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Search Results: 1 - 10 of 397361 matches for " J.F. Ojo "
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Identification of Optimal Models in Higher Order Integrated Autoregressive Models and Autoregressive Integrated Moving Average Models in the Presence of 2k-1 Subsets
J.F. Ojo
Journal of Modern Mathematics and Statistics , 2012,
Abstract: Significant efforts have been made in the study of the theory of integrated autoregressive models and autoregressive integrated moving average models, but less concerted effort has been made in the identification of optimal models which are of great importance in the forecasting of future values. Little attention has been focused on higher order integrated autoregressive models and autoregressive integrated moving average models which are always characterized by many parameters and the use of subsetting that eliminate redundant parameters in these higher order models. This study therefore focuses on identification of optimal models in higher order integrated autoregressive models and autoregressive integrated moving average models in the presence of 2k-1 subsets. The parameters of these models were estimated using Marquardt algorithm and Newton-Raphson iterative method and the statistical properties of the derived estimates were investigated. An algorithm was proposed to eliminate redundant parameters from the full order integrated autoregressive models and autoregressive integrated moving average models. To control the parameters of integrated autoregressive models and autoregressive integrated moving average models in the estimation procedure, the elements of 2k-1 subsets (when k=3) was used. To determine optimal models, residual variance, Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) were adopted.
On the Estimation and Performance of One-dimensional Autoregressive Integrated Moving Average Bilinear Time Series Models
J.F. Ojo
Asian Journal of Mathematics & Statistics , 2010,
Abstract: In this study, full and subset one-dimensional autoregressive integrated moving average bilinear models which are capable of achieving stationarity for all non linear series are proposed and were compared to determine which of them perform better. The parameters of the proposed models were estimated using Newton-Raphson iterative method and an algorithm is proposed to eliminate redundant parameters from the full models to have subset models. Akaike Information Criterion (AIC) was used to determine the order of the model. To determine the best model, the residual variance attached to the proposed full and subset models were studied. In the fitted models different sample sizes were used and the statistical properties of the derived estimates are investigated. It was found that the residual variance attached to the full bilinear model was smaller than the subset model and this was so because of the introduction of the d factor in our new models which has made us to capture trend and seasonality in the data, which in turn helps arrive at stationarity easily for any time series data set and at the same time made the full model a better model.
On the Performance and Estimation of Spectral and Bispectral Analysis of Time Series Data
J.F. Ojo
Asian Journal of Mathematics & Statistics , 2008,
Abstract: In this study, discrete spectral and bi-spectral analysis of time series data were considered to determine which of them perform better. The parameters of the spectral and bi-spectral models were estimated using Modified Newton Raphson Iterative method. Since the order of a model cannot be increased indiscriminately because of the closeness of some parameters to zero; discrete spectral and bi-spectral analysis model of orders one to five were fitted to the real series. Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) were used to determine the best order of the model. To determine the best model, the residual variance attached to the spectral and bi-spectral models was used. Order one and order four gave the best order in spectral and bi-spectral models, respectively. Residual variances of spectral and bi-spectral models compared favourably with each other. The residual variance of bi-spectral model was smaller than the residual variance of spectral model and this made us to conclude that bi-spectral analysis of time series data performed better than spectral analysis of time series data.
Forecasting in Subsets Autoregressive Models and Autoprojective Models
J.F. Ojo,T.O. Olatayo,O.O. Alabi
Asian Journal of Scientific Research , 2008,
Abstract: Full autoregressive models are always characterize by many parameters and this is a problem. Some of these parameters are redundant that is close to zero and there is the need to eliminate these parameters through the concept of subsetting. Subsets autoregressive models are free from redundant parameters thereby lowering the residual variance and forecasting with such models will always give a better forecast. Likewise auto projective models calculate on the basis of current knowledge what the errors would have been which gives us some guide to errors of the future. It is in the light of the above we considered the subsets autoregressive models and auto projective models, to see how these models will perform with regard to forecast. Exponential smoothening was used to forecast the future value in auto projective models while conditional least square predictor was used to forecast the future value in subset autoregressive models. An algorithm was proposed to eliminate redundant parameters from the full order autoregressive models and the parameters were estimated. To determine optimal models, residual variance, Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) were adopted. Results revealed that the residual variance attached to the subset autoregressive models is smaller than the residual variance attached to the auto projective models. We conclude that the forecast for subset autoregressive is preferred to the forecast for auto projective.
Phenomenological Model for the metal-insulator transition in two dimensions
Weisz, J.F;
Brazilian Journal of Physics , 2009, DOI: 10.1590/S0103-97332009000600017
Abstract: the resistivity measured in two-dimensional mosfet geometry is modeled by considering that the resistivity is a function of the temperature and the areal density of charges (electrons or holes). the logistics differential equation is proposed for the behaviour of the resistivity as a function of temperature, so that the two phases are obtained in a natural manner. at low temperatures, the drude model behaviour is assumed for the resistivity as a function of density. two characteristics then follow in a natural manner: the existance of a characteristic temperature for resistivity as a function of temperature, and the symmetry relationship. if the magnetic field is incorporated into the drude model, reasonable results are obtained for the qualitative behaviour of resistivity for weak fields.
Health Consequences of Obesity and Overweight
J.F. Babalola
Pakistan Journal of Social Sciences , 2012, DOI: 10.3923/pjssci.2011.118.124
Abstract: Obesity is a condition in which the natural energy reserve, stored in the fatty tissue of humans and other mammals is increased to a point where it is associated with certain health conditions or increased mortality. Although, obesity is an individual clinical condition, it is increasingly viewed as a serious and growing public health problem. Excessive body weight has been shown to predispose to various diseases particularly cardiovascular diseases, diabetes mellitus type 2, sleep apnea and osteoarthritis. Obese people are seen to be less active than lean people. A controlled increase in calorie intake of lean people did not make them less active; correspondingly when obese people lost weight they did not become more active. Weight stigma also known as weightism, weight bias and weight-based discrimination, refers to invidiously discriminatory attitudes towards overweight/obese individuals that influence interpersonal interactions. Weight stigma reflects internalized attitudes towards overweight and obese people and affects how these people are treated. Combined diet and exercise as well as drug therapy is effective for the prevention and management of obesity and overweight.
Hypercholesterolaemia in children and young adults – current management
J.F Raal
Journal of Endocrinology, Metabolism and Diabetes of South Africa , 2009,
Abstract: Atherosclerosis begins in childhood. Not uncommonly, the first presentation of atherosclerosis is sudden cardiac death. It therefore makes sense that risk-factor modification to prevent the development or delay the onset of atherosclerosis needs to begin early in life. Dietary intervention is the key component for the primary prevention of hyperlipidaemia. However, if diet and lifestyle fail to correct hyperlipidaemia, drug therapy may have to be considered. All children and adolescents with high-risk lipid disorders such as familial hypercholesterolaemia (FH), those with diabetes mellitus or other cardiovascular disease risk factors or with a family history of premature coronary artery disease should be considered for lipid-lowering therapy if diet and lifestyle intervention are ineffective. There are now numerous studies that have documented the safety and efficacy of statin therapy in both children and young adults. Based on these studies, it is now recommended that statin therapy be initiated in all male FH children from the age of ten years and at the onset of menses in females with FH. The initiation of statin therapy could be considered even earlier in FH children at high risk.
Three New Species of Mesosciophilid Gnats from the Middle-Late Jurassic of China (Insecta: Diptera: Nematocera: Mesosciophilidae)
J.F. Zhang
Pakistan Journal of Biological Sciences , 2008,
Abstract: Three extinct new species from the Callovian or Oxfordian (uppermost Middle Jurassic or lowermost Upper Jurassic) Daohugou beds in Inner Mongolia, China is described as Mesosciophila abstracta sp. n., Mesosciophilodes synchrona sp. n. and Paramesosciophilodes eximia sp. n. (Family Mesosciophilidae). All the records of mesosciophilid gnats are briefly reviewed.
Nigeria: a federation gone wrong
J.F. Kirsten
Koers : Bulletin for Christian Scholarship , 1996, DOI: 10.4102/koers.v61i4.613
Abstract: Due to its size, large population, oil-based economy and geographical location in West Africa. Nigeria is regarded as an important state in Africa. The country is also one of the longest surviving federal states on the continent and therefore represents an ongoing experiment in federalism in the Third World. Since its independence in 1960, however, Nigeria has been devastated by chronic political instability. This article tries to address the issue why this is the case and to identify ethnic-religious diversity and successive military regimes as the most important sources for the mentioned political unrest. The course and nature of political instability in Nigeria is pul in historical context - a context which also include the secession attempt by Riafra as one of the tragic highlights in the past of Nigeria. In conclusion, the author speculates on ways and options as to how secession attempts can be prevented and a larger amount of national political stability be achieved.
Africa: signs of hope?
J.F. Kirsten
Koers : Bulletin for Christian Scholarship , 2008, DOI: 10.4102/koers.v73i4.179
Abstract: The dawning of the 21st century generally brought new hope to African leaders and countless thousands of ordinary citizens of many countries on the continent. The first signs of a new turn of events shone through by the end of the last decade of the previous century. This was manifested by economic growth rates that started to pick up in a number of African states, by pro-democracy movements which in country after country succeeded in replacing authoritarian regimes, and by the winding down and termination of some of Africa’s most devastating wars. The results of this analysis confirm the above-mentioned positive political, economic and conflict trends in Africa. It is clearly a significant turn of events given the well-known political and economic predicament with which Africa is struggling. When this negative legacy and Cold War background of Africa is considered, the importance of present developments is clear to see. The identified heightened sense of purpose among the leaders and peoples of Africa and the changed mood and need among Africans to take charge of their own future that found expression in the New Partnership for Africa’s Development (NEPAD) are indeed significant and bode well for the future of the continent. A word of warning here is, however, necessary. Our conduct with Africa must be very cautious and we must guard against over-optimism and the exaggerated belief that Africa is now on a trajectory of sustained development and peace. We cannot generalise about Africa – for that the continent is just too big and diverse from a geographical, cultural, economic and political point of view.
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