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Input Level (input + level)
Selected AbstractsNonlinear response of N2O flux to incremental fertilizer addition in a continuous maize (Zea mays L.) cropping systemGLOBAL CHANGE BIOLOGY, Issue 10 2005Claire P. McSwiney Abstract The relationship between nitrous oxide (N2O) flux and N availability in agricultural ecosystems is usually assumed to be linear, with the same proportion of nitrogen lost as N2O regardless of input level. We conducted a 3-year, high-resolution N fertilizer response study in southwest Michigan USA to test the hypothesis that N2O fluxes increase mainly in response to N additions that exceed crop N needs. We added urea ammonium nitrate or granular urea at nine levels (0,292 kg N ha,1) to four replicate plots of continuous maize. We measured N2O fluxes and available soil N biweekly following fertilization and grain yields at the end of the growing season. From 2001 to 2003 N2O fluxes were moderately low (ca. 20 g N2O-N ha,1 day,1) at levels of N addition to 101 kg N ha,1, where grain yields were maximized, after which fluxes more than doubled (to >50 g N2O-N ha,1 day,1). This threshold N2O response to N fertilization suggests that agricultural N2O fluxes could be reduced with no or little yield penalty by reducing N fertilizer inputs to levels that just satisfy crop needs. [source] Evaluating the transport and removal of chromate using pyrite and biotite columnsHYDROLOGICAL PROCESSES, Issue 14 2007Chul-Min Chon Abstract To remove chromate from a wastewater, a porous permeable reactive barrier system (PRBS), using pyrite and biotite, was adapted. This study included bench-scale column experiments to evaluate the efficiency of the PRBS and investigate the reaction process. The total chromium concentration of the effluent from the biotite and pyrite columns reached the influent concentration of 0·10 mM after passing through more than 150 pore volumes (PVs) and 27 PVs respectively, and remained constant thereafter. The CrVI concentration in the effluent from the biotite column became constant at about 0·08 mM, accounting for approximately 80% of the influent concentration, after passing through 200 PVs. Moreover, in the pyrite column, the CrVI concentration remained at about 0·01 mM, 10% of the input level, after passing through 116 PVs. This shows that both columns maintained their levels of chromate reduction once the CrVI breakthrough curves (BTCs) had reached the steady state, though the steady-state output concentration of total chromium had reached the influent level. The variances of the iron concentration closely followed those of the chromium. The observed data for both columns were fitted to the predicted BTCs calculated by CXTFIT, a program for estimating the solute transport parameters from experimental data. The degradation coefficient µ of the total chromium BTCs for both columns was zero, suggesting the mechanisms for the removal of chromate limit the µ of the CrVI BTCs. The CrVI degradation of the pyrite column (6·60) was much greater than that of the biotite column (0·27). In addition, the CrVI retardation coefficient R of the pyrite column (253) was also larger than that of the biotite column (125). The R values for the total chromium BTCs from both columns were smaller than those of the CrVI BTC. Whereas the total chromium BTC for the pyrite column showed little retardation (1·5), the biotite column showed considerable retardation (80). The results for the 900 °C heat-treated biotite column were analogous to those of the control column (quartz sand). This suggests that the heat-treated biotite played no role in the retardation and removal of hexavalent chromium. The parameters of the heat-treated biotite were calculated to an R of 1·2 and µ of 0·01, and these values confirmed quantitatively that the heated biotite had little effect on the transport of CrVI. These solute transport parameters, calculated by CXTFIT from the data obtained from the column tests, can provide quantitative information for the evaluation of bench- or field-scale columns as a removal technology for CrVI in wastewater or contaminated groundwater. Copyright © 2006 John Wiley & Sons, Ltd. [source] VHF high-power tunable RF bandpass filter using microelectromechanical (MEM) microrelaysINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 5 2001Robert D. Streeter Abstract A VHF RF bandpass filter tuned through the use of MEM microrelays was operated at a 25 W RF power input level. The filter insertion loss was less than 1 dB at the tuned frequencies of operation, and the filter operating Q was about 10. The MEM microrelays were life tested for 53 million operating cycles at 25 W RF power, and no significant degradation to the contacts was noted. The development of the microrelay and the use of a CAE tool in the filter development are discussed. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 261,275, 2001. [source] Sensory-motor control mechanism for reaching movements of a redundant musculo-skeletal armJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 11 2005Kenji Tahara This paper studies the human arm's sensory-motor control mechanism in reaching movements. First, we formulate both the kinematics and dynamics of a two-link planar arm model with six redundant muscles. The nonlinear muscle dynamics is modeled based on several biological understandings. We then show the stability of the overall system and perform some numerical simulations. By considering the internal forces induced by the redundant muscles, we show that the damping factors in each joint can be regulated, and as the result, it can realize humanlike quasistraight line reaching movements. In addition, we also propose the gravity compensation method at the muscle input level and present the result of numerical simulation to verify the usefulness of this method. © 2005 Wiley Periodicals, Inc. [source] Elements Which Delimitate Technical Efficiency of Fish Farms in GhanaJOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 4 2010Edward E. Onumah The study aims to examine the technical efficiency and its determinants of fish farms in Ghana. The stochastic frontier function is employed using a cross-sectional data of 150 farmers. The results show that elasticities of mean output for all inputs are positive, whereas the computed return to scale reveals that, on average, fish farms exhibit increasing return to scale. The combined effect of operational and farm-specific factors influence technical efficiency although individual effects of some variables may not be significant. Mean technical efficiency is estimated to be 84%, indicating that the possibility of enhancing production given the present state of technology and input level can be achieved in the short run by increasing technical efficiency by 16% through adoption of practices of the best fish farm. [source] EFFECT OF OSMOTIC TREATMENT WITH CONCENTRATED SUGAR AND SALT SOLUTIONS ON KINETICS AND COLOR IN VACUUM CONTACT DRYINGJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 6 2007S.M.A. RAHMAN ABSTRACT An experimental study of osmotic dehydration (OD) of selected heat-sensitive products was carried out in a laboratory-scale vacuum contact dryer. Cubes of potato and apple were examined as model heat-sensitive objects. Experiments were conducted at different conduction heat input levels with wall temperatures in the range 35,45C under vacuum and also in pure vacuum without any external heat input. Detailed investigations were carried out of OD on drying performance, product temperature and color of the dried product. PRACTICAL APPLICATIONS Osmotic treatment of potato and apple samples using concentrated sugar solution shows better osmotic dehydration as well as drying rate in a vacuum contact drying system. This information may help to select the osmotic agent in any industrial application for faster drying rate in vacuum contact drying specially for food products. Moreover this work shows the analysis to find out the starting point of precipitation of osmotic agent inside the products in terms of drying time, temperature and moisture content. This information will be helpful for critical analysis in osmotic dehydration technique which in turns may help for optimum design. [source] Structural adjustment and soil degradation in Tanzania A CGE model approach with endogenous soil productivityAGRICULTURAL ECONOMICS, Issue 3 2001Henrik Wiig CGE model; Soil degradation; Economic growth; Structural adjustment Abstract In this paper, a model of the nitrogen cycle in the soil is incorporated in a Computable General Equilibrium (CGE) model of the Tanzanian economy, thus establishing a two-way link between the environment and the economy. For a given level of natural soil productivity, profit-maximising farmers choose input levels , and hence production volumes , which in turn influence soil productivity in the following years through the recycling of nitrogen from the residues of roots and stover and the degree of erosion. The model is used to simulate the effects of typical structural adjustment policies like a reduction in agro-chemicals' subsidies, reduced implicit export tax rate etc. After 10 years, the result of a joint implementation is a 9% higher Gross Domestic Product (GDP) level compared to the baseline scenario. The effect of soil degradation is found to represent a reduction in the GDP level of more than 5% for the same time period. [source] | ||||||||||