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The notion of sediment-transport capacity has been engrained in geomorphological and related literature for over 50 years, although its earliest roots date back explicitly to Gilbert in fluvial geomorphology in the 1870s and implicitly to eighteenth to nineteenth century developments in engineering. Despite cross fertilization between different process domains, there seem to have been independent inventions of the idea in aeolian geomorphology by Bagnold in the 1930s and in hillslope studies by Ellison in the 1940s. Here we review the invention and development of the idea of transport capacity in the fluvial, aeolian, coastal, hillslope, débris flow, and glacial process domains. As these various developments have occurred, different definitions have been used, which makes it both a difficult concept to test, and one that may lead to poor communications between those working in different domains of geomorphology. We argue that the original relation between the power of a flow and its ability to transport sediment can be challenged for three reasons. First, as sediment becomes entrained in a flow, the nature of the flow changes and so it is unreasonable to link the capacity of the water or wind only to the ability of the fluid to move sediment. Secondly, environmental sediment transport is complicated, and the range of processes involved in most movements means that simple relationships are unlikely to hold, not least because the movement of sediment often changes the substrate, which in turn affects the flow conditions. Thirdly, the inherently stochastic nature of sediment transport means that any capacity relationships do not scale either in time or in space. Consequently, new theories of sediment transport are needed to improve understanding and prediction and to guide measurement and management of all geomorphic systems.

The magnetization of three high-quality single crystals of YBa2Cu3O6+x, from slightly overdoped to heavily underdoped, has been measured using torque magnetometry. Striking effects in the angular dependence of the torque for the two underdoped crystals, a few degrees above the superconducting transition temperature (Tc) are described well by the theory of Gaussian superconducting fluctuations using a single adjustable parameter. The data at higher temperatures (T) are consistent with a strong cut-off in the fluctuations for T >∼ 1.1Tc. Numerical estimates suggest that inelastic scattering could be responsible for this cut-off.

The antiferromagnetic parent compounds of the iron pnictide superconductors exhibit unusual magnetic and electronic properties which may play a crucial role in the origin of unconventional pairing in these high temperature superconductors. Recent theoretical work [1] and angle-resolved photoemission spectroscopy measurements [2] suggest that the detection of small Fermi-surface pockets from quantum oscillation experiments in these compounds are associated with a Dirac-type dispersion, in support of a nodal spin density wave state which protects the metallic density of states at the Fermi surface from complete gapping [3]. In this work, we provide a further test of this scenario through quantum oscillation measurements using radio frequency techniques on high quality single crystal samples of SrFe2As2 in pulsed magnetic fields up to 60 T. By tracking the ratio of the quasiparticle effective cyclotron mass to the quantum oscillation frequency as a function of magnetic field angle, we observe a dependence consistent with the Fermisurface topology of a Dirac-type dispersion. We discuss the implications of this result on understanding the metallic state of the iron arsenide parent compounds. References [1] N. Harrison and S. E. Sebastian, Phys. Rev. B 80, 224512 (2009). [2] P. Richard, K. Nakayama, T. Sato, M. Neupane, Y.-M. Xu, J. H. Bowen, G. F. Chen, J. L. Luo, N. L. Wang, X. Dai, Z. Fang, H. Ding, and T. Takahashi, Phys. Rev. Lett. 104, 137001 (2010). [3] Y. Ran, F. Wang, H. Zhai, A. Vishwanath, and D.-H. Lee, Phys. Rev. B 79, 014505 (2009).

The antiferromagnetic parent compounds of the high pnictide superconductors play host to unusual magnetic and electronic properties which may be closely related to the presence of superconductivity in the doped compounds. Recent theoretical1 and experimental, 2 work have suggested the presence of small Fermi-surface pockets in these compounds with regions in k-space characterized by a Dirac-like dispersion. Here we test this scenario by performing quantum oscillation studies on high quality single crystal samples of SrFe2As2 to 60 T in pulsed magnetic elds. By tracking the ratio of the quasiparticle e ective mass m⋆ to the quantum oscillation frequency as a function of magnetic eld angle, we observe a dependence consistent with that expected for the Dirac dispersion scenario. We discuss the implications of this result on understanding the metallic state of the FeAs parent compounds. 1 N. Harrison and SE Sebastian, Phys. Rev. B. 80, 224512 (2009). 2 P. Richard P, K. Nakayama, T. Sato et. al., Phys. Rev. Lett. 104, 137001 (2010).