Absence of squirt singularities for the multi-phase Muskat problem

In this paper we study the evolution of multiple fluids with different constant densities in porous media. This physical scenario is known as the Muskat and the (multi-phase) Hele-Shaw problems. In this context we prove that the fluids do not develop squirt singularities.Comment: 16 page

A maximum principle for the Muskat problem for fluids with different densities

We consider the fluid interface problem given by two incompressible fluids with different densities evolving by Darcy's law. This scenario is known as the Muskat problem for fluids with the same viscosities, being in two dimensions mathematically analogous to the two-phase Hele-Shaw cell. We prove in the stable case (the denser fluid is below) a maximum principle for the $L^\infty$ norm of the free boundary.Comment: 16 page

Limnogeology in Southern South America: an overview

One of the major goals of Limnogeology is to provide clues on past Earth system environmental unevenness and feedbacks on longer time scales (100s-1,000s of years) than instrumental records, thus including periods with null or low anthropic influences on the environment. The multiproxy approach in the analysis of lake records allows to gain a wider overview than could be acquired from a single proxy data. Unlike the Northern Hemisphere, reconstructions of Late Pleistocene and Holocene environmental variability across Southern South America have been hampered by the paucity of complete and well-dated paleoclimate archives. However, last decades have been marked by a substantial increase of paleoclimatic research providing new data to analyze past climate variability from a regional perspective in Southern South America. This special issue include five articles applying a variety of proxy data (physical, chemical and biological) to elucidate climate and environmental changes on various time scales. Contributions cover a wide geographic distribution from the Antarctic Peninsula, Patagonia, Pampean region and NW Argentina up to the Río de la Plata Estuary. Results provide critical elements for further assessments of latitudinal paleo-circulation dynamics and hydroclimatic changes. The recent proliferation of limnogeological studies in Argentina and Uruguay evidence the reinforcement of regional research networks providing comparative and integrative analysis

Incompressible flow in porous media with fractional diffusion

In this paper we study the heat transfer with a general fractional diffusion term of an incompressible fluid in a porous medium governed by Darcy's law. We show formation of singularities with infinite energy and for finite energy we obtain existence and uniqueness results of strong solutions for the sub-critical and critical cases. We prove global existence of weak solutions for different cases. Moreover, we obtain the decay of the solution in $L^p$, for any $p\geq2$, and the asymptotic behavior is shown. Finally, we prove the existence of an attractor in a weak sense and, for the sub-critical dissipative case with $\alpha\in (1,2]$, we obtain the existence of the global attractor for the solutions in the space $H^s$ for any $s > (N/2)+1-\alpha$

Una visión paleolimnológica de la variabilidad hidroclimática reciente en el centro de Argentina: desde la pequeña edad de hielo al siglo XXI.

En este trabajo se presenta una revisión de diferentes estudios paleolimnológicos previamente publicados y desarrollados en la región subtropical Argentina, con la finalidad de efectuar comparaciones latitudinales de la respuesta hidrológica de estos sistemas lacustres frente a las variaciones de la circulación atmosférica asociada a la dinámica del Sistema Monzónico Sudamericano desde la Pequeña Edad de Hielo (PEH) hasta la actualidad. Con este objetivo se analizan y comparan los registros paleolimnológicos recientes (~ 250 años) de las lagunas Mar Chiquita (Córdoba), Melincué (Santa Fe) y Encadenadas del Oeste (Buenos Aires). La necesidad de analizar integradamente la variabilidad hidroclimática de alta (1 a 101 años) y baja frecuencia (102 años en adelante) en el centro de Argentina toma relevancia a partir del gran “salto hidroclimático” ocurrido durante la década de los años 70 en el sudeste del continente sudamericano. Este cambio caracterizado por un aumento notable en las precipitaciones ha sido registrado como uno de los mayores saltos hidrológicos ocurridos en ambientes continentales a nivel global. Debido a que algunos patrones de variabilidad climática se caracterizan por períodos largos, es difícil discernir si la variabilidad ambiental observada es natural o bien corresponde a una señal de cambio con múltiples forzantes (antrópicos + naturales). En este sentido las reconstrucciones hidroclimáticas basadas en indicadores múltiples (sedimentología, geoquímica, bioindicadores, isótopos estables) permiten conocer la variabilidad ambiental durante un período superior al percibido por los habitantes de una región afectada, aportando a la sociedad el conocimiento básico para abandonar la idea del clima estacionario, suministrando además herramientas para efectuar eficientemente la Gestión Integrada de los Recursos Hídricos. Las reconstrucciones paleohidrológicas y paleoambientales de las secuencias estudiadas indican que en general durante la finalización de la PEH predominaron condiciones áridas a lo largo de la región Pampeana, reflejadas por los niveles bajos a extremadamente bajos de las lagunas, con episodios de fases lacustres de niveles intermedios de menor duración. La PEH se habría extendido hasta la década de 1870/80 AD, momento que es indicado por el pasaje de sistemas lacustres efímeros a perennes. A partir de ca. 1870/80 AD y hasta 1976/77 AD se produce un mejoramiento climático progresivo a partir de un incremento sostenido de la humedad efectiva, que se refleja en los niveles intermedios alcanzados por las lagunas desde la segunda mitad del siglo XIX. Durante los últimos ~ 40 años se establecieron los niveles lacustres más altos registrados desde la PEH, dando lugar al establecimiento de las condiciones actuales de las lagunas. Los resultados obtenidos permiten perfeccionar los modelos planteados sobre la variabilidad hidroclimática pasada en las regiones ubicadas hacia el E-SE de la Diagonal Árida Sudamericana y aportan información crucial para descifrar la actividad del Sistema Monzónico Sudamericano en su zona de influencia más austral

El uso de parámetros magnéticos en estudios paleolimnológicos en Antártida

En esta contribución se describen las distintas técnicas y mediciones magnéticas utilizadas en Magnetismo Ambiental y Paleomagnetismo. Tales mediciones ofrecen útiles indicadores para realizar estudios relacionados con cambios climáticos y ambientales, así como herramientas de datación. Si bien es ampliamente conocida la utilidad de la susceptibilidad magnética, en primer lugar se discute el potencial y necesidad del uso de parámetros adicionales obtenidos a partir de mediciones de magnetizaciones remanentes (natural, anhistérica e isotérmica), histéresis magnética y estudios termomagnéticos. A continuación se presentan resultados magnéticos obtenidos en sedimentos lacustres del Archipiélago James Ross (NE de la Península Antártica) como un caso de estudio. Se complementa con estudios sedimentológicos, hidroquímicos, geoquímicos y de estadística multivariada, pero se pone énfasis en los parámetros magnéticos y su relación con los distintos procesos que ocurren en los sistemas lacustres antárticos. Se analiza además el uso de las paleointensidades relativas como herramienta de datación en lagunas antárticas

On the origin and processes controlling the elemental and isotopic composition of carbonates in hypersaline Andean lakes

H.J. and J.W.B. Rae acknowledge funding from the European Research Council under the European Union’s Horizon 2020 research and innovation program (grant agreement 805246).The Altiplano-Puna Plateau of the Central Andes hosts numerous lakes, playa-lakes, and salars with a great diversity and abundance of carbonates forming under extreme climatic, hydrologic, and environmental conditions. To unravel the underlying processes controlling the formation of carbonates and their geochemical signatures in hypersaline systems, we investigated coupled brine-carbonate samples in a high-altitude Andean lake using a wide suite of petrographic (SEM, XRD) and geochemical tools (δ2H, δ18O, δ13C, δ11B, major and minor ion composition, aqueous modelling). Our findings show that the inflow of hydrothermal springs in combination with strong CO2 degassing and evaporation plays an important role in creating a spatial diversity of hydro-chemical sub-environments allowing different types of microbialites (microbial mounds and mats), travertines, and fine-grained calcite minerals to form. Carbonate precipitation occurs in hot springs triggered by a shift in carbonate equilibrium by hydrothermal CO2 degassing and microbially-driven elevation of local pH at crystallisation. In lakes, carbonate precipitation is induced by evaporative supersaturation, with contributions from CO2 degassing and microbiological processes. Lake carbonates largely record the evaporitic enrichment (hence salinity) of the parent water which can be traced by Na, Li, B, and δ18O, although other factors (such as e.g., high precipitation rates, mixing with thermal waters, groundwater, or precipitation) also affect their signatures. This study is of significance to those dealing with the fractionation of oxygen, carbon, and boron isotopes and partitioning of elements in natural brine-carbonate environments. Furthermore, these findings contribute to the advancement in proxy development for these depositional environments.Peer reviewe

Seismic structure of the northern continental margin of Spain from ESCIN deep seismic profiles

By the end of the Carboniferous, the crust of the continental shelf in northwestern Spain was made up of deeply rooted structures related to the Variscan collision. From Permian to Triassic times the tectonic setting had changed to mainly extensional and the northern Iberian continental margin underwent rifting during Late Jurassic-Early Cretaceous times, along with sea-floor spreading and the opening of the Bay of Biscay until the Late Cretaceous. Subsequently, the northern Iberian margin was active during the north-south convergence of Eurasia and Iberia in the Tertiary. A multichannel seismic experiment, consisting of two profiles, one north-south (ESCIN-4) crossing the platform margin offshore Asturias, and another (ESCIN-3) crossing the platform margin to the northwest of Galicia, was designed to study the structure of the northern Iberian margin. The ESCIN-4 stacked section reveals inverted structures in the upper crust within the Le Danois Basin. North of the steep continental slope, ESCIN-4 shows a thick sedimentary package from 6 to 9.5 s, two-way travel time (TWT). Within this latter package, a 40-km-long, north-tapering wedge of inclined, mainly south-dipping reflections is thought to represent a buried, Alpine-age accretionary prism. In the north western part of the ESCIN-3 (ESCIN-3-1) stacked section, horizontal reflections from 6.5 to 8.5 s correspond to an undisturbed package of sediments lying above oceanic-type basement. In this part of the line, a few kilometres long, strong horizontal reflection at 11.2 s within the basement may represent an oceanic Moho reflection. Also, a band of reflections dips gently towards the southeast, from the base of the gently dipping continental slope. The part of ESCIN-3 line that runs parallel to the NW-Galicia coast (ESCIN-3-2), is characterized by bright, continuous lower crustal reflections from 8 to 10 s. Beneath the lower crustal reflectivity, a band of strong reflections dips gently toward the southwest from 10 to 13.5 s. The part of ESCIN-3 that parallels the northern margin (ESCIN 3-3), shows good reflectivity in all levels. Upper crustal reflections image the sedimentary fill of probable Mesozoic to recent basins. Mid-crustal reflectivity is characterized by dipping reflections until 8 s that are probably related to compressional Variscan features. The lower crustal level shows 'layered' reflections between 8 and 12 s. Dipping reflections are found below the continental Moho.J. Alvarez-Marrón held a post-doc research grant from the Ministry of Education and Science of Spain. The ESCI-N program was sponsored by the Spanish agencies CICYT (project GEO 90-0660) and FICYT, and STRIDE Program of the EU.Peer Reviewe

Ozone Eliminates SARS-CoV-2 from Difficult-to-Clean Office Supplies and Clinical Equipment.

Background: Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) continues to cause profound health, economic, and social problems worldwide. The management and disinfection of materials used daily in health centers and common working environments have prompted concerns about the control of coronavirus disease 2019 (COVID-19) infection risk. Ozone is a powerful oxidizing agent that has been widely used in disinfection processes for decades. The aim of this study was to assess the optimal conditions of ozone treatment for the elimination of heat-inactivated SARS-CoV-2 from office supplies (personal computer monitors, keyboards, and computer mice) and clinical equipment (continuous positive airway pressure tubes and personal protective equipment) that are difficult to clean. (2) Methods: The office supplies and clinical equipment were contaminated in an area of 1 cm2 with 1 × 104 viral units of a heat-inactivated SARS-CoV-2 strain, then treated with ozone using two different ozone devices: a specifically designed ozonation chamber (for low–medium ozone concentrations over large volumes) and a clinical ozone generator (for high ozone concentrations over small volumes). SARS-CoV-2 gene detection was carried out using quantitative real-time polymerase chain reaction (RT-qPCR). (3) Results: At high ozone concentrations over small surfaces, the ozone eliminated SARS-CoV-2 RNA in short time periods—i.e., 10 min (at 4000 ppm) or less. The optimum ozone concentration over large volumes was 90 ppm for 120 min in ambient conditions (24 °C and 60–75% relative humidity). (4) Conclusions: This study showed that the appropriate ozone concentration and exposure time eliminated heat-inactivated SARS-CoV-2 RNA from the surfaces of different widely used clinical and office supplies, decreasing their risk of transmission, and improving their reutilization. Ozone may provide an additional tool to control the spread of the COVID-19 pandemic.TRUEInstituto de Salud Carlos III, Madrid, Spain, and by the European Regional Development Funds (FEDER)Fundación Canaria del Instituto de Investigación Sanitaria de Canarias (FIISC), Las PalmasFundación Mapfre Guanarteme, Las PalmasGobierno de Canarias, Las Palmaspu

El uso de parámetros magnéticos en estudios paleolimnológicos en Antártida

En esta contribución se describen las distintas técnicas y mediciones magnéticasutilizadas en Magnetismo Ambiental y Paleomagnetismo. Tales mediciones ofrecen útilesindicadores para realizar estudios relacionados con cambios climáticos y ambientales,así como herramientas de datación. Si bien es ampliamente conocida la utilidad de lasusceptibilidad magnética, en primer lugar se discute el potencial y necesidad del uso deparámetros adicionales obtenidos a partir de mediciones de magnetizaciones remanentes(natural, anhistérica e isotérmica), histéresis magnética y estudios termomagnéticos. Acontinuación se presentan resultados magnéticos obtenidos en sedimentos lacustresdel Archipiélago James Ross (NE de la Península Antártica) como un caso de estudio.Se complementa con estudios sedimentológicos, hidroquímicos, geoquímicos y deestadística multivariada, pero se pone énfasis en los parámetros magnéticos y su relacióncon los distintos procesos que ocurren en los sistemas lacustres antárticos. Se analizaademás el uso de las paleointensidades relativas como herramienta de datación enlagunas antárticas