A THEORY OF DIGITAL DIVIDE: WHO GAINS AND LOSES FROM TECHNOLOGICAL CHANGES?

This paper attempts to answer the question: How does the income gap between workers and capitalists evolve over time in the period of ITC and globalization increasing international technology creation and transfers? The model bases on a Romer¡¯s type of variety expansion of intermediate goods. We assume that there are two types of agents supplying two different types of factors. Workers supply specific skill weighted labor by accumulating their specific skills that depreciate with an introduction of new intermediate goods. The other type of agents, R&D agents, produce and sell new varieties of intermediate goods monopolistically after inventing them. The model yields: Depending on the elasticity of substitution between the two factors and on the value of the factor share, an increase in the efficiency of technology creation (or lowering the barriers on the imports of intermediate goods) affects the growth rates of workers¡¯ and R&D agents¡¯ average income differently. First, if the elasticity of substitution is greater than one, in a certain stage of development, an advance in ITC or ¡®globalization¡¯ increases the growth rate of R&D agents¡¯ average income, while it decreases that of workers¡¯. Thus, the ¡®Digital Divide¡¯ happens. Conversely, if the elasticity of substitution is less than one, the result will be reversed. These results are intuitively obvious. Second, if an economy develops from a higher factor share of the workers to a sufficiently lower one, the growth rates of GNP, and the average incomes of both workers and R&D agents increase over time.Romer¡¯s Model, R&D, Specific Skill, Digital Divide

Two-Layered Superposition of Broadcast/Multicast and Unicast Signals in Multiuser OFDMA Systems

We study optimal delivery strategies of one common and $K$ independent messages from a source to multiple users in wireless environments. In particular, two-layered superposition of broadcast/multicast and unicast signals is considered in a downlink multiuser OFDMA system. In the literature and industry, the two-layer superposition is often considered as a pragmatic approach to make a compromise between the simple but suboptimal orthogonal multiplexing (OM) and the optimal but complex fully-layered non-orthogonal multiplexing. In this work, we show that only two-layers are necessary to achieve the maximum sum-rate when the common message has higher priority than the $K$ individual unicast messages, and OM cannot be sum-rate optimal in general. We develop an algorithm that finds the optimal power allocation over the two-layers and across the OFDMA radio resources in static channels and a class of fading channels. Two main use-cases are considered: i) Multicast and unicast multiplexing when $K$ users with uplink capabilities request both common and independent messages, and ii) broadcast and unicast multiplexing when the common message targets receive-only devices and $K$ users with uplink capabilities additionally request independent messages. Finally, we develop a transceiver design for broadcast/multicast and unicast superposition transmission based on LTE-A-Pro physical layer and show with numerical evaluations in mobile environments with multipath propagation that the capacity improvements can be translated into significant practical performance gains compared to the orthogonal schemes in the 3GPP specifications. We also analyze the impact of real channel estimation and show that significant gains in terms of spectral efficiency or coverage area are still available even with estimation errors and imperfect interference cancellation for the two-layered superposition system

"Effects of Stochastic Interest Rates and Volatility on Contingent Claims (Revised Version)"

We investigate the effects of the stochastic interest rates and the volatility f the underlying asset price on the contingent claim prices including futures and options prices. The futures price can be decomposed into the forward price and the additional terms and the options price can be decomposed into the Black-Scholes formula and several additional terms via the asymptotic expansion approach in the small disturbance asymptotics developed by Kunitomo and Takahashi(1995,1998,2001), which is based on Malliavin-Watanabe Calculus in stochastic analysis. We illustrate our new formulae and their numerical accuracy by using some modi ed CIR type processes for the short term interest rates and stochastic volatility.

Technological Change, Investment in Human Capital, and Economic Growth

This paper presents a theoretical model to analyze the effects of technology change on growth rates of income and human capital. We set up an overlapping generations model in which young agents invest in both width and depth of human capital in order to adopt new technologies. The model develops explicitly the micro-mechanism of the role of human capital in adopting new technologies as well as that of the process of human capital production. In our model an increase in the technology uncertainty decreases growth rates of income and human capital by lowering efficiencies both in creating new knowledge and in adopting new technologies. We also show that, depending on the initial structure of human capital and the uncertainty about the nature of new technologies, an economy can have multiple growth paths. Hence, increased inflows of new technologies with more uncertain characteristics may affect human capital accumulation and income growth adversely, leading the economy to a low growth trap. Keywords: education, endogenous growth, human capital investment, technology adoption.

Characteristics and applications of the short external cavity laser diode

The characteristics of the external cavity laser diode are investigated. Emphasis is placed on the short external cavity configuration. The general governing model equations which include the multiple reflection effect are derived. It is shown that the coupling coefficient becomes a complex function of the external cavity length and the near field beam size of the laser diode due to the diffraction loss of an open resonator. The validity of this open resonator model is proven experimentally by the asymmetry in optical power versus external cavity length characteristic curve. For analysis of the ultra short external cavity laser, it is necessary to include this complex coupling coefficient. As an example, the flying optical disk head is studied using this model. In some cases, especially when the external cavity length is longer than several micrometers, the external cavity may be simply regarded as a lossy resonator. With this constant loss per roundtrip approximation, the feedback operator can be reduced to the closed form. The stationary and transient solutions are investigated analytically and numerically. The single mode condition, and dynamical stability condition are derived. Also, the simple expression for the relaxation oscillation frequency of the short external cavity laser is given for the first time. With our model, it can not be expected to find the strange attractor for the constant biased autonomous operation. However, the chaotic behavior in the current modulated nonautonomous operation is investigated. It seems that the route to chaos in this system is not limited to the period-doubling route, which has been believed as the only route in the modulated solitary laser diode so far. Generally, it is suggested that the operating external cavity length should be close to the constructive interference position, as it will give superior properties. Some experimental results applying the short external cavity laser as a laser diode sensor are given