Quantitative analysis of the interplay between InAs quantum dots and wetting layer during the GaAs capping process.

A procedure to quantitatively analyse the relationship between the wetting layer (WL) and the quantum dots (QDs) as a whole in a statistical way is proposed. As we will show in the manuscript, it allows determining, not only the proportion of deposited InAs held in the WL, but also the average In content inside the QDs. First, the amount of InAs deposited is measured for calibration in three different WL structures without QDs by two methodologies: strain mappings in high-resolution transmission electron microscopy images and compositional mappings with ChemiSTEM x-ray energy spectrometry. The area under the average profiles obtained by both methodologies emerges as the best parameter to quantify the amount of InAs in the WL, in agreement with high-resolution x-ray diffraction results. Second, the effect of three different GaAs capping layer (CL) growth rates on the decomposition of the QDs is evaluated. The CL growth rate has a strong influence on the QD volume as well as the WL characteristics. Slower CL growth rates produce an In enrichment of the WL if compared to faster ones, together with a diminution of the QD height. In addition, assuming that the QD density does not change with the different CL growth rates, an estimation of the average In content inside the QDs is given. The high Ga/In intermixing during the decomposition of buried QDs does not only trigger a reduction of the QD height, but above all, a higher impoverishment of the In content inside the QDs, therefore modifying the two most important parameters that determine the optical properties of these structures.

Strain-balanced type-II superlattices for efficient multi-junction solar cells.

Multi-junction solar cells made by assembling semiconductor materials with different bandgap energies have hold the record conversion efficiencies for many years and are currently approaching 50%. Theoretical efficiency limits make use of optimum designs with the right lattice constant-bandgap energy combination, which requires a 1.0-1.15 eV material lattice-matched to GaAs/Ge. Nevertheless, the lack of suitable semiconductor materials is hindering the achievement of the predicted efficiencies, since the only candidates were up to now complex quaternary and quinary alloys with inherent epitaxial growth problems that degrade carrier dynamics. Here we show how the use of strain-balanced GaAsSb/GaAsN superlattices might solve this problem. We demonstrate that the spatial separation of Sb and N atoms avoids the ubiquitous growth problems and improves crystal quality. Moreover, these new structures allow for additional control of the effective bandgap through the period thickness and provide a type-II band alignment with long carrier lifetimes. All this leads to a strong enhancement of the external quantum efficiency under photovoltaic conditions with respect to bulk layers of equivalent thickness. Our results show that GaAsSb/GaAsN superlattices with short periods are the ideal (pseudo)material to be integrated in new GaAs/Ge-based multi-junction solar cells that could approach the theoretical efficiency limit.

Dose assessment to workers in a dicalcium phosphate production plant.

The production of dicalcium phosphate (DCP) uses phosphate rock (PR) as a raw material. Sedimentary phosphate rocks are enriched with relevant concentrations of natural radionuclides from the 238U decay chain (around 103 Bq·kg-1), leading to the need of controlling potential exposures to radiation of workers and members of the public in accordance with IAEA safety standards. Indeed, phosphate industries are classified as Naturally Occurring Radioactive Material (NORM) industries. Thus, the aim of this work is to assess the radiological risk of the workers in a DCP production plant located in the Iberian Peninsula (South-West Europe), which digests PR with hydrochloric acid. In the present study 238U, 230Th, 222Rn, 210Pb and 210Po concentrations in aerosols (indoor and outdoor areas) are reported. Aerosols showed concentrations between 0.42-92 mBq·m-3 for 238U, 0.24-33 mBq·m-3 for 230Th, 0.67-147 mBq·m-3 for 210Pb and 0.09-34 mBq·m-3 for 210Po. Long-term exposure (four months) of passive 222Rn detectors provided concentrations that ranged from detection limit (< DL) to 121 Bq·m-3 in outdoor areas and from < DL to 211 Bq·m-3 in indoor areas, similar to concentrations obtained from short-term measurements with active detectors from < DL to 117 Bq·m-3 in outdoor areas and from < DL to 318 Bq·m-3 in indoor places. 226Ra accumulation in ebonite and pipe scales were the most important contributions to the ambient dose equivalent H*(10), resulting in 0.07 (background)-27 µSv·h-1 with a median value of 1.1 µSv·h-1. Average 222Rn air concentrations were lower than the 300 Bq·m-3 limit and therefore, according to European Directive 2013/59/EURATOM, 222Rn concentration is excluded from the worker operational annual effective dose. Thus, considering the inhalation of aerosols and the external dose sources, the total effective dose determined for plant operators was 0.37 mSv·y-1.

General route for the decomposition of InAs quantum dots during the capping process.

The effect of the capping process on the morphology of InAs/GaAs quantum dots (QDs) by using different GaAs-based capping layers (CLs), ranging from strain reduction layers to strain compensating layers, has been studied by transmission microscopic techniques. For this, we have measured simultaneously the height and diameter in buried and uncapped QDs covering populations of hundreds of QDs that are statistically reliable. First, the uncapped QD population evolves in all cases from a pyramidal shape into a more homogenous distribution of buried QDs with a spherical-dome shape, despite the different mechanisms implicated in the QD capping. Second, the shape of the buried QDs depends only on the final QD size, where the radius of curvature is function of the base diameter independently of the CL composition and growth conditions. An asymmetric evolution of the QDs' morphology takes place, in which the QD height and base diameter are modified in the amount required to adopt a similar stable shape characterized by a averaged aspect ratio of 0.21. Our results contradict the traditional model of QD material redistribution from the apex to the base and point to a different universal behavior of the overgrowth processes in self-organized InAs QDs.

Trace metal partitioning over a tidal cycle in an estuary affected by acid mine drainage (Tinto estuary, SW Spain).

The Tinto River estuary is highly polluted with the acid lixiviates from old sulphide mines. In this work the behaviour of dissolved and particulate trace metals under strong chemical gradients during a tidal cycle is studied. The pH values range from 4.4 with low tide to 6.9 with high tide. Precipitation of Fe and Al is intense during rising tides and As and Pb are almost exclusively found in the particulate matter (PM). Sorption processes are very important in controlling the mobility (and hence bioavailability) of some metals and particularly affect Cu below pH 6. Above pH~6 Cu is desorbed, probably by the formation of Cu(I)-chloride complexes. Although less pronounced than Cu, also Zn desorption above pH 6.5 seems to occur. Mn and Co are affected by sorption processes at pH higher than ca. 6. Cd behaves conservatively and Ni is slightly affected by sorption processes.

VIS-UV ZnCdO/ZnO multiple quantum well nanowires and the quantification of Cd diffusion.

We report on the growth and microstructure analysis of high Cd content ZnCdO/ZnO multiple quantum wells (MQW) within a nanowire. Heterostructures consisting of ten wells with widths from 0.7 to 10 nm are demonstrated, and show photoluminescence emissions ranging from 3.03 to 1.97 eV. The wells with thicknesses ≦̸2 nm have high radiative efficiencies compared to the thickest ones, consistent with the presence of quantum confinement. However, a nanometric analysis of the Cd profile along the heterostructures shows the presence of Cd diffusion from the ZnCdO well to the ZnO barrier. This phenomenon modifies the band structure and the optical properties of the heterostructure, and is considered in order to correctly identify quantum effects in the ZnCdO/ZnO MQWs.

Geochemical behavior of metals and metalloids in an estuary affected by acid mine drainage (AMD).

The Tinto and Odiel rivers in southwest Spain drain the world's largest sulfide mineral formation: the Iberian Pyrite Belt which has been worked since 2,500 BC. The Tinto and Odiel estuarine zones include both an extensive area of salt marsh and an intensively industrialized urban area. As a consequence of pyrite oxidation, the Tinto and Odiel rivers are strongly acidic (pH < 3) with unusually high and quite variable metal concentrations. In this study, seasonally varying concentrations of dissolved major and trace elements were determined in the acid mine drainage affected estuary of the Ría de Huelva. During estuarine mixing, ore-derived metal concentrations exhibit excellent correlations with pH as the main controlling parameter. As pH increases, concentrations of dissolved ore-associated elements are attenuated, and this process is enhanced during the summer months. The decrease in Fe and Al concentrations ranged from 80 to 100 % as these elements are converted from dissolved to sediment-associated forms in the estuary. Coprecipitation/adsorption processes also removed between 60 and 90 % of the originally dissolved Co, Cu, Mn, Pb, Zn, and Th; however, Cd and Ni exhibited a greater propensity to remain in solution, with an average removal of approximately 60 %. On the other hand, As and U exhibited a different behavior; it is likely that these elements remain in dissolved forms because of the formation of U carbonates and soluble As species. Concentrations of As remain at elevated levels in the outer estuary (average = 48 µg L(-1)) which exceeds concentrations present in the Tinto River. Nevertheless, the estuary has recently witnessed improvements in water quality, as compared to results of several previous studies reported in the 1990s.

Mobility of Po and U-isotopes under acid mine drainage conditions: an experimental approach with samples from Río Tinto area (SW Spain).

Under acid mine drainage (AMD) conditions, the solubilities and mobilities of many elements are vastly different from conditions prevailing in most natural waters. Studies are underway in the Río Tinto area (Iberian Pyrite Belt), in order to understand the behavior and mobility of long-lived U-series radionuclides under AMD conditions. A set of leaching experiments utilizing typical country rocks from the Tinto River basin, waste rock pile composite materials, iron-rich riverbed sediments and gossan (weathered naturally rock) were performed towards this purpose. Initial leaching experiments using distilled water kept in contact with solid material for 300, 100, 50 and 1 h resulted in very low concentrations of U with (234)U/(238)U activity ratios close to equilibrium and activity concentrations of (210)Po < 0.03 mBq/g. Leaching experiments performed with sulfuric acid media (0.1 and 0.01 M), and contact times between the solid and solution for 24 h were conducted to quantify the amount of U-isotopes and (210)Po leached, and the radioactive disequilibria generated between the radionuclides in the leachate. These experiments show that Po mobility in acidic conditions (pH around 1-2) is very low, with (210)Po activity in the leachate to be 6% in average for the solid sample. By contrast, mobility of U-isotopes is higher than that of Po, around 1.2%.

Large negative thermal expansion of the Co subnetwork measured by EXAFS in highly disordered Nd1-xCox thin films with perpendicular magnetic anisotropy.

We have measured a negative thermal expansion (NTE) of the Co subnetwork in amorphous Nd1-xCox (0.78 < x < 0.84) thin films of the order of 1% in volume using linearly polarized EXAFS spectroscopy at RT and 10 K. The expansion, which is anisotropic, is uncorrelated with the perpendicular magnetic anisotropy (PMA) observed in all the films, but correlated with the method used to deposit them. The atomic environments of the Nd atoms resulted in such a strong disorder that Nd-Nd and Nd-Co environments were invisible to EXAFS, and only Co-Co atomic environments were detected. The information on the Nd subnetwork was obtained through its magnetic moment measured by XMCD. These measurements demonstrate an increasing interaction of neodymium atoms with their particular local crystal field as the temperature decreased, suggesting possible structural modifications at their sites. Since the magnetic moment of the cobalt subnetwork remains essentially constant with the temperature, it is proposed that its detected NTE may be caused by the mechanical response of the amorphous network to structural transformations at the Nd sites. These results support that the PMA in RE-TM alloys is localized at the RE sites. The complete absence of EXAFS oscillations in the Nd L3 EXAFS spectra is remarkable: it means that the coherence length of the photoemitted electrons in disordered matter can be strongly reduced from that expected by atomic calculations to the point of being less than first neighbor distances, which is contrary to the common belief that first neighbors are always visible by EXAFS.

Uranium behaviour in an estuary polluted by mining and industrial effluents: the Ría of Huelva (SW of Spain).

This paper describes a comprehensive study of the behaviour of U in the Ría of Huelva estuary, formed by the Tinto and Odiel rivers. This ecosystem is conditioned by two hydrochemical facts: one connected with the acid mining drainage (AMD) generated in the first section of the river basins, and another one related to the fertilizer industry located at the estuary. AMD gives a singular character to these rivers; low pH and high redox potential that keep high amounts of toxic elements and radionuclides in dissolution. Most of the data for dissolved U in estuaries indicate conservative mixing, but there are examples of non-conservative behaviour attributed to oxidation/reduction processes or solubility variations. In the Ría of Huelva estuary the U shows a non-conservative behaviour due to solubility changes produced by variations in the pH. A complete removal of riverine dissolved U is observed in a pH range of 4-6. At higher pH values, U release from suspended matter, and probably also from sediments into the dissolved phase is found.

[Visual fields defect as inicial presentation of neurosarcoidosis]. / Alteraciones campimétricas como manifestación inicial de una neurosarcoidosis.

CASE REPORT: A 29 year old man who suffered from progressive loss of peripherical vision in the previous few weeks. He was being studied for hormonal dysfunction. The visual field showed superior arciform defect in the right eye and a superior altitudinal defect in the left eye. The endocrinology study showed hypopituitarism secondary to a neurosarcoidosis. DISCUSSION: Neurosarcoidosis is very rare, and can produce irreversible visual fields defects. Prompt diagnosis and treatment are essential to maintain visual function.

Behavior of natural radionuclides in surficial sediments from an estuary impacted by acid mine discharge and industrial effluents in Southwest Spain.

The environmental degradation resulting from the acid mine drainage (AMD) and discharge from effluents of phosphogypsum (PG) piles in the watershed of Tinto and Odiel Rivers estuary over long periods of time has resulted in significant impact on the ecosystem of this estuary, resulting that the sediments are highly polluted by heavy metals and radionuclides from the discharge AMD and leachates from the PG. During resuspension of benthic sediments some of the radionuclides are desorbed making them bioavailable. In the present study, we investigate the spatial distribution of radionuclides U, Th and Ra and assess the factors and processes that caused the spatial distribution of these nuclides in this estuarine system. This study has global significance for other polluted environmental systems that are impacted by AMD and PG.

Alteraciones campimétricas como manifestación inicial de una neurosarcoidosis / Visual fields defect as inicial presentation of neurosarcoidosis

Caso clínico: Varón de 29 años que refería alteraciones progresivas de la visión periférica en las últimas semanas. Se encontraba en estudio por disfunción hormonal. La campimetría presentaba un defecto arciforme superior, en ojo derecho y defecto altitudinal superior en ojo izquierdo y el estudio endocrinológico reveló disfunción hormonal secundaria a neurosarcoidosis. Discusión: La neurosarcoidosis es un cuadro muy poco frecuente que puede producir alteraciones visuales irreversibles. Su diagnóstico y tratamientos precoces son fundamentales para preservar la función visual (AU)

Case report: A 29 year old man who suffered from progressive loss of peripherical vision in the previous few weeks. He was being studied for hormonal dysfunction. The visual field showed superior arciform defect in the right eye and a superior altitudinal defect in the left eye. The endocrinology study showed hypopituitarism secondary to a neurosarcoidosis. Discussion: Neurosarcoidosis is very rare, and can produce irreversible visual fields defects. Prompt diagnosis and treatment are essential to maintain visual function (AU)

Biotransformation of pineapple juice sugars into dietetic derivatives by using a cell free oxidoreductase from Zymomonas mobilis together with commercial invertase.

An easy procedure for cell free biotransformation of pineapple juice sugars into dietetic derivatives was accomplished using a commercial invertase and an oxidoreductase from Zymomonas mobilis. First, pineapple juice sucrose was quantitatively converted into glucose and fructose by invertase, thus increasing the concentration of each monosaccharide in the original juice to almost twice. In a second step, glucose-fructose oxidoreductase (GFOR) transformed glucose into gluconolactone, and fructose into the low calorie sweetener sorbitol. The advantage of using GFOR is simultaneous reduction of fructose and oxidation of glucose, allowing the continuous regeneration of the essential coenzyme NADP(H), that is tightly bound to the enzyme. The yield of GFOR catalyzed sugar conversion depends on initial pH and control of pH during the reaction. At optimal conditions (pH control at 6.2) a maximum of 80% (w/v) sugar conversion was obtained. Without pH control, GFOR is inactivated rapidly due to gluconic acid formation. Therefore, conversion yields are relatively low at the natural pH of pineapple juice. The application of this process might be more advantageous on juices of other tropical fruits (papaya, jackfruit, mango) due to their naturally given higher pH.

Metamorphic In(0.20)Ga(0.80)As p-i-n photodetectors grown on GaAs substrates for near infrared applications.

The growth and performance of top-illuminated metamorphic In(0.20)Ga(0.80)As p-i-n photodetectors grown on GaAs substrates using a step-graded In(x)Ga(1-x)As buffer is reported. The p-i-n photodetectors display a low room-temperature reverse bias dark current density of ~1.4×10(-7) A/cm(2) at -2 V. Responsivity and specific detectivity values of 0.72 A/W, 2.3×10(12) cm·Hz(1/2)/W and 0.69 A/W, 2.2×10(12) cm·Hz(1/2)/W are achieved for Yb:YAG (1030 nm) and Nd:YAG (1064 nm) laser wavelengths at -2 V, respectively. A high theoretical bandwidth-responsivity product of 0.21 GHz·A/W was estimated at 1064 nm. Device performance metrics for these GaAs substrate-based detectors compare favorably with those based on InP technology due to the close tuning of the detector bandgap to the target wavelengths, despite the presence of a residual threading dislocation density. This work demonstrates the great potential for high performance metamorphic near-infrared InGaAs detectors with optimally tuned bandgaps, which can be grown on GaAs substrates, for a wide variety of applications.

Isolation and basic characterization of a beta-glucosidase from a strain of Lactobacillus brevis isolated from a malolactic starter culture.

AIMS: To study glycosidase activities of a Lactobacillus brevis strain and to isolate an intracellular beta-glucosidase from this strain. METHODS AND RESULTS: Lactic acid bacteria (LAB) isolated from a commercially available starter culture preparation for malolactic fermentation were tested for beta-glycosidase activities. A strain of Lact. brevis showing high intracellular beta-D-glucosidase, beta-D-xylosidase and alpha-L-arabinosidase activities was selected for purification and characterization of its beta-glucosidase. The pure glucosidase from Lact. brevis has also side activities of xylosidase, arabinosidase and cellobiosidase. It is a homotetramer of 330 kDa and has an isoelectric point at pH 3.5. The K(m) for p-nitrophenyl-beta-D-glucopyranoside and p-nitrophenyl-beta-D-xylopyranoside is 0.22 and 1.14 mmol l(-1), respectively. The beta-glucosidase activity was strongly inhibited by gluconic acid delta-lactone, partially by glucose and gluconate, but not by fructose. Ethanol and methanol were found to increase the activity up to twofold. The free enzyme was stable at pH 7.0 (t(1/2) = 50 day) but not at pH 4.0 (t(1/2) = 4 days). CONCLUSIONS: The beta-glucosidase from Lact. brevis is widely different to that characterized from Lactobacillus casei (Coulon et al. 1998) and Lactobacillus plantarum (Sestelo et al. 2004). The high tolerance to fructose and ethanol, the low inhibitory effect of glucose on the enzyme activity and the good long-term stability could be of great interest for the release of aroma compounds during winemaking. SIGNIFICANCE AND IMPACT OF THE STUDY: Although the release of aroma compounds by LAB has been demonstrated by several authors, little information exists on the responsible enzymes. This study contains the first characterization of an intracellular beta-glucosidase isolated from a wine-related strain of Lact. brevis.

Structural and functional properties of Escherichia coli-derived nucleoplasmin. A comparative study of recombinant and natural proteins.

Fourier transform infrared spectroscopy, circular dichroism and prediction techniques have been used to investigate the conformational properties of nucleoplasmin isolated from oocytes and eggs of Xenopus. laevis and overexpressed in Escherichia coli. A simple and fast method allows purification of recombinant nucleoplasmin free of truncated and/or aggregated forms, and therefore provides a suitable sample to carry out the structural and functional comparison between these proteins. The secondary structure of the three proteins estimated from both spectroscopic techniques was very similar, and was found to be 31--33% loops, 27--34% beta structure, 22--26% turns and 9-14% alpha helix. Prediction studies, in good agreement with experimental data, also suggest that beta structure is the major regular conformation, and that loops and turns are the most abundant conformational features within the secondary structure of nucleoplasmin. Furthermore, the spectroscopic characterization of a truncated version of the protein, lacking 80 residues at the C-terminus, and the prediction data indicate that the secondary structure elements of the protein are segregated into two regions. The N-terminal fragment (comprising residues 1--120) which holds all the putative beta strands, and the solvent-exposed C-terminal region, that is suggested to be enriched in turn and loop structures. The phosphate/protein monomer molar ratios, obtained from chemical analysis and mass spectrometry, are 0, 3 and 7--10 for recombinant, oocyte and egg nucleoplasmin, respectively. Phosphorylation does not significantly affect the secondary structure of the protein, but clearly modulates its ability to decondense sperm nuclei and to remove basic proteins from DNA.

Acetabular dysplasia in the rat induced by injury to the triradiate growth cartilage.

An extraarticular lesion of the physeal component of the acetabular roof was performed by thermal cautery in young Wistar rats. Seventy-four animals were studied. The effects of the lesion on the pelvis, the hip joint, and the femur were analyzed during a 14-week period by radiographic, gross morphologic, morphometric, and histologic methods. Most hips developed dysplasia with a shallow and deformed acetabulum and a deformed and underdeveloped femoral head.

Experimental acetabular dysplasia associated with a lesion of iliopubic limb of the triradiate cartilage.

An experimental lesion was created in the iliopubic limb of the triradiate cartilage in young Wistar rats with the object of studying the role of this structure in the development of hip joint disorders. Roentgenographic, functional, morphologic, and morphometric results were evaluated during the following 12 weeks. Acetabular dysplasia, dislocation, or subluxation of the hip, deformities of the acetabulum and the femoral head, and bending and hypoplasia of the innominate bone were the most significant findings. It is concluded that a lesion of the iliopubic limb of the triradiate cartilage may be a cause of severe hip joint disorders such as acetabular dysplasia, subluxation, and dislocation.