Academic literature on the topic 'Debye decomposition'

We have developed an alternative formulation for Debye decomposition of complex electric conductivity spectra, by recasting it into a new set of parameters with a close relationship to the continuous formulation for the complex conductivity method. The procedure determines a relaxation time distribution (RTD) and two frequency-independent parameters that modulate the complex conductivity spectra. These two parameters represent (1) the direct current contribution and (2) the conductivity range spanned by the low- and high-frequency limits. The distribution of relaxation times quantifies the contribution of each distinct relaxation process. Assuming that characteristic times with insignificant contributions can be ignored, a minimum set of characteristic relaxation times is determined. Each contribution can then be associated with specific polarization processes that can be interpreted in terms of electrochemical or interfacial parameters of mechanistic models derived from inverted parameters obtained from the proposed approach. Synthetic tests show that the procedure can fit spectral induced polarization (SIP) data and successfully retrieve the RTD. We have applied the procedure to laboratory SIP data from experiments with sand and oil mixtures undergoing microbial degradation of hydrocarbons. The RTD reveals evidence of a length scale at which a new polarization process takes place as a result of the biodegradation process.

Abstract Twelve cubic sodalites |Na8X2|[T1T2O4]6 (T1 = Al3+, Ga3+; T2 = Si4+, Ge4+; X = Cl−, Br−, I−) were examined using high-temperature (HT) X-ray diffraction experiments and TGA-DSC measurements. Temperature-dependent structure data was obtained by Rietveld refinements. Decomposition temperatures were determined using TGA-DSC data for all compounds. The temperature-dependent volume expansion was used to determine Debye and Einstein temperatures using DEA fits. Distinct relations between thermal expansion, bond lengths and the decomposition temperature could not be found. Determination of Lindemann constants of all compounds enables a classification of the sodalites in three groups.

Mixture metal oxide system Co-Cr were prepared by decomposition of the precursor complexes obtained from a mixture Co-Cr nitrates with tartaric acid. The samples were subsequently submitted to chemical analysis, magnetic measurements, IR spectrometry, UV-Vis, thermal analysis, XRD, EXAFS and TPR. At 600oC was identificated a solid solution of CoCr2O4 with Co3O4. With Cu-CrK-edge EXAFS the local structure of samples calcinated of 420oC and 600oC was obtained. By theirs analysis was calculated: the lengths of M-O bounds, number of coordination (N), Debye-Waller factor (A1) and x metallic cations fraction in tetrahedral structures (spinelic centers). The TPR measurements were emphasized the existence of two reduction cycles.

We consider model A dynamics for a quench from the disordered into the ordered phase of SU (3) lattice gauge theory and the analogue 3d 3-state Potts model. For the gauge model this corresponds to a rapid heating from the confined to the deconfined phase. The exponential growth factors of low-lying structure function modes are numerically calculated. The linear theory of spinodal decomposition is used to determine the critical modes. This allows for the Debye screening mass estimation in an effective phenomeno-logical model. The quench leads to competing vacuum domains, which make the equilibration of the QCD vacuum after the heating non-trivial. The influence of such domains on the gluonic energy density is studied.

The characterization of the shallow subsurface constitutes a challenging issue in several applications of science and engineering. Among the other disciplines, hydrogeophysics deals with the use of geophysical methods for the exploration, management, and monitoring of soil and groundwater. One of the main topics is the study of the petrophysical relationships between electrical properties and hydraulic conductivity, mainly through the dependence of such physical parameters on textural properties. The general aim of this work consists in an investigation of porous materials typical of alluvial environments with spectral induced polarization (SIP) method. The driving question of the research is the feasibility of the use of SIP to characterize both the textural assemblage of the sediments and the fluid properties, in presence of interacting effects related to particles’ mineralogy, organic matter, sediments’ fabric, etc. The samples’ set is constituted by 19 unconsolidated materials collected in four sites of the Po plain south of Milano (Orio Litta, Senna Lodigiana, and Landriano) and west of Milano (Lozzolo), and saturated with seven NaCl-water solutions with electrical resistivity varying from 0.9 Ωm to 315 Ωm. The textural composition of the samples varies between slightly-sandy mud and gravelly sand, and the porosity of the repacked samples between 0.26 and 0.63. The measurements are executed with an experimental system designed and realized at the Laboratory of Hydrogeophysics of the Università degli Studi di Milano. The resistivity amplitude and phase spectra are firstly modelled with single-relaxation models (Cole-Cole and generalized Cole-Cole) in a bounded low-frequency interval. Besides a traditional optimization based on the root-mean-square error, an original multi-optimization approach with separated amplitude and phase errors is tested to obtain a set of optimal solutions and an uncertainty interval for each model parameter, in order to avoid the misinterpretation of petrophysical relationships with scarcely reliable parameters. Significant relationships are identified between DC-resistivity and water resistivity, and between chargeability and mud content. The 10-based logarithm of the relaxation time is inversely correlated with a characteristic diameter of the sample. On the other hand, a Debye-decomposition, multi-relaxation model is applied to identify several polarization processes, characterized by different relaxation times, over the whole frequency interval. In order to maintain the whole spectral information also in the search for electrical-textural relationships, a combination of cluster analysis (CA) and principal component analysis (PCA) is adopted. This constitutes a new approach to relate spectral electrical behaviour to litho-textural properties, avoiding the selection of individual parameters or individual investigation frequency. The CA permits to classify the samples on the basis of their electrical behaviour, and the PCA allows to interpret the variability within the database in terms of a series of parameters ordered by importance. A textural characterization (characteristic diameters, gravel and mud contents, uniformity coefficients) is associated to each cluster, based on the characteristics of the corresponding samples. Analogously, a typical range of water resistivity is attributed to each cluster. This association of variability ranges of electrical and sedimentological properties is then used to infer the sediments’ properties of samples external to the input database, with satisfactory results. The high flexibility of the hierarchical clustering also allows evaluating the differences in the inferred properties according to the number of selected clusters. Finally, some preliminary SIP tests are performed in the field; field and laboratory results are not completely comparable, due to the differences in porosity, water content, and scale of investigation. However, some peculiar characters of the laboratory spectra are recognized in the corresponding field spectra, thus supporting a future application of the proposed methodology to interpret the resistivity amplitude and phase distribution in the subsurface.

The nonequilibrium molecular dynamics (NEMD) approach is adopted in this work to calculate the in-plane lattice thermal conductivity of Silicon thin films. In the simulation, the Stillinger-Weber (SW) potential is employed to capture both two-body and three-body interactions. The periodic boundary conditions are applied in the in-plane directions of a thin film. An additional surface potential is added to atoms that are near the surfaces. This surface potential imposes a force normal to the plane to prevent atoms from evaporation. A constant heat flux is generated by injecting energy into the system somewhere and withdrawing energy somewhere else via the velocity rescaling method. After a sufficiently long simulation time, the time-averaged temperature distribution is calculated and then the thermal conductivity can be obtained by the Fourier’s law. When the average temperature of the system is lower than the Debye temperature (θD = 645 K for Si), quantum corrections to both the MD temperature and the thermal conductivity are carried out. To speed up the computation, the present MD tool is parallelized based on a spatial decomposition technique. In this study, we attempt to investigate the relationship among the model parameters of the surface potential, the surface roughness, and the specular reflection fraction at the boundary that is often used in many theoretical studies.