3,442 research outputs found

    Interactions between genetically distinct retroviruses.

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    Retroviruses can packaged two copies of their RNA genome into a single virion. If two different RNAs are co-packaged together, both strands can be used as templates to generate a single DNA provirus during reverse transcription. In this dissertation, we studied mechanisms that may allow genetically distinct retroviruses to exchange genetic information. First, we examined whether minus-strand DNA transfer could occur between R regions with diminished sequence homology. It was found the only very short stretches of homology were necessary and that minus-strand DNA transfer was not limited to the R region. Thus, it is possible that viruses with different R regions may interact through this mechanism. A second question that was addressed was whether RNAs containing the encapsidation sequences of two genetically distinct retroviruses could co-package into the same virion. Such an event is critical for any exchange of genetic material to occur during reverse transcription. In our experimental system, we were able to observe proviruses that contained sequences from the different RNAs. This indicates that RNA from different retroviruses can be co-packaged and exchange genetic information. We concluded from these experiments that it is possible for different retroviral species to interact, which could result in the generation of a recombinant retrovirus with a significantly altered phenotype than either of its parents. This may have far-reaching implications for retroviral evolution and pathogenesis. Finally, in a third experiment we observed that inserting sequences into the 3{dollar}\\sp\\prime{dollar} untranslated region of the spleen necrosis virus disrupted replication. We demonstrated that this defect was due to an impairment in env expression that is likely to occur at a post RNA processing step. These results suggest the disruption of a novel cis-acting element in SNV

    The Awakening Chinese Economy: Macro and Terms of Trade Impacts on 10 Major Asia-Pacific Countries

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    This paper analyzes the impact that terms of trade (TOT) are likely to have on the growth of the People’s Republic of China’s (PRC) neighboring countries. Two scenarios employing a dynamic computable general equilibrium framework are considered: (i) a convergence scenario, where historical trends are projected; and (ii) a baseline scenario, where technological progress in the PRC is placed in line with that of the United States (US). The results show that the PRC’s technological convergence leads to increased world prices for mining products, and lower world prices for manufactures, especially those exported extensively by the PRC. On the whole, however, the effects on the growth and TOT of the PRC’s neighboring countries are relatively small. The modelling framework used in this study explicitly captures the various offsetting effects that dampen the impact on TOT and contribute to the small impact on growth. In addition, the additional capital required to finance the PRC’s growth comes predominantly from domestic savings, placing little pressure on the global supply of capital. Thus, an awakening PRC is unlikely to make a dramatic entrance despite the country’s overall positive impact on the region – although there is nothing to fear, there is also only little to gain.computable general equilibrium; multicountry models; People’s Republic of China; terms of trade

    Excluded-Volume Effects in Tethered-Particle Experiments: Bead Size Matters

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    The tethered-particle method is a single-molecule technique that has been used to explore the dynamics of a variety of macromolecules of biological interest. We give a theoretical analysis of the particle motions in such experiments. Our analysis reveals that the proximity of the tethered bead to a nearby surface (the microscope slide) gives rise to a volume-exclusion effect, resulting in an entropic force on the molecule. This force stretches the molecule, changing its statistical properties. In particular, the proximity of bead and surface brings about intriguing scaling relations between key observables (statistical moments of the bead) and parameters such as the bead size and contour length of the molecule. We present both approximate analytic solutions and numerical results for these effects in both flexible and semiflexible tethers. Finally, our results give a precise, experimentally-testable prediction for the probability distribution of the distance between the polymer attachment point and the center of the mobile bead.Comment: 4 pages, 3 figure

    Are all regulatory compliant independent director appointments the same? An analysis of Taiwanese board appointments

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    Globally many regulators adopted a rules-based approach to independent director appointments stipulating ‘independence’ criteria. This paper investigates whether partitioning a regulatory compliant sample of independent director appointments by prior affiliation to the board influences the relationship between ownership and control rights, and performance. We report a significant positive relationship between board independence and controlling shareholders’ cash-flow rights for firms where the appointee had prior affiliation to the board, but no performance improvement. Firms where the regulatory compliant independent directors had no prior-affiliation to the board experienced significant improvement in firms’ next period Return-on-Assets. Appointing affiliated directors is indicative diminished board quality, which is consistent with the empirical evidence that controlling shareholders determine board quality to accommodate tunneling to extract the private benefits of control to compensate for significant additional costs associated with concentrated ownership (Yeh and Woidtke, 2005; Luo et al, 2012; Liu et al, 2015). The positive association between performance and unaffiliated independent directors suggests a desire to introduce expertise to receive benefits via improved firm performance which is consistent with the literature, mostly from studies of emerging markets, reporting a causal link from independent directors to firm performance (Choi et al, 2007; Dahya et al. 2008; Liu et al, 2015)

    The Awakening Chinese Economy: Macro and Terms of Trade Impacts on 10 Major Asia-Pacific Countries

    Get PDF
    This paper analyzes the impact that terms of trade (TOT) are likely to have on the growth of the People’s Republic of China’s (PRC) neighboring countries. Two scenarios employing a dynamic computable general equilibrium framework are considered: (i) a convergence scenario, where historical trends are projected; and (ii) a baseline scenario, where technological progress in the PRC is placed in line with that of the United States (US). The results show that the PRC’s technological convergence leads to increased world prices for mining products, and lower world prices for manufactures, especially those exported extensively by the PRC. On the whole, however, the effects on the growth and TOT of the PRC’s neighboring countries are relatively small. The modelling framework used in this study explicitly captures the various offsetting effects that dampen the impact on TOT and contribute to the small impact on growth. In addition, the additional capital required to finance the PRC’s growth comes predominantly from domestic savings, placing little pressure on the global supply of capital. Thus, an awakening PRC is unlikely to make a dramatic entrance despite the country’s overall positive impact on the region – although there is nothing to fear, there is also only little to gain

    Foundations for Studying Clinical Workflow: Development of a Composite Inter-Observer Reliability Assessment for Workflow Time Studies

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    The ability to understand and measure the complexity of clinical workflow provides hospital managers and researchers with the necessary knowledge to assess some of the most critical issues in healthcare. Given the protagonist role of workflow time studies on influencing decision makers, major efforts are being conducted to address existing methodological inconsistencies of the technique. Among major concerns, the lack of a standardized methodology to ensure the reliability of human observers stands as a priority. In this paper, we highlight the limitations of the current Inter-Observer Reliability Assessments, and propose a novel composite score to systematically conduct them. The composite score is composed of a) the overall agreement based on Kappa that evaluates the naming agreement on virtually created one-seconds tasks, providing a global assessment of the agreement over time, b) a naming agreement based on Kappa, requiring an observation pairing approach based on time-overlap, c) a duration agreement based on the concordance correlation coefficient, that provides means to evaluate the correlation concerning tasks duration, d) a timing agreement, based on descriptive statistics of the gaps between timestamps of same-task classes, and e) a sequence agreement based on the Needleman-Wunsch sequence alignment algorithm. We hereby provide a first step towards standardized reliability reporting in workflow time studies. This new composite IORA protocol is intended to empower workflow researchers with a standardized and comprehensive method for validating observers' reliability and, in turn, the validity of their data and results

    Bayesian atmospheric correction over land: Sentinel-2/MSI and Landsat 8/OLI

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    Mitigating the impact of atmospheric effects on optical remote sensing data is critical for monitoring intrinsic land processes and developing Analysis Ready Data (ARD). This work develops an approach to this for the NERC NCEO medium resolution ARD Landsat 8 (L8) and Sentinel 2 (S2) products, called Sensor Invariant Atmospheric Correction (SIAC). The contribution of the work is to phrase and solve that problem within a probabilistic (Bayesian) framework for medium resolution multispectral sensors S2/MSI and L8/OLI and to provide per-pixel uncertainty estimates traceable from assumed top-of-atmosphere (TOA) measurement uncertainty, making progress towards an important aspect of CEOS ARD target requirements. A set of observational and a priori constraints are developed in SIAC to constrain an estimate of coarse resolution (500 m) aerosol optical thickness (AOT) and total column water vapour (TCWV), along with associated uncertainty. This is then used to estimate the medium resolution (10–60 m) surface reflectance and uncertainty, given an assumed uncertainty of 5 % in TOA reflectance. The coarse resolution a priori constraints used are the MODIS MCD43 BRDF/Albedo product, giving a constraint on 500 m surface reflectance, and the Copernicus Atmosphere Monitoring Service (CAMS) operational forecasts of AOT and TCWV, providing estimates of atmospheric state at core 40 km spatial resolution, with an associated 500 m resolution spatial correlation model. The mapping in spatial scale between medium resolution observations and the coarser resolution constraints is achieved using a calibrated effective point spread function for MCD43. Efficient approximations (emulators) to the outputs of the 6S atmospheric radiative transfer code are used to estimate the state parameters in the atmospheric correction stage. SIAC is demonstrated for a set of global S2 and L8 images covering AERONET and RadCalNet sites. AOT retrievals show a very high correlation to AERONET estimates (correlation coefficient around 0.86, RMSE of 0.07 for both sensors), although with a small bias in AOT. TCWV is accurately retrieved from both sensors (correlation coefficient over 0.96, RMSE <0.32 g cm−2). Comparisons with in situ surface reflectance measurements from the RadCalNet network show that SIAC provides accurate estimates of surface reflectance across the entire spectrum, with RMSE mismatches with the reference data between 0.01 and 0.02 in units of reflectance for both S2 and L8. For near-simultaneous S2 and L8 acquisitions, there is a very tight relationship (correlation coefficient over 0.95 for all common bands) between surface reflectance from both sensors, with negligible biases. Uncertainty estimates are assessed through discrepancy analysis and are found to provide viable estimates for AOT and TCWV. For surface reflectance, they give conservative estimates of uncertainty, suggesting that a lower estimate of TOA reflectance uncertainty might be appropriate
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