Kinetic approaches to particle acceleration at cosmic ray modified shocks

Kinetic approaches provide an effective description of the process of particle acceleration at shock fronts and allow to take into account the dynamical reaction of the accelerated particles as well as the amplification of the turbulent magnetic field as due to streaming instability. The latter does in turn affect the maximum achievable momentum and thereby the acceleration process itself, in a chain of causality which is typical of non-linear systems. Here we provide a technical description of two of these kinetic approaches and show that they basically lead to the same conclusions. In particular we discuss the effects of shock modification on the spectral shape of the accelerated particles, on the maximum momentum, on the thermodynamic properties of the background fluid and on the escaping and advected fluxes of accelerated particles.Comment: 22 pages, 7 figures, accepted for publication in MNRA

Zooarchaeological evidence of functional and social differentiation in northern Italy between the Neolithic and Bronze ages

Many sites dating from the Neolithic to the Bronze Age have been investigated in northern Italy and have provided important zooarchaeological data. These sites are mostly settlements, but also places of worship and necropoli. While there are few zooarchaeological studies for the north-western part of Italy, the north-east and the Po Valley have been better investigated. Particularly important are the pile-dwellings and the Terramare sites of the Po Valley as they have a long chronological span, the animal bone assemblages are large and, therefore, highly statistically reliable, and have been excavated relatively recently. There is evidence of functional and social differentiation in the Bronze Age which coincided with the evolution of more complex societies. The most common type of functional differentiation began when human communities started to settle and is visible in the zooarchaeological record. Until the end of the Copper Age, animal bone assemblages are characterized by the presence of both domestic animals and a relatively important proportion of wild animals. In the early Bronze Age, domestic animals dominated, if not entirely, the assemblages, and a growing interest in secondary products is evident. From the Middle Bronze Age, the foundation of semi-permanent settlements multiplied in the Alpine area, in the internal areas (secondary valleys and areas far from the main watercourses) and at medium-high altitudes. This was coupled with the seasonal occupation of sites at a high altitude, used for the practice of vertical transhumance (alpine pasture). This phenomenon implies the existence of a settlement hierarchy and, therefore, of forms of social stratification within the framework of the settlement system. Unfortunately, the few zooarchaeological studies of sites located in the Emilia Apennines do not currently allow us to confirm the existence of such links between the mountain sites and those on the plain. Nevertheless, other evidence, such as the introduction of the horse, which is attested from the late Early Bronze Age onwards, can be interpreted as proof of social differentiation; the horse was, in fact, considered a status symbol of the emerging warrior elite. Very few animal burials, dated to the period studied, show the link between animal species (such as dog, cattle, deer) and cultural practices, although a number of examples of such a relationship are provided by the terramare necropoli. In conclusion, in light of current knowledge, it seems that zooarchaeology cannot confirm the existence of important forms of social stratification. This does not mean that they cannot necessarily be postulated: the complex use of territory and the evidently communal nature of funerary and cult ceremonies (which often involved animals) that characterize the Bronze Age make it difficult to exclude the existence of such stratification

Has education lost sight of children?

The reflections presented in this chapter are informed by clinical and personal experiences of school education in the UK. There are many challenges for children and young people in the modern education system and for the professionals who support them. In the UK, there are significant gaps between the highly selective education provided to those who pay privately for it and to the majority of those educated in the state-funded system. Though literacy rates have improved around the world, many children, particularly boys, do not finish their education for reasons such as boredom, behavioural difficulties or because education does not ‘pay’. Violence, bullying, and sexual harassment are issues faced by many children in schools and there are disturbing trends of excluding children who present with behavioural problems at school whose origins are not explored. Excluded children are then educated with other children who may also have multiple problems which often just make the situation worse. The experience of clinicians suggests that school-related mental health problems are increasing in severity. Are mental health services dealing with the consequences of an education system that is not meeting children’s needs? An education system that is testing- and performance-based may not be serving many children well if it is driving important decisions about them at increasingly younger ages. Labelling of children and setting them on educational career paths can occur well before they reach secondary schools, limiting potential very early on in their developmental trajectory. Furthermore, the emphasis at school on testing may come at the expense of creativity and other forms of intelligence, which are also valuable and important. Meanwhile the employment marketplace requires people with widely different skills, with an emphasis on innovation, creativity, and problem solving. Is education losing sight of the children it is educating

Direct measurement of the pion valence quark momentum distribution, the pion light-cone wave function squared

We present the first direct measurements of the pion valence quark momentum distribution which is related to the square of the pion light-cone wave function. The measurements were carried out using data on diffractive dissociation of 500 GeV/c $\pi^-$ into di-jets from a platinum target at Fermilab experiment E791. The results show that the $|q\bar {q}>$ light-cone asymptotic wave function, which was developed using perturbative QCD methods, describes the data well for $Q^2 \sim 10 ~{\rm (GeV/c)^2}$ or more. We also measured the transverse momentum distribution of the diffractive di-jets.Comment: 13 pages, 4 figure

Magnetic Fields, Relativistic Particles, and Shock Waves in Cluster Outskirts

It is only now, with low-frequency radio telescopes, long exposures with high-resolution X-ray satellites and gamma-ray telescopes, that we are beginning to learn about the physics in the periphery of galaxy clusters. In the coming years, Sunyaev-Zeldovich telescopes are going to deliver further great insights into the plasma physics of these special regions in the Universe. The last years have already shown tremendous progress with detections of shocks, estimates of magnetic field strengths and constraints on the particle acceleration efficiency. X-ray observations have revealed shock fronts in cluster outskirts which have allowed inferences about the microphysical structure of shocks fronts in such extreme environments. The best indications for magnetic fields and relativistic particles in cluster outskirts come from observations of so-called radio relics, which are megaparsec-sized regions of radio emission from the edges of galaxy clusters. As these are difficult to detect due to their low surface brightness, only few of these objects are known. But they have provided unprecedented evidence for the acceleration of relativistic particles at shock fronts and the existence of muG strength fields as far out as the virial radius of clusters. In this review we summarise the observational and theoretical state of our knowledge of magnetic fields, relativistic particles and shocks in cluster outskirts.Comment: 34 pages, to be published in Space Science Review

Tsunami risk communication and management: Contemporary gaps and challenges

Very large tsunamis are associated with low probabilities of occurrence. In many parts of the world, these events have usually occurred in a distant time in the past. As a result, there is low risk perception and a lack of collective memories, making tsunami risk communication both challenging and complex. Furthermore, immense challenges lie ahead as population and risk exposure continue to increase in coastal areas. Through the last decades, tsunamis have caught coastal populations off-guard, providing evidence of lack of preparedness. Recent tsunamis, such as the Indian Ocean Tsunami in 2004, 2011 Tohoku and 2018 Palu, have shaped the way tsunami risk is perceived and acted upon. Based on lessons learned from a selection of past tsunami events, this paper aims to review the existing body of knowledge and the current challenges in tsunami risk communication, and to identify the gaps in the tsunami risk management methodologies. The important lessons provided by the past events call for strengthening community resilience and improvement in risk-informed actions and policy measures. This paper shows that research efforts related to tsunami risk communication remain fragmented. The analysis of tsunami risk together with a thorough understanding of risk communication gaps and challenges is indispensable towards developing and deploying comprehensive disaster risk reduction measures. Moving from a broad and interdisciplinary perspective, the paper suggests that probabilistic hazard and risk assessments could potentially contribute towards better science communication and improved planning and implementation of risk mitigation measures

On the thermoelectricity of correlated electrons in the zero-temperature limit

The Seebeck coefficient of a metal is expected to display a linear temperature-dependence in the zero-temperature limit. To attain this regime, it is often necessary to cool the system well below 1K. We put under scrutiny the magnitude of this term in different families of strongly-interacting electronic systems. For a wide range of compounds (including heavy-fermion, organic and various oxide families) a remarkable correlation between this term and the electronic specific heat is found. We argue that a dimensionless ratio relating these two signatures of mass renormalisation contains interesting information about the ground state of each system. The absolute value of this ratio remains close to unity in a wide range of strongly-correlated electron systems.Comment: 15 pages, including two figure