Numerical study of the shape and integral parameters of a dendrite

We present a numerical study of sidebranching of a solidifying dendrite by means of a phase--field model. Special attention is paid to the regions far from the tip of the dendrite, where linear theories are no longer valid. Two regions have been distinguished outside the linear region: a first one in which sidebranching is in a competition process and a second one further down where branches behave as independent of each other. The shape of the dendrite and integral parameters characterizing the whole dendrite (contour length and area of the dendrite) have been computed and related to the characteristic tip radius for both surface tension and kinetic dominated dendrites. Conclusions about the different behaviors observed and comparison with available experiments and theoretical predictions are presented.Comment: 10 pages, 7 figures, Accepted for publication in Phys. Rev.

Sharp-Interface Limit of a Fluctuating Phase-Field Model

We present a derivation of the sharp-interface limit of a generic fluctuating phase-field model for solidification. As a main result, we obtain a sharp-interface projection which presents noise terms in both the diffusion equation and in the moving boundary conditions. The presented procedure does not rely on the fluctuation-dissipation theorem, and can therefore be applied to account for both internal and external fluctuations in either variational or non-variational phase-field formulations. In particular, it can be used to introduce thermodynamical fluctuations in non-variational formulations of the phase-field model, which permit to reach better computational efficiency and provide more flexibility for describing some features of specific physical situations. This opens the possibility of performing quantitative phase-field simulations in crystal growth while accounting for the proper fluctuations of the system.Comment: 21 pages, 1 figure, submitted to Phys. Rev.

Impedance characterization of calcia-stabilized zirconia as a function of applied field

Cubic stabilised-zirconias are well-known oxide ion conductors. They are used as solid electrolytes in oxygen sensors and in solid oxide fuel cells (SOFCs). However, it has been demonstrated recently that electronic conduction can be introduced into yttria-stabilised zirconia (YSZ), under the application of either (i) a small dc bias or (ii) for YSZ compositions with higher yttria content, by an increase in oxygen partial pressure (pO2) [1]. Such electronic conduction will have implications for materials that are to be used as ionically-conducting but electrically-insulating components in fuel cells and sensors. Please click Additional Files below to see the full abstract

Genetic study in patients operated dentally and anesthetized with articaine-epinephrine

Aims: In this study we wanted to figure out if there was a correlation between OPRM1 N40D, TRPV1 I316M, TRPV1 I585V, NOS3 −786T>C and IL6 −174C>G polymorphisms and the response to locally applied articaine-epinephrine anesthetic. Methods: In this observational study, 114 oral cell samples of patients anesthetized with articaine-epinephrine (54 from men 60 from women), were collected from dental centers in Madrid (Spain). High molecular weight DNA was obtained from oral mucosa cells. The analysis of OPRM1 N40D (rs1799971), TRPV1 I316M (rs222747), TRPV1 I585V (rs8065080) and IL6 −174C>G polymorphism was performed through real-time PCR allelic discrimination using TaqMan probes. Polymorphism NOS3 −786T> C (rs2070744) was analyzed using RFLP-PCR. Results: The studied polymorphisms are involved neither in the response to the anesthetic, nor in the intensity of perceived dental pain. However, in a subset of female patients we found that TRPV1 I316M was associated with a delayed onset of anesthesia. Conclusions: There is no association among these polymorphisms and the time elapsed between the application of the anesthetic and the onset of its effect

General Non-equilibrium Theory of Colloid Dynamics

A non-equilibrium extension of Onsager's canonical theory of thermal fluctuations is employed to derive a self-consistent theory for the description of the statistical properties of the instantaneous local concentration profile n(r,t) of a colloidal liquid in terms of the coupled time evolution equations of its mean value n(r,t) and of the covariance {\sigma}(r,r';t) \equiv of its fluctuations {\delta}n(r, t) = n(r, t) - n(r, t). These two coarse-grained equations involve a local mobility function b(r, t) which, in its turn, is written in terms of the memory function of the two-time correlation function C(r, r' ; t, t') \equiv <{\delta}n(r, t){\delta}n(r',t')>. For given effective interactions between colloidal particles and applied external fields, the resulting self-consistent theory is aimed at describing the evolution of a strongly correlated colloidal liquid from an initial state with arbitrary mean and covariance n^0(r) and {\sigma}^0(r,r') towards its equilibrium state characterized by the equilibrium local concentration profile n^(eq)(r) and equilibrium covariance {\sigma}^(eq)(r,r'). This theory also provides a general theoretical framework to describe irreversible processes associated with dynamic arrest transitions, such as aging, and the effects of spatial heterogeneities

Electrical Conductivity in Magnesium-Doped Al_2 O_3 Crystal at Moderate Temperatures

AC and DC electrical measurements between 273 and 800 K were used to characterize the electrical conductivity of Al_2 O_3:Mg single crystals containing [Mg]^{0} center. At low fields contacts are blocking. At high fields, electrical current flows steadily through the sample and the I-V characteristic corresponds to a directly biased barrier whit a series resistance (bulk resistance). AC measurements yield values for the junction capacitance as well as for the sample resistance, and provide perfectly reproducible conductivity values. The conductivity varies linearly whit the [Mg]^{0} concentration and a thermal activation energy of 0.68 eV was obtained, which agrees very well with the activation energy previously reported for motion of free holes.Comment: LaTeX, 6 pages, 3 eps figures included. Contributed Paper to the "International Conference on Defects in Insulating Materials" (ICDIM 2000), Johannesburg, South Africa, 3-7 April, 200