Influence of channel reservation on the handover calls flow in mobile network

In this paper the properties of handover traffic are analyzed in the system with channel reservation. The reservation of several traffic channels only for handover calls leads to probability of handover calls congestion decrease to the level of per mill or even lower. The congestion of all traffic channels in the neighbouring cells is the cause that handover traffic process deviates from the Poissonian distribution and this deviation is negligible, because handover calls congestion probability is very low. This low handover calls probability is also the reason why implementation of one equivalent cell instead of 6 neighbouring cells surrounding the central cell does not model satisfactory the traffic flow in the mobile network. The randomness of handover calls arrival to the central cell is tested by our originally developed simulation program. Coefficient of variation of time between handover calls arrival to the central cell is calculated as the result of simulation. We introduced the ratio of the coefficient of variation of the time between new handover calls appearance in the central cell to the value of this coefficient for surrounding cell as the measure of handover calls randomness: the nearer this ration to 1, the more random is handover calls arrival to the central cell.

Teachers’ Stances on Cell Phones in the ESL Classroom: Toward a “Theoretical” Framework

In the ongoing and constantly expanding discussion surrounding cell phones in the classroom, a theoretical complement to the practical side of the issue is gener- ally lacking. This is perhaps understandable. Many teachers are still trying to deal with the simple presence of cell phones in the class, and managing a classroom in which the presence and use of cell phones is a reality takes precedence over chart- ing some sort of theoretical framework. Yet perhaps it is now time to step back and consider such a framework. I offer just such a consideration, as well as some remarks about which theoretical positions might be most advisable in specific classroom contexts.Au débat portant sur les téléphones cellulaires en salle de classe, toujours actuel et s’élargissant sans cesse, il manque souvent une composante théorique pour venir compléter le côté pratique. Plusieurs enseignants tentent encore de composer avec la simple présence des téléphones cellulaires en classe, alors la gestion d’une classe où on les utilise prend le dessus sur la planification d’un cadre théorique. Il est peut-être temps, toutefois, de prendre un certain recul et de considérer un tel cadre. J’offre une telle proposition ainsi que certaines remarques par rapport aux positions théoriques les plus recommandables dans des contextes pédagogiques particuliers.

A Fourth-Order-Centered Finite-Volume Scheme for Regular Hexagonal Grids

Fourth-order-centered operators on regular hexagonal grids with the ZM-grid arrangement are described. The finite-volume method is used and operators are defined at hexagonal cell centers. The gradient operator is calculated from 12 surrounding cell center scalars. The divergence operator is defined from 12 surrounding cell corner vectors. A linear combination of local or interpolated values generates cell corner values used to calculate the operators. The flux-divergence operator applies the same cell corner values as those used in the gradient and divergence operators. The fourth-order convergence of the gradient and divergence operators is obtained in numerical tests using sufficiently smooth and differentiable test functions. The flux-divergence operator is formally second-order accurate. However, the results from a cone advection test show that the flux-divergence operator performs better than a commonly used second-order flux-divergence operator. Numerical dispersion and phase error are small because mean wind advection is computed with fourth-order accuracy.

The ultrastructure of Geotrichum candidum hyphae

Complete septa divide the hyphae of Geotrichum candidum into many compartments or cells. Two cell types are readily recognizable, (i) the apical cell, delimited by one septum and the surrounding cell wall, and (ii) the sub- or non-apical cell, delimited by two septa and the surrounding cell wall. Vacuolation of the apical cells is slight compared with that of subapical cells. Apical cells contain many vesicles, some of which are elongated and branched, possibly forming an interconnecting tubular network; other vesicles were observed distributed about the apical zone or aggregated to form an apical body (the Spitzenkörper). Vesicles are also evident in subapical cells, but only in association with developing septa. Golgi bodies were not observed in any cells, their function in vesicle production possibly being taken by a modification of part of the endoplasmic reticulum. Both cell types contained mitochondria with contrasting electron-staining properties. Some stages of mitosis were observed. The nucleus appears to retain its envelope throughout division and exhibits intranuclear microtubules attached to spindle plaques. Septa were formed by a centripetal deposition of wall material, plasmodesmata developing during this process. Another deposition of wall material occurs after the centripetal deposition thus allowing a secondary thickening of the septum to take place.