Parameter Estimation of a Class of Hidden Markov Model with Diagnostics

A stochastic volatility (SV) problem is formulated as a state space form of a Hidden Markov model (HMM). The SV model assumes that the distribution of asset returns conditional on the latent volatility is normal. This article analyzes the SV model with the student-t distribution and the generalized error distribution (GED) and compares these distributions with a mixture of normal distributions from Kim and Stoffer (2008). A Sequential Monte Carlo with Expectation Maximization (SMCEM) algorithm technique was used to estimate parameters for the extended volatility model; the Akaike Information Criteria (AIC) and forecast statistics were calculated to compare distribution fit. Distribution performance was assessed using simulation study and real data. Results show that, although comparable to the normal mixture SV model, the Student-t and GED were empirically more successful

Characterization of a thermostable Bacillus subtilis f-amylase isolated from decomposing peels of Cassava ( Manihot esculenta )

f-Amylase (\u3b1-1, 4 glucan maltohydrolase; E.C:3.2.1.2) is used in the food processing, brewing and distilling industries due to its capacity to produce maltose syrup from starch. Here, we report the purification and characterization of f-amylase from Bacillus subtilis isolated from cassava peel waste obtained from a milling factory in Ikenne-Remo, Ogun State, Nigeria. The enzyme was extracted, fractionated at 90% (NH4)2SO4 and further purified using DEAE-cellulose ion exchange chromatography. The molecular weight of the purified enzyme was estimated to be 34.67 Kd. The specific activity of the partially purified enzyme was approximately 1.35 units per mg of protein (Umg-1), Kinetic analysis of its starch hydrolysis activity gave a Km value of 2.496 \ub1 0.025% and a Vmax of 1.136 \ub1 0.055 units min-1. The optimum pH and temperature were determined to be 5.5 and 70 0C respectively, and the thermal stability curve gave a maximum activity of 9.75 U at 70oC for 60 min of incubation. Bacillus subtilis f-amylase is valuable for maltose production, which can be hydrolyzed further by other groups of amylase for the production of high cassava glucose syrup used as sweeteners in the food industry

Selective Phosphorylation Modulates the PIP2 Sensitivity of the CaM-SK Channel Complex

Phosphatidylinositol bisphosphate (PIP2) regulates the activities of many membrane proteins including ion channels through direct interactions. However, the affinity of PIP2 is so high for some channel proteins that its physiological role as a modulator has been questioned. Here we show that PIP2 is an important cofactor for activation of small conductance Ca2+-activated potassium channels (SK) by Ca2+-bound calmodulin (CaM). Removal of the endogenous PIP2 inhibits SK channels. The PIP2-binding site resides at the interface of CaM and the SK C-terminus. We further demonstrate that the affinity of PIP2 for its target proteins can be regulated by cellular signaling. Phosphorylation of CaM T79, located adjacent to the PIP2-binding site, by Casein Kinase 2 reduces the affinity of PIP2 for the CaM-SK channel complex by altering the dynamic interactions among amino acid residues surrounding the PIP2-binding site. This effect of CaM phosphorylation promotes greater channel inhibition by G-protein-mediated hydrolysis of PIP2

Phenotypic variation among five provenances of Pterocarpus angolensis in Zimbabwe and Zambia

The feasibility of utilising morphological markers for determining existing provenance variation in the African savanna tree Pterocarpus angolensis was assessed. Five provenances were used: Mtao, Gokwe, Nyazura, Chesa (Zimbabwe) and Kapirimposhi (Zambia). Two weeks after germination, seedlings were inoculated with mycorrhizal inoculum and raised in a glasshouse. Height and collar diameter were measured at one, three and five months of age (before stem dieback), and at 14 months (after stem dieback). At the time of dieback, percentage of seedlings losing leaves, stem dieback and mortality were recorded; numbers of new shoots produced in the recovery period were also determined. To further assess growth, leaf, stem and root dry biomass were measured after stem dieback at 14 months. At one month, Chesa seedlings were the tallest and Kapirimposhi seedlings were significantly shorter (p < 0.05) than the rest of the provenances. However, at three and five months of height growth no significant differences were observed. At one month, diameter growth was significantly different with the Kapirimposhi provenance having the smallest diameter (p < 0.05). At three and five months of seedling growth only the Gokwe provenance was significantly different from the rest of the provenances. By seven months of age, stem dieback was observed and foliage loss was over 60% in each of the five provenances. At 14 months of seedling growth after stem dieback the Nyazura and Kapirimposhi provenances were significantly shorter, whereas there were no significant differences in diameter growth and dry biomass from root, stem, leaf or root:shoot dry biomass ratio. Fourteen months after germination new shoots emerged from various axillary bud positions depending on the extent of dieback.Keywords: diameter, dieback, height, morphological markers, Pterocarpus angolensi

Comparison of the effects of mechanical scarification and gibberellic acid treatments on seed germination in Pterocarpus angolensis

Pterocarpus angolensis is a savanna tree species growing mostly in the miombo and undifferentiated woodlands found in the southern and central parts of Africa. Exploitation for its medicinal and commercial uses has led to a diminishing of wild populations. Artificial propagation, domestication and exploitation in a sustainable manner depend on detailed knowledge on germination of the seeds. The effects of eight potential dormancy-breaking treatments, compared with no treatment, on promoting the germination of P. angolensis seeds were examined. Five seed provenances were used, namely Mufulira and Chati from Zambia, and Gokwe, Matopos and Mtao from Zimbabwe. Seeds were treated by nicking to remove a small piece of seed coat near to the radical, soaking in cold water or an aqueous solution of gibberellic acid (GA3 at 10, 50, 100 or 1 000ppm; GA4/7 at 10 or 1 000ppm). Treatments with gibberellic acids, regardless of the concentration, had little effect on germination rates when compared with the control seeds. With nicking, high and rapid rates of germination occurred for all provenances within approximately 5d of sowing the seeds, suggesting that nicking alone could improve seed germination.Southern Hemisphere Forestry Journal 2007, 69(1): 63–7

RAPD markers demonstrate genetic diversity in Pterocarpus angolensis from Zimbabwe and Zambia

Understanding the availability, extent and apportionment of genetic variability in natural populations of the southern African savanna tree Pterocarpus angolensis can provide reliable information on the evolutionary history and phylogenetic relationships of P. angolensis populations. This information will aid strategies for successful domestication, conservation and sustainable exploitation of the species. In this study random amplified polymorphic DNA (RAPD) analysis was employed to assess genetic diversity of P. angolensis, characterising 60 genotypes originating from four Zimbabwean and two Zambian provenances. Four RAPD primers each generated 11 to 15 scorable bands, with a total of 50 reproducible bands of which 88% were polymorphic. Analysis of molecular variance partitioned the greatest proportion of variability to within population (80.82%). Euclidean distance gave a phiST value of 0.192, indicating a moderately high level of population differentiation. The degree of population diversity found in this study, with two clear strong population structures for most genotypes from Nyazura and Gokwe and the rest of the populations with slight weak structures, suggests that all provenances tested could be beneficially utilised in a domestication programme for P. angolensis. Keywords: domestication, genetic variation, population diversity, Pterocarpus angolensis, RAP

Economic Impact and Challenges of Jatropha curcas L. Projects in North-Western Province, Zambia: A Case of Solwezi District

Forest products, wood and non-wood, remain vital among smallholder households in Zambia with charcoal being the most sought after product. This has led to increased exploitation of forest trees to meet the needs for fuel wood, among others. However, Jatropha curcas plant has been identified as a potential fuel source. In the early 2000s, profit-making organizations encouraged smallholder households to grow Jatropha for use as an alternative fuel source. This paper reports on a study conducted in Solwezi between 2011 and 2014 to evaluate the impact of Jatropha cultivation for biofuel production. A sample of 100 small-scale farmers involved in Jatropha cultivation and key informants were interviewed to evaluate the impact of growing Jatropha at the small-scale level. Results show that farmers lost out on time; income from sale of edible non-wood forest products; and experienced reduction in maize (Zea mays) and bean (Phaseolus vulgaris) production, worsening household economic conditions. Farmers attributed this loss to unclear policy alignment on biofuel production by government. We therefore recommend that project implementation should involve interactions of all legislative bodies and any other concerned stakeholders. There is also a need to promote the value chain, from production to marketing, which focuses on minimizing detrimental effects on the livelihood of small-scale farmers

Characterization of a thermostable Bacillus subtilis ß-amylase isolated from decomposing peels of Cassava ( Manihot esculenta )

ß-Amylase (α-1, 4 glucan maltohydrolase; E.C:3.2.1.2) is used in the food processing, brewing and distilling industries due to its capacity to produce maltose syrup from starch. Here, we report the purification and characterization of ß-amylase from Bacillus subtilis isolated from cassava peel waste obtained from a milling factory in Ikenne-Remo, Ogun State, Nigeria. The enzyme was extracted, fractionated at 90% (NH4)2SO4 and further purified using DEAE-cellulose ion exchange chromatography. The molecular weight of the purified enzyme was estimated to be 34.67 Kd. The specific activity of the partially purified enzyme was approximately 1.35 units per mg of protein (Umg-1), Kinetic analysis of its starch hydrolysis activity gave a Km value of 2.496 ± 0.025% and a Vmax of 1.136 ± 0.055 units min-1. The optimum pH and temperature were determined to be 5.5 and 70 0C respectively, and the thermal stability curve gave a maximum activity of 9.75 U at 70oC for 60 min of incubation. Bacillus subtilis ß-amylase is valuable for maltose production, which can be hydrolyzed further by other groups of amylase for the production of high cassava glucose syrup used as sweeteners in the food industry