Multi-overlap simulations of spin glasses

We present results of recent high-statistics Monte Carlo simulations of the Edwards-Anderson Ising spin-glass model in three and four dimensions. The study is based on a non-Boltzmann sampling technique, the multi-overlap algorithm which is specifically tailored for sampling rare-event states. We thus concentrate on those properties which are difficult to obtain with standard canonical Boltzmann sampling such as the free-energy barriers F^q_B in the probability density P_J(q) of the Parisi overlap parameter q and the behaviour of the tails of the disorder averaged density P(q) = [P_J(q)]_av.Comment: 14 pages, Latex, 18 Postscript figures, to be published in NIC Series - Publication Series of the John von Neumann Institute for Computing (NIC

A minimal transfer conception for Verbmobil

In this paper we introduce the transfer conception MinT that is currently being developed for the prototype of the face-to-face translation system verbmobil. The acronym MinT stands for Minimal Transfer. MinT is a semantic-oriented transfer model that is based on some central ideas of the MRS-based approach outlined in [Copestake et al., 1995], and the Shake-and-Bake approach to machine translation sketched in [Whitelock, 1992]. The central idea of minimal transfer is to relate the source and target language semantic descriptions on a maximal abstract level, without falling back into the well-known problems of the Interlingua approach. Minimal transfer results in simultaneously decreasing the number of transfer rules and leaving a maximal set of options for lexicalization and grammaticalization up to the generator. In sum, MinT can be characterized as a semantic-oriented, unification-based and lexicalist transfer model. Its main knowledge base are transfer statements which provide the correspondences between underspecied semantic predicates of the source and target language. Transfer statements comprise both bilingual and monolingual correspondences. Bilingual correspondences, on the one hand, establish the equivalence between sets of semantic predicates of the source and target languages. They are formulated in a strictly declarative way and can be applied bidirectionally. In order to solve translational ambiguities, the roles and instances of a predicate are typed with fine-grained sorts that are supplied by an elaborated sort hierarchy. Monolingual correspondences, on the other hand, provide a solution to divergences in the logical structure of the languages involved. The idea is to allow the transfer component to initiate further compositional processes if this is motivated by the contrastive situation. Thus, the input structure is transformed into a logically equivalent semantic representation that is shared by the target language. This way, all contrastive knowledge is contained in the transfer component, which allows strict modularity of analysis and generation

Abstraction and underspecification in semantic transfer

This paper introduces the semantic transfer approach MinT (Minimal Transfer) that has been developed in the speech-to-speech MT system VERBMOBIL. As a unification-based and lexicalist semantic transfer model, it relies on some central ideas of the MRS-based transfer approach outlined in [Copestake et al., 1995]. It differs, however, from the latter in certain aspects: in MinT, the idea of abstraction and underspecification is worked out in much more detail and has been applied to a variety of translation phenomena. MinT relates SL and TL semantic descriptions on a maximally abstract level, which results in simultaneously decreasing the number of transfer rules and leaving a considerable amount of options for lexicalization and grammaticalization up to the generator. To preserve ambiguities that hold across the involved languages MinT processes underspecified semantic representations

Induction Mapping of the 3D-Modulated Spin Texture of Skyrmions in Thin Helimagnets

Envisaged applications of skyrmions in magnetic memory and logic devices crucially depend on the stability and mobility of these topologically non-trivial magnetic textures in thin films. We present for the first time quantitative maps of the magnetic induction that provide evidence for a 3D modulation of the skyrmionic spin texture. The projected in-plane magnetic induction maps as determined from in-line and off-axis electron holography carry the clear signature of Bloch skyrmions. However, the magnitude of this induction is much smaller than the values expected for homogeneous Bloch skyrmions that extend throughout the thickness of the film. This finding can only be understood, if the underlying spin textures are modulated along the out-of-plane z direction. The projection of (the in-plane magnetic induction of) helices is further found to exhibit thickness-dependent lateral shifts, which show that this z modulation is accompanied by an (in-plane) modulation along the x and y directions