Fluid Flow Properties of Slotted Flat- and Hollow-blade Impellers

Published data on flow field variation caused by various blade design patterns are scarce. Most designs exhibit significant flow separation and adverse pressure gradients effects that lower mixing efficiency. In view of the design potentials of the CFD methodology, the flow field variations caused by different blade designs could be classified in order to be able to predict the spread of the low pressure regions behind blades while retrofitting existing equipment towards energy-saving performance without decreasing the impeller blending and dispersing capacity related to the geometry considered. The aim of the present study is to reveal such variations for some conventional flat blade modifications. The performance of three flat and hollow blade design modifications comprising slotted and perforated blades are examined. The specific power drawn, pumping capacity, deformation rate and turbulence intensity are determined and compared. The impeller power effectiveness is discussed in terms of the strain deformation rate produced. Evidence for enhanced performance of slotted and perforated designs is presented

Stating Appointment Costs in SMS Reminders Reduces Missed Hospital Appointments: Findings from Two Randomised Controlled Trials

BACKGROUND: Missed hospital appointments are a major cause of inefficiency worldwide. Healthcare providers are increasingly using Short Message Service reminders to reduce 'Did Not Attend' (DNA) rates. Systematic reviews show that sending such reminders is effective, but there is no evidence on whether their impact is affected by their content. Accordingly, we undertook two randomised controlled trials that tested the impact of rephrasing appointment reminders on DNA rates in the United Kingdom. TRIAL METHODS: Participants were outpatients with a valid mobile telephone number and an outpatient appointment between November 2013 and January 2014 (Trial One, 10,111 participants) or March and May 2014 (Trial Two, 9,848 participants). Appointments were randomly allocated to one of four reminder messages, which were issued five days in advance. Message assignment was then compared against appointment outcomes (appointment attendance, DNA, cancellation by patient). RESULTS: In Trial One, a message including the cost of a missed appointment to the health system produced a DNA rate of 8.4%, compared to 11.1% for the existing message (OR 0.74, 95% CI 0.61-0.89, P<0.01). Trial Two replicated this effect (DNA rate 8.2%), but also found that expressing the same concept in general terms was significantly less effective (DNA rate 9.9%, OR 1.22, 95% CI 1.00-1.48, P<0.05). Moving from the existing reminder to the more effective costs message would result in 5,800 fewer missed appointments per year in the National Health Service Trust in question, at no additional cost. The study's main limitations are that it took place in a single location in England, and that it required accurate phone records, which were only obtained for 20% of eligible patients. We conclude that missed appointments can be reduced, for no additional cost, by introducing persuasive messages to appointment reminders. Future studies could examine the impact of varying reminder messages in other health systems. TRIAL REGISTRATION: Controlled-Trials.com 49432571

CFD – facilitated Prognosis of Bubble Bed Bioreactor Performance Based on Bubble Swarms Oscillation Analysis

Bubble column reactors are widely used as gas-liquid and gas liquid-solid contactors in biotechnology applications. A basic issue in biotechnology is oxygen availability related to gas hold-up distribution, since aerobic bioprocessing depends on the dissolved oxygen substrate. The aim of this study is to analyze oxygen availability in bubble column bioreactors in terms of specific spatial and temporal gas-liquid flow. 3D CFD simulation is used to simulate the dispersed gas-liquid flow field of a bubble column of ID 0.29 m equipped with metal distributing plate. The solution is based on the Euler/Euler approach, the standard k-ε model, and the standard wall function treatment. A single size particle model was employed. No mass transfer between the gas and the liquid phase was studied; oxygen transfer is discussed in terms of local and temporal gas hold-up distribution. Two cases of different viscosity are studied related to water-like and sugar-containing nutrient media cases, e.g. tap water and aqueous solution of 0.3 kg kg–1 saccharose, respectively. Conditions of oxygen availability for aerobic cell growth in a bio-fluid at condition of elevated viscosity are considered. The time-course of instantaneous oxygen delivery proportional to the dispersion capacity estimated as gas hold-up is uncovered. The results are presented in the form of contour plots and radial profiles of the local gas hold-up at different bed height positions. The oscillating behaviour of the gas hold-up is illustrated and summarized into oxygen availability plot related to position. Based on the CFD analysis, clues for rational bioprocess performance time-course could be inferred

CFD – facilitated Prognosis of Bubble Bed Bioreactor Performance Based on Bubble Swarms Oscillation Analysis

Bubble column reactors are widely used as gas-liquid and gas liquid-solid contactors in biotechnology applications. A basic issue in biotechnology is oxygen availability related to gas hold-up distribution, since aerobic bioprocessing depends on the dissolved oxygen substrate. The aim of this study is to analyze oxygen availability in bubble column bioreactors in terms of specific spatial and temporal gas-liquid flow. 3D CFD simulation is used to simulate the dispersed gas-liquid flow field of a bubble column of ID 0.29 m equipped with metal distributing plate. The solution is based on the Euler/Euler approach, the standard k-ε model, and the standard wall function treatment. A single size particle model was employed. No mass transfer between the gas and the liquid phase was studied; oxygen transfer is discussed in terms of local and temporal gas hold-up distribution. Two cases of different viscosity are studied related to water-like and sugar-containing nutrient media cases, e.g. tap water and aqueous solution of 0.3 kg kg–1 saccharose, respectively. Conditions of oxygen availability for aerobic cell growth in a bio-fluid at condition of elevated viscosity are considered. The time-course of instantaneous oxygen delivery proportional to the dispersion capacity estimated as gas hold-up is uncovered. The results are presented in the form of contour plots and radial profiles of the local gas hold-up at different bed height positions. The oscillating behaviour of the gas hold-up is illustrated and summarized into oxygen availability plot related to position. Based on the CFD analysis, clues for rational bioprocess performance time-course could be inferred

Fluid Flow Properties of Slotted Flat- and Hollow-blade Impellers

Published data on flow field variation caused by various blade design patterns are scarce. Most designs exhibit significant flow separation and adverse pressure gradients effects that lower mixing efficiency. In view of the design potentials of the CFD methodology, the flow field variations caused by different blade designs could be classified in order to be able to predict the spread of the low pressure regions behind blades while retrofitting existing equipment towards energy-saving performance without decreasing the impeller blending and dispersing capacity related to the geometry considered. The aim of the present study is to reveal such variations for some conventional flat blade modifications. The performance of three flat and hollow blade design modifications comprising slotted and perforated blades are examined. The specific power drawn, pumping capacity, deformation rate and turbulence intensity are determined and compared. The impeller power effectiveness is discussed in terms of the strain deformation rate produced. Evidence for enhanced performance of slotted and perforated designs is presented

The behavioralist as tax collector : using natural field experiments to enhance tax compliance

This paper presents results from two large-scale natural field experiments that tested the effect of social norm messages on tax compliance. Using administrative data from more than 200,000 individuals in the United Kingdom, we show that including social norm messages in standard reminder letters increases payment rates for overdue tax. This result offers a rare example of social norm messages affecting tax compliance behavior in a real world setting. We find no evidence that loss framing is more effective than gain framing. Descriptive norms appear to be more effective than injunctive norms. Messages referring to public services or financial information also significantly increased payment rates. The field experiments accelerated the collection of tax revenue at little cost

Redesigning the 'choice architecture' of hospital prescription charts: a mixed methods study incorporating in situ simulation testing.

Objectives: To incorporate behavioural insights into the user-centred design of an inpatient prescription chart (Imperial Drug Chart Evaluation and Adoption Study, IDEAS chart) and to determine whether changes in the content and design of prescription charts could influence prescribing behaviour and reduce prescribing errors. Design: A mixed-methods approach was taken in the development phase of the project; in situ simulation was used to evaluate the effectiveness of the newly developed IDEAS prescription chart. Setting: A London teaching hospital. Interventions/methods: A multimodal approach comprising (1) an exploratory phase consisting of chart reviews, focus groups and user insight gathering (2) the iterative design of the IDEAS prescription chart and finally (3) testing of final chart with prescribers using in situ simulation. Results: Substantial variation was seen between existing inpatient prescription charts used across 15 different UK hospitals. Review of 40 completed prescription charts from one hospital demonstrated a number of frequent prescribing errors including illegibility, and difficulty in identifying prescribers. Insights from focus groups and direct observations were translated into the design of IDEAS chart. In situ simulation testing revealed significant improvements in prescribing on the IDEAS chart compared with the prescription chart currently in use in the study hospital. Medication orders on the IDEAS chart were significantly more likely to include correct dose entries (164/164 vs 166/174; p=0.0046) as well as prescriber's printed name (163/164 vs 0/174; p<0.0001) and contact number (137/164 vs 55/174; p<0.0001). Antiinfective indication (28/28 vs 17/29; p<0.0001) and duration (26/28 vs 15/29; p<0.0001) were more likely to be completed using the IDEAS chart. Conclusions: In a simulated context, the IDEAS prescription chart significantly reduced a number of common prescribing errors including dosing errors and illegibility. Positive behavioural change was seen without prior education or support, suggesting that some common prescription writing errors are potentially rectifiable simply through changes in the content and design of prescription charts

Agitation Effects and Kinetic Constants of Exoglucomannan Production by Antarctic Yeast Strain in a Stirred Tank Bioreactor

Exoglucomannan production by Antarctic yeast Sporobolomyces salmonicolor AL1 is studied at semi-tech scale in a 5 L stirred tank bioreactor and the bioreaction kinetics is quantified. The organism’s unconventional response to agitation is analyzed in terms of the agitation-induced mechanical stress. The yeast maximum production activity was observed at agitation rate 400 rpm and conserved or decreased at further increase in mixing intensity. Referring to the relationship of cell growth and aeration intensity, the various production activity, oxygen availability and cell growth are considered as a starting point to elucidate the possible reasons for the anomaly. At suspicion of shear detrimental effect on the yeast cells, the hydrodynamic stress acting on cell particles is determined and the microorganism morphology at low and high mixing intensity is examined. Biological stability is registered and the agitation effect is attributed to depressed metabolic activity at the evolving dissolved oxygen tension rather than to direct effect of hydrodynamics. A kinetic model is proposed. The specific growth rate (µ, h–1) and growth-associated (g EPS g–1 cells), and non-growth associated (g EPS g–1 cells h–1) production constants are determined and compared with reported estimates for similar reference EPS fermentations. The model and its parameters are determined in well-mixed cultures and could be upgraded further to account for mixing non-ideality and mass transfer in larger vessels

Electronic States in Diffused Quantum Wells

In the present study we calculate the energy values and the spatial distributions of the bound electronic states in some diffused quantum wells. The calculations are performed within the virtual crystal approximation, $sp^3 s^*$ spin dependent empirical tight-binding model and the surface Green function matching method. A good agreement is found between our results and experimental data obtained for AlGaAs/GaAs quantum wells with thermally induced changes in the profile at the interfaces. Our calculations show that for diffusion lengths $L_{D}=20\div100$ {\AA} the transition (C3-HH3) is not sensitive to the diffusion length, but the transitions (C1-HH1), (C1-LH1), (C2-HH2) and (C2-LH2) display large "blue shifts" as L_{D} increases. For diffusion lengths $L_{D}=0\div20$ {\AA} the transitions (C1-HH1) and (C1-LH1) are less sensitive to the L_{D} changes than the (C3-HH3) transition. The observed dependence is explained in terms of the bound states spatial distributions.Comment: ReVTeX file, 7pp., no macros, 4 figures available on the reques