526 research outputs found
A Preliminary Analysis for Understanding Variations in Mountain Springs’ Water Availability under Climate Change in Aosta Valley
The availability of freshwater resources in alpine mountain areas has been affected by the impacts of climate change on groundwater storage mechanisms. A web of complex interactions characterizes climate systems, and several potential effects of climate change in such areas remain largely unknown. Therefore, examining how groundwater storage mechanisms are changing in response to climate-driven agents is becoming increasingly crucial.
To comprehend the existing relationship between changes in weather conditions and water availability in the Aosta Valley region (Northwestern Italy) and how their trends have changed over the last decade, a 7-year discharge series of different Aosta Valley springs (Promise, Alpe Perrot, Promiod, Cheserod) and precipitation data of the related meteorological stations (Aymaville-Viayes, La Thuile-Villaret, Champdepraz, Sant Vincent) were analyzed. The extent of the correlations between springs discharge measurements and hydrometeorological data was investigated. Besides, precipitation and flow rate trend analyses using the Mann–Kendall and Sen’s slope trend detection tests were performed. The Aymaville-Viayes, La Thuile-Villaret, Champdepraz, and Sant Vincent meteorological stations revealed an overall decreasing trend in annual rainfall (mm), with a slight increase in intensity (mm/day) as a result of the reduction in rainfall events (number of rainy days). Nonetheless, based on the analysis of flow rate data relating to the associated springs, Alpe Perrot, Cheserod, and Promise show an overall increasing trend of discharge over time. Although the Cheserod and Promise springs were not found to be highly correlated with rainfall, their aquifers appear to positively respond to the modified climate conditions, increasing the amount of groundwater stored. The moderate correlation values of these two springs can be a consequence of several factors such as aquifer features, distance from the weather station, and solid precipitation amounts that supply water in the following hydrogeological year.
Being able to continuously monitor the effects induced by changed climatic conditions on water reserves through simplified analysis approaches such as those presented in this paper is increasingly necessary. Moreover, implementing future studies through in-depth analyses of soil infiltration, groundwater recharge and storage mechanisms are required to predict the mountain aquifers’ behavior in changing climatic conditions
The nebular spectra of SN 2012aw and constraints on stellar nucleosynthesis from oxygen emission lines
We present nebular phase optical and near-infrared spectroscopy of the Type
IIP supernova SN 2012aw combined with NLTE radiative transfer calculations
applied to ejecta from stellar evolution/explosion models. Our spectral
synthesis models generally show good agreement with the ejecta from a MZAMS =
15 Msun progenitor star. The emission lines of oxygen, sodium, and magnesium
are all consistent with the nucleosynthesis in a progenitor in the 14 - 18 Msun
range. We also demonstrate how the evolution of the oxygen cooling lines of [O
I] 5577 A, [O I] 6300 A, and [O I] 6364 A can be used to constrain the mass of
oxygen in the non-molecularly cooled ashes to < 1 Msun, independent of the
mixing in the ejecta. This constraint implies that any progenitor model of
initial mass greater than 20 Msun would be difficult to reconcile with the
observed line strengths. A stellar progenitor of around MZAMS = 15 Msun can
consistently explain the directly measured luminosity of the progenitor star,
the observed nebular spectra, and the inferred pre-supernova mass-loss rate. We
conclude that there is still no convincing example of a Type IIP explosion
showing the nucleosynthesis expected from a MZAMS > 20 Msun progenitor.Comment: Accepted for publication in MNRA
Estimating Quasi-long-range Order via Renyi Entropies
We show how entanglement entropies allow for the estimation of
quasi-long-range order in one dimensional systems whose low-energy physics is
well captured by the Tomonaga-Luttinger liquid universality class. First, we
check our procedure in the exactly solvable XXZ spin-1/2 chain in its entire
critical region, finding very good agreement with Bethe ansatz results. Then,
we show how phase transitions between different dominant orders may be
efficiently estimated by considering the superfluid-charge density wave
transition in a system of dipolar bosons. Finally, we discuss the application
of this method to multispecies systems such as the one dimensional Hubbard
model. Our work represent the first proof of a direct relationship between the
Luttinger parameter and R\'enyi entropies in both bosonics and fermionic
lattice models.Comment: v2: minimal changes, 6 pages, 7 figures, accepted for publication in
Phys. Rev.
A metallicity study of 1987A-like supernova host galaxies
The origin of the blue supergiant (BSG) progenitor of Supernova (SN) 1987A
has long been debated, along with the role that its sub-solar metallicity
played. We now have a sample of 1987A-like SNe that arise from the core
collapse (CC) of BSGs. The metallicity of the explosion sites of the known BSG
SNe is investigated, as well as their association to star-forming regions. Both
indirect and direct metallicity measurements of 13 BSG SN host galaxies are
presented, and compared to those of other CC SN types. Indirect measurements
are based on the known luminosity-metallicity relation and on published
metallicity gradients of spiral galaxies. To provide direct estimates based on
strong line diagnostics, we obtained spectra of each BSG SN host both at the SN
explosion site and at the positions of other HII regions. Continuum-subtracted
Ha images allowed us to quantify the association between BSG SNe and
star-forming regions. BSG SNe explode either in low-luminosity galaxies or at
large distances from the nuclei of luminous hosts. Therefore, their indirectly
measured metallicities are typically lower than those of SNe IIP and Ibc. This
is confirmed by the direct estimates, which show slightly sub-solar values
(12+log(O/H)=8.3-8.4 dex), similar to that of the Large Magellanic Cloud (LMC),
where SN 1987A exploded. However, two SNe (1998A and 2004em) were found at near
solar metallicity. SNe IIb have a metallicity distribution similar to that of
BSG SNe. Finally, the association to star-forming regions is similar among BSG
SNe, SNe IIP and IIn. Our results suggest that LMC metal abundances play a role
in the formation of some 1987A-like SNe. This would naturally fit in a single
star scenario for the progenitors. However, the existence of two events at
nearly solar metallicity suggests that also other channels, e.g. binarity,
contribute to produce BSG SNe.Comment: 28 pages, 17 figures; accepted for publication (Astronomy and
Astrophysics); abstract abridged for arXiv submissio
Constraints on the origin of the first light from SN2014J
We study the very early lightcurve of supernova 2014J (SN 2014J) using the
high-cadence broad-band imaging data obtained by the Kilodegree Extremely
Little Telescope (KELT), which fortuitously observed M 82 around the time of
the explosion, starting more than two months prior to detection, with up to 20
observations per night. These observations are complemented by observations in
two narrow-band filters used in an H survey of nearby galaxies by the
intermediate Palomar Transient Factory (iPTF) that also captured the first days
of the brightening of the \sn. The evolution of the lightcurves is consistent
with the expected signal from the cooling of shock heated material of large
scale dimensions, \gsim 1 R_{\odot}. This could be due to heated material of
the progenitor, a companion star or pre-existing circumstellar environment,
e.g., in the form of an accretion disk. Structure seen in the lightcurves
during the first days after explosion could also originate from radioactive
material in the outer parts of an exploding white dwarf, as suggested from the
early detection of gamma-rays. The model degeneracy translates into a
systematic uncertainty of days on the estimate of the first light
from SN 2014J.Comment: Accepted by ApJ. Companion paper by Siverd et al, arXiv:1411.415
Critical properties and R\'enyi entropies of the spin-3/2 XXZ chain
We discuss entanglement and critical properties of the spin-3/2 XXZ chain in
its entire gapless region. Employing density-matrix renormalization group
calculations combined with different methods based on level spectroscopy,
correlation functions and entanglement entropies, we determine the sound
velocity and the Luttinger parameter of the model as a function of the
anisotropy parameter. Then, we focus on entanglement properties by
systematically studying the behavior of R\'enyi entropies under both open and
periodic boundary conditions, providing further evidence of recent findings
about entanglement entropies of excited states in conformal field theory.Comment: 8 pages, 10 figures; small text revisions and a new figure. Accepted
for publication in Phys. Rev.
Gap scaling at Berezinskii-Kosterlitz-Thouless quantum critical points in one-dimensional Hubbard and Heisenberg models
We discuss how to locate critical points in the
Berezinskii-Kosterlitz-Thouless (BKT) universality class by means of
gap-scaling analyses. While accurately determining such points using gap
extrapolation procedures is usually challenging and inaccurate due to the
exponentially small value of the gap in the vicinity of the critical point, we
show that a generic gap-scaling analysis, including the effects of logarithmic
corrections, provides very accurate estimates of BKT transition points in a
variety of spin and fermionic models. As a first example, we show how the
scaling procedure, combined with density-matrix-renormalization-group
simulations, performs extremely well in a non-integrable spin- XXZ model,
which is known to exhibit strong finite-size effects. We then analyze the
extended Hubbard model, whose BKT transition has been debated, finding results
that are consistent with previous studies based on the scaling of the
Luttinger-liquid parameter. Finally, we investigate an anisotropic extended
Hubbard model, for which we present the first estimates of the BKT transition
line based on large-scale density-matrix-renormalization-group simulations. Our
work demonstrates how gap-scaling analyses can help to locate accurately and
efficiently BKT critical points, without relying on model-dependent scaling
assumptions.Comment: 8 pages, 7 figure
Metallicity at the explosion sites of interacting transients
Context. Some circumstellar-interacting (CSI) supernovae (SNe) are produced
by the explosions of massive stars that have lost mass shortly before the SN
explosion. There is evidence that the precursors of some SNe IIn were luminous
blue variable (LBV) stars. For a small number of CSI SNe, outbursts have been
observed before the SN explosion. Eruptive events of massive stars are named as
SN impostors (SN IMs) and whether they herald a forthcoming SN or not is still
unclear. The large variety of observational properties of CSI SNe suggests the
existence of other progenitors, such as red supergiant (RSG) stars with
superwinds. Furthermore, the role of metallicity in the mass loss of CSI SN
progenitors is still largely unexplored. Aims. Our goal is to gain insight on
the nature of the progenitor stars of CSI SNe by studying their environments,
in particular the metallicity at their locations. Methods. We obtain
metallicity measurements at the location of 60 transients (including SNe IIn,
SNe Ibn, and SN IMs), via emission-line diagnostic on optical spectra obtained
at the Nordic Optical Telescope and through public archives. Metallicity values
from the literature complement our sample. We compare the metallicity
distributions among the different CSI SN subtypes and to those of other
core-collapse SN types. We also search for possible correlations between
metallicity and CSI SN observational properties. Results. We find that SN IMs
tend to occur in environments with lower metallicity than those of SNe IIn.
Among SNe IIn, SN IIn-L(1998S-like) SNe show higher metallicities, similar to
those of SNe IIL/P, whereas long-lasting SNe IIn (1988Z-like) show lower
metallicities, similar to those of SN IMs. The metallicity distribution of SNe
IIn can be reproduced by combining the metallicity distributions of SN IMs
(that may be produced by major outbursts of massive stars like LBVs) and SNe
IIP (produced by RSGs). The same applies to the distributions of the Normalized
Cumulative Rank (NCR) values, which quantifies the SN association to H II
regions. For SNe IIn, we find larger mass-loss rates and higher CSM velocities
at higher metallicities. The luminosity increment in the optical bands during
SN IM outbursts tend to be larger at higher metallicity, whereas the SN IM
quiescent optical luminosities tend to be lower. Conclusions. The difference in
metallicity between SNe IIn and SN IMs suggests that LBVs are only one of the
progenitor channels for SNe IIn, with 1988Z-like and 1998S-like SNe possibly
arising from LBVs and RSGs, respectively. Finally, even though linedriven winds
likely do not primarily drive the late mass-loss of CSI SN progenitors,
metallicity has some impact on the observational properties of these
transients. Key words. supernovae: general - stars: evolution - galaxies:
abundancesComment: Submitted to Astronomy and Astrophysics on 28/02/2015; submitted to
arXiv after the 1st referee repor
Synthetic gauge fields in synthetic dimensions: interactions and chiral edge modes
Synthetic ladders realized with one-dimensional alkaline-earth(-like) fermionic gases and subject to a gauge field represent a promising environment for the investigation of quantum Hall physics with ultracold atoms. Using density-matrix renormalization group calculations, we study how the quantum Hall-like chiral edge currents are affected by repulsive atom-atom interactions. We relate the properties of such currents to the asymmetry of the spin resolved momentum distribution function, a quantity which is easily addressable in state-of-art experiments. We show that repulsive interactions significantly enhance the chiral currents. Our numerical simulations are performed for atoms with two and three internal spin states
Reliability of spring recession curve analysis as a function of the temporal resolution of the monitoring dataset
Mountain springs represent one of the largest and most precious sources of potable water in Italy, necessary to meet the water needs of the population. Optimizing the present and future management strategies of mountain groundwater resources has become increasingly necessary. The accuracy and frequency of the flow rate (Q) measurements determine and restrict the processes that can be studied using spring hydrograph and recession curve analysis. Therefore, to properly define mountain aquifers’ hydrogeological properties, it turns out important to highlight the variation of the error in the estimation of the hydrogeological parameters as the time interval of sampling varies. In this paper, recession curve analysis was performed on two different mountain springs (Spring 1 and Spring 2) of north-western Italy, firstly considering available 4-h resolution measuring data and subsequently by resampling data to simulate longer sampling intervals of 1, 3, 7, 15, and 30 days. The resulting distribution of errors introduced by longer acquisition intervals underlined how the percentage error increases with increasing acquisition interval. For obtaining an adequate estimation of mountain aquifer hydrodynamic parameters, in place of continuous hourly data, 1-day and 3-day sampling intervals with associated errors respectively lower than 5% and 10% were found to be valid
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