Anisotropic focusing characteristics of micro-domain structures within crystalline Sr_0.61Ba_0.39Nb₂O₆ : the crystal ball

We report the anisotropic focusing characteristics of a spherically configured region of micro-domains that have been induced within a cubic shaped crystal of Ce:doped Sr0.61Ba0.39Nb2O6. The internal spherical structure focuses extraordinary polarised light, but not ordinary polarised. The spherical region, which is easily observed via scattering, is formed as the crystal cools down, after a repoling cycle through the Curie temperature, with an applied field. Analytic modelling of the thermal gradients that exist within the crystal during cooling reveals a small (< 1°) temperature difference between the central and outside regions. The similarity in shape between these temperature profiles and the observed scattering region suggests a possible mechanism for the growth of this spherical micro-domained structure

Faster scannerless GLR parsing

Analysis and renovation of large software portfolios requires syntax analysis of multiple, usually embedded, languages and this is beyond the capabilities of many standard parsing techniques. The traditional separation between lexer and parser falls short due to the limitations of tokenization based on regular expressions when handling multiple lexical grammars. In such cases scannerless parsing provides a viable solution. It uses the power of context-free grammars to be able to deal with a wide variety of issues in parsing lexical syntax. However, it comes at the price of less efficiency. The structure of tokens is obtained using a more powerful but more time and memory intensive parsing algorithm. Scannerless grammars are also more non-deterministic than their tokenized counterparts, increasing the burden on the parsing algorithm even further. In this paper we investigate the application of the Right-Nulled Generalized LR parsing algorithm (RNGLR) to scannerless parsing. We adapt the Scannerless Generalized LR parsing and filtering algorithm (SGLR) to implement the optimizations of RNGLR. We present an updated parsing and filtering algorithm, called SRNGLR, and analyze its performance in comparison to SGLR on ambiguous grammars for the programming languages C, Java, Python, SASL, and C++. Measurements show that SRNGLR is on average 33% faster than SGLR, but is 95% faster on the highly ambiguous SASL grammar. For the mainstream languages C, C++, Java and Python the average speedup is 16%

Temperature sensitivity of repoling in strontium barium niobate near to the glassy transition

We report the observation of an enhanced temperature sensitivity for transient repoling near to the domain freezing temperature in ferroelectric strontium barium niobate. This work has important consequences for the use of optical fields to control domain patterns in such materials. We model the repoling characteristics of the material using a Vogel-Fulcher type response and present results showing the degree of repoling as a function of field and temperature, for short duration repoling times

Free motion time-of-arrival operator and probability distribution

We reappraise and clarify the contradictory statements found in the literature concerning the time-of-arrival operator introduced by Aharonov and Bohm in Phys. Rev. {\bf 122}, 1649 (1961). We use Naimark's dilation theorem to reproduce the generalized decomposition of unity (or POVM) from any self-adjoint extension of the operator, emphasizing a natural one, which arises from the analogy with the momentum operator on the half-line. General time operators are set within a unifying perspective. It is shown that they are not in general related to the time of arrival, even though they may have the same form.Comment: 10 a4 pages, no figure

On the evolution of cosmic-superstring networks

We model the behaviour of a network of interacting (p,q) strings from IIB string theory by considering a field theory containing multiple species of string, allowing us to study the effect of non-intercommuting events due to two different species crossing each other. This then has the potential for a string dominated Universe with the network becoming so tangled that it freezes. We give numerical evidence, explained by a one-scale model, that such freezing does not take place, with the network reaching a scaling limit where its density relative to the background increases with N, the number of string types.Comment: Extra references added showing constraints on cosmic superstrings, 7 pages, 7 figure

Ballistic electron transport through magnetic domain walls

Electron transport limited by the rotating exchange-potential of domain walls is calculated in the ballistic limit for the itinerant ferromagnets Fe, Co, and Ni. When realistic band structures are used, the domain wall magnetoresistance is enhanced by orders of magnitude compared to the results for previously studied two-band models. Increasing the pitch of a domain wall by confinement in a nano-structured point contact is predicted to give rise to a strongly enhanced magnetoresistance.Comment: 4 pages, 2 figures; to appear in PRB as a brief repor

Cumulative incidence and treatment of non-simultaneous bilateral femoral neck fractures in a cohort of one thousand two hundred and fifty patients

Purpose In the Netherlands, over 20,000 patients sustain a hip fracture yearly. A first hip fracture is a risk factor for a second,