3,582,465 research outputs found

    Structural features and reactivity of (sparteine)PdCl_2: a model for selectivity in the oxidative kinetic resolution of secondary alcohols

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    The chiral ligand (−)-sparteine and PdCl_2 catalyze the enantioselective oxidation of secondary alcohols to ketones and thus effect a kinetic resolution. The structural features of sparteine that led to the selectivity observed in the reaction were not clear. Substitution experiments with pyridine derivatives and structural studies of the complexes generated were carried out on (sparteine)PdCl2 and indicated that the C1 symmetry of (−)-sparteine is essential to the location of substitution at the metal center. Palladium alkoxides were synthesized from secondary alcohols that are relevant steric models for the kinetic resolution. The solid-state structures of the alkoxides also confirmed the results from the pyridine derivative substitution studies. A model for enantioinduction was developed with C1 symmetry and Cl− as key features. Further studies of the diastereomers of (−)-sparteine, (−)-α-iso- and (+)-ÎČ-isosparteine, in the kinetic resolution showed that these C_2-symmetric counterparts are inferior ligands in this stereoablative reactio

    Inference on a structural break in trend with fractionally integrated errors

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    Perron and Zhu (2005) established the consistency, convergence rate and limiting distributions of parameter estimates in time trends with a change in slope with or without a concurrent level change for the cases with I(1) or I(0) errors. We extend their analysis to the general case of fractionally integrated errors with memory parameter d∗. Our results uncover interesting features; e.g., with a level shift allowed, the convergence rate for the break date estimate is the same for all d∗∈(−0.5,0.5). In other cases, it is decreasing as d∗ increases. We also provide results about the so-called spurious break issue

    Trend Estimation

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    Trend estimation deals with the characterization of the underlying, or long–run, evolution of a time series. Despite being a very pervasive theme in time series analysis since its inception, it still raises a lot of controversies. The difficulties, or better, the challenges, lie in the identification of the sources of the trend dynamics, and in the definition of the time horizon which defines the long run. The prevalent view in the literature considers the trend as a genuinely latent component, i.e. as the component of the evolution of a series that is persistent and cannot be ascribed to observable factors. As a matter of fact, the univariate approaches reviewed here assume that the trend is either a deterministic or random function of time.Time series models; unobserved components.

    Discrimination between deterministic trend and stochastic trend processes

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    Most of economic and financial time series have a nonstationary behavior. There are different types of nonstationary processes, such as those with stochastic trend and those with deterministic trend. In practice, it can be quite difficult to distinguish between the two processes. In this paper, we compare random walk and determinist trend processes using sample autocorrelation, sample partial autocorrelation and periodogram based metrics.Autocorrelation; Classification; Determinist trend; Kullback-Leibler; Periodogram; Stochastic trend; Time series

    Guide To Trend Mapping

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    A trend map is a visual depiction of relevant trends influencing the system around a given topic. Developing a trend map can help a group deepen their understanding of an issue through exploring related history, identifying key external factors, and tracking shifts in social and cultural norms. This guide will walk you through a feasibility assessment as well as how to prepare for and facilitate a trend mapping activity

    An Experimentally Derived Model for Stereoselectivity in the Aerobic Oxidative Kinetic Resolution of Secondary Alcohols by (Sparteine)PdCl_2

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    A model for asymmetric induction in palladium-catalyzed aerobic oxidative kinetic resolution is described. The model is based on coordination complexes and general reactivity trends of the parent (sp)PdCl2 catalyst. The first example of a nonracemic chiral palladium alkoxide complex is presented, and exhibits the subtle steric influences of the C1symmetric ligand sparteine

    Political Islam: the Shrinking Trend and the Future Trajectory of Islamic Political Parties in Indonesia

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    The trend of religious conservatism in Indonesian public sector is increasing nowadays. But the trend is not followed by the rise of political Islam‟s popularity. The Islamic political parties are precisely abandoned by their sympathizers because of some reasons. This paper tries to elaborate the reasons causing the erosion of Islamic parties‟ political legitimacy. Some fundamental problems such as inability to transform ideology into political platform, internal-factionalism, as well as the crisis of identity will be explained further. The experience from 2009 election can be used to revitalize their power and capacity for the better electability in the next 2014 election. But they seem to be unable to deal with the previous problems making the electability erosion in 2014 more potential and inevitable. Various strategies must be conducted by the parties such as consolidation, revitalizing their political communication strategy, widening political networks across various ideological and religious streams, and others. Without that, their existence would be subordinated by the secular parties to become the second class political players in this biggest Moslem country in the world
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