Graphite intercalation chemistry: An interpretive review

It was but five years ago that Forsman, and Ebert and Selig suggested independently that redox chemistry might be intrinsic to the formation of so-called acceptor compounds. Since then, much of the work in chemical aspects of intercalation has been specifically directed at verifying or disproving this hypothesis. The wealth of new data compiled in the process, coupled with a meticulous review of past evidence, confirms the essential role of oxidation in this genre of intercalation reactions.This review addresses two particular issues in the chemistry of acceptor type intercalants. First, how the oxidative or coordinating capability of a chemical species relates to its behavior as an intercalant. There has been considerable emphasis on the broad spectrum of interactions which exist, from weak charge transfer (Br₂ compounds), to oxidative intercalation (e.g., HNO₃), to reactions so vigorous that intercalation is only achieved with accompanying fluorination of the lattice and partial destruction of the sp² character of the carbon network (certain inorganic fluoride systems). Ebert and Selig have pointed out that detrimental oxidations of this sort are always an alternate reaction pathway in oxidative intercalation; the particular intercalant and reaction conditions determine which products will dominate. Secondly, what is the mechanism by which the intercalant interacts with the π-electron system and what are the reactive intermediates? In contrast to the previous topic—which relies on concrete evidence such as final product composition and properties for its resolution—here the approach has been largely hypothetical, relying on analogy to inorganic coordination compounds and organic π-systems which participate in charge transfer reactions. Here also lies, perhaps, the greatest future challenge to the intercalation chemist. For while the devising of possible reaction mechanisms is accomplished easily enough, experimental confirmation is always difficult. However, the past record of cooperation between chemist and physicist, experimenter and theoretician in intercalation science is an impressive one. If this question of mechanism is approached with the same gusto that has characterized past efforts, we should have some answers before long.     

Film insert molding as a novel weld‐line inhibition and strengthening technique

Specimens with weld lines were produced via conventional and film insert molding techniques using two types of materials as the substrate resin, i.e. a polycarbonate/acrylonitrile‐butadiene‐styrene (PC/ABS) blend and glass fiber‐filled polycarbonate (PC‐gf). The formation and morphology of the weld line region was assessed with and without the presence of 0.5‐mm‐thick PC film inserts. The weld line formation and characteristics were found to be dependent on the extent of interaction between the injected resin and the mold surface or the film insert. Better interfacial interaction between the substrate and film led to the distortion of the weld line orientation, which significantly enhanced the mechanical properties of the weld line. The incorporation of glass fibers into the substrate resin would usually reduce the resistance of the weld line towards tensile, flexural and impact loadings. However, with the attachment of film inserts, the mechanical properties of the weld line region have significantly improved, even with the presence of rigid fibers. Upon examination of tensile and impact fracture surfaces of film insert specimens, a unique orientation of fibers across the weld line (parallel to the flow direction and perpendicular to the weld line) could be observed at regions directly under the film. The combination of favorable properties from the unique fiber orientation and distortion of the weld line, as well as the ability of the film to effectively dissipate forces towards a larger area, have synergistically contributed towards the mechanical property enhancement of the weld line region in film insert moldings. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Dangerous misidentification of people due to flashback phenomena in posttraumatic stress disorder

Changes in the fatty acid composition of phospholipid and triglyceride fractions in Spirometra erinaceieuropaei plerocercoids were investigated after 0, 0.5, 1, 3, and 6 hr incubation at 10 C and 37 C with physiological saline containing 5 mM arachidonic acid and 10 mg/ml bovine serum albumin, pH 7.0. At 37 C, arachidonic acid was absorbed and incorporated rapidly into the triglyceride fraction (over 14.4% in composition), and decreased after 2-3 hr; at 10 C, the amount of triglyceride increased slowly and continued to a maximum of 12.9% during 6 hr of incubation. We used a simplified method to extract and purify prostaglandins from the plerocercoid of S. erinaceieuropaei. Prostaglandins were quantified using gas chromatography-mass spectrometry. Prostaglandin E2, PGD2, PGF2alpha, and 6-keto-PGF1alpha were detected under different incubation conditions. In the dose-dependent experiment, PGD2 was detected in plerocercoids incubated with 0.5, 1, 2, and 5 mM arachidonic acid, pH 7.0, at 25 C; PGE2 was detected with 2 and 5 mM arachidonic acid. In the time-dependent experiment, where plerocercoids were incubated with 5 mM arachidonic acid, pH 7.0 at 25 C, PGF2alpha was first detected at 15 min; thereafter, 6-keto-PGF1alpha was detected at 30 min and PGD2 and PGE2 were detected at 1 hr. Thromboxane B2 was not detected in either the dose-dependent or time-dependent experiments, and only PGE2 was detected in the incubation medium with 5 mM arachidonic acid at 1 hr. These results reveal that when plerocercoids change from reptilian to mammalian hosts, they are able to absorb and modify arachidonic acid bound to albumin and generate prostaglandins under suitable conditions. Prostaglandins exhibit potent biological functions for immunoresponses that may be relevant to parasitism and the success of larva migrans in S. erinaceieuropaei.     

Serial and Parallel FPGA-based Variable Block Size Motion Estimation Processors

H.264/AVC is the latest video coding standard adopting variable block size motion estimation (VBS-ME), quarter-pixel accuracy, motion vector prediction and multi-reference frames for motion estimation. These new features result in much higher computation requirements than previous coding standards. In this paper we propose a novel most significant bit (MSB) first bit-serial architecture for full-search block matching VBS-ME, and compare it with systolic implementations. Since the nature of MSB-first processing enables early termination of the sum of absolute difference (SAD) calculation, the average hardware performance can be enhanced. Five different designs, one and two dimensional systolic and tree implementations along with bit-serial, are compared in terms of performance, pixel memory bandwidth, occupied area and power consumption.

Entropy generation analysis of nanofluid flow in a circular tube subjected to constant wall temperature

Due to their improved thermal conductivity, nanofluids have the potential to be used as heat transfer fluids in thermal systems. However adding particles into nanofluids will increase the viscosity of the fluid flow. This demonstrates that there is a trade-off between heat transfer enhancement and viscosity. It might not be ideal to achieve a heat transfer enhancement along with a relatively high pumping power. This study presents an analytical investigation on the entropy generation of a nanofluid flow through a circular tube with a constant wall temperature. Nanofluid thermo-physical properties are obtained from literature or calculated from suitable correlations. The present study focuses on water based alumina and titanium dioxide nanofluids. Outcome of the analysis shows that titanium dioxide nanofluids offer lower total dimensionless entropy generation compared to that of alumina nanofluids. Addition of 4% titanium dioxide nanoparticles reduces the total dimensionless entropy generation by 9.7% as compared to only 6.4% reduction observed when using alumina. It is also noted that dimension configurations of the circular tube play a significant role in determining the entropy generation.     

CO2 methanation over Ni and Rh based catalysts: Process optimization at moderate temperature

H₂ was produced from aluminum/water reaction and reacted with CO₂ over Ni and Rh based catalysts to optimize the process conditions for CO₂ methanation at moderate temperature. Monometallic catalysts were prepared by incorporating Ni and Rh using nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O) and rhodium(III) chloride trihydrate (RhCl₃·3H₂O)as a precursor chemical. The preliminary study of the catalysts revealed higher activity and CH₄ selectivity for Rh based catalyst compared to that of Ni based catalyst. Further, Rh based catalyst was investigated using response surface methodology (RSM) involving central composite design. The quadratic model was employed to correlate the effects of variable parameters including methanation temperature, %humidity, and catalyst weight with the %CO₂ conversion, %CH₄ selectivity, and CH₄ production capacity. Analysis of variance revealed that methanation temperature and humidity play an important role in CO₂ methanation. Higher response values of CO₂ conversion (54.4%), CH₄ selectivity (73.5%) and CH₄ production capacity (8.4 μmol g^?1 min^?1) were noted at optimum conditions of 206.7°C of methanation temperature, 12.5% humidity and 100 mg of the catalyst. The results demonstrated the ability of Rh catalyst supported on palm shell activated carbon (PSAC) for CO₂ methanation at low temperature and atmospheric pressure.     

Comparison and Characterization of Compounds with Antioxidant Activity in Lycium barbarum Using High‐Performance Thin Layer Chromatography Coupled with DPPH Bioautography and Tandem Mass Spectrometry

Methanol extracts from 50 batches of Lycium barbarum (L. barbarum, wolfberry) in China were compared and characterized using high‐performance thin‐layer chromatography coupled with 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) bioautography (HPTLC‐DPPH) and electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry (ESI‐Q‐TOF‐MS/MS), respectively. Results showed that similar components occupying the major antioxidant activity existed in L. barbarum collected from different origins. However, the average antioxidant capacities of methanol extracts of L. barbarum collected in Ningxia were significantly higher than those of Qinghai, Xinjiang, Inner Mongolia, and Gansu, which may contribute to rational use of L. barbarum in China. Furthermore, the chemical structure of compound with the highest antioxidant capacity was tentatively identified as 2‐O‐β‐d ‐glucopyranosyl‐l ‐ascorbic acid using ESI‐Q‐TOF‐MS/MS analysis, which possessed high potentials to be used as an antioxidant biomarker for the quality control of L. barbarum. Results are helpful for the bioactivity‐based quality control of L. barbarum, and beneficial for the improvement of their performance in functional/health foods area, suggesting that HPTLC‐DPPH bioautography with ESI‐Q‐TOF‐MS/MS could be used as a routine approach for quality control of antioxidant components in L. barbarum.     

Microwave‐Assisted Extraction,Chemical Structures,and Chain Conformation of Polysaccharides from a Novel Cordyceps Sinensis Fungus UM01

Cordyceps sinensis is a well‐known tonic food with broad medicinal properties. The aim of the present study was to investigate the optimization of microwave‐assisted extraction (MAE) and characterize chemical structures and chain conformation of polysaccharides from a novel C. sinensis fungus UM01. Ion‐exchange and gel filtration chromatography were used to purify the polysaccharides. The chemical structure of purified polysaccharide was determined through gas chromatography‐mass spectrometry. Moreover, high performance size exclusion chromatography combined with refractive index detector and multiangle laser light scattering were conducted to analyze the molecular weight (M_w) and chain conformation of purified polysaccharide. Based on the orthogonal design L₉, optimal MAE conditions could be obtained through 1300 W of microwave power, with a 5‐min irradiation time at a solid to water ratio of 1:60, generating the highest extraction yield of 6.20%. Subsequently, the polysaccharide UM01‐S1 was purified. The UM01‐S1 is a glucan‐type polysaccharide with a (1→4)‐β‐d ‐glucosyl backbone and branching points located at O‐3 of Glcp with a terminal‐d ‐Glcp. The M_w, radius of gyration (R_g) and hydrodynamic radius (R_h) of UM01‐S1 were determined as 5.442 × 10⁶ Da, 21.8 and 20.2 nm, respectively. Using the polymer solution theory, the exponent (ν) value of the power law function was calculated as 0.38, and the shape factor (ρ = R_g/R_h) was 1.079, indicating that UM01‐S1 has a sphere‐like conformation with a branched structure in an aqueous solution. These results provide fundamental information for the future application of polysaccharides from cultured C. sinensis in health and functional food area.