Mechanical properties of friction stir welded armor grade Al–Zn–Mg alloy joints

The influence of different welding speeds and rotary speeds on the formation and mechanical properties of friction stir weld joints of armor grade aluminum alloy was presented. The developed weld joints were characterized by bend tests, micro-hardness tests, tensile tests, optical and scanning electron microscopies. Mechanical properties (i.e., micro-hardness, ultimate tensile strength and elongation to fracture) increased with the increase in rotary speed or decrease in welding speed. The effect of welding speed on micro-hardness of heat affected zones was more profound than the rotary speeds. The welding speeds and rotary speeds influenced the mechanical properties and their effects on various mechanical properties of the friction stir welded joints can be predicted with the help of regression models.     

Integrated safety assessment of Indian nuclear power plants for extreme events: Reducing impact on public mind

Nuclear energy professionals need to understand and address the catastrophe syndrome that of late seems to be increasingly at work in public mind in the context of nuclear energy. Classically the nuclear power reactor design and system evolution has been based on the logic of minimization of risk to an acceptable level and its quantification based on a deterministic approach and backed up by a further assessment based on the probabilistic methodology. However, in spite of minimization of risk, the reasons for anxiety and trauma in public mind that still prevails in the context of severe accidents needs to be understood and addressed. Margins between maximum credible accidents factored in the design and the ultimate load withstanding capacities of relevant systems need to be enhanced and guaranteed with a view to minimize release of radioactivity and avoid serious impact in public domain. A more realistic basis for management of an accident in public domain also needs to be quantified for this purpose. Assurance to public on limiting the consequences to a level that does not lead to a trauma is something that we need to be able to credibly demonstrate and confirm. The findings from Chernobyl reports point to significant psychological effects and related health disorders due to large scale emergency relocation of people that could have been possibly reduced by an order of magnitude without significant additional safety detriment. A combination of probabilistic and deterministic approaches should be evolved further to minimize consequences in public domain through enhancing safety margins and adding greater precision to quantitatively predicting accident progression and its management. The paper presents the case studies of the extreme external event such as tsunami and its impact on the coastal nuclear plants in India, the containment integrity assessment under the extreme internal event of over-pressurization and aircraft impact along with hydrogen deflagration/detonation-induced loadings. These are at the moment extremely burning issues due to the severe accidents of Fukushima, Chernobyl and Three Mile Island reactors. In the present day context identifying the extreme loadings in a separate category and the corresponding margin assessment is necessary in addition to the implementation of the mitigation and upgraded safety measures. Further, the paper attempts to address the question of public trauma in the event of a serious nuclear reactor accident, a need that has been felt in view of the recent Fukushima and earlier Chernobyl accidents and the resulting large scale relocation due to the present deficient policies and the inherent limitations of Linear No Threshold (LNT) principle.     

THEORETICAL EARTH TEMPERATURE PROFILES FOR DIFFERENT SOILS AND SOIL CONDITIONS

The annual temperature variations in earth with depth from the surface offers, by its natural characteristics, a phase lag and reduced variation in the maximum and minimum temperatures. The temperature profiles vary for different soils and soil conditions. Soil temperatures are found to be an explicit function of soil thermal properties, particularly the thermal diffusivity. The earth temperatures stabilize at certain depth, where the annual swings in temperature are negligible and this stabilizing depth varies for different soils. A simple first harmonic approximation method has been used to predict the temperature variations as a function of depth and time for different soils (ordinary light soil, heavy soil, organic soil and sand) and soil conditions (dry, damp and wet). The results are a helpful indicator for deciding external design temperatures for the design of earth sheltered or ground coupled spaces.     

Deposition and characterization of diamond-like nanocomposite coatings grown by plasma enhanced chemical vapour deposition over different substrate materials

Diamond-like nanocomposite (DLN) coatings have been deposited over different substrates used for biomedical applications by plasma-enhanced chemical vapour deposition (PECVD). DLN has an interconnecting network of amorphous hydrogenated carbon and quartz-like oxygenated silicon. Raman spectroscopy, Fourier transform–infra red (FT–IR) spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) have been used for structural characterization. Typical DLN growth rate is about 1  ${\upmu} $ m/h, measured by stylus profilometer. Due to the presence of quartz-like Si:O in the structure, it is found to have very good adhesive property with all the substrates. The adhesion strength found to be as high as 0·6 N on SS 316 L steel substrates by scratch testing method. The Young’s modulus and hardness have found to be 132 GPa and 14· 4 GPa, respectively. DLN coatings have wear factor in the order of 1 × 10^???7 mm ³ /N-m. This coating has found to be compatible with all important biomedical substrate materials and has successfully been deposited over Co–Cr alloy based knee implant of complex shape.     

Characterization and in vitro and in vivo evaluation of cross-linked chitosan films as implant for controlled release of citalopram

The aim of the present study is to develop cross-linked chitosan (CH) films that can release drug over an extended period of time and that too in a controlled manner. A solution of different percentages of CH, is prepared in 1% lactic acid, followed by addition of citalopram (CTP) and then reacted with increasing amounts of glutaraldehyde (GL) to obtain films with different cross-linking densities. Prepared films are characterized for their physical and mechanical properties. The films are then subjected to in vitro drug release studies using pH 7·4 phosphate buffer saline (PBS) as dissolution medium and cumulative amount of drug released is calculated. Kinetic analysis of drug release is performed using Power law model and Higuchi’s model. With increase in concentration of CH, water absorption capacity and mechanical strength are increased; whereas, water vapour permeability and elasticity of the films are decreased. The effect of cross-linking agent, GL, is such that with an increase in the amount of GL, water vapour permeability, water absorption capacity and elasticity of the films are decreased; whereas, mechanical strength increased to some extent and then decreased. In vitro release studies indicate that films containing 3% CH, cross-linked with 2–3% GL and films containing 4% CH, cross-linked 1% GL are able to sustain the drug release for a prolonged time along with releasing almost complete drug in a desired period. Out of these batches, films containing 3% CH, cross-linked with 2–3% GL are having sufficient strength, water vapour permeation, water absorption capacity and elongation at break for implantation purpose. The in vitro degradation studies and histopathological studies were carried out with a sample film (batch C3 as in table 1) in rabbit model. In vitro degradation study indicates that the films maintained their integrity for desired implantation. The histopathological studies under optical microscope indicates that on implanting, there is no evidence of any inflammation, any foreign body granuloma or any necrosis or hemorrhage. Tissue configuration remains unaltered after 30 days of implantation. So, it can be suggested that cross-linked CH films of above said composition can be used as implant for long term application in depression and related disorders.     

Electrochemical potentials of layered oxide and olivine phosphate with aluminum substitution: A first principles study

First-principles prediction of enhancement in the electrochemical potential of LiCoO₂ with aluminum substitution has been realized through earlier experiments. For safer and less expensive Li-ion batteries, it is desirable to have a similar enhancement for alternative cathode materials, LiFePO₄ and LiCoPO₄. Here, we present first-principles density functional theory based analysis of the effects of aluminum substitution on electrochemical potential of LiCoO₂, LiFePO₄ and LiCoPO₄. While Al substitution for transition metal results in increase in electrochemical potential of LiCoO₂, it leads to reduction in LiFePO₄ and LiCoPO₄. Through comparative topological analysis of charge density of these materials, we identify a ratio of Bader charges that correlates with electrochemical potential and determine the chemical origin of these contrasting effects: while electronic charge from lithium is transferred largely to oxygen in LiCoO₂, it gets shared by the oxygen and Co/Fe in olivine phosphates due to strong covalency between O and Co/Fe. Our work shows that covalency of transition metal–oxygen bond plays a key role in determining battery potential.     

TRANSIENT STABILITY SIMULATION OF UNBALANCED LARGE SCALE POWER SYSTEMS

ABSTRACT

Conventional transient stability analysis is performed on the basis of a balanced system representation. However, a typical power system may be unbalanced due to a variety of reasons, and the computations of sequence quantities due to these unbalances is necessary in order to facilitate the application of countermeasures. This paper presents an algorithm for the simulation of large scale power system dynamics under unbalanced operating conditions. This algorithm finds potential application in the simulation of systems with abnormal loads such as arc furnace and traction, and also in the realistic simulation of unbalanced faults in bulk power transmission systems.     

Preparation and bioactivity Of SiO2 functional films on titanium by PACVD

SiO2 functional films were deposited on the surface of titanium by plasma assisted chemical vapour deposition（PACVD） and the composition of films was studied by XPS. Samples deposited with SlOE films were immersed in different concentration simulated body fluid（SBF） for biomimetic deposition of hydroxyapatite（HA）. The results show that SiO2 functional films deposited on titanium surface with PACVD have good bioactivity. Hydroxyapatite is formed while titanium coated with SlOE is immersed in simulated body fluid for seven days.     

Retardation of Cs+ and Cl− Diffusion Using Blended Cement Admixtures

Diffusion of cesium chloride through thin plates of hardened cement pastes was studied. Blast-furnace slag and condensed silica fume were used as blending admixtures in an attempt to retard the diffusion of cesium and chloride ions. The curing and diffusion temperatures were varied from 27° to 60°C, and the water/solid ratio was varied from 0.30 to 0.40. Results indicate that the cesium ion diffuses more slowly than the chloride ion in hardened cement paste systems. Blending admixtures caused a further reduction in diffusivity for both ions, which is important for preventing corrosion or restricting radionuclide transport.