Low-Temperature Preparation and Magnetic Properties of Nanoparticle Iron-Doped Anatase TiO2

Nanoparticle iron (Fe)-doped anatase TiO₂ was prepared at a low temperature (100°C) and at room pressure. The product was obtained from a boiling solution of an amorphous TiO₂ gel mixed with an iron nitrate solution and stirred for 5 h. An amorphous TiO₂ gel was obtained from TiCl₃ solution and NH₄OH as a precipitating agent stirred at room temperature for 1 day. EDAX results on different selected areas of as-prepared Fe-doped anatase TiO₂ revealed a homogeneous composition of 17 at.% Fe. Fe–TiO₂ has a superparamagnetic state with a possibility of antiferromagnetism at low temperatures. Fe seems to substitute titanium ions without any evidence of other impurities such as Fe nanoclusters or Fe-based oxides.     

对减轻钢结构逐步破坏的改造方法的效应评估

根据GSA和DoD为预防结构逐步破坏而制订的规范中所推荐的APM方法,对提高重力荷载下,钢结构抗弯能力的三种改造方法的有效性进行了分析。主要采用的是三维非线性动力分析法。分析模型为6×3跨的18层钢结构,这个结构曾由于底层突然移除一根柱而遭受到破坏。对跨长为5,6,7·5,9m的4个建筑进行了分析。分别采用三种方法改造结构并对其进行了评估,即增加梁的强度、增加梁的刚度以及同时增加梁的强度与刚度。通过分析改造后梁的转角、约束力和位移延性这三个性能指标的增强效应,来评估相应改造方法的有效性。     

Claim management

Construction contracts are seldom ideal, and claims for time extensions or financial compensation often have to be made by one party on another. This paper is concerned with the typical causes of claims, how claims are analysed, and how they can be prevented. It also looks at the legal implications of CPM schedules, and at the importance of the efficient management of records.     

Incremental modified pushover analysis

The recently developed Incremental Dynamic Analysis (IDA) requires nonlinear time history analyses at different levels of intensity of an ensemble of ground motions, which is time‐consuming due to the high computational efforts involved. In the current study, a simplified method named as Incremental Modified Pushover (IMP) is developed and evaluated. In this method, the response of the structure is obtained using one pushover analysis at any specified level of ground motion intensity. The associated higher mode effects are explicitly considered when determining target roof displacement and lateral load pattern. In the bilinear idealization of the pushover curves, a new approach has been used. Moment resisting steel frames with 4, 8, 12 and 16 stories, as well as their corresponding soft‐story models are used for verifying the proposed method. The studied frames were subjected to seventeen different scaled earthquake ground motions. The results of the presented method, IMP, are verified in terms of maximum roof displacement, maximum inter‐story drift and maximum plastic hinge rotation at different ground motion intensities. The results show that the IMP method gives higher response values compared with IDA, which can be viewed as being more conservative. Copyright © 2008 John Wiley & Sons, Ltd.     

Studies of iron corrosion inhibition using chemical, electrochemical and computer simulation techniques

The inhibitive action of some benzimidazole derivatives namely 2-(2-furanyl)-1H-benzimidazole (FB), 2-(2-pyridyl) benzimidazole (PB) and 2-(4-thiazolyl) benzimidazole (TB), against the corrosion of iron in solutions of nitric acid has been studied using density function theory calculations (DFT), weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The calculated electronic parameters involved in the activity of the benzimidazole derivatives confirmed that the position of the side chain in the benzimidazole moiety affects the pattern of activity. The effectiveness of the benzimidazole derivatives is following the order TB > PB > FB. The same order is supported by the experimental chemical and electrochemical measurements. The relationships between inhibition efficiency of iron in 1.0 M HNO₃ and the molecular orbitals of the studied molecules as well as number of electrons transferred ΔN from the inhibitor molecules to the iron surface were calculated by DFT method. The inhibition efficiency increased with the increase in E_HOMO and decrease in E_LUMO-E_HOMO. TB had the highest inhibition efficiency because it had the highest HOMO energy and ΔN values, and it was most capable of offering electrons. Molecular modeling was used to evaluate the structural, electronic and reactivity parameters of the selected benzimidazole derivatives in relation to their effectiveness as corrosion inhibitors. Results obtained from weight loss, dc polarization and ac impedance measurements are in reasonably good agreement and show increased inhibitor efficiency with increasing inhibitor concentration.Data obtained from EIS were analyzed to model the corrosion inhibition process through equivalent circuit.     

On the Tribocorrosion Responses of Two Stainless Steels

Tribocorrosion has considerable effects on AISI 304L used in olive processing equipment. In fact, some investigations have been conducted to compare the tribocorrosion behavior of AISI 304L to UNS 2205 stainless steels sliding against alumina in olive pomace–tap water filtrate. The active and passive surface states involved in tribocorrosion mechanisms of the steels have accordingly been analyzed. Mechanical and corrosion wear components were quantified. It was revealed that the tribocorrosion mechanism was dominated by mechanical removal. The mechanical resistance of UNS 2205 proved to be more important than that of AISI 304L. Furthermore, UNS 2205 was more sensitive to corrosion under sliding than AISI 304L due to its two-phase microstructure.     

High-Resolution Patterning of Organic–Inorganic Photoresins for Tungsten and Tungsten Carbide Microstructures

Tungsten is an important material for high-temperature applications due to its high chemical and thermal stability. Its carbide, that is, tungsten carbide, is used in tool manufacturing because of its outstanding hardness and as a catalyst scaffold due to its morphology and large surface area. However, microstructuring, especially high-resolution 3D microstructuring of both materials, is a complex and challenging process which suffers from slow speeds and requires expensive specialized equipment. Traditional subtractive machining methods, for example, milling, are often not feasible because of the hardness and brittleness of the materials. Commonly, tungsten and tungsten carbide are manufactured by powder metallurgy. However, these methods are very limited in the complexity and resolution of the produced components. Herein, tungsten ion-containing organic–inorganic photoresins, which are patterned by two-photon lithography (TPL) at micrometer resolution, are introduced. The printed structures are converted to tungsten or tungsten carbide by thermal debinding and reduction of the precursor or carbothermal reduction reaction, respectively. Using TPL, complex 3D tungsten and tungsten carbide structures are prepared with a resolution down to 2 and 7 μm, respectively. This new pathway of structuring tungsten and its carbide facilitates a broad range of applications from micromachining to metamaterials and catalysis.     

Deriving a minimum distance-based collective preorder: a binary mathematical programming approach

Deriving the “closest” (minimal distance) collective judgment to all individual opinions is a complex aggregation problem that has been widely studied in group decision-making literature. However, most of the existing literature does not consider individual opinions expressed as partial preorders (i.e., a preference system which includes the incomparability relation). In this paper, we propose a method based on binary linear programming to derive a minimum distance-based collective preorder from individual preferences relational systems (p.r.s.). This method is threefold. First, each member determines a preorder (partial or total) over the set of alternatives. Second, an aggregation algorithm is proposed to derive at least one collective and not necessary transitive p.r.s. at minimum distance from all individual preorders. Third, a binary linear programming optimization will transform each non-transitive collective p.r.s. into a collective preorder (i.e. a transitive p.r.s.). The proposed method has three main advantages: (1) it deals with incomparability (partial preorders), (2) the relative importance of the members is explicitly considered and (3) the collective p.r.s. obtained after the aggregation step might be “exploited” according to different decision-making problematics (i.e. ranking, choice and sorting).     

Modeling railroad track structures using the finite segment method

In the finite segment method, the dynamics of a deformable body is described using a set of rigid bodies that are connected by elastic force elements. This approach can be used, as demonstrated in this investigation, in the simulation of some rail movements. In order to ensure that the rail geometry is not distorted as the result of the finite segment displacements, a new track model that consistently integrates the absolute nodal coordinate formulation (ANCF) geometry and the finite segment method is developed. ANCF finite elements define the track geometry in the reference configuration as well as the change in the geometry due to the movement of the finite segments of the track. Using ANCF geometry and the finite segment kinematics, the location of the wheel/rail contact point is predicted online and used to update the creepage expressions due to the finite segment displacements and rotations. The location of the wheel/rail contact point and the updated creepage expressions are used to evaluate the creep forces. A three-dimensional elastic contact formulation (ECF-A) which allows for wheel/rail separation is used in this investigation. The rail displacement due to the applied loads is modeled by a set of rigid finite segments that are connected by a set of spring-damper elements. Each rail finite segment is assumed to have six rigid body degrees of freedom. The equations of motion of the finite segments are integrated with the railroad vehicle system equations of motion in a sparse matrix formulation. The resulting dynamic equations are solved using a predictor–corrector numerical integration method that has a variable order and variable step size. The finite segments may be used to model specific phenomena that occur in railroad vehicle applications, including rail rotations and gauge widening. The procedure used in this investigation to implement the finite segment method in a general purpose multibody system (MBS) computer program is described. Two simple models are presented in order to demonstrate the implementation of the finite segment method in MBS algorithms. The limitations of using the finite segments approach for modeling the track structure and rail flexibility are also discussed.     

A heuristic approach for balancing mixed-model assembly line of type I using genetic algorithm

The mixed model assembly line is becoming more important than the traditional single model due to the increased demand for higher productivity. In this paper, a set of procedures for mixed-model assembly line balancing problems (MALBP) is proposed to make it efficiently balance. The proposed procedure based on the meta heuristics genetic algorithm can perform improved and efficient allocation of tasks to workstations for a pre-specified production rate and address some particular features, which are very common in a real world mixed model assembly lines (e.g. use of parallel workstations, zoning constraints, resource limitation). The main focus of this study is to study and modify the existing genetic algorithm framework. Here a heuristic is proposed to reassign the tasks after crossover that violates the constraints. The new method minimises the total number of workstation with higher efficiency and is suitable for both small and large scale problems. The method is then applied to solve a case of a plastic bag manufacturing company where the minimum number of workstations is found performing more efficiently.