Home About us Contact
|
Home About us Contact | ||
|
|
||
Whole Region (whole + region)
Selected AbstractsSpatial congruence between ecotones and range-restricted species: implications for conservation biogeography at the sub-continental scaleDIVERSITY AND DISTRIBUTIONS, Issue 3 2009Berndt J. Van Rensburg ABSTRACT Aim, To examine whether at a sub-continental scale range-limited species tend to occur close to areas of transition between vegetation boundaries more often than expected by chance. Location, South Africa and Lesotho. Methods, We examined the relationship between the distance of a grid square to ecological transition areas between vegetation types and both avian and frog range-limited species richness in the quadrat. We used quadrats at a spatial resolution of quarter degree (15, × 15,, 676 km2). Spatial congruence between areas representing range-restricted species and those representing ecological transition zones was assessed using a random draw technique. Results, Species richness and range size rarity are generally negatively correlated with distance to transition areas between vegetation communities when analysed for the whole region for both groups. Although this relationship becomes weaker after controlling for environmental energy and topographical heterogeneity, the explanatory power of distance to transition areas remains significant, and compared to the different biomes examined, accounts for most of the variation in bird richness (20%), frog richness (18%), range-restricted bird species (17%) and range-restricted frog species (16%) in the savanna biome. The random draw technique indicated that areas representing range-restricted species were situated significantly closer in space to those areas representing transition areas between vegetation communities than expected by chance. Main conclusions, We find that at the sub-continental scale, when examined for South Africa, areas of transition between vegetation communities hold concentrations of range-limited species in both birds and frogs. We find that South African endemic/range-limited birds and frogs are located closer to ecological transition zones than endemics and non-endemics combined. This has important implications for ongoing conservation planning in a biogeographical context. [source] Involvement of thiaminase II encoded by the THI20 gene in thiamin salvage of Saccharomyces cerevisiaeFEMS YEAST RESEARCH, Issue 2 2008Mari Onozuka Abstract The physiological significance of thiaminase II, which catalyzes the hydrolysis of thiamin, has remained elusive for several decades. The C-terminal domains of THI20 family proteins (THI20/21/22) and the whole region of PET18 gene product of Saccharomyces cerevisiae are homologous to bacterial thiaminase II. On the other hand, the N-terminal domains of THI20 and THI21 encode 2-methyl-4-amino-5-hydroxymethylpyrimidine kinase and 2-methyl-4-amino-5-hydroxymethylpyrimidine phosphate kinase involved in the thiamin synthetic pathway. In this study, it was first indicated that the C-terminal domains of the THI20 family and PET18 are not required for de novo thiamin synthesis in S. cerevisiae, using a quadruple deletion strain expressing the N-terminal domain of THI20. Biochemical analysis using cell-free extracts and recombinant proteins demonstrated that yeast thiaminase II activity is exclusively encoded by THI20. It appeared that Thi20p has an affinity for the pyrimidine moiety of thiamin, and HMP produced by the thiaminase II activity is immediately phosphorylated. Thi20p was found to participate in the formation of thiamin from two synthetic antagonists, pyrithiamin and oxythiamin, by hydrolyzing both antagonists and phosphorylating HMP to give HMP pyrophosphate. Furthermore, 2-methyl-4-amino-5-aminomethylpyrimidine, a presumed naturally occurring thiamin precursor, was effectively converted to HMP by incubation with Thi20p. It is proposed that the thiaminase II activity of Thi20p is involved in the thiamin salvage pathway by catalyzing the hydrolysis of HMP precursors in S. cerevisiae. [source] Measuring and partitioning the high-order linkage disequilibrium by multiple order Markov chainsGENETIC EPIDEMIOLOGY, Issue 4 2008Yunjung Kim Abstract A map of the background levels of disequilibrium between nearby markers can be useful for association mapping studies. In order to assess the background levels of linkage disequilibrium (LD), multilocus LD measures are more advantageous than pairwise LD measures because the combined analysis of pairwise LD measures is not adequate to detect simultaneous allele associations among multiple markers. Various multilocus LD measures based on haplotypes have been proposed. However, most of these measures provide a single index of association among multiple markers and does not reveal the complex patterns and different levels of LD structure. In this paper, we employ non-homogeneous, multiple order Markov Chain models as a statistical framework to measure and partition the LD among multiple markers into components due to different orders of marker associations. Using a sliding window of multiple markers on phased haplotype data, we compute corresponding likelihoods for different Markov Chain (MC) orders in each window. The log-likelihood difference between the lowest MC order model (MC0) and the highest MC order model in each window is used as a measure of the total LD or the overall deviation from the gametic equilibrium for the window. Then, we partition the total LD into lower order disequilibria and estimate the effects from two-, three-, and higher order disequilibria. The relationship between different orders of LD and the log-likelihood difference involving two different orders of MC models are explored. By applying our method to the phased haplotype data in the ENCODE regions of the HapMap project, we are able to identify high/low multilocus LD regions. Our results reveal that the most LD in the HapMap data is attributed to the LD between adjacent pairs of markers across the whole region. LD between adjacent pairs of markers appears to be more significant in high multilocus LD regions than in low multilocus LD regions. We also find that as the multilocus total LD increases, the effects of high-order LD tends to get weaker due to the lack of observed multilocus haplotypes. The overall estimates of first, second, third, and fourth order LD across the ENCODE regions are 64, 23, 9, and 3%. Genet. Epidemiol. 2008. © 2008 Wiley-Liss, Inc. [source] An enriched meshless method for non-linear fracture mechanicsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2004B. N. Rao Abstract This paper presents an enriched meshless method for fracture analysis of cracks in homogeneous, isotropic, non-linear-elastic, two-dimensional solids, subject to mode-I loading conditions. The method involves an element-free Galerkin formulation and two new enriched basis functions (Types I and II) to capture the Hutchinson,Rice,Rosengren singularity field in non-linear fracture mechanics. The Type I enriched basis function can be viewed as a generalized enriched basis function, which degenerates to the linear-elastic basis function when the material hardening exponent is unity. The Type II enriched basis function entails further improvements of the Type I basis function by adding trigonometric functions. Four numerical examples are presented to illustrate the proposed method. The boundary layer analysis indicates that the crack-tip field predicted by using the proposed basis functions matches with the theoretical solution very well in the whole region considered, whether for the near-tip asymptotic field or for the far-tip elastic field. Numerical analyses of standard fracture specimens by the proposed meshless method also yield accurate estimates of the J -integral for the applied load intensities and material properties considered. Also, the crack-mouth opening displacement evaluated by the proposed meshless method is in good agreement with finite element results. Furthermore, the meshless results show excellent agreement with the experimental measurements, indicating that the new basis functions are also capable of capturing elastic,plastic deformations at a stress concentration effectively. Copyright © 2003 John Wiley & Sons, Ltd. [source] The impact of the positive Indian Ocean dipole on Zimbabwe droughtsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2008D. Manatsa Abstract A comparative study of the impact of the anomalous positive Indian Ocean SST gradient, referred to as the Indian Ocean Dipole/Zonal Mode (IODZM), and El Niño-Southern Oscillation (ENSO) on Zimbabwe seasonal rainfall variability for the period 1940,1999, is documented. Composite techniques together with simple and partial correlation analyses are employed to segregate the unique association related to IODZM/ENSO with respect to the Zimbabwe seasonal rainfall. The analysis reveals that the IODZM impact on the country's summer rainfall is overwhelming as compared to that of ENSO when the two are in competition. The IODZM influence remains high (significant above 99% confidence level), even after the influence of ENSO has been removed, while that of ENSO collapses to insignificance (even at 90% confidence level) when the IODZM contribution is eliminated. The relationship between ENSO and Zimbabwe seasonal rainfall seems to be sustained through El Niño occurring in the presence of positive IODZM events. However, when the co-occurring positive IODZM and El Niño events are removed from the analysis, it is apparently clear that ENSO has little to do with the country's rainfall variability. On the other hand, positive IODZM is mostly associated with the rainfall deficits, whether or not it co-occurs with El Niño. However, the co-occurrence of the two events does not necessarily suggest that El Niño influences droughts through the positive IODZM events. The El Niño event components during co-occurrence seem to be unrelated (at least linearly) to the droughts, while the positive IODZM events display a relatively strong relationship that is significant above the 95% confidence level. It thus becomes important to extend the study of this nature to cover the whole of southern Africa, so that the extent of the impact of the phenomena can be realized over the whole region. Copyright © 2008 Royal Meteorological Society [source] Landscape patterns of indicator plants for soil acidity in the Bavarian AlpsJOURNAL OF BIOGEOGRAPHY, Issue 10 2003Sebastian Schmidtlein Abstract Aim, Electronic distribution atlases and lists of ecological indicator values are becoming important tools in plant geography. In this contribution, we combine a geographical and an ecological data bank, and map out patterns of indicator value spectra (instead of single or average values) across a physiographically complex landscape. For our study, we select indicators of soil pH and carbonate content as key environmental factors that strongly affect overall plant diversity patterns in the temperate zone. Our goal is to relate the distribution and diversity of plant groups that are indicators of soil pH and carbonate content to environmental controls at the landscape-scale, and thus contribute to a causal understanding of species pools. Location, We studied the Bavarian Alps, which represent the German portion of the Northern Alps. Methods, Based on the existing floristic survey, we calculated relative frequencies of nine classes of indicator plants for soil pH and carbonate content in grid cells. The resulting attribute matrix (cells by indicator class frequencies) was subjected to principal components analysis and to k-means clustering. Results were compared and mapped out in the grid array of the whole region, resulting in continuous and discrete representations of species pool structure. We used a geographical information system to derive physiographical landscape properties from a geological map and a digital elevation model, and analysed their statistical relationship with the shapes of indicator spectra. Results and Main conclusions, Averages of indicator values for soil pH and carbonate content follow the geological structure quite closely. Surprisingly, the diversity of indicator plant groups does not appear to be a function of geological or topographic heterogeneity. Rather, it seems to be related to areas of high elevation with uniform geology. The effect is a matter of additional acidophytes in high mountain areas and, in the high calcareous Alps, extreme calciphytes, while species with intermediate requirements are rarer than usual. For explanation, we suggest two facts: (1) a frequent lack of mature soils at high elevations and (2) particularities in soil genetic processes occurring under the harsh climatic conditions of high mountains. [source] GEOMETRICAL, THERMAL AND MECHANICAL PROPERTIES OF OLIVE FRUITSJOURNAL OF FOOD PROCESS ENGINEERING, Issue 2 2010MOHAMAD I. AL-WIDYAN ABSTRACT In Mediterranean countries, olive trees play a significant economical role. Knowledge of olive fruits properties is essential for the efficient handling of the product and optimizing oil yield. The lack of such knowledge at the local level triggered this study in an attempt to report the fruit's chemical composition and some major engineering properties. Established procedures were followed in conducting the measurements and calculations on fruit samples. The study examined four major varieties of olive fruits, including Spanish, Black Spanish, improved Nabali and Nabali Baladi for their chemical composition and other properties, including geometrical, thermal and frictional properties. Thermal properties, including thermal conductivity, heat capacity and thermal diffusivity, ranged from 0.41 to 0.47 W/(m·K), 2.35 to 2.39 kJ/(kg·K) and 2.88 × 10,7to 2.779 × 10,7 m2/s, respectively. The geometrical properties of the Spanish and Black Spanish were quite similar except for roundness and sphericity. Similar results were found for improved Nabali and Nabali Baladi. The properties of weight, density and packing coefficient ranged from 2.22 to 8.60 g, 890 to 1,230 kg/m3 and 0.43 to 0.52, respectively. The fruit's static friction coefficient over mild steel, aluminum and softwood surfaces ranged from 0.20 to 0.30, 0.21 to 0.29 and 0.22 to 0.33, respectively. PRACTICAL APPLICATIONS In Jordan and other Mediterranean countries, olive fruits are produced in large quantities every season. They are very widely used as pickled fruits or are processed in mills to extract their oil. Despite the fact that fruit properties are a necessary prerequisite for the efficient handling and processing of fruits, literature search indicated the lack of a comprehensive study of scientific merit that reports on the engineering properties of olive fruits. In addition, it is established that knowledge of the fruit properties leads to optimized handling and processing and results in knowledge-based development of all processes and equipment that deal with the fruits. The practical merit of this study stems from the fact that it reports on the key properties of a major product (olive fruits) that has social, cultural and economical significance throughout a whole region and is expanding throughout the globe. [source] | ||||||||||