21 research outputs found
An analytic approach to the dosimetry of a new BEBIG 60 Co high-dose-rate brachytherapy source
No full textWe present a simple analytic tool for calculating the dose rate distribution in water for a new BEBIG high-dose-rate (HDR) 60 Co brachytherapy source. In the analytic tool, we consider the active source as a point located at the geometric center of the 60 Co material. The influence of the activity distribution in the active volume of the source is taken into account separately by use of the line source-based geometric function. The exponential attenuation of primary 60 Co photons by the source materials ( 60 Co and stainless-steel) is included in the model. The model utilizes the point-source-based function, f(r) that represents the combined effect of the exponential attenuation and scattered photons in water. We derived this function by using the published radial dose function for a point 60 Co source in an unbounded water medium of radius 50 cm. The attenuation coefficients for 60 Co and the stainless-steel encapsulation materials are deduced as best-fit parameters that minimize the differe
On measuring literacy
No full textThe authors present a new approach to evaluating the level of effective literacy in a region or country, one that takes into account the presence in a household of a literate person. They characterize the approach and give an empirical illustration of its use. They designed the new measures of literacy because traditional measures of the literacy rate (R) ignore how the presence of literate person in the household affects literacy. They contend that literate household members generate a positive externality -- a kind of public good - for illiterate members. They believe their new measures will be superior to R in predicting or explaining other achievements that depend on literacy. They expect the rate of diffusion of a new technology for farming, for example, to be more closely linked to the effective literacy rate than to the usual literacy rate. If an agricultural extension worker leaves behind a brochure explaining how to plant and care for high-yielding varieties, an illiterate person who lives in a household with at least one literate member has access to that public good; an isolated illiterate - whose household has not literate members - may not have. Similarly, if the presence ( or absence) of one literate household member increases the chance of a child becoming literate, so the effective literacy rate should be a better predictor of future generations'literacy rate should be a better predictor of future generations'literacy levels. Some changes in policy emphasis might be expected if the new effective literacy measures are used. There might be a shift, for example, toward ensuring a better distribution of literacy across households or toward addressing more seriously the problem of female illiteracy. More work is needed to determine if a child in a household with a higher percentage of literate adults has more frequent access to literacy skills.Adult Outreach,Nonformal Education,ICT Policy and Strategies,Primary Education,Curriculum&Instruction,Nonformal Education,Gender and Education,Primary Education,Curriculum&Instruction,ICT Policy and Strategies
Effects of sediment erosion in guide vanes of Francis turbines
No full textErosive wear of turbine components has been a major operational challenge for the runoff-river hydropower plants across the basins of Himalaya in Asia. The hard mineral particles, which are carried by rivers reach the turbines and erode the surface in contact. In Francis turbines, guide vanes, cover plates, hub at runner inlet and blades at runner outlet are the most affected areas due to the sediment erosion. Several attempts have been made in the past to minimize the losses due to the sediment erosion in the hydraulic turbines. However, the problem has not been solved satisfactorily.
A dry clearance gap between the guide vanes and the cover plates usually exists in the Francis turbines, fromthe design. The deflection of cover plates and the erosion of the components causes the clearance gap to increase by multiple times of its design value. Inherit pressure difference between guide vane surfaces forces a leakage flow from the increased clearance gap. A systematic study of the characteristics of the leakage flow, and its effects on the flow conditions inside the Francis turbine distributor has not been reported yet. Such studies are necessary for the design optimization of the turbine components and to plan the effective maintenance schedules for repairing the eroded turbine parts.
The main objective of this work is to study the effects of sediment erosion in hydro turbines, with the focus on the flow around the guide vanes of a low specific speed Francis turbine. Experimental investigations of the characteristics of leakage flow from the increased clearance gap between eroded guide vanes and cover plates, has been the focus of this study.
A one-guide vane cascade has been developed to represent the flow inside a low specific speed Francis turbine distributor. Cases with five different sizes of clearance gap are investigated for the guide vane shaped with a symmetric profile. Particle Image Velocimetry techniques are applied for the flow measurement. All experiments have been carried out at the Waterpower Laboratory of Norwegian University of Science and Technology. Flow velocity exceeding 35 m/s, at the runner inlet of Francis turbine, is reported for the first time from such experimental studies.
The results show that, that the clearance gap up to 0.5 mm does not have significant effects on the flow parameters and hence can be accepted as the maximum limit. The leakage flow, with clearance gap more than 1 mm, is found to change the velocity components at the runner inlet significantly. The case with the clearance gap of 2 mm is found to have the highest effects on the flow velocities and is considered as the critical size. The total crosswise leakage flow, from the critical clearance gap, is measured to be more than 1% of the main flow. As the consequence of the leakage flow, the relative velocity at the runner inlet is found to increase locally up to three times from its design value. This local increase in relative velocity is identified as the cause to have severe erosion at the runner hub in the sediment-laden projects. The leakage flow also changes the pressure distribution around guide vane, causing the torque on the guide vane shaft to increase up to 28%.
Further investigation of the propagation of the leakage flow into the turbine runner, and its effects on the runner’s performance is necessary. Alternative designs of guide vane geometry, to minimize the differential pressure across is recommended as the future works
The effects of atomic oxygen on space coatings
No full textAmorphous silicon dioxide and aluminum oxide films are being considered by NASA for application on low earth orbit solar space reflectors as oxidation protective coatings. Using monolayer sensitive Variable Angle Spectroscopic Ellipsometry (VASE) the author has investigated the diffusion of atomic oxygen through deposited films of these materials. Atomic oxygen was generated in an RF plasma chamber using pure oxygen. Conversion of silver to silver oxide was used for the detection of atomic oxygen. Mainly, the grain boundary diffusion of oxygen was attributed to the diffusion of atomic oxygen through a deposited film. A new proposal, made by the author for improving the protective layer quality, was to deposit a thin aluminum layer on top of silver before depositing the silver oxide were also determined by VASE technique. To investigate the mechanisms of atomic oxygen diffusion through (grown) silicon dioxide films, the growth of silicon dioxide on top of silicon(111), caused by atomic oxygen diffusion, was monitored using VASE. A kink at about 30 Angstroms of silicon dioxide thickness was observed in the oxide growth curve for each of the plasma powers used by the author. Various theories were investigated for explaining the experimental data. The Murali and Murarka theory was found to be in reasonable agreement with the data. For an alternative explanation, a theory involving the formation of pores during the initial stages of oxide growth is proposed by the author. Development of these pores was probed using the VASE technique, and above about 30 Angstroms of oxide thickness, no further pore growth was found. The temperature and pressure dependencies of silicon dioxide growth were also investigated by the author. Finally the effects of atomic oxygen on Indium Tin Oxide (ITO) films were studied by the author using X-ray diffraction, optical transmission, VASE and resistivity measurements. It was found that increased ashing results in lower resistivity and increased optical absorption of the film, before reaching a saturation point
Computational modelling of meiotic entry and commitment
No full textIn response to developmental and environmental conditions, cells exit the mitotic cell cycle and enter the meiosis program to generate haploid gametes from diploid germ cells. Once cells decide to enter the meiosis program they become irreversibly committed to the completion of meiosis irrespective of the presence of cue signals. How meiotic entry and commitment occur due to the dynamics of the regulatory network is not well understood. Therefore, we constructed a mathematical model of the regulatory network that controls the transition from mitosis to meiosis in Schizosaccharomyces pombe. Upon nitrogen starvation, yeast cells exit mitosis and undergo conjugation and meiotic entry. The model includes the regulation of Mei2, an RNA binding protein required for conjugation and meiotic entry, by multiple feedback loops involving Pat1, a kinase that keeps cells in mitosis, and Ste11, a transcription activator required for the sexual differentiation. The model accounts for various experimental observations and demonstrates that the activation of Mei2 is bistable, which ensures the irreversible commitment to meiosis. Further, we show by integrating the meiosis-specific regulation with a cell cycle model, the dynamics of cell cycle exit, G1 arrest and entry into meiosis under nitrogen starvation. © 2017 The Author(s)
Mapping mangrove opportunities with open access data: A case study for Bangladesh
No full textMangroves protect coastal areas against hazards like storms or cyclones by attenuating waves and currents, and by trapping floating debris during extreme events. Bangladesh is a very vulnerable country to floods and cyclones, and part of its coastal system is thus being upgraded to a higher safety standard. These upgrades include embankment reinforcement and mangrove afforestation schemes seawards of the embankments. To further strengthen the implementation of combined green–grey infrastructure in future programs, identifying potential mangrove development sites near the polder systems is a necessary first step. We thus developed a tool to systematically identify mangrove sites throughout the coastal area based on open access data. This method identi-fies potential sites for mangrove development based on their distance from existing mangrove patches and suggests the required technique to implement the vegetation depending on the rate of coastline change. Our method showed that approximately 600 km of the coastal stretches placed seawards of embankments are within 10 km of existing mangroves, and could thus be potential sites for mangrove establishment. Out of those 600 km, we identified 140 km of coastline where the land-wards polders are particularly vulnerable to flooding. The sites with highest restoration potential and priority are located in Galachipa, Hatiya, Bhola, Manpura, Khangona, and Boro Moheshkhali. More detailed data collection and local assessments are recommended prior to executing mangrove afforestation schemes. Nevertheless, this method could serve as a useful systematic tool for feasi-bility studies that identify mangrove opportunities in data-scarce areas and help to prioritize data collection at the sites of highest interest.</p
Velocity and pressure measurements in guide vane clearance gap of a low specific speed Francis turbine
No full textIn Francis turbine, a small clearance gap between the guide vanes and the cover plates is usually required to pivot guide vanes as a part of governing system. Deflection of cover plates and erosion of mating surfaces causes this gap to increase from its design value. The clearance gap induces the secondary flow in the distributor system. This effects the main flow at the runner inlet, which causes losses in efficiency and instability. A guide vane cascade of a low specific speed Francis turbine has been developed for experimental investigations. The test setup is able to produce similar velocity distributions at the runner inlet as that of a reference prototype turbine. The setup is designed for particle image velocimetry (PIV) measurements from the position of stay vane outlet to the position of runner inlet. In this study, velocity and pressure measurements are conducted with 2 mm clearance gap on one side of guide vane. Leakage flow is observed and measured together with pressure measurements. It is concluded that the leakage flow behaves as a jet and mixes with the main flow in cross-wise direction and forms a vortex filament. This causes non-uniform inlet flow conditions at runner blades.Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI
The digital future of farming : a bibliometric analysis of big data in smart farming research
No full textRecent advancement of technology in the analytics of big data has sparked a transformative revolution in smart agriculture, enabling farmers to make informed decisions, optimize resources, and enhance productivity and sustainability. Tracking developmental progress is crucial to understanding how big data applications in smart farming are rapidly evolving with ongoing technological advancements. We conducted a bibliometric analysis of academic publications and documents published in Scopus-indexed peer-reviewed journals. A total of 2,154 publications, including journal articles (45 %), conference proceedings (30 %), book series (16 %), and books (9 %), were retrieved, with 96 % of the documents in the English language and two-thirds of the documents published within the last four years of this research study. The reviewed publications were predominantly focused on the disciplines of computer science (64 %), engineering (36 %), and agriculture and biological science (22 %). The contributions of authors from India, China, and the United States were the highest, accounting for half of the publications when combined. As an outcome of the bibliometric analysis, five research domains of big data, i.e., data-driven decision-making, sustainability and supply chain management, technology and innovation, data management and governance, and digital transformation were identified, suggesting positive development in this field. As an implication of this work, we have identified a need for greater global collaboration to achieve big data advancement and technology adaptation. We also discussed the implications of this work for research, practice, and policy. Despite the opportunities that big data brings for smart farming, economics, data governance, and data sharing and reliability remain prevalent issues. These issues need to be addressed for fully effective utilisation of big data in smart farming. © 2024 The Author(s
Working speed optimization of the fully automated vegetable seedling transplanter
No full textThe purpose of this study was to determine the optimal operating speeds for a low-speed automated vegetable transplanter that utilized a modified linkage cum hopper-type planting unit. A biodegradable seedling plug-tray feeding mechanism is employed by the transplanter. Using kinematic simulation software, the planter unit’s movement was simulated under various operating conditions. The resulting trajectories were compared based on variables like plant spacing, soil intrusion area, soil intrusion perimeter, and horizontal hopper displacement in the soil. It was discovered that the best results occurred at 200, 250, and 300 mm/s and 40, 50, and 60 rpm combinations. Following testing in a soil bin facility, it was discovered that the ideal operating speeds performed well when transplanting pepper seedlings, with measured plant spacing that was nearly identical to the theoretical spacing. While the planting angle in various speed combinations was found to be significantly different, but still within acceptable bounds, the planting depth in each case did not differ statistically. The optimal speed combinations that were chosen resulted in minimal damage to the mulch film. The best speeds for the transplanter were found through this investigation, and these speeds can be used as a foundation for refining the other mechanisms in the transplanter. © the Author(s), 2024
