On the use of external information in social network analysis

Network analysis focuses on links among interacting units (actors). Interactions are often derived from the presence of actors at events or activities (two-mode network) and this information is coded and arranged in a typical affiliation matrix. In addition to the relational data, interest may focus on external information gathered on both actors and events. Our aim is to explore the effect of external information on the formation of ties by setting a strategy able to decompose the original affiliation matrix by linear combinations of data vectors representing external information with a suitable matrix of coefficients. This allows to obtain peculiar relational data matrices that include the effect of external information. The derived adjacency matrices can then be analyzed from the network analysis perspective. In particular, we look for groups of structurally equivalent actors obtained through clustering methods. Illustrative examples and a real dataset in the framework of scientific collaboration will give a major insight into the proposed strategy.     

Reverse‐phase high‐performance liquid chromatography for the simultaneous determination of sildenafil and N‐desmethyl sildenafil in plasma of children

Sildenafil is a selective inhibitor of cGMP‐specific type 5 phosphodiesterase used for the treatment of pulmonary arterial hypertension (PAH) in the adults. In pediatrics, PAH treatment options include the off‐label use of sildenafil. Sildenafil is metabolized in the liver by cytocrome P450 into its active metabolite, N‐desmethyl sildenafil. The determination of plasma levels of sildenafil and N‐desmethyl sildenafil could be useful for therapy optimization and pharmacokinetic studies. We have developed and validated a method for the quantification of sildenafil and its metabolite in plasma of children by rapid extraction, using high‐performance liquid chromatography with ultraviolet detection. The calibration range was fitted at least square model (r² ≥ 0.999), with an accuracy and an intra‐ and inter‐day relative standard deviation <15% for both analytes. The mean recovery was 102.5% for sildenafil and 101.8% for N‐desmethyl sildenafil. This simple method could be successfully used in children with PAH under treatment with sildenafil.     

Unit Root Testing in Presence of a Double Threshold Process

In this paper we propose a double threshold process that generalizes the threshold autoregressive one widely known in the literature. It is characterized by a structure with two thresholds: the first regulates the switching between two autoregressive regimes; the second threshold regulates the switching between the two regimes of the stationary innovations. A testing procedure based on a Wald statistic has been given to evaluate the presence of unit roots in the process against stationarity. The asymptotic distribution of the statistic has been derived and the size and the power of the test have been evaluated through a Monte Carlo study where the proposed test is compared to two competing unit root testing procedures. The results clearly highlight the advantage obtained from the proposed test as the asymmetry of the generating process increases.     

Aggregation Processes of Perylene Bisimide Diimidazolium Salts

The supramolecular aggregation of three diimidazolium‐functionalized perylene bisimides, differing in the alkyl chain length was investigated. These salts form aggregates in solvents like chloroform, dichloromethane, and glycerol. Solvent‐, concentration‐, and temperature‐dependent spectroscopic studies were carried out, evidencing the occurrence of an isodesmic, enthalpy‐driven aggregation process, underpinned by π–π stacking and hydrogen bonding. Moreover, dynamic light scattering (DLS) measurements and SEM images revealed that these salts aggregate in chloroform into elongated structures.     

Independence and determination of probabilities

A non-atomic probability measure is determined by its specification of independent events. We give two proofs and related results.

     

Photochemical synthesis of perfluoropolyether (PFPE) nanocomposites containing PFPE oligomer stabilized magnetite nanoparticles

Magnetite nanoparticles were synthesized and their post-synthesis surface modification was carried out with triethoxy terminated perfluoropolyether (PFPE) oligomers. The surface-treated nanoparticles were then dispersed in a UV-curable difunctional methacrylic PFPE oligomer. Thin films prepared from the resulting stable suspensions were photopolymerized. The obtained nanocomposites showed good distribution of the surface-treated magnetite nanoparticles in the polymer matrix. The surface treatment of magnetite nanoparticles with perfluoropolyether oligomers thus was found to be effective in preventing nanoparticle segregation and aggregation, ensuring therefore an increased compatibility with the PFPE matrix.