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Copyright of Scientia et Technica is the property of Scientia et Technica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Scientia et Technica is the property of Scientia et Technica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The stochastic Milstein method is presented with weak approximation to find the neutron population density and the concentration of delayed neutron precursors, solving equations of stochastic point kinetics of a nuclear reactor. The set of equations is a non-linear stochastic differential and strongly coupled system. The proposed method uses two approximations in the first derivative and another in the attenuation of the covariance matrix. The results obtained agree with those reported in the calculation of the mean values for neutron density and precursor concentration. It is concluded that the numeric results also show good approximations when compared to deterministic model point kinetics, which is simulated by using the Runge-Kutta method of fourth order. [ABSTRACT FROM AUTHOR]

By using a four-interaction interionic potential, constant-energy (classical microcanonical ensemble) molecular dynamics simulations, at room temperature, A g + ionic positions in α-RbAg4I5 compound are reported. In this crystal structure (cubic with a = 11.23934(3) Å and P4132 as space group) a new site has been found. The unit cell has 16- A g + ions, and its disordered partial occupancies have been the subject of discussion. Some authors report 72 [ = 24(e) + 24(e) + 8(c) + 4(b) + 12(d) or Ag1, Ag2, Ag3, Ag4, Ag5] sites with equal vacancy probabilities (Bradley and Greene), 60 [ = 24(e) + 24(e) + 8(c) + 4(b) or Ag1, Ag2, Ag3, Ag4 respectively] with different probability (Geller), 56 [ = 24(e) + 24(e) + 8(c) + 4(b) or Ag1, Ag2, Ag3] with different probability and 4 sites having zero probability (Hull et al). We report 96 interstitial sites [ = 24(e) + 24(e) + 8(c) + 4(b) + 12(d) + 24(e) or Ag1, Ag2, Ag3, Ag4, Ag5, Ag6, respectively] with different probabilities. The new site was denoted as Ag6 with 0.77% similar to Ag5 (∼0.66%). Good results (occupancy probabilities) compared to experimental data were found. [ABSTRACT FROM AUTHOR]

A rigid-ion empirical pairwise potential for RbAg I including Coulomb (long range), Born–Mayer (short range), charge–dipole and dipole–quadrupole (Van der Waals) interactions, has been tested by molecular dynamics simulation with a statistical ensemble where the number of particle, volume, and total energy are constant, non-pressure (P = 0), and as space group were used. Structural (radial, pair, distribution function) and dynamical behaviour (mean square function) of rubidium, iodines, and silvers were evaluated and compared to experimental data reported at room temperature. The potential parameters were taken from different works. [ABSTRACT FROM AUTHOR]

Electrical Impedance Spectroscopy (EIS) was used to study the electrical properties of the (1 − x)CsHSeO4–xKHSeO4 binary system with concentrations x = 0.0 and 0.1. The results show a higher proton-conduction phase above 80°C for both concentrations, however, while DC conductivity of CsHSeO4 shows a gradual change to higher values in the 80–118°C temperature range, the 0.9CsHSeO4–0.1KHSeO4 concentration reveals an abrupt change at about 80°C to an intermediate temperature phase. The observed behavior for the doped sample was modeled using a trial free-energy density, based on the concentration of mobile ions, that takes into account the formation of defects, configurational and phonon entropies, and defect-defect interactions. By minimising the free-energy density one obtains two roots for the carrier concentration at a given temperature, which corresponds to a stable and metastable configuration. It is possible to characterise the phase behavior of the system by means of temperature and two model parameters, which depend on the crystalline properties of the system, but not on temperature. One can successfully explain the conductivity behavior of the system by changing the model parameters if it is assumed that its variations are due to the carriers density. [ABSTRACT FROM AUTHOR]

The solid electrolyte transition in NaI-AgI was studied by electrical conductivity measurements. The addition of NaI stabilizes the α - Β phase boundary of AgI, decreases the total ionic conductivity of a αAgI and modifies their values in the α y Β phases of AgI. The conductivity data were analyzed by considering that the ionic carrier density is the main source of ts variation through this solid electrolyte transition. Thus, by using a previously proposed model trial free-energy density for the equilibrium defects concentration, we were able to reproduce the conductivity change observed in NaI- AgI at 420 K. [ABSTRACT FROM AUTHOR]