Influence of mass diffusion in sea ice dynamical models

The mixing of floes of different thickness caused by repeated deformation of the ice cover is modeled as diffusion, and the mass balance equation for sea ice accounting for mass diffusion is developed. The effect of deformational diffusion on the ice thickness balance is shown to reach 1% of the divergence effect, which describes ridging and lead formation. This means that with the same accuracy the mass balance equation can be written in terms of mean velocity rather than mean mass-weighted velocity, which one should correctly use for a multicomponent fluid such as sea ice with components identified by floe thickness. Mixing (diffusion) of sea ice also occurs because of turbulent variations in wind and ocean drags that are unresolved in models. Estimates of the importance of turbulent mass diffusion on the dynamic redistribution of ice thickness are determined using empirical data for the turbulent diffusivity. For long-time-scale prediction (≫5 days), where unresolved atmospheric motion may have a length scale on the order of the Arctic basin and the time scale is larger than the synoptic time scale of atmospheric events, turbulent mass diffusion can exceed 10% of the divergence effect. However, for short-time-scale prediction, for example, 5 days, the unresolved scales are on the order of 100 km, and turbulent diffusion is about 0.1% of the divergence effect. Because inertial effects are small in the dynamics of the sea ice pack, diffusive momentum transfer can be disregarded.

Chirikov diffusion in the asteroidal three-body resonance (5,-2,-2)

The theory of diffusion in many-dimensional Hamiltonian system is applied to asteroidal dynamics. The general formulation developed by Chirikov is applied to the NesvornA1/2-Morbidelli analytic model of three-body (three-orbit) mean-motion resonances (Jupiter-Saturn-asteroid). In particular, we investigate the diffusion along and across the separatrices of the (5, -2, -2) resonance of the (490) Veritas asteroidal family and their relationship to diffusion in semi-major axis and eccentricity. The estimations of diffusion were obtained using the Melnikov integral, a Hadjidemetriou-type sympletic map and numerical integrations for times up to 10(8) years.

Clustering and diffusion in a symplectic map lattice with non-local coupling

We study a symplectic chain with a non-local form of coupling by means of a standard map lattice where the interaction strength decreases with the lattice distance as a power-law, in Such a way that one can pass continuously from a local (nearest-neighbor) to a global (mean-field) type of coupling. We investigate the formation of map clusters, or spatially coherent structures generated by the system dynamics. Such clusters are found to be related to stickiness of chaotic phase-space trajectories near periodic island remnants, and also to the behavior of the diffusion coefficient. An approximate two-dimensional map is derived to explain some of the features of this connection. (C) 2008 Elsevier Ltd. All rights reserved.

Modeling Information Diffusion in University Libraries: Assessing Peer Interaction Patterns as a Complex Dynamic System

This presentation was offered as part of the CUNY Library Assessment Conference, Reinventing Libraries: Reinventing Assessment, held at the City University of New York in June 2014.

Measurement of oxygen atom diffusion in Nb and Ta by anelastic spectroscopy

Impurity interstitial atoms present in metals with BCC structure can diffuse in the metallic matrix by jumps to energetically equivalent crystallographic sites. Anelastic spectroscopy (internal friction) is based on the measurement of mechanical loss or internal friction as a function of temperature. Due to its selective and nondestructive nature, anelastic spectroscopy is well suited for the study of diffusion of interstitial elements in metals. Internal friction measurements were made using the torsion pendulum technique with oscillation frequency of a few Hz, temperature interval from 300 to 700 K, heating rate of about 1 K/min, and vacuum better than 10-5 mbar. The polycrystalline Nb and Ta samples used were supplied by Aldrich Inc. The results obtained showed thermally activated relaxation structures due to stress-induced ordering of oxygen atoms around the Nb (or Ta) atoms of the metallic matrix. The results were interpreted by three methods and led to activation enthalpy values for the diffusion of oxygen in Nb and Ta of 1.15 eV and 1.10 eV, respectively.

Oxygen diffusion in Ti-10Mo alloys measured by mechanical spectroscopy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Blocking Radial Diffusion in a Double-Waved Hamiltonian Model

A non-twist Hamiltonian system perturbed by two waves with particular wave numbers can present Robust Tori, barriers created by the vanishing of the perturbing Hamiltonian at some defined positions. When Robust Tori exist, any trajectory in phase space passing close to them is blocked by emergent invariant curves that prevent the chaotic transport. We analyze the breaking up of the RT as well the transport dependence on the wave numbers and on the wave amplitudes. Moreover, we report the chaotic web formation in the phase space and how this pattern influences the transport.

An implicit BEM formulation to model strong discontinuities in solids

A boundary element method (BEM) formulation to predict the behavior of solids exhibiting displacement (strong) discontinuity is presented. In this formulation, the effects of the displacement jump of a discontinuity interface embedded in an internal cell are reproduced by an equivalent strain field over the cell. To compute the stresses, this equivalent strain field is assumed as the inelastic part of the total strain. As a consequence, the non-linear BEM integral equations that result from the proposed approach are similar to those of the implicit BEM based on initial strains. Since discontinuity interfaces can be introduced inside the cell independently on the cell boundaries, the proposed BEM formulation, combined with a tracking scheme to trace the discontinuity path during the analysis, allows for arbitrary discontinuity propagation using a fixed mesh. A simple technique to track the crack path is outlined. This technique is based on the construction of a polygonal line formed by segments inside the cells, in which the assumed failure criterion is reached. Two experimental concrete fracture tests were analyzed to assess the performance of the proposed formulation.

Vehicle influence on calcium hydroxide pastes diffusion in human and bovine teeth

The purpose of this study was to compare the pH and calcium ion liberation after use of calcium hydroxide pastes with different paste vehicles in human or bovine teeth. Ninety-two single-rooted human and bovine roots were used. The roots were instrumented and an external cavity preparation was performed. The roots were divided in to human and bovine groups. Each group was subdivided into four subgroups (SB) according to the vehicle:SB1, detergent; SB2, saline; SB3, polyethylenoglycol + camphorated paramonochlorophenol (Calen PMCC) and SB4, polyethylenoglycol + furacyn paramonochlorophenol (FPMC). Specimens were immersed into saline solution at 37 degrees C and after 7 and 14 days pH and calcium ion measurements were made. The results were analyzed by ANOVA and Tukey tests (P < 0.05). There was no statistical difference between bovine and human teeth in the pH analysis (P < 0.05), but bovine teeth provided larger calcium ion liberation than human teeth. Calen PMCC was statistically more effective for pH increase and calcium ion liberation in all analyses, followed by FPMC and saline. Detergent showed the lowest pH alterations and calcium ion liberation. The period of 14 days showed more calcium ionic liberation than the 7-day period.

SAXS measurements of the porosity in Cu(II)-doped SnO2 xerogels during crystallization

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Electrical Properties at Grain Boundaries Influenced by Cr3+ Diffusion in SnO2.ZnO.Nb2O5-Films Varistor Prepared by Electrophoresis Deposition

SnO2-based varistors are strong candidates to replace the ZnO-based varistors due to ordering fewer additives to improve its electrical behavior as well as by showing similar nonlinear characteristics of ZnO varistors. In this work, SnO2-nanoparticles based-varistors with addition of 1.0 %mol of ZnO and 0.05 %mol of Nb2O5 were synthesized by chemical route. SnO2.ZnO.Nb2O5-films with 5 μm of thickness were obtained by electrophoretic deposition (EPD) of the nanoparticles on Si/Pt substrate from alcoholic suspension of SnO2-based powder. The sintering step was carried out in a microwave oven at 1000 °C for 40 minutes. Then, Cr3+ ions were deposited on the films surface by EPD after the sintering step. Each sample was submitted to different thermal treatments to improve the varistor behavior by diffusion of ions in the samples. The films showed a nonlinear coefficient (α) greater than 9, breakdown voltage (VR) around 60 V, low leakage current (IF ≈ 10-6 A), height potential barrier above 0.5 eV and grain boundary resistivity upward of 107 Ω.cm.

Nitrogen diffusion in niobium under low pressure

The interaction among heavy interstitial atoms present in metals with bcc structure is studied using anelastic spectroscopy. This technique makes it possible to obtain information on interstitial concentration, precipitation, solubility limit, and diffusion. The diffusion coefficients of nitrogen in niobium were obtained using the relaxation parameters obtained from anelastic spectroscopy measurements for different oscillation frequencies of the system. The results showed the interstitial diffusion of nitrogen present in solid solution in niobium when submitted to different charges of nitrogen at a temperature of 1373 K and a partial pressure in the order of 10-4 Torr. The exponential variation of the pressure experimentally in function of the time was thus obtained.