In this article, the Recoil Distance Doppler-Shift (RDDS) method which is extensively used in nuclear structure physics to determine level lifetimes and absolute transition probabilities is reviewed. ...Especially, it is aimed to present new developments and variants of the technique which have evolved mainly in the past 25 years. After a short and comprehensive description of the basic elements of the plunger technique, the new variants are presented. This comprises the RDDS technique using γγ-coincidences, RDDS measurements in combination with particle detectors for selecting specific reaction channels, RDDS after Coulomb excitation, RDDS after fission and RDDS using a gas target. In addition, the concept of a differential plunger is discussed with respect to its specific features and typical experimental setups. Examples of differential plunger measurements with recoil tagging, recoil decay tagging and after deep inelastic reactions, Coulomb excitation in inverse reaction kinematics as well as after reactions with fast radioactive beams at energies of 50–100 MeV/u are given. The second focus of the review is dedicated to today’s plunger devices and related hardware. The concepts of specific plunger devices which accommodate the specific demands of the aforementioned RDDS applications including specific feedback systems for controlling target–stopper/degrader separations in-beam are presented. Also discussed are target and stopper/degrader foil related issues like foil preparation, mounting and stretching as well as specific features of the foil behavior in-beam (temperature, blistering, wrinkling and carbon build-up). The third focus is devoted to the data analysis. The concept of the Differential Decay Curve Method (DDCM) is presented as an alternative approach for the analysis of RDDS data measured as singles or as γγ-coincidences. For the latter, different gating possibilities are discussed, e.g. gating from above and gating from below the level of interest and gating on fractional components. Finally, the simulation of line-shapes and its application is presented.
Context.
Hydrodynamical simulations of planet-disk interactions suggest that planets may be responsible for a number of the substructures frequently observed in disks in both scattered light and dust ...thermal emission. Despite the ubiquity of these features, direct evidence of planets embedded in disks and of the specific interaction features like spiral arms within planetary gaps are still rare.
Aims.
In this study we discuss recent observational results in the context of hydrodynamical simulations in order to infer the properties of a putative embedded planet in the cavity of a transition disk.
Methods.
We imaged the transition disk SR 21 in
H
-band in scattered light with SPHERE/IRDIS and in thermal dust emission with ALMA band 3 (3 mm) observations at a spatial resolution of 0.1″. We combine these datasets with existing Band 9 (430
μ
m) and Band 7 (870
μ
m) ALMA continuum data.
Results.
The Band 3 continuum data reveals a large cavity and a bright ring peaking at 53 au strongly suggestive of dust trapping. The ring shows a pronounced azimuthal asymmetry, with a bright region in the northwest that we interpret as a dust overdensity. A similarly asymmetric ring is revealed at the same location in polarized scattered light, in addition to a set of bright spirals inside the millimeter cavity and a fainter spiral bridging the gap to the outer ring. These features are consistent with a number of previous hydrodynamical models of planet-disk interactions, and suggest the presence of a ∼1
M
Jup
planet at 44 au and PA = 11 deg. This makes SR21 the first disk showing spiral arms inside the millimeter cavity, and the first disk for which the location of a putative planet can be precisely inferred.
Conclusions.
The main features of SR 21 in both scattered light and thermal emission are consistent with hydrodynamical predictions of planet-disk interactions. With the location of a possible planet being well constrained by observations, it is an ideal candidate for follow-up observations to search for direct evidence of a planetary companion still embedded in its disk.
Context.
During the evolution of protoplanetary disks into planetary systems we expect to detect signatures that trace mechanisms such as planet–disk interaction. Protoplanetary disks display a large ...variety of structures in recently published high-spatial resolution images. However, the three-dimensional morphology of these disks is often difficult to infer from the two-dimensional projected images we observe.
Aims.
We aim to detect signatures of planet–disk interaction by studying the scattering surface of the protoplanetary disk around HD 34282.
Methods.
We spatially resolved the disk using the high-contrast imager VLT/SPHERE in polarimetric imaging mode. We retrieved a profile for the height of the scattering surface to create a height-corrected deprojection, which simulates a face-on orientation.
Results.
The detected disk displays a complex scattering surface. An inner clearing or cavity extending up to
r
< 0.′′28 (88 au) is surrounded by a bright inclined (
i
= 56°) ring with a position angle of 119°. The center of this ring is offset from the star along the minor axis with 0.′′07, which can be explained with a disk height of 26 au above the midplane. Outside this ring, beyond its southeastern ansa we detect an azimuthal asymmetry or blob at
r
~ 0.′′4. At larger separation, we detect an outer disk structure that can be fitted with an ellipse, which is compatible with a circular ring seen at
r
= 0.′′62 (=190 au) and a height of 77 au. After applying a height-corrected deprojection we see a circular ring centered on the star at 88 au; what had seemed to be a separate blob and outer ring could now both be part of a single-armed spiral.
Conclusions.
We present the first scattered-light image of the disk around HD 34282 and resolve a disk with an inner cavity up to
r
≈ 90 au and a highly structured scattering surface of an inclined disk at a large height
H
scat
∕
r
= 0.′′29 above the midplane at the inner edge of the outer disk. Based on the current data it is not possible to conclude decisively whether
H
scat
∕
r
remains constant or whether the surface is flared with at most
H
scat
∝
r
1.35
, although we favor the constant ratio based on our deprojections. The height-corrected deprojection allows for a more detailed interpretation of the observed structures, from which we discern the first detection of a single-armed spiral in a protoplanetary disk.
The influence of the Plata, the second largest river in South America, extends along a coastal strip of 1300 km. Historical hydrographic and wind data and numerical simulations are combined to ...determine the seasonal and interannual variability of the Plata plume and its relationship to the magnitude of the river discharge and the intensity and direction of the wind stress. Our results indicate that the seasonal variability of the river plume is controlled by the alongshore component of the wind stress. During El Niño the effects of the wind and precipitation anomalies tend to compensate each other, preventing anomalous northeastward plume extensions associated to large outflow events. Numerical experiments confirm this finding and indicate that during El Niño the discharge from the Plata River spreads offshore.
Many estuaries present natural harbor conditions with relatively calm and shallow waters that provide a connection between the ocean and continental waterways. The increase in the demand for goods by ...the constant growing of the world population has forced estuaries to be altered by human activities, such as dredging, in order to maintain a safe navigation system. The development of sophisticated morphological and hydrodynamic models opened a new perspective of assisting dredging operations inside different estuaries. Thus, the aim of this study is to apply a hydromorphodynamic model to simulate the bed evolution of the Patos Lagoon estuary, southern Brazil. The results of the simulation were applied in a dredge operation model to simulate dredging inside the waterway of the Rio Grande harbor, located inside the Patos Lagoon estuary. The salinity and current velocities inside the estuary were well represented by the model simulations. An annual mean discharge of 3 407 ms3 s−1 was calculated for the lagoon for the year 2004. The morphodynamic model successfully represented the silted and eroded scenarios for the estuarine channel. The dredge operation model results affirm that dredging of the channel causes significant variations in estuarine physical parameters such as salinity, current velocity and suspended sediment concentration. The bed evolution results indicate that a fast siltation of the channel occurs right after dredging stops, stabilizing the variations after a 60-day period.
•Silted areas were identified by the morphodynamic model.•Dredge polygons were defined over the silted areas.•The dredging model was applied on the dredge sectors defined.•Current velocities presented considerable reduction on a dredged scenario.•The results indicate intense siltation of the dredged areas until 60 days after the end of the operations.
We reviewed historical data on surface sediment composition/distribution and hydrodynamics of the Patos-Mirim lagoonal system, the largest coastal shallow limnological system of the world, located in ...eastern South America, which is ca.15,000 km2, the maximum length is almost 500 km and maximum depth is around 7 m. We inferred the geographical position of six mud depocenters in relation to the hydrodynamic conditions evolved from predominant winds and morphometry. Littoral zones of sediment resuspension dominated by sand were identified where current velocity was higher than 0.2 m s−1 and depth was <5 m. In addition, central zones were susceptible to deposition of fine sediment fractions, where current velocity was close to 0.1 m s−1 and depth was >5 m. Such conditions observed for the central zones represent appropriate morphodynamic controls for mud depocenter formation. The six permanent Holocene depocenters for the whole Patos-Mirim system were all dominated mostly by silty clayey facies and exhibited an Mz value equal to or higher than 7.5. Because of the dominance of the fine fraction, we propose them as future potential key-spots for monitoring the environmental quality of the system to assist regional sustainable management.
The palaeolimnological conditions of Mirim Lagoon, a large coastal shallow lagoon under the influence of historical human impacts related to the development of the primary sector of the economy were ...reconstructed. The first significant human impact consisted of locking the estuarine system to induce the transition from brackish to freshwater conditions. During this transition, the sedimentation rate consistently increased from pre-disturbance values of 0.25 cm yr−1 to >1 cm yr−1. A concomitant increase in nitrogen and carbon values was recorded indicating a related eutrophication process. The highest nutrient levels were achieved during the 1990s after the incorporation of cutting-edge technologies for agricultural production such as high-yielding varieties of rice resistant to climate variability and pests, and the use of inorganic fertilisers, pesticides and water supply controlled by irrigation. After 2011, the soybean production boosted and the area cultivated with this oilseed equalled the area of rice paddies, i.e., 2 × 105 ha. A sharp decrease in δ13C from −19 to −24‰ and in δ15N from 6 to 2‰ were observed in the sedimentary record, indicating a major shift in the composition of the organic matter after the agricultural intensification. Trace elements Cr, Cu, Ni and Zn showed a high positive correlation with Al and Fe, and enrichment factors near 1, indicating a natural and terrigenous source of these elements and also unpolluted conditions. However, the increase of As after 1990 and the positive correlation with Pb was associated with agricultural practices. All elemental ratios (K/Al, Ti/Al and V/Cr) showed constant pre-disturbance trends and a turning point ca. the 1990s. Microplastics were detected from the beginning of the 1990s and increased towards recent sediments, thus corroborating an anthropogenically impacted scenario. Therefore, the development of the primary sector of the economy exerted clear impacts on the environmental quality of the system.
Display omitted
•Mirim Lagoon estuary was transformed into a freshwater body in 1977.•Subsequent growth of the primary sector of the economy was documented.•Sedimentation increases and eutrophication symptoms were observed after 1990.•After 2011, the inclusion of soy cultivation changed the organic matter composition.•Mirim Lagoon is the final fate of agricultural production waste.
The Río de la Plata waters form a low salinity tongue that affects the circulation, stratification and the distributions of nutrients and biological species over a wide extent of the adjacent ...continental shelf. The plume of coastal waters presents a seasonal meridional displacement reaching lower latitudes (28°S) during austral winter and 32°S during summer. Historical data suggests that the wind causes the alongshore shift, with southwesterly (SW) winds forcing the plume to lower latitudes in winter while summer dominant northeasterly (NE) winds force its southward retreat. To establish the connection between wind and outflow variations on the distribution of the coastal waters, we conducted two quasi-synoptic surveys in the region of Plata influence on the continental shelf and slope of southeastern South America, between Mar del Plata, Argentina and the northern coast of Santa Catarina, Brazil. We observed that: (A) SW winds dominating in winter force the northward spreading of the plume to low latitudes even during low river discharge periods; (B) NE winds displace the plume southward and spread the low salinity waters offshore over the entire width of the continental shelf east of the Plata estuary. The southward retreat of the plume in summer leads to a volume decrease of low salinity waters over the shelf. This volume is compensated by an increase of Tropical waters, which dominate the northern shelf. The subsurface transition between Subantarctic and Subtropical Shelf Waters, the Subtropical Shelf Front, and the subsurface water mass distribution, however, present minor seasonal variations. Along shore winds also influence the dynamics and water mass variations along the continental shelf area. In areas under the influence of river discharge, Subtropical Shelf Waters are kept away from the coastal region. When low salinity waters retreat southward, NE winds induce a coastal upwelling system near Santa Marta Cape. In summer, solar radiation promotes the establishment of a strong thermocline that increases buoyancy and further enhances the offshore displacement of low salinity waters under the action of NE winds.
The Southern Brazilian Shelf (SBS) is a freshwater-influenced region, but studies on the dynamics of coastal plumes are sparse and lack in space-time resolution. Studies on the dynamics of the Patos ...Lagoon plume are even more limited. The aim of this paper is to investigate the influence of the principal physical forcing for the formation and behavior of the Patos Lagoon coastal plume. The study is carried out through 3D numerical modeling experiments and empirical orthogonal function (EOF) analysis. Results showed that the amount of freshwater is the principal physical forcing controlling the plume formation. The Coriolis effect enhances the northward transport over the shelf, while the tidal effects contribute to intensify horizontal and vertical mixing, which are responsible for spreading the freshwater over the shelf. The wind effect, on the other hand, is the main mechanism controlling the behavior of the Patos Lagoon coastal plume over the inner SBS in synoptic time scales. Southeasterly and southwesterly winds contribute to the northeastward displacement of the plume, breaking the vertical stratification of the inner continental shelf. Northeasterly and northwesterly winds favor ebb conditions in the Patos Lagoon, contributing to the southwestward displacement of the plume enhancing the vertical stratification along and across-shore. The EOF analysis reveals two modes controlling the variability of the plume on the surface. The first mode (explaining 70% of the variability) is associated to the southwestward transportation of the plume due to the dominance of north quadrant winds, while the second mode (explaining 19% of the variability) is associated to the intermittent migration of the plume northeastward due to the passage of frontal systems over the area. Large scale plumes can be expected during winter and spring months, and are enhanced during El Niño events.
High sea surface chlorophyll concentration on the Argentine Continental Shelf frequently extends to the deep ocean in the vicinity of the Brazil/Malvinas Confluence (BMC). The offshore transport of ...shelf waters likely plays a key role in the biogeochemical balance of the western South Atlantic and promotes the offshore transport of planktonic species. We analyze data from an oceanographic survey carried out in the western South Atlantic shelf between 31°S and 38°S in October 2013. We describe the distribution and circulation of the water masses and focus on the exchanges with the open ocean. On‐shelf subsurface intrusions of oceanic waters and river discharge supply nutrients to the shelf. A low‐salinity tongue of Río de la Plata (RDP) waters extends northward to 32°S. Below these waters Subantarctic and Subtropical Shelf Waters (SASW and STSW) meet to form the Subtropical Shelf Front. The main SASW branch, oversaturated in oxygen and with high‐fluorescence mixes with a detachment of Brazil Current waters at 38°S and is exported offshore along the BMC. A second branch of SASW reaches 33°S mixing along its way with RDP and STSW and returns southward after splitting into an onshore and an offshore branch. The offshore branch is exported to the open ocean through the BMC. These export routes are in overall qualitative agreement with those indicated by a high‐resolution reanalysis. We estimate a net off‐shelf transport (geostrophic 96.2% plus Ekman 3.8%) of 3.44 Sv to the open ocean between 32.1°S and 37.7°S. The majority of the offshore flow occurs between 34.7°S and 37.7°S.
Plain Language Summary
The western South Atlantic shelf is characterized by a northeastward flow of Subantarctic Shelf Water (SASW) that meets a southwestward flow of Subtropical Shelf Waters creating the Subtropical Shelf Front (STSF). The STSF is capped by low salinity layer derived from the Río de la Plata. The outer shelf region is swept by intense and opposing flows: the cold‐fresh Malvinas Current and the warm‐salty Brazil Current. Here, we analyze data from an oceanographic survey of the western South Atlantic shelf (31–38°S) in October 2013. We describe the distribution and circulation of the water masses with emphasis on the cross‐shelf exchange. On‐shelf subsurface intrusions of oceanic waters and river discharge supply nutrients to the shelf. We estimate an off‐shelf transport of 3.44 Sv. The majority of this flow is located at the Brazil‐Malvinas Confluence and at 33.5°S. A fraction of the exported shelf water is associated with high biological activity. This off‐shelf flow might also transfer planktonic eggs and larvae to the open ocean, modulating their abundance over the shelf. Moreover, the detrainment of high‐chlorophyll shelf waters may play an important role in the fertilization of the western South Atlantic.
Key Points
The circulation of the western South Atlantic shelf is determined based on in situ observations
We estimate a net offshore flow of 3.44 Sv from the shelf to the open ocean
Diluted AAIW and SACW intrusions and RDP waters supply nutrients to the continental shelf
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