Simulating Star Formation and Feedback in Galactic Disk Models

We use a high-resolution grid-based hydrodynamics method to simulate the multi-phase interstellar medium in a Milky Way-size quiescent disk galaxy. The models are global and three-dimensional, and include a treatment of star formation and feedback. We examine the formation of gravitational instabilities and show that a form of the Toomre instability criterion can successfully predict where star formation will occur. Two common prescriptions for star formation are investigated. The first is based on cosmological simulations and has a relatively low threshold for star formation, but also enforces a comparatively low efficiency. The second only permits star formation above a number density of 1000 cm^-3 but adopts a high efficiency. We show that both methods can reproduce the observed slope of the relationship between star formation and gas surface density (although at too high a rate for our adopted parameters). A run which includes feedback from type II supernovae is successful at driving gas out of the plane, most of which falls back onto the disk. This feedback also substantially reduces the star formation rate. Finally, we examine the density and pressure distribution of the ISM, and show that there is a rough pressure equilibrium in the disk, but with a wide range of pressures at a given location (and even wider for the case including feedbackComment: 14 pages, 12 figures, accepted to Astrophysical Journa

Micropalaeontology reveals the source of building materials for a defensive earthwork (English Civil War?) at Wallingford Castle, Oxfordshire

Microfossils recovered from sediment used to construct a putative English Civil War defensive bastion at Wallingford Castle, south Oxfordshire, provide a biostratigraphical age of Cretaceous (earliest Cenomanian) basal M. mantelli Biozone. The rock used in the buttress – which may have housed a gun emplacement – can thus be tracked to the Glauconitic Marl Member, base of the West Melbury Marly Chalk Formation. A supply of this rock is available on the castle site or to the east of the River Thames near Crowmarsh Gifford. Microfossils provide a unique means to provenance construction materials used at the Wallingford site. While serendipity may have been the chief cause for use of the Glauconitic Marl, when compacted, it forms a strong, almost ‘road base’-like foundation that was clearly of use for constructing defensive works. Indeed, use of the Glauconitic Marl was widespread in the area for agricultural purposes and its properties may have been well-known locally

Deviations from the Schmidt-Kennicutt relations during early galaxy evolution

We utilize detailed time-varying models of the coupled evolution of stars and the HI, H_2, and CO-bright H_2 gas phases in galaxy-sized numerical simulations to explore the evolution of gas-rich and/or metal-poor systems, expected to be numerous in the Early Universe. The inclusion of the CO-bright H_2 gas phase, and the realistic rendering of star formation as an H_2-regulated process (and the new feedback processes that this entails) allows the most realistic tracking of strongly evolving galaxies, and much better comparison with observations. We find that while galaxies eventually settle into states conforming to Schmidt-Kennicutt (S-K) relations, significant and systematic deviations of their star formation rates (SFRs) from the latter occur, especially pronounced and prolonged for ... ...This indicates potentially serious limitations of (S-K)-type relations as reliable sub-grid elements of star formation physics in simulations of structure formation in the Early Universe. We anticipate that galaxies with marked deviations from the S-K relations will be found at high redshifts as unbiased inventories of total gas mass become possible with ALMA and the EVLA.Comment: 13 pages, 3 figures, accepted for publication in the Astrophysical Journa

Magnetism and half-metallicity at the O surfaces of ceramic oxides

The occurence of spin-polarization at ZrO$_{2}$, Al$_{2}$O$_{3}$ and MgO surfaces is proved by means of \textit{ab-initio} calculations within the density functional theory. Large spin moments, as high as 1.56 $\mu_B$, develop at O-ended polar terminations, transforming the non-magnetic insulator into a half-metal. The magnetic moments mainly reside in the surface oxygen atoms and their origin is related to the existence of $2p$ holes of well-defined spin polarization at the valence band of the ionic oxide. The direct relation between magnetization and local loss of donor charge makes possible to extend the magnetization mechanism beyond surface properties

Follow-up monitoring in a cat with leishmaniosis and coinfections with Hepatozoon felis and ‘Candidatus Mycoplasma haemominutum’

Case summary A 6-year-old female neutered domestic shorthair cat from Cyprus was presented with multiple ulcerated skin nodules. Cytology and histopathology of the lesions revealed granulomatous dermatitis with intracytoplasmic organisms, consistent with amastigotes of Leishmania species. Biochemistry identified a mild hyperproteinaemia. Blood extraction and PCR detected Leishmania species, Hepatozoon species and ‘Candidatus Mycoplasma haemominutum’ (CMhm) DNA. Subsequent sequencing identified Hepatozoon felis. Additionally, the rRNA internal transcribed spacer 1 locus of Leishmania infantum was partially sequenced and phylogeny showed it to cluster with species derived from dogs in Italy and Uzbekistan, and a human in France. Allopurinol treatment was administered for 6 months. Clinical signs resolved in the second month of treatment with no deterioration 8 months post-treatment cessation. Quantitative PCR and ELISA were used to monitor L infantum blood DNA and antibody levels. The cat had high L infantum DNA levels pretreatment that gradually declined during treatment but increased 8 months post-treatment cessation. Similarly, ELISA revealed high levels of antibodies pretreatment, which gradually declined during treatment and increased slightly 8 months post-treatment cessation. The cat remained PCR positive for CMhm and Hepatozoon species throughout the study. There was no clinical evidence of relapse 24 months post-treatment. Relevance and novel information To our knowledge, this is the first clinical report of a cat with leishmaniosis with H felis and CMhm coinfections. The high L infantum DNA levels post-treatment cessation might indicate that although the lesions had resolved, prolonged or an alternative treatment could have been considere

Contrast Mechanisms for the Detection of Ferroelectric Domains with Scanning Force Microscopy

We present a full analysis of the contrast mechanisms for the detection of ferroelectric domains on all faces of bulk single crystals using scanning force microscopy exemplified on hexagonally poled lithium niobate. The domain contrast can be attributed to three different mechanisms: i) the thickness change of the sample due to an out-of-plane piezoelectric response (standard piezoresponse force microscopy), ii) the lateral displacement of the sample surface due to an in-plane piezoresponse, and iii) the electrostatic tip-sample interaction at the domain boundaries caused by surface charges on the crystallographic y- and z-faces. A careful analysis of the movement of the cantilever with respect to its orientation relative to the crystallographic axes of the sample allows a clear attribution of the observed domain contrast to the driving forces respectively.Comment: 8 pages, 8 figure