The Flattening of Globular Clusters

In the three nearest luminous galaxies, the Milky Way System, the Andromeda Galaxy and NGC 5128 the brightest globular clusters are rounder than the faintest ones. On the other hand (contrary to some previous results) the flattening of individual LMC clusters is found to be independent of their luminosities. This suggests the possibility that the relationship between the flattening and luminosity of clusters might depend on host galaxy luminosity. No significant differences are found between the intrinsic flattening distributions of Galactic old halo, Galactic young halo and Galactic bulge/disk clusters. Such a dependence might perhaps have been expected if tidal forces (which are largest at small Galactocentric distances) removed angular momentum from globular clusters. The preliminary conclusion by Norris that clusters with blue horizontal branches are more flattened than red HB clusters is not confirmed by the larger data base that is now available. In other words there is no evidence for the puzzling claimed correlation between the flattening and the horizontal branch morphology of Galactic globular clusters.Comment: 20 pages text + tables; 5 postscript figures. Astronomical Journal, in pres

Motivic classes of some classifying stacks

We prove that the class of the classifying stack $B PGL_n$ is the multiplicative inverse of the class of the projective linear group $PGL_n$ in the Grothendieck ring of stacks for $n = 2$ and $n = 3$ under mild conditions on the base field $k$. In particular, although it is known that the multiplicativity relation $\{T\} = \{S\}\cdot\{PGL_n\}$ does not hold for all $PGL_n$-torsors $T \to S$, it holds for the universal $PGL_n$-torsors for said $n$.Comment: 25 pages. Final versio

Factors for success in Swedish biogas

The energy sector of modern time is currently faced with several challenges. These are both production oriented and environmental oriented in nature. The energy of the future is intended to support an increasing demand while at the same time reduce its environmental affection. This stresses a development towards production methods of renewable energy. Among the existing methods, biogas is presented as an attractive alternative. Further, biogas is also perceived as an attractive business concept within the agricultural sector, since this sector contains a good supply of substrate that can be used in the biogas process. As an effect, biogas would enable renewable energy production in combination with biological waste treatment and thus there are several environmental benefits with using this method. The potential for producing biogas in Sweden today, is relatively unexploited. Studies shows that there still is a large potential for producing biogas in Sweden, where a large share is represented by agricultural products. This study aims at identifying factors that are important for a further development in agricultural based biogas production. The study have been based on interviews with 31 agricultural biogas producers, where the findings has been analyzed using resource based view and Diffusion theory. The study has shown that agricultural biogas production in Sweden needs to develop in order to become competitive. To enable such a development, factors such as support from external parties and investments in technological development is viewed as important.Energisektorn är i dagsläget en sektor som innehåller flera problem. Dels finns det miljömässiga som produktionsmässiga problem. Framtidens energi ska dels kunna bistå en ökande population med energi samtidigt som den ska minska sin miljöpåverkan. Detta kommer att kräva nya metoder för att producera energi. Biogas presenteras som ett attraktivt alternativ för att producera förnyelsebar energi. Vidare är biogas ett intressant affärskoncept inom jordbrukssektorn, då det finns god tillgång till substrat som kan användas i biogas processen. Effekten av biogas skulle innebära produktion av förnyelsebar energi kombinerat med biologisk avfallshantering. Således finns det flera miljömässiga effekter med biogas produktion. Potentialen för att producera biogas är i dagsläget i relativt liten i Sverige. Studier visar att det finns stor potential att utöka produktionen av biogas, där en stor andel beräknas komma från jordbruks produkter. Denna studie syftar till att identifiera framgångs faktorer för den Svenska jordbruksbaserade biogas produktionen, för att utforska möjligheterna till en fortsatt utveckling. Studien baseras på intervjuer från 31 jordbruksbaserade biogas producenter där insamlad data har analyserats med resursbaserad teori och spridnings teori. Studien visar att jordbruksbaserad biogas produktion är i behov av utveckling för att bli konkurrenskraftigt. För att möjligöra en sådan utveckling, pekas faktorer såsom inverkan från externa parter samt vidare satsningar i teknik ut som viktiga

Weak factorization and the Grothendieck group of Deligne-Mumford stacks

We construct a presentation for the Grothendieck group of Deligne-Mumford stacks over a field of characteristic zero. The generators for this presentation are smooth, proper Deligne-Mumford stacks and the relations are expressed in terms of stacky blow-ups. In the process we prove a version of the weak factorization theorem for Deligne-Mumford stacks.Comment: Final versio

Classifications of the Host Galaxies of Supernovae, Set II

Classifications on the DDO system are given for an additional 231 host galaxies of supernovae that have been discovered during the course of the Lick Observatory Supernova Search with the Katzman Automatic Imaging Telescope (KAIT). This brings the total number of hosts of supernovae discovered (or independently rediscovered) by KAIT, which have so far been classified on a homogeneous system, to 408. The probability that SNe Ia and SNe II have a different distribution of host galaxy Hubble types is found to be 99.7%. A significant difference is also found between the distributions of the host galaxies of SNe Ia and of SNe Ibc (defined here to include SNe Ib, Ib/c, and Ic). However, no significant difference is detected between the frequency distributions of the host galaxies of SNe II and SNe IIn. This suggests that SNe IIn are generally not SNe Ia embedded in circumstellar material that are masquerading as SNe II. Furthermore, no significant difference is found between the distribution of the Hubble types of the hosts of SNe Ibc and of SNe II. Additionally, SNe II-P and SNe II-L are found to occur among similar stellar populations. The ratio of the number of SNe Ia-pec to normal SNe Ia appears to be higher in early-type galaxies than it is in galaxies of later morphological types. This suggests that the ancestors of SNe Ia-pec may differ systematically in age or composition from the progenitors of normal SNe Ia. Unexpectedly, five SNe of Types Ib/c, II, and IIn (all of which are thought to have massive progenitors) are found in host galaxies that are nominally classified as types E and S0. However, in each case the galaxy classification is uncertain, or newly inspected images show evidence suggesting a later classification (abridged) ...Comment: Accepted for publishing in PAS

The Mass of the Centaurus A Group of Galaxies

The mass M, and the radius R_h, of the Centaurus A group are estimated from the positions and radial velocities of 30 probable cluster members. For an assumed distance of 3.9 Mpc it is found that R_h \sim 640 kpc. The velocity dispersion in the Cen A group is 114 \pm 21 km/s. From this value, and R_h = 640 kpc, the virial theorem yields a total mass of 1.4 \times 10^{13} M_{\sun} for the Cen A group. The projected mass method gives a mass of 1.8 \times 10^{13} M_{\sun}. These values suggest that the Cen A group is about seven times as massive as the Local Group. The Cen A mass-to-light ratio is found to be M/L_B = 155-200 in solar units. The cluster has a zero-velocity radius R_0 = 2.3 Mpc.Comment: 8 pages, 1 figure, in LaTeX format; to appear in the Astronomical Journal in January 200

Twisted support varieties

We define and study twisted support varieties for modules over an Artin algebra, where the twist is induced by an automorphism of the algebra. Under a certain finite generation hypothesis, we show that the twisted variety of a module satisfies Dade's Lemma and is one dimensional precisely when the module is periodic with respect to the twisting automorphism. As a special case we obtain results on DTr-periodic modules over Frobenius algebras.Comment: 22 pages, to appear in J. Pure Appl. Algebr