A celulose é o principal polímero derivado de fonte renovável de uso industrial tanto em termos de volume como em número de aplicações. A celulose é comercializada na forma de polpa, que se trata de uma commodity cuja principal aplicação é a indústria de papel e de derivados de celulose, tais como os seus éteres e ésteres. Com o advento das nanoceluloses, que podem ser obtidas diretamente da polpa química, se observa um expressivo aumento no interesse por esses materiais. A modificação superficial tanto das fibras (polpa) como das microfibrilas é de grande interesse, pois podem permitir a ampliação do uso desses materiais uma vez que suas propriedades poderiam ser modificadas. O desenvolvimento de métodos de modificação em meio aquoso da celulose em suspensão é de grande interesse em especial se realizado com o uso de agentes sustentáveis em contexto de química verde. Este trabalho visou a modificação da polpa de celulose por duas vias: química e física, realizadas inteiramente em meio aquoso e utilizando materiais de caráter renováveis. A modificação física da fibra de celulose \"never-dried\" foi feita pelo método de auto-montagem (Layer-by-Layer) com o par de polieletrólito quitosana / carboximetilcelulose (CH / CMC) em meio aquoso. Fibras modificadas foram submetidas à analise morfológica (MEV e microscopia confocal no método de absorção de dois fótons e EDS), propriedade mecânica (módulo elástico e limite de resistência à tração) e potencial zeta. O complexo CH / CMC depositado sobre as fibras apresentou uma espessura de aproximadamente 50 nm por camada e um aumento de aproximadamente 170% no limite de resistência a tração das folhas produzidos a partir das fibras, demonstrando uma forte interação fibra/polieletrólitos. Através da técnica de absorção de dois fótons foi possível identificar a deposição das camadas fora e dentro das fibras sem o uso de cromóforo. A modificação química da nanofibra de celulose foi feita pela enxertia de grupamentos furânicos na superfície da fibra, oxidada. Em seguida de uma reação com uma bismaleimida através da reação de \"click\" de Diels-Alder em meio aquoso. Os géis foram caracterizados por meio da técnica de calorimetria diferencial de varredura (DSC) e viscosimetria, com os quais pode-se verificar o efeito da termorreversibilidade uma vez que a 65°C ocorre gelificação do sistema e 95°C ocorre reversão do gel como resultado das reações DA e retro Diels-Alder. As modificações das fibras e nanofibras de celulose em meio aquoso foram bem-sucedidas, o que pode impulsionar o uso da polpa de celulose em novas aplicações originais como artefatos de papel fortes e géis biocompatíveis, visando a estratégia green chemistry. / Cellulose is the main polymer derived from renewable sources of industrial use, in terms of volume and number of applications. Cellulose is marketed in the pulp form, which is a commodity whose main application is the paper industry and derived from pulp, such as its ethers and esters. The advent of nanocelluloses, which can be obtained directly from the chemical pulp, there is an expressive increase in these materials. The superficial modification in fibers (pulp) and microfibrils is great interest, since they can allow the amplification of the use of these materials since their properties could be modified. The development of methods for modification of cellulose in aqueous suspension is of particular interest especially if carried out with sustainable agents in the context of green chemistry. This work aimed at the modification of the cellulose pulp by two routes: chemistry and physics, performed entirely in aqueous medium and using renewable character materials. The physical modification of the \"never-dried\" cellulose fiber was done by the self-assembly method (Layer-by-Layer) with the polyelectrolyte pair chitosan / carboxymethylcellulose (CH / CMC) in aqueous medium. Modified fibers were subjected to morphological analysis (SEM and confocal microscopy in two-photon absorption technique and EDS), mechanical properties (elastic modulus and tensile strength) and zeta potential. The CH / CMC complex deposited under the fibers had a thickness of approximately 50 nm per layer and an increase of approximately 170% in the tensile strength of the sheets in compare of unmodified fibers sheets, showing a strong interaction between fiber and polyelectrolyte. Through the technique of two-photon adsorption, it was possible to identify the layers deposition outside and inside the fibers without the use of chromophore. The chemical modification of the cellulose nanofiber was made by the grafting of furanic groups on the surface of the oxidized fiber. Following by reaction with a bismaleimide through the \"click\" reaction of Diels-Alder in aqueous medium. The thermoreversible hydrogels were characterized by differential scanning calorimetry (DSC) and viscosimetry, which the effect of thermoreversibility can be verified at 65 °C when the gelation of the system occurs and 95 °C gel reversion occurs because of DA and retro Diels-Alder reactions. Modifications of cellulose fibers and nanofibers in aqueous media have been successful, which may increase the use of cellulose pulp in novel applications such as strong paper artifacts and biocompatible gels, targeting the green chemistry strategy.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (p. 117-126).

<p>Wireless communication is of great importance for safety and entertainment purposes in vehicular networks. Vehicles on roads are required to share sensor data, road traffic information or digital maps with other vehicles on the road. To be able to do this, vehicles require to either communicate directly with each other or to be connected to a wireless communication-based access points on the road side. These wireless access points support short to medium range wireless communication through the protocol 802.11p. 802.11p is designed specifically for vehicular communication and it is an amended form of the widely used 802.11 protocol suit for wireless local area networks (WLAN). Vehicles are able to be associated with these wireless access points for exchange of information. While vehicles move along the road infrastructure, they change their point of attachment from one wireless access point to another wireless access point. During this process, connectivity to the access point breaks down until the vehicle is connected to a new access point in its area. This disconnection causes an interruption in the data flow. This interruption increases when vehicle requires a new IP address, i.e. when the vehicle is going to attach to an access point which is part of another network. In this thesis report, we give an overview of standard handover methods and their enhancements and propose a fast handover scheme for layer 3 of the communication stack. Based on the assumption that vehicles know their route in advance, we enhance the handover process and improve seamless connectivity. We also discuss different issues which are the cause of delay and how they can be overcome in our proposed solution.</p>

Eight years (1980-87) of twice-daily high-resolution radiosonde data from a tropical mid-Pacific island station are analyzed to generate time series of the planetary boundary layer (PBL) top pressure, an ageostrophic parameter (related to the divergence), and a parameter of mean PBL specific humidity. Sample spectra of these time series are calculated along with a spectra for nighttime outgoing longwave radiation (OLR) data (centered at a gridpoint near the island station) and compared in order to investigate the relationship between the ageostrophy and dynamical phenomena of the tropical Pacific. Methods of boundary layer top diagnosis are compared. Data derived methods include temperature inversion detection, humidity jump detection, and wind shear detection. The model based diagnosis method uses a Richardson number scheme. Comparisons between data derived methods and model based methods show good agreement. Correlation coefficients for comparisons are all above 0.91. In each sample spectra, the dominant peak corresponds to the frequency of the annual cycle. With an estimated annual cycle removed from each of the time series the nighttime (12 GMT) sample spectra for PBL top pressure shows a peak at a frequency that corresponds to the 30-60 day Intraseasonal Oscillation (ISO). Removal of an estimated annual cycle was unsuccessful for the daytime (0 GMT) sample spectra for PBL top pressure, PBL mean specific humidity, and the ageostrophic parameter. Sample spectra of the ageostrophic parameter show peaks in the ISO frequency range for both 12 GMT and 0 GMT even before removal of the annual cycle was attempted. The ISO range peaks remained in the 12 GMT ageostrophic parameter spectrum when the annual cycle was successfully removed. The nighttime OLR spectrum is dominated by the annual cycle peak and its harmonics. The OLR spectrum also shows a significant peak in the ISO range of periods. Removal of an estimated annual cycle intensifies the peak in the ISO range. The ageostrophic parameter time series is compared to the results of an EOF analysis performed on the same 8 years of radiosonde humidity measurements. The first three EOF modes of specific humidity give sample spectra which are dominated by the annual cycle. With the annual cycle removed the sample spectra of the first and third EOF modes of specific humidity both show significant peaks in the ISO frequency range, while the second EOF mode sample spectrum is dominated by two peaks at frequencies corresponding to periods of approximately 4 and 5 months. The presence of common frequencies in the ISO range of the power spectra of the ageostrophic parameter (a measure of divergence), the nighttime OLR (a measure of deep convection), the nighttime planetary boundary layer top, and the first EOF mode of specific humidity, lends support to theories that relate the ISO to the interaction of dynamics and moist processes. / Graduation date: 1995

It has been shown by Schlesinger and Mintz (1979) that the UCLA general circulation model (GCM) is able to simulate the observed negative correlation between the total amount of ozone in a vertical atmospheric column (the total ozone) and the eastward-propagating synoptic disturbances in the troposphere, with the total ozone maxima and minima located respectively at the troughs and ridges of the tropospheric waves. The goal of the present study was to understand how the GCM simulated this observed relationship. Our analysis shows that the transient-eddy total ozone disturbances were an omnipresent feature of the GCM January simulation in the northern hemisphere midlatitudes, just as they are in nature. It is also found that the transient-eddy total ozone disturbances in the northern hemisphere midlatitudes were closely related to the transient-eddy geopotential heights there throughout the entirety of the simulation. Furthermore, the correlations between these two quantities are negative up to the 72 mb level and attain their largest negative values at the 300 mb level. The analysis also shows that the transient-eddy disturbances in the stratosphere are out of phase with their counterparts in the troposphere, in accord with what would be expected from Dines compensation. In the GCM simulation there is a well-defined positive correlation between the total ozone and the ozone content in each of the model layers in the upper troposphere and lower and middle stratosphere. It is found that although layers 5-8 (19.3-150 mb) contain the largest percentage of the total ozone, it is predominantly layers 6-9 (37.3 -300 mb) that make the largest contribution to the temporal variations of total ozone. In accordance with the observations, a strong negative correlation is found between the simulated total ozone and the height of the simulated tropopause. However, changing the height of the tropopause cannot in itself change the total ozone, but rather only its partitioning between the stratosphere and the troposphere. Our analysis clearly shows that it is the ozone convergence and divergence in an atmospheric column, not the photochemical ozone production and destruction, which are responsible for the synoptic increases and decreases of total ozone. / Graduation date: 1988

Thesis (D. Sc.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1983. / "Funding was provided by the American Gas Association Project no. PR-153-126, the National Science Fundation under grant OCE-8014930, and NOAA-Sea Grant NA-79AA-D-00101 ; NA 79AA-D-00102." Includes bibliographical references (p. 201-205).

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1983. / Supervised by William D. Grant. Includes bibliographical references (leaves 201-205).

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1984. / Vita. Bibliography: p. 200-206.

The vertical structures of tropospheric temperature and moisture over the oceans have not been well observed to date. The Atmospheric Infrared Sounder (AIRS) aboard NASA?s Aqua satellite offers the opportunity to provide observed soundings of these variables. This thesis focuses on the validation and application of AIRS soundings in the tropical troposphere over the Atlantic Ocean, with emphasis on the Saharan Air Layer (SAL). SAL outbreaks occur every few days, producing a warm air mass that is particularly dry at the middle levels. These westward-propagating plumes inhibit convection and are thereby thought to possess a detrimental effect on African easterly waves and tropical cyclones (TCs). First, AIRS soundings are compared with concurrent Global Positioning System (GPS) dropwindsonde data released from NOAA?s Gulfstream-IV jet aircraft, for three TC cases. In SAL environments, temperature soundings from both instruments are usually consistent. Additionally, AIRS is able to capture the very dry air in the middle levels, but it generally underestimates the moisture in the boundary layer and often misses the sharp vertical moisture gradient at the SAL base (~850 hPa). In the moist tropical boundary layer, AIRS also exhibits a dry bias. Cloud cover also prevents AIRS from accurately sampling the low-level moisture. Next, total precipitable water is derived from AIRS soundings and averaged over daily, monthly and seasonal timescales. The significant monthly and interannual variability of the moisture distribution is found to be consistent with expectations. A peak in the probability density function of mixing ratio corresponding to dry air is observed in the lower-mid troposphere in early summer, consistent with the increased frequency of SAL outbreaks during this period. Finally, the relationship between dry air derived from AIRS and TC intensity is explored. As the amount of dry air increases, particularly in the southeast and northeast quadrants of the TC, the TC becomes more likely to weaken. In the presence of high wind shear or low sea surface temperature, the likelihood of weakening increases further. While these results highlight some shortcomings of the AIRS data, their importance and uniqueness are emphasized via new applications of AIRS soundings over data sparse regions.

The object ofthe present work is to experimentally study thecase ofa turbulent boundary layer subjected to an AdversePressure Gradient (APG) with separation and reattachment. Thisconstitutes a good test case for advanced turbulence modeling.The work consists ofde sign of a wind-tunnel setup, developmentofP article Image Velocimetry (PIV) measurements and evaluationtechniques for boundary layer flows, investigations ofs calingofb oundary layers with APG and separation and studies oftheturbulence structure ofthe separating boundary layer withcontrol by means ofs treamwise vortices. The accuracy ofP IV isinvestigated in the near-wall region ofa zero pressure-gradientturbulent boundary layer at high Reynolds number. It is shownthat, by careful design oft he experiment and correctly appliedvalidation criteria, PIV is a serious alternative toconventional techniques for well-resolved accurate turbulencemeasurements. The results from peak-locking simulationsconstitute useful guide-lines for the effect on the turbulencestatistics. Its symptoms are identified and criteria for whenthis needs to be considered are presented. Different velocityscalings are tested against the new data base on a separatingAPG boundary layer. It is shown that a velocity scale relatedto the local pressure gradient gives similarity not only forthe mean velocity but also to some extent for the Reynoldsshear-stress. Another velocity scale, which is claimed to berelated to the maximum Reynolds shear-stress, gives the samedegree of similarity which connects the two scalings. However,profile similarity achieved within an experiment is notuniversal and this flow is obviously governed by parameterswhich are still not accounted for. Turbulent boundary layerseparation control by means ofs treamwise vortices isinvestigated. The instantaneous interaction between thevortices and the boundary layer and the change in the boundarylayer and turbulence structure is presented. The vortices aregrowing with the boundary layer and the maximum vorticity isdecreased as the circulation is conserved. The vortices arenon-stationary and subjected to vortex stretching. Themovements contribute to large levels ofthe Reynolds stresses.Initially non-equidistant vortices become and remainequidistant and are con- fined to the boundary layer. Theamount ofi nitial streamwise circulationwas found to be acrucial parameter for successful separation control whereas thevortex generator position and size is ofseco ndary importance.At symmetry planes the turbulence is relaxed to a nearisotropic state and the turbulence kinetic energy is decreasedcompared to the case without vortices. <b>Keywords:</b>Turbulence, Boundary layer, Separation,Adverse Pressure Gradient (APG), PIV, control, streamwisevortices, velocity scaling.