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Flow System (flow + system)
Kinds of Flow System Selected AbstractsVariations in Grain Size Analysis with a Time-of-Transition Laser Sizer (Galai CIS-50) using a Gravitational Flow SystemPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 6 2004Björn Bohling Abstract This study deals with grain size analysis with a Laser Sizer Galai CIS-50. This device utilizes the time-of-transition method and is equipped with a module for measurements in the range 0.5 to 150,,m along with a gravitational flow system. Experiments were conducted using natural marine sediments. The aim was to determine possible explanations for discrepancies in the measured results that occurred between different operators of the Galai CIS-50. These discrepancies may be due to differences in the technique of inserting a sub-sample into the measurement system. Furthermore, the influence of the sample concentration and the flow velocity in the device's liquid flow cell is considered, since these factors can act as potential sources of inaccuracies and errors in the experimental setup. Strong variations in the results occurred, which were mainly due to problems in the detection of particles >20,,m. In the range>20,,m gaps appeared in the registration of the size distribution. An improvement in reproducibility was achieved by using a pipette instead of a beaker for the insertion step. Nevertheless, the standard deviation for mean grain sizes of natural marine sediments obtained with the Galai CIS-50 is still about 20%. [source] Laser Flash Photolysis in a O3/Cl2 Mixture at 266 nm in a Very Low-Pressure Flow System,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2005Jorge Codnia ABSTRACT The laser flash photolysis in a very low-pressure flow system with mass spectrometry detection technique was developed for the study of oxidation reactions of chlorofluorocarbons. In this work, we have studied the UV photolysis of O3 in the presence of Cl2 at room temperature, which presents two catalytic cycles of O3 depletion with efficiencies dependent on the partial pressures in the photoreactor. The ozone dissociation was initiated with fourth harmonic pulses of a Nd:YAG laser. The detection of the reactants and the final and intermediate reaction products was performed with real-time mass spectrometry. The variations of the O3, Cl2 and ClO concentration were measured. The equations system associated to a proposed kinetic scheme was solved numerically and excellent agreement with the experimental results was obtained. The results from this work allowed the determination of the wall loss rates of the O(1D), Cl and ClO radicals. [source] The short-term effect of latanoprost on intraocular pressure and pulsatile ocular blood flowACTA OPHTHALMOLOGICA, Issue 1 2002Gerasimos T. Georgopoulos ABSTRACT. Purpose:, There is evidence that ocular blood flow plays a critical role in the clinical course of glaucoma. Any reduction in ocular blood flow due to topical antiglaucoma treatment should therefore be avoided. This study aimed to evaluate the short-term effect of local latanoprost application on ocular hemodynamics. Methods:, Intraocular pressure (IOP), ocular pulse amplitude (OPA), ocular pulse volume (OPV), systemic blood pressure, heart rate and the pulsatile component of ocular blood flow (POBF) were recorded using a pneumotonometer linked to the Langham Ocular Blood Flow System in 24 patients in a prospective, open-label study before and after 1 week of topical latanoprost application in both eyes. Twenty of the subjects had primary open-angle glaucoma and four had ocular hypertension. Results:, After 1 week of latanoprost treatment, IOP decreased significantly 6.2 ± 2.9 mmHg in OD (P < 0.001) and 6.2 ± 3.2 mmHg in OS (P < 0.001). Pulsatile OBF increased significantly by 201.2 ± 167.4 µL/min in OD (P < 0.001) and 203.8 ± 187.3 µL/min in OS (P < 0.001). Ocular pulse amplitude and OPV showed statistically significant increases (P < 0.05 and P < 0.001 respectively). Blood pressure and heart rate did not change significantly. Conclusion:, Our results indicate that 1 week after latanoprost application, POBF, OPA and OPV were significantly increased in the eyes treated. More information on the perfusion of the optic nerve head is needed before the relevance of these findings to optic nerve head blood flow can be interpreted correctly. [source] An Integrated Microreactor System for Self-Optimization of a Heck Reaction: From Micro- to Mesoscale Flow Systems,ANGEWANDTE CHEMIE, Issue 39 2010Jonathan P. McMullen Aufbauen, anschalten, fertig: Die Kombination einer Rückkopplungssteuerung mit Durchflussoperationen in Mikroreaktoren (siehe Bild) ermöglicht eine vollautomatische Online-Reaktionsoptimierung. An einer Heck-Reaktion wird das Potenzial für eine schnelle Vielvariablen-Optimierung demonstriert, die mit minimalen Materialmengen auskommt. Die optimalen Bedingungen lassen sich schnell in einen 50-mal größeren Maßstab übertragen. [source] A Comparison of the Mixing Characteristics in Single- and Two-Phase Grid-Generated Turbulent Flow SystemsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 6 2004J.S. Moghaddas Abstract The mixing process is studied in grid-generated turbulent flow for single- and bubbly two-phase flow systems. Concentration and mixing characteristics in the liquid phase are measured with the aid of a PLIF/PLIF arrangement. A nearly isotropic turbulent flow field is generated at the center of the vertical pipe by using a honeycomb, three grids and a contraction. In two-phase flow experiments, air bubbles were injected into the flow from a rectangular grid, with mesh size M = 6 mm, which is placed midway between two circular grids each with a mesh size of M = 2 mm. For single-phase flow, the normalized mean concentration cross-stream profiles have rather similar Gaussian shapes, and the cross-stream profiles of the normalized root-mean-square (RMS) values of concentration were found to be quite similar. Cross-stream profiles of the mean concentration, for bubbly two-phase flow, were also found to be quite similar, but they did not have the Gaussian shape of the profiles for single-phase flow. Almost self-similar behavior was also found for the RMS values of the concentration in two-phase systems. The turbulent diffusion coefficient in the liquid phase was also calculated. At the center of the plume, the flow was found to have a periodic coherent structure, probably of vortex shedding character. Observations showed that the period of oscillation is higher in the case of two-phase flow than in single-phase flow. [source] Determination of Diazepam, Temazepam and Oxazepam at the Lead Film Electrode by Adsorptive Cathodic Stripping VoltammetryELECTROANALYSIS, Issue 17-18 2010Katarzyna Tyszczuk Abstract The determination of psychoactive 1,4-benzodiazepine drugs is of relevant interest in clinical, biomedical areas. Therefore a highly sensitive and simple voltammetric method for the determination of temazepam, diazepam and oxazepam at an in situ plated lead film electrode was developed. The method was successfully applied to the determination of diazepam and temazepam in pharmaceutical formulations with minimum sample manipulation and oxazepam in human urine samples without any separation steps. The determinations of oxazepam in human urine samples were performed in a flow system. Therefore a previous extraction procedure was not necessary to separate the active compound before its determination. [source] Electrical field-assisted solid-phase extraction coupled on-line to capillary electrophoresis-mass spectrometryELECTROPHORESIS, Issue 10 2008Gabriel Morales-Cid Abstract A substantial demand currently exists for analytical methods affording the determination of very low concentrations of analytes in complex matrices, such as those of environmental and biological samples, as simply as possible. However, the pretreatment of complex samples, which is unavoidable prior to CE-MS analysis, is usually complicated and time-consuming. In this work, we used voltage-assisted SPE for the first time as an alternative to conventional treatments for preconcentrating and purifying analytes. To this end, we used a simple flow system coupled on-line to CE-MS equipment. The system is quite robust and provides reproducible peak areas (the precision ranges from 2.5 to 3.8%). Also, it provides increased sensitivity affording the determination of trace amounts (nanogram per liter levels) of analytes in only a few milliliters of sample. The proposed system was applied to the determination of members of two compound families (viz. tetracyclines and amines). [source] Synthesis,Structure,Property Relationships for Hyperbranched Aminosilica CO2 AdsorbentsADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Jeffrey H. Drese Abstract Hyperbranched aminosilica (HAS) adsorbents are prepared via the ring-opening polymerization of aziridine in the presence of mesoporous silica SBA-15 support. The aminopolymers are covalently bound to the silica support and capture CO2 reversibly in a temperature swing process. Here, a range of HAS materials are prepared with different organic loadings. The effects of organic loading on the structural properties and CO2 adsorption properties of the resultant hybrid materials are examined. The residual porosity in the HAS adsorbents after organic loading, as well as the molecular weights and degrees of branching for the separated aminopolymers, are determined to draw a relationship between adsorbent structure and performance. Humid adsorption working capacities and apparent adsorption kinetics are determined from experiments in a packed-bed flow system monitored by mass spectrometry. Dry adsorption isotherms are presented for one HAS adsorbent with a high amine loading at 35 and 75,°C. These combined results establish the relationships between adsorbent synthesis, structure, and CO2 adsorption properties of the family of HAS materials. [source] Ground Water Sustainability: Methodology and Application to the North China PlainGROUND WATER, Issue 6 2008Jie Liu This article analyzes part of a ground water flow system in the North China Plain (NCP) subject to severe overexploitation and rapid depletion. A transient ground water flow model was constructed and calibrated to quantify the changes in the flow system since the predevelopment 1950s. The flow model was then used in conjunction with an optimization code to determine optimal pumping schemes that improve ground water management practices. Finally, two management scenarios, namely, urbanization and the South-to-North Water Transfer Project, were evaluated for their potential impacts on the ground water resources in the study area. Although this study focuses on the NCP, it illustrates a general modeling framework for analyzing the sustainability, or the lack thereof, of ground water flow systems driven by similar hydrogeologic and economic conditions. The numerical simulation is capable of quantifying the various components of the overall flow budget and evaluating the impacts of different management scenarios. The optimization modeling allows the determination of the maximum "sustainable pumping" that satisfies a series of prescribed constraints. It can also be used to minimize the economic costs associated with ground water development and management. Furthermore, since the NCP is one of the most water scarce and economically active regions in the world, the conclusions and insights from this study are of general interest and international significance. [source] Geochemical Factors Controlling Radium Activity in a Sandstone AquiferGROUND WATER, Issue 4 2006Tim Grundl Geochemical processes behind the occurrence of radium activities in excess of the U.S. EPA's drinking water limit of 5 pCi/L combined radium were investigated in a regional sandstone aquifer located in southeastern Wisconsin. Geochemical speciation modeling (PHREEQC 2.7) combined with a detailed understanding of the regional flow system provided by recent flow modeling efforts was used to determine that radium coprecipitation into barite controls radium activity in the unconfined portion of the aquifer. As the aquifer transitions from unconfined to confined conditions, radium levels rise and the water becomes more sulfate rich yet the aquifer remains at saturation with barite throughout. Calculations based on published distribution coefficients and the observed Ra:Ba atomic ratios indicate that barite contains ,12 ,g/kg coprecipitated radium. Confined portions of the aquifer have high concentrations of sulfate, and barium concentrations become too low to be an effective control on radium activity. Additional, as yet undefined, controls on radium are operative in the downgradient, confined portion of the aquifer. [source] Radon (222Rn) in Ground Water of Fractured Rocks: A Diffusion/Ion Exchange ModelGROUND WATER, Issue 4 2004Warren W. Wood Ground waters from fractured igneous and high-grade sialic metamorphic rocks frequently have elevated activity of dissolved radon (222Rn). A chemically based model is proposed whereby radium (226Ra) from the decay of uranium (238U) diffuses through the primary porosity of the rock to the water-transmitting fracture where it is sorbed on weathering products. Sorption of 226Ra on the fracture surface maintains an activity gradient in the rock matrix, ensuring a continuous supply of 226Ra to fracture surfaces. As a result of the relatively long half-life of 226Ra (1601 years), significant activity can accumulate on fracture surfaces. The proximity of this sorbed 226Ra to the active ground water flow system allows its decay progeny 222Rn to enter directly into the water. Laboratory analyses of primary porosity and diffusion coefficients of the rock matrix, radon emanation, and ion exchange at fracture surfaces are consistent with the requirements of a diffusion/ion-exchange model. A dipole-brine injection/withdrawal experiment conducted between bedrock boreholes in the high-grade metamorphic and granite rocks at the Hubbard Brook Experimental Forest, Grafton County, New Hampshire, United States (42°56,N, 71°43,W) shows a large activity of 226Ra exchanged from fracture surfaces by a magnesium brine. The 226Ra activity removed by the exchange process is 34 times greater than that of 238U activity. These observations are consistent with the diffusion/ion-exchange model. Elutriate isotopic ratios of 223Ra/226Ra and 238U/226Ra are also consistent with the proposed chemically based diffusion/ion-exchange model. [source] Ground Water Discharge and Nitrate Flux to the Gulf of MexicoGROUND WATER, Issue 3 2004Carolyn B. Dowling Ground water samples (37 to 186 m depth) from Baldwin County, Alabama, are used to define the hydrogeology of Gulf coastal aquifers and calculate the subsurface discharge of nutrients to the Gulf of Mexico. The ground water flow and nitrate flux have been determined by linking ground water concentrations to 3H/3He and 4He age dates. The middle aquifer (A2) is an active flow system characterized by postnuclear tritium levels, moderate vertical velocities, and high nitrate concentrations. Ground water discharge could be an unaccounted source for nutrients in the coastal oceans. The aquifers annually discharge 1.1 ± 0.01 × 108 moles of nitrate to the Gulf of Mexico, or 50% and 0.8% of the annual contributions from the Mobile-Alabama River System and the Mississippi River System, respectively. In southern Baldwin County, south of Loxley, increasing reliance on ground water in the deeper A3 aquifer requires accurate estimates of safe ground water withdrawal. This aquifer, partially confined by Pliocene clay above and Pensacola Clay below, is tritium dead and contains elevated 4He concentrations with no nitrate and estimated ground water ages from 100 to 7000 years. The isotopic composition and concentration of natural gas diffusing from the Pensacola Clay into the A3 aquifer aids in defining the deep ground water discharge. The highest 4He and CH4 concentrations are found only in the deepest sample (Gulf State Park), indicating that ground water flow into the Gulf of Mexico suppresses the natural gas plume. Using the shape of the CH4 -He plume and the accumulation of 4He rate (2.2 ± 0.8 ,cc/kg/1000 years), we estimate the natural submarine discharge and the replenishment rate for the A3 aquifer. [source] Variability of Isotope and Major Ion Chemistry in the Allequash Basin, WisconsinGROUND WATER, Issue 7 2003John F. Walker As part of ongoing research conducted at one of the U.S. Geological Survey's Water, Energy, and Biogeochem-ical Budgets sites, work was undertaken to describe the spatial and temporal variability of stream and ground water isotopic composition and cation chemistry in the Trout Lake watershed, to relate the variability to the watershed flow system, and to identify the linkages of geochemical evolution and source of water in the watershed. The results are based on periodic sampling of sites at two scales along Allequash Creek, a small headwater stream in northern Wisconsin. Based on this sampling, there are distinct water isotopic and geochemical differences observed at a smaller hillslope scale and the larger Allequash Creek scale. The variability was larger than expected for this simple watershed, and is likely to be seen in more complex basins. Based on evidence from multiple isotopes and stream chemistry, the flow system arises from three main source waters (terrestrial-, lake-, or wetland-derived recharge) that can be identified along any flowpath using water isotopes together with geochemical characteristics such as iron concentrations. The ground water chemistry demonstrates considerable spatial variability that depends mainly on the flow-path length and water mobility through the aquifer. Calcium concentrations increase with increasing flowpath length, whereas strontium isotope ratios increase with increasing extent of stagnation in either the unsaturated or saturated zones as waters move from source to sink. The flowpath distribution we identify provides important constraints on the calibration of ground water flow models such as that undertaken by Pint et al. (this issue). [source] Flowpath Delineation and Ground Water Age, Allequash Basin, WisconsinGROUND WATER, Issue 7 2003Christine D. Pint An analysis of ground water flowpaths to a lake and creek in northern Wisconsin shows the flow system in a geologically simple basin dominated by lakes can be surprisingly complex. Differences in source area, i.e., lakes or terrestrial, combined with the presence of intervening lakes, which may or may not capture underflowing ground water as water moves downgradient from recharge areas, contribute to a complex mix of flowpaths. The result is water of different chemistry and vastly different ages may discharge in close proximity. Flowpaths, travel times, and capture zones in the Allequash Basin in northern Wisconsin were delineated using particle tracking based on a calibrated steady-state ground water flow model. The flowpath analysis supports the conclusions of Walker et al. (2003) who made inferences about flowpath characteristics from isotope and major ion chemistry. Simulated particle tracking agreed with Walker et al.'s measurements of water source (lake or terrestrial recharge) in the stream subsurface and also supported their assertion that ground water with a high calcium concentration in the lower basin of Allequash Lake is derived from long flowpaths. Numerical simulations show that ground water discharging in this area originates more than 5 km away in a source area located upgradient of Big Muskellunge Lake, which is upgradient of Allequash Lake. These results graphically illustrate that in settings with multiple sources of water with different age characteristics and converging flowlines (like the Allequash Basin) it may be difficult to obtain accurate estimates of ground water age by chemical analyses of ground water. [source] A Numerical Model and Spreadsheet Interface for Pumping Test AnalysisGROUND WATER, Issue 4 2001Gary S. Johnson Curve-matching techniques have been the standard method of aquifer test analysis for several decades. A variety of techniques provide the capability of evaluating test data from confined, unconfined, leaky aquitard, and other conditions. Each technique, however, is accompanied by a set of assumptions, and evaluation of a combination of conditions can be complicated or impossible due to intractable mathematics or nonuniqueness of the solution. Numerical modeling of pumping tests provides two major advantages: (1) the user can choose which properties to calibrate and what assumptions to make; and (2) in the calibration process the user is gaining insights into the conceptual model of the flow system and uncertainties in the analysis. Routine numerical modeling of pumping tests is now practical due to computer hardware and software advances of the last decade. The RADFLOW model and spreadsheet interface presented in this paper is an easy-to-use numerical model for estimation of aquifer properties from pumping test data. Layered conceptual models and their properties are evaluated in a trial-and-error estimation procedure. The RADFLOW model can treat most combinations of confined, unconfined, leaky aquitard, partial penetration, and borehole storage conditions. RADFLOW is especially useful in stratified aquifer systems with no identifiable lateral boundaries. It has been verified to several analytical solutions and has been applied in the Snake River Plain Aquifer to develop and test conceptual models and provide estimates of aquifer properties. Because the model assumes axially symmetrical flow, it is limited to representing multiple aquifer layers that are laterally continuous. [source] A Model of Cells as Practical Approach to Simulate Spring Flow in the Itxina Karstic Aquifer, Basque Country, SpainGROUND WATER, Issue 3 2001J. Gárfias Soliz The aim of this study is to apply a parsimonious hydrologic model to the Itxina karstic aquifer that can predict changes in discharge resulting from variable inputs (recharge). The Itxina Aquifer was divided into four cells corresponding to different recharge areas. Each cell was treated as a tank to characterize the conditions within the cell. In the model, when the reservoir boundaries coincide with the position of the siphons, the signal simulated is sensitive to input pulses of the recharge. This supports the hypothesis that the siphons are the controlling mechanism in the flow system of the aquifer. The good agreement between predicted and measured discharges demonstrates the ability of the model to simulate the flow in the Itxina Aquifer. These results demonstrated that the hydraulic conductivity increases downstream within the aquifer. The hydraulic conductivities obtained by calibration varied between 4.2 × 10,3 m/s upstream of the aquifer, 6.0 × 10,2 m/s in the central region, and 9.5 × 10,1 m/s in the lower region of the aquifer. These values seem reasonable because the underground features in the principal caves show that the density of caves increases downstream in the Itxina Aquifer. The simple representation of the system produced results comparable to traditional ground water models with fewer data requirements and calibration parameters. [source] Environmental isotopic and hydrochemical characteristics of groundwater systems in Daying and Qicun geothermal fields, Xinzhou Basin, Shanxi, ChinaHYDROLOGICAL PROCESSES, Issue 22 2010Dongmei Han Abstract The conceptual hydrogeological model of the low to medium temperature Daying and Qicun geothermal fields has been proposed, based on hydrochemical characteristics and isotopic compositions. The two geothermal fields are located in the Xinzhou basin of Shanxi, China and exhibit similarities in their broad-scale flow patterns. Geothermal water is derived from the regional groundwater flow system of the basin and is characterized by Cl·SO4 -Na type. Thermal water is hydrochemically distinct from cold groundwater having higher total dissolved solids (TDS) (>0·8 g/l) and Sr contents, but relatively low Ca, Mg and HCO3 contents. Most shallow groundwater belongs to local flow systems which are subject to evaporation and mixing with irrigation returns. The groundwater residence times estimated by tritium and 14C activities indicate that deep non-thermal groundwater (130,160 m) in the Daying region range from modern (post-1950s) in the piedmont area to more than 9·4 ka BP (Before Present) in the downriver area and imply that this water belong to an intermediate flow system. Thermal water in the two geothermal fields contains no detectable active 14C, indicating long residence times (>50 ka), consistent with this water being part of a large regional flow system. The mean recharge elevation estimated by using the obtained relationship Altitude (m) = , 23·8 × ,2H (, ) , 121·3, is 1980 and 1880 m for the Daying and Qicun geothermal fields, respectively. The annual infiltration rates in the Daying and Qicun geothermal fields can be estimated to be 9029 × 103 and 4107 × 103 m3/a, respectively. The variable 86Sr/87Sr values in the thermal and non-thermal groundwater in the two fields reflect different lithologies encountered along the flow path(s) and possibly different extents of water-rock interaction. Based on the analysis of groundwater flow systems in the two geothermal fields, hydrogeochemical inverse modelling was performed to indicate the possible water-rock interaction processes that occur under different scenarios. Copyright © 2010 John Wiley & Sons, Ltd. [source] A kinetic and product study of reaction of chlorine atom with CH3CH2ODINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2004Mary A. Crawford The reaction of atomic chlorine with CH3CH2OD has been examined using a discharge fast flow system coupled to a mass spectrometer combined with the relative rate method (RR/DF/MS). At 298 ± 2 K, the rate constant for the Cl + CH3CH2OD reaction was determined using cyclohexane as a reference and found to be k3 = (1.13 ± 0.21) × 10,10 cm3 molecule,1 s,1. Mass spectral studies of the reaction products resulted in yields greater than 97% for the combined hydrogen abstraction at the , and , sites (3a + 3b) and less than 3% at the hydroxyl site (3c). As a calibration of the apparatus and the RR/DF/MS technique, the rate constant of the Cl + CH3CH2OH reaction was also determined using cyclohexane as the reference, and a value of k2 = (1.05 ± 0.07) × 10,10 cm3 molecule,1 s,1 was obtained at 298 ± 2 K, which was in excellent agreement with the value given in current literature. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 584,590, 2004 [source] Thermodynamic optimization of internal structure in a fuel cellINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2004Jose V. C. Vargas Abstract This paper shows that the internal structure (relative sizes, spacings) of a fuel cell can be optimized so that performance is maximized at the global level. The optimization of flow geometry begins at the smallest (elemental) level, where the fuel cell is modelled as a unidirectional flow system. The polarization curve, power and efficiency are obtained as functions of temperature, pressure, geometry and operating parameters. Although the model is illustrated for an alkaline fuel cell, it may be applied to other fuel cell types by changing the reaction equations and accounting for the appropriate energy interactions. The optimization of the internal structure is subjected to fixed total volume. There are four degrees of freedom in the optimization, which account for the relative thicknesses of the two (anode and cathode) diffusion layers, two reaction layers and the space occupied by the electrolyte solution. The available volume is distributed optimally through the system so that the total power is maximized. Numerical results show that the optima are sharp, and must be identified accurately. Temperature and pressure gradients play important roles, especially as the fuel and oxidant flow paths increase. The optimized internal structure is reported in dimensionless form. Directions for future improvements in flow architecture (constructal design) are discussed. Copyright © 2004 John Wiley & Sons, Ltd. [source] Fast and Enantioselective Production of 1-Aryl-1-propanols through a Single Pass, Continuous Flow ProcessADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2008Miquel Abstract A functional polymer 4, obtained by reaction of (R)-2-(1-piperazinyl)-1,1,2-triphenylethanol with a Merrifield resin, has been loaded in a packed bed reactor and used as catalyst for the continuous enantioselective production of 1-arylpropanols by ethylation of aromatic aldehydes. The high catalytic activity depicted by 4 allows the complete conversion of the substrates with the use of stoichiometric reagent ratios and unprecedently short residence times (down to 2.8,min). In practice, a single-pass operation can be used for all the studied aldehydes, and productions of up to 13.0 mol/g,h are recorded. The sequential operation of the flow system for the uninterrupted synthesis of a small library of enantiopure 1-arylpropanols is also reported. [source] Resolution of structure characteristics of AE signals in multiphase flow system,From data to informationAICHE JOURNAL, Issue 10 2009Yi-Jun He Abstract This investigation was performed to study the underlying structure characteristics of acoustic emission (AE) signals, which could be helpful not only to understand a relatively complete picture of hydrodynamics in multiphase flow systems, but also to extract the most useful information from the original signals with respect to a particular measurement requirement. However, due to AE signals are made up of emission from many acoustic sources at different scales, the resolution of AE signals is often very complicated and appears to be relatively poorly researched. In this study, the structure characteristics of AE signals measured both in gas,solid fluidized bed and liquid,solid stirred tank were researched in detail by resorting to wavelet transform and rescaled range analysis. A general criterion was proposed to resolve AE signals into three physical-related characteristic scales, i.e., microscale, mesoscale, and macroscale. Multiscale resolution of AE signals implied that AE signals in microscale represented totally the dynamics of solid phase and could be applied to measure particle-related properties. Furthermore, based on the structure characteristics of AE signals, useful features related to particles motion were extracted to establish two new prediction models, one for on-line measurements of particle size distribution (PSD) and average particle size in gas,solid fluidized bed and the other for on-line measurement of the suspension height in liquid,solid stirred tank. The prediction results indicated that (1) measurements of PSD and average particle size using AE method showed a fairly good agreement with that using sieve method both for laboratory scale and plant scale fluidized beds, and (2) measurements of the suspension height using AE method showed a fairly good agreement with that using visual method. The results thus validated that the extracted features based on analyses of structure characteristics of AE signals were very useful for establishing effective on-line measurement models with respect to some particular applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Odontocete suction feeding: Experimental analysis of water flow and head shapeJOURNAL OF MORPHOLOGY, Issue 12 2006Alexander J. WerthArticle first published online: 13 NOV 200 Abstract The role of cranial morphology in the generation of intraoral and oropharyngeal suction pressures in odontocetes was investigated by manipulating the jaw and hyolingual apparatus of submerged heads of three species presenting varied shapes. Hyoid and gular muscles were manually employed to depress and retract the tongue. Pressures were recorded at three locations in the oral cavity, as gape and site, speed, and force of pull were varied. A biomechanical model was also developed to evaluate pressure data. The species with the shortest, bluntest head and smallest mouth opening generated greater negative pressures. Suction generation diminished sharply as gape increased. Greatest negative pressures attained were around ,45 mmHg (,6,000 Pa), a magnitude deemed suitable for capture of small live prey. Odontocetes utilizing this bidirectional flow system should profit by evolution of a rounder mouth opening through progressive shortening and widening of the rostrum and jaws, a trend evident in cranial measurements from fossil and recent odontocetes. Blunt heads correlate with anatomical, ecological, and behavioral traits associated with suction feeding. Small-gape suction (with minimally opened jaws) could be used by odontocetes of all head and oral shapes to draw prey sufficiently close to the mouth for suction ingestion or grasping via dentition. Principal limitations of the experimental and mathematical simulations include assumption of a stationary odontocete with static (open or closed) jaws and potential scaling issues with differently sized heads and gapes. J. Morphol., 2006. © 2006 Wiley-Liss, Inc. [source] Adherence of Streptococcus mutans to various restorative materials in a continuous flow systemJOURNAL OF ORAL REHABILITATION, Issue 3 2004S. Eick summary, A continuous flow system was developed to evaluate the adhesion of Streptococcus mutans ATCC 25175 to filling materials (Ariston, Tetric, Dyract, Compoglass, Vitremer, Aqua Ionofil, Ketac Fil, amalgam, Galloy and ceramics as controls). Streptococcus mutans was added to saliva-coated test specimens, and a nutrient broth permanently supplied over a time period of 48 h and then the weight of plaque, the number and viability of the bacteria adhering to the materials were determined. The weights of artificial plaque on all filling materials tested were higher than those on ceramics, the highest values were measured on the glass,ionomers. The amount of plaque correlates with the surface roughness, whereas there was no correlation of the surface roughness with the number of colony-forming units (CFU) of S. mutans. The CFU of adhering S. mutans also depends on the viability of the bacteria. The plaque on Ketac Fil contained a high number of viable bacteria. The fluorides of glass,ionomers do not efficiently prevent the attachment and the viability of S. mutans. [source] Development of a silica monolith microbioreactor entrapping highly activated lipase and an experiment toward integration with chromatographic separation of chiral estersJOURNAL OF SEPARATION SCIENCE, JSS, Issue 17 2007Koei Kawakami Abstract Microbioreactors are effective for high-throughput production of expensive products from small amounts of substrates. Lipases are versatile enzymes for chiral syntheses, and are highly activated when immobilized in alkyl-substituted silicates by the sol,gel method. For practical application of sol,gel immobilized lipases to a flow system, a microbioreactor loaded with a macroporous silica monolith is well suited, because it can be easily integrated with a chromatographic separator for optical resolution. We attempted to develop a microbioreactor containing a silica monolith-immobilized lipase. A nonshrinkable silica monolith was first formed from a 4:1 mixture of methyltrimethoxysilane (MTMS) and tetramethoxysilane (TMOS). It was then coated with silica precipitates entrapping lipase, derived from a 4:1 mixture of n -butyltrimethoxysilane (BTMS) and TMOS. As a result, monolith treated with the BTMS-based silicate entrapping lipase exhibited approximately ten times higher activity than nontreated monolith-immobilized lipase derived from the MTMS-based silicate, in transesterification between glycidol and vinyl n -butyrate in isooctane. A commercially available chiral column was connected in series to the monolith microbioreactor, and a pulse of substrate solution was supplied at the inlet of the reactor. Successful resolution of the racemic ester produced was achieved in the chromatographic column. [source] ANALYTICAL REGRESSION STAGE ANALYSIS FOR DEVILS HOLE, DEATH VALLEY NATIONAL PARK, NEVADA,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 4 2006M.S. Bedinger ABSTRACT: Devils Hole is a collapse depression connected to the regional carbonate aquifer of the Death Valley ground water flow system. Devils Hole pool is home to an endangered pupfish that was threatened when irrigation pumping in nearby Ash Meadows lowered the pool stage in the 1960s. Pumping at Ash Meadows ultimately ceased, and the stage recovered until 1988, when it began to decline, a trend that continued until at least 2004. Regional ground water pumping and changes in recharge are considered the principal potential stresses causing long term stage changes. A regression was found between pumpage and Devils Hole water levels. Though precipitation in distant mountain ranges is the source of recharge to the flow system, the stage of Devils Hole shows small change in stage from 1937 to 1963, a period during which ground water withdrawals were small and the major stress on stage would have been recharge. Multiple regression analyses, made by including the cumulative departure from normal precipitation with pumpage as independent variables, did not improve the regression. Drawdown at Devils Hole was calculated by the Theis Equation for nearby pumping centers to incorporate time delay and drawdown attenuation. The Theis drawdowns were used as surrogates for pumpage in multiple regression analyses. The model coefficient for the regression, R2= 0.982, indicated that changes in Devils Hole were largely due to effects of pumping at Ash Meadows, Amargosa Desert, and Army 1. [source] Comparative assessment of the water balance and hydrology of selected Ethiopian and Kenyan Rift LakesLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 3 2008Tenalem Ayenew Abstract The study area is part of the East African Rift system, characterized by a cluster of lakes occupying an extremely faulted rift floor with geothermal manifestations. Some of the lakes illustrated contrasting water levels and size evolution over the last few decennia, believed to have been caused by various natural and anthropogenic factors. The relative importance of these factors, however, is unknown. This study attempts to present the hydrology of the lakes in a broader context, by giving more emphasis to lake water level fluctuations and to the water balance. These factors have far-reaching implications in regard to future management of the lake basin water. It also provides information on the relation of the groundwater with the lakes, and with the local and regional groundwater flow system from the adjacent highlands to the floor of the Rift. The methods utilized in this study include conventional hydrogeological field surveys, and hydrometeorological and data analyses, coupled with digital image processing and spatial analysis under a Geographic Information System environment. Ancillary supporting information has been obtained from environmental isotopes and hydrochemical data. The study results indicate the terminal Ethiopian lakes changed in size and water level significantly over the last half century. In contrast, the Kenyan lakes only exhibited slight changes. The lakes in both countries exhibit a striking similarity in their subsurface hydraulic connection, and are strongly governed by complex rift geological structures. Groundwater plays a vital role in the water balance of the study lakes. The study results indicate that future sustainable use of the study lakes demands that serious attention be given to the role of the groundwater component of the lake water balances. [source] Variations in Grain Size Analysis with a Time-of-Transition Laser Sizer (Galai CIS-50) using a Gravitational Flow SystemPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 6 2004Björn Bohling Abstract This study deals with grain size analysis with a Laser Sizer Galai CIS-50. This device utilizes the time-of-transition method and is equipped with a module for measurements in the range 0.5 to 150,,m along with a gravitational flow system. Experiments were conducted using natural marine sediments. The aim was to determine possible explanations for discrepancies in the measured results that occurred between different operators of the Galai CIS-50. These discrepancies may be due to differences in the technique of inserting a sub-sample into the measurement system. Furthermore, the influence of the sample concentration and the flow velocity in the device's liquid flow cell is considered, since these factors can act as potential sources of inaccuracies and errors in the experimental setup. Strong variations in the results occurred, which were mainly due to problems in the detection of particles >20,,m. In the range>20,,m gaps appeared in the registration of the size distribution. An improvement in reproducibility was achieved by using a pipette instead of a beaker for the insertion step. Nevertheless, the standard deviation for mean grain sizes of natural marine sediments obtained with the Galai CIS-50 is still about 20%. [source] Laser Flash Photolysis in a O3/Cl2 Mixture at 266 nm in a Very Low-Pressure Flow System,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2005Jorge Codnia ABSTRACT The laser flash photolysis in a very low-pressure flow system with mass spectrometry detection technique was developed for the study of oxidation reactions of chlorofluorocarbons. In this work, we have studied the UV photolysis of O3 in the presence of Cl2 at room temperature, which presents two catalytic cycles of O3 depletion with efficiencies dependent on the partial pressures in the photoreactor. The ozone dissociation was initiated with fourth harmonic pulses of a Nd:YAG laser. The detection of the reactants and the final and intermediate reaction products was performed with real-time mass spectrometry. The variations of the O3, Cl2 and ClO concentration were measured. The equations system associated to a proposed kinetic scheme was solved numerically and excellent agreement with the experimental results was obtained. The results from this work allowed the determination of the wall loss rates of the O(1D), Cl and ClO radicals. [source] Determination of lead content in medicinal plants by pre-concentration flow injection analysis,flame atomic absorption spectrometryPHYTOCHEMICAL ANALYSIS, Issue 6 2009Marina M. A. Campos Abstract Introduction , Although medicinal plants are widely used throughout the world, few studies have been carried out concerning the levels of heavy metal contaminants present. Such metals are highly toxic to living organisms even in low concentrations owing to their cumulative effect. The present paper describes the the development of a pre-concentration flow injection analysis-flame atomic absorption spectrometric system to determine the lead content in medicinal plants at the ppb level. Objective , To develop a pre-concentration flow injection analysis-flame atomic absorption spectrometric system to determine the lead content in medicinal plants at the ppb level. Methodology , A pre-concentration flow system was coupled to a flame atomic absorption spectrometer. The plant samples were analysed after nitroperchloric digestion. The proposed system was optimised by evaluating the following parameters: nature, concentration and volume of the eluent solution, elution flow rate, elution efficiency, pre-concentration flow rate and pre-concentration time. Results , The proposed system exhibited good performance with high precision and repeatability (RSD , 2.36%), excellent linearity (r = 0.9999), low sample consumption (10.5 mL per determination) and an analytical throughput of 55 samples/h. Lead concentrations ranged from 3.37 ± 0.25 to 7.03 ± 0.51 ,g/g in dry material. This concentration interval is greater than that previously published in the literature. Conclusion , The inclusion of a pre-concentration column in the flow manifold improved the sensitivity of the spectrometer. Thus, it was possible to determine the analyte at the ng/mL level in sample solutions of medicinal plants. This is a very important accomplishment, especially when the cumulative effect of heavy metals in living organisms is considered. Copyright © 2009 John Wiley & Sons, Ltd. [source] Determining acetylcholinesterase inhibitory activity in plant extracts using a fluorimetric flow assayPHYTOCHEMICAL ANALYSIS, Issue 3 2003In Kyung Rhee Abstract A fluorometric assay for acetylcholinesterase inhibitory activity was developed in a flow system using the fluorogenic substrate 7-acetoxy-1-methyl quinolinium iodide which is hydrolysed to the highly fluorescent 7-hydroxy-1-methyl quinolinium iodide. The detection limit of galanthamine is 0.5,µM, which is about 20 times more sensitive than in the colorimetric flow assay. In the presence of 30% methanol or of 5% acetonitrile, about 70% of the enzyme activity could still be detected. Various plant extracts have been screened using the described system including bulbs of Galanthus nivalis, Eucharis amazonica (E. × grandiflora), Crinum powelli and Nerine bowdenii (all members of the Amaryllidaceae), which showed strong AchE inhibitory activity. Copyright © 2003 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||