Dynamics of heavy and buoyant underwater pendulums

The humble pendulum is often invoked as the archetype of a simple, gravity driven, oscillator. Under ideal circumstances, the oscillation frequency of the pendulum is independent of its mass and swing amplitude. However, in most real-world situations, the dynamics of pendulums is not quite so simple, particularly with additional interactions between the pendulum and a surrounding fluid. Here we extend the realm of pendulum studies to include large amplitude oscillations of heavy and buoyant pendulums in a fluid. We performed experiments with massive and hollow cylindrical pendulums in water, and constructed a simple model that takes the buoyancy, added mass, fluid (nonlinear) drag, and bearing friction into account. To first order, the model predicts the oscillation frequencies, peak decelerations and damping rate well. An interesting effect of the nonlinear drag captured well by the model is that for heavy pendulums, the damping time shows a non-monotonic dependence on pendulum mass, reaching a minimum when the pendulum mass density is nearly twice that of the fluid. Small deviations from the model's predictions are seen, particularly in the second and subsequent maxima of oscillations. Using Time- Resolved Particle Image Velocimetry (TR-PIV), we reveal that these deviations likely arise due to the disturbed flow created by the pendulum at earlier times. The mean wake velocity obtained from PIV is used to model an extra drag term due to incoming wake flow. The revised model significantly improves the predictions for the second and subsequent oscillations.Comment: 15 pages, 8 figures, J. Fluid Mech. (in press

Human exposure assessment of fluoride from tea(Camellia Sinensis L.) with specific reference to human bioaccessibility studies

This study aims to determine the concentrations of fluoride in UK tea products and their infusions. This is related to the uptake and distribution of fluoride within tea plants Camellia sinensis (L.). Human oral bioaccessibility of fluoride from the consumption of tea infusions was estimated, using an in vitro approach. The possible health significance from fluoride exposure is discussed. Fluoride in tea products and the distribution within the tea plant was determined using a method, involving alkali fused digestion with ion chromatography and a conductivity detector for the instrumentation. For the aqueous infusions and the supernatants in the bioaccessibility experiments, ion selective electrode with a voltmeter was adopted. Mean fluoride concentrations in tea products and their infusions varied significantly (p<0.001; n=3) and were related to the type of tea product and the retail cost. The higher priced teas, such as Darjeeling, Assam and Oolong, had lower fluoride concentrations. The lower priced supermarket Economy ranged teas were significantly higher (p<0.05) in fluoride and exhibited concentrations similar to Chinese Brick tea, which is prepared using mature tea leaves. The higher quality products are prepared by selecting the finest tips of tea (buds), whereas an Economy products use coarser harvesting techniques to include mature leaves in the product. Fluoride affinity and tolerance of C. sinensis was assessed by a series of fluoride dosing experiments, ranging from 0 to 200 mg. Following fluoride dosing, a rapid uptake and accumulation occurred throughout the tea plants, resulting in partial necrosis of random leaves. Despite the necrosis, the plants tolerated the fluoride and continued to increase in height, although at a significantly slower rate (p<0.05) compared to the control plants. Accumulation of fluoride was observed to be mostly in the mature leaves followed by younger buds, then the roots. This relates to the part of the plant used to produce the tea types, with mature leaves for Economy products and the buds for the finer teas. The in vitro bioaccessibility assessment of fluoride estimated that over 91.4% of fluoride from a tea infusion is available in the human gastric compartment, with 92.1% in the gastro-intestinal compartment. The addition of milk reduced fluoride absorption in the gastric and gastro-intestinal compartments to 73.8 and 83.1%, respectively, possibly reacting to form calcium fluoride. Despite the percentage bioaccessibility, the concentration of fluoride available for absorption in the human gut was dependent upon choice of tea product. Based on an adult male, the findings suggest that consuming a litre of Economy tea can fulfil or exceed (75 to 120%) the recommended dietary reference intake (DRI) of fluoride at 4 mg a day, but only partially fulfil (25 to 40%) when consuming a more expensive Pure blend such as Assam. With regards to health, tea consumption is a source of fluoride in the diet and is highly available for absorption in the human gut. Tea alone can fulfil an adult fluoride DRI, but is dependent upon choice of tea product. Excess fluoride in the diet can lead to detrimental health effects such as fluorosis of the teeth and skeletal fluorosis and consuming economy branded tea can lead to a higher exposure

Rapid Rural-to-Urban Migration to Lima: A Need for a Sustainable Housing Reform

Over the past 70 years, Peru’s rapid urbanization has put great strain on the housing supply in the capital city of Lima. This article examines how the large migration waves to Lima have affected housing for lower-income groups and suggests how the city can mitigate the housing deficit through sustainable initiatives

Expert elicitation of cost, performance, and RD&D budgets for coal power with CCS

AbstractThere is uncertainty about the ex-ante returns to research, development, and demonstration programs in the United States on carbon capture and sequestration (CCS) technology. To quantify this uncertainty, we conducted a written expert elicitation of thirteen experts in fossil power and CCS technologies from the government, academia, and the private sector. We asked experts to provide their recommended budget and allocation of RD&D funds by specific fossil power and CCS technology and type of RD&D activity (i.e. basic research, applied research, pilot plants, and demonstration plants) for the United States. The elicitation instrument was structured around estimating the cost and performance of coal-fired power plants with and without CCS in the years 2010 and 2030 under four funding scenarios for federal fossil energy RD&D in the USA. The most important areas identified for basic research were chemical looping combustion and membrane technology. The most important area for commercial demonstration was integrated gasification combined cycle (IGCC). There was substantial disagreement between experts on both the current and future capital cost to build a new coal-fired power plant with CCS. There was also disagreement across experts as to whether the capital cost of a new coal plant with CCS would increase or decrease if federal RD&D funding stayed constant at current levels. However, there was a consensus among our experts that accelerated federal RD&D would (weakly) lower the capital cost requirements for a new coal plant with CCS. On average, experts estimated that if their recommended RD&D portfolio was implemented, the capital cost of new coal plants with CCS in 2030 would decrease by 10% in addition to the cost reductions/increases that would occur by 2030 through non-public RD&D related factors

"Deaf Learning": Using a Visual Method to Teach Written Language to the Deaf

The majority of deaf people prefer to use the visual channel for communication, choosing a national sign language instead of a spoken language. In many countries, Deaf education is still not bilingual, therefore deaf people frequently have problems with learning and using the written language of their country. The Erasmus+ project "Deaf Learning" addresses the need for a visually-oriented written language course for the levels from A1 to B2. The main target group is that of young deaf adults aged 16 to 25 years. A secondary target group are older deaf people who are interested in improving their written language competence

Capturing and Processing Born-Digital Files in the STOP AIDS Project Records: A Case Study

In September 2012, the Manuscripts Division of the Stanford University Libraries Department of Special Collections and University Archives completed a one-year National Historical Publications and Records Commission (NHPRC)-funded project to process the records of the STOP AIDS Project, an HIV prevention non-profit organization in San Francisco, California. This project marked the department’s first large-scale processing project to capture and process born-digital records. Building upon the nascent framework outlined by the AIMS white paper and the infrastructure developed by Stanford University Libraries, the project team captured born-digital records and implemented new processing strategies using digital forensics tools. This case study will document the strategies and workflows employed by the project team to capture and process the born-digital component of the STOP AIDS Project records. We will describe the successes, challenges and roadblocks encountered while forensically imaging 3.5 inch floppy disks, Zip disks, and CDs using Forensic Toolkit (FTK) Imager software. We will then outline our approach to processing nearly 30,000 unique digital files captured from the computer media using AccessData Forensic Toolkit (FTK) software, discuss our current delivery strategy, and offer some concluding thoughts