Spin dynamics simulations of the magnetic dynamics of RbMnF3_3 and direct comparison with experiment

Spin-dynamics techniques have been used to perform large-scale simulations of the dynamic behavior of the classical Heisenberg antiferromagnet in simple cubic lattices with linear sizes $L\leq 60$. This system is widely recognized as an appropriate model for the magnetic properties of RbMnF$_3$. Time-evolutions of spin configurations were determined numerically from coupled equations of motion for individual spins using a new algorithm implemented by Krech {\it etal}, which is based on fourth-order Suzuki-Trotter decompositions of exponential operators. The dynamic structure factor was calculated from the space- and time-displaced spin-spin correlation function. The crossover from hydrodynamic to critical behavior of the dispersion curve and spin-wave half-width was studied as the temperature was increased towards the critical temperature. The dynamic critical exponent was estimated to be $z=(1.43\pm 0.03)$, which is slightly lower than the dynamic scaling prediction, but in good agreement with a recent experimental value. Direct, quantitative comparisons of both the dispersion curve and the lineshapes obtained from our simulations with very recent experimental results for RbMnF$_3$ are presented.Comment: 30 pages, RevTex, 9 figures, to appear in PR

Lessons learned from synthetic research projects based on the ostrom workshop frameworks

A generalized knowledge of social-ecological relationships is needed to address current environmental challenges. Broadly comparative and synthetic research is a key method for establishing this type of knowledge. To date, however, most work on social-ecological systems has applied idiosyncratic methods to specific systems. Several projects, each based on the frameworks developed by Elinor Ostrom and colleagues, stand out for their application of consistent methods across a broad range of cases. In this paper we compare seven of these projects and draw conclusions regarding their potential benefits and the challenges that scholars can expect in conducting this type of research. The two main challenges that we identified are (1) the collective-action dilemmas that collaborators face in producing and maintaining the social and technical infrastructure that is needed for such projects; and (2) balancing complexity and comparability in the structure of the databases used and the associated methods for characterizing complex social-ecological cases. We discuss approaches for meeting these challenges, and present a guiding checklist of questions for project design and implementation to provide guidance for future broadly comparative research. © 2021 by the author(s). Published here under license by the Resilience Alliance.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Privatização dos serviços de extensão rural: uma discussão (des)necessária?

O artigo analisa e discute o tema da privatização dos serviços de extensão rural, conforme apresentado na literatura internacional. Inicialmente, a temática é situada no horizonte das discussões sobre a chamada Reforma do Estado, que pautaram as agendas sobre o desenvolvimento desde a década de 1980. Na seqüência, apresenta-se como o tema foi e vem sendo discutido à luz da teoria econômica e se examinam experiências de privatização em âmbito internacional. A análise dessas experiências mostra que a agenda inicial da privatização previa que os serviços de extensão rural, que estavam sob responsabilidade do Estado, passassem a ser integralmente assumidos pelo setor privado. No entanto, foi identificada uma série de limitações a tal intento e passou-se a proliferar os argumentos em favor de arranjos de privatização em que o Estado mantém um importante papel. Assim, o exame das experiências de privatização internacionais permitiu constatar que elas seguiram diferentes orientações. Um conjunto de experiências foi orientado pela noção de "Estado Mínimo" e outro conjunto de experiências teve como referência o Estado fomentador dos atores privados. A privatização continua sendo um processo atual e relevante e, portanto, sua discussão é considerada necessária.<br>The article analyzes and discusses the privatization of the rural extension services according to international literature. To start with, the subject is set in the horizon of the debate of the so called State Reform, which determined the agenda for the development since the 1980's. Next, we show how the subject has been treated so far having the economic theory as background and we examine experiments of privatization at international level. The analysis of such experiments reveals that the early agenda for the privatization took for granted that the rural extension services - which were a responsibility of the State - would be held completely by the private sectors. However, a series of obstacles appeared and arguments for models of privatization in which the State has a main role spread over. Therefore, the exam of international experiments of privatization led to the conclusion that they followed different orientations. One set of experiments was oriented by the notion of the "Minimum State" while the other had for reference the State as a supporter for private action. The privatization is a current and relevant process and, therefore, the discussion about it is considered necessary

Plantas com possível atividade hipolipidêmica: uma revisão bibliográfica de livros editados no Brasil entre 1998 e 2008 Plants with possible hypolipidemic activity: a review of books published in Brazil between 1998 and 2008

O objetivo deste trabalho foi realizar levantamento sobre as plantas medicinais indicadas para o tratamento da hiperlipidemia, hipercolesterolemia e/ou aterosclerose. Este estudo foi feito a partir da pesquisa bibliográfica em 32 livros publicados no Brasil entre 1998 e 2008, resultando em lista de 85 espécies distribuídas em 53 famílias, principalmente Asteraceae e Fabaceae, com 54 espécies exóticas e 31 nativas. As espécies mais citadas foram Allium sativum (Alliaceae), Cynara scolymus (Asteraceae), Curcuma longa (Zingiberaceae), Allium cepa (Alliaceae), Echinodorus grandiflorus (Alismataceae), Taraxacum officinale (Asteraceae), Vernonia condensata (Asteraceae), Cuphea carthagenensis (Lythraceae) e Curcuma zedoaria (Zingiberaceae). As espécies nativas, citadas em pelo menos 2 livros, foram investigadas para alguma evidencia científica relacionada a possíveis efeitos hipolipidêmico, hipocolesterolêmico e/ou contra aterosclerose. Somente foram encontrados estudos científicos, relacionados a estes efeitos, para as espécies nativas Cuphea carthagenensis e Echinodorus grandiflorum, indicando a necessidade de pesquisas que possam garantir a segurança e a eficácia do uso destas espécies.<br>The aim of this study was to survey medicinal plants indicated for the treatment of hyperlipidemia, hypercholesterolemia and/or atherosclerosis. This study was performed from a review of 32 books published in Brazil between 1998 and 2008, resulting in a list of 85 species belonging to 53 families, especially Asteraceae and Fabaceae, with 54 exotic and 31 native species. The species most often cited were Allium sativum (Alliaceae), Cynara scolymus (Asteraceae), Curcuma longa (Zingiberaceae), Allium cepa (Alliaceae), Echinodorus grandiflorus (Alismataceae), Taraxacum officinale (Asteraceae), Vernonia condensata (Asteraceae), Cuphea carthagenensis (Lythraceae) and Curcuma zedoaria (Zingiberaceae). Native species cited in at least 2 books were investigated for some scientific evidence related to possible hypolipidemic and hypocholesterolemic effects and/or action against atherosclerosis. Scientific studies related to these effects were found only for the native species Cuphea carthagenensis and Echinodorus grandiflorum, indicating the need for studies capable of assuring the safety and the efficacy as to the use of these species