Photoionization and transient Wannier-Stark ladder in silicon: First-principles simulations versus Keldysh theory

Nonlinear photoionization of dielectrics and semiconductors is widely treated in the framework of the Keldysh theory whose validity is limited to photon energies that are small compared to the band gap and relatively low laser intensities. The time-dependent density functional theory (TDDFT) simulations, which are free of these limitations, enable one to gain insight into nonequilibrium dynamics of the electronic structure. Here we apply TDDFT to investigate the photoionization of silicon crystal by ultrashort laser pulses in a wide range of laser wavelengths and intensities and compare the results with predictions of the Keldysh theory. Photoionization rates derived from the simulations considerably exceed the data obtained with the Keldysh theory within the validity range of the latter. Possible reasons for the discrepancy are discussed and we provide fundamental data on the photoionization rates beyond the limits of the Keldysh theory. By investigating the features of the Stark shift as a function of photon energy and laser field strength, a manifestation of the transient Wannier-Stark ladder states is revealed, which become blurred with increasing laser field strength. Finally, it is shown that the TDDFT simulations can potentially provide reliable data on the electron damping time that is of high importance for large-scale modeling

Probing the low-energy electron-scattering dynamics in liquids with high-harmonic spectroscopy

High-harmonic spectroscopy (HHS) is a nonlinear all-optical technique with inherent attosecond temporal resolution, which has been applied successfully to a broad variety of systems in the gas phase and solid state. Here, we extend HHS to the liquid phase, and uncover the mechanism of high-harmonic generation (HHG) for this phase of matter. Studying HHG over a broad range of wavelengths and intensities, we show that the cut-off (Ec) is independent of the wavelength beyond a threshold intensity, and find that Ec is a characteristic property of the studied liquid. We explain these observations within an intuitive semi-classical model based on electron trajectories that are limited by scattering to a characteristic length, which is connected to the electron mean-free path. Our model is validated against rigorous multi-electron time-dependent density-functional theory calculations in, both, supercells of liquid water with periodic boundary conditions, and large clusters of a variety of liquids. These simulations confirm our interpretation and thereby clarify the mechanism of HHG in liquids. Our results demonstrate a new, all-optical access to effective mean-free paths of slow electrons (≤10 eV) in liquids, in a regime that is inaccessible to accurate calculations, but is critical for the understanding of radiation damage to living tissue. Our work also establishes the possibility of resolving sub-femtosecond electron dynamics in liquids, which offers a novel, all-optical approach to attosecond spectroscopy of chemical processes in their native liquid environment

Inherited biotic protection in a Neotropical pioneer plant

Chelonanthus alatus is a bat-pollinated, pioneer Gentianaceae that clusters in patches where still-standing, dried-out stems are interspersed among live individuals. Flowers bear circum-floral nectaries (CFNs) that are attractive to ants, and seed dispersal is both barochorous and anemochorous. Although, in this study, live individuals never sheltered ant colonies, dried-out hollow stems - that can remain standing for 2 years - did. Workers from species nesting in dried-out stems as well as from ground-nesting species exploited the CFNs of live C. alatus individuals in the same patches during the daytime, but were absent at night (when bat pollination occurs) on 60.5% of the plants. By visiting the CFNs, the ants indirectly protect the flowers - but not the plant foliage - from herbivorous insects. We show that this protection is provided mostly by species nesting in dried-out stems, predominantly Pseudomyrmex gracilis. That dried-out stems remain standing for years and are regularly replaced results in an opportunistic, but stable association where colonies are sheltered by one generation of dead C. alatus while the live individuals nearby, belonging to the next generation, provide them with nectar; in turn, the ants protect their flowers from herbivores. We suggest that the investment in wood by C. alatus individuals permitting stillstanding, dried-out stems to shelter ant colonies constitutes an extended phenotype because foraging workers protect the flowers of live individuals in the same patch. Also, through this process these dried-out stems indirectly favor the reproduction (and so the fitness) of the next generation including both their own offspring and that of their siblings, alladding up to a potential case of inclusive fitness in plants

Analysis of biological diversity and miscegenation in the city of Puerto Madryn (Prov.of Chubut, Argentina)

En el marco del estudio de la composición genética de las poblaciones cosmopolitas de Argentina, se analizó una muestra poblacional de la localidad de Puerto Madryn (PM) con la finalidad de evaluar su diversidad biológica mediante la utilización de marcadores biparentales y uniparentales y comparar los resultados con los obtenidos previamente por nuestro equipo de investigación en seis poblaciones cosmopolitas de distintas regiones de la Argentina, aunque poniendo el énfasis a las correspondientes a la Región Patagónica. Las muestras biológicas fueron tomadas con consentimiento informado a 82 dadores de sangre no emparentados que concurrieron al Banco de Sangre y al Hospital Subzonal de dicha localidad, a quienes también se les realizó una encuesta genealógica. A partir de los datos proporcionados por los marcadores autosómicos se registró una contribución europea de 67.2%, amerindia de 29.4% y africana de 3.4%. A un origen amerindio fueron adscriptos el 59.9% y 8.7% de los linajes maternos y paternos, respectivamente, revelando un desigual aporte autóctono por género. El aporte europeo se vio representado principalmente por el Hg H (19.5%) y se detectaron sólo dos linajes subsaharianos. En PM las migraciones desde el centro del país han generado un fuerte impacto, reflejado en la mayor contribución de marcadores europeos respecto de dos muestras estudiadas previamente en Chubut (Comodoro Rivadavia y Esquel). Estas diferencias al interior de una misma provincia nos advierten que no puede abordarse el análisis de la constitución genética de las poblaciones sin dar cuenta de las particularidades regionales.In the frame of the study of the genetic composition of Argentinean cosmopolitan populations, a population sample of the city of Puerto Madryn (PM) was analyzed in order to evaluate its biological diversity using biparental and uniparental markers and compare the results with those previously obtained by our research team in six cosmopolitan populations from different regions of Argentina. The emphasis was laid on the populations of the Patagonia region. Biological samples were taken with informed consent from 82 unrelated blood donors, who attended the Regional Blood Bank and Hospital of the town and also underwent a genealogical survey. From the data obtained by analyzing autosomal markers, a European contribution of 67.2%, an Amerindian one of 29.4%, and an African one of 3.4% were estimated. The 59.9% and 8.7% of the maternal and paternal lineages, respectively, were ascribed to Native American origins, revealing an unequal gender indigenous contribution. The European contribution was mainly represented by H Hg (19.5%), and only two sub-Saharan lineages were detected. In PM, migrations from the center of the country have had a strong impact, as reflected in the greater contribution of European markers, with respect to the two samples previously studied in the province of Chubut (Comodoro Rivadavia and Esquel). These differences warn us of the necessity of accounting for the regional particularities when analyzing the genetic constitution of populations.Fil: Parolin, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Avena, Sergio Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Maimónides. Area de Investigaciones Biomédicas y Biotecnológicas. Centro de Estudios Biomédicos, Biotecnológicos, Ambientales y de Diagnóstico; Argentina. Universidad de Buenos Aires. Facultad de Filosofía y Letras. Instituto de Ciencias Antropologicas; ArgentinaFil: Fleischer, Silvina. Puerto Madryn. Hospital Subzonal Andrés Isola; ArgentinaFil: Pretell, Mariana. Puerto Madryn. Hospital Subzonal Andrés Isola; ArgentinaFil: Di Fabio Rocca, Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Filosofía y Letras. Instituto de Ciencias Antropologicas; Argentina. Universidad Maimónides. Area de Investigaciones Biomédicas y Biotecnológicas. Centro de Estudios Biomédicos, Biotecnológicos, Ambientales y de Diagnóstico; ArgentinaFil: Rodriguez, Debora A.. Universidad Maimonides. Area de Invest.biomedicas y Biotecnologicas; Argentina. Universidad Maimónides. Area de Investigaciones Biomédicas y Biotecnológicas. Centro de Estudios Biomédicos, Biotecnológicos, Ambientales y de Diagnóstico; ArgentinaFil: Dejean, Cristina B.. Universidad Maimónides. Area de Investigaciones Biomédicas y Biotecnológicas. Centro de Estudios Biomédicos, Biotecnológicos, Ambientales y de Diagnóstico; Argentina. Universidad de Buenos Aires. Facultad de Filosofía y Letras. Instituto de Ciencias Antropologicas; ArgentinaFil: Postillone, María Bárbara. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Filosofía y Letras. Instituto de Ciencias Antropologicas; Argentina. Universidad Maimónides. Area de Investigaciones Biomédicas y Biotecnológicas. Centro de Estudios Biomédicos, Biotecnológicos, Ambientales y de Diagnóstico; ArgentinaFil: Vaccaro, Maria S.. Universidad Maimónides. Area de Investigaciones Biomédicas y Biotecnológicas. Centro de Estudios Biomédicos, Biotecnológicos, Ambientales y de Diagnóstico; Argentina. Universidad de Buenos Aires. Facultad de Filosofía y Letras. Instituto de Ciencias Antropologicas; ArgentinaFil: Dahinten, Silvia Lucrecia V.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Manera, Guillermo. Puerto Madryn. Hospital Subzonal Andrés Isola; ArgentinaFil: Carnese, Francisco Raul. Universidad de Buenos Aires. Facultad de Filosofía y Letras. Instituto de Ciencias Antropologicas; Argentina. Universidad Maimónides. Area de Investigaciones Biomédicas y Biotecnológicas. Centro de Estudios Biomédicos, Biotecnológicos, Ambientales y de Diagnóstico; Argentin

Spatial Distribution of Dominant Arboreal Ants in a Malagasy Coastal Rainforest: Gaps and Presence of an Invasive Species

We conducted a survey along three belt transects located at increasing distances from the coast to determine whether a non-random arboreal ant assemblage, such as an ant mosaic, exists in the rainforest on the Masoala Peninsula, Madagascar. In most tropical rainforests, very populous colonies of territorially dominant arboreal ant species defend absolute territories distributed in a mosaic pattern. Among the 29 ant species recorded, only nine had colonies large enough to be considered potentially territorially dominant; the remaining species had smaller colonies and were considered non-dominant. Nevertheless, the null-model analyses used to examine the spatial structure of their assemblages did not reveal the existence of an ant mosaic. Inland, up to 44% of the trees were devoid of dominant arboreal ants, something not reported in other studies. While two Crematogaster species were not associated with one another, Brachymyrmex cordemoyi was positively associated with Technomyrmex albipes, which is considered an invasive species—a non-indigenous species that has an adverse ecological effect on the habitats it invades. The latter two species and Crematogaster ranavalonae were mutually exclusive. On the other hand, all of the trees in the coastal transect and at least 4 km of coast were occupied by T. albipes, and were interconnected by columns of workers. Technomyrmex albipes workers collected from different trees did not attack each other during confrontation tests, indicating that this species has formed a supercolony along the coast. Yet interspecific aggressiveness did occur between T. albipes and Crematogaster ranavalonae, a native species which is likely territorially dominant based on our intraspecific confrontation tests. These results suggest that the Masoala rainforest is threatened by a potential invasion by T. albipes, and that the penetration of this species further inland might be facilitated by the low density of native, territorially dominant arboreal ants normally able to limit its progression

Enhanced high-harmonic generation from chromium-doped magnesium oxide

High-order harmonic generation (HHG) from crystals offers a new source of coherent extreme ultraviolet (XUV) attosecond radiation.Comment: Significant change of conten

Estimation of Fish Biomass Using Environmental DNA

Environmental DNA (eDNA) from aquatic vertebrates has recently been used to estimate the presence of a species. We hypothesized that fish release DNA into the water at a rate commensurate with their biomass. Thus, the concentration of eDNA of a target species may be used to estimate the species biomass. We developed an eDNA method to estimate the biomass of common carp (Cyprinus carpio L.) using laboratory and field experiments. In the aquarium, the concentration of eDNA changed initially, but reached an equilibrium after 6 days. Temperature had no effect on eDNA concentrations in aquaria. The concentration of eDNA was positively correlated with carp biomass in both aquaria and experimental ponds. We used this method to estimate the biomass and distribution of carp in a natural freshwater lagoon. We demonstrated that the distribution of carp eDNA concentration was explained by water temperature. Our results suggest that biomass data estimated from eDNA concentration reflects the potential distribution of common carp in the natural environment. Measuring eDNA concentration offers a non-invasive, simple, and rapid method for estimating biomass. This method could inform management plans for the conservation of ecosystems