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The seeding of cells into an organ is an important step in cell therapy because the final functional properties of the organ are related to the initial cell distribution throughout the organ. However, vessel occlusion is a serious problem that prevents uniform distribution of the cells in the entire organ. Understanding the mechanism of vessel occlusion can help optimize the seeding process. In this study, the vessel occlusion phenomenon under perfusion conditions during cell seeding was investigated. First, we applied a microfluidic system that enabled the observation of the occlusion events during injection. Second, we applied a multiphase numerical model that can describe the cell–cell interactions and cell–fluid interactions to investigate the vessel occlusion phenomenon during the seeding process. In particular, the effects of cell concentration and flow rate were investigated. The results indicate the importance of cell–cell interactions and cell–vessel interactions for the occurrence of vessel occlusion. In addition, it is found that the probability of occurrence of vessel occlusion increases with the increase in cell concentration and decrease in flow rate. The simulation model can help determine the optimum parameters to enhance cell seeding efficiency.

An experimental and analytical study of the tonal trailing-edge noise of a symmetric NACA-0012 aerofoil and of a cambered SD7003 aerofoil has been achieved. It provides a complete experimental database for both aerofoils and improves the understanding of the underlying mechanisms. The analysis stresses the high sensitivity of the tonal noise phenomenon to the flow velocity and the angle of attack. Several regimes of the noise emission are observed depending on the aforementioned parameters. The contributions of the pressure and the suction sides are found to vary with the flow parameters too. A special attention has been paid to the role of the separation bubble in the tonal noise generation. Hot-wire measurements and flow visualization prove that the separation bubble is a necessary condition for the tonal noise production. Moreover, the bubble must be located close enough to the trailing edge. Several tests with small-scale upstream turbulence confirm the existence of the feedback loop. Analytical predictions with a classical trailing-edge noise model show a good agreement with the experimental data, they confirm the cause-to-effect relationship between the wall-pressure fluctuations and the radiated sound. Finally, previously reported works on fans and propellers are shortly re-addressed to show that the tonal noise associated with laminar-boundary-layer instabilities can take place in rotating blade technology.

This essay considers Deleuze and Guattari’s paradoxical claim that Marx’s critique of political economy implies as a universal history derived from the singular features of capitalism. In this critique, capitalism is defined by the commodity form, as a relationship of economic equivalence that replaces the bonds of dependence underlying other social formations. By negating relations of kinship and caste, capitalism reveals, a contrario, the universal foundation of other societies. As the “negative of all social formations,” capitalism conditions a universal history, defined, retrospectively, from the singular standpoint of a society, based upon the negation of kinship and caste. In this universal history, moreover, the negation of capitalism is identified with the possibility of a new and equally singular form of society. In Anti-Oedipus, the latter is defined as a “schizophrenic” condition liberated from the commodity as well as from the bonds of dependence that constituted the universal foundation of earlier societies.

This paper examines Jacques Derrida's deconstruction of Giorgio Agamben's account of the history of bio-politics in the Beast and the Sovereign. In this account, the ‘threshold of bio-political modernity’ is identified with the collapse of an allegedly immemorial distinction between life and the law. According to Derrida, however, this in-distinction between life and the law, which supposedly marks the historical emergence of the bio-political, is in fact an originary event. Agamben, therefore, announces a bio-political modernity that has always already existed. In this essay, I argue that Derrida, in the Beast and the Sovereign, fails to grasp the significance of one of the principal figures employed in Agamben's theory of the bio-political, the ‘threshold’. This figure, which Agamben opposes, elsewhere in his writings, to the Derridean notion of difference/deferral, does not refer to either an historical beginning or something that has always already existed. Rather, the threshold is defined as a particular moment in which an originary phenomenon becomes a decisive historical norm. In his ‘history’ of the bio-political, therefore, Agamben identifies the modernity of the latter in terms of the historical normalization of an in-distinction between law and life that has always already occurred.

The seeding of cells into an organ is an important step in cell therapy because the final functional properties of the organ are related to the initial cell distribution throughout the organ. However, vessel occlusion is a serious problem that prevents uniform distribution of the cells in the entire organ. Understanding the mechanism of vessel occlusion can help optimize the seeding process. In this study, the vessel occlusion phenomenon under perfusion conditions during cell seeding was investigated. First, we applied a microfluidic system that enabled the observation of the occlusion events during injection. Second, we applied a multiphase numerical model that can describe the cell-cell interactions and cell-fluid interactions to investigate the vessel occlusion phenomenon during the seeding process. In particular, the effects of cell concentration and flow rate were investigated. The results indicate the importance of cell-cell interactions and cell-vessel interactions for the occurrence of vessel occlusion. In addition, it is found that the probability of occurrence of vessel occlusion increases with the increase in cell concentration and decrease in flow rate. The simulation model can help determine the optimum parameters to enhance cell seeding efficiency.

The Ba Lai distributary channel of the Mekong River Delta was abandoned and infilled with sediment during the Late Holocene, providing a unique opportunity to investigate the sediment fill, timing and mechanisms of channel abandonment in tide-dominated deltaic systems. Based on analysis and age dating of four sediment cores, we show that the channel was active since 2.6 ka and was abandoned at 0.7 ka as marked by the abrupt disappearance of the sand fraction and increase in organic matter and sediment accumulation rate. We estimate that the channel might have been filled in a time range of 45–263 years after detachment from the deltaic network, with sediment accumulation rates of centimetres to decimetres per year, rapidly storing approximately 600 Mt of organic-rich mud. We suggest that the channel was abandoned due to a sediment buildup favoured by an increase in regional sediment supply to the delta. This study highlights that mechanisms for abandonment and infilling of tide-dominated deltaic channels do not entirely fit widely used models developed for fluvial-dominated environments. Their abandonment might be driven by autogenic factors related to the river-tidal and deltaic dynamics and favoured by allogenic factors (e.g., human impact and/or climate change).

A high-fidelity computational analysis carefully validated against concurrently obtained experimental results is employed to examine self-noise radiation of airfoils at transitional flow regimes, with a focus on elucidating the connection between the unsteady behavior of the laminar separation bubble (LSB) and the acoustic feedback-loop (AFL) resonant interactions observed in the airfoil boundary layers. The employed parametric study examines AFL sensitivity to the changes in the upstream flow conditions and the airfoil loading. Implicit Large-Eddy Simulations are performed for a NACA-0012 airfoil in selected transitional-flow regimes for which experimental measurements recorded characteristic multiple-tone acoustic spectra with a dual ladder-type frequency structure. The switch between the tone-producing and no-tone-producing regimes is traced to the LSB size and position as a function of the flow Reynolds number and the airfoil angle of attack, and further substantiated by the linear stability analysis. The results indicate a strong multi-tonal airfoil noise radiation associated with the AFL and attributed to the switch from the slowly-growing Tollmien–Schlichting to the fast-growing Kelvin–Helmholtz instabilities occurring in thin LSB regions when those are localized near the trailing-edge (TE) on either side of the airfoil. Such a process eventually results in the nonlinearly saturated flapping vortical modes (“rollers”) that scatter into acoustic waves at the TE.

Since the 1990s the Mekong River delta has suffered a large decline in sediment supply causing coastal erosion, following catchment disturbance through hydropower dam construction and sand extraction. However, our new geological reconstruction of 2500-years of delta shoreline changes show that serious coastal erosion actually started much earlier. Data shows the sandy coast bounding river mouths accreted consistently at a rate of +2 to +4 km2/year. In contrast, we identified a variable accretion rate of the muddy deltaic protrusion at Camau; it was 2/year before 1400 years ago but increased drastically around 600 years ago, forming the entire Camau Peninsula. This high level of mud supply had sharply declined by the early 20th century after a vast canal network was built on the delta. Since then the Peninsula has been eroding, promoted by the conjunction of mud sequestration in the delta plain driven by expansion of rice cultivation, and hysteresis of long-term muddy sedimentation that left the protrusion exposed to wave erosion. Natural mitigation would require substantial increases in sediment supply well above the pre-1990s levels.

Limited information is known about organophosphate esters (OPEs) in sediments of the Dong Nai River System (DNRS) in Vietnam and the influences of complex hydro-sedimentary dynamics on their fate. In this study, 48 surface sediment samples were collected from the Dong Nai-Soai Rap River and its tributary Vam Co River for the determination of 11 target OPEs, together with grain size and total organic carbon (TOC). The total concentrations of OPEs were in the range of 39.4 ng/g dw-373 ng/g dw (mean: 128 ng/g dw), and tris(1-chloro-2-propyl) phosphate (TCPP) was the predominant one with an average contribution of 81%, followed by tri-n-butyl phosphate (TNBP), tris(2-ethylhexyl) phosphate (TEHP). The composition profiles of OPEs at different locations of the DNRS showed no significant differences (p 0.05). In addition, the distribution of OPEs had been influenced by both human activities and the fluvial-tidal interactions. The highly frequent and various human activities in Ho Chi Minh City (HCMC) leaded to the highest total concentration of OPEs in the midstream site. Based on our dataset, TOC content and grain size of sediments had significant correlation with certain OPEs (p 0.05), and sediments with higher TOC content and finer grain size in the DNRS were more likely to be deposited in the downstream reach, contributing to the estuary of the DNRS was identified as another hotspot with the second highest concentration of OPEs. Furthermore, the distribution of OPEs in the transects had distinct characteristics, which reflected the joint influence of the human activities and fluvial-tidal interaction as well. However, the mechanism of their influence needed further investigation.

This essay proposes a reading of Nhất Linh’s “Going to the West” (Đi Tây, 1935). The travelogue presents a critique of colonialism that was prevalent among the interwar Vietnamese elite. In...

The current work reports on the results of high-accuracy two-dimensional and high-fidelity three-dimensional Navier–Stokes simulations of an SD7003 airfoil interacting with canonical upstream flow ...

As the world's third largest delta and one of the world's most important biodiversity hotspots, the Mekong Delta provides both ecological and food security for its inhabitants. Nevertheless, the delta has been threatened by climate change and human activities, particularly the proliferation of hydropower development across the Mekong Basin since the 1990s. However, compared to the well-studied Holocene Mekong Delta, our understanding of the recent 50-year evolution of the Mekong Delta is not sufficient to address these threats. In this study, we used 43-year Landsat images from 1973 to 2015 to investigate the entirety of the Mekong Delta's shoreline, land area and geomorphological changes. We compiled a new and comprehensive GIS database of the dams and irrigations of the Mekong Basin. The goal was to improve our knowledge of the recent evolution of the Mekong Delta and to link the potential impacts of dams and other factors. Our results show that the Mekong Delta is experiencing a significant decrease in the shoreline progradation rate. Currently, 66% of the entire delta shoreline is under erosion. The erosion segments are mainly located on the eastern side of the Ca Mau Peninsula and northwestern side of the delta in the Gulf of Thailand (GoT). Most parts of the shorelines in the estuarine area are still growing, although river sediment continues to decrease. Geomorphological asymmetries, discontinuous shoreline shifts, and sandy beach-ridge sets can be observed in multitemporal images. The entire Mekong Delta experienced a shift from growing to shrinking around 2005 with the gradual increase of the total accumulated installed capacity of the dams over the entire river basin. In the near future, the realization of planned dams, extension of irrigation, groundwater withdrawal, uncontrolled riverbed mining, delta subsidence, sea level rise, and other factors will accelerate the ongoing delta erosion.

The fluvial to marine transition zone (FMTZ) is the area of coastal rivers in which sedimentation is controlled by the interaction of fluvial and marine processes. This study examines the FMTZ of the Mekong River delta, along a total channel length of ~660 km. Methods consist of collection and analysis of channel bed sediment samples, measurements of channel morphological parameters, and recognition of mangrove, molluscan, and diatom species. The process regime, salinity, morphological, and sedimentary trends recognized were used to define two main tracts for this FMTZ: an upstream, fluvial-dominated tract and a downstream, tide-dominated tract. In more detail, they allow the identification of four subzones, from upstream to downstream: 1) fluvial-dominated, tide-affected; 2) fluvial-dominated, tide-influenced; 3) tide-dominated, fluvial-influenced; and 4) tide-dominated, fluvial-affected. Tide-induced water-level changes affect the entire study area and extend into Cambodia. Measured salinity intrusion extends ~15 km upstream of the river mouth during wet season, and ~50 km during dry season. Brackish water species of mangroves, mollusks, and diatoms, however, occur landward of these limits, suggesting that highly diluted brackish water may reach ~160 km upstream of the river mouth during the dry season. In the fluvial-dominated tract, channels are sinuous and show a seaward-deepening trend, whereas width is relatively constant. In the tide-dominated tract, channels are straight, and show seaward-widening and seaward-shallowing trends. Natural levees are present in the fluvial-dominated, tide-affected subzone, but are replaced by mangroves elsewhere along the FMTZ. In the fluvial-dominated tract, mud content is low, sand grain size fines seaward, and gravelly sand and sand are the dominant facies. In the tide-dominated tract, mud content is high, sand grain size is constant, recycled sand is common, and tidal rhythmites are the dominant facies. Mud pebbles are common in sediments throughout a large part of the FMTZ. These trends characterizing the FMTZ of the Mekong River delta seem to be present in other systems and likely represent a general FMTZ pattern. Nonetheless, minor differences may be observed between different types of systems, or because of differences in local conditions. The comprehensive description of trends and their mutual relationships along the FMTZ presented herein provides critical information that can form the basis of a general conceptual model and can help to better understand these complex zones.

International audience; River delta shorelines composed of sand may be characterized by complex spatial and temporal patterns of erosion and accretion even when sand supply is readily available. This is especially the case for deltas with multiple mouths subject to significant wave and tide influence. High-resolution topographical and wave and current measurements were conducted from 2010 to 2012 at Ba Ding beach, a popular resort located on the largest of the multiple inter-distributary plains of the Mekong River delta. Ba Dang beach is a mesotidal, multiple bar-trough system. The upper beach corresponds to the current active beach ridge in the sequence of ridges that have marked the progradation of the inter-distributary delta plains, and is capped by a low foredune that protects villages and agricultural land from marine flooding. During the low river-flow season, the beach is characterized by Northeast monsoon waves and strong longshore currents that transport sediment towards the southwest. Weaker longshore currents towards the northeast are generated by Southwest monsoon waves during the high river-flow season. Ba Dang beach underwent strong erosion between 2010 and 2012, following a phase of massive accretion. In 2012, this erosion resulted in breaching of the foredune, contributing to concerns that the Mekong delta had become vulnerable to retreat. The local erosion at Ba Dang needs to be considered, however, in the broader context of delta shoreline morphodynamics, which involves space- and time-varying patterns of beach accretion and erosion. These patterns are the present expressions of plan-view beach-ridge morphology in the delta, which is characterized by flaring and truncations that reflect changing beach morphodynamics in the course of deltaic progradation. We surmise that these patterns are related to complex interactions involving river water and sediment discharge, waves and wave-generated longshore currents, tidal currents, and shoreline orientation.

Along the fluvial to marine transition zone (FMTZ) of river deltas, the river-tidal dynamics exert a primary control on channel width, sinuosity, and bed elevation; however, other local factors, such as valley confinements, bifurcations, and confluences, can modify the channel morphology. Here, we report a case study of the major channel of the Ðồng Nai River System (DNRS) that shows complex morphological trends linked to multiple factors. This study is based on the analysis of satellite images and bathymetric maps of the studied channel, together with a digital elevation model of the area and additional climate and hydrology data. Our study shows that channel width, sinuosity, and bed elevation show mutual relationships and complex upstream to downstream trends linked to the river-tidal dynamics and valley confinements, together with more local effects due to bifurcations and confluences. The tidal dynamics is mainly responsible for the seaward-widening and seaward-shallowing trends and the abrupt decrease in channel sinuosity observed in the downstream tract of the channel, whereas the relatively constant channel width and sinuosity in the upstream tract suggest a control of the river dynamics. The studied channel also shows three areas of valley widening or exit, which are characterized by high channel sinuosity, the presence of minor and major bifurcations, and additional changes in channel width and bed elevation, and they are considered important nodes in this system. Valley-related nodes also show different active and inactive features, implying that the degree of activity and importance of these nodes likely varied through time, migrating from upstream to downstream due to the deltaic progradation.

Mangroves can deliver important socio-economic benefits and store significant volumes of carbon along tropical to temperate coastlines, but the distribution is controlled by complex geomorphologic, hydrodynamic and salinity conditions, as well as human-related pressures. In the Mekong delta, the interaction of tide, wave and riverine hydrodynamic processes clearly impacts sedimentation and mangrove distribution. Extensive mangroves presently occur along the northeastern delta margin (Can Gio, located 40 km southeast of Ho Chi Minh City), in an embayed, back-barrier environment subject to the highest tidal range (c. 4 m) and away from major fluvial distributary channels. However, the development of the Can Gio mangrove system during the Holocene evolution of the Mekong delta is not fully understood. This study aims to constrain the sedimentary evolution of the back-barrier mangrove in Can Gio based on stratigraphic, palynological and geochronological analyses of sediment cores. Two deep borehole cores (15 and 30 m deep) and four short auger cores (up to 4 m deep) were taken at the modern mangrove to characterize a 20-km-long shore-normal cross section dated with radiocarbon and optically-stimulated luminescence (OSL) ages. The cores consist of a thick (> 20 m) subtidal mud from the base of the Holocene unit to the level of 3–4 m deep below the ground level, overlain by carbonaceous, intertidal mud. Chronological data reveal major episode of subtidal mud aggradation from 6 to 3.5 ka, forming the topography for mangrove development. Radiocarbon ages in the overlying intertidal mud range from 4 ka to modern and show some inconsistencies with the stratigraphy, suggesting mangrove root penetration and sediment mixing. The beach-ridge structure and OSL ages of the Can Gio barrier indicate that barrier formation initiated just before 3.2 ka. The transition from subtidal to intertidal mud aggradation and initiation of barrier formation, are broadly correlated with the onset of the subaqueous delta progradation and shift to a wave-dominated regime in the central delta. However, after 3.5 ka, the Can Gio shoreline had negligible sediment accretion while the central delta prograded up to 50 km seawards. Reduced sediment supply to Can Gio is consistent with more asymmetric, southwestward-dominated longshore drift after 3.5 ka. The negligible progradation at Can Gio also indicates minor sediment supply from the nearby Dong Nai River, which prevented upper intertidal accretion and translation of mangroves into a flood plain.

Having developed in the later Quaternary Period, the Mui Ne dunefield, representing the upper-most portion of a major coastal barrier complex in SE Vietnam, formed by wind regimes associated with the Asian monsoon climate. The barrier complex is 100 km long and higher than 150 m in elevation but despite its large dimensions, research on its geomorphological and geological characterization is limited. Several active dune fields extend 2–10 km landwards from the coast while the rest of the barrier surface is stabilized. We applied ground-penetrating radar (GPR) and quartz optically-stimulated luminescence (OSL) dating to the transverse dunes of the Mui Ne dunefield to characterize the morphostratigraphy and recent aeolian sedimentation history. Currently the dunes have a relief of typically 5–10 m and a wavelength of 50–100 m. They are driven by the northeasterly winter monsoon winds and reversed with minor relief in response to the southwesterly summer monsoon. GPR profiles and OSL ages define three morphostratigraphic units: the modern, Holocene, and Pleistocene dune units. The GPR data of the modern dune unit is dominated by a series of steep reflections that dip exclusively towards the west reflecting the winter monsoon and is punctuated by reactivation surfaces. Evidence for the wind reversal is not preserved in the sediment successions but is represented by reactivation surfaces. Thus a subunit bounded by the reactivation surfaces defines annual deposition. The preservation potential of a subunit varies with the migration rate of the transverse dune, and in the fastest migrating dunes, approximately one subunit was preserved every year (1.1 ± 0.6 subunit/yr). The modern dunes are generally younger than 100 years and have migrated WSW at net rates of 0.6–2.5 m/yr. The Holocene dune unit is as thick as the modern unit although it spans a period, ten times longer, reflecting the lower preservation potential of the transverse dunes as sedimentary records, due to erosion associated with their migration. The rate of dune migration suggests that an aeolian contribution of coastal sands has occurred following the sea level highstand of the Middle Holocene, accounting for the extent of the active dunefields. This mode of the barrier accumulation is considered as an analogue for earlier highstand events. However, the dunefields only cover a fraction of the entire barrier. It is thus inferred that barrier formation occurred over a long period, probably encompassing several glacial-interglacial cycles. Sand accumulation during the lowstand, either by transport of sand from the subaerially exposed shelf and/or reworking of sand emplaced during the prior highstand, may contribute significantly to the barrier development.

Studies on the sediment distribution along the fluvial to marine transition zone are rare and have focused on large-scale systems. Here, we report a case study from the Dong Nai River System (DNRS), a small-scale, tide-dominated river delta from southern Vietnam. The study is based on 80 channel bed sediment samples, together with channel depth, temperature, and salinity measurements, identification of mangroves and mollusks, and grain-size analysis. Year-round meter-scale water-level fluctuations due to tides are present across the entire study area, whereas saline-water intrusion affects the entire studied part of the Vam Co Dong–Vam Co River and the majority of the studied part of the Dong Nai–Soai Rap River. The sediment distribution of both channels highlights the presence of a downstream area characterized by soft mud indicating active deposition, and upstream areas characterized by sand and gravel sediments with abundant bedrock clasts and other evidence of the extremely limited sedimentation (e.g., encrusting biostructures, borings, coating, and agglutinated mats). The coarser-grained sand and gravel are likely reworked from local bedrock and transported for short distances as also suggested by their angularity and the similarities with Pleistocene sedimentary and igneous rocks in the study area. The sediment of the DNRS is overall coarser and muddier than the sediment of the Mekong, likely reflecting the smaller scale of this system, the lower discharge, and the local sediment supply from the bedrock.

Understanding the relationship between depositional processes and their products in the fluvial–marine transition zone in tide-dominated depositional systems is fundamental to improving environmental and stratigraphic interpretations of long-term sedimentary records. The distributary channels of the Mekong Delta represent a typical example of a complex sedimentary environment characterized by strong fluvial and tidal interactions, and seasonal variability in hydro-sedimentary dynamic processes, particularly the migration of a salt wedge front linked to seasonal fluctuations in freshwater discharge. For this study, we analyzed grain size, magnetic susceptibility, and organic elemental geochemistry of channel-bed surficial sediments collected in 2015 from all distributary channels during the dry season and from the Mekong–Co Chien River during the flood season. This paper reports spatial and seasonal differences in the characteristics of channel-bed surficial sediments, which are closely linked to sediment sources and depositional processes during the dry and flood seasons. Distributary channels are characterized by coarse-grained sediments in the upper reaches and fine-grained sediments in the lower reaches, in both dry and flood seasons, reflecting the difference between the upstream fluvial-dominated environment and the downstream tide-dominated environment. Flood season samples from the Co Chien River show higher magnetic mineral contents and a terrestrial source of organic carbon compared with dry season samples, indicating sourcing from the drainage basin and trapping of suspended materials in the distributary channel due to the barrier effect of the saltwater wedge at the river mouth. Compared with the flood season, during the dry season the mud content was lower in the downstream reach close to the river mouth and higher in the upstream reach of the Co Chien River, and the content of magnetic minerals was lower in both reaches, indicating dissolution of magnetic minerals during early diagenesis. Furthermore, the lower C/N ratios (