Curved Herbig-Haro Jets: Simulations and Experiments

Herbig-Haro jets often show some degree of curvature along their path, in many cases produced by the ram pressure of a side-wind. We present simulations of both laboratory and astrophysical curved jets and experimental results from laboratory experiments. We discuss the properties and similarities of the laboratory and astrophysical flow, which show the formation of internal shocks and working surfaces. In particular the results illustrate how the break-up of the bow-shock and clumps in the flow are produced without invoking jet variability; we also discuss how jet rotation reduces the growth of the Rayleigh-Taylor instability in curved jets.Comment: 15 pages, 5 figure, accepted to be published in The Astrophysical Journa

Isospin structure of one- and two-phonon GDR excitations

Isospin is included in the description of Coulomb excitation of multiple giant isovector dipole resonances. In the excitation of even-even nuclei, a relevant portion of the excitation strength is shown to be associated with 1+ two-phonon states, which tends to be hindered or completely supressed in calculations in which the isospin degree of freedom is not considered. We find that the excitation cross sections is strongly dependent on the ground state isospin.Comment: 8 pages, 2 figure

Effective Widths and Effective Number of Phonons of Multiphonon Giant Resonances

We discuss the origin of the difference between the harmonic value of the width of the multiphonon giant resonances and the smaller observed value. Analytical expressions are derived for both the effective width and the average cross-section. The contribution of the Brink-Axel mechanism in resolving the discrepancy is pointed out.Comment: 9 pages, 4 figure

Aplicações de ferramentas de avaliação de impacto socioeconômico e ambiental para agricultura de precisão.

Foram avaliadas ferramentas para aplicação da avaliação de impacto socioeconômico e ambiental para o macroprograma 1 de agricultura de precisão. Duas em particular chamaram a atenção pelo potencial de resposta e foram detalhadas nesse trabalho como exemplos: a Matriz Insumo Produto, representando ferramentas de avaliação inovadoras a serem aplicadas na avaliação da AP e a avaliação tradicional pela Embrapa através do modelo Ambitec. Uma vez que a maioria das tecnologias propostas nesse projeto ainda não estão em fase finalística, optou-se por aplicar o modelo Ambitec nas tecnologias que atingiram a fase de uso pelo produtor e selecionou-se uma, o aplicador seletivo de herbicida Campo Limpo, desenvolvido pela Embrapa Pecuária Sul. O equipamento apresentou um baixo valor na avaliação do Ambitec Social, responsável pela dimensão social, principalmente devido ao baixo impacto econômico, mas um valor significativo em relação ao Ambitec agro, que avalia a dimensão ambiental. Isso pode indicar uma tecnologia que será plenamente aplicada à medida que demandas de ordem ambiental tornem a atividade agrícola mais restrita do que o momento atual

Nonlinear Enhancement of the Multiphonon Coulomb Excitation in Relativistic Heavy Ion Collisions

We propose a soluble model to incorporate the nonlinear effects in the transition probabilities of the multiphonon Giant Dipole Resonances based on the SU(1,1) algebra. Analytical expressions for the multi-phonon transition probabilities are derived. Enhancement of the Double Giant Resonance excitation probabilities in relativistic ion collisions scales as $(2 k +1)(2k)^{-1}$ for the degree of nonlinearity $(2k)^{-1}$ and is able to reach values $1.5-2$ compatible with experimental data. The enhancement factor is found to decrease with increasing bombarding energy. [KEYWORDS: Relativistic Heavy Ion Collisions,Double Giant Resonance]Comment: 12 pages, 2 figure

Quantum Tunneling in Nuclear Fusion

Recent theoretical advances in the study of heavy ion fusion reactions below the Coulomb barrier are reviewed. Particular emphasis is given to new ways of analyzing data, such as studying barrier distributions; new approaches to channel coupling, such as the path integral and Green function formalisms; and alternative methods to describe nuclear structure effects, such as those using the Interacting Boson Model. The roles of nucleon transfer, asymmetry effects, higher-order couplings, and shape-phase transitions are elucidated. The current status of the fusion of unstable nuclei and very massive systems are briefly discussed.Comment: To appear in the January 1998 issue of Reviews of Modern Physics. 13 Figures (postscript file for Figure 6 is not available; a hard copy can be requested from the authors). Full text and figures are also available at http://nucth.physics.wisc.edu/preprints