Explicit definition of PT\mathcal{PT} symmetry for non-unitary quantum walks with gain and loss

$\mathcal{PT}$ symmetry, that is, a combined parity and time-reversal symmetry is a key milestone for non-Hermite systems exhibiting entirely real eigenenergy. In the present work, motivated by a recent experiment, we study $\mathcal{PT}$ symmetry of the time-evolution operator of non-unitary quantum walks. We present the explicit definition of $\mathcal{PT}$ symmetry by employing a concept of symmetry time frames. We provide a necessary and sufficient condition so that the time-evolution operator of the non-unitary quantum walk retains $\mathcal{PT}$ symmetry even when parameters of the model depend on position. It is also shown that there exist extra symmetries embedded in the time-evolution operator. Applying these results, we clarify that the non-unitary quantum walk in the experiment does have $\mathcal{PT}$ symmetry.Comment: 14 pages, 8 figure

Elemental Spiking Neuron Model for Reproducing Diverse Firing Patterns and Predicting Precise Firing Times

In simulating realistic neuronal circuitry composed of diverse types of neurons, we need an elemental spiking neuron model that is capable of not only quantitatively reproducing spike times of biological neurons given in vivo-like fluctuating inputs, but also qualitatively representing a variety of firing responses to transient current inputs. Simplistic models based on leaky integrate-and-fire mechanisms have demonstrated the ability to adapt to biological neurons. In particular, the multi-timescale adaptive threshold (MAT) model reproduces and predicts precise spike times of regular-spiking, intrinsic-bursting, and fast-spiking neurons, under any fluctuating current; however, this model is incapable of reproducing such specific firing responses as inhibitory rebound spiking and resonate spiking. In this paper, we augment the MAT model by adding a voltage dependency term to the adaptive threshold so that the model can exhibit the full variety of firing responses to various transient current pulses while maintaining the high adaptability inherent in the original MAT model. Furthermore, with this addition, our model is actually able to better predict spike times. Despite the augmentation, the model has only four free parameters and is implementable in an efficient algorithm for large-scale simulation due to its linearity, serving as an element neuron model in the simulation of realistic neuronal circuitry

Buried double CuO chains in YBa2_2Cu4_4O8_8 uncovered by nano-ARPES

The electron dynamics in the CuO chains has been elusive in Y-Ba-Cu-O cuprate systems by means of standard angle-resolved photoemission spectroscopy (ARPES); cleaved sample exhibits areas terminated by both CuO-chain or BaO layers, and the size of a typical beam results in ARPES signals that are superposed from both terminations. Here, we employ spatially-resolved ARPES with submicrometric beam (nano-ARPES) to reveal the surface-termination-dependent electronic structures of the double CuO chains in YBa$_2$Cu$_4$O$_8$. We present the first observation of sharp metallic dispersions and Fermi surfaces of the double CuO chains buried underneath the CuO$_2$-plane block on the BaO terminated surface. While the observed Fermi surfaces of the CuO chains are highly one-dimensional, the electrons in the CuO-chains do not undergo significant electron correlations and no signature of a Tomonaga-Luttinger liquid nor a marginal Fermi liquid is found. Our works represent an important experimental step toward understanding of the charge dynamics and provides a starting basis for modelling the high-$T_c$ superconductivity in YBCO cuprate systems.Comment: 10 pages, 5 figures including supplementary material (4 pages, 2 figures

Observation of band crossings protected by nonsymmorphic symmetry in the layered ternary telluride Ta3SiTe6

We have performed angle-resolved photoemission spectroscopy of layered ternary telluride Ta3SiTe6 which is predicted to host nodal lines associated with nonsymmorphic crystal symmetry. We found that the energy bands in the valence-band region show Dirac-like dispersions which present a band degeneracy at the R point of the bulk orthorhombic Brillouin zone. This band degeneracy extends one-dimensionally along the whole SR high-symmetry line, forming the nodal lines protected by the glide mirror symmetry of the crystal. We also observed a small band splitting near EF which supports the existence of hourglass-type dispersions predicted by the calculation. The present results provide an excellent opportunity to investigate the interplay between exotic nodal fermions and nonsymmorphic crystal symmetry.Comment: 6 pages, 4 figure

Validation of the effect of mantle inelasticity and latitude dependence through the observed tidal parameters

第2回極域科学シンポジウム/第31回極域地学シンポジウム 11月16日（水） 国立国語研究

Optimal call admission control for voice traffic in cellular mobile communication networks

We propose a new call admission control (CAC) scheme for voice calls in cellular mobile communication networks. It is assumed thatthe rejection of a hand-off call is less desirable than that of a new call,for a hand-off call loss would cause a severe mental pain to a user. We consider the pains of rejecting new and hand-off calls as differentcosts. The key idea of our CAC is to restrict the admission of new calls in order to minimize the total expected costs per unit time over thelong term. An optimal policy is derived from a semi-Markov decision process in which the intervals between successive decision epochs areexponentially distributed. Based on this optimal policy, we calculate the steady state probability for the number of established voice connections in a cell. We then evaluate the probability of blocking new calls and the probability of forced termination of hand-odd calls. In the numerical experiments, it is found that the forced termination probability of hand-off calls is reduced significantly by our CAC scheme at the slight expense of the blocking probability of new calls and the channel utilization.Includes bibliographical reference

Emerging Stock Market Comovements and the Third-Country Effects

This paper investigates the effects of financial globalization; in particular cross-border capital flows in financial markets, on excess pairwise stock return comovements in emerging Asian countries during 2001-2012. Increased comovements in excess stock returns are mainly explained by the third-country effect from G7 countries, not by bilateral capital flows between Asian countries. That is, a high correlation of stock returns in emerging Asia is the result of synchronized capital flows from G7 countries into Asian financial markets, not by portfolio investment among Asian countries. This result provides evidence that “coupling” is still a reality in terms of stock returns in emerging Asia