Longitudinal instabilities affecting the moving critical layer laser-plasma ion accelerators

In this work we analyze the longitudinal instabilities of propagating acceleration structures that are driven by a relativistically intense laser at the moving plasma critical layer [1]. These instabilities affect the energy-spectra of the accelerated ion-beams in propagating critical layer acceleration schemes [2][3]. Specifically, using analytical theory and PIC simulations we look into three fundamental physical processes and their interplay that are crucial to the understanding of energy spectral control by making the laser-plasma ion accelerators stable. The interacting processes are (i) Doppler-shifted ponderomotive bunching [1][4] (ii) potential quenching by beam-loading [2] and (iii) two-stream instabilities. These phenomenon have been observed in simulations analyzing these acceleration processes [5][6][7]. From the preliminary models and results we present in this work, we can infer measures by which these instabilities can be controlled [8] for improving the energy-spread of the beams.Comment: submitted to the proceeding of the Advanced Accelerator Concepts workshop July 2014, San Jose, CA, US

Dundee Discussion Papers in Economics 179:Activism, separation of powers and development

We consider a model of constitutional (mechanism) design with separation of powers where different institutions are assigned different tasks. In this context, we define activism as an institution extending its mechanism of decision-making into the domain of other institution’s tasks. When members of the institutions are likely to be benevolent as well as non-benevolent, such activism in a limited form reduces the cost of achieving collusion-proofness and raises welfare. Hence the value of such activism can be potentially very high in the context of developing economies. But as the fraction of non-benevolent member increases, such activism turns excessive and reduces welfare. It is argued that developing economies are likely to get caught in the excessive activism trap because of the high levels of corruption and bribery

On the origin of the featureless soft X-ray excess emission from the Seyfert 1 galaxy ESO~198--G24

We present medium and high resolution X-ray spectral study of a Seyfert 1 galaxy ESO~198--G24 using a long (122 ks) XMM-Newton observation performed in February 2006. The source has a prominent featureless soft X-ray excess below 2\kev. This makes the source well suited to investigate the origin of the soft excess. Two physical models -- blurred reflection, and optically thick thermal Comptonization in a warm plasma, describe the soft-excess equally well resulting in similar fits in the 0.3-10\kev band. These models also yield similar fits to the broad-band UV (Optical Monitor) and X-ray data. XMM-Newton observations performed in 2000, 2001 and 2006 on this source show flux variability. From 2001 to 2006, the UV flux increased by $\sim23\%$ while the 2-10\kev X-ray flux as well as the soft-excess flux decreased by ~ 20. This observation can be described in the blurred reflection scenario by a truncated accretion disk whose inner-most radius had come closer to the blackhole. We find that the best-fit inner radius of the accretion disk decreases from R_{in}=4.93_{-1.10}^{+1.12}R_G to R_{in}<2.5R_G from 2001 to 2006. This leads to an increase in the UV flux and compressing the corona, leading to reduction of the powerlaw flux and therefore the soft-excess. The blurred reflection model seems to better describe the soft-excess for this source.Comment: Accepted for publication in the MNRA