Effective hadronic Lagrangian for charm mesons

An effective hadronic Lagrangian including the charm mesons is introduced to study their interactions in hadronic matter. Using coupling constants that are determined either empirically or by the SU(4) symmetry, we have evaluated the absorption cross sections of $J/\psi$ and the scattering cross sections of $D$ and $D^*$ by $\pi$ and $\rho$ mesons.Comment: 5 pages, 4 eps figures, presented at Strangeness 2000, Berkeley. Uses iopart.cl

Short-time critical dynamics at perfect and non-perfect surface

We report Monte Carlo simulations of critical dynamics far from equilibrium on a perfect and non-perfect surface in the 3d Ising model. For an ordered initial state, the dynamic relaxation of the surface magnetization, the line magnetization of the defect line, and the corresponding susceptibilities and appropriate cumulant is carefully examined at the ordinary, special and surface phase transitions. The universal dynamic scaling behavior including a dynamic crossover scaling form is identified. The exponent $\beta_1$ of the surface magnetization and $\beta_2$ of the line magnetization are extracted. The impact of the defect line on the surface universality classes is investigated.Comment: 11figure

Phase dynamics of inductively coupled intrinsic Josephson junctions and terahertz electromagnetic radiation

The Josephson effects associated with quantum tunneling of Cooper pairs manifest as nonlinear relations between the superconductivity phase difference and the bias current and voltage. Many novel phenomena appear, such as Shapiro steps in dc cuurent-voltage (IV) characteristics of a Josephson junction under microwave shining, which can be used as a voltage standard. Inversely, the Josephson effects provide a unique way to generate high-frequency electromagnetic (EM) radiation by dc bias voltage. The discovery of cuprate high-Tc superconductors accelerated the effort to develop novel source of EM waves based on a stack of atomically dense-packed intrinsic Josephson junctions (IJJs), since the large superconductivity gap covers the whole terahertz frequency band. Very recently, strong and coherent terahertz radiations have been successfully generated from a mesa structure of $\rm{Bi_2Sr_2CaCu_2O_{8+\delta}}$ single crystal which works both as the source of energy gain and as the cavity for resonance. It is then found theoretically that, due to huge inductive coupling of IJJs produced by the nanometer junction separation and the large London penetration depth of order of $\rm{\mu m}$ of the material, a novel dynamic state is stabilized in the coupled sine-Gordon system, in which $\pm \pi$ kinks in phase differences are developed responding to the standing wave of Josephson plasma and are stacked alternatively in the c-axis. This novel solution of the inductively coupled sine-Gordon equations captures the important features of experimental observations. The theory predicts an optimal radiation power larger than the one available to date by orders of magnitude, and thus suggests the technological relevance of the phenomena.Comment: review article (69 pages, 30 figures

Calibration and Irradiation Study of the BGO Background Monitor for the BEAST II Experiment

Beam commissioning of the SuperKEKB collider began in 2016. The Beam Exorcism for A STable experiment II (BEAST II) project is particularly designed to measure the beam backgrounds around the interaction point of the SuperKEKB collider for the Belle II experiment. We develop a system using bismuth germanium oxide (BGO) crystals with optical fibers connecting to a multianode photomultiplier tube (MAPMT) and a field-programmable gate array (FPGA) embedded readout board for monitoring the real-time beam backgrounds in BEAST II. The overall radiation sensitivity of this system is estimated to be $(2.20\pm0.26)\times10^{-12}$ Gy/ADU (analog-to-digital unit) with the standard 10 m fibers for transmission and the MAPMT operating at 700 V. Our $\gamma$-ray irradiation study of the BGO system shows that the exposure of BGO crystals to $^{60}$Co $\gamma$-ray doses of 1 krad has led to immediate light output reductions of 25--40%, and the light outputs further drop by 30--45% after the crystals receive doses of 2--4 krad. Our findings agree with those of the previous studies on the radiation hard (RH) BGO crystals grown by the low thermal gradient Czochralski (LTG Cz) technology. The absolute dose from the BGO system is also consistent with the simulation, and is estimated to be about 1.18 times the equivalent dose. These results prove that the BGO system is able to monitor the background dose rate in real time under extreme high radiation conditions. This study concludes that the BGO system is reliable for the beam background study in BEAST II

Space-time OFDM with adaptive beamforming: Performance in spatially correlated channels

Space-time block coding (STBC) has proved to be an effective means of exploring diversity branches and improving system performance. In a previous work we proposed an extension to that where the STBC was combined with adaptive eigenbeamforming, an approach that takes an advantage of spatial channel correlation and can provide further improvement for the overall system performance. In this paper, we investigate this new transmission structure for broadband orthogonal frequency division multiplexing (OFDM) systems in frequency-selective channels. Numerical analysis showed that systems employing this scheme would not undergo any diversity losses as it maintains the maximum achievable diversity advantage of space-time (ST) codes in realistic channel conditions. Simulation results showed that the proposed structure has a significant improvement in bit/symbol error rate performance in a spatially correlated channel over systems that utilize only space-time coding

Transmission of compressed multimedia data over wireless channels using space-time OFDM with adaptive beamforming

The transmission of multimedia data over wireless channels poses significant constraints on the communication system bandwidth, energy, and latency. To overcome these bottlenecks to wireless multimedia communication, various channel coding and transmit diversity schemes have been proposed. In previous work, we have shown that space-time block-coding (STBC) with adaptive beamforming (STBC-OFDM-AB) is an effective technique for improving the error-rate performance and channel capacity of wireless multimedia systems utilizing OFDM. In this paper, we introduce a transmission system for multimedia communication employing STBC-OFDM with adaptive beamforming incorporating a perceptually-based image compression coder - which consists of a 2-D discrete wavelet transform (DWT), an adaptive quantizer (with thresholding) and variable-length entropy encoding. Initial simulation results based on the transmission of compressed images, showed that the performance improvement introduced by STBC-OFDM-AB can be readily observed, and compared to other transmission methods is better suited to wireless multimedia communication

Multimedia transmission over wireless space-time-frequency coded OFDM

The transmission of multimedia data over wireless systems generally require network devices designed with a high communication bandwidth, power, and processing resources. To deal with these bottlenecks commonly associated with multimedia transmission, various diversity coding schemes have been proposed. We have previously shown that wireless OFDM systems based on space-time block-coding with adaptive beamforming (STBC-OFDM-AB) are well suited to multimedia communication. Recent studies have shown further performance gains in systems utilizing space-time-frequency (STF) coding. In this paper, we introduce a transmission system which combines STF coding with adaptive beamforming (STF-OFDM-AB). Simulation results based on the transmission of compressed images showed that the performance improvements introduced by STF-OFDM-AB can be readily observed

Adaptive transmit eigenbeamforming with orthogonal space-time block coding in correlated space-time channels

Conventional space-time codes can provide a significant improvement in system performance only if the signal paths are spatially uncorrelated, a condition that is hardly met in practice. In this paper, we mitigate this condition by combining a technique of eigenbeamforming, based on the channel correlation matrix, with orthogonal space-time block codes (O-STBC) at the transmitter side of the link. No feedback information from the receiver (the mobile station) is utilized in the proposed structure. Simulation results using 4-ary PSK signaling showed that this idea outperforms existing techniques in both uncorrelated and correlated channels in terms of bit-error rate and symbol-error rate