scholarly journals Sediment shell-content diminishes current-driven sand ripple development and migration

2021 ◽  
Vol 9 (5) ◽  
pp. 1335-1346
Author(s):  
Chiu H. Cheng ◽  
Jaco C. de Smit ◽  
Greg S. Fivash ◽  
Suzanne J. M. H. Hulscher ◽  
Bas W. Borsje ◽  
...  
Keyword(s):  
Direct Consequence ◽  
Sandy Sediment ◽  
Natural Sand ◽  
Significant Control ◽  
Ripple Formation ◽  
Marine Habitats ◽  
Biogenic Structures ◽  
Shell Content ◽  
Bed Roughness ◽  
And Migration

Abstract. Shells and shell fragments are biogenic structures that are widespread throughout natural sandy shelf seas and whose presence can affect the bed roughness and erodibility of the seabed. An important and direct consequence is the effect on the formation and movement of small bedforms such as sand ripples. We experimentally measured ripple formation and the migration of a mixture of natural sand with increasing volumes of shell material in a racetrack flume. Our experiments reveal the impacts of shells on ripple development in sandy sediment, providing information that was previously lacking. Shells expedite the onset of sediment transport while simultaneously reducing ripple dimensions and slowing down their migration rates. Moreover, increasing shell content enhances near-bed flow velocity due to the reduction of bed friction that is partly caused by a decrease in average ripple size and occurrence. This, in essence, limits the rate and magnitude of bed load transport. Given the large influence of shell content on sediment dynamics as well as the high shell concentrations found naturally in the sediments of shallow seas, a significant control from shells on the morphodynamics of sandy marine habitats is expected.

scholarly journals Sediment shell-content diminishes current-driven sand ripple development and migration

2021 ◽  
Author(s):  
Chiu H. Cheng ◽  
Jaco C. de Smit ◽  
Greg S. Fivash ◽  
Suzanne J. M. H. Hulscher ◽  
Bas W. Borsje ◽  
...  
Keyword(s):  
Direct Consequence ◽  
Bedload Transport ◽  
Sandy Sediment ◽  
Natural Sand ◽  
Significant Control ◽  
Ripple Formation ◽  
Marine Habitats ◽  
Biogenic Structures ◽  
Shell Content ◽  
And Migration

Abstract. Shells and shell fragments are biogenic structures that are widespread throughout natural sandy shelf seas and whose presence can affect the bed roughness and erodibility of the seabed. An important and direct consequence is the effect on the formation and movement of small bedforms such as sand ripples. We experimentally measured ripple formation and migration of a mixture of natural sand with increasing volumes of shell material in a racetrack flume. Our experiments reveal the impacts of shells on ripple development in sandy sediment, providing information that was previously lacking. Shells expedite the onset of sediment transport while simultaneously reducing ripple dimensions and slowing down their migration rates. Moreover, increasing shell content enhances near-bed flow velocity due to the reduction of bed friction that is partly caused by a decrease in average ripple size and occurrence. This, in essence, limits the rate and magnitude of bedload transport. Given the large influence of shell content on sediment dynamics on the one hand, and the high shell concentrations found naturally in the sediments of shallow seas on the other hand, a significant control from shells on the morphodynamics of sandy marine habitats is expected.

scholarly journals NBS1 interacts with Notch signaling in neuronal homeostasis

2020 ◽  
Vol 48 (19) ◽  
pp. 10924-10939
Author(s):  
Zhong-Wei Zhou ◽  
Murat Kirtay ◽  
Nadine Schneble ◽  
George Yakoub ◽  
Mingmei Ding ◽  
...  
Keyword(s):  
Notch Signaling ◽  
Notch Pathway ◽  
Direct Consequence ◽  
Nijmegen Breakage Syndrome ◽  
Neuron Development ◽  
Genetic Ablation ◽  
Notch Activity ◽  
And Migration

Abstract NBS1 is a critical component of the MRN (MRE11/RAD50/NBS1) complex, which regulates ATM- and ATR-mediated DNA damage response (DDR) pathways. Mutations in NBS1 cause the human genomic instability syndrome Nijmegen Breakage Syndrome (NBS), of which neuronal deficits, including microcephaly and intellectual disability, are classical hallmarks. Given its function in the DDR to ensure proper proliferation and prevent death of replicating cells, NBS1 is essential for life. Here we show that, unexpectedly, Nbs1 deletion is dispensable for postmitotic neurons, but compromises their arborization and migration due to dysregulated Notch signaling. We find that Nbs1 interacts with NICD-RBPJ, the effector of Notch signaling, and inhibits Notch activity. Genetic ablation or pharmaceutical inhibition of Notch signaling rescues the maturation and migration defects of Nbs1-deficient neurons in vitro and in vivo. Upregulation of Notch by Nbs1 deletion is independent of the key DDR downstream effector p53 and inactivation of each MRN component produces a different pattern of Notch activity and distinct neuronal defects. These data indicate that neuronal defects and aberrant Notch activity in Nbs1-deficient cells are unlikely to be a direct consequence of loss of MRN-mediated DDR function. This study discloses a novel function of NBS1 in crosstalk with the Notch pathway in neuron development.

SPATIAL AND TEMPORAL VARIABILITY IN RIPPLE FORMATION AND MIGRATION ACROSS A CORAL REEF FLAT AND LAGOON

2019 ◽  
Author(s):  
KURT ROSENBERGER ◽  
CURT STORLAZZI ◽  
ANDREW POMEROY ◽  
OLIVIA CHERITON ◽  
RYAN LOWE ◽  
...  
Keyword(s):  
Coral Reef ◽  
Temporal Variability ◽  
Reef Flat ◽  
Spatial And Temporal Variability ◽  
Ripple Formation ◽  
And Migration

scholarly journals Changes in growth and migration patterns of sea trout before and after the introduction of Atlantic salmon farming

2020 ◽  
Author(s):  
Sindre Håvarstein Eldøy ◽  
D Ryan ◽  
W K Roche ◽  
E B Thorstad ◽  
T F Næsje ◽  
...  
Keyword(s):  
Reproductive Potential ◽  
Growth Patterns ◽  
Anthropogenic Factors ◽  
Salmon Farming ◽  
Sea Trout ◽  
Marine Habitats ◽  
Management Measures ◽  
Before And After ◽  
And Migration ◽  
Visual Reading

Marine growth has strong implications for reproductive potential and ultimate fitness of sea trout. Hence, the effects of anthropogenic factors on marine growth are important when evaluating population responses and implementing management measures. Temporal changes in growth patterns of sea trout from three Norwegian and two Irish watercourses were examined, covering time spans of 25–65 years. Elemental chemistry Ba:Ca profiles and visual reading of fish scales were used to estimate smolt length and lifetime growth after first sea entry. Reduced growth after the first sea entry coincided with periods of nearby (<14 km) salmon-farming activity in impacted watersheds in both countries. Increased Ba:Ca levels were also recorded during these periods, likely indicating reduced residency in marine habitats caused by premature return to freshwater and estuaries. An increase in estimated length at first sea entry coinciding with salmon-farming activity, for groups of fish sampled after sea migration, suggests a size-selective marine mortality, with the smallest individuals experiencing a larger mortality.

Editorial: Governing the Poor – Migration and Poverty

2020 ◽  
Vol 66 (4) ◽  
pp. 363-385
Author(s):  
Lisa Marie Borrelli ◽  
Yann Bochsler
Keyword(s):  
Welfare Recipients ◽  
State Agencies ◽  
Special Issue ◽  
State Institutions ◽  
Significant Control ◽  
The Poor ◽  
Migration Control ◽  
And Migration ◽  
Media Practices ◽  
Policy Mechanisms

Abstract In contrast to the nexus between welfare and migration control, the link between migration and poverty (or rather the perception of poverty), has not received the same amount of political interest, but also public and scholarly attention. Yet, there are multiple ways in which migrants are rendered or perceived as poor in receiving states after having migrated. Hence, this special issue addresses the intersection of migration and poverty. The contributions cover various socio-legal, political and discursive aspects of how state institutions and non-state agencies address, and how poor citizens and migrant individuals in the broadest sense deal with, precariousness and discrimination in the states where they have settled or within which they have moved. In public and political discourse, migrant individuals are often portrayed as underserving, needy and dependent on the ‘receiving states’. Yet, what is often overlooked is how this assumed dependency is constructed by policies and laws, encouraged by media practices and everyday street-level implementation, to the degree that it demonises the foreign ‘other’, accused of misusing welfare assistance. At the same time, we find similar framings regarding marginalised citizens, such as welfare recipients, which discloses the moral character of social policies and a hierarchy of deservingness-recognition. Within the special issue, we critically discuss how such representations and policy mechanisms allow for the discriminatory circumscription of rights and services of the ‘poor’ and migrants that are deeply embedded in welfare chauvinist attitudes, causing significant control and surveillance by the state.

scholarly journals Supplementary material to "Sediment shell-content diminishes current-driven sand ripple development and migration"

2021 ◽  
Author(s):  
Chiu H. Cheng ◽  
Jaco C. de Smit ◽  
Greg S. Fivash ◽  
Suzanne J. M. H. Hulscher ◽  
Bas W. Borsje ◽  
...  
Keyword(s):  
Sand Ripple ◽  
Supplementary Material ◽  
Shell Content ◽  
And Migration

The influence of gravel mixed with sand on the formation and development of ripples.

2020 ◽  
Author(s):  
Katrien Van Landeghem ◽  
Irinios Yiannoukos ◽  
Connor McCarron ◽  
Jacob Morgan ◽  
Barney Clayton-Smith
Keyword(s):  
Sediment Transport ◽  
Critical Shear Stress ◽  
Bedload Transport ◽  
Migration Rates ◽  
Ripple Formation ◽  
Shelf Seas ◽  
Flow Speeds ◽  
And Migration ◽  
Sand And Gravel ◽  
Sediment Mixtures

<p>Coarse and bimodal sediment mixtures like sand and gravel are common in palaeo-glaciated shelf seas and in coastal environments. Their presence leads to more complex sediment transport and morphodynamic processes, depending on the ratio of sand to gravel in the bed. With increased pressure on our near-and offshore sea beds, there is a growing need to more accurately model sediment transport and bedform dynamics with an increasing focus on bimodal sand-gravel sediment mixtures. Revisiting the quantification of the hiding-exposure (HE) effect highlighted how differently sized grains in a bimodal mixture modify each other’s threshold of motion. The critical shear stress needed to mobilise the sand and gravel fractions increased by up to 75% and decreased by up to 64% respectively, compared to that needed to mobilise well-sorted sediment of similar size. Implementation of this newly quantified HE correction in current-and wave-driven models illustrated that its influence on bedload transport rates and bed morphodynamics was greatest for mixtures where gravel percentage ranges between 10 and 20 %. Laboratory experiments were therefore conducted to investigate ripple formation and bed dynamics in mixtures with gravel percentage between 0 and 25%. The development of initial bedforms was quicker in sand-gravel mixtures compared to those developed in pure sand, whilst final heights and migration rates of the developed ripples decreased with increasing fraction of gravel in the bed. During this presentation, a full comparison will be made of the morphology and “down-core” sedimentary properties of ripples formed at different flow speeds. If we want to use our seabeds cost-effectively and sustainably, we need a better understanding on the influence of a decreased mobilisation of the finer fractions and an increased mobilisation of the coarser fraction on the dynamics of beds with a bimodal sediment composition.</p>

scholarly journals Relaxin-like factor (RLF) serum concentrations and gubernaculum RLF receptor display in relation to pre- and neonatal development of rats

Reproduction ◽  
2001 ◽  
pp. 899-906 ◽  
Author(s):  
FR Boockfor ◽  
G Fullbright ◽  
EE Bullesbach ◽  
C Schwabe
Keyword(s):  
Developmental Stages ◽  
Direct Consequence ◽  
Biologically Active ◽  
Male Rat ◽  
Serum Concentrations ◽  
Rat Pups ◽  
Biological Responses ◽  
Phases Of Development ◽  
And Migration

Deletion of the relaxin-like factor (RLF) gene in mice causes retention of testicles and infertility. The development of a synthetic RLF has made it possible to investigate the events that connect the genomic event and the basic biological responses that cause gonadal positioning. Anti-RLF antibodies were raised against synthetic RLF, allowing determination of RLF concentrations during the critical period, testing for RLF receptors on the gubernaculum and exploration of the temporal relationship between receptor display and migration of the testes in developing rats. In male rat pups, serum RLF concentrations were high at day 2 before parturition (2.4 ng ml(-1)) and decreased sharply just before parturition. Thereafter, males and females had the same low serum concentrations until RLF concen-trations began to increase in males only, starting at day 10 after parturition and continuing until adult RLF concentrations (0.6 ng ml(-1)) were reached on day 39 after parturition. The testicles are descending into the scrotum during this phase of increasing RLF concentrations and are descended fully by day 19-21 after parturition, before adult hormone concentrations are established. The high prenatal serum RLF concentration coincides with high expression of RLF receptors in the gubernaculum tissue. Competitive binding of RLF per mg of membrane protein prepared from rat gubernacula at various developmental stages showed no increase in receptor density as sexual maturity was reached. Gubernaculum cells in primary culture showed an increased uptake of 5-bromo-2'-deoxyuridine in the presence of RLF compared with controls. These studies demonstrate that the synthetic RLF is biologically active and indicate that the cryptorchid phenotype INSL3(-/-) is a direct consequence of defective gubernaculum growth, caused by the absence of RLF during early phases of development.

scholarly journals TRANSIENT RIPPLE FORMATION AND SEDIMENT TRANSPORT

1986 ◽  
Vol 1 (20) ◽  
pp. 120
Author(s):  
Suphat Vongvisessomjai ◽  
L.C.J. Munasinghe ◽  
P.P. Gunaratna
Keyword(s):  
Sediment Transport ◽  
Surface Waves ◽  
Coastal Engineering ◽  
Transport Rate ◽  
Beach Morphology ◽  
Ripple Formation ◽  
Engineering Problems ◽  
Successful Measurement ◽  
And Migration ◽  
Rates Of Growth

A knowledge of sediment transport rates due to wave action is essential for an understanding of various coastal engineering problems. Many problems have to be resolved before successful measurement can be made for sediment transport rates due to waves. Since gradients of sediment transport cause changes of beach morphology, the sediment transport rate outside breaker can be determined from measured beach changes. Measurements of ripple growth and migration yield their mathematical descriptions in the same manner as those of surface waves. Expressions of sediment transport rates are then derived. It is found from the study that the sediment transport rates are strongly controlled by the rates of growth and migration of ripples.

scholarly journals THE CRITERION OF RIPPLE FORMATION BY WAVE ACTION

1988 ◽  
Vol 1 (21) ◽  
pp. 138
Author(s):  
Yoshito Tsuchiya ◽  
Masato Banno
Keyword(s):  
Experimental Data ◽  
Specific Gravity ◽  
Wave Action ◽  
Common Mechanism ◽  
Natural Sand ◽  
Water Particle ◽  
Acceleration Parameter ◽  
Ripple Formation ◽  
Unidirectional Flow ◽  
Grain Diameter

In this paper, we emphasize that there must exist a common mechanism governing ripple formation in the case of both waves where the acceleration effect exists, and unidirectional flow, where the acceleration effect is usually ignored. Using a light sediment with an immersed specific gravity of about 0.8, which is nearly one-half that of natural sand, a series of ripple formation experiments were performed in order to determine the formation criterion. Using the experimental data, along with data collected by other researchers the ripple-formation criterion was investigated in terms of the ratio of water particle orbital diameter to sediment grain diameter as an acceleration parameter, on the so-called Shields diagram. Emphasis is placed on the importance of this ratio in the criterion of ripple formation in relation to that by unidirectional flow.

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