496 research outputs found
First evidence of cryptotephra in palaeoenvironmental records associated with Norse occupation sites in Greenland
The Norse/Viking occupation of Greenland is part of a dispersal of communities across the North Atlantic coincident with the supposed Medieval Warm Period of the late 1st millennium AD. The abandonment of the Greenland settlements has been linked to climatic deterioration in the Little Ice Age as well as other possible explanations. There are significant dating uncertainties over the time of European abandonment of Greenland and the potential influence of climatic deterioration. Dating issues largely revolve around radiocarbon chronologies for Norse settlements and associated mire sequences close to settlement sites. Here we show the potential for moving this situation forward by a combination of palynological, radiocarbon and cryptotephra analyses of environmental records close to three âiconicâ Norse sites in the former Eastern Settlement of Greenland â Herjolfsnes, Hvalsey and GarĂ°ar (the modern Igaliku). While much work remains to be undertaken, our results show that palynological evidence can provide a useful marker for both the onset and end of Norse occupation in the region, while the radiocarbon chronologies for these sequences remain difficult. Significantly, we here demonstrate the potential for cryptotephra to become a useful tool in resolving the chronology of Norse occupation, when coupled with palynology. For the first time, we show that cryptotephra are present within palaeoenvironmental sequences located within or close to Norse settlement ruin-groups, with tephra horizons detected at all three sites. While shard concentrations were small at Herjolfsnes, concentrations sufficient for geochemical analyses were detected at Igaliku and Hvalsey. WDS-EPMA analyses of these tephra indicate that, unlike the predominantly Icelandic tephra sources reported in the Greenland ice core records, the tephra associated with the Norse sites correlate more closely with volcanic centres in the Aleutians and Cascades. Recent investigations of cryptotephra dispersal from North American centres, along with our new findings, point to the potential for cryptotephra to facilitate hypothesis testing, providing a key chronological tool for refining the timing of Norse activities in Greenland (e.g. abandonment) and of environmental contexts and drivers (e.g. climate forcing)
Relativistic Kinetics of Phonon Gas in Superfluids
The relativistic kinetic theory of the phonon gas in superfluids is
developed. The technique of the derivation of macroscopic balance equations
from microscopic equations of motion for individual particles is applied to an
ensemble of quasi-particles. The necessary expressions are constructed in terms
of a Hamilton function of a (quasi-)particle. A phonon contribution into
superfluid dynamic parameters is obtained from energy-momentum balance
equations for the phonon gas together with the conservation law for superfluids
as a whole. Relations between dynamic flows being in agreement with results of
relativistic hydrodynamic consideration are found. Based on the kinetic
approach a problem of relativistic variation of the speed of sound under phonon
influence at low temperature is solved.Comment: 23 pages, Revtex fil
Optimally squeezed spin states
We consider optimally spin-squeezed states that maximize the sensitivity of
the Ramsey spectroscopy, and for which the signal to noise ratio scales as the
number of particles . Using the variational principle we prove that these
states are eigensolutions of the Hamiltonian
and that, for large , the states become equivalent to the quadrature
squeezed states of the harmonic oscillator. We present numerical results that
illustrate the validity of the equivalence
Quantum coherence in a degenerate two-level atomic ensemble: for a transition
For a transition driven by a linearly polarized
light and probed by a circularly light, quantum coherence effects are
investigated. Due to the coherence between the drive Rabi frequency and Zeeman
splitting, electromagnetically induced transparency, electromagnetically
induced absorption, and the transition from positive to negative dispersion are
obtained, as well as the populations coherently oscillating in a wide spectral
region. At the zero pump-probe detuning, the subluminal and superluminal light
propagation is predicted. Finally, coherent population trapping states are not
highly sensitive to the refraction and absorption in such ensemble.Comment: 9 pages, 6 figure
On Slow Light as a Black Hole Analogue
Although slow light (electromagnetically induced transparency) would seem an
ideal medium in which to institute a ``dumb hole'' (black hole analog), it
suffers from a number of problems. We show that the high phase velocity in the
slow light regime ensures that the system cannot be used as an analog
displaying Hawking radiation. Even though an appropriately designed slow-light
set-up may simulate classical features of black holes -- such as horizon, mode
mixing, Bogoliubov coefficients, etc. -- it does not reproduce the related
quantum effects. PACS: 04.70.Dy, 04.80.-y, 42.50.Gy, 04.60.-m.Comment: 14 pages RevTeX, 5 figure
Genomic innovations, transcriptional plasticity and gene loss underlying the evolution and divergence of two highly polyphagous and invasive Helicoverpa pest species
BACKGROUND:
Helicoverpa armigera and Helicoverpa zea are major caterpillar pests of Old and New World agriculture, respectively. Both, particularly H. armigera, are extremely polyphagous, and H. armigera has developed resistance to many insecticides. Here we use comparative genomics, transcriptomics and resequencing to elucidate the genetic basis for their properties as pests.
RESULTS:
We find that, prior to their divergence about 1.5 Mya, the H. armigera/H. zea lineage had accumulated up to more than 100 more members of specific detoxification and digestion gene families and more than 100 extra gustatory receptor genes, compared to other lepidopterans with narrower host ranges. The two genomes remain very similar in gene content and order, but H. armigera is more polymorphic overall, and H. zea has lost several detoxification genes, as well as about 50 gustatory receptor genes. It also lacks certain genes and alleles conferring insecticide resistance found in H. armigera. Non-synonymous sites in the expanded gene families above are rapidly diverging, both between paralogues and between orthologues in the two species. Whole genome transcriptomic analyses of H. armigera larvae show widely divergent responses to different host plants, including responses among many of the duplicated detoxification and digestion genes.
CONCLUSIONS:
The extreme polyphagy of the two heliothines is associated with extensive amplification and neofunctionalisation of genes involved in host finding and use, coupled with versatile transcriptional responses on different hosts. H. armigera's invasion of the Americas in recent years means that hybridisation could generate populations that are both locally adapted and insecticide resistant
A Search for the Dark Matter Annual Modulation in South Pole Ice
Astrophysical observations and cosmological data have led to the conclusion
that nearly one quarter of the Universe consists of dark matter. Under certain
assumptions, an observable signature of dark matter is the annual modulation of
the rate of dark matter-nucleon interactions taking place in an Earth-bound
experiment. To search for this effect, we introduce the concept for a new dark
matter experiment using NaI scintillation detectors deployed deep in the South
Pole ice. This experiment complements dark matter search efforts in the
Northern Hemisphere and will investigate the observed annual modulation in the
DAMA/LIBRA and DAMA/NaI experiments. The unique location will permit the study
of background effects correlated with seasonal variations and the surrounding
environment. This paper describes the experimental concept and explores the
sensitivity of a 250 kg NaI experiment at the South Pole.Comment: FERMILAB-PUB-11-251-A
Geodesic rewriting systems and pregroups
In this paper we study rewriting systems for groups and monoids, focusing on
situations where finite convergent systems may be difficult to find or do not
exist. We consider systems which have no length increasing rules and are
confluent and then systems in which the length reducing rules lead to
geodesics. Combining these properties we arrive at our main object of study
which we call geodesically perfect rewriting systems. We show that these are
well-behaved and convenient to use, and give several examples of classes of
groups for which they can be constructed from natural presentations. We
describe a Knuth-Bendix completion process to construct such systems, show how
they may be found with the help of Stallings' pregroups and conversely may be
used to construct such pregroups.Comment: 44 pages, to appear in "Combinatorial and Geometric Group Theory,
Dortmund and Carleton Conferences". Series: Trends in Mathematics.
Bogopolski, O.; Bumagin, I.; Kharlampovich, O.; Ventura, E. (Eds.) 2009,
Approx. 350 p., Hardcover. ISBN: 978-3-7643-9910-8 Birkhause
Solubilization of Proteins in 2DE: An Outline
Protein solubilization for two-dimensional electrophoresis (2DE) has to break
molecular interactions to separate the biological contents of the material of
interest into isolated and intact polypeptides. This must be carried out in
conditions compatible with the first dimension of 2DE, namely isoelectric
focusing. In addition, the extraction process must enable easy removal of any
nonprotein component interfering with the isoelectric focusing. The constraints
brought in this process by the peculiar features of isoelectric focusing are
discussed, as well as their consequences in terms of possible solutions and
limits for the solubilization process
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