15 research outputs found
Middle East - North Africa and the millennium development goals : implications for German development cooperation
Closed-loop controlled combustion is a promising technique to improve the overall performance of internal combustion engines and Diesel engines in particular. In order for this technique to be implemented some form of feedback from the combustion process is required. The feedback signal is processed and from it combustionrelated parameters are computed. These parameters are then fed to a control process which drives a series of outputs (e.g. injection timing in Diesel engines) to control their values. This paper’s focus lies on the processing and computation that is needed on the feedback signal before this is ready to be fed to the control process as well as on the electronics necessary to support it. A number of feedback alternatives are briefly discussed and for one of them, the in-cylinder pressure sensor, the CA50 (crank angle in which the integrated heat release curve reaches its 50% value) and the IMEP (Indicated Mean Effective Pressure) are identified as two potential control variables. The hardware architecture of a system capable of calculating both of them on-line is proposed and necessary feasibility size and speed considerations are made by implementing critical blocks in VHDL targeting a flash-based Actel ProASIC3 automotive-grade FPGA
Changes in the concentration of organic acids in roots and leaves of carob-tree under Fe deficiency
Several fruit trees are able to cope with iron (Fe) deficiency when grown in calcareous soils in the Mediterranean region, although information regarding well adapted slow-growing species is scarce, and the mechanisms activated by these species are not described in the literature. A crucial issue related to tolerance is the need to transport Fe over relatively long distances inside the plant. To evaluate the possible role of organic acids in the movement of Fe in tolerant plants, we studied the concentration of low molecular weight organic acids in several organs of 1-year old carob plants grown for 55 days in nutrient solutions without Fe (0 mu M Fe) or with 1 mu M Fe and 10 mu M Fe. Roots, stems and leaves were harvested, and the biomass, Fe and organic acid contents quantified. Total leaf chlorophyll (Chl) was evaluated in young leaves over the experimental period and the activity of root ferric chelate-reductase (FC-R; EC 1.16.1.17) was determined after 35 days, when deficiency symptoms appeared. Iron chlorosis was observed only at the end of the experiment in plants grown in the absence of Fe, and these plants had a smaller DW of leaves and also significant greater activity of root FC-R. Iron deficiency (Fe0 and Fe1 treatments) induced significant changes in the concentrations of succinic, malic, citric and fumaric acids, which increased in roots, or in basal, middle and apical leaves. There were significant correlations between most organic acids (with the exceptions of 2-oxoglutaric and tartaric acids) and leaf Chl. Analysis of each type of leaf showed that more succinic and malic acids were present in young chlorotic leaves while the reverse was true for quinic acid. These changes in organic acids followed a root-to-foliage pathway that was similar in all leaf types and particularly evident in young chlorotic leaves. We hypothesised that it was associated with Fe transport from roots to aboveground tissues, as there were significant differences in Fe contents between treatments with and without Fe
Accumulation of Calcium in the Centre of Leaves of Coriander (Coriandrum sativum L.) is Due to an Uncoupling of Water and Ion Transport.
The aim of this study is to understand the parameters
regulating calcium ion distribution in leaves. Accumulation
of ions in leaf tissue is in part dependent on
import from the xylem. This import via the transpiration
stream is more important for ions such as calcium
that are xylem but not phloem mobile and cannot
therefore be retranslocated. Accumulation of calcium
was measured on bulk coriander leaf tissue (Coriandrum
sativum L. cv. Lemon) using ion chromatography
and calcium uptake was visualized using phosphorimages
of 45Ca2+. Leaves of plants grown in hydroponics
had elevated calcium in the centre of the leaf
compared with the leaf margin, while K+ was distributed
homogeneously over the leaf. This calcium was
shown to be localised to the mesophyll vacuoles using
EDAX. Stomatal density and evapotranspiration (water
loss per unit area of leaf) were equal at inner and outer
sections of the leaf. Unequal ion distribution but
uniformity of water loss suggested that there was
a difference in the extent of uncoupling of calcium and
water transport between the inner and outer leaf. Since
isolated tissue from the inner and outer leaf were able
to accumulate similar amounts of calcium, it is proposed
that the spatial variation of leaf calcium concentration
is due to differential ion delivery to the two
regions rather than tissue/cell-specific differences in
ion uptake capacity. There was a positive correlation
between whole leaf calcium concentration and the
difference in calcium concentration between inner and
outer leaf tissue. Exposing the plants to increased
humidity reduced transpiration and calcium delivery to
the leaf and abolished this spatial variation of calcium
concentration. Mechanisms of calcium delivery to
leaves are discussed. An understanding of calcium
delivery and distribution within coriander will inform
strategies to reduce the incidence of calcium-related
syndromes such as tip-burn and provides a robust
model for the transport of ions and other substances
in the leaf xylem