Measured Concentration Profiles Research Articles

Transport of small polar molecules across nonporous polymeric membranes: I. Experimental procedures and data analysis

The transient measurement of concentration profile within the liquid boundary layer close to the membrane interface and the flux of permeating species across the membrane coupled with transient model of membrane allows a more critical evaluation of membrane transport performance. The experimental procedure for transient measurement of pervaporation fluxes and data obtained for the {ethanol–water}/silicone rubber system and experimental set up for transient dialysis measurement by interferometry technique for the same system was described. A detailed analysis of optical effect accounting for the light deflection in a medium of varying refractive index profile was presented. A numerical procedure was described which is capable to handle the transient models consist of highly nonlinear partial differential equations. The potential of recovering the transport model parameters from the interference fringes was tested by using a hypothetical model system. The results obtained confirm that both the diffusive and equilibrium parameters can be recovered from the interference fringes. The possibility of recovering the transport model parameters for the {ethanol–water}/silicon rubber system from dialysis data and using those parameters for predicting pervaporation performance for the purpose of model validation will be described in forthcoming articles.

Soil and canopy CO2, 13CO2, H2O and sensible heat flux partitions in a forest canopy inferred from concentration measurements

A canopy scale model is presented that utilises Lagrangian dispersal theory to describe the relationship between source distribution and concentration within the canopy. The present study differs from previous studies in three ways: (1) source/sink distributions are solved simultaneously for CO 2 , 13 CO 2 , H 2 O and sensible heat to find a solution consistent with leaf-level constraints imposed by photosynthetic capacity, stomatal and boundary layer conductance, available energy and carbon isotopic discrimination during diffusion and carboxylation; (2) the model is used to solve for parameters controlling the nonlinear source interactions rather than the sources themselves; and (3) this study used plant physiological principles to allow the incorporation of within- and above-canopy measurements of the 13 C/ 12 C ratios of CO 2 as an additional constraint. Source strengths of CO 2 , H 2 O, sensible heat and 13 CO 2 within a Siberian mixed-coniferous forest were constrained by biochemical and energy-balance principles applied to sun and shaded leaves throughout the canopy. Parameters relating to maximum photosynthetic capacity, stomatal conductance, radiation penetration and turbulence structure were determined by the optimisation procedure to match modelled and measured concentration profiles, effectively inverting the concentration data. Ground fluxes of CO 2 , H 2 O and sensible heat were also determined by the inversion. Total ecosystem fluxes predicted from the inversion were compared to hourly averaged above-canopy eddy covariance measurements over a ten-day period, with good agreement. Model results showed that stomatal conductance and maximum photosynthetic capacity were depressed due to the low temperatures experienced during snow melt; radiation penetrated further than simple theoretical predictions because of leaf clumping and penumbra, and stability effects were important in the morning and evening. The inversion was limited by little vertical structure in the concentration profiles, particularly of water vapour, and by co-dependence of canopy parameters. DOI: 10.1034/j.1600-0889.2002.01356.x

Liquid–solid separation phenomena of two-phase turbulent flow in curved pipes

The present study is to contribute some knowledge of phase separation phenomena of liquid–solid two-phase turbulent flow in curved pipes and provide a basis for the invention and development of a new type of curved pipe separator. Firstly, the solid–liquid two-phase flows in two-dimensional (2D) curved channels were numerically simulated using a two-way coupling Euler–Lagrangian scheme. Phase distribution characteristics of 2D curved channel two-phase flow were examined under conditions of different particle size, liquid flowrate and coil curvature. Based on the numerical results, the dynamic effects and contributions to phase separation of particle-subjected forces, including centrifugal force, drag force, pressure gradient force, gravity force, buoyancy force, virtual mass force and lift force, were exposed by kinematic and dynamic analysis along particle trajectories. Secondly, measurement of particle size and concentration profiles in helically coiled tube two-phase flow was conducted using a nonintrusive Malvern 2600 particle sizer based on laser diffraction. Particle size and concentration distribution characteristics of helically coiled tube two-phase flow and the effect of secondary flow on phase separation were analyzed based on experimental data.

Suspension flows in open channels; experimental study

The vertical distribution of the concentration of suspended particles is usually determined by solving the diffusion-convection equation under appropriate boundary conditions. The exponent in the resulting Rouse equation is the Rouse number, defined as z′ = vss /κu. The -value has been subject of much research, being ⋛ 1. This study focuses on the experimental determination of the depth-averaged -value, given by the ratio of the sediment, ε s , and the momentum, ε m , diffusion coefficients. These coefficients were evaluated under laboratory conditions from measurements of instantaneous velocity and concentration profiles, obtained simultaneously by using a non-intrusive sonar instrument, the Acoustic Particle Flux Profiler (APFP). In suspension flows over a movable bed without bed forms the measured -values at capacity condition are smaller than unity, < 1. However, it could also be shown that for flows over a movable bed with bed forms the -values are larger than unity, > 1; this is notably the case in natural waterways.

FLUORINE ANALYSIS IN BIOGENIC AND GEOLOGICAL APATITE BY ANALYTICAL TRANSMISSION ELECTRON MICROSCOPY AND NUCLEAR REACTION ANALYSIS

ABSTRACT In this paper we present fluorine analysis by transmission electron microscopy (TEM-EDX) and measurement of concentration profiles by nuclear reaction analysis with a proton beam (PIGE and microPIGE) on various archaeological bone and dentine material. Fluorine is present as trace element in modern bone and dentine (100–1000 ppm) whose mineral phase consists of a poorly crystalline hydroxylapatite (Ca10(PO4)6 − x(CO3)x(OH)2+x). During the burial time, archaeological bone and dentine accumulate F in the apatite structure. TEM-EDX can evidence fluorine accumulation on a very localised, nanometric scale if its concentration exceeds 1 wt.%. On the contrary, PIGE and microPIGE permit detection of fluorine with a high sensitivity (limit of detection 30 ppm) on a microscopic or macroscopic level. Its spatial resolution can be of 10 µm, but is, however, insufficient to resolve the distribution of fluorine within the bone and dentine apatite nanocrystals. We show the complementarity of the information delivered by each technique on examples of ancient bone and dentine remains from different archaeological and geological sites, dating from the Neolithic Age to the Miocene. Furthermore, the potential to reveal detailed diagenetic changes of bone material of TEM-EDX and of PIGE is evaluated. This is important for the determination of information on the life style of prehistoric societies. Specifically, we show different steps of F enrichment depending on the age and the environment of the samples. Nevertheless, the fluorine content cannot be correlated to the age of the specimens, and high variations have been observed within one bone sample.

Intercomparison of ozone profiles measurements by a differential absorption lidar system and satellite instruments at Buenos Aires, Argentina

A ground-based DIfferential Absorption Lidar (DIAL) system has been implemented at CEILAP (CITEFA-CONICET) laboratory (34°33′S, 58°30′W), located in the Buenos Aires industrial suburbs. The goal is to perform measurements of the stratospheric ozone layer. Systematic measurements of ozone concentration profiles from ∼18 to ∼35 km altitude are performed since early 1999. Our measurements are carried out in 5 h in average during the night and in cloudless conditions. The DIAL system allows us to calculate directly the ozone profile from the lidar backscattering radiation since it is a self-calibrating technique. The signal processing takes into account the influence of the temperature profile on the ozone cross section. The temperature data are obtained from the radiosondes measurements performed at Ezeiza International Airport (34°30′S, 58°18′W), 27 km from DIAL station. The evolution of the stratospheric ozone profile is studied for different months. Results are compared with the data obtained by different satellites SAGE II, HALOE and GOME. The comparisons between our DIAL system and the satellite measurements show an agreement better than 20% for 20–35 km altitude range.

Validation of a Two-Pool Model for the Kinetics of ß2-Microglobulin

Secondary amyloidosis due to beta-2-microglobulin (beta2-m) is a serious long-term complication in patients on regular dialysis therapy. Beta2-m can be considered a middle-molecule marker used to facilitate the assessment of dialysis efficacy. For this purpose, a validated model that calculates characteristic efficacy parameters, such as Kt/V, TAC and generation rate, is needed. There is general agreement that beta2-m-kinetics should be described by a two-pool model, but little has been published to validate such an approach. We measured the beta2-m concentration profiles of eight stable patients during hemodialysis (HD) at the start of treatment, after 30 minutes, after 60 minutes, and every hour until the end. Thereafter they were measured at 10-minute intervals for an hour. The dialyser clearances were determined from the plasma concentrations in front of and behind the dialyser twice during each session - after 1 hour, and 4 hours from the start of treatment. The kinetic parameters of a two-pool model (e.g. the compartment volumes V1 and V2, the mass transfer coefficient K12 and the generation rate G) were determined from the optimal fit of the measured concentration profile. The table below summarises the results by giving the mean and standard deviation for each parameter: [table: see text]. Inter-individual differences in V1/V2 and K12 were high, ranging from 2.5 to 10.0 for V/V2 and from 26 to 140 for K12. Error analysis suggested that these wide ranges were due to the method and that in reality the probable range of V is 25-36% of TBW, of V1/V2 3.5-5.3, and of K12 30-80 ml/min. With standard values for these three parameters (V = 30% of TBW, V/V2 = 4.4 and K12 = 55 ml/m), equal for all patients, and their respective ranges, Kt/W can be calculated with a standard deviation of 13%. Kt/W > 1.2 secures the maximum possible beta2-m removal with three HD treatments a week. The parameters of a two-pool model of beta2-m kinetics can be derived from concentration profiles obtained under routine dialysis conditions, but accuracy is not completely satisfactory. Similar to the dialysis dose for urea (Kt/Vurea) the dialysis dose for beta2-m (Kt/Vbeta2-m) can be calculated from the pre- and post-dialysis concentrations of beta2-m, body weight, ultrafiltration and dialysis time. Kt/Vbeta2-m > 1.2 secures the maximum possible removal of beta2-m in HD with three sessions per week.

The carbon uptake of a mid latitude pine forest growing on sandy soil

Measurements of net ecosystem exchange (NEE) are described over a temperate coniferous forest in The Netherlands. The data show no loss of night-time fluxes at low values of friction velocity. Measurements of concentration profiles show a wide diurnal range in concentration values (50 ppm) during July in the summer compared to November in the late autumn (10 ppm). This is a result of photosynthetic activity during summer. The profiles also show the effect of respiration in the build up of the night-time profiles. The half-hourly day time NEE shows a relation with incoming short-wave radiation when separate classes of specific humidity deficit are defined. Quantum yield varies from 0.0197 to 0.0375. A linear relation was found between NEE and surface conductance at the ecosystem level. The annual carbon sequestration of the forest in 1997 is 338 g m −2 per year. It was estimated that respiration contributed 1221 g C m −2 per year to the NEE. This brings the gross primary production (GPP) of this forest to 1559 g C m −2 per year. The forest shows a clear growing season (positive uptake) of 249 days, but even during the winter the forest acts as a sink for a few hours around noon.

Direct Measurement of Transient Concentration Profiles in Adsorbent Particles and Chromatographic Columns by MRI

Magnetic resonance imaging (MRI) was applied as an in situ imaging technique to study transient adsorption/desorption and chromatographic processes in microporous adsorbents. Transient concentration profiles were measured for several different types of systems: the diffusion of water vapor into a bed of 4A zeolite, the movement of pulses of light hydrocarbons through a chromatographic column of 5A or 13X zeolite, and the transient adsorption/desorption of propane or water vapor in a single extrudate of 13X zeolite. The profiles are approximately as predicted from nonlinear diffusion theory and the effect of isotherm nonlinearity on the form of the transient profiles is clearly apparent. The possibility of distinguishing between the concentration profiles in the gaseous and adsorbed phases by MRI methods is also examined.

Aerial short-range dispersion of volatilized pesticides from an area source.

Owing to legal provisions, pesticides have to be applied in such a way that there is no unacceptable influence on human health and the environment at nearby non-target areas. In order to quantify their concentration over and downwind of agricultural target plots of 0.5-1 ha, covered by winter wheat and winter barely, the pesticides lindane, parathion and pirimicarb were applied. Over these plots the post-application volatilization rates of the pesticides were estimated indirectly from vertical concentration, wind and temperature profile measurements using the aerodynamic gradient technique. Philip's advection model was applied to take non-favourable fetch conditions into account. In addition, at a height of 1.6 m downwind of the area source, measurements of the horizontal concentration profile were made up to a distance of about 250 m at roughly 50-m intervals. The monitoring started immediately after spraying in the morning and continued for about 8-10 h, thus providing a worst-case situation because volatilization, and therefore pesticide concentration in the atmospheric surface layer, is then strongest. The concentration of the airborne pesticides over the downwind non-target area was also calculated by Philip's advection model. By using the Nash-Sutcliffe relative-difference measure between observed and calculated concentrations, a goodness-of-fit of 0.97 was obtained over the downwind non-target area, indicating that the Philip model is well suited for dispersion estimates in the near-field range.

In Situ Study of Alkane Conversion on Pt-Loaded Acidic Zeolites

The hydroisomerization of hexane on platinum-loaded acidic zeolites was studied with positron emission profiling (PEP), a tracer imaging technique based on the same principle as positron emission tomography. The unique character of PEP enables the determination of reaction parameters under in situ reaction conditions that are difficult to obtain via ex situ techniques. A numerical model, including the effects of adsorption, diffusion, and reaction, was used to fit the measured concentration profiles. Preexponential factors and activation energies for some of the elementary proton-activated reaction steps of the bifunctional reaction mechanism have been determined in different transient experiments for a variety of platinum-loaded acidic zeolites. An activation energy for dehydrogenation of 98 kJ/mol was found, in which the heat of adsorption appeared to be included. The heat of adsorption was found to be 61 kJ/mol. An upper value for the deprotonation energy of 100 kJ/mol was determined. This is in agreement with quantum mechanical calculations that have become available only recently.

Auger depth profiling of heat‐treated Au/Ni thin films

AbstractGold/nickel thin films heat treated in the temperature range 200–500°C, have been analysed for composition–depth profiles using Auger electron spectroscopy in combination with simultaneous Ar+ ion sputtering. The present investigation indicates that pronounced nickel diffusion through the gold layer takes place due to annealing at 500°C for 5 min, whereas a noticeable nickel diffusion through the gold layer needs 3 h of annealing at 200°C. The measured concentration profiles suggest diffusion mechanisms involving infinitely fast grain boundary diffusion coupled with defect‐enhanced diffusion into the grains. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Redistribution of Phosphorus and Carbon in Steel Weldments

Abstract The results of P and C redistribution measured in steel weldments are reported. Four sorts of steels were used in steel weldments preparation. The experimental specimens, having a diameter of 12 mm and a thickness of (4 + 4) mm were prepared in the form of sandwiches using electric shocks. The welded specimens were isothermally heated in the temperature range 500–1100°C. The concentration of P and C was measured by the use of an analytical complex JEOL JXA 8600/KEVEX. The measured curves N(P, x, t) and N(C, x, t) revealed uphill diffusion in the investigated steel weldments. The diffusivities D(P) and D(C), and the concentrations N(P, 0)± and N(C, 0)± at the weld interface x = 0 were evaluated from the measured concentration profiles N(P, x, t), N(C, x, t). The obtained D and N(0)± values made it possible to calculate the diffusion (βiP, βiC) and thermodynamic (eiP, eiC) interaction parameters; i ≡ C, Mn, P, Cr, Ni.

MACROPOROSITY AFFECTS WATER MOVEMENT AND PORE WATER SAMPLING IN PEAT SOILS

The measurement of chemical concentration profiles in pore water is a starting point for the analysis of biogeochemical processes in waterlogged peat soils. Concentration patterns may be obscured when macroporosity causes preferential flow in column experiments and when pore water is retrieved from the peat by suction. To investigate the magnitude of such effects, we used LiBr as a tracer in peat columns at outflow rates of 0, 2–3, and 8 mm d−1. The results were compared with modeled advective-diffusive migration rates. Twenty to fifty percent of the tracer was recovered from depths at which the tracer would have been absent if preferential flow had not occurred. At the high flow rate, the preferential flow was stronger, and the retrieved pore-water was probably in disequilibrium with the matrix. When pore water was retrieved by suction, linear concentration gradients decreased by about 30% through the recovery of water from different depths, and the quality of fitted linear gradients decreased from R2 = 0.99 to R2 = 0.82. When flow rates are low (<3 mm d−1) and pore water concentration values from samplers are aggregated or regressed, the obtained concentration profiles seem to represent the vertical distribution of chemical species reasonably well. The use and interpretation of pore water profiles in peat soils is problematic if flow rates are higher and if vertical gradients are based on individual or few data points that have been obtained by suction samplers.

Modelling night‐time ecosystem respiration by a constrained source optimization method

AbstractOne of the main challenges to quantifying ecosystem carbon budgets is properly quantifying the magnitude of night‐time ecosystem respiration. Inverse Lagrangian dispersion analysis provides a promising approach to addressing such a problem when measured mean CO2 concentration profiles and nocturnal velocity statistics are available. An inverse method, termed ‘Constrained Source Optimization’ or CSO, which couples a localized near‐field theory (LNF) of turbulent dispersion to respiratory sources, is developed to estimate seasonal and annual components of ecosystem respiration. A key advantage to the proposed method is that the effects of variable leaf area density on flow statistics are explicitly resolved via higher‐order closure principles. In CSO, the source distribution was computed after optimizing key physiological parameters to recover the measured mean concentration profile in a least‐square fashion. The proposed method was field‐tested using 1 year of 30‐min mean CO2 concentration and CO2 flux measurements collected within a 17‐year‐old (in 1999) even‐aged loblolly pine (Pinus taeda L.) stand in central North Carolina. Eddy‐covariance flux measurements conditioned on large friction velocity, leaf‐level porometry and forest‐floor respiration chamber measurements were used to assess the performance of the CSO model. The CSO approach produced reasonable estimates of ecosystem respiration, which permits estimation of ecosystem gross primary production when combined with daytime net ecosystem exchange (NEE) measurements. We employed the CSO approach in modelling annual respiration of above‐ground plant components (c. 214 g C m−2 year−1) and forest floor (c. 989 g C m−2 year−1) for estimating gross primary production (c. 1800 g C m−2 year−1) with a NEE of c. 605 g C m−2 year−1 for this pine forest ecosystem. We conclude that the CSO approach can utilise routine CO2 concentration profile measurements to corroborate forest carbon balance estimates from eddy‐covariance NEE and chamber‐based component flux measurements.

Depth carrier profiling in silicon carbide

The measurement of majority carrier concentration profiles in silicon carbide is critically discussed considering the most promising methods. Three different techniques are reviewed in detail: (1) capacitance–voltage measurements, (2) scanning capacitance microscopy and (3) spreading resistance profiling. The potentialities and the limitations of these methods are described and compared. The investigated samples include p- and n-type epitaxial layers with a doping concentration in the range 10 16–10 19 cm −3 and ion implanted samples at several doses. The applications of spreading resistance profiling and scanning capacitance microscopy in p- and n-type implanted samples are shown both for uniformly doped samples and single implantation profile. The carrier profiles measured by scanning capacitance microscopy can be quantified by calculations of a complete set of capacitance–voltage curves. Difficulties are presented when quantitative carrier concentration profiles should be calculated by the spreading resistance measurements.

Soil and canopy CO2, 13CO2, H2O and sensible heat flux partitions in a forest canopy inferred from concentration measurements

A canopy scale model is presented that utilises Lagrangian dispersal theory to describe the relationship between source distribution and concentration within the canopy. The present study differs from previous studies in three ways: (1) source/sink distributions are solved simultaneously for CO2, 13CO2, H2O and sensible heat to find a solution consistent with leaf-level constraints imposed by photosynthetic capacity, stomatal and boundary layer conductance, available energy and carbon isotopic discrimination during diffusion and carboxylation; (2) the model is used to solve for parameters controlling the nonlinear source interactions rather than the sources themselves; and (3) this study used plant physiological principles to allow the incorporation of within- and above-canopy measurements of the 13C/12C ratios of CO2 as an additional constraint. Source strengths of CO2, H2O, sensible heat and 13CO2 within a Siberian mixed-coniferous forest were constrained by biochemical and energy-balance principles applied to sun and shaded leaves throughout the canopy. Parameters relating to maximum photosynthetic capacity, stomatal conductance, radiation penetration and turbulence structure were determined by the optimisation procedure to match modelled and measured concentration profiles, effectively inverting the concentration data. Ground fluxes of CO2, H2O and sensible heat were also determined by the inversion. Total ecosystem fluxes predicted from the inversion were compared to hourly averaged above-canopy eddy covariance measurements over a ten-day period, with good agreement. Model results showed that stomatal conductance and maximum photosynthetic capacity were depressed due to the low temperatures experienced during snow melt; radiation penetrated further than simple theoretical predictions because of leaf clumping and penumbra, and stability effects were important in the morning and evening. The inversion was limited by little vertical structure in the concentration profiles, particularly of water vapour, and by co-dependence of canopy parameters.

Electrodialysis Kinetics by Laser Interferometry

A new approach to studying electromembrane systems by the laser interferometry method is proposed. Problems in the electrodialysis kinetics that had been solved by this method are reviewed. These include the determination of the size of diffusion boundary layers, the measurement of concentration profiles of solutions at a concentration polarization of ion-selective membranes in solutions of one and two components in isothermal and nonisothermal conditions, the verification of mathematical models for electrodialysis, and the measurement of local Sherwood numbers. A method for measuring concentration profiles in solutions at the interface with bodies of spherical symmetry following the imposition of a gradient of an electric potential on the system is offered. The results of studying the concentration polarization of an ion exchanger granules are analyzed.

On the effect of tracer density on axial dispersion in a batch oscillatory baffled column

In this paper, we report our modelling evaluation on the effect of tracer density on axial dispersion in a batch oscillatory baffled column (OBC). Tracer solution of potassium nitrite, its specific density ranged from 1.0 to 1.5, was used in the study, and was injected to the vertical column from either the top or bottom. Local concentration profiles are measured using conductivity probes at two locations along the height of the column. Using the experimental measured concentration profiles together with both ‘Tank-in-Series’ and ‘Plug Flow with Axial Dispersion’ models, axial dispersion coefficients were determined and used to describe the effect of specific tracer density on mixing in the OBC. The results showed that the axial dispersion coefficients evaluated by the two models are very similar in both magnitudes and trends, and the range of variations in such coefficients is generally larger for the bottom injection than for the top one. Empirical correlations linking the mechanical energy for mixing, the specific density of tracer and axial dispersion coefficient were established. Using these correlations, we identified the enhancements of up to 269% on axial dispersion for various specific tracer densities.

Spatial gradients in particle reinforced polymers characterized by X-ray attenuation and laser confocal microscopy

The goal of this work is to develop techniques for measuring gradients in particle concentration within filled polymers, such as thermosetting polymer encapsulants. A high concentration of filler particles is added to such materials to tailor physical properties such as thermal expansion coefficient. Sedimentation and flow-induced migration of particles can produce concentration gradients that are most severe near boundaries. Therefore, techniques for measuring local particle concentration should be accurate near boundaries. Particle gradients in an alumina-filled epoxy resin are measured with a spatial resolution of 0.2 mm using an X-ray beam attenuation technique, but an artifact reduces accuracy near the specimen's edge. Local particle concentration near an edge can be measured more reliably using microscopy coupled with image analysis. This is illustrated by measuring concentration profiles of glass particles having 40 μm median diameter using images acquired with a confocal laser fluorescence microscope. The mean of the measured profiles of volume fraction agrees to better than 3% with the expected value and the shape of the profiles agrees qualitatively with simple theory for sedimentation of monodisperse particles. Evidence that the microscopic method can be extended to smaller particles is provided by local concentration measurements on an epoxy polymer containing particles having diameters of the order of 1 μm.