ON THE TEMPERATURE DEPENDENCE OF PARAMAGNETIC RESONANCE IN THE CASE OF THE ISING MODEL

1961 ◽  
Vol 39 (12) ◽  
pp. 1733-1737 ◽  
Author(s):  
Y. Y. Lee
Keyword(s):  
Ising Model ◽  
Temperature Dependence ◽  
Approximation Method ◽  
Line Shape ◽  
Theoretical Study ◽  
Shape Function ◽  
Paramagnetic Resonance ◽  
One Dimensional ◽  
The One ◽  
Line Shape Function

The adequacy of the approximation method used by McMillan and Opechowski in their theoretical study of the temperature dependence of the paramagnetic resonance line shape function is very difficult to ascertain for the case of a typical paramagnetic crystal. For this reason the approximation method has been investigated for the very simple case of the one-dimensional Ising model. Exact expressions for the line shape function of the model are compared with expressions obtained by the approximation method mentioned above. The agreement between the two expressions is found to be very good in general, and extremely good at very low temperatures.

ON THE TEMPERATURE DEPENDENCE OF THE SHAPE OF PARAMAGNETIC RESONANCE LINES

1960 ◽  
Vol 38 (9) ◽  
pp. 1168-1186 ◽  
Author(s):  
Malcolm McMillan ◽  
W. Opechowski
Keyword(s):  
Thermal Expansion ◽  
General Theory ◽  
Temperature Dependence ◽  
Shape Function ◽  
Temperature Dependent ◽  
Paramagnetic Resonance ◽  
Effective Spin ◽  
Spin Lattice ◽  
Second Moments ◽  
Line Shape Function

A theory of the temperature dependence of the shape of paramagnetic resonance lines is developed for temperatures sufficiently low to make the effects of the spin–lattice interaction and thermal expansion negligible. General expressions for the first and second moments of the line shape function as functions of the temperature are obtained, and the approximations used are discussed in detail. These expressions are applied to the case of effective spin [Formula: see text] and 1. As an illustration of the general theory numerical results are given for the paramagnetic resonance lines of nickel fluosilicate. In this case the moments become strongly temperature dependent below 10 °K.

scholarly journals Rare temperature histories and cirrus ice number density in a parcel and a one-dimensional model

2014 ◽  
Vol 14 (23) ◽  
pp. 13013-13022 ◽  
Author(s):  
D. M. Murphy
Keyword(s):  
Temperature Dependence ◽  
Low Temperatures ◽  
Ice Crystals ◽  
Strong Increase ◽  
Number Density ◽  
Dimensional Model ◽  
One Dimensional ◽  
Slow Growth Rate ◽  
Wide Range ◽  
The One

Abstract. A parcel and a one-dimensional model are used to investigate the temperature dependence of ice crystal number density. The number of ice crystals initially formed in a cold cirrus cloud is very sensitive to the nucleation mechanism and the detailed history of cooling rates during nucleation. A possible small spread in the homogeneous freezing threshold due to varying particle composition is identified as a sensitive nucleation parameter. In a parcel model, the slow growth rate of ice crystals at low temperatures inherently leads to a strong increase in ice number density at low temperatures. This temperature dependence is not observed. The model temperature dependence occurs for a wide range of assumptions and for either homogeneous or, less strongly, heterogeneous freezing. However, the parcel model also shows that random temperature fluctuations result in an extremely wide range of ice number densities. A one-dimensional model is used to show that the rare temperature trajectories resulting in the lowest number densities are disproportionately important. Low number density ice crystals sediment and influence a large volume of air. When such fall streaks are included, the ice number becomes less sensitive to the details of nucleation than it is in a parcel model. The one-dimensional simulations have a more realistic temperature dependence than the parcel mode. The one-dimensional model also produces layers with vertical dimensions of meters even if the temperature forcing has a much broader vertical wavelength. Unlike warm clouds, cirrus clouds are frequently surrounded by supersaturated air. Sedimentation through supersaturated air increases the importance of any process that produces small numbers of ice crystals. This paper emphasizes the relatively rare temperature trajectories that produce the fewest crystals. Other processes are heterogeneous nucleation, sedimentation from the very bottom of clouds, annealing of disordered to hexagonal ice, and entrainment.

Sign in / Sign up

Export Citation Format

Share Document