Inhomogeneity of asteroid 2008 TC3 (Almahata Sitta meteorites) revealed through magnetic susceptibility measurements

Magnetic susceptibility measurements were performed on freshly fallen Almahata Sitta meteorites. Most recovered samples are polymict ureilites. Those found in the first four months since impact, before the meteorites were exposed to rain, have a magnetic susceptibility in the narrow range of 4.92 ± 0.08 log 10-9 Am2/kg close to the range of other ureilite falls 4.95 ± 0.14 log 10-9 Am2/kg reported by Rochette et al. (2009). The Almahata Sitta samples collected one year after the fall have similar values (4.90 ± 0.06 log 10-9 Am2/kg), revealing that the effect of one-year of terrestrial weathering was not severe yet. However, our reported values are higher than derived from polymict (brecciated) ureilites 4.38 ± 0.47 log 10-9 Am2/kg (Rochette et al. 2009) containing both falls and finds confirming that these are significantly weathered. Additionally other fresh-looking meteorites of non-ureilitic compositions were collected in the Almahata Sitta strewn field. Magnetic susceptibility measurements proved to be a convenient non-destructive method for identifying non-ureilitic meteorites among those collected in the Almahata Sitta strewn field, even among fully crusted. Three such meteorites, no. 16, 25, and 41, were analyzed and their composition determined as EH6, H5 and EL6 respectively (Zolensky et al., 2010). A high scatter of magnetic susceptibility values among small (< 5 g) samples revealed high inhomogeneity within the 2008 TC3 material at scales below 1-2 cm.

Almahata Sitta (=asteroid 2008 TC3) and the search for the ureilite parent body

This article explores what the recovery of 2008 TC3 in the form of the Almahata Sitta meteorites may tell us about the source region of ureilites in the main asteroid belt. An investigation is made into what is known about asteroids with roughly the same spectroscopic signature as 2008 TC3. A population of low-inclination near-Earth asteroids is identified with spectra similar to 2008 TC3. Five asteroid families in the Main Belt, as well as a population of ungrouped asteroids scattered in the inner and central belts, are identified as possible source regions for this near-Earth population and 2008 TC3. Three of the families are ruled out on dynamical and spectroscopic grounds. New near-infrared spectra of 142 Polana and 1726 Hoffmeister, lead objects in the two other families, also show a poor match to Almahata Sitta. Thus, there are no Main Belt spectral analogs to Almahata Sitta currently known. Space weathering effects on ureilitic materials have not been investigated, so that it is unclear how the spectrum of the Main Belt progenitor may look different from the spectra of 2008 TC3 and the Almahata Sitta meteorites. Dynamical arguments are discussed, as well as ureilite petrogenesis and parent body evolution models, but these considerations do not conclusively point to a source region either, other than that 2008 TC3 probably originated in the inner asteroid belt.

Origin and history of ureilitic material in the solar system: The view from asteroid 2008 TC3 and the Almahata Sitta meteorite

Asteroid 2008 TC3 (approximately 4m diameter) was tracked and studied in space for approximately 19h before it impacted Earth's atmosphere, shattering at 44-36km altitude. The recovered samples (>680 individual rocks) comprise the meteorite Almahata Sitta (AhS). Approximately 50-70% of these are ureilites (ultramafic achondrites). The rest are chondrites, mainly enstatite, ordinary, and Rumuruti types. The goal of this work is to understand how fragments of so many different types of parent bodies became mixed in the same asteroid. Almahata Sitta has been classified as a polymict ureilite with an anomalously high component of foreign clasts. However, we calculate that the mass of fallen material was 0.1% of the pre-atmospheric mass of the asteroid. Based on published data for the reflectance spectrum of the asteroid and laboratory spectra of the samples, we infer that the lost material was mostly ureilitic. Therefore, 2008 TC3 probably contained only a few percent nonureilitic materials, similar to other polymict ureilites except less well consolidated. From available data for the AhS meteorite fragments, we conclude that 2008 TC3 samples essentially the same range of types of ureilitic and nonureilitic materials as other polymict ureilites. We therefore suggest that the immediate parent of 2008 TC3 was the immediate parent of all ureilitic material sampled on Earth. We trace critical stages in the evolution of that material through solar system history. Based on various types of new modeling and re-evaluation of published data, we propose the following scenario. (1) The ureilite parent body (UPB) accreted 0.5-0.6Ma after formation of calcium-aluminum-rich inclusions (CAI), beyond the ice line (outer asteroid belt). Differentiation began approximately 1Ma after CAI. (2) The UPB was catastrophically disrupted by a major impact approximately 5Ma after CAI, with selective subsets of the fragments reassembling into daughter bodies. (3) Either the UPB (before breakup), or one of its daughters (after breakup), migrated to the inner belt due to scattering by massive embryos. (4) One daughter (after forming in or migrating to the inner belt) became the parent of 2008 TC3. It developed a regolith, mostly 3.8Ga ago. Clasts of enstatite, ordinary, and Rumuruti-type chondrites were implanted by low-velocity collisions. (5) Recently, the daughter was disrupted. Fragments were injected or drifted into Earth-crossing orbits. 2008 TC3 comes from outer layers of regolith, other polymict ureilites from deeper regolith, and main group ureilites from the interior of this body. In contrast to other models that have been proposed, this model invokes a stochastic history to explain the unique diversity of foreign materials in 2008 TC3 and other polymict ureilites.

The impact and recovery of asteroid 2008 TC3

In the absence of a firm link between individual meteorites and their asteroidal parent bodies, asteroids are typically characterized only by their light reflection properties, and grouped accordingly into classes. On 6 October 2008, a small asteroid was discovered with a flat reflectance spectrum in the 554-995nm wavelength range, and designated 2008 TC3 (refs 4-6). It subsequently hit the Earth. Because it exploded at 37km altitude, no macroscopic fragments were expected to survive. Here we report that a dedicated search along the approach trajectory recovered 47 meteorites, fragments of a single body named Almahata Sitta, with a total mass of 3.95kg. Analysis of one of these meteorites shows it to be an achondrite, a polymict ureilite, anomalous in its class: ultra-fine-grained and porous, with large carbonaceous grains. The combined asteroid and meteorite reflectance spectra identify the asteroid as F class, now firmly linked to dark carbon-rich anomalous ureilites, a material so fragile it was not previously represented in meteorite collections.

Man kan både sitta bredbent och med benen i kors : En kvalitativ studie om hur genusvetare praktiserar genuskunskap

There is an awareness of the importance of gender equality in most western societies, both at the political level and in everyday life. In academia, for instance, gender is nowadays a scientific field which indicates that there is a lot of knowledge about the subject. What we do not have much knowledge about is whether gender knowledge leads to changes in gender relations in practice. The aim of this study is to explore how gender scholars relate to using – practicing – gender knowledge. Key issues in this study are how gender scholars construct gender, how they practice gender theoretical knowledge, and their reflections of gender boundaries.             Theoretically, this study is mainly based on Sara Ahmed’s perspective on gender. The main finding of the study is that despite gender knowledge gender scholars tend to reproduce traditional gender orders. By identifying concepts such as reflected and unreflected masculinity/femininity, different ideals of masculinity/femininity are made visible. There seems to be an ideal among gender scholars to practice their gender knowledge. This ideal is practiced among “gender scholar women” by doing reflected masculinity and reflected femininity. Among “gender scholar men”, however, the ideal to practice gender knowledge by doing unreflected masculinity and reflected femininity seems to be a taboo at the same time. For men, it seems important to mark a distance to a certain type of femininity and to maintain the heterosexual – straight – line. For women, it seems desirable both to distance themselves from a certain type of masculinity and femininity and thereby follow alternative – queer – lines.

SINGULARITY THEORY AND FORCED SYMMETRY BREAKING IN EQUATIONS

A theory of bifurcation equivalence for forced symmetry breaking bifurcation problems is developed. We classify (O(2), 1) problems of corank 2 of low codimension and discuss examples of bifurcation problems leading to such symmetry breaking.

On the open-circuit interaction between methanol and oxidized platinum electrodes

In the present work, results of the interaction between methanol and oxidized platinum surfaces as studied via transients of open-circuit potentials are presented. The surface oxidation before the exposure to interaction with 0.5 M methanol was performed at different polarization times at 1.4 V vs reversible hydrogen electrode (RHE). In spite of the small changes in the initial oxide content, the increase of the pre-polarization time induces a considerable increase of the time needed for the oxide consumption during its interaction with methanol. The influence of the identity of the chemisorbing anion on the transients was also investigated in the following media: 0.1 M HClO4, 0.5 M H2SO4, and 0.5 M H2SO4 + 0.1 mM Cl-. It was observed that the transient time increases with the energy of anion chemisorption and, more importantly, without a change in the shape of the transient, meaning that free platinum sites are available at the topmost layer all over the transient and not only in the potential region of small oxide `coverage`. The impact of the pre-polarization time and the effect of anion chemisorption on the transients are rationalized in terms of the presence of surface and subsurface oxygen driven by place exchange.

Stabilizing Nonstationary Electrochemical Time Series

Electrochemical systems are ideal working-horses for studying oscillatory dynamics. Experimentally obtained time series, however, are usually associated with a spontaneous drift in some uncontrollable parameter that triggers transitions among different oscillatory patterns, despite the fact that all controllable parameters are kept constant. Herein we present an empirical method to stabilize experimental potential time series. The method consists of applying a negative galvanodynamic sweep to compensate the spontaneous drift and was tested for the oscillatory electro-oxidation of methanol on platinum. For a wide range of applied currents, the base system presents spontaneous transitions from quasi-harmonic to mixed mode oscillations. Temporal patterns were stabilized by galvanodynamic sweeps at different rates. The procedure resulted in a considerable increase in the number of oscillatory cycles from 5 to 20 times, depending on the specific temporal pattern. The spontaneous drift has been associated with uncompensated oscillations, in which the coverage of some adsorbed species are not reestablished after one cycle; i.e., there is a net accumulation and/or depletion of adsorbed species during oscillations. We interpreted the rate of the galvanodynamic sweep in terms of the time scales of the poisoning processes that underlies the uncompensated oscillations and thus the spontaneous slow drift.

Nanogravimetric study of the complex voltammetric response in the electro-oxidation of methanol on platinum

Instead of a time-invariant voltammetric profile, many electrochemical systems display a cycle-dependent current-potential response. This phenomenon has been referred to as complex voltammetric response and it has been observed during the electro-oxidation of several molecules such as methanol, ethanol, propanol and hydrogen. There are currently two explanations for the surface mechanism underlying this behavior. In one scenario, the complex voltammogram would result from the specific kinetic pathway taken during the forward sweep. In the other explanation, the phenomenon is discussed in terms of the interplay among the surface roughening and subsequent relaxation, and the ohmic drop coupled to a negative differential resistance. We report in this paper a nanogravimetric investigation of the complex voltammetric response in the electro-oxidation of methanol on platinum electrode in both acidic and alkaline media. Different periodic patterns composed of intercalated small and large hysteresis cycles were observed as a function of the applied voltage and the series resistance between the working electrode and the potentiostat. Independently, nanogravimetric results indicated no detectable difference in the delta-frequency versus voltage profile between small and large hysteresis cycles. These findings were interpreted as experimental evidence of the secondary, if any, role played by the very electrochemical reaction on the emergence of complex voltammetric response. (C) 2009 Elsevier Ltd. All rights reserved.

Kyrkorum och status : En studie om bänkplacering i 1700-talets Falun

Denna studie har som syfte att undersöka bänkrummets betydelse för vidmakthållandet av hierarkier och status i 1700-talets Falun. Materialet som används för att uppfylla detta syfte består främst av kyrkorådsprotokoll ifrån Kristine församling i Falun mellan 1744-1784. Utöver dessa kyrkorådsprotokoll används stundtals biografier för att kunna ge en djupare bild av vissa individer. Resultatet visar att det under den undersökta perioden råder en strikt uppdelning av kyrko-rummet. Det mest uppenbara är uppdelningen mellan kvinnor och män. Uppdelningen av kyr-korummet följer emellertid inte bara könstillhörighet utan även ett mönster för över- och un-derordning. Inflytelserika personer satt långt fram i kyrkan och detta gällde både på manssi-dan som kvinnosidan i kyrkan. Ju längre bak i kyrkan man satt desto lägre social status hade man. Att sitta utmed en vägg verkar inte heller ha varit förknippat med hög status i Falun. Bänkplaceringen i kyrkan blev ett sätt att upprätthålla skillnad mellan människor, dock inte helt utan utmaningar och undantag.

Barn utan språk? : En kvalitativ studie om pedagogers språkutvecklande arbete i förskolan och hur det synliggörs

Undersökningens syfte var att ta reda på hur pedagoger arbetar för att stödja barns andraspråksutveckling på en förskola. Mina frågeställningar var: Hur säger pedagogerna att de planerar för ett språkutvecklande arbete med flerspråkiga barn? Hur syns (synliggörs) möjligheter/begränsningar till språkutveckling i verksamheten? Hur arbetar pedagogerna med barn som ännu inte har uppnått jämförbar nivå i svenska som sina enspråkigt svenska kamrater? Jag genomförde två kvalitativa intervjuer med två pedagoger på den aktuella avdelningen samt åtta observationer i språkutvecklande situationer. Dessa situationer var samling, matsituationer, högläsning, valstund samt fri lek. Intervjuer samt observationer skedde under två dagar. Tekniken som jag använt mig av är inspelning med hjälp av diktafon och anteckningar. Resultatet visade att pedagogerna arbetar språkutvecklande främst i form av sånger samt högläsning. De uppmärksammar barnens kultur med hjälp av en världskarta samt bilder på flaggor där barnen kommer ifrån. Resultatet visar även att de ej uppmärksammar barnens kultur i den utsträckning de säger sig vilja vilket ses som en begränsning. Resultatet av observationerna visar att pedagogerna arbetar språkutvecklande med sånger samt högläsning och genom samtal med barnen. Samtalen vid matsituationer visade sig innehålla stora möjligheter till språkutveckling, medan möjligheterna till språkutveckling vid högläsningen visade sig bristfällig. Vid högläsningen skedde samtalet kring boken främst under själva läsningen, dock inget före eller efter läsningen, vilket ses som en begränsning till språkutveckling. Resultatet visade även att barnen i leken ofta lämnas ensamma i ett rum utan pedagog närvarande, och därigenom missar pedagogerna språkutvecklande tillfällen. Vid några tillfällen fanns pedagog närvarande i rummet utan att uppmärksamma barnens chans till språkutveckling. Vid samlingarna fanns möjligheter till språkutveckling som pedagogerna uppmärksammade, dock bestod mycket av tiden av tillsägelser till barnen att vara tysta eller sitta stilla, vilket kan inverka hämmande på möjligheter till språkutveckling.

Slöjdlärarare och den lokala pedagogiska planeringen : Ett arbete i hur slöjdlärare förhåller sig till den lokala pedagogiska planeringen i undervisningen

Syftet med mitt arbete är att få inblick i hur slöjdlärare arbetar med den Lokala pedagogiska planeringen (LPP) och vilken funktion den fyller. Studiens fokus ligger i hur slöjdlärana använder den lokala pedagogiska planeringen under lektioner och hur de arbetar fram den. För att få svar på mina frågeställningar genomförde jag intervjuer med slöjdlärare. Mitt resultat visar att slöjdlärana inte får mycket tid till att skriva sin LPP vilket leder till att de ofta får sitta hemma på sin fritid och skriva. De anser att den är ett bra stöd för dem själva och även för eleverna under lektionerna. Undersökningen visar även att lärarna har nytta av den lokala pedagogiska planeringen, som de menar är ett uppdrag som påförts dem "uppifrån". Genom undersökningen har jag fått större förståelse för vilken nytta den lokala pedagogiska planeringen kan ha för lärare och elever i undervisningen.

Främjande av en samverkan mellan programgemensamma och gymnasiegemensamma ämnen på yrkesprogrammen

Detta examensarbete presenterar hur gymnasielärare upplever ett ämnesövergripande samarbete som inbegriper undervisning med elever som har svenska som sitt första språk och elever som har svenska som sitta andraspråk. Ämneslärare på två gymnasieskolor delar med sig av sina reflektioner kring detta område. Resultatet av min undersökning visar fram vikten av att följa upp lärarnas strävan att ge ungdomarna en så allsidig gymnasieutbildning som möjligt där språk och ämne ingår och som följer läroplanens uppsatta kommunikativa mål. För att detta ska kunna förverkligas behöver dels nationella åtgärder och dels lokala åtgärder genomföras. Dessa åtgärder berör nationella kursmål såväl som genomförande av lokala ämnesövergripande samverkansplaner.