Study of Solution Polymerization of Styrene in the Presence of Poly(ethylene glycol)-RAFT Agents Possessing Benzoyl Xanthate Derivatives

In this work, Macro-Reversible addition fragmentation termination (RAFT) agents based on poly(ethylene glycol) (PEG) possessing different molecular weights and bearing benzoyl xanthate moieties were synthesized by the reaction of PEG potassium xanthate salts with benzoyl chloride, 4-methyl benzoyl chloride and 4-chloro benzoyl chloride. Controlled free radical polymerization of the styrene were carried out in the presence of these macro-RAFT agents using 2,2′-azobisizsobutyronitrile (AIBN) as an initiator to yield PS-b-PEG-b-PS block copolymers. The linear kinetic plot ln [M]_o/[M] vs. polymerization time indicated that was first order with reference to monomer concentration. The block copolymerization possessed controlled/living character. The controlled character of the RAFT polymerization of the styrene was confirmed by the formation of narrow polydispersity of the polymers, linear increases in the molecular weight with polymerization time and molecular weight of the products that agreed well with theoretical values. Polymers having relatively narrow molecular weight distributions and predetermined number average molecular weights were obtained by the RAFT polymerization of the styrene. However, molecular weights of the polymers deviated from the theoretical values when low molecular weight RAFT agents are used. The results indicate that PEG benzoyl xanthate RAFT agents can more efficiently control the polymerization comparing methyl or chlorobenzoyl derivatives. The block copolymers were characterized by spectroscopic and GPC methods.     

An incremental clustering algorithm based on hyperbolic smoothing

Clustering is an important problem in data mining. It can be formulated as a nonsmooth, nonconvex optimization problem. For the most global optimization techniques this problem is challenging even in medium size data sets. In this paper, we propose an approach that allows one to apply local methods of smooth optimization to solve the clustering problems. We apply an incremental approach to generate starting points for cluster centers which enables us to deal with nonconvexity of the problem. The hyperbolic smoothing technique is applied to handle nonsmoothness of the clustering problems and to make it possible application of smooth optimization algorithms to solve them. Results of numerical experiments with eleven real-world data sets and the comparison with state-of-the-art incremental clustering algorithms demonstrate that the smooth optimization algorithms in combination with the incremental approach are powerful alternative to existing clustering algorithms.     

Effect of the intense laser field on the valance band for Ga1−xAlxAs/GaAs heterostructure

The energy levels of holes in symmetric single quantum well under the laser field are theoretically calculated within the framework of the effective mass approximation. Results obtained show that the potential profile and energy levels can significantly be modified and controlled by intense laser field and the well width. The effect of the laser field and the well width on the energy difference changes the degree of the confinement, and thus this behavior can be used to study these systems in regions of interest, without the need for the growth of many different samples.     

Separable and low-rank continuous games

In this paper, we study nonzero-sum separable games, which are continuous games whose payoffs take a sum-of-products form. Included in this subclass are all finite games and polynomial games. We investigate the structure of equilibria in separable games. We show that these games admit finitely supported Nash equilibria. Motivated by the bounds on the supports of mixed equilibria in two-player finite games in terms of the ranks of the payoff matrices, we define the notion of the rank of an n-player continuous game and use this to provide bounds on the cardinality of the support of equilibrium strategies. We present a general characterization theorem that states that a continuous game has finite rank if and only if it is separable. Using our rank results, we present an efficient algorithm for computing approximate equilibria of two-player separable games with fixed strategy spaces in time polynomial in the rank of the game. This research was funded in part by National Science Foundation grants DMI-0545910 and ECCS-0621922 and AFOSR MURI subaward 2003-07688-1.     

Kinetic modeling of the reactions of C3H3+ with acetylene,deuteroacetylene, and diacetylene

The reactions of ?-C₃H₃⁺ (propargylium cation) with acetylene and diacetylene have been modeled kinetically. Data were obtained from Fourier Transform Ion Cyclotron Resonance (FTICR) experiments on these systems, which are themselves models for soot particle initiation. Acetylene forms an encounter complex with ?-C₃H₃⁺, but, in the absence of a third body collision, the complex decomposes to acetylene and c-C₃H₃⁺ (cyclopropenylium cation) at about 1/3 the rate it decomposes to acetylene and ?-C₃H₃⁺, in spite of the fact that c-C₃H₃⁺ is ca. 115 kJ/mol more stable than ?-C₃H₃⁺. The encounter complex is long enough lived, and energetic enough, to scramble deuterium in reactions between ?-C₃H₃⁺ and C₂D₂. These reactions have been successfully modeled, yielding a nearly statistical distribution of deuterium, and a rather large kinetic isotope effect. The more complex reactions of ?-C₃H₃⁺ with diacetylene have also been modeled.     

Antioxidant Properties and Phenolic Composition of Sideritis Species

The antioxidant properties and phenolic composition of 27 Sideritis species were studied. Plant samples were extracted with petroleum ether using a Soxhlet apparatus. The defatted plant materials were extracted with 70% methanol. Antioxidant activities of the extracts were measured using Fe⁺² induced linoleic acid peroxidation, as indicated by thiobarbituric acid reactive substance (TBARS) production. Free radical scavenging activities were determined based on 1,1-diphenyl-2-picrylhydrazyl radical (DPPH). Results were compared with standard BHT. Total phenol concentration of the extracts was estimated with Folin-Ciocalteu reagent using gallic acid as standard, and phenolic components were quantified by HPLC-DAD.     

Exact two-sample nonparametric test for quantile difference between two populations based on ranked set samples

Creation of a ranked set sample, by its nature, involves judgment ranking error within set units. This ranking error usually distorts statistical inference of the population characteristics. Tests may have inflated sizes, confidence intervals may have incorrect coverage probabilities, and the estimators may become biased. In this paper, we develop an exact two-sample nonparametric test for quantile shift between two populations based on ranked set samples. This test is based on two independent exact confidence intervals for the quantile of interest corresponding to the two populations and rejects the null hypothesis of equal quantiles if these intervals are disjoint. It is shown that a pair of 83 and 93% confidence intervals provide a 5 and 1% test for the equality of quantiles. The proposed test is calibrated for the effect of judgment ranking error so that the test has the correct size even under a wide range of judgment ranking errors. A small scale simulation study suggests that the test performs quite well for cycle sizes as small as 2.     

Effects of metal coating on self-assembled monolayers on gold. 2. Copper on an oligo(phenylene-ethynylene) monolayer

We report studies on the modifications induced by the evaporation of copper overlayers on a self-assembled monolayer (SAM) of the oligo(phenylene-ethynyl) dithiol, 1-thio-4-[4'-[(4'-thio)phenylethynyl]-1'-ethynyl]-benzene (TTPEB). These SAMs were characterized after deposition from a tetrahydrofuran solution on polycrystalline gold substrates and after copper evaporation and its subsequent removal by nitric acid. Monolayers were studied via cyclic voltammetry (CV), UV-vis multiwavelength ellipsometry, external reflectance infrared (IR) spectroscopy, and ion scattering spectroscopy (ISS). The results obtained indicate that TTPEB SAMs display the same packing characteristics before and after copper evaporation and removal. However, as shown by IR spectroscopy, the monolayers undergo a reorganization process that involves an increase in tilt angle accompanied by rotation of aromatic rings that results in a decrease in the average molecular twist angle. ISS data suggest that copper diffuses through the monolayer after copper evaporation, a result that is significant for applications of this molecule in molecular electronic devices.     

Intramolecular interactions in ethyl bis-(2,4-dinitrophenyl)acetate

The crystal structure of ethyl bis(2,4-dinitrophenyl)acetate, determined by room temperature X-ray diffraction, shows that this crowded molecule contains two short intramolecular interactions between nitro oxygen atoms and electron deficient carbon atoms. One mimics an early stage of the nucleophilic addition to a carbonyl group (O...C, 2.730 Å), and the other mimics an early stage of a Michael reaction (O...C, 2.854 Å). Crystal data: C₁₆H₁₂N₄O₁₀, M _r = 420.29, a = 10.079(1), b = 11.139(1), c = 16.162(1) Å, = 91.319(7)°, monoclinic, P2₁/c, Z = 4.     

Chemical composition and antimicrobial activity of the essential oil of <Emphasis Type="Italic">Anthemis wiedemanniana</Emphasis> from Turkey

The chemical composition and antimicrobial activity of the essential oil from aerial parts of Anthemis wiedemanniana, an endemic taxon of Turkey, were investigated. Linalool (12.75%), 1,8-cineole (8.49%), hexadecanoic acid (6.09%), and chrysanthenone (5.67%) were found to be the main components among the 122 compounds characterized in the essential oil of Anthemis wiedemanniana. Antimicrobial activities were reported against 12 microorganisms and five yeast-like fungi by the disc diffusion method. Published in Khimiya Prirodnykh Soedinenii, No. 1, pp. 40–43, January–February, 2007.