Comments on "Angular Momentum Transport in Quasi-Keplerian Accretion Disks"

Subramanian, Pujari and Becker (2004) claim that the correct expression for the angular momentum transport in an accretion disc, which is proportional to dOmega/dR, can be derived on the basis of the analysis of the epicyclic motion of gas parcels in adjacent eddies in the disc. We study their argument and show that their derivation contains several fundamental errors: 1) the biased choice of the desired formula from an infinite number of formulae; 2) the biased choice of parcel trajectories; and 3) confusion regarding the reference frames. Following 1) we could derive, for example, a (invalid) formula in which the angular momentum transport is proportional to dv_phi/dR, and from 2) we could even prove that the angular momentum transport is either inward or null. We present the correct approach to the problem of angular momentum transport in an accretion disc in terms of mean free path theory.Comment: 9 pages, 2 figures, to appear in Prog. Theor. Phys. Vol.113, No.6, 200

Deformation of hypernuclei studied with antisymmetirzed molecular dynamics

An extended version of the antisymmetrized molecular dynamics to study structure of $p$-$sd$ shell hypernuclei is developed. By using an effective $\Lambda N$ interaction, we investigate energy curves of $^9_\Lambda$Be, $^{13}_\Lambda$C and $^{20,21}_\Lambda$Ne as function of nuclear quadrupole deformation. Change of nuclear deformation caused by $\Lambda$ particle is discussed. It is found that the $\Lambda$ in p-wave enhances nuclear deformation, while that in s-wave reduces it. This effect is most prominent in $^{13}_\Lambda$C. The possibility of the parity inversion in $^{20}_\Lambda$Ne is also examined

Modification of triaxial deformation and change of spectrum in $^{25}_{\ \Lambda}MgcausedbyMg caused by \Lambda$ hyperon

The positive-parity states of $^{25}_{\ \Lambda}$Mg with a $\Lambda$ hyperon in $s$ orbit were studied with the antisymmetrized molecular dynamics for hypernuclei. We discuss two bands of $^{25}_{\ \Lambda}$Mg corresponding to the $K^\pi=0^+$ and $2^+$ bands of $^{24}$Mg. It is found that the energy of the $K^\pi = 2^+ \otimes \Lambda_s$ band is shifted up by about 200 keV compared to $^{24}$Mg. This is because the $\Lambda$ hyperon in $s$ orbit reduces the quadrupole deformation of the $K^\pi = 0^+ \otimes \Lambda_s$ band, while it does not change the deformation of the $K^\pi = 2^+ \otimes \Lambda_s$ band significantly.Comment: 19 pages, 3 figure

When Are Uninformed Boards Preferable?

In this paper, I analyze the optimal choice of board of directors using the dual- role model of boards in Adams and Ferreira (2007). In my model, shareholders choose either an informed board that brings additional private information to the firm or an uninformed board that merely considers the inside information already available within the firm. The board then randomly chooses a good chief executive officer (CEO) with inside information or a bad CEO without such information, and the CEO decides whether to consult with the board when making a project decision. I show that shareholders generally choose the informed board to maximize firm value by utilizing the private information available to the board. However, the shareholders optimally select the uninformed board if the CEO is reluctant to communicate with the informed board for fear it will reject the CEO’s decision. The uninformed board is also optimal when the board has a sufficiently large private benefit of monitoring the CEO, the shareholders feel burdened by any conflict between the CEO and the board, or the firm is involved in many unrelated businesses, especially when the inside information is valuable and the firm needs many outsiders to observe useful outside information. I use some of these implications and casual observation of real-world data to discuss recent trends in the board structure of Japanese firms

Multi-cluster dynamics in Λ13C^{13}_\Lambda{\rm C} and analogy to clustering in 12C^{12}{\rm C}

We investigate structure of $^{13}_\Lambda{\rm C}$ and discuss the difference and similarity between the structures of $^{12}{\rm C}$ and $^{13}_\Lambda{\rm C}$ by answering the questions if the linear-chain and gaslike cluster states, which are proposed to appear in $^{12}{\rm C}$, survives, or new structure states appear or not. We introduce a microscopic cluster model called, Hyper-Tohsaki-Horiuchi-Schuck-R\"opke (H-THSR) wave function, which is an extended version of the THSR wave function so as to describe $\Lambda$ hypernuclei. We obtained two bound states and two resonance (quasi-bound) states for $J^\pi=0^+$ in $^{13}_\Lambda{\rm C}$, corresponding to the four $0^+$ states in $^{12}{\rm C}$. However, the inversion of level ordering between the spectra of $^{12}{\rm C}$ and $^{13}_\Lambda{\rm C}$, i.e. that the $0_3^+$ and $0_4^+$ states in $^{13}_\Lambda{\rm C}$ correspond to the $0_4^+$ and $0_3^+$ states in $^{12}{\rm C}$, respectively, is shown to occur. The additional $\Lambda$ particle reduces sizes of the $0_2^+$ and $0_3^+$ states in $^{13}_\Lambda{\rm C}$ very much, but the shrinkage of the $0_4^+$ state is only a half of the other states. In conclusion, the Hoyle state becomes quite a compact object with ${^{9}_\Lambda{\rm Be}}+\alpha$ configuration in $^{13}_\Lambda{\rm C}$ and is no more gaslike state composed of the $3\alpha$ clusters. Instead, the $0_4^+$ state in $^{13}_\Lambda{\rm C}$, coming from the $^{12}{\rm C}(0_3^+)$ state, appears as a gaslike state composed of $\alpha+\alpha+^{5}_\Lambda{\rm He}$ configuration, i.e. the Hoyle analog state. A linear-chain state in a $\Lambda$ hypernucleus is for the first time predicted to exist as the $0_3^+$ state in $^{13}_\Lambda{\rm C}$ with more shrunk arrangement of the $3\alpha$ clusters along $z$-axis than the $3\alpha$ linear-chain configuration realized in the $^{12}{\rm C}(0_4^+)$ state.Comment: 9 pages, 6 figures, figures rearranged, accepted for publication in PL

Superdeformed Λ\Lambda hypernuclei with antisymmetrized molecular dynamics

The response to the addition of a $\Lambda$ hyperon is investigated for the deformed states such as superdeformation in $^{41}_\Lambda$Ca, $^{46}_\Lambda$Sc and $^{48}_\Lambda$Sc. In the present study, we use the antisymmetrized molecular dynamics (AMD) model. It is pointed out that many kinds of deformed bands appear in $^{45}$Sc and $^{47}$Sc. Especially, it is found that there exists superdeformed states in $^{45}$Sc. By the addition of a $\Lambda$ particle to $^{40}$Ca, $^{45}$Sc and $^{47}$Sc, it is predicted, for the first time, that the superdeformed states exist in the hypernuclei $^{41}_\Lambda$Ca and $^{46}_\Lambda$Sc. The manifestation of the dependence of the $\Lambda$-separation energy on nuclear deformation such as spherical, normal deformation and superdeformation is shown in the energy spectra of $^{41}_\Lambda$Ca, $^{46}_\Lambda$Sc and $^{48}_\Lambda$Sc hypernuclei.Comment: 24 pages, 8 figure