Search results for "Resistivity"
showing 10 items of 385 documents
On the Measurements of Numerical Viscosity and Resistivity in Eulerian MHD Codes
2016
We propose a simple ansatz for estimating the value of the numerical resistivity and the numerical viscosity of any Eulerian MHD code. We test this ansatz with the help of simulations of the propagation of (magneto)sonic waves, Alfven waves, and the tearing mode instability using the MHD code Aenus. By comparing the simu- lation results with analytical solutions of the resistive-viscous MHD equations and an empirical ansatz for the growth rate of tearing modes we measure the numerical viscosity and resistivity of Aenus. The comparison shows that the fast-magnetosonic speed and wavelength are the characteristic velocity and length, respectively, of the aforementioned (relatively simple) syst…
Finite difference time domain simulation of soil ionization in grounding systems under lightning surge conditions
2004
This paper proposes a Maxwell’s equations finite difference time domain (FDTD) approach for electromagnetic transients in ground electrodes in order to take into account the non linear effects due to soil ionization. A time variable soil resistivity method is used in order to simulate the soil breakdown, without the formulation of an initial hypothesis about the geometrical shape of the ionized zone around the electrodes. The model has been validated by comparing the computed results with available data found in technical literature referred to concentrated earths. Some application examples referred to complex grounding systems are reported to show the computational capability of the propos…
Infinite single-particle bandwidth of a Mott–Hubbard insulator
2016
The conventional viewpoint of the strongly correlated electron metal-insulator transition is that a single band splits into two upper and lower Hubbard bands at the transition. Much work has investigated whether this transition is continuous or discontinuous. Here we focus on another aspect and ask the question of whether there are additional upper and lower Hubbard bands, which stretch all the way out to infinity — leading to an infinite single-particle bandwidth (or spectral range) for the Mott insulator. While we are not able to provide a rigorous proof of this result, we use exact diagonalization studies on small clusters to motivate the existence of these additional bands, and we discu…
Zero Temperature Magnetoresistance of the HF Metal: Enigma of $$\mathrm{Sr}_{3}\mathrm{Ru}_{2}\mathrm{O}_{7}$$
2014
To understand the nature of field-tuned metamagnetic quantum criticality in the ruthenate \(\mathrm{Sr}_{3}\mathrm{Ru}_{2}\mathrm{O}_{7}\) is one of the significant challenges in the condensed matter physics. It is established experimentally that the entropy has a peak in the ordered phase. It is unexpectedly higher than that outside latter phase, while the magnetoresistivity varies abruptly near the ordered phase boundary. We demonstrate unexpected similarity between \(\mathrm{Sr}_{3}\mathrm{Ru}_{2}\mathrm{O}_{7}\) and HF metals expressing universal physics that transcends microscopic details. Our \(T-B\) phase diagram of \(\mathrm{Sr}_{3}\mathrm{Ru}_{2}\mathrm{O}_{7}\) explains main featu…
Results of proton irradiations of large area strip detectors made on high-resistivity Czochralski silicon
2004
Abstract We have processed full-size strip detectors on Czochralski grown silicon wafers with resistivity of about 1.2 kΩ cm. Wafers grown with Czochralski method intrinsically contain high concentrations of oxygen, and thus have potential for high radiation tolerance. Detectors and test diodes were irradiated with 10 MeV protons. The 1-MeV neutron equivalent irradiation doses were 1.6×1014 and 8.5×1013 cm−2 for detectors, and up to 5.0×1014 cm−3 for test diodes. After irradiations, depletion voltages and leakage currents were measured. Czochralski silicon devices proved to be significantly more radiation hard than the reference devices made on traditional detector materials.
Particle detectors made of high-resistivity Czochralski silicon
2005
We have processed pin-diodes and strip detectors on n- and p-type high-resistivity silicon wafers grown by magnetic Czochralski method. The Czochralski silicon (Cz-Si) wafers manufactured by Okmetic Oyj have nominal resistivity of 900 O cm and 1.9 kO cm for n- and p-type, respectively. The oxygen concentration in these substrates is slightly less than typically in wafers used for integrated circuit fabrication. This is optimal for semiconductor fabrication as well as for radiation hardness. The radiation hardness of devices has been investigated with several irradiation campaigns including low- and high-energy protons, neutrons, g-rays, lithium ions and electrons. Cz-Si was found to be more…
Small-polaron transport inLa0.67Ca0.33MnO3thin films
1998
We present a detailed study of the activated resistivity of ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_{3}$ films up to 600 K under the influence of high magnetic fields. Data in zero field can be explained by small polaron hopping as treated in the Friedman-Holstein theory. Based on the spin orientation of ferromagnetic clusters in a magnetic field, we develop a phenomenological model describing the temperature and field dependence of the resistivity with a minimum of free parameters. We find that the polarons have a magnetic contribution to their activation energy for hopping which depends on the variation of the spin order with increasing temperature and can be modified by a…
Transfer coefficients for evaporation of a system with a Lennard-Jones long-range spline potential
2007
International audience; Surface transfer coefficients are determined by nonequilibrium molecular dynamics simulations for a Lennard-Jones fluid with a long-range spline potential. In earlier work A. Røsjorde et al., J. Colloid Interface Sci. 240, 355 2001; J. Xu et al., ibid. 299, 452 2006, using a short-range Lennard-Jones spline potential, it was found that the resistivity coefficients to heat and mass transfer agreed rather well with the values predicted by kinetic theory. For the long-range Lennard-Jones spline potential considered in this paper we find significant discrepancies from the values predicted by kinetic theory. In particular the coupling coefficient, and as a consequence the…
Influence of disorder on anomalous Hall effect for Heusler compounds
2011
The anomalous Hall effect (AHE) is a long known but still not fully understood transport effect. Most theory papers focus on the influence of one particular contribution to the AHE. Actual measured experimental data, however, often are not in accord with idealized assumptions. In this work we discuss the data analysis for materials with low residual resistivity ratios. As prototypical materials we study half metallic Heusler compounds. Here the influence of defects and disorder is apparent in a material with a complex topology of the Fermi surface. Using films of different degree of disorder, we show how different scattering mechanisms can be separated. For ${\text{Co}}_{2}{\text{FeSi}}_{0.…
Violation of the Wiedemann-Franz Law in HF Metals
2014
Experimental observations of the much-studied compounds CeCoIn\(_5\) and YbRh\(_2\)Si\(_2\) at vanishing temperatures carefully probe the nature of their magnetic-field-tuned QCPs. The violation of Wiedemann-Franz (WF) law, along with jumps revealed both in the residual resistivity \(\rho _0\) and the Hall resistivity \(R_H\), provide vital clues to the origin of their non-Fermi-liquid behavior. The empirical facts point unambiguously to association of the observed QCP with FC forming flat bands.