Roughness exponents and grain shapes

In surfaces with grainy features, the local roughness $w$ shows a crossover at a characteristic length $r_c$, with roughness exponent changing from $\alpha_1\approx 1$ to a smaller $\alpha_2$. The grain shape, the choice of $w$ or height-height correlation function (HHCF) $C$, and the procedure to calculate root mean-square averages are shown to have remarkable effects on $\alpha_1$. With grains of pyramidal shape, $\alpha_1$ can be as low as 0.71, which is much lower than the previous prediction 0.85 for rounded grains. The same crossover is observed in the HHCF, but with initial exponent $\chi_1\approx 0.5$ for flat grains, while for some conical grains it may increase to $\chi_1\approx 0.7$. The universality class of the growth process determines the exponents $\alpha_2=\chi_2$ after the crossover, but has no effect on the initial exponents $\alpha_1$ and $\chi_1$, supporting the geometric interpretation of their values. For all grain shapes and different definitions of surface roughness or HHCF, we still observe that the crossover length $r_c$ is an accurate estimate of the grain size. The exponents obtained in several recent experimental works on different materials are explained by those models, with some surface images qualitatively similar to our model films.Comment: 7 pages, 6 figures and 2 table

Adiabatic Gate Teleportation

The difficulty in producing precisely timed and controlled quantum gates is a significant source of error in many physical implementations of quantum computers. Here we introduce a simple universal primitive, adiabatic gate teleportation, which is robust to timing errors and many control errors and maintains a constant energy gap throughout the computation above a degenerate ground state space. Notably this construction allows for geometric robustness based upon the control of two independent qubit interactions. Further, our piecewise adiabatic evolution easily relates to the quantum circuit model, enabling the use of standard methods from fault-tolerance theory for establishing thresholds.Comment: 4 pages, 1 figure, with additional 3 pages and 2 figures in an appendix. v2 Refs added. Video abstract available at http://www.quantiki.org/video_abstracts/0905090

Finite-size effects in roughness distribution scaling

We study numerically finite-size corrections in scaling relations for roughness distributions of various interface growth models. The most common relation, which considers the average roughness $$as scaling factor, is not obeyed in the steady states of a group of ballistic-like models in 2+1 dimensions, even when very large system sizes are considered. On the other hand, good collapse of the same data is obtained with a scaling relation that involves the root mean square fluctuation of the roughness, which can be explained by finite-size effects on second moments of the scaling functions. We also obtain data collapse with an alternative scaling relation that accounts for the effect of the intrinsic width, which is a constant correction term previously proposed for the scaling of$$. This illustrates how finite-size corrections can be obtained from roughness distributions scaling. However, we discard the usual interpretation that the intrinsic width is a consequence of high surface steps by analyzing data of restricted solid-on-solid models with various maximal height differences between neighboring columns. We also observe that large finite-size corrections in the roughness distributions are usually accompanied by huge corrections in height distributions and average local slopes, as well as in estimates of scaling exponents. The molecular-beam epitaxy model of Das Sarma and Tamborenea in 1+1 dimensions is a case example in which none of the proposed scaling relations works properly, while the other measured quantities do not converge to the expected asymptotic values. Thus, although roughness distributions are clearly better than other quantities to determine the universality class of a growing system, it is not the final solution for this task.Comment: 25 pages, including 9 figures and 1 tabl

Status epilepticus in the childhood. A Review of seven years

Rev Neurol. 2000 Mar 1-15;30(5):414-8. [Status epilepticus in the childhood. A review of seven years] [Article in Spanish] Oliveira D, Oliveira MJ, Alves V, Temudo T. Hospital Geral de Santo António, Porto, Portugal. Abstract INTRODUCTION: Status epilepticus is a neurological emergency that requires early and prompt treatment. PATIENTS AND METHODS: This retrospective study includes 32 children treated for status epilepticus at Hospital Geral de Santo António, from January 1992 to December 1998. We evaluated the clinical features, duration, aetiology and prognostic. RESULTS: Symptomatic or criptogenetic aetiology was present in 53% of children and idiopathic in 47%. 27% of episodes of status epilepticus were induced by fever. The most common neurological sequel was epilepsy (onset of new epilepsy in 20%; aggravated in 25%). Two children (10%) had major neurological sequelae after status epilepticus. CONCLUSION: In our study the duration of status epilepticus and sequelae seems to be related with aetiology. PMID: 10775965 [PubMed - indexed for MEDLINE

Kinetic modelling of epitaxial film growth with up- and downward step barriers

The formation of three-dimensional structures during the epitaxial growth of films is associated to the reflection of diffusing particles in descending terraces due to the presence of the so-called Ehrlich-Schwoebel (ES) barrier. We generalize this concept in a solid-on-solid growth model, in which a barrier dependent on the particle coordination (number of lateral bonds) exists whenever the particle performs an interlayer diffusion. The rules do not distinguish explicitly if the particle is executing a descending or an ascending interlayer diffusion. We show that the usual model, with a step barrier in descending steps, produces spurious, columnar, and highly unstable morphologies if the growth temperature is varied in a usual range of mound formation experiments. Our model generates well-behaved mounded morphologies for the same ES barriers that produce anomalous morphologies in the standard model. Moreover, mounds are also obtained when the step barrier has an equal value for all particles independently if they are free or bonded. Kinetic roughening is observed at long times, when the surface roughness w and the characteristic length $\xi$ scale as $w ~ t^\beta$ and $\xi ~ t^\zeta$ where $\beta \approx 0.31$ and $\zeta \approx 0.22$, independently of the growth temperature.Comment: 15 pages, 7 figure