ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

1

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A study of the structure of zinc polycarboxylate dental cements (1993)

Nicholson, J. W. ; Hawkins, S. J. ; Wasson, E. A.

Springer

Journal of materials science 4 (1993), S. 32-35

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ISSN: 1573-4838

Source: Springer Online Journal Archives 1860-2000

Topics: Medicine , Technology

Notes: Two examples of zinc polycarboxylate dental cement were studied, one of which was prepared from an aqueous solution of poly (acrylic acid) together with the zinc oxide powder, the other being prepared by adding water to a mixture of dried polyacid and zinc oxide powder. The changes in the properties of the resultant cements with length of storage in various media were determined. In all cases the maximum strength was achieved fairly rapidly, usually at 1 week, after which there was little or no increase. Cements stored in water achieved the lowest compressive strengths, whereas cements stored in highly desiccating conditions, over concentrated sulphuric acid, achieved very high (if variable) compressive strengths. There appeared to be very little difference between the water-activated and conventional cements. These results confirm previous findings that zinc polycarboxylate cements are relatively poorly hydrated compared with other polyelectrolyte biomaterials. This in turn implies that water does not play a structural role in these cements.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00122974

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2

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The incorporation of hydroxyapatite into glass-polyalkenoate (“glass-ionomer”) cements: a preliminary study (1993)

Nicholson, J. W. ; Hawkins, S. J. ; Smith, J. E.

Springer

Journal of materials science 4 (1993), S. 418-421

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ISSN: 1573-4838

Source: Springer Online Journal Archives 1860-2000

Topics: Medicine , Technology

Notes: The effect of adding finely divided hydroxyapatite (HAp) powder to glass-polyalkenoate cements has been studied. Two different glasses were used in cement formation, an oxide and a fluoride glass. Cements were prepared at a powder: liquid ratio of 2:1, higher ratios being unattainable because of the low bulk density (hence large volume fraction per unit mass) of HAp powder. For the oxide glass there was a steady reduction in compressive strength and an increase in working and setting times with increased loadings of HAp. By contrast, for the fluoride glass, there was a plateau region from 2.5 to 40% by mass HAp in the glass powder in which the compressive strengths and the working and setting times remained approximately constant. At HAp levels above 40%, as for the oxide glass, there was a significant reduction in strength and an increase in working and setting times. The presence of HAp in the cement was not found to inhibit the development of compressive strength with time for cements prepared from the fluoride-containing glass. Cements prepared from the oxide glass, by contrast, did not increase in strength with time and this feature was also not changed by the presence of HAp.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00122202

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Feeding behaviour in Littorina littorea: a study of the effects of ingestive conditioning and previous dietary history on food preference and rates of consumption (1990)

Imrie, D. W. ; McCrohan, C. R. ; Hawkins, S. J.

Springer

Hydrobiologia 193 (1990), S. 191-198

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ISSN: 1573-5117

Keywords: feeding ; preference ; learning ; phagostimulant ; intertidal

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Feeding responses of the generalist herbivore, Littorina littorea (L.), to the perceived ‘taste’ of macroalgae were assessed with respect to the effects of recent dietary intake and to overlapping versus nonoverlapping distributions of winkles and algae. The extent of grazing on artificial substrates impregnated with crude algal extracts was used as a measure of rate of response to the odour of preferred algae, and of feeding preference among less preferred algae, in a variety of designs. Adult L. littorea collected from a site where a range of algae were present showed preference among extracts of fucoids, whereas adults from a nearby site showed no such preference. Juvenile L. littorea of two weight cohorts collected from the former site responded faster to Porphyra umbilicalis extract-containing substrate than similar-sized animals from the latter site. Juveniles, fed either Porphyra, Ulva lactuca, or starved for two weeks in the laboratory, responded similarly to Ulva versus Porphyra extracts in a dose-dependent manner across a range of concentrations, although the Porphyra-maintained group consumed more of each, and the starved group less over seven days. Juveniles maintained on a mixed diet of Ulva and Porphyra consumed more Porphyra extract and less Ulva extract over the same period. These results are discussed in relation to the possible role of ingestive conditioning and previous dietary history in determining the occurrence and extent of chemically-mediated feeding preference in L. littorea.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00028076

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4

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Scraping a living: a review of littorinid grazing (1990)

Norton, T. A. ; Hawkins, S. J. ; Manley, N. L. ; [et al.]

Springer

Hydrobiologia 193 (1990), S. 117-138

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ISSN: 1573-5117

Keywords: feeding behaviour ; algal defences ; intertidal ecology

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Littorinid snails are predominantly herbivorous and the versatility of their radulae enables them to feed on a variety of macroscopic and microscopic plants in a diversity of habitats. Some are selective feeders preferring some species of algae to others, and rejecting some even after a prolonged period of starvation. Different species of snail exhibit different preferences. The factors affecting the attractiveness and edibility of food plants are discussed and food value considered. Foraging behaviour of littorinids is briefly reviewed in relation to the influence of chemical cues from the algae. Littorinids appear to be able to select or reject algae without having ingested them, having perceived the plants from a distance, moving towards favoured foods (or habitat-providing plants) and away from those that it rejects. The nature of the chemical cues emitted by the algae is discussed. Temporal patterns of foraging activity show some evidence of an endogenous component which can be overridden by responses to environmental conditions. These patterns place restraints on energy intake. The structural and chemical defences used by algae against littorinid grazing are considered. The importance of polyphenolic compounds is evaluated. The effects of grazing as a selective agency and a factor influencing algal populations are discussed. There is some evidence that life history patterns are a response to grazing. The influence of external physical factors, such as salinity on grazing pressure is demonstrated. Finally, the impact of littorinid snails on intertidal communities is assessed in relation to their abundance and biogeographical distribution. The relative importance of littorinids is contrasted on shores possessing or lacking limpets.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00028071

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