Simulations of energetic beam deposition: from picoseconds to seconds

We present a new method for simulating crystal growth by energetic beam deposition. The method combines a Kinetic Monte-Carlo simulation for the thermal surface diffusion with a small scale molecular dynamics simulation of every single deposition event. We have implemented the method using the effective medium theory as a model potential for the atomic interactions, and present simulations for Ag/Ag(111) and Pt/Pt(111) for incoming energies up to 35 eV. The method is capable of following the growth of several monolayers at realistic growth rates of 1 monolayer per second, correctly accounting for both energy-induced atomic mobility and thermal surface diffusion. We find that the energy influences island and step densities and can induce layer-by-layer growth. We find an optimal energy for layer-by-layer growth (25 eV for Ag), which correlates with where the net impact-induced downward interlayer transport is at a maximum. A high step density is needed for energy induced layer-by-layer growth, hence the effect dies away at increased temperatures, where thermal surface diffusion reduces the step density. As part of the development of the method, we present molecular dynamics simulations of single atom-surface collisions on flat parts of the surface and near straight steps, we identify microscopic mechanisms by which the energy influences the growth, and we discuss the nature of the energy-induced atomic mobility

Reconstruction of sound speed profile through natural generalized inverse technique

328-334An acoustic model has been developed for reconstruction of vertical sound speed in a near stable or stratified ocean. Generalized inverse method is utilised in the model development. Numerical experiments have been carried out to account for the noise while reconstructing the model parameters. The results (data kernel, generalized inverse operator, model parameter resolution, data resolution etc.) obtained thereof have been presented

Acoustic characteristics of the waters of the Bay of Bengal

263-267Acoustic eigen rays (rays connecting the source and receiver) have been identified and their turning depth, path length, travel time etc. evaluated. Acoustic intensity loss due to mean environmental conditions, vergence along acoustic rays and the low frequency absorption due to the presence of boric acid and magnesium sulphate, etc. have bren estimated. For a source-receiver distance of 300 km, computed intensity loss due to spreading for different eigen rays varies between 92 and 116 dB while that due to absorption is about 4.25 dB at 0.2 kHz and 15.25 dB at 0.4 kHz source frequencies for ranges of 300 km. This analysis can be applied to, for target detection and source localization problems

Acoustic propagation within a surface duct in the western Bay of Bengal

236-238Sound speed structure forms a surface duct in the upper 50 m layer in the western Bay of Bengal during late July A range-dependent acoustic ray computation shows that some rays emanating from a source within the upper 30 m, get trapped within this duct while the untrapped rays propagating as refracted bottom-reflected (RBR) rays. The extent of acoustic energy trapped depends on the critical angle of approximately 1 degree. When the source depth coincides with the axis of the surface duct, all the rays within the above critical angle get trapped fully. With further decrease in the source depth, the limit of energy trapping reduces to 0.5 of a degree. The intensity level for a trapped ray is 10-15 dB higher than that of an untrapped RBR ray. The leakage of + 0.6 degree ray out of the surface duct can clearly be seen as change in the intensity level of about 15-20 dB which is attributed to the weakening of the duct at that range

Computations Of Some Acoustic Ray Parameters In The Bay Of Bengal

235-245Methods to compute geometric path, travel time and intensity of sound rays were detailed following a range dependent numerical computer program to study the acoustic properties and their variability in the Bay of Bengal, utilising sound speed data derived from CTD profiles taken during winter and premonsoon along a section off Madras. Between the 2 seasons, intensity levels varied from - 74 to - 88 dB for distances of 200 km and the flight of the eigen rays presented significant differences. The results indicate the independent nature of the eigen rays for a given source-receiver pair

Atmospheric Pollutants & Rainfall

75-79The gaseous pollutants comprising sulphur dioxide, ammonia, chlorine and nitrogen oxides and the particulate pollutants comprising ammonium and chloride were measured at Poona over three to four consecutive monsoon periods commencing from 1970. The contrasting activities of the monsoon in 1972 and 1973 afforded opportunity to examine the association, if any, between the various components of pollution and rainfall. Analysis of the data suggested that the gaseous components, sulphur dioxide and ammonia and the particulate components, ammonium and chloride may be associated with rainfall. Possible explanations have been offered for the features suggested

Computation of diffusion coefficients for water of Ghauthami Godavari estuary using one-dimensional advection-diffusion model

185-187<span style="font-size: 12.0pt;font-family:" times="" new="" roman";color:black;mso-ansi-language:en-us;="" mso-fareast-language:en-us;mso-bidi-language:ar-sa"="">An analysis  of salinity, salt budget and diffusion coefficients based on the salinity data of Gauthami Godavari estuary for three different months (Nov. '95 Jan. '96, April '96) representing different seasons has been carried out. Diffusion coefficients vary quite randomly with distance between 90 - 4050 m2/s for consecutive months during Nov. '95 - Jan. '96 and between 10-869 m2/s for Jan. '96 - April. '96. The mean values of diffusion coefficients are found to be 1510 m2/s for consecutive months during Nov. '95 - Jan. '96, 174 <span style="mso-bidi-font-style: italic">m2/s for Jan. '96-April '96 and are attributed to the river run-off. The undulations in diffusion coefficients reflect the topographic features. The estuarine salt budget shows an increase of salt content by 62% from Nov. '95 - Jan. '96 and 32% from Jan. '96 - April. </span