Local Isometric immersions of pseudo-spherical surfaces and evolution equations

The class of differential equations describing pseudo-spherical surfaces, first introduced by Chern and Tenenblat [3], is characterized by the property that to each solution of a differential equation, within the class, there corresponds a 2-dimensional Riemannian metric of curvature equal to $-1$. The class of differential equations describing pseudo-spherical surfaces carries close ties to the property of complete integrability, as manifested by the existence of infinite hierarchies of conservation laws and associated linear problems. As such, it contains many important known examples of integrable equations, like the sine-Gordon, Liouville and KdV equations. It also gives rise to many new families of integrable equations. The question we address in this paper concerns the local isometric immersion of pseudo-spherical surfaces in ${\bf E}^{3}$ from the perspective of the differential equations that give rise to the metrics. Indeed, a classical theorem in the differential geometry of surfaces states that any pseudo-spherical surface can be locally isometrically immersed in ${\bf E}^{3}$. In the case of the sine-Gordon equation, one can derive an expression for the second fundamental form of the immersion that depends only on a jet of finite order of the solution of the pde. A natural question is to know if this remarkable property extends to equations other than the sine-Gordon equation within the class of differential equations describing pseudo-spherical surfaces. In an earlier paper [11], we have shown that this property fails to hold for all other second order equations, except for those belonging to a very special class of evolution equations. In the present paper, we consider a class of evolution equations for $u(x,t)$ of order $k\geq 3$ describing pseudo-spherical surfaces. We show that whenever an isometric immersion in ${\bf E}^3$ exists, depending on a jet of finite order of $u$, then the coefficients of the second fundamental forms are functions of the independent variables $x$ and $t$ only.Comment: Fields Institute Communications, 2015, Hamiltonian PDEs and Applications, pp.N

Informações meteorológicos para pesquisa e planejamento agrícola, referentes ao Município de Santo Antônio de Goiás-GO 2000.

Os dados meteorológicos aqui apresentados permitirão aos usuários do setor agrícola obter informações sobre as variações dos elementos climáticos do município de Santo Antônio de Goiás ? GO, a partir de observações contínuas das variáveis climáticas.bitstream/CNPAF/20192/1/doc_120.pdfPublicação On-line

A discussion about a start-up procedure of a doubly-fed induction generator system

The present work proposes a start-up procedure for a doubly-fed induction generator (DFIG) driven by a wind turbine. In the DFIG topology the stator is connected direct to the grid while the rotor is connected to a back-to-back converter. This structure requires some care during grid synchronization to avoid undesired overloads. The main goal of a start-up procedure is to reduce the stresses on the electrical and mechanical components during synchronization. In this work, it is achieved by equalization among the induced stator voltage, the voltage over the filter capacitor and the grid voltage. A phase-locked-loop (PLL) computes the grid voltage phase displacement required for the system control orientation and synchronization procedures. Previous to the starting-up, the output currents set-points of the grid-side converter and rotor-side converter are computed in order to produce the same grid voltage over the filter capacitors and on the stator terminals. The whole procedure is summarized in seven different steps: turbine acceleration by the pitch control, DC-link pre-charge; initialization of the filter current controllers; filter synchronization; DC-Link voltage adjust; rotor current controllers' initialization and stator synchronization. The proposed start-up procedure was tested in a 4 kW test bench and the description of each step as well as simulation and experimental results are presented throughout the paper.reviewe

Estudo comparativo entre técnicas de extração de DNA para o futuro diagnóstico do endossimbionte Wolbachia em Haematobia irritans.

Editores técnicos: João de Mendonça Naime, Caue Ribeiro, Maria Alice Martins, Elaine Cristina Paris, Paulino Ribeiro Villas Boas, Ladislau Marcelino Rabello

MOLYBDENUM CATALYZED ACID PEROXIDE BLEACHING OF EUCALYPTUS KRAFT PULP

Molybdenum catalyzed peroxide bleaching (PMo Stage) consists of pulp treatment with hydrogen peroxide under acidic conditions in the presence of a molybdenum catalyst. Molybdenum is applied in catalytic doses (50-200 mg/kg pulp) and may originate from various sources, including (NH4)6Mo7O24.4H2O, Na2MoO4.2H2O, siliconmolybdate, etc. This work is aimed at optimizing the PMo stage and evaluating its industrial application in the OAZDP sequence. Optimum PMo stage conditions for bleaching eucalyptus pulp were 90 ºC, pH 3.5, 2 h, 0.1 kg/adt Mo and 5 kg/adt H2O2. The PMo stage was more efficient to remove pulp hexenuronic acids than lignin. Its efficiency decreased with increasing pH in the range of 1.5-5.5, while it increased with increasing temperature and peroxide and molybdenum doses. The application of the PMo stage as replacement for the A-stage of the AZDP sequence significantly decreased chlorine dioxide demand. The PMo stage caused a decrease of 20-30% in the generation of organically bound chlorine. The quality parameters of the pulp produced during the PMo stage mill trial were comparable to those obtained with the reference A-stage

Forrageiras em regime de corte avaliadas pela técnica in vitro semi-automática de produção de gases.

O objetivo deste trabalho foi determinar, atraves da tecnica in vitro semi-automatica de producao de gases, os potenciais maximos de producao de gases, degradabilidade da materia seca (DMS) e as taxas de producao de gases (mi) e de degradacao da MS (c) do capim Elefante (Pennisetum purpureum) - cv. Napier, cana-de-acucar (Saccharum officinarum) - var. rb 72454 e de dois hibridos de sorgo com capim Sudao (Sorghum bicolor x Sorghum sudanense) - AG 2501 e BRS 800, avaliados em regime de corte. Foi utilizado o modelo de descricao matematica da cinetica ruminal proposto por FRANCE et al. (1993( ara determinacao dos potenciais maximos de producao de gases (A) de 237, 232, 217 e 213 ml/g MS e taxas de producao de gases (mi) de 0,028, 0,079, 0,022 ml/h, empregando-se a equacao sugerida por ORSKOV et al. (1980) , foram encontrados potenciais de degradabilidade da MS (A) de 68,7, 66,2, 65,9 e 65,8% e taxas de degradacao da MS (c) de 0,054, 0,033, 0,051 e 0,049 %/h para o capim Elefante, a cana-de-acucar, o Ag 2501 e o BRS 800, respectivamente. para todos os alimentos foram notadas altas correlacoes entre as producoes cumulativas de gases e as degradabilidades da MS