Embedding Fluid Research Articles

Thermal Effects on Optical Chirality, Mechanics, and Associated Symmetry Properties

A review is provided here about the thermal effects on optical chirality. To this goal, chiral objects dispersed in an embedding fluid are examined for their magnetoelectric coupling. Thermal effects on several chiral meta-atoms and their ensembles are examined. To this goal, DNA-like helical structures are examined in detail. The mechanical aspect of thermo-elasticity is reviewed along with transverse deformations while drawing analogies from condensed-matter physics. In this respect, the chirality-induced spin selection is reviewed along with the temperature-mediated electron–phonon interactions. A wide range of materials, such as polymers and biological cells, are also examined for temperature effects. A transition temperature delineating a sign flip in the chirality parameter is identified as well. Chirality-associated functionalities such as ratchet motions, switching, and modulations are investigated for their respective thermal effects. Issues of fabricating chiral meta-atoms are also discussed.

Suspension of discrete microscopic oscillators as a model of an ultrasonic metafluid

We present a model of ultrasonic metafluids---acoustic metamaterials in the form of suspensions of discrete microscopic oscillators coupled to the embedding fluid. Contrary to a common assumption about metamaterials, and as already established in the field of metafluids, the metafluid concept need not be based on position periodicity or correlation of the suspended micro-oscillators, and in this case not even on ideally designed micro-oscillators. For the speculation that metafluids may one day be produced as solutions of macromolecules, it is essential that the micro-oscillators be allowed to be randomly distributed in the host fluid and generally have irregular (modal) shapes. We formulate the detailed operating principle of such a metafluid model, give explicit formulas for its effective dynamic moduli in terms of the modal structure of the micro-oscillators, and discuss basic practical issues of performance optimization in terms of their mass and size.

Spatial modulation of Gaussian beam by dual-beam nonlinear Fabry-Perot interferometer

In this paper, a model of dual-beam nonlinear Fabry-Perot interferometer (DBNFPI) for laser Gaussian beam’s spatial modulation is proposed. It includes a thin film of oil red O sandwiched between two optical mirrors and is irradiated by two signal and pump laser Gaussian beams. The equation describing the output-input relation of intensities concerning pump intensity and the expression describing the spatial intensity distribution of output signal beam (OSB) are derived. The optical bistability of DBNFPI is numerically calculated with different pump intensities as well as the capability to spatially modulate the Gaussian beam is discussed. The different shapes of the OSB as: Gaussian, flat-top-Gaussian, ring-Gaussian, hollow-Gaussian, and multi-hollow-Gaussian are shown. The suitable range of pump intensity for particular shape of OSB is discussed, especially the hollow-Gaussian shape requirement for optically trapping microspheres having reflective index to be lower than that of embedding fluid.

Discrete embedded boundary method with smooth dependence on the evolution of a fluid‐structure interface

AbstractEmbedded boundary methods (EBMs) are robust solution methods for highly nonlinear fluid‐structure interaction (FSI) problems. They suffer, however, some disadvantages because they perform their computations on embedding, nonbody‐fitted fluid meshes. In particular, they tend to generate discrete events that introduce discontinuities in the semi‐discretization process and lead to numerical solutions that are insufficiently smooth for differentiation with respect to the evolution of a discrete, fluid/structure interface . This hinders their application to the gradient‐based solution of fluid‐structure optimization problems. Discrete events also promote spurious oscillations in the post‐processing of time‐dependent results computed at .z This paper addresses these issues in the context of Finite Volume method with Exact two‐material Riemann problems (FIVER), a comprehensive framework for developing EBMs for highly nonlinear, compressible, FSI problems. It revisits the concept of the status of a node of an embedding fluid mesh and introduces that of a smoothness indicator nodal function, to eliminate discrete events and achieve smoothness in the semi‐discretization process. It also introduces a moving least squares approach in the loads evaluation algorithm, to suppress spurious oscillations from integral quantities computed on . Equipped with these enhancements, FIVER is shown to deliver, for three different FSI applications, smooth results that are differentiable with respect to evolutions of .

Molecular chains under tension: Thermal and mechanical activation of statistically interacting extension and contraction particles.

This work introduces a methodology for the statistical mechanical analysis of polymeric chains under tension controlled by optical or magnetic tweezers at thermal equilibrium with an embedding fluid medium. The response of single bonds between monomers or of entire groups of monomers to tension is governed by the activation of statistically interacting particles representing quanta of extension or contraction. This method of analysis is capable of describing thermal unbending of the freely jointed or wormlike chain kind, linear or nonlinear contour elasticity, and structural transformations including effects of cooperativity. The versatility of this approach is demonstrated in an application to double-stranded DNA undergoing torsionally unconstrained stretching across three regimes of mechanical response including an overstretching transition. The three-regime force-extension characteristic, derived from a single free-energy expression, accurately matches empirical evidence.

51 Optimizing Urinalysis Turnaround Times in the Emergency Department

To improve urinalysis (UA) collection and result turnaround times (TAT) in the emergency department (ED). Prolonged ED stays negatively impact patient care quality, mortality, and satisfaction. Improving throughput requires timely diagnostic test results. Urinalyses are the third most commonly performed lab test after CBC and chemistry. Little has been published on successful strategies to improve collection and turnaround times for urinalyses. Initial process involved determination of current state by retrospective data query of urinalyses ordered in the ED of a Level 1 trauma center (annual volume of 117,000 patients). Turnaround times of urinalyses for all active ED patients ages 18 and up were compared over a 6-month period (June-November 2018). This included order time, collection time, and lab result time for 18,309 patients. Preliminary data analysis focused on areas most likely to result in shorter overall turnaround times. This was followed by a prospective 90-day pilot over 4500 UA samples, focusing on optimization strategies on collection which included (1) creation of a multidisciplinary taskforce, (2) development of EPIC orders with embedded fluid and in-and-out catheter orders, (3) UA tracker within EPIC that alerts nursing to collection delays, (4) team education addressing need to collect, (5) patient education on sample collection via provider scripts and educational signs, (6) and implementation of strategic algorithms to guide staff. Preliminary analysis of current state showed largest variance of times were from Time- to-Collection (120-240 minutes). Process changes focused on earlier UA collection as described above resulted in overall TAT decrease from 120 minutes to 90 min (26% decrease in total time). The time from Order to Collection was decreased from 87 minutes to 50 minutes (36% decrease). Times were also impacted by delays in transfer of specimen from ED to lab as well as lab processing; however, these times had much smaller range variance. It is of no surprise that EDs face a heightened degree of overcrowding. Although this is multi-factorial, urine collection can be one of the culprits predisposing providers to delays in disposition, which leads to extended lengths of stay for patients. UA TAT’s can be improved via process changes focused primarily on early collection of the sample. This is a novel project created with a focus on systems-based quality improvement. Through a multidisciplinary team approach involving providers, nurses, techs, and IT support, we developed simple pathways to expedite the collection process. Embedding fluid and catheterization orders within the initial UA order, using a UA tracker within EPIC alerting staff to collection delays, and team and patient education on importance of obtaining sample quickly were integral in reducing time to collection and overall TAT. The project is still ongoing. Our goal is to maintain a multidisciplinary team for process refinement, continue staff education, and optimize urine acquisition in the ED. It is our hope that these reductions in TAT will expedite dispositions and enhance overall patient care.

Active morphogenesis of epithelial monolayers

During typical early-stage embryo development, single-cell-thick tissues of tightly bound epithelial cells autonomously generate profound changes in their shape, forming the basis of organism anatomy. We report on a (covariant) active-hydrodynamic theory of such monolayer morphogenesis that is closed under its shape-changing dynamics-i.e., the degrees of freedom that encode monolayer geometry appear properly as broken-symmetry variables. In our theory, the salient physics of tissue-scale deformations emerges from a balance between the displacement and/or shear of a low-Reynolds-number embedding fluid (the "yolk") and cell-autonomous stresses, themselves a result of combining apical contractile stresses with an elastic-like mechanical response under the constraint of constant cell volume. The leading-order hydrodynamic instabilities include both passive constrained-buckling and active deformation, which can be further categorized by cell shape changes that are either "squamous to columnar" or "regular-prism to truncated-pyramid." The deformations resulting from the latter qualitatively reproduce in vivo observations of the onset of both mesoderm and posterior midgut invaginations, which take place during gastrulation in the model organism Drosophila melanogaster.

Bacterial swarmer cells in confinement: a mesoscale hydrodynamic simulation study.

A wide spectrum of Peritrichous bacteria undergo considerable physiological changes when they are inoculated onto nutrition-rich surfaces and exhibit a rapid and collective migration denoted as swarming. Thereby, the length of such swarmer cells and their number of flagella increases substantially. In this article, we investigated the properties of individual E. coli-type swarmer cells confined between two parallel walls via mesoscale hydrodynamic simulations, combining molecular dynamics simulations of the swarmer cell with the multiparticle particle collision dynamics approach for the embedding fluid. E. coli-type swarmer cells are three-times longer than their planktonic counter parts, but their flagella density is comparable. By varying the wall separation, we analyze the confinement effect on the flagella arrangement, on the distribution of cells in the gap between the walls, and on the cell dynamics. We find only a weak dependence of confinement on the bundle structure and dynamics. The distribution of cells in the gap changes from a geometry-dominated behavior for very narrow to fluid-dominated behavior for wider gaps, where cells are preferentially located in the gap center for narrower gaps and stay preferentially next to one of the walls for wider gaps. Dynamically, the cells exhibit a wide spectrum of migration behaviors, depending on their flagella bundle arrangement, and ranges from straight swimming to wall rolling.

Transient dynamics of a colloidal particle driven through a viscoelastic fluid

We study the transient motion of a colloidal particle actively dragged by an optical trap through different viscoelastic fluids (wormlike micelles, polymer solutions, and entangled λ-phage DNA). We observe that, after sudden removal of the moving trap, the particle recoils due to the recovery of the deformed fluid microstructure. We find that the transient dynamics of the particle proceeds via a double-exponential relaxation, whose relaxation times remain independent of the initial particle velocity whereas their amplitudes strongly depend on it. While the fastest relaxation mirrors the viscous damping of the particle by the solvent, the slow relaxation results from the recovery of the strained viscoelastic matrix. We show that this transient information, which has no counterpart in Newtonian fluids, can be exploited to investigate linear and nonlinear rheological properties of the embedding fluid, thus providing a novel method to perform transient rheology at the micron-scale.

Ultrasonic-Controled Microlens Arrays in Germanium for Optical Tweezers

The microlens arrays created by ultrasonic waves in acousto-optical material Germanium (Ge) is theoretically proposed. The simulated results show the proposed microlens arrays can be used for optical tweezers arrays to trap an assembly micro-beads. Moreover, with the control by changing of the ultrasonic intensity and frequency, the optical tweezers arrays will act as the dynamical one, which can sieve the beads in (X,Y) plane in the embedding fluid.

MICROLENS FOCAL LENGTH CONTROLING FOR OPTICAL TWEEZER ARRAYS BY ACOUSTO-OPTIC MODULATION IN GERMANIUM

The microlens arrays created by ultrasonic waves in acousto-optical material Germanium (Ge) is theoretically proposed. The simulated results show the proposed microlens arrays can be used for optical tweezers arrays to trap an assembly micro-beads. Moreover, with the control by changing of the ultrasonic intensity and frequency, the optical tweezers arrays will act as the dynamical one, which can sieve the beads in (X,Y) plane in the embedding fluid. The focal length of microlens in Germanium controling by frequency and intensity of ultrasonic wave is discussed.      Â

Modelling the mechanics and hydrodynamics of swimming E. coli.

The swimming properties of an E. coli-type model bacterium are investigated by mesoscale hydrodynamic simulations, combining molecular dynamics simulations of the bacterium with the multiparticle particle collision dynamics method for the embedding fluid. The bacterium is composed of a spherocylindrical body with attached helical flagella, built up from discrete particles for an efficient coupling with the fluid. We measure the hydrodynamic friction coefficients of the bacterium and find quantitative agreement with experimental results of swimming E. coli. The flow field of the bacterium shows a force-dipole-like pattern in the swimming plane and two vortices perpendicular to its swimming direction arising from counterrotation of the cell body and the flagella. By comparison with the flow field of a force dipole and rotlet dipole, we extract the force-dipole and rotlet-dipole strengths for the bacterium and find that counterrotation of the cell body and the flagella is essential for describing the near-field hydrodynamics of the bacterium.

A multiblob approach to colloidal hydrodynamics with inherent lubrication.

This work presents an intermediate resolution model of the hydrodynamics of colloidal particles based on a mixed Eulerian-Lagrangian formulation. The particle is constructed with a small set of overlapping Peskin's Immersed Boundary kernels (blobs) which are held together by springs to build up a particle impenetrable core. Here, we used 12 blobs placed in the vertexes of an icosahedron with an extra one in its center. Although the particle surface is not explicitly resolved, we show that the short-distance hydrodynamic responses (flow profiles, translational and rotational mobilities) agree with spherical colloids and provide consistent effective radii. A remarkable property of the present multiblob model is that it naturally provides zero relative mobility at some finite inter-particle distance. In terms of mutual friction, this divergent force accurately represents the "soft" lubrication regime of spherical colloids and permits to resolve the increase of the solution viscosity up to moderately dense systems with volume fraction up to about 0.50. This intermediate resolution model is able to recover highly non-trivial (many-body) hydrodynamics using small particles whose radii are similar to the grid size h (in the range [1.6 - 3.2] h). Considering that the cost of the embedding fluid phase scales such as the cube of the particle radius, this result brings about a significant computational speed-up. Our code Fluam works in Graphics Processor Units and uses Fast Fourier Transform for the Poisson solver, which further improves its efficiency.

Hydrodynamic interactions induce anomalous diffusion under partial confinement

Under partial confinement, the motion of colloidal particles is restricted to a plane or a line but their dynamics is influenced by hydrodynamic interactions mediated by the unconfined, three-dimensional flow of the embedding fluid. We demonstrate that this dimensionality mismatch induces a characteristic divergence in the collective diffusion coefficient of the colloidal subsystem. This result, independent of the specific interparticle forces in the colloid, is solely due to the kinematical constraint on the colloidal particles, and it is different from the known divergence of transport coefficients in purely one or two-dimensional fluids.

Multiple-component lattice Boltzmann equation for fluid-filled vesicles in flow

We document the derivation and implementation of extensions to a two-dimensional, multicomponent lattice Boltzmann equation model, with Laplace law interfacial tension. The extended model behaves in such a way that the boundary between its immiscible drop and embedding fluid components can be shown to describe a vesicle of constant volume bounded by a membrane with conserved length, specified interface compressibility, bending rigidity, preferred curvature, and interfacial tension. We describe how to apply this result to several, independent vesicles. The extended scheme is completely Eulerian, and it represents a two-way coupled vesicle membrane and flow within a single framework. Unlike previous methods, our approach dispenses entirely with the need explicitly to track the membrane, or boundary, and makes no use whatsoever of computationally expensive and intricate interface tracking and remeshing. Validation data are presented, which demonstrate the utility of the method in the simulation of the flow of high volume fraction suspensions of deformable objects.

Flow regimes of a fluid driven granular suspension

We discuss molecular dynamics simulations of a granular suspension driven in a channel by an embedding fluid. The flow has three different regimes: it is disordered at small packing fractions, \({\phi}\); above a transition point, \({\phi_m}\), flows becomes ordered in layers, but only in a fraction of samples; at higher \({\phi}\), if ordering is avoided, jamming is also encountered. In the disordered flow regime the velocity profile is power law, consistent with an Ostwald-de Waele constitutive relation. In the ordered regime, flow is concentrated in the bulk in a nearly solid plug having a flat velocity profile, with narrow shear regions at the boundaries. Interestingly, velocity fluctuations are approximately linear in the velocity in all regimes.

Stochastic transitions and jamming in granular pipe flow

We study a model granular suspension driven down a channel by an embedding fluid via computer simulations. We characterize the different system flow regimes and the stochastic nature of the transitions between them. For packing fractions below a threshold ϕ{m}, granular flow is disordered and exhibits an Ostwald-de Waele-type power-law shear-stress constitutive relation. Above ϕ{m}, two asymptotic states exist; disordered flow can persist indefinitely, yet, in a fraction of samples, the system self-organizes in an ordered form of flow where grains move in parallel ordered layers. In the latter regime, the Ostwald-de Waele relationship breaks down and a nearly solid plug appears in the center, with linear shear regions at the boundaries. Above a higher threshold ϕ{g}, an abrupt jamming transition is observed if ordering is avoided.

Deformation and clustering of red blood cells in microcapillary flows

The shape changes and clustering of red blood cells (RBCs) under flow in cylindrical microcapillaries are studied using a triangulated surface model for the membrane and a particle-based mesoscopic simulation technique for the embedding fluid. As the flow velocity increases, the RBCs make a transition from a discocyte shape at low velocities to a parachute shape at high velocities; close to the critical flow velocity, the RBC can also be found in a transient slipper shape. The transition and critical flow velocity are examined for various capillary diameters and RBC volume fractions (hematocrit HT). At high flow velocities and low hematocrits, the parachute-shaped RBCs can be found in clusters which are hydrodynamically stabilized. Here, the formation of a fluid vortex between neighboring cells, called bolus, develops which keeps the cells at a preferred distance. Decreasing the flow velocity towards the critical velocity, we observe an increasing frequency of drastic RBC shape fluctuations to slipper-shaped RBCs that can result in cluster breakup. These clusters resemble those seen in experiments using optical microscopy.

Nonlinear dynamics and self-organization of rotary molecular motor ensembles

The coupled nonlinear dynamics of rotary motor ensembles and an embedding fluid medium are simulated on the basis of Navier-Stokes equations. The model description considers space-dependent rotation of motors and a spatially inhomogeneous motor distribution as well as spatial fluctuations in molecular properties. The mutual influence of motor rotations and fluid dynamics as well as spatial inhomogeneities of their molecular properties are self-consistently included. Space-time simulations visualize the complex interplay between the fluid dynamics and motor rotation and show that the dynamic coupling to the environment via the velocity field as well as the spatial inhomogeneity and distribution of rotors determines the overall behavior of the motor complex. Depending on the initial molecular distribution, rotation frequency, and fluid dynamics a spatial self-organization or a chaotic behavior may arise.

On the slumping of high Reynolds number gravity currents in two-dimensional and axisymmetric configurations

The behaviour of an inviscid gravity current of finite volume which is released from behind a lock and then propagates over a horizontal boundary is considered, for the elucidation of the initial ‘slumping’ phase during which the nose propagates with a constant velocity. The shallow-water two-layer model is used and the necessary front condition is provided, for comparisons, by four different correlations for the nose Froude function. Analytical and numerical results are presented, which reveal the essential flow-field features for various values of the governing dimensionless parameter H, the initial depth ratio of the outer embedding fluid to that of the dense fluid in the lock. It is shown that in the two-dimensional configuration a clear-cut slumping stage develops for any value of H, but for H<2 this stage is complicated by jumps of the interface (backward and forward moving bores) and constrained maximal nose velocity. The two-layer model provides good qualitative and quantitative agreements with previously published measurements, but the one-layer model mispredicts the dependency of the slumping distance on H. In the axisymmetric configuration a clear-cut slumping stage develops only for values of H close to 1 (shallow ambient), and persists for a relatively short time and distance. The effect of the Froude correlations and implementation to box-model approximations are also discussed.