Dynamics of the Sharp Edges of Broad Planetary Rings

(Abridged) The following describes a model of a broad planetary ring whose sharp edge is confined by a satellite's m^th Lindblad resonance (LR). This model uses a streamline formalism to calculate the ring's internal forces, namely, ring gravity, pressure, viscosity, as well as a hypothetical drag force. The model calculates the streamlines' forced orbit elements and surface density throughout the perturbed ring. The model is then applied to the outer edge of Saturn's B ring, which is maintained by an m=2 inner LR with the satellite Mimas. Ring models are used to illustrate how a ring's perturbed state depends on the ring's physical properties: surface density, viscosity, dispersion velocity, and the hypothetical drag force. A comparison of models to the observed outer B ring suggests that the ring's surface density there is between 10 and 280 gm/cm^2. The ring's edge also indicates where the viscous torque counterbalances the perturbing satellite's gravitational torque on the ring. But an examination of seemingly conventional viscous B ring models shows that they all fail to balance these torques at the ring's edge. This is due ring self-gravity and the fact that a viscous ring tends to be nearly peri-aligned with the satellite, which reduces the satellite's torque on the ring and makes the ring's edge more difficult to maintain. Nonetheless, the following shows that a torque balance can still be achieved in a viscous B ring, but only in an extreme case where the ratio of the ring's bulk/shear viscosities satisfy ~10^4. However, if the dissipation of the ring's forced motions is instead dominated by a weak drag force, then the satellite can exert a much stronger torque that can counterbalance the ring's viscous torque.Comment: Accepted for publication in the Astrophysical Journal on April 3, 200

Fonders avkastning - en variabelanalys av fonders avkastning under ekonomisk upp- och nedgång

Vårt syfte är att ta reda på mer om vad som påverkar fonders avkastning och om detta skiljer sig åt i ekonomisk uppgångs- respektive nedgångsperiod. För att uppfylla vårt syfte har vi valt att genomföra regressionsanalys med avkastning som beroende variabel och variablerna: standardavvikelse, beta, storlek, TKA och omsättningshastighet som förklarande variabler. Detta har genomförts i en ekonomisk uppgångs- och en ekonomisk nedgångsperiod. Vi har använt portföljvalsteori med dess ingående variabler avkastning och risk. Även begrepp som kovarians, korrelation, effektiva fronten, mean variance, CAPM och beta gås igenom. Detta följs av det aktuella forskningsläget inom ämnet. Risk i form av standardavvikelse är den variabel som visar det starkaste sambandet med avkastning. Studerar man fondernas beta underpresterar fonderna jämfört med marknaden i både ekonomisk upp- och nedgångsperiod

Fonders avkastning -en variabelanalys av fonders avkastning under ekonomisk upp- och nedgång

Vårt syfte är att ta reda på mer om vad som påverkar fonders avkastning och om detta skiljer sig åt i ekonomisk uppgångs- respektive nedgångsperiod. För att uppfylla vårt syfte har vi använt oss av regressionsanalyser med avkastning som beroendevariabel och variablerna: standardavvikelse, beta, storlek, TKA och omsättningshastighet som förklarande variabler. Vi har använt portföljvalsteori med dess ingående variabler avkastning och risk. Även begrepp som CAPM och beta gås igenom. Detta följs av det aktuella forskningsläget inom ämnet. Risk i form av standardavvikelse är den variabel som uppvisar det starkaste sambandet med avkastning. Studerar man fondernas beta underpresterar fonderna jämfört med marknaden i både ekonomisk upp- och nedgång

Kinetic description of coagulation and fragmentation in dilute granular particle assemblies

We derive kinetic equations covering coagulation and fragmentation of granular gases including a combined dynamics of the mass spectrum and the velocity distribution. We will focus on coagulation, that can only occur at low impact velocities where attractive forces and dissipation prevent a post-collisional separation. We calculate an impact speed-dependent threshold velocity g_{\ab{c}} for coagulation to occur based on binary collision dynamics of viscoelastic granular particles including adhesive forces and determined by the masses, and the material of the colliding particles. Growth processes are immensely slowed down due to g_{\ab{c}} and the resulting restriction in phase space, and do furthermore depend on the ratio of threshold and thermal velocity of a considered particle ensemble. The Smoluchowski equation emerges from the general kinetic approach as a special case

Impact-generated dust clouds around planetary satellites: spherically symmetric case

An analytic model of an impact-generated, steady-state, spherically symmetric dust cloud around an atmosphereless planetary satellite (or planet-Mercury, Pluto) is constructed. The projectiles are assumed to be interplanetary micrometeoroids. The model provides the expected mass, density, and velocity distributions of dust in the vicinities of parent bodies. Applications are made to Jupiter's moon Ganymede and six outer satellites of Saturn. In the former case, the model is shown to be consistent with the measurements of the dust detector system onboard the Galileo spacecraft. In the latter case, estimates are given and recommendations are made for the planned experiment with the Cassini cosmic dust analyzer (CDA) during targeted flybys of the spacecraft with the moons. The best CDA pointing to maximize the number of detections is in the ram direction. With this pointing, measurements are possible within a few to about 20min from the closest approach, with maximum minute impact rates ranging from about 1 for Phoebe and Hyperion to thousands for Enceladus. Detections of the ejecta clouds will still be likely if CDA's angular offset from the ram direction does not exceed /45°. The same model can be applied to dust measurements by other space missions, like New Horizons to Pluto or BepiColombo to Mercury

Oxidative stress, hemoglobin content, superoxide dismutase and catalase activity influenced by sulphur baths and mud packs in patients with osteoarthritis

Background/Aim. It is weel-known that sulphur baths and mud paks demonstrate beneficial effects on patients suffering from degenerative knee and hip osteoarthritis (OA) through the increased activity of protective antioxidant enzymes. The aim of this study was to assess lipid peroxidation level, i.e. malondialdehyde concetration, in individuals with knee and/or hip osteoarthritis (OA), as well as to determine the influence of sulphur baths and mud packs application on the activity of superoxide dismutase (SOD) and catalase (CAT) in order to minimize or eliminate excessive free radical species production (oxidative stress). Methods. Thirty one patiens with knee and/or hip OA of both sexes were included in the study. All OA patients received mud pack and sulphur bath for 20 minutes a day, for 6 consecutive days a week, over 3 weeks. Blood lipid peroxidation, ie malondialdehyde concentration, superoxide dismutase and catalase activity were measured spectrophotometrically, before, on day 5 during the treatment and at the end of spa cure. Healthy volunteers (n = 31) were the controls. Results. The sulphur baths and mud packs treatment of OA patients caused a significant decrease in plasma malondialdehyde concentration compared to the controls (p < 0.001). The mean SOD activity before the terapy was 1 836.24 U/gHb, on day 5 it rose to 1 942.15 U/gHb and after the spa cure dropped to 1 745.98 U/gHb. Catalase activity before the therapy was 20.56 kU/gHb and at the end of the terapy decreased to 16.16 kU/gHb. The difference in catalase activity before and after the therapy was significant (p < 0.001), and also significant as compared to control (p < 0.001). At the end of the treatment significant increase of hemoglobin level and significant decrease of pain intensity were noticed. Conclusion. A combined 3-week treatment by sulphur bath and mud packs led to a significant decrease of lipid peroxidation in plasma, as well as pain intensity in the patients with OA. These changes were associated with changes in plasma activity of SOD and CAT and a significant increase of hemoglobin level suggesting their role in beneficial effect of spa therapy in the patients with OA

Impact-generated dust clouds around planetary satellites: spherically symmetric case

An analytic model of an impact-generated, steady-state, spherically symmetric dust cloud around an atmosphereless planetary satellite (or planet-Mercury, Pluto) is constructed. The projectiles are assumed to be interplanetary micrometeoroids. The model provides the expected mass, density, and velocity distributions of dust in the vicinities of parent bodies. Applications are made to Jupiter's moon Ganymede and six outer satellites of Saturn. In the former case, the model is shown to be consistent with the measurements of the dust detector system onboard the Galileo spacecraft. In the latter case, estimates are given and recommendations are made for the planned experiment with the Cassini cosmic dust analyzer (CDA) during targeted flybys of the spacecraft with the moons. The best CDA pointing to maximize the number of detections is in the ram direction. With this pointing, measurements are possible within a few to about 20min from the closest approach, with maximum minute impact rates ranging from about 1 for Phoebe and Hyperion to thousands for Enceladus. Detections of the ejecta clouds will still be likely if CDA's angular offset from the ram direction does not exceed /45°. The same model can be applied to dust measurements by other space missions, like New Horizons to Pluto or BepiColombo to Mercury