Spatial variation in sap flow velocity in semiarid region trees: its impact on stand‐scale transpiration estimates

In this study, we aimed to clarify spatial variations in xylem sap flow, and to determine the impacts of these variations on stand‐scale transpiration (E) estimates. We examined circumferential and radial variations in sap flow velocity (F_d) measured at several directions and depths in tree trunks of black locust (Robinia pseudoacacia) and native oak (Quercus liaotungensis), both of which have ring‐porous wood anatomy, in forest stands on the Loess Plateau, China. We evaluated the impacts of circumferential variations in F_d on stand‐scale transpiration estimates using a simple scaling exercise. We found significant circumferential variations in F_d in the outermost xylem in both species (coefficients of variation = 20–45%). For both species, F_d measured at the inner xylem was smaller than that of the outermost xylem and the F_d at the depth of > 10 mm was almost zero. The simple exercises showed that omitting circumferential variations in F_d affected the E estimate by 16–21%, which was less than the effects of omitting within‐tree radial and tree‐to‐tree variations in F_d in both species. These results suggest that circumferential variations in F_d can be a minor source of error for E estimates compared with within‐tree radial and tree‐to‐tree variations in F_d, regardless of the significant circumferential variations. Copyright © 2011 John Wiley & Sons, Ltd.     

Relationship between sinking organic matter and minerals in the shallow zone of the western Subarctic Pacific

We used time-series sediment trap data for four major components, organic matter and ballast minerals (CaCO₃, opal, and lithogenic matter) from 150, 540, and 1000 m in the western subarctic Pacific (WSAP), where opal is the predominant mineral in sinking particles, to develop four simple models for settling particles, including the “ballast model”. The ballast model is based on the concept that most of the organic matter “rain” in the deep sea is carried by the minerals. These four models are designed to simultaneously reproduce the flux of each major component of settling particles at 540 and 1000 m by using the data for each component at 150 m as initial values. Among the four models, the ballast model, which considers the sinking velocity increase with depth, was identified as the best using the Akaike information criterion as a measure of the model fit to data. This model successfully reproduced the flux of organic matter at 540 and 1000 m, indicating that the ballast model concept works well in the shallow zone of the WSAP on a seasonal timescale. This also suggests that ballast minerals not only physically protect the organic matter from degradation during the settling process but also enhance the sinking velocity and reduce the degree of decomposition.     

Molecular dynamics study of the crystal structure and phase relation of the GeO2 polymorphs

A two-body interatomic potential model for GeO₂ polymorphs has been determined to simulate the structure change of them by semi-empirical procedure, total lattice energy minimization of GeO₂ polymorphs. Based on this potential, two polymorphs of GeO₂; α-quartz-type and rutile-type, have been reproduced using the molecular dynamics (MD) simulation techniques. Crystal structures, bulk moduli, volume thermal expansion coefficients and enthalpies of these polymorphs of GeO₂ were simulated. In spite of the simple form of the potential, these simulated structural values, bulk moduli and thermal expansivities are in excellent agreement with the reliable experimental data in respect to both polymorphs. Using this potential, MD simulation was further used to study the structural changes of GeO₂ under high pressure. We have investigated the pressure-induced amorphization. As reported in previous experimental studies, quartz-type GeO₂ undergoes pressure-induced crystalline-to-amorphous transformation at room temperature, the same as other quartz compounds; SiO₂, AlPO₄. Under hydrostatic compression, in this study, α-quartz-type GeO₂ transformed to a denser amorphous state at 7.4 GPa with change of the packing of oxygen ions and increase of germanium coordination. At higher pressure still, rutile-type GeO₂ transformed to a new phase of CaCl₂-type structure as a post-rutile candidate. Received: 29 July 1996 / Revised, accepted: 30 April 1997     

Raman scattering and lattice vibrations of Ni2SiO4 spinel at elevated temperature

Raman spectra of Ni₂SiO₄ spinel (O _h ⁷ Z=8) have been measured in the temperature range from 20 to 600 °C and the Raman active vibrations (A _1g +E _g +3F _2g ) have been assigned. A calculation of the optically active lattice vibrations of this spinel has been made, assuming a potential function which combines general valence and short range force constants. The values of the force constants at 20 and 500 °C have been calculated from the vibrational frequencies of the observed Raman spectra and infrared (IR) spectral data. The Ni spinel at 20 °C has a prominently small Si-O bond stretching force constant of K(SiO)=2.356 ～ 2.680 md/Å and a large Ni-O bond stretching constant of K(NiO)=0.843 ～ 1.062 md/Å and these force constants at 500 °C decrease to K(SiO)=2.327 ～ 2.494 md/Å and K(NiO)=0.861 ～ 0.990 md/Å. The Si-O bond is noticeably weakened at high temperatures, despite the small thermal expantion from 1.657 Å (20 °C) to 1.660 Å (500 °C). These changes of the interatomic force constants of the spinel at high temperatures are in accord with the thermal structure changes observed by X-ray diffraction study. The weakened Si-O bond is consistent with the fact that Si atoms in the spinel lattice can diffuse at significant rates at elevated temperature.     

Wind fluctuations near a cold vortex-tropopause funnel system observed by the MU radar

Vertical and temporal variations of three-dimensional wind velocity associated with an upper-tropospheric cold vortex-tropopause funnel system were observed by an MST radar in Japan (the MU radar). Marked changes of vertical velocity and horizontal wind direction were found between the inside and outside of the cold vortex. The vertical velocity activity outside the vortex was asymmetric; it was most active in a sector before the vortex. Unsaturated internal gravity waves in their generation stage contribute predominantly to the vertical velocity activity, suggesting that tropospheric occluded cyclones may be a possible source of middle-atmospheric gravity waves through the geostrophic adjustment process.     

Internal gravity wave selection in the upper troposphere and lower stratosphere observed by the MU radar: Preliminary results

Marked wavelike variations of the lower stratospheric wind observed on 7–10 May, 1985 by an MST radar in Japan (by the MU radar) are analyzed assuming that they are induced by monochromatic internal inertio-gravity waves. These variations are mainly composed of two modes (periods: 22 and 24 hours), both of which have zonal phase velocities (C _X ) slower than the mean westerly wind (). A statistical analysis of the zonal phase velocity shows thatC _X above andC _X below the tropopause jet stream, which is considered to be a vivid proof of wave selection due to the tropospheric mean flow and upward wave emission from the tropopause jet. A comparison between the MU radar results and routine meteorological observations leads to the conclusion that the marked waves appear when the jet stream takes a maximum wind speed.     

Electron density distribution of FeTiO<Subscript>3</Subscript> ilmenite under high pressure analyzed by MEM using single crystal diffraction intensities

Many of ilmenites ABO₃ compounds bearing transition elements have semiconductive, ferroelectric and antiferromagnetic properties. The high-pressure diffraction studies of FeTiO₃ have been conducted up to 8.2 GPa using synchrotron radiation in KEK at Tsukuba with diamond anvil cell. The compression mechanism of FeTiO₃ ilmenite has been investigated by the structure refinements converged to the reliable factors R = 0.05. The deformations of the FeO₆ and TiO₆ octahedra were reduced with increasing pressure. In order to elucidate the electric conductivity change with pressure, electron density distribution of ilmenite have been executed by maximum entropy method (MEM) using single-crystal diffraction intensity data. MEM based on F _obs(hkl) of FeTiO₃ clearly shows electron density in comparison with the difference Fourier synthesis based on F _obs(hkl) − F _calc(hkl). The radial distribution of the electron density indicates electron localization around the cation positions. The bonding electron density found in bond Fe–O and Ti–O is lowered with pressure. The isotropic temperature factors B _iso become smaller with increasing pressure. Nevertheless the thermal vibration is considerably restrained by the compression, the electric conductivity is enhanced with pressure. Neither charge transfer nor electron hopping between Fe and Ti along the c axis in FeTiO₃ is plausible under high pressure. But the electric conductivity due to electron super-exchange in Fe–Fe and Ti–Ti has been clarified by the MEM electron density distribution. The anisotropy in the electric conductivity has been clarified.