Lateral Separation Research Articles

Dean-Flow Affected Lateral Focusing and Separation of Particles and Cells in Periodically Inhomogeneous Microfluidic Channels.

The purpose of the recent work is to give a better explanation of how Dean vortices affect lateral focusing, and to understand how cell morphology can alter the focusing position compared to spherical particles. The position and extent of the focused region were investigated using polystyrene fluorescent beads with different bead diameters (Ø = 0.5, 1.1, 1.97, 2.9, 4.8, 5.4, 6.08, 10.2, 15.8, 16.5 µm) at different flow rates (0.5, 1, 2 µL/s). Size-dependent focusing generated a precise map of the equilibrium positions of the spherical beads at the end of the periodically altering channels, which gave a good benchmark for focusing multi-dimensional particles and cells. The biological samples used for experiments were rod-shaped Escherichia coli (E. coli), discoid biconcave-shaped red blood cells (RBC), round or ovoid-shaped yeast, Saccharomyces cerevisiae, and soft-irregular-shaped HeLa cancer-cell-line cells to understand how the shape of the cells affects the focusing position at the end of the channel.

Perceived Safety Influencing Active Travel to School-A Built Environment Perspective.

Despite the many research studies on active school travel (AST), the number of children walking/cycling to school is decreasing as there is a lack of implementable research evidence. This review through database searches from 2000 to 2020 aims to identify research gaps and explore new perspectives. The articles are selected and screened methodically for systematic presentation of the review. An existing active school travel framework is used to structure and discuss this review paper on mediating factors influencing children's active travel to school, that is the perceived traffic safety, neighborhood safety, and distance to school. Perception of traffic safety could be ameliorated through lateral separation from the traffic, and this could be a new area of research. The neighborhood safety perception may require more research to validate the previous findings. Schools should be located within high-density residential development so that many children can walk to school.

Membrane curvature sensing by model biomolecular condensates.

Biomolecular condensates (BCs) are fluid droplets that form in biological cells by liquid-liquid phase separation. Their major components are intrinsically disordered proteins. Vast attention has been given in recent years to BCs inside the cytosol and nucleus. BCs at the cell membrane have not been studied to the same extent so far. However, recent studies provide increasingly more examples of interfaces between BCs and membranes which function as platforms for diverse biomolecular processes. Galectin-3, for example, is known to mediate clathrin-independent endocytosis and has been recently shown to undergo liquid-liquid phase separation, but the function of BCs of galectin-3 in endocytic pit formation is unknown. Here, we use dissipative particle dynamics simulations to study a generic coarse-grained model for BCs interacting with lipid membranes. In analogy to galectin-3, we consider polymers comprising two segments - one of them mediates multivalent attractive interactions between the polymers, and the other one has affinity for association with specific lipid head groups. When these polymers are brought into contact with a multi-component membrane, they spontaneously assemble into droplets and, simultaneously, induce lateral separation of lipids within the membrane. Interestingly, we find that if the membrane is bent, the polymer droplets localize at membrane regions curved inward. Although the polymers have no particular shape or intrinsic curvature, they appear to sense membrane curvature when clustered at the membrane. Our results indicate toward a generic mechanism of membrane curvature sensing by BCs involved in such processes as endocytosis.

Collision risk assessment of reduced aircraft separation minima in procedural airspace using advanced communication and navigation

With the advancement of Communication, Navigation and Surveillance (CNS) technologies such as space-based Automatic Dependent Surveillance-Broadcast/Contract (ADS-B/C), large separation minima may be reduced in procedural airspaces. It is of great significance to know the upper limit of the Reduced Separation Minima (RSM) for a procedural airspace and the corresponding consequences on collision risk with specifics of the advanced ADS-B and control intervention model. In this work, an interactive software is first developed for collision risk estimation. This software integrates the International Civil Aviation Organization (ICAO) collision risk models for lateral and longitudinal collision risk calculation for the Singapore procedural airspace. Results demonstrate that the lateral and longitudinal collision risk of Singapore procedural airspace with respect to current control procedures meets the ICAO Target Level of Safety (TLS) standard. Moreover, the feasibility of reducing the horizontal separations implemented in the Singapore procedural airspace with respect to advanced CNS techniques is investigated. It is found that if advanced CNS technologies are applied, then the current 50-NM lateral and longitudinal separation standards can be reduced to 22 NM (1 NM = 1.825 km) and 20 NM, respectively, to meet the TLS standards based on current demand. A method is then devised to expand the traffic demand by p for p ∈ [10%, 200%]. It is found that the minimum lateral and longitudinal separations can be reduced from 50 NM to be within the range of [23, 31] NM, and 20 NM, respectively, for p ∈ [10%, 200%], while the collision risk still meets the TLS standards.

Fluorescence Spectroscopic Analysis of Lateral and Transbilayer Fluidity of Exosome Membranes.

Exosomes are small extracellular vesicles (sEVs) involved in distal cell-cell communication and cancer migration by transferring functional cargo molecules. Membrane domains similar to lipid rafts are assumed to occur in exosome membranes and are involved in interactions with target cells. However, the bilayer membrane properties of these small vesicles have not been fully investigated. Therefore, we examined the fluidity, lateral domain separation, and transbilayer asymmetry of exosome membranes using fluorescence spectroscopy. Although there were some differences between the exosomes, TMA-DPH anisotropy showing moderate lipid chain order indicated that ordered phases comprised a significant proportion of exosome membranes. Selective TEMPO quenching of the TMA-DPH fluorescence in the liquid-disordered phase indicated that 40-50% of the exosome membrane area belonged to the ordered phase based on a phase-separated model. Furthermore, NBD-PC in the outer leaflet showed longer fluorescence lifetimes than those in the inner leaflets. Therefore, the exosome membranes maintained transbilayer asymmetry with a topology similar to that of the plasma membranes. In addition, the lateral and transbilayer orders of exosome membranes obtained from different cell lines varied, probably depending on the different membrane lipid components and compositions partially derived from donor cells. As these higher membrane orders and asymmetric topologies are similar to those of cell membranes with lipid rafts, raft-like functional domains are possibly enriched on exosome membranes. These domains likely play key roles in the biological functions and cellular uptake of exosomes by facilitating selective membrane interactions with target organs.

On the Stability of Particle–Particle Interaction during Gravitational Settling

The elevated energy demand and high dependency on fossil fuels have directed researchers’ attention to promoting and advancing hydraulic fracturing (HF) operations for a sustainable energy future. Even though previous studies have demonstrated that the proppant suspension and positioning in slickwater play a vital role during the shut-in stage of the HF operations, minimal experimental work has been conducted on the fundamental proppant–proppant interaction mechanisms, especially a complete mapping of the interactions. This study utilizes high-speed imaging to provide a 2D space- and time-resolved investigation of two-particle (proppant models: 2 mm Ø, 2.6 g·cm−3) interactions during gravitational settling in different initial spatial configurations and rheological properties. The mapping facilitates the identification of various interaction regimes and newly observed particle trajectories. Pure water results at a settling particle Reynolds number (Rep) ~ 470 show an unstable particle–particle interaction regime characterized by randomness while altering pure water to a 25% (v/v) water–glycerin mixture (Rep ~ 200) transitions an unstable interaction to a stable prominent repulsion regime where particles’ final separation distance can extend up to four times the initial distance. This indicates the existence of Rep at which the stability of the interactions is achieved. The quantified trajectories indicate that when particles are within minimal proximity, a direct relation between repulsion and Rep exists with varying repulsion characteristics. This was determined by observing unique bottle-shaped trajectories in the prominent repulsion regimes and further highlighted by investigating the rate of lateral separation distance and velocity characteristics. Additionally, a threshold distance in which the particles do not interact (or negligibly interact) and settle independently seems to exist at the normalized 2D lateral separation distance.

A Comparison of Spectrum-Splitting Configurations for High-Efficiency Photovoltaic Systems With Perovskite Cells

The recent development of inexpensive perovskite photovoltaic (PV) cells at a variety of band gap energies has opened the prospects for commercially viable spectrum-splitting PV systems. A variety of cell configurations exist for implementing spectrum splitting in PV modules. In this article, 3-junction and 4-junction hybrid spectrum-splitting systems are proposed that use volume holographic lens arrays for lateral spectral separation and absorptive filtering in semitransparent perovskite PV cells for vertical spectral separation. A 3-junction hybrid system is shown to have greater conversion efficiency (28.7%) than comparable systems using completely lateral (25.6%) or completely stacked (26.9%) cell arrangements. It is shown that a 4-junction hybrid system has a hypothetical conversion efficiency of 30.0% using perovskite PV cells that have been experimentally demonstrated in the literature with energy band gaps of 1.25 eV, 1.55 eV, 1.72 eV, and 2.30 eV.

Spin-locked scattering of unpolarized light by magnetoelectric coupling

Unpolarized light is ubiquitous in nature. It does not carry spin angular momentum but it can be converted to partially polarized light with spin angular momentum after scattering. In this work, we demonstrate that the unpolarized light not only possesses a definite spin state after scattering but also induces lateral separation of scattered light with opposite chiralities. Such spin-locked scattering of unpolarized light stems from the inherent property of magnetoelectric coupling of the scatterer. Moreover, the spin-locked scattering for arbitrary linearly polarized light is also investigated and compared with the case of unpolarized light. Our findings can broaden the application range of unpolarized light and open other avenues for spin-related phenomena induced by unpolarized light.

Wind-induced response of an offshore wind turbine under non-neutral conditions: A comparison with Hywind Scotland

In this study, aeroelastic simulations of a 5 MW spar wind turbine are performed by using simulated wind fields that are representative of surface layer marine atmospheric turbulence under different atmospheric stratifications. The spar floater’s motion responses from the simulations are then compared with the observations from Hywind Scotland’s 6 MW spar wind turbine. The platform’s pitch and yaw motions from the simulations are consistent with the observations, in terms of mean wind speed and atmospheric stratification. The simulations and the observations show that a stable atmosphere induces the lowest platform pitch and yaw motions compared to neutral and unstable stratifications. Nonetheless, the discrepancy of platform motions between stable and unstable conditions is more pronounced from the observations than in the simulations. Uncertainties associated with the estimation of the atmospheric stability and the modelling of the turbulence’s co-coherence for lateral separation may partly account for the discrepancies between the observed and the simulated motion responses of the spar wind turbine.

Schooling benefits from a system of active and passive hydrofoils

Fishes school to swim more efficiently while not much of fish schooling is understood from the perspective of fluid–structure interactions. To understand the benefits of fish schooling, we investigate thrust, efficiency, and wake structure of a two-hydrofoil system where the upstream hydrofoil is forced pitching (active) and the downstream hydrofoil is free pitching (passive). The streamwise and lateral separations between the two hydrofoils are 0.109c and 1.0D, respectively, where c is the chord length and D is the diameter of the leading edge. The active hydrofoil pitches with normalized amplitudes A∗=0.55 – 0.80 and normalized frequencies StD=0.23–0.33. It is found that the upstream active hydrofoil undergoes up to 38% thrust enhancement in the presence of the downstream passive hydrofoil while the downstream passive hydrofoil achieves the same thrust as the upstream active hydrofoil under certain conditions. The maximum combined thrust and efficiency achieved for the two-hydrofoil system are 95% and 180% higher than those for a single isolated hydrofoil. These are some reasons for fish swimming in school. Three distinct flow structures (vortex impingement flow, vortex trapping flow, and vortex splitting flow) are identified in the A∗– StD domain, where the vortex trapping flow provides the greatest thrust and efficiency enhancement.

An Improved Runway Operation Capacity Model for V-Open Multirunway Airports in China

Diverging runways are receiving considerable attention as replacements for parallel runways when constructing three or more runways in China. This has been prompted by the limitations associated with a single-direction airspace and associated regulations when using parallel runways. However, the operating efficiency of diverging runways is still greatly constrained by the separation standard for departing aircraft in CCAR-93TM-R5 and Decree of CAAC NO.123. To address these problems, an improved runway operation capacity model for a V-open multirunway airport is proposed to reduce the separation standard based on the equivalent lateral separation operation (ELSO) standard. A collision risk module is first proposed to assess the feasibility and safety of the proposed policy. Also, a novel runway capacity model for V-open multiple runways is then built to improve the operating efficiency for diverging runway. A series of comparative experiments based on actual flight data from Chengdu Tianfu International Airport demonstrated that reducing the divergence angle from 15° to 10° improved the runway operation capacity by about 8% based on the proposed improved policy. These research results could play a major role in facilitating appropriate amendments to the associated CAAC operation regulations.

Periodic Structural Defects in Graphene Sheets Engineered via Electron Irradiation.

Artificially-induced defects in the lattice of graphene are a powerful tool for engineering the properties of the crystal, especially if organized in highly-ordered structures such as periodic arrays. A method to deterministically induce defects in graphene is to irradiate the crystal with low-energy (<20 keV) electrons delivered by a scanning electron microscope. However, the nanometric precision granted by the focused beam can be hindered by the pattern irradiation itself due to the small lateral separation among the elements, which can prevent the generation of sharp features. An accurate analysis of the achievable resolution is thus essential for practical applications. To this end, we investigated patterns generated by low-energy electron irradiation combining atomic force microscopy and micro-Raman spectroscopy measurements. We proved that it is possible to create well-defined periodic patterns with precision of a few tens of nanometers. We found that the defected lines are influenced by electrons back-scattered by the substrate, which limit the achievable resolution. We provided a model that takes into account such substrate effects. The findings of our study allow the design and easily accessible fabrication of graphene devices featuring complex defect engineering, with a remarkable impact on technologies exploiting the increased surface reactivity.

A general Lagrangian tracking methodology for riverine flow and transport

AbstractThis article presents a new public domain tool for generalized Lagrangian particle tracking in rivers. The approach can be applied with a variety of two‐ and three‐dimensional flow solvers. Particle advection by the flow is incorporated using flow fields from the chosen solver assuming particles follow the Reynolds‐averaged flow, although some other simple passive and active particle behaviors are also treated. Turbulence effects are treated using a random walk algorithm with spatial step lengths randomly chosen from Gaussian distributions characterized by the diffusivity from the flow solver. Our work extends this concept to a general framework that is solver and coordinate system independent to allow easy comparisons between differing flow treatments. To better treat problems where detailed information is required in specific regions, the approach includes novel cloning and colligation algorithms which enhance local resolution at modest computational expense. We also provide tools for computing local concentrations and total exposure over a user‐specified time interval. Several examples of predictions are provided to illustrate applications of the technique, including examination of the role of curvature‐driven secondary flows, storage in lateral separation eddies, treatment of larval drift, treatment of fuel spill dispersion, river‐floodplain connections, and sedimentation in floodplain ponds by tie channel connections. We also demonstrate that the model can reproduce analytically derived concentration profiles for simple diffusivities. These examples show that the Lagrangian particle tracking approach and the extensions proposed here are broadly applicable and viable for treating difficult river problems with multiple temporal and spatial scales. The examples also illustrate the utility of the cloning/colligation extensions and show how these can decrease the computational effort required on problems where high local resolution is required. Enhancement of the tools and even broader applicability can be achieved through the inclusion of multiple particle populations and particle–particle interactions.

Electric double layer of spherical pH-responsive polyelectrolyte brushes in an electrolyte solution: A strong stretching theory accounting for excluded volume interaction and mass action law

In this paper, we study the electrostatics of pH-responsive polyelectrolyte-grafted spherical particles by using a strong stretching theory that takes into account the excluded volume interaction and the density of chargeable sites on the polyelectrolyte molecules. Based on free energy formalism, we obtain self-consistent field equations for determining the structure and electrostatics of spherical polyelectrolyte brushes. First, we find that the smaller the radius of the inner core, the longer the height of the polyelectrolyte brush. Then, we also prove that an increase in the excluded volume interaction yields a swelling of the polyelectrolyte brush height. In addition, we demonstrate how the effect of pH, bulk ionic concentration, and lateral separation between adjacent polyelectrolyte chains on the electrostatic properties of a spherical polyelectrolyte brush is affected by the radius of the inner core, the excluded volume interaction, and the chargeable site density.

Structural and electrostatic properties between pH-responsive polyelectrolyte brushes studied by augmented strong stretching theory.

In this paper, we study electrostatic and structural properties between pH-responsive polyelectrolyte brushes by using a strong stretching theory accounting for excluded volume interactions, the density of polyelectrolyte chargeable sites, and the Born energy difference between the inside and outside of the brush layer. In a free energy framework, we obtain self-consistent field equations to determine electrostatic properties between two pH-responsive polyelectrolyte brushes. We elucidate that in the region between two pH-responsive polyelectrolyte brushes, electrostatic potential at the centerline and osmotic pressure increase not only with excluded volume interaction but also with the density of chargeable sites on a polyelectrolyte molecule. Importantly, we clarify that when two pH-responsive polyelectrolyte brushes approach each other, the brush thickness becomes short and that a large excluded volume interaction and a large density of chargeable sites yield the enhanced contract of polyelectrolyte brushes. In addition, we also demonstrate how the influence of such quantities as pH, the number of Kuhn monomers, the density of charged sites, the lateral separation between adjacent polyelectrolyte brushes, and Kuhn length on the electrostatic and structural properties between the two polyelectrolyte brushes is affected by the exclusion volume interaction. Finally, we investigate the influence of the Born energy difference on the thickness of polyelectrolyte brushes and the osmotic pressure between two pH-responsive polyelectrolyte brushes.

A Car-Following Model Considering Driver’s Instantaneous Reaction Delay in Nonlane-Based Traffic Environments

Reaction delay is an indispensable factor in the operation and control process of drivers in a car-following scenario. Utilizing trajectory data obtained from an instrumented vehicle, this paper proposes a data-driven neural network car-following model incorporating instantaneous reaction delay of the drivers in nonlane-based (or disorderly) traffic systems. Considering instantaneous reaction delay as the time interval between relative speed and acceleration, a model is developed where the lateral descriptor of vehicle interaction (or centerline separation, CS) is found as a significant factor in modeling reaction delays in such disordered systems. Interestingly, reaction delays were found to increase with lateral separation between the interacting vehicles. Modeling results further indicate that the car-following model with instantaneous reaction delay outperformed the model with fixed reaction delay. In addition, the proposed model also showed better performance in terms of trajectory reproducing accuracy when compared with the classic car-following models. The results of this work justify the importance of considering CS in the development of algorithms for future autonomous traffic of disorderly traffic environments.

Effect of back pressure and divergent section contours on aerodynamic mixture separation using convergent–divergent micronozzles

A numerical investigation of the aerodynamic separation associated with converging–diverging two-dimensional planar micronozzles is reported. The impact of divergent section shapes such as linear, bell, and trumpet, the effect of different back pressure conditions, and the associated flow and separation features are studied. Simulations used the direct simulation Monte Carlo method and are validated with the available experimental data. The lateral separation effect is found to be influenced by the nozzle divergent section shape. The separation performance of micronozzles of different throat sizes indicates the dependence of the exit Kn on separation performance. The bell shape of the divergent section produced higher flow alignment, a thicker subsonic layer, more reduction in exit velocity, and lower separation performance than linear and trumpet shapes. The divergent section with a trumpet shape is preferred for higher species separation performance. The back pressure conditions at the exit of the nozzle are found to play a significant role in the curvature of streamlines and flow characteristics, which may play a vital role in mixture separation performance.

Database examination, multivariate analysis, and machine learning: Predictions of vapor intrusion attenuation factors

Traditional soil vapor intrusion (VI) models usually rely on preset conceptual scenarios, simplifying the influences of limiting environmental covariates in determining indoor attenuation factors relative to subsurface sources. This study proposed a technical framework and applied it to predict VI attenuation factors based on site-specific parameters recorded in the United States Environmental Protection Agency (USEPA)’s and the California Environmental Protection Agency (CalEPA)’s VI databases, which can overcome the limitations of traditional VI models. We examined the databases with multivariate analysis of variance to identify effective covariates, which were then employed to develop VI models with three machine learning algorithms. The results of multivariate analysis show that the effective covariates include soil texture, source depth, foundation type, lateral separation, surface cover, and land use. Based on these covariates, the predicted attenuation factors by these new models are generally within one order of magnitude of the observations recorded in the databases. Then the developed models were employed to generate the generic indoor attenuation factors to subsurface vapor (i.e., the 95th percentile of selected dataset), the values of which are different between the USEPA’s and CalEPA’s databases by one order of magnitude, although comparable to recommendations by the USEPA and literature, respectively. Such a difference may reflect the significant regional disparity in factors such as building structures or operational conditions (e.g., indoor air exchange rates), which necessitates generating generic VI attenuation factors on a state-specific basis. This study provides an alternative for VI risk screens on a site-specific basis, especially in states with a good collection of datasets. Although the proposed technical framework is used for the VI databases, it can be equally applied to other environmental science problems.

Three-dimensional dynamics of a pair of deformable bubbles rising initially in line. Part 2. Highly inertial regimes

The buoyancy-driven dynamics of a pair of gas bubbles released in line is investigated numerically, focusing on highly inertial conditions under which isolated bubbles follow non-straight paths. In an early stage, the second bubble always drifts out of the wake of the leading one. Then, depending on the ratios of the buoyancy, viscous and capillary forces which define the Galilei ( $Ga$ ) and Bond ( $Bo$ ) numbers of the system, five distinct regimes specific to such conditions are identified, in which the two bubbles may rise independently or continue to interact and possibly collide in the end. In the former case, they usually perform large-amplitude planar zigzags within the same plane or within two distinct planes, depending on the oblateness of the leading bubble. However, for large enough $Ga$ and low enough $Bo$ , they follow nearly vertical paths with small-amplitude erratic horizontal deviations. Increasing $Bo$ makes the wake-induced attraction toward the leading bubble stronger, forcing the two bubbles to realign vertically one or more times along their ascent. During such sequences, wake vortices may hit the trailing bubble, deflecting its path and, depending on the case, promoting or hindering further possibilities of interaction. In some regimes, varying the initial distance separating the two bubbles modifies their lateral separation beyond the initial stage. Similarly, minute initial angular deviations favour the selection of a single vertical plane of rise common to both bubbles. These changes may dramatically affect the fate of the tandem as, depending on $Bo$ , they promote or prevent future vertical realignments.

Vapor intrusion in buildings: Development of semi-empirical models including lateral separation between the building and the pollution source

Vapor intrusion in buildings: Development of semi-empirical models including lateral separation between the building and the pollution source