5,211 research outputs found
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
Coarsening Dynamics of Crystalline Thin Films
The formation of pyramid-like structures in thin-film growth on substrates
with a quadratic symmetry, e.g., {001} surfaces, is shown to exhibit
anisotropic scaling as there exist two length scales with different time
dependences. Analytical and numerical results indicate that for most
realizations coarsening of mounds is described by an exponent n=0.2357.
However, depending on material parameters, n may lie between 0 (logarithmic
coarsening) and 1/3. In contrast, growth on substrates with triangular
symmetries ({111} surfaces) is dominated by a single length scale and an
exponent n=1/3.Comment: RevTeX, 4 pages, 3 figure
Observation of a two-dimensional spin-lattice in non-magnetic semiconductor heterostructures
Tunable magnetic interactions in high-mobility nonmagnetic semiconductor
heterostructures are centrally important to spin-based quantum technologies.
Conventionally, this requires incorporation of "magnetic impurities" within the
two-dimensional (2D) electron layer of the heterostructures, which is achieved
either by doping with ferromagnetic atoms, or by electrostatically printing
artificial atoms or quantum dots. Here we report experimental evidence of a
third, and intrinsic, source of localized spins in high-mobility GaAs/AlGaAs
heterostructures, which are clearly observed in the limit of large setback
distance (=80 nm) in modulation doping. Local nonequilibrium transport
spectroscopy in these systems reveals existence of multiple spins, which are
located in a quasi-regular manner in the 2D Fermi sea, and mutually interact at
temperatures below 100 milliKelvin via the Ruderman-Kittel-Kasuya-Yosida (RKKY)
indirect exchange. The presence of such a spin-array, whose microscopic origin
appears to be disorder-bound, simulates a 2D lattice-Kondo system with
gate-tunable energy scales.Comment: 7 pages + 4 figs. To appear in Nature Physics. This is the original
submitted version. Final version will be posted six months after publication.
The Supplementary Information can be downloaded from:
http://www.physics.iisc.ernet.in/~arindam/Supplementary_Information_NPHYS-2006-08-0
0812B.pd
The Al Gamma-ray Line from Massive-Star Regions
The measurement of gamma rays from the diffuse afterglow of radioactivity
originating in massive-star nucleosynthesis is considered a laboratory for
testing models, when specific stellar groups are investigated, at known
distance and with well-constrained stellar population. Regions which have been
exploited for such studies include Cygnus, Carina, Orion, and
Scorpius-Centaurus. The Orion region hosts the Orion OB1 association and its
subgroups at about 450~pc distance. We report the detection of Al gamma
rays from this region with INTEGRAL/SPI.Comment: Contribution to Symposium "Nuclei in the Cosmos XIV", Niigata, Japan,
Jun 2016; 3 pages, 2 figures; accepted for publication in JPS (Japan Physical
Society) Conference Proceedings http://jpscp.jps.jp
Sensitivity of the magnetic state of a spin lattice on itinerant electron orbital phase
Spatially extended localized spins can interact via indirect exchange
interaction through Friedel oscillations in the Fermi sea. In arrays of
localized spins such interaction can lead to a magnetically ordered phase.
Without external magnetic field such a phase is well understood via a
"two-impurity" Kondo model. Here we employ non-equilibrium transport
spectroscopy to investigate the role of the orbital phase of conduction
electrons on the magnetic state of a spin lattice. We show experimentally, that
even tiniest perpendicular magnetic field can influence the magnitude of the
inter-spin magnetic exchange.Comment: To be published in PhysicaE EP2DS proceedin
Transport Through an Electrostatically Defined Quantum Dot Lattice in a Two-Dimensional Electron Gas
Quantum dot lattices (QDLs) have the potential to allow for the tailoring of
optical, magnetic and electronic properties of a user-defined artificial solid.
We use a dual gated device structure to controllably tune the potential
landscape in a GaAs/AlGaAs two-dimensional electron gas, thereby enabling the
formation of a periodic QDL. The current-voltage characteristics, I(V), follow
a power law, as expected for a QDL. In addition, a systematic study of the
scaling behavior of I(V) allows us to probe the effects of background disorder
on transport through the QDL. Our results are particularly important for
semiconductor-based QDL architectures which aim to probe collective phenomena.Comment: 6 pages, 4 figure
Beautiful Baryons from Lattice QCD
We perform a lattice study of heavy baryons, containing one () or
two -quarks (). Using the quenched approximation we obtain for the
mass of
The mass splitting between the and the B-meson is found to increase
by about 20\% if the light quark mass is varied from the chiral limit to the
strange quark mass.Comment: 11 pages, Figures obtained upon request from [email protected]
A Bayesian framework for verification and recalibration of ensemble forecasts: How uncertain is NAO predictability?
Predictability estimates of ensemble prediction systems are uncertain due to
limited numbers of past forecasts and observations. To account for such
uncertainty, this paper proposes a Bayesian inferential framework that provides
a simple 6-parameter representation of ensemble forecasting systems and the
corresponding observations. The framework is probabilistic, and thus allows for
quantifying uncertainty in predictability measures such as correlation skill
and signal-to-noise ratios. It also provides a natural way to produce
recalibrated probabilistic predictions from uncalibrated ensembles forecasts.
The framework is used to address important questions concerning the skill of
winter hindcasts of the North Atlantic Oscillation for 1992-2011 issued by the
Met Office GloSea5 climate prediction system. Although there is much
uncertainty in the correlation between ensemble mean and observations, there is
strong evidence of skill: the 95% credible interval of the correlation
coefficient of [0.19,0.68] does not overlap zero. There is also strong evidence
that the forecasts are not exchangeable with the observations: With over 99%
certainty, the signal-to-noise ratio of the forecasts is smaller than the
signal-to-noise ratio of the observations, which suggests that raw forecasts
should not be taken as representative scenarios of the observations. Forecast
recalibration is thus required, which can be coherently addressed within the
proposed framework.Comment: 36 pages, 10 figure
Thermoelectric Properties of Electrostatically Tunable Antidot Lattices
We report on the fabrication and characterization of a device which allows
the formation of an antidot lattice (ADL) using only electrostatic gating. The
antidot potential and Fermi energy of the system can be tuned independently.
Well defined commensurability features in magnetoresistance as well as
magnetothermopower are obsereved. We show that the thermopower can be used to
efficiently map out the potential landscape of the ADL.Comment: 4 pages, 3 figures; to appear in Appl. Phys. Let
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