Home About us Contact
|
Home About us Contact | ||
|
|
||
Conductive Layer (conductive + layer)
Selected AbstractsMagnetotelluric Investigation of the Hydrothermal System and Heat Source in the Muine-Toyoha Geothermal Area, Hokkaido, JapanRESOURCE GEOLOGY, Issue 3 2003Shinichi Takakura Abstract. Magnetotelluric (MT) surveys were carried out around the Muine volcano, Hokkaido, Japan, where it is expected that the heat and metal source forming the polymetallic Ag-Pb-Zn-Cu-In Toyoha deposit is present at depth. Measurements were performed at 20 sites, 18 of which were located along a WSW-ENE profile traversing the north ridge of Mt. Muine. A resistivity model obtained from 2D inversion of the MT data shows subsurface specific conductive and resistive features. Conductive layers are present at the surface of Mt. Muine. The low resistivity is probably due to the clay-rich rocks associated with the hydrothermal alteration. A high resistivity layer, which corresponds to the pre-Tertiary Usubetsu Formation, crops out east of Mt. Muine and dips westward. At the west foot of Mt. Muine, relatively high resistive layers are widely exposed. The resistivity increases with depth and exceeds 1000 ohm-m. This fact indicates that this region is not influenced by the recent hydrothermal activity. An extremely conductive zone about 3,6 km wide and 6,9 km thick exists at a depth of 2 km below Mt. Muine. This zone mostly corresponds to an elastic wave attenuation zone detected by a seismic survey. It is interpreted as a large hydrothermal reservoir or melted magma, which is a heat source of the hydrothermal system in this area. [source] Electrical conductivity and crustal structure beneath the central Hellenides around the Gulf of Corinth (Greece) and their relationship with the seismotectonicsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2000V. N. Pham A deep magnetotelluric sounding (MTS) investigation in the western part of the Gulf of Corinth has revealed a complex electrical image of the crustal structure. The geotectonic structure of the Parnassos unit and the Transition zone in the central Hellenides, overthrusting the Pindos zone both towards the west and towards the south, has been clearly identified by its higher resistivity and its intrinsic anisotropy related to the N,S strike of the Hellenides range. Subsequent N,S extension of the Gulf introduced another heterogeneous anisotropy characteristic that corresponds to E,W-trending normal faults on both sides of the Gulf. The 2-D modelling of the MTS results reveals the existence of a relatively conductive layer about 4 km thick at a depth greater than 10 km in the middle crust. It corresponds to a ductile detachment zone suggested by microseismic and seismic studies (King et al. 1985; Rigo et al. 1996; Bernard et al. 1997a). It may be attributed to the phyllite series lying between the allochthonous Hellenic nappes and the autochthonous Plattenkalk basement. Towards the east, under the Pangalos peninsula, approaching the internal Hellenides, the detachment zone could root deeply into the lower crust. Some strong local electrical anomalies are observed, reaching the conductive layer in the middle crust, such as that under the Mamousia fault and under the front of the overthrust of the Transition zone on the Pindos zone. Other anomalies affect only the shallower zones such as that beneath the Helike fault and in the Psaromita peninsula. These shallower anomalies provide complementary information to the study of spatial and temporal variations of the seismic anisotropy in relation to the short- and long-term tectonic activity of the Gulf (Bouin et al. 1996; Gamar et al. 1999). [source] Geophysical exploration for interlayer slip breccia gold deposits: example from Pengjiakuang gold deposit, Shandong Province, ChinaGEOPHYSICAL PROSPECTING, Issue 2 2004Z. Qingdong ABSTRACT Interlayer slipping breccia-type gold deposit , a new type of gold deposit, defined recently in the northern margin of the Jiaolai Basin, Shandong Province, China , occurs in interlayer slip faults distributed along the basin margin. It has the features of large orebody thickness (ranging from 14 m to 46 m, with an average thickness of 30 m), shallow embedding (0,50 m thickness of cover), low tenor of gold ore (ranging from 3 g/t to 5 g/t), easy mining and ore dressing. This type of gold deposit has promising metallogenic forecasting and potential for economic exploitation. A ground gamma-ray survey in the Pengjiakuang gold-ore district indicates that the potassium/thorium ratio is closely related to the mineralization intensity, i.e. the larger the potassium/thorium ratio, the higher the mineralization. The gold mineralized alteration zone was defined by a potassium/thorium ratio of 0.35. A seismic survey confirms the location of the top and bottom boundaries and images various features within the Pengjiakuang gold mineralization belt. The gold-bearing shovel slipped belt dips to the south at an angle of 50,55° at the surface and 15,20° at depth. The seismic profile is interpreted in terms of a structural band on the seismic section characterized by a three-layered model. The upper layer is represented by weakly discontinuous reflections that represent the overlying conglomerates. A zone of stronger reflections representing the interlayer slip fault (gold-bearing mineralized zone) is imaged within the middle of the section, while the strongest reflections are in the lower part of the section and represent metamorphic rocks at depth. At the same time, the seismic reflection survey confirms the existence of a granite body at depth, indicating that ore-forming fluids may be related to the granite. A CSAMT survey showed that the gold-bearing mineralized zone is a conductive layer and contains a low-resistivity anomaly ranging from 2 ,m to 200 ,m. [source] Experimental validation of the wavefield transform of electromagnetic fieldsGEOPHYSICAL PROSPECTING, Issue 5 2002Kaushik Das The wavefield transform is a mathematical technique for transforming low-frequency electromagnetic (EM) signals to a non-diffusive wave domain. The ray approximation is valid in the transform space and this makes traveltime tomography for 3D mapping of the electrical conductivity distribution in the subsurface possible. The transform, however, imposes stringent frequency bandwidth and signal-to-noise ratio requirements on the data. Here we discuss a laboratory scale experiment designed to collect transform quality EM data, and to demonstrate the practical feasibility of transforming these data to the wavefield domain. We have used the scalable nature of EM fields to design a time-domain experiment using graphite blocks to simulate realistic field conditions while leaving the time scale undisturbed. The spatial dimensions have been scaled down by a factor of a thousand by scaling conductivity up by a factor of a million. The graphite blocks have two holes drilled into them to carry out cross-well and borehole-to-surface experiments. Steel sheets have been inserted between the blocks to simulate a conductive layer. Our experiments show that accurate EM data can be recorded on a laboratory scale model even when the scaling of some features, such as drill-hole diameters, is not maintained. More importantly, the time-domain EM data recorded in cross-well and surface-to-borehole modes can be usefully and accurately transformed to the wavefield domain. The observed wavefield propagation delay is proportional to the direct distance between the transmitter and receiver in a homogeneous medium. In a layered medium, data accuracy is reduced and, hence, our results are not so conclusive. On the basis of the experimental results we conclude that the wavefield transform could constitute a valid approach to the interpretation of accurate, undistorted time-domain data if further improvement in the transform can be realized. [source] Schottky contacts to hydrogen doped ZnOPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2008R. Schifano Abstract High resistivity (,1 k, cm) hydrothermally grown single crystal ZnO wafers were modified by hydrogen implantation. The implantation has been performed with multiple energies in order to form a box-like profile with a depth of 4 ,m and two different concentrations of 8 × 1017 H/cm3 and 1.5 × 1018 H/ cm3. A subsequent annealing at 200 °C for 30 min in N2 resulted in the formation of a highly conductive layer. Pd con- tacts deposited on the implanted side showed rectifying behaviour by up to three orders of magnitude. However by capacitance vs. voltage (C ,V) technique a carrier concentration significantly lower than the one expected according to the implanted H content was measured suggesting the presence of a high density of compensating centers and/or an incomplete activation of H as a donor. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Scanning capacitance microscopy as a tool for the assessment of unintentional doping in GaNPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009Rachel A. Oliver Abstract Scanning capacitance microscopy (SCM) is a technique based on atomic force microscopy which provides information about the concentration and distribution of charge carriers in a semiconducting sample. As an imaging technique it provides an advantage over more conventional approaches such as secondary ion mass spectrometry and depth-profiling Hall voltage measurement since it provides a two-dimensional dataset rather than a one dimensional line profile. Here, we demonstrate the utility of SCM for GaN-based materials by assessing the unintentionally doped layer at the GaN/sapphire interface in a series of samples in which the growth conditions initially favoured the formation of three-dimensional islands, which later coalesced to form a two-dimensional film. Using SCM we observe that the width of the resulting conductive layer at the GaN/sapphire interface depends on the time taken to achieve coalescence but that the carrier density does not. We also assess and attempt to explain the roughness of the top surface of the conductive interface layer, which can only be addressed using an imaging technique. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A Dual-Electrode Approach for Highly Selective Detection of Glucose Based on Diffusion Layer Theory: Experiments and SimulationCHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2005Kang Wang Dr. Abstract A dual-electrode configuration for the highly selective detection of glucose in the diffusion layer of the substrate electrode is presented. In this approach, a glassy carbon electrode (GCE, substrate) modified with a conductive layer of glucose oxidase/Nafion/graphite (GNG) was used to create an interference-free region in its diffusion layer by electrochemical depletion of interfering electroactive species. A Pt microelectrode (tip, 5 ,m in radius) was located in the diffusion layer of the GNG-modified GCE (GNG-G) with the help of scanning electrochemical microscopy. Consequently, the tip of the electrode could sense glucose selectively by detecting the amount of hydrogen peroxide (H2O2) formed from the oxidization of glucose on the glucose oxidase layer. The influences of parameters, including tip,substrate distance, substrate potential, and electrolyzing time, on the interference-removing efficiency of this dual-electrode approach have been investigated systematically. When the electrolyzing time was 30 s, the tip,substrate distance was 1.8,a (9.0 ,m) (where a is the radius of the tip electrode), the potentials of the tip and substrate electrodes were 0.7 V and 0.4 V, respectively, and a mixture of ascorbic acid (0.3,mM), uric acid (0.3,mM), and 4-acetaminophen (0.3,mM) had no influence on the glucose detection. In addition, the current,time responses of the tip electrode at different tip,substrate distances in a solution containing interfering species were numerically simulated. The results from the simulation are in good agreement with the experimental data. This research provides a concept of detection in the diffusion layer of a substrate electrode, as an interference-free region, for developing novel microelectrochemical devices. [source] | |||||||||||||