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79 Thus, geochronology of sediment using 137Cs is based on the fact that the depth of the peak concentration in the sediment column corresponds to the year 1963; 137Cs is also used to estimate rates of soil loss from agricultural land (He and Walling, 2003). Note that 134Cs is produced mainly by the neutron activation reaction of 133Cs in nuclear reactors and is not produced during nuclear explosions. Therefore, 134Cs in the environment results from its release from a nuclear power plant during an accident. Furthermore, the half-life of 134Cs is 2 y, too short to allow detection of the isotope’s activity after several decades; thus, its presence clearly represents a recent accident. We are currently engaged in ongoing research on the sedimentary environment in the Mekong River delta to assess the deltaic environment and its conservation status (Saito et al., 2012). During a survey of the deltaic sediment in October 2011, we conducted a geomorphological study and also took core samples. We were surprised to detect Cs isotopes released from the FDNPP in the core, and surveyed the same station the next year. The present study focuses on the Cs isotopes in the core in order to study the seasonal variations of this deltaic environment. Sediment erosion revealed by study of Cs isotopes derived from the Fukushima Dai-ichi nuclear power plant accident

Empirical understanding of decadal- to centennial-scale deltaic shoreline changes in the past is essential for understanding the fate of coasts in the coming decades and centuries. We tested the effectiveness of quartz optically-stimulated luminescence (OSL) dating of beach ridges to constrain shoreline changes of the Mekong River delta over the last 3500 years. Forty-seven OSL ages have been analyzed from the Tra Vinh delta plain, central Mekong River delta. The Tra Vinh beach ridges are recurved and branching, showing the hierarchy of shoreline changes, which include discontinuous shifts c. 5 km seawards caused by the emergence and elongation of a delta-front bar/island, and subsequent downdrift accretion of spits. The spit accretion is interrupted by changes of shoreline orientation. Each of the discontinuous shifts resulted in a cluster of beach ridges, which is referred to as ridgeset. The beach ridge sediments were found to have excellent luminescence properties resulting in low age uncertainties of c. 5%. The OSL chronology agrees well with shoreline changes over recent decades and with radiocarbon ages of tidal flat sediment underlying the beach ridges. The chronology clearly illustrates the coastal progradation from 3500 years (relative to AD 2010) onwards. Two main types of beach ridge are present: recurved and trunk ridges. OSL ages of recurved ridges are consistently younger both downdrift and seawards, documenting decadal- to centennial-scale shoreline migration especially over the last 1500 years. Trunk ridges in contrast have less systematic ages because a trunk ridge is formed where the sediment is likely to have been reworked by waves. Ages of updrift trunk ridges characteristically show relatively young ages in each ridgeset, representing the extensive erosion and resedimentation of the updrift coast. Major changes in shoreline orientation occurred around 400–500 years, suggesting strengthening of the northeasterly winter monsoon at the beginning of the Little Ice Age. The rate of progradation of the Tra Vinh delta plain is described in two ways: frequency of the discontinuous shift, and growth rate of the delta plain area. Both suggest the coast has expanded regularly over the last 1000 years. A decrease in sand supply to the coast in the last few decades due to river dam construction and fluvial sand dredging is inferred, possibly affecting the behavior of the modern and future shorelines, which can be compared with the less human-influenced, centennial- to decadal-scale past shoreline changes reconstructed in this study.

The initial growth stage of a river delta can be defined either as the beginning geomorphologic expansion of the river-dominated coastal lowland or as the starting basinward-directed progradation of the geological/stratigraphic delta body. Differentiating between these two perspectives is necessary for understanding the sensitive reaction of a deltaic system to dynamic changes in sea-level and sediment availability. The Holocene evolution of the northeastern part of the Mekong River delta (Southern Vietnam) offers a great chance to depict these two different definitions and relate them genetically to each other since the transition between an old abrasion platform (inner delta) and the continental-shelf basin (outer delta) is well developed in this marginal part of the delta. The early stage of delta growth taking place during transgression-related inundation between 8 cal ka BP (maximum flooding) and 5.7 (6.0–4.8) cal ka BP (sea-level highstand) was characterized by tide-and saltwater-influenced nearshore conditions allowing extensive mangrove and tidal-flat deposits to aggradate on the wide abrasion platform. With the onset of regression around 4.8 cal ka BP the depositional center shifted immediately beyond the seaward margin of this estuarine platform and thus true deltaic progradation could develop leading to rapid construction of a delta body (and, in addition, to subsidence/tilting of the inner delta zone). Directly at the transition of these two deposystems, remains of shore-related deposits indicate the sudden breakdown of the estuarine platform conditions around 4.6 cal ka BP.

We consider the problem of verifying the correctness and completeness of the result of a keyword search. We introduce the concept of an authenticated web crawler and present its design and prototype implementation. An authenticated web crawler is a trusted program that computes a specially-crafted signature over the web contents it visits. This signature enables (i) the verification of common Internet queries on web pages, such as conjunctive keyword searches---this guarantees that the output of a conjunctive keyword search is correct and complete ; (ii) the verification of the content returned by such Internet queries---this guarantees that web data is authentic and has not been maliciously altered since the computation of the signature by the crawler. In our solution, the search engine returns a cryptographic proof of the query result. Both the proof size and the verification time are proportional only to the sizes of the query description and the query result, but do not depend on the number or sizes of the web pages over which the search is performed. As we experimentally demonstrate, the prototype implementation of our system provides a low communication overhead between the search engine and the user, and fast verification of the returned results by the user.

The geometry of river deltas is considered to refl ect the interplay of coastal processes, river discharge, and sediment supply. As ~25% of the world’s population lives on deltaic lowlands, prediction of delta growth is critical. Knowledge of processes responsible for delta geometries is not well established, although such knowledge is critical for the risk management of land use and settlements on deltas. The Mekong River delta of southern Vietnam is one of the largest deltas in the world and offers a unique opportunity to understand the sedimentary evolution of mixed tide- and wave-dominated large river deltas. We constrained the three-dimensional sedimentary evolution of the delta plains, based on optically stimulated luminescence dating of beach ridges coupled with radiocarbon-dated sediment cores. Results show that the beach shoreline in the lower delta plain initiated ca. 3.5 ka by aggradation on basement shoals. The delta plain propagated laterally during the late Holocene, evolving from bars that resulted in asymmetric bifurcation of the river mouth. Asymmetry was caused by the southwestward longshore sediment drift enhanced by the winter monsoon. Bars were successively formed on the wider side of the bifurcated river mouths, and subsequently accreted seaward, being stabilized by tide effects to result in shore-perpendicular elongate delta plains. Our work, based on the Mekong delta, demonstrates for the fi rst time that bar emergence is a key process in the long-term evolution of mixed tide- and wave-dominated deltas.

The aim of the study was to characterize a variety of sedimentary facies from the Mekong River delta (MRD) and to determine their geotechnical properties. The paper furthermore discusses the influences of sedimentary environment and conditions on geotechnical properties of the sedimentary facies. A core at the Vinhlong province, MRD, sufficiently presented the sedimentary facies of the area. Eight successive facies were identified based upon sedimentary properties. Characteristics of the unit showed development of sedimentary facies. Each sedimentary facies was formed under a different environment and revealed typical geotechnical properties. Estuarine channel, estuarine marine, delta front-mouth bar, and sub- to inter-tidal flat facies were formed under strong hydrodynamic conditions. The sediments are from clay to coarse sand and even pebbles, and the sedimentary structures are plentiful, such as intercalated clay, silt beddings and fine to coarse sand beddings with very different thicknesses. Strengths of these sedimentary facies vary significantly, which can be observed by cone penetration test (CPTU) results, but not by standard penetration test (SPT). The normalized values from CPTU show saw–tooth graphs with large variations, especially delta front-mouth bar and sub- to inter-tidal flat facies at shallower depth. The soil-behavior-types determined from the normalized values are plentiful from cohesionless to cohesive soils. As an example, an estuarine channel facies experiencing a large consolidation pressure, in relatively long-time (over 9920 yr BP) has geotechnical properties with heavily overconsolidated conditions and high strength. On the other hand, marsh, open bay, pro-delta and March/flood plain facies, which formed under relatively low hydrodynamic conditions, have simple and homogenous sedimentary properties. The sediments are commonly silt and clay, and sedimentary structures are very faint interbedded clay and silt laminae, and rarely very fine sand laminae. Strengths of these sedimentary facies increase linearly with depth, the normalized values are all rather constant with depth, and their soil behavior-type is only normally consolidated clays from CPTU results. It could be said that the particular sedimentary conditions in the late Pleistocene–Holocene deposits of MRD can be reasonably estimated by the CPTU test.

The Early Holocene initiation of the Mekong River delta, Vietnam, was investigated based on sedimentary facies, microfossil analyses, and radiocarbon dating of DT1 core taken from the upper delta plain. The DT1 core (105°38′51″E, 10°17′02″N, elevation + 2 m) is 51.5 m long and located in fill of a buried incised valley. This incised valley of the Paleo-Mekong River formed during the last glacial maximum, which is 20–30 km wide, has been traced spatially from the Cambodian border to the South China Sea coast by compilation of existing core data. The DT1 core records the history of the estuarine channel and delta systems of the Mekong River during the early to middle Holocene. The sedimentary facies, determined particularly from sedimentary structures, diatom and foraminifera assemblages, grain-size variation, and the accumulation rate, clearly show an upward-deepening succession in the lower part of the core from marsh or intertidal flat to subtidal-inner bay facies and an overlying upward-shallowing succession from prodelta to intertidal flat-floodplain. The boundary between the two successions, indicating the maximum flooding surface, occurred at approximately 8.0 ka, at the time that the Mekong River delta was initiated. The delta initiation and sediment facies succession are closely linked to Holocene sea-level changes, particularly a standstill from 8.0 to 7.5 ka after a rapid rise of sea level from 8.8 to 8.2 ka. During the further sea-level rise from 7.5 to 7.0 ka, sediments aggraded, forming topset sedimentary deposits.

Three radiocarbon-dated sediment cores from the northeastern Vietnamese Mekong River Delta have been analysed with a multiproxy approach (grain size, pollen and spores, macro-charcoal, carbon content) to unravel the palaeoenvironmental history of the region since the mid Holocene. During the mid-Holocene sea-level highstand a diverse, zoned and widespread mangrove belt (dominated by Rhizophora) covered the extended tidal flats. The subsequent regression and coeval delta progradation led to the rapid development of a back-mangrove community dominated by Ceriops and Bruguiera but also represented locally by e.g. Kandelia, Excoecaria and Phoenix. Along rivers this community seems to have endured even when the adjoining floodplain had already shifted to freshwater vegetation. Generally this freshwater vegetation has a strong swamp signature but locally Arecaceae, Fabaceae, Moraceae/ Urticaceae and Myrsinaceae are important and mirror the geomorphological diversity of the delta plain. The macro-charcoal record implies that natural burning of vegetation occurred throughout the records, however, the occurrence of the highest amounts of macro-charcoal particles is linked with modern human activity.

A mesotidal beach on the Mekong River delta coast exhibits unique patterns of river sediment discharge and experiences reversals of ocean wave directions in response to the summer and winter monsoons. We analyzed long-term changes of the shoreline since 1936 from past topographic maps and satellite images, and short-term changes in geomorphology and sedimentology by undertaking repeated field surveys between November 2005 and February 2008 along six shore-normal beach transects. The shoreline of the Mekong River delta coast has changed asymmetrically over the last 70 years in response to net southwestward sediment transport related to dry northeasterly winter monsoons. During the summer rainy season, large volumes of sediments are discharged from the river; at this time, wave direction is reversed in response to the relatively weak southwesterly summer monsoon. Mud and very fine sand in the surface sediments of the northeastern (updrift) beach transects tend to be removed during winter, suggesting that the sediment supplied from the river during summer is temporarily deposited near the river mouth and later transported southwestward during the winter monsoon. The relief of intertidal bars on the beach increased during winter in response to higher waves. However, previous studies have suggested that higher waves flatten bars. We hypothesize that the increase in relief that we observed is related to a wide and shallow subtidal delta-front platform that attenuates ocean waves at all times other than at high tide. The beach profile varies longshore: the accreting to stable beach dips seaward at a gradient of about 1/80 with up to three longshore intertidal bars, classified here as either slip-face bars or low-amplitude ridges. In contrast, the eroding beach profile is much steeper (1/20–1/40) and linear without intertidal bars, and is similar in form to a low-tide terrace. Because there is little variation of wave size and grain size within the study area, we consider that the spatial variation of the beach profile is related to the availability of sediment accumulated on the beach.

This paper explores the relationship between revolution and corruption in Jean Genet’s accounts of the Palestinian movement in his final work, Prisoner of Love. For Genet, corruption does not simply expose the actions of a revolutionary subject as an empty impersonation, performed for the actual ends of acquiring personal power and fortune. Rather, it exposes the ‘pretension’ inherent in the revolution it undermines as well as in the accumulation of value (for which the revolution is betrayed). For Genet, the misappropriation of money by the Palestinian leadership makes manifest the imaginary character of both devotion to a revolutionary cause and greed for the commodity-fetish (value). Corruption, in other words, betrays revolution as well as the ‘imaginary wealth and power’ which the ‘game of revolution’ attempts to destroy.

The objective of the current work is to compare variable-fidelity approaches for predictions of unsteady airfoil lift induced by an impinging turbulence based on the superposition of timeharmonic vortical gusts. First, analytical models are reviewed describing 2D, inviscid, timeharmonic gust-airfoil modal interactions. A low-fidelity model is then developed to predict the upstream turbulence response synthesized using a superposition of gust responses and based on the random flow generation (RFG) procedure. Finally, the results obtained using the proposed analytical inviscid model are compared against high-fidelity viscous simulations performed for NACA0012 and SD7003 airfoils.

As international concern for the survival of deltas grows, the Mekong River delta, the world’s third largest delta, densely populated, considered as Southeast Asia’s most important food basket and rich in biodiversity at the world scale, is also increasingly affected by human activities and exposed to subsidence and coastal erosion. Several dams have been constructed upstream of the delta and many more are now planned. We quantify from high-resolution SPOT 5 satellite images large-scale shoreline erosion and land loss between 2003 and 2012 that now affect over 50% of the once strongly advancing >600 km-long delta shoreline. Erosion, with no identified change in the river’s discharge and in wave and wind conditions over this recent period, is consistent with: (1) a reported significant decrease in coastal surface suspended sediment from the Mekong that may be linked to dam retention of its sediment, (2) large-scale commercial sand mining in the river and delta channels and (3) subsidence due to groundwater extraction. Shoreline erosion is already responsible for displacement of coastal populations. It is an additional hazard to the integrity of this Asian mega delta now considered particularly vulnerable to accelerated subsidence and sea-level rise and will be exacerbated by future hydropower dams.

The noise generation by moderate-Reynolds number airfoils is still a topic of major interest because of the wide area of its applications. However, the underlying mechanism is not totally clear. The present paper is dealing with an exhaustive experimental characterization addressing aerodynamic and acoustic quantities. The symmetric NACA-0012 airfoil and the slightly cambered SD7003 airfoil at moderate incidence (angles of attack varied from −5 to +7) are tested in the free-jet anechoic wind tunnel of Ecole Centrale de Lyon. Measurements of wall pressure, far-field acoustic pressure and velocity fluctuations using the hot-wire anemometry are described. In addition advanced post-processing techniques are applied, such as the time-frequency analysis and the bicoherence in order to highlight some non-linear features and/or intermittency. Three regimes of noise emission are identified depending on the configuration and flow velocity. The results complement the database started in previous investigations. They are used for comparison with numerical simulations presented in the second part of the paper.

Vietnam is a tropical to subtropical country located on the eastern Asian coast where the Red (Song Hong) and Mekong rivers discharge into the sea. The catchments of these two transboundary rivers cover parts of six countries, and their water and sediment discharges greatly influence the coastal seas of Vietnam. The impact of human activities include changes in the supply and distribution of water, sediments, and nutrients; changes in the relationships and balance among dynamically interacting factors and processes; and changes in the quality of the coastal and marine environments due to the increased use and accumulation of pollutants and the loss of habitats. These impacts have resulted in increasing unpredictability and severity of coastal problems such as floods, erosion, sedimentation, and saltwater intrusion; environmental pollution; and the degradation of ecosystems, with accompanying decrease in biodiversity and fishery productivity.

The current study conducts numerical experiments to assess possibility of employing synthetic-jet actuators (SJAs)as active noise control devices for reduction of airfoil acoustic radiation. High-accuracy numerical efforts employ a 6-order Navier-Stokes solver implementing low-pass filtering of poorly resolved high-frequency solution content to retain numerical accuracy and stability over the range of transitional flow regimes. In the adopted numerical procedure, the actuator is modeled without its resonator cavity through imposing a simple fluctuating-velocity boundary condition at the bottom of the actuator's orifice. The orifice cavity with the properly defined boundary condition is then embedded into the airfoil surface for conducting high-accuracy viscous analysis of SJA-based active noise control. The effects of SJA location and actuation frequency on airfoil sound radiation are examined both for uniform and non-uniform upstream flow conditions.

In the follow-up study to Ref. [1], we investigate a benchmark case of a robust nonlinear control of gustinduced limit-cycle oscillations (LCO) of an elastically-mounted transitional airfoil using synthetic-jet actuators (SJA) embedded in the airfoil design of a small-size unmanned air vehicle (UAV). The robust controller is particularly advantageous for high levels of uncertainty and nonlinearity present both in the UAV unsteady flight-path environment and the actuator’s response. In the adopted numerical procedure, the actuator is modeled through imposing a fluctuating-velocity boundary condition directly on the airfoil surface for conducting high-accuracy viscous analysis of SJA-based airfoil LCO control governed by the developed robust regulation law. The numerical studies conducted for selected SJA excitation parameters examine the thresholds of the actuator’s control authority to produce the desirable impact.

The Mekong River Delta, southern Vietnam, is a typical mixed tide and wave energy delta with a wide delta plain formed during the last 6 ka and is one of the largest deltas in the world. Three cores were taken from Bentre Province in the lower delta plain, with the objective to describe the sediment facies and to clarify the changes from tide-dominated to tide-wave-dominated delta of the Mekong River Delta during the Late Holocene. Three cores (BT1, BT2, and BT3) were obtained in 1997. Holocene sediments in BT1 and BT3, with thickness ranging from 10 to 20 m, were mainly composed of deltaic sediments unconformably overlying the Late Pleistocene sediments. The BT2 core, however, consisted of transgressive estuarine sediments covered by deltaic sediments infilling the paleo-Mekong River incised valley, which is more than 70 m deep and was formed during the last glacial period. The deltaic sediment facies and succession in the BT2 and BT3 cores taken from the outer delta plain, with beach ridges, were different from those of the BT1 core taken from the inland delta plain. The BT2 and BT3 cores provide a good example of tide- and wave-dominated delta sediments and were characterized by a coarsening-upward delta front facies covered by a fining-upward subtidal to intertidal flat facies, followed by a coarsening-upward foreshore/dune facies. These changes from the inland delta plain to the beach ridge delta plain were accompanied by changes in progradation rates and subaqueous delta topography caused by increased wave influence.

Evolutionary changes, delta progradation, and sediment discharge of the Mekong River Delta, southern Vietnam, during the late Holocene are presented based on detailed analyses of samples from six boreholes on the lower delta plain. Sedimentological and chronostratigraphic analyses indicate clearly that the last 3 kyr were characterized by delta progradation under increasing wave influence, southeastward sediment dispersal, decreasing progradation rates, beach-ridge formation, and steepening of the face of the delta front. Estimated sediment discharge of the Mekong River for the last 3 kyr, based on sediment-volume analysis, was 144±36 million t yr−1 on average, or almost the same as the present level. The constant rate of delta front migration and stable sediment discharge during the last 3 kyr indicate that a dramatic increase in sediment discharge owing to human activities, as has been suggested for the Yellow River watershed, did not occur. Although Southeast Asian rivers have been considered candidates for such dramatic increases in discharge during the last 2 kyr, the Mekong River example, although it is a typical, large river of this region, does not support this hypothesis. Therefore, estimates of the millennial-scale global pristine sediment flux to the oceans must be revised.

We examine a new robust nonlinear flight control technology that employs an array of synthetic-jet micro-actuators embedded in UAV wing design in order to completely eliminate moving parts (such as ailerons) thus greatly enhancing maneuverability required for small fixed-wing air vehicles operating, e.g., in tight urban environments. Estimated fast response times are critical in mitigating gust effects while greatly improving flight stability and control. The new controller design is particularly advantageous for high levels of uncertainty and nonlinearity present both in the unsteady flow-path environment and in the embedded actuator’s response. The current work focuses on a benchmark case of flutter control of 2-DOF elastically-mounted airfoil entering limit-cycle oscillations (LCO) due to impinging upstream flow disturbance. Preliminary parametric studies conducted for various SJA excitation amplitudes and frequencies examine the thresholds of the actuator’s control authority to produce a desirable impact.Copyright © 2014 by ASME

This work reports on high-accuracy numerical experiments focusing on examining turbulence effects on flow-acoustic resonant interactions observed for transitional airfoils at moderate Reynolds numbers. A recently developed approach is employed in numerical analysis to generate a three-dimensional, divergence-free, convected turbulent velocity field with prescribed integral characteristics by means of a time-dependent momentum source located in an arbitrary region of the computational domain upstream of a solid body. Numerical studies employ a 6-order Navier-Stokes solver implementing low-pass filtering of poorly resolved high-frequency solution content to retain numerical accuracy and stability over the range of transitional flow regimes. The results of parametric studies supported by linear stability analysis indicate significant effects of increasing turbulence intensity levels on the airfoil boundary-layer statistical moments and the related unsteady aerodynamic and acoustic airfoil responses.

A new robust nonlinear flight control technology is investigated that employs an array of synthetic-jet micro-actuators in UAV wing design in order to completely eliminate moving parts (such as ailerons) thus greatly enhancing maneuverability required for small fixed-wing air vehicles operating in tight urban environments. Estimated fast response times are also critical in mitigating gust effects while greatly improving flight stability and control. The new controller design is particularly advantageous for high levels of uncertainty and nonlinearity present both in the unsteady flow-path environment and in the embedded actuator’s response. The current work initiates a benchmark case study focusing on the flutter control of 1-DOF and 2-DOF responses of the transitional elastically-mounted airfoil entering limit-cycle oscillations (LCO) due to impinging upstream vortical flow disturbances including a deterministic gust and a stochastic turbulence with prescribed characteristics. The employed methodology combines lowand high-fidelity analysis tools to design and estimate synthetic-jet actuator’s impact on UAV robust flight control by incorporating a model of the embedded SJA actuator into numerical analyses of gust-airfoil interactions. Preliminary parametric studies conducted for various SJA excitation amplitudes and frequencies examine the thresholds of the actuator’s control authority to produce a desirable impact.

International audience; We discuss our recent experimental and preliminary numerical efforts examining resonant feedback mechanism of flow-acoustic interactions in airfoil transitional boundary layers. Experimentally recorded unsteady responses of loaded, transitional NACA0012 airfoil with tripped suction or pressure sides confirm the presence of shifted ladder-type tonal structures with dual velocity dependence in the acoustic signal previously reported in the literature. The installation of upstream grid generating low-intensity turbulence appears to eliminate the feedback mechanism leaving just a single velocity dependence for the dominant spectral components. Complementary numerical efforts employ a high-order Navier-Stokes solver implementing low-pass filtering of poorly resolved high-frequency solution content to retain numerical accuracy and stability over the range of transitional flow regimes. Within the scope of 2D analysis, the conducted numerical experiments particularly investigate the behavior of the boundary-layer statistical moments during the transitional flow regimes characterized by the presence of the acoustic feedback, and address sensitivity of the latter to the flow Reynolds number.

A detailed description of sediment facies, diatom, mollusca and foraminifer assemblages, and 14 C ages of the Mekong River Delta, Southern Vietnam, is presented in this paper. A 71 m long core, recovered in 1997 at the Bentre province in the eastern part of the Mekong River Delta, is divided into eight units and nine sediment facies on the basis of sedimentary properties, diatom and foraminifer assemblages, and 14 C ages. These units show facies changes from transgression to regression in relation to the late Pleistocene–Holocene sea-level changes. The Postglacial transgression caused by a sea-level rise led to infilling of the incised valley and formation of estuarine sediments and open bay muddy sediments in ascending order. Estuarine sediments consist of slightly oxidized yellowish–grey silty sand and intercalated greenish–grey and stiffly brownish–grey sandy silt and silty clay. The muddy facies, 13.5 m thick, is characterized by abundant marine planktonic diatoms and open-sea foraminifers. This facies indicates the maximum Holocene marine influence was around 5300 cal yr BP at the BT2 site. The regressive succession is composed of deltaic sediments from prodelta, delta front, sub- to inter-tidal flat and beach ridge in ascending order. 14 C ages indicate that the delta front passed the core site at approximately 4000–3000 cal yr BP. The coastal progradation rate was 17–18 m yr −1 during the 5300–3500 cal yr and decreased to 13–14 m yr −1 during the last 3500 cal yr.

The Mekong River Delta in Southern Vietnam is a tide-dominated delta and has been formed by the Mekong River system. The sediments are dominantly fine grained and were deposited in the receiving basin with slight inclination of pre-existing deposits in the South China Sea and Gulf of Thailand. Around 6000 to 5000 yr BP maximum Holocene transgression occurred and seawaves surrounded uplands of the Late Pleistocene terrace, basement rock and weathered land in the northern parts of the delta. Double notches were undercut by seawaves on the limestone hill in Hatien at about 4.5 and 2.5 m above present sea level. Marine deposits prevailed throughout the delta. During the highstand and regressions of relative sea level over the last 4550 yr BP, delta progradation has produced a great flat-plain of 62,520 km 2 . This extremely fast progradation could be due to: (a) very high sediment supply depositing in the slight inclination of the receiving basin; (b) neotectonic movements and relative sea-level changes; (c) widespread mangrove forests playing an important role to enhance sediment accumulation. Former mangrove marshy deposits were significantly developed in the Plain of Reeds and Longxuyen Quadrangle. Mangrove marshes have also been developing well in the Camau Peninsula and present coastlines. Moreover, regressions over the last 4550 yr BP have produced many distinct sets of relict beach ridges which are useful in distinguishing the former coastlines and evolutionary history of the delta.

Recent experimental and numerical efforts are discussed examining resonant feedback mechanism of flow-acoustic interactions in airfoil transitional boundary layers. Experimentally recorded unsteady responses of loaded, transitional NACA0012 airfoil with tripped suction or pressure sides confirm the presence of shifted ladder-type tonal structures with dual velocity dependence in surface pressure and acoustic signals previously reported in the literature. High-fidelity numerical efforts employ a 6thorder Navier-Stokes solver implementing low-pass filtering of poorly resolved high-frequency solution content to retain numerical accuracy and stability over the range of transitional flow regimes. 2D and 3D (ILES) numerical experiments investigate the behavior of the boundary-layer statistical moments during the transitional flow regimes characterized by the presence of separation regions and the resulting formation of amplified instability waves scattered into noise at the airfoil trailing edge and triggered by the acoustic feedback-loop interaction.

When we examine the status of children and families in the United States today, it is clear that the state of the wellbeing of children and families in America does not meet the standards of our leaders a decade ago. Today, our children suffer from poverty in a country of great wealth; they may lack the educational skills that will allow them to be competitive in the future job market. Many of their parents experience chronic unemployment or transience, as well as periods of family instability. The lives of many children are scarred by abuse and neglect. Many children live in homes or neighborhoods which expose them to domestic or community violence. They are involved in an educational system that does not allow them to develop their full learning potential. Still others are homeless or confront food insecurity on a daily basis. As Marian Wright Edelman states

Synthetic jet actuators (SJAs) have been primarily investigated as means of unsteady flow control on aircraft wing. The current work for the first time explores the effectiveness of SJAs for control of a low-speed airfoil acoustic radiation both with the uniform upstream flow conditions (with noise dominated by the trailing-edge sources) and in the presence of an upstream flow disturbance (with noise dominated by the leading-edge sources or stall-related phenomena depending on the disturbance character and amplitude). In the high-fidelity numerical study, the effect of the selected SJA location and other parameters characterizing SJA performance are determined. In the adopted numerical procedure, the actuator is modeled without its resonator cavity through imposing a simple fluctuating-velocity boundary condition at the bottom of the actuator’s orifice. The orifice cavity with the properly defined boundary condition is then embedded into the airfoil surface for conducting high-accuracy viscous analysis of SJA-based active noise control. The effects of the actuation on sound radiated by the airfoil both in presence and absence of the upstream flow disturbance are examined for a benchmark problem of time-harmonic gust interaction with a symmetric Joukowski airfoil.Copyright © 2012 by ASME

The current work reports on a comparison of high-fidelity 3D Navier-Stokes simulations of SD7003 airfoil interacting with canonical upstream flow disturbances against previous high-accuracy 2D simulations conducted for transitional flow regime. Three forms of upstream flow disturbance are considered including 1D and 2D time-harmonic gust, sharp-edge gust, and the Taylor vortex models. Results obtained for the airfoil unsteady aerodynamic responses to time-harmonic and sharp-edge gust perturbations with variable gust amplitude are discussed in comparison with linearized inviscid, incompressible unsteady aerodynamic theory. In addition, analysis of unsteady aerodynamic response for a large highamplitude Taylor vortex impinging on the airfoil is examined. It is shown that the less computationally expensive 2D simulations provide a sufficiently accurate analysis of the unsteady lift responses but fall short in drag and moment predictions.

This work complements a series of benchmark high-fidelity numerical studies investigating a low-speed airfoil response to canonical forms of impinging flow disturbances characteristic of unsteady urban environment. While previous parametric analyses examined aerodynamic effects induced by incident sharp-edge gust, time-harmonic gust, and Taylor vortex all representing deterministic perturbation models, the current study focuses on modeling airfoil interaction with upstream synthetic turbulence produced based on a random flow generation procedure. A previously introduced highly efficient approach is employed to generate a three-dimensional, divergence-free, convected turbulent velocity field with prescribed integral characteristics by means of a time-dependent momentum source located in an arbitrary region of the computational domain upstream of a solid body. In parametric 2D and 3D numerical studies, imposed and generated turbulence spectra as well as the resulting unsteady aerodynamic responses are examined for a set of parameters characterizing turbulent upstream flow conditions and airfoil loading.

The current work extends the numerical study of Ref. [1] focusing on the resonant feedback mechanism of flow-acoustic interactions in airfoil transitional boundary layers and its contribution to low-speed airfoil trailing-edge noise. Results of two different numerical studies conducted with loaded NACA0012 and unloaded Joukowski airfoils are reported. Computational efforts employ a high-order compressible Navier-Stokes solver implementing low-pass filtering of poorly resolved high-frequency solution content to retain numerical accuracy and stability over the range of flow regimes. Numerical experiments particularly investigate the behavior of the boundary-layer statistical moments during the transitional flow regimes characterized by the presence of the acoustic feedback, and address sensitivity of the latter to the flow Reynolds number, as well as to both external and internal boundary-layer excitations.

The current work proposes a new method to introduce an upstream turbulence for high-fidelity numerical simulations of unsteady flow-structure interactions. In particular, the approach to generate a threedimensional, divergence-free, convected perturbation velocity field by prescribing a momentum source in an arbitrary region of the computational domain upstream of a solid body is discussed. It is shown that the method can be efficiently employed in conjunction with the random flow generation (RFG) procedures for numerical analysis of airfoil response to synthetically-generated upstream turbulence with prescribed integral characteristics. Details of the numerical implementation of the method are discussed. Preliminary two-dimensional test studies are conducted to illustrate application of the proposed technique for analysis of the airfoil interaction with convected disturbance fields.

The current preliminary study initiates complementary experimental and numerical efforts to re-examine resonant feedback mechanism of flow-acoustic interactions in airfoil transitional boundary layers and its contribution to low-speed airfoil trailing-edge noise. Furthermore, the impact of impinging vortical flow disturbances and the corresponding interaction of leading and trailing edge noise sources is considered. Recorded unsteady responses of loaded, transitional NACA0012 airfoil with tripped suction or pressure sides indicate the presence of shifted ladder-type tonal structures with dual velocity dependence in the acoustic signal previously reported in the literature. The installation of upstream grid generating low-intensity turbulence appears to eliminate the feedback mechanism leaving just a single velocity dependence for the dominant spectral components. Numerical efforts employ a high-order Navier-Stokes solver implementing low-pass filtering of poorly resolved high-frequency solution content to retain numerical accuracy and stability over the range of flow regimes. Upstream flow disturbances are introduced inside the computational domain through a source term in the momentum equations.

Synthetic jet actuators (SJAs) may be carefully designed to alleviate the negative impact of impinging flow non-uniformities on the aircraft wing unsteady aerodynamic response. Current study investigates the effectiveness of SJAs for active control of unsteady flow over SD7003 low-Re airfoil in presence of a high-amplitude upstream flow disturbance characterized by a sharp-edge gust. In the employed numerical procedure, the actuator's dimensional scaling and excitation frequency effects are first examined for a specific SJA configuration using LEM model used in conjunction with RANS analysis to determine simple fluctuating-velocity boundary condition at the bottom of the actuator's orifice. The orifice with the properly defined boundary condition is then embedded into the airfoil surface for conducting highaccuracy viscous simulations of active flow control of gust-airfoil interaction. Results of numerical simulations indicate that the SJA positive effect on the airfoil response appears most significant with the actuator operating in resonance with von Karman shedding frequency.

The paper discusses results of 2D and 3D high-fidelity viscous simulations of SD7003 airfoil’s unsteady aerodynamic response to impinging vortical structures in the transitional flow regimes characteristic of Micro Air Vehicle (MAV) applications. Following a thorough review of previous studies characterizing various scales and configurations of urban flow disturbances, the numerical work focuses on the airfoil-vortex unsteady interaction investigated in the parametric space of variable vortex strength, size, position, sense of rotation, as well as the airfoil steady loading and the mean flow Reynolds number. The analysis reveals numerous details of the unsteady interaction processes and elucidates a complex interplay of viscous and inviscid unsteady phenomena and their resulting effect on the airfoil unsteady aerodynamic lift, drag and moment responses.

The current work completes a high-accuracy 2D study of nonlinear viscous interaction of SD7003 airfoil with nonuniform, unsteady incoming flow initiated in Ref. [1]. A laminar mean flow is considered with M=0.1 and Re=10,000 typical of MAV applications in which an encounter with upstream vortical flow structures may induce particularly significant aerodynamic and aeroelastic responses. Previous and new results obtained for the aerodynamic airfoil response to time-harmonic and sharp-edge gust perturbations with variable gust amplitude, frequency, dimension and duration are discussed in comparison with “equivalent” pitching simulations as well as corresponding predictions based on the linearized inviscid, incompressible unsteady aerodynamic theory. In addition, results obtained for the airfoil response to an upstream Taylor vortex are presented and compared against sharp-edge gust solutions. Preliminary 3D ILES computations of the vortex-airfoil interaction are also conducted and compared with 2D predictions in a transitional flow regime.

The current work conducts high-accuracy 2D and 3D Navier-Stokes simulations of the unsteady interaction of upstream non-uniform flow with unloaded, symmetrical, stationary Joukowski airfoil in the transitional flow regimes with M=0.5 and Re= 10, 5x10 and 10. An Implicit Large Eddy Simulations (ILES) procedure employs a high order low-pass filter operator which selectively damps the poorly resolved high-frequency solution content to retain numerical accuracy and stability over a wide range of flow regimes. The upstream flow non-uniformity is modeled by means of an efficient analytical model introducing an unsteady, incompressible, time-harmonic 2D vortical flow perturbation (gust) inside the computational domain through a source term in the momentum equations. Unsteady aerodynamic and aeroacoustic airfoil responses are examined with focus on interaction of the airfoil leading and trailing edge noise radiation sources.