Influences of laser welding parameters on the geometric profile of NI-base superalloy Rene 80 weld-bead

In the present study, autogenous laser butt joint welding parameters of Ni-base super alloy Rene 80 has been investigated by using a continuous wave 2.2?kW CO₂ laser. The experiments were performed based on the response surface methodology as a statistical design of experiment approach in order to investigate the effect of parameters on the response variations, achieving the mathematical equations and predicting the new results. Laser power (1,000?C2,200?W), welding speed (120?C360?cm/min), laser beam focal point position (?0.5?C0.5?mm) and inert gas pressure (0.2?C1?bar) were considered as the input process variables while welding surface width (W1), welding pool area (A), width of the weld-bead at the middle depth (W2), undercut welding and drop of welding were considered as the five process responses. Analyzed by statistical techniques, the results show that the welding bead profile is influenced by the laser heat input and input laser process parameters. Welding speed is known as the most important parameter with the reverse effect on process outputs. Inert gas pressure is the next significant parameter, and higher gas pressure causes welding geometry defects. Laser power has a direct influence on all investigated responses.     

Overcoat Free Magnetic Media for Lower Magnetic Spacing and Improved Tribological Properties for Higher Areal Densities

Surface modification with shallow embedding (≤1 nm) of carbon in the top layer of magnetic media is evaluated for its tribological and anti-oxidation properties. Cobalt is used as the magnetic material and carbon embedding is achieved by using the filtered cathodic vacuum arc technique at different ion energies, specifically of 20, 90, and 350 eV, in order to study the effect of ion energy on the embedding profiles. Simulations using the transport of ions in Matter software and X-ray photoelectron spectroscopy (XPS) are used to characterize the embedded layer and their surface chemical composition. XPS and transmission electron microscopy depth profiling results confirm the presence of a shallow mixed layer of carbon and cobalt for all three types of ion energies tested. However, embedding carried out at the ion energy of 90 eV produced a more uniform overcoat free mixed layer (≤1 nm) with improved anti-oxidation properties. Ball-on-disk wear tests and atomic force microscopy based scratch tests are conducted on the bare cobalt and modified cobalt surfaces. It is observed that the wear life and scratch resistance of the cobalt surface improved considerably after surface modification at the ion energy of 90 eV.     

Nested partitions for global optimization in nonlinear model predictive control

In Nonlinear Model Predictive Control (NMPC), the optimization problem may be nonconvex. It is important to find a global solution since a local solution may not be able to operate the process at desired setpoints. Also the solution must be available before the control input has to be applied to the process. In this paper, a stochastic algorithm called the Nested Partitions Algorithm (NPA) is used for global optimization. The NPA divides the search space into smaller regions and either concentrates search in one of these regions called the most promising region or backtracks to a larger region in the search space based on a performance index. To adapt the NPA to solve dynamic NMPC with continuous variables, a new partitioning scheme is developed that focuses on the first few control moves in the control horizon. The expected number of iterations taken by the NPA is presented. Convergence speed is improved by reducing the size of the starting most promising region based on a good starting point. The discrete sampling nature of the NPA may cause difficulty in finding the global solution in a continuous space. A gradient-based search is used with the NPA to overcome this difficulty. The solution quality is assessed in terms of the error from the actual global minimum. The algorithm is shown to give a feasible solution that provides asymptotic stability. Case studies are used to show the algorithm performance in terms of tracking setpoints, cost, solution quality and convergence time.     

Two layered Genetic Programming for mixed-attribute data classification

The important problem of data classification spans numerous real life applications. The classification problem has been tackled by using Genetic Programming in many successful ways. Most approaches focus on classification of only one type of data. However, most of the real-world data contain a mixture of categorical and continuous attributes. In this paper, we present an approach to classify mixed attribute data using Two Layered Genetic Programming (L2GP). The presented approach does not transform data into any other type and combines the properties of arithmetic expressions (using numerical data) and logical expressions (using categorical data). The outer layer contains logical functions and some nodes. These nodes contain the inner layer and are either logical or arithmetic expressions. Logical expressions give their Boolean output to the outer tree. The arithmetic expressions give a real value as their output. Positive real value is considered true and a negative value is considered false. These outputs of inner layers are used to evaluate the outer layer which determines the classification decision. The proposed classification technique has been applied on various heterogeneous data classification problems and found successful.     

Development and characterization of novel modified red mud nanocomposites based on poly(hydroxy ether) of bisphenol A

This study dealt with the use of various quantities of modified red mud as a nanofiller in a poly(hydroxy ether) of bisphenol A (Phe) based matrix. Phe‐based polymer nanocomposites reinforced with acidically and organically modified layered red mud were prepared by a conventional solvent‐casting technique. The best dispersion occurred in the polymer nanocomposites where the interactions between the functional groups of the polymer matrix and those of the organic substitution of the red mud appeared to be the highest. The particle size of the modified red mud was determined by field emission scanning electron microscopy. The as‐synthesized composite films were typically characterized by Fourier transform infrared spectroscopy and X‐ray diffraction. The dispersion of the modified fillers within the matrix was studied by transmission electron microscopy. The thermal properties measured by thermogravimetric analysis showed enhanced thermal stability of a series of composite materials. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Investigation on UV photodetector behavior of RF-sputtered ZnO by impedance spectroscopy

Ag/ZnO/Ag thin films representing metal/semiconductor/metal ultraviolet (UV) photodetectors were successfully prepared by RF magnetron sputtering. A UV light emitting diode was used as an illuminating source at 365 nm. The current-voltage characteristics of the device under UV illumination showed an enhancement in the forward current. Device modeling was carried out using impedance spectroscopy. The resistance of the device decreased as the light was switched from dark to UV. Moreover, the device showed further decrease in resistance at a bias voltage of up to 2 V.     

Mechanical,dielectric and EMI shielding response of styrene acrylonitrile,styrene acrylonitrile/polyaniline polymer blends,upon incorporation of few layer graphene at low filler loadings

The malfunction of electronic devices and many health-related issues may be caused due to electromagnetic interference (EMI) pollution. To overcome this problem a new set of material SAN/PANI/FLG hybrid composite with better EMI shielding properties is prepared using solution casting technique. Conductive polyaniline (PANI) is added (5 wt% and 10 wt%) to otherwise, an insulative polymer styrene acrylonitrile (SAN). Furthermore, few layer graphene (FLG) is added (0.1–1 wt%) to SAN/PANI polymer blends for preparation of SAN/PANI/FLG hybrid composites. The incorporation of PANI in SAN produces a phase separated morphology, whereas graphene appears in sheet like structure. For 0.1 wt% FLG/SAN/PANI-10 composite, total shielding effectiveness (SE_T) is enhanced from 1.1 to 24.3 dB (100 Hz), mainly due to enhanced dielectric characteristics. However, the maximum increase in tensile strength (49.6 MPa) and modulus (1.5 GPa) is observed for 0.5 wt% FLG/SAN/PANI-5.0 hybrid composite. The increase in dielectric properties and shielding efficiency of SAN/PANI/FLG may be credited to the accumulation of space charges or electric dipoles at the insulator conductor-interface.     

Online and stable parameter estimation based on normalized brain emotional learning model (NBELM)

Recently, a computational model of Amygdala based on the brain emotional learning is presented by psychologists. This brain emotional learning model (BELM) that has a neuro‐inspired architecture is utilized to train the weights which are in Amygdala and Orbitofrontal. In this paper, unknown parameters of dynamic systems are estimated by developing the normalized BELM (NBELM). To this end, after proving the stability of the model output, the sufficient condition for weights convergence is extracted while the sensitivity analysis is applied for this model. In order to evaluate the performance of NBELM, in the first example, the matrices of a twin rotor MIMO system are estimated and compared with the equation error method (EEM). In the second example, the nonlinear model of a servomotor is utilized as a case study. In the third example, the performance of the NBELM in experimental systems is validated using a reaction wheel with a DC motor. An important feature of the brain emotional system is its fast response, leading the NBELM to have a high speed performance in estimating the parameters of dynamic systems. A few number of adjustable parameters and low computing complexity also cause the NBELM to be an appropriate method for online estimation of the unknown parameters of dynamic systems.     

Multi-metric geographic routing for vehicular ad hoc networks

Wireless Networks - Maintaining durable connectivity during data forwarding in Vehicular Ad hoc Networks has witnessed significant attention in the past few decades with the aim of supporting most...     

Synthesis,Characterization and <Emphasis Type="Italic">in-vitro</Emphasis> Study of Chitosan/Gelatin/Calcium Phosphate Hybrid Scaffolds Fabricated Via Ion Diffusion Mechanism for Bone Tissue Engineering

In this study, biomimetic scaffolds were designed to investigate calcium phosphate formation via a double diffusion mechanism within a gelatin/chitosan hydrogel in biological pH and temperature. Three types of samples with initial percentages of chitosan (20, 30 and 40 wt. %) were prepared. Diffusion of calcium and phosphate ions through the hydrogel formed a precipitation layer. Samples were freeze dried to form porous scaffolds and soaked in glutaraldehyde to increase their mechanical properties. X-ray diffraction (XRD), Fourier transform infra-red (FTIR) spectroscopy and scanning electron microscopy (SEM) were employed to investigate the microstructure and to characterize the prepared scaffolds. Analysis of precipitation indicated the presence of brushite and hydroxyapatite. The amorphous calcium phosphate phase converted into crystalline hydroxyapatite after immersion in simulated body fluid which mimics the formation of hydroxyapatite in the human body. FTIR results suggested the presence of structural hydroxyl and phosphate bonds in the structure of the prepared scaffolds which could be due to the formation of hydroxyapatite. With increasing amount of chitosan in the composite scaffold, the water up-take ability was increased from 380 to 660 %, yield strength and Young’s modulus slightly decreased and the crystalinity of the precipitated phase increased. Mechanical properties obtained from the samples were in the range of cancellous bone. MTT assay results and alkaline phosphatase activity showed prepared scaffolds had proper biocompatibility.