Breaking Symmetry with Light: Ultra-Fast Ferroelectricity and Magnetism from Three-Phonon Coupling

A theory describing how ferroic properties can emerge transiently in the ultra-fast regime by breaking symmetry with light through three-phonon coupling is presented. Particular emphasis is placed on the special case when two exactly degenerate mid-infra-red or THz phonons are resonantly pumped, since this situation can give rise to an exactly rectified ferroic response with damping envelopes of ~ 1 ps or less. Light-induced ferroelectricity and ferromagnetism are discussed in this context, and a number of candidate materials that could display these phenomena are proposed. The same analysis is also applied to the interpretation of previous femto-magnetism experiments, performed in different frequency ranges (visible and near-infrared), but sharing similar symmetry characteristics.Comment: 10 page

Intraplanar couplings in the CuO_2 lattice of cuprate superconductors

We have investigated the doping dependencies of the basal areas in single-layer high-T_c cuprates La_{2-x}Sr_xCuO_4 and HgBa_2CuO_x, as well as in two-layer Y_{1-y}Ca_yBa_2Cu_3O_x and HgBa_2CaCu_2O_x. The basal areas not only tend to shrink on hole doping, as expected from single electron quantum chemistry, but exhibit also a "bulge'' around optimum doping. We attribute the "bulge'' to the effects of the strongly correlated quantum liquid on the CuO_2 lattice, rendering it nearly incompressible around optimum doping, but highly compressible in the weakly overdoped regime. Inhomogenous doping cannot account for this anomaly in the electronic compressibility of the CuO_2 lattice.Comment: 2 pages, 2 figures, to appear in Physica C (Proc. M2S-HTSC-VII

Ab initio calculation of spin fluctuation spectra using time dependent density functional perturbation theory, planewaves, and pseudopotentials

We present an implementation of time-dependent density functional perturbation theory for spin fluctuations, based on planewaves and pseudopotentials. We compute the dynamic spin susceptibility self-consistently by solving the time-dependent Sternheimer equation, within the adiabatic local density approximation to the exchange and correlation kernel. We demonstrate our implementation by calculating the spin susceptibility of representative elemental transition metals, namely bcc Fe, fcc Ni and bcc Cr. The calculated magnon dispersion relations of Fe and Ni are in agreement with previous work. The calculated spin susceptibility of Cr exhibits a soft-paramagnon instability, indicating the tendency of the Cr spins to condense in a incommensurate spin density wave phase, in agreement with experiment

Los vinos ibéricos en Roma (y Ostia) en el Medio Imperio (siglo II ‒ principios del III d. C.). Análisis y revisiones de datos

The excavations in the building known as the Terme di Elagabalo in Rome revealed large amounts of fragments. The amounts of Iberian wine-amphorae found in the Middle Imperial contexts of this site (2nd – early 3rd centuries AD) will be added to those found in other excavations carried out in Rome and Ostia in order to ponder over their presence in both cities during this period. Also, ancient sources will be analyzed so as to identify the quality of these wines (including also the defrutum), leading to a reflection (with theories derived from social sciences) regarding their consumers

Orbital ordering promotes weakly-interacting S=1/2 dimers in the triangular lattice compound Sr3Cr2O8

The weakly interacting S=1/2 dimers system Sr3Cr2O8 has been investigated by powder neutron diffraction and inelastic neutron scattering. Our data reveal a structural phase transition below room temperature corresponding to an antiferro-orbital ordering with nearly 90 degrees arrangement of the occupied 3z^2-r^2 d-orbital. This configuration leads to a drastic reduction of the inter-dimer exchange energies with respect to the high temperature orbital-disorder state, as shown by a spin-dimer analysis of the super-superexchange interactions performed using the Extended Huckel Tight Binding method. Inelastic neutron scattering reveals the presence of a quasi non-dispersive magnetic excitation at 5.4 meV, in agreement with the picture of weakly-interacting dimers

Probabilistic Modeling Approach to Crack Nucleation from Forging Flaws

Der Prozess der Rissbildung aus Schmiedefehlern ist in der Literatur kaum beschrieben. In dieser Arbeit wurde dies durch umfangreiche Experimente und verschiedene Modellierungsans ätze gründlich untersucht. Sie ist eine Fortsetzung des Probabilistic Fracture Mechanics (ProbFM) Projektes, welches eine konservative Bewertung des Versagensrisikos basierend auf dem Wachstum von Ermüdungsrissen aus inhärenten Schmiedefehlern in großen Hochleistungsgasturbinen ermöglicht. Der Fokus der Versuchsreihe lag auf der Charakterisierung von typischen Schmiedefehlern und der Quantifizierung der Nukleationslebensdauer durch zyklische Belastung des Materials. Die Nukleationslebensdauer wurde definiert als die Anzahl der Belastungszyklen, die erforderlich sind, um einen scharfen Riss aus einem anfänglichen Fehler zu erzeugen. Dieser Teil des Lebenszyklus wird normalerweise beim Design ignoriert und konservativ gleich null Zyklen angenommen. Aus den Experimenten wissen wir, dass dies nicht stimmt und dass oft etwa 50% der Lebensdauer auf den Nukleationsprozess entfallen. Das Hauptziel der Untersuchungen ist die Entwicklung eines effektiven Modellierungsansatzes zur Quantifizierung der Nukleationslebensdauer von Fehlern unter variierenden Belastungsbedingungen. Dieser Ansatz muss dann in ein Engineering- Tool eingebettet werden, welches zum Design realer Komponenten verwendet wird. Es wurden drei verschiedene Modellierungsansätze untersucht, von denen einer in ProbFM implementiert wurde. Im ersten Ansatz wird der Fehler als eingebettetes Ellipsoid innerhalb des Matrixmaterials mit einer Finite-Elemente-Methode modelliert. Das Dehnungsfeld um das Ellipsoid, das sich aus den angelegten Spannungen und Temperaturen ergibt, dient als Eingabe für die lokale probabilistische LCF Bewertung. Bei dieser Bewertung wird die Wahrscheinlichkeit für Rissbildung als Oberfl¨achenintegral der lokalen Hazarddichte berechnet. Die zugrunde liegende Modellannahme ist, dass die lokale LCF-Lebensdauer Weibull verteilt ist. Der zweite und dritte Versuch basieren auf der Annahme eines Fehlers, der als flacher Oberflächenbereich modelliert ist. Auch hier wird die lokale probabilistische LCF-Lebensdauer berechnet und, in einem Fall, mit einem Lebensdauermultiplikationsfaktor w und, in dem anderen Fall, mit einem Spannungskonzentrationsfaktor Kt korrigiert. Das flächenbasierte Modell mit dem kalibrierten Spannungskonzentrationsfaktor passt am besten zu den experimentellen Ergebnissen und wird zur Implementierung vorgeschlagen. Der Konservatismus wurde während der gesamten Analyse berücksichtigt, um ein zuverlässiges Modell zu gewährleisten, das für eine technische Anwendung geeignet ist. Das resultierende Modell wurde in einer Zuverlässigkeitsbewertung eines realen Rotorscheibendesigns vorgestellt. Die erhaltenen Ausfallwahrscheinlichkeiten sind geringer, wenn die Nukleationslebensdauer berücksichtigt wird, und die Lebensdauer der Komponenten kann potenziell verlängert werden

Micromagnetic modelling and imaging of vortex/merons structures in an oxide | metal heterostructure

Using micromagnetic simulations, we have modelled the formation of imprinted merons and anti-merons in cobalt overlayers of different thickness (1-8 nm), stabilised by interfacial exchange with antiferromagnetic vortices in α-Fe2O3. Structures similar to those observed experimentally could be obtained with reasonable exchange parameters, also in the presence of surface roughness. We produce simulated meron/antimeron images by magnetic force microscopy (MFM) and nitrogen-vacancy (N-V) centre microscopy, and established signatures of these topological structures in different experimental configurations

Occupy the semantic space! Opening up the language of better regulation

Policy agendas are often cast in semantic constructions that portray them as universally desirable outcomes. These semantic constructions protect and reinforce the power of dominant coalitions and make it hard to pursue alternatives. The semantic space is entirely occupied by the dominant concepts. At the same time, within the dominant coalition, ideational conflict is muted by decontesting concepts. Drawing on political theory, I show the presence of this double act of reducing the semantic space and decontesting concepts with the case of ‘better regulation’. Then I briefly extend the argument to other terms such as policy coherence, agile governance, smart cities and social value judgements. The critical discussion of the implications of dominant language brings in transparency, allows other coalitions to articulate their vision in a discursive level-playing-field, and offers citizens the possibility to discuss what is really ‘better’ and ‘for whom’

Better regulation and the Lisbon agenda

Conference paper given at the European Evaluation Society Conference: 'Evaluation in Society: Critical Connections', London, October 4th-6th 2006This paper assesses the congruence between the initiatives for regulatory reform known as ‘better regulation’ and the recently re-formulated ‘growth and jobs’ Lisbon agenda of the European Union. To do that, better regulation is re-conceptualised as meta-regulation - sets of rules on the process of rule-formulation, adoption, implementation, and evaluation. Meta-regulation has both structural and discursive properties. Better regulation discourse has been re-defined over the years. Its malleability has enabled policy-makers to address different objectives and to push for their shifting regulatory reform agendas. This explains how the better regulation pendulum has been able to swing between regulatory quantity (or de-regulation) and quality across time and even across the same country. In terms of structural properties, there is diversity across time and countries on fundamental issues such as the dominant stakeholders and the contents of regulatory impact assessment. ‘Better regulation’ has been re-defined by the Barroso Commission to fit in with the ‘growth and jobs’ priorities of Lisbon. This re-definition, however, has also narrowed the scope, the range of stakeholders, and the ambitions in terms of governance and regulatory legitimacy. Diversity, proliferation of objectives and better regulation rhetoric make the relationship between meta-regulation, the Lisbon agenda, and, looking at the long-term impact, the dynamics of the regulatory state problematic. The quality-quantity divide and the role played by credibility and regulatory legitimacy are critical for the development of meta-regulation and its impact on the regulatory state

The puzzle of regulatory competition

Our understanding of international competition in regulatory policies has not progressed much because conventional theories lead to a bewildering range of conclusions. Empirical evidence has shown the limitations of simplistic models. Fresh work should overcome the obsession with ‘races’ and ‘final outcomes’ of conventional theoretical approaches and start modelling real-world mechanisms of regulatory competition. The first part of the article shows the limitations of conventional theories. The second introduces eight problems that explanations of international regulatory competition should address. It also discusses how the articles presented here contribute to the solution to problematic aspects of the puzzle. The conclusion reports results achieved in terms of key concepts of regulatory competition, sequences of cooperation and competition, the role of non-unitary actors in networked regulatory action, and why regulatory competition is still limited, both in the EU and in transatlantic relations