Path integral Monte Carlo with importance sampling for excitons interacting with an arbitrary phonon bath

The reduced density matrix of excitons coupled to a phonon bath at a finite temperature is studied using the path integral Monte Carlo method. Appropriate choices of estimators and importance sampling schemes are crucial to the performance of the Monte Carlo simulation. We show that by choosing the population-normalized estimator for the reduced density matrix, an efficient and physically-meaningful sampling function can be obtained. In addition, the nonadiabatic phonon probability density is obtained as a byproduct during the sampling procedure. For importance sampling, we adopted the Metropolis-adjusted Langevin algorithm. The analytic expression for the gradient of the target probability density function associated with the population-normalized estimator cannot be obtained in closed form without a matrix power series. An approximated gradient that can be efficiently calculated is explored to achieve better computational scaling and efficiency. Application to a simple one-dimensional model system from the previous literature confirms the correctness of the method developed in this manuscript. The displaced harmonic model system within the single exciton manifold shows the numerically exact temperature dependence of the coherence and population of the excitonic system. The sampling scheme can be applied to an arbitrary anharmonic environment, such as multichromophoric systems embedded in the protein complex. The result of this study is expected to stimulate further development of real time propagation methods that satisfy the detailed balance condition for exciton populations.Comment: 16 pages, 5 figure

A Unifying Variational Perspective on Some Fundamental Information Theoretic Inequalities

This paper proposes a unifying variational approach for proving and extending some fundamental information theoretic inequalities. Fundamental information theory results such as maximization of differential entropy, minimization of Fisher information (Cram\'er-Rao inequality), worst additive noise lemma, entropy power inequality (EPI), and extremal entropy inequality (EEI) are interpreted as functional problems and proved within the framework of calculus of variations. Several applications and possible extensions of the proposed results are briefly mentioned

Learning How to Demodulate from Few Pilots via Meta-Learning

Consider an Internet-of-Things (IoT) scenario in which devices transmit sporadically using short packets with few pilot symbols. Each device transmits over a fading channel and is characterized by an amplifier with a unique non-linear transfer function. The number of pilots is generally insufficient to obtain an accurate estimate of the end-to-end channel, which includes the effects of fading and of the amplifier's distortion. This paper proposes to tackle this problem using meta-learning. Accordingly, pilots from previous IoT transmissions are used as meta-training in order to learn a demodulator that is able to quickly adapt to new end-to-end channel conditions from few pilots. Numerical results validate the advantages of the approach as compared to training schemes that either do not leverage prior transmissions or apply a standard learning algorithm on previously received data

The marriage market for immigrant families in Chosŏn Korea after the Imjin War: women, integration, and cultural capital

Challenging the myth of premodern Korea as ethnically homogenous, this study focuses on immigrant marriages in Chosŏn Korea following Japanese invasions (Imjin War, 1592-1598). By examining household registers and genealogies, I investigate the status of women who married into the families of Japanese and Ming Chinese immigrants and the social consequences of such marriages. The results unexpectedly indicate that immigrant families rarely intermarried, preferring integration with local families. As a means of acquiring social and cultural capital, Korean brides from elite families were vital to the success of immigrant families in forming social networks and in producing candidates for the civil service examinations, with failure to obtain such a bride proving a potential long-term obstacle to social advancement. There is a noticeable difference between families of Chinese and Japanese origin in this context due to the preference shown by Korean families for the descendants of Ming generals over Japanese defectors. Contributing to a growing number of studies that question whether the Korean family was fully "Confucianized" in the seventeenth century with a consequent decline in the status of women, this study argues that women possessed social and cultural capital and held particular value for immigrant familie

Power, policy and conflict: the politics of regional system of innovation in Gyeonggi province, South Korea

Academic literature has examined how change in a regional system of innovation involves interactions between various actors that participate in regional economic development. This thesis examines similar processes, but also explores the ways in which various factors characterize change in regional systems of innovation. Without making assumptions about the political nature of the interactions among actors and the contexts surrounding them, the thesis advances the idea of a non-economic approach to the processes of regional development and industrial policy. In this thesis, a strategic relational perspective to regional systems of innovation comprises the conceptual framework that provides an in-depth explanation of the analysis of experiences. The single case study is employed for the operationalization of the strategic-relational perspective in the context of Gyeonggi province, South Korea, as a highly industrialized region in a post catching-up economy. The fieldwork is based on the collection and analysis of interviews and participant observation. The interpretation of empirical evidence through the strategic relational perspective reveals tension in the governance context, which has not met the interests of regional policy makers concerning regional development and industrial policy in Gyeonggi province. Thus, the thesis portrays the parts played by the provincial government in the innovation system affecting innovative capacity and performance, and identifies the political tensions that emerged and that seemed to be important in these processes

The Very Dark Side of Internal Capital Markets: Evidence from Diversified Business Groups in Korea

This paper examines the capital allocation within Korean chaebol firms during the period from 1991 to 2000. We find strong evidence that, during the pre-Asian financial crisis period in the early 1990's, poorly performing firms with less investment opportunities invest more than well-performing firms with better growth opportunities. We also find the evidence of cross-subsidization among firms in the same chaebol group during the pre-crisis period. It appears that the existence of the "dark" side of internal capital markets explains most part of this striking phenomenon where "tunneling" practice has been common during the pre-crisis period. However, the inefficient capital allocation seems to disappear after the crisis as banks gain more power and market disciplines inefficient chaebol firms.