Alternative way of looking at shape resonances in atomic reactive collisions is proposed. The shape resonances in a certain collision system can be arranged systematically according to a universal measure of the difference between the collision energy and the top of the barrier produced by the sum of the intermolecular interaction and the centrifugal potential. Applying Wentzel-Krammers-Brillouin (WKB) approximation as a basis, one can show that the resonance peak heights and widths are given by very simple universal formulae.
In living cells, chemical reactions form complex networks. We developed a theoretical framework, called structural sensitivity analysis (SSA), to predict the sensitivity, i.e. the responses of concentrations and fluxes to perturbations of enzymes, from network structure alone. Responses turn out to exhibit two characteristic patterns, localization and hierarchy. We proved a general theorem connecting sensitivity with network topology, from which the characteristic patterns can be explained. Our results imply that network topology is an origin of biological robustness. Finally, we propose a strategy to identify missing reactions in database networks and determine real networks by combining our framework with experimental measurements.
We have observed extremely strong coupling between a superconducting flux qubit and a microwave LC resonator. The coupling energy is larger than the energies of the bare qubit and photons. The observed energy spectra are well described by the Rabi model, and they agree with selection rules that reflect the symmetry of the circuits. All our observations indicate the realization of an entangled ground state. Finally, the relation with the superradiant quantum phase transition is discussed.
The primordial abundances of the light elements produced in the Big Bang nucleosynthesis (BBN) provide important insights into the early universe. Accurate estimation of the primordial abundances is crucial to test the cosmological theories by comparing the predicted values with the observations. However, there remains a serious problem that the 7Li abundance does not agree with the standard BBN calculation. Since the BBN theory relies on nuclear reactions among the primordial light elements and their electroweak decays, nuclear experimental approaches toward solving the cosmological lithium problem are important.
Recently, we measured the cross sections of the 7Be (n, α)4He reaction at E=0.20–0.81 MeV close to the BBN energy window for the first time by measuring the time-reverse reaction. The obtained cross sections are significantly smaller than the theoretical estimation widely used in the BBN calculations. The present results suggest the 7Be (n, α)4He reaction rate is not large enough to solve the cosmological lithium problem.
Materials with low thermal conductivity are employed in many modern technologies, such as thermal management in electronic devices or thermoelectric energy conversion. In general, low values of thermal conductivity are found in disordered solids, glasses. The heat carriers are strongly scattered by disorder, and their lifetimes even reach the minimum time scale of thermal vibrations. For this reason, the value of the glass is generally considered as a lower bound for thermal conductivity of materials with homogeneous chemical composition. An appropriate design at the nano-scale, however, may allow one to reduce the thermal conductivity even below the glass limit. Indeed, recent experiments achieved ultra-low thermal conductivity through layered design of materials. In the layered materials, the interface between different layers blocks the propagation of the heat carriers and significantly reduces the thermal conductivity. Although both of glasses and layered materials show low values of thermal conductivity, the behavior of the heat carriers is different between them, thus the mechanism of the low thermal conductivity is different.