Materials Science

A computer oriented numerical approach to study the effects of variable viscosity and thermal conductivity of stagnation flow of a micropolar fluid towards a vertical permeable surface is investigated in this study. The external flow impinges normal to the heated plate and we have assumed the viscosity and thermal conductivity as the inverse linear function of temperature. The partial differential equations governing the problem under consideration have been transformed into a system of non-linear ordinary differential equations by the similarity transformation and solved them numerically by shooting method. Numerical results are carried out for various dimensionless parameters of the problem especially variable viscosity parameter, thermal conductivity parameter, micro-rotation parameter along with the Prandtl number. The results are presented graphically for velocity distribution, temperature distribution and micropolar distributions for various values of non-dimensional parameters. It is found that the effects of the parameters representing variable property of viscosity and thermal conductivity are significant.

Additive or constructive manufacturing is a manufacturing technology in which prototypes and functional parts are built through layer by layer addition of material directly by importing the STL file from CAD software to 3D printer. Unlike many manufacturing processes in which material destruction or erosion takes place in this technology material is successively added in a constructive manner to obtain physical 3D object. Due to its simplified product development process it has a wide range of applications in many distinct areas like Automobile, Aerospace, Architecture, bio medics and consumer goods. Since inception many additive manufacturing techniques were evolved and a variety of materials from the classes of metals, polymers, ceramics and composites are utilized. As the numbers of applications are increasing day to day the development of new materials has gained significant importance. In the current paper an over view of developed materials for additive manufacturing processes are reviewed and recent research developments in natural, diverse materials for additive manufacturing applications are discussed.

Most people see the telescope as the things for the movies, the science geeks and the rich and affluent, but are these feelings for real? This paper on the design and construction of an optical refracting telescope which is aimed at producing a low cost and portable telescope with less or no aberration effects using the materials we see around us every day goes a long way to answer the question that the telescope is for everybody that loves astronomy. Overall implementation of this work involves knowledge of the physics of optics; lenses to be precise. As a case study I used a double convex lens and the eyepiece of a microscope for the construction of the mini refractor telescope, my hypothesis is that using a double convex is better than using a Plano-convex because the two curved surfaces will cancel out the aberration effect of the individual sides. The resultant telescope was tested during the night and during the day and was used to focus objects at a distance of about 50m from the person with less aberration effect.

Cu₂Se particles have been synthesized by the hydrothermal method at a temperature of 200° C. The synthesized nanoparticles were characterized by a variety of techniques like XRD, UV, FTIR, SEM and EDAX. Experimental data reveals that the final product almost consists of hexagonal flakes in the [111] plane. The estimated optical band gap for the particles was found to be within the reported range.

A study on the DC performance of Nano Quantum Dot Transistor under illumination is presented. A device structure consist of Quantum Dots(QD) in the GaAs layer is considered for illumination. The photoconductive effect in the GaAs and QD layer which increases the 2DEG Channel electron concentration is considered. The I-V Characteristics of Quantum Dot Transistor, under dark and illumination condition have been calculated, plotted and discussed.

Exciton binding energy is obtained in a Zn_xCd_1-xTe/ZnTe strained quantum dot taking into account the phonon confinement effect. The effect of mismatch between the dielectric constants of the dot and the barrier (dielectric mismatch effect) is taken into account in our calculation. The calculations include the effect of exciton and the LO phonon interaction is derived by the effective potential (V_PB) between the electron and hole along with the self energy term (E_self). It is observed that  the potential taking into account the effects of phonon makes the  exciton binding energies more than  the obtained results using a Coulomb potential screened by a static dielectric constant and the optical properties of exciton  in a quantum dot are strongly affected by the confining potential and the quantum size.

The effect of Mn content on donor binding energy of a hydrogenic donor as a function of dot radius in a GaAs diluted magnetic semiconductor quantum dot is investigated. The Mn based GaAs material is the most thoroughly studied ferromagnetic dilute magnetic semiconductor which brings out the relationship between magnetic and semiconducting properties. All the calculations include the exchange interaction of Mn alloy content with an itinerant carrier. The worked out computation are performed within a single band effective mass approximation using variational technique. The binding energy is calculated by varying its dot radius, for various Mn incorporation in Mn based GaAs inner quantum dot surrounded by the GaAlAs outer barrier material.

The effects of magnetic field on the exciton binding energy and the Phosphorous alloy content in a cylindrical Phosphorous doped GaAs quantum dot are investigated with the geometrical confinement. The various Phosphorous alloy concentration in the (xin = <0.3) quantum dot has been taken into account. All the computations to get the electronic states are performed using variational procedure within the single band effective mass approximation by the magnetic field strength. The effect of strain due to the spontaneous and piezoelectric polarizations is included.

Electric field induced donor binding energy in a GaAs/AlGaAs finite quantum well are discussed. It is calculated with and without the inclusion of position dependent effective mass. We find the energy eigen values to obtain the subband energy and thereby the hydrogenic impurity binding energies. In all the calculation, we follow the variational formulism within the single band effective mass approximation. We find that results are different when the position dependent effective mass included in the Hamiltonian. Moreover, we find that the reduction of binding energy when the electric field is applied in the growth direction.

Pure and 0.1 mole % L-aspartic acid doped Ammonium Dihydrogen Phosphate (ADP) have been grown by solvent slow evaporation technique at room temperature. The grown crystals were characterized by powder X-ray diffraction, Uv-visible, FTIR and Raman FTIR analysis. The doping of L-aspartic acid was confirmed by FTIR spectrum and Raman FTIR. The Nonlinear optical property (SHG) of L-aspartic acid doped ADP was increased than the Pure ADP. Thermally stable for both pure and L-aspartic acid doped ADP crystal. Micro hardness studies were carried out on the grown crystal.