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• 28791. [Article] Tidal influence on downstream fining in gravel-bed rivers

  This research examines the downstream fining phenomenon as it operates in coastal gravel-bed rivers of Oregon. Downstream fining is a change in bed composition toward smaller sediment sizes in the downstream ...

  Citation × Citation Citation Abstract Copy Title: Tidal influence on downstream fining in gravel-bed rivers Author: Coles, Derron Rafiq This research examines the downstream fining phenomenon as it operates in coastal gravel-bed rivers of Oregon. Downstream fining is a change in bed composition toward smaller sediment sizes in the downstream direction. Changes in stream flow discharge and channel slope affect the rate of bed-load transport, thereby altering the downstream fining regime. This research focuses on ascertaining the rate of downstream fining and the characterization of tidal influence on bed-load transport in the lower-river reaches. For this purpose, a combination of physical and numerical analysis techniques were used. Variations of particle size distributions and specific gravity values were assessed along the main channel. Numerical analysis techniques included a MATLAB program for simulating bed-load transport as affected by tide. The numerical model developed for this investigation, TIMM (Tidally Influenced Movement Model) uses physically based excess shear stress as the underlying mechanism. Namely, an undulating water surface is applied to Shields criterion for incipient motion and bed-load transport. The Generalized Stream Tube model for Alluvial River Simulation version 2.1 (GSTARS 2.1), developed by the Bureau of Reclamation, was used to validate conclusions drawn from field data analyses. The five rivers of the Tillamook Basin were the sites of field data collection. The Tillamook Basin is located approximately 60 miles (96.6 kilometers) west of Portland, Oregon and 60 miles (96.6 kilometers) south of the Columbia River mouth at the Pacific Ocean. The basin has a total area of 570 square miles (1476 square kilometers) including Tillamook Bay, which is the second largest estuary in Oregon. All rivers empty into the Tillamook Bay. From north to south, the rivers are the Miami, Kilchis, Wilson, Trask and Tillamook. The Kilchis River was the primary field research site and the other four rivers allowed expansion of field research for added understanding of downstream fining. Bulk sampling of the armor and sub-armor layer of the Kilchis River was completed for five sidebars along the river, from river mile 0 to river mile 14 (0 - 22.5 km). Photo frame sampling was carried out for the armor layer of sidebars along the four additional rivers. In total, 21 sampling locations with 141 individual sampling points were used for the particle size analyses. Assessment of longitudinal variation in specific gravity of bed particles by size fraction was performed for all five rivers. Particle size analyses showed a distinct downstream fining trend. Kilchis River surface particle sizes decreased from 216 mm at river mile 14 (22.5 km) to 10 mm at river mile 0. Miami River surface particle sizes decreased from 43 mm at river mile 9 to 29 mm at river mile 1.5 (2.4 km). Wilson River surface particle sizes decreased from 51 mm at river mile 27 to 23 mm at river mile 0. Trask River surface particle sizes decreased from 55 mm at river mile 18 to 26 mm at river mile 4 (6.4 km). Diminution coefficients (rates of size reduction) were found to be 0.55 km⁻¹ for the armor layer and 0.48 km⁻¹ for the sub-armor layer of the Kilchis River. The R-squared values for the armor and sub-armor coefficients are 0.92 and 0.99, respectively. Results of regression analyses performed for the photo frame sampling data were 0.02, 0.03, and 0.04 km⁻¹ for the Miami, Wilson, and Trask Rivers, respectively. R-squared values of 0.19, 0.78, and 0.81, respectively. Diminution coefficients reported for all rivers were far outside the value reported for abrasion-dominated systems (0.089 km⁻¹), yet were within the range of diminution coefficients reported for selective sorting-dominated systems (0.001 to 0.05 km⁻¹). Average specific gravities for bed material were 2.78, 2.68, 2.73, 2.56, and 2.76 for the Miami, Kilchis, Wilson, Trask, and Tillamook Rivers, respectively. Simulations of sediment transport within the tidal portion of the Kilchis River (river mile 0 to 3 or 0 to 4.8 km) using TIMM at moderate river streamflow above the threshold for transport of material showed that tidal influence causes distinct deposition zones during periods of high, low, and moderate tide levels. Depositional zones were found to propagate downstream with increases in river discharge, such that at elevated river stage the location of depositional zones associated with tide levels were undistinguishable. It can be concluded that tide has a significant influence at flows below, and moderately above the threshold for transport. Simulations of a simplified version of the Kilchis River using GSTARS 2.1 produced comparable results to the TIMM simulations. GSTARS 2.1 was run using three scenarios, 1) a uniform bed and incoming sediment supply set at 7.9 mm, 2) a mixed bed with mean sediment diameter of 7.9 mm and coarser incoming sediment supply, and 3) a mixed bed with mean sediment diameter of 7.9 mm and finer incoming sediment supply. Each scenario had output data that show maximum deposition in the zone of tidal influence. The location of head of tide for the simplified Kilchis River was found to occur at river mile 5 instead of river mile 3 used for the head of tide in TIMM simulations. GSTARS 2.1 simulations showed that variations in particle size distribution of incoming sediment supply influence rates of downstream fining. An incoming sediment supply that had a coarser particle size distribution than the particle size distribution of the bed resulted in an observable increase in deposition of large particle sizes in the upstream reaches; however, there was no observable increase in deposition of large particle sizes in downstream reaches. An incoming sediment supply that had a finer particle size distribution than the particle size distribution of the bed resulted in an observable increase in deposition of smaller particles in the downstream reaches, with no observable increase in deposition of smaller sizes in the upstream reaches. Therefore, simulations show evidence that sediment supply of particles coarser than the bed causes increased rates of fining in reaches near the sediment source. Key contributions of this research are in the categories of methodology, numerical analysis, and basic understanding of the fate and transport of sediment in the zone of tidal influence. It has been shown that particle size data, collected in detail on sidebars, can be used in conjunction with specific gravity data to categorize in-stream particles based on probable origin and type. Characterization of sediment transport in the zone of tidal influence using numerical models showed the tide cycle influences the downstream fining trend in lower reaches by shifting the zone of deposition farther upstream than would the case without tidal influence, with a net effect of increasing the rate of downstream fining. Moreover, tidal influence was found to have an inverse relationship with water discharge. Finally, it was shown that numerical modeling of river reaches in the tidal zone should include consideration of tidal fluctuations in order to predict erosion and depositional areas more accurately. Title: Tidal influence on downstream fining in gravel-bed rivers Author: Coles, Derron Rafiq This research examines the downstream fining phenomenon as it operates in coastal gravel-bed rivers of Oregon. Downstream fining is a change in bed composition toward smaller sediment sizes in the downstream direction. Changes in stream flow discharge and channel slope affect the rate of bed-load transport, thereby altering the downstream fining regime. This research focuses on ascertaining the rate of downstream fining and the characterization of tidal influence on bed-load transport in the lower-river reaches. For this purpose, a combination of physical and numerical analysis techniques were used. Variations of particle size distributions and specific gravity values were assessed along the main channel. Numerical analysis techniques included a MATLAB program for simulating bed-load transport as affected by tide. The numerical model developed for this investigation, TIMM (Tidally Influenced Movement Model) uses physically based excess shear stress as the underlying mechanism. Namely, an undulating water surface is applied to Shields criterion for incipient motion and bed-load transport. The Generalized Stream Tube model for Alluvial River Simulation version 2.1 (GSTARS 2.1), developed by the Bureau of Reclamation, was used to validate conclusions drawn from field data analyses. The five rivers of the Tillamook Basin were the sites of field data collection. The Tillamook Basin is located approximately 60 miles (96.6 kilometers) west of Portland, Oregon and 60 miles (96.6 kilometers) south of the Columbia River mouth at the Pacific Ocean. The basin has a total area of 570 square miles (1476 square kilometers) including Tillamook Bay, which is the second largest estuary in Oregon. All rivers empty into the Tillamook Bay. From north to south, the rivers are the Miami, Kilchis, Wilson, Trask and Tillamook. The Kilchis River was the primary field research site and the other four rivers allowed expansion of field research for added understanding of downstream fining. Bulk sampling of the armor and sub-armor layer of the Kilchis River was completed for five sidebars along the river, from river mile 0 to river mile 14 (0 - 22.5 km). Photo frame sampling was carried out for the armor layer of sidebars along the four additional rivers. In total, 21 sampling locations with 141 individual sampling points were used for the particle size analyses. Assessment of longitudinal variation in specific gravity of bed particles by size fraction was performed for all five rivers. Particle size analyses showed a distinct downstream fining trend. Kilchis River surface particle sizes decreased from 216 mm at river mile 14 (22.5 km) to 10 mm at river mile 0. Miami River surface particle sizes decreased from 43 mm at river mile 9 to 29 mm at river mile 1.5 (2.4 km). Wilson River surface particle sizes decreased from 51 mm at river mile 27 to 23 mm at river mile 0. Trask River surface particle sizes decreased from 55 mm at river mile 18 to 26 mm at river mile 4 (6.4 km). Diminution coefficients (rates of size reduction) were found to be 0.55 km⁻¹ for the armor layer and 0.48 km⁻¹ for the sub-armor layer of the Kilchis River. The R-squared values for the armor and sub-armor coefficients are 0.92 and 0.99, respectively. Results of regression analyses performed for the photo frame sampling data were 0.02, 0.03, and 0.04 km⁻¹ for the Miami, Wilson, and Trask Rivers, respectively. R-squared values of 0.19, 0.78, and 0.81, respectively. Diminution coefficients reported for all rivers were far outside the value reported for abrasion-dominated systems (0.089 km⁻¹), yet were within the range of diminution coefficients reported for selective sorting-dominated systems (0.001 to 0.05 km⁻¹). Average specific gravities for bed material were 2.78, 2.68, 2.73, 2.56, and 2.76 for the Miami, Kilchis, Wilson, Trask, and Tillamook Rivers, respectively. Simulations of sediment transport within the tidal portion of the Kilchis River (river mile 0 to 3 or 0 to 4.8 km) using TIMM at moderate river streamflow above the threshold for transport of material showed that tidal influence causes distinct deposition zones during periods of high, low, and moderate tide levels. Depositional zones were found to propagate downstream with increases in river discharge, such that at elevated river stage the location of depositional zones associated with tide levels were undistinguishable. It can be concluded that tide has a significant influence at flows below, and moderately above the threshold for transport. Simulations of a simplified version of the Kilchis River using GSTARS 2.1 produced comparable results to the TIMM simulations. GSTARS 2.1 was run using three scenarios, 1) a uniform bed and incoming sediment supply set at 7.9 mm, 2) a mixed bed with mean sediment diameter of 7.9 mm and coarser incoming sediment supply, and 3) a mixed bed with mean sediment diameter of 7.9 mm and finer incoming sediment supply. Each scenario had output data that show maximum deposition in the zone of tidal influence. The location of head of tide for the simplified Kilchis River was found to occur at river mile 5 instead of river mile 3 used for the head of tide in TIMM simulations. GSTARS 2.1 simulations showed that variations in particle size distribution of incoming sediment supply influence rates of downstream fining. An incoming sediment supply that had a coarser particle size distribution than the particle size distribution of the bed resulted in an observable increase in deposition of large particle sizes in the upstream reaches; however, there was no observable increase in deposition of large particle sizes in downstream reaches. An incoming sediment supply that had a finer particle size distribution than the particle size distribution of the bed resulted in an observable increase in deposition of smaller particles in the downstream reaches, with no observable increase in deposition of smaller sizes in the upstream reaches. Therefore, simulations show evidence that sediment supply of particles coarser than the bed causes increased rates of fining in reaches near the sediment source. Key contributions of this research are in the categories of methodology, numerical analysis, and basic understanding of the fate and transport of sediment in the zone of tidal influence. It has been shown that particle size data, collected in detail on sidebars, can be used in conjunction with specific gravity data to categorize in-stream particles based on probable origin and type. Characterization of sediment transport in the zone of tidal influence using numerical models showed the tide cycle influences the downstream fining trend in lower reaches by shifting the zone of deposition farther upstream than would the case without tidal influence, with a net effect of increasing the rate of downstream fining. Moreover, tidal influence was found to have an inverse relationship with water discharge. Finally, it was shown that numerical modeling of river reaches in the tidal zone should include consideration of tidal fluctuations in order to predict erosion and depositional areas more accurately. Close

• 28792. [Image] Historical and scientific resources on Crater Lake National Park

  	"27 March 1998."; At head of title: Maines & Associates; Includes index
  	Citation × Citation Citation Abstract Copy Title: Historical and scientific resources on Crater Lake National Park Author: Maines, Rachel P. Year: 1998, 2010 "27 March 1998."; At head of title: Maines & Associates; Includes index Title: Historical and scientific resources on Crater Lake National Park Author: Maines, Rachel P. Year: 1998, 2010 "27 March 1998."; At head of title: Maines & Associates; Includes index Close

• 28793. [Image] Program development and design criteria for activity center/hotel facility at Rim Village: Crater lake National Park, Crater Lake, Oregon [volume 2]

  	2 v.: ill., maps, photos (some color); "Volume One: Program" and "Volume Two: Reference." Both volumes: "Prepared for the National Park Service, Denver Service Center." - Cover/Title pages; Volume Two ...
  	Citation × Citation Citation Abstract Copy Title: Program development and design criteria for activity center/hotel facility at Rim Village: Crater lake National Park, Crater Lake, Oregon [volume 2] Author: Project Team Year: 1989, 2009, 2010 2 v.: ill., maps, photos (some color); "Volume One: Program" and "Volume Two: Reference." Both volumes: "Prepared for the National Park Service, Denver Service Center." - Cover/Title pages; Volume Two includes "Wind tunnel study of snow conditions at Rim Village Crater Lake National Park," CPP Project 86-0361, prepared October 1987; Project Team consists of various architects and mechanical, structural, wind and civil engineering representatives and a snow consultant. Title: Program development and design criteria for activity center/hotel facility at Rim Village: Crater lake National Park, Crater Lake, Oregon [volume 2] Author: Project Team Year: 1989, 2009, 2010 2 v.: ill., maps, photos (some color); "Volume One: Program" and "Volume Two: Reference." Both volumes: "Prepared for the National Park Service, Denver Service Center." - Cover/Title pages; Volume Two includes "Wind tunnel study of snow conditions at Rim Village Crater Lake National Park," CPP Project 86-0361, prepared October 1987; Project Team consists of various architects and mechanical, structural, wind and civil engineering representatives and a snow consultant. Close

• 28794. [Image] Crater Lake National Park: Mazama Campground, Rim Village Corridor: supplement to the 1984 environmental assessment/development concept plan: amendment to the general management plan

  	ill., maps (some col.); Shipping list no.: 88-25-P; "October 1987."; "NPS D-2180A"--P. [3] of cover
  	Citation × Citation Citation Abstract Copy Title: Crater Lake National Park: Mazama Campground, Rim Village Corridor: supplement to the 1984 environmental assessment/development concept plan: amendment to the general management plan Author: United States. National Park Service Year: 1987, 2010 ill., maps (some col.); Shipping list no.: 88-25-P; "October 1987."; "NPS D-2180A"--P. [3] of cover Title: Crater Lake National Park: Mazama Campground, Rim Village Corridor: supplement to the 1984 environmental assessment/development concept plan: amendment to the general management plan Author: United States. National Park Service Year: 1987, 2010 ill., maps (some col.); Shipping list no.: 88-25-P; "October 1987."; "NPS D-2180A"--P. [3] of cover Close

• 28795. [Image] A review of the taxonomic status of pines including true firs within the pinus ponderosa forest in the southern portion of Crater Lake National Park, Oregon

  	ill.; Report title; "A report to the Superintendent, Crater Lake National Park, March 1982." - T.p.; Includes bibliographical references (p. 11-16)
  	Citation × Citation Citation Abstract Copy Title: A review of the taxonomic status of pines including true firs within the pinus ponderosa forest in the southern portion of Crater Lake National Park, Oregon Author: Mastrogiuseppe, R. J. Year: 1982, 2009 ill.; Report title; "A report to the Superintendent, Crater Lake National Park, March 1982." - T.p.; Includes bibliographical references (p. 11-16) Title: A review of the taxonomic status of pines including true firs within the pinus ponderosa forest in the southern portion of Crater Lake National Park, Oregon Author: Mastrogiuseppe, R. J. Year: 1982, 2009 ill.; Report title; "A report to the Superintendent, Crater Lake National Park, March 1982." - T.p.; Includes bibliographical references (p. 11-16) Close

• 28796. [Image] Organization of the Reclamation Service

  	An article summarizing the history of the United States Bureau of Reclamation; Photos of C.E. Grunsky, Consulting Engineer, and E.T. Perkins, author of this article, are included ; A map of Reclamation ...
  	Citation × Citation Citation Abstract Copy Title: Organization of the Reclamation Service Author: Perkins, E.T. Year: 1906, 2004 An article summarizing the history of the United States Bureau of Reclamation; Photos of C.E. Grunsky, Consulting Engineer, and E.T. Perkins, author of this article, are included ; A map of Reclamation Service projects current as of 1906 is included Title: Organization of the Reclamation Service Author: Perkins, E.T. Year: 1906, 2004 An article summarizing the history of the United States Bureau of Reclamation; Photos of C.E. Grunsky, Consulting Engineer, and E.T. Perkins, author of this article, are included ; A map of Reclamation Service projects current as of 1906 is included Close

• 28797. [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

• 28798. [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

• 28799. [Article] Beyond the Angle of Repose: A Review and Synthesis of Landslide Processes in Response to Rapid Uplift, Eel River, Northern Eel River, Northern California

  In mountainous settings, increases in rock uplift are often followed by a commensurate uptick in denudation as rivers incise and steepen hillslopes, making them increasingly prone to landsliding as slope ...

  Citation × Citation Citation Abstract Copy Title: Beyond the Angle of Repose: A Review and Synthesis of Landslide Processes in Response to Rapid Uplift, Eel River, Northern Eel River, Northern California Author: Roering, Joshua J., Mackey, Benjamin H., Handwerger, Alexander L., Booth, Adam M., Schmidt, David A., Bennett, Georgina L., Cerovski-Darriau, Corina Year: 2015 In mountainous settings, increases in rock uplift are often followed by a commensurate uptick in denudation as rivers incise and steepen hillslopes, making them increasingly prone to landsliding as slope angles approach a limiting value. For decades, the threshold slope model has been invoked to account for landslide-driven increases in sediment flux that limit topographic relief, but the manner by which slope failures organize themselves spatially and temporally in order for erosion to keep pace with rock uplift has not been well documented. Here, we review past work and present new findings from remote sensing, cosmogenic adionuclides, suspended sediment records, and airborne lidar data, to decipher patterns of landslide activity and geomorphic processes related to rapid uplift along the northward-migrating Mendocino Triple Junction in Northern California. From historical air photos and airborne lidar, we estimated the velocity and sediment flux associated with active, slow-moving landslides (or earthflows) in the mélange- and argillite-dominated Eel River watershed using the downslope displacement of surface markers such as trees and shrubs. Although active landslides that directly convey sediment into the channel network account for only 7% of the landscape surface, their sediment flux amounts to more than 50% of the suspended load recorded at downstream sediment gauging stations. These active slides tend to exhibit seasonal variations in velocity as satellite-based interferometry has demonstrated that rapid acceleration commences within 1 to 2 months of the onset of autumn rainfall events before slower deceleration ensues in the spring and summer months. Curiously, this seasonal velocity pattern does not appear to vary with landslide size, suggesting that complex hydrologic-mechanical feedbacks (rather than 1-D pore pressure diffusion) may govern slide dynamics. A new analysis of 14 years of discharge and sediment concentration data for the Eel River indicates that the characteristic mid-winter timing of earthflow acceleration corresponds with increased suspended concentration values, suggesting that the seasonal onset of landslide motion each year may be reflected in the export of sediments to the continental margin. The vast majority of active slides exhibit gullied surfaces and the gully networks, which are also seasonally active, may facilitate sediment export although the proportion of material produced by this pathway is poorly known. Along Kekawaka Creek, a prominent tributary to the Eel River, new analyses of catchment-averaged erosion rates derived from cosmogenic radionuclides reveal rapid erosion (0.76 mm/yr) below a prominent knickpoint and slower erosion (0.29 mm/yr) upstream. Such knickpoints are frequently observed in Eel tributaries and are usually comprised of massive (>10m) interlocking resistant boulders that likely persist in the landscape for long time periods (>105yr). Upstream of these knickpoints, active landslides tend to be less frequent and average slope angles are slightly gentler than in downstream areas, which indicates that landslide density and average slope angle appear to increase with erosion rate. Lastly, we synthesize evidence for the role of large, catastrophic landslides in regulating sediment flux and landscape form. The emergence of resistant blocks within the mélange bedrock has promoted large catastrophic slides that have dammed the Eel River and perhaps generated outburst events in the past. The frequency and impact of these landslide dams likely depend on the spatial and size distributions of resistant blocks relative to the width and drainage area of adjacent valley networks. Overall, our findings demonstrate that landslides within the Eel River catchment do not occur randomly, but instead exhibit spatial and temporal patterns related to baselevel lowering, climate forcing, and lithologic variations. Combined with recent landscape evolution models that incorporate landslides, these results provide predictive capability for estimating erosion rates and managing hazards in mountainous regions. Title: Beyond the Angle of Repose: A Review and Synthesis of Landslide Processes in Response to Rapid Uplift, Eel River, Northern Eel River, Northern California Author: Roering, Joshua J., Mackey, Benjamin H., Handwerger, Alexander L., Booth, Adam M., Schmidt, David A., Bennett, Georgina L., Cerovski-Darriau, Corina Year: 2015 In mountainous settings, increases in rock uplift are often followed by a commensurate uptick in denudation as rivers incise and steepen hillslopes, making them increasingly prone to landsliding as slope angles approach a limiting value. For decades, the threshold slope model has been invoked to account for landslide-driven increases in sediment flux that limit topographic relief, but the manner by which slope failures organize themselves spatially and temporally in order for erosion to keep pace with rock uplift has not been well documented. Here, we review past work and present new findings from remote sensing, cosmogenic adionuclides, suspended sediment records, and airborne lidar data, to decipher patterns of landslide activity and geomorphic processes related to rapid uplift along the northward-migrating Mendocino Triple Junction in Northern California. From historical air photos and airborne lidar, we estimated the velocity and sediment flux associated with active, slow-moving landslides (or earthflows) in the mélange- and argillite-dominated Eel River watershed using the downslope displacement of surface markers such as trees and shrubs. Although active landslides that directly convey sediment into the channel network account for only 7% of the landscape surface, their sediment flux amounts to more than 50% of the suspended load recorded at downstream sediment gauging stations. These active slides tend to exhibit seasonal variations in velocity as satellite-based interferometry has demonstrated that rapid acceleration commences within 1 to 2 months of the onset of autumn rainfall events before slower deceleration ensues in the spring and summer months. Curiously, this seasonal velocity pattern does not appear to vary with landslide size, suggesting that complex hydrologic-mechanical feedbacks (rather than 1-D pore pressure diffusion) may govern slide dynamics. A new analysis of 14 years of discharge and sediment concentration data for the Eel River indicates that the characteristic mid-winter timing of earthflow acceleration corresponds with increased suspended concentration values, suggesting that the seasonal onset of landslide motion each year may be reflected in the export of sediments to the continental margin. The vast majority of active slides exhibit gullied surfaces and the gully networks, which are also seasonally active, may facilitate sediment export although the proportion of material produced by this pathway is poorly known. Along Kekawaka Creek, a prominent tributary to the Eel River, new analyses of catchment-averaged erosion rates derived from cosmogenic radionuclides reveal rapid erosion (0.76 mm/yr) below a prominent knickpoint and slower erosion (0.29 mm/yr) upstream. Such knickpoints are frequently observed in Eel tributaries and are usually comprised of massive (>10m) interlocking resistant boulders that likely persist in the landscape for long time periods (>105yr). Upstream of these knickpoints, active landslides tend to be less frequent and average slope angles are slightly gentler than in downstream areas, which indicates that landslide density and average slope angle appear to increase with erosion rate. Lastly, we synthesize evidence for the role of large, catastrophic landslides in regulating sediment flux and landscape form. The emergence of resistant blocks within the mélange bedrock has promoted large catastrophic slides that have dammed the Eel River and perhaps generated outburst events in the past. The frequency and impact of these landslide dams likely depend on the spatial and size distributions of resistant blocks relative to the width and drainage area of adjacent valley networks. Overall, our findings demonstrate that landslides within the Eel River catchment do not occur randomly, but instead exhibit spatial and temporal patterns related to baselevel lowering, climate forcing, and lithologic variations. Combined with recent landscape evolution models that incorporate landslides, these results provide predictive capability for estimating erosion rates and managing hazards in mountainous regions. Close

• 28800. [Article] Improving estimates of forest disturbance by combining observations from Landsat time series with U.S. Forest Service Forest Inventory and Analysis data

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by Elsevier ...

  Citation × Citation Citation Abstract Copy Title: Improving estimates of forest disturbance by combining observations from Landsat time series with U.S. Forest Service Forest Inventory and Analysis data Author: Yang, Zhiqiang, Schroeder, Todd A., Healey, Sean P., et al., Moisen, Gretchen G. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/remote-sensing-of-environment/. Title: Improving estimates of forest disturbance by combining observations from Landsat time series with U.S. Forest Service Forest Inventory and Analysis data Author: Yang, Zhiqiang, Schroeder, Todd A., Healey, Sean P., et al., Moisen, Gretchen G. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/remote-sensing-of-environment/. Close