The Synthesis of Functionalised beta-Lactams

N-t-Butyldimethylsilyl imines were prepared readily by oxidation of the corresponding primary amines. The application of N-t-butyl-dimethylsilyl imines to the synthesis of monocyclic beta-lactams was examined via the ester-imine condensation reaction with silyl ketene acetals. Initial choice of Znl2 as Lewis acid for this reaction proved fruitful in certain instances. This reaction, performed in the presence of t-BuOH to suppress reaction of the initially formed N-metallo beta-amino ester with a further molecule of activated imine, followed by treatment with Grignard reagent, displays a modest trans selectivity in the product beta-lactams. However, difficulties were encountered during utilization of more highly functionalised N-t-butyldimethylsilyl imines. As a result, a second Lewis acid system was investigated. Utilization of trimethylsilyl trifluoromethanesulphonate (TMSOTf) as the Lewis acid component produced, in a one-pot process, a range of beta-lactams in a trans-selective manner. Chemical yields resulting from this approach were comparable to those achieved using Znl2 as Lewis acid and the diastereoselectivities found showed a modest increase over those induced in the earlier approach. Low temperature quenching of the derived from treatment of a non-enolisable aldehyde with lithium hexamethyldisilazide resulted in formation of the corresponding N,N,O-tris(trimethylsilyl) amine acetal. Treatment of these compounds with TMSOTf provides access to the same reactive iminium species as found in the reaction between N-silyl imines and TMSOTf and, as such, provides an alternative route to beta-lactam synthesis. Two functionalised silyl ketene acetals were prepared. Attempts to incorporate these substrates into the ester-imine condensation process met with only partial success. The cyclic silyl ketene acetal derived from delta-valerolactone was incorporated into a beta-lactam nucleus, although some atypical characteristics were observed in this system. As an alternative source of the electrophilic iminium species generated in the reaction between an imine or amine acetal with a Lewis acid, the reactivity of enamines was examined. Lewis acid catalysis did allow access to beta-amino esters from enamines, although certain aspects of this process are, as yet, unexplained

Diversity of Decline-Rate-Corrected Type Ia Supernova Rise Times: One Mode or Two?

B-band light-curve rise times for eight unusually well-observed nearby Type Ia supernovae (SNe) are fitted by a newly developed template-building algorithm, using light-curve functions that are smooth, flexible, and free of potential bias from externally derived templates and other prior assumptions. From the available literature, photometric BVRI data collected over many months, including the earliest points, are reconciled, combined, and fitted to a unique time of explosion for each SN. On average, after they are corrected for light-curve decline rate, three SNe rise in 18.81 +- 0.36 days, while five SNe rise in 16.64 +- 0.21 days. If all eight SNe are sampled from a single parent population (a hypothesis not favored by statistical tests), the rms intrinsic scatter of the decline-rate-corrected SN rise time is 0.96 +0.52 -0.25 days -- a first measurement of this dispersion. The corresponding global mean rise time is 17.44 +- 0.39 days, where the uncertainty is dominated by intrinsic variance. This value is ~2 days shorter than two published averages that nominally are twice as precise, though also based on small samples. When comparing high-z to low-z SN luminosities for determining cosmological parameters, bias can be introduced by use of a light-curve template with an unrealistic rise time. If the period over which light curves are sampled depends on z in a manner typical of current search and measurement strategies, a two-day discrepancy in template rise time can bias the luminosity comparison by ~0.03 magnitudes.Comment: As accepted by The Astrophysical Journal; 15 pages, 6 figures, 2 tables. Explanatory material rearranged and enhanced; Fig. 4 reformatte

Evidence for a Spectroscopic Sequence Among SNe Ia

In this Letter we present evidence for a spectral sequence among Type Ia supernovae (SNe Ia). The sequence is based on the systematic variation of several features seen in the near-maximum light spectrum. This sequence is analogous to the recently noted photometric sequence among SNe Ia which shows a relationship between the peak brightness of a SN Ia and the shape of its light curve. In addition to the observational evidence we present a partial theoretical explanation for the sequence. This has been achieved by producing a series of non-LTE synthetic spectra in which only the effective temperature is varied. The synthetic sequence nicely reproduces most of the differences seen in the observed one and presumably corresponds to the amount of 56Ni produced in the explosion.Comment: To appear in Astrophysical Journal Letters, uuencoded, gzipped postscript file, also available from http://www.nhn.uoknor.edu/~baron

Constraining the Progenitor Companion of the Nearby Type Ia SN 2011fe with a Nebular Spectrum at +981 Days

We present an optical nebular spectrum of the nearby Type Ia supernova 2011fe, obtained 981 days after explosion. SN 2011fe exhibits little evolution since the +593 day optical spectrum, but there are several curious aspects in this new extremely late-time regime. We suggest that the persistence of the $\sim5800$~\AA\ feature is due to Na I D, and that a new emission feature at $\sim7300$~\AA\ may be [Ca II]. Also, we discuss whether the new emission feature at $\sim6400$~\AA\ might be [Fe I] or the high-velocity hydrogen predicted by Mazzali et al. The nebular feature at 5200~\AA\ exhibits a linear velocity evolution of $\sim350$ $\rm km\ s^{-1}$ per 100 days from at least +220 to +980 days, but the line's shape also changes in this time, suggesting that line blending contributes to the evolution. At $\sim 1000$ days after explosion, flux from the SN has declined to a point where contribution from a luminous secondary could be detected. In this work we make the first observational tests for a post-impact remnant star and constrain its temperature and luminosity to $T \gtrsim 10^4$ $\rm K$ and $L \lesssim 10^4$ $\rm L_{\odot}$. Additionally, we do not see any evidence for narrow H$\alpha$ emission in our spectrum. We conclude that observations continue to strongly exclude many single-degenerate scenarios for SN 2011fe.Comment: 11 pages, 10 figures, published by MNRA

Indoor localisation through object detection within multiple environments utilising a single wearable camera

The recent growth in the wearable sensor market has stimulated new opportunities within the domain of Ambient Assisted Living, providing unique methods of collecting occupant information. This approach leverages contemporary wearable technology, Google Glass, to facilitate a unique first-person view of the occupants immediate environment. Machine vision techniques are employed to determine an occupant’s location via environmental object detection. This method provides additional secondary benefits such as first person tracking within the environment and lack of required sensor interaction to determine occupant location. Object recognition is performed using the Oriented Features from Accelerated Segment Test and Rotated Binary Robust Independent Elementary Features algorithm with a K-Nearest Neighbour matcher to match the saved key-points of the objects to the scene. To validate the approach, an experimental set-up consisting of three ADL routines, each containing at least ten activities, ranging from drinking water to making a meal were considered. Ground truth was obtained from manually annotated video data and the approach was previously benchmarked against a common method of indoor localisation that employs dense sensor placement in order to validate the approach resulting in a recall, precision, and F-measure of 0.82, 0.96, and 0.88 respectively. This paper will go on to assess to the viability of applying the solution to differing environments, both in terms of performance and along with a qualitative analysis on the practical aspects of installing such a system within differing environments