditions from 1950 to 2099 at 0.25° spatial resolution. Two future concentration pathways of RCP4.5 and RCP8.5 are considered for this analysis. Accounting for the combined effects of precipitation and temperature variations reveals a considerable aggravation in severity and extent of future drought in the western United States and a tendency toward more frequent and intense summer droughts across the Contiguous United States. Title: Centennial Drought Outlook Over the CONUS Using NASA-NEX Downscaled Climate Ensemble Author: Ahmadalipour, Ali, Moradkhani, Hamid, Svoboda, Mark Year: 2017 Drought is a natural hazard developing slowly and affecting large areas which may have severe consequences on society and economy. Due to the effects of climate change, drought is expected to exacerbate in various regions in future. In this study, the impact of climate change on drought characteristics is assessed, and statistical methods are employed to analyse the significance of projections. This is the first study utilizing 21 recently available downscaled global climate models generated by NASA (NEX-GDDP) to evaluate drought projections over various regions across the United States. Drought is investigated through a multi-model dual-index dual-scenario approach to probabilistically analyse drought attributes while characterizing the uncertainty in future drought projections. Standardized Precipitation Index and Standardized Precipitation Evapotranspiration Index values at the seasonal scale (3 months) are used to project and analyse meteorological drought conditions from 1950 to 2099 at 0.25° spatial resolution. Two future concentration pathways of RCP4.5 and RCP8.5 are considered for this analysis. Accounting for the combined effects of precipitation and temperature variations reveals a considerable aggravation in severity and extent of future drought in the western United States and a tendency toward more frequent and intense summer droughts across the Contiguous United States. Close

• 309. [Article] Simple GHz Resonator for Superconducting Materials Characterization

  This work examines the design and operation of a longitudinal resonant cavity, paired with monopole send and reciprocal patch receive antennae, that couples radio-frequency energy to a superconducting ...

  Citation × Citation Citation Abstract Copy Title: Simple GHz Resonator for Superconducting Materials Characterization Author: Jensen, Shauna Marie, Bass, Robert, Lichtenberger, Arthur W., Datesman, Aaron M. Year: 2015 This work examines the design and operation of a longitudinal resonant cavity, paired with monopole send and reciprocal patch receive antennae, that couples radio-frequency energy to a superconducting thin film carrying high current densities (~105 A/cm2). The dielectric substrate supporting the film penetrates the waveguide, which operates in an evanescent mode below the design cutoff frequency of 18 GHz. Oscillatory vortex motion in the thin film is found to produce a small (~0.1 mV) dc voltage. When the niobium film is patterned to form an aperture that permits resonant conditions within the waveguide volume, the measured voltage increases by an order of magnitude. The increase is explained in the framework of the Larkin-Ovchinnikov model for quasiparticle behavior inside a moving normal vortex core. Operated near the superconducting transition, this device is useful for materials characterization, including the possibility to extract parameters including the pinning force. The authors suggest that the device could be used to characterize the pinning potential or to explore quasiparticle dynamics in superconducting thin films. Title: Simple GHz Resonator for Superconducting Materials Characterization Author: Jensen, Shauna Marie, Bass, Robert, Lichtenberger, Arthur W., Datesman, Aaron M. Year: 2015 This work examines the design and operation of a longitudinal resonant cavity, paired with monopole send and reciprocal patch receive antennae, that couples radio-frequency energy to a superconducting thin film carrying high current densities (~105 A/cm2). The dielectric substrate supporting the film penetrates the waveguide, which operates in an evanescent mode below the design cutoff frequency of 18 GHz. Oscillatory vortex motion in the thin film is found to produce a small (~0.1 mV) dc voltage. When the niobium film is patterned to form an aperture that permits resonant conditions within the waveguide volume, the measured voltage increases by an order of magnitude. The increase is explained in the framework of the Larkin-Ovchinnikov model for quasiparticle behavior inside a moving normal vortex core. Operated near the superconducting transition, this device is useful for materials characterization, including the possibility to extract parameters including the pinning force. The authors suggest that the device could be used to characterize the pinning potential or to explore quasiparticle dynamics in superconducting thin films. Close

• 310. [Article] Microstructures and Stabilization Mechanisms of Nanocrystalline Iron-Chromium Alloys with Hafnium Addition

  The low thermal stability of nanocrystalline metals severely limits their applications at high temperatures. In this study, we investigate the nanocrystalline stabilization mechanisms for Fe-14Cr alloys ...

  Citation × Citation Citation Abstract Copy Title: Microstructures and Stabilization Mechanisms of Nanocrystalline Iron-Chromium Alloys with Hafnium Addition Author: Xu, Weizong, Li, Lulu, Saber, Mostafa, Koch, Carl C., Zhu, Yuntian, Scattergood, Ronald O. Year: 2015 The low thermal stability of nanocrystalline metals severely limits their applications at high temperatures. In this study, we investigate the nanocrystalline stabilization mechanisms for Fe-14Cr alloys with 1, 2, and 4 at. pct Hf addition at 1173 K (900 °C). Microstructural characterizations using aberration-corrected scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy reveal high density of HfO2 nanoparticles with sizes of ~4 nm dispersed throughout the ferritic matrix. This indicates that kinetic stabilization by HfO2 nanoparticle pinning is primarily responsible for the observed high thermal stability. In addition, some Hf and Cr segregation on grain boundaries is observed in the Fe-14Cr-4Hf, suggesting the existence of thermodynamic stabilization at high Hf content. Second-phase precipitations such as hafnium carbide, M23C6, and Fe-Cr-Hf intermetallic phase are also found in the Fe-14Cr-4Hf, but their large sizes and inter-spacing suggest that their contribution to stabilization is minimal. Title: Microstructures and Stabilization Mechanisms of Nanocrystalline Iron-Chromium Alloys with Hafnium Addition Author: Xu, Weizong, Li, Lulu, Saber, Mostafa, Koch, Carl C., Zhu, Yuntian, Scattergood, Ronald O. Year: 2015 The low thermal stability of nanocrystalline metals severely limits their applications at high temperatures. In this study, we investigate the nanocrystalline stabilization mechanisms for Fe-14Cr alloys with 1, 2, and 4 at. pct Hf addition at 1173 K (900 °C). Microstructural characterizations using aberration-corrected scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy reveal high density of HfO2 nanoparticles with sizes of ~4 nm dispersed throughout the ferritic matrix. This indicates that kinetic stabilization by HfO2 nanoparticle pinning is primarily responsible for the observed high thermal stability. In addition, some Hf and Cr segregation on grain boundaries is observed in the Fe-14Cr-4Hf, suggesting the existence of thermodynamic stabilization at high Hf content. Second-phase precipitations such as hafnium carbide, M23C6, and Fe-Cr-Hf intermetallic phase are also found in the Fe-14Cr-4Hf, but their large sizes and inter-spacing suggest that their contribution to stabilization is minimal. Close