On the quantum and classical scattering times due to charged dislocations in an impure electron gas

We derive the ratio of transport and single particle relaxation times in three and two - dimensional electron gases due to scattering from charged dislocations in semiconductors. The results are compared to the respective relaxation times due to randomly placed charged impurities. We find that the ratio is larger than the case of ionized impurity scattering in both three and two-dimensional electron transport.Comment: 4 pages, 3 figure

Effect of Ti and metal vacancies on the electronic structure, stability, and dehydrogenation of Na3AlH6: Supercell band-structure formalism and gradient-corrected density-functional theory

Electronic and structural properties of sodium-aluminum hexahydride (Na3AlH6) formed during the decomposition reaction of sodium alanate (NaAlH4) and the effects of Ti catalyst are studied using supercell approach and density-functional theory. The preferred site of Ti has been determined by substituting it at both the Na and Al sites and comparing the respective formation energies. The least unfavorable site for Ti is found to be the Al site. To examine the role of Ti substitution on the desorption of hydrogen, the energy cost to remove a H atom from the vicinity of Ti was calculated and compared with that from the pure Na3AlH6 The improvement in dehydrogenation of Na3AlH6 was found to be due to the weakening the Al-H bond caused by Ti substitution. We also studied the role of metal vacancies on hydrogen desorption. Although this desorption was exothermic, the energies to create these vacancies are high

Li- and B-decorated cis-polyacetylene: A computational study

By using density functional theory and the generalized gradient approximation, we show that Li-decorated cis-polyacetylene meets some of the requirements of an ideal hydrogen storage material. Unlike Ti-doped cis-polyacetylene, Li resists clustering and can reversibly store up to 10.8 wt %hydrogen in molecular form. However, molecular dynamics simulations show that Li can retain hydrogen only at cryogenic temperatures. On the other hand, B-doped cis-polyacetylene can store up to 7.5 wt % hydrogen, but it binds to hydrogen too strongly to be suitable for room temperature applications. The results are compared to those in Ti-doped cis-polyacetylene

Nanotechnology- future prospect in recent medicine: a review

Any damage at molecular or cellular level is the major culprit for disease & ill health. Nanotechnology, “the manufacturing technology of the 21st century," helps us economically build a broad range of complex molecular machines by manipulating matter on an atomic and molecular scale. Nanotech may be able to create many new materials and devices with at least one dimension sized from 1 to 100 nanometres with a vast range of applications, such as in medicine, electronics, biomaterials and energy production. Lots of new possibilities come into account in relation to use of nanotechnology in medicines. Nanotechnology in medicine involves applications of nanoparticles, also involves nano-robots to make repairs at the cellular levels. On the other hand, nanotechnology raises many of the same issues as any new technology, including concerns about the toxicity and environmental impact of nanomaterials

Magnetotransport properties of a polarization-doped three-dimensional electron slab

We present evidence of strong Shubnikov-de-Haas magnetoresistance oscillations in a polarization-doped degenerate three-dimensional electron slab in an Al$_{x}$Ga$_{1-x}$N semiconductor system. The degenerate free carriers are generated by a novel technique by grading a polar alloy semiconductor with spatially changing polarization. Analysis of the magnetotransport data enables us to extract an effective mass of $m^{\star}=0.19 m_{0}$ and a quantum scattering time of $\tau_{q}= 0.3 ps$. Analysis of scattering processes helps us extract an alloy scattering parameter for the Al$_{x}$Ga$_{1-x}$N material system to be $V_{0}=1.8eV$

Environmental Issues in Indian Freshwater Aquaculture

Aquaculture is assuming increasing importance in recent years on a global basis including the Indian subcontinent. With possibilities of obtaining high productivity levels among different farming system, there has been a flux between the farming practices and aquaculture is receiving greater investments both in public and private secto

Determination of the lowest energy structure of Ag8_8 from first-principles calculations

The ground-state electronic and structural properties, and the electronic excitations of the lowest energy isomers of the Ag$_8$ cluster are calculated using density functional theory (DFT) and time-dependent DFT (TDDFT) in real time and real space scheme, respectively. The optical spectra provided by TDDFT predict that the D$_{2d}$ dodecahedron isomer is the structural minimum of Ag$_8$ cluster. Indeed, it is borne out by the experimental findings.Comment: 4 pages, 2 figures. Accepted in Physical Review A as a brief repor