Crystallographic characterization of silicon nitride ceramics sintered with Y(2)O(3)-Al(2)O(3) or E(2)O(3)-Al(2)O(3) additions

Silicon nitride ceramics were sintered using Y(2)O(3)-Al(2)O(3) or E(2)O(3)-Al(2)O(3) (E(2)O(3) denotes a mixed oxide Of Y(2)O(3) and rare-earth oxides) as sintering additives. The intergranular phases formed after sintering was investigated using high-resolution X-ray diffraction (HRXRD). The use of synchrotron radiation enabled high angular resolution and a high signal to background ratio. Besides the appearance Of beta-Si(3)N(4) phase the intergranular phases Y(3)Al(5)O(12) (YAG) and Y(2)SiO(5) were identified in both samples. The refinement of the structural parameters by the Rietveld method indicated similar crystalline structure Of beta-Si(3)N(4) for both systems used as sintering additive. On the other hand, the intergranular phases Y(3)Al(5)O(12) and Y(2)SiO(5) shown a decrease of the lattice parameters, when E(2)O(3) was used as additive, indicating the formation of solid solutions of E(3)Al(5)O(12) and E(2)SiO(5), respectively. (C) 2007 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

A hybrid system for upper limb movement restoration in quadriplegics

Generally, quadriplegic individuals have difficulties performing object manipulation. Toward satisfactory manipulation, reach and grasp movements must be performed with voluntary control, and for that, grasp force feedback is essential. A hybrid system aiming at partial upper limb sensory-motor restoration for quadriplegics was built. Such device is composed of an elbow dynamic orthosis that provides elbow flexion/extension (range was approximately from 20 degrees to 120 degrees, and average angular speed was approximately 15 degrees/s) with forearm support, a wrist static orthosis and neuromuscular electrical stimulation for grasping generation, and a glove with force sensors that allows grasping force feedback. The glove presents two user interface modes: visual by light emitting diodes or audio emitted by buzzer. Voice control of the entire system (elbow dynamic orthosis and electrical stimulator) is performed by the patient. The movements provided by the hybrid system, combined with the scapular and shoulder movements performed by the patient, can aid quadriplegic individuals in tasks that involve reach and grasp movements.

Experimental results on the nonlinear H(infinity) control via quasi-LPV representation and game theory for wheeled mobile robots

In this paper, nonlinear dynamic equations of a wheeled mobile robot are described in the state-space form where the parameters are part of the state (angular velocities of the wheels). This representation, known as quasi-linear parameter varying, is useful for control designs based on nonlinear H(infinity) approaches. Two nonlinear H(infinity) controllers that guarantee induced L(2)-norm, between input (disturbances) and output signals, bounded by an attenuation level gamma, are used to control a wheeled mobile robot. These controllers are solved via linear matrix inequalities and algebraic Riccati equation. Experimental results are presented, with a comparative study among these robust control strategies and the standard computed torque, plus proportional-derivative, controller.

Chaos-Galerkin solution of stochastic Timoshenko bending problems

This paper presents an accurate and efficient solution for the random transverse and angular displacement fields of uncertain Timoshenko beams. Approximate, numerical solutions are obtained using the Galerkin method and chaos polynomials. The Chaos-Galerkin scheme is constructed by respecting the theoretical conditions for existence and uniqueness of the solution. Numerical results show fast convergence to the exact solution, at excellent accuracies. The developed Chaos-Galerkin scheme accurately approximates the complete cumulative distribution function of the displacement responses. The Chaos-Galerkin scheme developed herein is a theoretically sound and efficient method for the solution of stochastic problems in engineering. (C) 2011 Elsevier Ltd. All rights reserved.

Estimation of Mass Transfer Velocity Based on Measured Turbulence Parameters

The aim of this study is to quantify the mass transfer velocity using turbulence parameters from simultaneous measurements of oxygen concentration fields and velocity fields. The surface divergence model was considered in more detail, using data obtained for the lower range of beta (surface divergence). It is shown that the existing models that use the divergence concept furnish good predictions for the transfer velocity also for low values of beta, in the range of this study. Additionally, traditional conceptual models, such as the film model, the penetration-renewal model, and the large eddy model, were tested using the simultaneous information of concentration and velocity fields. It is shown that the film and the surface divergence models predicted the mass transfer velocity for all the range of the equipment Reynolds number used here. The velocity measurements showed viscosity effects close to the surface, which indicates that the surface was contaminated with some surfactant. Considering the results, this contamination can be considered slight for the mass transfer predictions. (C) 2009 American Institute of Chemical Engineers AIChE J, 56: 2005-2017; 2010

Digital versus Conventional Radiography for Imaging Fatigue Cracks in Riveted Lap Joints of Hybrid Glass Reinforced Fiber/Metal Laminate

A round robin program zoos conducted to assess the ability of three different X-radiographic systems for imaging internal fatigue cracks in riveted lap joints of composite glass reinforced fiber/metal laminate. From an engineering perspective, conventional film radiography and direct radiography have produced the best results, identifying and characterizing in detail internal damage on metallic faying surfaces of fastened glass reinforced fiber/metal laminate joints. On the other hand, computed radiographic images presented large projected geometric distortions and feature shifts due to the angular incident radiation beam, disclosing only partial internal cracking patterns.

Galerkin finite element method for incompressible thermofluid flows framed within the bond graph theory

In this paper a bond graph methodology is used to model incompressible fluid flows with viscous and thermal effects. The distinctive characteristic of these flows is the role of pressure, which does not behave as a state variable but as a function that must act in such a way that the resulting velocity field has divergence zero. Velocity and entropy per unit volume are used as independent variables for a single-phase, single-component flow. Time-dependent nodal values and interpolation functions are introduced to represent the flow field, from which nodal vectors of velocity and entropy are defined as state variables. The system for momentum and continuity equations is coincident with the one obtained by using the Galerkin method for the weak formulation of the problem in finite elements. The integral incompressibility constraint is derived based on the integral conservation of mechanical energy. The weak formulation for thermal energy equation is modeled with true bond graph elements in terms of nodal vectors of temperature and entropy rates, resulting a Petrov-Galerkin method. The resulting bond graph shows the coupling between mechanical and thermal energy domains through the viscous dissipation term. All kind of boundary conditions are handled consistently and can be represented as generalized effort or flow sources. A procedure for causality assignment is derived for the resulting graph, satisfying the Second principle of Thermodynamics. (C) 2007 Elsevier B.V. All rights reserved.

Characterization of the elastic-plastic region in AISI/SAE 1070 steel by the magnetic barkhausen noise

The magnetic Barkhausen energy in the rolling and transversal directions of AISI/SAE 1070 annealed surfaces is studied. The measurements were made in the samples under applied tension in the elastic-plastic region for different angular directions. The outcomes evidence that the magnetic anisotropy coefficient can be used to characterize the linear and nonlinear elastic limits of the material tinder tensile tresses. The results also show that the area of the curve corresponding to the angular dependence of the number of Barkhausen jumps with average energy presents a maximum value that corresponds to the elastic limit of the sample. (C) 2008 Elsevier Ltd. All rights reserved.

Discrete approximation to the global spectrum of the tangent operator for flow past a circular cylinder

This paper deals with the calculation of the discrete approximation to the full spectrum for the tangent operator for the stability problem of the symmetric flow past a circular cylinder. It is also concerned with the localization of the Hopf bifurcation in laminar flow past a cylinder, when the stationary solution loses stability and often becomes periodic in time. The main problem is to determine the critical Reynolds number for which a pair of eigenvalues crosses the imaginary axis. We thus present a divergence-free method, based on a decoupling of the vector of velocities in the saddle-point system from the vector of pressures, allowing the computation of eigenvalues, from which we can deduce the fundamental frequency of the time-periodic solution. The calculation showed that stability is lost through a symmetry-breaking Hopf bifurcation and that the critical Reynolds number is in agreement with the value presented in reported computations. (c) 2007 IMACS. Published by Elsevier B.V. All rights reserved.

Axial wedge effect in tilted hydrodynamic journal bearings

Hydrodynamic journal bearings are susceptible to static angular misalignment, resulting from improper assemblage, elastic and thermal distortion of the shaft and bearing housing, and also manufacturing errors. Several previous works on the theme, both theoretical and experimental, focused on the determination of the static properties of angular misaligned bearings. Although some reports show agreement between theoretical and experimental results, the increasingly severe operating conditions of hydrodynamic bearings (heavy loads and high rotational speeds) require more reliable theoretical formulations for the evaluation of the journal performance during the design process. The consideration of the angular misalignment in the derivation of the Reynolds equation is presented here in detail, showing that properly conducted geometric and magnitude-order analyses lead to the inclusion of an axial wedge effect term that influences the velocity and pressure fields in the lubricant film. Numerical results evidence that this axial wedge effect more significantly affects the hydrodynamic forces and static operational properties of tilted short journal bearings.

Geographic variation of sex pheromone and mitochondrial DNA in Diatraea saccharalis (Fab., 1794) (Lepidoptera: Crambidae)

(9Z,11E)-hexadecadienal and (Z11)-hexadecenal, the main sex pheromone components of the sugarcane borer, Diatraea saccharalis, were identified and quantified from four Brazilian and one Colombian populations using GC-EAD, GC-MS and GC analyses. Three different ratios were observed, 9:1,6:1, and 3:1. The pheromone concentration for the major component, (9Z,11E)-hexadecadienal, varied from 6.8 ng/gland to 21.9 ng/gland and from 1.7 ng/gland to 6.5 to the minor component, (Z11)-hexadecenal. The 25 D. saccharalis cytochrome oxidase II sequences that were analyzed showed low intra-specific variation and represented only 11 haplotypes, with the most frequent being the one represented by specimens from Sao Paulo, Parana, and Pernambuco states. Specimens from Colombia showed the highest genetic divergence from the others haplotypes studied. Data on the genetic variability among specimens, more than their geographic proximity, were in agreement with data obtained from analyses of the pheromone extracts. Our data demonstrate a variation in pheromone composition and a covariation in haplotypes of the D. saccharalis populations studied. (C) 2010 Elsevier Ltd. All rights reserved.

Canonical discriminant analysis applied to broiler chicken performance

The mechanisms involved in the control of growth in chickens are too complex to be explained only under univariate analysis because all related traits are biologically correlated. Therefore, we evaluated broiler chicken performance under a multivariate approach, using the canonical discriminant analysis. A total of 1920 chicks from eight treatments, defined as the combination of four broiler chicken strains (Arbor Acres, AgRoss 308, Cobb 500 and RX) from both sexes, were housed in 48 pens. Average feed intake, average live weight, feed conversion and carcass, breast and leg weights were obtained for days 1 to 42. Canonical discriminant analysis was implemented by SAS((R)) CANDISC procedure and differences between treatments were obtained by the F-test (P < 0.05) over the squared Mahalanobis` distances. Multivariate performance from all treatments could be easily visualised because one graph was obtained from two first canonical variables, which explained 96.49% of total variation, using a SAS((R)) CONELIP macro. A clear distinction between sexes was found, where males were better than females. Also between strains, Arbor Acres, AgRoss 308 and Cobb 500 (commercial) were better than RX (experimental), Evaluation of broiler chicken performance was facilitated by the fact that the six original traits were reduced to only two canonical variables. Average live weight and carcass weight (first canonical variable) were the most important traits to discriminate treatments. The contrast between average feed intake and average live weight plus feed conversion (second canonical variable) were used to classify them. We suggest analysing performance data sets using canonical discriminant analysis.

Cryptic vicariance in Gulf of California fishes parallels vicariant patterns found in Baja, California mammals and reptiles

Comparisons across multiple taxa can often clarify the histories of biogeographic regions. In particular, historic barriers to movement should affect multiple species and, thus, result in a pattern of concordant intraspecific genetic divisions among species. A striking example of such comparative phylogeography is the recent observation that populations of many small mammals and reptiles living on the Baja, California peninsula have a large genetic break between northern and southern peninsular populations. In the present study, I demonstrate that five species of near-shore fishes living on the Baja coastline of the Gulf of California share this genetic pattern. The simplest explanation for this concordant genetic division within both terrestrial and marine vertebrates is that the Baja peninsula was fragmented by a Plio-Pleistocene marine seaway and that this seaway posed a substantial barrier to movement for near-shore fishes. The genetic divisions within Gulf of California fishes also coincide with recognized biogeographic regions based on fish community composition and several environmental factors. It is likely that adaptation to regional environments and present-day oceanographic circulation limits gene exchange between biogeographic regions and helps maintain evidence of past vicariance.

Differential patterns of Male and Female mtDNA exchange across the Atlantic Ocean in the blue mussel, Mytilus edulis

Comparisons among loci with differing modes of inheritance can reveal unexpected aspects of population history. We employ a multilocus approach to ask whether two types of independently assorting mitochondrial DNAs (maternally and paternally inherited: F- and M-mtDNA) and a nuclear locus (ITS) yield concordant estimates of gene flow and population divergence. The blue mussel, Mytilus edulis, is distributed on both North American and European coastlines and these populations are separated by the waters of the Atlantic Ocean. Gene flow across the Atlantic Ocean differs among loci, with F-mtDNA and ITS showing an imprint of some genetic interchange and M-mtDNA showing no evidence for gene flow. Gene flow of F-mtDNA and ITS causes trans-Atlantic population divergence times to be greatly underestimated for these loci, although a single trans-Atlantic population divergence time (1.2 MYA) can be accommodated by considering all three loci in combination in a coalescent framework. The apparent lack of gene flow for M-mtDNA is not readily explained by different dispersal capacities of male and female mussels. A genetic barrier to M-mtDNA exchange between North American and European mussel populations is likely to explain the observed pattern, perhaps associated with the double uniparental system of mitochondrial DNA inheritance.

Positive selection on an acrosomal sperm protein, M7 lysin, in three species of the mussel genus Mytilus

Marine invertebrate sperm proteins are particularly interesting because they are characterized by positive selection and are likely to be involved in prezyogotic isolation and, thus, speciation. Here, we present the first survey of inter and intraspecific variation of a bivalve sperm protein among a group of species that regularly hybridize in nature. M7 lysin is found in sperm acrosomes of mussels and dissolves the egg vitelline coat, permitting fertilization. We sequenced multiple alleles of the mature protein-coding region of M7 lysin from allopatric populations of mussels in the Mytilus edulis species group (M. edulis, M. galloprovincialis, and M. trossulus). A significant McDonald-Kreitman test showed an excess of fixed amino acid replacing substitutions between species, consistent with positive selection. In addition, Kolmogorov-Smirnov tests showed significant heterogeneity in polymorphism to divergence ratios for both synonymous variation and combined synonymous and non-synonymous variation within M. galloprovincialis. These results indicate that there has been adaptive evolution at M7 lysin and, furthermore, shows that positive selection on sperm proteins can occur even when post-zygotic reproductive isolation is incomplete.