Showing papers by "Australian National University published in 1979"

Optimal Control: Linear Quadratic Methods

Abstract: This augmented edition of a respected text teaches the reader how to use linear quadratic Gaussian methods effectively for the design of control systems. It explores linear optimal control theory from an engineering viewpoint, with step-by-step explanations that show clearly how to make practical use of the material. The three-part treatment begins with the basic theory of the linear regulator/tracker for time-invariant and time-varying systems. The Hamilton-Jacobi equation is introduced using the Principle of Optimality, and the infinite-time problem is considered. The second part outlines the engineering properties of the regulator. Topics include degree of stability, phase and gain margin, tolerance of time delay, effect of nonlinearities, asymptotic properties, and various sensitivity problems. The third section explores state estimation and robust controller design using state-estimate feedback. Numerous examples emphasize the issues related to consistent and accurate system design. Key topics include loop-recovery techniques, frequency shaping, and controller reduction, for both scalar and multivariable systems. Self-contained appendixes cover matrix theory, linear systems, the Pontryagin minimum principle, Lyapunov stability, and the Riccati equation. Newly added to this Dover edition is a complete solutions manual for the problems appearing at the conclusion of each section.

The determination of the order of an autoregression

Abstract: SUMMARY It is shown that a strongly consistent estimation procedure for the order of an autoregression can be based on the law of the iterated logarithm for the partial autocorrelations. As compared to other strongly consistent procedures this procedure will underestimate the order to a lesser degree.

Stomatal conductance correlates with photosynthetic capacity

Abstract: Previous studies on the Physiology of stomata in higher plants suggest that stomata influence the rate of CO2 fixation in leaf mesophyll tissue. We believe that an equally important stomatal function has not been fully recognised; that stomatal aperture is determined by the capacity of the mesophyll tissue to fix carbon. We altered the capacity of leaves to fix carbon by various means, and found invariably that the diffusive conductance of the epidermis to CO2 transfer, g, (which mainly depends on the number and dimensions of the stomata) changes in nearly the same proportion as the rate of assimilation of CO2. Thus, the intercellular concentration of CO2 (ci), calculated as ci = ca–A/g (where ca is ambient concentration of CO2, A is assimilation rate of CO2), tends to remain constant providing ca is kept constant. We used routine techniques1 to measure A and estimate g in leaves placed singly in chambers. Conductance takes account of CO2 transfer through both stomata and leaf boundary layer, the conductance of the latter being 0.5 mol m−2 s−1.

Immobilisation of high level nuclear reactor wastes in SYNROC

Abstract: The elements occurring in high-level nuclear reactor wastes can be safely immobilised by incorporating them within the crystal lattices of the constituent minerals of a synthetic rock (SYNROC). The preferred form of SYNROC can accept up to 20% of high level waste calcine to form dilute solid solutions. The constituent minerals, or close structural analogues, have survived in a wide range of geochemical environments for periods of 20–2,000 Myr whilst immobilising the same elements present in nuclear wastes. SYNROC is unaffected by leaching for 24 h in pure water or 10 wt % NaCl solution at high temperatures and pressure whereas borosilicate glasses completely decompose in a few hours in much less severe hydrothermal conditions. The combination of these leaching results with the geological evidence of long-term stability indicates that SYNROC would be vastly superior to glass in its capacity to safely immobilise nuclear wastes, when buried in a suitable geological repository. A dense, compact, mechanically strong form of SYNROC suitable for geological disposal can be produced by a process as economical as that which incorporates radwaste in borosilicate glasses.

Elevated atmospheric partial pressure of CO2 and plant growth

Abstract: Cotton and maize plants were grown under full sunlight in glass houses containing normal ambient partial pressure of CO2 (330±20 μbar) and enriched partial pressure of CO2 (640 ±15 μbar) with four levels of nitrogen nutrient. In 40 day old cotton plants grown in high CO2, there was a 2-fold increase in day weight and a 1.6-fold increase in leaf area compared with plants grown in ambient CO2. In 30 day old maize plants there was only 20% increase in dry weight in plants grown in 640 μbar CO2 compared with plants grown in 330 μbar and no significant increase in leaf area. In both species, at both CO2 treatments, dry weight and leaf area decreased in similar proportion with decreased nitrogen nutrient. The increase of leaf area in cotton plants at high CO2 caused a reduction of total nitrogen on a dry weight basis. In cotton assimilation rate increased 1.5 fold when plants were grown with high nitrogen and high CO2. The increase was less at lower levels of nitrate nutrient. There was a 1.2 fold increase in assimilation rate in maize grown at high CO2 with high nitrate nutrient. Cotton and maize grown in high CO2 had a lower assimilation rate in ambient CO2 compared to plants grown in normal ambient air. This difference was due to the reduction in RuBP carboxylase activity. Water use efficiency was doubled in both cotton and maize plants grown at high CO2 in all nutrient treatments. However, this increase in water use efficiency was due primarily to reduced transpiration in some treatments and to increased assimilation in others. These data show that plant responses to elevated atmospheric partial pressure of CO2 depend on complex of partially compensatory processes which are not readily predictable.

Experimental deformation of partially-melted granite

Abstract: An account is given of the experimental deformation of partially-melted granite with melt fractions up to 25% at 800 °C and 300 MPa confining pressure in constant strainrate tests between 10−3 and 10−6 S−1, creep tests and cycling tests Microscopic study reveals that under these conditions most of the uniform deformation prior to macroscopic shear failure is accomplished by melt redistribution into films perpendicular to the least compressive stress, and by axial fracturing of grains, the latter occurring even at low macroscopic differential stress The strenght of the partially-melted rock at 10−5 S−1 is found to decrease gradually from about 250 MPa at 5 vol% melt to about 60 MPa at 15 % melt, and then to drop rapidly to less than 1 MPa at 24% melt The critical melt fraction separating granular-framework-controlled flow behaviour from suspension-like behaviour is deduced to be approximately 30 to 35 vol% At low melt fractions the deforming rock tends to take up externally available melt by a mechanism of dilatancy pumping The relevance of these results to natural conditions involving partially-melted rocks is discussed

Functional aspects of satellite DNA and heterochromatin.

Abstract: Publisher Summary This chapter discusses the functional aspects of satellite DNA and heterochromatin. Despite all attempts to formulate simple rules governing satellite evolution, it is now clear that each case so far analyzed has brought with it its own claims for generalization, none of which have proven sufficiently all-embracing. One initial hypothesis on satellite evolution was that satellites wax and wane with amazing rapidity in evolutionary terms, so that closely related species differ drastically in amount or type of satellite. However, improved methods of DNA sequencing have led to the suggestion that closely related species appear to modulate their satellites from a common library. Because some kinds of heterochromatin are now known to contain satellite DNA and because a large literature exists on the properties of heterochromatin, it is necessary to consider the relationships between heterochromatin and satellite DNA in some detail. The term “heterochromatin” was initially used to define chromosomes or chromosome segments which did not uncoil at mitotic telophase and so maintained a condensed or heteropycnotic state throughout interphase and into the subsequent prophase of the next division cycle.

Crystallization, fractionation and solidification of the Tuolumne intrusive series, Yosemite National Park, California

Abstract: Study of the Tuolumne Intrusive Series, a concentric texturally and compositionally zoned plutonic sequence in the eastern part of Yosemite National Park, was undertaken to develop and test a model for the origin of comagmatic plutonic sequences in the Sierra Nevada batholith. The granitoid units that make up the sequence are progressively younger and more felsic inward. The bulk of the rocks are granodiorite, but the outermost formation is quartz diorite, and the innermost one is granite porphyry. The compositional gradient changes both gradually within formations and abruptly between them. The change is greatest in the outer 1 km and lower toward the center of the sequence. Hornblende and biotite, abundant in the marginal rocks, decrease rapidly inward for 1 km as K-feldspar and quartz increase, but farther inward, they decrease slowly. The most conspicuous chemical changes are shown by the elements that are enriched in the mafic minerals. The compositional zoning indicates that with decreasing temperature, the sequence solidified from the margins inward. Solidification was interrupted repeatedly by surges of fluid core magma. The magma eroded the adjacent solidifying rock, and it expanded the area of the magma chamber at the exposed level by crowding the wall and roof rocks outward and upward and by breaking through the solidifying carapace into the wall rocks. The compositional zonation resulted from crystal fractionation that could have involved (1) preferential accretion of crystalline material present in the magma to the margins of the magma chamber, thus displacing the melt phase progressively inward, and/or (2) downward settling of crystals, probably accompanied by upward movement of melt and volatiles; the residual magma solidifying to form the granitoids. Although either mechanism can explain the observed relations, they lead to very different interpretations of the composition of the magma when the first exposed granitoids solidified at the margins of the magma chamber and as the sequence solidified inward.

Anatomical organization of the primary visual cortex (area 17) of the cat. A comparison with area 17 of the macaque monkey.

Abstract: Golgi and axonal transport techniques have been used to examine the organization of neurons within primary visual cortex, area 17, of the cat. This organization has been compared to that of the primate cortical area 17 as described in previous studies and it is discussed in relationship to the distribution of afferents from the dorsal lateral geniculate nucleus (dLGN). The visual cortex of the cat and monkey show strong similarities in the laminar positions of neurons projecting extrinsically and also in the restriction of spiny stellate neurons to a central lamina (lamina 4) receiving input from the dLGN. However, lamina 4B in the monkey, which contains spiny stellate neurons but does not receive direct input from the dLGN, has no direct counterpart in cat area 17. Axon projections of spiny stellate neurons in the other divisions of lamina 4 differ in cat and monkey: the small, closely packed neurons in the lowermost division of lamina 4 (4B in the cat, 4Cbeta in the monkey) project chiefly within lamina 4 in the cat whereas in the monkey they have a strong projection to lamina 3. In the cat, spiny stellate neurons of lamina 4A project upon lamina 3 whereas in the monkey those in the apparently equivalent zone, 4Calpha, project upon lamina 4B. Most non-spiny stellate neurons examined have precisely organized interlaminar axonal projections which differ from the axon trajectories of neighboring spiny neurons.

ACTION OF THE NEUROTOXIN KAINIC ACID ON HIGH AFFINITY UPTAKE OF l‐GLUTAMIC ACID IN RAT BRAIN SLICES

Abstract: Kainic acid is a linear competitive inhibitor (Kis 250 μm) of the ‘high affinity’ uptake of l-glutamic acid into rat brain slices Kainic acid inhibits the ‘high affinity’ uptake of l-glutamic, d-aspartic and l-aspartic acids to a similar extent Kainic acid is not actively taken up into rat brain slices and is thus not a substrate for the ‘high affinity’ acidic amino acid transport system or any other transport system in rat brain slices Kainic acid (300 μm) does not influence the steady-state release or potassium-stimulated release of preloaded d-aspartic acid from rat brain slices Kainic acid binds to rat brain membranes in the absence of sodium ions in a manner indicating binding to a population of receptor sites for l-glutamic acid Only quisqualic and l-glutamic acid inhibit kainic acid binding in a potent manner The affinity of kainic acid for these receptor sites appears to be some 4 orders of magnitude higher than for the ‘high affinity’l-glutamic acid transport carrier Dihydrokainic acid is approximately twice as potent as kainic acid as an inhibitor of ‘high affinity’l-glutamic acid uptake but is some 500 times less potent as an inhibitor of kainic acid binding and at least 1000 times less potent as a convulsant of immature rats on intraperitoneal injection Dihydrokainic acid might be useful as a ‘control uptake inhibitor’ for the effects of kainic acid on ‘high affinity’l-glutamic acid uptake since it appears to have little action on excitatory receptors N-Methyl-d-aspartic acid is a potent convulsant of immature rats, but does not inhibit kainic acid binding or ‘high affinity’l-glutamic acid uptake N-Methyl-d-aspartic acid might be useful as a ‘control excitant’ that activates different excitatory receptors to kainic acid and does not influence ‘high affinity’l-glutamic acid uptake

Transition to Mach reflexion of shock waves in steady and pseudosteady flow with and without relaxation

Abstract: Experiments were conducted in the free-piston shock tube and shock tunnel with dissociating nitrogen and carbon dioxide, ionizing argon and frozen argon to measure the transition condition in pseudosteady and steady flow. The transition condition in the steady flow, in which the wall was eliminated by symmetry, agrees with the calculated von Neumann condition. In the real gases this calculation assumed thermo-dynamic equilibrium after the reflected shock. In the pseudosteady flow of reflexion from a wedge the measured transition angle lies on the Mach-reflexion side of the calculated detachment condition by an amount which may be explained in terms of the displacement effect of the boundary layer on the wedge surface. A single criterion based on the availability of a length scale at the reflexion point explains the difference between the pseudosteady and steady flow transition condition and predicts a hysteresis effect in the transition angle when the shock angle is varied during steady flow. No significant effects on the transition condition due to finite relaxation length could be detected. However, new experiments in which interesting relaxation effects should be evident are suggested.

The SYNROC process: A geochemical approach to nuclear waste immobilization.

Abstract: The SYNROC process proposes to immobilize high-level wastes as dilute solid solutions (i.e. as integral parts of crystal lattices) in the constituent minerals of a synthetic rock formed from a mixture of oxides, principally, TiO2, BaO, ZrO2, Al2O3 and CaO. A new modification of SYNROC, comprising the titanate mineral assemblage Ba-hollandite (BaAl2Ti6O16), perovskite (CaTiO3) and zirconolite (CaZrTi2O7) has been developed. Experiments show that the entire spectrum of high-level waste elements can be incorporated in the crystal lattices of these 3 phases and in a few minor accessory phases. This titanate assemblage has proved to be exceptionally resistant to hydrothermal leaching and in this respect, amongst others, is demonstrably superior to alternative ceramic waste forms and to borosilicate glasses. The relative stabilities of various waste forms were compared in hydrothermal leaching experiments using both pure water and lOwt.% NaCl solutions (temperature range 300-1, 000°C; pressure range 300-5, 000 bars). Borosilicate glasses are almost completely decomposed and disintegrated after only 24 hours at 350°C and 1, 000 bars, and extensive losses of hazardous high-level waste elements occurred. The phase pollucite (CsAlSi2O6), which provides the site for Cs-fixation in alternative ceramic waste forms, likewise begins to decompose at 400°C, with total loss of Cs by 600°C. On the other hand, the hollandite-perovskite-zirconolite SYNROC assemblage proved to be exceptionally resistant to leaching, surviving unaltered extreme conditions up to 900°C and 5, 000 bars. Hazardous species e.g. Cs, U and Sr, were quantitatively retained by the hollandite, zirconolite and perovskite phases respectively. Geochemical studies of naturally-occurring minerals containing radwaste elements are relevant to the problem of radiation damage to SYNROC phases. These imply that the a-particle flux in SYNROC is unlikely to be enough to impair the ability to immobilize radwaste for the required period. SYNROC can be produced by mixing about 10wt.% radwaste calcine with appropriate amounts of inert oxides. Subsolidus hot-pressing at 1, 200-1, 300°C in sealed Ni containers results in a dense, compact, mechanically-strong material. The production of SYNROC in its terminal state and final encapsulation and sealing are accomplished in a single step, and moreover, volatile species e.g. Cs, Ru, are quantitatively retained during hot-pressing. In contrast to borosilicate glass technology, expensive equipment for volatile recovery and recycling is not required. These advantages are believed to make SYNROC economically competitive with borosilicate glass. Moreover, the simplicity of the hot-pressing process makes it very suitable for remote operation in hot cells. SYNROC phases have structures analogous to natural minerals which have survived a variety of geological conditions for millions of years while retaining certain high-level waste elements in their crystal lattices. This fact, coupled with the exceptional resistance exhibited by SYNROC in accelerated leaching tests, leads to considerable confidence in the long-term stability of SYNROC, and in its capacity to isolate high-level wastes from the biosphere for periods sufficiently long to permit their safe decay.

Lateralisation of function in the chicken fore-brain

Abstract: There is lateralisation of function in the chicken fore-brain This was revealed by examining the behavioral modifications produced by administration of cycloheximide into the left or right hemisphere on Day 2 of post-hatched life Visual discrimination learning of a task requiring a search for food was found to be performed either entirely or, at least, to a greater extent by the left hemisphere Visual habituation learning was not found to be lateralised The left hemisphere is more involved in auditory habituation than is the right; administration of cycloheximide to the left hemisphere slowed auditory habituation, as did bilateral administration, but treatment of the right hemisphere was ineffective There are indications that the right hemisphere plays a more important role in response to novelty A side-preference for response to stimuli seen by the left eye was demonstrated These results are discussed with reference to head orientation during development in the egg

Influence of Rate of Development of Leaf Water Deficits upon Photosynthesis, Leaf Conductance, Water Use Efficiency, and Osmotic Potential in Sorghum

Abstract: This study reports the effect of rate of development of leaf water deficits in soil-grown sorghum (Sorghum bicolor) on the relationship of net photosynthesis, leaf conductance, and water use efficiency to leaf water potential, and on the degree of solute accumulation (osmotic adjustment). Recovery of these processes on rewatering, and responses during a second stress cycle were also studied. The most rapid rate of stress (1.2 MPa day−1) resulted in no solute accumulation and the lowest rate of net photosynthesis and leaf conductance for any given leaf water potential during stress. Stress at 0.7 and 0.15 MPa day−1 led to equal solute accumulations of approximately 0.6 MPa, but net photosynthesis, leaf conductance, and water use efficiency at a given leaf water potential were lower with the faster rate of stress (0.7 MPa day−1). Additionally, leaf conductance at a given leaf turgor potential was lowest at the 1.2 MPa day−1 stress rate, slightly higher at the intermediate rate of stress, and clearly highest at the slowest rate of stress. Recovery of both net photosynthesis and leaf conductance upon rewatering was rapid, taking less than 3 days, but full recovery of osmotic potential took between 6 and 11 days. One slow stress cycle had no influence on relationships during a second cycle. The concept of a threshold leaf water potential for stomatal closure is discussed and the conclusion reached that stomatal closure occurs slowly over a wide range of leaf water potential (> 1.0 MPa), the range being greater for slower rates of stress.

Boninites, komatiites and ophiolitic basalts

Abstract: The rare Phanerozoic rock type boninite petrographically resembles Archaean basaltic komatiites and the range of boninite compositions overlaps that of basaltic komatiites. Quench amphibole and hydrous glass in the groundmass of boninites confirm earlier ideas that they may be the products of partial melting of peridotite in hydrous conditions, whereas basaltic komatiites have been assumed to result from fractionation of dry melts. Where field relationships are known, boninites are found either in ophiolites or a fore-arc tectonic environment.

Psychiatric disorder in Canberra. A standardised study of prevalence.

Abstract: A standardised survey of prevalence has been carried out in a general population. The epidemiological method employed is innovative in its use of two established instruments, the GHQ and the PSE, harnessed together in a two-phase design. 756 persons were interviewed, giving a response rate of 85 % in phase 1. 157 were then interviewed with the PSE in phase 2 within a few days, giving a response rate of 92 % in this weighted subsample. The point prevalence of non-psychotic morbidity, based on the distribution of GHQ scores, is higher than elsewhere in Australia, the excess being in Canberra males. The PSE data weighted back to represent the total population, show a distribution of morbidity in women which is remarkably similar to that in the very different population of Camberwell. The overall point prevalence of threshold and definite cases is 9.0 % 3.2. Case rates did not vary significantly with age or sex, but were higher in the separated, the single and the widowed. This study represents an advance in the reliable and economical detection of psychiatric morbidity at specified levels of severity in general populations.

Spatial variations in the geochemistry of quaternary lavas across the Sunda arc in Java and Bali

Abstract: Since Mesozoic time, Java and Bali have formed part of an evolving system of island arcs comprising the Sunda arc of Indonesia. The present tectonic setting is relatively simple with subduction occurring at the Java Trench to the south. A north-dipping Benioff seismic zone delineates an underthrust lithospheric slab to depths of approximately 600 km beneath the Java Sea. Quaternary lavas of the ‘normal island arc association’ range from tholeiites to high-K calc-alkaline lavas over Benioff zone depths from 120–250 km, respectively. More abundant calc-alkaline lavas lie between these extremes. High-K alkaline lavas are found over Benioff zone depths in excess of 300 km.

Electrophysiological analysis of fly retina. I: Comparative properties of R1-6 and R 7 and 8

Abstract: 1. Intracellular recordings have been made from the photoreceptor classes R1–6, R 7, and R 8 in the flies,Calliphora (wild) andMusca (white). 2. The half width of the angular sensitivity function (Δρ) inCalliphora R1–6 varies between 1.5° in the fovea and 3° in the lateral eye regions (Fig. 1). Light adaptation narrows these values by 20%. Both R 7 and R 8 haveΔρ values narrower than in R1–6, averaging 1.3° in foveal regions. InMusca (white)Δρ in R1–6=2.3° and in R7/8=1.5° (both values for foveal regions). 3. The presence of an adapting light of sufficient intensity to activate the pupil mechanism shifts the 490 nm peak of spectral sensitivity in R1–6 towards shorter wavelengths by 40–50 nm inCalliphora but not in the pupilless mutant, white, ofMusca (Fig. 2). The shift is independent of photopigment equilibria and has a time course similar to that of the pupil closure mechanism (Fig. 3). 4. There are two spectral classes of R7. Both have a single peak of sensitivity in the range 340–360 nm, but one is purely ultra-violet (UV) sensitive, having less than 10% sensitivity beyond 400 nm, whilst the other has a long tail of sensitivity extending to 500 nm. The majority of R 8 cells have a major peak of sensitivity at around 540 nm (Fig. 4). 5. Polarisation sensitivity (PS) inCalliphora R1–6 averages 2.0 when measured in the green, and is not significantly affected by light-adaptation. InMusca R1–6, PS averages 1.9. In R7, PS is similar inCalliphora (average 2.2), but reaches values of up to 6 inMusca. PS could not always be detected in R8 but values of up to 3.5 have been recorded inCalliphora. 6. Absolute sensitivities measured from the quantal flux required to generate a 50% maximum response using axial light of peak wavelength (APS50) are higher in R 7 and R 8 due to the higher voltage gain per quantum (Table 2). 7. All receptor classes light adapt in a similar manner and continue responding to increments of intensity under the brightest adapting regimes used. 8. These new results from identified receptors lead to a reappraisal of the possible roles of R1–6 and R 7 and 8 in optomotor responses elicited under different regimes of test pattern wavelength and intensity.

Predicting the multiple pathways of plant succession

Abstract: Classical concepts view succession as a deterministic, mechanistic regeneration of the disturbed community, and thus have limited applicability to fire-prone ecosystems, A recently developed multiple pathway succession model appears to have more realism and applicability in frequently disturbed ecosystems. It includes a set of species-specific attributes that are vital to reproduction and survival, and permits variable succession pathways depending on the stand's age (and thus species composition) when disturbed. Examples from Australia and the northern Rocky Mountains (USA) are presented, as are approaches to refining and improving the model.

Direct experimental verification of the Kelvin equation for capillary condensation

Abstract: THE thermodynamic properties of liquids trapped in microscopic pores or existing as very small, highly curved droplets are described by the Kelvin equation1. This equation forms the basis of critical nucleation theory2 and has been used in interpreting such diverse phenomena as adhesion3, the enhanced solubility of small particles2 and the retention and flow of liquids in porous materials4–6. The validity of the application of the Kelvin equation to such highly curved interfaces (where the mean radius of curvature can be in the range 1–100 nm) has been questioned1,4, but has never been tested by direct experiment. We have used multiple beam interferometry to observe the formation of capillary condensed liquid between crossed cylinders of molecularly smooth mica. We report here that the Kelvin equation is obeyed by cyclohexane menisci with mean radius of curvature as low as 4 nm. We further conclude that the application of the laws of thermodynamics, and the concept of a bulk surface tension, are valid in principle for such highly curved interfaces.

The escape factor in plasma spectroscopy—I. The escape factor defined and evaluated

Abstract: In plasma spectroscopy, it is frequently convenient to treat the effect of self-absorption parametrically, as a reduction in the spontaneous transition probability by a parameter known in the literature relating to laboratory sources as the escape factor. The concept of the escape factor is here developed in a systematic way, within a framework into which the many contributions of individual authors to particular aspects of the subject have been fitted. A general definition of the escape factor is presented from which other definitions are shown to follow. The escape factor has been evaluated for Gaussian, Lorentzian and Holtsmarkian profiles, for upper and lower limits to the source function and for infinite plane-parallel slab and infinite cylinder geometries. A comparison is made with other calculations of the escape factor from the literature. Where appropriate, reference is made to the astrophysical literature, particularly to that concerning the net radiative bracket.

Refined instrumental variable methods of recursive time-series analysis Part I. Single input, single output systems

Abstract: This paper is the first in a series concerned with a comprehensive evaluation of the refined instrumental variable-approximate maximum likelihood (IVAML) method of time-series analysis. The implementation of a recursive/iterative version of the refined IVAML algorithm for single input, single output systems is discussed in detail and the performance of the algorithm is evaluated by Monte-Carlo simulation analysis applied to five simulated stochastic systems. As conjectured, the algorithm appears to yield asymptotically efficient estimates of the time-series model parameters and, indeed, it seems to approach minimum variance estimation of the basic system model parameters for even low sample size and low signal/noise ratios. The noise model parameters are not estimated so well at the smaller sample sizes but the estimation performance appears similar to that of other competing methods of analysis, such as recursive maximum likelihood (RML). Subsequent papers on this same general topic will deal with extens...

Dihydromuscimol, thiomuscimol and related heterocyclic compounds as GABA analogues.

Abstract: A series of heterocyclic GABA analogues related to muscimol (5-aminomethyl-3-isoxazolol) were tested as depressants of the firing of GABA sensitive neurones on the cat spinal cord, and as inhibitors of the sodium-independent binding of GABA to rat brain membranes. Furthermore, the compounds were examined as inhibitors of GABA uptake into rat brain slices and as inhibitors of the activities of the GABA-metabolizing enzymes L-glutamate 1-carboxylyase and GABA:2-oxoglutarate aminotransferase. Dihydromuscimol [(RS)-4,5-dihydromuscimol] and thiomuscimol (5-aminomethyl-3-isothiazolol) were approximately equipotent to muscimol as bicuculline-sensitive depressants of neuronal firing and as inhibitors of GABA binding. The structurally related compounds isomuscimol (3-aminomethyl-5-isoxa-zolol) and azamuscimol (5-aminomethyl-3-pyrazolol) were much weaker than muscimol as GABA agonists. The affinity of the compounds for GABA receptor sites in vitro is in agreement with their relative potency as GABA receptor agonists in vivo. The rat brain synaptic membranes used for the GABA receptor binding studies were prepared by two procedures, which were shown to have a pronounced influence on the observed potency of the inhibitors of GABA binding. The compounds were weak or inactive as inhibitors of the uptake of GABA into rat brain slices and of the activity of GABA: 2-oxoglutarate aminotransferase in vitro. Azamuscimol and 2-methylaza-muscimol were moderately potent inhibitors.of the activity of L-glutamate 1-carboxylyase in vitro. This inhibition by azamuscimol was timedependent following pseudo-first-order kinetics, consistent with azamuscimol acting as a catalytic inhibitor. The structure of the heterocyclic rings of these zwitterionic compounds is a factor of critical importance for interaction with GABA receptors. The present structure-activity analysis demonstrates that heterocyclic GABA analogues having a high degree of delocalization of the negative charges have low affinity for the GABA receptors.