Drop rebound in clouds and precipitation

The possibility of rebound for colliding cloud drops was measured by determining the collection efficiency. The collection efficiency for 17 size pairs of relatively uncharged drops in over 500 experimental runs was measured using two techniques. The collection efficiencies fall in a narrow range of 0.60 to 0.70 even though the collection drop was varied between 63 and 326 microns and the size ratio from 0.05 to 0.33. In addition the measured values of collection efficiencies (Epsilon) were below the computed values of collision efficiencies (E) for rigid spheres. Therefore it was concluded that rebound was occurring for these sizes since inferred coalescence (epsilon = Epsilon/E) efficiencies are about 0.6 yo 0.8. At a very small size ratio (r/R = p = 0.05, R = 326 microns) the coalescence efficiency inferred is in good agreement with the experimental findings for a supported collector drop. At somewhat large size ratios the inferred values of epsilon are well above results of supported drop experiments, but show a slight correspondence in collected drop size dependency to two models of drop rebound. At a large size ratio (p = 0.73, R = 275) the inferred coalescence efficiency is significantly different from all previous results

An engine trade study for a supersonic STOVL fighter-attack aircraft, volume 1

The best main engine for an advanced STOVL aircraft flight demonstrator was studied. The STOVL aircraft uses ejectors powered by engine bypass flow together with vectored core exhaust to achieve vertical thrust capability. Bypass flow and core flow are exhausted through separate nozzles during wingborne flight. Six near term turbofan engines were examined for suitability for this aircraft concept. Fan pressure ratio, thrust split between bypass and core flow, and total thrust level were used to compare engines. One of the six candidate engines was selected for the flight demonstrator configuration. Propulsion related to this aircraft concept was studied. A preliminary candidate for the aircraft reaction control system for hover attitude control was selected. A mathematical model of transfer of bypass thrust from ejectors to aft directed nozzle during the transition to wingborne flight was developed. An equation to predict ejector secondary air flow rate and ram drag is derived. Additional topics discussed include: nozzle area control, ejector to engine inlet reingestion, bypass/core thrust split variation, and gyroscopic behavior during hover

UA3/1/7/2 Henry Cherry Campaign Letter

Form letter sent to supporters of Henry Cherry\u27s gubernatorial campaign

Clear air turbulence

Research on forecasting, detection, and incidents of clear air turbulenc

Design concepts for bioreactors in space

Microbial food sources are becoming viable and more efficient alternatives to conventional food sources especially in the context of Closed Ecological Life Support Systems (CELSS) in space habitats. Since bioreactor designs for terrestrial operation will not readily apply to conditions of microgravity, there is an urgent need to learn about the differences. These differences cannot be easily estimated due to the complex nature of the mass transport and mixing mechanisms in fermenters. Therefore, a systematic and expeditious experimental program must be undertaken to obtain the engineering data necessary to lay down the foundations of designing bioreactors for microgravity. Two bioreactor design concepts presented represent two dissimilar approaches to grappling with the absence of gravity in space habitats and deserve to be tested for adoption as important components of the life support function aboard spacecrafts, space stations and other extra-terrestrial habitats

Data From: Root Distributions Predict Shrub-Steppe Responses to Precipitation Intensity

Precipitation events are becoming more intense around the world, changing the way water moves through soils and plants. Plant rooting strategies that sustain water uptake under these conditions are likely to become more abundant (e.g., shrub encroachment). Yet, it remains difficult to predict species responses to climate change because we typically do not know where active roots are located or how much water they absorb. Here, we applied a water tracer experiment to describe forb, grass, and shrub root distributions. These measurements were made in 8 m by 8 m field shelters with low or high precipitation intensity. We used tracer uptake data in a soil water flow model to estimate how much water respective plant root tissues absorb over time. In low precipitation intensity plots, deep shrub roots were estimated to absorb the most water (93 mm yr-1) and shrubs had the greatest aboveground cover (27%). Grass root distributions were estimated to absorb an intermediate amount of water (80 mm yr-1) and grasses had intermediate aboveground cover (18%). Forb root distributions were estimated to absorb the least water (79 mm yr-1) and had the least aboveground cover (12%). In high precipitation intensity plots, shrub and forb root distributions changed in ways that increased their water uptake relative to grasses, predicting the increased aboveground growth of shrubs and forbs in these plots. In short, water uptake caused by different rooting distributions predicted plant aboveground cover. Our results suggest that detailed descriptions of active plant root distributions can predict plant growth responses to climate change in arid and semi-arid ecosystems

Introduction, Establishment, and Spread: 50 Years of Invasion Ecology Since Elton

While some may argue that Charles Elton was not a founder but rather a prophet of invasion ecology (Simberloff, this volume), Elton’s 1958 monograph The ecology of invasions by animals and plants (Methuen, London) inspired and informed many of today’s ecologists about the issues and problems of biological invasions. In addition, while many theories Elton proposed in his monograph (e.g., diversityinvasibility) have been questioned and his oversights (e.g., on propagule pressure) have been noted, there is no doubt that he has influenced entire directions of research. Thus, revisiting Elton’s influence on the field of invasion ecology 50 years after his monograph is clearly worthwhile

Root Niche Partitioning among Grasses, Saplings, and Trees Measured Using a Tracer Technique

Niche partitioning of resources by plants is believed to be a fundamental aspect of plant coexistence and biogeochemical cycles; however, measurements of the timing and location of resource use are often lacking because of the difficulties of belowground research. To measure niche partitioning of soil water by grasses, planted saplings, and trees in a mesic savanna (Kruger National Park, South Africa), we injected deuterium oxide into 102,000 points in 15, 154-m2 plots randomly assigned to one of five depths (0–120 cm) and one of three time periods during the 2008/2009 growing season. Grasses, saplings and trees all demonstrated an exponential decline in water uptake early in the season when resources were abundant. Later in the season, when resources were scarce, grasses continued to extract the most water from the shallowest soil depths (5 cm), but saplings and trees shifted water uptake to deeper depths (30–60 cm). Saplings, in particular, rapidly established roots to at least 1 m and used these deep roots to a greater extent than grasses or trees. Helping to resolve contradictory observations of the relative importance of deep and shallow roots, our results showed that grasses, saplings and trees all extract the most water from shallow soils when it is available but that woody plants can rapidly shift water uptake to deeper soils when resources are scarce. Results highlight the importance of temporal changes in water uptake and the problems with inferring spatial and temporal partitioning of soil water uptake from root biomass measurements alone