Showing papers by "University of Adelaide published in 1985"

Principles of CMOS VLSI Design: A Systems Perspective

Abstract: Introduction to CMOS Circuits. Introduction. MOS Transistors. MOS Transistor Switches. CMOS Logic. Circuit Representations. CMOS Summary. MOS Transistor Theory. Introduction. MOS Device Design Equation. The Complemenatry CMOS Inverter-DC Characteristics. Alternate CMOS Inverters. The Differential Stage. The Transmission Gate. Bipolar Devices. CMOS Processing Technology. Silicon Semiconductor Technology: An Overview. CMOS Technologies. Layout Design Rules. CAD Issues. Circuit Characterization and Performance Estimation. Introduction. Resistance Estimation. Capacitance Estimation. Inductance. Switching Characteristics. CMOS Gate Transistor Sizing. Power Consumption. Determination of Conductor Size. Charge Sharing. Design Margining. Yield. Scaling of MOS Transistor Dimensions. CMOS Circuit and Logic Design. Introduction. CMOS Logic Structures. Basic Physical Design of Simple Logic Gates. Clocking Strategies. Physical and Electrical Design of Logic Gates. 10 Structures. Structured Design Strategies. Introduction. Design Economics. Design Strategies. Design Methods. CMOS Chip Design Options. Design Capture Tools. Design Verification Tools. CMOS Test Methodolgies. Introduction. Fault Models. Design for Testability. Automatic Test Pattern Generation. Design for Manufacturability. CMOS Subsystem Design. Introduction. Adders and Related Functions. Binary Counters. Multipliers and Filter Structures. Random Access and Serial Memory. Datapaths. FIR and IIR Filters. Finite State Machines. Programmable Logic Arrays. Random Control Logic.

Non-radioactive hybridization probes prepared by the chemical labelling of DNA and RNA with a novel reagent, photobiotin

Abstract: A photo-activatable analogue of biotin, N-(4-azido-2-nitrophenyl)-N'-(N-d-biotinyl-3-aminopropyl)-N'-methyl-1,3- propanediamine (photobiotin), has been synthesized and used for the rapid and reliable preparation of large amounts of stable, non-radioactive, biotin-labelled DNA and RNA hybridization probes. Upon brief irradiation with visible light, photobiotin formed stable linkages with single- and double-stranded nucleic acids yielding probes which were purified from excess reagent by 2-butanol extraction and ethanol precipitation. Using single-stranded phage M13 DNA probes chemically labelled with one biotin per 100-400 residues and dot-blot hybridization reactions on nitrocellulose, as little as 0.5 pg (6 X 10(-18) mol) of target DNA was detected colorimetrically by avidin or streptavidin complexes with acid or alkaline phosphatase from three commercial sources. The sensitivity of detection of target RNA in dot-blots and Northern blots was equivalent to that obtained with 32p-labelled DNA probes. Photobiotin was also used for the labelling of proteins with biotin.

A review of the ecological effects of river regulation in Australia

Abstract: Responses to hydrologic change are an important theme in lotic ecology, and data for Australian rivers are accumulating in a rapid, butad hoc manner. Thia paper arranges recent contributions according to the major drainage divisions, which provide reasonably coherent environmental units. The east coastal rivers are exploited for storage, power generation and waste disposal, and Tasmanian rivers are regulated to serve hydro-electric power schemes. Most information refers to the Murray-Darling river system, which supplies irrigated agriculture in semi-arid inland areas of S.E. Australia, and is intensively regulated by dams, weirs and barrages. The Murray's flows are over-committed, if variability is taken into account, and there are environmental problems (e.g. erosion and salinity) associated with irrigation. The effects of regulation are seen also in the changed distributions of plants and animals associated with the Murray and its floodplain. In Australia the national effort is uncoordinated because research and management are developing independently of one another. Ecologists must become involved in the planning and implementation of strategies that are consistent, as far as possible, with offstream and instream needs.

Acute and chronic effects of domperidone on gastric emptying in diabetic autonomic neuropathy.

Abstract: Gastric emptying was studied with a double radioisotopic method in 12 patients with insulin-dependent diabetes mellitus complicated by autonomic neuropathy and in 22 control subjects. In the diabetics, the acute and chronic effects of oral domperidone on gastric emptying, symptoms of gastroparesis, and glycemic control were assessed. Gastric emptying of solid and liquid was slower in diabetics than controls (P less than 0.001). Acute administration of domperidone increased the rate of both solid and liquid emptying (P less than 0.005). Domperidone was most effective in those patients with the greatest delay in gastric emptying. After chronic administration (35-51 days), domperidone had no significant effect on solid emptying (P greater than 0.05), but was still effective in increasing liquid emptying (P less than 0.025). Symptoms of gastroparesis were less after domperidone (P less than 0.001).

Eleven new sequence variants of citrus exocortis viroid and the correlation of sequence with pathogenicity

Abstract: Full-length double-stranded cDNA was prepared from purified circular RNA of two new Australian field isolates of citrus exocortis viroid (CEV) using two synthetic oligodeoxynucleotide primers. The cDNA was then cloned into the phage vector M13mp9 for sequence analysis. Sequencing of nine cDNA clones of isolate CEV-DE30 and eleven cDNA clones of isolate CEV-J indicated that both isolates consisted of a mixture of viroid species and led to the discovery of eleven new sequence variants of CEV. These new variants, together with the six reported previously, form two classes of sequence which differ by a minimum of 26 nucleotides in a total of 370 to 375 residues. These two classes correlate with two biologically distinct groups when propagated on tomato plants where one produces severe symptoms and the other gives rise to mild symptoms. Two regions of the native structure of CEV, comprising 18% of the total residues, differ between the sequence variants of mild and severe isolates. Whether or not both of these regions are essential for the variation in pathogenicity has yet to be determined.

Biotic adaptations in temporary lentic waters, with special reference to those in semi-arid and arid regions

Abstract: Despite the obvious ubiquity, ecological importance and limnological interest of temporary waters, most limnological texts have little to say about them. Dussart (1966), Schwoerbel (1974), Golterman (1975), Moss (1980), Goldman & Horne (1983), and Wetzel (1983), to mention just a few recent and otherwise comprehensive texts of North American or European provenance, make scant if any reference. Cole’s (1983) text does better, but only those authors who live in or have lived in tropical or arid countries make extensive reference (e.g. Bayly & Williams, 1973; Beadle, 1981). Temporary waters are especially widespread in arid and semi-arid regions. Even the most cursory glance at maps of world climate will indicate the vast extent of these regions in Africa, Australia, the Middle East and Central Asia, parts of South America, and in W. North America. The paucity of permanent waters in arid and semi-arid regions means, of course, that temporary waters have an ecological significance much greater there than in more temperate regions. For example, throughout most of continental Australia, waterfowl are closely dependent for survival on the occurrence of temporary water-bodies (Frith, 1967). The limnological interest of temporary waters relates above all to the nature of the ecological stresses that assail their biota, and the nature of corresponding adaptation.

Microwave irradiation as a form of fixation for light and electron microscopy.

Abstract: Microwave irradiation was used to fix a wide range of surgical and autopsy specimens as well as tissue from freshly killed rats. Although there appeared to be varying optimum temperatures of fixation for different tissues, from a practical standpoint, the heating to 58 degrees C of tissues submerged in normal saline resulted in fixation of a quality comparable with that produced by conventional fixation to 10 per cent formalin. Microwave irradiation applied to tissues which had up to 1 h prior immersion in 10 per cent formalin also produced excellent preservation of cytomorphology, the time required for microwave fixation being no more than 150 s. This form of rapid heat fixation had no deleterious effects on special stains, sectioned as well as control fixed blocks and produced less shrinkage artefact than conventional formalin fixation. Immunocytochemical staining for more stable cytoplasmic antigens revealed no significant difference between microwave fixation compared with formalin fixation. The more labile membrane associated antigens of lymphocytes, however, were not preserved by either method of fixation. Microwave fixation was also found to be applicable to electron microscopy. Tissue samples immersed in 2.5 per cent glutaraldehyde and fixed in 90 s by irradiation to 50 degrees C showed excellent preservation of ultrastructural morphology.

The role of the necrotic periodontal membrane in cementum resorption and ankylosis

Abstract: Teeth replanted with non-vital periodontal membranes demonstrate a high incidence of root resorption and ankylosis. It has been suggested that necrotic periodontal membrane remnants actively stimulate resorption of the resistant cementum layer. The aim of this study was to examine resorption and ankylosis patterns following replantation of teeth with chemically denuded root surfaces and, by extrapolation from these data, to suggest a role for the necrotic periodontal membrane in resorption and ankylosis. Monkey incisors were replanted after endodontic therapy and immersion in 10% sodium hypochlorite. Teeth were either examined with scanning electron microscopy at intervals from 1 day to 8 wk, or subjected to light microscopic examination, using a morphometrical evaluation technique, at 8 wk post-replantation. Only a few macrophage-like cells, in relation to shallow resorption lacunae, were observed by 8 wk. Histologically, the alveolar bone had approached an apparently intact cementum surface in 93% of the morphometrically recorded points. This bone appeared to lie in close approximation to the cementum surface. Denuding the root surface of periodontal membrane prior to replantation demonstrated the resistance of the cementum to colonization and resorption in the absence of stimulation from necrotic periodontal membrane remnants. Furthermore, it revealed that bone replacing the periodontal membrane space grew from the alveolus towards the cementum, to which it appeared unable to fuse due to the absence of significant resorption. Thus, removal of a non-vital periodontal membrane may result in slower destruction of tooth substance following replantation of teeth with severely damaged periodontal membranes.

Culture factors affecting the success rate of in vitro fertilization and embryo transfer.

Abstract: The development of one-cell mouse zygotes to the blastocyst stage in vitro has been used as a quality control for the media and handling procedures employed for human in vitro fertilization and embryo transfer (IVF/ET). One-cell mouse zygotes were placed in culture in medium containing bovine serum albumin. Aliquots of the same batch of medium containing female patients' homologous serum were used for the fertilization and culture of human oocytes. The following procedures were associated with high rates of mouse embryo development and human pregnancies following IVF/ET: adequate gassing and equilibration of the medium, double-rinsing of pipets and catheters used to handle embryos, use of a HEPES-buffered medium for manipulating embryos in the absence of an atmosphere containing 5% CO2, control of excessive temperature in the vicinity of the embryos, and ET using medium containing 50% patient's serum. The institution of these procedures gave more consistent pregnancy rates. However, there was no obvious association between fertilization and cleavage of human oocytes and the quality of the medium ascertained by the mouse embryo development test. In a continuing trial, we are comparing two culture media (modified Tyrode's and a medium formulated on the composition of human fallopian tube fluid [HTF]) and two culture techniques (culture in medium under oil in petri dishes and in loosely capped tubes). Significantly more mouse zygotes developed in HTF medium compared to Tyrode's medium. In a randomized 2 X 2 factorial trial with human IVF/ET, the highest pregnancy rate occurred when fertilization and culture were carried out in HTF medium under oil, but numbers are not yet sufficient to show any statistical difference between treatments.

Activity of glutamine synthetase and glutamate dehydrogenase in trifolium subterraneum l. and allium cepa l: effects of mycorrhizal infection and phosphate nutrition

Abstract: Summary Activities of glutamate dehydrogenase and glutamine synthetase were determined using crude extracts of roots and shoots of mycorrhizal and non-mycorrhizal plants of Trifolium subterraneum L. and Allium cepa L., grown at different levels of fertilizer phosphate. Glutamate dehydrogenase activity was low in all tissues [0.1 to 1.6 μmol NAD(P)H oxidized min−1 gFW−1 tissue] and there was no consistent effect of mycorrhizal infection or phosphate nutrition on this activity. Glutamine synthetase (GS) activity (assayed by the transferase method) was in the range 1 to 40/iimol γ-glutamyl hydroxamate produced min−1 gFW−1. In general, activity of this enzyme was low in phosphate-deficient plants and was increased both by mycorrhizal infection and by improved phosphate supply. In T. subterraneum routine assays of GS were done on roots only. The effects of mycorrhizal infection in increasing enzyme activity in roots were similar whether natural soil inoculum (containing a mixture of several mycorrhizal fungi) or inoculum of Glomus mosseae Nichol. & Gerd. was used. Both increased phosphate supply and mycorrhizal infection increased nodulation of clover plants as well as GS activity, so that it was difficult to relate changes in GS activity to the interacting effects of mycorrhizal infection and phosphate nutrition. Onions had low GS activity in uninfected roots, compared with shoots. Again improved phosphate supply resulted in increased enzyme activity in both roots and shoots. However, the patterns of interaction between phosphate supply, P concentration in tissues, mycorrhizal infection and enzyme activity were different in the two tissues. In shoots, as expected, the effects were consistent with an indirect effect of mycorrhizal infection on enzyme activity, via improved P nutrition. In roots there appeared to be a ‘fungal effect’ superimposed on the phosphate effect. This was investigated by manipulating the amount of fungal tissue in mycorrhizal roots via differences in propagule density of G. mosseae in soil. Results were again consistent with the hypothesis that the mycorrhizal fungi contributed GS activity to the symbiotic root system. Fungal structures were separated from roots following digestion in cellulase and pectinase. GS activity was high in fungal tissue from young roots (29 to 31 d), but low in older infections (55 d). The high activity could not have been caused by contamination of fungal tissue by root cells. The digestion technique reduced GS activity in uninfected and infected root segments, so that results obtained with separated fungi are not quantitatively comparable with those obtained from extracts of fresh tissues. We conclude that vesicular-arbuscular mycorrhizal fungi are able to assimilate ammonium via GS. This ability would be important in increased uptake of nitrogen which is an inevitable prerequisite for increased growth following relief of phosphate stress. It is also consistent with the recent findings by others that hyphae of G. mosseae can absorb and translocate 15NH+4

The structure and genetic control of a new class of disulphide-linked proteins in wheat endosperm

Abstract: Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of unreduced total protein extracts from the endosperm of hexaploid wheat revealed three high molecular weight protein bands (triplet bands) in a zone of heavy background streaking. Electrophoretic examination of 135 hexaploid cultivars showed at least five different patterns of these triplet bands. Nine durum wheat cultivars showed a single band only. Analysis of nullisomic-tetrasomic and ditelocentric lines of ‘Chinese Spring’ wheat revealed that the slowest moving band (Tri-1) of the triplet was controlled by gene(s) on chromosome arm 1DS and the fastest moving band (Tri-3) by 1AS. The band with intermediate mobility (Tri-2) was found to be a hybrid aggregate of the subunits controlled by 1DS and 1AS. Using a non-reducing/reducing form of 2-dimensional (2-D) electrophoresis, these triplet bands were shown to be heterotetramers of four subunits designated D (M.W. 58,000), δ (22,000), A (52,000) and α (23,000) where Tri-1=DδDδ, Tri-2 = DδAα and Tri-3 = AαAα. With very low concentrations of 2-mercaptoethanol (ME), the tetramers dissociated into dimeric subunit pairs (Dδ, Aα), the monomers being observed with higher concentrations of ME. The structure of these subunit pairs resembles that of the subunit pairs in the globulin storage proteins of oats and some legumes. The 2-D method employed in this study was useful also for separating low molecular weight (LMW) subunits of glutenin from the monomeric gliadins which have similar electrophoretic mobility in 1-D separation. It was shown that at least four of these LMW glutenin subunits are controlled by genes on 1DS and 1AS and at least one subunit is controlled by gene(s) on 1BS. This electrophoretic separation method has proven useful in understanding the aggregation behaviour of the seed proteins of wheat.

Comparison of multimeric plus and minus forms of viroids and virusoids

Abstract: In order to investigate the mechanism of replication of viroids and virusoids, we have compared the replication intermediates of three members of each group in nucleic acid extracts of infected plants. Viroids were avocado sunblotch viroid (ASBV), citrus exocortis viroid (CEV) and coconut cadang cadang viroid (CCCV). Virusoids were from velvet tobacco mottle virus (VTMoV), solanum nodiflorum mottle virus (SNMV) and lucerne transient streak virus (LTSV). Analysis of intermediates was by the Northern hybridization technique with single-strand DNA and RNA probes prepared from recombinant DNA clones. The results obtained are discussed in terms of current models of viroid and virusoid replication.The plus RNA species consisted of an oligomeric series up to decamers based on the unit of full-length viroid or virusoid, which was always the major component, except for CEV where only monomer and dimer species were found. In the case of ASBV and the virusoids of VTMoV and SNMV, a minor, multimeric series of components (X-bands) was superimposed on the main oligomeric series.The complementary minus species proved more difficult to detect and characterise, with each viroid and virusoid exhibiting a unique pattern on Northern hybridization. However, they all had greater than unit-length minus species. In addition, minus species analogous to the plus X-bands were found in ASBV and CEV. The experimental difficulties encountered in this work are discussed in terms of the problem of detecting minus species by Northern analysis in the presence of excess complementary plus species.

Nucleotide sequence of cucumber mosaic virus RNA. 1. Presence of a sequence complementary to part of the viral satellite RNA and homologies with other viral RNAs.

Abstract: The nucleotide sequence of the 3389 residues of RNA 1 (Mr1.15 × 106) of the Q strain of cucumber mosaic virus (CMV) was determined, completing the primary structure of the CMV genome (8617 nucleotides). CMV RNA 1 was sequenced by the dideoxy-chain-termination method using M13 clones carrying RNA 1 sequences as well as synthetic oligonucleotide primers on RNA 1 as a template. At the 5′ end of the RNA there are 97 noncoding residues between the cap structure and the first AUG (98–100), which is the start of a single long openreading frame. This reading frame encodes a translation product of 991 amino acid residues (Mr 110791) and stops 319 nucleotide residues from the 3′ end of RNA 1. In addition to the conserved 3′ region present in all CMV RNAs (307 residues in RNA 1), RNAs 1 and 2 have highly homologous 5′ leader sequences, a 12-nucleotide segment of which is also conserved in the corresponding RNAs of brome mosaic virus (BMV). CMV satellite RNA can form stable base pairs with a region of CMV RNAs 1 and 2 including this 12-nucleotide sequence, implying a regulatory function. This conserved sequence is part of a hairpin structure in RNAs 1 and 2 of CMV and BMV and in CMV satellite RNA. The entire translation products of RNA 1 of CMV and BMV could be aligned with significant homology. Less prominent homologies were found with alfalfa mosaic virus RNA 1 translation product and with tobacco mosaic virus Mr-126000 protein.

The learning style of medical students

Abstract: Summary. Recent research indicates that students' learning styles and approaches to study may have a significant bearing on their academic success. A study was undertaken on first-, third-and final-year medical students to analyse their preferred learning styles and approaches to study, using the Lancaster Approaches to Learning Inventory. The results showed that students entering the medical school had preferences which were more similar to science students than arts students' . The medical students had high scores on reproducing orientation (surface approach) in all years tested. The first-year students had low scores on meaning orientation (deep approach) but the scores from students in later years showed a progressive rise. The implications of these results with regard to selection, teaching and assessment are explored. However, this preliminary study does not allow us to differentiate between the effect of student preference and that of the context and the environment in which they study.

An elementary proof of Gleason's theorem

Abstract: Gleason's theorem characterizes the totally additive measures on the closed sub-spaces of a separable real or complex Hilbert space of dimension greater than two. This paper presents an elementary proof of Gleason's theorem which is accessible to undergraduates having completed a first course in real analysis.

The limits of change

Abstract: (1985). The limits of change. Australasian Journal of Philosophy: Vol. 63, No. 1, pp. 1-10.

Virulence properties of strains of agrobacterium on the apical and Basal surfaces of carrot root discs.

Abstract: Most pathogenic strains of Agrobacterium are able to induce crown gall or hairy root on both the apical surface (facing the root tip) and the basal surface (facing the shoot) of carrot (Daucus carota L.) root discs. Tumorigenic strains carrying mutations in the shoot inhibition region of the T-DNA (TL-DNA genes 1 and 2) are markedly attenuated on the basal surface but remain virulent on the apical surface. Coinoculation of two attenuated tumorigenic strains, with mutations in gene 1 and gene 2, respectively, resulted in restoration of virulence on the basal surface. Wild type hairy root-inducing strains can be divided into two groups: those that are virulent on both apical and basal surfaces and those that are virulent only on the apical surface. α-Naphthalene acetic acid stimulated virulence of hairy root strain TR7, belonging to the latter group, on the basal surface. Attenuated virulence on the basal surface can be explained in terms of an auxin deficiency in the basal tissues and unidirectional auxin transport to the apical surface.

Reproduction in zebra finches: hormone levels and effect of dehydration

Abstract: -Zebra Finches (Poephila guttata) of arid Australia can breed continuously under favorable conditions. During droughts, however, breeding ceases but is said to begin again immediately after rain. We found that testis size in breeding birds did not change during, or between, reproductive cycles. Luteinizing hormone (irLH) levels in plasma, however, were significantly higher in males during early incubation (1.25 ng/ml), and in females during courtship (0.89 ng/ ml), than during other parts of the reproductive cycle. Plasma levels of the sex steroids were highest (1.06 ng/ml for androgen in males, 0.32 ng/ml for estrogens in females) at the same time that irLH levels were highest. Wild-caught Zebra Finches had, at capture, testes similar in size to those of aviary-breeding Zebra Finches, but after three weeks of dehydration (1 ml water/bird/week), testis size was significantly smaller and hematocrit was significantly higher: 54% vs. 50% for birds given unlimited access to water. When dehydrated birds were given unlimited access to water, testes grew significantly. Access to green grass or exposure to high relative humidity (85%) augmented the effects of the water on testis size. Spermatogenic activity in some dehydrated birds was high despite small gonad size; however, interstitial tissue was poorly developed, and plasma levels of sex steroids and irLH were low. We suggest that Zebra Finches normally maintain gonadal tissue in a functioning state unless severely dehydrated. Relief from dehydration is a necessary, but not sufficient, condition for the full expression of reproduction. For species that do not live in temporally uniform environments, the timing of reproduction can be a critical element in reproductive success. In many temperate zone birds, reproductive activity begins during the spring, when increasing daylength provides a dependable cue that indicates the approach of conditions favorable for reproduction (see reviews in Lofts and Murton 1968, Farner 1970, Farner and Lewis 1971, Wingfield and Farner 1980). Compared to daylength, other environmental cues that may play a role in controlling the timing of reproduction have received little attention (Moreau 1950, Marshall and Disney 1957, Marshall 1970, Immelmann 1971, Wingfield 1980, Earle 1981, Storey and Nicholls 1982). In some habitats, daylength may not be a reliable cue for reproduction because the onset of other favorable conditions is independent of the changes in daylength. Desert birds, for example, may encounter suitable conditions for reproduction only for brief periods after rainfall, and in such species rapid initiation of reproduction in response to rainfall, regardless of daylength or season, may maximize reproductive success. Such breeding in response to rain apparently occurs in the Zebra Finch (Poephila guttata, syn: Taeniopygia guttata castanotis) native to the arid interior of Australia. The reproductive state of Zebra Finches is not influenced by daylength (Marshall and Serventy 1958, Oksche et al. 1963, Sossinka 1975). In the mesic parts of their range, or in areas receiving agricultural irrigation, Zebra Finches breed year-round, except in the coldest winter months, with peaks in nesting attempts occurring in spring and in autumn (Frith and Tilt 1959, Kikkawa 1980). In arid central Australia, however, the species breeds following the irregular rains, regardless of the time of year (Immelmann 1965). Davies (1977), in a two-year study of Zebra Finches in Western Australia, found birds breeding in every month except March, April, and August, and suggested that both rainfall and temperature were important in the initiation of breeding. Immelmann (1963, 1965) reported that Zebra Finches copulated within a few hours of the beginning of the first rain following several months of drought, and began nesting and egglaying within one week. Zebra Finches are capable of producing many offspring under favorable conditions because (1) both members of the pair participate in nest building (Immelmann 1963), (2) a pair will nest repeatedly as long as conditions remain favorable (Ser-

Healed injuries in Early Cambrian trilobites from South Australia

Abstract: Examples of an undescribed species of the trilobite Redlichia from the Emu Bay Shale (Early Cambrian), Kangaroo Island, South Australia, show damage to the exoskeleton attributed to the action of predators. Injury was probably not lethal. The identity of the predators is unresolved, notwithstanding soft-part preservation within the fossil assemblage. Possible culprits include either a rare and presumably large animal such as an arthropod or conceivably cannibalism by Redlichia itself. This report provides new data on the occurrence of Cambrian predators, and casts further doubt on earlier suggestions that macrophagous predation was insignificant at this time. Aspects of trilobite predation during the Palaeozoic are reviewed, with emphasis placed on their ability to withstand substantial injuries and the possible repair mechanisms that promoted wound healing and survival.

The effect of varnishes and other surface treatments on water movement across the glass ionomer cement surface. II

Abstract: The aesthetic restorative glass ionomer cements undergo a rather prolonged setting reaction during which time they are susceptible to water uptake and water loss. If they can be maintained in isolation long enough in the oral cavity then the clinical result will be superior. A further series of surface treatments has been tested and it has been shown that immediate covering of the immature glass ionomer cement surface with light-activated bonding resin is the most effective method of limiting water movement across the surface. This restriction of water movement is not effective for all light-activated bonding resins suggesting that there may be a physico-chemical interaction occurring on the glass ionomer cement surface with certain of the resins.

Infectivity and in vitro mutagenesis of monomeric cDNA clones of citrus exocortis viroid indicates the site of processing of viroid precursors.

Abstract: Monomeric cDNA clones of citrus exocortis viroid (CEV) were constructed in the plasmid vector pSP6-4 and the infectivity of the clones plus in vitro-synthesized RNA transcripts determined by inoculation onto tomato seedlings. Infectivity was dependent on the site of the viroid molecule used for cloning and the orientation of the cDNA insert. Only the plus BamHI cDNA clone was infectious and produced progeny viroid with wild-type sequence at the region corresponding to the BamHI cloning site. Infectivity correlated with the terminal repetition of 11 nucleotides of viroid sequence, 5'GGATCCCCGGG 3', in the vector adjacent to the insert. The 11-nucleotide sequence lies within the highly conserved central region of viroids. Site-directed mutagenesis of a single nucleotide in the repeat at the 5'-end of the CEV insert to 5' GGATCCCC(T,A)GG 3' gave two point mutants. The two mutant CEV inserts, when excised from the vector, were not infectious. However, plasmid DNA and RNA transcripts from non-excised mutant CEV inserts were infectious. The progeny of one of these clones was examined and contained wild-type sequence. It was concluded that in vivo processing of longer-than-unit-length CEV occurs at one of three adjacent sites in the 11 nucleotide sequence and that the G nucleotide at position 97 is important for viroid replication.

Rhizanthella gardneri (Orchidaceae), its rhizoctonia endophyte and close association with Melaleuca uncinata (Myrtaceae) in Western Australia

Abstract: Summary Rhizanthella gardneri R. S. Rogers, a rare subterranean achlorophyllous orchid which grows in Western Australia near plants of the Myrtaceous shrub Meialeuca uncinata R. Br. ex Alton f., is associated with an undescribed species of Rhizoctonia which forms hyphal coils within cortical cells of the orchid rhizome. The Rhizoctonia also forms ectomycorrhizas with sheath and Hartig net on Meialeuca uncinata and other ectomycorrhizal plants including Eucalyptus. Seeds of R. gardneri may germinate without the Rhizoctonia but their growth soon ceases unless the protocorm is invaded by the fungus through the protocorm hairs. Two plants of R. gardneri raised from seed in association with Rhizoctonia ectomycorrhizas on M. uncinata have flowered after 15 months. The Rhizanthella endophyte stimulated germination of seed of R. gardneri but not seed of two chlorophyllous terrestrial orchids, Prasophyllum regium R. Rogers and Microtis unifolia (Forster f.) Reichb. f. However, germination of these two orchids was stimulated by five of six other Rhizoctonias, including Tkanatephorus cucumeris (Frank) Donk and two species of Tulasnella, also isolated from soil and litter from two Rhizanthella sites.

Equilibration, conflict and instruction: A new class‐oriented perspective

Abstract: Attention is directed to equilibration‐based instructional studies all of which parallel natural development in that they require the concurrent construction of both strategic and metastrategic knowledge (Kuhn and Phelps 1982, Kuhn 1983). The need for this concurrence is questioned, and theoretical arguments developed for an equilibration‐based alternative instructional strategy separating the two. It is argued that this latter strategy may provide an answer to the problematic retention of invalid ideas. A pilot study is reported providing tentative support for this viewpoint.

Two-dimensional simulation by turning bands

Abstract: Journel (1974) developed the turning-bands method which allows a three-dimensional data set with specified covariance to be obtained by the simulation of several one-dimensional realizations which have an intermediate covariance. The relationship between the threedimensional and one-dimensional covariance is straightforward and allows the one-dimensional covariance to be obtained immediately. In theory a dense uniform distribution of lines in three-dimensional space is required along which the one-dimensional realizations are generated; in practice most workers have been content to use the fifteen axes of the regular icosahedron. Many mining problems may be treated in two dimensions, and in this paper a turning-bands approach is developed to generate two-dimensional data sets with a specified covariance. By working in two dimensions, the area on which the data is simulated may be divided as finely as desired by the lines on which the one-dimensional realizations are first generated. The relationship between the two-dimensional and one-dimensional covariance is derived as a nontrivial integral equation. This is solved analytically for the onedimensional covariance. The method is applied to the generation of a two-dimensional data set with spherical covariance.

Unbridling the tongues of women: A biography of Catherine Helen Spence

Abstract: Catherine Helen Spence was a charismatic public speaker in the late nineteenth century, a time when women were supposed to speak only at their own firesides. In challenging the custom and convention that confined middle-class women to the domestic sphere, she was carving a new path into the world of public politics along which other women would follow, in the first Australian colony to win votes for women.

An H1 histone gene-specific 5′ element and evolution of H1 and H5 genes

Abstract: In previous studies we have shown that the H5 gene is not closely linked to the dispersed clusters of core and H1 histone genes. Here we emphasise features of H1 and H5 genes relevant to their expression in the chicken genome. Of particular note is an H1 gene-specific 5' element, 5' AAACACA 3' found upstream of all H1 genes studied to date. This "H1-box" is not found in the related H5 gene, which is expressed only in erythroid cells. A second aspect relates to generation of histone mRNA 3' termini. The H5 gene is shown to contain a remnant of the dyad symmetry element (as well as other conserved sequences) associated with core and H1-histone gene transcript 3' processing. However, it appears as if H5 has evolved a different mechanism in which the mRNA terminus (which is polyadenylated) is displaced downstream from the dyad element. The two clear differences noted here have the potential to affect transcriptional (H1-box) and post-transcriptional (3' terminus processing) regulation of H1 and H5 gene expression.