Glass veins in the unequilibrated eucrite Yamato 82202

The unequilibrated eucrite Yamato 82202 (Y82202) contains a network of relatively thick (up to 1 mm in width) glass veins. The host of the meteorite represents a monomict breccia composed of volcanic rock that crystallized > 4.3 Ga ago as a lava flow on the surface of 4 Vesta. The veins formed 3.90 ± 0.04 Ga ago, probably as a result of frictional melting associated with impact, under conditions of low effective oxygen fugacity and higher sulfur fugacity. The glass contains disordered structural elements characteristic of pyroxene and feldspar, reminiscent of the eucritic target lithology. The unequilibrated pyroxenes of the volcanic host and the pristine character of the glass indicate that this meteoritic material did not experience significant thermal metamorphism after initial crystallization of the lava. Hence, it was not affected by regional metamorphism caused by burial to a significant depth or by long-term contact metamorphism associated with a thick lava flow, large intrusion, or hot layer of impact ejecta. The meteorite resided at a shallow depth (though not at the surface) on 4 Vesta or on one of the vestoids until it was ejected and traveled to Earth, probably with other HED materials that have ³⁶Ar exposure ages of ∼13 Ma. These data suggest that the surface of the asteroid 4 Vesta has significant, though probably small, proportions of glass, as well as unequilibrated volcanic rock.     

Developing A National Groundwater-Monitoring Network In Korea

Since the 1960's, the groundwater resources of Korea have been developed without a proper regulatory system for monitoring and preservation, resulting in significant source depletion, land subsidence, water contamination, and sea-water intrusion. With the activation of the "Groundwater Law" in June 1994, the government initiated a project to develop a groundwater-monitoring network to describe general groundwater quality, to define its long-term changes, and to identify major factors affecting changes in groundwater quality and yield. In selecting monitoring locations nationwide, criteria considered are 1) spatial distribution, 2) aquifer characteristics of hydrogeologic units, 3) local groundwater flow regime, 4) linkage with surface hydrology observations, 5) site accessibility, and 6) financial situations. A total of 310 sites in 78 small hydrologic basins were selected to compose the monitoring network. Installation of monitoring wells is scheduled to start in 1995 for 15 sites; the remainder are scheduled to be completed by 2001. At each site, a nest of monitoring wells was designed; shallow and deep groundwater will be monitored for water temperature, pH, EC, DO and TDS every month. Water-level fluctuations will also be measured by automatic recorders equipped with pressure transducers. As a next step, the government plans to develop a groundwater-database management system, which could be linked with surface hydrologic data. RÉSUMÉ: Depuis les années 60, les ressources en eaux souterraines de la Corée ont été mises en valeur sans dispositif réglementaire adapté de surveillance et de protection, ce qui a provoqué la diminution significative des apports, la subsidence des sols, la contamination de l'eau et l'intrusion d'eau marine. Avec la mise en vigueur de la "Loi sur les Eaux Souterraines", en juin 1994, le gouvernement a lancé un programme de réalisation d'un réseau de surveillance des eaux souterraines afin de décrire la qualité générale des eaux souterraines, de définir les variations à long terme et d'identifier les principaux facteurs responsables des variations de la qualité et du débit des eaux souterraines. Pour sélectionner les sites de contrôle à l'échelle du pays, les critères retenus sont les suivants: 1) la répartition spatiale, 2) les caractères aquifères des unités hydrologiques, 3) le régime local des écoulements souterrains, 4) le lien avec les observations faites en hydrologie de surface, 5) l'accessibilité des sites et 6) le réseau de surveillance. La mise en place de piézomètres de contrôle a été programmé pour le début de 1995, sur 15 sites; le reste est prévu d'ici à 2001. Sur chaque site, un groupe de piézomètres de contrôle a été prévu; la température, le pH, la conductivité électrique et la minéralisation des eaux souterraines superficielles et profondes seront mesurés chaque mois. Les variations du niveau piézométrique seront aussi mesurées au moyen de capteurs de pression reliés à des chaînes d'acquisition. Dans une étape ultérieure, le gouvernement prévoit de créer un système de gestion d'une banque de données sur les eaux souterraines, qui seront reliées aux données sur les eaux de surface. RESUMEN: Desde los años 60, los recursos de agua subterránea en Corea han sido desarrollados sin un sistema de regulación adecuado de control y conservación. Esto ha resultado en una disminución de los recursos, problemas de subsidencia, contaminación de aguas e intrusión marina. Con la activación de la "Ley de Aguas Subterráneas" en junio de 1994, el gobierno inició un proyecto para la instalación de una red de control de agua subterráneas con el objeto de establecer su calidad, definir sus variaciones a largo plazo e identificar los factores principales que afectan tanto su calidad como el suministro. Los criterios para seleccionar los puntos de control en todo el país fueron: 1) su distribución espacial, 2) las características de las unidades hidrogeológicas, 3) el régimen de flujo local, 4) su relación con el comportamiento observado de las aguas superficiales, 5) su accesibilidad, y 6) criterios económicos. Se seleccionaron un total de 310 lugares, situados en 78 pequeñas cuencas hidrológicas, para formar la red de control. La instalación de los pozos de control está previsto que empiece en 1995 para 15 puntos; el resto se deberá completar hacia el año 2001. En cada localización seleccionada se ha previsto un conjunto de pozos con el objetivo de tomar medidas, tanto en aguas subsuperficiales como profundas, de temperatura del agua, pH, CE, DO y TSD, mensualmente. Las oscilaciones de niveles del agua también se medirán, mediante registros automáticos conectados a transductores de presión. Como paso siguiente, el gobierno tiene previsto desarrollar un sistema de gestión de bases de datos hidrogeológicas, que pudiera conectarse con los datos de hidrología superficial.     

The misorientation index: Development of a new method for calculating the strength of lattice-preferred orientation

Using orientation data from experimentally deformed olivine, we explore some practical problems with the J-index, a commonly applied measure of fabric strength. We show that the J-index is highly dependent on several factors, including the number of discrete data in the orientation distribution function (ODF), and arbitrary numerical parameters specified for its calculation. Because of this non-uniqueness, we conclude that the J-index is difficult to interpret and should only be applied with caution. As an alternative to the J-index, we propose a new measure of fabric strength that is based on the distribution of uncorrelated misorientation angles. This “M-index” is shown to be insensitive to the parameters specified for its calculation. For typical deformed olivine samples, we show that 150 discrete data are adequate to quantify fabric strength using the M-index technique. The M-index correlates well with seismic anisotropy, particularly for materials of the same fabric type. Therefore, we conclude that the M-index technique is well-suited for the quantification of fabric strength and the comparison of like materials.     

Ediacaran mafic magmatism recorded in Cambrian eclogites of the Ross orogen,Antarctica: Implications for the Neoproterozoic rifting episodes along the Pacific-Gondwana margin

We report the first finding of Ediacaran mafic magmatism in northern Victoria Land of the Ross orogen, Antarctica, based on ca. 600–590 Ma magmatic zircon cores in Cambrian eclogites. The mafic magmatism could be either linked to ca. 615–590 Ma incipient convergent margin magmatism in central segment of the Ross orogen, or ca. 600–580 Ma continental rift-related volcanism widespread in eastern Australia. The latter is preferred based on the trace-element compositions distinctive from those of arc-related basalts and the depleted mantle-like Hf isotopic compositions of zircon. Our results suggest dual rifting episodes during both the Ediacaran and Cryogenian (ca. 670–650 Ma) in the East Antarctic margin, correlative with those in eastern Australia. A spatial distribution of coeval rifting and subduction along the Ediacaran margin of East Antarctica is readily accounted for by rift inheritance; the upper- and lower-plate geometry resulting from detachment and transform faulting.     

Finite element method for strong reflection of water waves

In this study, the propagation of monochromatic water waves over an arbitrarily varying topography is numerically investigated. A finite element model is developed by formulating the diffraction of waves caused by depth changes. Not only the propagating mode but also the evanescent modes are included in the model. The model developed is applied to the study of strong reflection of monochromatic waves over a sinusoidally varying topography. Predicted reflection coefficients are compared with those of available laboratory experiments and the eigenfunction expansion method. A very good agreement is observed.     

Angular spectra of polarized Galactic foregrounds

It is believed that magnetic field lines are twisted and bend by turbulent motions in the Galaxy. Therefore, both Galactic synchrotron emission and thermal emission from dust reflects statistics of Galactic turbulence. Our simple model of Galactic turbulence, motivated by results of our simulations, predicts that Galactic disk and halo exhibit different angular power spectra. We show that observed angular spectra of synchrotron emission are compatible with our model. We also show that our model is compatible with the angular spectra of star-light polarization for the Galactic disk. Finally, we discuss how one can estimate polarized microwave emission from dust in the Galactic halo using star-light polarimetry.     

Semi‐active fuzzy control for seismic response reduction using magnetorheological dampers

A semi‐active fuzzy control strategy for seismic response reduction using a magnetorheological (MR) damper is presented. When a control method based on fuzzy set theory for a structure with a MR damper is used for vibration reduction of a structure, it has an inherent robustness, and easiness to treat the uncertainties of input data from the ground motion and structural vibration sensors, and the ability to handle the non‐linear behavior of the structure because there is no longer the need for an exact mathematical model of the structure. For a clipped‐optimal control algorithm, the command voltage of a MR damper is set at either zero or the maximum level. However, a semi‐active fuzzy control system has benefit to produce the required voltage to be input to the damper so that a desirable damper force can be produced and thus decrease the control force to reduce the structural response. Moreover, the proposed control strategy is fail‐safe in that the bounded‐input, bounded‐output stability of the controlled structure is guaranteed. The results of the numerical simulations show that the proposed semi‐active control system consisting of a fuzzy controller and a MR damper can be beneficial in reducing seismic responses of structures. Copyright © 2004 John Wiley & Sons, Ltd.     

Compressibility of natural soils subjected to long-term acidic contamination

This paper presents the results of a systematic analysis aimed at establishing whether acidic pore fluids can affect the properties of natural soils, in particular their compressibility. Marine deposits with different mineral compositions and undisturbed soil structure were collected for this research from three coastal areas in Japan. Pleistocene clays from the Osaka and Ariake Bays were obtained from boreholes at a depth of more than 10 m, whereas the Kawasaki mud, a relatively young deposit of Holocene, was dredged from the bed of the Tokyo Bay. Soil specimens were placed in special containers, which were designed to reproduce the process of long-term soil–water–chemical interaction, and leached with solutions of sulfuric acid for different periods of time, ranging from 1 to 9 months. At the end of each time interval, standard compression tests were performed to study the behavior of soil in an acidic environment. It was found that clay mineralogy and soil structure had a significant effect on the compressibility of clays at low pH. In the case of the Osaka and Ariake clays, the compressibility significantly increased with a decrease in pH values, a finding that was primarily attributed to changes in the soil’s structure. In contrast, the effect of acidic leaching on the properties of Kawasaki mud was observed to be the opposite. Laboratory data showed that in acidic medium the compressibility of soil decreased presumably due to the collapse of the diffuse double layer.     

Mapping beech (Fagus sylvatica L.) forest structure with airborne hyperspectral imagery

Estimating forest structural attributes using multispectral remote sensing is challenging because of the saturation of multispectral indices at high canopy cover. The objective of this study was to assess the utility of hyperspectral data in estimating and mapping forest structural parameters including mean diameter-at-breast height (DBH), mean tree height and tree density of a closed canopy beech forest (Fagus sylvatica L.). Airborne HyMap images and data on forest structural attributes were collected from the Majella National Park, Italy in July 2004. The predictive performances of vegetation indices (VI) derived from all possible two-band combinations (VI_(i,j) = (R_i − R_j)/(R_i + R_j), where R_i and R_j = reflectance in any two bands) were evaluated using calibration (n = 33) and test (n = 20) data sets. The potential of partial least squares (PLS) regression, a multivariate technique involving several bands was also assessed. New VIs based on the contrast between reflectance in the red-edge shoulder (756–820 nm) and the water absorption feature centred at 1200 nm (1172–1320 nm) were found to show higher correlations with the forest structural parameters than standard VIs derived from NIR and visible reflectance (i.e. the normalised difference vegetation index, NDVI). PLS regression showed a slight improvement in estimating the beech forest structural attributes (prediction errors of 27.6%, 32.6% and 46.4% for mean DBH, height and tree density, respectively) compared to VIs using linear regression models (prediction errors of 27.8%, 35.8% and 48.3% for mean DBH, height and tree density, respectively). Mean DBH was the best predicted variable among the stand parameters (calibration R² = 0.62 for an exponential model fit and standard error of prediction = 5.12 cm, i.e. 25% of the mean). The predicted map of mean DBH revealed high heterogeneity in the beech forest structure in the study area. The spatial variability of mean DBH occurs at less than 450 m. The DBH map could be useful to forest management in many ways, e.g. thinning of coppice to promote diameter growth, to assess the effects of management on forest structure or to detect changes in the forest structure caused by anthropogenic and natural factors.