"Voluntarily Separable Prisoner's Dilemma with Reference Letters"

We consider voluntarily separable repeated Prisoner's Dilemma in which a pair of players meet randomly and repeatedly play Prisoner's Dilemma only by mutual agreement. Fujiwara-Greve and Okuno-Fujiwara (2007) consider the case that once a partnership is dissolved there is no information flow to other partnerships. We consider the case that players can issue a reference letter to the partner if they entered cooperation periods, but the content of a letter is not verifiable. We show that the sheer existence of a letter shortens the trust-building periods of new matches and thus improves efficiency in equilibrium.

Product Architecture as a Coordination System (Japanese)

Baldwin and Clark (2000) brought the substantial attention to the concept of product architecture. This concept, particularly the concept of module architecture, defines a product system as a "coordination system," taking the viewpoint that a product system is an object that is used by human users or developed by human developers. In this paper, product architecture is defined as a design concept for a product system that calls for complex part-to-part coordination in order to fulfill the user's objectives, whereby we seek to show that module architecture can clarify (1) the functions of a product, and (2) the relationship between users' commands and corresponding product actions. By doing so, it becomes possible for human users or developers, whose actions and behaviors are instinctively "context dependent," to operate and use highly complex systems as well as to design and develop new systems by seeking an appropriate combination of division of labor and collaboration between human beings and product systems.

The Role of Money in Supporting the Pareto Optimality of Competitive Equilibrium in Consumption-Loan Type Models

Perhaps the single most enduring theme in economics is that of the social desirability of the competitive mechanism. In its modern form, this theme occurs as the two basic theorems of welfare economics (see, in particular, Arrow). Our central concern in this paper is with the validity of the first of these two theorems—that every competitive equilibrium yields a Pareto optimal allocation—in idealized yet plausible models of intertemporal allocation in a market economy

Robust prognostic prediction model developed with integrated biological markers for acute myocardial infarction

Commonly used prediction methods for acute myocardial infarction (AMI) were created before contemporary percutaneous coronary intervention was recognized as the primary therapy. Although several studies have used machine learning techniques for prognostic prediction of patients with AMI, its clinical application has not been achieved. Here, we developed an online application tool using a machine learning model to predict in-hospital mortality in patients with AMI. A total of 2, 553 cases of ST-elevation AMI were assigned to 80% training subset for cross validation and 20% test subset for model performance evaluation. We implemented random forest classifier for the binary classification of in-hospital mortality. The selected best feature set consisted of ten clinical and biological markers including max creatine phosphokinase, hemoglobin, heart rate, creatinine, systolic blood pressure, blood sugar, age, Killip class, white blood cells, and c-reactive protein. Our model achieved high performance: the area under the curve of the receiver operating characteristic curve for the test subset, 0.95: sensitivity, 0.89: specificity, 0.91: precision, 0.43: accuracy, 0.91 respectively, which outperformed common scoring methods. The freely available application tool for prognostic prediction can contribute to risk triage and decision-making in patient-centered modern clinical practice for AMI

Three-dimensional flow visualization system by holographic interferometry

A holographic system has been developed to visualize a three-dimensional fluid flow. The system consists principally of a thermoplastic film, a monochrome video camera, a microcomputer with image-processing capability and a printer. The system makes it possible to measure a slow flow. Two examples of such, the bimodal mixed-mode convection flows within a Bénard cell, are presented

"Bubble Economy and Financial System Failures After Its Crush: Form the Viewpoint of '1975' Regime"(in Japanese)

We analyze the performance of the Japanese Economy in the last 30 years. We do so by emphasizing the fact that an economy is a social system and people are concerned with social values and norms. We point out that the employment security, which became socially guaranteed during the aftermath of the first oil shock, and the coercion of unitarism, rather than plurarism, became prevalent in this period. These factors are behind the birth and continuation of financial bubble in the late 80's as well as the indecisiveness of financial policies in the 90's. They also positively affected the competitiveness of exporting industries but negatively affected regulated and non-tradable industries by regulation captures and accumulation of political rents. What is needed in Japan is to revive a value system that allow plural ways of thinking and improve adaptability.

"Communication and Coordination in Organizations" (in Japanese)

This paper analyzes a model of coordination where two agents attempt to coordinate their actions through communication. One agent (Sender) is engaged in finding the true state of nature in a stochastic environment and the action that best fits the state. The other agent (Receiver) in turn tries to ``understand'' the Sender's message and chooses his own action. Since the communication succeeds only probilistically, so does the coordination. In our model, two different modes of coordination are identified: the integral-type coordination based on the communication of soft information and the default-type coordination based on the predetermined default value. We find that the agents might choose the latter mode of coordination when the cost arising from the failed communication is high relative to the benefit from coordinating on the state-contingent best actions. Applications to the economics of organization are also discussed.