1,746 research outputs found
Metallicity dependence of HMXB populations
High-mass X-ray binaries (HMXBs) might have contributed a non-negligible
fraction of the energy feedback to the interstellar and intergalactic media at
high redshift, becoming important sources for the heating and ionization
history of the Universe. However, the importance of this contribution depends
on the hypothesized increase in the number of HMXBs formed in low-metallicity
galaxies and in their luminosities. In this work we test the aforementioned
hypothesis, and quantify the metallicity dependence of HMXB population
properties. We compile from the literature a large set of data on the sizes and
X-ray luminosities of HMXB populations in nearby galaxies with known
metallicities and star formation rates. We use Bayesian inference to fit simple
Monte Carlo models that describe the metallicity dependence of the size and
luminosity of the HMXB populations. We find that HMXBs are typically ten times
more numerous per unit star formation rate in low-metallicity galaxies (12 +
log(O/H) < 8, namely < 20% solar) than in solar-metallicity galaxies. The
metallicity dependence of the luminosity of HMXBs is small compared to that of
the population size. Our results support the hypothesis that HMXBs are more
numerous in low-metallicity galaxies, implying the need to investigate the
feedback in the form of X-rays and energetic mass outflows of these high-energy
sources during cosmic dawn.Comment: 9 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Runoff at the micro-plot and slope scale following wildfire, central Portugal
Through their effects on soil properties and vegetation/litter cover, wildfires can strongly enhance overland flow generation and accelerate soil erosion [1] and, thereby, negatively affect land-use sustainability as well as downstream aquatic and flood zones. Wildfires are a common phenomenon in present-day Portugal, devastating in an average year some 100.000 ha of forest and woodlands and in an exceptional year like 2003 over 400.000 ha. There therefore exists a clear need in Portugal for a tool that can provide guidance to post-fire land management by predicting soil erosion risk, on the one hand, and, on the other, the mitigation effectiveness of soil conservation measures. Such a tool has recently been developed for the Western U.S.A. [3: ERMiT] but its suitability for Portuguese forests will need to be corroborated by field observations.
Testing the suitability of existing erosion models in recently burned forest areas in Portugal is, in a nutshell, the aim of the EROSFIRE projects. In the first EROSFIRE project the emphasis was on the prediction of erosion at the scale of individual hill slopes. In the ongoing EROSFIRE-II project the spatial scope is extended to include the catchment scale, so that also the connectivity between hill slopes as well as channel and road processes are being addressed. Besides ERMiT, the principal models under evaluation for slope-scale erosion prediction are: (i) the variant of USLE [4] applied by the Portuguese Water Institute after the wildfires of 2003; (ii) the Morgan–Morgan–Finney model (MMF) [5]; (iii) MEFIDIS [6]. From these models, MEFIDIS and perhaps MMF will, after successful calibration at the slope scale, also be applied for predicting catchment-scale sediment yields of extreme events
Runoff and erosion at the micro-plot and slope scale in a small burnt catchment, central Portugal
Wildfires can have important impacts on hydrological processes and soil erosion in forest catchments, due to the destruction of vegetation cover and changes to soil properties. However, the processes involved are non-linear and not fully understood. This has severely limited the understanding on the impacts of wildfires, especially in the up-scaling from hillslopes to catchments; in consequence, current models are poorly adapted for burnt forest conditions.
The objective of this presentation is to give an overview of the hydrological response and sediment yield from the micro-plot to slope scale, in the first year following a wildfire (2008/2009) that burnt an entire catchment nearby the Colmeal village, central Portugal. The overview will focus on three slopes inside the catchment, with samples including:
• Runoff at micro-plot scale (12 bounded plots) and slope scale (12 open plots); • Sediments and Organic Matter loss at micro-plot scale (12 bounded plots) and slope scale (12 open plots plus 3 Sediment fences); • Rainfall and Soil moisture data; • Soil Water Repellency and Ground Cover data.
The analysis of the first year following the wildfire clearly shows the complexity of runoff generation and the associated sediment transport in recently burnt areas, with pronounced differences between hillslopes and across spatial scales as well as with marked variations through time.
This work was performed in the framework of the EROSFIRE-II project (PTDC/AGR-CFL/70968/2006) which has as overall aim to predict soil erosion risk in recently burnt forest areas, including common post-fire forest management practices; the project focuses on the simultaneous measurement of runoff and soil erosion at multiple spatial scales.The results to be presented in this session are expected to show how sediment is generated, transported and exported in the Colmeal watershed; and contribute to understand and simulate erosion processes in burnt catchments, including for model development and evaluation
The CWKB particle production and classical condensate in de Sitter spacetime
The complex time WKB approximation is an effective tool in studying particle
production in curved spacetime. We use it in this work to understand the
formation of classical condensate in expanding de Sitter spacetime. The CWKB
leads to the emergence of thermal spectrum that depends crucially on horizons
(as in de Sitter spacetime) or observer dependent horizons (as in Rindler
spacetime). A connection is sought between the horizon and the formation of
classical condensate. We concentrate on de Sitter spacetime and study the
cosmological perturbation of mode with various values of . We find
that for a minimally coupled free scalar field for , the one-mode
occupation number grows more than unity soon after the physical wavelength of
the mode crosses the Hubble radius and soon after diverges as , where . The results substantiates the previous works in this
direction. We also find the correct oscillation and behaviour of at
small from a single expression using CWKB approximation for various values
of . We also discuss decoherence in relation to the formation of
classical condensate. We also find that the squeezed state formalism and CWKB
method give identical results.Comment: 19 pages, revtex, 5 figure
One-Parameter Squeezed Gaussian States of Time-Dependent Harmonic Oscillator and Selection Rule for Vacuum States
By using the invariant method we find one-parameter squeezed Gaussian states
for both time-independent and time-dependent oscillators. The squeezing
parameter is expressed in terms of energy expectation value for
time-independent case and represents the degree of mixing positive and negative
frequency solutions for time-dependent case. A {\it minimum uncertainty
proposal} is advanced to select uniquely vacuum states at each moment of time.
We show that the Gaussian states with minimum uncertainty coincide with the
true vacuum state for time-independent oscillator and the Bunch-Davies vacuum
for a massive scalar field in a de Sitter spacetime.Comment: 13 Pages, ReVTeX, no figure
Squeezed States of the Generalized Minimum Uncertainty State for the Caldirola-Kanai Hamiltonian
We show that the ground state of the well-known pseudo-stationary states for
the Caldirola-Kanai Hamiltonian is a generalized minimum uncertainty state,
which has the minimum allowed uncertainty , where is a constant depending on the damping
factor and natural frequency. The most general symmetric Gaussian states are
obtained as the one-parameter squeezed states of the pseudo-stationary ground
state. It is further shown that the coherent states of the pseudo-stationary
ground state constitute another class of the generalized minimum uncertainty
states.Comment: RevTex4, 9 pages, no fingure; to be published in Journal of Physics
Asthma, obesity and diet
El asma y la obesidad son dos trastornos de gran
impacto en la salud pública que han aumentado su prevalencia
en los últimos años. Numerosos estudios han relacionado
ambas entidades.
La mayoría de los estudios prospectivos demuestran
que la obesidad es un factor de riesgo para el diagnóstico
“de novo” de asma. Además, los resultados de diversos
estudios sugieren que así como la ganancia de peso
aumenta el riesgo de asma, la pérdida mejora su evolución.
En general, los estudios prospectivos encuentran
una asociación positiva entre el índice de masa corporal
(IMC) basal y el posterior desarrollo de asma, lo que
sugiere que es el exceso de peso el que podría favorecer el
desarrollo de asma, aunque estos resultados no son tan
concluyentes cuando se estudia la asociación entre hiperreactividad
bronquial con el IMC.
Existen distintos factores que podrían explicar esta
asociación. La obesidad es capaz de reducir la compliance
pulmonar, los volúmenes pulmonares y el diámetro de de
las vías respiratorias periféricas, así como alterar los
volúmenes sanguíneos pulmonares y la relación ventilación-
perfusión. Además, el aumento del funcionamiento
normal del tejido adiposo en sujetos obesos conduce a un
estado proinflamatorio sistémico, que produce un
aumento de las concentraciones séricas de numerosas
citoquinas, fracciones solubles de sus receptores y quimiocinas.
Muchos de estos mediadores son sintetizados y
secretados por células del tejido adiposo y reciben el nombre
genérico de adipocinas, entre las que se incluyen IL-6,
IL-10, eotaxina, TNF- , TGF- 1, PCR, leptina y adiponectina.
Por último, se han identificado regiones específicas
del genoma humano que están relacionadas tanto con
el asma como con la obesidad.
La mayoría de los estudios apuntan a que la obesidad
es capaz de aumentar la prevalencia y la incidencia de
asma, aunque este efecto parece ser moderado. El tratamiento
de los asmáticos obesos debe incluir un programa
de control de peso.Asthma and obesity have a considerable impact on
public health and their prevalence has increased in recent
years. Numerous studies have linked both disorders.
Most prospective studies show that obesity is a risk factor
for asthma and have found a positive correlation between
baseline body mass index (BMI) and the subsequent
development of asthma, although these results are not
conclusive when studying the association between airway
hyperresponsiveness with BMI. Furthermore, several
studies suggest that whereas weight gain increases the
risk of asthma, weight loss improves the course of the illness.
Different factors could explain this association. Obesity
is capable of reducing pulmonary compliance, lung
volumes and the diameter of peripheral respiratory airways
as well as affecting the volume of blood in the lungs
and the ventilation-perfusion relationship. Furthermore,
the increase in the normal functioning of adipose tissue in
obese subjects leads to a systemic proinflammatory state,
which produces a rise in the serum concentrations of several
cytokines, the soluble fractions of their receptors and
chemokines. Many of these mediators are synthesized
and secreted by cells from adipose tissue and receive the
generic name of adipokines, including IL-6, IL-10,
eotaxin, TNF- , TGF- 1, PCR, leptin y adiponectin.
Finally, specific regions of the human genome which are
related to both asthma and obesity have been identified.
Most studies point out that obesity is capable of
increasing the prevalence and incidence of asthma,
although this effect appears to be modest. The treatment
of obese asthmatics must include a weight control progra
Algebraic approach in the study of time-dependent nonlinear integrable systems: Case of the singular oscillator
The classical and the quantal problem of a particle interacting in
one-dimension with an external time-dependent quadratic potential and a
constant inverse square potential is studied from the Lie-algebraic point of
view. The integrability of this system is established by evaluating the exact
invariant closely related to the Lewis and Riesenfeld invariant for the
time-dependent harmonic oscillator. We study extensively the special and
interesting case of a kicked quadratic potential from which we derive a new
integrable, nonlinear, area preserving, two-dimensional map which may, for
instance, be used in numerical algorithms that integrate the
Calogero-Sutherland-Moser Hamiltonian. The dynamics, both classical and
quantal, is studied via the time-evolution operator which we evaluate using a
recent method of integrating the quantum Liouville-Bloch equations \cite{rau}.
The results show the exact one-to-one correspondence between the classical and
the quantal dynamics. Our analysis also sheds light on the connection between
properties of the SU(1,1) algebra and that of simple dynamical systems.Comment: 17 pages, 4 figures, Accepted in PR
Processo de sobremoldação de vedante numa tampa plástica
O objeto da presente patente é o processo de sobremoldação de uma tampa
Plástica com vedante incorporado, na qual é injetado o material de maior dureza sobre o
De menor dureza. Este processo de sobremoldação é aplicado somente em bi-injecção
(utilização de dois materiais ou mais), em tampas plásticas rígidas para embalagens de
Forma redonda ou outras. A solução adotada passou por proteger o vedante (3) do fluxo
(9) do material da tampa (2) de modo a evitar que este cause deformações no vedante (3)
Durante o processo de enchimento. A forma de orientação precisa do fluxo (9) do sobre o
Material de menor dureza (3) evita a deformação deste ultimo recorrendo aos diferenciais
De pressão conjugados com a velocidade. Desta forma é possível injetar sobre um
Material de menor dureza (3), um material de maior dureza (2)
Dental pulp stem cells and Bonelike® for bone regeneration in ovine model
Development of synthetic bone substitutes has arisen as a major research interest in the need to find an alternative to autologous bone grafts. Using an ovine model, the present pre-clinical study presents a synthetic bone graft (Bonelike®) in combination with a cellular system as an alternative for the regeneration of non-critical defects. The association of biomaterials and cell-based therapies is a promising strategy for bone tissue engineering. Mesenchymal stem cells (MSCs) from human dental pulp have demonstrated both in vitro and in vivo to interact with diverse biomaterial systems and promote mineral deposition, aiming at the reconstruction of osseous defects. Moreover, these cells can be found and isolated from many species. Non-critical bone defects were treated with Bonelike® with or without MSCs obtained from the human dental pulp. Results showed that Bonelike® and MSCs treated defects showed improved bone regeneration compared with the defects treated with Bonelike® alone. Also, it was observed that the biomaterial matrix was reabsorbed and gradually replaced by new bone during the healing process. We therefore propose this combination as an efficient binomial strategy that promotes bone growth and vascularization in non-critical bone defects.This research was supported by Programa Operacional Regional do Norte (ON.2 – O Novo Norte), QREN, FEDER with the project ‘iBone Therapies: Terapias inovadoras para a regeneração óssea’, ref. NORTE-01-0247-FEDER-003262, and by the programme COMPETE – Programa Operacional Factores de Competitividade, Projects PEst-OE/AGR/UI0211/2011 and PEst-C/EME/UI0285/2013 funding from FCT. This research was also supported by Programa Operacional Competitividade e Internacionalizac¸~ao (P2020), Fundos Europeus Estruturais e de Investimento (FEEI) and FCT with the project ‘BioMate—A novel bio-manufacturing system to produce bioactive scaffolds for tissue engineering’ with reference PTDC/EMS-SIS/7032/2014 and by COMPETE 2020, from ANI—Projectos ID&T Empresas em Copromoção Programas Operacionais POCI, by the project ‘insitu.Biomas - Reinvent biomanufacturing systems by using an usability approach for in situ clinic temporary implants fabrication’ with the reference POCI-01-0247-FEDER-017771. The research was also supported by the research project ‘BEPIM III –Microdispositivos me´dicos com capacidades osteintegradoras por micoPIM’, with the reference POCI-01-0247-FEDER-017935, from Fundo Europeu de Desenvolvimento Regional (FEDER), by the Programa Operacional da Competitividade & Internacionalização. Ana Rita Caseiro (SFRH/BD/101174/2014) acknowledges FCT, for financial support
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