Note on the No-stress Boundary Condition at the Edge of the Ice Pack

The theoretical modelling of the large-scale motion of the arctic ice pack is receiving increasing attention as the economic importance of the region increases. One of the most widely used types of model is the so-called "viscous fluid" model. ... The boundary condition at the edge of the ice pack is an important feature of most such models. In some cases a no-slip condition seems appropriate, but in others, when the ice near the boundary has a low compactness (fraction of ice coverage) or the boundary occurs away from a coast, some other condition may be more appropriate. One that is often suggested is a no-stress condition, which is often assumed to imply that there is no velocity gradient perpendicular to the boundary. When the edge occurs away from a coast, the latter assumption is wrong. It suffices for present purposes to assume that we are dealing with an incompressible two-dimensional fluid. In this case the viscous force per unit of area (corresponding to volume in three dimensions) is del·(A del v), where A is an isotropic but possibly variable coefficient of eddy viscosity, and v, the large-scale averaged horizontal ice velocity, has components u and v in the x and y directions respectively. The notation del v ... is equivalent to the tensor [partial derivative of vi with respect to xj], where i and j vary independently over all coordinate directions, and (del·del v)i = Sum over the index j of (partial derivative with respect to xj of the partial derivative of vi with respect to xj). ... Since the viscous force is the divergence of the stress, the quantity A del v is often thought of as the eddy stress (or "internal ice stress"). That this is not true is easily seen by noting that the tensor A del v, to be referred to here as the "pseudo-stress" tensor, is not symmetrical. The non-diagonal elements of the stress tensor, which must be equal, are ½A(partial derivative of v with respect to x + partial derivative of u with respect to y). The distinction made here is irrelevant in determining the viscous forces, since the stress tensor and the pseudo-stress tensor differ by a tensor of zero divergence .... In large-scale ocean models which employ eddy viscosity, the stress itself is often required in connection with boundary conditions, particularly at the sea surface, or naviface .... Here, however, those who use the pseudo-stress are saved both by scale considerations and by the fact that w=0 (where w is the vertical or z-component of velocity), hence the (partial derivative of w with respect to x)=0 and the (partial derivative of w with respect to y)=0, at the naviface, so that the stress components there reduce to A(partial derivative of u with respect to z) and A(partial derivative of v with respect to z). In the "viscous liquid" model of an ice pack bounded by open water, we at last have a case in which the distinction between real stress and pseudo-stress assumes geophysical importance. ... Assuming (without loss of generality) that the edge is oriented with its outward normal in the first quadrant at an angle of theta to the x-axis, we have for the direction cosines: n1 = +cos(theta), n2 = +sin(theta), t1 = +sine(theta), t2= -cos(theta). The appropriate expression of the condition that there be no tangential stress at the boundary becomes: sin(2theta)(partial derivative of u with respect to x - partial derivative of v with respect to y) - cos(2theta)(partial derivative of v with respect to x - partial derivative of u with respect to y) = 0. ... If the boundary is oriented along a coordinate axis this reduces to (partial derivative of v with respect to x) + (partial derivative of u with respect to y) = 0, which qualitatively means that shears at the boundary are permitted, provided that they are part of a locally uniform rotation and do not produce deformation of the ice field. If one also wishes to assume zero normal stress at the boundary, there is an additional condition given by: (partial derivative of u with respect to x)cos² (theta) + (partial derivative of v with respect to y)sin²(theta) + ½(partial derivative of v with respect to x + partial derivative of u with respect to y)sin(2theta) = 0. These are purely mathematical deductions; the appropriateness of the physical conditions is a more difficult question which can only be answered experimentally. The physical condition of zero tangential stress qualitatively means that no deformation of the ice field can take place at the boundary. Techniques for measuring the deformation of the ice fields are now under development. It is suggested that it would be interesting to measure the deformation of ice fields near the boundary, even though a measurement of non-zero deformation (which the author suspects would be found, since external driving forces will in general tend to produce deformation) would not distinguish critically between the correctness of the boundary condition and the basic validity of the "viscous liquid" type of model

Ice Spirals off Barrow as Seen by Satellite

An eddy-like feature, similar to ones observed in the Kamchatka Current, has been observed off the Alaskan coast near Barrow at the boundary of the Chukchi and Beaufort Seas by the NOAA-5 satellite and radar imaging. Broken ice in the area was carried into a spiral pattern by complex current actions. Possible mechanisms for this phenomenon, including encounters between the Alaskan Coastal Current and the Beaufort Sea Gyre, local bathymetry, or sidewall friction effects caused by Point Barrow, are discussed

Large scale response of the ocean to sea ice formation,

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Meteorology, 1969.Vita.Includes bibliography.by Harold Solomon.Ph.D

Slow, stealthy and steady – capacity development to address land tenure issues in development programmes: experiences of the IFAD/GLTN TSLI-ESA Project

Land and natural resource tenure security is a central yet often neglected area for economic development and poverty reduction in the developing world. Land is fundamental to the lives of poor rural people. It is a source of food, shelter, income and social identity. Secure access to land reduces vulnerability to hunger and poverty. There are some 1.3 billion extremely poor people in the world, struggling to survive on less than US$1.25 a day, and close to a billion continue to suffer from chronic under-nourishment. About 70 per cent of these people live in the rural areas of developing countries. In most rural societies, the poorest people often have weak or unprotected tenure rights. This condition undermines them from using their land resource effectively. They also risk losing land they depend on to more powerful groups including private investors.Women and youth are particularly vulnerable because their land rights may be obtained through kinship relationships with men or families. If those links are severed, women and youth can lose their rights. When insufficient attention is paid to secure access by small-scale producers and to land tenure issues, development programmes can become part of the problem. Most development programmes continue to eschew land tenure issues because they are sticky and difficult issues to be addressed, at least, in the timeframe of a classic programme. As such, the tenure issues linger around and affect the outcome of the programmes. While many other issues are attributed to their failures, again, land tenure issues are swept under the carpet.This paper presents the experiences of implementing capacity development for strengthening tenure security in IFAD supported programmes in Eastern and Southern Africa. Most of the data was gathered during missions and many interactions with communities and staff of the about 20 IFAD supported programmes that TSLI-ESA worked with.In all programmes tenure issues were present, albeit to varying extents – be it those programmes promoting sustainable natural resources management, agricultural productivity, agricultural value chain development, and rural finance. Tenure issues were analysed during design missions, and if they were predicted to have significant impacts, appropriate interventions were designed and integrated in the programme plan documents. The tenure interventions were, however, not the primary objectives of the programmes hence, the scope, budget and detail of implementation tended to be less emphasized relative to the other ‘core’ interventions of the programmes.Furthermore, in some cases, potentially salient tenure issues were not very apparent at the design stage. In such cases land tenure interventions were not explicitly integrated into the programme design, mainly because their impacts on the outputs of the programme were, at least initially, calculated to be insignificant. Such issues were addressed retrospectively during the programme implementation following a programme re-design, an exercise that makes sure the programme bounce back on track.Key lessons, there is need to exhaustively consider implications of potential land tenure issues from the start including their anticipated consequences, and where possible include them in the programme plan. Secondly, there is need to integrate tenure issues in programme monitoring and evaluation system to keep track of tenure issues and their potential impact on programme delivery. There is need to provide evidence-based report to local and national authorities responsible for administration, management and policy for land and natural resources of any salient tenure security issues that are beyond the scope of, but have significant impact on, the programme being implemented. We recommend for establishment of centralized tenure desk at national or local level to attend to tenure issues from the various programmes, both public and private

Meaning in Small, Snyders and Pearce : an application of Lotman’s semiotics to ‘coloured’ literature

In this study, a semiotic point of view of selected literature written by ‘coloured’ writers is examined, using some of the semiotic theories of Jurij M. Lotman, one of the leading Soviet semioticians of the school of Tartu. Selected theories of Lotman are applied to ‘coloured’ literature. These include an examination of poetic language (based on Lotman’s theory of a primary and secondary modelling system), the iconicity of the text, the aesthetics of identity and opposition, the distinction between text and extra-text, and the relationship that exists between the extra-text, culture and code. The literary texts chosen for analysis are works by three contemporary ‘coloured’ writers, namely Adam Small, Peter Snyders and Robert Pearce, who have all contributed poetry, prose and drama to Afrikaans literature in general, and original Afrikaans literature in particular. The selected dramas are Joanie Galant-hulle (Small 1978), Political Joke (Snyders 1983) and Die Laaste Supper in Marabastad (Pearce 1988b)*. These writers’ works span approximately three consecutive decades and their work can be examined for commonality and differences. The three chosen dramas were written five years apart respectively; yet they reveal thematic similarities. The dramas also feature a common ‘deviant’ language code used by ‘coloured’ people and discussed in this study as original Afrikaans. This code, which is juxtaposed with standard Afrikaans, is one of the basic areas of interest that motivated the choice of subject for this study. The primary objective of this study is to examine the differentiation that Lotman makes between the various sign systems that operate in natural language (the primary modelling system) and poetic language (a secondary modelling system), and to determine whether these sign systems can be detected and are functional in ‘coloured’ literature. In addition, an investigation is made of the iconicity that operates in poetic language (which, according to Lotman, is the basis for differentiation), and to ascertain whether iconicity occurs in these examples of ‘coloured’ literature and to what extent it influences meaning. In the process, intratextual relations within the poetic text were scrutinised to establish whether the manipulation of language, devices and codes raises any particular expectation in the poetic text, and also to detect whether oppositionally constituted code-systems which set up their own patterns of expectation within the syntactic and lexical levels of the poetic text clash with and contradict prior expectations. In addition, an analysis has been made to determine whether a new understanding of the texts can be reached, based on Lotman’s aesthetics of identity and opposition, and to what extent the reader is forced to collaborate in the modelling process of the texts when the reader’s expectations are undermined by an aesthetics of opposition. The study has successfully corroborated and substantiated all the selected aspects of Lotman’s theory. The differentiation that Lotman makes between the primary and secondary language model is demonstrated especially by the iconicity that operates in poetic language. Examples are abundant in the selected literature and are conspicuous, especially through the manipulation of the language, devices and codes employed by the authors to defamiliarise objects so that they transcend their familiar characteristics and perceptions, and sometimes signify a totally new concept. In this way, readers’ expectations are subverted and they are invited to collaborate in the modelling process of the texts. These techniques are also an integral part of both the text and the extra-text, and their presence justifies Lotman’s claims that the meaning of a literary text cannot be understood outside its cultural or historical context. In retrospect, it can be argued that this research has opened up some additional avenues for an analysis of meaning in ‘coloured’ literature.Dissertation (MA (English))--University of Pretoria, 2004.Englishunrestricte

United States and Western Europe cooperation in planetary exploration

A framework was sought for U.S.-European cooperation in planetary exploration. Specific issues addressed include: types and levels of possible cooperative activities in the planetary sciences; specific or general scientific areas that seem most promising as the main focus of cooperative efforts; potential mission candidates for cooperative ventures; identification of special issues or problems for resolution by negotiation between the agencies, and possible suggestions for their resolutions; and identification of coordinated technological and instrumental developments for planetary missions