Phase-field investigation on the non-equilibrium interface dynamics of rapid alloy solidification

The departure from the equilibrium solid concentration at the solid-liquid interface was often observed during rapid solidification. The energetic associated non-equilibrium solute partitioning has been treated in detail, providing possible ranges of interface concentrations for a given growth condition. For analytical description of specific single-phase dendritic and cellular operating point selection, analytical models for solute partitioning under a given set of growth conditions have been developed and widely utilized in most of the theoretical investigations of rapid solidification. However, these solute trapping models are not rigorously verified due to the difficulty in experimentally measuring under rapid growth conditions. Moreover, since these solute trapping models include kinetic parameters which are difficult to directly measure from experiments, application of the solute trapping models or the associated analytic rapid solidification model is limited. These theoretical models for steady state rapid solidification which incorporate the solute trapping models do not describe the interdependency of solute diffusion, interface kinetics, and alloy thermodynamics. This research program is focused on critical issues that represent conspicuous gaps in current understanding of rapid solidification, limiting our ability to predict and control microstructural evolution at high undercooling, where conditions depart significantly from local equilibrium. Through careful application of phase-field modeling, using appropriate thin-interface and anti-trapping corrections and addressing important details such as transient effects and a velocity-dependent numerics, the current analysis provides a reasonable simulation-based picture of non-equilibrium solute partitioning and the corresponding oscillatory dynamics associated with single-phase rapid solidification and show that this method is a suitable means for a self-consistent simulation of transient behavior and operating point selection under rapid growth conditions. Moving beyond the limitations of conventional theoretical/analytical treatments of non-equilibrium solute partitioning, these results serve to substantiate recent experimental findings and analytical treatments for single-phase rapid solidification. In addition, the simulations carried out here predict, for the first time, the full scope of behavior, from the initial transient to the steady-state conditions, where departure from equilibrium partitioning may lead to oscillations in composition, velocity, and interface temperature or may lead to a far-from-equilibrium steady-state. Such predictive capability is a necessary prerequisite to more comprehensive modeling of morphological evolution and, therefore, of significant importance

"Suicide and Life Insurance"

In this paper, we investigate the nexus between life insurance and suicide behavior using OECD cross-country data from 1980 to 2002. Through semiparametric instrumental variable regressions with fixed effects, we find that for the majority of observations, there exists a positive relationship between suicide rate and life insurance density (premium per capita). Since life insurance policies pay death benefits even in suicide cases after the suicide exemption period, the presence of adverse selection and moral hazard suggests an incentive effect that leads to this positive relationship. The novelty of our analysis lies in the use of cross-country variations in the length of the suicide exemption period in life insurance policies as the identifying instrument for life insurance density. Our results provide compelling evidence suggesting the existence of adverse selection and moral hazards in life insurance markets in OECD countries.

"Joint Liability Borrowing and Suicide"

This paper shows that joint liability borrowing may put too much pressure on the borrower, mainly through the stigma in case of repayment failure, and leads to a vexing outcome|the suicide of the borrower. We provide a model of joint liability borrowing which facilitates credit market transaction ex ante but may induce suicides ex post in the bad state. We introduce some supportive evidence from a suicide survey in Japan.

"How Is Suicide Different in Japan?"

In this study, we analyze suicide rates among OECD countries with a particular effort made to gain insight into how suicide in Japan is different from suicides in other OECD countries. Several findings emerged from fixed effect panel regressions with country specific time-trend. First, the impacts of socioeconomic variables vary across different age-gender groups. Second, in general, better economic conditions such as high level of income and higher economic growth reduce suicide rate while income inequality increases suicide rate. Third, suicide rate is more sensitive to the economic factors captured by real GDP per capita, growth rate of real GDP per capita, and Gini index than to the social factors represented by divorce rate, birth rate, female labor participation rate, and alcohol consumption. Fourth, female and elderly generation suicides are more difficult to be accounted for. Finally, in accordance to the general belief, the suicide problem in Japan is very different from those of the other OECD countries. The impact of socioeconomic variables is greater in Japan than in other OECD countries. Moreover, the empirical result of significant Gini index in Japan is consistent with individuals' aversion to inequality and relative deprivation discussed in the recent literature.

"Those Who Are Left Behind: An Estimate of the Number of Family Members of Suicide Victims in Japan"

This paper contributes to the literature of suicide studies by presenting procedures and its estimates of the number of family members who lose their loved ones to suicide. Using Japanese aggregate level data, three main findings emerge: first, there are approximately five bereaved family members per suicide; second, in 2006, there were about 90,000 children who had lost a parent to suicide; and third, in 2006, there were about three million living family members who had lost a loved one to suicide. The direct production loss of bereaved family members in 2006 alone is estimated at approximately 197 million USD. These results are valuable in evaluating the cost-effectiveness of suicide prevention programs and in designing appropriate policy instruments.

Degradation of perchloroethylene and nitrate by high-activity modified green rusts

Green rusts (GRs), a group of layered Fe(II)-Fe(III) hydroxide salts, have been observed to be effective reductants for degrading organic and inorganic contaminants under suboxic conditions. Furthermore, the addition of a transition metal to GRs can produce high-activity modified green rusts (HMGRs) that demonstrate higher degradation rates. Methods of modifying GRs to obtain high reactivity for degradation of PCE and nitrate were developed and reduction kinetics of PCE and nitrate by HMGRs were characterized in this study. First, the most promising HMGRs were developed through screening tests. GRs modified with Pt, Cu, Ag, or Pb were found to be effective in improving degradation rates of PCE. GR-F(Pt) and GR-F(Cu) were chosen because they showed high reactivity and produced non-chlorinated by-products. Pt and Cu showed the capability of improving reduction kinetics of nitrate by GRs. GR-F(Pt) and GR-F(Cu) were selected for further study. Second, degradation of PCE by GR-F(Cu) and GR-F(Pt) was characterized using a batch reactor system. The reaction kinetics of PCE degradation by GR-F(Cu) and GR-F(Pt) was strongly dependent on pH over the range of pH 7.5-11, with the fastest rate at pH 11. Increasing concentrations of Cu(II) over the range of 0 to 5 mM resulted in improving the reduction kinetics by a factor of more than 400, although the rate at 7.5 mM of Cu(II) was unexpectedly lower than that at 5 mM. Surface saturation behavior was observed in the rates of dechlorination of PCE by GR-F(Cu). Finally, nitrate reduction by GR-F(Cu) and GR-F(Pt) was further studied to determine the effects on degradation rates of pH, Cu(II) addition, and initial nitrate concentration. A reaction model with four sequential steps was proposed to describe the process of nitrate being reduced to ammonium and GR being oxidized to magnetite. The reaction rates of nitrate reduction by GR-F(Cu) and GR-F(Pt) was highest at pH 9. The reaction rates of GR-NO3 were improved by three orders of magnitude when Cu(II) was added in the range of 0 to 2.5 mM, while reaction rate decreased at concentrations above 2.5 mM. Saturation behavior was also observed in nitrate reduction by GR-F(Cu)

"The Jump, Inertia, and Juvenization of Suicides in Japan"

This article investigates the abrupt jump in the number of suicide cases in Japan in 1998 and the subsequent persistency of this figure by utilizing a generalized decomposition formula. In particular, by considering the change in the demographic structure, we decompose the 1998 jump in the number of suicides and the cumulative changes from 1998 to 2007 by age and gender. Our results show that while the abrupt jump in the number of suicides in 1998 is mainly attributed to middleaged males, who are 40 to 59 years old, the consistently high number of suicides after 1998 is because of the suicides of people from the younger generation, i.e., the age group from 20 to 39 years. This "juvenization" in suicides is also reflected by the change in the means for committing suicide. Finally, aging is also identified as an impediment in combating the high suicide numbers.

Topology of Luminous Red Galaxies from the Sloan Digital Sky Survey

We present measurements of the genus topology of luminous red galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS) Data Release 7 catalog, with unprecedented statistical significance. To estimate the uncertainties in the measured genus, we construct 81 mock SDSS LRG surveys along the past light cone from the Horizon Run 3, one of the largest N-body simulations to date that evolved 7210^3 particles in a 10815 Mpc/h size box. After carefully modeling and removing all known systematic effects due to finite pixel size, survey boundary, radial and angular selection functions, shot noise and galaxy biasing, we find the observed genus amplitude to reach 272 at 22 Mpc/h smoothing scale with an uncertainty of 4.2%; the estimated error fully incorporates cosmic variance. This is the most accurate constraint of the genus amplitude to date, which significantly improves on our previous results. In particular, the shape of the genus curve agrees very well with the mean topology of the SDSS LRG mock surveys in the LCDM universe. However, comparison with simulations also shows small deviations of the observed genus curve from the theoretical expectation for Gaussian initial conditions. While these discrepancies are mainly driven by known systematic effects such as those of shot noise and redshift-space distortions, they do contain important cosmological information on the physical effects connected with galaxy formation, gravitational evolution and primordial non-Gaussianity. We address here the key role played by systematics on the genus curve, and show how to accurately correct for their effects to recover the topology of the underlying matter. In a forthcoming paper, we provide an interpretation of those deviations in the context of the local model of non-Gaussianity.Comment: 23 pages, 18 figures. APJ Supplement Series 201