2,067 research outputs found
The use of metabolomics to dissect plant responses to abiotic stresses
Plant metabolism is perturbed by various abiotic stresses. As such the metabolic network of plants must be reconfigured under stress conditions in order to allow both the maintenance of metabolic homeostasis and the production of compounds that ameliorate the stress. The recent development and adoption of metabolomics and systems biology approaches enable us not only to gain a comprehensive overview, but also a detailed analysis of crucial components of the plant metabolic response to abiotic stresses. In this review we introduce the analytical methods used for plant metabolomics and describe their use in studies related to the metabolic response to water, temperature, light, nutrient limitation, ion and oxidative stresses. Both similarity and specificity of the metabolic responses against diverse abiotic stress are evaluated using data available in the literature. Classically discussed stress compounds such as proline, gamma-amino butyrate and polyamines are reviewed, and the widespread importance of branched chain amino acid metabolism under stress condition is discussed. Finally, where possible, mechanistic insights into metabolic regulatory processes are discussed
Bi-HKT and bi-Kaehler supersymmetric sigma models
We study CKT (or bi-HKT) N = 4 supersymmetric quantum mechanical sigma
models. They are characterized by the usual and the mirror sectors displaying
each HKT geometry. When the metric involves isometries, a Hamiltonian reduction
is possible. The most natural such reduction with respect to a half of bosonic
target space coordinates produces an N = 4 model, related to the twisted
Kaehler model due to Gates, Hull and Rocek, but including certain extra F-terms
in the superfield action.Comment: 31 pages, minor corrections in the published versio
Monotone independence, comb graphs and Bose-Einstein condensation
The adjacency matrix of a comb graph is decomposed into a sum of monotone independent random variables with respect to the vacuum state. The vacuum spectral distribution is shown to be asymptotically the arcsine law as a consequence of the monotone central limit theorem. As an example the comb lattice is studied with explicit calculation
Localization of the Grover walks on spidernets and free Meixner laws
A spidernet is a graph obtained by adding large cycles to an almost regular
tree and considered as an example having intermediate properties of lattices
and trees in the study of discrete-time quantum walks on graphs. We introduce
the Grover walk on a spidernet and its one-dimensional reduction. We derive an
integral representation of the -step transition amplitude in terms of the
free Meixner law which appears as the spectral distribution. As an application
we determine the class of spidernets which exhibit localization. Our method is
based on quantum probabilistic spectral analysis of graphs.Comment: 32 page
The Momentum Constraints of General Relativity and Spatial Conformal Isometries
Transverse-tracefree (TT-) tensors on , with an
asymptotically flat metric of fast decay at infinity, are studied. When the
source tensor from which these TT tensors are constructed has fast fall-off at
infinity, TT tensors allow a multipole-type expansion. When has no
conformal Killing vectors (CKV's) it is proven that any finite but otherwise
arbitrary set of moments can be realized by a suitable TT tensor. When CKV's
exist there are obstructions -- certain (combinations of) moments have to
vanish -- which we study.Comment: 16 page
Wigner formula of rotation matrices and quantum walks
Quantization of a random-walk model is performed by giving a qudit (a
multi-component wave function) to a walker at site and by introducing a quantum
coin, which is a matrix representation of a unitary transformation. In quantum
walks, the qudit of walker is mixed according to the quantum coin at each time
step, when the walker hops to other sites. As special cases of the quantum
walks driven by high-dimensional quantum coins generally studied by Brun,
Carteret, and Ambainis, we study the models obtained by choosing rotation as
the unitary transformation, whose matrix representations determine quantum
coins. We show that Wigner's -dimensional unitary representations of
rotations with half-integers 's are useful to analyze the probability laws
of quantum walks. For any value of half-integer , convergence of all moments
of walker's pseudovelocity in the long-time limit is proved. It is generally
shown for the present models that, if is even, the probability measure
of limit distribution is given by a superposition of terms of scaled
Konno's density functions, and if is odd, it is a superposition of
terms of scaled Konno's density functions and a Dirac's delta function at the
origin. For the two-, three-, and four-component models, the probability
densities of limit distributions are explicitly calculated and their dependence
on the parameters of quantum coins and on the initial qudit of walker is
completely determined. Comparison with computer simulation results is also
shown.Comment: v2: REVTeX4, 15 pages, 4 figure
Conformally Einstein Products and Nearly K\"ahler Manifolds
In the first part of this note we study compact Riemannian manifolds (M,g)
whose Riemannian product with R is conformally Einstein. We then consider
compact 6--dimensional almost Hermitian manifolds of type W_1+W_4 in the
Gray--Hervella classification admitting a parallel vector field and show that
(under some regularity assumption) they are obtained as mapping tori of
isometries of compact Sasaki-Einstein 5-dimensional manifolds. In particular,
we obtain examples of inhomogeneous locally (non-globally) conformal nearly
K\"ahler compact manifolds
Charge degree of freedom and single-spin fluid model in YBa_2Cu_4O_8
We present a 17O nuclear magnetic resonance study in the stoichiometric
superconductor YBa_2Cu_4O_8. A double irradiation method enables us to show
that, below around 180 K, the spin-lattice relaxation rate of plane oxygen is
not only driven by magnetic, but also significantly by quadrupolar
fluctuations, i.e. low-frequency charge fluctuations. In the superconducting
state, on lowering the temperature, the quadrupolar relaxation diminishes
faster than the magnetic one. These findings show that, with the opening of the
pseudo spin gap, a charge degree of freedom of mainly oxygen character is
present in the electronic low-energy excitation spectrum.Comment: 4 pages, 3 figures, REVTE
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