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81.
Brush type of poly (3‐hydroxy butyrate), PHB, copolymer synthesis has been reported. Natural PHB was chlorinated by passing chlorine gas through PHB solution in CHCl3/CCl4 mixture (75/25 v/v) to prepare chlorinated PHB, PHB‐Cl, with the chlorine contents varying between 2.18 and 39.8 wt %. Toluene solution of PHB‐Cl was used in the atom transfer radical polymerization (ATRP) of methyl methacrylate, MMA, in the presence of cuprous bromide (CuBr)/2,2′‐bipyridine complex as catalyst, at 90°C. This “grafting from” technique led to obtain poly (3‐hydroxybutyrate)‐g‐poly(methylmethacrylate) (PHB‐g‐PMMA) brush type graft copolymers (cylindrical brush). The polymer brushes were fractionated by fractional precipitation methods and the γ values calculated from the ratio of the volume of nonsolvent to volume of solvent of brushes were ranged between 2.8 and 9.5 depending on the molecular weight, grafting density, and side chain length of the brushes, while the γ values of PHB, PHB‐Cl, and homo‐PMMA were 2.7–3.8, 0.3–2.4, and 3.0–3.9, respectively. The fractionated brushes were characterized by gel permeation chromatography, 1H‐NMR spectrometry, thermogravimetric analysis (TGA), and differential scanning calorimetry techniques. PHB‐g‐PMMA brush type graft copolymers showed narrower molecular weight distribution (mostly in range between 1.3 and 2.2) than the PHB‐Cl macroinitiator (1.6–3.5). PHB contents in the brushes were calculated from their TGA thermograms and found to be in range between 22 and 42 mol %. The morphologies of PHB‐g‐PMMA brushes were also studied by scanning electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
82.
Scanning transmission electron microscope tomography and atom-probe tomography are both three-dimensional techniques on the nanoscale. We demonstrate here the combination of the techniques by analyzing the very same volume of an Al-Ag alloy specimen. This comparison allows us to directly visualize the theoretically known artifacts of each technique experimentally, providing insight into the optimal parameters to use for reconstructions and assessing the quality of each reconstruction. The combination of the techniques for accurate morphology and compositional information in three dimensions at the nanoscale provides a route for a new level of materials characterization and understanding. 相似文献
83.
Electron tomography is a powerful technique that can probe the three-dimensional (3-D) structure of materials. Recently, this technique has been successfully applied to inorganic materials using Z-contrast imaging in a scanning transmission electron microscope to image nanomaterials in 3-D with a resolution of 1 nm in all three spatial dimensions. However, an artifact intrinsic to this technique limits the amount of information obtainable from any object, namely the missing wedge. One way to circumvent this problem is to acquire data from two perpendicular tilt axes, a technique called "dual axis tomography." This paper presents the first dual axis data at high resolution for inorganic materials, and by studying a CdTe tetrapod sample, demonstrates the increase in information obtained using this technique. 相似文献
84.
M. M. Quazi M. Ishak A. Arslan M. Nasir Bashir Imran Ali 《Journal of Adhesion Science and Technology》2018,32(6):625-641
This study highlights the scratch adhesion failure characterization and tribo-mechanical properties of physical vapor deposited (Cr, Ti) N coating on AA7075-T6 by using magnetron-sputtering technique. The surface morphology, microstructure and chemical composition of CrTi/CrTiN film were inspected by an optical microscope, scanning electron microscope (SEM) incorporated with energy dispersive X-ray spectroscopy (EDX) in addition to focused ion beam milling. The coating to substrate critical load of about 1261 mN was obtained, by employing coating deposition parameters of; DC power (300 W, RF power (200 W)), temperature (300 °C) and nitrogen flow rate (6%). Failure adhesion characteristics exhibited initial arc-tensile cracking followed by chipping and spallation that led to complete coating failure at Lc3. The tribo-mechanical aspects were evaluated by a pin-on-plate reciprocating testing unit, which showed a lower friction coefficient of 0.36 for CrTiN as compared with 0.43 for AA7075-T6. Subsequently, the wear depth was also reduced from 9.5 to 5.9 μm. It was revealed that the wear mechanism for AA7075-T6 was extensive deformation, abrasion and delamination, while the CrTiN exhibited slightly oxidative abrasive wear mode. 相似文献
85.
86.
Differently than in the past, today environmental problems have local, national and international concern. The environmental problems in the Black Sea region are a good example for this phenomenon. These problems have affected all six countries that have shores with the Black Sea. The current study analyses these problems in detail. It intends to detect potential reasons for problems and provide suggestions to solve these problems by considering the economic dimensions. In addition, the impact of problems on the city life is examined. Also, the roles and importance of voluntary organizations on solving environmental problems are emphasized. 相似文献
87.
Novel biosorbent 'maize bran' has been successfully utilized for the removal of Cr(VI) from aqueous solution. The effect of different parameters such as contact time, sorbate concentration, pH of the medium and temperature were investigated and maximum uptake of Cr(VI) was 312.52 (mgg(-1)) at pH 2.0, initial Cr(VI) concentration of 200mgL(-1) and temperature of 40 degrees C. Effect of pH showed that maize bran was not only removing Cr(VI) from aqueous solution but also reducing toxic Cr(VI) into less toxic Cr(III). The sorption kinetics was tested with first order reversible, pseudo-first order and pseudo-second order reaction and it was found that Cr(VI) uptake process followed the pseudo-second order rate expression. Mass transfer of Cr(VI) from bulk to the solid phase (maize bran) was studied at different temperatures. Different thermodynamic parameters, viz., DeltaG degrees , DeltaH degrees and DeltaS degrees have also been evaluated and it has been found that the sorption was feasible, spontaneous and endothermic in nature. The Langmuir and Freundlich equations for describing sorption equilibrium were applied and it was found that the process was well described by Langmuir isotherm. Desorption studies was also carried out and found that complete desorption of Cr(VI) took place at pH of 9.5. 相似文献
88.
Güray Arslan 《Materials and Structures》2008,41(1):113-122
This study presents alternative shear strength prediction equations for reinforced concrete (RC) beams with stirrups. The
shear strength is composed of the contribution of the nominal shear strength provided by stirrups and the nominal shear strength
provided by concrete. For the concrete contribution, cracking shear strength values estimated by Arslan’s equations are almost
same those obtained with ACI 318 simplified equation in terms of coefficient of variation (COV). However, mean values estimated
by ACI 318 tend to be more conservative comparing to the mean values obtained with Arslan’s equations. Thus, for the consideration
of concrete contribution to shear strength, Arslan’s equations are used. To obtain the shear strength of RC beams, shear strength
provided by stirrups is added to the concrete shear strength estimated by Arslan’s equations. Results of existing 339 beam
shear tests are used to investigate how accurate proposed equation estimates the shear strength of RC beams. Furthermore,
ACI 318 and TS500 provisions are also compared to the aforementioned test results. It is found that proposed equations for
beams with shear span to depth ratios (a/d) between 1.5 and 2.5 are also conservative with a lower COV than ACI 318 and TS500. However, when a/d ratios exceed 2.5 (both normal and high strength concrete beams), ACI 318, TS500 and proposed equations give similar COV
value. 相似文献
89.
Beliz Ozorhon David Arditi Irem Dikmen M. Talat Birgonul 《Canadian Metallurgical Quarterly》2008,24(1):12-20
Joint ventures have been an important research topic over the last few decades primarily because of their importance as a strategic alternative in global competition. Due to the inherent complexities of international joint ventures (IJVs), involving a mixture of different managerial systems, attitudes, and business strategies, such entities are very difficult to manage. In this study, the effect of strategic, organizational, and cultural fit between IJV partners and of interpartner relations on IJV performance is examined through a questionnaire survey. IJV performance is measured by means of two constructs: “project performance” and “performance of IJV management.” The results point out the significance of the quality of partner relations for a successful IJV operation. Findings of the study also suggest that the level of organizational fit between the partners has a moderate influence on IJV performance. It was observed that strategic fit between IJV partners affects interpartner relations extensively, which in turn affects IJV performance. IJV partners with compatible technical and managerial skills, financial resources, organizational size, workload, and project experiences are expected to achieve greater IJV success. 相似文献
90.
Nurkan Yagiz Yuksel Hacioglu Yunus Ziya Arslan 《Journal of Mechanical Science and Technology》2010,24(5):1177-1184
In this study, a sliding mode controlled dual arm robotic system was designed. Such multi-arm, collaborative and synchronous
robots typically are employed in hazardous situations such as radioactive materials transport explosives disposal and industrial
applications. In the present study, a high performance, robust, non-chattering sliding mode controller (SMC) was developed
for the purpose of safe load handling, transportation and trajectory realization. First, dynamic equations of robot/load interaction
were derived. Then, the robust SMC was designed for the dual arm robotic system. In order to test the robustness of the proposed
SMC, parameter variations and external disturbances were introduced to the system. Furthermore, for comparative purposes,
the conventional and widely used, PID controller was also applied to the dual arm robot. Significantly, it was found that
the SMC made smaller trajectory tracking errors than the PID controller. An overall analysis of the numerical results confirmed
that the dual-arm robotic systems with the proposed SMC can safely and effectively be used in hazardous applications. 相似文献