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Minimum Flow (minimum + flow)
Selected AbstractsEffects of floods versus low flows on invertebrates in a New Zealand gravel-bed riverFRESHWATER BIOLOGY, Issue 12 2006ALASTAIR M. SUREN Summary 1. Floods and low flows are hydrological events that influence river ecosystems, but few studies have compared their relative importance in structuring invertebrate communities. Invertebrates were sampled in riffles and runs at eight sites along 40 km of a New Zealand gravel-bed river every 1,3 months over 2.5 years, during which time a number of large flood and low flow events occurred. Flows were high in winter and spring, and low in summer and autumn. Four flow-related variables were calculated from hydrological data: flow on the day of sampling (Qsample), maximum and minimum flow between successive samples (Qmax and Qmin, respectively), and the number of days since the last bed-moving flood (Ndays). 2. The invertebrate community was summarised by relative densities of the 19 most abundant taxa and four biotic metrics [total abundance, taxon richness, the number of Ephemeroptera, Plecoptera and Trichoptera taxa (i.e. EPT richness), and per cent EPT]. Invertebrate density fluctuated greatly, and was high in summer and autumn, and low during winter and spring. Stepwise multiple regression (SMR) analysis was used to investigate relationships between the invertebrate community and season, flow, habitat and water temperature. 3. Seasonal variables were included in almost 50% of the SMR models, while flow-related variables were included in >75% of models. Densities of many taxa were negatively correlated to Qmin and Qmax, and positively correlated to Ndays, suggesting that while high flows reduced invertebrate densities, densities recovered with increasing time following a flood. Although season and flow were confounded in this study, many of the taxa analysed display little seasonal variation in abundance, suggesting that flow-related variables were more important in structuring communities than seasonal changes in density associated with life-cycles. 4. Five discrete flood and low flow events were identified and changes to invertebrate communities before and after these events examined. Invertebrate densities decreased more commonly after floods than after low flows, and there was a significant positive relationship between the number of taxa showing reductions in density and flood magnitude. Densities of most invertebrates either remained unchanged, or increased after low flow events, except for four taxa whose densities declined after a very long period (up to 9 months) of low flow. This decline was attributed to autogenic sloughing of thick periphyton communities and subsequent loss of habitat for these taxa. 5. Invertebrate communities changed more after floods and the degree of change was proportional to flood magnitude. Community similarity increased with increasing time since the last disturbance, suggesting that the longer stable flows lasted, the less the community changed. These results suggest that invertebrate communities in the Waipara River were controlled by both floods and low flows, but that the relative effects of floods were greater than even extended periods of extreme low flow. 6. Hydraulic conditions in riffles and runs were measured throughout the study. Riffles had consistently faster velocities, but were shallower and narrower than runs at all measured flows. Invertebrate density in riffles was expressed as a percentage of total density and regressed against the flow-related variables to see whether invertebrate locations changed according to flow. Significant negative relationships were observed between the per cent density of common taxa in riffles and Qsample, Qmax and Qmin. This result suggests either that these animals actively drifted into areas of faster velocity during low flows, or that their densities within riffles increased as the width of these habitats declined. [source] Some safety aspects on the design of sparger systems for the oxidation of organic liquidsPROCESS SAFETY PROGRESS, Issue 4 2006Manfred Weber Abstract This article summarizes all important parameters for a proper and safe design of the sparger system for large bubble columns, used for the oxidation of organic liquids with air or oxygen enriched air. As an example, this is done for the oxidation of cumene (isopropylbenzene), which is worldwide used in phenol processes. Based on data in the literature and newly measured flammability limits at 100° C and 5 barg, the potential hazards from uncontrolled gas reactions can be avoided, ultimately avoiding an explosion in the sparger system. For normal operation, a minimum flow of gas is necessary to ensure a uniform flow through all outlets, which are typically holes with a diameter of several millimeters. All holes should be directed towards the vessel bottom to self-drain the sparger. For start-up, a previous inerting of the sparger with nitrogen is preferable. Nevertheless, a certain amount of organic liquid may still be in the sparger system prior to start up. Therefore, the compressed air/oxygen should have a temperature below the Oxidation Initiation Temperature to avoid any initiation of a liquid phase oxidation within the sparger. In addition, the pressure in the sparger system should be high enough to keep the gas phase concentration of the organic liquid below the Lower Flammability Limit. © 2006 American Institute of Chemical Engineers Process Saf Prog, 2006 [source] Onset and Offset Phonation Threshold Flow in Excised Canine Larynges,THE LARYNGOSCOPE, Issue 7 2008Michael F. Regner Abstract Objectives/Hypothesis: In this study, we examined the hypothesis that the minimum flow required for phonation onset, the onset phonation threshold flow (PTF), is greater than the minimum flow to sustain phonation, the offset PTF. We also explored the hypothesis that the ratio of these two (PTF offset divided by PTF onset) falls within [0.707, 1.0]. Study Design: This was a methodology study to measure onset and offset PTFs in 10 excised canine larynges; their ratio (PTF offset divided by PTF onset) was predicted to fall in a specific domain. Methods: The onset and offset PTF and phonation threshold pressure (PTP) values were observed using 10 excised canine larynges mounted on a bench apparatus. The subglottal flow was increased until phonation was observed, and then decreased until phonation ceased; airflow and pressure measurements at critical conditions of phonation were observed as the PTF and PTP. Larynges with elongated vocal folds were then tested to observe PTF and determine if the hypothesis was observed in pathologic-like larynges. Results: The offset PTF was always less than the onset PTF (P , .0001) and 80.0% of the observed onset-offset PTF ratios were bound by [0.707, 1.0]. Conclusions: PTF onset or offset could be a useful diagnostic parameter of the voice, particularly when used in conjunction with PTP to describe laryngeal resistance and aerodynamic power. Further exploration of the relationship between onset and offset PTF values could augment clinical diagnostic ability and advance current theories on the physics of phonation. [source] Noninvasive Activity-based Control of an Implantable Rotary Blood Pump: Comparative Software Simulation StudyARTIFICIAL ORGANS, Issue 2 2010Dean M. Karantonis Abstract A control algorithm for an implantable centrifugal rotary blood pump (RBP) based on a noninvasive indicator of the implant recipient's activity level has been proposed and evaluated in a software simulation environment. An activity level index (ALI),derived from a noninvasive estimate of heart rate and the output of a triaxial accelerometer,forms the noninvasive indicator of metabolic energy expenditure. Pump speed is then varied linearly according to the ALI within a defined range. This ALI-based control module operates within a hierarchical multiobjective framework, which imposes several constraints on the operating region, such as minimum flow and minimum speed amplitude thresholds. Three class IV heart failure (HF) cases of varying severity were simulated under rest and exercise conditions, and a comparison with other popular RBP control strategies was performed. Pump flow increases of 2.54, 1.94, and 1.15 L/min were achieved for the three HF cases, from rest to exercise. Compared with constant speed control, this represents a relative flow change of 30.3, 19.8, and ,15.4%, respectively. Simulations of the proposed control algorithm exhibited the effective intervention of each constraint, resulting in an improved flow response and the maintenance of a safe operating condition, compared with other control modes. [source] | ||||||||||