Journal and Proceedings of
The Royal Society of New South Wales
Volume 134 Parts 3 and 4
River Bank Collapse on the Nepean River in the Wallacia Valley: Assessing Possible Causes by Historical and Geomechanical Methods
Docker, B.B., & Hubble, T.C.T.
Abstract: River banks of the Nepean River within the Wallacia Valley are subject to widespread upper bank collapse and erosion of the lower bank toe. An historical approach by aerial photograph analysis, and a geotechnical approach by slope stability modelling has been used to determine the influence of human-derived modifications on this morphological change. Widespread collapse of the Nepean's banks occurred primarily during a relatively wetter climatic period between 1949 and 1970 and was most noticeable on banks cleared of vegetation. Stability analyses conducted on representative bank profiles indicate the strong cause and effect relationship between devegetation and mass-failure of riverbanks. A riverbank of average morphological dimensions experiencing rapid drawdown presents as stable in the vegetated case and unstable in the devegetated case. Wind-wave erosion on the weir-lake has probably eroded bank toes by up to two metres. Changes in bank angles resulting from in-channel sand and gravel extraction also reduce bank stability although such activities largely post-date the main period of bank collapse and consequently they are not considered to be a major cause of failure. Human influence via devegetation and weir construction has been paramount in causing significant morphological change to this particular riverine environment.
Keywords
River-bank failure, Nepean River, Slope-Stability Modelling, Anthropogenic
Change, Devegetation
Heat Shock Events, Inhibition of Seed Germination and the Role of Growth Regulators in Stress Alleviation
Mohamad A. Kader
Abstract: The timing of heat stress after sowing is crucial in the success of pearl millet crops. Several heat shock events were evaluated and the impact of seed treatments on germination was investigated. Segmenting seed treatments into phases and sequencing growth regulators with water was also evaluated. Seven growth regulator-based seed treatments were applied to pearl millet seeds with the goal of improving the germination and early seedling growth under these heat shock events. Both gibberellic acid (GA3) and kinetin were sequenced with water in one or two cycles (growth regulator/water) for 4 hours. Otherwise, seeds were soaked in water alone for 4 hours. Heat shock (46oC) was administered on the first three days after sowing seeds, the fourth, the fifth or sixth day and in alternating form (shock/no shock). Results revealed that sequencing growth regulators with water advanced germination to a greater extent than growth regulators alone. Seed treatments increased the speed of germination over controls and the first three days after sowing were more sensitive to heat shock than days 4, 5 and 6. The physiology of seed response to heat shock is discussed.
Keywords
heat, germination, growth, stress
Factors in the Use of Breast Screening for Effective Secondary Prevention
Communicated by Professor A.G. Shannon
E. Thornton
Abstract: Although Australia has set up a breast screening program in each State and a National Breast Cancer Centre, there is a lack of understanding of mammography over a wide range of the community, both women and men, about its objectives, limitations and requirements for effective secondary prevention of breast cancer. Therefore it seems desirable to examine the criteria for selection of a disease for screening as established by the World Health Organisation and discuss these criteria in their applications to screening for breast cancer. The presentation is made in the light of the Australian system and what each criterion realistically implies. With regard to the marginal cost per year of life saved calculated for a range of different screening strategies for age groups and screening frequencies it appears that the Australian strategy (age 50--69 biennially) compares very well with the most effective screening strategy.
Keywords
Breast screening, mammography, Australia
Geodiversity Symposium, Australian Museum
F.L. Sutherland, Convenor
The following abstracts are associated with a special Geodiversity Symposium organised by the Geodiversity Research Centre at the Australian Museum to mark the retirement of Dr F.L. Sutherland from his Museum position. The Symposium was opened by Professor Evan Leitch, President of the Geological Society of Australia.
The abstracts cover the fields of research conducted by the Australian Museum during the tenure of Dr Sutherland in the past three decades and involved co-workers from the Museum and other institutions, both Australian and overseas.
The convenor hopes that by publishing these abstracts of the Symposium The Royal Society of NSW will be promoting the wide diversity of geological topics presented at the Symposium.
Communicated by Dr F.L. Sutherland
[ed. There are a total of 14 abstracts. Copies of these can be obtained from the Society.]
Thesis Abstract: Variation in the Anterior Mandible of Homo sapiens sapiens
Graham Knuckey
Abstract of a thesis submitted for the Degree of
Doctor of Philosophy,
University of New England, Armidale,
New South Wales, Australia.
One of the features that distinguishes humans from all other primates is the presence of a symphyseal buttress, or chin, on the basal margin of the buccal surface of the mandible. The presence and purpose of this buttress has been debated for two hundred years, culminating at the end of the twentieth century, in two main branches of thought; the adaptive hypothesis and the non-adaptive hypothesis.
With the passing of time the human craniofacial skeleton has reduced in size and the lower facial skeleton (which includes the mandible) has moved in under the cranial vault becoming in turn, less prognathic. The adaptive hypothesis suggests the chin appeared in humans as an adaptive response to these changes in size and shape and argues that as the mandible reduced in size to accommodate broader craniofacial size reductions, a buttress of bone developed at the mandibular symphysis, as a means of strengthening the anterior mandible against masticatory muscle stresses. This buttress was unnecessary in larger, ancestral hominids because their mandibles were sufficiently robust to begin with.
The non-adaptive hypothesis, however, maintains the symphyseal buttress is merely an artefact of evolution and that it does not actually exist as an adaptive trait at all . Rather, as the alveolar growth field in the mandible receded more rapidly than the basal growth field below it, the buttress of bone simply appeared between the two. The non-adaptive theorists argue the buttress has no adaptive significance, yet they concede it may have developed a functional role since first appearing on the mandible of Homo sapiens sapiens (commonly referred to as modern Homo sapiens).
Both adaptive and non-adaptive arguments are based upon the same underlying principle - that through time the human craniofacial skeleton has reduced in size, resulting in a buttress of bone appearing over the mandibular symphysis below the incisors. This thesis explores the underlying principle further and presents a model that suggests that as a direct result of this principle, symphyseal buttresses (chins) should be more prominent in human populations that are on average small. Specifically, a reduction in the lower craniofacial skeleton in humans has produced a response from the basal section of the anterior mandible, which has become increasingly prominent. The research presented here argues the result of this process should be an increase in symphyseal prominence in smaller human populations - bigger chins in smaller groups.
The model is tested using samples of crania from human populations originating in the Aleutian Islands; Australia (Australian Aborigines); Egypt (Pre- and Late Dynastic periods); mainland North America (African Americans, Caucasians, and Native Americans); South Africa (Sotho and Xhosa language groups); and the United Kingdom (Romano-Britons). It demonstrates that populations which are, on average smaller, do possess more prominent chins. There is also circumstantial evidence in support of a trend toward more prominent buttresses in the more gracile individuals within human populations, that is, the females.
Graham Knuckey
University of New England, Armidale,
New South Wales, Australia.