Estimating particle sizes, concentrations, and total mass of ash in volcanic clouds using weather radar

Observations of the March 19, 1982 ash eruption of Mount St. Helens, made by the National Weather Service (NWS, Portland, Oregon) on 5-cm radar, were used to estimate the volume of the ash cloud (2000 ±500 km3), the concentration of ash (0.2–0.6 g m−3). and the total mass of ash erupted (3–10×1011 g). The position of the cloud was also tracked by radar. Particle sizes in the ash cloud were estimated from settling velocities suggested by decreases in maximum ash cloud height with time as it moved away from the volcano. The March 19, 1982 ash blanket was sampled and mapped. Ash fallout times and accumulation rates were reconstructed from ground observations. Grain size distributions for various samples were used to obtain particle concentration (0.2 g m−3), total ashfall mass (1–3×1011 g), and radar reflectivity factor (4–5 mm6 m−3) for the ash cloud. Our preferred estimate for total ashfall mass (4×1011 g) is that obtained from the product of the ash cloud volume determined by radar (2000±500 km3) and the particle concentration inferred from ashfall data (0.2 g m−3). Previously published ashfall data for the May 18, 1980 Mount St. Helens eruption has been studied using our ashfall inversion technique to estimate 6-hour mean particle concentration (3 g m−3), the size distribution, total ashfall mass (5×1014 g), and radar reflectivity factors (7–60 mm6 m−3) for the ash cloud. A somewhat higher value (9 g m−3) for particle concentration was estimated from radar observations [Harris et al., 1981] for an ash cloud formed during the peak eruption rate at Mount St. Helens. The two independent estimates are consistent, given the many uncertainties of the problem. The reflectivity factors for very dense ash clouds (3–9 g m−3) are several orders of magnitude smaller than for severe weather considered routinely detectable by airborne weather radar and dangerous for aviation. Because volcanic ash clouds with particle concentrations of at least 0.2 g m−3 are produced in extremely small eruptions (in terms of total ashfall mass) of duration less than 1 minute, volcanic ash clouds must be considered an extremely serious hazard to in-flight aircraft, regardless of eruption magnitude. These factors should be considered in hazard evaluations for known volcanoes located near air routes. Radar observations and calculations can provide scientists monitoring eruptive activity with significant information for estimating duration of eruption, particle concentrations in ash clouds, total mass of solid material erupted, magma eruption rate, potential ashfall mass, ashfall locations and accumulation rates, and duration and amounts of ashfall. Detailed analysis of ashfall data and NWS radar observations of ash clouds from Mount St. Helens demonstrate that weather radar can yield such timely information during and following volcanic eruptions

Soluble tau species, not neurofibrillary aggregates, disrupt neural system integration in a tau transgenic model

Neurofibrillary tangles are a feature of Alzheimer disease and other tauopathies, and while they are generally believed to be markers of neuronal pathology, there is little evidence evaluating whether tangles directly impact neuronal function. To investigate the response of cells in hippocampal circuits to complex behavioral stimuli, we used an environmental enrichment paradigm to induce expression of an immediate-early gene, Arc, in the rTg4510 mouse model of tauopathy. These mice reversibly overexpress P301L tau and exhibit substantial neurofibrillary tangle deposition, neuronal loss, and memory deficits. Employing fluorescent in situ hybridization to detect Arc mRNA, we found that rTg4510 mice have impaired hippocampal Arc expression both without stimulation and in response to environmental enrichment; this likely reflects the combination of functional impairments of existing neurons and loss of neurons. However, tangle-bearing cells were at least as likely as non-tangle-bearing neurons to exhibit Arc expression in response to enrichment. Transgene suppression with doxycycline for 6 weeks resulted in increased percentages of Arc-positive cells in rTg4510 brains compared to untreated transgenics, restoring enrichment-induced Arc mRNA levels to that of wild-type controls despite the continued presence of neurofibrillary pathology. We interpret these data to indicate that soluble tau contributes to impairment of hippocampal function, while tangles do not preclude neurons from responding in a functional circuit

Sizes and shapes of 10-Ma Distal fall pyroclasts in the Ogallala gGroup, Nebraska

Size distributions of distal ashfall particles from correlated 10-Ma layers in Nebraska, measured using laser diffraction methods, are lognormal with mode diameters of ∼90 mm. This ashfall is ∼100% bubble-wall shards of rhyolite glass and apparently represents a distal ashfall from an eruption 1400 km away. Measured terminal velocities of these ash particles are 0.2–18 cm/s, consistent with Stokes Law settling of spherical particles with diameters of 9–50 mm. Surface area of the ash particles, measured with gas adsorption, is 20–30 times the surface area of equivalent Stokes spheres. These results highlight the effects of shape and atmospheric drag in distal ashfalls. They also highlight atmospheric transport and fallout of distal ashfall particles, because these deposits resemble many other ashfalls preserved in the Great Plains of North America throughout the Tertiary and Quaternary. Because the ashfalls preserve major mammalian death assemblages, they demonstrate that deposits with modes of optical diameters 1100 mm are still hazardous by aerodynamic definitions of lung disease risk and include particles substantially within hazardous PM10 ranges. The aerodynamically fine particle size may lead to substantial aeolian redistribution, causing local thicknesses of 12 m. Overall, the ashfall thicknesses observed are at least several times larger than would be expected based on exponential thinning from the volcano. Shape measurements of distal ash particles may be necessary to assess risk. The possible health risks in the central United States from a future rhyolitic eruption in the western United States may be significant

Using Classical Inference Methods to reveal individual-specific parameter estimates to avoid the potential complexities of WTP derived from population moments

nference estimation methods for logit models with Bayesian methods and suggested that the latter are more appealing on grounds of relative simplicity in estimation and in producing individual observation parameter estimates instead of population distributions. It is argued that one particularly appealing feature of the Bayesian approach is the ability to derive individual-specific willingness to pay measures that are claimed to be less problematic than the classical approaches in terms of extreme values and signs. This paper takes a close look at this claim by deriving both population derived WTP measures and individual-specific values based on the classical ‘mixed logit’ model. We show that the population approach may undervalue the willingness to pay substantially; however individual parameters derived using conditional distributions can be obtained from classical inference methods, offering the same posterior information associated with the Bayesian view. The technique is no more difficult to apply than the Bayesian approach – indeed the individual specific estimates are a by-product of the parameter estimation process. Our results suggest that while extreme values and unexpected signs cannot be ruled out (nor can they in the Bayesian framework), the overall superiority of the Bayesian method is overstated

Suspended Nanoscale Field Emitter Devices for High-Temperature Operation

In this work, we demonstrate suspended two- and four-terminal field emission devices for high-temperature operation. The planar structures were fabricated with tungsten on a 200-nm silicon nitride membrane. The insulator in the vicinity of the terminals was removed to minimize undesirable Frenkel–Poole emission and increase the resistance of leakage current pathways. The effects of temperatures up to 450 °C on Fowler–Nordheim emission characteristics and parasitic leakage resistance were studied. Turn-on voltages with magnitudes under 15 V that further decreased as a function of increasing temperature for the two-terminal device were reported. Gating at temperatures of 150 °C and 300 °C was shown for the four-terminal device, and corresponding transconductance and cutoff frequency values were computed

Urbanness and Its Implications for Logistics Strategy: A Revised Perspective

Due to rapid urbanization, logistics providers are dealing with the conundrum of misaligned strategies for urban environments. Logistics providers often see the urbanness of an activity region as a constraint, while at the same time urban actors view logistics activities within their immediate environment as disruption. These attitudes obscure the value that logistics can provide for urban areas. The current research synchronizes the notions of urban and logistics by reconceptualizing urbanness (i.e., an area’s state of being urban) from the logistics service provider’s perspective. Utilizing a conceptual abstraction technique, the concept of urbanness is revised and differentiated to redefine urban areas as value clusters looking to balance supply and demand globally while also providing access to service at the local urban level. Further, logistics service providers are seen as offering value to urban areas through network logistics and localized logistics. Identifying these differentiated value propositions suggests that transportation providers should respond to urbanness not as a constraint, but as a context where ambidextrous strategies provide the greatest return. Our conceptual revision of urbanness offers promising future avenues of research dealing with urban complexity and logistics providers value appropriation

Recovering costs through price and service differentiation: Accounting for exogenous information on attribute processing strategies in airline choice

The entry of low cost airlines has thrown out a challenge to all airlines to find ways of attracting passengers, through a mix of fare discounting, greater frequency, improved flight times and no-frill’s levels of on-board service. All of these competitive strategies have an impact on cost recovery. As airlines seek business in an increasingly heterogeneous passenger market, a greater understanding of what matters to potential passengers in choosing an airline grows in importance. Which attributes really do matter to specific classes of passengers? Traditional studies of passenger airline choice assume that all attributes matter, but some to a lesser extent. What happens to the empirical evidence on willingness to pay when specific attributes are totally ignored by particular passengers? In this paper, we examine the impact of individual-specific attribute processing strategies (APS) on the inclusion/exclusion of attributes on the parameter estimates and behavioural outputs of models of airline service and fare level choice. Current modelling practice assumes that whilst respondents may exhibit preference heterogeneity, they employ a homogenous APS with regards to how they process the presence/absence of attributes of stated choice (SC) experiments. We demonstrate how information collected exogenous of the SC experiment on whether respondents either ignored or considered each attribute of the SC task may be used in the estimation process, and how such information may be used to provide outputs that are APS segment specific. Accounting for the inclusion/exclusion of attributes has important implications on the willingness to pay for varying levels of service

Suspended Nanoscale Field Emitter Devices for High-Temperature Operation

In this work, we demonstrate suspended two- and four-terminal field emission devices for high-temperature operation. The planar structures were fabricated with tungsten on a 200-nm silicon nitride membrane. The insulator in the vicinity of the terminals was removed to minimize undesirable Frenkel–Poole emission and increase the resistance of leakage current pathways. The effects of temperatures up to 450 °C on Fowler–Nordheim emission characteristics and parasitic leakage resistance were studied. Turn-on voltages with magnitudes under 15 V that further decreased as a function of increasing temperature for the two-terminal device were reported. Gating at temperatures of 150 °C and 300 °C was shown for the four-terminal device, and corresponding transconductance and cutoff frequency values were computed

Consumer Self-Confidence: Refinements in Conceptualization and Measurement

The development and validation of measures to assess multiple dimensions of consumer self-confidence are described in this article. Scale-development procedures resulted in a six-factor correlated model made up of the following dimensions: information acquisition, consideration-set formation, personal outcomes, social outcomes, persuasion knowledge, and marketplace interfaces. A series of studies demonstrate the psychometric properties of the measures, their discriminant validity with respect to related constructs, their construct validity, and their ability to moderate relationships among other important consumer behavior variables

Quantitative shape measurements of distal volcanic ash

Large-scale volcanic eruptions produce fine ash (\u3c 200 μm) which has a long atmospheric residence time (1 hour or more) and can be transported great distances from the volcanic source, thus, becoming a hazard to aircraft and public health. Ash particles have irregular shapes, so data on particle shape, size, and terminal velocities are needed to understand how the irregular-shaped particles affect transport processes and radiative transfer measurements. In this study, a methodology was developed to characterize particle shapes, sizes , and terminal velocities for three ash samples of different compositions. The shape and size of 2,500 particles from 1) distal fallout (~100 km) of the October 14, 1974 Fuego eruption (basaltic), 2) the secondary maxima (~250 km) of the August 18, 1992 Spurr eruption (andesitic), and 3) the Miocene Ash Hollow member, Nebraska (rhyolitic) were measured using image analysis techniques. Samples were sorted into 10 to 19 terminal velocity groups (0.6-59.0 cm/s) using an air elutriation device. Grain size distributions for the samples were measured using laser diffraction. Aspect ratio, feret diameter, and perimeter measurements were found to be the most useful descriptors of how particle shape affects terminal velocity. These measurement values show particle shape differs greatly from a sphere (commonly used in models and algorithms). The diameters of ash particles were 10-120% larger than ideal spheres at the same terminal velocity, indicating that irregular particle shape greatly increases drag. Gas-adsorption derived surface areas are 1 to 2 orders of magnitude higher than calculated surface areas based on measured dimensions and simple geometry, indicating that particle shapes are highly irregular. Correction factors for surface area were derived from the ash sample measurements so that surface areas calculated by assuming spherical particle shapes can be corrected to reflect more realistic values