Search

Search Results

• 361. [Article] Riparian Shade Assessment and Restoration Priorities Analysis in the Damascus Urban Growth Boundary Expansion Area

  An important component of progressive urban planning is the protection and restoration of riparian environments, particularly in the Pacific Northwest where increasing stream temperatures threaten the ...

  Citation × Citation Citation Abstract Copy Title: Riparian Shade Assessment and Restoration Priorities Analysis in the Damascus Urban Growth Boundary Expansion Area Author: Leferink, Robin K. Year: 2007 An important component of progressive urban planning is the protection and restoration of riparian environments, particularly in the Pacific Northwest where increasing stream temperatures threaten the survival of endangered salmonids and other cold-water biota. Restoration projects are often led by watershed councils or other grassroots organizations with limited resources, and it is essential that these groups have an efficient and effective approach to determine priority areas where their efforts can be directed to achieve the greatest ecological benefit. The purpose of this project was to quantify existing riparian shade levels and identify priority reaches for shade restoration on Clackamas River basin streams in the Damascus area expansion of the Portland, Oregon urban growth boundary. Additionally, potential errors in the Metro Regional Land Information System (RLIS) Lite geographic information system (GIS) coverage of the area’s streams were identified and corrected where possible. Riparian shade levels were quantified through interpretation of digital aerial photographs using GIS. At the start of the shade analysis six 50 m reaches in the study area were surveyed using a spherical densiometer to calibrate the aerial photo interpretation. Following the analysis, the method accuracy was assessed by comparing GIS-derived shade classes with field data from 25 sites in the study area that were surveyed in 2003. Stream reaches were identified and prioritized for restoration based on riparian shade level, presence or absence of late-summer flow (as determined through field investigations), and GISevaluated stream aspect (i.e. the direction of stream flow). Generally, the headwaters were found to have less shade than the downstream areas and many of the headwater reaches were identified as the highest restoration priority. Of the 60.5 km of streams assessed in the riparian shade analysis, 24.7 km were identified as potential restoration reaches based on shade levels and late-summer flow conditions. These 24.7 km were further broken into five priority ranks, with 4.1 km of stream reaches assigned to the highest shade restoration priority class. Potential errors in the GIS stream coverage were identified in conjunction with the riparian shade assessment. Where possible, these errors were corrected based on the aerial photographs. Although in many cases access was limited, a total of 18 site visits were made to verify stream locations. The results of this watershed-scale restoration priorities analysis are being used by Clackamas River Basin Council and others to guide restoration planning in the new urban area. While focusing on the high priority stream reaches identified, restoration managers will also need to consider reach-scale factors including land use plans, riparian continuity, parcel size, and landowner cooperation in the final selection of restoration sites. The GIS stream layer corrections were provided to Metro and to the City of Damascus for use in their 2007 natural resource inventory. Title: Riparian Shade Assessment and Restoration Priorities Analysis in the Damascus Urban Growth Boundary Expansion Area Author: Leferink, Robin K. Year: 2007 An important component of progressive urban planning is the protection and restoration of riparian environments, particularly in the Pacific Northwest where increasing stream temperatures threaten the survival of endangered salmonids and other cold-water biota. Restoration projects are often led by watershed councils or other grassroots organizations with limited resources, and it is essential that these groups have an efficient and effective approach to determine priority areas where their efforts can be directed to achieve the greatest ecological benefit. The purpose of this project was to quantify existing riparian shade levels and identify priority reaches for shade restoration on Clackamas River basin streams in the Damascus area expansion of the Portland, Oregon urban growth boundary. Additionally, potential errors in the Metro Regional Land Information System (RLIS) Lite geographic information system (GIS) coverage of the area’s streams were identified and corrected where possible. Riparian shade levels were quantified through interpretation of digital aerial photographs using GIS. At the start of the shade analysis six 50 m reaches in the study area were surveyed using a spherical densiometer to calibrate the aerial photo interpretation. Following the analysis, the method accuracy was assessed by comparing GIS-derived shade classes with field data from 25 sites in the study area that were surveyed in 2003. Stream reaches were identified and prioritized for restoration based on riparian shade level, presence or absence of late-summer flow (as determined through field investigations), and GISevaluated stream aspect (i.e. the direction of stream flow). Generally, the headwaters were found to have less shade than the downstream areas and many of the headwater reaches were identified as the highest restoration priority. Of the 60.5 km of streams assessed in the riparian shade analysis, 24.7 km were identified as potential restoration reaches based on shade levels and late-summer flow conditions. These 24.7 km were further broken into five priority ranks, with 4.1 km of stream reaches assigned to the highest shade restoration priority class. Potential errors in the GIS stream coverage were identified in conjunction with the riparian shade assessment. Where possible, these errors were corrected based on the aerial photographs. Although in many cases access was limited, a total of 18 site visits were made to verify stream locations. The results of this watershed-scale restoration priorities analysis are being used by Clackamas River Basin Council and others to guide restoration planning in the new urban area. While focusing on the high priority stream reaches identified, restoration managers will also need to consider reach-scale factors including land use plans, riparian continuity, parcel size, and landowner cooperation in the final selection of restoration sites. The GIS stream layer corrections were provided to Metro and to the City of Damascus for use in their 2007 natural resource inventory. Close

• 362. [Article] Seasonal and Sex Differences in the Effects of Melatonin on Brain Arginine Vasotocin in Green Treefrogs (Hyla cinerea): Relationship to Melatonin Receptor 1a

  Critical life history events such as breeding, migration and hibernation must take place in the correct environmental context to minimize deleterious consequences on survival and reproductive fitness. ...

  Citation × Citation Citation Abstract Copy Title: Seasonal and Sex Differences in the Effects of Melatonin on Brain Arginine Vasotocin in Green Treefrogs (Hyla cinerea): Relationship to Melatonin Receptor 1a Author: Howard, Christina Marie Year: 2014 Critical life history events such as breeding, migration and hibernation must take place in the correct environmental context to minimize deleterious consequences on survival and reproductive fitness. Neuroendocrine mechanisms synchronizing internal physiological states with extrinsic environmental cues are vital to timing life history events appropriately. Secretion of the pineal hormone melatonin is sensitive to light and temperature cues, which provides a physiological indicator of time of day and time of year for organisms. Melatonin influences seasonal reproduction in a variety of vertebrates, likely by altering the synthesis and/or release of reproductive neuropeptides in the brain. The neuropeptides arginine vasotocin and its mammalian homologue, arginine vasopressin, are well-known modulators of reproductive and sociosexual behavior across vertebrate taxa, and are likely targets of melatonin in the context of seasonal reproduction. There is extensive evidence that vasotocin/vasopressin innervation in the brain is subject to seasonal variation, and that this variation is frequently sexually dimorphic. However, evidence that melatonin directly modulates this important neuropeptide system is lacking. Melatonin receptor 1a (MT1 in mammals) may be responsible for mediating melatonin's influence on brain vasotocin, as it is known to regulate seasonal reproduction in a variety of vertebrates. In the present study, I asked whether melatonin influences brain vasotocin in male green treefrogs (Hyla cinerea), and compared the distribution of melatonin receptor 1a in the brain of green treefrogs between sexes and seasons. Adult male and female green treefrogs were collected from field sites in Louisiana during the summer breeding season. Summer animals were acclimated to lab conditions for 3 weeks, then euthanized and their brains collected. Winter animals were maintained in the lab for four months under incrementally changing photo-, thermo-, and hygroperiod regimes that mimicked the transition to winter in their natural habitat, followed by euthanasia and brain collection. A subset of winter males (Experiment 1) were implanted with melatonin-filled or blank silastic capsules for a period of one month prior to euthanasia and brain collection. Brains of these males were processed for vasotocin immunohistochemistry. I quantified AVT-ir cell number in Experiment 1 males in the nucleus accumbens (NAcc), amygdala and caudal striatum (AMG), preoptic area (POA), suprachaismatic nucleus (SCN), and ventral hypothalamus (VH). Melatonin did not influence brain vasotocin-ir cell number in any brain region. Brains from untreated summer and winter males and females were collected and processed for MT1 immunohistochemistry. MT1-ir cells were quantified in the NAcc, striatum (STR), AMG, POA, SCN, and VH. In all regions quantified, reproductively active males had significantly more MT1-ir cells than nonreproductive males. Within the summer breeding season, males had significantly more MT1-ir cells in the NAcc than did reproductively active females. In all other regions there was no significant difference in MT1-ir cell number between reproductively active males and females. Collectively, these data suggest that melatonin modulates vasotocin via MT1. These findings assist in elucidating the neuroendocrine mechanisms by which vertebrates integrate seasonal cues with physiology to correctly time critical life history events. Title: Seasonal and Sex Differences in the Effects of Melatonin on Brain Arginine Vasotocin in Green Treefrogs (Hyla cinerea): Relationship to Melatonin Receptor 1a Author: Howard, Christina Marie Year: 2014 Critical life history events such as breeding, migration and hibernation must take place in the correct environmental context to minimize deleterious consequences on survival and reproductive fitness. Neuroendocrine mechanisms synchronizing internal physiological states with extrinsic environmental cues are vital to timing life history events appropriately. Secretion of the pineal hormone melatonin is sensitive to light and temperature cues, which provides a physiological indicator of time of day and time of year for organisms. Melatonin influences seasonal reproduction in a variety of vertebrates, likely by altering the synthesis and/or release of reproductive neuropeptides in the brain. The neuropeptides arginine vasotocin and its mammalian homologue, arginine vasopressin, are well-known modulators of reproductive and sociosexual behavior across vertebrate taxa, and are likely targets of melatonin in the context of seasonal reproduction. There is extensive evidence that vasotocin/vasopressin innervation in the brain is subject to seasonal variation, and that this variation is frequently sexually dimorphic. However, evidence that melatonin directly modulates this important neuropeptide system is lacking. Melatonin receptor 1a (MT1 in mammals) may be responsible for mediating melatonin's influence on brain vasotocin, as it is known to regulate seasonal reproduction in a variety of vertebrates. In the present study, I asked whether melatonin influences brain vasotocin in male green treefrogs (Hyla cinerea), and compared the distribution of melatonin receptor 1a in the brain of green treefrogs between sexes and seasons. Adult male and female green treefrogs were collected from field sites in Louisiana during the summer breeding season. Summer animals were acclimated to lab conditions for 3 weeks, then euthanized and their brains collected. Winter animals were maintained in the lab for four months under incrementally changing photo-, thermo-, and hygroperiod regimes that mimicked the transition to winter in their natural habitat, followed by euthanasia and brain collection. A subset of winter males (Experiment 1) were implanted with melatonin-filled or blank silastic capsules for a period of one month prior to euthanasia and brain collection. Brains of these males were processed for vasotocin immunohistochemistry. I quantified AVT-ir cell number in Experiment 1 males in the nucleus accumbens (NAcc), amygdala and caudal striatum (AMG), preoptic area (POA), suprachaismatic nucleus (SCN), and ventral hypothalamus (VH). Melatonin did not influence brain vasotocin-ir cell number in any brain region. Brains from untreated summer and winter males and females were collected and processed for MT1 immunohistochemistry. MT1-ir cells were quantified in the NAcc, striatum (STR), AMG, POA, SCN, and VH. In all regions quantified, reproductively active males had significantly more MT1-ir cells than nonreproductive males. Within the summer breeding season, males had significantly more MT1-ir cells in the NAcc than did reproductively active females. In all other regions there was no significant difference in MT1-ir cell number between reproductively active males and females. Collectively, these data suggest that melatonin modulates vasotocin via MT1. These findings assist in elucidating the neuroendocrine mechanisms by which vertebrates integrate seasonal cues with physiology to correctly time critical life history events. Close

• 363. [Article] Teacher Learning: Documentation, Collaboration, and Reflection

  Inspired by the Municipal preprimary schools of Reggio Emilia, Italy, two art studio teachers and a researcher have explored experiences and meaning in the atelier. When studio teachers document children's ...

  Citation × Citation Citation Abstract Copy Title: Teacher Learning: Documentation, Collaboration, and Reflection Author: Parnell, William A. Year: 2005 Inspired by the Municipal preprimary schools of Reggio Emilia, Italy, two art studio teachers and a researcher have explored experiences and meaning in the atelier. When studio teachers document children's thinking through digital photographs. transcribed audio tapes, quotations of a child's verbal thoughts, and copies of their work, an indescribable moment in teacher thinking interweaves with the child's learning, As teachers capture children's representations, investigate, interpret, and share their ideas with colleagues and community-an underlying question emerges. What are studio teachers' experiences o/teaching-learning in the atelier as they utilize documentation, collaboration, and reflection as a way to inform their practices? From this question, reader and researcher start a journey together into a six-month phenomenological study of studio teaching experiences. As a core member in the teaching team, the studio teacher resides in the atelier to bring teaching and learning together in a profound way, to bridge classroom experiences with representative arts, and to facilitate the community's learning about teaching-learning. The methods used to inform this study include observations, in-depth interviews, electronic journaling, description, photos, and interpretation of studio work. Overall, this study's methods inform the phenomenological research and construct an in-depth look at experiences in the artist's studio. The results of this research are retold through narratives focusing on experiences and meaning-making in the studios. Stories such as living with the cracked egg; isolation in the studio: gifts for others; rough stones polishing one another; and many others, utilize photographs to enhance meaning through picturesque artifacts. Essential themes, conclusions, and implications appear in the webbing of experiences and are explored in the final chapter. The themes include conceptual frameworks such as life eats entropy, serendipity and synergy and more. Conclusions are drawn and findings are made connecting studio experiences to participant voice, disequilibrium, listening, engaging, stepping back, and slowing time; demonstrating documentation as learning, revisiting, representation, and manageability; making meaning of collaboration as struggle, communication, and reconstruction; and reflecting back as purposeful and an act of teaching-learning. Overall, this research study exposes techniques, ideas, and wonderings from two studio teachers' and a researcher's experiences in the atelier. Title: Teacher Learning: Documentation, Collaboration, and Reflection Author: Parnell, William A. Year: 2005 Inspired by the Municipal preprimary schools of Reggio Emilia, Italy, two art studio teachers and a researcher have explored experiences and meaning in the atelier. When studio teachers document children's thinking through digital photographs. transcribed audio tapes, quotations of a child's verbal thoughts, and copies of their work, an indescribable moment in teacher thinking interweaves with the child's learning, As teachers capture children's representations, investigate, interpret, and share their ideas with colleagues and community-an underlying question emerges. What are studio teachers' experiences o/teaching-learning in the atelier as they utilize documentation, collaboration, and reflection as a way to inform their practices? From this question, reader and researcher start a journey together into a six-month phenomenological study of studio teaching experiences. As a core member in the teaching team, the studio teacher resides in the atelier to bring teaching and learning together in a profound way, to bridge classroom experiences with representative arts, and to facilitate the community's learning about teaching-learning. The methods used to inform this study include observations, in-depth interviews, electronic journaling, description, photos, and interpretation of studio work. Overall, this study's methods inform the phenomenological research and construct an in-depth look at experiences in the artist's studio. The results of this research are retold through narratives focusing on experiences and meaning-making in the studios. Stories such as living with the cracked egg; isolation in the studio: gifts for others; rough stones polishing one another; and many others, utilize photographs to enhance meaning through picturesque artifacts. Essential themes, conclusions, and implications appear in the webbing of experiences and are explored in the final chapter. The themes include conceptual frameworks such as life eats entropy, serendipity and synergy and more. Conclusions are drawn and findings are made connecting studio experiences to participant voice, disequilibrium, listening, engaging, stepping back, and slowing time; demonstrating documentation as learning, revisiting, representation, and manageability; making meaning of collaboration as struggle, communication, and reconstruction; and reflecting back as purposeful and an act of teaching-learning. Overall, this research study exposes techniques, ideas, and wonderings from two studio teachers' and a researcher's experiences in the atelier. Close

• 364. [Article] Where Is Portland Made? The Complex Relationship between Social Media and Place in the Artisan Economy of Portland, Oregon (USA)

  Portland, Oregon (USA) has become known for an artisanal or ‘maker’ economy that relies on a resurgence of place specificity (Heying), primarily expressed and exported to a global audience in the notion ...

  Citation × Citation Citation Abstract Copy Title: Where Is Portland Made? The Complex Relationship between Social Media and Place in the Artisan Economy of Portland, Oregon (USA) Author: Marotta, Stephen, Cummings, Austin, Heying, Charles H. Year: 2016 Portland, Oregon (USA) has become known for an artisanal or ‘maker’ economy that relies on a resurgence of place specificity (Heying), primarily expressed and exported to a global audience in the notion of ‘Portland Made’ (Roy). Portland Made reveals a tension immanent in the notion of ‘place’: place is both here and not here, both real and imaginary. What emerges is a complicated picture of how place conceptually captures various intersections of materiality and mythology, aesthetics and economics. On the one hand, Portland Made represents the collective brand-identity used by Portland’s makers to signify a products’ material existence as handcrafted, place-embedded, and authentic. These characteristics lead to certain assumptions about the concept of ‘local’ (Marotta and Heying): what meaning does Portland Made convey, and how is such meaning distributed? On the other hand, the seemingly intentional embedding of place-specificity in objects meant for distribution far outside of Portland begs another type of question: how does Portland come to be discursively representative of these characteristics, and how are such representations distributed to global audiences? How does this global distribution and consumption of immaterial Portland feed back into the production of material Portland? To answer these questions we look to the realm of social media, specifically the popular image-based service Instagram. For the uninitiated, Instagram is a web-based social media service that allows pictures to be shared and seen by anyone that follows a person or business’ Instagram account. Actions include posting original photos (often taken and posted with a cell phone), ‘liking’ pictures, and ‘hash-tagging’ posts with trending terms that increase visibility. Instagram presents us with a complex view of place as both material and virtual, sometimes reifying and sometimes abstracting often-contradictory understandings of place specificity. Many makers use Instagram to promote their products to a broad audience and, in doing so, makers participate in the construction of Portland’s mythology. In this paper, we use empirical insights to theorise makers’ role in shaping and cultivating the virtual and material aspects of place. Additionally, we discuss how makers navigate the complex relationships tied to the importance of place in their specific cultural productions. In the first section, we develop the notion of a curated maker subjectivity. In the second section, we consider the relationship between subjectivity and place. Both sections emphasize how Instagram mediates the relationship between place and subjectivity. Through spotlighting particular literatures in each section, we attempt to fill a gap in the literature that addresses the relationship between subjectivity, place, and social media. Through this line of analysis, we attempt to better understand how and where Portland is made, along with the implications for Portland’s makers. Title: Where Is Portland Made? The Complex Relationship between Social Media and Place in the Artisan Economy of Portland, Oregon (USA) Author: Marotta, Stephen, Cummings, Austin, Heying, Charles H. Year: 2016 Portland, Oregon (USA) has become known for an artisanal or ‘maker’ economy that relies on a resurgence of place specificity (Heying), primarily expressed and exported to a global audience in the notion of ‘Portland Made’ (Roy). Portland Made reveals a tension immanent in the notion of ‘place’: place is both here and not here, both real and imaginary. What emerges is a complicated picture of how place conceptually captures various intersections of materiality and mythology, aesthetics and economics. On the one hand, Portland Made represents the collective brand-identity used by Portland’s makers to signify a products’ material existence as handcrafted, place-embedded, and authentic. These characteristics lead to certain assumptions about the concept of ‘local’ (Marotta and Heying): what meaning does Portland Made convey, and how is such meaning distributed? On the other hand, the seemingly intentional embedding of place-specificity in objects meant for distribution far outside of Portland begs another type of question: how does Portland come to be discursively representative of these characteristics, and how are such representations distributed to global audiences? How does this global distribution and consumption of immaterial Portland feed back into the production of material Portland? To answer these questions we look to the realm of social media, specifically the popular image-based service Instagram. For the uninitiated, Instagram is a web-based social media service that allows pictures to be shared and seen by anyone that follows a person or business’ Instagram account. Actions include posting original photos (often taken and posted with a cell phone), ‘liking’ pictures, and ‘hash-tagging’ posts with trending terms that increase visibility. Instagram presents us with a complex view of place as both material and virtual, sometimes reifying and sometimes abstracting often-contradictory understandings of place specificity. Many makers use Instagram to promote their products to a broad audience and, in doing so, makers participate in the construction of Portland’s mythology. In this paper, we use empirical insights to theorise makers’ role in shaping and cultivating the virtual and material aspects of place. Additionally, we discuss how makers navigate the complex relationships tied to the importance of place in their specific cultural productions. In the first section, we develop the notion of a curated maker subjectivity. In the second section, we consider the relationship between subjectivity and place. Both sections emphasize how Instagram mediates the relationship between place and subjectivity. Through spotlighting particular literatures in each section, we attempt to fill a gap in the literature that addresses the relationship between subjectivity, place, and social media. Through this line of analysis, we attempt to better understand how and where Portland is made, along with the implications for Portland’s makers. Close

• 365. [Article] Investigation into Effects of Instability and Reactivity of Hydride-Passivated Silicon Nanoparticles on Interband Photoluminescence

  While silicon has long been utilized for its electronic properties, its use as an optical material has largely been limited due to the poor efficiency of interband transitions. However, discovery of visible ...

  Citation × Citation Citation Abstract Copy Title: Investigation into Effects of Instability and Reactivity of Hydride-Passivated Silicon Nanoparticles on Interband Photoluminescence Author: Radlinger, Christine Marie Year: 2017 While silicon has long been utilized for its electronic properties, its use as an optical material has largely been limited due to the poor efficiency of interband transitions. However, discovery of visible photoluminescence (PL) from nanocrystalline silicon in 1990 triggered many ensuing research efforts to optimize PL from nanocrystalline silicon for optical applications. Currently, use of photoluminescent silicon nanoparticles (Si NPs) is commercially limited by: 1) the instability of the energy and intensity of the PL, and 2) the low quantum yield of interband PL from Si NPs. Herein, red-emitting, hydrogen-passivated silicon nanoparticles (H-Si NPs) were synthesized by thermally-induced disproportionation of a HSiCl3-derived (HSiO1.5)n polymer. The H-Si NPs produced by this method were then subjected to various chemical and physical environments to assess the long-term stability of the optical properties as a function of changing surface composition. This dissertation is intended to elucidate correlations between the reported PL instability and the observed changes in the Si NP surface chemistry over time and as a function of environment. First, the stability of the H-Si NP surface at slightly elevated temperatures towards reactivity with a simple alkane was probed. The H-Si NPs were observed by FT-IR spectroscopy to undergo partial hydrosilylation upon heating in refluxing hexane, in addition to varying degrees of surface oxidation. The unexpected reactivity of the Si surface in n-hexane supports the unstable nature of the H-Si NP surface, and furthermore implicates the presence of highly-reactive Si radicals on the surfaces of the Si NPs. We propose that reaction of alkene impurities with the Si surface radicals is largely responsible for the observed surface alkylation. However, we also present an alternate mechanism by which Si surface radicals could react with alkanes to result in alkylation of the surface. Next, the energy and intensity stability of the interband PL from H-Si NPs in the presence of a radical trap was probed. Upon addition of (2,2,6,6,-tetramethyl-piperidin-1-yl)oxyl (TEMPO), the energy and intensity of the interband transition was observed to change over time, dependent on the reaction conditions. First, when the reaction occurred at 4ºC with minimal light exposure, the interband transition exhibited a gradual hypsochromic shift to between 595 nm and 655 nm, versus the λmax of the original low energy emission peak at 700 nm, depending on the amount of TEMPO in the sample. Second, when the reaction proceeded at room temperature with frequent exposure to 360 nm irradiation, the original interband transition at 660 nm was quenched while a new peak at 575 nm developed. Based on all the data collected and analyzed, we assign the 595 -- 655 nm transition as due to interband exciton recombination from Si NPs with reduced diameters relative to the original Si NPs. We furthermore assign the 575 nm transition as due to an oxide-related defect state resulting from rapid oxidation of photo-excited Si NPs. Title: Investigation into Effects of Instability and Reactivity of Hydride-Passivated Silicon Nanoparticles on Interband Photoluminescence Author: Radlinger, Christine Marie Year: 2017 While silicon has long been utilized for its electronic properties, its use as an optical material has largely been limited due to the poor efficiency of interband transitions. However, discovery of visible photoluminescence (PL) from nanocrystalline silicon in 1990 triggered many ensuing research efforts to optimize PL from nanocrystalline silicon for optical applications. Currently, use of photoluminescent silicon nanoparticles (Si NPs) is commercially limited by: 1) the instability of the energy and intensity of the PL, and 2) the low quantum yield of interband PL from Si NPs. Herein, red-emitting, hydrogen-passivated silicon nanoparticles (H-Si NPs) were synthesized by thermally-induced disproportionation of a HSiCl3-derived (HSiO1.5)n polymer. The H-Si NPs produced by this method were then subjected to various chemical and physical environments to assess the long-term stability of the optical properties as a function of changing surface composition. This dissertation is intended to elucidate correlations between the reported PL instability and the observed changes in the Si NP surface chemistry over time and as a function of environment. First, the stability of the H-Si NP surface at slightly elevated temperatures towards reactivity with a simple alkane was probed. The H-Si NPs were observed by FT-IR spectroscopy to undergo partial hydrosilylation upon heating in refluxing hexane, in addition to varying degrees of surface oxidation. The unexpected reactivity of the Si surface in n-hexane supports the unstable nature of the H-Si NP surface, and furthermore implicates the presence of highly-reactive Si radicals on the surfaces of the Si NPs. We propose that reaction of alkene impurities with the Si surface radicals is largely responsible for the observed surface alkylation. However, we also present an alternate mechanism by which Si surface radicals could react with alkanes to result in alkylation of the surface. Next, the energy and intensity stability of the interband PL from H-Si NPs in the presence of a radical trap was probed. Upon addition of (2,2,6,6,-tetramethyl-piperidin-1-yl)oxyl (TEMPO), the energy and intensity of the interband transition was observed to change over time, dependent on the reaction conditions. First, when the reaction occurred at 4ºC with minimal light exposure, the interband transition exhibited a gradual hypsochromic shift to between 595 nm and 655 nm, versus the λmax of the original low energy emission peak at 700 nm, depending on the amount of TEMPO in the sample. Second, when the reaction proceeded at room temperature with frequent exposure to 360 nm irradiation, the original interband transition at 660 nm was quenched while a new peak at 575 nm developed. Based on all the data collected and analyzed, we assign the 595 -- 655 nm transition as due to interband exciton recombination from Si NPs with reduced diameters relative to the original Si NPs. We furthermore assign the 575 nm transition as due to an oxide-related defect state resulting from rapid oxidation of photo-excited Si NPs. Close

• 366. [Article] Shifting Advertising Agency Structure and Evolving Technology

  As a senior at Portland State University I have been exposed to many real-life advertising situations. This immersion in the advertising world has been an invaluable experience that has given me significant ...

  Citation × Citation Citation Abstract Copy Title: Shifting Advertising Agency Structure and Evolving Technology Author: Norris, Sarah A. Year: 2017 As a senior at Portland State University I have been exposed to many real-life advertising situations. This immersion in the advertising world has been an invaluable experience that has given me significant insight into advertising agencies and their operations from multiple different positions throughout the typical firm. This experience has helped me shape my thesis into a question that is relevant not only for the advertising community as a whole but also as someone hoping to enter the field within the next few years. My goal for this thesis is not to simply gain total knowledge in one specific area of advertising, but to create an accurate perspective of the advertising ecosystem and all the businesses and people that interact with or depend on it, as it exists today. I will go in depth on all the aspects of the “advertising ecosystem” later in this paper,) I am using this terminology as an overarching term for all businesses that rely or drive any form of work related to advertising). These businesses can range from the advertising firm itself to the catering business that supplies sandwiches for a Nike photo-shoot. As a soon-to-be college graduate, it’s important to know exactly what the climate is for any potential field of work. I came to my topic by researching trends in the advertising ecosystem that have come about with the increased use of the Internet and technology in business. Almost everyone can not only advertise for themselves, but can also have access to a multitude of analytic tools that would previously have only been available to advertising and marketing professionals. There are a growing number of firms who use social media and low-cost creative departments, and whose success now threatens the larger advertising agencies. Because only a relatively few brands and companies have the funds to access larger more traditional firms, more small and micro businesses are turning to the only alternatives most of them can afford. For clarification, the traditional advertising firm is an all in-house firm that deals with every aspect of the advertising process from the PR to coupon development and media buying. These traditional firms are priced in one of three ways that I will explain further in my thesis. These firms tend to be more costly than most brands can afford. As I will discuss in my thesis the growing importance of small advertising firms has had reverberating effects on not only the industry but also the employees of the firms in question. Technology and the evolving tools of the Internet have allowed many brands and companies to reconsider the need for the traditional advertising agency, and has allowed for the growth of more non-traditional advertising shops. Title: Shifting Advertising Agency Structure and Evolving Technology Author: Norris, Sarah A. Year: 2017 As a senior at Portland State University I have been exposed to many real-life advertising situations. This immersion in the advertising world has been an invaluable experience that has given me significant insight into advertising agencies and their operations from multiple different positions throughout the typical firm. This experience has helped me shape my thesis into a question that is relevant not only for the advertising community as a whole but also as someone hoping to enter the field within the next few years. My goal for this thesis is not to simply gain total knowledge in one specific area of advertising, but to create an accurate perspective of the advertising ecosystem and all the businesses and people that interact with or depend on it, as it exists today. I will go in depth on all the aspects of the “advertising ecosystem” later in this paper,) I am using this terminology as an overarching term for all businesses that rely or drive any form of work related to advertising). These businesses can range from the advertising firm itself to the catering business that supplies sandwiches for a Nike photo-shoot. As a soon-to-be college graduate, it’s important to know exactly what the climate is for any potential field of work. I came to my topic by researching trends in the advertising ecosystem that have come about with the increased use of the Internet and technology in business. Almost everyone can not only advertise for themselves, but can also have access to a multitude of analytic tools that would previously have only been available to advertising and marketing professionals. There are a growing number of firms who use social media and low-cost creative departments, and whose success now threatens the larger advertising agencies. Because only a relatively few brands and companies have the funds to access larger more traditional firms, more small and micro businesses are turning to the only alternatives most of them can afford. For clarification, the traditional advertising firm is an all in-house firm that deals with every aspect of the advertising process from the PR to coupon development and media buying. These traditional firms are priced in one of three ways that I will explain further in my thesis. These firms tend to be more costly than most brands can afford. As I will discuss in my thesis the growing importance of small advertising firms has had reverberating effects on not only the industry but also the employees of the firms in question. Technology and the evolving tools of the Internet have allowed many brands and companies to reconsider the need for the traditional advertising agency, and has allowed for the growth of more non-traditional advertising shops. Close

• 367. [Article] Using Cultural Relevancy to Promote African American Brain Health

  African Americans are disproportionately more likely than older whites to develop Alzheimer’s disease and other dementias (ADOD). Despite these disparities, there is difficulty in motivating African Americans ...

  Citation × Citation Citation Abstract Copy Title: Using Cultural Relevancy to Promote African American Brain Health Author: Walker, Miya Year: 2017 African Americans are disproportionately more likely than older whites to develop Alzheimer’s disease and other dementias (ADOD). Despite these disparities, there is difficulty in motivating African Americans to engage in activities suitable to maintaining cognitive health (walking, social engagement, physical activity). The Sharing History through Active Reminiscence and Photo-imagery (SHARP) walking program (Croff, PI) combines these proactive activities in a culturally relevant way to create a motivational force to preserve cognitive health. SHARP engaged 19 African Americans aged 55 and older on 72 themed, 1-mile walks over 6 months in Portland, Oregon’s historically Black neighborhoods. This study examines participant responses to the SHARP walk “Afrocentrism” to illustrate how culture can be used to motivate walking and social engagement among older African Americans. The “Afrocentrism” walk presents three questions with historic neighborhood images, each approximately 10 minutes apart along the route: What are your memories of Afrocentric art? What did it mean to you and your community? Did you, your friends or family show your Afrocentrism in the 1960's, 70's and 80's? How? What did it mean to you? Do you have any memories about this [African clothing] shop? How were expressions of Afrocentrism accepted in the 1960's and 70's in Portland? Participant narratives were audio recorded. Narratives were then coded for common themes that gave insight to the importance of culture in health programming. Specific conversations amongst walking groups varied around the “Afrocentrism” prompts, however, walking groups reminisced over the same prominent people and places in the community. The commonality of participants shared neighborhood experiences creates a collective historical narrative and allows for connection to one another in ways that support connection to the neighborhood and to African American culture. This collective narrative informs researchers and allows for a deeper understanding of the Black experience, thus further facilitating the incorporation of culturally relevant prompts into the program. This is an essential way SHARP motivates participants to exercise and engage socially. Incorporating culture into health programs, as SHARP does, can be transferable to other health promotion programs to sustain retention and engagement. Title: Using Cultural Relevancy to Promote African American Brain Health Author: Walker, Miya Year: 2017 African Americans are disproportionately more likely than older whites to develop Alzheimer’s disease and other dementias (ADOD). Despite these disparities, there is difficulty in motivating African Americans to engage in activities suitable to maintaining cognitive health (walking, social engagement, physical activity). The Sharing History through Active Reminiscence and Photo-imagery (SHARP) walking program (Croff, PI) combines these proactive activities in a culturally relevant way to create a motivational force to preserve cognitive health. SHARP engaged 19 African Americans aged 55 and older on 72 themed, 1-mile walks over 6 months in Portland, Oregon’s historically Black neighborhoods. This study examines participant responses to the SHARP walk “Afrocentrism” to illustrate how culture can be used to motivate walking and social engagement among older African Americans. The “Afrocentrism” walk presents three questions with historic neighborhood images, each approximately 10 minutes apart along the route: What are your memories of Afrocentric art? What did it mean to you and your community? Did you, your friends or family show your Afrocentrism in the 1960's, 70's and 80's? How? What did it mean to you? Do you have any memories about this [African clothing] shop? How were expressions of Afrocentrism accepted in the 1960's and 70's in Portland? Participant narratives were audio recorded. Narratives were then coded for common themes that gave insight to the importance of culture in health programming. Specific conversations amongst walking groups varied around the “Afrocentrism” prompts, however, walking groups reminisced over the same prominent people and places in the community. The commonality of participants shared neighborhood experiences creates a collective historical narrative and allows for connection to one another in ways that support connection to the neighborhood and to African American culture. This collective narrative informs researchers and allows for a deeper understanding of the Black experience, thus further facilitating the incorporation of culturally relevant prompts into the program. This is an essential way SHARP motivates participants to exercise and engage socially. Incorporating culture into health programs, as SHARP does, can be transferable to other health promotion programs to sustain retention and engagement. Close

• 368. [Article] Google's Technology Strategy

  Google Inc. is a multinational public corporation invested in Internet search, cloud computing, and advertising technologies. Google hosts and develops a number of Internet-based services and products, ...

  Citation × Citation Citation Abstract Copy Title: Google's Technology Strategy Author: Murthy, Mamatha, Maheshwari, Priti, Neethirajan, Aarthi, Upadhyay, Jubin, Soysa, Dinesh, Taddesse, Neb Year: 2010 Google Inc. is a multinational public corporation invested in Internet search, cloud computing, and advertising technologies. Google hosts and develops a number of Internet-based services and products, and generates profit primarily from advertising through its Ad Words program. The company was founded in January 1996 by two Stanford students Larry Page and Sergey Brin and was first incorporated as privately held company on September 4, 1998. Its initial public offering followed on August 19, 2004. Google’s mission is to organize the world’s information and make it universally accessible and useful. This describes what the company actually plans to do on a day-by-day basis. By using its proprietary search technology and other internet based services and products, Google does help to organize information and make it both more accessible and more useful. Larry and Brin first started a simple search engine, Backrub in 1996 which based its search results on the number of “back links” pointing to a given web site. Backrub was unique as it was designed to work in a network of low-end PCs instead of expensive mainframes used by major search engines of the day. By 1998, Larry and Sergey tried to sell their technology but ended up having no takers. They moved out of the dorm and wrote a business plan. With the help of Bechtolsheim, one of the founders of Sun Microsystems, Google Inc. was born. Thus company thus started, has grown rapidly over the years becoming a market leader in the Search industry. Google runs over one million servers in datacenters around the world and processes over one billion search requests and about twenty-four petabytes of user –generated data every day. This rapid growth has triggered a chain of products, acquisitions and partnerships beyond the company’s core search engine. The company offers productivity software such as Gmail, social networking tools such as Orkut, Google Buzz, browser such as Google Chrome, the Picasa photo organization and editing application, Google Talk instant messaging application, Android mobile phone operating system, YouTube, Blogger and much more. Since its incorporation, Google continues to grow and its stock continues to rise from its initial price of $100/share to a high close of $704.79/share in October 2007. It has since dropped to $573/share as of December 2010, but still remains significantly higher. Google has a current market share of 66 percent in USA and 86 percent globally, thus is clearly a market leader. However, the dominant market position of Google's services has led to criticism of the company over issues including privacy, copyright, and censorship. Title: Google's Technology Strategy Author: Murthy, Mamatha, Maheshwari, Priti, Neethirajan, Aarthi, Upadhyay, Jubin, Soysa, Dinesh, Taddesse, Neb Year: 2010 Google Inc. is a multinational public corporation invested in Internet search, cloud computing, and advertising technologies. Google hosts and develops a number of Internet-based services and products, and generates profit primarily from advertising through its Ad Words program. The company was founded in January 1996 by two Stanford students Larry Page and Sergey Brin and was first incorporated as privately held company on September 4, 1998. Its initial public offering followed on August 19, 2004. Google’s mission is to organize the world’s information and make it universally accessible and useful. This describes what the company actually plans to do on a day-by-day basis. By using its proprietary search technology and other internet based services and products, Google does help to organize information and make it both more accessible and more useful. Larry and Brin first started a simple search engine, Backrub in 1996 which based its search results on the number of “back links” pointing to a given web site. Backrub was unique as it was designed to work in a network of low-end PCs instead of expensive mainframes used by major search engines of the day. By 1998, Larry and Sergey tried to sell their technology but ended up having no takers. They moved out of the dorm and wrote a business plan. With the help of Bechtolsheim, one of the founders of Sun Microsystems, Google Inc. was born. Thus company thus started, has grown rapidly over the years becoming a market leader in the Search industry. Google runs over one million servers in datacenters around the world and processes over one billion search requests and about twenty-four petabytes of user –generated data every day. This rapid growth has triggered a chain of products, acquisitions and partnerships beyond the company’s core search engine. The company offers productivity software such as Gmail, social networking tools such as Orkut, Google Buzz, browser such as Google Chrome, the Picasa photo organization and editing application, Google Talk instant messaging application, Android mobile phone operating system, YouTube, Blogger and much more. Since its incorporation, Google continues to grow and its stock continues to rise from its initial price of $100/share to a high close of $704.79/share in October 2007. It has since dropped to $573/share as of December 2010, but still remains significantly higher. Google has a current market share of 66 percent in USA and 86 percent globally, thus is clearly a market leader. However, the dominant market position of Google's services has led to criticism of the company over issues including privacy, copyright, and censorship. Close

• 369. [Article] Fundamental Properties of Functional Zinc Oxide Nanowires Obtained by Electrochemical Method and Their Device Applications

  We report on the fundamental properties and device applications of semiconductor nanoparticles. ZnO nanowires and CdSe quantum dots were used, prepared, characterized, and assembled into novel light-emitting ...

  Citation × Citation Citation Abstract Copy Title: Fundamental Properties of Functional Zinc Oxide Nanowires Obtained by Electrochemical Method and Their Device Applications Author: Nadarajah, Athavan Year: 2012 We report on the fundamental properties and device applications of semiconductor nanoparticles. ZnO nanowires and CdSe quantum dots were used, prepared, characterized, and assembled into novel light-emitting diodes and solar cells. ZnO nanowire films were grown electrochemically using aqueous soluble chloride-based electrolytes as precursors at temperatures below 90° C. Dopants were added to the electrolyte in the form of chloride compounds, which are AlCl3, CoCl2, CuCl2, and MnCl2. The optical, magnetic, and structural properties of undoped and transition-metal-ion doped ZnO nanowires were explored. Our results indicate that the as-grown nanowire structures have considerable internal strain, resulting in clearly visible lattice distortions in bright and dark-field transmission electron micrographs. Photo and electroluminescence studies indicate that the strain-induced defects strongly dominate any dopant-related effects. However, annealing at moderate temperature as well as laser annealing induces strain relaxation and leads to dopant activation. Hence, the optical and electrical properties of the nanowires significantly improve, allowing these nanowires to become feasible for use in the fabrication of solar cell and LED devices. In addition, the magnetic impurities incorporated into our ZnO nanowires show superparamagnetic behavior at room-temperature, while Al-doped and undoped ZnO nanowires show no magnetic behavior. The electroluminescence (EL) is achieved from a vertical hybrid p-n junction LED arrangement consisting of a hole-conducting polymer and n-type ZnO nanowires, our group was the first to report this vertical nanowire-based LED in Könenkamp et al., 2004 [12]. The observed EL spectra show an ultraviolet excitonic emission peak and a broad defect-related emission band in the visible range. After annealing at 380° C, the defect related EL peak exhibits a characteristic shift to higher wavelengths, where the magnitude of the shift is dependent on the dopant type. Aluminum incorporation exhibited the most improved exciton related-emission, leading to the emergence of a narrow excitonic luminescence peak around 390 nm, which is close to the bandgap of ZnO. The comparison of spectra obtained from temperature-dependent photoluminescence (PL) measurements, before and after thermal annealing, also indicates that the optical activity of impurities changes noticeably upon annealing. The internal quantum efficiency for PL is measured to be as high as 16 percent for Al-doped samples annealed at 380° C. The PL measurements also show that the excitonic luminescence is preferentially guided, while the defect related emission is more isotropically emitted. The nanostructured heterojunction solar cell is designed such that thin CdSe quantum dot films are embedded between a ZnO nanowire film and a hole-conducting polymer layer. This arrangement allows for enhanced light absorption and an efficient collection of photogenerated carriers. Here, we present a detailed analysis of the pyridine solution and 1,2- ethanedithiol ligand exchange processes of the quantum dots, deposition processes of this quantum dot layer, the conformality of this layer on deeply nanostructured samples, and the effect of a surfactant-aided thermal annealing process. Annealing creates a structural conversion of the quantum dot layers into an extremely thin continuous poly-crystalline film, with typical grain diameters of 30-50 nm. This transition is accompanied by a loss of quantum confinement and a significant improvement of the charge transport in the CdSe layer. The combination of the solution and ligand exchange of CdSe quantum dots, as well as the deposition and optimized annealing processes of this quantum dot layer, resulted in solar cells with an open-circuit voltage up to 0.6 V, a short circuit current of ~15 mA/cm2, an external quantum efficiency of 70 percent, and an energy conversion efficiency of 3.4 percent. This 3.4 percent efficiency is presently one of the best efficiencies obtained for this type of device. Title: Fundamental Properties of Functional Zinc Oxide Nanowires Obtained by Electrochemical Method and Their Device Applications Author: Nadarajah, Athavan Year: 2012 We report on the fundamental properties and device applications of semiconductor nanoparticles. ZnO nanowires and CdSe quantum dots were used, prepared, characterized, and assembled into novel light-emitting diodes and solar cells. ZnO nanowire films were grown electrochemically using aqueous soluble chloride-based electrolytes as precursors at temperatures below 90° C. Dopants were added to the electrolyte in the form of chloride compounds, which are AlCl3, CoCl2, CuCl2, and MnCl2. The optical, magnetic, and structural properties of undoped and transition-metal-ion doped ZnO nanowires were explored. Our results indicate that the as-grown nanowire structures have considerable internal strain, resulting in clearly visible lattice distortions in bright and dark-field transmission electron micrographs. Photo and electroluminescence studies indicate that the strain-induced defects strongly dominate any dopant-related effects. However, annealing at moderate temperature as well as laser annealing induces strain relaxation and leads to dopant activation. Hence, the optical and electrical properties of the nanowires significantly improve, allowing these nanowires to become feasible for use in the fabrication of solar cell and LED devices. In addition, the magnetic impurities incorporated into our ZnO nanowires show superparamagnetic behavior at room-temperature, while Al-doped and undoped ZnO nanowires show no magnetic behavior. The electroluminescence (EL) is achieved from a vertical hybrid p-n junction LED arrangement consisting of a hole-conducting polymer and n-type ZnO nanowires, our group was the first to report this vertical nanowire-based LED in Könenkamp et al., 2004 [12]. The observed EL spectra show an ultraviolet excitonic emission peak and a broad defect-related emission band in the visible range. After annealing at 380° C, the defect related EL peak exhibits a characteristic shift to higher wavelengths, where the magnitude of the shift is dependent on the dopant type. Aluminum incorporation exhibited the most improved exciton related-emission, leading to the emergence of a narrow excitonic luminescence peak around 390 nm, which is close to the bandgap of ZnO. The comparison of spectra obtained from temperature-dependent photoluminescence (PL) measurements, before and after thermal annealing, also indicates that the optical activity of impurities changes noticeably upon annealing. The internal quantum efficiency for PL is measured to be as high as 16 percent for Al-doped samples annealed at 380° C. The PL measurements also show that the excitonic luminescence is preferentially guided, while the defect related emission is more isotropically emitted. The nanostructured heterojunction solar cell is designed such that thin CdSe quantum dot films are embedded between a ZnO nanowire film and a hole-conducting polymer layer. This arrangement allows for enhanced light absorption and an efficient collection of photogenerated carriers. Here, we present a detailed analysis of the pyridine solution and 1,2- ethanedithiol ligand exchange processes of the quantum dots, deposition processes of this quantum dot layer, the conformality of this layer on deeply nanostructured samples, and the effect of a surfactant-aided thermal annealing process. Annealing creates a structural conversion of the quantum dot layers into an extremely thin continuous poly-crystalline film, with typical grain diameters of 30-50 nm. This transition is accompanied by a loss of quantum confinement and a significant improvement of the charge transport in the CdSe layer. The combination of the solution and ligand exchange of CdSe quantum dots, as well as the deposition and optimized annealing processes of this quantum dot layer, resulted in solar cells with an open-circuit voltage up to 0.6 V, a short circuit current of ~15 mA/cm2, an external quantum efficiency of 70 percent, and an energy conversion efficiency of 3.4 percent. This 3.4 percent efficiency is presently one of the best efficiencies obtained for this type of device. Close

• 370. [Article] Resolution and Reconstitution of the Photosystem I Reaction Center: Structure and Function of the Terminal Electron Acceptor FA/FB Polypeptide

  The Photosystem I core protein containing P700, A₀, A₁, and Fx has been isolated from Synechococcus sp. PCC 6301 and spinach Photosystem I complexes with 6.8 M urea followed by sucrose density ultracentrifugtion. ...

  Citation × Citation Citation Abstract Copy Title: Resolution and Reconstitution of the Photosystem I Reaction Center: Structure and Function of the Terminal Electron Acceptor FA/FB Polypeptide Author: Mehari, Tetemke Year: 1990 The Photosystem I core protein containing P700, A₀, A₁, and Fx has been isolated from Synechococcus sp. PCC 6301 and spinach Photosystem I complexes with 6.8 M urea followed by sucrose density ultracentrifugtion. The Photosystem I core protein has retained > 90% of Fx and 100% of P700 (determined by optical spectroscopy) but is totally devoid of iron-sulfur centers Fᴀ and Fв (determined by optical and ESR spectroscopy). SDS-PAGE indicates the retention of the 82-and 83-kDa reaction center polypeptides. The loss of Fᴀ and Fв is further reflected in the decline of acid labile sulfide from 11.8 ± 0.4 S²-/P700 in the Photosystem I complex to 4.6 ± 0.3 S²-/P700 in the Photosystem I core.protein. This preparation represents the first isolation of an intact reaction center core incorporating the redox centers P700 through Fx but totally lacking Fᴀ and Fʙ. Complete restoration of electron flow from P700 to Fᴀ/Fв was achieved by incubating a P700 and Fx-containing Photosystem I core protein with a freshly isolated 8.9-kDa, Fᴀ/Fв polypeptide. When illuminated during freezing, both Fᴀ and Fв become quantitatively reduced, and the ESR spectrum is nearly indistinguishable from Fᴀ and Fв in the control Photosystem I complex. In the reconstituted Photosystem I complex Fx is photochemically reduced only in the presence of Fᴀ- and Fв- and the broad high field resonance of Fx in the core protein appears upon reconstitution to be indistinguishable from Fx in the control Photosystem I complex. Optical flash photolysis after extensive washing confirms the complete restoration of the P700+ [Fᴀ/Fв]- backreaction, indicating quantitative rebinding of the 8.9-kOa polypeptide. This procedure.represents the first reconstitution of the Photosystem I complex from a purified Photosystem I core protein and a freshly isolated 8.9 kDa Fᴀ/Fв holoprotein, and makes possible independent manipulation of the two subunits that carry the entire electron acceptor system of Photosystem I. The Fᴀ/Fв iron-sulfur clusters in the 8.9 kDa polypeptide are easily degraded to the level of zero-valence sulfur during isolation from the Photosystem I complex. The level of degradation is minimized by working under anaerobic conditions and low temperature. It has been found that incubation of the purified Photosystem I core protein and the low molecular mass polypeptides (which includes the 8.9-kDa Fᴀ/Fв apoprotein) with a solution of FeCI₃, Na₂S and B-mercaptoethanol restores the light induced charge separation between P700 and Fᴀ/Fв. The optical and spectroscopic properties are indistinguishable from the control Photosystem one I complex. When a rebuilt spinach or Synechococcus sp. PeC 6301 Fᴀ/Fв polypeptide is rebound to a Photosystem I core protein from the same species, the reconstituted complexes show light-induced ESR spectra of Fᴀ/Fв with g-values identical to their respective controls. However, when the rebuilt spinach Fᴀ/Fв polypeptide is rebound to a Synechococcus sp. PCC 6301 Photosystem I core protein, the hybrid spinach Synechococcus sp. PCC 6301 Photo system complex shows a light-induced ESR spectrum of Fᴀ/Fв with g- values that differ slightly, but characteristically, from those of both spinach and Synechococcus sp. PCC 6301 control complexes. The hybrid spinach-Synechococcus sp. PCC 6301 Photosystem I complex was completely functional in light-induced charge separation between P700 and Fᴀ/Fв and showed a normal 30-ms room temperature charge recombination between P700+ and [Fᴀ/Fв]-. Accordingly, rebuilding of the Fᴀ and Fв iron-sulfur clusters is now possible and reconstitution of the Fᴀ/Fв holoprotein after chemical modification of the Fᴀ/Fв apoprotein or genetic modification of the psaC gene should reveal new findings about Photosystem I structure and function. Title: Resolution and Reconstitution of the Photosystem I Reaction Center: Structure and Function of the Terminal Electron Acceptor FA/FB Polypeptide Author: Mehari, Tetemke Year: 1990 The Photosystem I core protein containing P700, A₀, A₁, and Fx has been isolated from Synechococcus sp. PCC 6301 and spinach Photosystem I complexes with 6.8 M urea followed by sucrose density ultracentrifugtion. The Photosystem I core protein has retained > 90% of Fx and 100% of P700 (determined by optical spectroscopy) but is totally devoid of iron-sulfur centers Fᴀ and Fв (determined by optical and ESR spectroscopy). SDS-PAGE indicates the retention of the 82-and 83-kDa reaction center polypeptides. The loss of Fᴀ and Fв is further reflected in the decline of acid labile sulfide from 11.8 ± 0.4 S²-/P700 in the Photosystem I complex to 4.6 ± 0.3 S²-/P700 in the Photosystem I core.protein. This preparation represents the first isolation of an intact reaction center core incorporating the redox centers P700 through Fx but totally lacking Fᴀ and Fʙ. Complete restoration of electron flow from P700 to Fᴀ/Fв was achieved by incubating a P700 and Fx-containing Photosystem I core protein with a freshly isolated 8.9-kDa, Fᴀ/Fв polypeptide. When illuminated during freezing, both Fᴀ and Fв become quantitatively reduced, and the ESR spectrum is nearly indistinguishable from Fᴀ and Fв in the control Photosystem I complex. In the reconstituted Photosystem I complex Fx is photochemically reduced only in the presence of Fᴀ- and Fв- and the broad high field resonance of Fx in the core protein appears upon reconstitution to be indistinguishable from Fx in the control Photosystem I complex. Optical flash photolysis after extensive washing confirms the complete restoration of the P700+ [Fᴀ/Fв]- backreaction, indicating quantitative rebinding of the 8.9-kOa polypeptide. This procedure.represents the first reconstitution of the Photosystem I complex from a purified Photosystem I core protein and a freshly isolated 8.9 kDa Fᴀ/Fв holoprotein, and makes possible independent manipulation of the two subunits that carry the entire electron acceptor system of Photosystem I. The Fᴀ/Fв iron-sulfur clusters in the 8.9 kDa polypeptide are easily degraded to the level of zero-valence sulfur during isolation from the Photosystem I complex. The level of degradation is minimized by working under anaerobic conditions and low temperature. It has been found that incubation of the purified Photosystem I core protein and the low molecular mass polypeptides (which includes the 8.9-kDa Fᴀ/Fв apoprotein) with a solution of FeCI₃, Na₂S and B-mercaptoethanol restores the light induced charge separation between P700 and Fᴀ/Fв. The optical and spectroscopic properties are indistinguishable from the control Photosystem one I complex. When a rebuilt spinach or Synechococcus sp. PeC 6301 Fᴀ/Fв polypeptide is rebound to a Photosystem I core protein from the same species, the reconstituted complexes show light-induced ESR spectra of Fᴀ/Fв with g-values identical to their respective controls. However, when the rebuilt spinach Fᴀ/Fв polypeptide is rebound to a Synechococcus sp. PCC 6301 Photosystem I core protein, the hybrid spinach Synechococcus sp. PCC 6301 Photo system complex shows a light-induced ESR spectrum of Fᴀ/Fв with g- values that differ slightly, but characteristically, from those of both spinach and Synechococcus sp. PCC 6301 control complexes. The hybrid spinach-Synechococcus sp. PCC 6301 Photosystem I complex was completely functional in light-induced charge separation between P700 and Fᴀ/Fв and showed a normal 30-ms room temperature charge recombination between P700+ and [Fᴀ/Fв]-. Accordingly, rebuilding of the Fᴀ and Fв iron-sulfur clusters is now possible and reconstitution of the Fᴀ/Fв holoprotein after chemical modification of the Fᴀ/Fв apoprotein or genetic modification of the psaC gene should reveal new findings about Photosystem I structure and function. Close