Decreasing Concentration Profile Research Articles

Stochastic numerical computing to study MHD micropolar nanofluidic system along a rotating disk in the presence of partial slip conditions

The goal of investigation is to look at how a rotating disc affects the motion of magnetohydrodynamics micropolar nanofluid flow model (MHD-MPNFFM) in applied magnetic field and partial slip condition. Using suitable transformations, the PDEs of considered flow system are converted to ODEs. These obtained non-linear ODEs are then processed using the computational power of Lobatto IIIA approach to obtain a dataset of Artificial Intelligence neural networks model backpropagated with Bayesian Regularization procedure (AINM-BBRP) for variation of velocity slip parameters, magnetic field parameter, material parameters, Brownian motion parameter, thermophoresis parameter and Lewis number. To verify the current findings, a contrast to past study is included. Graphical representations of regression, efficiency, fit curve, error bars, and trained state analysis are presented using nftool. The velocity, temperature, microrotation, and concentration profiles were computed, and the findings were presented through graphs and tables. This is observed that velocity and microrotation or spin components are degraded by the slip action and magnetic field. Brownian motion parameter, thermophoresis parameter, and Lewis number all have rising temperature fields, however Brownian motion parameter and Lewis number have decreasing concentration profiles. The accuracy achieved in terms of relative error demonstrates the validity and significance of the solution process.

Numerical study of unsteady MHD flow of Williamson nanofluid in a permeable channel with heat source/sink and thermal radiation

The present research work is dedicated to examine the heat and mass transport phenomenon due to unsteady MHD flow of Williamson nanofluid between the permeable channel with heat source/sink. The influence of buoyancy and thermal radiation effects are also considered for the present model. The flow equations are reduced to an equivalent nonlinear coupled partial differential equations (PDE) through suitable transformation. The numerical simulation is performed to attain the solution of the nonlinear system via the Crank-Nicolson finite difference scheme. The influence of various emerging parameters on velocity, temperature and concentration profiles are developed. The magnetic parameter plays the significant role to enhance the heat transfer rate but reduces the velocity profile. The velocity of the fluid increases gradually with respect to time and this influence is dominant at the center of the channel. Additionally, the velocity profile exhibits the increasing behavior by varying the Reynolds number for a small time. In the entire study it is analyzed that the temperature profile increases for increasing values of Reynolds, thermophoresis, Brownian motion and heat source numbers, while a low temperature profile is attained for Biot numbers. The thermophoresis and Brownian motion parameters provide the decreasing concentration profile however, an increasing result is noticed for Biot numbers. An increase in the values of Williamson parameter $ \Lambda$ , illustrates the increase effects on the skin friction coefficient when $ \eta=1$ while it shows the decrease behavior at $ \eta=0$ . The effects of the Reynolds number on streamlines pattern is presented. It is noticed that the higher values of Re affects the stream line pattern.

Procedure for calculating the chloride diffusion coefficient and surface concentration from a profile having a maximum beyond the concrete surface

Chlorides induce local corrosion in the steel reinforcements when reaching the bar surface. The measurement of the rate of ingress of these ions, is made by mathematically fitting the so called “error function equation” into the chloride concentration profile, obtaining so the diffusion coefficient and the chloride concentration at the concrete surface. However, the chloride profiles do not always follow Fick’s law by having the maximum concentration at the concrete surface, but often the profile shows a maximum concentration more in the interior, which indicates a different composition and performance of the most external concrete layer with respect to the internal zones. The paper presents a procedure prepared during the time of the RILEM TC 178-TMC: “Testing and modeling chloride penetration in concrete”, which suggests neglecting the external layer where the chloride concentration increases and using the maximum as an “apparent” surface concentration, called C max and to fit the error function equation into the decreasing concentration profile towards the interior. The prediction of evolution should be made also from the maximum.

Neutral poly- and perfluoroalkyl substances in air and seawater of the North Sea

Concentrations of neutral poly- and perfluoroalkyl substances (PFASs), such as fluorotelomer alcohols (FTOHs), perfluoroalkane sulfonamides (FASAs), perfluoroalkane sufonamidoethanols (FASEs), and fluorotelomer acrylates (FTACs), have been simultaneously determined in surface seawater and the atmosphere of the North Sea. Seawater and air samples were taken aboard the German research vessel Heincke on the cruise 303 from 15 to 24 May 2009. The concentrations of FTOHs, FASAs, FASEs, and FTACs in the dissolved phase were 2.6-74, <0.1-19, <0.1-63, and <1.0-9.0 pg L(-1), respectively. The highest concentrations were determined in the estuary of the Weser and Elbe rivers and a decreasing concentration profile appeared with increasing distance from the coast toward the central part of the North Sea. Gaseous FTOHs, FASAs, FASEs, and FTACs were in the range of 36-126, 3.1-26, 3.7-19, and 0.8-5.6 pg m(-3), which were consistent with the concentrations determined in 2007 in the North Sea, and approximately five times lower than those reported for an urban area of Northern Germany. These results suggested continuous continental emissions of neutral PFASs followed by transport toward the marine environment. Air-seawater gas exchanges of neutral PFASs were estimated using fugacity ratios and the two-film resistance model based upon paired air-seawater concentrations and estimated Henry's law constant values. Volatilization dominated for all neutral PFASs in the North Sea. The air-seawater gas exchange fluxes were in the range of 2.5×10(3)-3.6×10(5) pg m(-2) for FTOHs, 1.8×10(2)-1.0×10(5) pg m(-2) for FASAs, 1.1×10(2)-3.0×10(5) pg m(-2) for FASEs and 6.3×10(2)-2.0×10(4) pg m(-2) for FTACs, respectively. These results suggest that the air-seawater gas exchange is an important process that intervenes in the transport and fate for neutral PFASs in the marine environment.

Atmospheric concentrations and air–sea exchanges of nonylphenol, tertiary octylphenol and nonylphenol monoethoxylate in the North Sea

Concentrations of nonylphenol isomers (NP), tertiary octylphenol ( t-OP) and nonylphenol monoethoxylate isomers (NP1EO) have been simultaneously determined in the sea water and atmosphere of the North Sea. A decreasing concentration profile appeared following the distance increasing from the coast to the central part of the North Sea. Air–sea exchanges of t-OP and NP were estimated using the two-film resistance model based upon relative air–water concentrations and experimentally derived Henry's law constant. The average of air–sea exchange fluxes was −12 ± 6 ng m −2 day −1 for t-OP and −39 ± 19 ng m −2 day −1 for NP, which indicates a net deposition is occurring. These results suggest that the air–sea vapour exchange is an important process that intervenes in the mass balance of alkylphenols in the North Sea.

Temporal and Longitudinal Characteristics of Volatile Organic Compound Emissions from Aeration Units of Publicly Owned Treatment Works

ABSTRACT The temporal and longitudinal characteristics of volatile organic compound (VOC) emissions from the aeration units of a publicly owned treatment works (POTWs) have been investigated by systematic monitoring and mathematical modeling. Field tests have been conducted at a 120-mgd wastewater treatment plant to investigate the hourly, weekly, and seasonal changes of VOC emissions. Variations of VOC emissions along the length of the aeration units have been tested and modeled. Most VOCs have decreasing concentration profiles. Henry's law coefficients and biodegradation constants for the detected compounds have been validated with the improved models and the field test data. More than one-half of the emissions were found to have been generated from the first one-third of the aeration unit length.

Emissions of hazardous air pollutants from aeration tanks

AbstractRegulated under the 1990 Clean Air Act Amendments (CAAA), Publicly Owned Treatment Works (POTWs) need to inventory and control their hazardous air pollutant (HAP) emissions, primarily from the aeration tanks. The spatial characteristics of hazardous air pollutants in the form of volatile organic compounds (VOCs) from the aeration units of POTWs have been investigated by systematic monitoring and mathematical modeling. Using a verified off‐gas sampling system and CC‐MS analytical method, a large wastewater treatment plant has been tested to understand the air emissions from its aeration basins. Variations of VOC emissions along the length of the aeration units have been tested and modeled. Most VOCs have decreasing concentration profiles. A simple PFR model has been developed to obtain the spatial information of the VOC fate. This model can be easily used to validate model parameters and accurately simulate the process especially in the case where the aeration tanks are operated with varied airflow rates along the tank length. Using this simple model, air emissions can be accurately estimated and the simulation results are useful to support an emissions control analysis. This study also reveals that simple multiplication of measured off‐gas concentration and total airflow over‐estimates the overall emissions.

Formation of Subthreshold Defects in Erbium Implanted Silicon

ABSTRACTIn this work we present the first quantitative approach to model subthreshold defects. Using cross-sectional Transmission Electron Microscopy (XTEM) and Convergent Beam Electron Diffraction (CBED), we studied subthreshold defects in Cz-silicon that followed a deep implantation of erbium, and their interaction with co-implantations. The analyzed Frank loops show an increasing size by a factor of five with increasing depth in the wafer. The ratios of the number of condensed silicon atoms to the implant doses support a “+0.4 model” for the erbium and a “+0.07 model” for the oxygen as a co-implant. Our results indicate that a “push away” mechanism produces the excess silicon atoms in the case of interstitial implant atoms. The observed loop size depth distributions helped to reveal the condensation mechanism of subthreshold defects. This mechanism is described by the relaxation of excess silicon atoms on primary defect clusters. The decreasing concentration profiles of the primary defect clusters together with the high diffusivity of silicon interstitials results in a number of condensed silicon atoms per loop that increases with the depth in the wafer.

Effect of magnesium supplementation and training on magnesium tissue distribution in rats.

The aim of this work is to study the effect of training and Mg supplementation on body pools of Mg and on Mg tissue distribution. Forty male Wistar rats were divided into four groups (n = 10): control group (C); trained group (T); Mg-supplemented group (+Mg); and trained and Mg-supplemented group (+MgT). The Mg supplement (1000 ppm of Mg) was given in the drinking water for 21 d. The training consisted of swimming during 60% of maximal swimming time obtained in the first session to exhaustion, during 3 wk (5 d a week). The variables measured were: erythrocytes (RBC), hemoglobin (Hb), hematocrit (Hto), total proteins (TP), and Mg in serum, RBC, liver, muscle, bone, and kidney. There was less Mg in liver, muscle, and erythrocyte in trained animals than in control or supplemented animals (T vs C, +MgT vs C and +MgT vs +Mg) (p < 0.01). Trained animals (T and +MgT) showed higher Mg kidney rates than the untrained ones (p < 0.01). There was less bone Mg in control (C) and in supplemented and trained (+MgT) groups than in trained (T) and in supplemented (+Mg) animals (p < 0.01). Serum Mg showed a decreasing concentration profile in the following order: +Mg, +MgT, T, C (p < 0.01). We conclude that Mg supplementation improves bone and serum Mg levels, but this does not affect Mg status in soft tissues. Maintained exercise leads to a diminution of Mg in the aforementioned soft tissues that is not noticeable in serum, probably provoked by an increase of renal excretion.

Polymers and copolymers at interfaces

We discuss the differences between the structure of homopolymers and multiblock copolymers at interfaces. As the surface concentration is increased, the former first lie on the surface and then progressively build up an adsorbed layer with a decreasing concentration profile. The latter first build up a layer of constant thickness. For sufficiently high concentrations, however, because the blocks repel each other, they tend to form loops that are extended in the direction normal to the surface. In this high concentration regime, the structure of the layer is reminiscent of that of grafted polymers. We do not consider the possibility of micelles forming in the solution.

Distributed-in-space product formation in vivo: linear kinetics

Distributed-in-space conversion of precursor substrate to product within an organ is explored when all formed product is released into the bloodstream. When precursor removal kinetics are linear (conversion occurring proportionately to concentration) and the process is uniformly distributed along the length, exponentially decreasing concentration profiles for precursor result. The vascular profile for product rises in complementary fashion; the sum of precursor and product is constant along the length. Symmetric permeability barriers are found to produce concentration stepdowns of precursor from blood to tissue and, for product, converse stepdowns from tissue to blood. Tracer precursor, introduced as an impulse input, within this steady state, is converted to product, details varying with the number of barriers. Nevertheless, a particular common feature is found in the solutions. The analytic expression for locally generated tracer product is found, in each case, to contain the impulse response to tracer product introduced at the origin. Therefore, to simplify experimental analysis and to superpose a set of constraints on computational approaches to parameter estimation, one should introduce, simultaneously with tracer precursor, tracer product labeled in an identifiably different manner.

A Tougaard background deconvolution study of the compositional depth profile in amorphous a-Si1−xCx:H alloys

A Tougaard background deconvolution analysis of the x-ray photoelectron spectra of an a-Si1−xCx:H film deposited on a silicon substrate by the radio-frequency plasma-enhanced chemical vapor deposition method has been performed. The analysis indicates that carbon and silicon atoms inhabit an exponentially decreasing concentration profile from the surface with different characteristic attenuation lengths. Oxygen has also been incorporated in the film with a similar concentration profile. The differential inelastic scattering cross section for the deconvolution has been obtained from reflection electron energy-loss spectroscopy. This nondestructive depth profile analysis appears to be a powerful tool for determining the uniformity of deposition of such films.

Precursor formation and soot inception in premixed ethylene flames

Absorption, fluorescence and scattering measurements were applied both in the ultraviolet and visible to rich premixed C2H4/O2 flames in the C/O range from 0.5 to 0.8. The concentration of soot and condensed hydrocarbon species were also measured by direct sampling along a lightly-sooting (C/O=0.65) and sooting (C/O=0.75) flame. The early formation in the flames of “particles” with typical average size around 2 nm (2500 a.m.u.), which do not absorb in the visible and fluoresce in the ultraviolet, was followed. These “transparent” particles were considered soot precursors on the basis of their decreasing concentration profile in correspondence of soot inception, as evaluated by both optical and chemical measurements. The soot inception process is characterized by the progressive aromatization of the “transparent” particles as shown by the progressive shift toward the visible of absorption and fluorescence. The internal rearrangement of a partially aromatic polymeric structure, more than a progressive formation of very large PAH structures, is proposed as the mechanism of soot inception.

Biogeochemistry of barium and strontium in a softwater lake

Vertical profiles of dissolved barium and strontium concentrations were measured over 12 months in the water column and near surface sediments of a seasonally anoxic softwater lake (Esthwaite Water, U.K.). The concentrations of these metals were also monitored in the major inflow. Depositional fluxes were determined by means of sediment traps. Biogeochemical processes operating in the lake result in (i) elevated dissolved barium concentrations in the hypolimnion during summer stratification, (ii) the major deposition flux of barium occurring over the summer months, (iii) partial dissolution of the barium deposition flux, to an extent sufficient to explain the observed net accumulation of hypolimnetic dissolved barium, and (iv) downward decreasing concentration profiles of dissolved barium and strontium in the sediment pore waters associated with continuous diagenetic removal. The observed water column behaviour of barium is probably due to uptake by, and release from, the algal standing crop and to the ciliated protozoa, Loxodes, located at the oxycline. Association with the dynamic iron cycle of the lake accounts for < 16% of the deposition flux of barium, as measured at the sediment surface. The influence of the biogeochemical cycling of barium and strontium is small compared with the overall dissolved budgets for the metals in the lake.

Measurements of atmospheric sea salt concentrations in Hawaii using a Tala kite

An inexpensive and convenient method to sample sea salt concentrations in the lowest few hundred meters of the atmosphere was tested in Hawaii. The string to a Tala kite flying at about 150 m was intersected by thin steel wires on which sea salt collected during one hour long flights. Measurements were taken at two beaches and inland of one of them. Sampled concentrations compared well with same day aircraft and tower measurements. A surf zone upwind of one of the beaches produced surface concentrations as high as 250 μg m -3 , while the other beach without such a zone had less than 35 μg m -3 . The high concentrations at the surf beach extended above 145 m. Concentrations at 100 m correlated best to wind speed at this level and less so to previous two-day mean upwind surf condition, cloudiness and shower activity. Simultaneous measurements at and inland of the surf beach showed the effects of boundary layer mixing with a much more uniformly decreasing concentration profile as opposed to a steep decrease up to about 40 m at the beach. DOI: 10.1111/j.1600-0889.1989.tb00136.x

A distributed model of peritoneal-plasma transport: tissue concentration gradients.

Peritoneal dialysis transport studies were carried out in anesthetized rats. Injections of [14C]EDTA were made by intravenous bolus or intraperitoneal dialysis solution, and blood and peritoneal fluid samples were collected for 1 h. After death and rapid freezing of the animal, transverse sections through the abdominal cavity were cut for quantitative macroautoradiography. The plasma-to-peritoneal transport experiments with a clinical dialysis solution resulted in essentially horizontal concentration profiles versus distance in all tissues except large intestine. Estimates of the extracellular tissue fraction were: small intestine, 0.34; large intestine, 0.28; stomach, 0.30; uterus, 0.66; liver 0.35; diaphragm, 0.16; and anterior abdominal wall, 0.15. Similar experiments with an isotonic salt solution resulted in larger (13-300%) extracellular fractions in all tissues. In contrast, peritoneal-to-plasma transport studies demonstrated decreasing concentration profiles in all visceral tissues, with the first 90% of the gradient contained in the initial 400 micron of tissue from the peritoneum. Parietal tissue gradients were less steep and had higher concentration levels deep within the tissue than visceral tissues. Computer simulations using a distributed model approach compared favorably with the experimental measurements and established the validity of this approach.