106,256 research outputs found
Bootstrap Approximation to Prediction MSE for State-Space Models with Estimated Parameters
No full textWe propose a simple but general bootstrap method for estimating the Prediction Mean Square Error (PMSE) of the state vector predictors when the unknown model parameters are estimated from the observed series. As is well known, substituting the model parameters by the sample estimates in the theoretical PMSE expression that assumes known parameter values results in under-estimation of the true PMSE. Methods proposed in the literature to deal with this problem in state-space modelling are inadequate and may not even be operational when fitting complex models, or when some of the parameters are close to their boundary values. The proposed method consists of generating a large number of series from the model fitted to the original observations, re-estimating the model parameters using the same method as used for the observed series and then estimating separately the component of PMSE resulting from filter uncertainty and the component resulting from parameter uncertainty. Application of the method to a model fitted to sample estimates of employment ratios in the U.S.A. that contains eighteen unknown parameters estimated by a three-step procedure yields accurate results. The procedure is applicable to mixed linear models that can be cast into state-space form. (Updated 6th October 2004
Small-area estimation with state-space models subject to benchmark constraints
No full textThis article shows how to benchmark small area estimators, produced by fitting separate state-space models within the areas, to aggregates of the survey direct estimators within a group of areas. State-space models are used by the U.S. Bureau of Labor Statistics (BLS) for the production of the monthly Employment and Unemployment State estimates. The computation of the benchmarked estimators and their variances is accomplished by incorporating the benchmark constraints within a joint model of the direct estimators in the different areas, which requires the development of a new filtering algorithm for state-space models with correlated measurement errors. No such algorithm has been developed before. The properties and implications of the use of the benchmarked estimators are discussed and illustrated using BLS unemployment series.
The problem of Small Area Estimation is how to produce reliable estimates of area (domain) characteristics, when the sample sizes within the areas are too small to warrant the use of traditional direct survey estimates. This problem is commonly handled by borrowing strength from either neighboring areas and/or from previous surveys, using appropriate cross-sectional/time series models. In order to protect against possible model breakdowns and for consistency in publication, it is often required to benchmark the area model dependent estimates to the direct survey estimate in a group of areas for which the survey estimate is sufficiently accurate. The latter estimate is a weighted sum of the direct estimates in the areas included in the group, so that the benchmarking process defines another way of borrowing strength across the areas
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Tiller Length vs. Tiller Weight: Applications to Plant Growth Studies
No full textThe growth and development of individual grass tillers is frequently monitored in intensive studies of plant response to treatments or environmental parameters. Since growth may be recognized as an increase in tiller weight or tiller length over time, knowledge of the relationship between them is important if researchers are to select the measure most appropriate for their needs. To make these comparisons, the mean weight and length of tillers from perennial ryegrass (Lolium perenne L.), colonial bentgrass (Agrostis tenuis Sibth.), softchess (Bromus mollis L.), and annual fescue (Vulpia Spp.) were measured on each of seven dates during the spring growing period, 1977. Sample sizes required to estimate mean tiller length were calculated on each date using Stein's two-stage procedure. The relationship between mean tiller weight and mean tiller length over time was evaluated by least squares analysis of a linear regression model. Results of these analyses indicated that mean tiller length can be estimated satisfactorily from a substantially smaller sample size than can mean tiller weight. In addition, a strong linear relationship was observed between mean tiller weight and mean tiller length over time. The strength and linear nature of this relationship suggests that both measures will yield similar relative growth curves when sequential observations are plotted over time. Actual growth curves plotted for perennial ryegrass and colonial bentgrass support this supposition. Therefore, since tiller lengths require a small sample size to estimate each mean, both time and money can be saved by basing growth analysis on observations of tiller length rather than on tiller weight.This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202
Exits Among U.S. Burley Tobacco Growers After the End of the Federal Tobacco Program
No full textThis study explores the relationship between family/farm characteristics and the probability of exiting burley tobacco farming in Tennessee, North Carolina, and Virginia. Following the termination of the federal tobacco program in 2004, 54% of burley tobacco–growing households in Tennessee, North Carolina, and Virginia exited burley tobacco farming by 2006. Tobacco yield, tobacco farm cash receipts, tobacco price, off-farm employment, and farm size are the most dominant variables discriminating between exiting and surviving tobacco farms. Data for this study came from a mail survey of burley tobacco producers in Tennessee, Virginia, and North Carolina in May 2006.burley tobacco, exit, federal tobacco program, Agribusiness, Agricultural and Food Policy, Crop Production/Industries, Environmental Economics and Policy, Financial Economics, Land Economics/Use, Risk and Uncertainty, C25, Q12, Q18,
DEVELOPMENT AND FIELD EVALUATION OF CULTIVATING ATTACHMENT TO POWER TILLER
No full textA power tiller operated three row cultivating attachment was developed and tested for interculture operation in soybean and sorghum crops. The field evaluation showed an effective field capacity of 0.22 ha/h and 0.107 ha/h in soybean and sorghum crops, respectively. The human energy requirement with power tiller cultivator was recorded to be 4.55 man-h/ha and 9.35 man-h/ha in soybean and sorghum crops, respectively. The respective weeding efficiencies were 51.2% and 48.3%. The cost of operation with power tiller cultivator and manual weeder was more or less same. The cost of operation with bullock drawn blade harrow (Kulpha) was about 1.5 times that of the power tiller cultivator and manual weeder
Performance of Light Weight Rotary Tiller for Different Agricultural Operations
No full textLight weight rotary tiller (Amar) was evaluated for seed bed preparation, interculture operation, puddling operation and basin preparation around the trees for finding its suitability. Overall discomfort rating of light weight rotary tiller was also measured during above operations. The average effective field capacity of rotary tiller was 0.042 ha/h for seedbed preparation under clay loam and silt clay loam soils. The average clod mean weight diameter (MWD) was observed 7.3 mm during seed bed preparation which was far below than the average clod size of 12 to 14 mm generally found in the final seed bed. The average depth of tilling (94 mm) achieved with this light weight rotary tiller may not be sufficient for sowing! planting of deep rooted crops. The overall discomfort rating on the IO-point VAD scale for operating duration of45 min was 3.36. The high slippage was observed during seed bed preparation due to low traction of iron wheel provided in light weight rotary tiller. The effective field capacity of rotary tiller during interculture operation was 0.04 ha/h, which was 85% more than manual system of interculture operation. The weeding efficiency was 84% with light weight rotary tiller during interculture operation in apple orchards. The mean overall discomfort ratings on a 1O-point VAD scale for an operating duration of35 min was 4.6, 5.4 and 7.6 for light weight rotary tiller, wheel hand hoe and manual system using spade, respectively. The interculture operation with light weight rotary tiller was found less tiring in comparison to interculture operation with wheel hand hoe and manual system. The average time required for basin preparation with rotary tiller was 4 min/basin, which was 1/3rd of time required in traditional system of basin preparation. However, cost of basin preparation was 5% higher with rotary tiller compared to traditional system due to involvement of high initial investment. The mean overall discomfort ratings recorded with rotary tiller after preparation of five basins was 5.5 in comparison to 7.9 with manual syste
Investigating the performance of electric mini tiller
No full textMini tiller is one of the agricultural machineries used for a secondary soil tillage for narrow fields. In general, it is equipped with a 4-stroke gasoline engine. Internal combustion engine is considered as one of the contributors to carbon emissions in the world, so it is necessary to find alternative energy uses. One of the famous alternative energies is electricity. Nowadays, the utilization of electrification in human life is widespread, for example, for an electric vehicle. However, the implementation of electrification in the agricultural sector has not been extensively adopted. This research investigated the performance and energy consumption of a local brand mini tiller (Cakar Baja) coupled with a Honda electric powertrain. Results showed that applying an electric mini tiller on flat and dry land can smoothly plough the soil. Furthermore, the field capacity of this electric mini tiller showed 0.11 ha/h with an effective field capacity of 0.07 ha/h. During performance testing, it showed a field efficiency of 80%, which means low energy use costs. This electric mini tiller demonstrates the opportunity to use it as future agricultural machinery for a household with a small agricultural ground
Development of a small-scale power tiller for farmers in developing countries: A case study of Benin
No full textThis study examines the labour of small-scale farmers during ploughing and develops a power tiller with the view of reducing the hardness of work and increasing the field operation capacity. The machine is designed and fabricated based on standard engineering principles for part-sizing and selection of materials. It is tested and the performance results obtained are compared to manual ploughing. Performance parameters were determined from fieldwork and laboratory experiments. The average depth, width of cut and operation speed were 14.84 cm, 24.56 cm and 3.48 km/h, respectively for power tiller compared with 10.62 cm, 18.97 cm and 0.49 km/h, respectively for manual ploughing. Average field efficiency and theoretical field capacity were 88.23%, and 0.096 ha/h, respectively for the power tiller compared with 96%, and 0.0136 ha/h for manual ploughing. Fuel consumption revealed for power tiller is 1.99 l/h. The field capacity of the machine was 0.075 ha/h which was higher than 0.013 ha/h for manual ploughing. The results show that the machine is suitable for small-scale farmers. Economic assessment of the power tiller is work to be done
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The elite haplotype OsGATA8-H coordinates nitrogen uptake and productive tiller formation in rice.
No full textExcessive nitrogen promotes the formation of nonproductive tillers in rice, which decreases nitrogen use efficiency (NUE). Developing high-NUE rice cultivars through balancing nitrogen uptake and the formation of productive tillers remains a long-standing challenge, yet how these two processes are coordinated in rice remains elusive. Here we identify the transcription factor OsGATA8 as a key coordinator of nitrogen uptake and tiller formation in rice. OsGATA8 negatively regulates nitrogen uptake by repressing transcription of the ammonium transporter gene OsAMT3.2. Meanwhile, it promotes tiller formation by repressing the transcription of OsTCP19, a negative modulator of tillering. We identify OsGATA8-H as a high-NUE haplotype with enhanced nitrogen uptake and a higher proportion of productive tillers. The geographical distribution of OsGATA8-H and its frequency change in historical accessions suggest its adaption to the fertile soil. Overall, this study provides molecular and evolutionary insights into the regulation of NUE and facilitates the breeding of rice cultivars with higher NUE
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