CONSTRUCTION OF ASYMMETRICAL RESPONSE SURFACE DESIGNS

The paper proposes several methods for constructing both rotatable and non-rotatable asymmetrical response surface designs. The idea of modified rotatable design is introduced. In most of the experiments conducted by the experimenter it is not necessary that all the factors under study may have equal number of levels The methods proposed will have wider use under these circumstances

Formation of Silicon Carbide Whiskers from Organic Precursors Via Sol-Gel Method

Silicon Carbide (SiC) was synthesized by carbothermal reduction of silica precursor and carbon precursor. The silica precursor was obtained from tetraethoxysilane. Sucrose was used as carbon source. Tetraethoxysilane (TEOS) was hydrolyzed in acidic water (pH = 2). The molar ratio of TEOS-H2O-EtOH was taken as 1:8:2 in the sol-gel processing. Hydrolysed silica sol was polymerized with sucrose to incorporate carbon precursor into the silica network. The gel thus obtained was dried in an oven at 70 oC and at 100 oC. The solid mass obtained on drying was heat treated at 1000 °C in nitrogen atmosphere to obtain the black glass. It was characterized by FTIR, SEM and TGA. The black glass was further heated to 1500 oC in argon to yield silicon carbide. this resulted in formation of β-SiC whiskers

Studies on synthesis and Reduction of Graphene Oxide from Natural Graphite by using Chemical Method

Graphene is a material with rapidly growing interest. It consists of flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice and is basic building block for all graphitic materials. Interest in Graphene is because of its excellent mechanical, electrical, thermal, optical properties and its very high specific surface area. Studies have been performed on wet oxidation of natural graphite by using Modified Hummers Method followed by exfoliation and reduction in order toВ  synthesise graphene from Graphite Oxide (GO). Acid route has been followed for oxidation whereas reduction has been carried out in water with hydrazine hydrate and Sodium Borohydrate. It results in to a material with characteristics that are comparable to those of pristine graphite. The reaction at every step has been characterized by using FTIR, TGA, XRD, Raman spectroscopy and surface area measurement

Separation of Cenospheres from Fly Ashes by Floatation Method

Fly-ashes are non-combustible mineral residues which are produced from coal in thermal power plants. Four different types of fly ashes were collected from different power station in Gujarat. Characterization through SEM shows that fly ash contains cenosphere i.e. gas bubble containing ceramic particle independent of their bulk density. Floatation technique was used for the separation of cenosphere from fly ash. Two solvents with extremely different densities were used for the separation of cenospheres. All methods gave approximately yield of less than 1% cenosphere in fly ash. Color of cenospheres varied from gray to almost white and the value of density range from 0.4 – 0.8 g/cc. Further, chemical composition analysis revealed that cenospheres do not contain any high concentration of hazardous elements

Synthesis and Characterization of Hydroxyapatite Nanoparticles using Sol-Gel Method

Hydroxyapatite (HAp) is a unique material having high adsorption capacity of heavy metals, high ion exchange capacity, high biological compatibility, low water solubility, high stability under reducing and oxidizing conditions, availability and low cost. Hydroxyapatite nanoparticles have been synthesized by Sol-gel method using Calcium nitrate tetrahydrate [Ca(NO3)2•4H2O] and Phosphorus pentaoxide (P2O5) as starting reactants. The addition of Phosphorus pentaoxide to Calcium nitrate tetrahydrate was carried out slowly with simultaneous stirring. After addition, solution was aged for 10 minutes for maturation. The precipitate was dried at 80 °C overnight and further heat treated at 550 °C for 2 hours. The dried and calcined particles were characterized by X-ray diffractometry, Fourier transform infra-red spectroscopy and Thermo gravimetric analysis. The particle size and morphology were studied using transmission electron microscopy. TEM examination of the treated powders displayed particles of polygon morphology with dimensions 20-50 nm in length. The FT-IR spectra for sample confirmed the formation of hydroxyapatite

Studies on Fabrication and Characterization of Nanoclay Reinforced Nylon-6 composites: Enhancement of Heat distortion Temperature

Organically modified nanoclay (cation exchange capacity of 135 to 145 meq/100 g) was used as nanophase reinforcement for fabrication of nylon-6 nanocomposites. The thickness of clay platelets varied form 1.2 nm to 1.3 nm with 3.485 nm as d-spacing. Nylon 6/nanoclay composites were fabricated with loading of 2.5, 5.0 and 10 wt. % nanoclay via direct melt compounding technique using conventional twinscrew extruder. Processing temperature profile from hopper to header was 230-240-245-260 °C and screw speed was maintained at 180 rpm. The nylon 6/clay nanocomposites were characterized for thermal and mechanical properties. The structural properties were characterized by Differential Scanning Calorimeter (DSC) and X-ray diffraction analysis. The tensile fracture morphology was analyzed by using Scanning Electron Microscope (SEM). DSC nonisothermal curves show an increase in the crystallization temperature with increasing degree of crystallinity. The crystallization rate of the nanoclay reinforced nylon 6 composites was found to be significantly faster than that for the pristine nylon 6 and suggests that the layered silicates act as nucleating centers. XRD result shows that addition of nanoclay by this technique favors the formation of γ-crystalline phase in nylon 6/nanoclay composites. Due to this, there is substantial enhancement in the tensile strength and Izod impact strength. A variation from 700 to 971 Kg/cm2 for tensile strength and from 3.0 to 3.4 Kg.cm/cm of notch for Izod impact strength. The detailed results are presented

Effect of Additional Particulate Reinforcement on the Properties of Fibrous Ceramic Matrix Composites

Composites, generally, consist of two phase i.e. matrix and reinforcement. Here in this work additional phase in terms of micro/nano particles was added in the fiber reinforced ceramic matrix composites and its effect on the final properties of composites was studied. Composites were prepared using sol derived from Tetraethoxysilane (TEOS) and Dimethyldiethoxysilane (DEDMS), and polycarbosilane (PCS) as matrix precursors and SiC fabric as reinforcement. To some composites another phase of solid, micro/nano powder precursor of SiC was added to decrease number of impregnation cycles. Latter composites resulted in higher density. Green composites were post-cured and pyrolyzed. Some of the composites were heated to 1500 °C in argon atmosphere. Composites were characterized for density, microstructure and mechanical properties. It revealed that the resulting matrix was solid glass and addition of SiC powder facilitated the rapid densification. Composites prepared with SiC nanoparticles as well as SiC fabric as reinforcement exhibit higher flexural strength than those made without nanoparticles. The fracture behaviour is also seen to be of mixed mode failure type

Resultant-based methods for plane curves intersection problems

http://www.springeronline.com/3-540-28966-6We present an algorithm for solving polynomial equations, which uses generalized eigenvalues and eigenvectors of resultant matrices. We give special attention to the case of two bivariate polynomials and the Sylvester or Bezout resultant constructions. We propose a new method to treat multiple roots, detail its numerical aspects and describe experiments on tangential problems, which show the efficiency of the approach. An industrial application of the method is presented at the end of the paper. It consists in recovering cylinders from a large cloud of points and requires intensive resolution of polynomial equations

Ultrahigh Surface Area Three-Dimensional Porous Graphitic Carbon from Conjugated Polymeric Molecular Framework

Porous graphitic carbon is essential for many applications such as energy storage devices, catalysts, and sorbents. However, current graphitic carbons are limited by low conductivity, low surface area, and ineffective pore structure. Here we report a scalable synthesis of porous graphitic carbons using a conjugated polymeric molecular framework as precursor. The multivalent cross-linker and rigid conjugated framework help to maintain micro- and mesoporous structures, while promoting graphitization during carbonization and chemical activation. The above unique design results in a class of highly graphitic carbons at temperature as low as 800 ??C with record-high surface area (4073 m2 g-1), large pore volume (2.26 cm-3), and hierarchical pore architecture. Such carbons simultaneously exhibit electrical conductivity >3 times more than activated carbons, very high electrochemical activity at high mass loading, and high stability, as demonstrated by supercapacitors and lithium-sulfur batteries with excellent performance. Moreover, the synthesis can be readily tuned to make a broad range of graphitic carbons with desired structures and compositions for many applications.clos

Work-Related Mental Health and Job Performance: Can Mindfulness Help?

Work-related mental health issues such as work-related stress and addiction to work impose a significant health and economic burden to the employee, the employing organization, and the country of work more generally. Interventions that can be empirically shown to improve levels of work-related mental health – especially those with the potential to concurrently improve employee levels of work performance – are of particular interest to occupational stakeholders. One such broad-application interventional approach currently of interest to occupational stakeholders in this respect is mindfulness-based interventions (MBIs). Following a brief explication of the mindfulness construct, this paper critically discusses current research directions in the utilization of mindfulness in workplace settings and assesses its suitability for operationalization as an organization-level work-related mental health intervention. By effecting a perceptual-shift in the mode of responding and relating to sensory and cognitive-affective stimuli, employees that undergo mindfulness training may be able to transfer the locus of control for stress from external work conditions to internal metacognitive and attentional resources. Therefore, MBIs may constitute cost-effective organization-level interventions due to not actually requiring any modifications to human resource management systems and practises. Based on preliminary empirical findings and on the outcomes of MBI studies with clinical populations, it is concluded that MBIs appear to be viable interventional options for organizations wishing to improve the mental health of their employees