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Search Results: 1 - 10 of 26229 matches for " Martin Tchamba "
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Spatio-Temporal Dynamic of Land Use and Land Cover in the Classified Forest of Djoli-Kera, South-Eastern, Chad  [PDF]
Lucie Félicité Temgoua, Behimnan Allaissem, Martin Tchamba, Goy Saradoum, Mbaiakambeye Mbaidje Osée, Marie Caroline Momo Solefack
Open Journal of Forestry (OJF) , 2018, DOI: 10.4236/ojf.2018.83019
Abstract: This study was carried out in the classified forest of Djoli-Kera found in the South-Eastern part of Chad. It aimed to analyze the spatial and temporal dy-namics of land cover between 1972 and 2013 and to determine the drivers of vegetation degradation. The databases used were made up of 4 Landsat satellite images (1MSS of 1972, 5TM of 1984, 7ETM+ of 1990 and 2010) and a spot 6 image of 2013, supplemented by field studies. Satellite images were processed using ENVI and ArcGIS software. Interview was used to identify the activities carried out by the local population. In 1972, the classified forest consisted of four types of land cover, the most important of which was open forest (51%), followed by wooded savannah (26%), tree savannah (21%) and sparse vegetation consisting of farms and fallows (2%). Gradually open forest and tree savannah disappeared. In 2013, the main types of land cover were shrub savannah (40%), sparse vegetation (28%), wooded savannah (12%), bare soil (12%) and dwellings (8%). Livestock, agriculture, wood collection and bushfires are perceived by local population as main drivers of forest cover change. Awareness-raising, monitoring and regulation of access to resources must be pursued, but also managers of the classified forest must accompany the local populations in the planting of trees and the setting up of more efficient farming systems to reduce pressure on the forest’s resources.
Human Elephant Conflict in the Waza-Logone Region of Northern Cameroon: An Assessment of Management Effectiveness
Tchamba, MN.,Foguekem, D.
Tropicultura , 2012,
Abstract: An investigation into the current level of humanelephant conflicts in the Waza Logone region was carried out during the 2005 rainy season to assess the effectiveness of conflict management. This was done by talking mainly to wildlife authorities, the local agricultural service, the local communities and consulting sequential reports from the nearest enumerators. The number of villages affected was declining in the dry season compared to the rainy season crop raiding. However, general pattern indicates a decline in the number of villages impacted by elephants since the 1992 to 1993 surveys, but comparatively more damaging as shown by the estimated costs. Therefore, the improve in ecological management of the Waza National Park and its elephant population has had a positive impact in the number of villages crop raided but has not definitely resolved the conflicts between man and elephant. Other approaches are needed to buttress the effort been undertaken in the region to date.
Large time behavior of solutions of viscous Hamilton-Jacobi Equations with superquadratic Hamiltonian
Thierry Wilfried Tabet Tchamba
Mathematics , 2009,
Abstract: We study the long-time behavior of the unique viscosity solution $u$ of the viscous Hamilton-Jacobi Equation $u_t-\Delta u + |Du|^m = f\hbox{in }\Omega\times (0,+\infty)$ with inhomogeneous Dirichlet boundary conditions, where $\Omega$ is a bounded domain of $\mathbb{R}^N$. We mainly focus on the superquadratic case ($m>2$) and consider the Dirichlet conditions in the generalized viscosity sense. Under rather natural assumptions on $f,$ the initial and boundary data, we connect the problem studied to its associated stationary generalized Dirichlet problem on one hand and to a stationary problem with a state constraint boundary condition on the other hand.
Aerial survey of Elephants (Loxodonta africana africana), other large mammals and human activities in Waza National Park, Cameroon
D Foguekem, MN Tchamba, P Omondi
African Journal of Environmental Science and Technology , 2010,
Abstract: Total aerial count of elephants, other large mammals and human activities in Waza National Park was conducted between 21st and 23rd February 2007. Total counts of elephants and other wildlife species were done and livestock numbers were estimated. A Cessna 206 Stationair six-seater aircraft fitted with GPS was used in navigation, recording survey paths and waypoints. A total of three different herds of 180 and 66 in the park along with a further 250 migrating elephant population towards Kalamaloue National Park were counted. The herds in the park were aggregated around central part of the park along watering point. The consideration of the number of the migrating herd then put the total Waza ecosystem elephant population at 496 individuals. The total number of carcasses recorded was 7 giving a carcass ratio of 2.85%. About 21,002 heads of livestock and over 50 farmlands and human settlement were estimated in the zone abutting the park. This signifies a high level of human pressures at the periphery and thus a high potential for loss of range for the elephants and illegal killing.
On the Large Time Behavior of Solutions of the Dirichlet problem for Subquadratic Viscous Hamilton-Jacobi Equations
Guy Barles,Alessio Porretta,Thierry Wilfried Tabet Tchamba
Mathematics , 2009,
Abstract: In this article, we are interested in the large time behavior of solutions of the Dirichlet problem for subquadratic viscous Hamilton-Jacobi Equations. In the superquadratic case, the third author has proved that these solutions can have only two different behaviors: either the solution of the evolution equation converges to the solution of the associated stationary generalized Dirichlet problem (provided that it exists) or it behaves like $-ct+\varphi (x)$ where $c\geq0$ is a constant, often called the "ergodic constant" and $\varphi$ is a solution of the so-called "ergodic problem". In the present subquadratic case, we show that the situation is slightly more complicated: if the gradient-growth in the equation is like $|Du|^m$ with $m>3/2,$ then analogous results hold as in the superquadratic case, at least if $c>0.$ But, on the contrary, if $m\leq 3/2$ or $c=0,$ then another different behavior appears since $u(x,t) + ct$ can be unbounded from below where $u$ is the solution of the subquadratic viscous Hamilton-Jacobi Equations.
Laterite Based Stabilized Products for Sustainable Building Applications in Tropical Countries: Review and Prospects for the Case of Cameroon
Patrick N. Lemougna,Uphie F. Chinje Melo,Elie Kamseu,Arlin B. Tchamba
Sustainability , 2011, DOI: 10.3390/su3010293
Abstract: Lateritic soils are formed in the tropics through weathering processes that favor the formation of iron, aluminum, manganese and titanium oxides. These processes break down silicate minerals into clay minerals such as kaolinite and illite. Iron and aluminum oxides are prominent in lateritic soils, and with the seasonal fluctuation of the water table, these oxides result in the reddish-brown color that is seen in lateritic soils. These soils have served for a long time as major and sub-base materials for the construction of most highways and walls of residential houses in tropical and sub-tropical countries of the world. Civil engineering applications of these lateritic soils are continually being developed with the use of different types of stabilizers. The stabilized soil-based products are as such viewed as environmentally-friendly and low-cost energy materials for sustainable building applications. This work aims at presenting a global view of what has been done in the field of lateritic soil improvement for construction purposes in tropical countries such as Cameroon. This shall be discussed through the presentation of the structure, composition and properties of lateritic soils, the various ways of improving their properties for construction purposes, the properties of products obtained and other prospects.
Antihepatotoxic Activity of Xylopia phloiodora Extracts on Some Experimental Models of Liver Injury in Rats
Paul F. Moundipa,Silvere Ngouela,Georges Alain Tchamba,Nico F. Njayou
International Journal of Pharmacology , 2007,
Abstract: The antihepatotoxic effects of Xylopia phloiodora extracts were evaluated in experimental models of liver injury in rats induced by CCl4 or paracetamol. Crude extract (CE), ether extract (EE) and essential oils from stem bark or leaves were tested. Hepatic function was accessed by measuring serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in rats. Liver malondialdehyde (MDA) and reduced glutathione were also measured in control and treated rats. X. phloiodora leaves (CE) and stem bark (CE) extracts showed hepatoprotective activities at doses equivalent to 2.5 g of plant/kg, since serum levels of ALT and AST in rats given the extracts were significantly low (p<0.05 and p<0.01, respectively) when compared to control CCl4-injured rats. Further studies were carried on the CE from stem bark of X. phloiodora which showed the highest level of protection against hepatitis. Further studies of the crude extract showed highest antihepatotoxic activity with the ether precipitate (PE) which was effective at 100mg/kg for hepatocurative activity in CCl4-injured rats. In experiments comparing the PE (100 mg kg-1) to a reference antihepatotoxic substance (silymarin) the PE exhibited a 71 and 80% hepatoprotection compared to the 80 and 90% one exhibited by silymarin in CCl4-and paracetamol-injured rats respectively. This study demonstrated that ether precipitate of Xylopia phloiodora was effective in protecting the liver from toxic hepatitis.
A Yield Mapping Procedure Based on Robust Fitting Paraboloid Cones on Moving Elliptical Neighborhoods and the Determination of Their Size Using a Robust Variogram  [PDF]
Martin Bachmaier
Positioning (POS) , 2010, DOI: 10.4236/pos.2010.11004
Abstract: The yield map is generated by fitting the yield surface shape of yield monitor data mainly using paraboloid cones on floating neighborhoods. Each yield map value is determined by the fit of such a cone on an elliptical neighborhood that is wider across the harvest tracks than it is along them. The coefficients of regression for modeling the paraboloid cones and the scale parameter are estimated using robust weighted M-estimators where the weights decrease quadratically from 1 in the middle to zero at the border of the selected neighborhood. The robust way of estimating the model parameters supersedes a procedure for detecting outliers. For a given neighborhood shape, this yield mapping method is implemented by the Fortran program paraboloidmapping.exe, which can be downloaded from the web. The size of the selected neighborhood is considered appropriate if the variance of the yield map values equals the variance of the true yields, which is the difference between the variance of the raw yield data and the error variance of the yield monitor. It is estimated using a robust variogram on data that have not had the trend removed.
Sources of inaccuracy when estimating economically optimum N fertilizer rates  [PDF]
Martin Bachmaier
Agricultural Sciences (AS) , 2012, DOI: 10.4236/as.2012.33037
Abstract: Nitrogen rate trials are often performed to determine the economically optimum N application rate. For this purpose, the yield is modeled as a function of the N application. The regression analysis provides an estimate of the modeled function and thus also an estimate of the economic optimum, Nopt. Obtaining the accuracy of such estimates by confidence intervals for Nopt is subject to the model assumptions. The dependence of these assumptions is a further source of inaccuracy. The Nopt estimate also strongly depends on the N level design, i.e., the area on which the model is fitted. A small area around the supposed Nopt diminishes the dependence of the model assumptions, but prolongs the confidence interval. The investigations of the impact of the mentioned sources on the inaccuracy of the Nopt estimate rely on N rate trials on the experimental field Sieblerfeld (Bavaria). The models applied are the quadratic and the linear-plus-plateau yield regression model.
Waiting for Redemption in The House of Asterion: A Stylistic Analysis  [PDF]
Martin Tilney
Open Journal of Modern Linguistics (OJML) , 2012, DOI: 10.4236/ojml.2012.22007
Abstract: The House of Asterion is a short story by Jorge Luis Borges that retells the classical myth of the Cretan Minotaur from an alternate perspective. The House of Asterion features the Minotaur, aka Asterion, who waits for “redemption” in his labyrinth. Many literary critics have suggested that the Borgesian labyrinth is a metaphor for human existence and the universe itself. Others have correctly interpreted Asterion’s ironic death at the hands of Theseus as his eagerly awaited redemption. Borges’ subversion of the reader’s expectations becomes the departure point for a systemic functional stylistic analysis of the story in one of its English translations, revealing how deeper-level meanings in the text are construed through its lexicogrammatical structure. A systemic functional stylistic reading suggests that on a higher level of reality, Asterion’s redemption is not only the freedom that death affords, but also a transformation that transcends his fictional universe. Asterion’s twofold redemption is brought about not only by the archetypal hero Theseus but also by the reader, who through the process of reading enables Asterion’s emancipation from the labyrinth.
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