概日時計中枢における翻訳後修飾を介したオーファン受容体Gpr176の活性調節

京都大学新制・課程博士博士(薬科学)甲第24558号薬科博第175号新制||薬科||19(附属図書館)京都大学大学院薬学研究科医薬創成情報科学専攻(主査)教授 土居 雅夫, 教授 竹島 浩, 教授 中山 和久学位規則第4条第1項該当Doctor of Pharmaceutical SciencesKyoto UniversityDFA

Thermal characterization of nm-thick black phosphorus based on Raman spectroscopy

As a new two-dimensional material, black phosphorus has attracted worldwide attention due to its extraordinary electronic and optoelectronic properties. Despite its importance for the performance of electronic devices, thermal properties of black phosphorus are still not well studied, which leads to incomplete understanding on phonon transport and interaction in black phosphorus. This is related to difficulties for preparing black phosphorus samples since black phosphorus is easily oxidized in air and the difficulty in characterizing this nm-thin material. In this work, black phosphorus is studied systematically with techniques developed based on Raman spectroscopy. Our study on black phosphorus involves identifying its crystalline orientation and measuring its interface thermal conductance and anisotropic in-plane thermal conductivity. In this work, the crystalline orientation of black phosphorus is identified with a newly developed technique, optothermal Raman spectroscopy. This technique utilizes the anisotropic heating effect of a linear polarized laser for crystalline orientation identification. It can distinguish the armchair direction and zigzag direction precisely regardless of excitation wavelength and sample thickness. This in-situ and nondestructive technique is required to identify the crystalline orientation of black phosphorus samples before their interface thermal conductance and anisotropic in-plane thermal conductivity are measured. Interface thermal conductance between black phosphorus and Si is measured with micro-Raman spectroscopy. It is found there is large interface thermal conductance between black phosphorus and its adjacent Si, which suggests black phosphorus can be used as new interface material for future devices. Also, interface thermal conductance shows a strong negative correlation to temperature, while no correlation to thickness. These results lead to the discovery of the temperature-related morphological variation of supported black phosphorus on Si. Frequency-resolved Raman spectroscopy is developed to measure the anisotropic in-plane thermal conductivity of black phosphorus. This technique is first used to measure thermal diffusivity of a c-Si cantilever, which has a reference value of thermal diffusivity. The validity of this technique is sufficiently verified since our measured thermal diffusivity is very close to its reference value. Our measurements on black phosphorus with thickness between 99.8 and 157.6 nm show the armchair thermal conductivity is 13.5~22 W m-1 K-1, and the zigzag thermal conductivity is 39.8~62.7 W m-1 K-1. These studies significantly advance our fundamental understanding of phonon transport and interaction in black phosphorus, which can further benefit the development of new-generation devices

Listen-and-Talk: Full-duplex Cognitive Radio Networks

In traditional cognitive radio networks, secondary users (SUs) typically access the spectrum of primary users (PUs) by a two-stage "listen-before-talk" (LBT) protocol, i.e., SUs sense the spectrum holes in the first stage before transmit in the second stage. In this paper, we propose a novel "listen-and-talk" (LAT) protocol with the help of the full-duplex (FD) technique that allows SUs to simultaneously sense and access the vacant spectrum. Analysis of sensing performance and SU's throughput are given for the proposed LAT protocol. And we find that due to self-interference caused by FD, increasing transmitting power of SUs does not always benefit to SU's throughput, which implies the existence of a power-throughput tradeoff. Besides, though the LAT protocol suffers from self-interference, it allows longer transmission time, while the performance of the traditional LBT protocol is limited by channel spatial correction and relatively shorter transmission period. To this end, we also present an adaptive scheme to improve SUs' throughput by switching between the LAT and LBT protocols. Numerical results are provided to verify the proposed methods and the theoretical results.Comment: in proceeding of IEEE Globecom 201

Distributed Cooperative Sensing in Cognitive Radio Networks: An Overlapping Coalition Formation Approach

Cooperative spectrum sensing has been shown to yield a significant performance improvement in cognitive radio networks. In this paper, we consider distributed cooperative sensing (DCS) in which secondary users (SUs) exchange data with one another instead of reporting to a common fusion center. In most existing DCS algorithms, the SUs are grouped into disjoint cooperative groups or coalitions, and within each coalition the local sensing data is exchanged. However, these schemes do not account for the possibility that an SU can be involved in multiple cooperative coalitions thus forming overlapping coalitions. Here, we address this problem using novel techniques from a class of cooperative games, known as overlapping coalition formation games, and based on the game model, we propose a distributed DCS algorithm in which the SUs self-organize into a desirable network structure with overlapping coalitions. Simulation results show that the proposed overlapping algorithm yields significant performance improvements, decreasing the total error probability up to 25% in the Q_m+Q_f criterion, the missed detection probability up to 20% in the Q_m/Q_f criterion, the overhead up to 80%, and the total report number up to 10%, compared with the state-of-the-art non-overlapping algorithm

Social Data Offloading in D2D-Enhanced Cellular Networks by Network Formation Games

Recently, cellular networks are severely overloaded by social-based services, such as YouTube, Facebook and Twitter, in which thousands of clients subscribe a common content provider (e.g., a popular singer) and download his/her content updates all the time. Offloading such traffic through complementary networks, such as a delay tolerant network formed by device-to-device (D2D) communications between mobile subscribers, is a promising solution to reduce the cellular burdens. In the existing solutions, mobile users are assumed to be volunteers who selfishlessly deliver the content to every other user in proximity while moving. However, practical users are selfish and they will evaluate their individual payoffs in the D2D sharing process, which may highly influence the network performance compared to the case of selfishless users. In this paper, we take user selfishness into consideration and propose a network formation game to capture the dynamic characteristics of selfish behaviors. In the proposed game, we provide the utility function of each user and specify the conditions under which the subscribers are guaranteed to converge to a stable network. Then, we propose a practical network formation algorithm in which the users can decide their D2D sharing strategies based on their historical records. Simulation results show that user selfishness can highly degrade the efficiency of data offloading, compared with ideal volunteer users. Also, the decrease caused by user selfishness can be highly affected by the cost ratio between the cellular transmission and D2D transmission, the access delays, and mobility patterns

Listen-and-Talk: Protocol Design and Analysis for Full-duplex Cognitive Radio Networks

In traditional cognitive radio networks, secondary users (SUs) typically access the spectrum of primary users (PUs) by a two-stage "listen-before-talk" (LBT) protocol, i.e., SUs sense the spectrum holes in the first stage before transmitting in the second. However, there exist two major problems: 1) transmission time reduction due to sensing, and 2) sensing accuracy impairment due to data transmission. In this paper, we propose a "listen-and-talk" (LAT) protocol with the help of full-duplex (FD) technique that allows SUs to simultaneously sense and access the vacant spectrum. Spectrum utilization performance is carefully analyzed, with the closed-form spectrum waste ratio and collision ratio with the PU provided. Also, regarding the secondary throughput, we report the existence of a tradeoff between the secondary transmit power and throughput. Based on the power-throughput tradeoff, we derive the analytical local optimal transmit power for SUs to achieve both high throughput and satisfying sensing accuracy. Numerical results are given to verify the proposed protocol and the theoretical results