Estimation in a class of nonlinear heteroscedastic time series models

Parameter estimation in a class of heteroscedastic time series models is investigated. The existence of conditional least-squares and conditional likelihood estimators is proved. Their consistency and their asymptotic normality are established. Kernel estimators of the noise's density and its derivatives are defined and shown to be uniformly consistent. A simulation experiment conducted shows that the estimators perform well for large sample size.Comment: Published in at http://dx.doi.org/10.1214/07-EJS157 the Electronic Journal of Statistics (http://www.i-journals.org/ejs/) by the Institute of Mathematical Statistics (http://www.imstat.org

Rayleigh’s quotient–based damage detection algorithm: Theoretical concepts, computational techniques, and field implementation strategies

This article proposes a Rayleigh’s quotient–based damage detection algorithm. It aims at efficiently revealing nascent structural changes on a given structure with the capability to differentiate between an actual damage and a change in operational conditions. The first three damage detection levels are targeted: existence, location, and severity. The proposed algorithm is analytically developed from the dynamics theory and the virtual energy principle. Some computational techniques are proposed for carrying out computations, including discretization, integration, derivation, and suitable optimization methods. Field implementation strategies are also considered for the purpose of online damage monitoring. In order to prove the efficiency of this strategy, one experimental and three numerical case studies were conducted. The proposed algorithm successfully detected the damage in all simulated cases and estimated the damage severity with acceptable accuracy. The conclusion is that the proposed algorithm was able to efficiently detect damage appearance in a range of structures for various damage levels and locations, and under different operational conditions. </jats:p

Assessing Potential Impact of a Farmer Field School Training on Perennial Crop in Cameroon

This study is an attempt of the combination of multiple data sources referring to the same time period and to the same farmer population, it aims at assessing the potential impact of a cocoa Farmer Field School Training on Integrated Pest Management in Cameroon. Using a combination of a latitudinal and a longitudinal comparison, the results indicate that FFS-trained farmers have significantly more knowledge about crop husbandry practices than those in the non-participant comparison group. A 32% production increase and 45% income increase relative to the non-participants was estimated in the latitudinal analysis. The longitudinal comparison is showing significant adoption rates of 94, 93, 90, 66 and 35 % respectively for shade management, phytosanitary harvest, pruning, improved spraying practices and grafting of improved materials. There was a 47 % reduction in the frequency of spraying fungicides and a 17 % reduction in the number of sprayers applied per treatment following the implementation of the training. Labour inputs increased significantly for pruning, phytosanitary harvest, and shade management but decreased for spraying. A partial budget analysis reveals that the IPM practices lowered overall costs of production by 11 % relative to previous practices. The two different analytical tools (longitudinal and latitudinal) are convergent in their results, showing more evidence about the higher potential impact of the farmer field school training on the restructuring process of the cocoa sector in Cameroonintegrated pest management, farmer field school, adoption rate, Agricultural and Food Policy, Community/Rural/Urban Development, Demand and Price Analysis, Environmental Economics and Policy, Farm Management, Food Consumption/Nutrition/Food Safety, Food Security and Poverty, Land Economics/Use, Marketing, Research and Development/Tech Change/Emerging Technologies,

Socio-Economic Impact of a Cocoa Integrated Crop and Pest Management Diffusion Knowledge Through a Farmer Field School Approach in Southern Cameroon

We focused on the Socio-Economic Evaluation of Farmer Field School Training on Integrated Pest Management in the humid forest region of Cameroon. The main objective was to assess the impact of training on integrated pest management (IPM) on cocoa farmer field school graduates. The results indicate that shade management, phytosanitary harvest, pruning, improved spraying practices and grafting of improved materials were adopted at the rate of 94, 93, 90, 66 and 35 % respectively, with the overall rate of adoption being 76 %. There was a 47 % reduction in the frequency of spraying fungicides and a 17 % reduction in the number of sprayers applied per treatment following the implementation of the training. Labour inputs increased significantly for pruning, phytosanitary harvest, and shade management but decreased for spraying. A partial budget analysis reveals that the IPM practices lowered overall costs of production by 11 % relative to previous practices. The poster presenting the synthesis of this work comprises a general introduction, a methodology and study area map, results and discussion which comprise two photographs of farmer field school activities, a graph and a table of different technical results, a short conclusion and recommendation.integrated pest management, farmer field school, adoption rate, Crop Production/Industries,

How close to detailed spectral calculations is the k-distribution method and correlated-k approximation of Kato et al. (1999) in each spectral interval?

International audienceThe k-distribution method and the correlated-k approximation of Kato et al. (1999) is a smart approach originally designed for broadband calculations of the solar radiation at ground level by dividing the solar spectrum in 32 spectral bands. The approach is a priori not suited for calculation of spectral irradiance. Nevertheless, this paper evaluates its performance when compared to more detailed spectral calculations serving as references for the spectral intervals no. 3 [283, 307] nm to 26 [1613, 1965] nm for clear and cloudy situations. The evaluation is based on numerical simulations. The clearer the sky, the greater the root mean square error (RMSE) in all bands. In the spectral intervals no. 3 and 4 [307, 328] nm, the irradiance is underestimated by large – approximately −90 % and −17 % in relative value -because the wavelength interval is large with respect to the absorption by ozone and a single value of ozone cross section is not enough for each interval. For each spectral interval from no. 5 [328, 363] nm to no. 18 [743, 791] nm, and for both global and direct radiation, the bias and the RMSE are less than 1.5 % of the irradiance in the corresponding interval under clear skies and may amount to 3 % in cloudy conditions. For greater wavelength intervals no. 19 to no. 26, the relative bias and RMSE show a tendency to increase with wavelength and may reach 8 % and 7 % for global and direct under clear skies respectively, and 11 % and 15 % under cloudy skies

Estimating the photosynthetically active radiation under clear skies by means of a new approach

International audienceThe k-distribution method and the correlated-k approximation of Kato et al. (1999) is a computa-tionally efficient approach originally designed for calculations of the broadband solar radiation by dividing the solar spectrum in 32 specific spectral bands from 240 to 4606 nm. This paper describes a technique for an ac-curate assessment of the photosynthetically active radiation (PAR) from 400 to 700 nm at ground level, under clear-sky conditions using twelve of these spectral bands. It is validated against detailed spectral calculations of the PAR made by the radiative transfer model libRadtran. For the direct and global PAR irradiance, the bias is −0.4 W m−2 (−0.2 %) and −4 W m−2 (−1.3 %) and the root mean square error is 1.8 W m−2 (0.7 %) and 4.5 W m−2 (1.5 %). For the direct and global Photosynthetic Photon Flux Density, the biases are of about +10.3 µmol m−2 s−1 (+0.8 %) and 1.9 µmol m−2 s−1 (−0.1 %) respectively, and the root mean square error is 11.4 µmol m−2 s−1 (0.9 %) and 4.0 µmol m−2 s−1 (0.3 %). The correlation coefficient is greater than 0.99. This technique provides much better results than two state-of-the-art empirical methods computing the daily mean of PAR from the daily mean of broadband irradiance

Further validation of the estimates of the downwelling solar radiation at ground level in cloud-free conditions provided by the McClear service: the case of Sub-Saharan Africa and the Maldives Archipelago

Being part of the Copernicus Atmosphere Monitoring Service (CAMS), the McClear service provides estimates of the downwelling shortwave irradiance and its direct and diffuse components received at ground level in cloud-free conditions, with inputs on ozone, water vapor and aerosol properties from CAMS. McClear estimates have been validated over several parts of the world by various authors. This article makes a step forward by comparing McClear estimates to measurements performed at 44 ground-based stations located in Sub-Saharan Africa and the Maldives Archipelago in the Indian Ocean. The global irradiance received on a horizontal surface (G) and its direct component received at normal incidence (BN) provided by the McClear-v3 service were compared to 1 min measurements made in cloud-free conditions at the stations. The correlation coefficient is greater than 0.96 for G, whereas it is greater than 0.70 at all stations but five for BN. The mean of G is accurately estimated at stations located in arid climates (BSh, BWh, BSk, BWk) and temperate climates without a dry season and a hot or warm summer (Cfa, Cfb) or with a dry and hot summer (Csa) with a relative bias in the range [−1.5, 1.5] % with respect to the means of the measurements at each station. It is underestimated in tropical climates of monsoon type (Am) and overestimated in tropical climates of savannah type (Aw) and temperate climates with a dry winter and hot (Cwa) or warm (Cwb) summer. The McClear service tends to overestimate the mean of BN. The standard deviation of errors for G ranges between 13 W m−2 (1.3 %) and 31 W m−2 (3.7 %) and that for BN ranges between 31 W m−2 (3.0 %), and 70 W m−2 (7.9 %). Both offer small variations in time and space. A review of previous works reveals no significant difference between their results and ours. This work establishes a general overview of the performances of the McClear service.</p