Measured Concentration Profiles Research Articles

Optical measurement of carrier concentration profile in n‐type semiconducting GaAs substrate

AbstractThe light absorption below the fundamental energy gap in n‐type GaAs has been investigated precisely. It is experimentally confirmed that there are the three different mechanisms: (a) the enhancement of fundamental absoption due to the shrinkage of energy gap and band filling by doping Si atoms, (b) deep‐level (EL2) absorption, and (c) free‐carrier absorption. It is found that the transmittance measurement at the wavelength longer than about 1000 nm in the free‐carrier absorption region is more useful and direct, compared with that near the fundamental absorption region from 900 nm to 950 nm, precisely to determine the carrier concentration in n‐type GaAs. The two‐dimensional profile of carrier concentration in a VB‐grown 3 ϕ GaAs substrate is measured in high spatial resolution with the short time less than 5 seconds by using a sophisticated near‐infrared transmittance‐measuring equipment. The absolute amount and homogeneity of carrier concentration can be assessed in the range from 0.3 to 3 × 1018 cm–3. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Leaching of Solutes from an Intensively Managed Peat Soil to Surface Water

In many peat land areas in The Netherlands target concentrations for nitrogen (N) and phosphorus (P) in surface water are exceeded. A considerable, but poorly quantified, fraction, of the N and P loading of surface water in these areas originate from the subsoil. Waterboards, responsible for the water management, are currently exploring options to improve surface water quality, whilst sustaining agricultural production. Therefore, insight into dynamics of nutrient pools in peat soils is required. The aim of this study was to measure concentration profiles (0–12 m) of the soil solution in an intensively managed grassland on peat soil and to explore the effects of a rise in surface water level on N and P loading of surface water, using budgeting approaches and two dimensional simulation modeling. The concentration profiles of N, P and Cl reflect by the presence of nutrient-rich anaerobic peat and a nearly impermeable marine clay in the subsoil. Concentrations of N, P and Cl tended to increase with depth till about 6 m and then decreased. In the top soil, inputs of N and P via fertilizers and animal manure were only partly retrieved in the soil solution, suggestion that biogeochemical processes, uptake and lateral transport processes had a dominant influence on dissolved N and P. Exploring scenario simulations showed that major drainage fluxes passed through the peat layer that transported nutrients to adjacent surface water. Raising surface water levels with 20 cm suppresses this kind of nutrient loading of surface water by more than 30%, but nutrient rich peat layers will remain persistent as a potential source of nutrients in surface water in many peat polders in the western part of The Netherlands.

Buoyancy Effects in Dead-End Reverse Osmosis: Visualization by Holographic Interferometry

Real-time holographic interferometry, previously used to measure concentration profiles in the polarized layer during membrane processes, has been applied to visualize the buoyancy effects on dead-end reverse osmosis of salts by rotating the cell 90° and 180° from its original position (0°). Sets of experiments have been carried out, each one with the membrane in a different gravitational orientation, using NaCl and Na2SO4 with a feed concentration ranging from 1 to 7 kg/m3 at a constant pressure of 600 kPa. The interferometric fringe patterns obtained in each membrane position were very different. At the 0° position, the evolution of the polarization layer was observed by means of several interferometric fringes parallel to the membrane surface. At 180° position, the interferometric fringe pattern obtained pointed out the existence of a natural convection or buoyancy flow in the vicinity of the membrane surface which prevented the growth of the polarization layer. Finally, with the membrane vertically pl...

Suction-lift sludge removal and non-Newtonian flow behaviour in circular secondary clarifiers: Numerical modelling and measurements

Abstract We present a computational fluid dynamics (CFD) model that predicts the sedimentation of activated sludge in a full-scale flat-bottom circular secondary clarifier that is equipped with a suction-lift sludge removal system. The axisymmetric single-phase model is developed using the general-purpose CFD solver Fluent. A convection–dispersion equation, which is extended to incorporate the sedimentation of activated sludge in the field of gravity, governs the mass transfer in the clarifier. Sludge removal by suction-lift in the near-bottom region of the clarifier is simulated using negative source terms on all field equations. The standard k–ɛ turbulence model is used to compute the turbulent motion, and our CFD model accounts for buoyancy flow and non-Newtonian flow behaviour of the activated sludge in the clarifier. The rheological flow behaviour was measured for varying sludge concentrations and temperatures. These measurements show that at low to moderate shear rates typical of secondary clarifiers, the relationship between shear stress and shear rate follows the Casson law for pseudo-plastic flow behaviour. The rheology study was carried out together with measurements of the settling velocity during on-site measurements. The well-known double-exponential law is used to describe the dependence of the settling velocity on the concentration. Light scattering was applied to measure the local sludge distribution in the clarifier. The computation of the local sludge distribution in the clarifier by the CFD model compares well with concentration profile measurements for two different treatment plant loadings. Our CFD computations show further that the sludge viscosity dominates the flow and the sedimentation of activated sludge within the sludge blanket.

Ultraviolet light absorber mobility in crosslinked coatings: Experiments and modeling

The diffusion of an ultraviolet absorber (UVA) across a concentration step change in an acrylic melamine clearcoat was measured via micro-ultraviolet spectroscopy. Concentration profiles were obtained after diffusion times of 4–200 h at steady temperatures of 70, 80, and 90 °C. The glass transition temperature of the coating was measured via dynamic mechanical analysis for each time–temperature pair, and T g was observed to increase with thermal aging, with a faster rate of increase at higher aging temperatures. The change in T g was modeled using a first-order dependence on the deviation from a long-time T g asymptote. The diffusion coefficient was then represented by a free volume expression, and the combination provided an accurate model of the measured concentration profiles. The time-dependent increases in glass transition temperature helped to explain why UVA diffusion does not alleviate concentration gradients created by photooxidation under natural weathering conditions.

Estimation of the Michaelis–Menten parameters for reductive dechlorination of chlorinated solvents

We present a rigorous mathematical study a non-competitive model employing the Michaelis–Menten kinetics for description of a reductive dechlorination of chlorinated ethenes. We start with the qualitative and quantitative analysis of a single equation and we describe the relevant properties of a solution. We also perform the sensitivity study with respect to the biotransformation reaction rates. This is afterwards applied to the whole reaction network. The theoretical results enable the use of regularization techniques for the recovery of missing reaction rates. These are determined from the measurements of concentration profiles of all chemical species using minimization of a suitable error functional. This technique is demonstrated on two numerical examples.

Enhancing activated sludge nitrification through seeding from a downstream nitrifying fixed-film reactor

An ASM1-based mathematical model was developed for the description of the combined activated sludge-biofilter system of the Southpest Wastewater Treatment Plant, Budapest, Hungary. This model includes the interactions of the activated sludge and biofilter units, i.e. the influence of both the clarified activated sludge effluent and the backwashed nitrifying and denitrifying microorganisms. Concentration profile measurements have been carried out throughout the combined system in order to track the biological processes. Optimization possibilities of the existing combined plant were investigated by mathematical simulations under the different detected operational conditions. In these studies concentration data measured on separate days and the appropriate flow rates of the preclarified influent and the recycled streams registered at the treatment plant were used. Simulation results showed that N-removal of the activated sludge unit could be highly intensified by appropriate aeration, that would facilitate the e fficient growth of backwashed biomass. However, in some cases, shortage of readily biodegradable carbon source proved to be the limit of the benefits available.

B212 標準添加LIF法によるジェット燃料火災中の―酸化窒素濃度・温度計測

An LIF imaging spectroscopy was applied to the quantitative measurements of NO concentration and temperature profiles in a jet fuel flame. The NO mole fractions were determined comparing the LIF signals of NO-seeded flame and non-seeded flame. A two-line thermometry technique was used for obtaining the temperature distributions. A narrow-band pass filter was used to sufficiently remove noise lights, and two-dimensional distributions of concentration and temperature of NO were obtained. The flame was stabilized inserting a honeycomb ceramic tube on the burner exit of preheated kerosene-air mixture. The result shows that NO is produced via the thermal NO mechanisms and that the NO concentration and temperature were higher in comparison with a methane-air premixed flame in a standard Bunsen burner.

Measurement of Fuel Concentration Profile at Leading Edge of Lifted Flame with Acetone Laser-Induced Fluorescence

This research proposes a study of the leading edge of the methane-air triple flame characteristics. Few experiment results are available for physical examination, so an experimental investigation must be conducted to understand the stability mechanisms in a mixture with a steep concentration gradient. To this end, applying acetone-laser-induced fluorescence (acetone-LIF) is studied for measuring concentration profiles at the leading edge of the flame. The results demonstrate that the lifted height is changed when acetone is added to the mixture. It correlates closely with increasing C2 radical behind the flame edge. Meanwhile, the OH radical luminous intensity measured with a spectroscope is not changed. Moreover, the burning velocity of methane-acetone-air mixture obtained by the Bunsen burner method remains constant. Therefore, the influence of acetone on burning intensity is small. Acetone LIF can thus be advantageous for measuring the local concentration gradient at the leading edge. The acetone LIF signals can be revised considering the thermal effect using the silicone oil vanishing plane. After temperature correction, the transition of the flammability limit width upstream of the flame at a steep concentration gradient can be observed as clearly as in the recent numerical result.

Molybdenum diffusion in thermally treated NANOPERM-type Fe 76Mo 8Cu 1B 15 alloy

Mo tracer diffusion in Fe 76Mo 8Cu 1B 15 alloy was studied using serial sectioning method in the temperature range 548–648 K. Sputtering by Ar + ions was applied as a sectioning technique. The measurement was carried out with the ribbon-like samples in as quenched state and in two states after pre-anneal 683 and 743 K/h. Measured concentration profiles consist of two distinct branches suggesting that two diffusion paths are operating. Diffusion coefficients D v calculated from the near-surface branch were attributed to Mo volume diffusion in amorphous phase, the higher ones, on the other hand are influenced by fast short-circuit diffusion.

Determination of the surface segregation ratio of P in Si(1 0 0) during solid-source molecular beam epitaxial growth

The surface segregation ratio as a function of growth temperature of a dopant is a fundamental property that must be known for that dopant to be used in device applications. Using low energy secondary ion mass spectrometry, a precise determination of the segregation ratio of P in Si(1 0 0) in the temperature interval from 380 °C to 650 °C has been made. The values of the surface segregation ratios determined are substantially less than previously reported. It has been observed that the source of the P dopant as well as the temperature during growth influences the segregation of P. Using a GaP decomposition source, the deposited P has been shown to be fully electrically active in the whole growth temperature interval by measurement of the carrier concentration profiles using spreading resistance profiling.

Open questions about polymer interfacial diffusion

The goal of understanding diffusion in bulk has been a large part of the agenda in polymer physics from the start of our discipline. It seemed obvious to researchers, many years ago, that this and other aspects of dynamics at the level of individual molecules surely underpinned the macroscopic properties, such as viscoelasticity and other properties discussed in this viewpoint. Great names are associated with the seminal understanding of diffusion in the bulk: we have Rouse, Zimm, Doi, Edwards, and de Gennes on the theoretical side, but on the experimental side, important work has been done by so many researchers that to single out individual names would not be meaningful. Nowadays, the study of the mechanisms and timescales of polymer diffusion in solution and in melts is a developed field of study that is summarized in textbooks. Interesting modern work does continue, for example, in understanding diffusion in blends and microstructured block copolymers. Although we should never claim that our understanding is definitive, polymer science has developed a rather mature understanding of how the dynamics depend on the chain length, chain architecture, and concentration. Why is the same not so for polymer dynamics at surfaces? Ultrahigh-vacuum surface science has studied surface diffusion for many years; polymer science has not. One basic limitation has been that the needed experimental tools have not been available. It is true that methods of dynamic light scattering have given insight into the global dynamics of polymer brushes. It is also true that in the field of polymer adsorption, work has approached this question from the perspective of understanding surface on–off (adsorption–desorption) kinetics. At the same time, it is also desirable to seek an understanding of in-plane polymer diffusion at surfaces, which is a distinctly different problem. In the past, techniques imported from other fields of science have enabled important advances. Secondaryion mass spectrometry and related methods from ultrahigh-vacuum surface science have been used to measure concentration profiles in multilayer thin films spin-coated onto solid supports, from which diffusion has been cleverly inferred. Neutron reflectometry has been used to study interdiffusion in thin films. Specular X-ray scattering has allowed us to study capillary fluctuations in thin films. X-ray scattering has even been used to assess segmental equilibration. These methods refer to thin melt films on solid supports. Atomic force microscopy and surface force apparatus are much used to measure how friction and surface forces are perturbed when polymer films are very thin. Correspondence to: S. Granick (E-mail: sgranick@uiuc. edu)

Internal Concentration Gradients of Guest Molecules in Nanoporous Host Materials: Measurement and Microscopic Analysis

Evolution of internal concentration profiles of methanol in 2-D pore structure of ferrierite crystal was measured in the pressure range of 0 to 80 mbar with the help of the recently developed interference microscopy technique. The measured profiles showed that both a surface barrier and internal diffusion controlled the kinetics of adsorption/desorption. Furthermore, they indicated that in the main part of the crystal, the z-directional 10-ring channels were not accessible to methanol and that the transport of methanol mainly occurred via 8-ring y-directional channels. The roof-like part of the crystal was almost instantaneously filled/emptied during adsorption/desorption, indicating accessible 10-ring channels in this section. The measured profiles were analyzed microscopically with the direct application of Fick's second law, and the transport diffusivity of methanol in ferrierite was determined as a function of adsorbed phase concentration. The transport diffusivity varied by more than 2 orders of magnitude over the investigated pressure range. Transport diffusivities, calculated from measured profiles from small and large pressure step changes, were all found to be consistent. Simulated concentration profiles obtained from the solution of Fick's second law with the calculated functional dependence of diffusivities on concentration compared very well with the measured concentration profiles, indicating validity and consistency of the measured data and the calculated diffusivities. The results indicate the importance of measuring the evolution of concentration profiles as this information is vital in determining (1) the direction of internal transport, (2) the presence of internal structural defects, and (3) surface/internal transport barriers. Such detailed information is available neither from common macroscopic methods since, they measure changes in macroscopic properties and use model assumptions to predict the concentration profiles inside, nor from microscopic methods, since they only provide information on average displacement of diffusing molecules.

Application of the Convection–Dispersion Equation to Modelling Oral Drug Absorption

Models of systemic drug absorption after oral administration are frequently based on a direct or a delayed first-order rate process. In practice, the use of the first-order approach to predict drug concentrations in blood plasma frequently yields a considerable mismatch between predicted and measured concentration profiles. This is particularly true for the upswing of the plasma concentration after oral administration. The current investigation explores an alternative model to describe the absorption rate based on the convection–dispersion equation describing the transport of chemicals through the GI tract. This equation is governed by two parameters, transport velocity and dispersion coefficient. One solution of this equation for a specific set of initial and boundary conditions was used to model absorption of paracetamol in a 22-year-old man after oral administration. The GI-tract passage rate in this subject was influenced by co-administration of drugs that stimulate or delay gastric emptying. The transport-limited absorption function is more accurate in describing the plasma concentration versus time curve after oral administration than the first-order model. Additionally, it provides a mechanistic explanation for the observed curve through the differences in GI-tract passage rate.

Transmission electron microscopy investigation of segregation and critical floating-layer content of indium for island formation inInxGa1−xAs

We have investigated ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ layers grown by molecular-beam epitaxy on $\mathrm{GaAs}(001)$ by transmission electron microscopy (TEM) and photoluminescence spectroscopy. $\mathrm{InGaAs}$ layers with In concentrations of 16, 25, and $28\phantom{\rule{0.2em}{0ex}}%$ and respective thicknesses of 20, 22, and 23 monolayers were deposited at $535\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. The parameters were chosen to grow layers slightly above and below the transition between the two- and three-dimensional growth mode. In-concentration profiles were obtained from high-resolution TEM images by composition evaluation by lattice fringe analysis. The measured profiles can be well described applying the segregation model of Muraki et al. [Appl. Phys. Lett. 61, 557 (1992)]. Calculated photoluminescence peak positions on the basis of the measured concentration profiles are in good agreement with the experimental ones. Evaluating experimental In-concentration profiles it is found that the transition from the two-dimensional to the three-dimensional growth mode occurs if the indium content in the In floating layer exceeds $1.1\ifmmode\pm\else\textpm\fi{}0.2$ monolayers. The measured exponential decrease of the In concentration within the cap layer on top of the islands reveals that the In floating layer is not consumed during island formation. In addition, ${\mathrm{In}}_{0.25}{\mathrm{Ga}}_{0.75}\mathrm{As}$ quantum wells were grown at different temperatures between $500\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and $550\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. The evaluation of concentration profiles shows that the segregation efficiency increases from $R=0.65$ to $R=0.83$. The strong increase of $R$ with the growth temperature is explained by the large growth rate of $1.5\phantom{\rule{0.3em}{0ex}}\mathrm{ML}∕\mathrm{s}$. Comparison with the temperature dependence of published segregation efficiencies obtained at lower growth rates reveals increasing temperature dependence and decreasing segregation efficiency with increasing growth rate.

Influence of thermal treatment upon the diffusion characteristics of Mo in Fe76Mo8Cu1B15 alloy

Mo tracer diffusion in Fe76Mo8Cu1B15 alloy was studied using serial sectioning method in the temperature range 548–648K. Sputtering by Ar+ ions was applied as a sectioning technique. The measurement was carried out with the ribbon-like samples in as quenched state (q) and in two states after pre-anneals 683K/1h (a1) and 743K/1h (a2). The volume fraction of crystalline phase was checked by the Mössbauer spectroscopy. Measured concentration profiles consist of two distinct branches suggesting that two diffusion paths are operating. Diffusion coefficients Dv calculated from the near-surface branch were attributed to Mo volume diffusion in amorphous phase. Their values obtained for (a1) are lower than those obtained for (q) which is due to relaxation of free volume. The higher values, on the other hand, obtained for (a2) are influenced by faster short-circuit diffusion, which was attributed to diffusion in interfacial amorphous phase. Short-circuit diffusivity, P, of Mo was evaluated from concentration tails using both LeClaire’s analysis and Divinski’s theory derived for transition type-A/B regime.

Measurement of concentration profiles over ZnO–Cr 2O 3/CeO 2–ZrO 2 monolithic catalyst in oxidative steam reforming of methanol

Oxidative steam reforming of methanol (OSRM) reaction was investigated over a novel monolithic ZnO–Cr 2O 3/CeO 2–ZrO 2 catalyst developed in our laboratory. A novel flat-bed reactor was designed to measure the concentration profiles of the monolithic catalyst beds under different operation conditions: water-to-methanol mole ratio (W/M) between 1 and 1.5; oxygen-to-methanol mole ratio (O/M) in the range of 0.1–0.3; space velocity ranging from 1840 to 2890 h − 1 ; and reaction temperature in the scale of 400–440 °C. On the basis of these results, reaction pathways for the OSRM were discussed. It is indicated that only three independent reactions dominate in our reaction system, namely, the partial oxidation of methanol, the steam reforming of methanol and the methanol decomposition reaction, whereas the water–gas shift and the reverse water–gas shift reactions should be ignored. In addition, the steam reforming of methanol proceeds along all the catalyst bed, whereas methanol decomposition and oxidation reactions occur mainly at the entrance of the catalyst bed.

Performance of pulsed plate bioreactor for biodegradation of phenol

Biodegradation of phenol was carried out using Nocardia hydrocarbonoxydans immobilised on glass beads, in a pulsed plate bioreactor. The effect of operating parameters like frequency of pulsation and amplitude of pulsation on the performance of pulsed plate bioreactor for biodegradation of phenol in a synthetic wastewater containing 500 ppm phenol was studied. Axial concentration profile measurements revealed that the pulsed plate bioreactor shows continuous stirred tank behaviour. As the amplitude was increased, percentage degradation increased, reaching 100% at amplitude of 4.7 cm and higher. Introduction of pulsation is found to increase the percentage degradation. Percentage degradation has increased with increase in frequency and 100% degradation was achieved at 0.5 s −1 and above. Biofilms developed in a non-pulsed bioreactor were thicker than those in the pulsed plate bioreactor. But biofilm thickness remained almost constant with increasing frequency. Biofilm density was found to be influenced by pulsation. The time required to reach steady state was more for pulsed reactor than the non-pulsed reactor and this start-up time had increased with increase in frequency of pulsation. The performance studies reveal that the pulsed plate bioreactor with immobilized cells has the potential to be an efficient bioreactor for wastewater treatment.

Measurement of Concentration Profiles by Holographic Interferometry and Modelling in Unstirred Batch Reverse Osmosis

An optical method (real-time holographic interferometry) has been used to visualize concentration changes in the vicinity of the membrane surface during the dead-end reverse osmosis of salt solutio...

In situ quantification of the concentration polarization layer in a hyperfiltration system

An experimental apparatus was constructed which allowed for in situ chemical sampling of a hyperfiltration (reverse osmosis) system inside the high-pressure reservoir. In this system – a columnar apparatus 50.6 cm in length and 5.1 cm in diameter – a 101.3 mM sodium chloride solution was advected towards an uncompressed sodium-saturated bentonite membrane. Twelve small-diameter stainless steel tubes were fitted to run parallel to the length of the experimental column—each tube terminating at a different position within the concentration polarization layer (CPL). Solution extracted from these different positions within the CPL showed a progressive buildup of solute toward the membrane's high-pressure interface. This measured concentration profile agrees favorably with the geometry of the CPL as predicted by solution of the continuity equation. These measurements constitute the first direct verification of the CPL's geometry under conditions where the fluid flow is directed toward the membrane and there is no cross-flow component.