Manual introductorio de ecotoxicología acuatica

El presente Manual muestra los métodos revisados de pruebas de toxicidad por agencias ambientales extranjeras, los cuales han sido adaptados empleando organismos que habitan el mar peruano. Se presenta la recopilación de las experiencias propias realizadas mediante la estandarización de protocolos que se han desarrollado desde 1988 en el Instituto del Mar del Perú.40 p.IMARP

Strong coupling between weakly guided semiconductor nanowire modes and an organic dye

The light-matter coupling between electromagnetic modes guided by a semiconductor nanowire and excitonic states of molecules localized in its surrounding media is studied from both classical and quantum perspectives, with the aim of describing the strong-coupling regime. Weakly guided modes (bare photonic modes) are found through a classical analysis, identifying those lowest-order modes presenting large electromagnetic fields spreading outside the nanowire while preserving their robust guided behavior. Experimental fits of the dielectric permittivity of an organic dye that exhibits excitonic states are used for realistic scenarios. A quantum model properly confirms through an avoided mode crossing that the strong-coupling regime can be achieved for this configuration, leading to Rabi splitting values above 100 meV. In addition, it is shown that the coupling strength depends on the fraction of energy spread outside the nanowire, rather than on the mode field localization. These results open up a new avenue towards strong-coupling phenomenology involving propagating modes in nonabsorbing media.The authors acknowledge the Spanish Ministerio de Economía, Industria y Competitividad for financial support through Grants No. MAT2014-53432-C5-5-R, No. FIS2015-69295-C3-2-P, and No. FIS2017-91413-EXP; the María de Maeztu program for Units of Excellence in R&D (MDM-2014-0377); and an FPU Fellowship (D.R.A.) and a Ramón y Cajal grant (J.F.). We also acknowledge funding from the European Research Council (ERC-2016-STG-714870

Directional emission from leaky and guided modes in GaAs nanowires measured by cathodoluminescence

8 págs.; 4 figs.We measure the polarization-resolved angular emission distribution from thin and thick GaAs nanowires (diameters ∼110 and ∼180 nm) with cathodoluminescence polarimetry. The nanowires, which horizontally rest on a thin carbon film, are excited by a 5 keV electron beam and emit band gap luminescence at a central wavelength of 870 nm. The emission can couple to different waveguide modes that propagate along the wire, are dependent on the wire diameter, and determine the directionality and polarization of the emission. Although each measured nanowire can support different modes, the polarized emission is dominated by the TM01 waveguide mode in all cases, independently of wire diameter. When exciting the nanowires close to the end facets, the thin and thick wires exhibit opposite directional emission. The emission from thin nanowires is dominated by a leaky TM01 mode that leads to emission toward the opposite end facet (emission to the right when exciting the left-side edge). For the thick wires, however, the TM01 mode is guided but also lossy due to absorption in the substrate. In such a case, the wires emit toward the excited end facet (to the left when exciting the left-side edge). The emission directionality switches for nanowire diameters in the range of 145-170 nm. We show that the measurements agree well with both a simple 1D current model and numerical simulations. The high spatial resolution of angle- and polarization-resolved cathodoluminescence spectroscopy provides detailed insight into the nanoscale emission and propagation of light in semiconductor nanowires. Copyright © 2016 American Chemical SocietyThis work is part of the Stichting voor Fundamenteel Onderzoek der Materie (FOM) as well as the Dutch Technology Foundation STW, which are financially supported by the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) and the Dutch Ministry of Economic Affairs. It is also part of NanoNextNL, a nanotechnology program funded by the Dutch Ministry of Economic Affairs, part of an industrial partnership program between Philips and FOM, and is supported by the European Research Council (ERC). The Spanish Ministerio de Economıía y Competitividad is also acknowledged for financial support through the grants NANOPLAS+ (FIS2012-31070) and LENSBEAM (FIS2015- 69295-C3-2-P).Peer Reviewe

Germination characteristics of Gymnocalycium monvillei (Cactaceae) along its entire altitudinal range

"Germination characteristics are important for understanding how species cope with environmental variation. The aims of this work were to analyze the effect of different temperatures (25 and 32 °C), water potentials (0, −0.2, −0.4, and −0.6 MPa), and light conditions (light vs. darkness) on the germination of five populations of the cactus Gymnocalycium monvillei (Lem.) Britton & Rose along its entire altitudinal distribution. The experiments to assess the effects of temperature, water potential, and light conditions were performed in germination chambers, and total germination (%) and mean germination time (T50) were recorded. Germination decreased in provenances from higher to lower altitudes, and the effect was very pronounced at temperatures of 32 °C. For all of the altitudinal provenances, germination decreased with lower water potential, with this effect being more pronounced at 32 °C. On the other hand, provenances at lower altitudes were less affected by lower water potentials than higher provenances. Provenances at all altitudes showed very low germination under dark conditions. T50 did not vary among altitudinal provenances at a temperature of 25 °C, but at 32 °C germination was slower at intermediate altitudes. Our results show that germination characteristics differ considerably among altitudinal provenances and seem to be important in determining the capacity of the species to inhabit such a broad gradient.

Are seed mass and seedling size and shape related to altitude? Evidence in Gymnocalycium monvillei (Cactaceae)

"Several studies reported a negative relationship between altitude and seed mass. In cactus species, seed mass has been also related to seedling morphology (size and shape). Here we studied Gymnocalycium monvillei (Lem.) Pfeiff. ex Britton & Rose, a cactus species with a wide altitudinal distribution, with the main aim of analyzing how altitude affects seed mass and seedling size (height and width) and shape (globose or columnar). We collected seeds from five sites along the entire altitudinal distribution of the species in the Córdoba Mountains (sites were located between 878 and 2230 m a.s.l.), encompassing a marked climatic gradient (6 °C of mean annual temperature difference between the extreme sites). Seed mass and seedling traits were measured in the laboratory. Seedling height increased with altitude, whereas seed mass was not related to this parameter. Seedlings became more globose (reduced surface/volume ratio) with decreasing altitude. Variation in seedling shape along the altitudinal gradient may be related to the contrasting climatic conditions to which seedlings are exposed, and could account for the wide altitudinal distribution of G. monvillei. Our results highlight the importance of seedling traits in the species’ response to climatic change.

Engineering bound states in the continuum at telecom wavelengths with non-Bravais lattices

Various optical phenomena can be induced in periodic arrays of nanoparticles by the radiative coupling of the local dipoles in each particle. Probably the most impressive example is bound states in the continuum (BICs), which are electromagnetic modes with a dispersion inside the light cone but infinite lifetime, i.e., modes that cannot leak to the continuum. Symmetry-protected BICs appear at highly symmetric points in the dispersion of periodic systems. Although the addition of nonequivalent lattice points in a unit cell is an easy and straightforward way of tuning the symmetry, BICs in such particle lattice, i.e., non-Bravais lattice, are less explored among periodic systems. Starting from a periodic square lattice of Si nanodisks, we have prepared three non-Bravais lattices by detuning size and position of the second disk in the unit cell. Diffraction-induced coupling excites magnetic/electric dipoles in each nanodisk, producing two surface lattice resonances at the $\Gamma$ point with a band gap in between. %of $\sim$ 41 meV. The high/low energy branch becomes a BIC for the size/position-detuned array, respectively, while both branches are bright (or leaky) when both size and position are detuned simultaneously. The role of magnetic and electric resonances in dielectric nanoparticles and the change of BIC to bright character of the modes is explained by the two different origins of BICs in the detuned arrays, which is further discussed with the aid of a coupled electric and magnetic dipole model. This study gives a simple way of tuning BICs at telecom wavelengths in non-Bravais lattices, including both plasmonic and dielectric systems, thus scalable to a wide range of frequencies.Comment: 26 pages, 5 figure

Combined effect of water potential and temperature on seed germination and seedling development of cacti from a mesic Argentine ecosystem

"Global climatic change will be associated with an increase of droughts and heat waves, which can affect seed germination and plant population dynamics. Cactus species from mesic ecosystems are likely to be more affected by these events than species from arid ecosystems. The aim of the study was to assess the combined effect of water potentials and temperatures on seed germination and seedling traits in six globose cactus species from Córdoba Mountains: Echinopsis candicans, Gymnocalycium bruchii, G. capillense, G. mostii, G. quehlianum and Parodia mammulosa. A factorial experiment was performed in which four water potential levels (0, ?0.2, ?0.4 and ?0.6 MPa) were combined with two temperature levels (25 and 32 °C). Germination (%) and mean germination time (T50) were recorded and seedling shape (width and length) was measured. In general, a decrease in water potential and an increase in temperature resulted in low germination, with different behaviors among species. At 32 °C and low water potentials, germination was low or null for almost all species. There was not a clear trend in the response of T50 to the treatments. Seedling development was highly and negatively affected by the combination of factors, particularly at low water potentials. The responses of the analyzed cactus species to low water potential were similar to those of cactus species from more arid ecosystems. Our results suggest that the studied species would be severely affected by changes in temperature and precipitation as predicted under a climate change scenario.

Celdas solares de tercera generación a base de puntos cuánticos y perovskitas

Third generation solar cells are photovoltaic devices fabricated with low cost materials and are attractive because the cost to efficiency ratio is significantly reduced. These devices are fabricated using semiconductor materials with a structure in the nanoscale. At these dimensions, these materials present interesting optical and electrical properties. Light absorption can be tuned by controlling particle size and there is also charge transport at the interfaces of the materials. Among the most studied solar cells in this generation are: the organic solar cells, the quantum dot sensitized solar cells and the perovskite solar cell. Different technologies require different manufacturing methods and distinct efficiencies. The quantum dot sensitized solar cells have a record of 12%, while the perovskite solar cells have a record of 24% in photoconversion efficiency.Las celdas solares de tercera generación son dispositivos fotovoltaicos fabricados con materiales de bajo costo y son atractivas debido a que reducen significativamente la razón costo/eficiencia. Este tipo de dispositivos son fabricados utilizando materiales semiconductores con estructuras a escala nanométrica, los cuales presentan propiedades ópticas y eléctricas muy interesantes, como es la sintonización de absorción de luz con el tamaño de la partícula y el trasporte de carga entre cada interface de los materiales. Las más estudiadas son: las celdas orgánicas, las sensibilizadas por puntos cuánticos y las celdas solares basadas en perovskitas. Cada tipo de tecnología presenta distintas formas de fabricación y distintas eficiencias. Las celdas solares sensibilizadas con puntos cuánticos actualmente presentan eficiencia de alrededor del 12%, mientras que las celdas de perovskita han llegado a tener hasta 24% de eficiencia

Room Temperature Exciton-Polariton Condensation in Silicon Metasurfaces Emerging from Bound States in the Continuum

We show the first experimental demonstration of room-temperature exciton-polariton (EP) condensation from a bound state in the continuum (BIC). This demonstration is achieved by strongly coupling stable excitons in an organic perylene dye with the extremely long-lived BIC in a dielectric metasurface of silicon nanoparticles. The long lifetime of the BIC, mainly due to the suppression of radiation leakage, allows for EP thermalization to the ground state before decaying. This property results in a condensation threshold of less than 5 \mu J cm^{-2}, one order of magnitude lower that the lasing threshold reported in similar systems in the weak coupling limit

Stability and relaxation mechanisms of citric acid coated magnetite nanoparticles for magnetic hyperthermia

Magnetite (Fe3O4) nanoparticles are proper materials for Magnetic Fluid Hyperthermia applications whenever these conjugate stability at physiological (neutral pH) medium and high specific dissipation power. Here, magnetite nanoparticles 9–12 nm in size, electrostatically stabilized by citric acid coating, with hydrodynamic sizes in the range 17–30 nm, and well dispersed in aqueous solution were prepared using a chemical route. The influence of media acidity during the adsorption of citric acid (CA) on the suspension’s long-term stability was systematically investigated. The highest content of nanoparticles in a stable suspension at neutral pH is obtained for coating performed at pH = 4.58, corresponding to the larger amount of CA molecules adsorbed by one carboxylate link. Specific absorption rates (SARs) of various magnetite colloids, determined calorimetrically at a radio frequency field of 265 kHz and field amplitude of 40.1 kA/m, are analyzed in terms of structural and magnetic colloid properties. Larger dipolar interactions lead to larger Néel relaxation times, in some cases larger than Brown relaxation times, which in the present case enhanced magnetic radio frequency heating. The improvement of suspension stability results in a decrease of SAR values, and this decrease is even large in comparison with uncoated magnetite nanoparticles. This fact is related to interactions between particles.Instituto de Física La Plat