bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nanoscaled Sn and Pb Particles Aligned in Al2O3 Tubes Obtained from Molecular Precursors
Authors: Veith Michael , Frères Jacqueline , König Peter , Schütt Oliver , Huch Volker , Blin Joel 
Published: August 2005

AbstractTin and lead nanoparticles and metal sponges were prepared by reducing Me2Si(NtBu)2Sn (7) and Me2Si(NtBu)2Pb (9) with [H2AlOtBu] (3), [HAl(OtBu)2] (13), [H2AlOSiMe2tBu] (8), and [(Me2tBuSiO)2AlH] (15). Together with dihydrogen and the metals in their elemental state the monomeric compounds [Me2Si(NtBu)2Al(OSiMe2tBu)(THF)] (10) and [Me2Si(NtBu)2Al(OtBu)(THF)] (11) can be obtained, to mention only two examples. Each monomer is stabilized by a THF molecule coordinated to aluminum, which on sublimation loses its donor molecule and dimerizes through Lewis acid–base interactions to the spiro compounds [Me2Si(NtBu)2AlOSiMe2tBu]2 (12) and [Me2Si(NtBu)2AlOtBu]2 (4), respectively. The molecular structures of 10, 11, and 12 were determined by single‐crystal X‐ray diffraction techniques. The reduction of 7 at –115 °C is gradually indicated by a color change of the reaction mixtures from red to dark brown with increasing temperature and depending on the reducing agent used. The tin powders that were obtained were identified as β‐tin using X‐ray powder diffraction techniques and their average crystallite size depends on the polarity of the solvent and hydride used. Under certain conditions metal sponges are formed. Pycnometric measurements were carried out on the tin and lead sponges. These showed almost the known densities for the metals when helium was used whereas significantly smaller ones were measured in water. Porous alumina membranes of different pore diameters were filled with tin and lead particles. Metal nanoparticles were prepared within the tubes of the membranes by reduction of the metal amides in the pores. The infiltration process can be repeated up to ten times increasing the amount of particles within the tubes monitored by SEM. The obtained brown or black membranes were characterized by SEM, EDX, and UV/Vis analysis. The filled membranes show sharp impervious ranges in the UV/Vis spectrum between 270 and 525 nm and could therefore be used as wavelength filters. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Cover Picture: Dithioacetals as Zwitterion Synthons (Eur. J. Org. Chem. 18/2005)
Authors: Luh Tien‐Yau , Lee Chin‐Fa 
Published: August 2005

AbstractThe cover picture shows recent advances in the synthetic applications of the dithioacetal functionality. With the aid of thiophilic organolithium or organocopper reagents, propargylic dithioacetals and related compounds have been shown to be useful for the synthesis of polysubstituted allenes, trisubstituted furans and pyrroles. An extension of this annulation reaction to the bidirectional iterative synthesis of furan‐containing oligoaryls and to cyclophane synthesis is described. Alternatively, convergent synthesis of such oligo aryls from propargylic dithioacetals is briefly discussed. Not only can the carbon–sulfur bonds in dithioacetals be readily displaced by carbon–carbon and/or carbon–heteroatom bonds, but a range of reactions involving polarity inversion in neighboring carbon atoms can also take place. Representative examples are presented in the Microreview by T.‐Y. Luh and C.‐F. Lee on p. 3875 ff.
Using cosmogenic nuclides to contrast rates of erosion and sediment yield in a semi‐arid, arroyo‐dominated landscape, Rio Puerco Basin, New Mexico
Authors: Bierman Paul R. , Reuter Joanna M. , Pavich Milan , Gellis Allen C. , Caffee Marc W. , Larsen Jennifer 
Published: August 2005

AbstractAnalysis of in‐situ‐produced 10Be and 26Al in 52 fluvial sediment samples shows that millennial‐scale rates of erosion vary widely (7 to 366 m Ma−1) through the lithologically and topographically complex Rio Puerco Basin of northern New Mexico. Using isotopic analysis of both headwater and downstream samples, we determined that the semi‐arid, Rio Puerco Basin is eroding, on average, about 100 m Ma−1. This rapid rate of erosion is consistent with estimates made using other techniques and is likely to result from a combination of easily eroded lithologies, sparse vegetation, and monsoon‐dominated rainfall. Data from 331 stream water samples collected by the US Geological Survey between 1960 and 1995 are consistent with basin‐wide, average chemical denudation rates of only about 1·4 m Ma−1; thus, the erosion rates we calculate may be considered rates of sediment generation because physical weathering accounts for almost 99 per cent of mass loss.The isotopic data reveal that sediment is generally well mixed downstream with the area‐weighted average sediment generation rate for 16 headwater samples (234 ton km−2 a−1 for basin area 170 to 1169 km2) matching well that estimated from a single sample collected far downstream (238 ton km−2 a−1, basin area = 14 225 km2). A series of 15 samples, collected from an arroyo wall and representing deposition through the late Holocene, indicates that 10Be concentration in sediment delivered by the fluvial system has not changed appreciably over the last 1200 years despite at least two cycles of arroyo cutting and filling. Other samples (n = 21) were collected along the drainage network.Rio Puerco erosion rates scale directly with a variety of metrics describing vegetation, precipitation, and rock erodibility. Using the headwater basins for calibration, the erosion rates for both the downstream samples and also the data set as a whole, are best modelled by considering a combination of relief and vegetation metrics, both of which co‐vary with precipitation and erodibility as inferred from lithology. On average, contemporary sediment yields, determined by monitoring suspended‐sediment discharge, exceed cosmogenically determined millennial‐scale erosion rates by nearly a factor of two. This discrepancy, between short‐term rates of sediment yield and long‐term rates of erosion, suggests that more sediment is currently being exported from the basin than is being produced. Because the failure of incised channel walls and the head cutting of arroyo complexes appear to be the main sources of channel sediment today, this incongruence between rates of sediment supply and sediment yield is likely to be transitory, reflecting the current status of the arroyo cycle and perhaps the influence of current or past land‐use patterns. Copyright © 2005 John Wiley & Sons, Ltd.
Fluvial bedrock incision in the active mountain belt of Taiwan from in situ‐produced cosmogenic nuclides
Authors: Schaller M. , Hovius N. , Willett S. D. , Ivy‐Ochs S. , Synal H.‐A. , Chen M.‐C. 
Published: August 2005

AbstractThe concentration of cosmogenic nuclides in rocks exposed at the Earth's surface is proportional to the total duration of their exposure. This is the basis for bedrock surface exposure dating and has been used to constrain valley lowering rates in the Taroko gorge, eastern Central Range, Taiwan. Taroko gorge contains a uniquely complete geomorphic record of fluvial valley lowering: continuous, fluvially sculpted surfaces are present in the lower 200 m of this marble gorge. Assuming no post‐fluvial erosion of the gorge wall, the concentration of in situ‐produced cosmogenic 36Cl measured in gorge wall marbles reveals exposure ages from 0·2 ka in the active channel to 6·5 ka at 165 m above the present river. These ages imply an average fluvial incision rate of 26 ± 3 mm a−1 throughout the middle and late Holocene. Taking into account lateral gorge wall retreat after initial thalweg lowering would give rise to calculated older exposure ages. Without considering gorge wall retreat, our estimates therefore represent maximum incision rates. Estimated maximum Holocene incision rates are higher than the long‐term exhumation rates derived from fission track dating. The long‐term gorge development governed by tectonic uplift is superimposed by short‐term variations in incision rates caused by climatic or regional tectonic changes. Copyright © 2005 John Wiley & Sons, Ltd.
Episodic incision of the Colorado River in Glen Canyon, Utah
Authors: Garvin Cristofer D. , Hanks Thomas C. , Finkel Robert C. , Heimsath Arjun M. 
Published: August 2005

AbstractIncision rates of the Colorado River are integral to understanding the development of the Colorado Plateau. Here we calculate episodic incision rates of the Colorado River based on absolute ages of two levels of Quaternary deposits adjacent to Glen Canyon, Utah, along the north flank of Navajo Mountain. Minimum surface ages are determined by a combination of cosmogenic radionuclide surface exposure ages, uranium series and soil‐development formation times. Bedrock incision rates of the Colorado River between c. 500 ka and c. 250 ka, and c. 250 ka to present are c. 0·4 m ka−1 and c. 0·7 m ka−1, respectively. These rates are more than double the rates reported in the Grand Canyon, suggesting that the Colorado River above Lees Ferry is out of equilibrium with the lower section of the river. We also determine incision rates of two tributaries to the Colorado River. Oak Creek and Bridge Creek flow off Navajo Mountain into Glen Canyon from the southeast. Oak Creek and Bridge Creek both have incision rates of c. 0·6 m ka−1 over the past c. 100 ka at points about 9 km away from the main stem of the Colorado River. Copyright © 2005 John Wiley & Sons, Ltd.
Erosion rates driven by channel network incision in the Bolivian Andes
Authors: Safran Elizabeth B. , Bierman Paul R. , Aalto Rolf , Dunne Thomas , Whipple Kelin X. , Caffee Marc 
Published: August 2005

AbstractThe Bolivian Andes flank one of Earth's major topographic features and dominate sediment input into the Amazon Basin. Millennial‐scale erosion rates and dominant controls on erosion patterns in this range are poorly known. To define these patterns, we present 48 erosion rate estimates, derived from analysis of in situ 10Be in quartz‐bearing alluvium collected from the Upper Beni River basin.Erosion rates, corrected for the non‐uniform distribution of quartz in the sample basins, range from 0·04 mm a−1 to 1·35 mm a−1 and thus integrate over 102–104 years. Mean and modal values are 0·42 (standard deviation: 0·29) and 0·2–0·4 mm a−1 respectively, within the range of long‐term average erosion rates in this area derived from apatite fission track thermochronology (0·1–0·6 mm a−1). Hence, our data do not record any significant variation in erosion rate over the last several million years. Mean and modal short‐term erosion rates for the Andes are an order of magnitude lower than rates in the Ganges River headwaters in the High Himalaya and an order of magnitude greater than rates typical of the European Alps.In the Upper Beni River region of the Bolivian Andes, short‐term, basin‐averaged erosion rates correlate with normalized channel steepness index, a metric of relative channel gradient corrected for drainage area. Neither normalized channel steepness index nor basin‐averaged erosion rate shows strong correlation with mean basin hillslope gradient or mean basin local relief because many hillslopes in the Upper Beni River region are at threshold values of slope and local relief. Patterns of normalized channel steepness index appear primarily to reflect tectonic patterns and transient adjustment to those patterns by channel networks. Climate and lithology do not appear to exert first‐order controls on patterns of basin‐averaged erosion rates in the Bolivian Andes. Copyright © 2005 John Wiley & Sons, Ltd.
Erosion rates over millennial and decadal timescales at Caspar Creek and Redwood Creek, Northern California Coast Ranges
Authors: Ferrier Ken L. , Kirchner James W. , Finkel Robert C. 
Published: August 2005

AbstractComparing millennial‐scale denudation rates from cosmogenic nuclides with decadal‐scale sediment yields can shed light on erosional processes and on the effects of land use on sediment delivery to streams. Detailed measurements of sediment fluxes in the Northern California Coast Ranges at Caspar Creek and Redwood Creek have provided estimates of physical erosion rates since 1963 and 1971, respectively. We used cosmogenic 10Be to measure millennial‐scale denudation rates averaged over 1400–8700 years at six catchments in Caspar Creek and four catchments in Redwood Creek. Our 10Be measurements at Caspar Creek imply denudation rates that are nearly spatially uniform across the entire catchment and average 0·09 ± 0·02 mm a−1. These millennial‐scale rates implied by cosmogenic 10Be are faster than physical erosion rates of 0·005 ± 0·001 mm a−1 to 0·046 ± 0·007 mm a−1 inferred from sediment flux measurements over the past few decades in the same catchments. At Redwood Creek, our cosmogenic 10Be measurements imply millennial‐scale denudation rates that vary across the catchment from 0·14 ± 0·03 mm a−1 to 0·44 ± 0·09 mm a−1, in contrast to physical erosion rates ranging from 0·038 ± 0·011 mm a−1 to 0·48 ± 0·09 mm a−1 derived from sediment flux measurements made over the past few decades at the same catchments. The decadal‐scale and millennial‐scale measurements tend to differ most at the smallest tributaries, but differ by less than a factor of three for the Caspar Creek and Redwood Creek catchments as a whole. These measurements suggest that denudation rates at Caspar Creek are slower than rock uplift rates of 0·3–0·4 mm a−1, implying that Caspar Creek is not in topographic steady state. Copyright © 2005 John Wiley & Sons, Ltd.
Ice sheet erosion patterns in valley systems in northern Sweden investigated using cosmogenic nuclides
Authors: Li Yingkui , Harbor Jon , Stroeven Arjen P. , Fabel Derek , Kleman Johan , Fink David , Caffee Marc , Elmore David 
Published: August 2005

AbstractErosion patterns associated with glaciation of trunk and hanging valley systems in northern Sweden were investigated using cosmogenic nuclide 10Be apparent exposure ages and inferred nuclide inheritance. Sequences of samples taken across valleys known to have been covered repeatedly by the Fennoscandian ice sheet revealed two primary patterns of erosion. In Vávlávágge the exposure age pattern is consistent with >2 m of glacial erosion during the last glacial cycle along the entire profile. At Rávtasvággi, Dievssavággi and Alisvággi, exposure ages in the valley bottom contrast with apparent exposure ages two to four times older on the valley sides. The older ages on the valley sides reflect cosmogenic nuclide inheritance due to limited (<2 m) bedrock erosion of the valley sides during the last glacial cycle. The pattern and scale of erosion in these valleys indicates that glacial valley formation is a result of multiple glacial cycles rather than the result of topographic modification during a single glacial cycle. Initial data comparing hanging valley and trunk valley sites do not show distinct differences in apparent exposure ages. Slightly older ages for samples from hanging valley bottoms may suggest nuclide inheritance indicating lower erosion than in trunk valley bottoms, as would be expected given the marked topographic step between hanging and trunk valleys. Although quantifying the amount of erosion depends on the assumed cosmogenic nuclide inheritance prior to the onset of erosion, the pattern of erosion is independent of this. Hence the observed pattern of cosmogenic nuclide concentrations provides constraints on spatial patterns of erosion and helps to refine understanding of the timing and extent of landform modification by glaciation. Copyright © 2005 John Wiley & Sons, Ltd.
Dating floodplain sediments using tree‐ring response to burial
Authors: Friedman Jonathan M. , Vincent Kirk R. , Shafroth Patrick B. 
Published: August 2005

AbstractFloodplain sediments can be dated precisely based on the change in anatomy of tree rings upon burial. When a stem of tamarisk (Tamarix ramosissima) or sandbar willow (Salix exigua) is buried, subsequent annual rings in the buried section resemble the rings of roots: rings become narrower, vessels within the rings become larger, and transitions between rings become less distinct. We combined observations of these changes with tree‐ring counts to determine the year of deposition of sedimentary beds exposed in a 150‐m‐long trench across the floodplain of the Rio Puerco, a rapidly filling arroyo in New Mexico. This method reliably dated most beds thicker than about 30 cm to within a year of deposition. Floodplain aggradation rates varied dramatically through time and space. Sediment deposition was mostly limited to brief overbank flows occurring every few years. The most rapid deposition occurred on channel‐margin levees, which migrated laterally during channel narrowing. At the decadal timescale, the cross‐section‐average sediment deposition rate was steady, but there was a shift in the spatial pattern of deposition in the 1980s. From 1936 to 1986, sediment deposition occurred by channel narrowing, with little change in elevation of the thalweg. After 1986 sediment deposition occurred by vertical aggradation. From 1936 to 2000 about 27 per cent of the arroyo cross‐section filled with sediment. The rate of filling from 1962 to 2000 was 0·8 vertical m/decade or 85 m2/decade. Published in 2005 by John Wiley & Sons, Ltd.
Contribution of deep‐seated bedrock landslides to erosion of a glaciated basin in southern Alaska
Authors: Arsenault Ann M. , Meigs Andrew J. 
Published: August 2005

AbstractLandslides represent a key component of catchment‐scale denudation, though their relative contribution to the erosion of glaciated basins is not well known. Bedrock landslide contribution was investigated on the surface of one of eleven glaciers on a glaciated ridge in the Chugach‐St Elias Range of southern Alaska, where the debris from four major landslides is easily distinguished from moraines and other supraglacial material. A series of aerial and satellite photos from 1972 to 2000 and field observations in 2001 and 2002 indicate that three of four landslides have fallen onto the surface of the glacier since about 1978. The landslides, which originated from the steeply dipping (60–70°) bedrock walls, were deposited onto the glacier in the ablation zone and are currently being transported downstream supraglacially. Individual glacial valleys with topographic relief of ∼400 m are cut into high‐grade metamorphic rock characterized by a steep north‐dipping foliation and fractured by numerous large joints. Measurements of landslide area and average thickness obtained from high‐resolution survey data indicate a total landslide volume of ∼2·3 × 105 m3. This volume suggests a basin‐averaged erosion rate from landslides of 0·48 mm a−1. An overall basin‐scale erosion rate of 0·7 to 1·7 mm a−1 can be inferred, but depends on the percentage of the total‐basin sediment yield contributed by supraglacial sources. A mean rockwall retreat rate of 6·7 mm a−1 is calculated and is considerably higher than published rates, which range from 0·04 to 4·0 mm a−1. Controls on landslide generation include seismicity, freeze–thaw processes, topography, rock strength, and debuttressing. It is likely all of these factors contribute to failure, although the primary controls for the landslides in this study are thought to be rock strength and topography. The absence of landslides on ten of the eleven glaciers on this ridge is attributed to landslide magnitude–frequency relationships and short temporal scale of this study. Large‐volume bedrock landslides (>100 000 m3) may have low frequency, occurring less than once in a 55‐year time frame. Copyright © 2005 John Wiley & Sons, Ltd.
Probabilistic formulation of conservation of cosmogenic nuclides: effect of surface elevation fluctuations on approach to steady state
Authors: Parker G. , Perg L. A. 
Published: August 2005

AbstractCosmogenic nuclides have provided a powerful tool for determining rates of landscape erosion. Once a steady‐state profile of cosmogenic nuclides is reached, the erosion rate becomes inversely proportional to the concentration of cosmogenic nuclides in the eroded sediment. Erosional landscapes are, however, subject to varying degrees of elevation fluctuations due to gullying, landsliding and bioturbation, for example. Here elevation fluctuation is described in terms of a probability density of deviation from mean elevation. A probabilistic formulation for the conservation of cosmogenic nuclides is derived so as to include the effect of the fluctuations. At steady state, the relation between the mean erosion rate and the concentration of cosmogenic radionucides in the eroded material becomes identical to that which would prevail in the absence of fluctuations. The fluctuations, however, can significantly lengthen the time required to reach steady state. Here the approach to steady state is studied in terms of (a) an impulsive increase in erosion rate starting from an antecedent steady state, and (b) a constant erosion rate but the initial absence of any cosmogenic nuclides. The problem allows an analytical solution. The effect of the fluctuations increases monotonically with increase in the ratio of the standard deviation of elevation fluctuations to the e‐folding penetration length of cosmic rays. Of prime importance to the practitioner is whether or not the concentration of cosmogenic nuclides in the eroded material has reached its steady‐state value. The central result of this paper is a simple plot allowing estimation of the time required to reach within a specified tolerance of the steady‐state value of this concentration. The time increases markedly with increase in the ratio defined above. The current formulation of the model is most applicable to weathering‐ or transport‐limited systems, e.g. badlands or landscapes dominated by deep‐seated landslides. Copyright © 2005 John Wiley & Sons, Ltd.
Quaternary relief generation by polythermal glacier ice
Authors: Staiger Jane K. W. , Gosse John C. , Johnson Jesse V. , Fastook James , Gray James T. , Stockli Daniel F. , Stockli Lisa , Finkel Robert 
Published: August 2005

AbstractThe juxtaposition of wet‐based erosive ice in valleys and cold‐based, non‐erosive ice atop felsenmeer‐covered interfluve plateaus has generated relief in the Torngat Mountains of northeastern Canada. Measurements of in situ terrestrial cosmogenic nuclide (TCN) concentrations from 31 bedrock sites, coupled with soils and geomorphology, indicate that erosion of the valleys has been >2 m during a single glacial–interglacial cycle. However, on summit plateaus the long‐term (over several glacial–interglacial cycles) erosion rate is <1·4 m Ma−1. TCN ratios reveal that the exposure plus ice‐cover history retained on some summit surfaces probably spans more than 800 ka despite complete ice cover as recently as 11 ka. A thermodynamic ice sheet model with a basal water calculation is used to calculate the sliding distance normalized by the duration of ice cover for the region. We formulate a general glacial erosion rule for the Torngat Mountains, which correlates TCN‐derived erosion rates for terrain once partially covered by cold‐based ice with modelled average ice basal sliding velocities. Erosion rates vary linearly with average sliding velocity by a glacial erosion coefficient of 5 × 10−7. Due to the significant distribution of cold‐based ice cover in this high latitude region, our estimates of net regional glacial erosion and glacial erosion coefficient are orders of magnitude lower than a previously published value. Copyright © 2005 John Wiley & Sons, Ltd.