1,721,069 research outputs found
Contagion and state dependent mutations
Full text linkEarly results of evolutionary game theory showed that the risk dominant equilibrium is uniquely selected on the long run by the best response dynamics with mutation. Bergin and Lipman (1996) qualified this result by showing that for a given population size the evolutionary process can select any strict Nash equilibrium if the probability of choosing a nonbest reply is state-dependent. This paper shows that the unique selection of the risk dominant equilibrium is robust with respect to state dependent mutation in local interaction games. More precisely, for a given mutation structure there exists a minimum population size beyond which the risk dominant equilibrium is uniquely selected. Our result is driven by contagion and cohesion among players, which exists only in local interaction settings and favors the play of the risk dominant strategy. Our result strengthens the equilibrium selection result of evolutionary game theor
Learning-by-doing and the choice of technology: the role of patience
Full text linkIf agents learn by doing and are myopic, less advanced firms might adopt new technologies while more advanced firms would stick with the old technology. This kind of overtaking can also occur if agents are forward looking and have high discount rates. However, overtaking never occurs if agents are sufficiently patient. A finite discount rate increases the set of states at which agents adopt new technologies, so more patient agents tend to upgrade their technology more frequently. Journal of Economic Literature Classification Numbers: D92, O14, O33
Market structure in congestible markets
No full textThis paper analyses market structure of industries that are subject to both positive and negative network effects. The size of a firm determines the quality of its product: when network effects are positive, a larger firm is of higher quality; when the effects are negative, a larger firm's product is of lower quality. Consumers have heterogeneous preferences towards quality (firm size), and firms compete in prices. Equilibria are characterised: for example, in any asymmetric equilibrium, it must be that congestion is not too severe. One consequence of this feature is that an increase in the number of firms in the industry can raise individual firms’ profits. Two factors can bound the number of firms in a free-entry equilibrium without fixed costs: expectations, and the ‘finiteness’ property (Shaked and Sutton, Review of Economic Studies 49 (1982) 3–13, Econometrica 51(5) (1983) 1469–1483) of price competition
Time-consistent policies
No full textIn many cases the optimal open-loop policy to influence agents who solve dynamic problems is time inconsistent. We show how to construct a time-consistent open-loop policy rule. We also consider an additional restriction under which the time-consistent open-loop policy is stationary. We use examples to illustrate the properties of these tax rules
Uncertainty, co-ordination and path dependence
No full textOur objective is to assess whether dynamics hinder or assist co-ordination in a agme with strategic complementarities. We study two dynamic aspects: different agents make decisions at different points in time; and extra information about a payoff-relevant state of nature becomes available over time. We find that the dynamic resolution of information matters most for uniqueness of equilibrium. This is demonstrated by showing that the condition for uniqueness is weaker when learning occurs. An important consequence of this result is the occurrence of path dependence: the order in which signals arrive matters, as well as the total amount of information received
제일원리 분자동역학을 이용한 비정질 실리콘과 실리콘 집합체에 관한 연구
No full text학위논문(박사) - 한국과학기술원 : 물리학과, 1996.2, [ ix, 97 p. ]We present the results of tight binding molecular dynamics calculations for studying the equilibrium structures and the bonding properties of Sin clusters up to n = 18. With a limited number of parameters in the tight binding scheme, the structures of minimum energy are well reproduced, compared to previous ab initio quantum mechanical calculations. We find the abundant cluster sizes of n = 4, 7, and 10, which are in good agreement with other theoretical and experimental results. For n ≥ 7, the surface-like compact structures with a pentagon or a hexagon base are found to be energetically favorable, resulting in the metallic nature of cluster bonding, while a core-based structure firstly appears for . We also present an efficient scheme of minimizing the energy functional related to the large-scale system in a self-consistent manner. In the framework of the preconditioned conjugate gradient minimization of the energy functional, we replaces the modified Jacobi relaxation for preconditioning and use for band by band minimization the restricted block Davidson algorithm, in which only the previous wave functions and the relaxation vectors are included additionally for subspace diagonalization. The present scheme is found to be comparable with the preconditioned conjugate gradient method for both large ordered and disordered Si systems, while it is more rapidly converged for systems with transition metal elements. We also present the explicit symmetric formulas for the nonlocal pseudopotential contribution to the stress tensor. The symmetric stress tensor can be derived by applying the scaling procedure of wavevectors , which satisfies the symmetric properties of ∂K_γ/∂ε_{αβ}=∂K_γ /∂ε_{βα}} for the symmetric strain . We note that this scaling procedure gives rise to the same expression for the stress tensor as that derived using a semilocal or a separable nonlocal pseudopotential. Using these highly efficient method of total energy calcu...한국과학기술원 : 물리학과
Stabilization strategy against disturbance for a quadruped robot
No full text학위논문(석사) - 한국과학기술원 : 기계공학전공, 2011.2, [ iv, 52 p. ]본 논문은 4족 보행로봇에 대하여 보행 중 외란에 대한 안정화 전략에 대한 연구이다. Walking Trunk, KOLT, SCOUT 등 대표적 4족 보행 로봇들이 개발되었지만, 동적 보행과 동시에 외란에 대한 안정화 전략에 대한 연구는 실험을 통해 증명된 바가 없다. 발바닥과 상체가 있는 2족 보행 로봇과 달리 Point contact을 하며 상체가 없는 4족 보행 로봇의 경우 적절한 발뻗기를 통해서 만이 안정화가 가능하다.
Swing Leg 가 Completely swing up 되었을 때 초기조건을 읽어 벌림 각 을 결정하고, 착지 전까지 다리를 벌린다. 착지 후 바뀐 Swing Leg가 다시 Swing up 될 때 까지 벌린 각을 다시 닫는다. swing leg가 swing up 되면 위 사항을 반복 한다. 특정 벌림 각 를 펴는 Dynamic equation을 세우고 Swing up 된 다리가 완전히 펴진 시각에 지면에 착지하도록 하는 벌림 각 α 를 해당 초기조건에 대한 벌림 각 으로 결정한다. Robot을 Line Contact에 따라 바라보면 Supporting Leg를 기준으로 두 개의 Swing Leg가 있다. 이 두 Swing Leg를 동시에 착지하도록 하는 것이 위 벌림 각 를 구하는 기준이 되는 것이다. 위와 같은 벌림 각 를 가질 때, 이 전략의 Stability를 Linearized poincare map을 사용하여 검증하였다. 또한 3-d simulator를 통해 검증하였다. 임의의 외란을 주어 걸음 횟수가 지남에 따라 필요한 벌림 각 가 작아짐을 관찰하였으며, 로봇의 기울기와 각속도 역시 0 에 가까이 수렴함을 보였다.
본 연구에서는 전략의 유효성을 보다 정확히 검증하기 위해 Motion Capture 장비를 사용하였다. 특히 기울기를 측정함에 있어 Body 에 Marker를 붙여 적외선 센서로 XYZ 공간상의 좌표를 기울기로 계산하여 Robot에 내장된 기울기 센서를 대체 하였다. 본 논문에서는 안정화 전략 뿐 아니라 Sensing 에 의한 불확정성을 Motion Capture 라는 객관적인 장비를 통해 배재할 수 있고 이를 실시간 사용할 수 있음을 제안한다.
마지막으로 설계한 전략을 실제 로봇에 적용하는 실험을 하였다. 먼저 외란이 없는 상태에서 전략을 적용하지 않고 걸었을 때와, 전략을 적용하고 걸었을 때의 차이점을 분석해본 결과, Normal Walking 시에도 Robot 자체적인 Perturbation 에 의해 초기조건이 (0,0) 이 아님을 관찰하였다. 전략을 적용하여 종전 보다 (0,0)에 가까운 보행 환경이 조성되었음을 Phase Portrait을 통해 확인하였다. 외란은 공을 던짐으로서 가하였고, 외란을 가했을 때 기존 보행 패턴만을 유지한 경우 쉽게 Tip Over 됨을 알았다. 마찬가지로 전략을 적용하고 외란을 가한 경우, Robot Body의 초기조건이 외란에 의해 바뀌었고, Simulation에서 얻은 Control Map에서 적정 벌림 각 를 찾아 지속적인 발 뻗음 동작을 통해 안정화에 성공하였다. 걸음 횟수가 지남에 따라 필요한 벌림 각 는 작아졌고 몸의 기울기와 각속도 역시 줄어 Neutrally stable 의 모습을 확인하였다. 실험을 통해 본 연구에서 제안한 안정화 전략이 유효 함을 증명 하였다.한국과학기술원 : 기계공학전공
실리콘 및 갈륨비소 내의 수소-이중-악셉터 복합체에 대한 연구
No full text학위논문(석사) - 한국과학기술원 : 물리학과, 1992.2, [ [ii], 37 p. ]The results of ab initio pseudopotential calculations to study the energetics of hydrogen-double acceptor complexes in crystalline Si and GaAs are presented. Double acceptors considered here are substitutional Be and Ga antisite in Si and GaAs, respectively. For both monatomic- and diatomic-hydrogen-double acceptor complexes, the C site which corresponds to the middle of the rhombus formed by two neighboring double acceptor-host bonds is found to be energetically most favorable for interstitial H atoms as stable position. Furthermore, these double acceptors are completely passivated by two hydrogen atoms in the form of diatomic-H-double acceptor complexes. Microscopic structures of these diatomic-H-double acceptor complexes are that two hydrogen atoms are positioned at two neighboring C sites. Small lattice relaxations are found for both monatomic- and diatomic-H-double acceptor complexes. In a recently proposed [111] substitutional-interstitial Be pair which was shown to be more stable than a single substitutional Be and is electrically inactive, atomic H is also positioned at the C site. A new hydrogen tunneling path going through a M site is proposed with an energy barrier of 0.4 eV.한국과학기술원 : 물리학과
Entry deterrence in durable-goods monopoly
No full textThere are industries that tend to remain monopolized, with successive generations of a good being introduced by an incumbent monopolist. This paper investigates the tendency of persistent leadership in durable goods industry. In particular it explores the implications of the durability of a good on the pricing and innovation behavior of both the incumbent monopolist and a potential entrant. It is shown that the durability of the good either acts as an entry barrier itself or creates an opportunity for the incumbent firm to deter entry by limit pricing. Moreover, we demonstrate that entry deterrence by limit pricing may cause underinvestment in innovation
A global game with strategic substitutes and complements
No full textWe study a global game in which actions are strategic complements over some region and strategic substitutes over another region. An agent's payoff depends on a market fundamental and the actions of other agents. If the degree of congestion is sufficiently large, agents strategies are non-monotonic in their signal about the market fundamental. In this case, a signal that makes them believe that the market fundamental is more favorable for an action may make them less likely to take the action, because of the risk of overcrowding
- …
