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Matrix Leads (matrix + lead)
Selected AbstractsEnhancing molecular discovery using descriptor-free rearrangement clustering techniques for sparse data setsAICHE JOURNAL, Issue 2 2010Peter A. DiMaggio Jr. Abstract This article presents a descriptor-free method for estimating library compounds with desired properties from synthesizing and assaying minimal library space. The method works by identifying the optimal substituent ordering (i.e., the optimal encoding integer assignment to each functional group on every substituent site of molecular scaffold) based on a global pairwise difference metric intended to capture smoothness of the compound library. The reordering can be accomplished via a (i) mixed-integer linear programming (MILP) model, (ii) genetic algorithm based approach, or (iii) heuristic approach. We present performance comparisons between these techniques as well as an independent analysis of characteristics of the MILP model. Two sparsely sampled data matrices provided by Pfizer are analyzed to validate the proposed approach and we show that the rearrangement of these matrices leads to regular property landscapes which enable reliable property estimation/interpolation over the full library space. An iterative strategy for compound synthesis is also introduced that utilizes the results of the reordered data to direct the synthesis toward desirable compounds. We demonstrate in a simulated experiment using held out subsets of the data that the proposed iterative technique is effective in identifying compounds with desired physical properties. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Transparent Nanocomposites of Radiopaque, Flame-Made Ta2O5/SiO2 Particles in an Acrylic Matrix,ADVANCED FUNCTIONAL MATERIALS, Issue 5 2005H. Schulz Abstract Mixed Ta2O5 -containing SiO2 particles, 6,14,nm in diameter, with closely controlled refractive index, transparency, and crystallinity are prepared via flame spray pyrolysis (FSP) at production rates of 6.7,100,g,h,1. The effect of precursor solution composition on product filler (particle) size, crystallinity, Ta dispersity, and transparency is studied using nitrogen adsorption, X-ray diffraction, optical microscopy, high-resolution transmission electron microscopy (HRTEM), and diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFTS). Emphasis is placed on the transparency of the composite that is made with Ta2O5/SiO2 filler and dimethylacrylate. Increasing Ta2O5 crystallinity and decreasing Ta dispersity on SiO2 decreases both filler and composite transparencies. Powders with identical specific surface area (SSA), refractive index (RI), and Ta2O5 content (24,wt.-%) show a wide range of composite transparencies, 33,78,%, depending on filler crystallinity and Ta dispersity. Amorphous fillers with a high Ta dispersity and an RI matching that of the polymer matrix lead to the highest composite transparency, 86,%. The composite containing 16.5,wt.-% filler that itself contains 35,wt.-% Ta2O5 has the optimal radiopacity for dental fillings. [source] The influence of fiber surface modification on the mechanical properties of coir-polyester compositesPOLYMER COMPOSITES, Issue 4 2001J. Rout Coir, an important lignocellulosic fiber, can be incorporated in polymers like unsaturated polyester in different ways for achieving desired properties and texture. But its high level of moisture absorption, poor wettability and insufficient adhesion between untreated fiber and the polymer matrix lead to debonding with age. In order to improve the above qualities, adequate surface modification is required. In our present work, fiber surface modification was effected through dewaxing, alkali (5%) treatment, aqueous graft copolymerization of methyl methacrylate (MMA) onto 5% alkali treated coir for different extents using CuSO4 , NaIO4 combination as an initiator system and cyanoexhylation with a view to improve the mechanical performance of coir-polyester composites. Mechanical properties like tensile strength (PS), flexural strength (ES) and impact strength (IS) of the composites as a function of fiber loading and fiber surface modification have been evaluated. Composites containing z5 wt% of fiber (untreated) improved tensile and flexural strength by 30% and 27% respectively in comparison to neat polyester. The work of fracture (impact strength) of the composite with 25 wt% fiber content was found to be 967 J/m. The elongation at break of the composites exhibits an increase with the introduction of fiber, All types of surface modification result In improved mechanical properties of the composites. Significant improvement in mechanical strength was also observed for composites prepared from 5% PMMA grafted fiber. [source] Fracture path prediction of diamond segment in a marble cutting discFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2008. UCUN ABSTRACT This study investigates the fracture path behaviour of diamond segments that have been brazed on a marble cutting disc. The segments are braze-joined using the oxy-gas welding technique. The micro-structure of the brazing zone and the disc were investigated using standard metallographic techniques and scanning electron microscope (SEM). Additionally, we used numerical modelling to study crack growth at the welding zone. Two dimensional linear elastic fracture mechanics principles were used to analyze propagation behaviour of the crack. Stress intensity factors were calculated using displacement correlation method. It was deduced from the SEM analysis of the fractured segment surface that the fracture occurred in the diamond segment due to stress concentration near the sharp corners of the diamond particles that are embedded into the matrix. The existence of such sharp artefacts within the matrix leads to the formation of cracks. [source] Synthesis and characterization of novel polyimide/SiO2 nanocomposite materials containing phenylphosphine oxide via sol-gel techniqueJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Canan Kizilkaya Abstract In this article, a series of novel polyimide/silica (PI/SiO2) nanocomposite coating materials were prepared from tetraethoxysilane (TEOS), ,-glycidyloxypropyltrimethoxysilane (GOTMS), and polyamic acid (PAA) via sol-gel technique. PAA was prepared by the reaction of 3,3,,4,4,-benzophenone tetracarboxylic dianhydride (BTDA) and bis (3-aminophenyl) phenyphosphine oxide (BAPPO) in N -methyl-2- pyrrolidone (NMP). BAPPO was synthesized hydrogenation of bis (3-nitrophenyl) phenyphosphine oxide (BNPPO) in the presence of Pd/C. The silica content in the hybrid coating materials was varied from 0 to 20 wt %. The molecular structures of the composite materials were analyzed by means of FT-IR and 29Si-NMR spectroscopy techniques. The physical and mechanical properties of the nanocomposites were evaluated by various techniques such as, hardness, contact angle, and optical transmission and tensile tests. These measurements revealed that all the properties of the nanocomposite coatings were improved noticeable, by the addition of sol-gel precursor into the coating formulation. Thermogravimetric analysis showed that the incorporation of sol-gel precursor into the polyimide matrix leads to an enhancement in the thermal stability and also flame resistance properties of the coating material. The surface morphology of the hybrid coating was characterized by scanning electron microscopy (SEM). SEM studies indicated that nanometer-scaled inorganic particles were homogenously dispersed throughout the polyimide matrix © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Selective migration in polyethylene/rubbery particles blends during capillary flowPOLYMER ENGINEERING & SCIENCE, Issue 4 2010C. Chartier Adding elastomeric particles (Sunigum®) into a polyethylene (PE) matrix leads to an increase of both viscosity and dynamic moduli in the molten state. This suspension effect is more pronounced if the particle's dispersion is improved with a compatibilizing agent. However, under capillary flow, the blends exhibit a more complex behavior with a strong violation of a viscosity mixing rule. To elucidate the origin of this observation, an analysis of extrudates by confocal micro Raman spectrometry has been carried out. A selective migration of the lowest viscosity component (at a given shear rate) toward the wall of the capillary die has been noted. This migration is inhibited by the addition of a compatibilizer. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source] Application of sulfur as a matrix for laser desorption/ionization in the characterization of halogenated fullerenesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 2 2002Alexey V. Streletskiy The application of sulfur as a matrix for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) analysis of highly chlorinated and fluorinated fullerenes is reported. Control over fluorofullerene fragmentation which resulted in the domination of the molecular peak C60F36, was achieved, with the optimal matrix-to-analyte ratio found to be 1000:1. We suggest the possible mechanism of the molecular ion formation according to the charge transfer between the sulfur anions and C60F36. For the first time the LDI and MALDI mass spectra of the highly chlorinated fullerene C60Clx(xmax,,,32) are presented. The formation of odd chlorine ions (positive and negative) is observed. We conclude that use of sulfur as a matrix leads to a significant decrease in fragmentation of the halogenated fullerenes. Copyright © 2001 John Wiley & Sons, Ltd. [source] | |||||||||||||