排序方式: 共有48条查询结果,搜索用时 31 毫秒
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A convenient one-step protocol for the synthesis of 4-amino-3,5-disubstituted pyrazoles has been developed. This method employs readily available diketo oximes as starting materials, and employs hydrazine hydrate for the cyclization and subsequent reduction of the intermediate nitroso compound. 相似文献
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Thomas Boucher CJ Carey Melinda Darby Dyar Sridhar Mahadevan Samuel Clegg Roger Wiens 《Journal of Chemometrics》2015,29(9):484-491
Laser‐induced breakdown spectroscopy (LIBS) is currently being used onboard the Mars Science Laboratory rover Curiosity to predict elemental abundances in dust, rocks, and soils using a partial least squares regression model developed by the ChemCam team. Accuracy of that model is constrained by the number of samples needed in the calibration, which grows exponentially with the dimensionality of the data, a phenomenon known as the curse of dimensionality. LIBS data are very high dimensional, and the number of ground‐truth samples (i.e., standards) recorded with the ChemCam before departing for Mars was small compared with the dimensionality, so strategies to optimize prediction accuracy are needed. In this study, we first use an existing machine learning algorithm, locally linear embedding (LLE), to combat the curse of dimensionality by embedding the data into a low‐dimensional manifold subspace before regressing. LLE constructs its embedding by maintaining local neighborhood distances and discarding large global geodesic distances between samples, in an attempt to preserve the underlying geometric structure of the data. We also introduce a novel supervised version, LLE for regression (LLER), which takes into account the known chemical composition of the training data when embedding. LLER is shown to outperform traditional LLE when predicting most major elements. We show the effectiveness of both algorithms using three different LIBS datasets recorded under Mars‐like conditions. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Aalseth CE Barbeau PS Colaresi J Collar JI Diaz Leon J Fast JE Fields N Hossbach TW Keillor ME Kephart JD Knecht A Marino MG Miley HS Miller ML Orrell JL Radford DC Wilkerson JF Yocum KM;CoGeNT Collaboration 《Physical review letters》2011,107(14):141301
Fifteen months of cumulative CoGeNT data are examined for indications of an annual modulation, a predicted signature of weakly interacting massive particle (WIMP) interactions. Presently available data support the presence of a modulated component of unknown origin, with parameters prima?facie compatible with a galactic halo composed of light-mass WIMPs. Unoptimized estimators yield a statistical significance for a modulation of ~2.8σ, limited by the short exposure. 相似文献
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Behnke E Behnke J Brice SJ Broemmelsiek D Collar JI Cooper PS Crisler M Dahl CE Fustin D Hall J Hinnefeld JH Hu M Levine I Ramberg E Shepherd T Sonnenschein A Szydagis M;COUPP Collaboration 《Physical review letters》2011,106(2):021303
Data from the operation of a bubble chamber filled with 3.5 kg of CF3I in a shallow underground site are reported. An analysis of ultrasound signals accompanying bubble nucleations confirms that alpha decays generate a significantly louder acoustic emission than single nuclear recoils, leading to an efficient background discrimination. Three dark matter candidate events were observed during an effective exposure of 28.1 kg day, consistent with a neutron background. This observation provides strong direct detection constraints on weakly interacting massive particle (WIMP)-proton spin-dependent scattering for WIMP masses >20 GeV/c2. 相似文献
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Indenbom MV van Der Beek CJ Konczykowski M Holtzberg F 《Physical review letters》2000,84(8):1792-1795
From magneto-optical imaging performed on heavy-ion-irradiated YBa(2)Cu(3)O(7-delta) single crystals, it is found that at fields and temperatures where strong single vortex pinning by individual irradiation-induced amorphous columnar defects is to be expected, vortex motion is limited by the nucleation of vortex kinks at the specimen surface. In the material bulk, vortex motion occurs through (easy) kink sliding. Depinning in the bulk determines the screening current only at fields comparable to or larger than the matching field, at which the majority of vortices is not trapped by an ion track. 相似文献