228 research outputs found
Approximating J -holomorphic curves by holomorphic ones
Abstract.: Given an almost complex structure J in a cylinder of (p > 1) together with a compatible symplectic form and given an arbitrary J-holomorphic curve without boundary in that cylinder, we construct an holomorphic perturbation of , for the canonical complex structure J 0 of , such that the distance between these two curves in W 1,2 and norms, in a sub-cylinder, are controled by quantities depending on J, and by the area of only. These estimates depend neither on the topology nor on the conformal class of . They are key tools in the recent proof of the regularity of 1-1 integral currents in [RT
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Exploring Locality in Ethereum Transactions
Early open blockchain designs face low throughput, high latency, and prohibitive costs for setting up a full node. New designs improve this with innovative mechanisms for handling transactions and the blockchain state, often assuming locality properties in the workload of transactions. Temporal locality allows efficient space management such as light nodes or snapshot-based bootstrap. Disjoint access parallelism, which depends on spatial locality, enables parallel processing of non-conflicting transactions. We analyze locality properties and their interplay in the largest transactional workload available to date, that of Ethereum. Our results show that, although transactions generally display good locality, a minority of accounts are responsible for caching- or parallelism-unfriendliness, calling for specific identification and handling in future blockchain designs
Antarctic Ozone Depletion and Trends in Tropopause Rossby Wave Breaking
Trends in summer tropopause Rossby wave breaking (RWB) are examined using meteorological reanalyses and model integrations. The reanalyses for the last 30 years show large increases in RWB on the equatorward side of the tropospheric jet and weak decreases on the poleward side. Comparable changes in RWB are found in general circulation model integrations whose stratospheric ozone differs between 1960 and 2000 levels, but not in integrations that differ only in their greenhouse gas concentrations and sea-surface temperatures. These results indicate that the formation of the ozone hole has led to changes in RWB frequency during southern summer
Desenganchados de la educación: procesos, experiencias, motivaciones y estrategias del abandono y del fracaso escolar
En este artículo, se presenta una parte de los resultados de una investigación sobre el fracaso y el abandono escolares llevada a cabo desde el Departamento de Sociología de la Universidad de Salamanca. La idea de partida, ya presentada en otras investigaciones, es que el abandono escolar prematuro es el resultado de un proceso progresivo de desvinculación de la escuela por parte de aquéllos que acaban abandonando antes de la obtención de un título post-obligatorio. Los diversos aspectos del proceso de fracaso deben observarse, desde este punto de vista, como síntomas de ese desenganche progresivo y previo por parte del alumno con respecto a la institución. El objetivo de este artículo es presentar los pasos y los elementos de este proceso a partir de la información con la que contamos. Para realizar este análisis, se ha recopilado una base de datos de expedientes (académicos, disciplinarios y de orientación) de alumnos entre 16 y más de 25 años que ya habían abandonado el sistema en el curso 2007-08, y se han realizado entrevistas con alumnos que han abandonado recientemente. A partir de esta información, se ha generado una serie de perfiles de comportamiento académico de los alumnos, se sientan las bases para realizar una crítica de la eficacia de las medidas de diversificación, y se corrobora la escasa importancia de los problemas disciplinarios en el proceso de abandono. Desde el punto de vista del alumnado, aparecen como elementos clave para el abandono: (1) la atracción relativa de la incorporación al empleo, (2) la desmotivación progresiva con la oferta vital de la escuela, (3) los cambios de centro, (4) el peso de los “malos profesores” y (5) la consideración del abandono como un éxito personal – como una victoria táctica–. Todos estos aspectos aparecen en los discursos de los alumnos como elementos clave en el proceso
First-principles modelling of molecular single-electron transistors
We present a first-principles method for calculating the charging energy of a
molecular single-electron transistor operating in the Coulomb blockade regime.
The properties of the molecule are modeled using density-functional theory, the
environment is described by a continuum model, and the interaction between the
molecule and the environment are included through the Poisson equation. The
model is used to calculate the charge stability diagrams of a benzene and
C molecular single-electron transistor
Health economic evaluation of Human Papillomavirus vaccines in women from Venezuela by a lifetime Markov cohort model
Abstract Background Cervical cancer (CC) and genital warts (GW) are a significant public health issue in Venezuela. Our objective was to assess the cost-effectiveness of the two available vaccines, bivalent and quadrivalent, against Human Papillomavirus (HPV) in Venezuelan girls in order to inform decision-makers. Methods A previously published Markov cohort model, informed by the best available evidence, was adapted to the Venezuelan context to evaluate the effects of vaccination on health and healthcare costs from the perspective of the healthcare payer in an 11-year-old girls cohort of 264,489. Costs and quality-adjusted life years (QALYs) were discounted at 5%. Eight scenarios were analyzed to depict the cost-effectiveness under alternative vaccine prices, exchange rates and dosing schemes. Deterministic and probabilistic sensitivity analyses were performed. Results Compared to screening only, the bivalent and quadrivalent vaccines were cost-saving in all scenarios, avoiding 2,310 and 2,143 deaths, 4,781 and 4,431 CCs up to 18,459 GW for the quadrivalent vaccine and gaining 4,486 and 4,395 discounted QALYs respectively. For both vaccines, the main determinants of variations in the incremental costs-effectiveness ratio after running deterministic and probabilistic sensitivity analyses were transition probabilities, vaccine and cancer-treatment costs and HPV 16 and 18 distribution in CC cases. When comparing vaccines, none of them was consistently more cost-effective than the other. In sensitivity analyses, for these comparisons, the main determinants were GW incidence, the level of cross-protection and, for some scenarios, vaccines costs. Conclusions Immunization with the bivalent or quadrivalent HPV vaccines showed to be cost-saving or cost-effective in Venezuela, falling below the threshold of one Gross Domestic Product (GDP) per capita (104,404 VEF) per QALY gained. Deterministic and probabilistic sensitivity analyses confirmed the robustness of these results
Photoprocessing of H2S on dust grains: building S chains in translucent clouds and comets
Stars and planetary system
Ensemble Dynamics and Bred Vectors
We introduce the new concept of an EBV to assess the sensitivity of model
outputs to changes in initial conditions for weather forecasting. The new
algorithm, which we call the "Ensemble Bred Vector" or EBV, is based on
collective dynamics in essential ways. By construction, the EBV algorithm
produces one or more dominant vectors.
We investigate the performance of EBV, comparing it to the BV algorithm as
well as the finite-time Lyapunov Vectors. We give a theoretical justification
to the observed fact that the vectors produced by BV, EBV, and the finite-time
Lyapunov vectors are similar for small amplitudes.
Numerical comparisons of BV and EBV for the 3-equation Lorenz model and for a
forced, dissipative partial differential equation of Cahn-Hilliard type that
arises in modeling the thermohaline circulation, demonstrate that the EBV
yields a size-ordered description of the perturbation field, and is more robust
than the BV in the higher nonlinear regime. The EBV yields insight into the
fractal structure of the Lorenz attractor, and of the inertial manifold for the
Cahn-Hilliard-type partial differential equation.Comment: Submitted to Monthly Weather Revie
An integrated approach of multiple correspondences analysis (MCA) and fuzzy AHP method for occupational health and safety performance evaluation in the land cargo transportation
Land cargo transportation is one of the components of the logistics chain with high impact on economic and social development worldwide. However, problems such as top logistics costs, deficiencies in transportation infrastructure and the failure to adopt good operating practices in aspects such as quality, environment, and occupational safety and health affect the ability of companies to comply with the agreements, requirements, and regulations of the clients and other interested parties. One of the most relevant problems for the sector is associated with the high accident rates that make this medium less advantageous compared to other means of transport with impact on operational costs, on logistics indicators, on compliance with legal regulations and customer satisfaction. However, although there are legal standards and management standards in occupational safety and health, evaluating performance can become a difficult and subjective process, due to the complexity of the land cargo transportation and the different interest groups involved. Besides, there is little information in the literature that provides solutions for the industry. Therefore, this document presents an integrated approach between multi-criterion decision making models (MCDM) and the Multiple Correspondences Analysis (MCA) to facilitate the evaluation and improvement of occupational health and safety performance, with a logical process, objective, robust and using both qualitative and quantitative techniques, with real application in the land cargo transportation sector. First, the multivariate method of Multiple Correspondences Analysis (MCA) was used for the evaluation of a sample of companies in the industry, considering the factors and sub-factors identified in the first stage and performing correlational analyzes among the variables. Subsequently, a multicriteria decision-making model was designed to determine the factors and sub-factors that affect occupational health and safety performance through the technique of the Fuzzy Analytic Hierarchy Process (FAHP). Finally, improvement strategies are proposed based on the approaches suggested in this document
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