Gamma phases in Cu-Al alloys and the influence of a square shaped phase in the electrochemical behavior of a Cu-13.6wt% Al alloy

The electrochemical behavior of Cu-xAl alloys, with 11 wt%less than or equal to x less than or equal to 15wt%, in 0.5 M H2SO4 was studied by means of open-circuit potential decay measurements, quasi-stationary and fast cyclic voltammetry, and electrochemical impedance spectroscopy. Some of the alloys (x less than or equal to 14%), when quenched formed martensitic structures. Alloys with greater than or equal to 13% showed a little square-shaped phase when quenched from temperatures around 800 degrees C. It was observed that in sulfuric medium, these formations were dealuminized differently than the martensitic phase. The values of the rest potentials are more influenced by the heat treatment rather than by the alloy composition. An anodic Tafel slope of ca. 60 mV/decade was observed for all the alloys, independently of the heat treatment. This is explained in terms of a competition between two processes: copper oxidation and copper(I) deproportionation. In the cyclic voltammetric experiments it was observed an anodic current peak, related with copper oxidation with a possible formation of some interfacial species, and a cathodic current peak during the reverse potential scan, associated with the reduction of soluble species and/or of the film. The AC Impedance data were interpreted in terms of electric equivalent circuits.

Differential response of the luteal phase and fertility in cattle following ovulation of the first-wave follicle with human chorionic gonadotropin or an agonist of gonadotropin-releasing hormone

A series of experiments with Holstein heifers was conducted to develop the capability of inducing accessory corpus luteum (CL) with a GnRH agonist (Buserelin, 8 mu g; GnRHa) or hCG; (3,000 IU) to increase plasma progesterone concentrations (Exp. 1, 2, and 3) and to test whether induction of accessory CL with hCG will increase conception rates in heifers (Exp. 4) and lactating cows (Exp. 5). In Exp. 1, heifers were treated on d 5 after estrus with GnRHa (n = 8) or saline (n = 7); heifers in Exp. 2 received hCG (n = 5) or saline (n = 4) on d 5. Experiment 3 allowed a contemporary evaluation of heifers treated on d 5 with GnRHa (n = 6), hCG (n = 6), saline (n = 6), or GnRHa at d 5 and hCG at the time of the induced ovulation (n = 5). The GnRHa and hCG were equally effective in inducing an accessory CL (93% induction rate), but the subsequent increase in progesterone concentrations was greater in hCG-treated heifers. A greater half life of hCG may provide longer LH-like stimulation of the first-wave follicle and subsequent developing accessory CL or a greater luteotropic effect on the original CL. Induction of an accessory CL with hCG on d 5 or 6 after insemination did not increase pregnancy rates in fertile heifers (Exp. 4: hCG = 64.8% vs control = 62.9%; n = 243) or lactating dairy cows during summer heat stress (Exp. 5: hCG = 24.2% vs control = 23.5%; n = 201).

Multi-wavelength holographic profilometry - art. no. 60272L

A novel method for surface profilometry by holography is presented. We used a diode laser emitting at many wavelengths simultaneously as the light source and a Bi12TiO20 (BTO) crystal as the holographic medium in single exposure processes. The employ of multi-wavelength, large free spectral range (FSR) lasers leads to holographic images covered of interference fringes corresponding to the contour lines of the studied surface. In order to obtain the relief of the studied surface, the fringe analysis was performed by the phase stepping technique (PST) and the phase unwrapping was carried out by the Cellular-automata method. We analysed the relief of a tilted flat metallic bar and a tooth prosthesis.

Relationship between predation by Podisus nigrispinus and developmental phase and density of its prey, Plutella xylostella

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Refractive and geometric lens characterization through multi-wavelength digital speckle pattern interferometry

Physical parameters of different types of lenses were measured through digital speckle pattern interferometry (DSPI) using a multimode diode laser as light source. When such lasers emit two or more longitudinal modes simultaneously the speckle image of an object appears covered of contour fringes. By performing the quantitative fringe evaluation the radii of curvature as well as the refractive indexes of the lenses were determined. The fringe quantitative evaluation was carried out through the four- and the eight-stepping techniques and the branch-cut method was employed for phase unwrapping. With all these parameters the focal length was calculated. This whole-field multi-wavelength method does enable the characterization of spherical and aspherical lenses and of positive and negative ones as well. (C) 2007 Elsevier B.V. All rights reserved.

Study of phase transition in (Pb,Ba)TiO(3) thin films

Dielectric and Raman scattering experiments were performed on polycrystalline Pb(1-x)Ba(x)TiO(3) thin films (x=0.40 and 0.60) as a function of temperature. The dielectric study on single phase compositions revealed that a diffuse-type phase transition occurred upon transformation of the cubic paraelectric to the tetragonal ferroelectric phase in all thin films, which showed a broadening of the dielectric peak. Diffusivity was found to increase with increasing barium contents in the composition range under study. In addition, the temperature dependence of Raman scattering spectra was investigated through the ferroelectric phase transition. The temperature dependence of the phonon frequencies was used to characterize the phase transitions. Raman modes persisted above the tetragonal to cubic phase transition temperature, although all optical modes should be Raman inactive. The origin of these modes was interpreted as a breakdown of the local cubic symmetry by chemical disorder. The lack of a well-defined transition temperature and the presence of broadbands in some temperature intervals above the paraferroelectric phase transition temperature suggest a diffuse-type phase transition. (C) 2008 American Institute of Physics.

Minimization of lead and copper interferences on spectrophotometric determination of cadmium using electrolytic deposition and ion-exchange in multi-commutation flow system

A new strategy for minimization of Cu2+ and Pb2+ interferences on the spectrophotometric determination of Cd2+ by the Malachite green (MG)-iodide reaction using electrolytic deposition of interfering species and solid phase extraction of Cd2+ in flow system is proposed. The electrolytic cell comprises two coiled Pt electrodes concentrically assembled. When the sample solution is electrolyzed in a mixed solution containing 5% (v/v) HNO3, 0.1% (v/v) H2SO4 and 0.5 M NaCl, Cu2+ is deposited as Cu on the cathode, Pb2+ is deposited as PbO2 on the anode while Cd2+ is kept in solution. After electrolysis, the remaining solution passes through an AG1-X8 resin (chloride form) packed minicolumn in which Cd2+ is extracted as CdCl4/2-. Electrolyte compositions, flow rates, timing, applied current, and electrolysis time was investigated. With 60 s electrolysis time, 0.25 A applied current, Pb2+ and Cu2+ levels up to 50 and 250 mg 1-1, respectively, can be tolerated without interference. For 90 s resin loading time, a linear relationship between absorbance and analyte concentration in the 5.00-50.0 μg Cd 1-1 range (r2 = 0.9996) is obtained. A throughput of 20 samples per h is achieved, corresponding to about 0.7 mg MG and 500 mg KI and 5 ml sample consumed per determination. The detection limit is 0.23 μg Cd 1-1. The accuracy was checked for cadmium determination in standard reference materials, vegetables and tap water. Results were in agreement with certified values of standard reference materials and with those obtained by graphite furnace atomic absorption spectrometry at 95% confidence level. The R.S.D. for plant digests and water containing 13.0 μg Cd 1-1 was 3.85% (n = 12). The recoveries of analyte spikes added to the water and vegetable samples ranged from 94 to 104%. (C) 2000 Elsevier Science B.V.

Enhanced multi-wavelength holographic profilometry by laser mode selection

The application of multi-wavelength holography for surface shape measurement is presented. In our holographic setup a Bi12TiO 20 (BTO) photorefractive crystal was the holographic recording medium and a multimode diode laser emitting in the red region was the light source in a two-wave mixing scheme. The holographic imaging with multimode lasers results in multiple holograms in the BTO. By employing such lasers the resulting holographic image appears covered of interference fringes corresponding to the object relief and the interferogram spatial frequency is proportional to the diode laser free spectral range (FSR). We used a Fabry-Perot étalon at the laser output for laser mode selection. Thus, larger effective values of the laser FSR were achieved, leading to higher-spatial frequency interferograms and therefore to more sensitive and accurate measurements. The quantitative evaluation of the interferograms was performed through the phase stepping technique (PST) and the phase map unwrapping was carried out through the Cellular-Automata method. For a given surface, shape measurements with different interferogram spatial frequencies were performed and compared, concerning measurement noise and visual inspection.

Hybrid three-phase HPF rectifier with programmable input current THD, using FPGA device and VHDL language

In this paper is proposed and analyzed a digital hysteresis modulation using a FPGA (Field Programmable Gate Array) device and VHDL (Hardware Description Language), applied at a hybrid three-phase rectifier with almost unitary input power factor, composed by parallel SEPIC controlled single-phase rectifiers connected to each leg of a standard 6-pulses uncontrolled diode rectifier. The digital control allows a programmable THD (Total Harmonic Distortion) at the input currents, and it makes possible that the power rating of the switching-mode converters, connected in parallel, can be a small fraction of the total average output power, in order to obtain a compact converter, reduced input current THD and almost unitary input power factor. Finally, the proposed digital control, using a FPGA device and VHDL, offers an important flexibility for the associated control technique, in order to obtain a programmable PFC (Power Factor Correction) hybrid three-phase rectifier, in agreement with the international standards (IEC, and IEEE), which impose limits for the THD of the AC (Alternate Current) line input currents. The proposed strategy is verified by experiments. © 2008 IEEE.

Una metodología eficiente para manejo de restricciones en algoritmos evolutivos multi-objetivo

This paper presents a new approach for solving constraint optimization problems (COP) based on the philosophy of lexicographical goal programming. A two-phase methodology for solving COP using a multi-objective strategy is used. In the first phase, the objective function is completely disregarded and the entire search effort is directed towards finding a single feasible solution. In the second phase, the problem is treated as a bi-objective optimization problem, turning the constraint optimization into a two-objective optimization. The two resulting objectives are the original objective function and the constraint violation degree. In the first phase a methodology based on progressive hardening of soft constraints is proposed in order to find feasible solutions. The performance of the proposed methodology was tested on 11 well-known benchmark functions.

Plant species identification using multi-scale fractal dimension applied to images of adaxial surface epidermis

This paper presents the study of computational methods applied to histological texture analysis in order to identify plant species, a very difficult task due to the great similarity among some species and presence of irregularities in a given species. Experiments were performed considering 300 ×300 texture windows extracted from adaxial surface epidermis from eight species. Different texture methods were evaluated using Linear Discriminant Analysis (LDA). Results showed that methods based on complexity analysis perform a better texture discrimination, so conducting to a more accurate identification of plant species. © 2009 Springer Berlin Heidelberg.

Coupling rate measurement of a novel multi-actuated piezoelectric device using optical interferometry

The class of piezoelectric actuators considered in this paper consists of a multi-flexible structure actuated by two or more piezoceramic devices that must generate different output displacements and forces at different specified points of the domain and in different directions. The devices were modeled by finite element using the software ANSYS and the topology optimization method. The following XY actuators were build to achieve maximum displacement in the X and Y directions with a minimum crosstalk between them. The actuator prototypes are composed of an aluminum structure, manufactured by using a wire Electrical Discharge Machining, which are bonded to rectangular PZT5A piezoceramic blocks by using epoxy resin. Multi-actuator piezoelectric device displacements can be measured by using optical interferometry, since it allows dynamic measurements in the kHz range, which is of the order of the first resonance frequency of these piezomechanisms. A Michelson-type interferometer, with a He-Ne laser source, is used to measure the displacement amplitudes in nanometric range. A new optical phase demodulation technique is applied, based on the properties of the triangular waveform drive voltage applied to the XY piezoelectric nanopositioner. This is a low-phase-modulation-depth-like technique that allows the rapid interferometer auto-calibration. The measurements were performed at 100 Hz frequency, and revealed that the device is linear voltage range utilized in this work. The ratio between the generated and coupled output displacements and the drive voltages is equal to 10.97 nm/V and 1.76 nm/V, respectively, which corresponds to a 16% coupling rate. © 2010 IEEE.

Evolutionary multi-move path-relinking for transmission network expansion planning

This paper presents the application of a new metaheuristic algorithm to solve the transmission expansion planning problem. A simple heuristic, using a relaxed network model associated with cost perturbation, is applied to generate a set of high quality initial solutions with different topologies. The population is evolved using a multi-move path-relinking with the objective of finding minimum investment cost for the transmission expansion planning problem employing the DC representation. The algorithm is tested on the southern Brazilian system, obtaining the optimal solution for the system with better performance than similar metaheuristics algorithms applied to the same problem. ©2010 IEEE.

Single-phase current-source-boost inverter for renewable energy sources

This paper presents a new methodology for the operation and control of a single-phase current-source (CS) Boost Inverter, considering that the conventional CS boost inverter has a right-half-plane (RHP) zero in its control-to-output transfer function, and this RHP zero causes the known non-minimum-phase effects. In this context, a special design with low boost inductance and a multi-loop control is developed in order to assure stable and very fast dynamics. Furthermore, the proposed inverter presents output voltage with very low total harmonic distortion (THD), reduced components and high power density. Therefore, this paper presents the inverter operation, the proposed control technique, the main simulation results and a prototype in order to demonstrate the feasibility of the proposal. © 2011 IEEE.

AC-DC three-phase multipulse converter with boost DC-DC stage and constant hysteresis control

This work proposes a new three-phase multipulse rectifier based on the delta autotransformer connection with DC-DC Boost stages and constant hysteresis control which has the objective of providing a reliable DC bus for on-board applications, electric motor drives and similars, always considering power quality issues. Thus, the proposal presents 0.99 power factor, 6% harmonic distortions in the currents from the mains and enhanced magnetic core utilization, which results in low weight and volume for the overall converter. The proposed control technique uses the simple constant hysteresis concept, thus leading to a low-cost but effective and reliable strategy. © 2011 IEEE.