Stripped-envelope supernovae were thought to be the explosions of very massive stars (& 20 M) that lost their outer layers of hydrogen and/or helium in strong stellar winds. However, recent studies have highlighted that most stripped-envelope supernovae seem to be arising from rela- tively lower-mass progenitor stars in the 12 20 M(sun) range, creating a mystery about the fate of the higher-mass stars. In this licentiate thesis, we review our knowledge of stripped-envelope supernovae, and present the astrophysical problem of their missing high-mass progenitors. The thesis focuses on observations of unique and rare stripped-envelope supernovae classified with modern optical surveys such as the intermediate Palomar Transient Factory (iPTF) and the Public European Southern Observatory Spectroscopic Survey of Transient Objects (PESSTO). In these surveys we have discovered stripped-envelope supernovae with long-lasting broad lightcurves, which are thought to be a marker for highly massive (& 20 M[sun]) progenitor stars. Despite this exciting association, there are only a handful of existing examples of stripped- envelope supernovae with broad lightcurves published in the literature, not numerous enough to account for the missing high-mass stars. During our efforts, the first object we focused on was OGLE-2014-SN-131, a long-lasting supernova in the southern sky initially classified by PESSTO. We re-classified it as a supernova Type Ibn interacting with a helium-rich circumstellar environment. Unlike all other Type Ibn’s in the literature, OGLE-2014-SN-131 was found to have a long rise-time and large lightcurve broadness. By modeling its bolometric lightcurve, we concluded that OGLE-2014-SN-131 must have had an unusually massive progenitor star. Furthermore, since an ordinary radioactive- decay model could not reproduce the lightcurve, we investigated both a magnetar and circum- stellar interaction as potential powering scenarios and favored the latter due to the signatures of interaction present in the spectra. Next, we looked for similar objects in the supernova dataset of the iPTF, which contains over 200 stripped-envelope supernovae. Searching in a sub-sample of 100 well-observed supernovae, we identified 11 to have unusually broad lightcurves. We also constrained the distribution of lightcurve broadness for iPTF stripped-envelope supernovae. The 11 with broad lightcurves will be studied carefully in a forthcoming paper. The first part of this forthcoming paper, which describes the careful statistical identification of these super-novae, is included in this thesis. In it we identify that 10% of the iPTF stripped-envelope supernova sample have broad lightcurves, which a surprisingly high fraction given their rarity in the published literature. Finally, we evaluate whether our estimate of the fraction of broad stripped-envelope supernovae could help explain the missing high-mass progenitors, and con- clude that they can only be a small fraction of the missing high-mass progenitors.

We present spectropolarimetric observations of the nearby Type Ia supernova SN 2014J in M82 over six epochs: +0, +7, +23, +51, +77, +109, and +111 days with respect to B-band maximum. The strong continuum polarization, which is constant with time, shows a wavelength dependence unlike that produced by linear dichroism in Milky Way dust. The observed polarization may be due entirely to interstellar dust or include a circumstellar scattering component. We find that the polarization angle aligns with the magnetic field of the host galaxy, arguing for an interstellar origin. Additionally, we confirm a peak in polarization at short wavelengths that would imply R-V < 2 along the light of sight, in agreement with earlier polarization measurements. For illustrative purposes, we include a two-component fit to the continuum polarization of our +51-day epoch that combines a circumstellar scattering component with interstellar dust where scattering can account for over half of the polarization at 4000 angstrom. Upon removal of the interstellar polarization signal, SN 2014J exhibits very low levels of continuum polarization. Asymmetries in the distribution of elements within the ejecta are visible through moderate levels of time-variable polarization in accordance with the Si II lambda 6355 absorption line. At maximum light, the line polarization reaches similar to 0.6% and decreases to similar to 0.4% 1 week later. This feature also forms a loop on theqRSP-uRSP plane, illustrating that the ion does not have an axisymmetric distribution. The observed polarization properties suggest that the explosion geometry of SN 2014J is generally spheroidal with a clumpy distribution of silicon.

Due to its proximity, SN. 1987A offers a unique opportunity to directly observe the geometry of a stellar explosion as it unfolds. Here we present spectral and imaging observations of SN. 1987A obtained similar to 10,000 days after the explosion with HST/STIS and VLT/SINFONI at optical and near-infrared wavelengths. These observations allow us to produce the most detailed 3D map of Ha to date, the first 3D maps for [Ca II] lambda lambda 7292, 7324, [O I] lambda lambda 6300, 6364, and Mg. II lambda lambda 9218, 9244, as well as new maps for [Si I]+[Fe II] 1.644 mu m and He I 2.058 mu m. A comparison with previous observations shows that the [Si I]+[Fe II] flux and morphology have not changed significantly during the past ten years, providing evidence that this line is powered by Ti-44. The time evolution of Ha shows that it is predominantly powered by X-rays from the ring, in agreement with previous findings. All lines that have sufficient signal show a similar large-scale 3D structure, with a north-south asymmetry that resembles a broken dipole. This structure correlates with early observations of asymmetries, showing that there is a global asymmetry that extends from the inner core to the outer envelope. On smaller scales, the two brightest lines, Ha and [Si I]+[Fe II] 1.644 mu m, show substructures at the level of similar to 200-1000 km s(-1) and clear differences in their 3D geometries. We discuss these results in the context of explosion models and the properties of dust in the ejecta.

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Current requirements of nonvolatile memory (NVM) are the high density cells, low-power consumption, high-speed operation and good reliability for the scaling down devices. However, all of the charges stored in the floating gate will leak into the substrate if the tunnel oxide has a leakage path in the conventional NVMs. Therefore, the tunnel oxide thickness is difficult to scale down in terms of charge retention and endurance. The nanocrystal nonvolatile memories are one of promising substitution, because the discrete storage nodes as the charge storage media have been effectively improve data retention under endurance test for the scaling down device. Many methods have been developed recently for the formation of nanocrystals. Generally, most methods need thermal treatment with high temperature and long duration. This procedure will influence thermal budget and throughput in current manufacture technology of semiconductor industry. And supercritical carbon dioxide (SCCO2) has been researched to the passivation of dielectric and reducing the activation energy. The research estimates SCCO2 is potential to form nanocrystals for these reason. This research is to discuss the feasibility of fabricating nanocrystal NVMs device with low temperature SCCO2. The low melting point metal material Sn is used for the attempts. In order to check if Sn can be used for fabricating nanocrystal NVMs device, the research selects the conventional thermal annealing method first. It uses rapid thermal annealing to improve the crystalline of nanocrystals and reliability of the memory device. Compare to different Sn containment or chemistry and different process, analyze the electric characteristics and materials chemistry. At last, select the Sn and SiO2 co-sputtering film to try the SCCO2 process and analyze these characteristics as well. Due to the novel technology, many physical mechanism and improvement of properties will be discuss following.

The mode of Ti and Sn action of anticancer compounds is still poorly understood. For each octahedral Ti(bzac)2 X2 and Sn(bzac)2 X2 (Hbzac = 1-benzoylacetone) complexes there are five possible isomers. It is not known which of these isomers is responsible for the anticancer activity. One of the Ti complex Ti(bzac)2(OEt)2 whose trade name is budotitane® is a anticancer drug on clinically trial base. Therefore we use VT-NMR (low temperature to high temperature) studies and their crystal structures (1a, 1b, and 2a) to examine their isomerization behavior, conversion rate constant k, and conversion barrier energy £GG‡. We suspect the antitumor activity of Ti and Sn compounds strongly depends on the unsubstituted phenyl rings of the £]-diketonato ligands in the outer sphere of the molecule. If these phenyl rings are replaced by methyl groups, the activity totally disappears. Therefore we propose that the anticancer activity of budotitane may be determined by a DNA intercalating mechanism. We further changed the ligand from Hbzac to FHnpac (FHnpac = 4, 4, 4-trifluoro-1-(naphthalen-3-yl) butane-1, 3-dione) in order to monitor their isomers exchange via 1H NMR. The related crystal structures (1a-NF, 1b-NF, and 2a-NF) were obtained fortunately. The stereochemistry of Ti and Sn complexes as well as their controlling factors is discussed.

Syftet med denna uppsats är att undersöka hur utrikesrapporteringen under 2013 såg ut i lokaltidningen Södermanlands Nyheter (SN) och storstadstidningen Svenska Dagbladet (SvD). Frågorna som ska besvaras handlar om vilka områden och ämnen som läsarna får ta del av i tidningen, och vem som rapporterar om utlandet. För att besvara frågeställningarna genomfördes en kvantitativ undersökning med kompletterande intervjuer med representanter för SN, SvD och TT Nyhetsbyrån. Materialet som samlades in var 159 texter från SN och 214 texter från SvD, vilket blev totalt 373 texter. Den teoretiska utgångspunkten kretsar främst kring nyhetsvärdering utifrån Galtung och Ruge samt Prakke, agenda-setting, gatekeeping, samt det västerländska mediala beroendet. I resultatet besvaras frågeställningarna genom en analys av texterna, och utrymme ges åt representanter från SN, SvD och TT:s för att bemöta det framkomna resultatet. Undersökningen visade att de länder och världsdelar som ligger nära Sverige, både geografiskt och kulturellt, får större uppmärksamhet i både SN och SvD. Ju längre bort ett land ligger, desto mindre regelbunden uppmärksamhet. Undersökningen visar också att olika ämnen dominerar i olika världsdelar. Exempelvis kretsar rapporteringen om Europa övervägande kring politik, medan rapporteringen kring Mellanöstern domineras av krig. SN använder bara TT:s utrikesnyheter. SvD gör stora uppslag och reportage själva, och använder TT:s material främst som utfyllnad. Vår undersökning visar att 303 av de totalt 373 texterna kommer från TT. Detta trots att SvD har flertalet utrikeskorrespondenter och stringers världen över. En stor del av TT:s utrikesmaterial kommer från de tre stora västerländska nyhetsbyråerna, AP, AFP och Reuters, vilket kan bidra till en västerländsk vinkling på nyheterna.

We present the results of an extensive observational campaign on the nearby Type Ibn SN 2015G, including data from radio through ultravioletwavelengths. SN2015Gwas asymmetric, showing late-time nebular lines redshifted by similar to 1000 km s(-1). It shared many features with the prototypical SN Ibn 2006jc, including extremely strong He I emission lines and a late-time blue pseudo-continuum. The young SN 2015G showed narrow P-Cygni profiles of He I, but never in its evolution did it showany signature of hydrogen -arguing for a dense, ionized and hydrogenfree circumstellar medium moving outward with a velocity of similar to 1000 km s(-1) and created by relatively recent mass-loss from the progenitor star. Ultraviolet through infrared observations show that the fading SN 2015G (which was probably discovered some 20 d post-peak) had a spectral energy distribution that was well described by a simple, single-component blackbody. Archival HST images provide upper limits on the luminosity of SN 2015G's progenitor, while non-detections of any luminous radio afterglow and optical non-detections of outbursts over the past two decades provide constraints upon its mass-loss history.

Cellulose, a major constituent of biomass, is a promising source of sustainable energy. A key step in the conversion of cellulose to a platform chemical is glucose isomerization to fructose. Sn-Beta zeolite catalyzes this reaction with high yield. The effect of methanol as a reaction medium on glucose transformations catalyzed by Sn-Beta has not been quantified. Here, density functional calculations are employed to elaborate on the effect of methanol medium, specifically to determine how reaction pathways and energy barriers are affected by methoxylation of Sn or Si groups at the active sites in Sn-Beta. Calculations suggest that the presence of the neighboring silanol group is necessary for glucose isomerization. If the silanol group is altered by methoxylation glucose epimerization is promoted and will likely occur. These results provide additional understanding of the active site of Sn-Beta for glucose transformations and are insightful for novel catalyst design and development.