Dangui-Mbani U.O.,University of Science and Technology Beijing |
Zheng L.,University of Science and Technology Beijing |
Tathy C.,Marien Ngouabi University
International Journal of Heat and Mass Transfer | Year: 2017
In this paper, an innovative constitutive model of modified Fourier's heat conduction law (Fick's diffusion law), which takes the effects of relaxation time, Philip n-diffusion flux on heat transfer (diffusion) and thermal diffusivity parameters into account, the n-diffusion Cattaneo telegraph equation is firstly proposed. The approximate analytical solutions are obtained by employing the Adomian decomposition method which coincide with exact solution in good agreement. Moreover, the involved parameters have strong effects on the temperature distribution which are presented graphically and discussed. The mathematical method and techniques employed in this paper also have the significance for some other problems in science and engineering. The results showed that the temperature oscillates and decreases with increasing and decreasing of thermal diffusivity and relaxation time parameters, without and with reaction term respectively, but the oscillations of temperature decay rapidly until reaching zero with decreasing of Philip n-diffusion parameter for spatial evolution with and without reaction term. The temperature decreases with increasing parameter of relaxation time, Philip n-diffusion or thermal diffusivity for temporal evolution. © 2017 Elsevier Ltd
Dargie G.C.,University of Leeds |
Dargie G.C.,University College London |
Lewis S.L.,University of Leeds |
Lewis S.L.,University College London |
And 5 more authors.
Nature | Year: 2017
Peatlands are carbon-rich ecosystems that cover just three per cent of Earth's land surface1, but store one-third of soil carbon2. Peat soils are formed by the build-up of partially decomposed organic matter under waterlogged anoxic conditions. Most peat is found in cool climatic regions where unimpeded decomposition is slower, but deposits are also found under some tropical swamp forests2,3. Here we present field measurements from one of the world's most extensive regions of swamp forest, the Cuvette Centrale depression in the central Congo Basin4. We find extensive peat deposits beneath the swamp forest vegetation (peat defined as material with an organic matter content of at least 65 per cent to a depth of at least 0.3 metres). Radiocarbon dates indicate that peat began accumulating from about 10,600 years ago, coincident with the onset of more humid conditions in central Africa at the beginning of the Holocene5. The peatlands occupy large interfluvial basins, and seem to be largely rain-fed and ombrotrophic-like (of low nutrient status) systems. Although the peat layer is relatively shallow (with a maximum depth of 5.9 metres and a median depth of 2.0 metres), by combining in situ and remotely sensed data, we estimate the area of peat to be approximately 145,500 square kilometres (95 per cent confidence interval of 131,900-156,400 square kilometres), making the Cuvette Centrale the most extensive peatland complex in the tropics. This area is more than five times the maximum possible area reported for the Congo Basin in a recent synthesis of pantropical peat extent2. We estimate that the peatlands store approximately 30.6 petagrams (30.6 × 1015 grams) of carbon belowground (95 per cent confidence interval of 6.3-46.8 petagrams of carbon)-a quantity that is similar to the above-ground carbon stocks of the tropical forests of the entire Congo Basin6. Our result for the Cuvette Centrale increases the best estimate of global tropical peatland carbon stocks by 36 per cent, to 104.7 petagrams of carbon (minimum estimate of 69.6 petagrams of carbon; maximum estimate of 129.8 petagrams of carbon). This stored carbon is vulnerable to land-use change and any future reduction in precipitation7,8. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
Koukouikila-Koussounda F.,University of Tübingen |
Malonga V.,Congolese Foundation for Medical Research |
Mayengue P.I.,Marien Ngouabi University |
Vouvoungui C.J.,Marien Ngouabi University |
Ntoumi F.,University of Tübingen
Malaria Journal | Year: 2012
Background: In order to prepare the field site for future interventions, the prevalence of asymptomatic Plasmodium falciparum infection was evaluated in a cohort of children living in Brazzaville. Plasmodium falciparum merozoite surface protein 2 gene (msp2) was used to characterize the genetic diversity and the multiplicity of infection. The prevalence of mutant P. falciparum chloroquine resistance transporter (pfcrt) allele in isolates was also determined. Methods. Between April and June 2010, 313 children below 10 years of age enrolled in the cohort for malaria surveillance were screened for P. falciparum infection using microscopy and polymerase chain reaction (PCR). The children were selected on the basis of being asymptomatic. Plasmodium falciparum msp2 gene was genotyped by allele-specific nested PCR and the pfcrt K76T mutation was detected using nested PCR followed by restriction endonuclease digestion. Results: The prevalence of asymptomatic P. falciparum infections was 8.6% and 16% by microscopy and by PCR respectively. Allele typing of the msp2 gene detected 55% and 45% of 3D7 and FC27 allelic families respectively. The overall multiplicity of infections (MOI) was 1.3. A positive correlation between parasite density and multiplicity of infection was found. The prevalence of the mutant pfcrt allele (T76) in the isolates was 92%. Conclusion: This is the first molecular characterization of P. falciparum field isolates in Congolese children, four years after changing the malaria treatment policy from chloroquine (CQ) to artemisinin-based combination therapy (ACT). The low prevalence of asymptomatic infections and MOI is discussed in the light of similar studies conducted in Central Africa. © 2012 Koukouikila-Koussounda et al; licensee BioMed Central Ltd.
Mayengue P.,Marien Ngouabi University |
Ndounga M.,Center dEtudes sur les Ressources Vegetales |
Malonga F.,Marien Ngouabi University |
Ntoumi F.,University of Tübingen
Malaria Journal | Year: 2011
Background: The characterization of malaria parasite populations circulating in an area is part of site characterization, as a basis for evaluating the impact of malaria interventions on genetic diversity, parasite species, and multiplicity of infection. The present study was aimed at analysing genetic diversity of Plasmodium falciparum merozoite surface proteins 1 and 2 (MSP-1 and MSP-2) and to determine the multiplicity of infection in clinical isolates collected from children living in the Southern district of Brazzaville in the Republic of Congo. Methods. A total of 125 isolates from patients with uncomplicated malaria attending Terinkyo and Madibou health centres were collected between January and June 2005 while evaluating the therapeutic efficacy of amodiaquine-artesunate combination. DNA was extracted and msp-1 and msp-2 genes were genotyped using allele-specific nested-PCR. Results: Out of 468 distinct fragments detected, 15 msp-1 and 20 msp-2 genotypes were identified. For the msp-1 gene, K1 family was the predominant allelic type carried alone or in association with RO33 and Mad20 types, whereas the 3D7 family was the most prevalent in the msp-2 gene. Overall, the mean multiplicity of infection was 2.2. Out of 125 samples, 104 (83%) harboured more than one parasite genotype. There was no statistical significant difference in the multiplicity of infection by either sex or age of patients. However, a statistically significant correlation was found between parasite densities and the number of genotypes. Conclusion: Polymorphism in P. falciparum clinical isolates from Brazzaville was high and mainly of multiple clones. The basis for the positive association between parasite densities and multiplicity of infection is discussed. © 2011Mayengue et al; licensee BioMed Central Ltd.
Kongo-Dia-Moukala J.U.,Jiangnan University |
Kongo-Dia-Moukala J.U.,Marien Ngouabi University |
Zhang H.,Jiangnan University
American Journal of Food Technology | Year: 2011
A number of operating parameters including temperature, pH, solvent/flour ratio and time influence the yield of protein during extraction. In order to effectively identify the good combinations of the extraction conditions, Response Surface Methodology (RSM) was employed to determine optimum conditions for extraction of protein from defatted corn. The coefficient of determination (0.9789) was good for the second-order model. Protein extraction from defatted corn was mainly affected by pH and solvent/flour ratio. From RSM-generated model, the optimum extraction conditions were 54°C, 11.55, 1:18 and 33 min for temperature, pH, solvent/flour ratio and time, respectively. Under these conditions, the experimental protein content was 69.25 mg mL -1 which agreed closely with the predicted value 71.23 mg mL -1. To ensure that the protein extract could be utilized for food application, some functional properties such as water holding capacity, oil holding capacity, emulsifying capacity, foaming capacity and foaming stability were evaluated. Defatted corn protein had a good water holding and foaming capacity. Thus, it can be used in food formulation systems. © 2011 Academic Journals Inc.
Mamonekene V.,Marien Ngouabi University |
Stiassny M.L.J.,American Museum of Natural History
Copeia | Year: 2012
A new species of Bathyaethiops is described from the Lkoumou River in the Kouilou-Nairi basin of the Republic of Congo. Bathyaethiops atercrinis, new species, is distinguished from its three central African congeners in the possession of 2124 scales in longitudinal series vs. 2842 scales, and from Brachypetersius altus by the possession of a short, abridged lateral line consisting of only six or seven pored scales vs. a complete lateral line of 2028 pored scales. The species is unique among congeners and related taxa in displaying marked sexual dichromatism and dimorphism of the supporting skeleton of the anal fin. The presence of B. atercrinis in the Lkoumou represents the first record of the genus in the Lower Guinean ichthyofaunal province and the first occurrence outside of the Congo basin. © 2012 by the American Society of Ichthyologists and Herpetologists.
Yoca S.E.,Marien Ngouabi University |
Quinet P.,University of Mons |
Quinet P.,University of Liège
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2014
A pseudo-relativistic Hartree-Fock model including a large amount of configuration-interaction effects has been used to compute radiative decay rates for allowed and forbidden transitions in Nd IV. Detailed comparisons of transition probabilities, oscillator strengths and radiative lifetimes with data previously published are also reported and discussed in the present work. © 2014 IOP Publishing Ltd.
Yoca S.E.,Marien Ngouabi University |
Quinet P.,University of Mons |
Quinet P.,University of Liège
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2013
Transition probabilities and oscillator strengths for electric dipole radiation in triply ionized praseodymium are reported for the first time in this paper. They were computed using a semi-empirical relativistic Hartree-Fock approach including core-polarization effects. Due to the lack of experimental data in the Pr IV spectrum, the accuracy of our results is estimated and discussed on the basis of comparisons between calculations performed with a similar physical model and laboratory measurements previously published for the isoelectronic ion Ce2+. In view of their great interest in optical materials and nanophotonics, radiative rates for forbidden lines within the 4f2 ground-state configuration of Pr3+ were also calculated in our work. © 2013 IOP Publishing Ltd.
Averti I.,Marien Ngouabi University |
Dominique N.,Marien Ngouabi University
Journal of Environmental Science and Technology | Year: 2011
The carbon budget of marginal forests that developed on the savannah in the Plateau Teke has not yet been studied despite increasing evidences of their spatial expansion. Measurements of litter fall, litter amount on forest floor and leaf litter decomposition was undertaken, on three plots in a Gallery Forest (GF) and three plots in a hill-slope forest clump (HF). The aim of the study was to study the dynamic of litter in two types of forest groves. Litterfall was collected biweekly for two years and averaged 1063 g m -2 y -1 in GF and 1097 g m -2 y -1 in HF, with leaves accounting for more than 95% of the total litterfall. The amount of litter on the floor was estimated twice within each plot and averaged 1824 g m -2 in GF and 1381 g m -2 in HF. The relative mass remaining after seven months of decomposition assessed in litterbags was 40% in GF and 33% in HF in 2007 and 44 and 53% in the 2008, with a strong impact of dry season. Despite differences in forest structure and species composition, litterfall, litter accumulation and decomposition rates were similar between the two types of forest groves. © 2011 Asian Network for Scientific Information.
Samba G.,Marien Ngouabi University |
Nganga D.,Marien Ngouabi University
International Journal of Climatology | Year: 2012
The interannual variability of rainfall amounts and rainy days is analysed from synoptic stations located in different climatic zones of Congo-Brazzaville over the common period 1932-2007. The annual and seasonal rainfall evolution is appreciated using standardized indices. Trends examined were based on the non-parametric Mann-Kendall test (the major synoptic stations point out alternative periods of anomalies-positive and negative). A majority of negative anomalies is recorded during the 1930s and 1940s. The decade 1950 shows mainly positive anomalies with the exception of 1958 which records a general precipitation deficit all across Congo. The decade 1960 is characterized by precipitation excess over the whole Congo. The decades 1980 and 1990 experience the largest rainfall deficit (about 10-20% below the long-term mean). The evolution of the precipitation at Brazzaville is particularly stable, although there are large positive anomalies during the 1990s. The transition between positive and negative anomalies decades is not uniform across Congo. The progressive non-parametric Mann-Kendall trend test shows that there is stability in the annual rainfall and rainy days over the southern area in the period 1932-2007. By contrast, the annual rainfall for the northern stations shows a significant decline since about the 1980s. In the south the decline is observable only in the evolution of the March-May seasonal rainfall. In most of the stations there is a precipitation increase during the September-November rainy season. © 2011 Royal Meteorological Society.