Skyrmion States In Chiral Liquid Crystals

Within the framework of Oseen-Frank theory, we analyse the static configurations for chiral liquid crystals. In particular, we find numerical solutions for localised axisymmetric states in confined chiral liquid crystals with weak homeotropic anchoring at the boundaries. These solutions describe the distortions of two-dimensional skyrmions, known as either \textit{spherulites} or \textit{cholesteric bubbles}, which have been observed experimentally in these systems. Relations with nonlinear integrable equations have been outlined and are used to study asymptotic behaviors of the solutions. By using analytical methods, we build approximated solutions of the equilibrium equations and we analyse the generation and stabilization of these states in relation to the material parameters, the external fields and the anchoring boundary conditions.Comment: 13 pages, 13 figures, Conference: PMNP 2017: 50 years of IST, Gallipoli (LE)- Italy June 17-24, 201

The model of an anomaly detector for HiLumi LHC magnets based on Recurrent Neural Networks and adaptive quantization

This paper focuses on an examination of an applicability of Recurrent Neural Network models for detecting anomalous behavior of the CERN superconducting magnets. In order to conduct the experiments, the authors designed and implemented an adaptive signal quantization algorithm and a custom GRU-based detector and developed a method for the detector parameters selection. Three different datasets were used for testing the detector. Two artificially generated datasets were used to assess the raw performance of the system whereas the 231 MB dataset composed of the signals acquired from HiLumi magnets was intended for real-life experiments and model training. Several different setups of the developed anomaly detection system were evaluated and compared with state-of-the-art OC-SVM reference model operating on the same data. The OC-SVM model was equipped with a rich set of feature extractors accounting for a range of the input signal properties. It was determined in the course of the experiments that the detector, along with its supporting design methodology, reaches F1 equal or very close to 1 for almost all test sets. Due to the profile of the data, the best_length setup of the detector turned out to perform the best among all five tested configuration schemes of the detection system. The quantization parameters have the biggest impact on the overall performance of the detector with the best values of input/output grid equal to 16 and 8, respectively. The proposed solution of the detection significantly outperformed OC-SVM-based detector in most of the cases, with much more stable performance across all the datasets.Comment: Related to arXiv:1702.0083

Whose poverty really matters when deciding aid volumes?

This study assesses the relevance of poverty in the determination of aid volumes. In particular, it investigates whether donors' decisions about aid volumes are more reactive to changes in domestic poverty than to those in the poverty of prospective aid recipients. This is particularly relevant at times of economic crisis, which may seriously affect the proportion of donors' budgets that is devoted to foreign assistance. The present study is based on the experience of a sample of members of the Development Assistance Committee of the Organisation for Economic Cooperation and Development (OECDDAC). It finds that faster and greater changes in the volume of foreign aid occurred in response to changes in poverty in the donor countries rather than in potential recipient countries. Furthermore, donors' attitude towards poverty in low-income countries differs from the one towards poverty in middle-income countries

Relevance of poverty and governance for aid allocation

The argument that aid can bolster growth and poverty reduction only in a conducive policy environment has generated attention on some conditions of the economic, political and institutional context in the recipient country which can allow aid to contribute to pro-poor growth. This has clear implications in terms of aid allocation. This paper tries to contribute to such discussion by proposing a combined framework to address the aid-growth-poverty-governance nexus. Results show that aid is more effective - both for poverty reduction and for growth - when its allocation is inspired by a poverty-focused perspective and, to a certain extent, by a conducive environment in the recipient country. A review of aid allocation over the past thirty years supports the criticism that this does not seem to be inspired by poverty-reducing aims, but it reveals as well how this has remarkably changed. It is highlighted how both donors' poverty-focused aid allocation and recipients' proper aid utilization are necessary to improve aid effectiveness. At the same time it is considered how the ongoing changes of the poverty landscape will require some changes of the aid architecture

Spacecraft dynamics under the action of Y-dot magnetic control law

The paper investigates the dynamic behavior of a spacecraft when a single magnetic torque-rod is used for achieving a pure spin condition by means of the so-called Y-dot control law. Global asymptotic convergence to a pure spin condition is proven on analytical grounds when the dipole moment is proportional to the rate of variation of the component of the magnetic field along the desired spin axis. Convergence of the spin axis towards the orbit normal is then explained by estimating the average magnetic control torque over one orbit. The validity of the analytical results, based on some simplifying assumptions and approximations, is finally investigated by means of numerical simulation for a fully non-linear attitude dynamic model, featuring a tilted dipole model for Earth׳s magnetic field. The analysis aims to support, in the framework of a sound mathematical basis, the development of effective control laws in realistic mission scenarios. Results are presented and discussed for relevant test cases

Group analysis of the membrane shape equation

A system of PDE describing bilayers amphiphilic membranes is studied by Lie group analysis. This algorithmic approach allows us to show all the symmetries of the system, to determine all possible symmetry reductions, to recover the axisymmetric solutions, obtained by other euristic methods, and finally to address the question of new similarity solutions.Comment: 28 pages, LaTe

Light Scattering by Cholesteric Skyrmions

We study the light scattering by localized quasi planar excitations of a Cholesteric Liquid Crystal known as spherulites. Due to the anisotropic optical properties of the medium and the peculiar shape of the excitations, we quantitatively evaluate the cross section of the axis-rotation of polarized light. Because of the complexity of the system under consideration, first we give a simplified, but analytical, description of the spherulite and we compare the Born approximation results in this setting with those obtained by resorting to a numerical exact solution. The effects of changing values of the driving external static electric (or magnetic) field is considered. Possible applications of the phenomenon are envisaged.Comment: 18 pages, 14 figure

The Climate of Spaces. On Architecture, Atmospheres and Time

This paper discusses the concept of climate in relation to architectural space. By elaborating on the notion of atmosphere, that today permeates a wide range of architectural research, I intend to expand its relevance by outlining a relationship between atmosphere and climate analogous to what occurs in meteorological studies. While climate represents a rather stable (if evolving) cycle of recurring conditions, atmospheric events are fleeting and less predictable. Equally, architectural spaces can establish a general climatic scaffolding that increases the possibility of particular atmospheres to unfold, without however evolving into a deterministic cause-effect relationship. By addressing and comparing philosophical notions and architectural questions, I intend to formulate a novel theorisation as a useful tool for both criticism and design

No man is an island: the impact of Social Capital on health

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