A Spitzer Study of Debris Disks in the Young Nearby Cluster NGC 2232: Icy Planets Are Common around ~1.5-3 M☉ Stars

We describe Spitzer IRAC and MIPS observations of the nearby 25 Myr old open cluster NGC 2232. Combining these data with ROSAT All-Sky Survey observations, proper motions, and optical photometry/spectroscopy, we construct a list of highly probable cluster members. We identify one A-type star, HD 45435, that has definite excess emission at 4.5-24 μm indicative of debris from terrestrial planet formation. We also identify 2-4 late-type stars with possible 8 μm excesses and 8 early-type stars with definite 24 μm excesses. Constraints on the dust luminosity and temperature suggest that the detected excesses are produced by debris disks. From our sample of B and A stars, stellar rotation appears to be correlated with 24 μm excess, a result that would be expected if massive primordial disks evolve into massive debris disks. To explore the evolution of the frequency and magnitude of debris around A-type stars, we combine our results with data for other young clusters. The frequency of debris disks around A-type stars appears to increase from ~25% at 5 Myr to ~50%-60% at 20-25 Myr. Older A-type stars have smaller debris disk frequencies: ~20% at 50-100 Myr. For these ages, the typical level of debris emission increases from 5 to 20 Myr and then declines. Because 24 μm dust emission probes icy planet formation around A-type stars, our results suggest that the frequency of icy planet formation is ηi ≳ 0.5-0.6. Thus, most A-type stars (≈1.5-3 M☉) produce icy planets

Non-Gaussianity and Excursion Set Theory: Halo Bias

We study the impact of primordial non-Gaussianity generated during inflation on the bias of halos using excursion set theory. We recapture the familiar result that the bias scales as $k^{-2}$ on large scales for local type non-Gaussianity but explicitly identify the approximations that go into this conclusion and the corrections to it. We solve the more complicated problem of non-spherical halos, for which the collapse threshold is scale dependent.Comment: 13 pages, 3 figures. v2 references added. Matches published versio

An analysis of judgemental bias in housing choice

Buying a home is among the most important choices that any individual is likely to make in their lifetime. It has lasting consequences for happiness, well-being and personal finances. Yet, given the infrequency with which such decisions are made; the difficulty getting information from an opaque and decentralised marketplace; and the high transactions costs involved, there is a significant risk that decision making may depart from the high standard imposed by the normative economic concept of 'rational choice'. This thesis uses the insights of the economic theory of choice - from behavioural economics in particular - to examine housing choice from a new perspective. It considers the potential for estate agents, knowingly or otherwise, to exploit behavioural biases in decision making to influence preference and, ultimately, choices over housing. This naturally is of interest to estate agents and policy makers involved in housing markets; but most importantly to individuals as decision makers: making better decisions relies on understanding when and where vulnerability to manipulation may lie. Using evidence from a series of classroom experiments with 280 student volunteers and from two online surveys with over 4,000 adult respondents, significant areas where individuals may be consistently vulnerable to manipulation of judgement are found and recorded. In particular, both student and adult respondents are susceptible to biases involving manipulation of the decision making context, known as the choice frame. Students also tend to rely on arbitrary `anchor' points to make value estimates, which results in significantly impaired judgements, even in the presence of incentives for accuracy. Finally, evidence of a significant new form of behavioural bias is found, in which elements of the choice frame have an unexpectedly negative impact on perceptions. This new bias is persistent across several experimental scenarios and is labelled the 'choice pollution effect'

Perfluoroalkanesulfonyl linker units for solid phase organic synthesis

Diversity linker units exploit the cleavage step in solid phase synthesis for the incorporation of further diversity into target molecules. A solid-supported perfluorosulfonyl linker unit would allow cleavage of substrates using transition-metal- catalysed cross-coupling reactions. This thesis describes several approaches towards a perfluoroalkanesulfonyl diversity linker from diiodoperfluoroalkanes. Early work concentrated on the reaction of diiodoperfluoroalkanes with eugenol. The resulting perfluoroalkyliodides were attached to Wang resin using Mitsunobu chemistry. However, stability problems prevented the generation of resin bound perfluoroalkanesulfonic acids and the route was abandoned. A bis-perfluoroalkanesulfonyl chloride linker unit was prepared from diiodoperfluoroalkanes by generation of the bis-sodium sulfite salt and subsequent chlorination. Optimisation studies using design software allowed preparation of multigram quantities in 60 - 70% yield. Model solution phase synthesis of bis- perfluoroalkanesulfonamides and bis-perfluoroalkanesulfonate esters showed the feasibility of attaching the bis-sulfonyl chloride to amino resins and loading phenols. Diversity cleavage was demonstrated using Suzuki and Stille reactions and optimised by screening parallel arrays of reaction conditions. Loading the bis-sulfonyl chloride onto TentaGel® gave access to solid supported porfluorosulfonate osters and diversity cleavage was shown using Suzuki reactions. However, the linkage to solid supports proved to be unstable and an additional spacer unit was required if the linker was to find widespread use. To this end, a second generation perfluoroalkanesulfonyl linker unit was developed from ally I alcohol and diiodoperfluoroalkanes. Oxidation to a perfluoroalkanesulfonyl chloride was achieved using a novel reaction employing N- chlorosuccinimide. Several methods for loading this linker unit onto a solid support were investigated but none were successful and this chemistry requires further development before it offers a practical perfluoroalkanesulfonyl diversity linker

Post-processing partitions to identify domains of modularity optimization

We introduce the Convex Hull of Admissible Modularity Partitions (CHAMP) algorithm to prune and prioritize different network community structures identified across multiple runs of possibly various computational heuristics. Given a set of partitions, CHAMP identifies the domain of modularity optimization for each partition ---i.e., the parameter-space domain where it has the largest modularity relative to the input set---discarding partitions with empty domains to obtain the subset of partitions that are "admissible" candidate community structures that remain potentially optimal over indicated parameter domains. Importantly, CHAMP can be used for multi-dimensional parameter spaces, such as those for multilayer networks where one includes a resolution parameter and interlayer coupling. Using the results from CHAMP, a user can more appropriately select robust community structures by observing the sizes of domains of optimization and the pairwise comparisons between partitions in the admissible subset. We demonstrate the utility of CHAMP with several example networks. In these examples, CHAMP focuses attention onto pruned subsets of admissible partitions that are 20-to-1785 times smaller than the sets of unique partitions obtained by community detection heuristics that were input into CHAMP.Comment: http://www.mdpi.com/1999-4893/10/3/9

Deep proteogenomics; high throughput gene validation by multidimensional liquid chromatography and mass spectrometry of proteins from the fungal wheat pathogen Stagonospora nodorum

BACKGROUND: Stagonospora nodorum, a fungal ascomycete in the class dothideomycetes, is a damaging pathogen of wheat. It is a model for necrotrophic fungi that cause necrotic symptoms via the interaction of multiple effector proteins with cultivar-specific receptors. A draft genome sequence and annotation was published in 2007. A second-pass gene prediction using a training set of 795 fully EST-supported genes predicted a total of 10762 version 2 nuclear-encoded genes, with an additional 5354 less reliable version 1 genes also retained. RESULTS: In this study, we subjected soluble mycelial proteins to proteolysis followed by 2D LC MALDI-MS/MS. Comparison of the detected peptides with the gene models validated 2134 genes. 62% of these genes (1324) were not supported by prior EST evidence. Of the 2134 validated genes, all but 188 were version 2 annotations. Statistical analysis of the validated gene models revealed a preponderance of cytoplasmic and nuclear localised proteins, and proteins with intracellularassociated GO terms. These statistical associations are consistent with the source of the peptides used in the study. Comparison with a 6-frame translation of the S. nodorum genome assembly confirmed 905 existing gene annotations (including 119 not previously confirmed) and provided evidence supporting 144 genes with coding exon frameshift modifications, 604 genes with extensions of coding exons into annotated introns or untranslated regions (UTRs), 3 new gene annotations which were supported by tblastn to NR, and 44 potential new genes residing within un-assembled regions of the genome. CONCLUSION: We conclude that 2D LC MALDI-MS/MS is a powerful, rapid and economical tool to aid in the annotation of fungal genomic assemblies