An antenna switching based NOMA scheme for IEEE 802.15.4 concurrent transmission

This paper introduces a Non-Orthogonal Multiple Access (NOMA) scheme to support concurrent transmission of multiple IEEE 802.15.4 packets. Unlike collision avoidance Multiple Access Control (MAC), concurrent transmission supports Concurrent-MAC (C-MAC) where packet collision is allowed. The communication latency can be reduced by C-MAC because a user can transmit immediately without waiting for the completion of other users’ transmission. The big challenge of concurrent transmission is that error free demodulation of multiple collided packets hardly can be achieved due to severe Multiple Access Interference (MAI). To improve the demodulation performance with MAI presented, we introduce an architecture with multiple switching antennas sharing a single analog transceiver to capture spatial character of different users. Successive Interference Cancellation (SIC) algorithm is designed to separate collided packets by utilizing the spatial character. Simulation shows that at least five users can transmit concurrently to the SIC receiver equipped with eight antennas without sacrificing Packet Error Rate

Three essays on the economics of U.S. water policy

The complicated relationship between human activities and water quality/quantity has interested many researchers. My primary research interest lies in environmental economics and water resource policy. This dissertation studies water quality and water quantity in the United States, especially groundwater. In particular, the first chapter, “The Conservation Reserve Program and Nutrient Pollution in Groundwater”, studies how the Conservation Reserve Program (CRP) affects groundwater quality in the United States. The second chapter of my dissertation, “Reliable Drinking Water Supply and Cities’ Resilience to Drought” (joint with Dr. David Keiser, Dr. Gabriel Lade, and Dr. Ivan Rudik), studies how differences in drinking water supply sources affect how cities adapt to and respond to extreme weather events. The third chapter of my dissertation, “The Effectiveness of Phosphorus Lawn Fertilizer Bans” (joint with Dr. David Keiser), studies the effectiveness of incomplete phosphorus lawn fertilizer bans in Florida by utilizing a restricted consumer scanner data and fixed effects model

低温光学顕微鏡による光合成タンパク質と細胞の励起-蛍光スペクトル分光

Tohoku University博士（理学）要約のみthesi

On large deformations of elastic circular arcs

Das Thema dieser Arbeit kommt von einem praktischen Greifersystem, dessen vereinfachter wesentlicher Teil aus zwei eingespannt-freien elastischen kreisförmigen Stäben besteht. Die Bewegung dieses Systems wird durch die Deformationen der elastischen kreisförmigen Stäbe unter der am freien Ende angreifenden Kraft erzeugt. Die Bögen können von jeder möglichen Form sein, von der Geraden bis zum gesamten geschlitzten Ring, und ihre Deformationen können beliebig groß sein. Nach Aufstellung eines mathematischen Modells in Form eines Randwertproblems mit drei Parametern (Kraft, Bogengeometrie) für eine Pendelgleichung wurden Vielfachheit und Stabilität der Lösungen der Pendelgleichung und der entsprechenden Stabkonfigurationen untersucht. Dazu wurde eine leistungsfähige Methode, die "Mannigfaltigkeitsmethode", entwickelt, die auf der Diskussion der Phasenkurven der Pendelgleichung basiert. Mit dieser Methode, gekoppelt mit numerischen Rechnungen, wurden die Bifurkationsdiagramme der Pendelgleichung für verschiedene Kombinationen der Parameter erhalten. Die Bifurkationsdiagramme zeigten Vielfachheit und die Änderungstendenz der Lösungen der Pendelgleichung und der Konfigurationen der verformten Bögen an. Die Bifurkationsdiagramme zeigen für unser Modell turningpoint-, pitchfork- und X-Bifurkationen sowie Hysteresis. Die Kraftparameterebene wurde nach der Zahl der Lösungen in Gebiete unterteilt. Die theoretische Untersuchung des Halbringes mittels elliptischer Integrale wurde durchgeführt, und das Resultat zeigt eine genaue Übereinstimmung mit den Ergebnissen der Mannifaltigkeitsmethode. Für die Stabilitätsuntersuchung versagen klassische Methoden, da das Randwertproblem für die Pendelgleichung keine trivialen Lösungen besitzt. Deshalb wurde die Pendelgleichung in eine parabolische partielle Differentialgleichung eingebettet, die Liapunovstabilität der stationären Lösungen definiert die "P-Stabilität" der Konfiguration des elastischen Stabes. Stabilitätsaussagen werden mit Hilfe der Methode der ersten Näherung und unter Benutzung der Bifurkationsfunktion gewonnen. Zum ursprünglichen praktischen Problem "Feder und Greifer" wurden als Ergebnisse Federcharakteristiken, insbesondere Kraft-Verschiebungs-Kennlinien für kreisbogenförmige Federn gefunden. Für Greifer, die aus zwei symmetrisch angeordneten elastischen Kreisbögen bestehen, wurden Zusammenhänge von Öffnungsweite, Haftreibungskoeffzient und Haltekraft gefunden. Die Methoden, die in dieser Arbeit eingeführt werden, besonders die Mannifaltigkeitsmethode und P-Stabilität, können für die Untersuchung von Bifurkation und Stabilität bei allgemeinen gewöhnlichen Dfferentialgleichungen nützlich sein

Openwifi : a free and open-source IEEE802.11 SDR implementation on SoC

Open source Software Defined Radio (SDR) project, such as srsLTE and Open Air Interface (OAI), has been widely used for 4G/5G research. However the SDR implementation of the IEEE802.11 (Wi-Fi) is still difficult. The Wi-Fi Short InterFrame Space (SIFS) requires acknowledgement (ACK) packet being sent out in 10μs/16μs(2.4 GHz/5GHz) after receiving a packet successfully, thus the Personal Computer (PC) based SDR architecture hardly can be used due to the latency (≥100μs) between PC and Radio Frequency (RF) front-end. Researchers have to do simulation, hack a commercial chip or buy an expensive reference design to test their ideas. To change this situation, we have developed an open-source full-stack IEEE802.11a/g/n SDR implementation — openwifi. It is based on Xilinx Zynq Systemon-Chip (SoC) that includes Field Programmable Gate Array (FPGA) and ARM processor. With the low latency connection between FPGA and RF front-end, the most critical SIFS timing is achieved by implementing Physical layer (PHY) and low level Media Access Control (low MAC) in FPGA. The corresponding driver is implemented in the embedded Linux running on the ARM processor. The driver instantiates Application Programming Interfaces (APIs) defined by Linux mac80211 subsystem, which is widely used for most SoftMAC Wi-Fi chips. Researchers could study and modify openwifi easily thanks to the modular design. Compared to PC based SDR, the SoC is also a better choice for portable and embedded scenario

A baseband wireless spectrum hypervisor for multiplexing concurrent OFDM signals

The next generation of wireless and mobile networks will have to handle a significant increase in traffic load compared to the current ones. This situation calls for novel ways to increase the spectral efficiency. Therefore, in this paper, we propose a wireless spectrum hypervisor architecture that abstracts a radio frequency (RF) front-end into a configurable number of virtual RF front ends. The proposed architecture has the ability to enable flexible spectrum access in existing wireless and mobile networks, which is a challenging task due to the limited spectrum programmability, i.e., the capability a system has to change the spectral properties of a given signal to fit an arbitrary frequency allocation. The proposed architecture is a non-intrusive and highly optimized wireless hypervisor that multiplexes the signals of several different and concurrent multi-carrier-based radio access technologies with numerologies that are multiple integers of one another, which are also referred in our work as radio access technologies with correlated numerology. For example, the proposed architecture can multiplex the signals of several Wi-Fi access points, several LTE base stations, several WiMAX base stations, etc. As it able to multiplex the signals of radio access technologies with correlated numerology, it can, for instance, multiplex the signals of LTE, 5G-NR and NB-IoT base stations. It abstracts a radio frequency front-end into a configurable number of virtual RF front ends, making it possible for such different technologies to share the same RF front-end and consequently reduce the costs and increasing the spectral efficiency by employing densification, once several networks share the same infrastructure or by dynamically accessing free chunks of spectrum. Therefore, the main goal of the proposed approach is to improve spectral efficiency by efficiently using vacant gaps in congested spectrum bandwidths or adopting network densification through infrastructure sharing. We demonstrate mathematically how our proposed approach works and present several simulation results proving its functionality and efficiency. Additionally, we designed and implemented an open-source and free proof of concept prototype of the proposed architecture, which can be used by researchers and developers to run experiments or extend the concept to other applications. We present several experimental results used to validate the proposed prototype. We demonstrate that the prototype can easily handle up to 12 concurrent physical layers

An analytically formulated structural strain method for fatigue evaluation of welded components incorporating nonlinear hardening effects

An analytically formulated structural strain method is presented for performing fatigue evaluation of welded components by incorporating nonlinear material hardening effects by means of a modified Ramberg‐Osgood power law hardening model. The modified Ramberg‐Osgood model enables a consistent partitioning of elastic and plastic strain increments during both loading and unloading. For supporting 2 major forms of welded structures in practice, the new method is applied for computing structural strain defined with respect to a through‐thickness section in plate structures and cross section in piping systems. In both cases, the structural strain is formulated as the linearly deformation gradient on their respective cross sections, consistent with the “plane sections remain plane” assumption in structural mechanics. The structural strain‐based fatigue parameter is proposed and has been shown effective in correlating some well‐known low‐cycle and high‐cycle fatigue test data, ranging from gusset‐to‐plate welded plate connections to pipe girth welds.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146966/1/ffe12900.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146966/2/ffe12900_am.pd