4,441 research outputs found
Superconductivity in higher titanium oxides
Recent renewal of the highest transition temperature in a conventional
superconductor of the sulfer hydride attracts much attention to exploring
simple compounds with the lighter elements, situated in unconventional
conditions. We report the discovery of superconductivity in simple oxides of
Ti4O7 and g-Ti3O5 in a thin-film form having deliberately tuned epitaxial
structures and off-stoichiometry. These higher titanium oxides join in a class
of simple-oxide superconductors, and g-Ti3O5 now holds the highest
superconducting transition temperature of 7.1 kelvin among them. The mechanism
behind the superconductivity is discussed on the basis of electrical
measurements and theoretical predictions. We conclude that superconductivity
arises from unstabilized bipolaronic insulating states.Comment: 25 pages, 4 figures in main text, 14 pages, 11 figures in
supplemental informatio
Statistical Mechanics of Dictionary Learning
Finding a basis matrix (dictionary) by which objective signals are
represented sparsely is of major relevance in various scientific and
technological fields. We consider a problem to learn a dictionary from a set of
training signals. We employ techniques of statistical mechanics of disordered
systems to evaluate the size of the training set necessary to typically succeed
in the dictionary learning. The results indicate that the necessary size is
much smaller than previously estimated, which theoretically supports and/or
encourages the use of dictionary learning in practical situations.Comment: 6 pages, 4 figure
Replica symmetry breaking in an adiabatic spin-glass model of adaptive evolution
We study evolutionary canalization using a spin-glass model with replica
theory, where spins and their interactions are dynamic variables whose
configurations correspond to phenotypes and genotypes, respectively. The spins
are updated under temperature T_S, and the genotypes evolve under temperature
T_J, according to the evolutionary fitness. It is found that adaptation occurs
at T_S < T_S^{RS}, and a replica symmetric phase emerges at T_S^{RSB} < T_S <
T_S^{RS}. The replica symmetric phase implies canalization, and replica
symmetry breaking at lower temperatures indicates loss of robustness.Comment: 5pages, 2 figure
The development of air shower in the iron absorber
The iron open-sandwich experiments to observe one dimensional development of individual air showers were carried out at Akeno Observatory. One dimensional energy flow, incident energy and production height of shower is estimated using the data of size and age obtained from the above experiment and simple calculation
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