148 research outputs found
On the small-scale stability of thermonuclear flames in Type Ia supernovae
We present a numerical model which allows us to investigate thermonuclear
flames in Type Ia supernova explosions. The model is based on a finite-volume
explicit hydrodynamics solver employing PPM. Using the level-set technique
combined with in-cell reconstruction and flux-splitting schemes we are able to
describe the flame in the discontinuity approximation. We apply our
implementation to flame propagation in Chandrasekhar-mass Type Ia supernova
models. In particular we concentrate on intermediate scales between the flame
width and the Gibson-scale, where the burning front is subject to the
Landau-Darrieus instability. We are able to reproduce the theoretical
prediction on the growth rates of perturbations in the linear regime and
observe the stabilization of the flame in a cellular shape. The increase of the
mean burning velocity due to the enlarged flame surface is measured. Results of
our simulation are in agreement with semianalytical studies.Comment: 9 pages, 7 figures, Uses AASTEX, emulateapj5.sty, onecolfloat.sty.
Replaced with accepted version (ApJ), Figures 1 and 3 are ne
Constraints on the high-density nuclear equation of state from the phenomenology of compact stars and heavy-ion collisions
A new scheme for testing nuclear matter equations of state (EsoS) at high
densities using constraints from neutron star phenomenology and a flow data
analysis of heavy-ion collisions is suggested. An acceptable EoS shall not
allow the direct Urca process to occur in neutron stars with masses below
, and also shall not contradict flow and kaon production data of
heavy-ion collisions. Compact star constraints include the mass measurements of
2.1 +/- 0.2 M_sun (1 sigma level) for PSR J0751+1807, of 2.0 +/- 0.1 M_sun from
the innermost stable circular orbit for 4U 1636-536, the baryon mass -
gravitational mass relationships from Pulsar B in J0737-3039 and the
mass-radius relationships from quasiperiodic brightness oscillations in 4U
0614+09 and from the thermal emission of RX J1856-3754. This scheme is applied
to a set of relativistic EsoS constrained otherwise from nuclear matter
saturation properties with the result that no EoS can satisfy all constraints
simultaneously, but those with density-dependent masses and coupling constants
appear most promising.Comment: 15 pages, 8 figures, 5 table
500 Days of SN 2013dy: spectra and photometry from the ultraviolet to the infrared
SN 2013dy is a Type Ia supernova for which we have compiled an extraordinary
dataset spanning from 0.1 to ~ 500 days after explosion. We present 10 epochs
of ultraviolet (UV) through near-infrared (NIR) spectra with HST/STIS, 47
epochs of optical spectra (15 of them having high resolution), and more than
500 photometric observations in the BVrRiIZYJH bands. SN 2013dy has a broad and
slowly declining light curve (delta m(B) = 0.92 mag), shallow Si II 6355
absorption, and a low velocity gradient. We detect strong C II in our earliest
spectra, probing unburned progenitor material in the outermost layers of the SN
ejecta, but this feature fades within a few days. The UV continuum of SN
2013dy, which is strongly affected by the metal abundance of the progenitor
star, suggests that SN 2013dy had a relatively high-metallicity progenitor.
Examining one of the largest single set of high-resolution spectra for a SN Ia,
we find no evidence of variable absorption from circumstellar material.
Combining our UV spectra, NIR photometry, and high-cadence optical photometry,
we construct a bolometric light curve, showing that SN 2013dy had a maximum
luminosity of 10.0^{+4.8}_{-3.8} * 10^{42} erg/s. We compare the synthetic
light curves and spectra of several models to SN 2013dy, finding that SN 2013dy
is in good agreement with a solar-metallicity W7 model.Comment: 22 pages, 18 figures, replaced with version accecpted for publication
in MNRA
Equation of State of Nuclear Matter at high baryon density
A central issue in the theory of astrophysical compact objects and heavy ion
reactions at intermediate and relativistic energies is the Nuclear Equation of
State (EoS). On one hand, the large and expanding set of experimental and
observational data is expected to constrain the behaviour of the nuclear EoS,
especially at density above saturation, where it is directly linked to
fundamental processes which can occur in dense matter. On the other hand,
theoretical predictions for the EoS at high density can be challenged by the
phenomenological findings. In this topical review paper we present the
many-body theory of nuclear matter as developed along different years and with
different methods. Only nucleonic degrees of freedom are considered. We compare
the different methods at formal level, as well as the final EoS calculated
within each one of the considered many-body schemes. The outcome of this
analysis should help in restricting the uncertainty of the theoretical
predictions for the nuclear EoS.Comment: 51 pages, to appear in J. Phys. G as Topical Revie
Staggering behavior of the low lying excited states of even-even nuclei in a Sp(4,R) classification scheme
We implement a high order discrete derivative analysis of the low lying
collective energies of even-even nuclei with respect to the total number of
valence nucleon pairs N in the framework of F- spin multiplets appearing in a
symplectic sp(4,R) classification scheme. We find that for the nuclei of any
given F- multiplet the respective experimental energies exhibit a Delta N=2
staggering behavior and for the nuclei of two united neighboring F- multiplets
well pronounced Delta N=1 staggering patterns are observed. Those effects have
been reproduced successfully through a generalized sp(4,R) model energy
expression and explained in terms of the step-like changes in collective modes
within the F- multiplets and the alternation of the F-spin projection in the
united neighboring multiplets. On this basis we suggest that the observed Delta
N=2 and Delta N=1 staggering effects carry detailed information about the
respective systematic manifestation of both high order alpha - particle like
quartetting of nucleons and proton (neutron) pairing interaction in nuclei.PACS
number(s):21.10.Re, 21.60.FwComment: 22 pages and 6 figures changes in the figure caption
The peculiar Type Ia supernova iPTF14atg: Chandrasekhar-mass explosion or violent merger?
iPTF14atg, a subluminous peculiar Type Ia supernova (SN Ia) similar to SN 2002es, is the first SN Ia for which a strong UV flash was observed in the early-time light curves. This has been interpreted as evidence for a single-degenerate (SD) progenitor system where such a signal is expected from interactions between the SN ejecta and the non-degenerate companion star. Here, we compare synthetic observables of multi-dimensional state-of-the-art explosion models for different progenitor scenarios to the light curves and spectra of iPTF14atg. From our models, we have difficulties explaining the spectral evolution of iPTF14atg within the SD progenitor channel. In contrast, we find that a violent merger of two carbon-oxygen white dwarfs with 0.9 and 0.76 M⊙, respectively, provides an excellent match to the spectral evolution of iPTF14atg from 10 d before to several weeks after maximum light. Our merger model does not naturally explain the initial UV flash of iPTF14atg. We discuss several possibilities like interactions of the SN ejecta with the circum-stellar medium and surface radioactivity from a He ignited merger that may be able to account for the early UV emission in violent merger models
Complex Risks from Old Urban Waste Landfills: Sustainability Perspective from Iasi, Romania
Landfills continue to represent the most frequent managerial practice for municipal solid wastes and an increasing and complex problem globally. In certain countries, a transition to an open society and free market is superimposed on the transition to sustainability, resulting in even higher complexity of management. This paper proposes an approach for problem-structuring of landfills in complex transitions: sustainability or unsustainability of a management approach is determined by a set of sustainability filters that are defined by sets of indicators and prioritized according the systemic concept of sustainability, which says that economy is embedded in society, which is embedded in nature. The writers exercise this approach with an old landfill in Iasi, Romania, and conclude for unsustainability, because the ecological sustainability filter is not successfully passed. Social and economic sustainability filters are also discussed in relation with the ecological sustainability indicators. The described approach allows a coherent, transdisciplinary synthesis of knowledge scattered across various disciplines, a pervasive problem in landfill management. The case study helps distinguish between generally true and context-dependent aspects.Peer reviewe
Lessons for sustainability from the world's most sustainable culture
Sustainable development is one of the key challenges faced by societies today. Yet it is not a new challenge; throughout history, societies have faced the need to live within environmental constraints. Some have done so well, and some poorly. One society which did well for tens of thousands of years is that of Aboriginal Australia. This paper explores some lessons from Aboriginal Australia which have resonance in the modern world and shows that countries which have learned those lessons are in fact more sustainable than those which have not. It thus suggests that there is much that the pantheon of human experience can teach the modern world as it endeavours to create a sustainable future
SNLS Spectroscopy: Testing for Evolution in Type Ia Supernovae
Aims: We present a quantitative study of a new data set of high redshift Type
Ia supernovae spectra, observed at the Gemini telescopes during the first 34
months of the Supernova Legacy Survey. During this time 123 supernovae
candidates were observed, of which 87 have been identified as SNe Ia at a
median redshift of z=0.720. Spectra from the entire second year of the survey
and part of the third year (59 total SNe candidates with 46 confirmed SNe Ia)
are published here for the first time. The spectroscopic measurements made on
this data set are used determine if these distant SNe comprise a population
similar to those observed locally. Methods: Rest-frame equivalent width and
ejection velocity measurements are made on four spectroscopic features.
Corresponding measurements are presented for a set of 167 spectra from 24 low-z
SNe Ia from the literature. Results: We show that there exists a sample at high
redshift with properties similar to nearby SNe. No significant difference was
found between the distributions of measurements at low and high redsift for
three of the features. The fourth feature displays a possible difference that
should be investigated further. Correlations between Type Ia SNe properties and
host galaxy morphology were also found to be similar at low and high z, and
within each host galaxy class we see no evidence for redshift-evolution in SN
properties. A new correlation between SNe Ia peak magnitude and the equivalent
width of SiII absorption is presented. We demonstrate that this correlation
reduces the scatter in SNe Ia luminosity distances in a manner consistent with
the lightcurve shape-luminosity corrections that are used for Type Ia SNe
cosmology. Conclusions: We show that this new sample of SNLS SNe Ia has
spectroscopic properties similar to nearby objects. (Abridged)Comment: Accepted for publication in Astronomy and Astrophysic
Workforce scheduling and routing problems: literature survey and computational study
In the context of workforce scheduling, there are many scenarios in which personnel must carry out tasks at different locations hence requiring some form of transportation. Examples of these type of scenarios include nurses visiting patients at home, technicians carrying out repairs at customers’ locations and security guards performing rounds at different premises, etc. We refer to these scenarios as workforce scheduling and routing problems (WSRP) as they usually involve the scheduling of personnel combined with some form of routing in order to ensure that employees arrive on time at the locations where tasks need to be performed. The first part of this paper presents a survey which attempts to identify the common features of WSRP scenarios and the solution methods applied when tackling these problems. The second part of the paper presents a study on the computational difficulty of solving these type of problems. For this, five data sets are gathered from the literature and some adaptations are made in order to incorporate the key features that our survey identifies as commonly arising in WSRP scenarios. The computational study provides an insight into the structure of the adapted test instances, an insight into the effect that problem features have when solving the instances using mathematical programming, and some benchmark computation times using the Gurobi solver running on a standard personal computer
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