404 research outputs found
Estimación de los parámetros de crecimiento del mero Epinephelus morio en la isla de Holbox Quintana Roo, México
Geochronology, Isotope Geochemistry and Petrogenesis of Tertiary Granitoids from Eastern Iran
Os granitóides sub-vulcânicos da zona de Chah-Shaljami fazem parte da faixa vulcânico-plutónica cenozóica do Bloco de Lut (Irão central-oriental). Tratam-se de quartzo-monzonitos, granodioritos e monzodioritos que, de acordo com a geoquÃmica de elementos maiores e vestigiais, são co-genéticos e têm caracterÃsticas de rochas calco-alcalinas ricas de potássio a shoshonÃticas, de ambiente de arco vulcânico. Numa amostra de quartzo-monzonito foi obtida uma idade Rb-Sr (rocha total - minerais) de 33.6±1 Ma; visto que esta amostra está praticamente livre de efeitos de alteração e que o arrefecimento foi provavelmente rápido, a idade de ~34 Ma deve corresponder à instalação magmática. Excepto em duas amostras, os valores iniciais de 87Sr/86Sr e εNd nos granitóides estudados estão concentrados nos intervalos de 0.7047 a 0.7051 e de +1.9 a +2.7, respectivamente, o que é consistente com uma fonte em cunha mantélica supra-subducção e indica que não houve contribuição crustal significativa na diversificação magmática; contudo, uma amostra tem (87Sr/86Sr)i superior e εNdt inferior, revelando que, ocasionalmente, a assimilação de rochas crustais também contribuiu para a variação geoquÃmica; uma outra amostra, fortemente afectada por alteração hidrotermal, afasta-se do grupo principal somente pelo relativamente elevado valor de (87Sr/86Sr)i, sugerindo que o processo hidrotermal envolveu fluidos crustais.Chah-Shaljami sub-volcanic granitoids belong to the Cenozoic volcanic-plutonic belt within the Lut Block (central eastern Iran). These intrusive rocks are mostly quartz monzonites, granodiorites and monzodiorites. Major and trace element geochemical evidence reveals that they are co-genetic and that they have features typical of high-K calc-alkaline to shoshonitic rocks from a volcanic arc setting. A Rb-Sr whole rock-mineral age of 33.6±1 Ma was obtained in a quartz monzonite sample; taking into account that this sample was almost unaffected by alteration and that cooling was probably fast, the ~34 Ma date is interpreted as the intrusion age. With the exception of two samples, initial 87Sr/86Sr ratios and εNd values of the studied granitoids are clustered in the restricted ranges from 0.7047 to 0.7051 and from +1.9 to +2.7, respectively, which fits into a supra-subduction mantle wedge source for the parental melts and indicates that, in general, crustal contribution for magma diversification was not relevant; however, one sample shows higher (87Sr/86Sr)i and lower εNdt, revealing that, occasionally, crustal rock assimilation also contributed to the geochemical variation; one other sample, strongly affected by hydrothermal alteration, departs from the main group only by higher (87Sr/86Sr)i, suggesting that its alteration involved crustal fluids
Diseño de un sistema automático de selección de frutos de café mediante técnicas de visión artificial
En el presente artÃculo se propone un sistema de visión artificial para la detección del fruto de café apto para producción. Para lograr esta detección se desarrollaron dos algoritmos, uno encargado de clasificar los frutos de café en maduros o no maduros, y otro que detecta la presencia de la plaga de la broca. Para el primero se extrajeron caracterÃsticas de color y se usó un clasificador bayesiano. Por otra parte, el algoritmo de detección de brocas busca zonas negras en la imagen, esto debido a que la evidencia dejada por esta plaga son orificios en la superficie del fruto. Además, se diseñó un sistema mecánico para el transporte de los frutos de café durante el proceso, y un mecanismo de extracción para separar los frutos, una vez estos sean clasificados por el algoritmo. Los resultados obtenidos mostraron una efectividad del 87%.In this Article, it is proposed a computer vision system, which can detect whether a coffee fruit is suitable for production
or not. In order to achieve this detection, two algorithms were developed, one to classify the coffee fruit in the ripe orunripe state, and the other to detect the presence of the ‘coffee berry borer’. The first one uses a Bayesian Classifier toidentify the color of the fruit, and the second algorithm searches for the holes made by the coffee berry borer on thesurface of the product. Moreover, a mechanical system was designed for the transportation and separation of the coffeefruits. In the first stage, coffees are transported as pictures of them are taken. At the end of this stage, the separationmechanism alters the path of the fruit based on the result of the classifier. The system proposed obtained aneffectiveness of 87%.
 
Diseño de un sistema automático de selección de frutos de café mediante técnicas de visión artificial
En el presente artÃculo se propone un sistema de visión artificial para la detección del fruto de café apto para producción. Para lograr esta detección se desarrollaron dos algoritmos, uno encargado de clasificar los frutos de café en maduros o no maduros, y otro que detecta la presencia de la plaga de la broca. Para el primero se extrajeron caracterÃsticas de color y se usó un clasificador bayesiano. Por otra parte, el algoritmo de detección de brocas busca zonas negras en la imagen, esto debido a que la evidencia dejada por esta plaga son orificios en la superficie del fruto. Además, se diseñó un sistema mecánico para el transporte de los frutos de café durante el proceso, y un mecanismo de extracción para separar los frutos, una vez estos sean clasificados por el algoritmo. Los resultados obtenidos mostraron una efectividad del 87%.In this Article, it is proposed a computer vision system, which can detect whether a coffee fruit is suitable for production
or not. In order to achieve this detection, two algorithms were developed, one to classify the coffee fruit in the ripe orunripe state, and the other to detect the presence of the ‘coffee berry borer’. The first one uses a Bayesian Classifier toidentify the color of the fruit, and the second algorithm searches for the holes made by the coffee berry borer on thesurface of the product. Moreover, a mechanical system was designed for the transportation and separation of the coffeefruits. In the first stage, coffees are transported as pictures of them are taken. At the end of this stage, the separationmechanism alters the path of the fruit based on the result of the classifier. The system proposed obtained aneffectiveness of 87%.
 
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Comparison of Microstructures and Mechanical Properties for Solid Cobalt-Base Alloy Components and Biomedical Implant Prototypes Fabricated by Electron Beam Melting
The microstructures and mechanical behavior of simple, as-fabricated, solid
geometries (with a density of 8.4 g/cm3), as-fabricated and fabricated and annealed
femoral (knee) prototypes all produced by additive manufacturing (AM) using electron
beam melting (EBM) of Co-26Cr-6Mo-0.2C powder are examined and compared in this
study. Microstructures and microstructural issues are examined by optical metallography,
SEM, TEM, EDS, and XRD while mechanical properties included selective specimen
tensile testing and Vickers microindentation (HV) and Rockwell C-scale (HRC) hardness
measurements. Orthogonal (X-Y) melt scanning of the electron beam during AM
produced unique, orthogonal and related Cr23C6 carbide (precipitate) cellular arrays with
dimensions of ~2μm in the build plane perpendicular to the build direction, while
connected carbide columns were formed in the vertical plane, parallel to the build
direction.Mechanical Engineerin
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Microstructure Architecture Development in Metals and Alloys By Additive Manufacturing Using Electron Beam Melting
The concept of materials with controlled microstructural architecture (MCMA) to
develop and fabricate structural materials with novel and possibly superior properties and
performance characteristics is a new paradigm or paradigm extension for materials science and
engineering. In the conventional materials science and engineering paradigm, structure
(microstructure), properties, processing, and performance features are linked in the development
of desirable materials properties and performance through processing methodologies which
manipulate microstructures. For many metal or alloy systems, thermomechanical treatment
combining controlled amounts of plastic deformation with heat treatment or aging cycles can
achieve improved mechanical properties beyond those attainable by conventional processing
alone (such as rolling or forging for example) through controlled microstructure development. In
this paper we illustrate a new concept involving the fabrication of microstructural architectures
by the process development and selective manipulation of these microstructures ideally defining
material design space. This allows for the additional or independent manipulation of material
properties by additive manufacturing (AM) using electron beam melting (EBM). Specifically we
demonstrate the novel development of a carbide (M23C6) architecture in the AM of a Co-base
alloy and an oxide (Cu2O) precipitate-dislocation architecture in the AM of an oxygen-containing Cu. While more conventional processing can produce various precipitate
microstructures in these materials, EBM produces spatial arrays of precipitate columns or
columnar-like features often oriented in the build direction. These microstructural architectures
are observed by optical microscopy and scanning and transmission electron microscopy.
Prospects for EBM architecture development in precipitation-hardenable Al alloys is also
discussed. In the EBM build process using precursor powders, the electron beam parameters
(including beam focus, scan speed and sequencing) produce localized, requisite thermodynamic
regimes which create or organize the precipitate-related spatial arrays. This feature demonstrates
the utility of AM not only in the fabrication of complex components, but also prospects for
selective property design using CAD for MCMA development: a new or extended processing-microstructure-property-performance paradigm for materials science and engineering in
advanced manufacturing involving solid free-form fabrication (SFF).Mechanical Engineerin
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Effect of Build Parameters and Build Geometries on Residual Microstructures and Mechanical Properties of Ti-6Al-4V Components Built by Electron Beam Melting (EBM)
In this study, involving additive manufacturing (AM) using electron beam melting (EBM), we
have examined build defects which result from beam tripping, porosities (including unmelted or
unsintered zones) due to excursions from optimal build parameters (especially variations in melt
scan beam current and scan speed), and gas bubbles trapped in atomized Ti-6Al-4V starting
powder as well as recycled powder, and retained in the build. At optimized build conditions we
have also examined microstructure-mechanical property (hardness, tensile strength, and
elongation) variations for multiple rake building and multiple melt scans using optical
metallography and scanning and transmission electron microscopy (SEM and TEM). These
build variances cause cooling rate variances which promote α-phase growth and variations in
dislocation density, as well as α-to-α' (martensite) phase changes, all of which produce some
degree of mechanical property variations. These features (especially α-to-α' phase changes) are
notable on comparing solid builds in comparison with a variety of mesh arrays where strut
dimension and build-element complexities alter the cooling rates in a significant way. We
illustrate these microstructure variations with corresponding variations in microindentation
hardness measurements made directly on fine mesh (strut) structures. Finally, we have examined
Ti-6Al-4V powder chemistries and solid build chemistries which for single-pass melt scans at
optimized build conditions are shown to be relatively constant up to 40 cycles of powder reuse
with the exception of Al content which was reduced by 10 to 15% in solid builds at optimized
conditions. However, Al loss in solid builds approached 25% for multiple (2 and 3) melt scans,
while no changes in Ar gas-bubble density were observed with changes in α-phase (grain) width
which increased from 3 µm for a single melt scan to 4.5 and 6 µm for 2 and 3 melt scans,
respectively. Corresponding Rockwell C-scale (HRC) hardness varied from 37, 36, and 35,
respectively; with ultimate tensile strengths exceeding 1.2 GPa at elongations of 12% or higher
for this melt scan sequence.Mechanical Engineerin
Higher order contributions to the effective action of N=2 super Yang-Mills
We apply heat kernel techniques in N=1 superspace to compute the one-loop
effective action to order for chiral superfields coupled to a non-Abelian
super Yang-Mills background. The results, when combined with those of
hep-th/0210146, yield the one-loop effective action to order for any N=2
super Yang-Mills theory coupled to matter hypermultiplets.Comment: 23 pages, references adde
Enhancing flame flashback resistance against Combustion Induced Vortex Breakdown and Boundary Layer Flashback in swirl burners
Swirl combustors have proven to be effective flame stabilisers over a wide range of operation conditions thanks to the formation of well-known swirl coherent structures. However, their employment for lean premixed combustion modes while introducing alternative fuels such as high hydrogenated blends results in many combustion instabilities. Under these conditions, flame flashback is considered one of the major instability problems that have the potential of causing considerable damage to combustion systems hardware in addition to the significant increase in pollutant levels. Combustion Induced Vortex Breakdown is considered a very particular mode of flashback instability in swirling flows as this type of flashback occurs even when the fresh mixture velocity is higher than the flame speed, a consequence of the interaction between swirl structures and swirl burner geometries. Improvements in burner geometries and manipulation of swirling flows can increase resistance against this type of flashback. However, increasing resistance against Combustion Induced Vortex Breakdown can lead to augmentation in the propensity of another flashback mechanism, Boundary Layer Flashback. Thus, this paper presents an experimental approach of a combination of techniques that increase Combustion Induced Vortex Breakdown resistance, i.e. by repositioning a central injector and using central air injection, while simultaneously avoiding Boundary Layer Flashback, i.e. by changing the wall boundary layer characteristics using microsurfaces on the nozzle wall. Results show that using these techniques together has promising potentials regarding wider stable operation for swirl combustors, enabling them to burn a broader variety of fuel blends safely, while informing developers of the improvements obtained with the combined techniques
Slow relaxation due to optimization and restructuring: Solution on a hierarchical lattice
Motivated by the large strain shear of loose granular materials we introduced
a model which consists of consecutive optimization and restructuring steps
leading to a self organization of a density field. The extensive connections to
other models of statistical phyics are discussed. We investigate our model on a
hierarchical lattice which allows an exact asymptotic renormalization
treatment. A surprisingly close analogy is observed between the simulation
results on the regular and the hierarchical lattices. The dynamics is
characterized by the breakdown of ergodicity, by unusual system size effects in
the development of the average density as well as by the age distribution, the
latter showing multifractal properties.Comment: 11 pages, 7 figures revtex, submitted to PRE see also:
cond-mat/020920
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