Asymmetric impacts of near-Earth asteroids on the Moon

Recent lunar crater studies have revealed an asymmetric distribution of rayed craters on the lunar surface. The asymmetry is related to the synchronous rotation of the Moon: there is a higher density of rayed craters on the leading hemisphere compared with the trailing hemisphere. Rayed craters represent generally the youngest impacts. The purpose of this paper is to test the hypotheses that (i) the population of Near-Earth asteroids (NEAs) is the source of the impactors that have made the rayed craters, and (ii) that impacts by this projectile population account quantitatively for the observed asymmetry. We carried out numerical simulations of the orbital evolution of a large number of test particles representing NEAs in order to determine directly their impact flux on the Moon. The simulations were done in two stages. In the first stage we obtained encounter statistics of NEAs on the Earth's activity sphere. In the second stage we calculated the direct impact flux of the encountering particles on the surface of the Moon; the latter calculations were confined within the activity sphere of the Earth. A steady-state synthetic population of NEAs was generated from a debiased orbital distribution of the known NEAs. We find that the near-Earth asteroids do have an asymmetry in their impact flux on the Moon: apex-to-antapex ratio of 1.32 +/- 0.01. However, the observed rayed crater distribution's asymmetry is significantly more pronounced: apex-to-antapex ratio of 1.65 +/- 0.16. Our results suggest the existence of an undetected population of slower (low impact velocity) projectiles, such as a population of objects nearly coorbiting with Earth; more observational study of young lunar craters is needed to secure this conclusion.Comment: 16 pages, 7 figures, accepted for publication in Astronomy & Astrophysic

Weather Risk and the Off-­Farm Labor Supply of Agricultural Households in India

As one of the measures to smooth income, this paper focuses on the diversification of labor allocation across activities. A key feature of this paper is that it pays particular attention to differences in the covariance between weather risk and agricultural wages and between weather risk and nonagricultural wages. We estimate a multivariate tobit model of labor allocation using household data from rural areas of Bihar and Uttar Pradesh, India. The regression results show that the share of the off­farm labor supply increases with the weather risk, and the increase is much larger in the case of nonagricultural wage work than in the case of agricultural wage work. Simulation results based on the regression estimates show that the sectoral difference is substantial, implying that empirical and theoretical studies on farmers' labor supply response to risk should distinguish between the types of off-­farm work involved.covariate risk, nonfarm employment, selfemployment, food security, India, Labor and Human Capital, Q12, O15, J22,

Weather Risk, Wages in Kind, and the Off-Farm Labor Supply of Agricultural Households in a Developing Country

This paper investigates the effects of weather risk on the off-farm labor supply of agricultural households in a developing country. Faced with the uninsurable risk of output and food price fluctuations, poor farmers in developing countries may diversify labor allocation across activities in order to smooth income in real terms.A key feature of this paper is that it distinguishes different types of off-farm labor markets: agriculture and nonagriculture on the one hand, and, wages paid in cash and wages paid in kind on the other. We develop a theoretical model of household optimization, which predicts that when farmers are faced with more production risk in their farm production, they find it more attractive to engage in nonagricultural work as a means of risk diversification, but the agricultural wage sector becomes more attractive when food security is an important issue for the farmers and agricultural wages are paid in kind. To test this prediction, we estimate a multivariate twolimit tobit model of labor allocation using household data from rural areas of Bihar and Uttar Pradesh, India. The regression results show that the share of the off-farm labor supply increases with weather risk, the increase is much larger in the case of nonagricultural work than in the case of agricultural wage work, and the increase is much larger in the case of agricultural wages paid in kind than in the cash wage case. Simulation results based on the regression estimates show that the sectoral difference is substantial, implying that empirical and theoretical studies on farmers' labor supply response to risk should distinguish between the types of off-farm work involved.covariate risk, non-farm employment, self-employment, food security, India

Nuclear dynamics in time-dependent picture

Using the time-dependent theory of quantum mechanics, we investigate nuclear electric dipole responses. The time evolution of a wave function is explicitly calculated in the coordinate-space representation. The particle continuum is treated with the absorbing boundary condition. Calculated time-dependent quantities are transformed into those of familiar energy representation. We apply the method to a three-body model for 11Li and to the mean-field model for 22O, then discuss properties of E1 response.Comment: 6 pages, 2 figures, Talk at the Sixth China Japan Joint Nuclear Physics Symposium, Shanghai, China, May 16-20, 200