69 research outputs found

    Multilayers for high-Tc superconducting electric field effect devices

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    Epitaxial multilayers, consisting of a PrBa2Cu3O7-x buffer layer, ultrathin YBa2Cu3O7-x and SrTiO3, have been grown for application in electric field effect devices. Different analytical techniques indicate a sharp interface between the layers and good dielectric properties of the SrTiO3-layer. First measurements show clear modification of the superconductor's current-voltage characteristics upon applying electric fields of 0.1-1 MV/cm

    Development of the mathematical model of catalytic cracking: identification of hydrocarbon of the vacuum distillate usin chromatomass- spectrometry

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    Information about composition of catalytic cracking raw materials and products is required fordevelopment of mathematical model of catalytic cracking. The results of laboratory investigation ondetermination of the composition of catalytic cracking vacuum distillate were performed in this work. Groupcomposition of the catalytic cracking raw materials was defined using liquid-adsorption chromatographicseparation on silica gel. Paraffin-naphthenic and aromatic fraction was indefined by chromato-massspectrometry

    General parenting and mothers’ snack giving behavior to their children aged 2–7

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    The increasing intake of energy-dense snacks among children is one of the contributing factors to childhood overweight. To understand children's snacking habits, snack choices of parents are essential to take into account. General parenting is one of the important factors that can influence the development of healthy eating patterns and weight status among children. Therefore, this study aims to explore how the key constructs of general parenting (nurturance, structure, behavioral control, overprotection and coercive control) relate to mothers’ snack choice for their children aged 2–7 years. The Dutch version of the validated Comprehensive General Parenting Questionnaire (CGPQ) was used to assess the key constructs of general parenting. An extensive, 13-day diary study with 136 Dutch mothers was used to measure the snacks mothers provided their children aged 2–4 years and 5–7 years. For both groups of mothers in our sample, differences were found on the scores of coercive control and overprotection. No differences between the mothers were present on the key constructs behavioral control, nurturance, and structure. Results give a first indication that more mothers who scored relatively higher on coercive control provided unhealthy products, like candy and cookies, and fewer mothers provided vegetables, compared to mothers who scored lower on coercive control. A higher score on coercive control combined with a higher score on overprotection was associated with fewer mothers providing unhealthy products like cookies and candies.</p

    The double [3+2] photocycloaddition reaction

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    One of a synthetic organic chemists‟ greatest challenges is to create step-efficient routes toward compounds with high molecular complexity. Therefore, reactions such as the meta photocycloaddition of an olefin to a benzene derivative, which provide more than one bond in a single step are of significant importance. It this remarkable reaction three new σ bonds, three new rings and up to six new stereocenters are formed simultaneously. Additional complexity can be added by tethering the two reacting partners together and this form of the reaction has found many uses in natural product synthesis. In this work a remarkable double [3+2] photocycloaddition reaction is reported that results in the formation of a complex cis, cis, cis, trans-[5, 5, 5, 5] fenestrane derivative from a simple flat aromatic acetal with two branching alkenes. During this dramatic transformation four carboncarbon bonds, five new rings and seven new stereocenters are created in a single one-pot process using only UV light. The reaction occurs in a sequential manner from the linear meta photocycloadduct, via a secondary [3+2] addition of the alkene across the cyclopropane of the adduct. In addition, an angular meta photocycloadduct also produced in the initial addition step, undergoes an alternative fragmentation-translocation photoreaction to afford a silphinene-like angular tricyclic compound. In this work the investigation of this newly discovered process is discussed via the synthesis and subsequent irradiation of a series of photosubstrates containing different functional groups in the arene-alkene tether. In addition, attempts toward the synthesis of alternative structures using the same double [3+2] photocycloaddition are reported

    Environmental Risk Assessment of Fluctuating Diazinon Concentrations in an Urban and Agricultural Catchment Using Toxicokinetic–Toxicodynamic Modeling

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    Temporally resolved environmental risk assessment of fluctuating concentrations of micropollutants is presented. We separated the prediction of toxicity over time from the extrapolation from one to many species and from acute to sublethal effects. A toxicokinetic–toxicodynamic (TKTD) model predicted toxicity caused by fluctuating concentrations of diazinon, measured by time-resolved sampling over 108 days from three locations in a stream network, representing urban, agricultural and mixed land use. We calculated extrapolation factors to quantify variation in toxicity among species and effect types based on available toxicity data, while correcting for different test durations with the TKTD model. Sampling from the distribution of extrapolation factors and prediction of time-resolved toxicity with the TKTD model facilitated subsequent calculation of the risk of undesired toxic events. Approximately one-fifth of aquatic organisms were at risk and fluctuating concentrations were more toxic than their averages. Contribution of urban and agricultural sources of diazinon to the overall risk varied. Thus using fixed concentrations as water quality criteria appears overly simplistic because it ignores the temporal dimension of toxicity. However, the improved prediction of toxicity for fluctuating concentrations may be small compared to uncertainty due to limited diversity of toxicity data to base the extrapolation factors on

    The tourism and economic growth enigma: Examining an ambiguous relationship through multiple prisms

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    This paper revisits the ambiguous relationship between tourism and economic growth, providing a comprehensive study of destinations across the globe which takes into account the key dynamics that influence tourism and economic performance. We focus on 113 countries over the period 1995-2014, clustered, for the first time, around six criteria that reflect their economic, political and tourism dimensions. A Panel Vector Autoregressive model is employed which, in contrast to previous studies, allows the data to reveal any tourism-economy interdependencies across these clusters, without imposing a priori the direction of causality. Overall, the economic-driven tourism growth hypothesis seems to prevail in countries which are developing, non-democratic, highly bureaucratic and have low tourism specialization. Conversely, bidirectional relationships are established for economies which are stronger, democratic and with higher levels of government effectiveness. Thus, depending on the economic, political and tourism status of a destination, different policy implications apply

    A Second Best Theory of Institutional Quality

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    This paper illustrates a theory of the second best where the constraints to the achievement of the optimum are of institutional nature. We consider the effects of corruption and bad governance on the public decision to privatize the provision of a service when contracts are incomplete and there is asymmetric information. We show that both corruption and bad governance are detrimental to welfare, but that removing only one of the two is not necessarily beneficial if the other is still present. The theory supplies a possible explanation to the controversial empirical evidence on the economic effects of corruption
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