Testate amoebae (Protozoa: Testacea) as bioindicators in the Late Quaternary deposits of the Bykovsky Peninsula, Laptev Sea, Russia

Testate amoebae (Protozoa: Testacea) were studied in the Late Quaternary permafrost depositsin the Siberian Arctic (Bykovsky Peninsula of the Laptev Sea coast, 71º40'-71º80'N and 129º-129º30'E). The studied Testacea associations reflect specific environmental conditions in paleocryosols,which were controlled by the local micro-relief as well as regional climate conditions. Totally, 86species, varieties, and forms of testate amoebae were found in 38 Pleistocene and Holocenesamples. The rhizopods indicate that soil conditions at ca 53,000 14C yr BP were probably rathersimilar to the modern cold and wet arctic tundra environment. More moisture and warmer soilconditions were relatively favourable for rhizopods ca 45,300-43,000 14C yr BP, but significantlydrier at about 42,000 14C yr BP. Drier and colder environmental conditions were also presentabout 39,300-35,000 14C yr BP. The Late Pleistocene samples, radiocarbon dated to 33,000-12,000 yr BP, are characterized by a low species diversity and density. This period may have beenextremely cold and dry, which is also supported by the polymorphism of some species.Hydrophilic Difflugia species (mostly obligate hydrobiotes) are broadly represented in theHolocene samples. The species composition and density of rhizopods in the majority of Holocenesamples suggest wet and relatively warm conditions. Changes in rhizopod assemblages during thelast 53,000 years were not very dramatic, mostly consisting of rare species and changes in thedominant species complexes during the Pleistocene and Holocene. However, these changes weremore drastic during the Pleistocene. They, probably, were at least partly responsible for thedisappearance of some rare testacean species such as Argynnia sp

GigaGauss solenoidal magnetic field inside of bubbles excited in under-dense plasma

Magnetic fields have a crucial role in physics at all scales, from astrophysics to nanoscale phenomena. Large fields, constant or pulsed, allow investigation of material in extreme conditions, opening up plethora of practical applications based on ultra-fast process, and studying phenomena existing only in exotic astro-objects like neutron stars or pulsars. Magnetic fields are indispensable in particle accelerators, for guiding the relativistic particles along a curved trajectory and for making them radiate in synchrotron light sources and in free electron lasers. In the presented paper we propose a novel and effective method for generating solenoidal quasi-static magnetic field on the GigaGauss level and beyond, in under-dense plasma, using screw-shaped high intensity laser pulses. In comparison with already known techniques which typically rely on interaction with over-dense or solid targets, where radial or toroidal magnetic field localized at the stationary target were generated, our method allows to produce gigantic solenoidal fields, which is co-moving with the driving laser pulse and collinear with accelerated electrons. The solenoidal field is quasi-stationary in the reference frame of the laser pulse and can be used for guiding electron beams and providing synchrotron radiation beam emittance cooling for laser-plasma accelerated electron and positron beams, opening up novel opportunities for designs of the light sources, free electron lasers, and high energy colliders based on laser plasma acceleration.Comment: 15 pages, 9 figures. Main text (without abstract, References and Appendix): 12 page

Nonlocal Andreev reflection at high transmissions

We analyze non-local effects in electron transport across three-terminal normal-superconducting-normal (NSN) structures. Subgap electrons entering S-electrode from one N-metal may form Cooper pairs with their counterparts penetrating from another N-metal. This phenomenon of crossed Andreev reflection -- combined with normal scattering at SN interfaces -- yields two different contributions to non-local conductance which we evaluate non-perturbatively at arbitrary interface transmissions. Both these contributions reach their maximum values at fully transmitting interfaces and demonstrate interesting features which can be tested in future experiments.Comment: 4 pages, 4 figure

Crossed Andreev reflection at spin-active interfaces

With the aid of the quasiclassical Eilenberger formalism we develop a theory of non-local electron transport across three-terminal ballistic normal-superconducting-normal (NSN) devices with spin-active NS interfaces. The phenomenon of crossed Andreev reflection (CAR) is known to play the key role in such transport. We demonstrate that CAR is highly sensitive to electron spins and yields a rich variety of properties of non-local conductance which we describe non-perturbatively at arbitrary voltages, temperature, spin-dependent interface transmissions and their polarizations. Our results can be applied to multi-terminal hybrid structures with normal, ferromagnetic and half-metallic electrodes and can be directly tested in future experiments.Comment: 11 pages, 7 figures; figures 6 and 7 are corrected; version published in Phys. Rev.

Permafrost, landscape and ecosystem responses to late Quaternary warm stages in Northeast Siberia

Permafrost, landscape and ecosystem responses to late Quaternary warm stages in Northeast Siberia S. Wetterich1, F. Kienast2, L. Schirrmeister1, M. Fritz1, A. Andreev3, P. Tarasov4 1Alfred Wegener Institute for Polar and Marine Research, Department of Periglacial Research, Potsdam, Germany; 2Senckenberg Research Institute and Natural History Museum, Research Station for Quaternary Palaeontology, Weimar, Germany; 3Institute of Geology and Mineralogy, University of Cologne, Germany; 4Institute of Geological Sciences, Free University Berlin, Germany Perennially frozen ground is widely distributed in Arctic lowlands and beyond. Permafrost responds sensitive to changes in climate conditions. Climate-driven dynamics of landscape, sedimentation and ecology in periglacial regions are frequently recorded in permafrost deposits. The study of late Quaternary permafrost can therefore reveal past glacial-interglacial and stadialinterstadial environmental dynamics. One of the most striking processes under warming climate conditions is the extensive thawing of permafrost (thermokarst) and subsequent surface subsidence. Thermokarst basins promote the development of lakes, whose sedimentological and paleontological records give insights into past interglacial and interstadial (warm). In this paper we present results of qualitative and quantitative reconstructions of climate and environmental conditions for the last Interglacial (MIS 5e, Kazantsevo; ca. 130 to 115 ka ago), the lateglacial Allerød Interstadial (ca. 13 to 11 uncal. ka BP), and the early Holocene (ca. 10.5 to 8 uncal. ka BP). The study was performed in course of the IPY project #15 ‘Past Permafrost’ with permafrost deposits exposed at the coasts of the Dmitry Laptev Strait (East Siberian Sea, East Siberia). The reconstruction based on fossil-rich findings of plants (pollen, macro-remains) and invertebrates (beetles, chironomids, ostracods gastropods). Interglacial vegetation dynamics are reflected in the pollen records by changes from early interglacial grass-sedge-tundra to shrub-tundra during the interglacial thermal optimum followed by grass-sedge-tundra vegetation at the end of the Kazantsevo warm period. Terrestrial beetle and plant remains prove the former existence of open forest tundra with Dahurian larch, grey alder and boreal shrubs interspersed with patches of steppes and meadows during the interglacial thermal optimum. Mean temperature reconstructions of the warmest month (MTWA, TJuly) for the interglacial thermal optimum are based on quantitative chironomid transfer functions revealed a TJuly of 12.9 ± 0.9 °C. The TJuly reconstructed by plant macrofossils amounts to 13.2 ± 0.5 °C, and the pollen-based TJuly reaches 14.3 ± 3.3 °C. Low net precipitation is reflected by steppe plants and beetles. The temperature reconstruction based on three independent approaches. Nethertheless, all methods consistently indicate an interglacial TJuly about 10 °C higher than today, which is interpreted as a result of a combination of increased insolation and higher climatic continentality during the last Interglacial. Grass-sedge dominated tundra vegetation occurred during the lateglacial to Holocene transition which was replaced by shrub tundra during the early Holocene. The presence of Salix and Betula pollen reflects temperatures about 4 °C higher than present between 12 to 11 uncal. ka BP, during the Allerød Interstadial, but shrubs disappeared in the following Younger Dryas stadial, reflecting a climate deterioration. Alnus fruticosa, Betula nana, Poaceae and Cyperaceae dominate early Holocene pollen spectra. Pollen-based reconstructions point to TJuly 4 °C warmer than present. Shrubs gradually disappeared from coastal areas after 7.6 uncal. ka BP when vegetation cover became similar to modern wet tundra. Thermokarst acted as response to warming conditions on landscape scale in permafrost regions. Concurrent changes in relief, hydrology and ecosystems are obvious and detectable by analyses of the paleontological record preserved in thermokarst deposits

Shot noise and Coulomb blockade of Andreev reflection

We derive low energy effective action for a short coherent conductor between normal (N) and superconducting (S) reservoirs. We evaluate interaction correction $\delta G$ to Andreev conductance and demonstrate a close relation between Coulomb effects and shot noise in NS systems. In the diffusive limit doubling of both shot noise power and charge of the carriers yields $|\delta G|$ four times bigger than in the normal case. Our predictions can be directly tested in future experiments.Comment: 4 pages, 2 figure