Eigen-analysis of Inviscid Fluid Structure Interaction (FSI) Systems with Complex Boundary Conditions

A method for extracting the eigenvalues and eigenmodes from complex coupled fluid-structure interaction (FSI) systems is presented. The FSI system under consideration in this case is a one-sided, inviscid flow over a finite-length compliant surface with complex boundary conditions, although the method could be applied to any FSI system. The flow is solved for the inviscid case using a boundary-element method solution of Laplace’s equation, while the finite compliant surface is solved through a finite-difference solution of the one-dimensional beam equation. The crux of the method lies in reducing the coupled fluid and structural equations down to a set of coupled linear differential equations. Standard Krylov subspace projection methods may then be used to determine the eigenvalues of the large system of linear equations. This method is applied to the analysis of hydroelastic FSI systems with complex boundary conditions that would be difficult or otherwise impossible to analyse using standard Galerkin methods. Specifically, the complex cases of inhomogeneous and discontinuous compliant wall properties and arbitrary hinge-joint conditions along the compliant surface are considered

Eigen-analysis of a Fully Viscous Boundary-Layer flow Interacting with a Finite Compliant Surface

A method and preliminary results are presented for the determination of eigenvalues and eigenmodes from fully viscous boundary layer flow interacting with a finite length one-sided compliant wall. This is an extension to the analysis of inviscid flow-structure systems which has been established in previous work. A combination of spectral and finite-difference methods are applied to a linear perturbation form of the full Navier-Stokes equations and one-dimensional beam equation. This yields a system of coupled linear equations that accurately define the spatio-temporal development of linear perturbations to a boundary layer flow over a finite-length compliant surface. Standard Krylov subspace projection methods are used to extract the eigenvalues from this complex system of equations. To date, the analysis of the development of Tollmien-Schlichting (TS) instabilities over a finite compliant surface have relied upon DNS-type results across a narrow (or even singular) spectrum of TS waves. The results from this method have the potential to describe conclusively the role that a finite length compliant surface has in the development of two-dimensional TS instabilities and other FSI instabilities across a broad spectrum

Hydraulic flow through a channel contraction: multiple steady states

We have investigated shallow water flows through a channel with a contraction by experimental and theoretical means. The horizontal channel consists of a sluice gate and an upstream channel of constant width $b_0$ ending in a linear contraction of minimum width $b_c$. Experimentally, we observe upstream steady and moving bores/shocks, and oblique waves in the contraction, as single and multiple steady states, as well as a steady reservoir with a complex hydraulic jump in the contraction occurring in a small section of the $b_c/b_0$ and Froude number parameter plane. One-dimensional hydraulic theory provides a comprehensive leading-order approximation, in which a turbulent frictional parametrization is used to achieve quantitative agreement. An analytical and numerical analysis is given for two-dimensional supercritical shallow water flows. It shows that the one-dimensional hydraulic analysis for inviscid flows away from hydraulic jumps holds surprisingly well, even though the two-dimensional oblique hydraulic jump patterns can show large variations across the contraction channel

Mean-field methods in evolutionary duplication-innovation-loss models for the genome-level repertoire of protein domains

We present a combined mean-field and simulation approach to different models describing the dynamics of classes formed by elements that can appear, disappear or copy themselves. These models, related to a paradigm duplication-innovation model known as Chinese Restaurant Process, are devised to reproduce the scaling behavior observed in the genome-wide repertoire of protein domains of all known species. In view of these data, we discuss the qualitative and quantitative differences of the alternative model formulations, focusing in particular on the roles of element loss and of the specificity of empirical domain classes.Comment: 10 Figures, 2 Table

The experiences of people bereaved by suicide regarding the press reporting of the death: qualitative study

Background: Media guidelines on suicide reporting of suicide have two purposes: to prevent further suicides, and to minimise distress to the bereaved, who are themselves at increased risk of suicide. We aimed to describe the subjective experiences of people bereaved by suicide regarding media reporting of the suicide of their friend or relative. / Methods: We conducted a cross-sectional study of staff and students aged 18–40 at 37 United Kingdom higher educational institutions in 2010 to recruit adults who had experienced bereavement by the suicide of a close contact. We analysed free-text responses to a question probing experiences of the press after the suicide, using thematic analysis to identify key themes. / Results: We analysed responses from 140 eligible respondents, and identified 3 main themes: value placed on respecting the privacy or wishes of the bereaved; respect accorded to the deceased; and the role of the press in promoting suicide prevention messages. Many respondents described negative experiences of the press, with sub-themes capturing distressing experiences relating to perceptions of journalists’ intrusive behaviour, failure to consult appropriately with the bereaved, journalists releasing private information, negatively misrepresenting the deceased, and breaching the anonymity of the deceased or bereaved. We identified considerable variation in people’s views over acceptable levels of detail reported in the press, and in some cases objections were in relation to journalists following media guidelines. These divergent views illustrate the tensions between the twin purposes of media guidelines: to prevent further suicides, and to protect the bereaved. / Conclusions: The findings from our British sample provide journalists with personal perspectives from bereaved relatives on the impact of media intrusion, speculation, and misrepresentation, and an insight into disparate views on the nature of information relatives feel comfortable disclosing. These findings suggest a need for journalists’ training to include exposure to such views, to heighten awareness of potentially distressing effects and the nuances of bereaved people’s preferences. This should aim to encourage journalists to consult with bereaved relatives more sensitively, whilst also remaining mindful of media guidelines on the reporting of suicide

How long does it take to pull an ideal polymer into a small hole?

We present scaling estimates for characteristic times $\tau_{\rm lin}$ and $\tau_{\rm br}$ of pulling ideal linear and randomly branched polymers of $N$ monomers into a small hole by a force $f$. We show that the absorbtion process develops as sequential straightening of folds of the initial polymer configuration. By estimating the typical size of the fold involved into the motion, we arrive at the following predictions: $\tau_{\rm lin}(N) \sim N^{3/2}/f$ and $\tau_{\rm br}(N) \sim N^{5/4}/f$, and we also confirm them by the molecular dynamics experiment.Comment: 4 pages, 3 figure

Statistical Mechanics of the Chinese Restaurant Process: lack of self-averaging, anomalous finite-size effects and condensation

The Pitman-Yor, or Chinese Restaurant Process, is a stochastic process that generates distributions following a power-law with exponents lower than two, as found in a numerous physical, biological, technological and social systems. We discuss its rich behavior with the tools and viewpoint of statistical mechanics. We show that this process invariably gives rise to a condensation, i.e. a distribution dominated by a finite number of classes. We also evaluate thoroughly the finite-size effects, finding that the lack of stationary state and self-averaging of the process creates realization-dependent cutoffs and behavior of the distributions with no equivalent in other statistical mechanical models.Comment: (5pages, 1 figure

Perceptions of the Use of Alcohol and Drugs after Sudden Bereavement by Unnatural Causes: Analysis of Online Qualitative Data

Bereavement is associated with an increased risk of psychiatric morbidity and all-cause mortality, particularly in younger people and after unnatural deaths. Substance misuse is implicated but little research has investigated patterns of drug or alcohol use after bereavement. We used a national online survey to collect qualitative data describing whether and how substance use changes after sudden bereavement. We conducted thematic analysis of free-text responses to a question probing use of alcohol and drugs after the sudden unnatural (non-suicide) death of a family member or a close friend. We analysed data from 243 adults in British Higher Education Institutions aged 18-40, identifying two main themes describing post-bereavement alcohol or drug use: (1) sense of control over use of drugs or alcohol (loss of control versus self-discipline), (2) harnessing the specific effects of drugs or alcohol. Across themes we identified age patterning in relation to substance misuse as a form of rebellion among those bereaved in childhood, and gender patterning in relation to men using alcohol to help express their emotions. The limitations of our sampling mean that these findings may not be generalizable from highly-educated settings to young people in the general population. Our findings describe how some young bereaved adults use drugs and alcohol to help them cope with traumatic loss, and suggest how clinicians might respond to any difficulties controlling substance use

The Association Between Personality Disorder Traits and Suicidality Following Sudden Bereavement: A National Cross-Sectional Survey

Personality disorder is associated with increased risk of suicidal behavior. The authors aimed to investigate the association between number of personality disorder traits and suicidality risk following sudden bereavement. A secondary analysis of cross-sectional data on 3,167 young adults in the United Kingdom who had experienced sudden bereavement investigated the association between number of traits (measured using a standardized screening instrument) and postbereavement suicide attempt and suicidal ideation. Using multivariable logistic regression, the authors found a linear relationship between number of traits and suicide attempt (adjusted odds ratio [AOR] = 1.36, 95% CI [1.23, 1.49]) and suicidal ideation (AOR = 1.31, 95% CI [1.25, 1.38]) following bereavement. This represented an increase in odds by 36% and 31%, respectively, for each additional personality trait. The authors suggest that individuals with a greater number of traits suggestive of a personality disorder diagnosis are at increased risk of suicidality after a negative life event

Use of Alcohol and Unprescribed Drugs after Suicide Bereavement: Qualitative Study

Studies describing the impact of suicide bereavement report an excess risk of suicide, suicide attempt, psychiatric illness, and drug and alcohol use disorders compared with the general population. However, the nature of patterns of drug and alcohol use after suicide bereavement is unclear. We used an online survey to collect qualitative data to understand whether and how drug and alcohol use changes after suicide bereavement. We conducted thematic analysis of free-text responses to a question capturing their use of alcohol and drugs after the suicide of a family member or a close friend. Analysing data from 346 adults in Britain aged 18–40, we identified three main themes describing the relationship of suicide bereavement to alcohol or drug use: (1) control over drug or alcohol use, (2) the perceived purpose of using drugs or alcohol, and (3) the attribution of drug or alcohol misuse to external factors. Overlying these themes were dimensions of control and of awareness of potential harms. This study highlights that increased use of drugs and alcohol after suicide bereavement may form part of a bereaved person’s coping strategies, and that sensitive approaches are needed when judging whether and when to intervene