The binding of benzene on Si(111)-(7×7): a theoretical modelling approach

Transgenic constructs intended to be stably established at high frequencies in wild popu- lations have been demonstrated to drive from low frequencies in experimental insect populations. Link- ing such population transformation constructs to genes which render them unable to transmit pathogens could eventually be used to stop the spread of vector-borne diseases like malaria and dengue. Generally, population transformation constructs with only a single transgenic drive mechanism have been envisioned. Using a theoretical modelling approach we describe the predicted properties of a construct combining autosomal Medea and underdominant population transformation systems. We show that when combined they can exhibit synergistic properties which in broad circumstances surpass those of the single systems. With combined systems, intentional population transformation and its reversal can be achieved readily. Combined constructs also enhance the capacity to geographically restrict transgenic constructs to targeted populations. It is anticipated that these properties are likely to be of particular value in attracting regulatory approval and public acceptance of this novel technology.

Download Full-text

What does 14 C uptake by phytoplankton really measure ? A theoretical modelling approach

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1982.0016 ◽

1982 ◽

Vol 214 (1196) ◽

pp. 351-368 ◽

Cited By ~ 65

Keyword(s):

Water Column ◽

External Medium ◽

Net Photosynthesis ◽

Compensation Point ◽

Theoretical Modelling ◽

Column Experiments ◽

Gross Photosynthesis ◽

Modelling Approach

The patterns of photosynthetic 14 C uptake predicted by four models, each of which incorporates different assumptions about the fate of carbon within a few hours of its fixation by phytoplankton, have been compared with the patterns of net 12 C uptake predicted by the same models. According to all models tested, 14 C will accumulate in the cells more rapidly (relative to its abundance) than 12 C, until an equilibrium is established between the 14 C : 12 C ratio inside the cells and that in the external medium. Since several hours are required for cells to approach this equilibrium, all models predict that measurements of photosynthesis based on 14 C uptake overestimate net photosynthesis in incubations of up to 6-12 h, and that this overestimation will be especially severe close to the compensation point, or at depth in a water column. Experiments showed approximately linear uptake of 14 C for up to 4-5 h. The only model predicting this pattern indicated that 14 C uptake was proportional to gross photosynthesis, and could not be used to estimate either respiration or net photosynthesis. Other physiological and ecological evidence suggests that the conventional assumption that the radiocarbon technique measures net photosynthesis should be re-examined.

Download Full-text

Why climate change will invariably alter selection pressures on phenology

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2014.1611 ◽

2014 ◽

Vol 281 (1793) ◽

pp. 20141611 ◽

Cited By ~ 58

Author(s):

Phillip Gienapp ◽

Thomas E. Reed ◽

Marcel E. Visser

Keyword(s):

Climate Change ◽

Environmental Variables ◽

Reaction Norm ◽

Theoretical Modelling ◽

Time Lags ◽

Selection Pressures ◽

Individual Fitness ◽

Consumer Reaction ◽

Environmentally Sensitive ◽

Modelling Approach

The seasonal timing of lifecycle events is closely linked to individual fitness and hence, maladaptation in phenological traits may impact population dynamics. However, few studies have analysed whether and why climate change will alter selection pressures and hence possibly induce maladaptation in phenology. To fill this gap, we here use a theoretical modelling approach. In our models, the phenologies of consumer and resource are (potentially) environmentally sensitive and depend on two different but correlated environmental variables. Fitness of the consumer depends on the phenological match with the resource. Because we explicitly model the dependence of the phenologies on environmental variables, we can test how differential (heterogeneous) versus equal (homogeneous) rates of change in the environmental variables affect selection on consumer phenology. As expected, under heterogeneous change, phenotypic plasticity is insufficient and thus selection on consumer phenology arises. However, even homogeneous change leads to directional selection on consumer phenology. This is because the consumer reaction norm has historically evolved to be flatter than the resource reaction norm, owing to time lags and imperfect cue reliability. Climate change will therefore lead to increased selection on consumer phenology across a broad range of situations.

Download Full-text

Some Problems in Understanding the Solar Corona

International Astronomical Union Colloquium ◽

10.1017/s025292110002491x ◽

1994 ◽

Vol 144 ◽

pp. 1-9

Author(s):

A. H. Gabriel

Keyword(s):

Solar Corona ◽

Solar Atmosphere ◽

Theoretical Modelling ◽

Total System ◽

Major Advance ◽

X Ray ◽

Proper Perspective ◽

Space Observations

The development of the physics of the solar atmosphere during the last 50 years has been greatly influenced by the increasing capability of observations made from space. Access to images and spectra of the hotter plasma in the UV, XUV and X-ray regions provided a major advance over the few coronal forbidden lines seen in the visible and enabled the cooler chromospheric and photospheric plasma to be seen in its proper perspective, as part of a total system. In this way space observations have stimulated new and important advances, not only in space but also in ground-based observations and theoretical modelling, so that today we find a well-balanced harmony between the three techniques.

Download Full-text