Imaging active topological defects in carbon nanotubes

A single-walled carbon nanotube (SWNT) is a wrapped single graphene layer, and its plastic deformation should require active topological defects--non-hexagonal carbon rings that can migrate along the nanotube wall. Although in situ transmission electron microscopy (TEM) has been used to examine the deformation of SWNTs, these studies deal only with diameter changes and no atomistic mechanism has been elucidated experimentally. Theory predicts that some topological defects can form through the Stone-Wales transformation in SWNTs under tension at 2,000 K, and could act as a dislocation core. We demonstrate here, by means of high-resolution (HR)-TEM with atomic sensitivity, the first direct imaging of pentagon-heptagon pair defects found in an SWNT that was heated at 2,273 K. Moreover, our in situ HR-TEM observation reveals an accumulation of topological defects near the kink of a deformed nanotube. This result suggests that dislocation motions or active topological defects are indeed responsible for the plastic deformation of SWNTs.     

Human walking animation based on foot reaction force in the three‐dimensional virtual world

This paper introduces a method that can generate continuous human walking motion automatically on an arbitrary path in a three‐dimensional (3D) modelled scene. The method is based on a physical approach that solves the boundary value problem. In the motion generation stage, natural‐looking walking motion, which includes plane walking, walking upstairs and downstairs and walking on a curved path, is created by applying dynamics and kinematics. The human body is approximated as a simple rigid skeleton model, and dynamic motion is created based on the ground reaction force of the human foot. To adapt to the 3D environment, the 3D walking path is divided into steps which are tagged with the parameters needed for motion generation, and step‐by‐step motion is connected end‐to‐end. Additional features include fast calculation and a reduced need for user control. The proposed method can produce interesting human motion and can create realistic computer animation scenes. Copyright © 2000 John Wiley & Sons, Ltd.     

Role of active oxygen transients in selective catalytic reduction of N2O with CH4 over Fe-zeolite catalysts

Sharp NO and O₂ desorption peaks, which were caused by the decomposition of nitro and nitrate species over Fe species, were observed in the range of 520–673 K in temperature-programmed desorption (TPD) from Fe-MFI after H₂ treatment at 773 K or high-temperature (HT) treatment at 1073 K followed by N₂O treatment. The amounts of O₂ and NO desorption were dependent on the pretreatment pressure of N₂O in the H₂ and N₂O treatment. The adsorbed species could be regenerated by the H₂ and N₂O treatment after TPD, and might be considered to be active oxygen species in selective catalytic reduction (SCR) of N₂O with CH₄. However, the reaction rate of CH₄ activation by the adsorbed species formed after the H₂ and N₂O or the HT and N₂O treatment was not so high as that of the CH₄ + N₂O reaction over the catalyst after O₂ treatment. The simultaneous presence of CH₄ and N₂O is essential for the high activity of the reaction, which suggests that nascent oxygen species formed by N₂O dissociation can activate CH₄ in the SCR of N₂O with CH₄.     

Continuous production of structured lipid containing γ-linolenic and caprylic acids by immobilized Rhizopus delemar lipase

Production of a structured lipid containing γ-linolenic acid (GLA) achieved by the continuous acidolysis of borage oil with caprylic acid (CA) using 1,3-specific Rhizopus delemar lipase as a catalyst. The lipase immobilized on a ceramic carrier was activated by feeding the borage oil/CA (1:2, w/w) mixture saturated with water into a column packed with the enzyme. However, the generation of partial glycerides (20%) in the reaction mixture showed that hydrolysis occurred concomitantly with acidolysis. The concomitant hydrolysis was completely repressed by feeding the oil/CA substrate mixture without adding additional water. When the substrate mixture was fed at 30°C and a flow rate of 4.5 mL/h into a column packed with 8 g of the carrier with immobilized lipase, the content of CA incorporated in glycerides was 50 to 55 mol%. The acidolysis activity scarcely changed even though the substrate mixture was continuously fed for 60 d; then it gradually decreased. The CA content in glycerides was decreased to 73% of the initial value after 100 d, but returned to the initial level when the flow rate was reduced to 3.1 mL/h. Molecular distillation was employed to separate the transesterified oil from the reaction mixture. No glycerides were detected in the distillate, and the transesterified oil was recovered as the residue (acid value, 2.6). Regiospecific analysis of the transesterified oil showed that only fatty acids at the 1- and 3-positions of borage oil were exchanged for CA. It was additionally found by high-performance liquid chromatography analysis that all the triglycerides contained one or two CA, and that the triglyceride with two GLA and one CA was also present, because the lipase acted on GLA very weakly.     

Revealing the Atomic Defects of WS2 Governing Its Distinct Optical Emissions

Defects and their spatial distribution are crucial factors in controlling the electronic and optical properties of semiconductors. By using scanning transmission electron microscopy and electron energy loss spectroscopy, the type of impurities/defects in WS₂ subdomains with different optical properties is successfully assigned. A higher population of Cr impurities is found in the W‐terminated edge domain, while the S‐terminated domain contains more Fe impurities, in accordance with the luminescence characteristics of chemical‐vapor‐grown WS₂ of a hexagonal shape. In agreement with the first‐principles calculations, the domains with Cr substitutional dopants exhibit strong trion emission. Fe atoms tend to gather into trimer configuration and introduce deep acceptor levels which compensate the n‐type doping and suppress trion emission. It is also discovered that the domain with higher luminescence but smaller defect concentration tends to get oxidized more rapidly and degrade the 2D structure with many triangular holes. Excitons tend to accumulate at the edges of the oxidized triangular holes and results in enhanced PL emission. The findings indicate that choosing stable elements as dopant and controlling the number of specific edge structures within a crystal domain of 2D transitional metal dichalcogenides can be a new route to improve the optical properties of these materials.     

Controllable Synthesis of Atomically Thin Type‐II Weyl Semimetal WTe2 Nanosheets: An Advanced Electrode Material for All‐Solid‐State Flexible Supercapacitors

Compared with 2D S‐based and Se‐based transition metal dichalcogenides (TMDs), Te‐based TMDs display much better electrical conductivities, which will be beneficial to enhance the capacitances in supercapacitors. However, to date, the reports about the applications of Te‐based TMDs in supercapacitors are quite rare. Herein, the first supercapacitor example of the Te‐based TMD is reported: the type‐II Weyl semimetal 1Td WTe₂. It is demonstrated that single crystals of 1Td WTe₂ can be exfoliated into the nanosheets with 2–7 layers by liquid‐phase exfoliation, which are assembled into air‐stable films and further all‐solid‐state flexible supercapacitors. The resulting supercapacitors deliver a mass capacitance of 221 F g^?1 and a stack capacitance of 74 F cm^?3. Furthermore, they also show excellent volumetric energy and power densities of 0.01 Wh cm^?3 and 83.6 W cm^?3, respectively, superior to the commercial 4V/500 µAh Li thin‐film battery and the commercial 3V/300 µAh Al electrolytic capacitor, in association with outstanding mechanical flexibility and superior cycling stability (capacitance retention of ≈91% after 5500 cycles). These results indicate that the 1Td WTe₂ nanosheet is a promising flexible electrode material for high‐performance energy storage devices.     

Large deformation simulations of geomaterials using moving particle semi-implicit method

Numerical simulation tools are required to describe large deformations of geomaterials for evaluating the risk of geo-disasters. This study focused on moving particle semi-implicit (MPS) method, which is a Lagrangian gridless particle method, and investigated its performance and stability to simulate large deformation of geomaterials. A calculation method was developed using geomaterials modeled as Bingham fluids to improve the original MPS method and enhance its stability. Two numerical tests showed that results from the improved MPS method was in good agreement with the theoretical value. Furthermore, numerical simulations were calibrated by laboratory experiments. It showed that the simulation results matched well with the experimentally observed free-surface configurations for flowing sand. In addition, the model could generally predict the time-history of the impact force. The MPS method could be a useful tool to evaluate large deformation of geomaterials.     

Engineering a hybrid pseudomonad to acquire 3,4-dioxygenase activity for polychlorinated biphenyls

We constructed a hybrid strain that acquired 3,4-dioxygenase activity for polychlorinated biphenyls (PCBs). This strain, KF707-D34, possessed a chimeric biphenyl dioxygenase gene, of which a portion of bphA1 (coding for a large subunit of biphenyl dioxygenase) of Pseudomonas pseudoalcaligenes KF707 was replaced with that of a PCB-degrader, Burkholderia cepacia LB400 by homologous recombination. KF707-D34 retained the ability to degrade 4,4'-dichlorobiphenyl via 2,3-dioxygenation in a fashion identical to that of KF707 and gained novel capability to degrade 2,5,4'-trichlorobiphenyl and 2,5,2',5'-tetrachlorobiphenyl via 3,4-dioxygenation in a fashion identical to that of LB400. Sequence analysis of bphA1 from KF707-D34 revealed that three nucleotides in the 3'-terminal region of KF707 bphA1 were changed to correspond to those in LB400 bphA1. The resulting BphA1 protein in KF707-D34 was changed at position 376 from threonine (Thr) to asparagine (Asn). The results demonstrate that a minor alteration of the amino acid sequence in BphA1 improved the PCB degradation capability in biphenyl-utilizing bacteria.     

Ag surfactant effects of TiO2 films prepared by sputter deposition

The surfactant effect of Ag on the thin film structure of TiO₂ by radio frequency magnetron sputtering has been investigated. Comparisons between the atomic force microscopy images revealed that the surface roughness of TiO₂ film mediated by Ag was smaller than that of the TiO₂ film without Ag. The surface segregation effect of Ag was confirmed using X-ray photoelectron spectroscopy. The results of X-ray diffraction revealed that the initial deposition of a 0.4 nm thick Ag surfactant layer onto a Fe buffer layer prior to the deposition of the TiO₂ film reduced the rutile (110) growth and enhanced the anatase (100) growth. It was concluded that Ag was an effective surfactant for changing the thin film structure of TiO₂ on the Fe buffer layer. The photocatalytic effect of the fabricated TiO₂ film was also investigated using the remote oxidation process. TiO₂ films with the Ag surfactant exhibited higher photocatalytic activity than conventionally deposited TiO₂ films.     

Large intrinsic energy bandgaps in annealed nanotube-derived graphene nanoribbons

The usefulness of graphene for electronics has been limited because it does not have an energy bandgap. Although graphene nanoribbons have non-zero bandgaps, lithographic fabrication methods introduce defects that decouple the bandgap from electronic properties, compromising performance. Here we report direct measurements of a large intrinsic energy bandgap of approximately 50 meV in nanoribbons (width, approximately 100 nm) fabricated by high-temperature hydrogen-annealing of unzipped carbon nanotubes. The thermal energy required to promote a charge to the conduction band (the activation energy) is measured to be seven times greater than in lithographically defined nanoribbons, and is close to the width of the voltage range over which differential conductance is zero (the transport gap). This similarity suggests that the activation energy is in fact the intrinsic energy bandgap. High-resolution transmission electron and Raman microscopy, in combination with an absence of hopping conductance and stochastic charging effects, suggest a low defect density.