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The effective heat of formation model enables heats of formation to be calculated as a function of concentration. By choosing the effective concentration at the growth interface to be that of the liquidus minimum, the model correctly predicL. first phase formation for 14 binary systems for which experimental data was found, except for the Au-Cu system which does not have a well-defined minimum on the liquidus curve.
D. J. Des Marais, NASA Ames Research Center MS 239-4 Moffett Field, CA 94035-1000, USA,
B. M. Jakosky, University of Colorado, Boulder LASP/Campus Box 392 Boulder, CO 80309-0392, USA,
B. M. Hynek, Department of Geological Sciences, Laboratory for Atmospheric and Space Physics 392 UCB, University of Colorado Boulder, CO 80309, USA
A central goal in Mars exploration is to determine whether life has ever existed there and, whether it did or not, the degree to which the Mars environment could have sustained life. To attain this goal, we can characterize the environmental context, identify places most likely to have sustained life and retained evidence of its presence, and search for “biosignatures,” namely features created only by life and that can persist long after they were formed. Life as we know it requires liquid water, source(s) of energy to sustain metabolism, and chemical building blocks for its cellular constituents. The availability of liquid water appears to be the primary limiting factor in near-surface Martian environments. Liquid water apparently was more widespread on the surface in ancient times and it has occurred within the crust at various times. Oscillations in the orbital obliquity of Mars probably influenced the distribution of water, and some evidence hints of recent liquid water. Observations by the Mars Exploration Rover (MER) Spirit in Gusev crater are consistent with the possibility that liquid water, nutrients and sources of chemical energy were simultaneously available to sustain habitable conditions in subsurface Columbia Hills materials at least some time in the distant (Noachian?) past. As of this writing Spirit rover has not yet determined that these conditions ever existed in a surface environment. MER Opportunity revealed that habitable environments might have persisted for an extended period of time in the Meridiani Planum region at some time in the distant past.
This study aimed to assess mother's/caregiver's understanding, practical application and cultural acceptability of a preliminary set of South African food-based dietary guidelines (FBDGs) for children aged 6–12 months living in the Little Karoo area of the Western Cape Province.
An observational, descriptive and cross-sectional study design was followed. Focus group interviews, recorded on videotape, were analysed for qualitative data. Quantitative questionnaires measured knowledge and comprehension of guidelines, perceived constraints to compliance with and importance of guidelines as well as socio demographic data prior to the focus group interviews.
Afrikaans-, English- and Xhosa-speaking communities of the Little Karoo area of the Western Cape Province of South Africa, including the urban areas of Oudtshoorn, Bongulethu, Bridgton, Toekomsrus and the adjacent rural areas of Dysselsdorp, Calitzdorp, Uniondale, Ladismith and Zoar.
Sixty-four mothers or caregivers to infants 6–12 months of age were included in the sample.
Information obtained through the questionnaires supported what was said during discussions. Although perceived as important by the majority of respondents, some of the guidelines were not well understood without prior explanation. Such guidelines were those pertaining to meal frequency and cup feeding, while application of the guideline to prolonged breast-feeding seemed the most problematic.
The FBDGs for this age group will have to be supported by extensive and appropriate educational material to be effective when introduced to the public. The fact that the applicability of the guideline to prolonged breast-feeding seemed to be the most problematic is a cause for concern.
Milled grass particles were coated with n-alkanes and suspended in a xanthan gum solution. Experiments snowed that grass particles could be coated uniformly with alkanes by means of a rotary evaporator. Further experiments showed that the grass particles, in stable xanthan gum suspension, could be accurately dispensed. The coefficients of variation of the alkane content per dose delivered by means of a dosing gun and syringe were 2·6 and 2·3%, respectively. There was no significant difference between the concentration of faecal alkanes derived from alkanes dosed in suspension-form and alkanes placed directly into the rumen.
Twenty-five patients who had each had inferior meatal antrostomies performed were endoscopically examined and assessed with acoustic rhinometry six weeks and six months after surgery. No significant increase in nasal cross-sectional area could be demonstrated at the site of the antrostomy in the post-operative cases, although the nasoantral window was found to be patent in 44 of the 50 nasal cavities.
Modern microbial mats are structurally coherent macroscopic accumulations of microorganisms. Mats are widely distributed on earth. They are found in a surprisingly large number of diverse environments from the equatorial zones to both polar regions. They vary in size from extensive terrestrial and hypersaline mats that cover areas several square kilometers in extent to minute mats only a few square centimeters in area found in small thermal springs. They vary in thickness from massive accumulations measured in meters, such as those in the Persian Gulf and the Red Sea region, to thin films less than a few millimeters in thickness. In addition to being highly varied in size, modern microbial mats are also very diverse in morphology, community structure, and physiological characteristics. What do such mats have in common? Under what conditions do they form? What is the basis of their diversity? What insight do they provide, if any, to the interpretation of the widespread stromatolites of the Proterozoic?
Microbial mats are accretionary cohesive microbial communities which are often laminated and found growing at the sediment-water (occasionally sediment-air) interface. Most mats stabilize unconsolidated sediment. The mats are comprised of the various microorganisms that accumulate along with their metabolic products. The most conspicuous of these products is usually a copious amount of extracellular polysaccharide which helps hold the cells together to form a cohesive structure.
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