A Semianalytical, Three Dimensional Model of Microstructure in Multiparticle, Multiphase Flow

This dissertation presents a three dimensional microgeodynamic model of grain-melt geometry in partially molten rocks. The isotropic unit cell of the partially molten rock is characterized by a face-centered-cubic symmetry, consisting of rhombic dodecahedral grains. The variation of surface tension between grain-grain and grain-melt contacts excites a coupled viscous flow within grains and the interstitial melt leading to a steady-state grain-melt geometry. The fractional area of intergranular contact, contiguity, is obtained from these models as a function of melt volume fraction, for melt fractions between 0.05 and 0.25. Comparison with previous results indicates that the contiguity in three dimensional models is lower than two dimensional models. We apply our model to the UltraLow Velocity Zones (ULVZ) in the Earth's core-mantle boundary. The observed seismic signature of the ULVZ can be explained by a melt volume fraction between 0.08 and 0.12

Explosive Volcanic Eruptions from Linear Vents on Earth, Venus and Mars: Comparisons with Circular Vent Eruptions

Conditions required to support buoyant convective plumes are investigated for explosive volcanic eruptions from circular and linear vents on Earth, Venus, and Mars. Vent geometry (linear versus circular) plays a significant role in the ability of an explosive eruption to sustain a buoyant plume. On Earth, linear and circular vent eruptions are both capable of driving buoyant plumes to equivalent maximum rise heights, however, linear vent plumes are more sensitive to vent size. For analogous mass eruption rates, linear vent plumes surpass circular vent plumes in entrainment efficiency approximately when L(sub o) > 3r(sub o) owing to the larger entrainment area relative to the control volume. Relative to circular vents, linear vents on Venus favor column collapse and the formation of pyroclastic flows because the range of conditions required to establish and sustain buoyancy is narrow. When buoyancy can be sustained, however, maximum plume heights exceed those from circular vents. For current atmospheric conditions on Mars, linear vent eruptions are capable of injecting volcanic material slightly higher than analogous circular vent eruptions. However, both geometries are more likely to produce pyroclastic fountains, as opposed to convective plumes, owing to the low density atmosphere. Due to the atmospheric density profile and water content on Earth, explosive eruptions enjoy favorable conditions for producing sustained buoyant columns, while pyroclastic flows would be relatively more prevalent on Venus and Mars. These results have implications for the injection and dispersal of particulates into the planetary atmosphere and the ability to interpret the geologic record of planetary volcanism

Tidningars syn på ungdomar : En kvalitativ studie

Syftet med denna uppsats har varit att förstå hur bilden av ungdomar konstrueras i svensk dags- och kvällspress. Problematiseringen av uppsatsämnet var den verklighet som konstrueras, i det här fallet bilden av ungdomar, som kan konstrueras till ett socialt problem. Den teoretiska utgångspunkten har varit socialkonstruktivistisk. Metoden för att förstå bilden av ungdomar var genom tolkning och analys av text. Två statligt utgivna rapporter valdes ut, därefter söktes via databas efter tidningsartiklar som berörde ämnena ungdom och de utvalda rapporterna. Undersökningen gjordes genom att först lästes, analyserades och tolkades de två statligt utgivna rapporerna och därefter gjordes desamma med tidningsartiklarna. Resultatet och analysen visade att dags-och kvällstidningsartiklarna har problemformuleringsprivilegium vad gäller den skrivna texten. Dels vad som skall skrivas om och på vilket sätt det skall skrivas från de två statligt utgivna rapporterna. I slutdiskussionen har vi skrivit om den ökande förståelsen som vi författare fått om den konstruerande tidningsartikelstexten samt makten som dags-och kvällstidningar besitter vad gäller den publicerade texten i sociala sammanhang