Drainage, sediment transport, and denudation rates on the Nanga Parbat Himalaya, Pakistan

The Nanga Parbat Himalaya presents some of the greatest relief on Earth, yet sediment production and denudation rates have only been sporadically addressed. We utilized field measurements and computer models to estimate bank full discharge, sediment transport, and denudation rates for the Raikot and Buldar drainage basins (north slope of Nanga Parbat) and the upper reach of the Rupal drainage basin (south slope).The overall tasks of determining stream flow conditions in such a dynamic geomorphic setting is challenging. No gage data exist for these drainage basins, and the overall character of the drainage basins (high relief, steep flow gradients, and turbulent flow conditions) does not lend itself to either ready access or complete profiling.Cross-sectional profiles were surveyed through selected reaches of these drainage basins. These data were then incorporated into software (WinXSPRO) that aids in the characterization (stage, discharge, velocity, and shear stress) of high altitude, steep mountain stream conditions.Complete field measurements of channel depths were rarely possible (except at several bridges where the middle of the channel could actually be straddled and probed) and, when coupled with velocity measurements, provided discrete points of field-measured discharge calculations. These points were then used to calibrate WinXSPRO results for the same reach and provided a confidence level for computer-generated results.Flow calculations suggest that under near bank full conditions, the upper Raikot drainage basin produces discharges of 61 cm and moves about 11,000 tons day⁻¹ (9980 tons day⁻¹) of sediment through its channel. Bank full conditions on the upper portion of the Rupal drainage basin generate discharges of 84 cm and moves only about 3800 tons day⁻¹ (3450 tons day⁻¹) of sediment. Although the upper Rupal drainage basin moves more water, the lower slope of the drainage basin (0.03) generates a much smaller shear stress (461 Pa) than does the higher slope (0.12) of the upper Raikot drainage basin (1925 Pa).Dissolved and suspended sediment loads were measured from water/sediment samples collected throughout the day and night over a period of 10 days at the height of the summer melt season but proved to be a minor variable in transport flux. Channel bed loads were measured using a pebble count method of bank material and then used to generate ratings curves of bed loads relative to discharge volumes. When coupled with discharge data and basin area, mean annual sediment yield and denudation rates for Nanga Parbat are produced. Denudation rates calculated in this fashion range from 0.2 mm year⁻¹ in the slower, more sluggish Rupal drainage basin to almost 6 mm year⁻¹ in the steeper, faster flowing Raikot and Buldar drainage basins.     

Predictive instantaneous optimal control of elastic structures during earthquakes

A predictive instantaneous optimal control (PIOC) algorithm is proposed for controlling the seismic responses of elastic structures. This algorithm compensates for the time delay that happens in practical control applications by predicting the structural response over a period that equals the time delay, and by substituting the predicted response in the instantaneous optimal control (IOC) algorithm. The unique feature of this proposed PIOC algorithm is that it is simple and at the same time compensates for the time delay very effectively. Numerical examples of single degree of freedom structures are presented to compare the performance of PIOC and IOC systems for various time delay magnitudes. Results show that a time delay always causes degradation of control efficiency, but PIOC can greatly reduce this degradation compared to IOC. The effects of the structure's natural periods and the choice of control gains on the degradation induced by the time delay are also analyzed. Results show that shorter natural periods and larger control gains are both more sensitive and more serious to the degradation of control efficiency. Finally, a practical application of PIOC is performed on a six‐story moment‐resisting steel frame. It is demonstrated that PIOC contributes significantly to maintain stability in multiple degree of freedom structures, and at the same time PIOC has a satisfactory control performance. Copyright © 2003 John Wiley & Sons, Ltd.     

Predictive instantaneous optimal control of inelastic structures during earthquakes

A new inelastic structural control algorithm is proposed by incorporating the force analogy method (FAM) with the predictive instantaneous optimal control (PIOC) algorithm. While PIOC is very effective in compensating for the time delay for elastic structures, the FAM is highly efficient in performing the inelastic analysis. Unlike conventional inelastic analysis methods of changing stiffness, the FAM analyzes structures by varying the structural displacement field, and therefore the state transition matrix needs to be computed only once. This greatly simplifies the computation and makes inelastic analysis readily applicable to the PIOC algorithm. The proposed algorithm compensates for the time delay that happens in practical control systems by predicting the inelastic structural response over a period that equals the magnitude of the time delay. A one‐story frame with both strain‐hardening and strain‐softening inelastic characteristics is analyzed using this algorithm. Results show that the proposed control algorithm is feasibile for any inelastic structures. While the control efficiency deteriorates with the increase in magnitude of the time delay, the PIOC maintains acceptable performance within a wide range of time delay magnitudes. Finally, a computer model of a six‐story moment‐resisting steel frame is analyzed to show that PIOC has good control results for real inelastic structures. Copyright © 2003 John Wiley & Sons, Ltd.     

Calcrete profile development in Quaternary alluvial sequences,southeast Spain: implications for using calcretes as a basis for landform chronologies

A detailed study of the morphology and micro‐morphology of Quaternary alluvial calcrete profiles from the Sorbas Basin shows that calcretes may be morphologically simple or complex. The ‘simple’ profiles reflect pedogenesis occurring after alluvial terrace formation and consist of a single pedogenic horizon near the land surface. The ‘complex’ profiles reflect the occurrence of multiple calcrete events during terrace sediment aggradation and further periods of pedogenesis after terrace formation. These ‘complex’ calcrete profiles are consequently described as composite profiles. The exact morphology of the composite profiles depends upon: (1) the number of calcrete‐forming events occurring during terrace sediment aggradation; (2) the amount of sediment accretion that occurs between each period of calcrete formation; and (3) the degree of pedogenesis after terrace formation. Simple calcrete profiles are most useful in establishing landform chronologies because they represent a single phase of pedogenesis after terrace formation. Composite profiles are more problematic. Pedogenic calcretes that form within them may inherit carbonate from calcrete horizons occurring lower down in the terrace sediments. In addition erosion may lead to the exhumation of older calcretes within the terrace sediment. Calcrete ‘inheritance’ may make pedogenic horizons appear more mature than they actually are and produce horizons containing carbonate embracing a range of ages. Calcrete exhumation exposes calcrete horizons whose morphology and radiometric ages are wholly unrelated to terrace surface age. Composite profiles are, therefore, only suitable for chronological studies if the pedogenic horizon capping the terrace sequence can be clearly distinguished from earlier calcrete‐forming events. Thus, a detailed morphological/micro‐morphological study is required before any chronological study is undertaken. This is the only way to establish whether particular calcrete profiles are suitable for dating purposes. Copyright © 2003 John Wiley & Sons, Ltd.     

Structural, chemical, and isotopic microanalytical investigations of graphite from supernovae

We report the results of coordinated ion microprobe and transmission electron microscope (TEM) studies of presolar graphites from the KE3 separate (1.65-1.72 g/cm³) of the Murchison CM2 meteorite. Isotopic analysis of individual graphites (1-12 μm) with the ion microprobe shows many to have large ¹⁸O excesses combined with large silicon isotopic anomalies, indicative of a supernova (SN) origin. Transmission electron microscopy (TEM) of ultramicrotome slices of these SN graphites revealed a high abundance (25-2400 ppm) of internal titanium carbides (TiCs), with a single graphite in some cases containing hundreds of TiCs. Isotopic compositions of individual TiCs by nanoscale resolution secondary ion mass spectrometry (NanoSIMS) confirmed their presolar origin. In addition to TiCs, composite TiC/Fe grains (TiCs with attached iron-nickel subgrains) and solitary kamacite internal grains were found. In the composite grains, the attached iron phase (kamacite [0-24 at. % Ni] or taenite [up to 60 at. % Ni]) was epitaxially grown onto one or more TiC faces. In contrast to the denser Murchison KFC1 graphites, no Zr-Ti-Mo carbides were observed. The average TiC diameters were quite variable among the SN graphites, from 30 to 232 nm, and were generally independent of the host graphite size. TiC grain morphologies ranged from euhedral to anhedral, with the grain surfaces exhibiting variable degrees of corrosion, and sometimes partially amorphous rims (3 to 15 nm thick). Partially amorphous rims of similar thickness were also observed on some solitary kamacite grains. We speculate that the rims on the internal grains are most plausibly the result of atom bombardment caused by drift of grains with respect to the ambient gas, requiring relative outflow speeds ∼100 km/s (i.e., a few percent of the SN mass outflow speed).Energy dispersive X-ray spectrometry (EDXS) of TiCs revealed significant V in solid solution, with an average V/Ti ratio over all TiCs of ∼83% of the solar value of 0.122. Significant variations about the mean V/Ti ratio were also seen among TiCs in the same graphite, likely indicating chemical equilibration with the surrounding gas over a range of temperatures. In general, the diversity in internal TiC properties suggests that TiCs formed first and had substantially diverse histories before incorporation into the graphite, implying some degree of turbulent mixing in the SN outflows.In most graphites, there is a decrease in the number density of TiCs as a function of increasing radial dis- tance, caused by either preferential depletion of TiCs from the gas or an acceleration of graphite growth with decreasing ambient temperature. In several graphites, TiCs showed a trend of larger V/Ti ratios with increasing distance from the graphite center, an indication of progressive equilibration with the surrounding gas before they were sequestered in the graphites. In all but one graphite, no trend was seen in the TiC size vs. distance from the graphite center, implying that appreciable TiC growth had effectively stopped before the graphites formed, or else that graphite growth was rapid compared to TiC growth. Taken together, the chemical variations among internal grains as well as the presence of partially amorphous rims and epitaxial Fe phases on some TiCs clearly indicate that the phase condensation sequence was TiC, followed by the iron phases (only found in some graphites) and finally graphite. Since graphite typically condenses at a higher temperature than iron at low pressures (<10⁻³ bars) in a gas with C > O and otherwise solar composition, the observed condensation sequence implies a relative iron enrichment in the gas or greater supersaturation of graphite relative to iron.The TEM observations allow inferences to be made about the physical conditions in the gas from which the grains condensed. Given the TiC sizes and abundances, the gas was evidently quite dusty. From the observed TiC size range of ∼20 nm to ∼500 nm (assuming ∼1 yr growth time and T ∼ 1800°K), we infer minimum Ti number densities in the gas to be ∼7 × 10⁴ to ∼2 × 10⁶ atoms/cc, respectively. Although the gas composition is clearly not solar, for scale, these number densities would correspond to a pressure range of ∼0.2 μbar to ∼5.0 μbar in a gas of solar composition. They also correspond to minimum TiC grain number densities of ∼3 × 10⁻⁴ to ∼0.2 grains/cc, assuming complete condensation of Ti in TiC. We estimate the maximum ratio of mean TiC grain separation distance in the gas to grain diameter from the Ti number densities as ∼3 × 10⁵ to ∼1 × 10⁶.     

Metal island growth and dynamics on molybdenite surfaces

In order to understand the adsorption mechanism of metal atoms to semiconducting surfaces, we have studied, as a model system, the vapor phase adsorption of Ag, Au, and Cu on the (001) surface of molybdenite (MoS₂) and the subsequent surface diffusion of these adsorbates. Our scanning tunneling microscopy (STM) images show that, depending on the type of metal atom that is adsorbed, islands of a characteristic size (2 nm for Ag, 8 to 10 nm for Cu, two distinct sizes of 2 nm and 8 to 10 nm for Au), shape (well rounded in the lateral extension) and thickness (one monolayer for Ag, 1 to 1.5 nm for Cu) are formed during the initial stages of deposition. Whole islands are observed to surface diffuse without loss of size or shape. Despite the relatively large size of the copper islands on molybdenite, these islands surface diffuse extensively, suggesting that the Cu-S interaction is weak. Surface diffusion is only hindered once individual islands start to coalesce. As copper islands accumulate, the size and shape of the original islands can still be recognized, supporting the conclusion that these characteristics are constant and that monolayer growth occurs by the aggregation of islands across the surface.The strength and the nature of the Ag-S(MoS₂) bond were further investigated by using molecular orbital calculations, ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling spectroscopy (STS). By applying quantum mechanical approaches using a two-dimensional periodic molybdenite slab and hexagonal MoS₂ clusters of different sizes with metal atoms adsorbed to them, it is possible to calculate the electron transfer between the mineral surface and the metal atom as well as the adsorption energy as a function of surface coverage. In addition, we used the results from the quantum mechanical runs to derive empirical potentials that model the characteristics of the forces within the crystal, within the adsorbed islands, and the metal and mineral surface. The combination of quantum mechanical calculations and empirical force field calculations explain the electronic structure and the highest stability of Ag islands that have seven atoms in diameter, which exactly agrees with the size of experimentally observed islands. UPS results also suggest that a specific new state is formed (approximately 4.5 eV into the valence band) which may describe the Ag-S bond because it does not occur in pure silver or molybdenite.This study shows how the combination of microscopic (STM), spectroscopic (STS, UPS), compositional (X-ray photoelectron spectroscopy, XPS) and molecular modeling (quantum mechanical and empirical) techniques is a useful approach to understand the nature of the metal to sulfide bond. Further insights may be gained concerning the natural association of certain metals with sulfides.     

Observation of gravity waves in a boreal forest

In this paper we report the results of the analysis of two 60-min wave events that occurred in a boreal aspen forest during the 1994 BOREAS (Boreal Ecosystems-Atmosphere Study) field experiment. High frequency wind and temperature data were provided by three 3-D sonic anemometer/thermometers and fourteen fine-wire thermocouples positioned within and above the forest. Wave phase speeds, estimated from information revealed by spectral analysis and linear plane wave equations, are 2.2 and 1.3 m s^-1 for the two events. The wavelengths are 130 m and 65 m respectively and are much larger than the vertical wave displacements. There is strong evidence from the present analysis and from the literature supporting our postulate that these waves are generated by shear instability. We propose that wind shear near the top of the stand is often large enough to reduce the gradient Richardson number below the critical value of 0.25 and thus is able to trigger the instability. When external conditions are favorable, the instability will grow into waves.     

Geochemistry of the Rare Earth Elements in Natural Terrestrial Waters：A Review of What Is Currently Knows

The range of observed chemical compositions of natural terrestrial waters varies greatly especially when compared to the essentially constant global composition of the oceans.The concentrations of the REEs in natural terrestrial waters also exhibit more variation than what was reported in seawater,In terrestrial waters ,pH values span the range from acid up to alkaline,In addition,terrestrial waters can range from very dilute waters through to highly concentrated brines.The REE concentrations and their behavior in natural terrestrial waters reflect these compositional ranges,Chemical weathering of rocks represents the source of the REEs to natural terrestrial waters and ,consequently,the REE signature of rocks can impart their REE signature to associated waters,In addition,Because of the typical low solubilities of the REEs both surface and solution complexation can be important in fractionating REEs in aqueous solution.Both of these processes are important in all natural terrestrial waters,however,their relative importance varies as a function of the overall solution composition,In alkaline waters,for example,Solution complexation of the REEs with carbonate ions appears to control their aqueous distributions whereas in acid waters,the REE signature of the labile fraction of the REEs is readily leached from the rocks.In circumneutral pH waters,both processes appear to be important and their relative significance has not yet been determined.