36,331 research outputs found
Roughness exponents and grain shapes
In surfaces with grainy features, the local roughness shows a crossover
at a characteristic length , with roughness exponent changing from
to a smaller . The grain shape, the choice of
or height-height correlation function (HHCF) , and the procedure to
calculate root mean-square averages are shown to have remarkable effects on
. With grains of pyramidal shape, 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
for flat grains, while for some conical grains it may
increase to . The universality class of the growth process
determines the exponents after the crossover, but has no
effect on the initial exponents and , 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 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 . 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 scale as and where
and , independently of the growth
temperature.Comment: 15 pages, 7 figure
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