60 research outputs found
Effect of catalyst on the producer gas composition from co-gasification of glycerol/fat mixtures
In this work, steam reforming of crude glycerol and animal fat mixtures was studied. The tests were carried out at temperatures of 700 °C and 750 °C in a fixed bed reactor using activated alumina or dolomite particles, to evaluate the catalytic capacity of these minerals in the removal of tar from the producer gas. The gas produced was quantified and analyzed by gas chromatography, and it was concluded that its composition is greatly influenced by the bed material used. The results obtained showed that dolomite is more effective in reducing the tar content, evidencing its ability to catalyze the tar reform reactions and promoting the water-gas shift reaction. Consequently, using dolomite as a catalyst, a producer gas with 47–48 vol% in H and 27–30 vol% in CO2 was obtained, while using a bed of alumina particles, a gas with a high CO content (45–48 vol%) and lower H content (34–37 vol%) was produced.This work was supported by Portugal 2020 (POCI-01-0145-FEDER-024067) and by Multi-year financing of FCT- Fundação para a Ciência e Tecnologia, Portugal (grant UIDB/04730/2020).info:eu-repo/semantics/publishedVersio
Constraining scalar fields with stellar kinematics and collisional dark matter
The existence and detection of scalar fields could provide solutions to
long-standing puzzles about the nature of dark matter, the dark compact objects
at the centre of most galaxies, and other phenomena. Yet, self-interacting
scalar fields are very poorly constrained by astronomical observations, leading
to great uncertainties in estimates of the mass and the
self-interacting coupling constant of these fields. To counter this,
we have systematically employed available astronomical observations to develop
new constraints, considerably restricting this parameter space. In particular,
by exploiting precise observations of stellar dynamics at the centre of our
Galaxy and assuming that these dynamics can be explained by a single boson
star, we determine an upper limit for the boson star compactness and impose
significant limits on the values of the properties of possible scalar fields.
Requiring the scalar field particle to follow a collisional dark matter model
further narrows these constraints. Most importantly, we find that if a scalar
dark matter particle does exist, then it cannot account for both the
dark-matter halos and the existence of dark compact objects in galactic nucleiComment: 23 pages, 8 figures; accepted for publication by JCAP after minor
change
Short-range correlations and meson exchange currents in photonucleon emission
One-nucleon emission processes induced by photon absorption are studied by
considering short-range correlations effects. At energies above the giant
resonance region the validity of the direct knock-out model has been tested by
comparison with continuum Random Phase Approximation results. Nucleon
re-scattering effects have been considered by using an optical potential. The
role of the electromagnetic convection, magnetization and meson exchange
currents has been investigated as a function of both excitation energy and
momentum transfer. The short-range correlation effects have been studied by
using various correlation functions. We found that the nucleon photo-emission
cross section is rather sensitive to the presence of short-range correlations
at large values of nucleon emission angle. In this region, however, the effects
of meson exchange currents are even larger than those produced by short-range
correlations.Comment: 37 pages, 20 figures in postscript, Text in LaTe
The scientific potential of space-based gravitational wave detectors
The millihertz gravitational wave band can only be accessed with a
space-based interferometer, but it is one of the richest in potential sources.
Observations in this band have amazing scientific potential. The mergers
between massive black holes with mass in the range 10 thousand to 10 million
solar masses, which are expected to occur following the mergers of their host
galaxies, produce strong millihertz gravitational radiation. Observations of
these systems will trace the hierarchical assembly of structure in the Universe
in a mass range that is very difficult to probe electromagnetically. Stellar
mass compact objects falling into such black holes in the centres of galaxies
generate detectable gravitational radiation for several years prior to the
final plunge and merger with the central black hole. Measurements of these
systems offer an unprecedented opportunity to probe the predictions of general
relativity in the strong-field and dynamical regime. Millihertz gravitational
waves are also generated by millions of ultra-compact binaries in the Milky
Way, providing a new way to probe galactic stellar populations. ESA has
recognised this great scientific potential by selecting The Gravitational
Universe as its theme for the L3 large satellite mission, scheduled for launch
in ~2034. In this article we will review the likely sources for millihertz
gravitational wave detectors and describe the wide applications that
observations of these sources could have for astrophysics, cosmology and
fundamental physics.Comment: 18 pages, 2 figures, contribution to Gravitational Wave Astrophysics,
the proceedings of the 2014 Sant Cugat Forum on Astrophysics; v2 includes one
additional referenc
A Deep Learning Neural Network to Classify Obesity Risk in Portuguese Adolescents Based on Physical Fitness Levels and Body Mass Index Percentiles: Insights for National Health Policies
The increasing prevalence of overweight and obesity among adults is a risk factor for many chronic diseases and death. In addition, obesity among children and adolescents has reached unprecedented levels and studies show that obese children and adolescents are more likely to become obese adults. Therefore, both the prevention and treatment of obesity in adolescents are critical. This study aimed to develop an artificial intelligence (AI) neural network (NNET) model that identifies the risk of obesity in Portuguese adolescents based on their body mass index (BMI) percentiles and levels of physical fitness. Using datasets from the FITescola® project, 654 adolescents aged between 10–19 years old, male: 334 (51%), female: n = 320 (49%), age 13.8 ± 2 years old, were selected to participate in a cross-sectional observational study. Physical fitness variables, age, and sex were used to identify the risk of obesity. The NNET had good accuracy (75%) and performance validation through the Receiver Operating Characteristic using the Area Under the Curve (ROC AUC = 64%) in identifying the risk of obesity in Portuguese adolescents based on the BMI percentiles. Correlations of moderate effect size were perceived for aerobic fitness (AF), upper limbs strength (ULS), and sprint time (ST), showing that some physical fitness variables contributed to the obesity risk of the adolescents. Our NNET presented a good accuracy (75%) and was validated with the K-Folds Cross-Validation (K-Folds CV) with good accuracy (71%) and ROC AUC (66%). According to the NNET, there was an increased risk of obesity linked to low physical fitness in Portuguese teenagers.This project was supported by the National Funds through the FCT—Portuguese Foundation for Science and Technology (project UIDB/04045/2021).info:eu-repo/semantics/publishedVersio
Star Formation and Dynamics in the Galactic Centre
The centre of our Galaxy is one of the most studied and yet enigmatic places
in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre
(GC) is the ideal environment to study the extreme processes that take place in
the vicinity of a supermassive black hole (SMBH). Despite the hostile
environment, several tens of early-type stars populate the central parsec of
our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and
inner radius ~0.04 pc, while the S-stars, i.e. the ~30 stars closest to the
SMBH (<0.04 pc), have randomly oriented and highly eccentric orbits. The
formation of such early-type stars has been a puzzle for a long time: molecular
clouds should be tidally disrupted by the SMBH before they can fragment into
stars. We review the main scenarios proposed to explain the formation and the
dynamical evolution of the early-type stars in the GC. In particular, we
discuss the most popular in situ scenarios (accretion disc fragmentation and
molecular cloud disruption) and migration scenarios (star cluster inspiral and
Hills mechanism). We focus on the most pressing challenges that must be faced
to shed light on the process of star formation in the vicinity of a SMBH.Comment: 68 pages, 35 figures; invited review chapter, to be published in
expanded form in Haardt, F., Gorini, V., Moschella, U. and Treves, A.,
'Astrophysical Black Holes'. Lecture Notes in Physics. Springer 201
The Lamb shift in muonic hydrogen
The long quest for a measurement of the Lamb shift in muonic hydrogen is over. Last year we measured the 2S1/2F=1–2P3/2F=2 energy splitting (Pohl et al., Nature, 466, 213 (2010)) in μp with an experimental accuracy of 15 ppm, twice better than our proposed goal. Using current QED calculations of the fine, hyperfine, QED, and finite size contributions, we obtain a root-mean-square proton charge radius of rp = 0.841 84 (67) fm. This value is 10 times more precise, but 5 standard deviations smaller, than the 2006 CODATA value of rp. The origin of this discrepancy is not known. Our measurement, together with precise measurements of the 1S–2S transition in regular hydrogen and deuterium, gives improved values of the Rydberg constant, R∞ = 10 973 731.568 160 (16) m⁻¹ and the rms charge radius of the deuteron rd = 2.128 09 (31) fm
Algumas propriedades físicas e hídricas de três solos na Chapada do Apodi, RN, cultivados com melão
Suplemento múltiplo com ionóforos para novilhos em pasto: consumo, fermentação ruminal e degradabilidade in situ
Controle associado de Alphitobius diaperinuse efeito de microrganismos eficazes no desenvolvimento de Beauveria bassiana
O objetivo deste trabalho foi avaliar a eficiência de Beauveria bassiana (Bb), terra diatomácea (TD) e microrganismos eficazes (EM-4), associados ou não, no controle de Alphitobius diaperinus, e o efeito de EM-4 no desenvolvimento de B. bassiana. Os agentes de controle (Bb, TD e EM-4), em diferentes concentrações e combinações, foram aplicados em uma mistura de cama-de-frango e ração, em que os insetos foram acondicionados por dez dias. Avaliaram-se, in vitro: a germinação, as unidades formadoras de colônia (UFC), o crescimento vegetativo e a produtividade de conídios de Bb em contato com suspensão aquosa de EM-4 (1%) não filtrada e filtrada. Os maiores índices de mortalidade foram observados nos tratamentos TD + Bb + EM-4 e TD + Bb, nas maiores concentrações. Verificou-se efeito não-aditivo sinérgico para TD + Bb nas três concentrações. Nos testes com EM-4 filtrado, não houve diferença em relação à testemunha quanto à germinação e às UFC, entretanto, o crescimento vegetativo e a produtividade de conídios foram negativamente afetados. O uso conjunto de B. bassiana e terra diatomácea, para o manejo de populações de A. diaperinus, pode reduzir o uso de produtos químicos
- …