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Selective Laser Melting (SLM) is an extremely versatile technology especially suited for the manufacturing of thin-walled parts. Micro-sized parts are highly influenced and dependent on the SLM processing parameters; thus being indispensable to assess the influence of processing parameters on SLM fabrication, as isolated parameters but also their interactions. In this study, the influence of SLM laser power and scanning speed on Ti6Al4V micro-pillars and micro-plates thickness was assessed by applying response surface methodology (RSM). These analyses resulted in four models that exhibit complex correlations of SLM process parameters, with non-linear equations, having coefficients of determination that assess the quality of the models. These developed models are accurate tools that can be used to optimize the micro manufacture of Ti6A14V thin-walled parts by SLM., This work is supported by FCT - Fundacao para a Ciencia e a Tecnologia through the grant SFRH/BPD/112111/2015 and the projects PTDC/EMS-TEC/5422/2014 and NORTE-01-0145-FEDER-000018-HAMaBICo. Additionally, this work is supported by FCT with the reference project UID/EEA/04436/2013, by FEDER funds through the COMPETE 2020 - Programa Operational Competitividade e Internacionalizacao (POCI) with the reference project POCI-01-0145-FEDER-006941.

Using neural networks as a prediction method, we attempt to demonstrate that forecasting of the Sun’s sunspot time series can be extended to the spatio-temporal case. We employ this machine-learning method to forecast not only in time but also in space (in this case, latitude) on a spatio-temporal dataset representing the solar sunspot diagram extending to a total of 142 years. The analysis shows that this approach seems to be able to reconstruct the overall qualitative aspects of the spatial-temporal series, namely the overall shape and amplitude of the latitude and time pattern of sunspots. This is, as far as we are aware, the first time that neural networks have been used to forecast the Sun’s sunspot butterfly diagram, and although the results are limited in the quantitative prediction aspects, it points to the way to use the full spatio-temporal series as opposed to just the time series for machine-learning approaches to forecasting. Additionally, we use the method to predict that the upcoming Cycle 25 maximum sunspot number will be around $R_{25}=57 \pm17$ . This implies a very weak cycle and, in fact, the weakest cycle on record.

SLM accuracy for fabricating porous materials is a noteworthy hindrance when aiming to obtain biomaterial cellular structures owing precise geometry, porosity, open-cells dimension and mechanical properties as outcomes. This study provides a comprehensive characterization of seventeen biomaterial Ti6Al4V-based structures in which experimental and numerical investigations (compression stress-strain tests) were carried out. Mono-material Ti6Al4V cellular structures and multi-material Ti6Al4V-PEEK cellular structures were designed, produced by SLM and characterized targeting orthopedic implants. In this work, the differences between the CAD design and the as-produced Ti6Al4V-based structures were obtained from image analysis and were used to develop predictive models. The results showed that dimensional deviations inherent to SLM fabrication are systematically found for different dimensional ranges. The present study proposes several mathematical models, having high coefficients of determination, that estimate the real dimensions, porosity and elastic modulus of Ti6Al4V-based cellular structures as function of the CAD model. Moreover, numerical analysis was performed to estimate the octahedral shear strain for correlating with bone mechanostat theory limits. The developed models can help engineers to design and obtain near-net shape SLM biomaterials matching the desired geometry, open-cells dimensions, porosity and elastic modulus. The obtained results show that by using these AM structures design it is possible to fabricate components exhibiting a strain and elastic modulus that complies with that of bone, thus being suitable for orthopedic implants., This work was supported by FCT (Fundacao para a Ciencia e a Tecnologia) through the grant SFRH/BD/128657/2017, the projects PTDC/EMS-TEC/5422/2014ADAPTPROSTHESIS, POCI-01-0145-FEDER-030353 (SMARTCUT), NORTE 010145_FEDER-000018-HAMaBICo and UID/EEA/04436/2019.

著者人数: 105名 (所属. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS): 鈴木, 大介), Number of authors: 105 (Affiliation. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS): Suzuki, Daisuke), Accepted: 2019-07-03, 資料番号: SA1190108000

In 2020, the Geophysical and Astronomical Observatory of the University of Coimbra will celebrate the 95th anniversary of its first spectroheliographic observation. Keeping a daily service of solar observations since then, making almost a century, led to one of the largest continuous solar data collections in the world. This long–term solar database is essential for studies where solar activity is involved. This work reviews the development of synoptic observations made at the Observatory of Coimbra since 1925 and presents a summary of some of the principal stages of the Observatory’s history since its founding in 1772. We refer the main technical improvements and present some perspectives for the near future. One of the most significant upgrades was the installation of a CCD camera in 2007. The transition from photographic emulsion to digital recording methods allowed the development of image analysis algorithms to process solar images and improved data sharing with other institutions. This upgrade enabled also to carry–out modern climate and space weather studies. This valuable advancement makes it possible to create a new catalogue of solar observations to be published in the future.

This study presents experimental and numerical results of a development prototype tool that includes blank-holder plates of variable stiffness. The application is analyzed for high-strength steel parts and tailor welded blanks manufactured from dissimilar steel grades using laser welding. A numerical model was constructed within the Ansys software platform incorporating appropriate material constitutive models parameters for high-strength Dual-Phase steels. The obtained results show a positive control of springback geometries. Experimental tests were performed on the relevant geometries. The presented numerical and experimental results constitute a validation of a variable-stiffness blank-holder approach for this particular case study., The funding support from Project I&DT AdvancedTOOLING CENTRO-01-0247- FEDER-011399 is acknowledged.

In this study the crashworthy performance of an ultimate safety toe cap model made of high-strength steel was evaluated. The structural response to impact loading conditions under normative requirements was properly related to the potential of light weight design for a significant thickness reduction. Two grades of fully martensitic steels were selected and numerical models modelling extensive plastic deformation and strain-rate dependence were performed. The mathematical description of the impact behaviour with the correlation of crashworthy properties was analysed and compared by applying two fundamental constitutive models: The Cowper-Symonds and Johnson-Cook constitutive equations. Experimental results of tensile testing at different strain rates and different directions of the sheet material were used to determine fundamental constitutive parameters for both steel alloys. The numerical simulation developed using an explicit dynamics software (ANSYS) was extensively compared to an experimental standard testing program of final prototypes. A local stiffening toe cap model with high energy absorption efficiency was also validated., The support from the Project S3 - Safety Slim Shoe, FCOMP-01-0202-FEDER-018458 with ICC-Lavoro is acknowledged. The authors would like to thank SSAB for supplying the steel sheets and for technical support during the prototype forming process., info:eu-repo/semantics/publishedVersion

The Astronomical Observatory of the University of Coimbra has a huge collection of solar images, acquired daily since 1926. From the beginning, only spectroheliograms in the CaiiK line has been recorded, and since 1989 in the H_alpha line also. Such dataset requires efficient tools to detect and analyze solar activity features. The objective of this work is to create a tool that allows to automatic detect sunspots, umbra, and penumbra, that can be applied to the entire dataset. To achieve this, two different approaches have been developed, one based on mathematical morphology and another based on the intensities of the digital levels of the pixels. Both approaches were applied to a subset of images with features identified visually by an experimented solar observer. The performance of both methods was compared through the metrics Precision, Recall and F-score. Another evaluation was made based on the catalogs from Heliophysics Features Catalog and the SILSO catalogue., Comment: submitted to Astronomy and Computing

This paper addresses the design of beams with web openings. The Vierendeel bending design procedures are described, and the related numerical equations are given. An automatic calculation model, for sections design is briefly described, and an input and output flowchart is also presented.

Auxetics are characterized by a negative Poisson’s ratio, expanding/contracting in tension/compression. Given this behavior, they are expected topossess high shear, fracture and indentation resistance, and superior damping. The lack of natural isotropic auxetics promoted an effort to designstructures that mimic this behavior, e.g. reentrant model. This last is based on honeycombs with inverted protruding ribs. Commonly, this modelis employed in lattices and has been thoroughly studied in terms of mechanical properties and deformation behavior. Given that the amount ofcells has an influence in the overall internal structural behavior, there seems to be an absence of data that determines the minimum number of cellsfor such structure to present internal static bulk properties. Recurring to FEA, this study determines the minimum number of cells to obtain anoverall face constrained auxetic lattice with internal bulk elastic behavior, namely in terms of normalized Young’s modulus and Poisson’s ratio. Itis shown that adding reentrant cells increases the Poisson’s ratio on an exponential rise to maximum function, reducing the normalized Young’smodulus on an exponential decay function. Fundamentally, a minimum number of 13 cells per row to obtain an internal bulk behavior in latticeswith constrained faces., Supported by the project iRAIL Innovation in Railway Systems and Technologies Doctoral Programme funds and by national funds through FCT – Portuguese Foundation for Science and Technology and was developed on the aim of the Doctoral grant PD/BD/114096/2015.

The present study proposes a dynamic constitutive material interface model that includes non-associated flow rule and high strain rate effects, implemented in the finite element code ABAQUS as a user subroutine. First, the model capability is validated with numerical simulations of unreinforced block work masonry walls subjected to low velocity impact. The results obtained are compared with field test data and good agreement is found. Subsequently, a comprehensive parametric analysis is accomplished with different joint tensile strengths and cohesion, and wall thickness to evaluate the effect of the parameter variations on the impact response of masonry walls.

info:eu-repo/semantics/publishedVersion

This data paper presents lightcurves of 101 near Earth asteroids (NEAs) observed mostly between 2014 and 2017 as part of the EURONEAR photometric survey using 11 telescopes with diameters between 0.4 and 4.2 m located in Spain, Chile, Slovakia and Romania. Most targets had no published data at the time of observing, but some objects were observed in the same period mainly by B. Warner, allowing us to confirm or improve the existing results. To plan the runs and select the targets, we developed the public Long Planning tool in PHP. For preliminary data reduction and rapid follow-up planning we developed the LiDAS pipeline in Python and IRAF. For final data reduction, flux calibration, night linkage and Fourier fitting, we used mainly MPO Canopus. Periods of 18 targets are presented for the first time, and we could solve or constrain rotation for 16 of them. We secured periods for 45 targets ( $$U\sim 3$$ ), found candidate periods for other 16 targets ( $$U\sim 2$$ ), and we propose tentative periods for other 32 targets ( $$U\sim 1$$ ). We observed 7 known or candidate binary NEAs, fiting 3 of them (2102 Tantalus, 5143 Heracles and 68348). We observed 8 known or candidate tumbling NEAs, deriving primary periods for 3 objects (9400, 242708 and 470510). We evidenced rapid oscillations (few minutes) and could fit fast tentative periods TP2 for 5 large newly suggested tumbling or binary candidates (27346, 112985, 285625, 377732, 408980), probably discovering at least one new binary NEA (2011 WO41). We resolved periods of 4 special objects which include two proposed space mission targets (163249 and 101955 Bennu), one very fast rotator NEA discovered by EURONEAR (2014 NL52) and the “Halloween asteroid” (2015 TB145). Using Mercator in simultaneous 3 band MAIA imaging, we could evidence for the first time clear variation in the color lightcurves of 10 NEAs. The periods derived from the g–r color lightcurves are found to match individual band period fits for 4 NEAs (27346, 86067, 112985 and 275976).

Context. The so-called Barbarian asteroids share peculiar, but common polarimetric properties, probably related to both their shape and composition. They are named after (234) Barbara, the first on which such properties were identified. As has been suggested, large scale topographic features could play a role in the polarimetric response, if the shapes of Barbarians are particularly irregular and present a variety of scattering/incidence angles. This idea is supported by the shape of (234) Barbara, that appears to be deeply excavated by wide concave areas revealed by photometry and stellar occultations. Aims. With these motivations, we started an observation campaign to characterise the shape and rotation properties of Small Main-Belt Asteroid Spectroscopic Survey (SMASS) type L and Ld asteroids. As many of them show long rotation periods, we activated a worldwide network of observers to obtain a dense temporal coverage. Methods. We used light-curve inversion technique in order to determine the sidereal rotation periods of 15 asteroids and the convergence to a stable shape and pole coordinates for 8 of them. By using available data from occultations, we are able to scale some shapes to an absolute size. We also study the rotation periods of our sample looking for confirmation of the suspected abundance of asteroids with long rotation periods. Results. Our results show that the shape models of our sample do not seem to have peculiar properties with respect to asteroids with similar size, while an excess of slow rotators is most probably confirmed.© 2017 ESO., N.P. acknowledges funding from the Portuguese FCT - Foundation for Science and Technology. CI-TEUC is funded by National Funds through FCT - Foundation for Science and Technology (project: UID/ Multi/00611/2013) and FEDER - European Regional Development Fund through COMPETE 2020 - Operational Programme Competitiveness and Internationalisation (project: POCI-01-0145-FEDER-006922). SARA observations were obtained under the Chilean Telescope Allocation Committee program CNTAC 2015B-4. P.H. acknowledges financial support from the Natural Sciences and Engineering Research Council of Canada, and thanks the staff of Cerro Tololo Inter-American Observatory for technical support. The work of A.M. was supported by grant no. 2014/13/D/ST9/01818 from the National Science Centre, Poland. The research of V.K. is supported by the APVV-15-0458 grant and the VVGS-2016-72608 internal grant of the Faculty of Science, P.J. Safarik University in Kosice. M.K. and O.E. acknowledge TUBITAK National Observatory for a partial support in using T100 telescope with project number 14BT100-648.

A widespread application of composite materials requires proper knowledge of both static and dynamic loading properties, particularly for automotive and transportation applications. In this study the behavior of unidirectional glass fiber reinforced polymeric composites under uniaxial loading is determined at quasi-static and intermediate strain rates in the range 0.6–500/s. The tensile tests were performed using different servo-hydraulic testing apparatus. Dynamic tests results are compared with the results of static tensile tests carried out on specimens with identical geometry. Experimental results show a significant increase of the tensile strength with increasing strain rate. The strain to failure is also observed to increase slightly for higher strain rates.

The compressive properties of open-cell aluminum foams are numerically studied using representative volume elements by means of the finite element method. Four face body centered cubic cell arrangements are analyzed, namely uniform-size with spherical pores and dual-size with spherical pores. The results demonstrated that a cell configuration with dual-size pore arrangement presents improved properties for applications subjected to compression loading. This is attributed to the introduction of secondary pores in the cell structure that provide an increase in the specific stiffness and strength of open-cell aluminum foams.

This study presents results regarding a numerical simulation of the plastic displacement of a road guardrail. An experimental study of two different guardrails was conducted in order to collect information regarding displacement due to a determined force behavior. These tests were then simulated in Ansys Workbench to recreate the elastic and plastic domain of the material. The guardrails are two meters long, supported by two simple cylinders while being pressed at the center by a third one. In order to explore the software two different mesh sizes were used to compare their efficiency, being concluded with the comparison between the force-displacement curves of numerical and experimental results.

This study presents experimental results on the behavior of aluminum alloy metal foams with controlled pore morphology in compression. Two types of metal foams were analyzed, having uniform cell structure and with a dual-size cell arrangement seeking optimized mechanical properties. The structures were manufactured by lost-wax casting using 3D printed components for internal structure definition. Results for stiffness and energy absorption were obtained and compared on weight efficiency basis. The results are indicative of higher efficiency of the dual-size structures that may be considered for use in components subjected to impact or compression loading.

Geometrical changes can improve stiffness substantially. The project S3 - Safety Slim Shoe presents the potential to reduce the weight in safety toe cap components combining a new geometric redesign deeply associated to local stiffeners to realize the full potential of AHSS - Advanced High Strength Steels. The investigation aimed to examine the potential energy absorption capacity for a substantial thickness reduction of slim toe cap models. In this paper the normative quasi-static compression test in the context of the experimental validation of the two last and approved prototype models were focused. A non-linear FEA - Finite Element Analysis of the elasto-plastic deformation mode was performed, and several numerical parameters such as: hardening effects of extrapolated True-Stress-Strain material curves and simulation convergence conditions were carried out. Experimental results of the toe cap deformation behavior confront a weight saving range of over 40%, compared with the original steel toe cap. The safety footwear, in the context of the global evolution of footwear, has adopted creative and different orientations. Particularly, as an active element in the prevention of accidents fitted in PPE - Personal Protective Equipment, it is appropriate that its optimization solutions amplify the market targets, mainly combining ergonomic aspects, biological and mechanical features since its conception. The toe cap is the main component for its weight contribution, approx. 35% of total weight for each safety footwear model, and due normative context demands with high deformation resistance and impact loading (1). Currently the toe cap protection takes a subdivided position on design selection and materials, with a clear definition of two distinctive conception trends: metallic and non-metallic models. If on one hand the metallic models, especially high carbon steels with Heat Treatment processes, emphasize the security concept by the implicit mechanical strength performance, on the other hand, the weight of these solutions is a disadvantage compared to the metal-free solutions, and relegates the first one for outdated and heavier footwear concept. The non-metallic solutions with higher trend effects in the global market call on low density materials such as: reinforced Polyester composites with glass fiber, HDPE - High Strength Polyethylene, and several advanced developments in the optimization of energy

This study presents an alternative approach for the absorption of impact energy that uses the internal pressurization of structures in the framework of a crash-adaptive response. Numerical simulations were conducted on axial impact of thin-walled tubular structures with circular cross section that serve as an approximation to a front crash box of a motor vehicle. The main objective of this work consists in studying the effect of internal pressurization of tubular structures in a crashworthiness application, as well as the possibility to obtain a reduction in wall thickness thus improving weight efficiency. A numerical study is presented for an internal pressure of 20 bar and tubular structures of circular section and 1.14 mm thickness. Numerical simulations were performed recurring to LS-DYNA explicit dynamics software while considering for the material a stainless steel alloy that is a material with interest for crashworthiness applications and manufacturing requisites due to its balance between strength, ductility and energy absorption. The results obtained allow concluding that recurring to internal pressurization it is feasible to reduce the wall thickness and have an impact resistance identical to the original while improving overall efficiency.

The aim of this study is to present a sensitivity analysis of geometric variables on the mechanical behavior of regular cellular solids. The cellular solids studied are named “spherical” and “elliptical”, if there is part of an empty sphere inside or if there is part of an empty revolved ellipse, respectively. Pure loads are applied separately, namely compression and shear, in order to study the influence of the variables on axial stress and axial displacement (compression) and shear stress and shear strain on shear. The sensitivity analysis is useful to establish limits for the studied variables in an optimization process and to know the influence of the variables on the results. In the case that a variable has little or no influence on the results; it must be evaluated if it is worth using it. In this work, the influence of two geometric variables, namely stacking and radius were studied for two types of regular cellular solids. The solids are composed by 7*7*7 base cells. The maximum axial stress and axial displacement were measured on compression for each model. On shear, the maximum shear stress and the maximum shear strain on the plane that is sensitive to the variation of the studied variable were taken. Three models were studied in each case. The influence of the studied geometric variables on the results are presented and discussed. It is found that all the variables have influence on the results, although in a different manner. (Abstract) KeywordsFEM;Optimization;Periodic Cellular solids;Sensitivity analysis;Optimization cellular solids

Simultaneous observations of microlensing events from multiple locations allow for the breaking of degeneracies between the physical properties of the lensing system, specifically by exploring different regions of the lens plane and by directly measuring the "microlens parallax". We report the discovery of a 30-55$M_J$ brown dwarf orbiting a K dwarf in microlensing event OGLE-2015-BLG-1319. The system is located at a distance of $\sim$5 kpc toward the Galactic bulge. The event was observed by several ground-based groups as well as by $Spitzer$ and $Swift$, allowing the measurement of the physical properties. However, the event is still subject to an 8-fold degeneracy, in particular the well-known close-wide degeneracy, and thus the projected separation between the two lens components is either $\sim$0.25 AU or $\sim$45 AU. This is the first microlensing event observed by $Swift$, with the UVOT camera. We study the region of microlensing parameter space to which $Swift$ is sensitive, finding that while for this event $Swift$ could not measure the microlens parallax with respect to ground-based observations, it can be important for other events. Specifically, for detecting nearby brown dwarfs and free-floating planets in high magnification events., 28 pages, 6 figures, 2 tables. Submitted to ApJ

(abridged) Context. Wide binaries are a potential pathway for the formation of hot Jupiters. The binary fraction among host stars is an important discriminator between competing formation theories, but has not been well characterised. Additionally, contaminating light from unresolved stars can significantly affect the accuracy of photometric and spectroscopic measurements in studies of transiting exoplanets. Aims. We observed 101 transiting exoplanet host systems in the Southern hemisphere in order to create a homogeneous catalogue of both bound companion stars and contaminating background stars. We investigate the binary fraction among the host stars in order to test theories for the formation of hot Jupiters, in an area of the sky where transiting exoplanetary systems have not been systematically searched for stellar companions. Methods. Lucky imaging observations from the Two Colour Instrument on the Danish 1.54m telescope at La Silla were used to search for previously unresolved stars at small angular separations. The separations and relative magnitudes of all detected stars were measured. For 12 candidate companions to 10 host stars, previous astrometric measurements were used to evaluate how likely the companions are to be physically associated. Results. We provide measurements of 499 candidate companions within 20 arcseconds of our sample of 101 planet host stars. 51 candidates are located within 5 arcseconds of a host star, and we provide the first published measurements for 27 of these. Calibrations for the plate scale and colour performance of the Two Colour Instrument are presented. Conclusions. We find that the overall multiplicity rate of the host stars is 38 +17 -13%, consistent with the rate among solar-type stars in our sensitivity range, suggesting that planet formation does not preferentially occur in long period binaries compared to a random sample of field stars., 19 pages, 9 figures. Accepted in A&A. Minor correction

The study of axial loading is essential to determine the properties of intervertebral disc. The objectives of this work are (1) to quantify the mechanical properties of porcine lumbar intervertebral discs under static and cyclic compressive loading, and (2) to determine the parameters of a five-parameter rheological model for porcine and compare them with those obtained for human lumbar intervertebral discs.Thus, the porcine lumbar motion segments were subjected to quasi-static and dynamic compression tests. The quasi-static tests were used to obtain the static stiffness coefficient at different strain rates, while the data from the cyclic compressive tests were used to both determine the dynamic stiffness coefficient and to be fitted in a 5-parameter model, in order to simulate the creep response of the porcine intervertebral discs.The results demonstrated that dynamic stiffness coefficient of porcine discs is between four and ten times higher than the static stiffness coefficient, depending on load applied. The parameters of the rheological model suggested a low permeability of nucleus and endplate during the fast response of porcine discs. In addition, the fast response in terms of displacement is four times higher than those documented for human discs.This study revealed that care must be taken on the comparison between porcine and human discs, since they present different behaviour under quasi-static and dynamic compressive loading.

Artificial light at night (ALAN), producing light pollution (LP), is not a matter restricted to astronomy anymore. Light is part of modern societies and, as a consequence, the natural cycle day-night (bright-dark) has been interrupted in a large segment of the global population. There is increasing evidence that exposure to certain types of light at night and beyond threshold levels may produce hazardous effects to humans and the environment. The concept of "dark skies reserves" is a step forward in order to preserve the night sky and a means of enhancing public awareness of the problem of spread of light pollution worldwide. The aim of this study was to assess the skyglow at two sites in Portugal, the Peneda-Gerês National Park (PNPG) and the region now known as Dark Sky Alqueva Reserve. The latter site was classified as a "Starlight Tourism Destination" by the Starlight Foundation (the first in the world to achieve this classification) following a series of night sky measurements in situ described herein. The measurements at PNPG also contributed to the new set of regulations concerning light pollution at this national park. This study presents the first in situ systematic measurements of night sky brightness, showing that at the two sites the skies are mostly in levels 3 to 4 of the Bortle 9-level scale (with level 1 being the best achievable). The results indicate that the sources of light pollution and skyglow can be attributed predominantly to contamination from nearby urban regions.

With static and dynamic load for the research background, this paper conducted a four-phase composite model for concrete damage test simulation of micro-mechanics. The two kinds of three-point bending beam load ware studied in case of failure process. The study found that the location of the main crack in the most disadvantaged section of beam shear in the vicinity. Crack is always along the aggregate and the mortar bond zone be extended. The main crack extension direction is always toward the load point. The main crack is showing a tortuous shape. Dynamic load and static load the stress - strain curve is basically similar shape, but basically the same as the starting point of the initial fracture. Stress wave in the sample after multiple visits, is the main reason leading to the breakdown of the sample. Dynamic load cases, the concrete elastic modulus higher than the static modulus of elasticity, numerical simulation results agree well with the experimental results.

This study presents experimental results of an approach consisting of local heating of aluminium alloy structures with the purpose of introducing a local change of material properties. Such modification can be precisely induced using a laser source, as detailed in this study. By a laser induced pre-treatment, the material properties are locally changed so that influencing the material flow is possible. It is therefore possible to improve deep drawing of high strength aluminium alloys. This technique can also be applied to thin-walled section aluminium tubes in order to act as local triggering of the deformation process reducing peak loads and inducing energy favourable folding modes. This study presents preliminary results of temperature, heating cycle and laser parameters influence in material properties and microstructure of a selected 6060-T5 aluminium alloy.

We re-examine the correlation between the colors and the inclinations of the Classical Kuiper Belt Objects (CKBOs) with an enlarged sample of optical measurements. The correlation is strong (rho=-0.7) and highly significant (>8 sigma) in the range 0-34 deg. Nonetheless, the optical colors are independent of inclination below ~12 deg, showing no evidence for a break at the reported boundary between the so-called dynamically "hot" and "cold" populations near ~5 deg. The commonly accepted parity between the dynamically cold CKBOs and the red CKBOs is observationally unsubstantiated, since the group of red CKBOs extends to higher inclinations. Our data suggest, however, the existence of a different color break. We find that the functional form of the color-inclination relation is most satisfactorily described by a non-linear and stepwise behavior with a color break at ~12 deg. Objects with inclinations >12 deg show bluish colors which are either weakly correlated with inclination or are simply homogeneously blue, whereas objects with inclinations, 9 pages, 4 figures, 3 tables. Accepted for publication in The Astronomical Journal (2008 August 21)

We present U-band photometry of Kuiper Belt objects taken to further investigate their color-orbit systematics. As at longer optical and near-infrared wavelengths, the U-band colors of Kuiper Belt objects show a wide range and a unimodal distribution. We find no evidence that color systematics in the Kuiper Belt are strongly wavelength-dependent. This observation is consistent with control of the reflection characteristics by a single (but unidentified) reddening material. No evidence is found for blue/ultraviolet absorption that can arise from charge transfer transitions in hydrated minerals in some primitive (C-type) asteroids. In the classical KBOs alone the U - B and other color indices are most strongly correlated with the Tisserand parameter measured with respect to Neptune.

Visible colors (BVRI) are a reasonable proxy for real spectra of Centaurs and Kuiper Belt Objects, which are rather linear in this range. Colors provide limited information but remain the best tool to study the bulk surface properties. We explore recurrent effects in the study of visible colors: i) how a correlation could be missed or weakened as a result of the data error bars, ii) the "risk" of missing an existing trend because of low sampling, and the possibility of making quantified predictions on the sample size needed to detect a trend at a given significance level, iii) the use of partial correlations to distinguish the mutual effect of two or more parameters, and iv) the sensitivity of the "reddening line" tool to the central wavelength of the filters used. We have compiled the visible colors of about 370 objects available in the literature and carried out an analysis per dynamical family. Our results show how a) data error bars impose a limit on the detectable correlations regardless of sample size and that therefore, once that limit is achieved, it is important to diminish the error bars, but it is pointless to enlarge the sampling with the same or larger errors; b) almost all dynamical families still require larger samplings to ensure the detection of correlations stronger than 0.5; c) the correlation strength between (V-R) vs. (R-I) is systematically lower than the one between (B-V) vs. (V-R) and is not related with error-bar differences between these colors; d) it is statistically equivalent to use any of the different flavors of orbital excitation or collisional velocity parameters regarding the color-inclination correlation of classical KBOs whereas the inclination and Tisserand parameter relative to Neptune cannot be separated from one another; and e) classical KBOs are the only dynamical family that shows neither (B-V) vs. (V-R) nor (V-R) vs. (R-I) correlations., 30 pages, 6 figures, 5 tables (2 long tables), accepted for publication in Astronomy & Astrophysics, abstract abridged

This study presents experimental results on the behaviour of aluminium alloy metal structures and foams manufactured by lost-wax casting and using 3D printed components for internal structure definition. Results for tensile tests, metallurgical properties, surface quality and geometry tolerances were obtained and discussed. The analysis focused on development geometries, used for adjusting manufacturing parameters and prototype geometries intended for geometrical and mechanical validation. The results are indicative of the viability of the method for producing foam structures suitable for mechanical loading., The authors are grateful to the Portuguese Foundation for Science and Technology (FCT) who financially supported this work, through the project PTDC/EME-PME/115668/2009., info:eu-repo/semantics/publishedVersion

The study of mechanical properties of intervertebral disc (IVD) is important for the evaluation of disc implants. To determine these properties, several animal spine models were used. The goal of this work is to determine and compare the dynamic stiffness coefficient (Kd) and initial creep behavior of porcine intervertebral disc with the human ones. Porcine lumbar “motion segments” were subjected to 1200 cycles of axial compressive loading at 1 Hz, and a mean load of 500 N. The results were fitted with a mathematical model. The Kd values are in same magnitude as the previously reported for human. The model showed a good adjust to the initial creep behavior and the obtained parameters present the same magnitude as the human discs, with exception of time constant. This work revealed that porcine MS is an interesting model to study both the dynamic behavior and initial creep response of human disc.

A newly developed strain rate dependent anisotropic continuum model is proposed for impact and blast applications in masonry. The present model adopted the usual approach of considering different yield criteria in tension and compression. The analysis of unreinforced block work masonry walls subjected to impact is carried out to validate the capability of the model. Comparison of the numerical predictions and test data revealed good agreement. Next, a parametric study is conducted to evaluate the influence of the tensile strengths along the three orthogonal directions and of the wall thickness on the global behavior of masonry walls., This work was performed under Project CH-SECURE, with reference TDC/ECM/120118/2010, funded by the Portuguese Foundation of Science and Technology - FCT. The authors acknowledge the support. The first author also acknowledges the support for the Strategic Planning of the School of Engineering from University of Minho.

We present 13 high-precision and four additional light curves of four bright southern-hemisphere transiting planetary systems: WASP-22, WASP-41, WASP-42 and WASP-55. In the cases of WASP-42 and WASP-55, these are the first follow-up observations since their discovery papers. We present refined measurements of the physical properties and orbital ephemerides of all four systems. No indications of transit timing variations were seen. All four planets have radii inflated above those expected from theoretical models of gas-giant planets; WASP-55b is the most discrepant with a mass of 0.63 Mjup and a radius of 1.34 Rjup. WASP-41 shows brightness anomalies during transit due to the planet occulting spots on the stellar surface. Two anomalies observed 3.1 d apart are very likely due to the same spot. We measure its change in position and determine a rotation period for the host star of 18.6 +/- 1.5 d, in good agreement with a published measurement from spot-induced brightness modulation, and a sky-projected orbital obliquity of lambda = 6 +/- 11 degrees. We conclude with a compilation of obliquity measurements from spot-tracking analyses and a discussion of this technique in the study of the orbital configurations of hot Jupiters., Comment: 13 pages, 8 tables, 11 figures. Version 2 is the final accepted version of the paper

The nature of the constitutive contact force law utilized to describe contact-impact events in solid contact interfaces plays a key role in predicting the response of multibody mechanical systems and in the simulation of engineering applications. The goal of this work is to present a comparative study on the most relevant existing viscoelastic contact force models. In the sequel of this process, their fundamental characteristics are examined and their performances evaluated. Models developed based on the Hertz contact theory and augmented with a damping term to accommodate the dissipation of energy during the impact process, which typically is a function of the coefficient of restitution between the contacting solids, are considered in this study. In particular, the identified contact force models are compared in the present study for simple solid impact problems with the sole purpose of comparing the performance of the various models and examining the corresponding system behavior. The outcomes indicate that the prediction of the dynamic behavior of contacting solids strongly depends on the selection of the contact force model., Fundação para a Ciência e a Tecnologia (FCT)

This study reports on modeling the mechanical behavior of high-strength steels subjected to impact loading. The materials studied were steel grades of interest for crashworthiness applications: dual-phase and transformation induced plasticity (TRIP) steels. The challenges associated with the numerical simulation of impact events involving these materials include the modeling of extensive plastic deformation, particularly the change of material properties with strain rate. Tensile testing was performed at different strain rates on the materials studied. The test results were used to compare and validate constitutive equations that provide a mathematical description of strain-rate dependence of the material properties. The Cowper–Symonds equation and modified variants were examined. The crashworthiness performance of thin-walled sections made of dual-phase and TRIP steels was also investigated. Axial crushing tests were performed at different speeds on top-hat and hexagonal tubes. The experimental results were compared with numerical simulations obtained using an explicit finite element program (LS-DYNA) and the original and modified Cowper–Symonds equations.

This study presents results concerning the stiffness and denting resistance of 6111-T4 aluminium alloy and AZ31B-H24 magnesium alloy. Experimental results of dynamic denting are compared with numerical simulations performed using LS-DYNA software. The experimental tests were performed on 0.9 and 1.09 mm thick plates clamped in a circular area with a diameter of 80 mm. Dynamic denting was accomplished by dropping different indenters from heights ranging from 0.36 to 1.7 m. The obtained experimental results enabled the properties of the two light alloys tested to be compared. The results of the numerical simulations display a good correlation with experiments if dynamic effects are introduced into the constitutive equation of the material through the Cowper-Symonds coefficients.

The original publication is available at http://iopscience.iop.org/1538-3881/; International audience; We report here the first detection of hectometer-size objects by the method of serendipitous stellar occultation. This method consists of recording the diffraction shadow created when an object crosses the observer's line of sight and occults the disk of a background star. One of our detections is most consistent with an object between Saturn and Uranus. The two other diffraction patterns detected are caused by Kuiper Belt objects beyond 100 AU from the Sun and hence are the farthest known objects in the solar system. These detections show that the Kuiper Belt is much more extended than previously believed and that the outer part of the disk could be composed of smaller objects than the inner part. This gives critical clues to understanding the problem of the formation of the outer planets of the solar system.

This study presents results of denting resistance of 6111-T4 aluminium alloy. Experimental results of dynamic denting were compared with numerical simulations performed using LS-DYNA software. The experimental tests were performed on 1mm thick plates clamped in a circular area with a diameter of 80mm. Dynamic denting was accomplished by dropping different indenters from heights ranging from 0.36 to 1.7 m. The obtained results indicate a high suitability of the aluminium alloy for use in automotive panels. The results of the numerical simulations display a good correlation with experiments if dynamic effects are introduced in the constitutive equation of the material through the Cowper-Symonds coefficients.

We present near-IR JHK broadband photometry for 17 Kuiper Belt objects (KBOs) and Centaurs. The observations were performed within the ESO Large Program on the Physical Properties of Kuiper Belt Objects and Centaurs from 2001 January to 2002 August. We used the ISAAC instrument at the ESO 8 m Very Large Telescope. We compiled visible-near-IR colors for a total of 51 published objects and performed a statistical analysis. Color-color correlations show that the same coloring process is probably acting on Centaur and KBO surfaces in the visible-near-IR range. Centaurs with H - K smaller than the Sun (0.06) systematically display the reddest B - V colors (at the 2.5 σ level). These Centaur surfaces are suspected of harboring material that has spectral signatures around 1.7-2.2 μm (water ice is a possibility; it was reported for the three objects that have published spectroscopy). We report no statistically significant evidence for a bimodal structure of the VJHK Centaur colors (Kolmogorov-Smirnov and dip tests on up to 17 objects). The Centaur H - K colors show some robust evidence (significance level >99.99%) for a continuous structure. We also report a statistically significant bimodal structure of the Centaur B - R distribution, which is compatible with the results published by Peixinho et al. in 2003 with different data. Classical KBOs show no trends at the 3 σ level. The V - J color is marginally correlated with perihelion distance q (which is consistent with results reported by Doressoundiram et al. in 2005 on B - R colors). Resonant and scattered disk objects are underrepresented (seven and nine objects, respectively) and show no statistically significant trend. Some of the marginal trends are mentioned as worthy of subsequent monitoring.

The improvements in vehicle crashworthiness observed in recent years have been closely linked to advanced high-strength steels that are currently being produced or in process of development. Amongst these, Dual-Phase and TRIP (Transformation Induced Plasticity) steels have presented excellent properties for use in crashworthy structures. For these steel grades an understanding of material behaviour at relevant strain rates is needed as well as constitutiv eequations suitable for use in analytic and numerical calculations. In this study the crashworthiness of thin-walled sections made of Dual-Phase and TRIP steels was investigated. Tensile tests were performed at different strain rates in a range of interest for crashworthiness problems. The results allowed the determination of parameters of Cowper-Symonds equation. Crush tests were performed at different speeds for top-hat and hexagonal tubes manufactured using laser welding. The experimental results were compared with numerical simulations obtained with LS-DYNA software. The influence of different material parameters on the accuracy of the simulations was examined.

We present here the latest B − V , V − R , and R − I color measurements obtained with the CFH12K mosaic camera of the 3.6-m Canada–France–Hawaii Telescope (CFHT). This work is the latest extension of the Meudon Multicolor Survey (2MS) and extends the total number of Centaurs and trans-neptunian objects (TNOs) in the dataset to 71. With this large and homogeneous dataset, we performed relevant statistical analyses to search for correlations with physical and orbital parameters and interrelations with related populations (cometary nuclei and irregular satellites). With a larger dataset, we confirm the correlations found for the Classical TNOs in our previous survey: some colors are significantly correlated with perihelion distance and inclination. The only exception is with the eccentricity. However, results strongly depend on which objects are considered Classicals, and with a dynamically more restricted definition these correlations are no longer present. We also find that strongly significant trends with orbital parameters are not detected for Centaurs, Plutinos or scattered disk objects (SDOs). We also make for the first time reliable statistical comparison between TNOs and related populations (e.g., Centaurs, irregular satellites, short period comets—i.e., SPCs). We find that (1) the colors of SPCs do not match either their TNO or Centaur precursors, and this suggests that some process modifies the surface of SPCs at entry into the inner Solar System. The only exception concerns colors of SDOs from which we could statistically assess that SPCs and SDOs could be drawn from a same single parent distribution. (2) Not surprisingly, Centaurs are compatible with each of the Edgeworth–Kuiper belt dynamical groups at a highly significant level except with the SDOs. (3) Centaurs' colors still present a strong dichotomy between a neutral/slightly red group (e.g., Chiron) and a very red group (e.g., Pholus). (4) The irregular satellite population is not compatible with any of the Centaur, Plutino or Classical populations; however, the similarity of their color properties with SDOs suggests that both groups can be extracted from the same parent distribution. However, due to the small number of Centaurs and SDOs these conclusions cannot be taken as definitive.

International audience; We report 43 new visible colors of Centaurs and TNOs, obtained at NTT and VLT telescopes under the "ESO large program on physical properties of Centaurs and TNOs." Merging these new measurements with those obtained during the first part of the program (Boehnhardt et al., 2002, Astron. Astrophys. 395, 297-303) and the "Meudon Multicolor Survey" (Doressoundiram et al., 2002, Astron. J. 124, 2279-2296) we have a unique dataset of 109 objects. We checked for correlations and trends between colors, physical and orbital parameters, carrying out an analysis based on Monte Carlo simulation to account for observational error bars. Centaurs show no evidence for correlation between V- R vs. R- I colors which raises the hypothesis that more than one single coloring process might be acting on their surfaces. Classical objects seem to be composed of two different color populations: objects with i4.5° display the whole range of colors from blue to very red. The possibility that the low inclined population is misguiding global conclusions is analyzed. Classical objects also show a stronger color-perihelion correlation for intrinsically brighter objects, corresponding to critical estimated sizes of different formation/evolutionary histories. Scattered disk objects show color resemblances with the classical objects at i>12°, hence surface reflectivities resemblances, pointing to a common origin. No color-aphelion trend is found for SDOs, as expected from the intense irradiation by galactic cosmic-rays beyond the solar wind termination shock. Plutinos show a color-absolute magnitude trend, in which all the intrinsically faintest objects are blue. We see many red Plutinos in highly inclined and highly eccentric orbits, that should have originated in a primordial inner disk under Gomes (2003, Icarus 161, 404-418) migration scenario. This seems to invalidate the assumption that objects originated in this inner disk are mainly blue. Finally, we also find six candidates for light-curve studies: four objects (1998 WU 31, 1999 OE 4, 1999 OX 3, and 2001 KP 77) present significant short term R-magnitude variability, and two objects (1999 XX 143 and 2000 GP 183) evidence possible color variations with rotation.

International audience

We report on observations of two bright Trans-Neptunian Objects (TNOs) - 1999 TC36 and 1998 SN165}- during two observational campaigns, as part of the Meudon Multicolor Survey of Outer Solar System Objects. V-J color was measured for 1999 TC36 (V-J=2.34+/-0.18), which combined with previous measured colors in the visible, indicate a red reflectivity spectrum at all wavelengths. Photometric V-band lightcurves were taken for both objects over a time span of around 8 hours. We have determined a possible rotational period of P=10.1+/-0.8 h for 1998 SN165, making it the seventh TNO with an estimated period. From its lightcurve variation of Dm=0.151(+0.022/-0.030), we have inferred an asymmetry ratio of a/b >=1.148(+0.024/-0.031). For 1999 TC36, we did not detect any rotational period or periodic signal variation within the uncertainties, but the analysis of its lightcurve hints to a slight systematic magnitude decrease.

The importance of the crest module design in the cortical bone region triggered a need to understand its geometry and its influence on stress management and bone stimulation., Supported by MCM Lda through a research grant (2012/24005) from TecMinho, Minho University, info:eu-repo/semantics/publishedVersion

This study presents alternative approaches for the improvement of crash energy absorption in representative automobile crashworthy structures. One such approach is the use of configurable crush initiators introduced through localized heating in tubular structures. The main objective is to improve the ability to absorb impact energy in a progressive and controlled manner by a local modification of material properties. In this manner, associated with the softening of the aluminium alloy, the deformation can be introduced precisely, forcing the tubular structure to deform in a mode of high energy absorption and reducing the maximum load in a controlled manner. An alternative approach for controllable energy absorption consists in the internal pressurization of structures in the framework of a crash-adaptive response. Within this strategy, the effect of internal pressurization of tubular structures in a crashworthiness application is investigated. The concept of internal pressurization can be implemented as a crash-adaptive structure therefore allowing different responses according to the intensity of shock.

The main goal of this work is to present numerical results on the behavior of aluminum metal foams in impact scenarios. One type of metal foam with uniform-size cell structures with spherical voids is taken into account in this work. The uniform-size cell configurations are closely compact and present only one type of voids (large voids). Metal foams with different spherical voids dimensions were analyzed in order to investigate their influence on the mechanical properties of these structures using explicit finite element method (FEM). Results for force-deformation curves, specific stiffness and yield strength were obtained and discussed.

The preservation of a cultural heritage has been, in nowadays, one important research topic. Some new techniques and materials have been studied. The use of Fibre Reinforced Polymer (FRP) is one of them. The static material properties of these materials when used in brick masonry are regularly studied. The dynamic studies are, however, almost non-existent. The development of a device capable to test dynamically the specimens already used in static tests is presented in this paper. It is described the construction of a drop weight tower to test FRP strips glued to brick masonry.

The intradiscal pressure has been essential for prevent the spinal complaints by forming a basis for clinical advice to promote the correct sitting postures. As a consequence, it is evident the need of an accurate method for measure the intradiscal pressure, to better understand the disc response to hydrostatic pressure fluctuations. Numerous reviews regarding disc mechanics are available, including intradiscal pressure benchmarks; however, an analysis on the techniques of intradiscal pressure measurement is needed. Therefore, this review will remain focused on the methodologies adopted for measure the intradiscal pressure in several conditions: for different daily activities, under external loads and for values where occurs annulus fibrosus disruption. The importance of the intradiscal pressure on disc function will be discussed as well as the some guidelines for design new measurement techniques will be defined.