11,507 research outputs found
Emissions of plant protection products from glasshouses to surface water in The Netherlands
Momenteel wordt een vast percentage van 0.1% gebruikt voor de emissie van gewasbeschermingsmiddelen vanuit kassen naar het oppervlaktewater. Metingsgegevens van waterschappen wijzen erop dat de emissie van gewasbeschermingsmiddelen en biociden naar het oppervlaktewater hoger zijn dan aangenomen wordt in de toelatingsprocedure. Dit rapport onderzoekt of nieuwe benaderingen nodig zijn. De onderzoeksresultaten duiden er op dat de werkelijke emissie sterk verschilt tussen verschillende gewassen, teeltsystemen en toedieningswijzen. Dit zou in de evaluatie van de emissie meegenomen moeten worden
Error Filtration and Entanglement Purification for Quantum Communication
The key realisation which lead to the emergence of the new field of quantum
information processing is that quantum mechanics, the theory that describes
microscopic particles, allows the processing of information in fundamentally
new ways. But just as in classical information processing, errors occur in
quantum information processing, and these have to be corrected. A fundamental
breakthrough was the realisation that quantum error correction is in fact
possible. However most work so far has not been concerned with technological
feasibility, but rather with proving that quantum error correction is possible
in principle. Here we describe a method for filtering out errors and
entanglement purification which is particularly suitable for quantum
communication. Our method is conceptually new, and, crucially, it is easy to
implement in a wide variety of physical systems with present day technology and
should therefore be of wide applicability.Comment: 23 pages (latex) and 4 postscript figure
On The Origin Of The Gamma Rays From The Galactic Center
The region surrounding the center of the Milky Way is both astrophysically
rich and complex, and is predicted to contain very high densities of dark
matter. Utilizing three years of data from the Fermi Gamma Ray Space Telescope
(and the recently available Pass 7 ultraclean event class), we study the
morphology and spectrum of the gamma ray emission from this region and find
evidence of a spatially extended component which peaks at energies between 300
MeV and 10 GeV. We compare our results to those reported by other groups and
find good agreement. The extended emission could potentially originate from
either the annihilations of dark matter particles in the inner galaxy, or from
the collisions of high energy protons that are accelerated by the Milky Way's
supermassive black hole with gas. If interpreted as dark matter annihilation
products, the emission spectrum favors dark matter particles with a mass in the
range of 7-12 GeV (if annihilating dominantly to leptons) or 25-45 GeV (if
annihilating dominantly to hadronic final states). The intensity of the
emission corresponds to a dark matter annihilation cross section consistent
with that required to generate the observed cosmological abundance in the early
universe (sigma v ~ 3 x 10^-26 cm^3/s). We also present conservative limits on
the dark matter annihilation cross section which are at least as stringent as
those derived from other observations.Comment: 13 pages, 11 figure
Refining the process of sharing problem-solving experience across domain: a hermeneutic study
Unstable coronal loops : numerical simulations with predicted observational signatures
We present numerical studies of the nonlinear, resistive magnetohydrodynamic
(MHD) evolution of coronal loops. For these simulations we assume that the
loops carry no net current, as might be expected if the loop had evolved due to
vortex flows. Furthermore the initial equilibrium is taken to be a cylindrical
flux tube with line-tied ends. For a given amount of twist in the magnetic
field it is well known that once such a loop exceeds a critical length it
becomes unstableto ideal MHD instabilities. The early evolution of these
instabilities generates large current concentrations. Firstly we show that
these current concentrations are consistent with the formation of a current
sheet. Magnetic reconnection can only occur in the vicinity of these current
concentrations and we therefore couple the resistivity to the local current
density. This has the advantage of avoiding resistive diffusion in regions
where it should be negligible. We demonstrate the importance of this procedure
by comparison with simulations based on a uniform resistivity. From our
numerical experiments we are able to estimate some observational signatures for
unstable coronal loops. These signatures include: the timescale of the loop
brightening; the temperature increase; the energy released and the predicted
observable flow speeds. Finally we discuss to what extent these observational
signatures are consistent with the properties of transient brightening loops.Comment: 13 pages, 9 figure
Isospin particle on with arbitrary number of supersymmetries
We study the supersymmetric quantum mechanics of an isospin particle in the
background of spherically symmetric Yang-Mills gauge field. We show that on
the number of supersymmetries can be made arbitrarily large for a
specific choice of the spherically symmetric SU(2) gauge field. However, the
symmetry algebra containing the supercharges becomes nonlinear if the number of
fermions is greater than two. We present the exact energy spectra and
eigenfunctions, which can be written as the product of monopole harmonics and a
certain isospin state. We also find that the supersymmetry is spontaneously
broken if the number of supersymmetries is even.Comment: 6 page
Redox reactions with empirical potentials: Atomistic battery discharge simulations
Batteries are pivotal components in overcoming some of today's greatest
technological challenges. Yet to date there is no self-consistent atomistic
description of a complete battery. We take first steps toward modeling of a
battery as a whole microscopically. Our focus lies on phenomena occurring at
the electrode-electrolyte interface which are not easily studied with other
methods. We use the redox split-charge equilibration (redoxSQE) method that
assigns a discrete ionization state to each atom. Along with exchanging partial
charges across bonds, atoms can swap integer charges. With redoxSQE we study
the discharge behavior of a nano-battery, and demonstrate that this reproduces
the generic properties of a macroscopic battery qualitatively. Examples are the
dependence of the battery's capacity on temperature and discharge rate, as well
as performance degradation upon recharge.Comment: 14 pages, 10 figure
High Rayleigh number convection with double diffusive fingers
An electrodeposition cell is used to sustain a destabilizing concentration
difference of copper ions in aqueous solution between the top and bottom
boundaries of the cell. The resulting convecting motion is analogous to
Rayleigh-B\'enard convection at high Prandtl numbers. In addition, a
stabilizing temperature gradient is imposed across the cell. Even for thermal
buoyancy two orders of magnitude smaller than chemical buoyancy, the presence
of the weak stabilizing gradient has a profound effect on the convection
pattern. Double diffusive fingers appear in all cases. The size of these
fingers and the flow velocities are independent of the height of the cell, but
they depend on the ion concentration difference between top and bottom
boundaries as well as on the imposed temperature gradient. The scaling of the
mass transport is compatible with previous results on double diffusive
convection
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