Suchergebnisse

In the space industry one of the most serious problems is charge storage on spacecrafts caused by plasma, solar-photoemission that causes damage to the spacecrafts. Therefore, the research by government and industry about spacecraft charging is thriving because there are still plenty of unknown faces in the space. A key first step for research of the phenomenon in ground-based laboratory test is to know well the most suitable experimental methods for measuring resistivity of spacecraft materials. This talk describes my investigations of the Classical Resistivity (constant voltage capacitor) Method to measure resistivity. I concentrate on understanding the differences between tests done in atmosphere and vacuum.

Abstract. Soil suction and resistivity strongly depend on the degree of soil saturation and, therefore, both are used for estimating water content variations. The main difference between them is that soil suction is measured using tensiometers, which give point information, while resistivity is obtained by tomography surveys, which provide distributions of resistivity values in large volumes, although with less accuracy. In this paper, we have related soil suction to electrical resistivity with the aim of obtaining information about soil suction changes in large volumes, and not only for small areas around soil suction probes. We derived analytical relationships between soil matric suction and electrical resistivity by combining the empirical laws of van Genuchten and Archie. The obtained relationships were used to evaluate maps of soil suction values in different ashy layers originating in the explosive activity of the Mt Somma-Vesuvius volcano (southern Italy). Our findings provided a further example of the high potential of geophysical methods in contributing to more effective monitoring of soil stress conditions; this is of primary importance in areas where rainfall-induced landslides occur periodically.

The utility of electrical resistivity as an indicator of magnetoionic performance in stoichiometrically and structurally similar thin-film systems is demonstrated. A series of highly nanocrystalline cobalt nitride (Co-N) thin films (85 nm thick) with a broad range of electrical properties exhibit markedly different magnetoionic behaviors. Semiconducting, near stoichiometric CoN films show the best performance, better than their metallic and insulating counterparts. Resistivity reflects the interplay between atomic bonding, carrier localization, and structural defects, and in turn determines the strength and distribution of applied electric fields inside the actuated films. This fact, generally overlooked, reveals that resistivity can be used to quickly evaluate the potential of a system to exhibit optimal magnetoionic effects, while also opening interesting challenges. ; Financial support by the European Research Council (SPIN-PORICS 2014-Consolidator Grant, Agreement No. 648454, and the MAGIC-SWITCH 2019-Proof of Concept Grant, Agreement No. 875018), the Spanish Government (MAT2017-86357-C3-1-R and PID2020- 116844RB-C21), the Generalitat de Catalunya (2017- SGR-292 and 2018-LLAV-00032) and the European Regional Development Fund (MAT2017-86357-C3-1-R and 2018-LLAV-00032) is acknowledged. This work was partially supported by the Impulse-und Net-working fund of the Helmholtz Association (FKZ VH-VI-442 Memriox), and the Helmholtz Energy Materials Characterization Platform (03ET7015). The PALS measurements were carried out at ELBE at the Helmholtz-Zentrum DresdenRossendorf e. V., a member of the Helmholtz Association. L.A. thanks MINECO for a Ramón y Cajal Contract (RYC-2013-12640). J.S. thanks the Spanish Fábrica Nacional de Moneda y Timbre for fruitful discussions. E.M. acknowledges support as a Serra Húnter Fellow. We acknowledge service from MiNa Laboratory at IMNCSIC.

In the papers of G.E. Archie and V.N. Dakhnov were presented formulas of dependence between resistivity (or conductivity) of soil and that of porous water. Such dependence shows that we need to know water resistivity, that means its study at each fieldwork area. In some areas places for groundwater are absent or restricted (boreholes, wells, springs) as places of surface water (rivers, streams, ponds, lakes). Can we measure water resistivity in pools? Immediately after rain such water has no relation with soil resistivity. The purpose of our study consists in determination the rules of ionic exchange between soil and rain water in time. In the paper [Brunet et al., 2010] the authors demonstrated results of water resistivity measurements at contact with soil in time. We wanted to check results of that experiment.

Resistivity method is widely used in shallow surface geophysics. Capacitive resistivity is one of techniques which help to extend usage of resistivity method for environmentc where galvanic coupling of electrodes is difficult, for instance, frozen ground, hard rocks and engineered structures (roads, railways and others). This technique allows fast field work without galvanic coupling electrodes. The main problem is complicated calculation of forward resistivity for simple model. In results, the limitations to the usage of the technique are not clear in theoretical and practical aspects. The authors determinate the limits of electrical properties and distances for capacity resistivity.

We report a detailed analysis of the electrical resistivity exponent of thin films of NdNiO3 as a function of epitaxial strain. Thin films under low strain conditions show a linear dependence of the resistivity versus temperature, consistent with a classical Fermi gas ruled by electron-phonon interactions. In addition, the apparent temperature exponent, n, can be tuned with the epitaxial strain between n = 1 and n = 3. We discuss the critical role played by quenched random disorder in the value of n. Our work shows that the assignment of Fermi/Non-Fermi liquid behaviour based on experimentally obtained resistivity exponents requires an in-depth analysis of the degree of disorder in the material. ; Qikai Guo and Saeedeh Farokhipoor acknowledge financial support from a China Scholarship Council (CSC) grant and a VENI grant (016.veni.179.053) of the Netherlands Organisation for Scientific Research (NWO), respectively. Francisco Rivadulla acknowledges support by the Ministry of Science of Spain (Project No. MAT2016-80762-R), the Conselleria de Cultura, Educacion e Ordenacion Universitaria. Xunta de Galicia (ED431F 2016/008, and Centro singular de investigación de Galicia accreditation 2016–2019, ED431G/09), the European Union (European Regional Development Fund (ERDF)) and the European Commission through the project 734187- SPI-COLOST (H2020-MSCA-RISE-2016). ; Peer reviewed

Particulate emission is a major problem in industrial processes, mainly power plants that make use of coal as a primary source of energy. Stringent emissions limits, set by government organisations requires industries to conform to these limits to ensure that air quality is sustained and with minimum pollutant present. Electrostatic precipitators are typically used to filter and collect these particulate emissions. Fly ash resistivity is a primary parameter in the collection of particulate emissions, and there is a resistivity range at which electrostatic precipitator collection is most efficient and anything outside this range limits, their operation. High resistivity ash results in back-corona discharge, whilst low resistivity results in particle re-entrainment into the flue gas stream. The purpose of this paper is to investigate and obtain a fly ash resistivity profile for existing power plants in South Africa. Ash samples obtained from power plants are, tested making use of an ash-resistivity test oven, in accordance with IEEE Standard 548-1984. This paper discusses obtained experimental results, to determine the resistivity profile at which South African power plant electrostatic precipitators operate. The electrical efficiency of the electrostatic precipitator system is evaluated based on the obtained resistivity profiles

Particulate emission is a major problem in industrial processes, mainly power plants that make use of coal as a primary source of energy. Stringent emissions limits, set by government organisations requires industries to conform to these limits to ensure that air quality is sustained and with minimum pollutant present. Electrostatic precipitators are typically used to filter and collect these particulate emissions. Fly ash resistivity is a primary parameter in the collection of particulate emissions, and there is a resistivity range at which electrostatic precipitator collection is most efficient and anything outside this range limits, their operation. High resistivity ash results in back-corona discharge, whilst low resistivity results in particle re-entrainment into the flue gas stream. The purpose of this paper is to investigate and obtain a fly ash resistivity profile for existing power plants in South Africa. Ash samples obtained from power plants are, tested making use of an ash-resistivity test oven, in accordance with IEEE Standard 548-1984. This paper discusses obtained experimental results, to determine the resistivity profile at which South African power plant electrostatic precipitators operate. The electrical efficiency of the electrostatic precipitator system is evaluated based on the obtained resistivity profiles

Under the terms of the Creative Commons Attribution (CC BY) license to their work. ; While graphene-based technology shows great promise for a variety of electronic applications, including radio-frequency devices, the resistance of the metal-graphene contact is a technological bottleneck for the realization of viable graphene electronics. One of the most important factors in determining the resistance of a metal-graphene junction is the contact resistivity. Despite the large number of experimental works that exist in the literature measuring the contact resistivity, a simple model of it is still lacking. In this paper, we present a comprehensive physical model for the contact resistivity of these junctions, based on the Bardeen Transfer Hamiltonian method. This model unveils the role played by different electrical and physical parameters in determining the specific contact resistivity, such as the chemical potential of interaction, the work metal-graphene function difference, and the insulator thickness between the metal and graphene. In addition, our model reveals that the contact resistivity is strongly dependent on the bias voltage across the metal-graphene junction. This model is applicable to a wide variety of graphene-based electronic devices and thus is useful for understanding how to optimize the contact resistance in these systems. ; We acknowledge support from SAMSUNG within the Global Innovation Program. The research leading to these results has received funding from Ministerio of Economía y Competitividad of Spain under the Project Nos. TEC2012-31330 and MAT2012-33911, and from the European Union Seventh Framework Programme under Grant Agreement No. 604391 Graphene Flagship. ; Peer Reviewed

Cadmium zinc telluride, CdZnTe, bulk single crystals doped with 1019 at./cm3 of indium in the initial melt were grown by vertical Bridgman technique. The samples were investigated by energy dispersive spectroscopy, cathodoluminiscence (CL), and current-voltage behavior at room temperature. The results shows that Cd and Te vacancy concentration depend on the indium and zinc concentrations. CL measurements indicate a relationship between radiative centers associated to Cd and Te vacancies and resistivity values. ; This work was partially supported by the following Projects: Grant Nos. MEC-ESP2006-09935, CM-S-0505/MAT-079, and FP7-SEC-2007-01 "European Commision," and Contract No. 14240/00/NL7SH "European Space Agency." One of the authors, V.C., thanks MEC, Spain for financial support. N.V. is grateful to Department of Science and Technology, Government of India for providing the BOYSCAST fellowship. The author J.R.F. is thankful to the Universidad Autónoma of Madrid for the financial suppor. ; Peer reviewed