47 research outputs found
Sequential Fragmentation / Transport Theory, Pyroclast Size-Density Relationships, and the Emplacement Dynamics of Pyroclastic Density Currents – A Case Study on the Mt. St. Helens (USA) 1980 Eruption
Pyroclastic density currents (PDCs) are the most dangerous hazard associated with explosive volcanic eruptions. Despite recent advancements in the general understanding of PDC dynamics, limited direct observation and/or outcrop scarcity often hinder the interpretation of specific transport and depositional processes at many volcanoes. This study explores the potential of sequential fragmentation / transport theory (SFT; cf. Wohletz et al. 1989), a modeling method capable of predicting particle mass distributions based on the physical principles of fragmentation and transport, to retrieve the transport and depositional dynamics of well-characterized PDCs from the size and density distributions of individual components within the deposits. The extensive vertical and lateral exposures through the May 18th, 1980 PDC deposits at Mt. St. Helens (MSH) provide constraints on PDC regimes and flow boundary conditions at specific locations across the depositional area. Application to MSH deposits suggests that SFT parameter distributions can be effectively used to characterize flow boundary conditions and emplacement processes for a variety of PDC lithofacies and deposit locations. Results demonstrate that (1) the SFT approach reflects particle fragmentation and transport mechanisms regardless of variations in initial component distributions, consistent with results from previous studies; (2) SFT analysis reveals changes in particle characteristics that are not directly observable in grain size and fabric data; (3) SFT parameters are more sensitive to regional transport conditions than local (outcrop-scale) depositional processes. The particle processing trends produced using SFT analysis are consistent with the degree of particle processing inferred from lithofacies architectures: for all lithofacies examined in this study, suspension sedimentation products exhibit much better processing than concentrated current deposits. Integrated field observations and SFT results provide evidence for increasing density segregation within the depositional region of the currents away from source, as well as for comparable density-segregation processes acting on lithic concentrations and pumice lenses within the current. These findings further define and reinforce the capability of SFT analysis to complement more conventional PDC study methods, significantly expanding the information gained regarding flow dynamics. Finally, this case study demonstrates that the SFT methodology has the potential to constrain regional flow conditions at volcanoes where outcrop exposures are limited
Sequential fragmentation/transport theory, pyroclast size–density relationships, and the emplacement dynamics of pyroclastic density currents — A case study on the Mt. St. Helens (USA) 1980 eruption
The Variable Responding Scale for Detection of Random Responding on the Multidimensional Pain Inventory
This study developed a scale for detecting random responding on the Multidimensional Pain Inventory (MPI). Ninety-five undergraduates (derivation sample) completed the MPI randomly, as did 2 cross-validation samples, 34 chronic pain patients (pain) and 115 health care professionals (health care). Up to 71% of random profiles appeared valid. For comparison in validity scale development, a clinical MPI sample (N = 507) was split into derivation and cross-validation samples. Given that responses to similar items should be consistent in nonrandom protocols, 8 pairs of highly intercorrelated items were selected. Absolute differences between pairs were summed into a variable responding (VR) scale; scores were contrasted across clinical and random groups. On the basis of derivation sample results, VR scale cut scores (from 12 to 17) were tested and found to discriminate accurately (p \u3c .001) between the cross-validation clinical and the healthcare and pain random responding samples. The potential clinical utility of the VR scale to identify random MPI protocols is supported
Do changes in cognitive factors influence outcome following multidisciplinary treatment for chronic pain? A cross-lagged panel analysis.
‘You've Gotta Learn how to Play the Game’: Homeless Women's Use of Gender Performance as a Tool for Preventing Victimization
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Thickness-dependent crossover from charge- to strain-mediated magnetoelectric coupling in ferromagnetic/piezoelectric oxide heterostructures.
Magnetoelectric oxide heterostructures are proposed active layers for spintronic memory and logic devices, where information is conveyed through spin transport in the solid state. Incomplete theories of the coupling between local strain, charge, and magnetic order have limited their deployment into new information and communication technologies. In this study, we report direct, local measurements of strain- and charge-mediated magnetization changes in the La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 system using spatially resolved characterization techniques in both real and reciprocal space. Polarized neutron reflectometry reveals a graded magnetization that results from both local structural distortions and interfacial screening of bound surface charge from the adjacent ferroelectric. Density functional theory calculations support the experimental observation that strain locally suppresses the magnetization through a change in the Mn-eg orbital polarization. We suggest that this local coupling and magnetization suppression may be tuned by controlling the manganite and ferroelectric layer thicknesses, with direct implications for device applications