Experimental Observation of the Thin-Shell Instability in a Collision-less Plasma

We report on the experimental observation of the instability of a plasma shell, which formed during the expansion of a laser-ablated plasma into a rarefied ambient medium. By means of a proton radiography technique, the evolution of the instability is temporally and spatially resolved on a timescale much shorter than the hydrodynamic one. The density of the thin shell exceeds that of the surrounding plasma, which lets electrons diffuse outward. An ambipolar electric field grows on both sides of the thin shell that is antiparallel to the density gradient. Ripples in the thin shell result in a spatially varying balance between the thermal pressure force mediated by this field and the ram pressure force that is exerted on it by the inflowing plasma. This mismatch amplifies the ripples by the same mechanism that drives the hydrodynamic nonlinear thin-shell instability (NTSI). Our results thus constitute the first experimental verification that the NTSI can develop in colliding flows.Funding agencies: EPSRC [EP/I031766/1, EP/K022415/1, EP/I029206/1, SFB-TR18, GRK1203, ENE2013-45661-C2-1-P, PEII-2014-008-P]; Vetenskapsradet [Dnr 2010-4063]; Triangle de la Physique RTRA network (ULIMAC)</p

Perspectives on the INternational CLassification of Diseases, 11th Revision (ICD-11); an international qualitative study to Understand and improve mental health Diagnosis using expertise by Experience: INCLUDE Study

Developed in collaboration with the WHO Department of Mental Health and Substance Abuse, this study conducted in the UK, India, and the US, integrated feedback from mental health service users into the development of the chapter on mental, behavioural, and neurodevelopmental disorders for the Eleventh Revision of the International Classification of Diseases and Related Health Problems (ICD-11). The ICD-11 is set for approval by the World Health Assembly in May, 2019. As a reporting standard and diagnostic classification system it will be highly influential on the policy, clinical practice, and research that affect mental health service users; yet this is the first study to systematically seek and collate service user perspectives on a major classification and diagnostic guideline. Focus groups were used to collect feedback on five diagnoses: depressive episode, generalised anxiety disorder, schizophrenia, bipolar type 1 disorder, and personality disorder. Participants were given the official draft diagnostic guidelines and a parallel lay translation. Data were thematically analysed. This formed the basis of co-produced recommendations for the WHO, which included features that could be added or revised to better reflect lived experience and changes to language that was confusing or objectionable to service users. The findings also indicated that an accessible lay language version of the ICD-11 could be beneficial for service users and their supporters

Evaluating laser-driven Bremsstrahlung radiation sources for imaging and analysis of nuclear waste packages

A small scale sample nuclear waste package, consisting of a 28 mm diameter uranium penny encased in grout, was imaged by absorption contrast radiography using a single pulse exposure from an X-ray source driven by a high-power laser. The Vulcan laser was used to deliver a focused pulse of photons to a tantalum foil, in order to generate a bright burst of highly penetrating X-rays (with energy >500 keV), with a source size of <0.5 mm. BAS-TR and BAS-SR image plates were used for image capture, alongside a newly developed Thalium doped Caesium Iodide scintillator-based detector coupled to CCD chips. The uranium penny was clearly resolved to sub-mm accuracy over a 30 cm2 scan area from a single shot acquisition. In addition, neutron generation was demonstrated in situ with the X-ray beam, with a single shot, thus demonstrating the potential for multi-modal criticality testing of waste materials. This feasibility study successfully demonstrated non-destructive radiography of encapsulated, high density, nuclear material. With recent developments of high-power laser systems, to 10 Hz operation, a laser-driven multi-modal beamline for waste monitoring applications is envisioned

Germinal center B cells govern their own fate via antibody feedback

Affinity maturation of B cells in germinal centers (GCs) is a process of evolution, involving random mutation of immunoglobulin genes followed by natural selection by T cells. Only B cells that have acquired antigen are able to interact with T cells. Antigen acquisition is dependent on the interaction of B cells with immune complexes inside GCs. It is not clear how efficient selection of B cells is maintained while their affinity matures. Here we show that the B cells’ own secreted products, antibodies, regulate GC selection by limiting antigen access. By manipulating the GC response with monoclonal antibodies of defined affinities, we show that antibodies in GCs are in affinity-dependent equilibrium with antibodies produced outside and that restriction of antigen access influences B cell selection, seen as variations in apoptosis, plasma cell output, T cell interaction, and antibody affinity. Feedback through antibodies produced by GC-derived plasma cells can explain how GCs maintain an adequate directional selection pressure over a large range of affinities throughout the course of an immune response, accelerating the emergence of B cells of highest affinities. Furthermore, this mechanism may explain how spatially separated GCs communicate and how the GC reaction terminates

Measurement of magnetic cavitation driven by heat flow in a plasma

We describe the direct measurement of the expulsion of a magnetic field from a plasma driven by heat flow. Using a laser to heat a column of gas within an applied magnetic field, we isolate Nernst advection and show how it changes the field over a nanosecond timescale. Reconstruction of the magnetic field map from proton radiographs demonstrates that the field is advected by heat flow in advance of the plasma expansion. This changes the dynamics of high energy density plasmas, in which heat flows and fields are strongly coupled, and may disrupt magnetised inertial confinement fusion schemes

Late-nineteenth-century chamber music and the cult of the classical adagio

Es una traducción de: Late-nineteenth-century chamber music and the cult of the classical adagio. "19th Century music" XXIII/1 (Verano 1999). Págs. 33-6

Vulnerable young people and substance use information-seeking: perceived credibility of different information sources and implications for services

This article presents exploratory qualitative data from a pragmatic sample (n== 11) of vulnerable young people (aged 13–18 years) in contact with youth services. Data were gathered during a substance-use services needs assessment project undertaken in a rural county in the United Kingdom. Semi-structured qualitative interviews explored engagement with services and narratives of episodes of substance-use information-seeking. A range of different information sources were reported, but consensus was expressed regarding source credibility. Parents, particularly mothers, and older siblings were perceived as the most credible. The range of information sources utilized by young people is discussed in terms of furthering research understanding of credibility of sources of information. Implications for services and for future research are discussed