Particle simulation study of electron heating by counter-streaming ion beams ahead of supernova remnant shocks

The growth and saturation of Buneman-type instabilities is examined with a particle-in-cell (PIC) simulation for parameters that are representative for the foreshock region of fast supernova remnant shocks. A dense ion beam and the electrons correspond to the upstream plasma and a fast ion beam to the shock-reflected ions. The purpose of the 2D simulation is to identify the nonlinear saturation mechanisms, the electron heating and potential secondary instabilities that arise from anisotropic electron heating and result in the growth of magnetic fields. We confirm that the instabilities between both ion beams and the electrons saturate by the formation of phase space holes by the beam-aligned modes. The slower oblique modes accelerate some electrons, but they cannot heat up the electrons significantly before they are trapped by the faster beam-aligned modes. Two circular electron velocity distributions develop, which are centred around the velocity of each ion beam. They develop due to the scattering of the electrons by the electrostatic wave potentials. The growth of magnetic fields is observed, but their amplitude remains low.

Electron-scale electrostatic solitary waves and shocks: the role of superthermal electrons

The propagation of electron-acoustic solitary waves and shock structures is investigated in a plasma characterized by a superthermal electron population. A three-component plasma model configuration is employed, consisting of inertial (“cold”) electrons, inertialess ? (kappa) distributed superthermal (“hot”) electrons and stationary ions. A multiscale method is employed, leading to a Korteweg-de Vries (KdV) equation for the electrostatic potential (in the absence of dissipation). Taking into account dissipation, a hybrid Korteweg-de Vries-Burgers (KdVB) equation is derived. Exact negative-potential pulse- and kink-shaped solutions (shocks) are obtained. The relative strength among dispersion, nonlinearity and damping coefficients is discussed. Excitations formed in superthermal plasma (finite ?) are narrower and steeper, compared to the Maxwellian case (infinite ?). A series of numerical simulations confirms that energy initially stored in a solitary pulse which propagates in a stable manner for large ? (Maxwellian plasma) may break down to smaller structures or/and to random oscillations, when it encounters a small-? (nonthermal) region. On the other hand, shock structures used as initial conditions for numerical simulations were shown to be robust, essentially responding to changed in the environment by a simple profile change (in width).

Welfare regimes and household income packaging in the European Union

This paper uses harmonized data for the member states of the European Union to analyse household income packaging from a 'welfare regimes' perspective. Using data from the third wave of the ECHP, it looks at how the role of welfare transfers in the income package varies across countries and welfare regimes, and assesses whether this is consistent with the predictions of welfare regime theory, having first elaborated some specific hypotheses in that regard. It finds that when one focuses on averages across countries categorized into regimes, many of these hypotheses about the role of transfers are in broad terms borne out by the evidence. However, when one focuses on individual countries rather than regime averages the picture is a good deal more complex and consistency with the range of hypotheses more limited. It is essential that this variation across countries is taken into account in interpreting and using welfare regime theory and typologies.

Persistent income poverty and deprivation in the European Union: An analysis of the first three waves of the European Community Household Panel

Poverty research has increasingly focused on persistent income poverty, both as a crucial social indicator and as a target for policy intervention. Such an approach can lead to an identification of a sub-set of poor individuals facing particularly adverse circumstances and/or distinctive problems in escaping from poverty. Here we seek to establish whether, in comparison with cross-sectional measures, persistent poverty measures also provide a better measure of exclusion from a minimally acceptable way of life and relate with other important variables in a logical fashion. Our analysis draws upon the first three waves of the ECHP and shows that a persistent poverty measure does constitute a significant improvement over its cross-sectional counterpart in the explanation of levels of deprivation. Persistent poverty is related to life-style deprivation in a manner that comes close to being uniform across countries. The measure of persistence also conforms to our expectations of how a poverty measure should behave in that, unlike relative income poverty lines, defining the threshold level more stringently enables us to identify progressively groups of increasingly deprived respondents. Overall the persistent poverty measure constitutes a significant advance on cross-sectional income measures. However, there is clearly a great deal relating to the process of accumulation and of erosion of resources, which is not fully captured in the persistent poverty measure. In the absence of such information, there is a great deal to be said for making use of both types of indictors in formulating and evaluating policies while we continue to improve our understanding of longer-term processes.

Income, deprivation, and economic strain. An analysis of the European community household panel

This paper is concerned with the relationship between household income and life-style deprivation, and their combined impact on households' perceptions of economic strain. It takes as a point of departure findings from a number of European countries showing that the relationship between income and deprivation is weaker than widely assumed and that relative income poverty lines may perform poorly in terms of identifying the most deprived households. It proceeds to examine how far these conclusions about income and deprivation can be generalized to the countries included in the first wave of the European Community Household Panel. Results show that five distinct dimensions of deprivation emerge from an overall European analysis and that these are consistent across individual countries. While a good deal of similarity is observed in the income-deprivation relationship, countries differ in the strength of relationship between income and what is termed 'current liferstyle deprivation' with the relationship being generally weakest in the richer countries. The implications of these findings for the use of relative income poverty lines are developed. Extending this analysis to an assessment of how income and deprivation combine to influence perceptions of economic strain, we show that within-nation reference group processes operating in a uniform manner across countries can account for the bulk of the variation in strain. Cross-national differences can be accounted for by corresponding variation in income and deprivation levels.

Persistent and consistent poverty in the 1994 and 1995 waves of the European Community Household Panel Survey

This paper focuses on the mismatch between income and deprivation measures of poverty. Using the first two waves of the European Community Household Panel Survey, a measure of relative deprivation is constructed and the overlap between the relative income poor and relatively deprived is examined, There is very limited overlap with the lowest relative income threshold. The overlap increases as the income threshold is raised, but it remains true that less than half those below the 60 percent relative income line are among the most deprived. Relative deprivation is shown to be related to the persistence of income poverty, but also to a range of other resource and need factors. Income and deprivation measures each contain information that can profitably be employed to enhance our understanding of poverty and a range of other social phenomena. This is illustrated by the manner in which both income poverty and relative deprivation are associated with self-reported difficulty making ends meet.

Magnetic field suppression in collision-less shocks generated during the expansion of a dense plasma into a rarefied medium

A two-dimensional numerical study of the expansion of a dense plasma through a more rarefied one is reported. The electrostatic ion-acoustic shock, which is generated during the expansion, accelerates the electrons of the rarefied plasma inducing a superthermal population which reduces electron thermal anisotropy. The Weibel instability is therefore not triggered and no self-generated magnetic fields are observed, in contrast with published theoretical results dealing with plasma expansion into vacuum. © The Author(s) 2013.

Dynamical characteristics of solitary waves, shocks and envelope modes in kappa-distributed non-thermal plasmas: an overview

Space plasmas provide abundant evidence of highly energetic particle population, resulting in a long-tailed non-Maxwellian distribution. Furthermore, the first stages in the evolution of plasmas produced during laser-matter interaction are dominated by nonthermal electrons, as confirmed by experimental observation and computer simulations. This phenomenon is efficiently modelled via a kappa-type distribution. We present an overview, from first principles, of the effect of superthermality on the characteristics of electrostatic plasma waves. We rely on a fluid model for ion-acoustic excitations, employing a kappa distribution function to model excess superthermality of the electron distribution. Focusing on nonlinear excitations (solitons), in the form of solitary waves (pulses), shocks and envelope solitons, and employing standard methodological tools of nonlinear plasmadynamical analysis, we discuss the role of excess superthermality in their propagation dynamics (existence laws, stability profile), geometric characteristics and stability. Numerical simulations are employed to confirm theoretical predictions, namely in terms of the stability of electrostatic pulses, as well as the modulational stability profile of bright- and dark-type envelope solitons.

Changing attitudes to gender roles: A longitudinal analysis of ordinal response data from the British household panel study

This article examines changes in attitudes to gender roles in contemporary Britain by using a first-order Markov process in which cumulative transition probabilities are logistic functions of a set of personal and socioeconomic characteristics of respondents. The data are taken from the British Household Panel Study (BHPS). The attitudinal responses examined take the form of ordinal responses concerning gender roles in 1991 and 2003. The likelihood function is partitioned to make possible the use of existing software for estimating model parameters. For the BHPS data, it was found that, depending on the value of the response in 1991, a variety of factors were important determinants of attitudes to gender roles by 2003.

Parametric study of non-relativistic electrostatic shocks and the structure of their transition layer

Nonrelativistic electrostatic unmagnetized shocks are frequently observed in laboratory plasmas and they are likely to exist in astrophysical plasmas. Their maximum speed, expressed in units of the ion acoustic speed far upstream of the shock, depends only on the electron-to-ion temperature ratio if binary collisions are absent. The formation and evolution of such shocks is examined here for a wide range of shock speeds with particle-in-cell simulations. The initial temperatures of the electrons and the 400 times heavier ions are equal. Shocks form on electron time scales at Mach numbers between 1.7 and 2.2. Shocks with Mach numbers up to 2.5 form after tens of inverse ion plasma frequencies. The density of the shock-reflected ion beam increases and the number of ions crossing the shock thus decreases with an increasing Mach number, causing a slower expansion of the downstream region in its rest frame. The interval occupied by this ion beam is on a positive potential relative to the far upstream. This potential pre-heats the electrons ahead of the shock even in the absence of beam instabilities and decouples the electron temperature in the foreshock ahead of the shock from the one in the far upstream plasma. The effective Mach number of the shock is reduced by this electron heating. This effect can potentially stabilize nonrelativistic electrostatic shocks moving as fast as supernova remnant shocks. 

Diffusive shock acceleration at laser-driven shocks: studying cosmic-ray accelerators in the laboratory

The non-thermal particle spectra responsible for the emission from many astrophysical systems are thought to originate from shocks via a first order Fermi process otherwise known as diffusive shock acceleration. The same mechanism is also widely believed to be responsible for the production of high energy cosmic rays. With the growing interest in collisionless shock physics in laser produced plasmas, the possibility of reproducing and detecting shock acceleration in controlled laboratory experiments should be considered. The various experimental constraints that must be satisfied are reviewed. It is demonstrated that several currently operating laser facilities may fulfil the necessary criteria to confirm the occurrence of diffusive shock acceleration of electrons at laser produced shocks. Successful reproduction of Fermi acceleration in the laboratory could open a range of possibilities, providing insight into the complex plasma processes that occur near astrophysical sources of cosmic rays.

Cosmic ray acceleration at oblique shocks

We show that the diffusion approximation breaks down for particle acceleration at oblique shocks with velocities typical of young supernova remnants. Higher order anisotropies flatten the spectral index at quasi-parallel shocks and steepen the spectral index at quasi-perpendicular shocks. We compare the theory with observed spectral indices.