Star formation and accretion in the circumnuclear disks of active galaxies

We explore the evolution of supermassive black holes (SMBH) centered in a circumnuclear disk (CND) as a function of the mass supply from the host galaxy and considering different star formation laws, which may give rise to a self-regulation via the injection of supernova-driven turbulence. A system of equations describing star formation, black hole accretion and angular momentum transport was solved for an axisymmetric disk in which the gravitational potential includes contributions from the black hole, the disk and the hosting galaxy. Our model extends the framework provided by Kawakatu et al. (2008) by separately considering the inner and outer part of the disk, and by introducing a potentially non-linear dependence of the star formation rate on the gas surface density and the turbulent velocity. The star formation recipes are calibrated using observational data for NGC 1097, while the accretion model is based on turbulent viscosity as a source of angular momentum transport in a thin viscous accretion disk. We find that current data provide no strong constraint on the star formation recipe, and can in particular not distinguish between models entirely regulated by the surface density, and models including a dependence on the turbulent velocity. The evolution of the black hole mass, on the other hand, strongly depends on the applied star formation law, as well as the mass supply from the host galaxy. We suggest to explore the star formation process in local AGN with high-resolution ALMA observations to break the degeneracy between different star formation models.Comment: 13 pages, 15 figures, 6 tables, accepted at A&

Infection Rates in a Traumatic Brain Injury Cohort Treated with Intravascular Cooling Catheters

Each year, in the United States, 235,000 individuals sustain a traumatic brain injury requiring hospitalization. Patient outcome from severe traumatic brain injury is improved with intensive care management of pathophysiological processes developing in the days following the injury. An important secondary complication of traumatic brain injury is fever, which is known to worsen neurologic outcome. Our institution has recently developed an approach to combat fever through the prophylactic use of intravascular cooling catheters, a treatment termed controlled normothermia. We have recently demonstrated that controlled normothermia reduces both core and brain temperature and can improve the intracranial milieu that may facilitate recovery. A major drawback to the systematic use of controlled normothermia is an increased risk of infection, or delayed diagnosis of infection by masking of fevers. In the current study, we evaluated whether "controlled normothermia", the prophylactic use of intravascular cooling catheters in severe traumatic brain injury, is associated with increased infection rates during the intensive care stay. Utilizing a matched cohort study and data from the Brain Trauma Research Center's database, a retrospective study was performed. The data was taken from the Brain Trauma Research Center's traumatic brain injury registry, and was matched on age, gender, and Glasgow Coma Score. After analysis, the results of the study indicated fewer infections in the controlled normothermia group; the rates of bloodstream infections were statistically lower in the controlled normothermia group. The current study demonstrates that prophylactic use of intravascular cooling catheters in severe traumatic brain injury is not associated with an increased risk of infection. The public health significance is that these results lend further support to the concept of controlled normothermia as a treatment for severe traumatic brain injury. Further study may prove that controlled normothermia is effective in improving neurologic outcomes from traumatic brain injury, which remain the leading cause of death under age 45 in the United States

Low-metallicity star formation: Relative impact of metals and magnetic fields

Low-metallicity star formation poses a central problem of cosmology, as it determines the characteristic mass scale and distribution for the first and second generations of stars forming in our Universe. Here, we present a comprehensive investigation assessing the relative impact of metals and magnetic fields, which may both be present during low-metallicity star formation. We show that the presence of magnetic fields generated via the small-scale dynamo stabilises the protostellar disc and provides some degree of support against fragmentation. In the absence of magnetic fields, the fragmentation timescale in our model decreases by a factor of ~10 at the transition from Z=0 to Z>0, with subsequently only a weak dependence on metallicity. Similarly, the accretion timescale of the cluster is set by the large-scale dynamics rather than the local thermodynamics. In the presence of magnetic fields, the primordial disc can become completely stable, therefore forming only one central fragment. At Z>0, the number of fragments is somewhat reduced in the presence of magnetic fields, though the shape of the mass spectrum is not strongly affected in the limits of the statistical uncertainties. The fragmentation timescale, however, increases by roughly a factor of 3 in the presence of magnetic fields. Indeed, our results indicate comparable fragmentation timescales in primordial runs without magnetic fields and Z>0 runs with magnetic fields.Comment: MNRAS in pres

Who’s the Fairest of them All?:A Comparison of Methods for Classifying Tone and Attribution in Earnings-related Management Discourse

We compare the relative and absolute performance of various machine learning algorithms and wordlists at replicating manual coding results for tone and attribution by domain experts in management performance commentary. Our suite of learning classifiers comprises Naïve Bayes, random forest, support vector machines, and an artificial neural network called multilayer perceptron. We use wordlists proposed by Henry (2006, 2008) and Loughran and McDonald (2010) to classify tone. Wordlists for attribution are based on the causal reasoning list from Language Inquirer and Word Count (LIWC), together with two self-constructed lists. We use a self-constructed wordlist to distinguish between internal and external attributions. We train learning classifiers using a large sample of manually annotated performance sentences. Results for all classifiers are assessed using a separate manually annotated holdout sample. Conclusions regarding the best classification method vary according to the classification task. None of the approaches are capable of identifying the presence of an attribution reliably. Even for more reliable classification tasks such as tone and attribution type, absolute measurement errors often exceed 20%. We conclude that while automated textual analysis methods offer important opportunities in certain settings, manual content analysis remains an essential tool for researchers interested in studying the properties and consequences of financial discourse

ITS2 data corroborate a monophyletic chlorophycean DO-group (Sphaeropleales)

<p>Abstract</p> <p>Background</p> <p>Within Chlorophyceae the ITS2 secondary structure shows an unbranched helix I, except for the '<it>Hydrodictyon</it>' and the '<it>Scenedesmus</it>' clade having a ramified first helix. The latter two are classified within the Sphaeropleales, characterised by directly opposed basal bodies in their flagellar apparatuses (DO-group). Previous studies could not resolve the taxonomic position of the '<it>Sphaeroplea</it>' clade within the Chlorophyceae without ambiguity and two pivotal questions remain open: (1) Is the DO-group monophyletic and (2) is a branched helix I an apomorphic feature of the DO-group? In the present study we analysed the secondary structure of three newly obtained ITS2 sequences classified within the '<it>Sphaeroplea</it>' clade and resolved sphaeroplealean relationships by applying different phylogenetic approaches based on a combined sequence-structure alignment.</p> <p>Results</p> <p>The newly obtained ITS2 sequences of <it>Ankyra judayi, Atractomorpha porcata </it>and <it>Sphaeroplea annulina </it>of the '<it>Sphaeroplea</it>' clade do not show any branching in the secondary structure of their helix I. All applied phylogenetic methods highly support the '<it>Sphaeroplea</it>' clade as a sister group to the 'core Sphaeropleales'. Thus, the DO-group is monophyletic. Furthermore, based on characteristics in the sequence-structure alignment one is able to distinguish distinct lineages within the green algae.</p> <p>Conclusion</p> <p>In green algae, a branched helix I in the secondary structure of the ITS2 evolves past the '<it>Sphaeroplea</it>' clade. A branched helix I is an apomorph characteristic within the monophyletic DO-group. Our results corroborate the fundamental relevance of including the secondary structure in sequence analysis and phylogenetics.</p

Essays in accounting and finance

In this thesis, I examine why there are distortions in investor portfolio selection, and show the consequence of these distortions on firms' investment decisions. The thesis consists of three essays. In the first essay, I examine the economic consequences of the mandatory adoption of IFRS in EU countries by showing which types of economies have the largest reduction in investment-cash flow sensitivity post-IFRS. I also examine whether the reduction in investment-cash flow sensitivity depends on firm size as well as economy type. I find that the investment-cash flow sensitivity of insider economies is higher than that of outsider economies pre-IFRS and that IFRS reduces the investment-cash flow sensitivity of insider economies more than that of outsider economies. Also, I find that small firms in insider economies have the highest sensitivity of investment to lagged cash flow pre-IFRS, and that they are no longer sensitive to lagged cash flow post-IFRS. Overall, my results suggest that IFRS adoption might have improved the functioning of capital markets in relation to small firms in insider economies. In the second essay, I show that the level of conditional accounting conservatism of foreign markets significantly influences decisions to diversify portfolios internationally. This could be either because conditional conservatism per se is attractive to international investors, or because the unmodelled factors that attract foreign investors to a country also cause these countries to adopt conditionally conservative accounting practices. We also find that the positive association between investor diversification decision and conditional conservatism is sensitive to the level of conditional conservatism of investors' home markets. If conditional conservatism serves to alleviate foreign investors' concerns related to insiders have asymmetric access to information then one would expect the chosen mode of entry into a foreign market (as foreign portfolio or direct investor) to be sensitive to the level of conditional conservatism. I find evidence supportive of this expectation.In the third and final essay, I document pieces of evidence suggesting that the stock ownership of politicians is a mechanism to establish mutual relations with firms. There is a positive association between the ownership of politicians and the contribution they receive from firms during the elections. This association is a function of how valuable it is to establish a mutual relation between politicians and firms. Politicians invest more in firms that favor their party and less in firms that oppose their party. The strength of the ownership-based relation with contributing firms is positively associated with the amount as well as the number of government contracts awarded to firms. When politicians divest the stock, the established relation with contributing firms breaks down. Such break-down, however, only exist when there are no other mechanisms enforcing politician-firm relation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Learning tone and attribution for financial text mining

Attribution bias refers to the tendency of people to attribute successes to their own abilities but failures to external factors. In a business context an internal factor might be the restructuring of the firm and an external factor might be an unfavourable change in exchange or interest rates. In accounting research, the presence of an attribution bias has been demonstrated for the narrative sections of the annual financial reports. Previous studies have applied manual content analysis to this problem but in this paper we present novel work to automate the analysis of attribution bias through using machine learning algorithms. Previous studies have only applied manual content analysis on a small scale to reveal such a bias in the narrative section of annual financial reports. In our work a group of experts in accounting and finance labelled and annotated a list of 32,449 sentences from a random sample of UK Preliminary Earning Announcements (PEAs) to allow us to examine whether sentences in PEAs contain internal or external attribution and which kinds of attributions are linked to positive or negative performance. We wished to examine whether human annotators could agree on coding this difficult task and whether Machine Learning (ML) could be applied reliably to replicate the coding process on a much larger scale. Our best machine learning algorithm correctly classified performance sentences with 70% accuracy and detected tone and attribution in financial PEAs with accuracy of 79%

Evidence for Interstitial Carbon in Nitrogenase FeMo Cofactor

The identity of the interstitial light atom in the center of the FeMo cofactor of nitrogenase has been enigmatic since its discovery. Atomic-resolution x-ray diffraction data and an electron spin echo envelope modulation (ESEEM) analysis now provide direct evidence that the ligand is a carbon species

SuperWASP Observations of the 2007 Outburst of Comet 17P/Holmes

We present wide-field imaging of the 2007 outburst of Comet 17P/Holmes obtained serendipitously by SuperWASP-North on 17 nights over a 42-night period beginning on the night (2007 October 22-23) immediately prior to the outburst. Photometry of 17P's unresolved coma in SuperWASP data taken on the first night of the outburst is consistent with exponential brightening, suggesting that the rapid increase in the scattering cross-section of the coma could be largely due to the progressive fragmentation of ejected material produced on a very short timescale at the time of the initial outburst, with fragmentation timescales decreasing from t(frag)~2x10^3 s to t(frag)~1x10^3 s over our observing period. Analysis of the expansion of 17P's coma reveals a velocity gradient suggesting that the outer coma was dominated by material ejected in an instantaneous, explosive manner. We find an expansion velocity at the edge of the dust coma of v(exp) = 0.55+/-0.02 km/s and a likely outburst date of t_0=2007 October 23.3+/-0.3, consistent with our finding that the comet remained below SuperWASP's detection limit of m(V)~15 mag until at least 2007 October 23.3. Modelling of 17P's gas coma indicates that its outer edge, which was observed to extend past the outer dust coma, is best explained with a single pulse of gas production, consistent with our conclusions concerning the production of the outer dust coma.Comment: 36 pages, 8 figures, accepted for publication in MNRA

Bird Cryptochrome 1a Is Excited by Blue Light and Forms Long-Lived Radical- Pairs

Cryptochromes (Cry) have been suggested to form the basis of light-dependent magnetic compass orientation in birds. However, to function as magnetic compass sensors, the cryptochromes of migratory birds must possess a number of key biophysical characteristics. Most importantly, absorption of blue light must produce radical pairs with lifetimes longer than about a microsecond. Cryptochrome 1a (gwCry1a) and the photolyase-homology-region of Cry1 (gwCry1-PHR) from the migratory garden warbler were recombinantly expressed and purified from a baculovirus/Sf9 cell expression system. Transient absorption measurements show that these flavoproteins are indeed excited by light in the blue spectral range leading to the formation of radicals with millisecond lifetimes. These biophysical characteristics suggest that gwCry1a is ideally suited as a primary light-mediated, radical-pair-based magnetic compass recepto