Chiral symmetry breaking in a uniform external magnetic field II. Symmetry restoration at high temperatures and chemical potentials

Chiral symmetry is dynamically broken in quenched, ladder QED at weak gauge couplings when an external magnetic field is present. In this paper, we show that chiral symmetry is restored above a critical chemical potential and the corresponding phase transition is of first order. In contrast, the chiral symmetry restoration at high temperatures (and at zero chemical potential) is a second order phase transition.Comment: Latex; 12 pages; 8 postscript figures include

High-Lundquist Number Scaling in Three-Dimensional Simulations of Parker's Model of Coronal Heating

Parker's model is one of the most discussed mechanisms for coronal heating and has generated much debate. We have recently obtained new scaling results in a two-dimensional (2D) version of this problem suggesting that the heating rate becomes independent of resistivity in a statistical steady state [Ng and Bhattacharjee, Astrophys. J., 675, 899 (2008)]. Our numerical work has now been extended to 3D by means of large-scale numerical simulations. Random photospheric footpoint motion is applied for a time much longer than the correlation time of the motion to obtain converged average coronal heating rates. Simulations are done for different values of the Lundquist number to determine scaling. In the high-Lundquist number limit, the coronal heating rate obtained so far is consistent with a trend that is independent of the Lundquist number, as predicted by previous analysis as well as 2D simulations. In the same limit the average magnetic energy built up by the random footpoint motion tends to have a much weaker dependence on the Lundquist number than that in the 2D simulations, due to the formation of strong current layers and subsequent disruption when the equilibrium becomes unstable. We will present scaling analysis showing that when the dissipation time is comparable or larger than the correlation time of the random footpoint motion, the heating rate tends to become independent of Lundquist number, and that the magnetic energy production is also reduced significantly.Comment: Accepted for publication in Astrophysical Journa

Competition in the advanced sale of service capacity

Pre-print of an article accepted for publication in International Journal of Revenue Management; authors' draft dated March 6, 2008; final version available at http://www.inderscience.com

Production Cost, Transaction Cost, and Outsourcing Strategy: A Game Theoretic Analysis

This paper presents a game theoretic analysis of the impact of both production and transaction costs on the single-or-multiple source purchasing decision. Both dyadic interactions involving a buyer and a seller, and triadic interactions involving a buyer and two suppliers, are examined to gain a more precise understanding of how small number interactions might influence transaction cost. We show that transaction cost is maximized when a buyer follows a single source strategy and learning specificity is present. Only if a buyer follows a multiple source strategy that splits the supply contract in such a way as to equalize the effects of learning specificity across the suppliers, will transaction cost be maximized and will a buyer be able to appropriate the efficiency gains achieved by its suppliers. Production and transaction costs interact to influence governance decisions. The equilibrium is such that a single (multiple) source strategy is optimal when efficiency gains due to the economies of scale are large (small), but those due to learning specificity are small (large). When both the effects of economies of scale and learning specificity are large, internalization is the optimal strategy

Advanced sale of service capacities: a theoretical analysis of the impact of price sensitivity on pricing and capacity allocations

Pre-print; author's draft dated March 27, 1999Should service firms sell in advance? Using a theoretical approach, we study the optimality of advanced sale of capacity for a monopolistic service firm and examine the impact of market price sensitivity on the optimal price and capacity allocations for advanced sale. We show that when firms undertake advanced sale, capacity utilization and profits are higher even though prices for sale in advance are discounted. In addition, we show that optimal pricing and capacity allocations for advanced sale depend on the expected price sensitivity at the time of consumption. When price sensitivity at the point of consumption is expected to be low (unchanged), it is optimal to allocate more (less) capacity for sale at time of consumption than in advance. Although optimal price and capacity allocations in advanced sale result in excess capacity, we show that having excess capacity is a strategic decision in that it is a dominant strategy

Broken time-reversal symmetry in Josephson junction involving two-band superconductors

A novel time-reversal symmetry breaking state is found theoretically in the Josephson junction between the two-gap superconductor and the conventional s-wave superconductor. This occurs due to the frustration between the three order parameters analogous to the two antiferromagnetically coupled XY-spins put under a magnetic field. This leads to the interface states with the energies inside the superconducting gap. Possible experimental observations of this state with broken time-reversal symmetry are discussed.Comment: 9 pages, 1 figur

New heat treatment to prepare high quality polycrystalline and single crystal MgB2 in single process

We report here on a new heat treatment to prepare both dense polycrystalline and single crystal MgB2 high quality samples in one single process. Resistivity measurements for polycrystalline part of the sample gives a residual resistivity ratio RRR=16.6 and a very low normal state resistivity rho(40K)= 0.28 microOhmcm. Both SEM and SQUID study on polycrystals reveal the high quality, dense character and well coupling of grain boundaries. On the other hand, the high quality single crystals have a unique shape that resembles the hexagonal crystal structure. SQUID measurements reveals very weak flux pinning character implying our single crystals to be very clean. In this study, we conclude that heat treatment is playing a major rule on the characteristics of both polycrystalline and single crystal MgB2. Samples are thoroughly characterized by x-ray, resistivity, dc SQUID and SEM