京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第21138号 / 農博第2264号 / 新制||農||1057(附属図書館) / 学位論文||H30||N5112(農学部図書室) / 京都大学大学院農学研究科食品生物科学専攻 / (主査)教授 谷 史人, 教授 保川 清, 教授 橋本 渉 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

The state-of-the-art organic solar cells (OSC) use bulk heterojunction (BHJ) blend architecture in the photo-active layer. The BHJ is formed by finely mixing polymer donor and small molecule acceptor, which was predominantly fullerene derivatives until the last five years. However, the emergence of non-fullerene acceptor (NFA) materials has been the viable alternative to overcome high synthetic costs, limited optical absorption, and poor bandgap tunability of fullerene-based acceptors. These unique properties of NFA has resulted in a rapid improvement of OSC efficiency and opened doors for wide variety of applications including building integrated photovoltaics, green houses and agrivoltaics. Despite these advantages, the shorter device lifetime under light and heat is a major concern for their commercialization. This dissertation is focused on improving poor photo- and thermal stability of high efficiency OSC based on the widely used NFA, ITIC and Y-series derivatives. The light-induced changes in the acceptor molecular structure and the active layer nanostructure results in the photo-induced traps in photo-aged devices. The selective addition of third component to the active layer impedes the changes in the active layer nanostructure and suppress trap formation. Under constant thermal stress, the growth of acceptor crystals results increases the trap-assisted recombination in thermally aged devices. Similar to photo-stability the selective addition of third or more component/s arrests the crystal growth by minimizing the Gibbs free energy. The results suggest that the fabricated hexanary and ternary OSC display a superior thermal stability than the respective binary devices. In addition, the hexanary devices displayed thickness independent thermal stability, which is essential for the active layer thermal stability printed via high throughput techniques.

In this work we present some of the general theory of shock waves and their stability properties. We examine the concepts of nonlinear stability and spectral stability, noting that for certain classes of equations the study of nonlinear stability is reduced to the analysis of the spectra of the linearized eigenvalue problem. A useful tool in the study of spectral stability is the Evans function, an analytic function whose zeros correspond to the eigenvalues of the linearized eigenvalue problem. We discuss techniques for numerical Evans function computation that ensure analyticity, allowing standard winding number arguments and rootfinding methods to be used to locate eigenvalues. The Evans function is then used to study the spectra of the high Lewis number combustion system, tracking eigenvalues in the right-half plane.

<p> Steady state response of a single degree of freedom system with impact damper, with the main emphasis of two impacts (symmetric or unsymmetric)/cycle motion, and its asymptotic stability criterion are derived analytically. Stability regions are determined for wide range of parameters of the impact damper by using digital computer. </p> <p> Experimental study is also made to verify the assumptions taken in the analytical solution and to obtain general response of the system for wide range of parameters of the impact damper. </p> <p> As a result, it is found that unsymmetric two impacts per cycle motion exists and is stable for a wide range of parameters of the impact damper. </p> <p> Also, it is found that three and four impacts/cycle motions exist and are stable. </p> <p> Stability boundaries are found to be a complicated function of the impact damper parameters. </p> / Thesis / Master of Engineering (MEngr)

We investigate the dynamics and stability of nonlinear time-delayed one-degree-of-freedom systems possessing quadratic and cubic nonlinearities and subjected to external and parametric disturbances. Due to the time-delay terms, the trivial solution of the unforced system undergoes Hopf bifurcations. We use the method of multiple scales to determine the normal forms of the Hopf bifurcations and hence determine whether they are locally supercritical or subcritical. Then, we use a combination of a path following scheme, the normal forms, and the method of harmonic balance to calculate and trace small- and large-amplitude limit cycles and use Floquet theory to ascertain their stability and hence generate global bifurcation diagrams. We validate these diagrams using numerical simulations. We apply the results to two important physical problems: machine-tool chatter in lathes and control of the sway of container cranes using time-delayed position feedback. We find that the Hopf bifurcations in machine tools are globally subcritical even when they are locally supercritical. We find multiple large-amplitude solutions coexisting with the linearly stable trivial solution. Consequently, there are three operating regions for machine tools: an unconditionally stable region, an unconditionally unstable region, and a conditionally stable region. In the latter region, the multiple responses lead to hysteresis. Then, we investigate the use of bifurcation control to transform the subcritical bifurcations into supercritical ones. We find that cubic-velocity feedback with appropriate gains can shrink or even eliminate the conditionally stable region. Then, we find that time-delayed acceleration feedback with an appropriate gain can completely eliminate the linear instability region. In contrast, we find that the Hopf bifurcations in controlled cranes are locally and globally supercritical. Finally, we investigate the effectiveness of time-delayed position feedback in rejecting external and parametric disturbances in ship-mounted cranes. / Ph. D.

The object of this study is to incorporate a nonlinear material law for wood in the finite element program ABAQUS to develop effective finite element models of glulam domes, and to investigate the buckling behavior of glulam domes using this finite element program. The material law is implemented with a FORTRAN subroutine. Results from thorough testing of the subroutine are presented. The dome is then modeled with I-DEAS and, analyzed with ABAQUS. The modeling procedure is briefly discussed, and the results from the stability analysis of the dome are presented. Finally, conclusions and further research scope based on this study are presented. / Master of Science

In recent years the problem of designing a feedback control law to stabilize a linear, time-varying uncertain system has received considerable attention. However, the problem is usually limited to the case of systems which satisfy the "matching" assumptions. Moreover, the question of the existence of a linear stabilizing control, if a nonlinear stabilizing control exists, is still unanswered. In the present work an attempt is made to design a stabilizing, linear, feedback control law for a specific second order, linear system which contains time-varying uncertainties into both the state and input matrices and does not satisfy the matching conditions. For specific values of the uncertainty bounds this system is quadratically stabilizable but not quadratically stabilizable via linear control. / Master of Science

Multiple STATCOM units in proximity have been adopted in power transmission systems in order to obtain better voltage regulation and share burdens. Throughout stability assessment in this dissertation, it is shown, for the first time, that STATCOMs could interact with each other in a negative way in the small-signal sense due to their control, causing voltage instability, while loads and transmission lines showed small effects. Since this voltage stability problem is induced by STATCOMs, d-q frame impedance-based stability analysis was used, for the first time, to explore the inherent power system instability problem with presence of STATCOMs as it provides an accurate understanding of the root cause of instability within the STATCOM control system. This dissertation first proposes the impedance model in d-q frame for STATCOMs, including dynamics from synchronization, current and voltage loops and reveals the significant features compared to other types of grid-tied converters that 1) impedance matrix strongly coupled in d and q channel due to nearly zero power factor, 2) different behaviors of impedances at low frequency due to inversed direction of reactive power and 3) coupled small-signal propagation paths on the voltage at point of common coupling from synchronization and ac voltage regulation. Using the proposed impedance model, this dissertation identifies the frequency range of interactions in a viewpoint of d-q frame impedances and pinpointed that the ac voltage regulation was the main reason of instability, masking the effects of PLL in power transmission systems. Due to the high impedance of STATCOMs compared to that of transmission lines around the frequency range of interactions, STATCOMs were seen to interact with each other through the transmission lines. A scaled-down 2-STATCOM power grid was built to verify the conclusions experimentally. / Ph. D. / STATCOMs have been proven a type of effective power electronics device for reactive power compensations and people are trying to install multiple STATCOMs in proximity in power systems in order to have better performances. This dissertation, for the first time, evaluates the operation of multiple STATCOMs in proximity and finds out that they could interact with each other in a negative way in the small-signal sense due to their control, causing voltage instability, while loads and transmission lines showed small effects. Since this voltage stability problem is induced by STATCOMs, d-q frame impedance-based stability analysis was used, for the first time, to explore the inherent power system instability problem with presence of STATCOMs as it provides an accurate understanding of the root cause of instability within the STATCOM control system. To this end, an impedance model of STATCOMs is proposed, which accurately explains the terminal behaviors of STATCOMs. Using the model, this dissertation identifies the frequency range of interactions in a viewpoint of d-q frame impedances and pinpointed that the ac voltage regulation was the main reason of instability, masking the effects of PLL in power transmission systems. All the above is validated experimentally in a scaled-down 2-STATCOM power system.

International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada / This paper analyzes the feature of frequency stability and modulation of airborne telemetry transmitters. According to the characteristic of telemetry information transmission, several methods for frequency stabilization and modulation are briefly compared. Emphasis is given to discuss frequency dividing phase- locked frequency modulation and on-off keying modulation and FM/on- off keying double modulation. With the view of raising frequency stability and modulation sensibility, extending the linear range of modulation, the contradiction between frequency stabilization and modulation should be coordinated properly. In addition, a compatible method between conventional telemetry channel and super fast signal telemetry channel is introduced. A satisfactory result has been acquired with those views and methods used in engineering application.

One of the central questions of materials science is which crystallographic structure a certain alloy or compound will adopt as a function of elemental composition, pressure and temperature. This question can be traced back all the way from the Bronze Age via the first steel makers of the Middle Ages and the metallurgists of the 19th century to the present day. Experiences drawn from centuries of alloy making have given rise to well-established rules of thumb for alloy development and detailed phase diagrams for equilibrium conditions. However, a rigorous theory for single-phase alloys out of equilibrium is less well established. This study employs state-of-the-art electronic structure calculations based on density functional theory to tackle this problem. This method employs a reformulation of quantum mechanics to solve the many-body Schrodinger equation that describes the system. In our case, the system is a titanium alloy, where titanium is substitutionally alloyed with elements such as aluminium, chromium, vanadium and molybdenum. We find that chromium and vanadium stabilise the β phase, while scandium destabilises it. The strength of this effect is directly proportional to the additional d-electrons present in the alloying element. The effect appears to be additive, and the positional effects of the alloying atoms appear to be small. Using the results from the calculations we can construct new phase diagrams and equations of state for these alloys. This gives us a theoretical confirmation for established rules of thumb and provides us with new insights when constructing new alloys.