Neutron-diffraction study of field-induced transitions in the heavy-fermion compound Ce2RhIn8

We present neutron diffraction measurements in high magnetic fields (0 to 14.5 T) and at low temperatures (2.5, 2.3, 0.77 and 0.068 K) on single crystals of the tetragonal heavy fermion antiferromagnet Ce2RhIn8. For B//[110] the field dependence of selected magnetic and nuclear reflections reveals that the material undergoes several transitions, the temperature dependence of which suggests a complex B-T phase diagram. We present the detailed evolution of the integrated intensities of selected reflections and discuss the associated field-induced transitions.Comment: 12 pages, 3 figures Proceeding Euro-conference "Properties of Condensed Matter probed by x-ray and neutron scattering"; to appear in Physica

Continuous measurements of greenhouse gases and atmospheric oxygen at the Namib Desert atmospheric observatory

A new coastal background site has been established for observations of greenhouse gases (GHGs) in the central Namib Desert at Gobabeb, Namibia. The location of the site was chosen to provide observations for a data-poor region in the global sampling network for GHGs. Semi-automated continuous measurements of carbon dioxide, methane, nitrous oxide, carbon monoxide, atmospheric oxygen, and basic meteorology are made at a height of 21 m a.g.l., 50 km from the coast at the northern border of the Namib Sand Sea. Atmospheric oxygen is measured with a differential fuel cell analyzer (DFCA). Carbon dioxide and methane are measured with an early-model cavity ring-down spectrometer (CRDS); nitrous oxide and carbon monoxide are measured with an off-axis integrated cavity output spectrometer (OA-ICOS). Instrument-specific water corrections are employed for both the CRDS and OA-ICOS instruments in lieu of drying. The performance and measurement uncertainties are discussed in detail. As the station is located in a remote desert environment, there are some particular challenges, namely fine dust, high diurnal temperature variability, and minimal infrastructure. The gas handling system and calibration scheme were tailored to best fit the conditions of the site. The CRDS and DFCA provide data of acceptable quality when base requirements for operation are met, specifically adequate temperature control in the laboratory and regular supply of electricity. In the case of the OA-ICOS instrument, performance is significantly improved through the implementation of a drift correction through frequent measurements of a reference cylinder

Nuclear Effects on Bremsstrahlung Neutrino Rates of Astrophysical Interest

We calculate in this work the rates for the neutrino pair production by nucleon-nucleon bremsstrahlung taking into account the full contribution from a nuclear one-pion-exchange potential. It is shown that if the temperatures are low enough ($T \leq 20 MeV$), the integration over the nuclear part can be done for the general case, ranging from the completely degenerate (D) to the non-degenerate (ND) regime. We find that the inclusion of the full nuclear contribution enhances the neutrino pair production by $nn$ and $pp$ bremsstrahlung by a factor of about two in both the D and ND limits when compared with previous calculations. This result may be relevant for the physical conditions of interest in the semitransparent regions near the neutrinosphere in type II supernovae, cooling of neutron stars and other astrophysical situations.Comment: 11 pages, no figures, LaTex file. submitted to PR

A Matrix Hyperbolic Cosine Algorithm and Applications

In this paper, we generalize Spencer's hyperbolic cosine algorithm to the matrix-valued setting. We apply the proposed algorithm to several problems by analyzing its computational efficiency under two special cases of matrices; one in which the matrices have a group structure and an other in which they have rank-one. As an application of the former case, we present a deterministic algorithm that, given the multiplication table of a finite group of size $n$, it constructs an expanding Cayley graph of logarithmic degree in near-optimal O(n^2 log^3 n) time. For the latter case, we present a fast deterministic algorithm for spectral sparsification of positive semi-definite matrices, which implies an improved deterministic algorithm for spectral graph sparsification of dense graphs. In addition, we give an elementary connection between spectral sparsification of positive semi-definite matrices and element-wise matrix sparsification. As a consequence, we obtain improved element-wise sparsification algorithms for diagonally dominant-like matrices.Comment: 16 pages, simplified proof and corrected acknowledging of prior work in (current) Section

Magnetic structure of CeRhIn_5 as a function of pressure and temperature

We report magnetic neutron-diffraction and electrical resistivity studies on single crystals of the heavy-fermion antiferromagnet CeRhIn$_{5}$ at pressures up to 2.3 GPa. These experiments show that the staggered moment of Ce and the incommensurate magnetic structure change weakly with applied pressure up to 1.63 GPa, where resistivity, specific heat and NQR measurements confirm the presence of bulk superconductivity. This work places new constraints on an interpretation of the relationship between antiferromagnetism and unconventional superconductivity in CeRhIn$_{5}$.Comment: 6 pages, 6 figures, submitted to Phys. Rev.

Magnetic Structure Of Cerhin5 As A Function Of Pressure And Temperature

We report magnetic neutron-diffraction and electrical resistivity studies on single crystals of the heavy-fermion antiferromagnet CeRhIn5 at pressures up to 2.3 GPa. These experiments show that the staggered moment of Ce and the incommensurate magnetic structure change weakly with applied pressure up to 1.63 GPa, where resistivity, specific heat and nuclear quadrupole resonance measurements confirm the presence of bulk superconductivity. This work places important constraints on an interpretation of the relationship between antiferromagnetism and unconventional superconductivity in CeRhIn 5.692244031244036Heffner, R.H., Norman, M.R., (1996) Comments Condens. Matter Phys., 17, p. 361Stewart, G.R., (2001) Rev. Mod. Phys., 73, p. 797Mathur, N.D., Grosche, F.M., Julian, S.R., Walker, I.R., Freye, D.M., Haselwimmer, R.K.W., Lonzarich, G.G., (1998) Nature (London), 394, p. 39Sato, N.K., Aso, N., Miyake, K., Shiina, R., Thalmeier, P., Varelogiannis, G., Geibel, C., Komatsubara, T., (2001) Nature (London), 410, p. 340Fisk, Z., Ott, H.R., Smith, J.L., (1986) Proceedings of the Sixth Annual Conference, , Los Alamos, NM, USA, (unpublished)Fisk, Z., Hess, D.W., Pethick, C.J., Pines, D., Smith, J.L., Thompson, J.D., Willis, J.O., (1988) Science, 239, p. 4835Miyake, K., Schmitt-Rink, S., Varma, C.M., (1986) Phys. Rev. B, 34, p. 6554Monthoux, P., Balatsky, A.V., Pines, D., (1991) Phys. Rev. Lett., 67, p. 3448Coleman, P., Pepin, C., (2002) Physica B, 312-313, p. 383Walker, I.R., Grosche, F.M., Freye, D.M., Lonzarich, G.G., (1997) Physica C, 282-287, p. 303Morin, P., Vettier, C., Flouquet, J., Konczykowski, M., Lassailly, Y., Mignot, J.M., Welp, U., (1988) J. Low Temp. Phys., 70, p. 377Jaccard, D., Wilhelm, H., Alami-Yadri, K., Vargoz, E., (1999) Physica B, 259-261, p. 1Jaccard, D., Behnia, K., Sierro, J., (1992) Phys. Lett. A, 163, p. 475Thompson, J.D., Parks, R.D., Borges, H., (1986) J. Magn. Magn. Mater., 54-57, p. 377Grosche, F.M., Julian, S.R., Mathur, N.D., Lonzarich, G.G., (1996) Physica B, 223-224, p. 50Movshovich, R., Graf, T., Mandrus, D., Thompson, J.D., Smith, J.L., Fisk, Z., (1996) Phys. Rev. B, 53, p. 8241Petrovic, C., Moshopoulou, E.G., Hundley, M.F., Sarrao, J.L., Fisk, Z., Thompson, J.D., (2000) Phys. Rev. Lett., 84, p. 4986Petrovic, C., Movshovich, R., Jaime, M., Pagliuso, P.G., Hundley, M.F., Sarrao, J.L., Fisk, Z., Thompson, J.D., (2001) Europhys. Lett., 53, p. 354Petrovic, C., Pagliuso, P.G., Hundley, M.F., Movshovich, R., Sarrao, J.L., Thompson, J.D., Fisk, Z., Monthoux, P., (2001) J. Phys.: Condens. Matter, 13, pp. L337Zheng, G.-Q., Tanabe, K., Mito, T., Kawasaki, S., Kitaoka, Y., Aoki, D., Haga, Y., Onuki, Y., (2001) Phys. Rev. Lett., 86, p. 4664Movshovich, R., Jaime, M., Thompson, J.D., Petrovic, C., Fisk, Z., Pagliuso, P.G., Sarrao, J.L., (2001) Phys. Rev. Lett., 86, p. 5152Fisher, R.A., Bouquet, F., Phillips, N.E., Hundley, M.F., Pagliuso, P.G., Sarrao, J.L., Fisk, Z., Thompson, J.D., (2002) Phys. Rev. B, 65, p. 224509Kawasaki, S., Mito, T., Kawasaki, Y., Zheng, G.-Q., Kitaoka, Y., Aoki, D., Haga, Y., Onuki, Y., cond-mat/0303123 (unpublished)Mito, T., Kawasaki, S., Zheng, G.-Q., Kawasaki, Y., Ishida, K., Kitaoka, Y., Aoki, D., Onuki, Y., (2001) Phys. Rev. B, 63, p. 220507Mito, T., Kawasaki, S., Zheng, G.-Q., Kawasaki, Y., Ishida, K., Kitaoka, Y., Aoki, D., Onuki, Y., (2002) Physica B, 312-313, p. 16Izawa, K., Yamaguchi, H., Matsuda, Y., Shishido, H., Settai, R., Onuki, Y., (2001) Phys. Rev. Lett., 87, p. 057002Pagliuso, P.G., Petrovic, C., Movshovich, R., Hall, D., Hundley, M.F., Sarrao, J.L., Thompson, J.D., Fisk, Z., (2001) Phys. Rev. B, 64, p. 100503Zapf, V.S., Freeman, E.J., Bauer, E.D., Petricka, J., Sirvent, C., Frederick, N.A., Dickey, R.P., Maple, M.B., (2002) Phys. Rev. B, 65, p. 014506Moshopoulou, E.G., Fisk, Z., Sarrao, J.L., Thompson, J.D., (2001) J. Solid State Chem., 158, p. 25Curro, N.J., Hammel, P.C., Pagliuso, P.G., Sarrao, J.L., Thompson, J.D., Fisk, Z., (2000) Phys. Rev. B, 62, pp. R6100Bao, W., Pagliuso, P.G., Sarrao, J.L., Thompson, J.D., Fisk, Z., Lynn, J.W., Erwin, R.W., (2000) Phys. Rev. B, 62, p. 14621(2003) Phys. Rev. B, 67, pp. 099903EMito, T., Kawasaki, S., Kawasaki, Y., Zheng, G.-Q., Kitaoka, Y., Aoki, D., Haga, Y., Onuki, Y., (2003) Phys. Rev. Lett., 90, p. 077004Bao, W., Trevino, S.F., Lynn, J.W., Pagliuso, P.G., Sarrao, J.L., Thompson, J.D., Fisk, Z., (2002) Appl. Phys. A Mater. Sci. Process. A, 74, p. 557Majumdar, S., Balakrishnan, G., Lees, M.R., Paul, D.McK., McIntyre, G.J., (2002) Phys. Rev. B, 66, p. 212502Kawasaki, S., (2002) Phys. Rev. B, 65, p. 020504Shishido, H., Settai, R., Araki, S., Ueda, T., Inada, Y., Kobayashi, T.C., Muramatsu, T., Onuki, Y., (2002) Phys. Rev. B, 66, p. 214510Kumar, R.S., Kohlmonn, H., Light, B.E., Cornelius, A.L., Raghavan, V., Darling, T.W., Sarrao, J.L., cond-mat/0209005 (unpublished)Moshopoulou, E.G., Fisk, Z., Sarrao, J.L., Thompson, J.D., (2001) J. Solid State Chem., 25, p. 158Pagliuso, P.G., Petrovic, C., Movshovich, R., Hall, D., Hundley, M.F., Sarrao, J.L., Thompson, J.D., Fisk, Z., (2001) Phys. Rev. B, 64, p. 100503Thompson, J.D., (1984) Rev. Sci. Instrum., 55, p. 231Bao, W., Aeppli, G., Lynn, J.W., Pagliuso, P.G., Sarrao, J.L., Hundley, M.F., Thompson, J.D., Fisk, Z., (2002) Phys. Rev. B, 65, p. 100505Cooper, M.J., (1968) Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr., A6, p. 624Cooper, M.J., Nathans, R., (1968) Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr., A6, p. 619Mignot, J.-M., Bourdarot, F., Llobet, A., Abanov, Ar., private communicationBlume, M., Freeman, A.J., Watson, R.E., (1962) J. Chem. Phys., 37, p. 1245Christianson, A.D., Lawrence, J.M., Pagliuso, R.G., Moreno, N.O., Sarrao, J.L., Thompson, J.D., Riseborough, P.S., Lacerda, A.H., (2002) Phys. Rev. B, 66, p. 193102Curro, N.J., Sarrao, J.L., Thompson, J.D., Pagliuso, P.G., Kos, S., Abanov, Ar., Pines, D., (2003) Phys. Rev. Lett., 90, p. 227202Knebel, G., Braithwaite, D., Canfield, P.C., Lapertot, G., Flouquet, J., (2002) High Press. Res., 22, p. 16

A holographic perspective on non-relativistic conformal defects

We study defects in non-relativistic conformal field theories. As in the well-studied case of relativistic conformal defects, we find that a useful tool to organize correlation functions is the defect operator expansion (dOPE). We analyze how the dOPE is implemented in theories with a holographic dual, highlighting some interesting aspects of the operator/state mapping in non-relativistic holography.Comment: 20 page

Magnetic Reconnection in Extreme Astrophysical Environments

Magnetic reconnection is a basic plasma process of dramatic rearrangement of magnetic topology, often leading to a violent release of magnetic energy. It is important in magnetic fusion and in space and solar physics --- areas that have so far provided the context for most of reconnection research. Importantly, these environments consist just of electrons and ions and the dissipated energy always stays with the plasma. In contrast, in this paper I introduce a new direction of research, motivated by several important problems in high-energy astrophysics --- reconnection in high energy density (HED) radiative plasmas, where radiation pressure and radiative cooling become dominant factors in the pressure and energy balance. I identify the key processes distinguishing HED reconnection: special-relativistic effects; radiative effects (radiative cooling, radiation pressure, and Compton resistivity); and, at the most extreme end, QED effects, including pair creation. I then discuss the main astrophysical applications --- situations with magnetar-strength fields (exceeding the quantum critical field of about 4 x 10^13 G): giant SGR flares and magnetically-powered central engines and jets of GRBs. Here, magnetic energy density is so high that its dissipation heats the plasma to MeV temperatures. Electron-positron pairs are then copiously produced, making the reconnection layer highly collisional and dressing it in a thick pair coat that traps radiation. The pressure is dominated by radiation and pairs. Yet, radiation diffusion across the layer may be faster than the global Alfv\'en transit time; then, radiative cooling governs the thermodynamics and reconnection becomes a radiative transfer problem, greatly affected by the ultra-strong magnetic field. This overall picture is very different from our traditional picture of reconnection and thus represents a new frontier in reconnection research.Comment: Accepted to Space Science Reviews (special issue on magnetic reconnection). Article is based on an invited review talk at the Yosemite-2010 Workshop on Magnetic Reconnection (Yosemite NP, CA, USA; February 8-12, 2010). 30 pages, no figure

Metagenomic study of the viruses of African straw-coloured fruit bats: detection of a chiropteran poxvirus and isolation of a novel adenovirus

Viral emergence as a result of zoonotic transmission constitutes a continuous public health threat. Emerging viruses such as SARS coronavirus, hantaviruses and henipaviruses have wildlife reservoirs. Characterising the viruses of candidate reservoir species in geographical hot spots for viral emergence is a sensible approach to develop tools to predict, prevent, or contain emergence events. Here, we explore the viruses of Eidolon helvum, an Old World fruit bat species widely distributed in Africa that lives in close proximity to humans. We identified a great abundance and diversity of novel herpes and papillomaviruses, described the isolation of a novel adenovirus, and detected, for the first time, sequences of a chiropteran poxvirus closely related with Molluscum contagiosum. In sum, E. helvum display a wide variety of mammalian viruses, some of them genetically similar to known human pathogens, highlighting the possibility of zoonotic transmission

Reptiles as food: Predation of Australian reptiles by introduced red foxes compounds and complements predation by cats

Context: Invasive species are a major cause of biodiversity loss across much of the world, and a key threat to Australia’s diverse reptile fauna. There has been no previous comprehensive analysis of the potential impact of the introduced European red fox, Vulpes vulpes, on Australian reptiles. Aims: We seek to provide an inventory of all Australian reptile species known to be consumed by the fox, and identify characteristics of squamate species associated with such predation. We also compare these tallies and characteristics with reptile species known to be consumed by the domestic cat, Felis catus, to examine whether predation by these two introduced species is compounded (i.e. affecting much the same set of species) or complementary (affecting different groups of species). Methods: We collated records of Australian reptiles consumed by foxes in Australia, with most records deriving from fox dietary studies (tallying >35 000 samples). We modelled presence or absence of fox predation records against a set of biological and other traits, and population trends, for squamate species. Key results: In total, 108 reptile species (~11% of Australia’s terrestrial reptile fauna) have been recorded as consumed by foxes, fewer than that reported for cats (263 species). Eighty-six species have been reported to be eaten by both predators. More Australian turtle species have been reported as consumed by foxes than by cats, including many that suffer high levels of predation on egg clutches. Twenty threatened reptile species have been reported as consumed by foxes, and 15 by cats. Squamate species consumed by foxes are more likely to be undergoing population decline than those not known to be consumed by foxes. The likelihood of predation by foxes increased with squamate species’ adult body mass, in contrast to the relationship for predation by cats, which peaked at ~217 g. Foxes, but not cats, were also less likely to consume venomous snakes. Conclusions: The two introduced, and now widespread, predators have both compounding and complementary impacts on the Australian reptile fauna. Implications: Enhanced and integrated management of the two introduced predators is likely to provide substantial conservation benefits to much of the Australian reptile fauna