Solid Freeform Fabrication of Functional Silicon Nitride Ceramics by Laminated Object Manufacturing 1

The processing of silicon nitride (Si3N4) structural ceramics by Laminated Object Manufacturing (LOM) using ceramic tape preforms was investigated. The key processing stages involved green shape formation (which used the LOM process), followed by the burnout of all organics, and final densification by pressureless sintering. Two material systems were considered. These were a) monolithic Si3N4 and b) a preceramic polymer infiltrated Si3N4. The raw materials for the process were tape preforms of Si3N4, which were fabricated by standard tape casting techniques. Mechanical property data obtained for the LOM processed Si3N4 showed high strength and fracture toughness values. The room temperature and high temperature (1260 o C) flexural strengths were in the range of 700-900 MPa and 360-400 MPa, respectively. The fracture toughness averaged from 5.5-7.5 MPa.m1/2. These strength and fracture toughness values are comparable to those reported for conventionally prepared Si3N4 ceramics. Thus, this research demonstrated that the LOM technique is a viable method for preparing functional Si3N4 ceramics with good physical and mechanical properties.Mechanical Engineerin

Studies on the Geology and Beneficiation of Chandak Magne-site Deposit from Pithoragarh District, Uttar Pradesh

Stringent operating conditions in modern steel making furnaces demand high quality basic refractories based on magnesia. Source of good quality natural magnesite cont-ains considerable amounts of SiO2 and fluxing agents. Therefore, appropriate measures are to be taken to ensure the availablity of good quality magnesite. Measures for meeting the demand of quality magnesite are follows:- i) Upgrading of the presently available natural magnesite by various beneficiation techniques ; ii) Production of high quality magnesia from sea water

Level Density of a Bose Gas and Extreme Value Statistics

We establish a connection between the level density of a gas of non-interacting bosons and the theory of extreme value statistics. Depending on the exponent that characterizes the growth of the underlying single-particle spectrum, we show that at a given excitation energy the limiting distribution function for the number of excited particles follows the three universal distribution laws of extreme value statistics, namely Gumbel, Weibull and Fr\'echet. Implications of this result, as well as general properties of the level density at different energies, are discussed.Comment: 4 pages, no figure

Pathological studies of Glaeosporium psidii causing die-back of guavas

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Resistivity due to a Domain Wall in Ferromagnetic Metal

The resistivity due to a domain wall in ferromagnetic metallic wire is calculated based on the linear response theory. The interaction between conduction electrons and the wall is expressed in terms of a classical gauge field which is introduced by the local gauge transformation in the electron spin space. It is shown that the wall contributes to the decoherence of electrons and that this quantum correction can dominate over the Boltzmann resisitivity, leading to a decrease of resisitivity by nucleation of a wall. The conductance fluctuation due to the motion of the wall is also investigated. The results are compared with recent experiments.Comment: 9 pages, 3 figure

Cloning and heterologous expression of a gene encoding lycopene-epsilon-cyclase, a precursor of lutein in tea (Camellia sinensis var assamica)

This report describes the cloning and expression of a gene lycopene epsilon cyclase, (LCYE) from Camellia sinensis var assamica which is a precursor of the carotenoid lutein in tea. The 1982 bp cDNA sequence with 1599 bp open reading frame of LCYE was identified from an SSH library constructed for quality trait in tea. 5’ and 3’ RACE (rapid-amplification of cDNA ends) was done to clone the full length cDNA of LCYE. Homology studies showed that the deduced amino acid sequence of LCYE gene had the highest sequence identity of up to 84% with Vitis vinefera. The cloned gene was successfully expressed in a PET based Escherichia coli expression system. The size of the expressed protein was 59615 Daltons. A suppression subtractive library was constructed using a quality clone H3111 (tester) and a garden series clone T3E3 (driver).Key words: Carotenoid, RACE, heterologous expression, lutein, tea

Structural Ceramics by Fused Deposition of Ceramics

Fused Deposition of Ceramics (FDC) is a SFF technique, based on FDMTM technology, for fabrication of advanced structural ceramics from powderlbinder filaments. In this study, in-situ reinforced (ISR) Si3N4 powder and polymer/wax based binder systems were used as filament material for FDC processing using a commercially available FDMTM system, 3D Modeler. Powderlbinder feedstocks were mixed using a torque rheometer and filaments were fabricated using a capillary rheometer and twin screw extruder. Green FDC components were built from these filaments and then characterized for inter-road and inter-layer bonding. Binder removal procedures were established for FDC green components to yield brown parts without distortion or shape change. Brown FDC parts were characterized for carbon residue, pore distribution and dimensional changes. Brown FDC parts were then sintered and the sintered density, microstructure, and shrinkage anisotropy were studied.Mechanical Engineerin