Supramolecular complexes: lamellar structure and crystalline transformation

Interfacial reaction of highly-branched polyethyleneimine (PEI) with octadecanoic acid (OA) was performed to prepare a series of supramolecular complexes (PEI(OA)_x). The complexes at solid state have typical lamellar structure, and the interlamellar distance can be modulated by the OA content. The long period values of the supramolecular complexes measured by SAXS were found to be dependent on the compositions, which are in good consistency with those measured by TEM. For example, the long period values from SAXS for PEI(OA)_0.76, PEI(OA)_1.03, and PEI(OA)_1.67 were 46.5, 62.7, and 56.2 Å, respectively. The corresponding data from TEM were 45.7, 60.7, and 56.6 Å, respectively. A model was proposed for the construction mode of the side alkyl chains (crystallization region) associated with PEI backbone (amorphous region), in which the side alkyl chains were arranged to be ‘end-to-end’ packing for the x=1 complex, while an ‘interdigitated structure’ of the side alkyl chains was deduced for the x>1 and x<1 complexes. Temperature variable FT-IR combination investigation of the scissoring band, rocking band, and stretching band of methylene (CH₂) and vibrational band of carbonyl group (CO) indicated that the crystalline form of the crystallization region in the lamellae can be transformed from orthorhombic to hexagonal with the temperature increasing, and vice versa.     

Synthesis of nanodispersed oxides of vanadium, titanium, molybdenum, and tungsten on mesoporous silica using atomic layer deposition

The advantages of the atomic layer deposition (ALD) method for preparation of tungsten, vanadium, titanium, and molybdenum oxide catalyst supported on mesoporous silica are discussed, with emphasis on the importance of synthesis conditions on dispersion, structure and activity of the resulting materials. A suite of complementary techniques such as DRS-UV/Vis, BET, ¹H-NMR, XRD, and TEM were used to study the structural properties of the supported metal oxides, and probe reactions such as 2-butanol dehydration and ethanol partial oxidation were used to demonstrate the potential advantages of the ALD-prepared catalysts. Specifically, highly dispersed oxides of titanium, molybdenum, and tungsten oxide on mesoporous silica were synthesized using the ALD method. It is also demonstrated that attainment of high dispersions of vanadium oxide on mesoporous silica requires the presence of at least a single layer of titanium oxide due to the well-known poor interaction between vanadia and silica. The highly dispersed catalysts prepared here by ALD methods exhibited superior catalytic performance relative to those prepared using conventional incipient wetness impregnation.     

Polybutadiene‐modified clay and its polystyrene nanocomposites

Vinylbenzyl chloride was allowed to react with a low‐molecular‐weight oligomer of butadiene in order to give a material that could then be used to alkylate an amine to form an ammonium salt. This ammonium salt was ion‐exchanged onto a clay to give a new organically modified clay, which was used to prepare polystyrene‐clay nanocomposites by solution and bulk polymerization and by melt blending. The nanocomposites were characterized by using X‐ray diffraction, transmission electron microscopy, thermogravimetric analysis, cone calorimetry, and the evaluation of mechanical properties. These systems show good nanodispersion and improvement in thermal and mechanical properties. J. Vinyl Addit. Technol. 10:44–51, 2004. © 2004 Society of Plastics Engineers.     

Functionally substituted tetramethylcyclopentadienes: Synthesis of 1-(p-hydroxyphenyl)-2,3,4,5-tetramethylcyclopentadiene and its use in the synthesis of an organometallic polymer

Reaction of 2,3,4,5-tetramethylcyclopent-2-enone (1) withp-LiC₆H₄OC-Me₂OMe, followed by treatment with aqueous acid afforded 1-(p-hydroxyphenyl)-2,3,4,5-tetramethylcyclopentadiene (2). This new ligand was then used in the synthesis of the functionally substituted organomolybdenum reagent (⁵-C₅Me₄-p-C₆H₅OH)Mo(CO)₂(NO) (3). Treatment of a preformed 1/1 styrene/maleic anhydride copolymer ( ) with 5 mol% 3 led to chemical incorporation of the organometallic species into the polymer. The final product contained 3 mol% of the organometallic moiety.     

The mechanism of CO oxidation over Cu(110): Effect of CO gas energy

The effect of the temperature of gas phase CO upon the kinetics of the oxygen titration reaction: CO_g +O_a CO_2,g, has been studied. It is found that the reaction's rate is independant of CO gas temperature between 300 and 623 K. The activation energy (6.5 kcal/mole), dependence upon CO pressure (first-order), and independence upon oxygen coverage for 0.1 _o 0.4 are all independant of the CO gas phase temperature. This result rules out any Eley-Rideal type mechanism whereby CO reacts directly from the gas phase with an oxygen adatom without first being accommodated to the surface temperature in an absorbed state. The result is instead interpretable in terms of a Langmuir-Hinshelwood mechanism.Camille and Henry Dreyfus Foundation Teacher-Scholar Fellowship.     

Low-Field Nuclear Magnetic Resonance Time Domain Characterization of Polyunsaturated Fatty Acid–Rich Linseed and Fish Oil Emulsions during Thermal Air Oxidation

Linseed contains high levels of polyunsaturated fatty acids (PUFA), such as α-linolenic acid (> 50% ALA-18:3), that are naturally protected against thermal oxidation by their encapsulation within linseed oil bodies (OB) by multiple components including antioxidant proteins and mucilage emulsifying agents. Linseed OB emulsions (LSE) can be produced by grinding linseed seeds, adding water, adjusting pH, and sonication. This is a process that can encapsulate externally added PUFA to minimize their thermal oxidation, as it does for the intrinsic ALA PUFA. Fish oil (FO) encapsulation into this LSE platform to form linseed fish oil emulsions (LSFE) offers the possibility of a nutritive delivery system of the biologically essential FO PUFA eicosapentaenoic acid and docosahexaenoic acid. In this study, ¹H low-field nuclear magnetic resonance (LF-NMR) is used to characterize LSE's and LSFE's chemical and structural properties as well as their stability and changes under thermal oxidation (55 °C for 96 hours). ¹H LF-NMR data processing was developed to generate one-dimensional (1D) T₁ (spin–lattice), 1D T₂ (spin–spin), and 2D (T₁ vs. T₂) relaxation time spectra that can characterize OB emulsions and monitor their time domain fingerprints (spectrum peaks) of chemical and structural changes during the oxidation process. The ¹H LF-NMR analysis were further supported and correlated with conventional peroxide value test, self-diffusion, droplet size distribution, zeta potential estimation of surface stability, and gas chromatography–mass spectrometry analysis of fatty acid profile changes under thermal oxidation conditions. The 1D and 2D LF-NMR relaxation spectra showed that the LSE and LSFE did not suffer intense oxidation process, due to PUFA assembly in OB oxidative protection. These results were further confirmed by the supportive analytical methodologies. The results of this study demonstrate the efficacy of ¹H LF-NMR methodology to monitor PUFA's rich oil and emulsion thermal oxidation.     

Extensions of principle component analysis with applications on vision based computing

This paper mainly focuses on the principle component analysis (PCA) and its applications on vision based computing. The underlying mechanism of PCA given and several significant factors, involved with subspace training are discussed theoretically in detail including principle components energy, residuals assessment, and decomposition computation. The typical extensions, including probabilistic PCA (PPCA), kernel PCA (KPCA), multi-dimensional PCA and robust PCA (RPCA), have been presented with critical analysis on both mechanisms and computations. Combining with the studies on, such as, image compression, visual tracking, image recognition and super-resolution image reconstruction, PCA and its extensions applied to computer vision are critically reviewed and evaluated on the targeted issues in each application as well as the role they played at specific tasks to the characteristics, cost and suitable situations of each PCA based vision processing technique.     

Upper Bounds on Number of Steals in Rooted Trees

Inspired by applications in parallel computing, we analyze the setting of work stealing in multithreaded computations. We obtain tight upper bounds on the number of steals when the computation can be modeled by rooted trees. In particular, we show that if the computation with n processors starts with one processor having a complete k-ary tree of height h (and the remaining n ? 1 processors having nothing), the maximum possible number of steals is \({\sum }_{i=1}^{n}(k-1)^{i}\binom {h}{i}\).     

A study of the graphical mediating representations used by collaborating authors

Abstract

Though they have access to sophisticated authoring support systems, many authors use conventional media for the earliest stages of generating and organising ideas. This paper gives an overview of a study of six pairs of collaborating authors who were videoed in aprewriting task and who also underwent a structured post-interview concerning their use of external representations in the study and in their everyday work. Pairs were studied so that the behaviour was more externalised, there were natural verbal protocols and these protocols could be interpreted by the interlocutor rather than by the researcher. The analysis focuses on the part that the mediating representations play in the cognitive task and in coordinating cooperative cognition. The properties of the marks produced and the affordances of conventional media are considered. The study is interpreted within a ‘shared cognitive’ framework which draws on insights from distributed cognition, socially shared cognition, situated action and most importantly from Soviet psychology. It is suggested that the mediating representations perform two important and highly related functions. First, they support ‘idea sketching’ which is a form of reflexive communication where the individual mediates her own creative cognition through external representations. Second, they mediate cooperative cognition, providing the common grounding necessary to coordinate shared thought.