395 research outputs found
On the random neighbor Olami-Feder-Christensen slip-stick model
We reconsider the treatment of Lise and Jensen (Phys. Rev. Lett. 76, 2326
(1996)) on the random neighbor Olami-Feder-Christensen stik-slip model, and
examine the strong dependence of the results on the approximations used for the
distribution of states p(E).Comment: 6pages, 3 figures. To be published in PRE as a brief repor
Factors that influence the position of the peri-implant soft tissues: a review
Introduction: The implantological rehabilitation of the anterior sector is one of the most demanding and complex treatments due to the necessity of obtaining an optimum esthetic result. At the level of the soft tissues, it involves obtaining the complete formation of the papilla and creating a harmonic contour of the gingival margin.Objective: A bibliographical review has been carried out on the factors that influence the final position of the soft tissues.Material and methods: A search has been carried out in the Pubmed database of articles written in English and Spanish. Articles that presented a clinical series of less than five patients and a monitoring of less than one year were excluded.Results: At the level of the papilla, there are two decisive factors that play an influential role: the formation of the biological width and the distance between the alveolar crest and the contact point. The position of the gingival margin depends mainly of the height and width of the facial bone, as well as on the biotype. The surgical technique, as well as certain prosthodontics aspects related to the implant, can influence the final position of the soft tissues.Conclusions: Although, today we know much more about the factors that influence the position of the soft tissues, there are still certain aspects that should be studied more in-depth, for example the influence of the micro and macro-structure of the implant in the position of the soft tissues
Random Neighbor Theory of the Olami-Feder-Christensen Earthquake Model
We derive the exact equations of motion for the random neighbor version of
the Olami-Feder-Christensen earthquake model in the infinite-size limit. We
solve them numerically, and compare with simulations of the model for large
numbers of sites. We find perfect agreement. But we do not find any scaling or
phase transitions, except in the conservative limit. This is in contradiction
to claims by Lise & Jensen (Phys. Rev. Lett. 76, 2326 (1996)) based on
approximate solutions of the same model. It indicates again that scaling in the
Olami-Feder-Christensen model is only due to partial synchronization driven by
spatial inhomogeneities. Finally, we point out that our method can be used also
for other SOC models, and treat in detail the random neighbor version of the
Feder-Feder model.Comment: 18 pages, 6 ps-figures included; minor correction in sec.
Equivalence of stationary state ensembles
We show that the contact process in an ensemble with conserved total particle
number, as simulated recently by Tome and de Oliveira [Phys. Rev. Lett. 86
(2001) 5463], is equivalent to the ordinary contact process, in agreement with
what the authors assumed and believed. Similar conserved ensembles and
equivalence proofs are easily constructed for other models.Comment: 5 pages, no figure
Allergy—A New Role for T Cell Superantigens of Staphylococcus aureus?
Staphylococcus aureussuperantigens (SAgs) are among the most potent T cell mitogensknown.They stimulate large fractions of T cells by cross-linking their T cell receptor withmajor histocompatibility complex class-II molecules on antigen presenting cells, resulting in Tcell proliferation and massive cytokine release. To date, 26 different SAgs have been described in thespeciesS. aureus; they comprise the toxic shock syndrome toxin (TSST-1), as well as 25 staphylococcalenterotoxins (SEs) or enterotoxin-like proteins (SEls). SAgs can cause staphylococcal food poisoningand toxic shock syndrome and contribute to the clinical symptoms of staphylococcal infection. Inaddition, there is growing evidence that SAgs are involved in allergic diseases. This review providesan overview on recent epidemiological data on the involvement ofS. aureusSAgs and anti-SAg-IgEin allergy, demonstrating that being sensitized to SEs—in contrast to inhalant allergens—is associatedwith a severe disease course in patients with chronic airway inflammation. The mechanisms by whichSAgs trigger or amplify allergic immune responses, however, are not yet fully understood. Here, wediscuss known and hypothetical pathways by which SAgs can drive an atopic diseas
Robust Dropping Criteria for F-norm Minimization Based Sparse Approximate Inverse Preconditioning
Dropping tolerance criteria play a central role in Sparse Approximate Inverse
preconditioning. Such criteria have received, however, little attention and
have been treated heuristically in the following manner: If the size of an
entry is below some empirically small positive quantity, then it is set to
zero. The meaning of "small" is vague and has not been considered rigorously.
It has not been clear how dropping tolerances affect the quality and
effectiveness of a preconditioner . In this paper, we focus on the adaptive
Power Sparse Approximate Inverse algorithm and establish a mathematical theory
on robust selection criteria for dropping tolerances. Using the theory, we
derive an adaptive dropping criterion that is used to drop entries of small
magnitude dynamically during the setup process of . The proposed criterion
enables us to make both as sparse as possible as well as to be of
comparable quality to the potentially denser matrix which is obtained without
dropping. As a byproduct, the theory applies to static F-norm minimization
based preconditioning procedures, and a similar dropping criterion is given
that can be used to sparsify a matrix after it has been computed by a static
sparse approximate inverse procedure. In contrast to the adaptive procedure,
dropping in the static procedure does not reduce the setup time of the matrix
but makes the application of the sparser for Krylov iterations cheaper.
Numerical experiments reported confirm the theory and illustrate the robustness
and effectiveness of the dropping criteria.Comment: 27 pages, 2 figure
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Neutrophil extracellular trap formation is elicited in response to cold physical plasma
Cold physical plasma is an ionized gas with a multitude of components, including hydrogen peroxide and other reactive oxygen and nitrogen species. Recent studies suggest that exposure of wounds to cold plasma may accelerate healing. Upon wounding, neutrophils are the first line of defense against invading microorganisms but have also been identified to play a role in delayed healing. In this study, we examined how plasma treatment affects the functions of peripheral blood neutrophils. Plasma treatment induced oxidative stress, as assessed by the oxidation of intracellular fluorescent redox probes; reduced metabolic activity; but did not induce early apoptosis. Neutrophil oxidative burst was only modestly affected after plasma treatment, and the killing of Pseudomonas aeruginosa and Staphylococcus aureus was not significantly affected. Intriguingly, we found that plasma induced profound extracellular trap formation. This was inhibited by the presence of catalase during plasma treatment but was not replicated by adding an equivalent concentration of hydrogen peroxide. Plasma-induced neutrophil extracellular trap formation was not dependent on the activity of myeloperoxidase or NADPH oxidase 2 but seemed to involve short-lived molecules. The amount of DNA release and the time course after plasma treatment were similar to that with the common neutrophil extracellular trap inducer PMA. After neutrophil extracellular traps had formed, concentrations of IL-8 were also significantly increased in supernatants of plasma-treated neutrophils. Both neutrophil extracellular traps and IL-8 release may aid antimicrobial activity and spur inflammation at the wound site. Whether this aids or exacerbates wound healing needs to be tested
On the robustness of scale invariance in SOC models
A random neighbor extremal stick-slip model is introduced. In the
thermodynamic limit, the distribution of states has a simple analytical form
and the mean avalanche size, as a function of the coupling parameter, is
exactly calculable. The system is critical only at a special point Jc in the
coupling parameter space. However, the critical region around this point, where
approximate scale invariance holds, is very large, suggesting a mechanism for
explaining the ubiquity of scale invariance in Nature.Comment: 6 pages, 4 figures; submitted to Physical Review E;
http://link.aps.org/doi/10.1103/PhysRevE.59.496
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