2,314 research outputs found
Classification of peacock feather reflectance using principal component analysis similarity factors from multispectral imaging data
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Iridescent structural colors in biology exhibit sophisticated spatially-varying reflectance properties that depend on both the illumination and viewing angles. The classification of such spectral and spatial information in iridescent structurally colored surfaces is important to elucidate the functional role of irregularity and to improve understanding of color pattern formation at different length scales. In this study, we propose a non-invasive method for the spectral classification of spatial reflectance patterns at the micron scale based on the multispectral imaging technique and the principal component analysis similarity factor (PCASF). We demonstrate the effectiveness of this approach and its component methods by detailing its use in the study of the angle-dependent reflectance properties of Pavo cristatus (the common peacock) feathers, a species of peafowl very well known to exhibit bright and saturated iridescent colors. We show that multispectral reflectance imaging and PCASF approaches can be used as effective tools for spectral recognition of iridescent patterns in the visible spectrum and provide meaningful information for spectral classification of the irregularity of the microstructure in iridescent plumage.This research was developed during a visiting research stay of Dr. JosĂ© M. Medina in the Departamento de Ă“ptica, Universidad de Granada, Spain. We thank to JosĂ© Medina and RosalĂa Ruiz who provided the peacock samples, to David Porcel and Juan de Dios Bueno from the Servicio de MicroscopĂa, (Centro de InstrumentaciĂłn CientĂfica, Universidad de Granada) for technical assessment, and to the Color Imaging Group (Universidad de Granada) for their hardware partial support. JMM and JAD acknowledge the Departmento de Ă“ptica, Universidad de Granada, Spain. PV acknowledges USAF funding (FA9550-10-1-0020)
An evolutionary approach to the delimitation of labour market areas: an empirical application for Chile
An evolutionary approach to the delimitation of labour market areas: an empirical application for Chile. Spatial Economic Analysis. Labour market areas (LMAs) are argued to represent a more appropriate policy framework than administrative units for the analysis of spatial labour market activity. This article develops LMAs for Chile by applying an evolutionary computation approach. This innovative approach defines LMAs through an optimization process by maximization of internal cohesion, subject to restrictions of minimum levels of self-containment and population. To evaluate the appropriateness of the LMAs, comparative analyses are performed between alternative delimitations based on different parameter configurations of the proposed method versus administrative boundaries and the most widely used method for official LMA delimitation, the travel-to-work areas method
Influence of charging conditions on simulated temperature-programmed desorption for hydrogen in metals
Failures attributed to hydrogen embrittlement are a major concern for metals
so a better understanding of damage micro-mechanisms and hydrogen diffusion
within the metal is needed. Local concentrations depend on transport phenomena
including trapping effects, which are usually characterised by a
temperature-programmed desorption method often referred to as Thermal
Desorption Analysis (TDA). When the hydrogen is released from the specimen
during the programmed heating, some desorption peaks are observed that are
commonly related to detrapping energies by means of an analytical procedure.
The limitations of this approach are revisited here and gaseous hydrogen
charging at high temperatures is simulated. This popular procedure enables
attaining high concentrations due to the higher solubility of hydrogen at high
temperatures. However, the segregation behaviour of hydrogen into traps depends
on charging time and temperature. This process and the subsequent cooling alter
hydrogen distribution are numerically modelled; it is found that TDA spectra
are strongly affected by the charging temperature and the charging time, both
for weak and strong traps. However, the influence of ageing time at room
temperature after cooling and before desorption is only appreciable for weak
traps
Cold Isostatic Pressing to Improve the Mechanical Performance of Additively Manufactured Metallic Components.
Additive manufacturing is becoming a technique with great prospects for the production of components with new designs or shapes that are difficult to obtain by conventional manufacturing methods. One of the most promising techniques for printing metallic components is binder jetting, due to its time efficiency and its ability to generate complex parts. In this process, a liquid binding agent is selectively deposited to adhere the powder particles of the printing material. Once the metallic piece is generated, it undergoes a subsequent process of curing and sintering to increase its density (hot isostatic pressing). In this work, we propose subjecting the manufactured component to an additional post-processing treatment involving the application of a high hydrostatic pressure (5000 bar) at room temperature. This post-processing technique, so-called cold isostatic pressing (CIP), is shown to increase the yield load and the maximum carrying capacity of an additively manufactured AISI 316L stainless steel. The mechanical properties, with and without CIP processing, are estimated by means of the small punch test, a suitable experimental technique to assess the mechanical response of small samples. In addition, we investigate the porosity and microstructure of the material according to the orientations of layer deposition during the manufacturing process. Our observations reveal a homogeneous distribution independent of these orientations, evidencing thus an isotropic behaviour of the material
Analysis of hydrogen permeation tests considering two different modelling approaches for grain boundary trapping in iron
The electrochemical permeation test is one of the most used methods for
characterising hydrogen diffusion in metals. The flux of hydrogen atoms
registered in the oxidation cell might be fitted to obtain apparent
diffusivities. The magnitude of this coefficient has a decisive influence on
the kinetics of fracture or fatigue phenomena assisted by hydrogen and depends
largely on hydrogen retention in microstructural traps. In order to improve the
numerical fitting of diffusion coefficients, a permeation test has been
reproduced using FEM simulations considering two approaches: a continuum 1D
model in which the trap density, binding energy and the input lattice
concentrations are critical variables and a polycrystalline model where
trapping at grain boundaries is simulated explicitly including a segregation
factor and a diffusion coefficient different from that of the interior of the
grain. Results show that the continuum model captures trapping delay, but it
should be modified to model the trapping influence on the steady state flux.
Permeation behaviour might be classified according to different regimes
depending on deviation from Fickian diffusion. Polycrystalline synthetic
permeation shows a strong influence of segregation on output flux magnitude.
This approach is able to simulate also the short-circuit diffusion phenomenon.
The comparison between different grain sizes and grain boundary thicknesses by
means of the fitted apparent diffusivity shows the relationships between the
registered flux and the characteristic parameters of traps
Pre-notched dog bone small punch specimens for the estimation of fracture properties
In recent years, the pre-notched or pre-cracked small punch test (P-SPT) has
been successfully used to estimate the fracture properties of metallic
materials for cases in which there is not sufficient material to identify these
properties from standard tests, such as CT or SENB specimens. The P-SPT
basically consists of deforming a pre-notched miniature specimen, whose edges
are firmly gripped by a die, using a high strength punch. The novelty of this
paper lies in the estimation of fracture properties using dog-bone-shaped
specimens with different confinement levels. With these specimens, three
confinement variations have been studied. The results obtained enable the
establishment of a variation of fracture properties depending on the level of
confinement of each miniature specimen and selection of the most appropriate
confinement for this goal
Trajectory Planning Under Time-Constrained Communication
In the present paper we address the problem of trajectory planning for scenarios in which some robot has to exchange information with other moving robots for at least a certain time, determined by the amount of information. We are particularly focused on scenarios where a team of robots must be deployed, reaching some locations to make observations of the environment. The information gathered by all the robots must be shared with an operation center (OP), thus some robots are devoted to retransmit to the OP the data of their teammates. We develop a trajectory planning method called Time-Constrained RRT (TC-RRT). It computes trajectories to reach the assigned primary goals, but subjected to the constraint determined by the need of communicating with another robot acting as moving relay, just during the time it takes to fulfill the data exchange. Against other methods in the literature, using this method it is not needed a task allocator to assign beforehand specific meeting points or areas for communication exchange, because the planner finds the best area to do it, simultaneously minimizing the time to reach the goal. Evaluation and limitations of the technique are presented for different system parameters
An overview of the lower cretaceous dinosaur tracksites from the mirambel formation in the iberian range (ne spain)
Up to now, the ichnological vertebrate record from the Barremian Mirambel Formation (NE Spain) has remained completely unknown despite the fact that osteological findings have been reported in recent years. Here we provide an overview of 11 new dinosaur tracksites found during a fieldwork campaign in the year 2011. The majority of these tracksites (seven) preserve small- to medium-sized tridactyl tracks here assigned to indeterminate theropods. Only one footprint presents enough characters to classify it as Megalosauripus isp. Ornithopod tracks identified as Caririchnium isp. and Iguanodontipodidae indet. and sauropod tracks are recorded at two tracksites. The footprints are preserved in a variety of paleoenvironmental conditions and thus display different kinds of preservation (true tracks, shallow undertracks, natural casts and undertrack casts). The ichnological record from the Mirambel Formation seems to be theropod dominated. This is a clear discrepancy with the osteological record identified in this formation, which shows a predominance of ornithopod dinosaurs
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