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171.
Dong‐Seon Won Jin‐Hyang Kim Hyo Jin No You Jin Cho Ju‐Yeon Lee Bum Ku Rhee Hee‐Dok Choi 《Polymer International》2010,59(2):162-168
Stabilization of electrically induced dipole alignment is one of the important criteria in the development of nonlinear optical (NLO) polymers for electro‐optic device applications. Polyurethanes for NLO applications have attracted attention because of their high thermal stability due to hydrogen bonding. In the work reported here, we designed and synthesized a new type of NLO polyurethane, in which the pendant NLO chromophores are part of the polymer backbone. This mid‐type NLO polymer is expected to have the merits of both main‐chain and side‐chain NLO polymers, namely stable dipole alignment and good solubility. 1‐[3,4‐Di‐(2‐hydroxyethoxy)phenyl]‐2‐(2‐thienyl)ethene was prepared and condensed with 3,3′‐dimethoxy‐4,4′‐biphenylenediisocyanate to yield a polyurethane. This polyurethane was reacted with tetracyanoethylene to give a novel Y‐type polyurethane (7) containing 1‐(3,4‐dioxyphenyl)‐2‐[5‐(1,2,2‐tricyanovinyl)‐2‐thienyl]ethenes as NLO chromophores, which constitute part of the polymer backbone. Polyurethane 7 is soluble in common organic solvents such as N,N‐dimethylformamide and dimethylsulfoxide. It shows a thermal stability up to 280 °C from thermogravimetric analysis with a glass transition temperature obtained from differential scanning calorimetry of ca 162 °C. The second harmonic generation (SHG) coefficient (d33) of a poled polymer film of he polyurethane at 1560 nm fundamental wavelength is ca 1.11 × 10?18 C. Polymer 7 exhibits an enhanced thermal stability and no significant SHG decay is observed below 150 °C, which is acceptable for NLO device applications. Copyright © 2009 Society of Chemical Industry 相似文献
172.
S.J. Yuan 《Corrosion Science》2009,51(6):1372-1385
The biofilm colonization dynamics of Pseudomonas NCIMB 2021 and Desulfovibrio desulfuricans (ATCC 27774) on 304 stainless steels (304 SS) was evaluated using atomic force microscopy (AFM) in simulated seawater-based media under aerobic and anaerobic conditions. Results showed that the biofilm formed on the coupon surface by the two strains of bacteria increased in the coverage, heterogeneity and thickness with exposure time, thus resulting in the deterioration of the steel substratum underneath the biofilm in the form of pitting corrosion. The depth of pits induced by D. desulfuricans was larger than that by Pseudomonas NCIMB 2021, which was mainly attributed to the enhanced corrosion of 304 SS coupons by the biogenic sulfide ions, as revealed by the results of X-ray photoelectron spectroscopy (XPS) and Tafel polarization curves. AFM was also used to determine cell attachment/detachment processes of the Pseudomonas and D. desulfuricans bacteria on the coupon surface by quantifying the tip-cell interaction forces. The interactive forces between the tip and the bacterial cell surface were considerably smaller than those between the tip and the cell-cell interface due to the accumulation of extra-cellular polymeric substances (EPS) for both strains. Furthermore, the adhesion forces over the Pseudomonas cells were verified to be more attractive than those of D. desulfuricans due to the former being a slime-producer. 相似文献
173.
M. Heck H.M. Ortner S. Flege U. Reuter W. Ensinger 《International Journal of Refractory Metals and Hard Materials》2008,26(3):197-206
Compacted graphite iron (CGI) is the material for the upcoming new generation of high-power diesel engines. Due to its increased strength compared to grey cast iron (CI) it allows an increase in the cylinder-pressures and therefore a better fuel economy and a higher power output are possible. First examples of such engines are the 3.3 L Audi V8 TDI and the 4.0 L BMW V8. The reason why CGI is not used to a larger extent in large scale production up to now is its much more difficult machinability as compared to conventional CI, especially at high cutting speeds. In modern transfer lines high cutting speeds are used in the cylinder-boring operation. And especially in these continuous cutting operations the tool life decreased due to the change from CI to CGI by about a factor of 20. As was found out previously by us, the difference in tool lifetime can be explained by the formation of a MnS-layer on the tool surface in the case of CI. This layer cannot form when machining CGI because the formation of MnS-inclusions is not possible in this material due to the higher magnesium content which in turn is responsible for the formation of the graphite vermicles. The MnS-layer acts as a lubricant and prevents the adhesion of workpiece particles. This is the reason for the greatly reduced wear of CI in high speed machining operations. This MnS-layer is inspected closer by X-ray diffraction, X-ray induced photoelectron spectrometry, atomic force microscopy and secondary ion mass spectrometry in this work. Furthermore, available information on the performance of MnS as lubricant in PM-steels is comparatively discussed. This knowledge led to an economic solution of high productivity machining of CGI. The key was to reduce the cutting speed, replacing single insert tools with multiple insert tools. This allowed to increase the feed rate. By increasing the feed rate in the same amount as decreasing the cutting speed, the same productivity can be realized. This concept is leading to a number of multiple insert tools thus realizing a high productivity machining of CGI cylinder-bores with multi-layer-coated carbide tools. 相似文献
174.
Dinesh Kumar Misra Sung Woo Sohn Won Tae Kim Do Hyang Kim 《Science and Technology of Advanced Materials》2008,9(4)
The plastic deformation of Ti45Zr16Be20Cu10Ni9 bulk metallic glass has been investigated by nanoindentation performed with loads ranging from 10 to 200 mN in a wide range of loading rates. The plastic flow in the alloy exhibited conspicuous serrations at low loading rates. The serrations, however, became less prominent as the rate of indentation increased. Atomic force microscopy showed a significant pile-up of materials around the indents, indicating that a highly localized plastic deformation occurred under nanoindentation. The possible mechanism governing the plastic deformation in bulk metallic glass specimens is tentatively discussed in terms of strain-induced free volume. 相似文献
175.
Marco Brucale Dr. Massimo Sandal Dr. Selena Di Maio Aldo Rampioni Dr. Isabella Tessari Dr. Laura Tosatto Marco Bisaglia Dr. Luigi Bubacco Prof. Bruno Samorì Prof. 《Chembiochem : a European journal of chemical biology》2009,10(1):176-183
α‐synuclein (α‐Syn) is an abundant brain protein whose mutations have been linked to early‐onset Parkinson's disease (PD). We recently demonstrated, by means of a single‐molecule force spectroscopy (SMFS) methodology, that the conformational equilibrium of monomeric wild‐type (WT) α‐Syn shifts toward β‐containing structures in several unrelated conditions linked to PD pathogenicity. Herein, we follow the same methodology previously employed for WT α‐Syn to characterize the conformational heterogeneity of pathological α‐Syn mutants A30P, A53T, and E46K. Contrary to the bulk ensemble‐averaged spectroscopies so far employed to this end by different authors, our single‐molecule methodology monitored marked differences in the conformational behaviors of the mutants with respect to the WT sequence. We found that all the mutants have a much higher propensity than the WT to adopt a monomeric compact conformation that is compatible with the acquiring of β structure. Mutants A30P and A53T show a similar conformational equilibrium that is significantly different from that of E46K. Another class of conformations, stabilized by mechanically weak interactions (MWI), shows a higher variety in the mutants than in the WT protein. In the A30P mutant these interactions are relatively stronger, and therefore the corresponding conformations are possibly more structured. The more structured and globular conformations of the mutants can explain their higher propensity to aggregate with respect to the WT. 相似文献
176.
G. POMPEO M. GIRASOLE G. LONGO A. CRICENTI D. BAILO F. RONCI A. MARAS† M. SERRACINO‡ & P. F. MORETTI§ 《Journal of microscopy》2008,230(2):218-223
Introduction: The aim of this study is to investigate the nanocrystallization of steels caused by the transformation from the austenitic to the martensitic phase induced by a severe plastic deformation (SPD) treatment. In this framework, we applied an air blast shot peening treatment, which is a simple protocol widely used for industrial purposes. Methods: AISI 286 and AISI 316 specimens were peened for different times and polished using diamond pastes in order to remove corrugations higher than 1 μm. The characterization of the steel surfaces was performed by atomic force microscopy (AFM) operating in contact mode. Additional EDXD measurements were performed to confirm the phase transition. Results and Discussion: An AFM‐based characterization at nanometric level of the steel surfaces is provided. When the peening exceeds a threshold time that, as expected, depends on the steel composition, a uniform nanostructuration is detected. It is well known that such rearrangement is associated to the growth of a martensitic phase. To date, AFM has been employed in this field only for few applications and to solve specific problems. On the other hand, our results demonstrate that this is a useful technique for the characterization of hardened surfaces, especially when non‐destructive sample preparation treatments are required. Moreover, we show that AFM can be a useful tool also for in situ industrial diagnostics of metallic parts. 相似文献
177.
Jian-Yi Sun Ming-Qi Liu Xiao-Yan Weng Li-Chun Qian Sai-Hong Gu 《Food chemistry》2007,104(3):1055-1064
The mature peptide of Thermomonospora fusca xylanase A (TfxA) was successfully expressed in Pichia pastoris under the control of AOX1 promoter. The activity of recombinant T. fusca xylanase A (reTfxA) in culture supernatant was 117.3 ± 2.4 U/mg, which is 3 times higher than that of the native TfxA. The optimal temperature and pH for reTfxA were 60 °C and 6.0, respectively. When treated at 70 °C and pH 6.0 for 2 min, the residual activity of the reTfxA was 70%. The reTfxA was very stable over a wide pH range (5.0–9.0). After incubation over pH 5.0–9.0 at 25 °C for 1 h, all the residual activity of reTfxA was over 80%. The Km and kcat values for reTfxA were 2.45 mg/ml and 139 s−1, respectively. HPLC analysis revealed that xylobiose (X2) was the main hydrolysis product released from birchwood xylan and wheat bran insoluble xylan by reTfxA. Hydrolysis results of xylooligosaccharides showed that reTfxA was an endo-acting xylanase and xylobiose, xylotriose (X3), xylotetraose (X4), xylopentaose (X5), and xylohexaose (X6) could be hydrolysed. This is the first report on the expression of reTfxA in yeast and on the determining and quantifying of the hydrolysis products released from xylans and xylooligosaccharides by reTfxA. 相似文献
178.
A set-up combining an AFM and an electrochemical cell has been used to study in situ the local corrosion of a 304L stainless steel in an aqueous chloride-containing solution. The focus was made on the sites where pits were initiated under controlled potential in order to establish whether or not the pits were randomly distributed at the nanoscale. Grain boundaries and surface stoichiometric inhomogeneities appeared to concentrate pit onsets significantly. The influence of the mechanical history of the material, especially soft surface strain hardening, on the location of the first pits has been shown. The study revealed that 70% of the pits initiated at strain hardened areas resulting from mechanical polishing. A plausible model has been suggested to explain such a behaviour. 相似文献
179.
Deok-Ho Kim Jungyul Park Moon K. Kim Keum-Shik Hong 《Journal of Mechanical Science and Technology》2008,22(11):2203-2212
Nowadays a mathematical model-based computational approach is getting more attention as an effective tool for understanding
the mechanical behaviors of biological systems. To find the mechanical properties of the proteins required to build such a
model, this paper investigates a real-time identification method based on an AFM nanomanipulation system. First, an AFM-based
bio-characterization system is introduced. Second, a second-order time-varying linear model representing the interaction between
an AFM cantilever and globular proteins in a solvent is presented. Finally, we address a real-time estimation method in which
the results of AFM experiments are designed to be inputs of the state estimator proposed here. Our attention is restricted
to a theoretical feasibility analysis of the proposed methodology. We simply set the mechanical properties of the particular
protein such as mass, stiffness, and damping coefficient in the system model prior to running the simulation. Simulation results
show very good agreement with the preset properties. We anticipate that the realization of the AFM-based bio-characterization
system will also provide an experimental validation of the proposed identification procedure in the future. This methodology
can be used to determine a model of protein motion for the purpose of computer simulation and for a real-time modification
of protein deformation.
This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim
Jungyul Park received the B.S. and M.S. degrees in mechanical design and production engineering from the Seoul National University in
1998 and 2000, respectively and received Ph.D. degree in School of Mechanical & Aerospace Engineering from the Seoul National
University, Korea in 2005. He is currently an assistant professor in the mechanical engineering department, Sogang University,
in Korea (since 2007). Previously he had worked at the Korea Institute of Science and Technology and at the biomedical engineering
department, Johns Hopkins University. His research interests are design, fabrication and analysis of BioMEMS, manipulation,
characterization and identification of cells/biomolecules using micro/nano technology, and precise control for micro/nano
manipulation. 相似文献
180.
Video rate atomic force microscopy (VideoAFM), with a frame rate of 14 frames/s and a tip velocity of up to 15 cms−1, is used to image polyethylene oxide films during crystal growth. The capabilities of VideoAFM when applied to semicrystalline polymer surfaces are explored. Image quality comparable to that found with conventional contact AFM is achieved but with a nearly 1000 times improvement in time resolution. By applying the technique to the real-time observation of crystal growth, different modes of rapid crystallization are followed in real time. Observation of the spherulite growth front allows measurement of growth rates at the lamellar scale, from which a factor of two difference in the rate of radial growth to the rate of tangential growth is observed, confirming that the elongated nature of spherulite lamellae is due to geometric constraints rather than an inherent fibrillar character. Measurements on screw dislocation growth, when large amounts of crystallizable material is trapped at the surface show that the terrace height does not influence the rate of crystal growth, confirming that under these conditions processes at the lamellar growth front control the rate of growth. When only a thin film of molten material is left on the surface of the already crystallized film dendritic growth is observed, implying a diffusion controlled process under these far from equilibrium conditions. 相似文献