scholarly journals Experimental Study of Erosion Threshold of Reconstituted Sediments

2011 ◽  
Author(s):  
Zhihui Ye ◽  
Liang Cheng ◽  
Zhipeng Zang
Keyword(s):  
Shear Stress ◽  
Steady Increase ◽  
Initial Increase ◽  
Threshold Condition ◽  
Seabed Sediment ◽  
Erosion Threshold ◽  
Sediment Types ◽  
Weight Content ◽  
Testing Facility ◽  
Seabed Sediments

Understanding of fundamental erosion characteristics of seabed sediments on which pipelines and other structures are founded is critical for the design of these facilities. The erosion threshold condition of cohesive sediments is not well understood because of the complexity and variability of natural sediments. Most of the existing methods for evaluating the erosion behaviours of seabed sediment are often applicable to the certain particular sediment types and test conditions. There appears to be a need for more research efforts in this area. In present research, the threshold of motion of four moderately consolidated mixtures was tested under unidirectional currents using a testing facility. Three threshold shear stress increase modes were observed, including initial increase mode, steady increase mode and equilibrium mode as mass content of mud Pm increases. A dimensionless threshold shear stress τ* is proposed to quantify the shear strength of these reconstituted mixtures, coupled with variation of coarse particle size. Finally, a predicting model is proposed to illustrate the trend of erosion threshold of the four mixtures as a function of mud weight content. Further understanding of erosion threshold can rely on the various consolidation conditions and different coarse and fine materials inputted in the mixture.

scholarly journals Sound Velocity Estimation of Seabed Sediment Based on Parametric Array Sonar

2020 ◽  
Vol 2020 ◽  
pp. 1-6
Author(s):  
Jingxin Ma ◽  
Haisen Li ◽  
Jianjun Zhu ◽  
Baowei Chen
Keyword(s):  
Parameter Estimation ◽  
Acoustic Parameter ◽  
Velocity Estimation ◽  
Parameters Estimation ◽  
Real Field ◽  
Sound Waves ◽  
Sediment Thickness ◽  
Seafloor Topography ◽  
Seabed Sediment ◽  
Seabed Sediments

Backscattered sound waves of seabed sediments are important information carriers in seafloor detection and acoustic characteristic parameters inversion. Most of the existing methods for estimating geoacoustic parameters are based on multiangle seabed backscattered signal processing and suitable for flat seafloor conditions with uniform sediment thickness. This usually deviates from the real field conditions and affects the accuracy of parameter estimation. In this paper, the sound ray propagation theory is studied and analysed under the condition of sloping seabed and uneven sediment thickness. Based on the phased parameter array sonar system, a method of acoustic parameters estimation of the sediment under inclined seabed conditions is proposed. The simulation results show that the new method shows good adaptability to different inclination angles of the seabed and solves the problem of accuracy of acoustic parameter estimation of the inclined seabed sediments. The model will greatly reduce the seafloor topography requirements in the sediment acoustic parameter inversion, such as velocity, layer thickness, and acoustic impedance.

scholarly journals The potential for mobile demersal fishing to reduce carbon storage and sequestration in seabed sediments

2021 ◽  
Author(s):  
Graham Epstein ◽  
Julie P Hawkins ◽  
Catrin R Norris ◽  
Callum M Roberts
Keyword(s):  
Sediment Resuspension ◽  
Order Estimate ◽  
Sediment Type ◽  
Seabed Sediment ◽  
Flocculent Material ◽  
Sediment Carbon ◽  
Carbon Stores ◽  
Seabed Sediments ◽  
Fish And Shellfish ◽  
The Impact

Subtidal marine sediments are one of the planet's primary carbon stores and strongly influence the oceanic sink for atmospheric CO2. By far the most pervasive human activity occurring on the seabed is bottom trawling and dredging for fish and shellfish. A global first-order estimate suggested mobile demersal fishing activities may cause 160-400 Mt of organic carbon (OC) to be remineralised annually from seabed sediment carbon stores. There are, however, many uncertainties in this calculation. Here, we discuss the potential drivers of change in seabed OC stores due to mobile demersal fishing activities and conduct a systematic review, synthesising studies where this interaction has been directly investigated. Mobile demersal fishing would be expected to reduce OC in seabed stores, albeit with site-specific variability. Reductions would occur due to lower production of flora and fauna, the loss of fine flocculent material, increased sediment resuspension, mixing and transport, and increased oxygen exposure. This would be offset to some extent by reduced faunal bioturbation and respiration, increased off-shelf transport and increases in primary production from the resuspension of nutrients. Studies which directly investigated the impact of demersal fishing on OC stocks had mixed results. A finding of no significant effect was reported in 51% of 59 experimental contrasts; 41% reported lower OC due to fishing activities, with 8% reporting higher OC. In relation to remineralisation rates within the seabed, 14 experimental contrasts reported that demersal fishing activities decreased remineralisation, with four reporting higher remineralisation rates. The direction of effects was related to sediment type, impact duration, study design and local hydrography. More evidence is urgently needed to accurately quantify the impact of anthropogenic physical disturbance on seabed carbon in different environmental settings, and incorporate full evidence-based carbon considerations into global seabed management.

scholarly journals Comprehensive detection device and physical testing for mechanical properties of seabed sediments and shallow gas

2021 ◽  
Vol 2083 (2) ◽  
pp. 022105
Author(s):  
Zhe Yun Li ◽  
Qing Li
Keyword(s):  
Mechanical Properties ◽  
Real Time ◽  
Gas Separation ◽  
Sensor Placement ◽  
Gas Detection ◽  
Shallow Gas ◽  
Seabed Sediment ◽  
Transmission Part ◽  
Seabed Sediments ◽  
Water Gas

Abstract In this paper, a comprehensive detection device for the mechanical properties of seabed sediments and shallow gas is designed, which is mainly composed of the seabed sediment mechanical properties detection part, the shallow gas detection part and the ultrasonic wireless transmission part. The mud water gas separation structure of the shallow gas detection part separates the shallow gas from the mud water, and then the methane concentration in the shallow gas is measured by the non-dispersive infrared methane sensor, which realizes the collection of the submarine shallow gas and the automatic real-time monitoring of the concentration. The measurement of the mechanical properties of seabed sediments realizes the real-time measurement of the three parameters of cone resistance, sidewall friction and pore water pressure, which characterize the mechanical properties of seabed sediments, through strain-sensitive elements. The ultrasonic wireless data transmission part is mainly for the data detected by the mechanical properties of the seabed sediments to be wirelessly transmitted to the sensor placement room through the ultrasonic transducer across the mud-water-gas separation structure. Finally, the data measured by the two parts are transmitted to the mother ship through the cable located in the sensor placement room. The experimental results show that it has the ability to comprehensively detect the mechanical properties of seabed sediments and shallow gas, and has strong operability.

scholarly journals Data heterogeneity and oldness, two difficulties to overcome for the world seabed sediment mapping

2021 ◽  
Vol 4 ◽  
pp. 1-7
Author(s):  
Thierry Garlan ◽  
Isabelle Gabelotaud ◽  
Elodie Marchès ◽  
Edith Le Borgne ◽  
Sylvain Lucas
Keyword(s):  
Global Scale ◽  
Single Product ◽  
Seabed Sediment ◽  
Bathymetric Data ◽  
The World ◽  
Data Heterogeneity ◽  
Sediment Data ◽  
The University ◽  
Seabed Sediments

Abstract. A global seabed sediment map has been developed since 1995 to provide a necessary tool for different needs. This project is not completely original since it had already been done in 1912 when the French hydrographic Office and the University of Nancy produced sedimentary maps of the European and North American coasts. Seabed sediments is one of the last geographical domains which can’t benefit of satellite data. Without this contribution, sediment maps need to use very old data mixed with the new ones to be able to reach the goal of a global map. In general, sediment maps are made with the latest available techniques and are replaced after a few decades, thus generating new cartographic works as if all the previous efforts had become useless. Such approach underestimates the quality of past works and prevents to have maps covering large areas. The present work suggests to standardize all kind of sedimentary data from different periods and from very different acquisition systems and integrate them into a single product. This process has already been done for bathymetric data of marine charts, we discuss in this article of the application of this method at a global scale for sediment data.

An immediate endothelial cell signaling response to lung ischemia

2001 ◽  
Vol 281 (4) ◽  
pp. L993-L1000 ◽  
Author(s):  
Chun Song ◽  
Abu B. Al-Mehdi ◽  
Aron B. Fisher
Keyword(s):  
Endothelial Cells ◽  
Shear Stress ◽  
Initial Response ◽  
Membrane Depolarization ◽  
Initial Increase ◽  
Amplex Red ◽  
Vascular Space ◽  
Endothelial Response ◽  
Intracellular Ca

Abrupt cessation of lung perfusion induces a rapid endothelial response that is not associated with anoxia but reflects loss of normal shear stress. This response includes membrane depolarization, H2O2generation, and increased intracellular Ca2+. We evaluated these parameters immediately upon nonhypoxic ischemia using fluorescence videomicroscopy to image in situ endothelial cells in isolated, ventilated rat lungs. Lungs labeled with 4-{2-[6-(dioctylamino)-2-naphthalenyl]ethenyl}1-(3-sulfopropyl)-pyridinium (di-8-ANEPPS; a membrane potential probe), Amplex Red (an extracellular H2O2probe), or fluo 3-AM (a Ca2+indicator) were subjected to control perfusion followed by global ischemia. Endothelial di-8-ANEPPS fluorescence increased significantly within the first second of ischemia and stabilized at 15 s, indicating membrane depolarization by ∼17 mV; depolarization was blocked by preperfusion with the K+channel agonist lemakalim. Increased H2O2, inhibitable by catalase, was detected in the vascular space at 1–2 s after the onset of ischemia. Increased intracellular Ca2+was detected 10–15 s after the onset of ischemia; the initial increase was inhibited by preperfusion with thapsigargin. Thus the temporal sequence of the initial response of endothelial cells in situ to loss of shear stress (i.e., ischemia) is as follows: membrane depolarization, H2O2release, and increased intracellular Ca2+.

scholarly journals Classifying seabed sediment type using simulated tidal-induced bed shear stress

2015 ◽  
Vol 367 ◽  
pp. 94-104 ◽  
Author(s):  
Sophie L. Ward ◽  
Simon P. Neill ◽  
Katrien J.J. Van Landeghem ◽  
James D. Scourse
Keyword(s):  
Shear Stress ◽  
Sediment Type ◽  
Bed Shear Stress ◽  
Seabed Sediment

Some Evidence for Light-induced Transfers of Fatty Acids in Euglena gracilis

1973 ◽  
Vol 28 (5-6) ◽  
pp. 270-284 ◽  
Author(s):  
P. Pohl
Keyword(s):  
Fatty Acids ◽  
Euglena Gracilis ◽  
Phosphatidyl Choline ◽  
Phosphatidyl Ethanolamine ◽  
Neutral Lipids ◽  
Steady Increase ◽  
Initial Increase ◽  
Phosphatidyl Glycerol ◽  
Subsequent Decrease ◽  
Monogalactosyl Diglyceride

Euglena gracilis was grown in the dark for 12 days. Subsequent incubation with sodium octanoate- l-14C in the dark for 6 hours resulted in a rather specific incorporation of radioactivity into the neutral lipids (primarily wax esters). Upon illumination of these cells in an identical medium without radiocarbon, the radioactivities in the neutral lipids decreased strongly, due to a decrease of the labeled wax acids (mainly 1 4:0) and wax alcohols (mainly C14). The radioactivities in phosphatidyl choline and phosphatidyl ethanolamine increased during the first 24 hours of illumination and thereafter decreased. This was caused by the initial increase and subsequent decrease of the labeled 14:0 and 16:0 acids in phosphatidyl choline and of the 14:0, 16:0 , and 18:1 acids in phosphatidyl ethanolamine. The chloroplast lipids (sulfolipid, phosphatidyl glycerol, monogalactosyl diglyceride, and digalactosyl diglyceride) exhibited a steady increase in radiocarbon content. This was due to an increase of label in the 16:0 fatty acid of the sulfolipid, in the 16:0 and trans3-16:1 fatty acids of the phosphatidyl glycerol, and in the saturated and unsaturated C16 and C18 fatty acids of the monogalactosyl and digalactosyl diglycerides. The labeled fatty acids of the above phospho- and glycolipids had comparably high specific radioactivities. Incorporation of radiocarbon into the last two carbon atoms of their methyl ends, however, was low. The glycerol and sugar moieties of the individual lipids incorporated relatively little radiocarbon. It is concluded that in Euglena gracilis the biosynthesis of long chain fatty acids is associated with specific lipids. Upon illumination, oxidative breakdown of the neutral lipids as well as transfers of fatty acids from the neutral lipids via phosphatidyl choline and phosphatidyl ethanolamine to the chloroplast lipids seem to be induced. The lipids involved appear to function as parts of a “lipid-bridge” for the acyl transfers.

Nonfrontier Deforestation in the Eastern Amazon

2010 ◽  
Vol 14 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Arlete Silva de Almeida ◽  
Thomas A. Stone ◽  
Ima Célia G. Vieira ◽  
Eric A. Davidson
Keyword(s):  
Land Use ◽  
Forest Cover ◽  
Secondary Forest ◽  
Average Rate ◽  
Landsat Imagery ◽  
Steady Increase ◽  
Initial Increase ◽  
Secondary Forests ◽  
Human Occupation

Abstract While interest in Amazonian deforestation mostly focuses on frontier areas, the amount of forest cover in areas already dominated by human settlement is also changing. Secondary forests play an increasingly important role for maintaining genetic diversity, hydrological functioning, and greenhouse gas emissions of altered landscapes, but secondary forests are also being converted to more intensive agricultural uses. Five dates of Landsat imagery from 1984 to 2002 were analyzed, covering 8000 km2 of the Zona Bragantina of the eastern part of the Brazilian state of Pará, which underwent its most intensive wave of deforestation several decades ago. However, even in this area of relatively long-term human occupation, ongoing decreases of forest cover were found, both in the small remaining areas of mature forest and in the more widespread areas of secondary forests, as human population increased and land use intensified. Although there was an initial increase in the area of secondary forest from 1984 to 1994, there has been a steady decline since then, from 75% secondary forest cover in 1994 to 54% in 2002. The amount of pasture was relatively stable from 1984 to 1994 but more recently has shown a steady increase, reaching 37% cover in 2002. The average rate of carbon loss over the 18-yr study period was 0.9 Mg C ha−1 yr−1 for the 8000 km2 study area. Forests in this long-settled region of eastern Amazonia continue to be degraded, resulting in the loss of ecosystem services and carbon stocks due to continued land-use change.

Laboratory investigation on erosion threshold shear stress of cohesive sediment in Karkheh Dam

2021 ◽  
Vol 80 (19) ◽  
Author(s):  
Rouhallah Fatahi Nafchi ◽  
Hossein Samadi-Boroujeni ◽  
Hamid Raeisi Vanani ◽  
Kaveh Ostad-Ali-Askari ◽  
Milad Khastar Brojeni
Keyword(s):  
Shear Stress ◽  
Laboratory Investigation ◽  
Cohesive Sediment ◽  
Erosion Threshold

scholarly journals Assessment of land use impact on hydraulic threshold conditions for gully head cut initiation

2016 ◽  
Vol 20 (7) ◽  
pp. 3005-3012 ◽  
Author(s):  
Aliakbar Nazari Samani ◽  
Qiuwen Chen ◽  
Shahram Khalighi ◽  
Robert James Wasson ◽  
Mohammad Reza Rahdari
Keyword(s):  
Land Use ◽  
Shear Stress ◽  
Soil Erosion ◽  
Critical Shear Stress ◽  
Gully Erosion ◽  
Threshold Condition ◽  
Stream Power ◽  
Threshold Phenomenon ◽  
Erosion Models ◽  
Dry Farming

Abstract. A gully as an accelerated erosion process is responsible for land degradation under various environmental conditions and has been known as a threshold phenomenon. Although the effects of gullying processes have been well documented, few soil erosion models have taken into account the threshold condition necessary for gully development. This research was devoted to determining the effects of land use change on hydraulic threshold condition and stream power of water flow through an in situ experimental flume (15 m  ×  0.4 m). Results indicated that head cut initiation and detachment rates showed a better correlation to stream power indices than shear stress (τcr). The threshold unit stream power value (ωu) for head cut initiation in rangeland, abandoned land, and dry farming land was 0.0276, 0.0149, and 4.5  ×  10−5 m s−1, respectively. Moreover, the micro-relief condition of soil surface and surface vegetation affected the flow regime of discharge and velocity. It is seen that the composite hydraulic criteria of Froude number (Fr) and discharge (Q) can clearly discriminate the land uses' threshold. In fact, the remarkable decrease of τcr in dry farming was related to the effect of tillage practice on soil susceptibility and aggregate strength. The findings indicated that using the unit steam power index instead of critical shear stress could increase the models' precision for prediction of head cut development. Compared to the Ephemeral Gully Erosion Model (EGEM) equation for critical shear stress, it is important to point out that for modelling of gully erosion, using single soil attributes can lead to an inaccurate estimation for τcr. In addition, based on the findings of this research, the use of threshold values of τcr  =  35 dyne cm−2 and ωu  =  0.4 cm s−1 in physically based soil erosion models is susceptible to high uncertainty when assessing gully erosion.

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