Hyperpycnal Discharge of Fluvial Sediment to the Ocean: Impact of Super‐Typhoon Herb (1996) on Taiwanese Rivers

Hyperpycnal events (when suspended sediment concentrations exceed 40 g/L) occur in small‐ and medium‐sized rivers throughout the world but are particularly common in Taiwan; they are often related to landslides or debris flows initiated and transported by typhoon floods. Super‐Typhoon Herb, which swept across Taiwan on July 31–August 2, 1996, triggered floods and landslides throughout the southern part of the island. Sediment concentrations in at least seven rivers (Taan, Choshui, Pachang, Erhjen, Tsengwen, Kaoping, and Peinan) approached or exceeded 40 g/L. Calculated sediment discharged from nine rivers (these seven as well as the Wu and Houlung, neither of which apparently reached hyperpycnal concentrations) during these 3 d was 217 million tons (MT)—most of it on August 1—of which ∼80% was discharged at hyperpycnal concentrations. Presumably, most of the sediments discharged by the Peinan River (to the southeast) and the Kaoping, Erhjen, Tsengwen, and Pachang rivers (to the southwest) were transported directly to the Huatong Basin and the South China Sea (via the Penghu Canyon system), respectively. The bulk of the typhoon‐derived sediment (142 MT), however, was discharged to the northwest (primarily by the Choshui River), and its fate remains unknown. It may have ultimately reached the Penghu Canyon system and thereby the South China Sea, but more probably it was transported northward (via the Taiwan Warm Current) toward China, the East China Sea, or (perhaps) the Okinawa Trough

Calculating highly fluctuated suspended sediment fluxes from mountainous rivers in Taiwan

Small drainage basins, highly fractured rock, high relief, and steep gradients make Taiwan watersheds particularly sensitive to episodic events such as typhoons and earthquakes, and to various types of anthropogenic disturbance. Here we analyze the characteristics of a long-term hydrological dataset from Taiwan and re-evaluate methods used to calculate sediment loads for Taiwan\u27s event-driven rivers. We suggest using the rating curve method stratified down to seasonal levels to reflect the rapid changes in the relationship between water discharge and suspended sediment load. A program is developed to determine the optimal time-interval for constructing rating curves, and is used to calculate hourly, daily, yearly, and long-term mean suspended sediment loads. Seasonal rating curves applied to hourly discharges are particularly critical to calculate sediment fluxes and concentrations in response to episodic events, particularly typhoons. The calculated cumulative long-term mean sediment fluxes for the Jhou-Shuei and Bei-Nan Rivers are considerably smaller than those calculated using monthly weighted average (MWA) method (Dadson et al. 2003). The MWA method likely over-estimates the mean load due to more frequent sediment observations during high-flow events

Trace metal fluxes to the ocean: The importance of high‐standing oceanic islands

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94592/1/grl16149.pd

Neodymium and Erbium Coordination Environments in Phosphate Glasses

The local structures of Nd3+ and Er3+ ions in two series of rare-earth (RE) phosphate glasses with nominal compositions xR203-(1-x)P2O5, where R=Nd and Er and 0.05≤x≤0.28, have been characterized by LIII-edge extended x-ray-absorption fine-structure spectroscopy (EXAFS). The RE coordination number depends on the R2O3 content, decreasing from 9.0 (10) oxygen nearest neighbors in ultraphosphate compositions (x\u3c0.15) to 6.4 (9) oxygen nearest neighbors for the metaphosphate (x∼0.25) compositions. The average Er-O bond distance decreases from 2.29 (1) to 2.23 (1) Å, and the average Nd-O bond distance decreases from 2.40 (1) to 2.37 (1) Å over the same compositional range. The changes in coordination environments are consistent with the conversion of isolated RE polyhedra to clustered RE polyhedra sharing common oxygens as the number of available terminal oxygens per RE ion decreases with increasing x

Overexpression of Fatty Acid Amide Hydrolase Induces Early Flowering in Arabidopsis thaliana

N-Acylethanolamines (NAEs) are bioactive lipids derived from the hydrolysis of the membrane phospholipid N-acylphosphatidylethanolamine (NAPE). In animal systems this reaction is part of the “endocannabinoid” signaling pathway, which regulates a variety of physiological processes. The signaling function of NAE is terminated by fatty acid amide hydrolase (FAAH), which hydrolyzes NAE to ethanolamine and free fatty acid. Our previous work in Arabidopsis thaliana showed that overexpression of AtFAAH (At5g64440) lowered endogenous levels of NAEs in seeds, consistent with its role in NAE signal termination. Reduced NAE levels were accompanied by an accelerated growth phenotype, increased sensitivity to abscisic acid (ABA), enhanced susceptibility to bacterial pathogens, and early flowering. Here we investigated the nature of the early flowering phenotype of AtFAAH overexpression. AtFAAH overexpressors flowered several days earlier than wild type and AtFAAH knockouts under both non-inductive short day (SD) and inductive long day (LD) conditions. Microarray analysis revealed that the FLOWERING LOCUS T (FT) gene, which plays a major role in regulating flowering time, and one target MADS box transcription factor, SEPATALLA3 (SEP3), were elevated in AtFAAH overexpressors. Furthermore, AtFAAH overexpressors, with the early flowering phenotype had lower endogenous NAE levels in leaves compared to wild type prior to flowering. Exogenous application of NAE 12:0, which was reduced by up to 30% in AtFAAH overexpressors, delayed the onset of flowering in wild type plants. We conclude that the early flowering phenotype of AtFAAH overexpressors is, in part, explained by elevated FT gene expression resulting from the enhanced NAE hydrolase activity of AtFAAH, suggesting that NAE metabolism may participate in floral signaling pathways

Near-Edge X-ray Absorption Fine Structure Study of Ion-beam-induced Phase Transformation in Gd2(Ti1-yZry)2O7

The structural and electronic properties of Gd2(Ti1−yZry)2O7 (y=0–1) pyrochlores following a 2.0-MeV Au2+ ion-beam irradiation (~5.0 X 1014 Au2+/cm2) have been investigated by Ti 2p and O 1s near-edge x-ray absorption fine structure (NEXAFS). The irradiation of Gd2(Ti1−yZry)2O7 leads to the phase transformation from the ordered pyrochlore structure (Fd3m) to the defect fluorite structure (Fm3m) regardless of Zr concentration. Irradiated Gd2(Ti1−yZry)2O7 with y≤0.5 are amorphous, although significant short-range order is present. Contrasting to this behavior, compositions with y≥0.75 retain crystallinity in the defect fluorite structure following irradiation. The local structures of Zr4+ in the irradiated Gd2(Ti1−yZry)2O7 with y≥0.75 determined by NEXAFS are the same as in the cubic fluorite-structured yttria-stabilized zirconia (Y–ZrO2), thereby providing conclusive evidence for the phase transformation. The TiO6 octahedra present in Gd2(Ti1−yZry)2O7 are completely modified by ion-beam irradiation to TiOx polyhedra, and the Ti coordination is increased to eight with longer Ti–O bond distances. The similarity between cation sites and the degree of disorder in Gd2Zr2O7 facilitate the rearrangement and relaxation of Gd, Zr, and O ions/defects. This inhibits amorphization during the ion-beam-induced phase transition to the radiation-resistant defect fluorite structure, which is in contrast to the ordered Gd2Ti2O7

Focal Contacts as Mechanosensors: Externally Applied Local Mechanical Force Induces Growth of Focal Contacts by an Mdia1-Dependent and Rock-Independent Mechanism

The transition of cell–matrix adhesions from the initial punctate focal complexes into the mature elongated form, known as focal contacts, requires GTPase Rho activity. In particular, activation of myosin II–driven contractility by a Rho target known as Rho-associated kinase (ROCK) was shown to be essential for focal contact formation. To dissect the mechanism of Rho-dependent induction of focal contacts and to elucidate the role of cell contractility, we applied mechanical force to vinculin-containing dot-like adhesions at the cell edge using a micropipette. Local centripetal pulling led to local assembly and elongation of these structures and to their development into streak-like focal contacts, as revealed by the dynamics of green fluorescent protein–tagged vinculin or paxillin and interference reflection microscopy. Inhibition of Rho activity by C3 transferase suppressed this force-induced focal contact formation. However, constitutively active mutants of another Rho target, the formin homology protein mDia1 (Watanabe, N., T. Kato, A. Fujita, T. Ishizaki, and S. Narumiya. 1999. Nat. Cell Biol. 1:136–143), were sufficient to restore force-induced focal contact formation in C3 transferase-treated cells. Force-induced formation of the focal contacts still occurred in cells subjected to myosin II and ROCK inhibition. Thus, as long as mDia1 is active, external tension force bypasses the requirement for ROCK-mediated myosin II contractility in the induction of focal contacts. Our experiments show that integrin-containing focal complexes behave as individual mechanosensors exhibiting directional assembly in response to local force

Oxygen and Phosphorus Coordination Around Iron in Crystalline Ferric Ferrous Pyrophosphate and Iron-phosphate Glasses with UO₂ or Na₂O

Fe K-edge x-ray absorption fine-structure (XAFS) measurements were performed on glass samples of (Fe3O4)0.3(P2O5)0.7 with various amounts of Na2O or UO2. Near-edge and extended-XAFS regions are studied and comparisons are made to several reference compounds. We find that iron in the base glass is ~25% divalent and that the Fe2+ coordination is predominantly octahedral, while Fe3+ sites are roughly split between tetrahedral and octahedral coordinations. Also, we measure roughly one FeñOñP link per iron. Substitution of Na2O or UO2 up to 15 mo1% primarily affects the first FeñO shell. The results are compared to data from the related material Fe3(P2O7)2

Research Program to Investigate the Fundamental Chemistry of Technetium

Technetium (99Tc, half-life = 2.13x105 years, b-emitter) is one of the radionuclides of major concern for nuclear waste disposal. This concern is due to the long half-life of 99Tc, the ease with which pertechnetate, TcO4 -, migrates in the geosphere, and the corresponding regulatory considerations. The problem of mobility of pertechnetate in the environment is compounded by the fact that pertechnetate is the thermodynamically stable form of technetium in aerobic environments. These two factors present challenges for the safe, long term immobilization of technetium in waste forms. Because of the stability of pertechnetate, technetium has been assumed to exist as pertechnetate in the aqueous phase of nuclear waste tanks. However, recent studies indicate that a significant fraction of the technetium is in a different chemical form. This program addresses the fundamental solution chemistry of technetium in the waste tank environment, and in a second part, the stability of technetium in various waste forms. The chemistry of this element will be studied in aqueous solutions at high pH, with various added salts such as nitrate, nitrite, and organic complexants, and as a function of radiation dose, to determine whether radiolysis effects can reduce TcO4 -. A separate facet of this research is the search for chemical forms of technetium that may be thermodynamically and/or kinetically stable and may be incorporated in various waste forms for long term storage. This phase of the program will address the problem of the possible oxidation of lower valent technetium species in various waste form matrices and the subsequent leaching of the highly soluble TcO4 -

Holographic analysis of diffraction structure factors

We combine the theory of inside-source/inside-detector x-ray fluorescence holography and Kossel lines/x ray standing waves in kinematic approximation to directly obtain the phases of the diffraction structure factors. The influence of Kossel lines and standing waves on holography is also discussed. We obtain partial phase determination from experimental data obtaining the sign of the real part of the structure factor for several reciprocal lattice vectors of a vanadium crystal.Comment: 4 pages, 3 figures, submitte