2,131 research outputs found
Learning cover context-free grammars from structural data
We consider the problem of learning an unknown context-free grammar when the
only knowledge available and of interest to the learner is about its structural
descriptions with depth at most The goal is to learn a cover
context-free grammar (CCFG) with respect to , that is, a CFG whose
structural descriptions with depth at most agree with those of the
unknown CFG. We propose an algorithm, called , that efficiently learns
a CCFG using two types of queries: structural equivalence and structural
membership. We show that runs in time polynomial in the number of
states of a minimal deterministic finite cover tree automaton (DCTA) with
respect to . This number is often much smaller than the number of states
of a minimum deterministic finite tree automaton for the structural
descriptions of the unknown grammar
Self-Reduction Rate of a Microtubule
We formulate and study a quantum field theory of a microtubule, a basic
element of living cells. Following the quantum theory of consciousness by
Hameroff and Penrose, we let the system to reduce to one of the classical
states without measurement if certain conditions are
satisfied(self-reductions), and calculate the self-reduction time (the
mean interval between two successive self-reductions) of a cluster consisting
of more than neighboring tubulins (basic units composing a microtubule).
is interpreted there as an instance of the stream of consciousness. We
analyze the dependence of upon and the initial conditions, etc.
For relatively large electron hopping amplitude, obeys a power law
, which can be explained by the percolation theory. For
sufficiently small values of the electron hopping amplitude, obeys an
exponential law, . By using this law, we estimate the
condition for to take realistic values
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{} 1000.Comment: 7 pages, 9 figures, Extended versio
Chiroptical properties of an alternatingly functionalized cellotriose bearing two porphyrin groups.
Right-handedness derived from bisporphyrins attached to a cellotriose backbone at O-6 and O''-6 positions is revealed for the first time. This cellotriose is proposed as a model of alternatingly functionalized cellulosics, which have promising properties for applications in optoelectronics and molecular receptors owing to the chirality and rigid backbone effects
Thermal conductivity of quantum magnetic monopoles in the frustrated pyrochlore Yb2Ti2O7
We report low-temperature thermal conductivity of pyrochlore
YbTiO, which contains frustrated spin-ice correlations with
significant quantum fluctuations. In the disordered spin-liquid regime,
exhibits a nonmonotonic magnetic field dependence, which is well
explained by the strong spin-phonon scattering and quantum monopole
excitations. We show that the excitation energy of quantum monopoles is
strongly suppressed from that of dispersionless classical monopoles. Moreover,
in stark contrast to the diffusive classical monopoles, the quantum monopoles
have a very long mean free path. We infer that the quantum monopole is a novel
heavy particle, presumably boson, which is highly mobile in a three-dimensional
spin liquid.Comment: 8 pages, 9 figure
Multiorbital analysis of the effects of uniaxial and hydrostatic pressure on in the single-layered cuprate superconductors
The origin of uniaxial and hydrostatic pressure effects on in the
single-layered cuprate superconductors is theoretically explored. A two-orbital
model, derived from first principles and analyzed with the fluctuation exchange
approximation gives axial-dependent pressure coefficients, , , with a hydrostatic response
for both La214 and Hg1201 cuprates, in qualitative
agreement with experiments. Physically, this is shown to come from a unified
picture in which higher is achieved with an "orbital distillation",
namely, the less the main band is hybridized with the
and orbitals higher the . Some implications for obtaining higher
materials are discussed.Comment: 6pages, 4 figure
Mechanisms Underlying Robustness and Tunability in a Plant Immune Signaling Network
SummaryThe plant immune signaling network needs to be robust against attack from fast-evolving pathogens and tunable to optimize immune responses. We investigated the basis of robustness and tunability in the signaling network controlling pattern-triggered immunity (PTI) in Arabidopsis. A dynamic network model containing four major signaling sectors, the jasmonate, ethylene, phytoalexin-deficient 4, and salicylate sectors, which together govern up to 80% of the PTI levels, was built using data for dynamic sector activities and PTI levels under exhaustive combinatorial sector perturbations. Our regularized multiple regression model had a high level of predictive power and captured known and unexpected signal flows in the network. The sole inhibitory sector in the model, the ethylene sector, contributed centrally to network robustness via its inhibition of the jasmonate sector. The model’s multiple input sites linked specific signal input patterns varying in strength and timing to different network response patterns, indicating a mechanism enabling tunability
Arabidopsis ABCG14 is essential for the root-to-shoot translocation of cytokinin.
Cytokinins are phytohormones that induce cytokinesis and are essential for diverse developmental and physiological processes in plants. Cytokinins of the trans-zeatin type are mainly synthesized in root vasculature and transported to the shoot, where they regulate shoot growth. However, the mechanism of long-distance transport of cytokinin was hitherto unknown. Here, we report that the Arabidopsis ATP-binding cassette (ABC) transporter subfamily G14 (AtABCG14) is mainly expressed in roots and plays a major role in delivering cytokinins to the shoot. Loss of AtABCG14 expression resulted in severe shoot growth retardation, which was rescued by exogenous trans-zeatin application. Cytokinin content was decreased in the shoots of atabcg14 plants and increased in the roots, with consistent changes in the expression of cytokinin-responsive genes. Grafting of atabcg14 scions onto wild-type rootstocks restored shoot growth, whereas wild-type scions grafted onto atabcg14 rootstocks exhibited shoot growth retardation similar to that of atabcg14. Cytokinin concentrations in the xylem are reduced by similar to 90% in the atabcg14 mutant. These results indicate that AtABCG14 is crucial for the translocation of cytokinin to the shoot. Our results provide molecular evidence for the long-distance transport of cytokinin and show that this transport is necessary for normal shoot development.open118380Ysciescopu
Influence of apical oxygen on the extent of in-plane exchange interaction in cuprate superconductors
In high Tc superconductors the magnetic and electronic properties are
determined by the probability that valence electrons virtually jump from site
to site in the CuO2 planes, a mechanism opposed by on-site Coulomb repulsion
and favored by hopping integrals. The spatial extent of the latter is related
to transport properties, including superconductivity, and to the dispersion
relation of spin excitations (magnons). Here, for three antiferromagnetic
parent compounds (single-layer Bi2Sr0.99La1.1CuO6+delta, double-layer
Nd1.2Ba1.8Cu3O6 and infinite-layer CaCuO2) differing by the number of apical
atoms, we compare the magnetic spectra measured by resonant inelastic x-ray
scattering over a significant portion of the reciprocal space and with
unprecedented accuracy. We observe that the absence of apical oxygens increases
the in-plane hopping range and, in CaCuO2, it leads to a genuine 3D
exchange-bond network. These results establish a corresponding relation between
the exchange interactions and the crystal structure, and provide fresh insight
into the materials dependence of the superconducting transition temperature.Comment: 9 pages, 4 figures, 1 Table, 42 reference
Current control system of the power supplies for LHD superconducting coils
The LHD is a fusion experimental facility using a large-scale superconducting coil system. The coil system includes six sets of superconducting coils, and six DC power supplies are used to charge them. For the current controllers of these power supplies, high accuracy of current control, fast response and robustness of the system are required. This paper describes the current control system for the LHD DC power supplies. First, the outline of the power system is presented, and then, the current controllers for the LHD are described. Finally, experimental results are presented and discussed in case of coil excitation using these control systems. The results show the various characteristics for each control system and indicate its possibility to control the system according to the requirements from a plasma experiment
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