Hyperfine Interactions in the Heavy Fermion CeMIn_5 Systems

The CeMIn_5 heavy fermion compounds have attracted enormous interest since their discovery six years ago. These materials exhibit a rich spectrum of unusual correlated electron behavior, and may be an ideal model for the high temperature superconductors. As many of these systems are either antiferromagnets, or lie close to an antiferromagnetic phase boundary, it is crucial to understand the behavior of the dynamic and static magnetism. Since neutron scattering is difficult in these materials, often the primary source of information about the magnetic fluctuations is Nuclear Magnetic Resonance (NMR). Therefore, it is crucial to have a detailed understanding of how the nuclear moments interact with conduction electrons and the local moments present in these systems. Here we present a detailed analysis of the hyperfine coupling based on anisotropic hyperfine coupling tensors between nuclear moments and local moments. Because the couplings are symmetric with respect to bond axes rather than crystal lattice directions, the nuclear sites can experience non-vanishing hyperfine fields even in high symmetry sites.Comment: 15 pages, 5 figure

On the Maximum Skidding Output of the "Timberjack 380" Forest Tractor

An analysis has been carried out of the skidding operations performed by the "Timberjack 380" forest tractor for an initial thinning of a Pinusradiata D. Don plantation. Knowing the maximum tractive force exerted by the tractor and allowing for the different resistances to forward movement (rolling friction, slope and load resistance), it has been calculated that the tractor can skid 10.1 m3 of material on a dry, compacted earth track, and 5.2 m3 on a wet track. An examination of the various phases of the operations shows that total time per trip to be expressed by the following relation: s„ su -aV where su (speed of tractor without load) = 151.45 m/ min a = 13.4352 V = volume transported d = skidding distance. On the basis of this relation and of the more general one expressing the output (P = 60 V/T), the maximum output was calculated for the "trip without load" phase and for the whole log removal phase. For the "trip with load" phase the maximum output, whatever the skidding distance, is obtained by transporting 5.636 m3, while, for the whole cycle, to achieve the maximum output the load should be 6.970 m3 over a distance of 800 m, and 8.180 m3 over a distance of 100 m. From the analysis carried out and the results obtained, it is clear that the tractor, to ensure maximum performance, should transport material having a high unit volume, such as that obtained from clearcut-ting operations

Local Magnetic Inhomogeneities in Lightly Doped BaFe2_2As2_2

We report $^{75}$As NMR measurements in BaFe$_2$As$_2$ doped with Ni. Like Co, Ni doping suppresses the antiferromagnetic and structural phase transitions and gives rise to superconductivity for sufficiently large Ni doping. The spin lattice relaxation rate diverges at $T_N$, with a critical exponent consistent with 3D ordering of local moments. In the ordered state the spectra quickly broaden inhomogeneously with doping. We extract the average size of the ordered moment as a function of doping, and show that a model in which the order remains commensurate but with local amplitude variations in the vicinity of the dopant fully explains our observations.Comment: 4 pages, 4 figure

NMR Evidence for Charge Inhomogeneity in Stripe Ordered La_{1.8-x}Eu_{0.2}Sr_{x}CuO_4

We report ^{17}O Nuclear Magnetic Resonance (NMR) results in the stripe ordered La_{1.8-x}Eu_{0.2}Sr_{x}CuO_4 system. Below a temperature T_q ~ 80K, the local electric field gradient (EFG) and the absolute intensity of the NMR signal of the planar O site exhibit a dramatic decrease. We interpret these results as microscopic evidence for a spatially inhomogeneous charge distribution, where the NMR signal from O sites in the domain walls of the spin density modulation are wiped out due to large hyperfine fields, and the remaining signal arises from the intervening Mott insulating regions.Comment: 4 pages, to appear in Phys. Rev. Let

Specific heat at the transition in a superconductor with fluctuating magnetic moments

In the heavy-fermion materials CeCoIn$_5$ and UBe$_{13}$, the superconducting order parameter is coupled to flucutating magnetization of the uncompensated part of the localized $f$-moments. We find that this coupling decreases the superconducting transition temperature and increases the jump of the specific-heat coefficient, which indicates entropy transfer from the magnetic to the superconducting degree of freedom at the transition temperature. Below the transition, we find that the magnetic fluctuations are suppressed. We discuss the relation of our results to experiments on CeCoIn$_5$ under pressure.Comment: 4 pages, 1 figur

A field study on human factor and safety performances in a downstream oil industry

afety culture and awareness by workers are pivotal tools for the implementation of systematic procedures aiming to risk mitigation in the process industry. The evaluation of human factors on safety performance can reveal unsafe attitudes and failures in training, supervision and management, whose correction greatly contribute to the enhancement of safety program. In this work, the role of human factors in an oil industry was studied by the collection of field data through a structured questionnaire filled by shift, daily and outsourced workers. A deep investigation on the variables involved in the process was carried out, firstly quantifying three conceptual key dimensions (individual, human resource management, equipment and technology) and then analyzing data by means of Response Surface Methodology (RSM), to identify the statistical significant factors and the overall level of safety awareness, behaviour and risk perception of the respondents

Long range order and two-fluid behavior in heavy electron materials

The heavy electron Kondo liquid is an emergent state of condensed matter that displays universal behavior independent of material details. Properties of the heavy electron liquid are best probed by NMR Knight shift measurements, which provide a direct measure of the behavior of the heavy electron liquid that emerges below the Kondo lattice coherence temperature as the lattice of local moments hybridizes with the background conduction electrons. Because the transfer of spectral weight between the localized and itinerant electronic degrees of freedom is gradual, the Kondo liquid typically coexists with the local moment component until the material orders at low temperatures. The two-fluid formula captures this behavior in a broad range of materials in the paramagnetic state. In order to investigate two-fluid behavior and the onset and physical origin of different long range ordered ground states in heavy electron materials, we have extended Knight shift measurements to URu$_2$Si$_2$, CeIrIn$_5$ and CeRhIn$_5$. In CeRhIn$_5$ we find that the antiferromagnetic order is preceded by a relocalization of the Kondo liquid, providing independent evidence for a local moment origin of antiferromagnetism. In URu$_2$Si$_2$ the hidden order is shown to emerge directly from the Kondo liquid and so is not associated with local moment physics. Our results imply that the nature of the ground state is strongly coupled with the hybridization in the Kondo lattice in agreement with phase diagram proposed by Yang and Pines.Comment: 9 pages, 13 figure