Dielectric confinement of excitons in type-I and type-II semiconductor nanorods.

We theoretically study the effect of the dielectric environment on the exciton ground state of CdSe and CdTe/CdSe/CdTe nanorods. We show that insulating environments enhance the exciton recombination rate and blueshift the emission peak by tens of meV. These effects are particularly pronounced for type-II nanorods. In these structures, the dielectric confinement may even modify the spatial distribution of the electron and hole charges. A critical electric field is required to separate electrons from holes, whose value increases with the insulating strength of the surroundings.

Ocean acidification effects on the stress response in a calcifying antarctic coastal organism: The case of Nacella concinna ecotypes.

Ocean acidification (OA) could become a serious threat for the Antarctic marine ecosystem over coming years, as the solubility of atmospheric CO2 and CaCO3 minerals increases at lower temperatures. We evaluated the effect of OA on the stress response of the limpet Nacella concinna by measuring gene expression levels. The experiment was performed with the two ecotypes (Littoral and Sublittoral) of the species during 54 days (IPCC, 2019 scenario RCP8.5; control, ~375 ppm; low-pH treatment, ~923 ppm). Exposure to low-pH treatment during 15 days triggered the down-regulation of two heat-shock protein genes (HSP70A, HSP70B) only in sublittoral individuals. Little variation in the relative expression values of all genes in both ecotypes was observed probably, due to a historical exposure to the substantial daily natural pH fluctuations recorded in the study area during the experiment. This study provides relevant baseline data for future OA experiments on coastal species in Antarctica.

Molecular mechanisms underlying responses of the Antarctic coral Malacobelemnon daytoni to ocean acidification.

Benthic organisms of the Southern Ocean are particularly vulnerable to ocean acidification (OA), as they inhabit cold waters where calcite-aragonite saturation states are naturally low. OA most strongly affects animals with calcium carbonate skeletons or shells, such as corals and mollusks. We exposed the abundant cold-water coral Malacobelemnon daytoni from an Antarctic fjord to low pH seawater (LpH) (7.68 ± 0.17) to test its physiological responses to OA, at the level of gene expression (RT-PCR) and enzyme activity. Corals were exposed in short- (3 days) and long-term (54 days) experiments to two pCO2 conditions (ambient and elevated pCO2 equaling RCP 8.5, IPCC 2019, approximately 372.53 and 956.78 µatm, respectively). Of the eleven genes studied through RT-PCR, six were significantly upregulated compared with control in the short-term in the LpH condition, including the antioxidant enzyme superoxide dismutase (SOD), Heat Shock Protein 70 (HSP70), Toll-like receptor (TLR), galaxin and ferritin. After long-term exposure to low pH conditions, RT-PCR analysis showed seven genes were upregulated. These include the mannose-binding C-Lectin and HSP90. Also, the expression of TLR and galaxin, among others, continued to be upregulated after long-term exposure to LpH. Expression of carbonic anhydrase (CA), a key enzyme involved in calcification, was also significantly upregulated after long-term exposure. Our results indicated that, after two months, M. daytoni is not acclimatized to this experimental LpH condition. Gene expression profiles revealed molecular impacts that were not evident at the enzyme activity level. Consequently, understanding the molecular mechanisms behind the physiological processes in the response of a coral to LpH is critical to understanding the ability of polar species to cope with future environmental changes. Approaches integrating molecular tools into Antarctic ecological and/or conservation research make an essential contribution given the current ongoing OA processes.

Correlation in narrow nanorods: a variational potential-configuration interaction scheme.

Full configuration interaction calculations for two electrons in narrow semiconductor nanorods are carried out employing different orbital basis sets. It is shown that the usual configurations built from single-particle states cannot yield a correct singlet-triplet energetic order regardless of the basis size, as they miss the correlation energy. Mean-field optimized orbitals partially correct this drawback. A new approach is introduced, based on a simple variational procedure, which yields robust results.

Restructuring of the sponge microbiome favors tolerance to ocean acidification.

Ocean acidification is increasing and affects many marine organisms. However, certain sponge species can withstand low-pH conditions. This may be related to their complex association with microbes. We hypothesized that species with greater microbial diversity may develop functional redundancy that could enable the holobiont to survive even if particular microbes are lost at low-pH conditions. We evaluated the effects of acidification on the growth and associated microbes of three ubiquitous Mediterranean sponges by exposing them to the present pH level and that predicted for the year 2100. We found marked differences among the species in the acquisition of new microbes, being high in Dysidea avara, moderate in Agelas oroides and null in Chondrosia reniformis; however, we did not observe variation in the overall microbiome abundance, richness or diversity. The relative abilities to alter the microbiomes contributes to survivorship in an OA scenario as demonstrated by lowered pH severely affecting the growth of C. reniformis, halving that of A. oroides, and unaffecting D. avara. Our results indicate that functional stability of the sponge holobiont to withstand future OA is species-specific and is linked to the species' ability to use horizontal transmission to modify the associated microbiome to adapt to environmental change.

Detrimental effects of ocean acidification on the economically important Mediterranean red coral (Corallium rubrum).

The mean predicted decrease of 0.3-0.4 pH units in the global surface ocean by the end of the century has prompted urgent research to assess the potential effects of ocean acidification on the marine environment, with strong emphasis on calcifying organisms. Among them, the Mediterranean red coral (Corallium rubrum) is expected to be particularly susceptible to acidification effects, due to the elevated solubility of its Mg-calcite skeleton. This, together with the large overexploitation of this species, depicts a bleak future for this organism over the next decades. In this study, we evaluated the effects of low pH on the species from aquaria experiments. Several colonies of C. rubrum were long-term maintained for 314 days in aquaria at two different pH levels (8.10 and 7.81, pHT ). Calcification rate, spicule morphology, major biochemical constituents (protein, carbohydrates and lipids) and fatty acids composition were measured periodically. Exposure to lower pH conditions caused a significant decrease in the skeletal growth rate in comparison with the control treatment. Similarly, the spicule morphology clearly differed between both treatments at the end of the experiment, with aberrant shapes being observed only under the acidified conditions. On the other hand, while total organic matter was significantly higher under low pH conditions, no significant differences were detected between treatments regarding total carbohydrate, lipid, protein and fatty acid composition. However, the lower variability found among samples maintained in acidified conditions relative to controls, suggests a possible effect of pH decrease on the metabolism of the colonies. Our results show, for the first time, evidence of detrimental ocean acidification effects on this valuable and endangered coral species.

Magnetic modulation of the tunnelling between defect states in antidot superlattices.

We show theoretically that the tunnelling between properly designed defects in periodic antidot lattices can be strongly modulated by applied magnetic fields. Further, transport channels made up of linear arrangements of tunnel-coupled defects can accommodate Aharonov-Bohm cages, suggesting a magnetic control of the transport through the system. Evidence supporting an unusual robustness of the caging effect against electron-electron interactions is also provided.

Orbital angular momentum of partially coherent beams.

The definition of the orbital angular momentum established for coherent beams is extended to partially coherent beams, expressed in terms of two elements of the beam matrix. This extension is justified by use of the Mercer expansion of partially coherent fields. General Gauss-Schell-model fields are considered, and the relation between the twist parameter and the orbital angular momentum is analyzed.

Beam propagation through uniaxial anisotropic media: global changes in the spatial profile.

The propagation of electromagnetic beams through uniaxial anisotropic media is investigated. The Maxwell equations are solved in the paraxial limit in terms of the plane-wave spectrum associated with each Cartesian field component. Attention is focused on the global changes in the spatial structure of the beam, which are described by means of the second-order intensity moment formalism. In particular, the propagation law for the intensity moments through this kind of media is obtained. As a consequence it is inferred that it is possible to improve the beam-quality parameter by using these media.

Spatial characterization of general partially polarized beams.

The spatial characterization of light beams given in terms of intensity moments is extended to partially polarized beams by means of a generalization of the Stokes-Mueller formalism. A simple classification scheme of partially polarized fields is proposed, and laws of propagation through nonpolarizing and polarizing optical systems are provided. Some invariant parameters are also investigated.

Quality improvement of partially polarized beams.

Improvement of the beam-quality parameter of partially polarized beams is investigated. We focus on the use of a Mach-Zehnder-type interferometric arrangement with crossed polarizers. The analysis has been carried out within the framework of the intensity moment formalism. Conditions are given under which the beam-quality parameter is optimized.

[Myoclonus as a manifestation of respiratory encephalopathy]. / Mioclonías como manifestación de la encefalopatía respiratoria.

The triad of mental abnormalities, neurologic disorders and abnormal electroencephalogram is central to respiratory encephalopathy. The development of myoclonus has been considered as a sign heralding the development of generalized seizures and coma. A patient with chronic bronchitis is reported in whom myoclonus was the predominant symptom. Myoclonus was generalized, symmetrical and synchronic, and electroencephalographic correlation was shown, with diffuse polyspike-high potential wave discharges coincident with myoclonus. Remarkably, they promptly responded to low doses of diazepam, with disappearance of clinical neurologic and electrical findings. These have not subsequently relapsed although the patient is not receiving specific therapy. The risk of the administration of diazepam was weighted against other specific drugs (clonacepam, pyracetam) which are probably better tolerated. The interest in the quicker response of diazepam prevailed. We propose the inclusion of myoclonus secondary to respiratory encephalopathy in the classification of myoclonic disorders.