14,098 research outputs found
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New organic-walled dinoflagellate cysts from recent sediments of central Asian seas
Recent to sub-recent sediments from the Caspian Sea, the Kara-Bogaz-Gol Bay, the Enseli lake and the Aral Sea contain the new organic-walled dinoflagellate cysts Caspidinium, Caspidinium rugosum and Impagidinium caspienense. Caspidinium rugosum has S-type paratabulation, dextral torsion and low relief intratabular ornamentation. Impagidinium caspienense has low intratabular suturo-cavate relief, parasutural septa irregular in height and a high septum at the junction of paraplate 1'''' and the sulcus. The accompanying species consist of Spiniferites cruciformis, Lingulodinium machaerophorum, Pyxidinopsis psilata, cysts of Pentapharsodinium dalei and Brigantedinium spp. Spiniferites cruciformis varies from specimens with a cruciform body with a well-developed postero-lateral membranous flange to specimens with a pear-shaped body, reduced processes and no flange. Sea-surface data from these Central Asian seas suggests that the two new taxa Caspidinium rugosum and Impagidinium caspienense are probably related to low salinity conditions (12-13)
A Universal Neutral Gas Profile for Nearby Disk Galaxies
Based on sensitive CO measurements from HERACLES and HI data from THINGS, we
show that the azimuthally averaged radial distribution of the neutral gas
surface density (Sigma_HI + Sigma_H2) in 33 nearby spiral galaxies exhibits a
well-constrained universal exponential distribution beyond 0.2*r25 (inside of
which the scatter is large) with less than a factor of two scatter out to two
optical radii r25. Scaling the radius to r25 and the total gas surface density
to the surface density at the transition radius, i.e., where Sigma_HI and
Sigma_H2 are equal, as well as removing galaxies that are interacting with
their environment, yields a tightly constrained exponential fit with average
scale length 0.61+-0.06 r25. In this case, the scatter reduces to less than 40%
across the optical disks (and remains below a factor of two at larger radii).
We show that the tight exponential distribution of neutral gas implies that the
total neutral gas mass of nearby disk galaxies depends primarily on the size of
the stellar disk (influenced to some degree by the great variability of
Sigma_H2 inside 0.2*r25). The derived prescription predicts the total gas mass
in our sub-sample of 17 non-interacting disk galaxies to within a factor of
two. Given the short timescale over which star formation depletes the H2
content of these galaxies and the large range of r25 in our sample, there
appears to be some mechanism leading to these largely self-similar radial gas
distributions in nearby disk galaxies.Comment: 7 pages, 4 figures, accepted for publication in the Astrophysical
Journa
Liquidity and fire sales
A “fire sale” occurs when the owner of a good offers it for sale at a price strictly below the price that some buyers would willingly pay for the good. He does so because the advantage of the quick sale made possible by the lower price outweighs the higher price that other potential buyers would pay, given the likely delay in locating these buyers in the latter case. Fire sales can occur only in illiquid markets. This paper generalizes earlier treatments of illiquid markets by assuming that the asset can be offered for sale at any time, rather than only after its owner loses his capacity to operate it profitably. Also, it specifies that profitability follows a random walk.Liquidity (Economics) ; Econometric models
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Natural and anthropogenic rapid changes in the Kara-Bogaz Gol over the last two centuries reconstructed from palynological analyses and a comparison to instrumental records
Palynological analyses (pollen and dinocysts) of a sediment core taken in the Kara-Bogaz Gol have been used to
reconstruct rapid and catastrophic environmental changes over the last two centuries (chronology based on 210Pb). A
natural cyclicity (65 years) of water level changes in the Caspian Sea and in the Kara-Bogaz Gol and anthropogenic
factors (building of a dam separating the CS and the KBG waters) combine to induce rapid changes in water levels of
the KBG, in the salinity of its waters and in vegetation cover of its surroundings. The impact of low water levels on
the dinocysts is marked by a lower diversity and the survival of two species that are typical of the KBG, the Caspian
Sea species present in the KBG having disappeared. During periods of higher water levels (AD 1871 to 1878), the
lake is surrounded by a steppe-like vegetation dominated by Artemisia; whereas during periods of low water levels
(AD 1878 to 1913 and AD 1955-1998), the emerged shore are colonised by Chenopodiaceae. The period of AD 1913
to 1955 corresponding to decreasing water levels has an extremely low pollen concentration and a maximum of
reworking of arboreal taxa. During the last low-level period, humans responded by abandoning the shores of the bay.
What happened to the KBG can be used as an example of what may happen in the future for the Aral Sea.
A problem of reworking of Tertiary dinocysts into modern deposits has been detected owing to the knowledge of the
modern dinoflagellate assemblages recently made available through a water survey. A comparison to modern surface
pollen samples from Central Asia (Anzali, Caspian Sea south and central basins, Aral Sea, Lake Balkhash, Lake
Issyk-Kul and the Chinese Tien-Shan range) allows us to establish the potential reworking of at least five arboreal
pollen taxa possibly by run-off and dust storms
Late Pleistocene and Holocene palaeoenvironments in and around the middle Caspian basin as reconstructed from a deep-sea core
This article has been made available through Open Access by the Brunel Open Access Publishing Fund.Late Pleistocene and/or Holocene high-resolution palynological studies are available for the south basin of the Caspian Sea (CS), the world's largest lake. However, the north and middle basins have not been the object of high-resolution palynological reconstructions. This new study presents the pollen, spores and dinoflagellate cysts records obtained from a 10m-long sediment core recovered in the middle basin, which currently has brackish waters and is surrounded by arid and semi-arid vegetation.An age-depth model built based on six radiocarbon dates on ostracod shells indicates that the sequence spans the period from 14.47 to 2.43cal.kaBP. The present palaeoenvironmental study focuses on the top 666cm, or from 12.44 to 2.43cal.kaBP.At the vegetation level, the Younger Dryas is characterised by an open landscape dominated by desert vegetation composed by Amaranthaceae with shrubs and salt-tolerant plants. However, although the Early Holocene is also characterised by desert vegetation, it is enriched in various shrubs such as Ephedra and Calligonum, but tree expansion is not important at the Holocene onset. After a major shift at 8.19cal.kaBP, the Middle Holocene displays now both the character of desert and of steppe, although some trees such as Quercus and Corylus slightly spread. The Late Holocene records steppe vegetation as dominant, with more tree diversity.Regarding the lacustrine signal, the dinocyst assemblage record fluctuates between slightly brackish conditions highlighted by Pyxidinopsis psilata and Spiniferites cruciformis, and more brackish ones - similar to the present day - with the dominance of Impagidinium caspienense. The Late Pleistocene is characterised by low salinities, related to the Khvalynian highstand. From 11.56cal.kaBP, slightly more saline waters are reconstructed with an increase of I.caspienense for a period of 1000 years, which could be attributed to the Mangyshlak lowstand. From 10.55cal.kaBP, low salinity conditions return with remains such as Anabaena and Botryococcus abundant until 8.83cal.kaBP, followed by a slow, progressive decrease of P. psilata and S. cruciformis until 4.11cal.kaBP, which is the main assemblage change at lacustrine scale. Since then, higher salinities, similar to the present one, are reconstructed. Finally, Lingulodinium machaerophorum starts its development only at 2.75cal.kaBP, in the Late Holocene.The present research revealed fundamental differences from previously published sea-level curves, in that a 6000yr-long highstand suggested by low salinities is shown between 10.55 and 4.11cal.kaBP. Amongst other arguments, using a comparison to a similar palynological regard but in the south basin, a N-S salinity gradient that is the reverse of the present one across the CS, suggests that the Amu Darya was flowing in the CS. Hence the CS levels during the Late Pleistocene and Holocene were influenced by a combination of precipitation over the high European latitudes and the indirect influence of the Indian summer monsoon over the Pamirs. © 2014.This study has been conducted within the European Contract INCO-Copernicus “Understanding the Caspian Sea erratic fluctuations” n IC15-CT96-0112. This was funded by the Centre National de la Recherche Scientifique within the framework of the INSUDYTEC (DYnamique de la Terre et du Climat) Program (France)
Mortgage default and mortgage valuation
We study optimal exercise by mortgage borrowers of the option to default. Also, we use an equilibrium valuation model incorporating default to show how mortgage yields and lender recovery rates on defaulted mortgages depend on initial loan-to-value ratios when borrowers default optimally. The analysis treats both the frictionless case and the case in which borrowers and/or lenders incur deadweight costs upon default. The model is calibrated using data on California mortgages. We find that the model's principal testable implication for default and mortgage pricing—that default rates and yield spreads will be higher for high loan-to-value mortgages—is borne out empirically.Mortgage loans ; Mortgage loans - California ; Default (Finance)
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