Computability of simple games: A characterization and application to the core

It was shown earlier that the class of algorithmically computable simple games (i) includes the class of games that have finite carriers and (ii) is included in the class of games that have finite winning coalitions. This paper characterizes computable games, strengthens the earlier result that computable games violate anonymity, and gives examples showing that the above inclusions are strict. It also extends Nakamura’s theorem about the nonemptyness of the core and shows that computable simple games have a finite Nakamura number, implying that the number of alternatives that the players can deal with rationally is restricted

Constraints on the mass of a habitable planet with water of nebular origin

From an astrobiological point of view, special attention has been paid to the probability of habitable planets in extrasolar systems. The purpose of this study is to constrain a possible range of the mass of a terrestrial planet that can get water. We focus on the process of water production through oxidation of the atmospheric hydrogen--the nebular gas having been attracted gravitationally--by oxide available at the planetary surface. For the water production to work well on a planet, a sufficient amount of hydrogen and enough high temperature to melt the planetary surface are needed. We have simulated the structure of the atmosphere that connects with the protoplanetary nebula for wide ranges of heat flux, opacity, and density of the nebular gas. We have found both requirements are fulfilled for an Earth-mass planet for wide ranges of the parameters. We have also found the surface temperature of planets of <= 0.3 Earth masses is lower than the melting temperature of silicate (~ 1500K). On the other hand, a planet of more than several Earth masses becomes a gas giant planet through runaway accretion of the nebular gas.Comment: 25 pages, 8 figures, to appear in the 01 September 2006 issue of Ap

First Detection of Near-Infrared Intraday Variations in the Seyfert 1 Nucleus NGC4395

We carried out a one-night optical V and near-infrared JHK monitoring observation of the least luminous Seyfert 1 galaxy, NGC4395, on 2004 May 1, and detected for the first time the intraday flux variations in the J and H bands, while such variation was not clearly seen for the K band. The detected J and H variations are synchronized with the flux variation in the V band, which indicates that the intraday-variable component of near-infrared continuum emission of the NGC4395 nucleus is an extension of power-law continuum emission to the near-infrared and originates in an outer region of the central accretion disk. On the other hand, from our regular program of long-term optical BVI and near-infrared JHK monitoring observation of NGC4395 from 2004 February 12 until 2005 January 22, we found large flux variations in all the bands on time scales of days to months. The optical BVI variations are almost synchronized with each other, but not completely with the near-infrared JHK variations. The color temperature of the near-infrared variable component is estimated to be T=1320-1710 K, in agreement with thermal emission from hot dust tori in active galactic nuclei (AGNs). We therefore conclude that the near-infrared variation consists of two components having different time scales, so that a small K-flux variation on a time scale of a few hours would possibly be veiled by large variation of thermal dust emission on a time scale of days.Comment: 4 pages including figures, accepted for publication in ApJ

Effects of Ram-Pressure from Intracluster Medium on the Star Formation Rate of Disk Galaxies in Clusters of Galaxies

Using a simple model of molecular cloud evolution, we have quantitatively estimated the change of star formation rate (SFR) of a disk galaxy falling radially into the potential well of a cluster of galaxies. The SFR is affected by the ram-pressure from the intracluster medium (ICM). As the galaxy approaches the cluster center, the SFR increases to twice the initial value, at most, in a cluster with high gas density and deep potential well, or with a central pressure of $\sim 10^{-2} cm^{-3} keV$ because the ram-pressure compresses the molecular gas of the galaxy. However, this increase does not affect the color of the galaxy significantly. Further into the central region of the cluster ($\lesssim 1$ Mpc from the center), the SFR of the disk component drops rapidly due to the effect of ram-pressure stripping. This makes the color of the galaxy redder and makes the disk dark. These effects may explain the observed color, morphology distribution and evolution of galaxies in high-redshift clusters. By contrast, in a cluster with low gas density and shallow potential well, or the central pressure of $\sim 10^{-3} cm^{-3} keV$, the SFR of a radially infalling galaxy changes less significantly, because neither ram-pressure compression nor stripping is effective. Therefore, the color of galaxies in poor clusters is as blue as that of field galaxies, if other environmental effects such as galaxy-galaxy interaction are not effective. The predictions of the model are compared with observations.Comment: 19 pages, 9 figures, to appear in Ap

Effective hadron masses and couplings in nuclear matter and incompressibility

The role of effective hadron masses and effective couplings in nuclear matter is studied using a generalized effective Lagrangian for sigma-omega model. A simple relation among the effective masses, the effective couplings and the incompressibility K is derived. Using the relation, it is found that the effective repulsive and the effective attractive forces are almost canceled to each other at the normal density. Inversely, if this cancellation is almost complete, K should be 250-350MeV.Comment: 13 pages of text, 16 figure

Quantum energy teleportation in a quantum Hall system

We propose an experimental method for a quantum protocol termed quantum energy teleportation (QET), which allows energy transportation to a remote location without physical carriers. Using a quantum Hall system as a realistic model, we discuss the physical significance of QET and estimate the order of energy gain using reasonable experimental parameters

Quantum enigma machines and the locking capacity of a quantum channel

The locking effect is a phenomenon which is unique to quantum information theory and represents one of the strongest separations between the classical and quantum theories of information. The Fawzi-Hayden-Sen (FHS) locking protocol harnesses this effect in a cryptographic context, whereby one party can encode n bits into n qubits while using only a constant-size secret key. The encoded message is then secure against any measurement that an eavesdropper could perform in an attempt to recover the message, but the protocol does not necessarily meet the composability requirements needed in quantum key distribution applications. In any case, the locking effect represents an extreme violation of Shannon's classical theorem, which states that information-theoretic security holds in the classical case if and only if the secret key is the same size as the message. Given this intriguing phenomenon, it is of practical interest to study the effect in the presence of noise, which can occur in the systems of both the legitimate receiver and the eavesdropper. This paper formally defines the locking capacity of a quantum channel as the maximum amount of locked information that can be reliably transmitted to a legitimate receiver by exploiting many independent uses of a quantum channel and an amount of secret key sublinear in the number of channel uses. We provide general operational bounds on the locking capacity in terms of other well-known capacities from quantum Shannon theory. We also study the important case of bosonic channels, finding limitations on these channels' locking capacity when coherent-state encodings are employed and particular locking protocols for these channels that might be physically implementable.Comment: 37 page

Instabilities and turbulence-like dynamics in an oppositely driven binary particle mixture

Using extensive particle-based simulations, we investigate out-of-equilibrium pattern dynamics in an oppositely driven binary particle system in two dimensions. A surprisingly rich dynamical behavior including lane formation, jamming, oscillation and turbulence-like dynamics is found. The ratio of two friction coefficients is a key parameter governing the stability of lane formation. When the friction coefficient transverse to the external force direction is sufficiently small compared to the longitudinal one, the lane structure becomes unstable to shear-induced disturbances, and the system eventually exhibits a dynamical transition into a novel turbulence-like phase characterized by random convective flows. We numerically construct an out-of-equilibrium phase diagram. Statistical analysis of complex spatio-temporal dynamics of the fully nonlinear turbulence-like phase suggests its apparent reminiscence to the swarming dynamics in certain active matter systems.Comment: 6 pages, 6 figures, accepted for publication in EP

Circularly-Polarized Light Emission from Semiconductor Planar Chiral Photonic Crystal

We proposed and demonstrated a scheme of surface emitting circularly polarized light source by introducing strong imbalance between left- and right-circularly polarized vacuum fields in an on-waveguide chiral grating structure. We observed circularly polarized spontaneous emission from InAs quantum dots embedded in the wave guide region of a GaAs-based structure. Obtained degree of polarization reaches as large as 25% at room temperature. Numerical calculation visualizes spatial profiles of the modification of vacuum field modes inside the structure with strong circular anisotropy.Comment: REVTeX4.1, 6pages, 3figure

Four-spin-exchange- and magnetic-field-induced chiral order in two-leg spin ladders

We propose a mechanism of a vector chiral long-range order in two-leg spin-1/2 and spin-1 antiferromagnetic ladders with four-spin exchanges and a Zeeman term. It is known that for one-dimensional quantum systems, spontaneous breakdown of continuous symmetries is generally forbidden. Any vector chiral order hence does not appear in spin-rotationally [SU(2)]-symmetric spin ladders. However, if a magnetic field is added along the S^z axis of ladders and the SU(2) symmetry is reduced to the U(1) one, the z component of a vector chiral order can emerge with the remaining U(1) symmetry unbroken. Making use of Abelian bosonization techniques, we actually show that a certain type of four-spin exchange can yield a vector chiral long-range order in spin-1/2 and spin-1 ladders under a magnetic field. In the chiral-ordered phase, the Z_2 interchain-parity (i.e., chain-exchange) symmetry is spontaneously broken. We also consider effects of perturbations breaking the parity symmetry.Comment: 8 pages, 1 figure, RevTex, published versio