Pressure study of nematicity and quantum criticality in Sr3_3Ru2_2O7_7 for an in-plane field

We study the relationship between the nematic phases of Sr$_3$Ru$_2$O$_7$ and quantum criticality. At ambient pressure, one nematic phase is associated with a metamagnetic quantum critical end point (QCEP) when the applied magnetic field is near the \textit{c}-axis. We show, however, that this metamagnetic transition does not produce the same nematic signatures when the QCEP is reached by hydrostatic pressure with the field applied in the \textit{ab}-plane. Moreover, a second nematic phase, that is seen for field applied in the \textit{ab}-plane close to, but not right at, a second metamagnetic anomaly, persists with minimal change to the highest applied pressure, 16.55 kbar. Taken together our results suggest that metamagnetic quantum criticality may not be necessary for the formation of a nematic phase in Sr$_3$Ru$_2$O$_7$

Asymptotic Stability of Ascending Solitary Magma Waves

Coherent structures, such as solitary waves, appear in many physical problems, including fluid mechanics, optics, quantum physics, and plasma physics. A less studied setting is found in geophysics, where highly viscous fluids couple to evolving material parameters to model partially molten rock, magma, in the Earth's interior. Solitary waves are also found here, but the equations lack useful mathematical structures such as an inverse scattering transform or even a variational formulation. A common question in all of these applications is whether or not these structures are stable to perturbation. We prove that the solitary waves in this Earth science setting are asymptotically stable and accomplish this without any pre-exisiting Lyapunov stability. This holds true for a family of equations, extending beyond the physical parameter space. Furthermore, this extends existing results on well-posedness to data in a neighborhood of the solitary waves.Comment: 60 pages, submitted to SIAM JM

A Modelling Approach to Generating User Acceptance Tests

Software testing, in particular acceptance testing, is a very important step in the development process of any application since it represents a way of matching the users’ expectations with the finished product´s capabilities. Typically considered as a cumbersome activity, many efforts have been made to alleviate the burden of writing tests by, for instance, trying to generate them automatically. However, testing still remains a largely neglected step. In this paper we propose taking advantage of existing requirement artifacts to semi-automatically generate acceptance tests. In particular, we use Scenarios, a requirement artifact used to describe business processes and requirements, and Task/Method models, a modelling approach taken from the Artificial Intelligence field. In order to generate User Acceptance tests, we propose a set of rules that allow transforming Scenarios (typically expressed in natural language), into Task/Methods that can in turn be used to generate the tests. Being high-level tests, close to the user experience, User Acceptance Tests verify that the expectations of the system are met from an end-user’s point of view. Using the proposed ideas, we show how the semi-automated generation of acceptance tests can be implemented by describing an ongoing development of a proof of concept web application designed to support the full process

Metamagnetic Quantum Criticality

A renormalization group treatment of metamagnetic quantum criticality in metals is presented. In clean systems the universality class is found to be of the overdamped, conserving (dynamical exponent z=3) Ising type. Detailed results are obtained for the field and temperature dependence of physical quantities including the differential susceptibility, resistivity and specific heat near the transition. An application of the theory is made to Sr3Ru2O7, which appears to exhibit a metamagnetic critical end-point at a very low temperature and a field of order 5-7T.Comment: 4 pages latex (Revtex 4) and 3 eps figure

Metamagnetic Quantum Criticality in Sr3Ru2O7

We consider the metamagnetic transition in the bilayer ruthenate, ${\rm Sr_3Ru_2O_7}$, and use this to motivate a renormalization group treatment of a zero-temperature quantum-critical end-point. We summarize the results of mean field theory and give a pedagogical derivation of the renormalization-group equations. These are then solved to yield numerical results for the susceptibility, the specific heat and the resistivity exponent which can be compared with measured data on ${\rm Sr_3Ru_2O_7}$ to provide a powerful test for the standard framework of metallic quantum criticality. The observed approach to the critical point is well-described by our theory explaining a number of unusual features of experimental data. The puzzling behaviour very near to the critical point itself, though, is not accounted for by this, or any other theory with a Fermi surface

Metamagnetism and critical fluctuations in high quality single crystals of the bilayer ruthenate Sr3Ru2O7

We report the results of low temperature transport, specific heat and magnetisation measurements on high quality single crystals of the bilayer perovskite Sr3Ru2O7, which is a close relative of the unconventional superconductor Sr2RuO4. Metamagnetism is observed, and transport and thermodynamic evidence for associated critical fluctuations is presented. These relatively unusual fluctuations might be pictured as variations in the Fermi surface topography itself. No equivalent behaviour has been observed in the metallic state of Sr2RuO4.Comment: 4 pages, 4 figures, Revtex 3.

Competing orders in M-theory: superfluids, stripes and metamagnetism

We analyse the infinite class of d = 3 CFTs dual to skew-whiffed AdS 4 × SE 7 solutions of D = 11 supergravity at finite temperature and charge density and in the presence of a magnetic field. We construct black hole solutions corresponding to the unbroken phase, and at zero temperature some of these become dyonic domain walls of an Einstein-Maxwell-pseudo-scalar theory interpolating between AdS 4 in the UV and new families of dyonic AdS 2 ×R 2 solutions in the IR. The black holes exhibit both diamagnetic and paramagnetic behaviour. We analyse superfluid and striped instabilities and show that for large enough values of the magnetic field the superfluid instability disappears while the striped instability remains. For larger values of the magnetic field there is also a first-order metamagnetic phase transition and at zero temperature these black hole solutions exhibit hyperscaling violation in the IR with dynamical exponent z = 3/2 and θ = −2

Quantum critical metamagnetism of sr(3)ru(2)o(7) under hydrostatic pressure

Contains fulltext : 92246.pdf (publisher's version ) (Open Access

A Modelling Approach to Generating User Acceptance Tests

International audienceSoftware testing, in particular acceptance testing, is a very important step in the development process of any application since it represents a way of matching the users’ expectations with the finished product´s capabilities. Typically considered as a cumbersome activity, many efforts have been made to alleviate the burden of writing tests by, for instance, trying to generate them automatically. However, testing still remains a largely neglected step. In this paper we propose taking advantage of existing requirement artifacts to semi-automatically generate acceptance tests. In particular, we use Scenarios, a requirement artifact used to describe business processes and requirements, and Task/Method models, a modelling approach taken from the Artificial Intelligence field. In order to generate User Acceptance tests, we propose a set of rules that allow transforming Scenarios (typically expressed in natural language), into Task/Methods that can in turn be used to generate the tests. Being high-level tests, close to the user experience, User Acceptance Tests verify that the expectations of the system are met from an end-user’s point of view. Using the proposed ideas, we show how the semi-automated generation of acceptance tests can be implemented by describing an ongoing development of a proof of concept web application designed to support the full process