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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Ubiquitous Internet in an integrated satellite-terrestrial environment: The SUITED solution

Conforto, P., Tocci, C., Losquadro, G., Spazio, A., Sheriff, Ray E., Chan, Pauline M.L., Hu, Yim Fun January 2002 (has links)
Yes / The current Internet architecture appears to not be particularly suited to addressing the emerging needs of new classes of users who wish to gain access to multimedia services made available by ISPs, regardless of their location, while in motion and with a guaranteed level of quality. One of the main objectives of so-called nextgeneration systems is to overcome the limitations of today¿s available Internet by adopting an approach based on the integration of different mobile and fixed networks. The SUITED project moves in this direction since it aims at contributing to the design and deployment of the global mobile broadband system (GMBS), a unique satellite/terrestrial infrastructure ensuring nomadic users access to Internet services with a negotiated QoS. A description of the main features of the GMBS architecture, characterized by the integration of a multisegment access network with a federated ISP network is given in this article. The GMBS multimode terminal is schematically described, and an overview of the so-called QoS-aware mobility management scheme, devised for such a heterogeneous scenario,is provided.
2

Investigating the Fluxes of Radio-Cesium (137Cs) in Sweden : Investigating the Fluxes of Radio-Cesium (137Cs) in Sweden

Masood, Hammad January 2022 (has links)
Technological advancement and the quest for power have gradually contaminated our environment, as industrialization, agriculture, and nuclear activities progressed. In the year 1986, a terrible nuclear incident occurred in Ukraine, in which the nuclear reactor exploded. The explosion resulted in the release of radionuclides with a massive concentration of 137Cs and 131I. Among these,137Cs was the most persistent one having a half-life of 30.2 years. The137Cs spread to Sweden due to advection, dispersion,and diffusion by wind, fallout over by precipitation via adsorption, and absorption in northern parts of Sweden experiencing a heterogeneous distribution. This fallout affected both the terrestrial and aquatic environments. This research aims to investigate where the 137Cs went and how its concentration changed with time in Swedish mushrooms, lakes, and in the Gulf of Bothnia. Also, to search for the environment that holds137Cs for a longer period and why it is so. More than 30 years have passed since the incident, and it isexpected that 137Cs would have decayed to values of its half-life. Swedish food authority recommends that up to 10,000 Bq/kg of 137Cs in mushrooms is safe for human consumption. The advocated limitsfor fish and seawater are 1500 Bq/kg and 40 Bq/kg, respectively.The method embraced to answer the research questions is based on data from the Swedish Radiation Safety Authority, the Radiant Earth project between Uppsala University and SLU, and also the data published in the literature. Decay models were generated for 137Cs.These models help in explaining the processes of accumulation and extraction of 137Cs. A closer look is also given to processes that have animpact on factors such as weathering, erosion, wind, washout, and bioturbation, and the rate of intake in environments. The aquatic environment, because Gävleborg was most affected during the incident, the highest value in the fish measured in the year 1988 was 23,508 Bq/kg. However, after 31 years (2016), the value was 4.5 Bq/kg. The values for Jämtland, Västerbotten, and Västernorrland were also almost equivalent to those for Gävleborg, estimated in the year 2016 to be around 4.5 Bq/kg. Observations of water data in Gävleborg show a wide range between 2-996 Bq/kg. In the Gulf of Bothnia, the highest 137Cs value recorded for sediment data in the year 2003 was 310 Bq/kg, and the lowest value of 181 Bq/kg was observed in the year 2015. In terrestrial environments, the maximum value recorded for Craterellus tubaeformis mushrooms was 522,000 Bq/kg in the year 1987. On the other hand, the lowest value recorded for Chanterelle mushrooms was 101.5 Bq/kg in the year 2017. Observations from a sample collected in Uppsala in the year 2017 indicates a value of 15 Bq/kg. Several mushroom species (Chanterelle, Craterellus tubaeformis) had distinct concentrations within the same geographical area and time, i.e., the Västernorrland in the year 2017.Due to weathering and erosion, when 137Cs reaches a water body (sea, ocean, estuary, river, lake or wetland), it dissolves in the water increasing its concentration. As a result, it increases the overall concentration of 137Cs in the fish. The results show that most of the 137Cs is locked in the sediments, with time buried under new sediment. However, due to resuspension and bioturbation, the contaminants may end up in the aquatic environment again. Models for lakes show irregular behaviour since their sizes are not as large as seas and small intakes depict high concentrations. Based on the mushroom results, 137Cs concentrations have been greatly reduced compared with Chernobyl levels. Different mushroom species exhibit different levels of 137Cs in the same area. Most radionuclides are found in the top layer of organic soil, making this layer crucial for taking up 137Cscontamination. Over time, these radionuclides, including 137Cs, are buried beneath the soil layers and cease to contribute to the system.
3

Harmful agents (PCDD/Fs, PCBs, and PBDEs) in Finnish reindeer (<em>Rangifer tarandus tarandus</em>) and moose (<em>Alces alces</em>)

Holma-Suutari, A. (Anniina) 18 November 2014 (has links)
Abstract In Finland there is a food monitoring program which has found elevated dioxin and polychlorinated biphenyl concentrations in the muscle of semi-domesticated reindeer (Rangifer tarandus tarandus) calves. This led to further research on the concentrations of persistent organic pollutants in reindeer muscle, liver, and other internal organs. The research was further expanded on wild moose (Alces alces) muscle and liver. The main objective of this thesis is to increase knowledge of polychlorinated dibenzo-p-dioxin (PCDD), polychlorinated dibenzofuran (PCDF), polychlorinated biphenyl (PCB), and polybrominated diphenyl ether (PBDE) pollution levels in the Finnish terrestrial environment, and in semi-domesticated reindeer and wild moose in particular. The research gives information of exposure conditions in the reindeer’s food chain, as well as species differences and individual variation in accumulation and distribution of pollutants in reindeer and moose. Local differences between the contaminant concentrations were explored. Toxic equivalencies (TEQs) set by the World Health Organization (WHO) of PCDD/Fs and PCBs were calculated in order to assess the validity of selling reindeer and moose tissue. It was observed that there is a species-, individual-, and tissue-specific accumulation of dioxins, dioxin-like PCB, and PBDE compounds in reindeer and moose. Varying exposure conditions mainly explain the differences, although taking into account the age of an individual animal, its metabolic patterns have a role, too. Reindeer placenta and milk proved to be important factors in the transporting of compounds from hind to calf. The highest PCDD/F and PCB concentrations (as WHO-TEQs) were observed in reindeer calves in the study area in which animals are fed in natural pastures only. Despite the findings, it was concluded that it is safe to eat reindeer and moose meat since the concentrations of dioxins and dioxin-like PCBs in the muscle are relatively low, and because of the low fat content in these animals. Reindeer liver, for its part, had quite a lot of dioxin-like compounds that may compromise its safety as food, at least on a regular basis. The study shows that Finnish semi-domesticated reindeer and wild moose are good indicator species of POP contamination in a terrestrial environment, reindeer describing the situation in northern parts of the country especially. / Tiivistelmä Suomalaisessa ruokamonitorointitutkimuksessa löydettiin kohonneita dioksiinien ja polykloorattujen bifenyylien pitoisuuksia puolivillin poron vasojen lihaksista. Se johti lisätutkimuksiin pysyvien orgaanisten yhdisteiden pitoisuuksista poron lihaksessa, maksassa ja muissa sisäelimissä. Tutkimus laajeni koskemaan myös hirven (Alces alces) lihasta ja maksaa. Väitöskirjatyö lisää tietämystä polykloorattujen dibentso-p-dioksiinien (PCDD), polykloorattujen dibentsofuraanien (PCDF), polykloorattujen bifenyylien (PCB) ja polybromattujen difenyylieettereiden (PBDE) pitoisuuksista suomalaisessa maaympäristössä ja erityisesti porossa ja hirvessä. Tutkimus antaa tietoa yhdisteille altistumisesta sekä viitteitä lajien- ja yksilöiden välisistä eroavai¬suuksista yhdisteiden kertymisessä ja niiden jakaantumisessa eri kudosten välillä. Alueellista vaihtelua yhdisteiden pitoisuuksissa selvitettiin myös. Maailman terveysjärjestön (WHO) asettamia PCDD/F- ja PCB-yhdisteiden toksisuusekvivalenttiarvoja (TEQ) tarkasteltaessa pystyttiin arvioimaan kemiallista elintarvikekelpoisuutta suhteessa EU:n antamiin sallittuihin pitoisuuksiin. Työssä havaittiin laji-, yksilö-, ikä- ja kudosspesifistä dioksiinien, dioksiinienkaltaisten PCB- ja PBDE-yhdisteiden kerääntymistä porossa ja hirvessä. Tämä on todennäköisimmin seurausta vaihtelevasta altistumisesta yhdisteille, mutta myös lajien metabolisissa toiminnoissa yksilön eri ikäkausina voi olla eroavaisuuksia. Poron istukan ja maidon havaittiin olevan tärkeitä yhdisteiden kulkeutumisessa emolta sikiölle ja vasalle. Korkeimmat dioksiinien ja dioksiinien kaltaisten PCB-yhdisteiden konsentraatiot (WHO-TEQ-pitoisuuksina) havaittiin poron vasoilla tutkimusalueella, jossa eläimet olivat laiduntaneet ainoastaan luonnonlaitumilla. Huolimatta havaituista haitta-ainepitoisuuksista todettiin, että sekä luonnostaan vähärasvaisen poron että hirvenlihan syönti on turvallista suhteellisen alhaisten dioksiinien ja dioksiininkaltaisten PCB-yhdisteiden pitoisuuksien perusteella. Poron maksa puolestaan sisälsi melko korkeita dioksiinien kaltaisten yhdisteiden pitoisuuksia, mikä voi vaikuttaa sen turvalliseen käyttöön elintarvikkeena ainakin usein syötynä. Suomalainen puolivilli poro ja villi hirvi sopivat hyvin POP-kontaminoitumisen indikaattoreiksi maaympäristössä; poron erityisesti kuvaten tilannetta maan pohjoisosissa.
4

The Climatic Response in the Partitioning of the Stable Isotopes of Carbon in Juniper Trees from Arizona

Arnold, Larry David January 1979 (has links)
Juniper trees (Juniperus osteosperma, J. monosperma, J. deppeana and J. scopulorum) grow under widely varying climatic and edaphic conditions throughout the American southwest. This study is chiefly concerned with a test of the climatic response in the partitioning of the stable isotopes of carbon in such trees. The relationships developed here, for example, might be used to extract paleoclimatic information from ancient juniper samples preserved in cave middens. In order to test for a climatic response in the leaf cellulose δ¹³C values, leaves from a total of 29 trees were sampled in the immediate vicinity of 9 meteorological stations across the state of Arizona. Care was taken to insure that 22 of the trees experienced only the temperature and precipitation values reflected by their site meteorological stations. As a cross-check, 7 trees exposed to temperature and/or precipitation levels clearly deviant from their site averages were also sampled. In general, each tree was sampled at four places, approximately 2 m above the ground. All leaf samples were reduced to cellulose (holocellulose) before combustion and analysis for their δ¹³C value. The δ¹³C value for each site was derived from an average of 2 to 4 trees per site, the value of each tree being the average of its individual samples. The one sigma 13C variation found between trees at any given site is ±0.38‰; within a single tree, ±0.36‰; and for repeat combustions, ±0.20‰. The δ¹³C values of the juniper sites were regressed against the temperature and precipitation of the individual months and running averages of months across the year using polynomial, multiple regression analysis. Temperature and precipitation were entered as separate variables in a general multiple regression model and also as a combined, single variable (T /P) in a more specific approach. The pattern formed by the multiple correlation coefficients, when plotted by months across the year, closely follows the seasonal variations in photosynthetic activity. Cellulose δ¹³C values have minimum correlation with temperature and precipitation (considered jointly) during summer months and maximum correlation during spring months. For an individual month, the temperature and precipitation (jointly) of April correlated at the highest level with a multiple adj. R = 0.994 and an F = 166; for a maximum seasonal response, March-May reached a multiple adj. R = 0.985, F = 66. The results using the combined, single variable (T /P) were nearly equivalent for the same months: April's adj. R = 0.957, F = 45; March-May's adj. R = 0.985 with an F = 132. The ability of T and P as independent predictors is considerably less than their ability in combination; e.g., 13C g(T) for March-May has an adj. R = 0.80 and 6 13C = h(P) has an adj. R = -0.67 compared to their in- concert adj. R value of 0.985. The results of this study, therefore, strongly support a high degree of climatic sensitivity in the partitioning of the stable isotopes of carbon in juniper leaf cellulose: the correlation coefficients and their F statistics are sufficiently high to consider temperature and precipitation (acting jointly) as accurate predictors of cellulose δ¹³C values in the system studied.
5

Stratigraphy and Depositional History of the Pantano Formation (Oligocene-Early Miocene), Pima County, Arizona

Balcer, Richard Allen January 1984 (has links)
The Pantano Formation comprises 1,250 m of alluvial, fluvial, lacustrine, and volcanic rocks deposited in a basin formed in response to regional extension during mid- Tertiary time in southeastern Arizona. During deposition, the locations and composition of sediment source areas varied as contemporaneous uplift occurred adjacent to the basin. The lower half of the formation was deposited as alluvial fans that prograded northward, westward, and southward; the upper half was deposited during southwestward retreat of alluvial fan deposition and the onset of lacustrine deposition. An andesite flow separates the two depositional regimes. Radiometric dates of 24.4 ± 2.6 m.y. B.P. for the andesite and 36.7 ± 1.1 m.y. B.P. for a rhyolitic tuff disconformably underlying the formation indicate that deposition occurred during Oligocene to early Miocene time. Proper stratigraphic sequencing and description, paleocurrent analysis, and gravel provenance study aided in understanding the depositional history of the formation.
6

Fire Frequency, Nutrient Concentrations and Distributions, and δ13C of Soil Organic Matter and Plants in Southeastern Arizona Grassland

Biggs, Thomas January 1997 (has links)
Over the past century, woody plants and shrubs have increased in abundance at the expense of grasslands in many semiarid regions. The availability and concentrations of nutrients influence the relative success of plants, but the effects of fire frequency on soil nutrients is unknown for semiarid grasslands. On the gunnery ranges of Fort Huachuca in southeastern Arizona, study sites were established to examine the effects of fire frequency on soil biogeochemistry, plant biochemistry, and δ¹³C values in soil organic matter (SOM). The sites were on homogeneous granitic alluvium where wildfire frequency history is known from 1973 to present and no cattle grazing has occurred in recent decades. Subplots represent fire frequencies of no burns, 3 fires per decade, and 5 fires per decade. The "no burn" plot has abundant C₃ Prosopis veleruina (mesquite) trees, whereas the burned plots are open C₄-dominated grasslands with scattered mesquite trees. Prosopis trees have altered SOM pools by the concentration of plant nutrients and the addition of isotopically light shrub litter. Frequent fires have altered the basic geochemistry and nutrient availabilities of the soil, and the changes appear to be significant enough to affect plant growth. Soil pH increases with burning frequency, and TOC, total nitrogen, and plant -available phosphorus show significant increases on the infrequently burned plot. Burning is advantageous for preservation or restoration of grasslands, as total living grass biomass is greater on the two burned plots. Root biomass is significantly lower on the "frequently burned" plot. Concentrations of the key nutrients nitrogen and phosphorus are reduced in plants on the burned sites compared to plants on the unburned site. Fires help re-distribute nutrients but evidence of nutrient concentrations and δ¹³C values are retained in SOM for many decades. Estimates of bulk carbon turnover rates range from 112 to 504 years. Evidence for modern C₃ shrub expansion is found in the shift of SOM δ¹³C values from values characteristic of C₄ grasses to C₃ shrubs in surface soil layers. δ¹³C(SOM) values indicate that the Holocene and Late Pleistocene were dominated by C₄ grasslands, and the pre-Late Pleistocene vegetation was a C₄-grass savanna with abundant C₃ plants.

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