The fabrication of graphitic thin films with highly dispersed noble metal nanoparticles by direct carbonization of block copolymer inverse micelle templates

Ordered arrays of Au or Ag nanoparticles supported on two-dimensional graphitic carbon films were prepared by direct carbonization of stabilized asymmetric polystyrene-block-poly(4-vinyl pyridine) (PS-b-P4VP) inverse micellar films loaded with metal precursors. Crosslinked PS-b-P4VP thin film templates with metal precursors selectively distributed in P4VP domains were converted to carbonaceous thin films having well-defined, highly dispersed metal nanoparticle (NP) arrays by ultraviolet (UV) irradiation under vacuum and subsequent carbonization. Mesoporous carbon films were also obtained after extracting the metal NPs by sonication in selected solvents. PS-b-P4VP was employed not only as carbon source, but also as template for introducing metal NPs in a nanopatterned configuration. The characteristic features and properties of thus generated hybrid carbon nanostructures were investigated by microscopy, UV–visible spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction measurement, and Raman spectroscopy.     

Improved performance of simulated moving bed process using column‐modified feed

A “FeedCol” strategy was developed to improve separation performance in simulated moving bed (SMB) processes. In the FeedCol operation, a short chromatographic column was simply added to the SMB unit and feed was supplied by a pulse input through the column to the SMB process. Because the feed was made in the shape of partially separated chromatographic peaks through the column, the purities in the raffinate and extract products were improved efficiently in the SMB process. All the performance parameters for a binary mixture with low selectivity (α = 1.1) were better for the FeedCol operation than for the conventional SMB operation (2‐2‐2‐2). Because the feed injection through the feed column was synchronized with the SMB process during the switching period, two new operating variables were introduced: injection length and injection time. Their effects on the suggested strategy were evaluated in terms of performance parameters through a detailed simulation study. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Preparation and characterization of polyimide/modified layered double hydroxide nanocomposites

Polyimide (PI)/modified layered double hydroxide (m‐LDH) nanocomposites were prepared in this study. For this work, m‐LDHs were prepared from layered double hydroxides (LDHs) through an anionic exchange reaction with pyromellitic dianhydride (PMDA), succinic acid or terephthalic acid. PMDA and 4,4′‐oxydianiline were used to make the poly(amic acid) precursor for PI. X‐ray diffraction and transmission electron microscopy measurements confirmed that the PMDA‐modified LDH (PMH) and terephthalic acid‐modified LDH (TMH) were well dispersed in the PI matrix. For the succinic acid‐modified LDH, some of the LDH was intercalated with the succinic acid molecules but most maintained its original structure. Thus, the PI/PMH and PI/TMH nanocomposites exhibited improved mechanical, thermal and electrical properties compared to pure PI. The PMH has aromatic groups and is expected to have better π–π interactions with the PI chains than the other m‐LDHs. Thus, the PI/PMH nanocomposites exhibited the best properties among the nanocomposites investigated. Copyright © 2010 Society of Chemical Industry     

连续时间模糊随机系统分析：状态空间模型分析

研究了连续时间模糊随机系统理论，给出了连续时间模糊随机系统的态变模糊订值映射的定义，讨论并解决了连续时间模糊随机系统的状态空间模型分析。     

Discomfort luminance level of head-mounted displays depending on the adapting luminance

The Images in an immersive head-mounted display (HMD) for virtual reality provide the sole source for visual adaptation. Thus, significant, near-instantaneous increases in luminance while viewing an HMD can result in visual discomfort. Therefore, the current study investigated the luminance change necessary to induce this discomfort. Based on the psychophysical experiment data collected from 10 subjects, a prediction model was derived using four complex images and one neutral image, with four to six levels of average scene luminance. Result showed that maximum area luminance has a significant correlation with the discomfort luminance level than average, median, or maximum pixel luminance. According to the prediction model, the discomfort luminance level of a head-mounted display was represented as a positive linear function in log₁₀ units using the previous adaptation luminance when luminance is calculated as maximum area luminance.     

Sodium azide and metal chelator effects on 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging compounds from methylene blue photosensitized lard

Thermal oxidation of edible oils can generate 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging compounds from oxidized lipids (RSOLs). However, effects of photosensitization on the formation of RSOLs have not been reported yet. Methylene blue (MB) photosensitization and involvement of singlet oxygen and transition metals on the RSOL formations were determined in stripped lard oils. RSOLs were formed in lard containing MB and visible light irradiation only. Addition of sodium azide decreased RSOLs with concentration dependent manner, which implies singlet oxygen was involved on the RSOL formation. Ethylenediammetetraacetic acid (EDTA), a well known metal chelator, accelerated the formation of RSOLs through protecting the decomposition of MB photosensitizer. Results from p‐anisidine values showed that RSOLs from photosensitization may not be formed from the same pathways compared to thermal oxidation. Practical application: Understanding mechanisms of lipid oxidation can help extend the shelf‐life of foods. Photosensitization plays important roles in accelerating the rates of lipid oxidation. The results of this study showed that foods containing photosensitizers can generate radical scavenging compounds from oxidized lipids (RSOLs) under visible light irradiation and singlet oxygen is involved in the formations of these compounds. However, these compounds may not share the same pathways with thermally oxidized lipids. Metal chelating agents accelerated the rates of lipid oxidation and formation of RSOLs which implies that metal chelators can act as prooxidant. Careful considerations are necessary on the addition of metal chelators because non‐polar photosensitizers can act a prooxidant.     

Powder preparation for a shell mold using a new coating process

A new coating process in the powder preparation for a shell mold has been developed to increase the fracture strength of the shell mold. It is due to the homogeneous formation of a glass phase on the starting particles and the increase in the glassification efficiency by the reduction in the loss of inorganic precursors. The inorganic binder system used for the new coating process is composed of tetraethyl orthosilicate (TEOS) and sodium methoxide (NaOMe) as the silica (SiO₂) and sodium oxide (Na₂O) precursors, respectively. Three different coating processes are employed for the powder preparation with a high glassification efficiency. In process I, the starting particles are coated with NaOMe, and then TEOS are coated on the particles treated with NaOMe. Process II is the reverse sequence of process I. Process III involves coating of the particles with a mixture of TEOS and NaOMe. The particles coated with an individual or mixture precursor were fixed with an organic binder and then heated at 1000 °C for 1 h. Molds prepared through the new coating processes, especially process III, show a higher fracture strength value compared with that of the conventional convert mold process, which may be caused by the increase in the glassification efficiency of the precursors. Powder prepared by process III shows a more uniform coating of the glass phase than those by other processes, resulting from an enhancement in the phase mixing between SiO₂ and NaOH molecules.     

Photocatalytic degradation and heat reflectance recovery of waterborne acrylic polymer/ZnO nanocomposite coating

This work aims to clarify the photocatalytic degradation mechanism and heat reflectance recovery performance of waterborne acrylic polymer/ZnO nanocomposite coating. To fabricate the nanocomposite coating, ZnO nanoparticles (nano-ZnO) were dispersed into acrylic polymer matrix at the various concentrations from 1 to 6% (by total weight of resin solids). The photocatalytic degradation of nanocomposite coating under ultraviolet (UV) light irradiation has been investigated by monitoring its weight loss and chemical/microstructural/morphological changes. As the topcoat layer, its heat reflectance recovery has been evaluated under UV/condensation exposure by using an artificial dirty mixture of 85 wt% nanoclay, 10 wt% silica particles (1–5 μm), 1 wt% carbon black, and 2 wt% engine oil. After 108-cycle UV/condensation exposure, infrared spectra and weight loss analysis indicated that the maximal degradation for nanocomposite coating is observed at 1 wt% nano-ZnO. On the other hand, after 96 hr of UV light exposure, the nanocomposite coating with1 wt% nano-ZnO could restore effectively the reflective index of solar-heat reflectance coating (from 58.45 to 80.78%). Finally, the photodegradation mechanism of this waterborne acrylic polymer coating has been proposed as the UV-induced formation of CC CO conjugated double bonds. As a result, its self-cleaning phenomenon can be achieved as the recovery of heat reflectance.     

A vacuum-sealed miniature X-ray tube based on carbon nanotube field emitters

ABSTRACT: A vacuum-sealed miniature X-ray tube based on a carbon nanotube field-emission electron source has been demonstrated. The diameter of the X-ray tube is 10 mm; the total length of the tube is 50 mm, and no external vacuum pump is required for the operation. The maximum tube voltage reaches up to 70 kV, and the X-ray tube generates intense X-rays with the air kerma strength of 108 Gy * cm2 min1. In addition, X-rays produced from the miniature X-ray tube have a comparatively uniform spatial dose distribution.     

Manipulating crystal growth and polymorphism by confinement in nanoscale crystallization chambers

The phase behaviors of crystalline solids embedded within nanoporous matrices have been studied for decades. Classic nucleation theory conjectures that phase stability is determined by the balance between an unfavorable surface free energy and a stabilizing volume free energy. The size constraint imposed by nanometer-scale pores during crystallization results in large ratios of surface area to volume, which are reflected in crystal properties. For example, melting points and enthalpies of fusion of nanoscale crystals can differ drastically from their bulk scale counterparts. Moreover, confinement within nanoscale pores can dramatically influence crystallization pathways and crystal polymorphism, particularly when the pore dimensions are comparable to the critical size of an emerging nucleus. At this tipping point, the surface and volume free energies are in delicate balance and polymorph stability rankings may differ from bulk. Recent investigations have demonstrated that confined crystallization can be used to screen for and control polymorphism. In the food, pharmaceutical, explosive, and dye technological sectors, this understanding and control over polymorphism is critical both for function and for regulatory compliance. This Account reviews recent studies of the polymorphic and thermotropic properties of crystalline materials embedded in the nanometer-scale pores of porous glass powders and porous block-polymer-derived plastic monoliths. The embedded nanocrystals exhibit an array of phase behaviors, including the selective formation of metastable amorphous and crystalline phases, thermodynamic stabilization of normally metastable phases, size-dependent polymorphism, formation of new polymorphs, and shifts of thermotropic relationships between polymorphs. Size confinement also permits the measurement of thermotropic properties that cannot be measured in bulk materials using conventional methods. Well-aligned cylindrical pores of the polymer monoliths also allow determination and manipulation of nanocrystal orientation. In these systems, the constraints imposed by the pore walls result in a competition between crystal nuclei that favors those with the fastest growth direction aligned with the pore axis. Collectively, the examples described in this Account provide substantial insight into crystallization at a size scale that is difficult to realize by other means. Moreover, the behaviors resulting from nanoscopic confinement are remarkably consistent for a wide range of compounds, suggesting a reliable approach to studying the phase behaviors of compounds at the nanoscale. Newly emerging classes of porous materials promise expanded explorations of crystal growth under confinement and new routes to controlling crystallization outcomes.