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By
Bandyopadhyay, A K; Sharma, J K N; Gopal, E S R
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1 Citations
We report here a systematic data analysis of the vapour pressure of argon at different amounts of the liquid phase to understand the thermodynamic behaviour of this inert gas around triple point. At the triple point plateau, the applied heat pulse melts a certain phase of solid argon into liquid and increases vapour pressure. It is observed that this vapour pressure attains the thermodynamic equilibrium pressure after a certain time interval. The expoential decay of the vapour pressure as a function of time at different fractions of the liquid phase shows two different features. In one region, the relexation time constant (τ) is low and is not varying with the liquid phase, while in the other region the value ofτ increases with the amount of the liquid phase. Further, the peak pressure from the equilibrium pressure (ΔP_{h}), obtained from the fitting parameters, shows a dip at around 50% of the liquid phase. A qualitative physical interpretation has been given to explain these results.
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By
Chatterjee, S; Vani, V; Gopal, E S R
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The effect of gravity on various thermodynamic properties near the gasliquid critical point has been calculated. Using a simple equation satisfying scaling requirements, an analytic expression for density profile is obtained, using which the effect on different thermodynamic properties can be easily calculated.
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By
Srinivasan, K R; Gopal, E S R
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7 Citations
The elastic constantsC_{11},C_{12} andC_{44} of sodium bromate single crystals have been evaluated using 10 MHz ultrasonic pulse echo superposition technique. The values areC_{11}=5.57_{8},C_{12}=1.07_{5},C_{44}=1.51_{0} (×10^{10} N/m^{2}) at 290 K and 6.35, 1.98 and 1.65 (×10^{10} N/m^{2}) at 77 K. The present room temperature values agree closely with the recent values of Gluyaset al. but the other earlier measurements show some scatter. A comparison between the elastic constants of sodium bromate and sodium chlorate is also made.
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By
Williams, I S; Street, R; Gopal, E S R
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12 Citations
A fully automated calorimeter has been designed and tested over the temperature range 200K–400K. The system may be used for measurements with an absolute accuracy of 0.2% of samples of approximate mass 50g and thermal capacity 15 JK^{−1}. The temperature of the sample is determined by a quartz crystal thermometer of resolution 100 µK which is not in direct thermal contact with the sample. The performance of the system is illustrated by results obtained on high purity copper, distilled water and K_{2}PbCu(NO_{2})_{6} which exhibits very sharp first order phase transitions at about 273.4K and 281.8K.
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By
Kumar, Anil; Gopal, E S R
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4 Citations
The electrical resistance of the binary liquid system cyclohexane + acetic anhydride is measured, in the critical region, both in the pure mixture and when the mixture is doped with small amounts (≈ 100 ppm) of H_{2}O/D_{2}O impurities.T_{c} was approached to aboutt=3×10^{−6} wheret=(T −T_{c})/T_{c}. The critical exponentb ≈ 0.35 in the fit of the resistance data to the equationdR/dT ∼t^{−b} does not seem to be affected appreciably by the impurities. There is a sign reversal ofdR/dt in the noncritical region. Binary liquid systems seem to violate the universality of the critical resistivity.
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By
Baranidharan, S; Gopal, E S R; Sasisekharan, V
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4 Citations
A method for generating aperiodic tilings with five fold symmetry is discussed here. Basic patterns formed within decagons can be used to fill two dimensional space, by matching such suitable patterns. It appears to be possible to generate perfect tilings without retracing already established coordinates imposing conditions at the initial stages of generating them. Various possible ways to generate tilings, when perfectness is not required, are discussed. The calculated diffraction patterns for some representative finite size tilings are shown. There are subtle differences in the intensities of peaks in the diffraction patterns corresponding to different finite size tilings constructed using intersecting decagons. These effects persist for a larger number of scatterers in weak peaks than in strong peaks. They are unaffected by an introduction of systematic disorder. These effects could be termed as the finite size boundary effects. There are also small shifts in the peak positions owing to the finite size effects. The possibility of formation of large approximate square cells in large tilings is shown.
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