On the Hopf–Schur group of a field

Let k be any field. We consider the Hopf–Schur group of k, defined as the subgroup of the Brauer group of k consisting of classes that may be represented by homomorphic images of finite-dimensional Hopf algebras over k. We show here that twisted group algebras and abelian extensions of k are quotients of cocommutative and commutative finite-dimensional Hopf algebras over k, respectively. As a consequence we prove that any tensor product of cyclic algebras over k is a quotient of a finite-dimensional Hopf algebra over k, revealing so that the Hopf–Schur group can be much larger than the Schur group of k.     

Formation of organic nanoparticles by electrospinning of volatile microemulsions

This study presents a method for one-step formation of poly(ethylene oxide) nanofibers incorporating nanoparticles of a poorly water-soluble compound. Using the new method reported here, nanofiber-nanoparticle composites are fabricated in one step by electrospinning of an oil-in-water microemulsion, in which a model material, propylparaben, has been dissolved within the volatile dispersed phase in the presence of a high-molecular-weight polymer. The approach is based on nanoscale confinement to the dispersed phase of an oil-in-water microemulsion with a volatile oil phase, in which the poorly water-soluble materials are dissolved. Thus, when the thermodynamically stable oil-in-water microemulsion is combined with the rapid evaporation of solvent inherent in the electrospinning process, the droplets are converted into organic nanoparticles embedded within a polymeric nanofiber. In addition to possessing process simplicity, this method exhibits a very high percentage of nanoparticle loading with desirable active material properties. Specifically, the diameter of the nanofibers is in the range of 60-185 nm, and propylparaben exists within the nanofiber as nanocrystals of 30-120 nm. These dimensions suggest that the nanofiber-nanocrystal composites could serve as a delivery system for water-insoluble materials.     

Sonochemical Coatings of ZnO and CuO Nanoparticles Inhibit Streptococcus mutans Biofilm Formation on Teeth Model

Antibiotic resistance has prompted the search for new agents that can inhibit bacterial growth. We recently reported on the antibiofilm activities of nanosized ZnO and CuO nanoparticles (NPs) synthesized by using sonochemical irradiation. In this study, we examined the antibacterial activity of ZnO and CuO NPs in a powder form and also examined the antibiofilm behavior of teeth surfaces that were coated with ZnO and CuO NPs using sonochemistry. Free ZnO and CuO NPs inhibited biofilm formation of Streptococcus mutans . Furthermore, by using the sonochemical procedure, we were able to coat teeth surfaces that inhibited bacterial colonization.     

Activation of a CH bond in polypyridine systems by acetyl hypofluorite made from F2

Activation of the relatively inactive polypyridine backbone with strong electrophilic fluorine, originating from acetyl hypofluorite (AcOF) enables attack of the acetoxy moiety at the α position to the heteroatom. Derivatives of bipyridine, phenanthroline and terpyridine systems have been acetoxylated or oxygenated within a few minutes usually in very good yields.     

Organic nanoparticles from microemulsions: Formation and applications

Microemulsions have already been recognized as convenient templates for nanoparticle synthesis. Spontaneous formation of the compartmentalized domains within the microemulsions leads to facile and low-cost preparation processes.In the past, microemulsions were mainly explored as precursors for the synthesis of inorganic nanoparticles. However, there is a constantly growing number of publications offering to exploit these systems to produce organic nanoparticles, and in recent years, a variety of methods have emerged in this field. The aim of this review is to survey the methods recently used to produce organic nanomaterials from microemulsions, and to give a perspective on particle design possibilities that can be achieved by various techniques. The structure of the initial microemulsion system, the chemical and technical aspects of preparation, the nature of additives and surface active agents, as well as the possible outcomes in terms of final particle characteristics, will be discussed for the various methods.     

New resonant cavity-enhanced absorber structures for mid-infrared detector applications

A new dielectric Fabry–Perot cavity was designed for a resonant enhancing optical absorption by a thin absorber layer embedded into the cavity. In this cavity, the front mirror is a subwavelength grating with ~ 100% retroreflection. For a HgCdTe absorber in a matching cavity of the new type, the design is shown to meet the combined challenges of increasing the absorbing efficiency of the entire device up to ~ 100?% and reducing its size and overall complexity, compared to a conventional resonant cavity enhanced HgCdTe absorber, while maintaining a fairly good tolerance against the grating’s fabrication errors.     

Universal behavior of optimal paths in weighted networks with general disorder

We study the statistics of the optimal path in both random and scale-free networks, where weights are taken from a general distribution P(w). We find that different types of disorder lead to the same universal behavior. Specifically, we find that a single parameter (S defined as AL(-1/v) for d-dimensional lattices, and S defined as AN(-1/3) for random networks) determines the distributions of the optimal path length, including both strong and weak disorder regimes. Here v is the percolation connectivity exponent, and A depends on the percolation threshold and P(w). We show that for a uniform P(w), Poisson or Gaussian, the crossover from weak to strong does not occur, and only weak disorder exists.     

Surface modification of crosslinked poly(styrene-divinyl benzene) micrometer-sized particles of narrow size distribution by ozonolysis

Micrometer-sized polystyrene template particles of narrow size distribution were prepared by dispersion polymerization of styrene in 2-methoxyethanol. Uniform micrometer-sized polystyrene/crosslinked poly(styrene-divinyl benzene) composite particles were formed by a single-step swelling process of the template particles with styrene, divinyl benzene and benzoyl peroxide, followed by polymerization at 70 degrees C. Uniform micrometer-sized crosslinked poly(styrene-divinyl benzene) particles of higher surface area were produced by dissolution of the template polystyrene part of the former composite particles with N,N-dimethylformamide. Hydroperoxide conjugated crosslinked poly(styrene-divinyl benzene) particles were produced by ozonolysis of these particles. The effect of ozonolysis conditions, such as exposure time and flow rate of the ozone, on the hydroperoxide conjugation to the crosslinked particles was also studied. Functionalization of the crosslinked poly(styrene-divinyl benzene) particles was performed by graft polymerization of vinylic monomers such as acrylonitrile and chloromethylstyrene on the hydroperoxide conjugated crosslinked particles. This was accomplished by raising the temperature (e.g., 70 degrees C) of deairated acetonitrile dispersions containing the hydroperoxide conjugated particles and the vinylic monomers. The influence of various polymerization parameters on the grafting yield, e.g., monomer concentration, conjugated hydroperoxide concentration, and temperature, was also elucidated.