Exact Floquet states of a driven condensate and their stabilities

We investigate the Gross-Pitaevskii equation for a classically chaotic system, which describes an atomic Bose-Einstein condensate confined in an optical lattice and driven by a spatiotemporal periodic laser field. It is demonstrated that the exact Floquet states appear when the external time-dependent potential is balanced by the nonlinear mean-field interaction. The balance region of parameters is divided into a phase-continuing region and a phase-jumping one. In the latter region, the Floquet states are spatiotemporal vortices of nontrivial phase structures and zero-density cores. Due to the velocity singularities of vortex cores and the blowing-up of perturbed solutions, the spatiotemporal vortices are unstable periodic states embedded in chaos. The stability and instability of these Floquet states are numerically explored by the time evolution of fidelity between the exact and numerical solutions. It is numerically illustrated that the stable Floquet states could be prepared from the uniformly initial states by slow growth of the external potential.Comment: 14 pages, 3 eps figures, final version accepted for publication in J. Phys.

Gluon mass generation in the PT-BFM scheme

In this article we study the general structure and special properties of the Schwinger-Dyson equation for the gluon propagator constructed with the pinch technique, together with the question of how to obtain infrared finite solutions, associated with the generation of an effective gluon mass. Exploiting the known all-order correspondence between the pinch technique and the background field method, we demonstrate that, contrary to the standard formulation, the non-perturbative gluon self-energy is transverse order-by-order in the dressed loop expansion, and separately for gluonic and ghost contributions. We next present a comprehensive review of several subtle issues relevant to the search of infrared finite solutions, paying particular attention to the role of the seagull graph in enforcing transversality, the necessity of introducing massless poles in the three-gluon vertex, and the incorporation of the correct renormalization group properties. In addition, we present a method for regulating the seagull-type contributions based on dimensional regularization; its applicability depends crucially on the asymptotic behavior of the solutions in the deep ultraviolet, and in particular on the anomalous dimension of the dynamically generated gluon mass. A linearized version of the truncated Schwinger-Dyson equation is derived, using a vertex that satisfies the required Ward identity and contains massless poles belonging to different Lorentz structures. The resulting integral equation is then solved numerically, the infrared and ultraviolet properties of the obtained solutions are examined in detail, and the allowed range for the effective gluon mass is determined. Various open questions and possible connections with different approaches in the literature are discussed.Comment: 54 pages, 24 figure

Achieving Bangladesh's Tourism Potential: Linkages to Export Diversification, Employment Generation and the 'Green Economy'

Bangladesh's international image is not as a popular tourism destination, and many people might be surprised to learn it has three World Heritage sites, including the Sundarbans tiger reserves. Moreover, it is part of important travel circuits for cultural and religious tourism, and has demonstrated potential for sports tourism. The objective of this working paper is to critically test the assertion that pro-poor "green" tourism is one of the best development options for the majority of least developed countries (LDCs) - a challenging task in Bangladesh in the face of the country's success as an exporter of readymade garments - by comparing tourism to the available alternatives with regard to the crucial government priorities of export diversification, employment generation and the "green economy". It is well-known that Bangladesh is under strong pressure to diversify its exports, to generate new employment (especially in rural areas), and to respond to critical environmental issues. The government has identified over 30 "thrust sectors" (including tourism) to help address these challenges, but otherwise tourism is rarely mentioned as a major trade and development option for Bangladesh. Within the limitations of data availability, this working paper reaches the conclusion that greater efforts to develop "green" tourism would be highly beneficial for facilitating rural development, environmental and cultural protection, gender equality, and export diversification in services. The most obvious current impediments are inadequate infrastructure, lack of investment and (typically election year) political conflict, but behind these factors appear to be a serious lack of stakeholder coordination, insufficient regulatory and administrative transparency and coherence, as well as some government reluctance to relinquish greater commercial autonomy in tourism to the private sector. This paper offers extensive analysis and some suggestions to help address the impediments, including the recommendation to create a Bangladesh Tourism Stakeholders Forum

Manpower Options in a Small Labor-Importing state: The Influence of Ethnic Composition on Kuwait's Development

International Migration, June 1992.Refereed Journal Articl

Against medical ethics: opening the can of worms

In a controversial paper, David Seedhouse argues that medical ethics is not and cannot be a distinct discipline with it own field of study. He derives this claim from a characterization of ethics, which he states but does not defend. He claims further that the project of medical ethics as it exists and of moral philosophy do not overlap. I show that Seedhouse's views on ethics have wide implications which he does not declare, and in the light of this argue that Seedhouse owes us a defence of his characterization of ethics. Further, I show that his characterization of ethics, which he uses to attack medical ethics, is a committed position within moral philosophy. As a consequence of this, it does not allow the relation between moral philosophy and medical ethics to be discussed without prejudice to its outcome. Finally, I explore the relation between Seedhouse's position and naturalism, and its implications for medical epistemology. I argue that this shows us that Seedhouse's position, if it can be defended, is likely to lead to a fruitful and important line of inquiry which reconnects philosophy and medical ethics