Premelting of ice adsorbed on a rock surface.

Considering ice-premelting on a quartz rock surface (i.e. silica) we calculate the Lifshitz excess pressures in a four layer system with rock-ice-water-air. Our calculations give excess pressures across (1) ice layer, (2) water layer, and (3) ice-water interface for different ice and water layer thicknesses. We analyse equilibrium conditions where the different excess pressures take zero value, stabilized in part by repulsive Lifshitz interactions. In contrast to previous investigations which considered varying thickness of only one layer (ice or water), here we present theory allowing for simultaneous variation of both layer thicknesses. For a given total thickness of ice and water, this allows multiple alternative equilibrium solutions. Consequently the final state of a system will depend on initial conditions and may explain variation in experimental measurements of the thicknesses of water and ice layers.

Trapping of Gas Bubbles in Water at a Finite Distance below a Water-Solid Interface.

Gas bubbles in a water-filled cavity move upward because of buoyancy. Near the roof, additional forces come into play, such as Lifshitz, double layer, and hydrodynamic forces. Below uncharged metallic surfaces, repulsive Lifshitz forces combined with buoyancy forces provide a way to trap micrometer-sized bubbles. We demonstrate how bubbles of this size can be stably trapped at experimentally accessible distances, the distances being tunable with the surface material. By contrast, large bubbles (≥100 µm) are usually pushed toward the roof by buoyancy forces and adhere to the surface. Gas bubbles with radii ranging from 1 to 10 µm can be trapped at equilibrium distances from 190 to 35 nm. As a model for rock, sand grains, and biosurfaces, we consider dielectric materials such as silica and polystyrene, whereas aluminium, gold, and silver are the examples of metal surfaces. Finally, we demonstrate that the presence of surface charges further strengthens the trapping by inducing ion adsorption forces.

Single-step fabrication process of 1-D photonic crystals coupled to nanocolumnar TiO2 layers to improve DSC efficiency.

The present work proposes the use of a TiO2 electrode coupled to a one-dimensional photonic crystal (1DPC), all formed by the sequential deposition of nanocolumnar thin films by physical vapor oblique angle deposition (PV-OAD), to enhance the optical and electrical performance of DSCs while transparency is preserved. We demonstrate that this approach allows building an architecture combining a non-dispersive 3 µm of TiO2 electrode and 1 µm TiO2-SiO2 1DPC, both columnar, in a single-step process. The incorporation of the photonic structure is responsible for a rise of 30% in photovoltaic efficiency, as compared with a transparent cell with a single TiO2 electrode. Detailed analysis of the spectral dependence of the photocurrent demonstrates that the 1DPC improves light harvesting efficiency by both back reflection and optical cavity modes confinement within the TiO2 films, thus increasing the overall performance of the cell.

Executive summary of the consensus document on the management of perioperative anemia in Spain.

Perioperative anemia is an independent risk factor for postoperative morbidity and mortality. However, conceptual, logistical and administrative barriers persist that hinder the widespread implementation of protocols for their management. The project coordinator convened a multidisciplinary group of 8 experienced professionals to develop perioperative anemia management algorithms, based on a series of key points (KPs) related to its prevalence, consequences, diagnosis and treatment. These KPs were assessed using a 5-point Likert scale, from "strongly disagree [1]" to "strongly agree [5]". For each KP, consensus was reached when receiving a score of 4 or 5 from at least 7 participants (>75%). Based on the 36 KPs agreed upon, diagnostic-therapeutic algorithms were developed that we believe can facilitate the implementation of programs for early identification and adequate management of perioperative anemia, adapted to the characteristics of the different institutions in our country.

Resonant photocurrent generation in dye-sensitized periodically nanostructured photoconductors by optical field confinement effects.

Herein we show experimental evidence of resonant photocurrent generation in dye-sensitized periodically nanostructured photoconductors, which is achieved by spectral matching of the sensitizer absorption band to different types of localized photon modes present in either periodic or broken symmetry structures. Results are explained in terms of the calculated spatial distribution of the electric field intensity within the configurations under analysis.

Large-scale synthesis of a silicon photonic crystal with a complete three-dimensional bandgap near 1.5 micrometres

Photonic technology, using light instead of electrons as the information carrier, is increasingly replacing electronics in communication and information management systems. Microscopic light manipulation, for this purpose, is achievable through photonic bandgap materials, a special class of photonic crystals in which three-dimensional, periodic dielectric constant variations controllably prohibit electromagnetic propagation throughout a specified frequency band. This can result in the localization of photons, thus providing a mechanism for controlling and inhibiting spontaneous light emission that can be exploited for photonic device fabrication. In fact, carefully engineered line defects could act as waveguides connecting photonic devices in all-optical microchips, and infiltration of the photonic material with suitable liquid crystals might produce photonic bandgap structures (and hence light-flow patterns) fully tunable by an externally applied voltage. However, the realization of this technology requires a strategy for the efficient synthesis of high-quality, large-scale photonic crystals with photonic bandgaps at micrometre and sub-micrometre wavelengths, and with rationally designed line and point defects for optical circuitry. Here we describe single crystals of silicon inverse opal with a complete three-dimensional photonic bandgap centred on 1.46 microm, produced by growing silicon inside the voids of an opal template of dose-packed silica spheres that are connected by small 'necks' formed during sintering, followed by removal of the silica template. The synthesis method is simple and inexpensive, yielding photonic crystals of pure silicon that are easily integrated with existing silicon-based microelectronics.

Optical analysis of the fine crystalline structure of artificial opal films.

Herein, we present a detailed analysis of the structure of artificial opal films. We demonstrate that, rather than the generally assumed face centered cubic lattice of spheres, opal films are better approximated by rhombohedral assemblies of distorted colloids. Detailed analysis of the optical response in a very wide spectral range (0.4 < or = a/lambda < or = 2, where a is the conventional lattice constant), as well as at perpendicular and off-normal directions, unambiguously shows that the interparticle distance coincides very approximately with the expected diameter only along directions contained in the same close-packed plane but differs significantly in directions oblique to the [111] one. A full description of the real and reciprocal lattices of actual opal films is provided, as well as of the photonic band structure of the proposed arrangement. The implications of this distortion in the optical response of the lattice are discussed.

Plasmonic Nanoparticles as Light-Harvesting Enhancers in Perovskite Solar Cells: A User's Guide.

In this Perspective we discuss the implications of employing metal particles of different shape, size, and composition as absorption enhancers in methylammonium lead iodide perovskite solar cells, with the aim of establishing some guidelines for the future development of plasmonic resonance-based photovoltaic devices. Hybrid perovskites present an extraordinarily high absorption coefficient which, as we show here, makes it difficult to extrapolate concepts and designs that are applied to other solution-processed photovoltaic materials. In addition, the variability of the optical constants attained from perovskite films of seemingly similar composition further complicates the analysis. We demonstrate that, by means of rigorous design, it is possible to provide a realistic prediction of the magnitude of the absorption enhancement that can be reached for perovskite films embedding metal particles. On the basis of this, we foresee that localized surface plasmon effects will provide a means to attain highly efficient perovskite solar cells using films that are thinner than those usually employed, hence facilitating collection of photocarriers and significantly reducing the amount of potentially toxic lead present in the device.

Origin of light-harvesting enhancement in colloidal-photonic-crystal-based dye-sensitized solar cells.

The effect of the presence of a photonic crystal on the optical absorption of dye-sensitized titanium oxide solar cells is theoretically investigated herein. Different configurations in which a colloidal crystal can be implemented in such devices are modeled, and their absorptances compared. Experimental results on light-harvesting enhancement recently reported for periodically structured photoelectrodes are satisfactorily explained in terms of the appearance of multiple resonant modes localized in the absorbing layer when this is deposited onto one of the optical lattice surfaces. Longer matter-radiation interaction times for such frequencies result in higher absorption of those modes when compared to standard dye-sensitized solar cells. The effect of the finite size and the different characteristics of the photonic crystal on the optical absorption amplification effect is also discussed, new perspectives for colloidal-crystal-based photovoltaics being proposed.

Absorption Enhancement in Organic-Inorganic Halide Perovskite Films with Embedded Plasmonic Gold Nanoparticles.

We report on the numerical analysis of solar absorption enhancement in organic-inorganic halide perovskite films embedding plasmonic gold nanoparticles. The effect of particle size and concentration is analyzed in realistic systems in which random particle location within the perovskite film and the eventual formation of dimers are also taken into account. We find a maximum integrated solar absorption enhancement of ∼10% in perovskite films of 200 nm thickness and ∼6% in 300 nm films, with spheres of radii 60 and 90 nm, respectively, in volume concentrations of around 10% in both cases. We show that the presence of dimers boosts the absorption enhancement up to ∼12% in the thinnest films considered. Absorption reinforcement arises from a double contribution of plasmonic near-field and scattering effects, whose respective weight can be discriminated and evaluated from the simulations.

Environmental Effects on the Photophysics of Organic-Inorganic Halide Perovskites.

The photophysical properties of films of organic-inorganic lead halide perovskites under different ambient conditions are herein reported. We demonstrate that their luminescent properties are determined by the interplay between photoinduced activation and darkening processes, which strongly depend on the atmosphere surrounding the samples. We have isolated oxygen and moisture as the key elements in each process, activation and darkening, both of which involve the interaction with photogenerated carriers. These findings show that environmental factors play a key role in the performance of lead halide perovskites as efficient luminescent materials.

Response of nanoparticle-based one-dimensional photonic crystals to ambient vapor pressure.

Herein we report an analysis of the variation of the optical properties of different nanoparticle-based one-dimensional photonic crystal architectures versus changes in the ambient vapor pressure. Gradual shift of the optical response provides us with information on the sorption properties of these structures and allow us to measure precise adsorption isotherms of these porous multilayers. The potential of nanoparticle-based one-dimensional photonic crystals as base materials for optical sensing devices is demonstrated in this way.

Growth dynamics of self-assembled colloidal crystal thin films.

A theoretical and experimental analysis of the growth dynamics of colloidal crystal films deposited by evaporation induced self-assembly is herein presented. We derive an expression for the film growth velocity from which we obtain an equation that describes the evolution of the forming crystal thickness with time. Its validity is confirmed by comparison to the experimental profiles of a large number of films grown under different conditions. We find that, on top of the already reported linear increase in film width over long distances in the growth direction, periodic variations of the friction force at the meniscus give rise to short-range thickness fluctuations that are the main source of spatial inhomogeneities observed in these lattices. The key parameters that determine the period and the intensity of these fluctuations are identified.

Tailoring photonic crystals with nanometer-scale precision using polyelectrolyte multilayers.

In this paper, we describe a rapid, accurate, and convenient method for postsynthetically tuning the optical properties of colloidal photonic crystals. High quality photonic crystal films are first synthesized and then coated iteratively with layers of water-soluble polyelectrolytes. The coating process results in nanometer-scale shifts in the photonic stop band, a process which has been monitored by theoretical modeling. The results suggest a fundamentally different, reproducible layering mechanism inside the confined spaces of the colloidal crystal where polyelectrolyte multilayers are less densely packed.

[Epidemiologic information on the improper use of psychoactive substances. Some strategies applied in Argentina]. / Información epidemiológica sobre el uso indebido de sustancias psicoactivas. Algunas estrategias aplicadas en la Argentina.

In seeking epidemiologic information on the improper use of psychoactive substances it makes good sense to take advantage of available institutional resources, especially in situations where more usual research resources are in short supply or altogether lacking. This article describes several studies that availed themselves of institutional resources in Argentina for the purpose of obtaining this type of information. One of these was carried out by personnel at several rehabilitation centers dealing with problems related to improper use of psychoactive substances; another obtained information from physicians and auxiliary personnel providing emergency treatment at three general hospitals; and another used the facilities of labor organizations to investigate workers' problems. All in all, these projects show how innovative approaches can help to obtain key substance abuse information; they could also serve as worthwhile models for those interested in carrying out similar work with limited resources.

[Psychoactive substance abuse. Basis for a regional epidemiologic surveillance system]. / Abuso de sustancias psicoactivas. Bases para un sistema de vigilancia epidemiológica regional.

A profile of alcohol and drug abusers in many a Latin American country features large groups with no or insufficient access to health services. In the light of such a situation, health resources should focus their efforts on addressing the effects instead of the causes of the problem. Both developing and strengthening local health systems should be a part of the overall effort. Every regional epidemiologic surveillance system must be decentralized, taking into account social participation, local limitations, as well as health personnel training. Placing an emphasis on research as an instrument for action is crucial for Latin America.