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In vitro blood flow behaviour in microchannels with simple and complex geometries

Garcia, Valdemar; Dias, Ricardo P.; Lima, R.
Fonte: InTech Publicador: InTech
Tipo: Parte de Livro
ENG
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Over the years, various experimental methods have been applied in an effort to understand the blood flow behaviour in microcirculation. The development of optical experimental techniques has contributed to obtain possible explanations on the way the blood flows through microvessels. In recent years, due to advances in computers, optics, and digital image processing techniques, it has become possible to combine a conventional particle image velocimetry (PIV) system with an inverted microscope and consequently improve both spatial and temporal resolution. The present review outlines our most relevant studies on the flow properties of blood at a microscale level by using current micro-PIV and confocal micro-PIV techniques. In this chapter, our recent studies about in vitro blood flow behaviour in microchannels both in straight and with complex geometries are presented. In straight microchannels we present some phenomena such as Fahraeus effect and Fahraeus-Lindqvist effect, the flow of particles and red blood cells (RBCs) in diluted suspensions, the flow of RBCs in concentrated suspensions, the cell-free layer and sedimentations effects. The most recent studies in blood flow through complex geometries such as bifurcations, confluences and stenosis are also reviewed. By using a chromatographic method...

Determinação das melhores condições de hidrólise física com ultrassom de potência em resíduos de amendoim

Polachini, Tiago Carregari
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Dissertação de Mestrado Formato: 107 f. : il., gráfs. tabs. color.
POR
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 2013/09344-4; Pós-graduação em Engenharia e Ciência de Alimentos - IBILCE; Nowadays, many resources are invested on developing new technologies for agroindustrial by-products utilization and process aiming at the second generation ethanol production. The peanut processing is one of the biggest waste producers, approximating to the waste from sugar cane culture. An emerging technology involved on residues treatment is the power ultrasound (US), which is being tested in areas such as cellulosic materials pretreatment and combined method to increase the reaction velocity in fermentative processes. In this work, powder peanut shells was obtained with an average particle size of 963,2 μm and density ranging according to its partice size. Its chemical characterization presented a dry matter composed by 37,1% of cellulose, 33,4% of hemicellulose and 15% of lignin. Initially, the acid suspension, which will be used in the physical hydrolysis, had its physical properties determined to allow the ultrasonic parameters calculation. Among the properties, there are density, rheological parameters and specific heat, where no influence of pH was verified. These properties could be modeled simultaneously as function of solid concentration and absolute temperature...

Multicellular oxidant defense in unicellular organisms.

Ma, M; Eaton, J W
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/09/1992 EN
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Although catalase is thought to be a major defense against hydrogen peroxide (H2O2), the catalase activity within individual Escherichia coli fails to protect against exogenous H2O2. Contrary to earlier reports, we find that dilute suspensions of wild-type and catalase-deficient E. coli are identical in their sensitivity to H2O2, perhaps because even wild-type, catalase-positive E. coli cannot maintain an internal/external concentration gradient of this highly diffusible oxidant. However, concentrated suspensions or colonies of catalase-positive E. coli do preferentially survive H2O2 challenge and can even cross-protect adjacent catalase-deficient organisms. Furthermore, high-density catalase-positive--but not catalase-negative--E. coli can survive and multiply in the presence of competitive, peroxide-generating streptococci. These observations support the concept that bacterial catalase may defend colonial, but not individual, E. coli against environmental H2O2. Group protection by the activity of enzymes that mitigate oxidative stress may have been a driving force in the evolution of multicellular organisms.

Viscoelasticity of packed erythrocyte suspensions subjected to low amplitude oscillatory deformation.

Drasler, W J; Smith, C M; Keller, K H
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1987 EN
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Concentrated adult erythrocyte suspensions were subjected to low amplitude oscillatory shear in a Weissenberg rheogoniometer equipped with a cone-and-plate assembly. The dynamic viscoelastic properties of the suspension were measured over a broad range of frequency by a numerical solution that accounted for fluid inertia. Variation of shear amplitude and cell volume percent, and comparison of buffered saline, plasma, and dextran as suspending media showed that the cellular elements had undergone small bending and shearing deformations. Studies of normal adult erythrocytes, hypotonically swollen cells, temperature-altered cells, and erythrocyte ghosts suggested that the method was evaluating membrane material properties. The normal membrane was found to exhibit a shear rate dependent elastic modulus that increased by more than a factor of 20 over a frequency range from 0.0076 Hz to 60 Hz. The membrane viscosity showed a substantial drop with frequency indicative of a frequency thinning phenomenon. At high frequency of deformation the viscous response of normal erythrocytes was no longer indicative of a membrane property due to the dominant influence of the internal hemoglobin solution. The studies generally supported the ability of the method to quantify relative membrane material properties and detect changes in membrane structure.

The rheology of three-phase suspensions at low bubble capillary number

Truby, J. M.; Mueller, S. P.; Llewellin, E. W.; Mader, H. M.
Fonte: The Royal Society Publishing Publicador: The Royal Society Publishing
Tipo: Artigo de Revista Científica
Publicado em 08/01/2015 EN
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We develop a model for the rheology of a three-phase suspension of bubbles and particles in a Newtonian liquid undergoing steady flow. We adopt an ‘effective-medium’ approach in which the bubbly liquid is treated as a continuous medium which suspends the particles. The resulting three-phase model combines separate two-phase models for bubble suspension rheology and particle suspension rheology, which are taken from the literature. The model is validated against new experimental data for three-phase suspensions of bubbles and spherical particles, collected in the low bubble capillary number regime. Good agreement is found across the experimental range of particle volume fraction (0≤ϕp≲0.5) and bubble volume fraction (0≤ϕb≲0.3). Consistent with model predictions, experimental results demonstrate that adding bubbles to a dilute particle suspension at low capillarity increases its viscosity, while adding bubbles to a concentrated particle suspension decreases its viscosity. The model accounts for particle anisometry and is easily extended to account for variable capillarity, but has not been experimentally validated for these cases.

On the rheology of concentrated fiber suspensions

Dinh, Steven Minh
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 362 leaves; 9350697 bytes; 9350492 bytes; application/pdf; application/pdf
ENG
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by Steven Minh Dinh.; Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1981.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.; Vita.; Bibliography: leaves 288-296.

Concentração de leveduras da fermentação alcoólica em hidrociclones

Bicalho, Isabele Cristina
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
POR
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No processo de fermentação para produção de etanol, as leveduras de Saccharomyces cerevisiae são recuperadas e recicladas para uma nova etapa de fermentação. Este processo de separação representa um grande desafio, pois as leveduras são pequenas e com baixa densidade. Para tal finalidade, o hidrociclone surge como uma alternativa interessante pois, além de utilizar o mesmo princípio de separação das centrífugas, requer baixo custo de manutenção e pode ser prontamente esterilizado. O presente trabalho teve como objetivo otimizar o processo de separação de leveduras da fermentação alcoólica utilizando hidrociclones. Para tanto, avaliou-se, através de estudos experimentais, a influência de variáveis geométricas e operacionais sobre o desempenho de hidrociclones. Um planejamento experimental fatorial (34) foi empregado e os resultados foram usados para a determinação de modelos matemáticos empíricos que descrevem a capacidade, eficiência total, a razão de líquido e a eficiência total reduzida como função de diferentes variáveis geométricas (diâmetro da alimentação, diâmetro do overflow e ângulo de tronco de cone) e da queda de pressão. A geometria “ótima” encontrada foi utilizada em um outro planejamento 3 níveis que visava avaliar o efeito da concentração e da queda de pressão sobre o desempenho deste hidrociclone. Os diâmetros dos dutos de alimentação e overflow estudados foram de 2...

Research on the specific viscosity of semi-concentrated fiber suspensions

Wan, Z.; Lin, J.; You, Z.; Ding, H.
Fonte: World Scientific Publ Co Pte Ltd Publicador: World Scientific Publ Co Pte Ltd
Tipo: Artigo de Revista Científica
Publicado em //2008 EN
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Zhanhong Wan, Jianzhong Lin, Zhenjiang You, Hai Ding

Emprego da flotação lamelar de alta taxa e convencional como pós-tratamento do efluente de sistema constituído de reator anaeróbio seguido de reator aeróbio tratando esgoto sanitário; Lamella design (high rate) and conventional flotation units applied to the post-treatment of the effluent from a system made up anaerobic reactor followed by aerobic reactor treating domestic sewage

Moretti, Renata Cristina
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 20/05/2005 PT
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O presente trabalho teve como objetivo o estudo da potencialidade de aplicação da flotação por ar dissolvido (FAD) lamelar (de alta taxa) e convencional como parte final de sistema de tratamento sequencial de esgoto sanitário, constituído de reatores anaeróbios de manta de lodo (UASB) seguidos de tanque de aeração. O trabalho, desenvolvido na Estação de Tratamento de Esgotos Jardim das Flores da cidade de Rio Claro, foi dividido em três etapas. Na primeira etapa, realizada com equipamento Flotateste, foram investigados os valores mais adequados de dosagens de polímero sintético catiônico, amido de araruta, cloreto férrico e associações entre cloreto férrico e polímero ou amido de araruta, de razão ar/sólidos (A/S), bem como de tempo e gradiente de mistura rápida e de floculação. Nessa etapa, os melhores desempenhos da FAD foram obtidos com o emprego de polímero catiônico, tanto isoladamente quanto associado ao cloreto férrico, sendo esta última condição imprescindível para maior remoção de fósforo. A flotação de liquor misto utilizando apenas o cloreto férrico como coagulante, apresentou desempenho extremamente insatisfatório, com a formação de flocos com características ruins de flotabilidade. Além disso...

Microcyst Germination in Myxococcus xanthus1

Ramsey, W. Scott; Dworkin, Martin
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1968 EN
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Germination of glycerol-prepared microcysts of Myxococcus xanthus was studied. The sequence of morphological events during germination resembled that of germinating fruiting body-microcysts. The turbidity drop of a culture of germinating microcysts could be described by McCormick's formula derived for germinating Bacillus spores. The rate of uptake of labeled glycine and acetate did not change during germination. Temperature, aeration, and pH optima for germination were the same as for vegetative cell growth. Germination was induced by protein hydrolysates and the individual amino acids glycine, alanine, valine, aspartic acid, and glutamic acid. A number of organic compounds, including sugars, alcohols, aldehydes, ketones, organic acids, and chelating agents, did not induce germination. The inorganic ions HPO42−, Mg++, Ca++, and NH4+ induced germination, although ionic strength was not a factor. Microcysts incubated in distilled water at concentrations greater than about 109 cells/ml germinated; supernatant fluid from such suspensions (germination factor) induced germination of less concentrated suspensions. The activity of germination factor was resistant to boiling, but was lost on charring and dialysis. Germination of microcysts and growth of vegetative cells was equally sensitive to a variety of metabolic inhibitors...

Dilatancy in the flow and fracture of stretched colloidal suspensions

Smith, M. I.; Besseling, R.; Cates, M. E.; Bertola, V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/01/2011
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Concentrated particulate suspensions, commonplace in the pharmaceutical, cosmetic and food industries, display intriguing rheology. In particular, the dramatic increase in viscosity with strain rate (shear thickening and jamming) which is often observed at high volume fractions, is of strong practical and fundamental importance. Yet manufacture of these products and their subsequent dispensing often involves flow geometries substantially different from that of simple shear flow experiments. Here we show that the elongation and breakage of a filament of a colloidal fluid under tensile loading is closely related to the jamming transition seen in its shear rheology. However, the modified flow geometry reveals important additional effects. Using a model system with nearly hard-core interactions, we provide evidence of surprisingly strong viscoelasticity in such a colloidal fluid under tension. With high speed photography we also directly observe dilatancy and granulation effects, which lead to fracture above a critical elongation rate.; Comment: 22pages, 4 figures

Effective shear and extensional viscosities of cocentrated disordered suspensions of rigid particles

Berlyand, Leonid; Panchenko, Alexander
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We study effective shear viscosity $\mu^\star$ and effective extensional viscosity $\lambda^\star$ of concentrated non-colloidal suspensions of rigid spherical particles. The focus is on the spatially disordered arrays. We use recently developed discrete network approximation techniques to obtain asymptotic formulas for the viscosities as the typical inter-particle distance $\delta$ tends to zero. For disordered arrays, the volume fraction alone does not determine the effective viscosity. Use of the network approximation allows us to study the dependence of the effective viscosities on variable distances between neighboring particles. Our analysis can be characterized as global because it goes beyond the local analysis of the flow between two particles. The principal conclusion in the paper is that, in general, asymptotic formulas obtained by global analysis are different from the formulas obtained from local analysis. In particular, the leading term in the asymptotics of $\mu^\star$ is of lower order than suggested by the local analysis (weak blow up), while the order of the leading term in the asymptotics of $\lambda^\star$ depends on the geometry of the particle array (either weak or strong blow up). We obtain geometric conditions on a random particle array that lead to the strong blow up of $\lambda^\star$...

Correlated particle dynamics in concentrated quasi-two-dimensional suspensions

Diamant, H.; Cui, B.; Lin, B.; Rice, S. A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We investigate theoretically and experimentally how the hydrodynamically correlated lateral motion of particles in a suspension confined between two surfaces is affected by the suspension concentration. Despite the long range of the correlations (decaying as 1/r^2 with the inter-particle distance r), the concentration effect is present only at short inter-particle distances for which the static pair correlation is nonuniform. This is in sharp contrast with the effect of hydrodynamic screening present in unconfined suspensions, where increasing the concentration changes the prefactor of the large-distance correlation.; Comment: 13 pages

S-Shaped Flow Curves of Shear Thickening Suspensions: Direct Observation of Frictional Rheology

Pan, Zhongcheng; de Cagny, Henri; Weber, Bart; Bonn, Daniel
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We study the rheological behavior of concentrated granular suspensions of simple spherical particles. Under controlled stress, the system exhibits an S-shaped flow curve (stress vs. shear rate) with a negative slope in between the low-viscosity Newtonian regime and the shear thickened regime. Under controlled shear rate, a discontinuous transition between the two states is observed. Stress visualization experiments with a novel fluorescent probe suggest that friction is at the origin of shear thickening. Stress visualization shows that the stress in the system remains homogeneous (no shear banding) if a stress is imposed that is intermediate between the high and low-stress branches. The S-shaped shear thickening is then due to the discontinuous formation of a frictional force network between particles upon increasing the stress.; Comment: 5 pages + 6 figures

Fluctuations and diffusion in sheared athermal suspensions of deformable particles

Gross, Markus; Krüger, Timm; Varnik, Fathollah
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We analyze fluctuations of particle displacements and stresses in a sheared athermal suspension of elastic capsules (red blood cells). Upon variation of the volume fraction from the dilute up to the highly concentrated regime, our numerical simulations reveal different characteristic power-law regimes of the fluctuation variances and relaxation times. In the jammed phase and at high shear rates, anomalous scaling exponents are found that deviate from pure dimensional predictions. The observed behavior is rationalized via kinetic arguments and a dissipation balance model that takes into account the local fluid flows between the particles. Our findings support the view that the rheology of dense suspensions is essentially governed by the non-affine displacements.; Comment: 6 pages, 6 figures

The Impact of non-DLVO Forces on the Onset of Shear Thickening of Concentrated Electrically Stabilized Suspensions

Kaldasch, Joachim; Senge, Bernhard; Laven, Jozua
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/07/2011
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This paper exposes an extension of an activation model previously published by the authors. When particles arranged along the compression axis of a sheared suspension, they may overcome the electrostatic repulsion and form force chains associated with shear thickening. A percolation based consideration, allows an estimation of the impact of the force chains on a flowing suspension. It suggests that, similar to mode-coupling models, the suspension becomes unstable before the critical stress evaluated from the activation model is reached. The theory is applicable only to discontinuous shear thickening, and the predictions are compared with results from two experimental studies on aqueous suspensions of inorganic oxides; in one of them hydration repulsion and in the other hydrophobic attraction can be expected. It is shown that the incorporation of non-DLVO forces greatly improve predictions of the shear thickening instability.

Rotational self-diffusion in suspensions of charged particles: simulations and revised Beenakker–Mazur and pairwise additivity methods

Makuch, Karol; Heinen, Marco; Abade, Gustavo Coelho; Nägele, Gerhard
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Article; PeerReviewed Formato: application/pdf; application/pdf
Publicado em 14/07/2015
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We present a comprehensive joint theory-simulation study of rotational self-diffusion in suspensions of charged particles whose interactions are modeled by the generic hard-sphere plus repulsive Yukawa (HSY) pair potential. Elaborate, high-precision simulation results for the short-time rotational self-diffusion coefficient, D^r, are discussed covering a broad range of fluid-phase state points in the HSY model phase diagram. The salient trends in the behavior of D^r as a function of reduced potential strength and range, and particle concentration, are systematically explored and physically explained. The simulation results are further used to assess the performance of two semi-analytic theoretical methods for calculating D^r. The first theoretical method is a revised version of the classical Beenakker–Mazur method (BM) adapted to rotational diffusion which includes a highly improved treatment of the salient many-particle hydrodynamic interactions. The second method is an easy-to-implement pairwise additivity (PA) method in which the hydrodynamic interactions are treated on a full two-body level with lubrication corrections included. The static pair correlation functions required as the only input to both theoretical methods are calculated using the accurate Rogers–Young integral equation scheme. While the revised BM method reproduces the general trends of the simulation results...

Self-diffusion in sheared suspensions by dynamic simulation

Foss, David R.; Brady, John F.
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 25/12/1999
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The behaviour of the long-time self-diffusion tensor in concentrated colloidal dispersions is studied using dynamic simulation. The simulations are of a suspension of monodisperse Brownian hard spheres in simple shear flow as a function of the Péclet number, Pe, which measures the relative importance of shear and Brownian forces, and the volume fraction, [phi]. Here, Pe = &[gamma]dot;a^2/D0, where &[gamma]dot; is the shear rate, a the particle size and D0 = kT/6[pi][eta]a is the Stokes–Einstein diffusivity of an isolated particle of size a with thermal energy kT in a solvent of viscosity [eta]. Two simulations algorithms are used: Stokesian Dynamics for inclusion of the many-body hydrodynamic interactions, and Brownian Dynamics for suspensions without hydrodynamic interactions. A new procedure for obtaining high-quality diffusion data based on averaging the results of many short simulations is presented and utilized. At low shear rates, low Pe, Brownian diffusion due to a random walk process dominates and the characteristic scale for diffusion is the Stokes–Einstein diffusivity, D0. At zero Pe the diffusivity is found to be a decreasing function of [phi]. As Pe is slowly increased, O(Pe) and O(Pe^3/2) corrections to the diffusivity due to the flow are clearly seen in the Brownian Dynamics system in agreement with the theoretical results of Morris & Brady (1996). At large shear rates...

Structure, diffusion and rheology of Brownian suspensions by Stokesian Dynamics simulation

Foss, David R.; Brady, John F.
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 25/03/2000
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The non-equilibrium behaviour of concentrated colloidal dispersions is studied using Stokesian Dynamics, a molecular-dynamics-like simulation technique for analysing suspensions of particles immersed in a Newtonian fluid. The simulations are of a monodisperse suspension of Brownian hard spheres in simple shear flow as a function of the Péclet number, Pe, which measures the relative importance of hydrodynamic and Brownian forces, over a range of volume fraction 0.316 [less-than-or-eq, slant] [phi] [less-than-or-eq, slant] 0.49. For Pe < 10, Brownian motion dominates the behaviour, the suspension remains well-dispersed, and the viscosity shear thins. The first normal stress difference is positive and the second negative. At higher Pe, hydrodynamics dominate resulting in an increase in the long-time self-diffusivity and the viscosity. The first normal stress difference changes sign when hydrodynamics dominate. Simulation results are shown to agree well with both theory and experiment.

High-Density Suspensions Formed Under Waves

Lamb, Michael P.; Parsons, Jeffrey D.
Fonte: Society for Sedimentary Geology Publicador: Society for Sedimentary Geology
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /05/2005
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We performed a series of laboratory experiments to investigate the interactions of a turbulent wave boundary layer with a predominantly silt-size sediment bed. Quasi-steady, turbulent, high-density suspensions (HDS) formed over a wide range of wave conditions and had near-bed (~1 mm above bed) concentrations ranging from 17 to 81 g/l scaling roughly with the wave orbital velocity. HDS were defined by the presence of a lutocline, an abrupt change in vertical concentration gradient. Despite the initial bed being 70% silt and 20% sand, HDS had significant near-bed sand fractions ranging from 27 to 78%. Winnowing of the bed caused more concentrated HDS to be coarser grained, which in turn caused the suspensions to be thinner because of the greater settling velocity of the sediment. Our experiments are consistent with a dynamic feedback model where suspended sediment is limited through sediment-induced stratification expressed with a bulk Richardson number. However, our computed values of the bulk Richardson number converge to a value that is an order of magnitude less than the critical value of 0.25 that is typically assumed. The experimental wave orbital velocities (15–60 cm/s) and periods (3–8 s), as well as the characteristics of the HDS and the bed in our experiments...