206 research outputs found
Transneptunian objects and Centaurs from light curves
We analyze a vast light curve database by obtaining mean rotational
properties of the entire sample, determining the spin frequency distribution
and comparing those data with a simple model based on hydrostatic equilibrium.
For the rotation periods, the mean value obtained is 6.95 h for the whole
sample, 6.88 h for the Trans-neptunian objects (TNOs) alone and 6.75 h for the
Centaurs. From Maxwellian fits to the rotational frequencies distribution the
mean rotation rates are 7.35 h for the entire sample, 7.71 h for the TNOs alone
and 8.95 h for the Centaurs. These results are obtained by taking into account
the criteria of considering a single-peak light curve for objects with
amplitudes lower than 0.15 mag and a double-peak light curve for objects with
variability >0.15mag. The best Maxwellian fits were obtained with the threshold
between 0.10 and 0.15mag. The mean light-curve amplitude for the entire sample
is 0.26 mag, 0.25mag for TNOs only, and 0.26mag for the Centaurs. The amplitude
versus Hv correlation clearly indicates that the smaller (and collisionally
evolved) objects are more elongated than the bigger ones. From the model
results, it appears that hydrostatic equilibrium can explain the statistical
results of almost the entire sample, which means hydrostatic equilibrium is
probably reached by almost all TNOs in the H range [-1,7]. This implies that
for plausible albedos of 0.04 to 0.20, objects with diameters from 300km to
even 100km would likely be in equilibrium. Thus, the great majority of objects
would qualify as being dwarf planets because they would meet the hydrostatic
equilibrium condition. The best model density corresponds to 1100 kg/m3.Comment: 21 pages, 8 figures. Astronomy & Astrophysics, in pres
A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century
The anthropogenically forced expansion of coastal hypoxia is a major environmental problem affecting coastal ecosystems and biogeochemical cycles throughout the world. The Baltic Sea is a semi-enclosed shelf sea whose central deep basins have been highly prone to deoxygenation during its Holocene history, as shown previously by numerous paleoenvironmental studies. However, long-term data on past fluctuations in the intensity of hypoxia in the coastal zone of the Baltic Sea are largely lacking, despite the significant role of these areas in retaining nutrients derived from the catchment. Here we present a 1500-year multiproxy record of near-bottom water redox changes from the coastal zone of the northern Baltic Sea, encompassing the climatic phases of the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA), and the Modern Warm Period (MoWP). Our reconstruction shows that although multicentennial climate variability has modulated the depositional conditions and delivery of organic matter (OM) to the basin the modern aggravation of coastal hypoxia is unprecedented and, in addition to gradual changes in the basin configuration, it must have been forced by excess human-induced nutrient loading. Alongside the anthropogenic nutrient input, the progressive deoxygenation since the beginning of the 1900s was fueled by the combined effects of gradual shoaling of the basin and warming climate, which amplified sediment focusing and increased the vulnerability to hypoxia. Importantly, the eutrophication of coastal waters in our study area began decades earlier than previously thought, leading to a marked aggravation of hypoxia in the 1950s. We find no evidence of similar anthropogenic forcing during the MCA. These results have implications for the assessment of reference conditions for coastal water quality. Furthermore, this study highlights the need for combined use of sedimentological, ichnological, and geochemical proxies in order to robustly reconstruct subtle redox shifts especially in dynamic, non-euxinic coastal settings with strong seasonal contrasts in the bottom water quality.Peer reviewe
Physicochemical characterization of the PEG8000-Na2SO4 aqueous two-phase system
The polyethylene glycol-sodium sulfate aqueous two-phase system has been characterized at 23 °C. Tielines
for the phase diagram were obtained experimentally. Phases in equilibrium were characterized by means
of the solvatochromic parameters π*, α, and β, which provide a measurement of the polarity/polarizability
and the H-bond donor and acceptor abilities, respectively. The ability of the phases to participate in hydrophobic
interactions was characterized by means of the free energy of transfer of a methylene group between the
conjugated phases, using the partition of a homologous series of dinitrophenylated amino acids. The results
show the effect of the presence of polymer and salt in the aqueous phase, and a comparison of both phases
with pure water is made.LSRE-PortoUniversidade Católica PortuguesaEscola Superior de Biotecnologia do PortoFundação para a Ciência e a Tecnologia (FCT
A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century
The anthropogenically forced expansion of coastal hypoxia is a
major environmental problem affecting coastal ecosystems and biogeochemical
cycles throughout the world. The Baltic Sea is a semi-enclosed shelf sea
whose central deep basins have been highly prone to deoxygenation during its
Holocene history, as shown previously by numerous paleoenvironmental studies.
However, long-term data on past fluctuations in the intensity of hypoxia in
the coastal zone of the Baltic Sea are largely lacking, despite the
significant role of these areas in retaining nutrients derived from the
catchment. Here we present a 1500-year multiproxy record of near-bottom water
redox changes from the coastal zone of the northern Baltic Sea, encompassing
the climatic phases of the Medieval Climate Anomaly (MCA), the Little Ice Age
(LIA), and the Modern Warm Period (MoWP). Our reconstruction shows that
although multicentennial climate variability has modulated the depositional
conditions and delivery of organic matter (OM) to the basin the modern
aggravation of coastal hypoxia is unprecedented and, in addition to gradual changes
in the basin configuration, it must have been forced by excess human-induced
nutrient loading. Alongside the anthropogenic nutrient input, the progressive
deoxygenation since the beginning of the 1900s was fueled by the combined
effects of gradual shoaling of the basin and warming climate, which amplified
sediment focusing and increased the vulnerability to hypoxia. Importantly,
the eutrophication of coastal waters in our study area began decades earlier
than previously thought, leading to a marked aggravation of hypoxia in the
1950s. We find no evidence of similar anthropogenic forcing during the MCA.
These results have implications for the assessment of reference conditions
for coastal water quality. Furthermore, this study highlights the need for
combined use of sedimentological, ichnological, and geochemical proxies in
order to robustly reconstruct subtle redox shifts especially in dynamic,
non-euxinic coastal settings with strong seasonal contrasts in the bottom
water quality.</p
TNOs are Cool: A survey of the trans-Neptunian region V. Physical characterization of 18 Plutinos using Herschel PACS observations
We present Herschel PACS photometry of 18 Plutinos and determine sizes and
albedos for these objects using thermal modeling. We analyze our results for
correlations, draw conclusions on the Plutino size distribution, and compare to
earlier results. Flux densities are derived from PACS mini scan-maps using
specialized data reduction and photometry methods. In order to improve the
quality of our results, we combine our PACS data with existing Spitzer MIPS
data where possible, and refine existing absolute magnitudes for the targets.
The physical characterization of our sample is done using a thermal model.
Uncertainties of the physical parameters are derived using customized Monte
Carlo methods. The correlation analysis is performed using a bootstrap Spearman
rank analysis. We find the sizes of our Plutinos to range from 150 to 730 km
and geometric albedos to vary between 0.04 and 0.28. The average albedo of the
sample is 0.08 \pm 0.03, which is comparable to the mean albedo of Centaurs,
Jupiter Family comets and other Trans-Neptunian Objects. We were able to
calibrate the Plutino size scale for the first time and find the cumulative
Plutino size distribution to be best fit using a cumulative power law with q =
2 at sizes ranging from 120-400 km and q = 3 at larger sizes. We revise the
bulk density of 1999 TC36 and find a density of 0.64 (+0.15/-0.11) g cm-3. On
the basis of a modified Spearman rank analysis technique our Plutino sample
appears to be biased with respect to object size but unbiased with respect to
albedo. Furthermore, we find biases based on geometrical aspects and color in
our sample. There is qualitative evidence that icy Plutinos have higher albedos
than the average of the sample.Comment: 18 pages, 8 figures, 8 tables, accepted for publication in A&
A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century
The anthropogenically forced expansion of coastal hypoxia is a major
environmental problem affecting coastal ecosystems and biogeochemical
cycles throughout the world. The Baltic Sea is a semi-enclosed shelf sea
whose central deep basins have been highly prone to deoxygenation
during its Holocene history, as shown previously by numerous
paleoenvironmental studies. However, long-term data on past fluctuations
in the intensity of hypoxia in the coastal zone of the Baltic Sea are
largely lacking, despite the significant role of these areas in
retaining nutrients derived from the catchment. Here we present a
1500-year multiproxy record of near-bottom water redox changes from the
coastal zone of the northern Baltic Sea, encompassing the climatic
phases of the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA),
and the Modern Warm Period (MoWP). Our reconstruction shows that
although multicentennial climate variability has modulated the
depositional conditions and delivery of organic matter (OM) to the basin
the modern aggravation of coastal hypoxia is unprecedented and, in
addition to gradual changes in the basin configuration, it must have
been forced by excess human-induced nutrient loading. Alongside the
anthropogenic nutrient input, the progressive deoxygenation since the
beginning of the 1900s was fueled by the combined effects of gradual
shoaling of the basin and warming climate, which amplified sediment
focusing and increased the vulnerability to hypoxia. Importantly, the
eutrophication of coastal waters in our study area began decades earlier
than previously thought, leading to a marked aggravation of hypoxia in
the 1950s. We find no evidence of similar anthropogenic forcing during
the MCA. These results have implications for the assessment of reference
conditions for coastal water quality. Furthermore, this study
highlights the need for combined use of sedimentological, ichnological,
and geochemical proxies in order to robustly reconstruct subtle redox
shifts especially in dynamic, non-euxinic coastal settings with strong
seasonal contrasts in the bottom water quality.</p
Comparison of lipid membrane-water partitioning with various organic solvent-water partitions of neutral species and ionic species: Uniqueness of cerasome as a model for the stratum corneum in partition processes
YesLipid membrane-water partitions (e.g., immobilized artificial membrane systems where the lipid membrane is a neutral phospholipid monolayer bound to gel beads) were compared to various organic solvent-water partitions using linear free energy relationships. To this end, we also measured the retention factors of 36 compounds (including neutral and ionic species) from water to liposomes made up of 3-sn-phosphatidylcholine and 3-sn-phosphatidyl-l-serine (80:20, mol/mol), employing liposome electrokinetic chromatography in this work. The results show that lipid membranes exhibit a considerably different chemical environment from those of organic solvents. For both neutral species and ionic species, partitions into the more polar hydroxylic solvents are chemically closer to partition into the lipid membrane as compared to partitions into the less polar hydroxylic solvents and into aprotic solvents. This means that solutes partition into the polar parts of lipid membranes, regardless of whether they are charged or not. In addition, cerasome (i.e., liposome composed mainly of stratum corneum lipids) was compared with regular phospholipid liposomes as a possible model for human stratum corneum in partitions. It was found that the cerasome-water partition exhibits a better chemical similarity to skin permeation. This is probably due to the unique structures of ceramides that occur in cerasome and in the stratum corneum lipid domain. We further show that membranes in membrane-water partitions exhibit very different properties
Evolutionary origins of abnormally large shoot sodium accumulation in non-saline environments within the Caryophyllales
The prevalence of sodium (Na) “hyperaccumulator” species, which exhibit abnormally large shoot sodium concentrations ([Na]shoot) when grown in non-saline environments, was investigated among angiosperms in general and within the Caryophyllales order in particular.
Shoot Na concentrations were determined in 334 angiosperm species, representing 35 orders, grown hydroponically in a non-saline solution.
Many Caryophyllales species exhibited abnormally large [Na]shoot when grown hydroponically in a non-saline solution. The bimodal distribution of the log-normal [Na]shoot of species within the Caryophyllales suggested at least two distinct [Na]shoot phenotypes within this order. Mapping the trait of Na-hyperaccumulation onto the phylogenetic relationships between Caryophyllales families, and between subfamilies within the Amaranthaceae, suggested that the trait evolved several times within this order: in an ancestor of the Aizoaceae, but not the Phytolaccaceae or Nyctaginaceae, in ancestors of several lineages formerly classified as Chenopodiaceae, but not in the Amaranthaceae sensu stricto, and in ancestors of species within the Cactaceae, Portulacaceae, Plumbaginaceae,Tamaricaceae and Polygonaceae.
In conclusion, a disproportionate number of Caryophyllales species behave as Na51 hyperaccumulators and multiple evolutionary origins of this trait can be identified within this order
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