1,363 research outputs found

    Synthesis of 3,3-disubstituted heterocycles by Pd-catalyzed arylallylation of unactivated alkenes

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    Finding new methods of carbon–carbon bond formation is a key goal in expanding current methodology for heterocycle formation. Because of their inherently non-planar shape, new methods of forming sp3-rich scaffolds are of particular importance. While there are methods for combining heterocyclisation and formation of new sp3–sp3 carbon–carbon bonds, these form the carbon– heteroatom bond rather than a carbon–carbon bond of the heterocycle. Here we show a new alkene arylallylation reaction that generates a heterocycle with concomitant formation of two new carbon– carbon bonds. Furthermore, we demonstrate that this process occurs through an isohypsic (redox neutral) mechanism. Overall, this carboallylation reaction gives a new route to the synthesis of 3,3- disubstituted heterocycles

    A double end fault location technique for distribution systems based on fault-generated transients

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    This paper presents a fault location technique for distribution systems. It is a two end impedance based technique that uses the fault generated transients to estimate the fault distance over a broad range of frequencies. Then, curve fitting is applied to find the final estimated fault distance. Firstly, the paper introduces the method for the system represented as a lumped RL model. Then, generalized to consider the distribution line capacitance. The technique accounts for presence of loading taps, heterogeneous feeder sections, single phase, two phase and three phase loads and unbalance in distribution system. Single line to ground, line to line, and three phase faults are considered at different fault resistance values up to 100 Ω. Also, the effect of fault inception angle and resolution of analogue to digital converter is investigated. IEEE 34 nodes system is used to evaluate the proposed method

    Fast fault location scheme for distribution systems based on fault transients

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    This paper presents a combined double-end and single-end fault locator for distribution systems. The technique lies under the impedance based category and uses the fault generated high frequency components to locate the faults. The combination of double-end and single-end allows the method to discriminate between faults on the main feeder and those on laterals. Also, the method only requires a short data window as it depends on the high frequency components. The evaluation of the method considers different system and fault parameters e.g. loading taps, loading unbalance, fault type and fault resistance. To validate the proposed technique, the IEEE 34 nodes system is used to simulate different test cases

    A data-based reduced-order model for dynamic simulation and control of district-heating networks

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    This study concerns the development of a data-based compact model for the prediction of the fluid temperature evolution in district heating (DH) pipeline networks. This so-called “reduced-order model” (ROM) is obtained from reduction of the conservation law for energy for each pipe segment to a semi-analytical input–output relation between the pipe outlet temperature and the pipe inlet and ground temperatures that can be identified from training data. The ROM basically is valid for generic pipe configurations involving 3D unsteady heat transfer and 3D steady flow as long as heat-transfer mechanisms are linearly dependent on the temperature field. Moreover, the training data can be generated by physics-based computational “full-order” models (FOMs) yet also by (calibration) experiments or field measurements. Performance tests using computational training data for a single-pipe configuration demonstrate that the ROM (i) can be successfully identified and (ii) can accurately describe the response of the outlet temperature to arbitrary input profiles for inlet and ground temperatures. Application of the ROM to two case studies, i.e. fast simulation of a small DH network and design of a controller for user-defined temperature regulation of a DH system, demonstrate its predictive ability and efficiency also for realistic systems. Dedicated cost analyses further reveal that the ROM may significantly reduce the computational costs compared to FOMs by (up to) orders of magnitude for higher-dimensional pipe configurations. These findings advance the proposed ROM as a robust and efficient simulation tool for practical DH systems with a far greater predictive ability than existing compact models

    Future land-use change in the Netherlands: an analysis based on a chain of models

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    Analyses of the impact of European policies on agricultural change are most often based on agricultural sector models. Such models have their limitations: they cannot specify the interaction between agriculture and the rest of the economy, and their spatial dimension is usually limited. Land use simulation models, on the other hand, usually depend on other models for assessing the demand for land. The consistency of those models with the assumptions and databases of the land use model is often not examined. This article reports on a research project where the links between a macroeconomic model, an agricultural sector model and a land use model were explicitly explored in order to arrive at a consistent model chain. This integrated framework was put to the test by applying it to two contrasting scenarios, which compare impact on agricultural incomes, land use and land management.land use, CAP, agricultural policy analyses, Netherlands, Agricultural and Food Policy, Land Economics/Use,

    Coupled Mg/Ca and clumped isotope analyses of foraminifera provide consistent water temperatures

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    The reliable determination of past seawater temperature is fundamental to paleoclimate studies. We test the robustness of two paleotemperature proxies by combining Mg/Ca and clumped isotopes (Δ47) on the same specimens of core top planktonic foraminifera. The strength of this approach is that Mg/Ca and Δ47 are measured on the same specimens of foraminifera, thereby providing two independent estimates of temperature. This replication constitutes a rigorous test of individual methods with the advantage that the same approach can be applied to fossil specimens. Aliquots for Mg/Ca and clumped analyses are treated in the same manner following a modified cleaning procedure of foraminifera for trace element and isotopic analyses. We analysed eight species of planktonic foraminifera from coretop samples over a wide range of temperatures from 2 to 29°C. We provide a new clumped isotope temperature calibrations using subaqueous cave carbonates, which is consistent with recent studies. Tandem Mg/Ca–Δ47 results follow an exponential curve as predicted by temperature calibration equations. Observed deviations from the predicted Mg/Ca-Δ47 relationship are attributed to the effects of Fe-Mn oxide coatings, contamination, or dissolution of foraminiferal tests. This coupled approach provides a high degree of confidence in temperature estimates when Mg/Ca and Δ47 yield concordant results, and can be used to infer the past δ18O of seawater (δ18Osw) for paleoclimate studies
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