Large Kinetic Power in FRII Radio Jets

We investigate the total kinetic powers (L_{j}) and ages (t_{age}) of powerful jets of four FR II radio sources (Cygnus A, 3C 223, 3C 284, and 3C 219) by the detail comparison of the dynamical model of expanding cocoons with observed ones. It is found that these sources have quite large kinetic powers with the ratio of L_{j} to the Eddington luminosity (L_{Edd}) resides in $0.02 <L_{j}/L_{Edd} <10$. Reflecting the large kinetic powers, we also find that the total energy stored in the cocoon (E_{c}) exceed the energy derived from the minimum energy condition (E_{min}): $2< E_{c}/E_{min} <160$. This implies that a large amount of kinetic power is carried by invisible components such as thermal leptons (electron and positron) and/or protons.Comment: 5 pages, accepted for publication in Astrophysics and Space Scienc

Digital Synthetic Aperture Acoustic Imaging for NDE

Real time synthetic aperture or synthetic focus techniques for acoustic imaging have been investigated and a prototype digital imaging system has been developed. It operates by exciting, with an impulse, one element from a transducer array, digitizing the return echoes, and storing them in a Random Access Memory. When this process has been repeated for all the array elements, the focus information is loaded from a mini computer. The system then generates a series of swept-focus lines, which are arranged perpendicular to the array face. Our processor handles typical input data at rates sufficient to generate real time images. As only one transducer at a time is excited it has been necessary to develop a high efficiency broadband transducer array with quarter wavelength matching layers. The array we have developed has an 11 dB return loss, a 2.7-4.3 MHz frequency range with a pulse response approximately 5 half cycles long. The digital processor operates at a 10- 16 MHz sample rate with 8 bit quantization. Theoretical and experimental images will be presented for a system with a 96 line display employing 8 and 32 active transducer elements, which has a resolution of \u3c 1 mm. We will also discuss methods of reducing the sidelobe responses in these systems. We have carried out experiments and theory, and we can considerably reduce the sidelobe level with input gain compression from the current experimental value of -12 dB to beyond -20 dB in our prototype 8 transducer system. In addition, we are investigating inverse filtering techniques for shortening the effective pulse length to 1 rf cycle to further improve the image quality and range resolution

Antiferromagnetic Heisenberg model on anisotropic triangular lattice in the presence of magnetic field

We use Schwinger boson mean field theory to study the antiferromagnetic spin-1/2 Heisenberg model on an anisotropic triangular lattice in the presence of a uniform external magnetic field. We calculate the field dependence of the spin incommensurability in the ordered spin spiral phase, and compare the results to the recent experiments in Cs$_{2}$CuCl$_{4}$ by Coldea et al. (Phys. Rev. Lett. 86, 1335 (2001)).Comment: 4 pages with 4 figures include

The Feedback-Regulated Growth of Black Holes and Bulges through Gas Accretion and Starbursts in Cluster Central Dominant Galaxies

We present an analysis of the growth of black holes through accretion and bulges through star formation in 33 galaxies at the centers of cooling flows. Most of these systems show evidence of cavities in the intracluster medium (ICM) inflated by radio jets emanating from their active galactic nuclei (AGN). We present a new and extensive analysis of X-ray cavities in these systems. We find that AGN are energetically able to balance radiative losses (cooling) from the ICM in more than half of our sample. Using a subsample of 17 systems, we examine the relationship between cooling and star formation. We find that the star formation rates are approaching or are comparable to X-ray and far UV limits on the rates of gas condensation onto the central galaxy. The remaining radiative losses could be offset by AGN feedback. The vast gulf between radiative losses and the sink of cooling material, which has been the primary objection to cooling flows, has narrowed and, in some cases, is no longer a serious issue. Using the cavity (jet) powers, we place strong lower limits on the rate of growth of supermassive black holes in central galaxies, and we find that they are growing at an average rate of ~ 0.1 solar masses per year, with some systems growing as quickly as ~ 1 solar mass per year. We find a trend between bulge growth (star formation) and black hole growth that is approximately in accordance with the slope of the local (Magorrian) relation between black hole and bulge mass. However, the large scatter in the trend suggests that bulges and black holes do not always grow in lock step. (Abridged)Comment: 17 pages, 6 figures, accepted to ApJ. Minor changes to text and figure

Perturbation Analysis of Superconductivity in the Trellis-Lattice Hubbard Model

We investigate pairing symmetry and transition temperature in the trellis-lattice Hubbard model. We solve the \'Eliashberg equation using the third-order perturbation theory with respect to the on-site repulsion $U$. We find that a spin-singlet state is very stable in a wide range of parameters. On the other hand, when the electron number density is shifted from the half-filled state and the band gap between two bands is small, a spin-triplet superconductivity is expected. Finally, we discuss a possibility of unconventional superconductivity and pairing symmetry in Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$.Comment: 7pages, 10 figures. To be published in J. Phys. Soc. Jp

Charge Ordering in Organic ET Compounds

The charge ordering phenomena in quasi two-dimensional 1/4-filled organic compounds (ET)_2X (ET=BEDT-TTF) are investigated theoretically for the $\theta$ and $\alpha$-type structures, based on the Hartree approximation for the extended Hubbard models with both on-site and intersite Coulomb interactions. It is found that charge ordered states of stripe-type are stabilized for the relevant values of Coulomb energies, while the spatial pattern of the stripes sensitively depends on the anisotropy of the models. By comparing the results of calculations with the experimental facts, where the effects of quantum fluctuation is incorporated by mapping the stripe-type charge ordered states to the S=1/2 Heisenberg Hamiltonians, the actual charge patterns in the insulating phases of $\theta$-(ET)_2MM'(SCN)_4 and $\alpha$-(ET)_2I_3 are deduced. Furthermore, to obtain a unified view among the $\theta$, $\alpha$ and $\kappa$-(ET)_2X families, the stability of the charge ordered state in competition with the dimeric antiferromagnetic state viewed as the Mott insulating state, which is typically realized in $\kappa$-type compounds, and with the paramagnetic metallic state, is also pursued by extracting essential parameters.Comment: 35 pages, 27 figures, submitted to J. Phys. Soc. Jp

Collective Charge Excitation in a Dimer Mott Insulating System

Charge dynamics in a dimer Mott insulating system, where a non-polar dimer-Mott (DM) phase and a polar charge-ordered (CO) phase compete with each other, are studied. In particular, collective charge excitations are analyzed in the three different models where the internal-degree of freedom in a dimer is taken into account. Collective charge excitation exists both in the non-polar DM phase and the polar CO phase, and softens in the phase boundary. This mode is observable by the optical conductivity spectra where the light polarization is parallel to the electric polarization in the polar CO phase. Connections between the present theory and the recent experimental results in kappa-(BEDT-TTF)2Cu2(CN)3 are discussed.Comment: 5 pages, 4 figure

The Heisenberg antiferromagnet on an anisotropic triangular lattice: linear spin-wave theory

We consider the effect of quantum spin fluctuations on the ground state properties of the Heisenberg antiferromagnet on an anisotropic triangular lattice using linear spin-wave theory. This model should describe the magnetic properties of the insulating phase of the kappa-(BEDT-TTF)_2 X family of superconducting molecular crystals. The ground state energy, the staggered magnetization, magnon excitation spectra and spin-wave velocities are computed as a function of the ratio between the second and first neighbours, J2/J1. We find that near J2/J1 = 0.5, i.e., in the region where the classical spin configuration changes from a Neel ordered phase to a spiral phase, the staggered magnetization vanishes, suggesting the possibility of a quantum disordered state. In this region, the quantum correction to the magnetization is large but finite. This is in contrast to the frustrated Heisenberg model on a square lattice, for which the quantum correction diverges logarithmically at the transition from the Neel to the collinear phase. For large J2/J1, the model becomes a set of chains with frustrated interchain coupling. For J2 > 4 J1, the quantum correction to the magnetization, within LSW, becomes comparable to the classical magnetization, suggesting the possibility of a quantum disordered state. We show that, in this regime, quantum fluctuations are much larger than for a set of weakly coupled chains with non-frustated interchain coupling.Comment: 10 pages, RevTeX + epsf, 5 figures Replaced with published version. Comparison to series expansions energies include