A simple deterministic self-organized critical system

We introduce a new continuous cellular automaton that presents self-organized criticality. It is one-dimensional, totally deterministic, without any kind of embedded randomness, not even in the initial conditions. This system is in the same universality class as the Oslo rice pile system, boundary driven interface depinning and the train model for earthquakes. Although the system is chaotic, in the thermodynamic limit chaos occurs only in a microscopic level.Comment: System slightly modified. New results on Liapunov exponents. Submitted for publication (8 pages

Exponential Distributions in a Mechanical Model for Earthquakes

We study statistical distributions in a mechanical model for an earthquake fault introduced by Burridge and Knopoff [R. Burridge and L. Knopoff, {\sl Bull. Seismol. Soc. Am.} {\bf 57}, 341 (1967)]. Our investigations on the size (moment), time duration and number of blocks involved in an event show that exponential distributions are found in a given range of the paramenter space. This occurs when the two kinds of springs present in the model have the same, or approximately the same, value for the elastic constants. Exponential distributions have also been seen recently in an experimental system to model earthquake-like dynamics [M. A. Rubio and J. Galeano, {\sl Phys. Rev. E} {\bf 50}, 1000 (1994)].Comment: 11 pages, uuencoded (submitted to Phys. Rev. E

Educação ambiental: uma ferramenta imprescindível para a vida do homem no planeta.

A educação ambiental se constitui numa forma abrangente de educação, que se propõe atingir todos os cidadãos, através de um processo pedagógico participativo permanente que procura incutir no educando uma consciência crítica sobre a problemática ambiental, compreendendo-se como crítica a capacidade de captar a gênese e a evolução de problemas ambientais

(2+1)-Gravity Solutions with Spinning Particles

We derive, in 2+1 dimensions, classical solutions for metric and motion of two or more spinning particles, in the conformal Coulomb gauge introduced previously. The solutions are exact in the $N$-body static case, and are perturbative in the particles' velocities in the dynamic two-body case. A natural boundary for the existence of our gauge choice is provided by some ``CTC horizons'' encircling the particles, within which closed timelike curves occur.Comment: 30 pages, LaTeX, no figure

Pauli-Lubanski scalar in the Polygon Approach to 2+1-Dimensional Gravity

In this paper we derive an expression for the conserved Pauli-Lubanski scalar in 't Hooft's polygon approach to 2+1-dimensional gravity coupled to point particles. We find that it is represented by an extra spatial shift $\Delta$ in addition to the usual identification rule (being a rotation over the cut). For two particles this invariant is expressed in terms of 't Hooft's phase-space variables and we check its classical limit.Comment: Some errors are corrected and a new introduction and discussion are added. 6 pages Latex, 4 eps-figure

Mapping the characteristics of network meta-analyses on antithrombotic therapies: an overview and critical appraisal

Objectives: A large number of network meta-analyses (NMAs) in the field of cardiac disease are available, yet the scientific literature lacks an updated straightforward synthesis of this evidence to ground the decision-making process. We aimed to map and critically appraise NMAs on antithrombotic therapies used as treatment or prophylaxis of cardiac diseases and cardiac surgical procedures. Methods: A systematic review of systematic reviews with meta-analysis was conducted following Cochrane Collaboration and Joanna Briggs recommendations (PROSPERO-CRD2020166468). Searches to identify NMAs meeting the eligibility criteria of this study were performed in PubMed and Scopus (Jan-2022). NMAs characteristics including metadata, statistical models’ description, and main pooled results were collected. The methodological quality of NMAs was evaluated using the PRISMA-NMA checklist and AMSTAR-2 tools. Descriptive statistical analyses with categorical variables reported as frequencies and continuous variables as the median and interquartile range (IQR) were performed (SPSS-Statistics v.25.0). Results: Overall, n=88 NMAs published between 2007-2022 were identified. The most evaluated clinical condition was atrial fibrillation (n=57; 64.7%); around one-third of the studies (38.6%) assessed cardiac surgical procedures. Only 28.4% NMAs had a registered study protocol. Fifty NMAs (56.8%) were published by authors from one single country China the most frequently. A median of 14 primary studies (IQR 5-20.75) (mostly randomized clinical trials) were included per NMA. A median of 40 (IQR 24-84.25) indirect meta-analyses per study were found. At least one network diagram for a given outcome was provided by 68 (77.2%) studies, yet only 22 (25.6%) performed treatment ranking analyses. Conflict of interest declarations and study funding were informed by 34 (38.6%) and 38 (43.2%) NMAs, respectively. Conclusions: Although there is a widespread of NMA-type studies assessing different antithrombotic agents for different cardiac conditions, the lack of standardized conduction and reporting of NMAs (poor-moderate methodological quality) may limit their comparison and results implementation into clinical practice.info:eu-repo/semantics/publishedVersio

Collective Decoherence of Nuclear Spin Clusters

The problem of dipole-dipole decoherence of nuclear spins is considered for strongly entangled spin cluster. Our results show that its dynamics can be described as the decoherence due to interaction with a composite bath consisting of fully correlated and uncorrelated parts. The correlated term causes the slower decay of coherence at larger times. The decoherence rate scales up as a square root of the number of spins giving the linear scaling of the resulting error. Our theory is consistent with recent experiment reported in decoherence of correlated spin clusters.Comment: 4 pages, 4 figure

Comportamento de sementes de pau-pretinho (Cenostigma tocantinum Ducke) quanto a tolerância à dessecação.

o presente trabalho teve por objetivo avaliar o comportamento das sementes de C. tocantinum, quanto a tolerância à dessecação

Electrical current-driven pinhole formation and insulator-metal transition in tunnel junctions

Current Induced Resistance Switching (CIS) was recently observed in thin tunnel junctions (TJs) with ferromagnetic (FM) electrodes and attributed to electromigration of metallic atoms in nanoconstrictions in the insulating barrier. The CIS effect is here studied in TJs with two thin (20 \AA) non-magnetic (NM) Ta electrodes inserted above and below the insulating barrier. We observe resistance (R) switching for positive applied electrical current (flowing from the bottom to the top lead), characterized by a continuous resistance decrease and associated with current-driven displacement of metallic ions from the bottom electrode into the barrier (thin barrier state). For negative currents, displaced ions return into their initial positions in the electrode and the electrical resistance gradually increases (thick barrier state). We measured the temperature (T) dependence of the electrical resistance of both thin- and thick-barrier states ($R_b$ and R$_B$ respectively). Experiments showed a weaker R(T) variation when the tunnel junction is in the $R_b$ state, associated with a smaller tunnel contribution. By applying large enough electrical currents we induced large irreversible R-decreases in the studied TJs, associated with barrier degradation. We then monitored the evolution of the R(T) dependence for different stages of barrier degradation. In particular, we observed a smooth transition from tunnel- to metallic-dominated transport. The initial degradation-stages are related to irreversible barrier thickness decreases (without the formation of pinholes). Only for later barrier degradation stages do we have the appearance of metallic paths between the two electrodes that, however, do not lead to metallic dominated transport for small enough pinhole radius.Comment: 10 pages, 3 figure