Chemical and Mechanical Properties of ZDDP Antiwear Films on Steel and Thermal Spray Coatings Studied by XANES Spectroscopy and Nanoindentation Techniques

X-ray Absorption Near Edge Structure (XANES) has been used to characterize the chemistry of tribochemical wear pads generated from a paraffinic base oil with a zinc-dialkyl-dithiophosphate additive on steel surfaces and high-velocity oxygen fuel (HVOF) thermal spray coatings. The phosphorus K- and L- edge XANES spectra show that the tribofilms formed on steel and the HVOF coatings have the same chemical nature. Also, mechanical properties of these tribofilms were examined by nanoindentation techniques using both Hysitron and Interfacial Force Microscopy (IFM) instruments. The elastic moduli extracted from indentation force-displacement (f-d) curves have demonstrated that tribofilms on steel and HVOF coatings have similar surface topography and mechanical properties.     

Highly Visible Light Activity of Nitrogen Doped TiO<Subscript>2</Subscript> Prepared by Sol–Gel Approach

A simple approach was explored to prepare N-doped anatase TiO₂ nanoparticles (N-TiO₂ NPs) from titanium chloride (TiCl₄) and ammonia (NH₃) via sol–gel method. The effects of important process parameters such as calcination temperatures, NH₃/TiCl₄ molar ratio (R _N) on crystallite size, structure, phase transformation, and photocatalytic activity of titanium dioxide (TiO₂) were thoroughly investigated. The as-prepared samples were characterized by ultraviolet–visible spectroscopy, x-ray diffraction, transmission electron microscopy, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. The photocatalytic activity of the samples was evaluated upon the degradation of methylene blue aqueous solution under visible-light irradiation. The results demonstrated that both calcination temperatures and NH₃/TiCl₄ molar ratios had significant impacts on the formation of crystallite nanostructures, physicochemical, as well as catalytic properties of the obtained TiO₂. Under the studied conditions, calcination temperature of 600°C and NH₃/TiCl₄ molar ratio of 4.2 produced N-TiO₂ with the best crystallinity and photocatalytic activity. The high visible light activity of the N-TiO₂ nanomaterials was ascribed to the interstitial nitrogen atoms within TiO₂ lattice units. These findings could provide a practical pathway capable of large-scale production of a visible light-active N-TiO₂ photocatalyst.     

Design and modelling of dispersion-engineered rib waveguide for ultra broadband mid-infrared supercontinuum generation

We report a dispersion-engineered As₂Se₃ chalcogenide glass rib waveguide structure for ultra broadband mid-infrared supercontinuum generation across molecular ‘fingerprint region’. The proposed rib waveguide structure offers non-linear coefficient as high as 18,250 W^?1 km^?1 at 2.5 μm. Supercontinuum spectrum spanning 2–15 μm, which not only covers the both atmospheric transparent windows (3–5 μm and 8–13 μm) in the mid-infrared domain but also covers the important molecular ‘fingerprint domain’, is obtained using only 4 mm-long rib waveguide structure. To the best of our knowledge, such broadband mid-infrared supercontinuum spectrum in As₂Se₃-based chalcogenide waveguide geometry is reported for the first time. The proposed design of rib waveguide has potential for robust, integrated and low-cost supercontinuum sources in various applications including frequency comb generation, chemical sensing, food quality control and early cancer diagnostics.     

飞机防滑控制系统的数字仿真研究

在数字仿真研究的基础上，结合国内外有关飞机防滑控制技术进展对防滑控制系统的评估指标、影响滑移速度控制—偏压调制型防滑系统性能的某些重要技术因素与进一步研究防滑控制的方向等问题作出了分析与评议．     

Effectiveness of filter gabions against slope failure due to heavy rainfall

Slope failures due to heavy rainfall events are phenomena that can cause serious damage to social infrastructures and the loss of lives. Based on previous studies, natural slope failures are generally shallow and originate at the slope toe where infiltrated rainwater has accumulated and saturated it. Hence, it is extremely important to prevent these initial failures from inducing entire slope failures. In the present study, firstly, 1 g model tests, called G series tests, were conducted. In the tests, a gabion filled with filter materials was placed at the slope toe of each model for reinforcement and to drain the accumulated rainwater from the slope toe. Filter gabions have been found to shrink the failure regions and to significantly extend the time until slope failures occur. The failure mechanism in the G series tests was almost similar to that in cases without filter gabions if focus was placed on the slope above the filter gabions. However, the drainage effect was small. Secondly, P series tests, in which a filter gabion with a pipe was introduced for each model, were conducted. The results of these tests indicated that the displacements significantly decreased as the diameter of the pipe and the depth of the pipe’s insertion to the surface layer increased. Water did not discharge through the pipe until the pore water pressure around the pipe reached positive values. The failures always started when a phreatic surface appeared on the slope surface. Thus, it is very important to prevent a phreatic surface from forming on the slope surface. The adequate arrangement of a filter gabion with a drainage pipe may increase the potential for slope stability.     

Design and control of a new linear magnetic actuator for squeeze film damper

A new model of a linear magnetic actuator (LMA) that can be applied to the controllable squeeze film damper (CSFD) was proposed, designed, and fabricated. To validate the operation of the proposed actuator, a mathematical model of the proposed LMA was derived through experiments. From the experimental results it was verified that the electromagnetic force depends upon the position of the mover (the outer damper ring of the CSFD) and the applied current. Also, the electromagnetic force varies symmetrically with the position of the mover within the working region. A self-tuning fuzzy PID controller was applied to control the position of the novel LMA. Further, the proposed LMA was assembled in the squeeze film damper (SFD), where the clearance can be controlled by LMA. To investigate the damping effect of the damper under various clearances by controlling the LMA, experiments on the rotor test-rig were conducted. From the experimental results, the proposed device, which is composed of SFD and LMA, was verified to be very effective for attenuation of the vibration of the rotor system. This paper was recommended for publication in revised form by Associate Editor Dong Hwan Kim Kyoung Kwan Ahn received the B.S. degree in the department of Mechanical Engineering from Seoul National University in 1990, the M. Sc. degree in Mechanical Engineering from Korea Advanced Institute of Science and Technology (KAIST) in 1992 and the Ph.D. degree with the title “A study on the automation of out-door tasks using 2 link electro-hydraulic manipulator” from Tokyo Institute of Technology in 1999. He is currently a Professor in the School of Mechanical and Automotive Engineering, University of Ulsan, Ulsan, Korea. His research interests are design and control of smart actuator using smart material, fluid power control and active damping control. He is a Member of IEEE, ASME, SICE, RSJ, JSME, KSME, KSPE, KSAE, KFPS, and JFPS. Truong Quoc Thanh received the B.S degree in the department of Mechanical Engineering from Hochiminh City University of Technology in 1998, and the M.Sc. degree with title “Dynamic stiffness method in calculation vibration of structure” from the master program of mechanics under Inter-University Cooperation Program between Liege University (Belgium) and HCMUT (Vietnam) in 2000. From 2000 to 2004, he worked as a lecturer in the mechanical department of Hochiminh City University of Technology. His teaching subjects are relevant in Advanced Manufacturing Methods, Measuring Technique and Manufacturing Technique. He is currently a Ph.D. candidate at the University of Ulsan. His research interests focus on designing and manufacturing of new actuators, vibration control theory and application theories.     

Antioxidants and stabilizers

Summary The efficiency of polyolefine melt stabilizer 2, 2-thiobis-(4,6-di-tert.butylphenol) (I) as a hydroperoxide decomposing antioxidant was studied under model conditions.tert.Butylhydroperoxide was used to simulate the reaction with polypropylene hydroperoxide. The reaction was performed at 85°C in chlorobenzene solution. Decomposition of tert.butylhydroperoxide by I and formation of the sulphoxide II and the sulphone III from sulphide I were followed quantitatively. Formation of small amounts of effective peroxidolytic species from II or III, responsible for acceleration of hydroperoxide decomposition was considered.     

Review of the lubrication of metallic surfaces by zinc dialkyl-dithiophosphates

Implementation of tighter environmental restrictions on combustion engine emissions has resulted in the need to create new, more environment friendly engine oil additives. By far the most studied and effective class of antiwear additive are the zinc dialkyl(aryl)-dithiophopshates (ZDDPs). To date, there is no single, effective replacement additive for ZDDP. In order to create an effective replacement, it is first necessary to understand how and why an additive works as well as it does, on all length scales from macro to nano. This comprehensive review of the literature over the last 50 years provides insight into the overall picture of ZDDP by focussing on their chemical characterization, film formation mechanisms, properties and structure with the intent of exposing gaps that still remain in understanding the conundrum of ZDDP.