Exact Results for the One-Dimensional Self-Organized Critical Forest-Fire Model

We present the analytic solution of the self-organized critical (SOC) forest-fire model in one dimension proving SOC in systems without conservation laws by analytic means. Under the condition that the system is in the steady state and very close to the critical point, we calculate the probability that a string of $n$ neighboring sites is occupied by a given configuration of trees. The critical exponent describing the size distribution of forest clusters is exactly $\tau = 2$ and does not change under certain changes of the model rules. Computer simulations confirm the analytic results.Comment: 12 pages REVTEX, 2 figures upon request, dro/93/

Different hierarchy of avalanches observed in the Bak-Sneppen evolution model

We introduce a new quantity, average fitness, into the Bak-Sneppen evolution model. Through the new quantity, a different hierarchy of avalanches is observed. The gap equation, in terms of the average fitness, is presented to describe the self-organization of the model. It is found that the critical value of the average fitness can be exactly obtained. Based on the simulations, two critical exponents, avalanche distribution and avalanche dimension, of the new avalanches are given.Comment: 5 pages, 3 figure

Unified Scaling Law for Earthquakes

We show that the distribution of waiting times between earthquakes occurring in California obeys a simple unified scaling law valid from tens of seconds to tens of years, see Eq. (1) and Fig. 4. The short time clustering, commonly referred to as aftershocks, is nothing but the short time limit of the general hierarchical properties of earthquakes. There is no unique operational way of distinguishing between main shocks and aftershocks. In the unified law, the Gutenberg-Richter b-value, the exponent -1 of the Omori law for aftershocks, and the fractal dimension d_f of earthquakes appear as critical indices.Comment: 4 pages, 4 figure

Crossover from Percolation to Self-Organized Criticality

We include immunity against fire as a new parameter into the self-organized critical forest-fire model. When the immunity assumes a critical value, clusters of burnt trees are identical to percolation clusters of random bond percolation. As long as the immunity is below its critical value, the asymptotic critical exponents are those of the original self-organized critical model, i.e. the system performs a crossover from percolation to self-organized criticality. We present a scaling theory and computer simulation results.Comment: 4 pages Revtex, two figures included, to be published in PR

Spatial-temporal correlations in the process to self-organized criticality

A new type of spatial-temporal correlation in the process approaching to the self-organized criticality is investigated for the two simple models for biological evolution. The change behaviors of the position with minimum barrier are shown to be quantitatively different in the two models. Different results of the correlation are given for the two models. We argue that the correlation can be used, together with the power-law distributions, as criteria for self-organized criticality.Comment: 3 pages in RevTeX, 3 eps figure

Assessing prospective chemistry teachers' understanding of gases through qualitative and quantitative analyses of their concept maps

Cataloged from PDF version of article.The use of concept mapping as a tool to measure the meaningful learning of students is the focus of this study. The study was carried out with 24 last year students (22 years old) from the Department of Chemistry Teaching at Fatih Faculty of Education, Karadeniz Technical University (KTU). Prospective Chemistry Teachers (PCT) were asked to create concept maps using a list of given concepts related to gases. An examination of the PCTs' maps revealed that the students could not form hierarchical maps even after being shown examples of the basic elements and meaningful propositions between the concepts. After being provided with feedback about their concept maps and trained to form non-hierarchical concept maps, the students were asked to create new maps. This time they were allowed to use either hierarchical or non-hierarchical maps. When their new maps were examined, we found that most of the PCTs formed non-hierarchical maps. However, they still could not form meaningful relationships between the given concepts. We also found that the PCTs had some misconceptions about gases and kinetic molecular theory that explains gas behavior. The study ended up with some suggestions and implications for educators and researchers related to pre-service teachers' training

Acute kidney injury is common, parallels organ dysfunction or failure, and carries appreciable mortality in patients with major burns: a prospective exploratory cohort study

Introduction: The purpose of this study was to determine the incidence, time course, and outcome of acute kidney injury after major burns and to evaluate the impact of possible predisposing factors ( age, gender, and depth and extent of injury) and the relation to other dysfunctioning organs and sepsis. Method: We performed an explorative cohort study on patients with a TBSA% (percentage burned of total body surface area) of 20% or more who were admitted to a national burn centre. Acute kidney injury was classified according to the international consensus classification of RIFLE ( Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease). Prospectively collected clinical and laboratory data were used for assessing organ dysfunction, systemic inflammatory response, and sepsis. Results: The incidence of acute kidney injury among major burns was 0.11 per 100,000 people per year. Of 127 patients, 31 (24%) developed acute kidney injury (12% Risk, 8% Injury, and 5% Failure). Mean age was 40.6 years (95% confidence interval [CI] 36.7 to 44.5), TBSA% was 38.6% (95% CI 35.5% to 41.6%), and 25% were women. Mortality was 14% and increased with increasing RIFLE class (7% normal, 13% Risk, 40% Injury, and 83% Failure). Renal dysfunction occurred within 7 days in 55% of the patients and recovered among all survivors. Age, TBSA%, and extent of full thickness burns were higher among the patients who developed acute kidney injury. Pulmonary dysfunction and systemic inflammatory response syndrome were present in all of the patients with acute kidney injury and developed before the acute kidney injury. Sepsis was a possible aggravating factor in acute kidney injury in 48%. Extensive deep burns (25% or more full thickness burn) increased the risk for developing acute kidney injury early (risk ratio 2.25). Conclusions: Acute kidney injury is common, develops soon after the burn, and parallels other dysfunctioning organs. Although acute kidney injury recovered in all survivors, in higher acute kidney injury groups, together with cardiovascular dysfunction, it correlated with mortality

Breakdown of self-organized criticality

We introduce two sandpile models which show the same behavior of real sandpiles, that is, an almost self-organized critical behavior for small systems and the dominance of large avalanches as the system size increases. The systems become fully self-organized critical, with the critical exponents of the Bak, Tang and Wiesenfeld model, as the system parameters are changed, showing that these systems can make a bridge between the well known theoretical and numerical results and what is observed in real experiments. We find that a simple mechanism determines the boundary where self-organized can or cannot exist, which is the presence of local chaos.Comment: 3 pages, 4 figure

Boundary conditions and defect lines in the Abelian sandpile model

We add a defect line of dissipation, or crack, to the Abelian sandpile model. We find that the defect line renormalizes to separate the two-dimensional plane into two half planes with open boundary conditions. We also show that varying the amount of dissipation at a boundary of the Abelian sandpile model does not affect the universality class of the boundary condition. We demonstrate that a universal coefficient associated with height probabilities near the defect can be used to classify boundary conditions.Comment: 8 pages, 1 figure; suggestions from referees incorporated; to be published in Phys. Rev.

Critical States in a Dissipative Sandpile Model

A directed dissipative sandpile model is studied in the two-dimension. Numerical results indicate that the long time steady states of this model are critical when grains are dropped only at the top or, everywhere. The critical behaviour is mean-field like. We discuss the role of infinite avalanches of dissipative models in periodic systems in determining the critical behaviour of same models in open systems.Comment: 4 pages (Revtex), 5 ps figures (included