21,012 research outputs found

    Modeling of the Terminal Velocities of the Dust Ejected Material by the Impact

    Get PDF
    We compute the distribution of velocities of the particles ejected by the impact of the projectile released from NASA Deep Impact spacecraft on the nucleus of comet 9P/Tempel 1 on the successive 20 hours following the collision. This is performed by the development and use of an ill-conditioned inverse problem approach, whose main ingredients are a set of observations taken by the Narrow Angle Camera (NAC) of OSIRIS onboard the Rosetta spacecraft, and a set of simple models of the expansion of the dust ejecta plume for different velocities. Terminal velocities are derived using a maximum likelihood estimator. We compare our results with published estimates of the expansion velocity of the dust cloud. Our approach and models reproduce well the velocity distribution of the ejected particles. We consider these successful comparisons of the velocities as an evidence for the appropriateness of the approach. This analysis provides a more thorough understanding of the properties of the Deep Impact dust cloud.Comment: Comments: 6 pages, 2 Postscript figures, To appear in the proceedings of "Deep Impact as a World Observatory Event - Synergies in Space, Time", ed. Hans Ulrich Kaeufl and Chris Sterken, Springer-Verla

    Non-covalent interactions at electrochemical interfaces : one model fits all?

    Get PDF
    Acknowledgements Funding from the DGI (Spanish Ministry of Education and Science) through Project CTQ2009-07017 is gratefully acknowledged. E.P.M.L. wishes to thank the Universidad Nacional de Co´rdoba, Argentina, for a grant within the ‘‘Programa de Movilidad Internacional de Profesores Cuarto Centenario’’.Peer reviewedPublisher PD

    The Economics of Biotechnology under Ecosystem Disruption

    Get PDF
    Economic analysis of chemical pesticide use has shown that the interactions between plants, pests, damage control technology and state of the ecosystem are important variables to be considered. Hence, a bio-economic model was developed for the assessment of Bt variety and pesticide-based control strategies of the cotton bollworm in China. The model simulates plant growth, the dynamics of pest populations and of natural enemies. The model predictions are used as major inputs for a stochastic partial budgeting procedure of alternative control strategies. Results show that: (1) productivity effects of Bt varieties and pesticide use depend on the action of natural control agents, and (2) the profitability of damage control measures increases with the severity of ecosystem disturbance. The findings highlight the importance of the choice of a counterfactual scenario in the assessment of the impact of agricultural biotechnology. Also, some doubts are raised whether the high benefits of Bt cotton varieties based on cross section comparisons are realistic.Research and Development/Tech Change/Emerging Technologies, Q57, Q55, O13, O3,

    Institutional Constraints for the Success of Agricultural Biotechnology in Developing Countries: The Case of Bt-Cotton in Shandong Province, China

    Get PDF
    The use of genetically engineered crop varieties has recently become one option to prevent pest damage in agriculture. The promoters of biotechnology stress the great potential for yield increase and pesticide reduction while the critics point out the potential risks for biodiversity and human health as well as institutional problems for implementation especially in developing countries. The objective of this paper is an in-depth economic analysis of Btcotton production in North East China under small-scale conditions and several years after technology introduction. Data were collected in 2002 (March - October) in Linqing County, a major cotton growing area of Shandong Province, China. Data collection comprised a seasonlong monitoring of Bt-cotton production with 150 farmers from five villages, and three complementary household interviews. In addition, plot-level biological testing was carried out to determine the actual Bt toxin concentration in the varieties that were used by the farmers. All farmers in the case study were growing insect resistant Bt-cotton varieties in 2002. Nevertheless, they sprayed high amounts of chemical pesticides that were almost entirely insecticides. A proportion of 40% of the pesticides applied belonged to the categories extremely or highly hazardous (WHO classes Ia and Ib). The paper reviews methodological issues inherent to impact assessment of crop biotechnology and identifies market and institutional failure as possible reasons for continued high pesticide use. The production function methodology with damage control function was applied and it was found that for both damage control inputs, i.e. Bt and insecticides the coefficients were not significantly different from zero. In contrast to studies that treat Bt varieties as dummy variable in economic models, in this research it was possible to specify Bt toxin concentration in cotton leaf samples as a continuous variable. The results of this study support the notion that introducing Biotechnology in developing countries without enabling institutions that assure proper use of the technology can considerably limit its benefits. Hence it is important to include institutional criteria in the evaluation of agricultural biotechnology especially in developing countries. --

    Probabilistic Combination of Noisy Points and Planes for RGB-D Odometry

    Full text link
    This work proposes a visual odometry method that combines points and plane primitives, extracted from a noisy depth camera. Depth measurement uncertainty is modelled and propagated through the extraction of geometric primitives to the frame-to-frame motion estimation, where pose is optimized by weighting the residuals of 3D point and planes matches, according to their uncertainties. Results on an RGB-D dataset show that the combination of points and planes, through the proposed method, is able to perform well in poorly textured environments, where point-based odometry is bound to fail.Comment: Accepted to TAROS 201

    Essays on American Depositary Receipts: New Fears, Investor Attention and Financial Bubbles

    Get PDF
    This dissertation consists of four chapters, focusing on American Depositary Receipts (ADRs) and how they are affected by new measures of investor sentiment, new proxies of investor attention, and financial bubble detection. ADRs are negotiable certificates of ownership in foreign companies that are traded in the U.S. financial markets. In Chapter I, I make a brief introduction of ADRs. The types of programs there are, the market capitalization and volume in general and to some specific countries. In Chapter II, I show that negative investor sentiment measures, derived from internet aggregate search indices, have a contemporaneous negative effect on ADR stock indices and a second-day reversal behavior. To build the sentiment measure, I apply a similar methodology developed in recent literature to construct the Financial and Economic Attitudes Revealed by Search (FEARS) index. Moreover, evidence shows that this effect is greater for Latin American ADR indices at the aggregate level and on a country-specific level than for other regions. After matching the sample during times of turmoil, the results are consistent with the literature that employs this sentiment proxy with U.S. stock indices. In Chapter III, I examine the effect of country-specific investor attention on ADR mispricing. Investor attention is measured by the amount of traffic a country profile receives on Wikipedia. A 2-Stage Least Squares (2SLS) model is employed to mitigate the potential endogeneity. Evidence shows that higher levels of investor attention have a negative impact on ADRs mispricing. In Chapter IV, I utilize the Generalized Supremum Augmented Dickey-Fuller test methodology to identify and time-stamp the beginning and the end of financial bubbles in ADR stock indices. Evidence shows that there are multiple bubble episodes in the general ADR index, which correspond to bubble episodes in the S&P 500 during the preceding months of the 2008-2009 financial crisis. Moreover, I also identify several bubble periods on Latin American, European, and Asian ADR indices