Raoult's Formalism in Understanding Low Temperature Growth of GaN Nanowires using Binary Precursor

Growth of GaN nanowires are carried out via metal initiated vapor-liquid-solid mechanism, with Au as the catalyst. In chemical vapour deposition technique, GaN nanowires are usually grown at high temperatures in the range of 900-1100 ^oC because of low vapor pressure of Ga below 900 ^oC. In the present study, we have grown the GaN nanowires at a temperature, as low as 700 ^oC. Role of indium in the reduction of growth temperature is discussed in the ambit of Raoult's law. Indium is used to increase the vapor pressure of the Ga sufficiently to evaporate even at low temperature initiating the growth of GaN nanowires. In addition to the studies related to structural and vibrational properties, optical properties of the grown nanowires are also reported for detailed structural analysis.Comment: 24 pages, 7 figures, journa

A detailed analysis of structure growth in f(R)f(R) theories of gravity

We investigate the connection between dark energy and fourth order gravity by analyzing the behavior of scalar perturbations around a Friedmann-Robertson-Walker background. The evolution equations for scalar perturbation are derived using the covariant and gauge invariant approach and applied to two widely studied $f(R)$ gravity models. The structure of the general fourth order perturbation equations and the analysis of scalar perturbations lead to the discovery of a characteristic signature of fourth order gravity in the matter power spectrum, the details of which have not seen before in other works in this area. This could provide a crucial test for fourth order gravity on cosmological scales.Comment: 27 pages and 35 figure

Geotechnical Aspects of Seismic Design of Bridges in New York City

Earthquake damage Civil engineering structure and bridges are no exception. Historically, bridges have proven to be vulnerable to earthquakes which cause damage to substructures and foundations and in some cases being totally destroyed as Superstructure collapse from their supporting elements. The bridges in New York City are required to comply with Specifications of American Association of State Highway and Transportation Officials (AASHTO) and New York State Department of Transportation (NYSDOT). The seismic design criteria has been recently introduced in these specifications and all bridge projects in New York City must comply with these requirements. The extent of seismic analysis required varies with bridge\u27s scope of rehabilitation or replacement scheme. The New York City Metropolitan area presents foundation engineers with a wide variety of soil profiles that varies from soft clay to compact glacial deposits. Local bedrock configurations are similarly extremely variable. The thickness and quality of the soil overburden generally plays a significant role in the seismic design of bridges. The paper summarizes the available geotechnical information regarding seismic design of bridges in New York City and discusses the geology, seismicity, seismic risk, various subsurface soils encountered in the area and their liquefaction potential. Seismic evaluation being performed on several of its important bridges is briefly presented

Studies on the Pyrolysis of Composite Solid Propellants leading to Ignition

Studies on the pyrolysis leading to ignition of polystyrene (PS)/ammonium perchlorate (AP), polyvinyl chloride (PVC)/AP and polyphenol formaldehyde (PPF)/AP  propellants revealed that the activation energy for the ignition strongly depends upon the binder. Double base propellants exhibit an empirical relationship between the ignition delay (~) and the oxidiser concentration; when the same equation is applied to composite solid propellants, the plot of In ~ vs In C (C=Concentration, %) yields a straight line with a knee corresponding to 65-70 per cent AP above which the dependence on ~ becomes less sensitive