6,852 research outputs found

    Individual Leadership in Guiding Change in Global Governance Institutions: Theory and Practice

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    It is increasingly accepted that in order for international organizations to address fully the panoply of threats and concerns at the international level the current structure of global governance, particularly the design of major international institutions, requires some level of reform. In different fields and at different levels, this reform has been discussed and debated, but has mostly stalled. Increasingly, it is the executive heads of an organization that are called upon to show stronger leadership during times of crisis and change. No longer viewed as merely managers or administrative posts, the leadership shown byexecutive heads of international organizations is now strongly linked with the effectiveness of these organizations. This working paper seeks to understand the role of leaders in driving, and responding to, change in international organizations. What does leadership, a term often used in relation to national politics, mean in the context of an international organization? How do leaders drive change within these bodies, and how do they effectively respond to external and internal challenges and threats? This paper argues that individual leaders, particularly during times of crisis, can play an important role in guiding change and reform. The first part discusses the concept of leadership in the context of international organizations, and discusses some of the ways in which executive heads can pursue change and reform in their organization. The second part turns to the specific example of the UN Secretary General, an executive head who, despite having a relatively minor role on paper, in some cases has been able to implement meaningful change in the organization. The paper argues that executive heads can and should show greater political leadership in reforming organizations and improving their effectiveness

    Path integral formulation of the tunneling dynamics of a superfluid Fermi gas in an optical potential

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    To describe the tunneling dynamics of a stack of two-dimensional fermionic superfluids in an optical potential, we derive an effective action functional from a path integral treatment. This effective action leads, in the saddle point approximation, to equations of motion for the density and the phase of the superfluid Fermi gas in each layer. In the strong coupling limit (where bosonic molecules are formed) these equations reduce to a discrete nonlinear Schrodinger equation, where the molecular tunneling amplitude is reduced for large binding energies. In the weak coupling (BCS) regime, we study the evolution of the stacked superfluids and derive an approximate analytical expression for the Josephson oscillation frequency in an external harmonic potential. Both in the weak and intermediate coupling regimes the detection of the Josephson oscillations described by our path integral treatment constitutes experimental evidence for the fermionic superfluid regime.Comment: 13 pages + 2 figure

    The vortex state in the BEC to BCS crossover: a path-integral description

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    We derive a path-integral description of the vortex state of a fermionic superfluid in the crossover region between the molecular condensate (BEC) regime and the Cooper pairing (BCS) regime. This path-integral formalism, supplemented by a suitable choice for the saddle point value of the pairing field in the presence of a vortex, offers a unified description that encompasses both the BEC and BCS limits. The vortex core size is studied as a function of the tunable interaction strength between the fermionic atoms. We find that in the BEC regime, the core size is determined by the molecular healing length, whereas in the BCS regime, the core size is proportional only to the Fermi wave length. The observation of such quantized vortices in dilute Fermi gases would provide an unambiguous proof of the realization of superfluidity in these gases.Comment: 10 pages, 2 figure

    Finite-temperature Wigner solid and other phases of ripplonic polarons on a helium film

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    Electrons on liquid helium can form different phases depending on density, and temperature. Also the electron-ripplon coupling strength influences the phase diagram, through the formation of so-called "ripplonic polarons", that change how electrons are localized, and that shifts the transition between the Wigner solid and the liquid phase. We use an all-coupling, finite-temperature variational method to study the formation of a ripplopolaron Wigner solid on a liquid helium film for different regimes of the electron-ripplon coupling strength. In addition to the three known phases of the ripplopolaron system (electron Wigner solid, polaron Wigner solid, and electron fluid), we define and identify a fourth distinct phase, the ripplopolaron liquid. We analyse the transitions between these four phases and calculate the corresponding phase diagrams. This reveals a reentrant melting of the electron solid as a function of temperature. The calculated regions of existence of the Wigner solid are in agreement with recent experimental data.Comment: 12 pages, 6 figures. arXiv admin note: text overlap with arXiv:1012.4576, arXiv:0709.4140 by other author

    Correlations in Free Fermionic States

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    We study correlations in a bipartite, Fermionic, free state in terms of perturbations induced by one party on the other. In particular, we show that all so conditioned free states can be modelled by an auxiliary Fermionic system and a suitable completely positive map.Comment: 17 pages, no figure
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