863 research outputs found
Mixing and transport of water in a karst catchment: a case study from precipitation via seepage to the spring
One of the best-known and largest karst areas in Germany, the Blautopf Catchment, offers unique access to waters of the unsaturated zone through a large cave system. It was investigated with stable isotopes (<sup>18</sup>O/<sup>16</sup>O and D/H ratios expressed in permille = &permil;) in precipitation, seepage- and groundwater as tracers for water flow, mixing, and storage. The precipitation showed a distinct seasonality with &delta;<sup>18</sup>O values between &minus;2.9 and &minus;24.6&permil; during summer and winter, respectively. However, the isotope signals in seepage water in the caves as well as the discharge were almost completely buffered and ranged around an average &delta;<sup>18</sup>O value of &minus;10&permil;. This value was also close to the long-term average value of local precipitation, &minus;9.3&permil;. The homogeneous isotopic composition of the Blautopf Spring was unexpected, as its highly variable discharge (0.3 to 32 m<sup>3</sup> s<sup>&minus;1</sup>) is typical for a fast responsive karst system. These isotopic similarities could be explained by nearly complete mixing of the water already in the vadose zone. The data set therefore presents a case study to narrow down zones of mixing in karst catchments. It also confirms the minor role of the fast conduit system in the water balance of the Blautopf Catchment
Storage and transport in cave seepage- and groundwater in a South German karst system
International audienceWe investigated one of the best-known and second largest karst areas in Germany (Blautopf Catchment) that offers a unique access waters of the unsaturated zone through a large cave system. As tracers for water flow and storage we measured stable isotopes (18O/16O and D/H ratios) in precipitation, seepage- and groundwater. The precipitation showed a distinct seasonal cycle with ?18O values between ?2.6 and ?22.6? during summer and winter, respectively. However, the isotope signals in seepage water in the caves as well as the discharge were completely buffered and ranged around an average ?18O value of ?10?. This value also matched the long-term average of the precipitation. In addition, the homogeneous isotopic composition of the Blautopf Spring was against expectation for its highly variable discharge (0.3 to 32 m3 s?1) that is typical for a fast responsive karst system. We explain the isotopic similarity between cave seepage and the Blautopf Spring (as an integral signal for groundwater) by nearly complete mixing of the water already in the vadose zone. The latter can be divided into the compartments soil, epikarst and rock matrix that all have good storage capacities and also allow diffusive exchange of solutes between mobile and less mobile matrix water. The above approach revealed new aspects about turnover and flow paths of the infiltrated water and thus helps to constrain the risk by pollution to the groundwater
The obscured hyper-energetic GRB 120624B hosted by a luminous compact galaxy at z = 2.20
Gamma-ray bursts are the most luminous explosions that we can witness in the
Universe. Studying the most extreme cases of these phenomena allows us to
constrain the limits for the progenitor models. In this Letter, we study the
prompt emission, afterglow, and host galaxy of GRB 120624B, one of the
brightest GRBs detected by Fermi, to derive the energetics of the event and
characterise the host galaxy in which it was produced. Following the
high-energy detection we conducted a multi-wavelength follow-up campaign,
including near-infrared imaging from HAWKI/VLT, optical from OSIRIS/GTC, X-ray
observations from the Chandra X-ray Observatory and at
sub-millimetre/millimetre wavelengths from SMA. Optical/nIR spectroscopy was
performed with X-shooter/VLT. We detect the X-ray and nIR afterglow of the
burst and determine a redshift of z = 2.1974 +/- 0.0002 through the
identification of emission lines of [OII], [OIII] and H-alpha from the host
galaxy of the GRB. This implies an energy release of Eiso = (3.0+/-0.2)x10^54
erg, amongst the most luminous ever detected. The observations of the afterglow
indicate high obscuration with AV > 1.5. The host galaxy is compact, with R1/2
< 1.6 kpc, but luminous, at L ~ 1.5 L* and has a star formation rate of 91 +/-
6 Msol/yr as derived from H-alpha. As other highly obscured GRBs, GRB 120624B
is hosted by a luminous galaxy, which we also proof to be compact, with a very
intense star formation. It is one of the most luminous host galaxies associated
with a GRB, showing that the host galaxies of long GRBs are not always blue
dwarf galaxies, as previously thought.Comment: 6 pages, 4 figures, 4 tables; accepted for publication in A&
Spectroscopy of superluminous supernova host galaxies. A preference of hydrogen-poor events for extreme emission line galaxies
Superluminous supernovae (SLSNe) are very bright explosions that were only
discovered recently and that show a preference for occurring in faint dwarf
galaxies. Understanding why stellar evolution yields different types of stellar
explosions in these environments is fundamental in order to both uncover the
elusive progenitors of SLSNe and to study star formation in dwarf galaxies. In
this paper, we present the first results of our project to study SUperluminous
Supernova Host galaxIES, focusing on the sample for which we have obtained
spectroscopy. We show that SLSNe-I and SLSNe-R (hydrogen-poor) often (~50% in
our sample) occur in a class of galaxies that is known as Extreme Emission Line
Galaxies (EELGs). The probability of this happening by chance is negligible and
we therefore conclude that the extreme environmental conditions and the SLSN
phenomenon are related. In contrast, SLSNe-II (hydrogen-rich) occur in more
massive, more metal-rich galaxies with softer radiation fields. Therefore, if
SLSNe-II constitute a uniform class, their progenitor systems are likely
different from those of H-poor SLSNe. Gamma-ray bursts (GRBs) are, on average,
not found in as extreme environments as H-poor SLSNe. We propose that H-poor
SLSNe result from the very first stars exploding in a starburst, even earlier
than GRBs. This might indicate a bottom-light initial mass function in these
systems. SLSNe present a novel method of selecting candidate EELGs independent
of their luminosity.Comment: Published version, matches proofs. Accepted 2015 February 13. 23
pages, 8 figures, 4 tables. Minor changes with respect to previous versio
Growth of InP on GaAs (001) by hydrogen-assisted low-temperature solid-source molecular beam epitaxy
Direct heteroepitaxial growth of InP layers on GaAs (001) wafers has been performed by solid-source molecular beam epitaxy assisted by monoatomic hydrogen (Hâ). The epitaxial growth has been carried out using a two-step method: for the initial stage of growth the temperature was as low as 200â°C and different doses of Hâ were used; after this, the growth proceeded without Hâ while the temperature was increased slowly with time. The incorporation of Hâ drastically increased the critical layer thickness observed by reflection high-energy electron diffraction; it also caused a slight increase in the luminescence at room temperature, while it also drastically changed the low-temperature luminescence related to the presence of stoichiometric defects. The samples were processed by rapid thermal annealing. The annealing improved the crystalline quality of the InP layers measured by high-resolution x-ray diffraction, but did not affect their luminescent behavior significantly
The optical counterpart of the bright X-ray transient Swift J1745-26
We present a 30-day monitoring campaign of the optical counterpart of the
bright X-ray transient Swift J1745-26, starting only 19 minutes after the
discovery of the source. We observe the system peaking at i' ~17.6 on day 6
(MJD 56192) to then decay at a rate of ~0.04 mag/day. We show that the optical
peak occurs at least 3 days later than the hard X-ray (15-50 keV) flux peak.
Our measurements result in an outburst amplitude greater than 4.3 magnitudes,
which favours an orbital period < 21 h and a companion star with a spectral
type later than ~ A0. Spectroscopic observations taken with the GTC-10.4 m
telescope reveal a broad (FWHM ~ 1100 km/s), double-peaked H_alpha emission
line from which we constrain the radial velocity semi-amplitude of the donor to
be K_2 > 250 km/s. The breadth of the line and the observed optical and X-ray
fluxes suggest that Swift J1745-26 is a new black hole candidate located closer
than ~7 kpc.Comment: 5 pages, 4 figures, accepted for publication in MNRA
Cyclobutene photochemistry. Adiabatic photochemical ring opening of alkylcyclobutenes
Abstract: The photochemistry of the cis and trans isomers of a series of dimethylbicyclo[n.2.O]alk-(n+2)-enes (n = 2-5) (bicyclic cyclobutene derivatives in which the C=C bond is shared by the two rings) in pentane solution is described. Irradiation of these compounds using monochromatic 193-or 214-nm light sources results in ring opening to yield the corresponding 1,2-bis(l-ethylidene)cycloalkanes (C,-C,) in high chemical and quantum yields. In all cases, the reaction proceeds with a high (70-90%) degree of disrotatory stereoselectivity. Quantum yields for direct cis,trans photoisomerization of the isomeric E,Eand E,Z-1,2-bis(l-ethylidene)cycloalkanes have also been determined. The product distributions from irradiation of the cyclobutenes are wavelength dependent, but for 214-nm excitation the isomeric diene distributions obtained from cyclobutene ring opening agree fairly closely with those calculated from the quantum yields for cis,trans photoisomerization of the isomeric dienes on the assumption that the process involves purely disrotatory ring opening to yield a single diene isomer in the lowest excited singlet state. The results are consistent with an orbital-symmetry-controlled, adiabatic mechanism for ring opening. Key words: photochemistry, cyclobutene, electrocyclic, adiabatic, conical intersection, orbital symmetry. Resume : On dCcrit la photochimie des isomkres cis et trans d'une sCrie de dimCthylbicyclo[n.2.0]alc-(n+2)-knes (n = 2-5) (dCrivts cyclobutknes bicycliques dans lesquels la liaison C% est partagCe entre deux cycles) en solution dans le pentane. L'irradiation de ces composCs utilisant des sources de lumikre monochromatique (193 ou 214 nm) provoque une ouverture de cycle qui conduit aux 1,2-bis(1-Cthylidbne)cycloalcanes (C,-C,) correspondants avec des rendements chimiques et quantiques tlevCs. Dans tous les cas, la reaction se produit avec un degrC ClevC (70-90%) de stCrCosClectivitt disrotatoire. On a determink les rendements quantiques pour la photoisomtrisation cis/trans des E,E-and E,Z-1,2-bis(1-Cthy1idkne)cycloaIcanes. Les distributions des produits dtrivant de l'irradiation des cyclobutknes dependent de la longueur d'onde, mais, pour l'excitation B 214 nm, les distributions des diknes isomkres obtenues pour l'ouverture de cycle du cyclobutkne sont en assez bon accord avec ceux calculCs ii partir des rendements quantiques pour la photoisomCrisation cis/trans des diknes isomkres en supposant que le processus implique une ouverture de cycle strictement disrotatoire pour conduire B un seul dikne isomkre dans 1'Ctat singulet excitC le plus bas. Les rtsultats sont en accord avec un mCcanisme, pour l'ouverture de cycle, qui serait adiabatique et sous contr6le d'une symCtrie des orbitales
Searching for differences in Swift's intermediate GRBs
Gamma-ray bursts are usually classified through their high-energy emission
into short-duration and long-duration bursts, which presumably reflect two
different types of progenitors. However, it has been shown on statistical
grounds that a third, intermediate population is needed in this classification
scheme, although an extensive study of the properties of this class has so far
not been done. The large amount of follow-up studies generated during the Swift
era allows us to have a suficient sample to attempt a study of this third
population through the properties of their prompt emission and their
afterglows. Our study is focused on a sample of GRBs observed by Swift during
its first four years of operation. The sample contains those bursts with
measured redshift since this allows us to derive intrinsic properties.
Intermediate bursts are less energetic and have dimmer afterglows than long
GRBs, especially when considering the X-ray light curves, which are on average
one order of magnitude fainter than long bursts. There is a less significant
trend in the redshift distribution that places intermediate bursts closer than
long bursts. Except for this, intermediate bursts show similar properties to
long bursts. In particular, they follow the Epeak vs. Eiso correlation and
have, on average, positive spectral lags with a distribution similar to that of
long bursts. Like long GRBs, they normally have an associated supernova,
although some intermediate bursts have shown no supernova component. This study
shows that intermediate bursts are different from short bursts and, in spite of
sharing many properties with long bursts, there are some differences between
them as well. We suggest that the physical difference between intermediate and
long bursts could be that for the first the ejecta are thin shells while for
the latter they are thick shells.Comment: Accepted for publication in Astronomy and Astrophysics. 16 pages, 17
figures, 5 table
Barnacle Allergy: Allergen Characterization and Cross-Reactivity with Mites
Background: Barnacles are a type of seafood with worldwide distribution and abundant along the shores of temperate seas. They are particularly appreciated and regularly consumed in Portugal as well as in
Spain, France and South America, but barnacle allergy is a rare condition of which there is only one reference in
the indexed literature. The molecular allergens and possible cross-reactivity phenomena implicated (namely with
mites) have not been established.
Objective: To demonstrate the IgE-mediated allergy to barnacle and to identify the proteins implicated as well as possible cross-reactivity phenomena with mites.
Methods: We report the clinical and laboratory data of five patients with documented IgE-mediated allergy to barnacle.
The diagnosis was based on a suggestive clinical history combined with positive skin prick tests (SPT) to barnacle â prick to prick method. Two barnacle extracts were prepared (raw and cooked barnacle) and sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) and IgE-immunoblotting were performed. An immunoblotting inhibition assay with Dermatophagoides pteronyssinus was also done in order to evaluate cross-reactivity.
Results: All patients had mite-related asthma and the allergic rhinoconjunctivitis; they all experienced mucocutaneous symptoms. All of them had positive SPT to barnacle, and the immunoblotting showed several
allergenic fractions with a wide molecular weight range (19 â 94 kDa). The D. pteronyssinus extract inhibited
several IgE-binding protein fractions in the barnacle extract.
Conclusions: We describe five patients with IgE-mediated barnacle allergy. We also describe a group of IgEbinding+
proteins between 30 and 75 kDa as the allergenic fractions of this type of Crustacea. Cross-reactivity with D. pteronyssinus was demonstrated in two cases
Climate change-related risks and adaptation potential in Central and South America during the 21st century
Climate-related risks in Central and South America have received increased attention and concern in science and policy, but an up-to-date comprehensive review and synthesis of risks and adaptation potential is currently missing. For this paper we evaluated over 200 peer-reviewed articles and grey literature documents published since 2012. We found that climate change in Central and South America during the 21st century may increase the risk to severe levels for the following topical risk clusters: (a) Food insecurity; (b) Floods and landslides; (c) Water scarcity; (d) Epidemics of vector-borne diseases; (e) Amazon Forest biome shift; (f). Coral bleaching; (g) Coastal risks of sea level rise, storm surges and erosion; (h) Systemic failure due to cascading impacts of hazards and epidemics. Our synthesis also identified feasible adaptation measures for each risk. The impacts of the risks will be heterogeneous throughout the region, with rural communities, Indigenous peoples, Afro-Latin Americans, women, disabled people, and migrants identified as being the most severely affected. We refer to a number of adaptation options for each risk. However, unabated climate change together with low adaptive capacity will strictly limit adaptation options. Immediate strengthening of policies for building adaptive capacity and increase of research on the risk-adaptation nexus in Central and South America are paramount. Our findings might contribute to guide the adjustment and emphasis of adaptation policies and climate risk management strategies from local to national level
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