Confinement Technique Research Articles

Practices of COVID-19 Pandemic Containment Measures among TVET Students in Kakamega County, Kenya

The COVID-19 pandemic affected all areas in the country. One area whose functioning had been significantly impacted by COVID-19 was education. The goal of this research was to determine practices of covid-19 pandemic containment measures among TVET students in Kakamega County. Cross-sectional research was conducted using a questionnaire. TVET students around the country filled out the survey after it was made available to them online. It was determined whether or not there was a statistically significant correlation between KAP (knowledge and attitude) and other socio-demographic factors by using chi-square testing. Using binary logistic regression, we were able to isolate and adjust for any confounding variables. SPSS was used for the statistical analysis (version 26). According to the respondents' demographic information, the vast majority of participants were male. Participants' average age was under 24. Majority of the respondents were single (n = 306, 78.1%) and were studying for diploma qualification (n = 238, 60.7%). In addition, most of them were in their second year of study (n = 192, 49.0%). With regard to practices, at least six practices were adhered to by 212 (54.1%) of the respondents. These eight PP include things like washing hands and using proper hygiene (70.7%), wearing of face masks (51.0%), and avoiding public places and maintaining a safe distance between individuals (50.9%). (74.0 percent and 64.3 percent respectively). According to the results of the binary logistic regression, females engaged in less harmful activities than men did with respect to COVID-19 (OR = 0.323, p 0.001). Age and academic year were also shown to have a role in the respondents' habits. Students aged 30 and over had a lower odd of engaging in negative behaviors than those aged 24 and under (OR = 0.631, p = 0.0083). In conclusion, over half of respondents were found to adhere to at least six measures, including hand washing and other forms of cleanliness, mask use, avoiding crowded areas, and keeping a safe space between themselves and others. However, a sizable percentage engaged in at least three harmful habits. Based on the findings of this research, the following are the recommended that for future studies, it will be important to get feedback from educators as well as students. The results of such research in the future would add to the body of data supporting the use of confinement techniques.

Abiotic microcompartments form when neighbouring droplets fuse: an electrochemiluminescence investigation.

Many studies have shown chemistry proceeds differently in small volumes compared to bulk phases. However, few studies exist elucidating spontaneous means by which small volumes can form in Nature. Such studies are critical in understanding the formation of life in microcompartments. In this study, we track in real-time the coalescence of two or more water microdroplets adsorbed on an electrified surface in a 1,2-dichloroethane continuous phase by electrogenerated chemiluminescence (ECL) imaging, uncovering the spontaneous generation of multiple emulsions inside the resulting water droplets. During the fusion of adsorbed water droplets with each other on the electrode surface, volumes of organic and water phases are entrapped in between and detected respectively as ECL not-emitting and emitting regions. The diameter of those confined environments inside the water droplets can be less than a micrometer, as described by scanning electron microscopy data. This study adds a new mechanism for the generation of micro- and nano-emulsions and provides insight into confinement techniques under abiotic conditions as well as new potential strategies in microfluidic devices.

Suppression of laser beam’s polarization and intensity fluctuation via a Mach–Zehnder interferometer with proper feedback

Long ground-Rydberg coherence lifetime is interesting for implementing high-fidelity quantum logic gates, many-body physics, and other quantum information protocols. However, the potential well formed by a conventional far-off-resonance red-detuned optical-dipole trap that is attractive for ground-state cold atoms is usually repulsive for Rydberg atoms, which will result in the rapid loss of atoms and low repetition rate of the experimental sequence. Moreover, the coherence time will be sharply shortened due to the residual thermal motion of cold atoms. These issues can be addressed by a one-dimensional magic lattice trap, which can form a deeper potential trap than the traveling wave optical dipole trap when the output power is limited. In addition, these common techniques for atomic confinement generally have certain requirements for the polarization and intensity stability of the laser. Here, we demonstrated a method to suppress both the polarization drift and power fluctuation only based on the phase management of the Mach–Zehnder interferometer for a one-dimensional magic lattice trap. With the combination of three wave plates and the interferometer, we used the instrument to collect data in the time domain, analyzed the fluctuation of laser intensity, and calculated the noise power spectral density. We found that the total intensity fluctuation comprising laser power fluctuation and polarization drift was significantly suppressed, and the noise power spectral density after closed-loop locking with a typical bandwidth of 1–3000 Hz was significantly lower than that under the free running of the laser system. Typically, at 1000 Hz, the noise power spectral density after locking was about 10 dB lower than that under the free running of a master oscillator power amplifier system. The intensity–polarization control technique provides potential applications for atomic confinement protocols that demand fixed polarization and intensity.

Extended Methods for 2D Confinement.

Physical confinement in microfluidic devices has become a common technique to induce and study cell migration in a large range of cell types. Confined migration was previously understudied due to the limitations of 2D migration assays but has emerged as an important mode of migration in the past decade. Furthermore, confinement improves the quality of the imaging and simplifies the analysis of trajectories by confining migration to the plane of acquisition. Protocols described in this chapter relate to methods extending the previously published 2D confinement technique. First, we explain a method to increase the complexity of the confinement chamber by microfabricating nanometer-sized PDMS grooves on the bottom surface, usually used for contact guidance studies. Then, we describe a method to perform the confinement on cells embedded inside a μm-thin 3D collagen gel. Finally, we describe an alternative method to confine cells based on agarose, so that cells can be fixed or drug perfused while being confined, which is currently not possible in the 2D confinement silicone-based device.

Spiral-based confinement in slabs for the seismic performance enhancement of steel-concrete composite frames

The seismic performance analysis of steel-concrete composite frames involves, as known, the interaction of several load-bearing components that should be properly designed, with multiple geometrical and mechanical parameters to account. Practical recommendations are given by the Eurocode 8 – Annex C for the optimal detailing of transversal rebars, so as to ensure the activation of conventional resisting mechanisms. In this paper, the attention is focused on the analysis of effects and benefits due to a novel confinement solution for the reinforced concrete (RC) slab. The intervention is based on the use of diagonal steel spirals, that are expected to enforce the improve the overall compressive response of the RC slab, thanks to the activation of an optimized strut-and-tie resisting mechanism. The final expectation is to first increase the resistance capacity of the slab, that can thus transfer higher compressive actions under seismic loads. Further, as shown, the same resisting mechanism can be beneficial for the yielding of steel rebars, depending on the final detailing of components, and thus possibly improve the ductility of the system To this aim, a refined Finite Element (FE) numerical analysis is carried out for several configurations of technical interest. The in-plane compressive behaviour and the activation of resisting mechanisms is explored for several spiral-confined slabs, based on various arrangements. Major advantage is take from literature experimental data on RC slabs, that are further investigated by introducing the examined confinement technique. As shown, once the spirals are optimally placed into the slab, the strength and ductility parameters of the concrete struts can be efficiently improved, with marked benefits for the overall resisting mechanisms of the slab, and thus for steelcomposite frames as a whole.

2D Oxides Realized via Confinement Heteroepitaxy

AbstractNovel confinement techniques facilitate the formation of non‐layered 2D materials. Here it is demonstrated that the formation and properties of 2D oxides (GaOx, InOx, SnOx) at the epitaxial graphene (EG)/silicon carbide (SiC) interface is dependent on the EG buffer layer properties prior to element intercalation. Using 2D Ga, it is demonstrated that defects in the EG buffer layer lead to Ga transforming to GaOx with non‐periodic oxygen in a crystalline Ga matrix via air oxidation at room temperature. However, crystalline monolayer GaO2 and bilayer Ga2O3 with ferroelectric wurtzite structure(FE‐WZ') can then be formed via subsequent high‐temperature O2 annealing. Furthermore, the graphene/X/SiC (X = 2D Ga or Ga2O3) junction is tunable from Ohmic to a Schottky or tunnel barrier depending on the interface species. Finally, using vertical transport measurements and electron energy loss spectroscopy analysis, the bandgap of 2D gallium oxide is identified as 6.6 ± 0.6 eV, significantly larger than that of bulk β‐Ga2O3 (≈4.8 eV), suggesting strong quantum confinement effects at the 2D limit. The study presented here is foundational for development of atomic‐scale, vertical 2D/3D heterostructure for applications requiring short transit times, such as GHz and THz devices.

Experimental Study on the Behaviour of Short Columns Confined by Waste Plastic Bags-Epoxy Composites

An experimental study was carried out to investigate the behaviour of short column confined by waste plastic bags and nylon strips and findings of this study are presented in this paper. Eight reinforced concrete (RC) short columns were casted. Among them two specimens were named as control, while remaining six specimens were divided into three groups [two specimens for each group] based on different confinement techniques investigated in this study. In retrofitting technique 1 (RT-1), RC short columns were externally confined by full wrap of plastic bags, while in retrofitting techniques 2 (RT-2) and 3 (RT-3), confinement was provided to the short columns by stirrups of nylon and plastic bags with 25 mm clear spacing, respectively. The testing under compression loading was performed on UTM of 100T capacity. From the results obtained, seismic parameters such as ductility, fracture energy before peak and after peak, factor k* and load-displacement response were studied. The results indicated that RC short column confined by RT-1 (full wrap) gives better performance in terms of ductility and fracture energy after peak. Increase in the ductility of RT-1 specimen was about 25% as compared to the control one. Moreover, post-peak fracture energy exhibited by short column confined through techniques RT-1 and RT-2 was 132 and 125 N/mm as compared to control one with 14 N/mm of fracture energy. The experimental observations further indicated that the failure of control specimen was sudden showing high brittleness while the failure of confined specimens by RT-1 and RT-2 techniques was observed to be gradual giving some warning before final failure.

Vorticity Confinement Technique and Blade Element Method for Accurate Propeller Modelling

Traditional CFD techniques are not effective in preserving wakes and vortices over larger distances and for longer times. Vorticity Confinement (VC) technique helps counter the numerical diffusion to preserve wakes and vortices. In the current study, VC was used to accurately model the propeller flow using two different propeller modelling techniques after being implemented into SU2, an open-source CFD solver. One resolves flow past the propeller by solving RANS equations in a rotating reference frame. Another is a simplified propeller modelling technique in which the propeller needs to be modelled as a disk, and the propeller loading is determined using the blade element method. In the first case, VC enabled tip and hub vortices to convect over larger distances from the propeller, along with an improved resolution of gradients in the tip vortex. With the latter technique, VC helped conserve the tangential velocities for longer distances.

Compression behavior of confined circular reinforced concrete with spiral CFRP rope with different slenderness ratios

NSM-CFRP strip cannot be wrapped around the column, the necessity for flexible near-surface mounted carbon fiber reinforced polymer (NSM-CFRP) material has recently arisen. Under concentric compression stress, twelve circular reinforced concrete columns (RC) with three slenderness ratios (17.3, 23.8, and 28.1) in addition to the spacing between ropes were investigated to assess the behavior of confined RC columns using NSM-CFRP rope. The results showed that the load capacity of RC columns was increased by using the NSM-CFRP rope and decreasing the spacing between the NSM-CFRP ropes. Furthermore, when the slenderness ratio is decreased, the load capacity of columns increases. Specimens with heights of 800 mm, 1100 mm, and 1300 mm reinforced with 150 mm spacing between CFRP ropes had a greater increase in capacity (3.3 times, 1.6 times, and 1.97) than control specimens of each height. The confinement technique using spiral CFRP rope at 150 mm spacing has the greatest impact on the load-carrying capacity of the RC column. Additionally, confining the RC column with spiral CFRP rope at a 150 mm spacing enhanced the bearing load capacity of the RC column with the lowest slenderness ratio more than the other slenderness ratios. Finally, when the slenderness ratio increases, the bearing load capacity and axial strain corresponding to the maximum axial stress decrease. The slenderness ratio had the greatest impact on the behavior of the RC column when there was a higher amount of CFRP rope or when the spacing between CFRP ropes was the lowest.

Analytical study and design approach of the axial and flexural response of reinforced masonry columns confined with FRP jackets

Using fiber-reinforced polymer (FRP) wraps has proven to be an effective and optimized confinement technique to upgrade the axial and flexural capacity of reinforced concrete (RC) and reinforced masonry (RM) columns. The axial capacity of FRP-confined masonry depends on both the compressive strength of masonry before strengthening and the confinement pressure provided by the FRP jacket. This study proposes a simplified methodology to design and analyze prismatic fully grouted reinforced masonry columns (RMCs) strengthened with FRP Jackets. The proposed design methodology included an analytical confinement model to predict the compressive strength gain in RMCs due to the effective confinement pressure provided by FRP jackets. The proposed procedure was also designed to predict the nominal capacity of RMCs for practical design applications, with columns subjected to both axial loading and bending moment. The essential parameters to perform detailed section analysis were established, and suggested expressions were proposed to obtain the parameter values. Practical values for the equivalent rectangular stress block parameters were proposed. The theoretical axial force-moment interaction diagrams obtained by the proposed procedure were compared with available experimental data. The experimental test results were in good agreement with the analytical predictions by a reasonable marginal error. Furthermore, the effect of five design variables on the axial-flexural interaction of FRP-wrapped RMCs was investigated. The variables considered in the parametric study were the number of FRP layers, radius of the corners, stiffness of the FRP composite, cross-sectional aspect ratio, and masonry compressive strength. The results showed that increasing the FRP layers, corner radius, and FRP jacket stiffness significantly enhanced the axial capacity of the FRP-confined RMCs. However, the increase in the masonry compressive strength and cross-sectional aspect ratio negatively affected the axial capacity gain ratio of FRP-strengthened RMCs.

Study of fire-damaged circular RC columns repaired using composite confinement techniques

Numerical and regression modelling of 21 undamaged, fire-damaged and repaired fire-damaged circular reinforced concrete (RC) columns was undertaken. The columns were exposed to temperatures of 300°C, 500°C and 900°C and tested for axial residual capacity. It was found that the concrete lost strength after exposure to a temperature of 300°C or above. Fire-damaged columns were then repaired using various composite confinement techniques. Strength was regained when carbon-fibre-reinforced polymer (CFRP) confinement was applied to the fire-damaged columns but it also increased the deformation and thus reduced the stiffness, which is undesirable. As an alternative, steel wire mesh, filled with cement–sand mortar and wrapped with CFRP was employed. A numerical model to predict the residual capacity of these columns was developed. The development of numerical techniques, including material properties, geometry, elements, loading, boundary conditions and contact algorithms for undamaged, fire-damaged and repaired fire-damaged columns is reviewed and summarised. Analytical equations were developed using linear, multiple and quadratic regression modelling. The results obtained using the proposed model and regression equations showed that these models offer a better alternative to experimental testing for the prediction of the post-fire performance of damaged and repaired RC columns.

Microstructure inducement of different tensile fracture mechanisms at 800 ℃ of directional solidified Ti-45Al-5Nb alloys produced by electromagnetic confinement

Directional solidified TiAl alloys have low density and good comprehensive high temperature performance, which is an ideal substitute material for high temperature structural parts. In this paper, Φ 16.5 mm directional solidified Ti-45Al-5Nb sample with full-lamellar microstructure was prepared successfully by electromagnetic confinement technique at 10 µm/s and relative tensile tests at 800 ℃ were also performed. The tensile strength of Ti-45Al-5Nb alloy at 800 ℃ is 765 MPa and the elongation is 16%. Moreover, results of tensile process characteristics and fracture analysis show that this material has two distinct fracture mechanisms at 800 ℃, which are cleavage fracture mechanism and microporous aggregation fracture mechanism. Two fracture mechanisms do not exist at the same time, and for a particular specimen, the fracture process is dominated by only one of them. Different fracture mechanisms are determined by the lamellar orientation difference and element segregation. When the orientation of adjacent grains is similar and the segregation is light, the fracture process is dominated by the cleavage fracture mechanism. Otherwise, proportion and scale of the γ phase at the grain boundary increase and the B2 phase is generated. In this case, the microporous aggregation fracture mechanism will dominate the fracture process.

Axial performance of grouted C-Shaped concrete block masonry columns jacketed by carbon and glass FRP

To overcome the relatively low ductility and capacity of masonry elements, the confinement technique may be an effective alternative for improving their performance, especially the columns. Fiber Reinforced Polymers (FRP) jacketing is a potential approach has benefits in terms of strength enhancement and gaining ductile behavior. Therefore, in this study, two types of FRP were used to improve column axial capacity and ductility: carbon and glass FRP. The effect of FRP wrapping on the compressive behavior of concrete masonry columns was investigated experimentally. Fully grouted scaled masonry columns constructed using C-shaped concrete blocks were wrapped with FRP jackets and tested under concentric compressive load until failure. For this purpose, 18 half-scale masonry prisms under variations in FRP jacketing and FRP thickness were developed and tested in six sets. The effect of FRP confinement on the unconfined masonry columns was evaluated. The CFRP and GFRP jacketing increased the peak strength and ultimate axial strain. Confinement improves post-peak performance by softening the descending stress–strain relationships. Increasing FRP jacket thickness improved the axial strain, strength, and ductility of masonry columns. The CFRP wrap gives 10 ∼ 16% more strength than GFRP. Ultimate strain enhanced by 76 % and 57 % for CFRP and GFRP respectively.

Localization of jet electrochemical additive manufacturing with a liquid confinement technique

Electrochemical additive manufacturing (ECAM) is a flexible additive manufacturing method to deposit metallic/metallic-alloys microstructures without any thermally induced residual stresses. The conventional ECAM process suffers from stray deposition leading to reduced dimensional accuracy. Therefore, this paper proposes a novel liquid confinement technique to improve the deposition localization in Jet-ECAM process. Dichloromethane was employed as a second liquid phase to confine and control the flow field distribution of electrolyte as well as localize electric field on the substrate. Thus, the stray deposition induced by spreading electrolyte and hence spreading electric field could be avoided, and the deposition localization was improved. Liquid-liquid two-phase flow model was developed to analyze the flow field characteristic of two-phase flow formed by electrolyte and dichloromethane. Both simulation and observation results indicated that the flow region of the electrolyte on the substrate was well confined by the dichloromethane. The experimental results showed that the deposition localization was improved about 43.84 % compared to that in traditional Jet-ECAM. The inter-electrode gap (IEG) had a significant effect on both electrolyte flow region and current density distribution on the substrate, which affected deposition quality. Additionally, high current density leads to coarsened grains and reduces the deposition quality. Moreover, increasing the reciprocating speed of nozzle could refine the grains of microstructure, but the deposition efficiency was reduced. By employing process parameters of IEG of 100 μm, electric current of 0.0015 A, and the reciprocating speed of 300 μm/s, micro-patterns including both lines and curves were well deposited with a width of 500 μm, height of 60 μm, and a radius of 2 mm (letters G and U) and 2.5 mm (letter D).

Improving the seismic capacity of steel–concrete composite frames with spiral-confined slabs

The seismic performance analysis of steel–concrete composite frames involves, as known, the interaction of several load-bearing components that should be properly designed, with multiple geometrical and mechanical parameters to account. Practical recommendations are given by the Eurocode 8 (EC8) – Annex C for the optimal detailing of transverse rebars, so as to ensure the activation of conventional resisting mechanisms. In this paper, the attention is focused on the analysis of effects and benefits due to a novel confinement solution for the reinforced concrete (RC) slab. The intervention is based on the use of diagonal steel spirals, that are expected to enforce the overall compressive response of the RC slab, thanks to the activation of an optimized strut-and-tie resisting mechanism. The final expectation is to first increase the resistance capacity of the slab that can thus transfer higher compressive actions under seismic loads. Further, as shown, the same resisting mechanism can be beneficial for the yielding of steel rebars, depending on the final detailing of components, and thus possibly improve the ductility of the system. To this aim, a refined finite element (FE) numerical analysis is carried out for several configurations of technical interest. The in-plane compressive behaviour and the activation of resisting mechanisms are explored for several spiral-confined slabs, based on various arrangements. Major advantage is taken from literature experimental data on RC slabs that are further investigated by introducing the examined confinement technique. The attention is hence given to the local and the global structural effects due to different arrangements for the proposed steel spirals. As shown, once the spirals are optimally placed into the slab, the strength and ductility parameters of the concrete struts can be efficiently improved, with marked benefits for the overall resisting mechanisms of the slab, and thus for the steel–composite frames as a whole.

Modelling of FRP and FRCM-Confined Masonry Columns: Critical Review for Design and Intervention Strategies

This paper presents a critical review of the most established analytical models for the prediction of the compressive strength of FRP and FRCM-confined masonry columns. In particular, two types of fibres are analysed, i.e. glass and basalt. A wide dataset available in the literature is used for the application of the analytical models and for the development of parametric analyses useful for the critical comparison of FRP vs. FRCM confinement technique and glass vs. basalt fibres to be adopted as reinforcement of masonry substrate. The effects of stiffness and strength of the reinforcement, the number of reinforcing layers, the compressive strength of masonry and the cross-section shape are investigated.

Numerical Investigation of HSC Columns Retrofitted by CFRP Materials under Combined Load

Repairing and retrofitting old civil engineering structures based on reinforced concrete represents a challenge for civil engineering societies all over the world. Environmental impacts such as corrosion and natural disasters like earthquakes can considerably weaken those structures. Reinforced concrete confinement technique using carbon fiber-reinforced polymers (CFRP) is considered as an innovative solution to strengthen the old and damaged structures. In this paper, a numerical simulation was carried out to evaluate the impact of the CFRP jacket as a confining composite material on the compressive strength and the ultimate strain of confined reinforced concrete. A FE model was developed, validated by comparing its results with the available experimental measurements, and finally assessed by performing a parametric study. Indeed, the parametric investigations had as their purpose the evaluation of the level of confinement (different number of plies), namely without plies, one plie, and three plies configuration, that were subjected to different eccentric loading modes e=0, e=25 and e=50 mm, in order to assess the interaction between the combined load that can be represented by compressive and flexural effect. The numerical results were, in fact, in good agreement with the experimental data. In addition, CFRP wrapping had a significant effect on the maximum load of eccentrically loaded columns compared to concentrically loaded columns by increasing the compressive strength with a value of 15% gain compared to the unconfined column. Doi: 10.28991/CEJ-2022-08-04-011 Full Text: PDF

Experimental and numerical evaluation of compression confinement techniques for HSC beams reinforced with different ratios of high strength steel reinforcement

This work presents experimental and numerical research to evaluate the compression confinement techniques of HSC beams reinforced with different ratios of high-strength steel reinforcement. Twelve specimens of high-strength reinforced concrete beams with two different compression confinement techniques were tested experimentally. The first method is used carbon fiber reinforced polymers sheets (CFRPs) around the compression zone, CF, and the steel fibers reinforced concrete is used in the compression zone by 1% of volume fraction, SF, in the second case. A 3-D finite element analysis was done; using the ANSYS program to simulate and idealize all experimental specimens. The numerical and experimental results of the RC beams were validated and compared in this work. The results showed that there is a good idealization using 3-D finite element models with the experimental specimens. Also, it was found that using the suggested techniques can increase the strength ratio and increase the ductility index depending on the tensile reinforcement ratios. Moreover, the energy absorption and the mode of failure were enhanced.

Experimental testing of novel hybrid rubberised concrete double skin tubular columns with filament wound CFRP tube under axial compressive loading

Rubberised concrete formed by using recycled scrap tyre chips as the substitution for natural aggregates, has recently emerged as an important research topic. Though it conserves the mineral aggregates, it is associated with reduced compressive strength. Different confinement techniques with fiber-reinforced polymer (FRP) wrapping and steel have been commonly used to restore the lost strength that also provided some other benefits such as enhanced ductility and energy dissipation capacity. In this paper, a novel hybrid double-skin tubular column termed as “Hybrid RuDSTC” consisting of rubberised concrete, filament wound circular CFRP tube, and cold-formed circular steel tube was developed and experimentally explored to evaluate its performance under axial load. The parameters of the experimental investigation were void ratio, slenderness ratio, and percentage rubber replacement. Results showed that the novel Hybrid RuDSTCs can provide a promising sustainable solution with greater strain capacity compared to their unconfined counterparts. Better strain and enhanced ductility of the hybrid RuDSTCs compared to non-rubberised hybrid DSTCs enable their use in seismic prone regions and mining infrastructure.

A phosphoinositide-based model of actin waves in frustrated phagocytosis

Phagocytosis is a complex process by which phagocytes such as lymphocytes or macrophages engulf and destroy foreign bodies called pathogens in a tissue. The process is triggered by the detection of antibodies that trigger signaling mechanisms that control the changes of the cellular cytoskeleton needed for engulfment of the pathogen. A mathematical model of the entire process would be extremely complicated, because the signaling and cytoskeletal changes produce large mechanical deformations of the cell. Recent experiments have used a confinement technique that leads to a process called frustrated phagocytosis, in which the membrane does not deform, but rather, signaling triggers actin waves that propagate along the boundary of the cell. This eliminates the large-scale deformations and facilitates modeling of the wave dynamics. Herein we develop a model of the actin dynamics observed in frustrated phagocytosis and show that it can replicate the experimental observations. We identify the key components that control the actin waves and make a number of experimentally-testable predictions. In particular, we predict that diffusion coefficients of membrane-bound species must be larger behind the wavefront to replicate the internal structure of the waves. Our model is a first step toward a more complete model of phagocytosis, and provides insights into circular dorsal ruffles as well.