A fast and compact elimination method of empty elements from a double‐array structure

A double‐array is a well‐known data structure to implement the trie. However, the space efficiency of the double‐array degrades with the number of key deletions because the double‐array keeps empty elements produced by the key deletion. This paper presents a fast and compact elimination method of empty elements using properties of the trie nodes that have no siblings. The present elimination method is implemented by C language. From simulation results for large sets of keys, the present elimination method is about 30–330 times faster than the conventional elimination method and maintains high space efficiency. Copyright © 2003 John Wiley & Sons, Ltd.     

Rod-like β-FeSi2 phase grown on Si (111) substrate

Pure Fe with coverage of 0.5-2.0 nm was deposited on Si (111) 7×7 surfaces by reactive deposition epitaxy (RDE) in an integrated ultrahigh vacuum (UHV) system. Transmission electron microscopy (TEM) confirmed that the as-deposited epitaxial phase exhibits rod-like and equilateral triangular morphology. The as-deposited phase was identified as c-FeSi₂ by electron diffraction and high-resolution transmission electron microscopy. It was found that there exists lattice distortion in epitaxial c-FeSi₂ phase. Upon annealing at 1073 K, the metastable c-FeSi₂ transforms into equilibrium β-FeSi₂ phase, the latter inherits completely the morphology of c-FeSi₂ phase. Based on RDE and subsequent annealing, a new fabrication technique to grow rod-like semiconducting β-FeSi₂ on a Si substrate has been proposed in the present work.     

Te concentration dependent photoemission and inverse-photoemission study of FeSe1?xTex

We have characterized the electronic structure of FeSe_1−xTe_x for various x values using soft x-ray photoemission spectroscopy (SXPES), high-resolution photoemission spectroscopy (HRPES) and inverse photoemission spectroscopy (IPES). The SXPES valence band spectral shape shows that the 2 eV feature in FeSe, which was ascribed to the lower Hubbard band in previous theoretical studies, becomes less prominent with increasing x. HRPES exhibits systematic x dependence of the structure near the Fermi level (E_F): its splitting near E_F and filling of the pseudogap in FeSe. IPES shows two features, near E_F and approximately 6 eV above E_F; the former may be related to the Fe 3d states hybridized with chalcogenide p states, while the latter may consist of plane-wave-like and Se d components. In the incident electron energy dependence of IPES, the density of states near E_F for FeSe and FeTe has the Fano lineshape characteristic of resonant behavior. These compounds exhibit different resonance profiles, which may reflect the differences in their electronic structures. By combining the PES and IPES data the on-site Coulomb energy was estimated at 3.5 eV for FeSe.     

On the onset of fracture as a silicon-based polymer converts into the ceramic phase

Silicon-based polymers evolve into refractory ceramics when heated gradually up to ~1000°C. The conversion is accompanied by the loss of gaseous species, and by a two-fold increase in density. The shrinkage can produce microcracks if the heating rate is too high, or if the specimen is too thick. This communication builds on earlier work whereby the measurement of gas evolution, and its relationship with viscous flow, are related to the onset of fracture in disk-shaped green (polymer) samples. The onset is determined as a function of the thickness of the disks, and of the heating rate. The results are presented in the form of a processing map. The overlay with gas evolution, and strain-rate measurements, suggest that fracture initiates with the release of hydrogen and methane, starting at temperatures near 750°C.     

Nanowrinkled and Nanoporous Polyethylene Membranes Via Entanglement Arrangement Control

Crystalline homopolymers, including polyethylene (PE), which has the simplest architecture, form a nanometer‐sized combination of crystalline and amorphous components, but their arrangement control, similar to self‐assembled phase‐separation of block‐copolymers, is usually difficult. However, molecular entanglements trapped between crystalline and amorphous components of homopolymers coincide with the segmental linking points on the interfaces of the microphase separation for block copolymers. Nanowrinkled PE membranes are prepared with a network of 30 nm‐thick homogeneous lamellae using a novel entanglement control technique composed of biaxial melt‐drawing and melt‐shrinking procedures, which are limited for highly entangled ultrahigh molecular weight materials. Such a network arrangement of nanowrinkling lamellae spreading on membrane surface and also across the membrane thickness improves the mechanical properties of both tensile strength and tearing strength. Subsequent cold‐drawing causes delamination of the lamellar interfaces, leading to the resultant nanoporous morphology composed of passing‐through channels that are several tens of nanometers in diameter, without any solvent processing.     

Synthesis of polyamides from sugar derived d-glucaric acid and xylylenediamines

d -Glucaric acid (GA) is the one of aldaric acids and is an important bio-based building block for polymers. In this study, poly(m-xylylene-acetyl glucaramide) and poly(p-xylylene-acetyl glucaramide) were synthesized from GA acetate and two kind of aromatic diamines by solution polymerization. The chemical structures of the polyamides were analyzed by nuclear magnetic resonance spectroscopy. The weight-average molecular weights ranged from 3.3 × 10³ to 1.15 × 10⁴ with a polydispersity of 1.6–1.9, depending on monomer ratio or monomer concentration in solution. The 10% decomposition temperature of the polymers was about 210 °C. Differential scanning calorimetry revealed that the polyamides exhibited no peaks attributed to crystallization or melting point, which indicated that the polyamides were amorphous. No crystalline pattern was observed in the X-ray diffractograms, supporting this result. Polarized optical microscopy observation revealed that the polyamides exhibited melting-like behavior at above 150 °C, which was attributed to glass-transition behavior. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47255.     

Supramolecular morphology of two-step melt-spun poly(dioxanone) fibers

Structure of poly(dioxanone) (PPDX) fibers produced through a two-step melt-spinning process with an additional short-period annealing above the melting temperature of PPDX was investigated and the effect of annealing on the degradation behavior was discussed. The morphological study carried out by etching the fibers using a phosphate or permanganate solution suggested that the fibers take a skin–core structure, and both the skin layer and the core region consist of a bundle of microfibrils. The micro-beam X-ray diffraction analysis revealed that the short-period annealing in the production process only slightly promotes the crystallization in the skin layer but contributes to increasing the packing of amorphous chains near the skin, which seems to be the controlling factor of the hydrolytic degradation behavior of the fibers.     

Energy state of InGaAs quantum dots on SiO2-patterned vicinal substrate

The optical properties of In_0.8Ga_0.2As self-assembled quantum dots (SAQDs) grown on GaAs wire structures formed by utilizing SiO₂-patterned exact and 5°-off (001) GaAs substrates have been studied with micro-photoluminescence (μ-PL). Single PL peak was occurred for In_0.8Ga_0.2As SAQDs grown on SiO₂-patterned exact (001) GaAs, whereas double PL peaks were showed for SAQDs grown on 5°-off (001) GaAs substrates as the width of the opening windows increased. The power-dependent μ-PL spectra show that the first and second peaks of these double peaks were originated from the well-defined ground and excited state, respectively. These results demonstrated that In_0.8Ga_0.2As SAQDs selectively grown by utilizing SiO₂-patterned 5°-off (001) GaAs substrates have well-defined zero-dimensional quantum states.     

Detection of Buckminsterfullerene in Usual Soots and Commercial Charcoals

Abstract

It was confirmed that soot produced by free burning of small hydrocarbons like benzene and cyclohexane generally contains less than 0.1 ppm of C₆₀. Small, but measurable amounts of C₆₀ were found in two samples of charcoal, providing the first indication of fullerene formation in the solid state.