Studies on erythropoiesis II. In vitro studies on red cell proliferation under varied oxygen tension

For the purpose to reveal the mechanism of the stimulated erythropoiesis in anemic condition, the author observed the numerical changes of the erythroblasts from normal rabbit bone marrow cultured under the environment of varied oxygen tensions, and revealed the following: 1. The erythroblasts incubated with air are increased after 24 to 48 hours and decreased gradually disappearing by 120 hours with a corresponding increase of erythrocytes. But no active proliferation of the stem cells or proerythroblasts is observed, all the cells have differentiated to erythrocytes. Hyperoxygen tension suppresses the increase of erythroblasts slightly, while hypoxygen tension stimulates the increase. Data suggest that the cell number destined to be ineffective erythropoiesis is regulated by oxygen tensions of the environment. 2. Basophilic erythroblasts are reduced in number from the beginning showing not any increasing tendency. The reducing rate is almost the same among those cultured under the hypo- and hyperoxygen tension, comparable to that incubated with air. 3. The hypoxygen tension brings about a marked increase in the number of orthochromatic erythroblasts with a decrease in polychromatic erythroblasts suggesting an accelerated cell differentiation, while the hyperoxygen tension elicits the suppression in the formation of orthochromatic erythroblasts with suppressed differentiation. Data also show the lack of denucleation mechanism in polychromatic stages in vitro differing from the case of the bone marrow of anemic animal.</p

Optical properties of unconventional superconductors

The optical conductivity measurements give a powerful tool to investigate the nature of the superconducting gap for conventional and unconventional superconductors. In this article, first, general analyses of the optical conductivity are given stemmed from the Mattis-Bardeen formula for conventional BCS superconductors to unconventional anisotropic superconductors. Second, we discuss the reflectance-transmittance (R-T) method which has been proposed to measure far-infrared spectroscopy. The R-T method provides us precise measurements of the frequency-dependent conductivity. Third, the optical conductivity spectra of the electron-doped cuprate superconductor Nd_{2-x}Ce_xCuO_4 are investigated based on the anisotropic pairing model. It is shown that the behavior of optical conductivity is consistent with an anisotropic gap and is well explained by the formula for d-wave pairing in the far-infrared region. The optical properties of the multiband superconductor MgB_2, i n which the existence of superconductivity with relatively high-T_c (39K) was recently announced, is also examined to determine the symmetry of superconducting gaps.Comment: 44 pages, 15 figure

The effects of costly exploration on optimal investment timing

This paper investigates a principal-agent model in which an owner (principal) optimizes a contract with a manager (agent) delegated to undertake an investment project. In the model, we explore the effects of costly exploration by which the manager learns the real value of development cost. We show that high exploration cost can lead to a pooling policy not contingent on project type. Further, and more notably, we show that, in the presence of asymmetric information, higher exploration cost leads to wealth transfer from owner to manager and can then play a positive role in preventing a greedy contract by the owner and improving social welfare.Real Options; Asymmetric Information; Costly Learning; Sequential Investment; Incentive Theory

Dynamic Model of Credit Risk in Relationship Lending: A Game- theoretic Real Options Approach

We develop a dynamic credit risk model for the case that banks compete to collect their loans from a firm falling in danger of bankruptcy. We apply a game-theoretic real options approach to investigate bankfs optimal strategies. Our model reveals that the bank with the larger loan amount, namely the main bank, provides an additional loan to support the deteriorating firm when the other bank collects its loan. This suggests that there exists rational forbearance lending by the main bank. Comparative statics show that as the liquidation value is lower, the optimal exit timing for the non-main bank comes at an earlier stage of business downturn and the optimal liquidation timing by the main bank is delayed further. As the interest rate of the loan is lower, the optimal exit timing for the non-main bank comes earlier. These analyses are consistent with the forbearance lending and exposure concentration of main banks observed in Japan.Credit risk, Relationship lending, Real option, Game theory, Concentration risk

Dynamic Model of Credit Risk in Relationship Lending: A Game- Theoretic Real Options Approach

We develop a dynamic credit risk model for the case in which banks compete to collect their loans from a firm in danger of bankruptcy. We apply a game-theoretic real options approach to investigate banksf optimal strategies. Our model reveals that the bank with the larger loan amount, namely, the main bank, provides an additional loan to support the deteriorating firm when the other bank collects its loan. This suggests that there exists rational forbearance lending by the main bank. Comparative statics show that as the liquidation value is lower, the optimal exit timing for the nonmain bank comes at an earlier stage in the business downturn and the optimal liquidation timing by the main bank is delayed further. As the interest rate of the loan is lower, the optimal exit timing for the non-main bank comes earlier. These analyses are consistent with the forbearance lending and exposure concentration of main banks observed in Japan.Credit risk; Relationship lending; Real option; Game theory; Concentration risk

Location of the innermost stable circular orbit of binary neutron stars in the post Newtonian approximations of general relativity

In this paper, we present results obtained from our recent studies on the location of the innermost stable circular orbit (ISCO) for binary neutron stars (BNSs) in several levels of post Newtonian (PN) approximations. We reach the following conclusion at present: (1) even in the Newtonian case, there exists the ISCO for binary of sufficiently stiff equation of state (EOS). If the mass and the radius of each star are fixed, the angular velocity at the ISCO $\Omega_{ISCO}$ is larger for softer EOS: (2) when we include the first PN correction, there appear roughly two kinds of effects. One is the effect to the self-gravity of each star of binary and the other is to the gravity acting between two stars. Due to the former one, each star of binary becomes compact and the tidal effect is less effective. As a result, $\Omega_{ISCO}$ tends to be increased. On the other hand, the latter one has the property to destabilize the binary orbit, and $\Omega_{ISCO}$ tends to be decreased. If we take into account both effects, however, the former effect is stronger than the latter one, and $\Omega_{ISCO}$ becomes large with increase of the 1PN correction: (3) the feature mentioned above is more remarkable for softer EOS if the mass and radius are fixed. This is because for softer EOS, each star has the larger central density and is susceptible to the GR correction: (4) there has been no self consistent calculation including all the 2PN effects and only exist studies in which one merely includes the effect of the 2PN gravity acting between two stars. In this case, the effect has the property to destabilize the binary orbit, so that $\Omega_{ISCO}$ is always smaller than that for the Newtonian case. If we include the PN effect of the self-gravity to each star, $\Omega_{ISCO}$ will increase.Comment: 33 pages ptptex file, 29 figures, to appear in Progress of Theoretical Physics Supplement No.128 (1997) `Perturbative and Numerical Approaches to Gravitational Radiation

Optimal Timing of Environmental Policy under Asymmetric Information

This paper examines the optimal timing strategy of environmental policy in the presence of agency conflict due to asymmetric information. When the policy maker delegates the adoption of environmental policy to agents, contracts must be designed to provide incentive for agents to truthfully reveal private information. Using a contingent claims approach, this paper shows that an underlying option value of social welfare can be decomposed into two components: a policy maker’s option and an agent’s option. The value of social welfare in the asymmetric information setting is strictly lower than that in the full-information setting. In particular, the implied adoption strategy in the asymmetric information setting differs significantly from that in the full-information setting