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The physical properties of rubber compounds are mainly determined by the filler dispersion within the rubber matrix, filler–rubber interaction, and chemical crosslink structure caused by sulfur. Carbon black or silica is typically used as a reinforcing filler in tire tread compounds; however, binary filler systems comprising the two types of filler are also currently being used to complement each other. This study used binary filler systems to manufacture vulcanizates and classified the vulcanizate structures as chemical crosslinks caused by sulfur, physical crosslinks caused by carbon black (carbon black–bound rubber), and silica–silane–rubber networks caused by silica and silane. The effect of each vulcanizate structure on the physical properties was also calculated. In the proposed binary filler system, silica chemically bonds with rubber molecules, unlike carbon black. Therefore, the crosslink density per unit of silica content was 19% higher than that of carbon black, in which rubber molecules were physically adsorbed on the surface. Tensile properties affected by 1 unit of crosslinking density for each filler were calculated, and silica was found to contribute more in the low-elongation range, whereas carbon black contributed more in the high-elongation range. Regarding tan δ at 60 °C and abrasion resistance per unit crosslink density of filler, carbon black made a greater contribution than silica, whereas silica had a greater contribution to wet traction and snow traction.

The purpose of this study is to reveal the impact of fashion social networking site (SNS) characteristic awareness on fashion product trust and consumer willingness to buy fashion products and present the basic data necessary to construct specific strategies for the market segment in which information is delivered, such as providing information on the promotion direction of brands and products. For research purposes, from 9 November 2018 to 22 November 2018, a professional online research institute was commissioned to investigate male and female adults in their 20s and 30s, and a total of 446 responses were analyzed for statistics using SPSS 25.0 and AMOS 25.0. The results of the study were as follows. Interaction and fashion information provision was found to have a significant effect on fashion product trust, and fashion product trust was found to have a positive effect on purchase intention. By comparing and analyzing the differences between groups that mostly used Facebook and those that used Instagram, the results showed that the impacts of interaction on fashion product trust and fashion product trust on purchase intention in both groups were significant, while fashion information provision was only significant for Instagram users. Fashion information provision is consumers obtaining the information they want from SNSs; during this process, new information is generated and shared. Facebook, however, is thought to be insignificant as many users have already been exposed to the information or advertising exposure of the event, which makes them less sympathetic to the information. The results of this study are expected to help fashion brands that utilize SNSs gain competitiveness in the online market and establish effective strategies for promoting fashion brands and products.

The tire industry has shown an increasing demand for the reduction in rolling resistance. Efforts have been made to improve the viscoelastic properties of tire compounds and reduce the weight of tires through optimization of the vulcanizate structure, which has become extremely complex. In this study, vulcanizates using carbon black and silica as binary fillers were prepared at various curing temperatures. Vulcanizate structures with respect to curing temperature were classified according to the chemical crosslink density by sulfur, carbon black bound rubber (i.e., physical crosslink due to carbon black), and silica-silane–rubber network. All properties exhibited a decreasing trend under the application of high curing temperatures, and the decrease in the crosslink density per unit content of filler with an increase in curing temperature was shown to be greater in carbon black than in silica. Mechanical and viscoelastic properties were also measured to evaluate the impact that the compound variates have on tire tread performance. These results serve as a guideline for determining the content and filler type and for setting the cure condition during the design of actual compound formulations to increase the crosslink density of rubber while retaining the necessary mechanical and viscoelastic properties for practical application.

Purpose: As human papillomavirus (HPV) is primarily responsible for the development of cervical cancer, significant efforts have been devoted to develop novel strategies for detecting and identifying HPV DNA in urine. The analysis of target DNA sequences in urine offers a potential alternative to conventional methods as a non-invasive clinical screening and diagnostic assessment tool for the detection of HPV. However, the lack of efficient approaches to isolate and directly detect HPV DNA in urine has restricted its potential clinical use. In this study, we demonstrated a novel approach of using polyethylenimine-conjugated magnetic polypyrrole nanowires (PEI-mPpy NWs) for the extraction, identification, and PCR-free colorimetric detection of high-risk strains of HPV DNA sequences, particularly HPV-16 and HPV-18, in urine specimens of cervical cancer patients. Materials and Methods: We fabricated and characterized polyethylenimine-conjugated magnetic nanowires (PEI/mPpy NWs). PEI/mPpy NWs-based HPV DNA isolation and detection strategy appears to be a cost-effective and practical technology with greater sensitivity and accuracy than other urine-based methods. Results: The analytical and clinical performance of PEI-mPpy NWs was evaluated and compared with those of cervical swabs, demonstrating a superior type-specific concordance rate of 100% between urine and cervical swabs, even when using a small volume of urine (300 µL). Conclusion: We envision that PEI-mPpy NWs provide substantive evidence for clinical diagnosis and management of HPV-associated disease with their excellent performance in the recovery and detection of HPV DNA from minimal amounts of urine samples.

Purpose: Recent developments in genomic and molecular methods have revolutionized the range of utilities of tumor-associated circulating biomarkers in both basic and clinical research. Herein, we present a novel approach for ultrasensitive extraction of cfDNA and CTCs, at high yield and purity, via the formation of magnetic nanowire networks. Materials and Methods: We fabricated and characterized biotinylated cationic polyethylenimine and biotinylated antibody cocktail-conjugated magnetic polypyrrole NWs (PEI/mPpy NW and Ab cocktail/mPpy NW, respectively). We applied these NWs to the extraction of cfDNA and CTC from the blood of 14 patients with lung cancer. We demonstrated reliable detection of EGFR mutations based on digital droplet PCR analysis of cfDNA and CTC DNA from patients with lung cancer. Results: The NW networks confined with a high density of magnetic nanoparticles exhibited superior saturation magnetization, which enabled rapid and high-yield capture whilst avoiding or minimizing damage and loss. The NW networks enabled the co-isolation of CTCs and cfDNA of high quality and sufficient quantities, thus allowing the amplification of rare and low-prevalence cancer-related mutations. Conclusion: The simple, versatile, and highly efficient nanowire network tool allows sensitive and robust assessment of clinical samples.

Low molecular O-carboxymethyl chitosan, a derivative of chitosan, was conjugated with a hydrophilic carboxymethyl group, following which the conjugate was modified with a furfuryl group. The chitosan derivative was cross-linked to encapsulate a model protein, bovine serum albumin (BSA), in the presence of Rose Bengal under visible light irradiation. The encapsulated BSA was slowly released from the matrix over 2 weeks. The modified chitosan exhibited antimicrobial activity and was non-cytotoxic to NIH3T3 fibroblasts. The wound healing effect of the cross-linked chitosan derivative was examined in Sprague-Dawley rats at 3, 7, and 14 days post-wounding. Cross-linked and murine epidermal growth factor (mEGF)-encapsulated chitosan derivatives healed wounds more rapidly in rats than non-encapsulated mEGF or chitosan derivative alone. Thus, visible light-curable chitosan has good potential for application as wound-healing matrix.

To photo-immobilize bone morphogenetic protein-2 (BMP-2), UV light-reactive gelatin (azidophenyl gelatin, Az-gel), which is introduced with an N-(4-azidobenzoyloxy) succinimide-containing an azide group, was prepared as a carrier of BMP-2. Characterization of the photo-reactivity of Az-gel was evaluated by the curing ratio and it was micropatterned using a photomask. The cross-linking ratio and an enzyme-linked immunosorbent assay, enzymelinked immunospecific assay (ELISA)-based BMP-2-release test were used to determine the optimal density of Azgel (1, 3, and 5%) and UV treatment time (10, 30, 60 s) of the BMP-2 carrier in collagen matrix. The results showed that 5% Az-gel with 60 s of UV treatment was the most efficient condition for cross-linking. Cytotoxicity assays using the C2C12 mouse myoblast cell line showed that there were no cytotoxic effects of Az-gel. Alkaline phosphatase activity and calcium ion detection assays to evaluate the osteoinductive activities were conducted in assumed optimal condition of Az-gel (5% and 60 s UV treatment) 14 days post-treatment. In our study, the osteoinductive activities were the highest in cells treated with BMP-2 and the photo-reactive Az-gel carrier compared to BMP-2 alone or untreated control cells in collagen matrix at all time points (3, 7, and 14 days).

A photoreactive azidophenyl hyaluronic acid (Az-HA) derivative for tissue augmentation was prepared by direct amide bond formation between the carboxyl groups of HA and the amine groups of 4-azidoaniline. 4-Azidoaniline was introduced to the carboxyl group of hyaluronic acid that was activated by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). The prepared Az-HA derivative was characterized by 1H NMR to measure the degree of modification. The Az-HA derivative was photo-cross-linked with varying UV irradiation times. Az-HA-20 hydrogels were formulated into injectable gels for soft tissue augmentation. The morphology, equilibrium swelling, rheological property, and in vitro degradation of hydrogels were examined. The cell cytotoxicity test of the Az-HA derivative was also examined. Az-HA-20 formed stronger hydrogels with higher storage modulus (Pa’) as UV irradiation time increased. Also, the in vitro degradation rate was lower as UV irradiation time increased. This study demonstrates that Az-HA-20 hydrogels have potential for use as injectable, biodegradable, and biocompatible hydrogels for tissue augmentation.

Titanium and its alloys have been used for a wide range of dental implant materials because of their biocompatible properties. Due to the osseointegration between the bone and implant surface that is required after implantation surgery, surface modification of titanium has been investigated. Even though bone morphogenetic protein-2 (BMP-2) and other growth factors have been applied to increase the efficiency of osseointegration, their short half-life has been a disadvantage. In this study, BMP-2 was photo-immobilized on a titanium surface using azidophenyl hyaluronic acid (Az-HA) as a matrix, and C2C12 cell lines were cultured on the modified surface. The photoreactive azidophenyl hyaluronic acid was prepared and characterized in a previous report. To demonstrate the osteoinductive effect of the photo-immobilized BMPs, alkaline phosphatase (ALP) activity assay, calcium detection assay, and alizarin red staining were conducted. Open image in new window

Carboxymethyl starch was modified by the incorporation of an azidophenyl group to prepare photoreactive starch, and characterized by Fourier transform infrared reflectance (FT-IR), proton nuclear magnetic resonance (1H-NMR), and ultraviolet (UV) spectroscopy. Photo-irradiation immobilized the Az-starch on a polystyrene plate and it was stably retained on the surface. The protein containing immobilized Az-starch was also immobilized on a stripe micropatterned plate. UV irradiation time and Az-starch concentration were used to alter the physical properties of Az-starch and consequently control the rate of epidermal growth factor (EGF) release. The Az-starch that released growth factor was not cytotoxic to 3T3-L1 fibroblast cells, and the immobilized EGF maintained its activity and induced cellular proliferation in vitro. These results suggest that Az-starch could be useful as a clinical synthetic material for medical applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Titanium (Ti) is widely used as an implant material. There are various kinds of Ti surface modification methods to facilitate effective osseointegration. In this study, UV-curable azido-LMC (azidophenyl low molecular weight chitosan) was used to modify the Ti surface. Here we suggest a novel Ti coating material that confers complex, diverse improvements to the Ti surface through a simple process. First, a cytotoxicity test of azido-LMC against osteoblast MG-63 was performed. The curing ratio dependent on UV irradiation time and concentration was determined by a comparison of weight. A 5% azido-LMC solution, which showed a wide curing ratio range, was used to investigate the surface properties. The contact angle value was measured to compare hydrophilicity, and osteoblast MG-63 cells were cultured on the coating surface. The Bradford assay was used to assess the protein immobilization capability. Hydroxyapatite, which has a beneficial influence on osseointegration, was included on the coating surface and observed by scanning electron microscopy. Surface roughness was measured by atomic force microscopy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

In this work, visible light-induced photocurable low molecular weight chitosan derivatives (F-LMC: furfuryl-low molecular weight chitosan) were prepared by nitrous acid decomposition followed by modification with furfuryl glycidyl ether. The structure of the decomposition products (LMC: low molecular weight chitosan) was characterized by FT-IR analysis. The structure and molecular weight of F-LMC, prepared from the decomposition products by modification with furfuryl glycidyl ether, were characterized by 1 H NMR and GPC analysis, respectively. F-LMC was initially water-soluble, but after the exposure to visible light, it became water-insoluble, indicating that F-LMC undergoes visible light-induced inter- and intra-molecular cross-linking. The cross-linking was determined by concentration of F-LMC and time of exposure to visible light. The cytotoxicity test using fibroblast 3T3 showed no toxicity of F-LMC. Cross-linked F-LMC surface inhibited cell adherence.

Adhesions occurring on a variety tissues and operation sites are a serious side effect of surgery and may require additional surgery for removal. Therefore, Furfuryl-fish gelatin (F-f.gel) was synthesized by introducing a furan ring to fish gelatin for application as an anti-adhesion agent. F-f.gel was cured by visible-light irradiation, which changed the material from a solution to a film. The prepared F-f.gel was characterized by proton nuclear mag- netic resonance spectroscopy ( 1 H NMR), substitution ratio, gel permeation chromatography (GPC), methyl thiazolyl tetrazolium (MTT) assay, and tests for measuring photo immobilization, water contact angle (WCA), and cell attach- ment. The results showed that F-f.gel was effective as an anti-adhesion agent.

Antimicrobial peptides exhibit high levels of antimicrobial activity against a broad range of spoilage and pathogenic microorganisms. Compared with bacteriocins produced by lactic acid bacteria, antimicrobial peptides from the genus Bacillus have been relatively less recognized despite their broad antimicrobial spectra. These peptides can be classified into two different groups based on whether they are ribosomally (bacteriocins) or nonribosomally (polymyxins and iturins) synthesized. Because of their broad spectra and high activity, antimicrobial peptides from Bacillus spp. may have great potential for applications in the food, agricultural, and pharmaceutical industries to prevent or control spoilage and pathogenic microorganisms. In this review, we introduce ribosomally synthesized antimicrobial peptides, the lantibiotic bacteriocins produced by members of Bacillus. In addition, the biosynthesis, genetic organization, mode of action, and regulation of subtilin, a well-investigated lantibiotic from Bacillus subtilis, are discussed.

The retention behavior of star-shaped polystyrene (PS) at the liquid chromatographic critical condition of linear PS was investigated. The star-shaped PS samples were prepared by anionic polymerization of styrene and subsequent linking of the polystyryl anions with divinylbenzene. The linking reaction yields a series of star-shaped PS with different number of branches of equal length. Three star-shaped PS samples with different arm molecular weight (MW) were prepared. To investigate the MW (hence the branch number) dependence of the LCCC (liquid chromatography at the critical condition) retention, the two-dimensional liquid chromatography method was used—first separating the polymers with respect to the molecular weight and subsequently separating the effluent by LCCC. Two different pore size columns were used for the LCCC separation to investigate the pore size dependence. The LCCC retention shows a very complex behavior. The retention time of the star-shaped PS shows a strong variation with MW (branch n...

Recently, distributed collaborative development environment has been recognized an alternative environment for product development in which multidisciplinary participants are naturally involving. Reuse of Product design information has long been recognized as one of core requirements for efficient product development. This paper addresses an image-based retrieval system to support product design information reuse. In the system, product images obtained from multi-modal devices are utilized to reuse design information. The proposed system conducts the segmentation of a product image by using a labeling method and generates an attributed relational graph (ARG) that represents properties of segmented regions and their relationships. The generated ARG is extended by integrating corresponding part/assembly information. In this manner, the reuse of assembly design information using a product image has been realized. The main advantages of the presented system are following. First, the system is not dependent to specific design tools, because it utilizes multimedia images that can be obtained easily from peripheral devices. Second ratio-based features extracted from images enable image retrievals that contain various sizes of parts. Third, the system has shown outstanding search performance, because we applied various information of segmented part regions and their relationships between parts.

The incremental addition of divinylbenzene was used to generate star polystyrenes in a nearly full conversion of a living polystyrenyl anion. The dramatic increase in the molecular weight of the star polystyrenes with a limited supply of the living polystyrene supported the formation of gradient-star polystyrenes through star-star coupling. The stoichiometric analysis of the star polymers revealed that their connection polymer had a shorter length than their branch polymer. The measured solution viscosity of the gradient-star polymers greatly deviated from a linear correlation with the molecular weight and was in parallel to a theoretical simulation based on a highly branched structure of the gradient-star polymer.

Structural and optical properties of InGaN/GaN triangular-shaped multiple quantum well (QW) structures were investigated under various conditions of growth parameters such as growth temperature, flow rate of Ga and/ or In composition, and well and barrier widths. The optical properties affected by the growth parameters were well correlated with an In band gap, which is determined by the potential depth and the In composition in the well region. The emission peak energy was almost independent of the barrier width due to the relaxation of the piezoelectric fields in the triangular-shaped QWs. Photoluminescence spectra of the InGaN/GaN multiple QW structures showed a parabolic curve centered at 2.66 eV. The optical property of the triangular-shaped multiple QWs was substantially improved due to formation of quantum dot-like In composition fluctuations.

Star polystyrenes were synthesized from polystyryllithium with an incremental procedure in which equally divided portions of divinylbenzene (DVB) were added periodically. When the addition of DVB was repeated, the content of the unreacted polystyryllithium dramatically decreased, and complete conversion was readily achieved. In the conventional linking reaction, however, in which all the required amounts of DVB were added at once, there was an incomplete conversion of the arm polymer. The arm number of star polymers also continuously increased upon the subsequent addition of DVB. The incremental-addition method effectively synthesized star polystyrene, minimizing uncoupled polystyrene and reproducibly controlling the arm number of star polystyrene without the formation of gel polymers. The intrinsic viscosity of star polystyrene was measured to determine the highly branched structure of star polystyrene prepared by incremental or one-shot addition.

We have studied structural and electrical properties of one dimensionally grown single crystalline gallium nitride (GaN) nanowires (NWs) for nanoscale devices using a metal-initiated metal-organic chemical vapor deposition (MOCVD). GaN nanowires were formed via the vapor-liquid-solid (VLS) mechanism with gold, iron, or nickel as growth initiators and were found to have triangular cross-sections with widths of 15 ∼ 200 nm and lengths of 5 ∼ 20 μm. TEM confirmed that the nanowires were single crystalline and were well oriented along the [210] or [110] direction on substrate depending on the metal initiators. For electrical transport properties of un-doped GaN nanowires, the back-gated field effect transistors (FET) were also fabricated by standard e-beam lithography. In our electrical measurement, the carrier concentration and mobility were 2 ∼ 4 × 10 18 cm -3 and 60 ∼ 70 cm2/V s, respectively.

Structural and optical properties of InGaN/GaN multiple triangular quantum well (QW) structures with different threading dislocation (TD) densities of 1.5×108 (sample A) and 4.5×108 cm-2 (sample B) have been studied. High resolution transmission electron microscopy and x-ray diffraction analysis showed more fluctuation of local In composition in the sample B, which was attributed to the stress field created by the dislocations as it provides a driving force for the migration of In atoms towards dislocations. Severe degradation of photoluminescence intensity of the sample B was also observed at < 50 K. The optical and structural properties of the InGaN/GaN triangular QW structures are overall substantially affected by the TD density.

Substantial improvement of electrical and optical properties of InGaN/GaN multiple quantum wells (MQWs) was obtained with a triangular band structure. Transmission electron microscopy (TEM) images from the–50 nm. The light-emitting diodes (LEDs) with the triangular QWs showed a lower operation voltage, a higher light output power, and higher intensities and narrower line widths of electroluminescence spectra than those with the rectangular QWs. Very bright and uniform light emission from the triangular MQW LEDs was also observed at a low injection current, but spatially non-uniform emission from the rectangular ones.

The effects of growth parameters on growth behavior of Pendeo-epitaxial GaN layers in (1100) patterned GaN seed stripes on sapphire were systematically investigated to improve the structural properties of the overgrown layers. It was found that the ratio of lateral to vertical growth rate (y) is strongly affected by changes in growth temperature, reactor pressure, and V/III ratio, which have an effect on the distribution of crystallographic tilt among the wing regions. Also, the crystallographic anisotropy, which was determined from the results of (0002) X-ray diffraction rocking curves taken perpendicular and parallel to the seed stripe direction, can be improved with relatively high V/III ratio.

We report the inhibition of a human recombinant geranylgeranyl diphosphate synthase (GGPPSase) by 23 bisphosphonates and six azaprenyl diphosphates. The IC50 values range from 140 nM to 690 microM. None of the nitrogen-containing bisphosphonates that inhibit farnesyl diphosphate synthase were effective in inhibiting the GGPPSase enzyme. Using three-dimensional quantitative structure-activity relationship/comparative molecular field analysis (CoMFA) methods, we find a good correlation between experimental and predicted activity: R2 = 0.938, R(cv)2 = 0.900, R(bs)2 = 0.938, and F-test = 86.8. To test the predictive utility of the CoMFA approach, we used three training sets of 25 compounds each to generate models to predict three test sets of three compounds. The rms pIC50 error for the nine predictions was 0.39. We also investigated the pharmacophore of these GGPPSase inhibitors using the Catalyst method. The results demonstrated that Catalyst predicted the pIC50 values for the nine test set compounds with an rms error of 0.28 (R2 between experimental and predicted activity of 0.948).

The effects of the indium flow rate on the properties of InGaN/GaN quantum wells have been investigated by using atomic force microscopy, photoluminescence (PL), transmission electron microscopy and high-resolution x-ray diffraction. The high-indium content InxGa1?x N/GaN (x > 0.3) quantum wells used in this study were grown on c-plane sapphire by using metal?organic chemical vapour deposition. The indium flow rate in the quantum well layers was varied while keeping other growth parameters fixed. With increasing indium flow rate, the indium solid composition in the well layers increases and the magnitudes of the indium spatial fluctuations increase. However, the defects increase and the quantum well structure degrades. As a result, the PL peak position was redshifted and the intensity was reduced. The transmission electron microscopy images show that the quantum-dot-like regions are clear for InxGa1?x N/GaN (x = 0.35). Temperature- and excitation-power-dependent photoluminescence spectra support the results of transmission electron microscopy measurements. In addition, the electroluminescence spectra of the light emitting diode shows that the dominant mechanism in InGaN/GaN quantum wells is a localized effect in the quantum-dot-like regions. The V-defects originate at threading dislocations and the inversion domain boundary due to higher misfit strain with increasing indium flow rate.

Deep level traps in Mg-doped Al0.1Ga0.9N/undoped GaN heterostructures grown by metalorganic vapor deposition with different Cp2Mg molar flow rates are studied by deep level transient spectroscopy (DLTS). Two distinct hole traps were observed, one with an activation energy of 0.18 eV (AD1) and the other with an activation energy of 0.88 eV (AD2) above the valence band maximum. From an analysis of the voltage dependence of DLTS spectra, the AD1 trap is associated with a defect in the Al0.1Ga0.9N/GaN interface based on the Poole–Frenkel model to interpret the enhancement of the thermal emission rate due to potential barrier lowering. The DLTS peak intensity of the AD2 trap steadily decreases with decreasing the Cp2Mg molar flow rate. It appears that the AD2 hole trap is strongly related to Mg-related deep levels, which contribute to the strong blue emission observed by photoluminescence measurements.

We have prepared high-quality In0.3Ga0.7N/GaN quantum wells (QWs) by metallorganic chemical vapour deposition and investigated their optical and structural properties using photoluminescence (PL), high-resolution x-ray diffraction (HRXRD) and cross-section and high-resolution transmission electron microscopy measurements. Growth parameters of the QWs were determined by adjusting the PL peak at around 2.7 eV (460 nm). PL peak intensity increases with the barrier thickness and then saturates and shows maxima when the number of wells is five or six in the In0.3Ga0.7N/GaN QWs. The results of transmission electron microscopy, PL and HRXRD show that the growth rate of the QW and barrier does not change with increasing number of wells in samples grown under optimum growth conditions, i.e. the period (well and barrier) thickness is constant. Based on the measurements of high-resolution transmission electron microscopy and temperature- and excitation-power-dependent PL, the dominant luminescent centre of In0.3Ga0.7N/GaN QWs is a quantum-dot-like localized state.

The abietane diterpenes—abietadiene, levopimaradiene, palustradiene, and neoabietadiene (1b–4b)—were prepared from the corresponding resin acids by diazomethane esterifications, LiAlH4 reductions, tosylations, and Zn/NaI reductions. Abietadiene was also obtained less efficiently by catechol borane reduction of abietadienal tosylhydrazone and Li/NH3 reduction of its 18-phenylthio derivative. These conjugated dienes were characterized by chromatographic properties (HPLC, TLC, GC), MS fragmentation patterns, optical rotations, and UV, IR, 1H NMR, and 13C NMR data. Assignments for the 1H and 13C NMR spectra were made by COSY, DEPT, HMQC, HMBC, NOE data, H–H coupling analysis, and comparisons with literature data. The four diterpenes were identified as cyclization products of recombinant abietadiene synthase, supporting their likely role in the biosynthesis of the abietane resin acids in conifer oleoresin.

The oleoresin secreted by grand fir (Abies grandis) is composed of resin acids derived largely from the abietane family of diterpene olefins as precursors which undergo subsequent oxidation of the C18-methyl group to a carboxyl function, for example, in the conversion of abieta-7,13-diene to abietic acid. A cDNA encoding abietadiene synthase has been isolated from grand fir and the heterologously expressed bifunctional enzyme shown to catalyze both the protonation-initiated cyclization of geranylgeranyl diphosphate to the intermediate (+)-copalyl diphosphate and the ionization-dependent cyclization of (+)-copalyl diphosphate, via a pimarenyl intermediate, to the olefin end products. Abietadiene synthase is translated as a preprotein bearing an N-terminal plastidial targeting sequence, and this form of the recombinant protein expressed in Escherichia coli proved to be unsuitable for detailed structure-function studies. Since the transit peptide-mature protein cleavage site could not be determined directly, a truncation series was constructed to delete the targeting sequence and prepare a "pseudomature" form of the enzyme that resembled the native abietadiene synthase in kinetic properties. Both the native synthase and the pseudomature synthase having 84 residues deleted from the preprotein converted geranylgeranyl diphosphate and the intermediate (+)-copalyl diphosphate to a nearly equal mixture of abietadiene, levopimaradiene, and neoabietadiene, as well as to three minor products, indicating that this single enzyme accounts for production of all of the resin acid precursors of grand fir. Kinetic evaluation of abietadiene synthase with geranylgeranyl diphosphate and (+)-copalyl diphosphate provided evidence for two functionally distinct active sites, the first for the cyclization of geranylgeranyl diphosphate to (+)-copalyl diphosphate and the second for the cyclization of (+)-copalyl diphosphate to diterpene end products, and demonstrated that the rate-limiting step of the coupled reaction sequence resides in the second cyclization process. The structural implications of these findings are discussed in the context of primary sequence elements considered to be responsible for binding the substrate and intermediate and for initiating the respective cyclization steps.

The photoelectric transient process of a 99 period Si0.823 Ge0.177 (17 A)/Si(24 A) superlattice (SL) was investigated by the photocurrent decay (PCD) method. Decay lifetimes of electrons and holes in SL and Si capping layers are extracted from the transient intensity and polarity of the PCD signal. The temperature and bias dependences of lifetime exhibit the thermal activation of heavy holes, the dissociation of free excitons and the thermal activations of shallow and deep levels. The heavy holes hop in and out of the well at low temperature and weak electric field, while they jump over the well region in a strong electric field or at high temperature. Lifetimes of electrons and holes are nearly the same in the Si capping layer, while the lifetime of holes is about one order of magnitude longer than that of electrons in the SL, mainly due to the quantum confinement of holes in the SL region.

Fragmentation of dialkyl peroxides and ozonides is strongly influenced by the choice of Lewis acid. TiCl4 promotes C–O ionization (SN1 reaction) of tertiary peroxides while SnCl4 and BF3·OEt2 promote O–O heterolysis (Hock reaction). The cationic intermediates are trapped with allyltrimethylsilane to afford allylated alkanes and homoallyl ethers. In the absence of a nucleophile, ozonides (1,2,4-trioxolanes) invariably undergo O–O heterolysis. However, the combination of allyltrimethylsilane and SnCl4 results in formation of 1,2-dioxolanes via trapping of intermediates derived from SN1 ionization.

We investigated the doping characteristics of Mg doped, Mg-Si co-doped, and Mg-Zn co-doped GaN films grown by metalorganic chemical vapor deposition. We have grown p-GaN film with a resistivity of 1.26 Ωcm and a hole density of 4.3 × 1017 cm−3 by means of Mg-Si co-doping technique. The Mg-Si co-doping characteristic was also explained effectively by taking advantage of the concept of competitive adsorption between Mg and Si during the growth. For Mg-Zn co-doping, p-GaN showing a low electrical resistivity (0.7 Ωcm) and a high hole concentration (8.5 × 1017 cm−3) was successfully grown without the degradation of structural quality of the film. Besides, the measured specific contact resistance for Mg-Zn co-doped GaN film is 5.0 × 10−4 cm2, which is lower value by one order of magnitude than that for only Mg doped GaN film (1.9 × 10−3Ωcm2).

Chlorofluorinated polyimides were prepared from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB), and 2,2′-dichloro-4,4′-diaminobiphenyl (DCB) for optical waveguide applications. The resulting optical polymers exhibited good thermal stability, controllable refractive index, and low optical loss in the optical communication wavelengths of 1.3 and 1.55 µm. The control of refractive indices of the polymers was achieved by copolymerization of 6FDA/PFMB and 6FDA/DCB. As the amount of DCB was increased, the refractive indices of polymer were increased. The effect of addition of chlorine on optical properties of polymers such as absorption loss in the near-IR region were also investigated. Rib-type optical waveguides were fabricated using these chlorofluorinated polyimides. These waveguides exhibited low loss of less than 0.4 dB/cm for both TE and TM polarizations. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 107–112, 1999

We have investigated the doping characteristics of Mg doped GaN films grown by metalorganic chemical vapor deposition. We have found that Mg doped GaN layer shows high electrical conductivity and good surface morphology, simultaneously, when the [Mg]/[Ga] ratio in gas phase is 7.6×10−3. If [Mg]/[Ga] ratios exceed an optimum value of 7.6×10−3, surface morphologies and electrical conduction properties become poor and blue emissions, considered as deep donor-to-acceptor-pair transitions in photoluminescence spectra, are dominant. Moreover, the Mg–Si codoping characteristics was explained effectively taking advantage of the concept of competitive adsorption between Mg and Si during the growth. Based on the experimental results, we suggest the methods to get a p-GaN showing high conductivity using Mg-Si codoping.

The origin of the radiative recombination leading to yellow luminescence (YL) has been elucidated by the study of luminescence properties of GaN films grown with two different gas feeding methods. GaN films were grown on a (0001) sapphire substrate in a rapid thermal chemical vapor deposition (RTCVD) reactor. GaN films emitted two different luminescence energies, 2.2 and 3.47 eV, depending on the introducing position of hydrogen gas in the growth reactor. The distribution of the TMGa flow and gas phase reactions in the reactor were investigated to understand the effect of the gas feeding methods on the optical properties of GaN films. The results suggest that YL is related to Ga vacancies in the grown films.

We studied the effects of the growth rate of a GaN buffer layer grown on a GaN epilayer. It was found that this growth rate plays a key role in improving the quality of the GaN film on a sapphire substrate and an optimum growth rate exists that yields the best crystal quality. A GaN film grown on a buffer layer with the optimum growth rate of 18.3 nm/min has an electron Hall mobility of 539 cm2/V s and a dislocation density of approximately 2×108 cm−2. These improvements of GaN film qualities are illustrated by the promotion of the lateral growth mode.

The material qualities of GaN overlayers grown on (0001) sapphire substrates by metal-organic chemical vapour deposition were investigated as a function of nitridation time. The nitridation of sapphire surface notably affects on the properties of the GaN overlayers, such as surface morphology and structural, optical and electrical properties. The GaN overlayer with a short nitridation time of 30 s shows a good surface morphology, a relatively low background Hall carrier concentration and a high electron mobility, but the defect-related emission around 550 nm increased. Furthermore, for the GaN overlayer with nitridation for 180 s, even though it has a low (102) full width at half-maximum of the high-resolution x-ray diffraction rocking curve, other material properties were degraded owing to the long nitridation time. It was found that material properties have a trade-off relationship with the variation of nitridation time.

A tetragonally distorted GaAs layer was grown on a Si(100) substrate by metalorganic chemical vapor deposition. From both the splitting and the shift of band-edge exciton lines in photoluminescence, the GaAs epilayer is found to be under biaxial tensile stress, which is quantitatively investigated using optical measurements, namely, Raman and temperature-dependent photoluminescence spectroscopy. The biaxial tensile stresses deduced from the intrinsic excitonic lines vary with temperature. The origin of the stress variation with temperature is discussed in detail. From the photoluminescence intensity ratios between the heavy- and light-hole excitonic transitions, the actual temperature where the conduction to heavy-hole band transition begins to predominate is found to be above 70 K.

We report the Si-doping-induced relaxation of residual stress in GaN epitaxial layers grown on (0001) sapphire substrate by the metalorganic vapor phase epitaxy technique. Micro-Raman spectroscopy is used to assess stress situation in the films with systematically modulated doping concentration from 4.0×1017 up to 1.6×1019 cm−3. As the Si-doping concentration increases, a monotonic decrease of the E2 phonon frequency is observed, which signifies gradual relaxation of the stress in the film. The layers are fully relaxed when electron concentration exceeds 1.6×1019 cm−3. The linear coefficient of shift in Raman frequency (ω) induced by the in-plane biaxial compressive stress (σ∥) is estimated to be Δω/Δσ∥=7.7 cm−1/GPa. We suggest that Si doping increases density of misfit dislocation, judging from linewidth of x-ray rocking curve.

The effects of growth parameters have been examined for the epitaxial growth of a void-free SiC film on a Si substrate. Experiments were performed under various growth conditions by pyrolyzing tetramethylsilane (TMS) in a rapid thermal chemical vapor deposition reactor. Void-free single crystalline SiC films were grown when the Si substrate was heated after the flow of TMS. The increase of TMS flow rate produced void-free SiC films but the crystallinity of the films varied from single crystalline to polycrystalline. The growth of void-free single crystalline SiC films was observed at substrate temperatures below 1000°C. The outdiffusion of Si atoms from the Si substrate surface and the void formation in the silicon side of the SiC/Si interface were investigated using various experimental techniques. The mechanism of the void formation is briefly discussed in this work.