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Search Results: 1 - 10 of 1721 matches for " Francisca Kemper "
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The chemistry of extragalactic carbon stars
Paul M. Woods,Catherine Walsh,Martin A. Cordiner,Francisca Kemper
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.21771.x
Abstract: Prompted by the ongoing interest in Spitzer Infrared Spectrometer spectra of carbon stars in the Large Magellanic Cloud, we have investigated the circumstellar chemistry of carbon stars in low-metallicity environments. Consistent with observations, our models show that acetylene is particularly abundant in the inner regions of low metallicity carbon-rich AGB stars -- more abundant than carbon monoxide. As a consequence, larger hydrocarbons have higher abundances at the metallicities of the Magellanic Clouds than in stars with solar metallicity. We also find the oxygen and nitrogen chemistry is suppressed at lower metallicity, as expected. Finally, we calculate molecular line emission from carbon stars in the Large and Small Magellanic Cloud and find that several molecules should be readily detectable with the Atacama Large Millimeter Array at Full Science operations.
The dust production rate of AGB stars in the Magellanic Clouds
Raffaella Schneider,Rosa Valiante,Paolo Ventura,Flavia dell Agli,Marcella Di Criscienzo,Hiroyuki Hirashita,Francisca Kemper
Physics , 2014, DOI: 10.1093/mnras/stu861
Abstract: We compare theoretical dust yields for stars with mass 1 Msun < mstar < 8 Msun, and metallicities 0.001 < Z < 0.008 with observed dust production rates (DPR) by carbon- rich and oxygen-rich Asymptotic Giant Branch (C-AGB and O-AGB) stars in the Large and Small Magellanic Clouds (LMC, SMC). The measured DPR of C-AGB in the LMC are reproduced only if the mass loss from AGB stars is very efficient during the carbon-star stage. The same yields over-predict the observed DPR in the SMC, suggesting a stronger metallicity dependence of the mass-loss rates during the carbon- star stage. DPR of O-AGB stars suggest that rapid silicate dust enrichment occurs due to efficient hot-bottom-burning if mstar > 3 Msun and Z > 0.001. When compared to the most recent observations, our models support a stellar origin for the existing dust mass, if no significant destruction in the ISM occurs, with a contribution from AGB stars of 70% in the LMC and 15% in the SMC.
Stellar dust production and composition in the Magellanic Clouds
F. Kemper
Physics , 2012, DOI: 10.5047/eps.2012.04.013
Abstract: The dust reservoir in the interstellar medium of a galaxy is constantly being replenished by dust formed in the stellar winds of evolved stars. Due to their vicinity, nearby irregular dwarf galaxies the Magellanic Clouds provide an opportunity to obtain a global picture of the dust production in galaxies. The Small and Large Magellanic Clouds have been mapped with the Spitzer Space Telescope from 3.6 to 160 {\mu}m, and these wavelengths are especially suitable to study thermal dust emission. In addition, a large number of individual evolved stars have been targeted for 5-40 {\mu}m spectroscopy, revealing the mineralogy of these sources. Here I present an overview on the work done on determining the total dust production rate in the Large and Small Magellanic Clouds, as well as a first attempt at revealing the global composition of the freshly produced stardust.
Using Extended Derksen Ideals in Computational Invariant Theory
Gregor Kemper
Mathematics , 2013,
Abstract: The main purpose of this paper is to develop new algorithms for computing invariant rings in a general setting. This includes invariants of nonreductive groups but also of groups acting on algebras over certain rings. In particular, we present an algorithm for computing invariants of a finite group acting on a finitely generated algebra over a Euclidean ring. This may be viewed as a first step in "computational arithmetic invariant theory." As a special case, the algorithm can compute multiplicative invariant rings. Other algorithms are applicable to nonreductive groups and are, when applied to reductive groups, often faster than the algorithms known to date. The main tool is a generalized and modified version of an ideal that was already used by Derksen in his algorithm for computing invariants of linearly reductive groups. As a further application, these so-called extended Derksen ideals give rise to invariantization maps, which turn an arbitrary ring element into an invariant. For the most part, the algorithms of this paper have been implemented.
The Transcendence Degree over a Ring
Gregor Kemper
Mathematics , 2011,
Abstract: For a finitely generated algebra over a field, the transcendence degree is known to be equal to the Krull dimension. The aim of this paper is to generalize this result to algebras over rings. A new definition of the transcendence degree of an algebra A over a ring R is given by calling elements of A algebraically dependent if they satisfy an algebraic equation over R whose trailing coefficient, with respect to some monomial ordering, is 1. The main result is that for a finitely generated algebra over a Noetherian Jacobson ring, the transcendence degree is equal to the Krull dimension.
High-resolution CO observation of the carbon star CIT 6 revealing the spiral structure and a nascent bipolar outflow
Hyosun Kim,Sheng-Yuan Liu,Naomi Hirano,Ronny Zhao-Geisler,Alfonso Trejo,Hsi-Wei Yen,Ronald E. Taam,Francisca Kemper,Jongsoo Kim,Do-Young Byun,Tie Liu
Physics , 2015,
Abstract: CIT 6 is a carbon star in the transitional phase from the asymptotic giant branch (AGB) to the protoplanetary nebulae (pPN). Observational evidences of two point sources in the optical, circumstellar arc segments in an HC$_3$N line emission, and a bipolar nebula in near-infrared provide strong support for the presence of a binary companion. Hence, CIT 6 is very attractive for studying the role of companions in the AGB-pPN transition. We have carried out high resolution $^{12}$CO $J=2-1$ and $^{13}$CO $J=2-1$ observations of CIT 6 with the Submillimeter Array combined with the Submillimeter Telescope (single-dish) data. The $^{12}$CO channel maps reveal a spiral-shell pattern connecting the HC$_3$N segments in a continuous form, and an asymmetric outflow corresponding to the near-infrared bipolar nebula. Rotation of the $^{12}$CO channel peak position may be related to the inner spiral winding and/or the bipolar outflow. An eccentric orbit binary is suggested for the presences of an anisotropic mass loss to the west and a double spiral pattern. The lack of interarm emission to the west may indicate a feature corresponding to the periastron passage of a highly eccentric orbit of the binary. Spatially-averaged radial and spectral profiles of $^{12}$CO $J=2-1$ and $^{13}$CO $J=2-1$ are compared with simple spherical radiative transfer models, suggesting a change of $^{12}$CO/$^{13}$CO abundance ratio from $\sim30$ to $\sim50$ inward in the CSE of CIT 6. The millimeter continuum emission is decomposed into extended dust thermal emission (spectral index $\sim-2.4$) and compact emission from radio photosphere (spectral index $\sim-2.0$).
Bacteria in milk from anterior and posterior mammary glands in sows affected and unaffected by postpartum dysgalactia syndrome (PPDS)
Nicole Kemper, Imke Gerjets
Acta Veterinaria Scandinavica , 2009, DOI: 10.1186/1751-0147-51-26
Abstract: In this study, the health status of 56 sows after farrowing was determined with special regard to mastitis and dysgalactia. Pooled milk samples from anterior and posterior glands were taken from both affected and non-affected animals and analysed bacteriologically for the presence of a wide spectrum of different pathogens.Mainly Escherichia coli, staphylococci and streptococci were detected in high percentages but without significant differences in healthy and diseased animals and anterior and posterior glands. However, the large percentages of coliform bacteria suggested a transmission route via faecal contamination.In this study, the prevalence of different bacteria in anterior and posterior glands in PPDS positive and negative sows was analysed. No significant differences in bacteria of healthy and diseased sows were assessed. Therefore, the development of clinical PPDS and actual infection seems to be largely dependant on individual resistance in single sows.In their first days of life, piglets are totally reliant on the sow for access to colostrum and milk. Every alteration in both milk yield and composition has highly sensitive impacts on weight gain and growth rate. Therefore, postparturient disorders, including dysgalactia in sows, are a very important disease complex economically [1]. They are reported world-wide, but subsumed under different terms depending on the geographical location. While mastitis, metritis and agalactia syndrome (MMA) [2,3] is the commonly used name in European countries, post-partum dysgalactia syndrome (PPDS or PDS) [4] has become widely accepted in English-speaking areas. At farm level, incidence is estimated to differ between 0.5% and 60% [5], with an average incidence of about 13% [6-11]. The syndrome is characterised by greatly reduced milk production within 12 to 48 hours post-partum that rapidly leads to piglet starvation. Even though metritis is often a part of the syndrome, mastitis is the central symptom, as shown by severa
Estado y antropología en México y Estados Unidos: reflexiones sobre los Proyectos Tarascos
Kemper, Robert V.;
Relaciones (Zamora) , 2011,
Abstract: the relation between "the state and anthropology", especially with regards its relevance to the development of anthropological work in michoacán, can be understood through an analysis of the tarasco project, one that comprised distinct periods of fieldwork and distinct academic and political proposals. those projects -including sáenz' work in carapan, swadesh in paracho, beals in cherán and foster in tzintzuntzan- represented a convergence produced by the interests of the governments of mexico and the united states; one that emerged, undoubtedly, from the special circumstances of the time; i.e., the end of the great depression and the period of world war ii. those studies were conducted thanks to substantial economic and logistical support provided by several governmental agencies in both mexico and the u.s. in that context, the anthropologists who participated in the tarasco project were not simple "intellectual intermediaries" but, rather, " institutional intermediaries" who fulfilled roles as agents of their respective governments.
Madre-padre-criatura: el dios andino transcorriente, Wiracocha
Claudette Kemper Columbus
Anthropologica , 1995,
Abstract: El artículo no presenta resumen.
Dos ejemplos del pensamiento andino no-lineal: los zorros de Arguedas y la illa andina
Claudette Kemper Columbus
Anthropologica , 1997,
Abstract: El artículo no presenta resumen.
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