823 research outputs found
Universal Central Extensions of Gauge Algebras and Groups
We show that the canonical central extension of the group of sections of a
Lie group bundle over a compact manifold, constructed in [NW09], is universal.
In doing so, we prove universality of the corresponding central extension of
Lie algebras in a slightly more general setting.Comment: 9 pages, LaTeX. Changes w.r.t. version 2: minor changes (final
version). To appear in J. Reine Angew. Mat
Homotheties and topology of tangent sphere bundles
We prove a Theorem on homotheties between two given tangent sphere bundles
of a Riemannian manifold of , assuming different
variable radius functions and weighted Sasaki metrics induced by the
conformal class of . New examples are shown of manifolds with constant
positive or with constant negative scalar curvature, which are not Einstein.
Recalling results on the associated almost complex structure and
symplectic structure on the manifold , generalizing the
well-known structure of Sasaki by admitting weights and connections with
torsion, we compute the Chern and the Stiefel-Whitney characteristic classes of
the manifolds and .Comment: 15 pages, to appear in Journal of Geometr
Dyson processes on the octonion algebra
We consider Brownian motion on symmetric matrices of octonions, and study the
law of the spectrum. Due to the fact that the octonion algebra is
nonassociative, the dimension of the matrices plays a special role. We provide
two specific models on octonions, which give some indication of the relation
between the multiplicity of eigenvalues and the exponent in the law of the
spectrum
Distribution of satellite galaxies in high redshift groups
We use galaxy groups at redshifts between 0.4 and 1.0 selected from the Great
Observatories Origins Deep Survey (GOODS) to study the color-morphological
properties of satellite galaxies, and investigate possible alignment between
the distribution of the satellites and the orientation of their central galaxy.
We confirm the bimodal color and morphological type distribution for satellite
galaxies at this redshift range: the red and blue classes corresponds to the
early and late morphological types respectively, and the early-type satellites
are on average brighter than the late-type ones. Furthermore, there is a {\it
morphological conformity} between the central and satellite galaxies: the
fraction of early-type satellites in groups with an early-type central is
higher than those with a late-type central galaxy. This effect is stronger at
smaller separations from the central galaxy. We find a marginally significant
signal of alignment between the major axis of the early-type central galaxy and
its satellite system, while for the late-type centrals no significant alignment
signal is found. We discuss the alignment signal in the context of shape
evolution of groups.Comment: 7 pages, 7 figures, accepted by Ap
On the twisted G/H topological models
The twisted G/H models are constructed as twisted supersymmetric gauged WZW
models. We analyze the case of , with , and discuss possible
generalizations. We introduce a non-abelian bosonization of the ghost
system in the adjoint of and in G/H. By computing chiral anomalies in the
latter picture we write the quantum action as a decoupled sum of ``matter",
gauge and ghost sectors. The action is also derived in the unbosonized version.
We invoke a free field parametrization and extract the space of physical states
by computing the cohomology of , the sum of the BRST gauge-fixing charge
and the twisted supersymmetry charge. For a given we briefly discuss the
relation between the various G/H models corresponding to different choices of
. The choice corresponds to the topological G/G theory.Comment: 27 page
A Theorem on the origin of Phase Transitions
For physical systems described by smooth, finite-range and confining
microscopic interaction potentials V with continuously varying coordinates, we
announce and outline the proof of a theorem that establishes that unless the
equipotential hypersurfaces of configuration space \Sigma_v ={(q_1,...,q_N)\in
R^N | V(q_1,...,q_N) = v}, v \in R, change topology at some v_c in a given
interval [v_0, v_1] of values v of V, the Helmoltz free energy must be at least
twice differentiable in the corresponding interval of inverse temperature
(\beta(v_0), \beta(v_1)) also in the N -> \infty and the
{\Sigma_v}_{v > v_c}, which is the consequence of the existence of critical
points of V on \Sigma_{v=v_c}, that is points where \nabla V=0.Comment: 10 pages, Statistical Mechanics, Phase Transitions, General Theory.
Phys. Rev. Lett., in pres
Connecting geodesics and security of configurations in compact locally symmetric spaces
A pair of points in a riemannian manifold makes a secure configuration if the
totality of geodesics connecting them can be blocked by a finite set. The
manifold is secure if every configuration is secure. We investigate the
security of compact, locally symmetric spaces.Comment: 27 pages, 2 figure
Physical States in G/G Models and 2d Gravity
An analysis of the BRST cohomology of the G/G topological models is performed
for the case of . Invoking a special free field parametrization of
the various currents, the cohomology on the corresponding Fock space is
extracted. We employ the singular vector structure and fusion rules to
translate the latter into the cohomology on the space of irreducible
representations. Using the physical states we calculate the characters and
partition function, and verify the index interpretation. We twist the
energy-momentum tensor to establish an intriguing correspondence between the
model with level and models
coupled to gravity.Comment: 42 page
Chalcone-based Selective Inhibitors of a C4 Plant Key Enzyme as Novel Potential Herbicides
Weeds are a challenge for global food production due to their rapidly evolving resistance against herbicides. We have identified chalcones as selective inhibitors of phosphoenolpyruvate carboxylase (PEPC), a key enzyme for carbon fixation and biomass increase in the C4 photosynthetic pathway of many of the world’s most damaging weeds. In contrast, many of the most important crop plants use C3 photosynthesis. Here, we show that 2′,3′,4′,3,4-Pentahydroxychalcone (IC50 = 600 nM) and 2′,3′,4′-Trihydroxychalcone (IC50 = 4.2 μM) are potent inhibitors of C4 PEPC but do not affect C3 PEPC at a same concentration range (selectivity factor: 15–45). Binding and modeling studies indicate that the active compounds bind at the same site as malate/aspartate, the natural feedback inhibitors of the C4 pathway. At the whole plant level, both substances showed pronounced growth-inhibitory effects on the C4 weed Amaranthus retroflexus, while there were no measurable effects on oilseed rape, a C3 plant. Growth of selected soil bacteria was not affected by these substances. Our chalcone compounds are the most potent and selective C4 PEPC inhibitors known to date. They offer a novel approach to combat C4 weeds based on a hitherto unexplored mode of allosteric inhibition of a C4 plant key enzyme
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