Growth rates of icicles

Experimental and theoretical studies on the growth rate of an icicle were carried out as a function of temperature, water-supply rate and wind speed; the relative humidity was also taken into account. The length of an icicle increases by the downward growth of thin dendritic crystals into the supercooled pendant water drop at the tip, and thus the growth is in the crystallographic a-axis direction. The diameter, on the other hand, increases by the freezing of a water film flowing down along the icicle wall. The ratio of measured length-and diameter-growth rates was large, namely 8–32.Both growth rates increased with decreasing temperature and increasing wind speed. The increase in water-supply rate led to the decrease in the length-growth rate but no significant change in the diameter-growth rate. These results could be well described by a numerical model of icicle growth which takes account of the dendritic growth at the tip and the wall and the effective heat transfer within the turbulent boundary layer around the icicle. A formation mechanism of ribs and hollows is discussed in relation to the flowing and freezing process of water on an icicle wall

Focus Groups and Political Marketing: Science and Democracy as Axiomatic?

Focus groups are an established and influential way of generating public opinion data. They have been extensively used by the British Labour Party and are more broadly associated with marketing. Focus groups, as referred to within much of the political marketing literature and used in political practice, are underpinned by two central but largely implicit claims: first, that the use of focus groups is scientific; second, this claim to science is conflated with the normative assertion that focus groups enhance the democratic process. This article renders explicit and disentangles these underlying assumptions that inform the theory and practice of focus groups. These theoretical concerns are illustrated by reference to the Labour Party, in particular its modernisation process during the build-up to the 1997 election. By separating and interrogating these basic premises two salient issues subsequently emerge. First, it is contended that the use of focus groups, in the political marketing literature and in political practice violates ‘scientific’ principles. Second, it is argued that over-reliance on focus groups challenges normative claims to democracy, by confining the potential for democratic debate to the few, rather than the many