To investigate the formation of grain boundary barriers, composite SnO(2)-Zn(2)SnO(4) varistor ceramics were prepared by traditional ceramic processing and, the electrical properties of grains and ...grain boundaries were evaluated by the measurement of complex impedances spectra. Calculated using the low frequency impedance data for each sample, a lower value about 0.09-0.32 eV and a higher value about 0.50-0.83 eV of activation energy E(a) was obtained in the temperature range of 50-110 and 140-200 degree C, respectively. The simulated results of complex impedances spectra by "Zsimpwin" software indicate that the equivalent circuit for SnO(2)-Zn(2)SnO(4) composite ceramics is connected in series by one RC and two QR parallels. The relaxations in the dielectric dispersion spectra at low frequency of ~1000 Hz suggest that one of the QR parallels is corresponding to oxygen vacancy. With increasing sintering temperature, the E(a) values related to oxygen vacancy decreased whereas, the values related to grain boundary barriers increase obviously. The results suggest that the oxygen vacancy is the key factor to the semi-conductance of SnO(2) grains and formation of grain boundary barriers.
Interactions mediated by layers of Io-casein and para-Io-casein have been calculated and compared using the self consistent field (SCF) approach, at pH and electrolyte concentrations found in milk. ...Our results show the interaction potentials at close separation distances to be repulsive for Io-casein, while they are attractive for para-Io-casein. We have also studied Io-casein chains stripped of their sugar moieties and highlighted the important role that the carbohydrate side chains play in the provision of steric forces. The point of transition from a repulsive to an attractive interaction is found to be rather sensitive to the degree of coverage of the surface by the protein chains. At I = 0.0025 chains per unit monomer area, the value is just over 40% renneted chains, whereas at I = 0.0032 this increases to 87%. At the coverage values higher than those we estimate for the surface of casein micelles, no transition is detected and the interactions remain repulsive even when all of Io-casein has been converted to para-Io-casein, as already shown by Mellema, Leermakers, and de Kruif (1999). At lower surface coverage values, the interaction potential curves for otherwise uncharged surfaces, covered with para-Io-casein, posses an energy barrier. We have demonstrated that the origin of this energy barrier is electrostatic, with para-Io-casein contributing a net positive charge to the surface. We have also explored the importance of the asymmetry in the distribution of charge between the para-Io-casein and the glycomacropeptide sides of the protein. The glycomacropeptide is net negative while para-Io-casein side is net positive at neutral pH. Our results suggest that on a negatively charged surface, such as the surface of casein micelles, this uneven distribution of charge is just as important in determining the conformation of Io-casein chains as is the difference in the hydrophobic and hydrophilic nature of the two sides of this protein.
The electrical properties of Cu(In,Ga)Se sub(2)/Mo junctions were characterized with respect of MoSe sub(2) orientation and Na doping level using an inverse transmission line method, in which the ...Cu(In,Ga)Se sub(2) (CIGS)/Mo contact resistance could be measured separately from the CIGS film sheet resistance. The MoSe sub(2) orientation was controlled by varying the Mo surface density, with the c-axis parallel and normal orientations favored on Mo surfaces of lower and higher density, respectively. The effect of Na doping was compared by using samples with and without a SiO sub(x) film on sodalime glass. The conversion of the MoSe sub(2) orientation from c-axis normal to parallel produced a twofold reduction in CIGS/Mo contact resistance. Measurements of the contact resistances as a function of temperature showed that the difference in CIGS/Mo contact resistance between the samples with different MoSe sub(2) orientations was due to different barrier heights at the back contact. Comparison between Na-doped and Na-reduced samples revealed that the contact resistance for the Na-reduced system was four times of that of the doped sample, which showed more pronounced Schottky-junction behavior at lower temperature, indicating that Na doping effectively reduced the barrier height at the back contact. Copyright copyright 2013 John Wiley & Sons, Ltd. The electrical properties of Cu(In,Ga)Se2/Mo junctions were successfully characterized in terms of contact resistance using modified (inverse) transmission line method, in which the Cu(In,Ga)Se2/Mo contact resistance could be measured separately from the CIGS film sheet resistance. The measurement showed that the substantial Na doping as well as the switching of MoSe2 structure toward c-axis parallel orientation could reduce the barrier height at back contact, favoring higher photovoltaic conversion efficiency.
To understand the microscopic mechanism of H diffusion in tritium permeation barrier (TPB), we have explored the energetics and mobility of neutral hydrogen in I--Al2O3 with hexagonal structure as ...well as sequioxide Er2O3 with cubic bixbyite structure using first-principles density-functional calculations. The comparison of the most energetically favorable H interstitial positions between I--Al2O3 and Er2O3 shows that crystal structure plays a critical role in determining migration barriers. Combining static and molecular-dynamics calculations with nudged elastic band method, we derive the temperature-dependent diffusivity of hydrogen or deuterium in I--Al2O3 and Er2O3 as D(T) = (2.37 A 10a7 m2/s) exp (a1.25 eV/kT) and D(T) = (1.72 A 10a7 m2/s) exp (a1.64 eV/kT), 1a3 orders of magnitude lower than the corresponding experimental data. The migration barrier for H diffusion between the planes defined by Er2O3 units along the a1 1 1a direction is found to be very small at 0.16 eV, while higher migration barriers of 0.41 eV and 1.64 eV are found for the diffusion across the planes. These results indicate that H diffusion in Er2O3 is favorable along the a1 1 1a direction. Quantum effects on H diffusion through I--Al2O3 and Er2O3 are discussed.
To understand the microscopic mechanism of H diffusion in tritium permeation barrier (TPB), we have explored the energetics and mobility of neutral hydrogen in alpha -Al sub(2)O sub(3) with hexagonal ...structure as well as sequioxide Er sub(2)O sub(3) with cubic bixbyite structure using first-principles density-functional calculations. The comparison of the most energetically favorable H interstitial positions between alpha -Al sub(2)O sub(3) and Er sub(2)O sub(3) shows that crystal structure plays a critical role in determining migration barriers. Combining static and molecular-dynamics calculations with nudged elastic band method, we derive the temperature-dependent diffusivity of hydrogen or deuterium in alpha -Al sub(2)O sub(3) and Er sub(2)O sub(3) as D (T) = (2.37 x 10 super(-7) m super(2)/s) exp (-1.25 eV/kT) and D (T) = (1.72 x 10 super(-7) m super(2)/s) exp (-1.64 eV/kT), 1-3 orders of magnitude lower than the corresponding experimental data. The migration barrier for H diffusion between the planes defined by Er sub(2)Ch units along the (111) direction is found to be very small at 0.16 eV, while higher migration barriers of 0.41 eV and 1.64 eV are found for the diffusion across the planes. These results indicate that H diffusion in Er sub(2)O sub(3) is favorable along the (111) direction. Quantum effects on H diffusion through alpha -Al sub(2)O sub(3) and Er sub(2)O sub(3) are discussed.
This work aims at analyzing if the perception of success and barriers of lean projects varies with the managers working position, measuring the perception's bias of the success and barriers of ...company managers. The research questions answered by this work are the following ones: is the perception of lean projects' success and lean practices implementation level biased by the position recovered by the respondent? Do respondents present a different perception of barriers experienced during lean project deployment, depending on their working position? A survey was carried out collecting information from top, middle and non-managers from 171 firms from 23 countries. Data were analysed through a Multiple Analysis of Variance in order to discover differences and similarities in lean projects' evaluation among various categories of managers and employees. Moreover, as existing literature highlighted that difficulties vary with the project progress, the Multiple Analysis of Variance was separately conducted for the start-up and the sustaining phase of the projects. Useful managerial advice can be extracted from the results since they evidence the existence of significantly different perceptions: the higher is the managerial position, the lower is the direct involvement in lean projects and the perception of success and barriers, and vice versa.
In this paper we consider Strong Stability Preserving (SSP) properties for explicit RungeaKutta (RK) methods applied to a class of nonlinear ordinary differential equations. We define new modified ...threshold factors that allow us to prove properties, provided that they hold for explicit Euler steps. For many methods, the stepsize restrictions obtained are sharper than the ones obtained in terms of the Kraaijevangeras coefficient in the SSP theory. In particular, for the classical 4-stage fourth order method we get nontrivial stepsize restrictions. Furthermore, the order barrier $p\le 4$ for explicit SSP RK methods is not obtained. An open question is the existence of explicit RK schemes with order $p\ge 5$ and nontrivial modified threshold factor. The numerical experiments done illustrate the results obtained.
Imbalance in the tissue microenvironment is the main obstacle to drug delivery and distribution in the human body. Before penetrating the pathological tissue microenvironment to the target site, ...therapeutic agents are usually accompanied by three consumption steps: the first step is tissue physical barriers for prevention of their penetration, the second step is inactivation of them by biological molecules, and the third step is a cytoprotective mechanism for preventing them from functioning on specific subcellular organelles. However, recent studies in drug-hindering mainly focus on normal physiological rather than pathological microenvironment, and the repair of damaged physiological barriers is also rarely discussed. Actually, both the modulation of pathological barriers and the repair of damaged physiological barriers are essential in the disease treatment and the homeostasis maintenance. In this review, we present an overview describing the latest advances in the generality of these pathological barriers and barrier-modulated nanomedicine. Overall, this review holds considerable significance for guiding the design of nanomedicine to increase drug efficacy in the future.
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