Consequences of fractal grade distribution for bulk sorting of a copper porphyry deposit

We show the presence of fractal ordering of copper grade in bore core data at short range in the Cadia Ridgeway porphyry deposit and measure its persistence after mining by monitoring the output of the mine every 20 s for a month using a large scale, zero field magnetic resonance sensor. A simple model is used to investigate this connection and its consequences for sorting of the ore. Fractal distributions, and their associated power laws, have two features highly favourable for segregating ore: a large proportion of low-grade pods and the large scale spatial clustering of grad

Fractional power-law susceptibility and specific heat in low temperature insulating state of o-TaS_{3}

Measurements of the magnetic susceptibility and its anisotropy in the quasi-one-dimensional system o-TaS_{3} in its low-T charge density wave (CDW) ground state are reported. Both sets of data reveal below 40 K an extra paramagnetic contribution obeying a power-law temperature dependence \chi(T)=AT^{-0.7}. The fact that the extra term measured previously in specific heat in zero field, ascribed to low-energy CDW excitations, also follows a power law C_{LEE}(0,T)=CT^{0.3}, strongly revives the case of random exchange spin chains. Introduced impurities (0.5% Nb) only increase the amplitude C, but do not change essentially the exponent. Within the two-level system (TLS) model, we estimate from the amplitudes A and C that there is one TLS with a spin s=1/2 localized on the chain at the lattice site per cca 900 Ta atoms. We discuss the possibility that it is the charge frozen within a soliton-network below the glass transition T_{g}~40 K determined recently in this system.Comment: 7 pages, 3 figures, submitted to Europhysics Letter

Rapid detection of arsenic minerals using portable broadband NQR

The remote real-time detection of specific arsenic species would significantly benefit in minerals processing to mitigate the release of arsenic into aquatic environments and aid in selective mining. At present, there are no technologies available to detect arsenic minerals in bulk volumes outside of laboratories. Here we report on the first room-temperature broadband 75As nuclear quadrupole resonance (NQR) detection of common and abundant arsenic ores in the Earth crust using a large sample (0.78 L) volume prototype sensor. Broadband excitation aids in detection of natural minerals with low crystallinity. We briefly discuss how the proposed NQR detector could be employed in mining operations. Key Points Transformation of chemical analysis method to geophysical detection technologyFirst NQR ore characterization of selected arsenic minerals in bulk volumesBroadband NQR sensor to detect arsenic minerals with low crystallinit

Magnetic Determination of Hc2H_{c2} under Accurate Alignment in (TMTSF)2_2ClO4_4

Cantilever magnetometry has been used to measure the upper critical magnetic field $H_{c2}$ of the quasi-one dimensional molecular organic superconductor (TMTSF)$_2$ClO$_4$. From simultaneous resistivity and torque magnetization experiments conducted under precise field alignment, $H_{c2}$ at low temperature is shown to reach 5T, nearly twice the Pauli paramagnetic limit imposed on spin singlet superconductors. These results constitute the first thermodynamic evidence for a large $H_{c2}$ in this system and provide support for spin triplet pairing in this unconventional superconductorComment: Submitted July 1, 2003, Accepted December 9, 2003, Physical Review Letter

Superconducting Magnetization above the Irreversibility Line in Tl2Ba2CuO6

Piezolever torque magnetometry has been used to measure the magnetization of superconducting Tl2Ba2CuO6. Three crystals with different levels of oxygen overdoping were investigated in magnetic fields up to 10 Tesla. In all cases, the magnetization above the irreversibility line was found to depart from the behaviour M ~ ln(Hc2/H) of a simple London-like vortex liquid. In particular, for a strongly overdoped (Tc = 15K) crystal, the remnant superconducting order above the irreversibility line is characterized by a linear diamagnetic response (M ~ H) that persists well above Tc and also up to the highest field employed.Comment: RevTeX, 11 pages, 7 encapsulated PostScript figures, submitted to Physical Review

Magnetic-Field Variations of the Pair-Breaking Effects of Superconductivity in (TMTSF)2ClO4

We have studied the onset temperature of the superconductivity Tc_onset of the organic superconductor (TMTSF)2ClO4, by precisely controlling the direction of the magnetic field H. We compare the results of two samples with nearly the same onset temperature but with different scattering relaxation time tau. We revealed a complicated interplay of a variety of pair-breaking effects and mechanisms that overcome these pair-breaking effects. In low fields, the linear temperature dependences of the onset curves in the H-T phase diagrams are governed by the orbital pair-breaking effect. The dips in the in-plane field-angle phi dependence of Tc_onset, which were only observed in the long-tau sample, provides definitive evidence that the field-induced dimensional crossover enhances the superconductivity if the field direction is more than about 19-degrees away from the a axis. In the high-field regime for H//a, the upturn of the onset curve for the long-tau sample indicates a new superconducting state that overcomes the Pauli pair-breaking effect but is easily suppressed by impurity scatterings. The Pauli effect is also overcome for H//b' by a realization of another state for which the maximum of Tc_onset(phi) occurs in a direction different from the crystalline axes. The effect on Tc_onset of tilting the applied field out of the conductive plane suggests that the Pauli effect plays a significant role in determining Tc_onset. The most plausible explanation of these results is that (TMTSF)2ClO4 is a singlet superconductor and exhibits Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states in high fields.Comment: 12 pages, 10 figures. To be published in J. Phys. Soc. Jpn. (vol.77, 2008

Thermodynamic and diamagnetic properties of weakly doped antiferromagnets

Finite-temperature properties of weakly doped antiferromagnets as modeled by the two-dimensional t-J model and relevant to underdoped cuprates are investigated by numerical studies of small model systems at low doping. Two numerical methods are used: the worldline quantum Monte Carlo method with a loop cluster algorithm and the finite-temperature Lanczos method, yielding consistent results. Thermodynamic quantities: specific heat, entropy and spin susceptibility reveal a sizeable perturbation induced by holes introduced into a magnetic insulator, as well as a pronounced temperature dependence. The diamagnetic susceptibility introduced by coupling of the magnetic field to the orbital current reveals an anomalous temperature dependence, changing character from diamagnetic to paramagnetic at intermediate temperatures.Comment: LaTeX, 10 pages, 10 figures, submitted to Phys. Rev.

Kondo effect in Ce(x)La(1-x)Cu(2.05)Si(2) intermetallics

The magnetic susceptibility and susceptibility anisotropy of the quasi-binary alloy system Ce(x)La(1-x)Cu(2.05)Si(2) have been studied for low concentration of Ce ions. The single-ion desc ription is found to be valid for x < 0.1. The experimental results are discussed in terms of t he degenerate Coqblin-Schrieffer model with a crystalline electric field splitting Delta = 330 K. The properties of the model, obtained by combining the lowest-order scaling and the pertur bation theory, provide a satisfactory description of the experimental data down to 30 K. The e xperimental results between 20 K and 2 K are explained by the exact solution of the Kondo mode l for an effective doublet.Comment: 11 pages, 13 Postscript figures, 1 tabl

Conformation and dynamics of human urotensin II and urotensin related peptide in aqueous solution

Conformation and dynamics of the vasoconstrictive peptides human urotensin II (UII) and urotensin related peptide (URP) have been investigated by both unrestrained and enhanced-sampling molecular-dynamics (MD) simulations and NMR spectroscopy. These peptides are natural ligands of the G-protein coupled urotensin II receptor (UTR) and have been linked to mammalian pathophysiology. UII and URP cannot be characterized by a single structure but exist as an equilibrium of two main classes of ring conformations, <i>open</i> and <i>folded</i>, with rapidly interchanging subtypes. The <i>open</i> states are characterized by turns of various types centered at K⁸Y⁹ or F⁶W⁷ predominantly with no or only sparsely populated transannular hydrogen bonds. The <i>folded</i> conformations show multiple turns stabilized by highly populated transannular hydrogen bonds comprising centers F⁶W⁷K⁸ or W⁷K⁸Y⁹. Some of these conformations have not been characterized previously. The equilibrium populations that are experimentally difficult to access were estimated by replica-exchange MD simulations and validated by comparison of experimental NMR data with chemical shifts calculated with density-functional theory. UII exhibits approximately 72% <i>open</i>:28% <i>folded</i> conformations in aqueous solution. URP shows very similar ring conformations as UII but differs in an <i>open:folded</i> equilibrium shifted further toward <i>open</i> conformations (86:14) possibly arising from the absence of folded N-terminal tail-ring interaction. The results suggest that the different biological effects of UII and URP are not caused by differences in ring conformations but rather by different interactions with UTR

Linear-T scattering and pairing from antiferromagnetic fluctuations in the (TMTSF)_2X organic superconductors

An exhaustive investigation of metallic electronic transport and superconductivity of organic superconductors (TMTSF)_2PF_6 and (TMTSF)_2ClO_4 in the Pressure-Temperature phase diagram between T=0 and 20 K and a theoretical description based on the weak coupling renormalization group method are reported. The analysis of the data reveals a high temperature domain (T\approx 20 K) in which a regular T^2 electron-electron Umklapp scattering obeys a Kadowaki-Woods law and a low temperature regime (T< 8 K) where the resistivity is dominated by a linear-in temperature component. In both compounds a correlated behavior exists between the linear transport and the extra nuclear spin-lattice relaxation due to antiferromagnetic fluctuations. In addition, a tight connection is clearly established between linear transport and T_c. We propose a theoretical description of the anomalous resistivity based on a weak coupling renormalization group determination of electron-electron scattering rate. A linear resistivity is found and its origin lies in antiferromagnetic correlations sustained by Cooper pairing via constructive interference. The decay of the linear resistivity term under pressure is correlated with the strength of antiferromagnetic spin correlations and T_c, along with an unusual build-up of the Fermi liquid scattering. The results capture the key features of the low temperature electrical transport in the Bechgaard salts