Search results for "conductivity"
showing 10 items of 1988 documents
Absence of correlated flux pinning by columnar defects in irradiated epitaxial Bi2Sr2CaCu2O8 thin films
1999
Abstract Using heavy-ion irradiation, we produced columnar defects of different density and orientation in epitaxial Bi 2 Sr 2 CaCu 2 O 8 thin films. Although this increases the normal state resistivity and the critical temperature is reduced proportionally to the volume fraction of damaged material, pinning-related quantities like critical current density, activation energy and depinning field are enhanced in external magnetic fields. Transport measurements in dependence of the magnetic field and its orientation consistently indicate two-dimensional pinning of pancake vortices at the columnar defects. We observe the absence of correlated flux pinning by columnar defects and compare to heav…
Ab initiocomputational study on the lattice thermal conductivity of Zintl clathrates[Si19P4]Cl4andNa4[Al4Si19]
2016
The lattice thermal conductivity of silicon clathrate framework ${\mathrm{Si}}_{23}$ and two Zintl clathrates, $[{\mathrm{Si}}_{19}{\mathrm{P}}_{4}]{\mathrm{Cl}}_{4}$ and ${\mathrm{Na}}_{4}[{\mathrm{Al}}_{4}{\mathrm{Si}}_{19}]$, is investigated by using an iterative solution of the linearized Boltzmann transport equation in conjunction with ab initio lattice dynamical techniques. At 300 K, the lattice thermal conductivities for ${\mathrm{Si}}_{23}, [{\mathrm{Si}}_{19}{\mathrm{P}}_{4}]{\mathrm{Cl}}_{4}$, and ${\mathrm{Na}}_{4}[{\mathrm{Al}}_{4}{\mathrm{Si}}_{19}]$ were found to be 43 W/(m K), 25 W/(m K), and 2 W/(m K), respectively. In the case of ${\mathrm{Na}}_{4}[{\mathrm{Al}}_{4}{\mathrm…
Effect of commercial mineral-based additives on composting and compost quality.
2009
Abstract The effectiveness of two commercial additives meant to improve the composting process was studied in a laboratory-scale experiment. Improver A (sulphates and oxides of iron, magnesium, manganese, and zinc mixed with clay) and B (mixture of calcium hydroxide, peroxide, and oxide) were added to source-separated biowaste:peat mixture (1:1, v/v) in proportions recommended by the producers. The composting process ( T , emissions of CO 2 , NH 3 , and CH 4 ) and the quality of the compost (pH, conductivity, C/N ratio, water-soluble NH 4 –N and NO 3 –N, water- and NaOH-soluble low-weight carboxylic acids, nutrients, heavy metals and phytotoxicity to Lepidium sarivum ) were monitored during…
Electron transport process in simple amorphous metals at moderately low temperatures
2001
Abstract The dependence of electroresistivity ϱ( T ) and electron contribution to thermoconductivity ϰ( T ) of simple amorphous metals is investigated. Calculation of kinetic coefficients is carried out in the nearly free electron approximation (Ziman theory). The form-factor was calculated in the quasiphonon model. In this approximation on the short wavelength part of “dispersion curve” a minimum exists (“roton-like minimum”). It is shown that at moderately low temperatures 10 K ≤ T ≤ 100 K the ratio ϱ(T) − ϱ(0) T 2 has a maximum and the T 2 [ ϰ ( T ) − ϰ (0)] is minimal in this temperature region. Such “anomaly” in the temperature dependence of the kinetic coefficient is due to additional…
Electrical resistivity of simple metal amorphous alloys at moderately low temperatures
2003
Abstract An approach is developed that allows to explain the unusual dependence of the electrical resistivity ρ(T) of amorphous alloys on temperature T. Interactions between the free electrons and the longitudinal acoustic excitations in the small-wavelength region (“the roton region”) are shown to cause such a behaviour of ρ(T) at moderately low temperatures. The features of the electron–phonon interactions in an amorphous alloy as compared to the crystal state case are discussed. The theory is illustrated by numerical calculations of the electrical resistivity ρ(T) for Mg–Zn and Cu–Sn amorphous alloys at the different alloy concentrations in the 0 K temperature range. Qualitative agreemen…
DC electrical resistivity of Nb-Doped BaTiO3 and EPR measurements
1992
DC electrical resistivity measurements along the c-axis of Nb-doped BaTiO3 single crystals are presented in a wide range of temperature, covering the four phases, with special attention to the rhomboedral one. The temperature dependence of the conductivity leads to convincing arguments in favour of a polaronic mechanism. Below the orthorhombic-rhomboedral transition point, a strong increase of the resistivity is observed. The correlation of this behavior with EPR analysis in the same temperature range, is consistent with a sharp trapping of the ''free'' electrons, when the temperature decreases.
Structural transitions and melting of copper clusters
1993
Molecular dynamics is used to study the melting and structural transitions of small copper clusters. The melting temperature is found to be proportional to the average coordination number. Small icosahedral clusters melt at slightly higher temperatures than the cubic structures. Small cuboctahedral clusters are not stable but transform via a nondiffusive transition to icosahedral structure.
3 Probing and Modelling of Galvanic Coupling Phenomena in Localized Corrosion
2011
The basic driving force of localized corrosion or corrosion protection in numerous cases is the galvanic coupling of which the dimensional aspect is fixed by a combination of scales regarding interfacial processes or properties. At the electrolyte–metal interface, it is necessary to consider the microstructure (including all real-time modification induced for example by applied stresses), the possible chemical changes at the surface of the material, and the electrolyte conductivity contribution, among others factors.
Unveiling signatures of topological phases in open kitaev chains and ladders
2019
In this work, the general problem of the characterization of the topological phase of an open quantum system is addressed. In particular, we study the topological properties of Kitaev chains and ladders under the perturbing effect of a current flux injected into the system using an external normal lead and derived from it via a superconducting electrode. After discussing the topological phase diagram of the isolated systems, using a scattering technique within the Bogoliubov de Gennes formulation, we analyze the differential conductance properties of these topological devices as a function of all relevant model parameters. The relevant problem of implementing local spectroscopic measurement…
Parameter identification for heterogeneous materials by optimal control approach with flux cost functionals
2021
The paper deals with the identification of material parameters characterizing components in heterogeneous geocomposites provided that the interfaces separating different materials are known. We use the optimal control approach with flux type cost functionals. Since solutions to the respective state problems are not regular, in general, the original cost functionals are expressed in terms of integrals over the computational domain using the Green formula. We prove the existence of solutions to the optimal control problem and establish convergence results for appropriately defined discretizations. The rest of the paper is devoted to computational aspects, in particular how to handle high sens…