Articles de revues : « DOWN STREEM LENGHT »

1

Shabtaie, S., et C. R. Bentley. « Ice-Thickness Map of the West Antarctic Ice Streams by Radar Sounding ». Annals of Glaciology 11 (1988) : 126–36. http://dx.doi.org/10.3189/s0260305500006443.

Texte intégral

Résumé :

Extensive radar ice-thickness sounding of ice streams A, B, and C, and the ridges between them, has been carried out. Closely spaced flight lines, as well as ties to numerous ground stations, have enabled us to compile a detailed ice-thickness map of the area. The map reveals a highly complex pattern of ice-thickness variations, which, because they are much larger than the surface relief, largely reflect the subglacial topography. Several cross-sectional profiles across the ice streams and ridges are shown, and a new configuration for Ice Stream A is presented.Ice Stream A is connected to Reedy Glacier and Horlick Ice Stream by subglacial troughs that converge down-stream. The single trough continues, at a depth of more than 1000 m below sea-level, beneath the entire length of the ice stream and adjacent part of Ross Ice Shelf. Ridge AB (part of which may be a remanent ice stream) overlies a deep bed with pronounced troughs at its headward end; the bed shoals rapidly down-stream to a height more than 500 m above the beds of the adjacent ice streams. Ice stream B1 overlies a subglacial trough that is deep inland and also shoals markedly toward the grounding line. Near its head. Ice Stream B2 is as much as 1000 m thinner than Ice Stream Bl, but then remains much more nearly constant in thickness along its length. Ridge BC is characterized by a smoother bed and less variation in bed depth than ridge AB. Ice Stream C, which is inactive, is particularly marked by uncorrelated maxima and minima in surface and bed topography.There are no distinct topographical steps that demarcate the transition from sheet to streaming flow at the head of the ice streams, and the ice streams are placed asymmetrically in some places with respect to their subglacial troughs. This may reflect a relative impermanence or transient behavior of the “Ross” ice streams.

Styles APA, Harvard, Vancouver, ISO, etc.

2

Shabtaie, S., et C. R. Bentley. « Ice-Thickness Map of the West Antarctic Ice Streams by Radar Sounding ». Annals of Glaciology 11 (1988) : 126–36. http://dx.doi.org/10.1017/s0260305500006443.

Texte intégral

Résumé :

Extensive radar ice-thickness sounding of ice streams A, B, and C, and the ridges between them, has been carried out. Closely spaced flight lines, as well as ties to numerous ground stations, have enabled us to compile a detailed ice-thickness map of the area. The map reveals a highly complex pattern of ice-thickness variations, which, because they are much larger than the surface relief, largely reflect the subglacial topography. Several cross-sectional profiles across the ice streams and ridges are shown, and a new configuration for Ice Stream A is presented. Ice Stream A is connected to Reedy Glacier and Horlick Ice Stream by subglacial troughs that converge down-stream. The single trough continues, at a depth of more than 1000 m below sea-level, beneath the entire length of the ice stream and adjacent part of Ross Ice Shelf. Ridge AB (part of which may be a remanent ice stream) overlies a deep bed with pronounced troughs at its headward end; the bed shoals rapidly down-stream to a height more than 500 m above the beds of the adjacent ice streams. Ice stream B1 overlies a subglacial trough that is deep inland and also shoals markedly toward the grounding line. Near its head. Ice Stream B2 is as much as 1000 m thinner than Ice Stream Bl, but then remains much more nearly constant in thickness along its length. Ridge BC is characterized by a smoother bed and less variation in bed depth than ridge AB. Ice Stream C, which is inactive, is particularly marked by uncorrelated maxima and minima in surface and bed topography. There are no distinct topographical steps that demarcate the transition from sheet to streaming flow at the head of the ice streams, and the ice streams are placed asymmetrically in some places with respect to their subglacial troughs. This may reflect a relative impermanence or transient behavior of the “Ross” ice streams.

Styles APA, Harvard, Vancouver, ISO, etc.

3

Perkin, Joshuah S., Keith B. Gido, Jeffrey A. Falke, Kurt D. Fausch, Harry Crockett, Eric R. Johnson et John Sanderson. « Groundwater declines are linked to changes in Great Plains stream fish assemblages ». Proceedings of the National Academy of Sciences 114, n^o 28 (26 juin 2017) : 7373–78. http://dx.doi.org/10.1073/pnas.1618936114.

Texte intégral

Résumé :

Groundwater pumping for agriculture is a major driver causing declines of global freshwater ecosystems, yet the ecological consequences for stream fish assemblages are rarely quantified. We combined retrospective (1950–2010) and prospective (2011–2060) modeling approaches within a multiscale framework to predict change in Great Plains stream fish assemblages associated with groundwater pumping from the United States High Plains Aquifer. We modeled the relationship between the length of stream receiving water from the High Plains Aquifer and the occurrence of fishes characteristic of small and large streams in the western Great Plains at a regional scale and for six subwatersheds nested within the region. Water development at the regional scale was associated with construction of 154 barriers that fragment stream habitats, increased depth to groundwater and loss of 558 km of stream, and transformation of fish assemblage structure from dominance by large-stream to small-stream fishes. Scaling down to subwatersheds revealed consistent transformations in fish assemblage structure among western subwatersheds with increasing depths to groundwater. Although transformations occurred in the absence of barriers, barriers along mainstem rivers isolate depauperate western fish assemblages from relatively intact eastern fish assemblages. Projections to 2060 indicate loss of an additional 286 km of stream across the region, as well as continued replacement of large-stream fishes by small-stream fishes where groundwater pumping has increased depth to groundwater. Our work illustrates the shrinking of streams and homogenization of Great Plains stream fish assemblages related to groundwater pumping, and we predict similar transformations worldwide where local and regional aquifer depletions occur.

Styles APA, Harvard, Vancouver, ISO, etc.

4

Gürkan, elin Ertürk. « Circumstantial evidence of effect of trout farming on length-weight relations of native fish species : Barbus oligolepis (Battalgil, 1941) and Squalius cii (Richardson, 1857) ». Journal of Aquaculture & ; Marine Biology 9, n^o 3 (2020) : 87–90. http://dx.doi.org/10.15406/jamb.2020.09.00282.

Texte intégral

Résumé :

This study was carried out to reveal how the aquaculture activities, located near the stream bed, effect the length-weight relations of native freshwater fish. Fish samples were collected on monthly for one year on the Kocabaş Stream (Çanakkale), a trout farm constructed next to stream. Fish specimens were collected from up and down sections of the trout farm and control station selected from another branch of the stream by electrofishing between August 2015-July 2016. The growth type sign; b value in length-weight relationship indicates that both species are in positive allometry at the down station and isometric growth at the upper station. Fish farm might affect the growth type of both species positively due to contribution of extra food resources originated from the farm via discharge of waste water of trout farm at the down section. However, this hypothesis should be tested by proper growth parameters of the fish species.

Styles APA, Harvard, Vancouver, ISO, etc.

5

Mua, Kang Edwin, et Kometa Sunday Shende. « The Response of Stream Competence to Topographic and Seasonal Variations in The Bamenda-Menchum Drainage Basin, North West Region, Cameroon ». Journal of Geography and Geology 11, n^o 2 (30 mai 2019) : 21. http://dx.doi.org/10.5539/jgg.v11n2p21.

Texte intégral

Résumé :

The flow direction of streams remains an establishing mechanism in understanding drainage basin function and stream competence. The ability of streams to erode, transport and deposit loads in fluvial geomorphology exert a benchmark precursor for slope dynamics given the differential geological outcrop of the Bamenda-Menchum basin. Such competence in stream network generates slope instability as materials continuously move down slope from the volcanic escarpment face of Bamenda highlands to the sedimentary lowland area of Lower Bafut-Menchum basin. This paper investigate the influence of stream flow direction and stream competence on slope dynamics and how such dynamism affects the development prospects of the drainage basin. Slope range was obtained from AVL/EBI.JHO measurement. Stream length, density and flow direction were gotten from GIS Arc 21. Stream depth, channel width, flow rate and sedimentation levels were measured. Gully depth on slopes and landslide angles were measured using 30m tape and a graduated pole. Questionnaires were used to collect information on the vulnerability of households to slope dynamics orchestrated by stream competence. Findings revealed that stream competence varies from the two geological basements and that the escarpment face respond to high flow gravity and hydraulic action contributing to rapid erosion and transportation of loads. The results equally showed that the Bamenda escarpment face that is linked to the crystalline rocks produce differential erosion and landslide. 76.7% of slope instability is explained by geological structure and seasonality effect in the basin while 23.3% of slope dynamics is explained by other variables not specified in the study. The lower basin remains liable to deposition of materials on river channels and flood plain. The accumulation of sand, stones and alluvial deposits are extracted and exploited for the development prospects of the basin. The study recommends channel and slope management by integrating slope development control policy in drainage basin management and development.

Styles APA, Harvard, Vancouver, ISO, etc.

6

Agarwal, N. K., et Gurnam Singh. « Documentation of fishes and physico-chemical characters of a stream Indrawati- a spring fed tributary of River Bhagirathi at Uttarkashi (Central Himalaya, Garhwal) India ». Environment Conservation Journal 13, n^o 3 (20 décembre 2012) : 117–24. http://dx.doi.org/10.36953/ecj.2012.130319.

Texte intégral

Résumé :

Most of the riverine resources in Garhwal region are mountainous and perennial either snow fed or spring originated. All these mountainous streams provide a good natural habitat for survival of hill stream fishes. Present communication deals with documentation of Ichthyofauna along with physico-chemical properties of a similar perennial spring fed stream Indrawati- a left side tributary of river Bhagirathi. It comes down from the hills of Baragari and through Joshiyara debouches into the river Bhagirathi at Uttarkashi (elevation 1128 masl). Major part of stream water is mainly abstracted for the irrigation purpose in the side lying fields all along its length. There is heterogeneity in the stream bed characteristics which results into the existence of varied fish fauna. Study reports eleven fish species from the stream belonging to two orders, three families and six genera. Fishes belonging to cyprinidae family are found more commonly than the cobitidae and sisoridae family. Fishery of the stream is of subsistence nature and is under intense pressure of anthropogenic activities. Fishes captured are of generally small sized. The physico-chemical characteristics recorded during the study period in the different seasons are water temperature (9.0-16.0 0C), velocity (.50 m-s-1.46 m-s), TDS (49 mg-l – 65 mg-l), pH (8.0 - 8.3), DO (7.3 mg-l – 10.5 mg-l), Free CO2 (0.10 mg-l – 0.30 mg-l) and turbidity (06-30 NTU).

Styles APA, Harvard, Vancouver, ISO, etc.

7

Gilbert, O. L., et V. J. Giavarini. « The Lichen Vegetation of Acid Watercourses in England ». Lichenologist 29, n^o 4 (juillet 1997) : 347–67. http://dx.doi.org/10.1006/lich.1997.0090.

Texte intégral

Résumé :

AbstractThe lichen vegetation of forty-five acid watercourses in England is described and related to ecological variables. The zonation scheme adopted for chalk and limestone streams that involves four overlapping bands of lichen vegetation related to length of submergence is also appropriate for this habitat. The flora involves around 90 species, a number of which are rarely recorded specialists. Evidence is presented that substratum chemistry is a more powerful ecological factor than water chemistry. An attempt has been made to relate the lichen flora to homogeneous stream segments from the headwaters down to the alluvial lowlands. An investigation into the effects of water quality showed that both suspended solids (silting) and eutrophication are highly deleterious to the lichen flora; the submerged and fluvial mesic zones are the first to be affected. The zonation across streams in England is compared with those reported from Germany and found to be closely similar.

Styles APA, Harvard, Vancouver, ISO, etc.

8

Amrender Singh, Bachhal, Vogstad Klaus, Lal Kolhe Mohan, Chougule Abhijit et Beyer Hans George. « Wake and Turbulence Analysis for Wind Turbine Layouts in an Island ». E3S Web of Conferences 64 (2018) : 06010. http://dx.doi.org/10.1051/e3sconf/20186406010.

Texte intégral

Résumé :

There is a big wind energy potential in supplying the power in an island and most of the islands are off-grid. Due to the limited area in island(s), there is need to find appropriate layout / location for wind turbines suited to the local wind conditions. In this paper, we have considered the wind resources data of an island in Trøndelag region of the Northern Norway, situated on the coastal line. The wind resources data of this island have been analysed for wake losses and turbulence on wind turbines for determining appropriate locations of wind turbines in this island. These analyses are very important for understanding the fatigue and mechanical stress on the wind turbines. In this work, semi empirical wake model has been used for wake losses analysis with wind speed and turbine spacings. The Jensen wake model used for the wake loss analysis due to its high degree of accuracy and the Frandsen model for characterizing the turbulent loading. The variations of the losses in the wind energy production of the down-wind turbine relative to the up-wind turbine and, the down-stream turbulence have been analysed for various turbine distances. The special emphasis has been taken for the case of wind turbine spacing, leading to the turbulence conditions for satisfying the IEC 61400-1 conditions to find the wind turbine layout in this island. The energy production of down-wind turbines has been decreased from 2 to 20% due to the lower wind speeds as they are located behind up-wind turbine, resulting in decreasing the overall energy production of the wind farm. Also, the higher wake losses have contributed to the effective turbulence, which has reduced the overall energy production from the wind farm. In this case study, the required distance for wind turbines have been changed to 6 rotor diameters for increasing the energy gain. From the results, it has been estimated that the marginal change in wake losses by moving the down-stream wind turbine by one rotor diameter distance has been in the range of 0.5 to 1% only and it is insignificant. In the full-length paper, the wake effects with wind speed variations and the wind turbine locations will be reported for reducing the wake losses on the down-stream wind turbine. The Frandsen model has been used for analysing turbulence loading on the down-stream wind turbine as per IEC 61400-1 criteria. In larger wind farms, the high turbulence from the up-stream wind turbines increases the fatigues on the turbines of the wind farm. In this work, we have used the effective turbulence criteria at a certain distance between up-stream and down-stream turbines for minimizing the fatigue load level. The sensitivity analysis on wake and turbulence analysis will be reported in the full-length paper. Results from this work will be useful for finding wind farm layouts in an island for utilizing effectively the wind energy resources and electrification using wind power plants.

Styles APA, Harvard, Vancouver, ISO, etc.

9

Jumper, G. W., W. C. Elrod et R. B. Rivir. « Film Cooling Effectiveness in High-Turbulence Flow ». Journal of Turbomachinery 113, n^o 3 (1 juillet 1991) : 479–83. http://dx.doi.org/10.1115/1.2927899.

Texte intégral

Résumé :

The mechanisms influencing film cooling effectiveness on a flat plate in high free-stream turbulence using a single row of 30 deg slant-hole injectors are examined. The primary area of focus is the area within 40 diameters downstream of injection. Of interest are blowing ratios for optimum film cooling effectiveness within 10 diameters downstream of injection, and the decay of film cooling effectiveness down the plate. Film cooling flow Reynolds numbers. Re, from 24,700 to 86,600 and free-stream turbulence intensities from 14 to 17 percent were examined. Changes in Reynolds number or free-stream turbulence broadened and increased the blowing ratios for optimum film cooling effectiveness. In comparison with tests conducted at 0.5 percent free-stream turbulence, higher free-stream turbulence causes a faster decay in film cooling effectiveness, or a reduction in the effective cooling length, and a reduction of the level of cooling effectiveness at the higher Reynolds numbers.

Styles APA, Harvard, Vancouver, ISO, etc.

10

Wang, D., K. Li et W. K. Teo. « Membrane vacuum stripping process for volatile organics removal from water using an asymmetric PVDF (polyvinylidene fluoride) hollow fiber membrane module ». Water Supply 1, n^o 5-6 (1 juin 2001) : 65–75. http://dx.doi.org/10.2166/ws.2001.0101.

Texte intégral

Résumé :

The vacuum membrane stripping process (VMS) for removing a VOC (trichloroethylene) from water was studied in a polyvinylidene fluoride (PVDF) hollow fiber membrane module containing 187 fibers with a length of 0.59 m. The porous PVDF asymmetric hollow fiber used was prepared by the wet phase inversion technique. The feed solution containing trichloroethylene (TCE) was passed through the lumen of the PVDF hollow fiber. Vapors of TCE and water were transported through the pores of the membrane into the shell side maintained at a sub-atmospheric pressure, and condensed in cold traps. The effects of down-stream pressure, solution temperature, feed concentration, and feed flow rate on TCE removal, TCE permeation flux, water permeation flux and TCE concentration of the permeated solution, as well as the mass transfer coefficient were investigated. The down stream pressure and solution temperature were identified as the major factors to control VOC removal and TCE concentration in the permeate stream. A small amount of the permeated solution with higher TCE concentration was obtained at the temperature of 50°C and pressure of 80 mmHg when about 90% TCE was removed from the water.

Styles APA, Harvard, Vancouver, ISO, etc.

11

Zheng, Yuan, R. S. Barlow et Jay P. Gore. « Spectral Radiation Properties of Partially Premixed Turbulent Flames ». Journal of Heat Transfer 125, n^o 6 (19 novembre 2003) : 1065–73. http://dx.doi.org/10.1115/1.1621902.

Texte intégral

Résumé :

Instantaneous spectral radiation intensities of three standard turbulent jet flames were measured and simulated in this study. In the simulation, a recently developed technique was adapted to reconstruct the local integral time and length scales in the flames. The simulated radiation properties, including mean, root mean square, probability density function, power spectral density and autocorrelation coefficient, were generally within 10% of the measurements. The macro time and length scales were found to increase with increasing distance from the axis and the radial averages of these scales were found to increase with down stream distance but decrease with Reynolds number.

Styles APA, Harvard, Vancouver, ISO, etc.

12

Antoniou, J., et G. Bergeles. « Development of the Reattached Flow Behind Surface-Mounted Two-Dimensional Prisms ». Journal of Fluids Engineering 110, n^o 2 (1 juin 1988) : 127–33. http://dx.doi.org/10.1115/1.3243524.

Texte intégral

Résumé :

Velocity and turbulence measurements are presented for the region after reattachment behind a two dimensional surface-mounted prism of varying length. The prism is mounted on the floor of an open circuit blow down wind tunnel and flow parameters for the developing boundary layer are deduced from the measurements; longitudinal integral time and length scales are estimated through autocorrelations. Reattchment on top of the prism, due to its increased length, affects the characteristics of the developing boundary layer; in this case the shear layer originating from the up-stream edge of the prism splits twice at reattachment points on top and behind the prism and the integral length scales of the turbulent eddies are found to be smaller due to the splitting.

Styles APA, Harvard, Vancouver, ISO, etc.

13

Clarke, T. S., et C. R. Bentley. « High-resolution radar on Ice Stream B2, Antarctica : measurements of electromagnetic wave speed in firn and strain history from buried crevasses ». Annals of Glaciology 20 (1994) : 153–59. http://dx.doi.org/10.3189/1994aog20-1-153-159.

Texte intégral

Résumé :

Two types of experiments were performed near Upstream B Camp on Ice Stream B2 using a high-resolution ground-penetrating radar system. In the first type of experiment, tracking a metal drill tip through the upper 85 m of the ice column indicated an approximately linear decrease of wave speed with depth down to 50 m, with a constant speed of 170 ± 4 m µs−1 below. We believe the (unexpected) linearity may have been caused by one or more buried crevasses. In the second experiment, a survey of a 250 km2 grid showed a population of buried crevasses at about 30 m depth that have an estimated burial age of 210 ± 25 years, which is taken to indicate that this ice has been exhibiting streaming behavior for at least that length of time. One 3 km segment along the edge of the survey area nearest the center of the stream showed virtually flat, undisrupted stratigraphy down to the maximum depth of our measurements. The fact that this ice was accelerated from near-zero speed to its present 440 m a−1 without cracking or folding suggests that this ice may have been incorporated into the ice stream as a solid block.

Styles APA, Harvard, Vancouver, ISO, etc.

14

Clarke, T. S., et C. R. Bentley. « High-resolution radar on Ice Stream B2, Antarctica : measurements of electromagnetic wave speed in firn and strain history from buried crevasses ». Annals of Glaciology 20 (1994) : 153–59. http://dx.doi.org/10.1017/s0260305500016384.

Texte intégral

Résumé :

Two types of experiments were performed near Upstream B Camp on Ice Stream B2 using a high-resolution ground-penetrating radar system. In the first type of experiment, tracking a metal drill tip through the upper 85 m of the ice column indicated an approximately linear decrease of wave speed with depth down to 50 m, with a constant speed of 170 ± 4 m µs−1 below. We believe the (unexpected) linearity may have been caused by one or more buried crevasses. In the second experiment, a survey of a 250 km2 grid showed a population of buried crevasses at about 30 m depth that have an estimated burial age of 210 ± 25 years, which is taken to indicate that this ice has been exhibiting streaming behavior for at least that length of time. One 3 km segment along the edge of the survey area nearest the center of the stream showed virtually flat, undisrupted stratigraphy down to the maximum depth of our measurements. The fact that this ice was accelerated from near-zero speed to its present 440 m a−1 without cracking or folding suggests that this ice may have been incorporated into the ice stream as a solid block.

Styles APA, Harvard, Vancouver, ISO, etc.

15

Schoenwolf, Gary C. « Cell movements driving neuruiation in avian embryos ». Development 113, Supplement_2 (1 avril 1991) : 157–68. http://dx.doi.org/10.1242/dev.113.supplement_2.157.

Texte intégral

Résumé :

Neuruiation, formation of the neural tube, a crucial event of early embryogenesis, is believed to be driven by the coordination of a number of diverse morphogenetic cell behaviors. Such behaviors include changes in cell number (division, death), cell shape and size (wedging, palisading and spreading), cell position (rearrangement or intercalation) and cell–cell and cell–matrix associations (including inductive interactions). The focus of this essay is on epiblast cell movements and their role in shaping and bending of the neural plate. Neuruiation is a multifactorial process requiring both intrinsic (within the neural plate) and extrinsic (outside the neural plate) forces. The origin and movements of three populations of epiblast cells have been studied in avian embryos by constructing quail/chick transplantation chimeras and by labeling cells in situ with identifiable, heritable markers. MHP (median hinge-point neurepithelial) cells originate principally from a midline epiblast area rostral to and overlapping Hensen's node. In addition, a few caudal MHP cells originate from paranodal epiblast areas. MHP cells stream down the length of the midline neuraxis in the wake of the regressing Hensen's node. This streaming occurs as a result of cell division (presumably oriented so that daughter cells are placed into the longitudinal plane rather than into the transverse plane) and rearrangement (intercalation), resulting in a narrowing of the width of the MHP region with a concomitant increase in its length. L (lateral neurepithelial) cells originate from paired epiblast areas flanking the rostral portion of the primitive streak, and they stream down the length of the lateral neuraxis concomitant with regression of Hensen's node. They do so both by oriented cell division and by intercalation. SE (surface epithelial) cells originate from the epiblast of the area pellucida, as far lateral as near the area pellucida area opaca border. From this area they stream medially, toward the forming lateral margins of the neural plate. Collectively, movements of the three populations of epiblast cells generate the convergent-extension movements characteristic of the epiblast during neuruiation. Heterotopic grafting has been used to assess the relationship between cell position and cell fate and to determine whether transplanted heterotopic cells can adopt the behaviors typical of the new site. For example, SE cells can replace L cells, changing their fate and adopting L-cell behavior. Similarly, prospective MHP and L cells both can change their fate and adopt the behavior of SE cells. L cells, when placed into prospective MHP-cell territory, move out of this territory by intermingling with adjacent host L cells. Likewise, prospective MHP cells placed into L-cell territory, move out of this territory by intermingling with host MHP cells. Collectively, these results suggest that cell fate is determined principally by the ultimate position of cells, and that adjacent, different cell populations are restricted from intermingling with one another. How positional information is specified, the nature of restriction of intermingling and the guidance cues used for cell navigation during streaming remain to be elucidated.

Styles APA, Harvard, Vancouver, ISO, etc.

16

Cai, Shixuan, Hongyan Shi, Guoqian Li, Qilu Xue, Lei Zhao, Fu Wang et Bo Hu. « 3D-Printed Concentration-Controlled Microfluidic Chip with Diffusion Mixing Pattern for the Synthesis of Alginate Drug Delivery Microgels ». Nanomaterials 9, n^o 10 (12 octobre 2019) : 1451. http://dx.doi.org/10.3390/nano9101451.

Texte intégral

Résumé :

Alginate as a good drug delivery vehicle has excellent biocompatibility and biodegradability. In the ionic gelation process between alginate and Ca2+, the violent reaction is the absence of a well-controlled strategy in the synthesizing calcium alginate (CaA) microgels. In this study, a concentration-controlled microfluidic chip with central buffer flow was designed and 3D-printed to well-control the synthesis process of CaA microgels by the diffusion mixing pattern. The diffusion mixing pattern in the microfluidic chip can slow down the ionic gelation process in the central stream. The particle size can be influenced by channel length and flow rate ratio, which can be regulated to 448 nm in length and 235 nm in diameter. The delivery ratio of Doxorubicin (Dox) in CaA microgels are up to 90% based on the central stream strategy. CaA@Dox microgels with pH-dependent release property significantly enhances the cell killing rate against human breast cancer cells (MCF-7). The diffusion mixing pattern gives rise to well-controlled synthesis of CaA microgels, serving as a continuous and controllable production process for advanced drug delivery systems.

Styles APA, Harvard, Vancouver, ISO, etc.

17

Hayes, Sean A., Morgan H. Bond, Chad V. Hanson, Andrew W. Jones, Arnold J. Ammann, Jeffrey A. Harding, Alison L. Collins, Jeffrey Perez et R. Bruce MacFarlane. « Down, up, down and “smolting” twice ? Seasonal movement patterns by juvenile steelhead (Oncorhynchus mykiss) in a coastal watershed with a bar closing estuary ». Canadian Journal of Fisheries and Aquatic Sciences 68, n^o 8 (août 2011) : 1341–50. http://dx.doi.org/10.1139/f2011-062.

Texte intégral

Résumé :

We investigated emigration behavior, habitat use, and Na+,K+-ATPase activity levels of juvenile steelhead trout (sea-run rainbow trout; Oncorhynchus mykiss ) in Scott Creek, a small coastal watershed with a seasonally closed estuary in central California, USA. Migratory fish moved downstream in the spring with elevated Na+,K+-ATPase activity levels. Larger fish (>150 mm) moved downstream during February and March, leaving the stream, whereas fish moving between April and June were typically smaller and tended to recruit to the estuary. The Na+,K+-ATPase activity levels of estuarine fish varied during the summer as a function of salinity and temperature, but overall levels declined from peak spring values. Many summer recruits were observed retreating upstream into the watershed when estuarine water quality declined in the fall. Rather than entering the ocean when winter storms reconnected the estuary with the ocean in early winter, many migrated downstream several months later during subsequent springs. The largest smolts observed (>190 mm fork length (LF)) were primarily those that had reared in the estuary the previous summer. Smolts were observed making a single migration from the upper watershed, but they were smaller (~120–190 mm LF) with potentially reduced marine survival. In summary, we observed fish moving between freshwater and estuarine habitats seasonally and adjusting their osmoregulatory physiology as needed.

Styles APA, Harvard, Vancouver, ISO, etc.

18

Ikhsan, Muhammad, Meylis Safriani, Cut Suciatina Silvia et Refvina Dari. « Prediction of Land Erosion Events in the Down Stream Kreung Meureubo Watershed West Aceh District ». International Journal of Engineering, Science and Information Technology 1, n^o 4 (3 novembre 2021) : 70–76. http://dx.doi.org/10.52088/ijesty.v1i4.173.

Texte intégral

Résumé :

This study aims to predict the occurrence of erosion in the downstream Krueng Meureubo watershed, West Aceh Regency. Erosion is the loss of topsoil due to rain splash which is analyzed as a factor of rain erosivity, but the occurrence of erosion is not necessarily calculated by the occurrence of rain alone, but many other factors, such as soil erodibility, slope and length of land, land cover and the presence or absence of land conservation efforts. the. The Krueng Meurebo watershed shows a large sediment transport, with an indication that the river is getting shallower caused by sediment deposition at the riverbed, this sediment comes from sediment carried through the process of soil erosion. The method used in analyzing the occurrence of soil erosion in this study is the USLE method and uses a Geographic Information System (GIS). The results obtained are the distribution of erosion rate values in 228 polygons, with the largest erosion rate value occurring in polygon 1 with an erosion rate of 8495.308 tons/ha/year. The smallest erosion rate occurs in polygons 30, 34, 35, 179, and 180, with an erosion rate of 0 meaning that there is no land erosion event, which occurs in organosol and glehumus and regosol soil types, land cover is settlements and water bodies. It is concluded that the occurrence of erosion in a land is very dependent on the type of soil and the type of land cover. It is recommended for land with large erosion events to take serious land conservation actions so that erosion events can be minimized and do not occur continuously which of course can cause the watershed to become critical. Conservation efforts can be carried out in various ways, one of which is by vegetative means using plants that can reduce the rate of soil erosion.

Styles APA, Harvard, Vancouver, ISO, etc.

19

Plewan, Thorsten, Ralph Weidner, Simon B. Eickhoff et Gereon R. Fink. « Ventral and Dorsal Stream Interactions during the Perception of the Müller-Lyer Illusion : Evidence Derived from fMRI and Dynamic Causal Modeling ». Journal of Cognitive Neuroscience 24, n^o 10 (octobre 2012) : 2015–29. http://dx.doi.org/10.1162/jocn_a_00258.

Texte intégral

Résumé :

The human visual system converts identically sized retinal stimuli into different-sized perceptions. For instance, the Müller-Lyer illusion alters the perceived length of a line via arrows attached to its end. The strength of this illusion can be expressed as the difference between physical and perceived line length. Accordingly, illusion strength reflects how strong a representation is transformed along its way from a retinal image up to a conscious percept. In this study, we investigated changes of effective connectivity between brain areas supporting these transformation processes to further elucidate the neural underpinnings of optical illusions. The strength of the Müller-Lyer illusion was parametrically modulated while participants performed either a spatial or a luminance task. Lateral occipital cortex and right superior parietal cortex were found to be associated with illusion strength. Dynamic causal modeling was employed to investigate putative interactions between ventral and dorsal visual streams. Bayesian model selection indicated that a model that involved bidirectional connections between dorsal and ventral stream areas most accurately accounted for the underlying network dynamics. Connections within this network were partially modulated by illusion strength. The data further suggest that the two areas subserve differential roles: Whereas lateral occipital cortex seems to be directly related to size transformation processes, activation in right superior parietal cortex may reflect subsequent levels of processing, including task-related supervisory functions. Furthermore, the data demonstrate that the observer's top–down settings modulate the interactions between lateral occipital and superior parietal regions and thereby influence the effect of illusion strength.

Styles APA, Harvard, Vancouver, ISO, etc.

20

Erf, Gisela F., Becky Lockhart, Olivia T. Bowen, Kristin Bateman et ReGina C. Finley. « Using the chicken feather as a window into cell-mediated tissue responses (99.12) ». Journal of Immunology 178, n^o 1_Supplement (1 avril 2007) : S196. http://dx.doi.org/10.4049/jimmunol.178.supp.99.12.

Texte intégral

Résumé :

Abstract Cell-mediated immune (CMI) responses are typically tested by injecting the skin and monitoring the skin reaction. In chickens, various integumental tissues are suitable to measure the CMI reaction, including the wattle, wing web, toe web and foot pad. Using the Smyth line chicken vitiligo model to study the spontaneous autoimmune destruction of pigment cells in feathers, we have found that one growing feather-tip (3 mm diameter by 8 mm length) yields generous amounts of material for down-stream gene-expression-, histological-, and cell population-analyses. Moreover, growing feathers are easily accessible for microinjection, removal of a feather is minimally invasive, and feathers are very suitable for repeated sampling during an immune response. To investigate the potential of the feather as a window into tissue immune responses, time-course studies were conducted comparing leukocyte infiltration in wattles, wing webs and growing feathers in response to injection of vehicle, PHA or LPS, and during the recall response to Mycobacterium butyricum. Based on histology and immunohistochemical staining, leukocyte infiltration profiles over a 72 hour period were similar in all three tissues tested. Hence, the feather provides excellent opportunity to monitor and assess CMI responses and immunomodulation strategies in situ and via down-stream analyses. Support: Arkansas Experiment Station Animal Health Grant

Styles APA, Harvard, Vancouver, ISO, etc.

21

Källo, Kristi, Henrik Baktoft, Niels Jepsen et Kim Aarestrup. « Great cormorant (Phalacrocorax carbo sinensis) predation on juvenile down-migrating trout (Salmo trutta) in a lowland stream ». ICES Journal of Marine Science 77, n^o 2 (4 décembre 2019) : 721–29. http://dx.doi.org/10.1093/icesjms/fsz227.

Texte intégral

Résumé :

Abstract Since in 1980s, the number of great cormorants (Phalacrocorax carbo sinensis) has increased all over its European distribution area. This has led to conflicts between bird conservation and fisheries. Mariager fjord in Denmark is an important feeding and transition area for a large population of migrating seatrout (Salmo trutta), but it also provides resting and breeding places for cormorants. Thus, juvenile anadromous salmonids migrating from the river to the sea may be exposed to high predation risk during a critical and vulnerable time in their development. A total of 31 123 down-migrating wild seatrout were tagged with Passive Integrated Transponder (PIT) tags in 2008, 2009, 2015, and 2016 in river Villestrup, the main tributary flowing into Mariager fjord. Tagged fish were measured and grouped by their developmental stage as parr, pre-smolt, or smolt. To quantify cormorant predation, nearby cormorant colonies and roosting sites were repeatedly scanned for PIT tags with a manual antenna to record tags from predated fish. Minimum predation rate was 27% but varied among years. Body length of the fish and predation risk were negatively correlated and the latter was dependent on the group of the fish. This study demonstrates a potential negative effect of predation by great cormorants on an important population of wild trout.

Styles APA, Harvard, Vancouver, ISO, etc.

22

OVCHINNIKOV, VICTOR, MEELAN M. CHOUDHARI et UGO PIOMELLI. « Numerical simulations of boundary-layer bypass transition due to high-amplitude free-stream turbulence ». Journal of Fluid Mechanics 613 (1 octobre 2008) : 135–69. http://dx.doi.org/10.1017/s0022112008003017.

Texte intégral

Résumé :

Direct numerical simulations (DNS) of bypass transition due to high-amplitude free-stream turbulence (FST) are carried out for a flat-plate boundary layer. The computational domain begins upstream of the plate leading edge and extends into the fully turbulent region. Thus, there is noad hoctreatment to account for the initial ingestion of FST into the laminar boundary layer. We study the effects of both the FST length scale and the disturbance behaviour near the plate leading edge on the details of bypass transition farther downstream. In one set of simulations, the FST parameters are chosen to match the ERCOFTAC benchmark case T3B. The inferred FST integral length scaleL11is significantly larger (RL=UL11/ν = 6580) than that employed in previous simulations of bypass transition (RL≃ 1000). An additional set of simulations was performed atRL= 1081 to compare the transition behaviour in the T3B case with that of a smaller value of FST length scale. The FST length scale is found to have a profound impact on the mechanism of transition. While streamwise streaks (Klebanoff modes) are observed at both values of the FST length scale, they appear to have clear dynamical significance only at the smaller value ofRL, where transition is concomitant with streak breakdown. For the T3B case, turbulent spots form upstream of the region where streaks could be detected. Spot precursors are traced to quasi-periodic spanwise structures, first observed as short wavepackets in the wall-normal velocity component inside the boundary layer. These structures are reoriented to become horseshoe vortices, which break down into young turbulent spots. Two of the four spots examined for this case had a downstream-pointing shape, similar to those found in experimental studies of transitional boundary layers. Additionally, our simulations indicate the importance of leading-edge receptivity for the onset of transition. Specifically, higher fluctuations of the vertical velocity at the leading edge of the plate result in higher levels of streamwise Reynolds stress inside the developing boundary layer, facilitating breakdown to turbulence.

Styles APA, Harvard, Vancouver, ISO, etc.

23

Asaduzzaman, M., et Md Moshiur Rahman. « Impacts of Tipaimukh Dam on the Down-stream Region in Bangladesh : A Study on Probable EIA ». Journal of Science Foundation 13, n^o 1 (22 mai 2016) : 3–10. http://dx.doi.org/10.3329/jsf.v13i1.27827.

Texte intégral

Résumé :

Amidst mounting protests both at home and in lower riparian Bangladesh, India is going ahead with the plan to construct its largest and most controversial 1500 mw hydroelectric dam project on the river Barak at Tipaimukh in the Indian state Manipur. In the process, however, little regard is being paid to the short and long-term consequences on the ecosystem, biodiversity or the local people in the rivers watershed and drainage of both upper and low reparian countries. This 390 m length and 162.8 m. high earthen-rock filled dam also has the potential to be one of the most destructive. In India too, people will have to suffer a lot for this mega project. The total area required for construction including submergence area is 30860 ha of which 20797 ha is forest land, 1195 ha is village land, 6160 ha is horticultural land, and 2525 ha is agricultural land. Cconstruction of the massive dam and regulate water flow of the river Barak will have long adverse effects on the river system of Surma and Kushiyara in the north-eastern region of Bangladesh which will obviously have negative impacts on ecology, environment, agriculture, bio-diversity, fisheries, socio-economy of Bangladesh. To assess the loss of Tipaimukh dam on downstream Bangladesh, an Eivironmental Impact Assessment (EIA) has been conducted based on probable affect parametes. Present study intends to depict Tipaimukh dam construction post scenerio in Bangladesh thru assessing probable loss and damage of the Tipaimukh dam construction. The most effective Batelle method of EIA has been applied in this study. It is found -5 scale severity impact will be imposed if the proposed dam is being construct after assessing values of each parameter. Journal of Science Foundation 2015;13(1):3-10DOI: http://dx.doi.org/10.3329/jsf.v13i1.27827

Styles APA, Harvard, Vancouver, ISO, etc.

24

Echelmeyer, Keith A., Barclay Kamb et Barclay Kamb. « Stress-Gradient Coupling in Glacier Flow : II. Longitudinal Averaging in the Flow Response to Small Perturbations in Ice Thickness and Surface Slope ». Journal of Glaciology 32, n^o 111 (1986) : 285–98. http://dx.doi.org/10.3189/s0022143000015616.

Texte intégral

Résumé :

AbstractAs a result of the coupling effects of longitudinal stress gradients, the perturbations ∆u in glacier-flow velocity that result from longitudinally varying perturbations in ice thickness ∆h and surface slope ∆α are determined by a weighted longitudinal average of ϕh∆h and ϕα∆α, where ϕh and ϕα are “influence coefficients” that control the size of the contributions made by local ∆h and ∆α to the flow increment in the longitudinal average. The values of ϕh and ϕα depend on effects of longitudinal stress and velocity gradients in the unperturbed datum state. If the datum state is an inclined slab in simple-shear flow, the longitudinal averaging solution for the flow perturbation is essentially that obtained previously (Kamb and Echelmeyer, 1985) with equivalent values for the longitudinal coupling length l and with ϕh = n + 1 and ϕα + n, where n is the flow-law exponent. Calculation of the influence coefficients from flow data for Blue Glacier, Washington, indicates that in practice ϕα differs little from n, whereas ϕh can differ considerably from n + 1. The weighting function in the longitudinal averaging integral, which is the Green’s function for the longitudinal coupling equation for flow perturbations, can be approximated by an asymmetric exponential, whose asymmetry depends on two “asymmetry parameters” μ and σ, where μ is the longitudinal gradient of ℓ(= dℓ/dx). The asymmetric exponential has different coupling lengths ℓ+ and ℓ− for the influences from up-stream and from down-stream on a given point of observation. If σ/μ is in the range 1.5–2.2, as expected for flow perturbations in glaciers or ice sheets in which the ice flux is not a strongly varying function of the longitudinal coordinate x, then, when dℓ/dx > 0, the down-stream coupling length ℓ+ is longer than the up-stream coupling length ℓ−, and vice versa when dℓ/dx < 0. Flow-, thickness- and slope-perturbation data for Blue Glacier, obtained by comparing the glacier in 1957–58 and 1977–78, require longitudinal averaging for reasonable interpretation. Analyzed on the basis of the longitudinal coupling theory, with 4ℓ + 1.6 km up-stream, decreasing toward the terminus, the data indicate n to be about 2.5, if interpreted on the basis of a response factor Ѱ + 0.85 derived theoretically by Echelmeyer (unpublished) for the flow response to thickness perturbations in a channel of finite width. The data contain an apparent indication that the flow response to slope perturbations is distinctly smaller, in relation to the response to thickness perturbations, than is expected on a theoretical basis (i.e. ϕα/ ϕh + (n/n + 1) for a slab). This probably indicates that the effective ℓ is longer than can be tested directly with the available data set owing to its limited range in x.

Styles APA, Harvard, Vancouver, ISO, etc.

25

Mustaffa, Z., N. Rajaratnam et David Z. Zhu. « An experimental study of flow into orifices and grating inlets on streets ». Canadian Journal of Civil Engineering 33, n^o 7 (1 juillet 2006) : 837–45. http://dx.doi.org/10.1139/l06-031.

Texte intégral

Résumé :

Findings are described from a laboratory-scale model of flow through orifices on manhole covers and through three types of grating inlets used by the City of Edmonton. The results demonstrated that the flow through these orifices can be calculated using an orifice equation with a coefficient of discharge equal to 0.616 in a ponding situation but decreasing with an increase in the Froude number of the flow. The roughness of the manhole cover was found to slow down this reduction. For the three gratings, the inflow can be calculated with an orifice type of equation when the gratings are submerged. The discharge coefficient in this equation is approximately constant for two of the gratings and decreases somewhat with an increase in the Froude number of the flow for the third grating if the specific energy of the approaching flow is used as the length scale.Key words: street inlet, street hydraulics, grating inlet, orifice flows.

Styles APA, Harvard, Vancouver, ISO, etc.

26

Echelmeyer, Keith A., et Barclay Kamb. « Stress-Gradient Coupling in Glacier Flow : II. Longitudinal Averaging in the Flow Response to Small Perturbations in Ice Thickness and Surface Slope ». Journal of Glaciology 32, n^o 111 (1986) : 285–98. http://dx.doi.org/10.1017/s0022143000015616.

Texte intégral

Résumé :

AbstractAs a result of the coupling effects of longitudinal stress gradients, the perturbations ∆uin glacier-flow velocity that result from longitudinally varying perturbations in ice thickness ∆hand surface slope ∆α are determined by a weighted longitudinal average ofϕh∆handϕα∆α, whereϕhandϕαare “influence coefficients” that control the size of the contributions made by local ∆hand ∆α to the flow increment in the longitudinal average. The values ofϕhandϕα depend on effects of longitudinal stress and velocity gradients in the unperturbed datum state. If the datum state is an inclined slab in simple-shear flow, the longitudinal averaging solution for the flow perturbation is essentially that obtained previously (Kamb and Echelmeyer, 1985) with equivalent values for the longitudinal coupling lengthland withϕh=n+ 1 andϕα+n, wherenis the flow-law exponent. Calculation of the influence coefficients from flow data for Blue Glacier, Washington, indicates that in practiceϕα differs little fromn, whereasϕhcan differ considerably fromn+ 1. The weighting function in the longitudinal averaging integral, which is the Green’s function for the longitudinal coupling equation for flow perturbations, can be approximated by an asymmetric exponential, whose asymmetry depends on two “asymmetry parameters”μand σ, whereμis the longitudinal gradient of ℓ(= dℓ/dx). The asymmetric exponential has different coupling lengths ℓ+and ℓ−for the influences from up-stream and from down-stream on a given point of observation. If σ/μis in the range 1.5–2.2, as expected for flow perturbations in glaciers or ice sheets in which the ice flux is not a strongly varying function of the longitudinal coordinatex, then, when dℓ/dx> 0, the down-stream coupling length ℓ+is longer than the up-stream coupling length ℓ−, and vice versa when dℓ/dx< 0. Flow-, thickness- and slope-perturbation data for Blue Glacier, obtained by comparing the glacier in 1957–58 and 1977–78, require longitudinal averaging for reasonable interpretation. Analyzed on the basis of the longitudinal coupling theory, with 4ℓ + 1.6 km up-stream, decreasing toward the terminus, the data indicatento be about 2.5, if interpreted on the basis of aresponse factor Ѱ+ 0.85 derived theoretically by Echelmeyer (unpublished) for the flow response to thickness perturbations in a channel of finite width. The data contain an apparent indication that the flow response to slope perturbations is distinctly smaller, in relation to the response to thickness perturbations, than is expected on a theoretical basis (i.e.ϕα/ ϕh+ (n/n+ 1) for a slab). This probably indicates that the effective ℓ is longer than can be tested directly with the available data set owing to its limited range inx.

Styles APA, Harvard, Vancouver, ISO, etc.

27

Sigalos, G., V. Loukaidi, S. Dasaklis et A. Alexouli-Livaditi. « ASSESSMENT OF THE QUANTITY OF THE MATERIAL TRANSPORTED DOWNSTREAM OF SPERCHIOS RIVER, CENTRAL GREECE ». Bulletin of the Geological Society of Greece 43, n^o 2 (23 janvier 2017) : 737. http://dx.doi.org/10.12681/bgsg.11239.

Texte intégral

Résumé :

It is well known that streams are an integral part of a natural ecosystem. The Sperchios valley is crossed by a large number of seasonal or permanent flow streams and rivers, out of which the Sperchios river can be distinguished, not only for its length but also for the area surrounded by the boundaries of its drainage system. The present study is aimed to estimate the quantity of the transported material at the mouth of Sperchios River. For this purpose we applied the Revised Universal Soil Loss Equation (RUSLE) model to the Sperchios drainage network in a Geographical Information Systems (GIS) environment. We estimated that approximately 2,308,000 tons per year are flooded mainly down the Sperchios drainage system, supporting the Malian delta.

Styles APA, Harvard, Vancouver, ISO, etc.

28

Maison, Alice, Cédric Flageul, Bertrand Carissimo, Yunyi Wang, Andrée Tuzet et Karine Sartelet. « Parameterizing the aerodynamic effect of trees in street canyons for the street network model MUNICH using the CFD model Code_Saturne ». Atmospheric Chemistry and Physics 22, n^o 14 (20 juillet 2022) : 9369–88. http://dx.doi.org/10.5194/acp-22-9369-2022.

Texte intégral

Résumé :

Abstract. Trees provide many ecosystem services in cities such as urban heat island reduction, water runoff limitation, and carbon storage. However, the presence of trees in street canyons reduces the wind velocity in the street and limits pollutant dispersion. Thus, to obtain accurate simulations of pollutant concentrations, the aerodynamic effect of trees should be taken into account in air quality models at the street level. The Model of Urban Network of Intersecting Canyons and Highways (MUNICH) simulates the pollutant concentrations in a street network, considering dispersion and physico-chemical processes. It can be coupled to a regional-scale chemical transport model to simulate air quality over districts or cities. The aerodynamic effect of the tree crown is parameterized here through its impact on the average wind velocity in the street direction and the vertical transfer coefficient associated with the dispersion of a tracer. The parameterization is built using local-scale simulations performed with the computational fluid dynamics (CFDs) code Code_Saturne. The two-dimensional CFD simulations in an infinite street canyon are used to quantify the effect of trees, depending on the tree characteristics (leaf area index, crown volume fraction, and tree height to street height ratio) using a drag porosity approach. The tree crown slows down the flow and produces turbulent kinetic energy in the street, thus impacting the tracer dispersion. This effect increases with the leaf area index and the crown volume fraction of the trees, and the average horizontal velocity in the street is reduced by up to 68 %, while the vertical transfer coefficient by up to 23 % in the simulations performed here. A parameterization of these effects on horizontal and vertical transfers for the street model MUNICH is proposed. Existing parameterizations in MUNICH are modified based on Code_Saturne simulations to account for both building and tree effects on vertical and horizontal transfers. The parameterization is built to obtain similar tree effects (quantified by a relative deviation between the cases without and with trees) between Code_Saturne and MUNICH. The vertical wind profile and mixing length depend on leaf area index, crown radius, and tree height to street height ratio. The interaction between the trees and the street aspect ratio is also considered.

Styles APA, Harvard, Vancouver, ISO, etc.

29

Lua, A. C., et R. F. Boucher. « Magnetic Filtration of Fine Particles from Gas Streams ». Proceedings of the Institution of Mechanical Engineers, Part E : Journal of Process Mechanical Engineering 207, n^o 2 (août 1993) : 109–22. http://dx.doi.org/10.1243/pime_proc_1993_207_214_02.

Texte intégral

Résumé :

Dust particles from the basic oxygen furnace steelmaking process were removed from air streams using a laboratory high-gradient magnetic filter. Particle sizes and number concentrations were determined by an optical particle spectrometer and were found to be largely in the submicrometre range. Dust loadability increased greatly when a magnetic field was applied and showed no deterioration in filter performance, even though the matrix had captured 10 times its own volume of dust. Particle penetrations of 1 per cent and less were achieved for submicrometre particles down to an optically measurable 0.24 μm diameter. Varying only one parameter at a time has isolated the individual effects of filter length, magnetic field, matrix packing fraction, gas velocity and wire size and aspect ratio. The dimensionless groups in an idealized single-wire model for high-gradient magnetic filtration are not adequate for a real filter. Other dimensionless parameters, viz. average dimensionless wire separation and cumulative dimensionless wire blockage, arise and are found to be important.

Styles APA, Harvard, Vancouver, ISO, etc.

30

MARCOU, C. « SPENDING BEACHES FOR A WAVE CANAL ». Coastal Engineering Proceedings 1, n^o 5 (29 janvier 2011) : 20. http://dx.doi.org/10.9753/icce.v5.20.

Texte intégral

Résumé :

The principal obstacle to the production of a pure wave in a laboratory-wave canal of short length is the presence of a wave reflected from the down-stream extremity of the canal. Different artifices are used to reduce the value of the coefficient of reflexion. It is of important to see that these setups occupy as small a length of the canal as possible. We have undertaken the study of a simple mechanism, easily constructed, whose parameters can be defined rigourously and whose action is consequently consistent. The different parameters can be varied systematically so that the values which give a minimum coefficient of reflection for • given Incident wave can be determined. The mechanism consists of a spending beach made of a thin aluminium plate ; the plate has the same width as the wave-canal, its lines of greatest slope being parallel to the plane of symmetry of the canal.

Styles APA, Harvard, Vancouver, ISO, etc.

31

Tereshchenko, Dmitry P., Egor A. Peganov, Sergei N. Smetanin, Alexander G. Papashvili, Evgeny V. Shashkov, Lyudmila I. Ivleva, Elizaveta E. Dunaeva, Irina S. Voronina et Milan Frank. « Measurement of Multi-Stokes Ultrashort Pulse Shapes of Synchronously Pumped Stimulated Raman Scattering on Combined Vibrational Modes in a BaWO4 Crystal ». Crystals 12, n^o 4 (2 avril 2022) : 495. http://dx.doi.org/10.3390/cryst12040495.

Texte intégral

Résumé :

Multi-Stokes ultrashort pulse shapes and their relative positions of synchronously pumped stimulated Raman scattering (SRS) on combined primary and secondary vibrational modes in a BaWO4 crystal are investigated. An original method of its simultaneous measurement with the help of a streak camera has been developed. The structure of SRS pulses at the pulse shortening effect down to the pulse duration, close to the dephasing time of the secondary Raman mode of the BaWO4 crystal, is registered and analyzed for the detuning of the Raman laser cavity length.

Styles APA, Harvard, Vancouver, ISO, etc.

32

Dotto, A., D. Barsi, D. Lengani, D. Simoni et F. Satta. « Effect of free-stream turbulence properties on different transition routes for a zero-pressure gradient boundary layer ». Physics of Fluids 34, n^o 5 (mai 2022) : 054102. http://dx.doi.org/10.1063/5.0086343.

Texte intégral

Résumé :

The natural and bypass routes to boundary-layer transition to turbulence are traditionally investigated independently in fluid mechanics applications. Nevertheless, in certain flow regimes both mechanisms could coexist and interact. In this work, large-eddy simulations (LES) were performed for a zero-pressure gradient boundary layer developing over a flat plate to investigate the transition mechanism for variable free-stream turbulent properties. Four different combinations of turbulence intensity and integral length scale were analyzed, and two main transition mechanisms were observed. High free-stream turbulence intensity instigates pure bypass transition through the amplification of a continuous Orr–Sommerfeld (O–S) mode that breaks down after secondary instability. Instead, at low free-stream turbulence intensity, discrete and continuous O–S modes interact and are both involved in the transition process. Visual inspection of the LES snapshots provides a detailed insight in Tollmien–Schlichting (TS) waves–streaks mutual interaction and clearly identifies two main mechanisms involved in turbulence breakdown. On one hand, TS waves trigger varicose instability of streaky structures. On the other hand, streaks cause secondary instability of TS waves with emerging Λ-structure formation. Then, dynamic mode decomposition (DMD) is applied to extract the main stability properties for both types of transition route and to highlight coherent structure dynamics, which is hardly observable in the literature. Specifically, for low-medium free-stream turbulence levels, DMD extracts unstable modes clearly related to streaks–TS waves interaction and leading to the formation of Λ structures. Therefore, the streaks–TS waves interaction is proved to be destabilizing and to trigger secondary instability leading to turbulence breakdown.

Styles APA, Harvard, Vancouver, ISO, etc.

33

Vlach, P., J. Dušek, M. Švátora et P. Moravec. « Growth analysis of chub, Leuciscus cephalus (L.), and dace, Leuciscus leuciscus (L.), in the Úpoř stream using growth data of recaptured marked fish ». Czech Journal of Animal Science 50, No. 7 (10 décembre 2011) : 329–39. http://dx.doi.org/10.17221/4174-cjas.

Texte intégral

Résumé :

The length growth of chub and dace was observed. The scale method was used as well as data gained from recaptured individuals which were marked with visible elastomer tags and platinum wire tags with a coloured code placed under the first bony ray of the dorsal fin. The length-weight relationship for chub could be explained by the equation w = 0.00001.l 3.067 (r2 = 0.96). The average condition coefficient reached 1.49. The growth was balanced, gradually slowing down. Von Bertallanffy growth equation had the form Lt = 245.47(1 – e–0.206(t + 0.0333)). The average value of instantaneous monthly growth rate (Gm) ranged between 0.4 and 4.3 (in %). Mean Gm of particular age groups gradually decreased. Gm varied seasonally, annually and in different parts of the stream. The length-weight relationship for dace was w = 0.000009.13.0948 (r2 = 0.97). The mean condition coefficient reached the value of 1.11. The length growth was balanced, gradually decreasing. Von Bertallanffy equation had the form Lt = 216.28(1 – e–0.2536(t + 0.26094)). The instantaneous monthly growth rate ranged between –1.57 and 10.38 (in percentage). This indicator fluctuated according to the age, season and year.

Styles APA, Harvard, Vancouver, ISO, etc.

34

Bakke, Paul D., Michael Hrachovec et Katherine D. Lynch. « Hyporheic Process Restoration : Design and Performance of an Engineered Streambed ». Water 12, n^o 2 (5 février 2020) : 425. http://dx.doi.org/10.3390/w12020425.

Texte intégral

Résumé :

Stream restoration designed specifically to enhance hyporheic processes has seldom been contemplated. To gain experience with hyporheic restoration, an engineered streambed was built using a gravel mixture formulated to mimic natural streambed composition, filling an over-excavated channel to a minimum depth of 90 cm. Specially designed plunge-pool structures, built with subsurface gravel extending down to 2.4 m, promoted greatly enhanced hyporheic circulation, path length, and residence time. Hyporheic process enhancement was verified using intra-gravel temperature mapping to document the distribution and strength of upwelling and downwelling zones, computation of vertical water flux using diurnal streambed temperature patterns, estimation of hyporheic zone cross section using sodium chloride tracer studies, and repeat measurements of streambed sand content to document evolution of the engineered streambed over time. Results showed that vertical water flux in the vicinity of plunge-pool structures was quite large, averaging 89 times the pre-construction rate, and 17 times larger than maximum rates measured in a pristine stream in Idaho. Upwelling and downwelling strengths in the constructed channel were larger and more spatially diverse than in the control. Streambed sand content showed a variety of response over time, indicating that rapid return to an embedded, impermeable state is not occurring.

Styles APA, Harvard, Vancouver, ISO, etc.

35

Kumaran, V. « Dense shallow granular flows ». Journal of Fluid Mechanics 756 (3 septembre 2014) : 555–99. http://dx.doi.org/10.1017/jfm.2014.412.

Texte intégral

Résumé :

AbstractSimplified equations are derived for a granular flow in the ‘dense’ limit where the volume fraction is close to that for dynamical arrest, and the ‘shallow’ limit where the stream-wise length for flow development ($\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}L$) is large compared with the cross-stream height ($h$). The mass and diameter of the particles are set equal to 1 in the analysis without loss of generality. In the dense limit, the equations are simplified by taking advantage of the power-law divergence of the pair distribution function $\chi $ proportional to $(\phi _{ad} - \phi )^{- \alpha }$, and a faster divergence of the derivative $\rho (\mathrm{d} \chi / \mathrm{d} \rho ) \sim (\mathrm{d} \chi / \mathrm{d} \phi )$, where $\rho $ and $\phi $ are the density and volume fraction, and $\phi _{ad}$ is the volume fraction for arrested dynamics. When the height $h$ is much larger than the conduction length, the energy equation reduces to an algebraic balance between the rates of production and dissipation of energy, and the stress is proportional to the square of the strain rate (Bagnold law). In the shallow limit, the stress reduces to a simplified Bagnold stress, where all components of the stress are proportional to $(\partial u_x/\partial y)^2$, which is the cross-stream ($y$) derivative of the stream-wise ($x$) velocity. In the simplified equations for dense shallow flows, the inertial terms are neglected in the $y$ momentum equation in the shallow limit because the are $O(h/L)$ smaller than the divergence of the stress. The resulting model contains two equations, a mass conservation equations which reduces to a solenoidal condition on the velocity in the incompressible limit, and a stream-wise momentum equation which contains just one parameter $\mathcal{B}$ which is a combination of the Bagnold coefficients and their derivatives with respect to volume fraction. The leading-order dense shallow flow equations, as well as the first correction due to density variations, are analysed for two representative flows. The first is the development from a plug flow to a fully developed Bagnold profile for the flow down an inclined plane. The analysis shows that the flow development length is $(\bar{\rho }h^3 / \mathcal{B})$, where $\bar{\rho }$ is the mean density, and this length is numerically estimated from previous simulation results. The second example is the development of the boundary layer at the base of the flow when a plug flow (with a slip condition at the base) encounters a rough base, in the limit where the momentum boundary layer thickness is small compared with the flow height. Analytical solutions can be found only when the stream-wise velocity far from the surface varies as $x^F$, where $x$ is the stream-wise distance from the start of the rough base and $F$ is an exponent. The boundary layer thickness increases as $(l^2 x)^{1/3}$ for all values of $F$, where the length scale $l = \sqrt{2 \mathcal{B}/ \bar{\rho }}$. The analysis reveals important differences between granular flows and the flows of Newtonian fluids. The Reynolds number (ratio of inertial and viscous terms) turns out to depend only on the layer height and Bagnold coefficients, and is independent of the flow velocity, because both the inertial terms in the conservation equations and the divergence of the stress depend on the square of the velocity/velocity gradients. The compressibility number (ratio of the variation in volume fraction and mean volume fraction) is independent of the flow velocity and layer height, and depends only on the volume fraction and Bagnold coefficients.

Styles APA, Harvard, Vancouver, ISO, etc.

36

BRZEK, BRIAN, SHEILLA TORRES-NIEVES, JOSÉ LEBRÓN, RAÚL CAL, CHARLES MENEVEAU et LUCIANO CASTILLO. « Effects of free-stream turbulence on rough surface turbulent boundary layers ». Journal of Fluid Mechanics 635 (10 septembre 2009) : 207–43. http://dx.doi.org/10.1017/s0022112009007447.

Texte intégral

Résumé :

Several effects of nearly isotropic free-stream turbulence in transitionally rough turbulent boundary layers are studied using data obtained from laser Doppler anemometry measurements. The free-stream turbulence is generated with the use of an active grid, resulting in free-stream turbulence levels of up to 6.2%. The rough surface is characterized by a roughness parameterk+≈ 53, and measurements are performed at Reynolds numbers of up toReθ= 11300. It is confirmed that the free-stream turbulence significantly alters the mean velocity deficit profiles in the outer region of the boundary layer. Consequently, the previously observed ability of the Zagarola & Smits (J. Fluid Mech., vol. 373, 1998, p. 33) velocity scaleU∞δ*/δ to collapse results from both smooth and rough surface boundary layers, no longer applies in this boundary layer subjected to high free-stream turbulence. In inner variables, the wake region is significantly reduced with increasing free-stream turbulence, leading to decreased mean velocity gradient and production of Reynolds stress components. The effects of free-stream turbulence are clearly identifiable and significant augmentation of the streamwise Reynolds stress profiles throughout the entire boundary layer are observed, all the way down to the inner region. In contrast, the Reynolds wall-normal and shear stress profiles increase due to free-stream turbulence only in the outer part of the boundary layer due to the blocking effect of the wall. As a consequence, there is a significant portion of the boundary layer in which the addition of nearly isotropic turbulence in the free-stream, results in significant increases in anisotropy of the turbulence. To quantify which turbulence length scales contribute to this trend, second-order structure functions are examined at various distances from the wall. Results show that the anisotropy created by adding nearly isotropic turbulence in the free-stream resides mostly in the larger scales of the flow. Furthermore, by analysing the streamwise Reynolds stress equation, it can be predicted that it is the wall-normal gradient of 〈u2v〉 term that is responsible for the increase in 〈u2〉 profiles throughout the boundary layer (i.e. an efficient turbulent transport of turbulence away from the wall). Furthermore, a noticeable difference between the triple correlations for smooth and rough surfaces exists in the inner region, but no significant differences are seen due to free-stream turbulence. In addition, the boundary layer parameters δ*/δ95,Handcfare also evaluated from the experimental data. The flow parameters δ*/δ95andHare found to increase due to roughness, but decrease due to free-stream turbulence, which has significance for flow control, particularly in delaying separation. Increases incfdue to high free-stream turbulence are also observed, associated with increased momentum flux towards the wall.

Styles APA, Harvard, Vancouver, ISO, etc.

37

McIntosh, S. C., et N. Qin. « The influence of transition onset location on the performance of shock control bumps ». Aeronautical Journal 117, n^o 1196 (octobre 2013) : 1037–51. http://dx.doi.org/10.1017/s0001924000008678.

Texte intégral

Résumé :

Abstract In order to investigate the robustness of three dimensional bumps on shock control for natural laminar-flow wings, the impact of transition onset location on the overall performance of the shock control device was studied. For a ramp bump, a moderate ramp start angle θ r =4° was found to effectively fix the location of the leading leg of the shock lambda, decreasing chord-wise movement in the main shock position resulting from variations in transition onset location. With increasing transition onset length from xtrans =0% chord to 45% chord, little influence was found regarding the overall performance of the shock control device but a down-stream movement of the secondary leg of the shock lambda in a range about 3% chord was observed. Change in the boundary-layer displacement thickness due to varying transition onset locations was identified as the primary mechanism responsible for this secondary shock leg movement.

Styles APA, Harvard, Vancouver, ISO, etc.

38

Chishty, Nadim, Anil Tripathi et Madhusudan Sharma. « Evaluation of acute toxicity of zinc, lead and cadmium to zooplanktonic community in upper Berach river system, Rajasthan, India ». South Asian Journal of Experimental Biology 2, n^o 1 (19 mars 2012) : 20–26. http://dx.doi.org/10.38150/sajeb.2(1).p20-26.

Texte intégral

Résumé :

Current study investigated through static bioassay, the acute toxicity of Zinc,Lead and Cadmium to fresh water zooplankters in the upper Berach riversystem which is a part of Gangetic river system. The river basin stretchesfrom Madar tank to Sarjana tank with a total length of 46 Km, including ninewater bodies i.e. Bada madar tank (73Â‹36Âf0ÂfÂfE and 24Â‹38Âf0ÂhN ), Chhotamadar tank, Fateh sagar lake, Udaisagar lake, UpÂ]stream pond (BichhdiÂ]I),DownÂ]stream pond(BichhdiÂ]II), Gadwa, Daroli and Sarjana tank (73Â‹ 57Âf10ÂhEand 24Â‹14Âf30Âh N). Whole zooplanktonic communities were exposed to different heavy metal stresses. Exposed zooplanktonic community included nine planktonic forms i.e. Heliodiaptomus viduus, Mesocyclops hyalinus, Heterocypris, Daphnia lumholtzi, Moina, Brachionus, Monostyla, Filinia. Cadmium was found to be most toxic and Zinc was least toxic to zooplankton. Ostracods and Cyclops were resistant forms and rotifers were sensitive forms in relation to metallic exposure. Sensitivity pattern observed during laboratory experiments was found to be in accordance with biodiversity variation of zooplankton in different ponds of Berach river system.

Styles APA, Harvard, Vancouver, ISO, etc.

39

KUMARAN, V. « Dense granular flow down an inclined plane : from kinetic theory to granular dynamics ». Journal of Fluid Mechanics 599 (6 mars 2008) : 121–68. http://dx.doi.org/10.1017/s002211200700002x.

Texte intégral

Résumé :

The hydrodynamics of the dense granular flow of rough inelastic particles down an inclined plane is analysed using constitutive relations derived from kinetic theory. The basic equations are the momentum and energy conservation equations, and the granular energy conservation equation contains a term which represents the dissipation of energy due to inelastic collisions. A fundamental length scale in the flow is the ‘conduction length’ δ=(d/(1-en)1/2), which is the length over which the rate of conduction of energy is comparable to the rate of dissipation. Here, d is the particle diameter and en is the normal coefficient of restitution. For a thick granular layer with height h ≫ δ, the flow in the bulk is analysed using an asymptotic analysis in the small parameter δ/h. In the leading approximation, the rate of conduction of energy is small compared to the rates of production and dissipation, and there is a balance between the rate of production due to mean shear and the rate of dissipation due to inelastic collisions. A direct consequence of this is that the volume fraction in the bulk is a constant in the leading approximation. The first correction due to the conduction of energy is determined using asymptotic analysis, and is found to be O(δ/h)2 smaller than the leading-order volume fraction. The numerical value of this correction is found to be negligible for systems of practical interest, resulting in a lack of variation of volume fraction with height in the bulk.The flow in the ‘conduction boundary layers’ of thickness comparable to the conduction length at the bottom and top is analysed. Asymptotic analysis is used to simplify the governing equations to a second-order differential equation in the scaled cross-stream coordinate, and the resulting equation has the form of a diffusion equation. However, depending on the parameters in the constitutive model, it is found that the diffusion coefficient could be positive or negative. Domains in the parameter space where the diffusion coefficients are positive and negative are identified, and analytical solutions for the boundary layer equations, subject to appropriate boundary conditions, are obtained when the diffusion coefficient is positive. There is no boundary layer solution that matches the solution in the bulk for parameter regions where the diffusion coefficient is negative, indicating that a steady solution does not exist. An analytical result is derived showing that a boundary layer solution exists (diffusion coefficient is positive) if, and only if, the numerical values of the viscometric coefficients are such that volume fraction in the bulk decreases as the angle of inclination increases. If the numerical values of the viscometric coefficients are such that the volume fraction in the bulk increases as the angle of inclination increases, a boundary layer solution does not exist.The results are extended to dense flows in thin layers using asymptotic analysis. Use is made of the fact that the pair distribution function is numerically large for dense flows, and the inverse of the pair distribution function is used as a small parameter. This approximation results in a nonlinear second-order differential equation for the pair distribution function, which is solved subject to boundary conditions. For a dissipative base, it is found that a flowing solution exists only when the height is larger than a critical value, whereas the temperature decreases to zero and the flow stops when the height becomes smaller than this critical value. This is because the dissipation at the base becomes a larger fraction of the total dissipation as the height is decreased, and there is a minimum height below which the rate of production due to shear is not sufficient to compensate for the rate of dissipation at the base. The scaling of the minimum height with dissipation in the base, the bulk volume fraction and the parameters in the constitutive relations are determined. From this, the variation of the minimum height on the angle of inclination is obtained, and this is found to be in qualitative agreement with previous experiments and simulations.

Styles APA, Harvard, Vancouver, ISO, etc.

40

Sołowczuk, Alicja, et Przemysław Gardas. « Effect of the Parking Lane Configuration on Vehicle Speeds in Home Zones in Poland ». Sustainability 12, n^o 2 (13 janvier 2020) : 588. http://dx.doi.org/10.3390/su12020588.

Texte intégral

Résumé :

Nowadays, traffic calming measures that are designed to influence the drivers’ behaviour in the first place and thus make them slow down (and increase the safety of traffic as a result) are used increasingly often in traffic engineering. As a rule of thumb, carefully planned street geometry and street furniture should advise the drivers of the traffic calmed area ahead of them, which makes them reduce the vehicle speed by influencing their perception. One of the most common treatments are road narrowings and horizontal deflections of the route of travel. The reduction of the vehicle speed increases the driver’s central visual area, which results in earlier and easier spotting of pedestrians that are about to cross the roadway. A reduction of noise and exhaust emissions is an additional benefit. However, the current sustainable design guidelines are not specific regarding how often the route should be deflected by alternate parking lanes and how frequently they should be placed in the home zones (woonerven in Dutch) in order to achieve the desired reduction of vehicle speed, noise, pollution, and exhaust emissions. This being so, the authors carried out a speed survey research on a chosen street that includes woonerf design features, as typically used in Poland, with carriageway narrowings being created by parking lanes differently sited along its length. Several speed measuring devices were deployed to automatically and simultaneously measure and record the vehicle speeds and volume of traffic at different test locations. The measurement data were subjected to statistical analyses, including conventional statistical tests. The alternative hypothesis, proposing that the vehicle speeds depend on the configuration of parking lanes and carriageway narrowings was confirmed in almost all cases. The results have confirmed that the siting of parking lanes is a relevant factor as far as speed reduction is concerned, with the degree of this reduction depending on the remaining travel lane width.

Styles APA, Harvard, Vancouver, ISO, etc.

41

SHYAMALA, S., et Dr G. AYYAPPAN. « Transient Solution of M[X]=G=1 With Second Optional Service, Bernoulli Schedule Server Vacation and Random Break Downs ». INTERNATIONAL JOURNAL OF MANAGEMENT & ; INFORMATION TECHNOLOGY 3, n^o 3 (31 mai 2013) : 45–55. http://dx.doi.org/10.24297/ijmit.v3i3.1722.

Texte intégral

Résumé :

In this model, we present a batch arrival non- Markovian queueingmodel with second optional service, subject to random break downs andBernoulli vacation. Batches arrive in Poisson stream with mean arrivalrate (> 0), such that all customers demand the rst `essential' ser-vice, wherein only some of them demand the second `optional' service.The service times of the both rst essential service and the second op-tional service are assumed to follow general (arbitrary) distribution withdistribution function B1(v) and B2(v) respectively. The server may un-dergo breakdowns which occur according to Poisson process with breakdown rate . Once the system encounter break downs it enters the re-pair process and the repair time is followed by exponential distributionwith repair rate . Also the sever may opt for a vacation accordingto Bernoulli schedule. The vacation time follows general (arbitrary)distribution with distribution function v(s). The time-dependent prob-ability generating functions have been obtained in terms of their Laplacetransforms and the corresponding steady state results have been derivedexplicitly. Also the mean queue length and the mean waiting time havebeen found explicitly.

Styles APA, Harvard, Vancouver, ISO, etc.

42

Mohammed-Taifour, A., Q. Schwaab, J. Pioton et J. Weiss. « A new wind tunnel for the study of pressure-induced separating and reattaching flows ». Aeronautical Journal 119, n^o 1211 (janvier 2015) : 91–108. http://dx.doi.org/10.1017/s0001924000010265.

Texte intégral

Résumé :

AbstractThe design, construction, and validation of a new academic wind tunnel is described in detail. The wind tunnel is of a classical, blow-down type and generates a pressure-induced, turbulent separation bubble on a flat test surface by a combination of adverse and favorable pressure gradients. The Reynolds number, based on momentum thickness just upstream of separation, is Reθ≃ 5,000 at a free-stream velocity ofUref= 25ms−1. The length of the separation bubble is estimated at 0°42 ± 0°02m by three different methods. Results of a numerical simulation demonstrate the absence of flow separation in the wind-tunnel contraction. This results in a turbulence level of about 0·05% in the test section. Oil-film visualisation experiments show that the flow near the wall is strongly three-dimensional in the recirculating region and that the topology of the limiting streamlines is consistent with experiments performed on configurations with fixed separation. Finally, spatial variations of the forward-flow fraction have been documented using a thermal-tuft probe and are shown to compare well with the results of the oil-film visualisation.

Styles APA, Harvard, Vancouver, ISO, etc.

43

Haller, M., B. Brümmer et G. Müller. « Results from the DAMOCLES ice-buoy campaigns in the transpolar drift stream 2007–2009 ». Cryosphere Discussions 7, n^o 4 (24 juillet 2013) : 3749–81. http://dx.doi.org/10.5194/tcd-7-3749-2013.

Texte intégral

Résumé :

Abstract. During the EU research project DAMOCLES 18 ice buoys were deployed in the region of the Arctic transpolar drift (TPD). Sixteen of them formed a square with 400 km side-length. The measurements lasted from 2007 to 2009. The properties of the TPD and the impact of synoptic weather systems on the ice drift are analysed. Compared to Nansen's drift with the vessel Fram the measured speed of the TPD is here almost twice as fast. Within the TPD, the speed increases by a factor of almost three from the North Pole to the Fram Strait region. The hourly buoy position fixes show that the speed is underestimated by 10–20% if positions were taken at only 1–3 days intervals as it is usually done for satellite drift estimates. The geostrophic wind factor Ui/Ug, i.e. the ratio of ice speed Ui and geostrophic wind speed Ug, in the TPD amounts to 0.012 on average, but with regional and seasonal differences. The constant Ui/Ug relation breaks down for Ug < 5 m s−1. The impact of synoptic weather systems is studied applying a composite method. Cyclones (anticyclones) cause cyclonic (anticyclonic) vorticity and divergence (convergence) of the ice drift. The amplitudes are twice as large for cyclones as for anticyclones. The divergence caused by cyclones corresponds to a 0.1–0.5%/6 h open water area increase based on the composite averages, but reached almost 4% within one day during a strong August 2007 storm. This storm also caused a~long-lasting (over several weeks) rise of Ui and Ui/Ug and changed the ice conditions in a way allowing ocean tidal motion to directly affect ice motion. The consequences of an increasing Arctic storm activity for the ice cover are discussed.

Styles APA, Harvard, Vancouver, ISO, etc.

44

Peterson, Curt D., et Sarah R. Doliber. « Groundwater Surface (GWS) Mapping by Ground Penetrating Radar (GPR) For Use in Protecting Freshwater Habitats, Water Quality, and Active Dune Landscapes, In the Florence Coastal Dune Sheet, Oregon, USA ». Journal of Geography and Geology 11, n^o 1 (26 février 2019) : 13. http://dx.doi.org/10.5539/jgg.v11n1p13.

Texte intégral

Résumé :

Ground penetrating radar (GPR) profiling was performed in the Florence (FLOR) coastal dune sheet to test relations between remotely-sensed groundwater surface (GWS) trends, measured groundwater phreatic surfaces, and overlying freshwater features/habitats. Following preliminary GPR testing, the GWS trend mapping was employed in the north FLOR dune aquifer (17 km in length and 5 km in width), in anticipation of increasing development pressures on aquifer groundwater withdrawal by the City of Florence, Oregon. Several available technologies, including continuously-towed GPR profiling (5-8 km/hr), real-time GPS positioning (±2 m horizontal), Lidar elevation control (±0.5 m NAVD88), and GIS mapping/surface trend analyses permitted upscaling to the large management area (40 km2) in the north FlOR dune aquifer. Totals of 95 km of GPR track-line, including 943 averaged shot points at 100 m track-line intervals (total ~100,000 shot points), were collected during a three-week field effort. The remotely sensed GWS, ranging from 1 to 14 m depth subsurface and 0 to 57 m elevation NAVD88, was ground-truthed in ponds, gaining-stream reaches, and monitored water wells. An area wide groundwater surface map confirmed a modeled dune-ramp aquifer, sloping (0.5-2.0 % gradients) to the Pacific Ocean shoreline and the dividing Siuslaw River valley. The continuous GPR profiles connected large dune barrage lakes, interdune valley window lakes, anadromous fish passage streams, and sensitive bog habitats to the locally-variable GWS (0.98 R2 correlation coefficient). These elevated freshwater features were shown not to be developed on perched dune soil aquitards or lake bottom mud seals, but rather they are directly dependent on the mounded, variably sloping, and very-shallow GWS in the regional dune aquifer. Shallow GWS depths also promote colonization of active dune surfaces by non-native invasive dune grasses. The freshwater lakes and ponds were shown to be susceptible to contaminant transport by down-gradient GWS flows from surrounding residential and resort development.

Styles APA, Harvard, Vancouver, ISO, etc.

45

Pierini, Stefano, Pierpaolo Falco, Giovanni Zambardino, Thomas A. McClimans et Ingrid Ellingsen. « A Laboratory Study of Nonlinear Western Boundary Currents, with Application to the Gulf Stream Separation due to Inertial Overshooting* ». Journal of Physical Oceanography 41, n^o 11 (1 novembre 2011) : 2063–79. http://dx.doi.org/10.1175/2011jpo4514.1.

Texte intégral

Résumé :

Abstract Various dynamical aspects of nonlinear western boundary currents (WBCs) have been investigated experimentally through physical modeling in a 5-m-diameter rotating basin. The motion of a piston with a velocity up that can be as low as up = 0.5 mm s−1 induces a horizontally unsheared current of homogeneous water that, flowing over a topographic beta slope, experiences westward intensification. First, the character of WBCs for various degrees of nonlinearity is investigated. By varying up, flows ranging from the highly nonlinear inertial Charney regime down to a weakly nonlinear regime can be simulated. In the first case, the dependence of zonal length scales on up is found to be in agreement with Charney’s theory; for weaker flows, a markedly different functional dependence emerges describing the initial transition toward the linear, viscous case. This provides an unprecedented coverage of nonlinear WBC dependence on an amplitude parameter in terms of experimental data. WBC separation from a wedge-shaped continent past a cape (simulating Cape Hatteras) due to inertial overshooting is then analyzed. By increasing current speed, a critical behavior is identified according to which a very small change of up marks the transition from a WBC that follows the coast past the cape to a WBC (nearly dynamically similar to a full-scale Gulf Stream) that separates from the cape without any substantial deflection, as with the Gulf Stream Extension. The important effect of the deflection angle of the continent is analyzed as well. Finally, the qualitative effect of a sloping sidewall along a straight coast is considered: the deflection of the flow away from the western wall due to the tendency to preserve potential vorticity clearly emerges.

Styles APA, Harvard, Vancouver, ISO, etc.

46

Roshka, N. M. « ORGANIZATION OF THE 5S RIBOSOMAL DNA INTERGENIC SPACER OF APAMEA MONOGLYPHA (LEPIDOPTERA) ». Biolohichni systemy 15, n^o 1 (2023) : 26–31. http://dx.doi.org/10.31861/biosystems2023.01.026.

Texte intégral

Résumé :

A significant part of the moth species, representatives of the superfamily Noctuoidea distributed on the territory of Ukraine, are pests of crops, which attracts special attention of researchers. In particular, host plants for the larvae of the Apamea species are cereals. For the correct identification of the pest moth speciesit is necessary to conduct molecular genetic studies to create molecular passports (barcoding). One of the convenient molecular markers used to compare low-ranking taxa is the 5S rDNA region represented by tandemly arranged clusters, where each repeat unit consists of a highly conserved coding region and a variable intergenic spacer (IGS). Since the molecular organization of 5S rDNA in moth species is still insufficiently studied, the aim of our work was to analyze the 5S rDNA IGS of A. monoglypha, a representative of the Apamea genus. For this, 5S rDNA repeats were amplified by PCR, and the obtained products were ligated into the pJet1.2 plasmid vector. The inserts of the three recombinant plasmids, ApMon1-1, ApMon1-2, and ApMon1-8, which were of the expected size, were sequenced. It was found that the A. monoglypha genome contains several structural IGS variants that differ both in length and nucleotide sequence. The level of similarity of the compared IGS sequences varied from 38.0 to 76.2%, indicating a high level of intragenomic polymorphism in this region. An AT-rich motif, a GC dinucleotide, and a cytosine residue up-stream of the coding region were identified as putative external promoter elements, which can be involved in the initiation of transcription. Furthermore, the oligo-T motif located immediately down-stream of the coding region is probably involved in the transcription termination.

Styles APA, Harvard, Vancouver, ISO, etc.

47

Bugaev, V. F. « Relationship between size-weight parameters of soсkeye salmon Oncorhynchus nerka smolts emigrated from Lake Azabachye (Kamchatka River basin) in 1979–2013 and abundance of mature fsh in the sea in 1982–2016 ». Izvestiya TINRO 195 (27 décembre 2018) : 128–39. http://dx.doi.org/10.26428/1606-9919-2018-195-128-139.

Texte intégral

Résumé :

Two groups of juvenile sockeye salmon are feeding in Lake Azabachye. They belong to the 2nd order stock of the lake (stock A) and to other 2nd order stocks of middle and down stream tributaries of the Kamchatka River which underyearlings migrate into the lake for feeding and wintering (group E). The main part of the stock A leaves the lake to the sea at the age 2+ (mainly 2.3) and the youngsters of the group E migrate to the sea at the age 1+ (mainly 1.3). The body length and weight parameters of the stock A smolts at the age 2+ and the group E smolts at the age 1+ could be similar or dissimilar in particular years. The maximal difference between the smots of these stocks is observed in the years with higher body length and weight for the stock A. Mean for 1979–2016 length and weight of smolts at abovementioned ages are evaluated as 98.42/87.46 mm and 10.40/7.38 g for the A/E stocks. For the stock A, statistically signifcant positive correlation is noted between size-weight parameters of smolts in the years of emigration and their abundance in the years of mass return. However, the regression has a shift between the periods of emigration/return of 1979–2000/1982–2003 and 2003–2013/2006–2016. The correlation is higher for the frst period (r = 0.820; P < 0.001 for body weight and r = 0.797; P < 0.001 for body length, n = 16) than for the second one with higher abundance (r = 0.669; P < 0.05 for body weight and r = 0.711; P < 0.05 for body length, n = 11). On opposite, the returns of the group E depend weakly on size-weight parameters of its smolts for the period of emigration/return of 1979–1997/1982–2000 (no data for return in 1999) and the dependence is insignifcant for the period of 2000–2013/2003–2016.

Styles APA, Harvard, Vancouver, ISO, etc.

48

Vorriberger, P. L., et I. M. Whillans. « Crevasse Deformation and Examples From Ice Stream B, West Antarctica (Abstract) ». Annals of Glaciology 11 (1988) : 211. http://dx.doi.org/10.1017/s0260305500006728.

Texte intégral

Résumé :

Crevasses are subject to rotation and bending according to the velocity field through which they travel. The objective of this study is to determine to what extent the velocity field can be inferred from measurements of the resulting shapes of crevasses. A quantitative model of crevasse deformation is developed, based on the following assumptions: (1) each crevasse is assumed to open perpendicularly to the principal extensional regional strain-rate, (2) the crevasse forms when the principal extensional strain-rate exceeds some specified critical value, and (3) velocity gradients are constant over the area of interest. The first two assumptions are reasonable and the third is necessary for an analytic solution of flow trajectories. The crevasse is carried along, rotated, and bent, and may continue to increase in length. Calculations are made for different velocity fields, and velocity fields are sought that produce crevasses similar to those found in three different areas of Ice Stream B. Hook-shaped crevasses occur just outside the chaotic zone at the ice-stream margin. These are similar to the curved marginal crevasses often found in the accumulation zone of valley glaciers. They are successfully modelled by combining strong lateral shear with slow flow of ice from the ice ridge into the ice stream. The curvature at the most sharply bent part of the crevasse is found to be a useful measure and, together with measurements of ice flow from the ridge, can be used to infer the rate of lateral shear. This rate compares favorably with the single measurement obtained so far (Bindschadler and others 1987). A pattern of splaying crevasses develops on the ice stream down-glacier of its narrowest part. These crevasses are similar to longitudinal crevasses found in the ablation zone of many valley glaciers. Models with linear variation in velocity cannot reproduce the observed pattern. However, we have been able to simulate higher-order variations by joining together successive linear models. The observed crevasse pattern is successfully produced if the side shearing varies as the third power of distance from the center of symmetry of the crevasse pattern. Such a variation is expected for a linear gradient in side-drag stress and a third-power constitutive relation for ice. The observed crevasse pattern is thus consistent with side drag varying linearly across the ice stream. The third example is the rotation of transverse crevasses, which occur in trains on the main part of the ice stream. This rotation is due to side shearing but its magnitude is also affected by turning of the flow line and by normal strain-rates. It is therefore possible to reproduce the observed pattern for a wide range of velocity fields, and so measurements of the orientation of transverse crevasses provide only an upper limit on side shearing within the main body of the ice stream. There are many other examples of crevasse patterns on Ice Stream Β and on other glaciers that can be studied in this way. We propose that important constraints can be placed on velocity gradients and on the flow dynamics by using quantitative modelling of crevasse shapes.

Styles APA, Harvard, Vancouver, ISO, etc.

49

A. B. Temimy, Alaa, et Adnan A. Abdulrasool. « THERMAL PERFORMANCE ENHANCEMENT OF A VERTICAL THERMOSYPHON HEAT PIPE BY FLOW CONTROL OF THE TWO PHASES ». Journal of Engineering and Sustainable Development 25, n^o 01 (1 janvier 2021) : 109–22. http://dx.doi.org/10.31272/jeasd.25.1.10.

Texte intégral

Résumé :

Heat Pipe (THP) has a continues evaporation/ condensation cycles of the working fluid. The flow patterns of the two phases is founds by previous published articles, as a non-steady complex spatial flow pattern. This type of the flow blocks the easy moving of the two-phases and limits the thermal performance of the THP. In this study, a copper tubes packing (TP) is simulated numerically to control/manage the flow streams of the two phases inside the THP. The simulated THP is 600mm length made of copper partially filled with water. The TP is consist of a two copper tubes attached contrary to each other with a neighboring openings. The upper tube (Riser tube) facilitate the moving of steam streams from evaporator section to the top of the condenser section. The lower tube (Down-comer tube) facilitate the moving of the condensate streams from the condenser section to the bottom of the evaporator section. The tested filling ratios are (40,50,55,60 and 70) % of evaporator section volume. The supplied heats are (50,75,100,150 and 200) W. The Computational Fluid Dynamics solution are done for a three dimensional model (3DCFD) using ANSYS/ Fluent R19.0 software. The simulation result of the steam volume fractions contours shows that the insertion of TP control the flow streams of both phases. Also prevent the formation of complex flow patterns then enhance the axial velocity vectors and reduce cross velocity vectors. The inserted TP provide a regular circulation paths for the working fluid phases and enhance evaporation /condensation processes. Hence it’s reduce the thermal resistance of the THP about 55% and enhance the thermal performance with the same percentage. In addition, the thermal performance of the enhanced TPTHP is not/a little influence due to the variation of the filling ratio.

Styles APA, Harvard, Vancouver, ISO, etc.

50

Haller, M., B. Brümmer et G. Müller. « Atmosphere–ice forcing in the transpolar drift stream : results from the DAMOCLES ice-buoy campaigns 2007–2009 ». Cryosphere 8, n^o 1 (20 février 2014) : 275–88. http://dx.doi.org/10.5194/tc-8-275-2014.

Texte intégral

Résumé :

Abstract. During the EU research project Developing Arctic Modelling and Observing Capabilities for Long-term Environmental Studies (DAMOCLES), 18 ice buoys were deployed in the region of the Arctic transpolar drift (TPD). Sixteen of them formed a quadratic grid with 400 km side length. The measurements lasted from 2007 to 2009. The properties of the TPD and the impact of synoptic weather systems on the ice drift are analysed. Within the TPD, the speed increases by a factor of almost three from the North Pole to the Fram Strait region. The hourly buoy position fixes would show that the speed is underestimated by 10–20% if positions were taken at only 1–3 day intervals as it is usually done for satellite drift estimates. The geostrophic wind factor Ui / Ug (i.e. the ratio of ice speed Ui and geostrophic wind speed Ug), in the TPD amounts to 0.012 on average, but with regional and seasonal differences. The constant Ui / Ug relation breaks down for Ug < 5 m s−1. The impact of synoptic weather systems is studied applying a composite method. Cyclones (anticyclones) cause cyclonic (anticyclonic) vorticity and divergence (convergence) of the ice drift. The amplitudes are twice as large for cyclones as for anticyclones. The divergence caused by cyclones corresponds to a 0.1–0.5% per 6 h open water area increase based on the composite averages, but reached almost 4% within one day during a strong August 2007 storm. This storm also caused a long-lasting (over several weeks) rise of Ui and Ui / Ug and changed the ice conditions in a way which allowed large amplitudes of inertial ice motion. The consequences of an increasing Arctic storm activity for the ice cover are discussed.

Styles APA, Harvard, Vancouver, ISO, etc.

Articles de revues sur le sujet « DOWN STREEM LENGHT »

Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres