Multi-scale numerical simulations of thermal expansion properties of CNT-reinforced nanocomposites

In this work, the thermal expansion properties of carbon nanotube (CNT)-reinforced nanocomposites with CNT content ranging from 1 to 15 wt% were evaluated using a multi-scale numerical approach, in which the effects of two parameters, i.e., temperature and CNT content, were investigated extensively. For all CNT contents, the obtained results clearly revealed that within a wide low-temperature range (30°C ~ 62°C), thermal contraction is observed, while thermal expansion occurs in a high-temperature range (62°C ~ 120°C). It was found that at any specified CNT content, the thermal expansion properties vary with temperature - as temperature increases, the thermal expansion rate increases linearly. However, at a specified temperature, the absolute value of the thermal expansion rate decreases nonlinearly as the CNT content increases. Moreover, the results provided by the present multi-scale numerical model were in good agreement with those obtained from the corresponding theoretical analyses and experimental measurements in this work, which indicates that this multi-scale numerical approach provides a powerful tool to evaluate the thermal expansion properties of any type of CNT/polymer nanocomposites and therefore promotes the understanding on the thermal behaviors of CNT/polymer nanocomposites for their applications in temperature sensors, nanoelectronics devices, etc.     

Development of high-rate anaerobic ammonium-oxidizing (anammox) biofilm reactors

To promptly establish anaerobic ammonium oxidation (anammox) reactors, appropriate seeding sludge with high abundance and activity of anammox bacteria was selected by quantifying 16S rRNA gene copy numbers of anammox bacteria by real-time quantitative PCR (RTQ-PCR) and batch culture experiments. The selected sludge was then inoculated into up-flow fixed-bed biofilm column reactors with nonwoven fabric sheets as biomass carrier and the reactor performances were monitored over 1 year. The anammox reaction was observed within 50 days and a total nitrogen removal rate of 26.0 kg-Nm(-3)day(-1) was obtained after 247 days. To our knowledge, such a high rate has never been reported before. Hydraulic retention time (HRT) and influent NH(4)(+) to NO(2)(-) molar ratio could be important determinant factors for efficient nitrogen removal in this study. The higher nitrogen removal rate was obtained at the shorter HRT and higher influent NH(4)(+)/NO(2)(-) molar ratio. After anammox reactors were fully developed, the community structure, spatial organization and in situ activity of the anammox biofilms were analyzed by the combined use of a full-cycle of 16S rRNA approach and microelectrodes. In situ hybridization results revealed that the probe Amx820-hybridized anaerobic anammox bacteria were distributed throughout the biofilm (accounting for more than 70% of total bacteria). They were associated with Nitrosomonas-like aerobic ammonia-oxidizing bacteria (AAOB) in the surface biofilm. The anammox bacteria present in this study were distantly related to the Candidatus Brocadia anammoxidans with the sequence similarity of 95%. Microelectrode measurements showed that a high in situ anammox activity (i.e., simultaneous consumption of NH(4)(+) and NO(2)(-)) of 4.45 g-N of (NH(4)(+)+NO(2)(-))m(-2)day(-1) was detected in the upper 800 microm of the biofilm, which was consistent with the spatial distribution of anammox bacteria.     

Structure-activity relationships of cyclic enediynes related to dynemicin A. II. Synthesis and antitumor activity of 9- and 12-substituted enediynes equipped with aryl carbamate moieties

Novel enediyne compounds 4-8, simple analogues of dynemicin A (1) equipped with the phenyl or 4-chlorophenyl carbamate moiety, were synthesized and evaluated for DNA-cleaving ability, in vitro cytotoxicity, and in vivo antitumor activity. As a result of the SAR study, it was revealed that the size and character of the substituents (R1 and R2) at the C9 position critically influenced both the stability and antitumor activity of the enediyne compounds. We found that the 9-deoxy compound 6a, a stable and less bulky enediyne having a hydrogen as the R1 and R2 substituents, showed a significant in vivo activity with a T/C of 215% at a daily dosage of 2.0 mg/kg for 4 days. The incorporation of an oxygen-containing functional group as the R3 substituent on a benzene ring resulted in considerable abolishing of both the in vitro and in vivo potencies. In a series of 9-acyloxy compounds, incorporation of the basic aromatic moiety such as 8e was effective for the in vitro activity, but it was ineffective for the in vivo activity. Furthermore, for the stereochemistry-activity relationships at the C9 position, the (9R*)-isomers of 8c, 8e, and 8f were found to show higher both in vitro and in vivo than the corresponding (9S*)-isomers. For the mechanistic studies, compound 6a underwent Bergman cycloaromatization via a diradical pathway under acidic conditions, whereas it scarcely showed DNA-cleaving activity due to the chemical stability of the aryl carbamate moiety under neutral conditions.     

Dual Raman features of double coaxial carbon nanotubes with N-doped and B-doped multiwalls

Double coaxial carbon nanotubes with nitrogen (N)-doped and boron (B)-doped multiwalls possess composite Raman characteristics, originating not only from the outer N-doped but also from inner B-doped layers. Both N and B dopings result in substantial shifts of the characteristic D band and G band of sp(2) carbon constituting nanotube walls but in different ways. The downshift of the G band is correlated with the decreases of electrical resistivity of carbon nanotubes regardless of N or B doping.     

Grating-coupled GaAs-GaAlAs lasers with distributed Bragg reflectors

Grating-coupled GaAs-GaAIAs lasers with 4th-order distributed Bragg reflectors have been successfully demonstrated with high efficiencies. The threshold current density, lasing spectrum and grating-coupled output power have been measured at room temperature. The output power from the grating at 1.5 Jth and its differential quantum efficiency have been measured to be 13.5 mW and 1.1%, respectively.     

Cloning and heterologous expression of a glucodextranase gene from Arthrobacter globiformis I42, and experimental evidence for the catalytic diad of the recombinant enzyme

The gene encoding a glucodextranase from Arthrobacter globiformis I42 was cloned and, subsequently, heterologously expressed in Escherichia coli. This glucodextranase gene consists of 1048 amino acid residues with a calculated molecular mass of 109,135 Da. The roles of two residues at the active site of A. globiformis I42 glucodextranase were examined by site-directed mutagenesis. Glutamic acid residues 458 and 656, which are part of the apparent catalytic residues, were found to be essential for hydrolase activity.     

Effects of substrate loading rate on biofilm structure

The effects of substrate surface loading rate on biofilm growth and structure were investigated by chemical, biochemical and microscopic methods. Three tubular reactors were operated at equal C:N ratio of 0.1, with substrate loading rates of 1.2, 0.6 and 0.3g-C/m(2)/day. Substrate loading positively influenced the biofilm growth rate. Denser biofilms with lower porosities were formed at higher substrate loading. Slowly growing biofilms having porous structures were found to have higher specific activities. Nitrification was suppressed under the higher substrate loading conditions even at the equal C:N ratio of 0.1, thus proving that the spatial competition between nitrifiers and heterotrophs as one limiting criteria for stable nitrification. The spatial organization of the ammonia oxidizers was biofilm structure related. The strain variability of ammonia oxidizers was substrate loading dependent. These findings suggest that substrate loading is a key parameter in determining biofilm structure and function.     

汽车发动机用无Co排气阀座圈材料的开发

烧结合金广泛地用于制作汽车发动机阀座圈（VSI）。就增高耐热与耐磨耗性能而言，在合金化设计上，烧结合金远比常规的锻钢与铸造合金灵活。特别足，一些高钻烧结材料由于耐磨耗与耐热性高而广泛用作排气阀座圈材料。鉴于近来将发动机的A／F比（空气／燃料比）调整到比常规的贫化（即空气／燃料比增高），排气阀座圈的工作环境趋于严酷。这种A／F比贫化的趋向旨在减少排出的废气和减低燃料消耗。另一方面。也需要不断地减少使用像钴之类环境负荷高的材料。同时，钴昂贵，减低钴含母有利于节省这些材料。这篇论文详细报道了无钴、无铅及有利于环境的排气阀座矧的开发与使用。     

Interfacial friction of helium films physisorbed on two-dimensional mesoporous hectorite

We report the slippage of ⁴He films physisorbed on a substrate of a two-dimensional mesoporous hectorite. Up to a certain coverage, a part of nonsuperfluid ⁴He films slipped from the oscillating substrate at low temperatures. From the temperature dependence of this slippage, it was found that the thermally activated process plays an important role in the frictional force of this system.     

STM probe-assisted site-control of self-organized InAs quantum dots on GaAs surfaces

A site-control technique for individual InAs quantum dots (QDs) has been developed by using scanning tunneling microscope (STM) probe-assisted nanolithography and self-organizing molecular-beam epitaxy. We find that nano-scale deposits can be created on a GaAs surface by applying voltage and current pulses between the surface and a tungsten tip of the STM, and that they act as “nano-masks” on which GaAs does not grow directly. Accordingly, subsequent thin GaAs growth produces GaAs nano-holes above the deposits. When InAs is supplied on this surface, QDs are self-organized at the hole sites, while hardly any undesirable Stranski-Krastanov QDs are formed in the flat surface region. Using this technique with nanometer precision, a QD pair with 45-nm pitch is successfully fabricated. An erratum to this article is available at .