Stability analysis of power systems described with detailed models by automatic method

The power system stability analysis is approached taking into explicit account the dynamic performance of generators internal voltages and control devices. The proposed method is not a direct method in the usual sense since conclusion for stability or instability is not exclusively based on energy function considerations but it is automatic since the conclusion is achieved without an analyst intervention. The stability test accounts for the nonconservative nature of the system with control devices such as the automatic voltage regulator (AVR) and automatic generation control (AGC) in contrast with the well-known direct methods. An energy function is derived for the system with machines forth-order model, AVR and AGC and it is used to start the analysis procedure and to point out criticalities. The conclusive analysis itself is made by means of a method based on the definition of a region surrounding the equilibrium point where the system net torque is equilibrium restorative. This region is named positive synchronization region (PSR). Since the definition of the PSR boundaries have no dependence on modelling approximation, the PSR test conduces to reliable results. (C) 2008 Elsevier Ltd. All rights reserved.

Comparison of agar gel immunodiffusion test, rapid slide agglutination test, microbiological culture and PCR for the diagnosis of canine brucellosis

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Population size and survivorship for juvenile lemon sharks (Negaprion brevirostris) on their nursery grounds at a marine protected area in Brazil

Os tubarões enfrentam muitos obstáculos para sobreviver nos primeiros anos de vida e muitas espécies ocupam áreas de berçário. Embora estimativas de sobrevivência, particularmente para jovens, sejam essenciais para acessar, monitorar e manejar efetivamente populações animais, existem poucos cálculos destas estimativas para populações de tubarões e poucas estimativas baseadas em métodos diretos para estes animais em suas áreas de berçário. Métodos de marcação e recaptura foram utilizados no presente estudo para estimar o tamanho populacional e a sobrevivência de jovens tubarões-limão (Negaprion brevirostris) em uma área de berçário na Reserva Biológica do Atol das Rocas, Brasil. Os indivíduos foram amostrados entre 1999 e 2003 e as estimativas de tamanho populacional variaram entre 12 a 100 indivíduos jovens e a taxa de sobrevivência entre 24 e 54%, com média de 44,6% durante o período de amostragem mais robusto. A população destes tubarões jovens diminuiu ao longo de nosso estudo, ainda que as taxas de sobrevivência tenham aumentado durante o mesmo período. Mesmo um nível moderado de pesca e a remoção de fêmeas maduras em áreas adjacentes podem afetar dramaticamente pequenas populações de tubarões num berçário pequeno e isolado como o Atol das Rocas. As taxas de sobrevivência e tamanho populacional relativamente mais baixos em Rocas podem ser resultado das diferenças nas características físicas deste berçário, comparadas a outros utilizados pela espécie no Atlântico norte-ocidental. Tais parâmetros comparativamente mais baixos no Atol das Rocas sugerem a fragilidade da população jovem de tubarões-limão neste berçário.

Estados ligados em um potencial delta duplo via transformada de Laplace

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Potenciais delta revisitados via transformada de Fourier

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

THE CRYSTAL-STRUCTURE OF BENZOYL-HISTIDINE MONOHYDRATE

The crystal structure of benzoyl-histidine monohydrate (BYLH hereafter), C-13H-12N-3O-3. H2O was determined from three dimensional data of 3012 independent reflections measured on a Enraf-Nonius (CAD4) single crystal diffractometer. The compound crystallizes in the orthorhombic space group P2(1)2(1)2(1) with cell dimensions alpha = 7.102(1) angstrom, b = 13.783(3) angstrom, c = 14.160(4) angstrom, V = 1385.92 angstrom-3, F.W. = 277.28, F(000) = 584 Q(calc) = 1.32 g cm-3 and Z = 4.The structure was solved with direct methods. All positional and anisotropic thermal parameters were refined by full-matrix least-squares calculations. The final reliability factor was R = 0.040, while the weighted one was Rw = 0.034. The H atoms found in the difference Fourier map were refined isotropically.The compound consists of a histidine molecule bound to a benzoyl group. There is also a cocrystallized water molecule stabilized through a hydrogen bridge.The 5-membered ring of the histidine has its tautomeric form, after the transfer of the H atom from the N(delta) to the N(epsilon) atom of the ring. There is an sp2 conformation around C6 while the conformation around C3 is that of sp3. The histidine ring forms with the benzene ring a dihedral angle of 109.8(1)-degree.All angle values and bond distances agree very well with the expected values in the literature.

Electronic spectra, ESR and crystal structure of tetrahedral halocuprates(II). The existence of cations (2tbpo·H+) with a very short hydrogen bond

Two compounds [2tbpo·H+)2[CuCl4]= (yellow) and (2tbpo·H+)2[CuBr4]= (dark purple) (tbpo = tribenzylphosphine oxide) have been prepared and investigated by means of crystal structure, electronic, vibrational and ESR spectra. The crystal structure of the (2tbpo·H+)2[CuCl4]= complex was determined by three-dimensional X-ray diffraction. The compound crystallizes in the space group P42/n with unit-cell dimensions a = 19.585(2), c = 9.883(1)Å, V = 3790 (1)Å3, Z = 2, Dm = 1.303 (flotation) Dx = 1.302 Mg m-3. The structure was solved by direct methods and refined by blocked full-matrix least-squares to R = 0.053 for 2583 observed reflections. Cu(II) is coordinated to four chlorides in a tetrahedral arrangement. Tribenzylphosphine oxide molecules, related by a centre of inversion, are connected by a short hydrogen bridge. Chemical analysis, electronic and vibrational spectra showed that the bromide compound is similar to the chloride one and can be formulated as (2tbpo·H+)2[CuBr4]=. The position of the dd transition bands, the charge transfer bands, the ESR and the vibrational spectra of both complexes are discussed. The results are compared with analogous complexes cited in the literature. © 1983.

Comparação de métodos para determinar biomassa na região amazônica

The aboveground biomass content of a region can be estimated by either direct or indirect methods. Direct methods correspond to the biomass content determination with scales and extrapolation of results to larger areas. It is a destructive and very laborious procedure. Indirect methods utilize formulas whose entrance parameters are obtained from forest inventories. Forest inventories are made with the purpose to plan exploration and land use and the inventory data are frequently not suitable for biomass estimation. Problems with both methods increase in the Amazon region, where little information is available on forest biomass. The objective of this paper is to establish, by comparing the application of the indirect and direct methods in the determination of the biomass, the more appropriate indirect formulation to represent the characteristic vegetation of a region in the amazonian forest. A 0.2 hectare area was chosen, which was part of a major forest clearing experiment conducted in Tomé Açu, a town located 250 km south of Belém, the capital of the Brazilian state of Pará. The entire biomass in the area was weighted with scales during the three weeks that followed the cut of the forest in July 1994. A detailed inventory was carried out in the area and then the indirect method was applied in the data. Seven different formulas for determining biomass were used. Comparison of the data of real mass and the mass obtained through the application of the seven formulas indicated that the more suitable for the region is given by FW = α · φβ · Hγ, where FW is total fresh weight (kg), φ is the diameter at breast height (cm), H is the total height of the tree and α, β and γ are regression coefficients (equal to 0.026, 1.529 and 1.747, respectively).

Crystal structure of BaBi2Ta2O9

The crystal structure of the Aurivillius compound Bi2BaTa2O9 prepared via the chemical route was determined by direct methods using EXPO97, and refined using the Rietveld method with conventional X-ray diffraction data. The structure was found to be tetragonal (space group I4/mmm, number 139) and Z = 2, isomorphic of the Bi2BaNb2O9 reported by Blake and co-workers in the literature (1997). Two refinements were performed using the two asymmetry functions of DBWS-9807 (release 20/May/99). The unit cell for each case are: a = 3.932 22(6) Å, c = 25.5053(6) Å (RA) and a = 3.93250(7) Å, c = 25.5069(6) Å (RCF). The differences for atom positions, interatomic distances and angles are in the range of one standard deviation. Final agreements factors are: Rwp = 7.97%, S = 1.84, RBragg = 4.28%(RA), Rwp = 7.98%, S = 1.84, RBragg = 4.30% (RCF). The occupancies of Ba and Bi in site 2b were refined but constrained to have their summation equal to 1.00. The same constraints were applied to the Ba and Bi of the 4e site. The results show that on site 2b there are 70% of Ba and 30% of Bi and on the site 4e there are 82% of Bi and 18% of Ba. The charge equilibrium is maintained for one standard deviation of the site occupancies. © 2000 International Centre for Diffraction Data.

Transient stability indices from a hybrid approach

This paper deals with hybrid method for transient stability analysis combining time domain simulation and a direct method. Nowadays, the step-by-step simulation is the best available tool for allowing the uses of detailed models and for providing reliable results. The main limitation of this approach involves the large time of computational simulations and the absence of stability margin. On the other hand, direct methods, that demand less CPU time, did not show ample reliability and applicability yet. The best way seems to be using hybrid solutions, in which a direct method is incorporated in a time domain simulation tool. This work has studied a direct method using the transient potential and kinetic energy of the critical machine only. In this paper the critical machine is identified by a fast and efficient method, and the proposal is new for using to get stability margins from hybrid approaches. Results from systems, like 16-machine, show stability indices to dynamic security assessment. © 2001 IEEE.

Utilização de índices de estabilidade transitória para a avaliação de segurança dinâmica

Indices that report how much a contingency is stable or unstable in an electrical power system have been the object of several studies in the last decades. In some approaches, indices are obtained from time-domain simulation; others explore the calculation of the stability margin from the so-called direct methods, or even by neural networks.The goal is always to obtain a fast and reliable way of analysing large disturbance that might occur on the power systems. A fast classification in stable and unstable, as a function of transient stability is crucial for a dynamic security analysis. All good propositions as how to analyse contingencies must present some important features: classification of contingencies; precision and reliability; and efficiency computation. Indices obtained from time-domain simulations have been used to classify the contingencies as stable or unstable. These indices are based on the concepts of coherence, transient energy conversion between kinetic energy and potential energy, and three dot products of state variable. The classification of the contingencies using the indices individually is not reliable, since the performance of these indices varies with each simulated condition. However, collapsing these indices into a single one can improve the analysis significantly. In this paper, it is presented the results of an approach to filter the contingencies, by a simple classification of them into stable, unstable or marginal. This classification is performed from the composite indices obtained from step by step simulation with a time period of the clearing time plus 0.5 second. The contingencies originally classified as stable or unstable do not require this extra simulation. The methodology requires an initial effort to obtain the values of the intervals for classification, and the weights. This is performed once for each power system and can be used in different operating conditions and for different contingencies. No misplaced classification o- - ccurred in any of the tests, i.e., we detected no stable case classified as unstable or otherwise. The methodology is thus well fitted for it allows for a rapid conclusion about the stability of th system, for the majority of the contingencies (Stable or Unstable Cases). The tests, results and discussions are presented using two power systems: (1) the IEEE17 system, composed of 17 generators, 162 buses and 284 transmission lines; and (2) a South Brazilian system configuration, with 10 generators, 45 buses and 71 lines.

Comparações entre equações de predição de consumo de capim-elefante cortado para vacas lactantes

This work aimed to compare intake prediction equations with values obtained by direct methods using chopped elephant-grass offered to crossbreed lactating cows with rumen canulas. The experimental design was a 3 x 3 Latin square (three animals and three cutting ages: 30, 45 and 60 days). The equations used for intake prediction (y) were: (1) y= -1.19 + 0.035(a+b) + 28.5c; (2) y= [%NDF on DM]*[NDF intake]/[(1- a - b)/KP+b/(c+kp)]/24; (3) y= -0.822 + 0.0748(a+b) + 40.7c and (4) equation 2 with values of intake measured directly. The predictions of NDF intake by equations were not different among treatments, instead of the difference among values measured directly: the 30 day-old had lower intake (5.29 kg/day) in relation to 45 (6.57 kg/day) and 60 (7.31 kg/day) day-old grasses. In general, equations overestimated the DM intake in relation to direct measuring (9.0 kg/cow/day), with exception of equation 3 which underestimated the intake (7.7 kg/day). The means of DM intake found by equations 1 and 2 (13.7 and 13.4 kg/cow/day, respectively) were similar between themselves and superior in relation to those found by equation 4 (9.7 kg/cow/day). The intakes measured directly were similar to those found in equation 4 and higher than those found by equation 3. The mean of rumen fill of 7.5 kg was superior to those of 5.2 kg estimated by equation. The prediction equations based on in situ degradability parameters do not supply estimates of DM intake, NDF intake and rumen fill in agreement with values obtained by direct methods.

Estudo geofísico de vazamento de combustíveis em posto de abastecimento

The geoelectrical methods have been widely used in research involving the evaluation and monitoring of areas with environmental risk. This paper presents the results of applying the Electrical Resistivity method by electrical profiling technique to investigate the fuel presence in soil and groundwater proceeding in station gas, located in an urban area Caçapava do Sul (RS), on soil in situ, from modification of Caçapava granite. The results suggest an association between low resistivity anomalies zone with potentially degraded from underground tanks worthless on the form of free phase, now represented as residual phase. The results of the model inversion are consistent with the standards expected for hydrocarbons present in the saturated zone. The electrical resistivity method proved to be an important tool for assessment and environmental monitoring in conjunction with direct methods of investigation.

Efeitos endócrinos, anti-inflamatórios e na atividade pedométrica após as administrações de flunixin meglumine e de meloxicam no pós-operatório de laparotomias em bezerros

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Enteroparasitoses caninas

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)