Hokkaido University

About: Hokkaido University is a education organization based out in Sapporo, Hokkaidô, Japan. It is known for research contribution in the topics: Catalysis & Population. The organization has 53925 authors who have published 115403 publications receiving 2651647 citations. The organization is also known as: Hokudai & Hokkaidō daigaku.

Mechanism of the mild functionalization of arenes by diboron reagents catalyzed by iridium complexes. Intermediacy and chemistry of bipyridine-ligated iridium trisboryl complexes.

Abstract: This paper describes mechanistic studies on the functionalization of arenes with the diboron reagent B2pin2 (bis-pinacolato diborane(4)) catalyzed by the combination of 4,4‘-di-tert-butylbipyridine (dtbpy) and olefin-ligated iridium halide or olefin-ligated iridium alkoxide complexes. This work identifies the catalyst resting state as [Ir(dtbpy)(COE)(Bpin)3] (COE = cyclooctene, Bpin = 4,4,5,5-tetramethyl-1,3,2-dioxaborolanyl). [Ir(dtbpy)(COE)(Bpin)3] was prepared by independent synthesis in high yield from [Ir(COD)(OMe)]2, dtbpy, COE, and HBpin. This complex is formed in low yield from [Ir(COD)(OMe)]2, dtbpy, COE, and B2pin2. Kinetic studies show that this complex reacts with arenes after reversible dissociation of COE. An alternative mechanism in which the arene reacts with the Ir(I) complex [Ir(dtbpy)Bpin] after dissociation of COE and reductive elimination of B2pin2 does not occur to a measurable extent. The reaction of [Ir(dtbpy)(COE)(Bpin)3] with arenes and the catalytic reaction of B2pin2 with arene...

The Group as the Container of Generalized Reciprocity

Abstract: The results of an experiment with 91 Japanese participants confirmed the hypothesis that players of a Prisoner's Dilemma game would cooperate more with an in-group member than with an out-group member in the simultaneous game but not in the sequential game. The game used in the experiment was constructed such that each player gave his or her partner a portion of his or her own endowment of 300 yen. The group membership was created on the basis of participant's preferences for Klee's or Kandinski's paintings; each participant played the game once with an in-group member and once with an out-group member. In the simultaneous game, the two players decided simultaneously how much to give to the partner without knowing what the partner would do. In the sequential game, the first player made the decision; then the second player followed with full information on the first player's behavior. All the participants in the sequential game in fact took the role of the first player. The differential effect of the partner's group membership had been predicted on the basis of Yamagishi and his colleagues' argument that expectations of generalized reciprocity from in-group members is the source of in-group favoritism in a minimal group. A group is clearly distinguished from a mere aggregate of people. People who sit in the waiting area of an airport, for example, hardly constitute a group, nor do all people who wear eyeglasses. They share certain characteristics such as sitting in the same place or wearing eyeglasses, but this does not make them a group. The defining feature

Dust in the Early Universe: Dust Formation in the Ejecta of Population III Supernovae

Abstract: Dust grains play a crucial role in the formation and evolution history of stars and galaxies in the early universe. We investigate the formation of dust grains in the ejecta of Population III supernovae, including pair-instability supernovae, which are expected to occur in the early universe, applying a theory of non-steady state nucleation and grain growth. Dust formation calculations are performed for core-collapse supernovae with progenitor mass Mpr ranging from 13 to 30 M? and for pair-instability supernovae with Mpr = 170 and 200 M?. In the calculations, the time evolution of gas temperature in the ejecta, which strongly affects the number density and size of newly formed grains, is calculated by solving the radiative transfer equation, taking account of the energy deposition of radioactive elements. Two extreme cases are considered for the elemental composition in the ejecta, unmixed and uniformly mixed cases within the He core, and formation of CO and SiO molecules is assumed to be complete. The results of calculations for core-collapse supernovae and pair-instability supernovae are summarized as follows: in the unmixed ejecta, a variety of grain species condense, reflecting the difference of the elemental composition at the formation site in the ejecta; otherwise only oxide grains condense in the uniformly mixed ejecta. The average size of newly formed grains spans a range of 3 orders of magnitude, depending on the grain species and the formation condition, and the maximum radius is limited to less than 1 ?m, which does not depend on the progenitor mass. The size distribution function of each grain species is approximately lognormal, except for Mg silicates, MgO, Si, and FeS in the unmixed case and Al2O3 in both cases. The size distribution function summed up over all grain species is approximated by a power-law formula whose index is -3.5 for the larger radius and -2.5 for the smaller one; the radius at the crossover point ranges from 0.004 to 0.1 ?m, depending on the model of supernovae. The fraction of mass locked into dust grains increases with increasing the progenitor mass: 2%-5% of the progenitor mass for core-collapse supernovae and 15%-30% for pair-instability supernovae whose progenitor mass ranges from 140 to 260 M?. Thus, if very massive stars populated the first generation of stars (Population III stars), a large amount of dust grains would be produced in the early universe. We also discuss the dependence of the explosion energy and the amount of 56Ni in the ejecta, as well as the efficiency of formation of CO and SiO molecules, on the formation of dust grains in the ejecta of supernovae.