Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Hydrodynamics”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 685 records · Page 38Linked to original sources
PubMed2005

On hydrodynamics of drag and lift of the human arm.

The work presents results on drag and lift measurement conducted in a low speed wind tunnel on a replica of the entire human arm. The selected model positions were identical to those during purely rotational front crawl stroke in quasi-static conditions. A computational fluid dynamics model using Fluent showed close correspondence with the experimental results and confirmed the suitability of low speed wind tunnel for the drag and lift measurement in quasi-static conditions. The obtained profiles of the hydrodynamic forces were similar to the dynamic data presented in an earlier study suggesting that shape drag is a major contributing factor in propulsive force generation. The aim of this study was to underline the importance of the entire arm analysis, the elbow angle and a newly defined angle of attack representing the angle of shoulder rotation. It was found that both the maximum value of the drag force at 160 degrees elbow flexion angle and the momentum generated by it exceed the respective magnitudes for the fully extended arm. The latter is underlined by a prolonged plateau of near maximum drag that was obtained at shoulder angle range of 50-140 degrees suggesting that optimal arm configuration in terms of propulsive force generation requires elbow flexion. Furthermore it was found that drag trend is not consistent with the widely assumed and used sinus wave profile. A gap in the existing experimental research was filled as for the first time the entire arm lift and drag was measured across the entire stroke range.

Air Movements↗
PubMed2006

Hydrodynamic thickness of petroleum oil adsorbed layers in the pores of reservoir rocks.

The hydrodynamic thickness delta of adsorbed petroleum (crude) oil layers into the pores of sandstone rocks, through which the liquid flows, has been studied by Poiseuille's flow law and the evolution of (electrical) streaming current. The adsorption of petroleum oil is accompanied by a numerical reduction in the (negative) surface potential of the pore walls, eventually stabilizing at a small positive potential, attributed to the oil macromolecules themselves. After increasing to around 30% of the pore radius, the adsorbed layer thickness delta stopped growing either with time or with concentrations of asphaltene in the flowing liquid. The adsorption thickness is confirmed with the blockage value of the rock pores' area determined by the combination of streaming current and streaming potential measurements. This behavior is attributed to the effect on the disjoining pressure across the adsorbed layer, as described by Derjaguin and Churaev, of which the polymolecular adsorption films lose their stability long before their thickness has approached the radius of the rock pore.

Journal Article↗
PubMed2006

3D simulations of hydrodynamic drag forces on two porous spheres moving along their centerline.

This paper numerically evaluates the hydrodynamic drag force exerted on two highly porous spheres moving steadily along their centerline through a quiescent Newtonian fluid over a Reynolds number ranging from 0.1 to 40. At creeping-flow limit, the drag forces exerted on both spheres were approximately identical. At higher Reynolds numbers the drag force on the leading sphere (sphere #1) was higher than the following sphere (sphere #2), revealing the shading effects produced by sphere #1 on sphere #2. At dimensionless diameter beta<2 (beta=d(f)/2k(0.5), d(f) and k are sphere diameter and interior permeability, respectively), the spheres can be regarded as "no-spheres" limit. At increasing beta for both spheres, the drag force on sphere #2 was increased because of the more difficult advective flow through its interior, and at the same time the drag was reduced owing to the stronger wake flow produced by the denser sphere #1. The competition between these two effects leads to complicated dependence of drag force on sphere #2 on beta value. These effects were minimal when beta became low.

Journal Article↗
PubMed2004

Using radiotracer techniques for coastal hydrodynamic model evaluation.

A three-dimensional (3D) water circulation and contaminant transport model of Manila Bay has been developed with the aim of better understanding the formation and movement of harmful algal blooms. Radiotracer techniques were used to evaluate the model by recording the dispersion of a tracer at depths of 2 and 15 m near the injection point. The selected tracer was 99mTc eluted from a molybdenum/technetium medical generator. The rationale for the choice of the tracer and the location of the injection is discussed. At 2 m the transport was dominated by the prevailing winds, and at 15 m by tidally induced currents. The development of the hydrodynamic model and its experimental evaluation were iterative processes. The experimental study confirmed the need for full 3D modelling of Manila Bay; quantified the impact of the prevailing wind field on contaminant dispersion near the injection point; and allowed the calculation of transverse dispersivity to guide the selection of parameter values used in the overall model.

Eutrophication↗
PubMed2006

Hydrodynamic plasmid DNA gene therapy model in liver transplantation.

BACKGROUND: There is great interest in the field of transplantation to genetically modify grafts to decrease preservation injury or allograft rejection. Although adenoviral gene transfer has been effective in experimental liver transplantation, viral toxicity and safety concerns limit potential use in clinical trials. Therefore, the purpose of this study was to develop a model of nonviral gene transfer in the liver transplant setting, allowing for efficient transgene expression. MATERIALS AND METHODS: Orthotopic syngeneic rat liver transplantation was performed with 3 h cold ischemia using University of Wisconsin (UW) preservation. A hydrodynamic gene transfer technique was developed where plasmid DNA was delivered to the liver graft by ex vivo rapid infusion of DNA in UW via the IVC with other vessels clamped. Expression plasmids for the marker genes luciferase and secreted human alpha1-antitrypsin (alpha1-AT) were used. Hepatic injury was assessed by graft histology and liver transaminases. Transgene expression was determined by hepatic luciferase relative light units activity (RLU) and serum alpha1-AT protein levels. Variables examined included the effect of (a) volume injected on the intravenous pressure in the liver graft; (b) injury to the liver, as measured by hepatic enzymes and histopathology; (c) variable expression between lobes; (d) volume of UW that the plasmid is administered in; (e) amount of DNA plasmid; (f) type of the promoter used; (g) clamp time; as well as (h) the time course of the marker gene expression. RESULTS: Control rats underwent standard orthotopic syngeneic rat liver transplantation and had no detectable hepatic luciferase activity or serum human alpha1-AT. The optimal DNA plasmid dose was found to be 400 mug/liver graft, as there was no increase in the luciferase expression by increasing the dose. Furthermore, cytomegalovirus promoter yielded greater expression than Rous sarcoma virus. A high injection pressure gradient allowed for more efficient transgene expression, but produced greater liver injury shown by elevated transaminases and centrilobular necrosis. Lowering injection volume from 75 to 50% of graft weight decreased liver injury by 4.5-fold. Although higher UW injection volumes were associated with increased expression, volumes of only 50% led to luciferase expression up to 10,000,000 RLU/mg; this expression was homogeneous between the different liver lobes. Human alpha1-AT was detected in recipient blood as early as 6 h, peaked at 24 h, and remained high for 5 days. CONCLUSIONS: We have developed a nonviral gene transfer technique where hydrostatic pressure across the cold-preserved liver vascular bed allows for efficient plasmid DNA delivery. This simple strategy should prove useful to genetically modify liver grafts in the transplantation setting.

Analysis of Variance↗
PubMed2004

Hydrodynamics of burst swimming fish larvae; a conceptual model approach.

Burst swimming of fish larvae is analysed from a hydrodynamic point of view. A picture of the expected flow pattern is presented based on information in literature on unsteady-flow patterns around obstacles in the intermediate Reynolds number region. It is shown that the acceleration stage of burst swimming under restricted conditions can be treated as a frictionless impulsive motion. The stream pattern resulting from this motion is presented and the efficiency of locomotion during the acceleration stage is calculated. The flow pattern in the post-acceleration stage is sketched and the origin of an interaction between the viscous and the reactive force contribution to the propulsive force in this stage is discussed. It is explained how this interaction can lead to an increase in propulsive efficiency. A conceptual model is developed describing the three stages in burst swimming locomotion: the acceleration stage, the post-acceleration stage and the gliding stage. Data from literature of the travel distance versus time relation of the common carp larva (Cyprinus carpio) of 5.5-mm length has been used to test the model results. The test appeared remarkably successful, and the model results for larger larvae up to 22 mm length are presented. The gliding distance as a function of larval length resulting from the model has been compared with experimental data from literature.

Animals↗
PubMed2005

Theoretical study on the body form and swimming pattern of Anomalocaris based on hydrodynamic simulation.

Anomalocarid arthropod is the largest known predatory animal of middle Cambrian. Studies on Anomalocaris have been piled up in the past two decades since the first reasonable reconstruction had achieved in 1980s. Recent finding of legs beneath lobes on Parapeytoia Yunnanensis shows arthropod affinities, however, many researchers believe that it must be a powerful swimmer by the use of developed lobes. In this work, we investigate swimming behaviour of Anomalocaris in water by performing hydrodynamical calculation. As a result of simulation using moving particle method possible swimming motion of Anomalocaris is obtained. In the computer we can change the morphology from known bauplan of Anomalocaris found as fossil record. It makes us possible to discuss on the variants of Anomalocaris at the intermediate state of evolution process. Such new methodology using computer reveals how and from where Anomalocaris evolved.

Animals↗
PubMed2006

Constructal pattern formation in stony corals, bacterial colonies and plant roots under different hydrodynamics conditions.

This paper explores a new application of the constructal theory, namely in describing and predicting the formation of dissimilar patterns inside elements of the same species under different hydrodynamics conditions. Our study proposes an explanation for the differences found in morphology of stony corals, bacterial colonies and plant roots. It specially provides an answer to the following question: have their shapes (architecture) been developed by chance, or do they represent the optimum structure serving their ultimate purpose? We show that in order to persist in time, these systems must evolve in such a way that an easy access to nutrients is ensured: their shapes develop in such a way as to minimize the time to reach the nutrient source. Moreover, it is also shown that it is the combination of a dispersive (diffusive) and a convective mechanism that allows for the maximization of nutrient transfer through use of the best of these mechanisms at a specific time. In the light of this outcome, it is straightforward to conclude why the existence of an optimal architecture makes sense: it is because there is an overriding natural tendency and because the system has the freedom to morph its shape in the search for an optimal attainment of this goal within a set of constraints imposed by the situation.

Animals↗
PubMed2004

Three-dimensional hydrodynamic-eutrophication model (HEM-3D): application to Kwang-Yang Bay, Korea.

The purpose of this paper is twofold: to describe the water quality model of Three-Dimensional Hydrodynamic-Eutrophication Model (HEM-3D) and to present an application of HEM-3D to a coastal system in Korea. HEM-3D, listed as a tool for the development of Total Maximum Daily Load by US Environmental Protection Agency, is a general-purpose modeling package for simulation of the flow field, transport, and eutrophication processes throughout the water column and of diagenetic processes in the benthic sediment. This paper describes the water quality model of HEM-3D with emphasis on its unique features. Excessive loadings of organic wastes have significantly deteriorated water quality conditions of Korean coastal waters. This paper presents an application of HEM-3D to Kwang-Yang Bay, a coastal system in Korea, which is one of the first water quality modeling efforts for Korean coastal waters accompanied by a relatively comprehensive field program. The current status of data availability for water quality modeling in Korea is discussed.

Environmental Monitoring↗
PubMed2004

Numerical simulation of organic chemicals in a marine environment using a coupled 3D hydrodynamic and ecotoxicological model.

For ecotoxicological risk assessment in a marine ecosystem, we constructed a coupled three-dimensional hydrodynamic and ecotoxicological model (EMT-3D), and applied it to Tokyo Bay. The model was calibrated with field data obtained in 2002. The results of sensitivity analysis for dissolved Bisphenol A showed that biodegradation rate was the most important factor for concentration change. Bioconcentration coefficient was the most important factor for Bisphenol A in phytoplankton. Therefore, the parameters must be carefully considered in the modeling. The mass balance results showed that standing stocks of Bisphenol A in water, in particulate organic carbon and in phytoplankton are 7.85 x 10(4), 1.78 x 10(2) and 3.44 x 10(-1) g, respectively. With respect to flux, biodegradation in the water column had the highest value of 1.06 x 10(3) g/day, and next were effluent to the open sea, partition to particulate organic carbon, and bioconcentration in phytoplankton.

Benzhydryl Compounds↗
PubMed2006

A 3D hydrodynamic fate and transport model for herbicides in Sacca di Goro coastal lagoon (Northern Adriatic).

Sacca di Goro is a shallow coastal microtidal lagoon with a surface area of 26 km2, and an average depth of about 1.5m. Fresh water pollutant loads from Po River branches and several drainage canals lead to anthropogenic eutrophication, frequent summer anoxia crises and chemical contamination. Such events not only affect the lagoon ecosystem but also cause serious economic losses, the lagoon being the second largest producer of clams in Italy. The present work aims at using a fate model coupled with COHERENS 3D hydrodynamic model to simulate and to explain the spatial distribution and temporal variations of s-triazines herbicides in the Sacca di Goro lagoon. The simulation results of spatial and temporal dynamic behaviour of atrazine, simazine and terbuthylazine have been compared with experimental data obtained during an annual monitoring programme.

Animals↗
PubMed2006

Review of solutions for 3D hydrodynamic modeling applied to aquaculture in South Pacific atoll lagoons.

A workshop organized in French Polynesia in November 2004 allowed reviewing the current methods to model the three-dimensional hydrodynamic circulation in semi-enclosed atoll lagoons for aquaculture applications. Mollusk (e.g. pearl oyster, clam) aquaculture is a major source of income for South Pacific countries such as French Polynesia or Cook Islands. This aquaculture now requires a better understanding of circulation patterns to improve the spatial use of the lagoons, especially to define the best area to set larvae collectors. The pelagic larval duration of the relevant species (<20 days) and the size of the semi-closed lagoons (few hundreds of km2) drive the specifications of the model in terms of the spatial and temporal scale. It is considered that, in contrast with fish, mollusk larvae movements are limited and that their cycle occurs completely in the lagoon, without an oceanic stage. Atolls where aquaculture is productive are generally well-bounded, or semi-closed, without significant large and deep openings to the ocean. Nevertheless part of the lagoon circulation is driven by oceanic water inputs through the rim, ocean swells, tides and winds. Therefore, boundary conditions of the lagoon system are defined by the spatial structure of a very shallow rim (exposition and number of hoas), the deep ocean swell climate, tides and wind regimes. To obtain a realistic 3D numerical model of lagoon circulation with adequate forcing, it is thus necessary to connect in an interdisciplinary way a variety of methods (models, remote sensing and in situ data collection) to accurately represent the different components of the lagoon system and its specific boundary conditions. We review here the current methods and tools used to address these different components for a hypothetical atoll of the Tuamotu Archipelago (French Polynesia), representative of the semi-closed lagoons of the South Pacific Ocean. We hope this paper will serve as a guide for similar studies elsewhere and we provide guidelines in terms of costs for all the different stages involved.

Animals↗
PubMedDate not supplied

Hydrodynamics of the spinal epidural space in pigs determined by constant-flow methods.

BACKGROUND AND OBJECTIVES: Impressive quantities of fluid can be infused into the epidural space of the spine without causing dramatic or sustained increases in pressure. The epidural space is considered "leaky," but questions remain about how fluid leaves the epidural space. We used constant-flow infusions of saline to gain insight into the hydrodynamics involved. METHODS: We infused saline at a constant rate into the lumbar epidural space of 6 anesthetized pigs while measuring pressure at the adjacent interspace. Three or 4 infusions were performed at different flow rates in each animal. RESULTS: Epidural space pressure in the absence of flow was consistently 2 to 3 mm Hg above right atrial pressure. During each infusion, pressure increased slowly to a steady plateau value between 15 and 70 mm Hg. When flow was stopped, pressure declined exponentially to the starting pressure. The presence of a plateau indicates that fluid leaving the epidural space ends up in a structure with high capacitance. Plateau pressures were linearly related to flow rate in each animal, indicating constant resistance to outflow. The flow-pressure relation showed neither a critical opening pressure nor moderating pressures with increased flow. CONCLUSIONS: Fluid leaves the porcine spinal epidural space through channels that are open at baseline rather than being recruited as epidural pressure increases. This behavior is inconsistent with the view that the epidural space behaves like a Starling resistor.

Animals↗
PubMed2005

Vibrational dephasing and hydrodynamic effects on vibrational relaxation rates in acetophenone: Raman bandshape analysis.

The isotropic component of Raman band for C=O stretching mode of acetophenone in solution was analyzed by estimating the correlation coefficient with reference to Lorentzian lineshape. In the intermediate region of solute/solvent concentration there is a sharp decrease in the correlation coefficient and there appears to be a transition from non-Lorentzian to Lorentzian lineshape. The vibrational relaxation rates have been estimated from the isotropic component of Raman band in different solvents. The rate is shown to be dependent on several macroscopic as well as microscopic properties of the solute-solvent system and intermolecular interactions. The hydrodynamic and dispersion forces appear to play a major role in determining the vibrational relaxation rate and the broadening of the bands.

Acetophenones↗
PubMed2006

Vibrational relaxation studies in methyl acetate: role of microenvironment and hydrodynamic forces.

The Raman spectra were recorded for the C=O stretching vibration of methyl acetate as solutions in various polar and non-polar solvents. The isotropic component was obtained and the vibrational relaxation rates were calculated. On the basis of dependence of isotropic Raman bandwidth on the hydrodynamic properties of the solute-solvent systems, the information was obtained on the microenvironment prevailing in the neighborhood of the C=O stretching mode. Significant correlation is observed between vibrational relaxation rate and solvent parameters namely viscosity, density, refractive index and molecular radius. Microviscosity, involving the size of solute and solvent molecules, is found to be crucial in determining the bandwidth, hence the relaxation rate. The microenvironment appears to play an important role in the vibrational relaxation process.

Acetates↗
PubMed2006

Preparation of biodiesel with the help of ultrasonic and hydrodynamic cavitation.

An alkali-catalyzed biodiesel production method with power ultrasonic (19.7 kHz) has been developed that allows a short reaction time and high yield because of emulsification and cavitation of the liquid-liquid immiscible system. Orthogonality experiments were employed to evaluate the effects of synthesis parameters. Furthermore, hydrodynamic cavitation was used for biodiesel production in comparison to ultrasonic method. Both methods were proved to be efficient, and time and energy saving for the preparation of biodiesel by transesterification of soybean oil.

Journal Article↗
PubMed2005

Increased hepatic transduction with reduced systemic dissemination and proinflammatory cytokines following hydrodynamic injection of helper-dependent adenoviral vectors.

Hydrodynamic injection of helper-dependent adenoviral vectors (HDAd) in mice results in increased hepatic transduction, reduced splenic and pulmonary transduction, and reduced levels of the proinflammatory cytokines IL-6 and IL-12 compared to conventional injection. These results indicate that hepatic transduction by HDAd, at least alone, does not necessarily provoke a severe innate inflammatory response. Instead, they suggest that systemic vector dissemination may play a major role in the severity of the innate inflammatory response. These results further suggest that the safety and efficacy of HDAd-mediated, liver-directed gene therapy may be improved if the vector could be preferentially, if not exclusively, targeted to liver.

Adenoviridae↗
PubMed2003

Near-wall micro-PIV reveals a hydrodynamically relevant endothelial surface layer in venules in vivo.

High-resolution near-wall fluorescent microparticle image velocimetry (micro-PIV) was used in mouse cremaster muscle venules in vivo to measure velocity profiles in the red cell-depleted plasma layer near the endothelial lining. micro-PIV data of the instantaneous translational speeds and radial positions of fluorescently labeled microspheres (0.47 microm) in an optical section through the midsagittal plane of each vessel were used to determine fluid particle translational speeds. Regression of a linear velocity distribution based on near-wall fluid-particle speeds consistently revealed a negative intercept when extrapolated to the vessel wall. Based on a detailed three-dimensional analysis of the local fluid dynamics, we estimate a mean effective thickness of approximately 0.33 micro m for an impermeable endothelial surface layer or approximately 0.44 micro m assuming the lowest hydraulic resistivity of the layer that is consistent with the observed particle motions. The extent of plasma flow retardation through the layer required to be consistent with our micro-PIV data results in near complete attenuation of fluid shear stress on the endothelial-cell surface. These findings confirm the presence of a hydrodynamically effective endothelial surface layer, and emphasize the need to revise previous concepts of leukocyte adhesion, stress transmission to vascular endothelium, permeability, and mechanotransduction mechanisms.

Animals↗