Mini High Velocity Clouds

Neutral hydrogen mapping of several small, very low column density High Velocity Clouds (HVC), using the Arecibo telescope, is reported. Some were found serendipitously superimposed at distinct velocities on largerHVCs; others were found to comprise the four most isolated low column density sources in the observations of Lockman et al. but proved to be individually much smaller than the Green Bank 140 Foot telescope beam. We call these clouds ``mini-HVC'' to distinguish them from the larger and denser Compact High Velocity Clouds (CHVC). Peak column densities are typically a few X 10^18 cm^-2 averaged over the Arecibo 3.2' beam, and diameters to our detection limit ~ 10^18 cm^-2 range from 9' to 35'. These column densities and angular diameters overlap with those for CHVC, but are typically smaller. We consider three possiblities: (1) that most mini-HVC are related to the Magellanic Stream, (2) that most mini-HVC are part of M31's retinue of CHVC, or (3) that the mini-HVC are simply the low column density tail of the distribution of CHVC. None of these possibilities can be rejected as yet, given the selection biases in our sample. We also discuss controversies about the amount of ionized hydrogen in CHVC and mini-HVC, which may be mainly ionized, and the implications of these small clouds for Lyman Limit Systems.Comment: Astronomical Journal, in pres

Minimum Tillage for Corn

Minimum tillage for corn discusses methods of planting, including strip processing, modified rototilling, hard ground listing, chisel plowing, wheel track planting, plow planting, and once-over tillage. Included are advantages and disadvantages of water infiltration, soil erosion and temperature, water evaporation, soil compaction and aeration, soil structure, and adaption to soil types. Problems, such as weed control, fertilizer placement, insect control, and the economics of minimum tillage, as also discussed

Minimum Tillage for Corn

This publication explains several minimum tillage planting methods such as strip processing, till, chisel, wheel track, and plow planting, modified rototilling, hard ground listing, and once-over tillage. Problems, advantages, and disadvantages of minimum tillage are also discussed

High Velocity Cloud Edges and Mini-HVCs

Arecibo mapping is reported of the neutral hydrogen distribution along selected directions out from the centers of two small High Velocity Clouds (HVC), W486 and W491. Both HVCs have a small inner region where the neutral hydrogen column density N_HI decreases slowly and a larger outer region where N_HI declines more rapidly, smoothly and exponentially from ~ 2 X 10^19 atoms cm^-2 down to < 10^18 atoms cm^-2. Line widths, and presumably temperature and turbulence, do not increase in the outermost regions. Therefore pressure decreases smoothly, making confinement by dark matter gravity more likely than confinement by external pressure. The more extended HVC, W491, has a superimposed small cloud (which we dub a ``mini-HVC''), offset by 66 km s^-1 in velocity along the line of sight with peak column density about 5 X 10^18 atoms cm^-2. Preliminary data toward future mapping of two more HVCs reveals two more mini-HVCs of similarly small size and central column density a bit less than 1 X 10^19 atoms cm^-2. We suggest that these three mini-HVCs are not physically associated with the HVCs on which they are superimposed, but are either very small outlyers of the extended Magellanic Stream HVC complex or more distant and/or smaller isolated CHVCs. The value of N_HI at the point where the neutral and ionized column densities are equal is ~ 2 X 10^19 atoms cm^-2 for the two mapped HVCs. Therefore the angular scalelength of the total hydrogen is appreciably larger than the observed HI scalelength. Previous distance estimates, related to absolute size and mass of the total hydrogen cloud, may have to be scaled down because of the undetected, more extended ionized hydrogen.Comment: 24 pages, 8 figures, ApJ in pres

Small changes at single nodes can shift global network dynamics

Understanding the sensitivity of a system's behavior with respect to parameter changes is essential for many applications. This sensitivity may be desired - for instance in the brain, where a large repertoire of different dynamics, particularly different synchronization patterns, is crucial - or may be undesired - for instance in power grids, where disruptions to synchronization may lead to blackouts. In this work, we show that the dynamics of networks of phase oscillators can acquire a very large and complex sensitivity to changes made in either their units' parameters or in their connections - even modifications made to a parameter of a single unit can radically alter the global dynamics of the network in an unpredictable manner. As a consequence, each modification leads to a different path to phase synchronization manifested as large fluctuations along that path. This dynamical malleability occurs over a wide parameter region, around the network's two transitions to phase synchronization. One transition is induced by increasing the coupling strength between the units, and another is induced by increasing the prevalence of long-range connections. Specifically, we study Kuramoto phase oscillators connected under either Watts-Strogatz or distance-dependent topologies to analyze the statistical properties of the fluctuations along the paths to phase synchrony. We argue that this increase in the dynamical malleability is a general phenomenon, as suggested by both previous studies and the theory of phase transitions.Comment: 14 pages, 8 figure

THE CO LUM BIA RIVER GORGE THE STORY OF THE RIVER AND TH E ROCKS

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Simulating the Clamped Tapered Beam Specimen Under Quasi-Static and Fatigue Loading Using Floating Node Method

As part of the NASA Advanced Composites Project (ACP), a sub-element has been designed to provide validation data for progressive damage analysis models. The clamped tapered beam is a cross-ply laminated composite specimen designed to validate the simulation of the onset of matrix cracks and their interaction with delaminations, including delamination migration. A tapered geometry was used to localize the first damage occurrence in the tapered region, without prescribing an initial crack. The boundary and loading conditions were chosen to favor delamination growth and subsequent migration after the first damage occurrence. The typical sequence of events consists of a matrix crack located at the tapered region, leading to delamination onset, followed by delamination growth and subsequent delamination migration to a different interface via a dominant matrix crack. The Clamped Tapered Beam (CTB) was tested in both quasi-static and fatigue regimes. The results obtained are used in this study to assess and validate a methodology based on the Floating Node Method (FNM) implemented as an Extended Interface Element. In this methodology, quasi-static and fatigue damage formation and development are modeled by combining FNM to represent crack networks, with Directional Cohesive Zone Elements (DCZE) and Virtual Crack Closure Technique (VCCT), respectively. Qualitatively, the methodology is capable of predicting the sequence of events and overall failure morphology. Quantitatively, the simulation results generally bound the experimental data, based on the range of the characterization data used. In this paper, the results from quasi static and fatigue simulations are compared and correlated with experimental data