Stepwise transition from deglacial/Early Holocene to modern-like conditions in the eastern Fram Strait, sub-Arctic north, inferred from planktic foraminifer fauna and sea surface temperatures

EGU2012-4750 The heat content of the Arctic Ocean is mainly controlled by the inflow of north-heading warm and saline Atlantic Water through eastern Fram Strait. The eastern Fram Strait is therefore ice-free all year, opposite to its perennially ice-covered western part where large amounts of Arctic sea ice are exported year-round to the Nordic Seas. The Early and Mid-Holocene phases (ca 12 to 5 cal ka BP) in the (sub-)Arctic have been especially marked not only by high summer insolation but also by rising sea level and the final disintegration of large ice sheets that had been established during the preceding glacial phase. Two sediment cores with multidecadal resolution from the Western Svalbard margin have been investigated for its planktic foraminiferal distribution, sea surface temperatures, planktic and benthic stable isotope ratios, and lithological parameters to derive information on the Holocene variability of the heat transport to the Arctic Ocean and related fluctuations of the marginal ice zone in the eastern Fram Strait. Planktic foraminifer fauna and a summer sea surface temperature reconstruction based on the modern analogue technique imply a stepwise transition from deglacial/Early Holocene to modern-like conditions in the eastern Fram Strait. Repeated short-term advances of the sea ice margin accompanied the generally strong heat transport to the Arctic Ocean during the Early to Mid-Holocene. Consistent with the decreasing solar insolation, cooler (sub-)surface conditions established after ca 5 cal ka BP most likely related to both a weakening of the Atlantic Water inflow and strong export of Arctic sea ice through Fram Strait. The Late Holocene Neoglacial phase was characterized by high contents of ice-rafted material and dominance of the cold water-indicating planktic foraminifer species Neogloboquadrina pachyderma. Cool Late Holocene conditions are reversed by a strong warming event likely caused by a significant strengthening of Atlantic heat advection to the Arctic during the present, anthropogenically influenced period

Study of the system of middle atmosphere-ionosphere using remote-sensing data

In the present investigation, the methods of statistical spectral analysis are employed for a study of the quasi-periodic changes of state parameters of the middle atmosphere and the ionosphere, taking into account oscillations with periods of several days. The considered oscillations are typical for planetary waves. The theory and empirical findings regarding transient planetary waves are utilized as a basis for the concepts employed in the data analysis and for the interpretation of the results. The results of the investigation show a presence of coherent variations in the time series of radiation density measurements and other state parameters for the middle atmosphere and the ionosphere. The existence of presumably dynamic coupling processes can be recognized in oscillations with periods of about 16 or 5 days

Short-term quantitative analysis of submarine bedform movement in the Sylt Outer Reef, North Sea

A new approach on optimizing and rectifying backscatter images from side-scan sonar were applied in the seafloor images of a marine protected area in the German part of the North Sea, to monitor bedform change. Hydro-acoustic data from 2017 to 2018 of side-scan and multibeam echosounder were evaluated using the Digital Shoreline Analysis System (DSAS) to quantify the movement pattern of submarine bedforms. Results were verified with grain-size analyses and underwater video footages. The new method provides the rate of change of bedform movement, net bedform movement, and linear regression rate, which can assist in the environmental monitoring of the marine protected area

Moire bands in twisted double-layer graphene

A moire pattern is formed when two copies of a periodic pattern are overlaid with a relative twist. We address the electronic structure of a twisted two-layer graphene system, showing that in its continuum Dirac model the moire pattern periodicity leads to moire Bloch bands. The two layers become more strongly coupled and the Dirac velocity crosses zero several times as the twist angle is reduced. For a discrete set of magic angles the velocity vanishes, the lowest moire band flattens, and the Dirac-point density-of-states and the counterflow conductivity are strongly enhanced

Deep far infrared ISOPHOT survey in "Selected Area 57", I. Observations and source counts

We present here the results of a deep survey in a 0.4 sq.deg. blank field in Selected Area 57 conducted with the ISOPHOT instrument aboard ESAs Infrared Space Observatory (ISO) at both 60 um and 90 um. The resulting sky maps have a spatial resolution of 15 x 23 sq.arcsec. per pixel which is much higher than the 90 x 90 sq.arcsec. pixels of the IRAS All Sky Survey. We describe the main instrumental effects encountered in our data, outline our data reduction and analysis scheme and present astrometry and photometry of the detected point sources. With a formal signal to noise ratio of 6.75 we have source detection limits of 90 mJy at 60 um and 50 mJy at 90 um. To these limits we find cumulated number densities of 5+-3.5 per sq.deg. at 60 um and 14.8+-5.0 per sq.deg.at 90 um. These number densities of sources are found to be lower than previously reported results from ISO but the data do not allow us to discriminate between no-evolution scenarios and various evolutionary models.Comment: 15 pages, 11 figures, accepted by Astronomy & Astrophysic

The Computational Complexity of Knot and Link Problems

We consider the problem of deciding whether a polygonal knot in 3-dimensional Euclidean space is unknotted, capable of being continuously deformed without self-intersection so that it lies in a plane. We show that this problem, {\sc unknotting problem} is in {\bf NP}. We also consider the problem, {\sc unknotting problem} of determining whether two or more such polygons can be split, or continuously deformed without self-intersection so that they occupy both sides of a plane without intersecting it. We show that it also is in NP. Finally, we show that the problem of determining the genus of a polygonal knot (a generalization of the problem of determining whether it is unknotted) is in {\bf PSPACE}. We also give exponential worst-case running time bounds for deterministic algorithms to solve each of these problems. These algorithms are based on the use of normal surfaces and decision procedures due to W. Haken, with recent extensions by W. Jaco and J. L. Tollefson.Comment: 32 pages, 1 figur

The modeling of medical expenditure data from a longitudinal survey using the generalized method of moments (GMM) approach

Medical expenditure data analysis has recently become an important problem in biostatistics. These data typically have a number of features making their analysis rather difficult. Commonly, they are heavily right-skewed, contain a large percentage of zeros, and often exhibit large numbers of missing observations because of death and/or the lack of follow-up. They are also commonly obtained from records that are linked to large longitudinal data surveys. In this manuscript, we suggest a novel approach to modeling these data through the use of generalized method of moments estimation procedure combined with appropriate weights that account for both dropout due to death and the probability of being sampled from among the National Long Term Care Survey (NLTCS) subjects. This approach seems particularly appropriate because of the large number of subjects relative to the length of observation period (in months). We also use a simulation study to compare our proposed approach with and without the use of weights. The proposed model is applied to medical expenditure data obtained from the 2004-2005 NLTCS-linked Medicare database. The results suggest that the amount of medical expenditures incurred is strongly associated with higher number of activities of daily living (ADL) disabilities and self-reports of unmet need for help with ADL disabilities

Andreev reflections on Y1-xCaxBa2Cu3O7-delta evidence for an unusual proximity effect

We have measured Andreev reflections between an Au tip and Y_{1-x}Ca_{x}Ba_{2}Cu_{3}O_{7 - \delta} thin films in the in-plane orientation. The conductance spectra are best fitted with a pair potential having the "d_{x^{2}-y^{2}+is" symmetry. We find that the amplitude of the "is" component is enhanced as the contact transparency is increased. This is an indication for an unusual proximity effect that modifies the pair potential in the superconductor near the surface with the normal metal.Comment: 4 pages, 4 figure

Highly-ordered graphene for two dimensional electronics

With expanding interest in graphene-based electronics, it is crucial that high quality graphene films be grown. Sublimation of Si from the 4H-SiC(0001) Si-terminated) surface in ultrahigh vacuum is a demonstrated method to produce epitaxial graphene sheets on a semiconductor. In this paper we show that graphene grown from the SiC$(000\bar{1})$ (C-terminated) surface are of higher quality than those previously grown on SiC(0001). Graphene grown on the C-face can have structural domain sizes more than three times larger than those grown on the Si-face while at the same time reducing SiC substrate disorder from sublimation by an order of magnitude.Comment: Submitted to Appl. Phys. Let