Emerging functions of mammalian mitochondrial fusion and fission

Mitochondria provide a myriad of services to the cell, including energy production, calcium buffering and regulation of apoptosis. How these diverse functions are coordinated among the hundreds of mitochondria in a given cell is largely unknown, but is probably dependent on the dynamic nature of mitochondria. In this review, we explore the latest developments in mitochondrial dynamics in mammals. These studies indicate that mitofusins and OPA1 are essential for mitochondrial fusion, whereas Fis1 and Drp1 are essential for mitochondrial fission. The overall morphology of the mitochondrial population depends on the relative activities of these two sets of proteins. In addition to the regulation of mitochondrial shape, these molecules also play important roles in cell and tissue physiology. Perturbation of mitochondrial fusion results in defects in mitochondrial membrane potential and respiration, poor cell growth and increased susceptibility to cell death. These cellular observations may explain why mitochondrial fusion is essential for embryonic development. Two inherited neuropathies, Charcot–Marie–Tooth type 2A and autosomal dominant optic atrophy, are caused by mutations in mitofusin 2 and OPA1, suggesting that proper regulation of mitochondrial dynamics is particularly vital to neurons. Mitochondrial fission accompanies several types of apoptotic cell death and appears important for progression of the apoptotic pathway. These studies provide insight into how mitochondria communicate with one another to coordinate mitochondrial function and morphology

Asymptotic behavior of the steady Navier-Stokes equation on the hyperbolic plane

We develop the asymptotic behavior for the solutions to the stationary Navier-Stokes equation in the exterior domain of the 2D hyperbolic space. More precisely, given the finite Dirichlet norm of the velocity, we show the velocity decays to $0$ at infinity. We also address the decay rate for the vorticity and the behavior of the pressure.Comment: 29 page

Convertible Bond Underpricing: Renegotiable Covenants, Seasoning and Convergence (Published in "Management Science", Vol. 53, No. 11, November 2007, pp. 1793.1814. )

We investigate the long-standing puzzle on the underpricings of convertible bonds. We hypothesize that the observed underpricing is induced by the possibility that a convertible bond might renegotiate on some of its covenants, e.g., an imbedded put option, in financial difficulties. Consistent with our hypothesis, we find that the initial underpricing is larger for lower rated bonds. The underpricing worsens if the issuer experiences subsequent financial difficulties. However, conditional on no rating downgrades, our main empirical result shows that convertible bond prices do converge to their theoretical prices within two years. This seasoning period is shorter for higher rated convertible bonds.

"Convertible Bond Underpricing: Renegotiable Covenants, Seasoning and Convergence"

We investigate the long-standing puzzle on the underpricings of convertible bonds. We hypothesize that the observed underpricing is induced by the possibility that a convertible bond might renegotiate on some of its covenants, e.g., an imbedded put option, in financial difficulties. Consistent with our hypothesis, we find that the initial underpricing is larger for lower rated bonds. The underpricing worsens if the issuer experiences subsequent financial difficulties. However, conditional on no rating downgrades, our main empirical result shows that convertible bond prices do converge to their theoretical prices within two years. This seasoning period is shorter for higher rated convertible bonds.

Naming Game on Networks: Let Everyone be Both Speaker and Hearer

To investigate how consensus is reached on a large self-organized peer-to-peer network, we extended the naming game model commonly used in language and communication to Naming Game in Groups (NGG). Differing from other existing naming game models, in NGG, everyone in the population (network) can be both speaker and hearer simultaneously, which resembles in a closer manner to real-life scenarios. Moreover, NGG allows the transmission (communication) of multiple words (opinions) for multiple intra-group consensuses. The communications among indirectly-connected nodes are also enabled in NGG. We simulated and analyzed the consensus process in some typical network topologies, including random-graph networks, small-world networks and scale-free networks, to better understand how global convergence (consensus) could be reached on one common word. The results are interpreted on group negotiation of a peer-to-peer network, which shows that global consensus in the population can be reached more rapidly when more opinions are permitted within each group or when the negotiating groups in the population are larger in size. The novel features and properties introduced by our model have demonstrated its applicability in better investigating general consensus problems on peer-to-peer networks.Comment: 11 pages, 6 figure