7,552 research outputs found
Organic farming without fossil fuels - life cycle assessment of two Swedish cases
Organic agriculture is dependent on fossil fuels, just like conventional agriculture, but this can be reduced by the use of on-farm biomass resources. The energy efficiency and environmental impacts of different alternatives can be assessed by life cycle assessment (LCA), which we have done in this project. Swedish organic milk production can become self-sufficient in energy by using renewable sources available on the farm, with biogas from manure as the main energy source. Thereby greenhouse gas (GHG) emissions from the production system can be reduced, both by substituting fossil fuels and by reducing methane emissions from manure. The arable organic farm studied in the project could be self-sufficient in energy by using the residues available in the crop rotation. Because of soil carbon losses, the greenhouse gas emission savings were lower with the use of straw ethanol, heat and power (9%) than by using ley for biogas production (35%).
In this research project, the system boundaries were set at energy self-sufficiency at farm or farm-cluster level. Heat and fuel were supplied as needed, and electricity production was equal to use on an annual basis. In practice, however, better resource efficiency can be achieved by making full use of available energy infrastructure, and basing production on resource availability and economic constraints, rather than a narrow self-sufficiency approach
Gamma-Ray Bursts from Primordial Quark Objects in Space
We investigate the possibility that gamma-ray bursts originate in a
concentric spherical shell with a given average redshift and find that this is
indeed compatible with the data from the third BATSE (3B) catalog. It is also
shown that there is enough freedom in the choice of unknown burst properties to
allow even for extremely large distances to the majority of bursts. Therefore,
we speculate about an early, and very energetic, origin of bursts, and suggest
that they come from phase transitions in massive objects of pure quark matter,
left over from the Big Bang.Comment: 11 pages, Latex, 3 postscript figures, to be publ in the Proc of the
Joint Meeting of the Networks 'The Fundamental Structure of Matter' and
'Tests of the Electroweak Symmetry Breaking', Ouranoupolis, Greece, May 199
Are there sharp fractional charges in Luttinger liquids?
We examine charge fractionalization by chiral separation in a one-dimensional
fermion system described by Luttinger liquid theory. The focus is on the
question of whether the fractional charges are quantum mechanically sharp, and
in the analysis we make a distinction between the global charge, which is
restricted by boundary conditions, and the local charge where a background
contribution is subtracted. We show, by way of examples, that fractional
charges of arbitrary values, all which are quantum mechanically sharp, can be
introduced by different initial conditions. Since the system is gapless,
excitations of arbitrary low frequency contribute to the fluctuations, it is
important to make a precise definition of sharp charges, and this we we do by
subtraction of the ground state contribution. We very briefly comment on the
relevance of our analysis for proposed experiments.Comment: One reference update
Solitons and Quasielectrons in the Quantum Hall Matrix Model
We show how to incorporate fractionally charged quasielectrons in the finite
quantum Hall matrix model.The quasielectrons emerge as combinations of BPS
solitons and quasiholes in a finite matrix version of the noncommutative
theory coupled to a noncommutative Chern-Simons gauge field. We also
discuss how to properly define the charge density in the classical matrix
model, and calculate density profiles for droplets, quasiholes and
quasielectrons.Comment: 15 pages, 9 figure
Two-vibron bound states in alpha-helix proteins : the interplay between the intramolecular anharmonicity and the strong vibron-phonon coupling
The influence of the intramolecular anharmonicity and the strong
vibron-phonon coupling on the two-vibron dynamics in an -helix protein
is studied within a modified Davydov model. The intramolecular anharmonicity of
each amide-I vibration is considered and the vibron dynamics is described
according to the small polaron approach. A unitary transformation is performed
to remove the intramolecular anharmonicity and a modified Lang-Firsov
transformation is applied to renormalize the vibron-phonon interaction. Then, a
mean field procedure is realized to obtain the dressed anharmonic vibron
Hamiltonian. It is shown that the anharmonicity modifies the vibron-phonon
interaction which results in an enhancement of the dressing effect. In
addition, both the anharmonicity and the dressing favor the occurrence of two
different bound states which the properties strongly depend on the interplay
between the anharmonicity and the dressing. Such a dependence was summarized in
a phase diagram which characterizes the number and the nature of the bound
states as a function of the relevant parameters of the problem. For a
significant anharmonicity, the low frequency bound states describe two vibrons
trapped onto the same amide-I vibration whereas the high frequency bound states
refer to the trapping of the two vibrons onto nearest neighbor amide-I
vibrations.Comment: may 2003 submitted to Phys. Rev.
Charge Fractionalization on Quantum Hall Edges
We discuss the propagation and fractionalization of localized charges on the
edges of quantum Hall bars of variable widths, where interactions between the
edges give rise to Luttinger liquid behavior with a non-trivial interaction
parameter g. We focus in particular on the separation of an initial charge
pulse into a sharply defined front charge and a broader tail. The front pulse
describes an adiabatically dressed electron which carries a non-integer charge,
which is \sqrt{g} times the electron charge. We discuss how the presence of
this fractional charge can, in principle, be detected through measurements of
the noise in the current created by tunneling of electrons into the system. The
results are illustrated by numerical simulations of a simplified model of the
Hall bar.Comment: 15 page
Belief Revision in Structured Probabilistic Argumentation
In real-world applications, knowledge bases consisting of all the information
at hand for a specific domain, along with the current state of affairs, are
bound to contain contradictory data coming from different sources, as well as
data with varying degrees of uncertainty attached. Likewise, an important
aspect of the effort associated with maintaining knowledge bases is deciding
what information is no longer useful; pieces of information (such as
intelligence reports) may be outdated, may come from sources that have recently
been discovered to be of low quality, or abundant evidence may be available
that contradicts them. In this paper, we propose a probabilistic structured
argumentation framework that arises from the extension of Presumptive
Defeasible Logic Programming (PreDeLP) with probabilistic models, and argue
that this formalism is capable of addressing the basic issues of handling
contradictory and uncertain data. Then, to address the last issue, we focus on
the study of non-prioritized belief revision operations over probabilistic
PreDeLP programs. We propose a set of rationality postulates -- based on
well-known ones developed for classical knowledge bases -- that characterize
how such operations should behave, and study a class of operators along with
theoretical relationships with the proposed postulates, including a
representation theorem stating the equivalence between this class and the class
of operators characterized by the postulates
Composite fermion wave functions as conformal field theory correlators
It is known that a subset of fractional quantum Hall wave functions has been
expressed as conformal field theory (CFT) correlators, notably the Laughlin
wave function at filling factor ( odd) and its quasiholes, and the
Pfaffian wave function at and its quasiholes. We develop a general
scheme for constructing composite-fermion (CF) wave functions from conformal
field theory. Quasiparticles at are created by inserting anyonic
vertex operators, , that replace a subset of the electron
operators in the correlator. The one-quasiparticle wave function is identical
to the corresponding CF wave function, and the two-quasiparticle wave function
has correct fractional charge and statistics and is numerically almost
identical to the corresponding CF wave function. We further show how to exactly
represent the CF wavefunctions in the Jain series as the CFT
correlators of a new type of fermionic vertex operators, ,
constructed from free compactified bosons; these operators provide the CFT
representation of composite fermions carrying flux quanta in the CF Landau level. We also construct the corresponding quasiparticle- and
quasihole operators and argue that they have the expected fractional charge and
statistics. For filling fractions 2/5 and 3/7 we show that the chiral CFTs that
describe the bulk wave functions are identical to those given by Wen's general
classification of quantum Hall states in terms of -matrices and - and
-vectors, and we propose that to be generally true. Our results suggest a
general procedure for constructing quasiparticle wave functions for other
fractional Hall states, as well as for constructing ground states at filling
fractions not contained in the principal Jain series.Comment: 26 pages, 3 figure
Edge Theories for Polarized Quantum Hall States
Starting from recently proposed bosonic mean field theories for fully and
partially polarized quantum Hall states, we construct corresponding effective
low energy theories for the edge modes. The requirements of gauge symmetry and
invariance under global O(3) spin rotations, broken only by a Zeeman coupling,
imply boundary conditions that allow for edge spin waves. In the generic case,
these modes are chiral, and the spin stiffness differs from that in the bulk.
For the case of a fully polarized state, our results agree with
previous Hartree-Fock calculations.Comment: 15 pages (number of pages has been reduced by typesetting in RevTeX);
2 references adde
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