Application of dynamical systems theory to the high angle of attack dynamics of the F-14

Dynamical systems theory has been used to study the nonlinear dynamics of the F-14. An eight degree of freedom model that does not include the control system present in operational F-14's has been analyzed. The aerodynamic model, supplied by NASA, includes nonlinearities as functions of the angles of attack and sideslip, the rotation rate, and the elevator deflection. A continuation method has been used to calculate the steady states of the F-14 as continuous functions of the control surface deflections. Bifurcations of these steady states have been used to predict the onset of wing rock, spiral divergence, and jump phenomena which cause the aircraft to enter a spin. A simple feedback control system was designed to eliminate the wing rock and spiral divergence instabilities. The predictions were verified with numerical simulations

Modeling for Active Control of Combustion and Thermally Driven Oscillations

Organized oscillations excited and sustained by high densities of energy release in combustion chambers have long caused serious problems in development of propulsion systems. The amplitudes often become sufficiently large to cause unacceptable structural vibrations. Because the oscillations are self-excited, they reach limiting amplitudes (limit cycles) only because of the action of nonlinear processes. Traditionally, satisfactory behavior has been achieved through a combination of trial-and-error design and testing, with control always involving passive means: geometrical modifications, changes of propellant composition, or devices to enhance dissipation of acoustic energy. Active control has been applied only to small-scale laboratory devices, but the limited success suggests the possibility of serious applications to full-scale propulsion systems. Realization of that potential rests on further experimental work, combined with deeper understanding of the mechanisms causing the oscillations and of the physical behavior of the systems. Effective design of active control systems will require faithful modeling of the relevant processes over broad frequency ranges covering the spectra of natural modes. This paper will cover the general character of the linear and nonlinear behavior of combustion systems, with special attention to acoustics and the mechanisms of excitation. The discussion is intended to supplement the paper by Doyle et al. concerned primarily with controls issues and the observed behavior of simple laboratory devices

The Impact of Agricultural Research in Tropical Africa: A Study of the Collaboration between the International and National Research Systems

CGIAR Study Paper on the problems and opportunities of international agricultural research in Sub Saharan Africa, and the impact of CGIAR Centers on African national agricultural research systems and on agricultural production and food security in Africa. Written by Hans E. Jahnke, Dieter Kirschke, and Johannes Lagermann and published as CGIAR Study Paper No. 21, part of the series comprising the CGIAR Impact Study of the 1980s

Application of dynamical systems theory to nonlinear aircraft dynamics

Dynamical systems theory has been used to study nonlinear aircraft dynamics. A six degree of freedom model that neglects gravity has been analyzed. The aerodynamical model, supplied by NASA, is for a generic swept wing fighter and includes nonlinearities as functions of the angle of attack. A continuation method was use to calculate the steady states of the aircraft, and bifurcations of these steady states, as functions of the control deflections. Bifurcations were used to predict jump phenomena and the onset of periodic motion for roll coupling instabilities and high angle of attack maneuvers. The predictions were verified with numerical simulations

Quantitative Indicators for Priorities in International Agricultural Research

FAO commissioned study by the German consulting firm Gesellschaft fur Agrarprojekte on the selection and use of quantitative indicators for establishing priorities in international agricultural research. The paper discusses the problems of research policy evaluation and the complexities of selecting suitable priority indicators. It describes the uses and limitations of commodity-oriented, resource-oriented, agroecological, and development indicators. Agenda document, TAC 32nd Meeting, October 1983

Supercurrent in Nodal Superconductors

In recent years, a number of nodal superconductors have been identified; d-wave superconductors in high T_c cuprates, CeCoIn$_5$, and \kappa-(ET)_2Cu(NCS)_2, 2D f-wave superconductor in Sr_2RuO_4 and hybrid s+g-wave superconductor in YNi_2B_2C. In this work we conduct a theoretical study of nodal superconductors in the presence of supercurrent. For simplicity, we limit ourselves to d-wave and 2D f-wave superconductors. We compute the quasiparticle density of states and the temperature dependence of the depairing critical current in nodal superconductors, both of which are accessible experimentally.Comment: revtex4, 6 pages, 7 figures; fixed typos, updated references, trimmed introductio

Mapeamento da favorabilidade da temperatura para Euschistus heros F. (Heteroptera: Pentatomidae) em soja na região sul do Brasil em cenários de clima atual e futuro.

Dentre as pragas que acometem a cultura da soja no Brasil destaca-se o percevejo-marrom Euschistus heros. O trabalho teve como objetivo avaliar os impactos potenciais das mudanças climáticas sobre E. heros a partir da determinação de faixas de favorabilidade para o aumento populacional deste, por meio do mapeamento de áreas favoráveis na região sul do Brasil em cenários de clima futuros projetados pelos modelos do IPCC. Faixas de temperatura variando de desfavorável a muito favorável foram propostas e integradas a um sistema de informações geográficas alimentados com dados de clima atual e projetados para as décadas de 2020, 2050 e 2080 para a confecção de mapas nos cenários A2 e B1. Com base em dados bibliográficos da biologia da praga, foi determinada a faixa de 26 a 28ºC como a mais favorável ao seu ciclo biológico. Abaixo de 14ºC foi determinado como desfavorável e entre 14 e 20ºC e acima de 30ºC como pouco favorável. Uma vez que os cenários futuros indicam incremento nas condições médias de temperatura, foi predito um aumento na área muito favorável ao estabelecimento de E. heros em relação ao clima atual no sul do Brasil, o qual foi mapeado como favorável entre os meses de dezembro a abril

Mapeamento da severidade da ferrugem asiática da soja na região sul do Brasil em cenários de clima atual e futuro.

Dentre as doenças que ocorrem na cultura da soja no Brasil destaca-se em importância a ferrugem asiática, causada pelo fungo Phakopsora pachyrhizi. O trabalho teve como objetivo avaliar o impacto potencial de alterações nos padrões de precipitação em cenários de clima futuro na severidade da ferrugem asiática na Região Sul do Brasil. Um modelo de predição da severidade foi integrado a um sistema de informação geográfica alimentado com dados de clima atual (1961-90) e futuro (2020, 2050 e 2080) predito pelos modelos do IPCC (cenários futuros A2 e B1) para a geração de mapas de severidade. Em cada um dos oito cenários possíveis, foi gerado um mapa mensal com a severidade delineada em cinco classes (0-100%) com base na chuva acumulada para os meses de outubro a abril. Os resultados mostram que, no período de maior ocorrência da ferrugem (dezembro a fevereiro), no cenário atual, o maior percentual de área da região (de 70 a 80% da área) apresentou severidade média entre 40 e 60%. Já nos cenários futuros, os modelos projetam um pequeno incremento na área geográfica nessa mesma classe, variando de 70 a 90%, para o mesmo período, sendo mais alto na década de 2080