Triangular buckling patterns of twisted inextensible strips

When twisting a strip of paper or acetate under high longitudinal tension, one observes, at some critical load, a buckling of the strip into a regular triangular pattern. Very similar triangular facets have recently been observed in solutions to a new set of geometrically-exact equations describing the equilibrium shape of thin inextensible elastic strips. Here we formulate a modified boundary-value problem for these equations and construct post-buckling solutions in good agreement with the observed pattern in twisted strips. We also study the force-extension and moment-twist behaviour of these strips by varying the mode number n of triangular facets

Pathogenic diversity of Phytophthora sojae pathotypes from Brazil.

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Variational formulation of ideal fluid flows according to gauge principle

On the basis of the gauge principle of field theory, a new variational formulation is presented for flows of an ideal fluid. The fluid is defined thermodynamically by mass density and entropy density, and its flow fields are characterized by symmetries of translation and rotation. The rotational transformations are regarded as gauge transformations as well as the translational ones. In addition to the Lagrangians representing the translation symmetry, a structure of rotation symmetry is equipped with a Lagrangian $\Lambda_A$ including the vorticity and a vector potential bilinearly. Euler's equation of motion is derived from variations according to the action principle. In addition, the equations of continuity and entropy are derived from the variations. Equations of conserved currents are deduced as the Noether theorem in the space of Lagrangian coordinate \ba. Without $\Lambda_A$, the action principle results in the Clebsch solution with vanishing helicity. The Lagrangian $\Lambda_A$ yields non-vanishing vorticity and provides a source term of non-vanishing helicity. The vorticity equation is derived as an equation of the gauge field, and the $\Lambda_A$ characterizes topology of the field. The present formulation is comprehensive and provides a consistent basis for a unique transformation between the Lagrangian \ba space and the Eulerian \bx space. In contrast, with translation symmetry alone, there is an arbitrariness in the ransformation between these spaces.Comment: 34 pages, Fluid Dynamics Research (2008), accepted on 1st Dec. 200

Action functionals for relativistic perfect fluids

Action functionals describing relativistic perfect fluids are presented. Two of these actions apply to fluids whose equations of state are specified by giving the fluid energy density as a function of particle number density and entropy per particle. Other actions apply to fluids whose equations of state are specified in terms of other choices of dependent and independent fluid variables. Particular cases include actions for isentropic fluids and pressureless dust. The canonical Hamiltonian forms of these actions are derived, symmetries and conserved charges are identified, and the boundary value and initial value problems are discussed. As in previous works on perfect fluid actions, the action functionals considered here depend on certain Lagrange multipliers and Lagrangian coordinate fields. Particular attention is paid to the interpretations of these variables and to their relationships to the physical properties of the fluid.Comment: 40 pages, plain Te

Wave Solutions of Evolution Equations and Hamiltonian Flows on Nonlinear Subvarieties of Generalized Jacobians

The algebraic-geometric approach is extended to study solutions of N-component systems associated with the energy dependent Schrodinger operators having potentials with poles in the spectral parameter, in connection with Hamiltonian flows on nonlinear subvariaties of Jacobi varieties. The systems under study include the shallow water equation and Dym type equation. The classes of solutions are described in terms of theta-functions and their singular limits by using new parameterizations. A qualitative description of real valued solutions is provided

Perfect Fluid Theory and its Extensions

We review the canonical theory for perfect fluids, in Eulerian and Lagrangian formulations. The theory is related to a description of extended structures in higher dimensions. Internal symmetry and supersymmetry degrees of freedom are incorporated. Additional miscellaneous subjects that are covered include physical topics concerning quantization, as well as mathematical issues of volume preserving diffeomorphisms and representations of Chern-Simons terms (= vortex or magnetic helicity).Comment: 3 figure

Oídio de trigo: avaliação de genótipos do programa de melhoramento genético da Embrapa em 2023.

Em 2023, foram caracterizados 234 genótipos de trigo, oriundos do melhoramento genético da Embrapa, para reação a oídio. Algumas linhagens vêm mantendo a resistência à doença desde 2019 e são candidatas à promoção para cultivares comerciais com bom comportamento para a doença, em campo.ODS 2, ODS 12

Strange Attractors in Dissipative Nambu Mechanics : Classical and Quantum Aspects

We extend the framework of Nambu-Hamiltonian Mechanics to include dissipation in $R^{3}$ phase space. We demonstrate that it accommodates the phase space dynamics of low dimensional dissipative systems such as the much studied Lorenz and R\"{o}ssler Strange attractors, as well as the more recent constructions of Chen and Leipnik-Newton. The rotational, volume preserving part of the flow preserves in time a family of two intersecting surfaces, the so called {\em Nambu Hamiltonians}. They foliate the entire phase space and are, in turn, deformed in time by Dissipation which represents their irrotational part of the flow. It is given by the gradient of a scalar function and is responsible for the emergence of the Strange Attractors. Based on our recent work on Quantum Nambu Mechanics, we provide an explicit quantization of the Lorenz attractor through the introduction of Non-commutative phase space coordinates as Hermitian $N \times N$ matrices in $R^{3}$. They satisfy the commutation relations induced by one of the two Nambu Hamiltonians, the second one generating a unique time evolution. Dissipation is incorporated quantum mechanically in a self-consistent way having the correct classical limit without the introduction of external degrees of freedom. Due to its volume phase space contraction it violates the quantum commutation relations. We demonstrate that the Heisenberg-Nambu evolution equations for the Quantum Lorenz system give rise to an attracting ellipsoid in the $3 N^{2}$ dimensional phase space.Comment: 35 pages, 4 figures, LaTe

Oídio de trigo: avaliação histórica de linhagens e cultivares do programa de melhoramento da Embrapa Trigo, em 2021.

Avaliar a reação ao oídio de linhagens e cultivares de trigo do programa de melhoramento genético da Embrapa Trigo, em 2021, além de apresentar o conjunto histórico de dados de avaliações de cada genótipo.ODS-2, ODS-1

Reação de gramíneas anuais de inverno à brusone da folha.

Genótipos de gramíneas anuais foram avaliados sob condições controladas quanto à resistência à brusone da folha. Os resultados apresentados demonstram que cultivares de trigo Brasil que se destacam quanto à resistência. A brusone da folha, doença causada por Pyricularia oryzae, tem causado danos importantes em cultivos de gramíneas anuais utilizados na produção de forragem na Região Sul do Brasil (RSB). O objetivo deste trabalho foi avaliar a reação à brusone da folha de gramíneas utilizadas como fonte de forragem e/ou produção de grãos na RSB. Plantas de 18 genótipos das seguintes espécies foram avaliadas: aveia-preta, aveia-branca, azevém, cevada e trigo. As plantas foram conduzidas em vasos de plástico com substrato até o estádio 14 da escala de Zadoks (quarta folha expandida) e submetidas à inoculação com suspensão de inóculo formada pela mistura de conídios de três isolados de P. oryzae Triticum (105 conídios mL-1)