Showing papers by "Australian National University published in 1981"

Sequence and organization of the human mitochondrial genome

Abstract: The complete sequence of the 16,569-base pair human mitochondrial genome is presented. The genes for the 12S and 16S rRNAs, 22 tRNAs, cytochrome c oxidase subunits I, II and III, ATPase subunit 6, cytochrome b and eight other predicted protein coding genes have been located. The sequence shows extreme economy in that the genes have none or only a few noncoding bases between them, and in many cases the termination codons are not coded in the DNA but are created post-transcriptionally by polyadenylation of the mRNAs.

Some relationships between the biochemistry of photosynthesis and the gas exchange of leaves.

Abstract: A series of experiments is presented investigating short term and long term changes of the nature of the response of rate of CO2 assimilation to intercellular p(CO2). The relationships between CO2 assimilation rate and biochemical components of leaf photosynthesis, such as ribulose-bisphosphate (RuP2) carboxylase-oxygenase activity and electron transport capacity are examined and related to current theory of CO2 assimilation in leaves of C3 species. It was found that the response of the rate of CO2 assimilation to irradiance, partial pressure of O2, p(O2), and temperature was different at low and high intercellular p(CO2), suggesting that CO2 assimilation rate is governed by different processes at low and high intercellular p(CO2). In longer term changes in CO2 assimilation rate, induced by different growth conditions, the initial slope of the response of CO2 assimilation rate to intercellular p(CO2) could be correlated to in vitro measurements of RuP2 carboxylase activity. Also, CO2 assimilation rate at high p(CO2) could be correlated to in vitro measurements of electron transport rate. These results are consistent with the hypothesis that CO2 assimilation rate is limited by the RuP2 saturated rate of the RuP2 carboxylase-oxygenase at low intercellular p(CO2) and by the rate allowed by RuP2 regeneration capacity at high intercellular p(CO2).

The composition and evolution of the continental crust: rare earth element evidence from sedimentary rocks

Abstract: The composition of the present-day upper crust, inferred from the uniformity of sedimentary rock r.e.e. (rare earth element) patterns, is close to that of granodiorite. A revised ‘andesite’ model is used to obtain total crustal composition. The lower crust is the composition remaining, assuming that the upper crust, one-third of the total, is derived from intracrustal partial melting. The upper-crustal r.e.e. pattern has pronounced Eu depletion (Eu/Eu* = 0.64), the lower-crustal pattern has Eu enrichment (Eu/Eu* = 1.17) and the total crust has no Eu anomaly relative to chondritic abundances. The Eu depletion in the upper crust is attributed to retention of Eu in plagioclase in the lower crust. Because plagioclase is not stable below 40 km (> 10 kbar), the anomaly is intracrustal in origin. The Archaean upper crust has a different r.e.e. pattern to that of the present-day upper crust, being lower in total r.e.e., and La/Yb ratios, and lacking an Eu anomaly. These data are used to infer the Archaean upper-crustal composition, which resembles that of the present-day total crust, except that Ni and Cr contents are higher. The Archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites. The latter have steep light r.e.e.-enriched-heavy r.e.e.-depleted patterns, consistent with equilibration with garnet and hence probable mantle derivation. There is little reason to suppose that the Archaean lower crust was different in composition from the upper crust, except locally where partial melting episodes occurred. The r.e.e. evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early Archaean, a massive increase (to about 70% of the total crust) between about 3000 and 2500 Ma B.P. and a slow increase until the present day. The change from Archaean to post-Archaean r.e.e. patterns in the upper crust is not isochronous, but is reflected in the sedimentary rock r.e.e. patterns at differing times in different continents. On the basis of a model composition for the mantle, 36% of the potassium, 30% of uranium, 15% of lanthanum and 3 % of ytterbium are concentrated in the present continental crust. This enrichment is related to ionic size and valency differences from common mantle cations (e.g. Mg, Fe). Pre-3.9 Ga B.P. crusts were obliterated by meteorite bombardment. No geochemical evidence exists for primordial anorthositic, sialic or mafic crusts.

Double-diffusive convection

Abstract: In this paper we present a rather personal view of the important developments in double-diffusive convection, a subject whose evolution has been the result of a close interaction between theoreticians, laboratory experimenters and sea-going oceano-graphers. More recently, applications in astrophysics, engineering and geology have become apparent. In the final section we attempt to draw some general conclusions and suggest that further progress will again depend on a close collaboration between fluid dynamicists and other scientists.

Hydration forces between mica surfaces in aqueous electrolyte solutions

Abstract: Surface forces between molecularly smooth mica sheets were measured in Na+ and K+ aqueous salt solutions (at ∼10−3 M) both at 21°C and, for the case of Na+, at 65°C. Additional short-range repulsive forces were found to be the same at both temperatures. In very low concentrations of electrolyte solution (∼5 × 10−6M) and in hydrochloric acid solutions (up to 1.2 × 10−3M) these forces were completely absent-giving force curves in very good agreement with DLVO theory. Analysis of these force-interaction results appears to prove conclusively the existence of counterion hydration forces on mica. These forces apparently also prevent both bubble coalescence and coagulation of latex colloids at high concentrations of electrolyte. The total interaction between charged colloidal surfaces should involve, as apparently in the case of mica, both short-range repulsive forces due to bound partially hydrated ions and a longer range repulsion due to hydrated counterions in the compressed double-layer. These “hydration” forces should be present in many colloidal systems and be dominant in those with high negative charge densities and little possibility of hydrogen bonding to adjacent water layers. Surfaces consisting of ionic species (e.g., Zwitterionic lecithin bilayers) should give rise to repulsive forces due to the surface ion hydration effects only.

Radial fingering in a Hele Shaw cell

Abstract: The results of experiments involving instability, known as fingering, in a circular Hele Shaw cell with inward and outward flow are presented. The width of fingers in this situation is examined, and an approximate equation for the growth of fingers is proposed. The equation rα = cos (nθ) is shown to fit the shape of long fingers.

The transition between spinel lherzolite and garnet lherzolite, and its use as a Geobarometer

Abstract: The equilibrium between spinel lherzolite and garnet lherzolite has been experimentally determined in the CaO-MgO-Al2O3-SiO2 system between 800° and 1,100° C. In confirmation of earlier work and predictions from thermodynamic data, it was found that theP-T slope of the reaction was close to zero, the equilibrium ranging from 16.1 kb at 800° C to 18.7 kb at 1,100° C (±0.3 kb).

Searching behaviour of desert ants, genusCataglyphis (Formicidae, Hymenoptera)

Abstract: 1. If a homing ant (Cataglyphis bicolor,C. albicans) gets lost, it does not perform a random walk but adopts a stereotyped search strategy. During its search the ant performs a number of loops of ever-increasing size, starting and ending at the origin and pointing at different azimuthal directions. This strategy ensures that the centre area where the nest is most likely to be, is investigated most extensively. 2. After one hour of continuous search the ant's search paths cover an area of about 104 m2. Nevertheless, the system of loops performed during this time is precisely centred around the origin. The ant's searching density does not depend on the azimuthal direction around the origin but only on the distance from the origin. It rapidly decreases with increasing distance. 3. The ant's searching pattern can be characterized by two functions: thed/t-function correlating distance (d) with time (t), and theα/t-function correlating azimuthal direction (α) with time. If fixes of the ant's position are taken every 10 s, the vectors pointing from the origin to successive fixes change their lengthsd systematically (α/t-function) and their directionsα randomly (α/t-function). What is especially characteristic of the ant's searching pattern is the oscillatingd/t-function which clearly demonstrates that the searching ant repeatedly returns to the origin, even after it has walked, within one hour, along a search trajectory of more than 1 km (the latter number refers toC. albicans-A). The ant's walking speed does not change within a search time of 1 h. 4. The distribution of changes in direction between successive segments of a search path,β, is usually unimodal with a mean of 0°, if complete search paths are considered. Nevertheless, within smaller periods of time, especially during the initial portions of the search the integrated angleβ may continuously change in the same direction. Such portions of the search crudely resemble a spiral which alternately expands and contracts. 5. Although all 3 species ofCataglyphis studied in this paper adopt the same general search strategy, there are some differences in the fine structure of the search:C. albicans-A departs further from the origin than any other species, and performs the most rapid turns. The tendency towards spiralling is most pronounced inC. albicans-B. 6. An efficient searching strategy is formulated, based on purely theoretical grounds. It is assumed that when the search begins the probability density function (PDF) for the location of the nest is Gaussian in two dimensions (a priori PDF). It is further assumed that the ant can never becompletely certain that a given area has been fully explored, so that it is only theprobability of encountering the nest within a certain region that decreases as the time spent in searching this region increases. Thus, the most promising region to search is specified by an a posteriori PDF which takes the ant's past performance into account. 7. A computer model is presented that searches in optimum fashion, as proposed above. In the model, motion of the ant is characterized in terms of radial and tangential components, with the tangential component varying randomly and the radial component varying according to the a posteriori PDF. The model successfully describes what the ants are actually doing (e.g., compare Figs. 17 and 18 with Fig. 3, Figs. 19 and 20 with Figs. 8–10, and Fig. 21a and b with Figs. 4 and 5), indicating that the searching behaviour ofCataglyphis is geared to find the nest as quickly as possible.

The translational and rotational drag on a cylinder moving in a membrane

Abstract: The translational and rotational drag coefficients for a cylinder undergoing uniform translational and rotational motion in a model lipid bilayer membrane is calculated from the appropriate linearized Navier–Stokes equations. The calculation serves as a model for the lateral and rotational diffusion of membrane-bound particles and can be used to infer the ‘microviscosity’ of the membrane from the measured diffusion coefficients. The drag coefficients are obtained exactly using dual integral equation techniques. The region of validity of an earlier asymptotic solution obtained by Saffman (1976) is elucidated.

The interaction of colloidal particles collected at fluid interfaces

Abstract: Simple approximate expressions are derived for the meniscus forces acting between spherical and cylindrical bodies at a fluid interface using a superposition approximation due to Nicolson (Proc. Cambridge Philos. Soc. 45, 288 (1949)). These expressions are correct to lowest order in the Bond number, B = (ϱB - ϱA)gR2/γAB, and are applicable to bodies that may be dissimilar in Bond number and wetting characteristics. Our results compare very favorably with the exact numerical calculations of Gifford and Scriven (Chem. Eng. Sci. 26, 287 (1971)) for parallel cylinders (for B ≲ 10−1). The small Bond number expressions derived herein are directly applicable to the interaction between particles of colloidal dimensions collected at fluid interfaces. Some sample calculations are given to illustrate the importance of capillary forces in interfacial coagulation processes. The extension of the theory to higher Bond number is discussed briefly.

Regional continuity in Australasian Pleistocene hominid evolution

Abstract: A reconstruction of the Indonesian male Homo erectus specimen Sangiran 17 reveals a suite of features that suggests regional morphological continuity in Australasia during the middle and late Pleistocene. Characteristics reflecting a morphological clade are established through a comparison with the males from Kow Swamp, the late Pleistocene Australian site with the largest number of hominid specimens. It is argued that the "center and edge" hypothesis could account for the initial appearance of regional variation, and that a dynamic model of geneflow and opposing selection provides the mechanism that maintained a long-standing dynamic clinal equilibrium in this area.

Fragmentation of Asia in the Permian

Abstract: Asia is a composite continent formed by the accretion of crustal blocks1–3. A likely sequence of events is that Siberia collided with a Kazakhstan block which together then collided with Europe along the Urals in Permo-Triassic times2. This was followed by the sucessive accretion of various blocks of south and east Asia to Siberia, culminating in the collision of India with Asia during the Cenozoic. Palaeomagnetic data have already demonstrated that the Kolyma and Sikhote Alin blocks of eastern Asia collided with the main continent along the late Mesozoic fold belts of Verkhoyansk and Sikhote Alin4. Furthermore, results from the Malay peninsula5 and Japan6 suggest that South-east Asia and Japan were situated near the Equator in Permian times and were therefore separated from the Asian continent. We report here some palaeomagnetic results from the Permian of the Sino-Korean and Yangtze blocks of China that show they were also situated near the Equator, were not in their present relationship to one another and were widely separated from Siberia.

Immunofluorescence microscopy of organized microtubule arrays in structurally stabilized meristematic plant cells.

Abstract: Cells were prepared for indirect immunofluorescence microscopy after paraformaldehyde fixation of multicellular root apices and brief incubation in cell wall-digesting enzymes. This allowed subsequent separation of the tissue into individual cells or short files of cells which were put onto coverslips coated with polylysine. Unlike spherical protoplasts made from living tissues, these preparations retain the same polyhedral shape as the cells from which they are derived. Cellular contents, including organized arrays of microtubules, are likewise structurally stabilized. Antibodies to porcine brain tubulin react with all types of microtubule array known to occur in plant meristematic cells, namely, interphase cortical microtubules, pre-prophase bands, the mitotic spindle, and phragmoplast microtubules. The retention of antigenicity in permeabilized, isolated, stabilized cells from typical, wall-enclosed plant cells has much potential for plant immunocytochemistry, and in particular should facilitate work on the role of microtubules in the morphogenesis of organized plant tissues.

The Area-Time Complexity of Binary Multiplication

Abstract: The problem of performing multtphcaUon of n-bit binary numbers on a chip is considered Let A denote the ch~p area and T the time reqmred to perform mult~phcation. By using a model of computation which is a realistic approx~mauon to current and anucipated LSI or VLSI technology, ~t is shown that A T 2.

Water and Microbial Stress

Abstract: Reference to a dictionary reveals that an object under stress is subjected to “demand upon energy” or is “constrained.” It is precisely these two aspects of microbial ecology that I have considered in this review, the stress being imposed by some factor directly associated with the water regime of the immediate environment. Such a topic is relevant to many branches of microbiology. Thus, those working in microbial physiology, soil microbiology, plant pathology, food preservation, biodegradation, and marine and lacustrine microbiology all find water and its biological availability to be an important factor influencing microbial activity and hence microbial ecology.

Regional specialization of the chick retina as revealed by the size and density of neurons in the ganglion cell layer.

Abstract: On the basis of both morphological criteria and survival after ganglion cell axotomy, three populations of cells can be recognized in the ganglion cell layer of the chick retina. These are: 1) Irregularly shaped cells, which are not affected by axotomy and lack Nissl stain. They comprise about 5% of the total cell population and are probably glial cells. 2) Small cells which have a distinctive teardrop-shaped perikarya, stain for Nissl substance, and are not affected by axotomy. They occur with a uniform density of about 4,000 cells/mm2 across the entire retina and comprise 30-35% of the total number of cells in the ganglion cell layer. It is suggested that these cells are displaced amacrine cells. 3) Cells which stain strongly for Nissl substance and disappear after axotomy. These cells comprise 60-65% of the population of cells in this layer. The density of the latter cells varies throughout the retina. A high-density region in the central area extends into the superior-temporal retina. This high-density region corresponds to a position in the lateral visual field extending into the infero-frontal field. The total number of these cells agrees with the reported number of the optic nerve fibres in the chick, (Rager and Rager, '78); therefore they are presumably ganglion cells. The size distribution of the presumptive ganglion cells varies in different parts of the retina. The only previous study of the distribution and size of cells in the ganglion cell layer of the avian retina did not distinguish between ganglion cells and displaced amacrine cells (Binggeli and Paule, '69). The present results are therefore likely to be a more accurate description of the total number of ganglion cells, the regional variations in their density, and the characteristics of their size than previously reported.

Comparisons of δ13C values in leaves of aquatic macrophytes from different habitats in Britain and Finland; some implications for photosynthetic processes in aquatic plants.

Abstract: The δ13C values of submerged aquatic plants from contrasting but relatively defined habitats, and the δ13C values of emergent, floating and submerged leaves of dimorphic aquatic plants, were measured. In many instances the δ13C values of dissolved inorganic carbon in the water were also measured. Plant δ13C values in the vicinity of-40 to-50‰ were found in rapidly flowing spring waters with carbonate δ13C values of-16 to-21‰, consistent with the notion that species such as Fontinalis antipyretica almost exclusively assimilate free CO2 via RuP2 carboxylase. Plant δ13C values in the vicinity of-10 to-15‰ in sluggish water with carbonate δ13C values of about-5‰ were observed, consistent with the notion that boundary layer diffusion and/or HCO3- uptake may determine the δ13C value of submerged aquatic plants in these circumstances. Comparisons of δ13C values of the same or related species growing in waters of similar carbonate δ13C value but different flow rates confirmed this view; more negative δ13C values were frequently associated with plants in fast moving water. In Britain, but not in Finland, the δ13C values of submerged leaves of dimorphic plants were almost invariably more negative than in aerial leaves. The δ13C value of carbonate from chalk streams and in acid springs indicate substantial inputs of respiratory CO2, as opposed to atmospheric carbon. The contributions of these variations in δ13C of the carbon source, and of isotope fractionation in diffusion, to the δ13C value of submerged parts of dimorphic plants is discussed.

The learning processes of australian university students: investigations of contextual and personological factors

Abstract: Summary. Two studies are reported which investigate sex, faculty, and age (academic year) differences in the study methods of students at an Australian university. Significant main effects were found, but there was little evidence of any interactions. Correlations with grade point average indicated that success in Science-based faculties was related to using a deep-level approach to study relatively infrequently adopted by these students. It would seem that it was the young students, the male students, and the students enrolled in Science-based faculties who were most in need of study methods counselling.

Population magnitudes and distribution of the major modal classes of cat retinal ganglion cell as estimated from HRP filling and a systematic survey of the soma diameter spectra for classical neurones.

Abstract: A survey of diameter spectra in presented for classic neurones of the cat retinal ganglion cell layer. From these, with the aid of retrograde HRP filling for central retina, a set of density distribution maps has been prepared for each of the major modes of the neuronal diameter spectrum. The total population of classical neurones, the presumed ganglion cells of Hughes ('75), confirms published values with a minimum of some 207,000 comprised 5,600 cells in the alpha mode, 80,700 cells in the beta mode, and 120,700 cells in the gamma mode. A proportion of classical neurones in the gamma mode do not fill by retrograde transport of HRP from either optic nerve or superior colliculus. Their morphology is characteristic and includes a conspicuous basophilic nuclear bar or fold; they remain subsequent to ganglion cell retrograde degeneration and resemble some profiles of the amacrine layer. It is presumed that they represent a class of displaced amacrine cells. Estimates based on ganglion cell identification by HRP filling indicate populations of about 80,000 cells in both the gamma and the beta modes and a total count of about 170,000 ganglion cells; a good agreement with Hughes and Wassle's ('76) optic nerve fibre count, but lower than the classic neurone count. It is concluded that the distribution maps for ganglion cells in each of the three modes of the soma diameter spectra are similar in form and resemble that of the total neurone density map. The ganglion cell population of the gamma mode in the visual streak is not found to increase in proportion relative to that of the beta mode, as has been reported elsewhere.