The Mechanics of Low Orbiting Satellites Implications in Communication

Low orbiting satellite communication networks will be competing with geosynchronous satellites for a share of the communications market. In world-wide communications that do not require immediate real time transmissions, low orbiting satellites are competitive with geosynchronous satellites because the system is reliable and low in cost. Since satellites are a clear example of Newtonian laws, the distinct patterns they make in their orbiting process are predictable. Newton\u27s law states that an object will remain in uniform motion unless acted upon by a force: a satellite remains in motion around the earth because there is no atmosphere to slow it down. A satellite stays in orbit because the pull of gravity inward is balanced by centrifugal energy outward. The rate which a satellite orbits the earth and the lifetime of the satellite depend on its altitude. Low orbiting satellites trace unique paths over the surface of the earth -- the satellite is accessible for communication if the path o the satellite comes within 1500 kilometers of a ground station. Unless there are 50 to 80 low orbiting satellites, the system is not useful for exclusive real time communication and thus requires a different operating structure. The low orbiting satellite will use a combination of two modes for communication: the transponder mode, and the store and forward mode

Flower Dance

https://digitalcommons.library.umaine.edu/mmb-ps/1517/thumbnail.jp

Advocating for Existence: The History of Environmental Justice Movements Surrounding the Port of Los Angeles

This thesis examines the forces and factors that gave rise to environmental justice movements surrounding the Port of Los Angeles in the early 21st Century. Through the spatial, economic, and migratory factors that shaped the region of Southeast Los Angeles, this thesis brings to light important tensions between port authorities, politicians, labor groups, employees, and communities that determined the economic and environmental fate of the region. These tensions came to a head through unique coalitions of labor and community-based environmental movements, ultimately achieving major regulatory wins and establishing initiatives that supported the financial and physical health of employees and communities. Through these moments of success, this thesis argues that centering environmental gains in environmental justice communities will ultimately prove to be the most promising path to climate solutions and healthy and thriving communities

Baroclinic boundary currents with downstream decreasing buoyancy: A study of an idealized Nordic Seas system

The dynamics of a baroclinic boundary current losing buoyancy along its path is analyzed both theoretically and using a numerical ocean-circulation model. A fundamental ingredient in our analysis is that the side boundaries of the ocean basin are sloping gently down to the deep ocean. Theoretically we find that the coastal boundary current develops two branches: one seaward baroclinic jetstream and one barotropic current, which is confined to the continental slope. The baroclinic jetstream decreases its transport as the buoyancy is lost from the surface layer. This decrease in transport is compensated by an increase in the barotropic flow on the slope. When the buoyancy is lost altogether, the entire volume transport occurs in the barotropic slope current. In our numerical experiments we focus on the penetration of warm water over a sill into a cold semi-enclosed basin. The flow enters as a baroclinic current with a thickness approximately equal to the sill depth and proceeds around the basin on essentially the same depth while being transformed to a barotropic slope current which leaves the basin over the sill. It should be noted that the circulation does not involve any renewal of the deep water in the cold basin, except in the initial spin up of the system. We suggest that our results can illuminate some basic aspects of the dynamics in the Nordic Seas, which are invaded by North Atlantic surface water over the Greenland-Scotland Ridge. One striking example; is the observations reported by Orvik et al. (2001), which show that the flow of Atlantic water along the Norwegian coast has two branches: A baroclinic jetstream and a shelf-bound barotropic current. The existence of this double-flow structure is to be expected from our theoretical considerations and numerical simulations

Analysis of the Impact of Public Comment on Regulatory Decision Making: The Arsenic Standards

A method for the characterization and analysis of public comment on an EPA standard was proposed. The arsenic emissions standard was chosen since it was the most commented upon standard ever promulgated by the Agency. The proposed method worked well, as participating groups were clearly defined and the intent of each of the groups was reasonable in relation to their inferred environmental ideology. The effectiveness of each of the major groups of commenters was measured by relating the number of comments submitted versus the number of changes made. Comments received on the risk assessment constituted 89 percent of all comments submitted, over half were submitted by citizens not belonging to any particular special interest group. Few changes were made to the risk assessment as a result of the comments and the effectiveness of the comments for all groups was less than two percent. Comments submitted on the technical issues of the standard were more successful in causing change to the proposed standard. The effectiveness of each group varied widely, but the average effectiveness was 20 times greater than for comments submitted on risk issues. Many changes dealt with the submittal of new cost and emissions data by the affected industries. To allow for a discussion of the comment process, Godschalk's Exchange Model was altered and applied to the standard. The Exchange Model indicated that the comment process was successful except in the Agency's response to the public comment. A group theory model was used to analyze the Agency's response to the comment. This model indicated that the changes made to the proposed standards by the EPA could not be explained rationally on the basis of public comment. Other factors which influence EPA must be considered when explaining the Agency's decisions in light of the public intent.Master of Science in Public Healt

Signals of tree volume and temperature in a high-resolution record of pollen accumulation rates in northern Finland

International audiencePollen accumulation rates (PARs) provide a potential proxy for quantitative tree volume (m3 ha 1) reconstruction with reliable absolute pollen productivity estimates (APPEs). We obtained APPEs for pine, spruce and birch at their range limits in northern Finland under two temperature periods ('warm' and 'cold') based on long-term pollen trap and tree volume records within a 14-km radius of each trap. APPEs (mean SE; 108 grains m 3 a 1) tend to be higher for the 'warm' periods (pine 123.8 24.4, birch 528.0 398.4, spruce 434.3 113.7) compared with the 'cold' periods (pine 95.5 37.3, birch 317.3 282.6, spruce 119.6 37.6), although the difference is only significant for spruce. Using an independent temperature record and the APPEs obtained, we reconstruct a low-frequency record of pine volume changes over the last 1000 years at Palomaa mire, where a high-resolution record of Pinus PARs is available. Five phases are distinguished in the reconstruction: moderate pine volume, AD 1080-1170; high volume, AD 1170-1340; low volume, AD 1340-1630; very low volume, AD 1630-1810; and rising pine volume, AD 1810- 1950. These phases do not coincide with periods of high or low June-July-August temperatures, and thus appear to reflect regional variations in tree volume, while high-frequency changes within each time-period block show variations in PARs in response to temperatur

The impact of land-use change on floristic diversity at regional scale in southern Sweden 600 BC-AD 2008

International audienceThis study explores the relationship between landuse and floristic diversity between 600BC and AD2008 in the uplands of southern Sweden. We use fossil pollen assemblages and the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model to quantitatively reconstruct land cover at a regional scale. Floristic richness and evenness are estimated using palynological richness and REVEALS-based evenness, respectively. We focus on the period AD350 to 750 to investigate the impact of an inferred, short-lived (<200 yr) period of land-use expansion and subsequent land abandonment on vegetation composition and floristic diversity. The observed vegetation response is compared to that recorded during the transition from traditional to modern land-use management at the end of the 19th century. Our results suggest that agricultural land use was most widespread between AD350 and 1850, which correlates broadly with high values of palynological richness. REVEALS-based evenness was highest between AD500 and 1600 which indicates a more equal cover among taxa during this time interval. Palynological richness increased during the inferred land-use expansion after AD350 and decreased during the subsequent regression AD550-750, while REVEALS-based evenness increased throughout this period. The values of palynological richness during the last few decades are within the range observed during the last 1650 yr. However, REVEALS-based evenness shows much lower values during the last century compared to the previous ca. 2600 yr, which indicates that the composition of presentday vegetation is unusual in a millennial perspective. Our results show that regional scale changes in land use have had clear impacts on floristic diversity in southern Sweden, with a vegetation response time of less than 20 to 50 yr. We show the importance of traditional land use to attain high biodiversity and suggest that ecosystem management should include a regional landscape perspective