Advanced Materials Research Vols. 488-489

Abstract: We have investigated the third order nonlinear optical properties of pyrrole Schiff bases synthesized by condensing pyrrole-2-carboxaldehyde with two different diamines. The nonlinear optical measurements were performed using the nano- second laser pulses at 532nm wavelengthby employing the Z-scan technique. The Z- scan spectra reveal a large negative non-linear refraction co-efficient .The nonlinear refractive index was found to be of the order of 10 ^-14cm2/W and the magnitude of third order susceptibility was of the order of 10 ^-13esu. These compounds exhibit good optical power limiting property under nano-second regime and TPA (Two Photon Absorption) is the dominating process leading to the non-linear behavior.

Abstract: In this paper, a reformulation of the Helmholtz integral equation for tridimesional acoustic radiation in a uniform subsonic flow is presented. An extension of the Sommerfeld radiation condition, for a free space in a uniform movement, makes possible the determination of the convected Green function, the elementary solution of the convected Helmholtz equation. The gradients of this convected Green function are, so, analyzed. Using these results, an integral representation for the acoustic pressure is established. This representation has the advantage of expressing itself in terms of new surface operators, which simplify the numerical study. For the case of a regular surface, the evaluation of the free term associated with the singular integrals shows that it is independent of the Mach number of the uniform flow. A physical interpretation of this result is offered. A numerical approximation method of the integral representation is developed. Furthermore, for a given mesh, an acoustic discretization criterion in a uniform flow is proposed. Finally, numerical examples are provided in order to validate the integral formula.

Abstract: Due to outstanding properties of γ–TiAl intermetallic such as high resistance against fatigue, oxidation, corrosion, creep, dynamic vibration, high working temperature and also its application in aerospace, automotive industry and turbojet engines; in this paper, powder mixed electrical discharge machining (PMEDM) of γ–TiAl intermetallic by means of different additive powders including aluminum (Al), graphite (Gr), silicon carbide (SiC), chrome (Cr) and iron (Fe) is investigated to compare the output characteristic of surface quality and roughness. The results indicate that aluminum powder produces the best surface finish, followed by silicon carbide, graphite, chrome and iron respectively. The experimental results show that in the determined settings of input machining parameters, aluminum powder can improve the surface roughness of TiAl sample about 32%.

Abstract: In order to improve the channel elecron mobility and decrease the surface roughness of SiC ,we have cleaned the SiC surfacre by hydrogen plasma with ECR–PEMOCVD plasma system. The surfaces were investigated by RHEED and X-ray Photoelectron Spectroscopy before and after hydrogen plasma cleanging. It indicated that the Si oxide content of SiC surface cleaned by hydrogen plasma for 18minutes is significantly higher than for 12 minutes and the SiC surface cleaned for 12 minutes at 200°C with ECR–PEMOCVD plasma system is the most smooth. The hydrogen plasma cleaning technology is very useful to improve the channel elecron mobility of MOS device.

Abstract: In recent years, supply chains have become increasingly vulnerable to risks resulting in poor financial performance and customer service. Managing the supply chain risks is a challenging task. Resilience and responsiveness based strategies are being attempted to build a robust supply chain. To select the appropriate mitigation strategies, supply chain risks are to be prioritized. Supply chain risk prioritization is a Multi Criteria Decision Making (MCDM) problem. MCDM models for supply chain risk prioritization needs attention. In this research, a hybrid Analytic Hierarch Process (AHP) and Preference Ranking Organization METHod for Enrichment Evaluation (PROMETHEE) approach is proposed for supply chain risk prioritization. A case example of a typical tractor industry is presented to illustrate the performance of the proposed approach.

Abstract: IT/IS represents a substantial financial investment for many organizations. Making IT project portfolio decision is difficult, because long lead times of IT project and market and technology dynamics lead to unavailable and unreliable collected data for portfolio management. This uncertainty has been modeled using fuzzy concepts. We need a collective model that will help decision-makers evaluate potential new investment projects in an easy, cost-effective, and collective manner. Hence, we propose a new approach based on the fuzzy multi-criteria decision model (FMCDM) and a fuzzy binary multi-objective linear programming model, featuring a 2-stage evaluation and selection process with 19 criteria for IT/IS investment. At the first stage, evaluation, all stakeholders in a corporation can decide the relative weights they give to the criteria when they evaluate a new IT/IS project by using linguistic values. Experts can also use linguistic values to evaluate all candidates easily. Only an Excel worksheet is needed to obtain an evaluation result. The results of FMCDM of the aforementioned are treated as input of a fuzzy binary mathematical programming model as coefficients of objective functions, which is the second stage of the proposed model. In the second stage, selection, we have developed a fuzzy binary mathematical programming model in order to find an optimum combination of investment portfolio considering a multi-objective measurement function in three ways: to maximize the benefit, to maximize the confidence level and to minimize the cost of projects in a complete ambiguous condition, when their initial investment costs, profits, confidence levels, resource requirements and total available budgets are assumed to be uncertain. We solve it in Lingo 10.0 through a Branch and Bound algorithm. In this paper, for the first time we have developed a model for IT/IS project portfolio selection in presence of uncertainty that is combination of fuzzy multi-criteria decision making and fuzzy mathematical programming with 19 criteria that is compatible with the nature of IT projects. We conduct a case study to show how this model can be used and discuss the results.

Abstract: The technology on network interconnection handoff with the QoS guarantee is becoming an important research issue in wireless mobile networks. Most of the current researches focus on the cell mobile networks, the schemes of which are comparatively complex in solving the QoS guarantee in mobile node handoff and the utilization rate of resource is lower. In order to reduce these disadvantages to the minimal extent, the model (HDBRA) on the mobile node handoff with service guarantee applied in the wireless mobile networks is presented in the paper based on the dynamic network bandwidth resource allocation in the real-time detection on the data flow state and network traffic-load in interconnection gateway nodes. And according to the state of the applications data in mobile node handoff, the model describes and analyzes in detail the dynamic resource allocation and reservation, and the release of the reserved resource as well. In the scheme, the real-time adjustment on resource allocation is achieved based on the real-time measurement on network traffic-load in interconnection gateway nodes and the method also achieves the balance on network traffic-load. Theoretic analysis and simulation test the correctness and validity of the model in the paper.

Abstract: Most of the steel structures used in industrial and non-industrial applications are exposed to outdoors weathering conditions. Organic coating typically protects them from corrosion. The maintenance actions can be done efficiently only if there is sufficient information of the condition. Therefore, the deterioration of the coating system and its lifetime has to be assessed accurately. This paper focuses on the development of parameters based on adhesion strength useful for that purpose. Three parameters are proposed, namely stress intensity factor, strain energy density, and J-integral.

Abstract: The (Ti,Cr)N thin films were deposited with various N₂ flow rates on silicon wafers by reactive unbalanced magnetron co-sputtering without heating and biasing substrates. The effects of N₂ flow rate on the structure and morphologies of the films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM) and energy dispersive x-ray spectroscopy (EDS). The results revealed that the (Ti,Cr)N thin films formed solid solutions with the fcc structure. The crystallite sizes calculated from Scherrer formula are about 13 nm. The root-mean-square roughness (Rrms) and the thickness (Tth) of the films were slightly decreased with the increase in N₂ flow rate. The cross-sectional morphology showed columnar structure corresponding to zone 2. In addition, the N atomic concentration was also increased with the increase in N₂ flow rate.

Abstract: Thermal oxidation is believed as an important phenomenon that naturally occurs on material subjected to elevated temperature such as NiAl-Al2O3 coated material. In the present study, thermal oxidation on this coated layer was prepared by heating processes of NiAl-Al2O3 coated on mild carbon steel. Deposition of NiAl-Al2O3 was performed by high-velocity oxy fuel (HVOF) process, whereas subsequent heating processes were performed at 3 different temperatures 600oC, 800oC and 1000oC. After the process, the effects of this thermal oxidation process on the phases formation, microstructure and qualitative toughness of thermally sprayed NiAl-Al2O3 coating were investigated. The results showed that significant amount of NiAl-Al2O3 phase was transformed into NiO phase by heating process at temperature higher than 800°C. In addition, decreasing of thickness of the coating layer was also found as the service temperature increases from 800 to 1000oC. Increasing of hardness was also observed as the heating temperature increases, which is predicted due to the formation of excessive oxide on the coating layer that in turn might impart the toughness of this layer. These conditions suggested that a careful determination of service temperature have to be taken in order to avoid excessive oxidation of the coating layer.