188 research outputs found
Visible-IR Colors and Lightcurve Analysis of Two Bright TNOs: 1999 TC36 and 1998 SN165
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.Comment: Accepted for publication in New Astronomy (13 pages, inc. 4 figures
Predicting the output dimensions, porosity and elastic modulus of additive manufactured biomaterial structures targeting orthopedic implants
This work was supported by FCT (Fundação para a CiĂȘncia e a Tecnologia) through the grant FRH/BD/128657/2017, the projects PTDC/EMS-TEC/5422/2014_ADAPTPROSTHESIS, POCI-01-0145-FEDER-030353 (SMARTCUT), NORTE 010145_FEDER-000018-HAMaBICo and UID/EEA/04436/2019.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. Monomaterial 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, opencells 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.info:eu-repo/semantics/publishedVersio
Coordinated thermal and optical observations of Trans-Neptunian object (20000) Varuna from Sierra Nevada
We report on coordinated thermal and optical measurements of trans-Neptunian
object (20000) Varuna obtained in January-February 2002, respectively from the
IRAM 30-m and IAA 1.5 m telescopes. The optical data show a lightcurve with a
period of 3.176+/-0.010 hr, a mean V magnitude of 20.37+/-0.08 and a
0.42+/-0.01 magnitude amplitude. They also tentatively indicate that the
lightcurve is asymmetric and double-peaked. The thermal observations indicate a
1.12+/-0.41 mJy flux, averaged over the object's rotation. Combining the two
datasets, we infer that Varuna has a mean 1060(+180/-220) km diameter and a
mean 0.038(+0.022/-0.010) V geometric albedo, in general agreement with an
earlier determination using the same technique.Comment: Accepted for publication in Astronomy & Astrophysics (7 pages,
including 3 figures
A study on the production of thin-walled Ti6Al4V parts by selective laser melting
Acknowledgements:
This work is supported by FCT - Fundação para a CiĂȘncia e a Tecnologia through the grant FRH/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 â Programa Operacional Competitividade e Internacionalização (POCI) with the reference project POCI-01-0145-FEDER-006941.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 micropillars 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 Ti6Al4V thin-walled parts by SLM.info:eu-repo/semantics/publishedVersio
The Color Distribution in the Edgeworth-Kuiper Belt
We have started since 1997 the Meudon Multicolor Survey of Outer Solar System
Objects with the aim of collecting a large and homogeneous set of color data
for Trans-Neptunian and Centaurs objects [...] We have a combined sample of 52
B-R color measurements for 8 Centaurs, 22 Classicals, 13 Plutinos, 8 Scattered
objects and 1 object with unidentified dynamical class. This dataset is the
largest single and homogeneous published dataset to date [...]. A strong
(color) correlation with mean excitation velocity points toward a space
weathering/impact origin for the color diversity. However, thorough modeling of
the collisional/dynamical environment in the Edgeworth-Kuiper belt needs to be
done in order to confirm this scenario. We found also that the Classical TNOs
consist in the superposition of two distinct populations: the dynamically Cold
Classical TNOs (red colors, low i, small sizes) and the dynamically Hot
Classical TNOs (diverse colors, moderate and high i, larger sizes). [...] Our
specific observation strategy [...] permitted us to highlight a few objects
suspected to have true compositional and/or texture variation on their
surfaces. These are 1998 HK151, 1999 DF9, 1999 OY3, 2000 GP183, 2000 OK67, and
2001 KA77 and should be prime targets for further observations [...]. Our
survey has also highlighted 1998 SN165 whose colors and dynamical properties
puts it in a new dynamical class distinct from the Classicals, its previously
assigned dynamical class.Comment: Accepted for publication in Astronomical Journal (38 pages, inc. 11
figures
Neptune Trojans and Plutinos: colors, sizes, dynamics, and their possible collisions
Neptune Trojans and Plutinos are two subpopulations of trans-Neptunian
objects located in the 1:1 and the 3:2 mean motion resonances with Neptune,
respectively, and therefore protected from close encounters with the planet.
However, the orbits of these two kinds of objects may cross very often,
allowing a higher collisional rate between them than with other kinds of
trans-Neptunian objects, and a consequent size distribution modification of the
two subpopulations.
Observational colors and absolute magnitudes of Neptune Trojans and Plutinos
show that i) there are no intrinsically bright (large) Plutinos at small
inclinations, ii) there is an apparent excess of blue and intrinsically faint
(small) Plutinos, and iii) Neptune Trojans possess the same blue colors as
Plutinos within the same (estimated) size range do.
For the present subpopulations we analyzed the most favorable conditions for
close encounters/collisions and address any link there could be between those
encounters and the sizes and/or colors of Plutinos and Neptune Trojans. We also
performed a simultaneous numerical simulation of the outer Solar System over 1
Gyr for all these bodies in order to estimate their collisional rate.
We conclude that orbital overlap between Neptune Trojans and Plutinos is
favored for Plutinos with large libration amplitudes, high eccentricities, and
small inclinations. Additionally, with the assumption that the collisions can
be disruptive creating smaller objects not necessarily with similar colors, the
present high concentration of small Plutinos with small inclinations can thus
be a consequence of a collisional interaction with Neptune Trojans and such
hypothesis should be further analyzed.Comment: 15 pages, 9 figures, 6 tables, accepted for publication in A&
Experimental and analytical study of the high-strain-rate compressive behavior of SFRC
The compressive behavior of steel-fiber-reinforced-concrete (SFRC) is dependent on the loading rate. This research investigates, experimentally and analytically, the effect of loading rate on the compressive behavior of SFRC designed to be used in prefabricated urban protective furniture. For this purpose, cylinder SFRC specimens were subjected to modified instrumented-drop-weightimpact tests at four dropping heights and quasi-static tests with four different strain rates. The inertia force was analytically obtained and also experimentally measured. The results demonstrate that by increasing the strain rate, elastic modulus, compressive strength, and energy dissipation capacity have increased. Three different models were proposed for predicting each mechanical characteristic, one in the range of quasi-static and the others in the range of impact corresponding to the split Hopkinson pressure bar and drop-weight-impact tests. The experimental dynamic to static ratios obtained for SFRC properties were discussed and compared with those proposed by present study and from other researchers. Three proposed models significantly improve the prediction the dynamic increase factor values in terms of compressive strength, modulus of elasticity and toughness.This paper is a part of the project âPufProtec â Prefabricated Urban Furniture Made by Advanced Materials for Protecting Public Builtâ with the reference of (POCI-01-0145-FEDER-028256) supported by FEDER and FCT funds. The first author appreciatively acknowledges the financial support of FCT-Fundação para a CiĂȘncia e Tecnologia for the Ph.D. Grant SFRH/BD/149246/2019
Experimental and analytical study of the high-strain rate flexural behavior of SFRC
Steel fiber-reinforced concrete (SFRC) with hooked-end steel fibers was created for use in urban furniture to protect against blast
and impact loads. Due to the variety of impact loads that these structures may experience, it is necessary to assess the impact of high strain
rates on the flexural behavior of SFRC. This study involved testing SFRC beams with 1% volume content of hooked-end fibers, which were
30 mm long and had an aspect ratio of 80. The beams were tested at different strain rates and in a three-point loading configuration. Four strain
rates were tested, ranging from 10â6 to 10â2 sâ1, and impact tests were conducted using a drop weight impact test machine and varying drop
heights, corresponding to strain rates ranging from 1 to 20 sâ1. Two load cells were used to measure the total impact force and one reaction
force, which were then used to assess the inertial force. Two accelerometers measured the maximum acceleration at the midspan of the beams.
The results included quasi-static and dynamic load-deflection relationships, dynamic flexural tensile strength, and failure mode of SFRC
specimens, as well as the relationship between the inertial force and strain rate. The study revealed that deflection capacity and flexural tensile
strength increased with loading rate. The study also provides dynamic to static property ratios, such as flexural tensile strength and fracture
energy, which are compared with those recommended by the CEB-FIP Model Code and other researchers.(undefined
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