3,087 research outputs found
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
Aplicações de ferramentas de avaliação de impacto socioeconômico e ambiental para agricultura de precisão.
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.
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
Photochemical efficiency of photosystem in Carapichea ipecacuanha under shading in different seasons of the year.
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 for
the degree of nonlinearity and is able to reach values
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
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