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• 11. [Article] Thermal Footprint Effect of Rooftop Urban Cooling Strategies

  Simulation results indicate that urban morphology plays an important role in determining the efficacy of rooftop urban cooling strategies for improving pedestrian thermal comfort. Results suggest that ...

  Citation × Citation Citation Abstract Copy Title: Thermal Footprint Effect of Rooftop Urban Cooling Strategies Author: Botham-Myint, Dylan, Recktenwald, Gerald W., Sailor, David J. Year: 2015 Simulation results indicate that urban morphology plays an important role in determining the efficacy of rooftop urban cooling strategies for improving pedestrian thermal comfort. Results suggest that a white roof has the greatest effect on near-surface air temperatures within the urban canyon when used on buildings of 1–2 stories height and almost no near-surface effect when applied to 4 story buildings. However, the near-surface effect is more substantial when complex urban morphology introduces enhanced vertical mixing. Of the cases studied the largest near-surface cooling benefit of implementing white roofs was found for the case when a taller building existed downwind from a building with a white roof. Using the Thermal Footprint Ratio it was found that by placing a tall building behind a building with a white roof in an otherwise uniform array of 2 story buildings, the cool roof would be twice as effective at reducing air temperatures at the pedestrian level. Calculations of the volumetric heat removal confirmed this result, indicating that the positioning of the tall building downwind of the modified roof would be 2.6 times as effective at cooling the pedestrian level air volume as compared to the case where all buildings were a uniform height. Title: Thermal Footprint Effect of Rooftop Urban Cooling Strategies Author: Botham-Myint, Dylan, Recktenwald, Gerald W., Sailor, David J. Year: 2015 Simulation results indicate that urban morphology plays an important role in determining the efficacy of rooftop urban cooling strategies for improving pedestrian thermal comfort. Results suggest that a white roof has the greatest effect on near-surface air temperatures within the urban canyon when used on buildings of 1–2 stories height and almost no near-surface effect when applied to 4 story buildings. However, the near-surface effect is more substantial when complex urban morphology introduces enhanced vertical mixing. Of the cases studied the largest near-surface cooling benefit of implementing white roofs was found for the case when a taller building existed downwind from a building with a white roof. Using the Thermal Footprint Ratio it was found that by placing a tall building behind a building with a white roof in an otherwise uniform array of 2 story buildings, the cool roof would be twice as effective at reducing air temperatures at the pedestrian level. Calculations of the volumetric heat removal confirmed this result, indicating that the positioning of the tall building downwind of the modified roof would be 2.6 times as effective at cooling the pedestrian level air volume as compared to the case where all buildings were a uniform height. Close

• 12. [Article] Bi-Material Assembly Subjected to Thermal Stress: Propensity to Delamination Assessed Using Interfacial Compliance Model

  It is shown that an engineering stress model suggested about 30 years ago for the approximate evaluation of the interfacial stresses in adhesively bonded or soldered bi-material assemblies experiencing ...

  Citation × Citation Citation Abstract Copy Title: Bi-Material Assembly Subjected to Thermal Stress: Propensity to Delamination Assessed Using Interfacial Compliance Model Author: Suhir, Ephraim Year: 2016 It is shown that an engineering stress model suggested about 30 years ago for the approximate evaluation of the interfacial stresses in adhesively bonded or soldered bi-material assemblies experiencing thermal loading and based on the concept of interfacial compliance can be employed also for the assessment of the assembly’s propensity to delamination. The analysis is limited to the shearing mode of failure and to the elastic stresses. A probabilistic extreme value distribution (EVD) approach can be used to consider the random nature of both the actual and the critical stress-energy-release-rates (SERR). The step-wise nature of the typical failure oriented accelerated test (FOAT) loading in the electronics reliability field (such as, e.g., temperature cycling) is addressed. The general concepts are illustrated by numerical examples. Title: Bi-Material Assembly Subjected to Thermal Stress: Propensity to Delamination Assessed Using Interfacial Compliance Model Author: Suhir, Ephraim Year: 2016 It is shown that an engineering stress model suggested about 30 years ago for the approximate evaluation of the interfacial stresses in adhesively bonded or soldered bi-material assemblies experiencing thermal loading and based on the concept of interfacial compliance can be employed also for the assessment of the assembly’s propensity to delamination. The analysis is limited to the shearing mode of failure and to the elastic stresses. A probabilistic extreme value distribution (EVD) approach can be used to consider the random nature of both the actual and the critical stress-energy-release-rates (SERR). The step-wise nature of the typical failure oriented accelerated test (FOAT) loading in the electronics reliability field (such as, e.g., temperature cycling) is addressed. The general concepts are illustrated by numerical examples. Close

• 13. [Article] Quench Factor Characterization of Steel Hardening: A Review

  A quench factor, Q, has been derived that quantifies the overall severity of the steel hardening process—quench severity by interrelating steel hardenability with quenching variables including: the specific ...

  Citation × Citation Citation Abstract Copy Title: Quench Factor Characterization of Steel Hardening: A Review Author: Otero, Rosa Lucia Simencio, Otero, Walker Roberto, Totten, George E., Canale, Lauralice C.F. Year: 2014 A quench factor, Q, has been derived that quantifies the overall severity of the steel hardening process—quench severity by interrelating steel hardenability with quenching variables including: the specific quenchant being used, agitation, bath temperature, etc. In this analysis, quench severity is quantified by a so-called “quench factor” (Q) that is a single numerical value that effectively indicates the extent to which a given steel can be hardened. This article provides a description of the concept and an overall review of applications where it has been successfully applied. Title: Quench Factor Characterization of Steel Hardening: A Review Author: Otero, Rosa Lucia Simencio, Otero, Walker Roberto, Totten, George E., Canale, Lauralice C.F. Year: 2014 A quench factor, Q, has been derived that quantifies the overall severity of the steel hardening process—quench severity by interrelating steel hardenability with quenching variables including: the specific quenchant being used, agitation, bath temperature, etc. In this analysis, quench severity is quantified by a so-called “quench factor” (Q) that is a single numerical value that effectively indicates the extent to which a given steel can be hardened. This article provides a description of the concept and an overall review of applications where it has been successfully applied. Close

• 14. [Article] A feasibility analysis of a directly sun-pumped carbon dioxide laser in space

  The possibility of using sunlight to pump a CW carbon dioxide laser has been analyzed. Such a laser could be of interest for such applications as space communication and power transmission. In order to ...

  Citation × Citation Citation Abstract Copy Title: A feasibility analysis of a directly sun-pumped carbon dioxide laser in space Author: Morimoto, Seiichi Year: 1979 The possibility of using sunlight to pump a CW carbon dioxide laser has been analyzed. Such a laser could be of interest for such applications as space communication and power transmission. In order to optically pump CO2 using sunlight, the intense vibrational-rotational absorption bands of CO2 in the 4.3 micron spectral region would have to be utilized. The total pumping power from sunlight can be calculated from the known data of the solar spectral irradiance outside the atmosphere and the infrared absorption by carbon dioxide at 4.3 microns. The pumping power is proportional to the collector area of the sunlight and is also dependent on the characteristics of the absorbing gas mixture, such as the gas composition, the gas temperature, the total pressure of the mixture, the partial pressure of CO2, and the absorption path length of the sunlight in the gas. To analyze the carbon dioxide laser system, a thermodynamic approach was used with a simplified CO2 chemical kinetic model. The gain and saturation intensity were obtained by solving a set of energy balance equations which describe the processes among the various vibrational modes. From those results, along with the estimated cavity losses, the output power was found. Title: A feasibility analysis of a directly sun-pumped carbon dioxide laser in space Author: Morimoto, Seiichi Year: 1979 The possibility of using sunlight to pump a CW carbon dioxide laser has been analyzed. Such a laser could be of interest for such applications as space communication and power transmission. In order to optically pump CO2 using sunlight, the intense vibrational-rotational absorption bands of CO2 in the 4.3 micron spectral region would have to be utilized. The total pumping power from sunlight can be calculated from the known data of the solar spectral irradiance outside the atmosphere and the infrared absorption by carbon dioxide at 4.3 microns. The pumping power is proportional to the collector area of the sunlight and is also dependent on the characteristics of the absorbing gas mixture, such as the gas composition, the gas temperature, the total pressure of the mixture, the partial pressure of CO2, and the absorption path length of the sunlight in the gas. To analyze the carbon dioxide laser system, a thermodynamic approach was used with a simplified CO2 chemical kinetic model. The gain and saturation intensity were obtained by solving a set of energy balance equations which describe the processes among the various vibrational modes. From those results, along with the estimated cavity losses, the output power was found. Close

• 15. [Article] Neutron-Scattering Study of Librations and Intramolecular Phonons in Rb_{2.6}K_{0.4}C_{60}

  We report the results of inelastic neutron-scattering measurements on Rb2.6K0.4C60. Librational modes were observed as broad peaks with maxima between 4.1 and 4.7 meV, as the temperature is lowered from ...

  Citation × Citation Citation Abstract Copy Title: Neutron-Scattering Study of Librations and Intramolecular Phonons in Rb_{2.6}K_{0.4}C_{60} Author: Reznik, D., Kamitakahara, W. A., Neumann, D. A., Copley, J. R. D., Fischer, J. E., Strongin, Robert M., Cichy, M. A., Smith, Amos B., III Year: 1994 We report the results of inelastic neutron-scattering measurements on Rb2.6K0.4C60. Librational modes were observed as broad peaks with maxima between 4.1 and 4.7 meV, as the temperature is lowered from 300 to 12 K. As in K3C60, no change in the width or position of the librational peak was observed when the sample was cooled through the superconducting transition. Thus any coupling of the librations to electronic states is small. The magnitude of the orientational potential barrier was estimated from the librational peak frequency. A flat background observed in the low-energy inelastic-scattering spectra is ascribed to two-phonon scattering. The density of states of intramolecular modes is similar to that of previously studied M3C60 compounds; modes at 53 and 66 meV in pure C60 are not observed in Rb2.6K0.4C60. Title: Neutron-Scattering Study of Librations and Intramolecular Phonons in Rb_{2.6}K_{0.4}C_{60} Author: Reznik, D., Kamitakahara, W. A., Neumann, D. A., Copley, J. R. D., Fischer, J. E., Strongin, Robert M., Cichy, M. A., Smith, Amos B., III Year: 1994 We report the results of inelastic neutron-scattering measurements on Rb2.6K0.4C60. Librational modes were observed as broad peaks with maxima between 4.1 and 4.7 meV, as the temperature is lowered from 300 to 12 K. As in K3C60, no change in the width or position of the librational peak was observed when the sample was cooled through the superconducting transition. Thus any coupling of the librations to electronic states is small. The magnitude of the orientational potential barrier was estimated from the librational peak frequency. A flat background observed in the low-energy inelastic-scattering spectra is ascribed to two-phonon scattering. The density of states of intramolecular modes is similar to that of previously studied M3C60 compounds; modes at 53 and 66 meV in pure C60 are not observed in Rb2.6K0.4C60. Close

• 16. [Article] Engineered Mushing Cooker

  This project revolves around building methanol cookers for dog mushers in the Iditarod and for the Denali Park Ranger Kennel in Denali National Park, Alaska. Traditional cookers are bulky, slow to burn, ...

  Citation × Citation Citation Abstract Copy Title: Engineered Mushing Cooker Author: Ritter, Aimee Year: 2016 This project revolves around building methanol cookers for dog mushers in the Iditarod and for the Denali Park Ranger Kennel in Denali National Park, Alaska. Traditional cookers are bulky, slow to burn, and use up a lot of fuel. Our goal has been to revolutionize the way mushing cookers look and perform. Our cookers are built to pack well in the sleds, heat up to 3 gallons of snowmelt, perform in arctic climates, use methanol (specifically HEET) for fuel, and be lightweight. A traditional cooker would use 3 to 4 bottles or more of HEET (36-48+oz.) and take at least 1 hour to heat up 3 gallons of water to the temperature needed to warm up frozen dog food. Our design takes 30 minutes and uses 2 to 3 bottles of HEET (24-36 oz). Additionally, it is square, making it easier to pack in a sled. The picture below shows the final product of the cooker that we sent to the musher Lisbet Norris for use in the 2016 Iditarod. Title: Engineered Mushing Cooker Author: Ritter, Aimee Year: 2016 This project revolves around building methanol cookers for dog mushers in the Iditarod and for the Denali Park Ranger Kennel in Denali National Park, Alaska. Traditional cookers are bulky, slow to burn, and use up a lot of fuel. Our goal has been to revolutionize the way mushing cookers look and perform. Our cookers are built to pack well in the sleds, heat up to 3 gallons of snowmelt, perform in arctic climates, use methanol (specifically HEET) for fuel, and be lightweight. A traditional cooker would use 3 to 4 bottles or more of HEET (36-48+oz.) and take at least 1 hour to heat up 3 gallons of water to the temperature needed to warm up frozen dog food. Our design takes 30 minutes and uses 2 to 3 bottles of HEET (24-36 oz). Additionally, it is square, making it easier to pack in a sled. The picture below shows the final product of the cooker that we sent to the musher Lisbet Norris for use in the 2016 Iditarod. Close

• 17. [Article] An in Situ Experimental Study of Grain Growth in a Nanocrystalline Fe91Ni8Zr1 Alloy

  Grain growth and microstructural evolution of thermally stabilized Fe91Ni8Zr1 were investigated by in situ and ex situ studies. Our investigations suggest that the microstructural evolution is fairly slow ...

  Citation × Citation Citation Abstract Copy Title: An in Situ Experimental Study of Grain Growth in a Nanocrystalline Fe91Ni8Zr1 Alloy Author: Kotan, Hasan, Darling, Kris A., Saber, Mostafa, Scattergood, Ronald O., Koch, Carl C. Year: 2013 Grain growth and microstructural evolution of thermally stabilized Fe91Ni8Zr1 were investigated by in situ and ex situ studies. Our investigations suggest that the microstructural evolution is fairly slow and the microstructure shows stabilization up to about 700 °C. Above this temperature, a certain fraction of grains grow abnormally into the nanocrystalline matrix, resulting in a bimodal microstructure and causing the complete loss of thermal stability. The reason for abnormal grain growth and the loss of thermal stability is identified as the appearance of the fcc γ-phase and consequent reduction in the total area of grain boundaries and the overall stored energy. Title: An in Situ Experimental Study of Grain Growth in a Nanocrystalline Fe91Ni8Zr1 Alloy Author: Kotan, Hasan, Darling, Kris A., Saber, Mostafa, Scattergood, Ronald O., Koch, Carl C. Year: 2013 Grain growth and microstructural evolution of thermally stabilized Fe91Ni8Zr1 were investigated by in situ and ex situ studies. Our investigations suggest that the microstructural evolution is fairly slow and the microstructure shows stabilization up to about 700 °C. Above this temperature, a certain fraction of grains grow abnormally into the nanocrystalline matrix, resulting in a bimodal microstructure and causing the complete loss of thermal stability. The reason for abnormal grain growth and the loss of thermal stability is identified as the appearance of the fcc γ-phase and consequent reduction in the total area of grain boundaries and the overall stored energy. Close

• 18. [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

• 19. [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

• 20. [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