12,229 research outputs found
Peer to Peer Optimistic Collaborative Editing on XML-like trees
Collaborative editing consists in editing a common document shared by several
independent sites. This may give rise to conficts when two different users
perform simultaneous uncompatible operations. Centralized systems solve this
problem by using locks that prevent some modifications to occur and leave the
resolution of confict to users. On the contrary, peer to peer (P2P) editing
doesn't allow locks and the optimistic approach uses a Integration
Transformation IT that reconciliates the conficting operations and ensures
convergence (all copies are identical on each site). Two properties TP1 and
TP2, relating the set of allowed operations Op and the transformation IT, have
been shown to ensure the correctness of the process. The choice of the set Op
is crucial to define an integration operation that satisfies TP1 and TP2. Many
existing algorithms don't satisfy these properties and are indeed incorrect
i.e. convergence is not guaranteed. No algorithm enjoying both properties is
known for strings and little work has been done for XML trees in a pure P2P
framework (that doesn't use time-stamps for instance). We focus on editing
unranked unordered labeled trees, so-called XML-like trees that are considered
for instance in the Harmony pro ject. We show that no transformation satisfying
TP1 and TP2 can exist for a first set of operations but we show that TP1 and
TP2 hold for a richer set of operations. We show how to combine our approach
with any convergent editing process on strings (not necessarily based on
integration transformation) to get a convergent process
Research report : Collaborative Peer 2 Peer Edition: Avoiding Conflicts is Better than Solving Conflicts
Collaborative edition is achieved by distinct sites that work independently
on (a copy of) a shared document. Conflicts may arise during this process and
must be solved by the collaborative editor. In pure Peer to Peer collaborative
editing, no centralization nor locks nor time-stamps are used which make
conflict resolution difficult. We propose an algorithm which relies on the
notion or semantics dependence and avoids the need of any integration
transformation to solve conflicts. Furthermore, it doesn't use any history file
recording operations performed since starting the edition process. We show how
to define editing operations for semi-structured documents i.e. XML-like trees,
that are enriched with informations derived for free from the editing process.
Then we define the semantics dependence relation required by the algorithm and
we present preliminary results obtained by a prototype implementation.Comment: 12 page
Intermediary LEO propagation including higher order zonal harmonics
Two new intermediary orbits of the artificial satellite problem are proposed.
The analytical solutions include higher order effects of the Geopotential, and
are obtained by means of a torsion transformation applied to the
quasi-Keplerian system resulting after the elimination of the parallax
simplification, for the first intermediary, and after the elimination of the
parallax and perigee simplifications, for the second one. The new
intermediaries perform notably well for low earth orbits propagation, are free
from special functions, and result advantageous, both in accuracy and
efficiency, when compared to the standard Cowell integration of the J2 problem,
thus providing appealing alternatives for onboard, short-term, orbit
propagation under limited computational resources.Comment: Celestial Mechanics and Dynamical Astronomy: Accepted September 25,
201
Equidistribution estimates for eigenfunctions and eigenvalue bounds for random operators
We discuss properties of -eigenfunctions of Schr\"odinger operators and
elliptic partial differential operators. The focus is set on unique
continuation principles and equidistribution properties. We review recent
results and announce new ones.Comment: Keywords: scale-free unique continuation property, equidistribution
property, observability estimate, uncertainty relation, Carleman estimate,
Schr\"odinger operator, elliptic differential equatio
Spin relaxation mechanism in graphene: resonant scattering by magnetic impurities
It is proposed that the observed small (100 ps) spin relaxation time in
graphene is due to resonant scattering by local magnetic moments. At
resonances, magnetic moments behave as spin hot spots: the spin-flip scattering
rates are as large as the spin-conserving ones, as long as the exchange
interaction is greater than the resonance width. Smearing of the resonance
peaks by the presence of electron-hole puddles gives quantitative agreement
with experiment, for about 1 ppm of local moments. While the local moments can
come from a variety of sources, we specifically focus on hydrogen adatoms. We
perform first-principles supercell calculations and introduce an effective
Hamiltonian to obtain realistic input parameters for our mechanism.Comment: 5 pages, 3 figures + Suppl. material (3 pages, 5 figures
Photo-induced gap closure in an excitonic insulator
We study the dynamical phase transition out of an excitonic insulator phase
after photo-excitation using a time-dependent extension of the selfconsistent
GW method. We connect the evolution of the photoemission spectra to the
dynamics of the excitonic order parameter and identify two dynamical phase
transition points marked by a slowdown in the relaxation: one critical point is
connected with the trapping in a nonthermal state with reduced exciton density
and the second corresponds to the thermal phase transition. The transfer of
kinetic energy from the photoexcited carriers to the exciton condensate is
shown to be the main mechanism for the gap melting. We analyze the low energy
dynamics of screening, which strongly depends on the presence of the excitonic
gap, and argue that it is difficult to interpret the static component of the
screened interaction as the effective interaction of some low energy model.
Instead we propose a phenomenological measure for the effective interaction
which indicates that screening has minor effects on the low energy dynamics
Management of Glaucoma in the Maltese Health Service
Glaucoma is a disease with characteristic changes of the optic nerve, visual field and raised intra ocular pressure. Its prevalence varies between, 1.6 to 8% and is dependent on the ethnic composition of the population and it is one of the leading causes of blindness in the developed world. There are 67 800 000 people worldwide suffering from glaucoma.1 In recent years, a number of highly potent topical medications have been introduced. These have substantially improved the conservative management of glaucoma. New laser techniques are also being used and safer operative techniques have been developed in order to cope with the more resistant cases of glaucoma. A previous study on `Glaucoma in Malta', conducted in 1989, established that 3% of Maltese population over the age of 40 suffers from glaucoma.2 This study was carried out in order to assess the management of glaucoma patients in the Maltese Government Health Service at the present time.peer-reviewe
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