Growth space requirements models for Prosopis africana (Guill & Perr) Taub tree species in Makurdi, Nigeria

All parts of Prosopis africana (Guill & Perr) Taub are used by rural communities in Nigeria, and this exposes it to degradation and a regeneration problems. There is lack of information on inventory on natural forest estates for management and decision-making. This species is facing a regeneration problem and overexploitation. The aim of this study was to developed model that can predict the growth space requirements for P. africana plantation establishment. Growing space was associated with crown size; seven crown and stem diameter relation models were tested on data recorded from P. africana trees in Makurdi-Nigeria; simple random sampling technique was used to collect data. The linear model (crown-stem diameter relation) provided the best model fitted with R2 values of 0.778 with adjusted R2 0.777. For optimum planting, fast growth and high production/yield the tree species would require a planting spacing of 4 x 4 meters; for example, that a dominant free-growing tree of diameter 52.90 cm would required 0.008 hectare of growing space with a stocking of 125 tree per hectare for P. africana. Stand density converges around 0.000016 m2. The baseline information provided by this study could serve as a guide for optimum planting distances and tree stocking in large scale plantations of P. africana species in Nigeria and international, this to avoid extinction of the economic tree

Seed banks as conservation tool for endangered wild plant species in ecozones of Nigeria

Seed banks have played the largest role in the conservation of endangered wild plant species in the world. The potential role of seed in the regeneration of plant species is threatened by a rapid decline in the longevity and viability of the seeds in their natural habitats. This study addresses the key role of seed banks in the conservation of floristic diversity. The increasing popularity of the seed bank as a tool in the conservation of wild plant species can be attributed to different significance, including; provision of immediate access to plant samples, allowing researchers and conservation biologists to evaluate them for properties such as new sources of medicines, nutrition, and genes. Also, wild plant seeds conserved in seed banks are immune to habitat destruction, diseases, and predators. The stored seeds can be used to reinstate species into existing, suitable habitats where they were once present, or to augment the diversity of small, genetically depleted populations. Conservation efforts, as sources for population reintroduction and restoration, have been cited as an important justification for seed banks. Thus, it is recommended that seed banks with state-of-the-art storage facilities should be established at the national and local levels; and all of such banks should be networked so that materials, knowledge, and expertise on particular wild plant species is available on a global scale.Key words: Conservation, Endangered, Floristic diversity, Plant species, Seeds bank, Storag

Set-Codes with Small Intersections and Small Discrepancies

We are concerned with the problem of designing large families of subsets over a common labeled ground set that have small pairwise intersections and the property that the maximum discrepancy of the label values within each of the sets is less than or equal to one. Our results, based on transversal designs, factorizations of packings and Latin rectangles, show that by jointly constructing the sets and labeling scheme, one can achieve optimal family sizes for many parameter choices. Probabilistic arguments akin to those used for pseudorandom generators lead to significantly suboptimal results when compared to the proposed combinatorial methods. The design problem considered is motivated by applications in molecular data storage and theoretical computer science

Structural properties of Co2TiSi films on GaAs(001)

Co2TiSi films were grown by molecular beam epitaxy on GaAs(001) and analyzed using reflection high-energy electron diffraction, and electron microscopy. In addition, X-ray diffraction was combined with lattice parameter calculations by density functional theory comparing the L21 and B2 structures and considering the influence of non-stoichiometry. Columnar growth is found and attributed to inhomogeneous epitaxial strain from non-random alloying. In films with thicknesses up to 13 nm, these columns may be the origin of perpendicular magnetization with the easy axis perpendicular to the sample surface. We found L21 and B2 ordered regions, however the [Co]/[Ti]-ratio is changing in dependence of the position in the film. The resulting columnar structure is leading to anisotropic B2-ordering with the best order parallel to the axes of the columns

Electrical detection of spin accumulation in a p-type GaAs quantum well

We report on experiments in which a spin-polarized current is injected from a $GaMnAs$ ferromagnetic electrode into a $GaAs$ quantum well through an AlAs barrier. The resulting spin polarization in the GaAs well is detected by measuring how the current, tunneling to a second $GaMnAs$ ferromagnetic electrode, depends on the orientation of its magnetization. Our results can be accounted for the non-relaxed spin splitting of the chemical potential, that is spin accumulation, in the $GaAs$ well. We discuss the conditions on the hole spin relaxation time in GaAs that are required to obtain the large effects we observe.Comment: 4 pages - 2 figues; one added note; some numbers corrected on page

Tuning of Human Modulation Filters Is Carrier-Frequency Dependent

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