3,505 research outputs found
Detection of Contact Binaries Using Sparse High Phase Angle Lightcurves
We show that candidate contact binary asteroids can be efficiently identified
from sparsely sampled photometry taken at phase angles >60deg. At high phase
angle, close/contact binary systems produce distinctive lightcurves that spend
most of the time at maximum or minimum (typically >1mag apart) brightness with
relatively fast transitions between the two. This means that a few (~5) sparse
observations will suffice to measure the large range of variation and identify
candidate contact binary systems. This finding can be used in the context of
all-sky surveys to constrain the fraction of contact binary near-Earth objects.
High phase angle lightcurve data can also reveal the absolute sense of the
spin.Comment: 4 pages, 4 figures, 1 table. Accepted for publication in ApJ
Detection of Additional Members of the 2003 EL61 Family via Infrared Spectroscopy
We have acquired near-infrared spectra of Kuiper belt objects 2003 UZ117,
2005 CB79 and 2004 SB60 with NIRC on the Keck I Telescope. These objects are
dynamically close to the core of the 2003 EL61 collisional family and were
suggested to be potential fragments of this collision by Ragozzine and Brown
(2007). We find that the spectra of 2003 UZ117 and 2005 CB79 both show the
characteristic strong water ice absorption features seen exclusively on 2003
EL61, its largest satellite, and the six other known collisional fragments. In
contrast, we find that the near infrared spectrum of 2004 SB60 is essentially
featureless with a fraction of water ice of less than 5%. We discuss the
implications of the discovery of these additional family members for
understanding the formation and evolution of this collisional family in the
outer solar system.Comment: 9 Pages, 2 figure
Modelação e Previsão do fluxo de Turismo em Portugal: Perspetivas para uma gestão estratégica
Purpose: The increase of Tourism in Portugal, as well as the companies related to it, it is necessary to analyze and forecast the flow of tourists so that the management of the business is endowed with a competitive strategy. Given the changes in the 'recent' dynamics of tourism data, this article discusses the contributions and limitations of using classical forecasting methodologies, when applied to this sector, namely to the number of overnight stays in tourist accommodation establishments in Portugal.
Methodology: The study focuses on the modeling and forecasting of time series related to the number of monthly overnight stays, in tourist accommodation establishments in Portugal, between January 2002 and March 2022. As a result of some suggestions contained in the scientific literature, it was resorted the Exponential Smoothing (ETS) methodologies. In computational terms, we used the Jupyter computational environment, with the Python programming language (version 3.7.3).
Findings: The results were presented and discussed through the analysis of two time series: (1) Total number of overnight stays in tourist accommodation establishments in Portugal – Total series; (2) Number of overnight stays spent by residents in Portugal in tourist accommodation establishments in Portugal – Residents series. Overall, from the analysis of the time series, there was a growth of Tourism in Portugal since 2002, with a visible drop in 2020, due to the pandemic situation. Regarding the ETS methodologies used in the modeling and forecasting, although they corresponded positively in the forecast of the Total series (with some error), the same did not happen in the Residents series. In this series, due to the recent dynamics that are completely atypical, it appears that the ETS methodologies, potentially more adequate, do not converge, in general. However, it is important to mention that it was the overnight stays of residents that, in the pandemic period, dictated the dynamics present in the Total series.
Research limitations: The literature points to a good performance of ETS methodologies in time series with characteristics present in the series under study (with the presence of a trend cycle and clear seasonality), a fact that motivated its choice. However, the difficulty of these methodologies in dealing with abrupt breaks in the data history was evident in this study. Despite how adjusted the forecasts are, the highlight is the non-convergence of some models that could be better adjusted to the historical data. In this sense, it is necessary to search for alternative forecasting methodologies, where Machine Learning methodologies, namely Deep Learning (Deep Neural Networks) have been pointed out in the scientific literature as quite promising. This will be the next step of the investigation.
Originality: Given the importance that Tourism has both in the economic and social dimension of Portugal, and being a very volatile and constantly changing sector, it is imperative to define a strategy for future action to understand how, internally, the sector can define policies to avoid situations of external dependence. In addition to a current analysis of the data history, resulting from an atypical period of pandemic, we need to critically evaluate the predictive capacity of (classical) econometric models, which can be used by the industry related to tourism. This not only contributes to a better understanding of the phenomenon under study, but also constitutes a tool to support decision-making.info:eu-repo/semantics/publishedVersio
High magnetic field thermal-expansion and elastic properties of CeRhIn
We report high magnetic field thermal-expansion and magnetostriction results
on CeRhIn single crystals. Several transitions, both first and second
order, are observed when the field is applied perpendicular to the
crystallographic c-axis. The magnetic field dependence of the thermal-expansion
coefficient above 15 K, where the magnetic correlations are negligible, can be
explained supposing an almost pure ground state doublet, in
apparent contradiction with neutron scattering experiments. Although the
spin-lattice interaction is relevant in this compound, the effect of the
magnetic correlations on the elastic properties is relatively weak, as revealed
by resonant ultrasound spectroscopy experiments.Comment: 5 pages, 6 figure
A logistic regression analysis of risk factors in ME/CFS pathogenesis
Background: Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a complex disease, whose exact
cause remains unclear. A wide range of risk factors has been proposed that helps understanding potential disease
pathogenesis. However, there is little consistency for many risk factor associations, thus we undertook an
exploratory study of risk factors using data from the UK ME/CFS Biobank participants. We report on risk factor
associations in ME/CFS compared with multiple sclerosis participants and healthy controls.
Methods: This was a cross-sectional study of 269 people with ME/CFS, including 214 with mild/moderate and 55
with severe symptoms, 74 people with multiple sclerosis (MS), and 134 healthy controls, who were recruited from
primary and secondary health services. Data were collected from participants using a standardised written
questionnaire. Data analyses consisted of univariate and multivariable regression analysis (by levels of proximity to
disease onset).
Results: A history of frequent colds (OR = 8.26, P <= 0.001) and infections (OR = 25.5, P = 0.015) before onset were
the strongest factors associated with a higher risk of ME/CFS compared to healthy controls. Being single (OR = 4.41,
P <= 0.001), having lower income (OR = 3.71, P <= 0.001), and a family history of anxiety is associated with a higher
risk of ME/CFS compared to healthy controls only (OR = 3.77, P < 0.001). History of frequent colds (OR = 6.31, P <
0.001) and infections before disease onset (OR = 5.12, P = 0.005), being single (OR = 3.66, P = 0.003) and having
lower income (OR = 3.48, P = 0.001), are associated with a higher risk of ME/CFS than MS. Severe ME/CFS cases were
associated with lower age of ME/CFS onset (OR = 0.63, P = 0.022) and a family history of neurological illness
(OR = 6.1, P = 0.001).
Conclusions: Notable differences in risk profiles were found between ME/CFS and healthy controls, ME/CFS and
MS, and mild-moderate and severe ME/CFS. However, we found some commensurate overlap in risk associations
between all cohorts. The most notable difference between ME/CFS and MS in our study is a history of recent
infection prior to disease onset. Even recognising that our results are limited by the choice of factors we selected to
investigate, our findings are consistent with the increasing body of evidence that has been published about the
potential role of infections in the pathogenesis of ME/CFS, including common colds/flu
Deposition of conductive materials on textile and polymeric flexible substrates
This paper describes the study, analysis and selection of textile and similar materials to be used as flexible substrates for thin conductive film deposition, in the context of integrating electronics into textiles. Kapton® polyimide was chosen as reference substrate material, was characterized regarding mechanical and electrical properties and was used as a basis for a comparison with several textile substrates. Samples were fabricated using physical vapour deposition (thermal evaporation) to deposit a thin layer of aluminium on top of Kapton and textile substrates. The measurement of electrical resistance of the thin aluminum films was carried out using the Kelvin method. To characterize the mechanical behaviour of the substrate and aluminum film, several mechanical tests were performed and results were compared between Kapton and these textile materials. The chemical composition of the textile substrates and aluminum films as well as the continuity of the films was characterized. This selection process identified the material that was closer to the behaviour of polyimide, a flexible, but non-elastic woven textile coated on both sides with PVC.FEDER funds in COMPETE program and by FCT, in the project FCOMP-01-0124-FEDER-02267
Caracterização de amido de pinhão modificado com soluções de ácido clorÃdrico 0,1 e 0,2M em presença de etanol e metanol.
O amido de pinhão possui propriedades interessantes, porém pouco foi estudado até o momento. Proveniente do Sul do Brasil, a semente da Araucária angustifolia serve de alimento para diversas culturas da região. Os amidos nativos de diversas fontes botânicas possuem caracterÃsticas de interesse industrial, porém algumas só são adquiridas ou melhoradas mediante a aplicação de agentes que modifiquem as estruturas originais dos grânulos, como ácidos e oxidantes. O presente trabalho teve como objetivo estudar propriedades do amido de pinhão nativo e este modificado, utilizando ácido clorÃdrico 0,1M e 0,2M, em meio etanólico e metanólico. Pelas curvas DSC foi possÃvel determinar as temperaturas ?onset?, de pico e de conclusão do processo de gelatinização das amostras, além de se determinar a entalpia envolvida no processo. Pelas imagens NC-AFM pode-se medir o tamanho dos grânulos dos amidos e a rugosidade dos mesmos antes e após as modificações. Por meio da técnica TG-DTG, foi possÃvel observar um perfil de perda de massa semelhante para todas as amostras, com 3 etapas definidas, sendo a 1ª referente à desidratação da amostra e a 2ª e 3ª referente à decomposição da matéria orgânica à cinzas. Através da análise de propriedade de pasta (RVA) se observou o perfil reológico das amostras, podendo determinar temperatura de pico, viscosidade final e retrogradação.CBRATEC
The formation of the solar system
The solar system started to form about 4.56 Gyr ago and despite the long
intervening time span, there still exist several clues about its formation. The
three major sources for this information are meteorites, the present solar
system structure and the planet-forming systems around young stars. In this
introduction we give an overview of the current understanding of the solar
system formation from all these different research fields. This includes the
question of the lifetime of the solar protoplanetary disc, the different stages
of planet formation, their duration, and their relative importance. We consider
whether meteorite evidence and observations of protoplanetary discs point in
the same direction. This will tell us whether our solar system had a typical
formation history or an exceptional one. There are also many indications that
the solar system formed as part of a star cluster. Here we examine the types of
cluster the Sun could have formed in, especially whether its stellar density
was at any stage high enough to influence the properties of today's solar
system. The likelihood of identifying siblings of the Sun is discussed.
Finally, the possible dynamical evolution of the solar system since its
formation and its future are considered.Comment: 36 pages, 7 figures, invited review in Physica Script
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