Tunable gap in stable arsenene nanoribbons opens the door to electronic applications.

Arsenic has been predicted to present significantly more diverse 2D phases than other elemental compounds like graphene. While practical applications must be based on finite arsenene samples, like nanoribbons, theory has so far focused on the infinite sheet. Our ab initio simulations show the clear contrast between the properties of arsenene nanoribbons and those of the monolayer, ranging from phase stability to electronic structure. We include nanoribbons derived from the buckled, puckered and square/octagon structures of bulk arsenene. The flexibility afforded by different parent structures, widths and edge passivations leads to a rich variety of semiconducting structures with tunable gaps.

Human Immune Protein C1q Selectively Disaggregates Carbon Nanotubes.

We atomistically compute the change in free energy upon binding of the globular domain of the complement protein C1q to carbon nanotubes (CNTs) and graphene in solution. Our modeling results imply that C1q is able to disaggregate and disperse bundles of large diameter multiwalled CNTs but not those of thin single-walled CNTs, and we validate this prediction with experimental observations. The results support the view of a strong binding with potential implications for the understanding of the immune response and biomedical applications of graphitic nanomaterials.

What will freestanding borophene nanoribbons look like? An analysis of their possible structures, magnetism and transport properties.

We report a density-functional theory study of the stability and electronic structure of two recently proposed borophene sheets with Pmmn symmetry and nonzero thickness. We then investigate nanoribbons (BNRs) derived from these nanostructures, with particular attention to technologically relevant properties like magnetism and electronic transport. We consider two perpendicular directions for the edges of the stripes as well as different lateral widths. We show that the Pmmn8 sheet, with 8 atoms in its unit cell and generated by two interpenetrating lattices, has a larger binding energy than the Pmmn2 sheet, with only 2 atoms per unit cell. We also use their phonon spectra to show that the mechanical stability of the Pmmn8 sheet is superior to that of the Pmmn2 sheet. Nanoribbons derived from Pmmn8 are not only more stable than those derived from Pmmn2, but also more interesting from the technological point of view. We find a rich variety of magnetic solutions, depending on the borophene "mother structure", edge orientation, width and, in the case of Pmmn8-derived BNRs, the sublattice of edge atoms. We show that one can build BNRs with magnetic moment in both, one or none of the edges, as well as with parallel or antiparallel magnetic coupling between the edges when magnetic; moreover, their electronic character can be semiconducting, metallic or half-metallic, creating a perfect spin valve at low bias. These different behaviors are reflected in their densities of states, spin density and electronic transport coefficients, which are analyzed in detail. Our work provides a complete overview of what one may expect if nanoribbons are cut out from Pmmn sheets with a view to potential technological applications.

Structural and electronic properties of zigzag InP nanoribbons with Stone-Wales type defects.

By means of density-functional-theoretic calculations, we investigate the structural and electronic properties of a hexagonal InP sheet and of hydrogen-passivated zigzag InP nanoribbons (ZInPNRs) with Stone-Wales (SW)-type defects. Our results show that the influence of this kind of defect is not limited to the defected region but it leads to the formation of ripples that extend across the systems, in keeping with the results obtained recently for graphene and silicene sheets. The presence of SW defects in ZInPNRs causes an appreciable broadening of the band gap and transforms the indirect-bandgap perfect ZInPNR into a direct-bandgap semiconductor. An external transverse electric field, regardless of its direction, reduces the gap in both the perfect and defective ZInPNRs.

Electronic properties of pure and p-type doped hexagonal sheets and zigzag nanoribbons of InP.

Unlike graphene, a hexagonal InP sheet (HInPS) cannot be obtained by mechanical exfoliation from the native bulk InP, which crystallizes in the zinc blende structure under ambient conditions. However, by ab initio density functional theory calculations we found that a slightly buckled HInPS is stable both in pristine form and when doped with Zn atoms; the same occurred for hydrogen-passivated zigzag InP nanoribbons (ZInPNRs), quasi-one-dimensional versions of the quasi-two-dimensional material. We investigated the electronic properties of both nanostructures, in the latter case also in the presence of an external transverse electric field, and the results are compared with those of hypothetical planar HInPS and ZInPNRs. The band gaps of planar ZInPNRs were found to be tunable by the choice of strength of this field, and to show an asymmetric behavior under weak electric fields, by which the gap can either be increased or decreased depending on their direction; however, this effect is absent from slightly buckled ZInPNRs. The binding energies of the acceptor impurity states of Zn-doped HInPS and ZInPNRs were found to be similar and much larger than that of Zn-doped bulk InP. These latter findings show that the reduction of the dimensionality of these materials limits the presence of free carriers.

Effect of temperature and cationic chain length on the physical properties of ammonium nitrate-based protic ionic liquids.

We report a systematic study of the effect of the cationic chain length and degree of hydrogen bonding on several equilibrium and transport properties of the first members of the alkylammonium nitrate protic ionic liquids (PILs) family (ethylammonium, propylammonium, and butylammonium nitrate) in the temperature range between 10 and 40 °C. These properties were observed by means of several experimental techniques, including density, surface tension, refractometry, viscosimetry, and conductimetry. The dilatation coefficients and compressibilities, as well as the Rao coefficients, were calculated, and an increase of these magnitudes with alkyl chain length was detected. Moreover, the surface entropies and enthalpies of the studied PILs were analyzed, and the temperature dependence of the surface tension was observed to be describable by means of a harmonic oscillator model with surface energies and critical temperatures that are increasing functions of the cationic chain length. Moreover, the refractive indexes were measured and the thermo-optic coefficient and Abbe numbers were calculated, and the contribution of the electrostrictive part seemed to dominate the temperature dependence of the electric polarization. The electric conductivity and the viscosity were measured and the influence of the degree of hydrogen bonding in the supercooled liquid region analyzed. Hysteresis loops were detected in freezing-melting cycles and the effect of the length of the alkyl chain of the cation on the size of the loop analyzed, showing that longer chains lead to a narrowing of the supercooled region. The temperature dependence of the conductivity was studied in the Vogel-Fulcher-Tamman (VFT) framework and the fragility indices, the effective activation energies, and the Vogel temperatures obtained. A high-temperature Arrhenius analysis was also performed, and the activation energies of conductivity and viscosity were calculated, showing that these transport processes are governed by two distinct mechanisms. The exponents of the fractional Walden rule for the different compounds were obtained. Finally, the ionicities and fragilities of the studied PILs were analyzed, proving that all the studied PILs are subionic and fragile liquids, with propylammonium nitrate showing the lowest fragility and the greater ionicity of all the studied compounds.

Molecular dynamics simulations of the structural and thermodynamic properties of imidazolium-based ionic liquid mixtures.

In this work, extensive molecular dynamics simulations of mixtures of alcohols of several chain lengths (methanol and ethanol) with the ionic liquids (ILs) composed of the cation 1-hexyl-3-methylimidazolium and several anions of different hydrophobicity degrees (Cl(-), BF(4)(-), PF(6)(-)) are reported. We analyze the influence of the nature of the anion, the length of the molecular chain of the alcohol, and the alcohol concentration on the thermodynamic and structural properties of the mixtures. Densities, excess molar volumes, total and partial radial distribution functions, coordination numbers, and hydrogen bond degrees are reported and analyzed for mixtures of the ILs with methanol and ethanol. The aggregation process is shown to be highly dependent on the nature of the anion and the size of the alcohol, since alcohol molecules tend to interact predominantly with the anionic part of the IL, especially in mixtures of the halogenated IL with methanol. Particularly, our results suggest that the formation of an apolar network similar to that previously reported in mixtures of ILs with water does not take place in mixtures with alcohol when the chloride anion is present, the alcohol molecules being instead homogeneously distributed in the polar network of IL. Moreover, the alcohol clusters formed in mixtures of [HMIM][PF(6)] with alcohol were found to have a smaller size than in mixtures with water. Additionally, we provide a semiquantitative analysis of the dependence of the hydrogen bonding degree of the mixtures on the alcohol concentration.

Surfactant self-assembly nanostructures in protic ionic liquids.

The existence and properties of mesoscopic self-assembly structures formed by surfactants in protic ionic liquid solutions are reported. Micellar aggregates of n-alkyltrimethylammonium (n = 10, 12, 14, 16) chlorides and bromides and of n-alkylpyridinium (n = 12, 16) chlorides in ethylammonium nitrate and propylammonium nitrate were observed by means of several experimental techniques, including surface tension, transmission electron micrography, dynamic light scattering, and potentiometry using surfactant-selective electrodes. The effect of the alkyl chain length of both solute and solvent molecules on the critical micelle concentration is discussed, and a Stauff-Klevens law is seen to apply to surfactant solutions in both protic ionic liquids. The counterion role is also a matter of study in the case of alkyltrimethylammonium-based surfactants, and the presently reported evidence suggests that the place of the surfactant counterion in the Hoffmeister's series could determine its effect on micellization in IL solution. The size distribution of the aggregates is also analyzed together with the Gibbs free energies of micellization and the minimum surface area per monomer in all of the studied cases. All of the hereby reported evidence suggests that the negative entropic contribution arising from the release of the solvent layer upon micellization is also the driving force of conventional surfactant self-association in protic ionic liquids.

Prediction of phonon thermal transport in thin GaAs, InAs and InP nanowires by molecular dynamics simulations: influence of the interatomic potential.

A number of different potentials are currently being used in molecular dynamics simulations of semiconductor nanostructures. Confusion can arise if an inappropriate potential is used. To illustrate this point, we performed direct molecular dynamics simulations to predict the room temperature lattice thermal conductivity λ of thin GaAs, InAs and InP nanowires. In each case, simulations performed using the classical Harrison potential afforded values of λ about an order of magnitude smaller than those obtained using more elaborate potentials (an Abell-Tersoff, as parameterized by Hammerschmidt et al for GaAs and InAs, and a potential of Vashishta type for InP). These results will be a warning to those wishing to use computer simulations to orient the development of quasi-one-dimensional systems as heat sinks or thermoelectric devices.

Magnetism of substitutional Fe impurities in graphene nanoribbons.

Using the generalized gradient approximation to exchange and correlation, we perform density functional calculations on an Fe atom at a single vacancy of graphene nanoribbons. Our results show that, after relaxation, the Fe atom is magnetic, in contrast to the behavior recently found for Fe at a single vacancy of the graphene sheet.

[Compliance with current dietary recommendations and geographical variability of diet in women participating in 7 screening programs for breast cancer in Spain]. / Cumplimiento de las recomendaciones dietéticas vigentes y variabilidad geográfica de la dieta en mujeres participantes en 7 programas de cribado de cáncer de mama en España.

INTRODUCTION: A healthy diet is especially important during menopause, a period which increases the risk of various health problems. We analyzed the diet of periand postmenopausal Spanish women and the degree of compliance with current recommendations. MATERIAL AND METHODS: We studied 3574 women 45-68 years old who attended breast cancer screening programmes in 7 centres (A Coruña, Barcelona, Burgos, Palma de Mallorca, Pamplona, Valencia and Zaragoza). Diet information was collected using a food frequency questionnaire validated for the Spanish population. For the assessment of compliance with current guidelines we used the recommendations by the Spanish Society of Community Nutrition for food groups intake and by the Spanish Federation of Nutrition, Food and Dietetics for energy, vitamins and minerals intake. RESULTS: The 29% of women were obese and 42% overweight. The average caloric intake was 2.053 kcal (SD 480). The general energy profile was: 43% of the energy from the carbohydrates, 36% from fats, and 20% from proteins. There was a low vitamin D intake in all centres of the study, with an overall mean intake of 2.14 mg/day. A deficit of vitamin E intake in A Coruña and Burgos was also detected. Intake of dairy products and vegetables was high in all the study centers. The consumption of fruits and vegetables was very heterogeneous, with high intakes observed in Mallorca and Valencia and low for both food groups in A Coruña. The olive oil intake was high in all centers except Burgos with 74.3% of the women studied below the recommended 3 servings per day. CONCLUSIONS: A diet with less fat and protein and a higher consumption of vegetables, nuts and foods rich in carbohydrate might balance the energy intake and improve the quality of the diet correcting the low intakes of vitamins D and E. These recommendations are especially important in cities far from the Mediterranean coast where more breaches have been detected over the current recommendations with a lower adherence to the Mediterranean diet.

A density-functional study of the vertical ionization potentials of the cluster Mn13.

Using the density-functional method SIESTA, nonlocal norm-conserving pseudopotentials and the generalized gradient approximation to exchange and correlation, we show that the two ionization energies of the photoionization spectrum of Mn(13) can be attributed to the presence of the ground state and an excited spin isomer of this species.

Pseudolattice theory of the surface tension of ionic liquid-water mixtures.

A theoretical model for ionic liquids (ILs) based on a pseudoreticular structural model for the bulk mixture is reported. The original Bahe-Varela pseudolattice theory of concentrated ionic solutions is modified and the short-range interactions modeled by a Lennard-Jones potential. In this framework, the surface tension of the pure IL is calculated and the correct dependence of this magnitude on the density of the liquid, as provided by the parachor, is recovered. The anions in the mixture are assumed to form a continuum structureless neutralizing background, and that the organic cations and water molecules are placed in the nodes of the pseudolattice. The surface pressure of IL-water mixtures is calculated using a localized model for the adsorption of particles in the surface of the mixture and a mean-field Bragg-Williams approximation for the chemical potential of the adsorbed particles in the pseudolattice. The theoretical predictions are tested with experimental data of several ionic liquid aqueous mixtures.

A density-functional study of the structures and electronic properties of neutral, anionic, and endohedrally doped In(x)P(x) clusters.

We report extensive ab initio calculations of the structures, binding energies, and magnetic moments of In(x)P(x) and In(x)P(x) (-) clusters (x=1-15) using a density-functional method that employs linear combinations of pseudoatomic orbitals as basis sets, nonlocal norm-conserving pseudopotentials, and the generalized gradient approximation for exchange and correlation. Our results, which are compared with those obtained previously for some of these clusters by means of all-electron calculations, show that hollow cages with alternating In-P bonds are energetically preferred over other structures for both the neutral and anionic species within the range x=6-15. We also consider the endohedrally doped X@In(10)P(10) (X=Cr,Mn,Fe,Co) and Ti@In(x)P(x) (x=7-12) clusters. Our results show that, except for Ti@In(7)P(7) and Ti@In(8)P(8), the transition metal atoms preserve their atomic spin magnetic moments when encapsulated in the InP cages, instead of suffering either a spin crossover or a spin quenching due to hybridization effects. We also show that the stabilities of some empty and doped InP cages can be explained on the basis of the jellium model.

Nonequilibrium nanothermodynamics.

Entropy production for a system outside the thermodynamic limit is formulated using Hill's nanothermodynamics, in which a macroscopic ensemble of such systems is considered. The external influence of the environment on the average nanosystem is connected to irreversible work with an explicit formula based on the Jarzynski equality. The entropy production retains its usual form as a sum of products of fluxes and forces and Onsager's symmetry principle is proven to hold for the average nanosystem, if it is assumed to be valid for the macroscopic ensemble, by two methods. The first one provides expressions that relate the coefficients of the two systems. The second gives a general condition for a system under an external force to preserve Onsager's symmetry.

Antioxidant status and odour profile in fresh beef from pasture or grain-fed cattle.

The main goal of the present work was to determine the overall antioxidant status in fresh meat from animals fed different diets and to differentiate them through their odour profiles. Attributes were evaluated in beef from pasture or grain-fed animals with (PE and GE) or without supplementation (P and G) with vitamin E (500UI/head/day). Fresh meat produced on pasture (P and PE) had higher total ferric reducing antioxidant power (FRAP) levels than meat from grain fed-animals (G and GE) (P<0.05). However, no differences were found on their ability to reduce ABTS(+) (2,2'-azino-bis-(3-ethylbenz-thiazoline-6-sulfonic acid)), indicating that total antioxidant activity was preferentially due to the reduction potential than to the quenching capacity of tissue homogenates. Two-fold glutathione (GSH and GSSG are the reduced and oxidised forms, respectively) levels were found in the P+PE group respect to G+GE meat (P<0.001). In addition, meat from pasture-fed animals presented a higher glutathione redox potential compared to grain-fed animals (-156.1±6.1 and -158.1±6.5 vs. -148.1±13 and -149.8±14.6 for P, PE G and GE, respectively), showing that the antioxidant status in fresh meat was affected by diet. Enzymatic activity of catalase and glutathione peroxidase were equivalent for all dietary groups. Only superoxide dismutase activity was slightly higher (P<0.05) in the P+PE group than in G+GE samples. Odour profile analysis was performed in relationship to antioxidant parameters. Significant linear correlation coefficients (P<0.05) were found for a set of sensors and the FRAP values. E-nose methodology successfully discriminated the odour characteristics of samples corresponding to pasture- or grain-based diet. Hence, it was possible to describe an analytical relationship between the odour profile and the antioxidant power of fresh meat.

[Retinal involvement in Gaucher's disease]. / La participation rétinienne dans la maladie de Gaucher.

Gaucher's disease, a storage disease, causes storage of the sphingolipid glucosylceramide in the reticulo endothelial system. The manifestations of such deposits within the retina consist of the appearance of numerous whitish spots, such as preretinian infiltrates. Several authors have noticed the higher frequency of appearance of such spots in splenectomized patients, with marked extrasplenic infiltration. In our case, the systemic infiltration was massive at the time of the ophthalmoscopic examination, as confirmed by the bone-marrow biopsy and computerized axial tomography study, in spite of the fact that the spleen had not been removed. Our hypothesis is that the appearance of the whitish preretinian deposits in the course of the disease is connected with the degree of systemic infiltration, stressing the importance of examination of the eye fundus in Gaucher's disease.

[Morbidity, vaccine coverage and immunity against measles, mumps and rubella in a Gallician population from 2 to 5 years old]. / Morbilidad, cobertura vacunal e immunidad frente a sarampión, parotiditis y rubéola en una población gallega de dos a cinco años.

Vaccine coverage, morbidity prevalence, and immunity to measles, rubella, and mumps, were estimated in 1985-1986 among a sample of 2 to 5 years old Galician children, studied through questionnaires and immunoenzymatic determinations of antibodies. According to the mothers, measles vaccine and measles-mumps-rubella vaccine were administered to 22.1% and 45.7%, respectively, of their children, whereas measles were reported in 17.9, mumps in 14.3%, and rubella in 2.9%. The seroconversion to rubella (50.7%) resulted significantly lower (p less than 0.001) than that to measles (75%) or mumps (68.6%). The three types of antibodies were found altogether in 32.1% of the subjects, and 5% of them showed none of these antibodies. The analysis of the serologic data stresses the need for reaching rapidly higher vaccination rates.