Gene orders have been shown to be generally unstable by comprehensive analyses in several complete genomes. In this study, we examined instability of genome structures within operons, where functionally related genes are clustered. We compared gene orders of known operons obtained from Escherichia coli and Bacillus subtilis with corresponding those of operons in 11 complete genome sequences. We found that in many cases, gene orders within operons could be shuffled frequently during evolution, although several operon structures, such as ribosomal protein operons, were well conserved. This suggests that shuffling of a genome structure is virtually neutral in long-term evolution. Moreover, degrees of instability of the operon structures depended on the genomes examined. Variation in degrees of instability of the genome structures was likely to be related to differences in amounts of insertion sequences. Effects on transcription regulation are also discussed in association with operon destruction.

Advances in single-photon sources (SPSs) and single-photon detectors (SPDs) promise unique applications in the field of quantum information technology. In this paper, we report long-distance quantum key distribution (QKD) by using state-of-the-art devices: a quantum-dot SPS (QD SPS) emitting a photon in the telecom band of 1.5 μm and a superconducting nanowire SPD (SNSPD). At the distance of 100 km, we obtained the maximal secure key rate of 27.6 bps without using decoy states, which is at least threefold larger than the rate obtained in the previously reported 50-km-long QKD experiment. We also succeeded in transmitting secure keys at the rate of 0.307 bps over 120 km. This is the longest QKD distance yet reported by using known true SPSs. The ultralow multiphoton emissions of our SPS and ultralow dark count of the SNSPD contributed to this result. The experimental results demonstrate the potential applicability of QD SPSs to practical telecom QKD networks.

The polar-angular dependence of the magnetization in electromotive force induced by the spin pumping has been investigated for a Ni 81 Fe 19 / Pt film to examine the model of the inverse spin-Hall effect ͑ISHE͒. In the experiment, the magnetization-direction dependence of the electromotive force is estimated directly by the simultaneous measurement of the ferromagnetic resonance field and the electromotive force signal. The experimental results are well reproduced by a calculation based on the Landau-Lifshitz-Gilbert equation combined with the ISHE model. J s J c FIG. 1. A schematic illustration of the inverse spin-Hall effect.J c , J s , and denote a charge current, the spatial direction of a spin current, and the spin-polarization vector of a spin current, respectively.

Background Co-occurrence networks—ecological associations between sampled populations of microbial communities inferred from taxonomic composition data obtained from high-throughput sequencing techniques—are widely used in microbial ecology. Several co-occurrence network methods have been proposed. Co-occurrence network methods only infer ecological associations and are often used to discuss species interactions. However, validity of this application of co-occurrence network methods is currently debated. In particular, they simply evaluate using parametric statistical models, even though microbial compositions are determined through population dynamics. Results We comprehensively evaluated the validity of common methods for inferring microbial ecological networks through realistic simulations. We evaluated how correctly nine widely used methods describe interaction patterns in ecological communities. Contrary to previous studies, the performance of the co-occurrence network methods on compositional data was almost equal to or less than that of classical methods (e.g., Pearson’s correlation). The methods described the interaction patterns in dense and/or heterogeneous networks rather inadequately. Co-occurrence network performance also depended upon interaction types; specifically, the interaction patterns in competitive communities were relatively accurately predicted while those in predator–prey (parasitic) communities were relatively inadequately predicted. Conclusions Our findings indicated that co-occurrence network approaches may be insufficient in interpreting species interactions in microbiome studies. However, the results do not diminish the importance of these approaches. Rather, they highlight the need for further careful evaluation of the validity of these much-used methods and the development of more suitable methods for inferring microbial ecological networks. Electronic supplementary material The online version of this article (10.1186/s12859-019-2915-1) contains supplementary material, which is available to authorized users.

We succeeded in efficiently generating single-photon pulses from an InAs/InP quantum dot at a wavelength of 1.5 μm. Our optical structure, named a single photon horn, can propagate over 95% photon pulses in InP substrate. We extracted the photon pulses through an anti-reflection coating on a substrate, and then we injected them into an objective lens. Total extraction efficiency from the quantum dot to the lens reached ∼11%, which was estimated using a photon correlation measurement. Furthermore we directly observed the single-photon pulse width ∼1.6 ns as an exciton lifetime in the quantum dot, which opens up the possibility of operating the single photon horn over 100 MHz.