Sublayer Structures Research Articles

Dilational rheological properties of extended anionic surfactants at decane-water interface

The dynamic interfacial dilational properties of extended surfactants octadecyl-(polypropylene oxide)m-(polyethylene oxide)n-carboxylic sodium (C18POmEOnC) with different numbers of polypropylene oxide (PO) and polyethylene oxide (EO) groups at the decane–water interface were investigated by means of oscillating drop method. The influences of interface ageing time, dilational frequency, bulk concentration and interfacial pressure on the dilational properties were investigated. The experimental results demonstrate that, at low concentrations, the adsorption film is predominantly influenced by diffusion exchange, while intermolecular interactions at the interface play a more significant role at high concentrations. Beyond the critical micelle concentration (CMC), the primary relaxation process in the adsorption film is driven by the formation of micellar structures. Additionally, the weak hydrophobic PO groups exhibit compressibility and extensibility, facilitating the formation of spring-like helical structures at the decane–water interface. As a result, the dilational modulus increases and the phase angle decreases in low concentration with the increase of PO number. With increasing concentration, the weak hydrophilic EO chains gradually transition from a partially flat state to an upright orientation toward the aqueous phase, forming sublayer structures through polar interactions. At this stage, the increase in EO group chain length has a more pronounced impact on the elastic modulus compared to PO groups. These experimental findings suggest the existence of a mechanistic model for the extended surfactant adsorption films.

Comparative In Vivo Imaging of Retinal Structures in Tree Shrews, Humans, and Mice.

Rodent models, such as mice and rats, are commonly used to examine retinal ganglion cell damage in eye diseases. However, as nocturnal animals, rodent retinal structures differ from primates, imposing significant limitations in studying retinal pathology. Tree shrews (Tupaia belangeri) are small, diurnal paraprimates that exhibit superior visual acuity and color vision compared with mice. Like humans, tree shrews have a dense retinal nerve fiber layer (RNFL) and a thick ganglion cell layer (GCL), making them a valuable model for investigating optic neuropathies. In this study, we applied high-resolution visible-light optical coherence tomography to characterize the tree shrew retinal structure in vivo and compare it with that of humans and mice. We quantitatively characterize the tree shrew's retinal layer structure in vivo, specifically examining the sublayer structures within the inner plexiform layer (IPL) for the first time. Next, we conducted a comparative analysis of retinal layer structures among tree shrews, mice, and humans. We then validated our in vivo findings in the tree shrew inner retina using ex vivo confocal microscopy. The in vivo and ex vivo analyses of the shrew retina build the foundation for future work to accurately track and quantify the retinal structural changes in the IPL, GCL, and RNFL during the development and progression of human optic diseases.

A Simple Model Generator for Radar Sounding Applications Based on Stochastic Media Model and gprMax

Ground penetrating radar (GPR), or more generically called radar sounding, is an established technique for probing subsurface objects and sublayer structures. Simulating pre-constructed models and comparing with the real-world observations can contribute to retrieve the geometrical and physical properties of subsurface objects. However, most GPR simulations are limited to geometrically simple models with homogeneous physical properties of subsurface media which are generally unable to represent the real-world situations. In this paper, we develop a simple model generator by combining the stochastic media model and gprMax, an open-source software for electromagnetic simulations, to jointly generate models with geometrically random fragments, which are forward models with minimum human intervention. These easily prepared and simulated models can enrich the model training datasets which can be further utilized in machine learning for GPR retrieval algorithms.

Ternary Phase-Field Simulations of the Skin-Sublayer Structures in Poly(vinylidene fluoride) Microporous Membranes Prepared by a Nonsolvent-Induced Phase Separation.

In this paper, the existing phase-field model based on the nonsolvent-induced phase separation (NIPS) method was optimized. Two-dimensional simulations using the relevant parameters of a poly(vinylidene fluoride) (PVDF) membrane system were carried out, simulating and analyzing the effects of changes in initial concentrations, concentration fluctuations, and diffusion rates of the solvent on the skin layer and sublayer structures of the membranes. These simulations modeled the process of preparing PVDF microporous membranes by the NIPS method to better understand the structural development of PVDF microporous membranes under different conditions. It was found that dense skin layers were formed at the mass-transfer exchange interface of the PVDF microporous membranes, whose number increased with the decrease of the concentration fluctuation, which has little effect on the structure of the sublayer. The initial concentration of PVDF and the diffusion rate of the solvent had a little impact on the number of skin layers yet played a relatively large role in the formation time of the skin layers and the structure of the sublayers. Also, the validity of the model was verified by corresponding experiments. Hence, the model can be applied to other PVDF ternary membrane systems by modifying specific thermodynamic and kinetic parameters.

Evolution of electron current layer during anti-parallel magnetic reconnection

Electron current layer (ECL) in the diffusion region plays an important role on energy dispassion and generation of a magnetic island during collisionless magnetic reconnection. In this study, kinetic simulations with high-resolution grids are performed to investigate the evolution of ECL during anti-parallel magnetic reconnection. It is found that ECL splits into two sublayers at the electron inertial scale, not long after the triggering of reconnection. The sublayers keep moving away from each other until reconnection rate reaches the maximum. We find the formation reason and maintaining mechanism of these sublayer structures of the ECL. When electrons flow toward the midplane, out-of-plane velocity is increased by the reconnection electric field. The deflection of magnetic field makes the out-of-plane component of velocity partly converted to the z direction. Electron flows pass through the mid-plane with super-Alfvenic speed. When they enter the other side, the increasing magnetic field makes velocity in the z direction gradually converted to the out-of-plane. Slowdown of the flows causes the density accumulation at the two sides of the mid-plane. The redistribution of electrons brings an extra pressure gradient to the ECS region, balancing the electric force and Ampere force.

Blisters on graphite surface: a scanning microwave microscopy investigation.

Scanning microwave microscopy (SMM) is based on the interaction between a sample and an electromagnetic evanescent field, in the microwave frequency range. SMM is usually coupled with a scanning probe microscopy (SPM) technique such as in our case, a scanning tunneling microscope (STM). In this way, the STM tip is used to control the distance between the probe and the sample while acting as an antenna for the microwave field. Thanks to the peculiarity of our home-made setup, the SMM is a suitable method to study blisters formed on HOPG surface as consequence of an electrochemical treatment. Our system has a “broad-band” approach that opens the way to perform local microwave spectroscopy over a broad frequency range. Moreover, microwaves have the ability to penetrate into the sample allowing the sub-surface characterization of materials. The application of the SMM to characterize blisters formed on the HOPG surface provides information on the sub-layer structures.

Tailoring both the surface pore size and sub-layer structures of PVDF membranes prepared by the TIPS process with a triple orifice spinneret

Membrane surface and sub-layer structures were tailored by extruding different types of solvents at the outer layer of the extruded polymer solution.

Numerical Characterisation of Active Drag and Lift Control for a Circular Cylinder in Cross-Flow

Synthetic jet actuators have shown promise to control drag and lift for a bluff body in cross-flow. Using unsteady RANS CFD modelling, a significant modification of the drag coefficient for a circular cylinder in cross-flow at R e = 3900 is achieved by varying the actuation frequency. The variation in actuation frequency corresponds to a range in Stokes number of 2.4 < S t o < 6.4. The trends in drag coefficient modification largely agree with the findings of past publications, achieving a maximum drag reduction at S t o = 4.9 for a fixed jet Reynolds number of the synthetic jet of R e U ¯ o = 12. A decrease in the adverse pressure gradient near the jet orifice correlated with a momentum increase in the viscous sublayer and stronger vortical structures at the rear of the cylinder. In these same conditions, a decrease in turbulence intensity was observed in the far field wake, which is a relevant finding in the context of wind and tidal turbine arrays.

The gradient structure of the NiTi surface layers subjected to tantalum ion beam alloying

The NiTi shape memory alloy has been modified by ion implantation with Ta to improve the surface and biological properties. The elemental and phase composition and structure of the surface and near-surface layers of NiTi specimens after the Ta ion implantation with the fluency D = 3 × 1017 cm-2 and D = 6 × 1017 cm-2 are examined. The methods of Auger electron spectroscopy (AES), transmission electron microscopy (TEM), and electron dispersion analysis (EDS) are used. It is found that a nonuniform distribution of elements along the depth of the surface layer after the ion implantation of NiTi specimens, regardless of the regime, is accompanied by the formation of a number of sublayer structures.

Effect of microstructure and mechanical properties difference between sub-layers on the performance of alternate hard and soft diamond-like carbon multilayer films

Alternate hard and soft diamond-like carbon (DLC) multilayer films with different modulus ratio and residual stress ratio between adjacent sub-layers were prepared by magnetron sputtering through alternating deposition bias. The microstructure, hardness and toughness of DLC films as well as their tribological properties under dry and water-lubricated sliding conditions were systematically studied in relation to the effects of modulus ratio and residual stress ratio between adjacent sub-layers. For multilayer DLC films with similar microstructure of adjacent sub-layers, the higher bias dominates the transformation from sp2 to sp3 carbon. As to multilayer DLC films with much different microstructure between adjacent sub-layers, the compact and ordered sub-layer structures formed under lower bias keeps growing even under higher deposition bias. Although multilayer strengthening effect is insignificant in multilayer DLC films, multilayer toughening effect is outstanding. Multilayer DLC films deposited at a substrate bias alternating between −120 and −160V have the highest toughness which is almost double of that of monolayer DLC films, because the multilayer structure with low modulus ratio contributes to reduce the stress concentration in harder sub-layer thereby inhibiting crack initiation. Moreover, multilayer DLC films show better wear resistance than monolayer DLC films under both dry and water-lubricated sliding conditions. It was found that the higher toughness inhibited abrasive wear on the sliding steel counterface and contributed to the formation of transfer film.

A Younger Dryas varve chronology from the Rehwiese palaeolake record in NE-Germany

The first 1400-year floating varve chronology for north-eastern Germany covering the late Allerød to the early Holocene has been established by microscopic varve counts from the Rehwiese palaeolake sediment record. The Laacher See Tephra (LST), at the base of the studied interval, forms the tephrochronological anchor point. The fine laminations were examined using a combination of micro-facies and μXRF analyses and are typical of calcite varves, which in this case provide mainly a warm season signal. Two varve types with different sub-layer structures have been distinguished: (I) complex varves consisting of up to four seasonal sub-layers formed during the Allerød and early Holocene periods, and, (II) simple two sub-layer type varves only occurring during the Younger Dryas. The precision of the chronology has been improved by varve-to-varve comparison of two independently analyzed sediment profiles based on well-defined micro-marker layers. This has enabled both (1) the precise location of single missing varves in one of the sediment profiles, and, (2) the verification of varve interpolation in disturbed varve intervals in the parallel core. Inter-annual and decadal-scale variability in sediment deposition processes were traced by multi-proxy data series including seasonal layer thickness, high-resolution element scans and total organic and inorganic carbon data at a five-varve resolution. These data support the idea of a two-phase Younger Dryas, with the first interval (12,675–12,275 varve years BP) characterised by a still significant but gradually decreasing warm-season calcite precipitation and a second phase (12,275–11,690 varve years BP) with only weak calcite precipitation. Detailed correlation of these two phases with the Meerfelder Maar record based on the LST isochrone and independent varve counts provides clues about regional differences and seasonal aspects of YD climate change along a transect from a location proximal to the North Atlantic in the west to a more continental site in the east.

Sublayer structure and reflection coefficient and their effects on concentration polarization and membrane performance in FO processes

We have demonstrated through experimental and theoretical study that membrane sublayer structure has significant influence on the performance in forward osmosis (FO) processes. Cellulose acetate (CA) hollow fiber membranes with different sublayer structures have been fabricated by varying the bore fluid composition during dry-jet wet spinning and then characterized in terms of pore structure of the selective layer, porosity of the sublayer, pure water permeability (PWP) coefficient, salt permeability coefficient and salt rejection. The water flux and reverse salt flux of these membranes are evaluated in the pressure-retarded osmosis (PRO) mode and FO mode. It is observed that varying the sublayer structure does not have apparent influence on the FO performance under the PRO mode but has significant influence on the performance under the FO mode. The different performance under different operation modes is resulted from more severe concentration polarization (CP) in the FO mode. The characteristics of the membrane sublayer structure are the origin of CP phenomenon in the FO mode. Through NF tests and FO tests with low draw solution concentrations on one of the membranes, the reflection coefficients ( σ 0) are determined as 0.77 and 0.99 for NaCl and MgCl 2 draw solutes, respectively. A low reflection coefficient indicates a low effective driving force in FO processes resulted from serious leakage of draw solutes from the draw solution to the feed. Thus, the reflection coefficient cannot be assumed to be equal to 1 and its significance must be considered when modeling FO performance using NaCl as the draw solute. The theoretical study reveals that the sublayer porosity, tortuosity and thickness have great impact on membrane performance when the draw solution flows against the sublayer. The desired FO membrane should have no sublayer. Since the phase inversed membrane may always have a sublayer, the preferred sublayer has high porosity, low tortuosity and small thickness. However, FO membranes for water reuse may have less structure requirements than those for seawater desalination.

Some Issues of Rough Surface Contact Plasticity at Micro- and Nano-Scales

ABSTRACTRough surface contact plasticity at microscale and nanoscale is of crucial importance in many new applications and technologies, such as nano-imprinting and nano-welding. This paper summarizes our recent progress in understanding contact plasticity from a multiscale point of view, and also presents our perspectives. We first discuss a contact model based on fractal roughness and continuum plasticity theory. Interestingly, our simple, elastic-plastic contact model of the Weierstrass-Archard type gives rise to many practical scaling relations of contact pressure, contact compliance etc. The usefulness of those predictions is discussed for experimental measurements of the thermal/electrical contact resistance. A material length scale can be introduced by a nonlocal plasticity theory, or implicitly by dislocation mechanics modeling. The recent work on micro-plasticity of surface steps gives a variety of surface yielding and hardening behaviors, depending on interface adhesion, roughness features and slip systems. As a consequence, a rough surface contact at mesoscale can lead to the formation of a boundary layer with sub-layer dislocation structures, which cannot be predicted by existing strain gradient plasticity theories. The micromechanical analysis of surface plasticity could serve as the connection between microscale bulk dislocation plasticity and nanoscale atomistic simulations.

Effect of adhesion strength of DLC to steel on the coating erosion mechanism

The wear of DLCs deposited onto steel substrates using a graphite arc-pulse sputtering technique in a corundum particle jet was studied. Two sample sets had different adhesion strength to the substrate due to different adhesive sublayer structures. It was found that the DLC itself does not wear, so that coating destruction occurs due to peeling. Analysis of the wear results for coatings having different (0.4–2.6 μm) thickness revealed that peeling is a result of two basic crack systems: (i) from the DLC surface inside the coating; and (ii) along the DLC–substrate interface.

Large-Eddy Simulations of the Atmospheric Boundary Layer Using a New Subgrid-Scale Model – II. Weakly and moderately stable cases

A series of simulations under weakly to moderately stable boundary layers (SBLs) have been performed using the proposed subgrid-scale (SGS) model implemented into the Terminal Area Simulation System (TASS). The proposed SGS model incorporates some aspects of the two-part eddy viscosity SGS model of Sullivan et al. (1994) and further refinements which include the dependence of SGS mixing length on stratification, two-part separation of the SGS eddy diffusivity of heat, and more realistic empirical forms of Monin–Obukhov similarity functions. The potential temperature profiles from simulations clearly show a three-layer structure: a stable surface layer of strong gradients, a middle layer of small gradients, and an inversion layer on the top. The wind speed profiles show the formation of low level jet (LLJ). However, the sub-layer structures under moderately SBLs differ from those under weakly SBLs. Both the momentum and heat fluxes decrease almost linearly in the lower part of the SBL. The near surface values of the normalized turbulent kinetic energy (TKE/u*2) in all simulations are about 4 which is much less than the typical value of 5.5 under the neutral condition. The decay of turbulence first occurs in the area with large values of Richardson number (Ri<0.2). Generally, instantaneous values of the TKE and Ri at the various grid points are negatively correlated, but there is not a unique relationship between the two parameters.

Metallizing of Silicon-Carbide Ceramics with Titanium Vapor

Silicon-carbide ceramic was metallized with titanium by the vapor-diffusion method, where pure titanium powder was used as a vapor source at temperatures between 973 and 1323K for up to 296.1ks in a dynamic vacuum atmosphere. The structure and composition of the metallized layers were investigated by scanning electron microscopy, electron-probe microanalysis, and X-ray diffraction analysis. At the initial stage of the metallization, titanium vapor reacted preferentially with the so called free carbon in the grain boundaries of SiC ceramics to form a titanium carbide, and then a metallized layer was grown laterally, forming the sublayer structures. This sub-layer structure was composed of five sub-layers; TiC (top surface), Ti5Si3 containing TiC (outer layer), TiC containing Ti5Si3 (middle layer), Ti5Si3 (inner layer) and Ti3SiC2 (bottom layer). Growth kinetics of each sub-layer and their total thicknesses obeyed the parabolic rate law, and the parabolic rate constants (kp) for the total layer varied between 10-16m2·s-1 at 1173K and 10-15m2·s-1 at 1323K. The activation energy (Qkp) obtained for the metallized layer was 153kJ·mol-1.

Structural properties of amorphous chalcogenide SeTe/CdSe superlattices

Structural perfection, periodicity and stability of novel amorphous chalcogenide SeTe/CdSe superlattices are investigated by means of small-angle X-ray diffraction. Interfacial roughness of about two atomic layers is estimated. Conclusions about the SeTe sublayer structures are deduced from the study of radial distribution function and Raman spectra of the superlattices.

Mass transfer modeling of asymmetric membrane formation by phase inversion

AbstractA derivation is presented of a ternary diffusion model to describe the mass transfer processes associated with the quench bath period of the phase inversion process for membrane formation. The complete governing equations, initial conditions, and boundary conditions in the casting film and coagulation bath are presented. Equations for ternary chemical potentials and diffusion coefficients are consistently based on constant specific volume formulations. The model is applied to the analysis of mass transfer paths and their effects on membrane structure formation. Precipitation times are determined for given sets of conditions by superposing calculated mass transfer paths on the ternary phase diagram and observing when the miscibility gap is crossed. Comparisons are made with an earlier reported study on the membrane‐forming system: water‐acetone‐cellulose acetate (CA). Agreement between predicted and measured precipitation times is found to be excellent. The polymer film composition profile at the moment of precipitation is shown to be a useful indicator of both skin and sublayer structures, allowing distinctions to be made between conditions leading to spongelike and fingerlike morphologies. The influence of model parameters on the mass transfer paths and associated polymer profiles is also discussed.

Flow measurements behind attached ring-type turbulence promoters

The flow field behind attached ring-type turbulence promoters of various sizes in a smooth pipe has been investigated by measuring the mean velocity and turbulence intensity profiles for downstream distances up to 100 promoter heights at a Reynolds number of 20 500 (based on pipe diameter and average velocity). Measurements have been limited to distances downstream of the flow reattachment region. The results indicate that for the smallest tested promoter with nondimensional height h+=12.5, the disturbance introduced does not have much influence in the core region and the flow behind the promoter reorganizes and recovers very quickly (within a streamwise distance equivalent to 20–30 promoter heights). On the other hand, for the largest promoter tested (h+=100), the flow in the core is significantly perturbed and the return of the flow to a self-preserving state has not been achieved, even at a downstream distance of 100 promoter heights. Furthermore,the mean velocity profile in the core region of the pipe with the largest promoter is much more uniform than the corresponding smooth pipe profile, indicating enhanced mixing. The longitudinal turbulence energy spectra in the sublayer, buffer layer, and logarithmic layer suggest that the sublayer structures are maintained and/or enhanced by large wallward motions originated in the core. These results are fairly consistent with the vortex model of Kobashi and Ichijo [Exp. Fluids 4, 49 (1986)].