579 research outputs found
Precise Experimental Investigation of Eigenmodes in a Planar Ion Crystal
The accurate characterization of eigenmodes and eigenfrequencies of
two-dimensional ion crystals provides the foundation for the use of such
structures for quantum simulation purposes. We present a combined experimental
and theoretical study of two-dimensional ion crystals. We demonstrate that
standard pseudopotential theory accurately predicts the positions of the ions
and the location of structural transitions between different crystal
configurations. However, pseudopotential theory is insufficient to determine
eigenfrequencies of the two-dimensional ion crystals accurately but shows
significant deviations from the experimental data obtained from resolved
sideband spectroscopy. Agreement at the level of 2.5 x 10^(-3) is found with
the full time-dependent Coulomb theory using the Floquet-Lyapunov approach and
the effect is understood from the dynamics of two-dimensional ion crystals in
the Paul trap. The results represent initial steps towards an exploitation of
these structures for quantum simulation schemes.Comment: 5 pages, 4 figures, supplemental material (mathematica and matlab
files) available upon reques
Palaeogeography and voyage modeling indicates early human colonization of Australia was likely from Timor-Roti
Anatomically Modern Humans (AMHs) dispersed rapidly through island southeast Asia (Sunda and Wallacea) and into Sahul (Australia, New Guinea and the Aru Islands), before 50,000 years ago. Multiple routes have been proposed for this dispersal and all involve at least one multi-day maritime voyage approaching 100 km. Here we use new regional-scale bathymetry data, palaeoenvironmental reconstruction, an assessment of vertical land movements and drift modeling to assess the potential for an initial entry into northwest Australia from southern Wallacea (Timor-Roti). From ∼70,000 until ∼10,000 years ago, a chain of habitable, resource-rich islands were emergent off the coast of northwest Australia (now mostly submerged). These were visible from high points close to the coast on Timor-Roti and as close as 87 km. Drift models suggest the probability of accidental arrival on these islands from Timor-Roti was low at any time. However, purposeful voyages in the summer monsoon season were very likely to be successful over 4–7 days. Genomic data suggests the colonizing population size was >72–100 individuals, thereby indicating deliberate colonization. This is arguably the most dramatic early demonstration of the advanced cognitive abilities and technological capabilities of AMHs, but one that could leave little material imprint in the archaeological record beyond the evidence that colonization occurred
Coherent THz Measurements at the Metrology Light Source
The Metrology Light Source MLS [1] is the first storage ring optimized for THz generation [2]. It applies a bunch shortening mode, based on a flexible momentum compaction factor optics. The short bunches emit coherent THz radiation. We report on measured THz signals as a function of different machine parameters. Two type of measurements are presented in this paper. The first part presents THz bursting thresholds for a variety of ring parameters compared with theoretical predictions and similar results achieved at BESSY II. The second part discusses an example of a special machine tuning, where the coherent THz signal suddenly and unexpectedly vanishes. Some measurements are shown to demonstrate this effect, a physical explanation is missing
Experimental Study of the Inductance of Pinned Vortices in Superconducting YBa2Cu3O7-d Films
Using a two-coil mutual inductance method, we have measured the complex
resistivity, rho_v(T,Be), of pinned vortices in c-axis pulsed laser deposited
YBa2Cu3O7-d films with magnetic field Be applied perpendicular to the film. At
low frequencies, (<100 kHz), rho_v is inductive and is inversely proportional
to the Labusch parameter, the average vortex pinning force constant, kappa_exp.
The observed weakening of kappa_exp with Be is consistent with a simple model
based on linear pinning defects. Adding classical thermal fluctuations to the
model in a simple way describes the observed linear T dependence of rho_v,
below ~15 K and provides reasonable values for the effective radius (.3 nm to
>.8 nm) of the defects and the depth of the pinning potential. The success of
this model implies that thermal supercurrent (phase) fluctuations have their
full classical amplitude down to 5 K for frequencies below the characteristic
depinning frequency. To date, no sufficient theory exists to explain the data
between ~15 K and the vortex glass melting temperature.Comment: 31 pages, 8 figures. Subm. to PR
Immunolocalization of dually phosphorylated MAPKs in dividing root meristem cells of Vicia faba, Pisum sativum, Lupinus luteus and Lycopersicon esculentum
Key message In plants, phosphorylated MAPKs display
constitutive nuclear localization; however, not all
studied plant species show co-localization of activated
MAPKs to mitotic microtubules.
Abstract The mitogen-activated protein kinase (MAPK)
signaling pathway is involved not only in the cellular
response to biotic and abiotic stress but also in the regulation
of cell cycle and plant development. The role of
MAPKs in the formation of a mitotic spindle has been
widely studied and the MAPK signaling pathway was
found to be indispensable for the unperturbed course of cell
division. Here we show cellular localization of activated
MAPKs (dually phosphorylated at their TXY motifs) in
both interphase and mitotic root meristem cells of Lupinus
luteus, Pisum sativum, Vicia faba (Fabaceae) and Lycopersicon esculentum (Solanaceae). Nuclear localization
of activated MAPKs has been found in all species. Colocalization
of these kinases to mitotic microtubules was
most evident in L. esculentum, while only about 50 % of
mitotic cells in the root meristems of P. sativum and V.
faba displayed activated MAPKs localized to microtubules
during mitosis. Unexpectedly, no evident immunofluorescence
signals at spindle microtubules and phragmoplast
were noted in L. luteus. Considering immunocytochemical
analyses and studies on the impact of FR180204 (an
inhibitor of animal ERK1/2) on mitotic cells, we hypothesize
that MAPKs may not play prominent role in the
regulation of microtubule dynamics in all plant species
Critical temperature and superfluid density suppression in disordered high- cuprate superconductors
We argue that the standard Abrikosov-Gorkov (AG) type theory of in
disordered -wave superconductors breaks down in short coherence length
high- cuprates. Numerical calculations within the Bogoliubov-de Gennes
formalism demonstrate that the correct description of such systems must allow
for the spatial variation of the order parameter, which is strongly suppressed
in the vicinity of impurities but mostly unaffected elsewhere. Suppression of
as measured with respect to the attendant decrease in the superfluid
density is found to be significantly weaker than that predicted by the AG
theory, in good agreement with experiment.Comment: REVTeX, 4 pages, 3 ps figures included [The version to appear in PRB
Sept. 1. Conclusions of the paper unchanged; several changes in text and
figures for added clarity, discussion of phase fluctuations added.
Landscape rules predict optimal superhighways for the first peopling of Sahul
Archaeological data and demographic modelling suggest that the peopling of Sahul required substantial populations, occurred rapidly within a few thousand years and encompassed environments ranging from hyper-arid deserts to temperate uplands and tropical rainforests. How this migration occurred and how humans responded to the physical environments they encountered have, however, remained largely speculative. By constructing a high-resolution digital elevation model for Sahul and coupling it with fine-scale viewshed analysis of landscape prominence, least-cost pedestrian travel modelling and high-performance computing, we create over 125 billion potential migratory pathways, whereby the most parsimonious routes traversed emerge. Our analysis revealed several major pathways—superhighways—transecting the continent, that we evaluated using archaeological data. These results suggest that the earliest Australian ancestors adopted a set of fundamental rules shaped by physiological capacity, attraction to visually prominent landscape features and freshwater distribution to maximize survival, even without previous experience of the landscapes they encountered
Interplay of disorder and magnetic field in the superconducting vortex state
We calculate the density of states of an inhomogeneous superconductor in a
magnetic field where the positions of vortices are distributed completely at
random. We consider both the cases of s-wave and d-wave pairing. For both
pairing symmetries either the presence of disorder or increasing the density of
vortices enhances the low energy density of states. In the s-wave case the gap
is filled and the density of states is a power law at low energies. In the
d-wave case the density of states is finite at zero energy and it rises
linearly at very low energies in the Dirac isotropic case
(\alpha_D=t/\Delta_0=1, where t is the hopping integral and \Delta_0 is the
amplitude of the order parameter). For slightly higher energies the density of
states crosses over to a quadratic behavior. As the Dirac anisotropy increases
(as \Delta_0 decreases with respect to the hopping term) the linear region
decreases in width. Neglecting this small region the density of states
interpolates between quadratic and back to linear as \alpha_D increases. The
low energy states are strongly peaked near the vortex cores.Comment: 12 REVTeX pages, 15 figure
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