Network Flow Models for Designing Diameter-Constrained Minimum Spanning and Steiner Trees

The Diameter-Constrained Minimum Spanning Tree Problem seeks a least cost spanning tree subject to a (diameter) bound imposed on the number of edges in the tree between any node pair. A traditional multicommodity flow model with a commodity for every pair of nodes was unable to solve a 20-node and 100-edge problem after one week of computation. We formulate the problem as a directed tree from a selected central node or a selected central edge. Our model simultaneously finds a central node or a central edge and uses it as the source for the commodities in a directed multicommodity flow model with hop constraints. The new model has been able to solve the 20-node, 100-edge instance to optimality after less than four seconds. We also present model enhancements when the diameter bound is odd (these situations are more difficult). We show that the linear programming relaxation of the best formulations discussed in this paper always give an optimal integer solution for two special, polynomially-solvable cases of the problem. We also examine the Diameter Constrained Minimum Steiner Tree problem. We present computational experience in solving problem instances with up to 100 nodes and 1000 edges. The largest model contains more than 250,000 integer variables and more than 125,000 constraints

PORQUE SE MOBILIZAM OS PROFESSORES? JUÍZOS PLURAIS SOBRE O QUE É “SER UM PROFISSIONAL DE ENSINO”. ANÁLISE EXPLORATÓRIA.

PORQUE SE MOBILIZAM OS PROFESSORES? JUÍZOS PLURAIS SOBRE O QUE É “SER UM PROFISSIONAL DE ENSINO”. ANÁLISE EXPLORATÓRIA

Porque se mobilizam os Professores? Juízos Plurais sobre o que é ser ?um profissional de ensino

A comunicação visa empreender, no quadro da Sociologia Pragmática de Boltanski e Thévenot, uma primeira abordagem ao movimento de contestação dos professores ao Estatuto da Carreira Docente (ECD) aprovado em 2007 enquanto questão intimamenteligadaà problemática de juízos morais e políticos plurais sobre o que é ser professor num contexto de incerteza.Procura-se apresentar alguns dos resultados das primeiras análises de dados empíricos recolhidos (através de fontes documentais e entrevistasrealizadas junto de porta-vozes dos professores o representantes sindicais da classe profissional) de forma a compreender que regimes de justificaçãoforam mobilizados para justificar as sucessivas críticas aos princípios de justiça que presidiram à reforma do ECD e para a receptibilidade da denúncia pública de injustiçaatravés da referência a ordens de grandeza decaráctermoral e político

Ultra-High-Energy Cosmic Ray Acceleration by Magnetic Reconnection in Newborn Accretion Induced Collapse Pulsars

We here investigate the possibility that the ultra-high energy cosmic ray (UHECR) events observed above the GZK limit are mostly protons accelerated in reconnection sites just above the magnetosphere of newborn millisecond pulsars which are originated by accretion induced collapse (AIC). We show that AIC-pulsars with surface magnetic fields $10^{12} G < B_{\star} \lesssim 10^{15}$ G and spin periods $1 ms \lesssim P_{\star} < 60 ms$, are able to accelerate particles to energies $\geq 10^{20}$ eV. Because the expected rate of AIC sources in our Galaxy is very small (\sim 10^{-5} yr^{-1}), the corresponding contribution to the flux of UHECRs is neglegible, and the total flux is given by the integrated contribution from AIC sources produced by the distribution of galaxies located within the distance which is unaffected by the GZK cutoff ($\sim 50$ Mpc). We find that the reconnection efficiency factor needs to be $\xi \gtrsim 0.1$ in order to reproduce the observed flux of UHECRs.Comment: Latex file, 16 pages, 2 figures, replaced with revised version accepted for publication in the ApJ letter

First order Fermi acceleration driven by magnetic reconnection

A box model is used to study first order Fermi acceleration driven by magnetic reconnection. It is shown, at least in this simple model, that the spectral index of the accelerated particles is related to the total compression in the same way as in diffusive shock acceleration and is not, as has been suggested, a universal $E^{-5/2}$ spectrum. The acceleration time-scale is estimated and some comments made about the applicability of the process.Comment: Accepted for MNRA

Sociodemographic and psychological characteristics influencing patients' willingness to participate in clinical trials

Background/Aims Clinical trials are fundamental for the development of new medicines and patient participation is based on free consent. Our study sought to identify psychological characteristics that may influence patient willingness to participate in a clinical trial. Methods A total of 100 participants were invited to participate with 80% positive response rate. The psychological characteristics of each patient were evaluated using the following validated psychometric scales: Self-Efficacy Scale, Curiosity, Exploration Inventory-Trait, Social Support Satisfaction, State-Trait Anxiety Inventory and Social Avoidance and Distress, and Fear of Negative Evaluation. Results Patients who agreed to participate in the clinical trial were significantly younger than those who refused (p=0.028). There were no differences in sex, lifestyle, employment status, monthly income or education. After adjusting for age and sex, patients who agreed to participate scored significantly higher in the following: self-efficacy total score (p<0.001), effectiveness in adversity (p<0.001), social effectiveness (p<0.001) and initiation and persistence (p<0.001); social support total score (p<0.001), family satisfaction (p=0.015), friendship satisfaction (p<0.001), social activities satisfaction (p=0.002) and intimacy (p<0.001); total curiosity score (p<0.001), absorption (p<0.001) and exploration (p<0.001). Compared with patients who agreed to participate, those who refused scored significantly higher for both state (p<0.001) and trait anxiety (p<0.001), fear of negative evaluation (p<0.001) and social avoidance and distress (p<0.001). Conclusions Patients who were willing to participate in clinical trials exhibited different psychological characteristics to patients who refused. Specifically, they were more curious and self-efficacious, less anxious and reported a higher level of social support than patients who declined to participate. Identifying characteristics that condition the individual's decision to participate in a clinical trial has important implications for the development of patient-focused communication strategies and improved recruitment approaches. ©This work was supported by BlueClinical, Ltd

ENTRE O PÚBLICO E O ÍNTIMO: TENSÕES PERANTE AS FRONTEIRAS INCERTAS DO ÍNTIMO E DO PÚBLICO EM CONFRONTO NA EDUCAÇÃO SEXUAL ESCOLAR

Entre o íntimo: tensões perante as fronteiras incertas do íntimo e o público em confronto na educação sexual escolar?