742 research outputs found
Recent Studies in Superconductivity at Extreme Pressures
Studies of the effect of high pressure on superconductivity began in 1925
with the seminal work of Sizoo and Onnes on Sn to 0.03 GPa and have continued
up to the present day to pressures in the 200 - 300 GPa range. Such enormous
pressures cause profound changes in all condensed matter properties, including
superconductivity. In high pressure experiments metallic elements, Tc values
have been elevated to temperatures as high as 20 K for Y at 115 GPa and 25 K
for Ca at 160 GPa. These pressures are sufficient to turn many insulators into
metals and magnetics into superconductors. The changes will be particularly
dramatic when the pressure is sufficient to break up one or more atomic shells.
Recent results in superconductivity to Mbar pressures wll be discussed which
exemplify the progress made in this field over the past 82 years.Comment: Proceedings of the 21st AIRAPT and 45th EHPRG International
Conference on High Pressure Science and Technology, Catania, Italy, Sept.
17-21, 200
Pressure-Induced Superconductivity in Sc to 74 GPa
Using a diamond anvil cell with nearly hydrostatic helium pressure medium we
have significantly extended the superconducting phase diagram Tc(P) of Sc, the
lightest of all transition metals. We find that superconductivity is induced in
Sc under pressure, Tc increasing monotonically to 8.2 K at 74.2 GPa. The Tc(P)
dependences of the trivalent d-electron metals Sc, Y, La, and Lu are compared
and discussed within a simple s-d charge transfer framework.Comment: to be published in Phys. Rev. B (Brief Reports
Expert elicitation of seasonal abundance of North Atlantic right whales Eubalaena glacialis in the mid-Atlantic
This work was supported in part by US Office of Naval Research (ONR) grants to E.F.: N00014-09-1-0896 at University of California, Santa Barbara and N00014-12-1-0274 at University of California, Davis. This work was also supported by ONR grant N000141210286 to the University of St Andrews. In addition, we gratefully acknowledge funding for this work from The Marine Alliance for Science and Technology for Scotland (MASTS). MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions.North Atlantic right whales (Eubalaena glacialis; henceforth right whales) are among the most endangered large whales. Although protected since 1935, their abundance has remained low. Right whales occupy the Atlantic Ocean from southern Greenland and the Gulf of St. Lawrence south to Florida. The highly industrialized mid-Atlantic region is part of the species’ migratory corridor. Gaps in knowledge of the species’ movements through the mid-Atlantic limit informed management of stressors to the species. To contribute to filling of these gaps, we elicited estimates of the relative abundance of adult right whales in the mid-Atlantic during four months, representing each season, from ten experts. We elicited the minimum, maximum, and mode as the number of individuals in a hypothetical population of 100 right whales, and confidence estimates as percentages. For each month-sex combination, we merged the ten experts’ answers into one distribution. The estimated modes of relative abundances of both sexes were highest in January and April (females, 29 and 59; males, 22 and 23) and lowest in July and October (females, five and nine; males, three and five). In some cases, our elicitation results were consistent with the results of studies based on sightings data. However, these studies generally did not adjust for sampling effort, which was low and likely variable. Our results supplement the results of these studies and will increase the accuracy of priors in complementary Bayesian models of right whale abundances and movements through the mid-Atlantic.Publisher PDFPeer reviewe
Studies on the Weak Itinerant Ferromagnet SrRuO3 under High Pressure to 34 GPa
The dependence of the Curie temperature Tc on nearly hydrostatic pressure has
been determined to 17.2 GPa for the weak itinerant ferromagnetic SrRuO3 in both
polycrystalline and single-crystalline form. Tc is found to decrease under
pressure from 162 K to 42.7 K at 17.2 GPa in nearly linear fashion at the rate
dTc/dP = -6.8 K/GPa. No superconductivity was found above 4 K in the pressure
range 17 to 34 GPa. Room-temperature X-ray diffraction studies to 25.3 GPa
reveal no structural phase transition but indicate that the average Ru-O-Ru
bond angle passes through a minimum near 15 GPa. The bulk modulus and its
pressure derivative were determined to be B =192(3) GPa and B' = 5.0(3),
respectively. Parallel ac susceptibility studies on polycrystalline CaRuO3 at 6
and 8 GPa pressure found no evidence for either ferromagnetism or
superconductivity above 4 K
Comparison of the pressure dependences of Tc in the trivalent d-electron superconductors
Whereas dhcp La superconducts at ambient pressure with Tc = 5 K, the other
trivalent d-electron metals Sc, Y, and Lu only superconduct if high pressures
are applied. Earlier measurements of the pressure dependence of Tc for Sc and
Lu metal are here extended to much higher pressures. Whereas Tc for Lu
increases monotonically with pressure to 12.4 K at 174 GPa (1.74 Mbar). Tc for
Sc reaches 19.6 K at 107 GPa, the 2nd highest value observed for any elemental
superconductor. At higher pressures a phase transition occurs whereupon Tc
drops to 8.31 K at 111 GPa. The Tc(P) dependences for Sc and Lu are compared to
those of Y and La. An interesting correlation is pointed out between the value
of Tc and the fractional free volume available to the conduction electrons
outside the ion cores, a quantity which is directly related to the number of d
electrons in the conduction band
On the Rankin-Selberg integral of Kohnen and Skoruppa
The Rankin-Selberg integral of Kohnen and Skoruppa produces the Spin
-function for holomorphic Siegel modular forms of genus two. In this paper,
we reinterpret and extend their integral to apply to arbitrary cuspidal
automorphic representations of . We show that the integral is
related to a non-unique model and analyze it using the approach of
Piatetski-Shapiro and Rallis.Comment: Final version. To appear in Math. Res. Let
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