Separation of particles by size from a suspension using the motion of a confined bubble

When confined in a liquid-filled circular cylinder, a long air bubble moves slightly faster than the bulk liquid as a small fraction of the liquid leaks through a very thin annular gap between the bubble and the internal wall of the cylinder. At low velocities, the thickness of this lubricating film formed around the bubble is set only by the liquid properties and the translational speed of the bubble and thus can be tuned in a simple fashion. Here, we use this setting to filter, based on size, micron-size particles that are originally dispersed in a suspension. Furthermore, we apply this process for separation of particles from a polydisperse solution. The bubble interface is free of particles initially, and particles of different sizes can enter the liquid film region. Particle separation occurs when the thickness of the lubricating liquid film falls between the diameters of the two different particles. While large particles will be collected at the bubble surface, smaller particles can leak through the thin film and reach the fluid region behind the bubble. As a result, the film thickness can be fine-tuned by simply adjusting the speed of a translating confined bubble, so as to achieve separation of particles by size based on the relative particle diameter compared to the film thickness

Bubble-Driven Detachment of Bacteria from Confined Microgeometries

Moving air–liquid interfaces, for example, bubbles, play a significant role in the detachment and transport of colloids and microorganisms in confined systems as well as unsaturated porous media. Moreover, they can effectively prevent and/or postpone the development of mature biofilms on surfaces that are colonized by bacteria. Here we demonstrate the dynamics and quantify the effectiveness of this bubble-driven detachment process for the bacterial strain Staphylococcus aureus. We investigate the effects of interface velocity and geometrical factors through microfluidic experiments that mimic some of the confinement features of pore-scale geometries. Depending on the bubble velocity U, at least three different flow regimes are found. These operating flow regimes not only affect the efficiency of the detachment process but also modify the final distribution of the bacteria on the surface. We organize our results according to the capillary number, , where μ and γ are the viscosity and the surface tension, respectively. Bubbles at very low velocities, corresponding to capillary numbers Ca 10–3, have lower detachment efficiencies and cause significant nonuniformities in the final distribution of the cells on the substrate. This effect is associated with the formation of a thin liquid film around the bubble at higher Ca. In general, at higher bubble velocities bacterial cells in the corners of the geometry are less influenced by the bubble passage compared to the central region

Rotational and ply-level uncertainty in response of composite shallow conical shells

This paper presents the quantification of rotational and ply level uncertainty of random natural frequency for laminated composite conical shells by using surrogate modeling approach. The stochastic eigenvalue problem is solved by using QR iteration algorithm. Sensitivity analysis is carried out to address the influence of different input parameters on the output natural frequencies. The sampling size and computational cost is reduced by employing the present approach compared to direct Monte Carlo simulation. The stochastic mode shapes are also depicted for a typical laminate configuration. Statistical analysis is presented to illustrate the results and its performance

Searching the genome of beluga (Huso huso) for sex markers based on targeted bulked segregant analysis (BSA)

In sturgeon aquaculture, where the main purpose is caviar production, a reliable method is needed to separate fish according to gender. Currently, due to the lack of external sexual dimorphism, the fish are sexed by an invasive surgical examination of the gonads. Development of a non-invasive procedure for sexing fish based on genetic markers is of special interest. In the present study we employed Bulked Segregant Analysis (BSA) methodology to search for DNA markers associated with the sex of the beluga sturgeon (Huso huso). DNA bulks (male and female) were created by combining equal amounts of genomic DNA from 10 fish of both sexes. A total of 101 decamer primers associated with the sex-specific sequences in non-sturgeon species was used for targeted screening of the bulks, resulting in 2846 bands that all of them were present in both sexes. Our results showed that sex chromosomes are weakly differentiated in the sturgeon genome and comprised sequences not complementary to the sex-specific primers in non-sturgeon species

Survey of the gram negaive bacterial pollution in some areas of Anzali Lagoon

For this survey, eight stations were selected in the Anzali Lagoon based on vicinity to the urban area, agricultural fields, in lets and out lets of the rivers. Sampling was carried out seasonally and in each season triplicate water samples were taken from surface layer of each station. Totally 96 water samples were collected during one year period in sterile condition.Samples were transferred to the laboratoray at 4ºC temperature using ice box. The pollution by Coliform was examind using standard technigue of MPN and for count of bacteria differential, specific test and pourplate method isolate was used. In this survey different genus of bacteria were isolated and identified as: E.Coli (%19.65), Shigella (%18.21), Klebsiella (%17.86), Proteus (%13.21), Enterobacter (%11.07), Morganella (%9.65), Salmonella (%3.92), Serratia (%2.5), Providencia (%2.14) and Citrobacter (%1.79) which belonged to family Enterobacteriacea. Also the most important isolated genus of Vibrionacea were Vibrio (%47.55), Aeromonas (%28.67) & Plesiomonas (%4.9) and nonfermented-bacilli containg Suedomonace (%18.88). There was significant differences in the bacterial pollution between stations (P<0.05). The highest Coliform count was recorded during summer amounting to (147.71±171.36) ind. 100 cm3 and also the highest Fecal Coliform count was observed in summer (135.125±173.19) ind. 100 cm3 in the water. Generally the pollution in summer was higher in comparison to rest of the year due to increasing temperature and decreasing water flow of rivers.Higher bacterial pollution during autum in comparison to winter was attributed to heavay rain, erosion of the soil, flooding of the rivers and run off of the waste waters. Pirbazar River, Psikhan and Shambe Bazaar Roga drained high volume of urban agricultural and animal waste waters.The western area of the lagoon which is the bigest part of the Anzali lagoon had the least pollution

Spontaneous formation of multilamellar vesicles from aqueous micellar solutions of sodium linear alkylbenzene sulfonate (NaLAS)

We report the spontaneous formation of multilamellar vesicles (MLVs) from low concentration (<30 wt%) aqueous micellar solutions of sodium linear alkylbenezene sulfonate (NaLAS) upon cooling, employing a combination of optical microscopy (OM), Small Angle Neutron Scattering (SANS), and Cryo-TEM. Upon cooling, MLVs grow from, and coexist with, the surfactant micelles, attaining diameters ranging from hundreds of nanometers to a few micrometers depending on the cooling rate, whilst the d-spacing of internal lamellae remains unchanged, at ≃3 nm. While microscale fluid and flow properties of the mixed MLVs and micellar phase depend on rate of cooling, the corresponding nanoscale structure of the surfactant aggregates, resolved by time-resolved SANS, remains unchanged. Our data indicate that the mixed MLV and micellar phases are in thermodynamic equilibrium with a fixed relative volume fraction determined by temperature and total surfactant concentration. Under flow, MLVs aggregate and consequently migrate away from the channel walls, thus reduce the overall hydrodynamic resistance. Our findings demonstrate that the molecular and mesoscopic structure of ubiquitous, low concentration NaLAS solutions, and in turn their flow properties, are dramatically influenced by temperature variation about ambient conditions

A microfluidic-multiwell platform for rapid phase mapping of surfactant solutions

Measurement of the phase behavior and (meta)stability of liquid formulations, including surfactant solutions, is required for the understanding of mixture thermodynamics, as well as their practical utilization. We report a microfluidic platform with a stepped temperature profile, imposed by a dual Peltier module, connected to an automated multiwell plate injector and optical setup, for rapid solution phase mapping. The measurement protocol is defined by the temperature step ΔT ≡ T1 − T2 (≲100 ○C), volumetric flow rate Q ≡ ΔV/Δt (≲50 μl/min), which implicitly set the thermal gradient ΔT/Δt (≃0.1–50 ○C/min), and measurement time (which must exceed the intrinsic timescale of the relevant phase transformation). Furthermore, U-shaped microchannels can assess the reversibility of such transformations, yielding a facile measurement of the metastable zone width of the phase diagram. By contrast with traditional approaches, the platform precisely controls the cooling and heating rates by tuning the flow rate, and the absolute temperature excursion by the hot and cold thermal profile, which remain stationary during operation, thus allowing the sequential and reproducible screening of large sample arrays. As a model system, we examined the transition from the micellar (L1) to the liquid crystalline lamellar phase (Lα), upon cooling, of aqueous solutions of sodium linear alkylbenzene sulfonate, a biodegradable anionic surfactant extensively employed in industry. Our findings are validated with quiescent optical microscopy and small angle neutron scattering data

Dynamics of long gas bubbles rising in a vertical tube in a cocurrent liquid flow

© 2019 American Physical Society. When a confined long gas bubble rises in a vertical tube in a cocurrent liquid flow, its translational velocity is the result of both buoyancy and mean motion of the liquid. A thin film of liquid is formed on the tube wall and its thickness is determined by the interplay of viscous, inertial, capillary and buoyancy effects, as defined by the values of the Bond number (Bo≡ρgR2/σ with ρ being the liquid density, g the gravitational acceleration, R the tube radius, and σ the surface tension), capillary number (Cab≡μUb/σ with Ub being the bubble velocity and μ the liquid dynamic viscosity), and Reynolds number (Reb≡2ρUbR/μ). We perform experiments and numerical simulations to investigate systematically the effect of buoyancy (Bo=0-5) on the shape and velocity of the bubble and on the thickness of the liquid film for Cab=10-3-10-1 and Reb=10-2-103. A theoretical model, based on an extension of Bretherton's lubrication theory, is developed and utilized for parametric analyses; its predictions compare well with the experimental and numerical data. This study shows that buoyancy effects on bubbles rising in a cocurrent liquid flow make the liquid film thicker and the bubble rise faster, when compared to the negligible gravity case. In particular, gravitational forces impact considerably the bubble dynamics already when B