4,208 research outputs found
How can organic agriculture contribute to long-term climate goals?
The EU countries aim to reduce their emissions of greenhouse gases (GHG) by 80-95% by 2050 (European Commission, 2011). The food sector accounts today for 25% of Swedish greenhouse gas emissions, most of which arise in agricultural production, so there is a need for radical reduction of GHG emissions in this sector. For organic farming in Sweden, this implies that it is time to move beyond the discussion on whether organic products have a lower or higher life-cycle climate impact than conventional products (Cederberg et al 2011). Instead, the interesting question is: What can and should be done to drastically reduce the climate impact of organic agriculture? The science-based response to that question is relevant for Swedish agriculture as a whole.
Development towards lower climate impact from organic agriculture requires further monitoring and technology development to reduce emissions of nitrous oxide, methane and carbon dioxide. But it also involves developing production systems that are more efficient in the use of nutrients, energy and land, as well as shifting focus from producing animal food towards more legume, grain, vegetable and fruit products
Crystalline phase of strongly interacting Fermi mixtures
We show that the system of weakly bound molecules of heavy and light
fermionic atoms is characterized by a long-range intermolecular repulsion and
can undergo a gas-crystal quantum transition if the mass ratio exceeds a
critical value. For the critical mass ratio above 100 obtained in our
calculations, this crystalline order can be observed as a superlattice in an
optical lattice for heavy atoms with a small filling factor. We also find that
this novel system is sufficiently stable with respect to molecular relaxation
into deep bound states and to the process of trimer formation.Comment: 4 pages, 1 color figure, published versio
Renormalization constants and beta functions for the gauge couplings of the Standard Model to three-loop order
We compute the beta functions for the three gauge couplings of the Standard
Model in the minimal subtraction scheme to three loops. We take into account
contributions from all sectors of the Standard Model. The calculation is
performed using both Lorenz gauge in the unbroken phase of the Standard Model
and background field gauge in the spontaneously broken phase. Furthermore, we
describe in detail the treatment of and present the automated setup
which we use for the calculation of the Feynman diagrams. It starts with the
generation of the Feynman rules and leads to the bare result for the Green's
function of a given process.Comment: 44 pages, 9 figures; v2: sign in eq.(29) corrected; final result
unchange
Versatile compact atomic source for high resolution dual atom interferometry
We present a compact Rb atomic source for high precision dual atom
interferometers. The source is based on a double-stage magneto-optical trap
(MOT) design, consisting of a 2-dimensional (2D)-MOT for efficient loading of a
3D-MOT. The accumulated atoms are precisely launched in a horizontal moving
molasses. Our setup generates a high atomic flux ( atoms/s) with
precise and flexibly tunable atomic trajectories as required for high
resolution Sagnac atom interferometry. We characterize the performance of the
source with respect to the relevant parameters of the launched atoms, i.e.
temperature, absolute velocity and pointing, by utilizing time-of-flight
techniques and velocity selective Raman transitions.Comment: uses revtex4, 9 pages, 12 figures, submitted to Phys. Rev.
Weakly bound dimers of fermionic atoms
We discuss the behavior of weakly bound bosonic dimers formed in a cold Fermi
gas at a large positive scattering length for the interspecies interaction.
We find the exact solution for the dimer-dimer elastic scattering and obtain a
strong decrease of their collisional relaxation and decay with increasing .
The large ratio of the elastic to inelastic rate is promising for achieving
Bose-Einstein condensation of the dimers and cooling the condensed gas to very
low temperatures.Comment: 4 pages, no figure
Three fermions in a box at the unitary limit: universality in a lattice model
We consider three fermions with two spin components interacting on a lattice
model with an infinite scattering length. Low lying eigenenergies in a cubic
box with periodic boundary conditions, and for a zero total momentum, are
calculated numerically for decreasing values of the lattice period. The results
are compared to the predictions of the zero range Bethe-Peierls model in
continuous space, where the interaction is replaced by contact conditions. The
numerical computation, combined with analytical arguments, shows the absence of
negative energy solution, and a rapid convergence of the lattice model towards
the Bethe-Peierls model for a vanishing lattice period. This establishes for
this system the universality of the zero interaction range limit.Comment: 6 page
Quantum interference of ultrastable twin optical beams
We report the first measurement of the quantum phase-difference noise of an
ultrastable nondegenerate optical parametric oscillator that emits twin beams
classically phase-locked at exact frequency degeneracy. The measurement
illustrates the property of a lossless balanced beam-splitter to convert
number-difference squeezing into phase-difference squeezing and, thus, provides
indirect evidence for Heisenberg-limited interferometry using twin beams. This
experiment is a generalization of the Hong-Ou-Mandel interference effect for
continuous variables and constitutes a milestone towards continuous-variable
entanglement of bright, ultrastable nondegenerate beams.Comment: 4 pages, 4 figs, accepted by Phys. Rev. Let
Runaway dilaton and equivalence principle violations
In a recently proposed scenario, where the dilaton decouples while
cosmologically attracted towards infinite bare string coupling, its residual
interactions can be related to the amplitude of density fluctuations generated
during inflation, and are large enough to be detectable through a modest
improvement on present tests of free-fall universality. Provided it has
significant couplings to either dark matter or dark energy, a runaway dilaton
can also induce time-variations of the natural "constants" within the reach of
near-future experiments.Comment: 4 pages, minor change
Optical control of photon tunneling through an array of nanometer scale cylindrical channels
We report first observation of photon tunneling gated by light at a different
wavelength in an artificially created array of nanometer scale cylindrical
channels in a thick gold film. Polarization properties of gated light provide
strong proof of the enhanced nonlinear optical mixing in nanometric channels
involved in the process. This suggests the possibility of building a new class
of "gated" photon tunneling devices for massive parallel all-optical signal and
image processing.Comment: 4 pages, 4 figure
Observation of anomalous spin-state segregation in a trapped ultra-cold vapor
We observe counter-intuitive spin segregation in an inhomogeneous sample of
ultra-cold, non-condensed Rubidium atoms in a magnetic trap. We use spatially
selective microwave spectroscopy to verify a model that accounts for the
differential forces on two internal spin states. In any simple understanding of
the cloud dynamics, the forces are far too small to account for the dramatic
transient spin polarizations observed. The underlying mechanism remains to be
elucidated.Comment: 5 pages, 3 figure
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