Model Of Layer Formation Research Articles

A mechanical model for surface layer formation on self-lubricating ceramic composites

To predict the thickness of a self-lubricating layer on the contact surface of ceramic composite material containing a soft phase during dry sliding test, a mechanical model was built to calculate the material transfer of the soft second phase in the composite to the surface. The tribological test, as a case, the contact situation of a composite disk sliding against a loaded pin was studied in the model. The macroscopic deformation of the composite was supposed to be elastic. Subsurface stresses were calculated by the Hamilton's formulae. Further, the squeezed second phase material of inclusions was analyzed microscopically based on the Hashin's equations of inelastic inclusions. Based on the mechanical model, the thickness of the transferred layer during the multi sliding passes was predicted. The influence of material parameters and loading conditions such as inclusion (second phase) concentration in the composite, yield strength of the inclusion material, normal load on the pin and friction force were studied. The model can be used to design and optimize self-lubricating ceramic composites for applications and resulting contact conditions.

Permeate flux decline during UF of oily wastewater: Experimental and modeling

Oily wastewaters in Tehran refinery has become a big issue of water and environment pollution to be solved urgently. The results of an experimental study on separation of oil from oily wastewaters are presented. A polyacrylonitrile (PAN, 20kDa) membrane as the ultrafiltration (UF) membrane and an outlet wastewater of API unit of Tehran refinery were employed and the interaction effects of different operating parameters such as transmembrane pressure (TMP), cross-flow velocity (CFV), temperature and pH on permeate flux and fouling resistance were investigated. In this research, Taguchi method (L9 orthogonal array (OA)) was used initially to plan a minimum number of experiments.In this work, Hermia's models were used to investigate the fouling mechanisms involved in UF of oily wastewaters. The results showed that the best fit to experimental data corresponds to the cake layer formation model followed by the intermediate blocking model for all the experimental conditions tested. A more detailed analysis of the fouling mechanisms was studied via dividing the filtration curves into different regions corresponding to the different fouling mechanisms. Intermediate blocking and cake layer formation or combinations of them were found to occur during the UF experiments depending on the operating conditions.

Estimation of the gel layer concentration in ultrafiltration: Comparison of different methods

Fouling is one of the major limitations of membrane applications. Gel layer formation is a common fouling mechanism that increases the membrane fouling resistance. In this work the estimation of the gel layer concentration was performed from experimental values obtained in several ultrafiltration experiments using three methods: the gel-polarization model, the mechanistic model for gel layer formation proposed by Song and an expression of the concentration polarization modulus developed for tubular membranes and turbulent flow. The results were compared and analyzed. Two types of monotubular ceramic membranes with different MWCO (5 and 15 KDa) were used in the experiments. Polyethylene glycol (PEG) of 35,000 Da in distilled water was used as feed. The experiments were performed at different feed flow rates (1–3 m/s), transmembrane pressures (0.1–0.5 MPa), temperatures (15–40EC) and constant feed concentrations (5–15 g/L). Values of the gel layer concentration estimated with the gel-polarization model diff...

Reconstruction of Zebrafish Early Embryonic Development by Scanned Light Sheet Microscopy

A long-standing goal of biology is to map the behavior of all cells during vertebrate embryogenesis. We developed digital scanned laser light sheet fluorescence microscopy and recorded nuclei localization and movement in entire wild-type and mutant zebrafish embryos over the first 24 hours of development. Multiview in vivo imaging at 1.5 billion voxels per minute provides "digital embryos," that is, comprehensive databases of cell positions, divisions, and migratory tracks. Our analysis of global cell division patterns reveals a maternally defined initial morphodynamic symmetry break, which identifies the embryonic body axis. We further derive a model of germ layer formation and show that the mesendoderm forms from one-third of the embryo's cells in a single event. Our digital embryos, with 55 million nucleus entries, are provided as a resource.

Analysis of membrane pore blocking models applied to the ultrafiltration of PEG

In this work Hermia's models [J. Hermia, Constant pressure blocking filtration laws—application to power-law non-newtonian fluids, Trans. Inst. Chem. Eng. 60 (1982) 183–187] were used to investigate the fouling mechanisms involved in the ultrafiltration of polyethylene glycol (PEG). Ultrafiltration experiments were performed at different feed flow rates (1, 2 and 3 m/s) and transmembrane pressures (0.1, 0.2, 0.3, and 0.4 MPa). Feed concentration and temperature were kept constant at 5 g/L and 25 °C, respectively. The results showed that the best fit to experimental data corresponded to the cake layer formation model followed by the intermediate blocking model for all the experimental conditions tested. A more detailed analysis of the fouling mechanisms consisted in dividing the filtration curves in different regions that corresponded to the different fouling mechanisms. Complete blocking, intermediate blocking and cake layer formation or a combination of them were found to occur during the ultrafiltration experiments depending on the operating conditions tested.

Modeling of white layer formation under thermally dominant conditions in orthogonal machining of hardened AISI 52100 steel

This paper presents a finite element model for white layer formation in orthogonal machining of hardened AISI 52100 steel under thermally dominant cutting conditions that promote martensitic phase transformations. The model explicitly accounts for the effects of stress and strain, transformation plasticity and the effect of volume expansion accompanying phase transformation on the transformation temperature. Model predictions of white layer depth are found to be in agreement with experimental values. The paper also analyzes the effect of white layer formation on residual stress evolution in orthogonal cutting of AISI 52100 hardened steel. Model simulations show that white layer formation does have a significant impact on the magnitude of surface residual stress and on the location of the peak compressive residual stress.

Recent formation and evolution of northern Martian polar layered deposits as inferred from a Global Climate Model

We present a time‐marching model which simulates the exchange of water ice between the Martian northern cap, the tropics, and a high‐latitude surface reservoir. Net annual exchange rates of water and their sensitivity to variations in orbital/rotational parameters are examined using the Martian water cycle modeled by the LMD three‐dimensional Global Climate Model. These rates are propagated over the last 10 Myr to follow the thickness of the reservoirs. The effect of a sublimation dust lag is taken account to test simple models of layer formation. Periods of high mean polar summer insolation (∼5–10 Ma ago) lead to a rapid exhaustion of a northern polar cap and a prolonged formation of tropical glaciers. The formation of a northern cap and of a high‐latitude icy mantle may have started 4 Ma ago with the average decrease of polar insolation. Tropical ice may have disappeared around 2.7 Ma ago, but small glaciers could have formed during the last peaks of polar summer insolation. Over the last 4 Myr, most of the present cap may have formed at the expense of tropical and high‐latitude reservoirs forming distinct layers at almost each ∼51‐kyr/120‐kyr insolation cycle. Layers thickness ranges from 10 to 80 m, variations being produced by the modulation of the obliquity with ∼2.4 and 1.3 Myr periods. Because only ∼30 insolation cycles have occurred since 4 Ma ago, we found an inconsistency between the recent astronomical forcing, the observed number of layers, and simple astronomically based scenarios of layers formation.

Perspectives on mucus secretion in reef corals

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 296:291-309 (2005) - doi:10.3354/meps296291 Perspectives on mucus secretion in reef corals B. E. Brown*, J. C. Bythell School of Biology, Newcastle University, Newcastle upon Tyne NE1 7RU, UK *Email: profbarbarabrown@aol.com ABSTRACT: The coral surface mucus layer provides a vital interface between the coral epithelium and the seawater environment and mucus acts in defence against a wide range of environmental stresses, in ciliary-mucus feeding and in sediment cleansing, amongst other roles. However, we know surprisingly little about the in situ physical and chemical properties of the layer, or its dynamics of formation. We review the nature of coral mucus and its derivation and outline the wide array of roles that are proposed for mucus secretion in corals. Finally, we review models of the surface mucus layer formation. We argue that at any one time, different types of mucus secretions may be produced at different sites within the coral colony and that mucus layers secreted by the coral may not be single homogeneous layers but consist of separate layers with different properties. This requires a much more dynamic view of mucus than has been considered before and has important implications, not least for bacterial colonisation. Understanding the formation and dynamics of the surface mucus layer under different environmental conditions is critical to understanding a wide range of associated ecological processes. KEY WORDS: Mucin · Mucopolysaccharide · Coral surface microlayer · CSM · Surface mucopolysaccharide layer · SML Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 296. Online publication date: July 12, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Noctilucent clouds and the mesospheric water vapour: the past decade

Abstract. The topic of this paper is the sensitivity of the brightness of noctilucent clouds (NLC) on the ambient water vapour mixing ratio f(H2O). Firstly, we use state-of-the-art models of NLC layer formation to predict NLC brightness changes in response to changes in the 80km mixing ratio f(H2O) for the two cases of ground-based 532nm lidar observations at 69° N and for hemispheric satellite SBUV observations at 252nm wavelength. In this study, we include a re-evaluation of the sensitivity of NLC brightness to changes in solar Lyman α flux. Secondly, we review observations of episodic changes in f(H2O) and those in NLC brightness, the former being available since 1992, the latter since 1979. To this review, we add a new series of observations of f(H2O), performed in the Arctic summer at the ALOMAR observatory. The episodic change exhibited by the Arctic summer means of f(H2O) turns out to be quite different from all those derived from annual means of f(H2O). The latter indicate that since 1996 a significant reduction of annually averaged upper mesospheric water vapour has occurred at low, mid, and high latitudes. These decreases of f(H2O) have been observed over the same time period in which a slow increase of SBUV NLC albedo has occurred. From this scenario and additional arguments we conclude that the cause for the observed long-term increase in NLC albedo remains to be identified. We close with comments on the very different character of decadal variations in NLC brightness and occurrence rate.

A model of AlN layer formation during ion nitriding of Al

A diffusion model of AlN layer formation by ion nitriding of Al is proposed based on the analysis of atomic transport during the process. This model is reduced to the following. Implantation of N ions to the surface of the specimen, named the reaction zone; extraction of Al from the substrate; diffusion transport of Al to the reaction zone through an AlN layer formed during the process; formation and growth of AlN in the reaction zone; sputtering of the AlN layer. Equations controlling the growth process have been obtained.

Magnetic Field Effects on Electrochemical Processes: A Theoretical Hydrodynamic Model

The effect of a static homogeneous magnetic field that is directed parallel to the planar electrode surface is analyzed in terms of a hydrodynamic boundary layer formation and equivalent mass transfer model for a semi-infinite electrode. The model predicts the decrease of the boundary layer thickness upon increasing either the magnetic field strength, B, or reagent bulk concentration, C*, with the power dependence corresponding to C*4/3B1/3. This permits the interpretation of the enhanced mass transfer at electrode surfaces via hydrodynamic principles.

Percolation in deposits for competitive models in (1+1)-dimensions

The percolation behaviour during the deposit formation, when the spanning cluster was formed in the substrate plane, was studied. Two competitive or mixed models of surface layer formation were considered in (1+1)-dimensional geometry. These models are based on the combination of ballistic deposition (BD) and random deposition (RD) models or BD and family deposition (FD) models. Numerically we find, that for pure RD, FD or BD models the mean height of the percolation deposit h ̄ grows with the substrate length L according to the generalized logarithmic law h ̄ ∝( ln(L)) γ , where γ=1 (RD), γ=0.88±0.02 (FD) and γ=1.52±0.02 (BD). For BD model, the scaling law between deposit density p and its mean height h ̄ at the point of percolation of type p−p ∞∝ h ̄ −1/ν h are observed, where ν h =1.74±0.02 is a scaling coefficient. For competitive models the crossover, corresponding to the RD or FD-like behaviour at small L and the BD-like behaviour at large L are observed.

Modeling of the Blast Furnace Burden Distribution by Evolving Neural Networks

A model of burden layer formation in the blast furnace is developed on the basis of layer thicknesses estimated from radar measurements of the burden (stock) level in the furnace. The dependence between the layer thickness and charging variables is modeled by neural networks. Parsimonious networks are determined by an evolutionary algorithm, which simultaneously trains weights and network connectivity. The efficiency of the training procedure is enhanced by tackling part of the numerical optimization by linear least squares. The resulting network models are utilized in a hybrid model, which considers practical constraints of the charging process in the furnace. The hybrid model is used to evaluate the impact of altered boundary conditions in novel charging programs.

Nucleation and Growth of Zinc Electrodeposited onto Electropolished and Mechanically Polished Steel Surfaces

SUMMARYNucleation and growth of zinc electrodeposition in acid sulphate bath on electropolished and mechanically polished low carbon steel surfaces was investigated. On both surfaces thin η-zine crystals were stacked on each other, although their orientation was different. Potentiostatic current-time plots and cyclic voltammetry were used to study the nucleation process. The results indicated that at pH 2 the nucleation process on both surfaces um instantaneous, and that the growth process was charge transfer controlled. The growth rate on the electropolished surface was higher than the mechanically polished surface under the same electrochemical conditions. Increasing temperature did not affect the nucleation mode; it only increased the growth rate. Increasing the pH from 2 to 4 caused deviation from instantaneous nucleation, so that on the mechanically polished surface the nucleation mode was fully progressive. The reason for this behavior was attributed to the number density of active nucleation sites on the steel surface. Cyclic voltammetry also confirmed the hydroxide layer formation model.

Percolation in models of thin film depositions.

We have studied the percolation behavior of deposits for different (2+1)-dimensional models of surface layer formation. The mixed model of deposition was used, where particles were deposited selectively according to the random (RD) and ballistic (BD) deposition rules. In the mixed one-component models with deposition of only conducting particles, the mean height of the percolation layer (measured in monolayers) grows continuously from 0.898 32 for the pure RD model to 2.605 for the pure BD model, but the percolation transition belongs to the same universality class, as in the two-dimensional (2D) random percolation problem. In two-component models with deposition of conducting and isolating particles, the percolation layer height approaches infinity as concentration of the isolating particles becomes higher than some critical value. The crossover transition from 2D to 3D percolation was observed with increase of the percolation layer height.

Kinetics of lipid layer formation at interfaces

A formal kinetic model of lipid layer formation at an interface in contact with a liposomal suspension is developed and investigated. Neglecting diffusion (for sufficiently high bulk concentrations) the kinetic scheme consists of two consecutive processes: (I) irreversible transformation of ‘soluble’ intact vesicles from the ‘subsurface’ layer into ‘adsorbed’ ones (‘defected’ or ‘ruptured’ liposomes, ‘mesophases’); and (II) irreversible transformation of the ‘adsorbed’ vesicles into a lipid monolayer. The resulting set of two differential equations is analyzed making use of the ‘steady-state concentration’ approach (with ‘adsorbed’ vesicles as intermediate compound). Numerical results illustrate the predicted kinetic behavior which depends on the relative magnitude of the rates of the two consecutive processes. Approximate analytical solutions in the case of a much slower process I are obtained in some limiting cases. The model is used to estimate rate constants from previously established experimental kinetic data at the air/water interface.

Sensor studies of the initial stages of the cadmium telluride film formation through vapor deposition

The results of sensor and electron-microscopic studies of the initial stages of cadmium telluride film formation through vapor deposition on a substrate at room temperature and on a substrate cooled by liquid nitrogen (highly nonequilibrium conditions) are reported. A piezoelectric quartz resonator is used as a sensor. The kinetic curves of the sensor analytical signal and photomicrographs are presented. A jumplike character of the nucleation process and a quasi-periodical growth mechanism for island films are disclosed. A sequence of new-phase island ensembles is formed in an analogous way. These islands increase the substrate surface coverage in a quasi-discrete manner. The experimental results are shown to agree with current theory of the first-order phase transitions and models of layer formation in highly nonequilibrium conditions.

A model for layer formation in stably stratified turbulence

Stably stratified turbulent flows are common in geophysics and astrophysics, and frequently exhibit layered structures in which large regions of nearly constant fluid density are separated by sharp density gradients. Experiments have demonstrated that, under suitable conditions, the stirring of a stably stratified fluid generates these layer structures. In this paper, a stochastic one-dimensional model is used to study layer formation in stably stratified turbulence. The results support mixing length arguments previously proposed to describe layers in steady state.

Lidar observations of a large high‐altitude sporadic Na layer during active aurora

A large sporadic Na layer was observed near 109 km during active aurora at Poker Flat, Alaska, on the night of 12–13 January 1996. This sporadic layer is significantly denser and broader than previously reported thermospheric sporadic layers; having a peak concentration equal to the peak concentration of the background Na layer, a FWHM of 4.7 km, and a column abundance of 40% of the background Na layer. The appearence of the Nas layer coincided with a significant OH temperature gradient across the sky but did not coincide with the presence of a discrete arc overhead nor a distinct signature in the local magnetometer data. The presence of such a large amount of neutral Na at these altitudes contradicts the current models of Nas layer formation. The observations are discussed in the light of other observations, current models, layered auroral phenomena, and meteoric ablation.

Reactive interaction between surfaces of lithium metal and electrolyte components

A brief overview concerning the nature of lithium “passivity” and the use of in-situ techniques in lithium research will be given in order to emphasize the important role of the properties of the phase boundary metal/electrolyte. The electrochemical behaviour of lithium is strongly influenced by the formation of a surface layer due to the reduction of the solvent and of the electrolyte. A model for layer formation at uncovered lithium surfaces will be suggested.