Is the σ\sigma meson dynamically generated?

We study the problem whether the $\sigma$ meson is generated `dynamically'. A pedagogical analysis on the toy O(N) linear sigma model is performed and we find that the large $N_c$ limit and the $m_\sigma\to \infty$ limit does not commute. The sigma meson may not necessarily be described as a dynamically generated resonance. On the contrary, the sigma meson may be more appropriately described by considering it as an explicit degree of freedom in the effective lagrangian.Comment: Contribution to ``Quark Confinement and Hadron Spectrum VII'', 2--7 Sept. 2006, Ponta Delgada, Acores, Portuga

On the scalar nonet in the extended Nambu Jona-Lasinio model

We discuss the lightest scalar resonances, $f_0(600)$, $\kappa(800)$, $a_0(980)$ and $f_0(980)$ in the extended Nambu Jona-Lasinio model. We find that the model parameters can be tuned, but unnaturally, to accommodate for those scalars except the $f_0(980)$. We also discuss problems encountered in the K Matrix unitarization approximation by using $N_c$ counting technique.Comment: 23 pages 3 eps figures, To appear in Nucl. Phys.

Performance analysis of contention based bandwidth request mechanisms in WiMAX networks

This article is posted here with the permission of IEEE. The official version can be obtained from the DOI below - Copyright @ 2010 IEEEWiMAX networks have received wide attention as they support high data rate access and amazing ubiquitous connectivity with great quality-of-service (QoS) capabilities. In order to support QoS, bandwidth request (BW-REQ) mechanisms are suggested in the WiMAX standard for resource reservation, in which subscriber stations send BW-REQs to a base station which can grant or reject the requests according to the available radio resources. In this paper we propose a new analytical model for the performance analysis of various contention based bandwidth request mechanisms, including grouping and no-grouping schemes, as suggested in the WiMAX standard. Our analytical model covers both unsaturated and saturated traffic load conditions in both error-free and error-prone wireless channels. The accuracy of this model is verified by various simulation results. Our results show that the grouping mechanism outperforms the no-grouping mechanism when the system load is high, but it is not preferable when the system load is light. The channel noise degrades the performance of both throughput and delay.This work was supported by the U.K. Engineering and Physical Sciences Research Council (EPSRC) under Grant EP/G070350/1 and by the Brunel University’s BRIEF Award

On the nature of the lightest scalar resonances

We briefly review the recent progresses in the new unitarization approach being developed by us. Especially we discuss the large $N_c$ $\pi\pi$ scatterings by making use of the partial wave $S$ matrix parametrization form. We find that the $\sigma$ pole may move to the negative real axis on the second sheet of the complex $s$ plane, therefore it raises the interesting question that this `$\sigma$' pole may be related to the $\sigma$ in the linear $\sigma$ model.Comment: Talk presented by Zheng at ``Quark Confinement and Hadron Spectroscopy VI'', 21--25 Sept. 2004, Cagliari, Italy. 3 pages with 2 figure

Switchable coupling between charge and flux qubits

We propose a hybrid quantum circuit with both charge and flux qubits connected to a large Josephson junction that gives rise to an effective inter-qubit coupling controlled by the external magnetic flux. This switchable inter-qubit coupling can be used to transfer back and forth an arbitrary superposition state between the charge qubit and the flux qubit working at the optimal point. The proposed hybrid circuit provides a promising quantum memory because the flux qubit at the optimal point can store the tranferred quantum state for a relatively long time.Comment: 5 pages, 1 figur

Recent Developments In Computational Fracture Mechanics At Cardiff

The following most recent developments in computational fracture mechanics at Cardiff University are reviewed: hybrid crack element (HCE) which can give directly the stress intensity factor (SIF) as well as the coefficients of higher order terms in the plane linear elastic crack tip asymptotic field; extended finite element method (XFEM) which avoids using a mesh conforming with the crack as is the case with the traditional FEM and gives highly accurate crack tip fields; penalty function technique for handling point loads; and compressed sparse row (CSR) storage scheme for efficient implementation of the above techniques. Possible future improvements are also discussed

The Shanxi Grand Theater: The “Renaissance” of Chinese Drama Land

ThispaperfocusesonTaiyuancity,asecond-tierChinesecitywithabrillianthistorythat had been gradually reduced to mediocrity. When an ambitious governor took office, he planned to carry out an urban revitalization process in which cultural facilities would become symbols of power and represent the city’s identity or define its character. The importation of western-style architecture and urban design for the performing arts offer a way out. The ‘perfect copies’ of European lifestyle, through the way of architectural, urbanism transplant, seemed to serve as a potent symbol of China authority’s ability to control and rearrange the worldwide intelligence for their citizen. The authors investigated Taiyuan and its performance spaces, examine the Shanxi Grand Theatre in terms of designs, layouts and uses, expectations, and disappointments in spatial terms both within and in relation to urban spaces, which epitomized China’s strategy on balancing the elite cultural monuments and social welfare