251 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
Effect of the number of vortices on the torque scaling in Taylor-Couette flow
Torque measurements in Taylor-Couette flow, with large radius ratio and large
aspect ratio, over a range of velocities up to a Reynolds number of 24 000 are
presented. Following a specific procedure, nine states with distinct number of
vortices along the axis were found and the aspect ratio of the vortices were
measured. The relationship between the speed and the torque for a given number
of vortices is reported. In the turbulent Taylor vortex flow regime, at
relatively high Reynolds number, a change in behaviour is observed
corresponding to intersections of the torque-speed curves for different states.
Before each intersection, the torque for a state with larger number of vortices
is higher. After each intersection, the torque for a state with larger number
of vortices is lower. The exponent, from the scaling laws of the torque, always
depends on the aspect ratio of the vortices. When the Reynolds number is
rescaled using the mean aspect ratio of the vortices, only a partial collapse
of the exponent data is found.Comment: 11 pages, 6 figure
Colors of Inner Disk Classical Kuiper Belt Objects
We present new optical broadband colors, obtained with the Keck 1 and Vatican
Advanced Technology telescopes, for six objects in the inner classical Kuiper
Belt. Objects in the inner classical Kuiper Belt are of interest as they may
represent the surviving members of the primordial Kuiper Belt that formed
interior to the current position of the 3:2 resonance with Neptune, the current
position of the plutinos, or, alternatively, they may be objects formed at a
different heliocentric distance that were then moved to their present
locations. The six new colors, combined with four previously published, show
that the 10 inner belt objects with known colors form a neutral clump and a
reddish clump in B-R color. Nonparametric statistical tests show no significant
difference between the B-R color distribution of the inner disk objects
compared to the color distributions of Centaurs, plutinos, or scattered disk
objects. However, the B-R color distribution of the inner classical Kuiper belt
objects does differ significantly from the distribution of colors in the cold
(low inclination) main classical Kuiper belt. The cold main classical objects
are predominately red, while the inner classical belt objects are a mixture of
neutral and red. The color difference may reveal the existence of a gradient in
the composition and /or surface processing history in the primordial Kuiper
Belt, or indicate that the inner disk objects are not dynamically analogous to
the cold main classical belt objects.Comment: Accepted for publication in A
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
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
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
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&
"TNOs are Cool": A survey of the trans-Neptunian region X. Analysis of classical Kuiper belt objects from Herschel and Spitzer observations
The classical Kuiper belt contains objects both from a low-inclination,
presumably primordial, distribution and from a high-inclination dynamically
excited population. Based on a sample of classical TNOs with observations at
thermal wavelengths we determine radiometric sizes, geometric albedos and
thermal beaming factors as well as study sample properties of dynamically hot
and cold classicals. Observations near the thermal peak of TNOs using infra-red
space telescopes are combined with optical magnitudes using the radiometric
technique with near-Earth asteroid thermal model (NEATM). We have determined
three-band flux densities from Herschel/PACS observations at 70.0, 100.0 and
160.0 m and Spitzer/MIPS at 23.68 and 71.42 m when available. We have
analysed 18 classical TNOs with previously unpublished data and re-analysed
previously published targets with updated data reduction to determine their
sizes and geometric albedos as well as beaming factors when data quality
allows. We have combined these samples with classical TNOs with radiometric
results in the literature for the analysis of sample properties of a total of
44 objects. We find a median geometric albedo for cold classical TNOs of 0.14
and for dynamically hot classical TNOs, excluding the Haumea family and dwarf
planets, 0.085. We have determined the bulk densities of Borasisi-Pabu (2.1
g/cm^3), Varda-Ilmare (1.25 g/cm^3) and 2001 QC298 (1.14 g/cm^3) as well as
updated previous density estimates of four targets. We have determined the
slope parameter of the debiased cumulative size distribution of dynamically hot
classical TNOs as q=2.3 +- 0.1 in the diameter range 100<D<500 km. For
dynamically cold classical TNOs we determine q=5.1 +- 1.1 in the diameter range
160<D<280 km as the cold classical TNOs have a smaller maximum size.Comment: 22 pages, 7 figures Accepted to be published in Astronomy and
Astrophysic
The impact of financial restatements on financial markets: A systematic review of the literature
Purpose: The purpose of this paper is to discuss the most relevant issues related to the impact of financial restatements in the dynamics of financial markets and identify several research gaps to be investigated in future research. Design/methodology/approach: The methodology is based on a systematic review of the literature described by Tranfield et al. (2003). The final sample includes 47 academic papers published from 1996 to 2019. Findings: Papers in this domain discuss three main topics: how the market prices the announcement of a financial restatement; how financial restatements affect the announcing firmâs cost of capital and how financial restatements affect firmsâ reputation. There are several issues to explore in future research, including whether financial restatements affect the dynamics of financial markets in Europe, whether the market fully and promptly assimilates the information content of a restatement, the role of financial analystsâ information disclosures in this process or how regulators may improve the way they provide investors with timely information about firmsâ restating problems. Research limitations/implications: There is always some degree of subjectivity in the definition of the keywords, search strings and selection criteria in a systematic review. These are all important aspects, as they delimitate the scope of the study and define the sample of papers to be reviewed. Practical implications: The answers to the research questions identified in this paper may provide regulators with information to improve financial accounting and reporting standards and strengthen investorsâ confidence in accounting information and the dynamics of financial markets. Originality/value: This paper systematically reviews the relevant literature exploring the connection between financial restatements and the dynamics of financial markets. It contributes to the academic community by identifying several research questions that may impact the theory and practice related to accounting quality and capital markets.info:eu-repo/semantics/acceptedVersio
Segregation pattern competition in a thin rotating drum
Results are presented of an experimental investigation into patterned size segregation of binary granular
mixtures in a thin rotating drum that is half full. It is observed that streaks of small particles are formed within
regions of large ones where the integer number of streaks is fixed over a range of rotation rate of the drum.
Different patterns form in adjacent parameter ranges and the dynamics associated with the exchange between
neighboring states is analyzed using angular spatiotemporal diagrams. These help to reveal properties of the
merging mechanism for streaks of small particles. We report experimental evidence that the merging of streaks
is mediated by the movement of a surplus material in a direction opposite to that of the rotation of the drum.
The excess material is distributed throughout the pattern and the extra streak eventually disappears
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