80 research outputs found
An expanded database of Southern Hemisphere surface sediment dinoflagellate cyst assemblages and their oceanographic affinities
Dinoflagellate cyst assemblages present a valuable proxy to infer
paleoceanographic conditions, yet factors influencing geographic
distributions of species remain largely unknown, especially in the Southern
Ocean. Strong lateral transport, sea-ice dynamics, and a sparse and uneven
geographic distribution of surface sediment samples have limited the use of
dinocyst assemblages as a quantitative proxy for paleo-environmental
conditions such as sea surface temperature (SST), nutrient concentrations,
salinity, and sea ice (presence). In this study we present a new set of
surface sediment samples (n=66) from around Antarctica, doubling the
number of Antarctic-proximal samples to 100 (dataset wsi_100)
and increasing the total number of Southern Hemisphere samples to 655
(dataset sh_655). Additionally, we use modelled ocean
conditions and apply Lagrangian techniques to all Southern Hemisphere sample
stations to quantify and evaluate the influence of lateral transport on the
sinking trajectory of microplankton and, with that, to the inferred ocean
conditions. k-means cluster analysis on the wsi_100 dataset
demonstrates the strong affinity of Selenopemphix antarctica with sea-ice presence and of Islandinium spp. with
low-salinity conditions. For the entire Southern Hemisphere, the k-means
cluster analysis identifies nine clusters with a characteristic assemblage.
In most clusters a single dinocyst species dominates the assemblage. These
clusters correspond to well-defined oceanic conditions in specific Southern
Ocean zones or along the ocean fronts. We find that, when lateral transport
is predominantly zonal, the environmental parameters inferred from the sea
floor assemblages mostly correspond to those of the overlying ocean surface.
In this case, the transport factor can thus be neglected and will not
represent a bias in the reconstructions. Yet, for some individual sites,
e.g. deep-water sites or sites under strong-current regimes, lateral
transport can play a large role. The results of our study further constrain
environmental conditions represented by dinocyst assemblages and the
location of Southern Ocean frontal systems.</p
The role of core excitations in the structure and decay of the 16+ spin-gap isomer in 96Cd
The first evidence for β-delayed proton emission from the 16+ spin gap isomer in 96Cd is presented. The data were obtained from the Rare Isotope Beam Factory, at the RIKEN Nishina Center, using the BigRIPS spectrometer and the EURICA decay station. βp branching ratios for the ground state and 16+ isomer have been extracted along with more precise lifetimes for these states and the lifetime for the ground state decay of 95Cd. Large scale shell model (LSSM) calculations have been performed and WKB estimates made for ℓ=0,2,4 proton emission from three resonance-like states in 96Ag, that are populated by the β decay of the isomer, and the results compared to the new data. The calculations suggest that ℓ=2 proton emission from the resonance states, which reside ∼5 MeV above the proton separation energy, dominates the proton decay. The results highlight the importance of core-excited wavefunction components for the 16+ state
Study of Isomeric States in <sup>198,200,202,206</sup>Pb and <sup>206</sup>Hg Populated in Fragmentation Reactions
Isomeric states in isotopes in the vicinity of doubly-magic 208Pb were
populated following reactions of a relativistic 208Pb primary beam impinging on a
9Be fragmentation target. Secondary beams of 198;200;202;206Pb and 206Hg were
isotopically separated and implanted in a passive stopper positioned in the focal
plane of the GSI Fragment Separator. Delayed γ rays were detected with the
Advanced GAmma Tracking Array (AGATA). Decay schemes were re-evaluated
and interpreted with shell-model calculations. The momentum-dependent
population of isomeric states in the two-nucleon hole nuclei 206Pb/206Hg was
found to differ from the population of multi neutron-hole isomeric states in
198;200;202Pb
CNS Delivery Via Adsorptive Transcytosis
Adsorptive-mediated transcytosis (AMT) provides a means for brain delivery of medicines across the blood-brain barrier (BBB). The BBB is readily equipped for the AMT process: it provides both the potential for binding and uptake of cationic molecules to the luminal surface of endothelial cells, and then for exocytosis at the abluminal surface. The transcytotic pathways present at the BBB and its morphological and enzymatic properties provide the means for movement of the molecules through the endothelial cytoplasm. AMT-based drug delivery to the brain was performed using cationic proteins and cell-penetrating peptides (CPPs). Protein cationization using either synthetic or natural polyamines is discussed and some examples of diamine/polyamine modified proteins that cross BBB are described. Two main families of CPPs belonging to the Tat-derived peptides and Syn-B vectors have been extensively used in CPP vector-mediated strategies allowing delivery of a large variety of small molecules as well as proteins across cell membranes in vitro and the BBB in vivo. CPP strategy suffers from several limitations such as toxicity and immunogenicity—like the cationization strategy—as well as the instability of peptide vectors in biological media. The review concludes by stressing the need to improve the understanding of AMT mechanisms at BBB and the effectiveness of cationized proteins and CPP-vectorized proteins as neurotherapeutics
Hot topics and application trends of the anammox biotechnology: a review by bibliometric analysis
Toward the limit of nuclear binding on the N=Z line : Spectroscopy of Cd 96
A γ-decaying isomeric state (τ1/2=197-17+19 ns) has been identified in Cd96, which is one α particle away from the last known bound N=Z nucleus, Sn100. Comparison of the results with shell-model calculations has allowed a tentative experimental level scheme to be deduced and the isomer to be interpreted as a medium-spin negative-parity spin trap based on the coupling of isoscalar (T=0) and isovector (T=1) neutron-proton pairs. The data also suggest evidence for the population of a 9+ T=1 state, which is predicted by shell-model calculations to be yrast. Such a low-lying T=1 state, which is unknown in lighter mass even-even self-conjugate nuclei, can also be interpreted in terms of the coupling of T=0 and T=1 neutron-proton pairs
Increased nutrient supply to the Southern Ocean during the Holocene and its implications for the pre-industrial atmospheric CO<sub>2</sub> rise
A rise in the atmospheric CO2 concentration of ~20 parts per million over the course of the Holocene has long been recognized as exceptional among interglacials and is in need of explanation. Previous hypotheses involved natural or anthropogenic changes in terrestrial biomass, carbonate compensation in response to deglacial outgassing of oceanic CO2, and enhanced shallow water carbonate deposition. Here, we compile new and previously published fossil-bound nitrogen isotope records from the Southern Ocean that indicate a rise in surface nitrate concentration through the Holocene. When coupled with increasing or constant export production, these data suggest an acceleration of nitrate supply to the Southern Ocean surface from underlying deep water. This change would have weakened the ocean’s biological pump that stores CO2 in the ocean interior, possibly explaining the Holocene atmospheric CO2 rise. Over the Holocene, the circum-North Atlantic region cooled, and the formation of North Atlantic Deep Water appears to have slowed. Thus, the ‘seesaw’ in deep ocean ventilation between the North Atlantic and the Southern Ocean that has been invoked for millennial-scale events, deglaciations and the last interglacial period may have also operated, albeit in a more gradual form, over the Holocene
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