4,384 research outputs found

    A practical comparison of firm valuation models: cash flow, dividend and income

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    Our research, based on a sample of listed Australian firms, indicates that the residual income model provides better estimates of firm value than two other commonly used models. It also provides advantages in that there is less need to forecast returns as far into the future and, with this model, a terminal value based upon a constant future return (or relatively low growth rates) can be used. This obviates the need to estimate an expected long-term growth rate, which is always problematic

    Temperature is a poor proxy for synergistic climate forcing of plankton evolution

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    This is the author accepted manuscript. The final version is available from The Royal Society via the DOI in this record.Abundance data available in Figshare via the link in this record.Changes in biodiversity at all levels from molecules to ecosystems are often linked to climate change, which is widely represented univariately by temperature. A global environmental driving mechanism of biodiversity dynamics is thus implied by the strong correlation between temperature proxies and diversity patterns in a wide variety of fauna and flora. Yet climate consists of many interacting variables. Species likely respond to the entire climate system as opposed to its individual facets. Here, we examine ecological and morphological traits of 12,629 individuals of two species of planktonic foraminifera with similar ecologies but contrasting evolutionary outcomes. Our results show that morphological and ecological changes are correlated to the interactions between multiple environmental factors. Models including interactions between climate variables explain at least twice as much variation in size, shape and abundance changes as models assuming that climate parameters operate independently. No dominant climatic driver can be identified: temperature alone explains remarkably little variation through our highly resolved temporal sequences, implying that a multivariate approach is required to understand evolutionary response to abiotic forcing. Our results caution against the use of a ‘silver bullet’ environmental parameter to represent global climate while studying evolutionary responses to abiotic change, and show that more comprehensive reconstruction of paleobiological dynamics requires multiple biotic and abiotic dimensions.NERC Advanced Research Fellowship NE/J018163/1Royal Society Wolfson Research Merit Awar

    The Dynamics of Diachronous Extinction Associated with Climatic Deterioration near the Neogene/Quaternary Boundary

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    This is the final version. Available on open access from Wiley via the DOI in this recordTo predict extinction we must understand the processes leading to terminal population decline. Once a critical threshold of population size is reached, small environmental perturbations can push a species over the cliff-edge to extinction, so the main drivers of extinction are the factors that cause the initial reduction in population size. Most studies of population decline leading up to extinction focus on modern species in a human-dominated world. The drivers of population decline leading to non-human mediated extinctions are less well known but changes in climate are arguably the most widely invoked mechanism. Here, we report data on >16,000 individuals of the planktonic foraminifer Globoconella puncticulata from six sites in the Atlantic Ocean along a 83 degree-long latitudinal transect, over a 600,000-year interval leading up to the species’ global extinction during the late Pliocene-earliest Pleistocene intensification of Northern Hemisphere glaciation. We show changes in geographic range, abundance and body size. We find that populations do not follow a North-to-South sequence in extinction as Earth cooled and developed large ice sheets in the high latitudes of the Northern Hemisphere. Instead, our results suggest that (1) populations are differentially adapted to local environmental conditions such as nutrient availability, (2) population dynamics in core populations differ from those at the edge of their range, and (3) individual population responses to external pressures are essential to understanding the drivers of global extinction. Our study demonstrates the potential to transform our understanding of extinction dynamics through spatially replicated sampling of the highly-resolved marine microfossil record

    The Red Sea, Coastal Landscapes, and Hominin Dispersals

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    This chapter provides a critical assessment of environment, landscape and resources in the Red Sea region over the past five million years in relation to archaeological evidence of hominin settlement, and of current hypotheses about the role of the region as a pathway or obstacle to population dispersals between Africa and Asia and the possible significance of coastal colonization. The discussion assesses the impact of factors such as topography and the distribution of resources on land and on the seacoast, taking account of geographical variation and changes in geology, sea levels and palaeoclimate. The merits of northern and southern routes of movement at either end of the Red Sea are compared. All the evidence indicates that there has been no land connection at the southern end since the beginning of the Pliocene period, but that short sea crossings would have been possible at lowest sea-level stands with little or no technical aids. More important than the possibilities of crossing the southern channel is the nature of the resources available in the adjacent coastal zones. There were many climatic episodes wetter than today, and during these periods water draining from the Arabian escarpment provided productive conditions for large mammals and human populations in coastal regions and eastwards into the desert. During drier episodes the coastal region would have provided important refugia both in upland areas and on the emerged shelves exposed by lowered sea level, especially in the southern sector and on both sides of the Red Sea. Marine resources may have offered an added advantage in coastal areas, but evidence for their exploitation is very limited, and their role has been over-exaggerated in hypotheses of coastal colonization

    Protease inhibitors and preterm delivery: another piece in the puzzle

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    BACKGROUND: Questions remain regarding preterm delivery (PTD) risk in HIV-infected women on antiretroviral therapy (ART), including the role of ritonavir (RTV)-boosted protease inhibitors, timing of ART initiation and immune status. METHODS: We examined data from the UK/Ireland National Study of HIV in Pregnancy and Childhood on women with HIV delivering a singleton live infant in 2007–2015, including those pregnancies receiving RTV-boosted protease inhibitor-based (n = 4184) or nonnucleoside reverse transcriptase inhibitors-based regimens (n = 1889). We conducted logistic regression analysis adjusted for risk factors associated with PTD and stratified by ART at conception and CD4^+ cell count to minimize bias by indication for treatment and to assess whether PTD risk differs by ART class and specific drug combinations. RESULTS: Among women conceiving on ART, lopinavir/RTV was associated with increased PTD risk in those with CD4^+ cell count 350 cells/”l or less [odds ratio 1.99 (1.02, 3.85)] and with CD4^+ cell count more than 350 cells/”l [odds ratio 1.61 (1.07, 2.43)] vs. women on nonnucleoside reverse transcriptase inhibitors-based (mainly efavirenz and nevirapine) regimens in the same CD4^+ subgroup. Associations between other protease inhibitor-based regimens (mainly atazanavir and darunavir) and PTD risk were complex. Overall, PTD risk was higher in women who conceived on ART, had low CD4^+ cell count and were older. No trend of association of PTD with tenofovir or any specific drug combinations was observed. CONCLUSION: Our data support a link between the initiation of RTV-boosted/lopinavir-based ART preconception and PTD in subsequent pregnancies, with implications for treatment guidelines. Continued monitoring of PTD risk is needed as increasing numbers of pregnancies are conceived on new drugs

    North Atlantic mid-latitude surface-circulation changes through the Plio-Pleistocene intensification of northern hemisphere glaciation

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    This is the final version. Available from American Geophysical Union (AGU) / Wiley via the DOI in this record.All new data presented are available at https://doi.pangaea.de/10.1594/PANGAEA.892805The North Atlantic Current (NAC) transports warm salty water to high northern latitudes, with important repercussions for ocean circulation and global climate. A southward displacement of the NAC and Subarctic Front, which separate subpolar and subtropical water masses, is widely suggested for the last glacial maximum (LGM) and may have acted as a positive feedback in glacial expansion at this time. However, the role of the NAC during the intensification of northern hemisphere glaciation (iNHG) ~3.5 to 2.5 Ma, is less clear. Here, we present new records from IODP Site U1313 (41°N) spanning ~2.8-2.4 Ma to trace the influence of Subarctic Front waters above this mid-latitude site. We reconstruct surface and permanent pycnocline temperatures and seawater Ύ18O using paired Mg/Ca-Ύ18O measurements on the planktic foraminifers Globigerinoides ruber and Globorotalia crassaformis, and determine abundances of the subpolar foraminifer Neogloboquadrina atlantica. We find that the first significant glacial incursions of Subarctic Front surface waters above Site U1313 did not occur until ~2.6 Ma. At no time during our study interval was (sub)surface reorganisation in the mid-latitude North Atlantic analogous to the LGM. Our findings suggest that LGM-like processes sensu stricto cannot be invoked to explain interglacial-glacial cycle amplification during iNHG. They also imply that increased glacial productivity at Site U1313 during iNHG was not only driven by southward deflections of the Subarctic Front. We suggest nutrient injection from cold-core eddies and enhanced glacial dust delivery may have played additional roles in increasing export productivity in the mid-latitude North Atlantic from 2.7 Ma.Funding for this research was provided by IODP France (CTB) and the German Research Foundation (DFG) (grant OF 2544/2 to OF). IB is grateful to the UK IODP for financial support for shipboard and post-cruise participation in IODP Exp. 306. CTB, KT, TDG, LV, CS, and ME acknowledge OSU Pythéas. MMR acknowledges support by the USGS Land Change Science Program. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. PAW acknowledges NERC UK IODP NE/F00141X/1 and a Royal Society Wolfson Merit Award

    Peptide exchange on MHC-I by TAPBPR is driven by a negative allostery release cycle.

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    Chaperones TAPBPR and tapasin associate with class I major histocompatibility complexes (MHC-I) to promote optimization (editing) of peptide cargo. Here, we use solution NMR to investigate the mechanism of peptide exchange. We identify TAPBPR-induced conformational changes on conserved MHC-I molecular surfaces, consistent with our independently determined X-ray structure of the complex. Dynamics present in the empty MHC-I are stabilized by TAPBPR and become progressively dampened with increasing peptide occupancy. Incoming peptides are recognized according to the global stability of the final pMHC-I product and anneal in a native-like conformation to be edited by TAPBPR. Our results demonstrate an inverse relationship between MHC-I peptide occupancy and TAPBPR binding affinity, wherein the lifetime and structural features of transiently bound peptides control the regulation of a conformational switch located near the TAPBPR binding site, which triggers TAPBPR release. These results suggest a similar mechanism for the function of tapasin in the peptide-loading complex
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