Phonons in Random Elastic Media and the Boson Peak

We show that the density of states of random wave equations, normalized by the square of the frequency, has a peak - sometimes narrow and sometimes broad - in the range of wave vectors between the disorder correlation length and the interatomic spacing. The results of this letter may be relevant for understanding vibrational spectra and light propagation in disordered solids

Mixing modes and measurement methods in longitudinal studies

Across the world longitudinal studies are facing falling response rates, at the same time cost imperatives are bringing into question the feasibility of large scale regular face-to-face data collection. While, the rapid development of communications technology and associated cultural changes is assumed to mean that study participants will increasingly expect to be able to answer surveys when and how it suits them. All of these factors are driving longitudinal studies to combine different modes of data collection both to increase response and to reduce costs. Mixing modes of data collection either across individuals at one point in time or within individuals over time, presents longitudinal researchers with a range of methodological challenges in both data collection and analysis. Within CLOSER, and beyond, studies are investigating different aspects of the implications of mixed mode data collection, and giving data users varying degrees of support and advice about issues that should be of concern. Drawing on evidence from across CLOSER’s longitudinal studies, this report reviews the latest evidence gathered on the effect of mixing modes and measurement methods on response, measurement issues and survey costs. The review also focuses on the implications for analysis of measures collected in different ways either across individuals at the same point in time or within individuals over time. Building on these reviews, we identify what further research is required in relation to both the design and analysis of mixed mode data collection. The contents of this report is based on a CLOSER workshop held in November 2016 (http://www.closer.ac.uk/event/mixing-modes-measurement-methods-longitudinal-studies/). The workshop and report were funded by a CLOSER Innovation grant awarded to Michaela Benzeval and Annette Jäckle (University of Essex), and Kate Tilling and Dr Andy Skinner (University of Bristol) and are part of a series of three reports (see Jäckle, Gaia, & Benzeval, 2017; Stone & Skinner, 2017)

METHOD for the IDENTIFICATION of REQUIREMENTS for DESIGNING REFERENCE PROCESSES

A reference process should consider to the needs and behaviours of the process users, as well as all relevant restrictions and boundary conditions within the company and its environment. Therefore, this contribution provides a method to synthesize relevant requirements on reference processes and supports the consideration of these requirements during the design of a new, company-specific reference process based on meta-models. The developed method was used to design a reference process for automotive predevelopment projects and its applicability and usefulness was evaluated successfully

Dynamical diversity and metastability in a hindered granular column near jamming

Granular media jam into a panoply of metastable states. The way in which these states are achieved depends on the nature of local and global constraints on grains; here we investigate this issue by means of a non-equilibrium stochastic model of a hindered granular column near its jamming limit. Grains feel the constraints of grains above and below them differently, depending on their position. A rich phase diagram with four dynamical phases (ballistic, activated, logarithmic and glassy) is revealed. The statistics of the jamming time and of the metastable states reached as attractors of the zero-temperature dynamics is investigated in each of these phases. Of particular interest is the glassy phase, where intermittency and a strong deviation from Edwards' flatness are manifest.Comment: 23 pages, 12 figure

Lipid droplets: A dynamic organelle moves into focus.

Lipid droplets (LDs) were perceived as static storage deposits, which passively participate in the energy homeostasis of both cells and entire organisms. However, this view has changed recently after the realization of a complex and highly dynamic LD proteome. The proteome contains key components of the fat mobilization system and proteins that suggest LD interactions with a variety of cell organelles, including the endoplasmic reticulum, mitochondria and peroxisomes. The study of LD cell biology, including cross-talk with other organelles, the trafficking of LDs in the cell and regulatory events involving the LD coat proteins is now on the verge of leaving its infancy and unfolds that LDs are highly dynamic cellular organelles

RfX: A Design Study for the Interactive Exploration of a Random Forest to Enhance Testing Procedures for Electrical Engines

Random Forests (RFs) are a machine learning (ML) technique widely used across industries. The interpretation of a given RF usually relies on the analysis of statistical values and is often only possible for data analytics experts. To make RFs accessible to experts with no data analytics background, we present RfX, a Visual Analytics (VA) system for the analysis of a RF's decision-making process. RfX allows to interactively analyse the properties of a forest and to explore and compare multiple trees in a RF. Thus, its users can identify relationships within a RF's feature subspace and detect hidden patterns in the model's underlying data. We contribute a design study in collaboration with an automotive company. A formative evaluation of RFX was carried out with two domain experts and a summative evaluation in the form of a field study with five domain experts. In this context, new hidden patterns such as increased eccentricities in an engine's rotor by observing secondary excitations of its bearings were detected using analyses made with RfX. Rules derived from analyses with the system led to a change in the company's testing procedures for electrical engines, which resulted in 80% reduced testing time for over 30% of all components

Excitations of attractive 1-D bosons: Binding vs. fermionization

The stationary states of few bosons in a one-dimensional harmonic trap are investigated throughout the crossover from weak to strongly attractive interactions. For sufficient attraction, three different classes of states emerge: (i) N-body bound states, (ii) bound states of smaller fragments, and (iii) gas-like states that fermionize, that is, map to ideal fermions in the limit of infinite attraction. The two-body correlations and momentum spectra characteristic of the three classes are discussed, and the results are illustrated using the soluble two-particle model.Comment: 7 pages, 5 figure

Thermodynamic picture of the glassy state

A picture for thermodynamics of the glassy state is introduced. It assumes that one extra parameter, the effective temperature, is needed to describe the glassy state. This explains the classical paradoxes concerning the Ehrenfest relations and the Prigogine-Defay ratio. As a second part, the approach connects the response of macroscopic observables to a field change with their temporal fluctuations, and with the fluctuation-dissipation relation, in a generalized non-equilibrium way.Comment: Proceedings of the Conference "Unifying Concepts in Glass Physics", ICTP, Trieste, 15 - 18 September 199

Binding between two-component bosons in one dimension

We investigate the ground state of one-dimensional few-atom Bose-Bose mixtures under harmonic confinement throughout the crossover from weak to strong inter-species attraction. The calculations are based on the numerically exact multi-configurational time-dependent Hartree method. For repulsive components we detail the condition for the formation of a molecular Tonks-Girardeau gas in the regime of intermediate inter-species interactions, and the formation of a molecular condensate for stronger coupling. Beyond a critical inter-species attraction, the system collapses to an overall bound state. Different pathways emerge for unequal particle numbers and intra-species interactions. In particular, for mixtures with one attractive component, this species can be viewed as an effective potential dimple in the trap center for the other, repulsive component.Comment: 10 pages, 10 figure