43,880 research outputs found

    Exchange and collective behavior of magnetic impurities in a disordered helical metal

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    We study the exchange interaction and the subsequent collective behavior of magnetic impurities embedded in a disordered two-dimensional (2D) helical metal. The exchange coupling follows a statistical distribution whose moments are calculated to the lowest order in (pF)1\left(p_F\ell\right)^{-1}, where pFp_F is the Fermi momentum of itinerant electrons and \ell is the mean free path. We find that i) the first moment of the distribution decays exponentially, and ii) the variance of the interaction is long-range, however, it becomes independent of the orientation of the localized magnetic moments due to the locking between spin and momentum of the electrons that mediate the interaction. As consequence, long-range magnetic order tends to be suppressed, and a spin glass phase emerges. The formalism is applied to the surface states of a three-dimensional (3D) topological insulator. The lack of a net magnetic moment in the glassy phase and the full randomization of spin polarization at distances larger than \ell excludes a spectral gap for surface states. Hence, non-magnetic disorder may explain the dispersion in results for photoemission experiments in magnetically-doped topological insulators.Comment: 5 pages, 3 figures; final version to appear in Physical Review B as a rapid communicatio

    Disintegrating Customary International Law: Reactions to Withdrawing from International Custom

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    Withdrawing from International Custom, a recent article by Curtis Bradley and Mitu Gulati, has sparked interest and debate. Bradley and Gulati’s article, develops with significant nuance and detail that, naturally, can be best understood by a careful reading of their work. In essence, it proposes a modification in customary international law (CIL) doctrine – a change that would permit states to unilaterally exit from existing customary international law. This Essay will act as a brief reflection on that article. In Part I, it will explore the analogies Withdrawing makes between CIL and contract and will argue, first that CIL and contract are not analogous and, second, that even to the extent that contract demonstrates how other doctrinal areas order exits from legal relationships, contract illustrates the point that unilateral exit is a recognized abdication of the exiting party’s obligations and that exit gives rise to legal liability. In Part II, it explores the analogies Withdrawing makes between governments and agents in order to unpack some of the theoretical political theory constructs on which Withdrawing relies, and to explore the limitations Withdrawing sets on the proposal for unilateral exit. Part III of this Essay will make an affirmative argument for symmetry between CIL formation doctrine and CIL disintegration doctrine. The current proposal anticipates that CIL formation would remain unchanged, but exit for any given state would be far more expeditious than is contemplated by current CIL exit formulations. This Part will illustrate that this proposal violates a strong presumption in favor of symmetrical entrenchment

    On Reading and Writing and Becoming a Teacher

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    The cartography of computational search spaces

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    This talk will present our recent findings and visual (static and animated) maps characterising combinatorial and computer program search spaces. We seek to lay the foundations for a new perspective to understand problem structure and improve heuristic search algorithms: search space cartography.   Heuristic methods operate by searching a large space of candidate solutions. The search space can be regarded as a spatial structure where each point (candidate solution) has a height (objective or fitness value) forming a fitness landscape surface. The performance of search algorithms crucially depends on the fitness landscape structure, and the study of landscapes offers an alternative to problem understanding where realistic formulations and algorithms can be analysed.   Most fitness landscapes analysis techniques study the local structure of search spaces. Our recently proposed model, Local Optima Networks, helps to study instead their global structure. This graph-based model provides fundamental new insight into the structural organisation and the connectivity pattern of a search space with given move operators.  Most importantly, it allows us to visualise realistic search spaces in ways not previously possible and brings a whole new set of network metrics for characterising them. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

    The Joys of Teaming

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    Panentheistic Elements in Wolfhart Pannenberg's Notion of God

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    In his exposition, Pannenberg dialectically explores the possibility of a redefinition of the notion of God and rejects the anthropomorphic analogies and the Greek understanding of God as nous in order to emphasize the idea of God as Spirit and thus facilitate the intersection between the natural sciences and Christian theology. Thus, based on the Hebrew notion of the spirit as “wind/breath” and using a naturalistic framework, Pannenberg offers an insightful yet panentheistic view of the Spirit of God as a field of force that binds the Three Persons of the Trinity

    N.T. Wright and the Body-Soul Predicament: The Presumption of Duality in Ontological Holism

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    N.T. Wright has offered Christian philosophers a proposal where it is apparently possible to hold the belief in the intermediate state-resurrection of the body and an ontological holism in the same sense at the same time. I argue that this not only creates a basic contradiction in Wright’s ontological paradigm, but also it is not a coherent and tenable proposal despite the fact one might eventually find a potential solution to such a quandary

    From Bison to Cattle: The Ecology of the Southern Plains 1500-1750

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    Bison made their home on the Southern Plains for millennia. However, their migratory patterns began to shift in the 17th and 18th centuries. My research investigated what caused this drastic shift and how it had far reaching effects on the ecology of the Southern Plains. Using archives from two prominent Catholic priests, I began to piece together why the bison left the Southern Plains. Rather than focus on the Europeans as the main players, I instead focused on the Indigenous peoples, the animals, and the land as the centralized actors in this project. I discovered that the introduction of cattle by the Spanish missions was the leading factor. As the cattle quickly consumed the resources, the bison had to find additional inhabitable spaces. Their swift departure from the Southern Plains resulted in upheaval for the Indigenous inhabitants and the ecology of the Plains themselves
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