Electronic and optical properties of double-walled armchair carbon nanotubes

Magnetoelectronic structures of double-walled armchair carbon nanotubes are calculated according to the tight-binding model. Their features are dominated by the intertube interactions, the symmetric configurations, the magnetic flux, and the Zeeman splitting. The drastic changes of the low energy states, such as energy dispersion, wave function, and Fermi level, which also rely on the different symmetries, are caused by the intertube interactions. The magnetic flux could change linear bands into parabolic bands, destroy state degeneracy, open an energy gap, and shift Fermi level. The magnetic flux and the intertube interactions, however, compete with each other in the metallic or semiconducting behavior. The Zeeman splitting would suppress the metal–semiconductor transition while the opposite is true of the magnetic flux. The main characteristics of energy bands are directly reflected in the magneto-optical absorption spectra. The different symmetric configurations can be distinguished by the absorption peaks, and the threshold absorption frequency is not identical with the energy gap.     

Gasoline permeation resistance of the as‐blow‐molded and annealed polyethylene,polyethylene/polyamide,and polyethylene/modified polyamide bottles

An investigation of the gasoline permeation resistance of the as‐blow‐molded and annealed polyethylene, polyethylene (PE)/polyamide (PA), and polyethylene/modified polyamide (MPA) bottles is reported. The gasoline permeation resistance improves dramatically after blending PA and MPA barrier resins in PE matrices during blow‐molding, and the order of barrier improvement corresponds to the order of barrier improvement of the barrier resins added in PE. Somewhat unexpectedly, the gasoline permeation rates of the annealed PE and/or PE/PA bottles annealed at 90°C or higher temperatures increase significantly with the annealing temperature and time. On the contrary, the gasoline permeation resistance of the annealed PE/MPA bottles increase significantly as the annealing temperature and/or time increase. For instance, the gasoline permeation rate of the PE/MPA bottle annealed at 120°C for 32 h is about 190 times slower than that of the as‐blow‐molded PE bottle. Further investigations found that, after blending the MPA and PA barrier resins in PE matrices, the relatively nonpolar hydrocarbon components present in the gasoline fuels were significantly blocked, without permeation during the permeation tests, in which the as‐blow‐molded PE/MPA bottle inhibited the permeation of hydrocarbon components more successfully than did the as‐blow‐molded PE/PA bottle. In contrast, the amounts of polar components that permeated through the as‐blow‐molded PE/PA and PE/MPA bottles were very small and about the same as the amount that permeated through the as‐blow‐molded PE bottle. Possible mechanisms accounting for these interesting behaviors are proposed in this study. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2827–2837, 2001     

Densification and Phase Development of Spodumene–Cordierite Glass Powder Mixtures

The sintering and crystallization of spodumene-cordierite glass-ceramics that are made from mixtures of Li₂O-Al₂O₃-SiO₂ (LAS) and MgO-Al₂O₃-SiO₂(MAS) glass powders were investigated. Pure LAS and MAS powders have good sinterability. However, the densification of LAS was drastically reduced when small amounts of MAS were added. When larger amounts of MAS were added, the amount of densification further increased. The decrease in the Li₂O content in the LAS glass promoted the densification of the mixed glass samples. The above-mentioned results can be explained by examining the crystallization temperature, which is influenced by the interactions between the LAS and MAS glass particles. The lower the temperature of crystallization, the less sintering occurred. For the sintered samples, the phase that crystallized from the MAS glass was alpha-cordierite, and that which crystallized from the LAS glass was ß-spodumene or high-quartz solid solution, depending on the Li₂O content in the LAS glass.     

Suppression of phosphor‐glass reactions in YAG:Ce phosphor‐embedded glasses

For high‐power white LED applications, YAG:Ce‐based yellow phosphors were embedded in a low‐T_g Bi₂O₃–B₂O₅–ZnO–Sb₂O₅ glass (BiG) by sintering route. A high‐T_g silicate glass (SiG) was also used for comparison. Dense (porosity<2%) phosphor‐glass composites were obtained after sintered at 800°C (for SiG) and 325°C (for BiG). XRD quantitative analysis indicates that the loss of phosphor content is in the range of 2.5%‐22%, caused by partial dissolution of phosphor particles into the glass matrix during sintering. The element distribution across the interface and within the reaction zone between phosphor and glass was analyzed by TEM/SEM‐EDS. The intrinsic emission characteristic of YAG:Ce is nearly not altered, possibly resulted from the slight modification of the YAG phase during sintering. Thus the final emission intensity of the sintered body is mainly determined by the residual amount of the YAG:Ce phase. Replace the high‐T_g SiG glass by the low‐T_g BiG glass, prenitridize the YAG:Ce phosphor, and change the sintering atmosphere from air to N₂ suppress the loss of phosphor during sintering. Therefore, the resulting loss of emission intensity of the phosphor‐embedded glass material can be reduced to only about 1.8%.     

Spinning and drawing properties of ultrahigh‐molecular‐weight polyethylene fibers prepared at varying concentrations and temperatures

The concentrations and temperatures of ultrahigh‐molecular‐weight polyethylene (UHMWPE) gel solutions exhibited a significant influence on their rheological and spinning properties. The shear viscosities of UHMWPE solutions increased consistently with increasing concentrations at a constant temperature above 80°C. Tremendously high shear viscosities of UHMWPE gel solutions were found as the temperatures reached 120–140°C, at which their shear viscosity values approached the maximum. The spinnable solutions are those gel solutions with optimum shear viscosities and relatively good homogeneity in nature. Moreover, the gel solution concentrations and spinning temperatures exhibited a significant influence on the drawability and microstructure of the as‐spun fibers. At each spinning temperature, the achievable draw ratios obtained for as‐spun fibers prepared near the optimum concentration are significantly higher than those of as‐spun fibers prepared at other concentrations. The critical draw ratio of the as‐spun fiber prepared at the optimum concentration approached a maximum value, as the spinning temperature reached the optimum value of 150°C. Further investigations indicated that the best orientation of the precursors of shish‐kebab‐like entities, birefringence, crystallinity, thermal and tensile properties were always accompanied with the as‐spun fiber prepared at the optimum concentration and temperature. Similar to those found for the as‐spun fibers, the birefringence and tensile properties of the draw fibers prepared at the optimum condition were always higher than those of drawn fibers prepared at other conditions but stretched to the same draw ratio. Possible mechanisms accounting for these interesting phenomena are proposed.     

Chitosan–Polyelectrolyte complexation for the preparation of gel beads and controlled release of anticancer drug. I. Effect of phosphorous polyelectrolyte complex and enzymatic hydrolysis of polymer

Enzymic hydrolyzed chitosan was employed to prepare chitosan–tripolyphosphate and chitosan–polyphosphoric acid gel beads using a polyelectrolyte complexation method for the sustained‐release of anticancer agent, 6‐mercaptopurine (6‐MP). pH responsive swelling ability, drug‐release characteristics, and morphology of the chitosan gel bead depends on polyelectrolyte complexation mechanism and molecular weight of the enzymic hydrolyzed chitosan. The complexation mechanism of chitosan beads gelled in pentasodium tripolyphosphate or polyphosphoric acid solution was ionotropic crosslinking or interpolymer complex, respectively. The drug‐release patterns of all chitosan gel beads in pH 6.8 seemed to be diffusional based, which might be in accordance with the Higuchi model, whereas release profiles of the chitosan–tripolyphosphate gel beads in pH 1.2 medium seemed to be non‐Fickian diffusion controlled due to the swelling or matrix erosion of the beads. The rate of 6‐MP releasing from chitosan–tripolyphosphate or chitosan–polyphosphoric acid gel matrix were significantly increased with the decreased molecular weight of enzymic hydrolyzed chitosan. However, the dissolution rates of 6‐MP entraped in chitosan–tripolyphosphate and chitosan–polyphosphoric acid gel matrix were significantly slower than the dissolution rate of the original drug. These results indicate that the chitosan–polyphosphoric acid gel bead is a better polymer carrier for the sustained release of anticancer drugs in simulated intestinal and gastric juice medium than the chitosan–tripolyphosphate gel beads. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1868–1879, 1999     

Spherulitic Growth of Apatite in a MgO─CaO─SiO2─P2O5 Glass

Differential thermal analysis, X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, and transmission electron microscopy were used to study the crystallization of a glass with a composition of 11.2 wt% MgO, 40.5 wt% CaO, 33.3 wt% SiO₂, and 15 wt% P₂O₅. A two-phase "composite," which was composed of apatite and an intermediate phase (H-phase), was formed under appropriate heat-treatment conditions. The spherulitic morphology of apatite phase transformed from "open sheaf" into ellipsoidal as samples were heated to a higher temperature. These phenomena were due to the intermediate H-phase becoming unstable at this temperature so that the retardation effect on the apatite dendritic growth disappeared.     

Effects of processing conditions on the quality of vacuum‐fried carrot chips

The effects of pretreatment and vacuum frying conditions on the quality of fried carrot chips were studied. The moisture and oil contents of fried carrot chips were significantly (p < 0.05) reduced when blanched carrot slices were pretreated by immersion in fructose solution and freezing prior to vacuum frying. Furthermore, more uniform porosity was observed on the vertical cross‐section of carrot chips when examined by scanning electron microscopy. During vacuum frying, the moisture content, colour and breaking force of carrot chips decreased while the oil content increased with increasing frying temperature and time. However, there was no apparent change in Hunter ΔE with time when the frying temperature was below 100 °C and the frying time was below 25 min. Results of this study suggest that vacuum frying at moderate temperature (90–100 °C) for 20 min can produce carrot chips with lower moisture and oil contents as well as good colour and crispy texture. Copyright © 2005 Society of Chemical Industry     

Knowledge-driven multidimensional indexing structure for biomedical media database retrieval.

Today, biomedical media data are being generated at rates unimaginable only years ago. Content-based retrieval of biomedical media from large databases is becoming increasingly important to clinical, research, and educational communities. In this paper, we present the recently developed entropy balanced statistical (EBS) k-d tree and its applications to biomedical media, including a high-resolution computed tomography (HRCT) lung image database and the first real-time protein tertiary structure search engine. Our index utilizes statistical properties inherent in large-scale biomedical media databases for efficient and accurate searches. By applying concepts from pattern recognition and information theory, the EBS k-d tree is built through top-down decision tree induction. Experimentation shows similarity searches against a protein structure database of 53 363 structures consistently execute in less than 8.14 ms for the top 100 most similar structures. Additionally, we have shown improved retrieval precision over adaptive and statistical k-d trees. Retrieval precision of the EBS k-d tree is 81.6% for content-based retrieval of HRCT lung images and 94.9% at 10% recall for protein structure similarity search. The EBS k-d tree has enormous potential for use in biomedical applications embedded with ground-truth knowledge and multidimensional signatures.