Evidence that particle acceleration in hotspots of FR II galaxies is not constrained by synchrotron cooling

We study the hotspots of powerful radiogalaxies, where electrons accelerated at the jet termination shock emit synchrotron radiation. The turnover of the synchrotron spectrum is typically observed between infrared and optical frequencies, indicating that the maximum energy of non-thermal electrons accelerated at the shock is ~TeV for a canonical magnetic field of ~100 micro Gauss. We show that this maximum energy cannot be constrained by synchrotron losses as usually assumed, unless the jet density is unreasonably large and most of the jet upstream energy goes to non-thermal particles. We test this result by considering a sample of hotspots observed at radio, infrared and optical wavelengths.Comment: 7 pages, 2 figures. To be appear in the proceedings of the conference "Cosmic ray origin - beyond the standard models" (San Vito di Cadore, Italy, September 2016

Particle acceleration and magnetic field amplification in the jets of 4C74.26

We model the multi-wavelength emission in the southern hotspot of the radio quasar 4C74.26. The synchrotron radio emission is resolved near the shock with the MERLIN radio-interferometer, and the rapid decay of this emission behind the shock is interpreted as the decay of the amplified downstream magnetic field as expected for small scale turbulence. Electrons are accelerated to only 0.3 TeV, consistent with a diffusion coefficient many orders of magnitude greater than in the Bohm regime. If the same diffusion coefficient applies to the protons, their maximum energy is only ~100 TeV.Comment: Accepted for publication in ApJ. 6 pages - 2 figures. Minor correction

Cosmic ray acceleration to ultrahigh energy in radio galaxies

The origin of ultrahigh energy cosmic rays (UHECRs) is an open question. In this proceeding, we first review the general physical requirements that a source must meet for acceleration to 10-100 EeV, including the consideration that the shock is not highly relativistic. We show that shocks in the backflows of radio galaxies can meet these requirements. We discuss a model in which giant-lobed radio galaxies such as Centaurus A and Fornax A act as slowly-leaking UHECR reservoirs, with the UHECRs being accelerated during a more powerful past episode. We also show that Centaurus A, Fornax A and other radio galaxies may explain the observed anisotropies in data from the Pierre Auger Observatory, before examining some of the difficulties in associating UHECR anisotropies with astrophysical sources.Comment: 6 pages, 4 figures. Proceedings of UHECR 2018, 8-12 October 2018, Paris, Franc

Amplification of perpendicular and parallel magnetic fields by cosmic ray currents

Cosmic ray (CR) currents through magnetised plasma drive strong instabilities producing amplification of the magnetic field. This amplification helps explain the CR energy spectrum as well as observations of supernova remnants and radio galaxy hot spots. Using magnetohydrodynamic (MHD) simulations, we study the behaviour of the non-resonant hybrid (NRH) instability (also known as the Bell instability) in the case of CR currents perpendicular and parallel to the initial magnetic field. We demonstrate that extending simulations of the perpendicular case to 3D reveals a different character to the turbulence from that observed in 2D. Despite these differences, in 3D the perpendicular NRH instability still grows exponentially far into the non-linear regime with a similar growth rate to both the 2D perpendicular and 3D parallel situations. We introduce some simple analytical models to elucidate the physical behaviour, using them to demonstrate that the transition to the non-linear regime is governed by the growth of thermal pressure inside dense filaments at the edges of the expanding loops. We discuss our results in the context of supernova remnants and jets in radio galaxies. Our work shows that the NRH instability can amplify magnetic fields to many times their initial value in parallel and perpendicular shocks.Comment: Published in MNRAS. 14 pages, 12 figures, 2 tables. Replacement corrects some typesetting error

Rietveld refinements of the crystal structures of Rb2XSi5O12 (X = Mn, Ni)

Poster Number: CCG06 Synthetic analogues of the silicate framework mineral leucite (KAlSi2O6) with the stoichiometry Rb2XSi5O12 (X = Mn, Ni) have been prepared by high temperature solid-state synthesis. Ambient temperature X-ray powder diffraction data have been collected on these samples. Analysis of these powder diffraction data show that these samples both consist of single phases [1] isostructural with the Pbca cation-ordered framework leucite structure of Cs2CdSi5O12 [2]. Rietveld refinement [3] shows that for X = Mn this crystal structure has complete Mn and Si cation order over the tetrahredrally coordinated sites (T-sites) in the silicate framework. However, for X = Ni, Rietveld refinement suggests that there may be some Ni and Si cation T-site cation disorder

Polymorphism in cyclohexanol

The crystal structures and phase behaviour of phase II and the metastable phases III0 and III of cyclohexanol, C6H11OH, have been determined using high-resolution neutron powder, synchrotron X-ray powder and single-crystal X-ray diffraction techniques. Cyclohexanol-II is formed by a transition from the plastic phase I cubic structure at 265 K and crystallizes in a tetragonal structure, space group P�4421c (Z0 = 1), in which the molecules are arranged in a hydrogen-bonded tetrameric ring motif. The structures of phases III0 and III are monoclinic, space groups P21/c (Z0 = 3) and Pc (Z0 = 2), respectively, and are characterized by the formation of hydrogen-bonded molecular chains with a threefold-helical and wave-like nature, respectively. Phase III crystallizes at 195 K from a sample of phase I that is supercooled to ca 100 K. Alternatively, phase III may be grown via phase III0, the latter transforming from supercooled phase I at ca 200 K. Phase III0 is particularly unstable and is metastable with respect to both I and II. Its growth is realised only under very restricted conditions, thus making its characterization especially challenging. The cyclohexanol molecules adopt a chair conformation in all three phases with the hydroxyl groups in an equatorial orientation. No evidence was found indicating hydroxyl groups adopting an axial orientation, contrary to the majority of spectroscopic literature on solid-state cyclohexanol; however, the H atom of the equatorial OH groups is found to adopt both in-plane and out-of-plane orientations

X-Ray synchronotron study of phase transforms in illite clays to extract information on sigillata manufacturing processes.

The technique of sigillata really began in central Italy during the first century B. C. with the development of red vitrified slips obtained through vitrification of a clay preparation. These ceramics, usually decorated with raised motifs and standardised shapes, quickly took over as semi luxury crockery. Given this success, this technique quickly extended to the entire Italian peninsula and then to the Mediterranean coast. From the very start of our era, great centres of production were set up in the south of Gaul. The aspect of sigillata comes from the nature and the texture of its slip. Studies have shown that sigillata slips of quality were obtained from a non calcareous clay while the local calcareous clay was used for the bodies. During firing the slips are vitrified and get a specific microstructure containing hematite and nanometric corundum crystals [1]. An investigation of the clays surrounding La Graufesenque site started and it seems that only the Trias levels are chemically compatible with the composition of antique slips. Apart from the in depth study of the mineralogical nature of these clays realized at a geological Laboratory, we have studied the structural transformations as a function of temperature of two of these clays, chosen for the quality of vitrification in the firing temperature range of sigillata [1030-1080°C]. The main difference between the chemical composition of these two clays is the amount of Mg (2.4 % and 4.5 % in oxide weight). Time-resolved measurements were made at Daresbury (station 2.3) up to 1100oC in oxidizing conditions. An abrupt increase of the hematite cell was observed around 850°C. Above 1000°C, the hematite peaks get sharper which indicate an increase of coherence length (Fig. 1). A spinel phase with cell parameter close to MgAl2O3 was detected from this temperature. As for the hematite, its coherence length increases with the temperature but also during the beginning of the cooling. For the clay sample with the smaller amount of Mg, a corundum phase with very small coherence length was detected above 1000°C. Slips were prepared from the last clay by modern potters and firing at 1050°C in oxidizing atmosphere. A mineral quantitative analysis performed using the Rietveld method revealed that the amount of spinel phase is very high while the corundum contributes to a small part of crystal phases. It is the inverse in the antique slip where the amount of Mg in oxide weight is around 1%. It is clear that the amount of Mg plays a key role in the corundum/spinel competition and that the present slips contain too much Mg. Two questions arise: (i) As the Trias levels are quite heterogeneous is it possible to find clay with less Mg? and (ii) Did the gallo-roman potters eliminated a great part of Mg during the slip preparation process? We discuss the merits of these two alternative hypotheses

X-ray Fluorescence Analysis of Feldspars and Silicate Glass: Effects of Melting Time on Fused Bead Consistency and Volatilisation

Reproducible preparation of lithium tetraborate fused beads for XRF analysis of glass and mineral samples is of paramount importance for analytical repeatability. However, as with all glass melting processes, losses due to volatilisation must be taken into account and their effects are not negligible. Here the effects of fused bead melting time have been studied for four Certified Reference Materials (CRM’s: three feldspars, one silicate glass), in terms of their effects on analytical variability and volatilisation losses arising from fused bead preparation. At melting temperatures of 1065 °C, and for feldspar samples, fused bead melting times shorter than approximately 25 min generally gave rise to a greater deviation of the XRF-analysed composition from the certified composition. This variation might be due to incomplete fusion and/or fused bead inhomogeneity but further research is needed. In contrast, the shortest fused bead melting time for the silicate glass CRM gave an XRF-analysed composition closer to the certified values than longer melting times. This may suggest a faster rate of glass-in-glass dissolution and homogenization during fused bead preparation. For all samples, longer melting times gave rise to greater volatilisation losses (including sulphates and halides) during fusion. This was demonstrated by a linear relationship between SO3 mass loss and time1/2, as predicted by a simple diffusion-based model. Iodine volatilisation displays a more complex relationship, suggestive of diffusion plus additional mechanisms. This conclusion may have implications for vitrification of iodine-bearing radioactive wastes. Our research demonstrates that the nature of the sample material impacts on the most appropriate fusion times. For feldspars no less than ~25 min and no more than ~60 min of fusion at 1065 °C, using Li2B4O7 as the fusion medium and in the context of feldspar samples and the automatic fusion equipment used here, strikes an acceptable (albeit non-ideal) balance between the competing factors of fused bead quality, analytical consistency and mitigating volatilisation losses. Conversely, for the silicate glass sample, shorter fusion times of less than ~30 min under the same conditions provided more accurate analyses whilst limiting volatile losses

Nanoparticulate nickel sulfides formed in low temperature aqueous solutions

The nature of the nickel sulfides formed in low temperature aqueous solutions is not well-understood. The material has some intrinsic interest to mineralogy, geochemistry and materials science as well as to biogeochemisty, especially as a possible catalyst involved in the origin and early evolution of life. We synthesized Ni sulfide under anoxic conditions at 25 C: (1) chemically, by the addition of 50 mL of 0.1 M NiSO4Æ7H2O to 100 mL of 0.05M Na2SÆ9H2O; (2) electrochemically, with a Ni foil and H2S gas. At pH 6 5, millerite (b-NiS) was produced electrochemically and NiS mixtures, including heazlewoodite (Ni3S2) and polydymite (Ni3S4), were obtained chemically. At pH >11, a- NiS was obtained from the chemical reaction. At pH 6–9, the product produced only two broad peaks (d = ca. 2.7 and 1.8 ) with conventional and synchrotron XRPD which could be assigned to a number of Ni sulfides. It has previously been referred to as ‘‘amorphous NiS’’ Jeong and Manthiram, 2001. Eight SAED reflections were collected which identified the material as godlevskite, orthorhombic NiS. HRTEM shows that the godlevskite particles are ca. 30 nm in diameter and plate-like. SAXS analyses show that the material is 6–8.5 nm thick. Godlevskite is structurally related to makinawite, tetragonal FeS, and is found naturally in similar parageneses-associated with the monosulfide solid solution products of high temperature nickel ores. Mackinawite is the black FeS precipitate from the reaction between Fe(II) and S(-II) in aqueous solution. It appears that, geochemically, godlevskite is the Ni analogue of mackinawite