Cooling-Rate Effects in Sodium Silicate Glasses: Bridging the Gap between Molecular Dynamics Simulations and Experiments

Although molecular dynamics (MD) simulations are commonly used to predict the structure and properties of glasses, they are intrinsically limited to short time scales, necessitating the use of fast cooling rates. It is therefore challenging to compare results from MD simulations to experimental results for glasses cooled on typical laboratory time scales. Based on MD simulations of a sodium silicate glass with varying cooling rate (from 0.01 to 100 K/ps), here we show that thermal history primarily affects the medium-range order structure, while the short-range order is largely unaffected over the range of cooling rates simulated. This results in a decoupling between the enthalpy and volume relaxation functions, where the enthalpy quickly plateaus as the cooling rate decreases, whereas density exhibits a slower relaxation. Finally, we demonstrate that the outcomes of MD simulations can be meaningfully compared to experimental values if properly extrapolated to slower cooling rates

Variation of effective attachment coefficient with pollution and its effect on atmospheric electric parameters over the Indian subcontinent

1-13A comprehensive model is developed for the calculation of effective attachment coefficient eff for polluted and unpolluted atmospheres. It is found that eff depends significantly on the aerosol size distribution. These calculated values of eff are then used to calculate the various atmospheric electric parameters, viz. conductivity, air-earth current, electric field, and potential over the Indian subcontinent taking into account the earth’s orography in 0.5° grid in latitude and longitude as well as the production of small ions due to cosmic rays and radioactivity. The electric parameters are found to increase with the latitude and the altitude of the ground. However, the latitudinal effect is very small compared to the orographic effect. The average electric field is nearly 98 V/m over land and 136 V/m over ocean. The electric field and potential are maximum while the conductivity is minimum during winter. With increase in pollution, current density and conductivity are found to decrease, whereas electric field and potential increase

On the enhancement of probability of ion induced nucleation on partially wettable, water insoluble planer substrate

138-146The nucleating behaviour of partially wettable, water insoluble planar substrate has been studied. The rate and probability of nucleation were found to be enhanced in ion induced nucleation. It is found that there exits a threshold for angle of contact above which the effect of ions is dominant. The effect of ions is more pronounced at low supersaturation rations and low temperatures for the material of large angle of contact w.r.t. water

The effect of a solar eclipse on atmospheric potential gradients

A continuous record of the atmospheric potential gradient during the period of the solar eclipse of 20th May, 1966 has been presented. The recorded values show a marked deviation from those normally observed at the same time of the day. It shows the potential gradient negative for most of the time, with a regular variation pattern having five clear peaks

Global electric circuit parameters over Indian subcontinent

320-324Some global electric circuit (GEC) parameters like electrical conductivity, air-earth current, electric field and electrostatic potential etc. have been calculated over Indian subcontinent taking into account the small scale (0.6° grid in latitude and longitude) orographic and latitudinal effects and the base conditions of conductivity profiles. It has been found that the electrical conductivity and air-earth current are larger over mountains than over ocean, while the electric field and the electrostatic potential are smaller over mountains. The theoretically calculated average value of electric field over sea surface is found to be in good agreement with the experimental observations. The values of all the parameters are found to increase with latitude, but the latitudinal variation is observed to be smaller than the orographic variation

Excess point-discharge current during rapid field-changes

The point-discharge current from an isolated artificial point is studied. The phenomenon is explained on the basis of a transient reversed 'local potential-gradient' developed around the point. It is shown that the relation of Chalmers (1962) can be used with some alterations to correlate this point-discharge current with atmospheric potential-gradient and wind speed. Agreement is found between observed and calculated values except at high wind speeds

Effect of ionization and particulate pollutants on GEC parameters over the Indian subcontinent

159-165The effect of ionization due to cosmic rays and radioactivity over the earth’s surface on global electric circuit (GEC) parameters like electrical conductivity, air-earth current and electric filed has been evaluated for the Indian subcontinent. In the first phase, the calculations were performed for a clean atmosphere, and in the second phase, the calculations were made for measured values of particulate concentrations in certain cities of India and also for 50 per cent increases. The results show a markable reduction in conductivity and increase in electric field under high particle concentrations

Effect of Corona on Ground Electric Field Beneath a Thundercloud

126-130The effect of corona space charge on growth rate of ground electric field beneath a thundercloud has been studied. The maximum electric fields have been calculated at the ground surface and aloft. It has been found that the corona limits the magnitude of the electrostatic field and also influences the time behaviour of the electric field at the ground surface. The computed results are found to be in good agreement with the available experimental observations