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Molecular dynamics study of the clustering in hard parallel squares
266
Current work on nucleation
This paper describes a computer simulation model which reproduces the random atomic processes which occur in condensation, evaporation, and surface diffusion (upon an idealized (100) crystalline substrate surface). Computer simulation experiments based on this model were carried out over a range of adatomadatom interaction energies and adsorption fluxes chosen so as to produce observable nucleation phenomena in a reasonably short computation time. The equilibrium distribution of cluster sizes and the critical cluster size were measured in a large number of cases and compared to predictions of the Walton-Rhodin atomistic nucleation theory. Very good agreement between the experimental and theoretical values was obtained. The nucleation rate was also measured for one particular set of parameters and found to agree satisfactorily with the atomistic theory prediction. Consequently, we conclude that within the limitation of the assumptions of the simulation model used, the Monte Carlo method is suitable for the simulation of the phenomena of heterogeneous nucleation. A number of suggestions are offered for the refinement and extension of this simulation method which may help to answer some of the unresolved questions of heterogeneous nucleation theory.
Molecular dynamics study of the clustering in hard parallel squares. By C. CARLIERand H. L. FRISCH; State University of New York, Albany, New York 12222, U.S.A. A molecular dynamics study of clustering in systems of 400 and 900 hard parallel squares shows that in the high density region, the distributions N(n) of clusters of size n depend only upon one dimensionless variable. Results are slightly different in the intermediate density fluid region. For all densities and values of the clustering distance parameter L, N(n) is a monotone decreasing function of n. A simple free volume theory predicts relatively well the results in the high density region. The clusters are relatively compact. From an exponential fit to the function N(n)/N(1) obtained for densities near the phase--transition region, one estimates the value of the parameters of the exponential law given by the classical theory of nuclation.
Heteromolecular nucleation theory applied to gas to particle conversion. By C. S. KIANG and D. STAUFFER; Physics Department, Clark College, Altanta, Georgia 30314, U.S.A. and V. A. Morrr~N; Atmospheric Sciences Research Center, State University of New York, Albany, New York 12222, U.S.A. and J. BRICARD; Physique des Aerosols, Facult6 des Sciences, Universit6 de Paris, France. An attempt has been made to explain gas to particle conversion with the beteromolecular nucleation theory, The theory is applied to a binary mixture of H 2 0 - H z S O , and H 2 0 - H N O a respectively in air. The resulting formation of critical sized clusters is calculated as function of relative humidity up to 99 per cent. Sulfuric acid resulting from gas phase reactions in the atmosphere has one of the lowest vapor pressures of all reaction products. Nitric acid with its relatively high vapour pressure would represent an upper limit for gas to particle conversion to occur under atmospheric conditions.
Homogeneous nudeafion in steam nozzle condensation. By D. BARSCHDORFF,W. J. DUNNING,P. P. WEGENER and B. J, C. Wu; Department of Engineering and Applied Science, Yale University, New Haven, Connecticut 06520, U.S.A.
(No abstract given; to be published in Nature.)
RecentstudiesenSO2 oxidation in the presence of liquid water. By S. BEILKE,D. LAMB and J. MILLER; Institut fur Metenrologie und Genphysik, OniversitAt, Frankfurt, West Germany. The following studies refer in a wide sense to problems of trace gas and atmospheric aerosol agglomoration on cloud droplets and rain droplets. Of particular interest is here the incorporation of atmospheric sulphur compounds like S02, H2S, and sulfate, which is an essential constituent of atmospheric aerosols. (In German.)
Condensation nuclei discriminator based on optical measurements during fog formation: A new tool for environmental research. By E. J. HART, K. H. SCHMIDT and K. N. VASUDEVAN;Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439, U,S.A.
(No abstract given.)
Current work on nucleation
This paper describes a computer simulation model which reproduces the random atomic processes which occur in condensation, evaporation, and surface diffusion (upon an idealized (100) crystalline substrate surface). Computer simulation experiments based on this model were carried out over a range of adatomadatom interaction energies and adsorption fluxes chosen so as to produce observable nucleation phenomena in a reasonably short computation time. The equilibrium distribution of cluster sizes and the critical cluster size were measured in a large number of cases and compared to predictions of the Walton-Rhodin atomistic nucleation theory. Very good agreement between the experimental and theoretical values was obtained. The nucleation rate was also measured for one particular set of parameters and found to agree satisfactorily with the atomistic theory prediction. Consequently, we conclude that within the limitation of the assumptions of the simulation model used, the Monte Carlo method is suitable for the simulation of the phenomena of heterogeneous nucleation. A number of suggestions are offered for the refinement and extension of this simulation method which may help to answer some of the unresolved questions of heterogeneous nucleation theory.
Molecular dynamics study of the clustering in hard parallel squares. By C. CARLIERand H. L. FRISCH; State University of New York, Albany, New York 12222, U.S.A. A molecular dynamics study of clustering in systems of 400 and 900 hard parallel squares shows that in the high density region, the distributions N(n) of clusters of size n depend only upon one dimensionless variable. Results are slightly different in the intermediate density fluid region. For all densities and values of the clustering distance parameter L, N(n) is a monotone decreasing function of n. A simple free volume theory predicts relatively well the results in the high density region. The clusters are relatively compact. From an exponential fit to the function N(n)/N(1) obtained for densities near the phase--transition region, one estimates the value of the parameters of the exponential law given by the classical theory of nuclation.
Heteromolecular nucleation theory applied to gas to particle conversion. By C. S. KIANG and D. STAUFFER; Physics Department, Clark College, Altanta, Georgia 30314, U.S.A. and V. A. Morrr~N; Atmospheric Sciences Research Center, State University of New York, Albany, New York 12222, U.S.A. and J. BRICARD; Physique des Aerosols, Facult6 des Sciences, Universit6 de Paris, France. An attempt has been made to explain gas to particle conversion with the beteromolecular nucleation theory, The theory is applied to a binary mixture of H 2 0 - H z S O , and H 2 0 - H N O a respectively in air. The resulting formation of critical sized clusters is calculated as function of relative humidity up to 99 per cent. Sulfuric acid resulting from gas phase reactions in the atmosphere has one of the lowest vapor pressures of all reaction products. Nitric acid with its relatively high vapour pressure would represent an upper limit for gas to particle conversion to occur under atmospheric conditions.
Homogeneous nudeafion in steam nozzle condensation. By D. BARSCHDORFF,W. J. DUNNING,P. P. WEGENER and B. J, C. Wu; Department of Engineering and Applied Science, Yale University, New Haven, Connecticut 06520, U.S.A.
(No abstract given; to be published in Nature.)
RecentstudiesenSO2 oxidation in the presence of liquid water. By S. BEILKE,D. LAMB and J. MILLER; Institut fur Metenrologie und Genphysik, OniversitAt, Frankfurt, West Germany. The following studies refer in a wide sense to problems of trace gas and atmospheric aerosol agglomoration on cloud droplets and rain droplets. Of particular interest is here the incorporation of atmospheric sulphur compounds like S02, H2S, and sulfate, which is an essential constituent of atmospheric aerosols. (In German.)
Condensation nuclei discriminator based on optical measurements during fog formation: A new tool for environmental research. By E. J. HART, K. H. SCHMIDT and K. N. VASUDEVAN;Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439, U,S.A.
(No abstract given.)