Statistical inference in mechanistic models: time warping for improved gradient matching

Inference in mechanistic models of non-linear differential equations is a challenging problem in current computational statistics. Due to the high computational costs of numerically solving the differential equations in every step of an iterative parameter adaptation scheme, approximate methods based on gradient matching have become popular. However, these methods critically depend on the smoothing scheme for function interpolation. The present article adapts an idea from manifold learning and demonstrates that a time warping approach aiming to homogenize intrinsic length scales can lead to a significant improvement in parameter estimation accuracy. We demonstrate the effectiveness of this scheme on noisy data from two dynamical systems with periodic limit cycle, a biopathway, and an application from soft-tissue mechanics. Our study also provides a comparative evaluation on a wide range of signal-to-noise ratios

Tackling youth anti-social behaviour in devolving Wales: a study of the tiered approach in Swansea

Taking youth anti-social behaviour as its focus, and drawing upon a recently completed study of the operation of the tiered approach to youth anti-social behaviour in Swansea, this article examines the important effects on youth justice of both devolution and the mediation of policy by practitioners. The discussion of the policy agendas of the Westminster and Welsh Assembly Governments and the accounts of stakeholders in Swansea is structured around the following themes: de-escalation and diversion; consistency and avoiding net-widening; inclusionary welfarism and multi-agency partnership; and voluntarism, engagement and compliance

Approximate parameter inference in systems biology using gradient matching: a comparative evaluation

Background: A challenging problem in current systems biology is that of parameter inference in biological pathways expressed as coupled ordinary differential equations (ODEs). Conventional methods that repeatedly numerically solve the ODEs have large associated computational costs. Aimed at reducing this cost, new concepts using gradient matching have been proposed, which bypass the need for numerical integration. This paper presents a recently established adaptive gradient matching approach, using Gaussian processes, combined with a parallel tempering scheme, and conducts a comparative evaluation with current state of the art methods used for parameter inference in ODEs. Among these contemporary methods is a technique based on reproducing kernel Hilbert spaces (RKHS). This has previously shown promising results for parameter estimation, but under lax experimental settings. We look at a range of scenarios to test the robustness of this method. We also change the approach of inferring the penalty parameter from AIC to cross validation to improve the stability of the method. Methodology: Methodology for the recently proposed adaptive gradient matching method using Gaussian processes, upon which we build our new method, is provided. Details of a competing method using reproducing kernel Hilbert spaces are also described here. Results: We conduct a comparative analysis for the methods described in this paper, using two benchmark ODE systems. The analyses are repeated under different experimental settings, to observe the sensitivity of the techniques. Conclusions: Our study reveals that for known noise variance, our proposed method based on Gaussian processes and parallel tempering achieves overall the best performance. When the noise variance is unknown, the RKHS method proves to be more robust

Ultrafast laser inscription: perspectives on future integrated applications

This paper reviews the recent advancements achieved using ultrafast laser inscription (ULI) that highlight the cross-disciplinary potential of the technology. An overview of waveguide fabrication is provided and the three distinct types of waveguide cross-section architectures that have so far been fabricated in transparent dielectric materials are discussed. The paper focuses on two key emergent technologies driven by ULI processes. First, the recently developed photonic devices, such as compact mode-locked waveguide sources and novel mid-infrared waveguide lasers are discussed. Secondly, the phenomenon and applications of selective etching in developing ultrafast laser inscribed structures for compact lab-on-chip devices are elaborated. The review further discusses the conceivable future of ULI in impacting the aforementioned fields.</p

Disclination Unbinding Transition in Quantum Hall Liquid Crystals

We derive the the long-wavelength elastic theory for the quantum Hall smectic state starting from the Hartree-Fock approximation. Dislocations in this state lead to an effective nematic model for $T>0$, which undergoes a disclination unbinding transition from a phase with algebraic orientational order into an isotropic phase. We obtain transition temperatures which are in qualitative agreement with recent experiments which have observed large anisotropies of the longitudinal resistivities in half-filled Landau levels, lending credence to the liquid crystal interpretation of experiments.Comment: Added explanation for spin dependence of anisotropic strength: The reason for this spin oscillation is simple: in the energetics of Eqs. (4-6), there is an energy scale $e^2/l_b$ that decreases with increasing filling factor $\nu$; simultaneously the matrix elements of the Coulomb interaction [Eq. (3)] increase with increasing LL index $L$, resulting in the observed spin dependenc

Cultural Heritage Destruction: Experiments with Parchment and Multispectral Imaging

This chapter describes a highly collaborative project in digital humanities, which used tools and expertise from a diverse range of disciplines: medical physics, image science, and conservation. We describe this collaboration through three examples: the use of phantoms taken from medical physics, a historically accurate model of parchment degradation, and a detailed description of the steps taken to run experiments and collect data within a manageable budget. Each example highlights how procedures from a discipline were adapted for the project through collaboration. Whilst conservation focuses on developing methods to best preserve cultural heritage documents, we describe an unusual collaboration between conservation and image science to document through multispectral imaging the deliberate damage of a manuscript. Multispectral imaging has been utilised to examine cultural heritage documents by providing information about their physical properties. However, current digitisation efforts concentrate on recording documents in their current state. In this project, we aimed at recording the process of macroscopic document degradation using multispectral imaging, and the digital recovery of the writing using standard image processing methodologies. This project’s success lay in the intersection of knowledge of the processes of parchment deterioration and the specific processes that occur when a document is imaged: this has permitted us to construct a more successful and informed experiment. The knowledge acquired during the project allows us to address the issues related to the recovery of information from damaged parchment documents, and to determine which research questions can be addressed, and through which imaging methodology

Extinction of the N=20 neutron-shell closure for 32Mg examined by direct mass measurements

The 'island of inversion' around $^{32}$Mg is one of the most important paradigm for studying the disappearance of the stabilizing 'magic' of a shell closure. We present the first Penning-trap mass measurements of the exotic nuclides $^{29-31}$Na and $^{30-34}$Mg, which allow a precise determination of the empirical shell gap for $^{32}$Mg. The new value of 1.10(3) MeV is the lowest observed shell gap for any nuclide with a canonical magic number.Comment: 6 pages, 4 figures, submitted to Physical Review

The re-birth of the "beat": A hyperlocal online newsgathering model

This is an Author's Accepted Manuscript of an article published in Journalism Practice, 6(5-6), 754 - 765, 2012, copyright Taylor & Francis, available online at: http://www.tandfonline.com/10.1080/17512786.2012.667279.Scholars have long lamented the death of the 'beat' in news journalism. Today's journalists generate more copy than they used to, a deluge of PR releases often keeping them in the office, and away from their communities. Consolidation in industry has dislodged some journalists from their local sources. Yet hyperlocal online activity is thriving if journalists have the time and inclination to engage with it. This paper proposes an exploratory, normative schema intended to help local journalists systematically map and monitor their own hyperlocal online communities and contacts, with the aim of re-establishing local news beats online as networks. This model is, in part, technologically-independent. It encompasses proactive and reactive news-gathering and forward planning approaches. A schema is proposed, developed upon suggested news-gathering frameworks from the literature. These experiences were distilled into an iterative, replicable schema for local journalism. This model was then used to map out two real-world 'beats' for local news-gathering. Journalists working within these local beats were invited to trial the models created. It is hoped that this research will empower journalists by improving their information auditing, and could help re-define journalists' relationship with their online audiences

Spontaneous Interlayer Coherence in Double-Layer Quantum Hall Systems: Symmetry Breaking Interactions, In-Plane Fields and Phase Solitons

At strong magnetic fields double-layer two-dimensional-electron-gas systems can form an unusual broken symmetry state with spontaneous inter-layer phase coherence. The system can be mapped to an equivalent system of pseudospin $1/2$ particles with pseudospin-dependent interactions and easy-plane magnetic order. In this paper we discuss how the presence of a weak interlayer tunneling term alters the properties of double-layer systems when the broken symmetry is present. We use the energy functional and equations of motion derived earlier to evaluate the zero-temperature response functions of the double-layer system and use our results to discuss analogies between this system and Josephson-coupled superconducting films. We also present a qualitative picture of the low-energy charged excitations of this system. We show that parallel fields induce a highly collective phase transition to an incommensurate state with broken translational symmetry.Comment: 26 pages, RevTex, 8 postscript figures (submitted to Phys. Rev. B