Influence of defects on the optical and structural properties of Ge dots embedded in an Si/Ge superlattice

In this work we studied the influence of high-energy proton irradiation on the optical and structural properties of an Si/Ge superlattice (SL) with embedded Ge quantum dots (QDs). The presence of QDs in the as-grown samples was established by transmission electron microscopy and photoluminescence (PL). The samples were irradiated with 2.0 MeV protons to fluences in the range 2×10¹²-2×10¹⁴ cm^-2. The structural characterization made by X-ray reciprocal space mapping, X-ray reflection and Rutherford backscattering/channelling has shown no changes in the as-grown heterostructure due to the irradiation. In spite of the expected high concentration of nonradiative recombination centres caused by the proton-induced damage, the PL emission from the Ge dots has been observed even for the highest irradiation fluence. The studied QD-in-SL structure has shown an extraordinarily high radiation hardness when compared with previously studied QD heterostructures.     

Characteristic Features of Gravitational Wave Lensing as Probe of Lens Mass Model

To recognize gravitational wave lensing events and being able to differentiate between similar lens models will be of crucial importance once one will be observing several lensing events of gravitational waves per year. In this work, the lensing of gravitational waves is studied in the context of LISA sources and wave-optics regime. While different papers before the studied microlensing effects enhanced by simultaneous strong lensing, the focus is on frequency (time) dependent phase effects produced by one lens that will be visible with only one lensed signal. It is shows how, in the interference regime (i.e., when interference patterns are present in the lensed image), one is able to i) distinguish a lensed waveform from an unlensed one, and ii) differentiate between different lens models. In pure wave-optics, on the other hand, the feasibility of the study depends on the signal-to-noise ratio of the signal and/or the amplitude of the lensing effect. To achieve these goals, the phase of the amplification factor of the different lens models and its effect on the unlensed waveform is studied, and the signal-to-noise calculation to provide some quantitative examples is exploited.     

A Highly Stabilizing Silver(I)‐Mediated Base Pair in Parallel‐Stranded DNA

The first parallel‐stranded DNA duplex with Hoogsteen base pairing that readily incorporates an Ag⁺ ion into an internal mispair to form a metal‐mediated base pair has been created. Towards this end, the highly stabilizing 6 FP ‐Ag⁺‐ 6 FP base pair comprising the artificial nucleobase 6‐furylpurine ( 6 FP ) was devised. A combination of temperature‐dependent UV spectroscopy, CD spectroscopy, and DFT calculations was used to confirm the formation of this base pair. The nucleobase 6 FP is capable of forming metal‐mediated base pairs both by the Watson–Crick edge (i.e. in regular antiparallel‐stranded DNA) and by the Hoogsteen edge (i.e. in parallel‐stranded DNA), depending on the oligonucleotide sequence and the experimental conditions. The 6 FP ‐Ag⁺‐ 6 FP base pair within parallel‐stranded DNA is the most strongly stabilizing Ag⁺‐mediated base pair reported to date for any type of nucleic acid, with an increase in melting temperature of almost 15 °C upon the binding of one Ag⁺ ion.     

Six‐Coordinate Group 13 Complexes: The Role of d Orbitals and Electron‐Rich Multi‐Center Bonding

Bonding in six‐coordinate complexes based on Group 13 elements (B, Al, Ga, In, Tl) is usually considered to be identical to that in transition‐metal analogues. We herein demonstrate through sophisticated electronic‐structure analyses that the bonding in these Group 13 element complexes is fundamentally different and better characterized as electron‐rich hypervalent bonding with essentially no role for the d orbitals. This characteristic is carried through to the molecular properties of the complex.     

Steric effects on alkyl cation affinities of maingroup-element hydrides

We have carried out an extensive exploration of gas‐phase alkyl cation affinities (ACA) of archetypal anionic and neutral bases across the periodic system using zeroth order regular approximation‐relativistic density functional theory at BP86/QZ4P//BP86/TZ2P. ACA values were computed for the methyl, ethyl, i‐propyl and t‐butyl cations and compared with the corresponding proton affinities (PA). One purpose of this work is to provide an intrinsically consistent set of values of the 298 K ACA of all anionic (XH) and neutral bases (XH_n) constituted by maingroup‐element hydrides of groups 14–17 and the noble gases (group 18) along the periods 1–6. Another purpose is to determine and rationalize the trend in affinity for a cation as the latter varies from proton to t‐butyl cation. This undertaking is supported by quantitative bond energy decomposition analyses. Correlations are established between PA and ACA values. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011     

Solubility of HFCs in lower alcohols

This work is inserted in a research program that consists mainly in the experimental and theoretical study of the effect of association between solute and solvent molecules in the solubility of gases in liquids.The solubilities of hydrofluorocarbons, HFCs, (CH₃F, CH₂F₂, CHF₃) in lower alcohols (methanol, ethanol, 1-propanol, 1-butanol) have been determined in the temperature range [284, 313] K, at atmospheric pressure. An automated apparatus based on Ben-Naim-Baer and Tominaga et al. designs was used, which provides an accuracy of 0.6%. A precision of the same order of magnitude was achieved.To represent the temperature dependence of the mole fraction solubilities, the equation R ln x₂ = A + B/T + C ln T was used. From this equation, the experimental Gibbs energies, enthalpies and entropies of solution at 298 K and 1 atm partial pressure of the gas, were calculated.A semiempirical correlation has been developed between the solubilities of HFCs in alcohols at 298 K and the Gutmann acceptor number of solvents, AN, and reduced dipole moment of the gases, μ*.     

Multiple response optimization for Cu, Fe and Pb determination in naphtha by graphite furnace atomic absorption spectrometry with sample injection as detergent emulsion

The present paper reports the optimization for Cu, Fe and Pb determination in naphtha by graphite furnace atomic absorption spectrometry (GF AAS) employing a strategy based on the injection of the samples as detergent emulsions. The method was optimized in relation to the experimental conditions for the emulsion formation and taking into account that the three analytes (Cu, Fe and Pb) should be measured in the same emulsion. The optimization was performed in a multivariate way by employing a three-variable Doehlert design and a multiple response strategy. For this purpose, the individual responses of the three analytes were combined, yielding a global response that was employed as a dependent variable. The three factors related to the optimization process were: the concentration of HNO₃, the concentration of the emulsifier agent (Triton X-100 or Triton X-114) in aqueous solution used to emulsify the sample and the volume of solution. At optimum conditions, it was possible to obtain satisfactory results with an emulsion formed by mixing 4 mL of the samples with 1 mL of a 4.7% w/v Triton X-100 solution prepared in 10% v/v HNO₃ medium. The resulting emulsion was stable for 250 min, at least, and provided enough sensitivity to determine the three analytes in the five samples tested. A recovery test was performed to evaluate the accuracy of the optimized procedure and recovery rates, in the range of 88-105%; 94-118% and 95-120%, were verified for Cu, Fe and Pb, respectively.     

Preparation, characterization and biocompatibility studies on risperidone-loaded solid lipid nanoparticles (SLN): high pressure homogenization versus ultrasound

The suitability of solid lipid nanoparticles (SLN) for the encapsulation of risperidone (RISP), an antipsychotic lipophilic drug, was assessed for oral administration. The hot high pressure homogenization (HPH) and the ultrasound (US) technique were used as production methods for SLN. All the studies on the SLN formulations were done in parallel, in order to compare the results and conclude about the advantages and limitations of both techniques. The particle sizes were in the nanometer range for all prepared SLN formulations and the zeta potential absolute values were high, predicting good long-term stability. Optical analyses demonstrated the achievement of stable colloidal dispersions. Physicochemical characterization of dispersions and bulk lipids, performed by differential scanning calorimetry (DSC) and X-ray assays, support prediction of occurrence of drug incorporation in the SLN and good long term stability of the systems. The toxicity of SLN with Caco-2 cells and the existence of contaminations derived from the production equipments were assessed by the (4,5-dimethylthiazol-2-yl)2,5-diphenyl-tetrazolium bromide (MTT) assay. The results showed 90% of cell viability after SLN exposure, with no significant differences within all prepared formulations (p > 0.05). From this study, we conclude that SLN can be considered as efficient carriers for RISP encapsulation. Moreover, HPH and US revealed to be both effective methods for SLN production.