30,228 research outputs found
Unstable manifolds and Schroedinger dynamics of Ginzburg-Landau vortices
The time evolution of several interacting Ginzburg-Landau vortices according
to an equation of Schroedinger type is approximated by motion on a
finite-dimensional manifold. That manifold is defined as an unstable manifold
of an auxiliary dynamical system, namely the gradient flow of the
Ginzburg-Landau energy functional. For two vortices the relevant unstable
manifold is constructed numerically and the induced dynamics is computed. The
resulting model provides a complete picture of the vortex motion for arbitrary
vortex separation, including well-separated and nearly coincident vortices.Comment: 23 pages amslatex, 5 eps figures, minor typos correcte
Planck pre-launch status: The HFI instrument, from specification to actual performance
Context. The High Frequency Instrument (HFI) is one of the two focal instruments of the Planck mission. It will observe the whole sky in six
bands in the 100 GHzâ1 THz range.
Aims. The HFI instrument is designed to measure the cosmic microwave background (CMB) with a sensitivity limited only by fundamental
sources: the photon noise of the CMB itself and the residuals left after the removal of foregrounds. The two high frequency bands will provide
full maps of the submillimetre sky, featuring mainly extended and point source foregrounds. Systematic effects must be kept at negligible levels
or accurately monitored so that the signal can be corrected. This paper describes the HFI design and its characteristics deduced from ground tests
and calibration.
Methods. The HFI instrumental concept and architecture are feasible only by pushing new techniques to their extreme capabilities, mainly:
(i) bolometers working at 100 mK and absorbing the radiation in grids; (ii) a dilution cooler providing 100 mK in microgravity conditions;
(iii) a new type of AC biased readout electronics and (iv) optical channels using devices inspired from radio and infrared techniques.
Results. The Planck-HFI instrument performance exceeds requirements for sensitivity and control of systematic effects. During ground-based
calibration and tests, it was measured at instrument and system levels to be close to or better than the goal specification
Parameter Estimation from Improved Measurements of the Cosmic Microwave Background from QUaD
We evaluate the contribution of cosmic microwave background (CMB) polarization spectra to cosmological parameter constraints. We produce cosmological parameters using high-quality CMB polarization data from the ground-based QUaD experiment and demonstrate for the majority of parameters that there is significant improvement on the constraints obtained from satellite CMB polarization data. We split a multi-experiment CMB data set into temperature and polarization subsets and show that the best-fit confidence regions for the ÎCDM six-parameter cosmological model are consistent with each other, and that polarization data reduces the confidence regions on all parameters. We provide the best limits on parameters from QUaD EE/BB polarization data and we find best-fit parameters from the multi-experiment CMB data set using the optimal pivot scale of k_p = 0.013 Mpc^(â1) to be {h^2Ω_c, h^2Ω_b, H_0, A_s, n_s, Ï} = {0.113, 0.0224, 70.6, 2.29 Ă 10^(â9), 0.960, 0.086}
Mit GrĂŒnfutter und Tageslicht strahlen HĂŒhnereier anders
Mit dem einfachen und schnellen Untersuchungsverfahren der Biophotonenanalyse lassen sich am Ei Unterschiede feststellen, die durch Haltungssystem, FĂŒtterung und Klimafaktoren bedingt sind
Satisfying the Einstein-Podolsky-Rosen criterion with massive particles
In 1935, Einstein, Podolsky and Rosen (EPR) questioned the completeness of
quantum mechanics by devising a quantum state of two massive particles with
maximally correlated space and momentum coordinates. The EPR criterion
qualifies such continuous-variable entangled states, where a measurement of one
subsystem seemingly allows for a prediction of the second subsystem beyond the
Heisenberg uncertainty relation. Up to now, continuous-variable EPR
correlations have only been created with photons, while the demonstration of
such strongly correlated states with massive particles is still outstanding.
Here, we report on the creation of an EPR-correlated two-mode squeezed state in
an ultracold atomic ensemble. The state shows an EPR entanglement parameter of
0.18(3), which is 2.4 standard deviations below the threshold 1/4 of the EPR
criterion. We also present a full tomographic reconstruction of the underlying
many-particle quantum state. The state presents a resource for tests of quantum
nonlocality and a wide variety of applications in the field of
continuous-variable quantum information and metrology.Comment: 8 pages, 7 figure
0.75 atoms improve the clock signal of 10,000 atoms
Since the pioneering work of Ramsey, atom interferometers are employed for
precision metrology, in particular to measure time and to realize the second.
In a classical interferometer, an ensemble of atoms is prepared in one of the
two input states, whereas the second one is left empty. In this case, the
vacuum noise restricts the precision of the interferometer to the standard
quantum limit (SQL). Here, we propose and experimentally demonstrate a novel
clock configuration that surpasses the SQL by squeezing the vacuum in the empty
input state. We create a squeezed vacuum state containing an average of 0.75
atoms to improve the clock sensitivity of 10,000 atoms by 2.05 dB. The SQL
poses a significant limitation for today's microwave fountain clocks, which
serve as the main time reference. We evaluate the major technical limitations
and challenges for devising a next generation of fountain clocks based on
atomic squeezed vacuum.Comment: 9 pages, 6 figure
To green or not to green: Establishing the economic value of green infrastructure investments in The Wicker, Sheffield.
Establishing the value of urban green infrastructure resources draws on a complex evaluation of social, economic and ecological influences. As a result planners have found it difficult to develop robust economic arguments to promote investments in urban greening. The Valuing Attractive Landscapes in the Urban Economy (VALUE) project facilitated a trans-national programme of investigations to establish economic values for a range of green infrastructure investments. This paper presents the results of a large-scale willingness to pay (WTP) survey (N: 510) for investments on Blonk Street, The Wicker, Sheffield. Using 3D visualisations of three alternative urban greening scenarios the research addressed the influence of green infrastructure on aesthetic quality, functionality and amenity. The evidence suggests that participants were WTP up ÂŁ10.56 or 2% more in monthly rent or additional mortgage payments to live in locations that have a high quality green infrastructure environment. The survey also examined the relationships between a range of socio-economic factors and WTP for green infrastructure (GI). WTP more rent was associated particularly with those in younger age groups and those with lower educational attainment. The paper concludes that investment in urban GI that is visibly greener, that facilitates access to GI and other amenities and that is perceived to promote multiple functions and benefits on a single site (i.e. multi-functionality) generate higher WTP values. The findings of the study support the wider literature evaluating the economic value of GI which argues that investment in urban greenspace can have a significant impact on local housing and commercial markets where it produces more attractive and functional landscapes
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