Bosonic Topological Insulators and Paramagnets: a view from cobordisms

We classify Bosonic Topological Insulators and Paramagnets in D<=4 spatial dimensions using the cobordism approach. For D<4 we confirm that the only such phase which does not fit into the group cohomology classification is the 3D Bosonic Topological Insulator protected by time-reversal symmetry whose surface admits an all-fermion topologically ordered state. For D=4 there is a unique "beyond group cohomology" phase. It is protected by gravitational anomalies of the boundary theory and is stable without any additional symmetry.Comment: 18 pages, latex. v2: an error in the last section has been corrected, affecting the classification in D=4. Other results unchange

Symmetry Protected Topological phases and Generalized Cohomology

We discuss the classification of SPT phases in condensed matter systems. We review Kitaev's argument that SPT phases are classified by a generalized cohomology theory, valued in the spectrum of gapped physical systems. We propose a concrete description of that spectrum and of the corresponding cohomology theory. We compare our proposal to pre-existing constructions in the literature.Comment: 27 pages, 10 figures. v2: citation updat

Enzymatic biomass utilization and modification

Environmental concerns, the requirements for energy and carbon efficiency as well as the need to reduce dependency on fossil feedstocks lead to a necessity to develop new bio-based processes and products that support sustainable development and create novel possibilities to boost Bioeconomy. Lignocellulosic biomass mainly composed of cellulose, hemicellulose and lignin is a renewable, abundant non-food starting material for various applications. Cellulases and related enzymes have for decades attracted substantial interest in various industrial applications. For the total hydrolysis of biomass to produce biofuels and other chemicals, mixtures of different (hemi)cellulolytic enzymes have been used, composed of cellobiohydrolases, endoglucanases, β-glucosidases, hemicellulases and helper activities that act in a synergistic manner. On the other hand, for the fibre-based applications usually tailored, or monocomponent enzyme preparations have been applied. The exact composition and proportions of the different enzymes depends in each case on the raw material used, and also on the biorefinery concept to be applied. Despite of the vast development of the lignocellulolytic enzymes, more efficient enzymes and enzyme cocktails are still needed. At VTT, novel cellulolytic enzymes have been discovered from environmental samples, culture collections, metagenomic libraries and genomic databases. Enzyme properties have also been improved by protein engineering. We have also analyzed the limiting factors in the hydrolysis, especially the role of hemicellulose and lignin. Molecular level mechanistic studies have paved way for development of more efficient enzymes. Besides biomass degradation, enzymes have been applied for fibre modification. Furthermore, protease deletion strains and strains with modified cellulase regulation pathways have made it possible to substantially increase protein production in Trichoderma reesei, the industrial production host. References: Igarashi K., Uchihashi, T., Koivula A., Wada, M., Kimura, S., Okamoto, T., Penttilä M., Ando, T. and Samejima, M. (2011) Traffic jams reduce hydrolytic efficiency of cellulase on cellulose surface. Science, 33, 1279-1282. Ilmén M., den Haan R, Brevnova E, McBride J, Wiswall E, Froehlich A, Koivula A, Voutilainen S.P, Siika-aho M, la Grange D.C., Thorngren N, Ahlgren S, Mellon M, Deleault K, Rajgarhia V, van Zyl W.H, Penttilä M (2011) High level secretion of cellobiohydrolases in Saccharomyces cerevisiae. Biotechnology for Biofuels 4, 30-45. Viikari, L., Vehmaanperä, J. and Koivula, A (2012) Lignocellulosic ethanol: from science to industry. Biomass and Bioenergy 46, 13-24. Nakamura, A., Tsukada, T., Auer,S., Furuta, T., Wada, M., Koivula,A., Igarashi, K., and Samejima M. (2013) Tryptophan residue at active-site tunnel entrance of Trichoderma reesei cellobiohydrolase Cel7A is important to initiate degradation of crystalline cellulose. J.Biol.Chem. 288, 13503-13510. Rahikainen, J. L., Moilanen, U., Nurmi-Rantala, S., Lappas, A., Koivula, A., Viikari, L., & Kruus, K. (2013). Effect of temperature on lignin-derived inhibition studied with three structurally different cellobiohydrolases. Bioresource Technology, 146, 118–25. Voutilainen S.P., Nurmi-Rantala, S., Penttilä M., and Koivula A. (2013) Engineering chimeric thermostable GH7 cellobiohydrolases in Saccharomyces cerevisiae. Appl. Microbiol. Biotechnol. 98, 2991-3001. Colabardini, A.C., Valkonen M; Huuskonen A; Siika-aho M; Koivula A; Goldman G.H; Saloheimo M (2016) Expression of two novel β-glucosidases from Chaetomium atrobrunneum in Trichoderma reesei and characterization of the heterologous protein products. Mol. Biotechnology. 58, 821-831

Subscriber churn in the Australian ISP market

Rapid growth in Internet use, combined with easy market entry by Internet service providers (ISPs), has resulted in a highly competitive supply of Internet services. Australian ISPs range in size from a few large national operators to niche ISPs focused on specialised service. With many ISPs currently not profitable, subscriber retention is an important aspect of survival. This study develops a model which relates the probability of subscriber churn to various service attributes and subscriber characteristics. Estimation results show that churn probability is positively associated with monthly ISP expenditure, but inversely related to household income. Pricing also matters with subscribers preferring ISPs which offer flat-rate pricing arrangements.

Radio-Loud Exoplanet-Exomoon Survey (RLEES): GMRT Search for Electron Cyclotron Maser Emission

We conducted the first dedicated search for signatures of exoplanet-exomoon interactions using the Giant Metrewave Radio Telescope (GMRT) as part of the radio-loud exoplanet-exomoon survey (RLEES). Due to stellar tidal heating, irradiation, and subsequent atmospheric escape, candidate `exo-Io' systems are expected to emit up to $10^6$ times more plasma flux than the Jupiter-Io DC circuit. This can induce detectable radio emission from the exoplanet-exomoon system. We analyze three `exo-Io' candidate stars: WASP-49, HAT-P 12, and HD 189733. We perform 12-hour phase-curve observations of WASP-49b at 400 MHz during primary $\&$ secondary transit, as well as first $\&$ third quadratures achieving a 3$\sigma$ upper-limit of 0.18 mJy/beam averaged over four days. HAT-P~12 was observed with GMRT at 150 and 325 MHz. We further analyzed the archival data of HD 189733 at 325 MHz. No emission was detected from the three systems. However, we place strong upper limits on radio flux density. Given that most exo-Io candidates orbit hot Saturns, we encourage more multiwavelength searches (in particular low frequencies) to span the lower range of exoplanet B-field strengths constrained here.Comment: 7 pages, 3 figures, accepted for publication in The Astronomical Journa