bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Numerical Analysis on FSWed Magnesium Alloy Thin Sheets Obtained Using “Pin” and “Pinless” Tool
Authors: Buffa Gianluca , Forcellese Archimede , Fratini Livan , Simoncini Michela
Published: February 2012

The present investigation aims at studying the effect of different tool geometries and process parameters on FSW of thin sheets in AZ31 magnesium alloy. In particular two properly designed tools, with shoulder diameters equal to 8 and 19 mm, were used; each of them was manufactured both in pin and pinless configurations. The effect of the different tool configurations and sizes, and welding parameters on mechanical properties of FSWed joints were analyzed in detail. The results were compared with those obtained on the base material. It was shown that FSWed joints are characterized by strength and ductility values lower than those of base material. Furthermore, the pin tool configuration, with a shoulder diameter of 8 mm, leads to the obtaining of strength and ductility values higher than those provided by the pinless one. A strong beneficial effect is obtained by increasing the shoulder diameter from 8 to 19 mm using the pinless configuration, whilst the FSW with the pin tool is critically affected by the welding conditions. The experimental work was joined to a numerical investigation based on finite element method (FEM) in order to study the material flow occurring during the welding process as well as the distribution of temperature, with the aim to identify a input window of the process parameters within which sound joints can be obtained.
Numerical and Experimental Studies on the Clinch-Bonding and Riv-Bonding Process
Authors: Neugebauer Reimund , Israel Markus , Mayer Bernd , Fricke Holger
Published: February 2012

A basic approach for lightweight construction on the basis of material design is to join different materials in one component. In practice bonding, joining-by-forming or the combination of both operations ore often used in these cases. The combination of bonding and mechanical joining has great potential. For assemblies, in automobile production for example, special features can be carried out, such as high strength and stiffness, leak-tightness, corrosion resistance, accuracy and crashworthiness. One challenge is the uncertainty about the stability of hybrid joining processes, which relies on deficits in the understanding of the adhesive flow during the joining operation. This article outlines how process understanding can be expanded due to numerical simulation. As a result, the mutual influences of mechanical joining and adhesive bonding are worked out numerically and experimentally.
Flexible Tooling System Using Reconfigurable Multi-Point Thermoforming Technology for Manufacturing Freeform Panels
Authors: Su S.Z. , Li M.Z. , Liu C.G. , Ji C.Q. , Setchi R. , Larkiola J. , Panteleev I. , Stead I. , Lopez R.
Published: February 2012

In this paper, authors present a highly flexible tooling system based on reconfigurable multi-point thermoforming (MPTF) methodology, which has been developed within an EU-granted FP7 project. The MPTF technology employs an actuated-punch matrix to dynamically configure a controllable tool working surface through digitally adjusting relative displacement of each punch in the matrix. Novel MPTF methods have been proposed through re-changing configurations of actuated-punch tooling system according to rapid thermoforming principles and relevant cladding applications. The tooling system includes an industrial-scale prototype of an MPTF tooling integrated with functional CAD/CAE/CAT software interfaces. The numerical simulation with an explicit FEM predicts the unexpected deformation defects of dimples and wrinkles regarding to discrete contact boundaries between punches and the sheet blank. Innovative techniques of variable blank-holder and deformable cushion have been implemented to suppress wrinkling and eliminate dimpling effectively. The tooling system has been successfully applied to manufacture complex double-curved panels, which are described as application examples. Compared with conventional fixed moulds, the flexible tooling offers robust, rapid and re-changeable means to make mould-less manufacturing large freeform panels.
Study of True Stress-Strain Curve after Necking for Application in Ductile Fracture Criteria in Tube Hydroforming of Aerospace Material
Authors: Saboori Mehdi , Champliaud Henri , Ghoulipor Javad , Gakwaya Augustin , Savoie Jean , Wanjara Priti
Published: February 2012

Tube hydroforming (THF) is an advanced metal forming process that is used widely in automotive industry, but the application of the THF process in aerospace field is comparatively new with many challenges due to high strength and limited formability of aerospace materials. The success of THF process largely depends on many factors, such as mechanical properties of the material, loading path during the process, tool geometry and friction condition. Due to complexity of this process, finite element modeling (FEM) can largely reduce the production cost. One of the important input in FEM is the material behavior during hydroforming process. The true stress-strain curve before necking can be easily determined, using either tensile testing or bulge testing, but for an accurate failure prediction in a large deformation, such as hydroforming, the study of true stress-strain curve after necking is important because it improves the quality of the analysis due to utilizing a real extended stress-strain curve. Hence, the objective of this research was to establish a methodology to determine the true stress-strain curve after necking in order to predict burst pressure in the THF of aerospace materials. Uniaxial tensile tests were performed on standard tensile samples (ASME E8M-04) to determine the true stress-strain before and after necking, using an analytical method presented in this study. To validate the approach, burst pressure in the THF process was predicted using the extended stress-strain curve in conjunction with Brozzo's decoupled fracture model. The approach was evaluated using data obtained from the free expansion (tube bulging) tests performed on stainless steel 321 tubes with 2 inches diameter and two different thicknesses, 0.9 mm and 1.2 mm. The comparison of the predicted and measured burst pressures was promising, indicating that the approach has the potential to be extended to predict formability limits in THF of complex shapes.
Grain Refinement Mechanism in Al–4B Master Alloy Added Pure Mg
Authors: Suresh Murugavel , Srinivasan Amirthalingam , Pillai Uma Thanu Subramonia , Pai Bellambettu Chandrasekhara
Published: February 2012

Al–4B master alloy has been prepared by the reaction of fluoride salt KBF4 with molten Al and different amounts of this master alloy (0.5, 1, 1.5 and 2 wt%) has been added to pure Mg to study in detail its effect on the grain refinement of pure Mg. Considerable reduction in grain size from 1300 to 210μm is obtained and maximum reduction is observed with 2 wt% master alloy addition. The grain refinement is caused by both the growth restriction effect of Al and the presence of potent AlB2 nucleant particles. Improvement in mechanical properties is obtained with Al–4B master alloy and is attributed to increase in grain boundary area due to the grain refinement and the particle strengthening due to AlB2.
Processing of V65 Aluminium Alloy Wires Processed from Hot and Warm Rolled Rods for Rivet Applications
Authors: Nayan Niraj , Murty S.V.S. Narayana , Sharma S.C. , Sinha Parameshwar Prasad
Published: February 2012

High shear strength of 25 kg/mm2 combined with a high plasticity makes Russian grade V65 aluminum alloys as potential candidate compared to AA2024 for riveting applications in aerospace industries. The lower content of magnesium over the AA 2024 alloy decreases the aging kinetics of this alloy because of the decreased vacancy concentration in the as-quenched alloy which in turn gives flexibility to carryout riveting operation even after 4 days after solution heat treat¬ment and natural aging at room temperature. This paper presents the processing and characterization of V65 aluminium alloy wires processed from hot and warm rolled rods. Mechanical properties of the wires have been evaluated in T6 and T4 tempers and correlated with microstructures. Detailed microstructural examination using optical microscopy and fractography of the tensile tested samples using scanning electron microscopy were carriedout.
Ultrafine Grained Steel Wire and its Formability
Authors: Torizuka Shiro , Muramastu Eijiro , Murty S.V.S. Narayana
Published: February 2012

While uniform elongation is a measure of ductility of the material, reduction in area in tensile tests is also an important measure of ductility. Ultrafine-grained steels with different carbon contents from ultralow carbon to high carbon were produced through warm caliber rolling. It was found that the reduction in area- tensile strength balance is far better than the conventional ferrite+pearlite steels and even superior to martensite steels for all materials. Formability of ultrafine-grained steel is examined by applying to form a M 1.7 micro screw using these ultrafine-grained steels. Screws are formed through the process of cold heading and rolling. Relationship between cold heading, rolling, uniform elongation and reduction in area are investigated to clarify the formability of ultrafine-grained steels. Low-carbon ultrafine-grained steel has excellent cold headability and favorable rolling properties, i.e., excellent formability. Reduction in area is a measure to determine formability on cold heading. Ultrafine grained steel wire with length of several hundred meter were developed with the technology of warm continuous multi-directional rolling. This wire also have a good formability which can form microscrews.
Equal Channel Angular Pressing of Aluminum-Alumina In Situ Metal Matrix Composite
Authors: Athreya C.N. , Mahesh V.P. , Brahmakumar M. , Rajan T.P.D. , Prabhu K. Narayan , Pai B.C. , Gupta R.K. , Ramkumar P.
Published: February 2012

The present investigation is on synthesis of in situ Al-alumina composite and to evaluate the effect of equal channel angular pressing on the refinement of the grain structure and enhancement in the hardness and the strength. The billets pressed in as cast condition has shown cracks during first pass. The billets pressed immediately after solution treatment for one pass and followed by ageing treatment immediately after pressing exhibited very high hardness of 125BHN against 95 BHN to that of the T6 condition of 6061 aluminium alloy. The microstructural refinement from 35 µm to 11 µm is obtained in annealed and ECAP 2 pass condition.
Comparisons of Sintered Technology with Powder Forging for Fe-P Soft Magnetic Alloys
Authors: Chaurasia Shailesh K. , Prakash Ujjwal , Chandra Kamlesh , Misra Prabhu S.
Published: February 2012

Sintered P/M ferrous compacts containing up to 0.8% phosphorous have attractive set of mechanical and magnetic properties. Large phosphorous additions increase the shrinkage during sintering to such a degree that the tolerances of the sintered component may become adversely affected. Further, the sintering process requires more time and energy and is hence costly. To overcome the above problems, powder forging route has been used. In this process encapsulated Fe- P based alloy powder is heated and forged it into slabs. These were hot rolled to produce sheet and wires. Phosphorous addition improves the final density of the resulting product. It also improves the soft magnetic properties. All the alloys exhibited excellent workability.
Effect of Ti Particle Size on Reaction Synthesis of Ti Aluminide
Authors: Gupta Rohit Kumar , Pant Bhanu , Agarwala Vijaya , Sinha Parameshwar Prasad
Published: February 2012

Titanium aluminide intermetallic was made through reaction synthesis (RS) process using elemental powders. Pressure assisted synthesis was carried out at high temperature under vacuum. Ti powder with two different particle sizes (200μm and 30μm average) were used in RS. Synthesized blocks were homogenized and characterized for chemical homogeneity, density, phase formation and microstructure evolution. Products near to theoretical density have been obtained with uniform chemistry after homogenization. Al3Ti as a major phase along with TiAl as minor phase was confirmed after RS and TiAl along with Ti3Al was observed after homogenization. Homogenization cycle was found to be different for the alloys made through different Ti particle sizes. Significant role of Ti particle size has been observed in this pressure assisted RS process.
Synthesis and Characterization of Nanostructure Magnesium Base Alloy by Mechanical Alloying for Hydrogen Storage Application
Authors: Selvaraj Rengasamy , Thirumurugan M. , Kumaran S. , Rao T. Srinivasa
Published: February 2012

Hydrogen storage is a key enabling technology for the advancement of hydrogen and fuel cell power technologies in transportation, stationary, and portable applications. The hydrogen transport from surface to the core of the metal powder particles is an important step during a hydrogenation reaction. Therefore, the hydrogen desorption kinetics are required for a complete understanding of the hydrogenation mechanism. In this present work, Mg-Ni-Nb systems were synthesized by mechanical alloying under optimized milling parameters (milling speed, milling time). The structural evolution (nanostructure, formation of intermetallic phases, etc) during ball milling was studied by X-ray diffraction. The activation energy of the mechanical alloyed powders was studied for Mg-Ni-Nb systems. Hydrogenation and dehydrogenation studies were carried out and understood the hydrogen interaction with Mg based alloys.
Fabrication and Optimization of Drilling Parameters in Heat Treated SiC Reinforced Functionally Graded Al Composites Using Taguchi Method
Authors: Vinoth Babu K. , Winowlin Jappes J.T. , Rajan T.P.D.
Published: February 2012

The present investigation is on the fabrication of SiC particles reinforced aluminum functionally graded disc and optimization of drilling process parameters using Taguchi method. The primary processing of A356-20%SiCpcomposite have been carried out by liquid metal stir casting technique followed by centrifugal casting leading to the formation of a functionally graded Al FGM disc with SiC particles segregating towards the outer periphery of the casting. The composite specimens are heat treated and used for the drilling studies. Taguchi method has been used to find the optimal drilling parameters for surface roughness and thrust force during drilling. The Taguchi Orthogonal arrays, signal-to-noise ratio (S/N) and Analysis of variance (ANOVA) are employed to study the performance characteristics in drilling operations of FGMMC using TiAlN coated carbide tools. The drilling parameters like cutting speed, feed and point angle in three different zones (15, 45, and 75 mm from the outer periphery) of FGMMC are optimized with considerations of surface roughness and thrust force.
Formation of Electroless Ni-B Coating on Boron Carbide Particles for Composite Processing
Authors: Deepa J.P. , Rajan T.P.D. , Pavithran C. , Pai Bellambettu Chandrasekhara
Published: February 2012

The present investigation is on formation of a uniform coating of Ni-B coating on the surface of B4C particle by electroless technique by varying process parameters and pH of the coating bath. The coating characteristics observed on majority of pH conditions on activated particles were mesh-like and at higher pH 12 the coated surface characteristics changes to patch like morphology. At lower alkaline condition there was not enough time for co-deposition to occur and the co-deposits appeared along with the coated particles. The studies with varying pH showed that pH 8 gives uniform coating of the entire particles surface with Ni-B and above which higher amount of co-deposited particles of Ni-B is also observed.
Thermally Activated Deformation of a High-Nitrogen Grade 316LN Stainless Steel under Compressive Loading
Authors: Samantaray Dipti , Mandal Sumantra , Albert Shaju K. , Bhaduri A.K. , Jayakumar Tammana
Published: February 2012

In this paper, the deformation behaviour of a high-nitrogen grade 316LN stainless steel (with 0.14%N) has been studied over a wide range of temperatures (1123-1423K) and strain rates (0.001-10 s-1). The key deformation controlling mechanisms have been investigated using thermal activation parameters, such as activation volume and activation enthalpy. The chromium nitride precipitates, dislocation intersections, both conservative and recovery, are found to be the key deformation controlling mechanism at different temperature–strain-rate domain during hot deformation of this material.
Development of Hardening and Tempering Cycle for High Strength Low Alloy Fastener Grade Steel
Authors: Kathikeyan M. K. , Gupta R.K. , Anil Kumar V. , Ramkumar P.
Published: February 2012

Medium carbon low alloy Ni-Cr-Mo steel is used in the fabrication of aerospace fasteners. It finds application in different heat treated conditions to meet the desired strength level. The alloy was realized through double melting route. Heat Treatment studies have been carried out by following different tempering temperatures to obtain varying strength levels ranging from 1200MPa to 1400MPa. Microstructural analysis has been carried out to find out reasons for variation in mechanical properties. Tempering cycle has been suggested to obtain fully tempered martensitic structure. This paper presents the different hardening and tempering cycles studied to obtain the desired strength level for the intended application.
Effect of Simulated Brazing Cycle on the Microstructure and Mechanical Properties of Cu-Cr-Zr-Ti Alloy
Authors: Krishna S. Chenna , Radhika K.V. , Thomas Tharian K. , Sudarshan Rao G. , Swathi Kiranmayee M. , Pant Bhanu
Published: February 2012

Cu-Cr-Zr-Ti alloys are widely used for fabrication of thrust chamber in liquid rocket engines, because of their high thermal conductivity and adequate strength. The alloy should be used in peak-aged condition to achieve the best combination of strength and conductivity. However, realization of final component involves forming and brazing operations which limit the usage of the alloy in peak aged condition. Therefore, an attempt has been made to study the effect of the simulated brazing treatment on the microstructure and mechanical properties using optical microscopy, electron microscopy, mechanical testing and hardness measurement. The high temperature brazing treatments resulted in tremendous grain growth. The measured hardness is observed to be in line with the grain size of the specimens. The hardness and tensile strength decreased in samples subjected to simulated brazing cycle, implying requirement for a post braze treatment. After the post brazing treatment the optimum mechanical properties have been achieved at room temperature. Low ductility was observed at 600°C in the samples subjected to simulated brazing cycle.
Metallurgical Failure Analysis-Few Case Studies
Authors: Manwatkar Sushant K. , Swathi Kiranmayee M. , Jha Abhay Kumar , Ramesh Narayanan P. , Sreekumar K. , Sinha Parameshwar Prasad
Published: February 2012

Advancement in material science has reached great heights both in terms of development and properties but still failures continue to happen. Failure is often accompanied by economic and human loss. Failures generally occur due to error of knowledge, error of performance and error of intent which comprises improper design and/or material selection, deficiency in processing and assembly. Failure analyst plays an important role in evaluating the causes of failure by using various analytical tools to arrive at the conclusion and suggests remedies to avoid its reoccurrence. This paper highlights the important steps in failure analysis with a few case studies demonstrated. Case studies include the failure of plumbing tube used in engine gimbal control system of liquid propulsion system, where failure was initiated due to process deficiency and its propagation was facilitated under fatigue loading. In the other case study discussed, failure of steel fasteners was due to hydrogen induced stress corrosion cracking (HISCC).
Electrical Properties of Nano Zinc Ferrites Prepared by Solution Combustion and Hydrothermal Methods
Authors: Daruka Prasad B. , Nagabhushan B.M. , Nagabhushana H. , Rudraswamy B. , Jnaneshwara D.M. , Shivakumara C. , Shivaprakash N.C. , Chakradar R.P.S. , Gnana Prakash A.P.
Published: February 2012

Zinc Ferrite (ZF) nanopowders relatively uniform size distributions ranging from 5 to 14 nm were prepared by solution combustion and hydrothermal methods. The PXRD showed cubic phase, spinel structure, and particle size in nanoscale. The SEM images confirm the agglomeration of the product composed of uniform nanoparticles of flakes type and spherical type in combustion and hydrothermal methods respectively. The purity check was done by FTIR. The optical band gap energy (Eg) obtained by UV-Vis spectra of the ZF nanopowders prepared by solution combustion and hydrothermal methods were found to be 1.985 eV and 1.99 eV respectively. The present study clearly shows that the distribution of the cations within the spinel lattice of the ferrite nanoparticles are strongly affected by the synthesis method used. Results suggest that the electrical properties depend on the particular method of preparation and sintering temperature of the prepared samples. The resistivity of the samples increased to the order of 103 by sintering the samples. It is observed that the activation energy (Ea) decreases with increasing the sintering temperature.
Thermal Barrier Coating on Metallic Substrates by Preceramic Route
Authors: Devapal Deepa , Sebastain T.V. , Prabhakaran P.V. , Packirisamy S.
Published: February 2012

A low cost, easily processable, multi layered functionally graded ceramic coating of thickness ~1000 µm was developed to protect metallic substrates from the risk of thermal oxidation. It consists of a four layered functionally graded coating consisting of aluminide layer followed by an intermediate zirconia as thermal insulative layer, an alumina layer serving as buffer layer with the outer most high emissivity layer to provide the required emissivity. All the layers were brush coated and the specimens were cured at 150°C. The solar absorptivity and emissivity of the coating was found to be 0.82 and 0.88 respectively. 15CDV6 plate of 150 x 150 x 5 mm was coated with multilayer thermal barrier coating of thickness ~ 1 mm. The coated sample was subjected to a heat flux of 8.5 W/cm2for 1035 secs to evaluate the thermo-responsive behaviour of the coating. Maximum back wall temperature measured was 299°C. The coating methodology is simple compared to complicated plasma techniques which can be applied on complex shaped substrates and all operations are carried out at low temperatures, below 150°C ensuring no deterioration of structural properties of the substrate.
Elimination of Twin Boundaries when Growing 3C-SiC Heteroepitaxial by Vapour-Liquid-Solid Mechanism on Patterned 4H-SiC Substrate
Authors: Lorenzzi Jean , Jegenyes Nikoletta , Lazar Mihai , Tournier Dominique , Carole Davy , Cauwet François , Ferro Gabriel
Published: February 2012

In this work we report on the study of twin boundary (TB) evolution during heteroepitaxial growth of 3C-SiC on patterned 4H-SiC(0001) substrate by vapour-liquid-solid (VLS) mechanism. Ge50Si50 melt was used at a temperature of 1450°C. 3C-SiC deposit was obtained on top and outside the mesas. Some lateral enlargement of these mesas was observed but it was systematically homoepitaxial. Elimination of TBs inside the 3C-SiC deposit on top of the mesas was observed for specific mesa shape and/or orientation of the sidewalls. Though three–fold or six-fold symmetry mesas are recommended for TB elimination, originally circular mesas lead also to the same result due to initial faceting toward hexagonal shape.
Electrical Characteristics of SiC UV-Photodetector Device from the P-I-N Structure Behaviour to the Junction Barrier Schottky Structure Behaviour
Authors: Biondo Stéphane , Lazar Mihai , Ottaviani Laurent , Vervisch Wilfried , Palais Olivier , Daineche R. , Planson Dominique , Milesi F. , Duchaine J. , Torregrosa Franck
Published: February 2012

In this paper, we deal with the study of Ultra Violet (UV) photodetector device based on SiC material undergoing a p-i-n structure process. Current density-voltage (J-V) measurements in reverse and forward bias, are performed on the UV photodetector device. Due to a very thin p+-type doping layer, a high reactivation annealing and the metallic contact deposit, experimental measurements point out Junction Barrier Schottky (JBS) device behaviour in spite of the p-i-n structure device process. To understand this involuntary phenomenon, these experimental characteristics are accompanied with an experimental study by the SIMS analysis.
High Temperature Capability of High Voltage 4H-SiC JBS
Authors: Berthou Maxime , Godignon Philippe , Vergne Bertrand , Brosselard Pierre
Published: February 2012

This paper presents the high blocking capability of the 4H-SiC tungsten Schottky and junction barrier Schottky (JBS) diodes at room temperature as well as at high operating temperature. First, we present the design of the proposed devices and the process employed for their fabrication. In a second part, their forward and reverse characteristics at room temperature will be presented. Our rectifiers exhibit blocking capability up to 9kV at room temperature. Then, we investigate the reverse current behaviour at 5kV from room temperature to 250°C under vacuum. JBS and Schottky devices that are capable to block 8kV at room temperature, show leakage current inferior to 100µA at 250°C when reverse biased at 5kV. It confirms the capability of Silicon Carbide to produce devices capable of operation at temperatures and voltages above the Silicon limits.
Nano-Analytical and Electrical Characterization of 4H-SiC MOSFETs
Authors: Beltran Ana Maria , Schamm-Chardon Sylvie , Mortet Vincent , Lefebvre Mathieu , Bedel-Pereira Elena , Cristiano Fuccio , Strenger Christian , Häublein Volker , Bauer Anton J.
Published: February 2012

4H-SiC presents great advantages for its use in power electronic devices working at particular conditions. However the development of MOSFETs based on this material is limited by mobility degradation. N-channel SiC MOSFETs were manufactured on p-type epitaxial and p-implanted substrates and the electron mobility in the inversion channels was measured to be correlated with their structural and chemical properties determined by transmission electron microscopy methods. With regard to what was previously discussed in the literature, transition layer formation and carbon distribution across the SiC-SiO2 interface are considered in relation with the measured low electron mobility of the MOSFETS.
CVD Growth of 3C-SiC on 4H-SiC Substrate
Authors: Henry Anne , Li Xun , Leone Stefano , Kordina Olof , Janzén Erik
Published: February 2012

The hetero epitaxial growth of 3C-SiC on nominally on-axis 4H-SiC is reported. A horizontal hot-wall CVD reactor working at low pressure is used to perform the growth experiments in a temperature range of 1200-1500 °C with the standard chemistry using silane and propane as precursors carried by a mix of hydrogen and argon. The optimal temperature for single-domain growth is found to be about 1350 °C. The ramp up-conditions and the gas-ambient atmosphere when the temperature increases are key factors for the quality of the obtained 3C layers. The best pre-growth ambient found is carbon rich environment; however time of this pre-treatment is crucial. A too high C/Si ratio during growth led to polycrystalline material whereas for too low C/Si ratios Si cluster formation is observed on the surface. The addition of nitrogen gas is also explored.
Microstructure and Transport Properties in Alloyed Ohmic Contacts to P-Type SiC and GaN for Power Devices Applications
Authors: Roccaforte Fabrizio , Frazzetto Alessia , Greco Giuseppe , Lo Nigro Raffaella , Giannazzo Filippo , Leszczyński Michał , Prystawko Pawel , Zanetti Edoardo , Saggio Mario , Raineri Vito
Published: February 2012

The formation of good Ohmic contacts to p-type silicon carbide (SiC) and gallium nitride (GaN) is an important physical and technological concern, because of the difficulty to find metals with low Schottky barriers to p-type wide band gap materials, and due to the high ionization energies of p-type dopant impurities. Typically, to overcome these issues, alloyed metallic compounds are used. In this work, the electrical properties of alloyed Ohmic contacts to p-type (Al-implanted) 4H-SiC and p-type (Mg-doped epilayers) GaN are presented and correlated with their microstructure. The impact of the surface preparation and annealing conditions are discussed, reporting the cases of Al/Ti contacts to p-SiC and Au/Ni contacts to p-GaN. The electrical characterization as a function of temperature allowed to define the dominant transport mechanism and to determine the barrier heights.
Comparison of Electrical Behavior of GaN-Based MOS Structures Obtained by Different PECVD Process
Authors: Al Alam Elias , Cortés Ignasi , Begou T. , Goullet Antoine , Morancho Frederique , Cazarré Alain , Regreny P. , Brault J. , Cordier Yvon , Besland Marie Paule , Isoird K.
Published: February 2012

MOS SiO2/GaN structures were fabricated with different surface preparation and different PECVD processes for the dielectric thin film deposition (ECR-PECVD and ICP-PECVD in continuous and pulsed modes). On the basis of C-V curves, the surface preparation steps, involving chemical etching with BOE, UV-Ozone oxidation and oxygen plasma oxidation, were compared in terms of resulting effective charge and interface trap density. A good SiO2/GaN interface quality was achieved for N-type MOS capacitances obtained both with continuousICPPECVD and ECR-PECVD deposition of the SiO2 dielectric. However, the interface quality is greatly reduced for MOS capacitors fabricated on P-type GaN.
Selective β-SiC/SiO2 Core-Shell NW Growth on Patterned Silicon Substrate
Authors: Attolini Giovanni , Rossi Francesca , Fabbri Filippo , Salviati Giancarlo , Bosi Matteo , Watts Bernard Enrico
Published: February 2012

β-SiC/SiO2 core-shell NWs have been synthesized on patterned silicon wafers in a CVD system, using carbon oxide as single precursor and nickel nitrate as catalytic element, in nitrogen or argon atmosphere at 1100°C. The coaxial structure and the crystallinity of the NW core are examined by (scanning) transmission electron microscopy. The patterning of the substrate allows to grow NWs in selected areas only, as imaged by SEM. Cathodoluminescence (CL) panchromatic images of the same areas point out that the light emitted under electron excitation is localized only in the area covered with NWs. The room-temperature CL spectrum has three different components peaked at 2.45 eV, related to the 3C-SiC near-band-edge emission, and at 2.75 and 3.75 eV, that are induced by the triplet and singlet states of oxygen-deficiency centers ODC(II) in silicon dioxide shell.
High Frequency 3C-SiC AFM Cantilever Using Thermal Actuation and Metallic Piezoresistive Detection
Authors: Boubekri Rachida , Cambril Edmond , Couraud L. , Bernardi Lorenzo , Madouri Ali , Martrou David , Gauthier Sébastien
Published: February 2012

One way to improve the force sensitivity of Atomic Force Microscopy (AFM) cantilevers is to increase their resonance frequency. SiC is an excellent material for that purpose due to its high Young’s modulus and low mass density. This size reduction makes conventional optical motion detection methods inappropriate. Here, we introduce self-sensing, self-excited high frequency AFM cantilevers. The motion detection is based on the measurement of a metallic piezoresistor incorporated in the cantilever. The motion excitation is performed by electrothermal actuation using another metallic circuit. Cantilevers with sizes as low as 4 μm in length, 1.2 μm in width and 0.5 μm in thickness were realized by using different steps of e-beam lithography, deposition of thin gold films to pattern the piezoresistor and the electrothermal actuation electrode. Dry etching SF6 plasma was used for etching the SiC cantilever and TMAH solution heated to 80°C to release the cantilever. In this case, a thigh control of underetching, which reduces the cantilever resonance frequency was required.
Influence of Filler Materials on Mechanical and Hot Corrosion Properties of Gas Tungsten Arc Welded AISI 304
Authors: Mohanraj R. , Rajesh Kumar D. , Yeswanth Kumar M. , Arivazhagan N. , Devendranath Ramkumar K. , Narayanan S.
Published: February 2012

This paper investigated the influence of filler materials such as E308L and ENiCu-7 utilized in the GTA welded AISI 304 with respect to mechanical and corrosion properties. It was found that E308L had shown better tensile strength and corrosion resistance as compared to ENiCu-7. A comparative analysis had been made on the different regions of the weldment subjected to cyclic air oxidation at 700°C. The corrosion products were examined using XRD and SEM/EDAX analysis.
Corrosion Resistance of Pulse-Electroplated Ni-W Alloys
Authors: Hou Kung Hsu , Chang Yun Feng , Ger Ming Der
Published: February 2012

Nickel-tungsten (Ni-W) plating process exhibited fewer environmental hazards and lower health hazards than conventional chromium bath processes did, because they had the potential to be substituted for certain future applications. This study attempted to develop Ni-W alloy coatings with different weight percentages of tungsten to produce by using nickel-tungsten citrate electrolyte baths that are deposited by pulse current power source techniques. The composition of the ratio of tungsten/nickel was controlled by the change from ion mass transfer rates for the interface between cathodes and electrolytes that were caused by adjustment by charging the over potential or rest that was regulated by the on-off time during pulse and reverse-pulse current. In this study, the corrosion resistance and the composition of the coatings related to the operating parameters were also discussed through the analyses of the experimental design method. Results were found that Ni-W alloy compositions governed through regulation of pulse and pulse-reverse parameters. The frequencies of electric current, Ton and Toff with pulse duty cycles had great impact on chemical composition and surface morphology for the deposits. Results of the electrochemical tests indicated the pulse plated Ni-W metal alloy coatings in which the corrosion resistance was superior to that of the alloy deposited by the direct current technique.
Investigation of Trapped Charges-Induced Stain Formation on RF-PECVD Diamond-Like Carbon Films
Authors: Seekumbor Eakkaphon , Jaroenapibal Papot , Lertwikool Nuansamorn , Yamwong Wittawat , Triroj Napat
Published: February 2012

This paper reports the investigation of a root cause of stain formation on the surfaces of diamond-like carbon (DLC) films. The DLC thin films are prepared using a radio-frequency plasma enhance chemical vapor deposition (RF-PECVD) technique with C2H4 as a carbon precursor gas. We have observed water spot-like stains on the DLC surfaces after treating the films with a dilute solution of dipropylene glycol monomethyl ether (DPGME). Low voltage-scanning electron microscopy (SEM) is employed to examine the thin layer of agglomerated stains on the surfaces. The results from capacitance-voltage (C-V) measurements show that as-deposited films inherit some trapped charge accumulations within the structure, thereby resulting in the pronounced shift in the flat-band voltage. These trapped charges make the films prone to surface stain formation. Post-annealing of the DLC films at 200 °C in N2 for 1 h has proven to reduce the trapped charge density, and therefore prevent stain formation on the DLC films.
ZnO Surface Acoustic Wave Sensor for the Enhanced Detection of DMMP
Authors: Bhasker Raj V. , Tomar Monika , Nimal A.T. , Parmar Yashoda , Sharma M.U. , Gupta Vinay
Published: February 2012

This article reports the development of ZnO coated one port Surface Acoustic Wave (SAW) resonators for the detection of DMMP (dimethyl methyl phosphonate), a simulant of chemical warfare agent Sarin at room temperature. For enhanced sensitivity high frequency SAW devices (433Mhz) were used. Frequency shift with DMMP exposure was found to increase with increase in thickness of ZnO film from 20 to 80 nm with maximum shift of 52 kHz. The cross sensitivity of the sensor with commonly available volatile organic compounds (VOCs), gases and water vapors has been performed and was found that the sensitivity towards other interferants is very less as compared to that of DMMP vapors. The sensing mechanism has been explained in detail. It has been shown that there was no significant change in the resistance of the film with exposure to DMMP vapors and hence the contribution of the acoustoelectric interaction is negligible. Further mass loading was not dominant. The negative differential frequency shifts proved that change in elasticity of the film with exposure to DMMP vapors is the dominant sensing mechanism.
O canto de anúncio de Scinax Belloni Faivovich, Gasparini & Haddad, 2010
Authors: Peres Juliana , Simon José Eduardo
Published: February 2012

Scinax belloni was recently described from the surroundings of the Forno Grande State Park, municipality of Castelo, state of Espírito Santo, southeastern Brazil. The present study describes the advertisement call of Scinax belloni based on recordings obtained in the type locality of the species, between 06th and 10th of January 2010. Three adult specimens were recorded in Rupicolous bromeliads (Alcantarea sp.). The call presents duration from 0,62 to 0,11s, and consists of 2 to 3 multi-pulsed notes. The frequency spectrum varies from 1.723 to 5.275 Hz, with the dominant frequency emitted on 3.078 Hz. The acoustic parameters differ from the data available for S. perpusillus, S. arduous and S. Peixotoi, emphasizing the value of the advertisement calls as diagnostic character among species of the Scinax perspusillus group.
Perfil de metilação do gene P16 em mucosa oral
Authors: Vargas Cruz Mariana , Azevedo Melo Estevão , Gomes Soares Aline , Fagundes Lima Oliveira Zilda , Vasconcelos de Podestá José Roberto , Alves Gouvêa Sônia , Ventorin von Zeidler Sandra , de Freitas Cordeiro-Silva Melissa
Published: February 2012

Oral cancer is the seventh most frequent type in our population and approximately 90% of these malignancies are squamous cell carcinoma. Genetic alterations in tumor suppressor genes increase the risk of tumor development, since these genes are associated with cycle cell control. Epigenetic changes involving cell cycle regulatory genes are related to the initiation and progression of various tumors. The hyper methylation of tumor suppressor gene p16 is found in many types of cancers and is associated with gene silencing. The aim of this study was to determine the methylation of the promoter region p16 in samples of normal oral mucosa from patients with oral squamous cell carcinoma. The technique of MS-PCR (Methylation-Specific Polymerase Chain Reaction), which allowed the distinction between methylated and non-methylated alleles in the promoter region p16, was used. This study analyzed 23 samples, and 17.4% tested positive for methylation. Among these, 50% were chronic users of tobacco and 25% alcohol. Aging may be associated with methylation of p16, since the average age of positive patients was 72 years and negative patients was 56 years. The results suggest that hyper methylation of the p16 can become important molecular marker for oral squamous cell carcinoma
Possíveis alternativas ao predomínio da lógica instrumental
Authors: Bellia Margoto Julia , Roberto Behr Ricardo
Published: February 2012

This essay contributes for the quarrel concerning the possibilities of construction of alternatives to the instrumental bureaucratic logic, essence of the model of society centered in the market, as Guerreiro Ramos points (1989). For such intention, a conceptual rescue on the bureaucratic model was made, under a critical approach and evidencing its permanent attempt of maintenance and occultation of an ideology of domination that historically perpetuates based on the triad power, control and alienation, in accordance with what supports Motta (1997). From this analysis, considerations are traded on the duality between the instrumental and substantive rationalities, this as representative of an alternative to the first one. In the sequence, it is presented what Guerreiro Ramos (1989) called par economic paradigm, which creates different categories of alternative enclaves that open space for innovative social performances, distant, in diverse aspects, of the predominant market logic. Finally, the need for the emergence of a distinctive rationality and opposed to the extreme link between means and purposes, it is clear from the analysis presented here and may even be perceived, though still very tentatively, in today’s society.
Soil organic carbon storage changes in coastal wetlands of the modern Yellow River Delta from 2000 to 2009
Authors: Yu J. , Wang Y. , Li Y. , Dong H. , Zhou D. , Han G. , Wu H. , Wang G. , Mao P. , Gao Y.
Published: February 2012

Abstract. Soil carbon sequestration plays an essential role in mitigating CO2 increases and the subsequently global greenhouse effect. The storages and dynamics of soil organic carbon (SOC) of 0–30 cm soil depth in different landscape types including beaches, reservoir and pond, reed wetland, forest wetland, bush wetland, farmland, building land, bare land (severe saline land) and salt field in the modern Yellow River Delta (YRD), were studied based on the data of the regional survey and laboratory analysis. The landscape types were classified by the interpretation of remote sensing images of 2000 and 2009, which was calibrated by field survey results. The results revealed an increase of 10.59 km2 in the modem YRD area from 2000 to 2009. The SOC density varied ranging from 0.73 kg m−2 to 21.60 kg m−2 at depth of 30 cm. There were ~3.97 × 106 t and 3.98 × 106 t SOC stored in the YRD in 2000 and 2009, respectively. The SOC storages changed greatly in beaches, bush wetland, farm land and salt field which were affected dominantly by anthropogenic activities. The area of the YRD increased greatly within 10 yr, however, the small increase of SOC storage in the region was observed due to landscape changes, indicating that the modern YRD was a potential carbon sink and anthropogenic activity was a key factor for SOC change.
Bolivia hoy: rupturas, inercias y desafios
Authors: Stefanoni Pablo
Published: February 2012

The arrival of Evo Morales to power in January of 2006 –supported with an unprecedent 54% of the votes– marked a milestone in Bolivian political history and opened the way to an ambitious project of re-foundation of the country. Those events were translated in the call for a Constituent Assembly and in the nationalization of hydrocarbons, within the framework of a strong “ruralización de la política”. More than five years of that one triumph has passed and after a re-election with 64% of the votes in December 2009 that consolidated the “evista” hegemonyhas declined.  Now the government faces a series of challenges tied to the effective materialization of the change proposed in the re-foundational speeches. This article analyses the novel experience of “Indians in the power” centered in the tension between the changes implemented and the inertias of the past in spheres such as the democratic radicalization, the social equality, the model of development, and the political project. All these themes affected by a powerful, and yet somehow vague objective: the decolonization of the country.
Ideology and Social Improvement in Bolivia during the 20th Century
Authors: Norris Brian
Published: February 2012

This essay relates improvements in social indicators in Bolivia during the Twentieth Century to ideological changes during the same period. During the Twentieth Century, most social indicators improved dramatically in Bolivia. Separately, scholars have vigorously debated ideologies, such as neoliberalism and its macroeconomic competitors, and the potential social impact of these ideologies. Despite the separate emphases on ideas and social outcomes, no systematic attempt has been made by scholars of Bolivia to link long–term ideological change to long–term social improvement in the country. This essay argues that it is probable that such a relationship exists, but it is important to consider mass ideology, which affects the whole of Bolivian society, in addition to elite ideology, which affects a much more limited portion of society.
"Without Him the Indians Would Leave and Nothing Would Get Done." The Changing Relationship Between the Caciques and the Audiencia of Charcas Following Francisco de Toledo’s Reforms
Authors: Thornton Jay David
Published: February 2012

Viceroy Francisco de Toledo’s 16th century population re–concentrations of the indigenous peoples of Charcas (modern day Bolivia) have been widely recognized as the most definitive attempt to transform indigenous Andean society along Iberian lines of settlement and government.  While the previously dispersed indigenous populations were resettled into a limited number of urban towns, native tribute obligations elevated, and Castilian forms of municipal government imposed, modern historiography is still debating the precise details of what Toledo’s reforms meant for the indigenous populations of this district. A review of decisions made by the Audiencia of Charcas and the contemporary correspondence of this court’s judges are examined to illustrate how the relationship between the high court and indigenous leaders ―caciques― changed through the period of Toledo’s reforms. This investigation reveals an explicit and previously underappreciated transformation in the political model from one where caciques frequently sought out and received legitimization from the Audiencia ―similar to the model used in the Inca system― to a situation where the caciques understood and utilized the Audiencia less as a partner in power and instead as a forum to be opportunistically used to obtain economic goods and privileges. Using the figure of the cacique as a proxy, this province–wide perspective on the changes engendered to native society by Toledo’s reforms is distinct from but complementary to the several more localized studies on the subject undertaken by other historians. The changes elucidated by these court records and official correspondence suggest the origins of the emergence of indigenous leaders whose skillful use of the colonial legal system would represent a hallmark of indigenous–Spanish relations for the rest of the colonial period.
THE EFFECTS OF CONSUMER ETHNOCENTRISM AND CONSUMER ANIMOSITY ON THE RE-PURCHASE INTENT: THE MODERATING ROLE OF CONSUMER LOYALTY
Authors: Akdogan M.Sukru , Ozgener Sevki , Kaplan Metin , Coskun Aysen
Published: February 2012

With the growth of international trade and travel, consumers are increasingly confronted with foreign products and services. But some negative attitudes towards foreign products can arise from several factors such as previous or ongoing political, military, economic, or diplomatic events. Thus, both consumer ethnocentrism and consumer animosity have become important constructs in marketing. The purpose of this study is to investigate whether consumer ethnocentrism and consumer animosity affect repurchase intent towards U.S. products and whether this impact is moderated by customer loyalty. The findings of the research indicate that consumer ethnocentrism increases consumer animosity for the sampling. The present study also denotes that both consumer ethnocentrism and animosity have a negative impact on repurchase intent toward U.S. products in Turkey. According to the results of regression analyses, customer loyalty may not be an important moderating factor between consumers’ animosity and repurchase intent toward U.S. products. However, customer loyalty moderated the relationship between consumer ethnocentrism and repurchase intent toward U.S. products. Further implications for Turkish consumers in supermarkets in the province of Nevşehir are discussed. The value of future research is also acknowledged