In Situ Synthesis and Microstructures of Tungsten Carbide-Nanoparticle-Reinforced Silicon Nitride-Matrix Composites

A W₂C-nanoparticle-reinforced Si₃N₄-matrix composite was fabricated by sintering porous Si₃N₄ that had been infiltrated with a tungsten solution. During the sintering procedure, nanometer-sized W₂C particles grew in situ from the reaction between the tungsten and carbon sources considered to originate mainly from residual binder. The W₂C particles resided in the grain-boundary junctions of the Si₃N₄, had an average diameter of ∼60 nm, and were polyhedral in shape. Because the residual carbon, which normally would obstruct sintering, reacted with the tungsten to form W₂C particles in the composite, the sinterability of the Si₃N₄ was improved, and a W₂C–Si₃N₄ composite with almost full density was obtained. The flexural strength of the W₂C–Si₃N₄ composite was 1212 MPa, ∼34% higher than that of standard sintered Si₃N₄.     

Monodisperse nanoparticles of poly(ethylene glycol) macromers and N‐isopropyl acrylamide for biomedical applications

Poly(ethylene glycol)‐based nanoparticles have received significant attention in the field of biomedicine. When they are copolymerized with pH‐ or temperature‐sensitive comonomers, their small size allows them to respond very quickly to changes in the environment, including changes in the pH, ionic strength, and temperature. In addition, the high surface‐to‐volume ratio makes them highly functionalized. In this work, nanoparticles composed of temperature‐sensitive poly(N‐isopropylacrylamide), poly(ethylene glycol) 400 dimethacrylate, and poly(ethylene glycol) 1000 methacrylate were prepared by a thermally initiated, free‐radical dispersion polymerization method. The temperature‐responsive behavior of the hydrogel nanoparticles was characterized by the study of their particle size with photon correlation spectroscopy. The size of the nanoparticles varied from 200 to 1100 nm and was a strong function of the temperature of the system, from 5 to 40°C. The thermal, structural, and morphological characteristics were also investigated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1678–1684, 2003     

Crack-wake shielding and small-scale crack-tip yielding as potential mechanisms for improving the delayed-failure resistance of silicon nitride at elevated temperatures

Requirements and microstructural design criteria for employing silicon nitride in long-term structural applications at elevated temperatures are discussed according to fracture mechanics concepts. Three least engineering parameters are considered: lifetime, flaw-tolerance and deformation under stress. “Ductile” materials are found by exploitation of small-scale crack-tip yielding which arises from the softening of their grain-boundary phase. These materials, however, are likely to exhibit poor deformation resistance. Materials with a “strong” grain boundary generally show a superior deformation behaviour but are liable to brittle fracture and static-fatigue strength degradation unless shielding mechanisms in the crack-wake be operative. The present analysis evaluates and compares these two classes of materials and the respective approaches commonly followed for their densification.     

Allelopathic Effects of Volatile Monoterpenoids Produced by <Emphasis Type="Italic">Salvia leucophylla</Emphasis>: Inhibition of Cell Proliferation and DNA Synthesis in the Root Apical Meristem of <Emphasis Type="Italic">Brassica campestris</Emphasis> Seedlings

Salvia leucophylla, a shrub observed in coastal south California, produces several volatile monoterpenoids (camphor, 1,8-cineole, -pinene, -pinene, and camphene) that potentially act as allelochemicals. The effects of these were examined using Brassica campestris as the test plant. Camphor, 1,8-cineole, and -pinene inhibited germination of B. campestris seeds at high concentrations, whereas -pinene and camphene did not. Root growth was inhibited by all five monoterpenoids in a dose-dependent manner, but hypocotyl growth was largely unaffected. The monoterpenoids did not alter the sizes of matured cells in either hypocotyls or roots, indicating that cell expansion is relatively insensitive to these compounds. They did not decrease the mitotic index in the shoot apical region, but specifically lowered mitotic index in the root apical meristem. Moreover, morphological and biochemical analyses on the incorporation of 5-bromo-2-deoxyuridine into DNA demonstrated that the monoterpenoids inhibit both cell-nuclear and organelle DNA synthesis in the root apical meristem. These results suggest that the monoterpenoids produced by S. leucophylla could interfere with the growth of other plants in its vicinity through inhibition of cell proliferation in the root apical meristem.     

Water electrolysis under microgravity: Part 1. Experimental technique

Water electrolysis was conducted in both alkaline (25 wt.% KOH, 2 wt.% KOH) and acid (0.1N H₂SO₄) solutions for 8 s under microgravity environment realized in a drop shaft. The gas bubble formation of hydrogen and oxygen on platinum electrodes was observed by CCD camera. In alkaline solutions, a bubble froth layer grew on the electrode surface. Hydrogen bubble size was smaller than that of oxygen. The current density at constant potential decreased continually with time. In spite of the growth of a bubble froth layer on the electrode, the electrolysis never stopped, apparently because fresh electrolyte is supplied to the electrode surface by microconvection induced by the gas bubble evolution. In acid solution, hydrogen gas bubbles frequently coalesced on the cathode surface, yielding a larger average bubble than that of oxygen. The current density did not vary at constant potentials from –0.4 to −0.8 V versus reversible hydrogen electrode (RHE), because the effective electrode surface area was significantly reduced by the larger bubble size compared to alkaline electrolyte. The present experiments indicate that, especially in a microgravity environment, the bubble evolution behavior and the resultant current–potential curves are significantly influenced by the wettability of the electrode in contact with the electrolyte.     

Balanced corpus of contemporary written Japanese

The balanced corpus of contemporary written Japanese (BCCWJ) is Japan’s first 100 million words balanced corpus. It consists of three subcorpora (publication subcorpus, library subcorpus, and special-purpose subcorpus) and covers a wide range of text registers including books in general, magazines, newspapers, governmental white papers, best-selling books, an internet bulletin-board, a blog, school textbooks, minutes of the national diet, publicity newsletters of local governments, laws, and poetry verses. A random sampling technique is utilized whenever possible in order to maximize the representativeness of the corpus. The corpus is annotated in terms of dual POS analysis, document structure, and bibliographical information. The BCCWJ is currently accessible in three different ways including Chunagon a web-based interface to the dual POS analysis data. Lastly, results of some pilot evaluation of the corpus with respect to the textual diversity are reported. The analyses include POS distribution, word-class distribution, entropy of orthography, sentence length, and variation of the adjective predicate. High textual diversity is observed in all these analyses.     

Microstructure and Thermal Shock Resistance of Molten Glass-Coated Carbon Materials Fabricated by Interfacial Control

Carbon substrates were coated completely with a molten silicate glass, where the wettability of carbon to glass was improved by infiltration and pyrolysis of perhydropolysilazane. Microstructures of the carbon–glass interface were dependent on P n ₂ during coating. Coating at lower P n ₂ induced the formation of cristobalite at the carbon–glass interface. When the coating was performed at higher P n ₂, the glass and carbon were strongly adhered, without the formation of cristobalite. Coating at higher P n ₂ improved the thermal shock resistance of the glass layer, because crack initiation was not induced by the phase transformation of cristobalite during the cooling process. In the case of coating at higher P n ₂, an oxynitride glass layer was formed at the glass subsurface by dissolution of N₂. A porous glass subsurface layer with uniform spherical micro-pores could be produced by soaking near the glass transition temperature in a steam environment. The porous layer with fine and homogeneous microstructure acts as a thermal shock absorbing layer, so that glass-coated carbon with a porous glass layer has excellent thermal shock resistance in addition to steam oxidation resistance.     

Higher-order structures and mechanical properties of stereocomplex-type poly(lactic acid) melt spun fibers

Equimolar blend of poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) was melt spun into fibers and the relations among the processing conditions, crystalline structures, thermal properties, and mechanical properties were investigated. Drawing and annealing were performed in order to obtain fiber mainly consisting of the stereocomplex crystal phase. Fibers drawn at various temperatures exhibited either amorphous, highly oriented homo crystal, or the mixture of homo and stereocomplex with a fairly low orientation depending on the drawing temperature. Annealing of the drawn fibers at an elevated temperature higher than the melting temperature of homo crystal increased the stereocomplex content significantly. The fractions of the homo and the stereocomplex crystals strongly depended on the higher-order structure of the drawn fibers and the annealing temperature.     

An Advanced Oscillation Mixing Method for Improving the Cooling Uniformity in Quenching

In quenching, the cooling uniformity is most important to diminish distortion occurring on work pieces. As a trial to accomplish uniform cooling, therefore, there exist various mixing methods of a quenchant and the quenchant circulation with an external pump has so far been the well accepted mixing method. However, this study proposes an advanced oscillation mixing method that can improve more the cooling uniformity in quenching. The proposed method includes a stirrer in oscillating motion, so that the simultaneous oscillating and mixing movements of the stirrer are considered to provide efecfively the uniform cooling characteristics for the quenchant. In comparison with the case of the circulation pump mixing, the investigation using the oscillation mixing method has demonstrated the following two experimental facts:(1) the short vapor blanket stage caused by the quick breakage of the oil vapor blanket and (2) the reduced variation of the quenching distortion.     

Origin of Hole-Trapping States in Solution-Processed Copper(I) Thiocyanate and Defect-Healing by I2 Doping

Solution-processed copper(I) thiocyanate (CuSCN) typically exhibits low crystallinity with short-range order; the defects result in a high density of trap states that limit the device's performance. Despite the extensive electronic applications of CuSCN, its defect properties are not understood in detail. Through X-ray absorption spectroscopy, pristine CuSCN prepared from the standard diethyl sulfide-based recipe is found to contain under-coordinated Cu atoms, pointing to the presence of SCN⁻ vacancies. A defect passivation strategy is introduced by adding solid I₂ to the processing solution. At small concentrations, the iodine is found to exist as I⁻ which can substitute for the missing SCN⁻ ligand, effectively healing the defective sites and restoring the coordination around Cu. Computational study results also verify this point. Applying I₂-doped CuSCN as a p-channel in thin-film transistors shows that the hole mobility increases by more than five times at the optimal doping concentration of 0.5 mol.%. Importantly, the on/off current ratio and the subthreshold characteristics also improve as the I₂ doping method leads to the defect-healing effect while avoiding the creation of detrimental impurity states. An analysis of the capacitance-voltage characteristics corroborates that the trap state density is reduced upon I₂ addition.