Showing papers by "Australian National University published in 1978"

Procedures for comparing and combining radiocarbon age determinations: a critique

Abstract: Archaeologists, along with other Quaternary researchers, seldom rely upon a single radiocarbon determination to provide an estimate of the age of the phenomenon which is the object of their study. There is an evident need for an explicitly formulated procedure for comparing sets of radiocarbon determinations from the same and from adjacent strata or sites, and for combining these where statistical and archaeological criteria indicate that this combination is warranted. The present contribution provides explicit modelling for a series of recommended procedures, a critique of previous methods, and paradigms for application of the recommended procedures.

Stomatal Behaviour and Environment

Abstract: Publisher Summary Stomata1 movement is a manifestation of strain in the epidermis, associated with change in the hydraulic pressure in the epidermal cells. This chapter discusses the role and behavior of stomata in the hydrology of the soil–plant–atmosphere system. Stomata operate in the light in such a way as to maintain positive turgor in the leaves, in the majority of crop plants and other species. The transient response of stomata to changes in environment which cause rapid changes in plant–water relations is quite dramatic. The nature of the stomatal response to change in water potential must involve the mechanical and hydraulic attributes of the stomatal apparatus. There is only a tenuous relationship between the potential of water in leaf tissue in bulk and the local potential of water to which an individual stoma responds in ways, which are also discussed. Thus the transient response of stomata to change in rate of evaporation may be a device which is designed to enhance the speed of the response to light.

The organization of turns at formal talk in the classroom

Abstract: Beginning with a consideration of some commonsense and professional conceptions of what a formal situation might comprise, this paper goes on to ask the question: where along a linear array which has its poles in exemplars of formal and informal speech-exchange systems, can classroom talk be placed? Its answer is given in part in the form of rules for the taking of turns in classrooms, these being modifications of those, already established in the literature, for natural conversation. These rules allow for and require that formal classroom situations be constructed so as to involve differential participation rights for parties to the talk depending on their membership of the social identity-class ‘student/teacher’. The analyses which follow examine some of the applications and violations of these rules found in audio and video recordings of naturally occurring classroom talk (and transcripts thereof) for their orderliness as orientations to these rules. It is argued that the rules provide a systematic basis for the ‘feelings’ of ‘formality’ that researchers and participants have of such situations and that a decision as to the ‘formality’ or otherwise of a social situation can be predicated on the degree of pre-allocation involved in the organization of turns at talk in the situation. (Configuration and distance in interaction, conversational analysis, turn-taking systems, classroom language, sociology of education; British and Australian English).

Transfer of specific cytotoxic T lymphocytes protects mice inoculated with influenza virus

Abstract: THERE is remarkably little information about the possible importance of cell-mediated immune responses in the protection of hosts during influenza virus infection. It has recently been found that specific cytotoxic T cells (Tc) can be recovered from the spleens of mice previously inoculated intranasally or intravenously with live virus1–4 and peak activity occurs about 6 d after virus inoculation. Furthermore, Tc are found in the lungs and the lymph nodes draining the lungs of infected mice in conditions which suggest that these cells might be important in host recovery from this infection5. Adoptive transfer of primary or secondary immune spleen cells to mice inoculated intranasally with a lethal dose of A/WSN virus caused a significant reduction of infectious virus levels in the lungs and prevented death6. The active cells in the transferred population were T lymphocytes. This report shows that the protective effects conferred by the transferred T cells in these conditions are largely, if not entirely, due to Tc.

Model-fitting approaches to the analysis of human behaviour

Abstract: Model-fitting methods are now prominent in the analysis of human behavioural variation. Various ways of specifying models have been proposed. These are identical in their simplest form but differ in the emphasis given to more subtle sources of variation. The biometrical genetical approach allows flexibility in the specification of non-additive factors. Given additivity, the approach of path analysis may be used to specify several environmental models in the presence of assortative mating. In many cases the methods should yield identical conclusions. Several statistical methods have been proposed for parameter estimation and hypothesis testing. The most suitable rely on the method of maximum likelihood for the estimation of variance and covariance components. Any multifactorial model can be formulated in these terms. The choice of method will depend chiefly on the design of the experiment and the ease with which a data summary can be obtained without significant loss of information. Examples are given in which the causes of variation show different degrees of detectable complexity. A variety of experimental designs yield behavioural data which illustrate the contribution of additive and non-additive genetical effects, the mating system, sibling and cultural effects, the interaction of genetical effects with age and sex. The discrimination between alternative hypotheses is often difficult. The extension of the approach to the analysis of multiple measurements and discontinuous traits is considered

Osmotic Adjustment in Leaves of Sorghum in Response to Water Deficits

Abstract: The relationships among the total water potential, osmotic potential, turgor potential, and relative water content were determined for leaves of sorghum (Sorghum bicolor [L.] Moench cvs. ;RS 610' and ;Shallu') with three different histories of water stress. Plants were adequately watered (control), or the soil was allowed to dry slowly until the predawn leaf water potential reached either -0.4 megapascal (MPa) (treatment A) or -1.6 MPa (treatment B). Severe soil and plant water deficits developed sooner after cessation of watering in ;Shallu' than in ;RS 610', but no significant differences in osmotic adjustment or tissue water relations were observed between the two cultivars. In both cultivars, the stress treatments altered the relationship between leaf water potential and relative water content, resulting in the previously stressed plants maintaining higher tissue water contents than control plants at the same leaf water potential. The osmotic potential at full turgor in the control sorghum was -0.7 MPa: stress pretreatment significantly lowered the osmotic potential to -1.1 and -1.6 MPa in stress treatments A and B, respectively. As a result of this osmotic adjustment, leaf turgor potentials at a given value of leaf water potential exceeded those of the control plants by 0.15 to 0.30 MPa in treatment A and by 0.5 to 0.65 MPa in treatment B. However, zero turgor potential occurred at approximately the same value of relative water content (94%) irrespective of previous stress history. From the relationship between turgor potential and relative water content there was an approximate doubling of the volumetric elastic modulus, i.e. a halving of tissue elasticity, as a result of stress preconditioning. The influence of stress preconditioning on the moisture release curve is discussed.

Solvable eight-vertex model on an arbitrary planar lattice

Abstract: Any planar set of intersecting straight lines forms a four-coordinated graph, or 'lattice', provided no three lines intersect at a point. For any such lattice an eight-vertex model can be constructed. Provided the interactions satisfy certain constraints (which are in general temperature-dependent), the model can be solved exactly in the thermodynamic limit, its local properties at a particular site being those of a related square lattice. A particular case is a solvable model on the Kagome lattice. It is shown that this model includes as special cases many of the models in statistical mechanics that have been solved exactly, notably the square, triangular and honeycomb Ising models, and the square eight-vertex model. Some remarkable equivalences between correlations on different lattices are also established.

Common strategies for light adaptation in the peripheral visual systems of fly and dragonfly

Abstract: 1 Intracellular recordings from photoreceptors and large monopolar cells (LMC's) of the flyCalliphora stygia, and the dragonflyHemicordulia tau, were used to examine the peripheral light adaptation processes of the insect compound eye 2 Photoreceptor and lamina adaptation mechanisms were separated by comparing the response waveforms and intensity/response functions (plotted as V/log I curves) of receptors (Figs 1 and 3) and LMC's (Figs 2 and 4), subjected to identical regimes of adaptation 3 Photoreceptor adaptation occurs in two phases, a rapid one lasting 100 ms, and a slow phase taking up to 60 s to complete (Fig 1) This adaptation shifts theV/logI curves to higher intensities without changing their shape or slope (Fig 3) Adaptation is negligible at low intensities but with stronger adaptation range sensitivity changes approach proportionality to background increments (Fig 7) 4 Lamina adaptation mechanisms adjust the LMCV/logI curve in response to new background levels within 200 ms, producing a phasic response waveform within which background signals are annihilated (Figs 1, 3, 8) The shape and amplitude of the saturated LMC ‘on’ and ‘off’ transient responses change with light adaptation (Figs 2, 3) 5 At all background intensities examined the slopes of the LMC V/log I curves remain about 8–10 times that of the photoreceptors under the same conditions, implying that lamina adaptation does not change the voltage gain of the first synapse We propose that light induced depolarisation of the lamina extracellular space subtracts away the standing background signal from the photoreceptor terminals 6 During dark adaptation the faster lamina mechanism can be superimposed upon slower photoreceptor processes (Fig 9) 7 A comparison of our findings with studies of higher order neurons of the compound eye suggests that peripheral adaptation mechanisms play an important role in determining the response of the entire visual system 8 The peripheral light adaptation processes of fly and dragonfly are similar, and the intensity/response functions of retinula cells and LMC's resemble those of vertebrate cones and bipolar cells respectively (Fig 11) We propose that this analogy has a functional basis Both vertebrate and invertebrate systems use a ‘log transform-subtraction-multiplication” strategy to match the response bandwidth of peripheral neurons to the expected intensity fluctuation about any one mean, and in so doing maximise the image detail sent to higher centres

Fast Algorithms for Manipulating Formal Power Series

Abstract: The classical algorithms require order n ~ operations to compute the first n terms in the reversion of a power series or the composition of two series, and order nelog n operations if the fast Founer transform is used for power series multiplication In this paper we show that the composition and reversion problems are equivalent (up to constant factors), and we give algorithms which require only order (n log n) ~/2 operations In many cases of practical importance only order n log n operations are required, these include certain special functions of power series and power series solution of certain differential equations Applications to root-finding methods which use inverse mterpolauon and to queuemg theory are described, some results on multivariate power series are stated, and several open questions are mentioned

Modes of optical waveguides

Abstract: A simple method is presented for finding the modes on those optical waveguides with a cladding refractive index that differs only slightly from the refractive index of the core. The method applies to waveguides of arbitrary refractive index profile, arbitrary number of propagating modes, and arbitrary cross section. The resulting modal fields and their progagation constants display the polarization properties of the waveguide contained within the ∇ ∊ term of the vector wave equation. Examples include modes on waveguides with circular symmetry and waveguides with two preferred axes of symmetry, e.g., an elliptical core. Only a minute amount of eccentricity is necessary for the well-known LP modes to be stable on an elliptical core, while the circle modes couple power among themselves.

Mitochondria and the control of intracellular calcium.

Abstract: Summary 1.Because the calcium (Ca) ion is intimately associated with so many biochemical and physiological phenomena, it is fundamental to understand how intracellular Ca is maintained and controlled. This review draws attention to the vital role played by mitochondria in controlling intracellular Ca and describes how transport of the ion into and out of mitochondria may itself be controlled. 2.The heterogeneous distribution of Ca is a property of most, if not all cells. This arises because the ion binds strongly to a variety of biological compounds, especially those containing oxyanions, which themselves have a heterogeneous distribution in cells, but mostly because of the existence in the cell of specific Ca-ion transport systems. 3.Although the concentration of total Ca in the cell may be quite high, a very large proportion of it is bound and non-diffusible; a small fraction is diffusible but unionized. The proportion of Ca that is ionized is probably much less than I% of the total 4.The mechanisms by which Ca is transported into and out of the mitochondrial matrix are discussed. Inward movement of the ion occurs in response to the membrane potential (negative inside) generated by respiration. The process is carrier-mediated and exhibits characteristics such as substrate specificity, high affinity for Ca, satur-ability, cooperativity, stimulation by permeant anions and is specifically inhibited by low concentrations of Ruthenium Red and lanthanum. The properties of the Ca carrier are geared therefore to facilitate rapid inward movement of Ca into the mitochondria. Such a carrier system is found in mitochondria isolated from a wide variety of tissues and species. 5.Ionized Ca appears not to be distributed across the inner mitochondrial membrane according to the Nernst equation, so the possibility exists that the ion is transported as Ca/H+ antiport or as Ca/anion symport. Alternatively, an efflux system coupled to inward movement of a cation may serve to prevent the [Ca ion]in/[Ca ion]out from attaining equilibrium. These components together contribute to a Ca-translocation cycle that permits Considerable flexibility in the overall control of Ca flux. 6.Evidence for Ca cycling in mitochondria is presented and the influence of physiological agents such as Mg, phosphoenolpyruvate, inorganic phosphate and adenine nucleotides, on the influx and efflux components are discussed in some detail. Moreover, various hormones administered in vivo are able to induce changes in mitochondrial Ca cycling. One important feature that emerges from this collection of data is that the ability of mitochondria to retain Ca is associated with their ability to retain also their adenine-nucleotide complement. 7.Various lines of research provide convincing evidence in support of the view that mitochondria play a major role in controlling cell Ca in vivo. Especially significant are the observations that the ‘activity’ of mitochondrial Ca transport can change during development in both insect and mammalian tissue, can depend on the hormonal status of the tissue and undergoes a permanent change in certain tumour cells. 8.Finally, consideration is given as to how the mitochondrial Ca transport system is able to modify Ca-sensitive enzyme activities by regulating the Ca concentration in specific environments. Some biological activities that might be susceptible to such control are discussed.

The number and distribution of ganglion cells in the cat's retina

Abstract: The number of ganglion cells in the cat's retina, and the pattern of their distribution over the retina, have been reinvestigated. Criteria are presented for the identification of ganglion cells in Nissl-stained whole mounts, most particularly for the distinction between small ganglion cells and neuroglial cells, by reference to retinas with no ganglion cells (obtained by nerve section) and to areas to retina containing a population of only small ganglion cells (obtained by optic tract section). Using these criteria, the number of ganglion cells was counted in four retinas (mean total 116,250). The number of large or "giant" cells (presumably the somas of Y-cells and of alpha-cells) varied from 4,200 to 7,100. Overall these cells comprised 4.0-6.3% of the total ganglion cell population. Their distribution over the retina showed a concentration around the area centralis, with a localized minimum density at the area centralis, and a concentration in the visual streak. These concentrations of large cells were quantitatively less than the concentrations of smaller cells in the area centralis and visual streak, so that the relative frequency of large cells was minimal (mean 1.6%) at the area centralis and increased steadily up to 5.5-6.9% in peripheral retina. Their relative frequency was distinctly lower along the visual streak than in peripheral retina above or below the streak.

The separation of visual axes in apposition compound eyes

Abstract: Measurements of the interommatidial angle (Δ ϕ ) and facet diameter ( D ) of the same ommatidia in a number of insects and crustaceans with large eyes have been related to the effective intensity at which the eye functions by the following theory. The highest spatial frequency which the eye is able to reconstruct as a pattern is limited by the interommatidial angle Δ ϕ , Which is the sampling angle, because two ommatidia are required to cover each cycle of the pattern. At the same time, the absolute modutlation of light in the receptors caused by the pattern depends on three interdependent factors. ( a ) The theoretical minimum angular sensitivity function, which has a width of θ/ D at the 50% level. The wavelength θ is taken as 0.5 μm. This component is not only the limiting angular resolving power of the lens: it reduces modulation caused by all patterns, with greater loss at higher spatial frequencies. Larger lenses increase resolution and sensitivity. ( b ) The effective light catching area of the rhabdom. This is the angular subtense of the rhabdom area (the receptor) as seen in the outside world (i.e. subtended through the posterior nodal point of the lens), and is the equivalent of the grain size in a film. Large receptors favour sensitivity at the expense of resolution. ( c ) The F value or focal ratio f/D , as in the camera, where F is the distance from the focal plane to the posterior nodal point. Larger F values increase sensitivity. The modulation resulting from these three factors is then set so that it exceeds the noise caused by the random arrival of photons at each ambient intensity. From this, the optimum value of the product D Δ ϕ (known as the eye parameter) can be calculated for eyes adapted to any ambient intensity. The same result is reached by a recent theory of Snyder, Stavenga & Laughlin (1977) who calculate the value of D Δ ϕ which allows the eye to reconstruct the maximum number of pictures despite photon noise. The eye parameter (divided by half the wavelength) is the ratio of the highest spatiai frequency passing the lens to the highest spatial frequency reconstructed by the eye. Compound eyes should have larger facets and interommatidial angles than predicted by diffraction theory alone because photon noise must be exceeded at all intensities. Theoretically, D Δ ϕ lies in the range 0.3 to 0.5 for bright light insects and is increased to 2.0 or more for those active in dim light. As well as depending on intensity, D Δ ϕ should depend on factors such as the typical angular velocity and level of intensity discrimination at which the eye is used. As D Δ ϕ can be measured from the outside of the eye, the theoretical predictions can be compared with measured values. Most of this paper consists of maps of the values of D Δ ϕ for eyes of a variety of arthropods from different habitats. The maps are made by a new convention in which the minimum theoretical field of each ommatidium is placed in angular coordinates as a circle of diameter θ/ D with centre on the axis at the place where it lies on the eye. To do this, a value of θ must be assumed. Every fifth facet is taken on most maps with the fields magnified five times. The overlap or separation of these circles of diameter θ/ D shows the local value of D Δ ϕ for any direction for each part of the eye. The method is independent of horizontal and vertical axes, of directions of facet rows, of regularity of facets and of eye radius. The problem of mapping a surface with double curvature upon a flat sheet was solved approximately by working with strips taken along the eye surface. Equal distances on the map then represent equal angles in any direction; with this projection there are no poles, and axes are arbitrary. Maps of D Δ ϕ reveal that compound eyes differ according to the intensity of light they normally encounter; eyes of animals which are active in bright light have smaller values of D Δ ϕ . The smallest value of about 0.3 is found in the forward facing acute zone of the sand wasp Bembix , which hovers while hunting in bright sunshine. The absolute limit set by diffraction of 0.25 (for square facets) is approached but never reached. Values of D Δ ϕ up to about 2.0 or even 4.0 are found in crepuscular animals which have apposition eyes. The interpretation is that the values of D and Δ ϕ are the result of a compromise between contrast sensitivity and resolution. An increase in aperture provides increased modulation and therefore increased sensitivity, but the additional angular resolving power which comes with the increased aperture is not used because sensitivity is also enhanced by an increase in the receptor size. The ommatidium then detects only the lower spatial frequencies (wider stripes) from the range which passes the lens. In an ommatidium optimized for any but the highest known intensities, both Δ ϕ and D (and therefore D Δ ϕ ) are larger than they would have to be if set at the diffraction limit. The maps also reveal that many apposition compound eyes have one or more regions of smaller Δ ϕ , called acute zones. None of the eyes are spherically symmetrical; all have gradients of both D and Δ ϕ , and all have regions where Δ ϕ varies in different directions on the eye surface. The acute zone is usually forward looking, but is upward looking in some insects which catch prey or mate in flight. In addition, some dragonflies have a lateral acute zone. In the acute zone the facet pattern is always more regular than elsewhere. Some acute zones, as in the locust ( Locusta ), the mantid Orthodera and the ghost crab Ocypode , are formed by reduction in Δ ϕ with little compensatory increase in D . Others such as the native bee Amegila , the dragonfly Austrogomphus , and the mantid shrimp Odontodactylus have larger values of D which match the decreasing Δ ϕ towards the centre of the acute zone, so that D Δ ϕ remains constant. Others again, particularly the wasp Bembix , the dragonflies Hemicordulia, Orthetrum and several mantids, show an increase in D which is insufficient to compensate for the large decrease in Δ ϕ , so that D Δ ϕ is smaller in the acute zone. A reduced D Δ ϕ in the acute zone may imply that it requires brighter light or more time than the rest of the eye in order to make full use of its increased sampling density. Mapping the regional differences of the theoretical resolving power of the ommatidia, and of the potential spatial resolution of different parts of the eye is only the first step towards understanding the functions of the different eye regions. The anatomical basis of the optics, the actual field sizes of receptors as measured physiologically, the part played by binocular overlap, the regional differences in the mechanisms of integration behind the eye, and the patterns of behaviour that are dependent on each eye region, remain to be elucidated.

Late Quaternary tectonic movements and sea-level changes at Timor and Atauro Island

Abstract: Flights of raised coral terraces on the north coast of East Timor and at Atauro Island, north of Timor, are described stratigraphically and dated by Th 230 -U 234 determinations. The exposures at southern Atauro enable detailed reconstruction of the history of transgressions and regressions, especially for the period 140,000 to 105,000 yr B.P. Sea-level changes identified in Barbados and New Guinea are closely confirmed. The Atauro uplift rate is 0.47 m/1,000 yr, as estimated from the highest position of shallow-water coral faunas in the reef, which is dated as 120,000 old. The extrapolated rate is used to estimate ages of higher reefs; these ages correlate quite well with periods of major glacio-eustatic rise indicated by the O 18 record of Pacific cores back to 700,000 yr B.P. Reefs from three sites along the north coast of Timor have been dated within the 84,000, 105,000, and 120,000 yr B.P. high sea-level periods and indicate uplift at 0.5 m/1,000 yr. A 120,000-yr-old reef from a fourth north Timor site, near Dili, indicates much slower uplift, about 0.03 m/1,000 yr.

Formative and proliferative cell divisions, cell differentiation, and developmental changes in the meristem of Azolla roots.

Abstract: The root of the water fern Azolla is a compact higher-plant organ, advantageous for studies of cell division, cell differentiation, and morphogenesis. The cell complement of A. filiculoides Lam. and A. pinnata R.Br. roots is described, and the lineages of the cell types, all derived ultimately from a tetrahedral apical cell, are characterised in terms of sites and planes of cell division within the formative zone, where the initial cells of the cell files are generated. Subsequent proliferation of the initial cells is highly specific, each cell type having its own programme of divisions prior to terminal differentiation. Both formative and proliferative divisions (but especially the former) occur in regular sequences. Two enantiomorphic forms of root develop, with the dispositions of certain types of cell correlating with the direction, dextrorse or sinistrorse, of the cell-division sequence in the apical cells. Root growth is determinate, the apical cell dividing about 55 times, and its cell-cycle duration decreasing from an initial 10 h to about 4 h during the major phase of root development. Sites of proliferation progress acropetally during aging, but do not penetrate into the zone of formative divisions. The detailed portrait of root development that was obtained is discussed with respect to genetic and epigenetic influences; quantal and non-quantal cell cycles; variation in cell-cycle durations; relationships between cell expansion and cell division: the role of the apical cell; and the limitation of the total number of mitotic cycles during root formation.

The functional organisation of locust ocelli

Abstract: This paper examines the optical and physiological organisation of locust ocelli with a view to understanding their function. The approach taken in this work has largely been to correlate quantitative measurements of the spectral, angular and absolute sensitivities of large second order neurons with radiometric data from the natural environment. The resulting estimates of the natural performance of these neurons form the basis for a hypothesis of their functional significance.

A Fortran Multiple-Precision Arithmetic Package

Abstract: : A collection of ANSI Standard FORTRAN subroutines for performing multiple-precision floating-point arithmetic and evaluating elementary and special functions is described. The subroutines are machine-independent and the precision is arbitrary, subject to storage limitations. In this paper the design of the package is discussed, some of the algorithms are described, and test results and an example are given. The complete package is available from the author.

Photosynthetic capacity and carbon allocation patterns in diverse growth forms of Eucalyptus.

Abstract: Eucalytptus species originating in Australian habitats differing in moisture regimes were examined under uniform growth conditions for their photosynthetic characteristics and allocation patterns. Species from the driest environments, the ‘mallee’ types, had the smallest leaf sizes and the highest leaf specific weights; and forest species, from moist coastal sites, had the largest and thinnest leaves. Photosynthetic rates on a dry weight basis were highly correlated with leaf nitrogen content in all species. Leaf nitrogen content on a dry weight basis varied little between species in nature; however, there were increasing amounts of nitrogen per unit leaf area as the habitat became drier because of the changes in specific leaf weight. This resulted in a greater light-saturated photosynthetic rate per leaf area of arid habitat species, which were presumably more efficient in water use as a consequence. A simple simulation model showed that changes in the allocation ratio to leaf weight reduces total leaf area in the expected direction without affecting total dry matter accumulation.

Leaf Conductance in Relation to Assimilation in Eucalyptus pauciflora Sieb. ex Spreng: Influence of Irradiance and Partial Pressure of Carbon Dioxide.

Abstract: Rates of assimilation and transpiration in Eucalyptus pauciflora Sieb. ex Spreng were measured at various ambient partial pressures of CO2 and various irradiances and were used to estimate leaf conductance and intercellular partial pressure of CO2. The responses of leaf conductance and rate of assimilation to change in intercellular partial pressure of CO2 were expressed in terms of feedback. They are small in the sense that their combined effect was to reduce disturbances in intercellular partial pressure of CO2 by 30% only. The magnitude of the feedback had no influence on the system as affected by irradiance, because the direct responses of conductance and rate of assimilation to changes in irradiance in the range 0.25 to 2 millieinsteins per meter per second were such that intercellular partial pressure was maintained almost constant.

Structure‐activity studies on the inhibition of gaba binding to rat brain membranes by muscimol and related compounds

Abstract: — A series of compounds structurally related to muscimol (5-aminomethyl-3-isoxazolol) was tested as inhibitors of the sodium-independent binding of GABA to membranes from rat brain. Muscimol, 5-(l-aminoethyl)-3-isoxazolol, 5-(2-aminoethyl)-3-isoxazolol (homomuscimol), and the bicyclic derivative 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP) were relatively potent inhibitors of GABA binding. THIP is an analogue of muscimol locked in a folded conformation. The structurally related compound 1,2,3,6-tetrahydropyridine-4-carboxylic acid (isoguvacine), a semirigid analogue of trans-4-aminocrotonic acid, was also a potent inhibitor of GABA binding. Apart from muscimol, these inhibitors of GABA binding did not influence the sodium-dependent,‘high-affinity’ uptake of GABA in rat brain slices, whereas the potent GABA uptake inhibitors guvacine and nipecotic acid did not influence GABA binding. The present results support previous findings that different conformational modes of GABA interact with GABA postsynaptic receptors and the neuronal GABA transport system in rat brain, and indicate that the ‘active conformation’ of GABA with respect to the receptors is partially folded and almost planar. Based on a comparison of the present results with previous in vivo studies the structural requirements for GABA-like activity in rat cerebral cortex and cat spinal cord seem to be somewhat different.

Normal Discrimination with Unclassified Observations

Abstract: Fisher's linear discriminant rule may be estimated by maximum likelihood estimation using unclassified observations. It is shown that the ratio of the relevant information contained in unclassified observations to that in classified observations varies from approximately one-fifth to two-thirds for the statistically interesting range of separation of the populations. Thus, more information may be obtained from large numbers of inexpensive unclassified observations than from a small classified sample. Also, all available unclassified and classified data should be used for estimating Fisher's linear discriminant rule.

The estimation of large social account matrices

Abstract: Formalization and extension of a recent proposal for adjusting initial unbalanced estimates of components of a matrix allows them to satisfy accounting requirements imposed by tabular form in an optimal manner. The proposal, which is based on linear combinations of initial unbiased estimates, has many potential applications in national income accounting, input-output construction, and demography, among other fields. Given that the adjustment procedure simply represents the first-order conditions resulting from the minimization of a quadratic loss function, it is possible to develop alternative procedures for minimizing the constrained loss function. These procedures, based on the conjugate gradient algorithm, prove to be much more efficient than the traditional solution, both in terms of the time taken and storage requirements, and the optimal adjustment of very large social account matrices becomes quite feasible. Application of these techniques to a social account matrix constructed for the Muda River District in West Malaysia indicate the feasibility and usefulness of the method. Statistical data are included.

Structural invariants of linear multivariable systems

Abstract: The class {∑} of all linear multivariable systems is partitioned into equivalence classes by the group consisting of all basis, all state feedback and all output injection transformations. This paper provides a new derivation of a set, of complete invariants and a corresponding canonical form first given by Morse. Strong reachability and strong observability concepts are the key tools. The method yields relatively simple proofs and economical matrix algorithms.

Triangular Potts model at its transition temperature, and related models

Abstract: Kelland has solved a restricted ice-type model on the triangular lattice. Here it is shown that this is equivalent to a restricted six-vertex model on the Kagome lattice, and to the g-state triangular (or hexagonal) Potts model at its transition temperature T c . This enables us to obtain the free energy, internal energy and latent heat of the Potts model at T c . The relation of this work to the operator method of Temperley and Lieb is explained, and this method is used to consider a generalized triangular Potts model which includes a three-site interaction on alternate triangles. It is shown that this model is self-dual. The results for the bond percolation problem on the triangular lattice give an excellent verification of series expansion predictions.

Aerobic glycolysis and lymphocyte transformation.

Abstract: 1. The role of enhanced aerobic glycolysis in the transformation of rat thymocytes by concanavalin A has been investigated. Concanavalin A addition doubled [U-(14)C]glucose uptake by rat thymocytes over 3h and caused an equivalent increased incorporation into protein, lipids and RNA. A disproportionately large percentage of the extra glucose taken up was converted into lactate, but concanavalin A also caused a specific increase in pyruvate oxidation, leading to an increase in the percentage contribution of glucose to the respiratory fuel. 2. Acetoacetate metabolism, which was not affected by concanavalin A, strongly suppressed pyruvate oxidation in the presence of [U-(14)C]glucose, but did not prevent the concanavalin A-induced stimulation of this process. Glucose uptake was not affected by acetoacetate in the presence or absence of concanavalin A, but in each case acetoacetate increased the percentage of glucose uptake accounted for by lactate production. 3. [(3)H]Thymidine incorporation into DNA in concanavalin A-treated thymocyte cultures was sensitive to the glucose concentration in the medium in a biphasic manner. Very low concentrations of glucose (25mum) stimulated DNA synthesis half-maximally, but maximum [(3)H]thymidine incorporation was observed only when the glucose concentration was raised to 1mm. Lactate addition did not alter the sensitivity of [(3)H]-thymidine uptake to glucose, but inosine blocked the effect of added glucose and strongly inhibited DNA synthesis. 4. It is suggested that the major function of enhanced aerobic glycolysis in transforming lymphocytes is to maintain higher steady-state amounts of glycolytic intermediates to act as precursors for macromolecule synthesis.