Nanostructured Crosslinkable Micropatterns by Amphiphilic Dendrimer Stamping

Summary: Microcontact printing was used to deposit stable, nanostructured, amphiphilic and crosslinkable patterns of poly(amidoamine organosilicon) (PAMAMOS)‐dimethoxymethylsilyl (DMOMS) dendrimer multilayers onto silicon wafers, glass, and polyelectrolyte multilayers. The effects of dendrimer ink concentration, contact time, and inking method, on the thickness, uniformity, and stability of the resulting patterns were studied using optical microscopy, fluorescence microscopy, atomic force microscopy (AFM), and contact‐angle analysis. Microarrayed dendrimer film thickness was found to be controllable by conditions used during spin self‐assembly.

Optical micrograph of the circular patterns, obtained from a 0.5% PAMAMOS dendrimer solution, on a glass substrate.     

Universality in three dimensional random-field ground states

We investigate the critical behavior of three-dimensional random-field Ising systems with both Gauss and bimodal distribution of random fields and additional the three-dimensional diluted Ising antiferromagnet in an external field. These models are expected to be in the same universality class. We use exact ground-state calculations with an integer optimization algorithm and by a finite-size scaling analysis we calculate the critical exponents , , and . While the random-field model with Gauss distribution of random fields and the diluted antiferromagnet appear to be in same universality class, the critical exponents of the random-field model with bimodal distribution of random fields seem to be significantly different. Received: 9 July 1998 / Received in final form: 15 July 1998 / Accepted: 20 July 1998     

Excluded Volume Effects for Frequency Moments of the Spin Autocorrelation Function of the Heisenberg Model on a Square Lattice at High Temperatures

The expansion coefficients in powers of time (or frequency moments) of the spin autocorrelation function are represented at the simple self-consistent approximation as a sum of weighted trees on a Bethe lattice. Using the computer numeration and the Monte Carlo method for self-avoidingly embedding these trees on the square lattice, we estimate the moments and the convergence radius of the expansion. We show that the moments decrease and the radius increases in consequence of the volume exclusion.     

Energy Gap and Charge Transfer in Doped Quasi-One-Dimensional π-Conjugated Organic Ferromagnetic

The effects of polarons along main chain and spin-soliton-like along side-radical lattice in doped quasi-one-dimensional π-conjugated organic ferromagnets are studied by selfconsistent method. It is shown that the gap of spin-down and spin-up mid energy bands of the system decreases because new energy levels of localization states appear. The stability of organic ferromagnetic system is weakened with decreasing of the gap. In addition, it is also shown that there is charge transfer between main chain and side-radical lattice of the doped system.     

Relativistic effects and the halogen dependencies in the 13C chemical shifts of CH4−nIn,CH4−nBrn,CCl4−nIn,and CBr4−nIn (n=0–4)

Linear and nonlinear halogen dependencies of the ¹³C magnetic shielding constants of CH_4−nI_n, CH_4−nBr_n, CCl_4−nI_n, and CBr_4−nI_n were fairly reproduced by the ab initio generalized unrestricted Hartree–Fock (GUHF)/finite perturbation (FP) method including spin‐orbit (SO) interaction and spin‐free relativistic (SFR) terms. As seen from the experimental trends, the calculated ¹³C chemical shifts in CCl_4−nI_n and CBr_4−nI_n depend linearly on n=0–4, while those in CH_4−nI_n and CH_4−nBr_n depend nonlinearly. We found that both the linear and nonlinear dependencies are due to the relativistic effects, and especially due to the Fermi–Contact (FC) term originating from the SO interaction. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 528–536, 2001     

Role-Aware Information Spread in Online Social Networks

Understanding the complex process of information spread in online social networks (OSNs) enables the efficient maximization/minimization of the spread of useful/harmful information. Users assume various roles based on their behaviors while engaging with information in these OSNs. Recent reviews on information spread in OSNs have focused on algorithms and challenges for modeling the local node-to-node cascading paths of viral information. However, they neglected to analyze non-viral information with low reach size that can also spread globally beyond OSN edges (links) via non-neighbors through, for example, pushed information via content recommendation algorithms. Previous reviews have also not fully considered user roles in the spread of information. To address these gaps, we: (i) provide a comprehensive survey of the latest studies on role-aware information spread in OSNs, also addressing the different temporal spreading patterns of viral and non-viral information; (ii) survey modeling approaches that consider structural, non-structural, and hybrid features, and provide a taxonomy of these approaches; (iii) review software platforms for the analysis and visualization of role-aware information spread in OSNs; and (iv) describe how information spread models enable useful applications in OSNs such as detecting influential users. We conclude by highlighting future research directions for studying information spread in OSNs, accounting for dynamic user roles.     

Thermal conversion of poly(paraphenylene–vinylene) precursor films: XPS and ESR studies

The conversion of the precursor into poly(phenylene–vinylene) (PPV) was studied by means of photoelectron spectroscopy (XPS) and electron spin resonance (ESR) on precursor films synthesized from the polymerization of pxylene-tetrahydrophenium halides. The sulfonium precursor containing chlorine or bromine was thermally converted to PPV and analyzed in situ using the spectrometers. It was found by XPS analysis that both halide precursors were thermally converted into polymer in a range of 190–250°C but traces of bromine were still present at >300 °C in the precursor containing Br. Furthermore, a small amount of oxygen in a ketone structure was also present in fully converted films. The ESR results corroborated the XPS experiments, showing a progressive disappearance of the radical distribution related to sulfur sites in a comparable temperature range. A discussion of the conversion process is given in terms of the modification of the core level spectra from XPS and the g distributions from ESR experiments. © 1997 John Wiley & Sons, Ltd.     

Evident solvent effect on propagation reactions during radical copolymerization of maleimide and alkene

The radical copolymerization of N-(2,6-dimethylphenyl)maleimide (DMPhMI) and 2,4,4-trimethylpentene (TP) was investigated in several solvents at 60°C. The copolymerization rate and the molecular weight of the resulting copolymers were dependent on the kind of solvent used. It was also revealed that the monomer reactivity ratios depended on the solvent; r₁ = 0.086 and r₂ = 0 in chloroform and r₁ = 0.25 and r₂ = 0 in benzene, where DMPhMI and TP are M₁ and M₂, respectively. The propagation rate constants were determined for the homopolymerization and copolymerization in chloroform and benzene using electron spin resonance spectroscopy. The homo- and crosspropagation rate constants (k₁₁ and k₁₂, respectively) were revealed to depend on the solvent: k₁₁ is 20 and 37 L/mol·s and k₁₂ is 230 and 150 L/mol·s in chloroform and in benzene, respectively. The interaction between the maleimide moiety and the solvent molecules was discussed based on the acceptivity of the solvents. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1515–1525, 1997