43,786 research outputs found
Sustainability assessment of wheat production using Emergy
Sustainability of crop production has to be given high priority when global biomass resources are limited. Here emergy evaluation is applied in order to assess sustainability of crop production exemplified by winter wheat. Emergy evaluation takes into account all inputs involved in a production system (i.e. renewable and non-renewable, local and imported) and transforms them into a common measure of direct and indirect solar energy requirement. The evaluation of winter wheat production is conducted by comparing conventional and organic management on two soil types using Danish reference conditions. The resource use efficiency of wheat production per kg biomass is higher using conventional management practices. This is due to high yield based on large use of non-renewable resources. The environmental loading ratio from organic management practices is about a third of the conventional implying that the organic management can be considered more sustainable
High purity bright single photon source
Using cavity-enhanced non-degenerate parametric downconversion, we have built
a frequency tunable source of heralded single photons with a narrow bandwidth
of 8 MHz, making it compatible with atomic quantum memories. The photon state
is 70% pure single photon as characterized by a tomographic measurement and
reconstruction of the quantum state, revealing a clearly negative Wigner
function. Furthermore, it has a spectral brightness of ~1,500 photons/s per MHz
bandwidth, making it one of the brightest single photon sources available. We
also investigate the correlation function of the down-converted fields using a
combination of two very distinct detection methods; photon counting and
homodyne measurement.Comment: 9 pages, 4 figures; minor changes, added referenc
Why Nature has made a choice of one time and three space coordinates?
We propose a possible answer to one of the most exciting open questions in
physics and cosmology, that is the question why we seem to experience four-
dimensional space-time with three ordinary and one time dimensions. We have
known for more than 70 years that (elementary) particles have spin degrees of
freedom, we also know that besides spin they also have charge degrees of
freedom, both degrees of freedom in addition to the position and momentum
degrees of freedom. We may call these ''internal degrees of freedom '' the
''internal space'' and we can think of all the different particles, like quarks
and leptons, as being different internal states of the same particle. The
question then naturally arises: Is the choice of the Minkowski metric and the
four-dimensional space-time influenced by the ''internal space''?
Making assumptions (such as particles being in first approximation massless)
about the equations of motion, we argue for restrictions on the number of space
and time dimensions. (Actually the Standard model predicts and experiments
confirm that elementary particles are massless until interactions switch on
masses.)
Accepting our explanation of the space-time signature and the number of
dimensions would be a point supporting (further) the importance of the
''internal space''.Comment: 13 pages, LaTe
Gravitational Lorentz anomaly from the overlap formula in 2-dimensions
In this letter we show that the overlap formulation of chiral gauge theories
correctly reproduces the gravitational Lorentz anomaly in 2-dimensions. This
formulation has been recently suggested as a solution to the fermion doubling
problem on the lattice. The well known response to general coordinate
transformations of the effective action of Weyl fermions coupled to gravity in
2-dimensions can also be recovered.Comment: 7 pages, late
Transition from Icosahedral to Decahedral Structure in a Coexisting Solid-Liquid Nickel Cluster
We have used molecular dynamics simulations to construct a microcanonical
caloric curve for a 1415-atom Ni icosahedron. Prior to melting the Ni cluster
exhibits static solid-liquid phase coexistence. Initially a partial icosahedral
structure coexists with a non-wetting melt. However at energies very close to
the melting point the icosahedral structure is replaced by a truncated
decahedral structure which is almost fully wet by the melt. This structure
remains until the cluster fully melts. The transition appears to be driven by a
preference for the melt to wet the decahedral structure.Comment: 7 pages, 6 figure
Fermionization, Number of Families
We investigate bosonization/fermionization for free massless fermions being
equivalent to free massless bosons with the purpose of checking and correcting
the old rule by Aratyn and one of us (H.B.F.N.) for the number of boson species
relative to the number of fermion species which is required to have
bosonization possible. An important application of such a counting of degrees
of freedom relation would be to invoke restrictions on the number of families
that could be possible under the assumption, that all the fermions in nature
are the result of fermionizing a system of boson species. Since a theory of
fundamental fermions can be accused for not being properly local because of
having anticommutativity at space like distances rather than commutation as is
more physically reasonable to require, it is in fact called for to have all
fermions arising from fermionization of bosons. To make a realistic scenario
with the fermions all coming from fermionizing some bosons we should still have
at least some not fermionized bosons and we are driven towards that being a
gravitational field, that is not fermionized. Essentially we reach the
spin-charge-families theory by one of us (N.S.M.B.) with the detail that the
number of fermion components and therefore of families get determined from what
possibilities for fermionization will finally turn out to exist. The
spin-charge-family theory has long been plagued by predicting 4 families rather
than the phenomenologically more favoured 3. Unfortunately we do not yet
understand well enough the unphysical negative norm square components in the
system of bosons that can fermionize in higher dimensions because we have no
working high dimensional case of fermionization. But suspecting they involve
gauge fields with complicated unphysical state systems the corrections from
such states could putatively improve the family number prediction.Comment: 30 pages, H.B. Nielsen presented the talk at Workshop
"What Comes Beyond the Standard Models", Bled, 09-17 of July, 201
- âŠ