Stagnant Fluid Research Articles

CFD study on rise and deformation characteristics of buoyancy-driven spheroid bubbles in stagnant Carreau model non-Newtonian fluids

The bubbles are almost ubiquitous in many chemical and processing industries; and many of the polymeric solutions obey non-Newtonian rheological characteristics. Therefore, in this work the rise and deformation characteristics of spheroid bubbles in Carreau model non-Newtonian fluids are numerically investigated using a level set method. To demonstrate the validity of the moving bubble interface, the present simulations are compared with existing numerical and experimental results available in the literature; and for these comparisons, the computational geometries are considered same as reported in corresponding literatures. The present bubble deformation characteristics are satisfactorily agreeing with their literature counterparts. After establishing the validity of the numerical solution procedure, the same method is applied to obtain the deformation characteristics of an air bubble in Carreau model non-Newtonian fluids. Further, the results in terms of the volume fraction images, streamlines, and viscosity profiles around the deforming bubbles are presented as function of the bubble rise time.

A new finding on the in-vivo crevice corrosion damage in a CoCrMo hip implant

A detailed investigation was performed to characterize the fretting wear and corrosion damage to the neck component of a CoCrMo stem from a metal-on-polyethylene implant retrieved after 99months. The stem was a low-carbon (0.07wt%) wrought Co-28Cr-6Mo alloy with no secondary carbide phases in the matrix (γ-phase). The original design of the neck surface contained an intentionally fabricated knurled profile with a valley-to-peak range of approximately 11μm. Roughness measurements indicated that the tip of the knurled profile was significantly damaged, especially in the distal medial region of the neck, with up to a 22% reduction in the mean peak-to-valley height (Ra) compared to the original profile. As a new finding, the channels between the peaks of the profile created an additional crevice site in the presence of stagnant body fluid within the head-neck taper junction. These channels were observed to contain the most severe corroded areas and surface oxide layers with micro-cracks. SEM/EDS, XRD and XPS evaluations identified the formation of Cr2O3 as a corrosion product. Also, decobaltification was found to occur in these corroded areas. The findings of this work indicate the important role of the knurled profile in inducing additional crevice corrosion.

Sugar export limits size of conifer needles.

Plant leaf size varies by more than three orders of magnitude, from a few millimeters to over one meter. Conifer leaves, however, are relatively short and the majority of needles are no longer than 6 cm. The reason for the strong confinement of the trait-space is unknown. We show that sugars produced near the tip of long needles cannot be exported efficiently, because the pressure required to drive vascular flow would exceed the greatest available pressure (the osmotic pressure). This basic constraint leads to the formation of an inactive region of stagnant fluid near the needle tip, which does not contribute to sugar flow. Remarkably, we find that the size of the active part does not scale with needle length. We predict a single maximum needle size of 5 cm, in accord with data from 519 conifer species. This could help rationalize the recent observation that conifers have significantly smaller leaves than angiosperms, and provide a biophysical explanation for this intriguing difference between the two largest groups of plants.

Renal Epithelial Function Can Be Altered by Hypoxia Inducible Mechanisms

Polycystic Kidney Disease (PKD) is characterized by fluid filled cysts which interfere with renal function and can lead to kidney failure. In cystic epithelia, hypoxia inducible factor 1α (HIF1α) and HIF2α were reported to be elevated [1]. Cyst expansion, stagnant fluid accumulation, and insufficient vascular supply may result in localized chronic ischemia‐hypoxia in cysts and as well as in normal epithelia adjacent to a cyst. We hypothesize that in normal epithelia near a cyst, the stabilization of HIF1α, a major regulator of cellular response to hypoxia, can cause altered paracellular and transcellular epithelial transport. Thus, increased level of HIF1α can be a triggering factor in the transformation of normal renal epithelia from an absorptive to a secretory phenotype, leading to cyst expansion.Cobalt chloride (CoCl2) was used at a concentration of 100 μM to stabilize HIF1α in the cellular nucleus. Using western blots, we confirmed that increased HIF1α levels in the nuclear extracts by CoCl2 also increased cellular erythropoietin (EPO) levels. Application of a HIF1α inhibitor, methyl 3‐[[2‐[4‐(2‐adamantyl)phenoxy]acetyl]amino]‐4‐hydroxybenzoate was found to suppress the increased level of EPO expression by CoCl2. Transcellular and paracellular transport studies were performed in a mouse cortical collecting duct cell line (mCCD 1296 (d)) which has a high monolayer transepithelial resistance (TER) value around 3000 Ω‐cm2 and a detectable 95% amiloride sensitive voltage value. A few paracellular transport studies were also carried out in Mardin‐Darby Canine Kidney (MDCK) epithelial cell line which has relatively low monolayer TER value around 400 Ω‐cm2 with no detectable voltage value. Short circuit current (Isc) was calculated using Ohm's law (I = V/R) to compare active ion transport. TER and voltage values were recorded using an Endohm chamber. Higher TER values in mCCD cells can reflect reduced paracellullar permeability which was verified by permeability assay using FITC‐conjugated dextran molecules (3 and 70 kDa). MTT assay was used in order to make sure CoCl2 treated and untreated groups maintained same level of cellular viability. Cells exposed to CoCl2 showed altered active ion transport in mCCD cells. Treatment with CoCl2 caused increased 70 kDa FITC‐dextran paracellular permeability both in mCCD and MDCK monolayers. In MDCK cell line, we performed a paracellular permeability experiment in which we used the HIF1α inhibitor along with CoCl2. The HIF1α inhibitor was found to block the effect of CoCl2 treatment on FITC‐dextran permeability to a certain extent. Thus, CoCl2 can alter epithelial transport most likely due to hypoxia inducible mechanisms. Currently, we are trying to strengthen the connection between HIF1α levels and renal epithelial function using HIF1α inhibitors in active and passive transport experiments in the presence of CoCl2 or another HIFα stabilizer, the iron chelator desferrioxamine.Support or Funding InformationThe project is supported by National Institute of Diabetes and Digestive and Kidney Diseases 1R15DK092716 to AR and Cleveland State University Dissertation Research Award to SN.

Flow of Newtonian fluids with different polarity in micro scale

Due to the great development of medicine, micro-electro mechanical systems (MEMS) and seepage theory of unconventional oil and gas, fluid flow especially liquid flow in micro scale is getting more and more attention. In micro scale, flow is affected by many factors which are negligible in macro scale, thus shows different characteristics compared to conventional theory, such as Navier-Stokes equations. Aiming to study the flow characteristics of deionized water and isopropanol in micro scale, a visual experimental device is established. The direct objective is to measure flow rate of experimental fluids under different pressure gradient, in microtubes with different radius. The pressure is measured directly by pressure transducer. Flow rate is measured indirectly by measuring the displacement of the meniscus in metering tube in a measureable time interval. The tubes are made of fused silica. We choose deionized water and isopropanol as experimental fluids because they both have hydroxide radical. The polarity of water and isopropanol is 10.2 and 4, respectively. The pressure gradient ranges 0.04–24.8 MPa/m. The radius of tubes range 1–7.5 μm. The length of experimental tubes ranges 8–49 cm. Uncertainty of all experiments is less than 3%. The results showed that fluid flow in microtubes with radius smaller than 7.5 μm did not conform to Navier-Stokes equations. Experimental flow rate is lower than theoretical value calculated by Poiseuile equation. The flow rate deviation ranges 7.53%–70.75%. Flow rate-pressure gradient curves showed nonlinear characteristics in all experiments. Based on the boundary layer theory of laminar flow, the thickness of boundary layer is calculated. Relationship between boundary layer thickness and its influencing factors is investigated. In this study, thickness of boundary layer is positively correlated with polarity and viscosity, while it is negatively correlated with pressure gradient and radius of the tube. There was a power function relationship between the thickness of boundary layer and pressure gradient. Coefficients and the powers are regressed for all eight experiments, and Poiseuille equation is corrected based on the thickness function of boundary layer. The fitting result is quite good. Polarity is an important factor affecting fluid flow in micro scale. In order to compare the flow characteristics of fluids with different polarity, the impact of viscosity is eliminated. The comparison shows that the stronger the polarity, the thicker the corrected thickness of boundary layer. In conclusion, fluid flow in microtubes is affected by pressure gradient, radius, viscosity and polarity of fluid and solid wall molecules. Under low pressure gradient, micro flow shows nonlinear characteristics, which declines as pressure gradient increases since the efficient flow space is enlarged continuously. When the pressure gradient is high, the thickness of boundary layer is constant, and the nonlinear flow converses to linear flow. The reason is that thickness of boundary layer decreases with pressure gradient. As for fluid solid interaction, it is the inter-attractive between –OH in fluid molecules and polarized silica wall. As a result, a stagnant fluid layer is formed near the wall. For fluid with greater polarity, the effect of fluid-solid interaction on micro flow is greater, and the normalized thickness of boundary layer is larger, the upper limit of nonlinear flow is higher as well.

Effects of flow interruption on transport and retention of iron oxide colloids in quartz sand

Due to the complexity of flow conditions as well as solid matrix and colloid surface properties, solid knowledge about the transport of iron oxide colloids in soils remains scarce. In order to analyze the influence of flow conditions on iron oxide colloid transport and retention, breakthrough behavior of negatively charged, organic matter-coated goethite (OMCG) colloids in saturated quartz sand columns was investigated under continuous and stagnant flow conditions. Classic DLVO and extended DLVO (XDLVO) interaction energies including Lewis acid/base parameters were evaluated using measurements of sessile drop contact angles and zeta potentials of OMCG colloids and quartz. Results elucidated that under continuous flow conditions, OMCG colloids were highly mobile, which was in agreement with calculated unfavorable attachment conditions revealed by predictions of both DLVO approaches. In contrast, during intervals of flow interruption, significant amounts of OMCG colloids were retained in the solid matrix and could not be remobilized via re-establishment of flow. The magnitude of colloid retention increased with the duration of flow interruption; OMCG colloids were almost completely immobilized after 112h. Further experiments were conducted in order to determine possible colloid retention mechanisms. Results indicated that the major cause for retention during flow stagnation was OMCG colloid capture at locations with attractive DLVO/XDLVO interactions, promoted by fast gravitational settling of colloids onto the solid matrix. We compared breakthrough curves to model predictions, where we demonstrated that an attachment term with a stagnant fluid switch was required in the mass balance in order to reproduce the measurements. We conclude that high mobility of OMCG colloids and prediction of that transport behavior with the applied DLVO approaches were only valid under continuous flow conditions. Under more discontinuous hydraulic conditions relevant in natural soils, such as flow interruption, OMCG colloid transport behavior was modified significantly.

Enhanced boiling heat transfer on plain and featured surfaces using acoustic actuation

Two-phase thermal management based on submerged boiling heat transfer has received considerable attention in recent years because of its potential to achieve high heat fluxes along with its relatively simple hardware and system-level coupling. However, this attractive heat transfer approach has been hampered by the critical heat flux (CHF) limit on the maximum heat transfer, which is caused by the dynamics of the vapor bubbles that form on the heated surface and the subsequent transition to film boiling that produces a large increase in the surface temperature. Recent work at Georgia Tech has exploited low-power ultrasonic acoustic forcing to enhance boiling heat transfer and increase the CHF limit by controlling the formation and evolution of the vapor bubbles and inhibiting the instabilities that lead to film boiling. These effects are investigated with plain and textured (surface-embedded microchannels) boiling heat transfer base surfaces. Even without acoustic actuation, the transfer of makeup fluid to the boiling sites in the presence of surface microchannels passively decreases the surface superheat and increases in the CHF by 218% compared to plain surfaces. Acoustic actuation has a profound effect on the onset and evolution of boiling by inducing interfacial forces that affect the bubbles’ contact line with the surface and lead to bubble detachment. Heat transfer measurements with acoustic actuation demonstrate a significant increase in the CHF as the acoustic field impedes the formation of large vapor columns and inhibits the instability that results in the collapse of these columns into a vapor film. The improvements in the CHF in stagnant bulk fluid exceed 66% for the plain surface (up to 183W/cm2), and 31% for the textured surface (up to 460W/cm2 with a 7°C reduction in surface superheat).

Ignition and flame characteristics of cryogenic hydrogen releases

In this work, under-expanded cryogenic hydrogen jets were investigated experimentally for their ignition and flame characteristics. The test facility described herein, was designed and constructed to release hydrogen at a constant temperature and pressure, to study the dispersion and thermo-physical properties of cryogenic hydrogen releases and flames. In this study, a non-intrusive laser spark focused on the jet axis was used to measure the maximum ignition distance. The radiative power emitted by the corresponding jet flames was also measured for a range of release scenarios from 37 K to 295 K, 2–6 barabs through nozzles with diameters from 0.75 to 1.25 mm. The maximum ignition distance scales linearly with the effective jet diameter (which scales as the square root of the stagnant fluid density). A 1-dimensional (stream-wise) cryogenic hydrogen release model developed previously at Sandia National Laboratories (although this model is not yet validated for cryogenic hydrogen) was exercised to predict that the mean mole fraction at the maximum ignition distance is approximately 0.14, and is not dependent on the release conditions. The flame length and width were extracted from visible and infra-red flame images for several test cases. The flame length and width both scale as the square root of jet exit Reynolds number, as reported in the literature for flames from atmospheric temperature hydrogen. As shown in previous studies for ignited atmospheric temperature hydrogen, the radiative power from the jet flames of cold hydrogen scales as a logarithmic function of the global flame residence time. The radiative heat flux from jet flames of cold hydrogen is higher than the jet flames of atmospheric temperature hydrogen, for a given mass flow rate, due to the lower choked flow velocity of low-temperature hydrogen. This study provides critical information with regard to the development of models to inform the safety codes and standards of hydrogen infrastructure.

Instability of a vortex sheet leaving a right-angled wedge

We examine the dynamics of a semi-infinite vortex sheet attached not to a semi-infinite plate but instead to a rigid right-angled wedge, with the sheet aligned along one of its edges. Our approach to this problem, which was suggested by David Crighton, accords well with the fundamental ethos of Crighton’s work, which was characterized by ‘the application of rigorous mathematical approximations to fluid mechanical idealizations of practically relevant problems’ (Ffowcs Williams, Annu. Rev. Fluid Mech., vol. 34, 2002, pp. 37–49). The resulting linearised unsteady potential flow is forced by an oscillatory dipole in the uniform stream passing along the top of the wedge, while there is stagnant fluid in the remaining quadrant. Spatial instability is considered according to well-established methods: causality is enforced by allowing the frequency to become temporarily complex. The essentially quadrant-type geometry replaces the usual Wiener–Hopf technique by the Mellin transform. The core difficulty is that a first-order difference equation of period 4 requires a solution of period unity. As a result, the complex fourth roots $(\pm 1\pm \text{i})$ of $-4$ appear in the complementary function. The Helmholtz instability wave is excited and requires careful handling to obtain explicit results for the amplitude of the instability wave.

Investigation of flow and thermal behavior in a pipe submerged in a hot fluid

Convection heat transfer through a pipe submerged in a stagnant fluid is experimentally studied over a range of flow and thermal conditions. The Reynolds number varied from 330 to 6670 while the Grashof number varied from 14,000 to 95,000. The ratio Gr/Re2 ranged from 0.0003 to 0.6 implying that the inertial effects were more predominant than the buoyancy effects. The wall heating influenced the mean flow structure in both the streamwise and vertical directions at higher Gr/Re2 values, where both velocity components peaked in the bottom region of the pipe. The Nusselt number values showed good agreement with the Gnielinski correlation in the turbulent regime at very low values of Gr/Re2 as well as with theoretical values at low Reynolds numbers. However, in the turbulent regime, the Nusselt number decreased with an increase in Gr/Re2. The results showed that the original flow regime (in the absence of heating) had a significant impact on the local temperature field as well as the mean flow structure. It was also concluded that at low Reynolds numbers when the contribution of buoyancy-driven flow (natural convection) was smaller than that of the inertia-driven flow (forced convection), the role of buoyancy was primarily limited to the initiation of instabilities in the laminar flow to trigger the transition into turbulence.

Effective thermal conductivity of unary particulate bed

AbstractEffective thermal conductivity of a unary (mono‐sized) pebble bed depends on the physical properties of solid pebbles, physical properties and flow rate of fluid, temperature, coordination number of pebbles, and void fraction. The pebble size also plays an important role on the effective thermal conductivity of a unary pebble bed. To date, no theoretical justification for the same has been reported. In this present study an attempt was made to justify theoretically the dependence of the effective thermal conductivity on pebble size of a unary pebble bed filled with a stagnant fluid. A mathematical model has been developed to determine the effective thermal conductivity of a unary pebble bed with stagnant fluid. Different particle sizes (10 μm to 10 mm) were considered and modes of heat transfer were assumed to be conduction and convention only. Radiation mode of heat transfer was not considered. It was found that the effective thermal conductivity depends on the pebble size and the estimated values of the same were in close agreement with the reported experimental results.

Modeling and Finite Element Formulation for Acoustic Problems Including Rotating Domains

A finite element formulation for the efficient numerical simulation of sound in computational domains, including rotating regions, is presented. The mathematical description is based on an arbitrary Lagrangian–Eulerian framework and results in a convective wave equation for the scalar acoustic potential. Numerically, the capability of nonconforming grids is explored by applying a Nitsche-type mortaring between stationary and rotating regions. The formulation can be applied to classical acoustics (stagnant fluid) as well as moving fluids in the case of aeroacoustics. The validation with the analytical solution of a rotating point source in three dimensions demonstrates the accuracy and robustness of the developed numerical scheme. Additionally, the convergence study shows that the intersection mesh operations needed in the nonconforming setting do not deteriorate the accuracy of the numerical solution.

Characterizing dispersivity and stagnation in porous media using NMR flow propagators

Low-field nuclear magnetic resonance (NMR) displacement probability distributions (flow propagators) are presented for water flowing through heterogeneous porous materials. Four sedimentary rocks have been chosen as example systems: Dolostone, Bentheimer sandstone, Berea sandstone, and Indiana limestone (in order of decreasing permeability). The fluid displacement is characterized by pre-asymptotic Stokes’ flow and so the probability distributions are bimodal, with peaks corresponding to stagnant fluid in dead-end pores and flowing fluid in the connected porosity. Cut-off Gaussian functions are used to fit the flowing and stagnant peaks independently. An effective dispersivity length scale Lv (also known as the mixing length scale) is estimated by fitting the portion of the probability distribution corresponding to the flowing fluid. For the relatively homogeneous Bentheimer sandstone, the ratio of effective dispersivity length scale to effective transport diameter dt is Lv/dt≈16, which is an order of magnitude larger than for randomly packed glass beads where Lv/dt≈1.8. We compare these dispersivity parameters to similar values extracted from a cumulant analysis of the entire propagator. Fitting a cut-off Gaussian avoids the usual complications of analyzing dispersion in the presence of the ubiquitous stagnant fluid, and results in a clear demonstration of the influence of long-range heterogeneities on the dispersivity for flow in real sedimentary rocks.

Fuel Assembly Oscillation-Induced Flow in Initially Stagnant Fluid

The effect of water on the dynamics response of fuel bundles in pressurized water reactors during external forcing is studied experimentally inside a large facility that houses a full-height bundle and is operated on an earthquake shake table. This configuration is directly relevant to earthquakes and loss-of-coolant accidents. Most data to date have been focused on structural response and some pointwise measurements of liquid velocity. Here, structure displacement coupled with velocity field are investigated with nonintrusive optical diagnostics in initially stagnant water. Data indicate that a flow develops as the structure oscillates: both a cross flow through the bundle and an axial pulsatile flow that was not anticipated. A physical mechanism is proposed as a source of this structure-induced flow that is driven by pressure gradients around the fuel bundle.

Instrumented flow-following sensor particles with magnetic position detection and buoyancy control

Abstract. A concept for buoyancy control and magnetic position detection has been developed for the improvement of instrumented flow-following sensor particles. The sensor particles are used for investigation of hydrodynamic and biochemical processes in large-scale vessels such as biogas fermenters, bioreactors and aerated sludge basins. Neutral buoyancy of the sensor particles is required for tracing of the fluid flows. Buoyancy control is performed by adjustment of the sensor particles' volume, which is altered by an integrated piston. A miniaturized linear actuator, namely a stepper motor with linear transmission, is operated by a microcontroller to drive the piston. The buoyancy control unit enables accurate automated taring of the sensor particles in the stagnant process fluid to achieve neutral buoyancy. Therefore, the measured vertical position of the sensor particle as a function of the hydrostatic pressure is used as feedback. It has an incremental density change of 0.0136 % as compared to water and a residual drift velocity of approximately 3.6 × 10−3 m s−1. Furthermore, a minimum density of 926 kg m−3 can be set by full extension of the piston, which allows floating of the sensor particles after a defined event, namely critical charge of battery, full data storage or the end of a fixed time cycle. Thus, recovery of the sensor particles can proceed easily from the fluid level. The sensor particles with a buoyancy control unit are tested for depths up to 15 m. Also, detection of a local magnetic position marker by the sensor particles has been implemented to enhance movement tracking. It was tested in a lab-scale biogas digester and was used for estimation of the liquid circulation time distribution and Peclét number to describe the macro-flow.

Interfacial Contamination Between Batches of Crude Oil Due to Dead-Legs in Pump Station Piping

Some oil pump station design layouts may contain multiple dead-legs. During the transportation of heavy crude through the pump station, these dead-legs will be filled with this crude. When a light crude batch is introduced next into the pipeline, following the heavy crude ahead, two phenomena will occur. First, contamination between batches at the interface of the two crudes will occur due to axial turbulent diffusion along the length of the pipeline itself. Second, as the light crude flows through the pump station and passes by each dead-leg containing still heavy crude from the preceding batch, the heavy crude trapped in these dead-legs will start to drain out into the passing light crude in the main run. This causes further contamination and spreading of the mixing zone between the two batches. These two different sources of contamination are addressed in this paper with the objective of accurately quantifying the extent of the contamination, with particular emphasis on the second phenomenon which could cause appreciable contamination particularly for large size and number of these dead-legs. A computational fluid dynamics (CFD) model has been developed to quantify the drainage rate of the contaminating crude into the main stream and its impact on widening the mixed zone (contamination spread) between the two batches. Two drainage mechanisms of the heavy crude in the dead-legs into the main stream of the light crude have been identified and quantified. The initial phase is a gravity-current-induced outflow of the initially stagnant fluid in the dead-leg, followed by a subsequent draining mechanism primarily induced by turbulent mixing and diffusion at the mouth of the dead-leg penetrating slightly into the dead-leg. It was found that the second mechanism takes a much longer time to drain the first, and that the break point in time where drainage switches from a predominantly gravity current to a turbulent diffusion appears to be at a specific time normalized with respect to the length of the dead-leg and the gravity current speed. The results show a consistent trend with actual interface contamination data obtained from the Keystone 2982 km pipeline from Hardisty (Canada) to the Patoka Terminal (U.S.A.).

Combined Effects of Slip Motion and Boundary Conditions on Enhanced Heat Transfer in Natural Convection Flows of Enclosed Nanofluids

The experimental studies dealing with natural convection of nanofluids in differentially heated enclosures demonstrate that the addition of nanoparticles to a pure base liquid is substantially detrimental, which can be ascribed to the formation of two stagnant fluid layers near the top and bottom adiabatic walls. Thus, if the horizontal walls are differentially heated instead of being perfectly insulated, the consequent development of a pair of concentration boundary layers near them may possibly imply a heat transfer enhancement. In this connection, a two-phase mixture model is employed to perform a numerical study of laminar natural convection in a square cavity containing water suspensions of alumina nanoparticles with a diameter of 33 nm and an average volume fraction in the range 0.001–0.04, assuming that Brownian diffusion and thermophoresis are the primary slip mechanisms between solid and liquid phases. The cavity is differentially heated at sides, whereas the horizontal walls are assumed to be either adiabatic or one heated and the other cooled, with a Rayleigh number in the range 4 × 105–3 × 106. It is found that the heating-from-below configuration is featured by periodic heat transfer, with a rate remarkably higher than that typical of the pure base liquid.

Coupled RapidCell and lattice Boltzmann models to simulate hydrodynamics of bacterial transport in response to chemoattractant gradients in confined domains

The RapidCell (RC) model was originally developed to simulate flagellar bacterial chemotaxis in environments with spatiotemporally varying chemoattractant gradients. RC is best suited for motility simulations in unbounded nonfluid environments; this limits its use in biomedical applications hinging on bacteria-fluid dynamics in microchannels. In this study, we eliminated this constraint by coupling the RC model with the colloidal lattice Boltzmann (LB) model. RC–LB coupling was accomplished by tracking positions of chemoreceptors on particle surfaces that vary with particles’ angular and translational velocities, and by including forces and torques due to particles’ tumbling and running motions in particle force- and torque-balance equations. The coupled model successfully simulated trajectories of particles in initially stagnant fluids in bounded domains, involving a chemoattractant contained in a confined zone with a narrow inlet or concentric multiringed inline obstacles, mimicking tumor vasculature geometry. Chemotactically successful particles exhibited higher attractant concentrations near the receptor clusters, transient increases in the motor bias, and transient fluctuations in methylated proteins at the cell scale, while exhibiting more frequent higher particle translation velocities and smaller angular velocities than chemotactically unsuccessful particles at the particle scale. In these simulations, the chemotactic particles reached the chemoattractant with the success rates of 20–72 %, whereas nonchemotactic particles would be unsuccessful. The coupled RC–LB model is the first step toward development of a multiscale simulation tool that bridges cell-scale signal and adaptation dynamics with particle-scale fluid-particle dynamics to simulate chemotaxis-driven bacterial motility in microchannel networks, typically observed in tumor vasculatures, in the context of targeted drug delivery.

Electro-hydrodynamic concentration of genomic length DNA.

We report a method of concentrating genomic length DNA within a microfluidic device, using a novel mechanism that combines polyelectrolyte migration with electrophoretic recirculation. Suitable combinations of geometry, pressure and voltage will trap long DNA molecules (>10 kbp) within a small volume (approximately 1 nL), amplifying the local concentration at rates in excess of 1000 fold per minute. The rate at which DNA accumulates is length dependent, while charged particles of similar size pass freely through the device. Experimental observations confirm that the rapid accumulation of DNA at the inlet is caused by an outward migration of the polyelectrolyte towards the capillary boundaries, followed by electrophoresis of DNA within the stagnant fluid layer next to the wall.

Open abdomen in gastrointestinal surgery: Which technique is the best for temporary closure during damage control?

To compare the 3 main techniques of temporary closure of the abdominal cavity, vacuum assisted closure (vacuum-assisted closure therapy - VAC), Bogota bag and Barker technique, in damage control surgery. After systematic review of the literature, 33 articles were selected to compare the efficiency of the three procedures. Criteria such as cost, infections, capacity of reconstruction of the abdominal wall, diseases associated with the technique, among others were analyzed. The Bogota bag and Barker techniques present as advantage the availability of material and low cost, what is not observed in the VAC procedure. The VAC technique is the most efficient, not only because it reduces the tension on the boarders of the lesion, but also removes stagnant fluids and debris and acts at cellular level increasing cell proliferation and division. Bogota bag presents the higher rates of skin laceration and evisceration, greater need for a stent for draining fluids and wash-ups, higher rates of intestinal adhesion to the abdominal wall. The Barker technique presents lack of efficiency in closing the abdominal wall and difficulty on maintaining pressure on the dressing. The VAC dressing can generate irritation and dermatitis when the drape is applied, in addition to pain, infection and bleeding, as well as toxic shock syndrome, anaerobic sepsis and thrombosis. The VAC technique, showed to be superior allowing a better control of liquid on the third space, avoiding complications such as fistula with small mortality, low infection rate, and easier capability on primary closure of the abdominal cavity.