Instituto Interdisciplinario de Ciencias Básicas

DFTB+ is a versatile community developed open source software package offering fast and efficient methods for carrying out atomistic quantum mechanical simulations. By implementing various methods approximating density functional theory (DFT), such as the density functional based tight binding (DFTB) and the extended tight binding method, it enables simulations of large systems and long timescales with reasonable accuracy while being considerably faster for typical simulations than the respective ab initio methods. Based on the DFTB framework, it additionally offers approximated versions of various DFT extensions including hybrid functionals, time dependent formalism for treating excited systems, electron transport using non-equilibrium Green's functions, and many more. DFTB+ can be used as a user-friendly standalone application in addition to being embedded into other software packages as a library or acting as a calculation-server accessed by socket communication. We give an overview of the recently developed capabilities of the DFTB+ code, demonstrating with a few use case examples, discuss the strengths and weaknesses of the various features, and also discuss on-going developments and possible future perspectives.

The extraordinary work hardening ability and fracture toughness of the face-centered cubic (fcc) high-entropy alloys render them ideal candidates for many structural applications. Here, the deformation and failure mechanisms of an equiatomic CrCoNi medium-entropyalloy (MEA) were investigated by powerful laser-driven shock experiments. Multiscale characterization demonstrates that profuse planar defects including stacking faults, nanotwins, and hexagonal nanolamella were generated during shock compression, forming a three-dimensional network. During shock release, the MEA fractured by strong tensile deformation and numerous voids was observed in the vicinity of the fracture plane. High defect populations, nanorecrystallization, and amorphization were found adjacent to these areas of localized deformation. Molecular dynamics simulations corroborate the experimental results and suggest that deformation-induced defects formed before void nucleation govern the geometry of void growth and delay their coalescence. Our results indicate that the CrCoNi-based alloys are impact resistant, damage tolerant, and potentially suitable in applications under extreme conditions.

Abstract Observational evidence shows the ubiquitous presence of ocean-emitted short-lived halogens in the global atmosphere 1–3 . Natural emissions of these chemical compounds have been anthropogenically amplified since pre-industrial times 4–6 , while, in addition, anthropogenic short-lived halocarbons are currently being emitted to the atmosphere 7,8 . Despite their widespread distribution in the atmosphere, the combined impact of these species on Earth’s radiative balance remains unknown. Here we show that short-lived halogens exert a substantial indirect cooling effect at present (−0.13 ± 0.03 watts per square metre) that arises from halogen-mediated radiative perturbations of ozone (−0.24 ± 0.02 watts per square metre), compensated by those from methane (+0.09 ± 0.01 watts per square metre), aerosols (+0.03 ± 0.01 watts per square metre) and stratospheric water vapour (+0.011 ± 0.001 watts per square metre). Importantly, this substantial cooling effect has increased since 1750 by −0.05 ± 0.03 watts per square metre (61 per cent), driven by the anthropogenic amplification of natural halogen emissions, and is projected to change further (18–31 per cent by 2100) depending on climate warming projections and socioeconomic development. We conclude that the indirect radiative effect due to short-lived halogens should now be incorporated into climate models to provide a more realistic natural baseline of Earth’s climate system.

Abstract CH 4 is the most abundant reactive greenhouse gas and a complete understanding of its atmospheric fate is needed to formulate mitigation policies. Current chemistry-climate models tend to underestimate the lifetime of CH 4 , suggesting uncertainties in its sources and sinks. Reactive halogens substantially perturb the budget of tropospheric OH, the main CH 4 loss. However, such an effect of atmospheric halogens is not considered in existing climate projections of CH 4 burden and radiative forcing. Here, we demonstrate that reactive halogen chemistry increases the global CH 4 lifetime by 6–9% during the 21st century. This effect arises from significant halogen-mediated decrease, mainly by iodine and bromine, in OH-driven CH 4 loss that surpasses the direct Cl-induced CH 4 sink. This increase in CH 4 lifetime helps to reduce the gap between models and observations and results in a greater burden and radiative forcing during this century. The increase in CH 4 burden due to halogens (up to 700 Tg or 8% by 2100) is equivalent to the observed atmospheric CH 4 growth during the last three to four decades. Notably, the halogen-driven enhancement in CH 4 radiative forcing is 0.05 W/m 2 at present and is projected to increase in the future (0.06 W/m 2 by 2100); such enhancement equals ~10% of present-day CH 4 radiative forcing and one-third of N 2 O radiative forcing, the third-largest well-mixed greenhouse gas. Both direct (Cl-driven) and indirect (via OH) impacts of halogens should be included in future CH 4 projections.

Cell membrane structure is proposed as a lipid matrix with embedded proteins, and thus, their emerging mechanical and electrostatic properties are commanded by lipid behavior and their interconnection with the included and absorbed proteins, cytoskeleton, extracellular matrix and ionic media. Structures formed by lipids are soft, dynamic and viscoelastic, and their properties depend on the lipid composition and on the general conditions, such as temperature, pH, ionic strength and electrostatic potentials. The dielectric constant of the apolar region of the lipid bilayer contrasts with that of the polar region, which also differs from the aqueous milieu, and these changes happen in the nanometer scale. Besides, an important percentage of the lipids are anionic, and the rest are dipoles or higher multipoles, and the polar regions are highly hydrated, with these water molecules forming an active part of the membrane. Therefore, electric fields (both, internal and external) affects membrane thickness, density, tension and curvature, and conversely, mechanical deformations modify membrane electrostatics. As a consequence, interfacial electrostatics appears as a highly important parameter, affecting the membrane properties in general and mechanical features in particular. In this review we focus on the electromechanical behavior of lipid and cell membranes, the physicochemical origin and the biological implications, with emphasis in signal propagation in nerve cells.

, Cl, and Br) by halogen chemistry, with a significant contribution from previously unconsidered bromine. These results show that higher recognition of the impact of anthropogenic halogens shall be given in haze pollution research and air quality regulation.

Active chlorine in the atmosphere is poorly constrained and so is its role in the oxidation of the potent greenhouse gas methane, causing uncertainty in global methane budgets. We propose a photocatalytic mechanism for chlorine atom production that occurs when Sahara dust mixes with sea spray aerosol. The mechanism is validated by implementation in a global atmospheric model and thereby explaining the episodic, seasonal, and location-dependent 13 C depletion in CO in air samples from Barbados [J.E. Mak, G. Kra, T. Sandomenico, P. Bergamaschi, J. Geophys. Res. Atmos. 108 (2003)], which remained unexplained for decades. The production of Cl can also explain the anomaly in the CO:ethane ratio found at Cape Verde [K. A. Read et al., J. Geophys. Res. Atmos. 114 (2009)], in addition to explaining the observation of elevated HOCl [M. J. Lawler et al., Atmos. Chem. Phys. 11 , 7617–7628 (2011)]. Our model finds that 3.8 Tg(Cl) y −1 is produced over the North Atlantic, making it the dominant source of chlorine in the region; globally, chlorine production increases by 41%. The shift in the methane sink budget due to the increased role of Cl means that isotope-constrained top–down models fail to allocate 12 Tg y −1 (2% of total methane emissions) to 13 C-depleted biological sources such as agriculture and wetlands. Since 2014, an increase in North African dust emissions has increased the 13 C isotope of atmospheric CH 4 , thereby partially masking a much greater decline in this isotope, which has implications for the interpretation of the drivers behind the recent increase of methane in the atmosphere.

Approximately 32 species of marine mammals of the Gulf of California (GC) share habitat and resources in this ecosystem. Unusually high 15 N values at the base of the food web in the GC permeate up all trophic levels, distinguishing the isotopic signature of the GC from other ecosystems in the Eastern North Pacific. Values of 13 C and 15 N were acquired from particulate organic matter (POM) of surface sediment, zooplankton, mollusks, crustaceans, fish, and marine mammals in the GC to construct a general trophic structure and were complemented with additional isotope data from the literature. Aims were to: estimate marine mammal trophic levels and habitat preferences; distinguish between GC residents and visitors; and assess potential trophic overlap among the most common and abundant cetacean species. Trophic level 1 (TL1), represented by POM, showed average ( SD) 13 C and 15 N values of -21.4 0.5 and 9.6 0.7 , bulk zooplankton (TL2) showed -18.8 0.7 and 11.8 1.4 , while TL3, represented by baleen whales, some fish, squid, and seabirds, showed 13 C values between -13 and -16 and 15 N values between 16.5 and 20 . Marine mammals occupied the entire coastal and pelagic isotope gradient ( 13 C values from -12 to -18.1 ), with most of the species at TL4 ( 15 N values from 17 to 23 ), whereas Orcinus orca occupied TL5 (25.8 maximum value). The odontocetes Mesoplodon peruvianus, Globicephala macrorhynchus, Grampus griseus, Kogia sima, Delphinus delphis, D. capensis, and Tursiops truncatus had both GC resident and visitor representatives, and the latter 3 species showed a significant degree of trophic and habitat overlap.

Abstract In contrast to the general stratospheric ozone recovery following international agreements, recent observations show an ongoing net ozone depletion in the tropical lower stratosphere (LS). This depletion is thought to be driven by dynamical transport accelerated by global warming, while chemical processes have been considered to be unimportant. Here we use a chemistry–climate model to demonstrate that halogenated ozone-depleting very short-lived substances (VSLS) chemistry may account for around a quarter of the observed tropical LS negative ozone trend in 1998–2018. VSLS sources include both natural and anthropogenic emissions. Future projections show the persistence of the currently unaccounted for contribution of VSLS to ozone loss throughout the twenty-first century in the tropical LS, the only region of the global stratosphere not projecting an ozone recovery by 2100. Our results show the need for mitigation strategies of anthropogenic VSLS emissions to preserve the present and future ozone layer in low latitudes.

Large anthropogenic 14 C datasets are widely used to generate summed probability distributions (SPDs) as a proxy for past human population levels. However, SPDs are a poor proxy when datasets are small, bearing little relationship to true population dynamics. Instead, more robust inferences can be achieved by directly modelling the population and assessing the model likelihood given the data. We introduce the R package ADMUR which uses a continuous piecewise linear (CPL) model of population change, calculates the model likelihood given a 14 C dataset, estimates credible intervals using Markov chain Monte Carlo, applies a goodness-of-fit test, and uses the Schwarz Criterion to compare CPL models. We demonstrate the efficacy of this method using toy data, showing that spurious dynamics are avoided when sample sizes are small, and true population dynamics are recovered as sample sizes increase. Finally, we use an improved 14 C dataset for the South American Arid Diagonal to compare CPL modelling to current simulation methods, and identify three Holocene phases when population trajectory estimates changed from rapid initial growth of 4.15% per generation to a decline of 0.05% per generation between 10 821 and 7055 yr BP, then gently grew at 0.58% per generation until 2500 yr BP. This article is part of the theme issue ‘Cross-disciplinary approaches to prehistoric demography’.

The catalytic depletion of Antarctic stratospheric ozone is linked to anthropogenic emissions of chlorine and bromine. Despite its larger ozone-depleting efficiency, the contribution of ocean-emitted iodine to ozone hole chemistry has not been evaluated, due to the negligible iodine levels previously reported to reach the stratosphere. Based on the recently observed range (0.77 ± 0.1 parts per trillion by volume [pptv]) of stratospheric iodine injection, we use the Whole Atmosphere Community Climate Model to assess the role of iodine in the formation and recent past evolution of the Antarctic ozone hole. Our 1980-2015 simulations indicate that iodine can significantly impact the lower part of the Antarctic ozone hole, contributing, on average, 10% of the lower stratospheric ozone loss during spring (up to 4.2% of the total stratospheric column). We find that the inclusion of iodine advances the beginning and delays the closure stages of the ozone hole by 3 d to 5 d, increasing its area and mass deficit by 11% and 20%, respectively. Despite being present in much smaller amounts, and due to faster gas-phase photochemical reactivation, iodine can dominate (∼73%) the halogen-mediated lower stratospheric ozone loss during summer and early fall, when the heterogeneous reactivation of inorganic chlorine and bromine reservoirs is reduced. The stratospheric ozone destruction caused by 0.77 pptv of iodine over Antarctica is equivalent to that of 3.1 (4.6) pptv of biogenic very short-lived bromocarbons during spring (rest of sunlit period). The relative contribution of iodine to future stratospheric ozone loss is likely to increase as anthropogenic chlorine and bromine emissions decline following the Montreal Protocol.

Task-specific ionic liquids (TSILs) represent a sub-family of ionic liquids characterized by their high specificity towards a target analyte or group of analytes. This characteristic has made them valuable tools for sample preparation, where selectivity represents a key aspect, especially when other species represent a significant source of interference or when non-specific detectors are used. This review presents an overview of TSILs applications for sample preparation from the last ten years, with a special emphasis on their use as liquid-liquid microextraction solvents or as functionalizing agents for sorbents applied to solid-phase microextractions. TSILs applications for the treatment of environmental, food and biological samples are reviewed, including reports devoted to speciation analysis, a relevant trend in recent years regarding elemental studies. Additionally, focus is made on the ‘task-specificity’ of the presented TSILs, including a description of the chemical characteristics that made them selective towards the studied analytes. Finally, future trends and gaps to be covered in the field are also discussed.

Abstract Unlike bromine, the effect of iodine chemistry on the Arctic surface ozone budget is poorly constrained. We present ship-based measurements of halogen oxides in the high Arctic boundary layer from the sunlit period of March to October 2020 and show that iodine enhances springtime tropospheric ozone depletion. We find that chemical reactions between iodine and ozone are the second highest contributor to ozone loss over the study period, after ozone photolysis-initiated loss and ahead of bromine.

We report on the search for overall kinematical or structural conditions that have allowed some Milky Way globular clusters to develop tidal tails. For this purpose, we built a comprehensive catalog of globular clusters with studies focused on their outermost regions and we classify the globular clusters in three categories: those with observed tidal tails, those with extra-tidal features that are different from tidal tails, and those without any signatures of extended stellar density profiles. When exploring different kinematical and structural parameter spaces, we found that globular clusters behave similarly, irrespective of the presence of tidal tails or any other kind of extra-tidal feature, or the absence thereof. In general, globular clusters whose orbits are relatively more eccentric and very inclined, with respect to the Milky Way plane, have undergone a larger amount of mass loss by tidal disruption. The latter has also accelerated the internal dynamics toward a comparatively more advanced stage of evolution. These outcomes show that it is not straightforward to find any particular set of parameter space and dynamical conditions that can definitely predict tidal tails along globular clusters in the Milky Way.

Atmospheric methane is both a potent greenhouse gas and photochemically active, with approximately equal anthropogenic and natural sources. The addition of chlorine to the atmosphere has been proposed to mitigate global warming through methane reduction by increasing its chemical loss. However, the potential environmental impacts of such climate mitigation remain unexplored. Here, sensitivity studies are conducted to evaluate the possible effects of increasing reactive chlorine emissions on the methane budget, atmospheric composition and radiative forcing. Because of non-linear chemistry, in order to achieve a reduction in methane burden (instead of an increase), the chlorine atom burden needs to be a minimum of three times the estimated present-day burden. If the methane removal target is set to 20%, 45%, or 70% less global methane by 2050 compared to the levels in the Representative Concentration Pathway 8.5 scenario (RCP8.5), our modeling results suggest that additional chlorine fluxes of 630, 1250, and 1880 Tg Cl/year, respectively, are needed. The results show that increasing chlorine emissions also induces significant changes in other important climate forcers. Remarkably, the tropospheric ozone decrease is large enough that the magnitude of radiative forcing decrease is similar to that of methane. Adding 630, 1250, and 1880 Tg Cl/year to the RCP8.5 scenario, chosen to have the most consistent current-day trends of methane, will decrease the surface temperature by 0.2, 0.4, and 0.6 °C by 2050, respectively. The quantity and method in which the chlorine is added, its interactions with climate pathways, and the potential environmental impacts on air quality and ocean acidity, must be carefully considered before any action is taken.

Dimethyl sulfide (DMS) produced by marine algae represents the largest natural emission of sulfur to the atmosphere. The oxidation of DMS is a key process affecting new particle formation that contributes to the radiative forcing of the Earth. In this study, atmospheric DMS and its major oxidation products (methanesulfonic acid, MSA; non-sea-salt sulfate, nss-SO42–) and particle size distributions were measured at King Sejong station located in the Antarctic Peninsula during the austral spring–summer period in 2018–2020. The observatory was surrounded by open ocean and first-year and multi-year sea ice. Importantly, oceanic emissions and atmospheric oxidation of DMS showed distinct differences depending on source regions. A high mixing ratio of atmospheric DMS was observed when air masses were influenced by the open ocean and first-year sea ice due to the abundance of DMS producers such as pelagic phaeocystis and ice algae. However, the concentrations of MSA and nss-SO42– were distinctively increased for air masses originating from first-year sea ice as compared to those originating from the open ocean and multi-year sea ice, suggesting additional influences from the source regions of atmospheric oxidants. Heterogeneous chemical processes that actively occur over first-year sea ice tend to accelerate the release of bromine monoxide (BrO), which is the most efficient DMS oxidant in Antarctica. Model-estimates for surface BrO confirmed that high BrO mixing ratios were closely associated with first-year sea ice, thus enhancing DMS oxidation. Consequently, the concentration of newly formed particles originated from first-year sea ice, which was a strong source area for both DMS and BrO was greater than from open ocean (high DMS but low BrO). These results indicate that first-year sea ice plays an important yet overlooked role in DMS-induced new particle formation in polar environments, where warming-induced sea ice changes are pronounced.

We report on the search for overall kinematical or structural conditions that have allowed some Milky Way globular clusters to develop tidal tails. For this purpose, we built a comprehensive catalog of globular clusters with studies focused on their outermost regions and we classify the globular clusters in three categories: those with observed tidal tails, those with extra-tidal features that are different from tidal tails, and those without any signatures of extended stellar density profiles. When exploring different kinematical and structural parameter spaces, we found that globular clusters behave similarly, irrespective of the presence of tidal tails or any other kind of extra-tidal feature, or the absence thereof. In general, globular clusters whose orbits are relatively more eccentric and very inclined, with respect to the Milky Way plane, have undergone a larger amount of mass loss by tidal disruption. The latter has also accelerated the internal dynamics toward a comparatively more advanced stage of evolution. These outcomes show that it is not straightforward to find any particular set of parameter space and dynamical conditions that can definitely predict tidal tails along globular clusters in the Milky Way.

Pastoral practices in the highlands of the Andes constitute a production strategy and a lifestyle involving a particular conception, perception and experience of space. Starting with the case of Susques in the Puna de Atacama (Jujuy Province, Argentina), we will analyse how, in a mountain environment, through intense seasonal mobility and a system of scattered settlements, shepherds are appropriating their domestic pasture territories. In turn, we propose that the mobilities are linked both to the use of strategic resources for animal breeding, in a mountain environment, and to the symbolic control of places of great importance for domestic groups. Throughout the text, we will work with the material which emerged from the fi eldwork that we have been developing in the area since 2004.

Abstract Tropospheric ozone ( ) is an important greenhouse gas and a surface pollutant. The future evolution of abundances and chemical processing are uncertain due to a changing climate, socioeconomic developments, and missing chemistry in global models. Here, we use an Earth System Model with natural halogen chemistry to investigate the changes in the budget over the 21st century following Representative Concentration Pathway (RCP)6.0 and RCP8.5 climate scenarios. Our results indicate that the global tropospheric net chemical change (NCC, chemical gross production minus destruction) will decrease , notwithstanding increasing or decreasing trends in ozone production and loss. However, a wide range of surface NCC variations (from −60 to 150 ) are projected over polluted regions with stringent abatements in precursor emissions. Water vapor and iodine are found to be key drivers of future tropospheric destruction, while the largest changes in production are determined by the future evolution of peroxy radicals. We show that natural halogens, currently not considered in climate models, significantly impact on the present‐day and future global burden reducing 30–35 Tg (11–15 ) of tropospheric ozone throughout the 21st century regardless of the RCP scenario considered. This highlights the importance of including natural halogen chemistry in climate model projections of future tropospheric ozone.

Abstract Question Biological soil crust ( BSC ) communities can be used in the identification and monitoring of degradation. A key question is how landscape‐scale livestock disturbance and other local‐scale factors influence BSC communities. We hypothesize that at the landscape scale, increased grazing pressure would lead to decreasing cover of BSC , but at the local scale biotic interactions between BSC and vascular plants would modulate the influence of grazing on BSC . Methods Spatially explicit sampling of vegetation composition and cover was conducted using point‐sampling methods in digital images along two disturbance gradients in the central Monte Desert in Argentina. Results The grazing gradient is the major determinant of changes in the structure of plant communities at the landscape scale. Approximately 1500 to 2000 m from a watering point, there is a threshold in vegetation structure associated with a nonlinear trend of the BSC , herb, grass and shrub cover. Bivariate spatial patterns show attraction between BSC and shrubs in the vicinity of settlements, and repulsion between BSC and both grasses and litter in less disturbed sites. Conclusion Grazing affects BSC directly through trampling and indirectly by altering vascular plant communities that interact with the BSC communities. Both these effects vary according to the spatial scale being considered. The results evidence that understanding of livestock impact in structuring arid ecosystems requires an integrated analysis of BSC and vascular plant communities at different spatial scales.