bluuebunny/crossref_metadata_2025 huggingface dataset:
As Instituições Financeiras Brasileiras Usam a PCLD para Gerenciamento de Capital?
Authors: Carvalho José Alves , Pereira João Vicente , Dantas José Alves
Published: June 2018

Este estudo teve por objetivo verificar se as instituições financeiras brasileiras utiliza a parcela discricionária da Provisão para Créditos de Liquidação Duvidosa (PCLD) como instrumento de gerenciamento de capital. Para esse propósito, foram analisados os dados trimestrais de 2000 a 2015 dos 50 maiores conglomerados e instituições financeiras com atuação no Sistema Financeiro Nacional (SFN). Na realização dos testes empíricos foram estimados modelos com uso de dados em painel com efeitos fixos seccionais, sendo consideradas duas variáveis representativas do nível de capital: o Índice de Basileia, medida regulamentar de requerimento de capital; e uma proxy baseada em informações contábeis. A discricionariedade no reconhecimento da PCLD, por sua vez, foi definida como o valor provisionado para perdas acima do mínimo estabelecido na Resolução CMN nº 2682 (1999). Os resultados dos testes revelaram que não há evidências de que os bancos brasileiros utilizem a discricionariedade na constituição da PCLD para fins de gerenciamento de capital. Por outro lado, reforçaram as evidências de estudos anteriores, nacionais e internacionais, sobre o tema, no sentido de que as instituições utilizam essa discricionariedade na PCLD com o propósito de gerenciamento de resultados. Mesmo quando aplicado sobre as instituições financeiras consideradas “menos” capitalizadas, os testes também não confirmaram a hipótese de gerenciamento de capital. O estudo contribui para as discussões em curso no âmbito dos reguladores contábeis e bancários sobre o modelo atual de provisão para perdas de crédito.
Properties of Polysiylate Binders for Sol-Silicate Pains
Authors: Loganina Valentina Ivanovna , Kislitsyna Svetlana Nikolaevna , Mazhitov Yerkebulan Bisengalievich
Published: June 2018

Information is provided on the composition of polysilicate solutions obtained by mixing liquid glass and silica sol. It was found that the introduction of the sol leads to an increase in the silicate module and contributes to an increase in the fraction of high-polymer fractions of the silicon-oxygen anions. The results of the kinetics of the variation of α-SiO2 and β-SiO2. It is shown, that coatings based on the polysilicate solutions are characterized by faster curing. The was found correlation between the content of high-polymer fractions of silicic anions in a polysilicate solution and the tensile strength of films. Increase in the g-SiO2 content promote increase in the tensile strength of films. The composition of sol silicate paint is developed. Coatings based on paint have a high performance property.
Concretes Using Modified Mineral Extenders
Authors: Yadykina Valentina V. , Lukash Evgeny A. , Gridchin Anatoly M.
Published: June 2018

The possibility of modification of mineral extenders with a specific surface of 350 m2/kg with ultraviolet irradiation is considered. Infrared spectroscopy confirmed that under the influence of ultraviolet irradiation, the bonds of OH-groups with SiO2 tetrahedra are weakened, that contributes to the formation of extenders of the acid centers of Lewis and Bronsted on the surface. The optimum time of ultraviolet exposure is determined, at which the concentration of active Lewis and Bronsted acid sites on the extenders surface increases by more than 100%. It was found that replacing 10% of cement mass with a modified extenders makes it possible to produce concretes with strength values 20-30% higher than for composites without extenders. Obtaining equal strength concrete is possible with replacing 20% of cement with modified extenders.
Radiation Effect on Heat and Mass Transfer by Natural Convection from a Horizontal Surface Embedded in a Porous Medium
Authors: Bano Nasreen , Makinde Oluwole Daniel , Singh B.B. , Sayyed Shoeb R.
Published: June 2018

This paper deals with the study of the heat and mass transfer characteristics of natural convection from a horizontalsurface embedded in a radiating fluid saturated porous medium. Similarity solutions for buoyancy induced heat and masstransfer from a horizontal surface, where the wall temperature and concentration are a power function of distance fromthe origin, are obtained by using an integral approach of Von Karman type. The effects of the governing parameters suchas buoyancy ratio, Lewis number, radiation parameter and the power-law exponent on local Nusselt and local Sherwoodnumbers have been investigated both numerically and graphically.
Numerical Approach at Flat Plate for Predicting the Film Cooling Effectiveness Part A: Effect Blowing Ratio
Authors: Kebir Farouk , Khorsi Azzeddine
Published: June 2018

Film cooling is vital for gas turbine blades to protect them from thermal stresses and high temperatures due to the hot gas flow in the blade surface. Film cooling is applied to almost all external surfaces associated with aerodynamic profiles that are exposed to hot combustion gases such as main bodies, end-walls, blade tips and leading edges. In a review of the literature, it was found that there are strong effects of free-stream turbulence, surface curvature and hole shape on film cooling performance also blowing ratio. The performance of the film cooling is difficult to predict due to the inherent complex flow fields along the surfaces of the airfoil components in the turbine engines. From all what we introducing the film cooling is reviewed through a discussion of the analyses methodologies, a physical description, and the various influences on film-cooling performance. Initially Computational analysis was done on a flat plate with hole inclined at 55° to the surface plate. This study focuses on the efficient computation of film cooling flows with three blowing ratio. The numerical results show the effectiveness cooling and heat transfer behavior with increasing injection blowing ratio M (0.5, 1, and 1.5). The influence of increased blade film cooling can be assessed via the values of Nusselt number in terms of reduced heat transfer to the blade. Predictions of film effectiveness are compared with experimental results for a circular jet at blowing ratios ranging from 0.5, 1.0 and 1.5. The present results are obtained at a free stream turbulence of 10%, which are the typical conditions upstream of the effectiveness is generally lower for a large stream-wise angle of 55°.
Non-Newtonian Power-Law Flows around Circular Cylinder under Aiding/Opposing Thermal Buoyancy
Authors: Laidoudi Houssem , Bouzit Mohamed
Published: June 2018

This paper presents a comprehensive computational work on hydrodynamic and thermal phenomena of upward flow separation around a confined circular cylinder by aiding/opposing thermal buoyancy. For that purpose, let us consider a confined flow of Non-Newtonian power-law fluid around a heated/cooled circular cylinder in a two-dimensional vertical channel. The effects of thermal buoyancy and power-Law index on the flow separation and the average Nusselt number are studied for the conditions: (10 ≤ Re ≤ 40), (0.4≤ n ≤ 1.2), (-0.5 ≤ Ri ≤ 0.8), Pr = 50 and blockage ratio β = 0.2. In the steady flow regime the results show that the augmentation of the power-law index in the absence of thermal buoyancy causes a separation to grow. The adding buoyancy effect delays the separation in different power-law indices gradually and at some critical value of the buoyancy parameter it completely disappears resulting a stuck flow around a cylinder, whereas the opposing buoyancy effect causes an earlier wake behind cylinder. Moreover, the recirculation length is calculated to support the above finding. The decrease in the power-Law index increases the heat transfer rate. The Nusselt numbers are computed to predict the heat transfer rates of power-law fluids under the aiding/opposing thermal buoyancy condition.
Biomechanical Variations in Female Runner’s Pre and Post Treadmill Running
Authors: Quan Wen Jing , Mei Qi Chang , Gu Yao Dong , Ren Feng , Sterzing Thorsten , Fernandez Justin
Published: June 2018

The growing popularity of endurance sports activities is associated with a growing number of running injuries among recreational runners. The aim of this study was to assess the kinematic and kinetic variation on biomechanical parameters before and after 5km of treadmill running in female runners. Fourteen habitually shod female runners were assessed during treadmill running at their self-selected 5km running speed. A VICON motion analysis system and a Novel Pedar insole plantar pressure measurement system were used to record kinematic and plantar pressure data. Key findings from the study were that the internal and external rotation angle of the ankle, hip and knee while pre-5k running showed significant differences to those evaluated post-5k. The peak values of ground reaction forces (GRF) recorded pre-5k running were larger than the forces measured post-5k running. Combining the inversion and eversion of the ankle in the coronal plane during the pushing off phase, post-5k running showed a bigger eversion angle than pre-5k running. These subtle differences may reﬂect adaptation of motor control in female runners during long distance running of 5km.
Development and Validation of a Numerical Model for the Mechanical Behavior of Knee Prosthesis Analyzed by the Finite Elements Method
Authors: Mestar Abdelkader , Zahaf Samir , Zina Noureddine , Boutaous Ahmed
Published: June 2018

The human knee is a complex joint (the largest joint of the human body). During the different daily activities, this joint is exposed to significant loads and movements, may in some cases exceed the limit of the mechanical capacities of its components, which shows that the pathologies are quite numerous at the level of the human knee and the treatment sometimes requires surgery to either repair or implant (implant total knee prosthesis). As we know very well, the success of a total knee implant is highly dependent on the initial stability of the femoral or tibial implant and the integration of femur and tibia bone tissue with these implants in the long term. Due to the optimal distribution of mechanical stresses in the surrounding bone. It is for this reason that the search for reasonable solutions to compensate the damaged knee prosthesis and reduce the stresses in the cortical bone and spongy has become a very important research axis. In this regard, we have proposed three models of prosthesis knee joint from available literature and study the distribution of Von-Mises stresses and strains in the differents composents of knee prosthesis, know the total displacement between the model intact and model artificial of knee, 3D modeling software Solidworks 2016 is used for 3D modeling of knee prosthesis and finite element analysis software ANSYS 16.2 is used for numerical estimation of von-Mises stresses and strains. We find in this study that the maximum stresses and strains of Von Mises at the level of the tibia and tibial bone decrease, that is to say that the cement and the elastomer play a very important role in the absorption of the stresses and their minimization. On the other hand, the four knee prostheses (Model I (Ti6Al4V), Model II (CoCrMo), Model III (316L SS), Model IV (ZrO2)) implanted by elastomer contribute significantly to the reduction of stresses in the patella bone compared to the Intact Model. In general, both models of the knee prosthesis and reinforced by a stress reduction system (cement, elastomer) gave a lower stress level in the tibia and tibial bone of a normal person compared to a healthy model. The results obtained provide a theoretical basis for choosing an appropriate surgical model.
The Role of Chitosan on Polyvinyl Chloride (PVC)-Glycerol Biocomposites for Blood Bag Application
Authors: Zahra Nabila Meutia , Siswanto Siswanto , Widiyanti Prihartini
Published: June 2018

The common blood bag in the market is made from a mixture of PVC and plasticizer. But the a number of occurrences where pockets of heavily polluted bacteria, blood requires blood bags which has the antibacterial characteristic. Antibacterial properties on the bags of blood can be raised with the addition of chitosan. This research aim is to know the influence of chitosan membrane biocomposite PVC-Glycerol against its biological and physical properties. Chitosan dissolved with a concentration of 0 wt/v%; wt/v 0.5%; 1 wt/v%; 1.5 v/wt% wt/v and 2 wt/v% mixed with glycerol with a 1:1 ratio. Then the mixture was mixed with PVC solution 15% and formed into a membrane by using the glass plates. Furthermore, the membranes are characterized using tensile test, hemolytic test, and antibacterial test. The physical characteristics of the tensile test indicate that the elongation percentage was 2.22 – 96.43% and tensile strength was 3.6-8 MPa. The test result of the hemolytic test and antibacterial test showed that biocomposite membrane of PVC-Glycerol-Chitosan are hemocompatible because it has a hemolysis percentage < 5%, while antibacterial test results showed that the membrane has a weak anti-bacterial due to bacterial inhibition zone diameter < 5 mm. Based on the characterization result, biocomposite membrane of PVC-Glycerol-Chitosan can be used for blood bag candidate.
Study of Microstructural and Mechanical Behavior of Mild Steel Wires Cold Drawn at TREFISOUD
Authors: Djimaoui Toufik , Zidani Mosbah , Nebbar Mohamed Chaouki , Abid T. , Farh Hichem , Helbert Anne Laure , Brisset Francois , Baudin Thierry
Published: June 2018

The aim of the present work is to study the evolution of microstructure, texture and mechanical properties during drawing of mild steel wire of type F8Z used in the manufacture of welding electrodes TREFISOUD. It was found that the as received wire has a ferritic-pearlitic microstructure corresponding to an isotopic state (without texture). This microstructure is relatively heterogeneous in the wire section. On the other hand, after strong drawing structure appears relatively homogeneous, throughout the section of the drawn wire. Also the deformation process by drawing causes the hardening of wire as a function of deformation with a reinforcing component of the fiber texture <110> // ND (majority), typical for bcc materials. Characterization methods used in this work is: Optical microscopy (OM), Scanning Electron Microscopy (SEM), the Electron Back Scattered Diffraction EBSD, Vickers microhardness and the tensile tests.
Rheological Properties of Sunflower Oil-in-Water Emulsion Containing Vinegar, Stabilized with Gelatinized Bambara Groundnut Flour
Authors: Adeyi Oladayo , Ikhu-Omoregbe Daniel Imwansi Ogiem , Jideani Victoria A.
Published: June 2018

The influence of vinegar concentrations on the rheological properties of 40% (w/w) sunflower oil-in-water emulsions stabilized with 7% (w/w) gelatinized bambara groundnut flour (BGNF) was investigated. The rheological properties of interest were steady shear, time dependent and viscoelastic characteristics. Rheological characterizations of the emulsions were carried out using a shear rate controlled rheometer. Both emulsions with and without vinegar were pseudoplastic, thixotropic and viscoelastic fluids. Vinegar however, significantly (p < 0.05) affected rheological properties of BGNF-stabilized emulsion. Presence of vinegar in the emulsion decreased extent of thixotropy, pseudoplasticity and viscoelasticity of BGNF-stabilized emulsions. The results indicated that the rheological properties of BGNF-stabilized emulsion can be controlled and manipulated using vinegar however, the presence of vinegar in BGNF-stabilized emulsion may be deleterious to the emulsion. The result provided the information to understand the influence of vinegar on the rheological properties of BGNF-stabilized emulsions for product and process development.
Effect of ZnO Film Thickness on its Optical and Structural Properties
Authors: Pérez-Cuapio Rene , Pacio Mauricio , Juarez Hector , Alvarado Jose Alberto , Guarneros Cesia , Bueno Carlos , Pacio Abraham
Published: June 2018

In this study, we report the effect of ZnO film thickness on its optical and structural properties. The sol solution was synthesized by sol-gel method and deposited on silicon substrates by spin coating technique. The ZnO films thickness was varied from 60 to 180 nm. The ZnO films obtained showed a highly preferred orientation along the (002) plane. It was also observed that the crystallite size was not affected by increasing thickness. Transmittance measurements indicated that the ZnO films have a high transparency in the visible range (~90 %), which remained constant with thickness. Morphological evolution measurements confirmed that the thinner ZnO film consist mostly of a porous layer which became homogeneous and compact to increase the thickness. Photoluminescence measurements exhibit a strong ultraviolet (UV) emission, and the emission intensity was improved with thickness due to crystallinity enhancement.
Preparation, Microstructure and Properties of Ti-6Al-4V Rods by Powder Compact Extrusion of TiH2/Al60V40 Powder Mixture
Authors: Luo Yi Fei , Xie Yue Huang , Liang Jia Miao , Zhang De Liang
Published: June 2018

Ti-6Al-4V (wt.%) alloy rods were prepared successfully using a low-cost and short powder metallurgy process that involves mixing TiH2 and Al60V40 powders, compacting the powder blend and extruding the powder compact at elevated temperatures. The microstructure and mechanical properties of Ti-6Al-4V alloy and the effects of particle size, oxygen content and heat treatment on them were investigated. The results showed that the microstructure and homogeneity of the extruded rods were strongly affected by the particle size of TiH2/Al60V40 powder blends. By changing tumbler mixing into low-energy ball milling, the TiH2/Al60V40 particle sizes decreased, and the volume fraction of undissolved V rich particles in the microstructure of the extruded rod substantially decreased from 8.6% to zero. High yield strength and ultimate tensile strength of 1154 and 1353 MPa respectively with a moderate elongation to fracture of 3.6% are achieved with the Ti-6Al-4V rod prepared by using the powder blend. The extruded Ti-6Al-4V rod prepared using the ball milled powder had a very high strength, but limited ductility due to a high oxygen content. Solution treatment and aging slightly increase the strength of Ti-6Al-4V rods at the cost of dramatic decrease of ductility.
The Challenges Associated with the Formation of Equiaxed Grains during Additive Manufacturing of Titanium Alloys
Authors: St John David H. , McDonald Stuart D. , Bermingham Michael J. , Mereddy Sri , Prasad Arvind , Dargusch Matthew
Published: June 2018

It is well established that columnar grain structures usually form when metal alloys are used to additively manufacture components. A challenging goal is to produce an equiaxed grain structure throughout the component to remove anisotropy and refine the grain size in order to improve its mechanical performance. The high cooling rates and associated high temperature gradients are the main reasons for the formation of columnar grains via epitaxial growth of each added layer of material. There appear to be limited strategies for promoting equiaxed nucleation of grains. In addition to cooling rate and temperature gradient, we explore other variables such as the potency of natural or added inoculant particles and the composition of the alloy, and their possible impact on the nucleation of equiaxed grains. Although changing the composition can help, finding a suitably potent nucleant particle is a major challenge. Operating parameters can also influence the microstructure and optimization to produce equiaxed grains may be possible. The limitations of these strategies and possible ways to overcome them are evaluated.
The Molecular Orbital Approach to Titanium Alloy Design
Authors: Morinaga Masahiko
Published: June 2018

The molecular orbital approach to alloy design is reviewed in this paper. This approachis based on the electronic structure calculations by the DV-Xα cluster method. New alloyingparameters are obtained for the first time by the calculations of titanium alloys and used for theprediction of phase stability and alloy properties. For example, it is shown that any titanium alloycan be classified into either the α, or α+β, or β type from the alloy composition by using the newalloying parameters. The corrosion resistance is also treatable along this approach. This theoreticalapproach is useful for the practical design of biomedical titanium alloys.
First Principle Study of Ti50Al50 Alloys
Authors: Modiba Rosinah , Chauke Hasani , Ngoepe Phuti
Published: June 2018

The study on the Ti-based materials and its application has been the interest of many research industries. These alloys are known to have an ordered B2 phase at high temperatures and transform to a stable low B19 martensitic phase. First principle approach has been used to study L10, B32, B2 and B19 Ti50Al50 alloys and the results compared well with the available experimental data. The equilibrium lattice constants are in good agreement with the experimental values (within 3% agreement). Furthermore, the elastic constants of these alloys are calculated, and revealed stability for L10 and B19 structures, while B2 and B32 gave C′<0 (condition of instability).
Mesenchymal Stem Cells Adhesion on Micro-to-Nano-Scaled Hierarchical Ti Implants Fabricated by Powder Metallurgy and Anodization
Authors: Zhao Da Peng , Zhang Yuan , Nie He Min , Yan Ming
Published: June 2018

The osseointegration of titanium (Ti) implants highly depends on their surface properties, including roughness, wettability and composition. Ti surfaces with micron-scale roughness have demonstrated more rapid bone apposition compared with polished ones. Besides, Ti implants with nanostructured surface also exhibit better cell adhesion and proliferation behavior. However, the optimal surface for bone regeneration is still unknown, partly due to the difficulty in fabricating surfaces with highly reproducible micron-and nanotopography. In this study, Ti implants with two hierarchies of roughness were fabricated by powder metallurgy, followed by anodization treatment to obtain self-assembled TiO2 nanotubes on the micro-roughened surface. X-ray diffraction (XRD), scanning electron microscopy (SEM), 3D Laser Scanning Microscope (3D LSM), and fluorescence microscope were used to investigate the properties of the samples. Ra of the powder metallurgy surface was about 5 μm, while, nanotubes of around 100 nm in diameter were observed after the anodization process. Compared with the reference samples, i.e., the ones with either smooth or single-level-structure surfaces, the ones with micro-to-nanoscaled hierarchical topography exhibited lower contact angle, higher protein adsorption and significantly improved mesenchymal stem cells (MSCs) early adhesion.
Effects of Open Atmosphere Solutionizing Treatment on the Microstructural and Mechanical Properties of Porous 60NiTi Parts
Authors: Khanlari Khashayar , Ramezani Maziar , Kelly Piaras , Hayat Muhammad Dilawer , Cao Peng , Neitzert Thomas Rainer
Published: June 2018

Titanium alloys have been widely used for medical implants due to their good biocompatibility and excellent corrosion resistance. 60NiTi, an intermetallic nickel-titanium alloy containing approximately 60 wt.% Ni and 40 wt.% Ti, is a promising material for medical components such as implants and prostheses. 60NiTi is hard with good biocompatibility, highly corrosion resistant and has relatively low stiffness. In this study, conventional press-and -sinter method was employed to produce porous 60NiTi parts suitable for general bone replacement applications such as spinal and cranial inserts. The effect of solution treatment in a non-protected furnace and water quenching on the mechanical and microstructural properties of 60NiTi were investigated. It was found that this procedure produces a hard integral ceramic layer, a complex mixture of nickel and titanium oxide compounds, on the surface and around the pores of 60NiTi parts. Results showed that this heat treatment procedure causes the embrittlement of the parts due to an increase in oxide content. However, the produced ceramic surface can also enhance the resistance to corrosion, which is beneficial from a biocompatibility point of view.
Mechanical Alloying of Ti-Based Materials
Authors: Chikwanda Hilda , Mahlatji L.
Published: June 2018

Mechanical alloying (MA) is a simple and versatile dry powder processing technique that has been used for the manufacture of both equilibrium and metastable phases of commercially useful and scientifically interesting materials. It owes its origin to an industry need to develop a nickel-based super alloy for gas turbine applications that had both oxide dispersion strengthening and precipitation hardening. This far-from equilibrium powder metallurgy processing technique involves fracturing, welding and re-welding of powder particles in a High Energy Ball Mill (HEBM). MA is an economically viable process with important technical advantages. Its utmost advantage is in the synthesis of novel alloys, e.g., alloying of ordinarily immiscible elements, that is not possible by any other technique. As MA is a completely solid-state processing technique, the limitations imposed by phase diagrams do not apply to it. The MA process is capable of producing different types of metastable effects in a variety of alloy systems. Some of the metastable effects achieved by MA are solid solution formation and amorphisation. MA has the possibility of producing superior and enhanced materials than those produces by conventional methods. In this work a review of MA and its present and potential applications for Ti-based materials are presented.
Contact Melting of Aluminum-Silicon Structures under Conditions of Thermal Shock
Authors: Skvortsov Arkady A. , Zuev Sergey M. , Koryachko Marina V.
Published: June 2018

The work is devoted to the study of contact melting in the Al-Si system, which is an aluminum film deposited on a silicon single-crystal substrate. The impulse action of high-density currents (j> 8.1010 A / m2) passing through an aluminum film is analyzed. It was found that under the considered electric heat loads in the system, the degradation processes associated with the appearance of a molten aluminum zone and subsequent contact melting in the metal-semiconductor system develop. From the analysis of contact melting processes, a technique for estimating the coefficients of multiphase diffusion in the system under consideration is a thin aluminum film-single-crystal silicon substrate.
Preparation of a Semiconductor Film with the Aid of a Superionic
Authors: Rakhymbekov Aitbai , Idrisova Aigul , Saduakasova Rosa , Nurbosynova Gulmira , Turlybekova Meruert
Published: June 2018

The actuality of the topic chosen by us lies in the fact that the effect of oxygen on the properties of semiconductors has not been studied sufficiently well, mainly because of the imperfections of methods for controlling the oxygen content in semiconductor materials. Almost in all such materials, oxygen is present either as an uncontrolled impurity or as a doping additive, or, in the case of oxide semiconductors, as in our case with a semiconductor film of vanadium dioxide, is part of the compound. The oxygen contained in the semiconductor film significantly affects the property of the material: in the first two cases, this influence is determined by the amount and state of the impurity, in the third - by the composition, or by the stoichiometry of the oxide compound. We set a goal to develop a technique for obtaining a semiconductor film of vanadium dioxide in a controlled atmosphere of oxygen. The semiconductor film thus obtained is used in holography to record and store optical information. For the production of VO2 films by oxidation in a controlled atmosphere, an apparatus including an oxygen pump based on stabilized zirconia dioxide has been developed. The principle of operation and the main characteristics of such an oxygen pump is the unique application of the property of the superionics - to carry through itself exclusively oxygen ions under the influence of a constant current field and a high temperature. The technique developed by us for obtaining a semiconductor film of vanadium dioxide in a controlled atmosphere of oxygen has no analog.
Ground Ancher Produced by Electric Discharge Technology, as Monolithic Reinforced Concrete Structure
Authors: Sokolov Nikolai S.
Published: June 2018

The construction of territories with problematic engineering and geological conditions in the presence of unstable, crossed relief is a complex geotechnical task. Therefore, the main purpose of the work is to study the features of the ground anchor, which is made by electric discharge technology, as a monolithic reinforced concrete structure. The questions related to the provision of safe methods of construction and erection works for the erection of any facility in such territories are related to a multifactor problem connected, primarily with the need to develop special geotechnical technologies tied to real engineering and geological conditions, loads from previously erected buildings and structures and, secondly, the actual implementation of them on a particular construction site. The case considered in the article from the geotechnical practice of construction of the facility is confirmed by the fact that due to the availability of modern design and construction and construction works, it is possible to solve any complex problems related to the issues of ensuring the stability of slopes.
Polyelectrolytes Efficiency in Grout Property Regulation
Authors: Agzamov Farit , Kabdushev Arman , Ismailov Abdulahat , Betzhanova Aizhan , Karabaeva Asel
Published: June 2018

Relevance of this study is concluded in the fact that high quality cementing requires regulation of the cement grouts’ properties using various chemicals. The objective of the work is based on the study of polyelectrolytes’ application efficiency used for regulation of cement slurries’ properties. In order to conduct the research the authors used the devices meeting the API requirements. Properties of cement slurry and cement were evaluated according to GOST 1581-96. In order to study the gas show emergence mechanism during the procedure of WOC (waiting on cement), the authors used a special experimental plant. It has been found that high efficiency during the research was shown by water soluble cationic polyelectrolyte (WSC-402), belonging to the class of cationic polymers. Also the paper considers its analog – cationic polyelectrolyte (PAK) released under the trade mark Praestol. Studying the mechanism of polyelectrolyte additives’ effect on cement showed that the chemicals can slow down the hydrating reaction of С3А in cement-water suspension, and prevent from the growth of gel strength of the grout, which causes drop in hydrostatic pressure of the cement grout column, provoking gas shows.
The Preparation of Highly Dispersed Pd/Gamma-Al2O3 Catalyst: The Relation of Attracting-Repelling Force and Pd Dispersion
Authors: Byun Mi Yeon , Kim Ji Sun , Park Jeong Wook , Park Dae Won , Lee Man Sig
Published: June 2018

The purpose of this study is to present the effect of attracting-repelling force on the dispersion and particle size of palladium (Pd) between Pd and γ-Al2O3. The Pd supported on γ-Al2O3 catalyst were prepared by deposition-precipitation method with two different ways. From the CO-Chemisorption results, Pd/γ-Al2O3 (R2-FM) catalyst has the highest Pd dispersion of 43.16%. The results showed that particle size and distribution of Pd influenced by the surface charge state of γ-Al2O3 support, indicating relation of attracting-repelling force between Pd precursor and γ-Al2O3 surface.
Effect of Solvents on Cadmium-Doped Zinc Oxide Nanoparticles Synthesised by Sol-Gel Technique
Authors: Nalumaga Hellen , Kim Kyung Nam , Kim Won Duck , Hwang Dong Ha
Published: June 2018

In this study, a comparative investigation of the effect of two solvents on cadmium-doped zincoxide (Cd-ZnO) nanoparticles synthesized via the sol-gel method is presented and discussed. Zinc acetate was used as the precursor with ethanol and methanol as solvents, and cadmium nitrate tetrahydrate was used as the cadmium dopant source. The properties of the synthesized ZnO nanoparticles were examined by XRD, SEM, TEM,TG-DTA and UV-vis spectroscopy (UV-vis). It was found that the crystallite sizes of the ZnO nanoparticles ranged from 35 to 50nm and had spherical shapes, and that the particle size decreased with Cd doping. Consequently, absorbance spectra showed that the Cd-doped ZnO nanoparticles extended the light absorption properties of the material into the visible region. Furthermore, the ZnO nanoparticles synthesized with ethanol had a relatively smaller sizethan methanol which resulted in higher absorbance of ZnO synthesized with ethanol than methanol.
The Preparation and Properties of Clay Bonded Silicon Carbide by Using Silicon Carbide Dusting Powder
Authors: Xu Shao Chun , Wang Zi Jing , Zhang Ya Ming , Zhi Qiang , Wang Xu Dong , Yang Jian Feng
Published: June 2018

In this paper, clay bonded silicon carbide was prepared through pressureless sintering process with silicon carbide dusting powder as raw materials and clay as sintering additive. The effects of the ball-milling method, sintering temperature and clay contents on the density, microstructure and mechanical properties of clay bonded silicon carbide refractory were studied. The planetary ball-milling was a good method to improve the density of the green body, and the density was increased simultaneously with an increase of the clay content. The liquid phase derived from low-melting eutectic mixtures of clay could prevent the superlative oxidation of silicon carbide. The mass increment of sintered samples decreased firstly and then increased at the sintering temperature range from 1250 to 1500 °C. The open porosity of samples decreased with the clay addition at a content range from 10 to 30 wt.%. The bending strength of the samples decreased firstly and then increased with the clay addition increasing. The optimum condition for preparing clay bonded silicon carbide with silicon carbide dusting powder was sintering at 1350 °C with 20 wt.% clay, and the obtained sample with a porosity of 24% achieved the bending strength of 78±7 MPa.
Electric Field Simulation of Typical Defects in the Epoxy/Paper Composites Insulated Tubular Bus
Authors: Li Cheng Lei , Liu Rui , Li Peng Hu , Li Wen Pei , Gao Nai Kui
Published: June 2018

Many failures had occurred in operation of insulated tubular bus because of the poor product quality, and its primary reason was that some defects were led into the insulation system in the production, then the local electric field would increase and then result in partial discharge, which could accelerate the aging and even breakdown of the materials. In this research, a 1/4 three-dimensional model was established according to the actual structure of insulated tubular bus, and the simulation results obtained from static electric field and quasi-static electric field were compared. Besides, the electric field distribution of insulated tubular bus with typical defects was simulated based on ANSYS software. These three defects were air void, moisture and damage of semi-conducting layer. The simulation results showed that the electric field distribution of insulated tubular bus with typical defects was more suitable with quasi-static electric field simulating. The maximum electric field value was different with different defects, and dependent on the location and size of defects.
Preparation and Characterization of Nanosize ZrO2 Particle for Highly Refractive Index Nanocomposite Depending on Zirconium Precursor and Concentration
Authors: Park Jeong Min , Lee Hee Seon , Lim Hyung Mi
Published: June 2018

The ZrO2 nanoparticles for highly refractive index nanocomposite are synthesized according to reaction temperature, zirconium precursor concentration, and kinds of precursor such as zirconium iso-propoxide (ZIP) and zirconium n-propoxide (ZNP). At lower reaction temperature the monoclinic phase is formed, whilst higher temperature favors the tetragonal and cubic phases. As the precursor concentration increased, the particle size of ZrO2 nanoparticle slightly increased. TEM images prove that the ZrO2 nanoparticles are spherical and monodisperse with a diameter of about 4 nm. The synthesized ZrO2 was modified methacryloxy propyltrimethoxy silane (MPS) for dispersibility in organic solvent. Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) illustrate that MPS are chemically attached to the surface of the ZrO2. The ZrO2 synthesized from ZNP and ZIP dispersed in o-phenylphenoxyethyl acrylate (OPPEA) is the highly transparent and the refractive index of this nanocomposite is 1.649 and 1.670, respectively.
The Preparation and Properties of Alumina Ceramics through a Two-Step Pressureless Sintering Process
Authors: Yuan Chang Suo , Wang Zi Jing , Zhi Qiang , Zhang Ya Ming , Wang Xu Dong , Yang Jian Feng
Published: June 2018

In this paper, a high-dense alumina ceramics were prepared through the two-step pressureless sintering process with high-purity alumina powder as raw materials and high-purity MgO as sintering aids. The effects of the sintering temperature in the first-step (T1) and the soaking time (t) in the second sintering step (T2) on the density, microstructure and mechanical properties of the alumina ceramics were studied. The results indicated that the relative density increased with the increase of T1 temperature whereas it increased and then decreased with the increase of MgO content. Higher T1 temperature and extended soaking time caused larger grain size, which accompanied with the Ostwald ripening of the grain and led to non-uniformity of grain size distribution. The addition of MgO was beneficial to the decrease in grain size due to pinning effect of the second phase. For samples with shorter soaking time, sintering with higher T1 temperature led to better mechanical properties because of its high density. However, for the long soaking time, all samples after sintering at different T1 temperature were fully-densified, so the grain size become to the dominant factor of strength, thus samples with lower T1 temperature exhibited better mechanical properties due to the refinement grain. Excessive addition of MgO resulted in defects, by which the strength increased firstly and then decreased slightly with the increased MgO content. For the samples with 2.5wt.% MgO, the optimum condition for the two-step pressureless sintering was T1=1450°C and T2=1400°C for 20h, and the obtained sample achieved the relative density of 96% and the strength of 507±32MPa.
Influence of Compaction Pressure on Density, Bending Strength, and Microstructures of Al2O3-SiC-ZrO2 Ceramic Matrix Composites with Nb2O5 Additives
Authors: Natalia Dewi Lestari , Wijanarko Risly , Angela Irene , Sofyan Bondan Tiara
Published: June 2018

Ceramic matrix composites (CMCs) are known to have high hardness, temperature and corrosion resistance, while being comparatively lightweight. One of many external factors that influence the mechanical properties of CMC is the compaction pressure given during fabrication process. Generally, greater amount of applied compaction pressure will result in improved final product density and bending strength. In this research, a type of CMCs was fabricated using Al2O3, SiC, and ZrO2 powder mixed with Nb2O5 additive of 81Al2O3-10SiC-5ZrO2-4Nb2O5 wt. % composition. Fabrication was done through mixing, compacting, and sintering process. Compaction was performed at 257, 308, and 359 MPa and finished with sintering process at 1400 °C for 4 h. Final samples were characterized by density measurement, 3-point bending strength testing, XRD for phase investigation, and microstructure observation using SEM-EDS. Results showing that samples with 308 MPa compaction pressure possessed the highest density and bending strength of 3.29 gr/cm3 and 14.91 MPa, respectively. These numbers however, declined on samples with higher compaction pressure of 359 MPa due to the formation of porosities caused by entrapped gas that failed to exit the sample of which compaction pressure was considered to be overwhelmingly high.
AC Conduction in Polyaniline Emeraldine Salt-Graphite Pellets
Authors: Manding Kenny Vienne S. , Lopez Jay Edson S. , Tapia Alvin Karlo Garcia
Published: June 2018

The conduction characteristics of Polyaniline emeraldine salt-Graphite (PAni-ES/Gr) pellets were characterized using an impedance analyzer. The pellets were prepared with varying mass fractions of PAni-ES and Gr. FTIR spectra have the stretching vibrations for PAni-ES and absence of peaks for Gr. PAni-ES showed aggregated particles while Gr appeared as sheets and flaky structures. The composition of the pellets was differentiated in the AC conductivity values. The critical frequency representing the transition from frequency-independent to frequency-dependent conductivity decreases with increasing Gr content. Lastly, the frequency-dependent conductivity behavior follows power-law behavior reflecting possible hopping mechanisms and random resistor-capacitor network.
Synthesis and Characterization of Aluminum Matrix Composites Reinforced with SiC-Graphene Core-Shell Nanoparticles
Authors: Zhang Jiang Shan , Chen Zhi Xin , Zhao Jing Wei , Jiang Zheng Yi
Published: June 2018

Graphene has been proved to be an excellent enhancer in metal matrix composites. Core-shell structured SiC nanoparticles and graphene nanosheets (GNSs) were fabricated and incorporated into aluminum matrix using ball milling in the current study. Graphite powder was exfoliated into thin GNSs, which are flexible to wrap SiC nanoparticles. The ductile aluminum particles were firstly flattened and then repeatedly welded and fractured into equalized particles during the ball milling of Al alloy-SiC-GNSs composite powder, which were observed using scanning electron microscopy and X-Ray diffraction. SiC-GNSs were embedded and dispersed into the aluminum matrix during the milling process.
Electrohydrodynamic (EHD) Bioprinting of Polycaprolactone Scaffolds
Authors: Altun Esra , Akyol Sibel , Ekren Nazmi , Kilic Osman , Gunduz Oguzhan
Published: June 2018

This study is combined a 3D printing and Electrohydrodynamic (EHD) methods to fabricate a 3D PCL scaffolds for tissue engineering. Various kV values were applied to the different PCL solutions to investigate the effect of the voltage on scaffolds. The morphology of 3D-EHD printed PCL scaffolds were characterized by an Optical Microscope. 10 wt.% PCL up to 3 kV was obtained best sample to use for tissue engineering scaffolds.
Comparative Evaluation of Forward Voltage Degradation due to Propagating and Converted Basal Plane Dislocations
Authors: Nishihara Yoshitaka , Kamei Koji , Momose Kenji , Osawa Hiroshi
Published: June 2018

This study investigated the relationship between the forward voltage degradation induced by SSF expansion and (a) BPD density in substrates and epitaxial layers of SiC, and (b) the temperature during the application forward current to the pin diodes. The Vf shift caused by the BPDs in the drift layer simply depended on the BPD density. However, no correlation was initially observed between the Vf shift and BPD density in the substrate; instead a strong correlation was observed between the Vf shift and the device temperature measured when applying the current stress. Thus when we selected samples which show the same temperature at that time, a correlation was observed between the Vf shift and the BPD density in the SiC substrate, with the slope corresponding to the former, drift layer relationship. Therefore, due to the high BPD density in the SiC substrate, suppressing the Vf shift due to BPD density in this region is highly important, and a combination of approaches is therefore proposed in order to reduce the overall forward voltage degradation.
Growth Conditions and In Situ Computed Tomography Analysis of Facetted Bulk Growth of SiC Boules
Authors: Arzig Matthias , Salamon Michael , Uhlmann Norman , Johansen Bertil A. , Wellmann Peter J.
Published: June 2018

Two 3inch SiC boules were grown in a PVT setup using source material of different packing density. During the growth, in-situ computed tomography of the growing boules showed differences in the development of the growth interface. A slightly bent growth interface was found for the smaller packing density. For the higher packing density the resulting crystal exhibits the onset of 6 pyramidal facets on its flanks. Besides that, strong anisotropic lateral growth was found on its (000-1) facet. Numerical simulations show an impact of the powder on the thermal gradient in the growth cell and therefore on the supersaturation. It is discussed that a higher supersaturation can account for the anisotropy in the growth rate of the [1-100] and the [11-20] direction.
High-Mobility SiC MOSFETs Using a Thin-SiO2/Al2O3 Gate Stack
Authors: Urresti Jesus , Arith Faiz , Vassilevski Konstantin , Tiwari Amit Kumar , Olsen Sarah , Wright Nick G. , O'Neill Anthony G.
Published: June 2018

We report the development of a low-temperature (600 °C) gate oxidation approach to minimize the density of interface traps (DIT) at the SiC/SiO2 interface, ultimately leading to a significantly higher channel mobility in SiC MOSFETs of 81 cm2·V-1·s-1, >11x higher than devices fabricated alongside but with a conventional 1150 °C gate oxide. We further report on the comparison made between the DIT and channel mobilities of MOS capacitors and n-MOSFETs fabricated using the low-and high-temperature gate oxidation.
Surface Engineering of SiC through Nanogrinding and CMP
Authors: Vacassy Robert , Gibson A. , Titov A. , Walters A. , Shindo T.
Published: June 2018

Processing silicon carbide (SiC) wafers to achieve an epi-ready quality finish typically requires many lapping and a very long chemical mechanical polishing (CMP) steps. In this paper, we report the thinning down of 6” SiC wafers to sub-nanometer surface finish in less than two hours. Three process steps (rough grinding, nanogrinding and CMP) are involved. Rough grinding thins down the wafer with fast feed rate and maintain excellent flatness. Nanogrinding allows the surface finish to improve down to a few nanometers. The last CMP step provides high planarization efficiency. Overall the throughput of SiC processing is substantially increased over current market solutions.
H3TRB Test on 650 V SiC JBS Diodes
Authors: Zorn Christian , Hoffmann Felix , Hanf Michael , Kaminski Nando , Allerstam Fredrik , Konstantinov Andrei , Neyer Thomas
Published: June 2018

Reliability characterization of SiC devices is an ongoing activity. For this work, 650 V SiC JBS diodes in TO247 housings were tested in H3TRB. After a test period of 4000 hours none of the devices had failed during the test and only two out of sixteen devices had failed during blocking curve measurements performed at intermediate time steps. This is significantly better performance than many silicon devices offer today. The failure spots of the failed devices were detected at the edge of the main junction appearing as semi-circular cavities in the aluminum metallization. All other devices did not even show deviations from their original blocking curves.