Up to 30% by mass of plant cell walls are comprised of hemicelluloses. The remainder is comprised of cellulose, lignin and extractives. Potential economic uses of hemicellulose include hydrogels, fibre additives in pulp mill paper-making and as a substrate for fermentation processes. Development of a fermentation process with sugars from hemicellulose has become of increasing interest due to their potential as a feedstock for fermentation-based liquid fuels and other bio-based chemicals. These can be incorporated into existing processes, in particular alkaline chemical pulping mills, where up to 50% of the hemicelluloses are today degraded and eventually combusted. The main objective of this project is to examine the solubility and aggregation properties of xylans (the predominant hemicellulose), as this will hopefully lead to better solubility-based separations for their recovery. This was done at Michigan State University by alkaline extraction at 85°C on milled birch wood, and at 130 and 170°C (both time-dependent) on birch chips, with 50 g/L sodium hydroxide. This was then followed by precipitation/aggregation experiments with ethanol, polyDADMAC (a polycationic flocculant) and by acidification. Characterisation was done by performing dynamic light scattering (DLS) and size exclusion chromatography (SEC) analysis on resolubilised recovered material from the different extraction conditions. From these, size distributions, molecular weights and degrees of polymerization (DP) could be estimated. The DP values for the extracted polymers were higher than the expected values for hardwood xylans, owing to the incoherent SEC chromatograms. This may be due to aggregate formation with other polymers or re-solubilisation issues of the hemicellulose precipitates. The estimated size range for model xylan was between 100 to 300 nm and the ethanol precipitates seemed to also lie around this region, as detected by DLS. One of the major factors contributing to the difficulty of analysing the results was the issue of re-solubilisation of the hemicellulose precipitates and flocculates. / <p>Validerat; 20120827 (anonymous); 2017-02-08 Nedladdad 414 gånger t.o.m. september 2016. Downloaded 414 times up until september 2016 (marisr)</p>

Globulettes have recently been found in the Rosette Nebula, the Carina Nebula and other nebulæ. They are expected to be seeds of brown dwarfs and free-floating planetary-mass objects. The size distribution in the Carina Nebula was found to follow a power-law, and the same power-function resulted in 880 +- 250 globulettes in total in the Rosette Nebula. Compared to the 145 observed objects in this nebula, many globulettes are beneath the resolution limit of the Nordic Optical Telescope, which was used to explore the Rosette Nebula. A simulation that arranged all these globulettes randomly in the nebula determined that some globulettes are captured by stars. They are believed to form into one or more planets, orbiting the star thereafter. The possibility that globulettes result into the formation of planets, orbiting a star, is some 4.75·10^2 per cent. According to this simulation, about 3.35·10^3 per cent of the stars with spectral type A to M host one or more planets that once have been globulettes. / <p>Validerat; 20101217 (root)</p>

As an orbiter cruising to Jupiter will encounter different plasma environments, variety of spacecraft surface charging is expected. This surface potential can lead to inaccurate and wrong in-situ plasma measurements of on-board sensors, which explain the interest in simulating the charging.In this thesis the spacecraft-plasma interactions for a future mission to Jupiter are modelled with the help of the Spacecraft Plasma Interaction System, taking the case of a Jupiter Ganymede Orbiter (JGO) and a Jupiter Europa Orbiter (JEO) as an archetype for a future mission.It is shown that in solar wind at Earth and Jupiter, spacecraft potentials of about 8 V for the JEO, and 10 V to 11 V for the JGO are expected. Furthermore, at a distance of 15 Jupiter radii from Jupiter, the JGO is expected to charge to an electric potential of 2 V, except in the planetary shadow, where it will charge to a high negative potential of -40 V. Moreover, close to the orbit of Callisto, JGO will charge to 12 V in the sun and to 4.6 V in eclipse, due to a high secondary electron emission yield. / <p>Validerat; 20120115 (anonymous)</p>

Different lubricant additives such as dialkyldithiophosphates (DTPs) of different metals have been extensively used as multifunctional additives to control wear and friction in mechanical systems. These additives can produce protective films on steel rubbing surfaces and, therefore, control friction and reduce wear. On the other hand, these additives contain large amounts of metals, phosphorus and sulfur, which can adversely affect the environment by degrading catalytic converters in automobiles. Boron based additives are recognized as friction modifiers, corrosion inhibitors, antioxidants, and effective antiwear additives. These additives are emerging as attractive alternatives for the additives already used in lubricants. The aim of the project is to investigate the tribological performance of some novel alkylborate dithiocarbamates.This project was performed in the following steps:1- Chemical synthesis of three different borated dialkyl dithiocarbamate additives with alkyl chains of different lengths.2- Tribological tests of novel compounds using a four ball tribometer.3- Surface analysis using an optical profiler (Veeco WYkO NT 1100) and Scanning Electron Microscopy coupled with X-ray Energy Dispersive Spectroscopy (SEM/EDS).The effect of the alkyl chain length in both DTC and the borate molecular moities of three B-DTC compounds on the tribological performance was studied. An increase in the alkyl chain length at the borate side improves antiwear properties in steel-steel contact. It was found that cyclo-N,N-alkylenedithiocarbamato-S-alkyl-di-n-alkyl-borate previously synthesized and studied [1], has the best antiwear performance compared with the other compounds synthesized in this work. All the novel additives were able to stabilize friction coefficient over a wide concentration range of the additives in the base oil. B-DTC additives with long alkyl chains show greater reduction in friction compared to the one with short alkyl chains. A possible explanation of this phenomenon is that longer chains have improved deposition process of additives on surfaces leading to a thicker and more stable tribofilm. EDS spectra show the presence of sulfur atoms on the rubbing surfaces lubricated by the base oil with B-DTC additives. / <p>Validerat; 20111001 (anonymous)</p>