958 research outputs found
Chlorine and Sulfur in Nearby Planetary Nebulae and H II Regions
We derive the chlorine abundances in a sample of nearby planetary nebulae
(PNe) and H II regions that have some of the best available spectra. We use a
nearly homogeneous procedure to derive the abundance in each object and find
that the Cl/H abundance ratio shows similar values in H II regions and PNe.
This supports our previous interpretation that the underabundance we found for
oxygen in the H II regions is due to the depletion of their oxygen atoms into
organic refractory dust components. For other elements, the bias introduced by
ionization correction factors in their derived abundances can be very
important, as we illustrate here for sulfur using photoionization models. Even
for low-ionization PNe, the derived sulfur abundances can be lower than the
real ones by up to 0.3 dex, and the differences found with the abundances
derived for H II regions that have similar S/H can reach 0.4 dex.Comment: 2 pages, 1 figure, proceedings of the IAU Symposium No. 283,
Planetary Nebulae: an Eye to the Futur
Ressenyes
Obra ressenyada: Horace FREELAND JUDSON, AnatomÃa del fraude cientÃfico. Barcelona: CrÃtica, 200
A non-local perturbation of the logistic equation in IR N
A logistic equation in the whole space is considered. In this problem, a non-local perturbation is included. We establish a new sub-supersolution method forgeneral nonlocal elliptic equations and, consequently, we obtain the existence ofpositive solutions of a nonlocal logistic equation.Ministerio de EconomÃa y Competitividad (MINECO). EspañaEuropean Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)Conselho Nacional de Desenvolvimento CientÃfico e Tecnológico. BrasilCoordenação de Aperfeiçoamento de Pessoal de Nivel Superior. Brasi
Oxygen enrichment in carbon-rich planetary nebulae
We study the relation between the chemical composition and the type of dust
present in a group of 20 Galactic planetary nebulae (PNe) that have high
quality optical and infrared spectra. The optical spectra are used, together
with the best available ionization correction factors, to calculate the
abundances of Ar, C, Cl, He, N, Ne, and O relative to H. The infrared spectra
are used to classify the PNe in two groups depending on whether the observed
dust features are representative of oxygen-rich or carbon-rich environments.
The sample contains one object from the halo, eight from the bulge, and eleven
from the local disc. We compare their chemical abundances with nucleosynthesis
model predictions and with the ones obtained in seven Galactic H II regions of
the solar neighbourhood.
We find evidence of O enrichment (by 0.3 dex) in all but one of the
PNe with carbon-rich dust (CRD). Our analysis shows that Ar, and especially Cl,
are the best metallicity indicators of the progenitors of PNe. There is a tight
correlation between the abundances of Ar and Cl in all the objects, in
agreement with a lockstep evolution of both elements. The range of
metallicities implied by the Cl abundances covers one order of magnitude and we
find significant differences in the initial masses and metallicities of the PNe
with CRD and oxygen-rich dust (ORD). The PNe with CRD tend to have intermediate
masses and low metallicities, whereas most of the PNe with ORD show higher
enrichments in N and He, suggesting that they had high-mass progenitors.Comment: Accepted for publication in MNRAS. 14 pages, 8 figures, 5 table
Analysis of an age-structured predator-prey model with disease in the prey
We study a nonlinear predator-prey model in which the prey population is affected by a mild disease, but has an effect on the death-rate and is assumed to have age structure. We assume that the predator population grows according to a logistic law. We prove the existence and uniqueness of a positive solution for this model.Patronato de la Fundación Cámara (Universidad de Sevilla
Sustainable enhancement of district heating and cooling configurations by combining thermal energy storage and life cycle assessment
District heating and cooling systems are designed and optimized to respond to the latest challenges of reducing energy demands while fulfilling comfort standards. Thermal energy storage (TES) with phase change materials can be employed to reduce the energy demands of buildings. This study considers a residential district located in Spain, where a general framework has been established to identify optimal combinations of energy conversion, delivery technologies, and operating rules. The Life Cycle Assessment (LCA) methodology was implemented within a mathematical model, and the objective function considered the minimization of environmental loads. Two environmental impact assessment methods were applied within the LCA methodology: IPCC 2013 GWP 100y and ReCiPe. Four optimal configurations were considered: a reference system (gas boiler and split-type air conditioners) and then three TES-based systems: one sensible (STES, water) and two latent (LTES1—paraffin emulsion and LTES2—sodium acetate trihydrate). Hourly environmental loads associated with electricity imports from the national grid were available. The conventional energy system always presented the worst performance from an environmental viewpoint, being penalized by the high consumption of natural gas. Regarding carbon emissions, LTES1 showed the lowest emissions, followed by STES and LTES2. Reductions in energy demands compensated the impact of paraffin, and results of STES are strongly dependent on tank design. However, considering the ReCiPe method, STES presented the lowest loads, followed by LTES1 and LTES2. Overall impacts of LTES1 with paraffin are higher than STES with water, mainly due to the paraffin and the high volume required
A nonlinear age-dependent model with spatial diffusion
The main goal of this paper is to study the existence and uniqueness of positive solution for a nonlinear age-dependent equation with spatial diffusion. For that, we mainly use properties of an eigenvalue problem related to the equation and the subsupersolution method. We justify that this method works for this kind of equation, in which appears a potential blowing-up and a non-local initial condition.Ministerio de Ciencia y TecnologÃ
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