778 research outputs found
Inferences from inventories of microbes in ecological vineyard settings
The effect of degraded soil conditions on microbial communities associating the rhizosphere and roots of grapevines was investigated within the frame of project CORE Organic Plus ReSolVe. Several relationships based on Dice cluster analyses of DGGE gel profiles suggest that fungal and bacterial communities from degraded and non-degraded areas differ. Results also suggest that composted organic amendments had an effect on community structures. However, the comparison of diversity indexes did not show differences between degraded and non-degraded plots. They suggested rich and even diversity of bacteria and fungi in any of the tested samples. Culture dependent analysis emphasized that a high diversity of Streptomyces spp. associates grapevine roots in degraded and non-degraded areas. Streptomyces species, best known for their potential to produce antibiotics, are increasingly depicted as beneficial plant associated bacteria
The interaction energy of well-separated Skyrme solitons
We prove that the asymptotic field of a Skyrme soliton of any degree has a
non-trivial multipole expansion. It follows that every Skyrme soliton has a
well-defined leading multipole moment. We derive an expression for the linear
interaction energy of well-separated Skyrme solitons in terms of their leading
multipole moments. This expression can always be made negative by suitable
rotations of one of the Skyrme solitons in space and iso-space.We show that the
linear interaction energy dominates for large separation if the orders of the
Skyrme solitons' multipole moments differ by at most two. In that case there
are therefore always attractive forces between the Skyrme solitons.Comment: 27 pages amslate
The Quest for Light Sea Quarks: Algorithms for the Future
As part of a systematic algorithm study, we present first results on a
performance comparison between a multibosonic algorithm and the hybrid Monte
Carlo algorithm as employed by the SESAM collaboration. The standard Wilson
fermion action is used on 32*16^3 lattices at beta=5.5.Comment: LaTeX, 3 pages, Lattice2001(algorithms
Meson decay constants from Nf=2 clover fermions
We present recent results for meson decay constants calculated on
configurations with two flavours of O(a)-improved Wilson fermions.
Non-perturbative renormalisation is applied and quark mass dependencies as well
as finite volume and discretisation effects are investigated. In this work we
also present a computation of the coupling of the light vector mesons to the
tensor current using dynamical fermions.Comment: 6 pages, contribution to Lattice2005(Hadron spectrum and quark
masses
On resonances and bound states of the 't Hooft-Polyakov monopole
We present a systematic approach to the linearised Yang-Mills-Higgs equations
in the background of a 't Hooft-Polyakov monopole and use it to unify and
extend previous studies of their spectral properties. We show that a
quaternionic formulation allows for a compact and efficient treatment of the
linearised equations in the BPS limit of vanishing Higgs self-coupling, and use
it to study both scattering and bound states. We focus on the sector of
vanishing generalised angular momentum and analyse it numerically, putting
zero-energy bound states, Coulomb bound states and infinitely many Feshbach
resonances into a coherent picture. We also consider the linearised
Yang-Mills-Higgs equations with non-vanishing Higgs self-coupling and confirm
the occurrence of Feshbach resonances in this situation.Comment: 33 pages, 7 figure
Generalized Parton Distributions from Lattice QCD
We perform a quenched lattice calculation of the first moment of twist-two
generalized parton distribution functions of the proton, and assess the total
quark (spin and orbital angular momentum) contribution to the spin of the
proton.Comment: 11 pages, 4 figures; final version, to be published in Phys. Rev.
Let
Quark Contributions to Nucleon Momentum and Spin from Domain Wall fermion calculations
We report contributions to the nucleon spin and momentum from light quarks
calculated using dynamical domain wall fermions with pion masses down to 300
MeV and fine lattice spacing a=0.084 fm. Albeit without disconnected diagrams,
we observe that spin and orbital angular momenta of both u and d quarks are
opposite, almost canceling in the case of the d quark, which agrees with
previous calculations using a mixed quark action. We also present the full
momentum dependence of n=2 generalized form factors showing little variation
with the pion mass.Comment: 7 pages, 5 figures, NT-LBNL-11-020, MIT-CTP-4323. Presented at the
29th International Symposium on Lattice Field Theory (Lattice 2011), Squaw
Valley, California, 10-16 Jul 201
A Chern-Simons approach to Galilean quantum gravity in 2+1 dimensions
We define and discuss classical and quantum gravity in 2+1 dimensions in the
Galilean limit. Although there are no Newtonian forces between massive objects
in (2+1)-dimensional gravity, the Galilean limit is not trivial. Depending on
the topology of spacetime there are typically finitely many topological degrees
of freedom as well as topological interactions of Aharonov-Bohm type between
massive objects. In order to capture these topological aspects we consider a
two-fold central extension of the Galilei group whose Lie algebra possesses an
invariant and non-degenerate inner product. Using this inner product we define
Galilean gravity as a Chern-Simons theory of the doubly-extended Galilei group.
The particular extension of the Galilei group we consider is the classical
double of a much studied group, the extended homogeneous Galilei group, which
is also often called Nappi-Witten group. We exhibit the Poisson-Lie structure
of the doubly extended Galilei group, and quantise the Chern-Simons theory
using a Hamiltonian approach. Many aspects of the quantum theory are determined
by the quantum double of the extended homogenous Galilei group, or Galilei
double for short. We study the representation theory of the Galilei double,
explain how associated braid group representations account for the topological
interactions in the theory, and briefly comment on an associated
non-commutative Galilean spacetime.Comment: 38 pages, 1 figure, references update
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