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1
Sobey, Rodney J., e Maarten W. Dingemans. "Rapidly Varied Flow Analysis of Undular Bore". Journal of Waterway, Port, Coastal, and Ocean Engineering 118, n. 4 (luglio 1992): 417–36. http://dx.doi.org/10.1061/(asce)0733-950x(1992)118:4(417).
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KIJIMA, Takuya, Katsuyuki NISHIDA e Nobuo SHUTO. "Numerical Computaion of a Rapidly Varied Flow with Free Surface". PROCEEDINGS OF HYDRAULIC ENGINEERING 34 (1990): 577–82. http://dx.doi.org/10.2208/prohe.34.577.
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Yang, Jinn-Chuang, Kun-Nan Chen e Hong-Yuan Lee. "An accurate computation for rapidly varied flow in an open channel". International Journal for Numerical Methods in Fluids 14, n. 3 (15 febbraio 1992): 361–74. http://dx.doi.org/10.1002/fld.1650140308.
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JHA, Akhilesh Kumar, Juichiro AKIYAMA e Masaru URA. "HIGHER ORDER FDS SCHEME FOR RAPIDLY VARIED 2-D FLOW SIMULATIONS". PROCEEDINGS OF HYDRAULIC ENGINEERING 43 (1999): 503–8. http://dx.doi.org/10.2208/prohe.43.503.
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Machalinska-Murawska, Justyna, e Michał Szydłowski. "Lax-Wendroff and McCormack Schemes for Numerical Simulation of Unsteady Gradually and Rapidly Varied Open Channel Flow". Archives of Hydro-Engineering and Environmental Mechanics 60, n. 1-4 (1 ottobre 2014): 51–62. http://dx.doi.org/10.2478/heem-2013-0008.
Testo completoAbstract (sommario):
Abstract Two explicit schemes of the finite difference method are presented and analyzed in the paper. The applicability of the Lax-Wendroff and McCormack schemes for modeling unsteady rapidly and gradually varied open channel flow is investigated. For simulation of the transcritical flow the original and improved McCormack scheme is used. The schemes are used for numerical solution of one dimensional Saint-Venant equations describing free surface water flow. Two numerical simulations of flow with different hydraulic characteristics were performed - the first one for the extreme flow of the dam-break type and the second one for the simplified flood wave propagation problem. The computational results are compared to each other and to arbitrary solutions.
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Kula, Anna, Ludwik Blaz e Patrycja Lobry. "Structure and Properties Studies of Rapidly Solidified Al-Mn Alloys". Key Engineering Materials 682 (febbraio 2016): 199–204. http://dx.doi.org/10.4028/www.scientific.net/kem.682.199.
Testo completoAbstract (sommario):
Rapid solidification (RS) combined with plastic consolidation by hot extrusion was used to produce Al alloys with additions of varied concentration of Mn. RS flakes were manufactured using an inert gas atomizing of the molten alloy and the spray deposition on the water-cooled cooper roll. Rods of 7mm in diameter were received using cold pressing of RS-flakes, vacuum degassing and hot extrusion procedures. Mechanical properties of as extruded materials were tested in hot compression at temperature range 293K - 773K. It was found that the flow stress was reduced monotonically with deformation temperature for all tested materials. RS alloys exhibit higher mechanical properties than those produced by conventional metallurgy methods. Higher mechanical properties of RS materials are ascribed to beneficial particles morphology obtained due to the rapid solidification. Development of fine Al6Mn particles was observed in all tested RS-materials.
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Vasquez, Jose A., Robert G. Millar e Peter M. Steffler. "Two-dimensional finite element river morphology model". Canadian Journal of Civil Engineering 34, n. 6 (1 giugno 2007): 752–60. http://dx.doi.org/10.1139/l06-170.
Testo completoAbstract (sommario):
We report the development and application of a river morphology model based on the two-dimensional depth-averaged hydrodynamic model River2D. This new movable bed version of River2D was applied to simulate the bed elevation changes in four experiments: bed aggradation due to sediment overload, bed degradation by sediment supply shut-off, knickpoint migration, and bar formation in a variable-width channel. Some conditions in these experiments involved quick changes in the upstream boundary conditions, rapidly varied flow, supercritical flow, hydraulic jumps, and secondary flows. The results of the model agreed well with measured data. Notable features of the model are the use of a flexible unstructured mesh based on triangular finite elements to provide higher spatial resolution in areas of interest and transcritical flow capabilities to simulate supercritical flow and hydraulic jumps over movable beds. Key words: numerical modeling, rivers, scour, sedimentation, two-dimensional, finite elements.
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Leat, P. T. "Facies variations in peralkaline ash-flow tuffs from the Kenya Rift Valley". Geological Magazine 122, n. 2 (marzo 1985): 139–50. http://dx.doi.org/10.1017/s0016756800031046.
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AbstractTwo late Quaternary ash-flow tuffs erupted as single flow units from the Menengai caldera volcano, Kenya, show marked facies variations. Dense welding of the tuffs close to source may have been promoted by their peralkaline trachyte compositions. Coarse, near-vent breccias are partly welded and were emplaced as lithic-rich parts of the body of pyroclastic flows. Non-welded tuff forms the bulk of the outflow sheets which include valley-fill deposits up to 520 m above the present caldera rim, indicating ash-flow generation by collapse of moderately high eruption columns. The flows overran varied topography which controlled development of ash-flow tuff facies. On hilly terrain, the flows became turbulent and separated into a lithic-rich, rapidly deposited part and a fine-grained lithic-and crystal-poor part which was subsequently deposited farther from source. Caldera walls belonging to an earlier caldera probably formed a major barrier to the spread of the second ash-flow from its site of collapse. There are many similarities in the facies variations in these peralkaline tuffs and subalkaline tuffs. Differences in welding characteristics and the shape of ash particles reflect the lower viscosity of peralkaline magma.
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Zerihun, Yebegaeshet T. "Modelling free surface flow with curvilinear streamlines by a non-hydrostatic model". Journal of Hydrology and Hydromechanics 64, n. 3 (1 settembre 2016): 281–88. http://dx.doi.org/10.1515/johh-2016-0028.
Testo completoAbstract (sommario):
Abstract This study addresses a particular phenomenon in open channel flows for which the basic assumption of hydrostatic pressure distribution is essentially invalid, and expands previous suggestions to flows where streamline curvature is significant. The proposed model incorporates the effects of the vertical curvature of the streamline and steep slope, in making the pressure distribution non-hydrostatic, and overcomes the accuracy problem of the Saint-Venant equations when simulating curvilinear free surface flow problems. Furthermore, the model is demonstrated to be a higher-order one-dimensional model that includes terms accounting for wave-like variations of the free surface on a constant slope channel. Test results of predicted flow surface and pressure profiles for flow in a channel transition from mild to steep slopes, transcritical flow over a short-crested weir and flow with dual free surfaces are compared with experimental data and previous numerical results. A good agreement is attained between the experimental and computed results. The overall simulation results reveal the satisfactory performance of the proposed model in simulating rapidly varied gravity-driven flows with predominant non-hydrostatic pressure distribution effects. This study suggests that a higher-order pressure equation should be used for modelling the pressure distribution of a curvilinear flow in a steeply sloping channel.
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Luo, Xue, Yu-meng Shen, Meng-nan Jiang, Xiang-feng Lou e Yin Shen. "Ocular Blood Flow Autoregulation Mechanisms and Methods". Journal of Ophthalmology 2015 (2015): 1–7. http://dx.doi.org/10.1155/2015/864871.
Testo completoAbstract (sommario):
The main function of ocular blood flow is to supply sufficient oxygen and nutrients to the eye. Local blood vessels resistance regulates overall blood distribution to the eye and can vary rapidly over time depending on ocular need. Under normal conditions, the relation between blood flow and perfusion pressure in the eye is autoregulated. Basically, autoregulation is a capacity to maintain a relatively constant level of blood flow in the presence of changes in ocular perfusion pressure and varied metabolic demand. In addition, ocular blood flow dysregulation has been demonstrated as an independent risk factor to many ocular diseases. For instance, ocular perfusion pressure plays key role in the progression of retinopathy such as glaucoma and diabetic retinopathy. In this review, different direct and indirect techniques to measure ocular blood flow and the effect of myogenic and neurogenic mechanisms on ocular blood flow are discussed. Moreover, ocular blood flow regulation in ocular disease will be described.
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Enders, Eva C., Michael H. Gessel e John G. Williams. "Development of successful fish passage structures for downstream migrants requires knowledge of their behavioural response to accelerating flow". Canadian Journal of Fisheries and Aquatic Sciences 66, n. 12 (dicembre 2009): 2109–17. http://dx.doi.org/10.1139/f09-141.
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Fish have evolved intrinsic flight responses, allowing pre-emptive avoidance of potentially threatening situations. To direct downstream migrant fish away from deleterious conditions at dams and other barriers, mechanical devices such as travelling screens and fish bypass systems are often installed. However, field observations suggest that if these structures create areas of rapidly accelerating flow, they do not effectively guide the fish. We studied the avoidance behaviour of actively migrating fall Chinook salmon ( Oncorhynchus tshawytscha ) smolts in controlled experiments of low-, medium-, and high-flow accelerations. We measured the response velocity (VR) and the velocity gradient (VG) over body length. Although VR varied significantly with flow conditions and increased with increasing water temperature, the median VG at the instant at which smolts displayed an avoidance response was similar over the range of accelerating flows tested. Results from this study present the first quantitative information about the avoidance behaviour of fish to flow acceleration and should provide data needed to help engineers and biologists develop effective systems to alleviate anthropogenically altered flow regimes. Furthermore, the devised experimental setup provides a valuable means to test the effects of accelerating flow on any downstream migrant fish species.
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He, S., C. Ariyaratne e A. E. Vardy. "Wall shear stress in accelerating turbulent pipe flow". Journal of Fluid Mechanics 685 (21 settembre 2011): 440–60. http://dx.doi.org/10.1017/jfm.2011.328.
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AbstractAn experimental study of wall shear stress in an accelerating flow of water in a pipe ramping between two steady turbulent flows has been undertaken in a large-scale experimental facility. Ensemble averaged mean and r.m.s. of the turbulent fluctuations of wall shear stresses have been derived from hot-film measurements from many repeated runs. The initial Reynolds number and the acceleration rate were varied systematically to give values of a non-dimensional acceleration parameter $k$ ranging from 0.16 to 14. The wall shear stress has been shown to follow a three-stage development. Stage 1 is associated with a period of minimal turbulence response; the measured turbulent wall shear stress remains largely unchanged except for a very slow increase which is readily associated with the stretching of existing turbulent eddies as a result of flow acceleration. In this condition of nearly ‘frozen’ turbulence, the unsteady wall shear stress is driven primarily by flow inertia, initially increasing rapidly and overshooting the pseudo-steady value, but then increasing more slowly and eventually falling below the pseudo-steady value. This variation is predicted by an analytical expression derived from a laminar flow formulation. The start of Stage 2 is marked by the generation of new turbulence causing both the mean and turbulent wall shear stress to increase rapidly, although there is a clear offset between the responses of these two quantities. The turbulent wall shear, reflecting local turbulent activities near the wall, responds first and the mean wall shear, reflecting conditions across the entire flow field, responds somewhat later. In Stage 3, the wall shear stress exhibits a quasi-steady variation. The duration of the initial period of nearly frozen turbulence response close to the wall increases with decreasing initial Reynolds number and with increasing acceleration. The latter is in contrast to the response of turbulence in the core of the flow, which previous measurements have shown to be independent of the rate of acceleration.
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MITTAL, SANJAY, e BHASKAR KUMAR. "Flow past a rotating cylinder". Journal of Fluid Mechanics 476 (10 febbraio 2003): 303–34. http://dx.doi.org/10.1017/s0022112002002938.
Testo completoAbstract (sommario):
Flow past a spinning circular cylinder placed in a uniform stream is investigated via two-dimensional computations. A stabilized finite element method is utilized to solve the incompressible Navier–Stokes equations in the primitive variables formulation. The Reynolds number based on the cylinder diameter and free-stream speed of the flow is 200. The non-dimensional rotation rate, α (ratio of the surface speed and freestream speed), is varied between 0 and 5. The time integration of the flow equations is carried out for very large dimensionless time. Vortex shedding is observed for α < 1.91. For higher rotation rates the flow achieves a steady state except for 4.34 < α < 4:70 where the flow is unstable again. In the second region of instability, only one-sided vortex shedding takes place. To ascertain the instability of flow as a function of α a stabilized finite element formulation is proposed to carry out a global, non-parallel stability analysis of the two-dimensional steady-state flow for small disturbances. The formulation and its implementation are validated by predicting the Hopf bifurcation for flow past a non-rotating cylinder. The results from the stability analysis for the rotating cylinder are in very good agreement with those from direct numerical simulations. For large rotation rates, very large lift coefficients can be obtained via the Magnus effect. However, the power requirement for rotating the cylinder increases rapidly with rotation rate.
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Freeman, T. C. A., T. S. Meese e M. G. Harris. "Discrimination of Optic Flow Components: Access to the Third Dimension?" Perception 25, n. 1_suppl (agosto 1996): 50. http://dx.doi.org/10.1068/v96l0909.
Testo completoAbstract (sommario):
A growing body of evidence suggests that optic flow is processed by specialised 2-D motion mechanisms. We asked whether the visual system has parallel, or rapid serial, access to representations of optic flow components in a spatial 4AFC task. Random-dot kinematograms (144 dots per interval) depicting expansion, rotation, deformation (horizontal shear+vertical shear) or one of these components summed with translation, were presented in four spatially abutting circular windows (2.65 deg in diameter), and were temporally modulated by half a cycle of a 300 ms cosine-wave. Within a session, stimuli were of the same type, but the target had opposite sign and was selected with a mouse and cursor with feedback. Systematic local cues were removed by randomising (i) the orientation of the windowing configuration, and (ii) the dot speeds between intervals (speed gradient varied between 2.4% and 6%; translation varied between 16 and 40 min arc s−1). Preliminary results (average SE=3.4%) showed that in the absence of translation, performance was close to chance (25% correct) for rotation (23% correct) and deformation (27% correct), but was good for expansion (61% correct). The addition of translation had no effect on rotation but improved deformation (58% correct) and impaired expansion (22% correct). In experiment 2, unlimited stimulus repetitions were allowed and performance improved (>93%) for all conditions, though, as predicted from experiment 1, reaction times were fastest for expansion and deformation-plus-translation. Importantly, only these two conditions produced unambiguous 3-D perceptions of the stimuli, suggesting that surface slant and motion in depth are coded by mechanisms more rapidly accessible than those subserving general extraction of 2-D motion.
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Emerson, Benjamin, e Tim Lieuwen. "Dynamics of harmonically excited, reacting bluff body wakes near the global hydrodynamic stability boundary". Journal of Fluid Mechanics 779 (21 agosto 2015): 716–50. http://dx.doi.org/10.1017/jfm.2015.450.
Testo completoAbstract (sommario):
This paper describes linear and nonlinear interactions between forced axial acoustic oscillations and the global mode of the reacting wake. This work is motivated by the problem of combustion instabilities, where acoustic oscillations associated with natural combustor modes excite hydrodynamic instabilities of the flow that, in turn, induce heat release oscillations. Wake flows with density stratification can be globally stable or unstable at high Reynolds numbers, and so the density change across the flame has significant influence on the natural flame and flow dynamics. Measurements were obtained in a facility in which flame density ratio, lip velocity and forcing frequency are independently varied using 5 kHz particle image velocimetry and Mie scattering measurements. By varying the density ratio, the hydrodynamic global mode growth rate can be systematically varied. In addition, measurements and analyses were performed where the forcing frequency is varied relative to the global mode frequency. While axial forcing excites a varicose response of the shear layers, the sinuous mode is the most rapidly growing. As expected, forcing at a frequency near the wake’s global mode frequency leads to rapid growth in vortical disturbance amplitude, and the symmetric vortices quickly stagger as they convect downstream leading to a large scale, sinuous flapping of the wake and flame. A linear, local stability analysis, together with a nonlinear analysis, help elucidate the physics that govern the vortex staggering. The study concludes with an analysis of the heat release dynamics. Significantly, the study shows that the heat release exhibits quite different sensitivities than the fluid dynamics; e.g. axial forcing of the flow near its global mode frequency leads to a reduction in heat release oscillations. This is true even though this forcing frequency maximizes the local degree of vortically induced flame flapping. Thus, the results of this study show some phenomena that contradict conventional notions, namely that conditions which align the frequency of a hydrodynamic global mode with that of an acoustic mode may lead to diminished forced heat release oscillations in bluff body combustors.
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Goedhart, Marc L., e Norman D. Smith. "Braided stream aggradation on an alluvial fan margin: Emerald Lake fan, British Columbia". Canadian Journal of Earth Sciences 35, n. 5 (1 maggio 1998): 534–45. http://dx.doi.org/10.1139/e97-128.
Testo completoAbstract (sommario):
Evolving bar and channel patterns were observed at the distal margin of an active alluvial fan at Emerald Lake, British Columbia, during peak midsummer flows. At the fan margin, bed slope is 0.024, sediment is predominantly coarse gravel, flow is shallow and fluctuating, and sediment transport and deposition are dominated by chutes and lobes. Flow unconfinement at the exit of rapidly formed shallow scour channels typically results in deposition of sediment lobes 0.2 m thick and 10-250 m2 in area. Closely spaced deposition of a number of these sediment lobes results in aggradation of composite sediment sheets. One such sheet, monitored daily over a 15 day period, deposited 129 m3 of gravel over 710 m2 of adjacent marsh sediment, locally extending the distal fan margin by 39 m. Thickness of the aggraded bed varied up to 0.37 m, depending on surface topography. During active deposition, individual lobe deposits formed simple unit bars that partly projected above the water surface. These bars caused local flow division that, together with avulsion of the dominant channel, initiated a braided stream pattern. Complex braid bars composed of several annealed lobe remnants are gradually exposed as waning discharge becomes confined to adjacent chutes. The newly aggraded fan margin is mainly composed of massive to crudely stratified imbricated gravel with interstratified, discontinuous, centimetre-thick finer grained layers. High-angle cross-stratification was not observed. Since chutes and lobes dominate sediment transport and deposition in streams at the distal margin of this rapidly aggrading fan, it is likely that similar deposits should be present in many ancient alluvial fan sequences, but as yet have gone largely unrecognized.
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Larinier, Michel, Lionel Dumond, Thierry Lagarrigue, Aurélien Frey e François Travade. "Performance of a large partial-depth guide wall to divert downstream migrating Atlantic salmon smolts at Tuilières dam, Dordogne River". Knowledge & Management of Aquatic Ecosystems, n. 421 (2020): 15. http://dx.doi.org/10.1051/kmae/2020010.
Testo completoAbstract (sommario):
From 2010 to 2016, an evaluation of the performance of a partial-depth guide wall associated with three surface bypasses to ensure the safe downstream migration of Atlantic salmon smolts was conducted at the Tuilières power plant on the Dordogne River in southwestern France. The objectives of this study, during which 603 smolts were monitored using radio telemetry, were (i) to determine their escapement rate (passage through routes other than turbines), (ii) to analyse their behaviour faced with the structure and (iii) to assess the permeability of the guide wall as a function of turbine and spilling flows. The rate of escapement through the surface bypass routes varied from approximately 15% to 85%. The turbine flow was the main factor influencing the guide wall efficiency. The contribution of secondary bypasses, while significant for low flows, decreased rapidly with the increase in turbine flows. The vast majority of fish arrived on the two downstream bays of the wall or directly in the area of the main bypass, with the guiding effect of the guide wall becoming less noticeable with the increase of turbine flow. A modification of the depth of the guide wall in 2014 slightly improved its efficiency (by 5–10%) for low turbine flows. Logistic regression models were used to describe the evolution of the efficiency of the facilty as a function of the turbine flow and the probability of direct passage under a bay as a function of average velocity under this bay.
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Adang, Laura A., Christopher H. Parsons e Dean H. Kedes. "Asynchronous Progression through the Lytic Cascade and Variations in Intracellular Viral Loads Revealed by High-Throughput Single-Cell Analysis of Kaposi's Sarcoma-Associated Herpesvirus Infection". Journal of Virology 80, n. 20 (15 ottobre 2006): 10073–82. http://dx.doi.org/10.1128/jvi.01156-06.
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ABSTRACT Kaposi's sarcoma-associated herpesvirus (KSHV or human herpesvirus-8) is frequently tumorigenic in immunocompromised patients. The average intracellular viral copy number within infected cells, however, varies markedly by tumor type. Since the KSHV-encoded latency-associated nuclear antigen (LANA) tethers viral episomes to host heterochromatin and displays a punctate pattern by fluorescence microscopy, we investigated whether accurate quantification of individual LANA dots is predictive of intracellular viral genome load. Using a novel technology that integrates single-cell imaging with flow cytometry, we found that both the number and the summed immunofluorescence of individual LANA dots are directly proportional to the amount of intracellular viral DNA. Moreover, combining viral (immediate early lytic replication and transcription activator [RTA] and late lytic K8.1) and cellular (syndecan-1) staining with image-based flow cytometry, we were also able to rapidly and simultaneously distinguish among cells supporting latent, immediate early lytic, early lytic, late lytic, and a potential fourth “delayed late” category of lytic replication. Applying image-based flow cytometry to KSHV culture models, we found that de novo infection results in highly varied levels of intracellular viral load and that lytic induction of latently infected cells likewise leads to a heterogeneous population at various stages of reactivation. These findings additionally underscore the potential advantages of studying KSHV biology with high-throughput analysis of individual cells.
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Tang, Weiyu, David John Kukulka, Wei Li e Rick Smith. "Comparison of the Evaporation and Condensation Heat Transfer Coefficients on the External Surface of Tubes in the Annulus of a Tube-in-Tube Heat Exchanger". Energies 13, n. 4 (20 febbraio 2020): 952. http://dx.doi.org/10.3390/en13040952.
Testo completoAbstract (sommario):
An experimental study was carried out to explore the heat transfer characteristics on the outside of smooth and enhanced tubes, during evaporation and condensation of R134A in the annulus of a tube-in-tube heat exchanger. The three-dimensional enhanced surface tube consisted of primary enhancement patterns and secondary patterns; results were compared to the performance of an equivalent smooth tube. The equivalent external diameter of the inside horizontal copper tubes used in this study was 19.05 mm, while the outer tube varied in size, allowing a comparison of heat transfer for different annulus dimensions. Tests were conducted with a fixed inlet/outlet vapor quality and a constant saturation temperature for varied mass velocities in the range of 30 to 100 kg/(m2∙s). For condensation, the ratio of heat transfer coefficient enhancement (enhanced tube/ smooth tube) was up to 1.78; this can be attributed to the turbulence increase, as well as liquid film re-distribution, produced from the dimples. Furthermore, the condensation heat transfer coefficient increased rapidly with increasing mass flux. For flow boiling in the annulus between the 1EHT tube and outer tube, the heat transfer coefficient during boiling was 11–36% higher when compared to the smooth tube at xave = 0.35, while the performance of the 1EHT tube was not as good as the smooth tube at xave = 0.5. The heat transfer deterioration can be explained by decreased effective nucleate flow boiling heat transfer area and the flow pattern transition between a slug/wavy-stratified flow to wavy-stratified flow.
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Yan, Yuhan, Dehai Song, Xianwen Bao e Yang Ding. "The Response of Lateral Flow to Peak River Discharge in a Macrotidal Estuary". Water 12, n. 12 (19 dicembre 2020): 3571. http://dx.doi.org/10.3390/w12123571.
Testo completoAbstract (sommario):
The Ou River, a medium-sized river in southeastern China, is selected to study the lateral flow response to rapidly varied river discharge, i.e., peak river discharge (PRD). A three-dimensional model based on the Finite-Volume Community Ocean Model is validated by in situ measurements from 15 June to 16 July 2005. PRD, which considers the extra buoyancy and longitudinal momentum in a short time, rebuilds the stratification and lateral flow. PRD, compared with low-discharge, generally makes stratification stronger and lateral flow weaker. PRD mainly rebuilds lateral flow by changing lateral advection, lateral Coriolis, and lateral-barotropic pressure gradient terms. After PRD, the salinity recovery time is longer than that of the flow because the impact on buoyancy lasts longer than that on longitudinal flow. Longitudinal flow is mostly affected by the momentum transferred during PRD; therefore, the recovery time is close to the flooding duration. However, the lateral flow is affected by the buoyancy, and its recovery time is generally longer than the flooding duration. The lateral flow recovery time depends on transect width, flow velocity and the variation caused by PRD. PRD occurs widely in global small-/medium-sized river estuaries, and the result of this work can be extended to other estuaries.
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Aadim, Kadhim A. "Diagnostics of low-pressure capacitively coupled RF discharge argon plasma". Iraqi Journal of Physics (IJP) 13, n. 27 (4 febbraio 2019): 76–82. http://dx.doi.org/10.30723/ijp.v13i27.266.
Testo completoAbstract (sommario):
Low-pressure capacitively coupled RF discharge Ar plasma has been studied using Langmuir probe. The electron temperature, electron density and Debay length were calculated under different pressures and electrode gap. In this work the RF Langmuir probe is designed using 4MHz filter as compensation circuit and I-V probe characteristic have been investigated. The pressure varied from 0.07 mbar to 0.1 mbar while electrode gap varied from 2-5 cm. The plasma was generated using power supply at 4MHz frequency with power 300 W. The flowmeter is used to control Argon gas flow in the range of 600 standard cubic centimeters per minute (sccm). The electron temperature drops slowly with pressure and it's gradually decreased when expanding the electrode gap. As the gas pressure increases, the plasma density rises slightly at low gas pressure while it drops little at higher gas pressure. The electron density decreases rapidly with expand distances between electrodes.
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Koyama, S., W. J. Lamm, J. Hildebrandt e R. K. Albert. "Flow characteristics of open vessels in zone 1 rabbit lungs". Journal of Applied Physiology 66, n. 4 (1 aprile 1989): 1817–23. http://dx.doi.org/10.1152/jappl.1989.66.4.1817.
Testo completoAbstract (sommario):
To describe the flow characteristics of vessels open in zone 1, we perfused isolated rabbit lungs with Tyrode's solution containing 1% albumin, 4% dextran, and papaverine (0.05 mg/ml). Lungs were expanded by negative pleural pressure (Ppl) of -10, -15, -20, and -25 cmH2O. Pulmonary arterial (Ppa) and venous (Ppv) pressures were varied relative to alveolar pressure (PA = 0) and measured 5–10 mm inside the pleura (i) and outside (o) of the lungs. With Ppa(o) at -2.5 cmH2O, we constructed pressure-flow (P-Q) curves at each Ppl by lowering Ppv(o) until Q reached a maximum, indicating fully developed zone 1 choke flow. Maximum flows were negligible until Ppl fell below -10 cmH2O, then increased rapidly at Ppl of -15 and -20 cmH2O, and at Ppl of -25 cmH2O reached about 15 ml.min-1.kg body wt-1. The Ppv(o) at which flow became nearly constant depended on degree of lung inflation and was 5–8 cmH2O more positive than Ppl. As Ppv(o) was lowered below Ppa(o), Ppv(i) remained equal to Ppv(o) until Ppv(i) became fixed at a pressure 2–3 cmH2O more positive than Ppl. At this point the choke flow was therefore located in veins near the pleural boundary. No evidence of choke flow (only ohmic resistance) was seen in the intrapulmonary segment of the vessels remaining open in zone 1. With Ppv(o) held roughly at Ppl, Q could be stopped by lowering Ppa(o), at which time Ppa(i) was several cmH2O above Ppv(i), showing that intrapulmonary vessel closure had occurred.(ABSTRACT TRUNCATED AT 250 WORDS)
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Retsinis, Eugene, e Panayiotis Papanicolaou. "Numerical and Experimental Study of Classical Hydraulic Jump". Water 12, n. 6 (21 giugno 2020): 1766. http://dx.doi.org/10.3390/w12061766.
Testo completoAbstract (sommario):
The present work is an effort to simulate numerically a classical hydraulic jump in a horizontal open channel with a rectangular cross-section, as far as the jump location and free surface elevation is concerned, and compare the results to experiments with Froude numbers in the range 2.44 to 5.38. The governing equations describing the unsteady one-dimensional rapidly varied flow have been solved with the assumption of non-hydrostatic pressure distribution. Two finite difference schemes were used for the discretization of the mass and momentum conservation equations, along with the appropriate initial and boundary conditions. The method of specified intervals has been employed for the calculation of the velocity at the downstream boundary node. Artificial viscosity was required for damping the oscillations near the steep gradients of the jump. An iterative algorithm was used to minimize the difference of flow depth between two successive iterations that must be less than a threshold value, for achieving steady state solution. The time interval varied in each iteration as a function of the Courant number for stability reasons. Comparison of the numerical results with experiments showed the validity of the computations. The numerical codes have been implemented in house using a Matlab® environment.
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Choi, C. E., C. W. W. Ng, G. R. Goodwin, L. H. D. Liu e W. W. Cheung. "Flume investigation of the influence of rigid barrier deflector angle on dry granular overflow mechanisms". Canadian Geotechnical Journal 53, n. 10 (ottobre 2016): 1751–59. http://dx.doi.org/10.1139/cgj-2015-0248.
Testo completoAbstract (sommario):
Mass-wasting processes are often intercepted using rigid barriers, which are sometimes equipped with deflectors to prevent overspilling. Despite the engineering value of deflectors, they are currently only installed using empirical and prescriptive approaches because flow interaction mechanisms are not well understood. A 5 m flume was used to study dry granular flow deposition and overflow processes with and without deflectors of varying angles. The deflector angle was varied as 0°, 30°, 45°, and 60° with respect to the horizontal plane. For the geometric and material parameters adopted in this study, experimental results reveal that deflector angles greater than 45° develop steep ramp-like deadzones that result in effective energy dissipation as approaching flow impacts the deflector, whereas deflectors less than 45° rapidly develop shallow ramp-like deadzones, which promote high-energy overflow. Deflectors of at least 45° are required to develop upward overflow launch angles, whilst deflectors of 30° or less result in downward overflow launch angles. Upward launch angles indicate that a steep deadzone develops and effectively dissipates flow energy. An orthogonal deflector increases launch lengths by 40% compared to a bare rigid barrier.
25
Wijitsopa, Kichaphum, Krit Somnuk, Thanansak Theppaya e Gumpon Prateepchaikul. "Continuous Transesterification for Ethyl Ester Production from Refined Palm Oil through Static Mixer". Applied Mechanics and Materials 705 (dicembre 2014): 64–68. http://dx.doi.org/10.4028/www.scientific.net/amm.705.64.
Testo completoAbstract (sommario):
In this study, the commercial grade of ethanol was used to produce the biodiesel from refined palm oil (RPO) through the continuous static mixer system. The ethanol, an alternative alcohol to adopt in the ethyl ester production, can be used instead of methanol, and this alcohol is more eco-friendly than methanol. The 6-meter in length of SUS304 static mixer reactor is an essential part of mixing the RPO and solution of ethanol and potassium hydroxide to accelerate the base-catalyzed transesterification. The ethanol were varied at the volumetric flow rate of 30, 40, 50, 60 vol.%, KOH as base-catalyst was varied with the weight to volume of oil of 10,12,14 gKOH.L-1, to investigate the suitable condition which can converted the glycerides to the maximum purity of ethyl ester. The results showed that all varied conditions, the ethyl ester conversion was rapidly increased from 0 to over 95 wt.% when the flowing mixtures flowed through the 1 meter of static mixer. Furthermore, the highest purity of ethyl ester from RPO was succeeded when the condition: the 60 vol.% ethanol, the 14 gKOH.L-1of catalyst, 5-meter of static mixer, and 75 oC temperature of RPO, was used in the continuous static mixer.
26
CARNEVALE, G. F., M. BRISCOLIN, R. C. KLOOSTERZIEL e G. K. VALLIS. "Three-dimensionally perturbed vortex tubes in a rotating flow". Journal of Fluid Mechanics 341 (25 giugno 1997): 127–63. http://dx.doi.org/10.1017/s0022112097005430.
Testo completoAbstract (sommario):
Numerical experiments are used to study the evolution of perturbed vortex tubes in a rotating environment in order to better understand the process of two-dimensionalization of unsteady rotating flows. We specifically consider non-axisymmetric perturbations to columnar vortices aligned along the axis of rotation. The basic unperturbed vortex is chosen to have a Gaussian cross-sectional vorticity distribution. The experiments cover a parameter space in which both the strength of the initial perturbation and the Rossby number are varied. The Rossby number is defined here as the ratio of the maximum amplitude of vorticity in the Gaussian vorticity profile to twice the ambient rotation rate. For small perturbations and small Rossby numbers, both cyclones and anticyclones behave similarly, relaxing rapidly back toward two-dimensional columnar vortices. For large perturbations and small Rossby numbers, a rapid instability occurs for both cyclones and anticyclones in which antiparallel vorticity is created. The tubes break up and then re-form again into columnar vortices parallel to the rotation axis (i.e. into a quasi-two-dimensional flow) through nonlinear processes. For Rossby numbers greater than 1, even small perturbations result in the complete breakdown of the anticyclonic vortex through centrifugal instability, while cyclones remain stable. For a range of Rossby numbers greater than 1, after the breakdown of the anticyclone, a new weaker anticyclone forms, with a small-scale background vorticity of spectral shape given approximately by the −5/3 energy spectral law.
27
NICOLLE, A., e I. EAMES. "Numerical study of flow through and around a circular array of cylinders". Journal of Fluid Mechanics 679 (27 maggio 2011): 1–31. http://dx.doi.org/10.1017/jfm.2011.77.
Testo completoAbstract (sommario):
This paper describes a study of the local and global effect of an isolated group of cylinders on an incident uniform flow. Using high resolution two-dimensional computations, we analysed the flow through and around a localised circular array of cylinders, where the ratio of array diameter (DG) to cylinder diameter (D) is 21. The number of cylinders varied from NC = 7 to 133, and they were arranged in a series of concentric rings to allow even distribution within the array with an average void fraction φ = NC(D/DG)2, which varied from 0.016 to 0.30. The characteristic Reynolds number of the array was ReG = 2100. A range of diagnostic tools were applied, including the lift/drag forces on each cylinder (and the whole array), Eulerian and Lagrangian average velocity within the array, and the decay of maximum vorticity with distance downstream. To interpret the flow field, we used vorticity and the dimensionless form of the second invariant of the velocity gradient tensor. A mathematical model, based on representing the bodies as point forces, sources and dipoles, was applied to interpret the results. Three distinct flow regimes were identified. For low void fractions (φ < 0.05), the cylinders have uncoupled individual wake patterns, where the vorticity is rapidly annihilated by wake intermingling downstream and the forces are similar to that of an isolated cylinder. At intermediate void fractions (0.05 < φ < 0.15), a shear layer is generated at the shoulders of the array and the force acting on the cylinders is steady. For high void fractions (φ > 0.15), the array generates a wake in a similar way to a solid body of the same scale. For low void fraction arrays, the mathematical model provides a reasonable assessment of the forces on individual bodies within the array, the Eulerian mean velocity and the upstream velocity field. While it broadly captures the change in the rate of decay of the maximum vorticity magnitude Ωmax downstream, the magnitude is underpredicted.
28
Kepecs, Adam, Naoshige Uchida e Zachary F. Mainen. "Rapid and Precise Control of Sniffing During Olfactory Discrimination in Rats". Journal of Neurophysiology 98, n. 1 (luglio 2007): 205–13. http://dx.doi.org/10.1152/jn.00071.2007.
Testo completoAbstract (sommario):
Olfactory perception relies on an active sampling process, sniffing, to rapidly deliver odorants from the environment to the olfactory receptors. The respiration cycle strongly patterns the flow of information into the olfactory systems, but the behavioral significance of particular sniffing patterns is not well understood. Here, we monitored the frequency and timing of nasal respiration in rats performing an odor-mixture–discrimination task that allowed us to test subjects near psychophysical limits and to quantify the precise timing of their behavior. We found that respiration frequencies varied widely from 2 to 12 Hz, but odor discrimination was dependent on 6- to 9-Hz sniffing: rats almost always entered and maintained this frequency band during odor sampling and their accuracy on difficult discrimination dropped when they did not. Moreover, the switch from baseline respiration to sniffing occurred not in response to odor delivery but in anticipation of odor sampling and was executed rapidly, almost always within a single cycle. Interestingly, rats also switched from respiration to rapid sniffing in anticipation of reward delivery, but in a distinct frequency band, 9–12 Hz. These results demonstrate the speed and precision of control over respiration and its significance for olfactory behavioral performance.
29
Kori, S. M., A. A. Mahessar, M. Channa, A. A. Memon e A. R. Kori. "Study of Flow Characteristics Over a Rounded Edge Drop Structure in Open Channel". Engineering, Technology & Applied Science Research 9, n. 3 (8 giugno 2019): 4136–39. http://dx.doi.org/10.48084/etasr.2584.
Testo completoAbstract (sommario):
Flow over a drop structure is a form of free overfall called hydraulic drop. Hydraulic drop changes the nature of flow abruptly from sub-critical to super-critical condition. Rapidly varied flow analysis is a complex phenomenon and involves remarkable characteristics. Some of the drop structures constructed in Sindh and Punjab provinces of Pakistan had gone through diverse failures, consequential in interruption of water supply to irrigation fields encountering substantial economic loss. In the present study experiments were carried out in the hydraulic laboratory of Mehran University of Engineering and Technology on round edged drop structure fitted in a horizontal rectangular flume (channel model). Data regarding hydraulic drop and hydraulic jump characteristics were collected during the experiment. The observed data included: flow discharge (Q), radius of rounded edge drop structure (r), height of the structure (h), hydraulic drop length (Ld), hydraulic jump length (Lj), depth of flow at toe of the jump (Y1) and tailwater depth (Y2). Applying dimensional analysis, the non-dimensional parameters of the observed data were calculated. Using statistical analysis, empirical relationships among the non-dimensional parameters were established for the appropriate design of the drop structure. The research results showed that the length and depth indices are functions of D=q2gh3 and r/h values. It was also found that for rounded-edge drop structure, the length of the stilling basin (LSB) reduces as r/h ratio increases
30
Wheeb, Ali Hussein. "Performance Evaluation of UDP, DCCP, SCTP and TFRC for Different Traffic Flow in Wired Networks". International Journal of Electrical and Computer Engineering (IJECE) 7, n. 6 (1 dicembre 2017): 3552. http://dx.doi.org/10.11591/ijece.v7i6.pp3552-3557.
Testo completoAbstract (sommario):
<p>The demand for internet applications has increased rapidly. Providing quality of service (QoS) requirements for varied internet application is a challenging task. One important factor that is significantly affected on the QoS service is the transport layer. The transport layer provides end-to-end data transmission across a network. Currently, the most common transport protocols used by internet application are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). Also, there are recent transport protocols such as DCCP (data congestion control protocol), SCTP (stream congestion transmission protocol), and TFRC (TCP-friendly rate control), which are in the standardization process of Internet Engineering Task Force (IETF). In this paper, we evaluate the performance of UDP, DCCP, SCTP and TFRC protocols for different traffic flows: data transmission, video traffic, and VOIP in wired networks. The performance criteria used for this evaluation include throughput, end to end delay, and packet loss rate. Well-known network simulator NS-2 used to implement the UDP, DCCP, SCTP, and TFRC protocols performance comparison. Based on the simulation results, the performance throughput of SCTP and TFRC is better than UDP. Moreover, DCCP performance is superior SCTP and TFRC in term of end-to-end delay.</p>
31
Sparrow, E. M., e G. M. Chrysler. "Turbulent Flow and Heat Transfer in Bends of Circular Cross Section: I—Heat Transfer Experiments". Journal of Heat Transfer 108, n. 1 (1 febbraio 1986): 40–47. http://dx.doi.org/10.1115/1.3246902.
Testo completoAbstract (sommario):
Experiments were performed to determine the local heat transfer characteristics of bends of circular cross section to which fluid was delivered either via a sharp-edged inlet or via a hydrodynamic development tube. The naphthalene sublimation technique, a mass transfer method, was used to facilitate the experiments. Bends subtending turning angles of 30, 60, and 90 deg were investigated, and the Reynolds number was varied between 5000 and 100,000. It was found that the local heat transfer coefficients at the outside of the bend were, for the most part, larger than those at the inside of the bend, but the deviations decreased as the Reynolds number increased. The streamwise distributions of the local transfer coefficient were markedly affected by the inlet condition; those for the sharp-edged inlet exhibited a universal shape, while the shapes of those for the tube-fed inlet depended both on the Reynolds number and on whether the distribution corresponded to the inside or the outside of the bend. In addition, the distributions for the case of the sharp-edged inlet exhibited higher local maxima and approached the fully developed regime more rapidly than did those for the tube-fed inlet. The heat transfer results were supplemented by flow visualization.
32
Seki, J. "Flow pulsation and network structure in mesenteric microvasculature of rats". American Journal of Physiology-Heart and Circulatory Physiology 266, n. 2 (1 febbraio 1994): H811—H821. http://dx.doi.org/10.1152/ajpheart.1994.266.2.h811.
Testo completoAbstract (sommario):
Red cell velocity was measured by a fiber-optic laser-Doppler anemometer microscope in microvessels of the mesentery of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto control rats (WKY) with high temporal resolution. Based on the velocity data, the propagation velocity of flow pulse along single microvessels as well as the arteriovenous distributions of the mean volumetric flow, the amplitude of flow pulsation, and the phase lag of the flow relative to the systemic pressure were analyzed in relationship to the vessel wall rheology and the network topology. The propagation velocity was 3.5–134 cm/s in arterioles of 12–43 microns in diameter, and it increased with increasing diameter. The mean volumetric flow exhibited a power law relationship to the vessel diameter, in which the exponents were 3.16 and 3.30 for arterioles and 3.03 and 2.85 for venules in SHR and WKY, respectively. The exponents for arterioles were > 3 (P < 0.1) and different between SHR and WKY (P < 0.12). The amplitude of the flow pulsation also varied in a power law with the vessel diameter, whose exponents for arterioles were 3.41 and 3.52 for SHR and WKY, respectively. The flow phase lag increased gradually with decreasing vessel diameter in arterioles and increased comparatively rapidly with increasing vessel diameter in venules, which suggests more compliant vessel walls for venules than arterioles. The slope of the increase in the flow phase lag with the vessel diameter in arterioles of SHR was larger than that for WKY (P < 0.05). This difference in the flow phase lag distribution and the difference in the exponent of the mean flow rate vs. diameter relationship may reflect that the number of small arterioles relative to large ones is reduced in SHR microvasculature compared with that in WKY.
33
Kramer, Stephan C., e Guus S. Stelling. "A conservative unstructured scheme for rapidly varied flows". International Journal for Numerical Methods in Fluids 58, n. 2 (20 settembre 2008): 183–212. http://dx.doi.org/10.1002/fld.1722.
Testo completo
34
Honig, C. R., J. L. Frierson e T. E. Gayeski. "Anatomical determinants of O2 flux density at coronary capillaries". American Journal of Physiology-Heart and Circulatory Physiology 256, n. 2 (1 febbraio 1989): H375—H382. http://dx.doi.org/10.1152/ajpheart.1989.256.2.h375.
Testo completoAbstract (sommario):
Calculations indicate that the PO2 in plasma falls to zero approximately 3 microns from an erythrocyte at O2 consumption (VO2) characteristic of myocardium (Federspiel, W.A., and A. Popel, Microvasc. Res. 32: 164-189, 1986). We measured distances between individual red cells along capillaries in rat hearts rapidly frozen in situ. Cell spacing varied widely even in branches of the same capillary. Plasma gaps between red cells were divided into two populations, those less than 5 microns and those greater than 5 microns. Mean gap lengths were 2.1 and 16.5 microns, respectively. Although the number of long plasma gaps was underestimated, gaps greater than 5 microns accounted for one-third of observed capillary length. Frozen muscles were also viewed in cross section. Because the depth of penetration of light was approximately equal to 3 microns, counts of red cell-containing capillary profiles in cross section depend on cell spacing as well as on number of cell-containing flow paths. Counts varied markedly with arterial O2 partial pressure, indicating that the capillary surface area functional for O2 transport changes in response to stress. The adaptive role of change in O2 flux density (flux per area) is discussed in light of new knowledge of tissue O2 gradients.
35
Zhang, Yan, e Hai Wei Xie. "The Convective Heat Transfer in Furcated Blood Vessels". Applied Mechanics and Materials 475-476 (dicembre 2013): 1599–602. http://dx.doi.org/10.4028/www.scientific.net/amm.475-476.1599.
Testo completoAbstract (sommario):
A finite element model was developed to simulate the 3-D velocity and temperature distributions in a vessel system including a bifurcated blood vessel and two branches. The effect of the angel between vessels and bifurcation ratio were taken into account, and the local Nusselt number at three typical radial angels and the mean Nusselt number on a section in the branching vessel were obtained. Results show that: the flow and temperature fields were highly unlike the distributions of a single vessel; the local Nusselt number were different at different radial angels; In the entrance region of the branching vessel the mean Nusselt number on a section was larger than that in a single vessel, and there was a maximum of mean Nusselt number whose value and location varied as the different furcating angel or bifurcation ratio; the mean Nusselt number decays rapidly at a small bifurcation ratio.
36
Suzuki, Satomi, Dave Stern e Tom Manzocchi. "The Use of Association-Rule Mining and High-Dimensional Visualization To Explore the Impact of Geological Features on Dynamic-Flow Behavior". SPE Journal 21, n. 06 (29 settembre 2016): 1996–2009. http://dx.doi.org/10.2118/174774-pa.
Testo completoAbstract (sommario):
Summary Because of computational advances in reservoir simulation with high-performance computing, it is now possible to simulate more than thousands of reservoir-simulation cases in a practical time frame. This opens a new avenue to reservoir-simulation studies, enabling exhaustive exploration of subsurface uncertainty and development/depletion options. However, analyzing the results of a large number of simulation cases still remains a challenging and overwhelming task. We propose a new method that enables the efficient analysis of massive reservoir-simulation results, often consisting of thousands of cases, by discovering interesting patterns of relationships among variables in large data sets. The method uses a well-known data-mining method, called association-rule mining, together with a high-dimensional visualization technique. We demonstrate the capability of the proposed method by using it to analyze the reservoir-simulation results from the Sensitivity Analysis of the Impact of Geological Uncertainty on Production (SAIGUP) project, which is an interdisciplinary reservoir-modeling project carried out earlier by Manzocchi et al. (2008a). To investigate the influence of geological features on oil recovery in shallow marine reservoirs, numerous reservoir models were built and flow-simulated in the SAIGUP project. In this paper, we analyze the simulation results from an ensemble of 9,072 models, which cover all possible combinations of several structural and sedimentological parameters individually varied to describe geological uncertainty. To be able to analyze the simulation results from such exhaustive sampling from high-dimensional model parameter space, it is crucial to efficiently decompose complex interactions between model parameters and to discover hidden impacts on flow response. By coupling the association-rule mining algorithm and high-dimensional visualization, such interactions and impacts are rapidly extracted and visualized in such a way that engineers and geoscientists can interpret meaningful sensitivities “at a glance.” This methodology provides a novel way to rapidly interpret flow response from a large ensemble of reservoir models without being overwhelmed by massive data.
37
Sendek, Michael E., e Mohamed A. Virji. "Development and Implementation of Network-Resident Clinical Laboratory Tools in an Integrated Health Delivery System". Laboratory Automation News 2, n. 3 (luglio 1997): 18–22. http://dx.doi.org/10.1177/221106829700200308.
Testo completoAbstract (sommario):
The conceptual approach to a system of network resident-training tools for use in a clinical pathology laboratory is described and specific modules developed for use in an integrated health care delivery system. The modules have been developed to be accessible throughout an organization, are amenable to customization, are designed for use by personnel with varied knowledge of laboratory techniques, and can be updated readily. The modules designed are for dry slide clinical chemistry analyses, white blood cell maturation sequence, and flow cytometry. The concept can be applied to other laboratory functions including point-of-care testing service. The modules incorporate flexibility of integrating text with digital images, sound and animation. The core of the system is based on readily available software for Internet. Therefore, the system of laboratory tools can provide the means for rapidly accessible, current data resources for a variety of purposes for a laboratory to operate in an integrated delivery system.
38
Nash, GB, BM Cooke, K. Marsh, A. Berendt, C. Newbold e J. Stuart. "Rheological analysis of the adhesive interactions of red blood cells parasitized by Plasmodium falciparum". Blood 79, n. 3 (1 febbraio 1992): 798–807. http://dx.doi.org/10.1182/blood.v79.3.798.798.
Testo completoAbstract (sommario):
Abstract Adhesion of parasitized red blood cells (RBCs) to vascular endothelium is thought to be a key factor in the pathology of falciparum malaria. However, quantitative analyses of the intercellular forces and of the effects of flow on adhesion have been lacking. We have characterized cytoadhesion of RBCs parasitized by the strains ITO4 (which can bind to receptors ICAM-1 or CD36) and FCR3A2 (which can bind to CD36 only) using micropipette manipulation and flow chamber techniques. Target cells were unfixed or glutaraldehyde-fixed human umbilical vein endothelial cells (HUVEC, bearing ICAM-1 only) or human amelanotic melanoma cells (C32, bearing CD36 and ICAM-1). In the static, micropipette assay, 60% to 70% of parasitized cells would adhere when tested at up to three successive sites. The percentage of cells adhering and the force required for their detachment (approximately 10(- 10) N) were similar for each combination of parasite strain and adhesion target (ITO4/HUVEC, ITO4/C32, FCR3A2/C32). In the flow chamber, efficiency of initial adhesion of parasitized cells was essentially constant (at about 1%) up to a stress of 0.1 Pa, and then decreased rapidly with increasing stress. Either receptor (ICAM-1 or CD36) could immobilize flowing cells at a physiologic flow stress (0.1 Pa), but the numbers of cells adhering varied for the different combinations (ITO4/C32 greater than ITO4/HUVEC greater than FCR3A2/C32). When flow was increased in steps, adhered cells were gradually washed off but many could withstand stresses at which they would not initially adhere. The force for detachment estimated in this way was similar to the pipette value, and again, was similar for the different combinations of strains and targets. Adhesion from flow depends on the affinity between surfaces being above a critical level, and once adhesion is established, the fracture energy determines resistance to disruption of adhesion. The results show that the fracture energy is greater than the affinity (ie, that adhesion becomes stabilized after it is initially established) and that the ratio of affinity to fracture energy is different for different receptor/ligand pairs, with ICAM-1 appearing to be the more efficient immobilizing receptor. Also, static and flow-based assays of adhesion clearly differ; the affinity is less critical in the static situation, so that most parasitized cells were capable of adhering in a static assay, but fewer did so under flow. Adhesiveness varied markedly from cell to cell, both for targets and parasitized cells.(ABSTRACT TRUNCATED AT 400 WORDS).
39
Nash, GB, BM Cooke, K. Marsh, A. Berendt, C. Newbold e J. Stuart. "Rheological analysis of the adhesive interactions of red blood cells parasitized by Plasmodium falciparum". Blood 79, n. 3 (1 febbraio 1992): 798–807. http://dx.doi.org/10.1182/blood.v79.3.798.bloodjournal793798.
Testo completoAbstract (sommario):
Adhesion of parasitized red blood cells (RBCs) to vascular endothelium is thought to be a key factor in the pathology of falciparum malaria. However, quantitative analyses of the intercellular forces and of the effects of flow on adhesion have been lacking. We have characterized cytoadhesion of RBCs parasitized by the strains ITO4 (which can bind to receptors ICAM-1 or CD36) and FCR3A2 (which can bind to CD36 only) using micropipette manipulation and flow chamber techniques. Target cells were unfixed or glutaraldehyde-fixed human umbilical vein endothelial cells (HUVEC, bearing ICAM-1 only) or human amelanotic melanoma cells (C32, bearing CD36 and ICAM-1). In the static, micropipette assay, 60% to 70% of parasitized cells would adhere when tested at up to three successive sites. The percentage of cells adhering and the force required for their detachment (approximately 10(- 10) N) were similar for each combination of parasite strain and adhesion target (ITO4/HUVEC, ITO4/C32, FCR3A2/C32). In the flow chamber, efficiency of initial adhesion of parasitized cells was essentially constant (at about 1%) up to a stress of 0.1 Pa, and then decreased rapidly with increasing stress. Either receptor (ICAM-1 or CD36) could immobilize flowing cells at a physiologic flow stress (0.1 Pa), but the numbers of cells adhering varied for the different combinations (ITO4/C32 greater than ITO4/HUVEC greater than FCR3A2/C32). When flow was increased in steps, adhered cells were gradually washed off but many could withstand stresses at which they would not initially adhere. The force for detachment estimated in this way was similar to the pipette value, and again, was similar for the different combinations of strains and targets. Adhesion from flow depends on the affinity between surfaces being above a critical level, and once adhesion is established, the fracture energy determines resistance to disruption of adhesion. The results show that the fracture energy is greater than the affinity (ie, that adhesion becomes stabilized after it is initially established) and that the ratio of affinity to fracture energy is different for different receptor/ligand pairs, with ICAM-1 appearing to be the more efficient immobilizing receptor. Also, static and flow-based assays of adhesion clearly differ; the affinity is less critical in the static situation, so that most parasitized cells were capable of adhering in a static assay, but fewer did so under flow. Adhesiveness varied markedly from cell to cell, both for targets and parasitized cells.(ABSTRACT TRUNCATED AT 400 WORDS).
40
Pashova, Katya, Elyes Dhaouadi, Ivaylo Hinkov, Ovidiu Brinza, Yves Roussigné, Manef Abderrabba e Samir Farhat. "Graphene Synthesis by Inductively Heated Copper Foils: Reactor Design and Operation". Coatings 10, n. 4 (25 marzo 2020): 305. http://dx.doi.org/10.3390/coatings10040305.
Testo completoAbstract (sommario):
We report on the design of a reactor to grow graphene via inductively heating of copper foils by radio frequency (RF) magnetic fields. A nearly uniform magnetic field induced by Helmholtz-like coils penetrates the copper foil generating eddy currents. While the frequency of the current is being rapidly varied, the substrate temperature increases from room temperature to ~1050 °C in 60 s. This temperature is maintained under Ar/H2 flow to reduce the copper, and under Ar/H2/CH4 to nucleate and grow the graphene over the entire copper foil. After the power cut-off, the temperature decreases rapidly to room temperature, stopping graphene secondary nucleation. Good quality graphene was obtained and transferred onto silicon, and coated with a 300 nm layer of SiO2 by chemical etching of the copper foil. After synthesis, samples were characterized by Raman spectroscopy. The design of the coils and the total power requirements for the graphene induction heating system were first estimated. Then, the effect of the process parameters on the temperature distribution in the copper foil was performed by solving the transient and steady-state coupled electromagnetic and thermal problem in the 2D domain. The quantitative effects of these process parameters were investigated, and the optimization analysis results are reported providing a root toward a scalable process for large-sized graphene.
41
Sun, Ya, Shi Guo Xu, Ping Ping Kang, Yan Zhao Fu e Tian Xiang Wang. "Impacts of Artificial Underground Reservoir on Groundwater Environment in the Reservoir and Downstream Area". International Journal of Environmental Research and Public Health 16, n. 11 (30 maggio 2019): 1921. http://dx.doi.org/10.3390/ijerph16111921.
Testo completoAbstract (sommario):
Artificial underground reservoirs have changed the hydrological cycle from its natural condition. This modification may trigger a series of negative environmental effects both at the local and regional levels. This study investigated the impact of the Wanghe artificial underground reservoir on groundwater flow and quality in the reservoir and its downstream area. Wanghe is a typical artificial underground reservoir scheme in China, which assumes the dual function of fresh-water preservation and control of seawater intrusion. The groundwater flow pattern has changed after the reservoir construction, and the water level in the reservoir rose rapidly. Evaluation of long-term groundwater level fluctuation suggested that the reservoir deprived the downstream aquifer of the runoff, which it received under the natural flow regime. A preliminary isotopic evaluation using 3H was developed to understand the groundwater flow and renewal rates in the study area. The uniform distribution of tritium levels in the reservoir indicated that the stored water was well-mixed in both horizontal and vertical directions. The intervention on groundwater circulation also made differences in groundwater renewal rates between stored and downstream water. Field investigations on groundwater nitrogen pollution showed that the construction of the artificial underground reservoir resulted in nitrate accumulation in the stored water. Agriculturally derived nitrate was the largest contributor, and
NO
3
−
concentration varied considerably over time due to fertilization and irrigation activities, rainfall, and denitrification.
NO
3
−
-N distributed homogeneously in the reservoir, which was attributed to the construction of the subsurface dam, land use pattern and artificial groundwater flow.
42
Islam, Md Fakhrul, Mehedi Hasan Rizvi, Towkir Ahmed Khan e Muhammad Hasanuzzaman. "Development of Ceramic Candle Filters by Slip Casting Process". Key Engineering Materials 608 (aprile 2014): 85–90. http://dx.doi.org/10.4028/www.scientific.net/kem.608.85.
Testo completoAbstract (sommario):
A well-defined porous ceramic having effective pore size less than 1 µm was fabricated by slip casting technique which provides a low-cost and single-stage filtration process. This single-stage filtration process removed suspended solids and pathogenic organism. In this study, diatomaceous earth was used as pore forming agent in clay based ceramic body. Varied amount of diatomaceous earth was used with fixed proportion of china clay, ball clay and lime stone. X-ray fluorescence spectroscopy (XRF) was used to determine the composition of raw materials and final sintered filter body. In terms of porosity and flow rate, 25% diatomaceous earth shows better filtration property. It was found that total porosity increased with decreasing milling time. As the firing temperature increased, porosity decreased rapidly after 1100 °C. However, the change of porosity in firing range of 1000 °C–1100 °C was found very small. Mercury intrusion porosimetry was used to measure the pore size and its distribution. An effective intra-particle pores in a range of 0.2-0.5 μm was identified. Inter- and intra-particle pores were observed using scanning electron microscope (SEM). Microbial removalefficiency of 99.99% was measured, while water flow rate was found in a range of 200-700 ml/hour.
43
Ahmad, Nadeem, e Takayuki Suzuki. "Study of dilution, height, and lateral spread of vertical dense jets in marine shallow water". Water Science and Technology 73, n. 12 (2 aprile 2016): 2986–97. http://dx.doi.org/10.2166/wst.2016.121.
Testo completoAbstract (sommario):
Abstract This study provides information for the design of sea outfalls to dispose of brine from desalination plants into shallow lagoons of the sea. The behavior of vertical dense jets was studied experimentally by discharging cold saline water vertically upward into a tank filled with hot freshwater under stagnant ambient conditions. The minimum return point dilution, μmin, was determined using thermocouples, and the maximum height, Zm, and the lateral spread, Rsp, of the fountains were determined by observing shadowgraph pictures. The flow was turbulent and the densimetric Froude number Fr0 varied from 9 to 18.8. Three mixing regimes were identified: deep, intermediate, and impinging mixing regimes. In the intermediate mixing regime, μmin and Zm were analyzed and compared with the results of deep water studies. The μmin and Zm values of fountains at an intermediate water depth were found to be higher than those of fountains at deep water depths. In the impinging regime, μmin decreases rapidly when a fountain starts to continuously impinge on the water surface, showing a noticeable disturbance in the water surface. Therefore, a good rule of thumb is to reduce the flow through multiport diffusers from desalination plants when the noticeable disturbance is observed from the top water surface.
44
Rab, MA, KA Olsson e ST Willatt. "Resistance to water uptake by irrigated potatoes on a duplex soil". Soil Research 28, n. 4 (1990): 487. http://dx.doi.org/10.1071/sr9900487.
Testo completoAbstract (sommario):
Resistances to water flow were analysed for the soil-root system of a potato crop growing on a duplex soil-where soil hydraulic properties varied with depth-under two irrigation regimes: 'wet' (irrigated weekly) and 'dry' (irrigated twice only during the growing season). The relative magnitudes of the soil and plant resistances controlling root water uptake were evaluated over depth and time using field-measured soil hydraulic properties and root length densities in successive soil layers. Resistance to water flow in the root system is likely to be the dominant resistance in the liquid phase, although soil resistance increased more rapidly than plant resistance with decreasing soil-water matric potential and root length density. Soil resistance reached similar values to plant resistance only when the soil-water matric potential was in the range -900 kPa to -1500 kPa (corresponding soil hydraulic conductivities of 10-7 and 10-8 m day-1 respectively), depending on the root length beneath unit ground area in the soil layer, La. Poor utilization of water from depth of this soil was attributed to resistance in the root system (possibly radial) associated with low La. Practical considerations for improved water management of the potato crop on clay soils are discussed.
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Nagato, Keisuke, Yuki Yajima e Masayuki Nakao. "Laser-Assisted Thermal Imprinting of Microlens Arrays—Effects of Pressing Pressure and Pattern Size". Materials 12, n. 4 (25 febbraio 2019): 675. http://dx.doi.org/10.3390/ma12040675.
Testo completoAbstract (sommario):
Polymer films with nano- or microstructured surfaces have been widely applied to optical devices, bioplates, and printed electronics. Laser-assisted thermal imprinting (LATI), in which a laser directly heats the surfaces of a mold and a thermoplastic polymer, is one of the high-throughput methods of replicating nano- or microstructures on polymer films. Only the surfaces of the mold and polymer film are heated and cooled rapidly, therefore it is possible to replicate nano- or microstructures on polymer films more rapidly than by using conventional thermal nanoimprinting. In this study, microlens arrays (MLAs) were replicated on polymethylmethacrylate (PMMA) films using LATI, and the effects of the pressing pressure (10−50 MPa) and the pattern size (33- and 5-μm pitch) of the MLA on the filling ratio were investigated by analyzing a microlens replicated using different laser-irradiation times (0.1−2 ms). The filling ratio increased with increasing pressing pressure and laser-irradiation time in the replication of MLAs with varying sizes, while the flow of the PMMA varied with the pressing pressure and laser-irradiation time. It was found that during filling, the shape of the polymer cross-sectional surface demonstrated a double and single peak in the 33- and 5-μm-pitch patterns, respectively. This was because the depth of the heated area in the 33-μm-pitch pattern was smaller than the pattern size, whereas that of the 5-μm-pitch pattern was comparable to (or larger) than the pattern size.
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Miller, Timothy L., e Nathaniel D. Reynolds. "A study of baroclinic instability in a cylindrical annulus with the temperature gradient imposed on the lower surface". Journal of Fluid Mechanics 233 (dicembre 1991): 495–518. http://dx.doi.org/10.1017/s0022112091000575.
Testo completoAbstract (sommario):
Laboratory experiments and numerical modelling studies have been performed for a rotating, thermally driven fluid system in a cylindrical annulus with a vertical rotation vector and axis of symmetry. The thermal forcing was through the imposition of an axisymmetric temperature gradient on a thermally conducting lower boundary, with additional heating through the outer sidewall. The upper and inner walls were nominally insulating. Flow patterns were observed in the experiments through the use of small, reflective flakes (Kalliroscope) in the working fluid, which was water. The rotation rate and temperature difference were varied to construct a regime diagram in thermal Rossby number–-Taylor number space. The curve separating axisymmetric flow from wave flow is ‘knee-shaped’, similar to the side-heated and -cooled baroclinic annulus which has been extensively investigated previously. Very near the transition curve, the initial wavenumber persists indefinitely, but well into the wave regime the initial wavenumber is higher than the equilibrated value. Far enough into the wave regime, the initial waves have wavenumbers several times that of the equilibrated value, and the initial disturbances form near the outer wall very early in the experiment. Numerical studies indicate that these waves are effective in distributing heat and that they occur in a region of positive static stability. These waves rapidly grow inward to fill the annulus and reduce in number as weaker waves are absorbed by the stronger ones. The period of transition between these waves and the equilibrated long-wave pattern is characterized by irregular flow. Closer to the transition curve, the temporal transition to longer waves as the flow equilibrates is simpler, with initial waves filling the annulus. In that case, the transition is characterized by a slow process of individual waves weakening and merging with adjacent waves.
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Mooney, T. Aran, Manuel Castellote, Ian T. Jones, Lori Quakenbush, Roderick Hobbs, Eric Gaglione e Caroline Goertz. "Local acoustic habitat relative to hearing sensitivities in beluga whales (Delphinapterus leucas)". Journal of Ecoacoustics 2, n. 2 (20 giugno 2018): 1. http://dx.doi.org/10.22261/jea.qzd9z5.
Testo completoAbstract (sommario):
Background noise can have a substantial effect on communication signals, however far less is known about how natural soundscapes may influence hearing sensitivity. Here we compare the audiograms of 26 wild beluga whales measured in their natural environment to a series of ecoacoustic measurements within a primary portion of their Bristol Bay summer habitat, the Nushagak Estuary in Bristol Bay, AK, USA. Environmental acoustic measurements were made during 2012 and 2016 using two different methods: a moored recorder and drifter buoys. Environmental noise curves varied substantially. Drifter recordings from the middle of Nushgak Estuary had the highest spectrum levels during ebb tides with acoustic energy from sediment transport extending well into higher frequencies (ca. 60 kHz), likely due to rapidly moving tidal flow and shifting sediment in that location. Drifter recordings near the estuary mouth and shallow tidal flats were lower amplitude. Noise levels generally varied during drifts (in one case up to ca. 6 dB) reflecting acoustic cues available to the local belugas. The moored recorder showed a substantially different spectral profile, especially at lower frequencies, perhaps due to its attachment to a pier piling and subsequent pier noise. Hearing sensitivity varied by individual and thresholds often fell above 1/3 octave-band noise levels, but not overall noise spectral density. Audiograms of the most sensitive animals closely paralleled the lowest ambient noise power spectral density curves, suggesting that an animal’s auditory dynamic range may extend to include its habitat’s quietest conditions. These data suggest a cautious approach is necessary when estimating the sound-sensitivity of odontocetes found in quiet environments as they may have sensitive auditory abilities that allow for hearing within the lowest noise-level conditions. Further, lower level ambient noise conditions could provide a conservative estimate of the maximal sensitivity of some cetacean populations within specific environments.
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BALZANO, ANDREA. "Semi-implicit modeling of 2D rapidly varied flows with transitions". Journal of Hydraulic Research 47, n. 3 (2009): 000. http://dx.doi.org/10.3826/jhr.2009.3250.
Testo completo
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Leng, Xinqian, e Hubert Chanson. "Integral turbulent scales in unsteady rapidly varied open channel flows". Experimental Thermal and Fluid Science 81 (febbraio 2017): 382–95. http://dx.doi.org/10.1016/j.expthermflusci.2016.09.017.
Testo completo
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Pallapothu, Surya K., e Adel M. Al Taweel. "Effect of Contaminants on the Gas Holdup and Mixing in Internal Airlift Reactors Equipped with Microbubble Generator". International Journal of Chemical Engineering 2012 (2012): 1–15. http://dx.doi.org/10.1155/2012/569463.
Testo completoAbstract (sommario):
The impact of contaminants on the gas holdup and mixing characteristics encountered in internal airlift reactors was investigated using a 200 L pilot scale unit equipped with a two-phase transonic sparger capable of generating microbubbles. Small dosages of a cationic surfactant (0–50 ppm of sodium dodecyl sulfonate (SDS)) were used to simulate the coalescence-retarding effect encountered in most industrial streams and resulted in the formation of bubbles that varied in size between 280 and 1,900 μm. Gas holdups as high as 0.14 were achieved in the riser under homogeneous flow regime when slowly coalescent systems were aerated at the relatively low superficial velocity of 0.02 ms−1, whereas liquid circulation velocities as high as 1.3 ms−1were achieved in conjunction with rapidly coalescent systems at the same superficial velocity. This excellent hydrodynamic performance represents a 5-fold improvement in the riser gas holdup and up to 8-fold enhancement in the liquid circulation velocity and is expected to yield good mixing and mass transfer performance at low energy dissipation rates.